[johnd_issaquah]

Hi all,

I'm using stepper motors to position sensitive measurement equipment (hydrophone). I have a problem with new stepper drives: they use a chopped voltage output, and the chopped signal produces electrical noise (EMI) in the measurement.

I have been using drives that are over 20 years old, and they were the constant-voltage (L/R) type drives that had a much smoother voltage changes, so they didn't affect the measurement. Now, I need to buy some new drives and motors, but I can't find the constant-voltage type. The new ones all use chopped voltage, which adds noise spikes to our measured signal. I understand that the chopped voltage gives better torque and speed performance, but I don't need that.

I tried extra shielding with the new drives, and I tried some motors that have integrated controllers and drives, so there's no cable to act as an antenna. These helped a bit, but a lot of noise remains.

Does anyone know where I can get new stepper drives that don't have chopped output? I couldn't justify the time to learn to build my own, since the steppers aren't the main focus of the project. Or, do you see any other solution to the noise?

Thanks.

[Al_The_Man]

Sounds like you need the older series resistance limiter type, but these are probably long gone for something off the shelf.
Have you tried connecting up supply commons and referencing them to earth GND?
Al.

[johnd_issaquah]

I think the supply commons are connected and grounded, but I don't think the supply plays much of a role in the noise issue; the main problem is with the chopped voltage signal out of the driver. I checked this by looking at the driver output on a scope: it has a square pulse, 1.5 usec long, repeated every 50 usec. Our measurement equipment picks up a matching noise pulse every 50 usec, so I'm sure that noise is from the driver's chopped output. I don't think any changes to the supply would help that, would they?

I was hoping that there might be a supplier somewhere that still has the older type of drive without chopping. Maybe I should also mention that I only measure when the motor is stopped: I alternate move - measure - move - measure - etc. So, if there was a drive that stopped chopping the voltage while the motor is stopped, that would solve the problem. I could turn off power to the drive in between moves, but I'm concerned that may allow a drift in position; I'd rather have a constant voltage to hold the position.

Thanks,
John

[PCW_MESA]

I think the supply commons are connected and grounded, but I don't think the supply plays much of a role in the noise issue; the main problem is with the chopped voltage signal out of the driver. I checked this by looking at the driver output on a scope: it has a square pulse, 1.5 usec long, repeated every 50 usec. Our measurement equipment picks up a matching noise pulse every 50 usec, so I'm sure that noise is from the driver's chopped output. I don't think any changes to the supply would help that, would they?

I was hoping that there might be a supplier somewhere that still has the older type of drive without chopping. Maybe I should also mention that I only measure when the motor is stopped: I alternate move - measure - move - measure - etc. So, if there was a drive that stopped chopping the voltage while the motor is stopped, that would solve the problem. I could turn off power to the drive in between moves, but I'm concerned that may allow a drift in position; I'd rather have a constant voltage to hold the position.

Thanks,
John

You might try a common mode choke on both the motor lead pairs and the driver power leads
(basically a big Ferrite bead like on a USB or video cable)

[James Newton]

The drive you are looking for is the Linistepper:
techref.massmind.org/techref/io/stepper/linistep/index.htm
Already used by companies which need low EMF to avoid messing up sensors.
https://www.facebook.com/Linistepper...89354987762005
And universities.
https://www.facebook.com/Linistepper...20992814598225
Just heard from UVA yesterday... they were having problems with one of their new V3 Linisteppers... now... why would I mention a client having problems? Well... because I actually SUPPORT people. And I know we will get them taken care of. I've offered to troubleshoot the driver here if they will return it, and I KNOW I will get it working correctly for them.

[johnd_issaquah]

The drive you are looking for is the Linistepper

James Newton: Thanks, the Linistepper does look like an ideal solution. But, I don't think I can justify the time to learn to assemble the kits myself, and there isn't someone else here who could do it. Can you offer them pre-assembled, or do you know another qualified source to do the assembly?

You might try a common mode choke on both the motor lead pairs and the driver power leads
(basically a big Ferrite bead like on a USB or video cable)

PCW_MESA: I tried ferrite beads on the motor and driver cables, and they reduced the noise a little bit, but not very much. If this is a better version of the beads, I'll keep it in mind. But, my first choice would be to eliminate the chopped-voltage driver, which would remove the noise completely. If I can't do that, I'll look more at the choke.
Thanks,
John

[James Newton]

James Newton: Thanks, the Linistepper does look like an ideal solution. But, I don't think I can justify the time to learn to assemble the kits myself, and there isn't someone else here who could do it. Can you offer them pre-assembled, or do you know another qualified source to do the assembly?

It's takes about an hour to solder up the kit. Full instructions are available here:
techref.massmind.org/techref/io/stepper/linistep/LiniV3_bld.htm

If you haven't soldered before, leave a note when you order and I'll include a free learn to solder kit which you can put together with this instruction.
https://docs.google.com/presentation...NiA&slide=id.p

It also lists some good sources for soldering irons, solder, tip cleaner and explains what goes wrong and how to fix it.

And if worse comes to worse, return the kit to me and I'll refund or fix it and return for the cost of shipping.

The nice thing is... if you fry the driver at some point in the future, you know how to fix it.