JPS5710171A - Original size detecting method of copying machine - Google Patents

Abstract

PURPOSE:To detect the presence or absence of an original as well as the size of original without disturbing the exposure route of copy, by using the contact glass whose thickness is changed in a constant ratio and irradiating light from the side of the large thickness to detect the light by a light receiver on the edge surface of the small thickness. CONSTITUTION:The contact glass part set into a device stand is constituted by oppositely bonding two sheets of glass 5 and 6 so that respective thickness changes in a constant ratio and the total thickness of the glass become substantially uniform. A light emitter 8 is provided to the edge part of a large thickness of the contact glass 5, and the light is made incident at an incident angle thetai. For instance, the incident angle is controlled, for example, to make the angle theta3 larger than the critical incident angle. Thus no light is made incident to a light receiver 9 when no original exists. On the other hand, when an original is put on the contact glass, an irregular reflection is caused at the white area of an original to be reflected again in to the glass. Then a part of the light reaches the receiver 9. The receiver 9 is provided in plural pieces in accordance with the sizes (B5-A4) of the original.