Patent Application
20100129110
The present invention relates to a developing device used in an electrophotographic image forming apparatus or the like, such as a laser beam printer or a copying machine and relates to a process cartridge including the developing device.
In an image forming apparatus using electrophotography, when its operation time is increased, there arise needs for exchange of a photosensitive drum, supply and exchange of a developer, and adjustment, cleaning and exchange of other devices (such as a charging device and a cleaning device). It was difficult for persons; other than a service person with expertise, to perform a maintenance operation of such process means. In order to eliminate the difficulty, a process cartridge integrally including image forming means, as a cartridge, such as the photosensitive drum, the developing device, the cleaning device, or the like has been put into practical use. As a result, in the case where there arose the need for the maintenance of the process means, a user himself (herself) was able to easily perform the maintenance and the exchange, thus being able to obtain a high-quality image inexpensively and easily. Such a process cartridge is provided with, e.g., a stirring member a developer stirring device in a developer container as a developer accommodating portion and drives the stirring member by transmitting a driving force from the outside of the container through a gear or the like. In order to transmit the driving force to the stirring member, a wall of the developer container is provided with a through hole through which one end portion of the stirring member passes and is connected to the gear located outside the container. For that reason, there is a possibility of an occurrence of leakage of the developer (toner) from the through hole portion. In view of the possibility, the toner leakage has been conventionally prevented by mounting a seal member having a lip portion contacting a full circumferential surface of a shaft of the stirring member (a portion contacting the shaft at an inner peripheral portion of a ring-like seal member) to the developer container.
However, in recent years, the image forming apparatus further improved in productivity and space saving has been required than ever. Also in the process cartridge, in order to meet a high-speed image forming process, the stirring member has been rotated at a speed higher than an conventional speed. Further, not only downsizing of the image forming apparatus but also downsizing of the process cartridge have been required. In order to downsize the process cartridge, a decrease in outer diameter of the above-described stirring member is effective. However, when the outer diameter of the stirring member is decreased, stirring and feeding properties with respect to the developer are lowered. In order to prevent the lowering in stirring and feeding properties, it is necessary to compensate for the lowered stirring and feeding properties by increasing the number of rotation of the stirring member. Thus, in recent years, the stirring member in the process cartridge has been rotated at a still higher speed than the conventional speed. However, when the stirring member is rotated at the high speed, the lip portion of the stirring member is abraded in a short time, so that a sealing property cannot be maintained. As described above, the image forming apparatus required to achieve the high productivity is simultaneously required to achieve a high durability in many cases, so that it becomes difficult to satisfy the required durability by the above-described contact-type seal member alone.
On the other hand, a sealing constituting using a magnet has also been known. In this constitution, a ring-like magnet (ring magnet) is provided by being passed through an end portion of the stirring member. A shaft portion of the stirring member facing an inner peripheral surface of the ring magnet is formed with a magnetic member to generate a magnetic field in a gap between the shaft portion of the stirring member and the ring magnet. The gap is filled with a magnetic developer by collecting the magnetic developer in the gap, thus performing sealing. However, even in the case of such magnetic sealing, when the number of rotation of the stirring member is increased, there arises a problem that toner contained in the developer is melted by frictional heat generated between the collected developer and the shaft portion of the stirring member and then is solidified again to cause locking of the stirring member. In order to solve this problem, weakening of a magnetic force of the magnetic is effective but simultaneously causes a lowering in sealing property, so that it is also difficult to satisfy the required durability.
In order to ensure the sealing property more reliably, a sealing constitution employing a magnetic sealing using a magnetic in combination with the seal member having the lip portion has been proposed (e.g., Japanese Laid-Open Patent Application (JP-A) Hei 11-296051).
However, in the case where the sealing is performed by using both of the magnetic member and the seal member as in JP-A Hei 11-296051, when the magnetic member and the seal member are provided adjacently to each other in order to downsize a developing device, the following problem arises. That is, an end of the lip portion of the seal member is buried in the collected magnetic powder (developer) and receives pressure from the magnetic powder which is about to be restored with respect to a direction along magnetic lines of force. In this case, a force by which the toner enters between the lip portion end and an outer peripheral surface (sealing surface) of a shaft member is increased. When the toner once enters between the lip portion end and the outer peripheral surface (sealing surface) of the shaft member, the toner acts like an abrading material in a gap created between the lip portion of the seal member fixed to the toner container and the outer peripheral surface of the shaft member which is in rotational motion, so that abrasion of the lip portion end is accelerated. When the abrasion of the lip portion end progresses, the lip portion end cannot retain a contact state with the outer peripheral surface of the shaft member, so that the toner leaks out of the created gap and reaches a shaft-supporting portion. In the case of a sliding shaft-supporting member, the toner melted by heat generated due to friction between the shaft member and the shaft-supporting member is solidified again, so that the stirring member is locked. In the case of a rolling ball shaft-supporting member (bearing), the toner enters the bearing, so that locking of the bearing is also caused to occur. In order to solve the above-described problem, it is considered that the lip portion of the seal member is disposed at a position in which the lip portion does not receive pressure from the magnetic powder collected by the magnetic member or is disposed so that the magnetic member and the seal member are spaced apart from each other with a distance such that an influence therebetween is negligible. However, a space with respect to a shaft direction of the stirring member is required correspondingly to the distance (gap) between the magnetic member and the seal member, so that elongation and increasing in size of a unit are caused to occur.
A principal object of the present invention is to provide a developing device capable of suppressing abrasion of an end of a seal member by magnetic powder collected by a magnetic member even when the magnetic member and the seal member are disposed closely to each other in order to realize downsizing of the developing device.
According to an aspect of the present invention, there is provided a developing device for developing with a developer a latent image formed on an image bearing member, the developing device comprising:
a container for containing the developer;
a stirring member, rotatably supported by the container, for stirring the developer in the container;
a magnetic member for forming a magnetic field in a gap between the container and a rotation shaft located at an end portion of the stirring member so as to magnetically confine magnetic particles in the gap;
a seal member, provided outside the magnetic member with respect to a rotation shaft direction of the stirring member, contacting a peripheral surface of the rotation shaft of the stirring member; and
a non-magnetic preventing portion, provided between the magnetic member and the seal member, for preventing the magnetic particles confined by the magnetic member from spreading toward the seal member.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
Hereinbelow, embodiments of the present invention will be described with reference to the drawings. Incidentally, it should be understood that dimensions, materials, shapes, relative positions, and the like of constituent elements of a developing device are not limited to those in the following embodiments unless otherwise specified.
In
Recording paper accommodated in a cassette 1 reaches, after being fed by a sheet feeding portion 2, registration rollers 3 by which oblique movement or the like of the recording paper is corrected, and then is sent toward a transfer belt 4 with appropriate timing. During this period, in accordance with an image information signal sent from an unshown image reading device or an output device (not shown) of a computer, latent images for respective color toner images are formed on photosensitive drums 11Y, 11M, 11C and 11K, respectively, as an image bearing member.
On the other hand, the recording paper sent from the registration rollers 3 is electrostatically attracted on (adsorbed by) the transfer belt 4 by which the recording paper is conveyed while passing under the respective color image forming portions 10Y, 10M, 10C and 10K.
At the respective image forming portions 10Y, 10M, 10C and 10K, exposure LED heads 12Y, 12M, 12C and 12K are disposed around the photosensitive drums 11Y, 11M, 11C and 11K, respectively. Further, around the photosensitive drums 11Y, 11M, 11C and 11K, developing devices 13Y, 13M, 13C and 13K and injection charging devices 14Y, 14M, 14C and 14K are disposed. The respective color toner images are formed on the surfaces of the photosensitive drums 11Y, 11M, 11C and 11K by an electrophotographic process. That is, the surfaces of the photosensitive drums 11Y, 11M, 11C and 11K are electrically charged to a predetermined potential by the injection charging devices 14Y, 14M, 14C and 14K. The charged surfaces of the photosensitive drums 11Y, 11M, 11C and 11K are exposed to light by the exposure LED heads 12Y, 12M, 12C and 12K, so that latent images are formed on the photosensitive drums 11Y, 11M, 11C and 11K. The latent images formed on the photosensitive drums 11Y, 11M, 11C and 11K are developed by the developing devices 13Y, 13M, 13C and 13K, so that the respective color toner images are formed.
Then, the respective color toner images are successively transferred onto the recording paper by the action of transfer means 5Y, 5M, 5C and 5K at transfer portions where the transfer belt comes close to the photosensitive drums 11Y, 11M, 11C and 11K.
The recording paper on which the four color toner images are transferred is separated from the transfer belt 4 by curvature and is conveyed to a fixing portion 6. The recording paper is heated and pressed at the fixing portion 6, so that the toner images are fixed on the recording paper. Thereafter, the recording paper is discharged on a sheet discharge tray 7, so that a copying operation is completed.
Next, a process cartridge 21 will be described with reference to
The process cartridge 21 is constituted by the photosensitive drum 11, the developing device 13, and the injection charging device 14 which are integrally supported through kit side plates 22 and 23 as shown in
The photosensitive drum 11 is not positioned to the kit side plates 22 and 23 but is positioned by being engaged with a drum shaft 51 when the photosensitive drum 11 is mounted in the apparatus main assembly. On the other hand, the developing device 13 and the injection charging device 14 are fixed to the kit side plates 22 and 23. Shaft supporting portions 24 and 25 of the kit side plates 22 and 23 are engaged with the drum shaft 51 and further a pin 23a projected from the kit side plate 23 is engaged in a minor diameter portion of an elongated hole portion 52a provided to a main assembly side plate 52, so that positioning among the kit side plates 22 and 23, the developing device 13, and the injection charging device 14 is performed.
A developing sleeve 13a of the developing device 13 and an injection sleeve 14a of the injection charging device 14 are assembled to the kit side plates 22 and 23 after a distance between the shaft supporting portion 24 and each of the sleeves 13a and 14a and a distance between the shaft supporting portion 25 and each of the sleeves 13a and 14a are adjusted with high precision. As a result, the developing sleeve 13a and the injection sleeve 14a are positioned to the drum shaft 51 with respect to a radial direction with high precision when the process cartridge 21 is mounted in the apparatus main assembly. Further, the photosensitive drum 11 is also positioned to the drum shaft 51, so that a clearance (SD gap) between the photosensitive drum 11 surface and each of the developing sleeve 13a and the injection sleeve 14a is set with high precision.
Driving shafts 81 and 91 shown in
Next, with reference to
In this embodiment, the developing device 13 includes a housing 33 as a developing container for containing the developer. The housing 33 is located oppositely to the photosensitive drum 11 as an image bearing member through an opening 34, at which the developing sleeve 13a as a developer carrying member is rotatably disposed. The housing 33 includes a developing chamber disposed closely to the developing sleeve 13a and a stirring chamber 16 disposed apart from the developing sleeve 13a. The developing chamber 15 and the stirring chamber 16 are partitioned by a partition wall 17. In a first feeding path 26 formed in the developing chamber provided in the developing container, a front-side stirring shaft, i.e., a first developer stirring member 31 is disposed in substantially parallel to a shaft line of the developing sleeve 13a. In a second feeding path 27 formed in the stirring chamber 16, a rear-side stirring shaft, i.e., a second developer stirring member 32 is disposed in substantially parallel to the shaft line of the developing sleeve 13a. These two (first and second) stirring members 31 and 32 circulatively feed the developer while stirring the developer in the developing chamber 15 and the stirring chamber 16, i.e., the first feeding path 26 and the second feeding path 27, respectively. Referring to
As shown in
The contact seal member 37 is formed with an elastic member such as a nitrile rubber or the like and is provided with a lip portion (contact portion) which contacts a circumferential shaft surface of a seal portion of the associated first or second developer stirring member 31 or 32. By linear contact between the lip portions and the associated seal portions of the first and second developer stirring members 31 and 32, inclusion of the toner therebetween is prevented. A cylindrical surface of the contact seal holder 38 in which the contact seal member 37 is engaged has a diameter larger than that of an outer peripheral surface of the contact seal member 37 by about several tens of microns. The contact seal member 37 and the contact seal holder 38 are fixed to each other by press-fitting engagement. Each of the ring magnet 30 and the contact seal holder 38 in which the contact seal member 37 is assembled is engaged and positioned at a cylindrical (inner) surface of the seal housing 20.
The contact seal holder 38 is provided with a projection projected toward the ring magnet 30. The projection runs against the ring magnet 30, so that a relative position between the ring magnet 30 and the contact seal member 37 is regulated. Further, by the projection, a space in which the developer is accommodatable between the ring magnet 30 and the contact seal member 37 is formed with respect to each of the shaft line directions of the first and second developer stirring members 31 and 32. By this space, the developer is temporarily accommodatable even when the developer confined by the ring magnet 30 leaks toward the contact seal member side.
A position of the seal unit 41 with respect to the shaft direction is regulated by regulating the end surface of the bearing 40 by each of the end surfaces of the driving gears 35 and 36 positions of which with respect to the shaft direction are regulated with an associated E-shaped metal member. The ring magnet 30 is disposed oppositely to the peripheral shaft surface of the associated first or second developer stirring member 31 or 32 with a predetermined gap. At a position where the inner peripheral surface of the ring magnet 30 and the core metal of the associated first or second developer stirring member 31 or 32 oppose each other, a magnetic field is formed therebetween. The magnetic developer is magnetically confined by the magnetic field generated from the ring magnet 30, thus being prevented from leaking out to the outside of the housing 33 through the associated through hole 28 or 29. Each of inner diameters of the through holes 28 and 29 and the through holes provided in the seal housings 20 is set to be smaller than an inner diameter of the ring magnet 30, so that a wall surface is formed with respect to the developer collected at the inner peripheral surface of the ring magnet 30. For example, in this embodiment, the inner diameter of the ring magnet 30 is 6.8 mm and on the other hand, the inner diameters of the through holes 28 and 29 and the through holes provided to the seal housings 20 are 5 mm. This is because the magnetic developer as magnetic particles collected at the inner peripheral surface of the ring magnet 30 can be prevented from erecting and spreading along the magnetic lines of force. As a result, the developer collected by the ring magnet 30 can be concentrated at the position in which the core metal and the inner peripheral surface of the ring magnet 30 oppose each other, so that the sealing property of the magnetic sealing can be improved. On the other hand, with respect to the rotation shaft line direction of the stirring member, a wall portion 39 as a preventing portion is provided between the ring magnet 30 and the contact seal member 37. The wall portion 39 in the present invention is formed with a non-magnetic member so as not to attract the magnetic developer collected by the magnetic lines of force of the ring magnet 30. In this embodiment, the wall portion 39 is formed integrally with the contact seal holder 38.
The wall portion 39 prevents, as described above, the developer collected by the ring magnet 30 from erecting along the magnetic lines of force and preventing the magnetic particles from spreading toward the outside of the developing container with respect to the rotation shaft line direction. As a result, pressure application to the lip portion of the contact seal member 37 by the contact of the magnetic particles with the lip portion is prevented.
Thus, even when the ring magnet 30 and the contact seal member 37 are provided adjacently to each other, a force for causing the developer collected by the ring magnet 30 to enter between the contact seal member 37 and the associated first or second stirring member 31 or 32 is reduced. As a result, durability of the contact seal member 37 is improved.
An effect of the wall portion 39 will be described with reference to
As described above, according to this embodiment, even when the constitution in which the ring magnet 30 and the contact seal member 37 are brought near to each other is employed, interference of the magnetic developer confined by the ring magnet 30 with the contact seal member 37 can be suppressed.
A larger effect of the wall portion 39 can be expected with a smaller gap between the wall portion 39 and the core metal of the associated first or second developer stirring member 31 or 32. The gap is set at 0.5 mm in this embodiment. That is, the following relationship is satisfied. With respect to a radial direction of each of the rotation shafts of the first and second developer stirring members 31 and 32, the gap between the wall portion 39 and the core metal of each of the first and second developer stirring members 31 and 32 is smaller than the gap between the ring magnet 30 and the core metal of each of the first and second developer stirring members 31 and 32.
The above-described ring magnet 30 is adjusted in magnetic force so as not to cause the locking by the toner melted at the magnetic sealing portion even when the first and second developer stirring members 31 and 32 are rotated at a high speed for a long time. For example, in this embodiment, a peak value of magnetic flux density at a center of the inner circumferential surface of the ring magnet 30 is set at 40 to 45 mT.
As described above, by juxtaposing the magnetic seal member constituted by the ring magnet 30 and the contact seal member 37, good durability is obtained through respective sealing effects of the magnetic seal member and the contact seal member 37 even in the case where the stirring members are rotated at high speeds. In addition, by providing the wall portion 39 between the ring magnet 30 and the contact seal member 37, it is possible to prevent the lowering in durability of the contact seal member 37 due to the influence of the developer collected by the magnetic seal member.
Incidentally, in this embodiment, the case where the core metals of the first and second developer stirring members 31 and 32 are constituted by the magnetic metal is described but the present invention is not limited thereto. For example, it is also possible to employ a constitution in which the core metal portion is also constituted by the resin material and is molded integrally with a sleeve member formed of the magnetic metal at a position where the core metal opposes the ring magnet 30 to form the magnetic field between the ring magnet 30 and the core metal.
In this embodiment, one side of each of the first and second developer stirring members 31 and 32 is described, it is possible to apply a similar sealing constitution to also the other side of each of the first and second developer stirring members 31 and 32.
Further, in this embodiment, the developer sealing constitution is described by taking the developing device as an example but the present invention is also suitably applicable to other units of the image forming apparatus. For example, the sealing constitution is also applicable to the injection charging device, a cleaning unit, collected toner feeding unit, a toner supply unit, and the like.
While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purpose of the improvements or the scope of the following claims.
This application claims priority from Japanese Patent Application No. 301213/2008 filed Nov. 26, 2008, which is hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-301213 | Nov 2008 | JP | national |
