Joints not independent
I am trying to set the PID position controller on my 7-DOF robotic arm using ros-control. However, the joints are not behaving independently. For instance when I move joint 2, joint 4 moves a bit as well. This makes the PID tuning complicated. How can I make the joints independent of each other so that I can set each joint's PID separately? Do you think that the problem is because of the inertial values?
Here is a video showing this behavior. I am giving a reference angle (position) to the last joint (the wrist joint). However as can be seen, the joints before are also moving even though I tuned the PID values of each joint. Also, when increasing the damping value, sometimes the link starts vibrating a lot.
https://youtu.be/GnTFysoRYjk
Also, when setting one of the joints (which is on a horizontal plane) as revolute, the link starts moving even when the set position is 0, however when changing it to continuous joint it behaves correctly. Why is this?
Thanks
Asked by sal14 on 2017-05-02 09:15:59 UTC
Answers
Thank you for the video showing the problem.
If I understood correctly, your problem is that you want to tune the PID of a joint on the base of the robot, but as you're doing it, other joints move too, right? They are moving because they're not "locked" and react to the forces generated by the joint you're controlling, just like they would in real life.
One thing you could do is changing your robot's description to use fixed joints on all joints except the one you're trying to tune.
Asked by chapulina on 2017-05-08 09:30:10 UTC
Comments
Thanks for your reply. I did tune each joint while setting the other joints as fixed. However, once each joint behaved correctly I replaced each joint back to revolute. But still, when moving certain joints, others still oscillate as in the video.
Asked by sal14 on 2017-05-08 16:12:21 UTC
Comments
It's a bit difficult to imagine what you're talking about without an example or images/videos, do you think you could add any of those to your question?
Asked by chapulina on 2017-05-02 09:43:17 UTC
I added a video to show such behavior. Thanks
Asked by sal14 on 2017-05-08 06:58:10 UTC