| 摘要 |
PROBLEM TO BE SOLVED: To automatically set charging biases to the optimum values, in an image forming apparatus that employs a non-contact type charging system using charging rollers and makes frequencies of the charging biases different from one another for each image formation mode according to the linear velocities of image formation processing. SOLUTION: A magenta image forming part 1M, a cyan image forming part 1C, a yellow image forming part 1Y, and a black image forming part 1Bk include photoreceptor drums 2a, 2b, 2c, and 2d respectively with which charging rollers 3a, 3b, 3c, and 3d are brought into contact, respectively. A charging bias in which a DC voltage and AC voltage are superimposed is applied to each of the charging rollers 3a, 3b, 3c, and 3d. The frequencies of the charging biases are made different according to the linear velocities for each image forming mode. During a period when images are not formed, the charging bias is varied to search a voltage value at which a DC current saturates, and then the charging bias is set on the basis of the found voltage value. The charging bias is set for each of the frequencies. COPYRIGHT: (C)2009,JPO&INPIT
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