While I don't fully know the exact details, I can tell you right
away, you cannot rely on software to eliminate the backlash within a
CNC system. For basic positioning, perhaps a little, but in
practice, no.
While software can compensate for the static deviation between where
it told the motor to position and where it really is based on
encoder feedback, the "Slop" is still there. During cutting, the
dynamic cutting forces will cause the axes to move around within the
mechanical slop. When drilling, the position will be off and the
holes will not be on size. When milling, all sorts of dimensional
problems pop up and in the end, you will have wished you took the
time the eliminate the mechancial backlash.
While there is backlash compensation within all CNC systems I have
used in the industrial world, it is primarily only used to
compensate for a very samll amount of backlash .001" or less
usually. Beyond that and it is time to correct the mechanical
problems.
So, don't waste your time or effort in thinking of a software
solution to backlash - backlash is a mechanical problem and must be
designed out of the system for even the most basic of machine
performance.
--- In
Homebrew_PCBs@yahoogroups.com, "Stefan Trethan"
<stefan_trethan@g...> wrote:
> On Tue, 28 Jun 2005 08:36:23 +0200, mikegw20 <mikegw20@h...> wrote:
>
> > Now I have never built a CNC anything and I am not overly
mechanical.
> > Right that is my qualifications out of the way...
> > I was thinking about high torque motors to drive a linear thread
and I
> > thought about those really cheap cordless drills. That is idea
pt1.
> > Now of course you need some sort of feedback for the position,
the
> > normal way would be to put a shaft encoder on the drive. My
thinking
> > is that if you used a linear encoder then you would get absoulte
> > positioning thereby negating the need for backlash
compensation. Now a
> > quick look around ebay reveals that linear encoders are not
cheap. So
> > has anyone used optical mice for a linear encoder? (idea pt b)
> > Here endith todays musings.
> > Mike
>
>
> cordless drills usually use a motor what the model-vehicle
builders would
> call similar to a "speed 600".
> Not a bad motor, and you can get replacements really cheap as well
as
> better motors the same size.
>
> I would try to find drills with metal gears for this purpose. I
recently
> bought a very cheap one with plastic gears, it is still working,
but i'm
> always expecting it to fail any time. It was cheaper than a
replacement
> battery for a better drill.
> There are often ebay lots of many drills.
>
>
> As for linear encoder, there are those striped plastic strips in
printers,
> but a much easier solution would be to use digital calipers and
use the
> data-out, 'cause you would get absolute position not only
relative.
> Probably more expensive than shaft encoders and certainly more
expensive
> than steppers.
>
>
> ST