Kinematic failure of Mocap model for simple lifting and lowering task

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1

Hi

I am having problems with my mocap model for a simple lifting and lowering task. The kinematic analysis continues to fail (Error message below). I have tried numerous ways to solve the issue such as altering marker position, starting position etc, however I am unable to solve the problem. Can you please help me debug the model (attached) and supply some advice.

Just to point out, the elbow markers were placed on the lateral epicondyle and the problem occurring seems to be taking place at the arms.

It must be noted that on some occasions the model will work and on other occasions it does not. For instance, the first C3D file (normal lift - file 004) works, second C3D file (semi-stooped lift - file 008) does not work and the third C3D file (stooped lift - file 014) does work. Markers were not altered throughout testing.

Thanks

Macro command : RunMotionAndParameterOptimizationSequence(5:5)> run

5.0) Kinematics (Operation: Main.Studies.MotionOptimization.Kinematics):
5.0.0) PreOperation (Operation: Main.Studies.MotionOptimization.Kinematics.PreOperation):
5.0.0.0) InitialConditions (Operation: Main.Studies.MotionOptimization.InitialConditions):
5.0.0.0) …Design variables have been updated.
5.0.0.1) …Load-time positions have been re-established.
5.0.0.2) …Kinematic analysis completed. The kinematic constraints have been resolved.
5.0.0.3) …Initial conditions are fully updated.
5.0) Kinematic analysis…
WARNING(OBJ.MCH.KIN6) : C:/U…s/k…n/D…s/A…y/A…o/Body/A…n/Arm/Jnt.any(46) : GHRot : Close to singular position : Orientation close to Gimbal Lock, i.e., first and third axis of rotation being parallel
Failed to resolve kinematic constraints. Newton relaxation too small. (final kin. error = 3.256412E-006)
Constraint no. 98 above error tolerance 0.000001, error = 0.000002.
Constraint no. 99 above error tolerance 0.000001, error = 0.000002.
Constraint no. 238 above error tolerance 0.000001, error = 0.000002.
Constraint no. 245 above error tolerance 0.000001, error = 0.000002.
Constraint no. 246 above error tolerance 0.000001, error = 0.000003.
5.138) …Kinematic analysis terminated
ERROR(OBJ.MCH.KIN3) : C:/U…s/k…n/D…s/A…y/A…o/A…n/E…s/M…g/M…l/Kinematics.any(74) : MotionOptimization.Kinematics : Kinematic analysis failed in time step 138

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Hi Kirsten,

I tried to fix your model.
Because your model does not seem to have enough number of markers,
so I had to add some extra drivers.

But I could not manage to make it working.

Because I may not have enough time to work on this model in this week,
I just attach the model which I’ve made so far.

Sorry, but we can see later in next week.

Best regards,
Moonki

3

Hi Moonki

Thanks for getting back to me. Next week will be great, thanks. So long I will have a look at the extra drivers inserted.

Quick question, what are the most important markers to have in order to not add extra drivers?

Unfortunately the motion capture system I am using only has two cameras, thus it is not possible to have markers on the spine and on the clavical or sternum. Is this a big problem? (too much data goes missing)

Regards,
Kirsten

4

Hi Kirsten,

The biggest problem of your model is that when two arms are fully stretched,
then the kinematics of your model will be in trouble.

So I would recommend you to add more markers in the arms(both for upper and lower arms).

We are working on a new concept which can be used for the implementation of joint range limit, but it will be released with the new AMS 6.1.X versions.

Best regards,
Moonki

5

Hi Moonki

Thanks! I will try and add these markers. When abouts will the new version be released?

Regards,
Kirsten

6

Hi Kirsten,

I’m not sure when it will be released.
Please keep your eyes on our websites.

Best regards,
Moonki

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