Target position out of range

[gunny]

Hi,

In my scene I have an anthropomorfich robot.
I run the simulation and I move the target object.
The robot moves correctly but when the target reach the physical limits it starts to moves in random positions, it seems to "bounce"...

I've tryied your redundantRobot sample and this doesn't happens.
I've searched through the ik options but I've not found any differences...

[coppelia]

Hello,

this happens because the IK module cannot satisfy the constraints (i.e. because the target configuration is impossible or unreachable). What you can do is:

• for your IK group, enable the option restore if position/orientation was not reached: in the IK dialog, select your IK group, then click Edit conditional parameters. Then check Restore if linear precision requirements were not fullfilled and Restore if angular precision requirements were not fullfilled
• define a second IK group, that should be positionned just after your original IK group. Use the same settings otherwise. Then specify DLS as the Claculation method. Adjust the damping as needed. Click Edit conditional parameters. Then specify Perform if IKGroup1 was performed and failed.

What above method does is use a non-damped resolution method by default (non-damped, i.e. Pseudo inverse is much faster but unstable if there is no solution), and if that non-damped resolution method fails, it uses a damped resolution method (i.e. Damped Least Squares (DLS), which is slower but more robust when a solution is not available)

The scene forwardAndInverseKinematics2.ttt goes one step further: it uses:

• a non-damped resolution method with 6 constraints (position and orientation). If that fails, it uses:
• a non-damped resolution method with 3 constraints (position only). If that fails too, it uses:
• a damped resolution method with 3 constraints (position only)

Cheers