Plasma Torch Height Control

  • Hi !

    I've been struggling with an issue for some time with my plasma setup : given the irregularities of the steel plates and the support grating, it is important to have a real-time control over the torch height above the workpiece.

    On my Hypertherm Powermax 65, I have an output which gives me a divided tension : tension between the torch and the workpiece divided by some value (contolled by jumpers).
    At first, I thought I could use this as an analog input in my KRC2 to change the tool "X" value during the execution of the program, but never found how to do it.

    If it is at all possible, that would be the most simple and elegant solution.

    Instead, I was advised to add an axis with a stepper motor on the toch support ; something similar to this : , albeit a bit less neet.
    The problem that I found is that these devices are not autonomous. They need a NC to trigger them and reset height to a nominal value after each cutting cycle.
    I could see the torch moving up and down to adjust for a bended steel plate, but from part to part, I ended up reaching the hardware limit of my rail.
    On a 3 axis tables, this "reset" job is done by the system's NC, but I'm not sure how I could manage that with the KRC2.

    Any ideas ?

  • What's an 'NC'?

    If the tool can accept a simple relay/pushbutton contact to reset the height, then all you really need to do is add an output on the KRC2. But how to go about that depends on what I/O architecture your KRC2 has installed.

    Dynamically changing the tool on-the-fly height only works if you use the Function Generator, which is a poorly-documented feature -- usually people buying KUKAbots purchase the ArcSense seam-tracking option for this kind of thing.

    If, OTOH, you only need to adjust your tool height for an area, instead of every mm along the cut, you could "touch off" to the area before cutting it, and perform a Tool or Base adjustement for that area.

  • Sorry, by NC I mean a controller.
    Those ready-made Torch Height Controllers don't have their own, and it makes sense because they need to know when they can reset to the default height (between two cuts).
    Kuka Arcsense seam tracking. Hmm... That *sounds* expensive :smiling_face:
    The "Function Generator" sounds nice. What can you tell me about that ?

    The " Touch off" idea wouldn't work well because some parts span the whole steel plate in at least one direction.
    But I'm nevertheless interested in how to adjust the Tool and Base.
    To be honnest, I do only offline programming, and generate only a single .src file per cycle, so I'm not used to having a master program calling subs.

  • The FG is the root technology underlying Seam Tracking, and in fact forms the underpinnings of RSI -- it's like RSI's grandparent, in some ways. FG or RSI are the only way to dynamically adjust robot paths on-the-fly.

    Unfortunately, while Seam Tracking is fairly well documented and supported, the FG is not. It is possible to "roll your own" FG operation, but the docs are very thin, and I've never actually done it.

    Tool and Base adjustments change the geometric context in which a program is performed. For example, if your torch gets bent, you could re-teach your Tool, and get your old programs to work without having to re-teach all the points. If your table got moved relative to the robot base, you could teach the robot the new Base of the table and that would "shift" all your programs to follow the table.
    This all assumes, of course, that your original Tool and Base values were correct. If you just programmed everything in Tool or Base Zero, for example (which too many people do), it becomes much harder to make use of Tool and/or Base shifts. Not impossible, but much harder. Doing it right the first time helps save you heartburn later.

    In your case, if your part had a localized "bump" that was right under a small circle you were trying to cut, you could perform a simple Base shift upwards by the height of the bump, and cut your circle. But, like you said, if you need to make a long cut across multiple bumps or ripples in the metal, a simple Base shift would not work.

  • Thanks a lot !!
    This looks like it might work : one of the examples is in fact "Using a distance sensor, a correction is to be made in the Z direction of the TTS." which is exactly what I need to do.
    Now, I just need to understand how it works.
    The manual starts with "The function generator included in the KRC software is easy to use...", and then proceeds to confuse the hell out of me, like any good KUKA documentation.

  • Hi there!
    I have the similar task, the topic appeared right on time. The problem is to implement AVC function on TIG welding system. During the arc burning the piwersource tramsmits real voltage to RC via interface - it's standard feature.
    The difference is that I have the correction parameter as 16 bit digital value, not an analogue. Seems kind of online value converter has to be written.

    OK then, back to fiddling with IOSYS.INI to get that analog input working.

    Thanks again !

    Please do not leave the topic, place any results here. So I'll post mine too.

  • On a KRC, analog values are actually passed to/from the robot as digital values, at the bus interface level. At the program level, the only real difference between analog and digital signals is in how you make use of them.

    For example, a 16-bit analog input to a KRC could be mapped in IOSYS.INI as either a digital "Word", or mapped to an ANIN. The ANIN would need to be set up such that the full 16-bit range of the incoming signal would be scaled to a Real value between 0.0 and 1.0 (or, if the input can be both positive and negative, -1.0 to 1.0), where 0 would represent no input, and 1.0 would represent the maximum value of the 16-bit signal (either 65535 for an unsigned input, or +/-32767 for a signed signal).

    In your program, you would still have to scale either signal mathematically, to match the actual voltage/force/current/flow/whatever that the analog sensor is reporting.

  • Hello.

    I have the same scenario...

    Plasma cutting that needs torch height control real time.

    The plasma generator outputs analog voltage that corresponds to torch distance from metal.

    I have setup devicenet 0-10V analog input to kss 5.6.12

    but how can go for next step ?

  • Plasma cutting that needs torch height control real time.

    Define "real time". Just to touch off before starting a cut, or constantly while the cut is running? Without the ArcTech SeamTracking option, or the RSI option, the latter is going to be extremely difficult.

  • Touch off before starting a cut and after that correction while cutting

    1-2 mm error to the height correction is not problem.

    What is the best solution for this ?

    I have made a linear axis with 200mm travel that can correct height independently from robot

    but i think with robot only without external linear axis will be the best solution.

  • In general, path adjustment in "real time" is not possible without using something like RSI or ArcTech with Seam Tracking.

    With some convoluted KRL programming, it is possible to get an approximation of real-time path control, but it would require breaking every path segment into multiple small approximated motions, and the correction will always lag the sensor input by at least $ADVANCE motions due to the Advance Run Pointer.

  • plasma cutting is done on a flat sheets of material. they may be warped a bit but in general they are pretty flat. in other words there is no need for rapid height adjustments.

    function generator manual is pretty short so not much to read. and it includes an example of height control. i would be looking into that.

    using separate axis is a possibility too. it would need to be configured as an asynchronous axis so it can move independently of the robot.

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

  • Hello ,

    I resolved with a external device

    THC (torch height control )

    Adquiered with Chinese supplier

    The THC received the signals from the plasma machine

    Note : the plasma must to be inverter because the THC received dividend arc voltage that comes from the plasma , and the signals "arc on" and" ok to move "

    The THC it's connected between the plasma and the robot via digital I/O

    The Robot moves and do the cutting figure the THC motor up Dow as required.

    Any details you can send me Message

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