Hi guys,
I am sasi, Graduate student, Mechanical engineering at University of Buffalo, NY. I am currently working on the project wherein I have to use the arm curl model in the repository and build an exo-skeleton around it to minimize the muscle forces. The arm is suppossed to lift a dumb-bell of given weight and the ex0-skeleton should aid the moment of the arm. The exo-skeleton in turn in actuated by a moment at its joint. I used the AnyOpt function to iteratively Optimize the moment such that the muscle forces are minimized. However, I realised that after a few iterations the muscle recuitment analysis fails. Is there any way in which I can prevent this from happening? I am attaching my code to this post. Your help in this is greatly appreciated.
P.S: I previously put this post on a wrong forum and I hope I got it right this time. Thanks Sylvian.
Thank you,
Sasi
Hi Sasi,
This is the god place for this post. Sorry for the inconvenience of making you posting again, but we want to keep this forum as well structured as possible.
It appears that the recruitement fails when the exoskeleton moment is to high. And i think this is related to the muscle configuration of you model. You changed some attachment points from the original simple arm, and you removed the elbow joint (so the rotation center is not fixed anymore). On the starting position confuguration there are no extensor muscles in your model. This should be avoided in general.
So it seems that due to this inacurate muscle configuration, when the effect of the exo moment is higher than the weight on the hand, then the system cannot be balanced.
My advice is to restore the elbow joint and review the muscle configuration.
Best regards, Sylvain.
Hi Sylvian,
First of all, thanks a lot for the reply. I attached a couple of extensor muscles to the model and now it seems to work. However, I could not restore the elbow joint owing to the degrees of freedom and constraints balance criterian. I tried disabling the ‘ShoulderExo’ joint and ‘PalmExo’ joint instead but the model failed. However, I would want to restore the elbow joint to bring more credibility to the model. Is there any way in which I can restore it and still satisfy the degrees of freedom and contraints criterian?
Once again, thanks a lot for the suggestions.
P.S: I am attaching my new code to this post.
Thank you,
Sasi
Hi Sasi,
You are right that you cannot restore the elbow joint directly beacause of the constraints balance. You must remove as much dof as you add to keep the balance.
By adding the elbow joint you add 5 constarints so you have to remove 5 somewhere else, more precisely on the exoskeleton (either directly removing the exoskeleton elbow joint or some of the Palmexo joint constraints and leaving only one linear constraint there).
Best regards, Sylvain.