focus and pixel size issues

Added by reinoud about 7 years ago

Dear folks,

after rigorous testing we are still having trouble getting a good focus. We have a Chinese made K-III (IIRC) and in general cutting goes quite well. However, engraving acrylic is our main job.

We added an low-pass filter between the PWM output for a smoother power control since the machine doesn't seem to have a low-pass filter. But without a scope we can only rely on simulation and some measurements made by a voltmeter but the results look OK now where we used to have interference issues. Maybe we ought to get back to the potmeter that shipped with it?

Is there a good way to test the focus? We tried the move up-down technique but when we go up or down with the platform (240V normal motor) we have to powercycle the machine since it crashes the cups hardware :( Should we use a very laser-insensitive material? It seems like around 23 mm is about the right position for perspex, but its an odd number.

Big pixels and half-pixels
Our pixels are not super, they are much bigger than with the old Chinese hardware on the same material. We blame this partially to focusing and/or dirty optics but cleaning them doesn't solve the issue.

We also got pixels that were `half'-pixels in that surrounding pixels were fine but a lone pixel is at times not marked correctly. We get better results when we slow down the engraving speed to say 40%.

We have several theories:

  • Could it be that the CO2 laser can't switch fast enough? But why was it better then with the Chinese hardware? Could it be laser-aging? So we get less good results than when it was new?
  • Could it be that the opto-coupler can't pull the laser enable line down fast enough? This would account for the half-pixels disappearing at slower speed, but not for the laser point size at slower speeds; that doesn't seem to be changing.

Any feedback would be much appreciated!
With regards,
Reinoud Zandijk