Developing unit

Abstract

A developing unit includes a developer container, a rotatable developing member, a magnet disposed inside the rotatable developing member, and a conduit portion including a suction port, a first conduit wall, and a second conduit wall. P1 is located downstream of P2 and upstream of P3. P1 is a point at which a line connecting a rotation center of the rotatable developing member and a distal end of the first catheter wall intersects an outer peripheral surface of the rotatable developing member. F [theta] > = 0 is satisfied in a range from P1 to P3 in a rotation direction of the rotatable developing member. F [theta] is a magnetic force in a tangential direction with respect to the outer peripheral surface of the rotatable developing member among magnetic forces acting on the carrier on the outer peripheral surface of the rotatable developing member.

Description

Technical Field

[0001] This disclosure relates to a developing unit that uses a developing agent to develop an electrostatic latent image formed on an image carrier member. Background Technology

[0002] Imaging devices such as copiers, printers, fax machines, or multifunction peripherals include a developing unit that attaches developer to the electrostatic latent image formed on the photosensitive drum and develops the latent image into a toner image. Two-component developers, comprising a toner and a carrier, are widely used as developers. In the developing unit, the amount of developer carried on the developing sleeve is controlled by a control member. Subsequently, as the developing roller rotates, the developer fed to the developing area facing the photosensitive drum is used to develop the electrostatic latent image on the photosensitive drum into a toner image in the developing area. Therefore, in the developing unit, toner may scatter when the developer is fed by the rotating developing sleeve.

[0003] When toner scatters, the scattered toner accumulates near the developing unit and the photosensitive drum. Subsequently, if the accumulated toner falls onto the developing sleeve or photosensitive drum due to vibrations during imaging or maintenance, image defects may occur. US 2021 / 0096500 A1 discloses a developing unit including a suction conduit that suctions away scattered toner to collect it and discharges it from the developing unit.

[0004] Here, to ensure the suction conduit effectively removes scattered toner, it is desirable to position the suction port near the developing sleeve. In this arrangement, near the suction port, air drawn into the conduit reaches the surface of the developing sleeve and collides with a carrier resting on its surface. Due to this air collision, the carrier may detach from the developing sleeve and may be drawn into the suction conduit along with the scattered toner. When the carrier reaches the suction path of the suction conduit, it deposits within the path, narrowing the cross-sectional area of ​​the flow path and preventing the desired airflow velocity from being achieved. Consequently, the scattered toner cannot be adequately suctioned. Furthermore, if a filter for collecting toner is installed in the suction conduit path, the filter may become clogged with the carrier, reducing suction force and further preventing the scattered toner from being adequately suctioned, potentially leading to image defects on a daily basis. The suction path of the conduit is also difficult to clean, which can result in insufficient suction of scattered toner, thus causing image defects on a daily basis.

[0005] US 2021 / 0096500 A1 discloses a configuration in which a recess is formed on the lower surface of the suction conduit path, and a carrier is collected by the recess to prevent carrier that has entered the body when aspirating scattered toner through the suction conduit. However, especially under operating conditions of high-speed imaging equipment, the amount of carrier separated from the developing sleeve tends to increase, the recess may become filled with carrier, and carrier may overflow from the recess. The carrier overflowing from the recess then enters the suction path and deposits in the suction path, and the scattered toner cannot be adequately aspirated, resulting in poor image quality on a daily basis. Summary of the Invention

[0006] One aspect of this disclosure is the inhibition of the carrier being aspirated into the catheter portion.

[0007] According to a first aspect of this disclosure, a developing unit includes: a developer container configured to contain a developer comprising a toner and a carrier; a rotatable developing member configured to carry the developer and feed the developer to a developing position, in which an electrostatic latent image formed on an image carrier is developed; a control unit configured to control the amount of developer carried on the outer peripheral surface of the rotatable developing member; and a magnet non-rotatably and fixedly disposed inside the rotatable developing member, the magnet including: a control pole disposed facing the control unit; a first feed pole disposed downstream of the control pole in the rotational direction of the rotatable developing member; and a second feed pole disposed adjacent to the first feed pole and downstream of the first feed pole in the rotational direction of the rotatable developing member, and having... The second feed electrode has a polarity different from that of the first feed electrode; a developing electrode disposed downstream of the second feed electrode in the rotational direction of the rotatable developing member and facing the image carrier member at the developing position; and a conduit portion comprising: a suction port, which is an inlet through which developer dispersed in the developing container is drawn through and extends upstream of the suction port in the rotational direction of the rotatable developing member; a first conduit wall disposed facing the rotatable developing member; and a second conduit wall disposed facing the rotatable developing member and facing the first conduit wall, and configured to form a space between the second conduit wall and the first conduit wall through which developer drawn from the suction port flows, the second conduit wall being located outside the first conduit wall in the radial direction of the rotatable developing member relative to the rotational center of the rotatable developing member. In the rotational direction of the rotatable developing member, the suction port is located upstream of a point on the outer peripheral surface of the rotatable developing member where the absolute value of the magnetic flux density of the developing electrode in the direction normal to the outer peripheral surface of the rotatable developing member becomes maximum, and downstream of a point on the outer peripheral surface of the rotatable developing member where the absolute value of the magnetic flux density of the control electrode in the direction normal to the outer peripheral surface of the rotatable developing member becomes maximum. In the rotational direction of the rotatable developing member, P1 is located downstream of P2 and upstream of P3. P1 is a point where the line connecting the rotation center of the rotatable developing member and the distal end of the first conduit wall on the suction port side intersects the outer peripheral surface of the rotatable developing member. P2 is a point on the outer peripheral surface of the rotatable developing member where the absolute value of the magnetic flux density of the first feed electrode in the direction normal to the outer peripheral surface of the rotatable developing member becomes maximum. P3 is a point on the outer peripheral surface of the rotatable developing member where the absolute value of the magnetic flux density of the second feed pole in the direction normal to the outer peripheral surface of the rotatable developing member becomes the maximum value.In the rotational direction of the rotatable developing member, Fθ ≥ 0 is satisfied within the range from P1 to P3. Fθ is the magnetic force acting on the carrier on the outer peripheral surface of the rotatable developing member in the tangential direction relative to the outer peripheral surface of the rotatable developing member. In the rotational direction of the rotatable developing member, the direction of Fθ from P1 to P3 is defined as the positive direction.

[0008] According to a second aspect of this disclosure, a developing unit includes: a developer container configured to contain a developer comprising a toner and a carrier; a rotatable developing member configured to carry the developer and feed the developer to a developing position, in which an electrostatic latent image formed on an image carrier is developed; a control unit configured to control the amount of developer carried on the outer peripheral surface of the rotatable developing member; and a magnet non-rotatably and fixedly disposed inside the rotatable developing member, the magnet comprising: a control pole disposed facing the control unit; a first feed pole disposed downstream of the control pole in the rotational direction of the rotatable developing member; and a second feed pole disposed adjacent to the first feed pole and downstream of the first feed pole in the rotational direction of the rotatable developing member, and having a relationship with the first feed pole. The device comprises: a feed electrode of different polarities; a developing electrode disposed downstream of the second feed electrode in the rotational direction of the rotatable developing member and facing the image carrier member at the developing position; and a conduit portion comprising: a suction port, which is an inlet through which developer dispersed in the developing container is drawn through, and the conduit portion extending upstream from the suction port in the rotational direction of the rotatable developing member; a first conduit wall disposed facing the rotatable developing member; and a second conduit wall disposed facing the rotatable developing member and facing the first conduit wall, and configured to form a space between the second conduit wall and the first conduit wall through which developer drawn from the suction port flows, the second conduit wall being located outside the first conduit wall in the radial direction of the rotatable developing member relative to the rotational center of the rotatable developing member. In the rotational direction of the rotatable developing member, the suction port is located upstream of a point on the outer peripheral surface of the rotatable developing member where the absolute value of the magnetic flux density of the developing electrode in the direction normal to the outer peripheral surface of the rotatable developing member becomes maximum, and downstream of a point on the outer peripheral surface of the rotatable developing member where the absolute value of the magnetic flux density of the control electrode in the direction normal to the outer peripheral surface of the rotatable developing member becomes maximum. In the rotational direction of the rotatable developing member, P1 is located downstream of P2 and upstream of P3. P1 is a point where the line connecting the rotation center of the rotatable developing member and the distal end of the first conduit wall on the suction port side intersects the outer peripheral surface of the rotatable developing member. P2 is a point on the outer peripheral surface of the rotatable developing member where the absolute value of the magnetic flux density of the first feed electrode in the direction normal to the outer peripheral surface of the rotatable developing member becomes maximum.P3 is a point on the outer peripheral surface of the rotatable developing member where the absolute value of the magnetic flux density of the second feed pole in the direction normal to the outer peripheral surface of the rotatable developing member becomes its maximum value. This satisfies (Bc + B2) / 2 ≥ B1 > Bc. Bc is the maximum absolute value of the magnetic flux density of the control pole in the direction normal to the outer peripheral surface of the rotatable developing member. B1 is the maximum absolute value of the magnetic flux density of the first feed pole in the direction normal to the outer peripheral surface of the rotatable developing member. B2 is the maximum absolute value of the magnetic flux density of the second feed pole in the direction normal to the outer peripheral surface of the rotatable developing member. The circumferential length of the rotatable developing member in the rotational direction from P4 to P3 is more than 1 / 4 of the circumferential length of the rotatable developing member in the rotational direction from P1 to P3. P4 is a point on the outer peripheral surface of the rotatable developing member that is closer to P1 than the following point: at this point, the absolute value of the magnetic flux density of the second feed pole in the direction normal to the outer peripheral surface of the rotatable developing member becomes half of the maximum value.

[0009] The features of this disclosure will become apparent from the accompanying drawings and the following description of embodiments. The following description of embodiments is by way of example. Attached Figure Description

[0010] Figure 1 A schematic cross-sectional view illustrating the construction of the imaging device according to the first embodiment.

[0011] Figure 2 A schematic cross-sectional view illustrating the construction of the developing unit according to the first embodiment.

[0012] Figure 3 A view showing the arrangement of the magnetic poles of the developing roller according to the first embodiment.

[0013] Figure 4 This is an enlarged cross-sectional view of the periphery of the developing roller and the guide tube according to the first embodiment.

[0014] Figure 5A This is a schematic diagram showing the relationship of forces acting on the carrier in the region TH downstream of P1 in the rotational direction of the developing sleeve, and a schematic diagram showing the case where the direction of the magnetic force Fθ acting on the carrier is the same as the suction direction into the catheter.

[0015] Figure 5B This is a schematic diagram showing the relationship of forces acting on the carrier in the region TH downstream of P1 in the rotational direction of the developing sleeve, and a schematic diagram showing the case where the direction of the magnetic force Fθ acting on the carrier is opposite to the suction direction into the catheter.

[0016] Figure 6 A graph showing the distribution of magnetic properties on the carrier acting on the developing sleeve according to Comparative Example 1.

[0017] Figure 7 A graph showing the distribution of magnetic properties on the carrier acting on the developing sleeve according to Comparative Example 2.

[0018] Figure 8 A graph showing the distribution of magnetic properties on the carrier acting on the developing sleeve according to Comparative Example 3.

[0019] Figure 9 This is an enlarged cross-sectional view of the periphery of the developing roller and the guide tube according to Comparative Example 4.

[0020] Figure 10 A graph illustrating the distribution of magnetic properties on the carrier acting on the developing sleeve according to the first embodiment.

[0021] Figure 11 A graph illustrating the distribution of magnetic properties on a carrier acting on a developing sleeve according to another example of the first embodiment.

[0022] Figure 12 A graph illustrating the distribution of magnetic properties on the carrier acting on the developing sleeve according to the second embodiment.

[0023] Figure 13 A graph showing the distribution of magnetic properties on the carrier acting on the developing sleeve according to Comparative Example 5. Detailed Implementation

[0024] First Embodiment

[0025] Reference Figures 1 to 11 The first embodiment will be described. First, reference will be made to... Figure 1 A schematic construction of the imaging apparatus according to this embodiment is described. Here, the X direction, Y direction, and Z direction, which are perpendicular to each other, are defined. In this embodiment, the X and Y directions are parallel to the horizontal plane, and the Z direction is perpendicular to the horizontal plane (vertical direction). The Y direction is the direction along the rotation axis of the developing sleeve 11, which will be described below.

[0026] Imaging equipment

[0027] In this embodiment, the imaging device 100 is a panchromatic imaging device, and for example, a multi-functional peripheral device (MFP) with copying, printing, and scanning functions. Figure 1As shown, the imaging device 100 includes imaging units PY, PM, PC, and PK, which perform processing in parallel to form toner images of four colors: yellow, magenta, cyan, and black, respectively. In the imaging device 100 according to this embodiment, a host device, such as a personal computer, is communicatively connected to a document reader or the device body connected to the main body (device body) of the imaging device. Therefore, based on image information from the host device, a panchromatic image of four colors—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 system.

[0028] The imaging units PY, PM, PC, and PK for the corresponding colors include primary chargers 22Y, 22M, 22C, and 22K; developing units 20Y, 20M, 20C, and 20K; exposure units 23Y, 23M, 23C, and 23K; photosensitive drums 21Y, 21M, 21C, and 21K; and cleaning units 25Y, 25M, 25C, and 25K. Additionally, the imaging device 100 includes a transfer unit 35 and a fixing unit 40. Since the imaging units PY, PM, PC, and PK for the corresponding colors have similar structures, the imaging unit PY will be described below as representative.

[0029] The photosensitive drum 21Y, used as an image-carrying component, is a photosensitive component with a photosensitive layer and is configured to rotate at a predetermined speed. This photosensitive layer is made of a resin (such as polycarbonate) containing an organic photoconductor (OPC). In this embodiment, the linear velocity of the surface of the photosensitive drum 21Y is set to 650 mm / s. The primary charger 22Y includes a corona discharge electrode disposed around the photosensitive drum 21Y and charges the surface of the photosensitive drum 21Y using the generated ions.

[0030] The exposure unit (optical writing unit) 23Y includes scanning optics and exposes the charged photosensitive drum 21Y based on image data to reduce the potential of the exposed portion, thereby forming a charge pattern (electrostatic latent image) corresponding to the image data. The developing unit 20Y transfers the developer contained therein to the photosensitive drum 21Y to develop the electrostatic latent image formed on the photosensitive drum 21Y. The developer is made by mixing a carrier and a toner corresponding to each color, and the electrostatic latent image is developed by the toner.

[0031] The transfer unit 35 includes primary transfer rollers 30Y, 30M, 30C, and 30K, an intermediate transfer belt 31, and a secondary transfer outer roller 33. The intermediate transfer belt 31 is wound around the primary transfer rollers 30Y, 30M, 30C, and 30K, the secondary transfer inner roller 32, and multiple rollers, and is supported in a traveling manner. The primary transfer rollers 30Y, 30M, 30C, and 30K, which serve as primary transfer components, are drawn from... Figure 1The top of each color corresponds sequentially to the following colors: yellow (Y), magenta (M), cyan (C), and black (K). The secondary transfer outer roller 33 is positioned outside the intermediate transfer belt 31 and is configured to allow recording material to pass between the secondary transfer outer roller 33 and the intermediate transfer belt 31, which is tensioned around the secondary transfer inner roller 32.

[0032] In the primary transfer section (primary transfer clamping section) T1, where the intermediate transfer belt 31 and the photosensitive drums 21Y, 21M, 21C, and 21K abut against each other, the toner images of corresponding colors formed on the photosensitive drums 21Y, 21M, 21C, and 21K are sequentially transferred (primarily transferred) to the intermediate transfer belt 31 by the primary transfer bias applied to the primary transfer rollers 30Y, 30M, 30C, and 30K. For example, for a full-color image of four colors, the toner image is sequentially transferred from the photosensitive drum 21Y to the intermediate transfer belt 31, forming a colored toner image in which a yellow layer, a magenta layer, a cyan layer, and a black layer are superimposed.

[0033] On the other hand, the recording material 50, housed in a recording material holding section (e.g., a cartridge) (not shown), is fed toward the transfer unit 35 via a feed roller (not shown). Synchronized with the toner image on the intermediate transfer belt 31, the recording material 50 is fed to a secondary transfer section (clamping section) T2, where the intermediate transfer belt 31, tensioned by the secondary transfer inner roller 32, and the secondary transfer outer roller 33, serving as a secondary transfer member, abut against each other. Then, in the secondary transfer section T2, the toner image formed on the intermediate transfer belt 31 is transferred a second time onto the recording material 50 by the secondary transfer bias applied to the secondary transfer outer roller 33. The recording material, on which the toner image has been transferred, is subjected to pressure and heat in the fixing unit 40. As a result, the toner on the recording material melts, and the color image is fixed onto the recording material. Afterward, the recording material 50 is discharged to the outside of the device.

[0034] After the first transfer process, toner and other residues remaining on the photosensitive drums 21Y, 21M, 21C, and 21K are collected by cleaning units 25Y, 25M, 25C, and 25K. As a result, the photosensitive drums 21Y, 21M, 21C, and 21K are ready for the next imaging process. Additionally, after the second transfer process, toner and other residues remaining on the intermediate transfer belt 31 are removed by the intermediate transfer belt cleaner 34.

[0035] Note that the imaging device 100 according to this embodiment can also use an imaging unit for a desired single color or an imaging unit for some of four colors to form a monochrome or multicolor image, such as a black monochrome image.

[0036] Developer repositories 26Y, 26M, 26C, and 26K are configured to correspond to developing units 20Y, 20M, 20C, and 20K, respectively, and are filled with replaceable vials, each containing developer corresponding to the colors yellow, magenta, cyan, and black, respectively, starting from the top. Developer repositories 26Y, 26M, 26C, and 26K are configured to feed (supply) developer to developing units 20Y, 20M, 20C, and 20K corresponding to the colors of the developer stored therein.

[0037] For example, the toner weight ratio of the developer contained in the bottle is 80% to 95%, and the toner weight ratio of the developer in developing units 20Y, 20M, 20C, and 20K is 5% to 10%. Therefore, when the toner is consumed due to development in developing units 20Y, 20M, 20C, and 20K, a developer containing toner corresponding to the amount consumed is supplied, and the toner weight ratio of the developer in developing units 20Y, 20M, 20C, and 20K remains constant.

[0038] Developing unit

[0039] Next, we will refer to Figure 2 and Figure 3 The developing units 20Y, 20M, 20C, and 20K are described in detail. Since developing units 20Y, 20M, 20C, and 20K have the same construction, developing unit 20Y will be described below. Figure 2 To show Figure 1 A conceptual diagram of the developing unit 20Y shown. Figure 3 A conceptual diagram illustrating the magnetic pole configuration of the developing magnet 12 disposed in the developing unit 20Y.

[0040] like Figure 2 As shown, the developing unit 20Y includes a developing roller 10, a first screw 41, and a second screw 42, and these components are housed in a developer container 60. The developer container 60 houses a two-component developer comprising a non-magnetic toner and a magnetic carrier. Specifically, the developer container 60 includes a first feed chamber 401 and a second feed chamber 402, and the developer is housed in both chambers. The first screw 41 is disposed in the first feed chamber 401, and the second screw 42 is disposed in the second feed chamber 402.

[0041] The developing roller 10 is a developer-carrying member that is driven to rotate and is positioned adjacent to the photosensitive drum 21Y such that the axis of rotation of the developing roller is substantially parallel to the axis of rotation of the photosensitive drum 21Y. The developing roller 10 includes a developing magnet (fixed magnet) 12 and a rotating developing sleeve 11. The developing magnet is disposed non-rotatingly inside the developing sleeve 11 to attract developer to the surface of the developing sleeve 11 by magnetic force. Then, the developing roller 10 carries the developer drawn from the first screw 41 based on magnetic attraction and uses the developer to develop the electrostatic latent image formed on the rotating photosensitive drum 21Y (on the image-carrying member).

[0042] Specifically, for example, a DC development bias voltage having the same polarity as the charging polarity of the primary charger 22Y is applied to the development sleeve 11 of the development unit 20Y, or a development bias voltage in which a DC voltage having the same polarity as the charging polarity of the primary charger 22Y is superimposed on an AC voltage is applied. As a result, reverse development is performed, in which toner charged to the same polarity as the charging polarity of the primary charger 22Y adheres to the electrostatic latent image formed by the exposure unit 23Y on the photosensitive drum 21Y.

[0043] The developing sleeve 11 is a non-magnetic cylindrical component and is driven to rotate about the rotation axis 19. The direction of rotation of the developing sleeve 11 is as follows: Figure 2 The direction indicated by arrow D11 is counterclockwise, and is the same as the rotation direction of the photosensitive drum 21Y in this embodiment (the direction indicated by arrow D21). Therefore, the developing sleeve 11 rotates so that the surface moves in the opposite direction to the surface of the photosensitive drum 21Y at the position facing the photosensitive drum 21Y (the facing portion).

[0044] The developing magnet 12 is disposed inside the developing sleeve 11 and includes multiple fan-shaped magnetic poles 101 to 107 and a fan-shaped low-magnetic-force portion 110, such as... Figure 3 As shown in the diagram, a space is provided between the inner periphery of the developing sleeve 11 and the outer periphery 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. Magnetic poles 101, 102, 103, 104, 105, 106, and 107 are arranged adjacent to each other in the direction of rotation of the developing sleeve 11, and are respectively N pole, S pole, N pole, S pole, N pole, S pole, and N pole. When the developing sleeve 11 rotates, each magnetic pole is fed with developer attracted by magnetic pole 101, as will be described below.

[0045] In this embodiment, a low-magnetic-force section 110, having a lower magnetic force than that of magnetic pole 107, is formed by a repulsive magnetic field generated by the cooperation between magnetic pole 107 and magnetic pole 101. Magnetic pole 101 is positioned downstream of magnetic pole 107 in the rotational direction of the developing sleeve 11 and has the same polarity as magnetic pole 107. The developer is stripped from the developing sleeve 11 by the low-magnetic-force section 110. Note that in this embodiment, the low-magnetic-force section 110 has almost no magnetic force, but it can have a low magnetic force, and for example, the magnetic force (the absolute value of the normal component Br of the magnetic flux density) can be less than 10 mT, or even less than 5 mT.

[0046] Magnetic pole 101 is the pole that draws developer from the first feed chamber 401, and may be referred to hereinafter as the draw pole 101. Magnetic pole 102, serving as the first magnetic pole, is a pole located at a position where the developing sleeve 11 is closest to the control scraper 43 (described hereinafter) which serves as a layer thickness control member, and may be referred to hereinafter as the cut pole 102. Magnetic pole 103, serving as the second magnetic pole, is a pole located downstream of the cut pole 102 in the rotational direction of the developing sleeve 11, and may be referred to hereinafter as the first feed pole 103. Magnetic pole 104, serving as the third magnetic pole, is a pole located downstream of the first feed pole 103 in the rotational direction of the developing sleeve 11, adjacent to the first feed pole 103, and having a different polarity than the first feed pole 103, and may be referred to hereinafter as the second feed pole 104. The magnetic pole 105, used as the fourth magnetic pole, is disposed downstream of the second feed pole 104 in the rotational direction of the developing sleeve 11 and is located at the position of the developing sleeve 11 closest to the photosensitive drum 21Y, and is hereinafter referred to as the developing pole 105. The magnetic pole 106 is disposed downstream of the developing pole 105 in the rotational direction of the developing sleeve 11, and is hereinafter referred to as the third feed pole 106. The magnetic pole 107 is disposed downstream of the third feed pole 106 in the rotational direction of the developing sleeve 11 and has the same polarity as the pick-up pole 101 disposed further downstream (where the low magnetic force portion 110 is inserted between the magnetic pole 107 and the pick-up pole 101), and is hereinafter referred to as the stripping pole 107.

[0047] The developer is flipped upwards as it is fed by the first screw 41 and supplied to the developing sleeve 11. Since the developer contains a magnetic carrier, it is constrained by the suction pole 101 of the developing magnet 12. Next, due to the rotation of the developing sleeve 11, the amount (layer thickness) of the developer carried on the developing sleeve 11 is controlled to a predetermined amount by the control scraper 43 as it passes through the cutting pole 102. The developer with its layer thickness controlled passes through the first feed pole 103 and the second feed pole 104 and is fed to the developing pole 105 facing the photosensitive drum 21Y, thus developing the latent image formed on the photosensitive drum 21Y. After the latent image formed on the photosensitive drum 21Y is developed, the developer on the developing sleeve 11 is fed by the rotation operation of the developing sleeve 11, passes through the third feed pole 106 towards the downstream side in the rotation direction, is released from the magnetic constraint between the absorb pole 101 and the stripping pole 107 with the same polarity, and is collected in the first feed chamber 401.

[0048] The first screw 41 and the second screw 42 are screw feed members that feed the developer in one direction while stirring it, and are arranged such that their axes of rotation are substantially parallel to each other. The axis of rotation of each screw is also substantially parallel to the axis of rotation of the developing roller 10.

[0049] like Figure 2 As shown, the first screw 41 is positioned between the developing roller 10 and the second screw 42, and the partition wall 61 of the developer container 60 is disposed between the first screw 41 and the second screw 42. The partition wall 61 of the developer container 60 extends along the rotation axis of the first screw 41 and the second screw 42. The partition wall 61 has a communication port (not shown) serving as a communication portion, which allows communication between the first feed chamber 401 (in which developer is fed by the first screw 41) and the second feed chamber 402 (in which developer is fed by the second screw 42). The communication port is an opening formed in the partition wall 61.

[0050] The developer feed directions of the first screw 41 and the second screw 42 are opposite to each other. The starting end (upstream end in the developer feed direction) and ending end (downstream end in the developer feed direction) of the first feed chamber 401, where the first screw 41 is located, communicate with the ending end and starting end of the second feed chamber 402, where the second screw 42 is located, via a communication port formed in the partition wall 61. Therefore, the developer circulates in the developer container 60 along the rotation direction of the first screw 41 and the second screw 42 and in the Y direction, and a portion of the developer is supplied toward the developing roller 10.

[0051] Developer supply port 62 (see Figure 2 It is positioned above the second screw 42 in the developer container 60 and connected to the developer memory 26Y (see...). Figure 1 The developer supply port 62 is configured to supply developer contained in a bottle filled in the developer reservoir 26Y to the second feed chamber 402, which is provided with the second screw 42. As described above, since the toner weight ratio of the developer contained in the bottle in the developer reservoir 26Y is greater than the toner weight ratio of the developer in the developing unit 20Y, the toner weight ratio of the developer in the developing unit 20Y can be kept constant by adjusting the amount of developer to be supplied to the second screw 42.

[0052] Toner concentration detection sensor 63 (see Figure 2 The toner concentration sensor 63 is configured to detect the toner concentration in the developer container 60. In this embodiment, the toner concentration detection sensor 63 is disposed in the second feed chamber 402. The toner concentration detection sensor 63 is a sensor that detects the permeability of the developer. The toner concentration corresponds to the amount of toner consumed in the developing unit 20Y, and is therefore used to control the supply of developer from the developer memory 26Y. For example, when the toner concentration is detected to be lower than a predetermined value, developer is supplied from the developer memory 26Y. Since the permeability of the developer varies with the toner concentration, the permeability can be used to detect the toner concentration.

[0053] A control scraper 43, serving as a layer thickness control component, is disposed adjacent to the developing roller 10 and is used to control the amount of developer supplied from the first feed chamber 401 to the developing roller 10. The control scraper 43 is configured such that its distal end faces the surface of the developing sleeve 11 with a gap therebetween, and the amount of developer (layer thickness) carried on the surface of the developing sleeve 11 is controlled based on this gap.

[0054] As described above, in this embodiment, a two-component development method is used as the development method, and a mixture of a magnetic carrier and a non-magnetic toner with a negative charge polarity is used as the developer. The non-magnetic toner acquires a negative charge through friction with the magnetic carrier, while the magnetic carrier acquires a positive charge. The non-magnetic toner is obtained by adding colorants, wax components, etc., to a resin such as polyester or styrene acrylate, then pulverizing or polymerizing it to form a powder, and then adding fine powders such as titanium dioxide or silicon dioxide to the surface. The magnetic carrier is obtained by applying a resin coating to the surface layer of a core, which is made of ferrite particles or resin particles obtained by mixing magnetic powder. In this embodiment, the toner concentration (the weight ratio of toner contained in the developer) in the initial state is 8%.

[0055] Generally, a two-component development method using toner and carrier is characterized by less stress on the toner compared to a one-component development method using a single-component developer. This is because the toner and carrier are charged to a predetermined polarity through frictional contact. On the other hand, prolonged use leads to an increase in the amount of contaminants (waste) adhering to the carrier surface, which gradually reduces the developer's ability to charge. As a result, problems such as haze and toner scattering occur. To extend the lifespan of a two-component development unit, increasing the amount of carrier contained in the development unit could be considered, but this is undesirable because it results in an increase in the size of the development unit.

[0056] To address the aforementioned problems associated with two-component developers, this embodiment employs an automatic carrier refresh (ACR) method. The ACR method involves gradually supplying new developer from the developer storage 26Y to the developing unit 20Y and gradually discharging electrically degraded developer from the discharge port (not shown) of the developing unit 20Y to suppress the accumulation of degraded carriers. Thus, the degraded carriers in the developing unit 20Y are gradually replaced with new carriers, and the electrical properties of the carriers in the developing unit 20Y can be maintained substantially constant.

[0057] catheter

[0058] In the developing unit 20Y, toner may scatter when developer is fed by the rotating developing sleeve 11. When toner scattering occurs, the scattered toner may accumulate near the developing unit 20Y and the photosensitive drum 21Y, and due to vibrations during imaging or maintenance, the accumulated toner may fall onto the developing sleeve 11 or the photosensitive drum 21Y. Therefore, the developing unit 20Y according to this embodiment includes a conduit 70 that draws in the scattered toner to collect the scattered toner and discharges the collected toner to the outside of the device. That is, the developing unit 20Y includes a conduit 70 for drawing in developer around the developing sleeve.

[0059] like Figure 2As shown, a suction conduit 70 is positioned above the developer container 60. The conduit 70 has a suction port 74 located upstream of the developing sleeve 11 closest to the photosensitive drum 21Y and downstream of the control blade 43 in the rotational direction of the developing sleeve 11 to draw in developer. The conduit 70 extends upstream of the suction port 74 in the rotational direction of the developing sleeve 11. The conduit 70 has a lower portion 72 serving as a first conduit wall and an upper portion 71 serving as a second conduit wall. The lower portion 72 is positioned to face a portion of the developing roller 10 and has a gap therebetween. The upper portion 71 is positioned to face the lower portion 72, and a space is formed between the upper portion 71 and the lower portion 72 through which developer drawn from the suction port 74 flows.

[0060] The lower portion 72 of the conduit is fixed to the developer container 60 to cover the first feed chamber 401, the developing roller 10, and the control scraper 43 from above. The lower portion 72 of the conduit has a shape in which two flat plates extending in the Y direction are joined together. The lower portion 72 of the conduit includes a first lower portion 72a and a second lower portion 72b, the first lower portion having an inclined surface that slopes upward from an end on the negative side (the Y side of the photosensitive drum 21) in the X direction toward the positive side (the side separated from the photosensitive drum 21Y) in the X direction, and the second lower portion extending from the portion that contacts the first lower portion 72a toward the positive side in the X direction.

[0061] The upper portion 71 of the catheter is disposed above the lower portion 72 of the catheter to cover the entire lower portion 72 from above. The upper portion 71 of the catheter has a shape in which two flat plates extending in the Y direction are joined together. The upper portion 71 of the catheter includes a first upper portion 71a and a second upper portion 71b, the first upper portion having an inclined surface that slopes upward from an end on the negative side in the X direction toward the positive side in the X direction, and the second upper portion extending from a portion that contacts the first upper portion 71a toward the positive side in the X direction.

[0062] The first lower portion 72a of the lower conduit 72 and the first upper portion 71a of the upper conduit 71 are arranged such that the upper surface of the first lower portion 72a and the lower surface of the first upper portion 71a face each other. The second lower portion 72b of the lower conduit 72 and the second upper portion 71b of the upper conduit 71 are also arranged such that the upper surface of the second lower portion 72b of the lower conduit 72 and the lower surface of the second upper portion 71b of the upper conduit 71 face each other. However, the second lower portion 72b and the second upper portion 71b are arranged to be more separated from each other on their positive sides in the X direction.

[0063] The upper part 71 of the guide tube is fixed to the developer container 60 such that the negative end in the X direction is positioned at a predetermined distance from the photosensitive drum 21Y. The negative end of the upper part 71 in the X direction faces the photosensitive drum 21Y downstream of the position where the photosensitive drum 21Y faces the developing roller 10 in the rotational direction of the photosensitive drum 21Y.

[0064] The lower end 72 of the guide tube, on the negative side in the X direction, is located between the position of the developing roller 10 facing the control scraper 43 and the position of the developing roller 10 facing the photosensitive drum 21Y in the rotation direction of the developing roller 10. The suction port 74 of the guide tube 70 is located between the lower end 72 of the guide tube on the negative side in the X direction and the upper end 71 of the guide tube.

[0065] The duct 70 has an exhaust port 81 at its positive end in the X direction and at its end in the Y direction, which opens toward the exhaust duct 82. The exhaust port 81 allows the space surrounded by the upper part 71 and the lower part 72 of the duct to communicate with the internal space of the exhaust duct 82. The exhaust duct 82 has a tubular shape, and the end of the exhaust duct 82 opposite to the end connected to the exhaust port 81 opens outward via a dust collection filter 84 and a fan 85.

[0066] In the duct 70, when the fan 85, which acts as an airflow generator, rotates, a flow path AP is created for drawing air from the gap 73 between the photosensitive drum 21Y and the upper part of the duct 71 (see...). Figure 4 Air drawn from gap 73 passes through region TH, which is surrounded by developing sleeve 11, photosensitive drum 21Y, and upper conduit 71, through suction port 74 formed by upper conduit 71 and lower conduit 72, and flows to exhaust conduit 82. Toner scattered in region TH (hereinafter referred to as "scattered toner") is fed to exhaust conduit 82 through flow path AP.

[0067] This toner dispersion is caused by the following mechanism: If the developer deteriorates when placed or used in a high-temperature and high-humidity environment, the charge on the toner decreases, and the electrostatic adhesion between the toner and the carrier weakens. Then, due to the centrifugal force generated when the developing sleeve 11 rotates or the impact force generated when the developer moves between the magnetic poles, the force attempting to separate the toner from the carrier becomes greater than the electrostatic adhesion between the carrier and the toner, and the toner may separate from the carrier, potentially resulting in toner dispersion.

[0068] As a method to prevent toner from leaking outside the developing unit, sealing the gap between the photosensitive drum and the developing unit with a polyurethane sheet or similar material could be considered. However, as mentioned above, if a sealing method that utilizes contact with the photosensitive drum 21Y is used to suppress leakage of toner in the region TH after development on the photosensitive drum 21Y, the toner image formed on the photosensitive drum 21Y will be disturbed. Therefore, this method is difficult to employ. Therefore, in this embodiment, as described above, the leaked toner is aspirated by the conduit 70.

[0069] Suppression of carrier separation from the developing sleeve

[0070] Simultaneously, when the toner is aspirated by the conduit 70, the carrier may also be unintentionally aspirated along with the toner because the developer on the surface of the developing sleeve 11 is exposed to the air flow path AP. This is due to the following mechanism.

[0071] like Figure 4 As shown, P1 represents the point where line α intersects the surface of the developing sleeve 11. Line α connects the distal end 72c of the lower part 72 of the conduit on the suction port 74 side (suction port side) and the rotation center O of the developing sleeve 11. Figure 5A and Figure 5B As a schematic diagram, it shows the forces acting on the carrier on the developing sleeve 11 in the region TH downstream of P1 in the rotational direction of the developing sleeve 11.

[0072] Due to the interaction between the magnetic poles arranged in the developing magnet 12, a magnetic force F acts on the carrier 200 on the developing sleeve 11. The magnetic force F is divided into a magnetic force Fr in the normal direction of the developing sleeve 11 and a magnetic force Fθ in the tangential direction (rotation direction D11) of the developing sleeve 11. In the normal direction of the developing sleeve 11, the magnetic force Fr and the centrifugal force Fc caused by the rotation of the developing sleeve 11 act on the carrier 200. At this time, the maximum static friction force Fm in the rotation direction of the developing sleeve 11 is Fm = μ(Fr - Fc), where μ is the coefficient of static friction between the carriers 200 or between the carrier 200 and the developing sleeve 11.

[0073] 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 due to wind pressure and the magnetic force Fθ, because the carrier 200 in region TH on the developing sleeve 11 is exposed to the airflow path AP leading to the duct 70. Here, when the force Fs > the maximum static friction force Fm, the carrier 200 may separate from the developing sleeve 11, and the separated carrier may be fed along the flow path AP towards the exhaust duct 82 along with the scattered toner.

[0074] In other words, such as Figure 5AAs shown, when the direction of the magnetic force Fθ is the same as the direction of air flow in the flow path AP (suction direction or wind load Fa direction) (opposite to the rotation direction of the developing sleeve 11), the force Fs = wind load Fa + magnetic force Fθ. Therefore, the force Fs may be greater than the maximum static friction force Fm, and the carrier may separate from the developing sleeve 11.

[0075] Therefore, in this embodiment, as Figure 5B As shown, in the region of the developing sleeve 11 where the developer is exposed to the airflow path AP, the magnetic flux density of a plurality of magnetic poles fixedly arranged in the developing magnet 12 is set such that the direction of the magnetic force Fθ is opposite to the direction of the wind load Fa (and the same as the rotation direction of the developing sleeve 11). Thus, the force Fs is equal to the wind load Fa minus the magnetic force Fθ, and the force Fs is less than the maximum static friction force Fm, making it difficult for the carrier to separate from the developing sleeve 11.

[0076] Here, the direction of the magnetic force Fθ acting on the carrier on the developing sleeve 11 will be described. 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 between the magnetic poles fixedly arranged in the developing magnet 12. That is, when the carrier 200 is located between the first feed pole 103 and the second feed pole 104, the direction of the magnetic force Fθ may be the same as or opposite to the rotation direction of the developing sleeve 11, depending on the influence of the magnetic flux density of the first feed pole 103 and the second feed pole 104 at the location of the carrier 200.

[0077] References are shown as comparative examples 1 and 2. Figure 6 and Figure 7 Describe the relationship between magnetic flux density and magnetic force Fθ. Figure 6 The graph shows the distribution of magnetic properties acting on the carrier in the developing sleeve 11 in the construction according to Comparative Example 1. In the construction according to Comparative Example 1, a developing magnet having multiple magnetic poles, including three magnetic poles 103P, 104P, and 105P, is disposed inside the developing sleeve 11 with a diameter of 25 mm. The absolute values ​​of the magnetic flux density |Br| of the three magnetic poles in the normal direction are substantially the same. Magnetic poles 103P, 104P, and 105P correspond to... Figure 3 The first feed pole 103, the second feed pole 104, and the developing pole 105 are shown. Magnetic poles 103P, 104P, and 105P are configured such that adjacent magnetic poles have different polarities.

[0078] exist Figure 6 In the graph, the angle on the developing sleeve 11 is plotted on the horizontal axis, while the absolute value of the magnetic flux density |Br| and the magnetic force Fθ are plotted on the vertical axis. This angle is defined as: the angle along the horizontal line H ( passing through the center of rotation O of the developing sleeve 11) Figure 4Among the points where the surface of the developing sleeve 11 intersects with the surface of the developing sleeve 11, point Q is located on the side opposite to the photosensitive drum 21Y (on the side in the positive direction of the X-axis from the rotation center O of the developing sleeve 11). Figure 4 The angle at which the magnetic flux density is 0 degrees is defined, and the rotation direction D11 of the developing sleeve 11 is defined as the positive direction. In the graph, the absolute value of the magnetic flux density |Br| is represented by 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 away from the surface of the developing sleeve 11 (on a perimeter with a diameter of 25.2 mm) is represented by a dashed line. The graph shown below was also obtained under the same conditions. In addition, the plus sign, as a symbol for the magnetic force Fθ, indicates that the direction of the force is the same as the rotation direction D11 of the developing sleeve 11. Furthermore, the direction of the arrow represented by the dashed line on the graph indicates the direction of the magnetic force Fθ.

[0079] The magnetic flux density and magnetic force (magnetic force) generated by the developing magnet will be described. In the description of this embodiment, Br, Bθ, Fr, and Fθ are defined as follows.

[0080] Br: Magnetic flux density at a point in the direction normal (perpendicular) to the outer peripheral surface (surface) of the developing sleeve 11.

[0081] Bθ: Magnetic flux density at a point in the tangential direction relative to the outer peripheral surface of the developing sleeve 11.

[0082] Fr: The magnetic force acting at a point in the direction normal to the outer peripheral surface of the developing sleeve 11 (however, the direction of attraction (towards the developing sleeve 11) is defined as the negative direction).

[0083] Fθ: The magnetic force acting at a point in the tangential direction relative to the outer peripheral surface of the developing sleeve 11 (however, the direction of rotation of the developing sleeve 11 is defined as the positive direction).

[0084] Unless otherwise stated, Br, Bθ, Fr and Fθ refer to the magnetic flux density or magnetic force at a point on the developing sleeve 11.

[0085] Methods for measuring magnetic force or magnetic flux density

[0086] Next, the method for measuring magnetic force in this embodiment will be described. The magnetic force described in this embodiment can be calculated using the calculation method described below. The magnetic force acting on the carrier is obtained using the following formula (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.

[0087] [Mathematical Formula 1]

[0088]

[0089] therefore,

[0090] [Mathematical Formula 2]

[0091]

[0092] If Br and Bθ are known from formula (2), then Fr and Fθ can be obtained. Here, the magnetic flux density Br is measured using the magnetic field measuring device “MS-9902” (product name) manufactured by FWBELL, where the distance between the probe (as a component of the measuring device) and the surface of the developing sleeve is set to about 100 μm.

[0093] Furthermore, Bθ can be obtained as follows: Using the measured magnetic flux density Br, the vector potential A at the location where the magnetic flux density Br is measured is calculated using formula (3). Z (R, θ).

[0094] [Mathematical Formula 3]

[0095]

[0096] The boundary condition is defined as A Z (R, θ), and solve the following equation to obtain A. Z (R, θ).

[0097] ▽ 2 A Z (R, θ) = 0. Then, Br and Bθ can be obtained through formulas (4) and (5).

[0098] [Mathematical Formula 4]

[0099]

[0100] [Mathematical Formula 5]

[0101]

[0102] Fr and Fθ can be obtained by applying Br and Bθ, which are measured and calculated as described above, to formula (1). According to the above formula, the magnetic flux density distribution that forms the desired Fr distribution in this embodiment can be obtained.

[0103] Typically, magnetic force points towards the side with higher magnetic flux density. Therefore, when the absolute values ​​of the magnetic flux density |Br| in the normal direction of adjacent magnetic poles are substantially the same, the magnetic force Fθ near the magnetic pole acts towards the position where the maximum value of the magnetic flux density in the normal direction, indicating the polarity of the magnetic pole, is located. For example, the magnetic force Fθ in the direction of magnetic pole 103P acts on a carrier positioned at approximately 120 degrees near magnetic pole 103P. That is, 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 magnetic force Fθ acts in a similar manner near magnetic poles 104P and 105P.

[0104] Furthermore, the direction of the magnetic force Fθ changes near the point where the magnetic poles change to opposite poles. For example, there is a point P11 at an angle of approximately 190 degrees where the polarity changes from magnetic pole 104P to magnetic pole 105P. Upstream of the point P11 in the direction of rotation D11, the magnetic force Fθ acting towards magnetic pole 104P acts on the carrier near point P11, and downstream of the point P11 in the direction of rotation D11, the magnetic force Fθ acting towards magnetic pole 105P acts on the carrier near point P11. This is because the magnitude of the magnetic influence of magnetic poles 104P and 105P switches with point P11 as the boundary.

[0105] on the other hand, Figure 7 The graph shows the distribution of magnetic properties acting on the carrier on the developing sleeve 11 in the construction according to Comparative Example 2. In the graph, similar to... Figure 6 The absolute value of the magnetic flux density |Br| is represented by a solid line, and the magnetic force Fθ acting on the carrier is represented by a dashed line. Similarly, in the construction according to Comparative Example 2, similar to Comparative Example 1, a developing magnet having multiple magnetic poles including three magnetic poles 103Q, 104Q, and 105Q is disposed inside a developing sleeve 11 with a diameter of 25 mm. The absolute values ​​of the magnetic flux density |Br| of these three magnetic poles in the normal direction are substantially the same. Magnetic poles 103Q, 104Q, and 105Q correspond to... Figure 3 The first feed pole 103, the second feed pole 104, and the developing pole 105 are shown. Magnetic poles 103Q, 104Q, and 105Q are configured such that adjacent magnetic poles have different polarities.

[0106] Figure 7The graph illustrates the case where the absolute value of the magnetic flux density |Br| in the normal direction of magnetic pole 105Q is greater than the absolute value of the magnetic flux density |Br| in the normal direction of magnetic pole 104Q. As the absolute value of the magnetic flux density |Br| in the normal direction of magnetic pole 105Q increases, the magnetic influence of magnetic pole 105Q on the carrier near magnetic pole 104Q becomes stronger. That is, when the absolute value of the magnetic flux density |Br| in the normal direction of magnetic pole 105Q becomes greater than the absolute value of the magnetic flux density |Br| in the normal direction of magnetic pole 104Q, the carrier present near magnetic pole 104Q is attracted to magnetic pole 105Q, and the magnetic force Fθ in the entire vicinity of magnetic pole 104Q always points towards magnetic pole 105Q (the rotation direction D11 of the developing sleeve 11). Naturally, the carrier near point P11 also points towards magnetic pole 105Q, where the direction of the magnetic force Fθ remains unchanged. In this way, the direction of the magnetic force Fθ changes according to the magnitude relationship between adjacent magnetic poles.

[0107] Next, we will use Figure 8 The graph shown describes the construction based on Comparative Example 3. Figure 8 The graph shows the distribution of magnetic properties acting on the carrier on the developing sleeve 11 in the construction according to Comparative Example 3. In the graph, similar to... Figure 6 The absolute value of the magnetic flux density |Br| is represented by a solid line, and the magnetic force Fθ acting on the carrier is represented by a dashed line. Similarly, in the construction according to Comparative Example 3, similar to Comparative Example 1, a developing magnet having multiple magnetic poles, including three magnetic poles 103R, 104R, and 105R, is disposed inside a developing sleeve 11 with a diameter of 25 mm. The absolute values ​​of the magnetic flux density |Br| of these three magnetic poles in the normal direction are substantially the same. Magnetic poles 103R, 104R, and 105R correspond to... Figure 3 The first feed pole 103, the second feed pole 104, and the developing pole 105 are shown. Magnetic poles 103R, 104R, and 105R are configured such that adjacent magnetic poles have different polarities.

[0108] exist Figure 8 In the curve diagram, P1 represents the point where line α intersects the surface of the developing sleeve 11. Line α connects the distal end 72c of the lower part 72 of the conduit on the suction port 74 side to the rotation center O of the developing sleeve 11, as referenced above. Figure 4 Furthermore, P2 represents the position where the absolute value of the magnetic flux density in the normal direction of the magnetic pole 103R on the developing sleeve 11 is the largest, while P3 represents the position where the absolute value of the magnetic flux density in the normal direction of the magnetic pole 104R on the developing sleeve 11 is the largest. Additionally, the sign of the magnetic force Fθ is positive in the direction from P1 to P3 (opposite to the direction of air flow in the flow path AP). The subsequent magnetic property distribution diagrams have a similar structure.

[0109] The absolute value of the magnetic flux density of the magnetic pole 105R positioned facing the photosensitive drum 21Y is typically greater than the absolute value of the magnetic flux density of the surrounding magnetic poles. This is to increase the magnetic bonding force between the carrier and the developing sleeve 11, and to suppress image defects caused by the carrier's incorrect attachment to the photosensitive drum 21Y. Furthermore, by increasing the absolute value of the magnetic flux density of the magnetic pole 105R, the magnetic brushes of the developer on the developing sleeve 11 become denser, resulting in a toner image with lower non-uniformity on the photosensitive drum 21Y.

[0110] Therefore, in Comparative Example 3, similar to Figure 7 In Comparative Example 2 shown, 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. Therefore, from P3 (which is the position where the absolute value of the magnetic flux density in the normal direction of magnetic pole 104R is the largest) upstream in the rotation direction of the developing sleeve 11 to the position where the absolute value of the magnetic flux density in the normal direction of magnetic pole 105R is the largest, the magnetic force Fθ acting on the carrier is positive.

[0111] However, the magnetic influence of magnetic pole 105R on magnetic pole 103R, which is upstream of magnetic pole 104R in the rotation direction of the developing sleeve 11, is relatively small. Near P2 (where the absolute value of the magnetic flux density in the normal direction of magnetic pole 103R is the largest), the magnetic force Fθ acts on the carrier on the developing sleeve 11 in the direction towards magnetic pole 103R. That is, the magnetic force Fθ is positive upstream of P2 in the rotation direction of the developing sleeve 11, and negative downstream of P2 in the same direction. Therefore, downstream of P2 in the rotation direction of the developing sleeve 11, in a portion of region TH, the direction of the magnetic force Fθ may coincide with the direction of airflow in the flow path AP (the direction of the wind load Fa), and in Comparative Example 3, the carrier is likely to separate from the developing sleeve 11.

[0112] Similarly, in this embodiment, P2 is the position where the absolute value of the magnetic flux density in the normal direction of the first feed pole 103 on the developing sleeve 11 is the largest, and P3 is the position where the absolute value of the magnetic flux density in the normal direction of the second feed pole 104 on the developing sleeve 11 is the largest. In this case, in the rotation direction of the developing sleeve 11, P1 is located downstream of P2 and upstream of P3. Furthermore, relative to the rotation direction of the developing sleeve, P1 is located in the range where the absolute value of the magnetic flux density in the normal direction of the first feed pole 103 is greater than 0. That is, position P1 is arranged downstream of P2 in the rotation direction of the developing sleeve 11 within the range where the polarity affects the magnetic flux density of the first feed pole 103, i.e., arranged in the range where the polarity affects the magnetic flux density of the first feed pole 103. Figure 8The absolute value of the magnetic flux density in the normal direction of magnetic pole 103R in the curve is within the range of positive values. This is because P1 is set such that the lower part 72 of the conduit covers the area near P2 to prevent the area on the developing sleeve 11 where the magnetic force Fθ acting on the carrier near the first feed pole 103 is negative from being exposed to the flow path AP, and to suppress the carrier from separating from the developing sleeve 11 near the first feed pole 103.

[0113] Here, in order to further improve the effect of the inhibitory carrier being aspirated into the catheter 70, it is conceivable to use, as follows: Figure 9 The configuration shown in Comparative Example 4 is illustrated. In Comparative Example 4, P1 is positioned near the location P2 where the absolute value of the magnetic flux density in the normal direction of the second feed pole 104 is the largest. However, since the lower part 72 of the guide tube deeply penetrates the area where a large amount of scattered toner is generated, the scattered toner is deposited on the lower surface of the lower part 72 facing the developing sleeve 11, and deposited toner TK is formed on the lower surface. The deposited toner TK may fall onto the photosensitive drum 21Y due to vibration or its own weight. Then, if the deposited toner TK falls onto the photosensitive drum 21Y, the toner image developed on the photosensitive drum 21Y is disturbed, resulting in a dotted defective image.

[0114] However, if the deposited toner TK falls vertically onto the developing sleeve 11 due to its own weight or vibration, the clumps of deposited toner TK will disperse on the developing sleeve 11, which may not result in a defective image. Therefore, when the tangent in the vertical direction of the developing sleeve 11 on the side closer to the photosensitive drum 21Y (the suction port 74 side) is defined as the vertical line G, P1 is preferably located in the horizontal direction further away from the photosensitive drum 21Y than the vertical line G. That is, P1 is preferably located downstream of position P2 in the rotational direction of the developing sleeve 11 up to the vertical line G, where the absolute value of the magnetic flux density in the normal direction of the first feed pole 103 is the largest. More preferably, P1 is located within the range where the polarity affects the magnetic flux density of the first feed pole 103, within which the risk of deposited toner TK is lower.

[0115] exist Figure 8In the curve diagram, P1 is located downstream of position P2 in the rotational direction of the developing sleeve 11 up to the vertical line G (P1 is located at approximately 130 degrees). At position P2, the absolute value of the magnetic flux density in the normal direction of magnetic pole 103R is the largest. The maximum value (absolute value) of the magnetic flux density in the normal direction of magnetic pole 103R is 87 mT, and the angle at 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, and the angle at 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.

[0116] In this specification, "near the developing sleeve 11" or "on the developing sleeve 11" refers to a position 100 μm away from the outer peripheral surface of the developing sleeve 11. That is, the magnetic force acting on the carrier on the developing sleeve 11 is the magnetic force acting on the carrier at a position 100 μm away from the outer peripheral surface of the developing sleeve 11.

[0117] exist Figure 8 In the graph, region TH extends from P1 to near the downstream magnetic pole 105R in the rotational direction of the developing sleeve 11, and is the region AP on the surface of the developing sleeve 11 where the developer is exposed to air during the suction of the scattered toner through the conduit 70. Figure 8 In Comparative Example 3 shown, the region in region TH where the magnetic force Fθ is negative (in the same direction as the air flow in the flow path AP) exists in the range of approximately 130 to 150 degrees. This is because the magnetic flux density of magnetic pole 104R is smaller upstream of the developing sleeve 11 in the rotation direction, and the magnetic influence of magnetic pole 103R is greater than that of magnetic pole 104R relative to the carrier near magnetic pole 103R, which increases the region where the magnetic force Fθ is negative downstream of P2 in the rotation direction of the developing sleeve 11. Therefore, in this region, as Figure 5A As shown, the force Fs = wind load Fa + magnetic force Fθ, and the force Fs becomes greater than the maximum static friction force Fm, causing the carrier to separate from the developing sleeve 11, thereby making it very likely that the carrier will be drawn into the conduit 70.

[0118] Therefore, in this embodiment, the following will refer to Figure 10As described, when the range from P1 to P3 in the rotational direction of the developing sleeve 11 is defined as R13, the tangential magnetic force acting on the carrier on the developing sleeve 11 is defined as Fθ, and the direction of Fθ from P1 to P3 in the rotational direction of the developing sleeve is defined as the positive direction, Fθ ≥ 0 is satisfied throughout the entire region R13. That is, the developing magnet 12 is configured such that the magnetic force Fθ is positive throughout the entire range R13 (in the direction opposite to the direction of air flowing through the flow path AP via the suction of the conduit 70).

[0119] Similarly, in this embodiment, it is similar to the above. Figure 7 and Figure 8 In Comparative Examples 2 and 3 shown, 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 feed electrode 104. Therefore, in the range from position P3 included in region TH to the vicinity of the developing electrode 105 located downstream in the rotation direction of the developing sleeve 11, the direction of the magnetic force Fθ must be the same as the rotation direction of the developing sleeve 11 (opposite to the direction of air flowing through the flow path AP by suction through the conduit 70). Therefore, in order to construct the magnetic force Fθ as positive throughout region TH, it is necessary to make the magnetic force Fθ positive within the range R13 from P1 to P3.

[0120] Therefore, when P4 is defined as the point on the side closer to P1 among the points where the normal component of the magnetic flux density of the second feed pole 104 on the developing sleeve 11 is half of its maximum value, and the range from P4 to P3 in the rotational direction of the developing sleeve 11 is defined as HW, the circumferential length of the developing sleeve 11 within the range HW is preferably 40% or more of the circumferential length of the developing sleeve 11 within the range R13. More preferably, the circumferential length of the developing sleeve 11 within the range HW is more than half of the circumferential length of the developing sleeve 11 within the range R13. In the following text, for convenience, the circumferential length of the developing sleeve 11 within the range HW can be simply referred to as "HW", and the circumferential length of the developing sleeve 11 within the range R13 can be simply referred to as "R13".

[0121] In other words, in this embodiment, when HW is defined as the range between points P4 and P3 on the first feed pole 103 side, at half the maximum value of the magnetic flux density of the second feed pole 104 on the surface of the developing sleeve 11, the range HW is preferably more than half of the range R13. That is, the developing magnet 12 is configured such that HW / R13 ≥ 1 / 2.

[0122] As a result, this enhances the magnetic influence of the second feed pole 104 on the first feed pole 103, thereby making the magnetic force Fθ acting on the carrier on the developing sleeve 11 positive within the range downstream of P1 in the rotational direction of the developing sleeve 11, where the polarity affects the magnetic flux density of the first feed pole 103. Therefore, within the entire range R13 exposed to the flow path AP, the magnetic force Fθ acts in the opposite direction to the direction of airflow through the flow path AP. As a result, as Figure 5B As shown, the force Fs = wind load Fa - magnetic force Fθ, and the force Fs may be less than the maximum static friction force Fm. Therefore, the carrier can be prevented from separating from the developing sleeve 11, and the carrier can be prevented from being drawn into the conduit 70. In the developing magnet 12, a portion of the magnet forming the second feed pole 104 in the circumferential direction can be cut off, or magnets with different magnetic forces can be embedded in the cut-off portion, thereby forming an asymmetric magnetic flux density like the second magnetic pole 104.

[0123] Figure 10 The magnetic property distribution according to this embodiment is shown. Figure 10 The graph illustrates the distribution of magnetic properties acting on the carrier on the developing sleeve 11 in the configuration according to this embodiment. In the graph, similar to... Figure 6 The absolute value of the magnetic flux density |Br| is represented by the solid line, and the magnetic force Fθ acting on the carrier is represented by the dashed line. Figure 10 In the curve diagram, the angle at P1 is 130 degrees, the maximum value (absolute value) of the magnetic flux density in the normal direction of the first feed pole 103 is 82 mT, the angle at P2 is 115 degrees, the maximum value (absolute value) of the magnetic flux density in the normal direction of the second feed pole 104 is 105 mT, the angle at 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.

[0124] Furthermore, the angle range of R13 is 48 degrees, the angle range of HW is 28 degrees, and HW / R13 = 58%. In this embodiment, since HW / R13 ≥ 1 / 2 is satisfied, the magnetic force Fθ is positive throughout the entire range of R13. Therefore, the carrier can be prevented from separating from the developing sleeve 11, thereby preventing the carrier from being aspirated into the catheter 70.

[0125] Reference Figure 8 (It is a graph showing the construction according to Comparative Example 3) and Figure 11 (It is a graph illustrating a construction according to another example of this embodiment) describes the use of... Figure 10 (It is a graph showing the construction according to this embodiment) The construction is compared. In Figure 8As mentioned above, the angle at 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 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 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.

[0126] In addition, Figure 8 In the curve graph, the angle range of R13 is 51 degrees, the angle range of HW is 17 degrees, HW / R13 = 33%, and Comparative Example 3 has a structure that does not satisfy HW / R13 ≥ 1 / 2. Therefore, since the magnetic force Fθ becomes negative within the range R13, the carrier is likely to separate from the developing sleeve 11, and the carrier cannot be sufficiently suppressed from being drawn into the catheter 70. On the other hand, unlike Comparative Example 3, this embodiment uses a developing magnet 12 with such... Figure 10 The magnetic field characteristics shown are constructed such that the carrier can be sufficiently suppressed from being drawn into the conduit 70.

[0127] Figure 11 The graph illustrates the distribution of magnetic properties acting on the carrier on the developing sleeve 11 in another example of the construction according to this embodiment. In the graph, similar to... Figure 6 The absolute value of the magnetic flux density |Br| is represented by the solid line, and the magnetic force Fθ acting on the carrier is represented by the dashed line. Figure 11 In the curve diagram, the angle at P1 is 130 degrees, the maximum value (absolute value) of the magnetic flux density in the normal direction of the first feed pole 103 is 82 mT, the angle at P2 is 116 degrees, the maximum value (absolute value) of the magnetic flux density in the normal direction of the second feed pole 104 is 105 mT, the angle at 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.

[0128] Furthermore, the angle range of R13 is 48 degrees, the angle range of HW is 20 degrees, HW / R13 = 42%, and another example of this embodiment has a structure that does not satisfy HW / R13 ≥ 1 / 2. However, since HW is a relatively large value and HW / R13 ≥ 40%, there is no region within the range R13 where the magnetic force Fθ is negative. Therefore, the carrier hardly separates from the developing sleeve 11, thereby suppressing the carrier from being drawn into the conduit 70. However, in another example of this embodiment, there is a region where the magnetic force Fθ is 0 at approximately 170 degrees, and the force used to counteract the wind load Fa is weak. Therefore, compared with Figure 10Compared to the configuration shown, the effect of inhibiting the carrier from being aspirated into the catheter 70 by inhibiting the carrier from separating from the imaging sleeve 11 is weaker.

[0129] Next, Table 1 shows the results of the investigation into whether the carrier was aspirated into the catheter 70 when R13 and HW were changed by altering the shape and arrangement of the magnets forming the first feed pole 103 and the second feed pole 104 in the imaging magnet 12.

[0130] Table 1

[0131] The method for evaluating whether the carrier has been aspirated is as follows: Ten consecutive pure white images are formed on an A3 sheet of paper, and the number of carriers attached to the dust collection filter 84 is checked. When no carrier is attached to the dust collection filter 84 in the ten consecutive pure white images formed on the A3 sheet of paper, 100 consecutive pure white images are formed on the A3 sheet of paper, and the number of carriers attached to the dust collection filter 84 is checked. The evaluation results of carrier aspiration are shown in Table 1 below.

[0132] Poor: When 10 images are formed on an A3 sheet of paper, more than 10 carriers are attached to the dust collection filter 84.

[0133] In the middle: When 10 images are formed on an A3 sheet of paper, approximately one carrier is attached to the dust collection filter 84.

[0134] Good: When 100 images are formed on A3 paper, approximately 1 carrier is attached to the dust collection filter 84.

[0135] When the minimum magnetic force Fθ in region TH, Fθmin, is positive (Fθmin > 0), it indicates that the direction of the magnetic force Fθ in region TH is opposite to the direction of the air flowing through flow path AP. Conversely, when the minimum magnetic force Fθ, Fθmin, in range R13 is negative (Fθmin < 0), it indicates that there exists a region within range R13 where the direction of the magnetic force Fθ is consistent with the direction of the air flowing through flow path AP. Furthermore, when the evaluation level is equal to or higher than "Medium," the target result for suppressing carrier suction is determined.

[0136] As can be seen from Table 1, in constructs 1 and 2, the ratio of range HW to range R13 is significantly less than 50%. Therefore, there is a region in range R13 where the minimum value Fθmin is negative, and no effect of suppressing carrier aspiration was observed.

[0137] In configuration 3, the ratio of range HW to range R13 is 42%, which is less than 50% but close to 50% and above 40%. Therefore, the minimum value Fθmin is not negative and is 0 (Fθmin=0). As a result, it exhibits a certain degree of effect in suppressing carrier aspiration. However, from the viewpoint of high productivity of the imaging device, as the speed of the developing sleeve 11 increases, the centrifugal force of the carrier applied to the developing sleeve 11 increases and the maximum static friction force Fm decreases, which may cause the carrier to be more likely to separate from the developing sleeve 11. Therefore, the minimum value Fθmin can be 0 to suppress the carrier from being aspirated into the conduit 70, but the minimum value Fθmin is preferably greater than 0 to exhibit a higher degree of effect.

[0138] In configurations 4, 5, and 6, the ratio of range HW to range R13 is greater than 50%. Because the magnetic influence of the second feed pole 104 also extends to the first feed pole 103, the magnetic force Fθ is positive throughout the entire range R13. Thus, the magnetic force Fθ acts to counteract the wind load Fa on the carrier on the developing sleeve 11 caused by the airflow path AP generated by the suction of toner through the conduit 70, thereby reducing the external force Fs (Fa-Fθ) relative to the maximum static friction force on the carrier. Therefore, carrier separation from the developing sleeve 11 can be suppressed. Consequently, in configurations 4, 5, and 6, carrier being drawn into the conduit 70 can be suppressed.

[0139] As described above, according to this embodiment, the separation of the carrier from the surface of the developing sleeve 11 can be suppressed. This separation occurs in a configuration where the suction port 74 of the conduit 70 is located near the developing sleeve 11 to effectively suction out scattered toner. That is, in the developing unit 20Y according to this embodiment, Fθ ≥ 0 is satisfied over the entire range R13 from P1 to P3. Preferably, the magnetic flux density of the plurality of magnetic poles fixedly arranged in the developing magnet 12 is set to satisfy HW / R13 ≥ 1 / 2, such that the direction of the magnetic force Fθ is opposite to the direction of the airflow path AP drawn into the conduit 70, i.e., Fθ > 0. Thus, the magnetic force Fθ acts on the carrier on the developing sleeve 11 to counteract the wind load Fa caused by the airflow path AP, and the force Fs, which is the resultant force of the wind load Fa and the magnetic force Fθ, becomes less than the maximum static friction force Fm of the carrier, thereby suppressing the separation of the carrier from the developing sleeve 11 and suppressing the carrier from being drawn into the conduit 70.

[0140] Second Embodiment

[0141] Reference Figure 12 and Figure 13The second embodiment is described below. This embodiment differs from the first embodiment in the magnetic flux density of the plurality of magnetic poles fixedly arranged in the developing magnet 12. Since other constructions and operations are similar to those in the first embodiment described above, the same constructions are indicated by the same reference numerals, and their descriptions and illustrations are omitted or simplified. Furthermore, the differences from the first embodiment will be primarily described below.

[0142] As described above in the first embodiment, the magnetic influence between adjacent magnetic poles depends on the magnitude relationship between their magnetic flux densities. Therefore, in order to make the direction of the magnetic force Fθ throughout the range R13 opposite to the direction of the airflow path AP through the conduit 70 (the 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 in the normal direction of the first feed pole 103 relatively smaller than the maximum absolute value of the magnetic flux density in the normal direction of the second feed pole 104. However, if the maximum absolute value of the magnetic flux density in the normal direction of the first feed pole 103 is smaller than the maximum absolute value of the magnetic flux density in the normal direction of the cutting pole 102, the magnetic force Fθ in the direction from the cutting pole 102 toward the first feed pole 103 decreases, and the developer coating formed on the developing sleeve 11 by the control scraper 43 becomes uneven. Therefore, the maximum absolute value of the magnetic flux density in the normal direction of the first feed pole 103 is set to be greater than the maximum absolute value of the magnetic flux density in the normal direction of the cut pole 102.

[0143] In this embodiment, when the maximum absolute value of the magnetic flux density in the normal direction of the cutting pole 102 is defined as Bc, the maximum absolute value of the magnetic flux density in the normal direction of the first feed pole 103 is defined as B1, and the maximum absolute value of the magnetic flux density in the normal direction of the second feed pole 104 is defined as B2, and the average value of Bc and B2 is defined as Bh = (Bc + B2) / 2, then Bh ≥ B1 > Bc, and HW / R13 ≥ 1 / 4. This allows for an increase in the magnetic influence of the second feed pole 104 on the carrier near the first feed pole 103 on the developing sleeve 11. As a result, the sign of the magnetic force Fθ can be positive throughout the range R13. That is, since the direction of the magnetic force Fθ is opposite to the direction of the airflow path AP through the conduit 70, carrier separation from the developing sleeve 11 can be suppressed within the range R13, and carrier being drawn into the conduit 70 can be suppressed.

[0144] Figure 12 The graph illustrates the distribution of magnetic properties acting on the carrier on the developing sleeve 11 in the configuration according to this embodiment. In the graph, similar to... Figure 6 The absolute value of the magnetic flux density |Br| is represented by the solid line, and the magnetic force Fθ acting on the carrier is represented by the dashed line. Figure 12 In the graph, the angle at P1 is set to 130 degrees, Bc is set to 45 mT, the angle at the location of the maximum absolute value of the magnetic flux density in the normal direction of the cutting pole 102 is set to 59 degrees, B2 is set to 105 mT, and the angle at the location of the maximum absolute value of the magnetic flux density in the normal direction of the second feed pole 104, P3, is set to 178 degrees. In this embodiment, since Bh = 75 mT, the magnetic characteristics are shown as follows: B1 is set to 52 mT and the angle at the location of the maximum absolute value of the magnetic flux density in the normal direction of the first feed pole 103, P2, is set to 115 degrees to satisfy Bh ≥ B1. Furthermore, the maximum absolute value of the magnetic flux density in the normal direction of the developing pole 105 is 175 mT, and the angle at this location is 210 degrees.

[0145] In this embodiment, the angle range of R13 is 48 degrees, the angle range of HW is 16 degrees, HW / R13 = 33%, and HW / R13 ≥ 1 / 4 is satisfied. In this configuration, it is confirmed that the magnetic force Fθ is positive throughout the entire region R13. As a result, the carrier can be suppressed from separating from the imaging sleeve 11, thereby suppressing the carrier from being aspirated into the catheter 70.

[0146] Reference Figure 13 (It is a graph showing the construction according to Comparative Example 5) Describes the use of... Figure 12 (It is a graph showing the construction according to this embodiment) for comparison. Figure 13 The graph shows the distribution of magnetic properties acting on the carrier on the developing sleeve 11 in the construction according to Comparative Example 5. In the graph, similar to... Figure 6 The absolute value of the magnetic flux density |Br| is represented by the solid line, and the magnetic force Fθ acting on the carrier is represented by the dashed line. Figure 13 In the curve diagram, the angle at P1 is set to 130 degrees, Bc is set to 45 mT, the angle at the position of the maximum absolute value of the magnetic flux density in the normal direction of the cutting pole 102 is set to 59 degrees, B2 is set to 105 mT, and the angle at the position of the maximum absolute value of the magnetic flux density in the normal direction of the second feed pole 104, P3, is set to 178 degrees.

[0147] In Comparative Example 5, Bh = 75 mT is satisfied, but B1 is set to 100 mT, and the angle at P2, the location of the maximum absolute value of the magnetic flux density in the normal direction of the first feed pole 103, is set to 118 degrees, indicating that the magnetic properties do not satisfy Bh ≥ B1. The maximum absolute value of the magnetic flux density in the normal direction of the developing pole 105 is 175 mT, and the angle at this location is 210 degrees. In Comparative Example 5, the angle range of R13 is 48 degrees, the angle range of HW is 16 degrees, and HW / R13 = 33%.

[0148] In this configuration according to Comparative Example 5, since the magnetic influence of the second feed pole 104 on the first feed pole 103 is reduced, the magnetic force Fθ becomes negative within the range where the polarity affects the magnetic flux density of the first feed pole 103. Therefore, the magnetic force Fθ acts on the carrier on the developing sleeve 11 in the same direction as the wind load Fa, and thus the force Fs (Fs = Fa + Fθ) opposing the maximum static friction force Fm of the carrier increases. As a result, the carrier cannot be sufficiently prevented from separating from the developing sleeve 11, and the carrier cannot be prevented from being drawn into the conduit 70.

[0149] As described above, in accordance with this embodiment Figure 12 The construction and according to Comparative Example 5 Figure 13 In the construction, HW / R13 is 33%, but the magnetic influence of the second feed pole 104 on the first feed pole 103 varies depending on whether the maximum value B1 of the magnetic flux density in the normal direction of the first feed pole 103 satisfies Bh≥B1>Bc. Therefore, the direction of the magnetic force Fθ within the range R13 is different.

[0150] Next, Table 2 shows the results of the investigation on whether the carrier was aspirated into the catheter 70 when the shape and arrangement of the magnets forming the cutting pole 102, the first feed pole 103 and the second feed pole 104 in the imaging magnet 12 were changed to alter Bc, B1, B2, R13 and HW.

[0151] Table 2

[0152] The carrier suction was evaluated in the same manner as described in the first embodiment. Furthermore, when the minimum value of the magnetic force Fθ within range R13, Fθmin, is positive (Fθmin>0), this indicates that the direction of the magnetic force Fθ is opposite to the direction of the air flowing through flow path AP throughout range R13. On the other hand, when the minimum value of the magnetic force Fθ within range R13, Fθmin, is negative (Fθmin<0), this indicates that there exists a region within range R13 where the direction of the magnetic force Fθ is consistent with the direction of the air flowing through flow path AP. Additionally, when the evaluation level is equal to or higher than "Medium," the target result regarding the suppression of carrier suction is determined.

[0153] As can be seen from Table 2, in configurations 11 to 15, the effect of inhibiting the carrier from being drawn into the conduit 70 is relatively poor. In configurations 11, 12, and 13, in the region where the maximum value B2 of the magnetic flux density in the normal direction of the second feed pole 104 is half of its maximum value, the width of the upstream side in the rotation direction of the developing sleeve 11 is narrower, and its magnetic influence on the first feed pole 103 is smaller, so there is a region where the minimum value Fθmin is negative. Furthermore, in configurations 14 and 15, since the maximum value B1 of the magnetic flux density in the normal direction of the first feed pole 103 is relatively larger than the maximum value B2 of the magnetic flux density in the normal direction of the second feed pole 104, the magnetic influence of the second feed pole 104 on the first feed pole 103 is reduced, thus there is a region where the minimum value Fθmin is negative. In this way, in structures 11 to 15, since the 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, the force Fs (Fs=Fa+Fθ) that resists the maximum static friction force Fm of the carrier becomes larger. As a result, the carrier cannot be sufficiently prevented from separating from the developing sleeve 11, and the carrier cannot be prevented from being drawn into the conduit 70.

[0154] In configurations 16 to 21, the minimum value of the magnetic force Fθ within the range R13, Fθmin, is positive. Therefore, since the 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) that counteracts the maximum static friction force Fm of the carrier becomes smaller. As a result, the effect of inhibiting the separation of the carrier from the developing sleeve 11 and inhibiting the carrier from being drawn into the conduit 70 is observed.

[0155] In configurations 16 and 17, B1 has the same magnitude relative to Bh, and the ratio of HW to R13 differs. However, both satisfy Bh ≥ B1 and HW / R13 ≥ 1 / 4. Therefore, the second feed pole 104 has a greater magnetic influence on the first feed pole 103, and the minimum value Fθmin is positive throughout the entire range of R13. When comparing configuration 12 with configurations 16 and 17, configuration 12 is identical to configurations 16 and 17 in terms of the magnitude of B1 relative to Bh. However, configuration 12 does not satisfy HW / R13 ≥ 1 / 4. Therefore, in configuration 12, the second feed pole 104 has a smaller magnetic influence on the first feed pole 103, resulting in a region where the minimum value Fθmin is negative.

[0156] Similarly, in constructs 19 and 20, B1 has the same magnitude relative to Bh, and the ratio of HW to R13 differs, but both satisfy Bh ≥ B1 and HW / R13 ≥ 1 / 4. Therefore, in constructs 19 and 20, the second feed pole 104 has a larger magnetic influence on the first feed pole 103, and the minimum value Fθmin is positive throughout the entire range of R13. When comparing construct 11 with constructs 19 and 20, construct 11 is essentially the same as constructs 19 and 20 in terms of the magnitude of B1 relative to Bh, but construct 11 does not satisfy HW / R13 ≥ 1 / 4. Therefore, in construct 11, the second feed pole 104 has a smaller magnetic influence on the first feed pole 103, resulting in a region where the minimum value Fθmin is negative.

[0157] When comparing configurations 20 and 21, the ratio of HW to R13 is the same, and HW / R13≥1 / 4 is satisfied in both configurations. The magnitudes of B1 and Bh are different, but both satisfy Bh≥B1. Therefore, in configurations 20 and 21, the second feed pole 104 has a greater magnetic influence on the first feed pole 103, and the minimum value Fθmin is positive throughout the entire range of R13.

[0158] When comparing configuration 13 with configuration 21, the magnitude of B1 relative to Bh is Bh = B1, and Bh ≥ B1 is satisfied in both configurations. However, configuration 13 does not satisfy the condition HW / R13 ≥ 1 / 4. Therefore, in configuration 13, the magnetic influence of the second feed pole 104 on the first feed pole 103 is relatively small, resulting in a region within the range R13 where the minimum value Fθmin is negative. That is, even if Bh ≥ B1 is satisfied, whether the minimum value Fθmin is positive or negative within the range R13 varies depending on whether HW / R13 ≥ 1 / 4 is satisfied.

[0159] As described above, according to this embodiment, the separation of the carrier from the surface of the developing sleeve 11 can be suppressed. This separation occurs in the configuration where the suction port 74 of the conduit 70 is located near the developing sleeve 11 to effectively suction out scattered toner. Specifically, in the developing unit 20Y according to this embodiment, the magnetic flux density of the plurality of magnetic poles fixedly arranged in the developing magnet 12 within the entire range R13 from P1 to P3 is set to satisfy Bh≥B1 and HW / R13≥1 / 4, such that the direction of the magnetic force Fθ is opposite to the direction of the airflow path AP drawn into the conduit 70, i.e., Fθ>0. Therefore, the magnetic force Fθ acts on the carrier on the developing sleeve 11 to counteract the wind load Fa caused by the airflow path AP, and thus, the force Fs, which is the resultant force of the wind load Fa and the magnetic force Fθ, becomes less than the maximum static friction force Fm of the carrier, thereby suppressing the separation of the carrier from the developing sleeve 11 and suppressing the carrier from being drawn into the conduit 70.

[0160] Similarly, in this embodiment, as in the first embodiment, it is preferable to satisfy HW / R13≥40%, and more preferably to satisfy HW / R13≥1 / 2.

[0161] Other embodiments

[0162] This disclosure is not limited to the construction of the embodiments described above. For example, the imaging device 100 is not limited to an MFP, but can be a copier, printer, or fax machine. In addition, the construction of the first screw 41 and the second screw 42 is not particularly limited, as long as the developer can be fed, and for example, a spiral scraper or a paddle scraper can be used.

[0163] According to this disclosure, it is possible to prevent the carrier from being aspirated into the catheter portion.

[0164] While this disclosure has been described with reference to embodiments, it should be understood that this disclosure is not limited to the disclosed embodiments. The scope of the following claims is accorded the broadest interpretation to cover all such modifications and equivalent structures and functions.

Claims

1. A developing unit, comprising: A developer container configured to contain a developer comprising a toner and a carrier; A rotatable developing member configured to carry and feed developer to a developing position, in which an electrostatic latent image formed on an image carrying member is developed; A control unit configured to control the amount of developer carried on the outer peripheral surface of the rotatable developing member; A magnet, which is non-rotatably and fixedly disposed inside the rotatable developing member, the magnet comprising: A control electrode, wherein the control electrode is configured to face the control unit; The first feed electrode is disposed downstream of the control electrode in the rotation direction of the rotatable developing member; A second feed electrode is disposed adjacent to the first feed electrode and downstream of the first feed electrode in the rotational direction of the rotatable developing member, and has a polarity different from that of the first feed electrode; and A developing electrode, wherein the developing electrode is disposed downstream of the second feed electrode in the rotational direction of the rotatable developing member and faces the image carrier member at the developing position; and The catheter portion includes: A suction port is an inlet through which developer dispersed in the developer container is drawn in, and extends upstream from the suction port in the direction of rotation of the rotatable developing member. A first catheter wall, the first catheter wall being configured to face the rotatable imaging member; and A second conduit wall is disposed facing the rotatable developing member and the first conduit wall, and is configured to form a space between the second conduit wall and the first conduit wall through which developer drawn from the suction port flows. The second conduit wall is located outside the first conduit wall in the radial direction of the rotatable developing member relative to the center of rotation of the rotatable developing member. In the rotational direction of the rotatable developing member, the suction port is located upstream of a point on the outer peripheral surface of the rotatable developing member where the absolute value of the magnetic flux density of the developing pole in the direction normal to the outer peripheral surface of the rotatable developing member becomes its maximum value, and the suction port is located downstream of a point on the outer peripheral surface of the rotatable developing member where the absolute value of the magnetic flux density of the control pole in the direction normal to the outer peripheral surface of the rotatable developing member becomes its maximum value. In the rotational direction of the rotatable developing member, P1 is located downstream of P2 and upstream of P3, wherein, P1 is a point at which the line connecting the center of rotation of the rotatable developing member and the distal end of the first conduit wall on the suction port side intersects the outer peripheral surface of the rotatable developing member. P2 is a point on the outer peripheral surface of the rotatable developing member where the absolute value of the magnetic flux density of the first feed pole in the direction normal to the outer peripheral surface of the rotatable developing member becomes its maximum value. P3 is a point on the outer peripheral surface of the rotatable developing member where the absolute value of the magnetic flux density of the second feed pole in the direction normal to the outer peripheral surface of the rotatable developing member becomes its maximum value. in, In the rotational direction of the rotatable developing member, Fθ ≥ 0 is satisfied within the range from P1 to P3, where, Fθ is the magnetic force acting on the carrier on the outer peripheral surface of the rotatable developing member in the tangential direction relative to the outer peripheral surface of the rotatable developing member. The direction of Fθ from P1 toward P3 in the rotational direction of the rotatable developing member is defined as the positive direction.

2. The developing unit according to claim 1, wherein, The circumferential length of the rotatable developing member in the rotational direction from P4 to P3 is more than 40% of the circumferential length of the rotatable developing member in the rotational direction from P1 to P3, where P4 is a point on the outer peripheral surface of the rotatable developing member closer to P1, where the absolute value of the magnetic flux density of the second feed pole in the normal direction relative to the outer peripheral surface of the rotatable developing member becomes half of its maximum value.

3. The developing unit according to claim 1, wherein, The circumferential length of the rotatable developing member in the rotational direction from P4 to P3 is more than half of the circumferential length of the rotatable developing member in the rotational direction from P1 to P3, where P4 is a point on the outer peripheral surface of the rotatable developing member closer to P1, where the absolute value of the magnetic flux density of the second feed pole in the normal direction relative to the outer peripheral surface of the rotatable developing member becomes half of its maximum value.

4. The developing unit according to claim 1, wherein, The condition (Bc+B2) / 2 ≥ B1 > Bc is satisfied, where, Bc is the maximum absolute value of the magnetic flux density of the control electrode in the direction normal to the outer peripheral surface of the rotatable developing member. B1 is the maximum absolute value of the magnetic flux density of the first feed pole in the direction normal to the outer peripheral surface of the rotatable developing member, and B2 is the maximum absolute value of the magnetic flux density of the second feed pole in the direction normal to the outer peripheral surface of the rotatable developing member, and in, The circumferential length of the rotatable developing member in the rotational direction from P4 to P3 is more than 1 / 4 of the circumferential length of the rotatable developing member in the rotational direction from P1 to P3, wherein... P4 is a point on the outer peripheral surface of the rotatable developing member that is closer to P1 than the following point: at this point, the absolute value of the magnetic flux density of the second feed pole in the direction normal to the outer peripheral surface of the rotatable developing member becomes half of its maximum value.

5. The developing unit according to claim 1 or 2, wherein, In the rotational direction of the rotatable developing member, P1 is located within the range in which the absolute value of the magnetic flux density of the first feed pole in the normal direction relative to the outer peripheral surface of the rotatable developing member is greater than 0.

6. The developing unit according to claim 1 or 2, wherein, Point P1 is located horizontally on the side farther from the image carrier than the vertical line G, which is the tangent in the vertical direction of the rotatable developing member on the side closer to the image carrier.

7. The developing unit according to claim 1 or 2, wherein, The second catheter wall extends in the rotational direction of the rotatable imaging member to the downstream end of the first catheter wall at the distal end on the suction port side.

8. The developing unit according to claim 1 or 2, wherein, The image-carrying member is configured to be rotatable, and Wherein, at the position where the rotatable developing member and the image carrying member face each other, the rotation direction of the rotatable developing member is opposite to the rotation direction of the image carrying member.

9. A developing unit, comprising: A developer container configured to contain a developer comprising a toner and a carrier; A rotatable developing member configured to carry and feed developer to a developing position, in which an electrostatic latent image formed on an image carrying member is developed; A control unit configured to control the amount of developer carried on the outer peripheral surface of the rotatable developing member; A magnet, which is non-rotatably and fixedly disposed inside the rotatable developing member, the magnet comprising: A control electrode, wherein the control electrode is configured to face the control unit; The first feed electrode is disposed downstream of the control electrode in the rotation direction of the rotatable developing member; A second feed electrode is disposed adjacent to the first feed electrode and downstream of the first feed electrode in the rotational direction of the rotatable developing member, and has a polarity different from that of the first feed electrode; and A developing electrode, wherein the developing electrode is disposed downstream of the second feed electrode in the rotational direction of the rotatable developing member and faces the image carrier member at the developing position; and The catheter portion includes: A suction port is an inlet through which developer dispersed in the developer container is drawn in, and extends upstream from the suction port in the direction of rotation of the rotatable developing member. A first catheter wall, the first catheter wall being configured to face the rotatable imaging member; and A second conduit wall is disposed facing the rotatable developing member and the first conduit wall, and is configured to form a space between the second conduit wall and the first conduit wall through which developer drawn from the suction port flows. The second conduit wall is located outside the first conduit wall in the radial direction of the rotatable developing member relative to the center of rotation of the rotatable developing member. In the rotational direction of the rotatable developing member, the suction port is located upstream of a point on the outer peripheral surface of the rotatable developing member where the absolute value of the magnetic flux density of the developing pole in the direction normal to the outer peripheral surface of the rotatable developing member becomes its maximum value, and the suction port is located downstream of a point on the outer peripheral surface of the rotatable developing member where the absolute value of the magnetic flux density of the control pole in the direction normal to the outer peripheral surface of the rotatable developing member becomes its maximum value. In the rotational direction of the rotatable developing member, P1 is located downstream of P2 and upstream of P3. P1 is a point at which the line connecting the center of rotation of the rotatable developing member and the distal end of the first conduit wall on the suction port side intersects the outer peripheral surface of the rotatable developing member. P2 is a point on the outer peripheral surface of the rotatable developing member where the absolute value of the magnetic flux density of the first feed pole in the direction normal to the outer peripheral surface of the rotatable developing member becomes its maximum value. P3 is a point on the outer peripheral surface of the rotatable developing member where the absolute value of the magnetic flux density of the second feed pole in the direction normal to the outer peripheral surface of the rotatable developing member becomes its maximum value. Among them, (Bc+B2) / 2≥B1>Bc, where, Bc is the maximum absolute value of the magnetic flux density of the control electrode in the direction normal to the outer peripheral surface of the rotatable developing member. B1 is the maximum absolute value of the magnetic flux density of the first feed pole in the direction normal to the outer peripheral surface of the rotatable developing member, and B2 is the maximum absolute value of the magnetic flux density of the second feed pole in the direction normal to the outer peripheral surface of the rotatable developing member, and Wherein, the circumferential length of the rotatable developing member in the rotation direction of the rotatable developing member within the range from P4 to P3 is more than 1 / 4 of the circumferential length of the rotatable developing member in the rotation direction of the rotatable developing member within the range from P1 to P3, wherein, P4 is a point on the outer peripheral surface of the rotatable developing member that is closer to P1 than the following point: at this point, the absolute value of the magnetic flux density of the second feed pole in the direction normal to the outer peripheral surface of the rotatable developing member becomes half of its maximum value.

10. The developing unit according to claim 9, wherein, The circumferential length of the rotatable developing member in the rotation direction of the rotatable developing member within the range from P4 to P3 is more than 40% of the circumferential length of the rotatable developing member in the rotation direction of the rotatable developing member within the range from P1 to P3.

11. The developing unit according to claim 9, wherein, The circumferential length of the rotatable developing member in the rotation direction of the rotatable developing member within the range from P4 to P3 is more than half of the circumferential length of the rotatable developing member in the rotation direction of the rotatable developing member within the range from P1 to P3.

12. The developing unit according to claim 9 or 10, wherein, In the rotational direction of the rotatable developing member, P1 is located within the range in which the absolute value of the magnetic flux density of the first feed pole in the normal direction relative to the outer peripheral surface of the rotatable developing member is greater than 0.

13. The developing unit according to claim 9 or 10, wherein, Point P1 is located horizontally on the side farther from the image carrier than the vertical line G, which is the tangent in the vertical direction of the rotatable developing member on the side closer to the image carrier.

14. The developing unit according to claim 9 or 10, wherein The second catheter wall extends in the rotational direction of the rotatable imaging member to the downstream end of the first catheter wall at the distal end on the suction port side.

15. The developing unit according to claim 9 or 10, in, The image-carrying member is configured to be rotatable, and Wherein, at the position where the rotatable developing member and the image carrying member face each other, the rotation direction of the rotatable developing member is opposite to the rotation direction of the image carrying member.

Images