Patent Application
20130236216
This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Application No. 2012-051312, filed on Mar. 8, 2012, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.
1. Field of the Invention
The present invention generally relates to a magnet roller for use in an image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction machine having at least two of these capabilities; and a developer bearer, a development device, a process cartridge, and an image forming apparatus including same.
2. Description of the Related Art
Electrophotographic image forming apparatuses typically include a latent image bearer, such as a drum-shaped or belt-shaped photoreceptor, on which electrostatic latent images are formed according to image data, and a development device to develop the electrostatic latent images. In electrophotographic image forming apparatuses, magnetic brush development methods using two-component developer consisting essentially of toner and magnetic carrier are widely used.
In magnetic brush development methods, developer is magnetically adsorbed onto an outer circumferential surface of the developer bearer, thus forming a magnetic brush. Then, in a development range formed between the developer bearer and the latent image bearer, toner is supplied from the magnetic brush to the electrostatic latent image formed on the latent image bearer, thereby developing it.
Developer bearers for use in such magnetic brush development methods typically include a cylindrical development sleeve constructed of a nonmagnetic material, and a magnet roller is provided disposed inside the development sleeve for generating magnetic force on the surface of the development sleeve. Magnetic carrier particles contained in developer are caused to stand on end on the development sleeve along the lines of the magnetic force thereon. Then, toner particles adhere to the magnetic carrier particles standing on end, forming a magnetic brush.
For example, JP-2001-165148-A proposes magnet rollers that include a cylindrical body and a pair of support portions provided on both sides of the body as shown in
A magnet roller 701 shown in
The magnet roller 701 shown in
A magnet roller 801 shown in
In view of the foregoing, one embodiment of the present invention provides a magnet roller that includes a roller-shaped body constructed of a magnetic field generating material, a first support rod provided to a first axial end of the body, and a second support rod provided to a second axial end of the body. At least one of the first and second support rods is constructed of a nonmagnetic material and includes a projecting part projecting outside the body from an end face of the body and a buried part united to the projecting part and positioned inside the body from the end face of the body. The buried part includes a reduced-area portion smaller in cross-sectional area perpendicular to an axial direction of the first and second support rods than a base end of the projecting part adjacent to the buried part.
In another embodiment, a developer bearer includes the above-described magnet roller and a hollow cylindrical rotator provided outside the magnet roller to rotate around an axis relative to the magnet roller.
In yet another embodiment, a development device includes the above-described magnet roller and a support rod mount to which the first and second support rods are fixed.
In yet another embodiment, an image forming apparatus includes a latent image bearer and the above-described development device to develop a latent image formed on the latent image bearer with developer.
In yet another embodiment, the latent image bearer and the development device are housed in a unit casing of a process cartridge that is removably installed in the image forming apparatus.
A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve a similar result.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views thereof, and particularly to
Referring to
It is to be noted that, in
The body 31 includes a roller body 32 constructed of a material capable of generating magnetic fields (hereinafter “magnetic field generating material”) and a rare-earth magnet block 141. It is preferred that the roller body 32 be substantially cylindrical and have an external diameter smaller than 12 mm. The term “cylindrical” used here is not limited to round columns but also includes polygonal prisms.
Examples of the magnetic field generating material forming the roller body 32 include, but not limited to, so-called plastic magnet and rubber magnets, which are produced by mixing high polymer with magnetic powders. Examples of magnetic powders include strontium (Sr) ferrite and barium (Ba) ferrite. Examples of high polymers include polyamides such as Polyamide 6 (PA6) or Polyamide 12 (P12); ethylenes such as ethylene ethyl (EEA) copolymers or ethylene vinyl acetate (EVA); chlorinated polymers such as chlorinated polyethylene (CPE); and rubbers such as acrylonitrile butadiene rubber. Needless to say, other materials capable of generating magnetic fields than those listed above can be used unless they conflict intended effects of the present embodiment.
The circumferential surface of the roller body 32 includes a flat face 32a extending in the direction of an axis P (hereinafter “P-axis direction”) of the roller body 32 over its long side entirely. That is, the roller body 32 is shaped as if a portion is cut out of a cylindrical shape along a chord of its circumference. The rare-earth magnet block 141 is fixed to the flat face 32a. With this configuration, the flat face 32a is provided with a main development pole extending over the long side of the roller body 32.
The shape of the body 31 is not limited to that illustrated in the drawings. Alternatively, for example, the body 31 may be constructed of a cylindrical body only, without the flat face 32a, made of a magnetic field generating material. Yet alternatively, instead of the flat face 32a, a groove extending over the entire length in the P-axis direction may be formed in the circumferential surface of the cylindrical roller body 32 constructed of a magnetic field generating material, and the rare-earth magnet block 141 may be inserted into the groove.
Additionally, the roller body 32 is provided with multiple stationary magnetic poles extending over the entire length of the roller body 32, each of which is either north (N) pole or south (S) pole. Those stationary magnetic poles are positioned in areas except the flat face 32a provided with the main development pole.
One of the stationary magnetic poles serves as a developer attracting pole or pump-up pole positioned facing an agitation screw 118 (shown in
At least another one of the stationary magnetic poles serves as a conveyance pole and is positioned between the developer attracting pole and the main development pole provided to the flat face 32a, positioned downstream from the conveyance pole in the direction in which developer is transported by the development sleeve 132. The conveyance pole causes magnetic force on the outer surface of the development sleeve 132 for transporting developer (hereinafter “pre-development developer”) that is not yet used for image development toward the photoreceptor drum 108.
The roller body 32 is further provided with a developer release pole for attenuating the magnetic force on the outer surface of the development sleeve 132, thereby causing developer to leave the development sleeve 132. The developer release pole is at substantially 180 degrees from the flat face 32a, that is, opposed to the flat face 32a. The developer release pole extends over the long side of the roller body 32.
The rare-earth magnet block 141 forms the main development pole when disposed on the flat face 32a of the roller body 32. The rare-earth magnet block 141 is shaped like a slim plate by magnetic field press or compression. Rare-earth magnets such as neodymium (Nd) magnet such as Nd—Fe—B or samarium (Sm) magnet such as Sm—Co and Sm—Fe—N can be used for the rare-earth magnet block 141 for attaining narrow range and high magnetic properties. Alternatively, the rare-earth magnet block 141 may be a plastic magnet or rubber magnet in which rare-earth magnetic powder is mixed with high polymer similarly to the roller body 32.
The pair of support portions 33 and 34 is constructed of a nonmagnetic material and is shaped like a cylinder or rod. The entire support portions 33 and 34 have an external diameter smaller than that of the body 31. The support portions 33 and 34 are fixed to the body 31 (the roller body 32 in particular) and project from the end faces 31a and 31b of the body 31.
In the present embodiment, the axis of the pair of support portions 33 and 34 (hereinafter also “first and second support portions 33 and 34”) is aligned with the axis of the body 31 (axis P in
For example, the support portions 33 and 34 can be constructed of nonmagnetic Steel Use Stainless (SUS) such as SUS303, SUS304, or SUS316 according to Japanese Industrial Standards (HS). Alternatively, any nonmagnetic material may be used as long as the support portions 33 and 34 can be fixed to the body 31 and a sufficient degree of rigidity can be secured. For example, hard synthetic resin such as polycarbonate may be used.
As shown in
An end portion 331a of the projecting part 331 is shaped as if a cylindrical shape is partly cut away along a chord of its circumference. That is, the positioning face 331c is formed in the circumferential surface at the end of the projecting part 331.
The buried part 332 has an external diameter reduced from that of the base portion 331b of the projecting part 331 and hereinafter also called a reduced-area portion 332. In other words, the buried part (reduced-area portion) 332 has a cross-sectional area reduced from that of the base portion 331b of the projecting part 331 in the direction perpendicular to the axis P. It is to be noted that the shape of the buried part 332 is not limited to round columns but may be shaped like a polygonal cylinder such as a square cylinder or a hexagonal cylinder.
Referring to
Descriptions area given below of a method of manufacturing an intermediate product in which the roller body 32 and the support portions 33 and 34 are united together, that is, the magnet roller 30 without the rare-earth magnet block 141.
This intermediate product can be produced by insert and injection molding using a mold 200 shown in
Additionally, as shown in
Shapes (width, height, and the like) and positions (i.e., the distance from the cavity 201) of the permanent magnets 205a through 205d are designed in accordance with the strength of magnetic force required at the respective stationary magnetic poles of the roller body 32. Even when the rare-earth magnet block 141 is relatively thin, high magnetic force similar to that of typical configurations can be attained by arranging the permanent magnets 205a through 205d such that a certain degree of orientation can be secured at the main development pole. It is to be noted that, to secure developer removal effect and the like, permanent magnets are also provided to other areas than those corresponding to the respective stationary magnetic poles.
Descriptions are given below of a configuration of the magnet roller 30 according to the present embodiment.
For example, the roller body 32 of the body 31 can be a plastic magnet constructed of anisotropic strontium ferrite, as the magnetic powder, and Polyamide 12 (P12), as the high polymer. For example, the roller body 32 is cylindrical and has an external diameter of 10 mm and a length of 223 mm. The flat face 32a of the roller body 32 has a width of 6 mm and a length of 223 mm. The flat face 32a is at a height of 5 mm from the center (axis P) of the roller body 32.
The rare-earth magnet block 141 is substantially planar and narrow, having a width of 3.5 mm, a peak height of 1.0 mm, and a length of 223 mm, for example. Further, a top face of the rare-earth magnet block 141 is curved at a radius of 5 mm (R5), for example. The rare-earth magnet block 141 can be bonded to the flat face 32a of the roller body 32 using glue or the like.
The pair of support portions 33 and 34 is constructed of SUS303 and fixed to the body 31 (the roller body 32 in particular) as a single unit by insertion and injection molding. The projecting part 331 of the first support portion 33 is cylindrical and has an external diameter of 6 mm and a length of 35 mm. The buried part 332 (reduced-area portion) is cylindrical and has an external diameter of 4 mm and a length of 10 mm. The projecting part 341 of the support portion 34 is cylindrical and has an external diameter of 6 mm and a length of 5 mm. The buried part 342 (reduced-area portion) is cylindrical and has an external diameter of 4 mm and a length of 10 mm.
The configuration of the magnet roller 30 is not limited to the description above.
Next, effects attained by the magnet roller 30 according to the present embodiment are described below.
Initially, comparative examples are described. A magnet roller according to a first comparative example is produced by monolithic molding and includes a body and support portions provided on both sides thereof. Both of the body and the support portions are constructed of a magnetic field generating material such as resin magnet. In such magnet rollers, as shown in
The support rod 903 includes a projecting part 903a positioned outside the end face 902a of the body 902 and a buried part 903b positioned inside the body 902 and continuous with the projecting part 903a. Similarly, the support rod 904 includes a projecting part 904a and a buried part 904b. The buried parts 903b and 904b have a thickness or width identical to that of the projecting part 903a and 904a.
When the support rods 903 and 904 are constructed of a nonmagnetic material having a high rigidity, durability of the magnet roller 901 shown in
The volume of the end portions of the body 902, however, may be reduced excessively if the buried parts 903b and 904b are excessively long to secure the rigidity of the support rods 903 and 904. In this case, the volume of the resin magnet in the end portions is insufficient, and, as shown in
Additionally, the thickness or width of the buried parts 903b and 904b is identical to that of the projecting parts 903a and 904a, which can also make the volume of the end portions of the body 902 insufficient. Accordingly, the magnetic flux density is lower in the end portions of the body 902 than in the center portion thereof.
In view of the foregoing, it is preferred to reduce differences in the magnetic flux density in the longitudinal direction (axial direction) of the magnet roller while securing a sufficient rigidity of the support portions.
In the magnet roller 30 according to the present embodiment, the support portions 33 and 34 are partly buried inside the body 31, and at least a part of the buried parts 332 and 342 of the support portions 33 and 34 are thinner than the projecting parts 331 and 341, that is, reduced in cross-sectional area from those of the projecting parts 331 and 341.
Accordingly, the volume of the buried parts 332 and 342 of the support portions 33 and 34 can be reduced from that of the comparative configuration in which the thickness of the buried parts are identical to that of the projecting parts.
With this configuration, a sufficient volume of the axial end portions of the body 31 can be secured. Simultaneously, the volume of the axial end portions of the body 31 can be adjusted by changing the cross-sectional area of the buried parts 332 and 342 (reduced-area portions), that is, the volume thereof. This adjustment enables inhibition of edge effects. Accordingly, as shown in
Additionally, a material having a high rigidity can be used for the support portions 33 and 34 to secure rigidity thereof since the material can be different from that of the body 31.
It is to be noted that the term “magnetic flux density” used here means the density of magnetic flux in the direction normal to the circumferential surface of the body 31 of the magnet roller 30 (or, in the area where the rare-earth magnet block 141 is provided, a virtual circumferential surface of the roller body 32 assuming that the roller body 32 is round in cross section).
The magnet roller 30 according to the present embodiment includes the roller-shaped body 31 constructed of the magnetic field generating material and the pair of rod-shaped, nonmagnetic support portions 33 and 34 provided to the axial end portions of the body 31. The support portions 33 and 34 respectively include the projecting parts 331 and 341 projecting from the end faces 31a and 31b of the body 31 and the buried parts 332 and 342 positioned inside the body 31 and continuous with the projecting parts 331 and 345. The cross section (perpendicular to the P-axis direction) of the buried parts 332 and 342 are reduced from that of the base portions 331b and 341b of the projecting part 331 and the 341. Although the entire buried parts 332 and 342 are reduced in cross section in the configuration shown in
Additionally, in the configuration shown in
Both of the support portions 33 and 34 are aligned with the axis P of the body 31. This adjustment enables inhibition of edge effects and reduction of axial differences in magnetic flux density on the circumferential surface of the magnet roller 30.
Additionally, the rod-shaped buried parts (reduced-area portions) 332 and 342 can be designed and manufactured easily, thus facilitating inhibition of differences in magnetic flux density on the circumferential surface of the magnet roller 30.
Aligning the axes of the support portions 33 and 34 with the axis P of the body 31 is advantageous to inhibit stress applied to the support portions 33 and 34, and the body 31 from being unbalanced.
Although the entire reduced-area portions (buried parts 332 and 342) are cylindrical in the above-described configuration, the shapes thereof are not limited thereto. For example,
In a magnet roller 30A shown in
Alternatively, a magnet roller 30B shown in
With the stepped reduced-area portion 332A shown in
Yet alternatively,
The following advantage can be attained in the configuration in which the buried part 332C has the latch shape constituted of the first portion 335e and the second portion 335f adjacent to the first portion 335e and smaller in cross section than the first portion 335e, and the first portion 335e is farther from the projecting part 331 than the second portion 335f. The body 31 can enter the step formed by the first and second portions 335e and 335f, engaging the buried part 332C. Thus, the body 31 can be latched, and the first support portion 33C can be inhibited from coming off from the body 31.
It is to be noted that, although the entire buried parts 332 and 342 are reduced in cross-sectional area and serve as the reduced-area portions in the above-described embodiment and variations, the buried parts 332 and 342 can be shaped otherwise.
For example,
When the buried part 332D has the reinforcement 335D1 identical in thickness to the base portion 331b of the projecting part 331, the first support portion 33 can has an increased rigidity. The axial length of the reinforcement 335D1 depends on the configuration of the magnet roller 30. For example, even if the axial length of the reinforcement 335D1 is 1 mm or 2 mm, the rigidity of the first support portion 33 can improve.
It is to be noted that, although
Further, although the pair of support portions 33 and 34 is nonmagnetic in the above-described configurations, alternatively, only one of the support portions 33 and 34 may be nonmagnetic, whereas the other support portion 33 or 34 may be constructed of the magnetic field generating material identical for the roller body 32 of the body 31 and integrated with the roller body 32. In other words, at least one of the support portions on the respective sides of the body is constructed of a nonmagnetic material, and the buried part of that support portion includes the reduced-area portion.
It is to be noted that, although the entire reduced-area portion is cylindrical or rod-shaped, the reduced-area portion can be shaped otherwise. For example, the entire buried portion may be shaped into a sphere having a diameter smaller than the external diameter of the base portion of the projection part of the support portion, and an outer surface thereof is partly connected to the projecting part.
Descriptions are given below of the development roller 115 serving as the developer bearer according to an embodiment.
The development sleeve 132 is nonmagnetic and rotatable around an axis of the development roller 115. While rotating, a part of the development sleeve 132 faces the main development pole and the respective stationary magnetic poles sequentially. The development sleeve 132 can be constructed of aluminum, Steel Use Stainless (SUS), or the like. As the material of the development sleeve 132, aluminum alloy excels in its lightness and easiness in processing. A6063, A5056, and A3003 are preferable as aluminum alloy. When stainless steel is used, SUS303, SUS304, and SUS316 are preferable.
Since the development roller 115 incorporates the above-described magnet roller 30, differences in magnetic flux density in the long size direction of the development sleeve 132, in particularly, the magnet roller 30, thus alleviating image density unevenness in the long side direction. Additionally, the rigidity of the magnet roller 30 of the development roller 115 can be secured, which can improve the durability of the development roller 115.
The development device 115 according to an embodiment is described with reference to
As shown in
The developer supply unit 114 includes a developer container 117, a supply screw 118a serving as a developer agitator, and a conveyance screw 118b. The supply screw 118a and the conveyance screw 118b are hereinafter also collectively referred to as agitation screws 118. For example, the developer container 117 is shaped like a box and has an axial length (i.e., a length in its longitudinal direction) equal or similar to an axial length of the photoreceptor drum 108. Additionally, a partition 119 extending in the longitudinal direction of the developer container 117 is provided inside the developer container 117. The partition 119 divides the developer container 117 into a first compartment 120 and a second compartment 121 that communicate with each other in both end portions in the longitudinal direction.
Developer is contained in both the first compartment 120 and the second compartment 121 of the developer container 117. Developer (illustrated in
For example, toner particles are spherical fine particles produced through an emulsion polymerization method or a suspension polymerization method. It is to be noted that, alternatively, toner may be produced by smashing synthetic resin blocks in which various colorants and pigments are mixed or dispersed. The toner particles have a mean particle diameter of within a range from about 3 μm to 7 μm. Alternatively, toner may be produced by pulverization.
The magnetic carrier 135 includes a core 136 coated with a resin coat 137, and alumina particles 138 are dispersed in the resin coat 137 as shown in
The core 136 is spherical and constructed of a magnetic material such as ferrite. The core 136 is covered with the resin coat 137 entirely. For example, the resin coat 137 contains a charge adjuster and a resin component, such as acrylic resin, in which thermoplastic resin and melamine resins are bridged together. The resin coat 137 is elastic and has a high degree of adhesion force. The alumina particles 138 are spherical and have an external diameter greater than the thickness of the resin coat 137. The alumina particles 138 are held by the adhesion force of the resin coat 137. The alumina particles 138 project outward from the outer face of the resin coat 137.
The agitation screws 118 are provided in the first and second compartments 120 and 121, respectively. The long axes of the agitation screws 118 parallel the longitudinal direction of the developer container 117, the development roller 115, and the photoreceptor drum 108. Each agitation screw 118 is rotatable about an axis of rotation. Each agitation screw 118 mixes the toner with the magnetic carrier and transports the developer in the axial direction while rotating.
In the configuration shown in the figures, the conveyance screw 118 in the first compartment 120 transports the developer from the axial end portion to which the toner is supplied to the other axial end portion (on the back side of the paper on which
In the above-described configuration, while mixing the supplied toner and the magnetic carrier 135, the developer supply unit 114 transports toner from one end to the other end of the first compartment 120 and further to an upstream end portion of the second compartment 121 in the developer conveyance direction therein. Toner and the magnetic carrier 135 in the developer are further mixed in the second compartment 121. Then, the developer is supplied to the surface (i.e., the circumferential surface) of the development roller 115 while transported it in the axial direction thereof.
The casing 125 is box-shaped and is attached to the developer container 117 of the developer supply unit 114. The casing 125 and the developer container 117 together cover the development roller 115 and the like. Additionally, an opening 125a is provided in a portion of the casing 125 facing the photoreceptor drum 108.
The development roller 115 is positioned between the second compartment 121 and the photoreceptor drum 108, adjacent to the opening 125a, with the support portions 33 and 34 of the magnet roller 30 fixed to the casing 125. The development roller 115 parallels both the photoreceptor drum 108 and the developer container 117. As described above, the development roller 115 is positioned across the predetermined gap from the photoreceptor drum 108.
The doctor blade 116 is provided in an end portion of the development device 113, on the side of the photoreceptor drum 108. The doctor blade 116 attached to the casing 125 at a position across a gap from the surface of the development sleeve 132. The doctor blade 116 removes the developer from the development sleeve 132 when the amount is excessive, that is, the thickness exceeds a predetermined thickness, and returns the excessive developer to the developer container 117, thereby adjusting the amount of developer conveyed to the development area 131.
After toner and the magnetic carrier 135 therein are agitated sufficiently in the developer supply unit 114, the developer is attracted to the surface of the development sleeve 132 by the magnetic force exerted by the stationary magnetic poles. The development sleeve 132 rotates and conveys the developer attracted to the surface thereof by the multiple magnetic poles to the development range 131. Then, the doctor blade 116 adjusts the amount of the developer carried on the development sleeve 132, and then the developer is attracted to the photoreceptor drum 108. Thus, developer is carried on and transported by the development roller 115 to the development area 131, and then develops the latent image formed on the photoreceptor drum 108 into the toner image.
Further, the developer used in image development is separated from the development roller 115 and returned to the developer container 117. The used developer is agitated with the developer contained in the second compartment 121 of the developer container 117 and is again used to develop the latent image formed on the photoreceptor drum 108.
Since the development device 113 incorporates the above-described development roller 115, differences in magnetic flux density in the long size direction of the development sleeve 132, in particularly, the magnet roller 30, thus alleviating image density unevenness in the long side direction. Additionally, the rigidity of the magnet roller 30 of the development roller 115 can be secured, which can improve the durability of the development device 113.
The process cartridge 106 according to an embodiment is described with reference to
In the configuration shown in
The cartridge casing 111 is removably insertable into an apparatus body 102 and houses the charge roller 109, the photoreceptor drum 108, the cleaning blade 112, and the development device 113. The charge roller 109 charges the surface of the photoreceptor drum 108 uniformly. The photoreceptor drum 108 is positioned across a gap from a development roller 115 of the development device 113. The photoreceptor drum 108 is shaped like a round or polygonal column and rotatable about an axis. Electrostatic latent images are formed on the outer surface of the photoreceptor drum 108 by optical writing. The development device 113 develops the latent image into toner image with toner. Then the toner image is transferred from the photoreceptor drum 108 onto a sheet of recording media. The cleaning blade 112 removes any toner remaining on the surface of the photoreceptor drum 108 after image transfer.
Since the process cartridge 106 incorporates the above-described development device 113, differences in magnetic flux density in the long size direction of the development sleeve 132, in particularly, the magnet roller 30, thus alleviating image density unevenness in the long side direction. Additionally, the rigidity of the magnet roller 30 of the development roller 115 can be secured, which can improve the durability of the process cartridge 106.
The image forming apparatus according to an embodiment is described with reference to
The image forming apparatus 101 forms multicolor images on sheets 107 of recording media by superimposing yellow (Y), magenta (M), cyan (C), and black (K) single color images one on another. It is to be noted that that the suffixes Y, M, C, and K attached to the end of each reference numeral indicate only that components indicated thereby are used for forming yellow, magenta, cyan, and black images, respectively, and hereinafter may be omitted when color discrimination is not necessary.
As shown in
The apparatus body 102 is shaped like a box, and is installed on the floor, for example. The apparatus body 102 contains the sheet feeder 103, the pair of registration rollers 110, the transfer unit 104, the fixing device 105, the multiple laser writing units 122, and the multiple process cartridges 106.
For example, multiple sheet feeders 103 are provided in a lower portion of the main body 102. The sheet feeder 103 includes a sheet cassette 123 for containing multiple recording sheets 107 that can be pulled out from and retracted into the main body 102 and a feed roller 124. The feed roller 124 is pressed against the recording sheet 107 on the top in the sheet cassette 123.
The pair of registration rollers 110 is positioned in a conveyance path through which the sheet 107 is fed from the sheet feeder 103 to the transfer unit 104. The pair of registration rollers 110 clamps the sheet 107 therebetween and forwards the recording sheet 107 to the nips between the process cartridges 106 and the transfer unit 104, timed to coincide with the arrival of the image to be transferred onto the sheet 107.
The transfer unit 104 is positioned above the sheet feeders 103 and includes a driving roller 127, a driven roller 128, the conveyance belt 129, and transfer rollers 130. The driving roller 127 is positioned on a downstream side in a sheet conveyance direction and driven by a driving source such as a motor. The driven roller 128 is rotatably supported by the apparatus body 102 and positioned on an upstream side in the sheet conveyance direction. The conveyance belt 129 is an endless belt and stretched around the driving roller 127 and the driven roller 128. As the driving roller 127 rotates, the conveyance belt 129 rotates around the driving roller 127 and the driven roller 128 counterclockwise in
Each transfer roller 130 is positioned facing via the conveyance belt 129 the photoreceptor drum 108 of the corresponding process cartridge 106, and the sheet 107 is nipped therebetween. The transfer rollers 130 press the sheet 107, which is fed from the sheet feeder 103, against the photoreceptor drums 108 of the respective process cartridges 106, thereby transferring the toner images from the photoreceptor drums 108 onto the sheet 107. Then, the transfer unit 104 forwards the sheet 107 to the fixing device 105.
The fixing device 105 is positioned downstream from the transfer unit 104 in the sheet conveyance direction and includes a pair of rollers 105a and 105b that clamps the recording sheet 107 therebetween. The fixing device 105 fixes the toner image on the sheet 107, clamped between the rollers 105a and 105b, with heat and pressure.
The laser writing units 122Y, 122M, 122C, and 122K are positioned in an upper portion of the image forming apparatus 101 and provided for the process cartridges 106Y, 106M, 106C, and 106K, respectively. The laser writing units 122 direct laser beams onto the surfaces of the photoreceptor drums 108 in the respective process cartridges 106, thus forming electrostatic latent images thereon after charge rollers 109 charge the surfaces of the photoreceptor drums 108 uniformly.
The process cartridges 106 are positioned between the transfer unit 104 and the respective laser writing units 122. The process cartridges 106 are removably insertable into the apparatus body 102 and disposed parallel to each other in the sheet conveyance direction.
In the image forming apparatus 101, images can be formed as follows. Initially, the photoreceptor drum 108 starts rotating, and the charge roller 109 charges the surface of the photoreceptor drum 108 uniformly. Then, the laser writing units 122 direct the laser beams onto the surfaces of the photoreceptor drums 108, thus forming electrostatic latent images thereon. When the latent image is conveyed to a development range 131 (shown in
The toner images are then transferred onto the sheet 107 when the sheet 107 transported by the feed roller 124 and the like of the sheet feeder 103 arrives at positions between the photoreceptor drums 108 and the conveyance belt 129. The image is fixed by the fixing device 105 on the recording sheet 107, and thus the image forming apparatus 101 forms the multicolor image thereon.
Since the image forming apparatus 101 incorporates the above-described process cartridges 106, differences in magnetic flux density in the long size direction of the development sleeve 132, in particularly, the magnet roller 30, thus alleviating image density unevenness in the long side direction. Additionally, the rigidity of the magnet roller 30 of the development roller 115 can be secured, which can improve the durability of the image forming apparatus 101.
Descriptions are given below of evaluation of the magnet rollers according to the above-described embodiment, its variations, and comparative examples, different in shape, produced by injection molding.
In the evaluation, axial differences in the magnetic flux density on the body of the magnet roller, the amount by which the support portion shifts, and image density unevenness were measured. In the description below, configuration 1 corresponds to the above-described embodiment, and it is assumed that variations 1, 2, and 3 are within the scope of the embodiment in a broad sense.
The magnet rollers evaluated were produced under molding conditions (resin temperature, mold temperature, injection time, pressure, pressuring time, and cooling time) below.
(Configuration 1)
As shown in
The first support portion 33 is rod-shaped and made of SUS303. The first support portion 33 is partly buried in the body 31 (inside the end face 31a) and united integrally thereto by injection molding. The second support portion 34 is formed integrally by injection molding and constructed of a material identical to that of the roller body 32. As shown in
(Variation 1)
As described above, the magnet roller 30A according to variation 1, shown in
(Variation 2)
As described above with reference to
(Variation 3)
As described above with reference to
In the magnet roller according to comparative example 1, one of the support portions (i.e., the first support portion) is integrated with the roller body 32 by injection molding and made of a material identical to that of the roller body 32. The first support portion projects 35 mm from the end face 31a of the body 31 and has an external diameter of 6 mm. Other than that, the comparative example is similar to the above-described configuration 1. That is, in the magnet roller according to comparative example 1, the body and the pair of support portions are formed as a single unit.
In the magnet roller according to comparative example 2, similarly to the one shown in
In the magnet roller according to comparative example 3, the first support portion is constructed of SUM steel (JIS standard) sulfur-containing free-cutting steel. Other than that, the comparative example 3 is similar to the above-described configuration 1. That is, in comparative example 3, the first support portion is magnetic.
(Evaluation of Differences in Magnetic Flux Density)
The magnetic flux density was measured while a probe for measuring magnetic flux density, disposed close to the main development pole (i.e., the rare-earth magnet block) of the magnet roller, was moved along the axis P from an axial center of the magnet roller to one end where the first support portion was provided. A magnetic flux density Ba at the axial center is deducted from a maximum magnetic flux density Bb among the measured values, thereby obtaining a difference ΔB, which was evaluated according to the following criterion. When there is no value greater than the magnetic flux density Ba at the axial center, a difference (absolute value) between the magnetic flux density Ba and a value measured at one end of the body of the magnet roller was regarded as the difference ΔB.
Excellent: the difference in magnetic flux density is lower than 5 mT,
Good: the difference in magnetic flux density is lower than 6 mT, and
Bad: the difference in magnetic flux density is greater than 6 mT
(Evaluation of Shift Amount of the First Support Portion)
The magnet roller was incorporated into the image forming apparatus according to the above-described embodiment and removed therefrom after 200,000 (two hundred thousand) sheets were output. Then, the amount by which the tip of the first support portion was shifted in the direction perpendicular to the axial direction from an initial position (where the tip was before 200,000 sheets were output) was measured. The shift amount of the first support portion was measured according to the following criterion.
Good: The shift amount is less than 5 μm, and
Bad: The shift amount is 5 μm or greater
(Evaluation of image density unevenness)
After solid images were printed on A4-size sheets using the above-described image forming apparatus, image density unevenness was evaluated according to the following criterion.
Good: Image density unevenness in the axial direction of the magnet roller is not observed visually.
Bad: Image density unevenness in the axial direction of the magnet roller is observed visually.
Descriptions are given below of overall evaluation of the embodiment, the variations thereof, and the comparative examples in view of the above-described difference in magnetic flux density, the shift amount of the first support portion, and image density unevenness.
Good: no item is deemed bad, and
Bad: One or greater items are deemed bad
Respective configurations and evaluation results are shown in Table 2 below.
In Table 2, “Image density” means uniformity of image density, and “Total” means total evaluation.
From Table 2, the following can be known.
In comparative example 1, since the first support portion is constructed of plastic magnet used for the body and integrated as a single unit with the body, axial differences in the magnetic flux density on the circumferential surface of the body are greater, causing image density unevenness. Further, the shift amount of the first support portion is greater, meaning that the rigidity is not sufficient.
In comparative example 2, since the projecting part and the buried part of an identical support portion have an identical thickness, the magnetic flux density at the axial end portion is smaller than the axial center portion, thereby causing image density unevenness.
Additionally, in comparative example 2, since the first support portion is magnetic, axial differences in the magnetic flux density on the circumferential surface of the body are greater, thereby causing image density unevenness.
By contrast, in the above-described embodiment and its variations, the first support portion is nonmagnetic, and at least a part of the buried portion thereof (reduced-area portion) is smaller in cross-sectional area than the base end portion of the projecting part. Accordingly, the volume of the first axial end portion of the body can be adjusted to inhibit edge effect, thereby keeping the axial differences in the magnetic flux density on the body within a suitable range. Thus, image density unevenness can be alleviated. Additionally, when the first support portion is constructed of a nonmagnetic material (such as SUS303) having high rigidity, the shift amount of the first support portion can be reduced, securing the rigidity.
From the evaluation results, it can be known that the embodiment and its variations can reduce edge effects and axial differences in the magnetic flux density of the magnet roller, and that a material having a high rigidity can be used for the support portions 33 and 34 to secure rigidity thereof since the material can be different from that of the body 31.
Additionally, regarding the above-described embodiment, multiple magnet rollers including the buried part 332 (reduced-area portion) having external diameters different from each other were produced, and axial changes in the magnetic flux density thereof were measured. Specifically, the magnetic flux density was measured sequentially while the probe for measuring magnetic flux density disposed close to the main development pole (i.e., the rare-earth magnet block) of the magnet roller was moved axially from the center portion of the magnet roller to one end where the first support portion was provided. The magnetic flux density Ba at the axial center is deducted from the maximum magnetic flux density Bb among the measured values, thereby obtaining the difference ΔB.
It can be known from
Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-051312 | Mar 2012 | JP | national |
