| 摘要 |
PURPOSE:To greatly enhance the capability of detecting a paper end and contrive a smaller printer, by a construction wherein a transparent plate having a different refractive index part at a position corresponding to the boundary between a light-emitting part and a light-receiving part of a reflection-type photo-sensor is provided directly above the sensor. CONSTITUTION:The reflection-type photo-sensor 5 provided on the lower side of a recording paper comprises the light-emitting part 5a and the light-receiving part 5b, and a transparent sensor cover 9 is provided thereon. A thin plate 9a provided in the cover 9 at a position corresponding to the boundary 5c between the part 5a and the part 5b is formed of a material different from that for the other part of the cover 9, and has a refractive index different from that of the other part, so that light is substantially totally reflected at this part, and light is prevented from entering the light-receiving part in the absence of the recording paper. The thin plate 9a may be formed of a material which perfectly shields light. Paper dust adhered to the cover 9 is removed by the end of the paper, and can not enter into the surface of the sensor 5. Accordingly, malfunctions can be prevented from occurring due to reflection of light at the surface of the dusting sensor cover, and sensitivity in paper end detection can be enhanced. In addition, since the reflection-type photo-sensor can be placed at the side of a small diameter press roller, the depth of the printer can be reduced. |
