Kinematic Error when running Inverse Dynamic Study

Hi,

I´m using a slightly adapted Gait Full Body Model found in AMMR 1.2, the AMS version is 5.0. As you know, for this model in the first step the Kinematic Optimization for the new c3d-motion is performed, in the second step the Inverse Dynamics is calculated.
Nothing special so far.

But for some motions an kinematic error occures for the ID Study, although the kinematic optimization was succesfully performed before.
Example Error:

7.0) InverseDynamics (Operation: Main.Studies.InverseDynamicStudy.InverseDynamics):
0) PreOperation (Operation: Main.Studies.InverseDynamicStudy.InverseDynamics.PreOperation):
.0) InitialConditions (Operation: Main.Studies.InverseDynamicStudy.InitialConditions):
.0) …Design variables have been updated.
.1) …Load time positions have been re-established.
.2) …Kinematic analysis completed. The kinematic constraints have been resolved.
.3) …Initial conditions are fully updated.
7.0) Inverse dynamic analysis…
Failed to resolve kinematic constraints (final kin. error = 6.630300E-006)
Constraint no. 160 above error tolerance 0.000001, error = 0.000007. - constr. #7 in ‘Main.Studies.InverseDynamicStudy.ModelEnvironmentConnection.JointsAndDrivers.JntDriverTrunk’
7.34) …Inverse dynamic analysis terminated
ERROR(OBJ.MCH.KIN3) : C:/D…s/q…2/D…p/A…2/A…n/B…E/V…S/VE_VP16_K01.main.any : InverseDynamicStudy.InverseDynamics : Kinematic analysis failed in time step 34

A workaround is to calculate the Inverse Kinematics again with a slightly different/optimized TrunkHeight (in this case) and optimizing some marker directions. But these additional recalculations are time consuming and till now not always lead to a successfully finished ID Study.

Now my question is:
What could cause the kinematic error in the ID Study?
Do you have an idea how to avoid this problem?

Thanks in advance,
Raphael

Hi Raphael,

It is hard to say what causes the error. The joint drivers used in the inverse dynamic should be quite robust. I would need to have a look at the model to find it.

One thing you can do now is change the kinematic tolerance. I can see the error is very small. You could safely set the tolerance to 1e-5 and it may solve it.

Best regards, Sylvain.

how do we set the tolarence to 1e-5?

Hi

In the study you enter a line like this

Kinematics.KinematicTol = 1e-005;

Best regards
Søren