This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application Nos. 2016-101803, filed on May 20, 2016, and 2017-022556, filed on Feb. 9, 2017, in the Japan Patent Office, the entire disclosure of each of which is hereby incorporated by reference herein.
Embodiments of the present disclosure generally relate to a developing device, and a process cartridge and an image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction peripheral having at least two of copying, printing, facsimile transmission, plotting, and scanning capabilities, that include the developing device.
Developing devices typically include a developing roller (i.e., a developer bearer) inside which a magnet roller is disposed and a casing having an opening. Through the opening, the developing roller is exposed and positioned opposite a photoconductor serving as a latent image bearer. Such developing devices develop a latent image on the photoconductor with powdered toner carried on the portion of the developing roller exposed from the opening.
According to an embodiment of this disclosure, a developing device includes a developer container to contain developer including toner and magnetic carrier, the developer container; a developer bearer to carry, by rotation, the developer to a developing range facing a latent image bearer; a communication opening in a wall defining the developer container; a toner conveyance passage connected to the communication opening; and a cylindrical magnet having a magnetic pole arrangement parallel to an axis of the cylindrical magnet. The cylindrical magnet is disposed such that a space enclosed by an inner face of the cylindrical magnet overlaps with the communication opening, on a cross section perpendicular to the axis of the cylindrical magnet.
In another embodiment, an image forming apparatus includes the latent image bearer to bear a latent image; and the developing device described above, to develop the latent image with the toner into a toner image.
Another embodiment provides a process cartridge to be removably installed in an image forming apparatus. The process cartridge includes the latent image bearer to bear a latent image, the developing device described above, and a holder to hold the latent image bearer and the developing device.
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:
The accompanying drawings are intended to depict embodiments of the present invention and should not be interpreted to limit the scope thereof The accompanying drawings are not to be considered as drawn to scale unless explicitly noted.
In describing 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
For example, the image forming apparatus 500 is a copier and includes a scanner 200 (i.e., an image reading device) disposed above an apparatus body 100.
The apparatus body 100 includes a process cartridge 1.
As illustrated in
The charging device 11 (i.e., a charger) includes a charging roller 11a and a removing roller 11b. A charging bias is applied to the charging roller 11a, and the charging roller 11a gives electrical charges to the surface of the photoconductor 10 to uniformly charge the photoconductor 10. The removing roller 11b removes substances, such as toner, adhering to the surface of the charging roller 11a.
The developing device 12 includes a first developer compartment V1 (a developer containing compartment), in which a first conveying screw 12b serving as a developer conveyor is disposed. The first conveying screw 12b has a spiral blade 12b 4 (illustrated in
The first and second developer compartments V1 and V2 contain two-component developer including magnetic carrier and negatively charged toner. Being rotated by a driver, the first conveying screw 12b transports the developer inside the first developer compartment V1 to the front side of the paper on which
Being rotated by the driver, the second conveying screw 12c inside the second developer compartment V2 transports the developer to the back side of the paper on which
A portion of the developer transported by the second conveying screw 12c is scooped onto the surface of the developing roller 12a due to the magnetic force exerted by the magnet roller. The developer doctor 12d is disposed across a predetermined gap from the surface of the developing roller 12a and adjusts the thickness of a layer of developer carried on the developing roller 12a, after which the developer is transported to a developing range B facing the photoconductor 10. Then, toner adheres to the electrostatic latent image on the photoconductor 10. Thus, a toner image is formed on the photoconductor 10. After the toner therein is thus consumed, the developer is returned to the second conveying screw 12c as the developing roller 12a rotates. The developer transported to the end of the second developer compartment V2 by the second conveying screw 12c is returned to the first developer compartment V1. Thus, the developer is circulated inside the developing device 12.
The developing device 12 further includes a toner concentration sensor 124 (illustrated in
Although this operation is performed to keep the density of the toner pattern (i.e., a reference pattern) on the photoconductor 10 constant, decreases in the density are inevitable when the toner bottle 20 becomes empty. In such a situation, even if the operation to supply the toner from the toner bottle 20 is executed for a certain length of time, the toner adhesion amount of the toner pattern, detected by the optical sensor, does not recover. Accordingly, in a case where the toner adhesion amount of the toner pattern, detected by the optical sensor, does not recover despite the operation to supply the toner from the toner bottle 20, a controller 60 (i.e., a determiner) illustrated in
After the toner bottle 20 is replaced in response to the determination of “toner end”, the following operation is executed to supply toner from the toner bottle 20 to the developing device 12. The developing roller 12a and the first and second conveying screws 12b and 12c illustrated in
The cleaning device 14 includes a cleaning blade 14a that contacts or abuts against the photoconductor 10 to scrape off the toner adhering to the photoconductor 10 after a transfer process. The cleaning device 14 further includes a toner collecting coil 14b disposed in a collected toner compartment W to transport the toner collected by the cleaning blade 14a. The collected toner is further transported by a toner conveyance device 50 (illustrated in
A transfer device 17 illustrated in
To make copies using the image forming apparatus 500 configured as described above, when a user presses a start button, the scanner 200 reads the contents of the document set therein. Simultaneously, a photoconductor driving motor drives the photoconductor 10, and the charging device 11 (refer to
When the user presses the start button, a pickup roller 27 sends out the sheet S (i.e., a transfer medium) from the selected sheet tray 22. One sheet S is separated from the rest by a sheet feeding roller 28 and a separation roller 29 and fed to a feeding path R1. In the feeding path R1, multiple conveyance roller pairs 30 transport the sheet S, and the sheet S is caught in a registration roller pair 23. The registration roller pair 23 forwards the sheet S to a transfer nip, where the transfer roller 16 contacts the photoconductor 10, timed to coincide with the arrival of the toner image on the photoconductor 10.
In the transfer nip, the transfer device 17 transfers the toner image onto the sheet S from the photoconductor 10. The cleaning device 14 (see
Meanwhile, the sheet S is guided to the fixing device 24. While passing between the heating roller 25 and the pressure roller 26, the sheet S is heated and pressed to fix the toner image on the sheet S. Subsequently, an ejection roller pair 31 discharges the sheet S to a sheet stack section 32.
Next, a configuration and operation of the developing device 12 illustrated in
A casing 121 illustrated in
At the downstream end of the second developer compartment V2 in the direction in which the second conveying screw 12c transports the developer, the developer moves to the first developer compartment V1, through the opening 121a at the end of the partition 122. Inside the first developer compartment V1, while stirring the developer, the first conveying screw 12b transports the developer in the direction opposite the direction in which the developer moves inside the second developer compartment V2. At the downstream end of the first developer compartment V1 in the direction in which the first conveying screw 12b transports the developer, the developer moves through the opening 121b to the second developer compartment V2. Thus, the first and second conveying screws 12b and 12c disposed in the first and second developer compartments V1 and V2, respectively, circulate the developer inside the developer containing compartment partitioned by the partition 122.
The upstream end of the first developer compartment V1 in the developer conveyance direction communicates with a toner supply passage 123. The toner supply inlet 12e is disposed in the toner supply passage 123. Through the toner supply inlet 12e, fresh toner and the toner collected by the cleaning device 14 are supplied. The first conveying screw 12b disposed in the first developer compartment V1 extends into the toner supply passage 123. The first developer compartment V1 communicates with the toner supply passage 123 through a communication opening 123a. The toner supplied from the toner supply inlet 12e is transported by the spiral blade 12b 4 (illustrated in
Descriptions are given of a mechanism for toner recycle with reference to
The toner conveyance device 50 illustrated in
Further, as illustrated in
As illustrated in
The cleaning blade 14a dams the residual toner remaining on the photoconductor 10 and removes the residual toner therefrom. The residual toner dammed up by the cleaning blade 14a is pushed by the subsequent toner on the photoconductor 10, and the dammed toner moves to the upper side of the cleaning blade 14a. The residual toner is further pushed to the collected toner compartment W and collected therein. In the collected toner compartment W, the toner collecting coil 14b conveys the collected toner toward the back end (one end in the axial direction) of the process cartridge 1.
As illustrated in
With reference to
When the value measured (detected) by the toner concentration sensor 124 illustrated in
The toner collected by the cleaning device 14 falls inside the connecting portion 14c (illustrated in
Referring to
To convey the collected toner to the waste-toner container 41, the motor 54b for opening and closing the shutter 54, illustrated in
Descriptions are given below of conveyance of the collected toner to the developing device 12, with reference
To convey the collected toner to the developing device 12, the motor 54b for opening and closing the shutter 54, illustrated in
The controller 60 controls the various devices according to control programs stored in the RAM 61 and the ROM 63. The controller 60 calculates the image area rate based on image data. Further, based on the calculated image area rate, the controller 60 controls opening and closing of the shutter 54.
Referring to
The predetermined number of sheets represents the number of sheets output in an estimated time for the toner collected by the cleaning blade 14a to reach the branching point in the collected-toner passage 55 branching into the route leading to the waste-toner container 41 and the route leading to the developing device 12. In other words, while the image forming operation is performed for outputting the predetermined number of sheets, the toner collected by the cleaning blade 14a during printing on the first page reaches the branching point. In the present embodiment, as illustrated in
As the image area rate decreases, the area of contact between the photoconductor 10 and the sheet S increases, and the possibility of adhesion of dust (e.g., paper dust) to the photoconductor 10 increases. Accordingly, when the image area rate per unit distance is smaller than the threshold (No at S2), it is a condition under which the amount of dust mixed in the collected toner is large. In this case, at S4, the shutter 54 is closed to convey the collected toner to the waste-toner container 41, and the collected toner is discarded. This is a condition under which the toner collected during printing on the predetermined number of sheets includes a large amount of dust, and the collected toner is conveyed to the waste-toner container 41 and discarded.
By contrast, when the image area rate per unit distance is equal to or greater than the threshold (Yes at S2), it is a condition under which the toner collected during printing on the predetermined number of sheets includes a small amount of dust. In this case, at S3, the shutter 54 is opened to supply the collected toner to the developing device 12 for reuse.
Although, in the above-described example, opening and closing the shutter 54 is controlled based on the image area rate per unit running distance of the developing device 12, the parameter for controlling opening and closing the shutter 54 is not limited thereto. For example, image area rate per page may be used instead. Specifically, when a predetermined number of sheets are output, the controller 60 calculates the image area rate per page based on the accumulated print area of images and the number of pages. The controller 60 controls opening and closing the shutter 54 based on the calculated image area rate per page. In the case of the image area rate per page, similarly, when the amount of dust mixed in the collected toner is large, the collected toner is conveyed to the waste-toner container 41. When the amount of dust mixed in the collected toner is small, the collected toner is conveyed to the developing device 12.
Next, a distinctive feature of the present embodiment is described below.
Inside the process cartridge 1 illustrated in
If air leaks from such connections, toner contained in the toner conveyance device 50 or the waste-toner container 41 may scatter out together with the leaking air, resulting in stains inside the image forming apparatus 500.
In view of the foregoing, in the present embodiment, the developing device 12 is designed to seal the communication opening 123a (i.e., opening on the side of the first developer compartment V1) with the developer contained inside the first developer compartment V1 to inhibit transmission of the internal pressure rise of the developing device 12 to the toner conveyance device 50. Features of the present embodiment are described in further detail below.
As illustrated in
One of the planar faces of the cylindrical magnet 130 is attached to the inner wall face 1210 of the first developer compartment V1 defining the communication opening 123a via a double-sided adhesive tape 131 as illustrated in
To seal the communication opening that connects an inside of the developing device with a toner conveyance passage outside the developing device, a bar-shaped magnet may be disposed adjacent to the communication opening. In this example, the communication opening is sealed with the magnetic ears of developer generated by the magnet. However, the magnetic force becomes weaker as the distance from the magnet increases. In a portion of the communication opening away from the magnet, sealing with the developer is weak and may be insufficient compared with a portion close to the magnet. Then, there is a risk that internal pressure rise of the developer containing compartment causes the toner to leak from the above-mentioned connections, allowing the toner to scatter.
By contrast, in the present embodiment, the cylindrical magnet 130 has the N pole on the side attached to the casing 121 and the S pole on the opposite side. Owing to this magnetic pole arrangement, as illustrated in
If the magnetic force is too strong, the developer accumulates around the magnet and inhibits rotation of the first conveying screw 12b. Then, the magnetic force causes adverse effects. The conveyance of developer may become insufficient, the developer may flow in reverse to the second conveying screw 12c, or the developer may adhere again to the developing roller. In the present embodiment, a magnet having a relatively weak magnetic force can be used, which attains the following advantage. While the adverse effects of the magnet, caused on the periphery of the magnet, can be suppressed, the developer can fill in and seal the gap between the first conveying screw 12b and the inner wall face 1210 of the casing 121 around the first conveying screw 12b. Accordingly, this structure inhibits leak of air from the connections such as the connection between the toner conveyance device 50 and the waste-toner container 41 and that between the toner conveyance device 50 and the developing device 12. Note that the position of the cylindrical magnet 130 is not limited to the inner wall face 1210 of the first developer compartment V1 defining the communication opening 123a as long as the cylindrical magnet 130 is disposed such that the space enclosed by the arc-shaped inner face of the cylindrical magnet 130 overlaps with the communication opening 123a when viewed in the axial direction of the cylindrical magnet 130. For example, the cylindrical magnet 130 can be inserted in the hole penetrating the wall of the casing 121 or the inner wall face of the toner supply passage 123 defining the communication opening 123a.
In a case where the first conveying screw 12b has a relatively small shaft diameter, the developer attracted to and adhering to the inner face of the cylindrical magnet 130 does not reach the surface of the shaft 12b0 of the first conveying screw 12b. Then, the developer fails to seal the gap between the first conveying screw 12b and the inner wall face of the casing 121 around the first conveying screw 12b. An approach to eliminate such an inconvenience may be narrowing the gap between the inner wall face of the cylindrical magnet 130 and the shaft 12b0 of the first conveying screw 12b. However, the spiral blade 12b 4 of the first conveying screw 12b is shortened if the shaft diameter of the first conveying screw 12b is increased to narrow the gap. Then, the performance of conveying toner supplied from the toner supply inlet 12e is degraded around the cylindrical magnet 130, inviting the risk of clogging of the toner supply passage 123 with toner. Keeping the dimensional accuracy of the shaft diameter is difficult.
Therefore, in the structure illustrated in
Next, variations of the first conveying screw 12b are described. The cost of the first conveying screw 12b having a magnetic shaft increases as the shaft diameter increases. Accordingly, in a variation illustrated in
While the shaft diameter is reduced by using a magnetic material for the shaft 12b0, increasing the length of the spiral blade 12b 4 of the first conveying screw 12b is required when developer having a low flow property is used. Accordingly, in another variation, as illustrated in
An experiment was performed to check the leak of air while changing the above-mentioned diameter D2 and the distance L1.
The results are presented, as either “Good” or “Poor”, in Table 1 below. “Good” means that air does not leak from the toner supply inlet 12e, and the toner supply passage 123 is not clogged with toner. “Poor” means that air leaks from the toner supply inlet 12e, or the toner supply passage 123 is clogged with toner.
In the experiment, the diameter D1 of the thin portion 132, the inner diameter D3 of the cylindrical magnet 130, the length L2 of the thick portion 133, and the tapered angle θ1 were constant as follows. The diameter D1 was 6 mm, the inner diameter D3 was 13 mm, the length L2 was 20 mm, and the tapered angle θ1 was 30 degrees. According to the results of the experiment, the leak of air is desirably suppressed by setting the distance L1 not longer than 2 mm when the diameter D2 is 11 mm and setting the distance L1 not longer than 0 mm when the diameter D2 is 9 mm. In the experiment, inhibition of leak of air was insufficient when the diameter D2 was equal to or smaller than 7 mm. Thus, according to the results of the experiment, the leak of air is desirably suppressed by setting the distance L1 to zero to 2 mm when the diameter D1 of the thin portion 132 is 6 mm and the diameter D2 of the thick portion 133 is 11 mm.
Note that, although the first conveying screw 12b used in the experiment, the results of which are presented in Table 1, has the shaft made of a nonmagnetic resin, the leak of air is more preferably inhibited when the shaft is made of a magnetic material or the shaft includes a magnetic shaft core and a resin coating covering the magnetic shaft core, as described above.
The structures described above are just examples, and the various aspects of the present specification attain respective effects as follows.
Aspect A
A developing device includes a developer container, such as the casing 121, to contain developer including toner and carrier; a developer bearer, such as the developing roller 12a, to bear the developer on a surface thereof and transport, by rotation, the developer to a developing range facing a latent image bearer, such as the photoconductor 10; a communication opening, such as the communication opening 123a, formed in a wall of the developer container; and a toner conveyance passage, such as the toner supply passage 123, to be connected to the communication opening. The developing device further includes a cylindrical magnet, such as the cylindrical magnet 130, having a magnetic pole arrangement parallel to an axis of the cylindrical magnet. The cylindrical magnet is disposed such that, on a cross section perpendicular to the axis of the cylindrical magnet, a space enclosed by an inner face of the cylindrical magnet overlaps with the communication opening.
In this aspect, the cylindrical magnet (i.e., a magnet cylinder) is used to generate the magnetic field to seal the communication opening with the magnetic ears of the developer. The lines of magnetic force exerted by the cylindrical magnet curl into and concentrating inside the cylinder. Such a cylindrical magnet is disposed with the space inside the cylinder overlapping with the communication opening as viewed in the axial direction of the cylinder. As a result, compared with the comparative example in which the bar-shaped magnet is used to generate the magnetic field to seal the communication with the magnetic ears, the communication opening can be sealed with a sufficient amount of developer even when the magnetic force of the cylindrical magnet is relatively weak. Accordingly, a magnet having a relative weak magnetic force is usable, and the adverse effects on the periphery of the magnet, caused by the magnet, can be suppressed.
Thus, this structure can preferably inhibit scattering of toner caused by internal pressure rise of the developer container while suppressing adverse effects on the periphery of the magnet, caused by the magnet.
Aspect B
In aspect A, the cylindrical magnet is disposed on an inner wall face (e.g., the inner wall face 1210) of the developer container defining the communication opening.
According to this aspect, the magnetic force lines curling from inside the cylinder generate a magnetic field to collect the developer entirely inside the cylinder. Accordingly, the communication opening can be sealed on the side of the developer container, with the developer. Accordingly, this structure can preferably inhibit scattering of toner caused by internal pressure rise of the developer container.
Aspect C
The developing device according to Aspect A or B further includes a conveying screw, such as the first conveying screw 12b, disposed in the developer container to stir and convey the developer therein. The conveying screw is inserted inside the cylindrical magnet so that the inner face of the cylindrical magnet faces the surrounds the conveying screw.
According to this aspect, the developer collected by the cylindrical magnet is magnetically retained by the magnetic ears generated in the gap between the inner face of the cylindrical magnet and the shaft (e.g., the shaft 12b0) of the conveying screw. Therefore, the gap between the shaft of the conveying screw and the communication opening is filled in, with the developer collected by the magnetic force of the cylindrical magnet. In this state, the developer container is shut off from the toner conveyance passage communicating with the communication opening, and the air is prevented from leaking out the developer container through the communication opening. Accordingly, this structure can preferably inhibit scattering of toner caused by internal pressure rise of the developer container.
Aspect D
In Aspect C, the shaft of the conveying screw is made of a magnetic material.
When the shaft of the conveying screw is made of a magnetic material, a portion of the shaft of the conveying screw facing the cylindrical magnet is magnetized by the magnetic field, and the developer is attracted and adheres to the magnetized portion of the shaft. With this structure, compared with a case where the conveying screw has a shaft made of a nonmagnetic material, the gap between the shaft of the conveying screw and the cylindrical magnet is preferably filled with the developer even when the shaft is relatively thin.
Aspect E
In Aspect C or D, the shaft of the conveying screw includes a magnetic portion, such as the magnetic shaft core 12b1, and a nonmagnetic coating, such as the coating 12b2, covering the magnetic portion.
According to this aspect, the diameter of the shaft is adjustable by the thickness of the coating 12b2 at a relatively low cost. With this structure, compared with a case where the conveying screw has a shaft made of a nonmagnetic material, the gap between the shaft of the conveying screw and the cylindrical magnet is preferably filled with the developer even when the shaft is relatively thin.
Aspect F
In any one of Aspects C through E, the conveying screw includes a first portion (e.g., the thin portion 132) having a first diameter and a second portion (e.g., the thick portion 133) having a second diameter larger than the first diameter. When the first diameter is 6 mm and the second diameter is 11 mm, a distance (e.g., the distance L1) from the cylindrical magnet to an end (e.g., the end 133E) of the second portion on the side of the cylindrical magnet in the axial direction of the conveying screw is 0 to 2 mm.
According to this aspect, while the conveying screw has the first portion having a smaller shaft diameter and a wider spiral blade (length of the blade in the direction extending from the shaft to the contour of the conveying screw is larger), the developer desirably seals the clearance between the conveying screw and the inner wall face of the developer container surrounding the conveying screw.
Aspect G
An image forming apparatus includes a latent image bearer, such as the photoconductor 10, and the developing device, such as the developing device 12, according to any one of Aspects A through F, to develop a latent image on the latent image bearer with the toner into a toner image.
This aspect prevents or reduces stains with toner inside the image forming apparatus.
Aspect H
The image forming apparatus according to Aspect G includes a transfer device, such as the transfer device 17, to transfer the toner image from the latent image bearer onto a transfer medium; a cleaning device, such as the cleaning device 14, to collect a substance (including toner) adhering to a surface of the latent image bearer after transferring of the toner image; a toner conveyance device, such as the toner conveyance device 50, to supply toner to the developing device; and a waste-toner container, such as the waste-toner container 41, to store waste toner collected by the cleaning device. The toner conveyance device includes a collected-toner passage (e.g., the collected-toner passage 55) to convey the toner collected by the cleaning device. The collected-toner passage branches into a waste-toner passage (e.g., the waste-toner passage 56) coupled to the waste-toner container and a collected-toner supply passage (e.g., the collected-toner supply passage 52) coupled to the toner conveyance passage (e.g., the toner supply passage 123) to supply toner to the developing device. The image forming apparatus further includes a passage selector (e.g., the shutter 54) to guide the collected toner inside the collected-toner passage to one of the collected-toner supply passage and the waste-toner passage.
According to this aspect, under such a condition that the toner collected by the cleaning device includes a large amount of dust (e.g., paper dust), the collected toner is conveyed to the waste-toner container 41. Thus, introduction of dust into the developing device is inhibited. By contrast, under such a condition that the amount of dust mixed in the collected toner is small, the collected toner is conveyed to the developing device 12. Thus, the collected toner is reused, thereby reducing the consumption of toner.
In this aspect, although the developing device is coupled, via the collected-toner passage, to the waste-toner container, the communication opening between the developing device and the collected-toner passage is sealed with the developer. Accordingly, a rise of pressure inside the developing device is not transmitted via the collected-toner passage to the waste-toner container. This aspect inhibits leak of toner, together with air, from the connection between the toner conveyance device and the waste-toner container. Accordingly, the waste toner inside the waste-toner container is prevented from scattering inside the image forming apparatus and from contaminating the interior of the image forming apparatus.
Aspect N
A process cartridge that is removably installable in an image forming apparatus includes at least the latent image bearer to bear a latent image, the developing device according to any one of Aspects A through C, and a holder, such as the common holder 1A, to hold, at least, the latent image bearer and the developing device.
With use of the process cartridge according to this aspect, contamination with toner inside the image forming apparatus is inhibited.
The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention.
Number | Date | Country | Kind |
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2016-101803 | May 2016 | JP | national |
2017-022556 | Feb 2017 | JP | national |
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Number | Date | Country | |
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20170336733 A1 | Nov 2017 | US |