Robot idle brake

    We have a KRC4 controller and a KR16 robot controlled by an external PLC.
    If there is some sort of error on the machine or it is down for any reason and the robot sits too long the brakes are applied. This is normally not a problem, but in some particular circumstances when the machine begins moving again at high speed the slight delay that is introduced by the brakes releasing causes problems. Is there a way to send a command/pulse to wake it up or eliminate/extend this idle timer?

    The system variable $BRK_DELAY_PRO (I think that's correct, I don't have my references handy) controls the delay time between the robot stopping and the brakes being applied. It's in the file /R1/MADA/$MACHINE.DAT.


    What kind of "problem" are you having, specifically? I've never encountered a motion issue with a modern KUKAbot transitioning between brake holding and servo holding -- I even did some tests with a laser tracker once looking for tiny motions, and found none.

    It is not a motion precision problem, it is a timing issue. There is not much leeway for paused motion in the process and that short time it takes to kick back into gear is enough to have it behind where it should be. The robot is dropping off a part into a running machine and if it falls far enough behind I have a stop setup for potential collision which gets triggered.

    Ah, I've had that problem. With high-speed stamping presses. I don't know your exact setup, but what we came up with was to manipulate $OV_PRO rather than simply use WAIT states. Basically, if the speed is turned down to 0, the robot stops moving physically, but as far as the brake controls are concerned, it's still in motion.


    Rather than simply slamming $OV_PRO to zero and back, what we did was look ahead to the status of the press, and the distance to the point where the robot would have to stop before colliding, and we ramped $OV_PRO proportionally -- as long as the press wasn't ready for the robot to enter, $OV_PRO kept dialing down as we got closer to the stop point, until it actually hit 0 before the robot reached the approximation radius where the WAIT command would actually be checked. It took some SPS acrobatics and some tuning time, but it worked quite well for eliminating the issue you describe.


    Unfortunately, there isn't any way I know of to make the robot transition from brakes to servo any faster -- there's some inherent hardware limitations there. There's also no way from turning the Brake Delay time up to "never"; I think it maxes out at a few minutes.

    That $OV_PRO variable may be exactly what I was looking for. I turned up the braking delay a bit for now and later I'll give the variable adjustment a shot.


    Is there a manual with a listing of system variables anywhere? I did not see anything regarding the braking variables in the KRL Reference guide or the Expert Programming manual.


    Thanks

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