Need Help!- 4th axis Stepper issues. Can someone give me a clue?

[TheProCreator]

Okay, I have a vertical Parker 5" precision rotary table. The table gear ratio is 1000 to 1. The unit came with a compumotor 100oz stepper motor. I have tried both parallel and series wiring. The motor slips at feed rates above 500mm per min. I also found that higher acceleration speeds performed better than slow. I am now trying a keling stepper rated at 425oz wired in series. This motor slips above 850mm per minute.

I want to get feed rates above 1000mm per min and I thought this would do. Is there something else that I could be doing to get a higher feed rate?

Please let me know if more info is needed.

Thanks!

[vger]

Not sure how XXXmm / min relates to rotation. What is the rotation rate in DEG/MIN ?

At 1000:1 with 200 steps/rev on the stepper you take 200,000 to go 360 deg. I think your max may be about 1 revolution per minute without getting into midband resonance on the motor.

Steve

[TheProCreator]

Apologies, the table ratio is 180 to 1. My motor tuning setting is 1000 per. So I'm really going 36,000 for a 360 deg turn. Without a scope how can I find the midband resonance?

[James Newton]

A microstepping driver may help reduce mid band resonance, or a mechanical damper on the shaft... I've heard that hockey pucks with a hole drilled through the middle work wonders, believe it or not.

Also, keep in mind that bipolar drivers drop torque faster than unipolar... they /start/ with higher torque (for the same amperage motor) but the bipolar drivers will typically drop off torque as speed increases faster than a unipolar driver (of the same etc...). And, you can buy a larger unipolar driver (more amps) for the same price. So you might want to try pushing the motors amp rating a bit with a unipolar microstepping driver.

I sell the Linistepper and SLAm drivers, but based on your massive oz/in rating, I doubt either of those is large enough for your big motor. What is the motor rated amperage and inductance? What voltage power supply do you have?

[vger]

ProCreator,

Ok... 180 to 1 then Mine is the same, but self made. I do often wish it would run a bit faster before the dreaded midband resonance. I actually tried hooking a DC servo motor to it with a variable speed control to get more speed, but without encoder feedback I could not do positioning. It worked OK that way for what I was doing. I took the stepper and linked it to the pot on the speed control so I could vary the speed.

I've seen the hocky puck thing james mentioned. Seemed to work although I haven't tried it. I do have a few unipolar steppers that have a damper already attached that I plan on using in the future with a different machine. They were pulled from some large HP laser printers.

Steve

[James Newton]

I love those laser printer stepper motors! Cheap (often free if you make nice with an office equipment repair place) and powerful.

[vger]

James,

Yeah, these werre rescued from the motor scrap barrel. There are a couple of computer recycler places here that I go by occasionally. Sometimes they have some pretty good stuff they are scrapping out. Came across a robotic tape archiver once that had the controller with it. It was 6 ft tall with aluminum extrusions (similar to 80/20 stuff) for the verticals and the electronics rack had the same. There was a 4 channel motion control board, 4 servo amps, and 4 servo motors. It also had a pair of 5 phase steppers (part of the tape gripper) along with their drivers. I had to pay the scrap price for the aluminum, and $50 for the motion control and amps as long as I took it apart for them...

Steve

[TheProCreator]

Looks like I'm good at a FR of 850. Kinda stinks that the MBR is keeping me from obtaining speeds near 1200. The motor is a dual shaft so is the idea that I hang a puck off the back? I also have Nylon stock perhaps that'll work......

[vger]

Yeah, off the back end should work. The steppers I have with the dampers are done that way. The dampers on them are a flat disk with a ring around it held together with rubber. Reminds me of the harmonic balancer on the front of a car engine. They were probably engineered for that specific motor. I was thinking I might try building my own for other motors but would have to experiment with the ring size and elastic dimensions.

Steve

[James Newton]

I don't think nylon stock will work as a damper... the material needs to be rubbery... flexible. Or have a flex coupling to the shaft like vgers. Does your controller do microstepping? If so try that mode, it should make it different.