Description

Class for modeling a universal joint between two two ChBodyFrame objects.

This joint is defined through 4 constraint equations between two marker frames, one on each body. Kinematically, these constraints impose the condition that the two marker origins coincide (3 constraints) and that two directions (one on each body) are always perpendicular. Together, these constraints model the cross in a physical universal joint.

#include <ChLinkUniversal.h>

Inheritance diagram for chrono::ChLinkUniversal:

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Collaboration diagram for chrono::ChLinkUniversal:

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Public Member Functions
	ChLinkUniversal (const ChLinkUniversal &other)

virtual ChLinkUniversal *	Clone () const override
	"Virtual" copy constructor (covariant return type).

virtual int	GetDOC_c () override
	Get the number of (bilateral) constraints introduced by this joint.

virtual ChCoordsys	GetLinkRelativeCoords () override
	Get the link coordinate system, expressed relative to Body2.

const ChFrame &	GetFrame1Rel () const
	Get the joint frame on Body1, expressed in Body1 coordinate system.

const ChFrame &	GetFrame2Rel () const
	Get the joint frame on Body2, expressed in Body2 coordinate system.

ChFrame	GetFrame1Abs () const
	Get the joint frame on Body1, expressed in absolute coordinate system.

ChFrame	GetFrame2Abs () const
	Get the joint frame on Body2, expressed in absolute coordinate system.

const ChVectorN< double, 4 > &	GetC () const
	Get the joint violation (residuals of the constraint equations)

void	Initialize (std::shared_ptr< ChBodyFrame > body1, std::shared_ptr< ChBodyFrame > body2, const ChFrame<> &frame)
	Initialize this joint by specifying the two bodies to be connected and a joint frame specified in the absolute frame. More...

void	Initialize (std::shared_ptr< ChBodyFrame > body1, std::shared_ptr< ChBodyFrame > body2, bool local, const ChFrame<> &frame1, const ChFrame<> &frame2)
	Initialize this joint by specifying the two bodies to be connected and the joint frames on each body. More...

virtual void	Update (double time, bool update_assets=true) override
	Perform the update of this joint at the specified time: compute jacobians and constraint violations, cache in internal structures.

virtual void	IntStateGatherReactions (const unsigned int off_L, ChVectorDynamic<> &L) override
	From item's reaction forces to global reaction vector. More...

virtual void	IntStateScatterReactions (const unsigned int off_L, const ChVectorDynamic<> &L) override
	From global reaction vector to item's reaction forces. More...

virtual void	IntLoadResidual_CqL (const unsigned int off_L, ChVectorDynamic<> &R, const ChVectorDynamic<> &L, const double c) override
	Takes the term Cq'L, scale and adds to R at given offset: R += cCq'*L. More...

virtual void	IntLoadConstraint_C (const unsigned int off, ChVectorDynamic<> &Qc, const double c, bool do_clamp, double recovery_clamp) override
	Takes the term C, scale and adds to Qc at given offset: Qc += c*C. More...

virtual void	IntToDescriptor (const unsigned int off_v, const ChStateDelta &v, const ChVectorDynamic<> &R, const unsigned int off_L, const ChVectorDynamic<> &L, const ChVectorDynamic<> &Qc) override
	Prepare variables and constraints to accommodate a solution: More...

virtual void	IntFromDescriptor (const unsigned int off_v, ChStateDelta &v, const unsigned int off_L, ChVectorDynamic<> &L) override
	After a solver solution, fetch values from variables and constraints into vectors: More...

virtual void	InjectConstraints (ChSystemDescriptor &descriptor) override
	Tell to a system descriptor that there are constraints of type ChConstraint in this object (for further passing it to a solver) Basically does nothing, but maybe that inherited classes may specialize this.

virtual void	ConstraintsBiReset () override
	Sets to zero the known term (b_i) of encapsulated ChConstraints.

virtual void	ConstraintsBiLoad_C (double factor=1, double recovery_clamp=0.1, bool do_clamp=false) override
	Adds the current C (constraint violation) to the known term (b_i) of encapsulated ChConstraints.

virtual void	ConstraintsLoadJacobians () override
	Adds the current jacobians in encapsulated ChConstraints.

virtual void	ConstraintsFetch_react (double factor=1) override
	Fetches the reactions from the lagrangian multiplier (l_i) of encapsulated ChConstraints. More...

virtual void	ArchiveOUT (ChArchiveOut &marchive) override
	Method to allow serialization of transient data to archives.

virtual void	ArchiveIN (ChArchiveIn &marchive) override
	Method to allow deserialization of transient data from archives. More...

Public Member Functions inherited from chrono::ChLink
	ChLink (const ChLink &other)

int	GetLeftDOF ()
	Get the number of free degrees of freedom left by this link, between two bodies.

virtual int	GetNumCoords () override
	Get the number of scalar variables affected by constraints in this link.

ChBodyFrame *	GetBody1 ()
	Get the constrained body '1', the 'slave' body.

ChBodyFrame *	GetBody2 ()
	Get the constrained body '2', the 'master' body.

virtual ChCoordsys	GetLinkAbsoluteCoords () override
	Get the link coordinate system in absolute reference. More...

virtual ChVector	Get_react_force () override
	Get reaction force, expressed in link coordinate system.

virtual ChVector	Get_react_torque () override
	Get reaction torque, expressed in link coordinate system.

virtual int	RestoreRedundant ()
	If some constraint is redundant, return to normal state //*OBSOLETE*.

virtual void	UpdateTime (double mytime)
	Given new time, current body state, update time-dependent quantities in link state, for example motion laws, moving markers, etc. More...

virtual void	Update (bool update_assets=true) override
	As above, but with current time.

virtual void	UpdatedExternalTime (double prevtime, double time)
	Called from a external package (i.e. a plugin, a CAD app.) to report that time has changed.

Public Member Functions inherited from chrono::ChLinkBase
	ChLinkBase (const ChLinkBase &other)

bool	IsValid ()
	Tells if the link data is currently valid. More...

void	SetValid (bool mon)
	Set the status of link validity.

bool	IsDisabled ()
	Tells if all constraints of this link are currently turned on or off by the user.

virtual void	SetDisabled (bool mdis)
	User can use this to enable/disable all the constraint of the link as desired.

bool	IsBroken ()
	Tells if the link is broken, for excess of pulling/pushing.

virtual void	SetBroken (bool mon)
	Set the 'broken' status vof this link.

bool	IsActive ()
	An important function! Tells if the link is currently active, in general, that is tells if it must be included into the system solver or not. More...

virtual ChFrame	GetAssetsFrame (unsigned int nclone=0) override
	Get the master coordinate system for the assets, in absolute reference. More...

virtual bool	IsRequiringWaking ()
	Tells if this link requires that the connected ChBody objects must be waken if they are sleeping. More...

Public Member Functions inherited from chrono::ChPhysicsItem
	ChPhysicsItem (const ChPhysicsItem &other)

ChSystem *	GetSystem () const
	Get the pointer to the parent ChSystem()

virtual void	SetSystem (ChSystem *m_system)
	Set the pointer to the parent ChSystem() and also add to new collision system / remove from old coll.system.

void	AddAsset (std::shared_ptr< ChAsset > masset)
	Add an optional asset (it can be used to define visualization shapes, es ChSphereShape, or textures, or custom attached properties that the user can define by creating his class inherited from ChAsset)

std::vector< std::shared_ptr< ChAsset > > &	GetAssets ()
	Access to the list of optional assets.

std::shared_ptr< ChAsset >	GetAssetN (unsigned int num)
	Access the Nth asset in the list of optional assets.

virtual unsigned int	GetAssetsFrameNclones ()
	Optionally, a ChPhysicsItem can return multiple asset coordinate systems; this can be helpful if, for example, when a ChPhysicsItem contains 'clones' with the same assets (ex. More...

virtual bool	GetCollide () const
	Tell if the object is subject to collision. More...

virtual void	SyncCollisionModels ()
	If this physical item contains one or more collision models, synchronize their coordinates and bounding boxes to the state of the item.

virtual void	AddCollisionModelsToSystem ()
	If this physical item contains one or more collision models, add them to the system's collision engine.

virtual void	RemoveCollisionModelsFromSystem ()
	If this physical item contains one or more collision models, remove them from the system's collision engine.

virtual void	GetTotalAABB (ChVector<> &bbmin, ChVector<> &bbmax)
	Get the entire AABB axis-aligned bounding box of the object. More...

virtual void	GetCenter (ChVector<> &mcenter)
	Get a symbolic 'center' of the object. More...

virtual void	StreamINstate (ChStreamInBinary &mstream)
	Method to deserialize only the state (position, speed) Must be implemented by child classes.

virtual void	StreamOUTstate (ChStreamOutBinary &mstream)
	Method to serialize only the state (position, speed) Must be implemented by child classes.

virtual void	Setup ()
	This might recompute the number of coordinates, DOFs, constraints, in case this might change (ex in ChAssembly), as well as state offsets of contained items (ex in ChMesh)

virtual void	SetNoSpeedNoAcceleration ()
	Set zero speed (and zero accelerations) in state, without changing the position. More...

virtual int	GetDOF ()
	Get the number of scalar coordinates (variables), if any, in this item. More...

virtual int	GetDOF_w ()
	Get the number of scalar coordinates of variables derivatives (usually = DOF, but might be different than DOF, ex. More...

virtual int	GetDOC ()
	Get the number of scalar constraints, if any, in this item.

virtual int	GetDOC_d ()
	Get the number of scalar constraints, if any, in this item (only unilateral constr.) Children classes might override this.

unsigned int	GetOffset_x ()
	Get offset in the state vector (position part)

unsigned int	GetOffset_w ()
	Get offset in the state vector (speed part)

unsigned int	GetOffset_L ()
	Get offset in the lagrangian multipliers.

void	SetOffset_x (const unsigned int moff)
	Set offset in the state vector (position part) Note: only the ChSystem::Setup function should use this.

void	SetOffset_w (const unsigned int moff)
	Set offset in the state vector (speed part) Note: only the ChSystem::Setup function should use this.

void	SetOffset_L (const unsigned int moff)
	Set offset in the lagrangian multipliers Note: only the ChSystem::Setup function should use this.

virtual void	IntStateGather (const unsigned int off_x, ChState &x, const unsigned int off_v, ChStateDelta &v, double &T)
	From item's state to global state vectors y={x,v} pasting the states at the specified offsets. More...

virtual void	IntStateScatter (const unsigned int off_x, const ChState &x, const unsigned int off_v, const ChStateDelta &v, const double T)
	From global state vectors y={x,v} to item's state (and update) fetching the states at the specified offsets. More...

virtual void	IntStateGatherAcceleration (const unsigned int off_a, ChStateDelta &a)
	From item's state acceleration to global acceleration vector. More...

virtual void	IntStateScatterAcceleration (const unsigned int off_a, const ChStateDelta &a)
	From global acceleration vector to item's state acceleration. More...

virtual void	IntStateIncrement (const unsigned int off_x, ChState &x_new, const ChState &x, const unsigned int off_v, const ChStateDelta &Dv)
	Computes x_new = x + Dt , using vectors at specified offsets. More...

virtual void	IntLoadResidual_F (const unsigned int off, ChVectorDynamic<> &R, const double c)
	Takes the F force term, scale and adds to R at given offset: R += c*F. More...

virtual void	IntLoadResidual_Mv (const unsigned int off, ChVectorDynamic<> &R, const ChVectorDynamic<> &w, const double c)
	Takes the Mv term, multiplying mass by a vector, scale and adds to R at given offset: R += cM*w. More...

virtual void	IntLoadConstraint_Ct (const unsigned int off, ChVectorDynamic<> &Qc, const double c)
	Takes the term Ct, scale and adds to Qc at given offset: Qc += c*Ct. More...

virtual void	VariablesFbReset ()
	Sets the 'fb' part (the known term) of the encapsulated ChVariables to zero.

virtual void	VariablesFbLoadForces (double factor=1)
	Adds the current forces (applied to item) into the encapsulated ChVariables, in the 'fb' part: qf+=forces*factor.

virtual void	VariablesQbLoadSpeed ()
	Initialize the 'qb' part of the ChVariables with the current value of speeds. More...

virtual void	VariablesFbIncrementMq ()
	Adds M*q (masses multiplied current 'qb') to Fb, ex. More...

virtual void	VariablesQbSetSpeed (double step=0)
	Fetches the item speed (ex. More...

virtual void	VariablesQbIncrementPosition (double step)
	Increment item positions by the 'qb' part of the ChVariables, multiplied by a 'step' factor. More...

virtual void	InjectVariables (ChSystemDescriptor &mdescriptor)
	Tell to a system descriptor that there are variables of type ChVariables in this object (for further passing it to a solver) Basically does nothing, but maybe that inherited classes may specialize this.

virtual void	ConstraintsBiLoad_Ct (double factor=1)
	Adds the current Ct (partial t-derivative, as in C_dt=0-> [Cq]*q_dt=-Ct) to the known term (b_i) of encapsulated ChConstraints.

virtual void	ConstraintsBiLoad_Qc (double factor=1)
	Adds the current Qc (the vector of C_dtdt=0 -> [Cq]*q_dtdt=Qc ) to the known term (b_i) of encapsulated ChConstraints.

virtual void	ConstraintsFbLoadForces (double factor=1)
	Adds the current link-forces, if any, (caused by springs, etc.) to the 'fb' vectors of the ChVariables referenced by encapsulated ChConstraints.

virtual void	InjectKRMmatrices (ChSystemDescriptor &mdescriptor)
	Tell to a system descriptor that there are items of type ChKblock in this object (for further passing it to a solver) Basically does nothing, but maybe that inherited classes may specialize this.

virtual void	KRMmatricesLoad (double Kfactor, double Rfactor, double Mfactor)
	Adds the current stiffness K and damping R and mass M matrices in encapsulated ChKblock item(s), if any. More...

Public Member Functions inherited from chrono::ChObj
	ChObj (const ChObj &other)

int	GetIdentifier () const
	Gets the numerical identifier of the object.

void	SetIdentifier (int id)
	Sets the numerical identifier of the object.

double	GetChTime () const
	Gets the simulation time of this object.

void	SetChTime (double m_time)
	Sets the simulation time of this object.

const char *	GetName () const
	Gets the name of the object as C Ascii null-terminated string -for reading only!

void	SetName (const char myname[])
	Sets the name of this object, as ascii string.

std::string	GetNameString () const
	Gets the name of the object as C Ascii null-terminated string.

void	SetNameString (const std::string &myname)
	Sets the name of this object, as std::string.

void	MFlagsSetAllOFF (int &mflag)

void	MFlagsSetAllON (int &mflag)

void	MFlagSetON (int &mflag, int mask)

void	MFlagSetOFF (int &mflag, int mask)

int	MFlagGet (int &mflag, int mask)

virtual std::string &	ArchiveContainerName ()

Additional Inherited Members
Protected Attributes inherited from chrono::ChLink
ChBodyFrame *	Body1
	first connected body

ChBodyFrame *	Body2
	second connected body

ChVector	react_force
	store the xyz reactions, expressed in local coordinate system of link;

ChVector	react_torque
	store the torque reactions, expressed in local coordinate system of link;

Protected Attributes inherited from chrono::ChLinkBase
bool	disabled
	all constraints of link disabled because of user needs

bool	valid
	link data is valid

bool	broken
	link is broken because of excessive pulling/pushing.

Protected Attributes inherited from chrono::ChPhysicsItem
ChSystem *	system
	parent system

std::vector< std::shared_ptr< ChAsset > >	assets
	set of assets

unsigned int	offset_x
	offset in vector of state (position part)

unsigned int	offset_w
	offset in vector of state (speed part)

unsigned int	offset_L
	offset in vector of lagrangian multipliers

Protected Attributes inherited from chrono::ChObj
double	ChTime
	the time of simulation for the object

Member Function Documentation

◆ ArchiveIN()

void chrono::ChLinkUniversal::ArchiveIN ( ChArchiveIn & marchive )

overridevirtual

Method to allow deserialization of transient data from archives.

Method to allow de serialization of transient data from archives.

Reimplemented from chrono::ChLink.

◆ ConstraintsFetch_react()

void chrono::ChLinkUniversal::ConstraintsFetch_react ( double factor = 1 )

overridevirtual

Fetches the reactions from the lagrangian multiplier (l_i) of encapsulated ChConstraints.

Mostly used after the solver provided the solution in ChConstraints. Also, should convert the reactions obtained from dynamical simulation, from link space to intuitive react_force and react_torque.

Reimplemented from chrono::ChPhysicsItem.

◆ Initialize() [1/2]

void chrono::ChLinkUniversal::Initialize	(	std::shared_ptr< ChBodyFrame >	body1,
		std::shared_ptr< ChBodyFrame >	body2,
		bool	local,
		const ChFrame<> &	frame1,
		const ChFrame<> &	frame2
	)

Initialize this joint by specifying the two bodies to be connected and the joint frames on each body.

If local = true, it is assumed that these quantities are specified in the local body frames. Otherwise, it is assumed that they are specified in the absolute frame.

Parameters

body1	first body frame
body2	second body frame
local	true if data given in body local frames
frame1	joint frame on body 1
frame2	joint frame on body 2

◆ Initialize() [2/2]

void chrono::ChLinkUniversal::Initialize	(	std::shared_ptr< ChBodyFrame >	body1,
		std::shared_ptr< ChBodyFrame >	body2,
		const ChFrame<> &	frame
	)

Initialize this joint by specifying the two bodies to be connected and a joint frame specified in the absolute frame.

Two local joint frames, one on each body, are constructed so that they coincide with the specified global joint frame at the current configuration. The kinematics of the universal joint are obtained by imposing that the origins of these two frames are the same and that the X axis of the joint frame on body 1 and the Y axis of the joint frame on body 2 are perpendicular.

Parameters

body1	first body frame
body2	second body frame
frame	joint frame (in absolute frame)

◆ IntFromDescriptor()

void chrono::ChLinkUniversal::IntFromDescriptor	(	const unsigned int	off_v,
		ChStateDelta &	v,
		const unsigned int	off_L,
		ChVectorDynamic<> &	L
	)

overridevirtual

After a solver solution, fetch values from variables and constraints into vectors:

Parameters

off_v	offset for v
v	vector to where the q 'unknowns' term of the variables will be copied
off_L	offset for L
L	vector to where L 'lagrangian ' term of the constraints will be copied

Reimplemented from chrono::ChPhysicsItem.

◆ IntLoadConstraint_C()

void chrono::ChLinkUniversal::IntLoadConstraint_C	(	const unsigned int	off,
		ChVectorDynamic<> &	Qc,
		const double	c,
		bool	do_clamp,
		double	recovery_clamp
	)

overridevirtual

Takes the term C, scale and adds to Qc at given offset: Qc += c*C.

Parameters

off	offset in Qc residual
Qc	result: the Qc residual, Qc += c*C
c	a scaling factor
do_clamp	apply clamping to c*C?
recovery_clamp	value for min/max clamping of c*C

Reimplemented from chrono::ChPhysicsItem.

◆ IntLoadResidual_CqL()

void chrono::ChLinkUniversal::IntLoadResidual_CqL	(	const unsigned int	off_L,
		ChVectorDynamic<> &	R,
		const ChVectorDynamic<> &	L,
		const double	c
	)

overridevirtual

Takes the term Cq'*L, scale and adds to R at given offset: R += c*Cq'*L.

Parameters

off_L	offset in L multipliers
R	result: the R residual, R += cCq'L
L	the L vector
c	a scaling factor

Reimplemented from chrono::ChPhysicsItem.

◆ IntStateGatherReactions()

void chrono::ChLinkUniversal::IntStateGatherReactions	(	const unsigned int	off_L,
		ChVectorDynamic<> &	L
	)

overridevirtual

From item's reaction forces to global reaction vector.

Parameters

off_L	offset in L vector
L	L vector of reaction forces

Reimplemented from chrono::ChPhysicsItem.

◆ IntStateScatterReactions()

void chrono::ChLinkUniversal::IntStateScatterReactions	(	const unsigned int	off_L,
		const ChVectorDynamic<> &	L
	)

overridevirtual

From global reaction vector to item's reaction forces.

Parameters

off_L	offset in L vector
L	L vector of reaction forces

Reimplemented from chrono::ChPhysicsItem.

◆ IntToDescriptor()

void chrono::ChLinkUniversal::IntToDescriptor	(	const unsigned int	off_v,
		const ChStateDelta &	v,
		const ChVectorDynamic<> &	R,
		const unsigned int	off_L,
		const ChVectorDynamic<> &	L,
		const ChVectorDynamic<> &	Qc
	)

overridevirtual

Prepare variables and constraints to accommodate a solution:

Parameters

off_v	offset for v and R
v	vector that will be copied into the q 'unknowns' term of the variables (for warm starting)
R	vector that will be copied into the F 'force' term of the variables
off_L	offset for L and Qc
L	vector that will be copied into the L 'lagrangian ' term of the constraints (for warm starting)
Qc	vector that will be copied into the Qb 'constraint' term of the constraints

Reimplemented from chrono::ChPhysicsItem.

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

/builds/uwsbel/chrono/src/chrono/physics/ChLinkUniversal.h
/builds/uwsbel/chrono/src/chrono/physics/ChLinkUniversal.cpp

Description

Public Member Functions

Additional Inherited Members

Member Function Documentation

◆ ArchiveIN()

◆ ConstraintsFetch_react()

◆ Initialize() [1/2]

◆ Initialize() [2/2]

◆ IntFromDescriptor()

◆ IntLoadConstraint_C()

◆ IntLoadResidual_CqL()

◆ IntStateGatherReactions()

◆ IntStateScatterReactions()

◆ IntToDescriptor()