Model a compliant stop element that acts to keep a mobilizer coordinate q within specified bounds. More...

#include <Force_MobilityLinearStop.h>

Inheritance diagram for SimTK::Force::MobilityLinearStop:

Public Member Functions
	MobilityLinearStop (GeneralForceSubsystem &forces, const MobilizedBody &mobod, MobilizerQIndex whichQ, Real defaultStiffness, Real defaultDissipation, Real defaultQLow=-Infinity, Real defaultQHigh=Infinity)
	Create a MobilityLinearStop force element on a particular generalized coordinate. More...

	MobilityLinearStop ()
	Default constructor creates an empty handle that can be assigned to refer to any MobilityLinearStop object. More...

MobilityLinearStop &	setDefaultBounds (Real defaultQLow, Real defaultQHigh)
	Provide new values for the default lower and upper bounds of this stop. More...

MobilityLinearStop &	setDefaultMaterialProperties (Real defaultStiffness, Real defaultDissipation)
	Provide new values for the default material properties of this stop, which are assumed to be the same for the upper and lower stops. More...

Real	getDefaultLowerBound () const
	Return the default value for the stop's lower bound (a generalized coordinate value). More...

Real	getDefaultUpperBound () const
	Return the default value for the stop's upper bound (a generalized coordinate value). More...

Real	getDefaultStiffness () const
	Return the default value for the stop material's stiffness k. More...

Real	getDefaultDissipation () const
	Return the default value for the stop's material's dissipation coefficient d. More...

void	setBounds (State &state, Real qLow, Real qHigh) const
	Change the values of the lower and upper bounds in the given state; these may differ from the default values supplied at construction. More...

void	setMaterialProperties (State &state, Real stiffness, Real dissipation) const
	Change the values of this stop's material properties in the given state; these may differ from the default values supplied at construction. More...

Real	getLowerBound (const State &state) const
	Return the value for the lower bound that is stored in the given state. More...

Real	getUpperBound (const State &state) const
	Return the value for the upper bound that is stored in the given state. More...

Real	getStiffness (const State &state) const
	Return the value for the stop material's stiffness k that is stored in the given state. More...

Real	getDissipation (const State &state) const
	Return the value for the stop material's dissipation coefficient d that is stored in the given state. More...

Public Member Functions inherited from SimTK::Force
void	disable (State &) const
	Disable this force element, effectively removing it from the System for computational purposes (it is still using its ForceIndex, however). More...

void	enable (State &) const
	Enable this force element if it was previously disabled. More...

bool	isDisabled (const State &) const
	Test whether this force element is currently disabled in the supplied State. More...

void	setDisabledByDefault (bool shouldBeDisabled)
	Normally force elements are enabled when defined and can be disabled later. More...

bool	isDisabledByDefault () const
	Test whether this force element is disabled by default in which case it must be explicitly enabled before it will take effect. More...

void	calcForceContribution (const State &state, Vector_< SpatialVec > &bodyForces, Vector_< Vec3 > &particleForces, Vector &mobilityForces) const
	Calculate the force that would be applied by this force element if the given state were realized to Dynamics stage. More...

Real	calcPotentialEnergyContribution (const State &state) const
	Calculate the potential energy contribution that is made by this force element at the given state. More...

	Force ()
	Default constructor for Force handle base class does nothing. More...

	operator ForceIndex () const
	Implicit conversion to ForceIndex when needed. More...

const GeneralForceSubsystem &	getForceSubsystem () const
	Get the GeneralForceSubsystem of which this Force is an element. More...

ForceIndex	getForceIndex () const
	Get the index of this force element within its parent force subsystem. More...

Public Member Functions inherited from SimTK::PIMPLHandle< Force, ForceImpl, 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 Force &other) const
	Determine whether the supplied handle is the same object as "this" PIMPLHandle. More...

void	disown (Force &newOwner)
	Give up ownership of the implementation to an empty handle. More...

PIMPLHandle &	referenceAssign (const Force &source)
	"Copy" assignment but with shallow (pointer) semantics. More...

PIMPLHandle &	copyAssign (const Force &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 ForceImpl &	getImpl () const
	Get a const reference to the implementation associated with this Handle. More...

ForceImpl &	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::PIMPLHandle< Force, ForceImpl, true >
typedef PIMPLHandle< Force, ForceImpl, PTR >	HandleBase

typedef HandleBase	ParentHandle

Protected Member Functions inherited from SimTK::Force
	Force (ForceImpl *r)
	Use this in a derived Force handle class constructor to supply the concrete implementation object to be stored in the handle base. More...

Protected Member Functions inherited from SimTK::PIMPLHandle< Force, ForceImpl, true >
	PIMPLHandle ()
	The default constructor makes this an empty handle. More...

	PIMPLHandle (ForceImpl *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 (ForceImpl *p)
	Set the implementation for this empty handle. More...

bool	hasSameImplementation (const Force &other) const
	Determine whether the supplied handle is a reference to the same implementation object as is referenced by "this" PIMPLHandle. More...

Detailed Description

Model a compliant stop element that acts to keep a mobilizer coordinate q within specified bounds.

This force element generates no force when the coordinate is in bounds, but when either the lower or upper bound is exceeded it generates a generalized force opposing further violation of the bound. The generated force is composed of a stiffness force (or torque, or generalized force) that is linear in the violation of the bound, and dissipation that is linear in the rate qdot.

Theory:

Given a mobilizer coordinate q and limits q_low and q_high, the generalized force generated here is:

      {           0,             q_low <= q <= q_high
  f = { min(0, -k*x*(1+d*qdot)), q > q_high, x=q-q_high (x>0, f<=0)
      { max(0, -k*x*(1-d*qdot)), q < q_low,  x=q-q_low  (x<0, f>=0)

where k is a stiffness parameter, and d is a dissipation coefficient.

Note that dissipation occurs both during compression and expansion, but we will never generate a "sticking" force. This is a Hunt and Crossley-like dissipation model. It has the nice property that the damping force is zero when you first touch the stop.

Constructor & Destructor Documentation

SimTK::Force::MobilityLinearStop::MobilityLinearStop	(	GeneralForceSubsystem &	forces,
		const MobilizedBody &	mobod,
		MobilizerQIndex	whichQ,
		Real	defaultStiffness,
		Real	defaultDissipation,
		Real	defaultQLow = `-Infinity`,
		Real	defaultQHigh = `Infinity`
	)

Create a MobilityLinearStop force element on a particular generalized coordinate.

Parameters

forces	subsystem to which this force element should be added
mobod	mobilizer to which the force should be applied
whichQ	to which of the mobilizer's generalized coordinates q should this force be applied (first is 0)?
defaultStiffness	default stop stiffness (>= 0)
defaultDissipation	default stop dissipation coefficient (>= 0)
defaultQLow	default lower bound (-Infinity)
defaultQHigh	default upper bound (+Infinity)

Note that if you have an integer value for the generalized coordinate (q) index, you have to cast it to a MobilizerQIndex here. The generalized coordinates are numbered starting with 0 for each mobilizer. Here is an example:

GeneralForceSubsystem forces;
MobilizedBody::Pin pinJoint(...);
MobilityLinearStop myStop(forces, pinJoint, MobilizerQIndex(0),
                          k, d, -Pi/4, Pi/4);

SimTK::Force::MobilityLinearStop::MobilityLinearStop ( )

inline

Default constructor creates an empty handle that can be assigned to refer to any MobilityLinearStop object.

Member Function Documentation

MobilityLinearStop& SimTK::Force::MobilityLinearStop::setDefaultBounds	(	Real	defaultQLow,
		Real	defaultQHigh
	)

Provide new values for the default lower and upper bounds of this stop.

This is a topological change because it affects the value that the containing System's default state will have when realizeTopology() is called. This is for use during construction, not for during a simulation where you should be using setBounds() to set the bounds in a State rather than in the System.

Parameters

defaultQLow	Default lower bound (generalized coordinate value); <= defaultQHigh. Set to `-Infinity` to disable the lower bound by default.
defaultQHigh	Default upper bound (generalized coordinate value); >= defaultQLow. Set to `Infinity` to disable the upper bound by default.

Returns: a writable reference to this modified force element

See Also: setBounds(), getDefaultLowerBound(), getDefaultUpperBound()

MobilityLinearStop& SimTK::Force::MobilityLinearStop::setDefaultMaterialProperties	(	Real	defaultStiffness,
		Real	defaultDissipation
	)

Provide new values for the default material properties of this stop, which are assumed to be the same for the upper and lower stops.

This is a topological change because it affects the value that the containing System's default state will have when realizeTopology() is called. This is for use during construction, not for during a simulation where you should be using setMaterialProperties() to set the material properties in a State rather than in the System.

Parameters

defaultStiffness	default stop stiffness (>= 0)
defaultDissipation	default stop dissipation coefficient (>= 0)

Returns: a writable reference to this modified force element

See Also: setMaterialProperties(), getDefaultStiffness(), getDefaultDissipation()

Real SimTK::Force::MobilityLinearStop::getDefaultLowerBound ( ) const

Return the default value for the stop's lower bound (a generalized coordinate value).

This is normally set at construction.

See Also: getDefaultUpperBound(), getLowerBound()

Real SimTK::Force::MobilityLinearStop::getDefaultUpperBound ( ) const

Return the default value for the stop's upper bound (a generalized coordinate value).

This is normally set at construction.

See Also: getDefaultLowerBound(), getUpperBound()

Real SimTK::Force::MobilityLinearStop::getDefaultStiffness ( ) const

Return the default value for the stop material's stiffness k.

This is normally set at construction.

See Also: getDefaultDissipation(), getStiffness()

Real SimTK::Force::MobilityLinearStop::getDefaultDissipation ( ) const

Return the default value for the stop's material's dissipation coefficient d.

This is normally set at construction.

See Also: getDefaultStiffness(), getDissipation()

void SimTK::Force::MobilityLinearStop::setBounds	(	State &	state,
		Real	qLow,
		Real	qHigh
	)		const

Change the values of the lower and upper bounds in the given state; these may differ from the default values supplied at construction.

Parameters

state	The State in which the bounds are changed.
qLow	Lower bound (generalized coordinate value); <= qHigh. Set to `-Infinity` to disable the lower bound.
qHigh	Upper bound (generalized coordinate value); >= qLow. Set to `Infinity` to disable the upper bound.

Changing these bounds invalidates Stage::Dynamics and above in the state since it can affect force generation.

See Also: setDefaultBounds(), getLowerBound(), getUpperBound()

void SimTK::Force::MobilityLinearStop::setMaterialProperties	(	State &	state,
		Real	stiffness,
		Real	dissipation
	)		const

Change the values of this stop's material properties in the given state; these may differ from the default values supplied at construction.

Parameters

state	The State in which the material properties are changed.
stiffness	The stop material stiffness k (>= 0).
dissipation	The stop material dissipation coefficient d (>= 0).

Changing these properties invalidates Stage::Dynamics and above in the state since it can affect force generation.

See Also: setDefaultMaterialProperties(), getStiffness(), getDissipation()

Real SimTK::Force::MobilityLinearStop::getLowerBound ( const State & state ) const

Return the value for the lower bound that is stored in the given state.

Note that this is not the same thing as the default lower bound that was supplied on construction.

See Also: getUpperBound(), setBounds(), getDefaultLowerBound()

Real SimTK::Force::MobilityLinearStop::getUpperBound ( const State & state ) const

Return the value for the upper bound that is stored in the given state.

Note that this is not the same thing as the default upper bound that was supplied on construction.

See Also: getLowerBound(), setBounds(), getDefaultUpperBound()

Real SimTK::Force::MobilityLinearStop::getStiffness ( const State & state ) const

Return the value for the stop material's stiffness k that is stored in the given state.

Note that this is not the same thing as the default stiffness that was supplied on construction.

See Also: getDissipation(), setMaterialProperties(), getDefaultStiffness()

Real SimTK::Force::MobilityLinearStop::getDissipation ( const State & state ) const

Return the value for the stop material's dissipation coefficient d that is stored in the given state.

Note that this is not the same thing as the default dissipation coefficient that was supplied on construction.

See Also: getStiffness(), setMaterialProperties(), getDefaultDissipation()

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

Force_MobilityLinearStop.h

Public Member Functions

Additional Inherited Members

Detailed Description

Theory:

Constructor & Destructor Documentation

Member Function Documentation