Patent Grant
10248069
The present invention relates to a developing apparatus used in an image forming apparatus adopting an electro-photographic system or an electrostatic recording system.
Hitherto, image forming apparatuses adopting an electro-photographic system are widely applied as copying machines, printers, plotters, facsimiles, and multifunction machines having a plurality of these functions. In these types of image forming apparatuses, toner charged in a developing apparatus is approximated to an image bearing member, and the toner is electrostatically attached to an electrostatic latent image on the image bearing member to develop the image, by which the image is formed. A developing apparatus is disposed in the image forming apparatus to develop the electrostatic latent image. A two-component developer including toner and carrier is used to develop the image in the developing apparatus, and the toner image is obtained by transferring toner from the developer borne on a developer bearing member to an electrostatic latent image on the image bearing member. The developer in the developing apparatus is conveyed by a conveyance screw serving as one example of an agitating conveyance member. At that time, toner density is detected by a density detection unit, such as a toner density detection sensor. A control unit of the image forming apparatus supplies the developer to the developing apparatus to realize an appropriate toner quantity based on the detected toner density.
A bulk density of toner within the developer is varied by fluctuation of surrounding environment and toner charge quantity, by which a detection result of the density detection unit may vary and erroneous detection may be output even in a state where the toner density is fixed. Therefore, stable conveyance of developer must be performed at a portion facing a detection surface of the density detection unit, and a plate-like agitating member may be disposed at a portion of the conveyance screw facing the detection surface of the density detection unit.
However, a gap is formed between the detection surface of the density detection unit and the agitating member of the developing apparatus, and the developer existing in the gap may be pressed onto the detection surface of the density detection unit at an end portion of the agitating member, causing accumulation of the developer. The bulk density of the accumulated developer is greater than the developer surrounding the accumulated developer and being conveyed, and the density detection unit may output erroneous detection. Especially if fluidity of the developer is reduced by long term use, the possibility of occurrence of erroneous detection is increased.
Recently, in order to downsize the image forming apparatus, there are cases where a density detection unit is disposed below a developer container. The lower the position of the density detection unit is, the more difficult it becomes to agitate and convey the developer on the detection surface of the density detection unit, and erroneous detection tends to be induced. If the density detection unit performs erroneous detection as described above, it may become impossible to maintain an appropriate toner charge quantity, and image defects such as fogging may be induced. In order to solve this problem, a technique is developed (refer to Japanese Unexamined Patent Application Publication No. 2011-22514) in which a magnetic plate is provided on an agitating member, a magnetic brush is formed by the magnetic carrier in the developer, and the magnetic brush is used to remove developer accumulation at a portion facing the detection surface of a density detection unit.
However, in the developing apparatus of the above-described Japanese Unexamined Patent Application Publication No. 2011-22514, a magnetic plate is provided on the agitating member, such that a fragment of the magnetic plate may be mixed into the developer, and abnormal image may occur. Further, since a magnetic plate is provided on the agitating member, the density detection unit detects the magnetic plate itself, and detection accuracy may be deteriorated. Moreover, since the magnetic plate is provided on the agitating member, costs may be raised by the addition of components. According to the above drawbacks, there were demands for a developing apparatus capable of removing accumulation of developer on the detection surface of the density detection unit, and enabling highly accurate detection of developer density.
According to one aspect of the present invention, a developing apparatus including a developer container configured to store a developer containing toner and carrier, a conveyance portion comprising a shaft portion supported rotatably within the developer container, and a conveying blade configured to rotate integrally with the shaft portion and convey the developer within the developer container in a conveyance direction of the developer along rotation of the shaft portion, a density detection unit arranged such that a detection surface exposed inside the developer container faces the conveyance portion, and configured to detect a density of the toner in the developer conveyed inside the developer container, and a projected portion projected from the shaft portion in a radial direction of the shaft portion such that a position of the projected portion overlaps with the detection surface in an axial direction of the shaft portion. The projected portion is shaped such that a part between both end portions of the projected portion in the axial direction is positioned upstream in a direction of rotation of the conveyance portion than the both end portions.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Now, an embodiment of the present invention will be described in detail with reference to
As illustrated in
The image forming portion 40 includes image forming units 50y, 50m, 50c and 50k, toner bottles 41y, 41m, 41c and 41k, exposing units 42y, 42m, 42c and 42k, an intermediate transfer unit 44, a secondary transfer portion 45, and a fixing portion 46. The image forming portion 40 is configured to form an image on a sheet S based on image information. The image forming apparatus 1 of the present embodiment corresponds to a full-color image, and the image forming units 50y, 50m, 50c and 50k are provided individually with a similar configuration for the four respective colors of yellow (y), magenta (m), cyan (c) and black (k). Therefore, color identifiers are added after the reference numbers for the respective configuration of the four toner colors in
In the present embodiment, a two-component developer, which is a mixture of nonmagnetic toner having negative chargeability and magnetic carrier, is used as developer. Toner can be generated by including coloring agents, wax components and so on in resin such as polyester or styrene, and grinding or polymerizing the same. A carrier is generated by applying a resin coating to a surface layer of a core composed of ferrite particles or resin particles formed by kneading magnetic powder.
The image forming unit 50 includes four image forming units 50y, 50m, 50c and 50k configured to form toner images of four colors. The respective image forming units 50 are equipped with a photosensitive drum 51 (51y, 51m, 51c and 51k) configured to form toner images, a charging roller 52 (52y, 52m, 52c and 52k), a developing apparatus 20 (20y, 20m, 20c and 20k), and a cleaning blade 59 (59y, 59m, 59c and 59k).
The photosensitive drum 51 has a photosensitive layer designed to have negative charging polarity arranged on an outer circumference surface of an aluminum cylinder, and rotates in a direction of an arrow at a predetermined processing speed (peripheral speed). The charging roller 52 contacts the surface of the photosensitive drum 51, and charges the surface of the photosensitive drum 51 uniformly. After the charge, an electrostatic image based on image information via the exposing units 42y, 42m, 42c and 42k is formed on the surface of the photosensitive drum 51. The photosensitive drum 51 bears the formed electrostatic image and rotates, by which the image is developed by toner in the developing apparatus 20. The detailed configuration of the developing apparatus 20 will be described later.
The developed toner image is primarily transferred to the intermediate transfer belt 44b described later. After primary transfer, the surface of the photosensitive drum 51 is discharged by a pre-exposure portion not shown. The cleaning blade 59 is arranged to contact the surface of the photosensitive drum 51, and cleans residuals such as transfer residual toner remaining on the surface of the photosensitive drum 51 after primary transfer.
The intermediate transfer unit 44 is arranged below the image forming units 50y, 50m, 50c and 50k. The intermediate transfer unit 44 includes a plurality of rollers such as a driving roller 44a, a driven roller 44d, and primary transfer rollers 44y, 44m, 44c and 44k, and an intermediate transfer belt 44b wound around these rollers. The primary transfer rollers 44y, 44m, 44c and 44k are respectively arranged to face the photosensitive drums 51y, 51m, 51c and 51k, and abutted against the intermediate transfer belt 44b.
By applying a transfer bias of positive polarity to the intermediate transfer belt 44b from the primary transfer rollers 44y, 44m, 44c and 44k, toner images having negative polarity formed on the photosensitive drums 51y, 51m, 51c and 51k are sequentially transferred to the intermediate transfer belt 44b in a superposed manner. The intermediate transfer belt 44b receives transfer of toner images formed by developing the electrostatic images on the surface of the photosensitive drums 51y, 51m, 51c and 51k, and moves.
The secondary transfer portion 45 includes a secondary transfer inner roller 45a and a secondary transfer outer roller 45b. In a state where a secondary transfer bias of positive polarity is applied to the secondary transfer outer roller 45b, a full-color image formed on the intermediate transfer belt 44b is transferred to the sheet S. The fixing portion 46 includes a fixing roller 46a and a pressure roller 46b. A sheet S is nipped and conveyed between the fixing roller 46a and the pressure roller 46b, by which the toner image transferred to the sheet S is heated and pressed, and fixed to the sheet S.
The controller 70 is configured of a computer, and as illustrated in
Now, an image forming operation according to the image forming apparatus 1 adopting the above configuration will be described.
As illustrated in
Meanwhile, along with the operation of forming the toner image, an uppermost sheet S in a sheet cassette is separated and fed. At a matched timing with the toner image on the intermediate transfer belt 44b, the sheet S is conveyed through a conveyance path to the secondary transfer portion 45. Further, image is transferred from the intermediate transfer belt 44b to the sheet S, and the sheet S is conveyed to the fixing portion 46, where unfixed toner image is heated and pressed and fixed to the surface of the sheet S, before the sheet S is discharged from the apparatus body 10.
Next, the developing apparatus 20 will be described in detail with reference to
The developer container 21 includes a partition wall 27 arranged approximately at a center portion and extending in a longitudinal direction. The developer container 21 is divided in a horizontal direction by the partition wall 27 into a developing chamber 21b and an agitating chamber 21c. The developer is stored in the developing chamber 21b and the agitating chamber 21c. The developing chamber 21b supplies the developer to the developing sleeve 24. The agitating chamber 21c is communicated with the developing chamber 21b, and the developer from the developing sleeve 24 is collected and agitated. Two communicating portions 27a and 27b are formed on both ends of the partition wall 27 formed between the developing chamber 21b and the agitating chamber 21c, communicating the developing chamber 21b and the agitating chamber 21c. According to the developing apparatus 20 of the present embodiment, the developing chamber 21b and the agitating chamber 21c are arranged in the horizontal direction, but the arrangement is not restricted thereto, and the developing apparatus can be formed in other ways, such as the developing chamber and the agitating chamber being arranged one above the other.
The first conveyance screw 22 is arranged in the developing chamber 21b substantially in parallel with the developing sleeve 24, and conveys the developer in the developing chamber 21b while agitating the developer. The first conveyance screw 22 includes a shaft portion 22a disposed rotatably in the developer container 21 with its axial direction Da arranged in a longitudinal direction, and a spiral-shaped conveying blade 22b rotated integrally with the shaft portion 22a and conveying the developer within the developer container 21 to a conveyance direction D1 of the developer along rotation.
The second conveyance screw 23 is arranged within the agitating chamber 21c approximately in parallel with the first conveyance screw 22, and conveys the developer within the agitating chamber 21c to an opposite direction as the first conveyance screw 22. The second conveyance screw 23 includes a shaft portion 23a disposed rotatably in the developer container 21, and a spiral-shaped conveying blade 23b rotated integrally with the shaft portion 23a and conveying the developer within the developer container 21 to the conveyance direction D1 along rotation. The developing chamber 21b and the agitating chamber 21c constitute a circulation path of the developer for conveying the developer while agitating the developer. The toner being agitated by the respective screws 22 and 23 is frictionally electrified to negative polarity by being rubbed with the carrier.
A return screw 23c is provided on a downstream end portion of the second conveyance screw 23 in the conveyance direction D1. A return screw 23c conveys the developer to a direction opposite to the conveyance direction D1 along rotation. In the agitating chamber 21c, a large part of the developer conveyed from the upstream side is pushed back by the return screw 23c and conveyed from the communicating portion 27a to the developing chamber 21b. A discharge port opening downward is formed on a downstream end portion of the agitating chamber 21c in the conveyance direction D1 of the developer, and the excessive developer in the agitating chamber 21c is pushed over the return screw 23c and discharged through the discharge port 29 to a discharge device not shown.
A supply port 28 opening upward is formed at an upstream end portion of the agitating chamber 21c in the conveyance direction D1 of the developer, and a hopper 41a of a toner bottle 41 is connected to the supply port 28. The hopper 41a stores a two-component developer for replenishment in which toner and carrier are mixed (usually, the ratio of toner/developer for replenishment is 100% through 80%). The toner supplied from the toner bottle 41 is replenished from the hopper 41a via the supply port 28 to the agitating chamber 21c. The hopper 41a has a screw-shaped replenishing screw not shown disposed at a lower portion therein, by which the developer can be supplied from the replenishing screw to the supply port 28. The amount of the replenishment developer replenished from the hopper 41a to the developer container 21 is roughly determined by the number of rotations of the replenishing screw. The number of rotations is determined by the controller 70 based on, for example, a video count value of image data or the detection result of the density detection sensor 75 disposed in the developer container 21.
The developing sleeve 24 bears the developer including nonmagnetic toner and magnetic carrier, and conveys the developer to an image developing region facing the photosensitive drum 51. The developing sleeve 24 is formed of a nonmagnetic material such as aluminum and nonmagnetic stainless steel, and in the present embodiment, it is formed of aluminum. A roller-shaped magnet roller 24m is disposed in a fixed manner in a non-rotating state with respect to the developer container 21 on the inner side of the developing sleeve 24. The magnet roller 24m has a plurality of magnetic poles N1, S1, N2, S2 and N3 on the surface thereof.
The developer within the developing apparatus 20 is borne on the developing sleeve 24 by the magnet roller 24m. Thereafter, layer thickness of the developer on the developing sleeve 24 is regulated by the regulation member 25, and along the rotation of the developing sleeve 24, the developer is conveyed to the image developing region facing the photosensitive drum 51. In the image developing region, the developer on the developing sleeve 24 is raised in a bristle state, and forms magnetic bristles. In a state where the magnetic bristles are in contact with the photosensitive drum 51, the toner is supplied to the photosensitive drum 51, and the electrostatic latent image on the photosensitive drum 51 is developed as toner image.
The density detection sensor 75 is attached to an outer side of the developer container 21, and arranged such that a detection surface 75a is exposed to an inner side of the developer container 21 through a through-hole 21d (refer to
In the present embodiment, a permeability sensor is used as the density detection sensor 75. The permeability sensor determines the density of the toner in the developer (referred to also as a ‘toner density’ hereinafter) by detecting an apparent change of permeability of the developer (detecting inductance) that drops if the toner density of the developer is increased. Upon computing the toner density, the controller 70 samples multiple points of output value of the permeability sensor, acquires the means of the samples, and takes out a DC component of the output value of the permeability sensor by cancelling vibrational components, for example. Then, the controller 70 calculates the toner density by referring to a table prepared by checking the relationship of the value and the toner density in advance.
Now, as illustrated in
The developing apparatus 20 equipped with the second conveyance screw 23 having the agitating panel 30 illustrated in
In a state where fluidity of the developer was high up to 60 minutes from start of operation, the developer was conveyed without being accumulated at the detection surface 75a of the density detection sensor 75, and the output was stable. Thereafter, however, the deterioration of the developer causes accumulation of the developer, by which the detection output is increased, causing erroneous detection and excessive replenishment of toner, and possibly inducing image defects such as fogging. If accumulation of the developer occurs near the detection surface 75a of the density detection sensor 75, even if fluidity of the developer is improved by repeated consumption and replenishment of the developer, it is difficult to demolish the accumulation of developer in the gap formed between the detection surface 75a and the agitating panel 30 and convey the accumulated developer, so that erroneous detection may not be solved. Recently, there are cases where the density detection sensor 75 is provided below the developer container 21 for downsizing of the image forming apparatus, and erroneous detection due to the accumulation of developer on the detection surface 75a of the density detection sensor 75 may occur more significantly.
Therefore, according to the present embodiment, an agitating portion, serving as a projected portion, 31 is provided to the shaft portion 23a of the second conveyance screw 23, the agitating portion 31 configured to remove the accumulation of developer on the detection surface 75a of the density detection sensor 75 and enable detection of density of the developer with high accuracy. The following describes the configuration of the agitating portion 31 in detail.
As illustrated in
The downstream side portion 31a and the upstream side portion 31b are communicated at an upstream portion in a direction of rotation R1. That is, the agitating portion 31 is designed such that a part 31m between both end portions 31e in the axial direction Da is positioned further upstream in the direction of rotation R1 than the both end portions 31e. Therefore, when viewed from a radial direction of the shaft portion 23a, the agitating portion 31 opens in a downstream side in the direction of rotation R1 and outward in the radial direction, and forms a concave portion 31c having a concaved shape closing in an upstream side in the direction of rotation R1. The concave portion 31c is arranged such that a width, in the axial direction Da, of a region surrounded by a line connecting the both end portions 31e and the concave portion 31c is narrowed from a downstream side toward an upstream side in the direction of the rotation R1. That is, viewed from the radial direction, the concave portion 31c has a width in the axial direction Da in the inner side region of the part 31m and the both end portions 31e that is narrowed from the downstream side toward the upstream side in the direction of rotation R1. Thereby, the agitating portion 31 collects the developer in a direction of rotation R1 along rotation of the second conveyance screw 23 so that the collected developer pushes and agitates a developer between the second conveyance screw 23 and the detection surface 75a of the density detection sensor 75. Further, the collected developer can push the developer existing between the second conveyance screw 23 and the density detection sensor 75 toward the direction of rotation R1, and agitate the developer.
In the present embodiment, a shaft diameter of the shaft portion 23a of the second conveyance screw 23 is 8 mm, an outer diameter of the conveying blade 23b is 16 mm, and a 1-mm clearance is provided between the conveying blade 23b and the inner wall of the developer container 21. Further, the detection surface 75a of the density detection sensor 75 is protruded by 2 mm from the inner wall of the developer container 21. Both the downstream side portion 31a and the upstream side portion 31b have a thickness of 1 mm in a direction along a circumferential surface of the shaft portion 23a, a height of 6 mm from a center to the shaft portion 23a, a height of 2 mm from the circumferential surface of the shaft portion 23a, and a 1-mm gap between the detection surface 75a of the density detection sensor 75.
The downstream side portion 31a and the upstream side portion 31b are connected, forming an obtuse angle θ of approximately 90°<θ≤120°. Therefore, the developer collected by the agitating portion 31 easily falls from a corner portion between the downstream side portion 31a and the upstream side portion 31b, such that the developer is suppressed from being aggregated at the corner portion and mixing with other developer.
The agitating portion 31 is arranged with a gap G between the conveying blade 23b of the second conveyance screw 23. Thereby, the developer collected at the time when the agitating portion 31 is positioned above the shaft portion 23a of the second conveyance screw 23 drops from the agitating portion 31, and the developer is conveyed by the second conveyance screw 23, according to which the aggregation of the collected developer is suppressed.
The operation of the second conveyance screw 23 being rotated to agitate and convey the developer in the above-described developing apparatus 20 will be described. As illustrated in
As described, according to the developing apparatus of the present embodiment, in a state where the second conveyance screw 23 is rotated, the developer is collected by the concaved part of the agitating portion 31. Then, the agitating portion 31 and the collected developer act to push the developer accumulated near the detection surface 75a of the density detection sensor 75 along with the rotation of the second conveyance screw 23. Thereby, the developer accumulated near the detection surface 75a of the density detection sensor 75 is either pushed directly or sheared. Thus, the accumulated developer on the detection surface 75a of the density detection sensor 75 can be removed, and the density of the developer can be detected with high accuracy.
According to the developing apparatus 20 of the present embodiment, the agitating portion 31 is formed of the downstream side portion 31a and the upstream side portion 31b. Therefore, the agitating portion 31 can be realized with a simple configuration, and the increase in size or complication of design of the agitating portion 31 can be suppressed.
Further according to the developing apparatus 20 of the present embodiment, the downstream side portion 31a and the upstream side portion 31b are connected to form an obtuse angle θ. Therefore, in a state where the agitating portion 31 is positioned above the shaft portion 23a, the developer collected by the agitating portion 31 easily falls from the corner portion between the downstream side portion 31a and the upstream side portion 31b, such that the developer can be suppressed from being aggregated at the corner portion and mixing into the other developer.
Now, the developing apparatus 20 equipped with the second conveyance screw 23 having the agitating portion 31 illustrated in
The developing apparatus 20 of the present embodiment described above illustrated an example in which the agitating portion 31 of the second conveyance screw 23 was composed of the downstream side portion 31a and the upstream side portion 31b, but the present invention is not restricted to this configuration. For example, as illustrated in
Also according to this case, in a state where the second conveyance screw 23 is rotated, developer is collected by the concave portion 32c of the agitating portion 32, and the developer accumulating near the detection surface 75a of the density detection sensor 75 is either directly pushed or sheared. Therefore, the accumulation of developer on the detection surface 75a of the density detection sensor 75 can be removed, and the density of the developer can be detected highly accurately. Even further, since the connecting portion 33 is disposed along the axial direction of the shaft portion 23a, a greater amount of developer can be collected by the agitating portion 32 compared to the configuration without the connecting portion 33, and the accumulation of the developer on the detection surface 75a of the density detection sensor 75 can be removed more effectively.
Further according to the agitating portion 32 illustrated in
According further to the developing apparatus 20 of the above-described embodiment, the agitating portion 31 of the second conveyance screw 23 is composed of multiple plate-shaped side portions, but the present embodiment is not restricted thereto. For example, as illustrated in
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2016-170336, filed Aug. 31, 2016, which is hereby incorporated by reference wherein in its entirety.
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