Detailed Description

template<typename T>
class drake::multibody::PlanarJoint< T >

This joint models a planar joint allowing two bodies to translate and rotate relative to one another in a plane with three degrees of freedom.

That is, given a frame F attached to the parent body P and a frame M attached to the child body B (see the Joint class's documentation), this joint allows frame M to translate within the x-y plane of frame F and to rotate about the z-axis, with M's z-axis Mz and F's z-axis Fz coincident at all times. The translations along the x- and y-axes of F, the rotation about the z-axis and their rates specify the state of the joint. Zero (x, y, θ) corresponds to frames F and M being coincident and aligned. Translation (x, y) is defined to be positive in the direction of the respective axes and the rotation θ is defined to be positive according to the right-hand-rule with the thumb aligned in the direction of frame F's z-axis.

Template Parameters

T	The scalar type, which must be one of the default scalars.

#include <drake/multibody/tree/planar_joint.h>

Public Types
template<typename Scalar >
using	Context = systems::Context< Scalar >

Public Member Functions
	PlanarJoint (const std::string &name, const Frame< T > &frame_on_parent, const Frame< T > &frame_on_child, Vector3< double > damping)
	Constructor to create a planar joint between two bodies so that frame F attached to the parent body P and frame M attached to the child body B translate and rotate as described in the class's documentation. More...

	~PlanarJoint () final

const std::string &	type_name () const final
	Returns a string identifying the type of `this` joint, such as "revolute" or "prismatic". More...

Vector3< double >	default_damping () const
	Returns `this` joint's default damping constant in N⋅s/m for the translational degrees and N⋅m⋅s for the rotational degree. More...

Vector2< double >	get_default_translation () const
	Gets the default position for `this` joint. More...

void	set_default_translation (const Vector2< double > &p_FoMo_F)
	Sets the default position of this joint. More...

double	get_default_rotation () const
	Gets the default angle for `this` joint. More...

void	set_default_rotation (double theta)
	Sets the default angle of this joint. More...

void	set_default_pose (const Vector2< double > &p_FoMo_F, double theta)
	Sets the default position and angle of this joint. More...

void	set_random_pose_distribution (const Vector2< symbolic::Expression > &p_FoMo_F, const symbolic::Expression &theta)
	Sets the random distribution that the position and angle of this joint will be randomly sampled from. More...

Does not allow copy, move, or assignment
	PlanarJoint (const PlanarJoint &)=delete

PlanarJoint &	operator= (const PlanarJoint &)=delete

	PlanarJoint (PlanarJoint &&)=delete

PlanarJoint &	operator= (PlanarJoint &&)=delete

Context-dependent value access
Vector2< T >	get_translation (const Context< T > &context) const
	Gets the position of `this` joint from `context`. More...

const PlanarJoint< T > &	set_translation (Context< T > *context, const Vector2< T > &p_FoMo_F) const
	Sets the `context` so that the position of `this` joint equals `p_FoMo_F`. More...

const T &	get_rotation (const systems::Context< T > &context) const
	Gets the angle θ of `this` joint from `context`. More...

const PlanarJoint< T > &	set_rotation (systems::Context< T > *context, const T &theta) const
	Sets the `context` so that the angle θ of `this` joint equals `theta`. More...

const PlanarJoint< T > &	set_pose (systems::Context< T > *context, const Vector2< T > &p_FoMo_F, const T &theta) const
	Sets the `context` so that the position of `this` joint equals `p_FoMo_F` and its angle equals `theta`. More...

Vector2< T >	get_translational_velocity (const systems::Context< T > &context) const
	Gets the translational velocity v_FoMo_F, in meters per second, of `this` joint's Mo measured and expressed in frame F from `context`. More...

const PlanarJoint< T > &	set_translational_velocity (systems::Context< T > *context, const Vector2< T > &v_FoMo_F) const
	Sets the translational velocity, in meters per second, of this `this` joint's Mo measured and expressed in frame F to `v_FoMo_F`. More...

const T &	get_angular_velocity (const systems::Context< T > &context) const
	Gets the rate of change, in radians per second, of `this` joint's angle θ from `context`. More...

const PlanarJoint< T > &	set_angular_velocity (systems::Context< T > *context, const T &theta_dot) const
	Sets the rate of change, in radians per second, of `this` joint's angle θ (see class documentation) to `theta_dot`. More...

Public Member Functions inherited from Joint< T >
	Joint (const std::string &name, const Frame< T > &frame_on_parent, const Frame< T > &frame_on_child, VectorX< double > damping, const VectorX< double > &pos_lower_limits, const VectorX< double > &pos_upper_limits, const VectorX< double > &vel_lower_limits, const VectorX< double > &vel_upper_limits, const VectorX< double > &acc_lower_limits, const VectorX< double > &acc_upper_limits)
	Creates a joint between two Frame objects which imposes a given kinematic relation between frame F attached on the parent body P and frame M attached on the child body B. More...

	Joint (const std::string &name, const Frame< T > &frame_on_parent, const Frame< T > &frame_on_child, const VectorX< double > &pos_lower_limits, const VectorX< double > &pos_upper_limits, const VectorX< double > &vel_lower_limits, const VectorX< double > &vel_upper_limits, const VectorX< double > &acc_lower_limits, const VectorX< double > &acc_upper_limits)
	Additional constructor overload for joints with zero damping. More...

virtual	~Joint ()

JointIndex	index () const
	Returns this element's unique index. More...

int	ordinal () const
	Returns this element's unique ordinal. More...

const std::string &	name () const
	Returns the name of this joint. More...

const RigidBody< T > &	parent_body () const
	Returns a const reference to the parent body P. More...

const RigidBody< T > &	child_body () const
	Returns a const reference to the child body B. More...

const Frame< T > &	frame_on_parent () const
	Returns a const reference to the frame F attached on the parent body P. More...

const Frame< T > &	frame_on_child () const
	Returns a const reference to the frame M attached on the child body B. More...

int	velocity_start () const
	Returns the index to the first generalized velocity for this joint within the vector v of generalized velocities for the full multibody system. More...

int	num_velocities () const
	Returns the number of generalized velocities describing this joint. More...

int	position_start () const
	Returns the index to the first generalized position for this joint within the vector q of generalized positions for the full multibody system. More...

int	num_positions () const
	Returns the number of generalized positions describing this joint. More...

bool	can_rotate () const
	Returns true if this joint's mobility allows relative rotation of the two frames associated with this joint. More...

bool	can_translate () const
	Returns true if this joint's mobility allows relative translation of the two frames associated with this joint. More...

std::string	position_suffix (int position_index_in_joint) const
	Returns a string suffix (e.g. More...

std::string	velocity_suffix (int velocity_index_in_joint) const
	Returns a string suffix (e.g. More...

const T &	GetOnePosition (const systems::Context< T > &context) const
	Returns the position coordinate for joints with a single degree of freedom. More...

const T &	GetOneVelocity (const systems::Context< T > &context) const
	Returns the velocity coordinate for joints with a single degree of freedom. More...

void	AddInOneForce (const systems::Context< T > &context, int joint_dof, const T &joint_tau, MultibodyForces< T > *forces) const
	Adds into `forces` a force along the one of the joint's degrees of freedom indicated by index `joint_dof`. More...

void	AddInDamping (const systems::Context< T > &context, MultibodyForces< T > *forces) const
	Adds into `forces` the force due to damping within `this` joint. More...

void	Lock (systems::Context< T > *context) const
	Lock the joint. More...

void	Unlock (systems::Context< T > *context) const
	Unlock the joint. More...

bool	is_locked (const systems::Context< T > &context) const

const VectorX< double > &	default_damping_vector () const
	Returns all default damping coefficients for joints that model viscous damping, of size num_velocities(). More...

const VectorX< T > &	GetDampingVector (const systems::Context< T > &context) const
	Returns the Context dependent damping coefficients stored as parameters in `context`. More...

void	set_default_damping_vector (const VectorX< double > &damping)
	Sets the default value of the viscous damping coefficients for this joint. More...

void	SetDampingVector (systems::Context< T > *context, const VectorX< T > &damping) const
	Sets the value of the viscous damping coefficients for this joint, stored as parameters in `context`. More...

	Joint (const Joint &)=delete

Joint &	operator= (const Joint &)=delete

	Joint (Joint &&)=delete

Joint &	operator= (Joint &&)=delete

const VectorX< double > &	position_lower_limits () const

const VectorX< double > &	position_upper_limits () const
	Returns the position upper limits. More...

const VectorX< double > &	velocity_lower_limits () const
	Returns the velocity lower limits. More...

const VectorX< double > &	velocity_upper_limits () const
	Returns the velocity upper limits. More...

const VectorX< double > &	acceleration_lower_limits () const
	Returns the acceleration lower limits. More...

const VectorX< double > &	acceleration_upper_limits () const
	Returns the acceleration upper limits. More...

const VectorX< double > &	default_positions () const
	Returns the default positions. More...

void	set_position_limits (const VectorX< double > &lower_limits, const VectorX< double > &upper_limits)
	Sets the position limits to `lower_limits` and `upper_limits`. More...

void	set_velocity_limits (const VectorX< double > &lower_limits, const VectorX< double > &upper_limits)
	Sets the velocity limits to `lower_limits` and `upper_limits`. More...

void	set_acceleration_limits (const VectorX< double > &lower_limits, const VectorX< double > &upper_limits)
	Sets the acceleration limits to `lower_limits` and `upper_limits`. More...

void	set_default_positions (const VectorX< double > &default_positions)
	Sets the default positions to `default_positions`. More...

void	SetDefaultPose (const math::RigidTransform< double > &X_FM)
	Sets this Joint's default generalized positions q₀ such that the pose of the child frame M in the parent frame F best matches the given pose. More...

math::RigidTransform< double >	GetDefaultPose () const
	Returns this Joint's default pose as a RigidTransform X_FM. More...

void	SetDefaultPosePair (const Quaternion< double > &q_FM, const Vector3< double > &p_FM)
	(Advanced) This is the same as SetDefaultPose() except it takes the pose as a (quaternion, translation vector) pair. More...

std::pair< Eigen::Quaternion< double >, Vector3< double > >	GetDefaultPosePair () const
	(Advanced) This is the same as GetDefaultPose() except it returns this Joint's default pose as a (quaternion, translation vector) pair. More...

Public Member Functions inherited from MultibodyElement< T >
virtual	~MultibodyElement ()

ModelInstanceIndex	model_instance () const
	Returns the ModelInstanceIndex of the model instance to which this element belongs. More...

template<typename MultibodyPlantDeferred = MultibodyPlant<T>>
const MultibodyPlantDeferred &	GetParentPlant () const
	Returns the MultibodyPlant that owns this MultibodyElement. More...

void	DeclareParameters (internal::MultibodyTreeSystem< T > *tree_system)
	Declares MultibodyTreeSystem Parameters at MultibodyTreeSystem::Finalize() time. More...

void	SetDefaultParameters (systems::Parameters< T > *parameters) const
	Sets default values of parameters belonging to each MultibodyElement in `parameters` at a call to MultibodyTreeSystem::SetDefaultParameters(). More...

	MultibodyElement (const MultibodyElement &)=delete

MultibodyElement &	operator= (const MultibodyElement &)=delete

	MultibodyElement (MultibodyElement &&)=delete

MultibodyElement &	operator= (MultibodyElement &&)=delete

Static Public Attributes
static constexpr char	kTypeName [] = "planar"
	The name for this Joint type. More...

Friends
template<typename >
class	PlanarJoint

Additional Inherited Members
Protected Member Functions inherited from Joint< T >
virtual void	DoSetDefaultPosePair (const Quaternion< double > &q_FM, const Vector3< double > &p_FM)
	Implementation of the NVI SetDefaultPose(). More...

virtual std::pair< Eigen::Quaternion< double >, Vector3< double > >	DoGetDefaultPosePair () const
	Implementation of the NVI GetDefaultPose(). More...

virtual const T &	DoGetOnePosition (const systems::Context< T > &) const
	Implementation of the NVI GetOnePosition() that must only be implemented by those joint subclasses that have a single degree of freedom. More...

virtual const T &	DoGetOneVelocity (const systems::Context< T > &) const
	Implementation of the NVI GetOneVelocity() that must only be implemented by those joint subclasses that have a single degree of freedom. More...

void	DoSetTopology (const internal::MultibodyTreeTopology &) override
	Implementation of the NVI SetTopology(). More...

const JointImplementation &	get_implementation () const
	Returns a const reference to the internal implementation of `this` joint. More...

bool	has_implementation () const
	Returns whether `this` joint owns a particular implementation. More...

std::pair< const Frame< T > , const Frame< T > >	tree_frames (bool use_reversed_mobilizer) const
	Utility for concrete joint implementations to use to select the inboard/outboard frames for a tree in the spanning forest, given whether they should be reversed from the parent/child frames that are members of this Joint object. More...

Protected Member Functions inherited from MultibodyElement< T >
	MultibodyElement ()
	Default constructor made protected so that sub-classes can still declare their default constructors if they need to. More...

	MultibodyElement (ModelInstanceIndex model_instance)
	Constructor which allows specifying a model instance. More...

	MultibodyElement (ModelInstanceIndex model_instance, int64_t index)
	Both the model instance and element index are specified. More...

template<typename ElementIndexType >
ElementIndexType	index_impl () const
	Returns this element's unique index. More...

int	ordinal_impl () const
	Returns this element's unique ordinal. More...

const internal::MultibodyTree< T > &	get_parent_tree () const
	Returns a constant reference to the parent MultibodyTree that owns this element. More...

const internal::MultibodyTreeSystem< T > &	GetParentTreeSystem () const
	Returns a constant reference to the parent MultibodyTreeSystem that owns the parent MultibodyTree that owns this element. More...

void	SetTopology (const internal::MultibodyTreeTopology &tree)
	Gives MultibodyElement-derived objects the opportunity to retrieve their topology after MultibodyTree::Finalize() is invoked. More...

systems::NumericParameterIndex	DeclareNumericParameter (internal::MultibodyTreeSystem< T > *tree_system, const systems::BasicVector< T > &model_vector)
	To be used by MultibodyElement-derived objects when declaring parameters in their implementation of DoDeclareParameters(). More...

systems::AbstractParameterIndex	DeclareAbstractParameter (internal::MultibodyTreeSystem< T > *tree_system, const AbstractValue &model_value)
	To be used by MultibodyElement-derived objects when declaring parameters in their implementation of DoDeclareParameters(). More...

Member Typedef Documentation

◆ Context

using Context = systems::Context<Scalar>

Constructor & Destructor Documentation

◆ PlanarJoint() [1/3]

PlanarJoint ( const PlanarJoint< T > & )

delete

◆ PlanarJoint() [2/3]

PlanarJoint ( PlanarJoint< T > && )

delete

◆ PlanarJoint() [3/3]

PlanarJoint	(	const std::string &	name,
		const Frame< T > &	frame_on_parent,
		const Frame< T > &	frame_on_child,
		Vector3< double >	damping
	)

Constructor to create a planar joint between two bodies so that frame F attached to the parent body P and frame M attached to the child body B translate and rotate as described in the class's documentation.

This constructor signature creates a joint with no joint limits, i.e. the joint position, velocity and acceleration limits are the pair (-∞, ∞). These can be set using the Joint methods set_position_limits(), set_velocity_limits() and set_acceleration_limits(). The first three arguments to this constructor are those of the Joint class constructor. See the Joint class's documentation for details. The additional parameters are:

Parameters

[in] damping Viscous damping coefficient, in N⋅s/m for translation and N⋅m⋅s for rotation, used to model losses within the joint. See documentation of default_damping() for details on modelling of the damping force and torque.

Exceptions

std::exception if any element of damping is negative.

◆ ~PlanarJoint()

~PlanarJoint ( )

final

Member Function Documentation

◆ default_damping()

Vector3<double> default_damping ( ) const

Returns this joint's default damping constant in N⋅s/m for the translational degrees and N⋅m⋅s for the rotational degree.

The damping force (in N) is modeled as fᵢ = -dampingᵢ⋅vᵢ, i = 1, 2 i.e. opposing motion, with vᵢ the translation rates along the i-th axis for this joint (see get_translational_velocity()) and fᵢ the force on child body B at Mo and expressed in F. That is, f_BMo_F = (f₁, f₂). The damping torque (in N⋅m) is modeled as τ = -damping₃⋅ω i.e. opposing motion, with ω the angular rate for this joint (see get_angular_velocity()) and τ the torque on child body B expressed in frame F as t_B_F = τ⋅Fz_F.

◆ get_angular_velocity()

const T& get_angular_velocity ( const systems::Context< T > & context ) const

Gets the rate of change, in radians per second, of this joint's angle θ from context.

See class documentation for the definition of this angle.

Parameters

[in] context The context of the model this joint belongs to.

Return values

theta_dot The rate of change of this joint's angle θ as stored in the context.

◆ get_default_rotation()

double get_default_rotation ( ) const

Gets the default angle for this joint.

Return values

theta The default angle of this joint.

◆ get_default_translation()

Vector2<double> get_default_translation ( ) const

Gets the default position for this joint.

Return values

p_FoMo_F The default position of this joint.

◆ get_rotation()

const T& get_rotation ( const systems::Context< T > & context ) const

Gets the angle θ of this joint from context.

Parameters

[in] context The context of the model this joint belongs to.

Return values

theta The angle of this joint stored in the context. See class documentation for details.

◆ get_translation()

Vector2<T> get_translation ( const Context< T > & context ) const

Gets the position of this joint from context.

Parameters

[in] context The context of the model this joint belongs to.

Return values

p_FoMo_F The position of this joint stored in the context ordered as (x, y). See class documentation for details.

◆ get_translational_velocity()

Vector2<T> get_translational_velocity ( const systems::Context< T > & context ) const

Gets the translational velocity v_FoMo_F, in meters per second, of this joint's Mo measured and expressed in frame F from context.

Parameters

[in] context The context of the model this joint belongs to.

Return values

v_FoMo_F The translational velocity of this joint as stored in the context.

◆ operator=() [1/2]

PlanarJoint& operator= ( PlanarJoint< T > && )

delete

◆ operator=() [2/2]

PlanarJoint& operator= ( const PlanarJoint< T > & )

delete

◆ set_angular_velocity()

const PlanarJoint<T>& set_angular_velocity	(	systems::Context< T > *	context,
		const T &	theta_dot
	)		const

Sets the rate of change, in radians per second, of this joint's angle θ (see class documentation) to theta_dot.

The new rate of change gets stored in context.

Parameters

[in]	context	The context of the model this joint belongs to.
[in]	theta_dot	The desired rates of change of `this` joint's angle in radians per second.

Returns: a constant reference to this joint.

◆ set_default_pose()

void set_default_pose	(	const Vector2< double > &	p_FoMo_F,
		double	theta
	)

Sets the default position and angle of this joint.

Parameters

[in]	p_FoMo_F	The desired default position of the joint
[in]	theta	The desired default angle of the joint

◆ set_default_rotation()

void set_default_rotation ( double theta )

Sets the default angle of this joint.

Parameters

[in] theta The desired default angle of the joint

◆ set_default_translation()

void set_default_translation ( const Vector2< double > & p_FoMo_F )

Sets the default position of this joint.

Parameters

[in] p_FoMo_F The desired default position of the joint

◆ set_pose()

const PlanarJoint<T>& set_pose	(	systems::Context< T > *	context,
		const Vector2< T > &	p_FoMo_F,
		const T &	theta
	)		const

Sets the context so that the position of this joint equals p_FoMo_F and its angle equals theta.

Parameters

[in]	context	The context of the model this joint belongs to.
[in]	p_FoMo_F	The desired position in meters to be stored in `context` ordered as (x, y). See class documentation for details.
[in]	theta	The desired angle in radians to be stored in `context`. See class documentation for details.

Returns: a constant reference to this joint.

◆ set_random_pose_distribution()

void set_random_pose_distribution	(	const Vector2< symbolic::Expression > &	p_FoMo_F,
		const symbolic::Expression &	theta
	)

Sets the random distribution that the position and angle of this joint will be randomly sampled from.

See class documentation for details on the definition of the position and angle.

◆ set_rotation()

const PlanarJoint<T>& set_rotation	(	systems::Context< T > *	context,
		const T &	theta
	)		const

Sets the context so that the angle θ of this joint equals theta.

Parameters

[in]	context	The context of the model this joint belongs to.
[in]	theta	The desired angle in radians to be stored in `context`. See class documentation for details.

Returns: a constant reference to this joint.

◆ set_translation()

const PlanarJoint<T>& set_translation	(	Context< T > *	context,
		const Vector2< T > &	p_FoMo_F
	)		const

Sets the context so that the position of this joint equals p_FoMo_F.

Parameters

[in]	context	The context of the model this joint belongs to.
[in]	p_FoMo_F	The desired position in meters to be stored in `context` ordered as (x, y). See class documentation for details.

Returns: a constant reference to this joint.

◆ set_translational_velocity()

const PlanarJoint<T>& set_translational_velocity	(	systems::Context< T > *	context,
		const Vector2< T > &	v_FoMo_F
	)		const

Sets the translational velocity, in meters per second, of this this joint's Mo measured and expressed in frame F to v_FoMo_F.

The new translational velocity gets stored in context.

Parameters

[in]	context	The context of the model this joint belongs to.
[in]	v_FoMo_F	The desired translational velocity of `this` joint in meters per second.

Returns: a constant reference to this joint.

◆ type_name()

const std::string& type_name ( ) const

finalvirtual

Returns a string identifying the type of this joint, such as "revolute" or "prismatic".

Implements Joint< T >.

Friends And Related Function Documentation

◆ PlanarJoint

friend class PlanarJoint

friend

Member Data Documentation

◆ kTypeName

constexpr char kTypeName[] = "planar"

static

The name for this Joint type.

The documentation for this class was generated from the following file:

drake/multibody/tree/planar_joint.h

Detailed Description

template<typename T> class drake::multibody::PlanarJoint< T >

Public Types

Public Member Functions

Static Public Attributes

Friends

Additional Inherited Members

Member Typedef Documentation

◆ Context

Constructor & Destructor Documentation

◆ PlanarJoint() [1/3]

◆ PlanarJoint() [2/3]

◆ PlanarJoint() [3/3]

◆ ~PlanarJoint()

Member Function Documentation

◆ default_damping()

◆ get_angular_velocity()

◆ get_default_rotation()

◆ get_default_translation()

◆ get_rotation()

◆ get_translation()

◆ get_translational_velocity()

◆ operator=() [1/2]

◆ operator=() [2/2]

◆ set_angular_velocity()

◆ set_default_pose()

◆ set_default_rotation()

◆ set_default_translation()

◆ set_pose()

◆ set_random_pose_distribution()

◆ set_rotation()

◆ set_translation()

◆ set_translational_velocity()

◆ type_name()

Friends And Related Function Documentation

◆ PlanarJoint

Member Data Documentation

◆ kTypeName

template<typename T>
class drake::multibody::PlanarJoint< T >