My 3rd Generation Scanner Build Thread

[StevePoling]

Apologies if this is the wrong place to ask this, and apologies if it is the stupidest thing you've heard today. But I got the impression that the problem of racking is caused by the weight of the glass (or plexiglass) in the thang you're pressing against the book.

Can you replace this rigid transparent material with a flexible transparent film that's held in tension around the framework? Ferinstance, consider that heat-shrink transparent film that you put on your windows to keep out drafts in the winter time. You could stretch that around a wood frame, (or carbon composite?), then give it a shot of hot air to stretch the thing into a rigid body. It'll form a stressed-skin structure that folks who know stuff prefer for stiffness with minimal weight. Then it'd be as light as a feather and you can lift it with less racking and no counterweights. I suppose then it would be too light to hold the pages flat...

Idunno. It's just an idea and ideas are a dime a dozen. I just hope this helps.

[daniel_reetz]

That's a pretty interesting idea -- something like the way model aircraft skins are doped?

I think the problem with implementation is that when the platen presses into the book, it has to be rigid. I don't think plastic film would be rigid enough to flatten out the pages. But I do like your line of thinking, please, keep the ideas coming. I have some weird ideas that I haven't posted here yet, but I hope to get some time to work on this soon, and I'll post some of them.

One thing that would help with the drawer slides is to bind the left and right one so they'd have to raise at the same time. This would be more easily accomplished with Karyudo's suggestion of having them together in the back.

[StevePoling]

It's all a function of how much stress you can put on the skin. airplanes, race cars, stick-frame houses they all get stiffness and light weight by loading a frame that tensions a skin. If you had infinite stress on an ideal membrane, it'd be stiffer than a pane of glass. And you can get the materials from your nearest unobtanium dealer.

Seriously, I don't know what can be done with 3M window film and a hardwood frame? But I've seen some pretty tight window seals. There's no flex in a drum surface. How much force is needed to exert on the paper? I don't know the requirements.

I originally imagined two square frames holding two pieces of film, but now I'm wondering if one hinged assembly that folds one way to travel, and folds the other way (and locks) to tension the film. And you could do whatever drum makers do to lock the film in place.

[daniel_reetz]

Well, I've had some setbacks -- namely, an infection in my jaw gone wild -- and I ran out of money and options and had to move out of my apartment. Now, after a brief stay in my workshop, plus doing a ton of odd jobs, I have all that paid for and I've moved into the basement of a house near my workshop. Just for the hell of it, here are some pics of my apartment after I emptied it out. All that was left on the last day was my bike, synth, and FTIR spectrometer. I built the first DIY book scanner here, so I guess the space is of historical interest.

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Life in the workshop was a bit messy, but was not long or bad.

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During that time, though, I got a lot of work done on this new scanner build. A whole lot of time and effort has gone into just seeing if things will work. One of my design constraints is that I want the majority of components for this scanner to be able to be produced with a laser cutter. Many high schools and universities have them, so if it can be laser cut, many students can have them and improve them. But to get the design to that stage, I had to find a suitable structural material.

I went to Menards, a local hardware store, and bought 1/4" regular plywood, 1/4" MDF, and 1/4" birch plywood. The first two failed to cut at all. They absorb too much laser energy and the kerf is just enormous. So they are unsuitable materials. However, the 1/4" "baltic birch" ply is actually not a quarter inch thick, it is 5mm thick. Not only that, but it is made with urea glue, which cuts neatly on the laser. There are two problems with 5mm Baltic Birch. The biggest problem is that it does not lay flat. Laser cutters fail horribly on non-flat materials. Even a deviation of 1/16" or a mm or two will put the material out of the focus of the beam. For the first few cuts, I tolerated this shitty situation, but for later cuts, I mounted the plywood to heavy aluminum blocks with double-sided tape. This caused a DRAMATIC improvement in cut quality and consistency, and made things work out well. The settings for the laser were 100% power, 15% speed, 600hz.

My nephew Benjamin is learning to use the cutter. He helped clean it and program up the test plywood parts.

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Now that I knew I could cut plywood, I had to figure out a way of sticking two pieces of it together. I decided on a screw and nut based system, and worked out the measurements. This system proved to work fantastically well. This little test box is incredibly strong. I can stand on it, no problem. This is how I will construct camera supports and the rear column.

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One constraint for my new scanner is that I want it to be acceptable as carry-on luggage. That means the dimensions cannot exceed 45 linear inches. 22x9x14. It also can't exceed the dimensions of my laser cutting bed -- 24x12". One solution that came to me the other day, though in hindsight it is totally obvious, is to make the base into a box instead of just a flat thing. That way it can be used to stow scanner parts, the power supply can be hidden inside, etc. So I started crafting one just to see how strong it would be. It seems that with a top and a brace or two, this will be acceptable in terms of strength.

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The next step was to reduce the size of the folding platen I was working on, and to cut it from plywood to test how strong it is. Results were pretty good -- strength seems acceptable. I toyed with the idea of a front-mounted plate which would stabilize it, but it doesn't seem quite right. I need to think of a way that the U-handle can stabilize the thing with a minimum of parts. Ideas welcome. Also, I need to figure out how to mount the platen to the hingalellogram in a way that it can be easily and quickly removed (because the platen can't fold with the column attached). If anyone has any clever ideas there, let me know.

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After re-cutting the folding platen, I realized that I could cut the folding base from plywood. Did that too.

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Finally, after lots of messing around with vertical slide mechanisms, I decided just to go with a hingalellogram for now. It is a smart mechanism and a compact one. And it preserves the original platen action of the first scanner I built, which I really like. So here are a few shots of where the hingalellogram is going. I think I'll use the black one.

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That's it for today. Gotta get back to work.

[daniel_reetz]

I should mention, much of the photography in this last post was by my brother, Poodus.

[fbonomi]

All that is quite exciting!

First of all, glad to seethat (if I understand correctly) your troubles are going better.

The little "nuts and bolts" box looks awesome, with a sort of steampunk-like look.

And the idea of cutting parts is brilliant. I quite see a (tiny) market for scanner kits.

Laser cutting forces you to flat materials, but the advantage would be that the things you produce can easily be shipped

I gues you already know ponoko. The forum there might be useful, and the free designs could give ideas.

There's a guy who sells a ScanDock, a support to photograph documents with an Iphone.

[daniel_reetz]

Some things are getting better, and some worse, but it's all a wash. At least for the moment my health problems are under control.

I have seen Ponoko and the iPhone scandock thingy. If I do ever decide to make a kit, I will probably use Ponoko's services, or the services of another shop like them, because my laser wouldn't withstand that kind of usage. Still, selling anything, kits, and all that are far from my mind now. My big idea is to make a portable scanner, and from there, we'll see what happens.

To that end, I have some more news to report. Tonight I made the first prototype folding glass platen, and it works beautifully! It's quite rigid and quite stable. I'm attaching some images of it here. The problem now is how to mount it and how to mount the handle to it... also keep in mind that in the final version, I don't think I'll have exposed tabs or screws. I'll just epoxy the glass right to the lasered folding bits.

Pictures:

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[daniel_reetz]

animation!

[fbonomi]

animation!

that gives me a strange feeling... were you moving the backgorund as well?

On a serious note, that's pretty slick

I will probably go for something similar, but not folding, just "dismantleable".

What are the sizes (esp. thickness) of glass & plywood?

I was thinking about something lighter....

[daniel_reetz]

that gives me a strange feeling... were you moving the backgorund as well?

I took the pics from different angles and then aligned them usingSIFT. The background shifts because it is being warped to accommodate the platen.

The glass is 1/8" thick, (sold as "doublestrength" at my hardware store). It is 10.5x13".
The plywood is 3 layers of 5mm baltic birch. Dimensions match the glass - 10.5" long. I'll share the art at some point.

The assembly is heavier than I thought it would be.