| 摘要 |
PROBLEM TO BE SOLVED: To reduce electrifying sound and to satisfactorily reproduce a small- spot picture while preventing a defective picture even in the case of high resolution or high process speed. SOLUTION: When a spot ratio which is the ratio of spot diameters of exposure beams for the size of one pixel obtained from pixel density of electrostatic latent image is α, the pixel density of electrostatic latent image is R (dot/mm), the process speed of a photosensitive drum 1 is V (mm/sec), the frequency of AC voltage applied from an electrifying source 9 is f (Hz) and the dot number per one period of electrifying bias is β (=R×V/f), the spot ratio α satisfies 2.5<=α and the dot number βsatisfies 4.2<=β<=7.0. When NESA sensitivity of the photosensitive drum 1 is γ (V.cm2/μm), the NESA sensitivity γ of the photosensitive drum 1 is set to satisfies 2000<=γand, thereby, the charge sound is reduced and the reproduction of small-spot picture can be excellently maintained while the defective picture is prevented even in the case of high resolution and high process speed. |
