# US 8,571,449 B2 · Development device, process cartridge, and image forming apparatus > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,571,449 B2 - Document ID: US8571449B2 - Status: Granted - Kind: B2 - Application number: 12/700,834 - Filed: 2010-02-05 - Published: 2010-08-12 - Granted: 2013-10-29 - Earliest claimed: 2009-02-06 - Assignees: Ricoh Company, Ltd. - Applicants: Yasuo Miyoshi; Norio Kudo; Yoshihiro Fujiwara; Tsukuru Kai; Hiroshi Hosokawa; Hiroaki Okamoto - Inventors: Yasuo Miyoshi; Norio Kudo; Yoshihiro Fujiwara; Tsukuru Kai; Hiroshi Hosokawa; Hiroaki Okamoto - Web page: https://patentgrep.com/patent/US8571449B2 ## CPC - G03G 15/0887: {Arrangements for conveying and conditioning developer in the developing unit, e.g. agitating, removing impurities or humidity} - G03G 15/0898: {for preventing toner scattering during operation, e.g. seals (sealing the donor member G03G15/0817; sealing the magnetic brush G03G15/0942)} - G03G 15/0921: {Details concerning the magnetic brush roller structure, e.g. magnet configuration} - G03G 2215/0609: magnetic brush - G03G: ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY ## Abstract A development device includes a developer containing part containing two-component developer, a cylindrical developer carrier to carry by rotation the developer to a development range, 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, 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, to transport the developer to a release position where the developer is separated from the developer carrier. ## Claims ### Claim 1 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 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. ### Claim 2 (depends on 1) The development device according to claim 1, wherein, 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°. ### Claim 3 (depends on 1) The development device according to claim 1, further comprising: 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. ### Claim 4 (depends on 3) The development device according to claim 3, 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. ### Claim 5 (depends on 4) The development device according to claim 4, wherein the developer attraction position at which the developer supplied from the developer containing part contacts the circumferential surface of the developer carrier is disposed downstream, in a direction in which the developer carrier rotates, from a point on the circumferential surface of the developer carrier at the top of the rotation of the developer carrier. ### Claim 6 (depends on 4) The development device according to claim 4, wherein the developer attraction position is disposed upstream, in a direction in which the developer carrier rotates, from a point on the circumferential surface of the developer carrier at the top of the rotation of the developer carrier, and 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 pre-development pole is disposed upstream, in the direction in which the developer carrier rotates, from the point on the circumferential surface of the developer carrier at the tope top of the rotation thereof. ### Claim 7 (depends on 3) The development device according to claim 3, wherein a first communication port and a second communication port through which the supply part and the circulation part communicate with each other are respectively formed in an upstream end portion and a downstream portion of the partition in a direction in which the first developer transport member transports the developer, and the second developer transport member transports the developer in a direction opposite the direction in which the first developer transport member transports the developer. ### Claim 8 (depends on 7) The development device according to claim 7, wherein the first communication port is disposed on a side away from the developer carrier. ### Claim 9 (depends on 1) The development device according to claim 1, wherein 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. ### Claim 10 (depends on 1) The development device according to claim 1, wherein, 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. ### Claim 11 (depends on 1) The development device according to claim 1, further comprising 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°. ### Claim 12 (depends on 1) An image forming apparatus, comprising: an image carrier on which a latent image is formed; a charging member disposed adjacent to the image carrier, to charge a surface of the image carrier; and the development device according to claim 1 disposed adjacent to the image carrier, to develop the latent image into a toner image. ### Claim 13 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°. ### Claim 14 (depends on 13) The development device according to claim 13, further comprising: 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. ### Claim 15 (depends on 14) The development device according to claim 14, 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. ### Claim 16 (depends on 15) The development device according to claim 15, wherein the developer attraction position at which the developer supplied from the developer containing part contacts the circumferential surface of the developer carrier is disposed downstream, in a direction in which the developer carrier rotates, from a point on the circumferential surface of the developer carrier at the top of the rotation of the developer carrier. ### Claim 17 (depends on 15) The development device according to claim 15, wherein the developer attraction position is disposed upstream, in a direction in which the developer carrier rotates, from a point on the circumferential surface of the developer carrier at the top of the rotation of the developer carrier, and 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 pre-development pole is disposed upstream, in the direction in which the developer carrier rotates, from the point on the circumferential surface of the developer carrier at the top of the rotation thereof. ### Claim 18 (depends on 14) The development device according to claim 14, wherein a first communication port and a second communication port through which the supply part and the circulation part communicate with each other are respectively formed in an upstream end portion and a downstream portion of the partition in a direction in which the first developer transport member transports the developer, and the second developer transport member transports the developer in a direction opposite the direction in which the first developer transport member transports the developer. ### Claim 19 (depends on 18) The development device according to claim 18, wherein the first communication port is disposed on a side away from the developer carrier. ### Claim 20 (depends on 13) The development device according to claim 13, wherein 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. ### Claim 21 (depends on 13) The development device according to claim 13, wherein, 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. ### Claim 22 (depends on 13) The development device according to claim 13, further comprising 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°. ### Claim 23 (depends on 13) An image forming apparatus, comprising: an image carrier on which a latent image is formed; a charging member disposed adjacent to the image carrier, to charge a surface of the image carrier; and the development device according to claim 13 disposed adjacent to the image carrier, to develop the latent image into a toner image. ### Claim 24 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. ### Claim 25 (depends on 24) The development device according to claim 24, wherein the developer attraction position at which the developer supplied from the developer containing part contacts the circumferential surface of the developer carrier is disposed downstream, in a direction in which the developer carrier rotates, from a point on the circumferential surface of the developer carrier at the top of the rotation of the developer carrier. ### Claim 26 (depends on 24) The development device according to claim 24, wherein the developer attraction position is disposed upstream, in a direction in which the developer carrier rotates, from a point on the circumferential surface of the developer carrier at the top of the rotation of the developer carrier, and 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 pre-development pole is disposed upstream, in the direction in which the developer carrier rotates, from the point on the circumferential surface of the developer carrier at the top of the rotation thereof. ### Claim 27 (depends on 24) The development device according to claim 24, wherein a first communication port and a second communication port through which the supply part and the circulation part communicate with each other are respectively formed in an upstream end portion and a downstream portion of the partition in a direction in which the first developer transport member transports the developer, and the second developer transport member transports the developer in a direction opposite the direction in which the first developer transport member transports the developer. ### Claim 28 (depends on 27) The development device according to claim 27, wherein the first communication port is disposed on a side away from the developer carrier. ### Claim 29 (depends on 24) The development device according to claim 24, wherein 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. ### Claim 30 (depends on 24) The development device according to claim 24, wherein, 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. ### Claim 31 (depends on 24) The development device according to claim 24, further comprising 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°. ### Claim 32 (depends on 24) An image forming apparatus, comprising: an image carrier on which a latent image is formed; a charging member disposed adjacent to the image carrier, to charge a surface of the image carrier; and the development device according to claim 24 disposed adjacent to the image carrier, to develop the latent image into a toner image. ### Claim 33 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. ### Claim 34 (depends on 33) The development device according to claim 33, further comprising: 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. ### Claim 35 (depends on 34) The development device according to claim 34, 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 the developer attraction position at which the developer supplied from the developer containing part contacts the circumferential surface of the developer carrier is disposed downstream, in a direction in which the developer carrier rotates, from a point on the circumferential surface of the developer carrier at the top of the rotation of the developer carrier. ### Claim 36 (depends on 34) The development device according to claim 34, 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, the developer attraction position is disposed upstream, in a direction in which the developer carrier rotates, from a point on the circumferential surface of the developer carrier at the top of the rotation of the developer carrier, and 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 pre-development pole is disposed upstream, in the direction in which the developer carrier rotates, from the point on the circumferential surface of the developer carrier at the top of the rotation thereof. ### Claim 37 (depends on 34) The development device according to claim 34, wherein a first communication port and a second communication port through which the supply part and the circulation part communicate with each other are respectively formed in an upstream end portion and a downstream portion of the partition in a direction in which the first developer transport member transports the developer, and the second developer transport member transports the developer in a direction opposite the direction in which the first developer transport member transports the developer. ### Claim 38 (depends on 37) The development device according to claim 37, wherein the first communication port is disposed on a side away from the developer carrier. ### Claim 39 (depends on 33) The development device according to claim 33, wherein, 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. ### Claim 40 (depends on 33) The development device according to claim 33, further comprising 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°. ### Claim 41 (depends on 33) An image forming apparatus, comprising: an image carrier on which a latent image is formed; a charging member disposed adjacent to the image carrier, to charge a surface of the image carrier; and the development device according to claim 33 disposed adjacent to the image carrier, to develop the latent image into a toner image. ### Claim 42 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. ### Claim 43 (depends on 42) The development device according to claim 42, further comprising: 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. ### Claim 44 (depends on 43) The development device according to claim 43, 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 the developer attraction position at which the developer supplied from the developer containing part contacts the circumferential surface of the developer carrier is disposed downstream, in a direction in which the developer carrier rotates, from a point on the circumferential surface of the developer carrier at the top of the rotation of the developer carrier. ### Claim 45 (depends on 43) The development device according to claim 43, 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, the developer attraction position is disposed upstream, in a direction in which the developer carrier rotates, from a point on the circumferential surface of the developer carrier at the top of the rotation of the developer carrier, and 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 pre-development pole is disposed upstream, in the direction in which the developer carrier rotates, from the point on the circumferential surface of the developer carrier at the top of the rotation thereof. ### Claim 46 (depends on 43) The development device according to claim 43, wherein a first communication port and a second communication port through which the supply part and the circulation part communicate with each other are respectively formed in an upstream end portion and a downstream portion of the partition in a direction in which the first developer transport member transports the developer, and the second developer transport member transports the developer in a direction opposite the direction in which the first developer transport member transports the developer. ### Claim 47 (depends on 46) The development device according to claim 46, wherein the first communication port is disposed on a side away from the developer carrier. ### Claim 48 (depends on 42) The development device according to claim 42, further comprising 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°. ### Claim 49 (depends on 42) An image forming apparatus, comprising: an image carrier on which a latent image is formed; a charging member disposed adjacent to the image carrier, to charge a surface of the image carrier; and the development device according to claim 42 disposed adjacent to the image carrier, to develop the latent image into a toner image. ### Claim 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; 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°. ### Claim 51 (depends on 50) The development device according to claim 50, further comprising: 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. ### Claim 52 (depends on 51) The development device according to claim 51, 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 the developer attraction position at which the developer supplied from the developer containing part contacts the circumferential surface of the developer carrier is disposed downstream, in a direction in which the developer carrier rotates, from a point on the circumferential surface of the developer carrier at the top of the rotation of the developer carrier. ### Claim 53 (depends on 51) The development device according to claim 51, 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, the developer attraction position is disposed upstream, in a direction in which the developer carrier rotates, from a point on the circumferential surface of the developer carrier at the top of the rotation of the developer carrier, and 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 pre-development pole is disposed upstream, in the direction in which the developer carrier rotates, from the point on the circumferential surface of the developer carrier at the top of the rotation thereof. ### Claim 54 (depends on 51) The development device according to claim 51, wherein a first communication port and a second communication port through which the supply part and the circulation part communicate with each other are respectively formed in an upstream end portion and a downstream portion of the partition in a direction in which the first developer transport member transports the developer, and the second developer transport member transports the developer in a direction opposite the direction in which the first developer transport member transports the developer. ### Claim 55 (depends on 54) The development device according to claim 54, wherein the first communication port is disposed on a side away from the developer carrier. ### Claim 56 (depends on 50) An image forming apparatus, comprising: an image carrier on which a latent image is formed; a charging member disposed adjacent to the image carrier, to charge a surface of the image carrier; and the development device according to claim 50 disposed adjacent to the image carrier, to develop the latent image into a toner image. ### Claim 57 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. ### Claim 58 (depends on 57) An image forming apparatus, comprising: an image carrier on which a latent image is formed; a charging member disposed adjacent to the image carrier, to charge a surface of the image carrier; and the development device according to claim 57 disposed adjacent to the image carrier, to develop the latent image into a toner image.