Description

A joint that enforces position and rotation between two frames on two bodies, using six rheonomic constraints.

That is, position and rotation of Body 1 are precisely enforced respect to Body 1 by using functions of time, where functions are defined via ChFunctionRotation and ChFunctionPosition objects. A typical usage scenario is where Body 2 is a fixed body, representing the absolute reference, so you move/rotate Body 1 in space according to the provided functions; this is the case for example where you have some data coming from a motion capture hardware following the motion, say, of a human head, and you want to replicate the motion of that head in 3D space. This joint imposes all the 6 DOFs of a body, including rotations, differently from the ChLinkTrajectory that imposes only the position but leaves rotation free. Note that if you are interested in simply imposing a straight motion, just use ChLinkMotorLinearPosition, and if you just need to impose a rotation on a shaft, just use the ChLinkMotorRotationAngle. Note: no compliance is allowed, so if the imposed motion hits an undeformable obstacle it mets a pathological situation and the solver result can be unstable/unpredictable. Think at it as a 6DOF servo drive with "infinitely stiff" control. By default it is initialized with no motion / no rotation, so by default is just like welding the two bodies, so it is up to the user to provide proper ChFunctionRotation and a proper ChFunctionPosition.

#include <ChLinkMotionImposed.h>

Inheritance diagram for chrono::ChLinkMotionImposed:

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Collaboration diagram for chrono::ChLinkMotionImposed:

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Public Member Functions
	ChLinkMotionImposed (const ChLinkMotionImposed &other)

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

void	SetPositionFunction (const std::shared_ptr< ChFunctionPosition > mf)
	Set the position function for a generic 3D rotation, as p=p(t) vector function. More...

std::shared_ptr< ChFunctionPosition >	GetPositionFunction () const
	Get the position function q=q(t).

void	SetRotationFunction (const std::shared_ptr< ChFunctionRotation > mf)
	Set the rotation function for a generic 3D rotation, as q=q(t) quaternion rotation function. More...

std::shared_ptr< ChFunctionRotation >	GetRotationFunction () const
	Get the rotation function q=q(t).

ChFrame &	GetFrameM2 ()
	For plotting etc: get the last computed value of imposed rotation and position, expressed as the "moving" ChFrame M respect to frame2.

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

void	Update (double mytime, bool update_assets) override
	Override all time, jacobian etc. updating.

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

virtual void	ConstraintsBiLoad_Ct (double factor=1) override
	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	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::ChLinkMateGeneric
	ChLinkMateGeneric (bool mc_x=true, bool mc_y=true, bool mc_z=true, bool mc_rx=true, bool mc_ry=true, bool mc_rz=true)

	ChLinkMateGeneric (const ChLinkMateGeneric &other)

virtual ChFrame	GetAssetsFrame (unsigned int nclone=0) override
	Get the master coordinate system for the assets (this will return the absolute coordinate system of the 'master' marker2)

ChFrame &	GetFrame1 ()
	Access the coordinate system considered attached to body1. More...

ChFrame &	GetFrame2 ()
	Access the coordinate system considered attached to body2. More...

bool	IsConstrainedX () const

bool	IsConstrainedY () const

bool	IsConstrainedZ () const

bool	IsConstrainedRx () const

bool	IsConstrainedRy () const

bool	IsConstrainedRz () const

void	SetConstrainedCoords (bool mc_x, bool mc_y, bool mc_z, bool mc_rx, bool mc_ry, bool mc_rz)
	Sets which movements (of frame 1 respect to frame 2) are constrained.

virtual void	Initialize (std::shared_ptr< ChBodyFrame > mbody1, std::shared_ptr< ChBodyFrame > mbody2, ChFrame<> mabsframe)
	Initialize the generic mate, given the two bodies to be connected, and the absolute position of the mate (the two frames to connect on the bodies will be initially coincindent to that frame). More...

virtual void	Initialize (std::shared_ptr< ChBodyFrame > mbody1, std::shared_ptr< ChBodyFrame > mbody2, bool pos_are_relative, ChFrame<> mframe1, ChFrame<> mframe2)
	Initialize the generic mate, given the two bodies to be connected, the positions of the two frames to connect on the bodies (each expressed in body or abs. More...

virtual void	Initialize (std::shared_ptr< ChBodyFrame > mbody1, std::shared_ptr< ChBodyFrame > mbody2, bool pos_are_relative, ChVector<> mpt1, ChVector<> mpt2, ChVector<> mnorm1, ChVector<> mnorm2)
	Initialization based on passing two vectors (point + dir) on the two bodies, which will represent the X axes of the two frames (Y and Z will be built from the X vector via Gram Schmidt orthonormalization). More...

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

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

virtual void	SetBroken (bool mon) override
	Ex:3rd party software can set the 'broken' status via this method.

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

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

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

const ChConstraintVectorX &	GetC () const
	Link violation (residuals of the link constraint equations).

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 &mdescriptor) 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...

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

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 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.

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

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 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...

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, bool full_update)
	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	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_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
Public Types inherited from chrono::ChLinkMateGeneric
using	ChConstraintVectorX = Eigen::Matrix< double, Eigen::Dynamic, 1, Eigen::ColMajor, 6, 1 >

Protected Member Functions inherited from chrono::ChLinkMateGeneric
void	SetupLinkMask ()

void	ChangedLinkMask ()

Protected Attributes inherited from chrono::ChLinkMateGeneric
ChFrame	frame1

ChFrame	frame2

bool	c_x

bool	c_y

bool	c_z

bool	c_rx

bool	c_ry

bool	c_rz

int	ndoc
	number of DOC, degrees of constraint

int	ndoc_c
	number of DOC, degrees of constraint (only bilaterals)

int	ndoc_d
	number of DOC, degrees of constraint (only unilaterals)

ChLinkMask	mask

ChConstraintVectorX	C
	residuals

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::ChLinkMotionImposed::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::ChLinkMateGeneric.

◆ GetLinkRelativeCoords()

virtual ChCoordsys chrono::ChLinkMotionImposed::GetLinkRelativeCoords ( )

inlineoverridevirtual

Get the link coordinate system, expressed relative to Body2 (the 'master' body).

This represents the 'main' reference of the link: reaction forces and reaction torques are expressed in this coordinate system. Note: differently from most other ChLinkMate -inherited links, that assume the frame2 as link coodrinate system, in this case we use the "moving" auxiliary frame M whose motion is concatenated to frame2 (in absolute coordinates, such moving frame will be cohincident with frame1 if the constraint is well assembled - in fact this makes constraint forces more intuitive, as one will get reaction forces and torques as applied to the frame1 of moving body 1).

Reimplemented from chrono::ChLinkMateGeneric.

◆ IntLoadConstraint_Ct()

void chrono::ChLinkMotionImposed::IntLoadConstraint_Ct	(	const unsigned int	off,
		ChVectorDynamic<> &	Qc,
		const double	c
	)

overridevirtual

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

Parameters

off	offset in Qc residual
Qc	result: the Qc residual, Qc += c*Ct
c	a scaling factor

Reimplemented from chrono::ChLinkMateGeneric.

◆ SetPositionFunction()

void chrono::ChLinkMotionImposed::SetPositionFunction ( const std::shared_ptr< ChFunctionPosition > mf )

inline

Set the position function for a generic 3D rotation, as p=p(t) vector function.

Use an object from one of the ChFunctionPosition inherited classes to this end. This function should be C0 continuous and, to prevent acceleration spikes, it should ideally be C1 continuous. The position is imposed to frame1 respect to frame2, in frame2 coordinate system.

◆ SetRotationFunction()

void chrono::ChLinkMotionImposed::SetRotationFunction ( const std::shared_ptr< ChFunctionRotation > mf )

inline

Set the rotation function for a generic 3D rotation, as q=q(t) quaternion rotation function.

Use an object from one of the ChFunctionRotation inherited classes to this end. This function should be C0 continuous and, to prevent acceleration spikes, it should ideally be C1 continuous. The position is imposed to frame1 respect to frame2, in frame2 coordinate system.

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

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

Description

Public Member Functions

Additional Inherited Members

Member Function Documentation

◆ ArchiveIN()

◆ GetLinkRelativeCoords()

◆ IntLoadConstraint_Ct()

◆ SetPositionFunction()

◆ SetRotationFunction()