CNC Repair Tip #12: Using Fanuc Parameter RMV
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When performing CNC repairs, you may find it useful to detach an axis that has disconnect alarms due to some other work that you are doing at the time.
For example, I was working with someone recently who was in the process scraping in a column on a large horizontal with a Fanuc 15M control. The column had to be removed from the machine and then re-installed many times during the process. He was using the Z axis motor to move the axis back and forth to generate a “print” or pattern on the turcite surfaces on the underside of the column (so the amount of contact could be seen). I noticed that although he only needed to move the Z axis, (the X axis motor was also connected and not generating any alarms) he was climbing up on top of the column and connecting the Y axis motor each time he put the column back on the machine. When I asked why, he said that it he was connecting the Y motor to eliminate the alarms of the Y axis that would arise at power on. These alarms were preventing all axis movement. I suggested that he try the following tip: Change NC parameter 12.7 for the Y axis to a 1.
NC parameter 12.7 is labeled RMV. The description from the Fanuc 16 and the Fanuc 16i/18i/21i Operation and Maintenance Handbook says ” Detach of the each axis is not performed (0)/ performed (1)”. In the comment section it states,” Parameter RMBx (No. 1005#7)”. NC parameter 1005.7 says “Setting to detach of axis control for each axis is not effective (0)/ effective (1).
So as long as RMBx is set to (1), the RMV parameter can be used to disregard and axis. In the case mentioned above, we used it to ignore the Y axis alarms and allow the Z axis to be moved with the motor while the scaping work continued.
One thing to note: since the Y axis is the gravity axis on this machine, when the RMV for Y was set to (1) and the machine came out of E-stop, the Y axis began descending unexpectedly. This happened because the Y axis brake was still releasing as it normally would, even though the Y motor was disregarded and not holding up the Y axis. Fortunatley, E-stop was pressed immediately and the brake held the axis from falling further. No damage was done, but you can see how this requires you to think about the consequences of “removing” and axis. You have to think about what other things will happen if you do it. YOU MUST ALSO REMEMBER TO SET THE RMV BACK TO (0) WHEN YOU’RE DONE! Imagine the spindle moving toward the fixture at full rapid with the Y axis unable to move because it’s detached. The machine will not stop the feed even though it has no control of the Y axis. Not a pretty image.
Another thing. I once used this on a Y axis on a horizontal with a 15-M Fanuc control and was surpised to see the Y axis falling at power on. The reason? Even though the Y axis had been “removed” form CNC control, the brake circuit still operated as usual. This meant that the brake coil was still energized at power on, releasing the axis to fall. EXTRA CAUTION MUST BE USED WHEN “REMOVING” A GRAVITY AXIS!
Another use for this could be to eliminate disconnection alarms of a fully integrated 4th or 4th/5th axis index table when it’s not being used and has been removed from the machine.
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Tagged With axis motor, cnc service, cnc services, detch, fanuc, Fanuc CNC, Fanuc Control, RMV, servo disconnect alarm, servo motor