Daniel Reetz, the founder of the DIY Book Scanner community, has recently started making videos of prototyping and shop tips. If you are tinkering with a book scanner (or any other project) in your home shop, these tips will come in handy. https://www.youtube.com/channel/UCn0gq8 ... g_8K1nfInQ

semi auto platen moto - motorized platen brainstorm

Built a scanner? Started to build a scanner? Record your progress here. Doesn't need to be a whole scanner - triggers and other parts are fine. Commercial scanners are fine too.
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dtic
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semi auto platen moto - motorized platen brainstorm

Post by dtic » 01 May 2014, 05:28

This thread is for brainstorming on semi automation by adding on platen motorization to existing scanner designs.

Background
Daniel's Hackerspace Scanner Kit and David Ladin's plastic pivot scanner are manually operated. Monson is prototyping a fully automated scanner. But there is also space for semi-automation that replaces some, but not all, manual operations. Semi auto won't save the operator much time but can reduce risk of repetitive strain injury from manually raising/lowering a platen thousands of times. This is a brainstorming thread, since I don't have a finished design and I'm not great at mechanics/electronics. I hope others will jump into the thread with ideas and prototyping and I'll try to contribute as best as I can.

Parts
A. ACTUATORS; a motor set up to move the platen up/down. Maybe a cordless drill motor or a strong stepper of the kind used in 3D printers. There are some tutorials around the internet on reusing a cordless drill motor for DIY projects. Counterweighting the platen allows for a weaker motor.
B. TRIGGERS; buttons, pedals or optical sensors for the user to manually use.
C. SENSORS for stopping the platen movement at the top of the scanner and when pressed down on the book.
D. ARDUINO/RASPI BOARD connecting everything. The SpreadPi camera control and image processing project will use a raspi. That device could maybe also control platen motorization.

Best case scenario
A semi auto design that is (1) inexpensive and uses widely available components (2) easy to assemble and set up, (3) matches or beats the speed of manual platen operation, (4) not too noisy and (5) safe for the user (no hands cut/mangled!). Combining 3 and 5 may be tricky.

a crude semi auto platen sketch
The motor controls a wheel that winds up/down a line vertically attached to the platen. Or (for the Landin scanner) the motor attaches to the pivot point on the platen arm. One button moves the platen upwards while pressed. Another button moves the platen downwards while pressed. Here the user has to keep track of when to manually stop the up/down motions.

a more sophisticated semi auto platen sketch
The motor is attached like above. The user press and hold a foot pedal which triggers platen up movement. At some preset top position a sensor detects the platen and then motor stops and holds the platen in place. The user releases the pedal and the motor lowers the platen until a sensor detects that the platen presses against the book (or a hand). Another sensor slows the motor right before hitting the book to avoid book damage. Here the user has both hands free and won't have to focus on stopping the motor at the right position. For safety an additional optical sensor could at all times detect hands under the platen and then move the platen up without a pedal press.

Of course all of the above is up for discussion!

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jck57
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Re: semi auto platen moto - motorized platen brainstorm

Post by jck57 » 01 May 2014, 16:19

Seems to me that the ultimate semi-auto scanner would do everything but flip pages. I imagine a speed control, an on/off hand switch, and a "deadman switch" footswitch. As long as the footswitch is depressed the cycle continuously repeats: Cameras fire, platen raises, timed pause, platen lowers, cameras fire. For safety, releasing the footswitch must immediately stop the process with no coast-down.

dtic
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Re: semi auto platen moto - motorized platen brainstorm

Post by dtic » 02 May 2014, 02:54

I like the idea of the platen movements cycling automatically. We could then have only two input controls. A button to start/stop the cycling process. And a safety control in the form of a hand detecting sensor or a foot pedal that moves the platen to the top position and waits. The sensor is more automatic than a pedal but could be slower, since for me at least the fastest possible manual cycles requires that I move the platen with one hand while turning the page with the other.

When to stop the platen upward move should be easy to sense, since the same position can be used every cycle. E.g. a wire on the platen connects to another wire. Sensing when to stop the platen downward move is trickier as the book thickness varies. With a stepper motor it might be good enough to have the motor attempt X number of steps from the top position, where X is the number that would move then platen next to the cradle if there was no book. The motor would then in practice push against the page a number of steps. I wonder if stepper motors would take damage by repeatedly doing so.

As for camera controls, that would be easy to add on I think. The SpreadPi project includes camera triggering. And auto camera is super easy if you connect the cameras to a PC. Simply attach a cheap wireless mouse to the scanner with the scanner wheel positioned so that the platen scrolls it on the way down. I have a zip tie with some tape attached to the platen which creates protruding "finger" that touches the scroll wheel. A script on the PC detects the scroll down and triggers, with some preset delay, the two cameras to shoot. Works very reliably.

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daniel_reetz
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Re: semi auto platen moto - motorized platen brainstorm

Post by daniel_reetz » 04 May 2014, 12:19

Scann sent me a message this morning with this machine:

http://pc.pcpress.rs/arhiva/tekst.asp?b ... kstID=9985

http://www.elconfidencial.com/cultura/2 ... al_122646/

A "Semi-Auto" scanner that appears to press the platen on the page. If the author is reading this, please say hello!!!
escaner-de-libros-inventado-por-voja-antoni.jpg
escaner-de-libros-inventado-por-voja-antoni.jpg (69.46 KiB) Viewed 6798 times

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daniel_reetz
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Re: semi auto platen moto - motorized platen brainstorm

Post by daniel_reetz » 04 May 2014, 12:20


dtic
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Re: semi auto platen moto - motorized platen brainstorm

Post by dtic » 04 May 2014, 17:02

Daniel: Nice to see a working DIY semi auto!

Some more brainstorming. I've again tested lifting a platen up with a cordless drill and some string. When the platen is counterweighted a much weaker motor will be enough I think. We can probably use parts common to 3D printers: a stepper motor, a timing belt, a toothed pulley, a bearing (or another pulley). And a motor shield for arduino or raspi. There are tons of kits and guides online for that. I guess the first step is to figure out what stepper motor to use.
Here is one example of such a kit, w/o stepper http://www.amazon.com/RepRap-Timing-Pul ... 00GFPC01Q/
belt2.jpg
belt2.jpg (28.1 KiB) Viewed 6787 times
Details on 3D printer components http://reprap.org/wiki/RepRap_Options

M@rtijn
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Re: semi auto platen moto - motorized platen brainstorm

Post by M@rtijn » 06 May 2014, 02:57

The belt could use a self made auto-adjusting idler arm tensioner.
tensioner.jpg
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dtic
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Re: semi auto platen moto - motorized platen brainstorm

Post by dtic » 06 May 2014, 15:40

M@rtijn: Nice but looks complex. Do you think a tensioner is strictly necessary? I've seen 3D printers that use only small clamps with two screws that hold the belts in place. If the belt starts to slack you unscrew, manually tighten it and secure the clamp again. Worth a try before moving on to tensioners.

Everyone: Stepper motor (or other motor) suggestions welcome! What stepper to use depends on the platen design of course. A vertical drawer slide moving platen can be counterweighted but there still some friction to deal with. I found a great stepper motor guide here. I'm thinking of using the Adafruit Motor Shield V2 and an Arduino.

M@rtijn
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Re: semi auto platen moto - motorized platen brainstorm

Post by M@rtijn » 17 May 2014, 02:48

Scotch Yoke Mechanism: http://youtu.be/hsaoTo1vuY4
Whitworth Quick Return Mechanism: http://youtu.be/UuTNtg7-Bwg

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daniel_reetz
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Re: semi auto platen moto - motorized platen brainstorm

Post by daniel_reetz » 17 May 2014, 09:28

You might consider prototyping with Makerslide. It's a bit expensive, but it gives you a ton of flexibility. I've used it in a few projects now. They even have a "camera slider kit" which has a motor mount and belt drive built in:

http://store.amberspyglass.co.uk/camera ... l-kit.html

Also, the "secret" history of Makerslide is that when Barton Dring took second place in the Instructables contest in which I won the laser cutter, he set out to make his own laser cutter using extrusion. He found that most extrusions suck for linear motion, and invented Makerslide.

One downside to Makerslide is that it is not a heavy-duty rail, the wheels can only take 6lbs each max. So on my projects I use a couple carriages to spread the load across many wheels.

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