Hi, I have a couple of M-20ib/25 robots doing machine tending operations. Multiple times over the last six months the robots have stopped hitting their taught points accurately. I teach all of the positions, and some time later (sometimes days, sometimes weeks) the robot will be moving to a position which is a few millimeters lower than where a taught it.
When this happens the Cartesian coordinates of the robot's actual position and the taught position are identical (and is even identical to the coordinates saved in previous controller backups), so it's not caused by a change in the taught coordinates. The robot's payload data is set properly as far as I can tell, and the payload is never more than half of the robot's rated 25kg capacity.
This is very bizarre to me. It's as if the robot's arm is sagging over time, but the robot is not reporting any mastering errors. Does anyone have any suggestions for what might be the cause or what I should check? Thanks!