How is min power calculated when not in constant power mode?

I understand the min power setting was removed with the latest version, as it apparently wasn’t doing anything outside of Grayscale mode. That being the case, can someone explain how the laser calculates power reductions when not set to “constant power mode”?

Machine Settings (stored on your controller) has its own Max/Min Power in addition to grayscale Layer’s Max/Min. And then there’s the grayscale value of a pixel.

The Layer Max/Min fits within the range of Machine Settings Max/Min, and the grayscale value is a portion inside that. That is, Machine Settings Max/Min is not a cap or clipping point

e.g. if Machine Settings Max/Min is 80%/15%, and Layer Max/Min is 50%/10%, then the actual PWM range will be 42.5%/21.5%. A 25% black pixel will get a pwm of 26.75%.

This also comes up when scaling back power for cornering vectors, but also the “Start Speed” comes into play.

Thank you for the reply, Danny – I wasn’t aware that the machine was using it’s own minimum value – I’ll have to research those settings. That said, with the exception of greyscale, does the latest release of Lightburn (the one that removes the min setting from the layer) use a min value of 0%, and leaves it to the machine to resolve the applicable range? Maybe it had always worked that way…

During vector cutting/scoring, when the laser starts/stops, does a corner, or takes a tight curve, there will be points where it’s slower than the target velocity. The machine aims to scale the power with the vector sum velocity in relation to the target speed. This scale is within the Machine Max/Min power setting.

Additionally, DC-excited tubes have a “dead zone” of about 0-15% of the rated output where they can’t operate. e.g. a 100W tube can be turned down to 15W, but there’s no way to get a stable 10W out of it. If you start at 15W and reduce the PWM, the power drops rapidly, and the lasing is unstable. It can produce 12W one moment and 5W the next.

So, Ruida has “start speed”- below this, it just uses Min Power but scales above that.

e.g. Machine Config is 80%/15%, start speed 5mm/s. Layer is 100%/0%, speed 100mm/s. But going around a corner, when it has an instantaneous velocity of 50mm/s, AFAIK the pwm should be 47.5% duty.
Below 5mm/s start speed, it’s a fixed 15%.

If the Layer was 70%/10% 100mm/s, then when doing 50mm/s the total should be 41% duty, halfway from 70% to 10% and that scale fits within the 80%-15% scale

During dithering (not grayscale), a pixel is either on or off, AND rastering is always done at constant velocity. So there is NO power scaling for reduced velocity, as we are in constant velocity. So, there is no use for Layer Min Power. Grayscale totally does use it, though.

If you have an analog current pot on the LPS, you want to set the current to your tube’s nominal rating for long tube life, then Machine Config Max Duty should be 100%.

If you don’t have an analog current pot on the LPS, then you want to set Machine Config Max Power to limit the current to the laser’s rating. Say 78% Max Power in Machine Config produce a rated 26mA… Then 100% power on the Layer will translate to 78% duty.

This means the Layers can’t ever demand a current over the limit no matter what, and in general you should be cutting at 100% and adjust speed for the fastest that still goes through. The Layer settings are user stuff and either of these two limits will avoid giving the user the ability to call for currents that exceed the tube rating.

Similarly, if you set Machine Config Min Power to 15%, then the Layer 0% Min Power will, I think, be 15% duty. Again, obfuscating the user settings so the user’s Layer doesn’t have to deal with it.

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