Plasma Application, Mach3 torch height control.

[halkintool]

Right now, my setup uses a pneumatic cylinder to control torch height up and down, and a handle to adjust to different plate thicknesses.

With the handle on my manual height adjustment, it would be quite easily to add a Z-axis. Im just wondering what would be required to interface the automatic torch height control with the mach. Do i need a THC board, or can I run a torch height control through software and my dspMC motion controller I/O?


Heres a little snippet from the plasma units manual,

MACHINE INTERFACE
The Pro-Cut 80 comes standard with a machine interface.
Interface signals provided include: arc start, arc
initiated, and arc voltage. These signals are accessible
through the 14 pin MS connector on the case
front.
ARC START:
The Arc Start circuit allows for triggering of the power
source to commence cutting. This circuit can be
accessed through pins K and M of the 14 pin MS connector.
The circuit has a 17 VDC nominal open circuit
voltage and requires a dry contact closure to activate.
ARC INITIATED:
The Arc Initiated circuit provides information as to
when a cutting arc has transferred to the work piece.
This circuit can be accessed through pins I and J of
the 14 pin MS connector. The circuit provides a dry
contact closure when the arc has transferred. Input to
this circuit should be limited to 0.3 A for either
120VAC or 30VDC.
ARC VOLTAGE:
The Arc Voltage circuit can be used for activating a
torch height control. This circuit can be accessed
through pins D and G of the 14 pin MS connector.
The circuit provides full electrode to work arc voltage
(no voltage divider, 335VDC maximum).
Users wishing to utilize the Machine Interface can
order a K867 Universal Adapter (please adhere to the
pin locations stated above) or manufacture a 14 pin
MS connector cable assembly.


Im not quite sure I understand what the ARC voltage pin outputs are going to look like. "The circuit provides full electrode to work arc voltage" I was hoping the machine would just give off an analog output to indicate arc voltage, what do you think?

[poppabear]

you need the adapter, call them and see if the adapter will give you a 0-10 signal for control

[halkintool]

From the description in the manual, it seems like they're just selling the cable. What would I expect the nature of the output to be?

0-335VDC?

[halkintool]

Would this work?

[halkintool]

Based on an analog 0-10V signal, does mach3 have the capability to control a Z axis?

[fer_mayrl]

I think there would be a couple of possibilities...

The only way mach can adjust the height of the torch while cutting is with the THC UP and THC DOWN inputs, which are digital TTL.

This said, the two options are:
1. Make a hardware interphase (beyond my capabilities) that interprets your 0-10v signal and translates it into either a torch up or torch down digital signal. you could even add PID cappabilities otherwise your control would be pretty minimal.

2. Make a brain read the 0-10v trough an analog interphase (PLC with analog inputs trough modbus) and interpret the voltage to make the torch up and down inputs work.

I could make a suggestion, but dont know it it would work or if you want to do it that way, the other options i gave you when it is all said and done will maybe cost more than a ready made THC unit from bob campbell, or sound logic, and the other provider which name escapes me right now. i think you will be amazed at the prices and features they have... besides its proven to work.

Have a chat with them and you make the decision.

Best regards
Fernando

[halkintool]

So there wouldnt be anyway of just writing a brain or modifying my M3 macro, to take an analog input and apply it to a Z axis?

Can Mach for example translate an analog signal as an encoder? I know some linear wire encoders use pots to determine position. If I could simulate an axis position with the voltage feedback from the plasma i could slave Z axis to it? It just seems to me that more hardware should not be required, given an analog signal you'd think you could write software to slave an axis to it.

Im building an oven right now, and i have a couple PID's kicking around I could probably use. All i would have to do is wire the PID and impliment a 1 or 2VDC power to the analog input on my servo amp, so when the voltage feedback comes out of range the PID puts the axis back to position. I dunno, just throwing out ideas.

Edit*

I just realized there is a download on the plugins page for a THC using an analog input.

I installed the plugin on my desktop here to take a look at it, it looks pretty good. I just wonder if its ever worked for anyone.

[fer_mayrl]

From what I know, there is no way to directly move the z axis with an input of button while it is running g-code.

I believe encoders send out pulses not proportional analog signals like 0 to 10v.

The linear wire encoders i believe they do not use encoders, just pots that divide a voltage, yes you could use something like that as an analog input and manipulate that value trough a brain or something like that. But a linear pot would have to be used with a "feeler" or foot that is always touching the surface of your material, If you can already tap the voltage of your plasma and translate that into a 0 to 10v signal, then the lienar pot would be redundant. You would really want to use that arc voltage as a reference since it is what really matters in the plasma process.

I have not tried the THC plugin that Brian wrote to accept an analog signal, you would have to ask him, but since in the description it says experimental-unsopported, i would believe it is not finished and would lack some features needed like arc dive and stuff like that. and since it is unsupported, i guess no changes will be made to it if requested.

Again, im no expert on this since i have never used plasma, torch height control or any type of analog signal control, im just calling it on the information I have read on this forum..

Best regards
Fernando

[BluePinnacle]

Hmm. Perhaps your Z axis would be better off controlled by the torch voltage system and X and Y controlled by Mach. Does mach accept jog inputs while running Gcode? I'm thinking you could emulate the pulses of a MPG easily in response to the torch signalling too high or too low.

Or just run the Z independently of the computer and just let it follow the work, using a "coolant" M-code to bring it to the workpiece and back, overriding the height control. Knowing more about your height control system would be a plus.

[halkintool]

Hmm. Perhaps your Z axis would be better off controlled by the torch voltage system and X and Y controlled by Mach. Does mach accept jog inputs while running Gcode? I'm thinking you could emulate the pulses of a MPG easily in response to the torch signalling too high or too low.

Or just run the Z independently of the computer and just let it follow the work, using a "coolant" M-code to bring it to the workpiece and back, overriding the height control. Knowing more about your height control system would be a plus.

It was suggested to run an independant height control system to control small adjustments to height, i could just use a PLC but id prefer to have everything integrated through 1 piece of software to avoid later complications etc. Seems more simple.