AU2007201595B2 - Developing device and image forming apparatus including same - Google Patents

Description

AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT ORIGINAL Name of Applicant/s: Fuji Xerox Co., Ltd. Actual Inventor/s: Takuya Iwamura and Hideaki Tanaka Address for Service is: SHELSTON IP 60 Margaret Street Telephone No: (02) 9777 1111 SYDNEY NSW 2000 Facsimile No. (02) 9241 4666 CCN: 3710000352 Attorney Code: SW Invention Title: DEVELOPING DEVICE AND IMAGE FORMING APPARATUS INCLUDING SAME The following statement is a full description of this invention, including the best method of performing it known to me/us: File: 53939AUP00 -2 DEVELOPING DEVICE AND IMAGE FORMING APPARATUS INCLUDING SAME CROSS-REFERENCE TO RELATED APPLICATIONS 5 This application is based on and claims priority from Japanese Patent Application No. 2006-129615 filed on May 8, 2006. Background of the Invention 10 Technical Field [0001] The present invention relates to a developing device that develops an electrostatic latent image on a photoreceptor with a developer, and an image forming apparatus including this developing device. 15 Related Art [0002] As described in Japanese Patent Application Laid Open (JP-A) No. 08-211745, there is a developing device in which a magnetic round bar for regulating the layer thickness of a developer to be transported to a development area of a photoreceptor, is 20 arranged in parallel with a developing roller with a space. In this developing device, lines of magnetic force are generated from the developing roller towards the round bar, and thereby the lines of magnetic force are controlled at the position opposing the round bar. Since any napping (magnetic brushing) is cut out when the developer is passing through the space between the 25 developing roller and the round bar, an excessive amount of the developer on the developing roller that is napping along the lines of magnetic force is squeegeed out. As a result, the thickness of the developer layer on the developer carrier is readily controlled. [0003] 30 However, since the round bar is made of a magnetic body, this developing device has a property in which the center of the round bar is attracted by a magnetic force of the developing roller and is deflected, and it is difficult to ensure the evenness of the space that has a great affect on the squeeging of developer. Furthermore, the developer is -3 restrained by a magnetic force in the vicinity of the round bar. In order to relieve this, it is needed to drive to rotate the round bar, and to arrange a blade for preventing the developer from going outside of the developing device due to the rotation. [0004] 5 If the round bar is a nonmagnetic body, this is advantageous in terms of mass productiveness and cost. However, since the line of magnetic force can not be controlled between the developer carrier and the round bar, the developer is not stably held on the developer carrier. [0005] 10 Moreover, when the developer is passing through a wedge-shaped space formed by the developer carrier and the round bar, it is compressed from the inlet to the center, and is affected by a releasing force as it goes toward the outlet. Therefore, waviness (slip) is generated on the surface of the developer and the layer thickness of the developer becomes uneven. 15 Summary [0006] The present invention takes the above phenomenon into consideration, with an 20 object of providing a developing device capable of forming a developer having an even layer thickness on a developer carrier, even if a developer regulating member of a nonmagnetic body is used, and an image forming apparatus including this. [0007] A first aspect of the present invention is a developing device including: a 25 developing roller that holds and rotates a developer to form a toner image on a photoreceptor; and a developer regulating member that is arranged to face the developing roller to form a space between the developer regulating member and the developing roller so as to regulate the layer thickness of the developer on the developing roller, wherein a developer layer thickness regulation region of a constant region with 30 respect to the developing roller and the developer regulating member is formed; the developer regulating member is nonmagnetic, and, in the space, the downstream side of the developing roller in the rotatory direction is wedge-shaped when viewed from one end side of the developing roller and the developer regulating member; and wherein the -4 developer regulating member is arranged so that, in the developer layer thickness regulation region, a layer thickness regulation region from the center of the developer regulating member to the downstream side in the rotatory direction of the developing roller is positioned in an area where the normal component of the magnetic flux density 5 of the developing roller is larger than the tangential component thereof. [0008] According to the above aspect, in the developer layer thickness regulation region of a constant region formed by the developing roller and the developer regulating member, a layer thickness regulation region from the center of the developer regulating 10 member to the downstream side in the rotatory direction of the developing roller is positioned in an area where the normal component of the magnetic flux density of the developing roller is larger than the tangential component thereof. As a result, the developer is napped (magnetic brushed) so as to rise along the lines of magnetic force. [0009] 15 That is, when the developer on the developing roller is passing through the space formed by the developing roller and the developer regulating member serving as a nonmagnetic body, it is compressed in the center of the developer layer thickness regulation region, and is gradually affected by a releasing force as it goes toward the downstream. However, since the normal component of the magnetic flux density is 20 large until the developer has passed through the region on the downstream side, the force for raising the developer against the developing roller is greater than the force for moving the developer in the circumferential direction of the developing roller. Thus, the developer is kept from slipping on the developing roller and is maintained in a predetermined position on the developing roller. 25 [0010] As a result, waviness generated on the surface of the developer is suppressed, and the layer thickness of the developer becomes even. [0011] In the above aspect, an angle of a line of magnetic force at a downstream 30 boundary of the downstream layer thickness regulation region may be 51.7* or more with respect to a part of the tangential line of the developing roller that is formed and extends from the downstream boundary on the surface of the developing roller to the downstream side.

-5 [0012] According to the above aspect, the napping of the developer in the downstream layer thickness regulation region is more stabilized. [0013] 5 In the above aspect, in the space , an upstream side of the developing roller in the rotatory direction is wedge-shaped when viewed from one end side of the developing roller and the developer regulating member, and the developer regulating member may be arranged so that, in the developer layer thickness regulation region, an upstream layer thickness regulation region is positioned in an area where the normal component of the 10 magnetic flux density of the developing roller is larger than the tangential component thereof. [0014] According to the above structure, the upstream layer thickness regulation region is positioned in an area where the normal component of the magnetic flux density is 15 larger than the tangential component thereof. Since the normal component is large, the force for raising the developer against the developing roller is greater. Thus, excessive developer on the developing roller is sufficiently squeegeed out, immediately before passing through the space between the developing roller and the developer regulating member. Moreover, by suppressing the amount of developer entering the wedge-shaped 20 space, and reducing the compression of the developer in the center of the space, the developer that has passed through the center of the space is less affected by releasing from compression, and thus the force for moving the developer in the circumferential direction of the developing roller can be reduced. As a result, the layer thickness of the developer that has passed through the space becomes even. 25 [0015] In the above aspect, the developer regulating member may be formed from a developer regulating roller, and the developer regulating roller may be arranged so that an angle is 20* or more between: a line linking the center of the developer regulating roller and the center of the developing roller; and a line linking the center of the 30 developing roller and a point where the normal component and the tangential component of the magnetic flux density of the developing roller on the upstream side become equal. [0016] -6 According to the above structure, since the angle of napping of the developer on the upstream side of the developing roller in the rotatory direction is stabilized with respect to the developer regulating roller, excessive developer on the developing roller is sufficiently squeegeed out. Moreover, by suppressing the amount of developer entering 5 the wedge-shaped space, and reducing the compression of the developer in the center of the space, the developer that has passed through the center of the space is less affected by releasing from compression, and thus the force for moving the developper in the circumferential direction of the developing roller can be reduced. Consequently, variation of the layer thickness of the developer after passing through the layer thickness 10 regulation region can be suppressed. [0017] As a result, even if respective members are positionally displaced due to production variations, any effect by the developer regulating roller and the developing roller on the operation for regulating the layer thickness of the developer is reduced, and 15 the layer thickness of the developer becomes even. [0018] In the above aspect, the structure may be such that: the downstream layer thickness regulation region is positioned between a line linking the center of the developing roller and the center of the developer regulating roller and a line linking the 20 center of the developing roller and tangential to the surface of the developer regulating roller at the downstream side; and the upstream layer thickness regulation region is positioned between a line linking the center of the developing roller and the center of the developer regulating roller and a line linking the center of the developing roller and tangential to the surface of the developer regulating roller at the upstream side. 25 [0019] According to the above structure, the developer regulating roller regulates the layer thickness of the developer in the downstream layer thickness regulation region and the upstream layer thickness regulation region. [0020] 30 In the above aspect, the developer may be a two-component developer containing a non-magnetic toner and a magnetic carrier. [0021] -7 According to the above structure, even if a two-component developer is used so as to maintain a high quality of color of the output image, the magnetic carrier adhered with the non-magnetic toner can be napped (magnetic brushed) on the developing roller so as to rise along the lines of magnetic force. 5 [0022] In the above aspect, the non-magnetic toner may be a chemical toner. [0023] If the non-magnetic toner is a chemical toner, variation in the shape of the non magnetic toner is suppressed, and fluidity is excellent. As a result, the transfer 10 performance onto a recording medium is improved. However, when the developer is passing through the space between the developing roller and the developer regulating member, waviness may be generated on the surface of the developer, and the layer thickness of the developer easily becomes uneven. However, according to the above structure, since the developer regulating member is arranged based on the magnetic flux 15 density of the developing roller, then even if the developer contains a chemical toner, the layer thickness of the developer becomes even. [0024] In the above aspect, the shape coefficient of the chemical toner may be 140 or less. 20 [0025] If the shape coefficient of the chemical toner is 140 or less, the shape thereof becomes close to spherical, and the fluidity is improved. As a result, the transfer performance onto a recording medium is further improved, but waviness may be generated on the surface of the developer, and the layer thickness of the developer easily 25 becomes uneven. However, according to the above structure, since the developer regulating member is arranged based on the magnetic flux density of the developing roller, the layer thickness of the developer becomes even. [0026] In the above aspect, the non-magnetic toner may be a resin carrier. 30 [0027] If the magnetic carrier is a resin carrier, the magnetic susceptibility is low. As a result, the lines of magnetic force have hardly affect thereon, and the layer thickness of the developer easily becomes uneven. However, according to the above structure, since -8 the developer regulating member is arranged based on the magnetic flux density of the developing roller, then even if the developer contains a resin carrier, the layer thickness of the developer becomes even. [0028] 5 A second aspect of the present invention is an image forming apparatus including any one of the above developing devices. [0029] According to the above structure, since the image forming apparatus includes any one of the above developing devices, the layer thickness of the developer becomes even, 10 image defects due to an excess or shortage of the amount of developer can be prevented, and image quality can be improved. [0030] According to the present invention, even if a nonmagnetic developer regulating member is used, an even layer thickness of developer can be formed on a developing 15 roller. Brief Description of the Drawings Embodiments of the present invention will be described in detail based on the 20 following figures, wherein: [0031] FIG. 1 shows a developing roller according to an exemplary embodiment of the present invention, being a side view showing the magnetic flux density in the normal direction of the developing roller and the magnetic flux density in the tangential 25 direction, on the developing roller; FIG. 2 shows the developing roller and a developer regulating roller according to an exemplary embodiment of the present invention, being a side view showing a state where a developer on the developing roller is passing through a space; FIG. 3 shows test results of angle a and unevenness of the developer layer 30 thickness of an output image, according to an exemplary embodiment of the present invention; -9 FIG. 4 shows a test result of angle 0 and thickness of the developer that has passed through the space, according to an exemplary embodiment of the present invention; FIG. 5 is a cross-sectional view viewed from above, showing the inside of the 5 developing device according to an exemplary embodiment of the present invention; FIG. 6 is a cross-sectional view viewed from the side, showing the inside of the developing device according to an exemplary embodiment of the present invention; FIG. 7 is a cross-sectional view viewed from the side, showing the inside of a process cartridge according to an exemplary embodiment of the present invention; and 10 FIG. 8 is a schematic block diagram showing an image forming apparatus according to an exemplary embodiment of the present invention. Description 15 [0032] An image forming apparatus 10 to which a developing device 64 of one exemplary embodiment of the present invention is applied, is described with reference to FIG. I to FIG. 8. [0033] 20 As shown in FIG. 8, in the image forming apparatus 10 is vertically arranged process cartridges 14 of four colors (yellow, magenta, cyan, and black in the present exemplary embodiment). As shown in FIG. 7, the process cartridge 14 includes a photoreceptor cartridge 62 having a photoreceptor 16, and a developing device 64 (detail described later). 25 [0034] The photoreceptor cartridge 62 includes a photoreceptor 16, a cleaning device 22 arranged around the photoreceptor 16, a charging roller 18, an eraser lamp 24, and a subtoner supply unit 66 arranged in the horizontal direction of the cleaning device 22. [0035] 30 The subtoner supply unit 66 is provided with a pair of supporting projections 78 extended in a direction orthogonal to the axial direction of the photoreceptor 16. The arrangement is such that by inserting these supporting projections 78 into a cartridge -10 receiver (not shown) of the image forming apparatus 10, the process cartridge 14 is installed in the image forming apparatus 10. [0036] Moreover, as shown in FIG. 8, at the bottom of the image forming apparatus 10 5 is provided a paper feeding cassette 26 containing sheet materials P. In the vicinity of the paper feeding cassette 26 is provided a pickup roller 28 that sends out a sheet material P at a predetermined timing. The sheet material P that has been sent out from the paper feeding cassette 26 by this pickup roller 28 is sent out via conveyance rollers 30 and registration rollers 32 to a sheet conveyance route 34, and then conveyed to a 10 conveyance device 48 described later. [0037] The process cartridges 14 shown in FIG. 7 are arranged in sequence of yellow, magenta, cyan, and black from the upstream side of the sheet conveyance route 34. To the side of the process cartridges 14 is arranged an exposure device 36 that irradiates 15 scanning light onto the process cartridges 14. [0038] Regarding the exposure device 36, in a casing 38 is arranged a semiconductor laser (not shown), a polygon mirror 40, image-forming lenses 44, and mirrors 46. Light from the semiconductor laser is deflected and scanned by the polygon mirror 40 and 20 irradiated onto the photoreceptors 16 via the image-forming lenses 44 and the mirrors 46. As a result, an electrostatic latent image corresponding to image data, is formed on the photoreceptor 16. [0039] Moreover, in a position facing the photoreceptors 16 on the other side of the 25 sheet conveyance route 34 is arranged a conveyance device 48. The conveyance device 48 includes a pair of tension rollers 51 and 52 provided along the side wall 1OA of the image forming apparatus 10, and a transfer belt 53 wrapped around these tension rollers 51 and 52. The tension roller 52 is rotated by a motor (not shown) so that the transfer belt 53 is moved. 30 [0040] In the vicinity of the tension roller 51 is arranged an attaching roller 55. By applying a voltage to this attaching roller 55, the sheet material P is electrostatically attached onto the transfer belt 53.

- 11 [0041] Moreover, in the positions facing the photoreceptors 16 of the respective colors on the backside of the transfer belt 53 are respectively arranged transfer rollers 54. By means of these transfer rollers 54, a later described toner image on the photoreceptor 16 5 is transferred onto the sheet material P that is conveyed by the transfer belt 53, and fixed thereon by the fixing device 56. Then, the sheet material P fixed with the toner image is discharged into a discharge tray 60 by discharge rollers 58. [0042] Next is a description of the developing device 64 in the present exemplary 10 embodiment, with reference to FIG. 6. [0043] As shown in FIG. 6, the developing device 64 includes; a development unit 68 that faces the photoreceptor 16 and develops the electrostatic latent image on the photoreceptor 16 with a two-component developer G formed from a non-magnetic toner 15 T and a magnetic carrier, and a main toner supply unit 70 that supplies this development unit 68 with the non-magnetic toner T. [0044] The development unit 68 has a housing 80. The housing 80 is provided on the lower side of the photoreceptor 16, and is formed with an opening 82 opened toward the 20 photoreceptor 16 side. Moreover, in this housing 80 is formed a developer containing chamber 84 capable of containing the developer G formed from the non-magnetic toner T and the magnetic carrier. [0045] Furthermore, in the housing 80 is provided a developing roller 86 so as to be 25 partially exposed from the opening 82 of the housing 80. The developing roller 86 is rotatably supported on the housing 80. Moreover, to an end of the developing roller 86 is fixed a gear (not shown). Rotatory power from the motor is transferred to the gear so as to rotate the developing roller 86 via the gear. [0046] 30 Furthermore, the developing roller 86 includes a rotatable and conductive thin cylindrical nonmagnetic sleeve 86A, and a fixed columnar magnet roller 86B. [0047] - 12 A columnar developer regulating roller 50 serving as a developer regulating member that regulates the layer thickness of the developer G on the developing roller 86, is arranged to face the nonmagnetic sleeve 86A with a space S. Details of the developer regulating roller 50 are described later. 5 [0048] As a result, the developing roller 86 attracts the magnetic carrier contained in the developer G with a magnetic force, and forms a magnetic brush of the developer G on the surface. The layer thickness of the developer G is regulated by the developer regulating roller 50, and the developer G is conveyed to the position facing the 10 photoreceptor 16. The electrostatic latent image formed on the photoreceptor 16 is developed as a toner image by the developer G on the developing roller 86. [0049] On the lower side of the developing roller 86 is arranged a first agitation conveyance auger 88 and a second agitation conveyance auger 89 along the axial 15 direction of the developing roller 86. [0050] As shown in FIG. 5, the first mixing conveyance auger 88 and the second mixing conveyance auger 89 respectively include rotating shafts 88A and 89A, and are respectively rotatably supported on the peripheral wall of the housing 80. Moreover, the 20 rotating shafts 88A and 89A of the first mixing conveyance auger 88 and the second mixing conveyance auger 89 are formed with spiral blades 88B and 89B that are spirally wrapped thereon at a predetermined pitch. [0051] Furthermore, to the ends of the rotating shafts 88A and 89A are respectively 25 fixed gears (not shown). When rotatory power from a motor (not shown) is transferred to the gears to respectively rotate the first mixing conveyance auger 88 and the second mixing conveyance auger 89 via the gears, the developer G contained in the developer containing chamber 84 is conveyed in the arrow direction in FIG. 5 while being mixed by the spiral blades 88B and 89B. 30 [0052] Between the first mixing conveyance auger 88 and the second mixing conveyance auger 89 is formed a partition wall 90. This partition wall 90 divides the inside of the developer containing chamber 84 into an area (first mixing path) 92 - 13 arranged with the first mixing conveyance auger 88, and an area (second mixing path) 93 arranged with the second mixing conveyance auger 89. [0053] In the longitudinal opposite ends of the partition wall 90 are formed 5 communication holes 94 and 95. By means of these communication holes 94 and 95, the first mixing path 92 and the second mixing path 93 are communicated. The developer G in the developer containing chamber 84 is conveyed while being mixed by the rotation of the first mixing conveyance auger 88 and the second mixingn conveyance auger 89 respectively in the first mixingn path 92 and the second mixing path 93, so that the 10 developer G is circulated between the first mixing path 92 and the second mixing path 93. [0054] As shown in FIG. 6, in the main toner supply unit 70 adjacent to the development unit 68 is provided a toner containing chamber 150 in which a supplementary toner T is 15 to be contained. In the toner containing chamber 150 is provided a toner mixing conveyance member 152 along the axial direction of the developing roller 86. [0055] The toner mixing conveyance member 152 includes a rotating shaft 152A, and is rotatably supported on the peripheral wall of the housing 80. On this rotating shaft 152A 20 is formed a blade 152B at a predetermined pitch. (0056] Furthermore, to an end of the rotating shaft 152A is fixed a gear (not shown). When rotatory power from a motor (not shown) is transferred to the gear to rotate the toner agitation conveyance member 152 via the gear, the non-magnetic toner T in the 25 toner containing chamber 150 is conveyed in the arrow direction in FIG. 5 while being mixed by the blade 152B. [0057] Between the toner containing chamber 150 and the developer containing chamber 84 is provided a wall 154. From the bottom of the wall 154, a curved wall 156 30 is extended to the toner containing chamber 150 side, and a partition wall 157 is extended to the developer containing chamber 84 side. As a result, between the bottom plate of the housing 80 and the walls 156 and 157 is provided a tunnel-like dispenser chamber 158.

- 14 [0058] As shown in FIG. 5, in the vicinity of one longitudinal end of the curved wall 156 is formed an opening 162 so that the toner containing chamber 150 and the dispenser chamber 158 are communicated with each other. As a result, the non 5 magnetic toner T contained in the toner containing chamber 150 is conveyed in the toner containing chamber 150 while being mixed by the toner mixing conveyance member 152, and then sent from the opening 162 to the dispenser chamber 158. [0059] On the other hand, in the vicinity of the other one longitudinal end of the 10 partition wall 157 is formed a toner supply port 164 so that the dispenser chamber 158 and the developer containing chamber 84 are communicated with each other. As a result, the non-magnetic toner T in the dispenser chamber 158 is conveyed in the dispenser chamber 158 while being mixed by the dispense auger 160, and sent from the toner supply port 164 to the developer containing chamber 84. 15 [0060] As shown in FIG. 6, the toner supply port 164 is formed so that the bottom end thereof is positioned lower than the surface of the developer G contained in the developer containing chamber 84. As a result, at least a part of the toner supply port 164 is immersed in the developer G contained in the developer containing chamber 84, and 20 the non-magnetic toner T that has been sent from the dispenser chamber 158 to the developer containing chamber 84 is submerged into the developer G and is readily mixed with the developer G contained in the developer containing chamber 84. In this manner, the structure is such that the developer G mixed by the first mixing conveyance auger 88 and the second mixing conveyance auger 89 is attached onto the surface of the 25 developing roller 86 by a magnetic force. [0061] In the image forming apparatus 10 of the above structure, images are formed in the following manner. [0062] 30 As shown in FIG. 8, firstly the charging roller 18 to which a voltage is applied, negatively and uniformly charges the surface of the photoreceptor 16 at a predetermined charge potential. [0063] - 15 Exposure is performed by the exposure device 36 so that the image part on the charged photoreceptor 16 has a predetermined potential for exposure, and an electrostatic latent image is formed. [0064] 5 That is, based on the image data supplied from a controller (not shown), the semiconductor laser (not shown) is turned on/off to modulate, and thereby a latent image corresponding to the image, is formed on the photoreceptor 16. [0065] Furthermore, as shown in FIG. 6, the developer G mixed by the dispense auger 10 160, the first mixing conveyance auger 88, and the second mixing conveyance auger 89 is attached onto the nonmagnetic sleeve 86A of the developing roller 86 of the developing device 64 by a magnetic force of the magnet roller 86B. Moreover, the developer G attached onto the nonmagnetic sleeve 86A passes through the space S between the developer regulating roller 50 and the developing roller 86, and thereby the 15 excessive portion is squeegeed out to even the layer thickness of the developer G. [0066] Moreover, to the each developing roller 86 is applied a predetermined developing bias voltage from a power unit (not shown) for each color. When the electrostatic latent image on the each photoreceptor 16 is passing through the position of the developing 20 roller 86, the toner of the developer G is adhered onto the electrostatic latent image by an electric force, and developed as a toner image. [0067] Then, as shown in FIG. 8, the sheet material P placed in the paper feeding cassette 26 is sent out to the sheet conveyance route 34 by the pickup roller 28, and 25 further conveyed at a predetermined timing by the conveyance rollers 30 and the registration rollers 32 to pass between the photoreceptors 16 and the transfer rollers 54, and the toner image is transferred onto the sheet material P. The transferred toner image is fixed by the fixing device 56, and the sheet material P fixed with the toner image is discharged into the discharge tray 60 by the discharge rollers 58. 30 [0068] Next is a description of the developing roller 86 and the developer regulating roller 50, with reference to FIG. 1. [0069] - 16 As shown in FIG. 1, the magnet roller 86B of the developing roller 86 has a total of five magnetic poles of N polarity NI and N2 and S polarity SI, S2, S3 which are arranged at predetermined spacing in sequence of S1, NI, S2, S3, and N2, in the circumferential direction. In the position facing the development area of the 5 photoreceptor 16 is arranged the developing pole S1. On the upstream side from this developing pole SI in the rotatory direction of the developing roller 86 is arranged the developer regulating pole N2 that regulates the amount of the developer on the surface of the nonmagnetic sleeve 86A, to face the developer regulating roller 50. Moreover, on the downstream side from the developing pole S1 but the upstream side from the 10 developer regulating pole N2 are arranged the developer peeling pole S2 and the developer scooping pole S3. Between the developing pole SI and the developer peeling pole S2 is arranged the conveying pole NI. [0070] The developing pole Sl generates lines of magnetic force in the direction for 15 shifting the developer G on the developing roller 86 in the direction of the photoreceptor 16. Moreover, since the developer peeling pole S2 and the developer scooping pole S3 having the same magnetic polarity are adjacent, lines of magnetic force are generated in the direction for separating the developer G on the developing roller 86 from the developing roller 86. Furthermore, the developer scooping pole S3 generates lines of 20 magnetic force in the direction for attaching the developer G contained in the developer containing chamber 84 (refer to FIG. 6) onto the developing roller 86. The developer regulating pole N2 generates lines of magnetic force in the direction for shifting the developer G toward the developer regulating roller 50. [0071] 25 By the lines of magnetic force generated by the respective magnetic poles, a predetermined magnetic flux is generated on the surface of the nonmagnetic sleeve 86A. If the magnetic flux density thereof is broken down into the normal component and the tangential component of the developing roller 86, this gives a magnetic flux density distribution as shown in FIG. 1. 30 [0072] Moreover, the columnar developer regulating roller 50 arranged to face the developer roller 86 is a nonmagnetic body, and is arranged with the space S between it and the nonmagnetic sleeve 86A. The developer G attached onto the developing roller - 17 86 rotating in the F direction passes through the space S, and thereby the developer regulating roller 50 squeegees excessive developer G. As a result, this gives a structure that regulates the layer thickness of the developer G on the developing roller 86. [0073] 5 Here, the layer thickness regulation region where the developer regulating roller 50 regulates the layer thickness of the developer G on the developing roller 86 includes a downstream layer thickness regulation region on the downstream side of the developer regulating roller 50, and an upstream layer thickness regulation region on the upstream side thereof. The downstream layer thickness regulation region is between a line linking 10 the center of the developing roller 86 and the center of the developer regulating roller 50, and a line passing through from the center of the developing roller 86 and tangential to the downstream surface of the developer regulating roller 50 (region B shown in FIG. 1). The upstream layer thickness regulation retion is between a line linking the center of the developing roller 86 and the center of the developer regulating roller 50, and a line 15 passing through from the center of the developing roller 86 and tangential to the upstream surface of the developer regulating roller 50 (region A shown in FIG. 1). [0074] In the exemplary embodiment, the developer regulating roller 50 is arranged so that the downstream layer thickness regulation region (region B) is positioned in an area 20 where the normal component of the magnetic flux density of the developing roller 86 is larger than the tangential component thereof. Since the normal component in the downstream layer thickness regulation region (region B) becomes large, the developer G is napped (magnetic brushed) so as to rise along the lines of magnetic force. [0075] 25 That is, the inlet of the space S between the developing roller 86 and the developer regulating roller 50 is wedge-like shaped, and when the developer G is passing through the space S, it is compressed in the center of the layer thickness regulation region, and is gradually affected by a releasing force as it goes toward the downstream. However, since up until the developer G has passed through the 30 downstream layer thickness regulation region, the normal component of the magnetic flux density is large and the developer G is raised, it becomes difficult to pass under the developer regulating roller 50, and the layer thickness of the developer G is evenly squeezed.

- 18 [0076] As a result, waviness generated on the surface of the developer G is suppressed, and the layer thickness of the developer G becomes even. [0077] 5 Moreover, since the layer thickness of the developer G becomes even, image defects due to an excess or shortage of the amount of developer G can be prevented. Therefore, by facilitating the accurate control of the development process, an image forming apparatus 10 having a high image quality can be provided. [0078] 10 Furthermore, in the case where a magnetic round bar is used as the developer regulating member as in the conventional manner, a means for preventing deflection due to the magnetic force is required. However, since a nonmagnetic round bar can be employed as the developer regulating roller 50 without adding a special means nor mechanism, the developing device 64 and the image forming apparatus 10 can be 15 provided at a lower price. [0079] As shown in FIG. 2, the developer regulating roller 50 is arranged so that an angle a of the lines of magnetic force on the downstream boundary H of the downstream layer thickness regulation region (region B) is 51.7* or more with respect to the 20 tangential direction of the developing roller 86 on the boundary H. As a result, the napping of the developer G in the downstream layer thickness regulation region (region B) is further oriented toward the normal direction of the developing roller 86, and thereby the napping of the developer G is more stabilized. The image is output onto the sheet material P and the unevenness of the amount of developer is visually observed. As 25 in FIG. 3, the result shows that an acceptable level is achieved as long as the angle a is 51.7* or more. [0080] Subsequently, by arranging the developer regulating roller 50 so that the angle a is 51.7* or more, a high quality image without unevenness can be obtained. 30 [0081] Moreover, as shown in FIG. 1, the developer regulating roller 50 is arranged so that the upstream layer thickness regulation region (region A) is positioned in an area - 19 where the normal component of the magnetic flux density of the developing roller 86 is greater than the tangential component thereof. [0082] As a result, as shown in FIG. 2, the developer G is napped (magnetic brushed) 5 along the lines of magnetic force in the upstream layer thickness regulation region (region A), and thus excessive developer is reliably squeegeed out by the developer regulating roller 50 immediately before passing through the space S. [0083] Furthermore, as shown in FIG. 1, the developer regulating roller 50 is arranged 10 so that the angle 0 between; a line linking the center of the developing roller 86 and the center of the developer regulating roller 50, and a line linking the center of the developing roller 86 and the point D where the normal component and the tangential component of the magnetic flux density of the upstream side of the developer regulating roller 50 become equal, is 200 or more. 15 [0084] As a result, on the upstream side of the developer regulating roller 50, the region where the normal component is larger than the tangential component is sufficiently ensured. [0085] 20 As shown in FIG. 4, the developing roller 86 having a diameter of 16 mm and the developer regulating roller 50 having a diameter of 5 mm are used for the test. The results show that if the angle 0 is 20* or more, there is hardly no affect on the layer thickness of the developer G after passing through the space S. That is, as long as the angle 0 is 20* or more, even if the angle 0 varies in the production process, the layer 25 thickness of the developer G after passing through the space S is hardly affected. [0086] Consequently, by arranging the developer regulating roller 50 so that the angle 0 is 200 or more, then even if the developer regulating roller 50 is positionally displaced due to production variations, variation of the layer thickness of the developer G after 30 passing through the space S can be suppressed. [0087] -20 In this manner, since the permissible width for variations in production can be more widely ensured, the yield of members can be improved and the production cost can be reduced. [0088] 5 Moreover, if a chemical toner having a smooth surface, a high fluidity, and a shape coefficient of 140 or less produced by a suspension polymerization method, an emulsion polymerization aggregation method, a dissolution granulation method or the like, is used as the non-magnetic toner of the two-component developer G so as to improve the transfer performance onto the sheet material P, then the shape of the non 10 magnetic toner becomes close to spherical, and the fluidity of the developer G is improved. As a result, when the developer G is passing through the space S, waviness is easily generated on the surface of the developer G. [0089] However, as described above, since the developer regulating roller 50 is arranged 15 based on the magnetic flux density of the developing roller 86, the layer thickness of the developer G becomes even. [0090] The calculation method of the toner shape coefficient is shown below. [0091] 20 Shape coefficient = (toner maximum diameter 2 / toner projected area) x (100r / 4) Furthermore, if a resin carrier is used as the magnetic carrier of the two component developer G so as to enable recycling, the magnetic susceptibility of the magnetic carrier is lowered. If the magnetic susceptibility becomes lower, the lines of magnetic force have less affect thereon, and the layer thickness of the developer easily 25 becomes uneven. [0092] However, as described above, since the developer regulating roller 50 is arranged based on the magnetic flux density of the developing roller 86, the layer thickness of the developer G becomes even. 30 [0093] Moreover, if the toner concentration is high, the magnetic susceptibility of the developer G is lowered, and thereby the developer retainability of the developing roller 86 is lowered. If the amount of the developer G is a lot at the time of layer formation of -21 the developer G, the formed layer becomes partially weak in retainability. However, as described above, since the developer regulating roller 50 is arranged based on the magnetic flux density of the developing roller 86, the layer thickness of the developer G becomes even. 5 [0094] The present invention has been described in detail with reference to specific exemplary embodiments. However, the present invention is not limited to these exemplary embodiments, and it will be apparent to a person skilled in the art that other various exemplary embodiments are applicable without departing from the scope of the 10 present invention. For example, in the above exemplary embodiments, the shape of the developer regulating roller 50 is made columnar so as to even the layer thickness of the developer G. However, the developer regulating roller serving as the layer thickness regulating member may be made in another shape such as triangle or hexagon so as to even the layer thickness of the developer G. 15 [0095] Moreover, in the above exemplary embodiments, a two-component developer is used for the explanation, however a magnetic toner or the like may be also used.

Claims (12)

1. A developing device comprising: a developing roller that holds and rotates a developer to form a toner image on a photoreceptor; and a developer regulating member 5 that is arranged to face the developing roller to form a space between the developer regulating member and the developing roller so as to regulate the layer thickness of the developer on the developing roller; a developer layer thickness regulation region of a constant dimention with respect to the developing roller and the developer regulating member being formed; 10 the developer regulating member being nonmagnetic, and in the space, the downstream side of the developing roller in the rotatory direction being wedge-shaped when viewed from one end side of the developing roller and the developer regulating member; and the developer regulating member being arranged so that, in the developer layer 15 thickness regulation region, a layer thickness regulation region from the center of the developer regulating member to the downstream side in the rotatory direction of the developing roller is positioned in an area where the normal component of the magnetic flux density of the developing roller is larger than the tangential component thereof. 20

2. The developing device according to claim 1, wherein an angle of a line of magnetic force at the downstream boundary of the downstream layer thickness regulation region is 51.70 or more with respect to a part of the tangential line of the developing roller that is formed, and extends from, the downstream boundary on the surface of the developing roller to the downstream side. 25

3. The developing device according to either one of claim I or claim 2, wherein, in the space, the upstream side of the developing roller in the rotatory direction is wedge shaped when viewed from one end side of the developing roller and the developer regulating member, and the developer regulating member is arranged so that, in the 30 developer layer thickness regulation region, an upstream layer thickness regulation region is positioned in an area where the normal component of the magnetic flux density of the developing roller is larger than the tangential component thereof. - 23

4. The developing device according to any one of claim I through claim 3, wherein the developer regulating member is formed from a developer regulating roller, and the developer regulating roller is arranged so that an angle is 200 or more between: a line linking the center of the developer regulating roller and the center of the developing 5 roller, and a line linking the center of the developing roller and a point where the normal component and the tangential component of the magnetic flux density of the developing roller on the upstream side become equal.

5. The developing device according to claim 4, wherein: the downstream layer 10 thickness regulation region is positioned between a line linking the center of the developing roller and the center of the developer regulating roller, and a line linking the center of the developing roller and tangential to the surface of the developer regulating roller at the downstream side; and the upstream layer thickness regulation region is positioned between a line linking the center of the developing roller and the center of the 15 developer regulating roller and a line linking the center of the developing roller and tangential to the surface of the developer regulating roller at the upstream side.

6. The developing device according to any one of claim 1 through claim 5, wherein the developer is a two-component developer comprising a non-magnetic toner and a 20 magnetic carrier.

7. The developing device according to claim 6, wherein the non-magnetic toner is a chemical toner. 25

8. The developing device according to claim 7, wherein a shape coefficient of the chemical toner is 140 or less.

9. The developing device according to any one of claim 6 through claim 8, wherein the non-magnetic toner is a resin carrier. 30

10. An image forming apparatus including the developing device according to any one of claim 1 through claim 9. - 24

11. A developing device substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples. 5

12. An image forming apparatus substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.