Developing device and image-forming device

Abstract

To provide a developing device capable of appropriately maintaining the amount of toner in a developing container.SOLUTION: A developing device 40 includes a developing container 50, a first conveyance member 42 and a second conveyance member 43, a developing roller 44, and a toner density sensor 46. The first conveyance member 42 and the second conveyance member 43 are rotatably supported by a first conveyance chamber 52 and a second conveyance chamber 53 of the developing container 50, and agitates a developer in the opposite direction of a longitudinal direction of the developing container 50 mutually and convey and circulate it. The first conveyance member 42 has a rotating shaft 42a, and a first spirally formed conveyance blade 42b. The first conveyance blade 42b has a cut section 42c partially cut in an opposing area of the toner density sensor 46.SELECTED DRAWING: Figure 4

Description

Technical Field

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

Background Art

[0002] In electrophotographic image forming apparatuses such as copiers and printers, a device that forms a toner image to be later transferred onto paper is widely used by supplying toner to an electrostatic latent image formed on the outer peripheral surface of an image carrier such as a photoreceptor drum and developing it. In order to continuously form a uniform image, the image forming apparatus conveys a developer containing toner accommodated in a developing container while stirring it inside the developing container. Further, in order to realize suitable image formation, the developing container is provided with a toner concentration sensor that detects the toner concentration inside the developing container.

[0003] A conventional developing device disclosed in Patent Document 1 includes a conveying screw having a plurality of blades formed spirally around a rotating shaft for conveying the developer. Further, the developing device includes an inductance sensor as a toner concentration sensor for detecting the toner concentration inside the developing container. Thereby, by measuring the toner concentration, various information such as the excess or deficiency of toner in the developing device and the circulation cycle of the replenishing developer can be obtained, and a uniform toner image can be formed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, if the conveyance speed of the developer in the developing container is increased by increasing the rotation speed of the conveyance screw or increasing the number of the spiral blades, there is a problem in that the toner concentration (detection value) may become unstable when the weight of the developer fluctuates. There was a concern that the detection value of the toner concentration becoming unstable would make it impossible to appropriately maintain the amount of toner in the developing container and prevent the realization of suitable image formation.

[0006] The present invention has been made in view of the above points, and an object thereof is to provide a developing device and an image forming device capable of appropriately maintaining the amount of toner in a developing container.

Means for Solving the Problem

[0007] To solve the above problems, a developing device of the present invention includes a developing container, a first conveyance member and a second conveyance member, a developer carrier, and a toner concentration sensor. The developing container has a first conveyance chamber and a second conveyance chamber that are arranged in parallel and communicate with each other at both longitudinal ends, and houses a developer containing toner to be supplied to an image carrier. The first conveyance member and the second conveyance member are rotatably supported in the first conveyance chamber and the second conveyance chamber, respectively, and convey and circulate the developer while stirring it in opposite directions in the longitudinal direction. The developer carrier is rotatably supported by the developing container so as to face the image carrier, and supplies the toner in the second conveyance chamber to the image carrier. The toner concentration sensor is disposed to face the first conveyance member or the second conveyance member on a wall portion along the longitudinal direction of the developing container, and detects the toner concentration in the developer. The first conveyance member and the second conveyance member each have a rotation shaft extending along the longitudinal direction of the developing container and conveyance blades formed spirally on an outer peripheral portion of the rotation shaft. The conveyance blades have a cut-out portion that is partially cut out in a region facing the toner concentration sensor.

Effect of the Invention

[0008] According to the configuration of the present invention, since the conveying blade has a cut-out portion in the region facing the toner concentration sensor, even if the conveyance speed of the developer increases, the developer is likely to stay near the toner concentration sensor. As a result, the detected value of the toner concentration can be stabilized, and it becomes possible to appropriately maintain the amount of toner in the developing container.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the following content.

[0011] FIG. 1 is a schematic cross-sectional front view of an image forming apparatus 1 according to an embodiment. FIG. 2 is a schematic cross-sectional front view around an image forming portion 20 of the image forming apparatus 1 of FIG. 1. As an example of the image forming apparatus 1 of the present embodiment, it is a tandem type color printer that transfers a toner image onto a sheet S using an intermediate transfer belt 31. The image forming apparatus 1 may be a so-called multifunction machine having functions such as printing, scanning (image reading), and facsimile transmission.

[0012] As shown in FIGS. 1 and 2, the image forming apparatus 1 includes a paper supply unit 3, a paper conveyance unit 4, an exposure unit 5, an image forming unit 20, a transfer unit 30, a fixing unit 6, a paper discharge unit 7, and a control unit 8 provided in its main body 2.

[0013] The paper supply unit 3 is disposed at the bottom of the main body 2. The paper supply unit 3 accommodates a plurality of sheets of paper S before printing and separates and feeds out the sheets of paper S one by one during printing. The paper conveyance unit 4 extends vertically along the side wall of the main body 2. The paper conveyance unit 4 conveys the sheet of paper S sent out from the paper supply unit 3 to the secondary transfer unit 33 and the fixing unit 6, and further discharges the sheet of paper S after fixing from the paper discharge port 4a to the paper discharge unit 7. The exposure unit 5 is disposed above the paper supply unit 3. The exposure unit 5 irradiates the image forming unit 20 with laser light controlled based on image data.

[0014] The image forming unit 20 is disposed above the exposure unit 5 and below the intermediate transfer belt 31. The image forming unit 20 includes a yellow image forming unit 20Y, a cyan image forming unit 20C, a magenta image forming unit 20M, and a black image forming unit 20B. These four image forming units 20 have the same basic configuration. Thus, in the following description, unless otherwise particularly limited, the identification symbols "Y", "C", "M", and "B" representing each color may be omitted.

[0015] The image forming unit 20 includes a photosensitive drum (image carrier) 21 rotatably supported in a predetermined direction (clockwise in FIGS. 1 and 2). The image forming unit 20 further includes a charging unit 22, a developing device 40, and a drum cleaning unit 23 disposed around the photosensitive drum 21 along its rotation direction. Note that a primary transfer unit 32 is disposed between the developing device 40 and the drum cleaning unit 23.

[0016] The photosensitive drum 21 is formed in a cylindrical shape extending in the horizontal direction and has a photosensitive layer formed of, for example, an amorphous silicon photosensitive member on its outer peripheral surface. The charging unit 22 charges the surface (outer peripheral surface) of the photosensitive drum 21 to a predetermined potential. The exposure unit 5 exposes the outer peripheral surface of the photosensitive drum 21 charged by the charging unit 22 to form an electrostatic latent image of the original image on the outer peripheral surface of the photosensitive drum 21. The developing device 40 supplies toner to this electrostatic latent image for development to form a toner image. Each of the four image forming units 20 forms a toner image of a different color. The drum cleaning unit 23 removes and cleans toner and the like remaining on the outer peripheral surface of the photosensitive drum 21 after the toner image is primarily transferred to the outer peripheral surface of the intermediate transfer belt 31. In this way, the image forming unit 20 forms an image (toner image) to be later transferred to the paper S.

[0017] The transfer unit 30 includes an intermediate transfer belt 31, primary transfer units 32Y, 32C, 32M, 32B, a secondary transfer unit 33, and a belt cleaning unit 34. The intermediate transfer belt 31 is disposed above the four image forming units 20. The intermediate transfer belt 31 is rotatably supported in a predetermined direction (counterclockwise in FIG. 1) and is an endless intermediate transfer member on which the toner images formed by each of the four image forming units 20 are sequentially superimposed and primarily transferred. The four image forming units 20 are arranged in a so-called tandem manner in a row from the upstream side to the downstream side in the rotation direction of the intermediate transfer belt 31.

[0018] The primary transfer units 32Y, 32C, 32M, 32B are disposed above the image forming units 20Y, 20C, 20M, 20B of each color with the intermediate transfer belt 31 interposed therebetween. The secondary transfer unit 33 is upstream of the fixing unit 6 with respect to the paper conveyance direction of the paper conveyance unit 4 and is downstream of the four image forming units 20Y, 20C, 20M, 20B with respect to the rotation direction of the intermediate transfer belt 31. The belt cleaning unit 34 is disposed downstream of the secondary transfer unit 33 with respect to the rotation direction of the intermediate transfer belt 31.

[0019] The primary transfer unit 32 transfers the toner image formed on the outer peripheral surface of the photosensitive drum 21 to the intermediate transfer belt 31. In other words, the toner image is primarily transferred to the outer peripheral surface of the intermediate transfer belt 31 by the primary transfer units 32Y, 32C, 32M, and 32B for each color. Then, as the intermediate transfer belt 31 rotates, the toner images of the four image forming units 20 are successively and continuously superimposed and transferred to the intermediate transfer belt 31 at a predetermined timing, whereby a color toner image in which toner images of four colors, yellow, cyan, magenta, and black, are superimposed is formed on the outer peripheral surface of the intermediate transfer belt 31.

[0020] The color toner image on the outer peripheral surface of the intermediate transfer belt 31 is transferred to the sheet S that has been fed in synchronization by the sheet conveyance unit 4 at the secondary transfer nip formed in the secondary transfer unit 33. The belt cleaning unit 34 removes and cleans deposits such as toner remaining on the outer peripheral surface of the intermediate transfer belt 31 after secondary transfer. In this way, the transfer unit 30 transfers (records) the toner image formed on the outer peripheral surface of the photosensitive drum 21 to the sheet S.

[0021] The fixing unit 6 is disposed above the secondary transfer unit 33. The fixing unit 6 heats and presses the sheet S onto which the toner image has been transferred to fix the toner image to the sheet S.

[0022] The sheet discharge unit 7 is disposed above the transfer unit 30. The sheet S on which the toner image has been fixed and the printing is completed is conveyed to the sheet discharge unit 7. The printed sheet (printed matter) is taken out from above by the sheet discharge unit 7.

[0023] The control unit 8 includes a CPU, an image processing unit, a storage unit, and other electronic circuits and components (none of which are shown). The CPU controls the operations of each component provided in the image forming apparatus 1 based on programs and data stored in the storage unit, and performs processes related to the functions of the image forming apparatus 1. Each of the paper supply unit 3, the paper conveyance unit 4, the exposure unit 5, the image forming unit 20, the transfer unit 30, and the fixing unit 6 receives individual commands from the control unit 8 and cooperates to perform printing on the paper S. The storage unit is composed of a combination of a non-volatile storage device such as a program ROM (Read Only Memory), a data ROM, etc., and a volatile storage device such as a RAM (Random Access Memory).

[0024] Subsequently, the configuration of the developing device 40 will be described with reference to FIG. 3 in addition to FIG. 2. FIG. 3 is a horizontal cross-sectional plan view of the developing device of the image forming unit in FIG. 2. Since the basic configurations of the developing devices 40 for each color are the same, the description of the components with the identification symbols representing each color and the explanations thereof are omitted. Also, in this description, the "axial direction" represents the axial direction of rotation of each of the photosensitive drum 21, the first conveying member 42, the second conveying member 43, and the developing roller 44 that extend parallel to each other (the depth direction of the paper surface in FIG. 2, the horizontal left-right direction in FIG. 3).

[0025] The developing device 40 supplies toner to the outer peripheral surface of the photosensitive drum 21. The developing device 40 is, for example, detachable from the main body 2 of the image forming apparatus 1. The developing device 40 includes a developing container 50, a first conveying member 42, a second conveying member 43, a developing roller (developer carrier) 44, a regulating blade 45, a toner density sensor 46, a scraper 47, and a holding unit 48.

[0026] The developing container 50 has an elongated shape extending along the axial direction of the photosensitive drum 21 and is arranged with its longitudinal direction horizontal. That is, the longitudinal direction of the developing container 50 is parallel to the axial direction of the photosensitive drum 21. The developing container 50 accommodates, as a developer containing toner to be supplied to the photosensitive drum 21, for example, a two-component developer containing toner and a magnetic carrier.

[0027] The developing container 50 includes a partition portion 51, a first conveyance chamber 52, a second conveyance chamber 53, a first communication portion 54, and a second communication portion 55.

[0028] The partition portion 51 is provided at the lower part inside the developing container 50. The partition portion 51 is disposed at a substantially central portion in a direction intersecting the longitudinal direction of the developing container 50 (the left - right horizontal direction in FIG. 2, the up - down direction in FIG. 3). The partition portion 51 is formed in a substantially plate shape extending in the longitudinal direction and the up - down direction of the developing container 50. The partition portion 51 divides the inside of the developing container 50 in a direction intersecting the longitudinal direction.

[0029] The first conveyance chamber 52 and the second conveyance chamber 53 are provided inside the developing container 50. The first conveyance chamber 52 and the second conveyance chamber 53 are formed by the inside of the developing container 50 being divided by the partition portion 51. The first conveyance chamber 52 and the second conveyance chamber 53 are arranged in parallel at substantially the same height.

[0030] The second conveyance chamber 53 includes the area around the arrangement area of the developing roller 44 in the developing container 50 and is arranged adjacent to the photoreceptor drum 21. The first conveyance chamber 52 is arranged in an area in the developing container 50 that is more separated from the photoreceptor drum 21 than the second conveyance chamber 53. In the first conveyance chamber 52, a developer supply port 52a is open, and the developer is supplied into the developing container 50 through the developer supply port 52a. In the first conveyance chamber 52, the developer is conveyed in the first direction f1 by the first conveyance member 42. In the second conveyance chamber 53, the developer is conveyed in the second direction f2 opposite to the first direction f1 by the second conveyance member 43.

[0031] The first communication portion 54 and the second communication portion 55 are respectively arranged outside both end portions in the longitudinal direction of the partition portion 51. The first communication portion 54 and the second communication portion 55 communicate the first conveyance chamber 52 and the second conveyance chamber 53 in a direction intersecting the longitudinal direction of the partition portion 51 (the left - right horizontal direction in FIG. 2, the up - down direction in FIG. 3), that is, in the thickness direction of the partition portion 51 having a substantially plate shape. In other words, the first communication portion 54 and the second communication portion 55 communicate with each other on both end portions in the longitudinal direction of the first conveyance chamber 52 and the second conveyance chamber 53.

[0032] The first communication part 54 connects the downstream end of the first conveyance chamber 52 in the first direction f1 and the upstream end of the second conveyance chamber 53 in the second direction f2. The developer is conveyed from the side of the first conveyance chamber 52 toward the side of the second conveyance chamber 53 through the first communication part 54. The second communication part 55 connects the downstream end of the second conveyance chamber 53 in the second direction f2 and the upstream end of the first conveyance chamber 52 in the first direction f1. The developer is conveyed from the side of the second conveyance chamber 53 toward the side of the first conveyance chamber 52 through the second communication part 55.

[0033] The first conveyance member 42 is disposed in the first conveyance chamber 52. The second conveyance member 43 is disposed in the second conveyance chamber 53. The first conveyance member 42 and the second conveyance member 43 are arranged in parallel at substantially the same height. The second conveyance member 43 extends in parallel in proximity to the developing roller 44. The first conveyance member 42 and the second conveyance member 43 are rotatably supported by the developing container 50 about an axis extending horizontally in parallel with the developing roller 44.

[0034] The basic configurations of the first conveyance member 42 and the second conveyance member 43 are the same. The first conveyance member 42 has first conveyance blades 42b formed in a spiral shape on the outer peripheral portion of a rotating shaft 42a extending along the longitudinal direction of the developing container 50. In the present embodiment, the first conveyance member 42 has two first conveyance blades 42b. The second conveyance member 43 has second conveyance blades 43b formed in a spiral shape on the outer peripheral portion of a rotating shaft 43a extending along the longitudinal direction of the developing container 50. In the present embodiment, the second conveyance member 43 has two second conveyance blades 43b.

[0035] The first conveyance member 42 conveys the developer while stirring it in the first direction f1 from the side of the second communication part 55 toward the side of the first communication part 54 along the axial direction of rotation in the first conveyance chamber 52. The second conveyance member 43 conveys the developer while stirring it in the second direction f2 from the side of the first communication part 54 toward the side of the second communication part 55 along the axial direction of rotation in the second conveyance chamber 53. That is, the first conveyance member 42 and the second conveyance member convey the developer while stirring it in opposite longitudinal directions, and circulate it in a predetermined circulation direction.

[0036] The developing roller 44 is positioned above the second conveying member 43 within the developing container 50 and is disposed opposite to the photosensitive drum 21. The developing roller 44 is rotatably supported by the developing container 50 about an axis extending parallel to the axis of the photosensitive drum 21.

[0037] A part of the outer peripheral surface of the developing roller 44 is exposed from the developing container 50, faces, and is close to the photosensitive drum 21. The developing roller 44 carries the toner supplied to the outer peripheral surface of the photosensitive drum 21 in the facing region with the photosensitive drum 21 on its outer peripheral surface. The developing roller 44 carries the toner in the second conveying chamber 53 of the developing container 50 and supplies it to the photosensitive drum 21. In other words, the developing roller 44 adheres the toner in the second conveying chamber 53 to the electrostatic latent image on the outer peripheral surface of the photosensitive drum 21 to form a toner image.

[0038] The regulating blade 45 is disposed on the upstream side in the rotation direction of the developing roller 44 in the facing region between the developing roller 44 and the photosensitive drum 21. The regulating blade 45 faces close to the developing roller 44 and is disposed with a predetermined gap provided between its tip and the outer peripheral surface of the developing roller 44. The regulating blade 45 extends over the entire axial direction of the developing roller 44. The regulating blade 45 regulates the layer thickness of the developer carried on the outer peripheral surface of the developing roller 44 passing through the gap between the tip of the regulating blade 45 and the outer peripheral surface of the developing roller 44.

[0039] The toner density sensor 46 is disposed on the wall portion along the longitudinal direction (first direction f1) of the first conveying chamber 52. The toner density sensor 46 is disposed opposite to the first conveying member 42. In the present embodiment, a headless sensor is used as the toner density sensor 46. The toner density sensor 46, which is a headless sensor, has its detection surface buried in the inner wall surface of the first conveying chamber 52. The toner density sensor 46 detects the toner density in the developer.

[0040] Specifically, the toner density sensor 46 is a permeability detection type sensor that obtains the toner density (mixing ratio of toner T to carrier C in the developer; T / C) by detecting changes in the magnetic permeability of the two-component developer. If the ratio of toner to carrier in the developer within the first conveyance chamber 52 changes, the magnetic permeability also changes, and accordingly, the output signal of the toner density sensor 46 also changes. The control unit 8 controls the start and stop of replenishment of the developer (toner and carrier) to the developing device 40 based on the output signal of the sensor received from the toner density sensor 46.

[0041] Regarding the toner density sensor 46, a scraper 47 is attached to the first conveyance member 42. The scraper 47 is fixed to the rotation shaft 42a of the first conveyance member 42 via a holding portion 48 in the region facing the toner density sensor 46. Details of the scraper 47 will be described later.

[0042] The developer in the developing container 50 circulates in a predetermined circulation direction between the first conveyance chamber 52 and the second conveyance chamber 53 through the first communication portion 54 and the second communication portion 55 due to the rotation of the first conveyance member 42 and the second conveyance member 43. At this time, the toner in the developing container 50 is agitated, charged, and carried on the outer peripheral surface of the developing roller 44. The developer carried on the outer peripheral surface of the developing roller 44 has its layer thickness regulated by the regulating blade 45 and is then conveyed to the region facing the developing roller 44 and the photosensitive drum 21 by the rotation of the developing roller 44. When a predetermined developing voltage is applied to the developing roller 44, due to the potential difference from the potential of the surface (outer peripheral surface) of the photosensitive drum 21, the toner in the developer carried on the outer peripheral surface of the developing roller 44 moves to the outer peripheral surface of the photosensitive drum 21 in the facing region. Thereby, the electrostatic latent image on the outer peripheral surface of the photosensitive drum 21 is developed with toner.

[0043] The developing container 50 further has a discharge portion 56. The discharge portion 56 is provided further downstream than the downstream end of the second transport chamber 53 in the second direction f2. The discharge portion 56 is connected to the second transport chamber 53. The interiors of the discharge portion 56 and the second transport chamber 53 communicate with each other. The inner diameter of the discharge portion 56 is smaller than the inner diameter of the second transport chamber 53. The discharge portion 56 has a developer discharge port 561.

[0044] Note that the rotation shaft 43a of the second transport member 43 extends continuously into the discharge portion 56. One end in the axial direction of the rotation shaft 43a is rotatably supported by the developing container 50 at the downstream end of the discharge portion 56 with respect to the second direction f2 of the second transport chamber 53.

[0045] The developer discharge port 561 is arranged at the downstream end of the discharge portion 56 with respect to the second direction f2 of the second transport chamber 53. The developer discharge port 561 opens, for example, below the rotation shaft 43a of the second transport member 43. The developer discharge port 561 discharges the surplus developer in the developing container 50 to the outside.

[0046] In addition to the second transport blades 43b, the second transport member 43 further includes a regulating blade 43c and a discharge blade 43d. These three blades are provided in the order of the second transport blade 43b, the regulating blade 43c, and the discharge blade 43d from the side of the second transport chamber 53 toward the discharge portion 56. Similar to the second transport blade 43b, the regulating blade 43c and the discharge blade 43d are provided integrally with the rotation shaft 43a and are formed in a spiral shape along the axial direction on the outer peripheral portion of the rotation shaft 43a.

[0047] The regulating blade 43c is located downstream of the second transport blade 43b with respect to the second direction f2 of the second transport chamber 53 and is arranged in the second transport chamber 53. The regulating blade 43c faces the connection portion between the second transport chamber 53 and the discharge portion 56 in the axial direction of the rotation shaft 43a.

[0048] The regulating blade 43c has a winding direction opposite to that of the second conveying blade 43b. Thereby, the regulating blade 43c blocks the developer conveyed to the vicinity of the downstream end in the second conveying chamber 53 and restricts the movement of the developer toward the discharge portion 56 side. Note that the pitch of the regulating blade 43c is smaller than the pitch of the second conveying blade 43b.

[0049] The outer peripheral portion of the regulating blade 43c has a predetermined interval (clearance) from the inner surface of the developing container 50. The developer that has reached a predetermined amount or more in the second conveying chamber 53 is conveyed as surplus developer from the gap between the outer peripheral portion of the regulating blade 43c and the inner surface of the developing container 50 toward the discharge portion 56.

[0050] The discharge blade 43d is located downstream of the regulating blade 43c with respect to the second direction f2 of the second conveying chamber 53 and is disposed in the discharge portion 56. The discharge blade 43d has the same winding direction as the second conveying blade 43b. That is, the conveying direction of the developer in the discharge portion 56 is the same as the second direction f2 of the second conveying chamber 53. Thereby, the discharge blade 43d conveys the surplus developer in the discharge portion 56 toward the developer discharge port 561. Note that the outer diameter of the discharge blade 43d is smaller than the outer diameters of the second conveying blade 43b and the regulating blade 43c. The pitch of the discharge blade 43d is smaller than the pitch of the second conveying blade 43b.

[0051] Subsequently, a more detailed configuration of the developing device 40 will be described with reference to FIGS. 4, 5, and 6 in addition to FIG. 3. FIG. 4 is a partial side view of the first conveying member 42 of the developing device 40 in FIG. 3. FIG. 5 is a partial side view of the first conveying member 42 as viewed from the opposite side of FIG. 4. FIG. 6 is a partial perspective view of the first conveying member 42 in FIG. 4.

[0052] As shown in FIGS. 4, 5, and 6, the first conveying member 42 has a cutout portion 42c. As shown in FIG. 3, the cutout portion 42c is formed in the facing area with the toner density sensor 46. In the cutout portion 42c located in the facing area with the toner density sensor 46, the first conveying blade 42b is partially cut along the longitudinal direction (first direction f1). In this embodiment, in the cutout portion 42c, the two first conveying blades 42bA and 42bB are each cut with different lengths in the axial direction of the rotating shaft 42a (the left - right horizontal direction in FIGS. 4 and 5).

[0053] According to the above configuration, since the first conveying blade 42b has the cutout portion 42c in the facing area with the toner density sensor 46, even if the conveying speed of the developer increases, the developer is likely to stay near the toner density sensor 46. Thereby, the detected value of the toner density can be stabilized, and it becomes possible to appropriately maintain the toner amount in the developing container 50.

[0054] The scraper 47 is fixed to the rotating shaft 42a of the first conveying member 42 via a holding portion 48 in the cutout portion 42c. As shown in FIG. 6, the scraper 47 is formed in a fan - shaped shape when viewed from the axial direction of the rotating shaft 42a. The scraper 47 is arranged so as to have substantially the same inclination as the inclination of the spiral - shaped first conveying blade 42b with respect to the axial direction of the rotating shaft 42a.

[0055] The scraper 47 is formed by laminating a fiber sheet such as felt or non - woven fabric on the surface of a base material made of a flexible film (elastic member) such as a PET (Polyethylene Terephthalate) film. The scraper 47 rotates together with the rotating shaft 42a to move the developer facing the toner density sensor 46. Then, new developer is fed into the facing area with the toner density sensor 46.

[0056] According to the above configuration, by providing the scraper 47 in the cutting portion 42c, excessive retention of the developer in the vicinity of the toner concentration sensor 46 can be suppressed. Therefore, it becomes possible to appropriately detect the toner concentration in the developing container 50.

[0057] The holding portion 48 is integrally formed on the outer peripheral portion of the rotary shaft 42a in the cutting portion 42c. Although the holding portion 48 is integrated with the rotary shaft 42a in the present embodiment, it may be provided as a separate member with respect to the rotary shaft 42a. The holding portion 48 holds the scraper 47 with the rotary shaft 42a interposed therebetween in a substantially axial direction of the rotary shaft 42a.

[0058] The holding portion 48 has circumferential end faces 48a that extend in the radial direction of the rotary shaft 42a at both circumferential ends of the rotary shaft 42a. As shown in FIG. 5, the circumferential end faces 48a face in a direction substantially orthogonal to the axial direction of the rotary shaft 42a. The circumferential end faces 48a of the holding portion 48 are disposed at the circumferential edge of the cutting portion 42c.

[0059] According to the above configuration, since the holding portion 48 of the scraper 47 has the circumferential end faces 48a, the action of moving the developer in the vicinity of the toner concentration sensor 46 can be enhanced by the circumferential end faces 48a that move with the rotation of the rotary shaft 42a. Thereby, excessive retention of the developer in the vicinity of the toner concentration sensor 46 can be suppressed. Therefore, it becomes possible to appropriately detect the toner concentration in the developing container 50.

[0060] Subsequently, the effects of the present embodiment will be described. FIG. 7 is a graph showing the transition of the mixing ratio (T / C) of toner to carrier in the developer in the developing apparatuses of the example and the comparative example. In each of the developing apparatus 40 of the example and the developing apparatus of the comparative example, the influence of the presence or absence and the axial length of the cutting portion 42c on the toner concentration in the developer (the mixing ratio of toner to carrier (hereinafter sometimes referred to as "T / C")) was evaluated.

[0061] In the developing device of the comparative example, no cutout portion is provided in the opposing regions of the two first conveying members with the toner density sensor. In the developing device 40 of Example 1, a cutout portion 42c is provided in the opposing region of one of the two first conveying vanes 42bA and 42bB with the toner density sensor 46. The axial length of the cutout portion 42c in Example 1 is three times (3L) the axial length L of the toner density sensor 46. In the developing devices 40 of Example 2 and Example 3, they are provided in the opposing regions of both of the two first conveying vanes 42bA and 42bB with the toner density sensor 46. The axial length of the cutout portion 42c in Example 2 is 1.5 times (1.5L) the axial length L of the toner density sensor 46, and the axial length of the cutout portion 42c in Example 3 is three times (3L). Table 1 shows the configuration conditions and evaluation results of the cutout portion 42c.

[0062]

Table 1

[0063] Regarding FIGS. 7 and Table 1, regarding the evaluation of the T / C variation, when the developer weight was varied by about 100 g with respect to the initial value of 250 g (340 g, 450 g), the variation of T / C was confirmed. In the "Evaluation of T / C Variation" in Table 1, the T / C variation could be suppressed within 1%, and the configurations with smaller variation widths were ranked as "◎ (best)", "○ (good)", and "△ (acceptable)" in order. Also, a configuration with a T / C variation exceeding 1% was regarded as "× (unacceptable)".

[0064] According to FIGS. 7 and Table 1, in all four configurations, when the developer weight increased from 250 g to 340 g, the T / C variation could be suppressed within 1%. However, in the developing device of the comparative example, when the developer weight increased from 340 g to 450 g, the T / C variation greatly exceeded 1%. On the other hand, in the developing devices 40 of Example 1, 2, and 3, even when the developer weight increased from 340 g to 450 g, the T / C variation could be suppressed within 1% in all cases. In particular, in Example 3, the suppression effect of the T / C variation is high.

[0065] According to the configuration of Example 1, by forming the cutout portion 42c in at least one of the two first transport vanes 42bA and 42bB, the T / C variation can be suppressed within 1%. That is, the detected value of the toner concentration (T / C) can be stabilized, and the toner amount in the developing container 50 can be appropriately maintained.

[0066] Also, according to the configuration of Example 2, since the cutout portion 42c has a length that is 1.5 times or more the length of the toner concentration sensor 46 with respect to the longitudinal direction (axial direction) of the developing container 50, the T / C variation can be suppressed within 1%. That is, the detected value of the toner concentration (T / C) can be stabilized, and the toner amount in the developing container 50 can be appropriately maintained.

[0067] Further, the developing device 40 uses a two-component developer in which the developer used for forming the toner image contains a magnetic carrier and toner, and has a developer discharge port 561 for discharging excess developer in the developing container 50 to the outside. When the developing device 40 has the developer discharge port 561, it is known that the weight of the developer in the developing container 50 is likely to vary. Therefore, by forming the cutout portion 42c in the first transport vane 42bA as described above in the developing device 40 having the developer discharge port 561, the detected value of the toner concentration (T / C) can be stabilized. That is, in the developing device 40, it becomes possible to more effectively maintain the appropriate toner amount in the developing container 50.

[0068] As described above, the embodiments of the present invention have been described, but the scope of the present invention is not limited thereto, and various modifications can be made without departing from the gist of the invention.

[0069] For example, in the above embodiment, the image forming apparatus 1 is a so-called tandem type color printing image forming apparatus that sequentially forms images of a plurality of colors, but it is not necessarily limited to such a model. The image forming apparatus may be a color printing image forming apparatus that is not of the tandem type or a monochrome printing image forming apparatus.

Industrial Applicability

[0070] The present invention can be used in a developing device and an image forming apparatus.

Explanation of Signs

[0071] 1 Image forming apparatus 2 Main body 20 Image forming section 21 Photoconductor drum (image carrier) 40 Developing device 42 First conveying member 42a Rotating shaft 42b, 42bA, 42bB First conveying blades 42c Cutting portion 43 Second conveying member 43a Rotating shaft 43b Second conveying blade 44 Developing roller (developer carrier) 45 Regulation blade 46 Toner density sensor 47 Scraper 48 Holding portion 48a Peripheral end face 50 Developing container 51 Partition portion 52 First conveying chamber 53 Second conveying chamber 56 Discharge portion 561 Developer discharge port

Claims

1. A developing device having a first transport chamber and a second transport chamber which are arranged in parallel and communicate with each other at both longitudinal ends thereof, and accommodating a developer containing toner to be supplied to an image carrier; A first transport member and a second transport member which are rotatably supported in the first transport chamber and the second transport chamber respectively, and transport and circulate the developer while stirring it in opposite directions in the longitudinal direction; A developer carrier which is rotatably supported on the developing device so as to face the image carrier and supplies the toner in the second transport chamber to the image carrier; A toner concentration sensor which is arranged to face the first transport member or the second transport member on a wall portion along the longitudinal direction of the developing device and detects the toner concentration in the developer; comprising; The first transport member and the second transport member have a rotation axis extending along the longitudinal direction of the developing device, and transport vanes formed spirally on the outer peripheral portion of the rotation axis; The developing device, wherein the transport vanes have a cut-out portion which is partially cut out in a region facing the toner concentration sensor.

2. The first transport member and the second transport member have a plurality of the transport vanes; The developing device according to claim 1, wherein the cut-out portion is formed in at least one of the plurality of transport vanes.

3. The developing device according to claim 1, wherein the cut-out portion has a length which is 1.5 times or more the length of the toner concentration sensor with respect to the longitudinal direction of the developing device.

4. The developing device according to claim 1, further comprising a scraper which is fixed to the rotation axis in the cut-out portion and moves the developer facing the toner concentration sensor.

5. The cut-out portion is formed on the rotation axis and includes a holding portion for holding the scraper; The developing device according to claim 4, wherein the holding portion extends in the radial direction of the rotating shaft at both circumferential ends of the rotating shaft and has a circumferential end face disposed at a circumferential edge of the cutting portion.

6. The developer is a two-component developer including a magnetic carrier and the toner, The developing container, a developer supply port for supplying the developer into the developing container, a developer discharge port formed at a downstream end of the second conveyance chamber with respect to the developer conveyance direction of the second conveyance chamber and discharging excess developer in the developing container to the outside, The developing device according to claim 1, characterized by comprising the above.

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

Images