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Author Topic: Plasma Application, Mach3 torch height control.  (Read 123681 times)

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Re: Plasma Application, Mach3 torch height control.
« Reply #40 on: June 04, 2009, 06:12:43 AM »
I am also trying to add a thc in my new plasma machine, and for now I have made the voltage divider and putted it inside of the plasma unit machine.
Before connecting the output of the voltage divider to the pokeys, I have tested the voltage divider output during cutting to make sure that the output would not damage the pokeys. I have measure the output with a simple, low cost multimeter, where in DC mode I register during normal cutting from 0.80V to 2.10V, that seams ok. The problem is during the piercing and if, for example the plate "ends" during cutting (both are limit situations), where the multimeter does not show a consistent value, and goes up to 20V for a brief instance.
I think that it is not possible to reach such a value, because the voltage divider is about 40x; and the 20V output from it was meaning that I would have 800V at the output of the plasma. I really think that is the multimeter that gets confused from the high frequency variations of the DC voltage during the limit situations (piercing and end plate).
The voltage divider also have a high speed voltage suppressor, that should take care of peak voltages if present.

Neverless I would like to receive a comment, before I have connected it to the computer and so on, of anyone that made such a voltage divider.
Thanks, Filipe

Offline poppabear

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Re: Plasma Application, Mach3 torch height control.
« Reply #41 on: June 04, 2009, 01:02:05 PM »
fourxfour2:

the problem is this: THC control is usually driven via the PP (very fast control 25K or higher). The Brians are at machs update loop time of 10hrtz (slow for your axis control), thus jerky.....

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 #42 on: August 16, 2009, 05:54:53 PM »


Mach already has all of the logic for dthc built in so there is no need to use anything else, my brain simply compares my value read in (in the process described above) with the value i have typed into dro 1036 i think, but its whatever is in the candcnc screenset for preset volts and moves up if the voltage is too low or down if its too high, the thc controls are there in the brain editor under thc up and thc dwn, and mach does the rest, if all criteria are met, arc ok signal is on and thc is turned on it will adjust the torch position.

Bingo youve got dthc



I have also been looking at how to do this with no pokeys, i think if i was to put a simple analogue to digital converter on my analogue voltage and reading in the pulses across the parrallel port using the spindle speed input or something which will measure frequency, this may also give the advantage of a wider working band, the limitation with my device is that i am taking a perhaps 10v variation and reducing it to perhaps 0.5v variation and then mathematically multiplying it back up, so there is error but in fairness to it i can make a 200mm long cut with one end of the material raised by 50mm and the cut height is pretty constant and when im hundreds in pocket i cant complain.


matt


Fisrt of thank you Matt for this great idea.

I think that I will try to do the suggestion with using the spindle speed input. The pulse signal should be easily generated by a tension to frequency converter such as the so cheap LM331.

Something like this (but only from the left to the optocoupler)



My only doubt compared to your pokeys solution is that with the LM331 I will only have one input which will prevent me to do the averaging that you perform in the brain while using several imputs on your pokeys...

Well I will see and keep you informed

JP
« Last Edit: August 16, 2009, 06:05:16 PM by freedom2000 »
Re: Plasma Application, Mach3 torch height control.
« Reply #43 on: August 17, 2009, 03:57:21 PM »
Thankyou for your kind words

I think the way you are talking about will work just fine, im not really sure if having more than one input is useful or not, i will be very interested to hear how you get on with that

matt
Re: Plasma Application, Mach3 torch height control.
« Reply #44 on: August 17, 2009, 04:05:46 PM »
For sure I will keep you  informed. As we say in France : "c'est la moindre des choses" !

BTW I am not yet sure how I can handle the negative voltage of the arc with the LM331... I will see !

I have just received the optocoupler today
still waiting for the LM331

And I have found into my plasma two devoted pins where to pick up the arc voltage  :o

I have tried to emulate the Torch Up and torch down with keyboards in Mach3... but I don't see any effect in the Z DRO when running...
Any idea ?

cheers
JP
Re: Plasma Application, Mach3 torch height control.
« Reply #45 on: September 27, 2009, 09:52:46 AM »
As someone mentioned, it is a good idea to have a transient suppressor in the voltage divider circuit to kill spikes caused by the collapse of the output transformer/choke of the plasma power supply. God forbid you should run unfiltered high frequency arc-start through a pokeys! Most modern small plasmas don't use HF. As far as averaging or smoothing the input (0-3.3 v) to torch-motion, a few trials with an RC network across the output of the voltage divider can give you control of the sensitivity or fussiness of the whole THC system. Make sure you use dividing resistors bigger than 1/4 watt if you are going to do this, however!  Hypertherm uses ohmic-contact probing as a secondary system for plate detection. Their main sensing is motor current at the torch lifter. This is adjustable but I will be danged if I can figure out how they do it with a PWM motor drive. This is a good project for anyone with the need for THC and I enjoy everyone's input very much!
Re: Plasma Application, Mach3 torch height control.
« Reply #46 on: September 27, 2009, 07:56:33 PM »
Jp,

i think if you cant see the dro changing its probably to do wit no having the thc enabled properly, personally i ecomend downloading the candcnc plugin, ensuring you have the thc on and a brain to make the keys emulate the signals.

I too enjoy peoples input on this, mkes for intesting reading

matt 
Re: Plasma Application, Mach3 torch height control.
« Reply #47 on: September 28, 2009, 02:19:49 AM »
Hi Matt,

In fact the plugin is not needed. My problem was only due to a missing THC On signal !!!

Now everything is in order and when emulating these signals (THCon, TCH up, THC down) Mach3 takes into account the height correction properly.

I have also progressed a bit.

Here is the schema of the electronics :

The voltage divider has been supressed as my Cut 50L provides a signal from 3V to 7V (when cutting) up to 90V when starting the arc.
The two diods on LM331 inputs are there to limit the voltage between -0.6V to 12.6V that is to the usefullrange of the torch signal.

I have not yet tested this schema excepted the inputs to the LM331.

For the moment I am finishing my CNC  !
More details here (in french) : http://www.usinages.com/ma-fraiseuse-v2-a-vos-critiques-svp-t8144-90.html


JP

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Re: Plasma Application, Mach3 torch height control.
« Reply #48 on: October 05, 2009, 08:41:35 AM »
I have tried to emulate the Torch Up and torch down with keyboards in Mach3... but I don't see any effect in the Z DRO when running...
Any idea ?

cheers
JP

Hi Matt,

In fact the plugin is not needed. My problem was only due to a missing THC On signal !!!

Now everything is in order and when emulating these signals (THCon, TCH up, THC down) Mach3 takes into account the height correction properly.

Hi JP. I too have been trying to simulate control of Torch Up/Down via keyboard emulation in ports n pins. I get the Torch Up/Down LEDs lighting on the Diagnostics page but no Z movement in the DRO. I've made a call to StartTHC (THCOn() throws a script syntax error) but this makes no difference. What am I missing?

Cheers

Ian
Re: Plasma Application, Mach3 torch height control.
« Reply #49 on: October 05, 2009, 02:54:19 PM »
Quote
Hi JP. I too have been trying to simulate control of Torch Up/Down via keyboard emulation in ports n pins. I get the Torch Up/Down LEDs lighting on the Diagnostics page but no Z movement in the DRO. I've made a call to StartTHC (THCOn() throws a script syntax error) but this makes no difference. What am I missing?
Ian
Hi Ian,

I have also emulated the torch on signal with a keyboard key. Then I have loaded a Gcode file at constant height.
When pressing the "torch on" key the cutting starts
when releasing the torch on key the cutting stops
when pressing the torch on + torch Up then the cutting height increases
with the torch down it decreases.

Well quite simple in fact
motion = torch on pressed
motion + torch up or down --> the height climbs or decreases

JP