JPS55115061A - Electrophotographic dry type developing device - Google Patents

Abstract

PURPOSE:To obtain the distinct cipied images corresponding to the images of different gradation characteristics by providing a means of suitably changing the thickness, shape and charging amount of the toner layer coated and charged on a developing roll to the chargint and coating member of the developing device. CONSTITUTION:A charging and coating member 4 is held by a guide plate 5 and is made vertically movable along this guide 5. At the upper end thereof, it is supported by a leaf spring 6, this leaf spring 6 being held at a fulcrum 7. In this way, a means which consists of the guide 5 and leaf spring 6 and changes the contact pressure upon the developing roll 1 is provided to the charging and coating member 4. Now, when the contact pressure is increased, the toner layer 3a on the developing roll 1 becomes relatively thin and this is suited for the reproduction of soft gradation images such as of photographs. Conversely, when the contact pressure is lowered, the toner layer 3a on the developing roll 1 is relatively thick and suited for the reproduction of images of hard gradation such as line drawings. In this way, the distinct copy images corresponding to the images of different gradation characteristics may be obtained.