Re: Re: Re: Can CNCPro users provide some input?

Message: 5
Date: Mon, 19 Mar 2001 15:49:45 -0600
From: "William Scalione" <wscalione@...>

<s>I have some Kollmorgan +/- 10V servo amps, but the Geckos accomplish the

>same thing for $129.00/axis. I'll hold those Kollmorgans for another
>project.

I was wishing that you wanted to unload them. ;) But, (AND THIS IS NO
REFLECTION ON GECKO! I LIKE THEIR PRODUCTS!) they do NOT do the
same thing. No way! No how! Whole other world! Pardon the scream but I
had to know that you are listening 'cause I like Mariss.

Kollmorgan controls velocity, Gecko controls position. Jon has it just
right in the post of his.

<snipped from Jon E>
The advantage to a true velocity servo, straight from the computer, is that
the VELOCITY is not quantized by the resolution. So, at very slow speeds,
the motion remains smooth.
<eos>

Stepped servo motion like that produced by the Gecko 3-- series may
well be fine for may uses, but it can not replace velocity control. The
way most machine tool builders are getting around this and using digital
signals like step and direction is by using very high resolution count
encoders. I've replaced units that spit out 250k ppr and have heard of
encoders that put out 1M ppr. Big bucks! These kinds of position
resolutions will approximate velocity control using drives like the Gecko
but they will not equal it.

And the 320 geckodrive has a max step rate around 250 Khz which would mean
60 RPM max on the encoder unit I have here. Nice resolution, but slow.
And EMC, at least isn't near ready to put out that many pps from a pure
software solution -- can't say about the other low cost cnc systems

Ray