EEVblog Electronics Community Forum
EEVblog => EEVblog Specific => Topic started by: EEVblog on December 30, 2023, 09:36:18 pm
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A closer look at the scanner array head from the dumpster FAX machine teardown.
00:00 - Linear Scanner Array
04:40 - CCD sensor grouping
08:24 - The optical zebra strip
11:30 - Under the x400 Olympus microscope
https://www.youtube.com/watch?v=KKMrT2HeRsQ (https://www.youtube.com/watch?v=KKMrT2HeRsQ)
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The optical zebra strip is likely settung the individual pixels and may work as mico-lenses. One kind of needs an optic to focus the light - otherwise the picture would spread out too much with the distance. The fax standard has a standard resolution of some 200 dpi for the fine mode. So one could check the distances.
The sensor part looks like it is made of several separate chips and the strage extra dots may be just there for alignment during the placement of the chips.
It looks like the sensor is not an old style CCD, but likely more a CMOS based sensor. A CCD would be simpler, with less parts directly linked to the sensors. This looks a bit like some amplifier per pixel.
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could the yellow dots be phosphor that get excited by UV LEDs ?
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@Dave , If it's not too much trouble, maybe you could zoom in on one of those strange square chips with your Olympious microscope and either we or you could take a guess based on that as to what those chips are.
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Quotes from youtube:
@WizardTim
The circle inside a square in the black area you theorize could be a light sensor is just a fiducial marker, they line up precisely at the breaks between each CCD die.
As for the strip of tiny lenses, it's called a "rod lens array", they're literally just normal lenses that focus the scanned page on the CCD, the image formed combines with other lenses in the array. This technique works without any of the distortions you'd expect because the CCD and page being scanned are at known fixed distances in a flat focal plane, change that however and the formed image with be trash, this is why this type of scanner cannot scan objects that aren't touching the glass like close to the spine of a book page. However not all scanners use the technique, particularly older ones that have a single small CCD sensor die but a complex optical path to shrink the image down, those scanners have a good usable working distance but are often larger and more expensive and pretty much obsolete, the HP 4C is an example of this alternate type of scanner.
@stuckathome5896
1. The lens array is a Gradient Index Lens Array (also called Selfoc®). It images the scanned document plane to the sensor plane - 1:1.
2. The sensor does not look like a CCD - It looks more like a CMOS sensor.
3. Color in scanners is usually achieved by multiple light sources (colored LEDS) rather than by multiple pixels.
could the yellow dots be phosphor that get excited by UV LEDs ?
You mean the post it note that was explained in the video?
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I know this is a long shot, but could someone please post either:
- A dimensioned/engineering drawing of the rod lens array/"optical zebra strip"
- or, reasonably accurate measurements of any rod lens array they have access to via a dumpster: specifically, the diameter of the rods, the centre-to-centre pitch of the rods, the length of the rods, and the working distance at each end (the distance from the rods to the paper; the distance from the rods to the CCD.)
- or, a physical actual zebra strip for me to play with (Sydney, Australia)
I'd be most appreciative!
Context: I've got a reasonably good optical simulation of how they work going (it's truly miraculous and wild what gradient refractive index optics can do!), but it's pointless doing simulations with made-up dimensions.