Changing control parameters of external axis

  • Hey!

    Info at the bottom (let me know what else you need)

    I'm having a lot of issues with an external axis of mine. When asked to move to a certain position programmatically, it will do the movement just fine, but stop and get a position error on ending the motion. The problem occurs no matter how I program the motion and with speeds as low as 20% rated and with with acc = 100). All machine parameters are set to default catalog values except transmission ratio, soft-limits and that the motor is set to endless.

    So far I've been recommended changing positioning window ($IN_POS_MA) and $TIME_POS, but none of these are that appealing process wise.

    The two remaining recommendations are drift compensation and controller tuning. The most plausible cause (in my opinion) would be the controller parameters, so I looked into that. I found that one of the control parameters (VelGain) differs from the catalog data by a factor of 10.

    The control parameters are all in the "CtrlE1.xml" file which is write-protected and clearly states at the top that the file is "Generated" and you should "NOT EDIT".

    Well, my guess is that I need to edit it anyway since the data is off.

    So, 2 questions.

    1) Do you agree, that the problem might be caused by the controller parameter?

    2) How would I go about changing these parameters?

    Thanks in advance!


    Controller: KRC4

    KSS: 8.5.8

    Kernel system version: KS V8.5.465

    Rob: KR60HA_3

    External axis: MG_64_KSP40 (MGS_64_110_35_S0)

    Catalog VelGain value:

    CtrlE1.xml VelGain value:


  • You still did not mention anything of your external axis, such as model, type, catalog type used by WoV etc.

    Parameters are locked for Kuka kinematics such as positioners and rails made by KUKA - for example linear rail KLxxxx, or positioners like KP1, KP2, KP3 or DKP....

    If your external axis is not KUKA productt, use different catalog that allows customizing.

    If axis moves but you get positioning error, check in position window. For rorary axis, that is small ... About 0.1 deg.

    But for linear axis units are different and valie is about 1.5 mm

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

  • It's a Kuka motor used for endless rotary motion.

    As I mentioned in the first post, the catalog number is MG_64_KSP40 (MGS_64_110_35_S0). If that number isn't sufficient, please let me know how I should reference the catalog numbers.

    It has been updated to use external kinematics v 42.18.7 and I'm working in WV 6.0.9_Build0584.

    Default position window is 0.1 deg (default) which I have had success with on other projects using the same motor.

    Positioning time is 512ms (default) which also has been successful on other projects using the same motor.

    The only difference I can find in projects that work and this one is the difference in the catalog suggested VelGain value of 0.011 and the actual VelGain value of 0.0011.


    I ended up using the SET_SYSTEM_DATA-function to change VelGain to the catalog value.

    All problems were fixed.

    ; Function:
    SET_SYSTEM_DATA("DRIVE", "E1", "VelGain.PTP", 0.011)
    SET_SYSTEM_DATA("DRIVE", "E1", "VelGain.CP", 0.011)
  • good job and thanks for an update.

    i also found from time to time that gains in some catalogs entries were off (1FK7042). in my case it was way too high (orders of magnitude larger than proper - clearly a typo). when value is too large it would affect not just that axis but every axis (even robot arm) became unstable and would continue to scream and move even after release of enabling switch so EStop was needed. solution was to edit the value of course.... (KSS8.3, don't recall WoV but this must have been 3.x or 4.x)

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

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