Re: [CAD_CAM_EDM_DRO] Re: Measuring backlash more accurately?

Randy Gordon-Gilmore wrote:

>I did an experiment after I posted. I had the Y backlash set at .001".
>Repeatedly jogging out and back .250" gave a reading of 0.000" on the
>indicator, sometimes varying .0005" or so.
>
>I set the backlash compensation to .0011", and was suddenly "losing" about
>.001" of travel each cycle--i.e. the Last Word was being deflected about
>.001" less each cycle.
>
>I set the backlash back to .001", and the movement was back to being about
>even. Same when I set the backlash to .0009".
>
>When I set the backlash to .0008", I was suddenly "gaining" about .001" of
>travel each cycle--the Last Word was being deflected about .001" more each
>cycle.
>
>I'm wondering if there is some interaction between the relative coarseness
>of the stepping, and how CNCPro inserts its backlash compensation. The
>steps are almost, but not quite half a thou, and trying to apply an even
>thou of backlash compensation might accumulate rounding errors(?)
>
>

Well, if it IS rounding errors, then you need a different program. It
would be absolutely useless
if it can't properly handle any reasonable backlash amount. This is
like a calculator that says
1-1=2!

But, I think it is a lot more likely that it is generating bursts of
step pulses at the
reversal that is causing your drivers to miss some of them. Anyway,
something having to
do with the timing of the step pulses alone, or the relationship between
step pulses and
changes of the direction line are most likely involved. You might make
sure the step
pulse polarity is going the right way for these drivers, too.

Jon