RE: [CAD_CAM_EDM_DRO] HELP ! on Westamp servo drives.

#)-----Original Message-----
#)From: elson [mailto:elson]On Behalf Of Jon Elson
#)Sent: Tuesday, July 31, 2001 9:14 PM
#)To: CAD_CAM_EDM_DRO@yahoogroups.com
#)Subject: Re: [CAD_CAM_EDM_DRO] HELP ! on Westamp servo drives.
#)
#)
#)"Ward M." wrote:
#)
#)> I have a Tree Ultra Precision 1000 lathe that I have been using
#)for about
#)> one year. As long as I've had it, there has been overtravel
#)(overshoot) in
#)> both X and Z axis. This occurs only during rapids and then can
#)produce an
#)> overshoot of up to 0.1 " on the Z axis. Turning the federate
#)override to 50
#)> or 60 % stops this, but then my programs need to call out twice
#)the required
#)> feed rate for proper cutting.
#)
#)That may not do any good, as you'll end up with feedrates close
#)to what they
#)were before. (Some controls allow feedrate override to change rapid rate,
#)others don't.)
#)

Yes, that's why I do this. I want the original feed rates, but this also
cuts the rapid rate in half, preventing the overshoot. There is only a
problem during full speed rapids, anything 50% of rapid or lower works fine.
When manually programming the G code, I can stop the rapid 0.15 or so away
from the part and then feed from there. The problem arises when using
canned cycles or CAM generated code. These usually rapid much closer than
this, and hit the part. Bad, very bad.......


#)> I believe that the servo amplifiers need
#)> adjustment, but I don't have any information or schematics for
#)these units.
#)> They are Westamp Model #30060-25 and are operating on a 90VDC
#)bus. There
#)> are six multi-turn pots on the edge of the board labeled AUX,
#)SIG, TAC, TC,
#)> CLM and BAL.
#)
#)AUX may do nothing, as it is an extra input that is not used in most servo
#)systems. SIG is a gain adjustment on the velocity command from the CNC
#)control. TAC is the gain of the tachometer. CLM sounds like
#)current limit.
#)BAL sounds like the DC offset adjustment to keep the amp from
#)drifting when the
#)
#)positioning loop is not closed. TC is a little vague, but is
#)probably Tach
#)Compensation,
#)or a way to adjust bandwidth of the velocity loop.
#)

<snip>

#)There is an analytical approach to this, using control theory,
#)but you need to
#)know motor and table inertia, motor and servo amp electrical
#)characteristics,
#)etc. to put into the calculations.
#)
#)


Yes, I have a scope and will be giving the tune-up a try soon. I'm still
hoping for a schematic or parts layout so the test points are more clear. I
can remove the amp from the lathe and trace out the circuit and make a
schematic but I am trying to avoid this. Prior to opening my machine shop,
I was working as an electrical engineer designing servo and video systems.
Unfortunately, I no longer have access to the frequency and network analysis
tools I once used. I suppose I could run a rough closed loop disturbance
analysis using a sweep generator and input a low level signal in the loop.
The results might be somewhat harder to interpret from a scope screen as
opposed to a frequency and phase domain system. What do you think?

Maybe I should just tune it as you have kindly suggested. This will no
doubt get it where it needs to be without the extra trouble and analysis.


Thanks,

Ward M.

wardmerk@...