Raster Laser Engraving software and methods

[lasersafe1]

Learned a very interesting thing about the Mach 3 laser engraving plugin today. Rather than enter the info twice, I'll direct you to the Mach 3 forum link that deals with the plugin.

http://www.machsupport.com/forum/index. ... l#msg87152

[bdring]

I am using a pretty slow computer. I am not near it, but I think it is a 2.9GHz AMD. I really should get a faster one. Please post pictures and parameters!

[lasersafe1]

I was actually setting it up to film for a Youtube video yesterday when I crashed the motor and burned up my Allegro driver. The replacement driver can't go below 1/10 step rate, so I can't get a good run until I can get another Allegro chip. Once I get it going I will definitely post all data along with the video.

[bdring]

Bummer...

Sounds like that would have made a better video

[lasersafe1]

I finally got my motor driver up and running again, but now I can't seem to get a good result out of the Mach 3 engraver plugin. It seems to be very dependent on image size, raster speed, etc. As an example, I can tell it to do a raster at 400"/min and the result is very dim and the laser barely turns on. When I enter the same exact information but change the requested raster speed to 2000"/min the laser turns on strong and I have to dial it down.

Much confusion.

I can't claim that it is working anymore because it always seems to overshoot the image and burn fuzzy around the edges of black. My image is pure black and white, so there shouldn't be any ambiguity about on-off. This can't have anything to do with the speed of my laser power supply, because the old Chinese driver card with Mosi-draw could give a nice clean edge.

I'm ready to purchase a card if someone builds one with a driver. I've been talking to someone working on a Propeller based driver and he thinks it's almost ready. If the xmos works I would be happy to purchase as well. I just need something that works! The Solustan LinkMotion didn't work at all for me, but I sure like the idea of making my PC simply see the engraver as a standard printer.

[bdring]

The propeller guy contacted me a few months ago. He is sharp and knows what we need. His board will do everything we want.

My XMOS board is only going to do engraving and may evolve to cutting as well, but I doubt it will ever compare with his. I plan to make my board open source, and not sell a "turn key" version. I will probably have some extra raw boards some day. There is talk in the XMOS forums of a Stamp style version that will make a home built version easier.

The Propeller and the XMOS are very similar. The Propellor has a lot more history and experience behind it making development easier. The XMOS is probably a little more powerful and has XC/C/C++ language support which is a plus. As far as CNC/Laser/etc requirements, they can hold their own against similarly priced FPGAs.

Mach3 Plugin

What is your steps per inch. Has that changed? The Mach3 plugin is probably sensitive to that. Just for my curiousity, could you post your steps per inch, plus a screen shot of the plugin screen just before you run it. There may be a sweet spot that Mach3 can work in.

[lasersafe1]

The steps per inch actually did change. Good catch. I replaced the relatively weak X motor (NEMA17) that had 0.9 degrees per step with a stronger motor at 1.8 degrees per step. So Mach 3 actually needs fewer steps per inch now, so my ultimate resolution may be suffering. I could now double my microstepping to compensate and give that a whirl.

[bdring]

This is just a theory....

The Mach3 plugin appears to send a single fixed length pulse per step. More steps per inch = more laser power per inch. I have very low steps per inch, so the plugin does not work at all for me. What is your actual steps per inch?

[lasersafe1]

Okay, your theory holds a little water, but here is where it leaks: Why then would it matter whether I tell it to scan at a different speed? Like I said before, when I told it to scan at a slower rate the image was dim. When I told it a higher rate I had more power. The needle on the ammeter went from barely moving to jumping 1/3 scale.

Here is some additional info from my experiment:

My image was 5.19 by 5.19 inches with 600dpi resolution and 1 bit depth. 600dpi is a big clue here because my X axis stepper is presently set to 250 steps per inch. This equates to an effective pixel resolution of 250 pixels per inch because the laser can't possibly be told to turn on or off for less than one step.

Looks like I would need to have at least 600 steps per inch if I wanted it to exactly fit within the 600dpi. This could be why I see ghosting on either side of the lines within an image. I'm going to raise my microstepping resolution and do some more experimentation.

More info from the setup: X Axis: 2000 in/min speed. 600 Acceleration. 250 steps per inch
Y Axis: 800 in/min speed. 150 Acceleration. 500 steps per inch.

[lasersafe1]

There is another way of looking at this. The Mach 3 engraver plugin is being asked to match a resolution that is not possible on the output. It is then up to the plugin to make its best judgement about turning on and off the laser during step outputs. This is a task that shouldn't be given to the plugin. You've seen how bad some image processing software is at nearest neighbor interpolation or other methods of image scale reduction. Sometimes it just turns out badly and I think that might be what I'm seeing. In the best of all worlds I would be giving it a pixel resolution that exactly matches the step resolution. I don't even want to play with my present 250 dpi effective resolution. I'm going to try to see if I can get it somewhere closer to 600. I will then "pre-process" the image with photoshop to make the image resolution exactly match the step resolution and see what happens.