Browse Prior Art Database

A LENSLESS RASTER INPUT SCANNER

IP.com Disclosure Number: IPCOM000024719D
Original Publication Date: 1981-Oct-31
Included in the Prior Art Database: 2004-Apr-02
Document File: 4 page(s) / 134K

Publishing Venue

Xerox Disclosure Journal

Abstract

A raster input scanner for reading documents typically consists of an illumination source, a collection optics using a lens, and a linear imaging array. The linear imaging array provides the scanning in one direction whereas the document motion provides scanning in the other direction. The lens images the document on the imaging array and one or more mirrors may be used to fold the optical path.

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XEROX DISCLOSURE JOURNAL

A LENSLESS RASTER INPUT SCANNER Jagdish C. Tandon
Jaies C. Stoffel

Proposed Classification
U.S. Cl. 358/285 Int. Cl. H04n 1/04

9 I

FIG. I

FIG. 2

Volume 6 Number 5 September/October 1981 287

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A LENSLESS RASTER INPUT SCANNER (Cont'd)

A raster input scanner for reading documents typically consists of an illumination source, a collection optics using a lens, and a linear imaging array. The linear imaging array provides the scanning in one direction whereas the document motion provides scanning in the other direction. The lens images the document on the imaging array and one or more mirrors may be used to fold the optical path.

It is here proposed, in order to exploit large arrays of photosensitive structures with dimensions in the 50ym - 100pm range, that image sensing by proximity be used. This eliminates the image forming optics and reduces the radiometric requirements by over two orders of magnitude.

A document scanner using this approach is shown in Figures 1 and 2. There a read bar, which is similar to a conventional imaging array in that it contains photosensor elements 6 and one or more shift registers 7, is used. Read bar 4 however differs from conventional imaging arrays in that the photosites are very close to one edge 8 of the substrate 5 and the shift registers 7 are only on one side (away from edge
8) of the array of photosensor elements 6. Read bar 4 can be fabricated using Silicon integrated circuit technology or thin film devices. The sensor elements 6 can be photodiode or CCD type. Read bar 4 is placed a precise distance 'd' from the document 9 to be scanned. The gap between document 9 and read bar 4 could be comprised of glass, air or some other transparent medium. Gap 'd' is very critical and determines the amount of light collected by the photosites, as well as, the system Modulation Transfer Function (MTF). The illumination source 10 is also linear and is placed close to edge 8 of the read bar to illuminate the portion of the document 9 just above the photosensor elements 6. Except for the photosensor elements, all of the read bar is covered with an opaque material.

The distance Id' will typically be equal to or less than the center-to-center spacing of the photosites.

For small gap distances Id', the solid angle subtended by each photosite at the document can be very...