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I am slowing learning EMC2 and have a few questions on THC.

I have a plasma machine that works good. I have successfully connected the ARKOK signal and it works. I have made a few parts. I am now trying to move the Z-Axis up and down with a THC unit. (It is a THC 300 from Cambell designs).

I have tried to follow the wiki and the examples but seem to be missing something.

From what i understand i have to decouple the axis.2.motor-pos-cmd from the stepgen.2.position-cmd

Which i have done with the following lines:

net zpos-cmd <= axis.2.motor-pos-cmd
net zpos-cmd-final => stepgen.2.position-cmd

I then create a move up bit and move down bit. Currently I have them connected to 2 switches I hold in my hand, when it works I will connect it to the correct pins on the THC unit.

newsig TorchMoveUp bit
linksp TorchMoveUp classicladder.0.out-13
newsig TorchMoveDown bit

linksp TorchMoveDown classicladder.0.out-12

I also create the max and minmum distance to move

newsig ZMinCord float
sets ZMinCord -0.15

newsig ZMaxCord float

sets ZMaxCord 1.0

I then set the maximum and minimum distances to move
linksp ZMaxCord sum2.0.in0
linksp zpos-cmd sum2.0.in1
linksp Absolute_Max sum2.0.out

linksp ZMinCord sum2.0.in0
linksp zpos-cmd sum2.0.in1
linksp Absolute_Min sum2.0.out


I then use a mux4 to select. If TorchMoveUp is selected I go to the absolute_Max, if TorchMoveDown is high, I go toward the absolute min.
linksp zposcommand => mux4.0.in0

linksp Absolute_Min => mux4.0.in2

linksp Absolute_Max => mux4.0.in1

linksp TorchMoveUp mux4.0.sel0

linksp TorchMoveDown mux4.0.sel1
linksp zpos-cmd-final mux4.0.out

From following the dallar example, I thought this was basically how it worked... However, I run a program everything is fine, then I press the switch to move up, it moves up a tiny amount and then gives me a joint following error.

A couple of things I am confused on, what is the feedrate it will be moving? The feedrate given in the program?
If I find my min and max from a sum command of the zpos command, will this change as the z pos command changes.

I do not have a float switch, so I set the zero of my torch to the top of the material. Command it to go to a certain height, it pierces through and then i want to invoke the Torch height control.

Any help would be appreciated. Thanks
Brian

Have you considered using the THC HAL component?
www.linuxcnc.org/docview/html//man/man9/thc.9.html

Your following error is because the stepgen feedback signal no longer needs matches the command signal. Ideally you need to subtract the THC offset from the stepgen feedback before passing it to the axis-fb pin. The THC HAL component does this, but might not suit your inputs.

I get very confused by the old-school newsig / linksp / linkps format, but let me have a look.

These lines could be combined as:
You are setting sum2.0.in0 to both Zmin and Zmax there, and linking zpos-cmd twice. That is probably an error.

Also, You can set the sum2 pins directly if you want, iecan just be

From following the dallar example, I thought this was basically how it worked... However, I run a program everything is fine, then I press the switch to move up, it moves up a tiny amount and then gives me a joint following error.

The quick and dirty solution would be to loop the axis feedback to itself, ie
net zpos-cmd axis.2.motor-pos-cmd axis.2.motor-pos-fb

But ideally you want to arrange to feedback the stepgen feedback with the THC offset subtracted, which will give you proper f-error detection of the commanded step rate exceeds what the stepgen can follow. (this is set only by the base thread period, and the axis limits are probably much, much, lower)

I was looking at the THC component and that looks exactly like what I need. However, it looks like I need to bring a scaled down voltage from the tip into this component. It does not look like it has a bit for just move up or down if you have an external box that sends those signals.

Would it be reasonable to just use some hal components and "fake" the voltage going into the THC component. Where if my external box says move up I could put a 6 into the THC component voltage and if it says move down I could put a 4 and have 5 when it is the correct height. Not sure if this makes sense, but I would rather use the component if possible.

Thanks for the help.

It might be simpler to edit the thc component and re-compile it.

You will find the current version at:
git.linuxcnc.org/gitweb?p=emc2.git;a=blo...02fa7bb54473;hb=HEAD

You can edit that, then recompile with
You might need to sudo that, and you might need to sudo apt-get install emc2-dev to get comp to work, but other than that it should be straightforward.

There are bit-type input pin declarations to copy, and the C-code function is quite short.

Brian,

At one point in time I did play with an up/down THC component for "smart" THC boxes but never did finish it . The current THC uses a velocity from the Mesa THC card that converts the voltage to pulses and it is what I use on my plasma table. An up/down one would be fairly easy to mod from the current THC comp. Andy is correct and you have to hijack the position and sub your own and lie about the feedback and say it is where EMC wants it to be.

John

Hello

I am a new user interested to use EMC with a plasma table THC .
I am tecnichian in electronics more than software developer , so is a liitle bit difficult for me change configuration .
I was reading about the HAL THC component and I am very intersted to use it .
Now my question is ...
It is necessary to use mesa board or can we use a small hardware ( voltage controlled oscillator )
to give the signal on the parallel port for THC control ?
Can we use ( as an example ) spindles inputs to "read" the torch volts ?
If some electronics is needed I will be happy to develop an open source schematic for that

Best regards to all
Roberto

Hi Roberto,

You do not need the mesa board, I use a parallel port. However, I do not read the voltage. I think the easiest thing for you to do is probably develop some hardware that will read the voltage and then decide whether to move up or down and send a signal to the computer on what to do, (since that is your strong point). That is basically what I do. I bought a THC controller from Campbell Designs and then connected that to the parallel port. I then modified the THC component per the suggestion by andypugh. I am by no means a great programmer, but it was fairly simple and it works fine for me. I can post it later if you like - I do not have it at this computer. One thing I am learning about EMC is you can basically do anything you want.

Any V-F converter would work, though the parallel port would limit your control loop bandwidth vs voltage resolution tradeoff somewhat. For example say that you can read the parallel port at 20 KHz so you can reliably sample an input square wave up 10 KHz. A t a 1 KHz servo thread you would only get ~10 counts full scale ( about 3 bits resolution) so you would have to low pass filter the velocity signal get a usable feedback signal (more voltage resolution), and this low pass filter will limit your Z Torch height axis control loop bandwidth.

Hello brianm,
Thanks for your answer . I was looking ( a lot ! ) in the web how to modify the thc component .
Basically I understand that may be changed and recompiled for suit the needs , but when I was trying to find more info i did not find nothing for a beginner .
Reading your reply and the reply from PCW ( many thanks too ) I come with a different appproach .
Would be relatively easy use the component input and "read analog values" like usb joisticks but I do not know the resolution and speed of this converters.
Also using Arduino to make the A/D conversion and why not something else like torch on, comparations etc...
There are also inxpensives USB SOUND CARDS that usually dont have ac coupling letting use them for dc A/D conversion ( but I dont know if HAL can use them.

At the end I think I will follow your idea !

Just will make a small external comparator and drive the voltage comparation from a parallel port pin (PWM) to set the voltage from Axis UI.
I will try also an experimental way to have the ARK_OK signal from the torch volt ( when working with a good ark I never saw voltages less than 80 v and more than 150 v )
Another experimental idea is to read the ARC_OK - UP - DOWN signals with just two pins ( when UP and Down signals are active will mean ARC_NO_OK ).

Now the big problem for me !
I NEED/WANT to learn how modify the thc component to do that.
Any help wil be greatly apreciated .
If everithing goes well I will be proud to post the hardware schematics and send some prototypes

Best regards
Roberto

hominux wrote:

Now the big problem for me !
I NEED/WANT to learn how modify the thc component to do that.
Any help wil be greatly apreciated .

This page explains how comp works, and how to recompile and install:
linuxcnc.org/docs/html/hal_comp.html

Basically make the changes you want to thc.comp then type comp --install thc.comp

Thanks a lot ! Looking for a lot but never find it !

My first impression is that, really, there are not limits on what can be done with EMC2.

I will begin to study just now .

Best regards

Hello all ,
Studying C language I was writing a .comp for interface a virtual jog wheel .
It has accelerated response , if the mouse wheel is turned slowly the out will be step by step.
but if you spin fast the mouse wheel it will be cubic steps .
I found useful for my plasma table ( just X Y ) but i think it may be useful for more axis too
If someone is interested ...

Best regards

Hi all

I was writing a new comp for thc boxes.

FIRST OF ALL I AM NOT A PROGRAMMER
So ,please, apologize if the program has a bad style

I believe is now ready for testings ( I am using it since two mounts and look fine ...)

BUT STILL EXPERIMENTAL (off course:-)

Hoping someone will find it useful

Hello guys
I'm new to EMC2 and Linux so i ask you kindly be very gentle.

I purchased from Agelkom Capacitive THC
The device is sending to pc four signals:

Torch UP
Torch Down
Torch in position (ARCOK)
Probe (Touch Plate)

As long it concern me, iti is a very useful device because it doesn't need to touch never sheet metal.

Can anyone can help me to integrate this device in EMC2?
Thank you in advance

their are configurations for Torch height controller within emc , see the examples for THC300
and also this post may help
www.linuxcnc.org/index.php/english/compo...mit=6&start=12#15198

are you connecting via a second parrell port ? , or other card