Patent ID: 7586592

Claim:
A sheet recognizing device which recognizes a sheet having a hue ink printed area in which a hue changes depending on a viewing angle, the sheet recognizing device comprising: a first light source for switching and projecting light of a plurality of colors at a predetermined angle to a surface of the sheet; a second light source for switching and projecting light of a plurality of colors from a vertical direction to the surface of the sheet; a first light-receiving element for receiving a light from the first light source and reflected on the surface of the sheet at the angle at which the hue of the hue ink printed area changes; a third light source for switching and projecting light of a plurality of colors at a predetermined angle to the back of the sheet; a second light-receiving element for receiving a light from the third light source and reflected on the back of the sheet at the angle at which the hue of the hue ink printed area changes; a third light-receiving element which is disposed on the back of the sheet so as to be opposite to the second light source; first computing means for computing a first color tone depending on the hue ink printed area on the basis of each light-reception output that is output corresponding to a light-reception amount received by the first light-receiving element based on a color of light from the first light source, or on the basis of each light-reception output that is output corresponding to a light-reception amount received by the second light-receiving element based on a color of light from the third light source; second computing means for computing a second color tone independent of the hue ink printed area on the basis of each light-reception output that is output corresponding to a light-reception amount received by the first light-receiving element based on a color of light from the second light source, or on the basis of each light-reception output that is output corresponding to a light-reception amount received by the third light-receiving element based on a color of light from the third light source; and sheet discriminating means for discriminating the sheet on the basis of results of the computation performed by the first computing means and the second computing means.