Re: Geckodrive

About (2): Quadrature outputs may look chaotic on a scope because of
ringing and motor non-linearity (electrical angle vs. mechanical
angle transfer function). The resulting phase modulation of the
signals is visually indecipherable. On the otherhand the differencing
register contents make perfect sense. I prefer to write its contents
to a G100 DAC output which I can then watch on a scope and observe
the results dynamically.

Motor inductance: Inductance and supply voltage have an indirect
effect. Motor power output is proportional to Vs / sqrt L. Increasing
Vs and/or decreasing L raises the speed to which the motor can
maintain its low-speed torque (approximately its holding torque). A
drive is a current source in this region, a voltage source above that
speed.

A nuance is motor current develops a 90 degree phase lag to voltage
because of inductance when the drive reverts to a voltage source.
While it is a current source current and voltage is in phase.

This 90 degree electrical phase lag translates into an additional 1.8
degree mechanical motor lag. A slow-turning motor will "skip steps"
if the lead/lag angle exceeds +/-1.8 degrees. That same motor will
stall if the lead/lag angle exceeds +0 or -3.6 degrees at high speeds.

Patents:

1) I do a patent search after, not before I work on an idea. I have a
real antipathy to copying someone else's work; if I search before
then I pollute my mindset with someone else's ideas at the expense of
my own originality. I feel reasonably assured the idea is original
because I'm not aware of any existing solution to what I'm addressing.

2) Patents are an expensive and poor way to protect ideas. Patenting
requires full disclosure of the practical method used to implement a
novel idea. Your only recourse to an infringer armed with your
revealed method is to sue and to my mind that is a losing proposition.

3) Better is to patent-protect yourself by revealing the idea but
keeping the practical method proprietary. This puts the idea in the
public domain, making it an unpatentable prior art. Since firmware is
involved, copyright protections come into play as well. Needless to
say there are other vital "nuances" involved in making this idea
practical that I'm keeping to myself for the reasons mentioned.

4) Finally, if someone does rip-off the idea, I always have more
ideas and second, the ripper-offer will always be two steps behind me
because he didn't originate the idea. It's a time thing; some have
tried but none have been commercially successful.

Mariss



--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Jack Hudler" <yahoo@...>
wrote:

>
> 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
>