laser raster engraving

skunkworks wrote: This is a good thread (printer port rasterizing..)

www.buildlog.net/forum/viewtopic.php?f=1...94599e5ac6cba9de2872

sam

I read this. Interesting. On Page 14, he starts to use Mesa hardware.... He said it was easier becasue the PWM signals are generated on the Mesa board... Good luck!

It starts using mesa hardware for cutting..
For raster engraving image he not finished because he says that this function must embedded to fpga
and modified linuxcnc code.
parport is useless because the speeds are low and engraving needs high speeds.
In raster engraving the speed of x axis must be constant and the laser fire synchronized with motion.

I am a little bit interested in this topic but I have a lot more to do to finish my current machine before I can buy into it. I'm not sure he has taken the right approach talking about programming the FGPA. I don't understand why he wanted to retain the base thread which is not usually used in a Mesa config. I think if I was going to do this I would write a HAL component that was installed on the servo thread. This would mean it was called every millisecond. He says he was working at 0.5ms pulses but the maths did not indicate that to me and I can't see how a parallel port could generate pulses at that frequency.

I would save the current position and compare the distance moved since the last pass through the component (or simply check the current velocity). Either way, you can calculate the distance moved in real time so you can synchronise the laser pulses with motion and turn a pin on and off to pulse the laser.

So now if you could take control of one of the Mesa stepgens (which is probably a simple as commanding an unused axis to run at a given velocity) you could pulse the laser at speeds of up to 10 Mhz until you tell it to alter the velocity. So as you run through the servo thread, check if the velocity has changed then alter the stepgen frequency from your custom component.

Another crazier idea might be to use one of the $69 Mesa THCAD-10 cards which converts a 0-10 volt signal to a frequency. The frequency alters from card to card but mine peaks at 925 kHz. I think though that maintaining a PWM 10 volt signal might not be as responsive as a stepgen.

The problem is currently - with external hardware (mesa) you can only change the laser intensity once every servo cycle (1 to 5khz give or take)

With the printer port rastering running a base thread - you can up that to 20 -40khz.

The only way around this is to somehow offload the raster information to the mesa card. Again - I know it has been discussed but no one has coded it. PCW would have more info.

sam

Chinese DC power supply for glass tubes have response rate <= 1ms according to the datasheet
and has 2 input ports one for turning on/off the laser beam (this is the only needed port for raster engraving)
and one analog input port that accepts 0v to 5v for specifying the power of the laser,
in this port you can put a potentiometer and tune the power of the laser manually
because the raster engraving implemented with 1bit black/white dithered images at constant power/speed.
The only thing controller need to do is to turn on the laser when read black pixel and turn off the laser when it reads white pixel in image.
Engraving must be at constant speed about 300mm/sec to 500mm/sec
the problem with parport is that can not achieve speeds like 300mm/sec because stepper drivers for this application have very high microstepping to avoid resonance (in my machine drivers set up with 5000 microstepping/step).
Wincnc controller that i think had same codebase with linuxcnc supports raster laser engraving but costs 2000usd with all hardware.

this is the power supply for laser www.aliexpress.com/item/Co2-Laser-Power-...60W/32581390817.html

I am pretty sure Wincnc does not share any code base with Linuxcnc. (We do have one machine running their hardware/software) Their older software based systems were Dos based and had more in common with Turbocnc.