JP7619913B2 - Developing device and image forming apparatus - Google Patents

Description

The present invention relates to a developing device and an image forming apparatus equipped with the developing device, and in particular to a developing device and an image forming apparatus that uses a two-component developer.

As a two-component development device using a developer containing toner and a non-magnetic carrier, a trickle development type development device is known in which new developer is replenished into the development device while some of the developer is discharged from an outlet. In this type of development device, the developer is circulated by being transported in a specific transport direction while being stirred by multiple transport screws in a circulation chamber. The circulation chamber is connected to a supply section that replenishes the developer and a discharge section that discharges the developer.

The fluidity of the developer changes depending on the conditions of use, etc., and there is a risk of clogging or retention during the process of being transported to the discharge section. If developer retention occurs, the amount of developer discharged from the discharge section will decrease, and the amount of developer in the circulation chamber will increase, or the developer pressure will increase, which can cause problems such as the developer not being stirred and transported smoothly.

For example, Patent Document 1 discloses a developing device that includes an agitation transport member that agitates and transports developer, a discharge section disposed at the downstream end of the agitation transport member in the developer transport direction, and a regulating member that regulates the amount of developer discharged. The agitation transport member has a spiral structure that transports developer, and a reverse spiral structure downstream adjacent to the spiral structure. The regulating member is intended to regulate the amount of developer that flows from the spiral structure to the reverse spiral structure in the agitation transport member that rotates at high speed.

JP 2020-118715 A

Normally, developer that has deteriorated or is in a high humidity environment is prone to a decrease in fluidity. In such cases, in the conventional developing device, a transport force acts on the developer with reduced fluidity that flows from the spiral structure to the reverse spiral structure in the opposite direction to the discharge section, making it difficult for the developer to be discharged. Furthermore, combined with the action of the regulating member, excess developer increases in the developing device, causing problems such as the developer not being discharged smoothly.

In addition, a reverse spiral structure is provided in the path to the discharge section, so that a transport force in the opposite direction to the discharge section acts on the developer. However, when the fluidity of the developer increases, the developer is more likely to scatter into the space above it, and is transported excessively to the discharge section, which causes problems such as an increase in the amount of developer discharged.

The present invention was made in consideration of the above problems, and its purpose is to provide a developing device that can suppress fluctuations in the amount of developer discharged and stabilize the amount of developer in the developing device, and an image forming apparatus equipped with such a developing device.

The solution of the present invention for achieving the above object is directed to a developing device having a circulation chamber that transports and agitates the developer to be supplied to a developer carrier in the axial direction of the developer carrier, the circulation chamber having a first chamber equipped with a first transport member that transports the developer in one direction in the axial direction, and a second chamber equipped with a second transport member that transports the developer in the other direction in the axial direction and supplies the developer to the developer carrier, the first chamber and the second chamber being connected via communication ports disposed at both ends of the second transport member, The first chamber is connected to an outlet chamber having a developer outlet at an end in the one direction, and the first transport member has a transport section having a spiral first blade that transports the developer in the one direction, a discharge section having a spiral second blade that is disposed in the discharge chamber and transports the developer to the outlet, and a reverse winding section that is disposed between the transport section and the discharge section and has a spiral third blade that is wound in the opposite direction to the first blade, and the third blade has a smaller outer diameter on the transport section side than on the discharge section side.

Furthermore, in the developing device having the above configuration, it is preferable that the outer diameter of the third blade on the conveying section side is smaller than the outer diameter of the first blade.

In addition, in the developing device having the above configuration, it is preferable that the third blade has an outer diameter that is equal over at least one helical pitch on the discharge section side.

In addition, in the developing device having the above configuration, a peripheral wall member that covers at least the upper portion of the outer periphery of the third blade may be provided on the discharge chamber side of the first chamber.

In addition, in the developing device having the above configuration, it is preferable that the peripheral wall member has a length in the axial direction that is at least equivalent to one helical pitch of the third blade.

In addition, in the developing device having the above configuration, the peripheral wall member is disposed with a gap from the outer periphery of the third blade, and the gap is preferably within 0.5 mm.

In addition, in the developing device having the above configuration, the peripheral wall member may have a protrusion that protrudes between the first chamber and the second chamber, or may be an elastic sheet-like member.

In addition, in the developing device having the above configuration, the first transport member may have a boundary portion between the reverse winding portion and the discharge portion that does not have a spiral blade, and a regulating member having a through hole with an inner diameter smaller than the outer diameter of the third blade is provided at the end of the first chamber on the discharge chamber side, so that the boundary portion is disposed within the through hole.

Furthermore, in the developing device having the above configuration, it is preferable that the helical pitch of the first blade is greater than the helical pitch of the third blade.

An image forming apparatus using a developing device having the above configuration also falls within the scope of the technical concept of the present invention.

The above configuration makes it possible to prevent developer from accumulating or being discharged in excess even if the fluidity of the developer fluctuates, thereby stabilizing the amount of developer in the developing device.

The present invention makes it possible to suppress fluctuations in the amount of developer discharged and stabilize the amount of developer in the developing device.

1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a perspective view showing a developing device according to the first embodiment of the present invention. 1 is a cross-sectional view showing a developing device according to a first embodiment of the present invention. This is a cross-sectional view taken along line AA in FIG. This is a cross-sectional view taken along the line B-B in FIG. FIG. 2 is an enlarged perspective view of a front portion of the developing device, with a portion cut away; 4 is a perspective view showing a front portion of a first transport screw provided in the developing device; FIG. FIG. 4 is a perspective view showing a mounting structure of a peripheral wall member in the developing device; FIG. 4 is a perspective view showing a state in which a peripheral wall member is attached to the developing device. FIG. 4 is a perspective view showing an attachment structure of a regulating member in the developing device. FIG. 4 is a perspective view showing a state in which a regulating member is attached to the developing device. FIG. 4 is a cross-sectional view illustrating a flow of developer in the developing device. 5 is a cross-sectional view illustrating a flow of developer in a comparative example of the present embodiment. FIG. FIG. 11 is a perspective view showing a front portion of a developing device according to a second embodiment of the present invention. FIG. 2 is a perspective view showing a front portion of the developing device. FIG. 11 is an explanatory diagram showing an enlarged front portion of a developing device according to a third embodiment of the present invention. FIG. 2 is a perspective view showing the developing device as viewed obliquely from above.

The developing device according to an embodiment of the present invention and the image forming apparatus equipped with the developing device will be described with reference to the drawings.

(Overall configuration of image forming apparatus)
1 is a cross-sectional view showing a schematic configuration of an image forming apparatus 1 according to an embodiment of the present invention. In the embodiment, the image forming apparatus 1 will be described by taking as an example a case in which the present invention is applied to a color multifunction machine that forms a color image on a sheet.

The image forming device 1 can be applied to various image forming devices including color printers, monochrome multifunction machines, monochrome printers, etc. As the recording medium sheet, paper or overhead projector sheets can be used. In addition, when the image forming device 1 is viewed from the front as shown in the figure, in the front-to-rear direction X, the front side (near side) of the image forming device 1 is the front direction X1, the back side (rear side) of the image forming device 1 is the rear direction X2, and in the left-to-right direction Y, the left side is the left direction Y1, and the right side is the right direction Y2, as described below.

The image forming device 1 is a multifunction device having a scanner function, a copy function, a printer function, a facsimile function, etc., and transmits an image of an original document read by the image reading device 18 to the outside (corresponding to the scanner function), and also forms an image of the read original document or an image received from the outside on a sheet in color or monochrome (corresponding to the copy function, printer function, and facsimile function).

The image forming apparatus 1 includes a charging device 12, an optical scanning device 11, a developing device 10, a photoconductor drum 13, a drum cleaning device 14, an image transfer section 15, a paper feed device 17, an image reading device 18, a fixing device 27, a sheet transport path 31, etc.

Image forming device 1 handles image data corresponding to color images using the colors black (K), cyan (C), magenta (M), and yellow (Y), or monochrome images using a single color (e.g., black). Image reading device 18 reads an original document or an original document transported from an original transport unit (ADF) to generate image data. Image transfer unit 15 of image forming device 1 is provided with four developing devices 10, four photosensitive drums 13, four drum cleaning devices 14, and four charging devices 12 for forming four types of toner images, and four image stations Pa, Pb, Pc, and Pd are configured to correspond to black, cyan, magenta, and yellow, respectively.

The drum cleaning device 14 removes and collects residual toner on the surface of the photoreceptor drum 13. The charging device 12 charges the surface of the photoreceptor drum 13. The optical scanning device 11 exposes the surface of the photoreceptor drum 13 to light to form an electrostatic latent image. The developing device 10 develops the electrostatic latent image on the surface of the photoreceptor drum 13 to form a toner image on the surface of the photoreceptor drum 13. Through this series of operations, a toner image of each color is formed on the surface of each photoreceptor drum 13.

An intermediate transfer roller 16 is disposed above the photosensitive drum 13 with an intermediate transfer belt 21 in between. The intermediate transfer belt 21 is an image carrier on which a toner image is formed, and is stretched around a transfer drive roller 22 and a transfer driven roller 23, rotating (moving in a circular motion) in the direction of arrow C. The toner images of each color formed on the surface of each photosensitive drum 13 are transferred (primary transfer) and superimposed, forming a color toner image on the surface of the intermediate transfer belt 21.

The transfer roller 26 of the secondary transfer section 25 forms a nip area (secondary transfer position) between itself and the intermediate transfer belt 21, and conveys the sheet conveyed through the sheet conveying path 31 by pinching it. When the sheet passes through the nip area, the toner image on the surface of the intermediate transfer belt 21 is transferred to the sheet, and the sheet is conveyed to the fixing device 27. Toner remaining on the intermediate transfer belt 21 is collected by the belt cleaning device 24.

The fixing device 27 includes a fixing roller 28 and a pressure roller 29 that rotate while sandwiching the sheet. The fixing device 27 sandwiches the sheet onto which the toner image has been transferred between the fixing roller 28 and the pressure roller 29, and applies heat and pressure to fix the toner image to the sheet.

The paper feeder 17 contains sheets used for image formation and is provided below the optical scanning device 11. The sheet is pulled out of the paper feeder 17 by the pickup roller 33, transported through the sheet transport path 31, and transported to the paper output tray 37 via the secondary transfer unit 25 and the fixing device 27 via the paper output roller 36. Various pairs of rollers are arranged on the sheet transport path 31, such as a registration roller 35 that stops the sheet, aligns the leading edge of the sheet, and then starts transporting the sheet in accordance with the transfer timing of the color toner image in the nip area between the intermediate transfer belt 21 and the transfer roller 26, multiple transport rollers 34 that promote the transport of the sheet, and a paper output roller 36.

When forming an image on the back side of the sheet as well as the front side, the sheet is transported in the reverse direction from the discharge rollers 36 to the sheet reversal transport path 32, the sheet is turned over, the sheet is guided again to the registration rollers 35, an image is formed on the back side in the same manner as on the front side, and the sheet is transported to the discharge tray 37.

(Embodiment 1)
FIG. 2 is a perspective view of the developing device 10 according to the first embodiment of the present invention as viewed from the front left side, and FIG.

The developing device 10 supplies non-magnetic toner contained in a two-component developer (developer) onto the surface of the photosensitive drum 13 by a development electric field formed between the photosensitive drum 13 and the developing device 10. As shown in FIG. 2, the developing device 10 has a housing 41 that is long in the front-rear direction X. As shown in FIG. 3, the housing 41 of the developing device 10 has an opening at a position facing the photosensitive drum 13. The photosensitive drum 13 is attached to a positioning portion 131 provided on the outside of the housing 41 as shown in FIG. 2, and is disposed facing this opening.

The developing roller 44 is a magnet roller that functions as a developer carrier, and is disposed in a position facing the photosensitive drum 13 within the housing 41. The developing roller 44 includes a sleeve portion that is formed in a non-magnetic cylindrical shape (not shown) and can rotate around the rotation axis 441, and a magnetic roll portion that is cylindrical and magnetic and disposed inside the sleeve portion. On the peripheral surface of the developing roller 44, a plurality of magnetic poles, each of which has a single polarity, are formed by the magnetism of the magnetic roll portion. In the illustrated embodiment, the developing roller 44 is provided so that the sleeve portion rotates in the rotation direction R3 around the rotation axis 441 disposed along the front-rear direction X. The developing roller 44 carries the developer on its surface and transports the toner contained in the carried developer to the surface of the photosensitive drum 13. The developer carried on the surface is regulated to a predetermined thickness by the regulating blade 45.

The rotation direction R3 of the developing roller 44 is set to be the same as the rotation direction R4 of the photosensitive drum 13 at the position facing the photosensitive drum 13. In the development area where the photosensitive drum 13 and the developing roller 44 face each other, the electrostatic latent image formed on the surface of the photosensitive drum 13 is developed with toner.

As shown in FIG. 3, the developing device 10 has a first chamber 51 and a second chamber 52 provided in the housing 41 as circulation chambers that transport and agitate the developer supplied to the developing roller 44 in the axial direction of the developing roller 44. The first chamber 51 and the second chamber 52 form a long space along the front-rear direction X in which the developer is contained. The first chamber 51 is provided with a first transport screw (first transport member) 60 that transports the developer in one direction in the front-rear direction X, which is the axial direction of the developing roller 44. The second chamber 52 is provided with a second transport screw (second transport member) 70 that transports the developer in the other direction in the front-rear direction X.

Figure 4 is a cross-sectional view taken along line A-A in Figure 3, and Figure 5 is a cross-sectional view taken along line B-B in Figure 4. As shown in Figure 4, the first chamber 51 and the second chamber 52 are adjacent to each other and are connected to each other via communication ports 541, 541 located at both ends of the second conveying screw 70. These communication ports 541, 541 are formed at both ends of a partition wall 54 that is provided in the housing 41 and extends in the front-rear direction X.

In the illustrated embodiment, the first transport screw 60 transports the developer in a forward direction X1 while stirring the developer, and the second transport screw 70 transports the developer in a rearward direction X2 opposite to the transport direction of the first transport screw 60 while stirring the developer.

Therefore, the developer contained in the first chamber 51 is transported in the first transport direction D1 while being stirred by the first transport screw 60, and reaches the second chamber 52 from the first chamber 51 by passing through the communication port 541 provided in the forward direction X1. The developer contained in the second chamber 52 is transported in the second transport direction D2 while being stirred by the second transport screw 70, and reaches the first chamber 51 from the second chamber 52 by passing through the communication port 541 provided in the rearward direction X2. In this way, the developer is transported so as to circulate between the first chamber 51 and the second chamber 52.

The first chamber 51 is also provided with a discharge chamber 53 at its end in the forward direction X1. As shown in FIG. 5, the discharge chamber 53 is provided at the downstream end of the first chamber 51 in the developer transport direction (first transport direction D1). As shown in FIGS. 2 and 5, a discharge section cover 43 is provided on the outside of the discharge chamber 53. The discharge chamber 53 is provided with a developer discharge port 531. A recovery container (not shown) is connected to the discharge port 531. Excess developer contained in the first chamber 51 is discharged from the discharge chamber 53 through the discharge port 531 to the recovery container.

As shown in FIG. 4, the second transport screw 70 disposed in the second chamber 52 has a helical blade 71 formed in a helical shape around the rotating shaft 72. The helical blade 71 rotates together with the rotating shaft 72 to send the developer in the second chamber 52 in the second transport direction D2. In contrast, the first transport screw 60 disposed in the first chamber 51 has a first helical blade (first blade) 61 and a second helical blade (second blade) 62 that are helically arranged around the rotating shaft 64, and a third helical blade (third blade) 63 that is helically arranged in a reverse direction to the first helical blade 61 and the second helical blade 62. The first helical blade 61, the second helical blade 62, and the third helical blade 63 are each integrally provided on the rotating shaft 64.

Figure 6 is an enlarged perspective view with a portion cut away of the front portion of the developing device 10, and Figure 7 is a perspective view showing the front portion of the first transport screw 60.

More specifically, the first transport screw 60 includes a transport section 610 having a first spiral blade 61 and transporting the developer in a first transport direction D1 (forward direction X1), a discharge section 620 having a second spiral blade 62 and disposed in the discharge chamber 53 and transporting the developer in the first transport direction D1, which is the direction of the discharge port 531, and a reverse winding section 630 having a third spiral blade 63 and applying a transport force to the developer in a second transport direction D2 (rear direction X2) opposite to the first transport direction D1. The transport section 610 is provided on the rear direction X2 side of the rotating shaft section 64 extending in the front-rear direction X, and the discharge section 620 is provided on the front direction X1 side. The reverse winding section 630 is provided on the rear direction X2 side between the transport section 610 and the discharge section 620. Furthermore, between the reverse winding section 630 and the discharge section 620, there is a boundary section 640 that consists of only the rotating shaft section 64, which does not have a spiral blade.

As shown in FIG. 7, the helical pitch P1 of the first helical blade 61 is set to be larger than the helical pitch P4 of the second helical blade 62, and larger than the helical pitches P2 and P3 of the third helical blade 63. In particular, the helical pitches P2 and P3 of the third helical blade 63 are smaller than the helical pitch P1 of the first helical blade 61, and are set at approximately 1/4 to 1/2 of the helical pitch P1. The helical pitches P1 to P4 relate to the distance the developer is transported when the first transport screw 60 rotates once, and a larger helical pitch can increase the transport force. In the illustrated embodiment, the helical pitch P2 and the helical pitch P3 are the same pitch.

Of the first helical blade 61, the second helical blade 62, and the third helical blade 63, the first helical blade 61 has the greatest number of spiral threads, followed by the second helical blade 62. In the illustrated embodiment, the third helical blade 63 has the fewest number of spiral threads, with three as shown. The developer enters between these helical blades, and the helical blades form the developer flow, so it can be said that the greater the number of threads, the greater the developer transport force.

Furthermore, the second spiral blade 62 has an outer diameter S4 that is smaller than the outer diameter S1 of the first spiral blade 61 and the outer diameters S3 and S2 of the third spiral blade 63. The third spiral blade 63 has an outer diameter S3 that is larger than the outer diameter S1 of the first spiral blade 61. In the first transport screw 60, the difference between the outer diameter S1 of the first spiral blade 61 and the outer diameter (shaft diameter) S5 of the rotating shaft portion 64 is related to the area of the first spiral blade 61, so it can be said that the larger the outer diameter of the first spiral blade 61, the greater the developer transport force.

The third spiral blade 63 has a smaller outer diameter S2 on the conveying section 610 side than on the discharge section 620 side. That is, as shown in FIG. 7, the third spiral blade 63 has a reverse-wound small diameter portion 631 having a small outer diameter S2 on the upstream side of the developer conveying direction (first conveying direction D1) from the conveying section 610, and a reverse-wound large diameter portion 632 having an outer diameter S3 on the downstream side. The outer diameter S2 of the reverse-wound small diameter portion 631 is smaller than the outer diameter S3 of the reverse-wound large diameter portion 632. Furthermore, the outer diameter S2 of the third spiral blade 63 on the conveying section 610 side is smaller than the outer diameter S1 of the first spiral blade 61. In addition, the rotating shaft portion 64 in the reverse-wound portion 630 is provided with an outer diameter S6 smaller than the outer diameter S5 of the rotating shaft portion 64 in the conveying section 610.

The reverse-wound large diameter portion 632 of the third spiral blade 63 is provided on the discharge section 620 side so as to have an outer diameter S3 that is equal to at least one pitch of the spiral pitch P2. As shown in FIG. 7, the reverse-wound large diameter portion 632 and the reverse-wound small diameter portion 631 are connected via a step 633 whose size corresponds to the difference in outer diameter. The reverse-wound large diameter portion 632 is provided with a spiral pitch P2, and the reverse-wound small diameter portion 631 is provided with a spiral pitch P3 that is equal to the spiral pitch P2. The reverse-wound large diameter portion 632 and the reverse-wound small diameter portion 631 may be connected in a shape that gradually decreases continuously from the outer diameter S3 to the outer diameter S2 without a step.

As a result, in the third spiral blade 63 of the reverse-wound portion 630, the conveying force acting on the developer in the second conveying direction D2 is weaker in the reverse-wound small diameter portion 631 of the outer diameter S2 than in the reverse-wound large diameter portion 632. In addition, since the third spiral blade 63 has the reverse-wound small diameter portion 631 on the conveying portion 610 side, as shown in FIG. 6, the outer periphery of the reverse-wound small diameter portion 631 has a space (gap) larger than the outer periphery of the reverse-wound large diameter portion 632. Therefore, the developer conveyed in the first conveying direction D1 through the conveying portion 610 by the first conveying screw 60 is easily able to enter the third spiral blade 63 due to the space on the outer periphery of the reverse-wound small diameter portion 631 on the conveying portion 610 side of the reverse-wound portion 630.

On the other hand, the third spiral blade 63 acts to transport the developer in the second transport direction D2, which is the opposite direction to the first transport direction D1. The outer periphery of the reverse-wound small diameter portion 631 also creates space above, so when the developer has high fluidity, it is easy for the developer to wrap around. Therefore, as shown in FIG. 6, a peripheral wall member 81 and a regulating member 83 are provided on the discharge chamber 53 side of the first chamber 51 to prevent excessive developer from being discharged. The peripheral wall member 81 is provided so as to cover at least the upper part of the outer periphery of the third spiral blade 63. The regulating member 83 is also provided at the boundary portion 640 of the first transport screw 60.

Figures 8A and 8B are perspective views showing the mounting structure of the peripheral wall member 81, and Figures 9A and 9B are perspective views showing the mounting structure of the regulating member 83. In Figures 8A and 8B, in order to make the drawings easier to see, the second conveying screw 70 arranged in the second chamber 52 across the partition wall 54 is omitted.

As shown in FIG. 8B, the peripheral wall member 81 is a protruding block body that protrudes between the first chamber 51 and the second chamber 52. In the illustrated embodiment, as shown in FIG. 8A, the peripheral wall member 81 has a cylindrical surface 811 that is arranged to face the outer periphery of the third spiral blade 63 of the first conveying screw 60, and a fixing portion 812 is provided above the cylindrical surface 811. The cylindrical surface 811 is formed in a curved shape with an inner diameter that can secure a gap between the outer diameter S3 of the reverse-wound large diameter portion 632 of the third spiral blade 63. In this case, the cylindrical surface 811 is provided on two sides so as to face both the first chamber 51 side and the second chamber 52 side.

The fixing portion 812 is attached to the inner surface of the mounting member 46 provided above the third spiral blade 63, and the peripheral wall member 81 is fixed thereto. Note that the peripheral wall member 81 is not limited to being provided above the third spiral blade 63 as shown in FIG. 8B, but may be provided so that two peripheral wall members 81 are arranged above and below with their protrusions butted together as shown in FIG. 9A, and integrally cover one side of the outer periphery of the third spiral blade 63 from above to below.

As shown in FIG. 9A, the restricting member 83 is a plate-shaped member having a through hole 831. The through hole 831 is formed with an inner diameter smaller than the outer diameter S3 of the reverse-wound large diameter portion 632 of the third spiral blade 63.

The regulating member 83 is fitted from the second helical blade 62 side in the front-rear direction X to the first conveying screw 60 arranged in parallel to the second conveying screw 70 via the partition wall 54. As shown in FIG. 9B, after the regulating member 83 is attached, the second helical blade 62 is fitted with a discharge case 532 having a discharge port 531. The discharge chamber 53 is provided in the internal space of this discharge case 532. As shown in FIG. 6, the regulating member 83 is disposed at the end of the first chamber 51 on the discharge chamber 53 side. The boundary portion 640 of the first conveying screw 60 is disposed within the through hole 831.

Figure 10 is a cross-sectional explanatory diagram showing the flow of developer in the developing device 10 according to embodiment 1. As shown in the figure, the peripheral wall member 81 has a length L1 in the axial direction (front-rear direction X) of the rotating shaft portion 64 that is long enough to cover the reverse-wound large diameter portion 632 of the third spiral blade 63. It is preferable that the peripheral wall member 81 is provided over at least one spiral pitch of the third spiral blade 63 (spiral pitches P2 and P3 shown in Figure 7).

The cylindrical surface 811 on the inner surface of the peripheral wall member 81 is disposed with a gap G1 from the outer periphery of the third spiral blade 63. For example, it is preferable that this gap G1 is set to 0.5 mm or less. In addition, at a minimum, a gap G2 is provided between the bottom surface of the first chamber 51 and the third spiral blade 63 and from the outer periphery of the reverse-wound large diameter portion 632.

A restricting member 83 is provided adjacent to the peripheral wall member 81 in the forward direction X1. As shown in FIG. 10, the through hole 831 of the restricting member 83 is formed with an inner diameter smaller than the outer diameter of the reverse-wound large diameter portion 632 of the third spiral blade 63, and is disposed on the outer periphery of the boundary portion 640.

Figure 11 is a cross-sectional view illustrating the flow of developer when neither the peripheral wall member 81 nor the regulating member 83 is provided, as a comparative example of this embodiment.

The fluidity of the developer changes depending on the conditions of use, such as humidity. In particular, when the fluidity decreases, as shown in FIG. 11, the developer transported in the first transport direction D1 by the first spiral blade 61A becomes more likely to clog, and even if it reaches the reverse-wound third spiral blade 63A, it becomes difficult for the developer to advance in the direction of the third spiral blade 63A.

Also, as shown in FIG. 11, if the third spiral blade 63A is formed with a constant outer diameter without having large and small diameter portions, the gap at the outer periphery of the third spiral blade 63A becomes narrow (the outer diameter S3 of the third spiral blade 63 is larger than the outer diameter S1 of the first spiral blade 61), and developer stagnation D11 is likely to occur, especially when the fluidity of the developer deteriorates. This may result in less developer being sent to the second spiral blade 62A, which may result in a decrease in the amount of developer discharged from the discharge chamber 53A.

On the other hand, developer with increased fluidity tends to float. Because space is created above the third spiral blade 63A, which does not have a peripheral wall member 81, developer with high fluidity tends to wrap around from above D12. As shown in FIG. 11, because no regulating member 83 is provided in the rear direction X2 of the discharge chamber 53A, the wrapped around developer tends to enter the discharge chamber 53A. In such a case, there is a risk that the amount of discharge from the discharge chamber 53A will increase.

In this way, if neither the peripheral wall member 81 nor the regulating member 83 is provided, the amount of developer discharged will fluctuate due to the influence of the fluidity of the developer, and there is a problem in that the amount of developer in the device will not be stable.

In contrast, in the developing device 10 according to this embodiment, as shown in FIG. 10, a peripheral wall member 81 is provided on the outer periphery of the third spiral blade 63, so that even if the developer has high fluidity, floating developer can be prevented from wrapping around or scattering from above the third spiral blade 63, and excessive developer flow toward the discharge section 620 can be prevented. In addition, a regulating member 83 is provided between the reverse winding section 630 and the discharge section 620, so that a through hole 831 with an inner diameter smaller than the outer diameter of the third spiral blade 63 acts as a resistance to the developer entering the discharge chamber 53, and excessive developer can be prevented from being sent to the discharge chamber 53.

Furthermore, since the third spiral blade 63 is configured with a reverse-wound small diameter portion 631 and a reverse-wound large diameter portion 632, even if the fluidity of the developer decreases, the developer transported in the first transport direction D1 can be prevented from stagnating or clogging in the reverse-wound portion 630.

For example, the outer periphery of the third spiral blade 63 has a gap G1 with the peripheral wall member 81 and a gap G2 with the bottom surface of the first chamber 51, and these gaps allow the developer with reduced fluidity to flow from the third spiral blade 63 toward the second spiral blade 62 without stagnation. In other words, the developer transported in the first transport direction D1 by the first spiral blade 61 and entering the space on the outer periphery of the reverse-wound small diameter portion 631 on the transport section 610 side of the reverse-wound section 630 and the developer transported in the second transport direction D2 from the reverse-wound large diameter portion 632 of the third spiral blade 63 collide with each other on the outer periphery of the reverse-wound small diameter portion 631, forming a circulating flow D10. Therefore, the developer is subjected to a shear force by the flow D10, and even if the developer has deteriorated in fluidity, the developer does not aggregate, so a constant amount of developer is always sent through the gap G2 in the first transport direction D1. In other words, a constant amount of developer can always be discharged from the discharge chamber 53A regardless of the fluidity of the developer.

As described above, the outer diameter (S6) of the rotating shaft 64 at the reverse winding section 630 and the discharge section 620 is smaller than the outer diameter (S5) at the transport section 610. This also ensures that the space for the developer to enter is as large as possible, making it easier for the developer to enter in the direction of the discharge section 620.

Therefore, regardless of whether the fluidity of the developer decreases or increases, it is possible to maintain an appropriate amount of developer discharge, and the amount of developer circulating in the first chamber 51 and the second chamber 52 can be stabilized.

(Embodiment 2)
12A and 12B are perspective views showing a front portion of a developing device 10 according to the second embodiment.

The peripheral wall member 81 provided on the discharge chamber 53 side of the first chamber 51 is preferably configured to cover at least the upper part of the outer periphery of the third spiral blade 63, and is not limited to the configuration shown in the first embodiment. For example, as shown in FIG. 12A, the peripheral wall member 81 may be provided with a curved cylindrical surface 813 that covers one side of the outer periphery of the third spiral blade 63 from above to below. In this case, the peripheral wall member 81 has cylindrical surfaces 813 provided symmetrically on both sides. In addition, fixing portions 814 are provided above and below the peripheral wall member 81. The cylindrical surface 813 has a length of at least one helical pitch of the third spiral blade 63 in the front-rear direction X.

As shown in FIG. 12B, the peripheral wall member 81 is fitted and attached from the second helical blade 62 side of the first conveying screw 60 to the side of the third helical blade 63. The peripheral wall member 81 narrows the gap around the outer periphery of the third helical blade 63 on the first conveying screw 60.

Even with this configuration, as in the first embodiment, even if the fluidity of the developer increases, the floating developer can be prevented from wrapping around or scattering from above or to the sides of the third spiral blade 63, and the developer can be prevented from flowing excessively toward the discharge section 620.

(Embodiment 3)
FIG. 13 is an explanatory diagram showing an enlarged view of the peripheral wall member 82 in the developing device 10 according to the third embodiment together with the front portion of the first transport screw 60, and FIG. 14 is a perspective view showing the peripheral wall member 82 as viewed obliquely from above.

In the first and second embodiments, a block-shaped peripheral wall member 81 is provided on the outer periphery of the first transport screw 60. The developing device 10 according to the present invention is not limited to this configuration, and the peripheral wall member 82 may be an elastic sheet-like member.

As shown in FIG. 13, the peripheral wall member 82 made of a sheet-like material is provided adjacent to the discharge chamber 53 in the rear direction X2 of the discharge chamber 53. Also, as shown in FIG. 14, the peripheral wall member 82 is provided in a substantially cylindrical shape so as to surround the third spiral blade 63 of the first conveying screw 60. The inner peripheral surface 821 of the peripheral wall member 82 is disposed with a gap between it and the third spiral blade 63. It is preferable that the length L2 of the peripheral wall member 82 in the front-rear direction X is set to a length that covers at least one pitch of the third spiral blade 63 in the forward direction X1 (e.g., equivalent to the spiral pitch P2 of the reverse-wound large diameter portion 632 shown in FIG. 7).

Even in this configuration, as in the first and second embodiments, it is possible to prevent floating developer from wrapping around or scattering from above or to the sides of the third spiral blade 63, and to prevent the developer from flowing excessively toward the discharge section 620.

By configuring the developing device 10 as described above, it is possible to suppress fluctuations in the amount of developer discharged from the discharge chamber 53 even if the fluidity of the developer changes. As a result, the amount of developer in the first chamber 51 and the second chamber 52 of the developing device 10 can be stabilized, and the developer pressure can be appropriately maintained, contributing to high-quality image formation.

The present invention is not limited to the above-described embodiments, and can be embodied in various other forms. For example, the shapes of the peripheral wall members 81, 82 are not limited to those shown in the above-described embodiments. Furthermore, the helical pitch and number of threads of the second helical blade 62 and the third helical blade 63 are not limited, and may be configured in any way. Therefore, the above-described embodiments are merely illustrative in all respects and should not be interpreted in a restrictive manner. The scope of the present invention is set forth in the claims, and is not bound by the specification. Furthermore, all modifications and changes that fall within the scope of the claims are within the scope of the present invention.

1 Image forming apparatus 10 Developing device 11 Optical scanning device 12 Charging device 13 Photoconductor drum 44 Developing roller (developer carrier)
441 Rotating shaft 51 1st chamber (circulation chamber)
52 Second room (circulation room)
53 Discharge chamber 531 Discharge port 54 Partition wall 541 Communication port 60 First conveying screw (first conveying member)
61 First spiral blade (first blade)
62 Second spiral blade (second blade)
63 Third spiral blade (third blade)
631 Reverse-wound small diameter portion 632 Reverse-wound large diameter portion 64 Rotating shaft portion 610 Conveying portion 620 Discharge portion 630 Reverse-wound portion 640 Boundary portion 70 Second conveying screw (second conveying member)
71 Spiral blade 72 Rotating shaft portion 81, 82 Peripheral wall member 811, 813 Cylindrical surface 812, 814 Fixing portion 83 Regulating member 831 Through hole

Claims (11)

A developing device having a circulation chamber that conveys and agitates a developer to be supplied to a developer carrier in an axial direction of the developer carrier,
the circulation chamber includes a first chamber including a first transport member that transports the developer in one direction in the axial direction, and a second chamber that includes a second transport member that transports the developer in the other direction in the axial direction and supplies the developer to the developer carrier;
the first chamber and the second chamber are connected via communication ports disposed at both ends of the second conveying member,
a discharge chamber having a developer discharge port is provided at an end of the first chamber in communication with the end of the first chamber,
The first conveying member is
a transport section including a spiral first blade for transporting the developer in the one direction;
a discharge portion provided in the discharge chamber and including a spiral second blade for feeding the developer in the one direction;
a reverse winding portion provided between the conveying portion and the discharge portion and including a third blade having a spiral shape that is reverse wound to the first blade,
the third blade has an outer diameter that is smaller on the conveying section side than on the discharge section side,
A developing device characterized in that an outer diameter of the third blade closest to the discharge portion is larger than an outer diameter of the first blade, and an outer diameter of a rotating shaft portion of the third blade is smaller than an outer diameter of a rotating shaft portion of the first blade .
2. The developing device according to claim 1,
The developing device, wherein the third blade has an outer diameter on the transport portion side smaller than an outer diameter of the first blade. 3. The developing device according to claim 1,
The developing device, wherein the third blade has a constant outer diameter over at least one helical pitch on the discharge portion side. In the developing device according to any one of claims 1 to 3,
a peripheral wall member that covers at least an upper portion of an outer periphery of the third blade, the peripheral wall member being provided on the discharge chamber side of the first chamber. 5. The developing device according to claim 4,
a peripheral wall member having a length in the axial direction that is at least equivalent to one helical pitch of the third blade; 6. The developing device according to claim 4,
a developing device, the peripheral wall member being disposed with a gap provided relative to an outer periphery of the third blade, the minimum gap being set to 0.5 mm or less.
In the developing device according to any one of claims 4 to 6,
The developing device according to claim 1, wherein the peripheral wall member has a protruding portion protruding between the first chamber and the second chamber. In the developing device according to any one of claims 4 to 6,
The developing device according to claim 1, wherein the peripheral wall member is a sheet-like member having elasticity. The developing device according to any one of claims 1 to 8,
the first conveying member includes a boundary portion between the reverse winding portion and the discharge portion that does not have a spiral blade,
A developing device characterized in that a regulating member having a through hole with an inner diameter smaller than the outer diameter of the third blade is provided at the end of the first chamber on the discharge chamber side, and the boundary portion is disposed within the through hole. The developing device according to any one of claims 1 to 9,
A developing device, wherein the helical pitch of the first blade is larger than the helical pitch of the third blade. An image forming apparatus equipped with the developing device according to any one of claims 1 to 10.

Images