| 摘要 |
PURPOSE:To obtain a uniform luminous energy, to detect a window at a high resolution and to scale down a detector by providing an optical fiber group with its end surface pointing the center of a light receiving part, which projects linear light beams on mails from an output part positioned on an arc. CONSTITUTION:Light beams from a dot-like light source 1 are made into parallel light beam by a convex lens 2, and enters the optical fiber group 3 from an optical input part 3a. The light beams coming out of the optical output part 3b of the fiber group 3 are projected on the irradiation surface 6 of the mail P, and the reflected light beams form an image on a line sensor 5 through a convex lens 4. Since the output part 3b is so formed that its end points a lens center 7 and the end surface of each end part is positioned on the arc with a radius R, the light receiving part can obtain a uniform luminous energy. As a part with the window of the mail P has a large directly reflected luminous energy, the luminous energy of the light that comes to a sensor 5 from the light source 1 becomes great. Accordingly the photoelectrically transferred amount is compared with the inbetween threshold of the photoelectrically transferred amounts of the part with the window and that without the window, and the presence or absence of the window, its size and position are detected.
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