Illumination – Light modifier – Reflector
Reexamination Certificate
1999-03-29
2001-05-29
Cariaso, Alan (Department: 2875)
Illumination
Light modifier
Reflector
C362S297000, C362S346000, C362S350000
Reexamination Certificate
active
06238066
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based on Japanese Application No. 10-97797, the content of which is hereby incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to an illumination system for illuminating a two-dimensional area. In one aspect, the present invention relates to an illumination system for a reading device, such as a scanner, for reading the image of an open and upwardly facing document or a thick document, such as a book.
BACKGROUND OF THE INVENTION
Conventional illumination devices used in reading devices for reading open-faced document images, such as those in books, are known to be arranged above and behind a document so that the device does not cast a shadow on the book binding area so that the light of a document image is not blocked from the image sensing means, and such that the direct reflection light of an illuminated document does not enter the image sensing means. Japanese Laid-Open Patent Application No.7-7605 discloses an illumination system which forms a secondary image via illumination light using an ovoid reflecting mirror to achieve a uniform illuminance distribution.
U.S. Pat. Nos. 4,747,033 and 4,891,739 disclose an illumination unit for a full exposure type copier (i.e., normally for a face-down document type), which does not form a secondary image using a light flux which has been reflected once.
In the construction of the aforesaid illumination systems, a reflecting mirror having an ovoid cross-section must be used to achieve a uniform luminance distribution on the document surface due to the inclination of the document surface relative to the illumination system. When the inclination of the document surface increases, it becomes difficult to maintain the light with a uniform luminance distribution on the document surface. This difficulty can be understood by considering a document illuminated by a linear light source without a reflecting mirror. In a linear light source wherein the light distributed in a direction perpendicular to the length direction (i.e., luminance intensity directional characteristic) has a uniform and infinite length, the luminance at a specific point on the document surface is proportional to the cosine of the entrance angle, and is inversely proportional to the distance from the light source. Thus, a reflecting mirror must be used to produce distributed light so as to reverse and correct this condition (e.g., refer to “Lectures in illumination engineering,” (New Edition), S. Seki, Tokyo Electrical Engineering College Press, p71-72 (5.21)). The aforesaid application discloses achieving a uniform luminance distribution by shifting the light source position from the focal point position of the ovoid mirror, but does not describe obtaining uniform luminance by the arrangement of the light source.
The specifications of the aforesaid United States patents disclose the provision of a donut-type light source and a two-dimensional curved reflecting mirror of a rotating body, but since this arrangement does not form a secondary image, the form of the reflecting mirror is increased, and the covering angle of the first reflecting area from the light source is reduced resulting in poor light use efficiency.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved illumination system.
Another object of the present invention is to provide an illumination system using a reflecting mirror of a type to form a secondary image of the illumination light, which is capable of increasing the covering angle of the light source on a first reflecting area, and which attains a uniform luminance distribution.
Still another object of the present invention is to provide a two-dimensional area tilted illumination system using a compact reflecting mirror.
Yet another object of the present invention is to provide a two-dimensional area tilted illumination system capable of uniform luminance distribution, which is located at a position opening above the document surface while preventing the light directly reflected from the document from entering the image sensing system, and which efficiently utilizes the light flux emitted by the light source.
These objects are attained by providing a two-dimensional area tilted illumination system comprising a long light source having a longitudinal axis and a reflecting mirror, cylindrical in shape, wherein the reflecting mirror has a generating line parallel to the longitudinal axis of the long light source. The surface of the reflecting mirror has a first area for illuminating an illumination area after the light flux emitted from the long light source is first reflected and converged, wherein the first area is shaped such that the intersection point of the light rays emitted from the light source and reflected at two ends of the first area is a position nearer to the long light source from the light rays emitted from the long light source and reflected from the first area so as to impinge the center of the illumination region.
The invention itself, together with further objects and corresponding advantages will be understood by reference to the following detailed description thereof taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4568179 (1986-02-01), Durbin et al.
patent: 4747033 (1988-05-01), Yasuda
patent: 4891739 (1990-01-01), Yasuda
patent: 5697699 (1997-12-01), Seo et al.
patent: 5791771 (1998-08-01), Bjorner et al.
Cariaso Alan
DelGizzi Ronald E.
Minolta Co. , Ltd.
Sidley & Austin
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