| 摘要 |
PURPOSE: To restrain the occurrence of horizontal stripe like image noise by specifying relative relation among the revolving speed of the polygon mirror of a laser beam irradiating device, the frequency of an AC component impressed on a contact electrifying device and system speed. CONSTITUTION: When the revolving speed of the polygon mirror is Fp (rps), the frequency of the AC voltage impressed on the electrifying device 2 is Fb (Hz) and the system speed (the circumferential speed of a photoreceptor drum) is Vp(cm/sec), Fp, Fb and Vp are set so that the relative relation among them may satisfy a condition that is|Fp-2×Fb|<Vp or|Fp-2×Fb|>Fp/2. Therefore, the occurrence of the horizontal stripe like image noise which can not be recognized as uneven gradation is restrained even when that is called a half image such as a dot pattern is formed in spite of 'beat' caused by the irragularity in the moving speed of the surface of the photoreceptor and the surface tilting of the polygon mirror based on the fluctuation of the electrosatic sttractive force of an electrifying brush 21 is the electrifying device 2 to the photoreceptor drum 1.
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