Simple 4th axis
01 Sep 2021 10:36 #219322
by RoberCNC
Simple 4th axis was created by RoberCNC
I'm going to start playing with a 4th axis, for now and by way of introduction and testing before getting into pulleys, reductions and jaw chucks, it will be a nema 23 coupled directly to the axis. What parameters would be recommended in relation to angular velocity, acceleration, etc. in the INI file?
I would also like to know how I could implement to make it work in indexed mode or speed mode, I know that's a way via MUX.
Thank you.
I would also like to know how I could implement to make it work in indexed mode or speed mode, I know that's a way via MUX.
Thank you.
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01 Sep 2021 11:44 #219323
by andypugh
Replied by andypugh on topic Simple 4th axis
To switch a stepper between position and speed control, the simplest way is probably to run the stepgen in velocity mode and run two different PID controllers. One has input and feedback in position, and the other velocity, but both output a velocity command. (to achieve this I would anticipate the position PID being strong on P and with a bit of I, and the velocity one being mainly FF0 and I term)
The following user(s) said Thank You: tommylight, RoberCNC
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01 Sep 2021 16:35 #219350
by RoberCNC
Replied by RoberCNC on topic Simple 4th axis
Thank you very much Andy, you will forgive my ignorance but I do not understand exactly what you are saying, would you be so kind to explain more in detail?
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02 Sep 2021 00:36 #219383
by andypugh
You do not need a velocity PID for velocity control of a velocity stepgen, you can run that part open-loop.
You will need a PID for position mode, though.
So, configure the stepgen as velocity-mode.
Connect a mux2 to choose between velocity command and the output of the position PID.
The position PID takes position (C axis?) as input and stepgen position as feedback.
Use some logic to simultaneously switch the mux and enable the PID when you want position control.
You might need something a bit clever if you want to switch from velocity mode to position mode after many revolutions, by default the position PID will want to unwind all the current stepgen turns.
Replied by andypugh on topic Simple 4th axis
Possibly because I over-complicated it.Thank you very much Andy, you will forgive my ignorance but I do not understand exactly what you are saying, would you be so kind to explain more in detail?
You do not need a velocity PID for velocity control of a velocity stepgen, you can run that part open-loop.
You will need a PID for position mode, though.
So, configure the stepgen as velocity-mode.
Connect a mux2 to choose between velocity command and the output of the position PID.
The position PID takes position (C axis?) as input and stepgen position as feedback.
Use some logic to simultaneously switch the mux and enable the PID when you want position control.
You might need something a bit clever if you want to switch from velocity mode to position mode after many revolutions, by default the position PID will want to unwind all the current stepgen turns.
The following user(s) said Thank You: RoberCNC
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03 Sep 2021 20:47 #219555
by RoberCNC
Replied by RoberCNC on topic Simple 4th axis
Thank you very much Andy, I will do a first initial configuration as you say, the first thing to see if I can move the axis and I will look for information about MUX2 and how to exchange modes. With whatever, I will consult you again and ask for help.
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