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SimTK::Force::MobilityLinearStop Class Reference

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...
 
MobilityLinearStopsetDefaultBounds (Real defaultQLow, Real defaultQHigh)
 Provide new values for the default lower and upper bounds of this stop. More...
 
MobilityLinearStopsetDefaultMaterialProperties (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 GeneralForceSubsystemgetForceSubsystem () 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...
 
PIMPLHandlereferenceAssign (const Force &source)
 "Copy" assignment but with shallow (pointer) semantics. More...
 
PIMPLHandlecopyAssign (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...
 
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 (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
forcessubsystem to which this force element should be added
mobodmobilizer to which the force should be applied
whichQto which of the mobilizer's generalized coordinates q should this force be applied (first is 0)?
defaultStiffnessdefault stop stiffness (>= 0)
defaultDissipationdefault stop dissipation coefficient (>= 0)
defaultQLowdefault lower bound (-Infinity)
defaultQHighdefault 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);

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
defaultQLowDefault lower bound (generalized coordinate value); <= defaultQHigh. Set to -Infinity to disable the lower bound by default.
defaultQHighDefault 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
defaultStiffnessdefault stop stiffness (>= 0)
defaultDissipationdefault 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
stateThe State in which the bounds are changed.
qLowLower bound (generalized coordinate value); <= qHigh. Set to -Infinity to disable the lower bound.
qHighUpper 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
stateThe State in which the material properties are changed.
stiffnessThe stop material stiffness k (>= 0).
dissipationThe 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: