3 pole DC motor failure mode?

Or internalised self destruction of one pair of drivers and nothing to do with motor playing up? Motor supply is 33V and 3 amp fuse , main drive motor for a photocopier, 3 poles and magnets. I have a parts mule for this copier but do not want to take all the frame apart to change the motor unnecessarily, the driver board is easy to get to. Other than lubricate the motor bearings and change the driver+speed/direction processing board over , anything else to check? Both motors measure 1.5 ohms all 3 ways between coils , also inside is 3 off

4 pin, presumably hall effect devices, can only see the pins. The electronics is for speed control, direction and braking. One pair of NPN+PNP TO220 drivers , 3 pairs in all, is all-pin shorted , well 1 to 3 ohm. Failed at switch on , knocking out fuses , no overheating or odd noises/smoke etc, Of course may have failed at final braking of the motor at last useage but as presumably braking is once per sheet cycle as not used for batch copying, seems unlikely it would happen to fail on the last of dozens of sheets
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N_Cook
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"Nutcase Kook"

** There is no way a 3 pole DC motor can handle 33V and survive. 6V is normal, 9V at most.

All got to do with arcing across the contacts on the comm.

... Phil

Reply to
Phil Allison

Maybe something to do with lack of lubrication, seems to run quiter now, perhaps a bearing stuck enough for overload. Seems to turn, by finger ,easier than before. Decided to solder 3 tell-tale small 28V bulbs to each coil and ground and power up with changed board. Overdriven by 33V at power up and half brightness but balanced in operation.

3 coil ,36 degree stepper motor rather than DC motor to be more exact. Will power up a few more times and then remove the telltales The hall-effect presumably for phase monitoring and an external 12 vane interupted slotted opto for speed and a PTO solenoid clutch to transfer power presumably at the right operational speed. Must vary that speed for different size paper and magnification. Anyone know where the braking fusnction comes in? perhaps the PTO system will not disengage reliably at speed and operational torque.
Reply to
N_Cook

If that truly is a stepper motor, the motor is the braking function. It simply keeps the last step phase energized. And being a stepper motor, you'll have either 4 or 6 wires and maybe a ground wire.

I would be willing to bet you have a servo motor there. If so, it most likely would have 3 wires in it and an internal feed back system. It could also have a mechanical brake, too. But I would venture to say the servo drive electronics is locking the motor in place as a function of brake.

Jamie

Reply to
Jamie

Anybody using a stepper as the only brake in the system had better not be holding any significant weight against gravity. A stepper that's lost sync might as well not even be there. Whatever that load is, one day it's _going_ to fall.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
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Reply to
Phil Hobbs

now,

and

Will

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at

If there is no binding of bearings etc there should be no load to speak of. It just turns the OPC drum and some rollers that feed paper through the system. The main load is probably the fuser roller as it is pushed against a backing roller to fuse the toner into the paper. Worst normal situation would be scrunched up paper jamming in the fuser section

Reply to
N_Cook

and

Will

for

at

I could not divide 360 by 12, it is 30 degree steps and turning by hand it has a stepper motor feel against the magnets and 12 magnetic steps. Ground is mechanical to the frame if any ground. 11 wires 3 are related to the coils, 1.5R between each to the other leaving 8 , the 3 hall effect have one common I could detect by probing with a needle, probably one other in common leaving 2 for each sensing part of the Halls. Separately there is a slotted opto. Without scoping or strobing or something I cannot tell whether PTO is coincident with starting or stopping. When I had the tell-tales in there (from common collector of each driver pair to ground) bright at startup, half bright for motor run , then off or too low a voltage to light the lamps for half a second then a second of half bright. Perhaps the bulbs off is the braking stage. In normal operation you see the axial fan which is directly coupled to this motor , ie not via PTO, kicks back before stopping. The motor control chippery is TC9192P, TA75358, NEC uPC494C, TA7712 and a

4013
Reply to
N_Cook

Sure, in a printer or something there's no big problem...over in the design group we've been having an argument about the applicability of steppers, and how their apparent simplicity and reliability is mostly an illusion, so it's sort of on the top of my mind just now. People have gotten killed by systems with steppers and no fail-safe brake.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
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Reply to
Phil Hobbs

That is a 3 phase servo/synchronous DC brushless motor.

Made pretty much the same way as your basic cooling fans with extra feed back to be able to lock rotor and slowly turn either direction to keep a lock.

These motors work very nicely in regards to holding things in position.

It's possible you have a 12 pole motor which would make it not the fastest motor but give you some torque and tight tracking.

That first chip in the list is a Phase lock Loop controller that can handle 2 motors.

The nice thing about these motors is due to the integrated feed back which has to be mechanically position correctly so the controller knows exactly where the rotor is in relation to the poles.

Jamie

Reply to
Jamie

message

now,

it

Ground

needle,

Halls.

voltage

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this

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Are you saying there could be microstepping involved, not perhaps with a copier but if that sort of motor was used in a plotter say

Reply to
N_Cook

There are different types of feed back systems and you must have the correct drive electronics per motor.

One of the most common ones I can think of that we use at work is that using a A+B and Z channel. The A+B can be used for both, direction detection and position. The Z is a index pulse and in the case of that motor, it could be at the corner of each pole. Or, it could be just one rotation and the driver just knows the number of poles there are and the PPR count and does the count after initial rotation.

Some systems simply generate a gray code which works very nicely too! In your case, it could be a 3 bit code which gives you an absolute position of rotor per pole. The 3 bit code should yield a combination of 8 places. Put that together with a 12 pole motor and you can have 96 positions for holding index. That's strange, that almost looks like the Font size per inch in windows by default! :)

You see the problem with using a 3 phase system like that for positioning and hold, the torque changes on the rotor are depending on what position of the pole you're in. So, it is common for a drive electronics to bias the drive to over come jitters between the poles and to do this, it needs to know exactly where the poles with relation to the PM is.

You said you had R's in the coils? that tells me the Q has been lowered so less ringing will develop, maybe.

Jamie

Reply to
Jamie

message

exact.

vane

transfer

reliably

function

there

position.

With this copier there is paper size selection from A5 to A3 nut more interestingly reduction or magnification from 64 percent to 154 percent by 1 percent steps, so need some pretty precise control of speed. I always thought it was feather action microswitches that set other parts of the operation as paper goes through the machine but they may be for timeout error determination and the real sequence process timing done via the hall-effects and slotted opto/vane system around the motor The motor is this, from the stock number, but no technical info known about the internals/specs

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Reply to
N_Cook

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