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Author Topic: Axes vibrating - analogue servos  (Read 64 times)

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Axes vibrating - analogue servos
« on: March 08, 2021, 04:54:43 AM »
Hi all,

I'm running an analogue servo system and have recently just changed the controller and have worked my way through the tuning process.
I've been having some issues getting the machine to run without vibration which at first I thought was. controller issue but now I'm not sure.

This is is an account of the simple tests I ran on the system and the results I got. I was wondering if someone might have had a similar experience and have some advice or places to look for a fix.

Jogging is smooth in X and Y.

With jogging now smooth I ran some old tool-paths to see how they would go.
They were not cutting anything as the spindle was not on.

What I noticed was strange.

On G-Code toolpath number 1, the machine would run through a profile cut. There were three depths but the profile was the same for all of the cuts. The Z moved up and down, but it was not anywhere near the table.
Somewhere on the third profile cut the machine would start to vibrate. It was hard to know exactly what line of code it was. I think it varied but was always in the third pass.
This seemed to be prevalent regardless of speed. I tried this 15 or so times and would vary the Feedrate with the FRO.

Because of this I decide to do a test.

I wrote the following code into the MDI.

G01 F2000

I copied the X and Y code 30 or 40 times so it effectively traced a box out.

I ran the MDI.

It generally started fine, but usually somewhere over halfway the machine would start to vibrate.
The vibration would normally go away and the program would finish.

At F2000 I never once made it through the program without a vibration somewhere.

I then increased to F3500mm/m.

Same problem.

I increased to F5000.

No vibration and the axes seemed smooth.

This is where it seems really strange to me.

I copied the exact code into a G-Code file.

I ran the file and everytime I pressed “Cycle Start” the machine would start the cycle and start vibrating straight away, always worse than the vibration that occurred whilst running on the MDI.
I increased the feedrate and the it always had the same outcome until l got to 5000mm/m and the machine stopped due to a PID fault.

So, to summarise.

Jogging seems fine at all feedrates.
Running “box” code in MDI seems to vibrate occasionally, but when increased feedrate to 5000mm/m it seems be smooth.
Running same “box” in G-Code vibrates consistently regardless of feedrate.
Running same “box” in G-Code stops with a PID fault at 5000mm/m.

Any thoughts?