Desktop 3D Scanner from Common (Geek) Household Supplies [Phase 1]

I got some good feedback on the 2D rotisserie scanner, and a few links that lead my mind in interesting directions. What I settled on for the 3D scanner was a notion called Structured Light.

So What's All This Structured Light Hoohaw Anyway?

The cool thing about structured light is that you only need a laser source, a camera, and some mechanism for sweeping the laser across the object.

As the next few sections will detail, it's not quite that simple, but it is very close to being that simple, and I'm a big fan of simple, especially

when it's me that's got to put all this junk together.

So the key to the whole process is that we know going into it that there is a fixed angle between the camera and the laser. Harnessing the twin powers of geometry and trigonometry, we can work out the height of the reflected laser light at any point.

Step One: The Laser Line-Painter

No mad science project is complete with out a laser. This is not a personal bias; simply a statement of fact. It is, if memory serves, set out in the declaration of principles in the 1997 conference proceedings for SIGMaST (Special Interest Group: Mad Science and Technology).

My first candidate was an ancient laser pointer that formed the key targeting element in my early Laser-Targeted Nerf Weaponry experiments in the mid 90s. This is a low-power, 1 mw laser, so anemic that it caries a simple "caution" sticker. I had some serious reservations, but pressed it into services in the first prototype.

Prototype of what, exactly?

The "structure" in structured light comes from the idea of projecting a known, regular pattern of light on an object, and figuring out the shape of the object by the way it distorts that pattern. The simplest pattern is a line (well, I suppose a dot is simpler, but it's less useful). So step one was taking the output of the laser pointer, a bright red dot, and turning it into a line.

Ok, not to belittle the customer service at Home Despot, but I swear, walk into that place and ask them where they keep their hexagonal laser reflectors, and you just get a blank stare.

I eventually tracked them down in the loose hardware section, filed under "nuts & bolts." They were very affordable, so I picked up a variety of sizes. The ultimate goal was to mount them on a small Lego motor, so I wanted to make sure I could attach a mount.

The first order of business was getting a useful reflecting surface. They were all a little battered and scratched, but a quick pass with the Dremel buffing wheel and some metal polish quickly brought out a decent shine (see image on right).

Already, there are some indications that this method leaves something to be desired. Even though the reflector is reflecting well, the surface is not especially smooth. These surface distortions will cause problems down the line.

But the great thing about mad science is, it's cheap! So why not follow through and see what happens. A bit of glue and a small Lego widget for attaching to the motor, and the Mark I line painter is one step closer to reality.

I was pretty impatient, but I managed to let the reflector set-up overnight. No reason risk flying debris!
The Mark I

The fast-spinning bolt reflects the laser beam in an arc. If the beam were pointed exactly at the shaft, you should get a spread of about 120 degrees.

I mounted the laser pointer off-center, so that the spread would not reflect back to the source, throwing the reflected beam off to one side. The device would not be particularly useful if the middle of the line were blocked by the laser itself.

You can see a couple of wires trailing off the laser.

This was a modification made for the Nerf Weaponry mod. I soldered wires to the contacts of the switch, so that I could activate the laser without having to press the awkward clip-switch. Not to spoil anything, but a little later on, I discover I'm in need of a bigger laser, so I'll document the process of making an external switch at that point.
   
Will it work? Find out on Page 2 >>