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Hi, Tom/JT.

I changed the max-velocity in the .ini file and also as per an earlier post by bubels I uncommented a line. (the Z-axis is controlled by thc.hal and not via G-code in the case of the Toma THC)

linuxcnc.org/index.php/english/forum/49-...works?start=20#50427

The Z-axis is probing correctly now.

I also cut a warped plate and it appears that the THC is working correctly.

A further question I have is if there is a way to switch off the THC when cutting small holes and arcs (via an M command?), or is this handled in the thc.hal?

Regards,
Ziggy

The F feed speed works for everything except G0, G33, G33.1 and G76. There is no ini setting for probe speed.

For example my plasma touchoff subroutine:

JT

The F for feed rate does not work when probing for material, so you need to set the correct speed in the .ini file for AXIS 2 under max_velocity.

Regards,
Tom

The F word sets maximum feed rate.

www.linuxcnc.org/docs/2.7/html/gcode/oth...html#sec:F-feed-rate

JT

All works fine, thanks for the hard work and effort. I like the simplicity, but is there a way to adjust the velocity of the Z-axis when probing the plate. I use a z-axis with rack and pinion.
Ziggy

PCW wrote:

You might take a look at the current implementation:

git.linuxcnc.org/gitweb?p=linuxcnc.git;a...ecffe87556e2;hb=HEAD

This is in the THC comp.

To add proportional control one possible approach would be to modify the THC
comp to use an external PID component (Linuxcnc's standard PID comp)

It looks as if this is getting close to the way I would like to see thc handled. i will be ordering my mesa cards soon , I was really waiting to see the latest info on the 7i76e card before committing to anything.

BTW , the neuron thc does exactly this , only problem is , it is a stand alone controller that has complete control over the z axis , linux or mach is only the coordinate plotter with no idea or control over z at all ,, the neuron is a very good thc , makes some of the finest cuts consistently that I have seen on a hobby class machine , but leaving the machine controller out of the loop is unacceptable to me.

per Andy
The complication is likely to be setting the behaviour when the arc is not yet established. What is the THCAD voltage output then, and what behaviour is required?

i would think there should be a way to let linux handle thc until arc is established , likewise turn control over to linux in tight corners (ie below set speed %) , short moves and overpasses as this is the way regular thc functions are handled
I'm not looking to do anything a typical low cost THC wouldn't do for anything other than following the metal at different feed rates based on a set target. another approach that has crossed my mind.. it is well documented what torch height will give the best cut for said material. although should the metal be rusty or pitted the voltage may not be accurate,, if the IHS set the height , then read the voltage from that height , let the machine maintain that height from that voltage , not a pre determined voltage that may or may not be right.
I'm hoping that I am explaining myself clearly here ,, in other words (just as a for instance) say 1/4 mild steel plate needs to be cut at .050 torch height .. the voltage may be 146 on a nice clean plate or 162 on a rusty plate , but both cut equally well at that height,, so the controller needs to sample the voltage of the cut that the touch off has established and maintain that voltage , what ever it may be ,,

cwalker1960 wrote:

It would seem that PID loop should be able to compare voltage and adjust such at whatever rate needed to track the material.

This should be relatively easy to set up. You would basically just need a PID component where the command value is the required voltage and the feedback is the actual voltage.
I would expect this to be an I-heavy PID loop.

The complication is likely to be setting the behaviour when the arc is not yet established. What is the THCAD voltage output then, and what behaviour is required?

You might take a look at the current implementation:

git.linuxcnc.org/gitweb?p=linuxcnc.git;a...ecffe87556e2;hb=HEAD

This is in the THC comp.

To add proportional control one possible approach would be to modify the THC
comp to use an external PID component (Linuxcnc's standard PID comp)

I talked to Peter at Mesanet trying to get a feel for the mesa thc and linux interaction with the information it provides. At present it is my understanding that linux just compares the voltage and bangs out an up or down move at a predetermined speed.. Knowing that linux is fully capable of sampling this information and with a proper closed loop is it not possible to get a better control over the THC? why would this information not be analyzed and adjust the torch z speed according to it's needs? It would seem that PID loop should be able to compare voltage and adjust such at whatever rate needed to track the material. IE the further target voltage is out of range the faster the correction is made and the closer the slower. If this is in fact how linuxcnc is addressing this then I am ready for the move. If it is not the way it is handled then I don't really see it as being significantly better than any of the other low cost (not so good IMO) solutions. I really want to know answers before i tear down a functioning machine ( although not as good as I would prefer) to make a serious changes and arrive at the same place I already am. there are many well proven stand alone thc that use a pid loop to follow the metal but being stand alone leaves the z axis out of control to the motion controller , linux or even mach has no idea where the z axis is. making an integral plate marker attached to the z axis almost unusable. While mach doesn't even have the capabilities to handle internally controlled loops, linux does if it can be implemented. And if I am completely mis understanding this whole scenario please lead me to the proper documentation so i can get on with making a better machine.
Can we have a plasma category?

Hi,

For some reason on the config that I did install, the values for the step increments for the THC, the travel height, pierce height and switch travel does not seem to always take effect immediately after I have changed them. For example, at first when I adjusted the switch travel it did work somewhat, but usually when I did change it, it had no effect on the movement of the torch after the plate was sensed.
With the step increments I slowly increased the value once because the torch was not moving up fast enough, I then change the value to something ridiculous like 2 mm and the effect seem to have took place but when I changed it back to a much smaller value, the torch still moved as if the value was 2. It was only fixed once I restarted LinuxCNC.

I did however 'fix' the problem by changing the default values to the values that I desired, and that works perfectly now.

Regards

I have tested and used those functions for a very long time and on a lot of machines and they do work properly all the time.
Can you explain exactly what is working and what not? It would help a lot at troubleshooting.
Regards,
Tom

Hi all,

I am back. I have been having some trouble with the THC user interface that shows the ARK OK, UP DOWN etc. signals. With the input values, such as the switch travel, travel height and gap width. When I change the standard values, it seems that the program does not recognizes the changes. Thus far I have manipulated the torch pierce height and switch travel values with the torch holder, but I have build a new torch holder which does not allow for such manipulation.

Any suggestions.

Regards

Hi Andy,

So I did tie up all the unused inputs to zero, and there was definitely an improvement. Another guy I talked too also suggested that I install a first order low pass filter on the arc voltage input from the plasma cutter, so I will try that as well to see if I can get and improvement.

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Thanks to all for helping me.