JP6496930B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to a so-called trickle-type developing device and an image forming apparatus including the developing device.

  Conventionally, as this type of developing device, for example, there is one described in Patent Document 1 below. A spiral auger is disposed inside the developing device. In the spiral auger, a forward spiral blade and a reverse spiral blade are provided on the rotation shaft, and an area where neither is provided is formed between the blades. Therefore, this region is only in the state of the rotating shaft, and the forward conveying force in the vicinity of the nozzle can be reduced. Thus, an appropriate amount of developer can be discharged according to the amount of developer in the developing device.

JP 2005-316161 A

  As described above, in the conventional developing device, the developer discharge amount is regulated by improving the configuration of the spiral auger. However, when the image forming apparatus operates at a low system speed, there is a problem that a large amount of old developer remains in the developing device as compared to when the image forming apparatus operates at a high speed.

  SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a developing device and an image forming apparatus capable of suppressing the remaining amount of old developer in the developing device regardless of the system speed.

According to one aspect of the present invention, a first transport path and a second transport path that communicate with each other through two openings, and the first transport path in the vicinity of one of the two openings, the discharge port A first transport member that transports at least the developer in the first transport path in the first direction, and a second direction different from the first direction in the developer in the second transport path. A second transport member that transports the first transport path, and a developer carrier that carries the developer transported through the first transport path or the second transport path, wherein the first transport member is provided on the first shaft. A first screw that applies a propulsive force in the first direction to the developer in the first transport path, and a first screw that is provided on the first shaft, and is opposite to the first direction in the developer on the third transport path. A second screw for applying a force of A first section is a portion of the cylindrical screw is not provided near, at least part of the diameter of the first section does not include a region along the outlet is greater than the diameter of other sections , Directed to the developer.

  Another embodiment of the present invention is directed to an image forming apparatus including the developing device.

  According to each of the above embodiments, it is possible to provide a developing device and an image forming apparatus that can reduce the amount of old developer remaining in the developing device regardless of the system speed.

FIG. 3 is a diagram when the inside of the image forming apparatus is viewed from the front side. It is a figure which shows the detailed structure of the developing device of FIG. FIG. 3 is a cross-sectional view when a cross section taken along line I-I ′ of FIG. 2 is viewed from the direction of arrow II. FIG. 3 is a diagram showing the amount of developer remaining in the developing tank when the developing device of FIG. 2 and the developing device according to the reference example are rotated at low speed, medium speed, and high speed, respectively. FIG. 3 is a schematic diagram for explaining a residual amount of developer when the developing device of FIG. 2 and the developing device of the reference example are rotated at high speed. FIG. 3 is a schematic diagram for explaining a residual amount of developer when the developing device of FIG. 2 and the developing device of the reference example are rotated at a low speed. It is a figure which shows the structure of the developing device which concerns on a 1st modification. It is a figure which shows the structure of the developing device which concerns on a 2nd modification.

  Hereinafter, a developing device and an image forming apparatus according to each embodiment will be described in detail with reference to the drawings.

<< First column: Definition >>
Some figures show an x-axis, a y-axis and a z-axis that are orthogonal to each other. The x axis and the z axis indicate the left and right direction and the up and down direction of the image forming apparatus 1. The y-axis indicates the front-rear direction of the image forming apparatus 1. More specifically, the y-axis direction is also a direction in which the photosensitive drum 5 and the developing roller 86 extend from the front side to the back side of the image forming apparatus 1.

  In addition, in the text and each figure, alphabetic small letters a, b, c, and d may be added as subscripts of reference numerals. a, b, c, and d represent yellow (Y), magenta (M), cyan (C), and black (K). For example, the photosensitive drum 5a means a Y-color photosensitive drum. In addition, although a subscript can be added but a subscript is not added to the reference symbol, it means four colors or each color. For example, the photosensitive drum 5 means YMCK all colors or each color photosensitive drum.

<< Second column: Overall configuration and printing operation of image forming apparatus >>
In FIG. 1, an image forming apparatus 1 is, for example, a copying machine, a printer, a facsimile machine, or a multifunction machine having these functions. Various types of images (typically, a typical electrophotographic system and a tandem system are used. A full-color image or a monochrome image) is printed on the paper M. For this purpose, the image forming apparatus 1 includes an image forming unit 2 for each color, an intermediate transfer belt 3, and a secondary transfer roller 4.

For example, the image forming units 2 for four colors are juxtaposed in the x-axis direction and include photosensitive drums 5 for corresponding colors.
Each photosensitive drum 5 has a cylindrical shape extending in the y-axis direction, and rotates in the direction of an arrow α, for example. Around each photosensitive drum 5, at least a charger 6, a trickle developer 8, and a primary transfer roller 9 are arranged from the upstream side to the downstream side in the rotation direction α.

Each charger 6 uniformly charges the peripheral surface of the rotating photosensitive drum 5.
An exposure device 7 is provided below each photosensitive drum 5. Each exposure device 7 irradiates a light beam B based on the image data to an exposure area immediately downstream of the charging area of the photosensitive drum 5, thereby forming an electrostatic latent image of a corresponding color.

  Each developing device 8 supplies a corresponding color two-component developer to a developing area immediately downstream of the exposure area of the corresponding photosensitive drum 5 to form a corresponding color toner image. The two-component developer includes at least a carrier and a corresponding color toner. Hereinafter, the two-component developer is simply referred to as a developer.

  The intermediate transfer belt 3 is a so-called endless belt, is wound around the outer peripheral surfaces of at least two rollers arranged in the x-axis direction, and rotates in the direction indicated by the arrow β, for example. The outer peripheral surface of the intermediate transfer belt 3 is in contact with the upper end of each photosensitive drum 5.

  Each primary transfer roller 9 opposes the corresponding photosensitive drum 5 with the intermediate transfer belt 3 interposed therebetween, and presses the inner peripheral surface of the intermediate transfer belt 3 from above, so that the photosensitive drum 5 and the intermediate transfer belt 3 A primary transfer region is formed between the two. The toner image formed on the photosensitive drum 5 is transferred to the rotating intermediate transfer belt 3 in the corresponding primary transfer region.

  The secondary transfer roller 4 presses the outer peripheral surface of the intermediate transfer belt 3 in the vicinity of the right end of the intermediate transfer belt 3, and places a secondary transfer region at a contact portion between the secondary transfer roller 4 and the intermediate transfer belt 3. Form. In the secondary transfer region, the image carried on the intermediate transfer belt 3 is transferred onto the paper M. The sheet M passes through a known fixing device and is then discharged to a tray as a printed matter.

  In the printing operation as described above, the conveyance speed of the paper M (that is, the system speed Vsys) is variable depending on various conditions. In the present embodiment, for example, 108.3 mm / s, 325 mm / s, and 502 mm. / S is set by a CPU (not shown).

  Also, four color cartridges 10 are arranged above the intermediate transfer belt 3. Each cartridge 10 contains unused developer, and when the remaining toner amount of the corresponding developing device 8 decreases, the corresponding developing device 8 is replenished with the developer.

《Third column: Detailed configuration and operation of developing device》
Next, the configuration and operation of each developing device 8 will be described in detail with reference to FIGS.
Each developing device 8 includes a developing tank 81, a first partition 82, and a second partition 83.
Each developing tank 81 is disposed along the corresponding photosensitive drum 5. More specifically, in the developing tank 81, a portion facing the developing area R3 is open, and the developing tank 81 is arranged so that the opening is close to the developing area R3. A first partition 82 extending in the y-axis direction protrudes substantially upward from the bottom of the developing tank 81, thereby dividing the inside of the developing tank 81 into a first transport path FP <b> 1 and a second transport path FP <b> 2.

  The first conveyance path FP1 is closer to the photosensitive drum 5 than the second conveyance path FP2, and is along the photosensitive drum 5. The second transport path FP2 is along the first transport path FP1. In addition, the two transport paths FP1 and FP2 communicate with each other through openings TH1 and TH2 provided at at least two places (for example, near the front side and the rear end) having different positions in the front-rear direction. As a result, a developer circulation path is formed inside each developer tank 81.

In the developed image 81, a third transport path FP3 extending in the y-axis negative direction communicates with an end portion on the y-axis negative direction side of the first transport path FP1. The third transport path FP3 is partitioned from the second transport path FP2 by the second partition wall 83.
Regarding the above-described transport paths FP1 to FP3, the cross-sectional shape along the zx plane is substantially circular over the entire y-axis direction. The inner diameter L of each of the transport paths FP1 to FP3 is, for example, 25 mm.
The developer of the corresponding color is stored in the developing tank 81 described above.

  Further, in each developing device 8, a replenishment port 84 is formed at the end of the second transport path FP2 on the y-axis negative direction side and on the upper wall of the developing tank 81, and the front side end of the third transport path FP3. In the section, a discharge port 85 is formed on the side surface of the developing tank 81. From the discharge port 85, the deteriorated developer is continuously discharged little by little throughout the development process. As the developer is discharged, unused developer is introduced from the corresponding color cartridge into the developing tank 81 through the supply port 84.

  Each developing device 8 includes a developing roller 86 having a receiving pole S2, a developing pole N1, and the like fixedly disposed in a rotatable sleeve, and further includes a developing roller 86 that is a typical example of a developer carrier. Prepare. The developing roller 86 is disposed in the developing tank 81 so as to be rotatable in the direction of the arrow γ so as to be close to the developing area R3 substantially parallel to the photosensitive drum 5 of the corresponding color and to also face the first transport path FP1. Passed. The developing roller 86 receives the developer from the first conveying member 87 described later at the receiving pole S2, and then carries the developer on the outer peripheral surface. The developing roller 86 rotates in the direction of the arrow γ to convey the carried developer to the developing pole N1 and supply it to the developing area R3 of the corresponding photosensitive drum 5.

  Each developing device 8 further includes a first conveying member 87 almost directly below the developing roller 86. The first conveying member 87 is close to the corresponding color developing roller 86 in a substantially parallel manner, and is rotatable counterclockwise (that is, in the direction of the arrow θ1) in plan view from the negative direction side of the y-axis. It is bridged over the roads FP1 and FP3. The first conveying member 87 rotates in the θ1 direction to agitate the developer in the first conveying path FP1 while supplying the developer to the receiving pole S2 of the corresponding color. Transport in the direction. When the developer is transported to the front end (end on the negative direction side of the y-axis) of the first transport path FP1, most of the developer is transferred from the first transport path FP1 to the second transport path FP2 via the communicating portion. The remaining developer is sent to the third transport path FP3. However, the transport force of the first transport member 87 in the third transport path FP3 is not so large, and further, there is a gap through which the developer can pass along the outermost periphery. A part of the developer sent to the third transport path FP3 is transported through the gap and discharged from the discharge port 85. Note that the developer conveyance direction in each of the conveyance paths FP1 to FP3 is indicated by black arrows in the drawing.

Next, a specific configuration example of the first transport member 87 will be described. The first conveying member 87 is made by, for example, resin molding, and includes at least a first shaft 88, a first screw 89, and a second screw 810.
The first shaft 88 is a rotating shaft extending in the y-axis direction. Further, the first shaft 83 is spanned over both the transport paths FP1 and FP3, is pivotally supported at both ends, and rotates in the θ1 direction (described above).

The first screw 89 has a spiral shape that advances in the y-axis direction while turning a portion corresponding to the first conveyance path FP1 in the first shaft 88 in the θ1 direction.
On the other hand, the second screw 810 has a spiral shape that advances in the negative direction of the y-axis while turning the portion corresponding to the third transport path FP3 in the first shaft 88 in the θ1 direction.
In the first shaft 88, no screw is formed in the first section P1 between the screws 89 and 810. Further, the first section P1 overlaps the opening TH2 in a plan view from the x-axis direction and exists in the vicinity of the opening TH2. At least a part of the outer diameter D1 of the first section P1 is a large-diameter portion that is larger than the outer diameter D2 of the other sections. The outer diameter D1 is, for example, 16 mm, and the outer diameter D2 is, for example, 8 mm.

  The developing device 8 further includes a second transport member 811. The second transport member 811 is preferably disposed in the second transport path FP2 substantially parallel to the first transport member 87 with both the partition walls 82 and 83 interposed therebetween, and is clockwise when viewed from the negative direction side of the y-axis (that is, , In the direction of the arrow θ2), and spans the second transport path FP2. The second transport member 811 rotates in the θ2 direction to stir the developer in the second transport path FP2, transports it in the y-axis direction as the second direction different from the first direction, and moves the communication portion. Through the second transport path FP2 to the first transport path FP1.

Next, a specific configuration example of the second transport member 811 will be described. The second transport member 811 includes a second shaft 812 and a third screw 813.
The second shaft 812 is a rotating shaft extending in the y-axis direction. The second shaft 812 is spanned over the second transport path FP2, is pivotally supported at both ends, and rotates in the θ2 direction (described above).
The third screw 813 has a spiral shape that advances in the y-axis direction while turning on the outer peripheral surface of the second shaft 812 in the direction opposite to the direction θ2.

<< 4th column: Action and effect of the embodiment >>
As is clear from the “problem to be solved by the invention”, the conventional developing device has an older developer when the image forming apparatus performs printing at a low system speed, compared to when the image forming apparatus performs printing at a high speed. There was a problem that many remained inside. With respect to the above problem, in the developing device 8, the first shaft 88 is provided with a large diameter portion. Hereinafter, the operation and effect of the developing device 8 having the above characteristics will be described in comparison with a reference example having no large diameter portion from the viewpoint of easy understanding.
First, the present inventor prepared a developing device 8 having a specification described in Table 1 below and a reference example.

  In addition, the inventor rotates the first conveying member 87 at each of the low speed, the medium speed, and the high speed with the same amount of developer stored in the developing device 8 and the reference example having the above specifications. The amount of developer remaining in the developing tank 81 was measured. The result is shown in FIG. In FIG. 4, the residual amount of developer in the developing unit 8 is plotted with Δ, and the reference example is plotted with ●. Further, the horizontal axis shows the rotation speed of the first conveying member 87 converted to the system speed Vsys.

  As shown in FIG. 4, at the time of high-speed rotation, the residual amount of developer was almost the same, about 495 g, in both the developing device 8 and the reference example. Moreover, it was substantially the same at the time of medium speed rotation, and was about 505 g. However, at the time of low speed rotation, the residual amount of developer in the developing device 8 was about 495 g, but the residual amount in the reference example was about 540 g. In other words, it has been found that the difference in the residual amount is as large as about 10% at the time of low-speed rotation as compared with that at high-speed rotation and medium-speed rotation. As described above, according to the developing device 8, when the image forming apparatus 1 performs printing at a low system speed, the old developer does not remain inside, and the system speed is increased as compared with when the image forming apparatus 1 performs printing at a medium high speed. Regardless, it is possible to prevent a large amount of old developer from remaining inside.

The inventor of the present invention considered the reason why the above operation / effect was obtained as follows.
First, the reason why there is almost no difference in the residual amount of developer between the developing device 8 and the reference example during high-speed rotation (that is, when the system speed Vsys is high). As shown in the upper part of FIG. 5, in the case of the reference example, neither the first screw 89 nor the second screw 810 is provided in the first section P <b> 1 of the first shaft 88. Here, for convenience of explanation, the propulsive force per unit area is assumed to be F1 for the developer from the first transport path FP1 toward the discharge port 85. On the other hand, the force per unit area is defined as F2 for the developer that is going to return from the discharge port 85 to the first transport path FP1. In the first transport path FP1 and the third transport path FP3, the propulsive force F1 is greatly attenuated in the first section P1, so that excessive discharge of the developer from the discharge port 85 is suppressed. At this time, the relationship between F1 and F2 is F1> F2. Assume that this relationship is an ideal state, and F1 and F2 are 2x and x.

  On the other hand, at the time of high speed rotation, the propulsive force F1 in the developing device 8 attenuates at the large diameter portion provided in the first section P1, as shown in the lower part of FIG. The propelling force F1 remains in the agent. Similarly, the force F2 is also attenuated by the large diameter portion. Here, if the pressure loss due to the large diameter portion is y with respect to the propulsive force F1, the pressure loss is 2y with respect to the force F2. This is because the balance between F1 and F2 should be taken into account at the portion beyond the end surface on the y-axis negative direction side of the large-diameter portion in the y-axis negative direction. Therefore, since the propulsive force F1 is 2x-y and the force F2 is x-2y, the relationship between F1 and F2 in the portion P2 of the developing device 8 is F1> F2 as in the reference example.

  As described above, as shown in FIG. 4, at the time of high speed rotation, the residual amount of developer is almost the same regardless of whether it is the developing device 8 or the reference example. For the same reason as during high-speed rotation, the remaining amount of developer is almost the same for both the developing device 8 and the reference example at the medium-speed rotation.

  Next, at the time of low speed rotation (that is, when the system speed Vsys is low), there remains a large difference in the residual amount of developer between the developing device 8 and the reference example, and the residual developer in the developing device 8. The reason why a large amount of the old developer does not remain inside regardless of the system speed Vsys will be described. In the reference example, as shown in the upper part of FIG. 6, the developer conveying force by the first screw 89 is originally small, and as a result, the propulsive force F <b> 1 does not attenuate so much in the first section P <b> 1. The amount of developer discharged is smaller than that during high-speed rotation or medium-speed rotation. At this time, the relationship between F1 and F2 is F1≈F2 = x. Therefore, in the reference example, during the low speed rotation, the developer discharge does not proceed and the residual amount increases as shown in FIG.

  On the other hand, when rotating at a low speed, the pressure loss due to the large-diameter portion is 2y for the force F2 if y is set for the propulsive force F1 as in the case of high-speed rotation and medium-speed rotation. Therefore, since the propulsive force F1 is xy and the force F2 is x-2y, the relationship between F1 and F2 at the end of the large diameter portion on the negative side in the y-axis is F1> F2. Therefore, in the developing device 8, the developer discharge proceeds at the low speed as well as at the high speed. As a result, as shown in FIG. 4, the residual amount becomes smaller than that of the reference example.

  As can be understood from the above consideration, the developing device 8 can prevent a large amount of old developer from remaining in the interior regardless of the system speed Vsys.

<5th column: Appendix>
In the above embodiment, L0 = 25 mm, D1 = 16 mm, and D2 = 8 mm. However, each value is not limited to the above, and preferably satisfies L0 / 2 ≧ D1> D2.

  With this configuration, the relationship between F1 and F2 at the end of the large-diameter portion on the y-axis negative direction side during low-speed rotation can be F1> F2. As a result, since the developer discharge proceeds, the developing device 8 can better prevent the old developer from remaining much in the interior regardless of the system speed Vsys.

  On the other hand, when L0 / 2 ≧ D1> D2 is not satisfied, the relationship between F1 and F2 approaches F1≈F2, so that the developer discharge does not proceed well during low speed rotation, as shown in FIG. The tendency for the residual amount to increase increases.

<Sixth column: first modification>
Further, as shown in FIG. 7, the length L1 in the first direction (y-axis negative direction) of at least a part of the first section P1 is preferably equal to or shorter than the first direction length L2 of the opening TH2. Further, in other sections other than the large diameter portion in the first section P1, the length L3 in the reverse direction of the first direction and the length L4 in the first direction on the basis of the large diameter portion may be substantially equal. preferable.

  With this configuration, it is possible to prevent the developer flow from the first transport path FP1 toward the opening TH2 from being blocked by the large-diameter portion, and to make the discharge amount from the discharge port 85 appropriate.

<Seventh column: second modification>
Further, as shown in FIG. 8, the developing roller 86 may be provided so as to be close to and along the second transport path FP2.

  The developing device according to the present invention can reduce the remaining of the old developer in the developing device regardless of the system speed, and is suitable for a trickle type developing device. Further, the image forming apparatus according to the present invention can reduce the remaining of the old developer in the developing device, and is suitable for a printer or the like.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 8 Developer FP1, FP2, FP3 1st conveyance path, 2nd conveyance path, 3rd conveyance path 85 Discharge port 86 Developing roller (developer carrier)
87,811 1st conveyance member, 2nd conveyance member 88 1st shaft 89 1st screw 810 2nd screw P1 1st area

Claims (4)

A first transport path and a second transport path communicating with each other through two openings;
A third conveying path in communication with the first conveying path in the vicinity of one of the two openings, and a discharge port provided;
A first conveying member that conveys at least the developer in the first conveying path in a first direction;
A second conveying member for conveying the developer in the second conveying path in a second direction different from the first direction;
A developer carrying member carrying the developer conveyed through the first conveying path or the second conveying path;
With
The first conveying member is
A first screw that is provided on the first shaft and applies a propulsive force in the first direction to the developer in the first conveyance path;
A second screw that is provided on the first shaft and applies a force in a direction opposite to the first direction to the developer in the third conveyance path,
In the first shaft, at least a part of the first section which is a cylindrical portion without a screw provided in the vicinity of the one opening and does not include a region along the discharge port . A developing device whose diameter is larger than the diameter of other sections.   The discharge port is provided at one end of the third transport path, and the first shaft in the third transport path is propelled in the first direction by the developer in the third transport path. The developing device according to claim 1, wherein a screw for applying force is not provided. The length L1 in the first direction of at least a part of the first section is equal to or less than the length L2 in the first direction of one of the two openings.
In the other section, the length L3 in the first direction of the section on the first direction side than at least a part of the first section, and the first direction than at least a part of the first section. The developing device according to claim 1 or 2, wherein a length L4 of the opposite side section in the first direction is substantially equal.   An image forming apparatus comprising the developing device according to claim 1.

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