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Pedersen VP2000 810M retrofit, severe servo hunting
03 Jul 2019 11:47 #138515
by Juckix
Replied by Juckix on topic Pedersen VP2000 810M retrofit, severe servo hunting
Z movement is achieved by lifting the bed rather than the spindle via a central ballscrew, and as far as I am aware there is no counterbalancing.
I tried a few different BIAS value (0.001-100, as well as negative values) without seeing any change in the oscillation. At values above 10 the machine jerks when motion is enabled, which is to be expected I guess.
Further, increased Integral values decreases the period of oscillation but seems to be necessary for a low f-error. I have a tune (something like P=10, D=0.1, FF1=0.01, FF2=0.001) which produces very little hunting (more like 0.002mm rather than 0.015) but has a completely unsatisfactory f-error while moving.
Lastly what I found a bit odd is that the hunting shows up as instant on the DRO, it basically jumps 0.015 up and down repeatedly without any inbetween.
I tried a few different BIAS value (0.001-100, as well as negative values) without seeing any change in the oscillation. At values above 10 the machine jerks when motion is enabled, which is to be expected I guess.
Further, increased Integral values decreases the period of oscillation but seems to be necessary for a low f-error. I have a tune (something like P=10, D=0.1, FF1=0.01, FF2=0.001) which produces very little hunting (more like 0.002mm rather than 0.015) but has a completely unsatisfactory f-error while moving.
Lastly what I found a bit odd is that the hunting shows up as instant on the DRO, it basically jumps 0.015 up and down repeatedly without any inbetween.
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03 Jul 2019 13:52 #138528
by andypugh
Replied by andypugh on topic Pedersen VP2000 810M retrofit, severe servo hunting
What is the physical size of a single encoder count?
You might need to add a little deadband to the PID.
You might need to add a little deadband to the PID.
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11 Jul 2019 14:42 - 11 Jul 2019 16:29 #139106
by Juckix
The slides are graduated to 0.004mm but it's hardware interpolated to 0.001mm. The latter number is the deadband set on X and Y and it works well there. Raising it leads to more severe hunting on those axes.
Replied by Juckix on topic Pedersen VP2000 810M retrofit, severe servo hunting
What is the physical size of a single encoder count?
You might need to add a little deadband to the PID.
The slides are graduated to 0.004mm but it's hardware interpolated to 0.001mm. The latter number is the deadband set on X and Y and it works well there. Raising it leads to more severe hunting on those axes.
Last edit: 11 Jul 2019 16:29 by Juckix. Reason: Wrong scale, clarification
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15 Jul 2019 11:42 #139414
by andypugh
Replied by andypugh on topic Pedersen VP2000 810M retrofit, severe servo hunting
I would suggest setting the BIAS to the same voltage as the Z shows steady state. It just helps make the PID tuning a bit more symmetric between up and down.
Did you decide if these were torque-mode or velocity-mode drives?
Did you decide if these were torque-mode or velocity-mode drives?
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