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

>> Such a beast would have dip switches to indicate
>> at setup time what the backlash was (in steps), and
>> upon detecting any reversal of direction, quickly
>> counts up through that selected number of steps
>> to take up the backlash.

Uhh .. doesn't the software in most systems do this already ?

Anyway, some time ago, I built and <mostly> finished the programming for
( and hence never installed ) a small unit with a PIC and an LCD to make
a one channel DRO.

Besides the quadrature inputs, though, there was also step and direction
inputs AND step and direction outputs. There was one last output, a
"pause" output to the software (CNCPro).

Each step and direction pulse IN was echoed to the step and direction
pulse OUT.

The step pulses were timed, and compared against the DRO.

Should enough steps be issued that resulted in no DRO activity, the
PAUSE output was asserted and additional steps issued until things
"matched up" again.

It seemed to me that for best operation, the DRO feedback must be at
least as fine a resolution as the stepper system. If the steppers are
4,000 steps per inch, then a .00025"/count DRO would be required to
more or less "correctly" compensate for the leadscrew.

However, even at lower resolutions of the DRO, it would still be
useful, there would simply be an uncorrectable error, roughly the size
of a quadrature step.

Seems that this would be a better anti-backlash system ...

Alan




--

Alan Rothenbush | The Spartans do not ask the number of the
Academic Computing Services | enemy, only where they are.
Simon Fraser University |
Burnaby, B.C., Canada | Agix of Sparta