THC Component
- islander261
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16 Mar 2016 16:42 #71730
by islander261
THC Component was created by islander261
Hello
This maybe really old ground but I couldn't find any earlier posts. Many of the commercial THCs use a PID loop to control the torch height based on the arc voltage. I notice that the THC component just uses a velocity error for correction. What is the reason for this? Was a PID tried and failed to work?
On other forums dedicated to plasma cutting one of the settings that seems to be needed for best cut quality is a delay between the start of torch motion and start of the THC height servo (torch moves at initial cutting height). This is allegedly to give the torch time to reach cut speed and the arc voltage to stabilize ( it is usually longer than just the time require to accelerate to cutting speed). Is this not needed with the THC component and the Mesa THCad card? If I want to add this functionally what is the recommended method?
One last thing, if I modify a component what is the correct etiquette for for crediting the original author for the starting point?
John
This maybe really old ground but I couldn't find any earlier posts. Many of the commercial THCs use a PID loop to control the torch height based on the arc voltage. I notice that the THC component just uses a velocity error for correction. What is the reason for this? Was a PID tried and failed to work?
On other forums dedicated to plasma cutting one of the settings that seems to be needed for best cut quality is a delay between the start of torch motion and start of the THC height servo (torch moves at initial cutting height). This is allegedly to give the torch time to reach cut speed and the arc voltage to stabilize ( it is usually longer than just the time require to accelerate to cutting speed). Is this not needed with the THC component and the Mesa THCad card? If I want to add this functionally what is the recommended method?
One last thing, if I modify a component what is the correct etiquette for for crediting the original author for the starting point?
John
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16 Mar 2016 17:30 - 16 Mar 2016 17:30 #71734
by PCW
Replied by PCW on topic THC Component
Might be easiest, at least at first to simply bring out the required pins
and wire them to an external PID component (I think I advocated this a couple years ago)
and wire them to an external PID component (I think I advocated this a couple years ago)
Last edit: 16 Mar 2016 17:30 by PCW.
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16 Mar 2016 17:36 - 16 Mar 2016 17:37 #71735
by mariusl
Regards
Marius
www.bluearccnc.com
Replied by mariusl on topic THC Component
The current THUD component is made for bit bang hardware. The PID loop or comparator is done in hardware and the THUD component just receives a signal to tell it to move the torch up or down. The inclusion of the crude velocity calculations are to do just that, crude velocity control.
THC is not a functional part of cnc control loops and hence the external control logic.
I suggest that you start your own component as the current THCUD does exactly what is required for bit bang hardware.
An external PID loop component would be welcomed by the community.
THC is not a functional part of cnc control loops and hence the external control logic.
I suggest that you start your own component as the current THCUD does exactly what is required for bit bang hardware.
An external PID loop component would be welcomed by the community.
Regards
Marius
www.bluearccnc.com
Last edit: 16 Mar 2016 17:37 by mariusl.
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- islander261
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16 Mar 2016 18:08 #71737
by islander261
Replied by islander261 on topic THC Component
Please pardon my ignorance in these maters. To add an external PID loop to the THC component I will need to:
1. Rework the THC component source code adding pins (input the PID output) and compile it.
2. Add another PID instance in HAL.
3. Create nets in HAL to connect pins to signals.
I think that my more immediate need will be to add the servo start delay, I know this has a dramatic effect with my present THC.
John
1. Rework the THC component source code adding pins (input the PID output) and compile it.
2. Add another PID instance in HAL.
3. Create nets in HAL to connect pins to signals.
I think that my more immediate need will be to add the servo start delay, I know this has a dramatic effect with my present THC.
John
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16 Mar 2016 19:34 - 16 Mar 2016 19:35 #71743
by mariusl
Regards
Marius
www.bluearccnc.com
Replied by mariusl on topic THC Component
You will have to create another component that will have the pins that you require as well as the code that is needed.
The current THCUD component will not work for PID. If you add the PID to the bit bang component you might break it for other users. Rather copy the component to use it as a template to start with but add and insert your own logic and code.
So you will typically create a component named THCPID for example.
Just for clarity - to use a PID loop
1: you will read an analog voltage of sorts from any hardware (THCAD from Mesa).
2: you will have to know what voltage you require the PID to track to.
3: you will create pins for hal to connect your component to an external PID component OR
4: you will write your own PID loop controller in the component. ( you already have a steady 1ms servo loop or any other that you want to create). So PID is not that hard to do.
5: you will connect your command signal to the Z axis in similar fashion as the THCUD component OR
you can provide the UP/DOWN signals from your PID component and connect them to the THCUD component that already exist
.
The current THCUD component will not work for PID. If you add the PID to the bit bang component you might break it for other users. Rather copy the component to use it as a template to start with but add and insert your own logic and code.
So you will typically create a component named THCPID for example.
Just for clarity - to use a PID loop
1: you will read an analog voltage of sorts from any hardware (THCAD from Mesa).
2: you will have to know what voltage you require the PID to track to.
3: you will create pins for hal to connect your component to an external PID component OR
4: you will write your own PID loop controller in the component. ( you already have a steady 1ms servo loop or any other that you want to create). So PID is not that hard to do.
5: you will connect your command signal to the Z axis in similar fashion as the THCUD component OR
you can provide the UP/DOWN signals from your PID component and connect them to the THCUD component that already exist
.
Regards
Marius
www.bluearccnc.com
Last edit: 16 Mar 2016 19:35 by mariusl.
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- islander261
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16 Mar 2016 20:16 #71744
by islander261
Replied by islander261 on topic THC Component
Thank you. I am thinking of starting with the plain THC component not the THCUD as I have a Mesa THCad card. The THC component already uses the encoder velocity pin as the input. I believe it also has has an input pin (THC.volts_requested) to hook desired arc voltage to.
John
John
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17 Mar 2016 06:38 #71764
by Rick G
Replied by Rick G on topic THC Component
The THC component...
linuxcnc.org/docs/html/man/man9/thc.9.html
Adjust the torch height based on the current arc voltage and the requested arc voltage.
It only makes corrections if the torch is on, the THC is on, the arc O.K. signal is good, the velocity is in range, etc.
I believe it is expected that the velocity will be reached and the arc will stabilize during the lead in portion of the cut.
Rick G
linuxcnc.org/docs/html/man/man9/thc.9.html
Adjust the torch height based on the current arc voltage and the requested arc voltage.
It only makes corrections if the torch is on, the THC is on, the arc O.K. signal is good, the velocity is in range, etc.
I believe it is expected that the velocity will be reached and the arc will stabilize during the lead in portion of the cut.
Rick G
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- islander261
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17 Mar 2016 15:14 #71799
by islander261
Replied by islander261 on topic THC Component
Thank you.
I have limited experience plasma cutting, we only do about 200lbs of 14ga a week here. Post cutting operations are a non trivial cost (time and materials) in our production setting so anything we can do to increase cut quality pays back quickly. With our current equipment I have found the use of a delay after motion starts until the THC starts servoing to be a requirement for good cut quality. The minimum delay we use is 3 times the movement distance required to come to full speed. The usual distance (time) is even greater. Now all of this maybe do to the poor design/performance of our current THC so using the Mesa THCad card and LCNC my make eliminate this requirement.
John
I have limited experience plasma cutting, we only do about 200lbs of 14ga a week here. Post cutting operations are a non trivial cost (time and materials) in our production setting so anything we can do to increase cut quality pays back quickly. With our current equipment I have found the use of a delay after motion starts until the THC starts servoing to be a requirement for good cut quality. The minimum delay we use is 3 times the movement distance required to come to full speed. The usual distance (time) is even greater. Now all of this maybe do to the poor design/performance of our current THC so using the Mesa THCad card and LCNC my make eliminate this requirement.
John
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17 Mar 2016 18:17 #71823
by BigJohnT
I have a thcpid as Peter advised but have not pushed it for no reason other than being busy. I'll be back Monday remind me.
JT
Replied by BigJohnT on topic THC Component
Hello
This maybe really old ground but I couldn't find any earlier posts. Many of the commercial THCs use a PID loop to control the torch height based on the arc voltage. I notice that the THC component just uses a velocity error for correction. What is the reason for this? Was a PID tried and failed to work?
On other forums dedicated to plasma cutting one of the settings that seems to be needed for best cut quality is a delay between the start of torch motion and start of the THC height servo (torch moves at initial cutting height). This is allegedly to give the torch time to reach cut speed and the arc voltage to stabilize ( it is usually longer than just the time require to accelerate to cutting speed). Is this not needed with the THC component and the Mesa THCad card? If I want to add this functionally what is the recommended method?
One last thing, if I modify a component what is the correct etiquette for for crediting the original author for the starting point?
John
I have a thcpid as Peter advised but have not pushed it for no reason other than being busy. I'll be back Monday remind me.
JT
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18 Mar 2016 15:18 #71867
by andypugh
You can delay THC activation using time in HAL. Distance is probably possible too.
Replied by andypugh on topic THC Component
With our current equipment I have found the use of a delay after motion starts until the THC starts servoing to be a requirement for good cut quality. The minimum delay we use is 3 times the movement distance required to come to full speed.
You can delay THC activation using time in HAL. Distance is probably possible too.
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