How do I prevent the robot from reaching its joint limits, where it theoretically shouldnt have to?

Cedricundert 2021-02-05

I am programming a Paletising programm for sheet metal parts and while testing the program, it often happened that after the program loop was executed without any problems, the robot rotated the Joint wrist 1 180 dg. This also meant, that wrist 3 had to counter the rotation to keep the Tool oriented correctly. This costs a lot of time between cycles which is unpractical and confused me a lot. But after the next cycle started, Wrist 1 rotated another 180 dg which caused the program to stop, since wrist 3 was now at its joint limit. I tried to solve this problem by limiting the joint wrist one in the safety installation, but that had no effect on the problem except that it stopped one cycle earlier (bc I limited the range of motion that greatly that it couldnt rotate 180 dg). This is really frustrating, since there is no way I can think of that could fix this. Could it be that the kinematics Calculation doesnt care at all about joint limits and just outputs the shortest delta angles? Im looking forward for any solutions, suggestions or even just insights how this problem occurs! Thanks in Advance

bcastets 2021-02-05

Which palletizing system are you using ? If you are using Robotiq palletizing solution (https://robotiq.com/applications/palletizing) with UR10 robot, please send your feedback to support@robotiq.com. We will advise to make sure the robot use the best trajectory.

Our software calculates optimal trajectories and manage this kind of problems.

If you are doing a custom program, you may be able to manage this issue by choosing the appropriate type of move: MoveL, MoveJ or MoveP.

Cedricundert 2021-02-08

I am doing a custom Program, since the robot I'm working on is mounted on a linear axis. One Question I have is why should the robot choose a different Joint Rotation for the same Position. I will certainly try out your proposal and thanks for the answer!

matthewd92 2021-02-08

When you are calculating the pose are you using quest in your calculation? There are always two joint solutions for any pose so you can force the calculation to return the solution that is closest to the desired joint angles.

Cedricundert 2021-02-08

No I'm not, it seems Logical that there are two Solutions for almost any pose, but I've never heard of "quest" to choose which one is gonna be used. How do you use this? Is this in UR script?

matthewd92 2021-02-08

Sory, dang autocorrect, qnear. Its a list of joint positions that the solution should be near, not the actual joint positions but the solution that is closer to these positions is the solution that is returned.

Cedricundert 2021-02-08

Ohh, thats Pretty smart! Thanks for the idea @matthewd92 , I will use a fixed Position for this, thank you so much, saved my week!!!

matthewd92 2021-02-08

Let us know if that fixes the problem you were having.