Developing device and image forming apparatus

Abstract

To provide a developing device that causes shear force to act on developer present at the bottom of a developer tank that is an area not affected by conveying force of a conveying member such as a screw, prevents adherence of the developer to a bottom wall of the developer tank, and conveys the developer in a conveyance direction, and an image forming apparatus.SOLUTION: A developing device according to the present disclosure comprises: a developer tank that stores developer; a conveying member that is provided in the developer tank and rotates in a predetermined rotation direction to convey the developer in a predetermined direction; and a developer carrier that carries, on its surface, a part of the developer conveyed by the conveying member. The conveying member has a rotation shaft, and a first spiral blade and a second spiral blade respectively provided in a spiral shape on an outer periphery of the rotation shaft. On an orthogonal section orthogonal to the rotation shaft, a first radius that is the distance from the center of the rotation shaft to a leading end of the first spiral blade, and a second radius that is the distance from the center of the rotation shaft to a leading end of the second spiral blade, are different in a length from each other.SELECTED DRAWING: Figure 6

Description

[Technical field]

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

[0002] 2. Description of the Related Art An electrophotographic image forming apparatus includes a developing device that develops an electrostatic latent image formed on an image carrier with toner.

[0003] For example, Patent Document 1 discloses a developing device equipped with a developing container that contains a developer including toner, and a stirring and transporting screw that has a shaft and blades arranged around the shaft and that rotates to transport the developer contained in the developing container to a developing sleeve (developer carrier) that supplies toner to an image carrier.

[0004] Furthermore, Patent Document 1 discloses a technology in which a member protruding from the inner wall of the developing container is provided in the gap between the inner wall of the developing container and the blades of the stirring screw, thereby preventing the expansion of a developer aggregation layer accumulated in the gap between the inner wall of the developing container and the stirring and conveying screw.

[0005] By configuring the developing container in this manner, when vibration is applied due to an external factor, a part of the developer aggregation layer is peeled off from the inner wall of the developing container and transported to the developing sleeve, and the developer aggregation layer is prevented from expanding, which would cause image defects if it becomes caught in the gap with a regulating member provided opposite the developing sleeve. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2012-42810 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, the developing device according to the above-mentioned document 1 can prevent the expansion of the developer aggregation layer that occurs in the gap between the inner wall of the developing container and the stirring and conveying screw (the blade), but cannot suppress the occurrence of the developer aggregation layer itself. Therefore, when the generated developer aggregation layer peels off from the inner wall of the developing container, it is conveyed to the developing sleeve and passes through the gap between the developing sleeve and the regulating blade, and is developed into an electrostatic latent image on the image carrier together with the aggregated mass, which may cause image defects.

[0008] In view of the above problems, the present disclosure provides a developing device and an image forming device that can suppress the generation of developer aggregation layers and adhesion to the inner walls, particularly the bottom wall, of a developer tank by changing the position at which the shear force generated by the rotation of a transport member acts on developer present in an area not reached by the transport force of a transport member such as a screw as the transport member rotates. [Means for solving the problem]

[0009] A developing device according to one embodiment of the present disclosure comprises a developing tank in which a developer is contained, a transport member provided in the developing tank and configured to rotate in a predetermined rotational direction to transport the developer in a predetermined direction, and a developer carrier configured to carry on its surface a portion of the developer transported by the transport member, wherein the transport member has a rotating shaft and a first helical blade and a second helical blade each configured in a spiral shape on the outer periphery of the rotating shaft, and in an orthogonal cross section perpendicular to the rotating shaft, a first radius which is the distance from the center of the rotating shaft to the tip of the first helical blade and a second radius which is the distance from the center of the rotating shaft to the tip of the second helical blade are different in size. Effect of the Invention

[0010] As described above, in the present disclosure, a conveying member such as a screw is configured so that the range of the conveying force varies with the rotation of the conveying member. With this configuration, the position where the shear force is generated by the rotation of the conveying member can be periodically changed for the developer present between the conveying member and the inner wall of the developing tank, and the developer present between the conveying member and the bottom wall of the developing tank can be effectively prevented from coagulating and sticking. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a side view of the image forming apparatus. [Diagram 2] 2 is a cross-sectional view of a developing device included in the image forming apparatus shown in FIG. [Diagram 3] FIG. [Figure 4] FIG. [Diagram 5] FIG. 5 is a side view of the conveying member shown in FIG. [Figure 6] FIG. 5 is a cross-sectional view of the conveying member shown in FIG. [Figure 7] FIG. 4 is a cross-sectional view showing a conveying member disposed in the developing tank, illustrating the positional relationship between a first spiral blade and a bottom wall of the developing tank. [Figure 8] FIG. 4 is a cross-sectional view showing a conveying member disposed in the developing tank, illustrating the positional relationship between a second spiral blade and a bottom wall of the developing tank. [Figure 9] 13 is a modified example of the conveying member. [Figure 10] FIG. 13 is a perspective view of a further modified example of the conveying member. [Figure 11] FIG. 11 is a side view of the conveying member shown in FIG. [Figure 12] 11 is a cross-sectional view of the conveying member shown in FIG. [Figure 13] 11 is a side view illustrating the positional relationship between a concentration sensor and a conveying member. FIG. [Figure 14] 4 is a perspective view illustrating the shapes of a first helical blade and a second helical blade in the vicinity of a concentration sensor. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the embodiments described below do not unduly limit the contents of the present disclosure described in the claims, and all of the configurations described in the embodiments are not necessarily essential as the means for solving the problems of the present disclosure.

[0013] <Image forming device> Fig. 1 is a side view of an image forming apparatus 1. As shown in Fig. 1, the image forming apparatus 1 is an electrophotographic image forming apparatus that forms an image using a developer, and includes an image reading device 2, a paper discharge device 3, a paper feed device 4, an image forming section 5, a developing device 100, etc.

[0014] The image forming apparatus 1 may be a multifunction machine having a scanner function, a copying function, a printer function, a facsimile function, and the like.

[0015] The image forming apparatus 1 is a color image forming apparatus, and the image forming section 5 includes a photoreceptor unit having a photoreceptor drum on whose surface a black, cyan, magenta, and yellow toner image is formed, respectively. The arrow X in Fig. 1 indicates the left-right direction when the image forming apparatus 1 is viewed from the front, and the direction of the arrow points to the right, and the arrow Z in Fig. 1 indicates the up-down direction when the image forming apparatus 1 is viewed from the front, and the direction of the arrow points upward. The arrow Y indicates the depth direction when the image forming apparatus 1 is viewed from the front, and the direction of the arrow points to the front side.

[0016] The developing device 100 will now be described.

[0017] <Developing device> FIG. 2 is a cross-sectional view of the developing device 100 included in the image forming apparatus 1 shown in FIG. 1. FIG. 3 is a perspective view of the developing device 100 viewed from the rear side, with a part of the developing tank 10 omitted to make the internal structure easier to understand. As shown in FIG. 2, the developing device 100 according to the present disclosure includes a developing tank 10 in which a developer containing a toner is accommodated, a transport member 20 for transporting the accommodated developer, a developer carrier 50 on whose surface the developer transported from the transport member 20 is carried and which supplies the toner to an image carrier 60, a layer regulating blade 70 for regulating the thickness of the developer carried on the surface of the developer carrier 50, and a developer supply port 14 for supplying the toner or developer to the developing tank 10. The developing device is disposed so as to face the developer carrier 50.

[0018] In this disclosure, a so-called two-component developer is used that contains a toner made of a non-magnetic resin material and a particle size of about 6 μm, and a carrier made of a magnetic material and a particle size of about 40 μm. However, a one-component developer made of a toner made of a magnetic material may also be used.

[0019] The developing tank 10 has a first chamber 10a and a second chamber 10b in which the developer is stored. The first chamber 10a and the second chamber 10b communicate with each other via a first communicating portion 13a provided at the end on the front side and a second communicating portion 13b provided at the end on the back side. The second chamber 10b further has an opening 12 that opens to face the longitudinal direction of the image carrier 60.

[0020] The transport member 20 is provided in the developing tank 10, and includes a first transport member 20a rotatably provided in the first chamber 10a and a second transport member 20b rotatably provided in the second chamber 10b. The first transport member 20a and the second transport member 20b are rotationally driven by a drive source (not shown).

[0021] Although details will be described later, each of the transport members 20 (20a, 20b) is a screw having a spiral blade, and transports the developer in a predetermined direction by rotating in a predetermined rotation direction. In other words, the transport member 20 is provided in the developer tank 10 so as to have a gap between the transport member 20 and the inner wall of the developer tank 10, and transports the contained developer in the predetermined direction by rotating in the predetermined direction.

[0022] For example, as shown in FIG. 3, the developer supplied from the developer supply port 14 of the developing tank 10 is transported from the rear side (-Y direction) of the first chamber 10a to the front side (+Y direction) by the rotating first transport member 20a. Next, the developer transported to the front end of the first chamber 10a is transported to the second chamber 10b through the first communication portion 13a that communicates with the second chamber 10b. Then, the developer transported to the second chamber 10b through the first communication portion 13a is transported from the front end to the rear end of the second chamber 10b by the rotating second transport member 20b. Then, the developer transported to the rear end of the second chamber 10b is transported to the first chamber 10a through the second communication portion 13b that communicates with the first chamber 10a. The developer transported to the first chamber 10a through the second communication portion 13b is transported again toward the front side of the first chamber 10a by the first transport member 20a.

[0023] The developer contained in developer tank 10 as described above is transported by first transport member 20a and second transport member 20b so as to circulate through first chamber 10a and second chamber 10b.

[0024] The developer carrier 50 is rotatably provided at a position corresponding to the opening 12 of the second chamber 10b, and is provided so as to face the image carrier 60 at the opening 12. Here, the developer carrier 50 carries a part of the developer transported by the second transport member 20b on its surface. In other words, the developer carrier 50 carries a part of the developer transported by the transport member 20 on its surface.

[0025] To explain in more detail, the developer carrier 50 has a sleeve (not shown) made of a non-magnetic metal material and driven to rotate by a drive source (not shown), and a plurality of magnets (not shown) arranged so as not to rotate inside the sleeve, with N poles and S poles arranged alternately around the circumference of the sleeve.

[0026] Due to the magnetic force generated by the non-rotating magnets, a part of the developer transported by the second transport member 20b is attracted to the sleeve side and supplied to the surface of the sleeve (the magnetic carrier is attracted together with the surrounding toner).

[0027] The developer supplied to the surface of the sleeve is transported to the opposing area (development area) with the image carrier 60 by the rotation of the sleeve (rotating in the direction of arrow R in Figure 2), but the layer is regulated by a layer regulating blade 70 provided along the way to ensure that the thickness is uniform.

[0028] Therefore, the layer regulating blade 70 is provided so that the portion facing the developer carrier 50 is spaced a predetermined distance, for example 0.8 mm in this disclosure, from the surface of the sleeve.

[0029] The developer on the sleeve, the thickness of which has been uniformly regulated in the longitudinal direction by the layer regulating blade 70 , is sent to the developing area facing the image carrier 60 , and forms a toner image on the surface of the image carrier 60 .

[0030] Furthermore, developing device 100 according to the present disclosure may be provided with a concentration sensor 80 that measures the toner concentration (amount of toner) contained in the developer. The concentration sensor 80 detects the amount of toner contained in developer tank 10. When the toner concentration detected by concentration sensor 80 falls below a predetermined value, developer containing toner is replenished from developer replenishing port 14 to developer tank 10.

[0031] Next, the conveying member 20 will be described in detail.

[0032] Fig. 4 is a perspective view of the conveying member 20. Fig. 5 is a side view of the conveying member 20 shown in Fig. 4. Fig. 6 is a cross-sectional view of the conveying member 20 shown in Fig. 4. As shown in Figs. 4, 5 and 6, the conveying member 20 has a rotating shaft 23, and a first helical blade 21 and a second helical blade 22 each provided in a helical shape on the outer periphery of the rotating shaft 23. Note that, although the figures show two helical blades, the number is not limited.

[0033] When the transport member 20 is rotated by a driving source (not shown), the first and second helical blades 21 and 22 also rotate to transport the developer contained in the developer tank 10 in a predetermined direction. In order to rotate the transport member 20 smoothly, a predetermined gap, for example, a gap of about 1 mm is provided between the end of the first and second helical blades 21 and 22 opposite the rotation shaft 23 and the inner wall of the developer tank 10. Therefore, the transport force of the first and second helical blades 21 and 22 does not directly act on the developer present in this gap, and the developer tends to move as if dragged by the movement of the developer transported by the first and second helical blades 21 and 22. Therefore, when the fluidity of the developer deteriorates after long use, the developer present in the gap is likely to aggregate and may stick to the bottom. The configuration of the transport member 20 for preventing the developer present in the gap from aggregating and sticking to the bottom will be described in detail below.

[0034] 6, the conveying member 20 is characterized in that, in an orthogonal cross section perpendicular to the rotating shaft 23, a first radius r1, which is the distance from the center O of the rotating shaft 23 to the tip of the first helical blade 21, and a second radius r2, which is the distance from the center O of the rotating shaft 23 to the tip of the second helical blade 22, are different in size. In order to make the first outer radius r1 and the second outer radius r2 different, the conveying member 20 may be provided with the first helical blade 21 and the second helical blade 22 that are at different heights from the surface of the rotating shaft 23 in the orthogonal cross section.

[0035] In the conveying member 20 of the present disclosure, the first radius r1 is smaller than the second radius r2 (r1 < r2). Specifically, the first radius r1 of the present disclosure is 8 mm and the second radius r2 is 8.5 mm, but they may be set to other values. By configuring the first radius r1 and the second radius r2 to be different in this way, the region where the conveying force of the first spiral blade 21 acts and the region where the conveying amount of the second spiral blade 22 acts can be changed in the radial direction. As a result, in the developer existing in the gap region, the position where the shearing force generated when the tips of the first spiral blade 21 and the second spiral blade 22 pass through can be changed in the radial direction. By alternately changing the position where this shearing force is generated in the radial direction, radial vibration is generated in the developer existing in the gap region, so that aggregation and sticking can be prevented. That is, since the vibration is periodically generated when the first spiral blade 21 and the second spiral blade 22 alternately pass through the gap region by rotation, aggregation and sticking can be prevented more effectively.

[0036] FIG. 7 is a view showing the conveying member 20 disposed in the developing tank 10, and is a cross-sectional view showing the positional relationship between the first spiral blade 21 (tip) and the bottom wall 11 of the developing tank 10. Similarly, FIG. 8 is a cross-sectional view showing the positional relationship between the second spiral blade 22 (tip) and the bottom wall 11 of the developing tank 10. The arrow S shown in FIGS. 7 and 8 is the rotation direction of the conveying member 20. Here, FIG. 7 shows a state where the first spiral blade 21 (tip) is in a position facing the bottom wall 11 of the developing tank 10, and FIG. 8 shows a state where the second spiral blade 22 (tip) is in a position facing the bottom wall 11 of the developing tank 10. That is, when the conveying member 20 shown in FIG. 7 is rotated half a turn, the conveying member 20 shown in FIG. 8 is obtained.

[0037] As shown in FIG. 7 and FIG. 8, in the orthogonal cross section, the first distance d1, which is the distance from the tip of the first spiral blade 21 to the bottom wall 11 of the developing tank 10, is preferably larger than the second distance d2, which is the distance from the tip of the second spiral blade 22 to the bottom wall 11 of the developing tank 10. That is, the first distance d1>the second distance d2. In the present disclosure, the first distance d1 is set to 1 mm, and the second distance d2 is set to 0.5 mm, but other values ​​may be used as long as the relationship is maintained. It is preferable that the first distance d1 is set to 1.2 mm or less. In this way, the position where the shear force generated when the tips of the first spiral blade 21 and the second spiral blade 22 pass through the developer present in the gap is generated can be reliably changed in the direction perpendicular to the inner wall of the developing tank 10 (up and down at the bottom). Therefore, the developer present in the gap can be effectively prevented from coagulating and adhering.

[0038] Furthermore, the second distance d2 is preferably in the range of 1 / 4 to 3 / 4 of the first distance d1. In the present disclosure, the range of the second distance d2 may be in the range of 0.25 mm to 0.75 mm, assuming that the first distance d1 is 1 mm. In this way, the position where the shear force occurs when the tips of the first spiral blade 21 and the second spiral blade 22 pass can be changed in a direction perpendicular to the inner wall of the developing tank 10 (up and down direction at the bottom wall 11), and the effect of the vibration generated as a result can be transmitted to the developer near the inner wall of the developing tank 10, especially near the bottom. Therefore, the developer present in the gap, especially the developer at the bottom, can be effectively prevented from coagulating and sticking.

[0039] A more preferred embodiment will be described below.

[0040] Fig. 9 is a modified example of the conveying member 20. The conveying member 20 shown in Fig. 9 is the same as the conveying member 20 described above in that the second radius r2 is larger than the first radius r1 (r2>r1) and the first distance d1 is larger than the second distance d2 (d1>d2).

[0041] In the orthogonal cross-section shown in FIG. 9, the feature portion of the modification is at a point having an inclined portion 40 that is inclined so as to approach the rotation axis 23 side from the tip toward the upstream side at the tip corner portion on the upstream side in the rotation direction of the second spiral blade 22. By configuring in this way, when the tip of the second spiral blade 22 passes through the developer existing in the gap, a vortex motion occurs in which the developer immediately scraped off at the second distance d2 moves in a direction spreading along the inclined portion 40. By the generation of this vortex motion, it is possible to effectively prevent the developer existing in the gap, particularly the developer at the bottom, from aggregating and sticking.

[0042] Note that the inclined portion 40 can also be formed as an arc. Further, the inclined portion 40 may be provided on the first spiral blade 21. In addition, although the inclined portion 40 of the present disclosure is provided over the entire tip surface so as to approach the rotation axis 23 side from the tip as it goes from the tip corner portion on the downstream side in the rotation direction of the conveying member 20 toward the upstream side, it may be provided on a part of the tip.

[0043] FIG. 10 is a perspective view of a further modification of the conveying member 20. FIG. 11 is a side view of the conveying member 20 shown in FIG. 10. FIG. 12 is a cross-sectional view of the conveying member 20 shown in FIG. 10.

[0044] As shown in FIGS. 10, 11, and 12, it is preferable that the first spiral blade 21 and the second spiral blade 22 are provided such that the magnitude relationship between the first radius r1 and the second radius r2 periodically alternates in the developer conveying direction.

[0045] Specifically, as shown in FIG. 11, in the region L1 on the left side of the figure of the conveying member 20, the first radius r1 of the first spiral blade 21 is configured to be larger than the second radius r2 of the second spiral blade 22 (r1>r2). On the other hand, in the region L2 on the right side of the figure of the conveying member 20, the second radius r2 of the second spiral blade 22 is configured to be larger than the first radius r1 of the first spiral blade 21 (r1<r2).

[0046] In other words, the feature of this further modified example is that the relationship between the first radius r1 of the first spiral blade 21 and the second radius r2 of the second spiral blade 22 is configured to be switched for each pitch described below in the developer transport direction.

[0047] The positional relationship between the first helical blade 21 and the second helical blade 22 will be described in detail.

[0048] 10, 11, and 12, the first spiral blade 21 and the second spiral blade 22 are arranged at positions 180° apart on either side of the center O of the rotation shaft 23 in the orthogonal cross section, and are arranged so as to be twisted while maintaining the same interval (pitch P) in the developer transport direction, and are configured so that the magnitude relationship between the first radius r1 and the second radius r2 is switched every time the developer advances at the pitch P in the developer transport direction. In the present disclosure, the first radius r1 is 8 mm, the second radius r2 is 8.5 mm, and the pitch P is 18 mm, but these may be changed depending on the developer used and the number of images output per unit time.

[0049] With this configuration, the amount of developer transported by each of the first and second helical blades 21 and 22 is switched for each pitch P, so that the average amount of developer transported in the developer transport direction by each of the first and second helical blades 21 and 22 can be made uniform. With this configuration, it is possible to reduce the variation in the detection of the toner concentration contained in the developer by the concentration sensor 80. Details will be described next.

[0050] Developing device 100 of the present disclosure includes a concentration sensor 80 that detects the toner concentration in developer tank 10. Concentration sensor 80 of the present disclosure is provided on the first communication portion 13a side of first chamber 10a included in developer tank 10.

[0051] Fig. 13 is a side view of the area of ​​the first chamber 10a where the concentration sensor 80 is provided, seen from the left side, illustrating the positional relationship between the concentration sensor 80 and the first conveying member 20a. Fig. 14 is a perspective view illustrating the shapes of the first helical blade 21 and the second helical blade 22 in the vicinity of the concentration sensor.

[0052] 13 and 14, the concentration sensor 80 is disposed at the bottom of the first chamber 10a so as to be aligned with the developer transport direction (the direction of the arrow in FIG. 13) of the first transport member 20a. Here, the length A of the concentration sensor 80 of the present disclosure in the developer transport direction is 8 mm.

[0053] In contrast, the first transport member 20a is configured such that the second radius r2 of the second spiral blade 22 is equal to the first radius r1 of the first spiral blade 21 in the region corresponding to the concentration sensor 80. More specifically, the second radius r2 of the region indicated by reference symbol C of the second spiral blade 22 shown in Fig. 13 is configured to be equal to the first radius r1 of the first spiral blade 21. Note that it is preferable to configure the length B of the region indicated by reference symbol C in the developer transport direction to be longer than the length A of the concentration sensor 80 in the developer transport direction. The length B in this disclosure is 14 mm.

[0054] With the above configuration, the tip of the first helical blade 21 and the tip of the second helical blade 22 pass through a position at the same distance from the concentration sensor 80. As a result, when the tip of the first helical blade 21 and the tip of the second helical blade 22 pass near the concentration sensor 80, the amount of developer present between each tip and the concentration sensor 80 becomes the same, so that it is possible to reduce the detection variation of the toner concentration contained in the developer transported by the tips of the first helical blade 21 and the second helical blade 22, respectively, and it becomes possible to detect the toner concentration with high accuracy.

[0055] Moreover, by combining with the configuration described in the further modified example, the variation in the detected toner concentration can be further reduced.

[0056] As described above, according to the developing device 100 and image forming apparatus 1 of the present disclosure, the position at which shear force is generated can be changed for the developer present at the bottom of the developing tank 10, which is an area not reached by the conveying force of the conveying member 20 such as a screw, thereby suppressing adhesion to the bottom wall 11 of the developing tank 10.

[0057] Although each embodiment and each example of the present disclosure have been described in detail above, it will be readily apparent to those skilled in the art that many modifications are possible without substantially departing from the novel features and effects of the present disclosure. Therefore, all such modifications are intended to be included within the scope of the present disclosure.

[0058] For example, a term described at least once in the specification or drawings together with a different term having a broader or similar meaning may be replaced with that different term anywhere in the specification or drawings. In addition, the configurations and operations of the developing device 100 and the image forming apparatus are not limited to those described in the embodiments and examples of the present disclosure, and various modifications are possible. [Explanation of symbols]

[0059] 1 image forming device, 2 image reading device, 3 paper discharge device, 4 paper feed device, 5 image forming unit, 10 developing tank, 10a first chamber (of developing tank), 10b second chamber (of developing tank), 11 bottom wall (of developing tank), 12 opening, 13a first communicating portion, 13b second communicating portion, 14 developer supply port, 20 conveying member, 20a first conveying member, 20b second conveying member, 21 first helical blade, 22 second helical blade, 23 rotating shaft, 40 slope, 50 developer carrier, 60 image carrier, 70 layer regulation blade, 80 concentration sensor, 100 developing device, d1 1st distance, d2 2nd distance, r1 1st radius, r2 2nd radius, O (rotation axis) center, P pitch, S rotation direction

Claims

1. A developer tank containing a developer; a transport member provided in the developing tank and configured to rotate in a predetermined direction to transport the developer in a predetermined direction; a developer carrier that carries, on its surface, a portion of the developer transported by the transport member; Equipped with The conveying member has a rotating shaft and a first helical blade and a second helical blade each provided in a helical shape on an outer periphery of the rotating shaft, A developing device characterized in that, in an orthogonal cross section perpendicular to the rotation shaft, a first radius, which is the distance from the center of the rotation shaft to the tip of the first helical blade, and a second radius, which is the distance from the center of the rotation shaft to the tip of the second helical blade, have different sizes.

2. In the orthogonal cross section, a first distance that is a distance from a tip of the first helical blade to a bottom wall of the developing tank is greater than a second distance that is a distance from a tip of the second helical blade to the bottom wall of the developing tank, 2. The development device of claim 1, wherein the second distance is in the range of 1 / 4 to 3 / 4 of the first distance.

3. the second radius is greater than the first radius; 2. The developing device according to claim 1, wherein the second spiral blade has, in the orthogonal cross section, an inclined portion at a tip corner on the upstream side of the rotation direction of the transport member, which is inclined from the tip to approach the rotation shaft side as it moves toward the upstream side.

4. 2. The developing device according to claim 1, wherein the first spiral blade and the second spiral blade are provided such that the magnitude relationship between the first radius and the second radius periodically changes in the developer transport direction.

5. the first helical blade and the second helical blade are disposed at positions spaced apart by 180° with respect to the center of the rotation shaft in the orthogonal cross section, and are disposed so as to be twisted at the same pitch in a transport direction of the developer, 5. The developing device according to claim 4, wherein the magnitude relationship between the first radius and the second radius is switched every time the developing device advances at the pitch in the transport direction.

6. a concentration sensor disposed at a bottom of the developer tank for determining a concentration of the developer; 2. The developing device according to claim 1, wherein the transport member is configured such that the first radius and the second radius are equal in size in a region corresponding to the density sensor.

7. An image forming apparatus comprising the developing device according to any one of claims 1 to 6, The image forming apparatus includes an image carrier, The image forming apparatus according to claim 1, wherein the developing device is disposed opposite the developer carrier.

Images