Re: Low cost Servo Controller

Les, I believe that Tech80 is the supplier to Industrial Computer
Source, the companys cataloge where I seen the LM628-629
board. That chip has been around for 10 years or so, and
companys are still using it in there motion boards. It seems
that the best way to evaluate the electronics, either build it
yourself or store bought, is to have the hardware allready
setup, like you will be doing. Another point about electronics is
the fact that one fellow may not be able to find a soulution to
a problem, and another guys come along and says, hey do it
this way, and you end up shaking your head at yourself. Part
of the fooling around with this stuff, I guess. That is a real nice
Index mill you have. I sure hope you will be able to make available
progress pictures on your CNC router, at your site.

Steve Carlisle

----------
From: Les Watts <leswatts@...>
To: CAD_CAM_EDM_DRO@onelist.com
Subject: Re: [CAD_CAM_EDM_DRO]Low cost Servo Controller
Date: Sunday, September 19, 1999 7:32 AM

From: Les Watts <leswatts@...>



Steve Carlisle wrote:

> From: "Steve Carlisle" <quatsein@...>
>
> I have seen a few LM628-629 based 3 axis boards that
> claim linear and circular interpolation. Computer Source
> is one that comes to mind.
>
> Steve Carlisle
>

I have a LM628 multi-axis board from Tech 80. I think they know more about
the LM628/9 than anyone else out there including
National.

On this board any axis with more than a certain user specified following
error will send an interrupt
to the host. The handler you write can adjust target accel, velocity, or
timing to maintain sync. Doing
so will slow the system down somewhat. Maximum update rate is 1 kHz even
though motor update
is 4kHz. This is due to latency of the LM628.

The multi LM628/9 boards are still considered fairly high performance as
far as servo update time
but lack feedforward capability unless you trick them with software
changing PID parameters on
the fly.

I suspect EMC with the STG card will outperform LM628/9 systems which is
why i'm here. The
big cnc router I am building uses very high feed rates and following error
is a big issue.

I have a comment on the servo power amp-
About a year ago I designed and built a large analog power amp (current
limit is set at 20 amps!)
and it took a month of weekends to get it going. But companies like Copley
Controls sell a 12 amp
h-bridge pwm amp for about $275. They will accept analog or pwm input I
believe. I think I will just
buy them rather than roll my own.

It makes more sense for me to be doing things like ball screw end machining
right now. This often
costs $300+ per screw from the manufacturer. To that end I bought a used
Boxford lathe with a Themac tool post grinder friday.
Now I don't have to go to my friends shop 30 miles away to get
the work done. I'll need the stuff for maintenance anyway. See how easy it
is to justify buying tools?
The other justification is even simpler- I want them.

Well, the sun is up so I'll go out and finish removing the horrible paint
job on the lathe so I will be
able to shoot new paint this week. My idea of a really good time.

Leslie M.Watts
Illinois Tool Works
Corporate Advanced Technology group
(847) 657-4559
http://www.netcom.com/~leswatts/leswp.html



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