N_Cook wrote:

Jamie t wrote in message
...

N_Cook wrote:


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.



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



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



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