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I am working with a Universal Robots UR5e. I am attempting to do a simple back and forth movement of 60 Degrees with Wrist 2, operating at 2 Hz (back and forth in 0.5s). Looking at the Joint Limits, the maximum Joint Speed is listed at 191 deg/sec, which should be plenty fast for this. However, I can't seem to get it to move faster than about 1 Hz. Even if I set the Robot Limits to Least Restricted, I max out at this speed.

I am using a movej command and setting t=0.100 to get the max speed. If I set it to t=0.250 I will still see the movement take over a second to go back and forth.

Does anyoneone have any suggestions for how to speed up the movement?

Thanks!

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  • $\begingroup$ Some additional information: It appears I can get the wrist to move faster if it's the ONLY wrist moving. If I make it a compound rotation (moving multiple wrists simultaneously) then the overall movement of Wrist 2 slows down. This seems strange to me, but maybe I misunderstand the spec? The datasheet specifically states 180 deg/sec for every joint and does not provide any caveats. $\endgroup$
    – user140011
    Jan 2, 2020 at 17:57

2 Answers 2

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Sounds like it could also be voltage sag in the power source that powers the servos.

Check the servo specs for the peak instantaneous current they draw under load, and multiply by 6 (or whatever concurrency you need).

If your power source can't robustly supply that total demand, its voltage will sag and the servos will operate slowly (at best), erratically (at worst), or not at all. Depending on the speed of the transients, an ordinary voltmeter might not be fast enough to measure the dropoff reliably.

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So it appears that although the documentation for movej() states that it is the time the robot will take to make the move, it's really closer to the time each joint will take to move. If I take my desired time to move and divide by 6 (number of joints), then the speed of movement is increased to be much closer to my goal. It isn't perfect, but it's much improved. I'd still like to hear what others have to say, but this is my best solution for now.

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