Stepper RPM and Accuracy Question. Please Help!

[David Bord]

In the process(although a bit behind Anthony at this point) of designing my Plasma Table.

It would be worlds easier to do direct drive with larger steppers. However, I am concerned with accuracy... I am buiding this table to cut tabs, brackets and chassis parts, so I want it to be more accurate than the plasma process itself. Hoping to stay in the .00X accuracy space.

I have read a few times on this board that you should have your steppers run in their optimum RPM range to get the best accuracy.

If the holding torque is the highest at the lowest RPM's, and the number of steps/required accuracy is within the desired range why wouldn’t it work well? I would think that having the most holding torque would provide the most resistance to losing steps. (if you are within an acceptable load range)

If you are using a high quality stepper drivers like Geckos, in say 1/4 step mode, would that increase your resolution by approx 4 times?

David

[CJL5585]

You are correct on all points. I am using direct drive coupled steppers with 10 micro step drives and 10 turn per inch ballscrews and the accuracy is better than 0.0005 of an inch.

Jerry

[ger21]

Originally Posted by David Bord If you are using a high quality stepper drivers like Geckos, in say 1/4 step mode, would that increase your resolution by approx 4 times? David

No. Read this. http://www.machinedesign.com/ASP/vie...strSite=MDSite

[bunalmis]

(http://www.machinedesign.com/ASP/vi...&strSite=MDSite)

I think this article not true. But i am not sure.

Why?

Two phase stepper motor has two coils. Phase currents are Ia and Ib.

If we write the currents, Ia=ISin(q) and Ib=ICos(q)

Yes Ia and Ib are functions of Sin and cos functions but if we calculate the
modul of current of vectors of this two current we can write;

Imod=ISqrt(2). (Modul off current)

Modul current independent Sin and Cos functions (microsteps) and motor produce constand torque for all off rotating angle.

My step motor rotate by 51200 mikrostep/rev and I can not breake by my fingers.

My English not good and i may be wrong understand this article.