| 摘要 |
PURPOSE:To detect the life of a photoreceptor drum with high accuracy at a low cost by extracting only fluctuations due to wearing in a detection current signal flowing out from the photoreceptor drum and amplifying the dynamic range of a detection signal through the use of a gain amplifier. CONSTITUTION:A primary current signal flowing from the photoreceptor drum 9 is converted into the detection signal 42 by a current-voltage converting circuit 30. Its output signal 42 is amplified in a full band by a first gain amplifier 43 and inputted to a clipper circuit 45 from an AC removing circuit 44. The clipper circuit 45 previously sets a value for taking out a section for detecting the life as a clip level. A level shifter 46 applies a bias to obtain an optimum value in the operating point of a second gain amplifier 47. Then, only the extracted detection signal is further amplified by the second gain amplifier 47, compared with the previously set value for setting the life of the photoreceptor drum 9 by a comparator 48 and then, outputted as a life generating signal 49 when it is judged that the drum 9 is used to the limit. |
