Choosing Position, Torque or Speed Mode

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JasonPORC
Posts: 26
Joined: Wed Jan 27, 2021 11:30 am
Acorn CNC Controller: No
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Choosing Position, Torque or Speed Mode

Post by JasonPORC »

Hi all. Newb question.

I've been finding a million opinions on the internet about choosing the best set up for my Servos, and I've finally decided to ask here.

My build plan is:

CNC Router with paired Y. Oak Board. Fixed Rail ATC. (ie no moving parts)

I have 4 Mitsubishi Motors. MR-JE-40, MR-JE-70, and 2 MR-JE-100's. All capable or running on P,T or Speed Mode. (Literature Attached below)

I'm pretty sure I do not want position mode. But beyond that, I just don't quite understand how they are different, and what is best for moving a router.

Any help, and or opinions are welcome with open arms. Thanks in advance. Cheers. :)
Jason
Attachments
Mitsubishi Servo Amplifier.pdf
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cncsnw
Posts: 1971
Joined: Wed Mar 24, 2010 5:48 pm

Re: Choosing Position, Torque or Speed Mode

Post by cncsnw »

You definitely do not want torque mode. Centroid's CNC11 and CNC12 software is targeted at velocity mode and position mode. This is in contrast to earlier generations, such as CNC7 and CNC10, which did target torque mode.

You should wire your interface cables to support both analog velocity mode and pulse-train position mode. Then you can experiment with both.

Generally, position mode is likely to be simpler to set up, because you would not need to do any PID gain tuning.

Position mode setups can be prone to loss of position while running, if your pulse command wiring is affected by electromagnetic noise. While switching to velocity mode would avoid that particular problem, it would be better to fix the wiring to mitigate the noise issue.

If I were building it, I would probably run it in velocity mode. That is because I have a lot of experience tuning velocity-mode systems, and get good results. If you are building your first (and perhaps only) system, that is an additional learning curve that you can avoid by using position mode.
JasonPORC
Posts: 26
Joined: Wed Jan 27, 2021 11:30 am
Acorn CNC Controller: No
Allin1DC CNC Controller: No
Oak CNC controller: Yes
MPU11 & GPIO4D -w/ 3rd Party Drives: No
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No
CNC Control System Serial Number: none

Re: Choosing Position, Torque or Speed Mode

Post by JasonPORC »

cncsnw wrote: Sat Mar 20, 2021 3:51 pm You definitely do not want torque mode. Centroid's CNC11 and CNC12 software is targeted at velocity mode and position mode. This is in contrast to earlier generations, such as CNC7 and CNC10, which did target torque mode.

You should wire your interface cables to support both analog velocity mode and pulse-train position mode. Then you can experiment with both.

Generally, position mode is likely to be simpler to set up, because you would not need to do any PID gain tuning.

Position mode setups can be prone to loss of position while running, if your pulse command wiring is affected by electromagnetic noise. While switching to velocity mode would avoid that particular problem, it would be better to fix the wiring to mitigate the noise issue.

If I were building it, I would probably run it in velocity mode. That is because I have a lot of experience tuning velocity-mode systems, and get good results. If you are building your first (and perhaps only) system, that is an additional learning curve that you can avoid by using position mode.
THANK YOU! See... I was off. I thought position mode was a no go. I'll look further into wiring it up for both as you mention. I too would rather wire properly to avoid noise and not use software to fix that.

Is PID gain tuning the same thing as "Auto Tune"? I know my drives have that option on them. Again... Newb here. :)

I guess I don't really know what "tuning" does for the drives/motors. Can you elaborate a bit more on that?

And we all know how this goes.... Wire one cabinet... next thing you know you're doing it a few more times for friends and a side hustle. lol I like learning so... here we are.
cncsnw
Posts: 1971
Joined: Wed Mar 24, 2010 5:48 pm

Re: Choosing Position, Torque or Speed Mode

Post by cncsnw »

Is PID gain tuning the same thing as "Auto Tune"?
No.

The drives may have an auto-tuning feature which allows them to set their internal current gains. Some do, some don't.

Centroid does not have an auto-tuning for PID gains in velocity mode. Centroid only has an autotune for drive response delay time in position mode, and for feed-forward terms (Kg, Kv1 and Ka) in torque mode.

Centroid PID gains in velocity mode you have to set for yourself, following some fairly standard (but poorly documented) procedures.
JasonPORC
Posts: 26
Joined: Wed Jan 27, 2021 11:30 am
Acorn CNC Controller: No
Allin1DC CNC Controller: No
Oak CNC controller: Yes
MPU11 & GPIO4D -w/ 3rd Party Drives: No
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No
CNC Control System Serial Number: none

Re: Choosing Position, Torque or Speed Mode

Post by JasonPORC »

Thank you again CNCSNW. Do you have any suggested reading I can do so that I can begin to understand this process better?

And I'm assuming there is a TB that addresses the PID gains procedure. I'll have a look.

Cheers!
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