Sunday, April 17, 2016

Book Scanner: Mechanically Complete

After agonizing about a broken fan on the 3D printer (yes, one successful print later, the 3D printer had a third part break), I started to wonder if I'd ever be able to print a camera mount for the book "scanner".

Yesterday, I had an idea (I would call it brilliant, but it was mine, and any ideas that come out of my head must be brilliant).  Instead of printing a plastic part... why not build it instead?  My brain went immediately to wood, as it would be the easiest to "mill" or to shape.  I was worried, though, about the wood splitting.  I needed some parts with a 60 degree surface to point the cameras at the glass platten. I kept thinking "sturdy", since the two parts had to hold a camera, and I did not want the cameras falling on the glass platten and breaking the glass and/or the cameras.  (Yes, wood was not my brilliant idea.)

Then something else hit my mind.  When I worked on the old Troybilt rototiller, I needed some steel for the recoil starter's dogs that engaged the pulley.  I had picked a piece of steel bar up, about 1/8" thick.  I thought about just welding three bars together and bolting it up to the aluminum extrusion meant to hold the mounts in place.

I grabbed the torch, and started heating the bar up.  Using a pair of ducks (commonly called "tongue and groove" pliers), I bent for the first angle.  The way it turned out was even better than I could comprehend.  I simply bent the first angle to 60 degrees, and cut off a length of it - I realized I didn't need the aluminum extrusion to support the cameras - the steel was sufficient.  I immediately built a matching one for the other camera, and drilled the holes.  One hole (the one on the 60 degree surface) needed to be tapped, so I grabbed my 1/4" taps and added some threads.  I put some threaded rod in place with a nut to lock it to the surface, and then the camera could just spin onto the mount.  Hooray!

Now to figure out the CHDK firmware hacks for the Canon cameras!

There are two glass plates, called "platten" (the German word for "plates" because scanners and copies have always called those parts "plattens") both set at 30 degrees from the main surface.  There are wooden supports underneath at the same angle for the plates to press against, so that when the plates are lowered against the supports, whatever is between them will be "flat".  The glass plates are mounted to two vertical drawer slides (you can see them in the above photo), with a cable (I used a vinyl-coated wire and pulleys) to lift both ends of the plates at the same time.  When the plates are down, you trigger a camera shot, then raise the plates, turn a page, and lower the plates.  Wash, rinse, and repeat.

The cameras are mounted onto 1/8" steel bar bent to 60 degrees.  This is because 60 degrees is perpendicular to 30 degrees (required for a straight-on shot of the page).  There are two cameras, one for each page.  Each camera will be loaded with CHDK (Canon Hacker Development Kit), a "firmware" designed to allow external control of the camera, or do things the native Canon firmware cannot do (e.g. saving the pictures as "RAW" images).  I simply need the CHDK firmware to allow me to remotely trigger a picture over a USB cable, and pull the picture down to the computer without filling up the camera card or with me trying to use the SD cards.  You CAN do this without the CHDK, but I'm just lazy.

The cable had to be attached to both drawer slides - I found that a single one had the thing going skewampus, and I didn't like that.  Getting the cables the same length was a little challenge, though nothing unsurmountable.

Here is what the view from the camera looks like (though, not the camera, just right next to the camera, since I am definitely too lazy to use a picture from the camera).

So, I just need to figure out the CHDK components (which I am definitely close to doing), and pick up a Raspberry Pi to act as the computer.  The Pi will be configured with a button so that all you have to do is raise the platten, turn a page, lower the platten, and press a button.  When done, the Pi should arrange all of the images and convert them into a PDF that can be loaded onto any tablet computer for your reading pleasure!

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