what the world needs now ... backlash aware stepper motor driver

While pondering how to cnc convert my bench
mill (bigger than an RF-45 but smaller than a
GEM500) which has 1" dia * 10 TPI acme leadscrews
with 10 thou backlash in the X axis and 8.5 thou
in the Y axis....

I thought it might be an idea for someone to
build backlash aware stepper motor drivers.

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.

Also, that range of steps represents the 'deadband'
where the motor driver does not have to respond to
any S&D inputs (thereby avoiding bad oscillations
caused by 'zero seeking').

For example, with the above mill and a 1.8 degree
stepper, 1 full step represents .100"/200 = 0.000 50"

and so 10 thou backlash would be 20 steps that the
driver would throw in on each axis reversal. That
would be '0001 0100' in binary, so upon initial setup
you'd toggle that into the dip switch on the driver
for that axis, and then backlash compensation would
more or less be automatic after that.

To compensate for the 8.5 thou backlash in the Y
axis, that represents 17 steps, so toggle '0001 0001'
into the Y axis stepper motor driver dip switches.

Simple.

Doug Fortune
http://www.cncKITS.com