Reflecting type overhead projector with automatically variable safety illumination
First Claim
Patent Images
1. A reflecting type overhead projector, for projecting an image of an at least partly transparent original upon a screen, comprising:
- a reflecting table for placing said original thereupon;
a light source lamp for projecting light rays towards said reflecting table, for illuminating said original when it is thus placed upon said reflecting table;
a projection lens for projecting an image of said original, when it is thus placed upon said reflecting table and illuminated by said light source lamp, upon said screen;
a photosensitive element in the vicinity of said reflecting table for responding to the intensity of light rays which said photosensitive element receives from said light source lamp;
and a control circuit which receives a signal from said photosensitive element, and which controls the intensity of the light emitted by said light source lamp; and
which, when said light source lamp is being supplied with full power so as to light it more brightly, and then the intensity of light radiation received by said photosensitive element drops substantially, supplies part power to said light source lamp so as to light it less brightly; and
, when said light source lamp is being supplied with part power so as to light it less brightly, and then the intensity of light radiation received by said photosensitive element rises substantially, supplies full power to said light source lamp so as to light it more brightly.
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Accused Products
Abstract
In a reflecting type overhead projector having a light source lamp and a projection lens above a reflecting table formed of a Fresnel lens and a mirror upon which an original to be projected is laid, there is provided a control circuit which switches over supply of electric power to the light source lamp between full and part power supply according to whether the intensity of the light beams from the light source lamp received by a photosensitive element provided in the vicinity of the reflecting table is higher or lower than a predetermined value.
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Citations
7 Claims
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1. A reflecting type overhead projector, for projecting an image of an at least partly transparent original upon a screen, comprising:
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a reflecting table for placing said original thereupon; a light source lamp for projecting light rays towards said reflecting table, for illuminating said original when it is thus placed upon said reflecting table; a projection lens for projecting an image of said original, when it is thus placed upon said reflecting table and illuminated by said light source lamp, upon said screen; a photosensitive element in the vicinity of said reflecting table for responding to the intensity of light rays which said photosensitive element receives from said light source lamp; and a control circuit which receives a signal from said photosensitive element, and which controls the intensity of the light emitted by said light source lamp; and
which, when said light source lamp is being supplied with full power so as to light it more brightly, and then the intensity of light radiation received by said photosensitive element drops substantially, supplies part power to said light source lamp so as to light it less brightly; and
, when said light source lamp is being supplied with part power so as to light it less brightly, and then the intensity of light radiation received by said photosensitive element rises substantially, supplies full power to said light source lamp so as to light it more brightly. - View Dependent Claims (3, 4, 5, 6, 7)
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2. A reflecting type overhead projector, for projecting an image of an at least partly transparent original upon a screen, comprising:
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a reflecting table for placing siad original upon; a light source lamp for projecting light rays towards said reflecting table, for illuminating said original when it is thus placed upon said reflecting table; a projection lens for projecting an image of said original, when it is thus placed upon said reflecting table and illuminated by said light source lamp, upon said screen; a photosensitive element in the vicinity of said reflecting table for responding to the intensity of light rays which said photosensitive element receives from said light source lamp; and a control circuit which receives a signal from said photosensitive element, and which controls the intensity of the light emitted by said light source lamp;
said control circuit supplying full or part power to said light source lamp, lighting said light source lamp more or less brightly, respectively, when the intensity of light radiation received by said photosensitive element is higher than a certain predetermined value, or drops to less than said certain predetermined value.
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Specification