Stepper Motor Resonance ?

["Tim & Heather Smith" <thdsmith-at-bigpond.com>]

Has anyone out there had any problems with resonance when driving stepper
motors?

I have a bridgeport mill onto which I have adapted steppers (Superior
Electric M111 ,torque is 500ish oz/in) and am running BDI 2.16.
The X axis I have has been limited to a top speed of about 600mm per min
(240rpm & 800Hz). I have occasionally lost some steps (due to lack of
torque), so made up a couple of reduction gearboxes (1:2.4) to over come
this.

The torque is OK now, but my rapid traverse speed is now limited to approx
250mm per min (240rpm & 800Hz). This is quite a pain....

In an effort to figure out what was going on, I used a function generator to
directly pulse the stepper drivers (Superior Electric STM103's) with the
motors disconnected from the lead screws.

I found the motors were stalling at around the same frequency, but if I
accelerated them quickly past this frequency they would run happily up to
over 3000Hz (or 900rpm) which would give me 930 mm per min. While I don't
need to travel this fast it would be good be able to get back to around
600mm/min again.

Is there a simple fix for this that I could try? or is there some thing I
could do to move the resonance frequency higher?


Thanks

Tim Smith