Developing device and image forming apparatus

Abstract

To provide a developing device that expands an area where it can develop an electrostatic latent image without increasing the size of the device.SOLUTION: A developing device comprises: a magnet roll that is composed of a roll part in a columnar shape having magnetism and a shaft part 233Y projecting in an axial direction from both ends of the roll part; a sleeve 231Y that is a non-magnetic material and formed into a cylindrical shape and stores the roll part therein; coupling parts 235Y that couple the sleeve 231Y to the shaft part 233Y with bearings on both ends of the sleeve 231Y; a magnetization part that generates magnetic fields at coupling ends 238Y where the sleeve 231Y is coupled to the coupling parts 235Y; and guiding means 251Y that guide a developer carried on the magnetization part from the ends toward the center of the sleeve.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a developing device and an image forming apparatus, and more particularly to a developing device that forms a toner image on an image carrier, and an image forming apparatus to which the developing device is attached. [Background technology]

[0002] Image forming devices, such as multi-function peripherals (MFPs), include a photosensitive drum and a developing device. The developing device magnetically supports a developer, including toner, in the form of a developing brush. The toner in the developing brush is transferred to an electrostatic latent image formed on the photosensitive drum, forming a toner image on the photosensitive drum. This toner image is then transferred to paper, forming an image on the paper. Therefore, the size of images that can be formed by an MFP is limited by the length of the axial direction parallel to the rotational axis of the photosensitive drum that the developing device can develop the electrostatic latent image. This is due to the limited axial length that the developing device can support the developing brush. For example, an image forming device equipped with a 297-mm developing device, which supports a developing brush with an axial length corresponding to A3 size (297 mm x 420 mm), can form an A3-size image. However, when forming an image on paper using an MFP, margins on the corners of the paper remain where no image can be formed. To eliminate this margin, an image forming device is used to form an A3 size image on SRA3 size (320mm x 450mm) paper, and the margin is then cut off from the SRA3 size paper on which the image has been formed, thereby aligning the paper and image to A3 size.

[0003] Due to limitations on the axial length that the developing device can carry the developing brush, toner cannot be carried at either end of the photosensitive drum. This can cause clumps of degraded toner to adhere to either end of the photosensitive drum, resulting in contamination. When an A3-sized image is formed on SRA3-sized paper with clumps of degraded toner adhering to either end of the photosensitive drum, vertical lines can appear in the margins. Meanwhile, the axial length of the developing device is limited by the demand for a more compact MFP body.

[0004] As a technology for extending the length over which a developing device can develop an electrostatic latent image formed on a photosensitive drum, for example, Japanese Patent Application Laid-Open No. 10-048956 describes a magnet roll that comprises a permanent magnet member that extends axially on its outer circumferential surface and is formed so that multiple magnetic poles appear in the circumferential direction, and a sleeve formed in a hollow cylindrical shape from a non-magnetic material, and that is formed so that the two can rotate relative to each other via a flange member that is attached to the end of the sleeve and has a bearing interposed therebetween, and that is characterized in that a magnetic field forming means that forms a magnetic field on the outer circumferential surface of the magnet roll is provided on the flange member.

[0005] However, in the magnet roll described in JP-A-10-048956, a magnetic field is formed in the flange member, and the magnetic field formed by the flange member causes the developing brush to stagnate in the portion of the sleeve where there is no permanent magnet member, resulting in a shortage of toner in the developer held in that portion, making it impossible to supply toner to the photosensitive drum. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 10-048956 Summary of the Invention [Problem to be solved by the invention]

[0007] SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device that expands the area in which an electrostatic latent image can be developed without increasing the size of the device.

[0008] Another object of the present invention is to provide an image forming apparatus in which the area in which an electrostatic latent image can be developed is expanded without increasing the size of the apparatus. [Means for solving the problem]

[0009] According to one aspect of the present invention, a developing device includes a magnet roll including a magnetic cylindrical roll portion and a shaft portion protruding from both ends of the roll portion in the axial direction; a sleeve formed into a cylindrical shape from a non-magnetic material and housing the roll portion therein; connecting portions that connect the sleeve to the shaft portion via bearings at both ends of the sleeve; a magnetized portion that generates a magnetic field at connecting ends where the sleeve is connected to the connecting portions; and a guide means that guides developer carried by the magnetized portion from the ends of the sleeve toward the center. The guide means includes a groove formed in the end of the sleeve so as to be inclined in a direction intersecting the axial direction. .

[0010] According to this aspect, the magnetized portion generates a magnetic field at the connecting end where the sleeve is connected to the connecting portion, and the developer carried by the magnetized portion is guided from the end toward the center of the sleeve. This prevents the developer from accumulating in the magnetized portion, and the developer carried by the magnetized portion can be replaced with new developer. As a result, it is possible to provide a developing device that expands the area in which electrostatic latent images can be developed without increasing the size of the device.

[0012] Also Since the grooves are formed at the end of the sleeve so as to be inclined in a direction intersecting the axial direction, a force in a direction intersecting the axial direction can be applied to the developer carried by the magnetized portion.

[0013] Preferably, the groove is located downstream in the rotation direction of the sleeve at the center side of the sleeve relative to the end sides.

[0014] According to this aspect, a force can be applied to the developer carried by the magnetized portion in a direction from the end side of the sleeve toward the center side.

[0015] Preferably, a plurality of grooves are arranged at predetermined intervals in the circumferential direction of the sleeve.

[0016] According to this aspect, since the plurality of grooves are arranged at predetermined intervals in the circumferential direction, a force can be applied to the developer carried by the magnetized portion over the entire circumferential direction of the sleeve.

[0017] Preferably, the device further comprises a magnetic sealing member that is magnetic and is arranged opposite a portion of the outer peripheral surface of the sleeve, and the guiding means includes an inclined surface formed on the inner peripheral surface of the magnetic sealing member so that the distance between the sleeve increases from the end of the sleeve toward the center.

[0018] In this aspect, an inclined surface is formed on the inner surface of the magnetic seal member such that the distance between the magnetic seal member and the sleeve increases from the end of the sleeve toward the center, thereby allowing the developer carried on the magnetic seal member to move from the end of the sleeve toward the center.

[0019] Preferably, the developer developer further comprises a housing having a storage space for storing developer and supporting the shaft portion, and the housing has a passage formed therein that connects the storage space with the space between the magnetic seal member and the sleeve.

[0020] According to this aspect, a path is formed that connects the space between the magnetic seal member and the sleeve with the containing space, so that the developer can be moved from the magnetic seal member to the containing space.

[0021] Preferably, the axial length of the portion of the sleeve that does not face the magnetic seal member is determined in accordance with the axial length of the image carrier disposed opposite the sleeve.

[0022] In this aspect, the axial length of the portion of the sleeve that does not face the magnetic seal member is determined in accordance with the axial length of the image carrier, so that toner can be supplied to the outside of the area where the image carrier carries the toner image, thereby improving the image quality of the marginal areas on the recording medium where no image is formed.

[0023] Preferably, the magnetized portion includes a magnetic film formed on the outer circumferential surface of the sleeve.

[0024] Preferably, the magnetized portion includes a magnetic cylindrical ring member that engages with the outer peripheral surface of the sleeve.

[0025] Preferably, the magnetized portion is a magnetic member embedded in the coupling portion.

[0026] According to still another aspect of the present invention, the above-described developing device is mounted in an image forming apparatus.

[0027] According to this aspect, it is possible to provide an image forming apparatus in which the area in which an electrostatic latent image can be developed is expanded without increasing the size of the apparatus. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a schematic cross-sectional view showing the internal configuration of an MFP according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing a developing device and a photosensitive drum together with peripheral members. [Figure 3] FIG. [Figure 4] FIG. [Figure 5] FIG. 2 is a perspective view of an end portion of the developing roller. [Figure 6] FIG. 2 is a cross-sectional view of an end portion of the developing roller. [Figure 7] FIG. 3 is a partial cross-sectional view taken along the line AA in FIG. 2. [Figure 8] FIG. 2 is a perspective view showing the positional relationship between a part of the developing roller and a magnetic seal. [Figure 9] FIG. 2 is a perspective view showing the inside of the housing. [Figure 10] FIG. 10 is an assembled perspective view of a part of the developing roller in the first modified example. [Figure 11]FIG. 10 is a perspective view of a part of a developing roller in a first modified example. [Figure 12] FIG. 10 is a cross-sectional view of an end portion of a developing roller in a first modified example. DETAILED DESCRIPTION OF THE INVENTION

[0029] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same components are designated by the same reference numerals. The names and functions of these components are also the same. Therefore, detailed description thereof will not be repeated.

[0030] FIG. 1 is a schematic cross-sectional view showing the internal configuration of an MFP according to one embodiment of the present invention. In FIG. 1 and certain figures described below, arrows indicating mutually orthogonal X, Y, and Z directions are used to clarify positional relationships. The X and Y directions are orthogonal to each other in a horizontal plane, and the Z direction corresponds to the vertical direction. Referring to FIG. 1, MFP (Multi Function Peripheral) 100 is an example of an image forming device, and includes a document reading unit 130 that reads a document, an automatic document feeder 120 that transports the document to document reading unit 130, an image forming unit 140 that forms an image on paper based on image data, and a paper feed unit 150 that supplies paper to image forming unit 140.

[0031] The document reading unit 130 exposes the image of a document set on a document glass 11 by an automatic document feeder 120 with an exposure lamp 13 attached to a slider 12 that moves below the document glass 11. Light reflected from the document is guided to a lens 16 by a mirror 14 and two reflecting mirrors 15 and 15A, and forms an image on a CCD (Charge Coupled Devices) sensor 18.

[0032] The reflected light that forms an image on the CCD sensor 18 is converted into image data as an electrical signal within the CCD sensor 18. The image data is converted into printing data in cyan (C), magenta (M), yellow (Y), and black (K) and output to the image forming unit 140.

[0033] Image forming unit 140 includes developing devices 24Y, 24M, 24C, and 24K, photoconductor drums 23Y, 23M, 23C, and 23K, exposure units 21Y, 21M, 21C, and 21K, primary transfer rollers 25Y, 25M, 25C, and 25K, and toner bottles 41Y, 41M, 41C, and 41K, corresponding to yellow, magenta, cyan, and black, respectively. Here, "Y," "M," "C," and "K" represent yellow, magenta, cyan, and black, respectively.

[0034] Developing devices 24Y, 24M, 24C, 24K, photosensitive drums 23Y, 23M, 23C, 23K, exposure units 21Y, 21M, 21C, 21K, primary transfer rollers 25Y, 25M, 25C, 25K, and toner bottles 41Y, 41M, 41C, 41K differ only in the color of the toner they handle, so here we will explain developing device 24Y, photosensitive drum 23Y, exposure unit 21Y, primary transfer roller 25Y, and toner bottle 41Y for forming yellow images.

[0035] Toner bottle 41Y contains yellow developer. The developer contains non-magnetic toner and magnetic carrier. Toner bottle 41Y rotates using a toner bottle motor as a drive source and discharges developer to the outside. The developer discharged from toner bottle 41Y is supplied to developing device 24Y. Toner bottle 41Y supplies developer to developing device 24Y when the remaining amount of developer contained in developing device 24Y falls below a predetermined lower limit.

[0036] The intermediate transfer belt 30 is suspended tightly by a drive roller 33 and a driven roller 34. When the drive roller 33 rotates counterclockwise in FIG. 1, the intermediate transfer belt 30 rotates counterclockwise in the drawing at a predetermined speed. As the intermediate transfer belt 30 rotates, the driven roller 34 rotates counterclockwise.

[0037] The developing device 24Y receives developer from a toner bottle 41Y and develops the electrostatic latent image formed on the photosensitive drum 23Y to form a toner image on the photosensitive drum 23Y. The toner image formed on the photosensitive drum 23Y is transferred onto the intermediate transfer belt 30 by a primary transfer roller 25Y. The timing at which the developing device 24Y transfers the toner image onto the intermediate transfer belt 30 is adjusted by detecting a reference mark attached to the intermediate transfer belt 30.

[0038] When forming a full-color image, the MFP 100 drives all of the developing devices 24Y, 24M, 24C, and 24K. As a result, yellow, magenta, cyan, and black toner images are superimposed on the intermediate transfer belt 30. When forming a monochrome image, the MFP 100 drives any one of the developing devices 24Y, 24M, 24C, and 24K. It is also possible to form an image using a combination of two or more of the developing devices 24Y, 24M, 24C, and 24K.

[0039] Paper of different sizes is set in paper feed cassettes 35, 35A, and 35B, respectively. The paper stored in paper feed cassettes 35, 35A, and 35B is supplied to the transport path by take-out rollers 36, 36A, and 36B attached to paper feed cassettes 35, 35A, and 35B, respectively, and sent to timing roller 31 by paper feed roller 37.

[0040] Timing roller 31 transports the paper transported by paper feed roller 37 to the nip between intermediate transfer belt 30 and secondary transfer roller 26, which is a transfer member. Secondary transfer roller 26 generates an electric field in the nip. The electric field force in this nip causes the toner image formed on intermediate transfer belt 30 to be transferred to the paper transported by timing roller 31. The paper with the transferred toner image is transported to fixing roller 32, where it is heated and pressed. This melts the toner and fixes it to the paper. The paper is then ejected to paper output tray 39. A belt cleaning blade 29 is provided upstream of developing device 24Y on intermediate transfer belt 30. The belt cleaning blade 29 removes any toner remaining on intermediate transfer belt 30 that has not been transferred to the paper.

[0041] Here, we will explain an example in which MFP 100 adopts a tandem system equipped with developing devices 24Y, 24M, 24C, and 24K that form four color toners on paper, but it may also adopt a four-cycle system in which four color toners are transferred sequentially onto paper using a single photosensitive drum.

[0042] Fig. 2 shows the developing device and the photosensitive drum together with the peripheral components. Fig. 2 is a cross-sectional view taken along a plane perpendicular to the rotation axis of the photosensitive drum. Fig. 2 shows the peripheral components of the developing device 24Y and the photosensitive drum 23Y, including an exposure unit 21Y to which yellow printing data is input, a charging roller 22Y, an intermediate transfer belt 30, a primary transfer roller 25Y disposed above the photosensitive drum 23Y across the intermediate transfer belt 30, and a drum cleaning blade 27Y.

[0043] The photosensitive drum 23Y is a cylindrical image carrier, with a photoconductive layer formed on the outer periphery of a conductive substrate such as aluminum. The photosensitive drum 23Y is supported on the housing of the MFP 100 so as to be rotatable about a rotationally symmetrical axis. Around the photosensitive drum 23Y, a charging roller 22Y, an exposure unit 21Y, a developing device 24Y, a primary transfer roller 25Y, and a drum cleaning blade 27Y are arranged in this order along the rotation direction of the photosensitive drum 23Y. The charging roller 22Y uniformly charges the surface of the photosensitive drum 23Y, which is an image carrier. The drum cleaning blade 27Y removes residual toner from the photosensitive drum 23Y.

[0044] After being charged by the charging roller 22Y, the photosensitive drum 23Y is irradiated with laser light emitted by the exposure unit 21Y. The exposure unit 21Y exposes an image-corresponding portion of the surface of the photosensitive drum 23Y. An electrostatic latent image is formed in the exposed portion of the photosensitive drum 23Y.

[0045] The developing device 24Y forms a toner image on the photosensitive drum 23Y using a developer made of carrier and toner. The developing device 24Y includes a housing 200Y, a first screw 201Y, a second screw 203Y, a developing roller 221Y, and a regulating blade 223Y.

[0046] The housing 200Y is a housing that houses the developer, the first screw 201Y, the second screw 203Y, the developing roller 221Y, and the regulating blade 223Y. A sensor that detects the amount of developer inside the housing 200Y is attached to the housing 200Y. If the amount of developer detected by the sensor is less than a predetermined value, the developer is supplied from the toner bottle 41Y to the housing 200Y.

[0047] A developing roller 221Y, a first screw 201Y, and a second screw 203Y are arranged side by side within the housing 200Y and are rotatably supported by the housing 200Y. The developing roller 221Y, the first screw 201Y, and the second screw 203Y extend in the Y direction.

[0048] The housing 200Y is a container extending in the Y direction and has two spaces, a first circulation tank Sp1 and a second circulation tank Sp2, separated by a partition wall 205Y extending in the Y direction. A first screw 201Y is provided in the first circulation tank Sp1, and a second screw 203Y is provided in the second circulation tank Sp2. Each of the first screw 201Y and the second screw 203Y has a shape in which spiral blades are provided on the outer circumferential surface of a cylindrical rotation shaft extending in the Y direction, and transports developer by rotating. The first circulation tank Sp1 and the second circulation tank Sp2 are storage spaces that store developer.

[0049] Openings are provided at both ends of the partition 205Y in the Y direction, and the first circulation tank Sp1 and the second circulation tank Sp2 are connected through these openings. As the first screw 201Y rotates, the developer in the first circulation tank Sp1 is transported to the positive side in the Y direction, and the developer transported to the end of the partition 205Y enters the second circulation tank Sp2 through the openings. As the second screw 203Y rotates, the developer in the second circulation tank Sp2 is transported to the negative side in the Y direction, and the developer transported to the end of the partition 205Y enters the first circulation tank Sp1 through the openings. In this way, the developer circulates through the first circulation tank Sp1 and the second circulation tank Sp2 by the first screw 201Y and the second screw 203Y.

[0050] The developing roller 221Y is provided in the first circulation tank Sp1, facing the first screw 201Y. Furthermore, the developing roller 221Y is exposed from the housing 200Y. The portion of the developing roller 221Y exposed from the housing 200Y faces the photosensitive drum 23Y. Specifically, the rotation shaft of the developing roller 221Y is rotatably supported by the housing 200Y so as to maintain a small gap between the developing roller 221Y and the photosensitive drum 23Y. The developer contains magnetic carrier and non-magnetic toner. The developing roller 221Y attracts the magnetic carrier together with the non-magnetic toner by the magnetic force of the roll portion 225Y disposed therein, and carries the developer transported by the first screw 201Y. Hereinafter, the collection of developer carried by the developing roller 221Y is referred to as a developing brush.

[0051] A regulating blade 223Y is disposed near the developing roller 221Y. The regulating blade 223Y is supported at both ends by the housing 200Y. The end of the regulating blade 223Y facing the developing roller 221Y is located upstream in the circumferential direction of the portion of the surface of the developing roller 221Y that is closest to the photosensitive drum 23Y.

[0052] For this reason, the amount of developer carried by the developing roller 221Y is limited by the regulating blade 223Y. Specifically, as the developing roller 221Y rotates, the developer carried by the developing roller 221Y that comes into contact with the regulating blade 223Y is no longer carried by the developing roller 221Y. The developer that passes through the gap between the regulating blade 223Y and the developing roller 221Y reaches a development region where the distance between the developing roller 221Y and the photosensitive drum 23Y is the shortest.

[0053] The developing roller 221Y applies toner to the photosensitive drum 23Y to develop the electrostatic latent image. Specifically, a developing bias is applied to the developing roller 221Y. As a result, the potential of the circumferential surface of the developing roller 221Y is lower than the potential (approximately 0 V) ​​of the portion of the circumferential surface of the photosensitive drum 23Y on which the electrostatic latent image is formed, and higher than the potential of the portion of the circumferential surface of the photosensitive drum 23Y on which the electrostatic latent image is not formed. The toner in the developer carried by the developing roller 221Y is negatively charged, and therefore adheres to the portion of the circumferential surface of the photosensitive drum 23Y on which the electrostatic latent image is formed. As a result, a toner image is formed by the negatively charged toner on the portion of the circumferential surface of the photosensitive drum 23Y on which the electrostatic latent image is formed.

[0054] The toner image formed on the photoreceptor drum 23Y is transferred onto the intermediate transfer belt 30, which is an image carrier, by the action of electric field force from the primary transfer roller 25Y. Toner that remains on the photoreceptor drum 23Y without being transferred is removed from the photoreceptor drum 23Y by the drum cleaning blade 27Y. The toner contains a cleaning component and a lubricating component. Therefore, the toner-carrying portion of the photoreceptor drum 23Y is cleaned while frictional force is reduced by the toner removed by the drum cleaning blade 27Y.

[0055] Fig. 3 is an external perspective view of the developing device. Fig. 3 is an oblique view of the developing device 24Y as viewed from the photosensitive drum 23Y side. The developing roller 221Y is housed inside the housing 200Y, and a portion of the surface of the developing roller 221Y extending in the Y direction is exposed from the housing 200Y. The developing device 24Y and the photosensitive drum 23Y are positioned so that the portion of the developing roller 221Y exposed from the housing 200Y faces the photosensitive drum 23Y.

[0056] Fig. 4 is a plan view of the developing roller. Fig. 5 is a perspective view of an end portion of the developing roller. Fig. 6 is a cross-sectional view of the end portion of the developing roller. With reference to Figs. 4 to 6, developing roller 221Y includes a sleeve 231Y, a magnet roll 232Y, and a connecting portion 235Y.

[0057] The sleeve 231Y has a cylindrical shape and is made of a non-magnetic material. A plurality of grooves parallel to the axial direction are formed on the outer peripheral surface of the sleeve 231Y. The plurality of grooves are arranged at predetermined intervals around the circumference of the sleeve 231Y.

[0058] The magnet roll 232Y includes a roll portion 225Y and a shaft portion 233Y. The roll portion 225Y has a cylindrical shape extending along the Y direction. The shaft portion 233Y protrudes in the axial direction from both ends of the roll portion 225Y. In the magnet roll 232Y, the roll portion 225Y is built into the sleeve 231Y, and both ends of the shaft portion 233Y are located outside the sleeve 231Y. The coupling portions 235Y connect the sleeve 231Y to the shaft portion 233Y at both ends of the sleeve 231Y via bearings 237Y. Therefore, the sleeve 231Y rotates relative to the magnet roll 232Y with the shaft portion 233Y as the rotation axis.

[0059] In this embodiment, the shaft portion 233Y is fixed to the housing 200Y. The coupling portion 235Y is connected to a drive source such as a motor via a gear. The sleeve 231Y rotates when the motor is driven, but the magnet roll 232Y does not rotate. The roll portion 225Y includes a magnetic member having multiple magnetic poles arranged parallel to the axial direction (Y direction) around the shaft portion 233Y. The magnetic member included in the roll portion 225Y includes a catch pole that draws up the developer from the first circulation tank Sp1, a regulating pole that is positioned opposite the regulating blade 223Y that regulates the amount of developer, a main pole that develops the electrostatic latent image formed on the photosensitive drum 23Y with toner, and a peeling pole that returns the remaining developer to the housing 200Y.

[0060] The coupling portion 235Y is coupled to the sleeve 231Y by being press-fitted into the interior of the sleeve 231Y from both ends of the sleeve 231Y. The portion of the sleeve 231Y that contacts the coupling portion 235Y and extends from the end toward the center is called a coupling end 238Y. The inner circumferential surface of the coupling end 238Y of the sleeve 231Y abuts against the outer circumferential surface of the coupling portion 235Y. Inside the sleeve 231Y, the coupling portions 235Y are located at the coupling ends 238Y at both ends of the sleeve 231Y, and the roll portion 225Y is located between the two coupling portions 235Y. Therefore, the axial length of the roll portion 225Y is shorter than the axial length of the sleeve 231Y. Therefore, the magnetic force of the roll portion 225Y alone is not enough to generate a developing brush of the developer at the coupling end 238Y of the sleeve 231Y.

[0061] In the present embodiment, the sleeve 231Y has a magnetic film formed on the outer peripheral surface of the connecting end 238Y. The magnetic film is formed by adhering or depositing magnetic material powder on the outer peripheral surface of the connecting end 238Y of the sleeve 231Y. This film generates a magnetic force sufficient to form a developing brush of the developer. This makes it possible to form a developing brush of the developer at the connecting end 238Y of the sleeve 231Y, and toner can be supplied to the photosensitive drum 23Y.

[0062] Furthermore, a plurality of grooves 251 are formed on the outer peripheral surface of the coupling end 238Y of the sleeve 231Y. The plurality of grooves are inclined so as to intersect with the rotation axis of the sleeve 231Y. Specifically, the end sides of the plurality of grooves are located downstream of the center side in the rotation direction of the sleeve 231Y. The plurality of grooves are also arranged at equal intervals in the circumferential direction of the coupling end 238Y of the sleeve 231Y.

[0063] The magnetic brush carried by the connecting end 238Y of the sleeve 231Y is affected by the magnetic field from the magnetic roll 232Y in addition to the magnetic field from the connecting end 238Y. As the sleeve 231Y rotates relative to the magnetic roll 232Y, the magnetic field at the connecting end 238Y fluctuates. In response to this magnetic field fluctuation, the magnetic brush carried by the connecting end 238Y collides with the multiple grooves. When the magnetic brush collides with the multiple grooves, it is subjected to a force that moves from the end toward the center in the axial direction. In this way, multiple grooves are formed in the connecting end 238Y, so the magnetic brush carried by the connecting end 238Y can be moved from the end toward the center.

[0064] The toner contained in the magnetic brush carried by the connecting end 238Y is transferred to the photosensitive drum 23Y, but the carrier remains at the connecting end 238Y. If the magnetic brush carried by the connecting end 238Y does not move, only the carrier remains, and the magnetic brush of the developer containing new toner cannot be carried. In this embodiment, multiple grooves are formed in the connecting end 238Y, so the magnetic brush carried by the connecting end 238Y moves from the end toward the center. This allows the magnetic brush carried by the connecting end 238Y to circulate, and toner can be supplied to the photosensitive drum 23Y.

[0065] FIG. 7 is a partial cross-sectional view taken along line AA in FIG. 2. FIG. 7 shows a cross section of one end of the developing device. Referring to FIG. 7, a coupling portion 235Y of the developing roller 221Y is connected to the housing 200Y via a bearing 236Y. Therefore, the coupling portion 235Y is rotatable relative to the housing 200Y. A shaft portion 233Y of the developing roller 221Y is fixed to the housing 200Y. A distance L1 in the figure indicates the axial length of the coupling end portion where the sleeve 231Y of the developing roller 221Y contacts the coupling portion 235Y.

[0066] A regulating blade 223Y is fixed to the housing 200Y at the top of the housing 200Y, facing the sleeve 231Y of the developing roller 221Y. The regulating blade 223Y is a plate-shaped member. The gap between the regulating blade 223Y and the sleeve 231Y is adjusted to a predetermined length.

[0067] A magnetic seal member 241Y is disposed in the housing 200Y, surrounding a portion of the end of the sleeve 231Y. The magnetic seal member 241Y is formed of a magnetic material and has a cylindrical shape with a cutout. The cross section of the magnetic seal member 241Y may be C-shaped. The magnetic seal member 241Y is disposed in the housing 200Y so that the cutout faces the photosensitive drum 23Y. The magnetic seal member 241Y attracts developer with its magnetic force, thereby attracting developer that is no longer supported by the sleeve 231Y and restricting movement of the magnetic seal member 241Y toward the opposite side of the sleeve 231Y. This prevents developer from entering the bearing 236Y, thereby preventing damage to the bearing 236Y. It also prevents developer from leaking out of the developing device 24Y.

[0068] FIG. 8 is a perspective view showing the positional relationship between a portion of the developing roller and the magnetic seal. Referring to FIG. 8, the inner diameter of the magnetic seal member 241Y is larger than the outer diameter of the sleeve 231Y. Therefore, the relative positions of the magnetic seal member 241Y and the sleeve 231Y are determined by the axial overlap length of the connecting end 238Y of the sleeve 231Y with the magnetic seal member 241Y. Distance L2 shown in FIG. 7 indicates the axial length of the magnetic seal member 241Y, and distance L3 indicates the axial overlap length of the magnetic seal member 241Y and the sleeve 231Y. Distance L3 is shorter than the axial length L1 of the connecting end 238Y of the sleeve 231Y. The length of the portion of the connecting end 238Y of the sleeve 231Y that does not overlap with the magnetic seal member 241Y in the axial direction is determined by the axial length of the photosensitive drum 23Y. The axial length of the photosensitive drum 23Y is the maximum axial length of the recording medium on which the MFP 100 forms an image, for example, the length of SRA3 paper in the short direction.

[0069] The magnetic sealing member 241Y has an inclined surface 242Y that intersects with the axial direction near the bottom end. Therefore, the distance between the inclined surface 242Y of the magnetic sealing member 241Y and the sleeve 231Y increases from the end toward the center of the sleeve 231Y. Therefore, the developer accumulated on the magnetic sealing member 241Y is likely to move downward along the inclined surface 242Y.

[0070] FIG. 9 is a perspective view showing the inside of the housing. FIG. 9 shows a state in which the developing roller 221Y is not installed. Referring to FIGS. 7 and 9, the housing 200Y has a path 243Y formed at the axial center of the magnetic seal member 241Y, which communicates with the first circulation tank (storage space) Sp1. Specifically, the path 243Y is formed by cutting out a portion of the partition wall surrounding the first circulation tank Sp1. As a result, the developer discharged from the magnetic seal member 241Y passes through the path 243Y and enters the first circulation tank Sp1. This allows the developer to circulate within the developing device 24Y.

[0071] <First Modification> Fig. 10 is an assembled perspective view of a portion of the developing roller in the first modified example. Fig. 11 is a perspective view of a portion of the developing roller in the first modified example. Fig. 12 is a cross-sectional view of an end portion of the developing roller in the first modified example. With reference to Figs. 10 to 12, in the developing roller 221Y, a ring member 261Y is assembled to the connecting end portion 238Y of the sleeve 231Y. The ring member 261Y is formed in a cylindrical shape from a magnetic material. A plurality of grooves 251 are formed in the outer peripheral surface of the ring member 261Y.

[0072] The inner diameter of the ring member 261Y is the same as or slightly smaller than the outer diameter of the connecting end 238Y of the sleeve 231Y. The ring member 261Y is fitted into the connecting end 238Y of the sleeve 231Y, thereby assembling the ring member 261Y to the connecting end 238Y of the sleeve 231Y. In the first modified example, the ring member 261Y fitted into the connecting end 238Y of the sleeve 231Y also generates a magnetic field, allowing the connecting end 238Y to support a magnetic brush.

[0073] <Second Modification> In the above-described embodiment, a magnetic film is formed by adhering or depositing magnetic material powder on the outer peripheral surface of the connecting end 238Y of the sleeve 231Y, but this is not limiting. A permanent magnet may be embedded in the portion of the connecting portion 235Y that fits into the sleeve 231Y. In the second modification, a magnetic field is also generated at the connecting end 238Y of the sleeve 231Y, allowing the connecting end 238Y to support a magnetic brush.

[0074] As described above, the developing device 24Y in this embodiment includes a magnet roll 232Y consisting of a magnetic cylindrical roll portion 225Y and a shaft portion 233Y protruding axially from both ends of the roll portion 225Y, a sleeve 231Y formed in a cylindrical shape from a non-magnetic material and housing the roll portion 225Y inside, and connecting portions 235Y that connect the sleeve 231Y to the shaft portion 233Y at both ends of the sleeve 231Y via bearings 237Y.

[0075] The sleeve 231Y includes a magnetized portion that generates a magnetic field at a coupling end 238Y where the sleeve 231Y couples with the coupling portion 235Y. The magnetized portion may be a magnetic film formed on the outer circumferential surface of the sleeve 231Y, or a magnetic cylindrical ring member 261Y that engages with the outer circumferential surface of the sleeve. Furthermore, the magnetized portion may be a permanent magnet embedded in the portion of the coupling portion 235Y that fits into the sleeve 231Y.

[0076] Furthermore, grooves 251 are formed on the outer peripheral surface of the connecting end 238Y of the sleeve 231Y so as to be inclined in a direction intersecting the axial direction. This allows a force in a direction intersecting the axial direction to be applied to the developing brush carried by the connecting end 238Y of the sleeve 231Y. This prevents the developer from accumulating at the connecting end 238Y of the sleeve 231Y, allowing the developer to circulate.

[0077] Furthermore, the groove 251 is located such that the center side of the sleeve 231Y is downstream of the end sides in the rotation direction of the sleeve 231Y. Therefore, a force can be applied to the developer in a direction from the end side to the center of the sleeve 231Y. Furthermore, since a plurality of grooves 251 are arranged at predetermined intervals in the circumferential direction of the sleeve 231Y, a force can be applied to the developer carried by the connecting end 238 over the entire circumferential direction of the sleeve 231Y.

[0078] Furthermore, the magnetic seal member 241Y, which is disposed opposite a portion of the outer circumferential surface of the sleeve 231Y, includes an inclined surface 242Y on its inner circumferential surface, where the distance from the sleeve 231Y increases from the end portion toward the center of the sleeve 231Y. This allows the developer carried on the magnetic seal member 241Y to move from the end portion toward the center of the sleeve 231Y.

[0079] Furthermore, a path 243 is formed in the housing 200Y, which connects the space between the magnetic seal member 241Y and the sleeve 231Y with the first circulation tank Sp1. This allows the developer to move from the magnetic seal member 241Y to the first circulation tank Sp1.

[0080] Furthermore, the axial length of the portion of the sleeve 231Y that does not face the magnetic seal member 241Y is determined corresponding to the axial length of the photosensitive drum 23Y disposed opposite the sleeve 231Y. This allows toner to be supplied to areas outside the area where the photosensitive drum 23Y carries the toner image. Therefore, the lubricating and cleaning components of the toner improve the cleaning efficiency of the drum cleaning blade 27Y in areas outside the area where the photosensitive drum 23Y carries the toner image. This improves the image quality of marginal areas where the toner image formed on the photosensitive drum 23Y is not transferred, on a recording medium onto which the toner image is transferred.

[0081] In the developing device 24Y of the present embodiment, the area in which the magnetic brush is supported by the sleeve 231Y can be expanded without increasing the axial length of the sleeve 231Y. Furthermore, since the developing device 24Y does not need to increase the axial length of the sleeve 231Y to expand the area in which the magnetic brush is supported, it is not necessary to increase the length of the MFP 100 in the Y direction.

[0082] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0083] 100 MFP, 21C, 21M, 21Y, 21K exposure unit, 22Y charging roller, 23C, 23M, 23Y, 23K photosensitive drum, 24C, 24M, 24Y, 24K developing device, 25Y primary transfer roller, 26 secondary transfer roller, 27Y drum cleaning blade, 29 belt cleaning blade, 30 intermediate transfer belt, 41C, 41M, 41Y, 41K toner bottle, 200Y housing, 201Y first screw, 203Y second screw, 205Y partition wall, 221Y developing roller, 223Y regulating blade, 225Y roll portion, 231Y sleeve, 232Y magnet roll, 233Y shaft portion, 235Y connecting portion, 236Y, 237Y bearing, 238Y connecting end portion, 241Y Magnetic seal member, 242Y inclined surface, 243 path, 251 groove, 261Y ring member, Sp1 first circulation tank, Sp2 second circulation tank.

Claims

1. a magnet roll including a magnetic cylindrical roll portion and shaft portions protruding in the axial direction from both ends of the roll portion; a sleeve formed in a cylindrical shape from a non-magnetic material and housing the roll portion therein; coupling portions at both ends of the sleeve for connecting the sleeve to the shaft portion via bearings; a magnetizing portion that generates a magnetic field at a coupling end where the sleeve is coupled to the coupling portion; a guide means for guiding the developer carried by the magnetized portion from the end portion of the sleeve toward the center thereof, The developing device, wherein the guide means includes a groove formed in the end of the sleeve so as to be inclined in a direction intersecting with the axial direction.

2. 2. The developing device according to claim 1, wherein the groove is located downstream in the rotation direction of the sleeve from the center side of the sleeve relative to the end side.

3. 3. The developing device according to claim 1, wherein a plurality of said grooves are arranged at predetermined intervals in the circumferential direction of said sleeve.

4. a magnetic seal member that is magnetic and that is disposed opposite a portion of the outer circumferential surface of the sleeve; The developing device according to any one of claims 1 to 3, wherein the guiding means includes an inclined surface formed on the inner peripheral surface of the magnetic seal member so that the distance between the magnetic seal member and the sleeve increases from the end of the sleeve toward the center.

5. a housing having a storage space for storing a developer and supporting the shaft portion; 5. The developing device according to claim 4, wherein said housing has a passage formed therein that connects said storage space with a space between said magnetic seal member and said sleeve.

6. 6. The developing device according to claim 4, wherein the axial length of the portion of the sleeve that does not face the magnetic seal member is determined in accordance with the axial length of an image carrier disposed opposite the sleeve.

7. 7. The developing device according to claim 1, wherein the magnetized portion includes a magnetic film formed on the outer peripheral surface of the sleeve.

8. 7. The developing device according to claim 1, wherein said magnetized portion includes a cylindrical ring member that is magnetic and engages with the outer peripheral surface of said sleeve.

9. 7. The developing device according to claim 1, wherein the magnetized portion is a magnetic member embedded in the connecting portion.

10. An image forming apparatus to which the developing device according to any one of claims 1 to 9 is attached.

Images