RE: [CAD_CAM_EDM_DRO] problem with gecko 201 dirve and cncpro

Scott -

If your motors have a shaft coming out of each end, you might want to put a
knob on the unused line and then set your motor running. Very gently touch
the knob and see if the motor seems smooth and not jerky. If you feel any
jerkiness at all, you are most likely losing steps because you're attempting
to run the motor too fast.

Can you switch the geckos into a half step mode (get 8000 steps /rev)? If so
do that and then program your controller to turn one revolution slowly (400
steps) Check whether or not the motor shaft makes a complete turn and
whether or not the table moves 0.050 inches. Then, move slowly and try for
an inch (8000 steps) The idea is to move the motor so slowly that you'll not
lose any steps just to verify that everything is working correctly.

Assuming that you can get an inch repeatably with half step, slow motion,
then try the same thing with the ten step microstepping mode. Again, work
slowly and just try to make one revolution. Now, if everything works
properly at slow speed, move back to "real speeds" and try the same
experiment, but try to put an oscilloscope on the step line. You're looking
for a smooth pulse train as the motors accelerate to speed, run at speed,
and then decelerate. With an XT machine, I'd be concerned that it simply
can't supply the pulse train and something's being lost.

Hope these suggestions help

-- Carol & Jerry Jankura
Strongsville, Ohio
So many toys, so little time....


|-----Original Message-----
|From: scott_in_tucson2002 [mailto:scott_in_tucson2002@...]
|Sent: Wednesday, February 13, 2002 5:22 PM
|To: CAD_CAM_EDM_DRO@yahoogroups.com
|Subject: [CAD_CAM_EDM_DRO] problem with gecko 201 dirve and cncpro
|
|
|Hello,
|
|I posted a message about this problem a couple of weeks ago, and
|have since had a chance to do some more research. My configuration
|is a sherline 5400 English milling machine, 3 gecko 201 (not the 'a'
|version) drives, two powermax II stepper motors & one sherline
|stepper, and an XT computer running the latest version of cncpro.
|
|There appears to be two problems:
|
|1) The steppers are 1.8 degree per step, and I compute this should
|be 40,000 pulses per inch (the gecko is a 10 microstep drive).
|However, it's taking approximately 52000-53000 pulses per inch.
|
|2) There is some kind of accuracy problem that I'm having trouble
|quantifying.
|
|Since problem #1 seems easier to quantify and more obvious than
|problem #2, I've decided to tackle it first. Yes, my machine _IS_
|the 5400 english model, and not the metric model. I've verified
|there are 20 rotations of the handwheel per inch.
|
|I've tried two different computers, a handful of parallel IO cables,
|and different parallel IO cards. I've also tried building and
|installing a buffer board to boost the parallel signal for driving
|the gecko's optocouplers. None of these attempts has produced any
|change.
|
|As a side note, I am getting some occasional humming from the
|motors, and only when the computer is connected (this led me to
|build the buffer board I mentioned above, which did reduce the
|humming, but did not effect the positional problems). The humming
|only occurs at certain phases where the motor is stopped.
|
|Does anyone have any clues as to what I should look to next?
|
|Thanks,
|Scott
|
|
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