Abstract: A developing device for an image forming apparatus and having a relatively hard first developing roller formed with fine N-S magnetic poles on the periphery thereof, and a relatively soft second developing roller for conveying toner electrostatically transferred thereto from the first roller toward a photoconductive drum. The toner is charged by friction while being passed through between the first roller and a blade, and then magnetically deposited on the first roller. At a position where the first and second rollers contact each other, the adequately charged toner is substantially evenly charged by friction and electrostatically transferred from the first roller to the second roller. The second roller conveys the toner toward the drum. The second roller has a surface roughness whose ratio to the mean particle size of the toner is selected to be less than or equal to 1.5.

Abstract: A developing unit incorporated in an image forming apparatus and having a waste toner container for collecting a waste toner and a fresh toner container containing a fresh toner and adjoining the waste toner container. When the waste toner container is filled with the waste toner, the developing unit causes the waste toner to enter the fresh toner container while preventing the fresh toner from entering the waste toner container. A wall separates the waste toner and fresh toner containers from each other and is formed with an opening. A shutter is associated with the opening and opens when the pressure inside the waste toner container increases due to the waste toner. The waste toner which enters the fresh toner container via the opening is agitated together with the fresh toner as far as possible and then fed to a developing roller or is collected in a container whose volume is variable.

Abstract: A developing device incorporated in an electrophotographic image forming apparatus using a dry developer. The device stores the developer in a hopper including an arcuate wall. Pressure sensors are mounted on the inner surface of the arcuate wall to determine the amount of developer existing in the hopper. A motor is controllably driven to change the rotation speed of an agitator or to change the period of intermittent rotation of the agitator in response to the outputs of the sensors. The rotation speed of the agitator may be changed in association with the load acting on the agitator. Further, while the motor is rotated at a constant speed, a gearing intervening between the motor and the agitator may have the gear ratio thereof changed to change the rotation speed of the agitator.

Abstract: A developing device of one-component developing type for use in the electrophotographic copying machine capable of developing latent image on the image carrier. The device comprises a developer carrying member having resistor layer on its surface layer, a regulation member for regulating the thickness of developer disposed on the developer carrying member, a replenishing member for replenishing developer onto the developer carrying member after finishing a process of developing, and a removing member for removing developer remaining on the developer carrying member after finishing a process of developing. The device sets the relationship of the time constants and the operational time periods in the form of inequalities, in order to obtain an optimum condition of developing. There are nine methods of setting the combination of time constant(s) and the operational time periods so as to satisfy the respective inequalities mentioned in the description of the invention.

Abstract: An apparatus having a plurality of replaceable parts. Replaceable parts to which the same life is assigned beforehand are replaced at the same time by hand or by use of a jig. Lives which are integral multiples of the shortest life which one of the replaceable parts has each is assigned to respective one of the other replaceable parts. Hence, when the life of a certain part has expired, the part having the shortest life is automatically replaced together with the part whose life has expired. The replaceable parts each is mounted on and locked to the apparatus and, when the life thereof has expired, unlocked from the apparatus. The expiration of the life is detected either electrically or mechanically, and the parts reached the end of the life is indicated. Before the life of a replaceable part expires, a spare part for replacing it is prepared by detecting that the life is about to expire. The deterioration of a part having a comparatively long life is measured to correct the time for replacing it.