Patent ID: 7310490

Claim:
A developing unit for an image forming apparatus, comprising: a developer receptacle for containing a developer comprising a non-magnetic toner and a magnetic carrier; a developer transferring means for supplying the developer of the developer receptacle to an electrostatic latent image formed on a photoconductive medium; a magnetic field generating means mounted to the developer transferring means and comprising magnetic poles; and a regulating means for restricting an amount of the developer transferred to the photoconductive medium by the developer transferring means, wherein a range of positions for the regulating means to control the developer transferred to the photoconductive medium satisfies the equations below: Fr=Br 2 +400×( dBr/dα ) 2 , Gr=dFr/dα, X≦Gr≦Y where, Br denotes a magnetism in a normal direction with respect to a surface of the developer transferring means, α denotes an angle of magnetic poles of a magnetic field generating means (N1 pole), Fr denotes a magnetic attraction force (in graphic representation), (dBr/dα) denotes a slope of a Br curve (differential), (dFr/dα) denotes a slope of an Fr curve (differential), and Gr is the range of the developer-regulating position.