Re: Looking for a servo amplifier.....

Jon & Matt,

Thanks for the excellent and knowledgeable responses and suggestions.

Jon, good idea to watch Ebay, you never know what'll show up there.

Matt, I went through the SD's recommended tuning procedure and the
results were so far off that the axis was not functioning. Their
tech suggested matching settings to the axis with the closest
loading, X. That worked very well. I noticed in matching, some of
the number of pot turns were off by large factors from the initial
recommended settings. Again, the BAL pot on the Y axis seems to have
no effect, the other axis BAL pots function correctly. That's the
main reason the SD tech suggested replacing the board.

In my current situation I don't have the time or inclination to go
too deeply into this problem. The machine is loaded at least 8 hours
a day for the near future. I don't mind spending a little money to
replace bad components if I have to just to keep things going here.

I do have concerns with taking the "replace the board" advice, that
seems to be the way techs fix CNC's these days. Very little analysis
of why or what is going on, fix the problem by a process of
elimination in replacing possibly suspect components, all at the
customer's expense.

The surest way to isolate my problem will be to either swap axis
motors or boards and follow the problem.


It would be nice to have a spare axis drive card and motor. I think
Dynapath still has PIC chips for my control to support a fourth axis.
That'd be a nice justification to spend the money.

thanks again,

Doug

--- In CAD_CAM_EDM_DRO@y..., Matt Shaver <mshaver@e...> wrote:
> dougrasmussen@c... wrote:
>
> > Matt,
> >
> > Yes, I have the tuning info, etc. The problem is the BAL pot
does
> > not seem to be active, the drive won't balance. When the control
is
> > put in Servo adjust mode to tune the axis lag, it's impossible to
get
> > the value adjusted properly. The axis lag is much higher in one
> > direction than the other, and impossible to adjust that
difference
> > out. This IM-balance causes in-position errors and occasionally
a
> > servo error during rapid, a while back I reset the max rapid down
to
> > 250 IPM to help eliminate errors.
>
> 1. Balance needs to be set with the signal input wires from the cnc
> disconnected. This adjustment is meant to compensate for offset
errors
> in the amp itself, not the output of the Servo I/F board in the
Delta
> 20. Disconnect the 15 pin Dsub connector from the Servo I/F board
(has
> three, 2 conductor grey cables coming out of it). You may need to
go to
> the setup screen and select the Test Mode that disables all axis
> movement (my memory is a little sketchy here) to keep from going
into
> e-stop due to following error while you adjust things.
>
> 2. Since you have big size 42 motors with 7V/1000RPM tachs, I would
> expect that a good starting point for adjustment would be:
>
> BAL, CMP and SIG - Midrange (all the way CCW, then 10 turns CW).
>
> TACH - 7k ohms from COMMON (TP1) to the TACH test point.
>
> CL and RMS- Maximum (all the way CW, then 1turn or so CCW to make
sure
> the wiper of the pot isn't off the end of the pot).
>
> With the signal input disconnected (as in 1 above) try to balance
the
> amp. If you can't get the motor shaft to stop turning, or at least
slow
> down to a bare creep, the amp has problems. If you can get the amp
to
> balance out, reconnect the signal inputs (and get out of the "stop
> everything" test mode). Jog the axis back and forth slowly, the
motion
> should be smooth. Now turn the CMP pot one or two turns CW and jog
again
> to make sure the motion is still smooth. Keep going CW a turn or
two at
> a time until you get rough running or oscillation, but in any case
I
> wouldn't go more than 8 turns CW from the starting point if
roughness or
> oscillation never develops. With that done, try to increase the
gain by
> turning the SIG pot one or two turns CW at a time and then jog a
little
> to test. If the axis starts running rough, back off a turn or two
CCW on
> the CMP pot to smooth it out. Since you want to run at high speed.
the
> idea is to get the gain (SIG) up as high as you can (but don't run
the
> wiper off the end of the pot) while still retaining smooth motion.
Don't
> go CCW past the center point on the CMP pot because the center
position
> is the minimum setting. When all this is done, disconnect the
signal
> input again and rebalance as best you can. The Y axis is the
hardest to
> adjust because it has the most weight (on a knee mill) to throw
around.
>
> > I tuned per my book, results were not good. Tech suggested using
the
> > test points off a good axis (X) card and tuning bad axis (Y) to
the
> > same reading. That improved axis performance a bit.
> >
> > This is the Y axis, which is notorious for allowing coolant to
leak
> > onto the motor. That was my problem 5 years ago, the motor got
> > coolant into the encoder area, new motor cured problem.
Performance
> > symtoms were similair to now, but the Servo Dynamics tech tells
me
> > the balance problem is strictly related to the amplifier card and
not
> > the motor.
> >
> > I do intend to switch motors between X & Y to make sure the
problem
> > doesn't follow the motor. Meanwhile due to work load I need to
keep
> > this machine running since it has the longest travel of my mills.
> >
> > Any thoughts?
>
> Try switching the motors for your own satisfaction. You could also
> switch the amps to see if the problem follows the amp, but you'll
really
> need to readjust their pots for it to be a fair test. Servo
Dynamics is
> a good company so you could get then to fix your amp if need be.
Worst
> case is a new amp at about $400, and since you have the work for
that
> machine...
>
> Matt
> (410) 521-3715