Developing device

Abstract

This provides a configuration that can suppress the scattering of toner accumulated in the guide section. [Solution] The third magnet 38 of the peeling roller 32 has a receiving electrode for receiving developer from the second developing roller 31, a transport electrode positioned downstream of the receiving electrode, and a peeling electrode positioned adjacent to the transport electrode and having a different polarity from the transport electrode. If the normal component of the magnetic flux density at any point on the outer surface of the peeling roller 32 is Br, the tangential component is Bθ, and the angle Φ of the magnetic tip at any point is arctan(Br / Bθ), then with respect to the rotation direction of the peeling roller 32, there is a point between point P1' on the outer surface of the peeling roller 32 corresponding to the tip position P1 of the guide member 45 and point P2' on the outer surface of the peeling roller 32 corresponding to the nearest position P2 of the guide member 45 where the absolute value of the angle Φ of the magnetic tip is 45° or more.

Description

Technical Field

[0001] The present disclosure relates to a developing device that develops an electrostatic latent image formed on an image carrier with a developer.

Background Art

[0002] As a developing device using a two-component developer composed of toner and a magnetic carrier, a configuration is common in which a magnet composed of a plurality of magnetic poles is provided inside a developing roller, and the developer is carried on the developing roller to develop an electrostatic latent image formed on an image carrier. [[ID=!13]]

[0003] Further, as a developing device, a configuration has been proposed in which a developer peeled off from a developing roller by a peeling roller disposed opposite to the side of the developing roller is collected and delivered to a developer circulation unit that circulates the developer (Patent Document 1). In the developing device described in Patent Document 1, a guide unit is provided below the peeling roller in the vertical direction to guide the developer peeled off from the peeling roller toward a conveying screw for conveying the developer to the developer circulation unit.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the case of the configuration described in Patent Document 1, in the process of delivering the developer from the developing roller to the peeling roller, there is a risk of toner scattering due to ear collapse between poles during conveyance when the peeling roller conveys the developer received from the developing roller to the peeling position, and toner scattering due to detachment during peeling. Some of the scattered toner rides on the airflow and accumulates on the guide unit directly below the peeling roller due to the influence of the airflow generated in the gap between the developing roller and the peeling roller.

[0006] If toner accumulated in the guide section falls to the area around the developing roller or the developer circulation section, the fallen toner mixes with the normal developer. This can cause unevenness in the amount of toner transferred to the photosensitive drum when developing the toner image on the drum, potentially resulting in uneven shading in the final output image.

[0007] One aspect of this disclosure is to provide a configuration that can suppress the scattering of toner accumulated in the guide section. [Means for solving the problem]

[0008] One aspect of the present disclosure includes a first chamber containing a developer including toner and a carrier; a first transport screw disposed in the first chamber for transporting the developer contained in the first chamber; a second chamber separated from the first chamber by a partition wall; a second transport screw disposed in the second chamber for transporting the developer contained in the second chamber; a first rotating body to which the developer is supplied, the first rotating body carrying and transporting the developer to a developing position for developing an electrostatic latent image formed on an image carrier; and a first magnet fixedly and non-rotatingly disposed inside the first rotating body, the first magnet located at the developing position. A first magnet having a first magnetic pole positioned opposite the image carrier, a second magnetic pole positioned downstream of the first magnetic pole with respect to the rotation direction of the first rotating body, and a third magnetic pole positioned adjacent to the second magnetic pole downstream of the second magnetic pole with respect to the rotation direction of the first rotating body and having the same pole as the second magnetic pole; a second rotating body positioned opposite the first rotating body and to which the developer is transferred from the first rotating body by the magnetic field generated by the first magnet, wherein a second rotating body carries and transports the developer in order to collect the developer in the second chamber after developing the electrostatic latent image A rotating body, a second magnet fixedly and non-rotatingly disposed inside the second rotating body, the second magnet having a fourth pole opposite to the second pole, a fifth pole positioned downstream of the fourth pole with respect to the rotational direction of the second rotating body, a sixth pole positioned adjacent to the fifth pole downstream with respect to the rotational direction of the second rotating body and opposite to the fifth pole, and a seventh pole positioned adjacent to the sixth pole downstream with respect to the rotational direction of the second rotating body and having the same pole as the sixth pole, and disposed opposite to the second rotating body, the developer The first rotating body and the second rotating body rotate in the same direction at positions opposite to each other, and the developer after developing the electrostatic latent image is transferred from the first rotating body to the second rotating body by the magnetic field generated between the second magnetic pole and the fourth magnetic pole, and when the normal component of the magnetic flux density at an arbitrary point on the outer surface of the second rotating body is Br, the tangential component of the magnetic flux density at the arbitrary point is Bθ, and the angle Φ of the magnetic tip at the arbitrary point is arctan(Br / Bθ), with respect to the rotation direction of the second rotating body,The developing apparatus is characterized in that, between the point on the outer surface of the second rotating body where a straight line passing through the end of the guide section opposite to the second transport screw and the center of rotation of the second rotating body intersects the outer surface of the second rotating body, and the nearest point on the outer surface of the second rotating body where the outer surface of the second rotating body is closest to the guide section, there is a location where the absolute value of the angle Φ of the magnetic tip is 45° or more. [Effects of the Invention]

[0009] One aspect of this disclosure provides a configuration that can suppress the scattering of toner accumulated in the guide section. [Brief explanation of the drawing]

[0010] [Figure 1] A schematic cross-sectional view of the image forming apparatus according to the embodiment. [Figure 2] A schematic cross-sectional view of the developing apparatus according to the embodiment. [Figure 3] A diagram showing the magnetic pole arrangement of the first developing roller according to the embodiment. [Figure 4] A diagram showing the magnetic pole arrangement of the second developing roller according to the embodiment. [Figure 5] A diagram showing the magnetic pole arrangement of a peeling roller according to an embodiment. [Figure 6] A diagram showing the arrangement of the second developing roller, peeling roller, and guide member according to the embodiment. [Figure 7] (a) Schematic diagram of the case where the angle of the magnetic tip is negative, (b) Schematic diagram of the case where the angle of the magnetic tip is positive. [Figure 8] (a) A graph showing the distribution of the normal and tangential components of the magnetic flux density on the peeling sleeve of the third magnet according to Comparative Example 1, and (b) A graph showing the angle of the magnetic tip on the peeling sleeve of the third magnet according to Comparative Example 1. [Figure 9] (a) A graph showing the distribution of the normal and tangential components of the magnetic flux density on the peeling sleeve of the third magnet according to Example 1, and (b) A graph showing the angle of the magnetic tip on the peeling sleeve of the third magnet according to the first embodiment. [Figure 10](a) Graph showing the distribution of the normal component and the tangential component of the magnetic flux density on the peeling sleeve of the third magnet according to Example 2, (b) Graph showing the angle of the magnetic spike on the peeling sleeve of the third magnet according to the second embodiment. [Figure 11] (a) Graph showing the distribution of the normal component and the tangential component of the magnetic flux density on the peeling sleeve of the third magnet according to Example 3, (b) Graph showing the angle of the magnetic spike on the peeling sleeve of the third magnet according to the third embodiment. [Figure 12] (a) Graph showing the distribution of the normal component and the tangential component of the magnetic flux density on the peeling sleeve of the third magnet according to Example 4, (b) Graph showing the angle of the magnetic spike on the peeling sleeve of the third magnet according to the fourth embodiment.

Embodiments for Carrying Out the Invention

[0011] The embodiments will be described with reference to FIGS. 1 to 12(b). First, the schematic configuration of the image forming apparatus of the present embodiment will be described with reference to FIG. 1.

[0012] [Image Forming Apparatus] The image forming apparatus 100 is a full-color image forming apparatus, and in the case of the present embodiment, for example, it is a MFP (Multi-Function Peripheral) having a copy function, a printer function, and a scan function. As shown in FIG. 1, the image forming apparatus 100 is provided with image forming units PY, PM, PC, and PK for performing image forming processes of four-color toner images of yellow, magenta, cyan, and black in parallel.

[0013] Each of the image forming units PY, PM, PC, and PK for each color has a primary charger 21Y, 21M, 21C, 21K, a developing device 1Y, 1M, 1C, 1K, an optical writing unit (exposure device) 22Y, 22M, 22C, 22K, a photosensitive drum 28Y, 28M, 28C, 28K, and a cleaning device 26Y, 26M, 26C, 26K. Further, the image forming apparatus 100 has a transfer device 2 and a fixing device 3. Since the configurations of the image forming units PY, PM, PC, and PK for each color are the same, hereinafter, the image forming unit PY will be described as a representative.

[0014] The photosensitive drum 28Y as a carrier is a photoreceptor having a photosensitive layer made of a resin such as polycarbonate containing an organic photoconductor (OPC), and is configured to rotate at a predetermined speed. In the present embodiment, the linear speed of the surface of the photosensitive drum 28Y is set to 650 mm / s. The primary charger 21Y is composed of a corona discharge electrode disposed around the photosensitive drum 28Y, and the surface of the photosensitive drum 28Y is charged by the generated ions.

[0015] The light writing unit 22Y incorporates a scanning optical device, and by exposing the charged photosensitive drum 28Y based on image data, the potential of the exposed portion is reduced, and a charge pattern (electrostatic latent image) corresponding to the image data is formed. The developing device 1Y transfers the contained developer to the photosensitive drum 28Y to develop the electrostactic latent image formed on the photosensitive drum 28Y. The developer is formed by mixing a carrier and toner corresponding to each color, and the electrostactic latent image is visualized by the toner.

[0016] The transfer device 2 includes primary transfer rollers 23Y, 23M, 23C, 23K, an intermediate transfer belt 24, and a secondary transfer roller 25. The intermediate transfer belt 24 is wound by the primary transfer rollers 23Y, 23M, 23C, 23K and a plurality of rollers and is supported so as to be able to run. The primary transfer rollers 23Y, 23M, 23C, 23K correspond to the respective colors of Y (yellow), M (magenta), C (cyan), and K (black) in order from the top in FIG. 1. The secondary transfer roller 25 is disposed outside the intermediate transfer belt 24, and is configured such that a recording material can pass between it and the intermediate transfer belt 24. The recording material is, for example, a sheet such as paper or a plastic sheet.

[0017] The toner images of each color formed on the photosensitive drums 28Y, 28M, 28C, and 28K are sequentially transferred onto the intermediate transfer belt 24 by the primary transfer rollers 23Y, 23M, 23C, and 23K, forming a color toner image with superimposed layers of yellow, magenta, cyan, and black. The formed toner image is then transferred to the recording material being transported from a cassette containing the recording material by the secondary transfer roller 25. The recording material on which the toner image has been transferred is then subjected to pressure and heat in the fixing device 3. This melts the toner on the recording material, fixing the color image to the recording material.

[0018] The developer storage units 27Y, 27M, 27C, and 27K are provided in accordance with the developing units 1Y, 1M, 1C, and 1K, respectively, and are loaded with replaceable bottles containing developer corresponding to the respective colors: yellow, magenta, cyan, and black, from top to bottom. The developer storage units 27Y, 27M, 27C, and 27K are configured to transport (replenish) the developer to the developing unit 1Y, 1M, 1C, and 1K corresponding to the color of the developer stored in them.

[0019] For example, the toner weight ratio of the developer stored in the bottle is 80-95%, while the toner weight ratio of the developer in developing units 1Y, 1M, 1C, and 1K is 5-10%. Therefore, when toner is consumed by developing in developing units 1Y, 1M, 1C, and 1K, developer containing an amount of toner corresponding to the consumption is replenished, and the toner weight ratio of the developer in developing units 1Y, 1M, 1C, and 1K is maintained at a constant level.

[0020] [Developing equipment] Next, developing units 1Y, 1M, 1C, and 1K will be described in detail using Figures 2 to 5. Since the configurations of developing units 1Y, 1M, 1C, and 1K are the same, developing unit 1Y will be described as a representative unit below. Figure 2 is a conceptual diagram illustrating developing unit 1Y shown in Figure 1, and Figures 3, 4, and 5 are conceptual diagrams illustrating the magnetic pole configurations of the first magnet 36, second magnet 37, and third magnet 38 arranged within developing unit 1Y.

[0021] As shown in Figure 2, the developing apparatus 1Y includes a first developing roller 30, a second developing roller 31, a peeling roller 32, a developer supply screw 42, a developer stirring screw 43, and a developer recovery screw 44, and these components are housed in a developing container 60.

[0022] The first developing roller 30 is a rotating developer carrier (rotating body) and is positioned adjacent to the photosensitive drum 28Y such that its axis of rotation is approximately parallel to the axis of rotation of the photosensitive drum 28Y. The first developing roller 30 has a first sleeve 33 as a rotating first developing sleeve (third rotating body) and a first magnet (fixed magnet, third magnet) 36 as a first developing magnet which is non-rotatingly positioned inside the first sleeve 33 and attracts the developer to the surface of the first sleeve 33 by magnetic force. The first developing roller 30 then attracts (carries) the developer drawn up from the developer supply screw 42 based on magnetic force and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y (on the image carrier) with the developer.

[0023] The first sleeve 33 (and the second sleeve 34, described later) of the developing device 1Y is subjected to, for example, a DC developing bias with the same polarity as the charging polarity of the primary charger 21Y, or a developing bias in which an AC voltage is superimposed with a DC voltage of the same polarity as the charging polarity of the primary charger 21Y. As a result, inverse development is performed in which toner charged with the same polarity as the charging polarity of the primary charger 21Y is deposited onto the electrostatic latent image formed by the optical writing unit 22Y. In this embodiment, the charging polarity of the primary charger 21Y and the DC voltage of the developing bias are set to negative, and inverse development is performed in which negatively charged toner is deposited onto the electrostatic latent image.

[0024] The first sleeve 33 is a non-magnetic cylindrical member with an outer diameter of 25 mm (radius r1 = 12.5 mm) and is rotationally driven around the rotation axis 39. The rotation direction of the first sleeve 33 is clockwise, as indicated by the arrow in Figure 2, and in this embodiment, it is in the opposite direction to the rotation direction of the photosensitive drum 28Y. Therefore, the first sleeve 33 and the photosensitive drum 28Y rotate in the same direction at positions opposite each other. In this embodiment, the linear velocity of the surface of the first sleeve 33 of the first developing roller 30 is set to 1.0 times (= 650 mm / s) the linear velocity of the surface of the photosensitive drum 28Y. Keeping the ratio of the linear velocity of the surface of the first sleeve 33 to the linear velocity of the surface of the photosensitive drum 28Y to approximately 1.0 times or more and 1.2 times or less is advantageous from the viewpoint of toner degradation. On the other hand, there are concerns about the development quality due to the reduced amount of toner supplied to the photosensitive drum 28Y. However, in this embodiment, two developing rollers 30 and 31 are provided, making it possible to maintain the amount of toner supplied to the photosensitive drum 28Y even when the linear velocity ratio is reduced.

[0025] The first magnet 36 is positioned inside the first sleeve 33 and has multiple magnetic poles 101 to 107, as shown in Figure 3. The solid lines of the magnetic poles 101 to 107 in Figure 3 indicate the positions (peak positions, pole positions) of the maximum values ​​of the distribution of the normal component of the magnetic flux density of the first magnet 36, respectively. A space is provided between the inner circumference of the first sleeve 33 and the outer circumference of the first magnet 36 to allow rotation of the first sleeve 33.

[0026] The developer adsorbed on the first sleeve 33 is transported toward the photosensitive drum 28Y by the rotation of the first sleeve 33, and develops the latent image formed on the photosensitive drum 28Y at the development position. After developing the latent image formed on the photosensitive drum 28Y, the developer on the first sleeve 33 is transported toward the vicinity of the second developing roller 31 by the rotation of the first sleeve 33. Then, near the closest proximity position between the first developing roller 30 and the second developing roller 31, the developer is detached from the first sleeve 33 by the magnetic field generated by the first magnet 36 contained in the first developing roller 30 and the second magnet 37 contained in the second developing roller 31, and the developer is transferred toward the second sleeve 34.

[0027] As described below, the second developing roller 31 of the developing apparatus 1Y in this embodiment is positioned vertically above the first developing roller 30. Therefore, the transfer of developer from the first sleeve 33 to the second sleeve 34 must also be performed vertically from downward to upward, against gravity. The first sleeve 33 and the second sleeve 34 are positioned with a 3 mm gap at their nearest contact point.

[0028] The second developing roller 31, acting as a developing roller, is a rotating developer carrier (rotating body) that is driven to rotate. It is positioned downstream of the first developing roller 30 with respect to the rotation direction of the photosensitive drum 28Y, and its rotation center O2 is positioned above the rotation center O1 of the first developing roller 30 with respect to the vertical direction. Developer is transferred from the first developing roller 30 by magnetic force (Figure 2). In this embodiment, the entire second developing roller 31 is positioned above the rotation center O1 of the first developing roller 30. The second developing roller 31, like the first developing roller 30, is positioned adjacent to the photosensitive drum 28Y, and its rotation axis is positioned approximately parallel to the rotation axis of the photosensitive drum 28Y. Therefore, the rotation axes of the second developing roller 31 and the first developing roller 30 are approximately parallel to each other.

[0029] Such a second developing roller 31 includes a second sleeve (second developing sleeve, first rotating body) 34 as a rotating developing sleeve, and a second magnet (second developing magnet, fixed magnet, first magnet) 37 as a developing magnet, which is non-rotatingly positioned inside the second sleeve 34 and attracts the developer to the surface of the second sleeve 34 by magnetic force. The second developing roller 31 receives the developer from the first developing roller 30 (first sleeve 33) based on magnetic force, attracts (carries) the developer, and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y with the developer. A peeling roller 32, which will be described later, is located to the side of the second developing roller 31.

[0030] The second sleeve 34 is a non-magnetic cylindrical member with an outer diameter of 25 mm (radius r2 = 12.5 mm) and is rotationally driven around the rotation axis 40. The rotation direction of the second sleeve 34 is clockwise, as shown by the arrow in Figure 2, and in this embodiment, it is in the opposite direction to the rotation direction of the photosensitive drum 28Y. Therefore, the second sleeve 34 and the photosensitive drum 28Y rotate in the same direction when they are facing each other. Also, the second sleeve 34 and the first sleeve 33 rotate in opposite directions when they are facing each other. In this embodiment, the linear velocity on the surface of the second sleeve 34 of the second developing roller 31 is set to be 1.2 times (= 780 mm / s) the linear velocity on the surface of the photosensitive drum 28Y.

[0031] The second magnet 37 is positioned inside the second sleeve 34 and has multiple magnetic poles 201 to 207, as shown in Figure 4. The solid lines on the magnetic poles 201 to 207 in Figure 4 indicate the positions (peak positions, pole positions) of the maximum values ​​of the distribution of the normal component of the magnetic flux density of the second magnet 37, respectively. A space is provided between the inner circumference of the second sleeve 34 and the outer circumference of the second magnet 37 to allow rotation of the second sleeve 34.

[0032] The developer adsorbed on the second sleeve 34 is transported toward the photosensitive drum 28Y by the rotation of the second sleeve 34, and develops the latent image formed on the photosensitive drum 28Y at the development position. After developing the latent image formed on the photosensitive drum 28Y, the developer remaining on the second sleeve 34 is transported toward the vicinity of the peeling roller 32 by the rotation of the second sleeve 34. Then, near the closest proximity position between the second developing roller 31 and the peeling roller 32, the developer is transferred from the second sleeve 34 to the third sleeve 35 of the peeling roller 32 by the magnetic fields generated by the second magnet 37 contained in the second developing roller 31 and the third magnet 38 contained in the peeling roller 32.

[0033] The peeling roller (recovery roller) 32, which acts as a peeling unit, is positioned on the opposite side of the photosensitive drum 28Y from the rotation center of the second sleeve 34, and peels off the developer from the second developing roller 31 after the electrostatic latent image on the photosensitive drum 28Y has been developed by the second developing roller 31. Specifically, the peeling roller 32 is a rotating developer carrier (rotating body), and is positioned between the second developing roller 31 and the developer recovery screw 44 such that its rotation center R is vertically above the rotation center O2 of the second developing roller 31.

[0034] Furthermore, the peeling roller 32 is positioned such that its axis of rotation is approximately parallel to the axis of rotation of the second developing roller 31. This peeling roller 32 has a third sleeve 35 as a rotating peeling sleeve (second rotating body) and a third magnet (peeling magnet, fixed magnet, second magnet) 38 which is positioned non-rotating inside the third sleeve 35 and attracts the developer to the surface of the third sleeve 35 by magnetic force, and is configured to transfer the developer from the second developing roller 31 based on magnetic force.

[0035] The third sleeve 35 is a non-magnetic cylindrical member with an outer diameter of 18 mm (radius of 9 mm) and is rotationally driven around the rotation axis 41. The rotation direction of the third sleeve 35 is counterclockwise, as indicated by the arrow in Figure 2, and in this embodiment, it is the opposite direction to the rotation direction of the second sleeve 34. Therefore, the third sleeve 35 and the second sleeve 34 rotate in the same direction at opposing positions (opposing parts).

[0036] The third magnet 38 is positioned inside the third sleeve 35 and has multiple magnetic poles 301 to 305, as shown in Figure 5. The solid lines of the magnetic poles 301 to 305 in Figure 5 indicate the positions (peak positions, pole positions) of the maximum values ​​of the distribution of the normal component of the magnetic flux density of the third magnet 38, respectively. A space is provided between the inner circumference of the third sleeve 35 and the outer circumference of the third magnet 38 to allow rotation of the third sleeve 35.

[0037] The developer adsorbed onto the third sleeve 35 is transported downstream in the direction of rotation by the rotational movement of the third sleeve 35, and at a position close to the developer recovery screw 44, is detached from the third sleeve 35 by the third magnet 38 contained in the peeling roller 32, and falls by its own weight toward the guide member 45 located vertically below. The developer that falls toward the guide member 45 is then guided toward the developer recovery screw 44 by its own weight.

[0038] The guide member 45 and the developer recovery screw 44 constitute a developer recovery unit 47, which is a recovery unit for recovering the developer peeled off from the third sleeve 35 on the peeling roller 32. The developer recovery screw 44 is located in the developer recovery chamber 47a and transports the developer contained in the developer recovery chamber 47a. Specifically, in the developer recovery unit 47, the developer recovery screw 44 is positioned so that its center of rotation is located below the center of rotation of the peeling roller 32 in the vertical direction, and it transports the developer received (recovered) from the peeling roller 32 while agitating it.

[0039] The guide member 45, acting as a guide, is positioned vertically below the peeling roller 32, and the closest proximity position P2 between the guide member 45 and the peeling roller 32 is vertically above the rotation center O2 of the second developing roller 31 (the rotation center of the second sleeve 34), guiding the developer peeled off by the peeling roller 32 toward the developer recovery screw 44. The guide member 45 is positioned opposite the peeling pole 305 of the third magnet 38 (described later) via the third sleeve 35. The tip position P1 of the guide member 45, which is the end opposite the developer recovery screw 44, is vertically above the rotation center O2 of the second developing roller 31.

[0040] Such a guide member 45 has an inclined surface 45a that serves as a guide surface for guiding the developer peeled off from the peeling roller 32. The inclined surface 45a is tilted so that the developer slides down by its own weight, in order to more reliably guide the peeled developer towards the developer recovery screw 44. That is, the inclined surface 45a is tilted horizontally such that the developer recovery screw 44 side (conveyor member side) is lower than the closest position P2 with respect to the peeling roller 32. In this embodiment, the gap between the peeling roller 32 and the guide member 45 at the closest position P2 is 1.8 mm, and the inclination angle of the inclined surface 45a of the guide member 45 is 8°.

[0041] The developer recovery screw (conveyor screw) 44, acting as a conveying member, conveys the recovered developer to the developer circulation section 46, which will be described below. That is, the developer recovery screw 44 is a screw conveying member used to convey the developer that has slid down the inclined surface 45a of the guide member 45 in one direction while agitating it. Furthermore, the developer recovery screw 44 is positioned such that its axis of rotation is approximately parallel to the axis of rotation of the second sleeve 34, and the center of rotation of the developer recovery screw 44 is located vertically above the center of rotation O2 of the second developing roller 31.

[0042] The developer circulation unit 46 is a supply unit for supplying developer to the first developing roller 30, and the developer circulation unit 46 has a regulating member 50, a developer supply screw 42, and a developer stirring screw 43. In the developer circulation unit 46, the developer is supplied to the first developing roller 30 while being agitated in the developer supply screw 42 and the developer stirring screw 43 and conveyed in a substantially horizontal direction. Also, as described above, the developer recovered by the developer recovery unit 47 falls by its own weight and is introduced into the developer circulation unit 46.

[0043] The developer supply screw 42, developer agitation screw 43, and developer recovery screw 44 are screw conveying members that convey the developer in one direction while agitating it. The developer supply screw 42 and developer agitation screw 43 are located below the developer recovery screw 44 in the vertical direction. Furthermore, these developer supply screw 42, developer agitation screw 43, and developer recovery screw 44 are arranged so that their rotation axes are approximately parallel to each other. The rotation axis of each of these screws is also approximately parallel to the rotation axis of the first developing roller 30.

[0044] The developer supply screw (first transport screw) 42 is located between the first developing roller 30 and the developer agitation screw 43, and a partition wall 48 of the developing container 60 is positioned between the developer supply screw 42 and the developer agitation screw 43. The partition wall 48 of the developing container 60 extends along the rotation axis direction of the developer supply screw 42 and the developer agitation screw 43. The partition wall 48 is provided with a communication opening (not shown) that connects the first transport path (first chamber) 61 through which the developer is transported by the developer supply screw 42 and the second transport path 62 through which the developer is transported by the developer agitation screw 43.

[0045] The developer agitated by the developer recovery screw (second transport screw) 44 falls by its own weight towards the developer supply screw 42 through a communication opening (not shown) formed in the partition wall 63 of the developing container 60 located between the developer recovery screw 44 and the developer supply screw 42. That is, the developer recovery chamber (second chamber) 47a where the developer recovery screw 44 is located is partitioned by the first transport path 61 and the partition wall 63, and the developer falls from the developer recovery chamber 47a to the first transport path 61 through the communication opening formed in the partition wall 63. The guide member 45 described above is formed integrally with the partition wall 63, and the developer recovery screw 44 is located above the partition wall 63.

[0046] The location of the communication port through which the developer agitated by the developer recovery screw 44 falls by its own weight and is introduced into the developer circulation section 46 is preferably positioned to avoid the area where the developer is supplied toward the first developing roller 30 (the intermediate portion with respect to the rotation axis direction of the developer supply screw 42). In this embodiment, the location of the communication port is set to include the downstream end (terminal end) in the developer transport direction of the first transport path 61 where the developer supply screw 42 is located.

[0047] The developer transport directions of the developer supply screw 42 and the developer agitation screw 43 are opposite to each other. The starting end (upstream end in the developer transport direction) and ending end (downstream end in the developer transport direction) of the first transport path 61 where the developer supply screw 42 is located, and the ending end and starting end of the second transport path 62 where the developer agitation screw 43 is located, are in communication with each other via a communication opening provided in the partition wall 48. Therefore, the developer circulates in the rotational direction of the developer supply screw 42 and the developer agitation screw 43, as indicated by the arrows in Figure 2, and in a substantially horizontal direction within the developing container 60, with a portion of it being supplied toward the first developing roller 30.

[0048] The developer supply port 51 (see Figure 2) is located above the developer agitation screw 43 in the developing container 60 and is connected to the developer storage section 27Y (see Figure 1). The developer supply port 51 is configured to supply the developer stored in the bottle loaded in the developer storage section 27Y to the second transport path 62 where the developer agitation screw 43 is located.

[0049] As described above, the toner weight ratio of the developer stored in the bottles of the developer storage unit 27Y is greater than the toner weight ratio of the developer in the developing device 1Y. Therefore, by adjusting the amount of developer supplied to the developer stirring screw 43, it is possible to maintain a constant toner weight ratio of the developer in the developing device 1.

[0050] The toner concentration detection sensor 49 (see Figure 2) is positioned to detect the toner concentration in the developer contained in the developer circulation unit 46. The toner concentration detection sensor 49 is a sensor that detects the magnetic permeability of the developer. The toner concentration corresponds to the amount of toner consumed in the developing device 1Y and is used to control the replenishment of developer from the developer storage unit 27Y. For example, if it is detected that the toner concentration has fallen below a predetermined value, developer is replenished from the developer storage unit 27Y. Since the magnetic permeability of the developer changes with the toner concentration, it is possible to detect the toner concentration using the magnetic permeability.

[0051] The regulating member 50 is positioned adjacent to the first developing roller 30 and is used to regulate the amount of developer supplied from the developer circulation unit 46 to the first developing roller 30. The regulating member 50 can be configured to regulate the amount of developer adsorbed onto the first developing roller 30 based, for example, on the gap between the surface of the first sleeve 33 of the first developing roller 30 and the end of the regulating member 50.

[0052] The developer in the developing container 60 is transported in a substantially horizontal direction while being agitated in the developer circulation unit 46, and then supplied to the first developing roller 30. From the first developing roller 30, it is transferred to the second developing roller 31 above it based on magnetic force. Next, it is transferred from the second developing roller 31 to the peeling roller 32 on the side of the second developing roller 31, again based on magnetic force. After that, it is peeled off the peeling roller 32 by a third magnet 38 embedded in the peeling roller 32, and then collected in the developer recovery unit 47 and introduced back into the developer circulation unit 46.

[0053] Furthermore, as described above, in this embodiment, a two-component development method is used as the development method, and the developer is a mixture of a negatively charged non-magnetic toner and a magnetic carrier. The non-magnetic toner becomes negatively charged through triboelectric charging with the magnetic carrier, and the magnetic carrier becomes positively charged. The non-magnetic toner is made by encapsulating colorants, wax components, etc., in a resin such as polyester or styrene acrylic, and then crushing or polymerizing it into a powder, to which fine powders such as titanium dioxide and silica are added to the surface. The magnetic carrier is made by coating the surface of a core consisting of resin particles mixed with ferrite particles or magnetic powder with resin. In this embodiment, the toner concentration in the developer in the initial state (weight ratio of toner contained in the developer) is 8%.

[0054] Furthermore, the magnetic carriers were 40 Am at an applied magnetic field of 1000 Oersted (79577 A / m). 2 / kg or more, 80Am 2 It is preferable to have a magnetization amount per unit weight of 63Am or less. Reducing the magnetization amount of the magnetic carrier has the effect of suppressing scavenging by the magnetic brush, but it becomes difficult for the magnetic carrier to adhere to the non-magnetic sleeve by the magnet inside the developing roller, which may cause image defects such as magnetic carrier adhesion to the photosensitive drum. Scavenging is a phenomenon in which the developed toner is scraped off by the magnetic carrier that has already been developed. Also, if the magnetization amount of the magnetic carrier is greater than the above range, image defects may occur due to the pressure of the magnetic brush as described above. In this embodiment, the magnetization amount per unit weight is 63Am 2 A magnetic carrier of / kg was used.

[0055] The magnetization of the magnetic carrier was measured using a BHV-30 oscillating magnetic field type automatic magnetic property recorder manufactured by RIKEN Electron Systems, Inc. The magnetic property value of the magnetic carrier was determined by creating an external magnetic field of 1000 oorsteds and measuring the magnetization strength at that time. The magnetic carrier was packed tightly into a cylindrical plastic container. The magnetization moment was measured in this state, and the actual weight with the sample inside was measured to determine the magnetization strength (Am). 2 Calculate the value of (kg).

[0056] The true specific gravity of the magnetic carrier is determined using a dry-type automatic density analyzer, AccuPic 1330, manufactured by Shimadzu Corporation. In this embodiment, the true specific gravity (density) is 4.6 g / cm³. 3 A magnetic carrier of the specified type was used. Furthermore, a magnetic carrier with a weight-average diameter of 35 μm (radius b = 17.5 μm) was employed.

[0057] Generally, two-component development systems using toner and carriers have the advantage of less stress on the toner than one-component development systems using a single-component developer, because they charge both the toner and carrier to a predetermined polarity by frictional contact. On the other hand, with prolonged use, the amount of dirt (spent) adhering to the carrier surface increases, and as a result, the ability to charge the toner gradually decreases. This results in problems such as fogging and toner scattering. Increasing the amount of carrier contained in the development unit could be considered to extend the lifespan of the two-component development unit, but this is undesirable because it would lead to a larger development unit.

[0058] To resolve the above-mentioned problems related to two-component developers, this embodiment employs an ACR (Auto Carrier Refresh) method. The ACR method is a method that suppresses the increase of degraded carriers by gradually supplying new developer from the developer storage unit 27Y into the developing device 1Y, and gradually discharging the developer with degraded charging performance from the discharge port (not shown) of the developing device 1Y. As a result, the degraded carriers in the developing device 1Y are gradually replaced with new carriers, making it possible to maintain the charging performance of the carriers in the developing device 1Y at a roughly constant level.

[0059] [About the magnetic poles of each magnet] Next, the magnetic pole configurations of the first magnet 36, second magnet 37, and third magnet 38, which are contained within the first developing roller 30, second developing roller 31, and peeling roller 32 shown in Figures 3, 4, and 5, will be described.

[0060] As shown in Figure 3, the first magnet 36 enclosed in the first developing roller 30 has a total of seven magnetic poles 101, 102, 103, 104, 105, 106, and 107. Of these, magnetic pole 107 is a transfer pole for transferring developer from the first developing roller 30 to the second developing roller 31. The magnetic poles 101 to 107 are arranged in numerical order in the rotational direction of the first sleeve 33. As described above, the solid lines of magnetic poles 101 to 107 shown in Figure 3 represent the position of the peak value (maximum value) of the magnitude of the normal component Br of the magnetic flux density of the first magnet 36 with respect to the surface of the first sleeve 33 (hereinafter sometimes simply referred to as "magnetic flux density Br" or "normal component Br"). The same applies to the magnetic poles 201 to 207 of the second magnet 37 shown in Figure 4, and the magnetic poles 301 to 305 of the third magnet 38 shown in Figure 5.

[0061] The magnetic pole 107, acting as a transfer pole, is used to transfer developer from the first sleeve 33 to the second sleeve 34 by a magnetic field generated in conjunction with the second magnet 37 of the second developing roller 31. Hereafter, the magnetic pole 107 may be referred to as the transfer pole 107. The magnetic pole 101 is an N pole and is used to attract the developer supplied from the developer supply screw 42 onto the first sleeve 33. The magnetic poles 102, 103, 104, 105, and 106 are S poles, N poles, S poles, N poles, and S poles, and are used to transport the developer attracted by the magnetic pole 101 upward as the first sleeve 33 rotates. The magnetic pole 107 is an N pole and, as described above, transfers the developer from the first sleeve 33 to the second sleeve 34 facing the first sleeve 33 by a magnetic field generated in conjunction with the magnetic pole 201 in the second magnet 37 enclosed in the second developing roller 31.

[0062] Furthermore, in this embodiment, a low-magnetic-force portion 110 is formed by a repulsive magnetic field generated in cooperation between a magnetic pole 101, which is positioned downstream of the transfer pole 107 with respect to the rotational direction of the first sleeve 33 and is the same pole as the transfer pole 107, and the transfer pole 107. This low-magnetic-force portion 110 facilitates the transfer of developer from the first sleeve 33 to the second sleeve 34. In this embodiment, the low-magnetic-force portion 110 has almost no magnetic force, but it may have a low magnetic force, for example, a magnetic pole with a magnetic force (normal component Br of magnetic flux density) of 5 mT or less. The same applies to the low-magnetic-force portion 210 of the second magnet 37 shown in Figure 4 and the low-magnetic-force portion 310 of the third magnet 38 shown in Figure 5.

[0063] As shown in Figure 4, the second magnet 37 enclosed in the second developing roller 31 has a total of seven magnetic poles 201, 202, 203, 204, 205, 206, and 207. Of these, magnetic pole 201 is the receiving pole for the second developing roller 31 to receive developer from the first developing roller 30. The magnetic poles 201 to 207 are arranged in numerical order in the rotational direction of the second sleeve 34.

[0064] The magnetic pole 201, acting as a receiving pole, is a magnetic pole that receives and adsorbs developer from the first sleeve 33 to the second sleeve 34 through a magnetic field generated in conjunction with the magnetic pole 107 of the first magnet 36 of the first developing roller 30. Hereafter, the magnetic pole 201 may be referred to as the receiving pole 201. The magnetic pole 207 is a magnetic pole that transfers developer from the second sleeve 34 to the third sleeve 35 through a magnetic field generated in conjunction with the third magnet 38 of the peeling roller 32.

[0065] Furthermore, the receiving pole 201 is an S pole, which is the opposite pole to the transfer pole 107, and is used to attract the developer from the first developing roller 30 (first sleeve 33) onto the second sleeve 34, as described above. The magnetic poles 202, 203, 204, 205, and 206 are N pole, S pole, N pole, S pole, and N pole, and are used to transport the developer attracted by the magnetic pole 201 upward as the second sleeve 34 rotates. The magnetic pole 207 is an S pole, and after the developer has passed through the developing area with the photosensitive drum 28Y corresponding to the magnetic pole (first magnetic pole) 203, it is transferred from the second sleeve 34 to the third sleeve 35 facing the second sleeve 34 by the magnetic field generated in conjunction with the magnetic pole 303 in the third magnet 38 enclosed in the peeling roller 32.

[0066] Furthermore, in this embodiment, a low-magnetic-force portion 210 is formed by a repulsive magnetic field generated in cooperation between a magnetic pole (second magnetic pole) 207, which is positioned upstream of the receiving pole 201 with respect to the rotational direction of the second sleeve 34 and is the same pole as the receiving pole (third magnetic pole) 201, and the receiving pole 201, resulting in a lower magnetic force than the magnetic pole 207. This low-magnetic-force portion 210 facilitates the transfer of developer from the first sleeve 33 to the second sleeve 34. In addition, the low-magnetic-force portion 210 prevents the developer from being attracted to the closest point between the first sleeve 33 and the second sleeve 34, thereby suppressing the pressure on the developer.

[0067] As shown in Figure 5, the third magnet 38 enclosed in the peeling roller 32 has multiple magnetic poles 301, 302, 303, 304, and 305. The magnetic poles 301 to 305 are arranged in numerical order in the rotational direction of the third sleeve 35.

[0068] The magnetic pole (fourth magnetic pole) 303 is an N pole opposite to the magnetic pole 207, and as described above, it is a magnetic pole for attracting the developer peeled off from the second sleeve 34 to the third sleeve 35, and hereafter, magnetic pole 303 may be referred to as the receiving pole 303. The magnetic poles 301, 302, and 304 are N pole, S pole, and S pole, and are used to transport the developer on the third sleeve 35 as the third sleeve 35 rotates. In particular, the magnetic pole (fifth magnetic pole) 304 is a magnetic pole for transporting the developer attracted by magnetic pole 303 downward as the third sleeve 35 rotates, and hereafter, magnetic pole 304 may be referred to as the transport pole 304. The magnetic pole (sixth magnetic pole) 305 is a north pole and, in conjunction with the same pole, the magnetic pole (seventh magnetic pole) 301, generates a repulsive magnetic field that detaches the developer adsorbed on the third sleeve 35 from the third sleeve 35. Hereafter, the magnetic pole 305 may be referred to as the detachment pole 305.

[0069] [Arrangement relationship between the second developing roller, peeling roller, and guide member] Next, the arrangement of the second developing roller 31, the peeling roller 32, and the guide member 45 in this embodiment will be explained using Figure 6. In this embodiment, as described above, the developer in the developing apparatus 1Y moves from the first sleeve 33 of the first developing roller 30 to the second sleeve 34 of the second developing roller 31, and then moves to the third sleeve 35 of the peeling roller 32. In recent years, as image forming apparatuses have become faster, the rotation speeds of the first developing roller 30, the second developing roller 31, and the peeling roller 32 have also increased. As a result, during the process of conveying the developer on each sleeve, when the magnetic particles formed on the sleeve between the poles of the magnets in each roller collapse, toner is more likely to detach from the carrier and scatter.

[0070] Furthermore, as described above, the high-speed rotation of the second developing roller 31 and the peeling roller 32 generates airflow, causing the detached toner to be scattered by the airflow. The airflow flows in the direction of rotation of each sleeve, and the airflow near the peeling roller 32 flows along the direction of rotation of the third sleeve 35. The scattered toner moves along this flow and collides with the guide member 45, accumulating from the tip position P1 of the guide member 45 to the closest position P2 between the peeling roller 32 and the guide member 45. Here, the tip position P1 is the end of the guide member 45 opposite to the developer recovery screw 44, in other words, the end on the second developing roller 31 side. The closest position P2 is the position of the guide member 45 that is closest to the peeling roller 32.

[0071] Furthermore, when airflow flows along the rotational direction of the third sleeve 35 near the peeling roller 32, the internal pressure of the developer recovery section 47 increases due to the taken-in airflow. This creates an airflow that escapes through the gap in the developer recovery section 47 to release the taken-in airflow. This airflow flows in the opposite direction to the rotational direction of the peeling roller 32, along the guide member 45 towards the tip of the guide member 45.

[0072] Due to this airflow, toner accumulated on the guide member 45 falls into the developing unit 1Y. This fallen toner then enters the developer in the developer circulation unit 46 before it is supplied to the first developing roller 30, or into the developer being transported by the first developing roller 30 or the second developing roller 31. When such toner mixes with the normal developer, it causes unevenness in the amount of toner contained in the developer. This results in unevenness in the amount of toner transferred to the photosensitive drum 28Y when developing the toner image on the photosensitive drum 28Y, and consequently, unevenness in density occurs in the final output image.

[0073] Therefore, in this embodiment, the magnetic tip on the peeling roller 32 is configured to contact the accumulated toner in a portion of the area between the tip position P1 of the guide member 45 and the closest position P2 between the peeling roller 32 and the guide member 45. The toner accumulated between the tip position P1 of the guide member 45 and the closest position P2 between the peeling roller 32 and the guide member 45 is then collected by the magnetic tip on the peeling roller 32.

[0074] Here, if the gap between the peeling roller 32 and the guide member 45 is narrowed at the nearest contact position P2 so that the magnetic tip on the peeling roller 32 is always in contact with the guide member 45, the gap between the peeling roller 32 and the guide member 45 will be sealed by the magnetic tip. As a result, the airflow near the peeling roller 32 that flows in the direction of rotation of the third sleeve 35 will be eliminated, making it easier for scattered toner to be scattered by the airflow that flows in the direction of rotation of the second sleeve 34. Then, the scattered toner will enter the developer in the developer circulation unit 46 before it is supplied to the first developing roller 30, or the developer being transported by the first developing roller 30 or the second developing roller 31. For this reason, it is undesirable to narrow the gap between the peeling roller 32 and the guide member 45 too much at the nearest contact position P2.

[0075] Therefore, it is preferable to form magnetic spikes on the peeling roller 32 (i.e., on the third sleeve 35) such that when scattered toner accumulates on the guide member 45, the magnetic spikes on the peeling roller 32 (i.e., on the third sleeve 35) come into contact with the accumulated toner. Here, the angle Φ of the magnetic spikes can be expressed as arctan(Br / Bθ), where Br is the normal component of the magnetic flux density B with respect to the third sleeve 35 and Bθ is the tangential component. That is, if Br is the normal component and Bθ is the tangential component of the magnetic flux density at any point on the third sleeve 35 (on the peeling sleeve), then the angle Φ of the magnetic spikes at this arbitrary point can be expressed as arctan(Br / Bθ).

[0076] Furthermore, in this embodiment, the angle Φ of the magnetic tip is defined as follows: Figures 7(a) and 7(b) are schematic diagrams illustrating the cases where the angle of the magnetic tip formed on the third sleeve 35 is negative and positive with respect to the rotation direction of the third sleeve 35. As shown in Figure 7(a), a negative (-) angle is defined as when the magnetic tip formed at an arbitrary point Q on the third sleeve 35 is inclined to tilt in the opposite direction to the rotation direction of the third sleeve 35 (arrow direction) with respect to a virtual line L passing through the arbitrary point Q and the rotation center R of the third sleeve 35. Also, as shown in Figure 7(b), a positive (+) angle is defined as when the magnetic tip formed at an arbitrary point Q on the third sleeve 35 is inclined to tilt in the direction of the rotation direction of the third sleeve 35 (arrow direction) with respect to a virtual line L passing through the arbitrary point Q and the rotation center R of the third sleeve 35.

[0077] In order to recover the scattered toner accumulated on the guide member 45 using the magnetic fin, the angle Φ of the magnetic fin formed on the peeling roller 32 in a portion of the area between the tip position P1 of the guide member 45 and the closest position P2 between the peeling roller 32 and the guide member 45 (i.e., between the intersection point P1' on the outer surface of the third sleeve 35, which is the point where a straight line passing through the end of the guide member 45 opposite to the developer recovery screw 44 and the rotation center R of the third sleeve 35 intersects the outer surface of the third sleeve 35, and the nearest contact point P2' on the outer surface of the third sleeve 35, which is the point on the outer surface of the third sleeve 35 that is closest to the guide member 45, in relation to the rotation direction of the third sleeve 35) should be 45° or more in absolute value. In other words, arctan(Br / Bθ)≧45° or arctan(Br / Bθ)≦-45° should be satisfied.

[0078] When the angle Φ of the magnetic tip is configured such that arctan(Br / Bθ)≧45°, as shown in Figure 7(b), the tip of the magnetic tip is tilted so that it is downstream of the direction in which the developer is transported by the third sleeve 35, relative to the surface side of the third sleeve 35 of the magnetic tip. The magnetic tip then strikes the toner on the guide member 45 in a manner that scrapes off the toner accumulated on the guide member 45. Therefore, when Φ≧45°, the toner accumulated on the guide member 45 can be efficiently collected. On the other hand, when the angle Φ of the magnetic tip is configured such that arctan(Br / Bθ)≦-45°, as shown in Figure 7(a), the tip of the magnetic tip is tilted so that it is upstream of the direction in which the developer is transported by the third sleeve 35, relative to the surface side of the third sleeve 35 of the magnetic tip (i.e., in the opposite direction to the above case). In this case, the magnetic tip is less likely to be disturbed when it collides with the toner accumulated on the guide member 45.

[0079] Furthermore, it is preferable that the angle Φ of the magnetic tip is 50° or more in absolute value in a portion of the area between the tip position P1 and the nearest point position P2. That is, it is preferable that arctan(Br / Bθ)≧50° or arctan(Br / Bθ)≦-50° be satisfied. Moreover, it is even more preferable that the angle Φ of the magnetic tip is 60° or more in absolute value in a portion of the area between the tip position P1 and the nearest point position P2. That is, it is even more preferable that arctan(Br / Bθ)≧60° or arctan(Br / Bθ)≦-60° be satisfied. The reason why a larger absolute value of the angle Φ of the magnetic tip is preferable is that it makes it easier to scrape off the toner accumulated on the guide member 45 with the magnetic tip.

[0080] The above-mentioned condition for the angle Φ of the magnetic tip can be met at any position between the tip position P1 and the nearest contact position P2, allowing the toner accumulated on the guide member 45 to be scraped off by the magnetic tip. However, it is preferable that the condition be met at the nearest contact position P2. At the nearest contact position P2 (i.e., the nearest contact point P2' on the outer surface of the third sleeve 35), it is preferable that the angle Φ of the magnetic tip is 45° or more in absolute value. Furthermore, it is even more preferable that the angle Φ of the magnetic tip is 50° or more in absolute value at the nearest contact position P2. Moreover, it is even more preferable that the angle Φ of the magnetic tip is 60° or more in absolute value at the nearest contact position P2.

[0081] On the other hand, at the tip position P1, if the angle Φ of the magnetic tip is on the positive side, there is a risk that the magnetic tip will be disturbed by the collision. For this reason, at the tip position P1 (i.e., the intersection point P1' on the outer surface of the third sleeve 35), it is preferable that the angle Φ of the magnetic tip is Φ≧-75°. In other words, if the magnetic tip is tilted to the negative side, it is less likely to collide with the tip position P1 of the guide member 45, and even if a collision does occur, the collision will be gentler, the magnetic tip will be less likely to be disturbed, and the toner on the guide member 45 can then be efficiently scraped off by the magnetic tip. For this reason, at the tip position P1, it is more preferable that the angle Φ of the magnetic tip is Φ≧-60°, and even more preferable that it is Φ≧-50°.

[0082] On the other hand, the narrower the gap between the peeling roller 32 and the guide member 45 at their closest proximity position P2, the easier it is for the magnetic tip to contact the toner on the guide member 45. However, if the gap is too narrow, it will be sealed by the magnetic tip, which is undesirable. Therefore, the gap (closest proximity distance) between the peeling roller 32 and the guide member 45 at their closest proximity position P2 is preferably 0.8 mm or more, more preferably 1.2 mm or more, and even more preferably 1.5 mm or more. However, if the gap between the peeling roller 32 and the guide member 45 at their closest proximity position P2 is too wide, there is a risk that the toner will fall off before the magnetic tip can contact the accumulated toner. For this reason, this gap is preferably 5 mm or less, more preferably 4 mm or less, and even more preferably 3 mm or less.

[0083] With this configuration, when toner scattered between the tip position P1 of the guide member 45 and the closest position P2 between the peeling roller 32 and the guide member 45 accumulates, the magnetic tip on the peeling roller 32 comes into contact with the toner. As a result, the toner that has accumulated before falling from the guide member 45 to the first developing roller 30 is collected by the magnetic tip on the peeling roller 32, thus suppressing the occurrence of unevenness in density on the image.

[0084] [Magnetic flux density distribution of the peeling roller] Next, the magnetic flux density distribution of the third magnet 38 for forming the magnetic ear on the peeling roller 32 as described above will be specifically explained using Comparative Example 1 and Examples 1 to 4 that satisfy the requirements of this embodiment. Note that the comparative example has the same configuration as the example except for the items described below.

[0085] Figures 8(a) and 8(b) show the magnetic flux density distribution of the third magnet 38 and the angle Φ of the magnetic tip for Comparative Example 1, and Figures 9(a) to 12(b) show the magnetic flux density distribution of the third magnet 38 and the angle Φ of the magnetic tip for Examples 1 to 4, respectively. In addition, Figures 8(a), 9(a), 10(a), 11(a), and 12(a) schematically show the distribution of the normal component Br of the magnetic flux density on the third sleeve 35 due to the third magnet 38 with a solid line, and the distribution of the tangential component Bθ of the magnetic flux density with a dashed line. Furthermore, Figures 8(b), 9(b), 10(b), 11(b), and 12(b) schematically show the angle Φ of the magnetic tip on the third sleeve 35 due to the third magnet 38 by plotting it in 1° increments. In Figures 8(a) to 812(b), the horizontal line H (Figure 6) passing through the rotation center R of the peeling roller 32 intersects the surface of the third sleeve 35, with the point on the second developing roller 31 side being defined as 0°, and the angles are indicated clockwise in Figure 6 (opposite to the direction of arrow U in Figure 6 (the rotation direction of the third sleeve 35)).

[0086] The normal component Br of the magnetic flux density more precisely refers to the component of magnetic flux density B normal to the third sleeve 35. The normal component Br of the magnetic flux density of each magnet was measured using a magnetic field measuring instrument (FWBELL "MS-9902") with a distance of approximately 100 μm between the probe, a component of the magnetic field measuring instrument, and the surface of the third sleeve 35. The tangential component Bθ of the magnetic flux density more precisely refers to the component of magnetic flux density B tangential to the third sleeve 35. The tangential component Bθ of the magnetic flux density can be calculated using the value of the normal component Br of the magnetic flux density from the following equation (1).

number

[0087] Table 1 also shows the absolute value of |Br|, the full width at half maximum, the peak angle of |Br|, and the inter-pole angle between the carrier pole 304 and the separation pole 305 of the third magnet 38. [Table 1]

[0088] Here, the full width at half maximum (FWHM) is the angle representing the width of the portion where the normal component Br of the magnetic flux density of each magnetic pole is half of its peak value. It is sometimes called the full width at half maximum to distinguish it from the half width at half maximum, but in this specification, the term "full width at half maximum" refers to the full width at half maximum. Furthermore, the peak angle of |Br| of the magnetic pole (the angle of the position where |Br| is at its maximum value (peak position)) is also expressed in a clockwise direction as shown in Figure 6, with the point on the second developing roller 31 side of the point where the horizontal line H passing through the rotation center R of the peeling roller 32 intersects the surface of the third sleeve 35 set to 0°.

[0089] Furthermore, the inter-pole angle is the angle between the peak positions of adjacent magnetic poles, and in Table 1, it is the angle between the peak position of the transport pole 304 and the peak position of the peeling pole 305. That is, the inter-pole angle is the angle between the line connecting the position on the third sleeve 35 where the absolute value |Br| of the normal component of the magnetic flux density of the transport pole 304 is maximum and the rotation center R of the third sleeve 35, and the line connecting the position on the third sleeve 35 where the absolute value |Br| of the normal component of the magnetic flux density of the peeling pole 305 is maximum and the rotation center R of the third sleeve 35. Note that the third magnet 38 of each peeling roller 32 in Comparative Example 1 and Examples 1 to 4 has the same configuration other than the distribution of magnetic flux density (for example, the number of magnetic poles and the order of their arrangement).

[0090] [Comparative Example 1] As shown in Figure 8(a), the magnetic flux density distribution of the peeling roller 32 in Comparative Example 1 has a gap between the transport pole 304 and the peeling pole 305 between the tip position P1 of the guide member 45 and the closest proximity position P2 between the guide member 45 and the peeling roller 32. Between the poles, the magnetic fins tilt until the angle Φ of the magnetic fins is almost 0°. As shown in Figure 7(b), the angle Φ of the magnetic fins on the peeling roller 32 in Comparative Example 1 is at most 41°, raising concerns about the ability of the magnetic fins to collect toner accumulated on the guide member 45 due to scattering.

[0091] [Example 1] On the other hand, the magnetic flux density distribution of the peeling roller 32 in Example 1, shown in Figure 9(a), shows that the peak of the normal component Br of the magnetic flux density of the transport pole 304 is at the closest proximity position P2 between the guide member 45 and the peeling roller 32. At the peak of the normal component Br, the angle of the magnetic tip is most likely to be steep, and as shown in Figure 9(b), the angle Φ of the magnetic tip on the peeling roller 32 in Example 1 is -49.7° at the tip position P1 of the guide member 45 (i.e., the intersection point P1' on the outer surface of the third sleeve 35). As a result, the tip of the magnetic tip collides with the toner accumulated on the guide member 45 at an angle opposite to the transport direction, allowing the magnetic tip to be recovered without disturbing it.

[0092] In order to allow the magnetic tip to enter the tip position P1 of the guide member 45 without disturbing it, as described above, it is preferable that the angle Φ of the magnetic tip satisfies Φ≧-75° at the tip position P1, more preferably Φ≧-60°, and even more preferably Φ≧-50°. The angle Φ of the magnetic tip at the tip position P1 in Example 1 satisfies this requirement.

[0093] Let's continue describing Example 1. After the magnetic tip enters the tip position P1 of the guide member 45 without disturbance, the angle of the magnetic tip gradually increases from the tip position P1 of the guide member 45 to the closest position P2 with respect to the peeling roller 32, and the angle Φ when passing the nearest contact position P2 (i.e., the nearest contact point P2' on the outer surface of the third sleeve 35) becomes 75.1°. As a result, the angle Φ of the magnetic tip at the nearest contact position P2 is tilted so that the tip of the magnetic tip faces downstream in the direction of developer transport by the third sleeve 35 relative to the toner accumulated on the guide member 45 (the state shown in Figure 7(b) above). Therefore, as described above, the toner accumulated on the guide member 45 can be recovered by scraping it off with the magnetic tip, and the toner recovery efficiency by the magnetic tip can be increased.

[0094] Therefore, in the configuration of Embodiment 1, the magnetic tip can be made to enter the tip position P1 of the guide member 45 without disturbing it, and the angle Φ of the magnetic tip is configured to be arctan(Br / Bθ)≧45° or arctan(Br / Bθ)≦-45° over the entire region from the tip position P1 of the guide member 45 to the closest position P2 with respect to the peeling roller 32 (i.e., the region from the intersection point P1' on the outer surface of the third sleeve 35 to the nearest contact point P2' with respect to the rotational direction of the third sleeve 35). As a result, the recovery efficiency of the toner deposited by the magnetic tip can be improved.

[0095] Furthermore, the nearest contact position P2 is the narrowest gap within the range from the tip position P1 of the guide member 45 to the closest contact position P2 with the peeling roller 32, so there is a risk of clogging due to accumulated toner. However, by using the configuration of Example 1, the magnetic tip can pass through the nearest contact position P2 at an angle that allows for high recovery by the magnetic tip, so that accumulated toner can be recovered without clogging at the nearest contact position P2.

[0096] As described above in Example 1, the above-mentioned effects can be obtained by positioning the peak position of the normal component Br of the magnetic flux density of the transport pole 304 at the closest proximity position P2 between the peeling roller 32 and the guide member 45, or in the vicinity of the nearest proximity position P2. For example, it is preferable that the peak position of the normal component Br of the magnetic flux density of the transport pole 304 be within ±10° of the nearest proximity position P2 with respect to the rotational direction of the third sleeve 35, that is, within a range of within 10° upstream or within a range of within 10° downstream when the nearest proximity position P2 is set to 0°.

[0097] [Example 2] The magnetic flux density distribution of the peeling roller 32 in Example 2, shown in Figure 10(a), shows a peak in the normal component Br of the magnetic flux density of the transport pole 304 at the tip position P1 of the guide member 45. The angle of the magnetic tip is most likely to be upright at the peak of the normal component Br, and as shown in Figure 10(b), the angle Φ of the magnetic tip on the peeling roller 32 in Example 2 is -89.2° at the tip position P1 of the guide member 45 (i.e., the intersection point P1' on the outer surface of the third sleeve 35). The magnetic tip then changes from a state where the angle of the magnetic tip is almost perpendicular to the toner accumulated on the guide member 45 to a state where the tip of the magnetic tip is tilted toward the downstream side in the transport direction of the developer by the third sleeve 35 as it approaches the closest proximity position P2 between the peeling roller 32 and the guide member 45. As a result, the toner accumulated on the guide member 45 can be recovered by scraping it off with the magnetic tip from the tip position P1 of the guide member 45, and the recovery efficiency of the toner on the guide member 45 by the magnetic tip can be increased.

[0098] To more reliably suppress developer scattering due to disturbance of the magnetic tip as it passes the tip position P1 of the guide member 45, it is preferable to change the angle of the magnetic tip to match the gap between the peeling roller 32 and the guide member 45 at the tip position P1 of the guide member 45. Specifically, when the gap between the peeling roller 32 and the guide member 45 is 0.8 mm or more and less than 1.2 mm, it is preferable to set the angle Φ of the magnetic tip to 45° ≤ arctan(Br / Bθ) ≤ 60°, and when the gap is 1.2 mm or more, it is preferable to set arctan(Br / Bθ) ≥ 60°. This allows the tip of the magnetic tip to not collide with the tip position P1 of the guide member 45, or to collide with it gently. Furthermore, it is possible to configure the magnetic tip to come into contact with the toner on the guide member 45 when scattered toner accumulates, without sealing the gap with the magnetic tip.

[0099] As described above in Example 2, the above-mentioned effects can be obtained by positioning the peak position of the normal component Br of the magnetic flux density of the transport pole 304 at the tip position P1, or in the vicinity of the tip position P1. For example, it is preferable that the peak position of the normal component Br of the magnetic flux density of the transport pole 304 be within ±10° of the tip position P1 with respect to the rotation direction of the third sleeve 35, that is, within a range of 10° upstream or within a range of 10° downstream when the tip position P1 is set to 0°.

[0100] [Example 3] The magnetic flux density distribution of the peeling roller 32 in Example 3, shown in Figure 11(a), is larger than that of Comparative Example 1, Example 1, and Example 2, in that the full width at half maximum (FWHM) of the peeling pole 305 extends further upstream in the transport direction of the third sleeve 35 beyond the nearest proximity position P2 between the guide member 45 and the peeling roller 32. Specifically, it is preferable that the FWHM of the peeling pole 305 includes a range of 29° or more upstream (upstream in the rotation direction) of the nearest proximity position P2 with respect to the rotation direction of the third sleeve 35. It is even more preferable that the FWHM of the peeling pole 305 includes a range of 31° or more upstream of the nearest proximity position P2 with respect to the rotation direction of the third sleeve 35. Furthermore, it is preferable that the FWHM of the peeling pole 305 includes a range of 33° or more upstream of the nearest proximity position P2 with respect to the rotation direction of the third sleeve 35.

[0101] In Example 3, even if the peak of the normal component Br of the magnetic flux density of the transport pole 304 is not positioned between the tip position P1 of the guide member 45 and the nearest proximity position P2 with respect to the peeling roller 32 (i.e., between the intersection point P1' on the outer surface of the third sleeve 35 and the nearest contact point P2' with respect to the rotational direction of the third sleeve 35), the full width at half maximum of the magnetic flux density of the peeling pole 305 is increased, thereby strengthening the normal component Br of the magnetic flux density of the peeling pole 305 at the nearest contact position P2, making it easier to set the angle of the magnetic tassels higher. As shown in Figure 11(b), the angle Φ of the magnetic tassels on the peeling roller 32 in Example 3 is 56.7° at the nearest proximity position P2 between the peeling roller 32 and the guide member 45 (i.e., the nearest contact point P2' on the outer surface of the third sleeve 35). The magnetic tassels are then tilted so that the tip of the magnetic tassels faces downstream in the direction of transport of the developer by the third sleeve 35 relative to the toner deposited on the guide member 45. Therefore, the toner accumulated on the guide member 45 can be collected by scraping it off with the magnetic tip.

[0102] [Example 4] The magnetic flux density distribution of the peeling roller 32 in Example 4, shown in Figure 12(a), is larger than that of Comparative Example 1 and Examples 1 to 3, because the inter-pole angle between the conveying pole 304 and the peeling pole 305 is larger. Narrowing the inter-pole angle increases the length of the magnetic head, but the magnetic head quickly collapses. Therefore, it is better to increase the inter-pole angle to prevent the magnetic head from collapsing.

[0103] In Example 4, even if the peak of the normal component Br of the magnetic flux density of the transport pole 304 is not positioned between the tip position P1 of the guide member 45 and the nearest proximity position P2 with respect to the peeling roller 32 (i.e., between the intersection point P1' on the outer surface of the third sleeve 35 and the nearest contact point P2' with respect to the rotational direction of the third sleeve 35), increasing the inter-pole angle between the transport pole 304 and the peeling pole 305 widens the effective angle between the normal component Br and the tangential component Bθ of the magnetic flux density of the transport pole 304, making it less likely for the angle of the magnetic fin to tilt. As shown in Figure 12(b), the angle of the magnetic fin on the peeling roller 32 in Example 4 is 67.8° at the tip position P1 of the guide member 45 (i.e., the intersection point P1' on the outer surface of the third sleeve 35). The magnetic fin is then tilted so that its tip faces downstream in the direction of transport of the developer by the third sleeve 35 relative to the toner deposited on the guide member 45. Therefore, the toner accumulated on the guide member 45 can be collected by scraping it off with the magnetic tip.

[0104] To prevent the magnetic tip from tipping over, it is preferable to set the inter-pole angle between the transport pole 304 and the peeling pole 305 to 20° or more, more preferably 30° or more, and even more preferably 40° or more. However, if the inter-pole angle is too large, the developer retention force will decrease and the developer may scatter, so it is preferable to set the inter-pole angle to 90° or less, more preferably 75° or less, and even more preferably 60° or less.

[0105] [Other embodiments] The present invention is not limited to the configuration of the embodiments described above. For example, the image forming apparatus 100 is not limited to an MFP, but may be a copier, printer, or facsimile machine. Furthermore, the configuration of the developer supply screw 42, the developer agitation screw 43, and the developer recovery screw 44 is not particularly limited as long as they can transport the developer, and for example, spiral blades or paddle-shaped blades can be applied.

[0106] Furthermore, although the above embodiment described the case where the first developing roller 30 is positioned upstream and the second developing roller 31 is positioned downstream with respect to the rotation direction of the photosensitive drum 28Y, the same effect can be obtained even when the second developing roller 31 is positioned upstream and the first developing roller 30 is positioned downstream.

[0107] Furthermore, although the above-described embodiment described a case where two developing rollers, a first developing roller 30 and a second developing roller 31, are arranged to develop the electrostatic latent image on the photosensitive drum, the present invention can also be applied to a configuration with only one developing roller. Also, although the above-described embodiment described a case where the third magnet 38 enclosed in the peeling roller 32 has five poles, the present invention can also be applied to a configuration where, for example, two poles are added between the receiving pole 303 and the transporting pole 304, resulting in a total of seven poles. In other words, the receiving pole 303 and the transporting pole 304 do not have to be adjacent to each other. [Explanation of symbols]

[0108] 1Y, 1M, 1C, 1K... Developing equipment 31...Second developing roller 32... Stripping roller 37. Second magnet 38. Third magnet 42. Developer supply screw 44. Developer recovery screw 45... Guide member 303... Receiving address 304... Transport pole 305... Stripping electrode

Claims

1. A first chamber containing the developer, including toner and carrier, A first transport screw is arranged in the first chamber and transports the developer contained in the first chamber, A second room separated from the first room by a partition wall, A second transport screw is located in the second chamber and transports the developer contained in the second chamber, A first rotating body to which the developer is supplied, the first rotating body carrying and transporting the developer to a developing position for developing an electrostatic latent image formed on an image carrier, A first magnet, which is fixedly and non-rotatingly arranged inside the first rotating body, having a first magnetic pole positioned opposite the image carrier at the development position, a second magnetic pole positioned downstream of the first magnetic pole with respect to the rotation direction of the first rotating body, and a third magnetic pole positioned adjacent to and downstream of the second magnetic pole with respect to the rotation direction of the first rotating body, and having the same pole as the second magnetic pole, A second rotating body is positioned opposite the first rotating body, and the developer is transferred from the first rotating body by the magnetic field generated by the first magnet, and the second rotating body carries and transports the developer in order to collect the developer in the second chamber after developing the electrostatic latent image, A second magnet, which is fixedly and non-rotatingly arranged inside the second rotating body, having a fourth magnetic pole opposite to the second magnetic pole, a fifth magnetic pole positioned downstream of the fourth magnetic pole with respect to the rotational direction of the second rotating body, a sixth magnetic pole positioned adjacent to the fifth magnetic pole downstream with respect to the rotational direction of the second rotating body and opposite to the fifth magnetic pole, and a seventh magnetic pole positioned adjacent to the sixth magnetic pole downstream with respect to the rotational direction of the second rotating body and having the same polarity as the sixth magnetic pole, A guide portion is positioned opposite the second rotating body and guides the developer to the second transport screw, Equipped with, The first rotating body and the second rotating body are rotating in the same direction at positions opposite each other. The magnetic field generated between the second and fourth magnetic poles causes the developer, after developing the electrostatic latent image, to be transferred from the first rotating body to the second rotating body. When Br is the normal component of the magnetic flux density at an arbitrary point on the outer surface of the second rotating body, Bθ is the tangential component of the magnetic flux density at the arbitrary point, and arctan(Br / Bθ) is the angle Φ of the magnetic tip at the arbitrary point, With respect to the rotation direction of the second rotating body, there is a point between the intersection point on the outer surface of the second rotating body, which is the point where a straight line passing through the end of the guide portion opposite to the second transport screw and the rotation center of the second rotating body intersects with the outer surface of the second rotating body, and the nearest point on the outer surface of the second rotating body, which is the point where the outer surface of the second rotating body is closest to the guide portion, where the absolute value of the angle Φ of the magnetic tip is 45° or more. A developing apparatus characterized by the following features.

2. With respect to the rotational direction of the second rotating body, between the intersection and the nearest contact point, there is a point where the absolute value of the angle Φ of the magnetic tip is 50° or more. The developing apparatus according to feature 1.

3. With respect to the rotational direction of the second rotating body, between the intersection and the nearest contact point, there is a point where the absolute value of the angle Φ of the magnetic tip is 60° or more. The developing apparatus according to feature 1.

4. With respect to the rotational direction of the second rotating body, the absolute value of the angle Φ of the magnetic tip is 45° or more over the entire region from the intersection to the nearest contact point. The developing apparatus according to feature 1.

5. The absolute value of the angle Φ of the magnetic tip at the nearest contact point is 45° or greater. The developing apparatus according to feature 1.

6. The absolute value of the angle Φ of the magnetic tip at the nearest contact point is 50° or more. The developing apparatus according to feature 1.

7. The absolute value of the angle Φ of the magnetic tip at the nearest contact point is 60° or more. The developing apparatus according to feature 1.

8. With respect to a virtual line passing through the arbitrary point and the center of rotation of the second rotating body, if the magnetic tip at the arbitrary point is tilted in the direction of rotation of the second rotating body, then the angle Φ of the magnetic tip is defined as positive. When the angle Φ of the magnetic tip is negative, in the case where the magnetic tip at the arbitrary point is tilted in the opposite direction to the rotation direction of the second rotating body with respect to a virtual line passing through the arbitrary point and the center of rotation of the second rotating body, The angle Φ of the magnetic tip at the aforementioned intersection satisfies Φ ≥ -75°. The developing apparatus according to feature 1.

9. With respect to a virtual line passing through the arbitrary point and the center of rotation of the second rotating body, if the magnetic tip at the arbitrary point is tilted in the direction of rotation of the second rotating body, then the angle Φ of the magnetic tip is defined as positive. When the angle Φ of the magnetic tip is negative, in the case where the magnetic tip at the arbitrary point is tilted in the opposite direction to the rotation direction of the second rotating body with respect to a virtual line passing through the arbitrary point and the center of rotation of the second rotating body, The angle Φ of the magnetic tip at the aforementioned intersection satisfies Φ ≥ -60°. The developing apparatus according to feature 1.

10. With respect to a virtual line passing through the arbitrary point and the center of rotation of the second rotating body, if the magnetic tip at the arbitrary point is tilted in the direction of rotation of the second rotating body, then the angle Φ of the magnetic tip is defined as positive. When the angle Φ of the magnetic tip is negative, in the case where the magnetic tip at the arbitrary point is tilted in the opposite direction to the rotation direction of the second rotating body with respect to a virtual line passing through the arbitrary point and the center of rotation of the second rotating body, The angle Φ of the magnetic tip at the aforementioned intersection satisfies Φ ≥ -50°. The developing apparatus according to feature 1.

11. The closest proximity distance between the second rotating body and the guide portion is 0.8 mm or more and 5 mm or less. The developing apparatus according to feature 1.

12. The closest proximity distance between the second rotating body and the guide portion is 1.2 mm or more and 4 mm or less. The developing apparatus according to feature 1.

13. The closest proximity distance between the second rotating body and the guide portion is 1.5 mm or more and 3 mm or less. The developing apparatus according to feature 1.

14. With respect to the rotational direction of the second rotating body, at locations between the intersection and the nearest contact point where the absolute value of the angle Φ of the magnetic tip is 45° or more, the magnetic tip is in contact with the guide portion. The developing apparatus according to feature 1.

15. The end of the guide portion opposite to the second transport screw is located vertically above the center of rotation of the first rotating body. The developing apparatus according to feature 1.

16. With respect to the rotation direction of the second rotating body, the angle from the point on the outer surface of the second rotating body where the absolute value of the normal component Br of the magnetic flux density of the fifth magnetic pole is maximum to the point on the outer surface of the second rotating body where the absolute value of the normal component Br of the magnetic flux density of the sixth magnetic pole is maximum is 20° or more. The developing apparatus according to feature 1.

17. With respect to the rotation direction of the second rotating body, the angle from the point on the outer surface of the second rotating body where the absolute value of the normal component Br of the magnetic flux density of the fifth magnetic pole is maximum to the point on the outer surface of the second rotating body where the absolute value of the normal component Br of the magnetic flux density of the sixth magnetic pole is maximum is 30° or more. The developing apparatus according to feature 1.

18. With respect to the rotation direction of the second rotating body, the angle from the point on the outer surface of the second rotating body where the absolute value of the normal component Br of the magnetic flux density of the fifth magnetic pole is maximum to the point on the outer surface of the second rotating body where the absolute value of the normal component Br of the magnetic flux density of the sixth magnetic pole is maximum is 40° or more. The developing apparatus according to feature 1.

19. The full width at half maximum of the normal component Br of the magnetic flux density of the sixth magnetic pole includes a range of 29° or more upstream of the nearest nearest point in the rotational direction of the second rotating body. The developing apparatus according to feature 1.

20. The full width at half maximum of the normal component Br of the magnetic flux density of the sixth magnetic pole includes a range of 31° or more upstream of the nearest nearest point in the rotational direction of the second rotating body. The developing apparatus according to feature 1.

21. The full width at half maximum of the normal component Br of the magnetic flux density of the sixth magnetic pole includes a range of 33° or more upstream of the nearest nearest point in the rotational direction of the second rotating body. The developing apparatus according to feature 1.

22. The center of rotation of the second body of revolution is located vertically above the center of rotation of the first body of revolution. The developing apparatus according to feature 1.

23. The rotation center of the second conveying screw is located vertically above the rotation center of the first conveying screw. The developing apparatus according to feature 1.

24. A third rotating body is positioned opposite the first rotating body and to which the developer contained in the first chamber is supplied, the third rotating body carrying and transporting the developer in order to develop the electrostatic latent image, A third magnet is fixedly positioned inside the third rotating body in a non-rotating manner, Furthermore, The first and third rotating bodies are rotating in opposite directions at positions opposite to each other. The first rotating body receives the developer from the third rotating body due to the magnetic field generated by the third magnet. The developing apparatus according to feature 1.

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