Browse Prior Art Database

FILM INTERMEDIATE RASTER INPUT SCANNER

IP.com Disclosure Number: IPCOM000025322D
Original Publication Date: 1984-Aug-31
Included in the Prior Art Database: 2004-Apr-04
Document File: 4 page(s) / 168K

Publishing Venue

Xerox Disclosure Journal

Abstract

A number of known Raster Input Scanners (RISI technologies exist such as a laser flying spot scanner. There, a multi-faceted polygon is used to scan the reading beam across a document original. The polygon is driven by a synchronous or DC motor, and the polygon facets are set up or made to very close angular tolerances with respect to one another to assure accuracy. Usually, the document original is moved in a linear fashion over a scan slit with video detection accomplished by means of a linear detector, a light pipe with detector, or a remote detector having a lengthwise intensity correction factor. For a full frame scanning system with a fixed document, other methods of achieving the detection may be used.

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8' L-J

287 Volume 9 Number 4 Julv/August 1984

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FILM INTERMEDIATE RASTER INPUT SCANNER (Con t'd)

A number of known Raster Input Scanners (RISI technologies exist such as a laser flying spot scanner. There, a multi-faceted polygon is used to scan the reading beam across a document original. The polygon is driven by a synchronous or DC
motor, and the polygon facets are set up or made to very close angular tolerances with respect to one another to assure accuracy. Usually, the document original is moved in a linear fashion over a scan slit with video detection accomplished by means of a linear detector, a light pipe with detector, or a remote detector having a lengthwise intensity correction factor. For a full frame scanning system with a fixed document, other methods of achieving the detection may be used.

The advantages of a flying spot scanner are analog video reproduction, generally good signal/noise ratio, and use of currently available technoloEies. The dis- advantages, however, are the need for a Constant Velocity Transport fCVTJ for handling the document original, relatively high component cost, limited speed, not panchromatic, and questionable reliability of the high speed rotational components.

Another scanner type uses a linear detector array. [Jsually, the array consists of a silicon chip having a line of discrete detectors in the form of diodes or charqe coupled devices. The scanner optical system images an illuminated line of the document onto the array, and the array detectors are addressed seauentially to produce a line of video. The resolution of this type of system is determined hv the number and spacing of the detectors that comprise the array and the MTF of the optics rather than by the spot size as in a flying spot scanner. And, for hiEh resolution, two or more arrays may be optically "stitched" together to view a single video line without interruption or loss. As with a flying spot system, the document original is normally moved past the scan slit.

For increased speed, the illumination intensity must be increased in order to maintain a reasonable signal/noise ratio at the detector array. However, typical transmission efficiencies of an optical system for a scanner of this type can be as low as 1 or 2%, requiring very high illumination levels.

The advantages of a linear detector array are: a simple optical system, self- synchronization, can be implemented with current semiconductor technology, reliability, and it is panchromatic. The disadvantages are that a CVT document transport system is required, the need for high illumination levels, poor signal/noise ratio, arrays with a high number of detectors are generally not available, and a quantized video output.

Both the flying spot scanner and the detector array have another significant problem when used as a RIS which stems from the fact that the high light levels required may present a potential sa...