Developing device
The developing device stabilizes developer transport to the regulating member using magnetic poles with varying flux densities, addressing inconsistent supply issues due to developer deterioration.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- CANON KK
- Filing Date
- 2024-12-25
- Publication Date
- 2026-07-07
Smart Images
Figure 2026112831000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a developing device that develops an electrostatic latent image formed on an image carrier with a developer.
Background Art
[0002] As a developing device, a configuration has been proposed in which two developing rollers that develop an electrostatic latent image formed on an image carrier with a developer are arranged side by side in the rotational direction of the image carrier (Patent Document 1). In the developing device described in Patent Document 1, among the two developing rollers, the developer is supplied from a supply screw to the developing roller located vertically below. The developer supplied to the developing roller is carried by the developing roller. Then, the developer carried by the developing roller is regulated in layer thickness by a regulating member arranged with a predetermined gap from the developing roller below the rotation center of the developing roller and on the upstream side of rotation of the developing roller from the lowest point of the developing roller, and is conveyed to a developing position facing the photosensitive drum.
[0003] Also, in the case of the configuration described in Patent Document 1, a space capacity regulating portion for regulating the capacity of the space for supplying the developer from the supply screw to the developing roller is provided between the supply screw and the developing roller. Further, an inclined portion that inclines downward from the end portion on the developing roller side of the space capacity regulating portion toward the regulating member is provided. The developer whose amount is regulated by the space capacity regulating portion is conveyed along the inclined portion toward the regulating member side.
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0005] As described in Patent Document 1, when supplying developer from a supply screw to a developing roller, the amount of developer is regulated by a space volume regulating section, and the developer is further transported along an inclined section to the regulating member side. In such a configuration, it is desirable not to obstruct the flow of developer toward the regulating member. If the flow of developer is obstructed, the amount of developer transported toward the regulating member side decreases, and there is a risk that the amount of developer carried on the developing roller cannot be stably regulated by the regulating member. In particular, when the developer deteriorates with use and its fluidity decreases, the transportability of the developer toward the regulating member side decreases, but even in such cases, it is desirable to maintain the amount of developer transported.
[0006] The present invention aims to provide a configuration that enables stable transport of developer to a regulating member. [Means for solving the problem]
[0007] One aspect of the present invention includes a developing roller for developing an electrostatic latent image formed on a rotating image carrier with a developer, having a rotating developing sleeve and a developing magnet non-rotatingly positioned inside the developing sleeve and attracting developer to the surface of the developing sleeve by magnetic force, a developing screw for supplying developer to the developing roller while agitating and conveying the developer, a regulating member for regulating the amount of developer carried on the developing sleeve, positioned vertically below the rotation center of the developing sleeve and upstream in the rotational direction of the developing sleeve from the lowest point in the vertical direction of the developing sleeve, facing the outer circumferential surface of the developing sleeve with a predetermined gap, and positioned between the developing roller and the developer supply screw, regulating the volume of the space for supplying developer from the developer supply screw to the developing roller, and extending downward from the end of the space volume regulating member on the developing roller side toward the regulating member The developing apparatus comprises an inclined portion that is tilted in one direction, and the developing magnet has a first magnetic pole that supports the developer supplied from the developer supply screw on the surface of the developing sleeve, a second magnetic pole that is positioned downstream of the first magnetic pole and adjacent to the first magnetic pole with respect to the rotational direction of the developing sleeve and faces the regulating member and the developing sleeve, and a third magnetic pole that is positioned downstream of the second magnetic pole and adjacent to the second magnetic pole with respect to the rotational direction of the developing sleeve, wherein the absolute value of the maximum value of the normal component of the magnetic flux density of the first magnetic pole on the developing sleeve is greater than the absolute value of the maximum value of the normal component of the magnetic flux density of the second magnetic pole on the developing sleeve, and the absolute value of the maximum value of the normal component of the magnetic flux density of the third magnetic pole on the developing sleeve is greater than the absolute value of the maximum value of the normal component of the magnetic flux density of the second magnetic pole on the developing sleeve. [Effects of the Invention]
[0008] According to the present invention, the developer can be stably transported to the regulating member. [Brief explanation of the drawing]
[0009] [Figure 1] A schematic cross-sectional view of the image forming apparatus according to the embodiment. [Figure 2] A schematic cross-sectional view of the developing apparatus according to the embodiment. [Figure 3] A diagram showing the magnetic pole arrangement of the first developing roller according to the embodiment. [Figure 4] A diagram showing the magnetic pole arrangement of the second developing roller according to the embodiment. [Figure 5] A diagram showing the magnetic pole arrangement of a peeling roller according to an embodiment. [Figure 6] A schematic cross-sectional view of the first developing roller and the area around the developer supply screw according to the embodiment. [Figure 7] A schematic cross-sectional view showing the relationship between the first developing roller, the regulating member, and the inclined portion according to the embodiment, and the area around the first developing roller and the developer supply screw. [Figure 8] A graph showing the magnetic flux density Br around the regulating pole of the first developing roller according to Example 1. [Figure 9] A graph showing the magnetic force Fθ around the regulating electrode of the first developing roller according to Example 1. [Figure 10] A graph showing the magnetic flux density Br around the regulating pole of the first developing roller according to Example 2. [Figure 11] A graph showing the magnetic force Fθ around the regulating electrode of the first developing roller according to Example 2. [Modes for carrying out the invention]
[0010] Embodiments will be described using Figures 1 to 11. First, the schematic configuration of the image forming apparatus of this embodiment will be described using Figure 1.
[0011] [Image forming apparatus] The image forming apparatus 100 is a full-color image forming apparatus, and in this embodiment, for example, it is an MFP (Multi-Function Peripheral) having a copy function, a printer function, and a scan function. As shown in Figure 1, the image forming apparatus 100 is equipped with parallel image forming units PY, PM, PC, and PK, which each perform the image forming process for four toner colors: yellow, magenta, cyan, and black.
[0012] The image forming units PY, PM, PC, and PK of each color include primary chargers 21Y, 21M, 21C, 21K, developing devices 1Y, 1M, 1C, 1K, optical writing units (exposure devices) 22Y, 22M, 22C, 22K, photosensitive drums 28Y, 28M, 28C, 28K, and cleaning devices 26Y, 26M, 26C, 26K. The image forming apparatus 100 also includes a transfer device 2 and a fixing device 3. Since the configurations of the image forming units PY, PM, PC, and PK of each color are the same, hereinafter, the image forming unit PY will be described as a representative.
[0013] The photosensitive drum 28Y as an image carrier is a photoreceptor having a photosensitive layer made of a resin such as polycarbonate containing an organic photoconductor (OPC), and is configured to rotate at a predetermined speed. In the present embodiment, the linear speed of the surface of the photosensitive drum 28Y is set to 650 mm / s. The primary charger 21Y is composed of a corona discharge electrode disposed around the photosensitive drum 28Y, and charges the surface of the photosensitive drum 28Y with the generated ions.
[0014] The optical writing unit 22Y incorporates a scanning optical device, and exposes the charged photosensitive drum 28Y based on image data, thereby reducing the potential of the exposed portion and forming a charge pattern (electrostatic latent image) corresponding to the image data. The developing device 1Y transfers the contained developer to the photosensitive drum 28Y to develop the electrostatic latent image formed on the photosensitive drum 28Y. The developer is formed by mixing a carrier and toner corresponding to each color, and the electrostatic latent image is visualized by the toner.
[0015] The transfer device 2 includes primary transfer rollers 23Y, 23M, 23C, 23K, an intermediate transfer belt 24, and a secondary transfer roller 25. The intermediate transfer belt 24 is wound by the primary transfer rollers 23Y, 23M, 23C, 23K and a plurality of rollers and is supported so as to be capable of running. The primary transfer rollers 23Y, 23M, 23C, 23K correspond to the respective colors of Y (yellow), M (magenta), C (cyan), and K (black) in order from the top in FIG. 1. The secondary transfer roller 25 is disposed outside the intermediate transfer belt 24 and is configured such that a recording material can pass between it and the intermediate transfer belt 24. Note that the recording material is, for example, a sheet such as paper or a plastic sheet.
[0016] The toner images of each color formed on the photosensitive drums 28Y, 28M, 28C, 28K are sequentially transferred onto the intermediate transfer belt 24 by the primary transfer rollers 23Y, 23M, 23C, 23K, and a color toner image in which layers of yellow, magenta, cyan, and black are superimposed is formed. The formed toner image is transferred by the secondary transfer roller 25 onto a recording material conveyed from a cassette or the like in which the recording material is accommodated. The recording material onto which the toner image has been transferred is subjected to pressure and heat in the fixing device 3. Thereby, the toner on the recording material is melted, and the color image is fixed onto the recording material.
[0017] The developer storage units 27Y, 27M, 27C, 27K are respectively provided corresponding to the developing devices 1Y, 1M, 1C, 1K, and bottles storing developers corresponding to the respective colors of yellow, magenta, cyan, and black are loaded therein so as to be replaceable in order from the top. The developer storage units 27Y, 27M, 27C, 27K are configured to be capable of conveying (supplying) the developer to the developing devices 1Y, 1M, 1C, 1K corresponding to the colors of the developers stored therein.
[0018] For example, the toner weight ratio of the developer stored in the bottle is 80-95%, while the toner weight ratio of the developer in developing units 1Y, 1M, 1C, and 1K is 5-10%. Therefore, when toner is consumed by developing in developing units 1Y, 1M, 1C, and 1K, developer containing an amount of toner corresponding to the consumption is replenished, and the toner weight ratio of the developer in developing units 1Y, 1M, 1C, and 1K is maintained at a constant level.
[0019] [Developing equipment] Next, developing units 1Y, 1M, 1C, and 1K will be described in detail using Figures 2 to 5. Since the configurations of developing units 1Y, 1M, 1C, and 1K are the same, developing unit 1Y will be described as a representative unit below. Figure 2 is a conceptual diagram illustrating developing unit 1Y shown in Figure 1, and Figures 3, 4, and 5 are conceptual diagrams illustrating the magnetic pole configurations of the first magnet 36, second magnet 37, and third magnet 38 arranged within developing unit 1Y.
[0020] As shown in Figure 2, the developing apparatus 1Y includes a first developing roller 30, a second developing roller 31, a peeling roller (recovery roller) 32, a developer supply screw 42, a developer stirring screw 43, and a developer recovery screw 44, and these components are housed in a developing container 60.
[0021] The first developing roller 30, acting as a developing roller, is a rotating developer carrier positioned adjacent to the photosensitive drum 28Y, such that its axis of rotation is approximately parallel to the axis of rotation of the photosensitive drum 28Y. The first developing roller 30 has a rotating first sleeve (first developing sleeve) 33 and a first magnet (fixed magnet, first developing magnet) 36 that is non-rotatingly positioned inside the first sleeve 33 and attracts the developer to the surface of the first sleeve 33 by magnetic force. The first developing roller 30 then attracts (carries) the developer drawn up from the developer supply screw 42 based on magnetic force and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y (on the image carrier) with the developer.
[0022] The first sleeve 33 (and the second sleeve 34, described later) of the developing device 1Y is subjected to, for example, a DC developing bias with the same polarity as the charging polarity of the primary charger 21Y, or a developing bias in which an AC voltage is superimposed with a DC voltage of the same polarity as the charging polarity of the primary charger 21Y. As a result, inverse development is performed in which toner charged with the same polarity as the charging polarity of the primary charger 21Y is deposited onto the electrostatic latent image formed by the exposure device 22Y. In this embodiment, the charging polarity of the primary charger 21Y and the DC voltage of the developing bias are set to negative, and inverse development is performed in which negatively charged toner is deposited onto the electrostatic latent image.
[0023] The first sleeve 33, which serves as the developing sleeve, is a non-magnetic cylindrical member with an outer diameter of 25 mm (radius r1 = 12.5 mm) and is rotationally driven around a rotation axis 39. The rotation direction of the first sleeve 33 is clockwise, as indicated by the arrow in Figure 2, and in this embodiment, it is opposite to the rotation direction of the photosensitive drum 28Y. Therefore, the first sleeve 33 and the photosensitive drum 28Y rotate in the same direction when they are facing each other. The first sleeve 33 rotates from vertically downward to vertically upward when it is facing the photosensitive drum 28Y.
[0024] In this embodiment, the linear velocity of the surface of the first sleeve 33 of the first developing roller 30 is set to 1.0 times (=650 mm / s) the linear velocity of the surface of the photosensitive drum 28Y. Keeping the ratio of the linear velocity of the surface of the first sleeve 33 to the linear velocity of the surface of the photosensitive drum 28Y to about 1.0 to 1.2 times is advantageous in terms of toner degradation. On the other hand, there is a concern that the amount of toner supplied to the photosensitive drum 28Y will decrease and the developing performance will decline, but in this embodiment, since there are two developing rollers 30 and 31, it is possible to maintain the amount of toner supplied to the photosensitive drum 28Y even if the linear velocity ratio is suppressed.
[0025] The first magnet 36 is positioned inside the first sleeve 33 and has multiple fan-shaped magnetic poles 101 to 107, as shown in Figure 3. The solid lines in the figure indicate the peak positions (maximum values) of the distribution of the normal component of the magnetic flux density of the magnetic poles 101 to 107 of the first magnet 36. A space is provided between the inner circumference of the first sleeve 33 and the outer circumference of the first magnet 36 to allow the rotation of the first sleeve 33.
[0026] The developer adsorbed on the first sleeve 33 (on the developing sleeve) is transported toward the photosensitive drum 28Y by the rotation of the first sleeve 33, developing the latent image formed on the photosensitive drum 28Y. After developing the latent image formed on the photosensitive drum 28Y, the developer on the first sleeve 33 is transported toward the vicinity of the second developing roller 31 by the rotation of the first sleeve 33. Then, near the closest proximity point between the first developing roller 30 and the second developing roller 31, the developer is detached from the first sleeve 33 by the magnetic field generated by the first magnet 36 contained in the first developing roller 30 and the second magnet 37 contained in the second developing roller 31, and transferred to the second sleeve 34. The first sleeve 33 and the second sleeve 34 are positioned with a 3 mm gap at their closest contact point.
[0027] The second developing roller 31 is a rotating developer carrier, positioned downstream of the first developing roller 30 with respect to the rotation direction of the photosensitive drum 28Y, and such that the rotation center R2 of the second sleeve 34 is above the rotation center R1 of the first sleeve 33 in the vertical direction, and the developer is transferred from the first developing roller 30 by magnetic force (Figure 2). In this embodiment, the entire second developing roller 31 is positioned above the rotation center R1 of the first developing roller 30. The second developing roller 31, like the first developing roller 30, is positioned adjacent to the photosensitive drum 28Y, such that its rotation axis is approximately parallel to the rotation axis of the photosensitive drum 28Y. Therefore, the rotation axes of the second developing roller 31 and the first developing roller 30 are approximately parallel to each other.
[0028] Such a second developing roller 31 has a rotating second sleeve (second developing sleeve) 34 and a second magnet (fixed magnet, second developing magnet) 37 that is positioned non-rotating inside the second sleeve 34 and attracts the developer to the surface of the second sleeve 34 by magnetic force. The second developing roller 31 receives the developer from the first developing roller 30 (first sleeve 33) based on magnetic force, attracts (carries) it, and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y with the developer. A peeling roller 32, which will be described later, is located to the side of the second developing roller 31.
[0029] The second sleeve 34 is a non-magnetic cylindrical member with an outer diameter of 25 mm (radius r2 = 12.5 mm) and is rotationally driven around the rotation axis 40. The rotation direction of the second sleeve 34 is clockwise, as shown by the arrow in Figure 2, and in this embodiment, it is in the opposite direction to the rotation direction of the photosensitive drum 28Y. Therefore, the second sleeve 34 and the photosensitive drum 28Y rotate in the same direction when they are facing each other. The second sleeve 34 rotates from vertically downward to vertically upward when it is facing the photosensitive drum 28Y. Also, the second sleeve 34 and the first sleeve 33 rotate in opposite directions when they are facing each other. In this embodiment, the linear velocity on the surface of the second sleeve 34 of the second developing roller 31 is set to be 1.2 times (= 780 mm / s) the linear velocity on the surface of the photosensitive drum 28Y.
[0030] The second magnet 37 is positioned inside the second sleeve 34 and has multiple fan-shaped magnetic poles 201 to 207, as shown in Figure 4. The solid lines in the figure indicate the peak positions (maximum values) of the distribution of the normal component of the magnetic flux density of the magnetic poles 201 to 207 of the second magnet 37. A space is provided between the inner circumference of the second sleeve 34 and the outer circumference of the second magnet 37 to allow the rotation of the second sleeve 34.
[0031] The developer adsorbed on the second sleeve 34 is transported toward the photosensitive drum 28Y by the rotation of the second sleeve 34, developing the latent image formed on the photosensitive drum 28Y. After developing the latent image formed on the photosensitive drum 28Y, the developer remaining on the second sleeve 34 is transported toward the vicinity of the peeling roller 32 by the rotation of the second sleeve 34. Then, near the closest proximity point between the second developing roller 31 and the peeling roller 32, the developer is transferred from the second sleeve 34 to the third sleeve 35 of the peeling roller 32 by the magnetic field generated by the second magnet 37 contained in the second developing roller 31 and the third magnet 38 contained in the peeling roller 32.
[0032] The peeling roller 32, which acts as a peeling unit, is positioned on the opposite side of the photosensitive drum 28Y from the rotation center of the second sleeve 34, and peels off the developer from the second developing roller 31 after the electrostatic latent image on the photosensitive drum 28Y has been developed by the second developing roller 31. Specifically, the peeling roller 32 is a rotating developer carrier, and is positioned between the second developing roller 31 and the developer recovery screw 44 such that its rotation center is above the rotation center R of the second developing roller 31.
[0033] Furthermore, the peeling roller 32 is positioned such that its axis of rotation is approximately parallel to the axis of rotation of the second developing roller 31. This peeling roller 32 has a rotating third sleeve 35 and a third magnet (fixed magnet) 38 that is positioned non-rotating inside the third sleeve 35 and attracts the developer to the surface of the third sleeve 35 by magnetic force, and is configured to transfer the developer from the second developing roller 31 based on magnetic force.
[0034] The third sleeve 35 is a non-magnetic cylindrical member with an outer diameter of 18 mm (radius of 9 mm) and is rotationally driven around the rotation axis 41. The rotation direction of the third sleeve 35 is counterclockwise, as indicated by the arrow in Figure 2, and in this embodiment, it is opposite to the rotation direction of the second sleeve 34. Therefore, the third sleeve 35 and the second sleeve 34 rotate in the same direction at positions facing each other.
[0035] The third magnet 38 is positioned inside the third sleeve 35 and has multiple magnetic poles 301 to 305, as shown in Figure 5. The solid lines in the figure indicate the peak positions (maximum values) of the distribution of the normal component of the magnetic flux density of the magnetic poles 301 to 305 of the third magnet 38. A space is provided between the inner circumference of the third sleeve 35 and the outer circumference of the third magnet 38 to allow rotation of the third sleeve 35.
[0036] The developer adsorbed onto the third sleeve 35 is transported downstream in the direction of rotation by the rotational movement of the third sleeve 35, and at a position close to the developer recovery screw 44, is detached from the third sleeve 35 by the third magnet 38 contained in the peeling roller 32, and falls by its own weight toward the guide member 45 located vertically below. The developer that falls toward the guide member 45 is then guided toward the developer recovery screw 44 by its own weight.
[0037] The guide member 45 and the developer recovery screw 44 constitute a developer recovery section 47, which is a recovery section for recovering the developer peeled off from the third sleeve 35 on the peeling roller 32. In the developer recovery section 47, the developer recovery screw 44 is positioned so that its center of rotation is located below the center of rotation of the peeling roller 32 in the vertical direction, and it conveys the developer received (recovered) from the peeling roller 32 while agitating it.
[0038] The guide member 45, acting as a guide, is positioned vertically below the peeling roller 32, and the closest point between the guide member 45 and the peeling roller 32 is positioned vertically above the rotation center R2 of the second sleeve 34, guiding the developer peeled off by the peeling roller 32 toward the developer recovery screw 44. Such a guide member 45 has a slope 45a to allow the developer to slide down by its own weight, in order to more reliably guide the peeled developer toward the developer recovery screw 44. The slope 45a is inclined horizontally such that the developer recovery screw 44 side is lower than the lower position of the peeling roller 32.
[0039] The developer recovery screw 44, which serves as both a recovery member and a transport unit, transports the recovered developer to the developer circulation unit 46, which will be described below. In other words, the developer recovery screw 44 is a screw transport member used to transport the developer that has slid down the slope of the guide member 45 in one direction while agitating it.
[0040] The developer circulation unit 46 is a supply unit for supplying developer to the first developing roller 30, and the developer circulation unit 46 includes a regulating member 50, a developer supply screw 42, and a developer stirring screw 43. In the developer circulation unit 46, the developer is supplied to the first developing roller 30 while being agitated in the developer supply screw 42 and the developer stirring screw 43 and transported in a substantially horizontal direction. That is, the developer supply screw 42 supplies the developer to the first developing roller 30 while agitating and transporting it. Also, as described above, the developer recovered by the developer recovery unit 47 falls by its own weight and is introduced into the developer circulation unit 46.
[0041] The developer supply screw 42, developer agitation screw 43, and developer recovery screw 44 are screw conveying members that convey the developer in one direction while agitating it. The developer supply screw 42 and developer agitation screw 43 are located below the developer recovery screw 44 in the vertical direction. Furthermore, these developer supply screw 42, developer agitation screw 43, and developer recovery screw 44 are arranged so that their rotation axes are approximately parallel to each other. The rotation axis of each of these screws is also approximately parallel to the rotation axis of the first developing roller 30.
[0042] The developer supply screw 42 is located between the first developing roller 30 and the developer agitation screw 43, and a partition wall 48 of the developing container 60 is positioned between the developer supply screw 42 and the developer agitation screw 43. The partition wall 48 of the developing container 60 extends along the rotation axis direction of the developer supply screw 42 and the developer agitation screw 43. The partition wall 48 is provided with a communication opening (not shown) that connects a first transport path 61 through which the developer is transported by the developer supply screw 42 and a second transport path 62 through which the developer is transported by the developer agitation screw 43.
[0043] The developer, agitated by the developer recovery screw 44, passes through a communication opening (not shown) formed in the partition wall 63 of the developing container 60 located between the developer recovery screw 44 and the developer supply screw 42, and falls towards the developer supply screw 42 by its own weight. The guide member 45 described above is formed integrally with the partition wall 63, and the developer recovery screw 44 is positioned above the partition wall 63.
[0044] The location of the communication port through which the developer agitated by the developer recovery screw 44 falls by its own weight and is introduced into the developer circulation section 46 is preferably positioned to avoid the area where the developer is supplied toward the first developing roller 30 (the intermediate portion with respect to the rotation axis direction of the developer supply screw 42). In this embodiment, the location of the communication port is set to include the downstream end (terminal end) in the developer transport direction of the first transport path 61 where the developer supply screw 42 is located.
[0045] The developer transport directions of the developer supply screw 42 and the developer agitation screw 43 are opposite to each other. The starting end (upstream end in the developer transport direction) and ending end (downstream end in the developer transport direction) of the first transport path 61 where the developer supply screw 42 is located, and the ending end and starting end of the second transport path 62 where the developer agitation screw 43 is located, are in communication with each other via a communication opening provided in the partition wall 48. Therefore, the developer circulates in the rotational direction of the developer supply screw 42 and the developer agitation screw 43, as indicated by the arrows in Figure 2, and in a substantially horizontal direction within the developing container 60, with a portion of it being supplied toward the first developing roller 30.
[0046] The developer supply port 55 (see Figure 2) is located above the developer agitation screw 43 in the developing container 60 and is connected to the developer storage section 27Y (see Figure 1). The developer supply port 55 is configured to supply the developer stored in the bottle loaded in the developer storage section 27Y to the second transport path 62 where the developer agitation screw 43 is located.
[0047] As described above, the toner weight ratio of the developer stored in the bottles of the developer storage unit 27Y is greater than the toner weight ratio of the developer in the developing device 1Y. Therefore, by adjusting the amount of developer supplied to the developer stirring screw 43, it is possible to maintain a constant toner weight ratio of the developer in the developing device 1.
[0048] The toner concentration detection sensor 49 (see Figure 2) is positioned to detect the toner concentration in the developer contained in the developer circulation unit 46. The toner concentration detection sensor 49 is a sensor that detects the magnetic permeability of the developer. The toner concentration corresponds to the amount of toner consumed in the developing device 1Y and is used to control the replenishment of developer from the developer storage unit 27Y. For example, if it is detected that the toner concentration has fallen below a predetermined value, developer is replenished from the developer storage unit 27Y. Since the magnetic permeability of the developer changes more than the toner concentration, it is possible to detect the toner concentration using the magnetic permeability.
[0049] The regulating member (regulating blade) 50 is positioned adjacent to the first developing roller 30 and is used to regulate the amount of developer supplied from the developer circulation unit 46 to the first developing roller 30. The regulating member 50 can be configured to regulate the amount of developer adsorbed onto the first developing roller 30 based, for example, on the gap between the surface of the first sleeve 33 of the first developing roller 30 and the end of the regulating member 50.
[0050] As will be explained in more detail later, a space volume regulating section 51 is provided between the developer supply screw 42 and the first developing roller 30 of the developer circulation section 46 to regulate the volume of the space through which the developer is supplied from the developer supply screw 42 to the first developing roller 30. Furthermore, the space volume regulating section 51 is also provided with an inclined section 52 that slopes downward from the end of the space volume regulating section 51 toward the regulating member 50. The amount of developer regulated by the space volume regulating section 51 is transported toward the regulating member 50 along the inclined section 52.
[0051] The developer in the developing container 60 is transported in a substantially horizontal direction while being agitated in the developer circulation unit 46, and then supplied to the first developing roller 30. From the first developing roller 30, it is transferred to the upper second developing roller 31 based on magnetic force. Next, it is transferred from the second developing roller 31 to the peeling roller 32 on the side of the second developing roller 31, again based on magnetic force. After that, it is peeled off the peeling roller 32 by a third magnet 38 embedded in the peeling roller 32, and then collected in the developer recovery unit 47 and introduced back into the developer circulation unit 46.
[0052] Furthermore, as described above, in this embodiment, a two-component development method is used as the development method, and the developer is a mixture of a negatively charged non-magnetic toner and a magnetic carrier. At this time, the non-magnetic toner becomes negatively charged due to triboelectric charging with the magnetic carrier, and the magnetic carrier becomes positively charged. The non-magnetic toner is made by encapsulating colorants, wax components, etc., in a resin such as polyester or styrene acrylic, and then crushing or polymerizing it into a powder, to which fine powders such as titanium dioxide and silica are added to the surface. The magnetic carrier is made by coating the surface of a core consisting of resin particles mixed with ferrite particles or magnetic powder with resin. In this embodiment, the toner concentration in the developer in the initial state (weight ratio of toner contained in the developer) is 8%.
[0053] Furthermore, the magnetic carriers are 40-80 Am at an applied magnetic field of 1000 Oersted. 2 It is preferable to have a magnetization amount per unit weight of / kg. Reducing the magnetization amount of the magnetic carrier has the effect of suppressing scavenging by the magnetic brush, but it becomes difficult for the magnetic field generating means to adhere to the non-magnetic cylinder, which may cause image defects such as magnetic carrier adhesion to the photosensitive drum. Also, if the magnetization amount of the magnetic carrier is greater than the above range, image defects may occur due to the pressure of the magnetic brush as described above. In this embodiment, 63Am 2 Magnetic carriers with a magnetization amount per unit weight of / kg were used.
[0054] The magnetization of the magnetic carrier was measured using the BHV-30 oscillating magnetic field type automatic magnetic property recorder manufactured by RIKEN Electron Co., Ltd. The magnetic property value of the magnetic carrier was determined by creating an external magnetic field of 1000 oorsteds and measuring the magnetization strength at that time. The magnetic carrier was packed tightly into a cylindrical plastic container. The magnetization moment was measured in this state, and the actual weight with the sample inside was measured to determine the magnetization strength (Am). 2 The true specific gravity of the magnetic carrier is determined using a dry-type automatic density analyzer, AccuPic 1330, manufactured by Shimadzu Corporation. In this example, the true specific gravity (density) is 4.6 g / cm³. 3A magnetic carrier of the specified type was used. Furthermore, a magnetic carrier with a weight-average diameter of 35 μm (radius b = 17.5 μm) was employed.
[0055] Generally, two-component development systems using toner and carriers have the advantage of less stress on the toner than one-component development systems using a single-component developer, because they charge both the toner and carrier to a predetermined polarity by frictional contact. On the other hand, with prolonged use, the amount of dirt (spent) adhering to the carrier surface increases, and as a result, the ability to charge the toner gradually decreases. This results in problems such as fogging and toner scattering. Increasing the amount of carrier contained in the development unit could be considered to extend the lifespan of the two-component development unit, but this is undesirable because it would lead to a larger development unit.
[0056] To resolve the above-mentioned problems related to two-component developers, this embodiment employs an ACR (Auto Carrier Refresh) method. The ACR method is a method that suppresses the increase of degraded carriers by gradually supplying new developer from the developer storage unit 27Y into the developing device 1Y, and gradually discharging the developer with degraded charging performance from the discharge port (not shown) of the developing device 1Y. As a result, the degraded carriers in the developing device 1Y are gradually replaced with new carriers, making it possible to maintain the charging performance of the carriers in the developing device 1Y at a roughly constant level.
[0057] [About the magnetic poles of each magnet] Next, the magnetic pole configurations of the first magnet 36, second magnet 37, and third magnet 38, which are contained within the first developing roller 30, second developing roller 31, and peeling roller 32 shown in Figures 3, 4, and 5, will be described.
[0058] As shown in Figure 3, the first magnet 36 enclosed in the first developing roller 30 has a seven-pole configuration with multiple magnetic poles 101, 102, 103, 104, 105, 106, and 107. The magnetic poles 101 to 107 are arranged in numerical order in the rotational direction of the first sleeve 33.
[0059] Magnetic pole 105 is an N pole and is positioned opposite the photosensitive drum 28Y via the first sleeve 33. It is a magnetic pole for developing the electrostatic latent image formed on the photosensitive drum 28Y. Magnetic pole 107, acting as a transfer pole, is an N pole and is a magnetic pole for transferring developer from the first sleeve 33 to the second sleeve 34 by the magnetic field generated in conjunction with the second magnet 37 of the second developing roller 31. Hereafter, magnetic pole 107 may be referred to as the transfer pole 107. Magnetic pole 101 (first magnetic pole) is an N pole and is used to attract the developer supplied from the developer supply screw 42 onto the first sleeve 33. That is, magnetic pole 101 is a magnetic pole that causes the developer supplied from the developer supply screw 42 to be supported on the surface of the first sleeve 33. Hereafter, magnetic pole 101 may be referred to as the pumping pole 101.
[0060] The magnetic pole 102 (second magnetic pole) is a south pole and is positioned opposite the regulating member 50 via the first sleeve 33, and adjusts the amount of developer transported on the first sleeve 33 as described above. That is, the magnetic pole 102 is positioned downstream of the pumping pole 101 and adjacent to the pumping pole 101 with respect to the rotational direction of the first sleeve 33, and is a magnetic pole that faces the regulating member 50 via the first sleeve 33, and hereafter the magnetic pole 102 may be referred to as the regulating pole 102. The magnetic poles 103, 104, and 106 are north poles, south poles, and south poles, respectively, and are used to transport the developer attracted by the magnetic pole 101 upward as the first sleeve 33 rotates. Of these, the magnetic pole 103 (third magnetic pole) is positioned downstream of the regulating pole 102 and adjacent to the regulating pole 102 with respect to the rotational direction of the first sleeve 33, and hereafter the magnetic pole 103 may be referred to as the transport pole 103.
[0061] Furthermore, the pumping pole 101 is positioned downstream of the transfer pole 107 with respect to the rotational direction of the first sleeve 33, and is the same pole as the transfer pole 107. The transfer pole 107 and the pumping pole 101 work together to form a low-magnetic-force portion 110 with lower magnetic force than the transfer pole 107 due to the repulsive magnetic field generated between them. This low-magnetic-force portion 110 causes the developer to peel off the first sleeve 33 and facilitates the transfer of the developer from the first sleeve 33 to the second sleeve 34. In this embodiment, the low-magnetic-force portion 110 has almost no magnetic force, but it may have a low magnetic force, for example, it may be a magnetic pole with a magnetic force (normal component Br of magnetic flux density) of 5mT or less. The same applies to the low-magnetic-force portion 210 of the second magnet 37 shown in Figure 4, and the low-magnetic-force portion 310 of the third magnet 38 shown in Figure 5.
[0062] As shown in Figure 4, the second magnet 37 enclosed in the second developing roller 31 has a seven-pole configuration with multiple magnetic poles 201, 202, 203, 204, 205, 206, and 207. Of these, magnetic pole 201 is the receiving pole for the second developing roller 31 to receive developer from the first developing roller 30. The magnetic poles 201 to 207 are arranged in numerical order in the rotational direction of the second sleeve 34.
[0063] The magnetic pole 201, acting as a receiving pole, is a magnetic pole that attracts developer from the first sleeve 33 to the second sleeve 34 by the magnetic field generated in conjunction with the magnetic pole 107 of the first magnet 36 of the first developing roller 30, and hereafter, the magnetic pole 201 may be referred to as the receiving pole 201. The magnetic pole 207 is a magnetic pole that transfers developer from the second sleeve 34 to the third sleeve 35 by the magnetic field generated in conjunction with the third magnet 38 of the peeling roller 32.
[0064] Furthermore, the receiving pole 201 is a south pole, opposite to the receiving pole 107, and is used to attract the developer from the first developing roller 30 (first sleeve 33) onto the second sleeve 34, as described above. The magnetic pole 203 is a south pole and is positioned opposite the photosensitive drum 28Y via the second sleeve 34, and is a magnetic pole for developing the electrostatic latent image formed on the photosensitive drum 28Y.
[0065] Magnetic poles 202, 204, 205, and 206 are north poles, north poles, south poles, and north poles, and are used to transport the developer attracted by magnetic pole 201 upward as the second sleeve 34 rotates. Magnetic pole 207 is a south pole, and after the developer has passed through the developing area with the photosensitive drum 28Y corresponding to magnetic pole 203, it is transferred from the second sleeve 34 to the third sleeve 35 facing the second sleeve 34 by a magnetic field generated in conjunction with magnetic pole 303 in the third magnet 38 enclosed in the peeling roller 32.
[0066] Furthermore, the magnetic pole 207 is positioned upstream of the receiving pole 201 with respect to the rotational direction of the second sleeve 34, and is the same pole as the receiving pole 201. The receiving pole 201 and the magnetic pole 207 work together to form a low-magnetic-force section 210, which has a lower magnetic force than the magnetic pole 207, due to the repulsive magnetic field generated between them. This low-magnetic-force section 210 causes the developer to peel off from the second sleeve 34 and facilitates the transfer of the developer from the first sleeve 33 to the second sleeve 34. In addition, the low-magnetic-force section 210 prevents the developer from being attracted to the closest point between the first sleeve 33 and the second sleeve 34, thereby suppressing the pressure on the developer.
[0067] As shown in Figure 5, the third magnet 38 enclosed in the peeling roller 32 has multiple magnetic poles 301, 302, 303, 304, and 305. The magnetic poles 301 to 305 are arranged in numerical order in the rotational direction of the third sleeve 35.
[0068] Magnetic pole 303 is an N pole opposite to magnetic pole 207 and is used to attract the developer peeled off from the second sleeve 34 to the third sleeve 35 as described above. Magnetic poles 301, 302, and 304 are N pole, S pole, and S pole, and are used to transport the developer on the third sleeve 35 as the third sleeve 35 rotates. In particular, magnetic pole 304 is used to transport the developer attracted by magnetic pole 303 downward as the third sleeve 35 rotates. Magnetic pole 305 is an N pole and is a peeling pole used to peel off the developer attracted to the third sleeve 35 from the third sleeve 35 by the repulsive magnetic field generated in conjunction with magnetic pole 301, which is of the same pole.
[0069] [Regarding the regulation of developer layer thickness] Next, the regulation of the amount of developer carried on the first developing roller 30, i.e., layer thickness regulation, will be explained using Figure 6. Figure 6 is a schematic cross-sectional view of the first developing roller 30 and the area around the developer supply screw 42, where arrows A and B indicate the direction in which the developer supplied from the developer supply screw 42 to the first developing roller 30 flows. Also, in Figure 6 and Figure 7, which will be described later, the dashed lines within the first magnet 36 indicate the magnet pieces corresponding to each magnetic pole constituting the first magnet 36. Between the developer supply screw 42 and the first developing roller 30, a space volume regulating section 51, an inclined section 52, and a regulating member 50 are arranged.
[0070] The regulating member 50 is positioned opposite the regulating pole 102 of the first developing roller 30, with a gap between it and the first developing roller 30. In this embodiment, the regulating member 50 is positioned vertically below the rotation center R1 of the first sleeve 33 of the first developing roller 30, and upstream of the first sleeve 33 in the rotational direction from the lowest point of the first sleeve 33 in the vertical direction, facing the outer surface of the first sleeve 33 with a predetermined gap, thereby regulating the amount of developer carried on the first sleeve 33. In other words, the regulating member 50 is positioned below the rotation center R1 of the first sleeve 33 and on the side of the rotation center R1 where the developer supply screw 42 is located, and is used to regulate the amount of developer supplied from the developer circulation unit 46 to the first developing roller 30.
[0071] The space volume regulating section 51 is used to regulate the space volume that defines the amount of developer accumulated between the first developing roller 30 and the developer supply screw 42. Without the space volume regulating section 51, a large amount of developer would be supplied from the developer supply screw 42 towards the regulating electrode 102 and the regulating member 50, creating a large developer accumulation which accelerates the deterioration of the developer. Furthermore, uneven pressure from the blades of the developer supply screw 42 may cause uneven developer layer thickness and density variations. The developer, which is agitated and conveyed by the developer supply screw 42, is drawn from the top of the space volume regulating section 51 towards the pumping electrode 101 of the first developing roller 30 in the direction of arrow A.
[0072] Furthermore, on the side of the space volume regulating section 51 that is closer to the first developing roller 30, there is an inclined section 52 that slopes downward toward the regulating member 50. The inclined section 52 slopes downward vertically from the end of the space volume regulating section 51 that is closer to the first developing roller 30. The developer carried on the surface of the first sleeve 33 by the pumping pole 101 is transported by the rotation of the first sleeve 33 toward the regulating pole 102 and the regulating member 50 by sliding down the inclined section 52 in the direction of arrow B. At the regulating pole 102, the developer, whose layer thickness is regulated by passing through the gap between the first developing roller 30 and the regulating member 50, is transported to the transport pole 103, magnetic poles 104 and 105, and at the magnetic pole 105, the electrostatic latent image on the photosensitive drum 28Y facing the first developing roller 30 is developed.
[0073] In this case, the developer flow indicated by arrows A and B depends on the magnetic force formed by each magnetic pole of the first developing roller 30. The developer flow indicated by arrow B affects the thickness of the layer formed by the regulating member 50. Therefore, if the amount of developer transported indicated by arrow B decreases, the regulating member 50 cannot stably regulate the thickness of the developer layer. In particular, developer that has deteriorated with use loses its fluidity. As the fluidity of the developer decreases, the layer thickness decreases, which may lead to a decrease in image density.
[0074] Therefore, in this embodiment, the transportability of the developer is improved by increasing the magnetic force Fθ of the first developing roller 30 in the developer transport direction (tangential direction of the first developing sleeve) within the range of region C shown in Figure 7. Figure 7 is a diagram similar to Figure 6, and is used to explain region C. Region C shows the relationship between the regulating member 50, the inclined portion 52, and the first developing roller 30. That is, region C is the area on the surface of the first sleeve 33 in the range of the rotation direction of the first sleeve 33, sandwiched between the rotation center R1 of the first sleeve 33 and the starting point of the downward inclination of the inclined portion 52 (the end on the space volume regulating portion 51 side) and the line L2 connecting the rotation center R1 of the first sleeve 33 and the tip of the regulating member 50.
[0075] The magnetic force settings described above are adjusted by adjusting the absolute value and slope of the magnetic flux density Br. This adjustment of Br can be done when magnetizing the first magnet 36. In addition, the size and shape of the multiple magnet pieces that make up the first magnet 36 may also be adjusted.
[0076] The magnetic force can be calculated using the following method. The magnetic force acting on a carrier can be calculated using the following equation (1). Here, μ0 is the permeability of vacuum, μ is the permeability of the carrier, b is the radius of the carrier, and B is the magnetic flux density.
number
[0077] Therefore, we obtain the following equation (2).
number
[0078] From equation (2) above, if Br and Bθ are known, Fr and Fθ can be determined. Here, the magnetic flux density Br was measured using the FWBELL "MS-9902" magnetic field meter (product name), with the distance between the probe, a component of the meter, and the surface of the developing sleeve set to approximately 100 μm.
[0079] Furthermore, Bθ can be determined as follows. The vector potential AZ(R,θ) at the measurement location of the magnetic flux density Br can be obtained using the measured magnetic flux density Br with the following equation (3).
number
[0080] Let the boundary conditions be AZ(R,θ). Solve the equation ∇2AZ(R,θ)=0 to find AZ(R,θ). Then, you can find Bθ using equation (4) below.
number
[0081] From the above, Fr and Fθ can be derived by substituting the measured and calculated Br and Bθ into equation (1). Such magnetic force settings are achieved by adjusting the absolute value and peak position of the magnetic flux density Br of the pumping pole and regulating pole.
[0082] In this embodiment, the absolute value of the maximum value of the normal component of the magnetic flux density of the regulating pole 102 on the first sleeve 33 is greater than the absolute value of the maximum value of the normal component of the magnetic flux density of the lifting pole 101 on the first sleeve 33. Furthermore, the absolute value of the maximum value of the normal component of the magnetic flux density of the carrier pole 103 on the first sleeve 33 is greater than the absolute value of the maximum value of the normal component of the magnetic flux density of the regulating pole 102 on the first sleeve 33. That is, the relationship between the magnitude of the absolute value |Br| of the maximum value of the normal component of the magnetic flux density of the magnetic poles on the first sleeve 33 is, Pumping pole 101 < Regulating pole 102 < Conveying pole 103 We are trying to satisfy this requirement.
[0083] [Example 1] As an example that satisfies the relationship of this embodiment, first, Example 1 will be described. In Example 1, as shown in Table 1, the relationship is that the magnitude of the absolute value |Br| of the maximum value of the normal component of the magnetic flux density of the magnetic pole on the first sleeve 33 is Pumping pole 101 < Regulating pole 102 < Conveying pole 103 This was done. In the following explanation, the relationship between the magnitudes of the magnetic poles as shown in the above equation represents the relationship between the magnitudes of the absolute values |Br| of the maximum values of the normal component of the magnetic flux density of the magnetic poles on the first sleeve 33. [Table 1]
[0084] On the other hand, in Comparative Example 1, Pumping pole 101 > Regulation pole 102 This was done so. In other words, in Comparative Example 1, the absolute value of the maximum value of the normal component of the magnetic flux density of the regulating pole 102 on the first sleeve 33 is made smaller than the absolute value of the maximum value of the normal component of the magnetic flux density of the pumping pole 101 on the first sleeve 33.
[0085] In Example 1, Example 2 (described later), Comparative Example 1, and Comparative Example 2 (described later), the absolute value |Br| of the maximum value of the normal component of the magnetic flux density of the magnetic pole 104 on the first sleeve 33 was set to 100 mT. Also, as shown in Figure 3, line M1 is defined as the line connecting position P1 where the absolute value of the normal component of the magnetic flux density of the lifting pole 101 on the first sleeve 33 is at its maximum value and the rotation center R1 of the first sleeve 33. Line M2 is defined as the line connecting position P2 where the absolute value of the normal component of the magnetic flux density of the regulating pole 102 on the first sleeve 33 is at its maximum value and the rotation center R1 of the first sleeve 33. In this case, the first pole angle α, which is the acute angle between line M1 and line M2, is preferably 30° or more. Furthermore, it is preferable that the first pole angle α is 60° or less. In other words, the angular difference between the pole positions at which the absolute value |Br| of the magnetic flux density of the pumping pole 101 and the regulating pole 102 is maximized is preferably 30° to 60°, and in this embodiment it was set to 40°.
[0086] Similarly, line M3 is defined as the line connecting position P3, where the absolute value of the normal component of the magnetic flux density of the transport pole 103 on the first sleeve 33 is at its maximum, and the rotation center R1 of the first sleeve 33. In this case, the second pole angle β, which is the angle (acute angle) between line M2 and line M3, is preferably 30° or more. Furthermore, it is preferable that the second pole angle β is 60° or less. That is, the angular difference between the pole positions where the absolute value |Br| of the magnetic flux density of the regulating pole 102 and the transport pole 103 is at its maximum is preferably 30° to 60°, and in this embodiment it was set to 50°. Also, as shown in Figure 7, when the first sleeve 33 is in a position facing the photosensitive drum 28Y and the second sleeve 34 is in a position facing the photosensitive drum 28Y, the angle (acute angle) γ of the inclined portion 52 with respect to the horizontal direction is preferably 15° or more. Furthermore, it is preferable that the angle γ is 45° or less. In other words, the angle of the inclined portion 52 is preferably 15° to 45°, and in this embodiment, it was set to 30°.
[0087] Figure 8 is a graph showing the magnetic flux density Br around the regulating pole 102 of the first developing roller 30 in Example 1 and Comparative Examples 1 and 2. Figure 9 is a graph showing the magnetic force Fθ around the regulating pole 102 of the first developing roller 30 in Example 1 and Comparative Examples 1 and 2. In Figures 8 and 9, the magnetic flux density Br and magnetic force Fθ for Example 1 are shown as solid lines, the magnetic flux density Br and magnetic force Fθ for Comparative Example 1 are shown as dotted lines, and the magnetic flux density Br and magnetic force Fθ for Comparative Example 2 are shown as dashed lines. In Figure 9, when Fθ is positive, it indicates that the direction of Fθ is toward the downstream direction in the rotational direction of the first sleeve 33, and when Fθ is negative, it indicates that the direction of Fθ is toward the upstream direction in the rotational direction of the first sleeve 33.
[0088] In Comparative Example 1, as shown in Figure 8, the absolute value |Br| of the maximum value of the normal component of the magnetic flux density of the regulating pole 102 is small relative to the pumping pole 101. Therefore, as shown in Figure 9, a large negative magnetic force Fθ acts at the upstream end of region C with respect to the rotational direction of the first sleeve 33 (developer transport direction), that is, a force that tries to return the developer from the regulating pole 102 to the pumping pole 101. In contrast, in Example 1, as shown in Figure 8, the absolute value |Br| of the maximum value of the normal component of the magnetic flux density of the regulating pole 102 is large relative to the pumping pole 101. Therefore, as shown in Figure 9, Fθ in region C is larger (more positive) than in the case of Comparative Example 1, and the flow of developer toward the regulating member 50 can be made smoother.
[0089] In Comparative Example 2, similar to Example 1, the absolute value |Br| of the maximum value of the normal component of the magnetic flux density of the transport pole 103 was made larger than that of the regulating pole 102, but the absolute value |Br| of the maximum value of the normal component of the magnetic flux density of the transport pole 103 was made the same as that of the regulating pole 102. In Comparative Example 2, as shown in Figure 9, with respect to the developer transport direction, Fθ is more positive at the upstream end of region C than in Comparative Example 1, but the result is almost the same as in Comparative Example 1 from the middle of region C onward with respect to the developer transport direction. In contrast, in Example 1, with respect to the developer transport direction, Fθ is more positive from the middle of region C onward than in the cases of Comparative Examples 1 and 2.
[0090] Based on the above, as in Example 1, Pumping pole 101 < Regulating pole 102 < Conveying pole 103 It can be seen that by satisfying this relationship, a high Fθ can be maintained in region C. Therefore, in this embodiment, the developer can be stably transported to the regulating member 50. That is, the developer supported by the pumping electrode 101 can be stably transported to the regulating member 50 side vertically downward, making it possible to stabilize the thickness of the developer layer over a long period of time. As a result, the occurrence of defects (e.g., reduction in density) in the image visualized by the toner contained in the developer can be suppressed.
[0091] Here, it is desirable that the absolute value |Br| of the maximum value of the normal component of the magnetic flux density Br of each pole differs by 5 mT or more, and more preferably by 10 mT or more. That is, it is preferable that the absolute value |Br| of the maximum value of the normal component of the magnetic flux density of the regulating pole 102 on the first sleeve 33 is 5 mT or more greater than the absolute value |Br| of the maximum value of the normal component of the magnetic flux density of the regulating pole 101 on the first sleeve 33, and more preferably by 10 mT or more. Furthermore, it is preferable that the absolute value |Br| of the maximum value of the normal component of the magnetic flux density of the regulating pole 102 on the first sleeve 33 is 5 mT or more greater than the absolute value |Br| of the normal component of the magnetic flux density of the carrier pole 103 on the first sleeve 33, and more preferably by 10 mT or more greater than the absolute value |Br| of the maximum value of the normal component of the magnetic flux density of the regulating pole 102 on the first sleeve 33.
[0092] This is because, if the difference in magnitude of the absolute value |Br| of the maximum value of the normal component of each magnetic flux density Br is small, depending on the component tolerance of the first magnet 36 of the first developing roller 30, the relative magnitudes of the absolute values |Br| of the maximum value of the normal component of each magnetic flux density may be reversed. For this reason, for example, as in Example 1, it is preferable to make the |Br| of the regulating pole 102 30mT or more larger than the |Br| of the pumping pole 101, and it is preferable to make the |Br| of the transport pole 103 20mT or more larger than the |Br| of the regulating pole 102.
[0093] In this embodiment, the magnetic pole downstream of the regulating pole 102 with respect to the rotational direction of the first sleeve 33 is designated as the transport pole 103. However, the magnetic pole downstream of the regulating pole 102 may also be a developing pole that faces the photosensitive drum 28Y and develops the electrostatic latent image with toner in the developer.
[0094] [Example 2] Next, as an example that satisfies the relationship of this embodiment, Example 2 will be described using Table 1, Figure 10, and Figure 11. In Example 2, the difference between |Br| of the regulating electrode 102 and |Br| of the pumping electrode 101 is larger than in Example 1. The other configurations of Example 2 are the same as in Example 1, so a detailed explanation will be omitted.
[0095] Figure 10 is a graph showing the magnetic flux density Br around the regulating pole 102 of the first developing roller 30 in Examples 1 and 2. Figure 11 is a graph showing the magnetic force Fθ around the regulating pole 102 of the first developing roller 30 in Examples 1 and 2. In Figures 10 and 11, the magnetic flux density Br and magnetic force Fθ for Example 1 are shown as solid lines, and the magnetic flux density Br and magnetic force Fθ for Example 2 are shown as dotted lines. In Figure 11, when Fθ is positive, it indicates that the direction of Fθ is toward the downstream direction in the rotational direction of the first sleeve 33, and when Fθ is negative, it indicates that the direction of Fθ is toward the upstream direction in the rotational direction of the first sleeve 33.
[0096] As shown in Figure 9, in Example 1, Fθ in region C is larger than in Comparative Examples 1 and 2. However, with respect to the developer transport direction, Fθ is negative at the upstream end of region C, and gradually increases as you move downstream in the developer transport direction, i.e., towards the position of the regulating member 50. Therefore, in Example 1, a small force acts at the upstream end of region C to return the developer to the pumping electrode 101.
[0097] Therefore, in Example 2, the relationship between the magnitude of the absolute value |Br| of the maximum value of the normal component of the magnetic flux density of each magnetic pole is the same as in Example 1. Pumping pole 101 < Regulating pole 102 < Conveying pole 103 To achieve this, and to make Fθ in region C larger, the difference between |Br| of the pumping electrode 101 and the regulating electrode 102 is made larger. As shown in Figure 11, in Example 2, Fθ is always a positive value in region C, and it can be seen that the developer transport flow can be improved. That is, in Example 2, the direction of the tangential magnetic force Fθ on the first sleeve 33 is in the direction downstream in the rotational direction of the first sleeve 33 throughout the entire region C. For this reason, for example, as in Example 2, it is preferable to make the |Br| of the regulating electrode 102 40mT or more larger than the |Br| of the pumping electrode 101.
[0098] As described above, by satisfying the conditions of pumping electrode 101 < regulating electrode 102 < transport electrode 103, and by increasing the |Br| difference between the pumping electrode 101 and the regulating electrode 102, the transport of the developer to the regulating member 50 can be made more stable. As a result, the thickness of the developer layer can be made more stable, and the occurrence of defects (e.g., reduction in density) in the image visualized by the toner contained in the developer can be further suppressed.
[0099] [Other embodiments] The present invention is not limited to the configuration of the embodiments described above. For example, the image forming apparatus 100 is not limited to an MFP, but may be a copier, printer, or facsimile machine. Furthermore, the configuration of the developer supply screw 42, the developer agitation screw 43, and the developer recovery screw 44 is not particularly limited as long as they can transport the developer, and for example, spiral blades or paddle-shaped blades can be applied.
[0100] Furthermore, although this embodiment describes the case where two developing rollers, a first developing roller 30 and a second developing roller 31, are arranged, the same effect can be obtained even when only one developing roller is arranged. Also, although this embodiment describes the case where the first magnet 36 enclosed in the first developing roller 30 has 7 poles, the same effect can be obtained even if the number of poles is reduced by one each for the north and south poles to 5 poles. [Explanation of symbols]
[0101] 1Y, 1M, 1C, 1K... Developing equipment 28Y, 28M, 28C, 28K... Photosensitive drum (image carrier) 30...First developing roller 31...Second developing roller 33...1st Sleeve 34...Second sleeve 35...3rd sleeve 36. First Magnet 37. Second magnet 50... Regulatory components 51...Space Capacity Regulation Section 52...Slope part 101... Pumping pole (first magnetic pole) 102...Regulating pole (second magnetic pole) 103... Carrier pole (3rd magnetic pole)
Claims
1. A developing roller having a rotating developing sleeve, a developing magnet positioned non-rotating inside the developing sleeve and attracting developer to the surface of the developing sleeve by magnetic force, and developing an electrostatic latent image formed on a rotating image carrier with developer, A developer supply screw that supplies the developer to the developing roller while agitating and conveying it, A regulating member is positioned vertically below the rotation center of the developing sleeve and upstream in the rotational direction of the developing sleeve from the lowest point in the vertical direction of the developing sleeve, facing the outer surface of the developing sleeve with a predetermined gap between them, and regulating the amount of developer carried in the developing sleeve. Between the developing roller and the developer supply screw, there is a space volume regulating unit that regulates the volume of the space through which the developer is supplied from the developer supply screw to the developing roller, The space volume restricting portion includes an inclined portion that slopes downward from the end on the developing roller side toward the restricting member, The aforementioned developing magnet is A first magnetic pole that supports the developer supplied from the developer supply screw on the surface of the developing sleeve, With respect to the rotational direction of the developing sleeve, the second magnetic pole is positioned downstream of the first magnetic pole and adjacent to the first magnetic pole, and is opposed to the regulating member and the developing sleeve, A third magnetic pole is positioned downstream of the second magnetic pole and adjacent to the second magnetic pole with respect to the rotational direction of the developing sleeve, It has, The absolute value of the maximum value of the normal component of the magnetic flux density of the first magnetic pole on the developing sleeve is greater than the absolute value of the maximum value of the normal component of the magnetic flux density of the second magnetic pole on the developing sleeve, and the absolute value of the maximum value of the normal component of the magnetic flux density of the third magnetic pole on the developing sleeve is greater than the absolute value of the maximum value of the normal component of the magnetic flux density of the second magnetic pole on the developing sleeve. A developing apparatus characterized by the following features.
2. The absolute value of the maximum value of the normal component of the magnetic flux density of the second magnetic pole on the developing sleeve is 5 mT or more greater than the absolute value of the maximum value of the normal component of the magnetic flux density of the first magnetic pole on the developing sleeve. The developing apparatus according to feature 1.
3. The absolute value of the maximum value of the normal component of the magnetic flux density of the third magnetic pole on the developing sleeve is 5 mT or more greater than the absolute value of the maximum value of the normal component of the magnetic flux density of the second magnetic pole on the developing sleeve. The developing apparatus according to feature 1.
4. The absolute value of the maximum value of the normal component of the magnetic flux density of the second magnetic pole on the developing sleeve is 30 mT or more greater than the absolute value of the maximum value of the normal component of the magnetic flux density of the first magnetic pole on the developing sleeve. The developing apparatus according to feature 1.
5. The absolute value of the maximum value of the normal component of the magnetic flux density of the second magnetic pole on the developing sleeve is 40 mT or more greater than the absolute value of the maximum value of the normal component of the magnetic flux density of the first magnetic pole on the developing sleeve. The developing apparatus according to feature 1.
6. The first pole angle, which is the angle between the line connecting the position on the developing sleeve where the absolute value of the normal component of the magnetic flux density of the first pole is at its maximum and the rotation center of the developing sleeve, and the line connecting the position on the developing sleeve where the absolute value of the normal component of the magnetic flux density of the second pole is at its maximum and the rotation center of the developing sleeve, is 30° or more. The developing apparatus according to feature 1.
7. The first pole-to-pole angle is 60° or less. The developing apparatus according to feature 6.
8. The second pole angle, which is the angle between the line connecting the position on the developing sleeve where the absolute value of the normal component of the magnetic flux density of the second pole is at its maximum and the rotation center of the developing sleeve, and the line connecting the position on the developing sleeve where the absolute value of the normal component of the magnetic flux density of the third pole is at its maximum and the rotation center of the developing sleeve, is 30° or more. The developing apparatus according to feature 1.
9. The angle between the second poles is 60° or less. The developing apparatus according to feature 8.
10. When the developing sleeve is in a position facing the image carrier, the angle of the inclined portion with respect to the horizontal direction is 15° or more. The developing apparatus according to feature 1.
11. When the developing sleeve is in a position facing the image carrier, the angle of the inclined portion with respect to the horizontal direction is 45° or less. The developing apparatus according to feature 10.
12. The direction of the tangential magnetic force Fθ on the developing sleeve is in the direction of the downstream direction of the developing sleeve's rotation, over the entire area on the surface of the developing sleeve within the range of the developing sleeve's rotation direction, which is sandwiched between the line connecting the rotation center of the developing sleeve and the end of the inclined portion on the side of the space volume restricting portion, and the line connecting the rotation center of the developing sleeve and the tip of the restricting member. The developing apparatus according to feature 1.
13. The developing sleeve is a first developing sleeve, the developing magnet is a first developing magnet, and the developing roller is a first developing roller. The device further comprises a second developing sleeve that rotates, a second developing magnet that is non-rotatingly positioned inside the second developing sleeve and attracts developer to the surface of the second developing sleeve by magnetic force, and a second developing roller that develops the electrostatic latent image formed on the rotating image carrier with the developer. The second developing roller is positioned downstream of the first developing roller with respect to the rotation direction of the image carrier, and above the center of rotation of the first developing roller with respect to the vertical direction, and the developer is transferred from the first developing roller by magnetic force. The developing apparatus according to any one of claims 1 to 12.