RE: [CAD_CAM_EDM_DRO] Re: Geckodrive

OK I'll accept 1 and 3. I never denied what you were seeing on the bench.
If you are reliably able to detect the lead/lag feedback from the stepper and
compensate for it then you have something here. I would encourage you search the
patent database for two reasons; not infringing and gather prior art for your
patent submission.

Does this system work regardless of motor inductance?

As for 2 I've seen this myself however; I only use high resolution microsteppers
50000+ spr; perhaps this a side effect of the installation with 25000 quadrature
encoders. It's very chaotic on an oscope.

-----Original Message-----
From: CAD_CAM_EDM_DRO@yahoogroups.com [mailto:CAD_CAM_EDM_DRO@yahoogroups.com]
On Behalf Of Mariss Freimanis
Sent: Saturday, April 29, 2006 2:44 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Re: Geckodrive

Well, then I guess I'm not seeing what I'm seeing on my lab bench.:-)

1) Parametric resonance is caused by a system (motor + drive) phase
lag of 180 degrees. It is corrected by adding a derivative component
(phase lead) to the system.

We do this in our drives using analog techniques, the G100 uses
digital PID feedback. Either way the motor will not resonate having
+80 degrees phase margin.

2) There is nothing "chaotic" even about a stalling motor. It simply
looses phase-lock with the rotating excitation field. The servo
summing node develops an increasing lag angle (where it is minus
where it should be). The controller decelerates the rotating field
until the motor "catches-up" and resynchronizes.

The trick is to keep this from happening in the first place. A step
motor's torque is a sine function of the lead/lag angle; constrain
this angle to +/- 1.8 degrees by how you control the rotating field
(accelerating/decelerating it in a PID loop) and the motor cannot
stall.

3) A step motor when operated PID closed-loop becomes an AC
servomotor just as a DC servomotor becomes an ordinary DC motor when
operated without a PID servo loop.

Mariss