Shoulder and Elbow model soft constraints

Main Forum
1

Hello,

I’ve posted my problem here: http://forum.anyscript.org/showthread.php?p=18974

To summarize:
I use an upper extremity marker set to drive my model of the trunk and right arm. I proceed to use the MotionAndParameterOptimizationModel and the InverseDynamicModel to calculate Joint Loading. When I switch the ‘OptimizeAnthropometricsOnOff’ on for the UpperArm and LowerArm the Elbow joint is disconnected after the Optimization. Because I do not know each segments length exactly, I need the Optimization to complete my movement (maximal reaching task). Otherwise the motion is not followed completely and the arm is not fully stretched or goes into gimbal lock.

I’ve also noticed an error in which the humerus is rotated 180 degrees. The Elbow C3D marker is shown on the medial side of the body and the humerus is rotated so it fits with the AnyBody marker. However the C3D marker is placed on the lateral epicondyle, so I don’t know why the humerus is twisted.

I’m informed that the typical solution would be to add some soft constraints to limit the rotation of the bones. However, I’m afraid I do not have the necessary skills yet to do this in a short time. I’ve registrered for a course later in March, but this will be too late for my deadline.

Because I tried some marker replacement I can’t find the disconnection of the elbow at the moment. However, I’ve added the twisted Humerus file to the model.

I’m using the AnyBody version : 6. 0. 4. 4327 (64-bit version) with folder AMMR.

2

Hans,
Your model does not load on my computer, I assume that you use a too old repository.
I suggest following fixes:

  • first make a better starting guess of the initial posture in the TrailSpecific/Mannequin file

  • move the position (sRel) of the elbow marker to the correct spot in the ModelSetup.any file

3

Hello Amir, thank you for the reply.

I’ve recently switched from AnyBody V5 to V6. I’ve improved the initial position and placed the RELB marker to the correct position. However, I still have some problems with an incorrectly twisted Humerus and overstretched Elbow which causes a Gimbal Lock. Because I don’t know the exact Bone Segment Lengths I would like to use the Optimization to correct for that.
I’m afraid I don’t know why the model doesn’t load at your computer. I’ve placed the model folder in the new repository and after a few adjustments to some functions it loaded.

Is there any way I can add/copy the constraints to the elbow from an other model? I haven’t found one so far.

Greets,

Hans

4

Hans,
I changed some paths so I could get it loading. As mentioned before, the initial guess on the starting position is wrong. I changed the ElbowFlexion to 90 and the ElboPronation to 0 and it went through looking fine.

You need to get a starting position/posture similar to what you recorded in your trial!