1981 Kitamura Fanuc 6MB DC spindle motor problem

[moldmker]

Having a problem with my old Kitamura VMC DC spindle motor and/or drive.

Machine:

1981 Kitamura Mycenter-2
Fanuc 6MB control
Approx 7 hp DC spindle motor w/ Fanuc 3 spindle drive
Running on 3 ph. rotary. conv.

Scenario:

Was running an easy cutting UHMW job when machine shut down.

Cycle power and come up to Not Ready screen.

Find that 2 out of 3 main fuses (35A) to spindle drive are open.

Inspect motor brushes and find a LARGE amount of carbon dust and copper
dust accumulated on brush holders. Enough copper dust to cause a short.

Replace fuses...un-hook motor leads from drive....powers up fine.
(I do not issue a spindle command )

The commutator is worn about .015"/side, slightly gouged, not burnt and not bridged across segments.

History:

I have cleaned/inspected the brushes about 6 months ago and they were dusty with carbon dust but not out of the norm. I polished/cleaned the commutator and inspected for any bridging. I do this fairly routinely.

I just finished a mild steel cutting job that taxed the spindle motor for about 20 hours total (not continuous).

Machine sees alot of 18 hr. continuous runs cutting UHMW

I have gotten occasional spindle overcurrent alarm in the past. Usually associated with an M3 command.

I have recently been running a program that requires me to manually lock the spindle. 3 times I failed to unlock the spindle and got the overcurrent alarm when trying to orient for the tool change.

Actions so far:

Pulled the motor, disassembled and cleaned everything. Turned the armature and scraped the arm. slots. Replaced bearings while torn down.

Megged the field windings which show OK.

Pulled out the motor leads from drive to motor and inspected, seems OK.

Replaced tach-generator wires since they seemed pinched and bent in areas.

Reinstall motor.

Powers up OK

Get a "Servo 401" when issuing a spindle command. Spindle makes about a 45 deg. turn and shuts down. Once got an Overcurrent LED but mostly no LEDs lit.

Kitamura tech says that the 401 error combined with the copper dust on the brushes indicates that motor will need rebuilt.

The rebuild cost is enough that it may be time to part ways with the machine.

One thing that I notice and do not recall before. The EMG relay LED is lit as soon as the power is turned on. Is this indicating that there is an emergency stop situation?? I have cycled the Estop button and made sure the toolchanger was at home positions.

Thanks...Bob

[underthetire]

Did you check the resistance in windings? Does the 45 deg start in the correct direction? Tach hooked up backwards? If all those are good, you probably lost a drive unit.

[Dan Fritz]

You blew fuses before, but did you check the SCRs? If an SCR is blown, it will take out a fuse as soon as you try to run the spindle.

Also, make sure that your spindle drive is getting 3-phase current. If one leg is out and your "single phasing", that would create trouble too.

[Al_The_Man]

Also did you Megger the brush holders to ground, often tracking is a problem that does not show up with low voltage ohmeter.
I have the same scenario with DC servo's.
Al.

[moldmker]

Originally Posted by underthetire Did you check the resistance in windings? ....

Just checked that today (...forgot to check before). I'm only getting about 3 ohms resistance on the field windings. Does that sound low??

Originally Posted by Dan Fritz You blew fuses before, but did you check the SCRs? If an SCR is blown, it will take out a fuse as soon as you try to run the spindle. Also, make sure that your spindle drive is getting 3-phase current. If one leg is out and your "single phasing", that would create trouble too.

The fuses are OK right now after several attempts to start the spindle.
The drive is getting 207-195-196 VAC

Originally Posted by Al_The_Man Also did you Megger the brush holders to ground, often tracking is a problem that does not show up with low voltage ohmeter. I have the same scenario with DC servo's. Al.

Yes....had to scrub quite a bit to get the readings down.

I tore the motor back off and it's strapped to a pallet ready for the motor shop to evaluate.

I have a customer who relies on me for his product delivery, so need to get back up and running in a week or 2.
(OTOH, borrowed a neighboring shops new Haas VM-3 and finished the current batch of parts in 30% my normal time....hmmmm)
Thanks for the replies so far.

[moldmker]

Originally Posted by Dan Fritz You blew fuses before, but did you check the SCRs?....

Dan, I (finally) checked the 12 SCRs and looks like one is shorted closed.

The p/n is NEC 25P8SG which I can't seem to find anywhere on the net.
I can call Fanucworld or other Fanuc sources to inquire on replacements.

Is there a substitute for this p/n?
Should I replace all 12?

Thanks
Bob

[Al_The_Man]

You might possibly to get away with changing an SCR from the opposing bank, 6 are used for each direction (FWD/REV), it is worth a try and just leave the open spot unconnected.
Al.