Intermittent Spindle Motor Fault 18M

[homchz]

Fanuc Motor: A06B-0751-B100#3000

For the past month I have been seeing an AL-31 from my spindle motor. Some weeks there is no issue what so ever, others it will trip out any time the spindle needs to restart.

AL-31 is a speed detection error. Currently the machine is used to flute and relieve reamers. First operation is fluting, upon completion the spindle rests, flutes are probed for location, spindle starts back up for relieving. 9 times out of 10 the fault happens right as the motor is trying to get back up to 6000 RPM for relieving (very few times does it happen when fluting begins but I have seen it. When I can see the fault happen the motor will make 4-5 very slow rotations then throw the error.

From what I can see:
1. Voltages to each phase are correct.
2. Parameters are the same as our saved parameters
3. The speed detection cable shows continuity through each lead. (Granted I do not have a Megohmmeter here to check other than low voltage)
4. Motor is wired correctly.
5. There is no mechanical restraint keeping the motor from turning (motor spins freely after fault).
6. This will happen with no load on motor (belts disconnected from spindle)
7. The feedback unit appears to be doing it job
8. Motor does not "feel" overheated upon fault

While I have call into Fanuc, the machine builder is at as much of a loss as I am. Here's to hoping someone else has seen a similar issue with their spindle motor.

Thanks in advance for any info shared.

[underthetire]

Built in sensor type? Bad sensor or out of adjustment. Gap should be .004-.006. Really need a scope to set it. If it is a built in type, also check the run out on the sensor ring<.0005