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Limitations of Glass CO₂ Tube Power Modulation
Electrical Response Time: The glass tube is powered by a high-voltage DC supply that produces continuous wave output. Switching and modulating this kind of supply is much slower and far less precise than RF-excited tubes, making low-power settings unstable and causing delayed or uneven laser response.

Nonlinear “Firing Threshold”: The CO₂ gas must ionize and sustain a plasma for lasing. Below a minimum current and voltage (the “lasing threshold”), the tube simply does not produce a beam. This means there is a baseline below which no light is generated, preventing true 0–100% analog modulation.

PWM (Pulse Width Modulation) Limits: Power is often controlled by pulsing the laser with PWM, but because the plasma response is slow, low duty cycles (such as 1–10%) do not produce proportional or stable output. That’s why at very low percentages, the laser may not actually fire.

Physical Characteristics: DC glass tubes are designed for simple on/off control or slow power changes rather than high-speed, fine power modulation. The ionized plasma cannot respond quickly to control signals.

RF CO₂ vs Glass Tube Modulation
RF-excited CO₂ lasers use radio frequency drivers, enabling extremely fast modulation, true analog control and very fine pulse shaping, with stable output down to low percentages of total power. Glass tubes, in contrast, cannot achieve high-speed or linear modulation due to their excitation mechanism.

Practical Implications
For cutting and engraving where power control below ~20% is needed, glass tube CO₂ lasers are less precise and often unreliable. They may not fire at low power settings or may not maintain beam stability at the edges of their modulation range.

H.O skrev: ↑6 oktober 2025, 07:02:31 Jag antar att du uteslutit allt mekaniskt, slapp rem som kuggar över p.g.a den höga accelerationen (t.ex)?

Ang. styrningen av lasern. Det är inte så enkelt att du har 3.3V logik på styrkortet och 5V på laserstyrningen eller att det sitter en optokopplare på lasern som styrkortet inte riktigt orkar driva - eller nått åt det hållet? Inget av det förklarar inte varför det verkar bli bättre när du ökar acceleration men det är en tanke i alla fall.

malman skrev: ↑6 oktober 2025, 12:35:28 En tanke till som slog mig....
Använder GrblHal på en teensy till cnc plasma styrning.
Där kan man justera tider för stegpulser mm.
Med för snålt ställda tider för step pulser skulle man också kunna tappa steg sporadiskt.... Finns det något motsvarande i detta styrsystem?

The MD556/DM556 class requires a minimum step pulse width of about 2.5 µs and a minimum DIR (direction) setup time of about 5 µs before the step edge; staying at or above these values is appropriate and reliable.

Key timings
Step pulse width: At least 2.5 µs high (and typically also 2.5 µs low if using 50% duty), which supports up to roughly 200 kHz input rate on DM556-class drives.

Direction setup time: Change DIR at least 5 µs before the active STEP edge to ensure the step is taken in the correct direction.

Max pulse frequency: Up to 200 kHz for DM556E/DM series; some MD556 datasheets list up to 400 kHz, but 200 kHz is a safe, widely stated capability.

Practical recommendations
Use ≥3 µs step high and ≥3 µs step low to add margin over the 2.5 µs minimum, especially with long cables or electrical noise.

Assert DIR at least 5–10 µs before issuing the next step pulse; many controllers use 10–20 µs to be conservative.

If approaching the stated max pulse rate, verify the specific model’s datasheet (MD556 vs DM556E) and test at the application’s cable length and supply voltage.