A Fanuc M710iC robot that I am interfacing to was working ok, except that there was a noise coming from the motors. J3 was making much noise and giving overcurrent alarm, and we changed the motor. The noise was less, and the alarm stopped.
Since then it has got worse, to the point that the robot is unusable. Motors have been swapped repeatedy, new CPU, Servo and other boards have been replaced, to no avail. A complete software-reinstall was done too. Still no good.
My feeling is that the PID values in the servo loop are wrong. Maybe too much gain. Perhaps the values are quite different to the default? Does anyone think this is plausible?
The robot had been in storage for a few years, and the batteries were dead upon re-powering, so all the original config is lost. Is it easy to get the as-shipped setting from Fanuc?
If you release the deadman, the noise stops. Press the deadman again, and as you take it out of fault the whiny noise starts again. It's hard to tell where it's coming from. Sounds like it's coming from all the axis motors. There is no program loaded, and nothing attached to the arm.
It does seem to be centered around J3. If you lift the arm, it will jerk at first, then move. Perhaps the brake is not being properly released?