A CNC machining center with Fanuc 6ME CNC system, the X axis speed is not stable, there is vibration when it reach to the position, sometimes even not reach the position, then the machine must be restarted to resume.

As the X axis vibration is not so frequent, and there is no abnormal noise, this could be related to the parameter setting of the close-loop-system. For example: the system gain is too high, or the integration time constant is too big, etc.

But after setting above parameters the problem is still there.

So set back to the original parameters, then check the servo motor and measuring system. Clean the speed generator and the commutator of the servo motor, then measure the speed generator and found the connection between motor axis and the speed generator was loosed, this was the cause.

Re-connect them and then restart the machine, the problem solved.