JP5887132B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to a developing device and an image forming apparatus.

  2. Description of the Related Art Two-component developers composed of toner and carrier are widely used in electrophotographic image forming apparatuses that are compatible with full color and high image quality. The developing device stirs the two-component developer in the developing tank to generate friction between the toner and the carrier, thereby charging the toner. The charged toner is supplied to the surface of the developing roller, and moves to the electrostatic latent image formed on the surface of the photosensitive drum from the developing roller by an electrostatic attraction force. As a result, a toner image based on the electrostatic latent image is formed on the photosensitive drum.

  Since the amount of developer carried on the developing roller by the electrostatic attraction force varies in the rotation direction of the developing roller, it is necessary to regulate the amount of developer to a constant amount. For this purpose, the developing devices described in Patent Documents 1 and 2 include a regulating member that regulates the developer amount upstream of the closest portion between the developing roller and the photosensitive drum in the rotation direction of the developing roller. . The regulating member is provided apart from the developing roller, and regulates the thickness of the developer carried on the developing roller and passing through the closest contact with the regulating member to a certain thickness or less.

JP 2001-255723 A JP 2008-256917 A

  The developer is agitated to charge as described above. The fluidity of the developer may be lowered by frictional heat generated at this time, and the developer may be loosely aggregated. Also, such a state may occur when the temperature inside the image forming apparatus becomes high. When the developer is in such a state, if the developing devices described in Patent Documents 1 and 2 are used, the pulsation state in which the density of the developer passing between the regulating member and the developing roller changes in a short period of time. Therefore, it becomes difficult to make the developer density on the surface of the developing roller uniform. As a result, density unevenness occurs when, for example, a halftone image is formed.

  SUMMARY An advantage of some aspects of the invention is to provide a developing device and an image forming apparatus capable of forming a developer layer having a uniform developer density on the surface of the developing roller.

The present invention is a developing device for supplying a developer to a photoreceptor,
A developing tank in which the developer is accommodated;
A developing roller that carries the developer in the developing tank and rotates around the axis, and conveys the carried developer toward the photoreceptor;
A regulating member that extends in the axial direction of the developing roller and regulates the amount of the developer carried on the developing roller to layer the developer.
A homogenizing member that extends in the axial direction downstream of the regulating member in the rotation direction of the developing roller, is carried by the developing roller, and homogenizes a developer layer regulated by the regulating member, An upstream portion protruding at a first curvature upstream of the closest contact point with the developing roller at a first curvature, and a second curvature smaller than the first curvature downstream of the closest contact point in the rotation direction. in a homogenizing member having a downstream portion which projects,
In the developing device, a distance from the upstream end portion in the rotation direction of the upstream portion to the regulating member is 5 mm or more and 30 mm or less .

The present invention also provides a first auxiliary line that is a virtual straight line that passes through the closest point of the homogenizing member with the developing roller and extends in the radial direction of the developing roller, and an upstream side of the upstream portion in the rotational direction. A distance from the second auxiliary line, which is a virtual straight line passing through the end point and parallel to the first auxiliary line, is 1.5 mm or more and 5 mm or less.

The present invention also provides a first auxiliary line that is a virtual straight line that passes through the closest point of the homogenizing member to the developing roller and extends in the radial direction of the developing roller, and a downstream side of the downstream portion in the rotational direction. The distance from the third auxiliary line, which is an imaginary straight line passing through the end point and parallel to the first auxiliary line, is 4 mm or more and 10 mm or less.

  Further, according to the present invention, the distance between the downstream end of the downstream portion in the rotational direction and the developing roller is determined between the closest point of the homogenizing member to the developing roller and the developing roller. A value obtained by subtracting the distance is 0 mm or more and 5 mm or less.

  Further, the present invention provides a distance between the closest point of the homogenizing member to the developing roller and the developing roller, a distance of the regulating member to the developing roller and the distance from the developing roller. Are equal to each other.

The present invention also provides an electrophotographic image forming apparatus,
A photoreceptor,
A developing tank in which the developer is accommodated, a developing roller that carries the developer in the developing tank and rotates around the axis, and conveys the carried developer toward the photoconductor, and an axial direction of the developing roller A developing device that includes a regulating member that extends to the developing roller and regulates the amount of the developer carried on the developing roller to layer the developer.
A homogenizing member that extends in the axial direction downstream of the regulating member in the rotation direction of the developing roller, is carried by the developing roller, and homogenizes a developer layer regulated by the regulating member, An upstream portion protruding at a first curvature upstream of the closest contact point with the developing roller at a first curvature, and a second curvature smaller than the first curvature downstream of the closest contact point in the rotation direction. in possess a homogenization member having a downstream portion which projects,
In the image forming apparatus, a distance from the upstream end portion in the rotation direction of the upstream portion to the regulating member is 5 mm or more and 30 mm or less .

  According to the present invention, since the portion of the homogenizing member upstream of the closest contact point with the developing roller is configured to protrude with the first curvature, the developer reservoir is formed in front of the homogenizing member. The As a result, when the developer whose fluidity has decreased passes in front of the regulating member, even if the amount of the developer passing in front of the regulating member instantaneously decreases, the density change is mitigated by the developer pool. The Further, since the portion of the homogenizing member on the downstream side from the closest contact point with the developing roller protrudes with the second curvature smaller than the first curvature, the pressure fluctuation of the developer is moderately reduced. Become. In this way, the homogenizing member can form a developer layer having a uniform developer density.

  In addition, according to the present invention, an appropriate developer pool is formed, so that the change in developer density can be further alleviated.

  Further, according to the present invention, the pressure fluctuation of the developer can be made gentler, so that the unevenness of the developer density can be reduced.

  Further, according to the present invention, the pressure fluctuation of the developer can be made gentler, so that the unevenness of the developer density can be reduced.

  Further, according to the present invention, the developer pressure in the developer reservoir is properly maintained, so that it is possible to prevent the developer from being compressed and aggregated in the developer reservoir.

  Further, according to the present invention, since the developer layer having a uniform developer density can be formed on the developing roller by the homogenizing member, it is possible to form a uniform halftone image without roughness.

1 is a schematic diagram illustrating a configuration of an image forming apparatus 100. FIG. 3 is a schematic diagram illustrating a configuration of a toner cartridge 300. FIG. FIG. 3 is a cross-sectional view of the toner cartridge 300 taken along line AA shown in FIG. 2 is a schematic diagram illustrating a configuration of a developing device 200. FIG. FIG. 5 is a cross-sectional view of the developing device 200 with the line BB shown in FIG. FIG. 5 is a cross-sectional view of the developing device 200 with the line CC shown in FIG. FIG. 2 is an enlarged view showing a developing roller 204, a doctor blade 206, and a homogenizing member 209. It is a figure for demonstrating an Example.

  First, the image forming apparatus 100 including the developing device 200 according to the embodiment of the present invention will be described. FIG. 1 is a schematic diagram illustrating a configuration of the image forming apparatus 100. The image forming apparatus 100 is a multifunction device having both a copying function, a printer function, and a facsimile function, and forms a full-color or monochrome image on a recording medium according to transmitted image information. The image forming apparatus 100 has three types of printing modes, ie, a copier mode (copy mode), a printer mode, and a facsimile mode, and an operation input from an operation unit (not shown), a personal computer, a portable terminal device, and an information recording medium A print mode is selected by a control unit (not shown) in response to reception of a print job from an external device using the memory device.

  The image forming apparatus 100 includes a toner image forming unit 20, a transfer unit 30, a fixing unit 40, a recording medium supply unit 50, a discharge unit 60, and a control unit unit (not shown). The toner image forming unit 20 includes photosensitive drums 21b, 21c, 21m, and 21y, charging units 22b, 22c, 22m, and 22y, an exposure unit 23, developing devices 200b, 200c, 200m, and 200y, a cleaning unit 25b, 25c, 25m, 25y, toner cartridges 300b, 300c, 300m, 300y, and toner supply pipes 250b, 250c, 250m, 250y. The transfer unit 30 includes an intermediate transfer belt 31, a driving roller 32, a driven roller 33, intermediate transfer rollers 34 b, 34 c, 34 m and 34 y, a transfer belt cleaning unit 35, and a transfer roller 36.

  The photosensitive drum 21, the charging unit 22, the developing device 200, the cleaning unit 25, the toner cartridge 300, the toner supply pipe 250, and the intermediate transfer roller 34 are black (b), cyan (c), magenta included in the color image information. In order to correspond to the image information of each color of (m) and yellow (y), four each are provided. In this specification, when distinguishing each member provided by four according to each color, an alphabet representing each color is added to the end of a number representing each member as a reference symbol, and when each member is collectively referred to Only numerals representing each member are used as reference numerals.

  The photosensitive drum 21 is supported by a drive unit (not shown) so as to be rotatable about an axis, and includes a conductive substrate (not shown) and a photoconductive layer formed on the surface of the conductive substrate. The conductive substrate can take various shapes, and examples thereof include a cylindrical shape, a columnar shape, and a thin film sheet shape. The photoconductive layer is formed of a material that exhibits conductivity when irradiated with light. As the photosensitive drum 21, for example, a cylindrical member (conductive base) formed of aluminum, and amorphous silicon (a-Si), selenium (Se), and the like formed on the outer peripheral surface of the cylindrical member, Alternatively, a film including a thin film (photoconductive layer) made of an organic optical semiconductor (OPC) can be used.

  The charging unit 22, the developing device 200, and the cleaning unit 25 are arranged in this order around the rotation direction of the photosensitive drum 21, and the charging unit 22 is arranged below the developing device 200 and the cleaning unit 25 in the vertical direction. The

  The charging unit 22 is a device that charges the surface of the photosensitive drum 21 to a predetermined polarity and potential. The charging unit 22 is installed along the longitudinal direction of the photosensitive drum 21 at a position facing the photosensitive drum 21. In the case of the contact charging method, the charging unit 22 is installed in contact with the surface of the photosensitive drum 21. In the case of the non-contact charging method, the charging unit 22 is installed so as to be separated from the surface of the photosensitive drum 21.

  The charging unit 22 is installed around the photosensitive drum 21 together with the developing device 200, the cleaning unit 25, and the like. The charging unit 22 is preferably installed at a position closer to the photosensitive drum 21 than the developing device 200, the cleaning unit 25, and the like. As a result, it is possible to reliably prevent the charging failure of the photosensitive drum 21.

  As the charging unit 22, a brush-type charging device, a roller-type charging device, a corona discharge device, an ion generation device, or the like can be used. The brush type charging device and the roller type charging device are contact charging type charging devices. As the brush type charging device, there are a type using a charging brush and a type using a magnetic brush. The corona discharge device and the ion generator are non-contact charging devices. Corona discharge devices include those using wire-like discharge electrodes, those using sawtooth discharge electrodes, and those using needle-like discharge electrodes.

  The exposure unit 23 is arranged such that light emitted from the exposure unit 23 passes between the charging unit 22 and the developing device 200 and is irradiated on the surface of the photosensitive drum 21. The exposure unit 23 irradiates the charged surface of the photosensitive drums 21b, 21c, 21m, and 21y with laser beams corresponding to the image information of the respective colors, so that each of the photosensitive drums 21b, 21c, 21m, and 21y is exposed. An electrostatic latent image corresponding to the image information of each color is formed on the surface. As the exposure unit 23, for example, a laser scanning unit (LSU) including a laser irradiation unit and a plurality of reflection mirrors can be used. As the exposure unit 23, an LED (Light Emitting Diode) array, a unit in which a liquid crystal shutter and a light source are appropriately combined, or the like may be used.

  The developing device 200 is a device that forms a toner image on the photosensitive drum 21 by developing the electrostatic latent image formed on the photosensitive drum 21 with toner. A toner supply pipe 250 that is a cylindrical member is connected to the upper part of the developing device 200 in the vertical direction. Details of the developing device 200 will be described later.

  The toner cartridge 300 is disposed vertically above the developing device 200 and stores unused toner. A toner supply pipe 250 is connected to the lower part of the toner cartridge 300 in the vertical direction. The toner cartridge 300 supplies toner to the developing device 200 via the toner supply pipe 250. Details of the toner cartridge 300 will be described later.

  The cleaning unit 25 is a member that removes the toner remaining on the surface of the photosensitive drum 21 after the toner image is transferred from the photosensitive drum 21 to the intermediate transfer belt 31 and cleans the surface of the photosensitive drum 21. . As the cleaning unit 25, for example, a plate-like member for scraping off toner and a container-like member for collecting the scraped toner are used.

  According to the toner image forming unit 20, the surface of the photosensitive drum 21 that is uniformly charged by the charging unit 22 is irradiated with laser light corresponding to image information from the exposure unit 23 to form an electrostatic latent image. . A toner image is formed by supplying toner from the developing device 200 to the electrostatic latent image on the photosensitive drum 21. This toner image is transferred to an intermediate transfer belt 31 described later. After the toner image is transferred to the intermediate transfer belt 31, the toner remaining on the surface of the photosensitive drum 21 is removed by the cleaning unit 25.

  The intermediate transfer belt 31 is an endless belt-like member that is disposed above the photosensitive drum 21 in the vertical direction. The intermediate transfer belt 31 is stretched by the driving roller 32 and the driven roller 33 to form a loop-shaped path, and moves in the direction of the arrow A4.

  The drive roller 32 is provided so as to be rotatable around its axis by a drive unit (not shown). The drive roller 32 moves the intermediate transfer belt 31 in the direction of the arrow A4 by its rotation. The driven roller 33 is provided so as to be able to rotate following the rotation of the driving roller 32, and generates a certain tension on the intermediate transfer belt 31 so that the intermediate transfer belt 31 does not loosen.

  The intermediate transfer roller 34 is provided in pressure contact with the photosensitive drum 21 via the intermediate transfer belt 31 and rotatable about its axis by a drive unit (not shown). As the intermediate transfer roller 34, for example, a metal (for example, stainless steel) roller having a diameter of 8 mm to 10 mm on which a conductive elastic member is formed can be used. The intermediate transfer roller 34 is connected to a power source (not shown) for applying a transfer bias, and has a function of transferring the toner image on the surface of the photosensitive drum 21 to the intermediate transfer belt 31.

  The transfer roller 36 is provided in pressure contact with the drive roller 32 via the intermediate transfer belt 31 and is rotatable about an axis by a drive unit (not shown). At the pressure contact portion (transfer nip portion) between the transfer roller 36 and the drive roller 32, the toner image carried and conveyed by the intermediate transfer belt 31 is transferred to a recording medium fed from a recording medium supply unit 50 described later. The

  The transfer belt cleaning unit 35 is provided so as to face the driven roller 33 through the intermediate transfer belt 31 and to be in contact with the toner image carrying surface of the intermediate transfer belt 31. The transfer belt cleaning unit 35 is provided for removing and collecting the toner on the surface of the intermediate transfer belt 31 after the toner image is transferred to the recording medium. If toner remains on the intermediate transfer belt 31 after the toner image is transferred to the recording medium, the residual toner may adhere to the transfer roller 36 due to the movement of the intermediate transfer belt 31. When toner adheres to the transfer roller 36, the toner contaminates the back surface of the recording medium to be transferred next.

  According to the transfer unit 30, when the intermediate transfer belt 31 moves while being in contact with the photosensitive drum 21, a transfer bias having a polarity opposite to the charging polarity of the toner on the surface of the photosensitive drum 21 is applied to the intermediate transfer roller 34. The toner image formed on the surface of the photosensitive drum 21 is transferred onto the intermediate transfer belt 31. The toner images of the respective colors respectively formed on the photosensitive drum 21y, the photosensitive drum 21m, the photosensitive drum 21c, and the photosensitive drum 21b are sequentially transferred onto the intermediate transfer belt 31 in this order, thereby transferring full color. A toner image is formed. The toner image transferred to the intermediate transfer belt 31 is conveyed to the transfer nip portion by the movement of the intermediate transfer belt 31, and transferred to the recording medium at the transfer nip portion. The recording medium on which the toner image is transferred is conveyed to a fixing unit 40 described later.

  The recording medium supply unit 50 includes a paper feed box 51, pickup rollers 52 a and 52 b, transport rollers 53 a and 53 b, registration rollers 54, and a paper feed tray 55. The paper feed box 51 is a container-like member that is provided in the lower part of the image forming apparatus 100 in the vertical direction and stores a recording medium inside the image forming apparatus 100. The paper feed tray 55 is a tray-like member that is provided on the outer wall surface of the image forming apparatus 100 and stores a recording medium outside the image forming apparatus 100. Examples of the recording medium include plain paper, color copy paper, overhead projector sheet, and postcard.

  The pickup roller 52a is a member that takes out recording media stored in the paper feed box 51 one by one and feeds it to the paper transport path A1. The transport rollers 53a are a pair of roller-like members provided so as to be in pressure contact with each other, and transport the recording medium toward the registration rollers 54 in the paper transport path A1. The pickup roller 52b is a member that takes out the recording medium stored in the paper feed tray 55 one by one and feeds it to the paper transport path A2. The transport rollers 53b are a pair of roller-like members provided so as to be in pressure contact with each other, and transport the recording medium toward the registration rollers 54 in the paper transport path A2.

  The registration rollers 54 are a pair of roller-like members provided so as to come into pressure contact with each other, and the toner image carried on the intermediate transfer belt 31 is conveyed to the transfer nip portion of the recording medium fed from the conveyance rollers 53a and 53b. In synchronization with this, the sheet is fed to the transfer nip portion.

  According to the recording medium supply unit 50, the recording medium is transferred from the paper feed box 51 or the paper feed tray 55 to the transfer nip portion in synchronization with the toner image carried on the intermediate transfer belt 31 being conveyed to the transfer nip portion. The toner image is transferred to the recording medium.

  The fixing unit 40 includes a heating roller 41 and a pressure roller 42. The heating roller 41 is controlled to have a predetermined fixing temperature. The pressure roller 42 is a roller that is in pressure contact with the heating roller 41. The heating roller 41 nips the recording medium together with the pressure roller 42 while heating, thereby melting and fixing the toner constituting the toner image on the recording medium. The recording medium on which the toner image is fixed is conveyed to a discharge unit 60 described later.

  The discharge unit 60 includes a conveyance roller 61, a discharge roller 62, and a discharge tray 63. The conveyance roller 61 is a pair of roller-like members provided so as to be in pressure contact with each other in the vertical direction above the fixing unit 40. The conveyance roller 61 conveys the recording medium on which the image is fixed toward the discharge roller 62.

  The discharge roller 62 is a pair of roller-like members provided so as to be in pressure contact with each other. In the case of single-sided printing, the discharge roller 62 discharges the recording medium on which single-sided printing has been completed to the discharge tray 63. In the case of duplex printing, the discharge roller 62 conveys the recording medium on which single-sided printing has been completed to the registration roller 54 via the paper conveyance path A <b> 3, and discharges the recording medium on which duplex printing has been completed to the discharge tray 63. The discharge tray 63 is provided on the upper surface in the vertical direction of the image forming apparatus 100 and stores a recording medium on which an image is fixed.

  Image forming apparatus 100 includes a control unit (not shown). The control unit unit is provided, for example, at an upper part in the vertical direction in the internal space of the image forming apparatus 100 and includes a storage unit, a calculation unit, and a control unit. The storage unit stores various setting values via an operation panel (not shown) arranged on the upper surface in the vertical direction of the image forming apparatus 100, detection results from sensors (not shown) arranged at various locations inside the image forming apparatus 100, external devices, and the like. The image information from is input. A program for executing various processes is written in the storage unit. Examples of the various processes include a recording medium determination process, an adhesion amount control process, and a fixing condition control process.

  As the storage unit, those commonly used in this field can be used, and examples thereof include a read only memory (ROM), a random access memory (RAM), and a hard disk drive (HDD). As the external device, an electric or electronic device that can form or acquire image information and can be electrically connected to the image forming apparatus 100 can be used. For example, a computer, a digital camera, a television receiver, a video recorder DVD (Digital Versatile Disc) recorder, HDDVD (High-Definition Digital Versatile Disc) recorder, Blu-ray disc recorder, facsimile apparatus, portable terminal apparatus, and the like.

  The calculation unit retrieves various data (image formation command, detection result, image information, etc.) written in the storage unit and various processing programs, and performs various determinations. The control unit performs operation control by sending a control signal to each device provided in the image forming apparatus 100 according to the determination result of the calculation unit.

  The control unit and the calculation unit include a processing circuit realized by a microcomputer, a microprocessor, or the like provided with a central processing unit (CPU). The control unit unit includes a main power source together with the processing circuit, and the power source supplies power not only to the control unit unit but also to each device provided in the image forming apparatus 100.

  FIG. 2 is a schematic diagram illustrating the configuration of the toner cartridge 300. FIG. 3 is a cross-sectional view of the toner cartridge 300 taken along line AA shown in FIG. The toner cartridge 300 is a device that supplies toner to the developing device 200 via the toner supply pipe 250. The toner cartridge 300 includes a toner storage container 301, a toner scooping member 302, a toner discharge member 303, and a toner discharge container 304.

  The toner storage container 301 is a container-like member having a substantially semi-cylindrical internal space. In the internal space, the toner scooping member 302 is rotatably supported, and unused toner is stored. The toner discharge container 304 is a container-like member having a substantially semi-cylindrical internal space provided along the longitudinal direction of the toner storage container 301, and supports the toner discharge member 303 rotatably in the internal space. The internal space of the toner storage container 301 and the internal space of the toner discharge container 304 communicate with each other via a communication port 305 formed along the longitudinal direction of the toner storage container 301. The toner discharge container 304 has a discharge port 306 formed in the lower part in the vertical direction. A toner supply pipe 250 is connected to the toner discharge container 304 at a discharge port 306.

  The toner scooping member 302 includes a rotation shaft 302a, a base body 302b, and a sliding portion 302c. The rotation shaft 302 a is a columnar member that extends along the longitudinal direction of the toner container 301. The base 302b is a plate-like member extending along the longitudinal direction of the toner container 301, and is attached to the rotating shaft 302a at the center in the width direction and the thickness direction. The sliding portion 302c is a flexible member attached to both ends in the width direction of the base body 302b, and is formed of, for example, polyethylene terephthalate (PET). In the toner pumping member 302, the base body 302b rotates as the rotary shaft 302a rotates about the axis thereof, and as a result, the sliding portions 302c provided at both ends in the width direction of the base body 302b are formed in the toner container 301. By rubbing the wall surface, the toner in the toner container 301 is pumped up to the toner discharge container 304.

  The toner discharge member 303 is a member that conveys the toner in the toner discharge container 304 toward the discharge port 306. The toner discharge member 303 is an auger screw-like member including a toner discharge rotation shaft 303a and a toner discharge blade 303b provided around the toner discharge rotation shaft 303a.

  According to the toner cartridge 300, unused toner in the toner container 301 is pumped up to the toner discharge container 304 by the toner pumping member 302. The toner drawn up in the toner discharge container 304 is conveyed to the discharge port 306 by the toner discharge member 303. The toner conveyed to the discharge port 306 is discharged from the discharge port 306 to the outside of the toner discharge container 304 and supplied to the developing device 200 via the toner supply pipe 250.

  FIG. 4 is a schematic diagram illustrating the configuration of the developing device 200. FIG. 5 is a cross-sectional view of the developing device 200 with the line BB shown in FIG. FIG. 6 is a cross-sectional view of the developing device 200 in which the line CC shown in FIG.

  The developing device 200 is a device that develops an electrostatic latent image formed on the surface of the photosensitive drum 21 by supplying toner to the surface of the photosensitive drum 21. The developing device 200 includes a developing tank 201, a first conveying member 202, a second conveying member 203, a developing roller 204, a developing tank cover 205, a doctor blade 206, a partition wall 207, and a toner concentration detection sensor 208. And a homogenizing member 209.

  The developing tank 201 is a member in which an internal space is formed by the side wall portions 201a and 201b and the bottom wall portion 201c, and stores the developer in the internal space. The side wall parts 201a and 201b and the bottom wall part 201c may be integrally formed, or may be separate members. The developing tank 201 is made of a resin material such as polyethylene, polypropylene, high impact polystyrene, and ABS resin (acrylonitrile-butadiene-styrene copolymer synthetic resin). The developer used in the present invention may be a one-component developer composed only of toner or a two-component developer containing toner and carrier.

  The developing tank 201 is provided with a developing tank cover 205 above the vertical direction, and a first conveying member 202, a second conveying member 203, a developing roller 204, a doctor blade 206, and a partition wall 207 are provided in the internal space. In addition, a toner concentration detection sensor 208 is provided at a lower portion (bottom portion) in the vertical direction of the developing tank 201.

Further, a homogenizing member 209 is provided outside the developing tank 201 so as to face the developing roller 204. The homogenizing member 209 is a member that is carried on the developing roller 204 and homogenizes the developer layer regulated by the doctor blade 206. In the present embodiment, homogenization member 209 is a part of the developing device 200, rather than homogenizing member 209 is part of the configuration of the developing device 200, is provided as part of the images forming apparatus 100 Also good. The homogenizing member 209 will be described in detail later.

The developing tank 201 is provided with an opening between the photosensitive drum 21 and the developing roller 204. The length _{L 1} in the longitudinal direction of the developer tank 201 is about 200Mm～400mm. The length _{L 2} in the width direction of the developer tank 201 is about 25Mm～80mm.

  The developing roller 204 includes a magnet roller, carries the developer in the developing tank 201 on the surface, and supplies toner contained in the carried developer to the photosensitive drum 21. A power supply (not shown) is connected to the developing roller 204, and a developing bias voltage is applied. The toner carried on the developing roller 204 moves to the photosensitive drum 21 in the vicinity of the photosensitive drum 21 by electrostatic force due to the developing bias voltage.

  The doctor blade 206 is a rectangular plate-like member extending in the axial direction of the developing roller 204, one end in the width direction is fixed to the developing tank 201, and the other end is provided at a distance from the surface of the developing roller 204. It is done. An interval (doctor gap) between the doctor blade 206 and the developing roller 204 is, for example, 0.4 mm to 2.0 mm. The doctor blade 206 is provided at a distance from the surface of the developing roller 204, thereby restricting the amount of developer carried on the developing roller 204 to a predetermined amount. The regulated developer is layered on the developing roller 204. As the material of the doctor blade 206, stainless steel, aluminum, synthetic resin, or the like can be used.

  The partition wall 207 is a member that extends along the longitudinal direction of the developing tank 201 at a substantially central portion in the width direction of the developing tank 201. The partition wall 207 is provided between the bottom wall portion 201 c of the developing tank 201 and the developing tank cover 205, and is provided so that both end portions in the longitudinal direction are separated from the side wall portions 201 a and 201 b of the developing tank 201. The partition 207 divides the internal space of the developing tank 201 into a first conveyance path P, a second conveyance path Q, a first communication path R, and a second communication path S.

  The second transport path Q is a substantially semi-cylindrical space extending along the longitudinal direction of the partition wall 207 and is a space facing the developing roller 204. The first transport path P is a substantially semi-cylindrical space extending along the longitudinal direction of the partition wall 207 and is a space facing the second transport path Q across the partition wall 207. The first communication path R is a space that communicates the first transport path P and the second transport path Q on the longitudinal end 207a side of the partition wall 207. The second communication path S is a space that communicates the first transport path P and the second transport path Q on the side of the other end 207 b in the longitudinal direction of the partition wall 207.

  The developing tank cover 205 is detachably provided above the developing tank 201 in the vertical direction, and has a supply port 205a. A toner supply pipe 250 is connected to the developing tank cover 205 at a supply port 205a. The supply port 205a is an opening in which an opening for supplying toner to the developing tank 201 is formed. The toner contained in the toner cartridge 300 passes through the toner supply pipe 250 and the opening, and then the developing tank 201. Supplied in.

  The supply port 205a is provided in the vicinity of the second communication path S in the vertical direction above the first transport path P. More specifically, the opening formed in the supply port portion 205 a is provided so as to face the first transport path P and be at the same position as the second communication path S in the longitudinal direction of the partition wall 207.

  The first transport member 202 is provided in the first transport path P. The first conveying member 202 conveys the developer in the developing tank 201 from the other end 207b in the longitudinal direction of the partition wall 207 toward the one end 207a in the longitudinal direction. Hereinafter, the developer conveyance direction by the first conveyance member 202 is referred to as a conveyance direction X.

  The first transport member 202 is an auger screw-like member including a first rotating shaft member 202a, a first spiral blade 202b, and a first gear 202c. The first rotating shaft member 202a is a columnar member having a diameter of 4 mm to 10 mm, and is connected to the first gear 202c at the downstream end in the transport direction X. The first rotating shaft member 202a is rotatably supported around the axis by a bearing (not shown) fixed to the side wall 201a of the developing tank 201 and a bearing (not shown) fixed to the side wall 201b of the developing tank 201.

A first spiral blade 202b that is a member that spirally surrounds the side surface is provided on the side surface of the first rotating shaft member 202a. The outer diameter L3 of the first spiral blade 202b is 12 mm to ₃₀ mm.

  The 1st rotating shaft member 202a, the 1st spiral blade 202b, and the 1st gear 202c are formed from resin materials, such as polyethylene, a polypropylene, high impact polystyrene, ABS resin, for example. The first rotating shaft member 202a, the first spiral blade 202b, and the first gear 202c are preferably integrally formed from the same material.

  The first conveying member 202 is rotated at 150 rpm to 400 rpm around the axis of the first rotating shaft member 202a via the first gear 202c by a rotation driving source such as a motor (not shown) provided in the image forming apparatus 100. To do. Accordingly, the first spiral blade 202b rotates around the axis of the first rotating shaft member 202a. As a result, the developer stored in the first transport path P is transported downstream in the transport direction X. The As described above, the supply port portion 205a of the developing tank cover 205 is formed in the vicinity of the second communication path S above the first conveyance path P in the vertical direction. First, it is supplied to the first transport path P, and then transported to the downstream side in the transport direction X of the first transport path P by the first transport member 202.

  The second transport member 203 is provided in the second transport path Q. The second transport member 203 transports the developer in the developing tank 201 from the longitudinal direction one end 207a side of the partition wall 207 toward the longitudinal other end 207b side. Hereinafter, the developer conveyance direction by the second conveyance member 203 is referred to as a conveyance direction Y.

  The second conveying member 203 is an auger screw-like member including a second rotating shaft member 203a, a second spiral blade 203b, and a second gear 203c. The second rotating shaft member 203a is a columnar member having a diameter of 4 mm to 10 mm, and is connected to the second gear 203c at the upstream end in the transport direction Y. The second rotating shaft member 203a is supported so as to be rotatable around the axis by a bearing (not shown) fixed to the side wall 201a of the developing tank 201 and a bearing (not shown) fixed to the side wall 201b of the developing tank 201.

A second spiral blade 203b that is a member that spirally surrounds the side surface is provided on the side surface of the second rotating shaft member 203a. Outer diameter _{L 4} of the second spiral blade 203b is 12Mm～30mm.

  The 2nd rotating shaft member 203a, the 2nd spiral blade 203b, and the 2nd gear 203c are formed from resin materials, such as polyethylene, a polypropylene, high impact polystyrene, ABS resin, for example. The second rotary shaft member 203a, the second spiral blade 203b, and the second gear 203c are preferably integrally formed from the same material.

  The second conveying member 203 is rotated at 150 rpm to 400 rpm around the axis of the second rotating shaft member 203a via the second gear 203c by a rotation driving source such as a motor (not shown) provided in the image forming apparatus 100. To do. Accordingly, the second spiral blade 203b rotates around the axis of the second rotating shaft member 203a. As a result, the developer stored in the second transport path Q is transported downstream in the transport direction Y. The

  A toner concentration detection sensor 208 shown in FIG. 4 is mounted at the bottom of the developing tank 201 below the second transport member 203 in the vertical direction so that the sensor surface is exposed to the second transport path Q. The toner concentration detection sensor 208 is electrically connected to a toner concentration control unit (not shown).

  The toner density control unit performs control to rotate the toner discharge member 303 and supply the toner into the developing tank 201 in accordance with the toner density detection result detected by the toner density detection sensor 208. More specifically, the toner density control unit determines whether or not the toner density detection result by the toner density detection sensor 208 is lower than a predetermined setting value. A control signal is sent to the driving section to rotate the toner discharging member 303 for a predetermined period.

  A power source (not shown) is connected to the toner concentration detection sensor 208. The power supply applies to the toner concentration detection sensor 208 a drive voltage for driving the toner concentration detection sensor 208 and a control voltage for outputting the toner concentration detection result to the toner concentration control unit. Application of a voltage to the toner concentration detection sensor 208 by the power supply is controlled by a control unit (not shown).

  As the toner concentration detection sensor 208, a general toner concentration detection sensor can be used. For example, a transmitted light detection sensor, a reflected light detection sensor, a magnetic permeability detection sensor, or the like can be used. Among these toner concentration detection sensors, it is preferable to use a magnetic permeability detection sensor. Examples of the magnetic permeability detection sensor include TS-L (trade name, manufactured by TDK Corporation), TS-A (trade name, manufactured by TDK Corporation), TS-K (trade name, manufactured by TDK Corporation), and the like. It is done.

  According to the developing device 200 configured as described above, the developer is in the order of the first conveyance path P, the first communication path R, the second conveyance path Q, and the second communication path S in the developing tank 201. It is circulated and conveyed. A part of the circulated developer is carried on the surface of the developing roller 204 in the second conveyance path Q, and the toner in the carried developer moves to the photosensitive drum 21 and is sequentially consumed. Is done. When the toner concentration detection sensor 208 detects that a predetermined amount of toner has been consumed, unused toner is supplied from the toner cartridge 300 into the first conveyance path P. The supplied toner is diffused in the already stored developer while being conveyed in the first conveyance path P.

  FIG. 7 is an enlarged view showing the developing roller 204, the doctor blade 206, and the homogenizing member 209. The homogenizing member 209 is provided downstream of the doctor blade 206 in the rotational direction G of the developing roller 204 and upstream of the developing roller 204 and the photosensitive drum 21 in the rotational direction G. It is a columnar member extending in the axial direction. Similar to the doctor blade 206, the homogenizing member 209 is formed of stainless steel, aluminum, synthetic resin, or the like.

When viewed developing roller 204 and homogenization member 209 in the axial direction, a point on homogenization member 209 that is closest to the developing roller 204, recently referred to as contact J _1. Shortest distance between the contact point _{J 1} and the developing roller 204 is, for example, 0.4 mm to 2.0 mm. A virtual straight line that passes through the closest point J ₁ and extends in the radial direction of the developing roller 204 is referred to as an auxiliary line H ₁ (first auxiliary line) .

When viewed homogenized member 209 in the axial direction, of the two parts being separated by the auxiliary line H _1, it referred to the portion of the rotational direction G upstream side to the first portion 209a, a portion of the rotational direction G downstream This is referred to as a second portion 209b. Furthermore, a portion (surface) facing the developing roller 204 in the first portion 209a is referred to as an upstream portion 209aa. A point J ₂ at the upstream end of the upstream portion 209aa in the rotational direction G is in contact with an auxiliary line H ₂ extending in the radial direction of the developing roller 204. In addition, a portion (surface) facing the developing roller 204 in the second portion 209b is referred to as a downstream portion 209ba. Point _{J 3} end of the rotational direction G downstream of the downstream portion 209ba is in contact with the auxiliary line _{H 3} extending in the radial direction.

Upstream portion 209aa is than nearest neighbor J ₁ toward the rotational direction G upstream, projecting in the first curvature. The first curvature is, for example, 1 to 1/5. Downstream portion 209ba recently towards the rotational direction G downstream of the contact point J _1, than the first curvature projecting a small second curvature. The second curvature is, for example, 0 to 1/20. Here, the curvature “0” means that the downstream portion 209ba is a flat surface. In the present embodiment, the second curvature is 0, and the downstream portion 209ba is a flat surface as shown in FIG.

  The homogenizing member 209 configured as described above is a member for homogenizing the layered developer carried on the developing roller 204 and passed in front of the doctor blade 206.

  When the developer passes in front of the doctor blade 206, the developer receives pressure in the rotational direction G from the subsequent developer and passes in front of the doctor blade 206 in a condensed state in the rotational direction G. Therefore, after passing in front of the doctor blade 206, the developer expands and becomes bulkier than when passing through the doctor blade 206. Here, assuming that a part of the developer is deteriorated and the fluidity is lowered, in the layered developer after passing through the doctor blade 206, the bulk increases and the bulk increases when the doctor blade 206 passes. The part which does not change occurs. In other words, the layered developer that should be of a uniform thickness originally becomes a pulsating state due to a decrease in the fluidity of the developer. As a result, the image density becomes uneven, and the image becomes rough in a halftone image or the like.

  In the present invention, a homogenizing member 209 is provided downstream of the doctor blade 206 in the rotational direction G, and an upstream portion 209aa of the homogenizing member 209 is configured to protrude upstream in the rotational direction G with a first curvature. Therefore, a developer pool is formed in front of the homogenizing member 209. As a result, when the developer whose fluidity has decreased passes in front of the doctor blade 206, the density change is mitigated by the developer pool even if the amount of the developer passing in front of the doctor blade 206 decreases instantaneously. Is done. The downstream portion 209ba of the homogenizing member 209 is configured to protrude downstream in the rotational direction G with a second curvature smaller than the first curvature, so that the pressure fluctuation of the developer becomes gentle. In this way, the homogenizing member 209 can form a developer layer having a uniform developer density on the developing roller 204.

  Therefore, the image forming apparatus 100 including the developing device 200 according to the present invention can form a developer layer having a uniform developer density by the developing device 200, and thus forms a uniform halftone image without roughness. be able to.

Hereinafter, an embodiment of the present invention will be described with reference to FIG. In each example, the values of the distances L _{5 to} L ₁₀ shown in FIG. 8 are made different. Here, the distance _{L 5} represents, in homogenizing member 209, the distance recently from contact _{J 1} to the point _{J 2} of the end of the upstream portion 209Aa, and more particularly, the auxiliary line _{H 1} (first auxiliary line) And the distance from the auxiliary line H ₄ (second auxiliary line) that passes through the point J ₂ and is parallel to the auxiliary line H ₁ (first auxiliary line) . The distance L ₆ is the distance from the closest point J ₁ to the point J ₃ at the end of the downstream portion 209ba in the homogenizing member 209. More specifically, the auxiliary line H ₁ (first auxiliary line) and the point This is the distance from the auxiliary line H ₅ (third auxiliary line) passing through J ₃ and parallel to the auxiliary line H ₁ (first auxiliary line) .

The distance L ₇ is the distance between the closest point J ₁ of the homogenizing member 209 and the developing roller 204, and more specifically, the auxiliary line H ₁ between the closest point J ₁ and the surface of the developing roller 204. The distance measured along. The distance L ₈ is a distance between the point J ₃ at the end of the downstream portion 209ba and the developing roller 204, and more specifically, the auxiliary line H ₃ between the point J ₃ and the surface of the developing roller 204. The distance measured along.

The distance L ₉ is the distance from point J ₂ of the end of the upstream portion 209aa of the homogenization member to a doctor blade 206, and more particularly, in contact with the surface of the rotational direction G downstream of the doctor blade 206, the developing roller a vertical auxiliary line _{H 6} to the axis 204, the distance between the auxiliary line _{H 7} parallel as auxiliary line _{H 6} point _{J 2.} The distance _{L 10} is the closest distance between the doctor blade 206 and the developing roller 204 (doctor gap).

In addition, each of the examples and the comparative examples was evaluated based on uneven image density of the halftone image. Specifically, using the developing devices of the examples and comparative examples, a halftone image is formed by setting the printing rate to 5%. For each halftone image, a spectral densitometer manufactured by X-Rite ( Using the product name: 939), the image density was measured at 10 arbitrary locations, and the standard deviation was calculated from each image density. The larger the standard deviation, the larger the image density unevenness. The evaluation criteria are as follows.
A: Standard deviation is 0.2 or less, and there is no unevenness in image density.
A: The standard deviation is larger than 0.2 and 0.50 or less, and there is almost no image density unevenness.
(Triangle | delta): A standard deviation is larger than 0.50 and is 1.00 or less, and image density nonuniformity is seen somewhat, but it is satisfactory practically.
X: The standard deviation is larger than 1.00, the image density unevenness is large, and the image appears rough.

Example 1
The distance L ₅ = 3 mm, the distance L ₆ = 7 mm, the distance L ₇ = 1 mm, the distance L ₈ = 3.5 mm, the distance L ₉ = 17 mm, and the distance L ₁₀ = 1 mm.

(Comparative Example 1)
The homogenizing member 209 was not provided.

(Comparative Example 2)
A member from which only the first portion 209a of the homogenizing member 209 in Example 1 was removed was installed instead of the homogenizing member 209.

The evaluation results of Example 1 and Comparative Examples 1 and 2 are as follows.

From Table 1, homogenization member 209, by the reservoir developer formed in the upstream portion 209Aa, recently compressing the developer in the vicinity of the contact J _1, gradually releasing the pressure of the developer in the downstream portion 209Ba, homogeneous It can be seen that a developer layer having a high developer density can be formed on the developing roller 204. In Comparative Example 2, although the image density unevenness is suppressed to some extent, the average value of the image density measured at 10 locations is significantly lower than that in Example 1, and the target image density is obtained. It is not suitable for actual use because it cannot be used.

(Example 2)
Example 1 was the same as Example 1 except that the distance L _{5 was} 1.5 mm.

(Example 3)
The same as Example 1 except that the distance L ₅ = 5 mm.

Example 4
Example 1 was the same as Example 1 except that the distance L _{5 was} 1 mm.

(Example 5)
Example 1 was the same as Example 1 except that the distance L _{5 was} 6 mm.

The evaluation results of Examples 1 to 5 are as follows.

Table 2, when the distance which L ₅ is 1.5mm or more 5mm or less, moderate puddle developer around the homogenization member 209 is formed, can be further relaxed change in developer density, as a result It can be seen that the unevenness of the developer concentration can be suppressed. Accordingly, the distance _{L 5} represents preferably set in a range of 1.5mm or 5mm or less.

(Example 6)
Example 1 was the same as Example 1 except that the distance L _{6 was set to} 4 mm.

(Example 7)
Example 1 was the same as Example 1 except that the distance L _{6 was set to} 10 mm.

(Example 8)
Example 1 was the same as Example 1 except that the distance L ₆ = 3 mm.

Example 9
Example 1 was the same as Example 1 except that the distance L ₆ = 11 mm.

The evaluation results of Examples 1 and 6 to 9 are as follows.

From Table 3, when the distance L ₆ is 4mm 10mm or more or less, it is possible to pressure variations of the developer by homogenizing member 209 more gradual, as a result, can be suppressed unevenness in the developer density I understand. Accordingly, the distance _{L 6} is preferably set in the range of 4mm or 10mm or less.

(Example 10)
Example 1 was the same as Example 1 except that the distance L _{8 was} 1 mm. Thus, in Example 10, the distance _{L 8} - Distance _L 7 = a 0 mm.

(Example 11)
Example 1 was the same as Example 1 except that the distance L _{8 was set to} 6 mm. Thus, in Example 11, the distance _{L 8} - the distance _L 7 = 5 mm.

(Example 12)
Example 1 was the same as Example 1 except that the distance L _{8 was set to} 7 mm. Thus, in Example 12, the distance _{L 8} - the distance _L 7 = 6 mm.

The evaluation results of Examples 1, 10 to 12 are as follows.

From Table 4, when the value of distance L ₈ -distance L ₇ is 0 mm or more and 5 mm or less, the pressure fluctuation of the developer by the homogenizing member 209 can be made more gradual, and as a result, the developer concentration unevenness can be reduced. It can be seen that it can be suppressed. Accordingly, the distance _{L 8} - Distance value of _{L 6} is preferably set in the range of 5mm or more 0 mm.

(Example 13)
The same as Example 1 except that the distance L _{9 was set to} 5 mm.

(Example 14)
Example 1 was the same as Example 1 except that the distance L _{9 was set to} 30 mm.

(Example 15)
The same as Example 1 except that the distance L _{9 was set to} 4 mm.

(Example 16)
Example 1 was the same as Example 1 except that the distance L _{9 was} 31 mm.

The evaluation results of Examples 1 and 13 to 16 are as follows.

Table 5, when the distance L ₉ is 5mm or more 30mm or less, moderate puddle developer around the homogenization member 209 is formed, it can be further relaxed change in developer density, as a result, development It can be seen that the uneven concentration of the agent can be suppressed. Accordingly, the distance _{L 9} is preferably set in a range of 5mm or 30mm or less.

(Example 17)
The same as Example 1 except that the distance L ₁₀ = 0.5 mm. Thus, in Example 17, the distance _{L 10} is smaller than the distance _{L 7.}

(Example 18)
The same as Example 1 except that the distance L _{10 was} 1.5 mm. Thus, in Example 18, the distance _{L 10} is greater than the distance _{L 7.}

The evaluation results of Examples 1, 17, and 18 are as follows.

From Table 6, when the distance L ₁₀ and the distance L ₇ are the same, the developer pressure in the developing agent accumulation caused by homogenization member 209 is properly maintained, the developer in the reservoir developer is agglomerated is compressed As a result, it can be seen that unevenness in the developer concentration can be suppressed. Therefore, it is preferable that the distance _{L 10} and the distance _{L 7} is set to be the same.

20 toner image forming unit 30 transfer unit 40 fixing unit 50 recording medium supply unit 60 discharge unit 100 image forming apparatus 200, 200b, 200c, 200m, 200y developing device 201 developing tank 204 developing roller 206 doctor blade 209 homogenizing member 209aa upstream portion 209ba downstream portion 250, 250b, 250c, 250m, 250y toner supply pipe 300, 300b, 300c, 300m, 300y toner cartridge

Claims (6)

A developing device for supplying a developer to a photoreceptor,
A developing tank in which the developer is accommodated;
A developing roller that carries the developer in the developing tank and rotates around the axis, and conveys the carried developer toward the photoreceptor;
A regulating member that extends in the axial direction of the developing roller and regulates the amount of the developer carried on the developing roller to layer the developer.
A homogenizing member that extends in the axial direction downstream of the regulating member in the rotation direction of the developing roller, is carried by the developing roller, and homogenizes a developer layer regulated by the regulating member, An upstream portion protruding at a first curvature upstream of the closest contact point with the developing roller at a first curvature, and a second curvature smaller than the first curvature downstream of the closest contact point in the rotation direction. in a homogenizing member having a downstream portion which projects,
The developing device , wherein a distance from the upstream end portion in the rotation direction of the upstream portion to the regulating member is 5 mm or more and 30 mm or less . A first auxiliary line that is a virtual straight line that passes through the closest point of the homogenizing member with the developing roller and extends in the radial direction of the developing roller, and a point of the upstream end of the upstream portion in the rotational direction. The developing device according to claim 1, wherein a distance from a second auxiliary line that is a virtual straight line parallel to the first auxiliary line is 1.5 mm or more and 5 mm or less. A first auxiliary line that is a virtual straight line that passes through the closest point of the homogenizing member with the developing roller and extends in the radial direction of the developing roller, and a point at the downstream end of the downstream portion in the rotational direction. The developing device according to claim 1 , wherein a distance from a third auxiliary line that is a virtual straight line parallel to the first auxiliary line is 4 mm or more and 10 mm or less.   A value obtained by subtracting the distance between the developing roller and the closest point of the homogenizing member to the developing roller from the distance between the downstream end of the downstream portion and the developing roller. The developing device according to claim 1, wherein the developing device is not less than 0 mm and not more than 5 mm. The distance between the closest point of the homogenizing member to the developing roller and the developing roller, and the distance between the closest point of the regulating member to the developing roller and the developing roller are equal. the developing device according to any one of claims 1-4, characterized. An electrophotographic image forming apparatus,
A photoreceptor,
A developing tank in which the developer is accommodated, a developing roller that carries the developer in the developing tank and rotates around the axis, and conveys the carried developer toward the photoconductor, and an axial direction of the developing roller A developing device that includes a regulating member that extends to the developing roller and regulates the amount of the developer carried on the developing roller to layer the developer.
A homogenizing member that extends in the axial direction downstream of the regulating member in the rotation direction of the developing roller, is carried by the developing roller, and homogenizes a developer layer regulated by the regulating member, An upstream portion protruding at a first curvature upstream of the closest contact point with the developing roller at a first curvature, and a second curvature smaller than the first curvature downstream of the closest contact point in the rotation direction. in possess a homogenization member having a downstream portion which projects,
An image forming apparatus , wherein a distance from the upstream end portion in the rotation direction of the upstream portion to the regulating member is 5 mm or more and 30 mm or less .

Images