JP2023051369A - Developing device and image forming apparatus - Google Patents

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

The present invention relates to a developing device and an image forming apparatus, and more particularly to a developing device for forming a toner image on an image carrier and an image forming apparatus to which the developing device is attached.

An image forming apparatus typified by an MFP (Multi Function Peripheral) includes a photosensitive drum and a developing device. The developing device carries developer containing toner as a developing brush by magnetic force. A toner image is formed on the photoreceptor drum by transferring the toner in the developing brush to the electrostatic latent image formed on the photoreceptor drum. An image is formed on the paper by transferring the toner image to the paper. Therefore, the size of an image that can be formed by the MFP is limited to the length that the developing device can develop the electrostatic latent image in the axial direction parallel to the rotating shaft of the photosensitive drum. This is because the axial length of the developing device that can carry the developing brush is limited. For example, it is possible to form an A3 size image in an image forming apparatus equipped with a developing device having an axial length of 297 mm corresponding to an A3 size (297 mm×420 mm) capable of carrying a developing brush. However, when an image is formed on a sheet of paper in an MFP, margins on which an image cannot be formed are generated at the corners of the paper. In order to eliminate this margin, an image forming apparatus is used to form an A3 size image on SRA3 size (320mm x 450mm) paper, and the margin is cut off from the SRA3 size paper on which the image is formed. , the paper and the image are aligned to A3 size.

Due to the limitation of the length in the axial direction in which the developing device can carry the developing brush, toner is not carried on both ends of the photosensitive drum. For this reason, deteriorated toner lumps adhere to both ends of the photosensitive drum, and the photosensitive drum may become dirty. When an A3 size image is formed on an SRA3 size sheet with deteriorated toner masses adhering to both ends of the photosensitive drum, vertical streaks may appear in the margins. On the other hand, the length of the developing device in the axial direction is restricted due to the demand for miniaturization of the main body of the MFP.

As a technique for extending the length over which an electrostatic latent image formed on a photosensitive drum can be developed by a developing device, for example, Japanese Patent Application Laid-Open No. 10-048956 discloses a device that extends axially and circumferentially on the outer peripheral surface. A permanent magnet member formed so that a plurality of magnetic poles appear in a direction, and a hollow cylindrical sleeve formed of a non-magnetic material are connected via a flange member provided at the end of the sleeve and having a bearing interposed therebetween. In the magnet roll formed to be relatively rotatable, the magnet roll is characterized in that a flange member is provided with magnetic field forming means for forming a magnetic field on the outer peripheral surface of the magnet roll.

However, in the magnet roll disclosed in Japanese Patent Application Laid-Open No. 10-048956, since a magnetic field is formed in the flange member, the developing brush is stagnated by the magnetic field formed by the flange member in a portion of the sleeve where the permanent magnet member does not exist. . For this reason, there is a problem that the toner in the developer held at that portion is insufficient, and the toner cannot be supplied to the photosensitive drum.

JP-A-10-048956

SUMMARY OF THE INVENTION One of the objects of the present invention is to provide a developing device with an expanded area capable of developing an electrostatic latent image without increasing the size of the device.

Another object of the present invention is to provide an image forming apparatus with an expanded area for developing an electrostatic latent image without increasing the size of the apparatus.

According to one aspect of the present invention, the developing device includes a magnetic roll formed of a cylindrical roll portion having magnetism, shaft portions protruding axially from both ends of the roll portion, and a cylindrical shape made of a non-magnetic material. , a sleeve in which the roll portion is housed, a coupling portion that connects the sleeve to the shaft portion via bearings at both ends of the sleeve, and a magnetic portion that generates a magnetic field at the coupling end where the sleeve is coupled to the coupling portion. and guide means for guiding the developer carried by the magnetized portion from the ends of the sleeve toward the center.

According to this aspect, the magnetized portion generates a magnetic field at the connecting end portion where the sleeve is connected to the connecting portion, and the developer carried by the magnetized portion is guided from the end portion of the sleeve toward the center. Therefore, it is possible to prevent the developer from accumulating in the magnetized portion and replace the developer carried in the magnetized portion with new developer. As a result, it is possible to provide a developing device with an expanded area capable of developing an electrostatic latent image without increasing the size of the device.

Preferably, the guide means includes a groove formed in the end of the sleeve so as to be inclined in a direction transverse to the axial direction.

According to this aspect, a groove that is inclined in a direction intersecting the axial direction is formed in the end portion of the sleeve, so that a force in the direction intersecting the axial direction can be applied to the developer carried by the magnetized portion.

Preferably, the grooves are positioned downstream in the rotational direction of the sleeve on the center side of the sleeve than on the end side.

According to this aspect, it is possible to apply a force in the direction from the end side of the sleeve toward the center side to the developer carried by the magnetized portion.

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

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

Preferably, a magnetic seal member having magnetism and arranged to face a part of the outer peripheral surface of the sleeve is further provided, and the guide means is such that the distance between the sleeve and the sleeve increases from the end portion toward the center of the sleeve. It includes an inclined surface formed on the inner peripheral surface of the magnetic seal member so as to be enlarged.

According to this aspect, since the inner peripheral surface of the magnetic seal member is formed with an inclined surface whose distance from the sleeve increases toward the center from the end portion of the sleeve, the developer carried on the magnetic seal member is formed. can be moved from the ends of the sleeve towards the center.

Preferably, the housing further comprises a housing that has a storage space for storing the developer and supports the shaft portion, and the housing is formed with a path that communicates the space between the magnetic seal member and the sleeve and the storage space. .

According to this aspect, a path is formed that communicates the space between the magnetic seal member and the sleeve with the storage space, so that the developer can be moved from the magnetic seal member to the storage space.

Preferably, the axial length of the portion of the sleeve that does not face the magnetic seal member is determined according to the axial length of the image carrier arranged to face the sleeve.

According to this aspect, the axial length of the portion of the sleeve that does not face the magnetic seal member is determined corresponding to the axial length of the image carrier. Toner can be supplied to the outside. Therefore, it is possible to improve the image quality of the blank portion where no image is formed on the recording medium.

Preferably, the magnetized portion includes a magnetic film formed on the outer peripheral surface of the sleeve.

Preferably, the magnetized portion includes a cylindrical ring member having magnetism and engaging with the outer peripheral surface of the sleeve.

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

According to still another aspect of the present invention, an image forming apparatus is equipped with the developing device described above.

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

1 is a schematic cross-sectional view showing an internal configuration of an MFP in one embodiment of the invention; FIG. FIG. 2 is a diagram showing a developing device and a photosensitive drum together with peripheral members; 2 is an external perspective view of a developing device; FIG. 4 is a plan view of a developing roller; FIG. 4 is a perspective view of an end portion of the developer roller; FIG. 4 is a cross-sectional view of an end portion of the developing roller; FIG. FIG. 3 is a partial cross-sectional view taken along line AA of FIG. 2; 4 is a perspective view showing the positional relationship between a portion of the developing roller and the magnetic seal; FIG. It is a perspective view showing the inside of a housing. FIG. 10 is an assembled perspective view of part of the developing roller in the first modified example; FIG. 11 is a perspective view of part of a developing roller in a first modified example; FIG. 11 is a cross-sectional view of an end portion of a developing roller in a first modified example;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are given the same reference numerals. Their names and functions are also the same. A detailed description thereof will therefore not be repeated.

FIG. 1 is a schematic cross-sectional view showing the internal configuration of an MFP in one embodiment of the invention. In FIG. 1 and certain figures to be described later, arrows indicating mutually orthogonal X, Y and Z directions are attached to clarify the positional relationship. The X and Y directions are perpendicular to each other in the horizontal plane, and the Z direction corresponds to the vertical direction. Referring to FIG. 1, an MFP (Multi Function Peripheral) 100 is an example of an image forming apparatus, and includes a document reading unit 130 that reads a document, an automatic document feeder 120 that conveys a document to the document reading unit 130, and an image forming apparatus. It includes an image forming section 140 that forms an image on a sheet based on data, and a sheet feeding section 150 that supplies the sheet to the image forming section 140 .

The document reading unit 130 exposes the image of the document set on the document glass 11 by the automatic document feeder 120 with the exposure lamp 13 attached to the slider 12 moving below. Reflected light 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 .

The reflected light imaged on the CCD sensor 18 is converted into image data as electrical signals within the CCD sensor 18 . The image data is converted into printing data of cyan (C), magenta (M), yellow (Y), and black (K) and output to image forming section 140 .

The image forming unit 140 includes developing devices 24Y, 24M, 24C and 24K, photosensitive drums 23Y, 23M, 23C and 23K, exposure units 21Y, 21M, 21C, 21K and 1, which correspond to yellow, magenta, cyan and black, respectively. It has secondary transfer rollers 25Y, 25M, 25C and 25K and toner bottles 41Y, 41M, 41C and 41K. Here, "Y", "M", "C" and "K" represent yellow, magenta, cyan and black respectively.

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, toner bottles 41Y, 41M, 41C , 41K differ only in the color of the toner handled, so here the developing device 24Y, the photosensitive drum 23Y, the exposure unit 21Y, the primary transfer roller 25Y and the toner bottle 41Y for forming a yellow image will be described.

The toner bottle 41Y contains a yellow developer. The developer includes non-magnetic toner and magnetic carrier. The toner bottle 41Y rotates using a toner bottle motor as a drive source, and discharges the developer to the outside. The developer discharged from the toner bottle 41Y is supplied to the developing device 24Y. The toner bottle 41Y supplies developer to the developing device 24Y when the remaining amount of developer contained in the developing device 24Y becomes equal to or less than a predetermined lower limit value.

The intermediate transfer belt 30 is suspended by a drive roller 33 and a driven roller 34 so as not to loosen. When the drive roller 33 rotates counterclockwise in FIG. 1, the intermediate transfer belt 30 rotates counterclockwise in the figure at a predetermined speed. As the intermediate transfer belt 30 rotates, the driven roller 34 rotates counterclockwise.

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

MFP 100 drives all developing devices 24Y, 24M, 24C, and 24K when forming a full-color image. As a result, yellow, magenta, cyan, and black toner images are superimposed on the intermediate transfer belt 30 . MFP 100 drives any one of developing devices 24Y, 24M, 24C, and 24K when forming a monochrome image. Also, an image can be formed by combining two or more of the developing devices 24Y, 24M, 24C, and 24K.

Sheets of different sizes are set in the sheet feed cassettes 35, 35A, and 35B. Sheets accommodated in paper feed cassettes 35, 35A, and 35B are supplied to the transport path by take-out rollers 36, 36A, and 36B attached to paper feed cassettes 35, 35A, and 35B, respectively. It is sent to timing roller 31 .

The timing roller 31 conveys the paper conveyed by the paper feed roller 37 to the nip portion between the intermediate transfer belt 30 and the secondary transfer roller 26 as a transfer member. The secondary transfer roller 26 generates an electric field at the nip portion. The toner image formed on the intermediate transfer belt 30 is transferred onto the sheet conveyed by the timing roller 31 due to the action of the electric field force at this nip portion. The paper onto which the toner image has been transferred is conveyed to the fixing roller 32 and is heated and pressed by the fixing roller 32 . As a result, the toner is melted and fixed on the paper. After that, the paper is discharged to the paper discharge tray 39 . A belt cleaning blade 29 is provided on the intermediate transfer belt 30 upstream of the developing device 24Y. The belt cleaning blade 29 removes toner remaining on the intermediate transfer belt 30 without being transferred to the paper.

Although the MFP 100 employs a tandem system having the developing devices 24Y, 24M, 24C, and 24K that form toners of four colors on paper, one photoreceptor drum can develop toners of four colors. A four-cycle method in which toner is sequentially transferred onto paper may be employed.

FIG. 2 is a diagram showing a developing device and a photosensitive drum together with peripheral members. FIG. 2 is a cross-sectional view taken along a plane perpendicular to the rotating shaft of the photosensitive drum. In FIG. 2, as members around the developing device 24Y and the photosensitive drum 23Y, an exposure unit 21Y to which yellow printing data is input, a charging roller 22Y, an intermediate transfer belt 30, and an upper portion of the photosensitive drum 23Y. shows the primary transfer roller 25Y and the drum cleaning blade 27Y arranged with the intermediate transfer belt 30 interposed therebetween.

The photoreceptor drum 23Y is a cylindrical image carrier, and a photoconductive layer is formed on the outer periphery of a conductive substrate such as aluminum. Photoreceptor drum 23Y is rotatably supported by the housing of MFP 100 about an axis of rotational symmetry. 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 order along the rotation direction of the photosensitive drum 23Y around 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 transfer residual toner on the photosensitive drum 23Y.

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 on the surface of the photosensitive drum 23Y. An electrostatic latent image is formed on the exposed portion of the photosensitive drum 23Y.

The developing device 24Y forms a toner image on the photosensitive drum 23Y using a developer composed 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.

The housing 200Y is a housing that accommodates the developer, the first screw 201Y, the second screw 203Y, the developing roller 221Y, and the regulating blade 223Y. A sensor for detecting the amount of developer in the housing 200Y is attached to the housing 200Y. When 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.

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

The housing 200Y is a container extending in the Y direction and has two spaces, a first circulation bath Sp1 and a second circulation bath 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 wings are provided on the outer peripheral surface of a cylindrical rotating shaft extending in the Y direction, and conveys the developer by rotating. The first circulation bath Sp1 and the second circulation bath Sp2 are storage spaces for storing the developer.

Openings are provided at both ends of the partition wall 205Y in the Y direction, and the first circulation bath Sp1 and the second circulation bath Sp2 are connected. 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 wall 205Y enters the second circulation tank Sp2 through the opening. 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 wall 205Y enters the first circulation tank Sp1 through the opening. Thus, the developer circulates through the first circulation bath Sp1 and the second circulation bath Sp2 by the first screw 201Y and the second screw 203Y.

The developing roller 221Y is provided inside the first circulation tank Sp1 so as to face the first screw 201Y. Furthermore, the developing roller 221Y is exposed from the housing 200Y. A portion of the developing roller 221Y exposed from the housing 200 faces the photosensitive drum 23Y. Specifically, the rotating shaft of the developing roller 221Y is rotatably supported by the housing 200Y so that the developing roller 221Y is kept at a slight distance from the photosensitive drum 23Y. The developer contains a magnetic carrier and a 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 arranged therein, and carries the developer conveyed by the first screw 201Y. Hereinafter, a collection of developer carried by the developing roller 221Y is referred to as a developing brush.

A regulating blade 223Y is arranged near the developing roller 221Y. The regulating blade 223Y is supported by the housing 200Y at both ends thereof. The end of the regulating blade 223Y facing the developing roller 221Y is positioned upstream in the circumferential direction from the portion of the surface of the developing roller 221Y that is closest to the photosensitive drum 23Y.

Therefore, the amount of developer carried by the developing roller 221Y is restricted by the regulating blade 223Y. Specifically, as the developing roller 221Y rotates, the developer carried by the developing roller 221Y is not carried by the developing roller 221Y in contact with the regulating blade 223Y. The developer passing through the gap between the regulation blade 223Y and the developing roller 221Y reaches the developing area where the distance between the developing roller 221Y and the photosensitive drum 23Y is the shortest.

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 peripheral surface of the developing roller 221Y is lower than the potential (approximately 0 V) of the portion of the peripheral surface of the photoreceptor drum 23Y where the electrostatic latent image is formed, and the potential of the electrostatic latent image of the photoreceptor drum 23Y. It will be higher than the potential of the non-imaged areas. Since the toner in the developer carried by the developing roller 221Y is negatively charged, it adheres to the portion of the peripheral surface of the photosensitive drum 23Y where the electrostatic latent image is formed. As a result, a toner image is formed by negatively charged toner on the portion of the circumferential surface of the photosensitive drum 23Y where the electrostatic latent image is formed.

The toner image formed on the photosensitive drum 23Y is transferred onto the intermediate transfer belt 30, which is an image carrier, by the action of the electric field force by the primary transfer roller 25Y. Toner remaining on the photoreceptor drum 23Y without being transferred is removed from the photoreceptor drum 23Y by the drum cleaning blade 27Y. Toners contain cleaning and lubricating components. Therefore, the portion of the photosensitive drum 23Y that carries the toner is cleaned while the frictional force is reduced by the toner removed by the drum cleaning blade 27Y.

FIG. 3 is an external perspective view of the developing device. FIG. 3 is a perspective view of the developing device 24Y viewed from the photosensitive drum 23Y side. The developing roller 221Y is accommodated 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.

FIG. 4 is a plan view of the developing roller. FIG. 5 is a perspective view of the end of the developer roller. FIG. 6 is a cross-sectional view of the end of the developer roller. 4 to 6, developing roller 221Y includes a sleeve 231Y, a magnet roll 232Y, and a coupling portion 235Y.

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 in the outer peripheral surface of the sleeve 231Y. The plurality of grooves are arranged at predetermined intervals in the circumferential direction of the sleeve 231Y.

The magnet roll 232Y includes a roll portion 225Y and a shaft portion 233Y. The roll portion 225Y has a columnar shape extending along the Y direction. The shaft portion 233Y axially protrudes from both ends of the roll portion 225Y. In the magnet roll 232Y, the roll portion 225Y is built in the sleeve 231Y, and both ends of the shaft portion 233Y are positioned outside the sleeve 231Y. The connecting portion 235Y connects 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.

In the present embodiment, shaft portion 233Y is fixed to housing 200Y. The coupling portion 235Y is connected to a drive source such as a motor via gears. Driven by the motor, the sleeve 231Y rotates and the magnet roll 232Y does not rotate. The roll portion 225Y includes a magnetic member having a plurality of magnetic poles arranged parallel to the axial direction (Y direction) around the shaft portion 233Y. The magnetic members included in the roll portion 225Y are a catch pole for pumping up the developer from the first circulation tank Sp1, a regulation pole facing the regulation blade 223Y for regulating the amount of developer, and a photosensitive drum 23Y. It has a main pole for developing the electrostatic latent image with toner and a stripping pole for returning the remaining developer to the housing 200Y.

The connecting portion 235Y is connected to the sleeve 231Y by being press-fitted into the sleeve 231Y from both ends of the sleeve 231Y. A portion extending from the end of the sleeve 231Y toward the center and in contact with the coupling portion 235Y is referred to as a coupling end portion 238Y. The inner peripheral surface of the coupling end portion 238Y of the sleeve 231Y and the outer peripheral surface of the coupling portion 235Y are in contact with each other. Inside the sleeve 231Y, the connecting portions 235Y are positioned at the connecting ends 238Y at both ends of the sleeve 231Y, and the roll portion 225Y is positioned between the two connecting portions 235Y. Therefore, the axial length of the roll portion 225Y is shorter than the axial length of the sleeve 231Y. Therefore, at the connecting end portion 238Y of the sleeve 231Y, the magnetic force of the roll portion 225Y alone does not generate enough magnetic force to form the developing brush of the developer.

The sleeve 231Y in this embodiment has a magnetic film formed on the outer peripheral surface of the coupling end portion 238Y. The magnetic film is formed by adhering or vapor-depositing magnetic material powder to the outer peripheral surface of the coupling end 238Y of the sleeve 231Y. This film generates enough magnetic force to form a developing brush of developer material. Therefore, it is possible to form a developing brush of developer at the connecting end portion 238Y of the sleeve 231Y, and to supply toner to the photosensitive drum 23Y.

A plurality of grooves 251 are formed on the outer peripheral surface of the coupling end portion 238Y of the sleeve 231Y. A plurality of grooves are inclined so as to intersect the rotation axis of the sleeve 231Y. Specifically, in the plurality of grooves, the end side of the sleeve 231Y is positioned downstream in the rotational direction of the sleeve 231Y with respect to the central side. Also, the plurality of grooves are arranged at equal intervals in the circumferential direction of the coupling end portion 238Y of the sleeve 231Y.

The magnetic brush carried by the coupling end 238Y of the sleeve 231Y is affected by the magnetic field from the magnet roll 232Y in addition to the magnetic field from the coupling end 238Y. As the sleeve 231Y rotates relative to the magnet roll 232Y, the magnetic field at the coupling end 238Y varies. In response to this magnetic field variation, the magnetic brush carried by the coupling end 238Y impinges on the plurality of grooves. The magnetic brush receives a force directed toward the center from the axial ends when colliding with the plurality of grooves. Since a plurality of grooves are formed in the coupling end portion 238Y in this manner, the magnetic brush supported by the coupling end portion 238Y can be moved from the end portion toward the center.

The toner contained in the magnetic brush carried by the connecting end 238Y is transferred to the photoreceptor drum 23Y, but the carrier remains on the connecting end 238Y. If the magnetic brush carried by the coupling end 238Y does not move, only the carrier remains, and the magnetic brush of developer containing new toner cannot be carried. In this embodiment, since a plurality of grooves are formed in the coupling end portion 238Y, the magnetic brush carried by the coupling end portion 238Y moves from the end portion toward the center. Therefore, the magnetic brush carried by the connecting end portion 238Y can be circulated, and toner can be supplied to the photosensitive drum 23Y.

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

A regulation blade 223Y is fixed to the housing 200Y above the housing 200Y so as to face the sleeve 231Y of the developing roller 221Y. The regulation blade 223Y is a plate-like member. A gap between the regulation blade 223Y and the sleeve 231Y is adjusted to a predetermined length.

A magnetic seal member 241Y that partially surrounds the end of the sleeve 231Y is arranged in the housing 200Y. The magnetic seal member 241Y is made of a material having magnetism and has a tubular shape with a notch in part. The magnetic seal member 241Y may have a C-shaped cross section. The magnetic seal member 241Y is arranged in the housing 200Y so that the cutout portion faces the photoreceptor drum 23Y. Since the magnetic seal member 241Y attracts the developer with a magnetic force, it attracts the developer that is no longer carried by the sleeve 231Y, and restricts the movement of the magnetic seal member 241Y to the opposite side of the sleeve 231Y. This prevents the developer from entering the bearing 236Y and prevents the bearing 236Y from malfunctioning. Further, it is possible to prevent the developer from leaking out of the developing device 24Y.

FIG. 8 is a perspective view showing the positional relationship between part of the developing roller and the magnetic seal. Referring to FIG. 8, the inner diameter of magnetic seal member 241Y is larger than the outer diameter of sleeve 231Y. Therefore, the relative position between the magnetic seal member 241Y and the sleeve 231Y is determined by the length of the coupling end portion 238Y of the sleeve 231Y that overlaps the magnetic seal member 241Y in the axial direction. A distance L2 shown in FIG. 7 indicates the length of the magnetic seal member 241Y in the axial direction, and a distance L3 indicates the length of overlap between the magnetic seal member 241Y and the sleeve 231Y in the axial direction. The distance L3 is shorter than the axial length L1 of the coupling end 238Y of the sleeve 231Y. The length of the portion where the coupling end portion 238Y of the sleeve 231Y does not overlap 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 value of the axial length of the recording medium on which the MFP 100 forms an image, for example, the length of the SRA3 paper in the lateral direction.

The magnetic seal member 241Y has an inclined surface 242Y that intersects with the axial direction in the vicinity of the lowermost end. Therefore, the distance between the inclined surface 242Y of the magnetic seal member 241Y and the sleeve 231Y increases from the ends of the sleeve 231Y toward the center. Therefore, the developer accumulated on the magnetic seal member 241Y can easily move downward along the inclined surface 242Y.

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 assembled. 7 and 9, the housing 200Y is formed with a path 243Y communicating with the first circulation tank (accommodating space) Sp1 on the axial center side of the magnetic seal member 241Y. Specifically, the path 243Y is formed by cutting out part of the partition 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. Therefore, the developer can be circulated in the developing device 24Y.

<First modification>
FIG. 10 is an assembled perspective view of part of the developing roller in the first modified example. FIG. 11 is a perspective view of part of the developing roller in the first modified example. FIG. 12 is a cross-sectional view of the end portion of the developing roller in the first modified example. 10 to 12, in developing roller 221Y, ring member 261Y is assembled to connecting end portion 238Y of sleeve 231Y. The ring member 261Y is made of a magnetic material and formed in a cylindrical shape. A plurality of grooves 251 are formed on the outer peripheral surface of the ring member 261Y.

The inner diameter of the ring member 261Y is the same as or slightly smaller than the outer diameter of the coupling end portion 238Y of the sleeve 231Y. The ring member 261Y is assembled to the coupling end portion 238Y of the sleeve 231Y by fitting the ring member 261Y to the coupling end portion 238Y of the sleeve 231Y. Also in the first modified example, since the ring member 261Y fitted to the coupling end portion 238Y of the sleeve 231Y generates a magnetic field, the coupling end portion 238Y can carry the magnetic brush.

<Second modification>
In the embodiment described above, a magnetic film is formed by adhering or evaporating magnetic material powder to the outer peripheral surface of the coupling end portion 238Y of the sleeve 231Y, but the present invention is not limited to this. A permanent magnet may be embedded in the portion of the coupling portion 235Y that enters the sleeve 231Y. Also in the second modification, since a magnetic field is generated at the coupling end portion 238Y of the sleeve 231Y, the magnetic brush can be carried by the coupling end portion 238Y.

As described above, the developing device 24Y in the present embodiment includes the magnet roll 232Y including the cylindrical roll portion 225Y having magnetism and the shaft portions 233Y projecting axially from both ends of the roll portion 225Y, and the non-magnetic roll portion 232Y. It comprises a sleeve 231Y which is made of a material and has a cylindrical shape and accommodates the roll portion 225Y therein, and coupling portions 235Y which connect the sleeve 231Y to the shaft portion 233Y via bearings 237Y at both ends of the sleeve 231Y.

Sleeve 231Y includes a magnetized portion that produces a magnetic field at coupling end 238Y that couples with coupling portion 235Y. The magnetized portion may be a magnetic film formed on the outer peripheral surface of the sleeve 231Y, or may be a cylindrical ring member 261Y that is magnetic and engages the outer peripheral surface of the sleeve. Furthermore, the magnetized portion may be a permanent magnet embedded in the portion of the coupling portion 235Y that enters the sleeve 231Y.

A groove 251 is formed on the outer peripheral surface of the coupling end portion 238Y of the sleeve 231Y so as to be inclined in a direction crossing the axial direction. Therefore, it is possible to apply a force in a direction crossing the axial direction to the developing brush carried by the coupling end portion 238Y of the sleeve 231Y. Therefore, the developer can be circulated without remaining at the coupling end portion 238Y of the sleeve 231Y.

Further, the groove 251 is positioned downstream in the rotational direction of the sleeve 231Y with respect to the center side of the sleeve 231Y relative to the end side. Therefore, it is possible to apply a force to the developer in the direction from the end side of the sleeve 231Y toward the center side. Further, since a plurality of grooves 251 are arranged at predetermined intervals in the circumferential direction of the sleeve, force can be applied to the developer carried by the coupling end portion 238 over the entire circumferential direction of the sleeve 231Y.

In addition, an inclined surface 242Y is provided on the inner peripheral surface of the magnetic seal member 241Y arranged to face a part of the outer peripheral surface of the sleeve 231Y, the distance from the sleeve 231Y increasing from the end portion of the sleeve 231Y toward the center. including. Therefore, the developer carried on the magnetic seal member 241Y can be moved from the ends of the sleeve 231Y toward the center.

Further, a path 243 is formed in the housing 200Y to communicate the space between the magnetic seal member 241Y and the sleeve 231Y and the first circulation tank Sp1. Therefore, the developer can be moved from the magnetic seal member 241Y to the first circulation tank Sp1.

The axial length of the portion of the sleeve 231Y that does not face the magnetic seal member 241Y is determined according to the axial length of the photosensitive drum 23Y that faces the sleeve 231Y. Therefore, the toner can be supplied to the outside of the area where the photosensitive drum 23Y carries the toner image. Therefore, in the area outside the area where the photoreceptor drum 23Y carries the toner image, the cleaning efficiency of the drum cleaning blade 27Y is improved due to the lubricating and cleaning components of the toner. Therefore, in the recording medium onto which the toner image formed on the photosensitive drum 23Y is transferred, the image quality of the blank portion where the toner image is not transferred can be improved.

In the developing device 24Y of the present embodiment, the sleeve 231Y can extend the area where the magnetic brush is carried without increasing the axial length of the sleeve 231Y. Furthermore, since the developing device 24Y does not need to extend the axial length of the sleeve 231Y in order to extend the area for carrying the magnetic brush, it is not necessary to extend the length of the MFP 100 in the Y direction.

It should be considered that the embodiments disclosed this time are illustrative in all respects and not restrictive. The scope of the present invention is indicated by the scope of the claims rather than the above description, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims.

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 regulation blade, 225Y Roll part 231Y Sleeve 232Y Magnet roll 233Y Shaft part 235Y Coupling part 236Y, 237Y Bearing 238Y Coupling end part 241Y Magnetic seal member 242Y Inclined surface 243 Path 251 Groove 261Y Ring member Sp1 First Circulation tank, Sp2 Second circulation tank.

Claims (11)

a magnet roll comprising a cylindrical roll portion having magnetism and shaft portions projecting in the axial direction from both ends of the roll portion;
a cylindrical sleeve made of a non-magnetic material, in which the roll portion is housed;
connecting portions for connecting the sleeve to the shaft portion via bearings at both ends of the sleeve;
a magnetizing portion that generates a magnetic field at a coupling end where the sleeve couples with the coupling portion;
and a guide means for guiding the developer carried by the magnetized portion from the end portion of the sleeve toward the center thereof. 2. The developing device according to claim 1, wherein said guide means includes a groove formed in an end portion of said sleeve so as to be inclined in a direction crossing said axial direction. 3. The developing device according to claim 2, wherein the groove is located downstream of the end portion side in the rotational direction of the sleeve on the center side of the sleeve. 4. The developing device according to claim 2, wherein a plurality of said grooves are arranged at predetermined intervals in the circumferential direction of said sleeve. further comprising a magnetic seal member having magnetism and arranged to face a portion of the outer peripheral surface of the sleeve,
5. The method according to any one of claims 1 to 4, wherein the guide means includes an inclined surface formed on the inner peripheral surface of the magnetic seal member so that the distance from the sleeve increases from the end of the sleeve toward the center. Developing device according to any one of the above. further comprising a housing that has a storage space that stores developer and supports the shaft,
6. The developing device according to claim 5, wherein said housing has a path connecting a space between said magnetic seal member and said sleeve and said housing space. 7. The axial length of the portion of the sleeve that does not face the magnetic seal member is determined according to the axial length of the image carrier arranged to face the sleeve. The developing device described in . 8. The developing device according to claim 1, wherein said magnetized portion includes a magnetic film formed on the outer peripheral surface of said sleeve. 8. The developing device according to claim 1, wherein said magnetized portion includes a cylindrical ring member having magnetism and engaging with an outer peripheral surface of said sleeve. 10. The developing device according to claim 1, wherein said magnetized portion is a magnetic member embedded in said coupling portion. An image forming apparatus equipped with the developing device according to any one of claims 1 to 10.

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