| 摘要 |
The residual potential and charging potential of the surface of a photosensitive drum 20 , or the charging potential and exposure potential of the surface of the photosensitive drum 20 are detected by an exposure sensor 28 . The lifetime of the photosensitive drum 20 is judged in accordance with the difference between the detected charging potential and residual potential, or the difference between the detected charging potential and exposure potential.
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