| 摘要 |
PURPOSE:To prevent detecting efficiency from being deteriorated by dirt on light emitting and receiving surfaces in case of optically detecting the density of a picture formed in a toner density detection area by using plural optical fibers as light transmitting and receiving means to transmit light. CONSTITUTION:A sub-light exposer 28, light emitter 29 and light receiver 30 are fitted to a sub-electrostatic latent image formation area 1b of a photosensitive element 1 so as to be opposed each other. A light source 32 is emitted according to a timing pulse from a CPU and the photosensitive element 1 is exposed through a light guide 31 and the sub-exposer 28. After development, light is sent through a light transmitting fiber 34 and the light emitter 29 and the reflected light of light from the light emitter 29 is received by the light receiver 30. The received light is sent to a photoelectric conversion element through a fiber 39. Conversion signals obtained from respective fibers (a), (b), (c) are sent to a comparator and an output from the comparator is sent to an OR circuit. Thus, picture density can be precisely detected even if a part of the light receiver and light emitter is dirt. |
