Found new EMC issue with motion control

During testing I found a new EMC issue. This time its the motion controller. When increasing the arc power, the dynomotion card suddenly becomes unreachable and the CAM software chrashes. I was afraid this would happen, since I’ve seen it in other CNC milling machines that use the Dynomotion card, so I took many precautions. However, the issue still popped up. My card is mounted in a shielded enclosure and has galvanic isolation on all used interfaces (including the USB interface). Even now the issue still persists. This is a mayor problem now which will consume quite some debugging time.

I know its EMC since the card works perfectly when the arc is turned off. The current counter measures are:

  • 4 stage common mode filter on mains power
  • Shielded enclosure
  • USB optical isolator
  • Interfaces to stepper drivers are all optically isolated
  • USB ferrite bead located next to the controller
  • Low noise linear power supply

 

Suggestions anyone for additional measures?……..

The picture below shows the current state of the motion control cabinet (click the image for large picture).

 

Comments

  1. Adolfo

    Hi Mike
    I understand you very well, i had similar problems, the solution that works for me was disconect the generator stage from the ground main, and not let electrical contact between generator box and control box
    Anyway, you can try this:
    – put a 100nf ceramic capacitor on control board power connector
    – take care with usb cables, not all usb cables works well
    – use a shorter cable to conect the control board (avoid loop)
    – i would try to connect the control board to the usb isolator and this to the pc (avoid the usb wall)
    – try to use and isolated 5v power supply for the board
    – don’t connect the main ground with the control board ground

    regards

  2. Post
    Author
    mikebax

    Hi Ghislain, its been a while since I updated my website. I’ve resolved all EMC issues with my machine now.
    I plan to construct a cage in the future, but this gives some practical implimentation problems, and since the issues have been resolved I’m in no hurry to create one.
    Thanks for the link, it might help others who visit this website!

  3. Ben Tubbing

    Dear Mike,
    I am impressed by your work!
    My name is Ben Tubbing, Dutch, now living in Brussels, studied in Delft. I built a first spark eroder die sinker in 1996, for making components for a miniature gas turbine.
    Recently, I redid the electronics, and built a 150V, 5A switched mode supply. It took effort, but what I have now is fairly simple. It is a switched current source with an inductor, delivering constant current to the gap. The controller just a comparator plus some timer chips plus the power fet / driver. Works very nicely. Position control for the die sinker is done by spark breakdown voltage, a window comparator and a couple of ttl chips. And it is easy to boost the current by adding lower voltage current sources, I will add another 10A module soon. At this moment, I am making the new generation mechanics.
    To see a previous project, search for “fusion 360 gallery inconel spark erosion”, then you should see ” copper dies for …..”.
    Let me know if you are interested to know more, I will be happy to share knowledge.
    Email ben@bjdt.be.

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