Function of the elbow joint

Main Forum
1

Hi Support-Team!

I am using:
AnyBody 5
Repository 1.3.1
App FreePostureHandSR

The definition of the elbow joint in JNTSR.any is:

//Definition of elbow flexion extension joint
AnyRevoluteJoint FE = {
Axis = x;
AnyRefNode &HumerusFE = ..Seg.Humerus.fe;
AnyRefNode &UlnaFE = ..Seg.Ulna.fe

//Next three definitions equal to spherical joint
//Definition of proximal forearm pronation supination joint
AnyKinRotational PSRotProximal = {
Axis1 = x;
Axis2 = y;
Axis3 = z;
Type = RotAxesAngles;

AnyRefNode &RadiusPs = ..Seg.Radius.PointPS2;
AnyRefNode &UlnaPs = ..Seg.Ulna.ps2;

};//End pronation supination joint proximal

//Definition of forearm pronation supination joint
AnyKinLinear PSLinProximal = {
Ref=0;

AnyRefNode &UlnaPs = ..Seg.Ulna.ps2;
AnyRefNode &RadiusPs = ..Seg.Radius.PointPS2;

};//End pronation supination joint proximal

AnyKinEq PSProximalConstraints = {
AnyKinLinear &Jnt = .PSLinProximal;
Reaction.Type = {Off,Off,Off};
};

AnyReacForce PSProximalReacForce =
{
AnyKinMeasureOrg RadiusHumerus = {
MeasureOrganizer = {0};
AnyKinLinear Lin =
{
Ref = 0;
AnyRefFrame &Radius = ....Seg.Radius.PointPS2.PointPS2Rot.PS2Reac;
AnyRefFrame &Humerus = ....Seg.Humerus.fe;
};
};

AnyKinMeasureOrg RadiusUlna = {
  MeasureOrganizer = {0,2};
  AnyKinLinear Lin = 
  {
    Ref = 0;
    AnyRefFrame &Ulna = ....Seg.Ulna.ps2.ps2Reac;
    AnyRefFrame &Radius = ....Seg.Radius.PointPS2.PointPS2Rot.PS2Reac;
  };
};

};

//This is measure which will be used by the applications
AnyKinMeasureOrg PS = {
AnyKinRotational &Jnt = .PSRotProximal;
MeasureOrganizer = {0};
};
//End definitions of spherical joint

AnyKinEq PSLinDistalConstraint = {

//Definition of distal forearm pronation supination joint 
AnyKinLinear PSLinDistal = {
  Ref = 0; //Uses coordinate system of the first defined segment

  AnyRefNode &UlnaPs = ...Seg.Ulna.ps2.usRot;
  AnyRefNode &RadiusPs = ...Seg.Radius.PS;
};//End pronation supination joint distal

MeasureOrganizer = {0,2};
};

The first part of the joint is no problem.
Just a revolute Joint for the flexion.

The second part is harder to understand.
There is a spherical joint for the proximal part consisting of three other joints?
A rotational joint, a linaer joint and a measure?

How does they work together?

Why is the distal part just a linear joint?
Isn't it a linear and rotational motion between ulna and radius in the distal forearm?

Is there any reference or description of the elbow joint in AnyBody?

thanks again for the help

Julian

2

Hi Julian,

The proximal part consist of three linear constraints, equivalent to a spherical joint. This is done with PSProximalConstraints. PSLinProximal and PSRotProximal are measures but have no constraints apply to it, so they are not joints.

The two linear constraint of the distal part are on the radial directions (considering the pronation/supination axis). So they are equivalent to a sort of shperical joint sliding on the pronation/supination axis.

The combination of the proximal spherical joint and the distal sliding-spherical joint is then equivalent to a revolute joint (5 constraints in total).

Best regards, Sylvain.