For building a Femur COSYS that I can reconstruct in a FEA-Model I plan to use the mechanical proximal-distal Axis and also the cylinder axis of the femur epicondyle as descript by Klein Horsman.

By doing so I found a bug in the AnyBody Code.

Picture 1.

The y-Component is in the Horsman definition positive but in the AnyBody-Model negative. The black line in the knee joint should have the same axis as the cylinder.

Changing sign of the first RotMat in the “AnyRefNode CylCenter” about the x-Axis from 2.46 to -2.46 the problem is solved.

ARel = RotMat(…Sign*-2.46*pi/180,x) * RotMat(…Sign*-21.70*pi/180,y)*RotMat(Ci*pi,x) ;

The same is true for the knee joint. As defined in the Horsman thesis the Knee Joint axis is:

Rotation axis X Y Z

Knee -0.53 -0.11 0.84

But with the AnyBody Code the ARel of The KneeJoint is:

ARel = {{0.8457278, 0, 0.5336145}, {0.06928131, 0.9915357, -0.1098042}, {-0.5290979, 0.129834, 0.8385694}}

The sign is not Correct of the ARel(1,3) entry.

ARel = RotMat(…Sign*-7.46*pi/180,x) * RotMat(…Sign*-32.25*pi/180,y) RotMat(…SignAxisRot*pi/180,x);

If I change the Sign of -7.46 to 7.46 the bug is solved.

Then the ARel Axes of the KneeJoint is:

ARel = {{0.8457206, 0.003505665, -0.5336145}, {-0.07339077, 0.99124, -0.1098042}, {0.5285551, 0.1320261, 0.8385694}}

This would be the same as the axis of Klein Horsman.