On Tue, 23 Sep 2014 19:20:17 -0500, Karl Townsend
wrote:


You need to ping Tim Wescott who sometimes posts here - he's the guru.

What? Who? Huh?

Maybe I've been sleeping under a rock, didn't know this.


I've been fighting a buzzing at stop in my Galilmc.com controlled AMC
servo amps and DC servos. 9 out of 10 times the servo will stop
smoothly, the tenth it will oscilate about 1 or 2 encoder counts so
rapidly it makes a buzzing noise.

Rate gain is turned up too high.

Adding the low pass filter to PID helped (see below for manual
description) but i ended up reducing P,I and D by huge amounts to stop
it. Now the system is sluggish. FWIW, Galil has servo tuning software
to automatically tune your system. that worked for many years till
this issue popped up.

Comments?

Karl





PL
FUNCTION: Pole
DESCRIPTION:
The PL command adds a low-pass filter in series with the PID
compensation. The digital transfer
function of the filter is (1 - n) / (Z - n) and the equivalent
continuous filter is A/(S+A) where
A is the filter cutoff frequency: A=(1/T) ln (1 / n) rad/sec and T is
the sample time.
To convert from the desired crossover (-3 dB) frequency in Hertz to
the value given to PL, use the
following formula:

whe
n is the argument given to PL
T is the controller’s servo loop sample time in seconds (TM divided by
1,000,000)
fc is the crossover frequency in Hertz

n 0 0.2 0.4 0.6 0.8 0.999
Fc(HZ) ?‡ (off) 256 145 81 36 0



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