THCAD Noise / THC comp movement
03 Nov 2016 07:01 #82367
by azeri
Replied by azeri on topic THCAD Noise / THC comp movement
Hi there,
About hardware limits, i use 400W Yaskaawa servos (3000 rpm, max 4000) with 15:1 gear reduction on both X and Y, and i use Yaskawa 100W servo (3000rpm, max 4000) direct to 5mm/rev ball screw, wich gives me up to 15000 mm/min and no problem with 1000mm/min acceleration.
About numbers, all my system works on mm, not on inches.
About PID on THC, there is a thread on this forum of BigJohn and other user discussing it, but there are not attachments, i found BigJohns THC comp with P, wich i still need to test (attached here).
I have thought about redoing THC comp ,but not as discussed here, to work with Linuxcnc "new" PID component, i'm going to think about it.
About hardware limits, i use 400W Yaskaawa servos (3000 rpm, max 4000) with 15:1 gear reduction on both X and Y, and i use Yaskawa 100W servo (3000rpm, max 4000) direct to 5mm/rev ball screw, wich gives me up to 15000 mm/min and no problem with 1000mm/min acceleration.
About numbers, all my system works on mm, not on inches.
About PID on THC, there is a thread on this forum of BigJohn and other user discussing it, but there are not attachments, i found BigJohns THC comp with P, wich i still need to test (attached here).
I have thought about redoing THC comp ,but not as discussed here, to work with Linuxcnc "new" PID component, i'm going to think about it.
The following user(s) said Thank You: Rick G
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03 Nov 2016 10:26 #82370
by rodw
This is quite interesting. Can you post a link to the discussion you referred to? I found a few relevant articles but I don't think I found that one. Here's the threads I found on this topic. It seems we've rediscovered what we've collectively forgotten yet again.
forum.linuxcnc.org/24-hal-components/30600-thc-component#71823
forum.linuxcnc.org/38-general-linuxcnc-q...d-control-loop#65832
forum.linuxcnc.org/38-general-linuxcnc-q...plasma-thc-questions
One thing I've learnt is that the default Plasma setup is generic and not designed for the Mesa THCAD. It would be good to get some history behind the PID code you've attached.. Eg is it in use, working or just a first cut.
I do have a stand alone THC here but when I ordered my Mesa 7i67e, International postage costs made it a no brainer to grab the Mease THCAD at the same time.
It will be quite a while before I get enough built to play with this.
Replied by rodw on topic THCAD Noise / THC comp movement
Hi there,
About PID on THC, there is a thread on this forum of BigJohn and other user discussing it, but there are not attachments, i found BigJohns THC comp with P, wich i still need to test (attached here).
I have thought about redoing THC comp ,but not as discussed here, to work with Linuxcnc "new" PID component, i'm going to think about it.
This is quite interesting. Can you post a link to the discussion you referred to? I found a few relevant articles but I don't think I found that one. Here's the threads I found on this topic. It seems we've rediscovered what we've collectively forgotten yet again.
forum.linuxcnc.org/24-hal-components/30600-thc-component#71823
forum.linuxcnc.org/38-general-linuxcnc-q...d-control-loop#65832
forum.linuxcnc.org/38-general-linuxcnc-q...plasma-thc-questions
One thing I've learnt is that the default Plasma setup is generic and not designed for the Mesa THCAD. It would be good to get some history behind the PID code you've attached.. Eg is it in use, working or just a first cut.
I do have a stand alone THC here but when I ordered my Mesa 7i67e, International postage costs made it a no brainer to grab the Mease THCAD at the same time.
It will be quite a while before I get enough built to play with this.
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03 Nov 2016 11:23 #82371
by Rick G
Replied by Rick G on topic THCAD Noise / THC comp movement
azeri,
Thanks for posting the thc pid, I had not seen that.
I do in fact have a modified thc comp I plan on testing this weekend and will try the thc pid you posted also.
Rick G
Thanks for posting the thc pid, I had not seen that.
I do in fact have a modified thc comp I plan on testing this weekend and will try the thc pid you posted also.
Rick G
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03 Nov 2016 18:06 #82384
by rodw
So if adjustments required by a pid mean that the z axis has to move more than one click as the bit bang approach does, isn't this required? However, rather than the arbitrary delay proposed by Rick, shouldn't we wait for the previous command to finish before adding another adjustment?
Eg
Perhaps this implies that PID based THC should be fully self contained. Will a stepper based system have different control requirements to a servo based system? I've been doing a bit of reading on pid algorithims and they don't look to hard to code.
Replied by rodw on topic THCAD Noise / THC comp movement
Perhaps modify the code to only apply a correction after so many cycles to give the z a chance to get into position.
So request a Z correction, wait 10 cycles before next correction can be made.
Rick G
So if adjustments required by a pid mean that the z axis has to move more than one click as the bit bang approach does, isn't this required? However, rather than the arbitrary delay proposed by Rick, shouldn't we wait for the previous command to finish before adding another adjustment?
Eg
if(still_moving)
do_nothing;
else
do_adjust_pid;Perhaps this implies that PID based THC should be fully self contained. Will a stepper based system have different control requirements to a servo based system? I've been doing a bit of reading on pid algorithims and they don't look to hard to code.
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03 Nov 2016 18:19 #82385
by andypugh
No, they are extremely simple.
This will work, but needs re-tuning if you change the servo thread frequency. That's not normally something that folk do, though.
Replied by andypugh on topic THCAD Noise / THC comp movement
I've been doing a bit of reading on pid algorithims and they don't look to hard to code.
No, they are extremely simple.
error = command - actual
I = I + error * Igain
P = error * Pgain
D = (error - old_error) * Dgain
out = P + I + D
old_error = errorThis will work, but needs re-tuning if you change the servo thread frequency. That's not normally something that folk do, though.
The following user(s) said Thank You: rodw
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03 Nov 2016 19:02 #82387
by azeri
Replied by azeri on topic THCAD Noise / THC comp movement
Hi there,
posted code is not mine, is BigJohT's published code. I think i started reading about it on this post:
forum.linuxcnc.org/27-driver-boards/3980...mesa-guru-s?start=60
but let me check somewhere else...
Best Regards,
Aitor.
posted code is not mine, is BigJohT's published code. I think i started reading about it on this post:
forum.linuxcnc.org/27-driver-boards/3980...mesa-guru-s?start=60
but let me check somewhere else...
Best Regards,
Aitor.
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03 Nov 2016 20:56 - 03 Nov 2016 21:28 #82390
by rodw
Very interesting thread. Got me to delve deeper.
Digging through the source, there are actually 2 versions of the THC component.
THC.comp for Mesa Hardware
THCUD.comp which for other hardware
The correct one (THC.comp) for the Mesa Card for V 2.7 is here
www.linuxcnc.org/docs/2.7/html/man/man9/thc.9.html
with source here
github.com/LinuxCNC/linuxcnc/blob/master.../components/thc.comp
You will see that the PID control has not been incorporated into the current stable release.
So I think you need to check which THC version you have deployed in your build.
Replied by rodw on topic THCAD Noise / THC comp movement
Hi there,
posted code is not mine, is BigJohT's published code. I think i started reading about it on this post:
forum.linuxcnc.org/27-driver-boards/3980...mesa-guru-s?start=60
but let me check somewhere else...
Best Regards,
Aitor.
Very interesting thread. Got me to delve deeper.
Digging through the source, there are actually 2 versions of the THC component.
THC.comp for Mesa Hardware
THCUD.comp which for other hardware
The correct one (THC.comp) for the Mesa Card for V 2.7 is here
www.linuxcnc.org/docs/2.7/html/man/man9/thc.9.html
with source here
github.com/LinuxCNC/linuxcnc/blob/master.../components/thc.comp
You will see that the PID control has not been incorporated into the current stable release.
So I think you need to check which THC version you have deployed in your build.
Last edit: 03 Nov 2016 21:28 by rodw. Reason: Removed some incorrect information
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03 Nov 2016 21:17 - 03 Nov 2016 21:18 #82393
by azeri
Replied by azeri on topic THCAD Noise / THC comp movement
Dear rodw,
i cant see any PID there. and the source (where i cant see PID neither) is for master branch, wich if im not wrong is now the 2.8-pre.
Of course, for us, THC comp is the good one, but on some threads, THCUD and THC are mixed.
Best Regards,
Azeri.
i cant see any PID there. and the source (where i cant see PID neither) is for master branch, wich if im not wrong is now the 2.8-pre.
Of course, for us, THC comp is the good one, but on some threads, THCUD and THC are mixed.
Best Regards,
Azeri.
Last edit: 03 Nov 2016 21:18 by azeri.
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03 Nov 2016 21:20 #82394
by rodw
Replied by rodw on topic THCAD Noise / THC comp movement
Oops, my mistake, I just realised I was wrong. Gotta get to work.
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