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IndustryArena Forum > CNC Electronics > Servo Motors / Drives > X and Y axis not moving as commanded.
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  1. #1
    Join Date
    Dec 2017
    Posts
    17

    X and Y axis not moving as commanded.

    I am having a bit of an issue with my CNC and will need help to diagnose and troubleshoot the issue. I am using stepperonline T6 servo on my X and Y and I have computed the steps per unit to 1000. I have measured backlash to be 0.01mm on both X and Y. When I issue a command for the machine to move 270mm, it always move 269.75mm consistently. For a move of 200mm, it moves 199.98mm. This issue is persistent on both my X and Y. The annoying thing is that the errors are not linear. Initially, I thought the servos were not properly tuned so I did the same test on the X axis but with a closed loop stepper motor and the machined moved 269.60mm instead of 270mm. I am using cncdrive AXBB-E. I have checked all the ball screws for binding and misalignment and everything looks fine.

    https://www.cnczone.com/forums/attac...d=506042&stc=1

  2. #2
    Join Date
    Apr 2004
    Posts
    5770

    Re: X and Y axis not moving as commanded.

    Are you applying backlash compensation? That can have somewhat random results.
    Andrew Werby
    Website

  3. #3
    Join Date
    Dec 2017
    Posts
    17

    Re: X and Y axis not moving as commanded.

    I do not have backlash compensation enabled.

  4. #4
    Join Date
    Apr 2004
    Posts
    5770

    Re: X and Y axis not moving as commanded.

    Are these values that are appearing in your DROs, or are they measured? They don't seem to be consistent, so I'm suspecting "thread drunkenness" in your screws. Unless you're using expensive ground ball screws, some errors are to be expected, and are worse in the cheaper grades. Another thing that can cause this is loose mounting of the screws. Put a dial indicator on the stage experiencing errors, and see if it's possible to change the reading by pushing or pulling on it.
    Andrew Werby
    Website

  5. #5
    Join Date
    Jan 2024
    Posts
    6

    Re: X and Y axis not moving as commanded.

    Examine the mechanical components further. Although you've checked for binding and misalignment of the ball screws, there could still be other subtle issues within the machine's structure that might affect the movement accuracy.

  6. #6
    Join Date
    Dec 2017
    Posts
    17

    Re: X and Y axis not moving as commanded.

    Those are values measured with a digital caliper. My ball screw is "fairly" straight with about 0.2mm bend in the middle.

  7. #7
    Join Date
    Apr 2024
    Posts
    23

    Re: X and Y axis not moving as commanded.

    I'm having the same problem kind of but haven't even started yet lol. I've been researching this video though.

    https://www.youtube.com/watch?v=TJDbKQzKXYc

  8. #8
    Join Date
    Jun 2024
    Posts
    1

    Re: X and Y axis not moving as commanded.

    Are you applying backlash compensation? That can have somewhat random results.

  9. #9
    Join Date
    Dec 2017
    Posts
    17

    Re: X and Y axis not moving as commanded.

    I fixed my issue by having the ball screws replaced. Everything looks good now.

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