Hi all,

Rather than trying to convince myself (or you !) on "voltage stories" I decided to try my schema  

Here is the result on you tube http://www.youtube.com/watch?v=8w3nAoKZghw

It's only a prototype just including the voltage divider that I had put after the bridge rectifier.

The Vss is connected both to the minus signal of the bridge and to the minus power supply of the PIC (exactly as on my schema)
The PIC itself is powered by a small mobile phone 220V to 5V DC power supply

The analog to digital input is used to flash two leds :
- one indicating a torch voltage between 40V and 150V
- one indicating a torch voltage greater than 150V (off if Vtorch < 150V)

The input torch voltage is absolutely not filtered so a few spikes may occur... But the basic function is demonstrated  

Why does it work ?
Because a "voltage" by itself is nothing... it must be "voltage difference". When wiring together the 0V of my PIC and the minus of the bridge output, I fix the "minus bridge" to 0V
When some electrons are flowing from the bridge minus to the bridge +, then the bridge v+ climbs, thus it is seen as a signal between 0 and 5V on the divider.

I have also connected an oscilloscope on the bridge and measured the signals between :
- the plasma ground and the torch tip --> it's a negative voltage (as foreseen)
- the bridge - and the bridge + --> it's a positive signal (as foreseen)
- the plasma ground and the bridge + --> it's a negative signal ... but I don't use it  


JP

JP,
I like it, i like it alot....

You tie the bridge to power supply negative to make them common, i had wondered about it but never imagined you could do it without having problems like drawing loads of current or destroying the pic when you fire the plasma, youve just solved a wholeload of problems!!!

The killer partnow really is in the filtering of the voltage from the torch to take out any spikes or component destroying hf.

I presume you are planning on using the pic for ad conversion then feeding the frequency output to mach through the pp??

Id love to see how that works

Matt

JP,
I like it, i like it alot....

You tie the bridge to power supply negative to make them common, i had wondered about it but never imagined you could do it without having problems like drawing loads of current or destroying the pic when you fire the plasma, youve just solved a wholeload of problems!!!

The killer partnow really is in the filtering of the voltage from the torch to take out any spikes or component destroying hf.

I presume you are planning on using the pic for ad conversion then feeding the frequency output to mach through the pp??

Id love to see how that works

Matt

Thanks Matt !!!

By the way the pic is protected for under and overvoltage with internal dodes put on all the I/O pins --> there is almost no way to destruct it (if the intensity of current is within the range...)

I need to filter the voltage only to get a proper measure to make the THC work !

I will not send the "index" signal to Mach3 but only the UP/DOWN and torch OK signals.
All the computations can be done in real time into the PIC.

The tricky issue is that I will not have the "Voltage consigne" from Mach3 either...
But I can monitor the firs ms of cutting when the torch is properly positionned in height and when there is yet no significant deformation of the metal.
So :
- mach3 height positonning
- piercing
- start of move
- PICK UP of torch voltage and use it as reference
- monitor torch voltage and deliver UP/DOWN signals

JP

Jp,

Personally id like to be able to set the voltage from mach for each cut, you could communicate it to the pic either using an analogue output if you have a modbus device or by using binary over 5 or 6 inputs, just a thought, be sure to let us know how you get on

Matt

Jp,

Personally id like to be able to set the voltage from mach for each cut, you could communicate it to the pic either using an analogue output if you have a modbus device or by using binary over 5 or 6 inputs, just a thought, be sure to let us know how you get on

Matt

Well,

My Pic is fully used (in terms of IO pins), I only have one remaining input pin left...
I could use it to communicate with Mach3 using serial protocol RS232
I know how to do it with the PIC but not from Mach3 ...

May be with a script, but how ?

Any idea  Matt ?

JP

The short answer is no....

i think there may be a serial out command that is supported by mach in vb, its either serial out or in because i remember looking at it to see if i could get the plasma volatge in that way but i couldnt get 2 way communication.

In some ways i doo like the idea of referencing the voltage fromt he start of the cut too, saves a lot of messing, you just leave it to do its thing, set the feedrate to what gives you best results and it does the rest, i think it would be very interesting to be able to see what that was doing until you learned to trust it, for instance if i make 5 pierces and start cutting do i get pretty well the same voltage preset each time?? how close is it to what is in the book?? etc etc...

keep up the good work jp

i think there may be a serial out command that is supported by mach in vb, its either serial out or in because i remember looking at it to see if i could get the plasma volatge in that way but i couldnt get 2 way communication.

In some ways i doo like the idea of referencing the voltage fromt he start of the cut too, saves a lot of messing, you just leave it to do its thing, set the feedrate to what gives you best results and it does the rest, i think it would be very interesting to be able to see what that was doing until you learned to trust it, for instance if i make 5 pierces and start cutting do i get pretty well the same voltage preset each time?? how close is it to what is in the book?? etc etc...

keep up the good work jp

Hi Matt,

I have found a way to send informations from Mach3 to the serial COM you want. Just copy paste this code into any button and run it :

Sub main()
  Set MSComm1=CreateObject("MSCOMMLib.MSComm")
    MSComm1.Settings = "9600,n,8,1"
    MSComm1.CommPort = 5
    MSComm1.InBufferCount = 0
    MSComm1.PortOpen = True
      If Err Then
         MsgBox "COM" & MSComm1.CommPort & ": not opened, Sorry!"
         Exit Sub
         Else
         message "port opened"
          Sleep(1000)
         'MsgBox "COM" & MSComm1.CommPort & ": opened !"

      End If
    MSComm1.Output="Torch Voltage sent by JP : " & GetOEMDRO(83) & Chr(13)
    'MsgBox "COM" & MSComm1.CommPort & "output ok"
    message "torch voltage sent"
    Sleep(1000)
    MSComm1.PortOpen = False
   
    Set MSComm1 = Nothing
End Sub   


The port that I choose is port COM5, you can change it if you don't have COM5...
I have checked that it works, the port is properly receiving the DRO value.

BTW, what are the DRO's for THC ?

I will try to update my PIC code to monitor the voltages as you propose.

Cheers
JP

I cant remember what the numbers are, the ones i found were from the candcnc screenset, to be honest i have been using my own numbers, we should set a standard if scott is going to write us a plugin.

I cant tell you what numbers i used, i got a new plasma with hf start a few days ago, needless to say it blew the **** out of the motherboard!!

Matt

Hey gents,

    Here is what Mach can do, Brian wrote a Serial plugin and a  PID loop plugin that went to a PLC for THC, I have copies of both, and they could be combined to do the PIC acros the serial if thats what you want..........  BUT..............

    I realize people say modbus and other technologies i.e. pokeys/usb is too slow, both Modbus, plugins, run in Machs 10hrtz update loop.  so 1/10th of a second. I find it hard to believe that you Z axis can move THAT much in 1/10th of a second, due to acceleration/decelration times, inertia ect.

From what I understand back in the day, when Brian did the THC plugin for analog PLC control, he said it worked ok acxross the modbus.  Currently in mach, (that I am aware of), there is no "FAST"  analog input stuff, i.e. attached to a Para Port etc.  I suspect that if you think Mach is TOO slow for your PID loop then you will need to do a stand alone PID and Z axis hiegth control.  Note: this may change in the future with mach version 4, as brian says that updates are running at 50hrtz.......  so.......

but at any rate, If you want to use the Modbus with a device like a PLC, or one of Aurturos boards, or Peter Holmans board, or...?? it really doesnt matter, Pokeys on USB.........  it all will currently ultimatly run inside machs 10hrts loop, ther e is a 40 hurtz loop available in the plugin but it is only for VERY fast code, other wize you crash mach. So I dont really fool with it much.......

Since I am NOT a THC user, someone else will have to do a Screen Set for it, the plugin can be tied into the screen set or what ever......  you can touch and do all kinds of stuff with mach from a plugin.......  Further I use MSI installers on all my plugins now, so when you run one of mine, it installs the plugin, the screen set, the xml, (the modbus config if applicable), Macros, Bitmaps, help file, read me......etc.

it is easy to make the PID loop user adjustable, via dialog boxes........   Personally for industrial applications I prefer a PLC that has a proven track record of reliablity in an industrial enviroment.  A Automation Direct DL05, with an Analog module would probably run you around $200-300 so that may be getting OUT of the realm of Cheap.....

I do some "beginner" programming of Pics, but I only have a "learners" PIC board, and no real world experience in using them. But, programming, is programmming.....

scott

Thanks Scott for these informations.

On my side, as I am an hobbyist, I do not plan to use modbus and so I look for the cheapest solution available.
A Pic + a few componants could give a "standalone" THC for less than 10$ 

A believe that Mach3 is fast enough on the Z axis to achieve a proper motion when ready the UP/DOWN signals on the // port.
All the rest could be done in the PIC at a rate of 0,1s per measure (roughly).

To save a few pins on my PIC I wanted to send some DRO to my board via a standard serial port (not modbus).
I don't care about the speed of this serial link as these parameters will just be sent for initialisation purpose from a VBscript attached to a button. So I don't need real time.

Well I go on with my breadboard solution... Just to see !


JP