Patent ID: 8331834
Filing Date: 2012-12-11
Classification: G03G

Abstract:
1. A developing unit, comprising: a developer bearing member to bear a two-component developer including magnetic carrier particles and toner particles on a surface thereof, the developer bearing member including: a developer container disposed adjacent to the developer bearing member, including a developer storing chamber to store the two-component developer therein; an agitation/conveyance member disposed in the developer container to convey the two-component developer in an axial direction of the developer bearing member while agitating the two-component developer; and a developer regulating member disposed opposite the developer bearing member to regulate the thickness of a layer of the two-component developer held on the developer bearing member, wherein the two-component developer conveyed in the developer container is attracted by the magnetic force exerted by the magnetic field generator to the developer bearing member, is regulated by the developer regulating member, then passes through a development region of the developer bearing member facing an image bearing member, and returns to the developer container, the magnetic field generator including first and second magnetic poles with an identical polarity disposed adjacent to each other and downstream from the development region in a direction of rotation of the developer bearing member to generate respective magnetic forces for removing the two-component developer from the developer bearing member after the two-component developer passes through the development region, the second magnetic pole disposed downstream from the first magnetic pole in a direction of conveyance of developer by the developer bearing member and proximate to the developer regulating member to generate a magnetic force to attract the two-component developer from the developer storing chamber in the developer container for forming a magnetic brush of the two-component developer on the developer bearing member regulated by the developer bearing member, the developer bearing member including a developer-releasing region to release the two-component developer from the developer bearing member using a release force corresponding to magnetic forces generated by the first and second magnetic poles, the magnetic field generator being disposed such that the release force exerted on the two-component developer in the developer-releasing region on the developer bearing member has a single local maximum point, the developer bearing member being disposed higher than a top surface of the two-component developer stored in the developer storing chamber so that the developer-releasing region on the developer bearing member remains separated from the top surface of the two-component developer in the developer storing chamber as the developer bearing member rotates, a component of a magnetic flux density of the magnetic field generated by the magnetic field generator in a direction normal to the developer-releasing region on the developer bearing member being directed to a same direction as the first and second magnetic poles across the developer-releasing region without forming a local maximum point.