Another plasma component...

phillc54 wrote:

P.S.
Yes, I would be interested in being able to provide ohmic probing as well.

From a system perspective, this is pretty easy. Just provide one more pin that is ORed with the float switch and use the output for probing.

The other thing I had trouble with was the probe becoming enabled while cutting. So becasue I used a gcode touch off routine, I set a digital output from the gcode before the probing sequence and reset it at the end of the routine. I then ANDed that with the probe input so it would only trigger when we were in the probing sequence. I Was thinking I could then sense when the probe/ohmic sensing was triggered while cutting (digital output not asserted) and wondered if I made an immediate offset that was equivalent to the cut height. I've had the gear to add Ohmic sensing here for a month and have not had time to modify the machine to implement it. (I need to fit a bigger drag chain as part of this).

Dunno if my ramblings help...

Rod

I OR2 the ohmic probe signal and the float switch signal and feed the output to the probe input on my current system. Out of an abundance of caution my ohmic sensing circuit is only connected to the work and the torch shield through a relay (well actually 2 because I only have SPST relays on my chinacom relay board) when actually doing the probing. I do have a GUI button so I can do a test connection for trouble shooting a shorted torch tip (happens more often than you think with the Finecut consumables I use). I did this even though the opto isolator I use is good to 2Kv or so isolation. I know this means that I can't use it for plate contact sensing when I am actually cutting but I don't need that because of my torch break away sensing switch (sensitive enough that the torch mount usually doesn't come all the way off the Z). Your A120 when used with the automation torch doesn't need this because the built in firmware will throw an error and shut off the torch if this happens, on US machines the 85psi led will light indicating this error. I believe we discussed my ohmic sensing setup in some detail in the recent past.

Phill

I didn't notice any problems during my installation. I was actually quite surprised by the lack of them. Thanks to Rod I didn't even have to look into the problem, straight to Synaptic to find the the required library wasn't installed and install it.

Today's adventure is find out why I have lost my hal widgets out of my Glade setup. I went through a bunch screwing around to get them installed a few months ago and now they are gone.

John

All

I don't know why this happens. When I try to open any of the plasmac glade files by right clicking on it in the file browser and selecting Glade to open it I don't get all the hal widgets in the left pane and I get error messages where they should be on the preview screen. Now if I start Glade from start menu or from the desktop short cut it starts with all the widgets loaded and if I open a plasmac Glade file from the file menu it opens correctly. Oh well I don't have time to fight this.

A bigger problem is that some of the files won't open in Glade... I opened some of those files with a text editor and found some names to contain special characters. So for instance the file plasmac_buttons.glade works when you run linuxcnc and select a configuration that uses it but if you try and open it with Glade you get nothing, not even a warning. I think this may have something to do with the problem:All of the files that won't open in Glade have a similar problem with special characters in the file names.

John

John , glad you are up and running. Yes, my Ohmic sensing is somewhat based on your ideas shared earlier except I'm using a 24 volt isolated slimline DIN rail power supply instead of your 12 volt wall wart. The biggest problem is as a carry over from the machine upgrade is there is not enough room in my drag chain any more so I have to upgrade the tray it sits on to upgrade it. I've been able to fold up a new one but its not installed yet.

Phill

Thanks, I am quite accomplished at causing Glade to crash but this is new one on me. That is why my first move is to always open a Glade file in a text editor and check for funny stuff.

John

Phill

The ability for the operator to easily check for a shorted torch is very important, it should be easy like a button and indicator on the GUI. When using ohmic sensing the float switch is always used as a Z minimum limit if it isn't ORed with ohmic signal.

I really tried hard to get just the float switch to work for probing. I tried many combinations of counter balance springs and never could get it right. If I had enough force negation with the springs then the float assembly would oscillate and over shoot when under THC. When I had it stiff enough so there was no oscillation or over shoot then the thin sheet is deflected a random amount. Actually at Z accelerations that are fast enough to cut corrugated sheet the response of the torch and float assembly get to be a problem.

Please find attached the Gcode probing subroutine I currently use. It is not perfect. The biggest problem is if the probing problem isn't fixed with a retry the subroutine exits with an error code when it should just jump back to the top with the program paused and the error message displayed. This is in imperial units because it was never met for an international audience. The distance sanity check works ok for the thin sheet I use, it has never been tested on thick material that will not deform or rock under the pressure from the torch.

The best for someone doing hobby or job shop work will be a way to select whether to use ohmic sensing or the float switch. This could be a check box in a setup pane and/or a gcode command sent by the PP that depends on the selected tool.

Do you know if anyone has used the plasmac component on a live machine?

John