Input external torque in a specified joint

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Stephen Garza
Posts: 2
Joined: Mon Dec 23, 2013 9:13 pm

Input external torque in a specified joint

Post by Stephen Garza » Fri Sep 19, 2014 3:17 pm

I have experimental data which contains torque information from an assistive device. I assume the axis of rotation is around the knee flexion joint. So I have the torque information throughout the gait.
I am trying to implement an external torque around a knee flexion axis. So far I have found three possible methods:
-Using OpenSim's inverse dynamic tool to create a custom grf xml file which specifies an external torque applied to a specific body.
- How should I introduce this torque into grf.mot file
-Using OpenSim's existing 'TorqueActuator' function to implement the applied torque.
- This function has an optimalForce input as a constant, is it possible to implement a variant force as a function of time ?
-Creating a custom actuator as explained in the the following link:
http://simtk-confluence.stanford.edu:80 ... d+Actuator
- The examples are showing linear spring or damper models. Is it possible to model a torsional spring around a joint.

Please let me know the method you think best suits this issue or if you have any other suggestions.

-Stephen

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James Dunne
Posts: 1231
Joined: Thu Oct 04, 2007 11:51 pm

Re: Input external torque in a specified joint

Post by James Dunne » Thu Oct 02, 2014 4:19 pm

Hi Stephen,

You will need to apply a prescribed force to the model;
https://simtk.org/api_docs/opensim/api_ ... Force.html

Hope that helps,
-james

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Stephen Garza
Posts: 2
Joined: Mon Dec 23, 2013 9:13 pm

Re: Input external torque in a specified joint

Post by Stephen Garza » Wed Oct 22, 2014 7:02 pm

Hi James,

Can you tell me about the advantages of using this method over the ExternalForce method?

Also, can you explain how I would implement the prescribed force function using force inputs as a function of time inside of an xml structure? I could not find a clear example in the documentation that explained how to do this.

Right now I currently have force and center of pressure data for the grfs, as well as the magnitudes of the torques vs. time that I wish to apply to the model.

Thank you very much for your advice.
Sincerely,
Stephen Garza

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zhong hongchuan
Posts: 1
Joined: Wed Apr 17, 2019 2:56 am

Re: Input external torque in a specified joint

Post by zhong hongchuan » Wed Apr 17, 2019 3:04 am

Hello, my situation is similar to yours, I am sorry that I am a beginner, I would like to consult you about the first solution, how to apply torque to grf files,Do you just modify the corresponding column files?Why can't I run a CMC program after I change it? :?:

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