Developing device

Abstract

The suction port 74 of the duct 70 is positioned near the developing sleeve 11, providing a configuration that can suppress the suction of the carrier into the duct 70. [Solution] The line α connecting the tip 72c of the lower part 72 of the duct on the suction port 74 side and the rotation center O of the developing sleeve 11 intersects the surface of the developing sleeve 11 at point P1. P2 is the position on the developing sleeve 11 where the absolute value of the magnetic flux density in the normal direction of the first transport pole 103 is maximum, and P3 is the position where the absolute value of the magnetic flux density in the normal direction of the second transport pole 104 is maximum. In this case, P1 is located downstream of P2 and upstream of P3 with respect to the rotation direction of the developing sleeve 11. The range from P1 to P3 with respect to the rotation direction of the developing sleeve 11 is defined as R13. The tangential magnetic force Fθ acting on the carrier on the developing sleeve 11 is positive when the direction from P1 to P3 with respect to the rotation direction of the developing sleeve 11 is defined as Fθ≧0 throughout the entire range of R13.

Description

Technical Field

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

Background Art

[0002] Image forming apparatuses such as copiers, printers, facsimiles, and multifunctional devices include a developing device that attaches a developer to an electrostatic latent image formed on a photosensitive drum and develops it into a toner image. As the developer, a two-component developer containing toner and carrier is widely used. In the developing device, the amount of the developer carried on the developing sleeve is regulated by a regulating member, and then the developer conveyed to the developing area facing the photosensitive drum as the developing roller rotates is used to develop the electrostatic latent image on the photosensitive drum into a toner image in the developing area. Therefore, in the developing device, toner is likely to scatter as the developing sleeve rotates to convey the developer.

[0003] When toner scattering occurs, the scattered toner accumulates near the developing device and the photosensitive drum. Then, due to vibrations during image formation or maintenance, the accumulated toner may fall onto the developing sleeve or the photosensitive drum, which may cause image defects. Patent Document 1 discloses a developing device provided with a suction duct for sucking scattered toner in order to collect the scattered toner and discharge it outside the unit.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In order to effectively suck up scattered toner using a suction duct, it is desirable to place the air intake port near the developing sleeve. In this configuration, the air drawn into the duct near the air intake port reaches the surface of the developing sleeve and collides with the carrier supported on the surface of the developing sleeve. This collision of air can cause the carrier to detach from the developing sleeve and be sucked into the suction duct along with the scattered toner. When the carrier reaches the suction path of the suction duct, it accumulates within the suction path, narrowing the cross-sectional area of ​​the flow path, preventing the necessary airflow from being obtained, and as a result, the scattered toner cannot be adequately sucked up. Furthermore, if a filter for toner collection is installed in the suction duct path, the carrier can clog the filter, reducing the suction power and preventing adequate suction of scattered toner, which could lead to routine image defects. Since this duct suction path is difficult to clean, it could lead to routine image defects due to insufficient suction of scattered toner.

[0006] Furthermore, Patent Document 1 discloses a configuration in which a recess is formed on the lower surface of the suction duct to collect carriers that enter when scattered toner is sucked up by the suction duct, in order to prevent carriers that have entered into the main body, the carriers collected by the recess. However, especially under operating conditions such as high-speed operation of the image forming apparatus, the amount of carrier separation from the developing sleeve tends to increase, so the recess may become filled with carriers and may overflow from the recess. Then, the carriers that overflow from the recess may enter the suction path and accumulate, making it impossible to adequately suck up scattered toners, which could lead to a situation where image defects occur on a daily basis.

[0007] The present invention aims to provide a configuration in which the duct's suction port is positioned near the developing sleeve, thereby suppressing the suction of the carrier into the duct. [Means for solving the problem]

[0008] One aspect of the present invention comprises a developing container for containing a developer including toner and a carrier; a rotating developing sleeve; a developing magnet positioned non-rotating inside the developing sleeve and attracting the developer to the surface of the developing sleeve by magnetic force; a developing roller for developing an electrostatic latent image formed on a rotating image carrier with the developer; a layer thickness regulating member for regulating the layer thickness of the developer supported on the surface of the developing sleeve; and a duct for sucking up the developer around the developing sleeve, wherein the developing magnet is positioned where the developing sleeve is closest to the layer thickness regulating member. The duct has a first magnetic pole, a second magnetic pole positioned downstream of the first magnetic pole with respect to the rotational direction of the developing sleeve, a third magnetic pole positioned downstream of the second magnetic pole and adjacent to the second magnetic pole with respect to the rotational direction of the developing sleeve, and having a different polarity from the second magnetic pole, and a fourth magnetic pole positioned downstream of the third magnetic pole with respect to the rotational direction of the developing sleeve, and positioned where the developing sleeve is closest to the image carrier, and the duct is upstream of the position where the developing sleeve is closest to the image carrier with respect to the rotational direction of the developing sleeve, and is further upstream than the layer thickness regulating member The duct is located downstream and has a suction port for drawing in developer, and extends upstream from the suction port in the rotational direction of the developing sleeve. The duct has a first duct wall positioned to face a part of the developing roller with a gap between them, and a second duct wall positioned opposite the first duct wall and forming a space between it and the first duct wall for the developer drawn in from the suction port to flow. The point where the line connecting the tip of the first duct wall on the suction port side and the rotational center of the developing sleeve intersects the surface of the developing sleeve is defined as P1, and the normal direction of the second magnetic pole on the developing sleeve. Let P2 be the position where the absolute value of the magnetic flux density is maximum, and P3 be the position where the absolute value of the magnetic flux density in the direction normal to the third magnetic pole on the developing sleeve is maximum. Then, P1 is located downstream of P2 and upstream of P3 with respect to the rotation direction of the developing sleeve, and the range from P1 to P3 with respect to the rotation direction of the developing sleeve is defined as R13. If Fθ is the tangential magnetic force among the magnetic forces acting on the carrier on the developing sleeve, and Fθ is positive in the direction from P1 to P3 with respect to the rotation direction of the developing sleeve,This developing apparatus is characterized by satisfying Fθ≧0 throughout the entire R13 region.

[0009] One aspect of the present invention comprises a developing container for containing a developer including toner and a carrier; a rotating developing sleeve; a developing magnet positioned non-rotating inside the developing sleeve and attracting the developer to the surface of the developing sleeve by magnetic force; a developing roller for developing an electrostatic latent image formed on a rotating image carrier with the developer; a layer thickness regulating member for regulating the layer thickness of the developer supported on the surface of the developing sleeve; and a duct for sucking up the developer around the developing sleeve, wherein the developing magnet is positioned where the developing sleeve is closest to the layer thickness regulating member. The duct has a first magnetic pole, a second magnetic pole positioned downstream of the first magnetic pole with respect to the rotational direction of the developing sleeve, a third magnetic pole positioned downstream of the second magnetic pole and adjacent to the second magnetic pole with respect to the rotational direction of the developing sleeve, and having a different polarity from the second magnetic pole, and a fourth magnetic pole positioned downstream of the third magnetic pole with respect to the rotational direction of the developing sleeve, and positioned where the developing sleeve is closest to the image carrier, and the duct is upstream of the position where the developing sleeve is closest to the image carrier with respect to the rotational direction of the developing sleeve, and is further upstream than the layer thickness regulating member The duct is located downstream and has a suction port for drawing in developer, and extends upstream from the suction port in the rotational direction of the developing sleeve. The duct has a first duct wall positioned to face a part of the developing roller with a gap between them, and a second duct wall positioned opposite the first duct wall and forming a space between it and the first duct wall through which the developer drawn in from the suction port flows. The point where the line connecting the tip of the first duct wall on the suction port side and the rotational center of the developing sleeve intersects the surface of the developing sleeve is defined as P1, and the normal direction of the second magnetic pole on the developing sleeve If we define P2 as the position where the absolute value of the magnetic flux density in the direction is maximum, and P3 as the position on the developing sleeve where the absolute value of the magnetic flux density in the direction normal to the third magnetic pole is maximum, then P1 is located downstream of P2 and upstream of P3 with respect to the rotational direction of the developing sleeve, and if we define Bc as the maximum value of the absolute value of the magnetic flux density in the direction normal to the first magnetic pole, B1 as the maximum value of the absolute value of the magnetic flux density in the direction normal to the second magnetic pole, and B2 as the maximum value of the absolute value of the magnetic flux density in the direction normal to the third magnetic pole, then Bh = (Bc + B2) / 2,This developing apparatus satisfies the condition Bh≧B1>Bc, defines R13 as the range from P1 to P3 in the rotational direction of the developing sleeve, defines P4 as the point on the developing sleeve closest to P1 where the normal component of the magnetic flux density of the third magnetic pole takes half of its maximum value, and defines HW as the range from P4 to P3 in the rotational direction of the developing sleeve, and satisfies HW / R13≧1 / 4. [Effects of the Invention]

[0010] According to the present invention, by arranging the duct's suction port near the developing sleeve, the suction of the carrier into the duct can be suppressed. [Brief explanation of the drawing]

[0011] [Figure 1] A schematic cross-sectional view of the image forming apparatus according to the first embodiment. [Figure 2] A schematic cross-sectional view of the developing apparatus according to the first embodiment. [Figure 3] A diagram showing the magnetic pole arrangement of a developing roller according to the first embodiment. [Figure 4] An enlarged cross-sectional view of the developing roller and duct area according to the first embodiment. [Figure 5] A schematic diagram showing the relationship of forces acting on the carrier in the region TH in the rotational direction of the developing sleeve, relative to P1, illustrating (a) the case where the direction of the magnetic force Fθ acting on the carrier is the same as the suction direction of the duct, and (b) the case where the direction of the magnetic force Fθ acting on the carrier is opposite to the suction direction of the duct. [Figure 6] A graph showing the distribution of magnetic properties acting on the carrier on the developing sleeve according to Comparative Example 1. [Figure 7] A graph showing the distribution of magnetic properties acting on the carrier on the developing sleeve according to Comparative Example 2. [Figure 8] A graph showing the distribution of magnetic properties acting on the carrier on the developing sleeve according to Comparative Example 3. [Figure 9] Enlarged cross-sectional view of the developing roller and duct area according to Comparative Example 4. [Figure 10]Graph showing the distribution of magnetic properties acting on the carrier on the developing sleeve according to the first embodiment. [Figure 11] Graph showing the distribution of magnetic properties acting on the carrier on the developing sleeve according to another example of the first embodiment. [Figure 12] Graph showing the distribution of magnetic properties acting on the carrier on the developing sleeve according to the second embodiment. [Figure 13] Graph showing the distribution of magnetic properties acting on the carrier on the developing sleeve according to Comparative Example 5.

Mode for Carrying Out the Invention

[0012] <First Embodiment> The first embodiment will be described with reference to FIGS. 1 to 11. First, the schematic configuration of the image forming apparatus of the present embodiment will be described with reference to FIG. 1. Here, the X direction, Y direction, and Z direction that intersect perpendicularly to each other are defined. In the present embodiment, the X direction and Y direction are parallel to the horizontal plane, and the Z direction is perpendicular to the horizontal plane (vertical direction). Further, the Y direction is a direction along the rotation axis direction of the developing sleeve 11 described later.

[0013] [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 that respectively perform image forming processes of four-color toner images of yellow, magenta, cyan, and black in parallel. The image forming apparatus 100 of the present embodiment is connected to a document reading apparatus connected to the image forming apparatus main body (apparatus main body) or a host device such as a personal computer is communicably connected to the apparatus main body. Therefore, according to the image information from the host device, a four-color full-color image of yellow (Y), magenta (M), cyan (C), and black (K) can be formed on a recording material (recording paper, plastic sheet, cloth, etc.) using an electrophotographic method.

[0014] The image forming units PY, PM, PC, and PK of each color have a primary charger 22Y, 22M, 22C, 22K, a developing device 20Y, 20M, 20C, 20K, an exposure device 23Y, 23M, 23C, 23K, a photosensitive drum 21Y, 21M, 21C, 21K, and a cleaning device 25Y, 25M, 25C, 25K. Further, the image forming apparatus 100 has a transfer device 35 and a fixing device 40. Since the configurations of the image forming units PY, PM, PC, and PK of each color are the same, hereinafter, the image forming unit PY will be described as a representative.

[0015] The photosensitive drum 21Y as an image 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 21Y is set to 650 mm / s. The primary charger 22Y is composed of a corona discharge electrode disposed around the photosensitive drum 21Y, and charges the surface of the photosensitive drum 21Y with the generated ions.

[0016] The exposure device (light writing unit) 23Y incorporates a scanning optical device, and by exposing the charged photosensitive drum 21Y 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 20Y transfers the contained developer to the photosensitive drum 21Y to develop the electrostatic latent image formed on the photosensitive drum 21Y. The developer is formed by mixing a carrier and toner corresponding to each color, and the electrostatic latent image is visualized by the toner.

[0017] The transfer device 35 includes primary transfer rollers 30Y, 30M, 30C, 30K, an intermediate transfer belt 31, and a secondary transfer outer roller 33. The intermediate transfer belt 314 is wound around the primary transfer rollers 30Y, 30M, 30C, 30K, the secondary transfer inner roller 32, and multiple rollers, and is supported so as to be able to move. The primary transfer rollers 30Y, 30M, 30C, and 30K, which serve as primary transfer members, correspond to the colors Y (yellow), M (magenta), C (cyan), and K (black), respectively, from top to bottom in Figure 1. The secondary transfer outer roller 33 is positioned outside the intermediate transfer belt 31 and is configured so that the recording material can pass between it and the intermediate transfer belt 31 stretched over the secondary transfer inner roller 32.

[0018] The toner images of each color formed on the photosensitive drums 21Y, 21M, 21C, and 21K are sequentially transferred (primary transfer) onto the intermediate transfer belt 31 in the primary transfer section (primary transfer nip) T1 where the intermediate transfer belt 31 and the photosensitive drums 21Y, 21M, 21C, and 21K come into contact, by the action of a primary transfer bias applied to the primary transfer rollers 30Y, 30M, 30C, and 30K. For example, over time, when a four-color full-color image is created, the toner images are transferred onto the intermediate transfer belt 31 in order from the photosensitive drum 21Y, forming a color toner image with superimposed layers of yellow, magenta, cyan, and black.

[0019] Meanwhile, the recording material 50, housed in a recording material storage unit (e.g., a cassette) not shown, is transported to the transfer device 35 via transport rollers not shown. The recording material 50 is transported to the secondary transfer section (nip section) T2, where the intermediate transfer belt 31, stretched by the secondary transfer inner roller 32, and the secondary transfer outer roller 33, which acts as a secondary transfer member, come into contact, in synchronization with the toner image on the intermediate transfer belt 31. The toner image formed on the intermediate transfer belt 31 is then secondarily transferred onto the recording material 50 in the secondary transfer section T2 by the action of a secondary transfer bias applied to the secondary transfer outer roller 33. The recording material on which the toner image has been transferred is then subjected to pressure and heat in the fixing device 40. This melts the toner on the recording material, fixing the color image to the recording material. After that, the recording material 50 is discharged from the machine.

[0020] After the primary transfer process, any toner or other deposits remaining on the photosensitive drums 21Y, 21M, 21C, and 21K are recovered by the cleaning devices 25Y, 25M, 25C, and 25K. This prepares the photosensitive drums 21Y, 21M, 21C, and 21K for the next image forming process. In addition, any toner or other deposits remaining on the intermediate transfer belt 31 after the secondary transfer process are removed by the intermediate transfer belt cleaner 34.

[0021] Furthermore, the image forming apparatus 100 of this embodiment can also form monochrome or multicolor images using a color image forming unit for a desired monochrome color or several of the four colors, such as a monochrome black image.

[0022] The developer storage units 26Y, 26M, 26C, and 26K are provided in accordance with the developing units 20Y, 20M, 20C, and 20K, 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 26Y, 26M, 26C, and 26K are configured to transport (replenish) the developer to the developing unit 20Y, 20M, 20C, and 20K corresponding to the color of the developer stored in them.

[0023] 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 20Y, 20M, 20C, and 20K is 5-10%. Therefore, when toner is consumed during development in developing units 20Y, 20M, 20C, and 20K, developer containing an amount of toner corresponding to the consumption is replenished, and the toner weight ratio of the developer in developing units 20Y, 20M, 20C, and 20K is maintained at a constant level.

[0024] [Developing equipment] Next, developing units 20Y, 20M, 20C, and 20K will be described in detail using Figures 2 and 3. Since the configurations of developing units 20Y, 20M, 20C, and 20K are the same, developing unit 20Y will be described as a representative unit below. Figure 2 is a conceptual diagram illustrating the developing unit 20Y shown in Figure 1, and Figure 3 is a conceptual diagram illustrating the magnetic pole configuration of the developing magnet 12 located inside the developing unit 20Y.

[0025] As shown in Figure 2, the developing apparatus 20Y has a developing roller 10, a first screw 41, and a second screw 42, and these components are housed in a developing container 60. The developing container 60 contains a two-component developer containing a non-magnetic toner and a magnetic carrier. Specifically, the developing container 60 has a first transport chamber 401 and a second transport chamber 402, and the developer is housed in the first transport chamber 401 and the second transport chamber 402. The first screw 41 is located in the first transport chamber 401, and the second screw 42 is located in the second transport chamber 402.

[0026] The developing roller 10 is a rotating developer carrier, positioned adjacent to the photosensitive drum 21Y, such that its axis of rotation is approximately parallel to the axis of rotation of the photosensitive drum 21Y. The developing roller 10 includes a rotating developing sleeve 11 and a developing magnet (fixed magnet) 12 that is non-rotatingly positioned inside the developing sleeve 11 and attracts the developer to the surface of the developing sleeve 11 by magnetic force. The developing roller 10 then attracts (carries) the developer drawn up from the first screw 41 based on magnetic force and develops the electrostatic latent image formed on the rotating photosensitive drum 21Y (on the image carrier) with the developer.

[0027] Specifically, the developing sleeve 11 of the developing device 20Y is subjected to a developing bias, for example, a DC developing bias with the same polarity as the charging polarity of the primary charger 22Y, or a developing bias in which an AC voltage is superimposed with a DC voltage with the same polarity as the charging polarity of the primary charger 22Y. As a result, inverse developing is performed, in which toner charged with the same polarity as the charging polarity of the primary charger 22Y is deposited onto the electrostatic latent image formed on the photosensitive drum 21Y by the exposure device 23Y.

[0028] The developing sleeve 11 is a non-magnetic cylindrical member and is rotationally driven around the rotation axis 19. The rotation direction of the developing sleeve 11 is counterclockwise, as shown by arrow D11 in Figure 2, and in this embodiment, it is the same direction as the rotation direction of the photosensitive drum 21Y (direction of arrow D21). Therefore, when the developing sleeve 11 is in a position opposite to the photosensitive drum 21Y (opposing part), its surface rotates in the opposite direction to the surface of the photosensitive drum 21Y.

[0029] The developing magnet 12 is positioned inside the developing sleeve 11 and, as shown in Figure 3, has a plurality of fan-shaped magnetic poles 101 to 107 and a fan-shaped low-magnetic-force section 110. A space is provided between the inner circumference of the developing sleeve 11 and the outer circumference of the developing magnet 12 to allow the developing sleeve 11 to rotate. In this embodiment, the developing magnet 12 has a total of seven magnetic poles. The magnetic poles 101, 102, 103, 104, 105, 106 and 107 are positioned adjacent to each other with respect to the rotation direction of the developing sleeve 11, and are, in order, N pole, S pole, N pole, S pole, N pole, S pole, N pole. Each magnetic pole then transports the developer attracted by magnetic pole 101 as the developing sleeve 11 rotates, as will be described later.

[0030] 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 located downstream of the magnetic pole 107 with respect to the rotational direction of the developing sleeve 11 and is the same pole as the magnetic pole 107, and the magnetic pole 107. This low-magnetic-force portion 110 causes the developer to peel off from the developing sleeve 11. In this embodiment, the low-magnetic-force portion 110 has almost no magnetic force, but it may have a low magnetic force, for example, its magnetic force (the absolute value of the normal component Br of the magnetic flux density) may be 10 mT or less, or even 5 mT or less.

[0031] Magnetic pole 101 is a magnetic pole that draws up the developer from the first transport chamber 401, and may hereafter be referred to as the draw-up pole 101. Magnetic pole 102 as the first magnetic pole is a magnetic pole positioned closest to the regulating blade 43, which will be described later as a layer thickness regulating member, when the developing sleeve 11 is in the closest position, and may hereafter be referred to as the cut pole 102. Magnetic pole 103 as the second magnetic pole is a magnetic pole positioned downstream of the cut pole 102 with respect to the rotation direction of the developing sleeve 11, and may hereafter be referred to as the first transport pole 103. Magnetic pole 104 as the third magnetic pole is a magnetic pole positioned downstream of the first transport pole 103 with respect to the rotation direction of the developing sleeve 11, adjacent to the first transport pole 103, and is a magnetic pole of the opposite pole to the first transport pole 103, and may hereafter be referred to as the second transport pole 104. The fourth magnetic pole, pole 105, is located downstream of the second transport pole 104 with respect to the rotational direction of the developing sleeve 11, and is positioned where the developing sleeve 11 is closest to the photosensitive drum 21Y. Hereafter, it may be referred to as the developing pole 105. The magnetic pole 106 is located downstream of the developing pole 105 with respect to the rotational direction of the developing sleeve 11, and is hereafter referred to as the third transport pole 106. The magnetic pole 107 is located downstream of the third transport pole 106 with respect to the rotational direction of the developing sleeve 11, and is the same pole as the pump pole 101 located further downstream across the low-magnetic-force section 110. Hereafter, it may be referred to as the stripping pole 107. to have

[0032] The developer is lifted up by the first screw 41 as it is transported and supplied onto the developing sleeve 11. Since the developer contains a magnetic carrier, it is restrained by the pumping pole 101 of the developing magnet 12. Next, as the developing sleeve 11 rotates, the amount of developer (layer thickness) carried on the developing sleeve 11 is restricted to a predetermined amount by the regulating blade 43 as it passes through the cutting pole 102. The developer with restricted layer thickness passes through the first transport pole 103 and the second transport pole 104 and is transported to the developing pole 105 facing the photosensitive drum 21Y, where it develops the latent image formed on the photosensitive drum 21Y. After developing the latent image formed on the photosensitive drum 21Y, the developer on the developing sleeve 11 is transported by the rotational movement of the developing sleeve 11, passes through the third transport pole 106 downstream in the direction of rotation, is released from magnetic constraint force between the pumping pole 101 and the stripping pole 107 which have the same polarity, and is collected in the first transport chamber 401.

[0033] The first screw 41 and the second screw 42 are screw conveying members that transport the developer in one direction while agitating it, and are arranged so that their rotation axes are approximately parallel to each other. The rotation axes of each of these screws are also approximately parallel to the rotation axis of the developing roller 10.

[0034] As shown in Figure 2, the first screw 41 is located between the developing roller 10 and the second screw 42, and a partition wall 61 of the developing container 60 is positioned between the first screw 41 and the second screw 42. The partition wall 61 of the developing container 60 extends along the rotation axis direction of the first screw 41 and the second screw 42. The partition wall 61 is provided with a communication opening (not shown) that connects the first conveying chamber 401, through which the developer is conveyed by the first screw 41, and the second conveying chamber 402, through which the developer is conveyed by the second screw 42. The communication opening is an opening formed in the partition wall 61.

[0035] The developer transport directions of the first screw 41 and the second screw 42 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 chamber 401 where the first screw 41 is located, and the ending end and starting end of the second transport chamber 402 where the second screw 42 is located, are in communication through a communication opening formed in the partition wall 61. Therefore, the developer circulates in the rotational direction of the first screw 41 and the second screw 42, and within the developing container 60 in the Y direction, with a portion of it being supplied toward the developing roller 10.

[0036] The developer supply port 62 (see Figure 2) is located above the second screw 42 in the developing container 60 and is connected to the developer storage section 26Y (see Figure 1). The developer supply port 62 is configured to supply the developer stored in the bottles loaded in the developer storage section 26Y to the second transport chamber 402 where the second screw 42 is located. As described above, the toner weight ratio of the developer stored in the bottles of the developer storage section 26Y is greater than the toner weight ratio of the developer in the developing device 20Y. Therefore, by adjusting the amount of developer supplied to the second screw 42, it is possible to maintain a constant toner weight ratio of the developer in the developing device 20Y.

[0037] The toner concentration detection sensor 63 (see Figure 2) is positioned to detect the toner concentration in the developer in the developing container 60. In this embodiment, the toner concentration detection sensor 63 is located in the second transport chamber 402. 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 20Y and is used to control the replenishment of developer from the developer storage unit 26Y. For example, when it is detected that the toner concentration has fallen below a predetermined value, developer is replenished from the developer storage unit 26Y. Since the magnetic permeability of the developer changes more than the toner concentration, it is possible to detect the toner concentration using the magnetic permeability.

[0038] The regulating blade 43, acting as a layer thickness regulating member, is positioned adjacent to the developing roller 10 and is used to regulate the amount of developer supplied from the first transport chamber 401 to the developing roller 10. The regulating blade 43 is positioned so that its tip faces the surface of the developing sleeve 11 with a gap between them, and based on this gap, it regulates the amount of developer (layer thickness) carried on the surface of the developing sleeve 11.

[0039] 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 by 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%.

[0040] 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.

[0041] 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 26Y into the developing device 20Y, and gradually discharging the developer with degraded charging performance from the outlet (not shown) of the developing device 20Y. As a result, the degraded carriers in the developing device 20Y are gradually replaced with new carriers, making it possible to maintain the charging performance of the carriers in the developing device 20Y at a roughly constant level.

[0042] [duct] The developing unit 20Y is prone to toner scattering as the developer is transported by the rotating developing sleeve 11. When toner scattering occurs, the scattered toner accumulates near the developing unit 20Y and the photosensitive drum 21Y, and vibrations during image formation or maintenance may cause the accumulated toner to fall onto the developing sleeve 11 or the photosensitive drum 21Y. Therefore, the developing unit 20Y of this embodiment is equipped with a duct 70 for sucking up the scattered toner in order to collect it and discharge it outside the machine. In other words, the developing unit 20Y has a duct 70 for sucking up the developer around the developing sleeve.

[0043] As shown in Figure 2, the duct (suction duct) 70 is located on top of the developing container 60. The duct 70 has a suction port 74 for sucking up developer, located upstream of the position where the developing sleeve 11 is closest to the photosensitive drum 21Y with respect to the rotational direction of the developing sleeve 11, and downstream of the regulating blade 43, and extends upstream from the suction port 74 in the rotational direction of the developing sleeve 11. The duct 70 also has a lower duct 72 as a first duct wall and an upper duct 71 as a second duct wall. The lower duct 72 is positioned opposite a part of the developing roller 10 with a gap in between. The upper duct 71 is positioned opposite the lower duct 72 and forms a space between it and the lower duct 72 through which the developer sucked in from the suction port 74 flows.

[0044] The lower duct portion 72 is fixed to the developing container 60 so as to cover the first transport chamber 401, the developing roller 10, and the regulating blade 43 from above. The lower duct portion 72 has a shape formed by joining two flat plates that extend in the Y direction. The lower duct portion 72 also has a first lower portion 72a having an inclined surface that slopes upward from the end on the negative X side (photosensitive drum 21Y side) toward the positive X side (side away from the photosensitive drum 21Y), and a second lower portion 72b that slopes toward the positive X side from the portion that contacts the first lower portion 72a.

[0045] The upper duct portion 71 is positioned above the lower duct portion 72 so as to cover the entire lower duct portion 72 from above. The upper duct portion 71 has a shape formed by joining two flat plates that extend in the Y direction. The upper duct portion 71 has a first upper portion 71a having an inclined surface that slopes upward toward the positive side in the X direction from the end on the negative side in the X direction, and a second upper portion 71b that slopes toward the positive side in the X direction from the portion that contacts the first upper portion 71a.

[0046] The first lower portion 72a of the lower duct 72 and the first upper portion 71a of the upper duct 71 are arranged so that the upper surface of the first lower portion 72a and the lower surface of the first upper portion 71a face each other. Similarly, the second lower portion 72b of the lower duct 72 and the second upper portion 71b of the upper duct 71 are arranged so that the upper surface of the second lower portion 72b of the lower duct 72 and the lower surface of the second upper portion 71b of the upper duct 71 face each other. However, the second lower portion 72b and the second upper portion 71b are arranged so that they are further apart from each other as you move toward the positive X direction.

[0047] The upper part of the duct 71 is fixed to the developing container 60 such that its negative end in the X direction is positioned at a predetermined distance from the photosensitive drum 21Y. The negative end in the X direction of the upper part of the duct 71 faces the photosensitive drum 21Y at a position downstream of the photosensitive drum 21Y in the rotational direction of the photosensitive drum 21Y, rather than at a position where the photosensitive drum 21Y faces the developing roller 10.

[0048] The negative X-direction end of the lower duct 72 is located between the position where the developing roller 10 faces the regulating blade 43 and the position where the developing roller 10 faces the photosensitive drum 21Y, with respect to the rotational direction of the developing roller 10. The space between the negative X-direction end of the lower duct 72 and the upper duct 71 serves as the suction port 74 of the duct 70.

[0049] The duct 70 has an outlet 81 at its positive X-direction end and at its Y-direction end, which opens to the exhaust duct 82. The outlet 81 connects the space enclosed by the upper part 71 and lower part 72 of the duct with the internal space of the exhaust duct 82. The exhaust duct 82 has a cylindrical shape, and the end opposite to the end connected to the outlet 81 is open to the outside via a dust collection filter 84 and a fan 85.

[0050] As the fan 85, which acts as an airflow generator, rotates in the duct 70, an airflow path AP (see Figure 4) is created, through which air is drawn in from the gap 73 between the photosensitive drum 21Y and the upper part of the duct 71. The air drawn in from the gap 73 passes through the region TH enclosed by the developing sleeve 11, the photosensitive drum 21Y, and the upper part of the duct 71, passes through the suction port 74 formed by the upper part of the duct 71 and the lower part of the duct 72, and flows into the exhaust duct 82. This airflow path AP transports the toner scattered in region TH (hereinafter referred to as "scattered toner") to the exhaust duct 82.

[0051] The cause of this toner scattering is as follows: Deterioration of the developer due to being left in a high-temperature, high-humidity environment or due to use reduces the charge of the toner, and the electrostatic adhesion force with the carrier decreases. Then, the force that tries to separate the toner from the carrier due to the centrifugal force caused by the rotation of the developer sleeve 11 and the shock caused by the movement of the developer between the magnetic poles becomes greater than the electrostatic adhesion force between the carrier and the toner, and the toner may detach from the carrier, resulting in toner scattering.

[0052] One possible method to prevent this scattered toner from leaking outside the developing device is to seal the gap between the photosensitive drum and the developing device with a urethane sheet or the like. However, as mentioned above, if a sealing method that contacts the photosensitive drum 21Y is adopted to suppress scattered toner leakage in the region TH after toner has been developed on the photosensitive drum 21Y, the toner image formed on the photosensitive drum 21Y will be disturbed. For this reason, this method is not feasible. Therefore, in this embodiment, as mentioned above, scattered toner is sucked up by the duct 70.

[0053] [Suppression of carrier separation from developing sleeve] By the way, when scattered toner is sucked up by duct 70, the developer on the surface of the developing sleeve 11 is exposed to the air passage AP, so unintended carriers may be sucked up along with the toner. The reason for this is as follows:

[0054] As shown in Figure 4, let P1 be the point where the line α connecting the tip 72c of the suction port 74 side (suction port side) of the lower part 72 of the duct and the rotation center O of the developing sleeve 11 intersects the surface of the developing sleeve 11. Schematic diagrams showing the forces acting on the carriers on the developing sleeve 11 in region TH downstream of P1 in the rotational direction of the developing sleeve 11 are shown in Figures 5(a) and (b).

[0055] A magnetic force F acts on the carrier 200 on the developing sleeve 11 due to the interaction between the magnetic poles arranged on the developing magnet 12. The magnetic force F can be divided into a magnetic force Fr in the direction normal to the developing sleeve 11 and a magnetic force Fθ in the direction tangential to the developing sleeve 11 (direction of rotation D11). In the direction normal to the developing sleeve 11, the magnetic force Fr and the centrifugal force Fc due to the rotation of the developing sleeve 11 act on the carrier 200. At this time, if the coefficient of static friction between the carriers 200s themselves, or between the carrier 200 and the developing sleeve 11, is μ, then the maximum static friction force Fm = μ(Fr-Fc) in the direction of rotation of the developing sleeve 11 is obtained.

[0056] On the other hand, the force Fs acting on the carrier 200 in the rotational direction of the developing sleeve 11 is the resultant force of the wind load Fa acting due to wind pressure and the magnetic force Fθ, because the carrier 200 on the developing sleeve 11 in region TH is exposed to the airflow path AP to the duct 70. Here, if force Fs > maximum static friction force Fm, the carrier 200 may detach from the developing sleeve 11, and the detached carrier may be transported along the airflow path AP toward the exhaust duct 82 along with the scattered toner.

[0057] In other words, as shown in Figure 5(a), when the direction of the magnetic force Fθ is the same as the direction in which air flows in the flow path AP (attraction direction, direction of wind load Fa) (opposite to the rotation direction of the developing sleeve 11), the force Fs = wind load Fa + magnetic force Fθ. For this reason, the force Fs tends to become larger than the maximum static friction force Fm, and the carrier tends to separate from the developing sleeve 11.

[0058] Therefore, in this embodiment, as shown in Figure 5(b), the magnetic flux density of multiple magnetic poles fixed to the developing magnet 12 is configured such that in the region where the developer on the developing sleeve 11 is exposed to the airflow channel AP, the direction of the magnetic force Fθ is opposite to the direction of the wind load Fa (same direction as the rotation direction of the developing sleeve 11). Then, by setting the force Fs = wind load Fa - magnetic force Fθ and making the force Fs small compared to the maximum static friction force Fm, the carriers from the developing sleeve 11 are less likely to separate.

[0059] Here, we will explain the direction of the magnetic force Fθ acting on the carrier on the developing sleeve 11. The magnetic force Fθ changes depending on the position of the carrier on the developing sleeve 11 and the configuration of the magnetic flux density distribution of the magnetic poles fixedly positioned on the developing magnet 12. In other words, when a carrier 200 is present between the first transport pole 103 and the second transport pole 104, the direction of the magnetic force Fθ can be either in the same direction as or opposite to the rotation direction of the developing sleeve 11, depending on the influence of the magnetic flux density of the first transport pole 103 and the second transport pole 104 at the position where the carrier 200 is located.

[0060] The relationship between magnetic flux density and magnetic force Fθ will be explained using Figures 6 and 7, which are shown as Comparative Examples 1 and 2. The graph in Figure 6 shows the distribution of magnetic properties acting on the carrier on the developing sleeve 11 in the configuration of Comparative Example 1. In the configuration of Comparative Example 1, a developing magnet having multiple magnetic poles, including three magnetic poles 103P, 104P, and 105P, which have similar absolute values ​​of magnetic flux density |Br| in the normal direction, is arranged inside the developing sleeve 11 with a diameter of 25 mm. Magnetic poles 103P, 104P, and 105P correspond to the first transport pole 103, the second transport pole 104, and the developing pole 105 shown in Figure 3, respectively. Furthermore, magnetic poles 103P, 104P, and 105P are arranged so that adjacent magnetic poles are opposite poles.

[0061] Furthermore, in the graph in Figure 6, the horizontal axis represents the angle on the developing sleeve 11, and the vertical axis represents the absolute value of the magnetic flux density |Br| and the magnetic force Fθ. The angle is defined as 0 degrees at point Q (Figure 3), which is on the opposite side of the photosensitive drum 21Y (the side in the positive X-axis direction from the rotation center O of the developing sleeve 11) from the point where the horizontal line H (Figure 4), passing through the rotation center O of the developing sleeve 11, intersects the surface of the developing sleeve 11, with the rotation direction D11 of the developing sleeve 11 being considered positive. In the graph, the absolute value of the magnetic flux density |Br| is shown as a solid line, and the magnetic force Fθ acting on a carrier with a diameter of 35 μm and a relative permeability of 5, at a position 100 μm from the surface of the developing sleeve 11 (on the circumference of a circle with a diameter of 25.2 mm), is shown as a dashed line. The same conditions are used for the derivation in the graphs shown hereafter. The sign of the magnetic force Fθ indicates that a positive sign indicates a force in the same direction as the rotation direction D11 of the developing sleeve 11. Furthermore, the direction of the arrows indicated by the dashed lines on the graph represents the direction of the magnetic force Fθ.

[0062] The magnetic flux density and magnetic force (magnetic force) produced by the developing magnet will be explained. For the purposes of this explanation, Br, Bθ, Fr, and Fθ are defined as follows. Br: Magnetic flux density in the direction normal (perpendicular) to the outer surface (surface) of the developing sleeve 11 at a certain point. Bθ: Magnetic flux density in the tangential direction to the outer surface of the developing sleeve 11 at a certain point. Fr: Magnetic force acting in the direction normal to the outer surface of the developing sleeve 11 at a certain point (where the attractive direction (direction toward the developing sleeve 11) is negative). Fθ: Magnetic force acting tangentially to the outer surface of the developing sleeve 11 at a certain point (where the rotational direction of the developing sleeve 11 is considered positive).

[0063] Unless otherwise specified, Br, Bθ, Fr, and Fθ refer to the magnetic flux density or magnetic force at a certain point on the developing sleeve 11.

[0064] [Method for measuring magnetic force or magnetic flux density] Next, the method for measuring magnetic force in this embodiment will be described. The magnetic force described in this embodiment can be calculated by the calculation method described below. The magnetic force acting on the carrier can be obtained by the following equation (1). Here, μ0 is the permeability of vacuum, μ is the permeability of the carrier, b is the radius of the carrier, and B is the magnetic flux density.

number

number

[0065] From equation (2), if Br and Bθ are known, Fr and Fθ can be determined. Here, the magnetic flux density Br was measured using the FWBELL MS-9902 magnetic field meter (product name), with the distance between the probe, a component of the meter, and the surface of the developing sleeve set to approximately 100 μm.

[0066] Furthermore, Bθ can be determined as follows: Vector potential A at the measurement location of magnetic flux density Br. Z (R,θ) is calculated using the measured magnetic flux density Br.

number

number

number

[0067] By substituting the measured and calculated Br and Bθ into equation (1), Fr and Fθ can be derived. Furthermore, following the above equation, the magnetic flux density distribution that forms the Fr distribution required in this embodiment can be obtained.

[0068] Generally, magnetic force is directed towards areas with greater magnetic flux density. Therefore, if the absolute values ​​|Br| of the magnetic flux density in the normal direction of adjacent magnetic poles are similar, the magnetic force Fθ near a magnetic pole acts toward the position of the maximum value of the magnetic flux density in the normal direction that indicates the polarity of that magnetic pole. For example, a carrier near magnetic pole 103P, located near an angle of 120 degrees, will experience a magnetic force Fθ acting toward magnetic pole 103P. In other words, upstream of 120 degrees in the rotation direction D11, the magnetic force Fθ acts in the same direction as the rotation direction of the developing sleeve 11, while downstream of 120 degrees in the rotation direction D11, the magnetic force Fθ acts in the opposite direction to the rotation direction of the developing sleeve 11. The same magnetic force Fθ acts in the vicinity of magnetic poles 104P and 105P.

[0069] Furthermore, the direction of the magnetic force Fθ also changes near the point where the magnetic poles change to opposite poles. For example, there is a point P11 near 190 degrees where the polarity changes from magnetic pole 104P to magnetic pole 105P. In the vicinity of this polarity-changing point P11, a magnetic force Fθ acts toward magnetic pole 104P upstream of point P11 in the rotation direction D11, and a magnetic force Fθ acts toward magnetic pole 105P downstream of point P11 in the rotation direction D11. This is because the magnitude of the magnetic influence of magnetic pole 104P and magnetic pole 105P switches at point P11.

[0070] On the other hand, the graph in Figure 7 shows the distribution of magnetic properties acting on the carrier on the developing sleeve 11 in the configuration of Comparative Example 2. Similar to Figure 6, the graph shows the absolute value of magnetic flux density |Br| as a solid line and the magnetic force Fθ acting on the carrier as a dashed line. In the configuration of Comparative Example 2, similar to Comparative Example 1, a developing magnet having multiple poles, including three poles 103Q, 104Q, and 105Q with similar absolute values ​​of magnetic flux density |Br| in the normal direction, is arranged inside the developing sleeve 11 with a diameter of 25 mm. The magnetic poles 103Q, 104Q, and 105Q correspond to the first transport pole 103, the second transport pole 104, and the developing pole 105 shown in Figure 3, respectively. Furthermore, the magnetic poles 103Q, 104Q, and 105Q are arranged such that adjacent poles are opposite poles.

[0071] The graph in Figure 7 shows the case where the absolute value of the magnetic flux density normal to pole 105Q, |Br|, is greater than that of pole 104Q. As the absolute value of the magnetic flux density normal to pole 105Q, |Br|, increases, the magnetic influence of pole 105Q on carriers near pole 104Q also becomes stronger. In other words, when the absolute value of the magnetic flux density normal to pole 105Q, |Br|, becomes larger than that of pole 104Q, carriers present near pole 104Q are attracted to pole 105Q, and the magnetic force Fθ in the vicinity of pole 104Q always points in the direction of pole 105Q (the rotation direction D11 of the developing sleeve 11). Naturally, the direction of the magnetic force Fθ of carriers near point P11 also does not change and points in the direction of pole 105Q. Thus, the direction of the magnetic force Fθ changes depending on the relative magnitudes of adjacent magnetic poles.

[0072] Next, we will explain using the graph of the configuration of Comparative Example 3 shown in Figure 8. The graph in Figure 8 shows the distribution of magnetic properties acting on the carrier on the developing sleeve 11 in the configuration of Comparative Example 3. In the graph, as in Figure 6, the absolute value of the magnetic flux density |Br| is shown by a solid line, and the magnetic force Fθ acting on the carrier is shown by a dashed line. In the configuration of Comparative Example 3, as in Comparative Example 1, a developing magnet having multiple magnetic poles, including three magnetic poles 103R, 104R, and 105R, which have similar absolute values ​​of magnetic flux density |Br| in the normal direction, is arranged inside the developing sleeve 11 with a diameter of 25 mm. Magnetic poles 103R, 104R, and 105R correspond to the first transport pole 103, the second transport pole 104, and the developing pole 105 shown in Figure 3, respectively. Furthermore, magnetic poles 103R, 104R, and 105R are arranged so that adjacent magnetic poles are opposite poles.

[0073] In the graph of Figure 8, P1 is the point where the line α connecting the tip 72c on the suction port 74 side of the lower part of the duct 72 and the rotation center O of the developing sleeve 11 intersects the surface of the developing sleeve 11, as explained in Figure 4 above. P2 is the position on the developing sleeve 11 where the absolute value of the magnetic flux density in the direction normal to the magnetic pole 103R is maximum, and P3 is the position on the developing sleeve 11 where the absolute value of the magnetic flux density in the direction normal to the magnetic pole 104R is maximum. The sign of the magnetic force Fθ is considered positive in the direction from P1 to P3 (opposite to the direction in which air flows in the flow path AP). The subsequent diagrams of the magnetic property distribution have a similar configuration.

[0074] The absolute value of the magnetic flux density of the magnetic pole 105R, which is positioned opposite the photosensitive drum 21Y, is usually greater than the absolute value of the magnetic flux density of the surrounding magnetic poles. This is to increase the magnetic constraint force of the carrier on the developing sleeve 11 and suppress image defects caused by the carrier accidentally adhering to the photosensitive drum 21Y. In addition, by increasing the absolute value of the magnetic flux density of the magnetic pole 105R, the aim is to make the magnetic particles of the developer on the developing sleeve 11 denser and to form a toner image with less unevenness on the photosensitive drum 21Y.

[0075] Therefore, in Comparative Example 3, similar to Comparative Example 2 shown in Figure 7, the absolute value of the magnetic flux density of magnetic pole 105R is greater than that of magnetic pole 104R, and the magnetic influence of magnetic pole 105R extends to magnetic pole 104R. Furthermore, the magnetic force Fθ acting on the carrier is positive from the upstream side in the rotational direction of the developing sleeve 11, above P3, which is the position where the absolute value of the magnetic flux density in the direction normal to magnetic pole 104R is maximum, up to the position where the absolute value of the magnetic flux density in the direction normal to magnetic pole 105R is maximum.

[0076] However, with respect to the magnetic pole 103R, which is upstream of the magnetic pole 104R in the rotational direction of the developing sleeve 11, the magnetic influence of magnetic pole 105R is small. Therefore, a magnetic force Fθ acts on the carriers on the developing sleeve 11 in the direction toward magnetic pole 103R near P2, where the absolute value of the magnetic flux density in the direction normal to magnetic pole 103R is maximum. In other words, upstream of P2 in the rotational direction of the developing sleeve 11, the magnetic force Fθ is positive, and downstream of P2 in the rotational direction of the developing sleeve 11, the magnetic force Fθ is negative. For this reason, downstream of P2 in the rotational direction of the developing sleeve 11, in a part of region TH, the direction of the magnetic force Fθ may coincide with the direction of airflow in the flow path AP (direction of wind load Fa), and in Comparative Example 3, carrier separation from the developing sleeve 11 is likely.

[0077] In this embodiment as well, P2 is defined as the position on the developing sleeve 11 where the absolute value of the magnetic flux density in the normal direction of the first transport pole 103 is maximum, and P3 is defined as the position on the developing sleeve 11 where the absolute value of the magnetic flux density in the normal direction of the second transport pole 104 is maximum. In this case, P1 is located downstream of P2 and upstream of P3 with respect to the rotational direction of the developing sleeve 11. Furthermore, P1 is located in a range where the absolute value of the magnetic flux density in the normal direction of the first transport pole 103 is greater than 0 with respect to the rotational direction of the developing sleeve. That is, the position of P1 is downstream of P2 in the rotational direction of the developing sleeve 11 and is located in the range where the polarity of the magnetic flux density of the first transport pole 103 extends, i.e., in the graph of Figure 8, the absolute value of the magnetic flux density in the normal direction of the magnetic pole 103R is positive. This is because P1 is positioned such that the lower part 72 of the duct covers the vicinity of P2, preventing the region on the developing sleeve 11 where the magnetic force Fθ acting on the carrier near the first transport pole 103 is negative from being exposed to the flow path AP, thereby suppressing the separation of the carrier from the developing sleeve 11 near the first transport pole 103.

[0078] To further enhance the effect of suppressing carrier attraction to the duct 70, a configuration like that shown in Comparative Example 4 in Figure 9 can be considered. In Comparative Example 4, P1 is positioned near P2, where the absolute value of the magnetic flux density in the direction normal to the second transport pole 104 is maximum. However, because the lower part of the duct 72 penetrates deeply into the area where a lot of scattered toner is generated, scattered toner accumulates on the lower surface of the lower part of the duct 72 facing the developing sleeve 11, and accumulated toner TK is generated on this lower surface. The accumulated toner TK may fall onto the photosensitive drum 21Y due to vibration or its own weight. If the accumulated toner TK falls onto the photosensitive drum 21Y, the toner image developed on the photosensitive drum 21Y will be distorted, resulting in a dot-like defective image.

[0079] However, if the accumulated toner TK falls vertically due to its own weight or vibration and lands on the developing sleeve 11, the clump of accumulated toner TK may break apart on the developing sleeve 11, and a defective image may not occur. For this reason, if the vertical tangent of the developing sleeve 11 on the side closer to the photosensitive drum 21Y (the side with the suction port 74) is defined as the vertical line G, it is preferable that P1 be located further away from the photosensitive drum 21Y than the vertical line G in the horizontal direction. That is, it is preferable that P1 be located downstream of the position P2 where the absolute value of the magnetic flux density in the normal direction of the first transport pole 103 is maximum, and within the range up to the vertical line G. More preferably, P1 is located within the range where the polarity of the magnetic flux density of the first transport pole 103 extends, which reduces the risk of accumulated toner TK formation.

[0080] In the graph of Figure 8, P1 is positioned (approximately 130 degrees) downstream of the developing sleeve 11 in the rotational direction from position P2, where the absolute value of the magnetic flux density in the direction normal to magnetic pole 103R is maximum, to the vertical line G. Furthermore, the maximum value (absolute value) of the magnetic flux density in the direction normal to magnetic pole 103R was set to 87 mT, and the angle at this position P2 was set to 117 degrees. The maximum value (absolute value) of the magnetic flux density in the direction normal to magnetic pole 104R was set to 99 mT, and the angle at this position P3 was set to 181 degrees. The maximum value (absolute value) of the magnetic flux density in the direction normal to magnetic pole 105R was set to 171 mT, and the angle at this position was set to 211 degrees.

[0081] In this specification, "near the developing sleeve 11" or "on the developing sleeve 11" refers to a position 100 μm away from the outer surface of the developing sleeve 11. That is, the magnetic force acting on the carrier on the developing sleeve 11 is the same as the magnetic force acting on the carrier at a position 100 μm away from the outer surface of the developing sleeve 11.

[0082] In the graph of Figure 8, the region TH extends from P1 downstream of the developing sleeve 11 in the direction of rotation to the vicinity of magnetic pole 105R. This region is where the developer on the surface of the developing sleeve 11 is exposed to the airflow channel AP when the scattered toner is sucked up by the duct 70. In Comparative Example 3 shown in Figure 8, there is a region in this region TH where the magnetic force Fθ is negative (in the same direction as the airflow in channel AP) in the range of 130 to 150 degrees. This is because the magnetic flux density of magnetic pole 104R is small on the upstream side in the direction of rotation of the developing sleeve 11, and the magnetic influence of magnetic pole 103R is greater than the magnetic influence of magnetic pole 104R on the carriers near magnetic pole 103R. As a result, the region where the magnetic force Fθ is negative downstream of the developing sleeve 11 in the direction of rotation is wider than at P2. Therefore, in this region, as shown in Figure 5(a), the force Fs = wind load Fa + magnetic force Fθ, and the force Fs becomes larger than the maximum static friction force Fm, causing the carrier to separate from the developing sleeve 11 and making it easier for the carrier to be attracted to the duct 70.

[0083] Therefore, in this embodiment, as shown in Figure 10 which will be described later, the range from P1 to P3 with respect to the rotation direction of the developing sleeve 11 is defined as R13, and the tangential magnetic force among the magnetic forces acting on the carrier on the developing sleeve 11 is defined as Fθ, and when Fθ is positive in the direction from P1 to P3 with respect to the rotation direction of the developing sleeve, Fθ ≥ 0 is satisfied throughout the entire range R13. That is, the developing magnet 12 is configured such that the magnetic force Fθ is positive (opposite to the direction of air flowing through the flow path AP due to the attraction of the duct 70) throughout the entire range R13.

[0084] In this embodiment as well, similar to Comparative Examples 2 and 3 shown in Figures 7 and 8 above, the absolute value of the magnetic flux density of the developing electrode 105 is greater than the absolute value of the magnetic flux density of the second transport electrode 104. Therefore, the direction of the magnetic force Fθ in the range from position P3 included in region TH to the vicinity of the developing electrode 105 on the downstream side in the rotational direction of the developing sleeve 11 is necessarily in the same direction as the rotational direction of the developing sleeve 11 (opposite to the direction of the air flowing through the flow path AP due to the attraction of the duct 70). For this reason, in order to configure the system so that the magnetic force Fθ is positive throughout the entire region TH, it is sufficient to make the magnetic force Fθ positive within the range R13 from P1 to P3.

[0085] To achieve this, it is preferable that the circumferential length on the developing sleeve 11 in the HW range be 40% or more of the circumferential length on the developing sleeve 11 in the R13 range, where P4 is the point on the developing sleeve 11 closest to P1 among the points on the developing sleeve 11 where the normal component of the magnetic flux density of the second transport pole 104 takes half of its maximum value, and HW is defined as the range from P4 to P3 with respect to the rotational direction of the developing sleeve 11.

[0086] In other words, in this embodiment, when HW is defined as the range between points P4 and P3 on the surface of the developing sleeve 11 on the first transport pole 103 side, which is half of the maximum value of the magnetic flux density of the second transport pole 104, it is preferable that the range HW be half or more of the range R13. That is, the developing magnet 12 is configured such that HW / R13 ≥ 1 / 2.

[0087] As a result, the magnetic influence of the second transport pole 104 on the first transport pole 103 increases, and the magnetic force Fθ acting on the carrier on the developing sleeve 11 in the area where the polarity of the magnetic flux density of the first transport pole 103 extends, downstream of P1 in the rotational direction of the developing sleeve 11, can be made positive. Therefore, throughout the entire area R13 exposed to the flow path AP, the magnetic force Fθ is in the opposite direction to the direction of the air flowing through the flow path AP, so as shown in Figure 5(b), force Fs = wind load Fa - magnetic force Fθ, and the force Fs can be made smaller than the maximum static friction force Fm. This suppresses carrier separation from the developing sleeve 11 and suppresses carrier attraction to the duct 70. Note that by cutting out a part of the circumferential direction of the magnet forming the second transport pole 104 of the developing magnet 12, or by embedding a magnet with a different magnetic force in the cut-out part, an asymmetrical magnetic flux density like that of the second magnetic pole 104 can be formed.

[0088] Figure 10 shows the magnetic properties distribution of this embodiment. The graph in Figure 10 shows the distribution of magnetic properties acting on the carrier on the developing sleeve 11 in the configuration of this embodiment. In the graph, as in Figure 6, the absolute value of the magnetic flux density |Br| is shown by a solid line, and the magnetic force Fθ acting on the carrier is shown by a dashed line. In the graph in Figure 10, the angle at P1 is 130 degrees, the maximum value (absolute value) of the magnetic flux density in the normal direction of the first carrier pole 103 is 82 mT, the angle at this position P2 is 115 degrees, the maximum value (absolute value) of the magnetic flux density in the normal direction of the second carrier pole 104 is 105 mT, the angle at this position P3 is 178 degrees, the maximum value (absolute value) of the magnetic flux density in the normal direction of the developing pole 105 is 175 mT, and the angle at this position is 210 degrees.

[0089] Furthermore, the angle range of R13 is 48 degrees and the angle range of HW is 28 degrees, resulting in R13 / HW = 58%. In this embodiment, since the configuration satisfies R13 / HW ≥ 1 / 2, the magnetic force Fθ is positive throughout the entire range of R13. Therefore, the separation of carriers from the developing sleeve 11 is suppressed, and carrier attraction to the duct 70 can be suppressed.

[0090] As a comparison to Figure 10, which is a graph showing the configuration of this embodiment, we will explain using Figure 8, which is a graph showing the configuration of Comparative Example 3, and Figure 11, which is a graph showing the configuration of another example of this embodiment. In Figure 8, as described above, the angle of P1 is 130 degrees, the maximum value (absolute value) of the magnetic flux density in the normal direction of magnetic pole 103R is 87 mT, the angle at this position P2 is 117 degrees, the maximum value (absolute value) of the magnetic flux density in the normal direction of magnetic pole 104R is 99 mT, the angle at this position P3 is 181 degrees, the maximum value (absolute value) of the magnetic flux density in the normal direction of magnetic pole 105R is 171 mT, and the angle at this position is 211 degrees.

[0091] Furthermore, in the graph in Figure 8, the angle range of R13 is 51 degrees and the angle range of HW is 17 degrees, resulting in R13 / HW = 33%. Comparative Example 3 does not satisfy R13 / HW ≥ 1 / 2. Therefore, since the magnetic force Fθ is negative within the range R13, carrier separation from the developing sleeve 11 is likely to occur, and carrier attraction to the duct 70 cannot be sufficiently suppressed. In contrast, in this embodiment, the magnetic field characteristics of the developing magnet 12 are configured as shown in Figure 10, so unlike Comparative Example 3, it is possible to sufficiently suppress the occurrence of carrier attraction to the duct 70.

[0092] The graph in Figure 11 shows the distribution of magnetic properties acting on the carrier on the developing sleeve 11 in an alternative configuration of this embodiment. Similar to Figure 6, the graph shows the absolute value of the magnetic flux density |Br| as a solid line, and the magnetic force Fθ acting on the carrier as a dashed line. In the graph of Figure 11, the angle at P1 is 130 degrees, the maximum value (absolute value) of the magnetic flux density normal to the first carrier pole 103 is 82 mT, the angle at this position P2 is 116 degrees, the maximum value (absolute value) of the magnetic flux density normal to the second carrier pole 104 is 105 mT, the angle at this position P3 is 178 degrees, the maximum value (absolute value) of the magnetic flux density normal to the developing pole 105 is 175 mT, and the angle at this position is 210 degrees.

[0093] Furthermore, the angle range of R13 is 48 degrees and the angle range of HW is 20 degrees, resulting in R13 / HW = 42%. In this alternative embodiment, the configuration does not satisfy R13 / HW ≥ 1 / 2. However, since HW is a relatively large value, HW / R13 ≥ 40% is satisfied, and no region where the magnetic force Fθ is negative occurs within the range R13. Therefore, carrier separation from the developing sleeve 11 is less likely to occur, and carrier attraction to the duct 70 can be suppressed. However, in this alternative embodiment, a region where the magnetic force Fθ is zero exists near 170 degrees, and the force canceling out the wind load Fa is weak. For this reason, the effect of suppressing carrier attraction to the duct 70 by suppressing carrier separation from the developing sleeve 11 is weaker than in the configuration shown in Figure 10.

[0094] Next, Table 1 shows the results of an investigation into whether or not carrier attraction occurred to the duct 70 when R13 and HW were changed by altering the shape and arrangement of the magnets forming the first transport pole 103 and the second transport pole 104 of the developing magnet 12. [Table 1]

[0095] The presence or absence of carrier suction was evaluated as follows: Ten consecutive solid white images were formed on A3 paper, and the number of carriers adhering to the dust collection filter 84 was checked. If no carriers were found adhering to the dust collection filter 84 in the ten solid white images formed on A3 paper, 100 consecutive solid white images were formed on A3 paper, and the number of carriers adhering to the dust collection filter 84 was checked. The evaluation of carrier suction shown in Table 1 is as follows. ×: When 10 images are formed on A3 paper, more than 10 carriers adhere to the dust collection filter 84. △: When 10 images are formed on A3 paper, approximately one carrier adheres to the dust collection filter 84. ○: When 100 images are formed on A3 paper, approximately one carrier adheres to the dust collection filter 84.

[0096] If the sign of the minimum value of magnetic force Fθ in region TH is positive (Fθmin>0), it indicates that the direction of the magnetic force Fθ is opposite to the direction of the air flowing through channel AP throughout region TH. On the other hand, if the sign of the minimum value of magnetic force Fθ in range R13 is negative (Fθmin<0), it indicates that there is a region within range R13 where the direction of the magnetic force Fθ coincides with the direction of the air flowing through channel AP. Furthermore, if the evaluation level is "△" or higher, it is judged that the target results regarding carrier attraction suppression have been obtained.

[0097] As is clear from Table 1, in configurations 1 and 2, the ratio of range HW to range R13 is significantly less than 50%, resulting in a region within range R13 where the minimum value Fθmin is negative, and no inhibitory effect on carrier attraction was observed.

[0098] In configuration 3, the ratio of range HW to range R13 is 42%, which is close to 50% but not quite 50%, and since it is above 40%, the minimum value Fθmin is not negative and is zero (Fθmin=0). As a result, it shows a certain effect in suppressing carrier attraction. However, from the perspective of high productivity of the image forming apparatus, if the speed of the developing sleeve 11 increases, the centrifugal force acting on the carrier on the developing sleeve 11 increases, and the maximum static friction force Fm decreases, which may cause the carrier to detach from the developing sleeve 11 more easily. Therefore, in order to suppress carrier attraction into the duct 70, the minimum value Fθmin can be zero, but in order to achieve a more effective result, it is preferable that the minimum value Fθmin is greater than zero.

[0099] Configurations 4, 5, and 6 are configurations in which the ratio of range HW to range R13 is greater than 50%. Because the magnetic influence of the second transport pole 104 extends to the first transport pole 103, the magnetic force Fθ is positive throughout the entire range R13. As a result, the magnetic force Fθ acts to counteract the wind load Fa acting on the carrier on the developing sleeve 11 due to the airflow path AP generated by the suction of scattered toner by the duct 70, so the external force Fs(Fa-Fθ) relative to the maximum static friction force of the carrier becomes small. Therefore, the separation of the carrier from the developing sleeve 11 can be suppressed. As a result, in configurations 4, 5, and 6, carrier suction into the duct 70 was suppressed.

[0100] As described above, according to this embodiment, the separation of carriers from the surface of the developing sleeve 11, which occurred when the suction port 74 of the duct 70 was located near the developing sleeve 11 in order to effectively suck up scattered toner, can be suppressed. That is, in the developing apparatus 20Y of this embodiment, Fθ≧0 is satisfied over the entire range R13 from P1 to P3. Preferably, the magnetic flux density of the multiple magnetic poles fixed to the developing magnet 12 is configured to satisfy R13 / HW≧1 / 2 so that the direction of the magnetic force Fθ is opposite to the direction of the airflow path AP due to the suction of the duct 70, i.e., Fθ>0. Then, the magnetic force Fθ acts on the carriers on the developing sleeve 11 in a way that cancels out the wind load Fa due to the airflow path AP, and the force Fs, which is the resultant force of the wind load Fa and the magnetic force Fθ, becomes smaller than the maximum static friction force Fm of the carrier, thereby suppressing the separation of carriers from the developing sleeve 11 and suppressing the attraction of carriers to the duct 70.

[0101] <Second Embodiment> A second embodiment will be described with reference to Figures 12 and 13. In this embodiment, the configuration of the magnetic flux density of the multiple magnetic poles fixedly arranged on the developing magnet 12 differs from that of the first embodiment. Since the other configurations and operations are the same as those of the first embodiment described above, the same reference numerals are used for similar components, and their descriptions and illustrations are omitted or simplified. The following description will focus on the differences from the first embodiment.

[0102] As explained in the first embodiment described above, the magnetic influence of adjacent magnetic poles depends on the relative magnitudes of their magnetic flux densities. Therefore, in order to make the direction of the magnetic force Fθ across the entire range R13 opposite to the direction of the airflow path AP by the duct 70 (same direction as the rotation direction D11 of the developing sleeve 11), it is effective to make the maximum absolute value of the magnetic flux density normal to the first transport pole 103 relatively smaller than the maximum absolute value of the magnetic flux density normal to the second transport pole 104. However, if the maximum absolute value of the magnetic flux density normal to the first transport pole 103 is made smaller than the maximum absolute value of the magnetic flux density normal to the cut pole 102, the magnetic force Fθ in the direction from the cut pole 102 to the first transport pole 103 will decrease, resulting in uneven developer coating on the developing sleeve 11 by the regulating blade 43. Therefore, the maximum absolute value of the magnetic flux density in the normal direction of the first carrier pole 103 is set to be greater than the maximum absolute value of the magnetic flux density in the normal direction of the cut-off pole 102.

[0103] In this embodiment, if we define Bc as the maximum absolute value of the magnetic flux density normal to the cut pole 102, B1 as the maximum absolute value of the magnetic flux density normal to the first transport pole 103, and B2 as the maximum absolute value of the magnetic flux density normal to the second transport pole 104, and define Bh = (Bc + B2) / 2 as the average of Bc and B2, then we satisfy Bh ≥ B1 > Bc, and the configuration HW / R13 ≥ 1 / 4. This makes it possible to increase the magnetic influence of the second transport pole 104 on the carriers on the developing sleeve 11 near the first transport pole 103. As a result, the sign of the magnetic force Fθ can be made positive throughout the entire range R13. In other words, since the direction of the magnetic force Fθ is opposite to the direction of the airflow path AP by the duct 70, carrier separation from the developing sleeve 11 can be suppressed in the range R13, and carrier attraction to the duct 70 can be suppressed.

[0104] The graph in Figure 12 shows the distribution of magnetic properties acting on the carrier on the developing sleeve 11 in the configuration of this embodiment. Similar to Figure 6, the graph shows the absolute value of the magnetic flux density |Br| as a solid line and the magnetic force Fθ acting on the carrier as a dashed line. In the graph of Figure 12, the angle of P1 is set to 130 degrees, Bc to 45 mT, the angle at the position of the maximum absolute value of the magnetic flux density in the normal direction of the cut pole 102 is set to 59 degrees, B2 to 105 mT, and the angle of the position P3 at the maximum absolute value of the magnetic flux density in the normal direction of the second carrier pole 104 is set to 178 degrees. In this embodiment, since Bh = 75 mT, the magnetic properties shown are set to satisfy Bh ≥ B1, with B1 set to 52 mT and the angle of the position P2 at the maximum absolute value of the magnetic flux density in the normal direction of the first carrier pole 103 set to 115 degrees. Furthermore, the maximum absolute value of the magnetic flux density in the normal direction of the developing electrode 105 was set to 175 mT, and the angle at that position was set to 210 degrees.

[0105] Furthermore, in this embodiment, the angle range of R13 is 48 degrees and the angle range of HW is 16 degrees, so HW / R13 = 33%, satisfying HW / R13 ≥ 1 / 4. With this configuration, it was confirmed that the magnetic force Fθ is positive across the entire range of R13. As a result, the separation of carriers from the developing sleeve 11 was suppressed, and the attraction of carriers to the duct 70 was suppressed.

[0106] As a comparison to Figure 12, which is a graph showing the configuration of this embodiment, we will use Figure 13, which is a graph showing the configuration of Comparative Example 5, to explain the configuration. The graph in Figure 13 shows the distribution of magnetic properties acting on the carrier on the developing sleeve 11 in the configuration of Comparative Example 5. Also, in the graph, as in Figure 6, the absolute value of the magnetic flux density |Br| is shown by a solid line, and the magnetic force Fθ acting on the carrier is shown by a dashed line. In the graph of Figure 13, the angle of P1 is set to 130 degrees, Bc to 45 mT, the angle at the position of the maximum value of the absolute value of the magnetic flux density in the normal direction of the cut pole 102 is set to 59 degrees, B2 to 105 mT, and the angle of the position P3, where the absolute value of the magnetic flux density in the normal direction of the second carrier pole 104 is set to 178 degrees.

[0107] In Comparative Example 5, Bh = 75 mT, but by setting B1 to 100 mT and the angle of position P2, where the absolute value of the magnetic flux density in the normal direction of the first transport pole 103 is maximum, to 118 degrees, the magnetic properties show that Bh ≥ B1. In Comparative Example 5, the maximum absolute value of the magnetic flux density in the normal direction of the developing pole 105 was set to 175 mT, and the angle of that position was set to 210 degrees. Also, in Comparative Example 5, the angle range of R13 was 48 degrees and the angle range of HW was 16 degrees, resulting in HW / R13 = 33%.

[0108] In the configuration of Comparative Example 5, the magnetic influence of the second transport pole 104 on the first transport pole 103 is reduced, resulting in a negative magnetic force Fθ in the range affected by the polarity of the magnetic flux density of the first transport pole 103. As a result, a magnetic force Fθ acts on the carrier on the developing sleeve 11 in the same direction as the wind load Fa, increasing the force Fs (Fs = Fa + Fθ) that opposes the maximum static friction force Fm of the carrier. Consequently, carrier separation from the developing sleeve 11 cannot be sufficiently suppressed, and carrier attraction to the duct 70 cannot be prevented.

[0109] As described above, in the configuration of Figure 12 of this embodiment and the configuration of Figure 13 of Comparative Example 5, R13 / HW is 33% in both cases. However, the magnetic influence of the second carrier pole 104 on the first carrier pole 103 differs depending on whether the maximum value B1 of the magnetic flux density in the normal direction of the first carrier pole 103 satisfies Bh≧B1>Bc, and therefore the direction of the magnetic force Fθ in the range R13 is different.

[0110] Next, Table 2 shows the results of an investigation into whether or not carrier attraction occurred to the duct 70 when Bc, B1, B2, R13, and HW were changed by altering the shape and arrangement of the magnets forming the cut pole 102, the first transport pole 103, and the second transport pole 104 of the developing magnet 12. [Table 2]

[0111] The evaluation of whether or not carrier attraction occurs is the same as the method described in the first embodiment. Furthermore, if the minimum value of magnetic force Fθ in range R13, Fθmin, is positive (Fθmin>0), it indicates that the direction of magnetic force Fθ is opposite to the direction of air flowing through channel AP throughout range R13. On the other hand, if the minimum value of magnetic force Fθ, Fθmin, is negative (Fθmin<0) within range R13, it indicates that there is a region within range R13 where the direction of magnetic force Fθ coincides with the direction of air flowing through channel AP. In addition, if the evaluation level is "△" or higher, it is judged that the target result regarding carrier attraction suppression has been obtained.

[0112] As is clear from Table 2, configurations 11 to 15 were configurations that had a low effect in suppressing carrier attraction to the duct 70. In configurations 11, 12, and 13, the width of the developing sleeve 11 on the upstream side in the rotational direction of half of the maximum value B2 of the magnetic flux density normal to the second transport pole 104 was narrow, and the magnetic influence on the first transport pole 103 was small, resulting in a region where the minimum value Fθmin was negative. In configurations 14 and 15, the maximum value B1 of the magnetic flux density normal to the first transport pole 103 was relatively large compared to the maximum value B2 of the magnetic flux density normal to the second transport pole 104, resulting in a small magnetic influence of the second transport pole 104 on the first transport pole 103, and a region where the minimum value Fθmin was negative. Thus, in configurations 11 to 15, a magnetic force Fθ acts on the carrier on the developing sleeve 11 in the same direction as the wind load Fa within the range R13. As a result, the force Fs (Fs = Fa + Fθ) that opposes the maximum static friction force Fm of the carrier becomes large, and the separation of the carrier from the developing sleeve 11 cannot be sufficiently suppressed, and the attraction of the carrier to the duct 70 cannot be suppressed.

[0113] Configurations 16 to 21 are configured such that the minimum value of the magnetic force Fθ in the range R13, Fθmin, is positive. Therefore, since a magnetic force Fθ acts on the carrier in the opposite direction to the wind load Fa throughout the entire range R13, the force Fs (Fs = Fa - Fθ) opposing the maximum static friction force Fm of the carrier becomes smaller, which suppresses carrier separation from the developing sleeve 11 and suppresses carrier attraction to the duct 70.

[0114] Configurations 16 and 17 have the same magnitude of B1 relative to Bh, but different ratios of HW to R13. Since both satisfy Bh≧B1 and HW / R13≧1 / 4, the magnetic influence of the second carrier pole 104 on the first carrier pole 103 is large, and the minimum value Fθmin is positive across the entire range R13. Looking at configuration 12 in comparison to configurations 16 and 17, the magnitude of B1 relative to Bh is the same for configurations 15 and 16. However, configuration 12 does not satisfy HW / R13≧1 / 4. Therefore, in configuration 12, the magnetic influence of the second carrier pole 104 on the first carrier pole 103 is small, and a region where the minimum value Fθmin is negative occurs.

[0115] Similarly, looking at configurations 19 and 20, the magnitude of B1 relative to Bh is the same, but the ratio of HW to R13 is different, and both satisfy Bh≧B1 and HW / R13≧1 / 4. For this reason, in configurations 19 and 20, the magnetic influence of the second carrier pole 104 on the first carrier pole 103 is large, and the minimum value Fθmin is positive throughout the entire range R13. Looking at configuration 11 as a comparison between configurations 19 and 20, the magnitude of B1 relative to Bh is roughly the same in configuration 11 as in configurations 19 and 20, but configuration 11 does not satisfy HW / R13≧1 / 4. For this reason, in configuration 11, the magnetic influence of the second carrier pole 104 on the first carrier pole 103 is small, and a region where the minimum value Fθmin is negative occurs.

[0116] Comparing configuration 20 and configuration 21, the ratio of HW to R13 is the same in both, satisfying HW / R13 ≥ 1 / 4. Although the magnitude of B1 relative to Bh is different, both configurations satisfy Bh ≥ B1. For this reason, in configurations 20 and 21, the magnetic influence of the second carrier pole 104 is large on the first carrier pole 103, and the minimum value Fθmin is positive across the entire range R13.

[0117] Looking at configuration 13 in comparison to configuration 21, the magnitude of B1 relative to Bh is Bh=B1 in both configurations, satisfying Bh≧B1. However, configuration 13 does not satisfy the condition HW / R13≧1 / 4. As a result, in configuration 13, the magnetic influence of the second carrier pole 104 on the first carrier pole 103 is reduced, and a region occurs in the range R13 where the minimum value Fθmin is negative. In other words, even if Bh≧B1 is satisfied, the sign of the minimum value Fθmin in the range R13 changes depending on whether HW / R13≧1 / 4 is satisfied or not.

[0118] As described above, according to this embodiment, the separation of carriers from the surface of the developing sleeve 11, which occurred when the suction port 74 of the duct 70 was located near the developing sleeve 11 in order to effectively suck up scattered toner, can be suppressed. That is, in the developing apparatus 20Y of this embodiment, the magnetic flux density of the multiple magnetic poles fixed to the developing magnet 12 is configured such that Bh≧B1 and HW / R13≧1 / 4, so that the direction of the magnetic force Fθ is opposite to the direction of the airflow path AP due to the suction of the duct 70, i.e., Fθ>0, throughout the entire range R13 from P1 to P3. Then, the magnetic force Fθ acts on the carriers on the developing sleeve 11 in a way that cancels out the wind load Fa due to the airflow path AP, so that the force Fs, which is the resultant force of the wind load Fa and the magnetic force Fθ, becomes smaller than the maximum static friction force Fm of the carrier, thereby suppressing the separation of carriers from the developing sleeve 11 and suppressing the suction of carriers to the duct 70.

[0119] In this embodiment as well, it is preferable that HW / R13 ≥ 40%, and even more preferable that HW / R13 ≥ 1 / 2, as in the first embodiment.

[0120] <Other Embodiments> The present invention is not limited to the configurations 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 first screw 41 and the second screw 42 is not particularly limited as long as they can transport the developer, and for example, spiral blades or paddle-shaped blades can be applied. [Explanation of Symbols]

[0121] 10. Developing roller 11. Developing sleeves 12. Developing Magnet 20Y, 20M, 20C, 20K...Developing device 21Y, 21M, 21C, 21K... Photosensitive drum (image carrier) 43. Regulating blade (layer thickness regulating member) 60... Developing container 70...Duct 71...Upper part of the duct (wall of the second duct) 72...Lower part of the duct (First duct wall) 72c...tip 74...Suction port 100...Image forming apparatus 102...Cut pole (first magnetic pole) 103...First transport pole (second magnetic pole) 104...Second carrier pole (third magnetic pole) 105...Development pole (4th magnetic pole)

Claims

1. A developing container containing a developer including toner and carrier, A developing roller having a rotating developing sleeve, a developing magnet positioned non-rotating inside the developing sleeve and attracting developer to the surface of the developing sleeve by magnetic force, and developing an electrostatic latent image formed on a rotating image carrier with developer, A layer thickness regulating member that regulates the thickness of the developer layer supported on the surface of the developing sleeve, The system includes a duct for sucking up the developer around the developing sleeve, The aforementioned developing magnet is The developing sleeve is positioned closest to the layer thickness regulating member, and the first magnetic pole is located there. With respect to the rotational direction of the developing sleeve, the second magnetic pole is positioned downstream of the first magnetic pole, With respect to the rotational direction of the developing sleeve, a third magnetic pole is positioned downstream of the second magnetic pole, adjacent to the second magnetic pole, and having a different polarity from the second magnetic pole. A fourth magnetic pole is positioned downstream of the third magnetic pole with respect to the rotational direction of the developing sleeve, and is positioned where the developing sleeve is closest to the image carrier, It has, The duct has a suction port for drawing in developer, located upstream of the position where the developing sleeve is closest to the image carrier with respect to the rotational direction of the developing sleeve, and downstream of the layer thickness regulating member, and extends from the suction port upstream in the rotational direction of the developing sleeve. The duct comprises a first duct wall positioned opposite a part of the developing roller with a gap in between, and a second duct wall positioned opposite the first duct wall, forming a space between it and the first duct wall through which the developer drawn in from the suction port flows. When the line connecting the tip of the first duct wall on the suction port side and the rotation center of the developing sleeve intersects the surface of the developing sleeve at point P1, the position on the developing sleeve where the absolute value of the magnetic flux density in the normal direction of the second magnetic pole is maximum is P2, and the position on the developing sleeve where the absolute value of the magnetic flux density in the normal direction of the third magnetic pole is maximum is P3, The P1 is located downstream of the P2 and upstream of the P3 with respect to the rotational direction of the developing sleeve. With respect to the rotation direction of the developing sleeve, the range from P1 to P3 is defined as R13, and the tangential magnetic force acting on the carrier on the developing sleeve is Fθ, and when the direction from P1 to P3 with respect to the rotation direction of the developing sleeve is defined as positive for Fθ, The entire region of R13 satisfies Fθ≧0. A developing apparatus characterized by the following features.

2. If we define P4 as the point on the developing sleeve where the normal component of the magnetic flux density of the third magnetic pole takes half of its maximum value, and the point closer to P1 is defined as HW as the range from P4 to P3 with respect to the rotational direction of the developing sleeve, The circumferential length on the developing sleeve in the range HW is 40% or more of the circumferential length on the developing sleeve in the range R13. The developing apparatus according to feature 1.

3. If we define P4 as the point on the developing sleeve where the normal component of the magnetic flux density of the third magnetic pole takes half of its maximum value, and the point closer to P1 is defined as HW as the range from P3 to P4 with respect to the rotational direction of the developing sleeve, The circumferential length on the developing sleeve in the range HW is at least half the circumferential length on the developing sleeve in the range R13. The developing apparatus according to feature 1.

4. P1 is located downstream of P2 with respect to the rotational direction of the developing sleeve, and is in a range where the absolute value of the magnetic flux density in the direction normal to the second magnetic pole is greater than 0. The developing apparatus according to feature 1.

5. If we define the vertical line G as the tangent to the image carrier among the vertical tangents of the developing sleeve, The P1 is located on the side further away from the image carrier than the vertical line G in the horizontal direction. The developing apparatus according to feature 1.

6. The developing sleeve rotates such that, at the portion facing the image carrier, its surface moves in the opposite direction to the surface of the image carrier. The developing apparatus according to feature 1.

7. When Bc is the maximum absolute value of the magnetic flux density in the normal direction of the first magnetic pole, B1 is the maximum absolute value of the magnetic flux density in the normal direction of the second magnetic pole, B2 is the maximum absolute value of the magnetic flux density in the normal direction of the third magnetic pole, and Bh = (Bc + B2) / 2 is the average of Bc and B2, Bh ≥ B1 > Bc Satisfying the conditions, If we define P4 as the point on the developing sleeve where the normal component of the magnetic flux density of the third magnetic pole takes half of its maximum value, and the point closer to P1 is defined as HW as the range from P4 to P3 with respect to the rotational direction of the developing sleeve, HW / R13≧1 / 4 The developing apparatus according to claim 1, characterized in that it satisfies the following conditions.

8. A developing container containing a developer including toner and carrier, A developing roller having a rotating developing sleeve, a developing magnet positioned non-rotating inside the developing sleeve and attracting developer to the surface of the developing sleeve by magnetic force, and developing an electrostatic latent image formed on a rotating image carrier with developer, A layer thickness regulating member that regulates the thickness of the developer layer supported on the surface of the developing sleeve, The system includes a duct for sucking up the developer around the developing sleeve, The aforementioned developing magnet is The developing sleeve is positioned closest to the layer thickness regulating member, and the first magnetic pole is located there. With respect to the rotational direction of the developing sleeve, the second magnetic pole is positioned downstream of the first magnetic pole, With respect to the rotational direction of the developing sleeve, a third magnetic pole is positioned downstream of the second magnetic pole, adjacent to the second magnetic pole, and having a different polarity from the second magnetic pole. A fourth magnetic pole is positioned downstream of the third magnetic pole with respect to the rotational direction of the developing sleeve, and is positioned where the developing sleeve is closest to the image carrier, It has, The duct has a suction port for drawing in developer, located upstream of the position where the developing sleeve is closest to the image carrier with respect to the rotational direction of the developing sleeve, and downstream of the layer thickness regulating member, and extends from the suction port upstream in the rotational direction of the developing sleeve. The duct comprises a first duct wall positioned opposite a part of the developing roller with a gap in between, and a second duct wall positioned opposite the first duct wall, forming a space between it and the first duct wall through which the developer drawn in from the suction port flows. When the line connecting the tip of the first duct wall on the suction port side and the rotation center of the developing sleeve intersects the surface of the developing sleeve at point P1, the position on the developing sleeve where the absolute value of the magnetic flux density in the normal direction of the second magnetic pole is maximum is P2, and the position on the developing sleeve where the absolute value of the magnetic flux density in the normal direction of the third magnetic pole is maximum is P3, The P1 is located downstream of the P2 and upstream of the P3 with respect to the rotational direction of the developing sleeve. When Bc is the maximum absolute value of the magnetic flux density in the normal direction of the first magnetic pole, B1 is the maximum absolute value of the magnetic flux density in the normal direction of the second magnetic pole, B2 is the maximum absolute value of the magnetic flux density in the normal direction of the third magnetic pole, and Bh = (Bc + B2) / 2 is the average of Bc and B2, Bh ≥ B1 > Bc Satisfying the conditions, When the range from P1 to P3 in the rotational direction of the developing sleeve is defined as R13, and the point on the developing sleeve where the normal component of the magnetic flux density of the third magnetic pole takes half of its maximum value is defined as P4, and the range from P4 to P3 in the rotational direction of the developing sleeve is defined as HW, HW / R13≧1 / 4 satisfies A developing apparatus characterized by the following features.

9. P1 is located downstream of P2 with respect to the rotational direction of the developing sleeve, and is in a range where the absolute value of the magnetic flux density in the direction normal to the second magnetic pole is greater than 0. The developing apparatus according to feature 8.

10. If we define the vertical line G as the tangent to the image carrier among the vertical tangents of the developing sleeve, The P1 is located on the side further away from the image carrier than the vertical line G in the horizontal direction. The developing apparatus according to feature 8.

11. The developing sleeve rotates such that, at the portion facing the image carrier, its surface moves in the opposite direction to the surface of the image carrier. The developing apparatus according to feature 8.

Images