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Alexandre_PareAlexandre_Pare Posts: 56 Crew
edited August 2016 in Troubleshooting
Hi Pros,
I had several discussions with colleagues, clients and other UR users about the accuracy of the UR robots. When we are programming pick and place applications where the robot is always picking for the same positions, the repeatability of the robot is fine. However, some people trying to move the robot around using specific distances that are sent to the robot. For example, there are some people trying to create some parametric motion. Something like giving the dimension of a rectangle and have the robot move along the edge of the rectangle. Also when using vision systems, the vision system is sending distance offset from a known origin frame. In these cases, when you ask the robot to move let's say 1000mm, it may actually move 1000mm+-5mm. I discuss this with some pros and they mentioned that calibrating the UR would help. However this calibration requires some serious work. So before suggesting this option I was wondering if some pros did try this out and if they can put some numbers on the accuracy improvement of either calibration methods suggested by UR? For those who have not heard about UR calibrations, here is a link to the UR support website where you will find info on this.

Alexandre Pare, Eng.
Application Engineer
Robotiq
[email protected]

Comments

  • Kaleb_RodesKaleb_Rodes Posts: 52Founding Pro, Partner, Beta Tester VIsion 1.1 Program, Tactile Sensor Beta Testers, Beta Tester Camera URCap 1.2.0-beta Handy
    @Alexandre_Pare I emailed UR about this a couple months ago. Here is the response I received from them:

    "Every CB3 (or higher) robot comes fully calibrated by this process.  Every spare part joint has also started its existence as part of a robot that was likewise calibrated.  It's required for every robot.  Because of the True Absolute Encoders, however, once done it never really needs to be done again, though, so we do not typically offer it as a service.

    Why do you ask?  If you're looking to (for instance) ensure the repeatability of a robot after replacing a joint, there's a process called Key Waypoints that can update an entire program based on reteaching a few high-accuracy waypoints.  The manual also recommends performing a Zero Calibration after replacing a joint, but I am not sure most of our customers actually do this or notice a problem from not doing it."

    Kaleb Rodes
    Applications Engineer
    Behco
  • Alexandre_PareAlexandre_Pare Posts: 56 Crew
    @Kaleb_Rodes , thanks. I did not get a chance to test this on a CB3 or later. I will check how it behaves. Have you seen an improvement on accuracy since this procedure is in place?


    Alexandre Pare, Eng.
    Application Engineer
    Robotiq
    [email protected]
  • Kaleb_RodesKaleb_Rodes Posts: 52Founding Pro, Partner, Beta Tester VIsion 1.1 Program, Tactile Sensor Beta Testers, Beta Tester Camera URCap 1.2.0-beta Handy
    @Alexandre_Pare no, I have not tested this out - only took UR's word on it. When I get a chance I can run a few tests then post my results back here!
    Kaleb Rodes
    Applications Engineer
    Behco
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