Thank you very much for posting!
Regarding infrared, sure, I'd be happy to hear what you've come up with. It wouldn't be much use for BW, but it could be a godsend for color.
Regarding the light situation, you're certainly right. Moving the light source would help minimize any recurring patterns. Our issue so far has been to find
a light source that is flat, light, even, high cri, and reasonably priced. There's been a lot of development the last few years with LEDs, and hopefully
some good options will appear fairly soon. One manufacturer we contacted plans on coming out with a high cri led mat by the end of the year. I do like flash
for it's high cri, brightness, and short duration, but making a moving source with flash might be challenging.
Taking pictures of just the light source to use to minimize any irregularities is certainly an option, but ideally I'd like to avoid it.
Your laser idea to help with stitching is interesting and certainly worth investigating. Hopefully precise and repeatable positioning of the samples will
help with stitching the mosaic with a structured panorama type setting, ala a gigapan. Another option is to increase magnification so that grain and defects
provide enough control points.
Moving on to mechanical motions, I've taken apart some free scanners and printers in the last few days, and you're right, they use belts and pulleys.
In addition, they tend to use one bearing rod, as opposed to two parallel rods, with one side of the carriage sliding on a flat metal surface. While this
method gives up some resistance to going out of alignment, it's a neat way to avoid binding.
Since we don't need to take pictures while anything is moving, we don't really need super smoothness of motion. Hopefully the steppers will be fairly precise using whole steps.
Daniel Moore and I have investigated countless rails, sliders, x-y systems..... Many could be made to work, but the better ones are quite pricey.
The trick is finding something for a reasonable cost that others could easily source. It also matters
whether we are going to go with a moving platen system, which would require very high accuracy in the z-plane, or a system that slides the carrier on a sheet of glass.
We are planing on using an Arduino, mine should be arriving this afternoon, and thank you very much for the code. It's terrific that we have someone
with experience using an Arduino helping out on the project.