I have a laser that is mounted as an extra ‘spindle’ on my CNC machine. The motion system is powerful and can keep up with speeds needed for a laser no problem.
However, because the toolhead is large and heavy, the motion system has a smoothed out acceleration profile to reduce jerkiness. This means that moves are not at full speed instantaneously, it ramps up to speed and ramps down into corners etc. Meanwhile, for a consistent burn, the laser power output must compensate for this variation in speed when burning a line. How is this calibrated in Lightburn? What settings should be tweaked to account for accelerating/decelerating and modulating the laser output when the speed is not constant?
It’s not, because the controller calculates it during path planning.
Which requires a controller running firmware with laser hardware in mind, because otherwise it just assumes the spindle will run at full speed all the time and can keep up with the chip load.
If it’s running a GRBL descendant, then $31=1 to turn on laser mode is your friend.
If it’s running LinuxCNC, then HAL tinkering is in order, starting with this doc:
Their forum has many threads on the topic that I haven’t been following.
OK, thanks. I am already setting to Laser mode, so that’s covered. What is strange is that I can run my CNC without the smooth motion profile, and the burns are as expected. As soon as I run a firmware build for my machine that has these jerk compensation acceleration curves (which are so much more graceful), the laser is not producing enough power, almost as though it is being throttled down. Hence, I wondered whether Lightburn is reading the speed and acceleration settings of the controller and compensating somehow?
No, the firmware does, as Ed mentioned. If you have a smooth acceleration, the smoothed power output might be too low for your laser. LB has an option to compensate for this in fill operations: overscan. You can use this parameter to adjust the distance the mechanics have for reaching the desired speed.
To the best of my admittedly limited knowledge: no.
All LightBurn does is set the power and speed for an entire layer, then hand the job to the controller, which then figures out how to apply those parameters to each motion / vector within the design.
Makes sense tbh. I will have to look at how the acceleration model is affecting laser output on the firmware side. It is probably a simple case of not using the smoothed motion when running in Laser mode. The trouble is…it’s determined at firmware build, so not easily switchable in the controller parameters. Oh well. Thanks both for the help.