Re: [CAD_CAM_EDM_DRO] Re: what the world needs now ... backlash aware stepper motor drive r

Are you suggesting that the "add reverse steps to take up backlash" should
not be used in the interim, before more advanced control software can be
written? Do you think that it makes the machine work less well compared
with no backlash compensation at all? Obviously, I am assuming that we are
trying to control a machine that has backlash for whatever reason. Not
trying to incite anything, just honestly asking questions that I do not know
the answer to.

Thank you,

Daniel J. Statman, Statman Designs
www.statmandesigns.com

----- Original Message -----
From: "CL" <datac@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Monday, February 11, 2002 6:44 PM
Subject: Re: [CAD_CAM_EDM_DRO] Re: what the world needs now ... backlash
aware stepper motor drive r


> Right On Peter.....
>
> Backlash seems to be a concern for many. Yet, unless it is a very large
> machine with a lot of mass, Backlash Compensation has some downfalls (with
an
> economy control). On a smaller machine without the usual weight and mass,
> backlash can end up as you describe - Messy.
>
> I think it only works on a non-contact machine if there is enough friction
in
> the machine to allow it to ride "one way or another", letting the software
> straighten things out, Or a much heavier machine where you can be assured
that
> an Axis simply does NOT MOVE unless the motors moved it !
>
> One thing I do not think inexpensive control "users" really think about,
is
> that backlash is NOT just "add a few steps - subtract a few steps"
according
> to direction. Especially if and when Continuous Contouring is applied.
I
> had a very good discussion with Art at Ability Sytems once, as he
explained
> what is involved with doing compensation **correctly**. A straight line
> motion, one way, then the other is real easy - a no brainer. But, when you
add
> in all of the moves a CNC machine >really< makes, the "add some-subtract
some"
> falls flat on its face. Thats where the marks come in.
>
> Even acceleration and deceleration factors as applied to cutting force and
> chip removal will affect just "What" amount of backlash is necessary. How
do
> you make such a calculation to hit that correctly ??
>
> Thus, its why Indexer does not yet have backlash comp. Art said it can be
done
> right, but will take some time. He plans on adding it in the future, but
even
> then as the problem really is described, I don't see how it could ever be
a
> perfect situation.
>
> I know a lot of guys are caught stumbling all over the issue of backlash
comp,
> but, In many circumstances, that very simple "add-Subtract" technique is
the
> one applied. Don't be fooled by some "Label" on a product indicating it
> *includes backlash compensation* and expecting miracles no matter what the
> cost of the control. Things will vary from installation to installation
and
> machine to machine.
>
> That is why I am such a proponent to just stick in something better for a
> leadscrew right off the bat.
>
> To each his own................... Ballscrews are nice..... But maybe the
> Rolled Leadscrews and A/B Nut will fit your hobby budget better.
>
> If your really budget minded (or your wife will throw you out if you spend
too
> much on this "thing" your building), well, I guess the threaded rod at the
> hardware store looks pretty good too.
>
> Peter wrote:
>
> > Having backlash compensation may be ok for light duty (i.e. low side
> > force) CNC applications like plasma cutting. My experience with
> > backlash compensation in my Flashcut CNC system is that while you can
> > completely compensate (in theory) for the backlash in the acme screws,
> > it still results in poor machining surface finish.
>
> (snip)
>
>
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