THC Velocity lock and void lock

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17 Sep 2020 12:17 #182535 by phillc54

Just been talking to a customer and realized that there is a very important use for Void Lock. It is used when one does chain cutting on a job and it is not always possible to route the cut path to miss a previous kerf.
Please keep this feature!!

I am pretty sure it is staying there, just did not have the chance to give it a thorough test and report back to Phill .

Yep, I have no intention of removing it. IMHO even if only one person uses a feature then that is a good enough reason to keep it.

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17 Sep 2020 12:21 #182536 by rodw
It just goes to show how few people are interested in void lock as we do not have any issues raised. Phill has tested a method and included it in Plasmac. I would prefer to use a different method that tracks the dv/dt (change in voltage over change in time).

Its just so hard and time consuming to test as you have to do lots of cutting and plot results in halscope.

You should give the Plasmac method a run and report back!

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17 Sep 2020 12:27 #182537 by phillc54

It just goes to show how few people are interested in void lock as we do not have any issues raised. Phill has tested a method and included it in Plasmac. I would prefer to use a different method that tracks the dv/dt (change in voltage over change in time).

Its just so hard and time consuming to test as you have to do lots of cutting and plot results in halscope.

You should give the Plasmac method a run and report back!

The PlasmaC method uses the change in voltage each servo period.

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17 Sep 2020 12:34 #182539 by rodw
My method which I started working on before plasmac (after reading some papers) calculates a moving average and then it has a bench mark over the last n readings. The theory is that the dv/dt when crossing a kerf is exponentially larger than what is caused from simple warpage so its a very responsive signal of kerf crossing. Who knows which is the better method?

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17 Sep 2020 13:19 #182542 by mariusl
I think that it does need testing. I had to turn it off on the last machine I did as it was coming on even during normal cutting. I don't have access to a machine currently but I will be doing another machine soon. I will test if it is not done by then.

Regards
Marius


www.bluearccnc.com

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17 Sep 2020 13:41 #182545 by rodw

I think that it does need testing. I had to turn it off on the last machine I did as it was coming on even during normal cutting. I don't have access to a machine currently but I will be doing another machine soon. I will test if it is not done by then.


I did not have that problem and there is a dv/dt threshold you can alter to control sensitivity. I had it working except for a false trigger at the end of a cut as that causes a spike too. I decided to rewrite it to be clearer (as a state machine) once I understood the behaviour but broke it and have never got back to it.

And yes, we can't have false triggers. I had a few while testing.

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17 Sep 2020 13:51 #182546 by mariusl

I think that it does need testing. I had to turn it off on the last machine I did as it was coming on even during normal cutting. I don't have access to a machine currently but I will be doing another machine soon. I will test if it is not done by then.


I did not have that problem and there is a dv/dt threshold you can alter to control sensitivity. I had it working except for a false trigger at the end of a cut as that causes a spike too. I decided to rewrite it to be clearer (as a state machine) once I understood the behaviour but broke it and have never got back to it.

And yes, we can't have false triggers. I had a few while testing.


That kind of error will not do any harm. If it is at the end of the cut and the THC is disabled it will do no harm. I think.

Regards
Marius


www.bluearccnc.com

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13 Jul 2021 05:05 #214481 by grijalvap
Hi, I have finally Tested the QTplasmaC in the field, everithing works fine it is great piece of software thanks to all for this great work.
I see an inprovement oportunity in the void lock section.
I did set up the plasma void lock to 200% and it worked well for 14G steel and 45 amps consumables in a hyperterm 85 plasma
then I changed the material to 3/16 steel and the consumables to 85A.
I see false trigers during the down part of travel in parts with inclination.
I see the comments from RODW about the dv/dt method  and I agree with that method because you have  "historical averange value" from previuos interactions, however i did someting similar in the past and never coud make it work well, since diferent materials have diferent voltage and kerf.  so I was thinking if we can tie the void lock treshold to te material.
then have a diferent one for each mairial.

Any thogths?

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13 Jul 2021 05:30 #214487 by phillc54
Currently it measures the change in voltage each servo cycle and reacts if it is greater than the threshold for n number of cycles, I don't see how giving it a dv/dt value will improve it. I think what we need are the threshold values and/or cycles required for different materials etc.
It works for me at 100% and 2 cycles with what I do but all of my cutting is only 1.6mm or 2mm with a 30A machine.
Without any decent feedback on this it have not bothered to do any more as I am limited to what mt machine can do. A couple of users have had an issue and after I made suggestions I didn't hear back so I realyy have no clue as to whether they were succesful or not. Rod consistenly saying that the plasmac algorithm is wrong has been of no help at all. 

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13 Jul 2021 05:48 #214489 by grijalvap
undertand, I will make some measurements and give you some data and plots,

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