basic stepper drive but lots of problems :(

[aidaniel]

hello,

i have set up a basic stepper motor and drive to drive a slide on a custom machine i have been building.

the drive is a "leadshine M542" running a "FL42STH38-1684B" bi polar 4 wire motor. these are controlled by an allen bradley PLC via some optocouplers.

for starters it has a fun habit of reversing its directions (forward becomes reverse and reverse becomes forward) with no change from the outputs of the PLC. secondly i cannot get it to do more then 300rpm at 2khz (i would like to run closer to 1000-1200rpm) and when i try to wind up the hz it just begins to stall and hum. the motor system is being driven at 24V dc and the control is being driven at 5V dc.

can someone please offer some guidance as to why these things would be happening

regards Aiden

LRD Engineering - Home

[wayneb]

Originally Posted by aidaniel hello, i have set up a basic stepper motor and drive to drive a slide on a custom machine i have been building. the drive is a "leadshine M542" running a "FL42STH38-1684B" bi polar 4 wire motor. these are controlled by an allen bradley PLC via some optocouplers. for starters it has a fun habit of reversing its directions (forward becomes reverse and reverse becomes forward) with no change from the outputs of the PLC. secondly i cannot get it to do more then 300rpm at 2khz (i would like to run closer to 1000-1200rpm) and when i try to wind up the hz it just begins to stall and hum. the motor system is being driven at 24V dc and the control is being driven at 5V dc. can someone please offer some guidance as to why these things would be happening regards Aiden LRD Engineering - Home

G'day Aiden

I'm about to setup with the same drivers as well. I don't think you will get much more speed without going to a higher voltage.

Cheers Wayne

[RomanLini]

I think 1200 RPM is getting way out of the ballpark for a bipolar motor, especially at 24 volts.

That driver appears to be limited to 24v DC max. To get those kind of RPMs reliably you need to go to a faster motor driver setup, like a unipolar motor and a 40v driver, or if you must keep that bipolar motor maybe a bipolar driver capable of 60 or 70 volts.

[seadog]

Your problem sounds amazingly similar to a problem I had. At slow speeds things would work just fine but at high speeds the motor would "miss" and the speed was erratic. What I finally figured out was that the optical device could not keep up with high speeds. I replaced it with transistors and all was good.

[tivoidethuong]

please use higer voltage for drive, ex 40VDC

b.r

[IsotopeJ]

Hi Aiden,

Double-check your opto-isolators like was said before, but if you're getting a clean signal to the driver, I would suspect it's your motor, not the electronics.

Steppers have a tendency to resonate, which will cause the symptoms you're describing. This happens more at higher speeds, and with higher-voltage per coil motors. What happens is when you move a step, the coils in the motor build up a magnetic field which has to collapse. The higher the voltage in the coil, the longer it takes to collapse. When you try to drive it too fast you're not giving it enough time to dissipate the magnetic field and it will stall, vibrate, or change direction erratically. This is why unipolar setups can be driven faster than bipolar, since you aren't immediately using the same coil.

The other thing that affects this is the mass (actually the "moment of inertia") of the shaft you are driving. If you are driving a heavy/thick leadscrew, it will reduce the highest usable speed that you can drive any given motor before it resonates.

You probably can't change the mass of your drive system, so the last thing I can suggest is to set up your driver to do micro-stepping if you haven't already. A quality driver doing microstepping can help limit resonance. In the end, though, it may just be that your 50oz-in motor just isn't beefy enough to go that fast. :-/

Cheers,
Isotope

[IsotopeJ]

I realize that talk of voltage might sound confusing, because increasing driver voltage might help as others have suggested. The reason is at 24v and high speed maybe the coils don't have time to reach their max current. Driving at a higher voltage overcomes the back EMF of the coils and can push the current into the coils faster, ensuring you reach the maximum power of the motor. I guess I should have said "the current through the coils" not "the voltage in the coils."

Isotope