THC that works

It's been a while since I assembled my plasma cutting table. 2012 to be exact and the software I'm running is still version 2.5. Years past I have searched for an implementable torch height controller. The best solutions previously for those who had plasma machines without integrated status outputs was an external THC module. I purchased a Proma thc controller and have successfully installed and wired the up, down and arc okay inputs into a second parallel port card on my computer. I can read the inputs using the on screen monitors. I have also assembled a touch switch on the head of my torch. My machine uses the traditional stepper motors.

A year or so back I worked quite a while trying to adapt code from A2 Mechshop Gantry Plasma Machines website to implement the files into my machine. They had a piece of python code that looked like it would do everything I needed and more, but it was so complicated and machine specific that I did not have much luck getting it to work. Their implementation used gpio cards and servos and there just wasn't enough documentation to decipher what parts I needed to add to my own config and and hal files to make it work. They presented only a completed HAL file and Python file for their specific machine. Cutting and pasting was just a disaster as I could never tell what was machine specific and what parts I needed, and how they were different between machines.

So a couple of questions that maybe some of you plasma guys running the 2.7 software can answer about the current state of affairs to bring me up to speed.

1) Do any of the newer releases of Linuxcnc have built in support for THC? Dallur-thc and Plasma-thc in the earlier versions never seemed complete to me, nor could I find enough info to make them work.

I also looked at the TOMA THC documentation but did not have any luck making that work either due to the minimal instructions.

2) Is there a step by step guide anywhere to installing a THC component?

It seems difficult (at least for me) to know exactly what files to add stuff to, what stuff goes in each type of file, what order the files need to be executed in and how to troubleshoot when the whole thing come crashing down. There seems to be a is a huge jump in "how to's" between monitoring a I/o pin with the HAL monitor and netting pins together, then suddenly you get presented with a "THC State Controller system schematic" designed for servos and GIPO cards that is really difficult to navigate.

Thanks for some feedback.

Engineer wrote:

1) Do any of the newer releases of Linuxcnc have built in support for THC? Dallur-thc and Plasma-thc in the earlier versions never seemed complete to me, nor could I find enough info to make them work.

2) Is there a step by step guide anywhere to installing a THC component?

Answers
1) Not yet but there is support in this experimental branch github.com/LinuxCNC/linuxcnc/tree/dgarr/external_offsets
2) No but there are quite a few notes in the experimental branch about how to move from the sim to a real machine

You need to look at the hpid.ini or hpid_mm.ini and their corresponding .ngc files under configs/sim/axis/external_offsets/

The text cut from hpid.txt below would lead me to believe that this work is looking at the next generation of TH control software, using a scaled analog input representing the arc voltage. A year ago I would have been gung-ho to have looked at this, as I had my plasma cutter torn to pieces and was fooling with voltage dividers, op amps, comparators, isolators and the like. At that time, the only software implementations that I saw utilized digital inputs torch up, torch down, and arc okay, I resigned myself to purchase the Proma hardware as that was a cost effective thing to do, rather than reinvent the wheel. Using this new approach may be superior, but would obsolete my Proma THC hardware (two steps backwards). Can you direct me to any implementations that use the external controller and straight digital inputs? Thanks.


The torch controller is simulated (sim_torch.hal) by connecting the z axis external offset output (axis.z.eoffset) to a scale component (sim:tovolts) and scaling by a factor of 1000 so that a 0.004 inch (0.1 mm) z offset height corresponds to a about a 4 volt torch voltage. The simulated torch voltage is passed through a lowpass filter component (sim:torch) to simulate the bandwidth-limited measurement of torch voltage. The bandwidth is set by the filter gain setting pin (sim:torch.gain). (See the lowpass filter man page for the relationship of lowpass gain and filter bandwidth). The delay to achieve arc-ok is simulated by a oneshot component (sim:arcwait), the delay time is set by the pin sim:arcwait.width. Key parameters are set with inifile settings:

I'm not so sure if obsoleting your proma is 2 steps backwards

The only config I've used for plasma is the experimental branch I shared with you. Yes, the sim includes a simulated torch but the intent is that you replace this with a real torch in a live config. And yes, this is next generation stuff light years ahead of most external THC's

I'm not sure if you've seen it but you could consider this one which is supposed to work well with proma.
forum.linuxcnc.org/49-basic-configuratio...hc-config-that-works

Also there is a THCUD component which may also do what you want
linuxcnc.org/docs/html/man/man9/thcud.9.html

Added Files

Aw fooey, lost my message when I opened the editor to attach files, so I will write it again.

I have more or less successfully implemented the toma THC files on my unit. Some difficulties converting the metric setup to the imperial one with velocities and measurements, particularly the defaults. Some in vcp some in ini.

Still having some issues with z axis velocity. Changing the max velocity, max acceleration, and stepgen maxaccel in my ini file all affect the z axis for homing operations, but the z axis wants to move too fast under thc software control. I have to crank up the amperage to the z drive board to make it work and it sill skips sometimes and the motor just howls.

Perhaps there is some place in the software to scale the thc speed of the z axis separately ?

I also attached an error file, as this happens every time I try to close and restart linuxcnc without rebooting the computer. Really a hassle. I tried some reset functions in the parport.hal file but that doesn't seem to be helping. There were some suffixes on the parport commands in the toma files, but I don't know what they do or why they were there. My parport commands from the stepconf setup didn't have any suffixes. Is that contributing to my issue?

I have been seeing the torch run away in the up direction at the direction as directed by the Proma THC control. I have experimented with 120 volts setpoint, plus or minus 10 but not convinced this is the right approach. Seems torch height is wavey at about 3-6 mm and a bit unstable. Making the steps smaller on the control panel seems to make the runaway condition worse. I figured making it react slower would stabilize it but it seems to go too high easier. Thoughts? Course my cutting speed is too slow after trying to get the z axis under control.