Development device, process cartridge, and image forming apparatus

A development device, comprising:

• a developer containing part containing two-component developer including toner and magnetic carrier particles;
• a cylindrical developer carrier to carry by rotation the developer supplied from the developer containing part to a development range where the developer carrier faces an image carrier;
• a first developer transport member disposed in the developer containing part, to supply the developer to the developer carrier while transporting the developer in an axial direction of the developer carrier;
• and
• a magnetic field generator disposed inside the developer carrier, having three developer-carrying magnetic poles each capable of generating a magnetic field to keep the developer on a circumferential surface of the developer carrier,
• the three developer-carrying magnetic poles consisting of a development pole to generate a first magnetic field in the development range, a pre-development pole to generate a second magnetic field to transport the developer supplied from the developer containing part to the development range, and a post-development pole to generate a third magnetic field disposed between the first magnetic field and the second magnetic field, wherein
• the second magnetic field causes the developer supplied from the developer containing part to be attracted to the circumferential surface of the developer carrier at a developer attraction position, the first magnetic field and the second magnetic field keep the developer on the circumferential surface of the developer carrier from the developer attraction position to the development range, and the first magnetic field and the third magnetic field keep the developer on the circumferential surface of the developer carrier from the development range to a release position where the developer is separated from the developer carrier, and
• when positions where magnetic flux density in a normal direction to the circumferential surface of the developer carrier is maximum in the pre-development pole, the development pole, and the post-development pole are respectively referred to as a pre-development magnetic flux density peak position, a development magnetic flux density peak position, and a post-development magnetic flux density peak position, and an angle θ3 is formed by a first line connecting a center of rotation of the developer carrier and the post-development magnetic flux density peak position and a second line connecting a center of rotation of the developer carrier and the pre-development magnetic flux density peak position, with the angle θ3 extending from the first line to the second line on a virtual plane perpendicular to an axial direction of the developer carrier so as to not include the development magnetic flux density peak position, the angle θ3 is not smaller than 180°.

A development device, comprising:

• a developer containing part containing two-component developer including toner and magnetic carrier particles;
• a cylindrical developer carrier to carry by rotation the developer supplied from the developer containing part to a development range where the developer carrier faces an image carrier;
• a first developer transport member disposed in the developer containing part, to supply the developer to the developer carrier while transporting the developer in an axial direction of the developer carrier;
• a magnetic field generator disposed inside the developer carrier, having three developer-carrying magnetic poles each capable of generating a magnetic field to keep the developer on a circumferential surface of the developer carrier,
• the three developer-carrying magnetic poles consisting of a development pole to generate a first magnetic field in the development range, a pre-development pole to generate a second magnetic field to transport the developer supplied from the developer containing part to the development range, and a post-development pole to generate a third magnetic field disposed between the first magnetic field and the second magnetic field, wherein
• the second magnetic field causes the developer supplied from the developer containing part to be attracted to the circumferential surface of the developer carrier at a developer attraction position, the first magnetic field and the second magnetic field keep the developer on the circumferential surface of the developer carrier from the developer attraction position to the development range, and the first magnetic field and the third magnetic field keep the developer on the circumferential surface of the developer carrier from the development range to a release position where the developer is separated from the developer carrier;
• a partition dividing the developer containing part into a supply part including a first developer supply member and a circulation part disposed beneath the supply part;
• and
• a second developer transport member disposed in the circulation part, to transport the developer in the circulation part in the axial direction of the developer carrier, wherein
• an end portion of the partition on a side closer to the developer carrier is disposed above the developer carrier, and
• the developer moves by gravity from the end portion of the partition to the circumferential surface of the developer carrier.

A development device, comprising:

• a developer containing part containing two-component developer including toner and magnetic carrier particles;
• a cylindrical developer carrier to carry by rotation the developer supplied from the developer containing part to a development range where the developer carrier faces an image carrier;
• a first developer transport member disposed in the developer containing part, to supply the developer to the developer carrier while transporting the developer in an axial direction of the developer carrier;
• and
• a magnetic field generator disposed inside the developer carrier, having three developer-carrying magnetic poles each capable of generating a magnetic field to keep the developer on a circumferential surface of the developer carrier,
• the three developer-carrying magnetic poles consisting of a development pole to generate a first magnetic field in the development range, a pre-development pole to generate a second magnetic field to transport the developer supplied from the developer containing part to the development range, and a post-development pole to generate a third magnetic field disposed between the first magnetic field and the second magnetic field, wherein
• the second magnetic field causes the developer supplied from the developer containing part to be attracted to the circumferential surface of the developer carrier at a developer attraction position, the first magnetic field and the second magnetic field keep the developer on the circumferential surface of the developer carrier from the developer attraction position to the development range, and the first magnetic field and the third magnetic field keep the developer on the circumferential surface of the developer carrier from the development range to a release position where the developer is separated from the developer carrier, and
• a peak of magnetic flux density in a normal direction to the circumferential surface of the developer carrier in the second magnetic field generated by the pre-development pole is not greater than 40 mT.

A development device, comprising:

• a developer containing part containing two-component developer including toner and magnetic carrier particles;
• a cylindrical developer carrier to carry by rotation the developer supplied from the developer containing part to a development range where the developer carrier faces an image carrier;
• a first developer transport member disposed in the developer containing part, to supply the developer to the developer carrier while transporting the developer in an axial direction of the developer carrier;
• and
• a magnetic field generator disposed inside the developer carrier, having three developer-carrying magnetic poles each capable of generating a magnetic field to keep the developer on a circumferential surface of the developer carrier,
• the three developer-carrying magnetic poles consisting of a development pole to generate a first magnetic field in the development range, a pre-development pole to generate a second magnetic field to transport the developer supplied from the developer containing part to the development range, and a post-development pole to generate a third magnetic field disposed between the first magnetic field and the second magnetic field, wherein
• the second magnetic field causes the developer supplied from the developer containing part to be attracted to the circumferential surface of the developer carrier at a developer attraction position, the first magnetic field and the second magnetic field keep the developer on the circumferential surface of the developer carrier from the developer attraction position to the development range, and the first magnetic field and the third magnetic field keep the developer on the circumferential surface of the developer carrier from the development range to a release position where the developer is separated from the developer carrier, and
• when Br1 represents a peak value of magnetic flux density at a position where magnetic flux density in a normal direction to the circumferential surface of the developer carrier is maximum in the first magnetic field generated by the development pole, and Br2 represents a peak value of magnetic flux density at a position where magnetic flux density in a normal direction to the circumferential surface of the developer carrier is maximum in the third magnetic field generated by the post-development pole, Br1>Br2.

A development device, comprising:

• a developer containing part containing two-component developer including toner and magnetic carrier particles;
• a cylindrical developer carrier to carry by rotation the developer supplied from the developer containing part to a development range where the developer carrier faces an image carrier;
• a first developer transport member disposed in the developer containing part, to supply the developer to the developer carrier while transporting the developer in an axial direction of the developer carrier;
• a magnetic field generator disposed inside the developer carrier, having three developer-carrying magnetic poles each capable of generating a magnetic field to keep the developer on a circumferential surface of the developer carrier,
• the three developer-carrying magnetic poles consisting of a development pole to generate a first magnetic field in the development range, a pre-development pole to generate a second magnetic field to transport the developer supplied from the developer containing part to the development range, and a post-development pole to generate a third magnetic field disposed between the first magnetic field and the second magnetic field, wherein
• the second magnetic field causes the developer supplied from the developer containing part to be attracted to the circumferential surface of the developer carrier at a developer attraction position, the first magnetic field and the second magnetic field keep the developer on the circumferential surface of the developer carrier from the developer attraction position to the development range, and the first magnetic field and the third magnetic field keep the developer on the circumferential surface of the developer carrier from the development range to a release position where the developer is separated from the developer carrier;
• and
• a range on the circumferential surface of the developer carrier where magnetic force in a direction tangential to the circumferential surface of the developer carrier is zero, disposed downstream from a post-development magnetic flux density peak position where magnetic flux density in a normal direction to the circumferential surface of the developer carrier is maximum in the third magnetic field generated by the post-development pole in a direction in which the developer carrier rotates and upstream from a pre-development magnetic flux density peak position where magnetic flux density in a normal direction to the circumferential surface of the developer carrier is maximum in the second magnetic field generated by the pre-development pole in a direction in which the developer carrier rotates,
• wherein an angle formed by a line connecting a given point in the range where magnetic force in the tangent direction is zero and a center of rotation of the developer carrier and a horizontal line is not greater than 50°.

A development device, comprising:

• a developer containing part containing two-component developer including toner and magnetic carrier particles;
• a cylindrical developer carrier to carry by rotation the developer supplied from the developer containing part to a development range where the developer carrier faces an image carrier;
• a first developer transport member disposed in the developer containing part, to supply the developer to the developer carrier while transporting the developer in an axial direction of the developer carrier;
• a magnetic field generator disposed inside the developer carrier, having three developer-carrying magnetic poles each capable of generating a magnetic field to keep the developer on a circumferential surface of the developer carrier,
• the three developer-carrying magnetic poles consisting of a development pole to generate a first magnetic field in the development range, a pre-development pole to generate a second magnetic field to transport the developer supplied from the developer containing part to the development range, and a post-development pole to generate a third magnetic field disposed between the first magnetic field and the second magnetic field, wherein
• the second magnetic field causes the developer supplied from the developer containing part to be attracted to the circumferential surface of the developer carrier at a developer attraction position, the first magnetic field and the second magnetic field keep the developer on the circumferential surface of the developer carrier from the developer attraction position to the development range, and the first magnetic field and the third magnetic field keep the developer on the circumferential surface of the developer carrier from the development range to a release position where the developer is separated from the developer carrier,
• each of the developer-carrying magnetic poles has a maximum density of magnetic flux in a normal direction to the circumferential surface of the developer carrier of 10 mT or greater;
• a partition dividing the developer containing part into a supply part including a first developer supply member and a circulation part disposed beneath the supply part;
• and
• a second developer transport member disposed in the circulation part, to transport the developer in the circulation part in the axial direction of the developer carrier, wherein
• an end portion of the partition on a side closer to the developer carrier is disposed above the developer carrier,
• the developer moves by gravity from the end portion of the partition to the circumferential surface of the developer carrier, and
• when Br1 represents a peak value of magnetic flux density at a position where magnetic flux density in a normal direction to the circumferential surface of the developer carrier is maximum in the first magnetic field generated by the development pole, and Br2 represents a peak value of magnetic flux density at a position where magnetic flux density in a normal direction to the circumferential surface of the developer carrier is maximum in the third magnetic field generated by the post-development pole, Br1>Br2.