Detailed Description

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

This joint models a screw joint allowing two bodies to rotate about one axis while translating along that same axis with one degree 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 (while rotating) along an axis â. Axis â is constant and has the same measures in both frames F and M, that is, â_F = â_M. The rotation about the â_F axis and its rate specify the state of the joint. Zero (θ) corresponds to frames F and M being coincident and aligned. The translation distance is defined positive when child body B translates along the direction of â, and the rotation θ is defined to be positive according to the right-hand-rule with the thumb aligned in the direction of the â_F axis.

Template Parameters

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

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

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

Public Member Functions
	ScrewJoint (const std::string &name, const Frame< T > &frame_on_parent, const Frame< T > &frame_on_child, double screw_pitch, double damping)
	Constructor to create a screw 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...

	ScrewJoint (const std::string &name, const Frame< T > &frame_on_parent, const Frame< T > &frame_on_child, const Vector3< double > &axis, double screw_pitch, double damping)
	Constructor to create a screw 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...

	~ScrewJoint () final

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

const Vector3< double > &	screw_axis () const
	Returns the normalized axis of motion of `this` joint as a unit vector. More...

double	screw_pitch () const
	Returns `this` joint's amount of translation in meters occurring over a one full revolution. More...

double	default_damping () const
	Returns `this` joint's default damping constant N⋅m⋅s for the rotational degree. More...

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

void	set_default_translation (const double &z)
	Sets the default translation 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_random_pose_distribution (const Vector1< symbolic::Expression > &theta)
	Sets the random distribution that the angle of this joint will be randomly sampled from. More...

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

ScrewJoint &	operator= (const ScrewJoint &)=delete

	ScrewJoint (ScrewJoint &&)=delete

ScrewJoint &	operator= (ScrewJoint &&)=delete

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

const ScrewJoint< T > &	set_translation (Context< T > *context, const T &z) const
	Sets the `context` so that the translation of `this` joint equals to (z). More...

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

const ScrewJoint< 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...

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

const ScrewJoint< T > &	set_translational_velocity (systems::Context< T > *context, const T &vz) const
	Sets the translational velocity, in meters per second, of this `this` joint's Mo along frame F's â-axis to `vz`. 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 ScrewJoint< 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...

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 constexpr char	kTypeName [] = "screw"
	The name for this Joint type. More...

Friends
template<typename >
class	ScrewJoint

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...

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

◆ ScrewJoint() [1/4]

ScrewJoint ( const ScrewJoint< T > & )

delete

◆ ScrewJoint() [2/4]

ScrewJoint ( ScrewJoint< T > && )

delete

◆ ScrewJoint() [3/4]

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

Constructor to create a screw 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 the axis â set to the z-axis and no joint limits, i.e. the joint angular position, angular velocity and angular acceleration limits are the pair (-∞, ∞). These can be set using the Joint methods set_position_limits(), set_velocity_limits() and set_acceleration_limits() in radians, radians/s, radians/s² units. 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]	screw_pitch	Amount of translation in meters occurring over a one full screw revolution. It's domain is (-∞, ∞). When the screw pitch is negative, positive rotation will result in translating towards the negative direction of z-axis. When the screw pitch is zero, this joint will behave like a revolute joint.
[in]	damping	Viscous damping coefficient, N⋅m⋅s/rad for rotation, used to model losses within the joint. See documentation of default_damping() for details on modelling of the damping torque.

Exceptions

std::exception if damping is negative.

◆ ScrewJoint() [4/4]

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

Constructor to create a screw 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 angular position, angular velocity and angular acceleration limits are the pair (-∞, ∞). These can be set using the Joint methods set_position_limits(), set_velocity_limits() and set_acceleration_limits() in radians, radians/s, radians/s² units. 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]	axis	A vector in ℝ³ specifying the axis of motion for this joint. The coordinates of `axis` expressed in frames F and M are the same at all times, that is, `axis_F = axis_M`. In other words, `axis_F` (or `axis_M`) is the eigenvector of `R_FM` with eigenvalue equal to one. This vector can have any length, only the direction is used.
[in]	screw_pitch	Amount of translation in meters occurring over a one full screw revolution. It's domain is (-∞, ∞). When the screw pitch is negative, positive rotation will result in translating towards the negative direction of â-axis. When the screw pitch is zero, this joint will behave like a revolute joint.
[in]	damping	Viscous damping coefficient, N⋅m⋅s/rad for rotation, used to model losses within the joint. See documentation of default_damping() for details on modelling of the damping torque.

Exceptions

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

◆ ~ScrewJoint()

~ScrewJoint ( )

final

Member Function Documentation

◆ default_damping()

double default_damping ( ) const

Returns this joint's default damping constant N⋅m⋅s for the rotational degree.

The damping torque (in N⋅m) is modeled as τ = -damping⋅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⋅Fâ_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()

double get_default_translation ( ) const

Gets the default position for this joint.

Return values

z	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()

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

Gets the translation of this joint from context.

Parameters

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

Return values

z	The translation of `this` joint stored in the `context` as (z). See class documentation for details.

◆ get_translational_velocity()

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

Gets the translational velocity vz, 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

vz	The translational velocity of `this` joint as stored in the `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]

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

delete

◆ operator=() [2/2]

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

delete

◆ screw_axis()

const Vector3<double>& screw_axis ( ) const

Returns the normalized axis of motion of 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.

◆ screw_pitch()

double screw_pitch ( ) const

Returns this joint's amount of translation in meters occurring over a one full revolution.

◆ set_angular_velocity()

const ScrewJoint<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_rotation()

void set_default_rotation ( double theta )

Sets the default angle of this joint.

This will change the default_translation too, because they are not independent in this joint.

Parameters

[in] theta The desired default angle of the joint

◆ set_default_translation()

void set_default_translation ( const double & z )

Sets the default translation of this joint.

This will change the default_rotation too, which are not independent in this joint.

Parameters

[in] z The desired default translation of the joint

Exceptions

std::exception if pitch is very near zero.

◆ set_random_pose_distribution()

void set_random_pose_distribution ( const Vector1< symbolic::Expression > & theta )

Sets the random distribution that the 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 ScrewJoint<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 ScrewJoint<T>& set_translation	(	Context< T > *	context,
		const T &	z
	)		const

Sets the context so that the translation of this joint equals to (z).

Parameters

[in]	context	The context of the model this joint belongs to.
[in]	z	The desired translation in meters to be stored in `context` as (z). See class documentation for details.

Returns: a constant reference to this joint.

◆ set_translational_velocity()

const ScrewJoint<T>& set_translational_velocity	(	systems::Context< T > *	context,
		const T &	vz
	)		const

Sets the translational velocity, in meters per second, of this this joint's Mo along frame F's â-axis to vz.

The new translational velocity gets stored in context.

Parameters

[in]	context	The context of the model this joint belongs to.
[in]	vz	The desired translational velocity of `this` joint in meters per second along F frame's â-axis.

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.

◆ 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

◆ ScrewJoint

friend class ScrewJoint

friend

Member Data Documentation

◆ kTypeName

constexpr char kTypeName[] = "screw"

static

The name for this Joint type.

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

drake/multibody/tree/screw_joint.h

Detailed Description

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

Public Types

Public Member Functions

Static Public Attributes

Friends

Additional Inherited Members

Member Typedef Documentation

◆ Context

Constructor & Destructor Documentation

◆ ScrewJoint() [1/4]

◆ ScrewJoint() [2/4]

◆ ScrewJoint() [3/4]

◆ ScrewJoint() [4/4]

◆ ~ScrewJoint()

Member Function Documentation

◆ default_damping()

◆ get_angular_velocity()

◆ get_default_rotation()

◆ get_default_translation()

◆ get_rotation()

◆ get_translation()

◆ get_translational_velocity()

◆ GetDamping()

◆ operator=() [1/2]

◆ operator=() [2/2]

◆ screw_axis()

◆ screw_pitch()

◆ set_angular_velocity()

◆ set_default_rotation()

◆ set_default_translation()

◆ set_random_pose_distribution()

◆ set_rotation()

◆ set_translation()

◆ set_translational_velocity()

◆ SetDamping()

◆ type_name()

Friends And Related Function Documentation

◆ ScrewJoint

Member Data Documentation

◆ kTypeName

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