Developing device

Abstract

A developing device includes first and second chambers, a partition wall, first and second feed screws, a developing roller, a supply roller, a first magnet including first magnetic poles, a second magnet including second to fourth magnetic poles, and a guide portion. Relative to a rotation direction of the supply roller, a position where a magnetic flux density of the fourth magnetic pole in a normal direction is 20% of a maximum value thereof downstream of the third magnetic pole is a first position, a position where a line connecting a lowermost end of the guide portion and a center of the supply roller intersects with an outer peripheral surface of the supply roller is a second position, a position where a line connecting an uppermost end of the first feed screw and the center of the supply roller intersects with the outer peripheral surface of the supply roller is a third position, and the first position is located downstream of the second position and upstream of the third position.

Description

Technical Field

[0001] The present invention relates to a developing apparatus comprising a supply roller and a developing roller. Background Technology

[0002] In developing apparatuses, a conventional developing apparatus using a two-component developer is known, which comprises a toner containing non-magnetic particles and a carrier containing magnetic particles (hereinafter, the two-component developer is simply referred to as the developer). As such a developing apparatus, a structure using a so-called hybrid developing type has been proposed, which includes a developing roller as a rotatable developing member and a supply roller as a rotatable supply member, wherein the developing roller is arranged opposite to a photosensitive drum as an image carrying member, and the supply roller is arranged opposite to the developing roller (Japanese Patent Application Publication No. (JP-A) 2009-198582).

[0003] In this hybrid type of developing apparatus, the developer is carried on a supply roller, which is equipped with a magnet. The developer delivered by the rotation of the supply roller forms a toner layer on the developing roller, and then the electrostatic latent image on the photosensitive drum is developed using the toner supplied from the developing roller.

[0004] In the developing apparatus disclosed in JP-A 2009-198582, a supply roller is disposed above a feed member for feeding developer into the developing apparatus. A magnet disposed inside the supply roller includes a main magnetic pole located opposite the developing roller. Furthermore, relative to the rotation direction of the supply roller, the magnet includes a stripping magnetic pole disposed downstream of the main magnetic pole for stripping developer from the supply roller, and a pick-up magnetic pole disposed downstream of and adjacent to the stripping magnetic pole for picking up developer from the developing container onto the supply roller. Additionally, a non-magnetic region is provided between the stripping magnetic pole and the pick-up magnetic pole.

[0005] In the configuration disclosed in JP-A 2009-198582, the developing container includes a wall member extending from a position opposite to the stripping magnet to below the supply roller around the periphery of the supply roller. Consequently, there is a tendency for developer stripped from the supply roller to remain between the supply roller and the wall member, and for this developer to be drawn back onto the supply roller by the pick-up magnet. That is, as the supply roller rotates, there is a tendency for so-called developer movement to occur, causing the developer carried on the supply roller and supplying toner to the developing roller to be stripped from the supply roller and then drawn back onto the supply roller. When this developer movement occurs as the supply roller rotates, toner is supplied from a developer with a low toner ratio, resulting in a decrease in the quality of the output image. Summary of the Invention

[0006] The main objective of this invention is to provide a developing apparatus that includes a supply roller and a developing roller, and is capable of suppressing the movement of the developer as the supply roller rotates.

[0007] According to one aspect of the invention, a developing apparatus is provided, comprising: a first chamber configured to contain a developer comprising a toner and a carrier; a second chamber forming a developer circulation channel between itself and the first chamber; a partition wall configured to separate the first chamber and the second chamber; a first feed screw disposed in the first chamber and configured to feed the developer in a first direction; a second feed screw disposed in the second chamber and configured to feed the developer in a second direction opposite to the first direction; a developing roller configured to carry and convey the toner to a developing position where an electrostatic image formed on an image carrier member is developed; and a supply roller disposed opposite to the developing roller and configured to carry and convey developer supplied from the first chamber and supply toner only to the developing roller, supplying rotation of the roller at the position where the supply roller and the developing roller are opposite to each other. The direction is opposite to the rotation direction of the developing roller; a first magnet, which is non-rotatable and fixedly disposed inside the developing roller, and includes a first magnetic pole; a second magnet, which is non-rotatable and fixedly disposed inside the supply roller, and includes: a second magnetic pole disposed opposite to the first magnetic pole at a position opposite the developing roller to the supply roller, and having a different polarity from the first magnetic pole; a third magnetic pole disposed downstream of the second magnetic pole relative to the rotation direction of the supply roller; and a fourth magnetic pole disposed upstream of the second magnetic pole and downstream of the third magnetic pole relative to the rotation direction of the supply roller, and adjacent to the third magnetic pole, and having the same polarity as the third magnetic pole; and a guide portion configured to guide developer stripped from the supply roller into a first chamber by a repulsive magnetic field formed by the third and fourth magnetic poles, the lowermost end of the guide portion being close to the uppermost end of the partition wall, wherein the guide portion overlaps with the supply roller in the direction of gravity, and wherein when: A first position is a position located downstream of the position where the magnetic flux density of the third magnetic pole is highest in the normal direction of the outer peripheral surface of the supply roller, and upstream of the position where the magnetic flux density of the fourth magnetic pole is highest in the normal direction of the outer peripheral surface of the supply roller, relative to the rotation direction of the supply roller. At the first position, the magnetic flux density of the fourth magnetic pole in the normal direction is 20% of its highest value. When viewed in a cross section perpendicular to the rotation axis of the supply roller, the position where the straight line connecting the lowermost end of the guide portion and the rotation center of the supply roller intersects the outer peripheral surface of the supply roller is the second position. And when viewed in a cross section perpendicular to the rotation axis of the supply roller, the position where the straight line connecting the uppermost end of the first feed screw and the rotation center of the supply roller intersects the outer peripheral surface of the supply roller is the third position, the first position is downstream of the second position and upstream of the third position relative to the rotation direction of the supply roller.

[0008] According to another aspect of the present invention, a developing apparatus is provided, comprising: a first chamber configured to contain a developer comprising a toner and a carrier; a second chamber forming a circulation channel for the developer between itself and the first chamber; a partition wall configured to separate the first chamber and the second chamber; a first feed screw disposed in the first chamber and configured to feed the developer in a first direction; a second feed screw disposed in the second chamber and configured to feed the developer in a second direction opposite to the first direction; a developing roller configured to carry and convey the toner to a developing position where an electrostatic image formed on an image carrier member is developed; and a supply roller disposed opposite to the developing roller and configured to carry and convey the developer supplied from the first chamber and supply toner only to the developing roller, supplying rotation of the roller at the position where the supply roller and the developing roller are opposite to each other. The direction is opposite to the rotation direction of the developing roller; a first magnet, which is non-rotatable and fixedly disposed inside the developing roller, and includes a first magnetic pole; a second magnet, which is non-rotatable and fixedly disposed inside the supply roller, and includes: a second magnetic pole disposed opposite to the first magnetic pole at a position opposite the developing roller to the supply roller, and having a different polarity from the first magnetic pole; a third magnetic pole disposed downstream of the second magnetic pole relative to the rotation direction of the supply roller; and a fourth magnetic pole disposed upstream of the second magnetic pole and downstream of the third magnetic pole relative to the rotation direction of the supply roller, and adjacent to the third magnetic pole, and having the same polarity as the third magnetic pole; and a guide portion configured to guide developer stripped from the supply roller into a first chamber by a repulsive magnetic field formed by the third and fourth magnetic poles, the lowermost end of the guide portion being close to the uppermost end of the partition wall, wherein the guide portion overlaps with the supply roller in the direction of gravity, and wherein when: A first position is a position located downstream of the position where the magnetic flux density of the third magnetic pole is highest in the normal direction of the outer peripheral surface of the supply roller, and upstream of the position where the magnetic flux density of the fourth magnetic pole is highest in the normal direction of the outer peripheral surface of the supply roller, relative to the rotation direction of the supply roller. At the first position, the magnetic flux density of the fourth magnetic pole in the normal direction is 20% of the absolute value of the difference between the highest value of the magnetic flux density of the fourth magnetic pole in the normal direction and the average value of the magnetic flux density in the normal direction in the region where the absolute value is less than 5 mT. When viewed in a section perpendicular to the rotation axis of the supply roller, the position where the straight line connecting the lowermost end of the guide portion and the rotation center of the supply roller intersects the outer peripheral surface of the supply roller is the second position. And when viewed in a section perpendicular to the rotation axis of the supply roller, the position where the straight line connecting the uppermost end of the first feed screw and the rotation center of the supply roller intersects the outer peripheral surface of the supply roller is the third position, the first position is downstream of the second position and upstream of the third position relative to the rotation direction of the supply roller.

[0009] Other features of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0010] Figure 1 This is a schematic structural cross-sectional view of the imaging device in the first embodiment.

[0011] Figure 2 This is a control block diagram of the imaging device in the first embodiment.

[0012] Figure 3 This is a cross-sectional view of the developing apparatus according to the first embodiment.

[0013] Figure 4 It is a cross-sectional view of a developing apparatus based on a comparative example.

[0014] Figure 5 It is a graph showing the magnetic strength (magnetic properties) generated by each magnetic pole when the magnetic poles of the magnetic rollers in the supply rollers of each of the first embodiment and the comparative example are spread out on a plane.

[0015] Figure 6 Part (a) is a table relating to the starting position of the magnetic force of the magnetic pole in Example 1 (starting magnetic force position). Figure 6 Part (b) is a table relating to the starting position of the magnetic force of the drawing pole in the comparative example.

[0016] Figure 7 This is a cross-sectional view of the developing apparatus according to the second embodiment.

[0017] Figure 8 It is a graph showing the magnetic strength (magnetic properties) generated by each magnetic pole when the magnetic poles of the magnetic roller in the supply roller according to the second embodiment are spread out on the plane.

[0018] Figure 9 This is a table related to the starting position of the magnetic force of the magnetic pole in Example 2 (starting magnetic force position). Detailed Implementation

[0019] <First Embodiment>

[0020] Will use Figures 1 to 6 The first embodiment is described. Incidentally, in this embodiment, an example is described of applying the developing apparatus to a tandem full-color printer as an imaging device.

[0021] [Imaging equipment]

[0022] First, we will use Figure 1 A schematic structure of the imaging device 100 is described.

[0023] Figure 1The imaging device 100 shown is an electrophotographic full-color printer, which includes imaging sections PY, PM, PC, and PK for four colors (yellow, magenta, cyan, and black) in its main assembly. In this embodiment, an intermediate transfer tandem type is used, wherein the imaging sections PY, PM, PC, and PK are arranged along the rotation direction of the intermediate transfer belt 6, which will be described later. The imaging device 100 forms a toner image (picture) on the recording material S based on an image signal from a host device, such as a personal computer communicatively connected to the main assembly or a document reader (not shown) connected to the main assembly. The recording material S can include sheet materials such as paper, plastic film, or cloth.

[0024] The toner image formation process will be described. First, the imaging portions PY, PM, PC, and PK will be described. The imaging portions PY, PM, PC, and PK are basically the same in composition, except that the colors of the toners differ from one another: yellow, magenta, cyan, and black, respectively. Therefore, in the following description, the imaging portion PY used for yellow will be described as an example, and the descriptions of the other imaging portions PM, PC, and PK will be omitted.

[0025] The imaging section PY mainly consists of a photosensitive drum 1, a charging device 2, a developing device 4, and a cleaning device 8. In this embodiment, the intermediate transfer belt 6 is positioned above the imaging sections PY, PM, PC, and PK, and the exposure device 3 is positioned below the imaging sections PY, PM, PC, and PK. The photosensitive drum 1, which serves as both an image carrier and a photosensitive component, includes a photosensitive layer with negative or positive charge polarity formed on the outer peripheral surface of an aluminum cylinder, and rotates at a predetermined processing speed (circumferential speed).

[0026] The charging device 2 charges the surface of the photosensitive drum 1 to, for example, a uniform negative or positive dark area potential, according to the charging characteristics of the photosensitive drum 1. In this embodiment, the charging device 2 is a rotatable charging roller that contacts the surface of the photosensitive drum 1. After charging, an electrostatic latent image is formed on the surface of the photosensitive drum 1 by the exposure device (laser scanner) 3 based on image information. The photosensitive drum 1 carries the formed electrostatic image and moves cyclically, and the electrostatic latent image is developed by the developing device 4 using toner. Details of the structure of the developing device 4 will be described later. The toner in the developer consumed by imaging is supplied from a toner cartridge (not shown) along with a carrier.

[0027] The toner image developed from the electrostatic latent image is initially transferred onto the intermediate transfer belt 6 by a primary transfer roller 61, which is positioned opposite the photosensitive drum 1 across an intermediate transfer belt 6, supplied with a predetermined pressure and a primary transfer bias. After the primary transfer, the surface of the photosensitive drum 1 is discharged by a pre-exposure portion (not shown). A cleaning device 8 removes residual substances, such as residual toner, remaining on the surface of the photosensitive drum 1 after the primary transfer.

[0028] The intermediate transfer belt 6 is stretched by the stretching roller 62 and the inner secondary transfer roller 63. The intermediate transfer belt 6 is driven by the inner secondary transfer roller 63, which is also the drive roller, along... Figure 1 The image moves in the direction of arrow R1. The imaging processes for various colors performed by the imaging sections PY, PM, PC, and PK are all executed at timings where the relevant color toner image is superimposed on the upstream color toner image initially transferred onto the intermediate transfer belt 6 in the direction of movement relative to the intermediate transfer belt 6. As a result, a full-color toner image is ultimately formed on the intermediate transfer belt 6 and conveyed towards the secondary transfer section T2. ​​The secondary transfer section T2 is a transfer clamping part formed by the outer secondary transfer roller 64 and a portion of the intermediate transfer belt 6 stretched by the inner secondary transfer roller 63. Incidentally, residual toner after passing through the secondary transfer section T2 is removed from the surface of the intermediate transfer belt 6 by a belt cleaning device (not shown).

[0029] In contrast to the toner image formation process, which sends the toner image to the secondary transfer section T2, a transfer (feed) process is performed at a similar timing to transfer the recording material S to the secondary transfer section T2. ​​During this transfer process, the recording material S is fed from a sheet cassette (not shown) and other components, and is sent to the secondary transfer section T2 synchronously with the imaging timing. In the secondary transfer section T2, a secondary transfer voltage is applied to the internal secondary transfer roller 63.

[0030] Through the aforementioned imaging and transport processes, in the secondary transfer section T2, the toner image is transferred a second time from the intermediate transfer belt 6 onto the recording material S. Subsequently, the recording material S is conveyed to the fixing device 7, where it is heated and pressurized to melt the toner image and fix it onto the recording material S. Therefore, the recording material S with the toner image fixed on it is discharged onto the discharge tray by the discharge roller.

[0031] [Controller]

[0032] Imaging device 100 includes a controller 20, which performs various controls, such as the imaging operations described above. The operation of various parts of imaging device 100 is controlled by the controller 20 disposed within imaging device 100. A series of imaging operations are controlled by an operation section located on the upper part of the main device assembly, or by the controller 20 via a network based on corresponding imaging signals.

[0033] like Figure 2As shown, the controller 20 includes a CPU (Central Processing Unit) 21, a ROM (Read-Only Memory) 22, and a RAM (Random Access Memory) 23, which serve as computing control devices. The CPU 21 controls various parts of the imaging device 100 and simultaneously reads programs corresponding to the control process stored in the ROM 22. Operational data and input data are stored in the RAM 23, and the CPU 21 performs control based on the aforementioned programs by referring to the data stored in the RAM 23.

[0034] The controller 20 generates drive signals for each part by processing image information by the image processing unit 24, and controls the operation of each part (e.g., the drive unit 9 for driving the exposure unit 3 and the developing unit 4) by the imaging controller 25, thereby controlling the toner supply to the developing unit 4 by the supply controller 26. The drive unit 9 includes drive motors for driving the developing roller 50, the supply roller 51, the first feed screw 44, and the second feed screw 45, which will be described later.

[0035] The controller is connected to a toner concentration sensor 58, an optical sensor 80, a temperature and humidity sensor 81, a bias power supply 82, etc. The toner concentration sensor 58 will be described later. The optical sensor 80 is positioned opposite the surface of the intermediate transfer belt 6 and detects the concentration of the block image formed on the intermediate transfer belt 6 as a control toner image. Based on the concentration of the block image detected by the optical sensor 80, toner supply control to the developing apparatus 4 is performed. The bias power supply 82 is a power source for applying voltage to the developing roller 50 and the supply roller 51, as described later.

[0036] A temperature and humidity sensor 81, as an example of a detection device, is provided, for example, in a portion of the wall of the stirring chamber 43 downstream in the toner delivery (feed) direction to detect temperature and humidity information in the developing apparatus 4. The controller 20 calculates the absolute water content in the developing apparatus 4 based on the information about the temperature and humidity in the developing apparatus 4, which is the detection result of the temperature and humidity sensor 81. That is, the temperature and humidity sensor 81 detects information about the absolute water content within the developing container 40. Incidentally, in this embodiment, the controller 20 calculates information about volumetric absolute humidity as information about the absolute water content. Furthermore, while this embodiment describes the controller 20 calculating information about volumetric absolute humidity as information about the absolute water content, the invention is not limited to this; rather, the controller 20 can calculate information about weight absolute humidity as information about the absolute water content.

[0037] [Two-component developer]

[0038] Next, the developer used in this embodiment will be described. In this embodiment, a two-component developer comprising non-magnetic toner particles (toner) and magnetic carrier particles (carrier) is used as the developer, and the two-component developer has a mixing coating ratio of 8.0% by weight of the toner on the carrier. The toner is colored resin particles containing binder resin, colorant, and other desired additives, and external additives such as colloidal silica powder are added to its surface from the outside. Depending on the charging characteristics of the photosensitive drum 1, the toner is, for example, a negatively or positively charged polyester resin material, and the volume average particle size is about 7.0 micrometers. The carrier includes, for example, magnetic metal particles such as iron, nickel, and cobalt, whose surfaces are oxidized, and the volume average particle size is about 40 micrometers or more and about 50 micrometers or less.

[0039] In this embodiment, a developer comprising a carrier having a weight-average particle size of 45 micrometers, containing Mn-Mg as the main component, and having a saturation magnetization of 60 emu / g (a value obtained by the MSV method) is used as the developer. Toner particles with an intermediate diameter of 7 micrometers in the volume distribution measured by a Coulter counter are used as the toner. Furthermore, a mixture of toner and carrier at a toner concentration of 12% is used as the developer.

[0040] [Developing apparatus]

[0041] Next, we will use Figure 3 The developing apparatus 4 is described in detail. The developing apparatus 4 in this embodiment is a so-called contact developing type developing apparatus, in which a thin layer consisting only of toner is formed on the developing roller 50 by a magnetic brush of a two-component developer formed on the supply roller 51, and then the toner is sent to the electrostatic latent image formed on the photosensitive drum 1 by a developing bias obtained by the superposition of DC and AC applied to the developing roller 50 for developing.

[0042] like Figure 3As shown, the developing apparatus 4 includes a developing container 40, a developing roller 50 as a rotatable developing member, and a supply roller 51 as a rotatable supply member. The developing container 40 contains a developing agent comprising a non-magnetic toner and a magnetic carrier. The developing container 40 includes a developing chamber 42 as a first chamber, a stirring chamber 43 as a second chamber, and a partition wall 41 as a partition wall. The stirring chamber 43 is disposed adjacent to the developing chamber 42, such that it at least partially overlaps with the developing chamber 42 when viewed in a horizontal direction. The partition wall 41 separates the developing chamber 42 and the stirring chamber 43. The partition wall 41 has openings 41a as communication portions on each of its opposite ends relative to the longitudinal direction (the direction of the rotation axes of the developing roller 50 and the supply roller 51), establishing communication between the developing chamber 42 and the stirring chamber 43. The developing container 40 forms a circulation channel along which the developing agent circulates between the developing chamber 42 and the stirring chamber 43 via the openings 41a in the partition wall 41.

[0043] In this embodiment, a partition wall 41 is disposed approximately in the central portion of the developing container 40. Thus, the developing container 40 is divided by the partition wall 41, such that the developing chamber 42 and the stirring chamber 43 are adjacent to each other in the horizontal direction. In the developing chamber 42 and the stirring chamber 43, a rotatable first feed screw 44 and a second feed screw 45 are configured for stirring and circulating the developing agent.

[0044] A first feed screw 44, serving as a first feed component, is disposed at the bottom of the developing chamber 42 (in the first chamber) substantially parallel to and opposite to the supply roller 51 along the rotation axis (longitudinal direction) of the supply roller 51. The first feed screw 44 includes a rotating shaft 44a and blades 44b spirally disposed around the rotating shaft 44a. A second feed screw 45, serving as a second feed component, is disposed at the bottom of the stirring chamber 43 (in the second chamber) substantially parallel to and opposite to the first feed screw 44. The second feed screw 45 includes a rotating shaft 45a and blades 45b spirally disposed around the rotating shaft 45a.

[0045] The first feed screw 44 and the second feed screw 45 rotate in the directions of arrow R4 and arrow R3, respectively, thereby feeding developer into the developing chamber 42 and the stirring chamber 43, respectively. The developer fed by the rotation of the first feed screw 44 and the second feed screw 45 circulates between the developing chamber 42 and the stirring chamber 43 through openings 41a at each opposite end of the partition wall 41. The toner is stirred by the first feed screw 44 and the second feed screw 45, thereby becoming triboelectrically charged to either a negative or positive polarity through friction with the carrier.

[0046] In the stirring chamber 43, the toner concentration sensor 58 ( Figure 2The second feed screw 45 is positioned facing the toner concentration sensor 58. For example, a permeability sensor used to detect the permeability of the developer in the developing container 40 is used as the toner concentration sensor 58. Based on the detection result of the toner concentration sensor 58, the controller 20 causes the toner cartridge to supply toner to the stirring chamber 43 through the toner supply port (not shown).

[0047] like Figure 3 As shown, the developing roller 50 and the supply roller 51 are vertically positioned above the developing chamber 42 and the stirring chamber 43. Viewed from the direction of the rotation axis of the supply roller 51, the developing roller 50 is positioned diagonally above the supply roller 51 between the supply roller 51 and the photosensitive drum 1. The supply roller 51 and the developing roller 50 are positioned opposite each other in the opposing portion P1, and their rotation axes are substantially parallel to each other. The developing roller 50 is opposite the photosensitive drum 1 on the opening side of the developing container 40. Each of the developing roller 50 and the supply roller 51 is configured to rotate about its rotation axis. Each of the developing roller 50 and the supply roller 51 is driven by a drive portion 9 (… Figure 2 The developing roller 50 and the supply roller 51 rotate in opposite directions in the opposite part P1, and their rotational speed is variable through the drive part 9.

[0048] The supply roller 51 is along Figure 3 A non-magnetic cylindrical roller (with a diameter of, for example, 20 mm or more and 25 mm or less (20 mm in this embodiment)) that rotates counterclockwise is rotatably disposed around the periphery of a non-rotating cylindrical magnetic roller 51a, which is disposed on the inner circumference side and serves as a magnetic field generating device and a second magnet. That is, the magnetic roller 51a is non-rotatably fixed and disposed inside the supply roller 51. The magnetic roller 51a comprises five components, which, on their surfaces opposite to the supply roller 51, are arranged in a specified order relative to the rotation direction of the supply roller 51, including a pick-up magnetic pole S2, a control magnetic pole N2, a holding magnetic pole S1, a main magnetic pole N1, and a stripping magnetic pole S3. Incidentally, in this embodiment, a magnetic roller with five magnetic poles is used, but a magnetic roller with more than five magnetic poles, such as a magnetic roller with seven magnetic poles, can also be used.

[0049] The main magnetic pole N1 is positioned opposite the supply roller 51 and the developing roller 50, and its polarity differs from that of the receiving magnetic pole S4 (described later) of the magnetic roller 51a in the developing roller 50. The holding magnetic pole S1 is positioned upstream of and adjacent to the main magnetic pole N1, with its rotational direction relative to the supply roller 51, and its polarity differs from that of the main magnetic pole N1. The control magnetic pole N2 is positioned upstream of and adjacent to the holding magnetic pole S1, at which the control blade 52 (described later) is opposite the supply roller 51, and its polarity is the same as that of the main magnetic pole N1. The pick-up magnetic pole S2 is positioned upstream of and adjacent to the control magnetic pole N2, with a different polarity than the control magnetic pole N2, and is used to pick up developer from the developing container 40 onto the supply roller 51. Specifically, the pick-up magnetic pole S2 is positioned above the developing chamber 42 opposite to the first feed screw 44. The stripping magnetic pole S3 is positioned upstream of and adjacent to the pick-up magnetic pole S2 relative to the rotation direction of the supply roller 51, and has the same polarity as the pick-up magnetic pole S2. The pick-up magnetic pole S2, the control magnetic pole N2, the holding magnetic pole S1, the main magnetic pole N1, and the stripping magnetic pole S3 are arranged adjacent to each other in a specified order relative to the rotation direction of the supply roller 51.

[0050] The supply roller 51 carries a developer containing a non-magnetic toner and a magnetic carrier, and rotatably delivers the developer to the opposite portion P1 opposite the developing roller 50. That is, the supply roller 51 is positioned opposite the developing roller 50 and supplies the developer from the developing container 40 to the developing roller 50. In this embodiment, the supply roller 51 has a cylindrical shape, for example, 20 mm in diameter, and is made of a non-magnetic material such as aluminum or non-magnetic stainless steel; in this embodiment, it is formed of aluminum. Furthermore, the supply roller 51 undergoes sandblasting, resulting in a surface roughness of, for example, Rz = 30 micrometers on its outer peripheral surface.

[0051] A control blade 52, acting as a control member, is positioned upstream of the supply roller 51 relative to the rotation direction of the supply roller 51, opposite to the developing roller 50, and controls the amount of developer carried on the supply roller 51. Specifically, the control blade 52 is a plate-shaped member disposed within the developing container 40, with its free end facing the outer peripheral surface of the supply roller 51 where the control magnetic pole N2 of the magnetic roller 51a is located. A predetermined gap is provided between the free end of the control blade 52 and the supply roller 51. Furthermore, the magnetic flux of developer carried on the surface of the supply roller 51 is cut by the control blade 52, thereby controlling the layer thickness of the developer. Specifically, the control blade 52 comprises a metal plate (e.g., a stainless steel plate) disposed along the longitudinal direction of the supply roller 51, and the developer passes between the free end of the control blade 52 and the supply roller 51, such that the developer is conveyed while the amount of developer is controlled to a certain level. The control blade 52 is formed from a magnetic member, such as SUS430, in an L-shape, with a thickness of, for example, approximately 1.5 mm, and is positioned such that... Figure 3 In the case of a position offset 3° to 5° counterclockwise relative to the control magnetic pole N2, it is fixed in the developing container 40 and extends along the rotation axis of the supply roller 51.

[0052] Incidentally, the control blade 52 can be a magnetic (material) component or a non-magnetic component (material). With a magnetic material, there is an advantage that the gap between the free end of the control blade 52 and the supply roller 51 can be large, thus reducing the likelihood of foreign matter clogging. On the other hand, with a magnetic material, there is a tendency for the developer to be confined by the magnetic field between the free end of the control blade 52 and the supply roller 51, thus making it prone to developer degradation due to friction. Incidentally, a configuration can be adopted in which the control blade 52 is a magnetic component applied to a portion of a non-magnetic component. By doing so, the advantages of a magnetic component are somewhat lost, but developer degradation can be suppressed. In this embodiment, a control blade composed solely of a magnetic component is used as the control blade 52. Therefore, there is a tendency for developer degradation, but by combining it with the magnetic roller 51a, described later in this embodiment, developer degradation can be suppressed.

[0053] The developer contained in the developing chamber 42 is attracted to the surface of the supply roller 51 by the pick-up magnetic pole S2 opposite to the supply roller 51 and conveyed toward the control blade 52. The developer is upright by the control magnetic pole N2 opposite to the control blade 52, and its layer thickness is controlled by the control blade 52. The developer layer passes through the holding magnetic pole S1 and is carried and conveyed to the opposite portion P1 opposite to the photosensitive drum 1, and then the toner is supplied to the surface of the developing roller 50 in a state where a magnetic flux is formed by the main magnetic pole N1 opposite to the developing area. A supply bias voltage in the form of a superposition of DC voltage and AC voltage is applied to the supply roller 51.

[0054] The developing roller 50 is positioned opposite the photosensitive drum 1, and the developer is transferred to the developing position by the rotation of the developing roller 50, where the electrostatic latent image formed on the photosensitive drum 1 is developed. In other words, the developing roller 50 is movable along... Figure 3 The developing roller 50 is a non-magnetic roller that rotates counterclockwise and is configured to rotate around a magnetic roller 50a, which serves as a first magnet. The magnetic roller 50a includes a single receiving magnetic pole S4 disposed on its inner circumferential surface and does not rotate. The developing roller 50 is capable of developing an electrostatic latent image on the photosensitive drum 1 in a developing region opposite to the photosensitive drum 1 by rotating while carrying toner. The supply roller 51 and the developing roller 50 are opposite each other in their opposing portions P1 with a predetermined gap. The polarity of the receiving magnetic pole S4 of the magnetic roller 50a of the developing roller 50 is different from the polarity of the main magnetic pole N1 opposite to the receiving magnetic pole S4.

[0055] A developing bias voltage, which is a superposition of DC and AC voltages, is applied to the developing roller 50. The developing bias voltage and the supply bias voltage are respectively controlled by a bias power supply 82 (which is an example of a voltage application section) via a bias control circuit. Figure 2 It is applied to the developing roller 50 and the supply roller 51.

[0056] That is, the bias power supply 82 applies a voltage including DC and AC components between the developing roller 50 and the supply roller 51.

[0057] The toner remaining on the developing roller 50 that was not used for development is transferred again to the opposing portion P1 between the developing roller 50 and the supply roller 51, and is collected by the supply roller 51 due to friction with the magnetic flux on the supply roller 51. In the stripping zone formed by the repulsion of the stripping magnetic pole S3 and the suction magnetic pole S2 located downstream of the rotation direction of the supply roller 51, the magnetic flux is stripped from the supply roller 51. The stripped developer falls into the developing chamber 42 and is agitated and fed together with the developer circulating within the developing container 40, and is again attracted to the suction magnetic pole S2, and then conveyed by the supply roller 51.

[0058] [The relationship between the magnetic roller supplying the roller and the developing container]

[0059] Next, the relationship between the developing container 40 of the developing apparatus 4 and the magnetic roller 51a of the supply roller 51 will be described. Incidentally, in the following description, "upstream" and "downstream" simply refer to "upstream" and "downstream" relative to the rotation direction of the supply roller 51, respectively.

[0060] like Figure 3As shown, the developing container 40 includes a wall member 90 extending from a position opposite to the stripping magnetic pole S3 to below the supply roller 51 around its periphery. The wall member 90 extends to a position opposite to a low magnetic field region (a region where the absolute value of the magnetic flux density Br, the normal component of the magnetic flux density Br at the surface of the supply roller 51, is 5 mT or less) located between the downstream portion of the stripping magnetic pole S3 and the upstream portion of the pick-up magnetic pole S2 relative to the rotational direction of the supply roller 51. Specifically, the wall member 90 extends between the supply roller 51 and the second feed screw 45 in the stirring chamber 43, with its free end near the upper end of the partition wall 41. That is, as... Figure 3 As shown, the partition wall 41 overlaps with the supply roller 51 relative to the gravity direction (Z direction), and the wall member 90 overlaps with the supply roller 51 relative to the gravity direction (Z direction).

[0061] Furthermore, in the wall member 90, the portion extending from the portion constituting the outer wall of the developing container 40 towards the upper end of the partition wall 41 is referred to as the extension portion 90a. In the extension portion 90a, a flat surface portion 90b opposite to the supply roller 51 between the second feed screw 45 and the supply roller 51 is formed to reach at least the downstream position of the wall member 90 relative to the supply roller 51. That is, the extension portion 90a includes a surface as a flat surface that is opposite to the supply roller 51 in the region from a position located downstream of the connecting portion connected to the portion constituting the outer wall of the developing container 40 to the free end of the extension portion 90a, relative to the rotational direction of the supply roller 51. However, in this embodiment, the surface may be formed as a concave curved surface when viewed from the supply roller 51 side, or a concave curved surface when viewed from the second feed screw 45 side.

[0062] As described above, when the supply roller 51 rotates counterclockwise from the stripping magnet S3, the magnetic brush (i.e., the developer) is stripped from the supply roller 51 in a low magnetic field region located downstream of the stripping magnet S3 relative to the rotation direction of the supply roller 51. As the developer is stripped from the supply roller 51, the stripped developer gradually falls from the supply roller 51 in a vertically downward direction between the supply roller 51 and the wall member 90 of the developing container 40 located opposite the supply roller 51, due to the rotational force of the supply roller and gravity.

[0063] Therefore, the developer stripped from the supply roller 51 falls onto the flat surface portion 90b of the wall member 90, and is subsequently introduced into the developing chamber 42 through the flat surface portion 90b, whereby the developer is collected by the first feed screw 44 and agitated together with the developer in the developing chamber 42. However, the developer stripped from the supply roller 51 falls onto the extension portion 90a of the wall member 90 located above the second feed screw 45 earlier than the developer is collected by the first feed screw 44, and is stored in the area between the supply roller 51 and the extension portion 90a.

[0064] Here, as in Figure 4 In the comparative developing apparatus 4A shown, when the magnetic force of the picking magnet S2 extends to a position opposite to the extension 90a of the wall member 90, the developer on the extension 90a is again attracted to the supply roller 51. That is, as the supply roller 51 rotates, a so-called developer movement occurs, causing the developer carried on the supply roller 51 and supplying toner to the developing roller 50 to be stripped off from the supply roller 51, and then picked up again onto the supply roller 51. Figure 4 The construction of the comparative example shown is similar to Figure 3 The structure is the same, except that the width of the component of the picking magnetic pole S2 relative to the rotation direction of the supply roller 51 is larger. Figure 3 The structure extends further upstream.

[0065] When the position of the upstream end of the area affected by the magnetic force of the magnetic pole S2 relative to the rotation direction of the supply roller 51 is taken as the magnetic force initiation position (magnetic force initiation position), in order to prevent the developer on the extension 90a from being attracted to the supply roller 51 again by the magnetic pole S2, the magnetic force initiation position can preferably be located downstream of the line between the downstreammost position 91 of the connecting wall member 90 and the rotation center position of the supply roller 51. The downstreammost position 91 is also the downstreammost position of the extension 90a. In this embodiment, the downstreammost position 91 is the intersection between the extension 90a of the wall member 90 above the second feed screw 45 and the partition wall 41 between the first feed screw 44 and the second feed screw 45.

[0066] When the line connecting the downstream position 91 of the connecting wall member 90 and the rotation center position of the supply roller 51 is considered as a dashed line α, when the magnetic force that attracts the developer to the supply roller 51 through the magnetic pole S2 exists in the upstream region of the dashed line α relative to the rotation direction of the supply roller 51, this magnetic force attracts the developer on the extension 90a of the wall member 90 to the supply roller 51. Figure 4 In the comparative example, the upstream end of the magnetic pole S2 component is located further upstream of the dashed line α, so that the starting position of the magnetic force is upstream of the dashed line α. Therefore, as described above, in the configuration of the comparative example, there is a tendency for the developer to move as the supply roller 51 rotates.

[0067] Therefore, in this embodiment, a region affected by the magnetic force of the suction magnetic pole S2 is provided downstream of the dashed line α between the downstreammost position 91 of the connecting wall member 90 and the rotation center position of the supply roller 51, relative to the rotation direction of the supply roller 51. That is, relative to the rotation direction of the supply roller 51, the suction magnetic pole S2 is configured such that the starting position of the suction magnetic force is downstream of position α1, and the line (dashed line α) between the downstreammost position 91 of the connecting wall member 90 and the rotation center position of the supply roller 51 intersects the surface of the supply roller 51.

[0068] On the other hand, when the starting position of the magnetic force of the pick-up magnet S2 moves excessively downstream of the rotation direction of the supply roller 51, the developer in the developing chamber 42 cannot be picked up by the magnetic force of the pick-up magnet S2. In order to stably pick up the developer by the pick-up magnet S2, it is desirable that the magnetic force of the pick-up magnet S2 has a sufficient influence on the region with the highest height of the developer surface on the first feed screw 44.

[0069] The inventors have demonstrated that during the rotation of the first feed screw 44, the developer absorption characteristics are stable when the magnetic force of the absorbent pole S2 contributes to the highest position 92 relative to the height direction. Therefore, in this embodiment, the starting position of the absorbent magnetic force is located upstream of the highest position 92 relative to the vertical direction of the blade 44b of the first feed screw 44, relative to the rotation direction of the supply roller 51. That is, the starting position of the absorbent magnetic force is set upstream of position β1 relative to the position β1 where the dashed line β connecting the highest position 92 of the first feed screw 44 and the rotation center position of the supply roller 51 intersects with the surface of the supply roller 51, thereby stabilizing the developer absorption characteristics of the supply roller 51.

[0070] Relative to the rotation direction of the supply roller 51, the region between the dashed line α connecting the downstream position 91 of the connecting wall member 90 and the rotation center position of the supply roller 51, and the dashed line β connecting the highest position 92 of the first feed screw 44 and the rotation center position of the supply roller 51, is designated as region A. In this case, in this embodiment, the starting position of the magnetic force generated by the magnetic pole S2 is located in region A. Specifically, as... Figure 3 As shown, the upstream end of the pick-up magnetic pole S2 component is located in region A relative to the rotation direction of the supply roller 51. This suppresses developer movement caused by the stripping magnetic pole S3 in the downstream low magnetic field region as the supply roller 51 rotates, and further stabilizes the developer pick-up characteristics from the developing chamber 42.

[0071] Figure 5 It shows when Figure 3 The graph shows the magnetic force intensity (magnetic flux density Br) generated by each magnetic pole when the magnetic poles of the magnetic roller 51a in the supply roller 51 of the developing apparatus 4 are unfolded on the plane.

[0072] Incidentally, the magnetic flux density Br precisely refers to the component of the magnetic flux density B perpendicular to the surface of the supply roller 51 in the normal direction. In the following text, in some cases, "magnetic flux density Br in the normal direction" is simply referred to as "magnetic flux density" or "magnetic force." When magnetic flux density is simply referred to as "magnetic flux density" or "magnetic force," it refers to "magnetic flux density Br in the normal direction." The magnetic flux density Br of each magnetic roller (relative to the normal direction) in Example 1 and Comparative Example 1 was measured using a magnetic field measuring device ("MS-9902," manufactured by FW BELL), where the distance between the probe, which is a component of the magnetic field measuring device, and the surface of the supply roller 51 was approximately 100 micrometers.

[0073] In addition, Figure 5 In the graph, the horizontal axis represents the angle (in degrees) when the counterclockwise direction is taken as the positive direction from the closest position (0°) between the supply roller 51 and the developing roller 50. The vertical axis represents the magnitude of the magnetic flux density Br (in mT), where the magnitude is positive on the N pole side and negative on the S pole side. Furthermore, N1, S3, S2, N2, and S1 represent the positions (maximum value positions) of the relevant magnetic poles of the magnetic roller 51a in the supply roller 51. That is, each of N1, S3, S2, N2, and S1 is the position where the magnetic flux density Br (the normal component of the magnetic flux density B at the surface of the supply roller 51) of the relevant magnetic pole of the magnetic roller 51a in the supply roller 51 becomes the highest value (maximum value).

[0074] Furthermore, the line represented by α shows the position of the dashed line α between the downstream position 91 of the connecting wall member 90 and the rotation center position of the supply roller 51, as shown in the reference. Figure 3 As stated above. Figure 5 In the diagram, the position of the dashed line α is 195° counterclockwise from the closest position of the supply roller 51 and the developing roller 50.

[0075] Furthermore, the line represented by β shows the position of the dashed line β connecting the highest position 92 of the first feed screw 44 and the rotation center position of the supply roller 51, as shown in the reference. Figure 3 As stated above. Figure 5 In the diagram, the position of the dashed line β is 240° counterclockwise from the closest position of the supply roller 51 relative to the developing roller 50. Figure 5 In the diagram, the magnetic characteristics of the developing apparatus in Example 1 are represented by solid lines, where the reference... Figure 3 The conditions of the described embodiment are met, refer to Figure 4 The magnetic properties of the comparative developing apparatus are represented by dashed lines.

[0076] Next, the location where the magnetic force initiation position is set in the magnetic characteristics will be described. In this case, the position where the absolute value of the magnetic flux density Br of the picking magnetic pole S2 in the normal direction at the surface of the downstream supply roller 51 of the stripping magnetic pole S3 is 20% of its highest value (maximum value) is taken as the magnetic force initiation position. When the magnitude of the magnetic flux density Br at the magnetic force initiation position is a ratio lower than 15% of the highest value (maximum value) of the magnetic flux density Br of the picking magnetic pole S2, the magnitude of the magnetic flux density Br becomes approximately 5 mT relative to the magnitude of the magnetic flux density Br of the picking magnetic pole S2, which is 40 mT to 50 mT. For this reason, the magnitude of the magnetic flux density Br does not change compared to the magnitude of the magnetic flux density Br in the low magnetic force region, making it difficult to define from which position the contribution of the magnetic force of the picking magnetic pole S2 begins. Therefore, in this embodiment, the magnetic force initiation position is set at a point on the surface of the downstream supply roller 51 of the stripping magnetic pole S2 where the absolute value of the magnetic flux density Br in the normal direction becomes 20% of its maximum value. Incidentally, in this embodiment, the magnetic force initiation position is set at a point on the surface of the supply roller 51 where the absolute value of the magnetic flux density Br in the normal direction of the stripping magnetic pole S2 becomes 20% of its maximum value, but the invention is not limited thereto. Depending on the environment, in some cases, the developer is drawn onto the surface of the supply roller 51 starting from a point where the absolute value of the magnetic flux density Br in the normal direction of the stripping magnetic pole S2 becomes 15% of its maximum value. Therefore, in order to further enhance the effect of suppressing developer movement when the supply roller 51 rotates, it is preferable to set the magnetic force starting position at a position where the absolute value of the magnetic flux density Br of the magnetic pole S2 in the normal direction at the surface of the supply roller 51 becomes 15% of its highest value (maximum value), and then design the downstream position 91 of the wall member 90.

[0077] exist Figure 5 In the example where the starting position for magnetic attraction is set at 20% of the absolute value of the magnetic flux density Br of the attracting magnetic pole S2, the starting position for magnetic attraction in Example 1 is represented by a white circle, while the starting position for magnetic attraction in the comparative example is represented by a black circle (dot). As described above, the dashed line α between the downstream position 91 of the connecting wall member 90 and the rotation center position of the supply roller 51 is a line showing the magnetic properties that affect the movement of the developer on the rotation of the supply roller 51. Figure 5 It can be clearly seen that the black circle indicating the starting position of the magnetic attraction in the comparative example is located upstream of the dashed line α relative to the rotation direction of the supply roller 51. On the other hand, the white circle indicating the starting position of the magnetic attraction in Example 1 is located downstream of the dashed line α relative to the rotation direction of the supply roller 51.

[0078] Figure 6 Part (a) shows the pole angle [degrees] of each magnetic pole and the magnitude of the highest (maximum) value of the magnetic flux density Br of each magnetic pole in Example 1, and shows the magnetic property value [mT] and the extraction angle [degrees] (magnetic position at the start of extraction) of magnetic pole S2 in Example 1. In addition, the angles [degrees] of the dashed lines α and β are also shown. Figure 6 Part (b) shows the magnitude of the pole angle [degrees] of each magnetic pole and the maximum value (maximum value) of the magnetic flux density Br of each magnetic pole in the comparative example, and shows the magnetic property value [mT] of the magnetic pole S2 used for extraction and the angle [degrees] of the starting position of the extraction magnetic force in the comparative example.

[0079] In this embodiment with the above-described structure, it is possible to suppress the movement of developer as the supply roller 51 rotates after the toner on the supply roller 51 is consumed by moving to the developing roller 50, and unlike the comparative example, it is possible to suppress the inconvenience of the image density decreasing as imaging progresses.

[0080] <Second Embodiment>

[0081] Will use Figures 7 to 9 The second embodiment is described. In this embodiment, the starting position for drawing magnetic force differs from that in the first embodiment. Other constructions and functions are similar to those in the first embodiment; therefore, similar constructions are omitted from the description and illustrations, or briefly described by adding the same reference numerals or symbols, and the differences from the first embodiment will be described primarily below.

[0082] In the first embodiment, relative to the rotation direction of the supply roller 51, the pick-up magnetic pole S2 is configured such that the starting position of the pick-up magnetic force is downstream of position α1, and the line (dashed line α) connecting the downstreammost position 91 of the wall member 90 and the rotation center position of the supply roller 51 at position α1 intersects the surface of the supply roller 51. Therefore, the movement of developer stored in the region between the wall member 90 and the supply roller 51 as the supply roller 51 rotates is suppressed.

[0083] However, for the developer movement that occurs as the supply roller 51 rotates, the pick-up magnet S2 attracts not only the developer stored between the wall member 90 and the supply roller 51, but also the developer floating between the wall member 90 and the supply roller 51. Furthermore, the developing apparatus 4B of this embodiment rotates counterclockwise similarly to the first embodiment, but at this time, an airflow generated by the rotation of the supply roller 51 is produced between the wall member 90 and the developing container 40 opposite to the supply roller 51. Due to the influence of this airflow, the developer stripped in the low magnetic field region downstream of the stripping magnet S3 flows along the space between the supply roller 51 and the developing container 40, while simultaneously floating between the supply roller 51 and the developing container 40. The developer is then carried until this space reaches the region above the first feed screw 44.

[0084] In this embodiment, the developer floats to the downstream position 91 of the wall member 90 (the intersection with the partition wall 41). Then, when the airflow passes through this position, the developer is drawn in by the first feed screw 44, thus suppressing the effect of the floating developer. Therefore, when the floating developer is attracted to the pick-up magnet S2 before passing through this position, there is a tendency for the developer to move more or less with the rotation of the supply roller 51.

[0085] In this embodiment, the space where the developer floats due to this airflow is considered to be the region where a vertical line is drawn from the downstream position 91 of the wall member 90 to the supply roller 51, as described below, and its relationship to the starting position of the magnetic attraction is defined. Incidentally, in this embodiment, as Figure 7 As shown, the partition wall 41 overlaps with the supply roller 51 relative to the direction of gravity (Z direction), and the wall member 90 also overlaps with the supply roller 51 relative to the direction of gravity (Z direction). Furthermore, the extension 90a of the wall member 90 is formed such that the flat surface portion 90b opposite to the supply roller 51 between the second feed screw 45 and the supply roller 51 reaches at least the downstream position 91 of the wall member 90 relative to the rotational direction of the supply roller 51. That is, the extension 90a includes a flat surface extending from a position downstream of the connecting portion that forms the outer wall of the developing container 40 relative to the rotational direction of the supply roller 51 to the free end of the extension 90a opposite to the supply roller 51.

[0086] In the above embodiments, such as Figure 7 As shown, a vertical line γ of the flat surface portion 90b of the wall member 90 extends from the downstream position 91 of the wall member 90 towards the surface of the supply roller 51. The position where this vertical line γ intersects the surface of the supply roller 51 is considered position γ1. Furthermore, the pick-up magnetic pole S2 is arranged such that the starting position of the pick-up magnetic force is downstream of position γ1.

[0087] In other words, in this embodiment, at the downstream position 91 of the wall member 90 relative to the rotation direction of the supply roller 51, when a straight line is drawn vertically toward the supply roller 51, the position γ1 on the supply roller 51 is used as a position to determine whether developer movement caused by airflow has occurred. Furthermore, by setting the starting position of the magnetic force of the suction pole S2 downstream of position γ1 relative to the rotation direction of the supply roller 51, the re-attraction of developer floating between the supply roller 51 and each of the developing container 40 and the wall member 90 to the suction pole S2 is suppressed before the developer is collected by the first feed screw 44.

[0088] Furthermore, in this embodiment, similar to the first embodiment, the position where the absolute value of the magnetic flux density Br of the picking magnetic pole S2 in the direction normal to the surface of the supply roller 51 becomes 20% (preferably 15%) downstream of the stripping magnetic pole S3 is considered the starting position of the picking magnetic force. Also, similar to the first embodiment, the starting position of the picking magnetic force is set upstream of position β1 relative to the rotation direction of the supply roller 51, and the dashed line β connecting the highest position 92 of the first feed screw 44 and the rotation center position of the supply roller 51 at position β1 intersects the surface of the supply roller 51.

[0089] Here, the area between the vertical line γ and the dashed line β, relative to the rotation direction of the supply roller 51, is considered region B. In this case, in this embodiment, the starting position of the magnetic force of the picking pole S2 is located in region B. Specifically, as Figure 7 As shown, the upstream end of the pick-up magnetic pole S2 component is located in region B relative to the rotation direction of the supply roller 51. This further suppresses developer movement caused by the rotation of the supply roller 51 as the developer, which is stripped by the stripping magnetic pole S3 in the downstream low magnetic region, is drawn from the developing chamber 42. Furthermore, it stabilizes the developer pick-up characteristics from the developing chamber 42.

[0090] Figure 8 It shows when Figure 7 The graph shows the magnetic force intensity (magnetic flux density Br) generated by each magnetic pole when the magnetic poles of the magnetic roller 51a in the supply roller 51 of the developing apparatus 4 are unfolded on the plane. Figure 8 The curve is similar to Figure 5 The graph shows the magnetic properties of the developing apparatus of Example 2 (with reference to...). Figure 7 The conditions of the described embodiment are met; the dashed line indicates a reference. Figure 4 The magnetic characteristics of the developing apparatus are described in the comparative example. Furthermore, the line indicated by the symbol γ is a perpendicular line γ of the flat surface portion 90b of the wall member 90, which extends from the downstreammost position 91 of the wall member 90 toward the surface of the supply roller 51, as shown above. Figure 7 As stated above.

[0091] exist Figure 8 In Example 1, the magnetic force initiation position is set at 20% of the absolute value of the magnetic flux density Br of the magnetic pole S2, representing its highest value. In the comparative example, the magnetic force initiation position is represented by a white circle, while in the latter, it is represented by a black circle (dot). As described above, the vertical line γ extending from the downstream position 91 towards the supply roller 51 illustrates the magnetic properties that influence the developer movement caused by the rotation of the supply roller 51. Figure 8 It is evident that the black circle indicating the starting position of the magnetic force in the comparative example is located upstream of the vertical line γ relative to the rotation direction of the supply roller 51. On the other hand, the white circle indicating the starting position of the magnetic force in Embodiment 2 is located downstream of the vertical line γ relative to the rotation direction of the supply roller 51.

[0092] Figure 9 The pole angles [degrees] and the maximum values ​​(maximum values) of the magnetic flux density Br of each magnetic pole in Example 2 are shown, along with the magnetic property value [mT] and the extraction angle [degrees] (the starting position of the extraction magnetic force) of the extraction pole S2 in Example 2. Furthermore, the angles [degrees] between the vertical line γ and the dashed line β are also shown. Incidentally, from... Figure 8 and Figure 9 Between and Figure 5 and Figure 6 A comparison between parts (a) reveals that the magnetic roller 51a of the supply roller 51 in Embodiment 2 uses the same construction as the magnetic roller 51a of the supply roller 51 in Embodiment 1.

[0093] In this embodiment with the above-described structure, similar to the first embodiment, it is possible to suppress developer movement as the supply roller 51 rotates after the toner on the supply roller 51 has been consumed by moving to the developing roller 50. Furthermore, unlike the comparative example, it is possible to suppress the inconvenience of image density decreasing as imaging progresses. In particular, when the magnetic force initiation position is defined as in this embodiment, it is possible to effectively suppress developer movement caused by airflow generated by the rotation of the supply roller 51 as it rotates. Therefore, compared to the structure of the first embodiment, when many images are formed by the imaging device, density reduction can be better suppressed.

[0094] <Third Embodiment>

[0095] A third embodiment will be described. In this embodiment, the method for obtaining the starting position of the magnetic force differs from that of the first and second embodiments. Other constructions and functions are similar to those in the first and second embodiments; therefore, similar constructions are omitted from the description and illustrations, or are briefly described by adding the same reference numerals or symbols and are omitted from the illustrations. Hereinafter, the differences from the first embodiment will be described primarily.

[0096] In the first and second embodiments described above, the magnetic characteristics used as the starting position of the magnetic force of the attracting magnetic pole S2 are such that the absolute value of the magnetic flux density Br of the attracting magnetic pole S2 becomes 20% (preferably 15%) of the absolute value of its highest value (maximum value). However, when the starting position of the magnetic force is set in the manner described above, in the low magnetic force region downstream of the stripping magnetic pole S3, when the magnetic flux density Br, which is a value in the low magnetic force region, is relatively large (e.g., about 10 mT), or when the magnetic flux density Br is on the opposite polarity side, it is difficult to set the magnetic characteristics of the starting position of the magnetic force of the attracting magnetic pole S2 according to the ratio of the absolute value of the magnetic flux density Br of the attracting magnetic pole S2 to the absolute value of its highest value (maximum value), as in the first and second embodiments.

[0097] Therefore, in this embodiment, the magnetic force change value is obtained in the following manner, and the position where the value becomes 20% (preferably 15%) of the magnetic force change value is used as the magnetic force absorption start position. Furthermore, on the upstream side of the absorption magnetic pole S2 and the downstream side of the stripping magnetic pole S3, the region where the absolute value of the magnetic flux density Br in the normal direction at the surface of the supply roller 51 becomes a predetermined value or less is a low magnetic force region. For example, the predetermined value is 5 mT. That is, in this embodiment, the low magnetic force region is the region where the absolute value of the magnetic flux density Br in the normal direction at the surface of the supply roller 51 is 5 mT or less. Next, relative to the rotation direction of the supply roller 51, the absolute value of the difference between the maximum value of the magnetic flux density Br of the absorption magnetic pole S2 in the normal direction at the surface of the supply roller 51 and the average value of the magnetic flux density Br in the aforementioned low magnetic force region is taken as the magnetic force change value. Furthermore, the position where the value becomes 20% (preferably 15%) of this magnetic force change value is considered the magnetic force absorption start position.

[0098] Specifically, the change in magnetic force between the low magnetic region and the magnetic pole is calculated according to the following formula 1.

[0099] [Magnetic force change value] = [Highest value (maximum value) of magnetic flux density Br at the magnetic pole] - [Average value of magnetic flux density Br in the low magnetic force region]... (Formula 1)

[0100] Here, when the angle moves from the position with the lowest magnetic flux density Br in the low magnetic region to the position with a 5-degree increment in each of the upstream and downstream directions relative to the rotation direction of the supply roller 51, the average value of a total of 11 points is taken as the average value of the magnetic flux density Br in the low magnetic region. Incidentally, the method of obtaining the average value is not limited to this, but can be, for example, by averaging the absolute values ​​of the magnetic flux density Br at any number of equidistant positions in the region where the absolute value of the magnetic flux density Br is a predetermined value or less, on the upstream side of the picking magnetic pole S2 and the downstream side of the stripping magnetic pole S3.

[0101] In this embodiment, for the magnetic force change value obtained by Formula 1 above, 20% (preferably 15%) of the obtained magnetic force change value is calculated, and the position (angle) corresponding to the magnetic force of the magnetic properties upstream of the picking magnetic pole S2 relative to the rotation direction of the supply roller 51 is defined as the picking magnetic force start position. Furthermore, as in the first embodiment, the picking magnetic pole S2 is set such that the picking magnetic force start position is downstream of position α1, and the line (dashed line α) connecting the downstreammost position 91 of the wall member 90 and the rotation center position of the supply roller 51 intersects the surface of the supply roller 51 at position α1. Alternatively, as in the second embodiment, the picking magnetic pole S2 is set such that the picking magnetic force start position is downstream of position γ1 relative to the rotation direction of the supply roller 51, and the perpendicular line γ drawn from the downstreammost position 91 of the wall member 90 toward the surface of the supply roller 51 at position γ1 intersects the surface of the supply roller 51.

[0102] In the above embodiment, even if the magnetic force changes in the low magnetic force region, the starting position of the magnetic force of the attracting magnetic pole S2 can be appropriately calculated.

[0103] <Other Embodiments>

[0104] The above embodiments describe the application of the present invention to a developing apparatus used in a tandem imaging device. However, the present invention is also applicable to developing apparatuses used in another type of imaging device. Furthermore, the imaging device is not limited to an imaging device for panchromatic images, but can also be an imaging device for monochrome images or an imaging device for single-color (single-color) images. Alternatively, by adding necessary devices, equipment, and housing structures, the imaging device can be implemented for various purposes, such as printers, various printing presses, copiers, fax machines, and multifunction printers.

[0105] Furthermore, regarding the structure of the developing apparatus, as described above, the structure is not limited to a structure in which the developing chamber and the stirring chamber are arranged in a horizontal direction; it can also be a structure in which the developing chamber and the stirring chamber are arranged in a direction inclined relative to the horizontal direction. In short, it is possible to use only a configuration in which the developing chamber, as the first chamber, and the stirring chamber, as the second chamber, are arranged adjacent to each other, so that they partially overlap when viewed in the horizontal direction.

[0106] Although the invention has been described with reference to exemplary embodiments, it should be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be interpreted in the broadest sense so as to encompass all such modifications and equivalent structures and functions.

Claims

1. A developing apparatus, comprising: The first chamber is configured to contain a developer containing toner and carrier; The second chamber forms a developer circulation channel between itself and the first chamber; A partition wall, which is constructed to separate the first chamber from the second chamber; A first feed screw is disposed in the first chamber and configured to feed developer in a first direction; A second feed screw is disposed in the second chamber and configured to feed the developer in a second direction opposite to the first direction; A developing roller is configured to carry and transport toner to a developing position, where an electrostatic image formed on an image-carrying member is developed. A supply roller, which is disposed opposite to the developing roller, is configured to carry and convey developer supplied from the first chamber, and to supply toner only to the developing roller. In the position where the supply roller and the developing roller are opposite to each other, the rotation direction of the supply roller is opposite to the rotation direction of the developing roller. A first magnet, which is non-rotatable and fixedly disposed inside the developing roller, includes a first magnetic pole; A second magnet, which is non-rotatable and fixedly disposed inside the supply roller, and comprises: The second magnetic pole is positioned opposite the first magnetic pole at a location where the supply roller and the developing roller are opposite each other, and its polarity is different from that of the first magnetic pole. The third magnetic pole, whose rotational direction relative to the supply roller is positioned downstream of the second magnetic pole, and The fourth magnetic pole is positioned upstream of the second magnetic pole and downstream of the third magnetic pole relative to the rotation direction of the supply roller, and is adjacent to the third magnetic pole, and has the same polarity as the third magnetic pole. and The guiding section is configured to guide the developer stripped from the supply roller into the first chamber via a repulsive magnetic field formed by the third and fourth magnetic poles, with the lowermost end of the guiding section close to the uppermost end of the partition wall. The guide portion overlaps with the supply roller relative to the direction of gravity, and in when: A position relative to the rotation direction of the supply roller, located downstream of the position where the magnetic flux density of the third magnetic pole is highest in the normal direction of the outer peripheral surface of the supply roller, and upstream of the position where the magnetic flux density of the fourth magnetic pole is highest in the normal direction of the outer peripheral surface of the supply roller, is the first position. At the first position, the magnetic flux density of the fourth magnetic pole in the normal direction is 20% of its highest value. Viewed in a cross-section perpendicular to the rotation axis of the supply roller, the position where the straight line connecting the lowermost end of the guide portion and the rotation center of the supply roller intersects the outer peripheral surface of the supply roller is the second position. Viewed in a cross-section perpendicular to the rotation axis of the supply roller, the position where the straight line connecting the uppermost end of the first feed screw and the rotation center of the supply roller intersects the outer peripheral surface of the supply roller is the third position. hour, The first position is located downstream of the second position and upstream of the third position, relative to the rotation direction of the supply roller.

2. The developing apparatus according to claim 1, wherein, The fourth position is a position located downstream of the position where the magnetic flux density of the third magnetic pole is highest in the normal direction and upstream of the position where the magnetic flux density of the fourth magnetic pole is highest in the normal direction relative to the rotation direction of the supply roller. When the magnetic flux density of the fourth magnetic pole in the normal direction at the fourth position is 15% of its highest value, the fourth position is located downstream of the second position and upstream of the first position relative to the rotation direction of the supply roller.

3. The developing apparatus according to claim 1 or 2, wherein, The guide portion includes a flat surface portion opposite the supply roller, the flat surface portion extending to the lowermost end of the guide portion, and When viewed in a section perpendicular to the axis of rotation, the fifth position is the location where the perpendicular line drawn from the lowest end of the guide portion toward the outer peripheral surface of the supply roller intersects with the outer peripheral surface of the supply roller. Relative to the rotation direction of the supply roller, the first position is located downstream of the fifth position and upstream of the third position.

4. The developing apparatus according to claim 1 or 2, characterized in that, When viewed in a section perpendicular to the axis of rotation of the supply roller, the lowermost end of the guide portion is located above the center of rotation of the second feed screw.

5. The developing apparatus according to claim 1 or 2, characterized in that, The partition wall overlaps with the supply roller in the direction of gravity.

6. A developing apparatus, comprising: The first chamber is configured to contain a developer containing toner and carrier; The second chamber forms a developer circulation channel between itself and the first chamber; A partition wall, which is constructed to separate the first chamber from the second chamber; A first feed screw is disposed in the first chamber and configured to feed developer in a first direction; A second feed screw is disposed in the second chamber and configured to feed the developer in a second direction opposite to the first direction; A developing roller is configured to carry and transport toner to a developing position, where an electrostatic image formed on an image-carrying member is developed. A supply roller, which is disposed opposite to the developing roller, is configured to carry and convey developer supplied from the first chamber, and to supply toner only to the developing roller. In the position where the supply roller and the developing roller are opposite to each other, the rotation direction of the supply roller is opposite to the rotation direction of the developing roller. A first magnet, which is non-rotatable and fixedly disposed inside the developing roller, includes a first magnetic pole; A second magnet, which is non-rotatable and fixedly disposed inside the supply roller, and comprises: The second magnetic pole is positioned opposite the first magnetic pole at a location where the supply roller and the developing roller are opposite each other, and its polarity is different from that of the first magnetic pole. The third magnetic pole, whose rotational direction relative to the supply roller is positioned downstream of the second magnetic pole, and The fourth magnetic pole is positioned upstream of the second magnetic pole and downstream of the third magnetic pole relative to the rotation direction of the supply roller, and is adjacent to the third magnetic pole, and has the same polarity as the third magnetic pole. and The guiding section is configured to guide the developer stripped from the supply roller into the first chamber via a repulsive magnetic field formed by the third and fourth magnetic poles, with the lowermost end of the guiding section close to the uppermost end of the partition wall. The guide portion overlaps with the supply roller in the direction of gravity, and in when: A first position is a position located downstream of the position where the magnetic flux density of the third magnetic pole in the normal direction of the outer peripheral surface of the supply roller is the highest, and upstream of the position where the magnetic flux density of the fourth magnetic pole in the normal direction of the outer peripheral surface of the supply roller is the highest, relative to the rotation direction of the supply roller. At the first position, the magnetic flux density of the fourth magnetic pole in the normal direction is 20% of the absolute value of the difference between the highest value of the magnetic flux density of the fourth magnetic pole in the normal direction and the average value of the magnetic flux density in the region where the absolute value of the magnetic flux density in the normal direction is less than 5 mT. Viewed in a cross-section perpendicular to the rotation axis of the supply roller, the position where the straight line connecting the lowermost end of the guide portion and the rotation center of the supply roller intersects the outer peripheral surface of the supply roller is the second position. Viewed in a cross-section perpendicular to the rotation axis of the supply roller, the position where the straight line connecting the uppermost end of the first feed screw and the rotation center of the supply roller intersects the outer peripheral surface of the supply roller is the third position. hour, The first position is located downstream of the second position and upstream of the third position, relative to the rotation direction of the supply roller.

7. The developing apparatus according to claim 6, wherein a fourth position is a position located downstream of the position where the magnetic flux density of the third magnetic pole in the normal direction is highest and upstream of the position where the magnetic flux density of the fourth magnetic pole in the normal direction is highest relative to the rotation direction of the supply roller, and the fourth position is located downstream of the second position and upstream of the first position relative to the rotation direction of the supply roller when the magnetic flux density of the fourth magnetic pole in the normal direction at the fourth position is 15% of the absolute value of the difference.

8. The developing apparatus according to claim 6 or 7, characterized in that, The guide section includes a flat surface portion opposite the supply roller, which extends to the lowermost end of the guide section, and When viewed in a section perpendicular to the axis of rotation, the fifth position is the location where the perpendicular line drawn from the lowest end of the guide portion toward the outer peripheral surface of the supply roller intersects with the outer peripheral surface of the supply roller. Relative to the rotation direction of the supply roller, the first position is located downstream of the fifth position and upstream of the third position.

9. The developing apparatus according to claim 6 or 7, characterized in that, When viewed in a section perpendicular to the axis of rotation of the supply roller, the lowermost end of the guide portion is located above the center of rotation of the second feed screw.

10. The developing apparatus according to claim 6 or 7, wherein the partition wall overlaps with the supply roller in the direction of gravity.

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