Torsional Spring

[Pia Stefanek]

Hi,

I want to model a torsional spring as described in https://simtk-confluence.stanford.edu/d ... bolic+Cost for the knee Joint. Could someone explain the variable Parameters: upper/lower Limit/stiffness.
If I unterstood correctly then the lower and upper Limit describe the range of Motion. If i want to model the spring for the full range of knee Motion I have to Chose -120 for the lower Limit and 10 for the upper Limit.
The lower stiffness describes the stiffness of the spring at -120 degrees and the upper stiffness describes the stiffness of the spring at 10 degrees.
So if I want the stiffness to be continuous, could I set the lower and the upper stiffness to 10Nm/degree?
Is this correct?

Thanks for your help.

[Thomas Uchida]

The properties for the CoordinateLimitForce class are described on the following page in the doxygen documentation (under the "Property declarations" heading"): https://simtk.org/api_docs/opensim/api_ ... Force.html.

[Pia Stefanek]

Thank you very much for your answer. I think I understood the Parameters now. But could you tell me if it is possible to calculate the resulting torque curve when applying the torsional spring during Walking? I really want to understand how the torsional spring works so I tried to simulate a constant Joint angle (-10 Degrees) and first calculated the resulting Joint torque. Then I applied the torsional spring (lower stiffness 10, lower limit -1, Transition 0.1, damping 0.01). Then I compared the torque curves (with and without torsional spring) and saw that the torque with the spring had lower values than the torque curve without the spring. I added the resulting file to my post. The curve linkskonstant is the torque curve with the spring, the curve linksohne is the torque curve without a spring. The other curves are torque curves with different spring Parameters.Now I like to know if I can somehow calculate the torque curve with the spring from the torque curve without the spring?

I really hope someone can help me and say if it is possible or not.
Thank you very much.
Pia