Center Spot Sheetcam Post

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12 Sep 2019 23:08 #145000 by phillc54
Replied by phillc54 on topic Center Spot Sheetcam Post
Looking at the performance of JTknives spotting has just about convinced me that voltage level is the way to go.

I think that using a timer has too many variables with relay response and machine response that it will not be consistent.

I will make a test comp but I won't get a chance today as I have other commitments.
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13 Sep 2019 01:47 - 13 Sep 2019 01:50 #145016 by docwelch
Replied by docwelch on topic Center Spot Sheetcam Post
As another data point, I have a one month old Hypertherm Powermax 45xp that shows the same behavior with spotting. When the torch moves to the first position, it moves to pierce height and fires the torch (110ms creates a nice dimple for me in 18g material). When the machine moves to the next location, it goes to pierce height but does not fire. The air is flowing from the first pierce. but when it tries to fire the second time, it turns off the air. Moving to the third pierce, everything works again.

Putting a G4 P20 between the first and second location does make it all work correctly. I tried a G4 P10 but it did not work. It seemed I had to wait long enough for the air to turn off (20 seconds). I suspect this is some "feature" of the machine itself but have not had a chance to call and ask Hypertherm.

I had considered just setting up my post processor to make a second tiny move and attempt to fire the torch a second time before moving to the actual second location. I think that would work but certainly is not very elegant.

Of note, the GUI showed 70V when the torch fired. For 18g material, the cut chart recommends 78V.

I use my own design board with a TLP222AF (solid state relay chip) to turn on/off the torch. The data sheet indicates a max turn on time of 2mS and max turn off time of 0.5mS.

Please let me know when you get the new version ready - I would be happy to test.

Steven
Last edit: 13 Sep 2019 01:50 by docwelch. Reason: Added that I would be willing to help test
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13 Sep 2019 06:25 #145026 by phillc54
Replied by phillc54 on topic Center Spot Sheetcam Post
Is 110ms long enough for the machine to set the transfer signal, I am guessing here that it is not so the machine goes into a fail mode that requires time to reset.

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13 Sep 2019 08:08 #145032 by phillc54
Replied by phillc54 on topic Center Spot Sheetcam Post
Attached is the experimental plasmac component for voltage based spotting.

It uses Centre Spot Torch On Time (which is for this exercise Voltage Threshold) in the following ways:
  • If the value is below the voltage reached for your Arc OK then this is the voltage the torch will turn off at.
  • If the value is above the voltage reached for your Arc OK and the value is below 300 then the torch will turn off when Arc OK is received.
  • If the value is above 300 then the torch will turn off (value - 300) milli-seconds after Arc OK is received.
    e.g. a value of 450 would turn the torch off 150 mS after receiving Arc OK
I know it is a bit funky but I want it to be reasonably flexible for testing purposes without too many changes.

I haven't added an arc fail timer yet so if the torch doesn't fire then it will just wait with the torch on signal active.

If you rename your existing plasmac.comp (which is probably in ~/linuxcnc-dev/src/hal/components) to plasmac.comp.old then copy this one to that directory then rebuild as you normally do then it should be installed.
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13 Sep 2019 08:20 #145034 by rodw
Replied by rodw on topic Center Spot Sheetcam Post
Phill, did you allow for machines that have an ArcOK signal?
It seems to me that is the problem Stefan and the Doctor had because we were trying to turn the arc off before the ArcOK was issued.

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13 Sep 2019 08:23 #145035 by phillc54
Replied by phillc54 on topic Center Spot Sheetcam Post
Rod,

The second and third points rely on the Arc OK signal.

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13 Sep 2019 10:05 #145043 by tommylight
It was my opinion (and still is) that time based marking will not work as every plasma cutter has a different response time. This is mainly due to use of RC (resistor / capacitor) time delays in them so the reaction time is not consistent.
On an old Hypertherm MAX 45 or similar, the time from signal to fire the torch to when it actually fires the torch is from 3 to 5 seconds, and it varies a lot especially when there is a short period between fires.
Maybe the new ones use proper timers, but i have not seen any of those yet.

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13 Sep 2019 10:29 #145047 by phillc54
Replied by phillc54 on topic Center Spot Sheetcam Post

tommylight wrote: It was my opinion (and still is) that time based marking will not work as every plasma cutter has a different response time. .

Yes, I think the results here are a confirmation of that.
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13 Sep 2019 11:03 #145048 by rodw
Replied by rodw on topic Center Spot Sheetcam Post
Well from what I saw in its present format as coded, this feature is not usable if you have an arcOK signal as you can't go shorter than this time frame and on my machine thats a pretty big divot.

I'm sorry my cool idea wasted Phill's time.

I Agree there is a lot of unknown latency in the system once the spindle on signal is enabled. I think some halscope plots are in order.

I started to write a separate component today that commenced the timer when the arc was sensed by my hypersensing component. My torch on relay turns off in 2 usec so any latency will be in the machine.

I do know somebody who had great success using current to set an ArcOK signal and also for spotting. But he hacked his machine, added a current sensor and built and programmed his own external THC using a microprocessor.

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13 Sep 2019 11:36 #145051 by tommylight
There are cheap current sensors that can be used for this or diy versions of it with hal sensors, they do require a bit of work and opening the plasma if using the DC side, but even that can be measured at the cables.
Measuring AC side is easier but it does require rectifying and filtering and so does the DC cable side.
Reed relay on the DC cable might work fast enough.
Do any of you have a reed relay to test that ?
Or any satelite dish motor, they have 2 of those inside.
3 windings are enough.

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