Force Reporter Problem

[Jonathan Mortensen]

I am trying to create a model that can do dynamic simulations of the head and neck. I found that adding SpringGeneralizedForce objects with stiffness and damping allow the model to solve correctly. However, adding these objects makes a strange error occur with my residual forces. The residual forces grow linearly, and do not respond to their inputs. Any idea why this is happening or how to fix it?

OsimProblem.PNG (15.46 KiB) Viewed 300 times

All the residual forces and moments follow this same pattern, linear increase and no reaction to input whatsoever.

[Jonathan Mortensen]

Any help?

[Dimitar Stanev]

Hi,

From your description it is very difficult to understand the problem. Please provide more details.

However, adding these objects makes a strange error occur with my residual forces. The residual forces grow linearly, and do not respond to their inputs.

What is your motion, what you want to analyze, what algorithms you use, why you added residual forces, why you want them to respond? Note that residual forces are typically used to compliment the muscle forces in case that the latter are not able to produce the desired torques, and typically you want to minimize the residuals. If you alter your model somehow, e.g. add a passive force, this force may cause large forces in the model and alter the behavior and predictions. So why you want to add the SpringGeneralizedForce?

Best

[Jonathan Mortensen]

I am analyzing motions of the head and neck. I have found the head to be very unstable without some element of stiffness and damping, so I added the SpringGeneralizedForce. I have the residual actuators there to make sure that static optimization or CMC will actually solve. The problem is that the residual actuators aren't responding to their input during FWD. Their force just ramps up linearly, no matter what the their activation level. It seems like the SpringGeneralizedForce being in the model is somehow overriding the residual actuators.

[Dimitar Stanev]

Seems strange indeed. So you have run CMC and you plot the activation and the torque produced by a reserve actuator. They should agree. Is this happening for other actuators too? I think that you may have missed something in the actuator.xml file. Can you post the actuator file and a short description of the degrees of freedom of your model?

Best