Developing device

Abstract

To provide a configuration that can prevent a reduction in productivity in a hybrid development type developing device.SOLUTION: A developing device has a developing roller that develops an electrostatic latent image formed on a photoconductor drum, a supply roller that supplies developer to the developing roller, and a regulation blade that regulates the amount of developer carried on the supply roller. A magnet roller inside the supply roller has a main pole located at a position facing the developing roller, and a regulation pole N2 arranged upstream of the main pole at a position where the regulation blade 52 faces the supply roller. A position of the regulation pole N2 where the magnetic flux density Bθ in a normal direction on a surface of the supply roller becomes 0 is located on the downstream side of an upstream end 52a of the regulation blade 52 with respect to a forward direction being the direction of rotation of the supply roller during image formation.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a developing device used in an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine having a plurality of these functions.

Background Art

[0002] Conventionally, in a developing device, a two-component developer (hereinafter abbreviated as developer) containing non-magnetic toner particles and magnetic carrier particles is known to be used. As such a developing device, a configuration using a so-called hybrid developing method has been proposed, which includes a developing roller as a developing rotating body disposed opposite to a photosensitive drum as an image carrier, and a supply roller as a supply rotating body disposed opposite to the developing roller (Patent Document 1).

[0003] In a developing device using such a hybrid developing method, the developer is carried on a supply roller having a magnet disposed inside, a toner layer is formed on the developing roller from the developer conveyed by the rotation of the supply roller, and an electrostatic latent image on the photosensitive drum is developed with toner from the developing roller.

[0004] In the developing device described in Patent Document 1, the main pole of the magnet disposed inside the supply roller is disposed at a position facing the developing roller, and the receiving pole having a different polarity from the main pole is disposed at a position facing the supply roller inside the developing roller. Further, a regulating member for regulating the amount of the developer carried on the supply roller is disposed upstream of the main pole with respect to the rotation direction of the supply roller. Further, the configuration described in Patent Document 1 includes a toner receiving member disposed below the developing roller for receiving toner falling from the developing roller, and vibration generating means for vibrating the toner receiving member.

[0005] In the configuration described in Patent Document 1, the toner receiving member is vibrated during non-image formation and the supply roller is rotated in the opposite direction to that during image formation. This causes the toner that has fallen and accumulated in the area sandwiched between the toner receiving member and the supply roller to be carried along the surface of the supply roller, passing through the gap between the supply roller and the regulating member, and being collected in the developing container. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2008-233223 [Overview of the project] [Problems that the invention aims to solve]

[0007] As described above, in the configuration described in Patent Document 1, the toner receiving member is vibrated and the supply roller is rotated in the opposite direction to that during image formation. If this operation is performed frequently, productivity will decrease. Therefore, it is desirable to improve the recovery efficiency of toner that rotates along with the surface of the supply roller and passes through the gap between the supply roller and the regulating member.

[0008] The present invention aims to provide a configuration that can suppress a decrease in productivity in a hybrid development system. [Means for solving the problem]

[0009] The developing apparatus of the present invention comprises: a developing container containing a developer including toner and a carrier; a developing rotating body positioned opposite an image carrier and rotating to transport the developer to a developing position for developing an electrostatic latent image formed on the image carrier; a supply rotating body positioned opposite the developing rotating body and rotating to supply the developer from the developing container to the developing rotating body; a regulating member positioned opposite the supply rotating body and regulating the amount of developer carried on the supply rotating body; a first magnet fixedly positioned inside the developing rotating body in a non-rotating manner; and a second magnet fixedly positioned inside the supply rotating body in a non-rotating manner, wherein the developing apparatus is capable of executing a mode in which the supply rotating body rotates in the opposite direction to that during image formation when not forming an image. The first magnet is positioned so that the developing rotating body faces the supply rotating body with respect to the rotation direction of the developing rotating body, and has a receiving pole for receiving developer from the supply rotating body; the second magnet is positioned so that the supply rotating body faces the developing rotating body with respect to the rotation direction of the supply rotating body, and has a main pole having the opposite polarity to the receiving pole, and a regulating pole positioned upstream of the main pole, where the regulating member faces the supply rotating body, and the position where the tangential magnetic flux density of the regulating pole on the surface of the supply rotating body is 0 is located downstream of the upstream end of the regulating member with respect to the forward direction, which is the rotation direction of the supply rotating body during image formation. [Effects of the Invention]

[0010] According to the present invention, a decrease in productivity can be suppressed in a hybrid development system. [Brief explanation of the drawing]

[0011] [Figure 1] A schematic cross-sectional view of the image forming apparatus according to the first embodiment. [Figure 2] A control block diagram of an image forming apparatus according to the first embodiment. [Figure 3] A cross-sectional view of a developing apparatus according to the first embodiment. [Figure 4] An enlarged cross-sectional view of the area around the toner receiving member according to the first embodiment. [Figure 5] A schematic diagram illustrating magnetic flux lines, magnetic ears, and ear angles. [Figure 6] (a) A graph showing the relationship between the angle of the supply roller and the magnetic flux density Br in the normal direction, and (b) A graph showing the relationship between the angle of the supply roller and the magnetic flux density Bθ in the tangential direction, centered on the arrangement area of ​​the regulating blades according to Examples 1-1, 1-2 and the Comparative Example. [Figure 7] (a) A graph showing the relationship between the angle of the supply roller and the magnetic flux density Br in the normal direction, and (b) A graph showing the relationship between the angle of the supply roller and the magnetic flux density Bθ in the tangential direction, centered on the arrangement area of ​​the regulating blades according to Examples 2-1, 2-2 and the Comparative Example. [Figure 8] A graph showing the relationship between the angle of the supply roller and the magnetic flux density Br in the normal direction, with an enlarged view of the region centered on the regulating pole in Example 2-1. [Figure 9] (a) A graph showing the relationship between the angle of the supply roller and the magnetic flux density Br in the normal direction, and (b) A graph showing the relationship between the angle of the supply roller and the magnetic flux density Bθ in the tangential direction, centered on the arrangement area of ​​the regulating blade according to Example 3, 1-2 and the Comparative Example. [Figure 10] A graph showing an enlarged view of the region centered on the regulating pole in Example 3, illustrating the relationship between the angle of the supply roller and the magnetic flux density Br in the normal direction and the magnetic flux density Bθ in the tangential direction. [Modes for carrying out the invention]

[0012] <First Embodiment> The first embodiment will be described with reference to Figures 1 to 6. In this embodiment, the developing apparatus is described in the case where it is applied to a tandem-type full-color printer as an example of an image forming apparatus.

[0013] [Image forming apparatus] First, the schematic configuration of the image forming apparatus 100 according to the present embodiment will be described with reference to FIG. 1. The image forming apparatus 100 shown in FIG. 1 is an electrophotographic full-color printer having image forming units PY, PM, PC, and PK of four colors (yellow, magenta, cyan, and black) inside the apparatus main body. In the present embodiment, the image forming units PY, PM, PC, and PK are arranged in an intermediate transfer tandem system along the rotation direction of an intermediate transfer belt 6, which will be described later. The image forming apparatus 100 forms a toner image (image) on a recording material S in accordance with an image signal from a host device such as a document reading apparatus (not shown) connected to the apparatus main body or a personal computer communicably connected to the apparatus main body. Examples of the recording material include sheet materials such as paper, plastic film, and cloth.

[0014] The toner image forming process will be described. First, the image forming units PY, PM, PC, and PK will be described. However, the image forming units PY, PM, PC, and PK are substantially the same in configuration except that the toner colors are different, i.e., yellow, magenta, cyan, and black. Therefore, hereinafter, the yellow image forming unit PY will be described as a representative example, and the description of the other image forming units PM, PC, and PK will be omitted.

[0015] The image forming unit PY mainly includes a photosensitive drum 1, a charging device 2, a developing device 4, a cleaning device 8, and the like. In the present embodiment, the intermediate transfer belt 6 is disposed above each of the image forming units PY, PM, PC, and PK, and the exposure device 3 is disposed below. The photosensitive drum 1, which serves as an image carrier and a photoreceptor, has a photosensitive layer formed on the outer peripheral surface of an aluminum cylinder so as to have a negative or positive charging polarity and rotates at a predetermined process speed (peripheral speed).

[0016] The charging device 2 charges the surface of the photosensitive drum 1 to a uniform negative or positive dark potential according to, for example, the charging characteristics of the photosensitive drum 1. In this embodiment, the charging device 2 is a charging roller that contacts and rotates on the surface of the photosensitive drum 1. On the surface of the photosensitive drum 1, after charging, an electrostatic latent image is formed based on image information by an exposure device (laser scanner) 3. The photosensitive drum 1 carries the formed electrostatic latent image, moves in a circular motion, and is developed with toner by a developing device 4. The detailed configuration of the developing device 4 will be described later. The toner in the developer consumed in image formation is replenished together with a carrier from a toner cartridge (not shown).

[0017] The developed toner image is given a predetermined pressing force and a primary transfer bias by a primary transfer roller 61 disposed opposite with the photosensitive drum 1 and the intermediate transfer belt 6 interposed therebetween, and is primarily transferred onto the intermediate transfer belt 6. The surface of the photosensitive drum 1 after primary transfer is discharged by a pre-exposure unit (not shown). The cleaning device 8 cleans residues such as transfer residual toner remaining on the surface of the photosensitive drum 1 after primary transfer.

[0018] The intermediate transfer belt 6 is stretched by a stretching roller 62 and a secondary transfer inner roller 63. The intermediate transfer belt 6 is driven to move in the direction of arrow R1 in the figure by the secondary transfer inner roller 63 which is also a driving roller. The image formation processes for each color processed by the above-described image formation units PY, PM, PC, and PK are performed at a timing to sequentially overlap on the toner image of the color upstream in the moving direction primarily transferred onto the intermediate transfer belt 6. As a result, finally, a full-color toner image is formed on the intermediate transfer belt 6 and conveyed to the secondary transfer unit T2. The secondary transfer unit T2 is a transfer nip portion formed by a portion of the intermediate transfer belt 6 stretched around the secondary transfer inner roller 63 and a secondary transfer outer roller 64. Incidentally, the transfer residual toner after passing through the secondary transfer unit T2 is removed from the intermediate transfer belt 6 by a belt cleaning device (not shown).

[0019] The process of transporting the recording material S to the secondary transfer section T2 is performed at the same timing as the toner image formation process that is delivered to the secondary transfer section T2. ​​In the transport process, the recording material S is fed from a sheet cassette (not shown) or the like and delivered to the secondary transfer section T2 in accordance with the image formation timing. In the secondary transfer section T2, a secondary transfer voltage is applied to the secondary transfer roller 63.

[0020] Through the image formation and transport processes described above, the toner image is transferred from the intermediate transfer belt 6 to the recording material S in the secondary transfer section T2. ​​The recording material S is then transported to the fixing device 7, where it is heated and pressurized, causing the toner image to melt and fix onto the recording material S. The recording material S, with the toner image fixed in this manner, is then discharged to the discharge tray by the discharge roller.

[0021] [Control Unit] The image forming apparatus 100 is equipped with a control unit 20 for performing various controls, such as the image forming operations described above. The operation of each part of the image forming apparatus 100 is controlled by the control unit 20 provided in the image forming apparatus 100. The series of image forming operations are controlled by the control unit 20 according to the operation unit on the top surface of the apparatus body or the input signals via the network.

[0022] As shown in Figure 2, the control unit 20 includes a CPU (Central Processing Unit) 21, ROM (Read Only Memory) 22, RAM (Random Access Memory) 23, etc., as calculation control means. The CPU 21 controls each part of the image forming apparatus 100 while reading programs corresponding to control procedures stored in the ROM 22. The RAM 23 stores working data and input data, and the CPU 21 performs control by referring to the data stored in the RAM 23 based on the aforementioned programs, etc.

[0023] The control unit 20 processes image information in the image processing unit 24 to generate drive signals for each part, the image forming control unit 25 controls the operation of each part such as the drive unit 9 that drives the exposure device 3 and the developing device 4, and the replenishment control unit 26 controls the replenishment of toner to the developing device 4. The drive unit 9 has drive motors that drive the developing roller 50, supply roller 51, first transport screw 44, and second transport screw 45, which will be described later.

[0024] The control unit 20 is connected to a toner density sensor 58, an optical sensor 80, a temperature and humidity sensor 81, a bias power supply 82, and the like. The toner density sensor 58 will be described later. The optical sensor 80 is positioned facing the surface of the intermediate transfer belt 6 and detects the density of the patch image, which is a control toner image formed on the intermediate transfer belt 6. Depending on the density of the patch image detected by the optical sensor 80, the supply of toner to the developing device 4 is controlled. The bias power supply 82 is a power supply that applies voltage to the developing roller 50 and the supply roller 51, as will be described later.

[0025] The temperature and humidity sensor 81 is provided, for example, on a part of the wall of the stirring chamber 43 on the downstream side in the toner transport direction, to detect information regarding the temperature and humidity inside the developing apparatus 4 as an example of a detection means. The control unit 20 calculates the absolute moisture content inside the developing apparatus 4 based on the information regarding the temperature and humidity inside the developing apparatus 4, which is the detection result of the temperature and humidity sensor 81. That is, the temperature and humidity sensor 81 detects information regarding the absolute moisture content inside the developing container 40. In this embodiment, the control unit 20 calculates information regarding volumetric absolute humidity as information regarding absolute moisture content. In this embodiment, the case in which the control unit 20 calculates information regarding volumetric absolute humidity as information regarding absolute moisture content is described, but it is not limited to this, and information regarding gravimetric absolute humidity may be calculated as information regarding absolute moisture content.

[0026] [Two-component developer] Next, the developer used in this embodiment will be described. In this embodiment, a two-component developer is used in which the mixed coverage rate of toner to a carrier containing non-magnetic toner particles (toner) and magnetic carrier particles (carrier) is 8.0% by weight. The toner is a colored resin particle containing a binder resin, a colorant, and other additives as needed, and an external additive such as colloidal silica fine powder is applied to its surface. The toner used in this embodiment is a negatively charged or positively charged polyester resin depending on the charging characteristics of the photosensitive drum 1, and the volume average particle size is approximately 7.0 μm. The carrier used in this embodiment consists of magnetic metal particles such as iron, nickel, and cobalt whose surfaces have been oxidized, and the volume average particle size is approximately 40 μm to 50 μm.

[0027] [Developing equipment] Next, the developing device 4 will be described in detail with reference to Figure 3. The developing device 4 of this embodiment is a so-called touchdown developing device that uses a magnetic brush made of a two-component developer formed on the supply roller 51 to form a thin layer of toner only on the developing roller 50, and then uses a developing bias, which is a superposition of DC and AC applied to the developing roller 50, to propel the toner towards the electrostatic latent image formed on the photosensitive drum 1, thereby performing development.

[0028] As shown in Figure 3, the developing apparatus 4 comprises a developing container 40, a developing roller 50 as a developing rotating body, and a supply roller 51 as a supply rotating body. The developing container 40 contains a developer containing non-magnetic toner and a magnetic carrier. The developing container 40 has a developing chamber 42 as a first chamber, an agitation chamber 43 as a second chamber, and a partition wall 41 as a partition wall. The agitation chamber 43 is positioned adjacent to the developing chamber 42 such that at least a portion of it overlaps with the developing chamber 42 when viewed from the horizontal direction. The partition wall 41 separates the developing chamber 42 and the agitation chamber 43. The partition wall 41 has openings 41a formed at both ends in the longitudinal direction (direction of the rotation axis of the developing roller 50 and the supply roller 51) as communication parts that connect the developing chamber 42 and the agitation chamber 43. The developing container 40 forms a circulation path for circulating the developer between the developing chamber 42 and the agitation chamber 43 via the openings 41a provided in the partition wall 41.

[0029] In this embodiment, a partition wall 41 is provided approximately in the center of the developing container 40. As a result, the developing container 40 is divided by the partition wall 41 so that the developing chamber 42 and the stirring chamber 43 are adjacent to each other horizontally. The developing chamber 42 and the stirring chamber 43 are respectively equipped with a rotatable first conveying screw 44 and a second conveying screw 45 for stirring and circulating the developer.

[0030] The first conveying screw 44, as the first conveying member, is positioned at the bottom of the developing chamber 42 (inside the first chamber) along the rotation axis direction (longitudinal direction) of the supply roller 51, and is positioned substantially parallel to and opposite the supply roller 51. The first conveying screw 44 has a rotating shaft 44a and blades 44b arranged spirally around the rotating shaft 44a. The second conveying screw 45, as the second conveying member, is positioned at the bottom of the stirring chamber 43 (inside the second chamber) substantially parallel to the first conveying screw 44. The second conveying screw 45 has a rotating shaft 45a and blades 45b arranged spirally around the rotating shaft 45a.

[0031] The first transport screw 44 and the second transport screw 45 rotate in the directions of arrows R4 and R3, respectively, transporting the developer within the developing chamber 42 and the agitation chamber 43. The developer transported by the rotation of the first transport screw 44 and the second transport screw 45 circulates between the developing chamber 42 and the agitation chamber 43 through the openings 41a at both ends of the partition wall 41. The toner is agitated by the first transport screw 44 and the second transport screw 45, causing it to rub against the carrier and become negatively or positively charged by friction.

[0032] In the stirring chamber 43, a toner concentration sensor 58 (Figure 2) is positioned facing the second transport screw 45. For example, a permeability sensor that detects the permeability of the developer in the developing container 40 is used as the toner concentration sensor 58. Based on the detection result of the toner concentration sensor, the control unit 20 supplies toner from the toner cartridge to the stirring chamber 43 via the toner supply port (not shown).

[0033] As shown in Figure 3, the developing roller 50 and the supply roller 51 are positioned vertically above the developing chamber 42 and the agitation chamber 43. The developing roller 50 is located between the developing roller 50 and the photosensitive drum 1, diagonally above the supply roller 51 when viewed from the direction of the supply roller 51's rotation axis. The supply roller 51 and the developing roller 50 are positioned facing each other in the opposing section P1, with their rotation axes approximately parallel. The developing roller 50 faces the photosensitive drum 1 on the opening side of the developing container 40. The developing roller 50 and the supply roller 51 are each provided to be rotatable about their respective rotation axes. The developing roller 50 and the supply roller 51 are driven to rotate counterclockwise (in the direction of arrows R6 and R5) in Figure 3 by a drive unit 9 (Figure 2) provided in the main body of the apparatus. That is, the developing roller 50 and the supply roller 51 rotate in opposite directions in the opposing section P1, and their rotation speeds are made variable by the drive unit 9.

[0034] The supply roller 51 is a non-magnetic cylindrical roller (for example, a cylindrical roller with a diameter of 20 mm to 25 mm (20 mm in this embodiment)) that rotates counterclockwise in Figure 3, and is rotatably mounted around a magnetic field generating means provided on its inner circumference and a non-rotating cylindrical magnet roller 51a, which is the second magnet. That is, the magnet roller 51a is fixedly positioned inside the supply roller 51 in a non-rotating manner. The magnet roller 51a has five pieces, each having a pumping pole S2, a regulating pole N2, a holding pole S1, a main pole N1, and a peeling pole S3 arranged in order with respect to the rotation direction of the supply roller on the surface facing the supply roller 51. Although this embodiment uses a magnet roller with five poles, it may have other poles, for example, a magnet roller with seven poles.

[0035] The main pole N1 is positioned where the supply roller 51 faces the developing roller 50, and has opposite polarity to the receiving pole S4 of the magnet roller 50a inside the developing roller 50, which will be described later. The holding pole S1 is positioned adjacent to the upstream of the main pole N1 with respect to the rotation direction of the supply roller 51, and has opposite polarity to the main pole N1. The regulating pole N2 is positioned adjacent to the upstream of the holding pole S1 with respect to the rotation direction of the supply roller 51, and is positioned where the regulating blade 52, which will be described later, faces the supply roller 51, and has the same polarity as the main pole N1. The pumping pole S2 is positioned adjacent to the upstream of the regulating pole N2, has opposite polarity to the regulating pole N2, and is a magnetic pole for pumping the developer from the developing container 40 to the supply roller 51. Specifically, the pumping pole S2 is positioned above the developing chamber 42, facing the first transport screw 44. The peeling electrode (stripping electrode) S3 is positioned adjacent to the upstream of the pumping electrode S2 with respect to the rotational direction of the supply roller 51, and has the same polarity as the pumping electrode S2. The pumping electrode S2, regulating electrode N2, holding electrode S1, main electrode N1, and peeling electrode S3 are positioned adjacent to each other in this order with respect to the rotational direction of the supply roller 51.

[0036] The supply roller 51 carries a developer containing non-magnetic toner and a magnetic carrier, and rotates and conveys it to the portion P1 opposite the developing roller 50. That is, the supply roller 51 is positioned opposite the developing roller 50 and rotates to supply the developer from inside the developing container 40 (inside the developing container) to the developing roller 50. The supply roller 51 is, for example, cylindrical with a diameter of 20 mm and is made of a non-magnetic material such as aluminum or non-magnetic stainless steel, and in this embodiment it is made of aluminum. Furthermore, the outer surface of the supply roller 51 is blast-treated so that the surface roughness is, for example, Rz30 μm.

[0037] The regulating blade 52, acting as a regulating member, is positioned upstream of the position facing the developing roller 50 with respect to the rotational direction of the supply roller 51, and regulates the amount of developer carried on the supply roller 51. Specifically, the regulating blade 52 is a plate-shaped member and is provided in the developing container 40 such that its tip faces the outer circumferential surface of the supply roller 51 where the regulating pole N2 of the magnetic roller 51a is located. A predetermined gap is provided between the tip of the regulating blade 52 and the outer circumferential surface of the supply roller 51. The magnetic particles of the developer carried on the surface of the supply roller 51 are cut by the regulating blade 52, thereby regulating the thickness of the developer layer. Specifically, the regulating blade 52 is made of a metal plate (for example, a stainless steel plate) positioned in the longitudinal direction of the supply roller 51, and the developer is transported in a regulated amount as it passes between the tip of the regulating blade 52 and the supply roller 51. The regulating blade 52 is made of a magnetic material such as SUS430 with a thickness of about 1.5 mm, and is fixed to the developing container 40 so as to extend in the direction of the rotation axis of the supply roller 51.

[0038] The regulating blade 52 can be made of either a magnetic or non-magnetic material. If a magnetic material is used, the distance between the tip of the regulating blade 52 and the supply roller 51 can be increased, which has the advantage of making it less likely for foreign matter to get stuck. On the other hand, if a magnetic material is used, the developer may be constrained by the magnetic field between the tip of the regulating blade 52 and the supply roller 51, which may make it easier for the developer to deteriorate due to friction. The regulating blade 52 may also be configured by attaching a magnetic material to a part of a non-magnetic material. In this case, some of the advantages of a magnetic material are lost, but it is possible to suppress the deterioration of the developer. In this embodiment, the regulating blade 52 is made of only a magnetic material. Therefore, there is a concern about the deterioration of the developer, but by using the magnetic roller 51a of this embodiment, which will be described later, in combination, it is possible to suppress the deterioration of the developer.

[0039] The developer contained in the developing chamber 42 is adsorbed onto the surface of the supply roller 51 by the pumping electrode S2 facing the developing chamber 42 and transported toward the regulating blade 52. The developer is raised by the regulating electrode N2 facing the regulating blade 52, and the layer thickness is regulated by the regulating blade 52. The developer layer is carried and transported via the holding electrode S1 to the portion P1 facing the developing roller 50, and with a magnetic head formed by the main electrode N1 facing the developing region, toner is supplied to the surface of the developing roller 50 by the potential difference ΔV between Vmag (DC: DC component) applied to the supply roller 51 and Vslv (DC: DC component) applied to the developing roller 50, and by the magnetic field. A supply bias (Vmag), which is a superposition of DC voltage and AC voltage, is applied to the supply roller 51.

[0040] The developing roller 50 is positioned opposite the photosensitive drum 1 and, by rotating, transports the developer to the developing position where the electrostatic latent image formed on the photosensitive drum 1 is developed. Specifically, the developing roller 50 is a non-magnetic roller that rotates counterclockwise in Figure 3 and is rotatably mounted around a non-rotating magnet roller 50a, which is a first magnet with one receiving pole S4 on its inner circumference. The developing roller 50 carries toner and, by rotating, can develop the electrostatic latent image on the photosensitive drum 1 in the developing region P2, which is the opposing region opposite the photosensitive drum 1. The supply roller 51 and the developing roller 50 face each other with a predetermined gap in their opposing portion P1. The receiving pole S4 of the magnet roller 50a within the developing roller 50 has opposite polarity to the opposing main pole N1.

[0041] In other words, the thickness of the toner layer on the developing roller 50 changes depending on the resistance of the developer and the difference in rotational speed between the supply roller 51 and the developing roller 50, but it can be controlled by ΔV. Increasing ΔV makes the toner layer on the developing roller 50 thicker, and decreasing ΔV makes it thinner. Generally, a range of ΔV between 100V and 350V is appropriate during development. The thin layer of toner formed on the developing roller 50 by contact with the magnetic brush on the supply roller 51 is transported to the area opposite the photosensitive drum 1 and the developing roller 50 by the rotation of the developing roller 50.

[0042] A developing bias (Vslv) consisting of a superimposed DC voltage and AC voltage is applied to the developing roller 50. Due to the potential difference between the developing roller 50 and the photosensitive drum 1, toner is ejected from the developing roller 50 to the photosensitive drum 1, and the electrostatic latent image on the photosensitive drum 1 is developed. The developing bias and supply bias are applied to the developing roller 50 and the supply roller 51 from a bias power supply 82 (Figure 2), which is an example of a voltage application unit, via a bias control circuit. That is, the bias power supply 82 applies a voltage containing DC and AC components between the developing roller 50 and the supply roller 51.

[0043] Toner remaining on the developing roller 50 that is not used for developing is transported again to the opposing section P1 between the developing roller 50 and the supply roller 51, where it is rubbed by the magnetic fins on the supply roller 51 and collected by the supply roller 51. The magnetic fins are detached from the supply roller 51 in a detachment region created by the repulsion between the detachment electrode S3 and the pumping electrode S2, which are located downstream of the supply roller 51 in the direction of rotation. The detached developer falls into the developing chamber 42, is mixed and transported with the developer circulating in the developing container 40, is again attracted to the pumping electrode S2 and transported by the supply roller 51.

[0044] [Collection of accumulated toner] In the developing apparatus 4 of this embodiment as described above, at the point where the developing roller 50 and the supply roller 51 face each other, only the toner is carried on the developing roller 50 by a magnetic brush formed on the supply roller 51, and any toner not used for development is peeled off the developing roller 50. As a result, toner scattering is likely to occur near the point where the developing roller 50 and the supply roller 51 face each other. Furthermore, if the toner floating in the developing apparatus accumulates around the regulating blade 52, and the accumulated toner aggregates and adheres to the developing roller 50, the aggregated toner may be output to the image, resulting in what is known as toner drop and potentially causing image defects.

[0045] Therefore, in this embodiment, there is a toner receiving member 53 and a vibration motor 54. The toner receiving member 53 is positioned below the developing roller 50 and is inclined downward as the regulating blade 52 approaches the position facing the supply roller 51. In this embodiment, the toner receiving member 53 is positioned longitudinally above the regulating blade 52 and receives toner falling from the developing roller 50. The vibration motor 54, as a vibration generating means, vibrates the toner receiving member 53. In addition, in this embodiment, a mode can be executed in which the supply roller 51 is rotated in the opposite direction to that during image formation when no image is being formed. In this mode, the vibration motor 54 is vibrated when no image is being formed, and the supply roller 51 is rotated in the opposite direction to that during image formation. This allows the magnetic brush on the supply roller 51 to collect the accumulated toner and effectively suppresses toner accumulation around the regulating blade 52. The details will be explained below.

[0046] As shown in Figure 3, a toner receiving support member 55 is provided near the developing roller 50 on the right side wall of the developing container 40, protruding inward from the developing container 40. The toner receiving support member 55 is positioned along the longitudinal direction of the developing container 40 (the direction perpendicular to the plane of the paper in Figure 3), and its upper surface faces the supply roller 51 and the developing roller 50, forming a wall that slopes downward from the developing roller 50 toward the supply roller 51. A toner receiving member 53 is attached to the upper surface of the toner receiving support member 55 along the longitudinal direction to receive toner that is peeled off from the developing roller 50 and falls.

[0047] The toner receiving member 53 is made of sheet metal and is supported by the toner receiving support member 55 via two coil springs 56 positioned on both sides in the longitudinal direction. A vibration motor 54 is supported approximately in the longitudinal center of the toner receiving member 53. A sheet member is attached to the surface of the toner receiving member 53. The sheet member is made of a material that is less resistant to toner adhesion than the toner receiving member 53 in order to suppress toner adhesion to the toner receiving member 53. Examples of materials for the sheet member include fluororesin sheets.

[0048] Furthermore, a film-like sealing member 57 is provided at the upper end of the toner receiving support member 55. The sealing member 57 extends longitudinally (in the direction perpendicular to the plane of the paper in Figure 6) such that its tip contacts the surface of the photosensitive drum 1 (the contact portion is omitted in Figure 2), and has the function of shielding the toner in the developing container 40 from leaking out.

[0049] The vibration motor 54 has an output shaft to which an excitation weight is fixed. The vibration motor 54 is fixed such that the output shaft 43a is aligned with the longitudinal direction of the toner receiving member 53. The excitation weight has a cam shape and is asymmetrical with respect to the output shaft. When the output shaft rotates at a speed above a predetermined speed, an uneven centrifugal force is applied to the excitation weight. This centrifugal force is transmitted to the output shaft, causing the vibration motor 54 to vibrate. Note that the shape of the excitation weight is not limited to a cam shape and can be any shape such that its center of gravity is offset from the output shaft.

[0050] By rotating the output shaft of the vibration motor 54 at high speed (for example, around 10,000 rpm) while the developing device 4 is in operation, the vibration weight also rotates at high speed along with the output shaft. At this time, an uneven centrifugal force is applied to the vibration weight, causing the vibration motor 54 to vibrate via the output shaft. As a result, the toner receiving member 53 to which the vibration motor 54 is fixed also vibrates. Due to the vibration of the toner receiving member 53, the toner accumulated on the toner receiving member 53 is detached and shaken off. This suppresses the accumulation of toner on the toner receiving member 53, even when the supply roller 51 and developing roller 50 in the developing device 4 are rotating at high speed and the amount of floating toner is large.

[0051] Figure 4 will be used to explain the configuration around the toner receiving member 53 in more detail. Only the edge 53a on the supply roller 51 side of the toner receiving member 53 is in contact with the toner receiving support member 55, while the opposite edge 53b (on the photosensitive drum 1 side) is a free end. The approximate center of the toner receiving member 53 in the width direction (left-right direction in Figure 4) is supported by the toner receiving support member 55 via a coil spring 56. As a result, the toner receiving member 53 is configured to swing with the edge 53a as the pivot point.

[0052] Furthermore, the toner receiving member 53 is positioned such that the toner receiving surface 53c facing the developing roller 50 is inclined upward from the supply roller 51 side toward the photosensitive drum 1 side, and the toner dropping surface 53d facing the supply roller 51 is positioned to be approximately vertical.

[0053] When the vibration motor 54 is vibrated during non-image formation, the toner receiving member 53 vibrates such that the amplitude increases as it moves towards the edge 53b, with the edge 53a as the pivot point. Due to the vibration of the toner receiving member 53, as shown in Figure 4, the toner accumulated on the toner receiving surface 53c of the toner receiving member 53 slides down along the slope of the toner receiving surface 53c (in the direction of the arrow in Figure 4) and falls into the region R sandwiched between the toner dropping surface 53d and the supply roller 51.

[0054] The timing for vibrating the toner receiving member 53 and rotating the supply roller 51 in the reverse direction, that is, the timing for executing the mode, may be performed at the end of each image forming operation, or at predetermined timings during non-image forming, such as when the number of formed images reaches a predetermined number or when the temperature inside the developing device 4 exceeds a predetermined level. Non-image forming refers to the time when the developing device 4 is not developing the electrostatic latent image on the photosensitive drum 1. Therefore, even during the execution of an image forming job in which images are formed by command, for example, the timing between consecutive images (so-called inter-page intervals) is considered non-image forming, and the above-mentioned mode may be executed during inter-page intervals.

[0055] Furthermore, the timing for vibrating the toner receiving member 53 and the timing for rotating the supply roller 51 in the opposite direction may be the same or different. Also, the vibration of the toner receiving member 53 may be automatically performed according to the number of images formed, by vibrating the toner receiving member 53 each time a predetermined number of images are formed, or the vibration of the toner receiving member 53 may be performed at a timing manually set by the user.

[0056] Here, in order to return the toner that has fallen into area R to the developing chamber 42, the supply roller 51 is rotated in the opposite direction to that during image formation (clockwise in Figure 3) when not forming an image. By rotating the supply roller 51 in the opposite direction, the toner that has fallen and accumulated in area R is carried along by the surface of the supply roller 51, passes through the gap between the supply roller 51 and the regulating blade 52, and is forcibly returned to the developing chamber 42. At this time, the developing roller 50 is also rotated in the opposite direction to that during image formation.

[0057] On the other hand, if the developing roller 50 and the supply roller 51 are rotated in reverse, there is a risk that the developer in the developing container 40 may overflow from the toner supply port, or that uneven distribution of the developer in the developing container 40 may occur, causing noise in the toner density sensor 58. For this reason, after rotating the developing roller 50 and the supply roller 51 in reverse, it is preferable to rotate the developing roller 50 and the supply roller 51 in the forward direction, which is the rotation direction during image formation, for a certain period of time.

[0058] Here, when the developing roller 50 and the supply roller 51 are rotated in reverse, the magnetic force and arrangement of the regulating pole N2 facing the regulating blade 52 are adjusted so that the bristles of the magnetic brush formed on the supply roller 51 become longer, thereby improving the scraping effect of toner accumulated on the tip of the regulating blade 52.

[0059] Figure 5 schematically shows the magnetic flux lines on the supply roller 51 due to the regulating pole N2 of the magnetic roller 51a of the supply roller 51. The magnetic flux lines extend from the regulating pole N2 of the magnetic roller 51a toward the adjacent pumping pole S2 and holding pole S1. The magnetic brush is formed along the magnetic flux lines. Therefore, the position where the bristles of the magnetic brush are longest in the direction normal to the surface of the supply roller 51 is the position where the tangential component Bθ = 0 of the magnetic flux density B with respect to the supply roller 51. In other words, when the angle between the magnetic flux lines and the surface of the supply roller 51 is denoted as the bristle angle φ, this is when the bristle angle is 90 degrees. The position where Bθ = 0 is formed around the regulating pole N2 of the magnetic roller 51a is where the bristles of the magnetic brush are longest, and the scraping effect of accumulated toner is highest.

[0060] When the brush head angle φ is 45 degrees and 60 degrees, the length of the magnetic brush bristles normal to the surface of the supply roller 51 is approximately 87% and 71%, respectively, compared to when the brush head angle φ is 90 degrees. Furthermore, as the magnetic field lines move away from the surface of the supply roller 51, the bristles bend to flatten out, so the length of the magnetic brush bristles normal to the surface of the supply roller 51 becomes shorter than described above. As the brush head angle φ flattens out, the scraping effect of the magnetic brush bristles on deposited toner decreases.

[0061] Therefore, in this embodiment, the position where the tangential magnetic flux density Bθ on the surface of the supply roller 51 of the restricting pole N2 is 0 is located downstream of the upstream end of the restricting blade 52 with respect to the forward direction, which is the rotation direction of the supply roller 51 during image formation. Preferably, the position where the tangential magnetic flux density Bθ on the surface of the supply roller 51 of the restricting pole N2 is 0 is located downstream of the downstream end of the restricting blade 52 with respect to the forward direction. This will be explained in detail below.

[0062] [Magnetic roller for supply roller] Examples 1-1 and 1-2 of the restricting pole N2 of the magnet roller 51a of the supply roller 51 of this embodiment will be described with reference to Figures 6(a) and (b), in comparison with the comparative example. Figure 6(a) is a schematic diagram showing the distribution of magnetic flux density Br on the supply roller 51 due to the magnet roller 51a, and Figure 6(b) is a schematic diagram showing the distribution of magnetic flux density Bθ on the supply roller 51 due to the magnet roller 51a. More precisely, magnetic flux density Br refers to the component of magnetic flux density B in the direction normal to the supply roller 51, and magnetic flux density Bθ refers to the component of magnetic flux density B in the direction tangential to the supply roller 51.

[0063] The magnetic flux density Br (normal direction) of each magnet roller in the examples and comparative examples was measured using a magnetic field measuring instrument (FWBELL "MS-9902") with a distance of approximately 100 μm between the probe, a component of the magnetic field measuring instrument, and the surface of the supply roller. The tangential magnetic flux density Bθ on the surface of the supply roller 51 was calculated using the value of Br measured by the above method from the following equation 1.

number

[0064] The magnetic flux density Bθ of the regulating pole N2 of the magnet roller 51a in Examples 1-1 and 1-2 will be described in detail based on Figures 6(a) and (b), including comparative examples. Here, Examples 1-1 and 1-2 are those in which the magnet roller 51a of this embodiment is used, and are represented by dashed and dotted lines, respectively. Comparative examples are represented by solid lines.

[0065] Furthermore, as shown in Figure 4, the positional relationship between the upstream end 52a and the downstream end 52b, which are on both sides of the rotation direction of the supply roller 51 at the tip of the regulating blade 52, the joint between the toner receiving surface 53c and the toner dropping surface 53d (53e), and the magnetic flux density Bθ is also shown in Figures 6(a) and (b). The arrows in Figures 6(a) and (b) indicate the direction of transport of the developer (the rotation direction of the supply roller 51 (forward direction)).

[0066] As shown in Figure 6(b), according to the positional relationship between the magnetic flux density Bθ=0 of the regulating pole N2 of the comparative example and the upstream end 52a of the regulating blade 52, the position where the magnetic brush bristles extend the most at magnetic flux density Bθ=0 is 2 degrees upstream of the upstream end 52a of the regulating blade 52 with respect to the forward direction of the supply roller 51. In other words, the configuration allows the magnetic bristles of the magnetic brush to extend the most in the regulating region of the developer.

[0067] As described above, the efficiency of collecting deposited toner by the bristles of the magnetic brush decreases as the bristles angle φ becomes flatter. According to our research, the deposited toner is efficiently collected when the bristles angle φ is 60 degrees or more. As shown in Figure 5, according to the magnetic flux densities Br and Bθ of the comparative example, the region E where the bristles angle φ is 60 degrees or more is approximately ±9 degrees with respect to the forward direction of the supply roller 51, relative to the position where Bθ=0. That is, the angular difference in the region E where the bristles angle φ is 60 degrees or more is within the range of an angular difference of 9 degrees centered on the position where Bθ=0.

[0068] In this embodiment, with a diameter of 20 mm for the supply roller 51, a gap between the supply roller 51 and the regulating blade 52, and a plate thickness for the regulating blade 52, the angular difference between the downstream end 52b and the upstream end 52a of the regulating blade 52 is approximately 8 degrees in the forward direction of the supply roller 51. Therefore, the angular difference between the Bθ=0 position of the regulating pole N2 and the downstream end 52b of the regulating blade 52 in the comparative example is approximately 10 degrees, which is larger than the 9-degree angular difference centered at Bθ=0 where the toner angle φ is 60 degrees or more, indicating that the recovery efficiency of the toner deposited in region R is low.

[0069] Therefore, in the case of the comparative example configuration, the efficiency of toner recovery by the toner recovery mode (toner recovery mode) is low in response to the increased toner scattering due to the increased speed of the image forming apparatus and the reduction in toner particle size. This leads to an increase in the frequency of this toner recovery mode, resulting in a decrease in productivity.

[0070] Next, Examples 1-1 and 1-2 will be described. In Examples 1-1 and 1-2, the magnitude of the magnetic flux density Br of the regulating pole N2 is the same as in the comparative example, but the relationship between the regulating blade 52 and the magnetic flux density Bθ is configured as follows in order to improve the efficiency of recovering deposited toner.

[0071] As described above, in order to efficiently recover the toner deposited in region R, it is preferable that a region with a brush angle of 60 degrees or more, formed by the restricting electrode N2, exists in region R. Therefore, in Example 1-1, the magnitude of the magnetic flux density Br formed by the restricting electrode N2 is the same as in the comparative example, and with respect to the forward direction of the supply roller 51, the position where the magnetic flux density Bθ=0 is at least downstream of the upstream end 52a of the restricting blade 52.

[0072] In Example 1-1, the position where the magnetic flux density Bθ=0 was set to be 2 degrees downstream in the forward direction from the upstream end 52a. That is, a region with a spike angle of 60 degrees or more formed by the regulating pole N2 exists in region R, resulting in improved toner recovery efficiency by the toner recovery mode compared to the comparative example.

[0073] Furthermore, in order to improve the efficiency of toner recovery using the toner recovery mode, it is preferable that the position of magnetic flux density Bθ=0 be located downstream in the forward direction from the downstream end 52b of the regulating blade 52. This is because the Bθ=0 position where the magnetic bristles extend the most is reliably located in region R, and the region with a bristle angle of 60 degrees or more extends over a wide area of ​​region R. In Example 1-2, the Bθ=0 position was set to 2 degrees downstream in the forward direction from the downstream end 52b of the regulating blade 52.

[0074] In the comparative example, Example 1-1, and Example 1-2 described above, evaluation tests were conducted to assess image defects due to toner fallout. The evaluation conditions were a temperature and humidity of 30°C and 80%, an image duty cycle of 30%, and the frequency of the accumulated toner recovery mode set to once every 100 images formed. The image forming speed of the image forming apparatus was set to 60, 80, and 100 ppm for evaluation. The evaluation was performed by visually inspecting the output images. A circle was used to indicate that no toner fallout (where aggregated toner is output to the image) was observed, a triangle to indicate slight toner fallout, and an "X" to indicate that toner fallout was observed and had a significant impact on image quality. The evaluation results are shown in Table 1. [Table 1]

[0075] As is clear from Table 1, compared to the comparative example, both Example 1-1 and Example 1-2 showed improved toner recovery efficiency using the accumulated toner recovery mode, and were able to suppress image defects due to toner fallout while maintaining productivity.

[0076] Furthermore, the position of B=0 formed by the regulating pole N2 may be set to a position downstream in the forward direction from the upstream end 52a and downstream end 52b of the regulating blade 52, taking into account the manufacturing tolerance of the magnet roller 51a compared to Examples 1-1 and 1-2. That is, if the manufacturing tolerance of Bθ=0 at the regulating pole N2 of the magnet roller 51a is ±3 degrees, it is preferable that the center value of the Bθ=0 position be 3 degrees downstream in the forward direction from the upstream end 52a and downstream end 52b.

[0077] Furthermore, if the position B=0 formed by the restricting electrode N2 is located downstream in the forward direction from the joint 53e between the toner receiving surface 53c and the toner dropping surface 53d, which is the downstream end in the forward direction of region R, the bristles of the magnetic brush will extend the most in the region where no toner is present, reducing the toner recovery rate by the toner recovery mode. Therefore, it is preferable that the position B=0 formed by the restricting electrode N2 be located upstream in the forward direction from the joint 53e.

[0078] The area with the most toner accumulation in region R is around the downstream end 52b of the regulating blade 52. Also, as mentioned earlier, the region where the brush head angle φ, which provides the highest recovery efficiency, is 60 degrees or more has an angular difference of approximately 9 degrees centered around the position Bθ=0. For this reason, the position Bθ=0 is preferably within a range of 10 degrees or less downstream in the forward direction from the downstream end 52b of the regulating blade 52.

[0079] Furthermore, in this embodiment, a non-magnetic metal plate is used as the regulating blade 52. However, the regulating blade 52 may also be a magnetic metal plate from which magnetic flux lines extend toward the regulating blade 52 from a position downstream of the regulating blade 52. This improves the recovery effect of toner that has fallen into region R when the supply roller 51 is rotated in reverse.

[0080] Furthermore, the relationship between the position of the regulating blade 52 and the magnetic flux density distribution can be measured as follows. Typically, the magnet roller 51a of the supply roller 51 has a shaft, and the end of the shaft has a so-called D-cut shape. The D-cut portion is fixed to the developing container 40 with a pole-setting member to achieve the desired magnetic pole arrangement. The distribution of magnetic flux density Br with respect to the D-cut (plane angle) of the magnet roller 51a can be measured with the magnetic field measuring instrument described above. On the other hand, by measuring the position of the regulating blade 52 with respect to the axis center of the magnet roller 51a, the relationship between the position of the regulating blade 52 and the magnetic flux density distribution can be determined. The position of the regulating blade 52 with respect to the axis center of the magnet roller 51a can be measured using measuring instruments such as a protractor, but if you want to know it accurately, you can use a general three-dimensional measuring machine (for example, Mitutoyo's CRYSTA-ApexS series three-dimensional measuring machine).

[0081] Furthermore, although this embodiment employs a configuration using a vibration motor 54, toner can still accumulate in region R even in configurations that do not use vibration generating means such as a vibration motor 54, due to toner scattering caused by, for example, the tilting of the magnetic brush bristles after passing the regulating electrode N2. For this reason, the arrangement of the regulating blade 52 and the configuration of the magnetic flux density distribution described above are also applicable to configurations without vibration generating means.

[0082] <Second Embodiment> The second embodiment will be described using Figures 7(a) to 8 with reference to Figures 3 and 4. This embodiment modifies the distribution of the magnetic flux density of the regulating pole N2 compared to the first embodiment. Since the other configurations and operations are the same as those of the first embodiment described above, the same reference numerals are used for similar components, and their descriptions and illustrations are omitted or simplified. The following description will focus on the differences from the first embodiment.

[0083] In this embodiment as well, the position where the tangential magnetic flux density Bθ on the surface of the supply roller 51 of the regulating pole N2 is zero is located downstream of the upstream end of the regulating blade 52 with respect to the forward direction, which is the rotational direction of the supply roller 51 during image formation. Preferably, the position where the tangential magnetic flux density Bθ on the surface of the supply roller 51 of the regulating pole N2 is zero is located downstream of the downstream end of the regulating blade 52 with respect to the forward direction.

[0084] On the other hand, in this embodiment, unlike the first embodiment, the distribution of magnetic flux density Br in the normal direction on the surface of the supply roller 51 of the restricting pole N2 satisfies 2≧X / Y>1, where the position where the magnetic flux density Br is maximum is the first position (point A), the second position (point B1) is upstream of the first position in the forward direction of the supply roller 51 and the position where the magnetic flux density Br in the normal direction on the surface of the supply roller 51 of the restricting pole N2 is 0, the third position (point B2) is downstream of the first position in the forward direction and the position where the magnetic flux density Br in the normal direction on the surface of the supply roller 51 of the restricting pole N2 is 0, and the angular difference between the first position and the second position in the forward direction is X, and the angular difference between the first position and the third position in the forward direction is Y. Preferably, 4≧X / Y>1 is satisfied.

[0085] Figure 7(a) schematically shows the distribution of magnetic flux density Br on the supply roller 51 by the magnetic roller 51a in the comparative example and Examples 2-1 and 2-2, and Figure 7(b) schematically shows the distribution of magnetic flux density Bθ on the supply roller 51 by the magnetic roller 51a.

[0086] Furthermore, Figures 7(a) and (b), similar to Figures 6(a) and (b), show the upstream end 52a and downstream end 52b, which are the sides of the supply roller 51 at the tip of the regulating blade 52 in the direction of rotation, the joint between the toner receiving surface 53c and the toner dropping surface 53d (53e), the positional relationship of the magnetic flux density Bθ, and the direction of transport of the developer (direction of rotation of the supply roller 51 (forward direction), indicated by the arrow).

[0087] In Examples 2-1 and 2-2, the magnitude of the magnetic flux density Br of the regulating pole N2 is approximately the same as in the comparative example, but the relationship between the regulating blade 52 and the magnetic flux density Bθ is configured as follows to improve the efficiency of toner recovery. The difference between Examples 2-1 and 2-2 and Examples 1-1 and 1-2 is that while the shape of the magnetic flux density Br of the regulating pole N2 and the adjacent pumping pole S2 and holding pole S1, as well as the angle of the maximum value and the positional relationship with the regulating blade 52, are approximately the same as in the comparative example, the shape of the magnetic flux density Br distribution of the regulating pole N2 is asymmetrical.

[0088] Here, the asymmetric shape of the magnetic flux density Br of the regulating pole N2 in Example 2-1 will be explained using Figure 8. Figure 8 is an enlarged view of the magnetic flux density Br around the regulating pole N2 of Example 2-1 described in Figure 7(a). Point A is the position where the magnitude of the magnetic flux density Br in the normal direction is maximum. Points B1 and B2 are points where the magnetic flux density Br is 0. With respect to the forward direction of the supply roller 51, point B1 is upstream of point A and point B2 is downstream of point A, and these are the positions where the magnetic flux density Br is 0. X indicates the angular difference between point A and point B1, and Y indicates the angular difference between the positions of point A and point B2.

[0089] Specifically, in Example 2-1, the ratio of the angular difference (Y) between points A and B2 on the regulating pole N2 to the angular difference (X) between point A and point B1 is approximately 1:2. That is, 2 ≥ X / Y > 1 is satisfied. In contrast, the ratio of the angular difference between points A and B2 on the regulating pole N2 to the angular difference between point A and point B1 is approximately 1:1.

[0090] To position the magnetic flux density Bθ=0 point further downstream in the forward direction, the maximum value of the magnetic flux density Br must be positioned downstream in the forward direction. To minimize the influence on adjacent poles, the position of magnetic flux density Br=0 must be approximately the same as in the comparative example. Therefore, by adjusting the ratio of the angular difference between points A and B2 of the regulated pole N2 to the angular difference between points A and B1, the position of magnetic flux density Bθ=0 can be changed while minimizing the influence on adjacent poles.

[0091] In the configuration of Example 2-1, the shape of the magnetic flux density Br of the magnetic pole adjacent to the regulating pole N2 is maintained compared to the comparative example, so the function of other magnetic poles is not impaired. In addition, in Example 2-1, the position where the magnetic flux density Bθ=0 is at least downstream of the upstream end 52a of the regulating blade 52 in the forward direction, and is 2 degrees downstream of the upstream end 52a, similar to Example 1-1. That is, the region with a tooth angle of 60 degrees or more formed by the regulating pole N2 exists in region R, improving the recovery efficiency of deposited toner by the deposited toner recovery mode compared to the comparative example, and achieving a recovery efficiency equivalent to that of Example 1-1.

[0092] Furthermore, in order to improve the efficiency of toner recovery using the toner recovery mode, it is preferable that the position of magnetic flux density Bθ=0 is located downstream of the downstream end 52b of the regulating blade 52 in the forward direction. This is because the Bθ=0 position where the magnetic bristles extend the most is reliably located in region R, and the region with a bristle angle of 60 degrees or more extends over a wide area of ​​region R.

[0093] In Example 2-2, the asymmetry of the shape of the magnetic flux density Br distribution of the regulating pole N2 was improved. Specifically, in Example 2-2, the ratio of the angular difference between the positions of points A and B2 of the regulating pole N2 to the angular difference between points A and B1 is approximately 1:4. That is, 4≧X / Y>1 is satisfied. As a result, Bθ=0 in Example 2-2 is at approximately the same position as the downstream end 52b of the regulating blade 52, resulting in improved toner recovery efficiency compared to the comparative example and Example 2-1.

[0094] The desirable position of the angle at which B=0 of the regulating pole N2, and the material of the regulating blade 52, are the same as in the first embodiment. Furthermore, in this embodiment, the arrangement of the regulating blade 52 and the configuration of the magnetic flux density distribution described above are also applicable to configurations without vibration generating means.

[0095] <Third Embodiment> The third embodiment will be described using Figures 9(a) to 10 with reference to Figures 3 and 4. This embodiment modifies the distribution of the magnetic flux density of the regulating pole N2 compared to the first embodiment. Since the other configurations and operations are the same as those of the first embodiment described above, the same reference numerals are used for similar components, and their descriptions and illustrations are omitted or simplified. The following description will focus on the differences from the first embodiment.

[0096] In this embodiment as well, the position where the tangential magnetic flux density Bθ on the surface of the supply roller 51 of the regulating pole N2 is zero is located downstream of the upstream end of the regulating blade 52 with respect to the forward direction, which is the rotational direction of the supply roller 51 during image formation. Preferably, the position where the tangential magnetic flux density Bθ on the surface of the supply roller 51 of the regulating pole N2 is zero is located downstream of the downstream end of the regulating blade 52 with respect to the forward direction.

[0097] On the other hand, in this embodiment, unlike the first embodiment, the position where the magnetic flux density Br in the normal direction on the surface of the supply roller 51 of the regulating pole N2 is maximum is defined as the first position (point A), the position downstream of the first position in the forward direction of the supply roller 51 where the magnetic flux density Bθ in the tangential direction on the surface of the supply roller 51 of the regulating pole N2 is 0 is defined as the fourth position (point D), the angular difference between the first position and the fourth position in the forward direction is defined as Z, and the angular difference between the first position and the upstream end 52a of the regulating blade 52 in the forward direction is defined as Ga, such that Z ≥ Ga. Preferably, when the angular difference between the first position and the downstream end 52b of the regulating blade 52 in the forward direction is defined as Gb, Z ≥ Gb is defined.

[0098] As described above, in Examples 1-2, the position where the magnetic flux density Bθ=0 of the regulating pole N2 was set to be downstream of the supply roller 51 in the forward direction from the downstream end 52b of the regulating blade 52, compared to the comparative example. According to the inventors' investigation, when the magnetic flux density Bθ of the regulating pole N2 is located downstream of the regulating blade 52, the fluidized bed of the developer around the cutting position is narrow. In other words, the change in the shear surface due to the pole position variation caused by the part tolerances and mounting tolerances of the regulating pole N2 is small, and the change in the layer thickness with respect to the pole position variation of the regulating pole N2 is small. On the other hand, when the magnetic flux density Br of the regulating pole N2 is located upstream of the regulating blade 52, the change in the layer thickness with respect to the variation in the gap between the supply roller 51 and the regulating blade 52 is large.

[0099] In Example 3, we propose a configuration that improves the efficiency of toner recovery while keeping the change in layer thickness in response to fluctuations in the gap between the supply roller 51 and the regulating blade 52 approximately the same as in the comparative example.

[0100] Figure 9(a) schematically shows the distribution of magnetic flux density Br on the supply roller 51 by the magnetic roller 51a in the comparative example and Examples 1-2 and Example 3, and Figure 9(b) schematically shows the distribution of magnetic flux density Bθ on the supply roller 51 by the magnetic roller 51a.

[0101] Furthermore, Figures 9(a) and (b), similar to Figures 6(a) and (b), show the upstream end 52a and downstream end 52b, which are on both sides of the rotation direction of the supply roller 51 at the tip of the regulating blade 52, the joint between the toner receiving surface 53c and the toner dropping surface 53d (53e), the positional relationship of the magnetic flux density Bθ, and the transport direction of the developer (rotation direction of the supply roller 51 (forward direction), arrow).

[0102] The difference between Example 3 and Examples 1-2 is that the shape of the magnetic flux density Br distribution of the regulating pole N2 is asymmetrical, so that the magnitude and location of the maximum value of the magnetic flux density Br are approximately the same as in the comparative example, while the position of Bθ=0 is set to a position downstream in the forward direction of the supply roller 51 rather than upstream end 52a of the regulating blade 52. As a result, the accumulation toner recovery efficiency is improved compared to the comparative example.

[0103] Here, the asymmetric shape of the magnetic flux density Br of the restricting pole N2 in Example 3 will be explained using Figure 10. Figure 10 is an enlarged view of the magnetic flux density Br and magnetic flux density Bθ around the restricting pole N2 of Example 3 described in Figures 9(a) and (b). Point A is the position where the magnitude of the magnetic flux density Br is maximum. Point D is the point where the magnetic flux density Bθ is 0. Z indicates the angle difference between point A and point D.

[0104] Specifically, in Example 3, the angular difference (Z) between points A and D on the regulating electrode N2 is approximately 10 degrees. In contrast, the angular difference (Z) between points A and D on the regulating electrode N2 in the Comparative Example is approximately 2 degrees.

[0105] In the comparative example, if Ga is the angular difference between point A and the upstream end 52a of the regulating blade 52, then Ga = 5 degrees, and the position where the magnetic flux density Bθ = 0 is upstream of the upstream end 52a of the regulating blade 52.

[0106] In Example 3, the position of point A is the same as in the Comparative Example, so Ga = 5 degrees. On the other hand, the angular difference (Z) between the positions of point A and point D is 10 degrees. That is, Z ≥ Ga. Therefore, the position where the magnetic flux density Bθ = 0 (point D) is located downstream of the upstream end 52a of the regulating blade 52. As a result, in Example 3, while improving the accumulation toner recovery efficiency compared to the Comparative Example, the change in layer thickness due to fluctuations in the gap between the supply roller 51 and the regulating blade 52 is configured to be approximately the same as in the Comparative Example.

[0107] Therefore, it is preferable that the angular difference (Z) between point A and point D is greater than the angular difference (Ga) between point A and the upstream end 52a of the regulating blade 52. Furthermore, it is preferable that the angular difference (Z) between point A and point D is greater than the angular difference (Gb) between point A and the downstream end 52b of the regulating blade 52. That is, it is preferable that Z ≥ Gb is satisfied.

[0108] According to the configuration of Embodiment 3, the accumulation toner recovery efficiency can be improved while suppressing changes in layer thickness due to fluctuations in the gap between the supply roller 51 and the regulating blade 52. The desirable position of the angle at which B=0 of the regulating pole N2 and the material of the regulating blade 52 are the same as in the first embodiment. Furthermore, in this embodiment, the arrangement of the regulating blade 52 and the configuration of the magnetic flux density distribution described above are also applicable to configurations without vibration generating means.

[0109] <Other Embodiments> In the embodiments described above, the present invention was explained in the case where it is applied to a developing apparatus used in a tandem-type image forming apparatus. However, the present invention is also applicable to developing apparatuses used in other types of image forming apparatuses. Furthermore, the image forming apparatus is not limited to full color; it may be monochrome or monocolor. Alternatively, by adding necessary equipment, fixtures, and housing structures, it can be implemented in various applications such as printers, various printing machines, copiers, fax machines, and multifunction devices.

[0110] Furthermore, regarding the configuration of the developing apparatus, as mentioned above, it is not limited to a configuration where the developing chamber and agitation chamber are arranged horizontally, but may also be arranged in a direction inclined to the horizontal. In short, it is sufficient if the developing chamber (as the first chamber) and the agitation chamber (as the second chamber) are arranged adjacent to each other so that at least a portion of them overlap when viewed from the horizontal. [Explanation of Symbols]

[0111] 1. Photosensitive drum (image carrier) 4. Developing equipment 40... Developing container 41. Partition wall 41a...Opening (communication part) 42...Development chamber (1st chamber) 43. Stirring chamber (second chamber) 44. First conveying screw (first conveying component) 45...Second conveying screw (second conveying component) 50. Developing roller (developing rotating body) 50a...Magnetic roller (first magnet) 51. Supply roller (supply rotating body) 51a...Magnetic roller (second magnet) 52. Regulatory blade (regulatory component)

Claims

1. a developer container that contains a developer including a toner and a carrier; a developing roller that carries and transports the toner to a developing position where the electrostatic image formed on the image carrier is developed; a supply roller disposed opposite to the developing roller, which carries and transports the developer supplied from the developing container and supplies only the toner to the developing roller, the supply roller rotating in a direction opposite to the developing roller during image formation at a position opposite to the developing roller; a first magnet having a first magnetic pole and fixedly disposed inside the developing roller in a non-rotatable manner; a second magnet disposed inside the supply roller in a non-rotatable and fixed manner, the second magnet having a second magnetic pole, the second magnetic pole being a different polarity from the first magnetic pole, disposed at a position where the supply roller faces the developing roller and disposed opposite the first magnetic pole, and a third magnetic pole disposed upstream of the second magnetic pole in the rotation direction of the supply roller during image formation; a regulating member disposed opposite the third magnetic pole and regulating an amount of developer carried by the supply roller, A mode in which the supply roller is rotated in a direction opposite to a direction in which the supply roller is rotated during image formation can be executed during non-image formation, With respect to the rotation direction of the supply roller during image formation, a position where the magnetic flux density of the third magnetic pole in a tangential direction to the outer circumferential surface of the supply roller becomes zero is downstream of the upstream end of the regulating member and upstream of the second magnetic pole. A developing device characterized by the above.

2. With respect to the rotation direction of the supply roller during image formation, a position where the magnetic flux density of the third magnetic pole in a tangential direction to the outer circumferential surface of the supply roller becomes zero is downstream of the downstream end of the regulating member and upstream of the second magnetic pole.

2. The developing device according to claim 1,

3. a position where the magnetic flux density of the third magnetic pole in a normal direction to the outer circumferential surface of the supply roller is maximized is defined as a first position; a second position is a position that is upstream of the first position and downstream of the second magnetic pole in the rotation direction of the supply roller during image formation, and where a magnetic flux density in a normal direction to an outer circumferential surface of the supply roller is zero; a third position is a position that is downstream of the first position and upstream of the second magnetic pole with respect to a rotation direction of the supply roller during image formation, and where a magnetic flux density in a normal direction to an outer circumferential surface of the supply roller is zero; An angle between the first position and the second position with respect to a rotation direction of the supply roller during image formation is defined as X, When the angle between the first position and the third position is defined as Y with respect to the rotation direction of the supply roller during image formation, 2≧X / Y>1 Fulfill 3. The developing device according to claim 1, wherein the developing device is a developing unit.

4. a position where the magnetic flux density of the third magnetic pole in a normal direction to the outer circumferential surface of the supply roller is maximized is defined as a first position; a second position is a position that is upstream of the first position and downstream of the second magnetic pole in the rotation direction of the supply roller during image formation, and where a magnetic flux density in a normal direction to an outer circumferential surface of the supply roller is zero; a third position is a position that is downstream of the first position and upstream of the second magnetic pole with respect to a rotation direction of the supply roller during image formation, and where a magnetic flux density in a normal direction to an outer circumferential surface of the supply roller is zero; An angle between the first position and the second position with respect to a rotation direction of the supply roller during image formation is defined as X, When the angle between the first position and the third position is defined as Y with respect to the rotation direction of the supply roller during image formation, 4≧X / Y>1 Fulfill 3. The developing device according to claim 1, wherein the developing device is a developing unit.

5. a position where the magnetic flux density of the third magnetic pole in a normal direction to the outer circumferential surface of the supply roller is maximized is defined as a first position; a fourth position is a position that is downstream of the first position and upstream of the second magnetic pole in the rotation direction of the supply roller during image formation, and where the magnetic flux density of the third magnetic pole in a tangential direction to the outer circumferential surface of the supply roller is zero; an angle between the first position and the fourth position with respect to a rotation direction of the supply roller during image formation is defined as Z; When the angle between the first position and the upstream end of the regulating member with respect to the rotation direction of the supply roller during image formation is Ga, Z≧Ga Fulfill 5. The developing device according to claim 1, wherein the developing device is a developing unit.

6. a position where the magnetic flux density of the third magnetic pole in a normal direction to the outer circumferential surface of the supply roller is maximized is defined as a first position; a fourth position is a position that is downstream of the first position and upstream of the second magnetic pole in the rotation direction of the supply roller during image formation, and where the magnetic flux density of the third magnetic pole in a tangential direction to the outer circumferential surface of the supply roller is zero; an angle between the first position and the fourth position with respect to a rotation direction of the supply roller during image formation is defined as Z; When the angle between the first position and the downstream end of the regulating member with respect to the rotation direction of the supply roller during image formation is Gb, Z ≧ Gb Fulfill 5. The developing device according to claim 1, wherein the developing device is a developing unit.

7. a toner receiving member disposed below the developing roller and receiving the toner falling from the developing roller; and a vibration means for vibrating the toner receiving member, In the above mode, the supply roller can be rotated in a direction opposite to the direction of rotation of the supply roller during image formation while the vibration means is vibrating the toner receiving member during non-image formation.

7. The developing device according to claim 1, wherein the developing device is a developing unit.

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