Re: [CAD_CAM_EDM_DRO] stepper to servo transition

Hi Bruce,

Those are some really interesting projects.

There are two main advantages to full servo control:

1) The controller always knows exactly where the machine is, even after
a tool crash or emergency stop. If the machine has home switches of some
sort then this does not really matter anyway

2) An intelligent controller can dynamically vary the amount of
following error allowed depending on the type of move. For instance when
making a rapid move accuracy is not important so you can allow a large
following error. This is handy if you want to wring every last bit of
performance out of the machine but not that important otherwise.

For your application I doubt if either of these are important. If you
are happy with your existing step/dir software then I would suggest that
you stick with it. If it ain't broke don't fix it :-)

Les


taomc57 wrote:

>
>
> Greetings all,
>
> I am new to this group (and Yahoo in general), and hope my query
> falls within the group's subject. I am writing in hopes that your
> collective wisdom can help guide a decision I am trying to make.
>
> Some background-- I have been building my own NC machines since
> 1990, although you might find that term a bit of a stretch when
> applied to some of my stuff. All the gory details can be found on
> my site: "The Art of Motion Control" -- http://www.taomc.com In a
> nut shell, my obsession with DIY CNC has evolved from creating my
> own shop tools (plasma cutting, routing, milling, engraving)
> to "live performance" machines-- NC machines as kinetic sculptures.
> And, as another branch, to educational projects and materials.
> The "art machines" section of my site covers the former; "teaching
> machines" the latter.
>
> I am now working on a large scale installation of a four-axis device
> I call "Ribbon Dancer." All my work thus far has relied upon open-
> loop steppers. I have extensive experience with them, and have
> written software that allows me to fluidly move 3-axis systems along
> paths I create in AutoCAD, sending a step/direction stream out the
> PC's printer port. For this large and very public piece, I think a
> closed loop system will be necessary-- which has prompted me to
> consider using servos (the budget is ample). I have begun to get my
> feet wet in this regard, and now realize that this is a deep
> subject. I was drawn to this group because of the direct experience
> that many of you have in bridging the gap between steppers and
> servos. I have read the FAQ, and searched the archives-- I hope I
> did not miss a section which directly addresses this.
>
> I am documenting the Ribbon Dancer project at:
> http://www.taomc.com/art_machines/ribbondancer.htm
>
> My specific question is this: Am I "hobbling" myself if I use step
> and direction control for a servo system? After playing with servos
> for the past month (see the scrapbook link) I need no convincing of
> their performance advantage. But, now I need to create a bridge to
> my "choreography." Thanks for any / all input.
>
> Bruce Shapiro
> Artist-in-residence
> Science Museum of Minnesota
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