Simbody  3.5
SimTK::Constraint::ConstantAngle Class Reference

This constraint consists of a single constraint equation that enforces that a unit vector v1 fixed to one body (the "base body") must maintain a fixed angle theta with respect to a unit vector v2 fixed on the other body (the "follower body"). More...

+ Inheritance diagram for SimTK::Constraint::ConstantAngle:

Public Member Functions

 ConstantAngle (MobilizedBody &baseBody_B, const UnitVec3 &defaultAxis_B, MobilizedBody &followerBody_F, const UnitVec3 &defaultAxis_F, Real angle=Pi/2)
 
 ConstantAngle ()
 Default constructor creates an empty handle. More...
 
ConstantAnglesetAxisDisplayLength (Real)
 
ConstantAnglesetAxisDisplayWidth (Real)
 
Real getAxisDisplayLength () const
 
Real getAxisDisplayWidth () const
 
ConstantAnglesetDefaultBaseAxis (const UnitVec3 &)
 
ConstantAnglesetDefaultFollowerAxis (const UnitVec3 &)
 
ConstantAnglesetDefaultAngle (Real)
 
MobilizedBodyIndex getBaseMobilizedBodyIndex () const
 
MobilizedBodyIndex getFollowerMobilizedBodyIndex () const
 
const UnitVec3getDefaultBaseAxis () const
 
const UnitVec3getDefaultFollowerAxis () const
 
Real getDefaultAngle () const
 
const UnitVec3getBaseAxis (const State &) const
 
const UnitVec3getFollowerAxis (const State &) const
 
Real getAngle (const State &) const
 
Real getPositionError (const State &) const
 
Real getVelocityError (const State &) const
 
Real getAccelerationError (const State &) const
 
Real getMultiplier (const State &) const
 
Real getTorqueOnFollowerBody (const State &) const
 
- 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 SimbodyMatterSubsystemgetMatterSubsystem () const
 Get a const reference to the matter subsystem that contains this Constraint. More...
 
SimbodyMatterSubsystemupdMatterSubsystem ()
 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 MobilizedBodygetMobilizedBodyFromConstrainedBody (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 MobilizedBodygetAncestorMobilizedBody () 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 MobilizedBodygetMobilizedBodyFromConstrainedMobilizer (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 SimbodyMatterSubtreegetSubtree () 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_< SpatialVecgetConstrainedBodyForcesAsVector (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
 
void setIsConditional (bool isConditional)
 (Advanced) Mark this constraint as one that is only conditionally active. More...
 
bool isConditional () const
 (Advanced) Get the value of the isConditional flag. More...
 
- 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...
 
PIMPLHandlereferenceAssign (const Constraint &source)
 "Copy" assignment but with shallow (pointer) semantics. More...
 
PIMPLHandlecopyAssign (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
 Synonym for Rod constraint. More...
 
typedef Ball CoincidentPoints
 Synonym for Ball constraint. More...
 
typedef Ball Spherical
 Synonym for Ball constraint. More...
 
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...
 
PIMPLHandleoperator= (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 consists of a single constraint equation that enforces that a unit vector v1 fixed to one body (the "base body") must maintain a fixed angle theta with respect to a unit vector v2 fixed on the other body (the "follower body").

This can be done with a single constraint equation as long as theta is sufficiently far away from 0 and +/-Pi (180 degrees), with the numerically best performance at theta=Pi/2 (90 degrees).

Warning
Do not use this constraint to align the vectors, that is for angles near 0 or +/- Pi; performance will noticeably degrade within a few degrees of these limits and numerical integration will eventually fail at the limits.

If you want to enforce that two axes are aligned with one another (that is, the angle between them is 0 or +/-Pi), that takes two constraint equations since the only remaining rotation is about the common axis. (That is, two rotational degrees of freedom are removed; that can't be done with one constraint equation – the situation is analogous to the inability of a Rod (distance) constraint to keep two points at 0 distance.) Instead, you can use two ConstantAngle constraints on pairs of vectors perpendicular to the aligned ones, so that each ConstantAngle is set to the optimal 90 degrees.

This constraint is enforced by an internal scalar torque applied equal and opposite on each body, about the mutual perpendicular to the two vectors.

The assembly condition is the same as the run-time constraint: the bodies must be rotated until the vectors have the right angle between them.

Constructor & Destructor Documentation

SimTK::Constraint::ConstantAngle::ConstantAngle ( MobilizedBody baseBody_B,
const UnitVec3 defaultAxis_B,
MobilizedBody followerBody_F,
const UnitVec3 defaultAxis_F,
Real  angle = Pi/2 
)

Default constructor creates an empty handle.

Member Function Documentation

ConstantAngle& SimTK::Constraint::ConstantAngle::setAxisDisplayLength ( Real  )
ConstantAngle& SimTK::Constraint::ConstantAngle::setAxisDisplayWidth ( Real  )
Real SimTK::Constraint::ConstantAngle::getAxisDisplayLength ( ) const
Real SimTK::Constraint::ConstantAngle::getAxisDisplayWidth ( ) const
ConstantAngle& SimTK::Constraint::ConstantAngle::setDefaultBaseAxis ( const UnitVec3 )
ConstantAngle& SimTK::Constraint::ConstantAngle::setDefaultFollowerAxis ( const UnitVec3 )
ConstantAngle& SimTK::Constraint::ConstantAngle::setDefaultAngle ( Real  )
MobilizedBodyIndex SimTK::Constraint::ConstantAngle::getBaseMobilizedBodyIndex ( ) const
MobilizedBodyIndex SimTK::Constraint::ConstantAngle::getFollowerMobilizedBodyIndex ( ) const
const UnitVec3& SimTK::Constraint::ConstantAngle::getDefaultBaseAxis ( ) const
const UnitVec3& SimTK::Constraint::ConstantAngle::getDefaultFollowerAxis ( ) const
Real SimTK::Constraint::ConstantAngle::getDefaultAngle ( ) const
const UnitVec3& SimTK::Constraint::ConstantAngle::getBaseAxis ( const State ) const
const UnitVec3& SimTK::Constraint::ConstantAngle::getFollowerAxis ( const State ) const
Real SimTK::Constraint::ConstantAngle::getAngle ( const State ) const
Real SimTK::Constraint::ConstantAngle::getPositionError ( const State ) const
Real SimTK::Constraint::ConstantAngle::getVelocityError ( const State ) const
Real SimTK::Constraint::ConstantAngle::getAccelerationError ( const State ) const
Real SimTK::Constraint::ConstantAngle::getMultiplier ( const State ) const
Real SimTK::Constraint::ConstantAngle::getTorqueOnFollowerBody ( const State ) const

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