Tuning 2 servo at same time (master/slave axis)

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rdpdo2002
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Joined: Sat Mar 23, 2019 6:34 pm

Tuning 2 servo at same time (master/slave axis)

Post by rdpdo2002 » Fri Mar 29, 2019 1:55 pm

Hello,

I need to tune an axis with 2 servo (master/slave). I think I will do that like if it was an unique servo, so I will view the step response of only one servo (the master ?) Is it correct ?

I don't think it is possible to view the response of the 2 servo simultaneously ?


Do you have some special recommandation to tune a master/slave axis ? Some error to avoid ?

Thanks you very much.

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TomKerekes
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Re: Tuning 2 servo at same time (master/slave axis)

Post by TomKerekes » Fri Mar 29, 2019 6:41 pm

Please see this wiki article.

HTH
Regards,

Tom Kerekes
Dynomotion, Inc.

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cnc_freak
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Re: Tuning 2 servo at same time (master/slave axis)

Post by cnc_freak » Sat May 16, 2020 5:42 am

Is there a way to observe in step response screen the position of the slave axis together with the position of the master?

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TomKerekes
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Re: Tuning 2 servo at same time (master/slave axis)

Post by TomKerekes » Sat May 16, 2020 9:48 pm

Hi cnc_freak,
Is there a way to observe in step response screen the position of the slave axis together with the position of the master?
Not with the Step Response Screen. Since they both follow the same trajectory if you verify one follows the trajectory properly and also the other that is usually sufficient.

Otherwise you could use a User C Program to capture the data and then analzye it yourself with some application like Excel. See the CaptureXYMotionPosDest.c example.
Regards,

Tom Kerekes
Dynomotion, Inc.

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cnc_freak
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Re: Tuning 2 servo at same time (master/slave axis)

Post by cnc_freak » Wed May 27, 2020 7:39 pm

It's not very clear to me about tuning the master/slaves axis. The slave should follow the master. Do i need to but anything in the slave configuration. Should i copy the p,i,d,max error etc ,parameters which i find by tuning the master, or does not have any influence.
Regards.

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TomKerekes
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Re: Tuning 2 servo at same time (master/slave axis)

Post by TomKerekes » Wed May 27, 2020 8:18 pm

Hi cnc_freak,
It's not very clear to me about tuning the master/slaves axis. The slave should follow the master.
They actually independently follow the same trajectory.


Do i need to but anything in the slave configuration. Should i copy the p,i,d,max error etc ,parameters which i find by tuning the master, or does not have any influence.
Both axes need to be configured independently. If both axes are identical then the same parameters may work for both, but this is not necessarily the case. Often while homing the axes are moved independently (not slaved) so the axes can be "squared".

HTH
Regards,

Tom Kerekes
Dynomotion, Inc.

awjennin
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Joined: Wed Apr 08, 2020 1:17 am

Re: Tuning 2 servo at same time (master/slave axis)

Post by awjennin » Tue Sep 20, 2022 12:58 am

Good evening Tom !

My machine is similar; a gantry system with independent ballscrews for the left and right sides. The right-side stepper motor is the master axis, and has a feedback mechanism (optical encoder), while the left-side stepper motor is the slave axis and has no feedback. My question and application are similar therefore I think its OK to piggyback on the original thread : )

I have read the forums and the wiki, however i'm not sure I fully understand what signals are passed to the slave axis.
Will the master's pre-control-loop commands be mirrored and sent to the slave axis (left image), or will the output of the masters control loop be passed to the slave (right image)?
ctrl_loop_ms.png
ctrl_loop_ms.png (11.3 KiB) Viewed 137 times
Thanks and kind regards!

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TomKerekes
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Re: Tuning 2 servo at same time (master/slave axis)

Post by TomKerekes » Tue Sep 20, 2022 4:58 pm

Hi Jennin,

What type of Drives and Configuration Modes are you using?

Normally your left diagram is used where basically both Axes are commanded to the same Destination.

With an exception when the Master is Closed Loop Step/Dir (or Closed loop Microstep with SnapAmp) and the Slave is Open Loop Step/Dir (or Open Loop Microstep). In this case the Master Output represents a correction of a number of extra +/- steps that were required to get the Master Axis Encoder to be at the commanded Destination. In this case the Master's Output is also applied to the Slave.

This is different from your right diagram where the Slave would try to follow the actual encoder position of the Master which I don't think would really make sense.

You might see this Closed Loop Step/Dir page.
Regards,

Tom Kerekes
Dynomotion, Inc.

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