Advanced Search

Sorry for the late message. Unfortunately I had to give the project less priority. 
At the moment very busy with my full time work, my own company and graduating from my bachelor mechanical engineering next to a more than full-time job. 

I am slowly designing further on the mechanical part during my breaks. The hardware will be a pc that runs on plasmac in combination with a mesa board and a thcad. 

The drive will be a belt, I do not believe that this stretch is noticeable under the load of plasma cutting. Much cheaper and simpler in design than rack and pinion.

 

I want EtherCAT as an interface.

I forgot to mention I am planning to use Ethercat too. A Beckhoff 5151 encoder interface arrived today. I also have a THCAD10 here which may allow reading of 0-10 volt using it. I will use a Beckhoff 2502 for PWM signal for laser.

I started a build for new CNC plasma table so here's my starting point.

CPU Ryzen 5 6C/12T 3.2Ghz 32G RAM, 550G SSD, Dual Ethernet ports
Ubuntu 24.04.02 - I know it's not "debian" but is what all other machines here run. Compatibility and support are the key deciding factors
PREEMPT-RT installed, Fairly minimal system with snap completely removed.
Stepper Drives (4ea) Stepper Online DM542T - have had excellent results with these in the past
Stepper Motors (4ea) Stepper Online 23HS30-2804S - again have worked well in past
Custom built frame from 2x2 16ga steel tubing. All Linear Rails SBR20. All Ball Screws SFU1605
Motion Controller Mesa Electronics 7i95T & THCAD2 - ordered and expected arrival in next few days
LinuxCNC version 2.10 being built from source.

I can successfully build the rip version without error and it appears to work correctly however as I mentioned I do not have the 7i95T in hand quite yet and it's not listed as an option in the opening config choices.

To get the full package I'm working to compile to get the .deb version and having some make problems.

Problem 1
I get lots of errors during the build of man pages. Some work but many report this error and often multiple times.

Making manpage sampler.9
<unknown>:1: SyntaxWarning: invalid escape sequence '\S'

I suspect this has to do with the fact that Ubuntu 24.04 uses python3.12. I haven't dug into to it but have had many problems in many projects with python version compatibility and this is known issue from 3.11 to 3.12. Any suggestions on how to fix this are welcome and sooner or later it'll have to be addressed anyway.


Problem 2
This is the end summary of the build

Compiling module_helper/module_helper.c
<command-line>: error: "_FORTIFY_SOURCE" redefined [-Werror]
<command-line>: note: this is the location of the previous definition
Compiling localized message catalog ../share/locale/ar/LC_MESSAGES/linuxcnc.mo
Compiling localized message catalog ../share/locale/bg/LC_MESSAGES/linuxcnc.mo
cc1: all warnings being treated as errors
make[2]: *** [Makefile:278: objects/module_helper/module_helper.o] Error 1
make[2]: *** Waiting for unfinished jobs....
make[2]: Leaving directory '/home/plasma/Documents/linuxcnc-source-dir/src'
dh_auto_build: error: cd src && make -j12 build-software returned exit code 2
make[1]: *** [debian/rules:55: override_dh_auto_build-arch] Error 2
make[1]: Leaving directory '/home/plasma/Documents/linuxcnc-source-dir'
make: *** [debian/rules:43: build] Error 2
dpkg-buildpackage: error: debian/rules build subprocess returned exit status 2

The _FORTIFY_SOURCE error shows up many times as well and probably isn't the only problem.

Again I know it's not debian but Ubuntu is derived from debian and the rip version compiles and works so I've very optimistic once I work out a few kinks this will too.

cc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
Copyright (C) 2023 Free Software Foundation, Inc.

Thanks for any and all suggestions. Mike

 Great! Let's move ahead.

Let's talk about 0-10 volt range first.
The Mesa THCAD is a voltage to frequency converter. The THCAD10 has a 10 volt full scale. The THCAD 5 has a 5 volt full scale. The newer THCAD2 can be configured to either have a 10v or 5v full scale range. For your hardware, the 10v range sounds best.
We read the frequency using an encoder A input (usually on a Mesa card) and then scale it internally back to a voltage. Usually we set the THCAD's on board frequency divider so we read 1/32 of the frequency when sending it to Linuxcnc.

To receive a frequency, we would simply connect your hardware direct to an encoder A input and not use a THCAD.

It would be easy to apply a mathematical function to the encoder frequency to convert to a voltage in a real time component written in C.

There are other options to read both voltage and frequency. For example, appropriate Ethercat slaves for both voltage and frequency are available.
I think for Ethercat I would prefer 0-10 volt.

Finally, I might mention that for plasma torch height control, we adjust the height using external offsets (this offset is external to the motion controller). A scaled count (much like a MPG) allows us to take the input and output a height adjustment of the error. But because you output a distance, it might be possible to manage height control via one of Linuxcnc's PIDS.
 
Anyway, if you have a contact us option on your website, let me know, and I will reach out to take things further.

fantastic.

There is still a possibility of implementation, so I would like to adapt it to LinuxCNC as much as possible.

I am not sure if it makes practical sense to process data multiple times, which loses measurement accuracy and introduces additional errors at each stage C/f -> U -> f ...

i can made frequency output directly in sensor.

I see that the THCAD5 card processes voltage to frequencies in the range of 100 kHz - 1 MHz, but I can adapt to any frequency (lower frexuancy could be directly monitored in many "less efficient" controllers and send via cable easyer ), it can also be a PWM output or serial communication, which I can send a ready-to-use height without the need for the CNC system to process the signal, which in my opinion would be the best option.

In your opinion, what would be the best option?

Send one to Rod, her can make it work easily as he has THCAD that turn 0-10V to frequency, and he is very detailed when testing stuff.
I do not have a laser (i do have a big box of lasers, but He-Ne ones at low power) so i can not help with testing it. I can attach it to a plasma torch and see how long it lasts with all the interference plasma causes, but that is it. Oh yeah, Rod can also test this, as he has plasma machines.

Hello LinuxCNC community,We are a group of engineering students working on our semester project – building a CNC plasma cutter using LinuxCNC as the control system.Since we are developing the machine from scratch and learning LinuxCNC at the same time, we would greatly appreciate the opportunity to discuss and receive guidance from experienced users. We are particularly interested in understanding potential challenges, key considerations, and best practices for setting up LinuxCNC for our machine.Brief Overview of Our Machine:

• CNC plasma cutter with X, Y, and Z axes
• Z-axis with a ball screw and linear guides
• Floating head with a proximity sensor as a probe input
• Plasma cutter with a voltage divider and THC (Torch Height Control)
• LinuxCNC control, likely using Mesa hardware
• Torch Height Control (THC) integration via Mesa THCAD-2
• Voltage divider (50:1) for plasma voltage feedback
• Probing system for automatic height sensing before cutting

We have already explored various existing solutions, but we would love to hear from those with practical experience in setting up and running a CNC plasma cutter with LinuxCNC.Some key topics we would like input on:

• Choosing the right hardware (drivers, Mesa cards, sensors)
• Configuring LinuxCNC (HAL, INI, probe input, THC integration)
• Common challenges and pitfalls when setting up a plasma cutter
• Best practices for calibration and fine-tuning

If anyone is willing to share their expertise or discuss this with us in more detail, we would greatly appreciate it. A virtual meeting would also be very valuable for us.Thank you in advance for your time and help.Best regards,
Ibrahim Al-N and the 4.semster students at Absalon Kalundborg (Denmark) 

It is possible to do ohmic sensing from the tip. At least it is on a Hypertherm 30XP using relay ohmic, I imagine it would work the same with a THCAD. I have been doing this for a few years now without any issues. The only mod to my torch from memory was to insert a diode, the inspiration was from   here  and  here .

Got a THCAD2 from www.welectron.com in Germany a few days back, not installed yet as it was freezing lately.
Updates when i get to using it a bit, although i see no apparent reason for any difference from THCAD10 and THCAD300 i used before.

For now I am using the period as a base for calculating the frequency. Looks good so far. I will have to test for a while, but I think it should be fine now. Thank you for all your inputs!

there is no comparison. Linuxcnc's QTplasmac, a Mesa 7i96 and a THCAD2 will give you a high end system for almost nothing. Its feature set is very extensive. The difference is that the THC is managed internally by Linuxcnc, not an external THC so the system knows much more about what I'd going on and has much more ability to provide consistent results.
This is quite an old video but it shows what you can do

And the cut recovery features

nothing comes close!

I think one can not take for granted that EL3061's signal ground is the same potential as the workpiece ground. If you are lucky it might work, but to be on the safe side the torch signals should be isolated and free to float.

I had a quick look at the manual and I saw something that indicated the drop to zero was an index mark. My guess is that one of the PDOs needs to be set to remove it.

As I said earlier in the Ethercat world, a 0-10 volt analog input is probably a better choice but I have not tried one (assuming the plasma cutter has a voltage divider).. The EL3061 for example offers 500 volt isolation which is similar to the Mesa THCAD. To scale the voltage you would just need to use a mult2 component, send the output to QTplasmac and set the Qtplasmac offset to zero and the scale to 1.

If the pulse length method works for you it is even better. 100 ns resolution between two rising edges gives 0.1 Hz resolution and seems to be updated every cycle.
 

Yes, indeed. However since the drops seem to be random, I am not sure if it is related.

The manual also states that no frequency measurement is possible if the counter is blocked by the gate, but that in this case the period can be measured regardless.

And further: If an encoder signal is only present at input A/A and the frequency/period is to be measured, the terminal must be set to “Enable FWD count” in CoE 0x8000:03 [} 155].