Re: Stepper Mid-band stabilization, formerly: Gecho 210 step multiplier

Paul,

Step motors are fun to design drives for because they have so many
bad vices.

Step motors exhibit to main resonance regions, generally called low
speed resonance and mid-band instability.

Low speed resonance occurs when the motor is stepped at its resonant
frequency or sub-harmonic. Typically it may be 80 Hz, so you will
also get a resonance at 40 Hz and sometimes at 20 Hz step rates. This
resonance has a high "Q" value, meaning it has a very narrow
bandwidth of just a few Hz. Microstepping is the method of choice to
tame this resonance. At 10 microsteps/step, the motor moves only 1/10
as far as for a full step and reaches only 1/10 the velocity. Since
resonant energy is the old M * V^2 / 2 thing, it has only 1% of the
resonant energy compared to a full step.

Mid-band resonance occurs when the drive appears as a voltage source
to the motor, typically at 5 to 15 revolutions per second. Here
second-order damping must be used to cure that.

The two are entirely seperate and unrelated vices.

Mariss

--- In CAD_CAM_EDM_DRO@y..., "Paul R. Hvidston" <paul_hvidston@y...>
wrote:

> Interesting, Mariss. I thought I read somewhere that half- and

microstepping

> eliminated or reduced exciting the system into mid-band resonance.

Thanks

> for the great technical description. I still find this stuff

fascinating.

> I've done disk servo PID loops, and industrial PMAC servo systems

years ago,

> but nothing with steppers.
>
> I'll leave the (stepper) driving to you!
>
> Regards,
>
> Paul R. Hvidston, N6MGN
> ACKSYS Engineering
> Upland, CA