On Dec 31 2008, 1:10*pm, Ned Simmons wrote:
On Tue, 30 Dec 2008 20:29:14 -0800 (PST), oldjag



wrote:

The amps are Servomate Randtronics. They have the following Pot
adjustments: GAN = Gain, TAC = tachometer input, AUX=auxillary, (not
used), BAL=Balance, SIG=Signal and CLM=current limit. *Standard
preliminary setup is to MAX out, (20 turns CW) the CLM and the TAC,
set the BAL in the middle, adjust SIG to get the A/D out from the
servo control board to the Servo amps around 0.65V during a 20 in/min
feed, and use the BAL to get the voltage the sam in both directions.
Also the gain gets adjusted up to instability and backed off a few
turns. *The problem is with the base settings the servos are vibrating
like crazy. *Backing off the Sig kills the vibration, but with the sig
backed off to where the vibration stops, the servos are very slow to
respond, and the A/D voltage gets to only .45 volts. *Things checked
so far:
1.)Tach inputs to servo amp are okay and correct polarity.
2.)Encoder pulses look good on A, B and Z channels on scope at the
servo control board.
3.)Backlash on the ballscrews is less than 0.0002"
4.)Main cap on servo amp 80Vdc supply checks out okay.
5.) +12V and -12V Servo amp supply looks good.
6.) Position display is reading in the correct direction and is
accurate.
7.) A/D signal from servo amp looks noisy, but I don't know what
normal looks like.

At this point I'm not sure what to check next. *Vendor thinks maybe
problem is the new encoders, but I'm not convinced.

Presumably the encoders connect to the motion (CNC) controller. You've
changed the encoder resolution, so to get best performance you need to
change the gains in the PID loop in the controller. As you've found,
fussing with the amp's gain will stabilize the loop at the expense of
performance, but I don't think you'll be able to get the stiffness
back without tuning the PID loop in the controller. *Do you have
access to the proportional, integral, and derivative gains in the
controller?

--
Ned Simmons

Ned;

There are no pots for Prop, Integral, or Derivative on these amps.