Re: Renishaw scales giving 5.0 um to 0.2 um

["Matt Shaver" <mshaver-at-erols.com>]

> From: Jon Elson <jmelson-at-artsci.wustl.edu>
> Why this happens is that when the table position needs to
> be moved just a hair the other way, the motor picks up
> speed crossing the backlash, while the encoder doesn't
> sense any movement.  Then, the motor takes up all the
> backlash, and the Acme screw suddenly moves the table
> too far before it can stop.  Then the process repeats in
> the other direction.

Yes, and if you tune P, I, and D to dampen out this tendency to oscillate,
then you'll be very disappointed with the axis' performance at higher speeds
and accelerations. Backlash compensation won't help this either because the
backlash is INSIDE the servo drive/position feedback loop itself.

Matt