Neil, >> What's the best strategy for controlling a laser?
My machine uses 2 axes to move the laser optic to the right position. I've got this much working satisfactorily. Now I need to control the laser power. I was planning to use a 3rd axis for this, let's call it Z. My plan was to use the sign of the Z position to control the laser-enable signal, and the magnitude of the Z position to control the laser power. But maybe this is a stupid idea... I don't know. << It is often a conundrum as to whether it is better to treat the laser as spindle or an axis. If you are doing cutting, it is more like a spindle, but if you are doing engraving it is more like an axis. In your case, making it an axis is probably the better choice. It has the advantage of being able to design in 3D and have it look like the intended engraving (also in 3D). At least that is the plan, but see below. >> For example, let's say I wanted to cut/burn a dashed line. It would be preferable if the optic could keep moving at a constant speed, and the beam would just turn on and off at the appropriate positions. Would I be able to do that if the beam was controlled by the Z axis position? << Yes, but with some limitations. Make sure you understand the consequences of section "3.1.4 Planning Moves" in the user manual (http://linuxcnc.org/docs/EMC2_User_Manual.pdf). If you have very small vector lengths and/or are running at high speed, the system will slow down as described in that section. One method of minimizing this is to, in the G-Code, use very small values for Z, then scale up to the range of the controlling output, be it an analog or pwm. Further there are timing limitations such as the servo period which is going to dictate how the maximum rate at which you can change the laser power. If your servo period is set to 1ms for example, then the quickest you will be able to adjust the laser power is 1ms. Further, the laser itself has a maximum rate at which the power can be changed, typically 5Khz (200 microseconds) or slower. Lasers used for high speed laser engraving will often simply gate the enable, thus turning the laser on and off, rather than adjust the laser power. >> This thing moves pretty fast.. maybe 25 to 30 inches per second, and I'm not sure if I'll be able to turn the beam on and off with enough precision. << 30 IPS with a 1ms servo loop means a maximum theoretical resolution of 30 thousandths. >> Later, I'll need to compensate for the linear velocity of the optic, so that it burns with less power when it is moving slowly. This will require computing the real-time velocity vector in x-y space and using that to control the laser power. << See Feedcomp: http://linuxcnc.org/docs/html/man/man9/feedcomp.9.html Regards, Eric ------------------------------------------------------------------------------ This SF Dev2Dev email is sponsored by: WikiLeaks The End of the Free Internet http://p.sf.net/sfu/therealnews-com _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
