Developing device and image forming apparatus including the same

Abstract

To provide a developing device that can be reduced in size at low cost and prevents the occurrence of a reduction in image quality.SOLUTION: A developing device 2 has a developer tank 28, and a rotatable developing roller 21. The developer tank 28 has: a first chamber 29 provided with a first screw 22 that conveys developer in a first conveyance direction F1 of the developing roller 21; a second chamber 30 provided with a second screw 23 that conveys the developer in a second conveyance direction F2, and having a second bottom 30a located above a first bottom 29a; and two communication parts 31a, 31b at both ends of the first chamber 29 and the second chamber 30 in the direction of a rotation axis 21a. The developing roller 21 is arranged above the second screw 23. The first and second screws 22 and 23 move the developer in the first and second conveyance directions F1 and F2 respectively at substantially the same speed. The conveyance amount of developer moved in the first conveyance direction F1 by the first screw 22 per unit time is larger than the conveyance amount of developer moved in the second conveyance direction F2 by the second screw 23 per unit time.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a developing device that agitates a developer and an image forming apparatus including the same. [Background technology]

[0002] BACKGROUND ART Conventionally, in image forming devices such as copiers, facsimile machines, printers, and multifunction machines, a toner image is formed on a photosensitive drum by a developing device, and this toner image is then transferred and fixed onto paper, thereby forming an image on the paper.

[0003] A two-component developer containing toner and a non-magnetic carrier is generally used as the developer for forming a toner image. A typical developing device has a first chamber and a second chamber, each equipped with a first transport member and a second transport member for agitating and transporting the developer. The developer is transported in the first chamber in the opposite direction to the developer in the second chamber. The downstream side of the first chamber is connected to the upstream side of the second chamber, and the upstream side of the first chamber is connected to the downstream side of the second chamber, forming a developer circulation path between the first chamber and the second chamber.

[0004] To achieve a smaller developing device, a developing device has been proposed in which the second chamber is located above the first chamber and the developing roller is positioned above the second chamber. In such a developing device, when developer moves from the first chamber to the second chamber, the difference in height between the first and second chambers can cause the developer to be impeded. If the developer is impeded, the developer level in the first or second chamber may become unstable, such as the developer level being higher downstream than upstream. This can lead to problems such as uneven developer levels at both axial ends of the developing roller. If the developer level in the second chamber, which supplies developer to the developing roller, becomes unstable, the developer carried by the developing roller may become uneven, which can affect the toner image formed on the photosensitive drum, reducing development performance and the quality of images formed on paper.

[0005] To prevent such problems, for example, Patent Document 1 discloses a developing device having a supply chamber in which a supply screw is disposed and an agitation chamber in which an agitation screw is disposed and which forms a circulation path with the supply chamber, the supply chamber being located above the agitation chamber, the developer being supplied from the supply chamber to a developing roller located further above the supply chamber, and the supply screw and the agitation screw rotating at different speeds.The developing device disclosed in Patent Document 1 has the effect of minimizing fluctuations in the liquid level of the developer, and minimizing fluctuations in the liquid level of the developer even when, for example, the amount of developer fluctuates. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4998602 Summary of the Invention [Problem to be solved by the invention]

[0007] As described above, the developing device disclosed in Patent Document 1 has little fluctuation in the liquid level of the developer in the supply chamber, which can prevent unevenness in the developer carried on the developing roller.

[0008] However, in the developing device disclosed in Patent Document 1, the supply screw and the agitating screw have different rotational speeds. This results in different agitation performance in the supply chamber and the agitating chamber. This may result in insufficient agitation of the developer. Furthermore, different rotational speeds between the supply screw and the agitating screw may require additional gears, which may increase the number of parts, resulting in increased costs and larger size.

[0009] The present disclosure has been made in consideration of the above-mentioned circumstances, and its purpose is to provide a developing device that can be made small and low cost and that is less likely to cause a deterioration in image quality, and an image forming apparatus equipped with the same. [Means for solving the problem]

[0010] A developing device according to one aspect of the present disclosure is a developing device having a developing tank that contains a developer, and a rotatable developing roller that carries the developer on its surface, wherein the developing tank has a first chamber provided with a first screw that transports the developer in a first transport direction, which is one direction along the direction of the rotation axis of the developing roller, a second chamber provided with a second screw that transports the developer in a second transport direction, which is the opposite direction to the first direction, and whose bottom is located above the bottom of the first chamber, and two communication portions that connect the first chamber and the second chamber at both ends in the direction of the rotation axis of the first chamber and the second chamber, respectively, and the developer roller is positioned above the second screw in the second chamber, the first screw and the second screw have approximately the same transport speed for moving the developer in each transport direction, and the first screw moves a greater amount of developer per unit time in each transport direction.

[0011] This allows the developer to be smoothly transported and sufficiently agitated in the first and second chambers even if the first and second chambers are not horizontally positioned to reduce size. In particular, when the developer moves from the first chamber to the second chamber, the developer can be transported smoothly without any disruption. This reduces the risk of image quality degradation. Furthermore, because the rotation speeds of the first screw and the second screw are approximately the same, the configuration is simple, does not require large size, and allows for low-cost miniaturization.

[0012] Furthermore, in the above-described developing device, the first screw may have a first shaft parallel to the rotation axis, and one or more first blades having a pitch in the rotation axis direction of a predetermined distance may be formed on the outer periphery of the first shaft; the second screw may have a second shaft parallel to the rotation axis, and one or more second blades having the same pitch in the rotation axis direction as the first helical blade may be formed on the outer periphery of the second shaft; a first cross-sectional area obtained by subtracting the cross-sectional area of the first helical blade and the cross-section perpendicular to the rotation axis direction of the first helical blade and the first shaft from the cross-sectional area of a circle equal to the outer diameter of the first helical blade may be larger than a second cross-sectional area obtained by subtracting the cross-sectional area of the second helical blade and the cross-section perpendicular to the rotation axis direction of the second helical blade and the second shaft from the cross-sectional area of a circle equal to the outer diameter of the second helical blade; and the rotational speeds of the first screw and the second screw may be approximately the same.

[0013] This allows the amount of developer transported by the first screw when it makes one rotation to be greater than the amount of developer transported by the second screw when it makes one rotation, with a simple configuration.

[0014] In the developing device described above, the number of the first blades may be less than the number of the second blades.

[0015] This allows the amount of developer transported by the first screw when it makes one rotation to be greater than the amount of developer transported by the second screw when it makes one rotation, with a simple configuration.

[0016] In addition, in the above-mentioned developing device, the outer diameter of the first blade may be approximately the same as the outer diameter of the second blade, and the difference between the outer diameter of the first blade and the outer diameter of the first shaft may be greater than the difference between the outer diameter of the second blade and the outer diameter of the second shaft.

[0017] This allows the amount of developer transported by the first screw when it makes one rotation to be greater than the amount of developer transported by the second screw when it makes one rotation, with a simple configuration.

[0018] In addition, in the above-mentioned developing device, the transport space in the first chamber, which is the space connecting the two communicating portions, may have a cylindrical shape extending in the direction of the rotation axis, and the first screw may be arranged in the transport space.

[0019] This makes it possible to prevent the developer from leaking to the outside without increasing the size.

[0020] In addition, in the above-mentioned developing device, an upper space extending upward may be formed above the second screw at the position of the second chamber to which a communication portion that guides the developer transported by the first screw to the second chamber is connected.

[0021] As a result, even if a problem occurs such as a change in the amount of developer, the developer can be smoothly transported and sufficiently agitated in the first and second chambers.

[0022] An image forming apparatus according to an aspect of the present disclosure is characterized by including the above-described developing device.

[0023] This allows the developer to be smoothly transported and sufficiently agitated in the developing device, making it possible to form high-quality images without causing deterioration in image quality. [Effects of the Invention]

[0024] According to the present disclosure, it is possible to provide a developing device that can be made small at low cost and that is less likely to cause a deterioration in image quality, and an image forming apparatus including the same. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a perspective front view showing a schematic configuration of an image forming apparatus according to a first embodiment of the present disclosure. [Figure 2] 1 is a schematic cross-sectional view of the periphery of a developing device in an image forming apparatus according to a first embodiment of the present disclosure. [Figure 3]FIG. 2 is a perspective view showing the configuration of a developing device in the image forming apparatus according to the first embodiment of the present disclosure. [Figure 4] 1 is a perspective view of an image forming apparatus according to a first embodiment of the present disclosure, with a part of a developing device removed to expose the internal configuration. FIG. [Figure 5] FIG. 2 is a side view showing the configuration of a first screw in the image forming apparatus according to the first embodiment of the present disclosure. [Figure 6] 2 is a cross-sectional view showing the configuration of a first screw in the image forming apparatus according to the first embodiment of the present disclosure. FIG. [Figure 7] FIG. 2 is a side view showing the configuration of a second screw in the image forming apparatus according to the first embodiment of the present disclosure. [Figure 8] 3 is a cross-sectional view showing the configuration of a second screw in the image forming apparatus according to the first embodiment of the present disclosure. FIG. [Figure 9] FIG. 10 is a perspective view showing a configuration of a first screw in an image forming apparatus according to a second embodiment of the present disclosure. [Figure 10] FIG. 10 is a cross-sectional view showing the configuration of a first screw in an image forming apparatus according to a second embodiment of the present disclosure. [Figure 11] FIG. 10 is a perspective view showing a configuration of a second screw in an image forming apparatus according to a second embodiment of the present disclosure. [Figure 12] FIG. 10 is a cross-sectional view showing the configuration of a second screw in an image forming apparatus according to a second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0026] Embodiments of the present disclosure will be described with reference to the drawings.

[0027] (First embodiment) An image forming apparatus according to a first embodiment of the present disclosure will be described with reference to the drawings. Fig. 1 is a perspective front view showing a schematic configuration of an image forming apparatus 100 according to a first embodiment of the present disclosure.

[0028] In the coordinate system shown in FIG. 1 and subsequent figures, the X-axis direction is the left-right direction (horizontal direction) when viewing the image forming apparatus 100 from the front, with the positive and negative X-axis directions representing the left and right sides, respectively. The Y-axis direction is the depth direction (front-to-back direction) perpendicular to the X-axis, with the positive and negative Y-axis directions representing the front side, which is the operator's side, and the rear side, which is the opposite side of the operator, respectively. The Z-axis direction represents the up-down direction, i.e., the vertical direction, with the positive and negative Z-axis directions representing the upper side (upward) and lower side (downward), respectively. When only components of the image forming apparatus 100 are shown without the image forming apparatus 100 itself, the coordinate system shows the state in which the components are incorporated into the image forming apparatus 100.

[0029] The image forming apparatus 100 is a multifunction machine having a copy function, a scanner function, a facsimile function, and a printer function, and includes an image reading device 102 and an image forming apparatus main body 101 .

[0030] The image reading device 102 includes an image reading unit 130 and an original feeder 160 (automatic document feeder (ADF)). The original feeder 160 is provided above the image reading unit 130 and is supported so as to be openable and closable relative to the image reading unit 130.

[0031] The image reading unit 130 includes an original placement table 130a on which an original G is placed, a scanning optical system 130c that is movable in the sub-scanning direction F from an original reading position 130b to read the original, and an original reading unit 130d.

[0032] When the document feeder 160 is opened, the document placement table 130a above the image reading unit 130 is opened, allowing the document G to be placed manually. The document G placed on the document placement table 130a is read by the document reading unit 130d as the scanning optical system 130c moves in the sub-scanning direction F, and is converted into image data.

[0033] The document feeder 160 transports one or more documents G loaded on a document loading tray 161 one by one to a document reading position 130b, and then discharges the documents onto a document discharge tray 162. The documents G passing through the document reading position 130b are read by a document reading unit 130d via the scanning optical system 130 and converted into image data.

[0034] As described above, the image reading unit 130 scans the scanning optical system 130c to read the document placed on the document table 130a or reads the document G conveyed by the document feeder 160, and generates image data.

[0035] The image forming apparatus main body 101 includes an image forming section 50, an optical scanning device 1, an intermediate transfer belt device 70, a secondary transfer device 11, a fixing device 12, a sheet transport path S, a paper feed cassette 18, and a sheet discharge tray 141.

[0036] The image forming device 100 handles image data corresponding to color images using the colors black (K), cyan (C), magenta (M), and yellow (Y), or monochrome images using a single color (e.g., black).

[0037] The image forming unit 50 of the image forming apparatus 100 has four image stations Pa, Pb, Pc, and Pd corresponding to the colors black, cyan, magenta, and yellow. Each of these image stations Pa, Pb, Pc, and Pd includes a developing device 2, a photosensitive drum 3, a drum cleaning device 4, and a charging roller 5, and four types of toner images are formed by these image stations Pa, Pb, Pc, and Pd. In other words, the image forming apparatus 100 is provided with four developing devices 2, four photosensitive drums 3, four drum cleaning devices 4, and four charging rollers 5, each corresponding to black, cyan, magenta, and yellow.

[0038] The photosensitive drum 3 comprises a grounded aluminum cylinder and a photosensitive layer that is insulating in areas not exposed to light and conductive in areas exposed to light. The photosensitive layer is formed on the outer periphery of the aluminum cylinder, and the surface of the photosensitive drum 3, i.e., the surface of the photosensitive layer, is charged to a predetermined potential by a charging roller 5. An optical scanning device (exposure device) 1 exposes the surface of the photosensitive drum 3, which is charged to a predetermined potential, to light to form an electrostatic latent image. A developing device 2 develops the electrostatic latent image on the surface of the photosensitive drum 3 with toner, forming a toner image on the surface of the photosensitive drum 3. The toner image formed on the surface of the photosensitive drum 3 is intermediately transferred to an intermediate transfer belt 71 (described later). Residual toner remaining on the photosensitive drum 3 without being intermediately transferred to the intermediate transfer belt 71 is removed and collected by a drum cleaning device 4. After intermediate transfer, the surface of the photosensitive drum 3 is irradiated with light by a discharger 8, erasing the electrostatic latent image formed by the optical scanning device 1. Then, the surface of the photosensitive drum 3 is again charged to a predetermined potential by the charging roller 5, and an electrostatic latent image is again formed by the optical scanning device 1. This series of operations is repeated, and a toner image of each color is formed on the surface of each photosensitive drum 3.

[0039] The image forming apparatus 100 also includes toner cartridges 90a, 90b, 90c, and 90d containing toner of each color to replenish the toner consumed when a toner image is formed on the surface of the photosensitive drum 3. When a toner image is formed at each of the image stations Pa, Pb, Pc, and Pd, the toner consumed is replenished from the corresponding toner cartridges 90a, 90b, 90c, and 90d to the developing device 2 of each of the image stations Pa, Pb, Pc, and Pd by a replenishment device (not shown).

[0040] The toner images formed on the photosensitive drums 3 of the image stations Pa, Pb, Pc, and Pd are transferred onto the intermediate transfer belt 71 of the intermediate transfer belt device 70 as described above.

[0041] The intermediate transfer belt device 70 includes an intermediate transfer roller 6, an endless intermediate transfer belt 71, an intermediate transfer drive roller 72, an intermediate transfer driven roller 73, and a cleaning device 9. The intermediate transfer belt 71 is an endless belt that can rotate, and is wound around the intermediate transfer drive roller 72 and the intermediate transfer driven roller 73. In other words, the intermediate transfer belt 71 is stretched around the intermediate transfer drive roller 72 and the intermediate transfer driven roller 73. There are four intermediate transfer rollers 6, each of which is provided inside the intermediate transfer belt 71 so as to form four types of toner images corresponding to each color. The intermediate transfer rollers 6 bring the intermediate transfer belt 71 into contact with the corresponding photosensitive drum 3, and intermediately transfer the toner images of each color formed on the surface of the photosensitive drum 3 onto the intermediate transfer belt 71.

[0042] As described above, the image forming apparatus 100 sequentially transfers and superimposes the toner images of each color formed on the surface of each photosensitive drum 3, forming a single-color or multi-color toner image on the surface of the intermediate transfer belt 71, which is stretched between the intermediate transfer drive roller 72 and the intermediate transfer driven roller 73. The toner image formed on the intermediate transfer belt 71 is secondarily transferred onto the sheet P by the secondary transfer device 11, which will be described later. Residual toner remaining on the intermediate transfer belt 71 without being secondarily transferred onto the sheet P is removed and collected by the cleaning device 9.

[0043] The secondary transfer device 11 forms a transfer nip area TN between the secondary transfer roller 11a and the intermediate transfer belt 71, and conveys a sheet P conveyed through the sheet conveying path S by sandwiching it in the transfer nip area TN. When the sheet P passes through the transfer nip area TN, the toner image on the surface of the intermediate transfer belt 71 is transferred to the sheet P, and the sheet P is conveyed to the fixing device 12.

[0044] The fixing device 12 includes a fixing roller 41 and a pressure roller 42 that rotate while sandwiching the sheet P. The fixing device 12 sandwiches the sheet P, on which the toner image has been transferred, between the fixing roller 41 and the pressure roller 42, and applies heat and pressure to fix the toner image to the sheet P. Specifically, a heater, which is a heat source, is disposed inside the fixing roller 41, and the heat generated by the heater heats the surface of the fixing roller 41 that comes into contact with the sheet P on which the toner image has been transferred.

[0045] The paper feed cassette 18 is a cassette for storing sheets P used for image formation and is provided below the optical scanning device 1. The sheets P are pulled out of the paper feed cassette 18 by a pickup roller 16 and transported one by one to a sheet transport path S. The sheet P transported to the sheet transport path S passes through a secondary transfer device 11 and a fixing device 12, is transported to a discharge roller 17, and is discharged to a sheet discharge tray 141 in a discharge section 140. The sheet transport path S is provided with a transport roller 13, a registration roller 14, and a discharge roller 17. The transport roller 13 promotes the transport of the sheet P. The registration roller 14 temporarily stops the sheet P and aligns the leading edge of the sheet P. The registration roller 14 then begins transporting the stopped sheet P in time with the toner image on the intermediate transfer belt 71 reaching the transfer nip area TN. As described above, the toner image on the intermediate transfer belt 71 is transferred to the sheet P in the transfer nip area TN after the registration roller 14 begins transporting the sheet P.

[0046] Although FIG. 1 shows one sheet feed cassette 18, the present invention is not limited to this, and a configuration may be provided in which a plurality of sheet feed cassettes 18 are provided, each of which may hold a different type of sheet P.

[0047] Furthermore, when forming an image on the back side of the sheet P in addition to the front side, the image forming apparatus 100 switches back the sheet P that has reached the discharge rollers 17 and transports it to a sheet reversal path Sr. The image forming apparatus 100 inverts the sheet P transported in the opposite direction and guides it again to the registration rollers 14. Furthermore, the image forming apparatus 100 forms an image on the back side of the sheet P guided to the registration rollers 14 in the same manner as on the front side, and then transports the sheet P to the sheet discharge tray 141.

[0048] Next, the configuration around the developing device 2 will be described with reference to the drawings. FIG. 2 is a schematic cross-sectional view of the developing device 2 and its periphery in the image forming apparatus 100 according to the first embodiment of the present disclosure. FIG. 3 is a perspective view showing the configuration of the developing device 2 in the image forming apparatus 100 according to the first embodiment of the present disclosure. FIG. 4 is a perspective view of the developing device 2 in the image forming apparatus 100 according to the first embodiment of the present disclosure, with a portion removed to expose the internal configuration. Note that FIG. 2 is a cross-sectional view of one of the image stations constituting the image forming unit 50, viewed from the front at the center position in the depth direction. Also, FIG. 4 shows a state in which a restricting member and a cover have been removed from the state shown in FIG. 3, exposing the first screw and the second screw.

[0049] Developing device 2 has developing tank 28 that contains developer including toner, and developing roller 21 that carries the developer contained in developing tank 28 on its surface and is rotatable around rotation axis 21a. More specifically, as shown in Fig. 2, developing device 2 includes developing roller 21, regulating member 80, cover 81, first screw 22, second screw 23, and developing tank 28 that has first chamber 29, second chamber 30, and communication portions 31a, 31b.

[0050] Here, as shown particularly in Figure 4, the developer tank 28 has a first chamber 29 provided with a first screw 22 that transports the developer containing the stored toner in a first transport direction F1 (from the front side to the back side in the Y-axis direction), which is one direction along the direction of the rotation axis 21a of the developing roller 21, a second chamber 30 that is provided with a second screw 23 that transports the developer containing the stored toner in a second transport direction F2 (from the back side to the front side in the Y-axis direction), which is the opposite direction to the one direction along the direction of the rotation axis 21a of the developing roller 21, and has a bottom located above the first chamber 29 (above in the Z-axis direction), and two communication portions 31a, 31b that connect the first chamber 29 and the second chamber 30 at both ends of the first chamber 29 and the second chamber 30 in the direction of the rotation axis 21a of the developing roller 21, respectively.

[0051] The developing roller 21 is disposed in the second chamber 30 facing the photosensitive drum 3 and above the second screw 23 (above in the Z-axis direction). The developing roller 21 is driven to rotate (in a predetermined direction R1 around the rotation axis 21a of the developing roller 21) by a drive source (not shown). Similarly, the first screw 22 and the second screw 23 are driven to rotate in predetermined directions S1 and S2, respectively, by a drive source (not shown). More specifically, at the rear end of the developing device 2, a plurality of gears (not shown) are disposed for rotating the developing roller 21 and the first and second screws 22 and 23. One of the gears is provided with a coupling member. When the developing device 2 is attached to the image forming apparatus 100, this coupling member engages with a coupling member connected to a drive source (not shown) provided in the image forming apparatus 100. Therefore, when the drive source (not shown) is rotated, the developing roller 21, the first screw 22, and the second screw 23 are rotated in the predetermined directions S1 and S2 in the developing device 2 attached to the image forming apparatus 100. The direction of the rotation axis 21a of the developing roller 21 is parallel to the Y-axis direction, which is the front-to-back direction, and the rotation axes of the photosensitive drum 3, the first screw 22 and the second screw 23 are also arranged so that they are parallel to the Y-axis direction.

[0052] Next, how the developer contained in the developer tank 28 is supplied to the developing roller 21 will be described.

[0053] When first screw 22 is rotated in direction S1 by a drive source (not shown), the developer contained in first chamber 29 of developer tank 28 is transported toward the rear side (in the Y-axis direction). The developer transported to the rear end by first screw 22 is sent to second chamber 30 via communication portion 31a. The developer transported to second chamber 30 via communication portion 31a is transported toward the front side (in the Y-axis direction) when second screw 23 is rotated in direction S2 by a drive source (not shown). The developer transported to the front end by second screw 23 is sent to first chamber 29 via communication portion 31b, and is transported toward the rear side again by first screw 22. In this way, the developer is transported so as to circulate between first chamber 29 and second chamber 30, which are connected by communication portions 31a and 31b, respectively. A portion of the developer transported through second chamber 30 is supplied to the surface of developing roller 21. The developer supplied to the surface of the developing roller 21 is regulated by the regulating member 80 so that the layer thickness is uniform. Therefore, the regulating member 80 is arranged so that the layer thickness of the developer carried on the outer circumferential surface of the developing roller 21 is uniform in the Y-axis direction, which is the front-to-rear direction. Specifically, the regulating member 80 is formed from a metal plate with a predetermined thickness (for example, an aluminum plate with a thickness of 1 mm), and is arranged so that the gap between the tip of the regulating member 80 and the outer circumferential surface of the developing roller 21 is uniform in the Y-axis direction, which is the front-to-rear direction (an example of a gap is 0.8 mm). Therefore, when the developing roller 21 is rotated in a predetermined direction by the drive source, the developer carried on the surface of the developing roller 21 is regulated to a uniform thickness in the Y-axis direction by the gap with the tip of the regulating member 80, thereby making it possible to form a uniform toner image with no uneven density in the Y-axis direction.

[0054] The developer, whose layer thickness has been made uniform by the regulating member 80, is sent to the opposing region DN of the developing roller 21 by the rotation of the developing roller 21, where the toner contained in the developer develops the electrostatic latent image formed on the surface of the photosensitive drum 3. When this type of development is performed continuously, the toner in the storage chamber 28 is consumed, so toner is replenished by a replenishment device (not shown) from toner cartridges 90a, 90b, 90c, and 90d corresponding to the developing device 2. For this reason, the developing device 2 further has a supply port 82 (see FIGS. 3 and 4) for receiving toner from these toner cartridges 90a, 90b, 90c, and 90d. The supply port 82 is located further toward the end than the communication portion 31b, and the toner (which may be developer) supplied from the supply port 82 is transported in the first transport direction F1 by the first screw 22.

[0055] Here, the positional relationship between the developing roller 21, the first screw 22, and the second screw 23 in the developing device 2 according to the first embodiment will be described in more detail. As shown in FIG. 2, the first screw 22 is disposed so as to be diagonally lower than the second screw 23, which is disposed below the developing roller 21. In other words, the first bottom 29a, which is the bottom of the first chamber 29 housing the first screw 22, is disposed at the lowest position, and the second bottom 30a, which is the bottom of the second chamber 30 housing the second screw 23, is disposed so as to be diagonally higher than the first screw 22. This arrangement reduces the space required in the left-right direction (X-axis direction) compared to a configuration in which the first screw 22 and the second screw 23 are disposed side by side in the horizontal direction (i.e., disposed at the same position in the Z-axis direction). This allows the image forming apparatus 100 to be made more compact.

[0056] However, with this configuration, the communicating portion 31a that sends the developer from the first chamber 29 to the second chamber 30 is configured so that its bottom slopes upward from the first chamber 29 toward the second chamber 30, which creates the problem that the developer transported by the first screw 22 does not easily move into the second chamber 30.

[0057] Therefore, the developing device 2 according to the first embodiment is configured so that the cross section perpendicular to the first transport direction F1, which is the direction in which the developer is transported in the first chamber 29, has a circular shape that is slightly larger than the outer diameter of the first transport screw 22 (see FIG. 2). Specifically, the cover 81 is attached to the developer tank 28 so as to cover part of the outer periphery of the first transport screw 22. As a result, the transport space in the first chamber 29, which is the space connecting the communication portions 31a and 31b, has a cylindrical shape that extends in the direction of the rotation axis 21a of the developing roller 21, and the first screw 22 is disposed in this transport space.

[0058] By configuring the transport space in this manner, the amount of developer transported through the first chamber 29 in the first transport direction F1 can be limited to a constant amount, and even if developer accumulates in the communicating portion 31a, which has a bottom that slopes upward toward the second chamber 30, it can be reliably pushed up into the second chamber 30.

[0059] Additionally, an upper space 88 is formed above the second screw 23 corresponding to the communicating portion 31a. The upper space 88 is formed above the second screw 23 near the communicating portion 31a, which is the portion where the developer moves from the first chamber 29 to the second chamber 30. In other words, the upper space 88 extending upward is formed above the second screw 23 at a position in the second chamber 30 where the communicating portion 31a, which guides the developer transported by the first screw 22 to the second chamber 30, is connected. This upper space 88 allows the surface position of the developer in the second chamber 30 to rise due to the developer being transported to the second chamber 30 via the communicating portion 31a, which has a bottom that slopes upward toward the second chamber 30, and enables the developer to be reliably transported in the second transport direction F2 by the second screw 23.

[0060] Next, the configurations of the first screw 22 and the second screw 23 will be described with reference to the drawings.

[0061] FIG. 5 is a side view showing the configuration of the first screw 22 in the image forming apparatus 100 according to the first embodiment of the present disclosure. FIG. 6 is a cross-sectional view showing the configuration of the first screw 22 in the image forming apparatus 100 according to the first embodiment of the present disclosure. FIG. 7 is a side view showing the configuration of the second screw 23 in the image forming apparatus 100 according to the first embodiment of the present disclosure. FIG. 8 is a cross-sectional view showing the configuration of the second screw 23 in the image forming apparatus 100 according to the first embodiment of the present disclosure. Note that FIGS. 5 and 7 show the first screw 22 and the second screw 23 as viewed in a direction perpendicular to the longitudinal direction (Y-axis direction), and are views showing a portion of each. Also, FIGS. 6 and 8 are cross-sectional views of the first screw 22 and the second screw 23 taken along a plane perpendicular to the longitudinal direction.

[0062] As shown in FIGS. 5 and 6 , the first screw 22 includes a first shaft 24, a first blade (first helical blade) 26 spirally formed around the first shaft 24, and a first metal shaft 86 disposed in the center of the first shaft 24. The first blade 26 (first screw 22) has a two-thread structure, with two first blades 26 (first screw 22) provided around the first shaft 24. In the first screw 22, the pitch (pitch in the Y-axis direction) of the first blades 26 is p1, and the distance between adjacent first blades 26 is p11. In the first embodiment, the pitch p1 of the first blades 26 is, for example, 30 mm, and the distance p11 between adjacent first blades 26 is 15 mm. The outer diameter CS1 of the first blade 26 is 14 mm, and the outer diameter C1 of the first shaft 24 is 6 mm. Here, the amount Q1 of developer moved in the first transport direction F1 when the first screw 22 makes one rotation is calculated by multiplying the first cross-sectional area, which is the cross-sectional area of a circle equal to the outer diameter CS1 of the first blade 26 minus the cross-sectional area of the two first blades 26 and the cross-sectional area of the cross section perpendicular to the rotation axis 21a of the first shaft 24, by the length of the pitch p1. In the first embodiment, the value of Q1 is 2.9 cm3. In other words, the amount Q1 of developer transported by the rotation of the first screw 22 is determined by the volume of the first groove portion 84 formed between adjacent first blades 26.

[0063] 7 and 8, the second screw 23 includes a second shaft 25, a second blade (second helical blade) 27 spirally formed around the second shaft 25, and a second metal shaft 87 disposed in the center of the second shaft 25. The second blades 27 (second screw 23) have a three-thread structure, with three second blades 27 provided around the second shaft 25. In the second screw 23, the pitch (pitch in the Y-axis direction) of the second blades 27 is p2, and the distance between adjacent second blades 27 is p21. In the first embodiment, the pitch p2 of the second blades 27 is, for example, 30 mm, and the distance p21 between adjacent second blades 27 is 10 mm. The outer diameter CS2 of the second blade 27 is 14 mm, and the outer diameter C2 of the second shaft 25 is 6 mm. Here, the amount Q2 of developer moved in the second transport direction F2 when the second screw 23 makes one rotation is calculated by multiplying a second cross-sectional area, which is obtained by subtracting the cross-sectional areas of the three second blades 27 and the cross-sectional area of a cross section perpendicular to the rotation axis 21a of the second shaft 24 from the cross-sectional area of a circle equal to the outer diameter CS2 of the second blade 27, by the length of the pitch p2. In the first embodiment, the value of Q2 is 2.47 cm3. In other words, the amount Q2 of developer transported by the rotation of the second screw 23 is determined by the volume of the second groove portion 85 formed between adjacent second blades 27. In other words, the first cross-sectional area of the first screw 22 is configured to be larger than the second cross-sectional area of the second screw 23.

[0064] Here, the first screw 22 and the second screw 23 are driven at the same rotational speed. In other words, the rotational speeds of the first screw 22 and the second screw 23 are substantially the same, and the pitch p1 of the first blade 26 and the pitch p2 of the second blade 27 are the same, 30 mm, so the moving speed of the developer moving in the first transport direction F1 within the first chamber 29 is the same as the phase speed of the developer moving in the second transport direction F2 within the second chamber 30. Therefore, the frictional charging opportunity between the toner and the carrier is the same when moving through the first chamber 29 and when moving through the second chamber 30, so the charge amount of the toner can be stabilized without changing.

[0065] Furthermore, by setting the amount Q2 of developer transported by the second screw 23 to approximately 85% of the amount Q1 of developer transported by the first screw 22, the amount of developer transported from the communication portion 31a to the communication portion 31b can be reduced relative to the amount of developer sent to the communication portion 31a by the first screw 22, and a sufficient amount of toner can be secured in the upper space 88. Therefore, a sufficient amount of developer can be secured to be transported by the second screw 23, so that the developer can be stably supplied to the developing roller 21. In other words, the upper surface position (liquid surface) of the developer transported by the second screw 23 can be made uniform in the Y-axis direction (parallel to the direction of the rotational axis 21a of the developing roller 21), so that the developer can be uniformly supplied to the rotational axis 21a of the developing roller 21. As described above, the developing roller 21 is disposed above the second screw 23, and there is a space above the second screw 23. Therefore, even if there is developer above the second screw 23, the second screw 23 can transport the developer in the second transport direction F2, including the developer above the second screw 23. In other words, since the developer above the second screw 23 is also transported, a sufficient amount of developer can be transported to the first chamber 29 in which the first screw 22 is disposed. In other words, the first screw 22 and the second screw 23 are configured to have substantially the same transport speed for moving the developer in each transport direction (first direction F1 and second direction F2), and the transport amount of the developer moved per unit time in each transport direction is greater by the first screw 22 than by the second screw 23. This stabilizes the charge amount of the toner, and allows the developer to be smoothly transported via the communication portion 31a to the second chamber 30, which is disposed above the first chamber 29 in which the first screw 22 is disposed.

[0066] Furthermore, because the rotation speeds of the first screw 22 and the second screw 23 are approximately the same, the rotation mechanisms for these screws can be configured simply. For example, if both the first screw 22 and the second screw 23 are driven by the driving force of a single motor, the rotation mechanisms for each screw can be similar, which prevents an increase in the number of gears and makes it possible to easily rotate the first screw 22 and the second screw 23. This prevents an increase in manufacturing costs and an increase in the size of the image forming apparatus 100.

[0067] In the first embodiment, the first screw 22 has a two-row configuration and the second screw 23 has a three-row configuration, but the number of rows is not limited to these numbers, as a similar effect can be obtained if the number of rows of the first screw 22 (first blades 26) is less than the number of rows of the second screw 23 (second blades 27). In other words, a similar effect can be obtained if the number of first blades 26 is less than the number of second blades, so the number of rows of each screw 22, 23 can be determined so as to adjust the conveying amount of the first screw 22 and the conveying amount of the second screw 23 in accordance with the other configurations. In other words, as long as this relationship can be maintained, the first screw 22 of the first embodiment has a first axis 24 parallel to the rotational axis 21a of the developing roller 21, and one or more first blades 26 having a pitch p1 in the direction of the rotational axis 21a of a predetermined distance are formed on the outer periphery of the first axis 24, and the second screw 23 has a second axis 25 parallel to the rotational axis 21a of the developing roller 21, and one or more second blades 27 having a pitch p2 in the direction of the rotational axis 21a of the developing roller 21 that is the same as the pitch p1 of the first blades 26 are formed on the outer periphery of the second axis 25.

[0068] As described above, according to the developing device 2 according to the first embodiment 100, the second chamber 30 provided with the second screw 23 is disposed above the first chamber 29 provided with the first screw 22, and the first screw 22 has a two-thread configuration and the second screw 23 has a three-thread configuration. Therefore, the rotation speeds of the first screw 22 and the second screw 23 are substantially the same, the pitches p1 and p2 are substantially the same, the outer diameters of the first blade 26 and the second blade 27 are substantially the same, and the outer diameters of the first shaft 24 and the second shaft 25 are substantially the same. In this configuration, the developer moves smoothly when it moves from the first chamber 29 to the second chamber 30 or when it moves from the second chamber 30 to the first chamber 29. As a result, the developer is transported smoothly in the first chamber 29 and the second chamber 30, and is transported stably with little fluctuation in the developer surface (liquid level). Therefore, the developer supplied from the second chamber 30 and carried on the developing roller 21 is carried evenly on the developing roller 21 without unevenness, and the quality of the formed image is less likely to deteriorate. Also, because the rotation speed of the first screw 22 and the rotation speed of the second screw 23 are approximately the same, the developer agitation performance does not differ greatly between the first chamber 29 and the second chamber 30, and the developer can be agitated uniformly. Furthermore, because this can be achieved with a simple configuration, the manufacturing cost of the image forming apparatus 100 does not increase, and the image forming apparatus 100 does not become larger.

[0069] In the first embodiment, the rotation directions of the first screw 22 and the second screw 23 are opposite to each other, but depending on the configuration of the first blade 26 and the second blade 27, it is also possible to have the same rotation direction but opposite conveying directions. (Second embodiment) A second embodiment of the present disclosure will be described below. Note that the second embodiment differs from the first embodiment in that, instead of the first screw 22 and the second screw 23 in the first embodiment, a first screw 122 and a second screw 123 having different configurations are provided, but other points are the same as those of the first embodiment. Therefore, the following will describe the differences, and will omit a description of the other configurations. Note that the same members as in the first embodiment are assigned the same reference numerals.

[0070] A developing device 2 according to a second embodiment will be described with reference to the drawings. FIG. 9 is a perspective view showing the configuration of a first screw 122 in an image forming apparatus 100 according to a second embodiment of the present disclosure. FIG. 10 is a cross-sectional view showing the configuration of the first screw 122 in an image forming apparatus 100 according to a second embodiment of the present disclosure. FIG. 11 is a perspective view showing the configuration of a second screw 123 in an image forming apparatus 100 according to a second embodiment of the present disclosure. FIG. 12 is a cross-sectional view showing the configuration of the second screw 123 in an image forming apparatus 100 according to a second embodiment of the present disclosure. Note that FIGS. 9 and 11 only show a portion of each of the first screw 122 and the second screw. The first screw 122 and the second screw 123 are actually longer than shown in the drawings. Also, FIGS. 10 and 12 are cross-sectional views of the first screw 122 and the second screw 123 taken along a plane perpendicular to the longitudinal direction.

[0071] 9 and 10, the first screw 122 includes a first shaft 124, a first blade 126 spirally formed around the first shaft 124, and a first metal shaft 186 disposed in the center of the first shaft 124, and the first blade 126 (first screw 122) has a two-thread structure. Here, the pitch (pitch in the Y-axis direction) of the first blades 126 is, for example, 30 mm. The distance between adjacent first blades 126 is, for example, 15 mm. The outer diameter of the first blade 126 is DS1, and the outer diameter of the first shaft 124 is D1. In the second embodiment, the outer diameter DS1 of the first blade 126 is, for example, 14 mm, and the outer diameter D1 of the first shaft 124 is, for example, 6 mm. Here, the amount Q1 of developer moved in the first transport direction F1 when the first screw 122 makes one rotation is the amount obtained by multiplying the first cross-sectional area, which is the cross-sectional area of a circle equal to the outer diameter DS1 of the first blade 126 minus the cross-sectional area of the cross section perpendicular to the rotation axis 21a of the two first blades 126 and the first shaft 124, by the pitch length. In the second embodiment, the value of Q1 is 2.9 cm3.

[0072] 11 and 12, the second screw 123 includes a second shaft 125, a second blade 127 spirally formed around the second shaft 125, and a second metal shaft 187 disposed in the center of the second shaft 125. The second blade 127 (second screw 123) has a two-thread structure similar to the first blade 126. Here, the pitch (pitch in the Y-axis direction) of the second blade 127 is, for example, 30 mm, which is the same value as the pitch of the first blade 126. The interval between adjacent second blades 127 is, for example, 15 mm. The outer diameter of the second blade 127 is DS2, and the outer diameter of the second shaft 125 is D2. In the second embodiment, the outer diameter DS2 of the second blade 127 is, for example, 14 mm, and the outer diameter D2 of the second shaft 125 is, for example, 8 mm, which is larger than the outer diameter D1 of the first shaft 124, which is 6 mm. Here, the amount Q2 of developer moved in the second transport direction F2 when the second screw 123 makes one rotation is the amount obtained by multiplying the second cross-sectional area, which is obtained by subtracting the cross-sectional area of the two second blades 127 and the cross-section perpendicular to the rotation axis 21a of the second shaft 124 from the cross-sectional area of a circle equal to the outer diameter DS2 of the second blade 126, by the pitch length. In the second embodiment, the value of Q2 is 2.55 cm3.

[0073] As described above, the outer diameters DS1 and DS2 are the same, and the outer diameters D1 and D2 are different. In other words, the outer diameter DS1 of the first blade 126 is substantially the same as the outer diameter DS2 of the second blade 127, and the difference between the outer diameter DS1 of the first blade 126 and the outer diameter D1 of the first shaft 124 is greater than the difference between the outer diameter DS2 of the second blade 127 and the outer diameter D2 of the second shaft. This results in the volumes of the first groove 184 and the second groove 185 being different. Specifically, the volume of the first groove 184 is greater than the volume of the second groove 185. Therefore, the amount of developer transported per one rotation of the first screw 122 is greater than the amount of developer transported per one rotation of the second screw 123.

[0074] Here, during operation of the developing device 2, the first screw 122 and the second screw 123 rotate at approximately the same speed, and therefore the first screw 122, which is located on the lower side, transports a greater amount of developer than the second screw 123, which is located on the upper side. Generally, when developer moves from the first chamber 29 to the upper second chamber 30, the movement of the developer in the communication portion 31b may be impeded due to gravity. However, in the second embodiment, the amount of developer transported in the first chamber 29 is greater than the amount of developer transported in the second chamber 30, and therefore the developer can move quickly from the first chamber 29 to the upper second chamber 30 without being impeded.

[0075] Furthermore, because the rotation speeds of the first screw 122 and the second screw 123 are approximately the same, the rotation mechanisms for these screws can be configured simply. For example, when both the first screw 122 and the second screw 123 are driven by the driving force of a single motor, the respective rotation mechanisms can be made similar, which prevents an increase in the number of gears and makes it possible to easily rotate the first screw 122 and the second screw 123. This prevents an increase in manufacturing costs and prevents the image forming apparatus 100 from becoming larger.

[0076] In the second embodiment, both the first screw 122 and the second screw 123 have a two-thread configuration, but other numbers of threads may be used as long as the first screw 122 (first blade 126) and the second screw 123 (second blade 127) have the same number of threads. By making the outer diameters DS1 and DS2 approximately the same and the outer diameter D1 smaller than the outer diameter D2, the volume of the first groove portion 184 can be easily made larger than the volume of the second groove portion 185, and the conveying amount of the first screw 122 can easily be made larger than the conveying amount of the second screw 123 at the same rotation speed.

[0077] As described above, according to the developing device 2 of the second embodiment 100, the second chamber 30 provided with the second screw 123 is disposed above the first chamber 29 provided with the first screw 122, and both the first screw 122 and the second screw 123 have a two-thread configuration, the pitch of the first blade 126 and the pitch of the second blade 127 are substantially the same, the outer diameters DS1 and DS2 are substantially the same, and the outer diameter D1 is smaller than the outer diameter D2. Therefore, in a configuration in which the rotation speeds of the first screw 122 and the second screw 123 are substantially the same, the developer moves smoothly when it moves from the first chamber 29 to the second chamber 30 or when it moves from the second chamber 30 to the first chamber 29. As a result, the developer is transported smoothly in the first chamber 29 and the second chamber 30, and is transported stably with little fluctuation in the developer liquid level. Therefore, the developer supplied from the second chamber 30 and carried on the developing roller 21 is carried evenly on the developing roller 21 without unevenness, and the quality of the formed image is less likely to deteriorate. Also, because the rotation speed of the first screw 122 and the rotation speed of the second screw 123 are substantially the same, the developer agitation performance does not differ greatly between the first chamber 29 and the second chamber 30, and the developer can be sufficiently agitated. Furthermore, because this can be achieved with a simple configuration, the manufacturing cost of the image forming apparatus 100 does not increase, and the image forming apparatus 100 does not become larger.

[0078] The present disclosure is not limited to the above-described embodiments, but can be implemented in various other forms. Therefore, these embodiments are merely examples in all respects and should not be interpreted as limiting. The scope of the present disclosure is defined by the claims and is not bound by the text of the specification. Furthermore, all modifications and variations within the equivalent range of the claims are within the scope of the present disclosure. [Explanation of symbols]

[0079] 1 Optical scanning device 2. Developing device 3 Photosensitive drum 4 Drum cleaning device 5 Charging roller 6 Intermediate transfer roller 8 Static eliminator 9 Cleaning Device 11 Secondary transfer device 11a Secondary transfer roller 12 Fixing device 13 Conveyor roller 14 Registration roller 16 Pickup roller 17 Ejection roller 18 Paper cassette 21 Developing roller 21a Rotation axis 22, 122 First screw 23, 123 Second screw 24, 124 1st axis 25, 125 2nd axis 26, 126 1st feather 27, 127 2nd feather 28 Developer tank 29 Room 1 29a 1st bottom 30 Room 2 30a 2nd bottom 31a, 31b communication part 41 Fuser roller 42 Pressure roller 50 Image forming unit 70 Intermediate transfer belt device 71 Intermediate transfer belt 72 Intermediate transfer drive roller 73 Intermediate transfer driven roller 80 Regulatory member 81 Cover 82 Developer supply port 84, 184 First groove 85, 185 Second groove 86, 186 First metal shaft 87, 187 Second metal shaft 88 Upper space 90a, 90b, 90c, 90d toner cartridges 100 Image forming device 101 Image forming apparatus main body 102 Image reader 130 Image reading unit 130a Document stand 130b Document reading unit 130c Scanning Optical System 130d Document reading unit 140 Discharge section 141 Sheet output tray 160 Document feeder 161 Document tray 162 Document output tray C1, CS1, C2, CS2 outer diameter D1, DS1, D2, DS2 Outer diameter F Sub-scanning direction F1 First conveying direction F2 Second conveying direction Sr sheet inversion pathway S Sheet transport path S1, S2, R1 direction DN opposing area TN Transfer Nip Area G Manuscript P-sheet Pa, Pb, Pc, Pd imaging station p1, p2 pitch p11, p21 interval

Claims

1. A developing device having a developer tank containing a developer, and a rotatable developing roller carrying the developer on its surface, The developing tank is a first chamber provided with a first screw that transports the developer in a first transport direction that is one direction along the direction of the rotation axis of the developing roller; a second chamber including a second screw for transporting the developer in a second transport direction opposite to the one direction, the second chamber having a bottom located above the bottom of the first chamber; two communication portions that communicate the first chamber with the second chamber, respectively, at both ends of the first chamber and the second chamber in the direction of the rotation axis, the developer roller is disposed above the second screw in the second chamber; the first screw and the second screw move the developer in the respective transport directions at substantially the same transport speed, a conveyance amount of the developer per unit time in each of the conveyance directions of the first screw being greater than that of the second screw;

2. 2. The developing device according to claim 1, The first screw has a first axis parallel to the rotation axis, and one or more first blades having a pitch of a predetermined distance in the direction of the rotation axis are formed on the outer periphery of the first axis, The second screw has a second axis parallel to the rotation axis, and one or more second blades having the same pitch in the rotation axis direction as the first helical blade are formed on the outer periphery of the second axis, a first cross-sectional area obtained by subtracting the cross-sectional area of the first helical blade and the cross-section perpendicular to the rotational axis direction of the first helical blade and the first shaft from the cross-sectional area of a circle equal to the outer diameter of the second helical blade, the first cross-sectional area being larger than a second cross-sectional area obtained by subtracting the cross-sectional area of the second helical blade and the cross-section perpendicular to the rotational axis direction of the second shaft from the cross-sectional area of a circle equal to the outer diameter of the second helical blade, and the first screw and the second screw have approximately the same rotational speed.

3. 3. The developing device according to claim 2, The developing device, wherein the number of the first blades is smaller than the number of the second blades.

4. 3. The developing device according to claim 2, The outer diameter of the first blade is substantially the same as the outer diameter of the second blade, a difference between an outer diameter of the first blade and an outer diameter of the first shaft being larger than a difference between an outer diameter of the second blade and an outer diameter of the second shaft;

5. 2. The developing device according to claim 1, In the first chamber, a transfer space that connects the two communication portions has a cylindrical shape that extends in the direction of the rotation axis, The developing device, wherein the first screw is disposed in the transport space.

6. 2. The developing device according to claim 1, A developing device characterized in that an upper space extending upward is formed above the second screw at the position of the second chamber where a communicating portion that guides the developer transported by the first screw to the second chamber is connected.

7. An image forming apparatus comprising the developing device according to any one of claims 1 to 6.

Images