Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: Scary on November 13, 2020, 02:37:04 AM

Title: Another THC problem
Post by: Scary on November 13, 2020, 02:37:04 AM
Hi All,
I am fighting a THC problem at the minute and it is very strange.

For starters the basics are:- yes I have a registered version of Mach3, yes I have tried the "enable THC even in off" both active and not active and I have written "StartTHC()" in the M3 VB script and "EndTHC()" in M5. I have the three diagnostic LEDs working correctly for THC on, Torch Up and Torch Down on the given signals.

The "THC ON" input is working and when signal low creates a feed hold, once high again program continues. So to me this is working as expected. The issue is that I have no Z-axis control whatsoever when arc active (THC ON) is on or off. I have tried to use the THC  input signals, Emulated inputs from keystroke hotkeys and have tried to manually jog the Z axis up and down to no avail. I can not get any Z axis movement whatsoever but the diagnostic LED's are giving the inputs to move.

Is there a command in VB or G/M code that allows axis override while program is running or is there a setting that I have missed in Mach itself? I know there is "JogOn()" command and I have considered putting it in my M3 script but from my understanding this is to move the axis with position input and then "JogOff()" once executed, not for external jog signals or am I not understanding it correctly. 

Title: Re: Another THC problem
Post by: TPS on November 13, 2020, 03:11:35 AM
witch Motion Controller are you using? THC is only working on a few Controllers.
Title: Re: Another THC problem
Post by: Scary on November 13, 2020, 03:30:15 AM
I am using an old RnRMotion card I have had lying around from other projects. Can you explain why the card would be a problem, not saying that this is not the problem, just trying to understand. Mach is receiving the signals but wont output anything. Is there a way to insert a MDI input while program is running? I could then run a brain or VB script to command the Z axis movement via G code while the main code is running?
Title: Re: Another THC problem
Post by: TPS on November 13, 2020, 03:47:26 AM
Hi Scary,
i am affraid your Controller does not Support THC, did a quick Google check, but maybe i am wrong.

receiving the input's ,and Show the on LED's, is only the easy part of THC.

THC (up/down) reactions have to be very fast, so they Need to be controlled by the part (Software) witch creates
the pulse/dir signal's. In your case by the Motion Controller.

any other part (VB or brain) would be to slow and not able to act the actual pulse stream.

hope i was able in my bad bavarian english to explain.
Title: Re: Another THC problem
Post by: Scary on November 13, 2020, 03:55:36 AM
Ok, thanks heaps for the info. I think I am understanding now. Mach3 is giving block info to the board and the board is executing it, the board will not accept interrupt signals to do other commands whilst executing the current block of information and therefore ignores the commands.

My question now is what board does have THC support and what do I look for?

Apologies for all the questions, I prefer to learn and understand the issues rather than just "do this" without learning.

Just a thought, I wonder if I could run the Z-axis on its own breakout board with a separate address and therefore eliminate the control logic block of the other board?
Title: Re: Another THC problem
Post by: TPS on November 13, 2020, 04:09:39 AM
there are a couple of boards with THC on the market
witch one is the best? i realy don't know, i would prefer one witch has Ethernet Connection,
especialy on an Plasma Setup.

maybe someone with Plasma and THC experiance can help.

Title: Re: Another THC problem
Post by: Scary on November 13, 2020, 04:12:11 AM
Once again, Thanks heaps for the info.
Title: Re: Another THC problem
Post by: Scary on November 13, 2020, 05:00:38 AM
FYI to all.
I have created a temporary workaround.  I have run the step/dir pins from between the mach3 breakout board and the stepper driver through a DPDT solid state relay. I have connected the relay signal to the arc ok output and have also left the arc ok signal connected to the mach3 input pin to utilise the feed hold function if arc is extinguished. Then I have connected the torch up and down outputs from the THC unit to an Arduino board and have programmed it to output a square wave and direction to control the Z axis. These outputs are connected to the N/O side of the relay and the mach3 output through the N/C side. The common is connected to the stepper driver.

Keep in mind that I am only just starting to test this but so far it looks ok. The theory is that when no arc, the Z axis stepper driver is connected to the mach3 board and mach can move Z axis as it wishes. When the arc ok signal is active, the SS relay disconnects the mach3 signal and connects the Arduino board and the Arduino converts the up down signals from the THC to step direction outputs that are now connected to the Z axis. The Z axis stepper can now move up/down according to the THC unit and mach3 has no THC functionality needed. Once arc off, the SS relay swaps control back to Mach3 and Mach continues on as normal.

As I have stated, this is a relatively untested TEMPORARY workaround and I will be getting a THC capable board as this does not allow the use of limits etc but my plasma table is too big of a toy to have sitting idle and I am impatient!