Detailed Description

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

This Joint allows two bodies to translate relative to one another along a common axis.

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 frames F and M to translate with respect to each other along an axis â. The translation distance is defined positive when child body B translates along the direction of â. Axis â is constant and has the same measures in both frames F and M, that is, â_F = â_M.

Template Parameters

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

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

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

Public Member Functions
	PrismaticJoint (const std::string &name, const Frame< T > &frame_on_parent, const Frame< T > &frame_on_child, const Vector3< double > &axis, double pos_lower_limit=-std::numeric_limits< double >::infinity(), double pos_upper_limit=std::numeric_limits< double >::infinity(), double damping=0)
	Constructor to create a prismatic joint between two bodies so that frame F attached to the parent body P and frame M attached to the child body B, translate relatively to one another along a common axis. More...

	~PrismaticJoint () override

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

const Vector3< double > &	translation_axis () const
	Returns the axis of translation for `this` joint as a unit vector. More...

double	default_damping () const
	Returns `this` joint's default damping constant in N⋅s/m. More...

void	set_default_damping (double damping)
	Sets the default value of viscous damping for this joint, in N⋅s/m. More...

double	position_lower_limit () const
	Returns the position lower limit for `this` joint in meters. More...

double	position_upper_limit () const
	Returns the position upper limit for `this` joint in meters. More...

double	velocity_lower_limit () const
	Returns the velocity lower limit for `this` joint in meters per second. More...

double	velocity_upper_limit () const
	Returns the velocity upper limit for `this` joint in meters per second. More...

double	acceleration_lower_limit () const
	Returns the acceleration lower limit for `this` joint in meters per second squared. More...

double	acceleration_upper_limit () const
	Returns the acceleration upper limit for `this` joint in meters per second squared. More...

double	get_default_translation () const
	Gets the default translation. More...

void	set_default_translation (double translation)
	Sets the `default_positions` of this joint (in this case a single translation) More...

void	set_random_translation_distribution (const symbolic::Expression &translation)

void	AddInForce (const systems::Context< T > &context, const T &force, MultibodyForces< T > *multibody_forces) const
	Adds into `multibody_forces` a given `force`, in Newtons, for `this` joint that is to be applied along the joint's axis. More...

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

PrismaticJoint &	operator= (const PrismaticJoint &)=delete

	PrismaticJoint (PrismaticJoint &&)=delete

PrismaticJoint &	operator= (PrismaticJoint &&)=delete

Context-dependent value access
const T &	get_translation (const Context< T > &context) const
	Gets the translation distance of `this` mobilizer from `context`. More...

const PrismaticJoint< T > &	set_translation (Context< T > *context, const T &translation) const
	Sets `context` so that the generalized coordinate corresponding to the translation distance of `this` joint equals `translation`. More...

const T &	get_translation_rate (const Context< T > &context) const
	Gets the rate of change, in meters per second, of `this` joint's translation distance (see get_translation()) from `context`. More...

const PrismaticJoint< T > &	set_translation_rate (Context< T > *context, const T &translation_dot) const
	Sets the rate of change, in meters per second, of `this` joint's translation distance to `translation_dot`. More...

const T &	GetDamping (const Context< T > &context) const
	Returns the Context dependent damping coefficient stored as a parameter in `context`. More...

void	SetDamping (Context< T > *context, const T &damping) const
	Sets the value of the viscous damping coefficient for this joint, stored as a parameter in `context`. 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 const char	kTypeName [] = "prismatic"

Protected Member Functions
void	DoAddInOneForce (const systems::Context< T > &, int joint_dof, const T &joint_tau, MultibodyForces< T > *forces) const final
	Joint<T> virtual override called through public NVI, Joint::AddInForce(). More...

void	DoAddInDamping (const systems::Context< T > &context, MultibodyForces< T > *forces) const override
	Joint<T> override called through public NVI, Joint::AddInDamping(). More...

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...

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...

Friends
template<typename >
class	PrismaticJoint

Member Typedef Documentation

◆ Context

using Context = systems::Context<Scalar>

Constructor & Destructor Documentation

◆ PrismaticJoint() [1/3]

PrismaticJoint ( const PrismaticJoint< T > & )

delete

◆ PrismaticJoint() [2/3]

PrismaticJoint ( PrismaticJoint< T > && )

delete

◆ PrismaticJoint() [3/3]

PrismaticJoint	(	const std::string &	name,
		const Frame< T > &	frame_on_parent,
		const Frame< T > &	frame_on_child,
		const Vector3< double > &	axis,
		double	pos_lower_limit = `-std::numeric_limits< double >::infinity()`,
		double	pos_upper_limit = `std::numeric_limits< double >::infinity()`,
		double	damping = `0`
	)

Constructor to create a prismatic joint between two bodies so that frame F attached to the parent body P and frame M attached to the child body B, translate relatively to one another along a common axis.

See this class's documentation for further details on the definition of these frames and translation distance. The first three arguments to this constructor are those of the Joint class constructor. See the Joint class's documentation for details. The additional parameter axis is:

Parameters

[in]	axis	A vector in ℝ³ specifying the translation axis for this joint. Given that frame M only translates with respect to F and there is no relative rotation, the measures of `axis` in either frame F or M are exactly the same, that is, `axis_F = axis_M`. This vector can have any length, only the direction is used.
[in]	pos_lower_limit	Lower position limit, in meters, for the translation coordinate (see get_translation()).
[in]	pos_upper_limit	Upper position limit, in meters, for the translation coordinate (see get_translation()).
[in]	damping	Viscous damping coefficient, in N⋅s/m, used to model losses within the joint. The damping force (in N) is modeled as `f = -damping⋅v`, i.e. opposing motion, with v the translational speed for `this` joint (see get_translation_rate()).

Exceptions

std::exception	if the L2 norm of `axis` is less than the square root of machine epsilon.
std::exception	if damping is negative.
std::exception	if pos_lower_limit > pos_upper_limit.

◆ ~PrismaticJoint()

~PrismaticJoint ( )

override

Member Function Documentation

◆ acceleration_lower_limit()

double acceleration_lower_limit ( ) const

Returns the acceleration lower limit for this joint in meters per second squared.

◆ acceleration_upper_limit()

double acceleration_upper_limit ( ) const

Returns the acceleration upper limit for this joint in meters per second squared.

◆ AddInForce()

void AddInForce	(	const systems::Context< T > &	context,
		const T &	force,
		MultibodyForces< T > *	multibody_forces
	)		const

Adds into multibody_forces a given force, in Newtons, for this joint that is to be applied along the joint's axis.

The force is defined to be positive in the direction along this joint's axis. That is, a positive force causes a positive translational acceleration along the joint's axis.

◆ default_damping()

double default_damping ( ) const

Returns this joint's default damping constant in N⋅s/m.

◆ DoAddInDamping()

void DoAddInDamping	(	const systems::Context< T > &	context,
		MultibodyForces< T > *	forces
	)		const

overrideprotectedvirtual

Joint<T> override called through public NVI, Joint::AddInDamping().

Therefore arguments were already checked to be valid. This method adds into forces a dissipative force according to the viscous law f = -d⋅v, with d the damping coefficient (see default_damping()).

Reimplemented from Joint< T >.

◆ DoAddInOneForce()

void DoAddInOneForce	(	const systems::Context< T > &	,
		int	joint_dof,
		const T &	joint_tau,
		MultibodyForces< T > *	forces
	)		const

finalprotectedvirtual

Joint<T> virtual override called through public NVI, Joint::AddInForce().

Therefore arguments were already checked to be valid. For a PrismaticJoint, we must always have joint_dof = 0 since there is only a single degree of freedom (num_velocities() == 1). joint_tau is the linear force applied along the joint's axis, on the body declared as child (according to the prismatic joint's constructor) at the origin of the child frame (which is coincident with the origin of the parent frame at all times).

Implements Joint< T >.

◆ get_default_translation()

double get_default_translation ( ) const

Gets the default translation.

Wrapper for the more general Joint::default_positions().

Returns: The default translation of this stored in default_positions_.

◆ get_translation()

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

Gets the translation distance of this mobilizer from context.

Parameters

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

Returns: The translation coordinate of this joint read from context.

◆ get_translation_rate()

const T& get_translation_rate ( const Context< T > & context ) const

Gets the rate of change, in meters per second, of this joint's translation distance (see get_translation()) from context.

Parameters

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

Returns: The rate of change of this joint's translation read from context.

◆ GetDamping()

const T& GetDamping ( const Context< T > & context ) const

Returns the Context dependent damping coefficient stored as a parameter in context.

Refer to default_damping() for details.

Parameters

[in] context The context storing the state and parameters for the model to which this joint belongs.

◆ operator=() [1/2]

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

delete

◆ operator=() [2/2]

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

delete

◆ position_lower_limit()

double position_lower_limit ( ) const

Returns the position lower limit for this joint in meters.

◆ position_upper_limit()

double position_upper_limit ( ) const

Returns the position upper limit for this joint in meters.

◆ set_default_damping()

void set_default_damping ( double damping )

Sets the default value of viscous damping for this joint, in N⋅s/m.

Exceptions

std::exception if damping is negative.

Precondition: the MultibodyPlant must not be finalized.

◆ set_default_translation()

void set_default_translation ( double translation )

Sets the default_positions of this joint (in this case a single translation)

Parameters

[in] translation The desired default translation of the joint

◆ set_random_translation_distribution()

void set_random_translation_distribution ( const symbolic::Expression & translation )

◆ set_translation()

const PrismaticJoint<T>& set_translation	(	Context< T > *	context,
		const T &	translation
	)		const

Sets context so that the generalized coordinate corresponding to the translation distance of this joint equals translation.

Parameters

[in]	context	The context of the MultibodyTree this joint belongs to.
[in]	translation	The desired translation in meters to be stored in `context`.

Returns: a constant reference to this joint.

◆ set_translation_rate()

const PrismaticJoint<T>& set_translation_rate	(	Context< T > *	context,
		const T &	translation_dot
	)		const

Sets the rate of change, in meters per second, of this joint's translation distance to translation_dot.

The new rate of change translation_dot gets stored in context.

Parameters

[in]	context	The context of the MultibodyTree this joint belongs to.
[in]	translation_dot	The desired rate of change of `this` joints's translation in meters per second.

Returns: a constant reference to this joint.

◆ SetDamping()

void SetDamping	(	Context< T > *	context,
		const T &	damping
	)		const

Sets the value of the viscous damping coefficient for this joint, stored as a parameter in context.

Refer to default_damping() for details.

Parameters

[out]	context	The context storing the state and parameters for the model to which `this` joint belongs.
[in]	damping	The damping value.

Exceptions

std::exception if damping is negative.

◆ translation_axis()

const Vector3<double>& translation_axis ( ) const

Returns the axis of translation for this joint as a unit vector.

Since the measures of this axis in either frame F or M are the same (see this class's documentation for frame definitions) then, axis = axis_F = axis_M.

◆ type_name()

const std::string& type_name ( ) const

overridevirtual

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

Implements Joint< T >.

◆ velocity_lower_limit()

double velocity_lower_limit ( ) const

Returns the velocity lower limit for this joint in meters per second.

◆ velocity_upper_limit()

double velocity_upper_limit ( ) const

Returns the velocity upper limit for this joint in meters per second.

Friends And Related Function Documentation

◆ PrismaticJoint

friend class PrismaticJoint

friend

Member Data Documentation

◆ kTypeName

const char kTypeName = "prismatic"

static

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

drake/multibody/tree/prismatic_joint.h

Detailed Description

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

Public Types

Public Member Functions

Static Public Attributes

Protected Member Functions

Friends

Member Typedef Documentation

◆ Context

Constructor & Destructor Documentation

◆ PrismaticJoint() [1/3]

◆ PrismaticJoint() [2/3]

◆ PrismaticJoint() [3/3]

◆ ~PrismaticJoint()

Member Function Documentation

◆ acceleration_lower_limit()

◆ acceleration_upper_limit()

◆ AddInForce()

◆ default_damping()

◆ DoAddInDamping()

◆ DoAddInOneForce()

◆ get_default_translation()

◆ get_translation()

◆ get_translation_rate()

◆ GetDamping()

◆ operator=() [1/2]

◆ operator=() [2/2]

◆ position_lower_limit()

◆ position_upper_limit()

◆ set_default_damping()

◆ set_default_translation()

◆ set_random_translation_distribution()

◆ set_translation()

◆ set_translation_rate()

◆ SetDamping()

◆ translation_axis()

◆ type_name()

◆ velocity_lower_limit()

◆ velocity_upper_limit()

Friends And Related Function Documentation

◆ PrismaticJoint

Member Data Documentation

◆ kTypeName

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