Ground contact of a lower limb prosthesis

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1

Hi there!

We are working on a simulation of a prosthetic leg, using the GaitLowerExtremity model. Basically we removed the lower leg of the model and replaced it with a segment, representing the prosthesis. Adding joints and other elements, we have the model running fine now.
To model the contact with the ground, we added a ConditionalContactClass (similar to a force plate) to the environment, pointing to a node on the bottom of the prosthesis. That looks like this:

ConditionalContactClass FootGroundContact (
  BaseObject = .GlobalRef,
  TargetObject = .Prosthesis.Segs.Foot.GroundContact,
  DisplayTriggerVolume = 1,
  DisplayTargetNode =0
  ) = {
    UserDefinedLimitLow = -0.15;
    UserDefinedLimitHigh = 0.02;
    UserDefinedRadiusLimit = 5;
    Strength = 1000;
    StaticFrictionCoefficient = 0.4;
    NormalDirection = Y;
    FrictionDirection1 = X;
    FrictionDirection2 = Z;
  };

That works rather well, but does not allow to model a contact of the real surface geometry of the prosthesis part with the ground (for example showing the change of pressure point during rolling off).

My question is: Is there a similar way to simulate the contact of a surface geometry to a “simulated force plate”?

Any help would be appreciated.

Best regards,

Martin

2

Hi Martin,

It seems that you used only one conditional contact element.

If you want to see the smooth transition of pressure,
then I would recommend you to define more AnyRefNode objects in your .Prosthesis.Segs.Foot segment.

For example, you can define more AnyRefNode objects on the surface of prosthesis by manually. Of course it may be a hard work.
After this work, then you can define more conditional contact elements as you want.

If you want to calculate the COP due to this conditional contact forces,
please refer to the previous post(by Søren):
http://forum.anyscript.org/showthread.php?t=2671

I hope this may help you.

Best regards,
Moonki

3

Thanks for the fast response, Moonki.

I am going to use several conditional contact elements, as you proposed.

If it works, I am fine with it.

All the best,

Martin

4