Reaction forces at the exoskeleton attachment points

Hello,

I am trying to understand how to obtain a realistic measure of the reaction forces applying at the exoskeleton attachment points. At the moment, my model is simple and consists of two links connected by a hinge joint at the knee. As shown in the attached imaged, I am using AnyReacForce to get my model kinetically running. Also I can observe a graph corresponding to the AnyReacForce as shown on the attachment. Does these values represent the reaction forces when the exoskeleton is connected to the human thigh using a rigid attachment in the real world?

Can I use 12 AnyGeneralMuscle to replace each AnyReacForce code segments in my model, and obtain more realistic results? I actually attempted this approach by providing two coincident nodes (one from exo and one from human thigh) as base and target, but I am getting a 'overload muscle configuration massage' continuously. Not sure if my code or usage is incorrect.

Also please let me know if there is any other better alterative for my task.

Best regards
Jeevan

Hi Jeevan,

The AnyReacForce you have implemented acts on an AnyKinLinear. Thus, it will provide the reaction force only along the AnyKinLinear. It will NOT provide any reaction moments along those axes. In the real world, this should be equivalent to a spherical joint rather than a rigid attachment (where I assume you also block rotations).

If you add 12 AnyGeneralMuscles, I believe, you are also intending to add the muscles on rotational measures? This you have not implemented in your code with AnyReacForce and is, therefore, a different system of constraints. But, more generally, yes AnyReacForce and AnyGeneralMuscle should provide you with the same results. This depends on the strength of the muscles relative to the force you are expecting from the muscle. You can think of AnyReacForce as AnyGeneralMuscle with infinite strength (if that makes sense). For the overload muscle configuration message, maybe the strength of the AnyGeneralMuscle you used is too low for the force/moment that it must generate?

Overall, if you are interested in investigating interface force at the attachment points, using AnyGeneralMuscle can be a suitable approach as it is not limited to the degrees of freedom in the system like AnyReacForce. But please always be aware of possible interaction between the human muscles and interface force, independent of the approach you are using.

Best regards,
Dave