MultibodyPlant is a Drake system framework representation (see systems::System) for the model of a physical system consisting of a collection of interconnected bodies.
See Multibody Kinematics and Dynamics for an overview of concepts/notation.
| MultibodyPlant |
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The ports whose names begin with model_instance_name[i] represent groups of ports, one for each of the model instances, with i ∈ {0, ..., N-1} for the N model instances. If a model instance does not contain any data of the indicated type the port will still be present but its value will be a zero-length vector. (Model instances world_model_instance()
and default_model_instance()
always exist.)
The ports shown in green are for communication with Drake's SceneGraph system for dealing with geometry.
MultibodyPlant provides a user-facing API for:
A MultiBodyPlant may contain multiple model instances. Each model instance corresponds to a set of bodies and their connections (joints). Model instances provide methods to get or set the state of the set of bodies (e.g., through GetPositionsAndVelocities() and SetPositionsAndVelocities()), connecting controllers (through get_state_output_port() and get_actuation_input_port()), and organizing duplicate models (read through a parser). In fact, many MultibodyPlant methods are overloaded to allow operating on the entire plant or just the subset corresponding to the model instance; for example, one GetPositions() method obtains the generalized positions for the entire plant while another GetPositions() method obtains the generalized positions for model instance.
Model instances are frequently defined through SDFormat files (using the model
tag) and are automatically created when SDFormat files are parsed (by Parser). There are two special multibody::ModelInstanceIndex values. The world body is always multibody::ModelInstanceIndex 0. multibody::ModelInstanceIndex 1 is reserved for all elements with no explicit model instance and is generally only relevant for elements created programmatically (and only when a model instance is not explicitly specified). Note that Parser creates model instances (resulting in a multibody::ModelInstanceIndex ≥ 2) as needed.
See num_model_instances(), num_positions(), num_velocities(), num_actuated_dofs(), AddModelInstance() GetPositionsAndVelocities(), GetPositions(), GetVelocities(), SetPositionsAndVelocities(), SetPositions(), SetVelocities(), GetPositionsFromArray(), GetVelocitiesFromArray(), SetPositionsInArray(), SetVelocitiesInArray(), SetActuationInArray(), HasModelInstanceNamed(), GetModelInstanceName(), get_state_output_port(), get_actuation_input_port().
The state of a multibody system x = [q; v]
is given by its generalized positions vector q, of size nq
(see num_positions()), and by its generalized velocities vector v, of size nv
(see num_velocities()). As a Drake System, MultibodyPlant implements the governing equations for a multibody dynamical system in the form ẋ = f(t, x, u)
with t being time and u the actuation forces. The governing equations for the dynamics of a multibody system modeled with MultibodyPlant are [Featherstone 2008, Jain 2010]:
q̇ = N(q)v (1) M(q)v̇ + C(q, v)v = τ
where M(q)
is the mass matrix of the multibody system, C(q, v)v
contains Coriolis, centripetal, and gyroscopic terms and N(q)
is the kinematic coupling matrix describing the relationship between q̇ (the time derivatives of the generalized positions) and the generalized velocities v, [Seth 2010]. N(q)
is an nq x nv
matrix. The vector τ ∈ ℝⁿᵛ
on the right hand side of Eq. (1) is the system's generalized forces. These incorporate gravity, springs, externally applied body forces, constraint forces, and contact forces.
Drake has the capability to load multibody models from SDFormat and URDF files. Consider the example below which loads an acrobot model:
As in the example above, for models including visual geometry, collision geometry or both, the user must specify a SceneGraph for geometry handling. You can find a full example of the LQR controlled acrobot in examples/multibody/acrobot/run_lqr.cc.
AddModelFromFile() can be invoked multiple times on the same plant in order to load multiple model instances. Other methods are available on Parser such as AddAllModelsFromFile() which allows creating model instances per each <model>
tag found in the file. Please refer to each of these methods' documentation for further details.
Probably the simplest way to add and wire up a MultibodyPlant with a SceneGraph in your Diagram is using AddMultibodyPlantSceneGraph().
Recommended usages:
Assign to a MultibodyPlant reference (ignoring the SceneGraph):
This flavor is the simplest, when the SceneGraph is not explicitly needed. (It can always be retrieved later via GetSubsystemByName("scene_graph").)
Assign to auto, and use the named public fields:
or taking advantage of C++17's structured binding
This is the easiest way to use both the plant and scene_graph.
Assign to already-declared pointer variables:
This flavor is most useful when the pointers are class member fields (and so perhaps cannot be references).
MultibodyPlant users can register geometry with a SceneGraph for essentially two purposes; a) visualization and, b) contact modeling.
Before any geometry registration takes place, a user must first make a call to RegisterAsSourceForSceneGraph() in order to register the MultibodyPlant as a client of a SceneGraph instance, point at which the plant will have assigned a valid geometry::SourceId. At Finalize(), MultibodyPlant will declare input/output ports as appropriate to communicate with the SceneGraph instance on which registrations took place. All geometry registration must be performed pre-finalize.
Multibodyplant declares an input port for geometric queries, see get_geometry_query_input_port(). If MultibodyPlant registers geometry with a SceneGraph via calls to RegisterCollisionGeometry(), users may use this port for geometric queries. The port must be connected to the same SceneGraph used for registration. The preferred mechanism is to use AddMultibodyPlantSceneGraph() as documented above.
In extraordinary circumstances, this can be done by hand and the setup process will include:
Refer to the documentation provided in each of the methods above for further details.
MultibodyPlant's point contact model looks for model parameters stored as geometry::ProximityProperties by geometry::SceneGraph. These properties can be obtained before or after context creation through geometry::SceneGraphInspector APIs as outlined below. MultibodyPlant expects the following properties for point contact modeling:
Group name | Property Name | Required | Property Type | Property Description |
---|---|---|---|---|
material | coulomb_friction | yes¹ | CoulombFriction<T> | Static and Dynamic friction. |
material | point_contact_stiffness | no² | T | Penalty method stiffness. |
material | hunt_crossley_dissipation | no²⁴ | T | Penalty method dissipation. |
material | relaxation_time | yes³⁴ | T | Parameter for a linear Kelvin–Voigt model of dissipation. |
¹ Collision geometry is required to be registered with a geometry::ProximityProperties object that contains the ("material", "coulomb_friction") property. If the property is missing, MultibodyPlant will throw an exception.
² If the property is missing, MultibodyPlant will use a heuristic value as the default. Refer to the section Penalty method point contact for further details.
³ When using a linear Kelvin–Voigt model of dissipation (for instance when selecting the SAP solver), collision geometry is required to be registered with a geometry::ProximityProperties object that contains the ("material", "relaxation_time") property. If the property is missing, an exception will be thrown.
⁴ We allow to specify both hunt_crossley_dissipation and relaxation_time for a given geometry. However only one of these will get used, depending on the configuration of the MultibodyPlant. As an example, if the SAP solver is specified (see set_discrete_contact_solver()) only the relaxation_time is used while hunt_crossley_dissipation is ignored. Conversely, if the TAMSI solver is used (see set_discrete_contact_solver()) only hunt_crossley_dissipation is used while relaxation_time is ignored. Currently, a continuous MultibodyPlant model will always use the Hunt & Crossley model and relaxation_time will be ignored.
Accessing and modifying contact properties requires interfacing with geometry::SceneGraph's model inspector. Interfacing with a model inspector obtained from geometry::SceneGraph will provide the default registered values for a given parameter. These are the values that will initially appear in a systems::Context created by CreateDefaultContext(). Subsequently, true system parameters can be accessed and changed through a systems::Context once available. For both of the above cases, proximity properties are accessed through geometry::SceneGraphInspector APIs.
Before context creation an inspector can be retrieved directly from SceneGraph as:
After context creation, an inspector can be retrieved from the state stored in the context by the plant's geometry query input port:
Once an inspector is available, proximity properties can be retrieved as:
Several MultibodyElements expose parameters, allowing the user flexible modification of some aspects of the plant's model, post systems::Context creation. For details, refer to the documentation for the MultibodyElement whose parameters you are trying to modify/access (e.g. RigidBody, FixedOffsetFrame, etc.)
As an example, here is how to access and modify rigid body mass parameters:
Another example, working with automatic differentiation in order to take derivatives with respect to one of the bodies' masses:
Add multibody elements to a MultibodyPlant with methods like:
All modeling elements must be added before Finalize() is called. See Finalize stage for a discussion.
Please refer to Contact Modeling in Drake for details on the available approximations, setup, and considerations for a multibody simulation with frictional contact.
MultibodyPlant implements the System energy and power methods, with some limitations.
See Drake issue #12942 for more discussion.
Once the user is done adding modeling elements and registering geometry, a call to Finalize() must be performed. This call will:
T | The scalar type, which must be one of the default scalars. |
#include <drake/multibody/tree/multibody_element.h>
Public Member Functions | |
Does not allow copy, move, or assignment | |
MultibodyPlant (const MultibodyPlant &)=delete | |
MultibodyPlant & | operator= (const MultibodyPlant &)=delete |
MultibodyPlant (MultibodyPlant &&)=delete | |
MultibodyPlant & | operator= (MultibodyPlant &&)=delete |
Input and output ports | |
These methods provide access to the Drake System input and output ports as depicted in the MultibodyPlant class documentation. Actuation values can be provided through a single input port which describes the entire plant, or through multiple input ports which each provide the actuation values for a specific model instance. See AddJointActuator() and num_actuators(). Output ports provide information about the entire MultibodyPlant or its individual model instances. | |
const systems::OutputPort< T > & | get_body_poses_output_port () const |
Returns the output port of all body poses in the world frame. More... | |
const systems::OutputPort< T > & | get_body_spatial_velocities_output_port () const |
Returns the output port of all body spatial velocities in the world frame. More... | |
const systems::OutputPort< T > & | get_body_spatial_accelerations_output_port () const |
Returns the output port of all body spatial accelerations in the world frame. More... | |
const systems::InputPort< T > & | get_actuation_input_port (ModelInstanceIndex model_instance) const |
Returns a constant reference to the input port for external actuation for a specific model instance. More... | |
const systems::InputPort< T > & | get_actuation_input_port () const |
Returns a constant reference to the input port for external actuations for all actuated dofs regardless the number of model instances that have actuated dofs. More... | |
const systems::InputPort< T > & | get_applied_generalized_force_input_port () const |
Returns a constant reference to the vector-valued input port for applied generalized forces, and the vector will be added directly into tau (see System dynamics). More... | |
const systems::InputPort< T > & | get_applied_spatial_force_input_port () const |
Returns a constant reference to the input port for applying spatial forces to bodies in the plant. More... | |
const systems::InputPort< T > & | get_geometry_query_input_port () const |
Returns a constant reference to the input port used to perform geometric queries on a SceneGraph. More... | |
const systems::OutputPort< T > & | get_state_output_port () const |
Returns a constant reference to the output port for the multibody state x = [q, v] of the model. More... | |
const systems::OutputPort< T > & | get_state_output_port (ModelInstanceIndex model_instance) const |
Returns a constant reference to the output port for the state xᵢ = [qᵢ vᵢ] of model instance i. More... | |
const systems::OutputPort< T > & | get_generalized_acceleration_output_port () const |
Returns a constant reference to the output port for generalized accelerations v̇ of the model. More... | |
const systems::OutputPort< T > & | get_generalized_acceleration_output_port (ModelInstanceIndex model_instance) const |
Returns a constant reference to the output port for the generalized accelerations v̇ᵢ ⊆ v̇ for model instance i. More... | |
const systems::OutputPort< T > & | get_generalized_contact_forces_output_port (ModelInstanceIndex model_instance) const |
Returns a constant reference to the output port of generalized contact forces for a specific model instance. More... | |
const systems::OutputPort< T > & | get_reaction_forces_output_port () const |
Returns the port for joint reaction forces. More... | |
const systems::OutputPort< T > & | get_contact_results_output_port () const |
Returns a constant reference to the port that outputs ContactResults. More... | |
const systems::OutputPort< T > & | get_geometry_poses_output_port () const |
Returns the output port of frames' poses to communicate with a SceneGraph. More... | |
Construction | |
To add modeling elements like bodies, joints, force elements, constraints, etc. to a MultibodyPlant, use one of the following construction methods. Once all modeling elements have been added, the Finalize() method must be called. A call to any construction method after a call to Finalize() causes an exception to be thrown. After calling Finalize(), you may invoke MultibodyPlant methods that perform computations. See Finalize() for details. | |
MultibodyPlant (double time_step) | |
This constructor creates a plant with a single "world" body. More... | |
template<typename U > | |
MultibodyPlant (const MultibodyPlant< U > &other) | |
Scalar-converting copy constructor. See System Scalar Conversion. More... | |
const RigidBody< T > & | AddRigidBody (const std::string &name, ModelInstanceIndex model_instance, const SpatialInertia< double > &M_BBo_B) |
Creates a rigid body with the provided name and spatial inertia. More... | |
const RigidBody< T > & | AddRigidBody (const std::string &name, const SpatialInertia< double > &M_BBo_B) |
Creates a rigid body with the provided name and spatial inertia. More... | |
template<template< typename > class FrameType> | |
const FrameType< T > & | AddFrame (std::unique_ptr< FrameType< T >> frame) |
This method adds a Frame of type FrameType<T> . More... | |
template<template< typename Scalar > class JointType> | |
const JointType< T > & | AddJoint (std::unique_ptr< JointType< T >> joint) |
This method adds a Joint of type JointType between two bodies. More... | |
template<template< typename > class JointType, typename... Args> | |
const JointType< T > & | AddJoint (const std::string &name, const Body< T > &parent, const std::optional< math::RigidTransform< double >> &X_PF, const Body< T > &child, const std::optional< math::RigidTransform< double >> &X_BM, Args &&... args) |
This method adds a Joint of type JointType between two bodies. More... | |
const WeldJoint< T > & | WeldFrames (const Frame< T > &frame_on_parent_P, const Frame< T > &frame_on_child_C, const math::RigidTransform< double > &X_PC=math::RigidTransform< double >::Identity()) |
Welds frame_on_parent_P and frame_on_child_C with relative pose X_PC . More... | |
template<template< typename Scalar > class ForceElementType, typename... Args> | |
const ForceElementType< T > & | AddForceElement (Args &&... args) |
Adds a new force element model of type ForceElementType to this MultibodyPlant. More... | |
const JointActuator< T > & | AddJointActuator (const std::string &name, const Joint< T > &joint, double effort_limit=std::numeric_limits< double >::infinity()) |
Creates and adds a JointActuator model for an actuator acting on a given joint . More... | |
ModelInstanceIndex | AddModelInstance (const std::string &name) |
Creates a new model instance. More... | |
void | Finalize () |
This method must be called after all elements in the model (joints, bodies, force elements, constraints, etc.) are added and before any computations are performed. More... | |
Constraints | |
Set of APIs to define constraints. To mention a few important examples, constraints can be used to couple the motion of joints, to create kinematic loops, or to weld bodies together. Currently constraints are only supported for discrete MultibodyPlant models and not for all discrete solvers, see set_discrete_contact_solver(). If the model contains constraints not supported by the discrete solver, the plant will throw an exception at Finalize() time. At this point the user has the option to either change the contact solver with set_discrete_contact_solver() or in the MultibodyPlantConfig, or to re-define the model so that such a constraint is not needed. | |
int | num_constraints () const |
Returns the total number of constraints specified by the user. More... | |
ConstraintIndex | AddCouplerConstraint (const Joint< T > &joint0, const Joint< T > &joint1, const T &gear_ratio, const T &offset=0.0) |
Defines a holonomic constraint between two single-dof joints joint0 and joint1 with positions q₀ and q₁, respectively, such that q₀ = ρ⋅q₁ + Δq, where ρ is the gear ratio and Δq is a fixed offset. More... | |
Geometry | |
The following geometry methods provide a convenient means for associating geometries with bodies. Ultimately, the geometries are owned by SceneGraph. These methods do the work of registering the requested geometries with SceneGraph and maintaining a mapping between the body and the registered data. Particularly, SceneGraph knows nothing about the concepts inherent in the MultibodyPlant. These methods account for those differences as documented below. Geometry registration with rolesGeometries can be associated with bodies via the All geometry registration methods return a geometry::GeometryId GeometryId. This is how SceneGraph refers to the geometries. The properties of an individual geometry can be accessed with its id and geometry::SceneGraphInspector and geometry::QueryObject (for its state-dependent pose in world). Body frames and SceneGraph framesThe first time a geometry registration method is called on a particular body, that body's frame B is registered with SceneGraph. As SceneGraph knows nothing about bodies, in the SceneGraph domain, the frame is simply notated as F; this is merely an alias for the body frame. Thus, the pose of the geometry G in the SceneGraph frame F is the same as the pose of the geometry in the body frame B; The model instance index of the body is passed to the SceneGraph frame as its "frame group". This can be retrieved from the geometry::SceneGraphInspector::GetFrameGroup(FrameId) method. Given a GeometryId, SceneGraph cannot report what body it is affixed to. It can only report the SceneGraph alias frame F. But the following idiom can report the body: const MultibodyPlant<T>& plant = ...; const SceneGraphInspector<T>& inspector = ...; const GeometryId g_id = id_from_some_query; const FrameId f_id = inspector.GetFrameId(g_id); const Body<T>* body = plant.GetBodyFromFrameId(f_id); See documentation of geometry::SceneGraphInspector on where to get an inspector. In MultibodyPlant, frame names only have to be unique in a single model instance. However, SceneGraph knows nothing of model instances. So, to generate unique names for the corresponding frames in SceneGraph, when MultibodyPlant registers the corresponding SceneGraph frame, it is named with a "scoped name". This is a concatenation of | |
geometry::SourceId | RegisterAsSourceForSceneGraph (geometry::SceneGraph< T > *scene_graph) |
Registers this plant to serve as a source for an instance of SceneGraph. More... | |
geometry::GeometryId | RegisterVisualGeometry (const Body< T > &body, const math::RigidTransform< double > &X_BG, const geometry::Shape &shape, const std::string &name, const geometry::IllustrationProperties &properties) |
Registers geometry in a SceneGraph with a given geometry::Shape to be used for visualization of a given body . More... | |
geometry::GeometryId | RegisterVisualGeometry (const Body< T > &body, const math::RigidTransform< double > &X_BG, const geometry::Shape &shape, const std::string &name, const Vector4< double > &diffuse_color) |
Overload for visual geometry registration; it converts the diffuse_color (RGBA with values in the range [0, 1]) into a geometry::DrakeVisualizer-compatible set of geometry::IllustrationProperties. More... | |
geometry::GeometryId | RegisterVisualGeometry (const Body< T > &body, const math::RigidTransform< double > &X_BG, const geometry::Shape &shape, const std::string &name) |
Overload for visual geometry registration; it relies on the downstream geometry::IllustrationProperties consumer to provide default parameter values (see Geometry Queries and Roles for details). More... | |
const std::vector< geometry::GeometryId > & | GetVisualGeometriesForBody (const Body< T > &body) const |
Returns an array of GeometryId's identifying the different visual geometries for body previously registered with a SceneGraph. More... | |
geometry::GeometryId | RegisterCollisionGeometry (const Body< T > &body, const math::RigidTransform< double > &X_BG, const geometry::Shape &shape, const std::string &name, geometry::ProximityProperties properties) |
Registers geometry in a SceneGraph with a given geometry::Shape to be used for the contact modeling of a given body . More... | |
geometry::GeometryId | RegisterCollisionGeometry (const Body< T > &body, const math::RigidTransform< double > &X_BG, const geometry::Shape &shape, const std::string &name, const CoulombFriction< double > &coulomb_friction) |
Overload which specifies a single property: coulomb_friction. More... | |
const std::vector< geometry::GeometryId > & | GetCollisionGeometriesForBody (const Body< T > &body) const |
Returns an array of GeometryId's identifying the different contact geometries for body previously registered with a SceneGraph. More... | |
void | ExcludeCollisionGeometriesWithCollisionFilterGroupPair (const std::pair< std::string, geometry::GeometrySet > &collision_filter_group_a, const std::pair< std::string, geometry::GeometrySet > &collision_filter_group_b) |
Excludes the collision geometries between two given collision filter groups. More... | |
geometry::GeometrySet | CollectRegisteredGeometries (const std::vector< const Body< T > * > &bodies) const |
For each of the provided bodies , collects up all geometries that have been registered to that body. More... | |
const Body< T > * | GetBodyFromFrameId (geometry::FrameId frame_id) const |
Given a geometry frame identifier, returns a pointer to the body associated with that id (nullptr if there is no such body). More... | |
std::optional< geometry::FrameId > | GetBodyFrameIdIfExists (BodyIndex body_index) const |
If the body with body_index belongs to the called plant, it returns the geometry::FrameId associated with it. More... | |
geometry::FrameId | GetBodyFrameIdOrThrow (BodyIndex body_index) const |
If the body with body_index belongs to the called plant, it returns the geometry::FrameId associated with it. More... | |
State accessors and mutators | |
The following state methods allow getting and setting the kinematic state variables
There are also utilities for accessing and mutating portions of state or actuation arrays corresponding to just a single model instance. | |
Eigen::VectorBlock< const VectorX< T > > | GetPositionsAndVelocities (const systems::Context< T > &context) const |
Returns a const vector reference [q; v] to the generalized positions q and generalized velocities v in a given Context. More... | |
VectorX< T > | GetPositionsAndVelocities (const systems::Context< T > &context, ModelInstanceIndex model_instance) const |
Returns a vector [q; v] containing the generalized positions q and generalized velocities v of a specified model instance in a given Context. More... | |
void | GetPositionsAndVelocities (const systems::Context< T > &context, ModelInstanceIndex model_instance, EigenPtr< VectorX< T >> qv_out) const |
(Advanced) Populates output vector qv_out representing the generalized positions q and generalized velocities v of a specified model instance in a given Context. More... | |
Eigen::VectorBlock< VectorX< T > > | GetMutablePositionsAndVelocities (systems::Context< T > *context) const |
(Advanced – see warning) Returns a mutable vector reference [q; v] to the generalized positions q and generalized velocities v in a given Context. More... | |
void | SetPositionsAndVelocities (systems::Context< T > *context, const Eigen::Ref< const VectorX< T >> &q_v) const |
Sets generalized positions q and generalized velocities v in a given Context from a given vector [q; v]. More... | |
void | SetPositionsAndVelocities (systems::Context< T > *context, ModelInstanceIndex model_instance, const Eigen::Ref< const VectorX< T >> &q_v) const |
Sets generalized positions q and generalized velocities v from a given vector [q; v] for a specified model instance in a given Context. More... | |
Eigen::VectorBlock< const VectorX< T > > | GetPositions (const systems::Context< T > &context) const |
Returns a const vector reference to the vector of generalized positions q in a given Context. More... | |
VectorX< T > | GetPositions (const systems::Context< T > &context, ModelInstanceIndex model_instance) const |
Returns a vector containing the generalized positions q of a specified model instance in a given Context. More... | |
void | GetPositions (const systems::Context< T > &context, ModelInstanceIndex model_instance, EigenPtr< VectorX< T >> q_out) const |
(Advanced) Populates output vector q_out with the generalized positions q of a specified model instance in a given Context. More... | |
Eigen::VectorBlock< VectorX< T > > | GetMutablePositions (systems::Context< T > *context) const |
(Advanced – see warning) Returns a mutable vector reference to the generalized positions q in a given Context. More... | |
Eigen::VectorBlock< VectorX< T > > | GetMutablePositions (const systems::Context< T > &context, systems::State< T > *state) const |
(Advanced) Returns a mutable vector reference to the generalized positions q in a given State. More... | |
void | SetPositions (systems::Context< T > *context, const Eigen::Ref< const VectorX< T >> &q) const |
Sets the generalized positions q in a given Context from a given vector. More... | |
void | SetPositions (systems::Context< T > *context, ModelInstanceIndex model_instance, const Eigen::Ref< const VectorX< T >> &q_instance) const |
Sets the generalized positions q for a particular model instance in a given Context from a given vector. More... | |
void | SetPositions (const systems::Context< T > &context, systems::State< T > *state, ModelInstanceIndex model_instance, const Eigen::Ref< const VectorX< T >> &q_instance) const |
(Advanced) Sets the generalized positions q for a particular model instance in a given State from a given vector. More... | |
Eigen::VectorBlock< const VectorX< T > > | GetVelocities (const systems::Context< T > &context) const |
Returns a const vector reference to the generalized velocities v in a given Context. More... | |
VectorX< T > | GetVelocities (const systems::Context< T > &context, ModelInstanceIndex model_instance) const |
Returns a vector containing the generalized velocities v of a specified model instance in a given Context. More... | |
void | GetVelocities (const systems::Context< T > &context, ModelInstanceIndex model_instance, EigenPtr< VectorX< T >> v_out) const |
(Advanced) Populates output vector v_out with the generalized velocities v of a specified model instance in a given Context. More... | |
Eigen::VectorBlock< VectorX< T > > | GetMutableVelocities (systems::Context< T > *context) const |
(Advanced – see warning) Returns a mutable vector reference to the generalized velocities v in a given Context. More... | |
Eigen::VectorBlock< VectorX< T > > | GetMutableVelocities (const systems::Context< T > &context, systems::State< T > *state) const |
(Advanced) Returns a mutable vector reference to the generalized velocities v in a given State. More... | |
void | SetVelocities (systems::Context< T > *context, const Eigen::Ref< const VectorX< T >> &v) const |
Sets the generalized velocities v in a given Context from a given vector. More... | |
void | SetVelocities (systems::Context< T > *context, ModelInstanceIndex model_instance, const Eigen::Ref< const VectorX< T >> &v_instance) const |
Sets the generalized velocities v for a particular model instance in a given Context from a given vector. More... | |
void | SetVelocities (const systems::Context< T > &context, systems::State< T > *state, ModelInstanceIndex model_instance, const Eigen::Ref< const VectorX< T >> &v_instance) const |
(Advanced) Sets the generalized velocities v for a particular model instance in a given State from a given vector. More... | |
void | SetDefaultState (const systems::Context< T > &context, systems::State< T > *state) const override |
Sets state according to defaults set by the user for joints (e.g. More... | |
void | SetRandomState (const systems::Context< T > &context, systems::State< T > *state, RandomGenerator *generator) const override |
Assigns random values to all elements of the state, by drawing samples independently for each joint/free body (coming soon: and then solving a mathematical program to "project" these samples onto the registered system constraints). More... | |
VectorX< T > | GetActuationFromArray (ModelInstanceIndex model_instance, const Eigen::Ref< const VectorX< T >> &u) const |
Returns a vector of actuation values for model_instance from a vector u of actuation values for the entire model. More... | |
void | SetActuationInArray (ModelInstanceIndex model_instance, const Eigen::Ref< const VectorX< T >> &u_instance, EigenPtr< VectorX< T >> u) const |
Given the actuation values u_instance for all actuators in model_instance , this method sets the actuation vector u for the entire model to which this actuator belongs to. More... | |
VectorX< T > | GetPositionsFromArray (ModelInstanceIndex model_instance, const Eigen::Ref< const VectorX< T >> &q) const |
Returns a vector of generalized positions for model_instance from a vector q_array of generalized positions for the entire model model. More... | |
void | GetPositionsFromArray (ModelInstanceIndex model_instance, const Eigen::Ref< const VectorX< T >> &q, EigenPtr< VectorX< T >> q_out) const |
(Advanced) Populates output vector q_out and with the generalized positions for model_instance from a vector q of generalized positions for the entire model. More... | |
void | SetPositionsInArray (ModelInstanceIndex model_instance, const Eigen::Ref< const VectorX< T >> &q_instance, EigenPtr< VectorX< T >> q) const |
Sets the vector of generalized positions for model_instance in q using q_instance , leaving all other elements in the array untouched. More... | |
VectorX< T > | GetVelocitiesFromArray (ModelInstanceIndex model_instance, const Eigen::Ref< const VectorX< T >> &v) const |
Returns a vector of generalized velocities for model_instance from a vector v of generalized velocities for the entire MultibodyPlant model. More... | |
void | GetVelocitiesFromArray (ModelInstanceIndex model_instance, const Eigen::Ref< const VectorX< T >> &v, EigenPtr< VectorX< T >> v_out) const |
(Advanced) Populates output vector v_out with the generalized velocities for model_instance from a vector v of generalized velocities for the entire model. More... | |
void | SetVelocitiesInArray (ModelInstanceIndex model_instance, const Eigen::Ref< const VectorX< T >> &v_instance, EigenPtr< VectorX< T >> v) const |
Sets the vector of generalized velocities for model_instance in v using v_instance , leaving all other elements in the array untouched. More... | |
Working with free bodies | |
A MultibodyPlant user adds sets of Body and Joint objects to | |
std::unordered_set< BodyIndex > | GetFloatingBaseBodies () const |
Returns the set of body indexes corresponding to the free (floating) bodies in the model, in no particular order. More... | |
math::RigidTransform< T > | GetFreeBodyPose (const systems::Context< T > &context, const Body< T > &body) const |
Gets the pose of a given body in the world frame W. More... | |
void | SetFreeBodyPose (systems::Context< T > *context, const Body< T > &body, const math::RigidTransform< T > &X_WB) const |
Sets context to store the pose X_WB of a given body B in the world frame W. More... | |
void | SetFreeBodyPose (const systems::Context< T > &context, systems::State< T > *state, const Body< T > &body, const math::RigidTransform< T > &X_WB) const |
Sets state to store the pose X_WB of a given body B in the world frame W, for a given context of this model. More... | |
void | SetDefaultFreeBodyPose (const Body< T > &body, const math::RigidTransform< double > &X_WB) |
Sets the default pose of body . More... | |
const math::RigidTransform< double > & | GetDefaultFreeBodyPose (const Body< T > &body) const |
Gets the default pose of body as set by SetDefaultFreeBodyPose(). More... | |
void | SetFreeBodySpatialVelocity (systems::Context< T > *context, const Body< T > &body, const SpatialVelocity< T > &V_WB) const |
Sets context to store the spatial velocity V_WB of a given body B in the world frame W. More... | |
void | SetFreeBodySpatialVelocity (const systems::Context< T > &context, systems::State< T > *state, const Body< T > &body, const SpatialVelocity< T > &V_WB) const |
Sets state to store the spatial velocity V_WB of a given body B in the world frame W, for a given context of this model. More... | |
void | SetFreeBodyRandomPositionDistribution (const Body< T > &body, const Vector3< symbolic::Expression > &position) |
Sets the distribution used by SetRandomState() to populate the free body's x-y-z position with respect to World. More... | |
void | SetFreeBodyRandomRotationDistribution (const Body< T > &body, const Eigen::Quaternion< symbolic::Expression > &rotation) |
Sets the distribution used by SetRandomState() to populate the free body's rotation with respect to World. More... | |
void | SetFreeBodyRandomRotationDistributionToUniform (const Body< T > &body) |
Sets the distribution used by SetRandomState() to populate the free body's rotation with respect to World using uniformly random rotations. More... | |
void | SetFreeBodyPoseInWorldFrame (systems::Context< T > *context, const Body< T > &body, const math::RigidTransform< T > &X_WB) const |
Sets context to store the pose X_WB of a given body B in the world frame W. More... | |
void | SetFreeBodyPoseInAnchoredFrame (systems::Context< T > *context, const Frame< T > &frame_F, const Body< T > &body, const math::RigidTransform< T > &X_FB) const |
Updates context to store the pose X_FB of a given body B in a frame F. More... | |
const Body< T > & | GetUniqueFreeBaseBodyOrThrow (ModelInstanceIndex model_instance) const |
If there exists a unique base body that belongs to the model given by model_instance and that unique base body is free (see HasUniqueBaseBody()), return that free body. More... | |
bool | HasUniqueFreeBaseBody (ModelInstanceIndex model_instance) const |
Return true if there exists a unique base body in the model given by model_instance and that unique base body is free. More... | |
Kinematic and dynamic computations | |
These methods return kinematic results for the state supplied in the given Context. Methods whose names being with | |
const math::RigidTransform< T > & | EvalBodyPoseInWorld (const systems::Context< T > &context, const Body< T > &body_B) const |
Evaluate the pose X_WB of a body B in the world frame W. More... | |
const SpatialVelocity< T > & | EvalBodySpatialVelocityInWorld (const systems::Context< T > &context, const Body< T > &body_B) const |
Evaluates V_WB, body B's spatial velocity in the world frame W. More... | |
const SpatialAcceleration< T > & | EvalBodySpatialAccelerationInWorld (const systems::Context< T > &context, const Body< T > &body_B) const |
Evaluates A_WB, body B's spatial acceleration in the world frame W. More... | |
const std::vector< geometry::PenetrationAsPointPair< T > > & | EvalPointPairPenetrations (const systems::Context< T > &context) const |
Evaluates all point pairs of contact for a given state of the model stored in context . More... | |
math::RigidTransform< T > | CalcRelativeTransform (const systems::Context< T > &context, const Frame< T > &frame_F, const Frame< T > &frame_G) const |
Calculates the rigid transform (pose) X_FG relating frame F and frame G. More... | |
math::RotationMatrix< T > | CalcRelativeRotationMatrix (const systems::Context< T > &context, const Frame< T > &frame_F, const Frame< T > &frame_G) const |
Calculates the rotation matrix R_FG relating frame F and frame G. More... | |
void | CalcPointsPositions (const systems::Context< T > &context, const Frame< T > &frame_B, const Eigen::Ref< const MatrixX< T >> &p_BQi, const Frame< T > &frame_A, EigenPtr< MatrixX< T >> p_AQi) const |
Given the positions p_BQi for a set of points Qi measured and expressed in a frame B, this method computes the positions p_AQi(q) of each point Qi in the set as measured and expressed in another frame A, as a function of the generalized positions q of the model. More... | |
T | CalcTotalMass (const systems::Context< T > &context) const |
Calculates the total mass of all bodies in this MultibodyPlant. More... | |
T | CalcTotalMass (const systems::Context< T > &context, const std::vector< ModelInstanceIndex > &model_instances) const |
Calculates the total mass of all bodies contained in model_instances. More... | |
Vector3< T > | CalcCenterOfMassPositionInWorld (const systems::Context< T > &context) const |
Calculates the position vector from the world origin Wo to the center of mass of all bodies in this MultibodyPlant, expressed in the world frame W. More... | |
Vector3< T > | CalcCenterOfMassPositionInWorld (const systems::Context< T > &context, const std::vector< ModelInstanceIndex > &model_instances) const |
Calculates the position vector from the world origin Wo to the center of mass of all non-world bodies contained in model_instances, expressed in the world frame W. More... | |
Vector3< T > | CalcCenterOfMassTranslationalVelocityInWorld (const systems::Context< T > &context) const |
Calculates system center of mass translational velocity in world frame W. More... | |
Vector3< T > | CalcCenterOfMassTranslationalVelocityInWorld (const systems::Context< T > &context, const std::vector< ModelInstanceIndex > &model_instances) const |
Calculates system center of mass translational velocity in world frame W. More... | |
SpatialMomentum< T > | CalcSpatialMomentumInWorldAboutPoint (const systems::Context< T > &context, const Vector3< T > &p_WoP_W) const |
This method returns the spatial momentum of this MultibodyPlant in the world frame W, about a designated point P, expressed in the world frame W. More... | |
SpatialMomentum< T > | CalcSpatialMomentumInWorldAboutPoint (const systems::Context< T > &context, const std::vector< ModelInstanceIndex > &model_instances, const Vector3< T > &p_WoP_W) const |
This method returns the spatial momentum of a set of model instances in the world frame W, about a designated point P, expressed in frame W. More... | |
void | CalcSpatialAccelerationsFromVdot (const systems::Context< T > &context, const VectorX< T > &known_vdot, std::vector< SpatialAcceleration< T >> *A_WB_array) const |
Given the state of this model in context and a known vector of generalized accelerations known_vdot , this method computes the spatial acceleration A_WB for each body as measured and expressed in the world frame W. More... | |
VectorX< T > | CalcInverseDynamics (const systems::Context< T > &context, const VectorX< T > &known_vdot, const MultibodyForces< T > &external_forces) const |
Given the state of this model in context and a known vector of generalized accelerations vdot , this method computes the set of generalized forces tau that would need to be applied in order to attain the specified generalized accelerations. More... | |
void | CalcImplicitTimeDerivativesResidual (const systems::Context< T > &context, const systems::ContinuousState< T > &proposed_derivatives, EigenPtr< VectorX< T >> residual) const |
MultibodyPlant implements the systems::System::CalcImplicitTimeDerivativesResidual method when the plant is modeled as a continuous-time system, returning one residual for each multibody state. More... | |
void | CalcForceElementsContribution (const systems::Context< T > &context, MultibodyForces< T > *forces) const |
Computes the combined force contribution of ForceElement objects in the model. More... | |
VectorX< T > | CalcGravityGeneralizedForces (const systems::Context< T > &context) const |
Computes the generalized forces tau_g(q) due to gravity as a function of the generalized positions q stored in the input context . More... | |
void | MapVelocityToQDot (const systems::Context< T > &context, const Eigen::Ref< const VectorX< T >> &v, EigenPtr< VectorX< T >> qdot) const |
Transforms generalized velocities v to time derivatives qdot of the generalized positions vector q (stored in context ). More... | |
void | MapQDotToVelocity (const systems::Context< T > &context, const Eigen::Ref< const VectorX< T >> &qdot, EigenPtr< VectorX< T >> v) const |
Transforms the time derivative qdot of the generalized positions vector q (stored in context ) to generalized velocities v . More... | |
System matrix computations | |
Methods in this section compute and return various matrices that appear in the system equations of motion. For better performance, prefer to use direct computations where available rather than work with explicit matrices. See Kinematic and dynamics computations for available computations. For example, you can obtain the mass matrix, Coriolis, centripetal, and gyroscopic "bias" terms, and a variety of Jacobian and actuation matrices. | |
void | CalcMassMatrixViaInverseDynamics (const systems::Context< T > &context, EigenPtr< MatrixX< T >> M) const |
Performs the computation of the mass matrix M(q) of the model using inverse dynamics, where the generalized positions q are stored in context . More... | |
void | CalcMassMatrix (const systems::Context< T > &context, EigenPtr< MatrixX< T >> M) const |
Performs the computation of the mass matrix M(q) of the model, as a function of the generalized positions q stored in context . More... | |
void | CalcBiasTerm (const systems::Context< T > &context, EigenPtr< VectorX< T >> Cv) const |
Computes the bias term C(q, v)v containing Coriolis, centripetal, and gyroscopic effects in the multibody equations of motion: More... | |
Matrix3X< T > | CalcBiasTranslationalAcceleration (const systems::Context< T > &context, JacobianWrtVariable with_respect_to, const Frame< T > &frame_B, const Eigen::Ref< const Matrix3X< T >> &p_BoBi_B, const Frame< T > &frame_A, const Frame< T > &frame_E) const |
For each point Bi affixed/welded to a frame B, calculates a𝑠Bias_ABi, Bi's translational acceleration bias in frame A with respect to "speeds" 𝑠, where 𝑠 is either q̇ (time-derivatives of generalized positions) or v (generalized velocities). More... | |
SpatialAcceleration< T > | CalcBiasSpatialAcceleration (const systems::Context< T > &context, JacobianWrtVariable with_respect_to, const Frame< T > &frame_B, const Eigen::Ref< const Vector3< T >> &p_BoBp_B, const Frame< T > &frame_A, const Frame< T > &frame_E) const |
For one point Bp affixed/welded to a frame B, calculates A𝑠Bias_ABp, Bp's spatial acceleration bias in frame A with respect to "speeds" 𝑠, where 𝑠 is either q̇ (time-derivatives of generalized positions) or v (generalized velocities). More... | |
void | CalcJacobianSpatialVelocity (const systems::Context< T > &context, JacobianWrtVariable with_respect_to, const Frame< T > &frame_B, const Eigen::Ref< const Vector3< T >> &p_BoBp_B, const Frame< T > &frame_A, const Frame< T > &frame_E, EigenPtr< MatrixX< T >> Js_V_ABp_E) const |
For one point Bp fixed/welded to a frame B, calculates J𝑠_V_ABp, Bp's spatial velocity Jacobian in frame A with respect to "speeds" 𝑠. More... | |
void | CalcJacobianAngularVelocity (const systems::Context< T > &context, const JacobianWrtVariable with_respect_to, const Frame< T > &frame_B, const Frame< T > &frame_A, const Frame< T > &frame_E, EigenPtr< Matrix3X< T >> Js_w_AB_E) const |
Calculates J𝑠_w_AB, a frame B's angular velocity Jacobian in a frame A with respect to "speeds" 𝑠. More... | |
void | CalcJacobianTranslationalVelocity (const systems::Context< T > &context, JacobianWrtVariable with_respect_to, const Frame< T > &frame_B, const Eigen::Ref< const Matrix3X< T >> &p_BoBi_B, const Frame< T > &frame_A, const Frame< T > &frame_E, EigenPtr< MatrixX< T >> Js_v_ABi_E) const |
For each point Bi affixed/welded to a frame B, calculates J𝑠_v_ABi, Bi's translational velocity Jacobian in frame A with respect to "speeds" 𝑠. More... | |
void | CalcJacobianCenterOfMassTranslationalVelocity (const systems::Context< T > &context, JacobianWrtVariable with_respect_to, const Frame< T > &frame_A, const Frame< T > &frame_E, EigenPtr< Matrix3X< T >> Js_v_ACcm_E) const |
Calculates J𝑠_v_ACcm_E, point Ccm's translational velocity Jacobian in frame A with respect to "speeds" 𝑠, expressed in frame E, where point CCm is the center of mass of the system of all non-world bodies contained in this MultibodyPlant. More... | |
void | CalcJacobianCenterOfMassTranslationalVelocity (const systems::Context< T > &context, const std::vector< ModelInstanceIndex > &model_instances, JacobianWrtVariable with_respect_to, const Frame< T > &frame_A, const Frame< T > &frame_E, EigenPtr< Matrix3X< T >> Js_v_ACcm_E) const |
Calculates J𝑠_v_ACcm_E, point Ccm's translational velocity Jacobian in frame A with respect to "speeds" 𝑠, expressed in frame E, where point CCm is the center of mass of the system of all non-world bodies contained in model_instances. More... | |
Vector3< T > | CalcBiasCenterOfMassTranslationalAcceleration (const systems::Context< T > &context, JacobianWrtVariable with_respect_to, const Frame< T > &frame_A, const Frame< T > &frame_E) const |
Calculates abias_ACcm_E, point Ccm's translational "bias" acceleration term in frame A with respect to "speeds" 𝑠, expressed in frame E, where point Ccm is the composite center of mass of the system of all bodies (except world_body()) in the MultibodyPlant. More... | |
MatrixX< double > | MakeStateSelectorMatrix (const std::vector< JointIndex > &user_to_joint_index_map) const |
This method allows users to map the state of this model, x, into a vector of selected state xₛ with a given preferred ordering. More... | |
MatrixX< double > | MakeActuatorSelectorMatrix (const std::vector< JointActuatorIndex > &user_to_actuator_index_map) const |
This method allows user to map a vector uₛ containing the actuation for a set of selected actuators into the vector u containing the actuation values for this full model. More... | |
MatrixX< T > | MakeActuationMatrix () const |
This method creates an actuation matrix B mapping a vector of actuation values u into generalized forces tau_u = B * u , where B is a matrix of size nv x nu with nu equal to num_actuators() and nv equal to num_velocities(). More... | |
MatrixX< double > | MakeActuatorSelectorMatrix (const std::vector< JointIndex > &user_to_joint_index_map) const |
Alternative signature to build an actuation selector matrix Su such that u = Su⋅uₛ , where u is the vector of actuation values for the full model (ordered by JointActuatorIndex) and uₛ is a vector of actuation values for the actuators acting on the joints listed by user_to_joint_index_map . More... | |
Introspection | |
These methods allow a user to query whether a given multibody element is part of this plant's model. These queries can be performed at any time during the lifetime of a MultibodyPlant model, i.e. there is no restriction on whether they must be called before or after Finalize(). These queries can be performed while new multibody elements are being added to the model. These methods allow a user to retrieve a reference to a multibody element by its name. An exception is thrown if there is no element with the requested name. If the named element is present in more than one model instance and a model instance is not explicitly specified, std::logic_error is thrown. | |
double | time_step () const |
The time step (or period) used to model this plant as a discrete system with periodic updates. More... | |
bool | is_finalized () const |
Returns true if this MultibodyPlant was finalized with a call to Finalize(). More... | |
const RigidBody< T > & | world_body () const |
Returns a constant reference to the world body. More... | |
const BodyFrame< T > & | world_frame () const |
Returns a constant reference to the world frame. More... | |
int | num_bodies () const |
Returns the number of bodies in the model, including the "world" body, which is always part of the model. More... | |
const Body< T > & | get_body (BodyIndex body_index) const |
Returns a constant reference to the body with unique index body_index . More... | |
bool | IsAnchored (const Body< T > &body) const |
Returns true if body is anchored (i.e. More... | |
bool | HasBodyNamed (std::string_view name) const |
int | NumBodiesWithName (std::string_view name) const |
bool | HasBodyNamed (std::string_view name, ModelInstanceIndex model_instance) const |
const Body< T > & | GetBodyByName (std::string_view name) const |
Returns a constant reference to a body that is identified by the string name in this MultibodyPlant. More... | |
const Body< T > & | GetBodyByName (std::string_view name, ModelInstanceIndex model_instance) const |
Returns a constant reference to the body that is uniquely identified by the string name and model_instance in this MultibodyPlant. More... | |
std::vector< BodyIndex > | GetBodyIndices (ModelInstanceIndex model_instance) const |
Returns a list of body indices associated with model_instance . More... | |
const RigidBody< T > & | GetRigidBodyByName (std::string_view name) const |
Returns a constant reference to a rigid body that is identified by the string name in this model. More... | |
const RigidBody< T > & | GetRigidBodyByName (std::string_view name, ModelInstanceIndex model_instance) const |
Returns a constant reference to the rigid body that is uniquely identified by the string name in model_instance . More... | |
std::vector< const Body< T > * > | GetBodiesWeldedTo (const Body< T > &body) const |
Returns all bodies that are transitively welded, or rigidly affixed, to body , per these two definitions: More... | |
int | num_joints () const |
Returns the number of joints in the model. More... | |
const Joint< T > & | get_joint (JointIndex joint_index) const |
Returns a constant reference to the joint with unique index joint_index . More... | |
bool | HasJointNamed (std::string_view name) const |
bool | HasJointNamed (std::string_view name, ModelInstanceIndex model_instance) const |
Joint< T > & | get_mutable_joint (JointIndex joint_index) |
Returns a mutable reference to the joint with unique index joint_index . More... | |
std::vector< JointIndex > | GetJointIndices (ModelInstanceIndex model_instance) const |
Returns a list of joint indices associated with model_instance . More... | |
template<template< typename > class JointType = Joint> | |
const JointType< T > & | GetJointByName (std::string_view name, std::optional< ModelInstanceIndex > model_instance=std::nullopt) const |
Returns a constant reference to a joint that is identified by the string name in this MultibodyPlant. More... | |
template<template< typename > class JointType = Joint> | |
JointType< T > & | GetMutableJointByName (std::string_view name, std::optional< ModelInstanceIndex > model_instance=std::nullopt) |
A version of GetJointByName that returns a mutable reference. More... | |
int | num_frames () const |
Returns the number of Frame objects in this model. More... | |
const Frame< T > & | get_frame (FrameIndex frame_index) const |
Returns a constant reference to the frame with unique index frame_index . More... | |
bool | HasFrameNamed (std::string_view name) const |
bool | HasFrameNamed (std::string_view name, ModelInstanceIndex model_instance) const |
const Frame< T > & | GetFrameByName (std::string_view name) const |
Returns a constant reference to a frame that is identified by the string name in this model. More... | |
const Frame< T > & | GetFrameByName (std::string_view name, ModelInstanceIndex model_instance) const |
Returns a constant reference to the frame that is uniquely identified by the string name in model_instance . More... | |
std::vector< FrameIndex > | GetFrameIndices (ModelInstanceIndex model_instance) const |
Returns a list of frame indices associated with model_instance . More... | |
int | num_actuators () const |
Returns the number of joint actuators in the model. More... | |
int | num_actuated_dofs () const |
Returns the total number of actuated degrees of freedom. More... | |
int | num_actuated_dofs (ModelInstanceIndex model_instance) const |
Returns the total number of actuated degrees of freedom for a specific model instance. More... | |
const JointActuator< T > & | get_joint_actuator (JointActuatorIndex actuator_index) const |
Returns a constant reference to the joint actuator with unique index actuator_index . More... | |
JointActuator< T > & | get_mutable_joint_actuator (JointActuatorIndex actuator_index) const |
Returns a mutable reference to the joint actuator with unique index actuator_index . More... | |
bool | HasJointActuatorNamed (std::string_view name) const |
bool | HasJointActuatorNamed (std::string_view name, ModelInstanceIndex model_instance) const |
const JointActuator< T > & | GetJointActuatorByName (std::string_view name) const |
Returns a constant reference to an actuator that is identified by the string name in this MultibodyPlant. More... | |
const JointActuator< T > & | GetJointActuatorByName (std::string_view name, ModelInstanceIndex model_instance) const |
Returns a constant reference to the actuator that is uniquely identified by the string name and model_instance in this MultibodyPlant. More... | |
int | num_force_elements () const |
Returns the number of ForceElement objects. More... | |
const ForceElement< T > & | get_force_element (ForceElementIndex force_element_index) const |
Returns a constant reference to the force element with unique index force_element_index . More... | |
template<template< typename > class ForceElementType = ForceElement> | |
const ForceElementType< T > & | GetForceElement (ForceElementIndex force_element_index) const |
Returns a constant reference to a force element identified by its unique index in this MultibodyPlant. More... | |
const UniformGravityFieldElement< T > & | gravity_field () const |
An accessor to the current gravity field. More... | |
UniformGravityFieldElement< T > & | mutable_gravity_field () |
A mutable accessor to the current gravity field. More... | |
int | num_model_instances () const |
Returns the number of model instances in the model. More... | |
const std::string & | GetModelInstanceName (ModelInstanceIndex model_instance) const |
Returns the name of a model_instance . More... | |
bool | HasModelInstanceNamed (std::string_view name) const |
ModelInstanceIndex | GetModelInstanceByName (std::string_view name) const |
Returns the index to the model instance that is uniquely identified by the string name in this MultibodyPlant. More... | |
std::string | GetTopologyGraphvizString () const |
Returns a Graphviz string describing the topology of this plant. More... | |
int | num_positions () const |
Returns the size of the generalized position vector q for this model. More... | |
int | num_positions (ModelInstanceIndex model_instance) const |
Returns the size of the generalized position vector qᵢ for model instance i. More... | |
int | num_velocities () const |
Returns the size of the generalized velocity vector v for this model. More... | |
int | num_velocities (ModelInstanceIndex model_instance) const |
Returns the size of the generalized velocity vector vᵢ for model instance i. More... | |
int | num_multibody_states () const |
Returns the size of the multibody system state vector x = [q v]. More... | |
int | num_multibody_states (ModelInstanceIndex model_instance) const |
Returns the size of the multibody system state vector xᵢ = [qᵢ vᵢ] for model instance i. More... | |
VectorX< double > | GetPositionLowerLimits () const |
Returns a vector of size num_positions() containing the lower position limits for every generalized position coordinate. More... | |
VectorX< double > | GetPositionUpperLimits () const |
Upper limit analog of GetPositionsLowerLimits(), where any unbounded or unspecified limits will be +infinity. More... | |
VectorX< double > | GetVelocityLowerLimits () const |
Returns a vector of size num_velocities() containing the lower velocity limits for every generalized velocity coordinate. More... | |
VectorX< double > | GetVelocityUpperLimits () const |
Upper limit analog of GetVelocitysLowerLimits(), where any unbounded or unspecified limits will be +infinity. More... | |
VectorX< double > | GetAccelerationLowerLimits () const |
Returns a vector of size num_velocities() containing the lower acceleration limits for every generalized velocity coordinate. More... | |
VectorX< double > | GetAccelerationUpperLimits () const |
Upper limit analog of GetAccelerationsLowerLimits(), where any unbounded or unspecified limits will be +infinity. More... | |
VectorX< double > | GetEffortLowerLimits () const |
Returns a vector of size num_actuators() containing the lower effort limits for every actuator. More... | |
VectorX< double > | GetEffortUpperLimits () const |
Upper limit analog of GetAccelerationsLowerLimits(), where any unbounded or unspecified limits will be +infinity. More... | |
ContactModel | get_contact_model () const |
Returns the model used for contact. See documentation for ContactModel. More... | |
int | num_visual_geometries () const |
Returns the number of geometries registered for visualization. More... | |
int | num_collision_geometries () const |
Returns the number of geometries registered for contact modeling. More... | |
std::optional< geometry::SourceId > | get_source_id () const |
Returns the unique id identifying this plant as a source for a SceneGraph. More... | |
bool | geometry_source_is_registered () const |
Returns true if this MultibodyPlant was registered with a SceneGraph. More... | |
Friends | |
template<typename U > | |
class | MultibodyPlant |
class | MultibodyPlantTester |
class | internal::MultibodyPlantModelAttorney< T > |
class | internal::MultibodyPlantDiscreteUpdateManagerAttorney< T > |
Related Functions | |
(Note that these are not member functions.) | |
template<typename T > | |
AddMultibodyPlantSceneGraphResult< T > | AddMultibodyPlantSceneGraph (systems::DiagramBuilder< T > *builder, double time_step, std::unique_ptr< geometry::SceneGraph< T >> scene_graph=nullptr) |
Makes a new MultibodyPlant with discrete update period time_step and adds it to a diagram builder together with the provided SceneGraph instance, connecting the geometry ports. More... | |
template<typename T > | |
AddMultibodyPlantSceneGraphResult< T > | AddMultibodyPlantSceneGraph (systems::DiagramBuilder< T > *builder, std::unique_ptr< MultibodyPlant< T >> plant, std::unique_ptr< geometry::SceneGraph< T >> scene_graph=nullptr) |
Adds a MultibodyPlant and a SceneGraph instance to a diagram builder, connecting the geometry ports. More... | |
Contact modeling | |
Use methods in this section to choose the contact model and to provide parameters for that model. Currently Drake supports an advanced compliant contact model we call Hydroelastic contact and a penalty-based point contact model as a reliable fallback. Hydroelastic contactTo understand how material properties enter into the modeling of contact traction in the hydroelastic model, the user is referred to [R. Elandt 2019] for details. For brevity, here we limit ourselves to state the relationship between the material properties and the computation of the normal traction or "pressure" E = Eᵃ⋅Eᵇ/(Eᵃ + Eᵇ), d = E/Eᵃ⋅dᵃ + E/Eᵇ⋅dᵇ = Eᵇ/(Eᵃ+Eᵇ)⋅dᵃ + Eᵃ/(Eᵃ+Eᵇ)⋅dᵇ The effective hydroelastic modulus computation is based on that of the effective elastic modulus in the Hertz theory of contact. Dissipation is weighted in accordance with the fact that the softer material will deform more and faster and thus the softer material dissipation is given more importance. Hydroelastic modulus has units of pressure, i.e.
We use a Hunt & Crossley dissipation model parameterized by a dissipation constant with units of inverse of velocity, i.e. The dissipation can be specified in one of two ways:
The hydroelastic modulus can be specified in one of two ways:
With the effective properties of the pair defined as above, the hydroelastic model pressure field is computed according to: p(x) = E⋅ε(x)⋅(1 - d⋅vₙ(x))₊ where we defined the effective strain: ε(x) = εᵃ(x) + εᵇ(x) which relates to the quasi-static pressure field p₀(x) (i.e. when velocity is neglected) by: p₀(x) = E⋅ε(x) = Eᵃ⋅εᵃ(x) = Eᵇ⋅εᵇ(x) that is, the hydroelastic model computes the contact patch assuming quasi-static equilibrium. The separation speed [Elandt 2019] R. Elandt, E. Drumwright, M. Sherman, and A. Ruina. A pressure field model for fast, robust approximation of net contact force and moment between nominally rigid objects. Proc. IEEE/RSJ Intl. Conf. on Intelligent Robots and Systems (IROS), 2019. Penalty method point contactCurrently MultibodyPlant uses a rigid contact model that is, bodies in the model are infinitely stiff or ideal rigid bodies. Therefore, the mathematical description of the rigid contact model needs to include non-penetration constraints among bodies in the formulation. There are several numerical methods to impose and solve these constraints. In a penalty method approach, we allow for a certain amount of interpenetration and we compute contact forces according to a simple law of the form: fₙ = k(1+dẋ)x where the normal contact force k = (k₁⋅k₂)/(k₁+k₂) d = (k₂/(k₁+k₂))⋅d₁ + (k₁/(k₁+k₂))⋅d₂ These parameters are optional for each geometry. For any geometry not assigned these parameters by a user Pre-Finalize, MultibodyPlant will assign default values such that the combined parameters of two geometries with default values match those estimated using the user-supplied "penetration allowance", as described below. These are ad-hoc parameters which need to be tuned as a trade-off between:
There is no exact procedure for choosing these coefficients, and estimating them manually can be cumbersome since in general they will depend on the scale of the problem including masses, speeds and even body sizes. However, MultibodyPlant aids the estimation of these coefficients using a heuristic function based on a user-supplied "penetration allowance", see set_penetration_allowance(). The penetration allowance is a number in meters that specifies the order of magnitude of the average penetration between bodies in the system that the user is willing to accept as reasonable for the problem being solved. For instance, in the robotics manipulation of ordinary daily objects the user might set this number to 1 millimeter. However, the user might want to increase it for the simulation of heavy walking robots for which an allowance of 1 millimeter would result in a very stiff system. As for the dissipation coefficient in the simple law above, MultibodyPlant chooses the dissipation coefficient d to model inelastic collisions and therefore sets it so that the penetration distance x behaves as a critically damped oscillator. That is, at the limit of ideal rigid contact (very stiff penalty coefficient k or equivalently the penetration allowance goes to zero), this method behaves as a unilateral constraint on the penetration distance, which models a perfect inelastic collision. For most applications, such as manipulation and walking, this is the desired behavior. When set_penetration_allowance() is called, MultibodyPlant will estimate reasonable penalty method coefficients as a function of the input penetration allowance. Users will want to run their simulation a number of times and assess they are satisfied with the level of inter-penetration actually observed in the simulation; if the observed penetration is too large, the user will want to set a smaller penetration allowance. If the system is too stiff and the time integration requires very small time steps while at the same time the user can afford larger inter-penetrations, the user will want to increase the penetration allowance. Typically, the observed penetration will be proportional to the penetration allowance. Thus scaling the penetration allowance by say a factor of 0.5, would typically results in inter-penetrations being reduced by the same factor of 0.5. In summary, users should choose the largest penetration allowance that results in inter-penetration levels that are acceptable for the particular application (even when in theory this penetration should be zero for perfectly rigid bodies.) For a given penetration allowance, the contact interaction that takes two bodies with a non-zero approaching velocity to zero approaching velocity, takes place in a finite amount of time (for ideal rigid contact this time is zero.) A good estimate of this time period is given by a call to get_contact_penalty_method_time_scale(). Users might want to query this value to either set the maximum time step in error-controlled time integration or to set the time step for fixed time step integration. As a guidance, typical fixed time step integrators will become unstable for time steps larger than about a tenth of this time scale. For further details on contact modeling in Drake, please refer to the section Contact Modeling in Drake of our documentation. Modeling DissipationWe use a dissipation model inspired by the model in [Hunt and Crossley, 1975], parameterized by a dissipation constant with units of inverse of velocity, i.e. To be more precise, compliant point contact forces are modeled as a function of state x: f(x) = f₀(x)⋅(1 - d⋅vₙ(x))₊ where here Similarly, Drake's hydroelastic contact model incorporates dissipation at the stress level, rather than forces. That is, pressure p(x) = p₀(x)⋅(1 - d⋅vₙ(x))₊ where [Hunt and Crossley 1975] Hunt, KH and Crossley, FRE, 1975. Coefficient of restitution interpreted as damping in vibroimpact. Journal of Applied Mechanics, vol. 42, pp. 440–445. | |
void | set_contact_model (ContactModel model) |
Sets the contact model to be used by this MultibodyPlant, see ContactModel for available options. More... | |
void | set_discrete_contact_solver (DiscreteContactSolver contact_solver) |
Sets the contact solver type used for discrete MultibodyPlant models. More... | |
DiscreteContactSolver | get_discrete_contact_solver () const |
Returns the contact solver type used for discrete MultibodyPlant models. More... | |
void | set_contact_surface_representation (geometry::HydroelasticContactRepresentation representation) |
Sets the representation of contact surfaces to be used by this MultibodyPlant. More... | |
geometry::HydroelasticContactRepresentation | get_contact_surface_representation () const |
Gets the current representation of contact surfaces used by this MultibodyPlant. More... | |
void | SetContactSolver (std::unique_ptr< contact_solvers::internal::ContactSolver< T >> solver) |
For use only by advanced developers wanting to try out their custom contact solvers. More... | |
void | SetDiscreteUpdateManager (std::unique_ptr< internal::DiscreteUpdateManager< T >> manager) |
For use only by advanced developers wanting to try out their custom time stepping strategies, including contact resolution. More... | |
void | AddPhysicalModel (std::unique_ptr< internal::PhysicalModel< T >> model) |
For use only by advanced developers wanting to try out their new physical models. More... | |
const std::vector< std::unique_ptr< internal::PhysicalModel< T > > > & | physical_models () const |
For use only by advanced developers. More... | |
void | set_penetration_allowance (double penetration_allowance=MultibodyPlantConfig{}.penetration_allowance) |
Sets the penetration allowance used to estimate the coefficients in the penalty method used to impose non-penetration among bodies. More... | |
double | get_contact_penalty_method_time_scale () const |
Returns a time-scale estimate tc based on the requested penetration allowance δ set with set_penetration_allowance(). More... | |
void | set_stiction_tolerance (double v_stiction=MultibodyPlantConfig{}.stiction_tolerance) |
static geometry::HydroelasticContactRepresentation | GetDefaultContactSurfaceRepresentation (double time_step) |
Return the default value for contact representation, given the desired time step. More... | |
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delete |
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delete |
|
explicit |
This constructor creates a plant with a single "world" body.
Therefore, right after creation, num_bodies() returns one.
MultibodyPlant offers two different modalities to model mechanical systems in time. These are:
time_step
is strictly greater than zero.time_step
equals exactly zero.Currently the discrete model is preferred for simulation given its robustness and speed in problems with frictional contact. However this might change as we work towards developing better strategies to model contact. See Choice of Time Advancement Strategy for further details.
[in] | time_step | Indicates whether this plant is modeled as a continuous system (time_step = 0 ) or as a discrete system with periodic updates of period time_step > 0 . See Choice of Time Advancement Strategy for further details. |
time_step = 0
does not support joint limits for simulation, these are ignored. MultibodyPlant prints a warning to console if joint limits are provided. If your simulation requires joint limits currently you must use a discrete MultibodyPlant model.std::exception | if time_step is negative. |
|
explicit |
Scalar-converting copy constructor. See System Scalar Conversion.
ConstraintIndex AddCouplerConstraint | ( | const Joint< T > & | joint0, |
const Joint< T > & | joint1, | ||
const T & | gear_ratio, | ||
const T & | offset = 0.0 |
||
) |
Defines a holonomic constraint between two single-dof joints joint0
and joint1
with positions q₀ and q₁, respectively, such that q₀ = ρ⋅q₁ + Δq, where ρ is the gear ratio and Δq is a fixed offset.
The gear ratio can have units if the units of q₀ and q₁ are different. For instance, between a prismatic and a revolute joint the gear ratio will specify the "pitch" of the resulting mechanism. As defined, offset
has units of q₀
.
if | joint0 and joint1 are not both single-dof joints. |
std::exception | if the MultibodyPlant has already been finalized. |
const ForceElementType<T>& AddForceElement | ( | Args &&... | args | ) |
Adds a new force element model of type ForceElementType
to this
MultibodyPlant.
The arguments to this method args
are forwarded to ForceElementType
's constructor.
[in] | args | Zero or more parameters provided to the constructor of the new force element. It must be the case that ForceElementType<T>(args) is a valid constructor. |
ForceElementType | The type of the ForceElement to add. As there is always a UniformGravityFieldElement present (accessible through gravity_field()), an exception will be thrown if this function is called to add another UniformGravityFieldElement. |
ForceElementType<T>
specialized on the scalar type T of this
MultibodyPlant. It will remain valid for the lifetime of this
MultibodyPlant. const FrameType<T>& AddFrame | ( | std::unique_ptr< FrameType< T >> | frame | ) |
This method adds a Frame of type FrameType<T>
.
For more information, please see the corresponding constructor of FrameType
.
FrameType | Template which will be instantiated on T . |
frame | Unique pointer frame instance. |
this
MultibodyPlant. const JointType<T>& AddJoint | ( | std::unique_ptr< JointType< T >> | joint | ) |
This method adds a Joint of type JointType
between two bodies.
For more information, see the below overload of AddJoint<>
.
const JointType<T>& AddJoint | ( | const std::string & | name, |
const Body< T > & | parent, | ||
const std::optional< math::RigidTransform< double >> & | X_PF, | ||
const Body< T > & | child, | ||
const std::optional< math::RigidTransform< double >> & | X_BM, | ||
Args &&... | args | ||
) |
This method adds a Joint of type JointType
between two bodies.
The two bodies connected by this Joint object are referred to as parent and child bodies. The parent/child ordering defines the sign conventions for the generalized coordinates and the coordinate ordering for multi-DOF joints.
Note: The previous figure also shows Pcm which is body P's center of mass and point Bcm which is body B's center of mass.
As explained in the Joint class's documentation, in Drake we define a frame F attached to the parent body P with pose X_PF
and a frame M attached to the child body B with pose X_BM
. This method helps creating a joint between two bodies with fixed poses X_PF
and X_BM
. Refer to the Joint class's documentation for more details.
name | A string that uniquely identifies the new joint to be added to this model. A std::runtime_error is thrown if a joint named name already is part of the model. See HasJointNamed(), Joint::name(). | |
[in] | parent | The parent body connected by the new joint. |
[in] | X_PF | The fixed pose of frame F attached to the parent body, measured in the frame P of that body. X_PF is an optional parameter; empty curly braces {} imply that frame F is the same body frame P. If instead your intention is to make a frame F with pose X_PF equal to the identity pose, provide RigidTransform<double>::Identity() as your input. When non-nullopt, adds a FixedOffsetFrame named {name}_parent . |
[in] | child | The child body connected by the new joint. |
[in] | X_BM | The fixed pose of frame M attached to the child body, measured in the frame B of that body. X_BM is an optional parameter; empty curly braces {} imply that frame M is the same body frame B. If instead your intention is to make a frame M with pose X_BM equal to the identity pose, provide RigidTransform<double>::Identity() as your input. When non-nullopt, adds a FixedOffsetFrame named {name}_child . |
[in] | args | Zero or more parameters provided to the constructor of the new joint. It must be the case that JointType<T>( const std::string&, const Frame<T>&, const Frame<T>&, args) is a valid constructor. |
JointType | The type of the Joint to add. |
JointType<T>
specialized on the scalar type T of this
MultibodyPlant. It will remain valid for the lifetime of this
MultibodyPlant.Example of usage:
std::exception | if this MultibodyPlant already contains a joint with the given name . See HasJointNamed(), Joint::name(). |
const JointActuator<T>& AddJointActuator | ( | const std::string & | name, |
const Joint< T > & | joint, | ||
double | effort_limit = std::numeric_limits<double>::infinity() |
||
) |
Creates and adds a JointActuator model for an actuator acting on a given joint
.
This method returns a constant reference to the actuator just added, which will remain valid for the lifetime of this
plant.
[in] | name | A string that uniquely identifies the new actuator to be added to this model. A std::runtime_error is thrown if an actuator with the same name already exists in the model. See HasJointActuatorNamed(). |
[in] | joint | The Joint to be actuated by the new JointActuator. |
[in] | effort_limit | The maximum effort for the actuator. It must be strictly positive, otherwise an std::exception is thrown. If +∞, the actuator has no limit, which is the default. The effort limit has physical units in accordance to the joint type it actuates. For instance, it will have units of N⋅m (torque) for revolute joints while it will have units of N (force) for prismatic joints. |
this
plant. std::exception | if joint.num_velocities() > 1 since for now we only support actuators for single dof joints. |
ModelInstanceIndex AddModelInstance | ( | const std::string & | name | ) |
Creates a new model instance.
Returns the index for the model instance.
[in] | name | A string that uniquely identifies the new instance to be added to this model. An exception is thrown if an instance with the same name already exists in the model. See HasModelInstanceNamed(). |
void AddPhysicalModel | ( | std::unique_ptr< internal::PhysicalModel< T >> | model | ) |
For use only by advanced developers wanting to try out their new physical models.
With this method MultibodyPlant takes ownership of model
and calls its DeclareSystemResources() method at Finalize(), giving specific physical model implementations a chance to declare the system resources it needs.
model | After this call the model is owned by this MultibodyPlant. |
std::exception | if called post-finalize. See Finalize(). |
this
MultibodyPlant will no longer support scalar conversion to or from symbolic::Expression after a call to this method. const RigidBody<T>& AddRigidBody | ( | const std::string & | name, |
ModelInstanceIndex | model_instance, | ||
const SpatialInertia< double > & | M_BBo_B | ||
) |
Creates a rigid body with the provided name and spatial inertia.
This method returns a constant reference to the body just added, which will remain valid for the lifetime of this
MultibodyPlant.
Example of usage:
[in] | name | A string that identifies the new body to be added to this model. A std::runtime_error is thrown if a body named name already is part of model_instance . See HasBodyNamed(), Body::name(). |
[in] | model_instance | A model instance index which this body is part of. |
[in] | M_BBo_B | The SpatialInertia of the new rigid body to be added to this MultibodyPlant, computed about the body frame origin Bo and expressed in the body frame B. |
this
MultibodyPlant. const RigidBody<T>& AddRigidBody | ( | const std::string & | name, |
const SpatialInertia< double > & | M_BBo_B | ||
) |
Creates a rigid body with the provided name and spatial inertia.
This method returns a constant reference to the body just added, which will remain valid for the lifetime of this
MultibodyPlant. The body will use the default model instance (more on model instances).
Example of usage:
[in] | name | A string that identifies the new body to be added to this model. A std::runtime_error is thrown if a body named name already is part of the model in the default model instance. See HasBodyNamed(), Body::name(). |
[in] | M_BBo_B | The SpatialInertia of the new rigid body to be added to this MultibodyPlant, computed about the body frame origin Bo and expressed in the body frame B. |
this
MultibodyPlant. std::exception | if additional model instances have been created beyond the world and default instances. |
Vector3<T> CalcBiasCenterOfMassTranslationalAcceleration | ( | const systems::Context< T > & | context, |
JacobianWrtVariable | with_respect_to, | ||
const Frame< T > & | frame_A, | ||
const Frame< T > & | frame_E | ||
) | const |
Calculates abias_ACcm_E, point Ccm's translational "bias" acceleration term in frame A with respect to "speeds" 𝑠, expressed in frame E, where point Ccm is the composite center of mass of the system of all bodies (except world_body()) in the MultibodyPlant.
abias_ACcm is the part of a_ACcm (Ccm's translational acceleration) that does not multiply ṡ, equal to abias_ACcm = J̇𝑠_v_ACcm ⋅ s. This allows a_ACcm to be written as a_ACcm = J𝑠_v_ACcm ⋅ ṡ + abias_ACcm.
[in] | context | The state of the multibody system. |
[in] | with_respect_to | Enum equal to JacobianWrtVariable::kQDot or JacobianWrtVariable::kV, indicating whether the Jacobian abias_ACcm is partial derivatives with respect to 𝑠 = q̇ (time-derivatives of generalized positions) or with respect to 𝑠 = v (generalized velocities). |
[in] | frame_A | The frame in which abias_ACcm is measured. |
[in] | frame_E | The frame in which abias_ACcm is expressed on output. |
abias_ACcm_E | Point Ccm's translational "bias" acceleration term in frame A with respect to "speeds" 𝑠, expressed in frame E. |
std::exception | if Ccm does not exist, which occurs if there are no massive bodies in MultibodyPlant (except world_body()). |
std::exception | if composite_mass <= 0, where composite_mass is the total mass of all bodies except world_body() in MultibodyPlant. |
std::exception | if frame_A is not the world frame. |
SpatialAcceleration<T> CalcBiasSpatialAcceleration | ( | const systems::Context< T > & | context, |
JacobianWrtVariable | with_respect_to, | ||
const Frame< T > & | frame_B, | ||
const Eigen::Ref< const Vector3< T >> & | p_BoBp_B, | ||
const Frame< T > & | frame_A, | ||
const Frame< T > & | frame_E | ||
) | const |
For one point Bp affixed/welded to a frame B, calculates A𝑠Bias_ABp, Bp's spatial acceleration bias in frame A with respect to "speeds" 𝑠, where 𝑠 is either q̇ (time-derivatives of generalized positions) or v (generalized velocities).
A𝑠Bias_ABp is the term in A_ABp (Bp's spatial acceleration in A) that does not include 𝑠̇, i.e., A𝑠Bias_ABp is Bi's translational acceleration in A when 𝑠̇ = 0.
A_ABp = J𝑠_V_ABp ⋅ 𝑠̇ + J̇𝑠_V_ABp ⋅ 𝑠 (𝑠 = q̇ or 𝑠 = v), hence A𝑠Bias_ABp = J̇𝑠_V_ABp ⋅ 𝑠
where J𝑠_V_ABp is Bp's spatial velocity Jacobian in frame A for speeds s (see CalcJacobianSpatialVelocity() for details on J𝑠_V_ABp).
[in] | context | The state of the multibody system. |
[in] | with_respect_to | Enum equal to JacobianWrtVariable::kQDot or JacobianWrtVariable::kV, indicating whether the spatial accceleration bias is with respect to 𝑠 = q̇ or 𝑠 = v. |
[in] | frame_B | The frame on which point Bp is affixed/welded. |
[in] | p_BoBp_B | Position vector from Bo (frame_B's origin) to point Bp (regarded as affixed/welded to B), expressed in frame_B. |
[in] | frame_A | The frame that measures A𝑠Bias_ABp. Currently, an exception is thrown if frame_A is not the World frame. |
[in] | frame_E | The frame in which A𝑠Bias_ABp is expressed on output. |
V_ABp = J𝑠_V_ABp ⋅ 𝑠 which upon vector differentiation in A gives A_ABp = J𝑠_V_ABp ⋅ 𝑠̇ + J̇𝑠_V_ABp ⋅ 𝑠 Since J̇𝑠_V_ABp is linear in 𝑠, A𝑠Bias_ABp = J̇𝑠_V_ABp ⋅ 𝑠 is quadratic in 𝑠.
std::exception | if with_respect_to is not JacobianWrtVariable::kV |
std::exception | if frame_A is not the world frame. |
void CalcBiasTerm | ( | const systems::Context< T > & | context, |
EigenPtr< VectorX< T >> | Cv | ||
) | const |
Computes the bias term C(q, v)v
containing Coriolis, centripetal, and gyroscopic effects in the multibody equations of motion:
M(q) v̇ + C(q, v) v = tau_app + ∑ (Jv_V_WBᵀ(q) ⋅ Fapp_Bo_W)
where M(q)
is the multibody model's mass matrix and tau_app
is a vector of generalized forces. The last term is a summation over all bodies of the dot-product of Fapp_Bo_W
(applied spatial force on body B at Bo) with Jv_V_WB(q)
(B's spatial Jacobian in world W with respect to generalized velocities v). Note: B's spatial velocity in W can be written V_WB = Jv_V_WB * v
.
[in] | context | The context containing the state of the model. It stores the generalized positions q and the generalized velocities v. |
[out] | Cv | On output, Cv will contain the product C(q, v)v . It must be a valid (non-null) pointer to a column vector in ℛⁿ with n the number of generalized velocities (num_velocities()) of the model. This method aborts if Cv is nullptr or if it does not have the proper size. |
Matrix3X<T> CalcBiasTranslationalAcceleration | ( | const systems::Context< T > & | context, |
JacobianWrtVariable | with_respect_to, | ||
const Frame< T > & | frame_B, | ||
const Eigen::Ref< const Matrix3X< T >> & | p_BoBi_B, | ||
const Frame< T > & | frame_A, | ||
const Frame< T > & | frame_E | ||
) | const |
For each point Bi affixed/welded to a frame B, calculates a𝑠Bias_ABi, Bi's translational acceleration bias in frame A with respect to "speeds" 𝑠, where 𝑠 is either q̇ (time-derivatives of generalized positions) or v (generalized velocities).
a𝑠Bias_ABi is the term in a_ABi (Bi's translational acceleration in A) that does not include 𝑠̇, i.e., a𝑠Bias_ABi is Bi's translational acceleration in A when 𝑠̇ = 0.
a_ABi = J𝑠_v_ABi ⋅ 𝑠̇ + J̇𝑠_v_ABi ⋅ 𝑠 (𝑠 = q̇ or 𝑠 = v), hence a𝑠Bias_ABi = J̇𝑠_v_ABi ⋅ 𝑠
where J𝑠_v_ABi is Bi's translational velocity Jacobian in frame A for s (see CalcJacobianTranslationalVelocity() for details on J𝑠_v_ABi).
[in] | context | The state of the multibody system. |
[in] | with_respect_to | Enum equal to JacobianWrtVariable::kQDot or JacobianWrtVariable::kV, indicating whether the translational acceleration bias is with respect to 𝑠 = q̇ or 𝑠 = v. |
[in] | frame_B | The frame on which points Bi are affixed/welded. |
[in] | p_BoBi_B | A position vector or list of p position vectors from Bo (frame_B's origin) to points Bi (regarded as affixed to B), where each position vector is expressed in frame_B. Each column in the 3 x p matrix p_BoBi_B corresponds to a position vector. |
[in] | frame_A | The frame that measures a𝑠Bias_ABi. Currently, an exception is thrown if frame_A is not the World frame. |
[in] | frame_E | The frame in which a𝑠Bias_ABi is expressed on output. |
3 x p
matrix, where p is the number of points Bi. v_ABi = J𝑠_v_ABi ⋅ 𝑠 which upon vector differentiation in A gives a_ABi = J𝑠_v_ABi ⋅ 𝑠̇ + J̇𝑠_v_ABi ⋅ 𝑠 Since J̇𝑠_v_ABi is linear in 𝑠, a𝑠Bias_ABi = J̇𝑠_v_ABi ⋅ 𝑠 is quadratic in 𝑠.
std::exception | if with_respect_to is not JacobianWrtVariable::kV |
std::exception | if frame_A is not the world frame. |
Vector3<T> CalcCenterOfMassPositionInWorld | ( | const systems::Context< T > & | context | ) | const |
Calculates the position vector from the world origin Wo to the center of mass of all bodies in this MultibodyPlant, expressed in the world frame W.
[in] | context | Contains the state of the model. |
p_WoScm_W | position vector from Wo to Scm expressed in world frame W, where Scm is the center of mass of the system S stored by this plant. |
std::exception | if this has no body except world_body(). |
std::exception | if mₛ ≤ 0 (where mₛ is the mass of system S). |
Vector3<T> CalcCenterOfMassPositionInWorld | ( | const systems::Context< T > & | context, |
const std::vector< ModelInstanceIndex > & | model_instances | ||
) | const |
Calculates the position vector from the world origin Wo to the center of mass of all non-world bodies contained in model_instances, expressed in the world frame W.
[in] | context | Contains the state of the model. |
[in] | model_instances | Vector of selected model instances. If a model instance is repeated in the vector (unusual), it is only counted once. |
p_WoScm_W | position vector from world origin Wo to Scm expressed in the world frame W, where Scm is the center of mass of the system S of non-world bodies contained in model_instances. |
std::exception | if model_instances is empty or only has world body. |
std::exception | if mₛ ≤ 0 (where mₛ is the mass of system S). |
Vector3<T> CalcCenterOfMassTranslationalVelocityInWorld | ( | const systems::Context< T > & | context | ) | const |
Calculates system center of mass translational velocity in world frame W.
[in] | context | The context contains the state of the model. |
v_WScm_W | Scm's translational velocity in frame W, expressed in W, where Scm is the center of mass of the system S stored by this plant. |
std::exception | if this has no body except world_body(). |
std::exception | if mₛ ≤ 0 (where mₛ is the mass of system S). |
Vector3<T> CalcCenterOfMassTranslationalVelocityInWorld | ( | const systems::Context< T > & | context, |
const std::vector< ModelInstanceIndex > & | model_instances | ||
) | const |
Calculates system center of mass translational velocity in world frame W.
[in] | context | The context contains the state of the model. |
[in] | model_instances | Vector of selected model instances. If a model instance is repeated in the vector (unusual), it is only counted once. |
v_WScm_W | Scm's translational velocity in frame W, expressed in W, where Scm is the center of mass of the system S of non-world bodies contained in model_instances. |
std::exception | if model_instances is empty or only has world body. |
std::exception | if mₛ ≤ 0 (where mₛ is the mass of system S). |
void CalcForceElementsContribution | ( | const systems::Context< T > & | context, |
MultibodyForces< T > * | forces | ||
) | const |
Computes the combined force contribution of ForceElement objects in the model.
A ForceElement can apply forces as a spatial force per body or as generalized forces, depending on the ForceElement model. ForceElement contributions are a function of the state and time only. The output from this method can immediately be used as input to CalcInverseDynamics() to include the effect of applied forces by force elements.
[in] | context | The context containing the state of this model. |
[out] | forces | A pointer to a valid, non nullptr, multibody forces object. On output forces will store the forces exerted by all the ForceElement objects in the model. |
std::exception | if forces is null or not compatible with this model, per MultibodyForces::CheckInvariants(). |
VectorX<T> CalcGravityGeneralizedForces | ( | const systems::Context< T > & | context | ) | const |
Computes the generalized forces tau_g(q)
due to gravity as a function of the generalized positions q
stored in the input context
.
The vector of generalized forces due to gravity tau_g(q)
is defined such that it appears on the right hand side of the equations of motion together with any other generalized forces, like so:
Mv̇ + C(q, v)v = tau_g(q) + tau_app
where tau_app
includes any other generalized forces applied on the system.
[in] | context | The context storing the state of the model. |
v
for this
so that the inner product v⋅tau_g
corresponds to the power applied by the gravity forces on the mechanical system. That is, v⋅tau_g > 0
corresponds to potential energy going into the system, as either mechanical kinetic energy, some other potential energy, or heat, and therefore to a decrease of the gravitational potential energy. void CalcImplicitTimeDerivativesResidual | ( | const systems::Context< T > & | context, |
const systems::ContinuousState< T > & | proposed_derivatives, | ||
EigenPtr< VectorX< T >> | residual | ||
) | const |
MultibodyPlant implements the systems::System::CalcImplicitTimeDerivativesResidual method when the plant is modeled as a continuous-time system, returning one residual for each multibody state.
In particular, the first num_positions() residuals are given by
q̇_proposed - N(q)⋅v
and the final num_velocities() residuals are given by
CalcInverseDynamics(context, v_proposed)
including all actuator and applied forces.
VectorX<T> CalcInverseDynamics | ( | const systems::Context< T > & | context, |
const VectorX< T > & | known_vdot, | ||
const MultibodyForces< T > & | external_forces | ||
) | const |
Given the state of this model in context
and a known vector of generalized accelerations vdot
, this method computes the set of generalized forces tau
that would need to be applied in order to attain the specified generalized accelerations.
Mathematically, this method computes:
tau = M(q)v̇ + C(q, v)v - tau_app - ∑ J_WBᵀ(q) Fapp_Bo_W
where M(q)
is the model's mass matrix, C(q, v)v
is the bias term containing Coriolis and gyroscopic effects and tau_app
consists of a vector applied generalized forces. The last term is a summation over all bodies in the model where Fapp_Bo_W
is an applied spatial force on body B at Bo
which gets projected into the space of generalized forces with the transpose of Jv_V_WB(q)
(where Jv_V_WB
is B's spatial velocity Jacobian in W with respect to generalized velocities v). Note: B's spatial velocity in W can be written as V_WB = Jv_V_WB * v
. This method does not compute explicit expressions for the mass matrix nor for the bias term, which would be of at least O(n²)
complexity, but it implements an O(n)
Newton-Euler recursive algorithm, where n is the number of bodies in the model. The explicit formation of the mass matrix M(q)
would require the calculation of O(n²)
entries while explicitly forming the product C(q, v) * v
could require up to O(n³)
operations (see [Featherstone 1987, §4]), depending on the implementation. The recursive Newton-Euler algorithm is the most efficient currently known general method for solving inverse dynamics [Featherstone 2008].
[in] | context | The context containing the state of the model. |
[in] | known_vdot | A vector with the known generalized accelerations vdot for the full model. Use the provided Joint APIs in order to access entries into this array. |
[in] | external_forces | A set of forces to be applied to the system either as body spatial forces Fapp_Bo_W or generalized forces tau_app , see MultibodyForces for details. |
known_vdot
. void CalcJacobianAngularVelocity | ( | const systems::Context< T > & | context, |
const JacobianWrtVariable | with_respect_to, | ||
const Frame< T > & | frame_B, | ||
const Frame< T > & | frame_A, | ||
const Frame< T > & | frame_E, | ||
EigenPtr< Matrix3X< T >> | Js_w_AB_E | ||
) | const |
Calculates J𝑠_w_AB, a frame B's angular velocity Jacobian in a frame A with respect to "speeds" 𝑠.
J𝑠_w_AB ≜ [ ∂(w_AB)/∂𝑠₁, ... ∂(w_AB)/∂𝑠ₙ ] (n is j or k) w_AB = J𝑠_w_AB ⋅ 𝑠 w_AB is linear in 𝑠 ≜ [𝑠₁ ... 𝑠ₙ]ᵀ
w_AB
is B's angular velocity in frame A and "speeds" 𝑠 is either q̇ ≜ [q̇₁ ... q̇ⱼ]ᵀ (time-derivatives of j generalized positions) or v ≜ [v₁ ... vₖ]ᵀ (k generalized velocities).
[in] | context | The state of the multibody system. |
[in] | with_respect_to | Enum equal to JacobianWrtVariable::kQDot or JacobianWrtVariable::kV, indicating whether the Jacobian J𝑠_w_AB is partial derivatives with respect to 𝑠 = q̇ (time-derivatives of generalized positions) or with respect to 𝑠 = v (generalized velocities). |
[in] | frame_B | The frame B in w_AB (B's angular velocity in A). |
[in] | frame_A | The frame A in w_AB (B's angular velocity in A). |
[in] | frame_E | The frame in which w_AB is expressed on input and the frame in which the Jacobian J𝑠_w_AB is expressed on output. |
[out] | J𝑠_w_AB_E | Frame B's angular velocity Jacobian in frame A with respect to speeds 𝑠 (which is either q̇ or v), expressed in frame E. The Jacobian is a function of only generalized positions q (which are pulled from the context). The previous definition shows J𝑠_w_AB_E is a matrix of size 3 x n , where n is the number of elements in 𝑠. |
std::exception | if J𝑠_w_AB_E is nullptr or not of size 3 x n . |
void CalcJacobianCenterOfMassTranslationalVelocity | ( | const systems::Context< T > & | context, |
JacobianWrtVariable | with_respect_to, | ||
const Frame< T > & | frame_A, | ||
const Frame< T > & | frame_E, | ||
EigenPtr< Matrix3X< T >> | Js_v_ACcm_E | ||
) | const |
Calculates J𝑠_v_ACcm_E, point Ccm's translational velocity Jacobian in frame A with respect to "speeds" 𝑠, expressed in frame E, where point CCm is the center of mass of the system of all non-world bodies contained in this
MultibodyPlant.
[in] | context | contains the state of the model. |
[in] | with_respect_to | Enum equal to JacobianWrtVariable::kQDot or JacobianWrtVariable::kV, indicating whether the Jacobian J𝑠_v_ACcm_E is partial derivatives with respect to 𝑠 = q̇ (time-derivatives of generalized positions) or with respect to 𝑠 = v (generalized velocities). |
[in] | frame_A | The frame in which the translational velocity v_ACcm and its Jacobian J𝑠_v_ACcm are measured. |
[in] | frame_E | The frame in which the Jacobian J𝑠_v_ACcm is expressed on output. |
[out] | J𝑠_v_ACcm_E | Point Ccm's translational velocity Jacobian in frame A with respect to speeds 𝑠 (𝑠 = q̇ or 𝑠 = v), expressed in frame E. J𝑠_v_ACcm_E is a 3 x n matrix, where n is the number of elements in 𝑠. The Jacobian is a function of only generalized positions q (which are pulled from the context). |
std::exception | if CCm does not exist, which occurs if there are no massive bodies in MultibodyPlant (except world_body()). |
std::exception | if mₛ ≤ 0 (where mₛ is the mass of all non-world bodies contained in this MultibodyPlant). |
void CalcJacobianCenterOfMassTranslationalVelocity | ( | const systems::Context< T > & | context, |
const std::vector< ModelInstanceIndex > & | model_instances, | ||
JacobianWrtVariable | with_respect_to, | ||
const Frame< T > & | frame_A, | ||
const Frame< T > & | frame_E, | ||
EigenPtr< Matrix3X< T >> | Js_v_ACcm_E | ||
) | const |
Calculates J𝑠_v_ACcm_E, point Ccm's translational velocity Jacobian in frame A with respect to "speeds" 𝑠, expressed in frame E, where point CCm is the center of mass of the system of all non-world bodies contained in model_instances.
[in] | context | contains the state of the model. |
[in] | model_instances | Vector of selected model instances. If a model instance is repeated in the vector (unusual), it is only counted once. |
[in] | with_respect_to | Enum equal to JacobianWrtVariable::kQDot or JacobianWrtVariable::kV, indicating whether the Jacobian J𝑠_v_ACcm_E is partial derivatives with respect to 𝑠 = q̇ (time-derivatives of generalized positions) or with respect to 𝑠 = v (generalized velocities). |
[in] | frame_A | The frame in which the translational velocity v_ACcm and its Jacobian J𝑠_v_ACcm are measured. |
[in] | frame_E | The frame in which the Jacobian J𝑠_v_ACcm is expressed on output. |
[out] | J𝑠_v_ACcm_E | Point Ccm's translational velocity Jacobian in frame A with respect to speeds 𝑠 (𝑠 = q̇ or 𝑠 = v), expressed in frame E. J𝑠_v_ACcm_E is a 3 x n matrix, where n is the number of elements in 𝑠. The Jacobian is a function of only generalized positions q (which are pulled from the context). |
std::exception | if mₛ ≤ 0 (where mₛ is the mass of all non-world bodies contained in model_instances). |
std::exception | if model_instances is empty or only has world body. |
void CalcJacobianSpatialVelocity | ( | const systems::Context< T > & | context, |
JacobianWrtVariable | with_respect_to, | ||
const Frame< T > & | frame_B, | ||
const Eigen::Ref< const Vector3< T >> & | p_BoBp_B, | ||
const Frame< T > & | frame_A, | ||
const Frame< T > & | frame_E, | ||
EigenPtr< MatrixX< T >> | Js_V_ABp_E | ||
) | const |
For one point Bp fixed/welded to a frame B, calculates J𝑠_V_ABp, Bp's spatial velocity Jacobian in frame A with respect to "speeds" 𝑠.
J𝑠_V_ABp ≜ [ ∂(V_ABp)/∂𝑠₁, ... ∂(V_ABp)/∂𝑠ₙ ] (n is j or k) V_ABp = J𝑠_V_ABp ⋅ 𝑠 V_ABp is linear in 𝑠 ≜ [𝑠₁ ... 𝑠ₙ]ᵀ
V_ABp
is Bp's spatial velocity in frame A and "speeds" 𝑠 is either q̇ ≜ [q̇₁ ... q̇ⱼ]ᵀ (time-derivatives of j generalized positions) or v ≜ [v₁ ... vₖ]ᵀ (k generalized velocities).
[in] | context | The state of the multibody system. |
[in] | with_respect_to | Enum equal to JacobianWrtVariable::kQDot or JacobianWrtVariable::kV, indicating whether the Jacobian J𝑠_V_ABp is partial derivatives with respect to 𝑠 = q̇ (time-derivatives of generalized positions) or with respect to 𝑠 = v (generalized velocities). |
[in] | frame_B | The frame on which point Bp is fixed/welded. |
[in] | p_BoBp_B | A position vector from Bo (frame_B's origin) to point Bp (regarded as fixed/welded to B), expressed in frame_B. |
[in] | frame_A | The frame that measures v_ABp (Bp's velocity in A). Note: It is natural to wonder why there is no parameter p_AoAp_A (similar to the parameter p_BoBp_B for frame_B). There is no need for p_AoAp_A because Bp's velocity in A is defined as the derivative in frame A of Bp's position vector from any point fixed to A. |
[in] | frame_E | The frame in which v_ABp is expressed on input and the frame in which the Jacobian J𝑠_V_ABp is expressed on output. |
[out] | J𝑠_V_ABp_E | Point Bp's spatial velocity Jacobian in frame A with respect to speeds 𝑠 (which is either q̇ or v), expressed in frame E. J𝑠_V_ABp_E is a 6 x n matrix, where n is the number of elements in 𝑠. The Jacobian is a function of only generalized positions q (which are pulled from the context). Note: The returned 6 x n matrix stores frame B's angular velocity Jacobian in A in rows 1-3 and stores point Bp's translational velocity Jacobian in A in rows 4-6, i.e., J𝑠_w_AB_E = J𝑠_V_ABp_E.topRows<3>(); J𝑠_v_ABp_E = J𝑠_V_ABp_E.bottomRows<3>();Note: Consider CalcJacobianTranslationalVelocity() for multiple points fixed to frame B and consider CalcJacobianAngularVelocity() to calculate frame B's angular velocity Jacobian. |
std::exception | if J𝑠_V_ABp_E is nullptr or not sized 6 x n . |
void CalcJacobianTranslationalVelocity | ( | const systems::Context< T > & | context, |
JacobianWrtVariable | with_respect_to, | ||
const Frame< T > & | frame_B, | ||
const Eigen::Ref< const Matrix3X< T >> & | p_BoBi_B, | ||
const Frame< T > & | frame_A, | ||
const Frame< T > & | frame_E, | ||
EigenPtr< MatrixX< T >> | Js_v_ABi_E | ||
) | const |
For each point Bi affixed/welded to a frame B, calculates J𝑠_v_ABi, Bi's translational velocity Jacobian in frame A with respect to "speeds" 𝑠.
J𝑠_v_ABi ≜ [ ∂(v_ABi)/∂𝑠₁, ... ∂(v_ABi)/∂𝑠ₙ ] (n is j or k) v_ABi = J𝑠_v_ABi ⋅ 𝑠 v_ABi is linear in 𝑠 ≜ [𝑠₁ ... 𝑠ₙ]ᵀ
v_ABi
is Bi's translational velocity in frame A and "speeds" 𝑠 is either q̇ ≜ [q̇₁ ... q̇ⱼ]ᵀ (time-derivatives of j generalized positions) or v ≜ [v₁ ... vₖ]ᵀ (k generalized velocities).
[in] | context | The state of the multibody system. |
[in] | with_respect_to | Enum equal to JacobianWrtVariable::kQDot or JacobianWrtVariable::kV, indicating whether the Jacobian J𝑠_v_ABi is partial derivatives with respect to 𝑠 = q̇ (time-derivatives of generalized positions) or with respect to 𝑠 = v (generalized velocities). |
[in] | frame_B | The frame on which point Bi is affixed/welded. |
[in] | p_BoBi_B | A position vector or list of p position vectors from Bo (frame_B's origin) to points Bi (regarded as affixed to B), where each position vector is expressed in frame_B. |
[in] | frame_A | The frame that measures v_ABi (Bi's velocity in A). Note: It is natural to wonder why there is no parameter p_AoAi_A (similar to the parameter p_BoBi_B for frame_B). There is no need for p_AoAi_A because Bi's velocity in A is defined as the derivative in frame A of Bi's position vector from any point affixed to A. |
[in] | frame_E | The frame in which v_ABi is expressed on input and the frame in which the Jacobian J𝑠_v_ABi is expressed on output. |
[out] | J𝑠_v_ABi_E | Point Bi's velocity Jacobian in frame A with respect to speeds 𝑠 (which is either q̇ or v), expressed in frame E. J𝑠_v_ABi_E is a 3*p x n matrix, where p is the number of points Bi and n is the number of elements in 𝑠. The Jacobian is a function of only generalized positions q (which are pulled from the context). |
std::exception | if J𝑠_v_ABi_E is nullptr or not sized 3*p x n . |
Jq̇_v_ABi = Jq_p_AoBi
. In other words, point Bi's velocity Jacobian in frame A with respect to q̇ is equal to point Bi's position Jacobian from Ao (A's origin) in frame A with respect to q. [∂(v_ABi)/∂q̇₁, ... ∂(v_ABi)/∂q̇ⱼ] = [∂(p_AoBi)/∂q₁, ... ∂(p_AoBi)/∂qⱼ]Note: Each partial derivative of p_AoBi is taken in frame A.
void CalcMassMatrix | ( | const systems::Context< T > & | context, |
EigenPtr< MatrixX< T >> | M | ||
) | const |
Performs the computation of the mass matrix M(q)
of the model, as a function of the generalized positions q stored in context
.
This method employs the Composite Body Algorithm, which is known to be the fastest O(n²) algorithm to compute the mass matrix of a multibody system.
[in] | context | The context containing the state of the model. |
[out] | M | A valid (non-null) pointer to a squared matrix in ℛⁿˣⁿ with n the number of generalized velocities (num_velocities()) of the model. This method aborts if M is nullptr or if it does not have the proper size. |
void CalcMassMatrixViaInverseDynamics | ( | const systems::Context< T > & | context, |
EigenPtr< MatrixX< T >> | M | ||
) | const |
Performs the computation of the mass matrix M(q)
of the model using inverse dynamics, where the generalized positions q are stored in context
.
Use CalcMassMatrix() for a faster implementation using the Composite Body Algorithm.
[in] | context | The context containing the state of the model. |
[out] | M | A valid (non-null) pointer to a squared matrix in ℛⁿˣⁿ with n the number of generalized velocities (num_velocities()) of the model. This method aborts if H is nullptr or if it does not have the proper size. |
The algorithm used to build M(q)
consists in computing one column of M(q)
at a time using inverse dynamics. The result from inverse dynamics, with no applied forces, is the vector of generalized forces:
tau = M(q)v̇ + C(q, v)v
where q and v are the generalized positions and velocities, respectively. When v = 0
the Coriolis and gyroscopic forces term C(q, v)v
is zero. Therefore the i-th
column of M(q)
can be obtained performing inverse dynamics with an acceleration vector v̇ = eᵢ
, with eᵢ
the standard (or natural) basis of ℛⁿ
with n the number of generalized velocities. We write this as:
M.ᵢ(q) = M(q) * e_i
where M.ᵢ(q)
(notice the dot for the rows index) denotes the i-th
column in M(q).
void CalcPointsPositions | ( | const systems::Context< T > & | context, |
const Frame< T > & | frame_B, | ||
const Eigen::Ref< const MatrixX< T >> & | p_BQi, | ||
const Frame< T > & | frame_A, | ||
EigenPtr< MatrixX< T >> | p_AQi | ||
) | const |
Given the positions p_BQi
for a set of points Qi
measured and expressed in a frame B, this method computes the positions p_AQi(q)
of each point Qi
in the set as measured and expressed in another frame A, as a function of the generalized positions q of the model.
[in] | context | The context containing the state of the model. It stores the generalized positions q of the model. |
[in] | frame_B | The frame B in which the positions p_BQi of a set of points Qi are given. |
[in] | p_BQi | The input positions of each point Qi in frame B. p_BQi ∈ ℝ³ˣⁿᵖ with np the number of points in the set. Each column of p_BQi corresponds to a vector in ℝ³ holding the position of one of the points in the set as measured and expressed in frame B. |
[in] | frame_A | The frame A in which it is desired to compute the positions p_AQi of each point Qi in the set. |
[out] | p_AQi | The output positions of each point Qi now computed as measured and expressed in frame A. The output p_AQi must have the same size as the input p_BQi or otherwise this method aborts. That is p_AQi must be in ℝ³ˣⁿᵖ . |
p_BQi
and p_AQi
must have three rows. Otherwise this method will throw a std::exception. This method also throws a std::exception if p_BQi
and p_AQi
differ in the number of columns. math::RotationMatrix<T> CalcRelativeRotationMatrix | ( | const systems::Context< T > & | context, |
const Frame< T > & | frame_F, | ||
const Frame< T > & | frame_G | ||
) | const |
Calculates the rotation matrix R_FG
relating frame F and frame G.
[in] | context | The state of the multibody system, which includes the system's generalized positions q. Note: R_FG is a function of q. |
[in] | frame_F | The frame F designated in the rigid transform R_FG . |
[in] | frame_G | The frame G designated in the rigid transform R_FG . |
R_FG | The RigidTransform relating frame F and frame G. |
math::RigidTransform<T> CalcRelativeTransform | ( | const systems::Context< T > & | context, |
const Frame< T > & | frame_F, | ||
const Frame< T > & | frame_G | ||
) | const |
Calculates the rigid transform (pose) X_FG
relating frame F and frame G.
[in] | context | The state of the multibody system, which includes the system's generalized positions q. Note: X_FG is a function of q. |
[in] | frame_F | The frame F designated in the rigid transform X_FG . |
[in] | frame_G | The frame G designated in the rigid transform X_FG . |
X_FG | The RigidTransform relating frame F and frame G. |
void CalcSpatialAccelerationsFromVdot | ( | const systems::Context< T > & | context, |
const VectorX< T > & | known_vdot, | ||
std::vector< SpatialAcceleration< T >> * | A_WB_array | ||
) | const |
Given the state of this model in context
and a known vector of generalized accelerations known_vdot
, this method computes the spatial acceleration A_WB
for each body as measured and expressed in the world frame W.
[in] | context | The context containing the state of this model. |
[in] | known_vdot | A vector with the generalized accelerations for the full model. |
[out] | A_WB_array | A pointer to a valid, non nullptr, vector of spatial accelerations containing the spatial acceleration A_WB for each body. It must be of size equal to the number of bodies in the model. On output, entries will be ordered by BodyIndex. |
std::exception | if A_WB_array is not of size num_bodies() . |
SpatialMomentum<T> CalcSpatialMomentumInWorldAboutPoint | ( | const systems::Context< T > & | context, |
const Vector3< T > & | p_WoP_W | ||
) | const |
This method returns the spatial momentum of this
MultibodyPlant in the world frame W, about a designated point P, expressed in the world frame W.
[in] | context | Contains the state of the model. |
[in] | p_WoP_W | Position from Wo (origin of the world frame W) to an arbitrary point P, expressed in the world frame W. |
L_WSP_W,spatial | momentum of the system S represented by this plant, measured in the world frame W, about point P, expressed in W. |
MultibodyPlant<T> plant; // ... code to load a model .... const Vector3<T> p_WoScm_W = plant.CalcCenterOfMassPositionInWorld(context); const SpatialMomentum<T> L_WScm_W = plant.CalcSpatialMomentumInWorldAboutPoint(context, p_WoScm_W);
SpatialMomentum<T> CalcSpatialMomentumInWorldAboutPoint | ( | const systems::Context< T > & | context, |
const std::vector< ModelInstanceIndex > & | model_instances, | ||
const Vector3< T > & | p_WoP_W | ||
) | const |
This method returns the spatial momentum of a set of model instances in the world frame W, about a designated point P, expressed in frame W.
[in] | context | Contains the state of the model. |
[in] | model_instances | Set of selected model instances. |
[in] | p_WoP_W | Position from Wo (origin of the world frame W) to an arbitrary point P, expressed in the world frame W. |
L_WSP_W,spatial | momentum of the system S represented by the model_instances, measured in world frame W, about point P, expressed in W. |
MultibodyPlant<T> plant; // ... code to create a set of selected model instances, e.g., ... const ModelInstanceIndex gripper_model_instance = plant.GetModelInstanceByName("gripper"); const ModelInstanceIndex robot_model_instance = plant.GetBodyByName("end_effector").model_instance(); const std::vector<ModelInstanceIndex> model_instances{ gripper_model_instance, robot_model_instance}; const Vector3<T> p_WoScm_W = plant.CalcCenterOfMassPositionInWorld(context, model_instances); SpatialMomentum<T> L_WScm_W = plant.CalcSpatialMomentumInWorldAboutPoint(context, model_instances, p_WoScm_W);
std::exception | if model_instances contains an invalid ModelInstanceIndex. |
T CalcTotalMass | ( | const systems::Context< T > & | context | ) | const |
Calculates the total mass of all bodies in this MultibodyPlant.
[in] | context | Contains the state of the model. |
The | total mass of all bodies or 0 if there are none. |
T CalcTotalMass | ( | const systems::Context< T > & | context, |
const std::vector< ModelInstanceIndex > & | model_instances | ||
) | const |
Calculates the total mass of all bodies contained in model_instances.
[in] | context | Contains the state of the model. |
[in] | model_instances | Vector of selected model instances. This method does not distinguish between welded, joint connected, or floating bodies. |
The | total mass of all bodies belonging to a model instance in model_instances or 0 if model_instances is empty. |
geometry::GeometrySet CollectRegisteredGeometries | ( | const std::vector< const Body< T > * > & | bodies | ) | const |
For each of the provided bodies
, collects up all geometries that have been registered to that body.
Intended to be used in conjunction with CollisionFilterDeclaration and CollisionFilterManager::Apply() to filter collisions between the geometries registered to the bodies.
For example:
Changing the order will cause exceptions to be thrown.
std::exception | if this MultibodyPlant was not registered with a SceneGraph. |
const math::RigidTransform<T>& EvalBodyPoseInWorld | ( | const systems::Context< T > & | context, |
const Body< T > & | body_B | ||
) | const |
Evaluate the pose X_WB
of a body B in the world frame W.
[in] | context | The context storing the state of the model. |
[in] | body_B | The body B for which the pose is requested. |
X_WB | The pose of body frame B in the world frame W. |
std::exception | if Finalize() was not called on this model or if body_B does not belong to this model. |
const SpatialAcceleration<T>& EvalBodySpatialAccelerationInWorld | ( | const systems::Context< T > & | context, |
const Body< T > & | body_B | ||
) | const |
Evaluates A_WB, body B's spatial acceleration in the world frame W.
[in] | context | The context storing the state of the model. |
[in] | body_B | The body for which spatial acceleration is requested. |
A_WB_W | Body B's spatial acceleration in the world frame W, expressed in W (for point Bo, the body's origin). |
std::exception | if Finalize() was not called on this model or if body_B does not belong to this model. |
const SpatialVelocity<T>& EvalBodySpatialVelocityInWorld | ( | const systems::Context< T > & | context, |
const Body< T > & | body_B | ||
) | const |
Evaluates V_WB, body B's spatial velocity in the world frame W.
[in] | context | The context storing the state of the model. |
[in] | body_B | The body B for which the spatial velocity is requested. |
V_WB_W | Body B's spatial velocity in the world frame W, expressed in W (for point Bo, the body's origin). |
std::exception | if Finalize() was not called on this model or if body_B does not belong to this model. |
const std::vector<geometry::PenetrationAsPointPair<T> >& EvalPointPairPenetrations | ( | const systems::Context< T > & | context | ) | const |
Evaluates all point pairs of contact for a given state of the model stored in context
.
Each entry in the returned vector corresponds to a single point pair corresponding to two interpenetrating bodies A and B. The size of the returned vector corresponds to the total number of contact penetration pairs. If no geometry was registered, the output vector is empty.
std::exception | if called pre-finalize. See Finalize(). |
void ExcludeCollisionGeometriesWithCollisionFilterGroupPair | ( | const std::pair< std::string, geometry::GeometrySet > & | collision_filter_group_a, |
const std::pair< std::string, geometry::GeometrySet > & | collision_filter_group_b | ||
) |
Excludes the collision geometries between two given collision filter groups.
void Finalize | ( | ) |
This method must be called after all elements in the model (joints, bodies, force elements, constraints, etc.) are added and before any computations are performed.
It essentially compiles all the necessary "topological information", i.e. how bodies, joints and, any other elements connect with each other, and performs all the required pre-processing to enable computations at a later stage.
If the finalize stage is successful, the topology of this MultibodyPlant is valid, meaning that the topology is up-to-date after this call. No more multibody elements can be added after a call to Finalize().
At Finalize(), state and input/output ports for this
plant are declared.
For a full account of the effects of Finalize(), see Finalize() stage.
std::exception | if the MultibodyPlant has already been finalized. |
bool geometry_source_is_registered | ( | ) | const |
Returns true
if this
MultibodyPlant was registered with a SceneGraph.
This method can be called at any time during the lifetime of this
plant to query if this
plant has been registered with a SceneGraph, either pre- or post-finalize, see Finalize().
const systems::InputPort<T>& get_actuation_input_port | ( | ModelInstanceIndex | model_instance | ) | const |
Returns a constant reference to the input port for external actuation for a specific model instance.
This input port is a vector valued port, which can be set with JointActuator::set_actuation_vector().
this
plant. std::exception | if called before Finalize(). |
std::exception | if the model instance does not exist. |
const systems::InputPort<T>& get_actuation_input_port | ( | ) | const |
Returns a constant reference to the input port for external actuations for all actuated dofs regardless the number of model instances that have actuated dofs.
The input actuation is assumed to be ordered according to model instances. This input port is a vector valued port, which can be set with JointActuator::set_actuation_vector().
this
plant. std::exception | if called before Finalize(). |
std::exception | if individual actuation ports are connected. |
const systems::InputPort<T>& get_applied_generalized_force_input_port | ( | ) | const |
Returns a constant reference to the vector-valued input port for applied generalized forces, and the vector will be added directly into tau
(see System dynamics).
This vector is ordered using the same convention as the plant velocities: you can set the generalized forces that will be applied to model instance i using, e.g., SetVelocitiesInArray(i, model_forces, &force_array)
.
std::exception | if called before Finalize(). |
const systems::InputPort<T>& get_applied_spatial_force_input_port | ( | ) | const |
Returns a constant reference to the input port for applying spatial forces to bodies in the plant.
The data type for the port is an std::vector of ExternallyAppliedSpatialForce; any number of spatial forces can be applied to any number of bodies in the plant.
Returns a constant reference to the body with unique index body_index
.
std::exception | if body_index does not correspond to a body in this model. |
const systems::OutputPort<T>& get_body_poses_output_port | ( | ) | const |
Returns the output port of all body poses in the world frame.
You can obtain the pose X_WB
of a body B in the world frame W with:
As shown in the example above, the resulting std::vector
of body poses is indexed by BodyIndex, and it has size num_bodies(). BodyIndex "zero" (0) always corresponds to the world body, with pose equal to the identity at all times.
std::exception | if called pre-finalize. |
const systems::OutputPort<T>& get_body_spatial_accelerations_output_port | ( | ) | const |
Returns the output port of all body spatial accelerations in the world frame.
You can obtain the spatial acceleration A_WB
of a body B in the world frame W with:
As shown in the example above, the resulting std::vector
of body spatial accelerations is indexed by BodyIndex, and it has size num_bodies(). BodyIndex "zero" (0) always corresponds to the world body, with zero spatial acceleration at all times.
std::exception | if called pre-finalize. |
const systems::OutputPort<T>& get_body_spatial_velocities_output_port | ( | ) | const |
Returns the output port of all body spatial velocities in the world frame.
You can obtain the spatial velocity V_WB
of a body B in the world frame W with:
As shown in the example above, the resulting std::vector
of body spatial velocities is indexed by BodyIndex, and it has size num_bodies(). BodyIndex "zero" (0) always corresponds to the world body, with zero spatial velocity at all times.
std::exception | if called pre-finalize. |
ContactModel get_contact_model | ( | ) | const |
Returns the model used for contact. See documentation for ContactModel.
double get_contact_penalty_method_time_scale | ( | ) | const |
Returns a time-scale estimate tc
based on the requested penetration allowance δ set with set_penetration_allowance().
For the penalty method in use to enforce non-penetration, this time scale relates to the time it takes the relative normal velocity between two bodies to go to zero. This time scale tc
is artificially introduced by the penalty method and goes to zero in the limit to ideal rigid contact. Since numerical integration methods for continuum systems must be able to resolve a system's dynamics, the time step used by an integrator must in general be much smaller than the time scale tc
. How much smaller will depend on the details of the problem and the convergence characteristics of the integrator and should be tuned appropriately. Another factor to take into account for setting up the simulation's time step is the speed of the objects in your simulation. If vn
represents a reference velocity scale for the normal relative velocity between bodies, the new time scale tn = δ / vn
represents the time it would take for the distance between two bodies approaching with relative normal velocity vn
to decrease by the penetration_allowance δ. In this case a user should choose a time step for simulation that can resolve the smallest of the two time scales tc
and tn
.
const systems::OutputPort<T>& get_contact_results_output_port | ( | ) | const |
Returns a constant reference to the port that outputs ContactResults.
std::exception | if called pre-finalize, see Finalize(). |
geometry::HydroelasticContactRepresentation get_contact_surface_representation | ( | ) | const |
Gets the current representation of contact surfaces used by this
MultibodyPlant.
DiscreteContactSolver get_discrete_contact_solver | ( | ) | const |
Returns the contact solver type used for discrete MultibodyPlant models.
const ForceElement<T>& get_force_element | ( | ForceElementIndex | force_element_index | ) | const |
Returns a constant reference to the force element with unique index force_element_index
.
std::exception | when force_element_index does not correspond to a force element in this model. |
const Frame<T>& get_frame | ( | FrameIndex | frame_index | ) | const |
Returns a constant reference to the frame with unique index frame_index
.
std::exception | if frame_index does not correspond to a frame in this plant. |
const systems::OutputPort<T>& get_generalized_acceleration_output_port | ( | ) | const |
Returns a constant reference to the output port for generalized accelerations v̇ of the model.
this
plant. std::exception | if called before Finalize(). |
const systems::OutputPort<T>& get_generalized_acceleration_output_port | ( | ModelInstanceIndex | model_instance | ) | const |
Returns a constant reference to the output port for the generalized accelerations v̇ᵢ ⊆ v̇ for model instance i.
this
plant. std::exception | if called before Finalize(). |
std::exception | if the model instance does not exist. |
const systems::OutputPort<T>& get_generalized_contact_forces_output_port | ( | ModelInstanceIndex | model_instance | ) | const |
Returns a constant reference to the output port of generalized contact forces for a specific model instance.
this
plant. std::exception | if called before Finalize(). |
std::exception | if the model instance does not exist. |
const systems::OutputPort<T>& get_geometry_poses_output_port | ( | ) | const |
Returns the output port of frames' poses to communicate with a SceneGraph.
const systems::InputPort<T>& get_geometry_query_input_port | ( | ) | const |
Returns a constant reference to the input port used to perform geometric queries on a SceneGraph.
See SceneGraph::get_query_output_port(). Refer to section Geometry of this class's documentation for further details on collision geometry registration and connection with a SceneGraph.
const Joint<T>& get_joint | ( | JointIndex | joint_index | ) | const |
Returns a constant reference to the joint with unique index joint_index
.
std::exception | when joint_index does not correspond to a joint in this model. |
const JointActuator<T>& get_joint_actuator | ( | JointActuatorIndex | actuator_index | ) | const |
Returns a constant reference to the joint actuator with unique index actuator_index
.
std::exception | if actuator_index does not correspond to a joint actuator in this tree. |
Joint<T>& get_mutable_joint | ( | JointIndex | joint_index | ) |
Returns a mutable reference to the joint with unique index joint_index
.
std::exception | when joint_index does not correspond to a joint in this model. |
JointActuator<T>& get_mutable_joint_actuator | ( | JointActuatorIndex | actuator_index | ) | const |
Returns a mutable reference to the joint actuator with unique index actuator_index
.
std::exception | if actuator_index does not correspond to a joint actuator in this tree. |
const systems::OutputPort<T>& get_reaction_forces_output_port | ( | ) | const |
Returns the port for joint reaction forces.
A Joint models the kinematical relationship which characterizes the possible relative motion between two bodies. In Drake, a joint connects a frame Jp
on parent body P with a frame Jc
on a child body C. This usage of the terms parent and child is just a convention and implies nothing about the inboard-outboard relationship between the bodies. Since a Joint imposes a kinematical relationship which characterizes the possible relative motion between frames Jp and Jc, reaction forces on each body are established. That is, we could cut the model at the joint and replace it with equivalent forces equal to these reaction forces in order to attain the same motions of the mechanical system.
This output port allows to evaluate the reaction force F_CJc_Jc
on the child body C, at Jc
, and expressed in Jc for all joints in the model. This port evaluates to a vector of type std::vector<SpatialForce<T>> and size num_joints() indexed by JointIndex, see Joint::index(). Each entry corresponds to the spatial force F_CJc_Jc
applied on the joint's child body C (Joint::child_body()), at the joint's child frame Jc
(Joint::frame_on_child()) and expressed in frame Jc
.
std::exception | if called pre-finalize. |
std::optional<geometry::SourceId> get_source_id | ( | ) | const |
Returns the unique id identifying this
plant as a source for a SceneGraph.
Returns nullopt
if this
plant did not register any geometry. This method can be called at any time during the lifetime of this
plant to query if this
plant has been registered with a SceneGraph, either pre- or post-finalize, see Finalize(). However, a geometry::SourceId is only assigned once at the first call of any of this plant's geometry registration methods, and it does not change after that. Post-finalize calls will always return the same value.
const systems::OutputPort<T>& get_state_output_port | ( | ) | const |
Returns a constant reference to the output port for the multibody state x = [q, v] of the model.
this
plant. std::exception | if called before Finalize(). |
const systems::OutputPort<T>& get_state_output_port | ( | ModelInstanceIndex | model_instance | ) | const |
Returns a constant reference to the output port for the state xᵢ = [qᵢ vᵢ] of model instance i.
(Here qᵢ ⊆ q and vᵢ ⊆ v.)
this
plant. std::exception | if called before Finalize(). |
std::exception | if the model instance does not exist. |
VectorX<double> GetAccelerationLowerLimits | ( | ) | const |
Returns a vector of size num_velocities()
containing the lower acceleration limits for every generalized velocity coordinate.
These include joint and free body coordinates. Any unbounded or unspecified limits will be -infinity.
std::exception | if called pre-finalize. |
VectorX<double> GetAccelerationUpperLimits | ( | ) | const |
Upper limit analog of GetAccelerationsLowerLimits(), where any unbounded or unspecified limits will be +infinity.
VectorX<T> GetActuationFromArray | ( | ModelInstanceIndex | model_instance, |
const Eigen::Ref< const VectorX< T >> & | u | ||
) | const |
Returns a vector of actuation values for model_instance
from a vector u
of actuation values for the entire model.
This method throws an exception if u
is not of size MultibodyPlant::num_actuated_dofs().
Returns all bodies that are transitively welded, or rigidly affixed, to body
, per these two definitions:
This method can be called at any time during the lifetime of this
plant, either pre- or post-finalize, see Finalize().
Meant to be used with CollectRegisteredGeometries
.
The following example demonstrates filtering collisions between all bodies rigidly affixed to a door (which could be moving) and all bodies rigidly affixed to the world:
body
. This does not return the bodies in any prescribed order. std::exception | if body is not part of this plant. |
const Body<T>& GetBodyByName | ( | std::string_view | name | ) | const |
Returns a constant reference to a body that is identified by the string name
in this
MultibodyPlant.
std::exception | if there is no body with the requested name. |
std::exception | if the body name occurs in multiple model instances. |
this
MultibodyPlant with a given specified name. const Body<T>& GetBodyByName | ( | std::string_view | name, |
ModelInstanceIndex | model_instance | ||
) | const |
Returns a constant reference to the body that is uniquely identified by the string name
and model_instance
in this
MultibodyPlant.
std::exception | if there is no body with the requested name. |
this
MultibodyPlant with a given specified name. std::optional<geometry::FrameId> GetBodyFrameIdIfExists | ( | BodyIndex | body_index | ) | const |
If the body with body_index
belongs to the called plant, it returns the geometry::FrameId associated with it.
Otherwise, it returns nullopt.
geometry::FrameId GetBodyFrameIdOrThrow | ( | BodyIndex | body_index | ) | const |
If the body with body_index
belongs to the called plant, it returns the geometry::FrameId associated with it.
Otherwise this method throws an exception.
std::exception | if the called plant does not have the body indicated by body_index . |
const Body<T>* GetBodyFromFrameId | ( | geometry::FrameId | frame_id | ) | const |
Given a geometry frame identifier, returns a pointer to the body associated with that id (nullptr if there is no such body).
std::vector<BodyIndex> GetBodyIndices | ( | ModelInstanceIndex | model_instance | ) | const |
Returns a list of body indices associated with model_instance
.
const std::vector<geometry::GeometryId>& GetCollisionGeometriesForBody | ( | const Body< T > & | body | ) | const |
Returns an array of GeometryId's identifying the different contact geometries for body
previously registered with a SceneGraph.
this
plant, either pre- or post-finalize, see Finalize(). Post-finalize calls will always return the same value.
|
static |
Return the default value for contact representation, given the desired time step.
Discrete systems default to use polygons; continuous systems default to use triangles.
const math::RigidTransform<double>& GetDefaultFreeBodyPose | ( | const Body< T > & | body | ) | const |
Gets the default pose of body
as set by SetDefaultFreeBodyPose().
[in] | body | Body whose default pose will be retrieved. |
VectorX<double> GetEffortLowerLimits | ( | ) | const |
Returns a vector of size num_actuators()
containing the lower effort limits for every actuator.
Any unbounded or unspecified limits will be -infinity.
std::exception | if called pre-finalize. |
VectorX<double> GetEffortUpperLimits | ( | ) | const |
Upper limit analog of GetAccelerationsLowerLimits(), where any unbounded or unspecified limits will be +infinity.
std::unordered_set<BodyIndex> GetFloatingBaseBodies | ( | ) | const |
Returns the set of body indexes corresponding to the free (floating) bodies in the model, in no particular order.
std::exception | if called pre-finalize, see Finalize(). |
const ForceElementType<T>& GetForceElement | ( | ForceElementIndex | force_element_index | ) | const |
Returns a constant reference to a force element identified by its unique index in this
MultibodyPlant.
If the optional template argument is supplied, then the returned value is downcast to the specified ForceElementType
.
ForceElementType | The specific type of the ForceElement to be retrieved. It must be a subclass of ForceElement. |
std::exception | if the force element is not of type ForceElementType or if there is no ForceElement with that index. |
const Frame<T>& GetFrameByName | ( | std::string_view | name | ) | const |
Returns a constant reference to a frame that is identified by the string name
in this
model.
std::exception | if there is no frame with the requested name. |
std::exception | if the frame name occurs in multiple model instances. |
this
model with a given specified name. const Frame<T>& GetFrameByName | ( | std::string_view | name, |
ModelInstanceIndex | model_instance | ||
) | const |
Returns a constant reference to the frame that is uniquely identified by the string name
in model_instance
.
std::exception | if there is no frame with the requested name. |
std::exception | if model_instance is not valid for this model. |
this
model with a given specified name. std::vector<FrameIndex> GetFrameIndices | ( | ModelInstanceIndex | model_instance | ) | const |
Returns a list of frame indices associated with model_instance
.
math::RigidTransform<T> GetFreeBodyPose | ( | const systems::Context< T > & | context, |
const Body< T > & | body | ||
) | const |
Gets the pose of a given body
in the world frame W.
std::exception | if body is not a free body in the model. |
std::exception | if called pre-finalize. |
const JointActuator<T>& GetJointActuatorByName | ( | std::string_view | name | ) | const |
Returns a constant reference to an actuator that is identified by the string name
in this
MultibodyPlant.
std::exception | if there is no actuator with the requested name. |
std::exception | if the actuator name occurs in multiple model instances. |
this
MultibodyPlant with a given specified name. const JointActuator<T>& GetJointActuatorByName | ( | std::string_view | name, |
ModelInstanceIndex | model_instance | ||
) | const |
Returns a constant reference to the actuator that is uniquely identified by the string name
and model_instance
in this
MultibodyPlant.
std::exception | if there is no actuator with the requested name. |
std::exception | if model_instance is not valid for this model. |
this
MultibodyPlant with a given specified name. const JointType<T>& GetJointByName | ( | std::string_view | name, |
std::optional< ModelInstanceIndex > | model_instance = std::nullopt |
||
) | const |
Returns a constant reference to a joint that is identified by the string name
in this
MultibodyPlant.
If the optional template argument is supplied, then the returned value is downcast to the specified JointType
.
JointType | The specific type of the Joint to be retrieved. It must be a subclass of Joint. |
std::exception | if the named joint is not of type JointType or if there is no Joint with that name. |
std::exception | if model_instance is not valid for this model. |
this
MultibodyPlant with a given specified name. std::vector<JointIndex> GetJointIndices | ( | ModelInstanceIndex | model_instance | ) | const |
Returns a list of joint indices associated with model_instance
.
ModelInstanceIndex GetModelInstanceByName | ( | std::string_view | name | ) | const |
Returns the index to the model instance that is uniquely identified by the string name
in this
MultibodyPlant.
std::exception | if there is no instance with the requested name. |
this
MultibodyPlant with a given specified name. const std::string& GetModelInstanceName | ( | ModelInstanceIndex | model_instance | ) | const |
Returns the name of a model_instance
.
std::exception | when model_instance does not correspond to a model in this model. |
JointType<T>& GetMutableJointByName | ( | std::string_view | name, |
std::optional< ModelInstanceIndex > | model_instance = std::nullopt |
||
) |
A version of GetJointByName that returns a mutable reference.
Eigen::VectorBlock<VectorX<T> > GetMutablePositions | ( | systems::Context< T > * | context | ) | const |
(Advanced – see warning) Returns a mutable vector reference to the generalized positions q in a given Context.
std::exception | if the context is nullptr or if it does not correspond to the Context for a multibody model. |
Eigen::VectorBlock<VectorX<T> > GetMutablePositions | ( | const systems::Context< T > & | context, |
systems::State< T > * | state | ||
) | const |
(Advanced) Returns a mutable vector reference to the generalized positions q in a given State.
std::exception | if the state is nullptr or if context does not correspond to the Context for a multibody model. |
state
comes from this multibody model. Eigen::VectorBlock<VectorX<T> > GetMutablePositionsAndVelocities | ( | systems::Context< T > * | context | ) | const |
(Advanced – see warning) Returns a mutable vector reference [q; v]
to the generalized positions q and generalized velocities v in a given Context.
std::exception | if context is nullptr or if it does not correspond to the context for a multibody model. |
Eigen::VectorBlock<VectorX<T> > GetMutableVelocities | ( | systems::Context< T > * | context | ) | const |
(Advanced – see warning) Returns a mutable vector reference to the generalized velocities v in a given Context.
std::exception | if the context is nullptr or if it does not correspond to the Context for a multibody model. |
Eigen::VectorBlock<VectorX<T> > GetMutableVelocities | ( | const systems::Context< T > & | context, |
systems::State< T > * | state | ||
) | const |
(Advanced) Returns a mutable vector reference to the generalized velocities v in a given State.
std::exception | if the state is nullptr or if context does not correspond to the Context for a multibody model. |
state
comes from this multibody model. VectorX<double> GetPositionLowerLimits | ( | ) | const |
Returns a vector of size num_positions()
containing the lower position limits for every generalized position coordinate.
These include joint and free body coordinates. Any unbounded or unspecified limits will be -infinity.
std::exception | if called pre-finalize. |
Eigen::VectorBlock<const VectorX<T> > GetPositions | ( | const systems::Context< T > & | context | ) | const |
Returns a const vector reference to the vector of generalized positions q in a given Context.
std::exception | if context does not correspond to the Context for a multibody model. |
VectorX<T> GetPositions | ( | const systems::Context< T > & | context, |
ModelInstanceIndex | model_instance | ||
) | const |
Returns a vector containing the generalized positions q of a specified model instance in a given Context.
num_positions(model_instance)
associated with model_instance
by copying from context
. std::exception | if context does not correspond to the Context for a multibody model or model_instance is invalid. |
void GetPositions | ( | const systems::Context< T > & | context, |
ModelInstanceIndex | model_instance, | ||
EigenPtr< VectorX< T >> | q_out | ||
) | const |
(Advanced) Populates output vector q_out with the generalized positions q of a specified model instance in a given Context.
model_instance
and is populated by copying from context
. std::exception | if context does not correspond to the Context for a multibody model or model_instance is invalid. |
Eigen::VectorBlock<const VectorX<T> > GetPositionsAndVelocities | ( | const systems::Context< T > & | context | ) | const |
Returns a const vector reference [q; v]
to the generalized positions q and generalized velocities v in a given Context.
std::exception | if context does not correspond to the Context for a multibody model. |
VectorX<T> GetPositionsAndVelocities | ( | const systems::Context< T > & | context, |
ModelInstanceIndex | model_instance | ||
) | const |
Returns a vector [q; v]
containing the generalized positions q and generalized velocities v of a specified model instance in a given Context.
num_positions(model_instance) + num_velocities(model_instance)
associated with model_instance
by copying from context
. std::exception | if context does not correspond to the Context for a multibody model or model_instance is invalid. |
void GetPositionsAndVelocities | ( | const systems::Context< T > & | context, |
ModelInstanceIndex | model_instance, | ||
EigenPtr< VectorX< T >> | qv_out | ||
) | const |
(Advanced) Populates output vector qv_out representing the generalized positions q and generalized velocities v of a specified model instance in a given Context.
num_positions(model_instance) + num_velocities(model_instance)
associated with model_instance
and is populated by copying from context
. std::exception | if context does not correspond to the Context for a multibody model or model_instance is invalid. |
std::exception | if qv_out does not have size num_positions(model_instance) + num_velocities(model_instance) |
VectorX<T> GetPositionsFromArray | ( | ModelInstanceIndex | model_instance, |
const Eigen::Ref< const VectorX< T >> & | q | ||
) | const |
Returns a vector of generalized positions for model_instance
from a vector q_array
of generalized positions for the entire model model.
This method throws an exception if q
is not of size MultibodyPlant::num_positions().
void GetPositionsFromArray | ( | ModelInstanceIndex | model_instance, |
const Eigen::Ref< const VectorX< T >> & | q, | ||
EigenPtr< VectorX< T >> | q_out | ||
) | const |
(Advanced) Populates output vector q_out and with the generalized positions for model_instance
from a vector q
of generalized positions for the entire model.
This method throws an exception if q
is not of size MultibodyPlant::num_positions().
VectorX<double> GetPositionUpperLimits | ( | ) | const |
Upper limit analog of GetPositionsLowerLimits(), where any unbounded or unspecified limits will be +infinity.
const RigidBody<T>& GetRigidBodyByName | ( | std::string_view | name | ) | const |
Returns a constant reference to a rigid body that is identified by the string name
in this
model.
std::exception | if there is no body with the requested name. |
std::exception | if the body name occurs in multiple model instances. |
std::exception | if the requested body is not a RigidBody. |
this
model with a given specified name. const RigidBody<T>& GetRigidBodyByName | ( | std::string_view | name, |
ModelInstanceIndex | model_instance | ||
) | const |
Returns a constant reference to the rigid body that is uniquely identified by the string name
in model_instance
.
std::exception | if there is no body with the requested name. |
std::exception | if the requested body is not a RigidBody. |
std::exception | if model_instance is not valid for this model. |
this
model with a given specified name. std::string GetTopologyGraphvizString | ( | ) | const |
Returns a Graphviz string describing the topology of this plant.
To render the string, use the Graphviz tool, dot
. http://www.graphviz.org/
Note: this method can be called either before or after Finalize()
.
const Body<T>& GetUniqueFreeBaseBodyOrThrow | ( | ModelInstanceIndex | model_instance | ) | const |
If there exists a unique base body that belongs to the model given by model_instance
and that unique base body is free (see HasUniqueBaseBody()), return that free body.
Throw an exception otherwise.
std::exception | if called pre-finalize. |
std::exception | if model_instance is not valid. |
std::exception | if HasUniqueFreeBaseBody(model_instance) == false. |
Eigen::VectorBlock<const VectorX<T> > GetVelocities | ( | const systems::Context< T > & | context | ) | const |
Returns a const vector reference to the generalized velocities v in a given Context.
std::exception | if context does not correspond to the Context for a multibody model. |
VectorX<T> GetVelocities | ( | const systems::Context< T > & | context, |
ModelInstanceIndex | model_instance | ||
) | const |
Returns a vector containing the generalized velocities v of a specified model instance in a given Context.
num_velocities(model_instance)
associated with model_instance
by copying from context
. std::exception | if context does not correspond to the Context for a multibody model or model_instance is invalid. |
void GetVelocities | ( | const systems::Context< T > & | context, |
ModelInstanceIndex | model_instance, | ||
EigenPtr< VectorX< T >> | v_out | ||
) | const |
(Advanced) Populates output vector v_out with the generalized velocities v of a specified model instance in a given Context.
num_velocities(model_instance)
associated with model_instance
and is populated by copying from context
. std::exception | if context does not correspond to the Context for a multibody model or model_instance is invalid. |
VectorX<T> GetVelocitiesFromArray | ( | ModelInstanceIndex | model_instance, |
const Eigen::Ref< const VectorX< T >> & | v | ||
) | const |
Returns a vector of generalized velocities for model_instance
from a vector v
of generalized velocities for the entire MultibodyPlant model.
This method throws an exception if the input array is not of size MultibodyPlant::num_velocities().
void GetVelocitiesFromArray | ( | ModelInstanceIndex | model_instance, |
const Eigen::Ref< const VectorX< T >> & | v, | ||
EigenPtr< VectorX< T >> | v_out | ||
) | const |
(Advanced) Populates output vector v_out with the generalized velocities for model_instance
from a vector v
of generalized velocities for the entire model.
This method throws an exception if v
is not of size MultibodyPlant::num_velocities().
VectorX<double> GetVelocityLowerLimits | ( | ) | const |
Returns a vector of size num_velocities()
containing the lower velocity limits for every generalized velocity coordinate.
These include joint and free body coordinates. Any unbounded or unspecified limits will be -infinity.
std::exception | if called pre-finalize. |
VectorX<double> GetVelocityUpperLimits | ( | ) | const |
Upper limit analog of GetVelocitysLowerLimits(), where any unbounded or unspecified limits will be +infinity.
const std::vector<geometry::GeometryId>& GetVisualGeometriesForBody | ( | const Body< T > & | body | ) | const |
Returns an array of GeometryId's identifying the different visual geometries for body
previously registered with a SceneGraph.
this
plant, either pre- or post-finalize, see Finalize(). Post-finalize calls will always return the same value. const UniformGravityFieldElement<T>& gravity_field | ( | ) | const |
An accessor to the current gravity field.
bool HasBodyNamed | ( | std::string_view | name | ) | const |
true
if a body named name
was added to the MultibodyPlant. std::exception | if the body name occurs in multiple model instances. |
bool HasBodyNamed | ( | std::string_view | name, |
ModelInstanceIndex | model_instance | ||
) | const |
true
if a body named name
was added to the MultibodyPlant in model_instance
. std::exception | if model_instance is not valid for this model. |
bool HasFrameNamed | ( | std::string_view | name | ) | const |
true
if a frame named name
was added to the model. std::exception | if the frame name occurs in multiple model instances. |
bool HasFrameNamed | ( | std::string_view | name, |
ModelInstanceIndex | model_instance | ||
) | const |
true
if a frame named name
was added to model_instance
. std::exception | if model_instance is not valid for this model. |
bool HasJointActuatorNamed | ( | std::string_view | name | ) | const |
true
if an actuator named name
was added to this model. std::exception | if the actuator name occurs in multiple model instances. |
bool HasJointActuatorNamed | ( | std::string_view | name, |
ModelInstanceIndex | model_instance | ||
) | const |
true
if an actuator named name
was added to model_instance
. std::exception | if model_instance is not valid for this model. |
bool HasJointNamed | ( | std::string_view | name | ) | const |
true
if a joint named name
was added to this model. std::exception | if the joint name occurs in multiple model instances. |
bool HasJointNamed | ( | std::string_view | name, |
ModelInstanceIndex | model_instance | ||
) | const |
true
if a joint named name
was added to model_instance
. std::exception | if model_instance is not valid for this model. |
bool HasModelInstanceNamed | ( | std::string_view | name | ) | const |
true
if a model instance named name
was added to this model. bool HasUniqueFreeBaseBody | ( | ModelInstanceIndex | model_instance | ) | const |
Return true if there exists a unique base body in the model given by model_instance
and that unique base body is free.
std::exception | if called pre-finalize. |
std::exception | if model_instance is not valid. |
bool is_finalized | ( | ) | const |
Returns true
if this MultibodyPlant was finalized with a call to Finalize().
bool IsAnchored | ( | const Body< T > & | body | ) | const |
Returns true
if body
is anchored (i.e.
the kinematic path between body
and the world only contains weld joints.)
std::exception | if called pre-finalize. |
MatrixX<T> MakeActuationMatrix | ( | ) | const |
This method creates an actuation matrix B mapping a vector of actuation values u into generalized forces tau_u = B * u
, where B is a matrix of size nv x nu
with nu
equal to num_actuators() and nv
equal to num_velocities().
The vector u of actuation values is of size num_actuators(). For a given JointActuator, u[JointActuator::index()]
stores the value for the external actuation corresponding to that actuator. tau_u
on the other hand is indexed by generalized velocity indexes according to Joint::velocity_start()
.
O(n)
complexity, making a full B matrix has O(n²)
complexity. For most applications this cost can be neglected but it could become significant for very large systems. MatrixX<double> MakeActuatorSelectorMatrix | ( | const std::vector< JointActuatorIndex > & | user_to_actuator_index_map | ) | const |
This method allows user to map a vector uₛ
containing the actuation for a set of selected actuators into the vector u containing the actuation values for this
full model.
The mapping, or selection, is returned in the form of a selector matrix Su such that u = Su⋅uₛ
. The size nₛ of uₛ is always smaller or equal than the size of the full vector of actuation values u. That is, a user might be interested in only a given subset of actuators in the model.
This selection matrix is particularly useful when adding PID control on a portion of the state, see systems::controllers::PidController.
A user specifies the preferred order in uₛ via user_to_actuator_index_map
. The actuation values in uₛ are a concatenation of the values for each actuator in the order they appear in user_to_actuator_index_map
. The full vector of actuation values u is ordered by JointActuatorIndex.
MatrixX<double> MakeActuatorSelectorMatrix | ( | const std::vector< JointIndex > & | user_to_joint_index_map | ) | const |
Alternative signature to build an actuation selector matrix Su
such that u = Su⋅uₛ
, where u is the vector of actuation values for the full model (ordered by JointActuatorIndex) and uₛ is a vector of actuation values for the actuators acting on the joints listed by user_to_joint_index_map
.
It is assumed that all joints referenced by user_to_joint_index_map
are actuated. See MakeActuatorSelectorMatrix(const std::vector<JointActuatorIndex>&) for details.
std::exception | if any of the joints in user_to_joint_index_map does not have an actuator. |
MatrixX<double> MakeStateSelectorMatrix | ( | const std::vector< JointIndex > & | user_to_joint_index_map | ) | const |
This method allows users to map the state of this
model, x, into a vector of selected state xₛ with a given preferred ordering.
The mapping, or selection, is returned in the form of a selector matrix Sx such that xₛ = Sx⋅x
. The size nₛ of xₛ is always smaller or equal than the size of the full state x. That is, a user might be interested in only a given portion of the full state x.
This selection matrix is particularly useful when adding PID control on a portion of the state, see systems::controllers::PidController.
A user specifies the preferred order in xₛ via user_to_joint_index_map
. The selected state is built such that selected positions are followed by selected velocities, as in xₛ = [qₛ, vₛ]
. The positions in qₛ are a concatenation of the positions for each joint in the order they appear in user_to_joint_index_map
. That is, the positions for user_to_joint_index_map[0]
are first, followed by the positions for user_to_joint_index_map[1]
, etc. Similarly for the selected velocities vₛ.
std::exception | if there are repeated indexes in user_to_joint_index_map . |
void MapQDotToVelocity | ( | const systems::Context< T > & | context, |
const Eigen::Ref< const VectorX< T >> & | qdot, | ||
EigenPtr< VectorX< T >> | v | ||
) | const |
Transforms the time derivative qdot
of the generalized positions vector q
(stored in context
) to generalized velocities v
.
v
and q̇
are related linearly by q̇ = N(q)⋅v
. Although N(q)
is not necessarily square, its left pseudo-inverse N⁺(q)
can be used to invert that relationship without residual error, provided that qdot
is in the range space of N(q)
(that is, if it could have been produced as q̇ = N(q)⋅v
for some v
). Using the configuration q
stored in the given context
this method calculates v = N⁺(q)⋅q̇
.
[in] | context | The context containing the state of the model. |
[in] | qdot | A vector containing the time derivatives of the generalized positions. This method aborts if qdot is not of size num_positions(). |
[out] | v | A valid (non-null) pointer to a vector in ℛⁿ with n the number of generalized velocities. This method aborts if v is nullptr or if it is not of size num_velocities(). |
void MapVelocityToQDot | ( | const systems::Context< T > & | context, |
const Eigen::Ref< const VectorX< T >> & | v, | ||
EigenPtr< VectorX< T >> | qdot | ||
) | const |
Transforms generalized velocities v to time derivatives qdot
of the generalized positions vector q
(stored in context
).
v
and qdot
are related linearly by q̇ = N(q)⋅v
. Using the configuration q
stored in the given context
this method calculates q̇ = N(q)⋅v
.
[in] | context | The context containing the state of the model. |
[in] | v | A vector of generalized velocities for this model. This method aborts if v is not of size num_velocities(). |
[out] | qdot | A valid (non-null) pointer to a vector in ℝⁿ with n being the number of generalized positions in this model, given by num_positions() . This method aborts if qdot is nullptr or if it is not of size num_positions(). |
UniformGravityFieldElement<T>& mutable_gravity_field | ( | ) |
A mutable accessor to the current gravity field.
int num_actuated_dofs | ( | ) | const |
Returns the total number of actuated degrees of freedom.
That is, the vector of actuation values u has this size. See AddJointActuator().
int num_actuated_dofs | ( | ModelInstanceIndex | model_instance | ) | const |
Returns the total number of actuated degrees of freedom for a specific model instance.
That is, the vector of actuation values u has this size. See AddJointActuator().
std::exception | if called pre-finalize. |
int num_actuators | ( | ) | const |
Returns the number of joint actuators in the model.
int num_bodies | ( | ) | const |
Returns the number of bodies in the model, including the "world" body, which is always part of the model.
int num_collision_geometries | ( | ) | const |
Returns the number of geometries registered for contact modeling.
This method can be called at any time during the lifetime of this
plant, either pre- or post-finalize, see Finalize(). Post-finalize calls will always return the same value.
int num_constraints | ( | ) | const |
Returns the total number of constraints specified by the user.
int num_force_elements | ( | ) | const |
Returns the number of ForceElement objects.
int num_frames | ( | ) | const |
Returns the number of Frame objects in this model.
Frames include body frames associated with each of the bodies, including the world body. This means the minimum number of frames is one.
int num_joints | ( | ) | const |
Returns the number of joints in the model.
int num_model_instances | ( | ) | const |
Returns the number of model instances in the model.
int num_multibody_states | ( | ) | const |
Returns the size of the multibody system state vector x = [q v].
This will be num_positions()
plus num_velocities()
.
int num_multibody_states | ( | ModelInstanceIndex | model_instance | ) | const |
Returns the size of the multibody system state vector xᵢ = [qᵢ vᵢ] for model instance i.
(Here qᵢ ⊆ q and vᵢ ⊆ v.) will be num_positions(model_instance)
plus num_velocities(model_instance)
.
std::exception | if called pre-finalize. |
int num_positions | ( | ) | const |
Returns the size of the generalized position vector q for this model.
int num_positions | ( | ModelInstanceIndex | model_instance | ) | const |
Returns the size of the generalized position vector qᵢ for model instance i.
std::exception | if called pre-finalize. |
int num_velocities | ( | ) | const |
Returns the size of the generalized velocity vector v for this model.
int num_velocities | ( | ModelInstanceIndex | model_instance | ) | const |
Returns the size of the generalized velocity vector vᵢ for model instance i.
std::exception | if called pre-finalize. |
int num_visual_geometries | ( | ) | const |
Returns the number of geometries registered for visualization.
This method can be called at any time during the lifetime of this
plant, either pre- or post-finalize, see Finalize(). Post-finalize calls will always return the same value.
int NumBodiesWithName | ( | std::string_view | name | ) | const |
|
delete |
|
delete |
const std::vector<std::unique_ptr<internal::PhysicalModel<T> > >& physical_models | ( | ) | const |
For use only by advanced developers.
geometry::SourceId RegisterAsSourceForSceneGraph | ( | geometry::SceneGraph< T > * | scene_graph | ) |
Registers this
plant to serve as a source for an instance of SceneGraph.
This registration allows MultibodyPlant to register geometry with scene_graph
for visualization and/or collision queries. The string returned by this->get_name()
is passed to SceneGraph's RegisterSource, so it is highly recommended that you give the plant a recognizable name before calling this. Successive registration calls with SceneGraph must be performed on the same instance to which the pointer argument scene_graph
points to. Failure to do so will result in runtime exceptions.
scene_graph | A valid non nullptr to the SceneGraph instance for which this plant will sever as a source, see SceneGraph documentation for further details. |
this
plant in scene_graph
. It can also later on be retrieved with get_source_id(). std::exception | if called post-finalize. |
std::exception | if scene_graph is the nullptr. |
std::exception | if called more than once. |
geometry::GeometryId RegisterCollisionGeometry | ( | const Body< T > & | body, |
const math::RigidTransform< double > & | X_BG, | ||
const geometry::Shape & | shape, | ||
const std::string & | name, | ||
geometry::ProximityProperties | properties | ||
) |
Registers geometry in a SceneGraph with a given geometry::Shape to be used for the contact modeling of a given body
.
More than one geometry can be registered with a body, in which case the body's contact geometry is the union of all geometries registered to that body.
[in] | body | The body for which geometry is being registered. |
[in] | X_BG | The fixed pose of the geometry frame G in the body frame B. |
[in] | shape | The geometry::Shape used for visualization. E.g.: geometry::Sphere, geometry::Cylinder, etc. |
[in] | properties | The proximity properties associated with the collision geometry. They must include the (material , coulomb_friction ) property of type CoulombFriction<double>. |
std::exception | if called post-finalize or if the properties are missing the coulomb friction property (or if it is of the wrong type). |
geometry::GeometryId RegisterCollisionGeometry | ( | const Body< T > & | body, |
const math::RigidTransform< double > & | X_BG, | ||
const geometry::Shape & | shape, | ||
const std::string & | name, | ||
const CoulombFriction< double > & | coulomb_friction | ||
) |
Overload which specifies a single property: coulomb_friction.
geometry::GeometryId RegisterVisualGeometry | ( | const Body< T > & | body, |
const math::RigidTransform< double > & | X_BG, | ||
const geometry::Shape & | shape, | ||
const std::string & | name, | ||
const geometry::IllustrationProperties & | properties | ||
) |
Registers geometry in a SceneGraph with a given geometry::Shape to be used for visualization of a given body
.
[in] | body | The body for which geometry is being registered. |
[in] | X_BG | The fixed pose of the geometry frame G in the body frame B. |
[in] | shape | The geometry::Shape used for visualization. E.g.: geometry::Sphere, geometry::Cylinder, etc. |
[in] | name | The name for the geometry. It must satisfy the requirements defined in drake::geometry::GeometryInstance. |
[in] | properties | The illustration properties for this geometry. |
std::exception | if called post-finalize. |
std::exception | if scene_graph does not correspond to the same instance with which RegisterAsSourceForSceneGraph() was called. |
geometry::GeometryId RegisterVisualGeometry | ( | const Body< T > & | body, |
const math::RigidTransform< double > & | X_BG, | ||
const geometry::Shape & | shape, | ||
const std::string & | name, | ||
const Vector4< double > & | diffuse_color | ||
) |
Overload for visual geometry registration; it converts the diffuse_color
(RGBA with values in the range [0, 1]) into a geometry::DrakeVisualizer-compatible set of geometry::IllustrationProperties.
geometry::GeometryId RegisterVisualGeometry | ( | const Body< T > & | body, |
const math::RigidTransform< double > & | X_BG, | ||
const geometry::Shape & | shape, | ||
const std::string & | name | ||
) |
Overload for visual geometry registration; it relies on the downstream geometry::IllustrationProperties consumer to provide default parameter values (see Geometry Queries and Roles for details).
void set_contact_model | ( | ContactModel | model | ) |
Sets the contact model to be used by this
MultibodyPlant, see ContactModel for available options.
The default contact model is ContactModel::kHydroelasticWithFallback.
std::exception | iff called post-finalize. |
void set_contact_surface_representation | ( | geometry::HydroelasticContactRepresentation | representation | ) |
Sets the representation of contact surfaces to be used by this
MultibodyPlant.
See geometry::HydroelasticContactRepresentation for available options. See GetDefaultContactSurfaceRepresentation() for explanation of default values.
void set_discrete_contact_solver | ( | DiscreteContactSolver | contact_solver | ) |
Sets the contact solver type used for discrete MultibodyPlant models.
std::exception | iff called post-finalize. |
void set_penetration_allowance | ( | double | penetration_allowance = MultibodyPlantConfig{}.penetration_allowance | ) |
Sets the penetration allowance used to estimate the coefficients in the penalty method used to impose non-penetration among bodies.
Refer to the section Contact by penalty method for further details.
std::exception | if penetration_allowance is not positive. |
void set_stiction_tolerance | ( | double | v_stiction = MultibodyPlantConfig{}.stiction_tolerance | ) |
Currently MultibodyPlant uses the Stribeck approximation to model dry friction. The Stribeck model of friction is an approximation to Coulomb's law of friction that allows using continuous time integration without the need to specify complementarity constraints. While this results in a simpler model immediately tractable with standard numerical methods for integration of ODE's, it often leads to stiff dynamics that require an explicit integrator to take very small time steps. It is therefore recommended to use error controlled integrators when using this model or the discrete time stepping (see Choice of Time Advancement Strategy). See Continuous Approximation of Coulomb Friction for a detailed discussion of the Stribeck model.
Sets the stiction tolerance v_stiction
for the Stribeck model, where v_stiction
must be specified in m/s (meters per second.) v_stiction
defaults to a value of 1 millimeter per second. In selecting a value for v_stiction
, you must ask yourself the question, "When two objects are ostensibly in stiction, how much slip am I willing
to allow?" There are two opposing design issues in picking a value for vₛ. On the one hand, small values of vₛ make the problem numerically stiff during stiction, potentially increasing the integration cost. On the other hand, it should be picked to be appropriate for the scale of the problem. For example, a car simulation could allow a "large" value for vₛ of 1 cm/s (1×10⁻² m/s), but reasonable stiction for grasping a 10 cm box might require limiting residual slip to 1×10⁻³ m/s or less. Ultimately, picking the largest viable value will allow your simulation to run faster and more robustly. Note that v_stiction
is the slip velocity that we'd have when we are at edge of the friction cone. For cases when the friction force is well within the friction cone the slip velocity will always be smaller than this value. See also Continuous Approximation of Coulomb Friction.
std::exception | if v_stiction is non-positive. |
void SetActuationInArray | ( | ModelInstanceIndex | model_instance, |
const Eigen::Ref< const VectorX< T >> & | u_instance, | ||
EigenPtr< VectorX< T >> | u | ||
) | const |
Given the actuation values u_instance
for all actuators in model_instance
, this method sets the actuation vector u for the entire model to which this actuator belongs to.
This method throws an exception if the size of u_instance
is not equal to the number of degrees of freedom of all of the actuated joints in model_instance
.
[in] | u_instance | Actuation values for the actuators. It must be of size equal to the number of degrees of freedom of all of the actuated joints in model_instance . |
[out] | u | The vector containing the actuation values for the entire model. |
void SetContactSolver | ( | std::unique_ptr< contact_solvers::internal::ContactSolver< T >> | solver | ) |
For use only by advanced developers wanting to try out their custom contact solvers.
solver | The contact solver to be used for simulations of discrete models with frictional contact. Discrete updates will use this solver after this call. |
this
MultibodyPlant will no longer support scalar conversion to or from symbolic::Expression after a call to this method. void SetDefaultFreeBodyPose | ( | const Body< T > & | body, |
const math::RigidTransform< double > & | X_WB | ||
) |
Sets the default pose of body
.
If body.is_floating()
is true, this will affect subsequent calls to SetDefaultState(); otherwise, this value is effectively ignored.
[in] | body | Body whose default pose will be set. |
[in] | X_WB | Default pose of the body. |
|
override |
Sets state
according to defaults set by the user for joints (e.g.
RevoluteJoint::set_default_angle()) and free bodies (SetDefaultFreeBodyPose()). If the user does not specify defaults, the state corresponds to zero generalized positions and velocities.
std::exception | if called pre-finalize. See Finalize(). |
void SetDiscreteUpdateManager | ( | std::unique_ptr< internal::DiscreteUpdateManager< T >> | manager | ) |
For use only by advanced developers wanting to try out their custom time stepping strategies, including contact resolution.
With this method MultibodyPlant takes ownership of manager
.
manager | After this call the new manager is used to advance discrete states. |
std::exception | if called pre-finalize. See Finalize(). |
this
MultibodyPlant will no longer support scalar conversion to or from symbolic::Expression after a call to this method. void SetFreeBodyPose | ( | systems::Context< T > * | context, |
const Body< T > & | body, | ||
const math::RigidTransform< T > & | X_WB | ||
) | const |
Sets context
to store the pose X_WB
of a given body
B in the world frame W.
std::exception | if body is not a free body in the model. |
std::exception | if called pre-finalize. |
void SetFreeBodyPose | ( | const systems::Context< T > & | context, |
systems::State< T > * | state, | ||
const Body< T > & | body, | ||
const math::RigidTransform< T > & | X_WB | ||
) | const |
Sets state
to store the pose X_WB
of a given body
B in the world frame W, for a given context
of this
model.
std::exception | if body is not a free body in the model. |
std::exception | if called pre-finalize. |
state
comes from this MultibodyPlant. void SetFreeBodyPoseInAnchoredFrame | ( | systems::Context< T > * | context, |
const Frame< T > & | frame_F, | ||
const Body< T > & | body, | ||
const math::RigidTransform< T > & | X_FB | ||
) | const |
Updates context
to store the pose X_FB
of a given body
B in a frame F.
Frame F must be anchored, meaning that it is either directly welded to the world frame W or, more generally, that there is a kinematic path between frame F and the world frame W that only includes weld joints.
std::exception | if called pre-finalize. |
std::exception | if frame F is not anchored to the world. |
void SetFreeBodyPoseInWorldFrame | ( | systems::Context< T > * | context, |
const Body< T > & | body, | ||
const math::RigidTransform< T > & | X_WB | ||
) | const |
Sets context
to store the pose X_WB
of a given body
B in the world frame W.
[in] | context | The context to store the pose X_WB of body_B . |
[in] | body_B | The body B corresponding to the pose X_WB to be stored in context . |
X_WB | The pose of body frame B in the world frame W. |
std::exception | if body is not a free body in the model. |
std::exception | if called pre-finalize. |
void SetFreeBodyRandomPositionDistribution | ( | const Body< T > & | body, |
const Vector3< symbolic::Expression > & | position | ||
) |
Sets the distribution used by SetRandomState() to populate the free body's x-y-z position
with respect to World.
std::exception | if body is not a free body in the model. |
std::exception | if called pre-finalize. |
void SetFreeBodyRandomRotationDistribution | ( | const Body< T > & | body, |
const Eigen::Quaternion< symbolic::Expression > & | rotation | ||
) |
Sets the distribution used by SetRandomState() to populate the free body's rotation
with respect to World.
std::exception | if body is not a free body in the model. |
std::exception | if called pre-finalize. |
void SetFreeBodyRandomRotationDistributionToUniform | ( | const Body< T > & | body | ) |
Sets the distribution used by SetRandomState() to populate the free body's rotation with respect to World using uniformly random rotations.
std::exception | if body is not a free body in the model. |
std::exception | if called pre-finalize. |
void SetFreeBodySpatialVelocity | ( | systems::Context< T > * | context, |
const Body< T > & | body, | ||
const SpatialVelocity< T > & | V_WB | ||
) | const |
Sets context
to store the spatial velocity V_WB
of a given body
B in the world frame W.
std::exception | if body is not a free body in the model. |
std::exception | if called pre-finalize. |
void SetFreeBodySpatialVelocity | ( | const systems::Context< T > & | context, |
systems::State< T > * | state, | ||
const Body< T > & | body, | ||
const SpatialVelocity< T > & | V_WB | ||
) | const |
Sets state
to store the spatial velocity V_WB
of a given body
B in the world frame W, for a given context
of this
model.
std::exception | if body is not a free body in the model. |
std::exception | if called pre-finalize. |
state
comes from this MultibodyPlant. void SetPositions | ( | systems::Context< T > * | context, |
const Eigen::Ref< const VectorX< T >> & | q | ||
) | const |
Sets the generalized positions q in a given Context from a given vector.
Prefer this method over GetMutablePositions().
std::exception | if context is nullptr, if context does not correspond to the Context for a multibody model, or if the length of q is not equal to num_positions() . |
void SetPositions | ( | systems::Context< T > * | context, |
ModelInstanceIndex | model_instance, | ||
const Eigen::Ref< const VectorX< T >> & | q_instance | ||
) | const |
Sets the generalized positions q for a particular model instance in a given Context from a given vector.
std::exception | if the context is nullptr, if context does not correspond to the Context for a multibody model, if the model instance index is invalid, or if the length of q_instance is not equal to num_positions(model_instance) . |
void SetPositions | ( | const systems::Context< T > & | context, |
systems::State< T > * | state, | ||
ModelInstanceIndex | model_instance, | ||
const Eigen::Ref< const VectorX< T >> & | q_instance | ||
) | const |
(Advanced) Sets the generalized positions q for a particular model instance in a given State from a given vector.
std::exception | if the context is nullptr, if context does not correspond to the Context for a multibody model, if the model instance index is invalid, or if the length of q_instance is not equal to num_positions(model_instance) . |
state
comes from this MultibodyPlant. void SetPositionsAndVelocities | ( | systems::Context< T > * | context, |
const Eigen::Ref< const VectorX< T >> & | q_v | ||
) | const |
Sets generalized positions q and generalized velocities v in a given Context from a given vector [q; v].
Prefer this method over GetMutablePositionsAndVelocities().
std::exception | if context is nullptr, if context does not correspond to the context for a multibody model, or if the length of q_v is not equal to num_positions() + num_velocities() . |
void SetPositionsAndVelocities | ( | systems::Context< T > * | context, |
ModelInstanceIndex | model_instance, | ||
const Eigen::Ref< const VectorX< T >> & | q_v | ||
) | const |
Sets generalized positions q and generalized velocities v from a given vector [q; v] for a specified model instance in a given Context.
std::exception | if context is nullptr, if context does not correspond to the Context for a multibody model, if the model instance index is invalid, or if the length of q_v is not equal to num_positions(model_instance) + num_velocities(model_instance) . |
void SetPositionsInArray | ( | ModelInstanceIndex | model_instance, |
const Eigen::Ref< const VectorX< T >> & | q_instance, | ||
EigenPtr< VectorX< T >> | q | ||
) | const |
Sets the vector of generalized positions for model_instance
in q
using q_instance
, leaving all other elements in the array untouched.
This method throws an exception if q
is not of size MultibodyPlant::num_positions() or q_instance
is not of size MultibodyPlant::num_positions(model_instance)
.
|
override |
Assigns random values to all elements of the state, by drawing samples independently for each joint/free body (coming soon: and then solving a mathematical program to "project" these samples onto the registered system constraints).
void SetVelocities | ( | systems::Context< T > * | context, |
const Eigen::Ref< const VectorX< T >> & | v | ||
) | const |
Sets the generalized velocities v in a given Context from a given vector.
Prefer this method over GetMutableVelocities().
std::exception | if the context is nullptr, if the context does not correspond to the context for a multibody model, or if the length of v is not equal to num_velocities() . |
void SetVelocities | ( | systems::Context< T > * | context, |
ModelInstanceIndex | model_instance, | ||
const Eigen::Ref< const VectorX< T >> & | v_instance | ||
) | const |
Sets the generalized velocities v for a particular model instance in a given Context from a given vector.
std::exception | if the context is nullptr, if context does not correspond to the Context for a multibody model, if the model instance index is invalid, or if the length of v_instance is not equal to num_velocities(model_instance) . |
void SetVelocities | ( | const systems::Context< T > & | context, |
systems::State< T > * | state, | ||
ModelInstanceIndex | model_instance, | ||
const Eigen::Ref< const VectorX< T >> & | v_instance | ||
) | const |
(Advanced) Sets the generalized velocities v for a particular model instance in a given State from a given vector.
std::exception | if the context is nullptr, if context does not correspond to the Context for a multibody model, if the model instance index is invalid, or if the length of v_instance is not equal to num_velocities(model_instance) . |
state
comes from this MultibodyPlant. void SetVelocitiesInArray | ( | ModelInstanceIndex | model_instance, |
const Eigen::Ref< const VectorX< T >> & | v_instance, | ||
EigenPtr< VectorX< T >> | v | ||
) | const |
Sets the vector of generalized velocities for model_instance
in v
using v_instance
, leaving all other elements in the array untouched.
This method throws an exception if v
is not of size MultibodyPlant::num_velocities() or v_instance
is not of size MultibodyPlant::num_positions(model_instance)
.
double time_step | ( | ) | const |
The time step (or period) used to model this
plant as a discrete system with periodic updates.
Returns 0 (zero) if the plant is modeled as a continuous system. This property of the plant is specified at construction and therefore this query can be performed either pre- or post-finalize, see Finalize().
const WeldJoint<T>& WeldFrames | ( | const Frame< T > & | frame_on_parent_P, |
const Frame< T > & | frame_on_child_C, | ||
const math::RigidTransform< double > & | X_PC = math::RigidTransform< double >::Identity() |
||
) |
Welds frame_on_parent_P
and frame_on_child_C
with relative pose X_PC
.
That is, the pose of frame C in frame P is fixed, with value X_PC
. If X_PC
is omitted, the identity transform will be used. The call to this method creates and adds a new WeldJoint to the model. The new WeldJoint is named as: P.name() + "_welds_to_" + C.name().
std::exception | if the weld produces a duplicate joint name. |
const RigidBody<T>& world_body | ( | ) | const |
Returns a constant reference to the world body.
const BodyFrame<T>& world_frame | ( | ) | const |
Returns a constant reference to the world frame.
|
related |
Makes a new MultibodyPlant with discrete update period time_step
and adds it to a diagram builder together with the provided SceneGraph instance, connecting the geometry ports.
[in,out] | builder | Builder to add to. |
[in] | time_step | The discrete update period for the new MultibodyPlant to be added. Please refer to the documentation provided in MultibodyPlant::MultibodyPlant(double) for further details on the parameter time_step . |
[in] | scene_graph | (optional) Constructed scene graph. If none is provided, one will be created and used. |
builder
must be non-null. T | The scalar type, which must be one of the default scalars. |
|
related |
Adds a MultibodyPlant and a SceneGraph instance to a diagram builder, connecting the geometry ports.
[in,out] | builder | Builder to add to. |
[in] | plant | Plant to be added to the builder. |
[in] | scene_graph | (optional) Constructed scene graph. If none is provided, one will be created and used. |
builder
and plant
must be non-null. T | The scalar type, which must be one of the default scalars. |
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friend |
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friend |
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friend |
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friend |