Wanted: constant movement during linear movement with G1 and G0 sequences

I'm currently working on my laser cutter based on the repetier firmware (tried 0.9.1 and 1.0.x). Cutting ist (mostly) working perfektly, but now I'm trying to engrave. For this, I'm exporting data from inkscape. I've drawn a schematical diagram of the movement:
Pseudo gcode:
G0 x1 F1000
G0 X4 F500
G1 X7 F500
G0 X10 F500

From top to Bottom:
-in blue the G0 moves. it starts outside of the engraving area and is meant to be used as acceleration/deceleration outside of the engraving area
-in yellow the G1 movement with laser on
-in grey the speed I would expect. accelerate, move constantly over a wide range and decelerate on the end and sometimes (in the example between 4 and 7) activate the laser
-in orange the speed i have. The laser head accelerates and decelerates on every G0 / G1 command, wasting unbelieveble amounts of time and leading to moments of near-zero speed parts while the laser is on, which leads to uneven engraving depths.

Is there a way, that I can have a constant speed through G0/G1 changes?


  • If jerk is higher 2*max speed all speed changes are without acceleration. With the slow speed used here that should be no problem. You need to have it anyway so you can use speed to change color. Or you need a pwm controlled laser that you programmed to use pwm as default implementation does not do it.
  • A laser power control will be included, but it will not solve the problem, because CO2 laser tubes can not be used under a certain power (about 25% in my case)

    The speed in my example was really just an example. I tried all speeds from near zero to about 2000mm/s and it makes no difference.

    I'm still wondering, why there is a difference between those two examples below:

    Starting at 0/0:

    G1 x10 Fxyz
    G1 X20 Fxyz
    which will lead to a acceleration at the beginning (near X0) an deceleration at the end (near X20)


    G0 X10 Fxyz
    G1 X20 Fxyz
    which leeds to 2x acc (at X0 and C20) and 2x dec (at X10 and X20)
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