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Detector Geometry for Raster Scanning

IP.com Disclosure Number: IPCOM000078455D
Original Publication Date: 1973-Jan-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 56K

Publishing Venue

IBM

Related People

Barkhuff, ED: AUTHOR [+2]

Abstract

In a facsimile scanner, it is sometimes impossible to locate the photodetector in close proximity to the copy. In locating the photodetector at a distance from the scanned document the problem arises of maintaining constant response levels as the scanning light spot traverses the scanned line. A solution is to employ two or more photodetectors and sum their outputs. If the positions of the photodetectors are properly determined, as described below, the summed response will be substantially uniform.

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Detector Geometry for Raster Scanning

In a facsimile scanner, it is sometimes impossible to locate the photodetector in close proximity to the copy. In locating the photodetector at a distance from the scanned document the problem arises of maintaining constant response levels as the scanning light spot traverses the scanned line. A solution is to employ two or more photodetectors and sum their outputs. If the positions of the photodetectors are properly determined, as described below, the summed response will be substantially uniform.

Fig. 1 shows two detectors arranged in this manner. The scanning beam SB traverses scan line SL in a flying spot motion, while the document is moved perpendicular to the scan line to provide two dimensional scanning. The document is assumed to be a Lambertain diffuser. The photodetectors are located at a distance L from the document plane and separated from each other by a distance H. The photodetectors and the scan line lie in a common plane perpendicular to the document. D is the distance between the projection of the scanned spot on the plane of the photodetectors and photocell I.

Each photodetector has a sensitive area oriented parallel to the document. It is assumed that the dimensions of the sensitive area are small compared to the dimensions of H and L.

Response of each photodetector is proportional to the fourth power of the cosine of the angle of incidence on the photodetector of the light reflected from the scanning spot. One co...