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Author Topic: Jerky movements in complex toolpaths.  (Read 9112 times)

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Re: Jerky movements in complex toolpaths.
« Reply #10 on: July 27, 2016, 11:53:19 PM »
well I heard back from CS labs. They said the difference in voltage shouldnt be an issue. The also suggested I change some parameters to help with servo tuning. While the servos ended up with a better tune when I was done, I have exactly the same issue. Essentially, When running a program, I end up with a following error 10 TIMES the amount of error I get when jogging back and forth at full speed.

I'm wondering If I should take the plunge and set the machine to run in mach4. I need thing thing to be able to haul ass and cut molds and I just don't see it ever performing close to what it did before I installed mach3. I'm submitted a service ticket to machsupport weeks ago and never heard back from them. I even emailed Brian directly but haven't heard back. I suppose he's busy.

Offline Tweakie.CNC

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Re: Jerky movements in complex toolpaths.
« Reply #11 on: July 28, 2016, 01:58:15 AM »
Just a wild thought and grasping at straws here but have you looked at your CAD/CAM generated toolpath - if it contains many short lines this could cause jerky motion (particularly with arcs and contours).

Tweakie.

(nothing to do with the problem but the diode, below the 3PR relay, appears to be connected incorrect polarity).
PEACE
Re: Jerky movements in complex toolpaths.
« Reply #12 on: July 28, 2016, 02:30:57 AM »
It definitely has lots of very short lines and arcs and contours. Shouldn't mach be able to handle that with look ahead and constant velocity?

Offline Tweakie.CNC

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Re: Jerky movements in complex toolpaths.
« Reply #13 on: July 28, 2016, 02:50:51 AM »
Well yes it should but I recently changed the aspect ratio of a previously produced milled panel contour and regenerated the toolpath (in CAD/CAM) – this converted all my nice smooth arcs into many straight lines – the result was terribly rough motion from my mill.
Mach3 is good but it’s not perfect and I ended up redrawing the panel to the new dimensions, recreating the toolpath then everything was bliss.

Tweakie.
PEACE

Offline SimonRafferty

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Re: Jerky movements in complex toolpaths.
« Reply #14 on: December 25, 2020, 11:15:26 AM »
I don't know if you found a solution to this - but I'll tell you mine all the same!

I had the same issue.  CS Support wasn't really much  help, but I found a comment on line suggesting that a faster PC fixed it for them.  I was running a new i3 with 8GB 2GHz - so it isn't slow by any means.  My servos (Fanuc with Ultra3000) were perfectly tuned & lightning fast.  Running in test mode from the Ultra3000, or even a pulse generator they moved smoothly.

Connected to the CSMIO however, they were lumpy / jerky as hell.  Looking at the scope in the U3000, I could see the step pulses were coming in erratically.

I tried it with a i7 16Gb 4GHz - and now the axis are smooth.

I fail to understand why a motion controller needs a fast PC.  The jerkyness appeared even on straight line moves G0 Z500 kind of thing where I imagine the PC would just send one coordinate to the controller which would deliver the pulses at the required frequency.  However, it appears to send continuously - maybe so you can stop in the middle of a move?  It seems even more daft when the old PC with Mach3 & a parallel port BoB could drive them just fine.

The upshot is - if your servos are jerky, use a faster PC.