KUKA External Axis Limit rotation direction

    Hi everyone,

    I'm working with a KRC 4 (8.5.8) controller and an external axis Kuka External Kinematics 400V (MGU6800-235_KSP64) configured as an endless rotation axis.

    I would know if there is a possibility to limit the rotation direction: I need the axis rotates clockwise all the time and not on the contrary.

    I would appreciate knowing if anyone has tried it before or knows if it is possible.

    Thanks in advance!

  • Lemster68 December 12, 2023 at 2:53 PM

    Approved the thread.

    Thanks Fubini,

    But changing the sign of the gear ratio RAT_MOT_AX it seems I will only change the direction of rotation (positive becomes negative and vice versa). Isn´t it?

    I need the axis moves only in one direction (positive or negative but always the same direction of rotation). I need that with the robot working in AUT and also in T1 (disabling one of the movements (+/-) buttons if possible or similar).

    Quote from MDFB

    But changing the sign of the gear ratio RAT_MOT_AX it seems I will only change the direction of rotation (positive becomes negative and vice versa). Isn´t it?

    Thats correct. I misunderstood your initial question. Blocking a certain direction is afaik not possible. Only solution I could think about is implementing a monitoring function in submit and do everything yourself.

    Fubini

    Quote from MDFB

    I need the axis rotates clockwise all the time and not on the contrary.

    Under what circumstances? What motion commands are you using?

    Also, I'm not sure it's feasible to keep an Endless axis turning in one direction permanently. IIRC, there is an overflow limit on the resolver count that will be exceeded (eventually -- it might take several thousand rotations) and force motion in the other direction, or a re-Master of the axis.

    Thanks for your answer.

    I need the axis rotating in only one direction because we need too much precision in the position of the axis, I explain it better:

    We are working with Mx Automation (an interface to program the robot on a PLC), so in order to improve the precision on the axis position we have installed an encoder with an inductive sensor to count each flank when the axis is on the 'cero' position. When we rotate in one direction the flanks are precise but if we change the direction (the operator in manual or the automatic program in any movement) the flank will be executed in the other side of the inductive sensor, introducing an error in the position.

    Quote from MDFB

    When we rotate in one direction the flanks are precise but if we change the direction (the operator in manual or the automatic program in any movement) the flank will be executed in the other side of the inductive sensor, introducing an error in the position.

    That's normal -- you have backlash in your axis assembly.

    How long do you have to run the axis in one direction in a single process? Standard practice in situations like this is to "unwind" the axis between cycles. So if a process cycle runs the axis from 0 to 1000deg, in between cycles you would rotate it back to 0 before starting the next cycle. That way, when precision is critical, the axis would always rotate in a single direction.

    Quote from Fubini

    You also need to have in mind then that you will eventually also use precision the higher the axis value gets. The number of valid after comma decimals is limited. In essence the REALs in KRL are not exactly but similar to floating point precision.

    Yes, as the integer portion of the REAL gets larger, the available number of digits on the right of the decimal point gets smaller.

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