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Author Topic: Plasma Application, Mach3 torch height control.  (Read 123658 times)

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Re: Plasma Application, Mach3 torch height control.
« Reply #20 on: March 04, 2009, 02:57:57 PM »
Dave,

just shout if you need any help

matt
Re: Plasma Application, Mach3 torch height control.
« Reply #21 on: March 05, 2009, 05:00:15 AM »
Okay Matt I'm Shouting....
I got bad news for the people I ordered the pokeys from, they are out of stock, should have sometime in the next two weeks, ugh!!!
Any way I'm getting a grasp on what you have done IE: voltage devider and all some of that... its the brain(which every time I type that word I get a chuckle..wish I had a _____).. anyway if you could send me a copy of (LOL) your brain and the screens, or post them up here so other people can grasp also.
If not I understand And I'll keep working on it.
The brain thing still makes me laugh.

Dave
Re: Plasma Application, Mach3 torch height control.
« Reply #22 on: March 05, 2009, 08:31:36 AM »
dave,

due to miss spelling i tend to refewr to them as brians, ill fetch them off the shop machine and post them up for you to have a look at..

matt
Re: Plasma Application, Mach3 torch height control.
« Reply #23 on: March 08, 2009, 04:50:35 PM »
here are the three brains i ue, i ll let you look at them to try to work it out before i tell you how it works!

matt
Re: Plasma Application, Mach3 torch height control.
« Reply #24 on: March 09, 2009, 01:33:40 AM »
Thanks Matt, I'll take a look when I get home, as I'm at work right now,
One other question, after I understand more about how this is done I had a thought...
could you use a current transducer, say one that puts out the o-5v,or one that is 4-20ma, to the pokeys to do something similar.
Maybe you have tried this
Thanks again
Dave
Re: Plasma Application, Mach3 torch height control.
« Reply #25 on: March 09, 2009, 03:01:33 AM »
dave,

if ive got you right you mean a transducer which will put out a 0-5v signal dependant on the current in the plasma line?

if thats what you mean it wont do what you want,

since the plasma power supply delivers a fixed current (set to whatever the knob on the front is) as the rsistance the arc feels varies the voltage must also

since V=IR

I=V/R

I is constant so an increase in resistance decreases the voltage

since the plasma is cutting the same pice of plate all thetime the defining factor for resistance is the distance the arc has to "jump" across to get to the plate, or torch to works distance so giving the arc voltage direct proportionality to the torch to work distance.

Sorry if i told you something you already know

btw you must be 0-3.3v for the pokeys

matt
Re: Plasma Application, Mach3 torch height control.
« Reply #26 on: March 09, 2009, 08:21:59 AM »
Thanks matt I never looked at it that way.

Offline poppabear

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Re: Plasma Application, Mach3 torch height control.
« Reply #27 on: March 10, 2009, 06:12:39 PM »
Awesome Work Matt!!!  Keep at it, following this one with interest!!

scott
Commercial Mach3 & Mach 4, Design/Build/Retrofit CNC and Industrial machines.
http://www.ss-systems-llc.com/
Re: Plasma Application, Mach3 torch height control.
« Reply #28 on: March 19, 2009, 02:09:21 AM »
Okay Matt I had a look at the brains and I do kind of understand the First one (dthc1.) but the other two I can't make out the #'s or what any of the words say...  I don't know what I'm doing wrong, If I have the screen scroll unchecked then I can't see any of the oem dro#'s or mod#'s ...I know its some thing I'm doing wrong but I can't figure it out ( have been through all the videos couple of times)
And what I can read of those two screens ....I really don't understand!!!!

Then one last thing since the pokeys has so many inputs that aren't used can  a brain be used  to go ahead and probe the plate first, reset the Z dro and the go from there..Just thinking out loud.
Re: Plasma Application, Mach3 torch height control.
« Reply #29 on: March 19, 2009, 03:06:44 AM »
second question first,

yes it can, what cam program do you use? i have sheetcam, it has the probing for the material built into the post processor i use so at the start of each cut the z xis moves down until it trips a switch on the floating part of the z axis (the torch holder is in a slot so it can slide upward when it touches the metal and is pushed back down by a spring) then it moves back up a distance you specify in the post before it pierces then down to cut height after the peirce delay. It works absolutely perfect and i really wouldnt be without it, i make no changes to the setup for material thickness, if i have a slightly warped plate and nedd to pierce on top of a hump it doesnt matter. All you have to do for hardware is construct the floating torch holder with a switch on it and connect it to the z home input to mach and dial in your required offset in mach.

first question second,

ive just looked at the brains here and i get the same trouble, it reduces them so small you cant see what they are doing, i dont think its you i had someone else pm about it and they said they couldnt read them either so ill explain the functionality.

the first brain (dthc1 i think) reads the values from pins 44,45,46 (The analogue inputs which work) and has a no operation block to connect them to an oem dro which doesnt have a designation, so this reads a raw value from each pin and puts it into a dro number where the next brain can read it from. Easy, the reson the brain is so big is because it does it 8 times for each input, so 24 times in total, this is slow and boring to make, is there a copy and paste function? The idea of this is that you can average all of these values to get a better reading.

the next brain (dthc2 i think) has inputs which are all the oem dros written to in the previous brain, now we are gonna do something with the data. Each of these dros inputs is connected to a block which adds them together, beware you can only have 8 inputs to a operation block so you have to add the first eight together, then the secons, then the third and then add all three of them together to get a total, once you have a total put it through another operation block where it divided by 24 ( to average it) and then terminate with writing it to another unused oem dro.

the third brain (dthc i think) Has an input of the oem dro you wrote the average value to in the last brain which is then put through a formula block to turn it into arc voltage (did i explain how i did that?) and written to oem dro 1036 (i think but check in the screenset) which should write it to the screen in the tip volts dro.

the next line has an oem dro 1036 input and an oem dro 1035 (i think but the one for target volts) input and then a compare operation, if 1036 is higher than 1035, voltage is too high so its then terminated with a thc down block

the next line is identical but the inverse, comopare oem dro 1036 to 1035, if 1036 is lower, volatge is too low so terminate with thc up block.

i have added a couple of extras in to mine so that there is no move if the torch voltage is less than 0.8 or mare than 1.2 times the target volatge but i think it is important for you to get this far before making it more complicated, you could also put in a deadband so that if the readings were close there was no move, mine doesnt have that, i havent tried it since unfortunately time for tinkering with the plasma cutter has dried up recently adn the odd post here is all im managing at the moment.

dont hesitate to shout back if i ve confused you with my spelling!

matt