The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

The New Hotness

  • CO₂ Laser Tube Current: Analog RiseTime Target

    Given that the CO₂ laser power supply seems just as happy with an analog input as a digital PWM signal, one might wonder about the bandwidth of each mode. Rather than feeding the supply with a function generator, raster-scanning a grayscale target should suffice.

    For example, this would generate five square waves:

    Gray bars 10-90
    Gray bars 10-90

    The bars are 10 pixels wide, so scaling the image at 254 dpi makes them 1 mm wide:

    LightBurn - bandwidth test pattern setup
    LightBurn – bandwidth test pattern setup

    As before, the first and last bars are 100% (white), with 0% (black) bars just inboard. The other bars are 10% and 90% to stay a little bit away from the 0 V and 5 V limits. I set Lightburn to invert the colors so that 100% = full power and 0% = beam off.

    Engraving the pattern at 100 mm/s makes each bar 10 ms wide and the risetimes and falltimes are easy to see:

    Tube Current - analog - gray bars 10-90 - 100mm-s - 10 ma-div
    Tube Current – analog – gray bars 10-90 – 100mm-s – 10 ma-div

    [Edit: Clicked the wrong picture.]

    Although it’s a bit handwavy, a 1.5-ish ms risetime suggests a single pole (ordinary RC) time constant τ = 700 µs = 1.5 ms/2.2, so the controller’s output filter cutoff would be around 200 Hz = 1/(2π τ).

    The laser tube current looks a little slower than that, so there’s a definite tradeoff among engraving speed, edge crispness, and power level.

    More study is definitely needed …