Re: Digest Number 19

I would be willing to help build theprinted circuit card. But take a look at
the PIC chip from JR Kerr
They have a PIC-Servo chip that has PID filter and all in a $30 chip.
The web site is www.jrkerr.com The pic servo may decrease the effort
substanially. I have tried a single axis version of the chip and it is
fast. The only problem I ran into was that he sells a PIC-Step chip that
allows use of the parallel port and existing step and direction software.
The servo runs very slowly on a 486-33SX. The best I could get was about 200
RPM with a 200 line encoder. A 500 line encoder only yielded 100 RPM
It may have been due to the 486-33SX but by using the ISA bus it would run
and 2000 RPM. When I ran the pic servo using the RS232 port I was able to
get well over 5000 RPMs.
Dan
-----Original Message-----
From: Tom Kulaga <tkulaga@...>
To: CAD_CAM_EDM_DRO@onelist.com <CAD_CAM_EDM_DRO@onelist.com>
Date: Friday, May 21, 1999 10:00 PM
Subject: Re: [CAD_CAM_EDM_DRO] Digest Number 19

>From: Tom Kulaga <tkulaga@...>
>
><PTENGIN@...> wrote:
>> In looking over information from Mitutoyo, they offer BCD and several
>>other output cards for the KC and other DRO systems. I have one of these
>>(KC) systems and was suspecting the output could be used to inteface to a
>>CNC. Also, in the MSC catalog, Mitutoyo used to list a linear spar to

digital

>>output converter box. Peter
>
>One big problem using the output of the linear encoders of the DRO to
>control servos is that *any* backlash between the drive motor and the
>workpiece can cause some pretty bad instability (for controls
>newbies, the instability I'm talking about is a tendancy for the
>motor to oscillate around the target position, buzzing like crazy in
>the best case, or slamming back and forth in the worst). There are
>ways around it, but none of them are cheap, assuming you are faced
>with the normal HSM budget. And no, even zero-backlash ballscrews
>won't be enough to eliminate the backlash unless you're running VERY
>light loads at low speeds. I had once guessed otherwise, but found
>out fast that I was wrong.
>
>If you plan to use steppers, well, you're running open-loop already,
>but I guess you could use the linear encoders as feedback to correct
>for missed steps. This assumes that you'll be writing a custom
>program to run the steppers, unless there's software out there to
>take advantage of the encoder feedback. I haven't seen any, but then
>again, I haven't looked. :)
>
>-Tom Kulaga
>
>
>
>
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