On Sat, 10 Sep 2011 14:46:27 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

Ignoramus13208 fired this volley in
m:

Lloyd, this will work just fine. It is a known approach. If your DRO
is absolute, you can also avoid homing.


The scales are not absolute, but do have a built-in home index, so switches
(or choppers) would not be required except to provide an over-limit panic
stop. The fact that the index is built into the scale would, I think,
further improve repeatablilty of homing. I've seen home switches go
"wonky" over time, and choppers can get dirty, and not repeat the same home
position twice in a row.

LLoyd
Greetings LLoyd,
First of all, where are you getting the cheap magnetic scales?
Secondly, the biggest problem with using scales instead of a motor
shaft mounted encoder is backlash and resonance. As the control moves
the motor to correct the positional error if it has to turn the motor
shaft a lot before the scale moves then the motor can overshoot and
then this can lead to resonance problems. Inaccurate ballscrews aren't
a problem, just loose ballscrews.
Eric