Developing device

Abstract

To provide a configuration capable of suppressing dragging a developer with rotation in a hybrid-development-method developing device.SOLUTION: With respect to a rotational direction of a supplying roller 51, a section between the most upstream position and the most downstream position, which is downstream of a position where magnetic flux density Br of a peeling pole S3 in a normal direction is maximum and upstream of a position where magnetic flux density Br of a scooping pole S2 in the normal direction is maximum and in which magnetic attraction force in the normal direction on a surface of the supplying roller 51 is 0, is a low magnetic force section NM. In this case, the most upstream position of the low magnetic force section NM with respect to the rotational direction of the supplying roller 51 is located above a rotation center of the supplying roller 51 in a vertical direction and is opposed to a wall portion 71. At the most upstream position of the low magnetic force section NM, an absolute value of magnetic flux density Bθ in a tangential direction on the surface of the supplying roller 51 is larger than an absolute value of the magnetic flux density Br in the normal direction on the surface of the supplying roller 51.SELECTED DRAWING: Figure 5

Description

[Technical field]

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

[0002] Conventionally, there have been known developing devices that use a two-component developer (hereinafter, abbreviated as developer) containing non-magnetic toner particles and magnetic carrier particles. As such a developing device, a configuration using a so-called hybrid development method has been proposed, which has a developing roller as a developing rotor arranged opposite a photosensitive drum as an image carrier, and a supply roller as a supply rotor arranged opposite the developing roller (Patent Documents 1 and 2).

[0003] In a developing device using such a hybrid development method, a developer is carried on a supply roller with a magnet inside, and a toner layer is formed on the developing roller from the developer transported by the rotation of the supply roller, and the 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 magnet disposed inside the supply roller has a first magnetic pole disposed at a position facing the developing roller. In addition, the magnet has a second magnetic pole disposed downstream of the first magnetic pole in the rotation direction of the supply roller for peeling off the developer from the supply roller, and a third magnetic pole disposed adjacent to the downstream of the second magnetic pole for drawing up the developer from the developing container to the supply roller. A low magnetic force section is provided between the second magnetic pole and the third magnetic pole. In addition, in the developing device described in Patent Document 2, a wall portion of the developing container is disposed facing the low magnetic force section. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2009-198582 A [Patent Document 2] JP 2017-21278 A Summary of the Invention [Problem to be solved by the invention]

[0006] Here, when the second magnetic pole is located relatively downstream in the rotation direction of the supply roller and the most upstream position of the low magnetic force section is located below the rotation center of the supply roller, the developer peeled off from the supply roller in the low magnetic force section is likely to receive a force toward the third magnetic pole located downstream in the rotation direction as the supply roller rotates. This makes it easy for the developer that has consumed toner and is short of toner to be attracted to the supply roller again by the magnetic force of the third magnetic pole after being peeled off from the supply roller, causing dragging of the developer. When dragging of the developer occurs in this way, toner is supplied to the development roller from a developer with a low toner ratio, resulting in a decrease in the quality of the output image.

[0007] On the other hand, even if the second magnetic pole is located relatively upstream in the rotation direction of the supply roller and the most upstream position of the low magnetic force section is located above the rotation center of the supply roller, as described in Patent Document 2, if a wall portion exists opposite the low magnetic force section, the developer peeled off from the supply roller is likely to receive a force in a direction away from the supply roller as the supply roller rotates, as described in Patent Document 2. At this time, the developer peeled off from the supply roller may bounce off the wall portion and fly back toward the supply roller again. As a result, even with such a configuration, the developer is likely to rotate, and the quality of the output image may be reduced.

[0008] SUMMARY OF THE DISCLOSURE An object of the present invention is to provide a configuration capable of suppressing the co-rotation of developer in a developing device using a hybrid development method. [Means for solving the problem]

[0009] The developing device of the present invention includes a developing container that contains a developer containing toner and a carrier, a developing roller that is disposed opposite an image carrier and rotates to transport the developer to a development position where an electrostatic latent image formed on the image carrier is developed, a supply roller that is disposed opposite the developing roller and rotates to supply the developer in the developing container to the developing roller, a regulating member that is disposed opposite the supply roller and regulates the amount of developer carried by the supply roller, a first magnet that is fixedly disposed inside the developing roller and non-rotatable, and a second magnet that is fixedly disposed inside the supply roller and non-rotatable, the first magnet being a first magnetic pole that is disposed at a position where the supply roller faces the developing roller, a second magnetic pole that is disposed downstream of the first magnetic pole in the rotational direction of the supply roller, and a second magnetic pole that is upstream of the first magnetic pole and downstream of the second magnetic pole in the rotational direction of the supply roller. and a second magnet having a third magnetic pole arranged adjacent to the second magnetic pole and having the same polarity as the second magnetic pole, the developing container has a wall portion at a position facing a part of the supply roller, and in relation to the rotation direction of the supply roller, when a low magnetic force section is defined as a section between a most upstream position and a most downstream position where a magnetic attraction force in the normal direction on the surface of the supply roller is 0, downstream of a position where a magnetic flux density Br in the normal direction of the second magnetic pole is maximum and upstream of a position where a magnetic flux density Br in the normal direction of the third magnetic pole is maximum, the most upstream position of the low magnetic force section is located vertically above the center of rotation of the supply roller and faces the wall portion, and at the most upstream position of the low magnetic force section, an absolute value of a magnetic flux density Bθ in the tangential direction on the surface of the supply roller is greater than an absolute value of a magnetic flux density Br in the normal direction on the surface of the supply roller.

[0010] The developing device of the present invention includes a developing container that contains a developer containing a toner and a carrier, a developing roller that is disposed opposite an image carrier and rotates to transport the developer to a development position where an electrostatic latent image formed on the image carrier is developed, a supply roller that is disposed opposite the developing roller and rotates to supply the developer in the developing container to the developing roller, a regulating member that is disposed opposite the supply roller and regulates the amount of developer carried by the supply roller, a first magnet that is fixedly disposed inside the developing roller so as to be non-rotating, and a second magnet that is fixedly disposed inside the supply roller so as to be non-rotating, the first magnetic pole being disposed at a position where the supply roller faces the developing roller, a second magnetic pole being disposed downstream of the first magnetic pole in the rotational direction of the supply roller, and a second magnetic pole that is upstream of the first magnetic pole and downstream of the second magnetic pole in the rotational direction of the supply roller. and a second magnet having a third magnetic pole arranged adjacent to the second magnetic pole and having the same polarity as the second magnetic pole, the developing container has a wall portion at a position facing a part of the supply roller, and when a low magnetic force section is defined as a section between a most upstream position and a most downstream position where a magnetic attraction force in the normal direction on the surface of the supply roller is zero, downstream of a position where a magnetic flux density Br in the normal direction of the second magnetic pole is maximum and upstream of a position where a magnetic flux density Br in the normal direction of the third magnetic pole is maximum with respect to the rotation direction of the supply roller, the most upstream position of the low magnetic force section is located vertically above the center of rotation of the supply roller and faces the wall portion, and the direction of the magnetic flux density Bθ in the tangential direction on the surface of the supply roller does not reverse between the most upstream position of the low magnetic force section and a point half the way through the low magnetic force section with respect to the rotation direction of the supply roller.

[0011] The developing device of the present invention includes a developing container that contains a developer containing a toner and a carrier, a developing roller that is disposed opposite an image carrier and rotates to transport the developer to a development position where an electrostatic latent image formed on the image carrier is developed, a supply roller that is disposed opposite the developing roller and rotates to supply the developer in the developing container to the developing roller, a regulating member that is disposed opposite the supply roller and regulates the amount of developer carried by the supply roller, a first magnet that is fixedly disposed inside the developing roller and non-rotatable, and a second magnet that is fixedly disposed inside the supply roller and non-rotatable, the first magnet being a first magnetic pole that is disposed at a position where the supply roller faces the developing roller, a second magnetic pole that is disposed downstream of the first magnetic pole with respect to the rotation direction of the supply roller, and a second magnetic pole that is upstream of the first magnetic pole and downstream of the second magnetic pole and forward of the first magnetic pole with respect to the rotation direction of the supply roller. and a second magnet arranged adjacent to the second magnetic pole and having a third magnetic pole of the same polarity as the second magnetic pole, the developing container has a wall portion at a position facing a part of the supply roller, and is characterized in that, in terms of the rotation direction of the supply roller, the low magnetic force section is defined as a section between a most upstream position and a most downstream position where a magnetic attraction force in the normal direction on the surface of the supply roller is zero, downstream of a position where a magnetic flux density Br in the normal direction of the second magnetic pole is maximum and upstream of a position where a magnetic flux density Br in the normal direction of the third magnetic pole is maximum, the most upstream position of the low magnetic force section is located vertically above the center of rotation of the supply roller and faces the wall portion, and a product of an absolute value and a half-width of a peak value of the magnetic flux density Br in the normal direction of the second magnetic pole on the surface of the supply roller is 1.5 times or more of a product of an absolute value and a half-width of a peak value of the magnetic flux density Br in the normal direction of the third magnetic pole. Effect of the Invention

[0012] According to the present invention, in a developing device using a hybrid development method, the developer can be prevented from being carried around. [Brief description of the drawings]

[0013] [Figure 1]1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a developing device according to the embodiment. [Diagram 3] 1A is a partially enlarged schematic cross-sectional view of a developing device according to Comparative Example 1, and FIG. 1B is a schematic view showing the state of a magnetic field in the vicinity of a low magnetic force section. [Figure 4] 11A is a partially enlarged schematic cross-sectional view of a developing device according to Comparative Example 2, and FIG. 11B is a schematic view showing the state of a magnetic field in the vicinity of a low magnetic force section. [Diagram 5] 3A is a schematic cross-sectional view of a part of a developing device according to an embodiment, and FIG. 3B is a schematic view showing a state of a magnetic field around a low magnetic force section. [Figure 6] 10 is a graph showing the magnetic flux density distribution and the magnetic attraction force distribution of a magnet roller inside a supply roller according to Comparative Example 2. [Figure 7] 5 is a graph showing a magnetic flux density distribution and a magnetic attraction force distribution of a magnet roller inside a supply roller according to Example 1. [Figure 8] 10 is a graph showing a magnetic flux density distribution and a magnetic attraction force distribution of a magnet roller inside a supply roller according to Example 2. [Figure 9] 11 is a graph showing the magnetic flux density distribution and the magnetic attraction force distribution of the magnet roller inside the supply roller according to the third embodiment. [Figure 10] 13 is a graph showing the magnetic flux density distribution and the magnetic attraction force distribution of the magnet roller inside the supply roller according to Example 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The embodiment will be described with reference to Figures 1 to 7. Note that in this embodiment, a developing device is applied to a tandem type full-color printer as an example of an image forming apparatus.

[0015] [Image forming device] First, a schematic configuration of an 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) in the main body of the apparatus. In this embodiment, an intermediate transfer tandem type is adopted in which the image forming units PY, PM, PC, and PK are arranged 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 response to an image signal from a document reading device (not shown) connected to the main body of the apparatus or a host device such as a personal computer connected to the main body of the apparatus so as to be able to communicate with the main body of the apparatus. Examples of the recording material include sheet materials such as paper, plastic film, and cloth.

[0016] 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 configured almost identically except for the toner colors, yellow, magenta, cyan, and black. Therefore, the following description will be given using the yellow image forming unit PY as an example, and the description of the other image forming units PM, PC, and PK will be omitted.

[0017] The image forming unit PY is mainly composed of a photosensitive drum 1, a charging device 2, a developing device 4, a static eliminator 5, a cleaning device 8, etc. In this embodiment, an intermediate transfer belt 6 is disposed above each of the image forming units PY, PM, PC, and PK, and an exposure device 3 is disposed below them. The photosensitive drum 1, which serves as an image carrier and photosensitive member, has a photosensitive layer formed to have a negative or positive charging polarity on the outer circumferential surface of an aluminum cylinder, and rotates in the direction of arrow R2 in the figure at a predetermined process speed (circumferential speed).

[0018] The charging device 2 charges the surface of the photosensitive drum 1 to a uniform negative or positive dark potential according to the charging characteristics of the photosensitive drum 1. In this embodiment, the charging device 2 is a charging roller that rotates in contact with the surface of the photosensitive drum 1. After charging the surface of the photosensitive drum 1, an electrostatic latent image (electrostatic image) is formed on the surface of the photosensitive drum 1 by an exposure device (laser scanner) 3 based on image information. The photosensitive drum 1 carries the formed electrostatic latent image and moves around, and the image is developed with toner by the 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 carrier from a toner cartridge (not shown).

[0019] A predetermined pressure and a primary transfer bias are applied to the developed toner image by a primary transfer roller 61 disposed opposite the photosensitive drum 1 with the intermediate transfer belt 6 sandwiched therebetween, and the toner image is primarily transferred onto the intermediate transfer belt 6. After the primary transfer, the surface of the photosensitive drum 1 is neutralized by a static eliminator 5. A cleaning device 8 cleans off residual matter such as transfer residual toner remaining on the surface of the photosensitive drum 1 after the primary transfer.

[0020] The intermediate transfer belt 6 is tensioned by a tension roller 62 and a secondary transfer inner roller 63. The intermediate transfer belt 6 is driven by the secondary transfer inner roller 63, which is also a drive roller, so as to move in the direction of the arrow R1 in the figure. The image forming process of each color processed by the above-mentioned image forming units PY, PM, PC, and PK is performed at a timing to sequentially superimpose the toner image of the color upstream in the moving direction that has been primarily transferred onto the intermediate transfer belt 6. As a result, a full-color toner image is finally formed on the intermediate transfer belt 6 and is conveyed to the secondary transfer unit T2. The secondary transfer unit T2 is a transfer nip portion formed by a part of the intermediate transfer belt 6 tensioned by the secondary transfer inner roller 63 and the secondary transfer outer roller 64. Note that 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).

[0021] A process of transporting the recording material S to the secondary transfer portion T2 is executed at the same timing as the process of forming the toner image sent to the secondary transfer portion T2. ​​In the transport process, the recording material S is fed from the sheet cassette 11 and sent to the secondary transfer portion T2 in accordance with the image formation timing. In the secondary transfer portion T2, a secondary transfer voltage is applied to the inner secondary transfer roller 63.

[0022] Through the above image forming process and conveying process, the toner image is secondarily transferred from the intermediate transfer belt 6 to the recording material S at the secondary transfer portion T2. ​​Thereafter, the recording material S is conveyed to the fixing device 7, and is heated and pressurized by the fixing device 7, thereby melting and fixing the toner image onto the recording material S. The recording material S on which the toner image has been fixed in this manner is discharged by discharge rollers 12 onto a discharge tray (not shown).

[0023] [Two-component developer] Next, the developer used in this embodiment will be described. In this embodiment, a two-component developer is used as the developer, in which the mixture coverage of the toner with respect to the 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 necessary, and an external additive such as colloidal silica fine powder is added to the surface of the toner. The toner is, for example, a polyester resin with negative or positive charging properties according to the charging properties of the photosensitive drum 1, and has a volume average particle size of about 7.0 μm. The carrier is, for example, made of magnetic metal particles such as iron, nickel, cobalt, etc., whose surfaces are oxidized, and has a volume average particle size of about 40 μm to 50 μm.

[0024] In this embodiment, the developer used is a carrier mainly composed of Mn-Mg with a weight average diameter of 45 μm and a saturation magnetization of 60 emu / g as determined by the MSV method, and the toner particles are 7 μm in median diameter of the volume distribution measured by a Coulter counter. The toner and carrier are mixed to a toner concentration of 12%, and used as the developer. The toner has a positive charging characteristic.

[0025] [Developing device] Next, the developing device 4 will be described in detail with reference to Fig. 2. The developing device 4 of this embodiment is a so-called touch-down developing type developing device, which forms a thin layer of only toner on the developing roller 50 with a magnetic brush made of a two-component developer formed on a supply roller 51, and develops the toner by flying it to the electrostatic latent image formed on the photosensitive drum 1 with a developing bias in which a direct current and an alternating current are superimposed and applied to the developing roller 50.

[0026] As shown in FIG. 2, the developing device 4 includes a developing container 40, a developing roller 50 as a developing rotator, and a supply roller 51 as a supply rotator. The developing container 40 includes a housing 70 and a developer storage section 40a disposed at a lower portion of the housing 70. The housing 70 includes a wall portion 71 and an opening 72. The wall portion 71 is disposed at a position facing a part of the supply roller 51. In the case of the present embodiment, the wall portion 71 is disposed on the opposite side of the supply roller 51 from a regulating blade 52 described later, with the supply roller 51 interposed therebetween. At this position, the wall portion 71 is disposed so as to follow the outer peripheral surface of the supply roller 51. The opening 72 is formed at a position facing the photosensitive drum 1 of the developing container 40, and the developing roller 50 faces the photosensitive drum 1 through the opening 72.

[0027] The developer storage section 40a stores a developer including a non-magnetic toner and a magnetic carrier. The developer storage section 40a has a developing chamber 42 as a first chamber, a stirring chamber 43 as a second chamber, and a partition wall 41 as a partition wall. The stirring chamber 43 is disposed adjacent to the developing chamber 42 so that at least a part of the stirring chamber 43 overlaps with the developing chamber 42 when viewed in the horizontal direction. The partition wall 41 separates the developing chamber 42 from the stirring chamber 43. The partition wall 41 has openings as communication parts that communicate the developing chamber 42 and the stirring chamber 43 at both ends in the longitudinal direction (the direction of the rotation axis of the developing roller 50 and the supply roller 51). The developer storage section 40a forms a circulation path that circulates the developer between the developing chamber 42 and the stirring chamber 43 via the openings provided in the partition wall 41.

[0028] In this embodiment, a partition wall 41 is provided in the approximate center of the developer accommodating section 40a. As a result, the developer accommodating section 40a is partitioned by the partition wall 41 so that the developing chamber 42 and the stirring chamber 43 are adjacent to each other in the horizontal direction. A first transport screw 44 and a second transport screw 45 that can rotate to stir and circulate the developer are disposed in the developing chamber 42 and the stirring chamber 43, respectively.

[0029] The first transport screw 44 as the first transport member is disposed at the bottom of the developing chamber 42 (inside the first chamber) along the rotation axis direction (longitudinal direction) of the supply roller 51, facing the supply roller 51 substantially parallel to the supply roller 51. The first transport screw 44 has a rotating shaft 44a and a blade 44b provided in a spiral shape around the rotating shaft 44a. The second transport screw 45 as the second transport member is disposed at the bottom of the mixing chamber 43 (inside the second chamber) substantially parallel to the first transport screw 44. The second transport screw 45 has a rotating shaft 45a and a blade 45b provided in a spiral shape around the rotating shaft 45a.

[0030] The first transport screw 44 and the second transport screw 45 rotate in the directions of arrows R4 and R3, respectively, to transport the developer within the developing chamber 42 and the mixing 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 mixing chamber 43 through openings at both ends of the partition wall 41. The toner is stirred by the first transport screw 44 and the second transport screw 45, and rubs against the carrier, becoming frictionally charged to a negative or positive polarity.

[0031] As shown in FIG. 2, the developing roller 50 and the supply roller 51 are disposed vertically above the developing chamber 42 and the stirring chamber 43 inside the housing 70. The developing roller 50 is disposed between the photosensitive drum 1 and obliquely above the supply roller 51 when viewed from the direction of the rotation axis of the supply roller 51. That is, the developing roller 50 is disposed so that its rotation axis is located above the rotation axis of the supply roller 51. The supply roller 51 and the developing roller 50 are disposed so as to face each other at the closest position P1 with their rotation axes substantially parallel to each other. The closest position P1 is a position where the supply roller 51 and the developing roller 50 face each other on a line connecting the rotation centers of the supply roller 51 and the developing roller 50. The developing roller 50 faces the photosensitive drum 1 on the opening 72 side of the housing 70. The developing roller 50 and the supply roller 51 are disposed so as 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 Fig. 2. That is, the developing roller 50 and the supply roller 51 rotate in opposite directions (reverse directions) at the closest position P1, and the rotational speed is variable.

[0032] The supply roller 51 is a non-magnetic cylindrical roller that rotates counterclockwise in FIG. 2, and is provided rotatably around a cylindrical magnetic roller 51a that is a magnetic field generating means and a second magnet provided on the inner circumference side and does not rotate. That is, the magnetic roller 51a is fixedly arranged inside the supply roller 51 so as not to rotate. The magnetic roller 51a has five pieces, and on the surface facing the supply roller 51, it has a pumping pole (third magnetic pole) S2, a regulating pole (fourth magnetic pole) N2, a holding pole S1, a main pole (first magnetic pole) N1, and a peeling pole (second magnetic pole) S3, which are arranged in order with respect to the rotation direction of the supply roller. Note that, although a magnetic roller with five poles is used in this embodiment, it may be other than five poles, for example, a magnetic roller with seven poles may be used.

[0033] The main pole N1 is disposed at a position where the supply roller 51 faces the developing roller 50, and has a polarity opposite to that of a receiving pole S4 of the magnet roller 50a in the developing roller 50, which will be described later. The holding pole S1 is disposed adjacent to the upstream side of the main pole N1 with respect to the rotation direction of the supply roller 51, and has a polarity opposite to that of the main pole N1. The regulating pole N2 is disposed adjacent to the upstream side of the holding pole S1 with respect to the rotation direction of the supply roller 51, and at a position where a 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 disposed adjacent to the upstream side of the regulating pole N2, has a polarity opposite to that of the regulating pole N2, and is a magnetic pole for pumping up the developer from the developer storage section 40a to the supply roller 51. Specifically, the pumping pole S2 is disposed above the developing chamber 42, facing the first transport screw 44. The peeling pole (stripping pole) S3 is disposed adjacent to the upstream of the pumping pole S2 in the rotation direction of the supply roller 51, and has the same polarity as the pumping pole S2. The pumping pole S2, the regulating pole N2, the holding pole S1, the main pole N1, and the peeling pole S3 are disposed adjacent to each other in this order in the rotation direction of the supply roller 51.

[0034] The supply roller 51 carries developer having non-magnetic toner and magnetic carrier, and rotates to transport it to the closest position P1 to the development roller 50. That is, the supply roller 51 is disposed opposite the development roller 50, and rotates to supply the developer in the developer accommodating portion 40a (inside the development container) to the development roller 50. The supply roller 51 has, for example, a plurality of groove-shaped recesses arranged periodically in the circumferential direction on its outer circumferential surface along the direction of the rotation axis. These recesses assist in the transport of the developer carried by the supply roller 51.

[0035] The regulating blade 52 as a regulating member is disposed upstream of the position (closest position P1) facing the developing roller 50 with respect to the rotation direction of the supply roller 51, and regulates the amount of developer carried by the supply roller 51. That is, the regulating blade 52 is a plate-shaped member, and is provided in the developing container 40 so that its tip faces the outer circumferential surface of the supply roller 51 on which the regulating pole N2 of the magnet roller 51a is disposed. A predetermined gap is provided between the tip of the regulating blade 52 and the outer circumferential surface of the supply roller 51. Then, the magnetic brush of the developer carried on the surface of the supply roller 51 is cut off by the regulating blade 52, thereby regulating the layer thickness of the developer. Specifically, the regulating blade 52 is made of a metal plate (e.g., a stainless steel plate) disposed in the longitudinal direction of the supply roller 51, and the developer passes between the tip of the regulating blade 52 and the supply roller 51, so that the developer is conveyed in a state where the developer is regulated to a certain amount. The regulating blade 52 is formed in an L-shape from a magnetic material such as SUS430 having a thickness of approximately 1.5 mm, and is arranged opposite a position offset counterclockwise by 3 to 5° in the illustrated example from the peak position of the magnetic flux density of the regulating pole N2, and is fixed to the developing container 40 so as to extend in the direction of the rotational axis of the supply roller 51.

[0036] The developing roller 50 is disposed opposite the photosensitive drum 1, and conveys a developer to a developing position where the electrostatic latent image formed on the photosensitive drum 1 is developed by rotating. That is, the developing roller 50 is a non-magnetic roller that rotates counterclockwise in FIG. 2, and is provided rotatably around a magnet roller 50a as a non-rotating first magnet having one receiving pole (fifth magnetic pole) S4 provided on the inner periphery side. The developing roller 50 can develop the electrostatic latent image on the photosensitive drum 1 in a developing area P2, which is an opposing area facing the photosensitive drum 1, by carrying toner and rotating. The supply roller 51 and the developing roller 50 face each other with a predetermined gap at their closest position P1. The receiving pole S4 of the magnet roller 50a in the developing roller 50 is of a polarity opposite to the main pole N1 facing the supply roller 51 and the developing roller 50 via the supply roller 51 and the developing roller 50.

[0037] A supply bias in which a DC voltage and an AC voltage are superimposed is applied to the supply roller 51. A development bias in which a DC voltage and an AC voltage are superimposed is also applied to the development roller 50. The development bias and the supply bias are applied to the development roller 50 and the supply roller 51 from a bias power supply, which is an example of a voltage application unit, via a bias control circuit. That is, the bias power supply applies a voltage including a DC component and an AC component between the development roller 50 and the supply roller 51. Due to the potential difference between the voltage applied to the supply roller 51 and the voltage applied to the development roller 50, the toner is supplied from the supply roller 51 to the development roller 50, and due to the effect of the AC component, the toner on the development roller 50 after development is completed is collected by the supply roller 51.

[0038] That is, the toner remaining on the developing roller 50 that has not been used for development is transported again to the closest position P1 between the developing roller 50 and the supply roller 51, where it is rubbed by the magnetic brush on the supply roller 51 and collected by the supply roller 51. The magnetic brush is peeled off from the supply roller 51 in a peeling region (low magnetic force section) created by the repulsion of the peeling pole S3 and the pumping pole S2 arranged downstream in the rotation direction of the supply roller 51. The peeled developer falls into the developing chamber 42, where it is mixed and transported with the developer circulating in the developing container 40, and is attracted to the pumping pole S2 again and transported by the supply roller 51.

[0039] The toner shielding member 53 is a conductive cylindrical member that is disposed opposite the developing roller 50 and has the same potential as that of the supply roller 51 applied thereto. As a result, the toner passing through the toner shielding member 53 and the developing roller 50 is pressed against the developing roller 50, thereby suppressing the amount of toner passing through. As a result, it is possible to suppress the scattered toner generated at the closest position P1 between the supply roller 51 and the developing roller 50 from passing between the toner shielding member 53 and the developing roller 50 and leaking out of the developing device 4 through the opening 72, thereby preventing the inside of the image forming apparatus 100 from becoming dirty.

[0040] As described above, the magnet roller 51a inside the supply roller 51 has the main pole (development pole or delivery pole) N1 at a position substantially opposite the development roller 50. If the rotation direction is counterclockwise from the main pole N1, the holding pole (transport pole) S1 is located upstream of the main pole N1 in the rotation direction, the regulating pole (bristle cutting pole) N2 is located substantially opposite the regulating blade 52, and further upstream of the regulating pole N2, the pumping pole S2 and the peeling pole (separation pole) S3 are arranged in this order. The pumping pole S2 and the peeling pole S3 are of the same pole, and a low magnetic force section is formed between the peak position of the magnetic flux density of the pumping pole S2 and the peak position of the magnetic flux density of the peeling pole S3.

[0041] Here, the low magnetic force section refers to a section in which the magnetic force that the carrier in the developer on the supply roller 51 receives in the direction of the developing roller 50 from the magnet roller 51a inside the supply roller 51 is substantially zero. In this embodiment, the low magnetic force section is a section in which the absolute value of the magnetic flux density Br (also called the magnetic flux density Br in the normal direction), which is the normal component of the magnetic flux density B on the surface of the supply roller 51, is 5 mT or less.

[0042] The magnet roller 50a inside the developing roller 50 has only one pole, and a receiving pole S4 that is opposite to the main pole N1 of the supply roller 51 is disposed at a position substantially opposite to the supply roller 51. In this embodiment, the main pole N1 of the supply roller 51 and the receiving pole S4 of the developing roller 50 are disposed as follows with respect to the closest position P1 of the supply roller 51 and the developing roller 50. That is, the main pole N1 is disposed so that the peak position of the magnetic flux density is slightly downstream of the closest position P1 in the rotation direction R5 of the supply roller 51. Also, the receiving pole S4 of the developing roller 50 is disposed so that the peak position of the magnetic flux density is upstream of the closest position P1 in the rotation direction R6 of the developing roller 50. This is to prevent ghosts and carrier adhesion.

[0043] The peak position of the magnetic flux density of the regulating pole N2 of the supply roller 51 is shifted upstream by 3 to 5° with respect to the rotation direction R5 of the supply roller 51 relative to the position facing the regulating blade 52.

[0044] Here, the movement of the developer in the supply roller 51 and the developing roller 50 in the developing device 4 of this embodiment will be described. The developer in the developing chamber 42 is drawn up to the supply roller 51 by the drawing-up pole S2 of the supply roller 51. The drawn-up developer is carried and transported by the supply roller 51 as the supply roller 51 rotates in the direction of the arrow R5, and the thickness of the developer layer is regulated by the regulating blade 52 disposed substantially opposite the regulating pole N2. Thereafter, the developer is transported to the retaining pole S1 and the main pole N1 as the supply roller 51 rotates.

[0045] At the main pole N1 substantially opposed to the developing roller 50, the toner in the developer moves from the supply roller 51 to the developing roller 50 due to the effect of the voltages applied to the supply roller 51 and the developing roller 50. The developing roller 50 rotates in the direction of the arrow R6 to transport the toner to a position opposed to the photosensitive drum 1, and develops the electrostatic latent image on the photosensitive drum 1.

[0046] At the main pole N1, the developer on the supply roller 51, which has become deficient in toner due to the movement of toner to the developing roller 50, is transported to the peeling pole S3 as the supply roller 51 rotates, and the developer is peeled off from the supply roller 51 in the low magnetic force section formed between the peeling pole S3 and the pumping pole S2. The peeled off developer falls into the developing chamber 42. The dropped developer mixes with the developer in the developing chamber 42 due to the stirring effect of the first transport screw 44, resolving the toner shortage, and is then pumped up to the supply roller 51 by the pumping pole S2 of the supply roller 51 again.

[0047] At this time, if the developer peeled off from the supply roller 51 does not mix with the developer in the developing chamber 42 and is instead pumped up again by the pumping pole S2 of the supply roller 51, causing dragging, there is a risk of the quality of the output image being reduced due to a lack of toner in the developer. The present embodiment aims to suppress the occurrence of such dragging, and the configuration of this embodiment will be described in detail below with reference to a comparative example. In the following description, the term "upstream" refers to the upstream side in the direction of rotation of the supply roller 51, and the term "downstream" refers to the downstream side in the direction of rotation of the supply roller 51.

[0048] 3(a) and 3(b) show the developing device 4A of Comparative Example 1, 4(a) and 4(b) show the developing device 4B of Comparative Example 2, and 5(a) and 5(b) show the developing device 4 of Example 1 according to the present embodiment. 3(a), 4(a), and 5(a) are enlarged cross-sectional views of the periphery of the supply roller 51. In addition, in each of FIGS. 3(a), 4(a), and 5(a), a low magnetic force section formed between the peak position of the magnetic flux density of the peeling pole S3 and the peak position of the magnetic flux density of the pumping pole S2 (i.e., downstream of the position where the magnetic flux density Br in the normal direction of the peeling pole S3 is maximum with respect to the rotation direction of the supply roller 51 and upstream of the position where the magnetic flux density Br in the normal direction of the pumping pole S2 is maximum) is shown as a range NM surrounded by a dotted line (hereinafter, also referred to as low magnetic force section NM).

[0049] 3(b), 4(b), and 5(b) are schematic diagrams showing the state of the magnetic field formed by the magnet rollers 51a1, 51a2, and 51a inside the supply roller 51. These schematic diagrams show the state of the magnetic field in the low magnetic force section NM. In these schematic diagrams, the surface of the cylindrical supply roller 51 of each developing device 4, 4A, and 4B is shown by a straight line for the sake of convenience.

[0050] [Comparative Example 1] 3(a) and 3(b), the developing device 4A of Comparative Example 1 will be described. As described above, the developer on the supply roller 51, which has become deficient in toner due to the movement of toner to the development roller 50, is transported to the peeling pole S3 as the supply roller 51 rotates, and the developer is peeled off from the supply roller 51 in the low magnetic force section NM formed between the peeling pole S3 and the drawing pole S2.

[0051] Specifically, the developer on the supply roller 51 is transported to the peeling pole S3 as the supply roller 51 rotates, and the developer is peeled off from the supply roller 51 at an upstream position in the low magnetic force section NM. In the developing device 4A of Comparative Example 1, the most upstream position of the low magnetic force section NM is located vertically below the center of rotation of the supply roller 51. Therefore, in the developing device 4A of Comparative Example 1, the developer is peeled off below the center of rotation of the supply roller 51. When the developer is peeled off below the center of rotation of the supply roller 51, it is likely to be attracted to the supply roller 51 again by the magnetic force of the pick-up pole S2 located downstream in the rotation direction of the supply roller 51, causing co-rotation.

[0052] The likelihood of the developer dragging also depends on the direction in which the developer scraped off in the low magnetic force section NM flies. This point will be explained next. As shown in FIG. 3(b), in the case of Comparative Example 1, the magnetic field lines extend between the peeling pole S3 and the pumping pole S2 so as to repel each other. In other words, the magnetic field lines extending from the surface of the supply roller 51 extend in the direction of the peeling pole S3 upstream of the low magnetic force section NM, and in the direction of the pumping pole S2 downstream of the low magnetic force section NM. When the magnetic flux density and half-width of the two magnetic poles (the peeling pole S3 and the pumping pole S2 in this example) that form the low magnetic force section NM are not significantly different, the magnetic field lines extend in this way.

[0053] Usually, the magnetic brush of the developer on the supply roller 51 is formed along the magnetic lines. The magnetic lines may be said to represent the trajectory of the magnetic brush transported on the supply roller 51, and the magnetic brush advances in the normal direction (downstream of the rotation direction of the supply roller 51) of the magnetic lines. Therefore, the developer peeled off upstream of the low magnetic force section NM flies in the normal direction (facing the downstream side of the rotation direction of the supply roller 51) of the magnetic lines at that position (the direction of the arrow F in the figure). The direction of the arrow F roughly coincides with the rotation direction of the supply roller 51. Therefore, when the developer is peeled off below the rotation center of the supply roller 51 as in Comparative Example 1, the peeled off developer flies in the rotation direction of the supply roller 51, so that the developer is attracted to the supply roller 51 again by the magnetic force of the pick-up pole S2 downstream of the rotation direction of the supply roller 51, and thus the developer is likely to rotate together. In particular, when the supply roller 51 is rotated at a high speed as the image forming apparatus is increased in speed, the developer is more likely to rotate together.

[0054] [Comparative Example 2] Next, the developing device 4B of Comparative Example 2 will be described with reference to Figures 4(a) and (b). In the developing device 4B of Comparative Example 2, the most upstream position of the low magnetic force section NM formed between the peeling pole S3 and the pumping pole S2 is located vertically above the center of rotation of the supply roller 51, which is different from Comparative Example 1. On the other hand, the state of the magnetic field in the low magnetic force section NM is generally similar to that of Comparative Example 1. This is because the magnetic flux density and half-width of the two magnetic poles (in this example, the peeling pole S3 and the pumping pole S2) that form the low magnetic force section NM are not significantly different from those of Comparative Example 1.

[0055] The direction in which the developer scraped off upstream of the low magnetic force section NM flies is shown by the arrow F in Figures 4(a) and (b). Looking at Figure 4(a), by positioning the low magnetic force section NM above the center of rotation of the supply roller 51, the flying direction of the scraped off developer is directed away from the scooping pole S2 (in the horizontal direction), which is thought to make it difficult for the developer to be dragged along.

[0056] However, according to the inventor's investigation, the co-rotation was not necessarily improved in the developing device 4B of Comparative Example 2. This is believed to be due to the following reasons. In the developing device 4B of Comparative Example 2, the wall portion 71 of the housing 70 is present so as to be aligned with the supply roller 51. This is a common configuration that is implemented for the purpose of making effective use of space, etc.

[0057] In this way, if wall portion 71 of housing 70 is present along supply roller 51, there is a risk that the developer peeled off from supply roller 51 will fly in the direction of arrow F, as shown by the dotted arrow in Figure 4(a), hit wall portion 71, bounce off, and fly back toward supply roller 51.

[0058] Furthermore, in the schematic diagram of FIG. 4(b) showing the state of the magnetic field around the low magnetic force section NM of the developing device 4B of Comparative Example 2, the magnetic lines of force extend so as to repel each other between the peeling pole S3 and the drawing pole S2. In other words, the magnetic lines of force extending from the surface of the supply roller 51 extend toward the peeling pole S3 upstream of the low magnetic force section NM. Therefore, the normal direction (direction of the arrow F in FIG. 4(b)) of the magnetic lines (facing the downstream side in the rotation direction of the supply roller 51) is more or less directed in the direction away from the surface of the supply roller 51. Since the wall 71 of the housing 70 exists in the direction away from the surface of the supply roller 51, the developer peeled off from the supply roller 51 is more likely to fly toward the wall 71 and bounce off the wall 71. In this way, if the bounce off the wall 71 occurs, it becomes easier for the developer to rotate when the device is operated at a high speed, and this may result in a decrease in the quality of the output image.

[0059] [Example 1] 5(a) and (b), a developing device 4 of Example 1, which is a configuration of this embodiment, will be described. In the developing device 4 of Example 1, the most upstream position of the low magnetic force section NM formed between the peeling pole S3 and the drawing pole S2 is located vertically above the center of rotation of the supply roller 51, which is the same as in Comparative Example 2. As a result, like Comparative Example 2, the flying direction of the peeled off developer is toward a direction away from the drawing pole S2 (in the horizontal direction), making it difficult for the developer to be entrained.

[0060] On the other hand, the state of the magnetic field in the low magnetic force section NM is significantly different between Example 1 and Comparative Example 2. As shown in FIG. 4B, in Comparative Example 2, the magnetic field lines extending from the surface of the supply roller 51 extend in a repulsive manner, and extend in the direction of the peeling pole S3 upstream of the low magnetic force section NM and in the direction of the pumping pole S2 downstream of the low magnetic force section NM. On the other hand, as shown in FIG. 5B, in Example 1, the magnetic field lines extend in the direction of the pumping pole S2 regardless of the location in the low magnetic force section NM. This is because, in Comparative Example 2, the magnetic field lines generally extend from the peeling pole S3 toward the upstream main pole N1 and from the pumping pole S2 toward the downstream regulating pole N2, whereas in Example 1, the magnetic field lines extend toward the regulating pole N2 not only from the pumping pole S2 but also from the peeling pole S3.

[0061] In the case of Comparative Example 2, the magnetic flux density and half-width of the two magnetic poles (separating pole S3 and pumping pole S2) that form the low magnetic force section NM are not significantly different. In contrast, in the case of Example 1, the magnetic flux density and half-width of the two magnetic poles (separating pole S3 and pumping pole S2 in this example) that form the low magnetic force section NM are significantly different, with the magnetic flux density and half-width of the separated pole S3 being larger than those of the pumping pole S2. For this reason, it is considered that in Example 1, unlike Comparative Example 2, the magnetic field lines extend from the separated pole S3 to the regulating pole N2 downstream of the pumping pole S2.

[0062] According to the inventor's investigation, in the developing device 4 of Example 1 as described above, even when the wall portion 71 of the housing 70 is present so as to be aligned with the supply roller 51, the co-rotation is unlikely to occur, unlike the case of Comparative Example 2. This is for the following reason.

[0063] FIG. 5(b) shows the state of the magnetic field around the low magnetic force section NM in the case of Example 1. As described above, the magnetic brush of the developer on the supply roller 51 is formed along the magnetic field lines, and the developer peeled off upstream of the low magnetic force section NM flies in the normal direction (the direction of the arrow F in the figure) of the magnetic field lines (facing the downstream side in the rotation direction of the supply roller 51) in the upstream part of the low magnetic force section NM. In the case of Comparative Example 2 shown in FIGS. 4(a) and (b), the direction of the arrow F was directed away from the surface of the supply roller 51. In contrast, in the case of Example 1 shown in FIGS. 5(a) and (b), the magnetic field lines extend in a different way from Comparative Example 2, and the direction of the arrow F is directed toward the surface of the supply roller 51.

[0064] Therefore, in the case of Comparative Example 2, the developer peeled off upstream of the low magnetic force section NM was separated from the surface of the supply roller 51 and flew toward the wall 71 of the housing 70. In contrast, in the case of Example 1, the force is applied toward the surface of the supply roller 51, so that the developer is unlikely to fly toward the wall 71 as in Comparative Example 2. In fact, in the case of Example 1, the developer is separated while being subjected to a force in a direction in which it is pressed against the surface of the supply roller 51, so that the developer separated from the supply roller 51 follows a trajectory as shown by the dotted arrow in FIG. 5(a). As a result, in the developing device 4 of Example 1, even when the wall 71 of the housing 70 exists so as to be aligned with the supply roller 51, it is considered that the developer was unlikely to rotate together with the supply roller 51, unlike the case of Comparative Example 2.

[0065] In order to obtain the effect of suppressing the entrainment, it is important that the most upstream position of the low magnetic force section NM formed between the peeling pole S3 and the pumping pole S2 is located vertically above the center of rotation of the supply roller 51. Otherwise, there is a risk that the developer will fly in the direction of the pumping pole S2. The effect can be obtained if the most upstream position of the low magnetic force section NM is located even slightly above the center of rotation of the supply roller 51 in the vertical direction. However, the most upstream position of the low magnetic force section NM is preferably located 3° or more upstream of the horizontal line L passing through the center of rotation of the supply roller 51 in the direction of rotation of the supply roller 51, and more preferably 6° or more upstream.

[0066] [Magnetic flux density distribution] Next, the magnetic flux density distribution on the surface of the supply roller 51 around the low magnetic force section NM formed between the peeling pole S3 and the pumping pole S2 of the supply roller 51 of Example 1 will be described with reference to Fig. 6 and Fig. 7 while comparing with Comparative Example 2. Fig. 6 and Fig. 7 are diagrams that respectively show the distribution of the magnetic flux density Br in the normal direction and the magnetic flux density Bθ in the tangential direction on the surface of the supply roller 51 of the magnet rollers 51a1 and 51a inside the supply roller 51 of Comparative Example 2 and Example 1.

[0067] More precisely, the magnetic flux density Br refers to the component of the magnetic flux density B in the normal direction relative to the supply roller 51. Hereinafter, the "magnetic flux density Br in the normal direction" may be referred to simply as the "magnetic flux density" according to convention. When simply referring to the "magnetic flux density", it refers to the "magnetic flux density Br in the normal direction on the surface of the supply roller 51". The magnetic flux density Br in the normal direction on the surface of the supply roller 51 in Example 1 and Comparative Example 2 was measured using a magnetic field measuring device (FWBELL's "MS-9902") with the distance between a probe, which is a component of the magnetic field measuring device, and the surface of the developing sleeve 24 being approximately 100 μm.

[0068] 6 and 7 also show an outline of the magnetic attraction force Fr that attracts the developer (carrier) toward the center of the supply roller 51 (i.e., the magnetic attraction force in the normal direction to the surface of the supply roller 51). Hereinafter, the "magnetic attraction force Fr in the center direction of the supply roller 51" may be simply referred to as the "magnetic attraction force." When simply referred to as the "magnetic attraction force," it refers to the "magnetic attraction force Fr in the normal direction to the surface of the supply roller 51." The magnetic attraction force Fr of the supply roller 51 can be derived from the magnetic flux density Br in the normal direction, and is expressed by the following formula 1.

number

[0069] In formula 1, μ is the magnetic permeability of the magnetic carrier, μ0 is the magnetic permeability of a vacuum, and b is the radius of the magnetic carrier. The magnetic flux density Bθ in the tangential direction on the surface of the supply roller 51 is calculated from formula 2 below using the value of Br measured by the above method.

number

[0070] In Fig. 6 and Fig. 7, the magnetic flux density Br in the normal direction of Comparative Example 2 and Example 1 is shown by a solid line, the magnetic flux density Bθ in the tangential direction is shown by a dashed line, and the magnetic attraction force Fr (dotted line) of each is also shown on the second axis. The low magnetic force section NM refers to a region where the magnetic attraction force Fr is equal to or less than 0 or close to 0, but there are cases where it is difficult to understand due to variations occurring near 0. For this reason, in this embodiment, the "low magnetic force section NM" is defined as a section between the most upstream position and the most downstream position where the magnetic attraction force Fr in the normal direction on the surface of the supply roller 51 is 0 between the peeling pole (second magnetic pole) S3 and the pumping pole (third magnetic pole) S2 with respect to the rotation direction of the supply roller 51. The low magnetic force section NM is also shown at the same time in Fig. 6 and Fig. 7. By comparing these, the following can be understood.

[0071] First, in the case of Comparative Example 2 shown in Fig. 6, it can be seen that the tangential magnetic flux density Bθ (dashed line) crosses 0 mT relatively upstream of the low magnetic force section NM (i.e., the direction of the magnetic flux density Bθ is reversed). This means that a repulsive magnetic field in which the horizontal direction of the magnetic flux density changes is likely to be formed between the peeling pole S3 and the pumping pole S2 that form the low magnetic force section NM.

[0072] 7, the tangential magnetic flux density Bθ (dashed line) does not cross 0 mT until relatively downstream of the low magnetic force section NM (i.e., the direction of the magnetic flux density Bθ does not reverse). This means that the horizontal direction of the magnetic flux density is unlikely to change (difficult to reverse) between the peeling pole S3 and the pumping pole S2 that form the low magnetic force section NM, and a repulsive magnetic field is unlikely to be formed.

[0073] 6, the absolute value of the tangential magnetic flux density Bθ (dashed line) is smaller than the absolute value of the normal magnetic flux density Br (solid line) at the most upstream position of the low magnetic force section NM. This means that the magnetic field lines extend in a relatively vertical direction from the surface of the supply roller 51.

[0074] 7, the absolute value of the tangential magnetic flux density Bθ (dashed line) is greater than the absolute value of the normal magnetic flux density Br (solid line) at the most upstream position of the low magnetic force section NM. This means that the magnetic field lines extend from the surface of the supply roller 51 while being relatively horizontal.

[0075] As described above, from the magnetic flux density distribution, it can be seen that a repulsive magnetic field is difficult to form and the magnetic lines of force are likely to extend while lying down upstream of the low magnetic force section NM between the separating pole S3 and the pumping pole S2 in the case of Example 1. This can explain the state in which the magnetic lines of force extend from the separating pole S3 to the regulating pole N2 downstream of the pumping pole S2 as shown in Fig. 5(b), and conversely, it can be said to represent the conditions under which the magnetic lines of force extend in this way.

[0076] Therefore, as in Example 1, magnetic field lines extend from the peeling pole S3 to the regulating pole N2 downstream of the pumping pole S2, causing the developer peeled off upstream of the low magnetic force section NM to fly toward the surface of the supply roller 51, and the conditions for suppressing the accompanying rotation due to bouncing off the wall portion 71 as occurred in Comparative Example 2 are expressed as follows.

[0077] The first condition is that the tangential magnetic flux density Bθ does not cross 0 mT (does not reverse) until the downstream region of the low magnetic force section NM. This makes it difficult for a repulsive magnetic field to be formed in the upstream region of the low magnetic force section NM where the developer is peeled off from the supply roller 51, and makes it easier for magnetic lines of force to extend from the peeling pole S3 to the regulating pole N2 downstream of the pumping pole S2.

[0078] The above-mentioned effect of suppressing co-rotation can be obtained if the tangential magnetic flux density Bθ crosses 0 mT downstream of the center position of the low magnetic force section NM. That is, the direction of the tangential magnetic flux density Bθ on the surface of the supply roller 51 does not reverse between the most upstream position of the low magnetic force section NM and a point halfway through the low magnetic force section NM with respect to the rotation direction of the supply roller 51. In other words, the position where the direction of the tangential magnetic flux density Bθ first reverses in the low magnetic force section NM is downstream of a point halfway through the low magnetic force section NM from the most upstream position.

[0079] However, in order to obtain a sufficient effect of suppressing co-rotation, it is preferable that the magnetic flux density Bθ crosses 0 mT within the downstream 1 / 3, and more preferably within the downstream 1 / 4. That is, it is preferable that the direction of the tangential magnetic flux density Bθ does not reverse between the most upstream position of the low magnetic force section NM and the downstream 1 / 3 of the low magnetic force section NM (in other words, from the most upstream position to the 2 / 3 position) in relation to the rotation direction of the supply roller 51. In other words, it is preferable that the position where the direction of the tangential magnetic flux density Bθ first reverses in the low magnetic force section NM is downstream of the 2 / 3 position from the most upstream position.

[0080] Moreover, it is more preferable that the direction of the tangential magnetic flux density Bθ does not reverse between the most upstream position of the low magnetic force section NM and a point 1 / 4 downstream of the low magnetic force section NM (in other words, from the most upstream position to a point 3 / 4). In other words, it is more preferable that the position where the direction of the tangential magnetic flux density Bθ in the low magnetic force section NM first reverses is downstream of a point 3 / 4 from the most upstream position. In the magnetic flux density distribution of Example 1 shown in FIG. 7, the tangential magnetic flux density Bθ (dashed line) crosses 0 mT in an area within the downstream 1 / 4.

[0081] The second condition is that the absolute value of the magnetic flux density Bθ in the tangential direction at the most upstream position of the low magnetic force section NM is greater than the absolute value of the magnetic flux density Br in the normal direction. This makes it easier for the magnetic field lines to extend relatively horizontally from the surface of the supply roller 51. As mentioned above, when the developer is peeled off from the supply roller 51, the developer receives a force in the normal direction of the magnetic field lines at that position. Therefore, if the magnetic field lines extend horizontally from the surface of the supply roller 51 at the most upstream position of the low magnetic force section NM (the position where the developer is peeled off), the developer receives a force more in the direction of the surface of the supply roller 51, which has the effect of suppressing co-rotation.

[0082] The effect of suppressing co-rotation can be obtained if, at the most upstream position of the low magnetic force section NM, the absolute value of the magnetic flux density Bθ in the tangential direction on the surface of the supply roller 51 is greater than the absolute value of the magnetic flux density Br in the normal direction on the surface of the supply roller 51. However, in order to fully obtain the effect of suppressing co-rotation, the absolute value of the magnetic flux density Bθ in the tangential direction at the most upstream position of the low magnetic force section NM is preferably greater than 1.35 times the absolute value of the magnetic flux density Br in the normal direction, and more preferably greater than 1.7 times.

[0083] That is, the ratio Bθ / Br between the absolute value of the magnetic flux density Bθ in the tangential direction and the absolute value of the magnetic flux density Br in the normal direction is preferably 1.35 or more, and more preferably 1.7 or more.

[0084] Table 1 lists Bθ / Br, which is the ratio of the absolute value of the tangential magnetic flux density Bθ to the absolute value of the normal magnetic flux density Br at the most upstream position of the low magnetic force section NM for Comparative Example 2 and Example 1. Table 1 also lists Examples 2 to 4, which will be described later. Table 1 also lists an evaluation of the occurrence of co-rotation. [Table 1]

[0085] From Table 1, in Example 1, the absolute value of the magnetic flux density Bθ (dashed line) in the tangential direction was 1.8 times the absolute value of the magnetic flux density Br (solid line) in the normal direction, which was greater than 1.7 times. Although the effect of suppressing co-rotation can be obtained by satisfying only one of the above two conditions, it is more preferable to satisfy both conditions simultaneously.

[0086] [Configuration of peeling pole and pumping pole] Next, in order to obtain a magnetic flux density distribution in the low magnetic force section NM as in the first embodiment, how to configure the two magnetic poles forming the low magnetic force section NM, that is, the separation pole S3 and the pumping pole S2, will be described.

[0087] As shown in Fig. 5B, in the developing device 4 of the first embodiment, magnetic lines of force also extend from the stripping pole S3 to the regulating pole N2 downstream of the pumping pole S2. The conditions for the magnetic lines of force to extend in this manner are related to the magnetic flux density Br and the half-width. As mentioned above, if the magnetic flux density Br and the half-width of the stripping pole S3 and the pumping pole S2 are approximately the same, a repulsive magnetic field is formed between the stripping pole S3 and the pumping pole S2, as shown in Fig. 4B.

[0088] On the other hand, if the magnetic flux density Br or half-width of the peeled pole S3 is sufficiently larger than that of the pumping pole S2, as shown in Figure 5 (b), the magnetic field lines extend from the peeled pole S3 to the regulating pole N2 downstream of the pumping pole S2. This is because there are sufficiently more magnetic field lines coming from the peeled pole S3 than from the pumping pole S2. The number of magnetic field lines is roughly proportional to the "peak value (absolute value) [mT] x half-width [°] of the magnetic flux density Br in the normal direction", which corresponds to the area of ​​the magnetic flux density Br. Therefore, the condition for the magnetic field lines to extend from the peeled pole S3 to the regulating pole N2 downstream of the pumping pole S2 is that the area of ​​the magnetic flux density Br of the peeled pole S3, "peak value (absolute value) [mT] x half-width [°] of the magnetic flux density Br in the normal direction", is sufficiently larger than the area of ​​the magnetic flux density Br of the pumping pole S2.

[0089] Table 2 shows the magnetic flux density Br, half-width, and area in the normal direction of the peeling pole S3, the pumping pole S2, and the regulating pole N2 in Comparative Example 2, Example 1, and Examples 2 to 4 described later. The area ratio of the peeling pole S3 shows the ratio of the area of ​​the peeling pole S3 (peak value (absolute value) [mT] × half-width [°] of the magnetic flux density Br in the normal direction of the peeling pole S3) to the area of ​​the pumping pole S2 (peak value (absolute value) [mT] × half-width [°] of the magnetic flux density Br in the normal direction of the pumping pole S2). In addition, the area ratio of the regulating pole N2 indicates the ratio of the area of ​​the regulating pole N2 (peak value (absolute value) [mT] × half-width [°] of the magnetic flux density Br in the normal direction of the regulating pole N2) to the area of ​​the pumping pole S2 (peak value (absolute value) [mT] × half-width [°] of the magnetic flux density Br in the normal direction of the pumping pole S2). [Table 2]

[0090] As shown in Table 2, the peak value (absolute value) of the magnetic flux density Br in the normal direction of the peeling pole S3 of the supply roller 51 of Comparative Example 2 was 24 [mT] and the half-value width was 58 [°], and the peak value (absolute value) of the magnetic flux density Br in the normal direction of the pumping pole S2 was 42 [mT] and the half-value width was 30 [°]. The areas of the magnetic flux density Br of the peeling pole S3 and the pumping pole S2, "peak value (absolute value) [mT] × half-value width [°] of the magnetic flux density Br in the normal direction," are 1392 and 1260, respectively, which are approximately the same. Specifically, the area of ​​the peeling pole S3 of Comparative Example 2 is 1.10 times that of the pumping pole S2 (area ratio 1.10).

[0091] On the other hand, the peak value (absolute value) of the magnetic flux density Br in the normal direction of the peeling pole S3 of the supply roller 51 in Example 1 was 41 [mT], the half-width was 58 [°], and the peak value (absolute value) of the magnetic flux density Br in the normal direction of the pumping pole S2 was 42 [mT], and the half-width was 30 [°]. The areas of the magnetic flux density Br of the peeling pole S3 and the pumping pole S2, "peak value (absolute value) [mT] x half-width [°] in the normal direction of the magnetic flux density Br", are 2378 and 1260, respectively, and the area of ​​the peeling pole S3 is 1.89 times larger than the area of ​​the pumping pole S2. As a result, it is considered that the magnetic field lines extend from the peeling pole S3 to the regulating pole N2 downstream of the pumping pole S2, and the co-rotation is suppressed.

[0092] The supply rollers 51 of Examples 2 to 4, which were created by modifying the supply roller 51 of Example 1, will be described below. The peak values ​​and half-width values ​​of the magnetic flux density Br of the supply rollers 51 of Examples 2 to 4 are listed in Table 2, as in Example 1. Furthermore, as in FIG. 7 of Example 1, the magnetic flux density distribution and magnetic attraction force of the magnet of the supply roller 51 of Example 2 are shown in FIG. 8, the magnetic flux density distribution and magnetic attraction force of the magnet of Example 3 are shown in FIG. 9, and the magnetic flux density distribution and magnetic attraction force of the magnet of Example 4 are shown in FIG. 10. The developing devices 4 of Examples 2 to 4 are the same as those of Example 1 except for the magnet of the supply roller 51, so a description will be omitted except for the differences.

[0093] [Example 2] As shown in Table 2, the supply roller 51 of Example 2 has a smaller peak value of magnetic flux density Br in the normal direction of the peeling pole S3 compared to Example 1, but is larger than Comparative Example 1, with an area ratio of 1.52 times. When co-rotation was checked with the supply roller 51 of Example 2, the effect of suppressing co-rotation was obtained, but the result was slightly inferior to that of Example 1. That is, co-rotation hardly occurred in Example 1, but some co-rotation occurred in Example 2, although not as much as in Comparative Example 2 and with almost no effect on the output image (Table 1).

[0094] Considering the results of Example 1 and Example 2 together, when the ratio of the areas of the magnetic flux density Br of the peeling pole S3 and the pumping pole S2 (peak value (absolute value) [mT] × half-width [°] in the normal direction) is 1.5 or more, the effect of suppressing co-rotation is obtained, and it is preferable that the peeling pole S3 is 1.8 or more. In other words, the effect of suppressing co-rotation is obtained by making the product of the absolute value of the peak value and half-width of the magnetic flux density Br in the normal direction of the peeling pole (second magnetic pole) S3 on the surface of the supply roller 51 1.5 times or more the product of the absolute value of the peak value and half-width of the magnetic flux density Br in the normal direction of the pumping pole (third magnetic pole) S2. In addition, the product of the absolute value and half-width of the peak value of the magnetic flux density Br in the normal direction of the peeling pole S3 is preferably 1.8 times or more the product of the absolute value and half-width of the peak value of the magnetic flux density Br in the normal direction of the magnetic pole of the pumping pole S2.

[0095] Next, looking at the magnetic flux density distribution of Example 2 shown in FIG. 8, the tangential magnetic flux density Bθ also crosses 0 mT in the region within the downstream 1 / 4 of the low magnetic force section NM in Example 2, which also explains the suppression of co-rotation in Example 2. On the other hand, as shown in Table 1, the absolute value of the tangential magnetic flux density Bθ at the most upstream position of the low magnetic force section NM was 1.4 times the absolute value of the normal magnetic flux density Br. As mentioned above, the magnetic flux density Bθ is preferably greater than 1.35 times the magnetic flux density Br, and more preferably 1.7 times or more. In contrast, Example 2 is 1.4 times, which is 1.35 times or more but 1.7 times or less. Considering that Example 1 was 1.8 times and 1.7 times or more, it can be explained that Example 2 has a co-rotation suppression effect, but the result is slightly inferior to Example 1.

[0096] [Example 3] Next, Example 3 will be described. As shown in Table 2, the supply roller 51 of Example 3 has a smaller half-width of the peeling pole S3 than those of Comparative Example 2 and Example 1, but the magnetic flux density Br in the normal direction is large, and the area ratio is 2.12 times. When the co-rotation was confirmed with the supply roller 51 of Example 3, it was found that it could be suppressed to the same extent as Example 1 (Table 1). Therefore, it can be seen that even if the half-width is narrow as in Example 3, it is possible to suppress the co-rotation by increasing the magnetic flux density Br in the normal direction. This indicates that it is not either the magnetic flux density Br in the normal direction or the half-width, but the area obtained by multiplying both of them, "peak value (absolute value) [mT] x half-width [°] of the magnetic flux density Br in the normal direction", that has an effect on suppressing the co-rotation.

[0097] 9, the magnetic flux density Bθ in the tangential direction crosses 0 mT in the region within the downstream 1 / 4 of the low magnetic force section NM in Example 3 as well. As shown in Table 1, the absolute value of the magnetic flux density Bθ in the tangential direction at the most upstream position of the low magnetic force section NM is 2.45 times the absolute value of the magnetic flux density Br in the normal direction, which is more preferable, 1.7 times or more, as in Example 1. From these points, it can be explained that Example 3 has a high effect of suppressing the co-rotation of the supply roller 51.

[0098] [Example 4] Next, Example 4 will be described. As shown in Table 2, the supply roller 51 of Example 4 has the same magnetic flux density Br and half-width of the peeling pole S3 and the drawing pole S2 as Example 1. However, when the co-rotation was checked with the supply roller 51 of Example 4, the effect was obtained but the result was slightly inferior to that of Example 1. That is, while the co-rotation hardly occurred in Example 1, the co-rotation occurred slightly in Example 4, although not to the same extent as in Example 2 and with almost no effect on the output image (Table 1). This is considered to be due to the following reasons.

[0099] As shown in Table 2, the supply roller 51 of Example 4 has a smaller magnetic flux density Br of the regulating pole N2 of the opposite polarity downstream of the pumping pole S2 than that of Example 1. As a result, the area obtained by multiplying the magnetic flux density Br of the regulating pole N2 by the half-width, i.e., the peak value (absolute value) [mT] of the magnetic flux density Br in the normal direction × half-width [°], is also smaller than that of Example 1. From this, it is considered that in Example 4, the area of ​​the magnetic flux density of the peeling pole S3 is sufficiently larger than that of the pumping pole S2, and a sufficient number of magnetic lines of force extend from the peeling pole S3, but the area of ​​the magnetic flux density of the regulating pole N2 is small, making it difficult for the magnetic lines of force to extend in the direction of the regulating pole N2, thereby reducing the effect of suppressing co-rotation.

[0100] The extension of the magnetic field lines in the low magnetic force section NM depends greatly on the two poles (peeling pole S3 and pumping pole S2) that form the low magnetic force section NM. However, when the area of ​​the magnetic pole of a different polarity (regulating pole N2 in this example) located downstream of the magnetic pole on the downstream side of the low magnetic force section NM (pumping pole S2 in this example) becomes smaller, the effect of suppressing co-rotation is affected. That is, the regulating pole (fourth magnetic pole) N2 is located upstream of the main pole (first magnetic pole) N1 and downstream of the pumping pole (third magnetic pole) S2 in the rotation direction of the supply roller 51, and is adjacent to the pumping pole S2, and is a different polarity from the pumping pole S2, and the area of ​​this regulating pole N2 affects the co-rotation.

[0101] Taking the magnetic poles of this embodiment as an example, it is important that the area of ​​the regulating pole N2 is at least larger than the area of ​​the pumping pole S2. As in the fourth embodiment, the area of ​​the regulating pole N2 is preferably 1.25 times or more larger than the area of ​​the pumping pole S2, and more preferably 1.5 times or more larger as in the first embodiment. That is, the product of the absolute value and the half-width of the peak value of the magnetic flux density Br in the normal direction of the regulating pole N2 is preferably 1.25 times or more larger than the product of the absolute value and the half-width of the peak value of the magnetic flux density Br in the normal direction of the pumping pole S2. Also, it is more preferable that the product of the absolute value and the half-width of the peak value of the magnetic flux density Br in the normal direction of the regulating pole N2 is 1.5 times or more larger than the product of the absolute value and the half-width of the peak value of the magnetic flux density Br in the normal direction of the pumping pole S2.

[0102] Next, looking at the magnetic flux density distribution of Example 4 shown in Fig. 10, the tangential magnetic flux density Bθ in Example 4 crosses 0 mT in a region between 1 / 3 and 1 / 4 downstream of the low magnetic force section NM. In Example 1, the tangential magnetic flux density Bθ crosses 0 mT in a region within 1 / 4 downstream of the low magnetic force section NM, while in Example 4, it crosses 0 mT further upstream than in Example 1. This is thought to reflect the fact that the area of ​​the regulating pole N2 in Example 4 is small, making it difficult for the magnetic field lines from the separation pole S3 to extend in the direction of the regulating pole N2.

[0103] From the above, as described above, the effect of suppressing co-rotation can be obtained if the tangential magnetic flux density Bθ crosses 0 mT downstream of the center position of the low magnetic force section NM. However, to fully obtain the effect of suppressing co-rotation, it is preferable that the magnetic flux density Bθ crosses 0 mT in an area within the downstream 1 / 3 of the low magnetic force section NM, more preferably within the downstream 1 / 4.

[0104] On the other hand, in Example 4, as also shown in Table 1, the absolute value of the tangential magnetic flux density Bθ at the most upstream position of the low magnetic force section NM was 1.7 times the absolute value of the normal magnetic flux density Br. Since it was 1.8 times in Example 1, there was no significant change in Example 4 compared to Example 1. From the above, it is possible to explain why the effect of suppressing co-rotation is reduced in Example 4 compared to Example 1, but the degree of reduction is only slight.

[0105] As described above with reference to FIG. 2, Examples 1 to 4, which satisfy the requirements of this embodiment, are provided with a main pole N1 of a different polarity upstream of the peeling pole S3 of the supply roller 51. The main pole N1 is substantially opposed to the developing roller 50, and the developing roller 50 is provided with a magnet roller 50a inside, which is made up of the main pole N1 and one receiving pole S4 of a different polarity, in an area substantially opposed to the supply roller 51. The magnet roller 50a (receiving pole S4) of the developing roller 50 is not necessarily required, but providing the magnet roller 50a (receiving pole S4) as in this embodiment tends to slightly increase the effect of suppressing co-rotation. This is believed to be due to the following reasons.

[0106] The extension of the magnetic field lines in the low magnetic force section NM depends greatly on the two poles (separation pole S3 and pumping pole S2 in this example) that form the low magnetic force section NM. However, as described in the explanation of the fourth embodiment, the opposite pole (regulation pole N2) downstream also has some effect on the effect of suppressing co-rotation. According to the inventor's study, the opposite pole (main pole N1) upstream can also have some effect on the effect of suppressing co-rotation.

[0107] In order to obtain the effect of suppressing the co-rotation, as shown in FIG. 5, it is important that the magnetic field lines extend from the upstream magnetic pole (separation pole S3) that forms the low magnetic force section NM toward the opposite pole (regulation pole N2) further downstream of the downstream magnetic pole (pumping pole S2) that forms the low magnetic force section NM. If the magnetic field lines easily extend from the separation pole S3 toward the opposite pole (main pole N1) upstream, it is considered that the magnetic field lines will not easily extend from the separation pole S3 toward the regulation pole N2. At this time, as in this embodiment, if a different magnetic pole (receiving pole S4) exists inside the developing roller 50 substantially opposite the main pole N1, the magnetic field lines will extend more to the receiving pole S4 of the developing roller 50 that is close to the main pole N1. Therefore, the magnetic field lines will not easily extend between the separation pole S3 and the main pole N1. Then, it is considered that the magnetic field lines will easily extend from the separation pole S3 to the regulation pole N2, and the effect of suppressing the co-rotation will be easily obtained.

[0108] As described above, by arranging a magnetic pole (receiving pole S4) that is a different pole inside the developing roller 50 approximately opposite to the upstream different pole (main pole N1) of the two poles that form the low magnetic force section NM of the supply roller 51, the effect of suppressing co-rotation can be further achieved.

[0109] As described above, by adopting the configuration of this embodiment, it is possible to suppress the occurrence of toner drag after the toner on the supply roller 51 moves to the developing roller 50 and is consumed. As a result, it is possible to prevent the problem of the image density decreasing as the image formation proceeds, as in the comparative example.

[0110] [Other embodiments] In the above-described embodiments, the present invention has been described as being applied to a developing device used in a tandem-type image forming apparatus. However, the present invention can also be applied to developing devices used in other types of image forming apparatus. In addition, the image forming apparatus is not limited to being full-color, and may be monochrome or mono-color. Alternatively, by adding necessary devices, equipment, and housing structures, the present invention can be embodied in various applications such as printers, various printing machines, copiers, FAX machines, and multi-function machines.

[0111] In addition, the configuration of the developing device is not limited to the above-mentioned configuration in which the developing chamber and the stirring chamber are arranged horizontally, but may be arranged in a direction inclined with respect to the horizontal direction. In short, it is sufficient that the developing chamber as the first chamber and the stirring chamber as the second chamber are arranged adjacent to each other so as to overlap at least partially when viewed from the horizontal direction. [Explanation of symbols]

[0112] 1...Photosensitive drum (image carrier) 4. Developing device 40...Developing container 50 Developing roller 50a···Magnet roller (first magnet) 51 Supply roller 51a···Magnet roller (second magnet) 52 Regulating blade (regulating member) 71...Wall part N1: Main pole (first magnetic pole) N2 Regulating pole (fourth magnetic pole) S2: Pumping pole (third pole) S3: Stripping pole (second magnetic pole) S4: Receiving pole (fifth magnetic pole) NM: Low magnetic field

Claims

1. A developing container containing a developer including toner and carrier, A developing roller that carries and transports the toner to a developing position for developing an electrostatic image formed on an image carrier, A supply roller is positioned opposite the developing roller, and carries and transports the developer supplied from the developing container and supplies only the toner to the developing roller. A regulating member is positioned opposite the supply roller and regulates the amount of developer carried on the supply roller, A first magnet having a first magnetic pole is positioned inside the developing roller in a non-rotating, fixed manner, A second magnet is fixedly positioned inside the supply roller in a non-rotating manner, A second magnetic pole is positioned opposite to the first magnetic pole and is of the opposite pole to the first magnetic pole, A third magnetic pole positioned downstream of the second magnetic pole with respect to the rotational direction of the supply roller, The supply roller comprises a second magnet having a fourth magnetic pole which is located downstream of the third magnetic pole and adjacent to the third magnetic pole with respect to the rotational direction of the supply roller, and which has the same pole as the third magnetic pole, With respect to the rotational direction of the supply roller, the position where the magnetic flux density of the third magnetic pole in the direction normal to the supply roller is maximum is downstream of the position on the supply roller where the supply roller is closest to the developing roller, and upstream of the position on the supply roller where the regulating member is closest to the supply roller. With respect to the rotational direction of the supply roller, there exists a region downstream from the position where the magnetic pole density of the third magnetic pole in the normal direction of the supply roller is maximum, and upstream from the position where the magnetic pole density of the fourth magnetic pole in the normal direction of the supply roller is maximum, in which the absolute value of the magnetic flux density in the normal direction of the supply roller is 5 [mT] or less. The uppermost position of the region in the rotational direction of the supply roller is located vertically above the rotational center of the supply roller. The absolute value of the tangential magnetic flux density of the supply roller at the upstreammost position in the region is greater than the absolute value of the normal magnetic flux density of the supply roller at the upstreammost position in the region. A developing apparatus characterized by the following features.

2. The ratio of the absolute value of the tangential magnetic flux density of the supply roller at the upstreammost position in the region to the absolute value of the magnetic flux density in the normal direction of the supply roller at the upstreammost position in the region is 1.35 or greater. The developing apparatus according to feature 1.

3. The ratio of the absolute value of the tangential magnetic flux density of the supply roller at the upstreammost position in the region to the absolute value of the magnetic flux density in the normal direction of the supply roller at the upstreammost position in the region is 1.7 or greater. The developing apparatus according to feature 1.

4. In the section from the uppermost position of the region to a position half a distance downstream of the region with respect to the rotational direction of the supply roller, the direction of the magnetic pole density in the tangential direction of the supply roller does not reverse. The developing apparatus according to feature 1.

5. In the section from the uppermost position of the region to a position located two-thirds downstream of the region with respect to the rotational direction of the supply roller, the direction of the magnetic pole density in the tangential direction of the supply roller does not reverse. The developing apparatus according to feature 1.

6. In the section from the uppermost position of the region to a position located 3 / 4 of the way downstream of the region with respect to the rotational direction of the supply roller, the direction of the magnetic pole density in the tangential direction of the supply roller does not reverse. The developing apparatus according to feature 1.

7. The product of the absolute value of the maximum magnetic flux density of the third magnetic pole in the normal direction of the supply roller and the full width at half maximum of the magnetic flux density of the third magnetic pole in the normal direction of the supply roller is 1.5 times or more the product of the absolute value of the maximum magnetic flux density of the fourth magnetic pole in the normal direction of the supply roller and the full width at half maximum of the magnetic flux density of the fourth magnetic pole in the normal direction of the supply roller. The developing apparatus according to feature 1.

8. The product of the absolute value of the maximum magnetic flux density of the third magnetic pole in the normal direction of the supply roller and the half-width of the magnetic flux density of the third magnetic pole in the normal direction of the supply roller is 1.8 times or more the product of the absolute value of the maximum magnetic flux density of the fourth magnetic pole in the normal direction of the supply roller and the half-width of the magnetic flux density of the fourth magnetic pole in the normal direction of the supply roller. The developing apparatus according to feature 1.

9. The second magnet is positioned upstream of the second magnetic pole and downstream of the fourth magnetic pole with respect to the rotational direction of the supply roller, and adjacent to the fourth magnetic pole, and further has a fifth magnetic pole that is opposite to the fourth magnetic pole. The product of the absolute value of the maximum magnetic flux density of the fifth magnetic pole in the normal direction of the supply roller and the half-width of the magnetic flux density of the fifth magnetic pole in the normal direction of the supply roller is 1.25 times or more the product of the absolute value of the maximum magnetic flux density of the fourth magnetic pole in the normal direction of the supply roller and the half-width of the magnetic flux density of the fourth magnetic pole in the normal direction of the supply roller. The developing apparatus according to feature 1.

10. The fifth magnetic pole is positioned opposite the regulating member. The developing apparatus according to feature 9.

11. The second magnet is positioned upstream of the second magnetic pole and downstream of the fourth magnetic pole with respect to the rotational direction of the supply roller, and adjacent to the fourth magnetic pole, and further has a fifth magnetic pole that is opposite to the fourth magnetic pole. The product of the absolute value of the maximum magnetic flux density of the fifth magnetic pole in the normal direction of the supply roller and the full width at half maximum of the magnetic flux density of the fifth magnetic pole in the normal direction of the supply roller is 1.5 times or more the product of the absolute value of the maximum magnetic flux density of the fourth magnetic pole in the normal direction of the supply roller and the full width at half maximum of the magnetic flux density of the fourth magnetic pole in the normal direction of the supply roller. The developing apparatus according to feature 1.

12. The fifth magnetic pole is positioned opposite the regulating member. The developing apparatus according to feature 11.

13. With respect to the rotation direction of the supply roller, the upstreammost position in the region is located downstream of the position where the magnetic flux density of the third magnetic pole in the normal direction of the supply roller is maximum, and upstream of the position where the magnetic flux density of the fourth magnetic pole in the normal direction of the supply roller is maximum, and is located 3° or more upstream of the point where a horizontal line passing through the rotation center of the supply roller intersects the outer surface of the supply roller. The developing apparatus according to feature 1.

14. With respect to the rotation direction of the supply roller, the upstreammost position in the region is located downstream of the position where the magnetic flux density of the third magnetic pole in the normal direction of the supply roller is maximum, and upstream of the position where the magnetic flux density of the fourth magnetic pole in the normal direction of the supply roller is maximum, and is located 6° or more upstream of the point where a horizontal line passing through the rotation center of the supply roller intersects the outer surface of the supply roller. The developing apparatus according to feature 1.

Images