Re: [CAD_CAM_EDM_DRO] Re: Slight Servo Problem

mmurray701 wrote:

>Hi Jon,
>
>Thanks for the reply. The control program is Turbocnc for now and
>the problem is still there at all times, even with the computer
>turned off. The encoders are all the same, 250cpr and the Geckos
>step multiplier is set at 5x. The encoder wires are bundled with the
>motor wires but I am using sheilded wires and it hasnt picked up or
>lost any steps so far. I know this is a common problem but I got
>lucky here.
>
>I'm assuming that deadband is a neutral region where the controller
>doesnt try and correct position right? If so then this makes sense
>and would probably help it. How would you go about changing the
>deadband on a Gecko 340?
>

Other than installing and removing the anti-dither jumper, you can't.
It is built into the digital logic of the Gecko, you can just turn it
on or off. It is adjustable in EMC, but that has no bearing here, since you
aren't using that program. I've seen a lot of variability in Gecko 320/340
systems with the Ametek motors, though. I think the high resistance of
these motors really defeats the range of gains and loop compensations
available with the Gecko drives. I have a client in town who has a machine
with 3 Gecko 320s and Ametek motors. His machine simply does not
seem "stiff" around the null point. I can move the motors about 10 degrees
either side of the null before it starts to apply serious torque to correct
the offset. You can leave the motor anywhere over a/- 5 degree range,
say, and it will sit there without moving, sometimes for a minute or more.
It SHOULD control the motor position a LOT tighter than that. Mariss
says that if left more than 1 encoder count away from the null, it will
go all the way to full current within a couple of mS. My experience
with that machine is it DOES not perform that way. I'm going to borrow
a Gecko from my client and do some more testing here to try to understand
the behavior of the drive better.

Anyway, Mariss recommends putting a 1000 uF capacitor (I think that's the
value) right at the drive's power input terminals if your main power supply
capacitor is more than 18" away, by wire length. It seems to make a
difference
in drive performance, too. (I did this at my client's site, but I
hooked the
cap up wrong, and it blew up and made a mess. I haven't gotten back there
to try again.)

Jon