THC experimental

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19 Jan 2017 15:32 - 03 Feb 2017 05:50 #86156 by Rick G
THC experimental was created by Rick G
We have been using the Mesa THCAD and JT's THC for a while now and the combination works great.
Occasionally the question of using it on corrugated or dramatically bent work comes up.

If you keep your correction factor small all is well on relatively flat work, but the torch height control may react too slowly for rapid changes in height.
If you then increase the correction factor too large the torch will over correct and start oscillating up and down across the cut.
This seems to be because the THC is calling for more and more corrections before the z axis can react and reach it's new commanded position.
So there can be a constant overshoot up and down across the cut.

Here is an experimental edited version of your THC comp.
The hope is to allow larger corrections without oscillating up and down for say cutting corrugated steel.

Currently
THC voltage => lowpass.0 => THCR.comp => lowpass.1 =>
The math is in long form to try to make it easier to read.

The major changes...
Do not make a correction until the Z axis has gotten to within the Z tolerance of the last correction position it was sent to with a possible delay period.

The size of the correction is proportional to the difference in voltage up to the maximum voltage change.
So if the maximum voltage change setting is 5 volts and the z correction setting is .01".
A voltage difference of 2.5 volts would mean a correction of .005".
5 / 2.5 = 2
.01 / 2 = .005
The correction is then averaged with the last correction and sent out.

Several pins have been added to bring out to the panel for testing.
Also the THC correction factor can be brought out to the panel so can be set low for flat work and higher when needed
There is some redundancy in that the original concept was to have the THC self contained, but there seems to be a benefit to using the lowpass.
We have been swamped at work and so have not been in the shop for almost a month now, but plan to clean it up when time allows.

For some testing we cut out 4" x 3" rectangles in light gauge steel.
We then bent them and cut .4" x 3" rectangles.
The bend is roughly 1" change in height over 1 1/2" of Y travel.


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Last edit: 03 Feb 2017 05:50 by Rick G.
The following user(s) said Thank You: BigJohnT, rodw

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19 Jan 2017 17:29 #86172 by BigJohnT
Replied by BigJohnT on topic THC experimental
Hi Rick,

Not fully understanding the code yet, just took a quick look and want to say thanks for sharing this. What is the Z delay and where do you get or connect that to?

JT

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19 Jan 2017 17:41 #86177 by tommylight
Replied by tommylight on topic THC experimental
There is still a bit of jumping or bunny hopping as i like to call it on the flat part, but that is quite impressive. Good job !
Regards,
Tom

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19 Jan 2017 23:03 - 28 Jan 2017 22:01 #86208 by rodw
Replied by rodw on topic THC experimental
Awesome, thanks Rick, a few of us have been waiting for you to post this. (but it will still be a while before I can turn a torch on). I'm going to review in detail.
Last edit: 28 Jan 2017 22:01 by rodw.

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20 Jan 2017 15:09 #86254 by Rick G
Replied by Rick G on topic THC experimental
Morning John,

Thee idea of the z delay was to wait so many cycles between the last correction move and the next voltage reading to give the voltage a chance to stabilize before making the next correction. I just set it to 0 for now. In the little bit of testing I have done it has not proven beneficial to set it higher yet. It just seems to make things a bit lazy.

Rick G

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20 Jan 2017 15:58 #86259 by Rick G
Replied by Rick G on topic THC experimental
Tom,

Thanks for testing.

If the commanded correction is too great it can still overshoot, Say there is a 2 volt change and a 2 volt change equals .005" and the commanded correction is .010" it will overshoot, but only by one commanded position not possibly several. So if it does hop they should be small hops. Sort of like a narrow band O2 sensor searching for the right mix.
Of course the goal was no hops.
I set up Hal Scope and monitored Z up and Z down to try and find the best settings.
The z axis seems to move smother with a low Z correction which is why I think the Z correction should be brought out to the panel and set low for a smooth quality cut on flat work and higher for bent work so it can follow the contour.
There are several settings to adjust.
Besides the voltage tolerance and the Z correction amount there is "Voltage difference for full correction" which is used to calculate the proportional size of the z correction based on the voltage difference. The low pass gain can also be adjusted.

Rick G

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20 Jan 2017 18:25 #86268 by tommylight
Replied by tommylight on topic THC experimental
Rick, if you are referring to me, i did not test it, i just had a look at the code.
It is nice that it limits the amount of correction so it does not jump a lot, and makes for nicer cuts even when the correction value is set high.
On the configs i use, i have a setting on the panel for the amount of correction to be applied to Z axis with every up or down pulse, so when cutting flat i set it at a lower value to get smooth cuts, and set it higher when cutting easily bending material or slopes, makes cuts with a bit of bunny hoping but gets the job done nicely.
Will have to wait till the next run of ordering Mesa boards to get a THCAD and play with it, gona take a while.
First order of business is finishing the Elumatec retrofit, still a lot to do as i am limited with the time i can spend there, usually 2-4 hours a day. To cold even with heating, dang i miss the summer.
Regards,
Tom
P.S.
I did register with Texas Instruments, and they will happily ship samples of some voltage to frequency converters, but there is no Kosovo in the shipping states. I really hate that since US is the first state that recognised it as an independent state. That is the reason i have to find ways of getting stuff from abroad, and that takes a lot of time.

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22 Jan 2017 06:35 #86395 by rodw
Replied by rodw on topic THC experimental
Rick, I've been slaving away at implementing the current THC.comp in master and after implementing corner lock in my GUI, I found that the pin is never used in the current code.
pin in float vel_tol "Velocity Tolerance (Corner Lock)";

github.com/LinuxCNC/linuxcnc/blob/master.../components/thc.comp

I see your code does use the vel-tol pin. I wonder if there has been a regression in the current master code?

Looks like I'm going to learn how to compile HAL components now...

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22 Jan 2017 21:32 #86428 by Rick G
Replied by Rick G on topic THC experimental
rodw,

There seems to be a few versions of the THC out there. That one uses a parameter that you can set / change in Hal.
If you are working on your panel you might want to bring the THC correction amount out to the panel also as Tommylight has mentioned.

Rick G
The following user(s) said Thank You: rodw, grijalvap

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22 Jan 2017 21:55 #86431 by tommylight
Replied by tommylight on topic THC experimental
Did anyone have a look at that config to see the panel? It has everything needed except the voltage.
I am refering to the config i use, thread is something like "thc that works".
There is also a version of it that uses voltage and has voltage setings on the panel, named vldthc or similar, also on this forum. Those are the panels that have everything you might need for a thc, the only thing i can think of worth adding are presets for say 3mm 5mm and 10mm with respective feeds and voltages and other settings.
I might add that after i finish this job of retrofiting the Elumatec.
Regards,
Tom

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