over shooting of target coordiniate then stepping back

[polytone]

]I've got gecko 320's driving clifton brushed servos via Mach 2. (w/ball screws)
On a G00 or G01 command the system is consistantly over shooting the target by .001 or so then stepping back to right on the money. This is on all 3 axis, monitored with a dial indicator.
I've tried many different velocity/acceleration config tunings in mach 2 to no avail. Gecko says it's gotta be the software, Mach 2 says it's the Gecko drivers gain setting. Anybody have experience with this sort of problem?

[ViperTX]

I would suspect the software if it were a "closed loop system", but it's not.....so it has to be a problem with the positional error signal coming back to the gecko.....how much backlash does this system have....are your ballscrews shifting at all....is the error always the same regardless of how much you move??

[DAB_Design]

What feedrate are you trying with a G01? If it's too fast, it may just be the mass of the indicator moving an extra .001, then moving back to where it's supposed to be after the machine has stopped.

[polytone]

The over shoot is consistant even very slow feedrates on all 3 axis . I can actually hear the pulses stepping the servo back to the target. It's a new machine, backlash isn't an issue.

[ViperTX]

Originally Posted by polytone The over shoot is consistant even very slow feedrates on all 3 axis . I can actually hear the pulses stepping the servo back to the target. It's a new machine, backlash isn't an issue.

Wow, so you don't need an oscilloscope...that's cool.

If you had an oscope you could monitor the DIR and see if the SW is sending pulses to step back....I suspect not....does anyone know how the gecko handles the error signal...is it just a buffer that fills up and turns on the error signal LED when the max. allowable error count is reached???

[Dan Mauch]

You may have the gain and the dampening set too high or to low. Remeber to adjust the gain and dampening equally.

[polytone]

I'm experimenting with a 4:1 timing belt ratio. I tried it on one axis and it seemed to help. Also in conjuntion with tweaking the gain and damping trim pots on tha gecko 320.