JP5332276B2 - Developing device, process cartridge, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device of multi-stage development system, which prevents developer from being firmly fixed to the lengthwise end of a second developer carrier, and also to provide a process cartridge and image forming apparatus. <P>SOLUTION: A developer regulating member 23c has narrow sections 23c1 at its lengthwise ends, each section 23c1 being narrower in a gap N2 between a first developer carrier 23a1 and the member 23c itself than the lengthwise middle section. The lengthwise range of each narrow section 23c1 of the developer regulating member 23c is formed so as to include a range W2 in which the magnetic force of the receiving magnetic pole H22 of a second developer carrier 23a2 stabilizes from the lengthwise end to the lengthwise center. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, or a complex machine thereof, and a developing device and a process cartridge installed therein, and particularly includes a toner and a carrier. The present invention relates to a multistage developing type developing device, a process cartridge, and an image forming apparatus using a plurality of developer carrying members carrying a two-component developer.

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, a two-component developer composed of toner and carrier (including the case where an additive or the like is added) is applied to a plurality of developer carriers (developing rollers). Development devices that carry and carry out a development process are known (see, for example, Patent Document 1 and Patent Document 2).
Such a developing method using a plurality of developer carriers is called a “multi-stage developing method”, and is often used particularly for high-speed image forming apparatuses having a high process linear velocity.

  Specifically, the multistage developing type developing device is disposed along the traveling direction of the image carrier such that a plurality of developer carriers are opposed to the image carrier such as a photosensitive drum. Then, according to the toner consumption in the developing device, the toner is appropriately supplied into the developing device from a toner supply port provided in a part of the developing device. The replenished toner is agitated and mixed together with the developer in the developing device by a developer conveying member such as a conveying screw (screw auger). Part of the stirred and mixed developer is supplied to the first developing roller (first developer carrying member) by the developer conveying member. The developer carried on the first developing roller is regulated to an appropriate amount by a doctor blade (developer regulating member) and then reaches a position facing the photosensitive drum (image carrier). Thereafter, the developer on the first developing roller that has passed the position facing the photosensitive drum is carried on the second developing roller at the position of the receiving magnetic pole of the second developing roller (second developer carrying member). . The developer carried on the second developing roller reaches the position facing the photosensitive drum, and then separates from the second developing roller and returns to the developing device. Thus, in the first development area where the first developing roller and the photosensitive drum face each other and the second development area where the second development roller and the photosensitive drum face each other, the toner in the two-component developer is A toner image is formed by adhering to the latent image on the photosensitive drum.

  On the other hand, in Patent Document 3, Patent Document 4, etc., the doctor blade (the gap between the doctor blade and the developing roller) at the end in the longitudinal direction is narrower than the doctor gap at the center in the longitudinal direction. A technique for providing a step at the tip of (developing doctor) is disclosed.

JP 2007-322915 A JP-A-2005-55574 JP 2004-246103 A Japanese Patent No. 4038405

  In the conventional multi-stage development type developing device, there is a problem that the developer is fixed (filming) to the end portion in the longitudinal direction of the second developer carrier. If a large amount of developer adheres to the end in the longitudinal direction of the second developer carrier, the surface of the image carrier is damaged by the adhered developer, and the image quality of the output image decreases. There was a case.

  On the other hand, in the techniques described in Patent Document 3 and Patent Document 4 described above, when a plurality of developing rollers are divided and arranged in the longitudinal direction, the development carried on the developing roller in a region where adjacent developing rollers overlap. The total amount of agents and the amount of developer carried on each developing roller in an area where adjacent developing rollers do not overlap are intended to be equal in the longitudinal direction. Is not a solution.

  The present invention has been made to solve the above-described problems, and does not cause a problem that the developer adheres to the end portion in the longitudinal direction of the second developer carrying member. An apparatus, a process cartridge, and an image forming apparatus are provided.

The inventor of the present application has come to know the following matters as a result of repeated studies to solve the above-mentioned problems.
That is, although the magnetic force of the receiving magnetic pole of the second developer carrier is stable at the longitudinal center, the magnetic force is unstable at both longitudinal ends. Then, in the vicinity of the region where the magnetic force of the receiving magnetic pole is unstable (the end in the width direction) in this way, it is received on the second developer carrier compared to the central portion in the longitudinal direction where the magnetic force of the receiving magnetic pole is stable. In some cases, the amount of developer (or agent height) per unit area is extremely large. As described above, at a portion where the amount of developer carried on the second developer carrying member is large, the developer receives a large compressive force at a position facing the image carrying member, and eventually on the second developer carrying member. It will stick to.
Such a phenomenon is caused by the fact that the first developer conveying member that supplies the developer to the first developer carrying member while conveying the developer in the longitudinal direction and the developer separated from the second developer carrying member. In the developing device in which the second developer conveying member that conveys in the longitudinal direction is installed, it becomes prominent at the end in the longitudinal direction corresponding to the upstream side in the conveying direction of the first developer conveying member. This is because the amount of developer (the amount of developer per unit area) supplied onto the first developer carrier by the first developer transport member is larger on the upstream side in the transport direction than on the downstream side in the transport direction. is there. That is, the amount of developer delivered from the first developer carrier to the second developer carrier at the longitudinal end of the second developer carrier corresponding to the upstream side of the first developer conveyance member in the conveyance direction is As a whole, the amount of the developer carried on the second developer carrying member tends to be extremely large, and a portion where the amount of the developer is extremely increased tends to be generated.

The present invention is based on the matters described above. That is, the developing device according to the first aspect of the present invention accommodates the developer and develops the latent image formed on the image carrier. A developing device, which faces the image carrier and also has a first developer carrier that carries a developer, and the first developer carrier that faces the image carrier and passes through a position facing the image carrier. A second developer carrier that receives and carries a part or all of the developer on the one developer carrier by a magnetic pole; and is opposed to the first developer carrier and on the first developer carrier. A developer regulating member that regulates the amount of developer carried, wherein the developer regulating member has a narrow portion narrower than the central portion in the longitudinal direction in the gap in the longitudinal direction with respect to the first developer carrier. Provided at the end of the developer regulating member. Longitudinal extent of the serial narrow portion is formed to include a longitudinal end portion of said receiving magnetic pole of said second developer carrying member, said developer regulating member, toward the longitudinal center from said narrow portion And a tapered portion where the gap with the first developer carrier gradually increases .

  According to a second aspect of the present invention, there is provided the developing device according to the first aspect, wherein the developer regulating member includes a nonmagnetic member formed of a nonmagnetic material and a magnetic member formed of a magnetic material. And a member.

  A developing device according to a third aspect of the present invention is the developing device according to the second aspect, wherein the narrow portion is formed in the magnetic member.

A developing device according to a fourth aspect of the present invention is the developing device according to any one of the first to third aspects, wherein the developing device is opposed to the first developer carrying member and conveys the developer in the longitudinal direction. The first developer carrying member for supplying the developer to the first developer carrying member, and a position below the first developer carrying member and facing the second developer carrying member. And a second developer conveying member that conveys the developer separated from the second developer carrying member, wherein the narrow portion of the developer regulating member is in a conveying direction of the first developer conveying member It is provided at the end in the longitudinal direction corresponding to the upstream side.

A process cartridge according to a fifth aspect of the present invention is a process cartridge that is detachably installed on the main body of the image forming apparatus, and the developing device according to any one of the first to fourth aspects. And the image carrier.

An image forming apparatus according to a sixth aspect of the present invention includes the developing device according to any one of the first to fourth aspects and the image carrier.

  In the present application, the “process cartridge” refers to a charging unit that charges the image carrier, a developing unit (developing device) that develops a latent image formed on the image carrier, and a cleaning on the image carrier. At least one of the cleaning units and the image carrier are defined as a unit that is integrated and detachably installed on the image forming apparatus main body.

  In the present invention, the gap between the developer regulating member and the first developer carrier is optimized in accordance with the region where the magnetic force of the receiving magnetic pole of the second developer carrier is unstable. It is possible to provide a multistage developing type developing device, a process cartridge, and an image forming apparatus that do not cause a problem that the developer adheres to the end in the longitudinal direction of the body.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

Embodiment 1 FIG.
A first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
The writing units 2A to 2D are devices for writing an electrostatic latent image on the photosensitive drum 21 (image carrier) after the charging process based on image information. The writing units 2A to 2D are optical scanning devices using polygon mirrors 3A to 3D, optical elements 4A to 4D, and the like. An LED array can be used as the writing unit instead of the optical scanning device.
The paper feeding unit 61 stores a recording medium P such as recording paper or OHP, and feeds the recording medium P toward the transfer belt 30 during image formation.

The transfer belt 30 is an endless belt for transferring the toner image formed on the photosensitive drum 21 onto the recording medium P by electrostatically attracting and transporting the recording medium P to the surface thereof. An adsorption roller 64 and a belt cleaner 65 are provided on the outer peripheral surface.
The transfer roller 24 that faces the photosensitive drum 21 via the transfer belt 30 includes a cored bar and a conductive elastic layer that covers the cored bar. The conductive elastic layer of the transfer roller 24 is prepared by blending and dispersing a conductive agent such as carbon black, zinc oxide or tin oxide in an elastic material such as polyurethane rubber or ethylene-propylene-diene polyethylene (EPDM). It is an elastic body whose (volume resistivity) is adjusted to medium resistance.

The fixing unit 66 includes a heating roller 68 and a pressure roller 67, and fixes the toner image on the recording medium P to the recording medium P by pressure and heat.
The four process cartridges 20Y, 20C, 20M, and 20BK arranged in the vertical direction along the transfer belt 30 are for forming toner images of yellow, cyan, magenta, and black, respectively.

On each of the process cartridges 20Y, 20C, 20M, and 20BK, agent cartridges 28Y, 28C that supply a carrier (magnetic carrier) and toner (toner particles) of each color (yellow, cyan, magenta, black) to the developing device 23, 28M and 28BK are installed.
The process cartridges 20Y, 20C, 20M, and 20BK and the agent cartridges 28Y, 28C, 28M, and 28BK can be attached to and detached from the apparatus main body 1 by opening the transfer belt 30 around the rotation support shaft.

  The image forming apparatus according to the first embodiment is a composite image forming apparatus that functions as a copier and a printer. When functioning as a copying machine, the image information read from the scanner is subjected to various image processing such as A / D conversion, MTF correction, gradation processing, etc., and converted into writing data. In the case of functioning as a printer, image processing is performed on image information in a format such as a page description language or a bitmap transmitted from a computer or the like, and converted into write data.

  At the time of image formation, exposure light corresponding to the image information of black, magenta, cyan, and yellow is irradiated from the writing units 2A to 2D to the process cartridges 20BK, 20M, 20C, and 20Y, respectively. That is, exposure light (laser light) emitted from each light source passes through the polygon mirrors 3A to 3D, the optical elements 4A to 4D, and is irradiated onto each photosensitive drum 21. Thus, a toner image corresponding to the exposure light is formed on the photosensitive drum 21 (image carrier) of each process cartridge 20BK, 20M, 20C, 20Y. Then, this toner image is transferred to the recording medium P.

  The recording medium P fed from the paper feeding unit 61 is transported to the position of the transfer belt 30 at the timing of the registration roller 63 and the timing. The suction roller 64 disposed at the transfer position of the transfer belt 30 causes the transfer medium 30 to suck the recording medium P that has been transferred by applying a voltage. The recording medium P that moves as the transfer belt 30 travels in the direction of the arrow sequentially passes through the positions of the process cartridges 20Y, 20C, 20M, and 20BK, and the toner images of the respective colors are superimposed and transferred.

  The recording medium P on which the color toner image is transferred is separated from the transfer belt 30 and reaches the fixing unit 66. The toner image on the recording medium P is fixed on the recording medium P by being heated while being sandwiched between the heating roller 68 and the pressure roller 67. On the other hand, the surface of the transfer belt 30 after the recording medium P is separated reaches the position of the belt cleaner 65, and dirt such as toner adhering to the surface is cleaned.

Next, the process cartridge and the agent cartridge in the image forming apparatus will be described in detail.
The process cartridges 20Y, 20C, 20M, and 20BK have substantially the same structure, and the agent cartridges 28Y, 28C, 28M, and 28BK have substantially the same structure. The alphabet (Y, C, M, BK) is removed for illustration. In addition, the writing unit is illustrated by removing the alphabet (A to D).

  FIG. 2 is an enlarged view showing the process cartridge 20 and the agent cartridge 28 installed in the apparatus main body 1. FIG. 3 is an enlarged view showing the developing device 23 installed in the process cartridge 20. 4 is a cross-sectional view of the circulation path in the developing device 23 as viewed from the direction of the arrow X shown in FIG. 3 in the longitudinal direction. FIG. 5 is a cross-sectional view showing a Y1-Y1 cross section of the circulation path in the developing device 23 of FIG. 6 is a cross-sectional view showing a Y2-Y2 cross section of the circulation path in the developing device 23 of FIG.

As shown in FIG. 2, the process cartridge 20 includes a photosensitive drum 21 as an image carrier, a charging unit 22, a developing device 23 (developing unit), and a cleaning unit 25, and is a premix developing unit. System (development system in which carrier is replenished / discharged as appropriate) is adopted.
The photosensitive drum 21 as an image carrier is a negatively charged organic photosensitive member, and is rotationally driven counterclockwise by a rotation driving mechanism (not shown).

The charging unit 22 is a charging roller having elasticity, in which a medium-resistance foamed urethane layer in which a urethane resin, carbon black as conductive particles, a sulfurizing agent, a foaming agent, and the like are formed in a roller shape on a core metal. The material of the middle resistance layer of the charging unit 22 is urethane, ethylene-propylene-diene polyethylene (EPDM), butadiene acrylonitrile rubber (NBR), silicone rubber, isoprene rubber, etc. It is also possible to use a rubber material in which a conductive material such as the above is dispersed or a foamed material of these materials.
The cleaning unit 25 is provided with a cleaning brush (or cleaning blade) that is in sliding contact with the photosensitive drum 21, and mechanically removes and collects untransferred toner on the photosensitive drum 21.

  In the developing device 23, two developing rollers 23a1 and 23a2 as developer carrying members are disposed so as to be close to the photosensitive drum 21, and the photosensitive drum 21 and the magnetic brush are in contact with each other at both opposing portions. A development area is formed. In the developing device 23, a developer G (two-component developer) composed of toner T and carrier C is accommodated. The developing device 23 develops the electrostatic latent image formed on the photosensitive drum 21 (forms a toner image). The configuration and operation of the developing device 23 will be described in detail later.

Here, the developing device 23 in the first embodiment is of a premix developing system, and a new carrier C (developer G) is appropriately supplied from the agent cartridge 28 into the developing device 23, and The deteriorated developer G is discharged toward the agent storage container 70 installed outside the developing device 23.
Referring to FIG. 2, the agent cartridge 28 accommodates developer G (toner T and carrier C) to be supplied into the developing device 23 therein. The agent cartridge 28 functions as a toner cartridge that supplies new toner T to the developing device 23, and also functions as a supply unit that supplies new carrier C to the developing device 23. Specifically, the shutter mechanism 80 is based on the information of the toner density (the ratio of the toner in the developer G) detected by the magnetic sensor 26 (see FIG. 4) installed in the developing device 23. The developer G is appropriately supplied from the agent cartridge 28 into the developing device 23.
In the first embodiment, the mixing ratio (toner concentration) of the toner T with respect to the carrier C in the developer G of the agent cartridge 28 is set to be relatively high.
The supply pipe 29 is for reliably guiding the developer G (toner T and carrier C) supplied from the agent cartridge 28 into the developing device 23. That is, the developer G discharged from the agent cartridge 28 is supplied into the developing device 23 via the supply pipe 29.

Next, an image forming process performed on the photosensitive drum 21 will be described.
Referring to FIG. 2, when the photosensitive drum 21 is driven to rotate counterclockwise, first, the surface of the photosensitive drum 21 is uniformly charged at the position of the charging unit 22. Thereafter, the surface of the charged photosensitive drum 21 reaches the irradiation position of the exposure light L, and an exposure process by the writing unit 2 is performed. That is, by selectively removing the charge on the photosensitive drum 21 in accordance with the image information by irradiation with the exposure light L, a difference (potential contrast) from the potential of the non-image portion that has not been irradiated is generated, and electrostatic latent Form an image. In this exposure step, the charge generation material receives light in the photosensitive layer of the photosensitive drum 21 to generate charges, and among these holes, the holes cancel out the charged charges on the surface of the photosensitive drum 21.

Thereafter, the surface of the photosensitive drum 21 on which the latent image is formed reaches a position facing the developing device 23. The electrostatic latent image on the photosensitive drum 21 comes into contact with the magnetic brush on the developing rollers 23a1 and 23a2, and the negatively charged toner T in the magnetic brush is attached and visualized.
Specifically, the developer G pumped up by the magnetic force generated by the magnetic pole of the upper developing roller 23a1 is made into an appropriate amount by a doctor blade 23c as a developer regulating member, and then the developing region (the developing region (opposite part to the photosensitive drum 21)). This is a region where the two developing rollers 23a1 and 23a2 and the photosensitive drum 21 face each other). The carrier C spiked in the development area rubs the photosensitive drum 21. At this time, the toner T mixed with the carrier C is negatively charged due to friction with the carrier C. On the other hand, the carrier C is positively charged. A predetermined developing bias is applied to the developing rollers 23a1 and 23a2 from a power supply unit (not shown). As a result, an electric field is formed between the developing rollers 23a1 and 23a2 and the photosensitive drum 21, and the negatively charged toner T is selectively attached only to the image portion on the photosensitive drum 21 by the electric field, and the toner image. Form.

Thereafter, the surface of the photosensitive drum 21 on which the toner image is formed reaches a position facing the transfer belt 30 and the transfer roller 24. Then, the toner image on the photosensitive drum 21 is transferred onto the recording medium P conveyed to the facing position in accordance with this timing. At this time, a predetermined voltage is applied to the transfer roller 24.
Thereafter, the recording medium P to which the toner image is transferred passes through the fixing unit 66 and is discharged from the discharge roller 69 to the outside of the apparatus.

On the other hand, toner T (untransferred toner) remaining on the photosensitive drum 21 without being transferred to the recording medium P during the transfer process reaches the portion facing the cleaning unit 25 while adhering to the photosensitive drum 21. The untransferred toner on the photosensitive drum 21 is removed and collected by the cleaning unit 25.
Thereafter, the surface of the photosensitive drum 21 passes through a static elimination unit (not shown), and a series of image forming processes on the photosensitive drum 21 is completed.

Hereinafter, the configuration and operation of the developing device 23 will be described in detail.
Referring to FIG. 3, the developing device 23 includes a first developing roller 23a1 as a first developer carrier, a second developing roller 23a2 as a second developer carrier, transport screws 23b1 to 23b3 (auger screws), It includes a doctor blade 23c as a developer regulating member, a carrier collecting roller 23k, a scraper 23m, a discharge screw 23n, and the like. Further, in the developing device 23, three developer transport portions B1 to B3 that transport the developer G to form a circulation path are formed.

  The first developing roller 23a1 as the first developer carrying member and the second developing roller 23a2 as the second developer carrying member are each made of a nonmagnetic material such as aluminum, brass, stainless steel, conductive resin, etc. in a cylindrical shape. The formed sleeve is configured to be rotated clockwise by a rotation driving mechanism (not shown). Magnets 23a12 and 23a22 for forming a magnetic field are fixed in the sleeves 23a11 and 23a21 of the developing rollers 23a1 and 23a2 so as to cause the developer G to rise on the peripheral surfaces of the sleeves 23a11 and 23a21 (see FIG. 9). You can refer to it.) The carrier C in the developer G rises in a chain shape on the sleeves 23a11 and 23a21 so as to follow the normal magnetic field lines emitted from the magnets 23a12 and 23a22. The charged toner T is attached to the carrier C that is spiked in a chain shape to form a magnetic brush. The magnetic brush is transferred in the same direction (clockwise) as the sleeves 23a11 and 23a21 by the rotation of the sleeves 23a11 and 23a21.

  The doctor blade 23c as a developer regulating member is installed on the upstream side of the developing area, and regulates the developer carried on the first developing roller 23a1 to an appropriate amount. The doctor blade 23c according to the first embodiment is a plate-like member having a thickness of about 2 mm formed of a nonmagnetic metal material (including a weak magnetic metal material) such as SUS316 or XM7.

More specifically, referring to FIG. 8, a plurality of magnets 23a12 and 23a22 are provided around the first developing roller 23a1 (first developer carrier) and the second development roller 23a2 (second developer carrier) by magnets 23a12 and 23a22. Magnetic poles H11 to H15, H21 to H24 are formed.
Specifically, around the first developing roller 23a1 (first developer carrying member), a main magnetic pole H11 formed at a position facing the photosensitive drum 21, and between the doctor blade 23c and the main magnetic pole H11 are formed. Doctor magnetic pole H12 formed, pumping magnetic pole H13 formed at a position facing the first conveying screw 23b1, delivery magnetic pole H15 formed at a position facing the second developing roller 23a2, delivery magnetic pole H15 and pumping magnetic pole H13, A conveying magnetic pole H14 formed between the two is disposed.
Around the second developing roller 23a2 (second developer carrier), a main magnetic pole H21 formed at a position facing the photosensitive drum 21 and a position facing the first developing roller 23a1 (delivery magnetic pole H15). The receiving magnetic pole H22, the conveying magnetic pole H24 formed at a position facing the carrier collecting roller 23k, and the agent separating magnetic pole H23 formed at a position facing the second developer conveying portion B2 are disposed.

  First, the pumping magnetic pole H13 acts on a carrier as a magnetic body, and the developer G accommodated in the first developer transport unit B1 is carried on the first developing roller 23a1. Part of the developer G carried on the developing roller 23a1 is scraped off at the position of the doctor blade 23c, and returned to the first developer conveying portion B1. On the other hand, at the position of the doctor blade 23c where the magnetic force by the doctor magnetic pole H12 acts, the doctor blade 23c and the developing roller 23a1 pass through the doctor gap N1 (see also FIG. 9) and are carried on the developing roller 23a1. The developer G rises at the position of the main magnetic pole H11 and comes into sliding contact with the photosensitive drum 21 in the first development area. Thereafter, the developer G that has passed the position facing the photosensitive drum 21 is conveyed to the position of the delivery magnetic pole H15 (position facing the second developing roller 23a2). A part or all of the developer G on the first developing roller 23a1 is received and carried on the second developing roller 23a2 by the receiving magnetic pole H22 of the second developing roller 23a2. Thereafter, the developer G carried on the second developing roller 23a2 rises at the position of the main magnetic pole H21 and comes into sliding contact with the photosensitive drum 21 in the second developing region. Thereafter, the developer G that has passed through the position facing the photosensitive drum 21 reaches the position of the agent separation magnetic pole H23 after passing through the transport magnetic pole H24. Then, the repelling magnetic field acts on the carrier, and the developer G after the developing process carried on the second developing roller 23a2 is detached from the second developing roller 23a2. The detached developer G is collected in the second developer transport section B2 and transported in the longitudinal direction (the direction perpendicular to the paper surface of FIG. 8) by the second transport screw 23b2. Then, the developer is circulated through a developer circulation path to be described later. Further, during the operation of the developer described above, a first development area where the first development roller 23a1 and the photosensitive drum 21 face each other, a second development area where the second development roller 23a2 and the photosensitive drum 21 face each other, 2, the toner in the two-component developer G adheres to the latent image on the photosensitive drum 21 to form a toner image.

Referring to FIG. 3, the three conveying screws 23 b 1 to 23 b 3 are each formed with a screw portion in a spiral shape on a shaft portion, and the developer G accommodated in the developing device 23 is disposed in the longitudinal direction (FIG. 3), while stirring and mixing.
The first transport screw 23b1 as the first developer transport member is disposed at a position facing the first developing roller 23a1 in the first developer transport section B1, and transports the developer G in the horizontal direction. At the same time, the developer 23a is supplied onto the first developing roller 23a1.

The second transport screw 23b2 as the second developer transport member is installed in the second developer transport section B2. The second transport screw 23b2 is disposed below the first transport screw 23b1 and at a position facing the second developing roller 23a2. Then, the developer G separated from the second developing roller 23a2 (the developer G forcibly separated from the second developing roller 23a2 by the agent separation pole H23 after the developing step) is conveyed in the horizontal direction (FIG. 4). This is the left-hand conveyance indicated by the white arrow in FIG.
The first transport screw 23b1 and the second transport screw 23b2 are arranged so that the rotation axis is substantially horizontal, like the developing rollers 23a1 and 23a2 and the photosensitive drum 21.

  The third transport screw 23b3 as the third developer transport member is installed in the third developer transport unit B3. The third conveyance screw 23b3 is disposed obliquely with respect to the horizontal direction so as to linearly connect the downstream side of the conveyance path by the second conveyance screw 23b2 and the upstream side of the conveyance path by the first conveyance screw 23b1. (See FIG. 4). The third transport screw 23b3 transports the developer G transported by the second transport screw 23b2 to the upstream side of the transport path by the first transport screw 23b1, and from the downstream side of the transport path by the first transport screw 23b1. The developer G circulated through the drop path 23f is transported to the upstream side of the transport path by the first transport screw 23b1 (the transport is obliquely upward to the right as indicated by the white arrow in FIG. 4).

A transport path (first developer transport section B1) by the first transport screw 23b1, a transport path by the second transport screw 23b2 (second developer transport section B2), and a transport path (first transport by the third transport screw 23b3). 3 developer transport section B3) is isolated from the wall.
Referring to FIG. 4, the downstream side of the second developer transport unit B2 and the upstream side of the third developer transport unit B3 communicate with each other via the first relay unit 23g. In addition, the downstream side of the third developer conveyance unit B3 and the upstream side of the first developer conveyance unit B1 are communicated with each other via the second relay unit 23h. In addition, the downstream side of the first developer transport unit B1 and the upstream side of the third developer transport unit B3 communicate with each other via a drop path 23f.

With such a configuration, a circulation path for circulating the developer G in the longitudinal direction in the developing device 23 is formed by the three developer conveying portions B1 to B3 (conveying screws 23b1 to 23b3). Here, when the developing device 23 is operated, the developer accommodated in the device flows in a state as indicated by the oblique lines in FIG. Referring to FIG. 4, in the first developer conveying section B1, the developer surface on the downstream side is lower than the upstream agent surface because part of the developer being conveyed is the first. This is because it is supplied to one developing roller 23a1. That is, the developer that has not been supplied to the first developing roller 23a1 moves to the upstream side of the third developer conveying portion B3 via the dropping path 23f.
Note that a magnetic sensor 26 (toner density sensor) is installed in the third developer conveying section B3. Then, based on the toner density information detected by the magnetic sensor 26, the developer G having a predetermined toner density is supplied from the agent cartridge 28 into the developing device 23. In the first embodiment, the toner concentration of the developer G in the developing device 23 is controlled to be 4 to 7% by weight.

4 and 5, a part of the developer G accommodated in the developing device 23 is discharged to the outside (agent storage container 70) on the wall portion of the first developer conveying portion B1. A discharge port 23d (discharge means) is provided. Specifically, the discharge port 23d has a predetermined developer surface (upper surface) of the developer that is supplied to the developing device 23 from the agent cartridge 28 into the developing device 23 to increase the amount of developer in the device and is conveyed to that position. When the height is exceeded, the excess developer G is discharged toward the agent storage container 70. That is, the excess developer G exceeds the lower portion of the discharge port 23 d, is discharged from the discharge port 23 d, and gravity falls toward the agent storage container 70 via the discharge path 71. As described above, the carrier deteriorated by being contaminated by the base resin or the external additive of the toner T is automatically discharged to the outside of the developing unit, so that deterioration of the image quality can be suppressed even over time.
Although not shown in FIG. 2, FIG. 4, etc., a discharge screw 23n for conveying the developer discharged from the discharge port 23d in the horizontal direction is installed in the discharge path 71 ( See FIG. 3).

  Further, a bypass for returning a part of the developer G to the upstream side of the circulation path without passing through the position where the discharge port 23d (discharge means) is disposed in the developer circulation path in the developing device 23. A path is formed. Specifically, referring to FIG. 4 and FIG. 6, the opening 23e is the first developer transport unit B1 and upstream of the discharge port 23d (a position relatively close to the discharge port 23d). Is provided. The opening 23e serves as the inlet of the bypass path, and the outlet of the bypass path is disposed in the transport path (near the center in the longitudinal direction) by the third transport screw 23b3.

  As described above, by providing the bypass path in the developer circulation path in the developing device 23, even if the developer in the developing device has a wavy deviation or the like, the amount of developer discharged from the discharge port 23d varies. It is possible to suppress a problem that the developer exceeding the necessary amount is discharged from the developing device 23.

  FIG. 7 is a diagram illustrating a state in which the developer is wavy in the developer circulation path in the developing device 23. As described above, there is a case where a wavy deviation with a large height difference occurs in the developer circulation path. Such a wave-like bias appears remarkably immediately after the operation of the developing device 23 is started (immediately after restarting). When such a wave-like deviation occurs, conventionally, all of the developer (a developer having a height Z2 in FIG. 7) located higher than the lower portion of the discharge port 23d is discharged. It was discharged from the outlet 23d. Since the developer discharged in this way is not originally intended to be discharged, if such a phenomenon occurs repeatedly, the amount of developer in the developing device 23 becomes insufficient, and the developer As a result, the deterioration state of the toner becomes unstable or the charge amount of the toner decreases, which causes problems such as a decrease in image density on the output image.

  In contrast, in the first embodiment, since the opening 23e leading to the bypass path is provided on the upstream side of the discharge port 23d, a part of the developer at a position higher than the lower portion of the discharge port 23d is discharged. Without being discharged from the outlet 23d, it is returned to the transport path in the third transport screw 23b3 through the opening 23e. As a result, it is possible to suppress a problem that the developer is excessively discharged from the discharge port 23d.

Here, the height of the lower portion of the opening 23e in the bypass path is configured to be higher by the height Z1 than the height of the lower portion of the discharge port 23d.
As a result, among the developers located higher than the lower portion of the discharge port 23d, the developer corresponding to the height (Z2-Z1) is not discharged from the discharge port 23d, and is discharged from the third transport screw 23b3 through the opening 23e. It will be returned to the transport path. Accordingly, it is possible to reliably prevent the problem that the developer is excessively discharged from the discharge port 23d while maintaining the original function of the discharge unit. Here, the distance R in the longitudinal direction between the discharge port 23d and the opening 23e is preferably as short as possible.

Here, referring to FIG. 3 (not shown in FIG. 2, FIG. 4, etc.), in the first embodiment, below the second developing roller 23a2 (downstream in the rotational direction), A carrier collecting roller 23k is installed at a position facing the photosensitive drum 21. Further, a scraper 23m is installed at a position where it abuts on the carrier collecting roller 23k.
The carrier collecting roller 23k is a cylindrical body made of stainless steel or the like in which a magnet for forming a predetermined magnetic field is fixed, and the carrier that moves (flys) from the inside of the developing device 23 and adheres to the photosensitive drum 21. It is for collecting. The carrier collecting roller 23k is driven to rotate counterclockwise in FIG. Most of the carriers collected and carried by the carrier collecting roller 23k are transferred onto the second developing roller 23a2 by the conveying magnetic pole H24 at a position facing the second developing roller 23a2, and the second developing roller 23a2 It is separated from the second developing roller 23a2 at the position of the agent separating pole H23 and collected in the second developer conveying portion B2. On the other hand, the carrier remaining and carried on the carrier collecting roller 23k without moving onto the second developing roller 23a2 is mechanically scraped by the scraper 23m and collected in the second developer conveying section B2. The In this way, by installing the carrier collecting roller 23k, the carrier adhering to the photosensitive drum 21 can be collected in the developing device 23, so that the occurrence of abnormal images (firefly images, whiteout images) is suppressed. In addition, the shortage of carriers in the developing device 23 is suppressed.

In the first embodiment, the outer diameters of the developing rollers 23a1 and 23a2 are 30 mm, the linear velocity on the outer peripheral surface of the developing rollers 23a1 and 23a2 is 748 mm / second, the outer diameter of the carrier collecting roller 23k is 16 mm, The linear velocity on the outer peripheral surface of the collecting roller 23k is 10.6 mm / second, the process linear velocity (the linear velocity on the outer peripheral surface of the photosensitive drum 21 and the conveyance speed of the recording medium P) is 440 mm / second, Is set to about.
The carrier C used in the first embodiment has a particle diameter of 55 μm and a saturation magnetization of about 96 emu / g. Further, the toner T used in the first embodiment has a particle diameter of about 6.8 μm.

In the following, the configuration and operation of the developing device 23 that are characteristic in the first embodiment will be described in detail with reference to FIGS.
FIG. 9 is a schematic diagram showing the longitudinal relationship of the doctor blade 23c, the first developing roller 23a1, and the second developing roller 23a2. FIG. 10 is a schematic view showing the state of the developer G carried on the first developing roller 23a1 and the second developing roller 23a2.

  As shown in FIG. 9 and FIG. 10, a narrow portion where the gap (doctor gap) with the first developing roller 23 a 1 is narrower than the central portion in the longitudinal direction at both longitudinal ends of the doctor blade 23 c (developer regulating member). 23c1 is provided. In other words, the doctor blade 23c is formed in a concave shape so that the doctor gap N2 at both ends in the longitudinal direction is narrower than the doctor gap N1 at the center in the longitudinal direction (N1> N2). In the first embodiment, the doctor gap N2 of the narrow portion 23c1 (both ends in the longitudinal direction) is set to 0.32 ± 0.03 mm, and the doctor gap N1 other than the narrow portion 23c1 (central portion in the longitudinal direction) is 0. .42 ± 0.03 mm. In the first embodiment, the gap (development gap) between the first developing roller 23a1 and the photosensitive drum 21 is set to about 0.25 mm, and the gap (development) between the second developing roller 23a2 and the photosensitive drum 21 is set. The gap) is also set to about 0.25 mm.

Here, referring to FIG. 9, in the longitudinal range X of the narrow portion 23c1 of the doctor blade 23c, the magnetic force of the receiving magnetic pole H22 of the second developing roller 23a2 is stable from the longitudinal end portion toward the longitudinal central portion. It is formed so as to include a range W2 (unstable region) up to.
Specifically, the magnetic force (normal magnetic flux density) by the receiving magnetic pole H22 of the second developing roller 23a2 has a distribution such that both ends in the longitudinal direction are inclined when viewed in the longitudinal direction. In other words, the receiving magnetic pole H22 includes a stable region W1 at the longitudinal center where the magnetic force is stable and an unstable region W2 at both ends in the longitudinal direction where the magnetic force is unstable. The longitudinal range X of the narrow portion 23c1 of the doctor blade 23c includes the unstable region W2 of the receiving magnetic pole H22, and is longer than the unstable region W2 toward the center in the longitudinal direction. Specifically, in the present embodiment, the length X in the longitudinal direction of the narrow portion 23c1 is set to 17.5 mm. Further, the range X of the narrow portion 23c1 is outside the effective image area (the range in the width direction in which image formation can be performed on the maximum recording medium P capable of passing paper) provided in the central portion in the longitudinal direction. It is formed to become.

  With such a configuration, the amount of developer per unit area received on the second developing roller 23a2 (or in the vicinity of the unstable region W2 (both ends in the width direction) of the receiving magnetic pole H22 as compared to the stable region W1 (or The problem that the part where the agent height) increases extremely is suppressed. Specifically, as shown in FIG. 10 (A), at the doctor gap position, at both ends in the longitudinal direction of the first developing roller 23a1, the developer having a smaller amount of developer than the central portion in the longitudinal direction is caused by the narrow portion 23c1. Supported. Here, since the magnetic force of the magnet 23a12 acts to some extent at both ends of the developing roller 23a1 beyond the magnetizing range of the magnet 23a12, a slight amount of developer is carried around the magnetizing range. The The small amount of developer moves toward the center when it is carried on the second developing roller 23a2 by the receiving magnetic pole H22 at a position facing the second developing roller 23a2, and the stable region W1. Is carried on the second developing roller 23a2 by a developer amount substantially equal to the developer amount (agent height) (developer surrounded by a broken line). That is, the developer amount (agent height) of the developer received and carried on the second developing roller 23a2 by the receiving magnetic pole H22 is substantially uniform over the longitudinal direction. Therefore, the problem that the developer is fixed (filming) on the second developing roller 23a2 and the photosensitive drum 21 is damaged by the fixed developer is suppressed.

  On the other hand, when the narrow portion 23c1 is not provided in the doctor blade 230c as in the conventional developing device shown in FIG. 10B, the magnet 23a12 is attached at both longitudinal ends of the first developing roller 23a1. The amount (developer height) of the developer carried beyond the magnetic range is also increased. Therefore, when such a large amount of developer is carried on the second developing roller 23a2 by the receiving magnetic pole H22, it moves in the direction of the center portion and is larger than the developer amount (agent height) in the stable region W1. A very large amount of developer is carried on the second developing roller 23a2 (developer surrounded by a broken line). That is, the amount of developer received and carried on the second developing roller 23a2 by the receiving magnetic pole H22 (the amount of developer per unit area) is extremely large at both ends in the longitudinal direction compared to the central portion in the longitudinal direction. End up. In a portion where the amount of developer carried on the second developing roller 23a2 is large, the developer receives a large compressive force at a position facing the photosensitive drum 21, and eventually adheres to the second developing roller 23a2. (Filming).

Such a phenomenon is particularly noticeable at the end portion in the longitudinal direction corresponding to the upstream side in the conveyance direction of the first conveyance screw 23b1 (the right side in FIG. 4). This is because, as described above with reference to FIG. 4, the amount of developer supplied onto the first developing roller 23a1 by the first conveying screw 23b1 is larger on the upstream side in the conveying direction than on the downstream side in the conveying direction. is there. That is, the amount of developer delivered from the first developing roller 23a1 to the second developing roller 23a2 is generally large at the longitudinal end portion of the second developing roller 23a1 corresponding to the upstream side of the first conveying screw 23b1 in the conveying direction. Thus, the amount of developer carried beyond the magnetizing range of the first developing roller 23a1 is increased, and therefore, a portion where the amount of developer carried on the second developing roller 23a2 is extremely increased is likely to occur. .
In the first embodiment, the narrow portion 23c1 of the doctor blade 23c is provided at both ends in the longitudinal direction. However, in consideration of the phenomenon described above, the narrow portion 23c1 of the doctor blade 23c is disposed upstream in the transport direction of the first transport screw 23b1. It can also be provided only at the longitudinal end corresponding to the side. Furthermore, the doctor gap N2 of the narrow portion 23c1 corresponding to the downstream side in the transport direction of the first transport screw 23b1 is set larger than the doctor gap N2 of the narrow portion 23c1 corresponding to the upstream side of the first transport screw 23b1 in the transport direction. You can also

FIG. 11 is a graph showing changes in the degree of occurrence of developer sticking (filming) to the second developing roller 23a2 when the length X of the narrow portion 23a1 of the doctor blade 23c is changed.
In FIG. 11, the horizontal axis indicates the development gap (the gap between the second development roller 23a2 and the photosensitive drum 21), and the vertical axis indicates the developer amount per unit area carried on the second development roller 23a2. (The amount of developer in the stable region W1). In FIG. 11, a solid line S13 is a boundary line where developer sticking does not occur when the length X of the narrow portion 23a1 is set to 13 mm (when the range X of the narrow portion 23a1 is shorter than the unstable region W2). The solid line S15 is a boundary line where developer sticking does not occur when the length X of the narrow portion 23a1 is set to 15 mm (when the range X of the narrow portion 23a1 is longer than the unstable region W2). The range in the upper left of the solid line S13 or S15 in FIG. 11 (the range in the direction of the white arrow) is a range in which developer fixation (filming) does not occur on the second developing roller 23a2.
From the result of FIG. 11, it can be seen that by optimizing the range X of the narrow portion 23a1 of the doctor blade 23c, the problem that the developer sticks to the second developing roller 23a2 is surely reduced. This means that by optimizing the range X of the narrow portion 23a1 of the doctor blade 23c, it is possible to narrow the development gap and achieve high image quality of the output image without causing fixing of the developer. It is.

Further, the inventor of the present application shakes the length X of the narrow portion 23a1 of the doctor blade 23c by three levels of 13 mm, 15 mm, and 17 mm, operates the image forming apparatus for a predetermined time, and the developer adheres to the second developing roller 23a2. When the length X of the narrow portion 23a1 was 13 mm, the developer stuck to the second developing roller 23a2, whereas the length X of the narrow portion 23a1 was 15 mm and 17 mm. Sometimes, the developer did not adhere to the second developing roller 23a2. In this confirmation experiment, the developing gap (the gap between the second developing roller 23a2 and the photosensitive drum 21) is set to 0.25 mm, and the unit area carried on the second developing roller 23a2 is unit. The amount of developer (the amount of developer in the stable region W1) was set to 30 mg / cm ² .
As described above, when the range X in the longitudinal direction of the narrow portion 23a1 is too short, a sufficient amount of developer is carried beyond the magnetized range of the magnet 23a12 at the longitudinal end portion of the first developing roller 23a1. However, the amount of developer (agent height) per unit area carried on the end of the second developing roller 23a2 in the longitudinal direction by the receiving magnetic pole H22 cannot be reduced. In the first embodiment, since the longitudinal range X of the narrow portion 23a1 is optimized, the amount of developer carried beyond the magnetized range of the magnet 23a12 is sufficiently reduced, and the receiving magnetic pole H22 is received. Thus, the amount of developer (agent height) carried on the second developing roller 23a2 can be made uniform over the longitudinal direction. Accordingly, it is possible to suppress a problem that the developer adheres to the second developing roller 23a2.

  As described above, in the first embodiment, the doctor blade 23c (developer regulating member) is matched with the region W2 where the magnetic force of the receiving magnetic pole H22 of the second developing roller 23a2 (second developer carrier) becomes unstable. ) And the first developing roller 23a1 (first developer carrier) are optimized, so that the problem that the developer G adheres to the end in the longitudinal direction of the second developing roller 23a2 is ensured. Can be deterred.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 12 is a schematic view of the doctor blade of the developing device in the second embodiment as viewed in the longitudinal direction, and corresponds to FIG. 9 in the first embodiment. In the developing device according to the second embodiment, the shape of the doctor blade 23c as a developer regulating member is different from that of the first embodiment.

  Similarly to the first embodiment, the developing device 23 according to the second embodiment also includes a first developing roller 23a1, a second developing roller 23a2, transport screws 23b1 to 23b3, a doctor blade 23c, a carrier collecting roller 23k, A scraper 23m, a discharge screw 23n, and the like are included. Then, at both ends in the longitudinal direction of the doctor blade 23c (developer regulating member), the narrow portion 23c1 is provided in the range X longer than the unstable region W2 of the receiving magnetic pole H22, as in the first embodiment. .

Here, as shown in FIG. 12, the doctor blade 23c according to the second embodiment is provided with a tapered portion 23c2 in which the doctor gap gradually increases from the narrow portion 23c1 toward the central portion in the longitudinal direction. That is, the tapered portion 23c2 is provided so that the shape of the boundary of the narrow portion 23c1 becomes gentle.
With such a configuration, the developer carried on both ends of the first developing roller 23a1 beyond the magnetizing range of the first developing roller 23a1 is moved toward the center on the second developing roller 23a2 at the position of the receiving magnetic pole H22. There is almost no difference between the amount of developer (agent height) and the amount of developer (agent height) in the stable region W1 when the toner is moved and supported on the surface. That is, the amount of developer carried on the second developing roller 23a2 by the receiving magnetic pole H22 is further uniformized in the longitudinal direction. Therefore, a problem that the developer adheres to the second developing roller 23a2 and the photoreceptor drum 21 is damaged by the stuck developer is suppressed.

  As described above, in the second embodiment as well, in the same manner as in the first embodiment, the second developing roller 23a2 (second developer carrier) is matched with the region W2 in which the magnetic force of the receiving magnetic pole H22 becomes unstable. Since the doctor gap N2 between the doctor blade 23c (developer regulating member) and the first developing roller 23a1 (first developer carrier) is optimized, the developer G is placed at the longitudinal end of the second developing roller 23a2. Can be reliably prevented.

Embodiment 3 FIG.
A third embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 13 is a cross-sectional view illustrating a part of the developing device according to the third embodiment, and corresponds to FIG. 8 according to the first embodiment. FIG. 14 is a schematic view of the doctor blade as viewed in the longitudinal direction, and corresponds to FIG. 9 in the first embodiment.
The developing device according to the third embodiment is different from that of the first embodiment in that a doctor blade 23c as a developer regulating member is composed of a nonmagnetic member 23cA and a magnetic member 23cB.

  The developing device 23 according to the third embodiment also has a first developing roller 23a1, a second developing roller 23a2, transport screws 23b1 to 23b3, a doctor blade 23c, a carrier collecting roller 23k, as in the above embodiments. A scraper 23m, a discharge screw 23n, and the like are included.

  Here, as shown in FIGS. 13 and 14, the doctor blade 23c in the third embodiment includes a nonmagnetic plate 23cA as a nonmagnetic member formed of a nonmagnetic material and a magnetic member formed of a magnetic material. As a magnetic plate 23cB. The nonmagnetic plate 23cA is a plate-like member having a thickness of about 2 mm formed of a nonmagnetic metal material (including a weak magnetic metal material) such as SUS316 or XM7. Further, the magnetic plate 23cB is a thin plate made of a magnetic metal material such as SUS430 and having a thickness of about 0.3 mm, and is inside the nonmagnetic plate 23cA (the side facing the first conveying screw 23b1). Is installed. A narrow portion 23cB1 is provided in a range X at both ends in the longitudinal direction of the magnetic plate 23cB of the doctor blade 23c and longer than the unstable region W2 of the receiving magnetic pole H22. As in the second embodiment, a tapered portion can be provided from the narrow portion 23cB1 of the magnetic plate 23cB toward the central portion in the longitudinal direction.

With this configuration, the amount of developer carried on the second developing roller 23a2 by the receiving magnetic pole H22 is made uniform over the longitudinal direction, as in the above embodiments. Therefore, a problem that the developer adheres to the second developing roller 23a2 and the photoreceptor drum 21 is damaged by the stuck developer is suppressed.
In particular, when the narrow portion 23cB1 is provided in the magnetic plate 23cB as in the third embodiment, the narrow portion is provided in the nonmagnetic plate 23cA (for example, the configuration as in the first embodiment). As compared with the above, the doctor gap N12 of the narrow portion 23cB1 can be widened. This is because the magnetic plate 23cB has an action of attracting the developer due to magnetism as compared with the nonmagnetic plate 23cA. Therefore, even if the doctor gap N11 is larger than the doctor gap N10 of the nonmagnetic plate 23cA, the doctor gap N11 is reduced. This is because the amount of developer that slips through becomes equal. Therefore, even if the doctor gap N12 of the narrow portion 23cB1 of the magnetic plate 23cB is set to be relatively wide, the same effect as in the first embodiment can be obtained. And since the doctor gap N12 of the narrow part 23cB1 of the doctor blade 23c can be set relatively wide, the adjustment work of the doctor gap is simplified in the manufacturing process, and the doctor blade 23c comes into contact with the first developing roller 23a1. Can be suppressed.

  As described above, also in the third embodiment, in the same manner as in each of the embodiments described above, it is adjusted to the region W2 in which the magnetic force of the receiving magnetic pole H22 of the second developing roller 23a2 (second developer carrier) becomes unstable. Since the doctor gap N12 between the doctor blade 23c (developer regulating member) and the first developing roller 23a1 (first developer carrier) is optimized, the developer G is formed at the longitudinal end of the second developing roller 23a2. Can be reliably prevented.

In each of the above embodiments, the present invention is applied to the multistage developing type developing device 23 in which three developer conveying portions B1 to B3 are installed. However, the number of developer conveying portions is two or less or four. The present invention can also be applied to a multistage developing type developing apparatus installed as described above. Even in this case, the same effects as those of the above embodiments can be obtained.
Moreover, in each said embodiment, although the 3rd conveyance screw 23b3 was arrange | positioned diagonally with respect to the horizontal direction, the 3rd conveyance screw 23b3 can also be arrange | positioned horizontally.
Further, in each of the above-described embodiments, the discharge port 23d is provided in the wall portion of the first developer conveyance portion B1, but the discharge port 23d can also be provided in the wall portions of the other developer conveyance portions B2 and B3.

  In each of the above embodiments, the developer G (toner T and carrier C) is supplied from the agent cartridge 28 toward the developing device 23. However, only the carrier C may be supplied from the cartridge toward the developing device 23. it can. In that case, a toner cartridge containing only toner is installed separately from the agent cartridge (carrier cartridge), and the toner contained in the toner cartridge is appropriately directed toward the developing device 23 based on the detection result of the magnetic sensor 26. I will supply it. Furthermore, the present invention can be applied to a developing device that is not a premix developing system and supplies only toner from a cartridge without supplying a carrier. Even in these cases, the same effects as those of the above embodiments can be obtained.

In each of the above embodiments, the present invention is applied to an image forming apparatus in which a part of the image forming unit is configured by the process cartridge 20. However, the application of the present invention is not limited to this, and the present invention can naturally be applied to an image forming apparatus in which the image forming unit is not formed into a process cartridge. Specifically, the present invention can naturally be applied even when the developing device 23 is configured as a unit that is detachably attached to the image forming apparatus main body.
Further, in each of the above embodiments, the present invention is applied to the developing device 23 in which two developing rollers 23a1 and 23a2 are installed. However, in the multi-stage developing type developing device in which three or more developing rollers are installed. Of course, the present invention can be applied. Even in this case, the same effects as those of the above embodiments can be obtained.

  Further, in each of the above embodiments, the present invention is applied to the multistage developing type developing device in which the conveying screws 23b1 and 23b2 are installed in the vertical direction. However, the multistage developing in which a plurality of conveying screws are installed in the horizontal direction. Type developing device or multi-stage developing type developing device in which a paddle-like developer conveying member for conveying the developer in the short direction is installed instead of the first conveying screw 23b1 for conveying the developer in the longitudinal direction (for example, The present invention can also be applied to, for example, Patent Document 2). Even in such a case, the same effect as in each of the above embodiments can be obtained by using a doctor blade configured in the same manner as in each of the above embodiments.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the embodiments can be modified as appropriate in addition to those suggested in the embodiments. Is clear. In addition, the number, position, shape, and the like of the constituent members are not limited to the above embodiments, and can be set to a number, position, shape, and the like that are suitable for carrying out the present invention.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is an enlarged view showing a process cartridge installed in the image forming apparatus of FIG. 1. It is an enlarged view which shows a developing device. It is sectional drawing which looked at the circulation path in a developing device to the longitudinal direction. It is sectional drawing which shows the Y1-Y1 cross section in the circulation path | route of FIG. It is sectional drawing which shows the Y2-Y2 cross section in the circulation path | route of FIG. FIG. 5 is a diagram illustrating a state in which a wavy bias is generated in the developer in the circulation path of FIG. 4. FIG. 6 is a magnetic force distribution diagram showing magnetic poles formed on a first developing roller and a second developing roller. It is the schematic which shows the relationship of the longitudinal direction of a doctor blade and the magnetic distribution of the receiving magnetic pole of a 2nd developing roller. FIG. 4 is a schematic diagram illustrating a state of developer carried on a first developing roller and a second developing roller. It is a graph which shows the change of the generation | occurrence | production degree of a developer adherence to the 2nd developing roller when changing the length of the narrow part of a doctor blade. It is the schematic which shows the doctor blade in Embodiment 2 of this invention. It is the schematic which shows the principal part of the developing device in Embodiment 3 of this invention. It is the schematic which shows the doctor blade installed in the developing device of FIG.

Explanation of symbols

1 image forming apparatus body (apparatus body),
20, 20Y, 20C, 20M, 20BK Process cartridge,
21 Photosensitive drum (image carrier),
23 Developing device (developing part),
23a1 first developing roller (first developer carrier),
23a2 second developing roller (second developer carrier),
23b1 first conveying screw (first developer conveying member),
23b2 second transport screw (second developer transport member),
23b3 third transport screw (third developer transport member),
23c Doctor blade (developer regulating member),
23cA non-magnetic plate (non-magnetic member), 23cB magnetic plate (magnetic member),
23c1, 23cB1 Narrow part,
23c2 taper part,
H22 receiving magnetic pole,
G developer (two-component developer), T toner, C carrier.

Claims (6)

A developing device for containing a developer and developing a latent image formed on an image carrier,
A first developer carrying member facing the image carrier and carrying a developer;
A second developer carrier that receives a part or all of the developer on the first developer carrier that is opposed to the image carrier and that has passed through a position facing the image carrier, and is received and carried by a magnetic pole; ,
A developer regulating member that faces the first developer carrying member and regulates the amount of the developer carried on the first developer carrying member;
With
The developer regulating member includes a narrow portion at a longitudinal end that is narrower than a central portion in the longitudinal direction with respect to the first developer carrier.
Longitudinal extent of said narrow portion of said developer regulating member is formed to include a longitudinal end portion of said receiving magnetic pole of said second developer carrying member,
The developing device according to claim 1, wherein the developer regulating member further includes a tapered portion in which the gap with the first developer carrier gradually increases from the narrow portion toward the central portion in the longitudinal direction .   The developing device according to claim 1, wherein the developer regulating member includes a nonmagnetic member made of a nonmagnetic material and a magnetic member made of a magnetic material.   The developing device according to claim 2, wherein the narrow portion is formed in the magnetic member. A first developer conveying member facing the first developer carrying member and supplying the developer to the first developer carrying member while conveying the developer in the longitudinal direction;
A second developer transport that transports the developer that is disposed below the first developer transport member and is opposed to the second developer carrier and separated from the second developer carrier. Members,
With
The narrow portion of the developer regulating member is provided at an end in a longitudinal direction corresponding to an upstream side in the transport direction of the first developer transport member. The developing device described. A process cartridge that is detachably installed on the main body of the image forming apparatus,
5. A process cartridge in which the developing device according to claim 1 and the image carrier are integrated. An image forming apparatus comprising the developing device according to claim 1 and the image carrier.

Images