Developing device and image forming apparatus

Abstract

To provide a developing device that can prevent the density of a visible image from being relatively reduced, the visible image being developed in an area part corresponding to a part in a developing area on the downstream side in a first conveyance direction of a first conveyance path where developer supplied to a developer passing body is conveyed.SOLUTION: A developing device comprises: a developer passing body that holds developer and passes through a developing area; a first conveyance path through which the developer supplied to the developer passing body is conveyed; a second conveyance path through which the developer fed to the first conveyance path is conveyed; a first connection part that is connected with a frontward part at an upstream end in a second conveyance direction of the second conveyance path at a frontward part at a downstream end in a first conveyance direction of the first conveyance path; and a first conveying member where a spiral forward conveying blade that rotates in the first conveyance path and forwardly conveys the developer in the first conveyance direction is provided on its rotation shaft. The first conveying member is provided with a spiral backward conveying blade that backwardly conveys the developer in a direction opposite to the first conveyance direction at least at a part of a portion of the rotation shaft adjacent to the first connection part such that an end on the downstream side in the backward direction reaches at least an end on the upstream side in the first conveyance direction of the first connection part.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a developing device and an image forming apparatus. [Background technology]

[0002] The following Patent Document 1 describes a developing device having an agitation chamber equipped with a transport screw, a developing chamber equipped with a transport screw and a developing sleeve, and two communication ports connecting the agitation chamber and the developing chamber for transferring two-component developer, one of which is a downstream communication port located downstream in the direction in which the transport screw transports the two-component developer in the developing chamber, and in which the transport screw in the developing chamber has a forward-wound spiral blade on its rotating shaft that transports the developer in the above direction up to the downstream communication port. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-40139 A (paragraph 0020, Figure 2, etc.) Summary of the Invention [Problem to be solved by the invention]

[0004] This invention provides a developing device and an image forming apparatus that can suppress a relative decrease in density of a visible image developed in a region of the development area corresponding to the portion downstream in the first transport direction of the first transport path through which the developer supplied to the development passing body is transported, compared to a case in which a first transport member has a spiral forward transport blade attached to a rotating shaft for forward transporting the developer in the first transport direction in the first transport path, the forward transport blade being arranged at least until it reaches the downstream end in the first transport direction of a first connecting portion that connects to a second transport path just before the downstream end in the first transport direction of the first transport path. [Means for solving the problem]

[0005] This invention (1) is, a developer passing member that passes through a development area while holding a developer; a first transport path through which the developer to be supplied to the developing passage is transported; a second transport path through which the developer to be fed to the first transport path is transported; a first connection portion that connects a front portion of a downstream end of the first transport path in a first transport direction to a front portion of an upstream end of the second transport path in a second transport direction; a first transport member having a rotating shaft provided with a spiral forward transport blade that rotates in the first transport path to forward transport the developer in a first transport direction; Equipped with the first transport member is provided such that a downstream end of the forward transport blade in the first transport direction is located at a position away from the developing area on the first transport direction downstream side, and, The first transport member is a developing device in which a spiral reverse transport blade for reversely transporting developer in a direction opposite to the first transport direction is provided on at least a portion of the rotating shaft adjacent to the first connection portion, such that the downstream end of the reverse direction reaches at least the upstream end of the first connection portion in the first transport direction.

[0006] The present invention (2) is the developing device according to the above invention (1), wherein the reverse transport blade is provided across a boundary between the first transport path and the first connection portion. This invention (3) is the developing device of invention (1) above, wherein the downstream end of the reverse transport blade in the reverse direction passes beyond the upstream end of the first connection portion in the first transport direction and enters the first transport path.

[0007] This invention (4) is a developing device according to any one of inventions (1) to (3) above, wherein the downstream end of the reverse transport blade in the reverse direction is arranged to be located downstream in the first transport direction of the downstream end of the part of the developing passing body that faces the development area. The invention (5) is a developing device according to any one of the above inventions (1) to (4), wherein the downstream end of the reverse transport blade in the reverse direction is inserted into the first transport path by a length of one pitch or less.

[0008] This invention (6) is a developing device according to any one of inventions (1) to (5) above, wherein the reverse transport blade is arranged to be at least three pitches downstream in the first transport direction from a position that is the upstream end of the first connection part of the first transport path in the first transport direction. The invention (7) is the developing device according to the above invention (6), wherein the reverse transport blade is provided over the entire area of ​​the portion of the first transport path adjacent to the first connection portion. This invention (8) is a developing device according to the invention (6) above, wherein the first transport member is provided with the forward transport blade on a portion of the rotating shaft that is downstream in the first transport direction from the upstream end of the reverse transport blade in the reverse direction. This invention (9) is a developing device according to the above invention (6), in which the first transport member is provided with a plate-shaped transport blade downstream of the upstream end of the reverse transport blade in the reverse direction for transporting developer to the second transport path.

[0009] This invention (10) is the developing device of invention (6), (7) or (9) above, wherein an injection port for injecting developer into the second transport path is provided above a portion of the second transport path adjacent to the first connection portion. This invention (11) is a developing device according to the above invention (8), in which a discharge outlet for discharging a portion of the developer is provided in a portion of the first transport path where the forward transport blade is located downstream of the upstream end of the reverse transport blade in the reverse direction, or in a portion downstream of the forward transport blade in the first transport direction. This invention (12) is the developing device according to the above invention (9), wherein the first connection portion is provided continuously up to a position facing the plate-shaped transport blade.

[0010] Moreover, the present invention (13) is an image forming apparatus comprising a latent image carrier on which a latent image is held, and a developing device that develops the latent image on the latent image carrier with a developer, the developing device being configured as the developing device according to any one of the above inventions (1) to (12). Effect of the Invention

[0011] According to the above invention (1), a relative decrease in density of a visible image developed in a region of the development area corresponding to a portion downstream in the first transport direction of the first transport path through which the developer supplied to the development passing body is transported can be suppressed compared to a case in which a first transport member having a spiral forward transport blade attached to a rotating shaft that rotates in the first transport path to forward transport the developer in the first transport direction is provided with the forward transport blade extending at least to the downstream end in the first transport direction of a first connecting portion that connects with the second transport path just before the downstream end in the first transport direction of the first transport path.

[0012] According to the above invention (2), it is easier to increase the amount of developer present in the downstream portion of the first transport path in the first transport direction, compared to when the reverse transport blade is provided up to the boundary with the first connection portion in the first transport path. According to the above invention (3), it is easier to increase the amount of developer present in the downstream portion of the first transport path in the first transport direction, compared to a case in which the downstream end of the reverse transport blade is arranged so as not to pass beyond the upstream end of the first connection part in the first transport direction and enter the first transport path.

[0013] According to the above invention (4), it is possible to suppress density fluctuations in the image developed in the area corresponding to the part downstream in the first transport direction of the development area, compared to a case in which the downstream end of the reverse transport blade in the reverse direction is not positioned downstream in the first transport direction of the downstream end of the part of the development passing body that faces the development area. According to the above aspect (5), an increase in the driving load on the first transport member can be suppressed compared to a case where the end of the reverse transport blade on the downstream side in the reverse direction is inserted into the first transport path by a length longer than one pitch.

[0014] According to the above aspect (6), the developer transported in the first transport direction through the first transport path is more likely to remain in the first transport path, thereby suppressing a relative decrease in density of the visible image developed in the area corresponding to the downstream side of the development area. According to the above invention (7), compared to the case where the reverse transport blade is provided in a part of the portion adjacent to the first connection portion of the first transport path, it is possible to ensure that the developer transported forward in the first transport direction through the first transport path moves to the second transport path through the first connection portion, while suppressing a relative decrease in the density of the visible image developed in the area corresponding to the downstream side of the development area. According to the above invention (8), the developer transported forward through the first transport path downstream in the first transport direction by the first transport member does not continue to be transported forward by the forward transport blade provided in a portion in the first transport direction downstream of the upstream end of the reverse transport blade in the reverse direction, but is sent to the second transport path through the first connection portion by the reverse transport blade located upstream in the first transport direction of the forward transport blade. According to the above aspect (9), even if part of the developer transported by the plate-shaped transport blade enters the reverse transport blade side, the developer is sent to the second transport path through the first connection portion by the reverse transport blade.

[0015] According to the above invention (10), even if a portion of the developer injected from the injection port into the second transport path enters the portion adjacent to the first connection portion of the first transport path, the developer is sent so as to be returned to the second transport path by the reverse transport blade. According to the above invention (11), a portion of the developer is effectively discharged from the discharge outlet while suppressing a relative decrease in density of a visible image developed in the portion corresponding to the downstream side in the first transport direction, compared to a case in which no discharge outlet is provided in a portion where a forward transport blade is present in a portion downstream of the upstream end of the reverse transport blade in the reverse direction of the first transport path, or in a portion downstream of the forward transport blade in the first transport direction. According to the above invention (12), compared to a case where the first connection portion is not provided continuously up to a position facing the plate-shaped transport blade, the developer is more easily transported to the second transport path through the first connection portion by the plate-shaped transport blade, and even if part of the developer gets into the side of the reverse transport blade, it can be transported to the second transport path through the first connection portion by the reverse transport blade.

[0016] According to the above invention (13), the relative decrease in density of the visible image developed in the area of ​​the development region corresponding to the portion downstream in the first transport direction of the first transport path through which the developer supplied to the development passing body is transported can be suppressed compared to a case in which a first transport member having a spiral forward transport blade attached to a rotating shaft which rotates in the first transport path to transport the developer forward in the first transport direction, the forward transport blade being provided at least until it reaches the downstream end in the first transport direction of the first connecting portion which connects the first transport path to the second transport path just before the downstream end in the first transport direction of the first transport path, and a decrease in the relative density of the image portion due to the relative decrease in density of the visible image can also be suppressed. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram of an image forming apparatus according to a first embodiment. [Diagram 2] FIG. 2 is a schematic diagram of a developing device according to the first embodiment. [Diagram 3] 3 is a schematic diagram of the developing device in FIG. 2 with the upper part of the housing removed. [Figure 4] FIG. 2 is an enlarged schematic view of a part of the developing device. [Diagram 5] FIG. 2 is a schematic diagram showing a part of the developing device from another perspective. [Figure 6] FIG. 11 is a schematic diagram of a developing device according to a second embodiment. [Figure 7] FIG. 7 is a schematic diagram of the developing device in FIG. 6 with the upper part of the housing removed. [Figure 8] FIG. 2 is an enlarged schematic view of a part of the developing device. [Figure 9] FIG. 2 is a schematic diagram showing a part of the developing device from another perspective. [Figure 10] FIG. 2 is a schematic diagram of a developing device obtained by partially modifying the developing device according to the first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0019] First embodiment. FIG. 1 is a diagram showing an image forming apparatus 1 using a developing device 6A according to a first embodiment of the present invention. The arrows indicated by the symbols X, Y, and Z in each drawing such as Fig. 1 indicate the left-right direction (horizontal direction), the up-down direction (vertical direction), and the front-back direction (horizontal direction), respectively. Also, the circle at the intersection of the X and Y arrows in the drawing indicates that the Z direction is pointing vertically downward on the drawing (paper surface).

[0020] <Image forming device> The image forming apparatus 1 according to the first embodiment is an apparatus that forms an image on a recording paper 9, which is an example of a recording medium, by electrophotography. The image forming apparatus 1 is configured as a printer that forms an image corresponding to image information input from an externally connected device such as an information terminal.

[0021] As shown in FIG. 1, the image forming apparatus 1 includes, within the internal space of a housing 10 having a required external shape, an image forming device 2 that forms a toner image composed of toner as a developer based on image information and transfers the toner image onto a recording paper 9, which is an example of a recording medium, a paper feeding device 4 that stores and supplies the recording paper 9 to be supplied to a position where the image forming device 2 performs transfer, a fixing device 5 that fixes the toner image transferred by the image forming device 2 onto the recording paper 9, and a control means (not shown). 1 indicates a main transport path along which the recording paper 9 is transported inside the housing 10. The dotted and dashed lines in FIG.

[0022] The image forming device 2 has a photosensitive drum 21, which is an example of a latent image holder on which a latent image is formed and held, and is configured by arranging equipment such as a charging device 22, an exposure device 23, a developing device 6A, a transfer device 25, and a cleaning device 26 around the photosensitive drum 21.

[0023] Of these, the photosensitive drum 21 is a drum-shaped photosensitive body that rotates in the direction indicated by the arrow A around a rotation axis (not shown) that extends along the depth direction Z. The charging device 22 is a device that charges the outer circumferential surface (image forming surface) of the photosensitive drum 21 to a required surface potential. The charging device 22 is configured to include a charging member such as a roll that is brought into contact with the image forming area of ​​the outer circumferential surface of the photosensitive drum 21 and is supplied with a charging current. The exposure device 23 is a device that exposes the charged outer circumferential surface of the photosensitive drum 21 based on image information to form an electrostatic latent image.

[0024] The developing device 6A is a device that develops the electrostatic latent image formed on the outer peripheral surface of the photosensitive drum 21 with a developer (toner) of a corresponding predetermined color (e.g., black) to form a toner image, which is an example of a visible image. The developing device 6A will be described in detail later. The transfer device 25 is a device that electrostatically transfers the toner image formed on the outer peripheral surface of the photosensitive drum 21 onto the recording paper 9. The transfer device 25 is configured to include a transfer member such as a roll that comes into contact with the outer peripheral surface of the photosensitive drum 21 and is supplied with a transfer current. The cleaning device 26 is a device that cleans the outer peripheral surface of the photosensitive drum 21 by scraping off and removing unnecessary matter such as unnecessary toner and paper powder adhering to the outer peripheral surface of the photosensitive drum 21. In the image forming apparatus 2, each portion where the photosensitive drum 21 and the transfer device 25 face each other becomes a transfer position TP where the toner image is transferred.

[0025] The paper feeder 4 is disposed below the image forming device 2. The paper feeder 4 is configured by arranging devices such as a container 41 that stores recording paper 9 and a delivery device 43 that delivers the recording paper 9 one sheet at a time. The recording paper 9 may be any medium such as plain paper, coated paper, or thick paper that can be transported within the housing 10 and to which a toner image can be transferred and fixed, and there are no particular restrictions on its material, shape, etc. The recording medium represented by the recording paper 9 may be any medium that can be transported within the housing 10 and to which a toner image can be transferred and fixed.

[0026] The fixing device 5 is disposed at a position above the transfer position TP of the image forming device 2. The fixing device 5 is configured by arranging devices such as a heating rotor 51 and a pressure rotor 52 in the internal space of a housing 50 in which an inlet and an outlet for the recording paper 9 are formed. In the fixing device 5, the heating rotator 51 and the pressure rotator 52 are arranged so as to be in contact with each other in a substantially horizontal state. In the fixing device 5, the portion where the heating rotator 51 and the pressure rotator 52 contact each other is configured as a fixing processing portion (nip portion) FN which performs processing such as heating and pressure for fixing the unfixed toner image to the recording paper 9.

[0027] The main transport path for the recording paper 9 within the housing 10 is configured by an arrangement of multiple transport rolls 45a, 45b, 45c that clamp and transport the recording paper 9, and multiple guide members (not shown) that ensure a transport space for the recording paper 9 and guide the transport of the recording paper 9.

[0028] In the image forming apparatus 1, when a control means (not shown) receives a command for an operation of forming an image, the image forming device 2 performs a charging operation, an exposing operation, a developing operation and a transfer operation, while the paper feeding device 4 performs an operation of feeding the recording paper 9 to the transfer position TP. As a result, a toner image is formed on the photosensitive drum 21, and then the toner image is transferred onto the recording paper 9 supplied from the paper feeder 4 to the transfer position TP.

[0029] Next, in the image forming apparatus 1, the recording paper 9 onto which the toner image has been transferred is introduced into the nip portion FN in the fixing device 5, where a fixing operation is performed. As a result, the unfixed toner image is fixed onto the recording paper 9 . After the fixing is completed, the recording paper 9 is transported by, for example, transport rolls 45b and 45c, and then discharged to and stored in the discharge storage section 12 provided on the upper surface of the housing 10. In this manner, the image forming operation in which a toner image is formed on one side of the recording paper 9 is completed.

[0030] <Developing device> Next, the developing device 6A according to the first embodiment will be described in detail.

[0031] 2, the developing device 6A has a housing 60 consisting of a container-like lower part 60a that opens upward and a lid-like upper part 60b that closes the upper part 60a. The housing 60 is provided with an opening 61 for development and a storage part 62 that stores the developer 8. As the developer 8, for example, a two-component developer containing a non-magnetic toner and a magnetic carrier is used.

[0032] The opening 61 is a rectangular opening that is long in the depth direction Z facing the development area Ed where a latent image is developed in a portion extending along the rotation axis of the photosensitive drum 21, and its inside is connected to the storage section 62. A developing roll 71, which is an example of a development passing body that holds the developer 8 and passes through the development area Ed, is rotatably arranged in a lower part 60a on the inside of the opening 61 in the housing 60.

[0033] The developing roll 71 is composed of a cylindrical developing sleeve 71a that holds the developer 8 and rotates, and a magnet roll 71b that is fixedly disposed in the internal space of the developing sleeve 71a. The developing sleeve 71a is made of a non-magnetic material. As shown in Fig. 3, the shafts 71c and 71d at both ends of the developing sleeve 71a are rotatably attached to the left and right side walls 62c and 62d of the storage section 62, and the developing sleeve 71a is rotated in the direction indicated by the arrow B by the rotational power of a rotation drive device (not shown). A developing bias is supplied between the developing sleeve 71a and the photosensitive drum 21 from a power supply device (not shown). The magnet roll 71b has a plurality of magnetic poles arranged on the surface of the developing sleeve 71a, which generate magnetic forces that perform functions such as adsorption (pickup), retention, transport, and peeling of the developer 8.

[0034] As shown in Figures 2 and 3, the storage section 62 is provided with a first transport path 63 along which the developer 8 to be supplied to the developing roll 71 is transported, and a second transport path 64 along which the developer 8 to be sent to the first transport path 63 is transported. The first transport path 63 and the second transport path 64 are groove-shaped portions extending substantially parallel to the developing roll 71, and are separated by a partition wall 65 provided between them, while being connected to each other at connection parts 67, 68 provided to penetrate the front parts of both ends. As a result, the first transport path 63 and the second transport path 64 are configured as circulating transport paths in which the developer 8 is circulated and transported, with the developer 8 being moved and handed over to the opposite transport path at the connection parts 67, 68, respectively.

[0035] The connection portion 67 is a first connection portion that connects a front portion of the downstream end of the first transport path 63 in a first transport direction D1, which is the direction in which the developer 8 is transported, to a front portion of the upstream end of the second transport path 64 in a second transport direction D2, which is the direction in which the developer 8 is transported. The connection portion 68 is a second connection portion that connects a front portion of the upstream end of the first transport path 63 in the first transport direction D1 to a front portion of the downstream end of the second transport path 64 in the second transport direction D2.

[0036] In the first transport path 63, a first screw auger 72 is disposed as an example of a first transport member that transports the developer 8 forward in the first transport direction D1 while stirring the developer 8. The first screw auger 72 is provided such that a forward transport blade 72b for forward transporting the developer 8 in the first transport direction D1 is wound in a spiral shape around a round bar-shaped rotation shaft 72a that is arranged to rotate within the first transport path 63. This spiral forward transport blade 72b is provided so as to describe a spiral with a predetermined height, inclination angle, and pitch Pa. The first screw auger 72 is provided with a reverse conveying blade 74A that conveys in the reverse direction R1 opposite to the first conveying direction D1, wound in a spiral shape around a portion of the rotating shaft 72a adjacent to the first connecting portion 67. The spiral reverse conveying blade 74A is wound in the opposite direction to the winding direction of the forward conveying blade 72b with respect to the rotating shaft 72a, and is provided to draw a spiral with a predetermined height, inclination angle, and pitch Pb. The spiral reverse conveying blade 74A will be described in more detail below.

[0037] In the second transport path 64, a second screw auger 73 is disposed as an example of a second transport member that transports the developer 8 forward in the second transport direction D2 while stirring the developer 8. The second screw auger 73 is arranged so that a round rod-shaped rotating shaft 73a is rotated within the second transport path 64, and a forward transport blade 73b for forward transporting the developer 8 in the second transport direction D2 is spirally wound around the round rod-shaped rotating shaft 73a at a predetermined height, inclination angle and pitch. The second screw auger 73 is provided with a reverse transport blade 73c, which transports the developer in a direction R2 opposite to the second transport direction D2, wound in a spiral shape at a predetermined height, inclination angle, and pitch in a direction opposite to the winding direction of the forward transport blade 73b, on a part of the rotating shaft 73a adjacent to the second connecting portion 68. The reverse transport blade 73c prevents the developer 8 from accumulating at the downstream end of the second transport path 64 in the second transport direction D2.

[0038] The rotational power transmitted to the developing sleeve 71a of the developing roll 71 is distributed to the first screw auger 72 and the second screw auger 73 via a gear train mechanism (not shown), so that the first screw auger 72 and the second screw auger 73 rotate in a required direction, for example, in the direction of the arrow shown in FIG. 2, at a required speed.

[0039] A trimmer plate 74 is disposed in a portion of the upper portion 60b of the housing 60 near the opening 61, as an example of an adjustment member for adjusting the amount (layer thickness) of the developer 8 held by the developing roll 71. The trimmer plate 74 is attached so that its lower end portion faces the surface of the developing roll 71 (the developing sleeve 71a) at a predetermined distance and in parallel with the direction of the rotation axis of the developing sleeve 71a.

[0040] The developing device 6A operates as follows.

[0041] When the time comes for the developing operation to be performed in the developing device 6A, as shown in FIG. 2, the developing sleeve 71a of the developing roll 71 starts to rotate in the direction indicated by the arrow B, and the first screw auger 72 and the second screw auger 73 also start to rotate in the directions indicated by the respective arrows.

[0042] 2 and 3, in the second transport path 64, the developer 8 is transported forward in the second transport direction D2 while being stirred by the spiral forward transport blade 73b of the rotating second screw auger 73. At this time, the toner of the developer 8, which is a two-component developer, is triboelectrically charged to a required polarity (e.g., negative polarity) by the carrier. In addition, the developer 8 transported forward to the downstream side of the second transport direction D2 of the second transport path 64 is sent to the first transport path 63 side while also receiving a reverse transport force by the spiral reverse transport blade 73c at the second connection part 68, as exemplified by the dashed arrow D3 in FIG.

[0043] In the first transport path 63, the developer 8 is transported forward in the first transport direction D1 while being stirred by the spiral forward transport blade 72b of the rotating first screw auger 72. At this time, a part of the forwardly transported developer 8 (mainly toner) is attracted to and supplied to the outer circumferential surface of the developing sleeve 71a of the developing roll 71 by magnetic force and electrostatic force. In addition, the developer 8 transported forward to the downstream side of the first transport direction D1 of the first transport path 63 is sent to the second transport path 64 side while also receiving a reverse transport force by the spiral reverse transport blade 74A at the first connection portion 67, as exemplified by the dashed arrow D4 in FIG. 3.

[0044] Furthermore, in the developing roll 71, the developer 8, which is a two-component developer, forms a spike-like magnetic brush and is held on the outer peripheral surface of the rotating developing sleeve 71a, and is then transported in the direction indicated by arrow B and passes through a trimmer plate 74. At this time, the developer 8 held on the outer peripheral surface of the developing sleeve 71a is made to pass through the development area Ed on the photosensitive drum 21 after the amount held is adjusted by restricting the passage of excess developer 8 by the trimmer plate 74.

[0045] In the development area Ed, the toner of the developer 8 on the outer circumferential surface of the development sleeve 71a of the development roll 71 is reciprocated by a development electric field formed between the photosensitive drum 21 and the developer 8 by supplying a development bias, and some of the toner adheres to the latent image portion on the photosensitive drum 21 by electrostatic force and is used to develop the latent image. At this time, some of the toner and carrier of the developer 8 that is not used for development is peeled off from the development sleeve 71a in the storage section 62 after passing through the development area Ed and is returned to the first transport path 63.

[0046] 3, in the developing device 6A, the density of the toner image developed in the area portion Edj corresponding to the downstream portion of the first transport path 63 in the first transport direction D1 of the development area Ed may be relatively lower than the density of the toner image developed in the other portion than the area portion Edj. The density of the toner image is actually observed as the density of the image portion fixed on the recording paper 9. The area portion Edj occupies, for example, about 1 to 50% of the entire development area Ed. Such a phenomenon that the density of the toner image developed in the area portion Edj decreases tends to occur more easily as the length of the development area Ed in the direction of the rotation axis becomes longer (for example, as the length becomes 165 mm or more).

[0047] <Detailed configuration of the developing device> Therefore, in this developing device 6A, as shown in Figures 3 and 4, a spiral reverse conveying blade 74A is provided on at least a portion of the rotating shaft 72a of the first screw auger 72 adjacent to the first connection portion 67, so that its downstream end 74As in the reverse direction R1 at least reaches the upstream end 67a of the first connection portion 67 in the first conveying direction D1.

[0048] As shown in FIG. 4, the spiral reverse conveyance blade 74A in the first embodiment is provided in a state where the downstream end 74As in the reverse direction R1 enters the first conveyance path 63 beyond the upstream end 67a of the first connection portion 67 in the first conveyance direction D1. In other words, the spiral reverse conveyance blade 74A at this time is provided in a state of straddling the boundary M with the first connection portion 67 in the first conveyance path 63. Further, the spiral reverse conveyance blade 74A in the first embodiment is provided so as to exist over the entire area of the portion of the rotation shaft 72a adjacent to the first connection portion 67.

[0049] From the viewpoint of, for example, slightly blocking a part of the developer 8 being forwardly conveyed on the downstream side of the first conveyance path 63 in the first conveyance direction D1, the pitch Pb of the spiral reverse conveyance blade 74A is set to a value smaller than the pitch Pa of the forward conveyance blade 72b (Pb < Pa), preferably a value smaller than half of the pitch Pa of the forward conveyance blade 72b. Also, the inclination angle of the spiral reverse conveyance blade 74A with respect to the axis of the rotation axis 72a of the spiral is set to a value larger than the inclination angle of the forward conveyance blade 72b, for example, a value close to a perpendicular angle of about 80 to 90°.

[0050] Furthermore, as shown in FIG. 3, the downstream end 74As of the spiral reverse conveyance blade 74A is provided at a position downstream of the first conveyance direction D1 from the downstream end Ede in the first conveyance direction of the portion facing the development region Ed of the developing roll 71 without exceeding the downstream end Ede in the first conveyance direction. When the downstream end 74As of the spiral reverse conveyance blade 74A is provided at a position upstream of the downstream end Ede in the first conveyance direction D1 of the development region Ed in the first conveyance direction D1, the developer 8 in the downstream portion of the first conveyance path 63 is easily moved and fluctuated by the spiral reverse conveyance blade 74A of the first screw auger 72, and the development corresponding to the downstream portion becomes unstable and the density of the toner image developed fluctuates.

[0051] 4, the spiral reverse transport blade 74A is provided such that its downstream end 74As enters the first transport path 63 by a length of about 1 / 4 pitch. When the downstream end 74As of the spiral reverse transport blade 74A enters the first transport path 63, it is preferable that the length of the entry is one pitch or less. If the entry pitch exceeds one pitch, the amount of developer 8 moving to the second transport path 64 decreases and the amount of developer 8 present in the first transport path 63 increases, and the drive load for rotating the first screw auger 72 is likely to increase. Incidentally, at this time, the downstream end 72be of the spiral forward transport blade 72b of the first screw auger 72 in the first transport direction D1 is provided with a gap in the axial direction of the rotation shaft 72a from the downstream end 74As of the spiral reverse transport blade 74A, as shown in Fig. 4. By providing this gap, the moving speed of the forward transported developer 8 decreases immediately before it reaches the downstream end 74As of the spiral reverse transport blade 74A, and this makes it easier for the developer 8 to accumulate while suppressing the developer 8 from becoming unruly when it reaches the downstream end 74As of the spiral reverse transport blade 74A and is subjected to the action of reverse transport.

[0052] In this developing device 6A, when the screw auger 72 rotates, its spiral reverse transport blade 74A rotates so as to temporarily block the path of the developer 8 being transported forward in the first transport path 63 at a portion (at the boundary M) near the upstream end 67a of the first connection portion 67 in the first transport path 63. As a result, when the developer 8 in the first conveying path 63 is conveyed forward in the first conveying direction D1 by the rotating first screw auger 72 and moves downstream of the first conveying path 63, a portion of the developer 8 being conveyed forward comes into contact with the spiral reverse conveying blade 74A and is blocked, thereby suppressing movement downstream in the first conveying direction D1 of the first conveying path 63 and movement toward the first connection portion 67.

[0053] As a result, in the downstream portion of the first transport path 63, as shown in Fig. 5 by the broken line 80A representing the developer surface, the amount (bulk) of the developer 8 is the same as or slightly increased compared to the amount in the upstream or central portion of the first transport path 63. Furthermore, this makes it easier for the developing roll 71 to attract a sufficient amount of developer 8 (mainly toner) from the downstream side of the first transport path 63, and approximately the same amount of developer 8 as in the upstream or central portion of the first transport path 63 is supplied.

[0054] In this regard, in the case of the first screw auger 72 in which the spiral forward transport blade 72b is provided at a position that reaches or extends beyond the downstream end 67a of the first connection portion 67 of the first transport path 63 in the first transport direction D1, the amount of developer 8 downstream of the first connection portion 67 in the first transport direction D1 may be less than the amount of developer 8 in the portion up to that point, as illustrated by the dashed dotted line 80B in Figure 5, where the developer surface of the developer 8 is shown.

[0055] Therefore, in this developing device 6A, development is performed in a state where the developer 8 is supplied in an amount substantially the same as that in the area portions other than the area portion Edj, even in the area of ​​the developing roll 71 corresponding to the area portion Edj that corresponds to the downstream portion of the development area Ed in the first transport direction D1 of the first transport path 63. As a result, in the developing device 6A, the density of the toner image developed in the portion of the developing roll 71 corresponding to the above-mentioned area portion Edj is prevented from decreasing relatively compared to the density of the toner image developed in portions other than the area portion Edj, compared to the case where the spiral forward conveying blade 72b is extended at least to reach the downstream end 67a of the first connection portion 67 of the first conveying path 63 in the first conveying direction D1. Furthermore, in the image forming apparatus 1 using the developing device 6A, the decrease in relative density of the image portion caused by the decrease in density of the toner image is also suppressed.

[0056] In addition, in this developing device 6A, as illustrated by the dotted line in Figures 2 and 5, an injection port 82 for injecting developer 8 (mainly only toner) into the second conveying path 64 may be provided above the portion adjacent to the first connection portion 67 of the second conveying path 64.

[0057] In this case, even if a portion of the developer 8 injected from the injection port 82 into the second transport path 64 enters the portion adjacent to the first connection portion 67 of the first transport path 63, the developer 8 that entered is sent by the reverse transport blade 74A so as to be returned to the second transport path 64. As a result, the developer 8 injected from the injection port 82 into the second transport path 64 is sent satisfactorily into the second transport path 64 and transported forward in the second transport direction D2 while being agitated by the second screw auger 73.

[0058] Second embodiment. FIG. 6 is a diagram showing a developing device 6B according to a second embodiment of the present invention. The developing device 6B according to the second embodiment is different from the developing device 6A according to the first embodiment in that a part of the basic structure has been changed and a part (such as the spiral reverse transport blade) of the first screw auger 72 has been changed, but the rest of the configuration is the same. Therefore, in the following description, the common components are denoted by the same reference numerals used in the first embodiment, and the description thereof will be omitted unless necessary.

[0059] The developing device 6B is configured by adding an intermediate transport roll 76, a movement assist member 77, a third screw auger 78, a second trimmer plate 79, etc. to the developing device 6A according to the first embodiment.

[0060] The relay transport roll 76 is an example of a developer transport body that is positioned above the first screw auger 72 and holds a portion of the developer 8 transported forward by the first screw auger 72, and then relays and transports it toward the developing roll 71. The intermediate transport roll 76 is similar to the developing roll 71, and is composed of a cylindrical transport sleeve 76a that holds and rotates the developer 8, and a magnet roll 76b that is fixedly disposed in the internal space of the transport sleeve 76a. The transport sleeve 76a is made of a non-magnetic material. The transport sleeve 76a is rotated in the direction indicated by the arrow C by being distributed with the rotational power transmitted to the developing roll 71 or the first screw auger 72. The magnet roll 76b has a plurality of magnetic poles disposed on the surface of the transport sleeve 76a that generate magnetic forces that perform the functions of adsorbing (pickup), holding and transporting the developer 8, peeling it off, etc.

[0061] The movement assist member 77 is a non-magnetic member that is disposed between the portion of the developing roll 71 upstream of the trimmer plate 74 in the rotation direction B and the relay transport roll 76, and has an inclined surface 77a that receives the developer 8 sent from the relay transport roll 76 and moves it to the developing roll 71.

[0062] The third screw auger 78 is an example of a third transport member that transports at least a portion of the developer 8C that has passed through the development area Ed of the developing roll 71 and then peeled off so as to eventually return to the second transport path 64. The third screw auger 78 is provided below the developing roll 71 in the lower part 60a of the housing 60 in a state parallel to the rotation axis of the developing roll 71, and is disposed in a third transport path 66 along which the developer 8C peeled off from the developing roll 71 is transported. As shown in Figures 6 and 7, the third transport path 66 is a groove-shaped portion in which a portion facing the portion of the developing roll 71 that peels off the developer 8 is opened and connected, and is connected to the first transport path 63 via a third connection portion 69 that penetrates the first connection portion 67 in the first transport path 63 at a front portion of the downstream end in the third transport direction (depth direction Z in this example) along which the developer 8C is transported.

[0063] The third screw auger 78 is arranged so that a round rod-shaped rotating shaft 78a is rotated within the third transport path 66, and a forward transport blade 78b, which forward transports the developer 8C peeled off from the developing roll 71 in the third transport direction, is spirally wound around the rotating shaft 78a at a predetermined height, inclination angle and pitch. Furthermore, the third screw auger 78 is provided with a plurality of plate-shaped transport blades 78c rising from the rotary shaft 78a at a portion of the rotary shaft 78a adjacent to the third connection portion 69, for sending the developer 8C to the first transport path 63 adjacent to the first connection portion 67. The third screw auger 78 is also provided with a reverse transport blade 78d spirally wound around a portion of the rotary shaft 78a downstream of the plate-shaped transport blades 78c in the third transport direction.

[0064] The second trimmer plate 79 is an example of a second adjustment member that adjusts the amount (layer thickness) of the developer 8 held by the transport sleeve 76a. The second trimmer plate 79 is attached in a state where one end of the second trimmer plate 79 faces the surface of the intermediate transport roll 76 (the transport sleeve 76a) at a predetermined interval and is parallel to the direction of the rotation axis of the transport sleeve 76a.

[0065] Next, the first screw auger 72 in the developing device 6B is provided so that a reverse transport blade 74B, which transports in the opposite direction R1 to the first transport direction D1, is spirally wound around a portion of the rotating shaft 72a, but not the entire area, adjacent to the first connection portion 67.

[0066] 7 and 8, the spiral reverse conveying blade 74B may be provided with a length of at least three pitches from a position (part of boundary M) that is an end 67a on the upstream side of the first connecting portion 67 of the first conveying path 63 in the first conveying direction D1 downstream in the first conveying direction D1 with respect to the rotating shaft 72a, and is provided with a length of, for example, about three and a half pitches. In this respect, it differs from the first screw auger 72 in the first embodiment. Also, the spiral reverse conveying blade 74B has the same configuration as the spiral reverse conveying blade 74A in the first embodiment 1, except for the range in which it is provided.

[0067] 9 and other drawings, the first screw auger 72 in the developing device 6B is provided with a plate-shaped transport blade 75 for transporting the developer 8C transported from the third transport path 66 to the second transport path 64 on a portion of the rotation shaft 72a upstream of an end 74Be on the upstream side in the reverse direction R1 of the spiral reverse transport blade 74B. This differs from the first screw auger 72 in the first embodiment in that the plate-shaped transport blade 75 is not provided. The plate-shaped conveying blades 75 are also called paddles, and a plurality of conveying blades 75 are provided to rise from the rotation shaft 72a. As the plate-shaped conveying blades 75, for example, a plate member having approximately the same width as the opening width of the third connecting portion 69 along the third conveying direction D5 is used.

[0068] 8 and other drawings, the first screw auger 72 is provided with a spiral reverse transport blade 74C for reversely transporting the developer 8 in the reverse direction R1 in a portion between the plate-shaped transport blade 75 of the rotating shaft 72a and the downstream end of the first transport path 63 in the first transport direction D1. The reverse transport blade 74C prevents the developers 8, 8C from accumulating at the downstream end of the first transport path 63 in the first transport direction D1.

[0069] The developing device 6B operates as follows.

[0070] When the time comes for the developing operation to be performed in the developing device 6B, as shown in FIG. 6, the developing sleeve 71a of the developing roll 71 starts to rotate in the direction indicated by arrow B, and the transport sleeve 76a of the intermediate transport roll 76, the first screw auger 72, the second screw auger 73, and the third screw auger 78 also start to rotate in the directions indicated by the respective arrows.

[0071] 6 and 7, in the second transport path 64, the developer 8 is transported forward in the second transport direction D2 while being agitated by the spiral forward transport blade 73b of the rotating second screw auger 73. The developer 8 transported forward to the downstream side of the second transport direction D2 of the second transport path 64 is sent to the first transport path 63 side while also receiving a reverse transport force from the spiral reverse transport blade 73c at the second connection portion 68, as illustrated by the dashed arrow D3 in FIG.

[0072] In the first transport path 63, the developer 8 is transported forward in the first transport direction D1 while being agitated by the spiral forward transport blade 72b of the rotating first screw auger 72. At this time, above the first transport path 63, a portion of the developer 8 being transported forward by the first screw auger 72 is held on the outer peripheral surface of the transport sleeve 76a of the intermediate transport roll 76 by magnetic force, and is then transported by rotation of the transport sleeve 76a in the direction of arrow C.

[0073] When the developer 8 held and transported on the transport sleeve 76a passes through the second trimmer plate 79, the excess developer 8 is restricted from passing by the second trimmer plate 79, and the amount held is adjusted. The excess developer 8 falls back into the first transport path 63 and is transported forward in the first transport direction by the first screw auger 72, but some of it may be held by the intermediate transport roll 76 again. By making the second trimmer plate 79 return the excess developer 8 held on the intermediate transport roll 76 to the first transport path 63, the amount of developer 8 present in the portion of the first transport path 63 downstream in the first transport direction D1 is prevented from decreasing, and the amount is maintained to a certain extent.

[0074] Next, the developer 8 held and transported on the transport sleeve 76a is peeled off from the surface of the transport sleeve 76a at a position before passing over the inclined surface 77a of the movement assist member 77, and is transferred to the inclined surface 77a. The peeled developer 8 slides along the non-magnetic inclined surface 77a and moves to the developing roll 71, where it is attracted to the surface of the developing sleeve 71a of the developing roll 71 by magnetic force or the like and is supplied. On the other hand, the developer 8 transported forward to the downstream side of the first transport direction D1 of the first transport path 63 is sent to the second transport path 64 side while also receiving a reverse transport force from the spiral reverse transport blade 74B at the first connection portion 67, as illustrated by the dashed arrow D4 in Figure 7.

[0075] Furthermore, in the developing roll 71, the developer 8, which is a two-component developer that is supplied while sliding along the inclined surface 77a of the movement auxiliary member 77, forms and is held on the outer peripheral surface of the rotating developing sleeve 71a by forming a spike-like magnetic brush, and is then transported in the direction indicated by the arrow B and passes through the trimmer plate 74. At this time, the developer 8 held on the outer peripheral surface of the developing sleeve 71a is allowed to pass through the development area Ed on the photosensitive drum 21 after the amount held is adjusted by restricting the passage of any excess developer 8 by the trimmer plate 74.

[0076] In the development area Ed, a part of the toner of the developer 8 held on the outer circumferential surface of the developing sleeve 71a of the developing roll 71 and transported adheres to the latent image portion on the photosensitive drum 21 by electrostatic force and is used to develop the latent image. At this time, a part of the toner and carrier of the developer 8C that is not used for development is peeled off from the developing sleeve 71a in the storage section 62 after passing through the development area Ed, and is transported to drop into the third transport path 66.

[0077] In the third transport path 66, as shown in FIG. 9, the developer 8C that has been peeled off from the developing sleeve 71a and dropped is forward transported downstream in the third direction D5 by the forward transport blade 78b of the rotating third screw auger 78. Furthermore, the developer 8C conveyed forward to the downstream side of the third conveying path 66 in the third conveying direction D5 is conveyed to the first conveying path 63 by the plate-shaped conveying blade 77c at a portion adjacent to the third connecting portion 69. Next, the developer 8C conveyed to the first conveying path 63 is conveyed to the second conveying path 64 by the plate-shaped conveying blade 75 of the first screw auger 72, as illustrated by the arrow D6 in Fig. 9. Finally, the developer 8C conveyed to the second conveying path 64 is conveyed forward in the second conveying direction D2 by the second screw auger 73 and mixed with the developer 8 already present in the second conveying path 64.

[0078] In this developing device 6B, when the first screw auger 72 rotates, its spiral reverse transport blade 74B functions in the same manner as the spiral reverse transport blade 74A in the first embodiment, and rotates so as to temporarily block the path of the developer 8 being transported forward in the first transport path 63 at a portion (at the boundary M) near the upstream end 67a of the first connection portion 67 in the first transport path 63. As a result, when the developer 8 in the first conveying path 63 is conveyed forward in the first conveying direction D1 by the rotating first screw auger 72 and moves downstream of the first conveying path 63, a portion of the developer 8 being conveyed forward comes into contact with the spiral reverse conveying blade 74B and is blocked, thereby suppressing movement downstream in the first conveying direction D1 of the first conveying path 63 and movement toward the first connection portion 67.

[0079] As a result, in the downstream portion of the first transport path 63, as shown by the broken line 80A of the developer surface in Fig. 9, the amount (bulk) of the developer 8 becomes the same as or slightly increased compared to the amount in the upstream or central portion of the first transport path 63. Moreover, this makes it easier for the developing roll 71 to attract a sufficient amount of developer 8 (mainly toner) from the downstream side of the first transport path 63, and approximately the same amount of developer 8 as in the upstream or central portion of the first transport path 63 is supplied.

[0080] In this regard, when the spiral forward transport blade 72b of the first screw auger 72 is provided at a position that reaches or extends beyond the end 67a downstream in the first transport direction D1 of the first connection portion 67 of the first transport path 63, the amount of developer 8 downstream in the first transport direction D1 of the first connection portion 67 may be less than the amount of developer 8 in the upstream portion, as illustrated by the dotted line 80B in Figure 9, where the developer surface of the developer 8 is indicated.

[0081] Therefore, in this developing device 6B, even in the portion of the developing roll 71 corresponding to the area portion Edj corresponding to the portion of the development area Ed downstream in the first transport direction D1 of the first transport path 63, development is performed in which developer 8 is supplied in an amount substantially the same as in the area portions other than the area portion Edj. As a result, in the developing device 6B, the density of the toner image developed in the portion of the developing roll 71 corresponding to the above-mentioned area portion Edj is prevented from decreasing relatively compared to the density of the toner image developed in portions other than the area portion Edj, as compared to the case where the spiral forward conveying blade 72b is extended at least to reach the downstream end 67a of the first connection portion 67 of the first conveying path 63 in the first conveying direction D1. Also in the image forming apparatus 1 (FIG. 1) using this developing device 6B, the decrease in relative density of the image portion caused by the decrease in density of the toner image is suppressed.

[0082] In the developing device 6B, a spiral reverse transport blade 74B is provided on the first screw auger 72 upstream of the plate-shaped transport blade 75 in the first transport direction D1. For this reason, even if part of the developer 8C transported by the plate-shaped transport blade 75 enters the reverse transport blade 74B side, the developer 8C is sent to the second transport path 64 through the first connection portion 67 by the reverse transport blade 74B.

[0083] 7 and 8, in the developing device 6B, the first connection portion 67 is provided continuously up to a position facing the plate-shaped transport blade 75. Therefore, compared to a case where the first connection portion 67 is not provided continuously up to a position facing the plate-shaped transport blade 75, the developer 8C conveyed by the plate-shaped transport blade 75 is more easily conveyed to the second transport path 64 through the first connection portion 67, and even if part of the developer 8C enters the side of the spiral reverse transport blade 74B, it can be conveyed to the second transport path 64 through the first connection portion 67 by the reverse transport blade 74B.

[0084] In addition, in this developing device 6B as well, an injection port 82 for injecting developer 8 (mainly only toner) into the second conveying path 64 may be provided above the portion adjacent to the first connection portion 67 of the second conveying path 64, as illustrated by the two-dot chain lines in Figures 6 to 8.

[0085] In this case, even if a part of the developer 8 injected from the injection port 82 into the second transport path 64 gets into the portion of the first transport path 63 adjacent to the first connection portion 67, the developer 8 that got in is sent so as to be returned to the second transport path 64 by one or both of the reverse transport blade 74B and the plate-shaped transport blade 75. As a result, the developer 8 injected from the injection port 82 into the second transport path 64 is sent well into the second transport path 64 and transported forward in the second transport direction D2 while being agitated by the second screw auger 73.

[0086] Variations. The present invention is not limited to the contents exemplified in the first and second embodiments, and includes, for example, the following modified examples.

[0087] FIG. 10 is a diagram illustrating a part of a developing device 6C which is a partial modification of the developing device 6A according to the first embodiment. The developing device 6C is provided with an extension conveying path 84 in the shape of a groove whose cross section is relatively smaller than that of the first conveying path 63 and whose bottom surface is raised by one step, which is extended from the developing device 6A in the downstream end of the first conveying path 63 in the first conveying direction D1, and a discharge port 85 for discharging a part of the developer 8 is provided on the bottom surface at the end side of the extension conveying path 84. This discharge port 85 is for recovering a part of the developer 8 that is not used in the developing operation and whose performance required for development has deteriorated. The discharge port 85 is connected to a recovery container (not shown) that contains the recovered developer.

[0088] In addition, this developing device 6C has an extended rotating shaft 72c with a relatively small diameter extended from the end downstream in the first conveying direction D1 of the rotating shaft 72a of the first screw auger 72, and the extended rotating shaft 72c is rotatably attached to the side wall portion 62d of the storage section 62. Furthermore, in this developing device 6C, a spiral extended forward transport blade 72d that transports the paper in the extended transport direction D8 is provided on an extended rotation shaft 72c that is a portion further upstream of an end 74Ae on the upstream side in the reverse direction R1 of the reverse transport blade 74A of the first screw auger 72. The extended forward transport blade 72d has a smaller height and pitch than the forward transport blade 72b, and has a larger inclination angle.

[0089] In this developing device 6C, a portion of the developer 8 being transported forward through the first transport path 63 downstream in the first transport direction D1 by the first screw auger 72 is blocked by the reverse transport blade 74A, and the remaining portion enters the side of the extended forward transport blade 72d. However, the developer 8 transported forward along the first transport path 63 to the downstream side in the first transport direction D1 is not likely to continue to be transported forward by the extended forward transport blade 72d due to the presence of the reverse transport blade 74A, and is sent to and handed over to the second transport path 64 through the first connection portion 67 by the reverse transport blade 74A that is present upstream of the extended forward transport blade 72d in the first transport direction D1. In other words, most of the developer 8 flows in a circulating manner.

[0090] In addition, when a plate-shaped conveying blade 75 is provided next to the spiral reverse conveying blade 74B as in the first screw auger 72 in the second embodiment, or when a spiral extended forward conveying blade 72d is provided next to the spiral reverse conveying blade 74A as in the first screw auger 72 in the above-mentioned modified example, the spiral reverse conveying blade 74B and the spiral extended forward conveying blade 72d may be arranged to be at least three pitches downstream in the first conveying direction D1 from a position (boundary M) that is the upstream end 67a of the first connection portion 67 of the first conveying path 63 in the first conveying direction D1.

[0091] In this case, if the reverse transport blade 74B is provided so as to have a length of at least three pitches, the developer 8 transported forward in the first transport direction D1 on the first transport path 63 is likely to remain at the downstream end of the first transport path 63, and the relative decrease in density of the image portion due to the decrease in density of the toner image is also suppressed. In this case, the reverse transport blade 74A and the reverse transport blade 74B ensure that the developer 8 transported forward in the first transport direction D1 on the first transport path 63 moves to the second transport path 64 through the first connection portion 67, while suppressing the relative decrease in density of the toner image developed in the portion corresponding to the area portion Edj on the downstream side of the development area Ed. Furthermore, even if nothing is provided next to the spiral reverse transport blade 74A like the first screw auger 72 in the first embodiment 1, it may be provided so as to have a length of at least three pitches downstream from the boundary M in the first transport direction D1.

[0092] The image forming apparatus is not limited to the image forming apparatus 1 having the configuration exemplified in the first embodiment, etc., and may be an image forming apparatus of any configuration as long as the developing devices 6A, 6B exemplified in this invention are applicable. For example, the image forming apparatus may employ an image forming apparatus that employs an intermediate transfer method as the image forming device 2, or may employ an image forming apparatus capable of forming a multi-color image instead of a monochromatic image. The developing passing body in the developing device is not limited to the developing roll 71, and may be in a form other than a roll. [Explanation of symbols]

[0093] 1. Image forming device 6A,6B…Developing device 8... Developer 21...Photosensitive drum (an example of a latent image carrier) 60…Housing 63…First conveying route 64…Second transport path 67…First connection part 67a... upstream end in the first conveying direction 71...Developing roll (an example of a developing passing body) 71de: downstream end in the first transport direction of the portion facing the development area 72...First screw auger (an example of a first conveying member) 72a...Rotating shaft 72b...Spiral forward conveying blade 72d...Spiral extended forward conveying blade (an example of a spiral forward conveying blade) 74A, 74B...Spiral reverse conveying blades 74As, 74Bs: Downstream end in the reverse direction 75...Plate-shaped conveying blade 82…Inlet 85…Discharge port D1: First conveying direction D2: Second conveying direction D8…Extended conveying direction (an example of the forward conveying direction) Ed…Development area M … Boundary with the first connection part of the first transport path R1…Reverse direction

Claims

1. a developer passing member that passes through a development area while holding a developer; a first transport path through which the developer to be supplied to the developing passage is transported; a second transport path through which the developer to be fed to the first transport path is transported; a first connection portion that connects a front portion of a downstream end of the first transport path in a first transport direction to a front portion of an upstream end of the second transport path in a second transport direction; a first transport member having a rotating shaft provided with a spiral forward transport blade that rotates in the first transport path to forward transport the developer in a first transport direction; Equipped with the first transport member is provided such that a downstream end of the forward transport blade in the first transport direction is located at a position away from the developing area on the first transport direction downstream side, Furthermore, the first transport member has a spiral reverse transport blade that reversely transports the developer in the opposite direction to the first transport direction, provided on at least a portion of the portion of the rotating shaft adjacent to the first connection portion, such that the downstream end of the reverse direction at least reaches the upstream end of the first connection portion in the first transport direction.

2. The developing device according to claim 1 , wherein the reverse transport blade is provided across a boundary between the first transport path and the first connection portion.

3. 2. The developing device according to claim 1, wherein the downstream end of the reverse transport blade in the reverse direction extends beyond the upstream end of the first connecting portion in the first transport direction and enters the first transport path.

4. The developing device according to any one of claims 1 to 3, wherein the downstream end of the reverse transport blade in the reverse direction is arranged to be located downstream in the first transport direction of the downstream end of the portion of the developing passing body that faces the development area.

5. 5. The developing device according to claim 1, wherein a downstream end of the reverse transport blade in the reverse direction is inserted into the first transport path by a length of one pitch or less.

6. The developing device according to any one of claims 1 to 5, wherein the reverse transport blade is arranged to be at least three pitches downstream in the first transport direction from a position that is the upstream end of the first connection portion of the first transport path in the first transport direction.

7. 7. The developing device according to claim 6, wherein the reverse transport blade is provided over the entire area of ​​the portion of the first transport path adjacent to the first connection portion.

8. 7. The developing device according to claim 6, wherein the first transport member has the forward transport blade provided on a portion of the rotating shaft that is downstream in the first transport direction from an upstream end of the reverse transport blade in the reverse direction.

9. 7. The developing device according to claim 6, wherein the first transport member is provided with a plate-shaped transport blade that transports the developer to the second transport path downstream of an upstream end of the reverse transport blade in the reverse direction.

10. 10. The developing device according to claim 6, further comprising an injection port for injecting developer into the second transport path, the injection port being provided above a portion of the second transport path adjacent to the first connection portion.

11. 9. The developing device according to claim 8, wherein an outlet for discharging a portion of the developer is provided in a portion of the first transport path downstream of the upstream end of the reverse transport blade in the reverse direction, where the forward transport blade is located, or in a portion downstream of the forward transport blade in the first transport direction.

12. The developing device according to claim 9 , wherein the first connection portion is provided continuously up to a position facing the plate-shaped transport blade.

13. a latent image holder on which a latent image is held, and a developing device for developing the latent image on the latent image holder with a developer; An image forming apparatus, comprising the developing device according to claim 1 .

Images