Can't get Kuka LBR_iiwa_7_R800 IK to work

[tmmurcko]

Hello everyone,

I can't seem to get the kaka arm IK solver to work. I went through the tutorial, and I drag my target dummy and the arm just doesn't move. I tried with another robot (the redunantRobot), and it worked fine. Absolutely no idea what I'm doing wrong seeing how I know my process is right since I got it to work on another robot.

Anyone run into a similar problem?

Thanks in advance,
Tim

[jacobi]

I met similar problems before.
This problem also happens to the UR robot.
Basically, I think this is due to that there are two joint axes which are almost parallel.
The robot may have several IK solutions which are close in the numerical space, and this causes the IK algorithm to become unstable.

I use the hybrid operation to overcome the problem.
However the robot will drop down a little and then return to the inital position for the first few 100 ms.

We know that some robots can operate well without using hybrid operation mode, e.g. the twoRobots.ttt scene etc.
While other robobts may have the hybrid operation mode set as default, e.g. the 7-DoF robot model.

[coppelia]

Hello,

this problem can happen when you start your IK when your robot is in a singular configuration. Singular configurations should be avoided at all costs with IK, since IK doesn't know how to handle those situations (unless you use a damped resolution method). Best is to put your arm in an initial non-singular configuration (or to use a damped resolution method)

Cheers

[tmmurcko]

Hey guys, thanks for your responses.

I tried putting all of the joints into IK mode, selected hybrid operation, selected DLS calculation method rather than pseudo inverse, and tried bending a few joints to be in a better position at the start of simulation, but it's still not working. All I can do is drag around the target dummy.

Any additional thoughts?

Thanks,
Tim

[coppelia]

Tim,

please share your scene file with us.

Cheers

[tmmurcko]

Coppelia,

Well, I don't know what I did but it's working now...I opened up the scene this morning, redid the steps and now it works. I probably missed something silly when I went through adding the hybrid operation or something.

Thanks for the help!

Tim