Dual X Servo

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28 Apr 2013 05:23 #33300 by juwi
Dual X Servo was created by juwi
Hi

www.linuxcnc.org/index.php/english/forum...in-closed-loop#23714

Andy told me "simply" to:

"connect axis.1.motor-pos-cmd to both PID modules in the HAL"

How is this done? If I just change:

net a-pos-cmd axis.3.motor-pos-cmd
to
net a-pos-cmd axis.1.motor-pos-cmd

There comes an "net already connected" error on Startup...

HAL File is attached, INI too, A axis is second Y axis

Help?

best regards
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28 Apr 2013 05:52 - 28 Apr 2013 05:52 #33301 by juwi
Replied by juwi on topic Dual X Servo
michas_kleine.hal:164: Signal 'y-pos-cmd' can not add OUT pin 'axis.3.motor-pos-cmd', it already has OUT pin 'axis.1.motor-pos-cmd'
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Last edit: 28 Apr 2013 05:52 by juwi.

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28 Apr 2013 07:27 #33308 by andypugh
Replied by andypugh on topic Dual X Servo

Hi
www.linuxcnc.org/index.php/english/forum...in-closed-loop#23714
Andy told me "simply" to:
"connect axis.1.motor-pos-cmd to both PID modules in the HAL"
How is this done?


I just tried to make your HAL file work as suggested, and I have realised that it is rather important to know if you intend to use index-homing on both sides of the gantry.

I think I need to have a good long think about how to do homing on a gantry axis that uses servos and trivkins.

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28 Apr 2013 07:30 #33309 by andypugh
Replied by andypugh on topic Dual X Servo
This is the HAL file I came up with, but I can't really test it.
The main point is that the HAL is now assuming a 3-axis machine, but with 4 PID controllers and 4 motors to drive.
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The following user(s) said Thank You: juwi

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28 Apr 2013 07:53 #33311 by juwi
Replied by juwi on topic Dual X Servo
michas_kleine.hal:111: Pin 'axis.0.motor-pos-cmd' was already linked to signal 'x1-pos-cmd'

exactly my problem...

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28 Apr 2013 08:25 #33312 by juwi
Replied by juwi on topic Dual X Servo

Hi
www.linuxcnc.org/index.php/english/forum...in-closed-loop#23714
Andy told me "simply" to:
"connect axis.1.motor-pos-cmd to both PID modules in the HAL"
How is this done?


I just tried to make your HAL file work as suggested, and I have realised that it is rather important to know if you intend to use index-homing on both sides of the gantry.

I think I need to have a good long think about how to do homing on a gantry axis that uses servos and trivkins.


Homing is almost irrelevant, because I can home the machine by hand - its quite small - or by a special homing config with gantrykins...

My Problem is that hal forbids to add more than one outs to a net...

best regards

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28 Apr 2013 19:03 #33323 by andypugh
Replied by andypugh on topic Dual X Servo

My Problem is that hal forbids to add more than one outs to a net...


Yes, only one of the pins in the net can be an output (such as axis.0.motor-pos-cmd). This is logical, as otherwise the value of the net is ambiguous.

To use one output to drive multiple inputs you can use any of the following structures.

net x-pos axis.0.motor-pos-cmd => pid.0.command pid.1.command

or

net x-pos axis.0.motor-pos-cmd=> pid.0.command
net x-pos pid.1.command

or

net x-pos axis.0.motor-pos-cmd
net x-pos pid.0.command
net x-pos pid.1.command

So, each signal (the label directly after the "net" command) can have only one output pin connected, but can have as many input pins as you need.

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28 Apr 2013 19:07 #33324 by juwi
Replied by juwi on topic Dual X Servo
This works, but leads to a following error on the slave axis after exceeding max-ferror...

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28 Apr 2013 19:12 #33325 by andypugh
Replied by andypugh on topic Dual X Servo
If the motors point in different directions then you will need a negative encoder scale on one of them.

Each PID component needs to be connected to the same command position pin, but to its own feedback position pin.

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28 Apr 2013 19:26 #33327 by juwi
Replied by juwi on topic Dual X Servo
I write on my mobile, therefore short...

I left everything of the slave axis as it was, just connect the pid.commanded from y.pos to both. Result is following error after exceeding fferror-max.

Both are setup identical and rotate in the same direction...

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