Patent ID: 9599926
Date: 2017-03-21
CPC Classifications: G03G

Claim:
1. A developing unit, comprising: a developing container configured to store a developer including a non-magnetic toner and a magnetic carrier; a developing sleeve configured to bear the developer on a surface thereof, and to rotate; a developer regulating member configured to regulate an amount of the developer born on the developing sleeve; and a magnetic field generating portion configured to be fixed within the developing sleeve, and to have a plurality of fixed magnetic poles which generate a magnetic field which bears the developer on the developing sleeve, wherein the magnetic field generating portion includes (i) a cut pole which is disposed to oppose the developer regulating member and is closest to the developer regulating member among the magnetic poles, (ii) a drawing-up pole which is disposed adjacent to the cut pole on an upstream side in a direction of rotation of the developing sleeve and has an opposite polarity from the cut pole, and (iii) a peeling pole which is disposed adjacent to the drawing-up pole on the upstream side in the direction of rotation of the developing sleeve and has a same polarity as the drawing-up pole, and when a magnetic force in a direction toward a center of the developing sleeve is Fr, and a magnetic force in a tangential direction of the surface of the developing sleeve is Fθ, in a peak-to-peak area which is a region from a peak of magnetic flux density of the drawing-up pole to a peak of magnetic flux density of the cut pole, the magnetic field generating portion is configured to be arranged such that a distribution of Fr in a circumferential direction of the developing sleeve has an Fr flat area in which Fr is substantially constant or an Fr attenuation area in which Fr attenuates toward the cut pole side from the drawing-up pole side, and Fθ is oriented toward the same direction as the direction of rotation of the developing sleeve in the entire peak-to-peak area, and when an increase amount of Fr per unit angle is ΔFr, the Fr flat area satisfies ΔFr≦+5×10