QT-28N spindle motor control encoder problem

[Fred Raud]

Well to make a long story short, a bone head machinist removed the fan off of our Mazak QT 28's spindle motor because it started to smoke . Eventually the spindle motor got too hot, and the clickson/bimetal switch prevented the windings from going into meltdown. But not before eventually grenading the fr sf-2 18.5kw drive. We have had it repaired, (replacing all 6 igbt's the main board and power supply. Then it had the annoying problem of doing a error 39 on the maztrol, 32 on the drive of over current at 1000rpm in reverse.. Sent the drive out for testing again.. is fine.. So i decided to dive into the spindle motor. Windings ohm out at 2.1 Ohms, and motor meg's at 10Megaohms @ 1000v. I pulled the spindle motor out, and besides being packed with chips (because of the lack of motor fan) i found the encoder pickup had been chewed by the encoder wheel (most likely from expansion and lack of cooling. Now i am trying to find a good replacement pickup for this encoder.. In the manual it only lists the pulse generator as a unit ( which i believe is the amplifier and pickup.) tamagawa seiki TS1860N2. Anyone have some insight???? Even if i had the specs on the pickup.

Mike

[Fred Raud]

Does anyone have a clue to what the voltage to the amplifier board is so that i can test the output of the pickup..?? i have a scope and would like to test it before i get the drive back.

[Al_The_Man]

Is this the small circuit board with about 4 pots on that sits over the gear-like wheel, If so I should have the scope details as it has to be adjusted by double beam scope.
If this is a Mitsubishi Mazak then Mitsubishi Canada have an excellent support staff, I can give you a name/number if you need it.
Al.

[Fred Raud]

It is the pickup on the back side of the motor that runs to that small board ( the amplifier) mounted in the electrical junction box of the motor. The machine has a FR-SF 18.5k spindle drive with a sa-26A motor. .. I have a double probe scope and everything looks ok..both waves for PA and PB are equal after i adjusted them ( offset and peak to peak) But from what i found off the MEAU site, the peak to peak voltage should be 3V and it is at 6v.. i can't get them anlower than 5.98.
The drive recently blew up and was repaired.. and we keep getting a error 32 inverter over curent. it seems to happen quite frequently and randomly on either start up or during stopping. next thing i am going to check is the settings on the sf-ca board to see if infact the current sens outp[ut is 10v when this happens... i'm at a real road block here... i thought it might be the encoder.. and while i had the motor out, threw new bearings in it.. and reset the gap on the encoder pickup to the wheel.. it runs about 95 deg phase a to phase b off the amplifier. and will try rotating the pickup slightly to try and get it to 90.. but i think i may be barking up the wrong tree... if you have mitsu canada's number that would be great!!!

Mike

[Fred Raud]

I think i have the problem licked. Put the new encoder in.. and still the same problem. So out comes the damn motor again. Took the motor down to a good motor repair shop, and they found like i did the sator is fine, windings and insulation all good. But what they did find were that a couple of the rotor bars had opened, which causes the choppy rotation at low speeds. And if the open bars happen to be near a pole at the time of accel or decel, it will cause more current in the the bars next to it, which will also cause huge current in that leg on the sator side...

So now i am looking for a rotor or a place to get one used or new for a SJ-26B mitsu spindle motor.. Or a complete motor.

[Al_The_Man]

Glad you found the problem, I must have missed your post on the 19th, I have never seen a modern motor go open on the rotor bars as most are usually cast in and then turned, unlike in the old days where the copper was riveted on the end and/or silver soldered.
Al.

[Fred Raud]

I'm gonna set this machine on fire! New motor and the drive blew up again.....
I would like to check to see what the accel and decel times are for the spindle motor paramaters on the nc side. The control is a t32, and the books that came with the machine don't show machine paramater group 8, (the s) parameters. Anyone have an idea what the s paramaters are??

[Al_The_Man]

I have sent you a PM with the Mits contact.
Al.

[itmancnc]

Don't know were you are with respect to the problem, but I don't think it is a parameter issue, seems to be a PLG (feedback, Pulse Logic Generator) adjustment. Typically when a PLG is missadjusted you hear growling at slow speeds. I am in Washington state and may be able to assist you. Thanks

[onthebumper]

6y p-p is way off for that PLG. It should definitely be 3v p-p. 95 degrees won't hurt it. If you can't get it adjusted below 6v then increase the gap between the sensor and the gear. Be careful with the sensor face as it is very sensitive. If it comes in contact with the gear or is gouged then throw it in the garbage and order a new one from Mitsubishi. Make sure the gear is in good shape too. If the motor fan was off of the motor I am wondering if anything hit the gear. You will see this on the scope as noise though.
Also make sure you are adjusting the PLG in open loop. Do this one the drive by changing parameter 00 to a 1. Let me know if you need instructions on how to do this.

[Fred Raud]

Well long time but here is the update. Ended up sending the drive to mitsubishi in toronto, 8 grand later it has never worked better.. Recommendation, do not send the drive to anyone else. ended up costing 9G in shipping back and forth, as well as encoders, motor ect, when it was that the drive was never repaired right in the first place from a non mitsu company..