Raster speeds not matching actual laser head speeds

How can I speed up raster engravings?

Max speed is set to 600mm/s with acceleration at 1500mm/s, but there’s no way the head is actually moving at that speed, seems more like 50mm/s. A 100x100mm greyscale engraving takes 20 mins+.

Seems like it accelerates and decelerates between each pixel which is the limiting factor. Using LaserGRBL produces raster gcode that runs the head at the actual speed I set it to, but doesn’t offer things like overscan.

55w CO2 running GRBL. Using closed loop steppers with linear rails. Firmware settings match the speeds I’m using in LB. Don’t know if I’m actually hitting 600mm/s, but I do know that the machine can run a lot quicker than what it does with gcode produced by LB.

Any help here appreciated. Thanks.

Forgot to mention, I’m using M3 in GRBL1.1e as the newer version didn’t seem to let me adjust power/speed on the fly in LaserGRBL which I use as a gcode sender. Is switching to a newer version with M4 the answer here?

I think there are a number of things to unwind here.

  1. Scale of speed - is this a DIY build? How have you determined the target/expected speed range of your machine? The max speed of your machine will ultimately be determined by physics.
  2. Processing speed - Are you really running your system on Arduino? If so, which one? Typical Arduino running Atmega328 can process something like 200 instructions per second. Grayscale engraving in particular is especially instruction heavy. I suspect this is why you’re getting a slowdown at the pixel level.
  3. LaserGRBL vs LightBurn - Like for like code should have like for like performance from the controller. So whatever LaserGRBL is generating must not be the equivalent of what LightBurn is generating. Have you done grayscale at the same DPI for both?

From a machine capability perspective you should experimentally determine the max capable speed and acceleration using rapid moves (not images or grayscale). That will address the top expected speed. Getting to higher speeds would require either a reduction in laser head mass or increase in motor performance.

Processing performance is most easily solved with a board upgrade. There are a number of affordable 32-bit boards available.

I suggest you start with a time study. Line up some measurement markers on your bed and setup some high speed video. Review the video footage and calculate acceleration and speed making sure you account for time to accelerate/decelerate.

I don’t know if it’s the answer but I see no good reason not to use a newer version of GRBL. Laser mode is extremely useful. It’s possible you’ll get a performance difference depending on how this has been implemented in firmware but I’m not aware of any specific performance benefit claims.

The issue with adjustment of power/speed using LaserGRBL seems odd. I don’t see why that would be the case and is likely solvable.

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