Re: Slight Servo Problem

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:

>
>
> 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

Well mine havent got this problem. Mine are very stiff, cant turn
them much at all before its solid again, but i'm using a fairly high
resoloution encoder. Is it possible that this guys encoder counts
are this far apart?

Mark