Velocity Feed Forward Servo Parameter Definitions and Correlations Questions

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Catch42
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11 Apr 2023 23:51 - 11 Apr 2023 23:52 #268855 by Catch42

Velocity Feed Forward Servo Parameter Definitions and Correlations Questions was created by Catch42

Hello,

This is my first post on this forum, so be gentle.

I have a gantry style router that I am looking to retrofit to LinuxCNC. This will be my first use with LinuxCNC and I am trying to gather as much information as I can before taking down my running machine. I have access to the working machine config and I am trying to save as many working parameters as possible to hopefully aid in the transition. The machine currently uses Panasonic AC Servos with Velocity Feed Forward parameters.

The following are the parameters that I have values for;

PID_deltaT
PIVFF_Kp
PIVFF_Ki
PIVFF_Kv
PIVFF_bias
PIVFF_saturation
PIVFF_windup
DAC_offset
DAC_gain
ENC_offset
ENC_gain
max_following_error

Though I have found definitions for several of them, I haven't been able to find all of them(which makes me weary of any of them...lol).

Any help correlating these terms to LinuxCNC tuning parameters would be greatly appreciated!

Will any of these values be useful when tuning the servos in LinuxCNC, or am I better off starting from scratch?
Are there any additional Values I should be searching for?

I am planning on using a Mesa 7i77 board for the retrofit. Will this board and/or LinuxCNC support Velocity Feed Forward?

Thank you in advance for any help or guidance you can give!

Last edit: 11 Apr 2023 23:52 by Catch42.

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andypugh
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12 Apr 2023 12:29 #268895 by andypugh

Replied by andypugh on topic Velocity Feed Forward Servo Parameter Definitions and Correlations Questions

I am not sure what is meant by "velocity feed forward" in the sense of servos, or indeed in the sense of drives.

A position-controlled drive might conceivably have a secondary input for speed feed-forward, but I have never heard of that being a thing.

If the drives take +/-10V input then they are almost certainly velocity-controlled drives where the output speed of the motors is directly proportional to the input voltage.

The LinuxCNC PID controller does support velocity-feed-forward. (and also accelleration feed-forward, and even position). These are the FF1, FF2 and FF0 parameters of the PID component respectively.

So, can you clarify what currently feeds-forward to what?

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