class frictionContact

A unilateral constraint for a frictional contact between a link and a fixed surface.

Inheritance:

Public Methods

frictionContact(void)

constructor

frictionContact(link* l, const triple &xlink, const triple &cworld, const triple &n, double tol, part* p = NULL)

constructor.

frictionContact(link* l, link* l2, const triple &xlink, const triple &xlink2, const triple &n, double tol, part* p = NULL, part* p2 = NULL)

constructor.

inline int dim(void) const

the dimension of the constraint (3 for frictionContacts)

Inherited from contactConstraint:

Public Methods

virtual int updateConstants(const triple &xlink, const triple &cworld, const triple &n, double tol)

Inherited from uconstraint:

Inherited from constraint:

Public Fields

mechanism* mech

ptrList* otherMechs

linkForceRecord* frec

matrix Jc

double cDotTol

vector C

vector Cdot

int jdirty

int* _hasPosLimit

double* maxForce

double* minForce

vector prevF

int eindex

int iindex

int fdindex

int inSystem

double kp

double kv

Public Methods

inline int index(void) const

virtual int correctDrift(int i) const

inline virtual double computeCorrection(int i, int includeVel)

inline virtual int hasPosLimit(int i) const

inline virtual int hasNegLimit(int i) const

inline virtual int hasForceLimits(void) const

inline virtual void allocatePosLimits(void)

virtual void print(int printVal = 0)

virtual int createConstraintEquations(void)

virtual int deleteConstraintEquations(void)

virtual int setDynamicValues(void)

virtual const double* getCoefficients(int whichDof) const

virtual int resize(int newSize)

virtual int setDirtyFlags(void)

virtual int updateFlags(void)

inline virtual int isBilateral(void) const

inline virtual int isFrictional(int i) const

virtual int eval(int onlyConst = 0)

inline virtual double computeFStep(vector &a, vector &da, vector &f, vector &df, int i)

inline virtual double computeAStep(vector &a, vector &da, vector &f, vector &df, int i)

virtual int satisfied(const vector &a, const vector &f, int j)

inline virtual int needsImpulse(int i)

int computeJacobian(void)

virtual int violated(void)

virtual int applyToMech(mechanism* m, int subtract = 0)

int getGeneralizedForce(vector &gf)

virtual const linkForceRecord* getForces(void)

Inherited from dynoObject:

Public Fields

dynamicSystem* ds

int active

int stateSize

Public Methods

inline virtual int getState(double* state)

inline virtual int setState(const double* state)

inline virtual int reset(void)

Inherited from synObject:

Public Fields

static int staticClassID

int objectID

int verboseLevel

Public Methods

virtual const char* className(void) const

virtual synObject* copy(void) const

virtual int isOfType(int typeNum, int derivedOk)

static int setStaticClassID(void)

virtual int classID(void) const

Documentation

A unilateral constraint for a frictional contact between a link and a fixed surface. Friction constraints are fairly complex in relation to other constraint types. For static friction (i.e. when the tangential velocity is zero), the constraint equations are:

 1.  an >= 0                        (normal acceleration must be non-negative)
 2.  fn >= 0                        (normal force must be non-negative)
 3.  fn*an >= 0                     (normal force and/or normal acceleration 
                                     must be zero)
 4.  sqrt(fx*fx + fy*fy) <= muS*fn  (magnitude of the frictional force 
                                     must be less than muS*magnitude 
                                     of normal force)
 5.  ax*fx + ay*fy <= 0             (frictional force must be at least
                                     partially opposed to the tangential 
                                     acceleration)
 

For dynamic friction, the last two conditions above are replaced by:

 4.  fx = -fn*muD*vx/sqrt(vx+vy) 
` 5.  fy = -fn*muD*vy/sqrt(vx+vy) 
 

These two conditions ensure that the frictional force has magnitude muD*fn and is directly opposed to the tangential velocity.

Note that contact between multiple movable links is not yet implemented (it shouldn't be hard, but I haven't needed it yet.)

frictionContact(void)

constructor

frictionContact(link* l, const triple &xlink, const triple &cworld, const triple &n, double tol, part* p = NULL)

constructor. l is the link acted on by the contact. xlink is the world-space location of contact point on the link and cworld is the world-space location of the contact point on the fixed surface. n is the surface normal at cworld and points outward from the fixed surface. tol is the tolerance on interpenetration for the contact. Ideally xlink and cworld are the same; however, since there is a depth tolerance involved, some interpenetration always occurs. cworld is thus used to compute the amount of constraint violation and corrective acceleration.

frictionContact(link* l, link* l2, const triple &xlink, const triple &xlink2, const triple &n, double tol, part* p = NULL, part* p2 = NULL)

constructor. l is the link acted on by the contact. xlink is the world-space location of contact point on the link and cworld is the world-space location of the contact point on the fixed surface. n is the surface normal at cworld and points outward from the fixed surface. tol is the tolerance on interpenetration for the contact. Ideally xlink and cworld are the same; however, since there is a depth tolerance involved, some interpenetration always occurs. cworld is thus used to compute the amount of constraint violation and corrective acceleration.

inline int dim(void) const

the dimension of the constraint (3 for frictionContacts)

Direct child classes:

rollingContact

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