| 摘要 |
PROBLEM TO BE SOLVED: To steadily form a toner image of high image quality for a long time by variably controlling, according to a print rate, a speed at which a toner carrier carries toner to a latent image carrier. SOLUTION: A drive-roll driving device 108 controls the rotating speed of a developing roll in three gradations, A, B and C. For example, it detects the print rates of print information by classifying it in three gradations that are less than 6%, 6% to less than 11%, and 11% and more, and sets the rotating speeds A, B and C of the developing roll so that they match the development of electrostatic latent images of the respective print rates classified in the three gradations. Under such drive control, the developing roll is driven at a low rotating speed A [rotating speed (S/D) ratio 1.3] in the case of a print rate of less than 6%, driven at a medium rotating speed B (S/D ratio 1.5-1.6) in the case of 60% to less than 11%, and driven at a high rotating speed C (S/D ratio 1.8) in the case of 11% or more, thereby achieving high image quality print while maintaining the long life characteristics of the device. |
