Random Axis 5/6 rotations - PTP Movement

[jbledsoe2]

I am working on a fixed hot wire cutting simulation, to test on our DFL's Kuka robot. The robot would pick up a block of foam, and then follow the movement to cut the desired shape, on a stationary hot wire that is placed about 1.5m in front of the robot's center, and 1800mm high.

My geometry (points, planes, lines, etc.) is all fine, but when I would simulate the movement, the 5th and 6th axes start doing extra rotations for no reason, even though the x,y,z of the points are oriented correctly. We had a similar problem with LIN movement, so I switched to only PTP movement to correct this, but still happens.

When I move my geometry down, even by 100mm, then the movement works correctly, with no extra flips or problems... I don't really know if this is just a bug in the simulation, or an actual problem for the robot. Since it is not as convenient to change the hot wire height every time (other people are also using the robot, based on the 1800mm height), I have tried many other things, such as moving the wire to the sides or back and forth, or changing the 'STATUS' to try different options. Only statuses 010 or 110 seem to work decently, and still nothing else works 100% correctly except to move the wire and geometry down.

Please help if you have any solutions, or better knowledge about configuring the 'status' to correct this...!

Thanks,
Joanna

[Johannes @ Robots in Architecture]

Hello Joanna,

What you are seeing are so called singularities, which basically happen when two robot axis "overlap" - in this case, it's the A4 and A6. This video shows it quite nicely: https://www.youtube.com/watch?v=zlGCurgsqg8
In general - this applies to all 6-axis robots - you want to minimize these positions. In a best case, these singularities only cause the robot to slow down (i.e. the tooltip moves slowly, while there is much movement in the back), in a worst case the robot may stop with an error message that the required speed exceeded the allowed maximum.
As you've experienced, just slightly moving the toolpath will solve these issues.
Status defines the posture of the robot, with 010 and 110 switching the rotation of A4. Take a look at the PDFs that came with the robot for a detailed explanation - or send me an eMail if you cannot find them.

Best,
Johannes