SimTK::Constraint::BallRollingOnPlane Class Reference

This constraint enforces continuous contact and non-slip rolling between a spherical surface fixed on one body and a half space (flat surface) fixed on another. More...

#include <Constraint.h>

Inheritance diagram for SimTK::Constraint::BallRollingOnPlane:

Public Member Functions
	BallRollingOnPlane (MobilizedBody &planeBody_P, const UnitVec3 &defaultPlaneNormal_P, Real defaultPlaneHeight, MobilizedBody &ballBody_B, const Vec3 &defaultBallCenter_B, Real defaultBallRadius)
	Create a BallOnPlane constraint and define the default plane and ball geometry. More...
	BallRollingOnPlane ()
	Default constructor creates an empty handle. More...
BallRollingOnPlane &	setPlaneDisplayHalfWidth (Real)
Real	getPlaneDisplayHalfWidth () const
BallRollingOnPlane &	setDefaultPlaneNormal (const UnitVec3 &)
BallRollingOnPlane &	setDefaultPlaneHeight (Real)
BallRollingOnPlane &	setDefaultBallCenter (const Vec3 &)
BallRollingOnPlane &	setDefaultBallRadius (Real)
MobilizedBodyIndex	getPlaneMobilizedBodyIndex () const
MobilizedBodyIndex	getBallMobilizedBodyIndex () const
const UnitVec3 &	getDefaultPlaneNormal () const
Real	getDefaultPlaneHeight () const
const Vec3 &	getDefaultBallCenter () const
Real	getDefaultBallRadius () const
const UnitVec3 &	getPlaneNormal (const State &) const
Real	getPlaneHeight (const State &) const
const Vec3 &	getBallCenter (const State &) const
Real	getBallRadius (const State &) const
Real	getPositionError (const State &) const
Vec3	getVelocityError (const State &) const
Vec3	getAccelerationError (const State &) const
Vec3	getMultipliers (const State &) const
Real	getNormalForce (const State &) const
	Return the signed magnitude of the normal force applied by the plane to the ball at the contact point, in the direction of the plane normal; negative indicates sticking. More...
Vec2	getFrictionForceOnBallInPlaneFrame (const State &) const
	Return the friction force vector being applied by the plane to the ball at the contact point, expressed in the plane frame. More...
Public Member Functions inherited from SimTK::Constraint
	Constraint ()
	Default constructor creates an empty Constraint handle that can be used to reference any Constraint. More...
	Constraint (ConstraintImpl *r)
	For internal use: construct a new Constraint handle referencing a particular implementation object. More...
void	disable (State &) const
	Disable this Constraint, effectively removing it from the system. More...
void	enable (State &) const
	Enable this Constraint, without necessarily satisfying it. More...
bool	isDisabled (const State &) const
	Test whether this constraint is currently disabled in the supplied State. More...
bool	isDisabledByDefault () const
	Test whether this Constraint is disabled by default in which case it must be explicitly enabled before it will take effect. More...
void	setDisabledByDefault (bool shouldBeDisabled)
	Normally Constraints are enabled when defined and can be disabled later. More...
	operator ConstraintIndex () const
	This is an implicit conversion from Constraint to ConstraintIndex when needed. More...
const SimbodyMatterSubsystem &	getMatterSubsystem () const
	Get a const reference to the matter subsystem that contains this Constraint. More...
SimbodyMatterSubsystem &	updMatterSubsystem ()
	Assuming you have writable access to this Constraint, get a writable reference to the containing matter subsystem. More...
ConstraintIndex	getConstraintIndex () const
	Get the ConstraintIndex that was assigned to this Constraint when it was added to the matter subsystem. More...
bool	isInSubsystem () const
	Test whether this Constraint is contained within a matter subsystem. More...
bool	isInSameSubsystem (const MobilizedBody &mobod) const
	Test whether the supplied MobilizedBody is in the same matter subsystem as this Constraint. More...
int	getNumConstrainedBodies () const
	Return the number of unique bodies directly restricted by this constraint. More...
const MobilizedBody &	getMobilizedBodyFromConstrainedBody (ConstrainedBodyIndex consBodyIx) const
	Return a const reference to the actual MobilizedBody corresponding to one of the Constrained Bodies included in the count returned by getNumConstrainedBodies(). More...
const MobilizedBody &	getAncestorMobilizedBody () const
	Return a const reference to the actual MobilizedBody which is serving as the Ancestor body for the constrained bodies in this Constraint. More...
int	getNumConstrainedMobilizers () const
	Return the number of unique mobilizers directly restricted by this Constraint. More...
const MobilizedBody &	getMobilizedBodyFromConstrainedMobilizer (ConstrainedMobilizerIndex consMobilizerIx) const
	Return a const reference to the actual MobilizedBody corresponding to one of the Constrained Mobilizers included in the count returned by getNumConstrainedMobilizers(). More...
const SimbodyMatterSubtree &	getSubtree () const
	Return a subtree object indicating which parts of the multibody tree are potentially affected by this Constraint. More...
int	getNumConstrainedQ (const State &, ConstrainedMobilizerIndex) const
	Return the number of constrainable generalized coordinates q associated with a particular constrained mobilizer. More...
int	getNumConstrainedU (const State &, ConstrainedMobilizerIndex) const
	Return the number of constrainable mobilities u associated with a particular constrained mobilizer. More...
ConstrainedUIndex	getConstrainedUIndex (const State &, ConstrainedMobilizerIndex, MobilizerUIndex which) const
	Return the index into the constrained mobilities u array corresponding to a particular mobility of the indicated ConstrainedMobilizer. More...
ConstrainedQIndex	getConstrainedQIndex (const State &, ConstrainedMobilizerIndex, MobilizerQIndex which) const
	Return the index into the constrained coordinates q array corresponding to a particular coordinate of the indicated ConstrainedMobilizer. More...
int	getNumConstrainedQ (const State &) const
	Return the sum of the number of coordinates q associated with each of the constrained mobilizers. More...
int	getNumConstrainedU (const State &) const
	Return the sum of the number of mobilities u associated with each of the constrained mobilizers. More...
QIndex	getQIndexOfConstrainedQ (const State &state, ConstrainedQIndex consQIndex) const
	Map one of this Constraint's constrained q's to the corresponding index within the matter subsystem's whole q vector. More...
UIndex	getUIndexOfConstrainedU (const State &state, ConstrainedUIndex consUIndex) const
	Map one of this Constraint's constrained U's (or mobilities) to the corresponding index within the matter subsystem's whole u vector. More...
void	getNumConstraintEquationsInUse (const State &state, int &mp, int &mv, int &ma) const
	Find out how many holonomic (position), nonholonomic (velocity), and acceleration-only constraint equations are currently being generated by this Constraint. More...
void	getIndexOfMultipliersInUse (const State &state, MultiplierIndex &px0, MultiplierIndex &vx0, MultiplierIndex &ax0) const
	Return the start of the blocks of multipliers (or acceleration errors) assigned to this Constraint. More...
void	setMyPartInConstraintSpaceVector (const State &state, const Vector &myPart, Vector &constraintSpace) const
	Set the part of a complete constraint-space vector that belongs to this constraint. More...
void	getMyPartFromConstraintSpaceVector (const State &state, const Vector &constraintSpace, Vector &myPart) const
	Get the part of a complete constraint-space vector that belongs to this constraint. More...
Vector	getPositionErrorsAsVector (const State &) const
	Get a Vector containing the position errors. More...
Vector	calcPositionErrorFromQ (const State &, const Vector &q) const
Matrix	calcPositionConstraintMatrixP (const State &) const
Matrix	calcPositionConstraintMatrixPt (const State &) const
Matrix	calcPositionConstraintMatrixPNInv (const State &) const
void	calcConstraintForcesFromMultipliers (const State &, const Vector &lambda, Vector_< SpatialVec > &bodyForcesInA, Vector &mobilityForces) const
	This operator calculates this constraint's body and mobility forces given the complete set of multipliers lambda for this Constraint. More...
Vector	getVelocityErrorsAsVector (const State &) const
	Get a Vector containing the velocity errors. More...
Vector	calcVelocityErrorFromU (const State &, const Vector &u) const
Matrix	calcVelocityConstraintMatrixV (const State &) const
Matrix	calcVelocityConstraintMatrixVt (const State &) const
Vector	getAccelerationErrorsAsVector (const State &) const
	Get a Vector containing the acceleration errors. More...
Vector	calcAccelerationErrorFromUDot (const State &, const Vector &udot) const
Vector	getMultipliersAsVector (const State &) const
	Get a Vector containing the Lagrange multipliers. More...
void	getConstraintForcesAsVectors (const State &state, Vector_< SpatialVec > &bodyForcesInG, Vector &mobilityForces) const
	Given a State realized through Acceleration stage, return the forces that were applied to the system by this Constraint, with body forces expressed in Ground. More...
Vector_< SpatialVec >	getConstrainedBodyForcesAsVector (const State &state) const
	For convenience, returns constrained body forces as the function return. More...
Vector	getConstrainedMobilityForcesAsVector (const State &state) const
	For convenience, returns constrained mobility forces as the function return. More...
Real	calcPower (const State &state) const
	Calculate the power being applied by this Constraint to the system. More...
Matrix	calcAccelerationConstraintMatrixA (const State &) const
Matrix	calcAccelerationConstraintMatrixAt (const State &) const
Public Member Functions inherited from SimTK::PIMPLHandle< Constraint, ConstraintImpl, true >
bool	isEmptyHandle () const
	Returns true if this handle is empty, that is, does not refer to any implementation object. More...
bool	isOwnerHandle () const
	Returns true if this handle is the owner of the implementation object to which it refers. More...
bool	isSameHandle (const Constraint &other) const
	Determine whether the supplied handle is the same object as "this" PIMPLHandle. More...
void	disown (Constraint &newOwner)
	Give up ownership of the implementation to an empty handle. More...
PIMPLHandle &	referenceAssign (const Constraint &source)
	"Copy" assignment but with shallow (pointer) semantics. More...
PIMPLHandle &	copyAssign (const Constraint &source)
	This is real copy assignment, with ordinary C++ object ("value") semantics. More...
void	clearHandle ()
	Make this an empty handle, deleting the implementation object if this handle is the owner of it. More...
const ConstraintImpl &	getImpl () const
	Get a const reference to the implementation associated with this Handle. More...
ConstraintImpl &	updImpl ()
	Get a writable reference to the implementation associated with this Handle. More...
int	getImplHandleCount () const
	Return the number of handles the implementation believes are referencing it. More...

Additional Inherited Members
Public Types inherited from SimTK::Constraint
typedef Rod	ConstantDistance
typedef Ball	CoincidentPoints
typedef Ball	Spherical
typedef Weld	CoincidentFrames
Public Types inherited from SimTK::PIMPLHandle< Constraint, ConstraintImpl, true >
typedef PIMPLHandle < Constraint, ConstraintImpl, PTR >	HandleBase
typedef HandleBase	ParentHandle
Protected Member Functions inherited from SimTK::PIMPLHandle< Constraint, ConstraintImpl, true >
	PIMPLHandle ()
	The default constructor makes this an empty handle. More...
	PIMPLHandle (ConstraintImpl *p)
	This provides consruction of a handle referencing an existing implementation object. More...
	PIMPLHandle (const PIMPLHandle &source)
	The copy constructor makes either a deep (value) or shallow (reference) copy of the supplied source PIMPL object, based on whether this is a "pointer semantics" (PTR=true) or "object (value) semantics" (PTR=false, default) class. More...
	~PIMPLHandle ()
	Note that the destructor is non-virtual. More...
PIMPLHandle &	operator= (const PIMPLHandle &source)
	Copy assignment makes the current handle either a deep (value) or shallow (reference) copy of the supplied source PIMPL object, based on whether this is a "pointer sematics" (PTR=true) or "object (value) semantics" (PTR=false, default) class. More...
void	setImpl (ConstraintImpl *p)
	Set the implementation for this empty handle. More...
bool	hasSameImplementation (const Constraint &other) const
	Determine whether the supplied handle is a reference to the same implementation object as is referenced by "this" PIMPLHandle. More...

Detailed Description

This constraint enforces continuous contact and non-slip rolling between a spherical surface fixed on one body and a half space (flat surface) fixed on another.

This requires one holonomic (position) constraint equation enforcing contact, and two nonholonomic (velocity) contraint equations enforcing the non-slip condition in the plane. Note that this is a bilateral constraint and will push or pull as necessary to keep the sphere in contact with the plane, and that rolling is enforced regardless of the amount of normal force begin generated. If you want to make this unilateral, you must handle switching it on and off separately; when this constraint is enabled it always enforces the contact and no-slip conditions.

We define the contact point on the ball to be the unique point CB on the sphere surface at which the radius vector is antiparallel to the plane's normal vector, that is, the point of the sphere directly below the sphere center if the plane's normal is considered the "up" direction. Then the contact point CP on the plane is defined to be the point on the plane that is directly below the center; that is, the intersection of the antiparallel radius vector and the halfspace surface. Note that in general CB != CP; the sphere contact point and plane contact point will be separated along the plane normal by a small distance, limited to the constraint tolerance after assembly. Now we define the contact point C=(CB+CP)/2, the point in space that is half way between the sphere's contact point and the plane's contact point. Equal and opposite forces are applied to the ball body B and the plane body P, at the station on each body that is coincident with C.

The holonomic constraint we enforce is that point C should be touching the plane. We enforce this with the condition that ~C_P*n_P = h, that is, given the contact point C measured and expressed in the plane body's frame, the height of that point in the direction of the plane normal should be the height of the plane.

The assembly condition is the same as the run-time constraint: the point of the sphere where the inward normal is the same as the halfspace normal must be brought into contact with the halfspace surface.

Constructor & Destructor Documentation

SimTK::Constraint::BallRollingOnPlane::BallRollingOnPlane	(	MobilizedBody &	planeBody_P,
		const UnitVec3 &	defaultPlaneNormal_P,
		Real	defaultPlaneHeight,
		MobilizedBody &	ballBody_B,
		const Vec3 &	defaultBallCenter_B,
		Real	defaultBallRadius
	)

Create a BallOnPlane constraint and define the default plane and ball geometry.

SimTK::Constraint::BallRollingOnPlane::BallRollingOnPlane ( )

inline

Default constructor creates an empty handle.

Member Function Documentation

BallRollingOnPlane& SimTK::Constraint::BallRollingOnPlane::setPlaneDisplayHalfWidth

(

Real

)

Real SimTK::Constraint::BallRollingOnPlane::getPlaneDisplayHalfWidth

(

)

const

BallRollingOnPlane& SimTK::Constraint::BallRollingOnPlane::setDefaultPlaneNormal

(

const UnitVec3 &

)

BallRollingOnPlane& SimTK::Constraint::BallRollingOnPlane::setDefaultPlaneHeight

(

Real

)

BallRollingOnPlane& SimTK::Constraint::BallRollingOnPlane::setDefaultBallCenter

(

const Vec3 &

)

BallRollingOnPlane& SimTK::Constraint::BallRollingOnPlane::setDefaultBallRadius

(

Real

)

MobilizedBodyIndex SimTK::Constraint::BallRollingOnPlane::getPlaneMobilizedBodyIndex

(

)

const

MobilizedBodyIndex SimTK::Constraint::BallRollingOnPlane::getBallMobilizedBodyIndex

(

)

const

const UnitVec3& SimTK::Constraint::BallRollingOnPlane::getDefaultPlaneNormal

(

)

const

Real SimTK::Constraint::BallRollingOnPlane::getDefaultPlaneHeight

(

)

const

const Vec3& SimTK::Constraint::BallRollingOnPlane::getDefaultBallCenter

(

)

const

Real SimTK::Constraint::BallRollingOnPlane::getDefaultBallRadius

(

)

const

const UnitVec3& SimTK::Constraint::BallRollingOnPlane::getPlaneNormal

(

const State &

)

const

Real SimTK::Constraint::BallRollingOnPlane::getPlaneHeight

(

const State &

)

const

const Vec3& SimTK::Constraint::BallRollingOnPlane::getBallCenter

(

const State &

)

const

Real SimTK::Constraint::BallRollingOnPlane::getBallRadius

(

const State &

)

const

Real SimTK::Constraint::BallRollingOnPlane::getPositionError

(

const State &

)

const

Vec3 SimTK::Constraint::BallRollingOnPlane::getVelocityError

(

const State &

)

const

Vec3 SimTK::Constraint::BallRollingOnPlane::getAccelerationError

(

const State &

)

const

Vec3 SimTK::Constraint::BallRollingOnPlane::getMultipliers

(

const State &

)

const

Real SimTK::Constraint::BallRollingOnPlane::getNormalForce

(

const State &

)

const

Return the signed magnitude of the normal force applied by the plane to the ball at the contact point, in the direction of the plane normal; negative indicates sticking.

Vec2 SimTK::Constraint::BallRollingOnPlane::getFrictionForceOnBallInPlaneFrame

(

const State &

)

const

Return the friction force vector being applied by the plane to the ball at the contact point, expressed in the plane frame.

---

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

• Constraint.h