Z-axis overshooting

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01 Nov 2022 15:20 - 01 Nov 2022 15:26 #255667 by Jurre
Z-axis overshooting was created by Jurre
Hi,

I  am trying to cut some files. The X and Y axis seem to be doing okay, but the Z axis is overshooting the max depth. The first few moves go just fine. I am using a raspberry pi 4 with the Mesa 7i76e. The Gcode files are generated with Vcarve, where the max depth is set to -3mm. After a few moves the DRO still says the max depth is -3 mm but in reality it is much deeper. When I bring the tool up to the top of the material (0mm) the DRO reads +9mm (when it is supposed to be 0). 
In another topic on this forum they suggested to increase the servo_period to 2000000 instead of 1000000, and lower the P values to 500 instead of 1000. I have tried this without any result.
I am using the HY-DIV268N-5A TB6600 motor drivers but I cant find the exact values for the step time etc, I'm not sure these values have to do anything with this problem? I've tried some different values there but with the same result. 
I hope anybody has a suggestion!
Jurre 
 

File Attachment:

File Name: CNC_V7_2022-11-01.hal
File Size:12 KB

 

File Attachment:

File Name: CNC_V7_2022-11-01.ini
File Size:5 KB
 
Attachments:
Last edit: 01 Nov 2022 15:26 by Jurre. Reason: Added some information

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01 Nov 2022 18:32 #255680 by PCW
Replied by PCW on topic Z-axis overshooting
If you only lose Z position moving down, it may be that you are losing
steps. I would suggest reducing the the Z (joint3) acceleration to see if
the step loss stops.

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01 Nov 2022 22:06 #255700 by JT
Replied by JT on topic Z-axis overshooting
I also suggest doing a step timing test as shown in the documents.
linuxcnc.org/docs/stable/html/config/ste...ostics.html#_testing

JT

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01 Nov 2022 22:25 #255702 by Clive S
Replied by Clive S on topic Z-axis overshooting
Could it also be that tool pull out is responsible ?

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01 Nov 2022 23:54 #255715 by tommylight
Replied by tommylight on topic Z-axis overshooting

Could it also be that tool pull out is responsible ?

This can pull the tool out of it's jaws whenever it is tightened just a bit under "fully tightened", especially deep side cuts.
So yes, it can easily over power a stepper motor, and since all the motor/spindle/rails/etc are driven by that motor, more chances for skipping.
Lover the Z axis velocity to very slow,
lower the acceleration,
increase the motor current in the drive if the motor can handle it,
use much longer timings in the ini file for that axis/joint
check the motor for heat, if overdriven, it will skip.
check the z axis mechanically, no bindings or locking during motion
add counter weight or pneumatic lifter if the Z axis is to heavy.

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02 Nov 2022 00:57 #255732 by andypugh
Replied by andypugh on topic Z-axis overshooting
I will also add that lengthening the servo period is extremely unlikely to help with the problem as described and you should revert those changes.

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22 Nov 2022 22:06 #257387 by Jurre
Replied by Jurre on topic Z-axis overshooting
Hi!

It took me a while to get back to my machine. It turned out the velocity and acceleration were to high. Thanks for all the suggestions!
The following user(s) said Thank You: tommylight

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