Hypersensing with THCAD - better way to do ohmic sensing

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14 Nov 2020 08:21 - 14 Nov 2020 08:34 #189303 by stivemaster13

It does not cause a delay in operation and does not allow a drop of water to remain in the nozzle!

It does, about 2 seconds for every probe, so some of us doing about 2400 probes per session can not afford that. Pretty sure Rod and Stefan had more than that.


I can not understand you ? What does it take 2 seconds? What I have written takes a maximum of 40 ms at the UCCNC. On Mach3 it takes 50ms.
This trick works even on our transformer sources, to which we have added an interruption of the cooling cycle, which generally lasts 15 seconds!

I have another question - does anyone have observations (ie the graph of the voltage change) that PlasmaC (or actually THCAD) sees when the burner touches the material during cutting? And is this being handled in any way, like an emergency?
I ask in terms of what I went through while developing our THC.
Last edit: 14 Nov 2020 08:34 by stivemaster13.

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14 Nov 2020 08:53 #189305 by rodw

I can not understand you ? What does it take 2 seconds? What I have written takes a maximum of 40 ms at the UCCNC. On Mach3 it takes 50ms.
This trick works even on our transformer sources, to which we have added an interruption of the cooling cycle, which generally lasts 15 seconds!


The hypersensing method we've devised (which thefabricator03 is not yet using) seems to have solved the problem and its in use by quite a few now on several different brands of machines.

I have another question - does anyone have observations (ie the graph of the voltage change) that PlasmaC (or actually THCAD) sees when the burner touches the material during cutting? And is this being handled in any way, like an emergency?
I ask in terms of what I went through while developing our THC.


When I first started with plasma and linuxcnc before Plasmac, I did lot of halscope plots and had the torch hit the material many times. I don't recall observing any behaviour that was measurable. I did collect a lot of data and analysed it statistically. For that particular machine I measured 7.53 volts per mm of height. At 1.75mm cut height, I guess it wold hit the table on a fall of about 13 volts.

With Plasmac it has never hit the table.

You could disable downward height adjustments if the torch voltage fell by say 7-10 volts from the original sample. That would let the torch rise to cut height if it sorted itself out.

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14 Nov 2020 10:39 #189316 by stivemaster13

I can not understand you ? What does it take 2 seconds? What I have written takes a maximum of 40 ms at the UCCNC. On Mach3 it takes 50ms.
This trick works even on our transformer sources, to which we have added an interruption of the cooling cycle, which generally lasts 15 seconds!


The hypersensing method we've devised (which thefabricator03 is not yet using) seems to have solved the problem and its in use by quite a few now on several different brands of machines.

I have another question - does anyone have observations (ie the graph of the voltage change) that PlasmaC (or actually THCAD) sees when the burner touches the material during cutting? And is this being handled in any way, like an emergency?
I ask in terms of what I went through while developing our THC.


When I first started with plasma and linuxcnc before Plasmac, I did lot of halscope plots and had the torch hit the material many times. I don't recall observing any behaviour that was measurable. I did collect a lot of data and analysed it statistically. For that particular machine I measured 7.53 volts per mm of height. At 1.75mm cut height, I guess it wold hit the table on a fall of about 13 volts.

With Plasmac it has never hit the table.

You could disable downward height adjustments if the torch voltage fell by say 7-10 volts from the original sample. That would let the torch rise to cut height if it sorted itself out.




Your first quote is my answer to a question. This does not mean that I underestimate in any way what you have achieved so far. On the contrary, all the time it is important for me to eliminate all the unfavorable factors that affect the good work!
In this sense is my other question. Sopita further you will see that no matter how well THC works, collisions collide and that is why even controllers with a price of 6500 pounds have such protection.
It can be done in two ways. One is to keep an eye on Probe contact, but this is dangerous with some burners. The way you connected THCAD will not work. The other way is to set a fixed distance to be set for upward movement along the Z axis if the monitored voltage drops sharply below a certain threshold.
I say this as an occasion to think, because it is obviously too early in your development.
For me, when we started developing our own THC in order to achieve the best possible result, we did (as far as we could, of course) a retro design by Burny Inova.
Here is a very good read.

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14 Nov 2020 11:33 #189318 by rodw
Thanks for the link, I learnt something.

Its coming back to me now. Pre-Plasmac, I did get some issues with the torch touching the material, Because we were using gcode probing, when this happened, Linuxcnc would pause motion becasue the probe was triggered unexpectedly. So I made some changes so this probe signal was ignored while cutting. I did think of revising the action so the torch was lifted if the probe was enabled.

But before I did that I migrated to Plasmac and focussed my efforts to ensure my findings were incorporated into the emerging Plasmac controller.

Then we worked on the Hypersensing and I realised that it would not be possible to sense material contact while cutting. I suspect in time that will be possible but not with current hardware.

But yet again you have not grasped the fact that Plasmac is far more sophisticated than the Kaliburn system you linked to. Plasmac is integrated to the motion controller and an up/down THC isn't.

The other advantage is that Plasmac has hundreds (maybe thousands) of testers. Not one of those testers has raised the need for material sensing while cutting. If they had reported this as an issue, I am sure a solution would have been developed. Such is the power of open source.
The following user(s) said Thank You: thefabricator03, dvn4life1972

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14 Nov 2020 12:30 - 14 Nov 2020 12:38 #189323 by stivemaster13
Well, if you say so.
However, can you still explain exactly how you solved the problem with the sharp rise in voltage when going through a hole. As far as I understand you have worked on this. Hypertherm as you can see used for a limit of 12 volts (unfortunately it is not written for what period of time).
We used 15 volts for 300 ms (the same could be done with a sharp drop in voltage in a collision. Only here we need an active action - raising the torch)
In addition, in my opinion, an analysis of the curvature of the part is needed in order to be able to reduce the reaction rate of the axis. Otherwise, if we assume that our THC regulates by more than 5000 mm / min, then the speed becomes dangerous and means that a collision may occur after passing the hole. Simply because it will not be able to stop immediately.

And is it possible to add a record of the cut distance from the consumable? In this way, it is very easy to keep track of the time to change. Is this a very valuable feature of branded Plasma CNCs?

Hey Rod, I'm constructive all the time, I hope you understand. Despite the strange English, I'm not picky.
Last edit: 14 Nov 2020 12:38 by stivemaster13.
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14 Nov 2020 13:20 #189329 by tommylight
Just cut some 2mm alu sheet, mildly wobbly, at 7m/m and the THC tracked perfectly not touching the surface ever. :)

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14 Nov 2020 15:54 #189341 by snowgoer540
Plasmac currently pauses motion if the float switch is activated during a cut.

I think rods .comp is set to ignore the ohmic sensing while cutting though.

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14 Nov 2020 18:06 #189356 by tommylight

Plasmac currently pauses motion if the float switch is activated during a cut.

Yes it does !
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14 Nov 2020 18:41 #189361 by stivemaster13
I did not mean the cutting speed but the one with which the THC itself regulates.

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14 Nov 2020 18:54 #189366 by tommylight
The THC speed will depend on a lot of factors, so to remove one of those factors i made the Z axis capable of moving at 12m/m aaand had to slow them down to 6m/m or even less. PlasmaC has THC speed settable in the Config panel, it is at 10 by default and i do change it sometimes depending on what i am cutting, thinner material at 12 and thicker at 8 works best for me. If i set it at 15 it will track so fast that when it gets to the end of the material when hand cutting it risks putting a hole on the water table about 7cm below the material. :)
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