Re: true closed loop vs. hobby closed loop

There seems to be a little misunderstanding about how the G320
performs, so I ran some experiments.

Signal source: G2002REV3
Motor: Minertia TO6M (NEMA-34)
Power Supply: Sorensen DCR 60-18B lab supply
Encoder: 500 line (2,000 steps / rev)
Drive: G320
Scope: Tektronix TDS-360 (200MHz digital sampling scope)

Test:

The G2002 was programmed to move 25 revolutions at 2,400 RPM CW, then
25 revolutions at 2,400 RPM CCW. The rate of acceleration was a 0.004
second linear ramp to 2,400 RPM.

The sampling scope was attached to the POSITION ERROR test point of
the G320. The trigger was set to NORMAL and the vertical scale was
100mV differential to 5VDC (2 error counts equals 80mV).

This is a vicious rate of acceleration. The motor had to be clamped
because it jumped off of the bench on the first try.

The test results showed a maximum following error of only 5 counts
(0.9 degrees) on the 2,400 RPM CW to 2,400 RPM CCW slope. That is a
net change of 4,800 RPM in 0.0078 seconds. More practically seaking,
that would be a 0.0005" following error if you were to go 480 IPM
forward to 480 IPM backwards in 0.008 seconds on a 5 TPI leadscrew!

I have some terrific 'scope pics that show this data but it seems I
cannot post to the "Files" and "Photos" section anymore.

In any case, the actual, measured following error is far far better
than what has been mentioned on this thread. Nothing like actually
measuring something.

If anyone wants, I can e-mail the 'scope pics.

Mariss

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
> Well, without some interface between the Dan Mauch card and the
Gecko,
> it would probably be unreliable. You can't expect ground to be the
same at
> the computer and the Gecko drive. An opto-coupler to repeat the
encoder
> signals would be a very good idea.
>
> You could set the following error to be quite a bit less than the
128
> counts,
> or set up the sliding scale so it would be low at lower speeds.
You
> might try
> for +/- 10 counts at zero speed, and 25 counts per inch/second of
velocity.
> But, my experience with Gecko 320s has been that the allowable error
> band at idle is a lot larger than it is supposed to be.
>
> >On the Gecko G201/G210 if I were to ground terminal 7 (DISABLE)
then
> >you should be able to drive the system manually, using the encoder
to
> >feed the DRO, just as you say, correct?
> >
> >
> Oh, we're talking steppers here, I see. Yes, that is right. I
can't
> say anything
> about loop stability with steppers and G201, and especially G210s,
which
> have another control loop inside them (the pulse multiplier).
>
> >Sorry for the basic level questions, but I just got EMC working on
my
> >laptop this weekend (WOO HOO!) and I am now going about the
business
> >of getting my Bridgeport Series 1 CNC retrofitted with new drives
> >(same old motors). Anyone have any luck fitting handle to the old
> >Bridgeport CNC machines? I can easily get one on the Z drive.
The Y
> >drive I couls maybe see how I can modify the belt cover and put a
> >handle in. What about the X?
> >
> >
> This is a BOSS? The X leadscrew doesn't turn on a BOSS. The nut,
buried
> DEEP in the knee is what turns. I can see handwheels on this being
almost
> impossible! How about flexible shafts?
>
> J