## Description

A joint to enforce 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 2 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 ChLinkLockTrajectory that imposes only the position but leaves rotation free.

Notes

• 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.
• 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. 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 coincident 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).

#include <ChLinkMotionImposed.h>

## Public Member Functions

"Virtual" copy constructor (covariant return type).

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

std::shared_ptr< ChFunctionPositionGetPositionFunction () const
Get the position function q=q(t).

void SetRotationFunction (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< ChFunctionRotationGetRotationFunction () const
Get the rotation function q=q(t).

ChFrameGetFrameM2 ()
For plotting etc: get the last computed value of imposed rotation and position, expressed as the "moving" ChFrame M respect to frame2.

virtual ChFramed GetFrame2Rel () const override
Get the link frame 2, relative to body 2.

virtual void LoadKRMMatrices (double Kfactor, double Rfactor, double Mfactor) override
Add the current stiffness K matrix in encapsulated ChKRMBlock item(s), if any. More...

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

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

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

ChSystemGetSystem () const
Get the pointer to the parent ChSystem().

virtual void SetSystem (ChSystem *m_system)
Set the pointer to the parent ChSystem(). More...

void AddVisualModel (std::shared_ptr< ChVisualModel > model)
Add an (optional) visualization model. More...

std::shared_ptr< ChVisualModelGetVisualModel () const
Access the visualization model (if any). More...

void AddVisualShape (std::shared_ptr< ChVisualShape > shape, const ChFrame<> &frame=ChFrame<>())
Add the specified visual shape to the visualization model. More...

std::shared_ptr< ChVisualShapeGetVisualShape (unsigned int i) const
Access the specified visualization shape in the visualization model (if any). More...

void AddVisualShapeFEA (std::shared_ptr< ChVisualShapeFEA > shapeFEA)
Add the specified FEA visualization object to the visualization model. More...

std::shared_ptr< ChVisualShapeFEAGetVisualShapeFEA (unsigned int i) const
Access the specified FEA visualization object in the visualization model (if any). More...

virtual unsigned int GetNumVisualModelClones () const
Return the number of clones of the visual model associated with this physics item. More...

void AddCamera (std::shared_ptr< ChCamera > camera)
Attach a ChCamera to this physical item. More...

std::vector< std::shared_ptr< ChCamera > > GetCameras () const
Get the set of cameras attached to this physics item.

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

virtual void AddCollisionModelsToSystem (ChCollisionSystem *coll_sys) const
Add to the provided collision system any collision models managed by this physics item. More...

virtual void RemoveCollisionModelsFromSystem (ChCollisionSystem *coll_sys) const
Remove from the provided collision system any collision models managed by this physics item. More...

virtual void SyncCollisionModels ()
Synchronize the position and bounding box of any collsion models managed by this physics item.

virtual ChAABB GetTotalAABB () const
Get the axis-aligned bounding box (AABB) of this object. More...

virtual ChVector3d GetCenter () const
Get a symbolic 'center' of the object. More...

virtual void Setup ()
Perform setup operations. More...

void UpdateVisualModel ()
Utility function to update only the associated visual assets (if any).

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

virtual unsigned int GetNumCoordsPosLevel ()
Get the number of coordinates at the position level. More...

virtual unsigned int GetNumCoordsVelLevel ()
Get the number of coordinates at the velocity level. 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 IntStateGetIncrement (const unsigned int off_x, const ChState &x_new, const ChState &x, const unsigned int off_v, ChStateDelta &Dv)
Computes Dt = x_new - x, 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 M*v term, multiplying mass by a vector, scale and adds to R at given offset: R += c*M*w. More...

virtual void IntLoadLumpedMass_Md (const unsigned int off, ChVectorDynamic<> &Md, double &err, const double c)
Adds the lumped mass to a Md vector, representing a mass diagonal matrix. More...

virtual void InjectVariables (ChSystemDescriptor &descriptor)
Register with the given system descriptor any ChVariable objects associated with this item.

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

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

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...

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

Adds the current link-forces, if any, (caused by springs, etc.) to the 'fb' vectors of the ChVariables referenced by encapsulated ChConstraints.

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

int GetIdentifier () const
Get the unique integer identifier of this object. More...

void SetTag (int tag)
Set an object integer tag (default: -1). More...

int GetTag () const
Get the tag of this object.

void SetName (const std::string &myname)
Set the name of this object.

const std::string & GetName () const
Get the name of this object.

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

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

virtual std::string & ArchiveContainerName ()

Protected Member Functions inherited from chrono::ChObj
int GenerateUniqueIdentifier ()

Protected Attributes inherited from chrono::ChPhysicsItem
ChSystemsystem
parent system

std::shared_ptr< ChVisualModelInstancevis_model_instance
instantiated visualization model

std::vector< std::shared_ptr< ChCamera > > cameras
set of cameras

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
object simulation time

std::string m_name
object name

int m_identifier
object unique identifier

int m_tag
user-supplied tag

## ◆ ArchiveIn()

 void chrono::ChLinkMotionImposed::ArchiveIn ( ChArchiveIn & archive_in )
overridevirtual

Method to allow deserialization of transient data from archives.

Method to allow de serialization of transient data from archives.

overridevirtual

Add the current stiffness K matrix in encapsulated ChKRMBlock item(s), if any.

The K matrix is loaded with scaling value Kfactor.

## ◆ SetPositionFunction()

 void chrono::ChLinkMotionImposed::SetPositionFunction ( 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 ( 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: