"Bob Engelhardt" wrote in message
...
RogerN wrote:
I have an older Anilam CNC Bridgeport and Anilam CNC lathe. They both
use motors with tach feedback, the mill uses DRO scales for position
feedback to control and the lathe uses encoders coupled to the
ballscrews. I replaced the original amplifiers with AMC amplifiers
similar to those in your link, they work great.

How does you system use both tach feedback & encoders? It seems like the
encoders would give all the feedback that's needed.

... and I can browse the internet while on the lathe. :-)

A definite advantage G.

Bob

The tach feedback goes to the drive, the encoder goes to the controller. I
learned the most about my system due to a lot of backlash in it when I first
bought it. Due to shims and being out of adjustment, my CNC mill had around
a half turn of the handle of play. Lucky the problem wasn't in the
ballscrews, it's just that the bearings traveled in their holders for a
little bit before moving the table.

Here's how it responded. If the table was out a half thou per my DRO
scales, the handwheel would move slowly until it was in position, if it were
a thou out, that handwheel would move around twice as fast, almost
unnoticeable while running, I noticed the backlash when watching the
handwheel moving while a half thou out. So, the control knows it's a half
thou out, sends a move command proportional to the error (.0005") and the
motor moves in the correct direction at a controlled speed, thanks to the
tach feedback, until it gets in position. What I like about this system is
that it positions accurately and is stable even with backlash in the screws.
It goes off of table position, not just motor position, and does accurate
work. The performance improved when I got the shims correct to eliminate
the backlash. If it weren't for the tach feedback, the system wouldn't have
been stable with the backlash. This doesn't excuse sloppy equipment, but it
is nice to know the system is stable and accurate even with some backlash.

RogerN