# US 10,481,521 B2 · Developing device having spaced cover portion and frame > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,481,521 B2 - Document ID: US10481521B2 - Status: Granted - Kind: B2 - Application number: 15/926,169 - Filed: 2018-03-20 - Published: 2018-10-04 - Granted: 2019-11-19 - Earliest claimed: 2017-03-30 - Assignees: Canon Kabushiki Kaisha - Applicants: Canon Kabushiki Kaisha - Inventors: Yukihiro Soeta; Masafumi Takahashi; Ryohei Terada; Yushi Sadamitsu; Yasuhiro Shimoi; Yutaka Koga - Web page: https://patentgrep.com/patent/US10481521B2 ## CPC - G03G 15/0808: {characterised by the developer supplying means, e.g. structure of developer supply roller} - G03G 15/0815: {characterised by the developer handling means after the developing zone and before the supply, e.g. developer recovering roller} - G03G 15/0921: {Details concerning the magnetic brush roller structure, e.g. magnet configuration} - G03G 15/0812: {characterised by the developer regulating means, e.g. structure of doctor blade} - 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: ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY ## Abstract A developing device includes a rotatable developing member configured to carry a developer containing toner and a carrier to a developing position, a first frame configured to accommodate the developer, a second frame mounted on the first frame and configured to cover part of an outer peripheral surface of the rotatable developing member, and a cover portion provided opposite to the rotatable developing member. The following relationship is satisfied: L1≤L2+L3, and L2≤L3, where with respect to the radial direction of the rotatable developing member, L1 is a minimum of the clearance formed between the second frame and the rotatable developing member, L2 is a minimum of the clearance formed between the rotatable developing member and the cover portion, and L3 is a minimum of the clearance formed between the second frame and the cover portion. ## Claims ### Claim 1 A developing device comprising: a rotatable developing member configured to carry a developer containing toner and a carrier to a developing position where an electrostatic latent image formed on an image bearing member is developed; a first frame configured to accommodate the developer; a second frame mounted on said first frame and configured to cover part of an outer peripheral surface of said rotatable developing member; a regulating portion provided opposite to said rotatable developing member and configured to regulate, at a position closest to said rotatable developing member, an amount of the developer carried on said rotatable developing member, said regulating portion being positioned below a rotation center of said rotatable developing member in a state that said developing device is in a position where the electrostatic latent image formed on the image bearing member is developed; a magnet provided fixedly inside said rotatable developing member and configured to generate a magnetic field for peeling off the developer, passed through the developing position, from an outer peripheral surface of said rotatable developing member, said magnet including a plurality of magnetic poles including a first magnetic pole and a second magnetic pole which is provided adjacently to said first magnetic pole on a side downstream, with respect to a rotational direction of said rotatable developing member, of a first peak position where magnetic flux density of said first magnetic pole is a maximum and which has the same polarity as said first magnetic pole; a cover portion provided opposite to said rotatable developing member along the outer peripheral surface of said rotatable developing member and provided between said second frame and said rotatable developing member over a rotational axis direction of said rotatable developing member, said cover portion being disposed so as to form a clearance between itself and said rotatable developing member with respect to a radial direction of said rotatable developing member and to form a clearance between itself and said second frame with respect to the radial direction of said rotatable developing member, wherein as seen in a cross section perpendicular to the rotational axial direction of said rotatable developing member in a state that said developing device is in the position where the electrostatic latent image formed on the image bearing member is developed, with respect to the rotational direction of said rotatable developing member, a most upstream end of said cover portion is positioned downstream of the developing position and upstream of a most upstream position of a half-width of magnetic flux density of said first magnetic pole, and with respect to the rotational direction of said rotatable developing member, a most downstream end of said cover portion is positioned downstream of the first peak position and upstream of a position where the magnetic flux density of said first magnetic pole is a minimum on a side downstream of the first peak position and upstream of a second peak position where magnetic flux density of said second magnetic pole is a maximum, wherein the following relationship is satisfied: L1≤L2+L3, and L2≤L3, where with respect to the radial direction of said rotatable developing member, L1 is a minimum of the clearance formed between said second frame and said rotatable developing member, L2 is a minimum of the clearance formed between said rotatable developing member and said cover portion, and L3 is a minimum of the clearance formed between said second frame and said cover portion. ### Claim 2 (depends on 1) The developing device according to claim 1, wherein as seen in the cross section perpendicular to the rotational axial direction of said rotatable developing member in a state that said developing device is in the position where the electrostatic latent image formed on the image bearing member is developed, the most upstream end of said cover portion with respect to the rotational direction of said rotatable developing member is positioned downstream of an uppermost position of said rotatable developing member with respect to a direction of gravitation. ### Claim 3 (depends on 1) The developing device according to claim 1, wherein as seen in the cross section perpendicular to the rotational axial direction of said rotatable developing member in a state that said developing device is in the position where the electrostatic latent image formed on the image bearing member is developed, the most downstream end of said cover portion with respect to the rotational direction of said rotatable developing member is positioned within a range of the half-width of the magnetic flux density of said first magnetic pole. ### Claim 4 (depends on 1) The developing device according to claim 1, wherein said magnet further includes a third magnetic pole which is provided adjacently to said first magnetic pole on a side upstream of the first peak position with respect to the rotational direction of said rotatable developing member and which has a polarity different from the polarity of said first magnetic pole, wherein as seen in the cross section perpendicular to the rotational axial direction of said rotatable developing member in a state that said developing device is in the position where the electrostatic latent image formed on the image bearing member is developed, with respect to the rotational direction of said rotatable developing member, the most upstream end of said cover portion is positioned upstream of a position where the magnetic flux density is a minimum on a side upstream of the first peak position and downstream of a third peak position where magnetic flux density of said third magnetic pole is a maximum. ### Claim 5 (depends on 1) The developing device according to claim 1, wherein said magnet further includes a third magnetic pole which is provided adjacently to said first magnetic pole on a side upstream of the first peak position with respect to the rotational direction of said rotatable developing member and which has a polarity different from the polarity of said first magnetic pole, wherein as seen in the cross section perpendicular to the rotational axial direction of said rotatable developing member in a state that said developing device is in the position where the electrostatic latent image formed on the image bearing member is developed, with respect to the rotational direction of said rotatable developing member, the most upstream end of said cover portion is positioned downstream of a third peak position where magnetic flux density of said third magnetic pole is a maximum. ### Claim 6 (depends on 1) The developing device according to claim 1, wherein L2 is 1.5mm to 3.0mm, and L3 is 2.0mm to 3.5mm.