US 2010/0061773 A1Published application

Developing apparatus

AssigneeCanon Kabushiki Kaisha

InventorsKazukiyo AKASHI, Tomoyuki SAKAMAKI

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Abstract

A developing apparatus in which a first magnet of a first developing sleeve includes a first magnetic pole near a potion opposing to an image bearing member, and a second magnetic pole being downstream of the first magnetic pole; and a second magnet of a second developing sleeve includes a third magnetic pole near a portion opposing to the first sleeve. Assuming that a magnetic force obtained by combining normal direction forces Fr1 and Fr2 of magnetic forces generated by the first and second magnets, respectively, near the first sleeve is Fr, a center direction component of the first sleeve of the force Fr becomes positive between the first magnetic pole and a peak value position of the second magnetic pole, and a center direction component of the force Fr becomes negative between the peak value position and the closest position between both sleeves.

A developing apparatus for developing an electrostatic image formed on an image bearing member, comprising:

a developer container, which contains a magnetic developer;
a first developer carrying member rotatably provided to the developer container, for carrying the magnetic developer to feed the magnetic developer to a first developing portion;
a second developer carrying member rotatably provided to the developer container in the same direction as the first developer carrying member, for carrying the magnetic developer delivered from the first developer carrying member to feed the magnetic developer to a second developing portion;
first magnetic field generating means arranged to be fixed in the first developer carrying member, wherein the first magnetic field generating means includes a first magnetic pole arranged in the vicinity of a portion opposing to the image bearing member, and a second magnetic pole arranged to be adjacent to a downstream side of a movement direction of the first developer carrying member with respect to the first magnetic pole, and having a polarity opposite to the first magnetic pole;
and
second magnetic field generating means arranged to be fixed in the second developer carrying member, wherein the second magnetic field generating means includes a third magnetic pole which is arranged in the vicinity of a portion opposing to the first developing carrying member, and has a polarity opposite to the second magnetic pole,
wherein a peak position where a strength of a magnetic field of the second magnetic pole becomes a peak with respect to a circumferential direction of the first developer carrying member is provided upstream of a closest position between the first developer carrying member and the second developer carrying member in the movement direction of the first developer carrying member, when it is assumed that a magnetic force, which is obtained by combining a magnetic force of the first magnetic field generating means and a magnetic force of the second magnetic field generating means in the vicinity of the first developer carrying member, is set Fr, and a direction toward a center of the first developer carrying member is positive, a component obtained in the direction of the center of the first developer carrying member of the force Fr is positive at least between the first magnetic pole and the peak position, and the component obtained in the direction of the center of the first developer carrying member of the force Fr is negative between the peak position and the closest position.

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Abstract

Claims4