Re: [CAD_CAM_EDM_DRO] Control Box Isolation--Geckos

Jon,

Thanks for the advice. We will check these options out ASAP.

Tom

----- Original Message -----
From: Jon Elson <jmelson@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, April 03, 2001 1:51 PM
Subject: Re: [CAD_CAM_EDM_DRO] Control Box Isolation--Geckos


>
>
> Tom Eldredge wrote:
>
> > Todd, and those following this thread,
> >
> > I am using servo motors on our plasma cutter that run on 18 volts. I
know
> > that is the lower limit for the Geckos. I wonder if that could be
related
> > to why I am having such jerky motion? We are using 32 pitch rack and 22
> > teeth pinions for drive. The jerkiness is in about .60 (real roughly)
jerks
> > as the servo motors move.
>
> Not likely to be the supply voltage. I assume you have the jerkiness when
the
> plasma machine is off?
>
> If so, then it is a servo loop compensation problem. If there is any
backlash
> between the servo motors and the encoders, you will have vibrations and
hunting
> behavior. Backlash between the motor and the table motion can also cause
> jerking, as the system bumps from one side of the gears to the other.
>
> If you can disconnect the gearing, so the servo motor is relieved from the
> table load, see if it still jerks. If not, that confirms my hypothesis.
>
> One possible way that the 18 V supply could cause the problem is that the
> motor resistance is so high that 18 V cannot produce the acceleration
required
> of the servo. So, error accumulates until the servo drive is at 95%
(limit)
> duty cycle, and then the servo overshoots the desired position. So,
raising
> the voltage might help, but it is a bit of a long shot. If you have a
scope, you
> might try to see if the servo is going to max duty cycle.
>
> But, more likely, the mass of the table is lagging behind the required
position
> or velocity needed, and the servo overshoots. If so, then increasing
voltage
> will effectively increase gain, and it will get WORSE. If it does get
worse,
> that tells you what the problem is. Without tachs and linear compensation
> of the servo loops, I don't know how to fix it from here. Maybe Mariss
> has some suggestions for compensation of the system.
>
> Jon
>
>
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