Drake
RevoluteJoint< T > Class Template Referencefinal

This Joint allows two bodies to rotate relatively to one another around a common axis. More...

#include <drake/multibody/multibody_tree/joints/revolute_joint.h>

Public Types

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

Public Member Functions

 RevoluteJoint (const std::string &name, const Frame< T > &frame_on_parent, const Frame< T > &frame_on_child, const Vector3< double > &axis, double damping=0)
 Constructor to create a revolute joint between two bodies so that frame F attached to the parent body P and frame M attached to the child body B, rotate relatively to one another about a common axis. More...
 
 RevoluteJoint (const std::string &name, const Frame< T > &frame_on_parent, const Frame< T > &frame_on_child, const Vector3< double > &axis, double lower_limit, double upper_limit, double damping=0)
 Constructor to create a revolute joint between two bodies so that frame F attached to the parent body P and frame M attached to the child body B, rotate relatively to one another about a common axis. More...
 
const Vector3< double > & revolute_axis () const
 Returns the axis of revolution of this joint as a unit vector. More...
 
double damping () const
 Returns this joint's damping constant in N⋅m⋅s. More...
 
double lower_limit () const
 Returns the lower limit for this joint in radians. More...
 
double upper_limit () const
 Returns the upper limit for this joint in radians. More...
 
void AddInTorque (const systems::Context< T > &context, const T &torque, MultibodyForces< T > *forces) const
 Adds into forces a given torque for this joint that is to be applied about the joint's axis. More...
 
Does not allow copy, move, or assignment
 RevoluteJoint (const RevoluteJoint &)=delete
 
RevoluteJointoperator= (const RevoluteJoint &)=delete
 
 RevoluteJoint (RevoluteJoint &&)=delete
 
RevoluteJointoperator= (RevoluteJoint &&)=delete
 
Context-dependent value access

These methods require the provided context to be an instance of MultibodyTreeContext.

Failure to do so leads to a std::logic_error.

const Tget_angle (const Context< T > &context) const
 Gets the rotation angle of this mobilizer from context. More...
 
const RevoluteJoint< T > & set_angle (Context< T > *context, const T &angle) const
 Sets the context so that the generalized coordinate corresponding to the rotation angle of this joint equals angle. More...
 
const Tget_angular_rate (const Context< T > &context) const
 Gets the rate of change, in radians per second, of this joint's angle (see get_angle()) from context. More...
 
const RevoluteJoint< T > & set_angular_rate (Context< T > *context, const T &angle) const
 Sets the rate of change, in radians per second, of this this joint's angle 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, const VectorX< double > &lower_limits, const VectorX< double > &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...
 
virtual ~Joint ()
 
const std::string & name () const
 Returns the name of this joint. More...
 
const Body< T > & parent_body () const
 Returns a const reference to the parent body P. More...
 
const Body< 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 num_dofs () const
 Returns the number of degrees of freedom for this joint. 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...
 
const VectorX< double > & lower_limits () const
 Returns a vector of size num_positions() storing the lower limits for each generalized position for this joint. More...
 
const VectorX< double > & upper_limits () const
 Returns a vector of size num_positions() storing the upper limits for each generalized position for this joint. More...
 
const TGetOnePosition (const systems::Context< T > &context) const
 Returns the position coordinate for joints with a single degree of freedom. More...
 
const TGetOneVelocity (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...
 
 Joint (const Joint &)=delete
 
Jointoperator= (const Joint &)=delete
 
 Joint (Joint &&)=delete
 
Jointoperator= (Joint &&)=delete
 

Protected Member Functions

void DoAddInOneForce (const systems::Context< T > &, int joint_dof, const T &joint_tau, MultibodyForces< T > *forces) const override
 Joint<T> 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 >
void DoSetTopology (const MultibodyTreeTopology &)
 
const JointImplementationget_implementation () const
 Returns a const reference to the internal implementation of this joint. More...
 

Friends

template<typename >
class RevoluteJoint
 
class JointTester
 

Detailed Description

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

This Joint allows two bodies to rotate relatively to one another around 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 rotate with respect to each other about an axis â. The rotation angle's sign is defined such that child body B rotates about axis â according to the right hand rule, with thumb aligned in the axis direction. Axis â is constant and has the same measures in both frames F and M, that is, â_F = â_M.

Template Parameters
TThe scalar type. Must be a valid Eigen scalar.

Instantiated templates for the following kinds of T's are provided:

  • double
  • AutoDiffXd

They are already available to link against in the containing library. No other values for T are currently supported.

Member Typedef Documentation

◆ Context

using Context = systems::Context<Scalar>

Constructor & Destructor Documentation

◆ RevoluteJoint() [1/4]

RevoluteJoint ( const RevoluteJoint< T > &  )
delete

◆ RevoluteJoint() [2/4]

RevoluteJoint ( RevoluteJoint< T > &&  )
delete

◆ RevoluteJoint() [3/4]

RevoluteJoint ( const std::string &  name,
const Frame< T > &  frame_on_parent,
const Frame< T > &  frame_on_child,
const Vector3< double > &  axis,
double  damping = 0 
)
inline

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

See this class's documentation for further details on the definition of these frames and rotation angle. This constructor signature creates a joint with no joint limits, i.e. the joint limits are the pair (-∞, ∞). 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]axisA vector in ℝ³ specifying the axis of revolution for this joint. Given that frame M only rotates with respect to F and their origins are coincident at all times, the measures of axis in either frame F or M are exactly the same, 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. This method aborts if axis is the zero vector.
[in]dampingViscous damping coefficient, in N⋅m⋅s, used to model losses within the joint. 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_rate()).
Exceptions
std::exceptionif damping is negative.

◆ RevoluteJoint() [4/4]

RevoluteJoint ( const std::string &  name,
const Frame< T > &  frame_on_parent,
const Frame< T > &  frame_on_child,
const Vector3< double > &  axis,
double  lower_limit,
double  upper_limit,
double  damping = 0 
)
inline

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

See this class's documentation for further details on the definition of these frames and rotation angle. 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]axisA vector in ℝ³ specifying the axis of revolution for this joint. Given that frame M only rotates with respect to F and their origins are coincident at all times, the measures of axis in either frame F or M are exactly the same, 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. This method aborts if axis is the zero vector.
[in]lower_limitLower limit, in radians, for the rotation coordinate (see get_angle()).
[in]upper_limitUpper limit, in radians, for the rotation coordinate (see get_angle()).
[in]dampingViscous damping coefficient, in N⋅m⋅s, used to model losses within the joint. 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_rate()).
Exceptions
std::exceptionif damping is negative.
std::exceptionif lower_limit > upper_limit.

Member Function Documentation

◆ AddInTorque()

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

Adds into forces a given torque for this joint that is to be applied about the joint's axis.

The torque is defined to be positive according to the right-hand-rule with the thumb aligned in the direction of this joint's axis. That is, a positive torque causes a positive rotational acceleration according to the right-hand-rule around the joint's axis.

Note
A torque is the moment of a set of forces whose resultant is zero.

◆ damping()

double damping ( ) const
inline

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

◆ DoAddInDamping()

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

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

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

Reimplemented from Joint< T >.

◆ DoAddInOneForce()

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

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

Therefore arguments were already checked to be valid. For a RevoluteJoint, we must always have joint_dof = 0 since there is only a single degree of freedom (num_velocities() == 1). joint_tau is the torque applied about the joint's axis, on the body declared as child (according to the revolute joint's constructor) at the origin of the child frame (which is coincident with the origin of the parent frame at all times). The torque is defined to be positive according to the right-hand-rule with the thumb aligned in the direction of this joint's axis. That is, a positive torque causes a positive rotational acceleration (of the child body frame) according to the right-hand-rule around the joint's axis.

Implements Joint< T >.

◆ get_angle()

const T& get_angle ( const Context< T > &  context) const
inline

Gets the rotation angle of this mobilizer from context.

Parameters
[in]contextThe context of the MultibodyTree this joint belongs to.
Returns
The angle coordinate of this joint stored in the context.

◆ get_angular_rate()

const T& get_angular_rate ( const Context< T > &  context) const
inline

Gets the rate of change, in radians per second, of this joint's angle (see get_angle()) from context.

Parameters
[in]contextThe context of the MultibodyTree this joint belongs to.
Returns
The rate of change of this joint's angle as stored in the context.

◆ lower_limit()

double lower_limit ( ) const
inline

Returns the lower limit for this joint in radians.

◆ operator=() [1/2]

RevoluteJoint& operator= ( RevoluteJoint< T > &&  )
delete

◆ operator=() [2/2]

RevoluteJoint& operator= ( const RevoluteJoint< T > &  )
delete

◆ revolute_axis()

const Vector3<double>& revolute_axis ( ) const
inline

Returns the axis of revolution 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 frames's definitions) then, axis = axis_F = axis_M.

◆ set_angle()

const RevoluteJoint<T>& set_angle ( Context< T > *  context,
const T angle 
) const
inline

Sets the context so that the generalized coordinate corresponding to the rotation angle of this joint equals angle.

Parameters
[in]contextThe context of the MultibodyTree this joint belongs to.
[in]angleThe desired angle in radians to be stored in context.
Returns
a constant reference to this joint.

◆ set_angular_rate()

const RevoluteJoint<T>& set_angular_rate ( Context< T > *  context,
const T angle 
) const
inline

Sets the rate of change, in radians per second, of this this joint's angle to theta_dot.

The new rate of change theta_dot gets stored in context.

Parameters
[in]contextThe context of the MultibodyTree this joint belongs to.
[in]theta_dotThe desired rate of change of this joints's angle in radians per second.
Returns
a constant reference to this joint.

◆ upper_limit()

double upper_limit ( ) const
inline

Returns the upper limit for this joint in radians.

Friends And Related Function Documentation

◆ JointTester

friend class JointTester
friend

◆ RevoluteJoint

friend class RevoluteJoint
friend

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