| 摘要 |
PROBLEM TO BE SOLVED: To stabilize image density, regardless of the differences among density sensors and variations in service life of the density sensors. SOLUTION: Light is emitted from a light-emitting element 13a toward a density detection patch image P formed on a photoreceptor drum 1. The light reflected from it is received by a light-receiving element 13b, thereby detecting an amount of receiving light. For example, if the density sensor 13 is soiled by a toner t due to the end of service life, the amounts of receiving light from the patch images P having the same density are changed. To counteract this, the amount of soil on the density sensor 13 is detected by a soil detection means 13f, by using the amount of receiving light reflected from a patch image non- forming area on the photoreceptor drum 1 before the end of service life (before being soiled: reference time) and the amount of receiving reflected light after the end of the service life (after being soiled: measurement time). Based upon the result of the detection, the output of the density sensor when measuring the patch image density is corrected according to a conversion table, thereby adjusting it to an output used at the reference time. |
