I finally have the controller working perfectly. I have been super busy, so I haven't been able to produce a video yet. This thing is awesome!
After a few experiments it is changing my outlook on PWM. If I am wishing to do a vector cut, then by all means PWM is used to set the power level. The rapid on/off during a vector cut is done through the second control input to the power supply, the TTL that one might associate with an interlock.
This control method is also used during a raster. This changes how we have been thinking of grey scale. We can set the "power level" to the maximum burn depth we would want for a raster at a given speed. This power level setting sets the PWM frequency. The grey scale occurs because it is rapidly turning the laser on and off with the other TTL input.
Confused yet? This should clear things up.
First lets look at a typical grey scale image:
Next we will zoom in on the grey scale and we can clearly see the different levels of grey:
Now we do a little trick so the laser can create a "pseudo-grey" image. Yes, it might look like crap in this photo, but the output on the laser blends it all together:
Zooming in on this image we can see that the processed image is actually pure black and white with bit density creating the appearence of grey scale:
This image processing is done with normal image processing software. The CorelDraw software can do it immediately before launching the laser plugin. PhotoShop and other packages can also do it. The conversion is called "Dither".
If starting from a color image, we first convert to greyscale. In photoshop, select IMAGE, MODE, GREYSCALE.
Once we have a greyscale we select IMAGE, MODE, BITMAP.
Now we have some choices to make.
1. The
resolution will be important because it will select the ultimate "density" of the black and white pixels. We shouldn't select a pixel resolution that is higher than our machine can produce. This will require experimentation on your machine because it is a function of step size and focused laser spot size.
2. The
method of diffusion will also make a difference depending on the type of image and the material being processed. In my example above I selected a "diffusion dither" method that creates a more randomized placement pattern of the black and white pixels.
This is going to need much more experimentation on my part to get it right, but my first run was pretty nice. I will show a picture later since I'm away from my machine.
Another VERY interesting surprise in the ultimate outcome was the fact that I can indeed acheive an anolog depth control into the wood. It can make true 3D depths varying from 0 to about .2 inches with nice rounded transitions. I wasn't expecting this. I thought that this could only be done with regular 3D CNC milling. HOW, WHY? I don't know for sure but it must be some slight overlaps in the burned holes allow the edges to be knocked down in the hole next door. Lame explaination, but it just works.
When you first finish the burn it looks ....well... burnt. After cleaning the burn with the Orange hand cleaner and toothbrush for a minute, the black burns disappear and the original wood shows through with different cut depths. Perhaps this is the part that helps knock down the hole edges to blend it all together. This is way too cool!