| 摘要 |
PURPOSE:To exactly detect developer concentration by coating the face of a detection window on the side in contact with a developer with a light transmitting synthetic resin high in releasability and having electrification characteristics same in polarity as a toner. CONSTITUTION:The base plate of the detection window 33 of a developing device 25 is made of glass 332, and the outside face of the window 33 is provided with a vapor deposited film 331 to be used as a dichroic mirror for selective reflection and transmission of light. The face of the window 33 in contact with the developer 252 is coated with the transparent synthetic resin sheet 333 specified in thickness, high in releasability, having electrification characteristics, and made of a tetrafluoroethylene-perfluoroalkoxyethylene copolymer. Near infrared rays past the window 33 illuminate the developer 252, and its reflected light is again transmitted through the window 33, reflected with a reflective mirror 31, or directly guided through an optical fiber 34 fixed to a detection head 30, and allowed to project a light receiving element 45 through the opening 43 of a side plate 41, and a color separation filter 44. |
