Abstract: In an image forming apparatus, a photosensitive drum 7 is previously charged to have a surface potential by a charger 7. A latent image is formed on the charged photosensitive drum 7 by projecting an optical image thereon. The latent image is developed by a developer which is charged in the developing unit and supplied from the developing unit 18. The developed latent image is transferred to and fixed on a paper. Environmental conditions such as temperature, humidity and atmospheric pressure around the photosensitive drum are detected by temperature, humidity and pressure detectors, and image densities of the image on the photosensitive drum are detected by a density sensor. The surface potential of the drum and the charge amount of developer are charged and controlled in accordance with the image densities and the environmental conditions, so that a high quality image is formed on the paper even if environmental conditions are changed.

Abstract: An image forming apparatus comprises a rotatable, drum-shaped photosensitive member carrying thereon a latent image responsive to an original image, a first developing roller adapted to supply a first developing agent to the photosensitive member while rotating, thereby developing the latent image, second developing roller adapted to supply the second developing agent to the photosensitive member while rotating, thereby developing the latent image and a first and second motor assembly for rotating the photosensitive member and selectively rotating the first and second developing rollers to move the photosensitive member relatively to the first developing roller at a first relative speed when the first developing roller is rotated and to move the photosensitive member relatively to the second developing roller at a second relative speed different from the first relative speed when the second developing roller is rotated.

Abstract: An electronic copying apparatus comprises a movable optical unit with a mirror lens defining a first light path between an original and the mirror lens and a second light path between the mirror lens and a photosensitive body, which include a ratio of optical distances controlled according to the copying magnification, and driving belts to move the photosensitive body according to the correlation as followsV.sub.P = .vertline.V.sub.L (1-.alpha.).vertline.where V.sub.P is a moving speed of the photosensitive body, V.sub.L is a moving speed of the optical unit and .alpha. is a copying magnification.