CN111487850A - Developing device and image forming apparatus - Google Patents

Abstract

In the developing device and the image forming apparatus according to the embodiment, at least one of the first developer conveyance member and the second developer conveyance member includes a first conveyance unit, a second conveyance unit, a third conveyance unit, and a conveyance reduction unit. The first conveying section has a spiral first paddle unit, and conveys the developer in the first conveying chamber in the direction of the rotation axis by rotation of the first paddle unit. The second conveying section is disposed downstream of the first conveying section in the direction of the rotation axis, has a second paddle portion having a reverse spiral shape with respect to the first paddle portion, and conveys the developer to the upstream side of the first conveying section in the direction of the rotation axis by rotation of the second paddle portion. The third conveying section is disposed downstream of the second conveying section, and conveys the developer that has passed the second conveying section and entered the downstream side to the discharge port. The conveyance reducing unit is provided between the first conveyance unit and the second conveyance unit, and reduces a conveyance amount of the developer in a rotation axis direction.

Description

Developing device and image forming apparatus

Technical Field

Embodiments of the present invention generally relate to a developing device and an image forming apparatus.

Background

An image forming apparatus is provided which forms an electrostatic latent image on an image carrier formed of a photoreceptor or the like. The electrostatic latent image is developed by a developing device and visualized as a toner image. One of the developing devices is a two-component developing system using a two-component developer. Such a developing device accommodates a two-component developer including a carrier and a toner in a developing container. The developing container is provided therein with an agitating member, which supplies the developer to the developing roller while agitating and conveying the developer.

In the developing device of the two-component development method, the toner is consumed by the developing action, and the carrier is not consumed and remains in the developing device. The carrier deteriorates with increasing stirring time, and the charging performance to the toner decreases. Therefore, a developing device that suppresses the decrease in the charging performance of the carrier has been proposed. The developing device replenishes developer containing carrier and toner into the developing container, and discharges the excessive developer to the outside of the container.

The discharge amount of the developer is increased or decreased according to the rotation speed of the stirring member. When the stirring member is rotated at a high speed, etc., the developer may be undesirably discharged in a large amount. In particular, in the case where the image forming apparatus is switchable in process speed, the discharge amount of the developer varies. In this case, the change in the amount of developer in the developing container (saturated residual developer amount) becomes large. Further, when the same developing device is mounted in a plurality of types of image forming apparatuses having different processing speeds, the amount of saturated residual developer also varies greatly.

Disclosure of Invention

The developing device and the image forming apparatus of the embodiment have an image carrier, a receiving portion, a first developer conveying member, and a second developer conveying member. The image carrier carries a developer containing toner. The accommodating portion has a first conveying chamber and a second conveying chamber, and accommodates the developer carried by the image carrier. The accommodating portion has a discharge port. The discharge port discharges the excess developer inside the housing portion to the outside of the housing portion.

At least one of the first developer conveying member and the second developer conveying member has a first conveying portion, a second conveying portion, a third conveying portion, and a conveyance reducing portion.

The first conveying section has a spiral first paddle unit, and conveys the developer in the first conveying chamber in the direction of the rotation axis by rotation of the first paddle unit.

The second conveying section is disposed downstream of the first conveying section in the direction of the rotation axis, has a second paddle portion that is formed in a reverse spiral shape with respect to the first paddle portion, and conveys the developer in the direction of the rotation axis toward the upstream side of the first conveying section by rotation of the second paddle portion.

The third conveying section is disposed downstream of the second conveying section, and conveys the developer that has passed the second conveying section and entered the downstream side to the discharge port.

The conveyance reducing unit is provided between the first conveying unit and the second conveying unit, and reduces a conveyance amount of the developer in the rotation axis direction.

Drawings

Fig. 1 is an external view showing an example of an image forming apparatus according to an embodiment.

Fig. 2 is a diagram showing an example of a schematic configuration of an image forming apparatus according to the embodiment.

Fig. 3 is a sectional view of a developing device of the image forming apparatus according to the embodiment.

Fig. 4 is a plan view of the developing device of the embodiment.

Fig. 5 is a perspective view of a mixer of the developing device of the embodiment.

Fig. 6 is a plan view of the periphery of the conveyance reducing portion of the developing device according to the embodiment.

Fig. 7 is a front view of the periphery of the conveyance reducing portion of the developing device of the embodiment.

Fig. 8 is a graph showing a correlation between the saturated residual developer amount and the rotational speed of the mixer in the developing device according to the embodiment, in accordance with the axial length of the conveyance reducing portion.

Fig. 9 is a graph showing a correlation between the saturated residual developer amount and the rotational speed of the mixer of the developing device of the embodiment according to the arrangement of the communication port.

Fig. 10 is a graph showing a relationship between the saturated residual developer amount and the rotation speed of the mixer in the developing device according to the embodiment depending on the presence or absence of the upper space.

Detailed Description

Hereinafter, the developing device 12a and the image forming apparatus 1 according to the embodiment will be described with reference to the drawings.

Fig. 1 is an external view showing an example of an image forming apparatus 1 according to the embodiment. For example, the image forming apparatus 1 is a Multi-Function Peripheral (MFP). The image forming apparatus 1 reads an image formed on a sheet-like recording medium (hereinafter referred to as a "sheet") such as paper, and generates digital data (image file). The image forming apparatus 1 forms an image on a sheet using toner based on digital data.

The image forming apparatus 1 includes a display unit 110, an image reading unit 120, an image forming unit 130, and a sheet tray 140.

The display unit 110 operates as an output interface and displays characters and images. The display unit 110 also operates as an input interface and receives a user instruction. For example, the display unit 110 is a touch panel type liquid crystal display.

The image reading section 120 is, for example, a color scanner. Examples of the color scanner include cis (contact Image sensor), ccd (charge Coupled devices), and the like. The image reading section 120 reads an image formed on a sheet using a sensor, and generates digital data.

The image forming portion 130 forms an image on a sheet using toner. The image forming unit 130 forms an image based on the image data read by the image reading unit 120 or the image data received from an external device. For example, an image formed on a sheet is an output image called a hard copy, a printout, or the like.

The sheet tray 140 supplies sheets used in image output to the image forming portion 130.

Fig. 2 is a diagram showing an example of a schematic configuration of the image forming apparatus 1 according to the embodiment. The image forming apparatus 1 is an electrophotographic image forming apparatus. The image forming apparatus 1 is a 5-drum tandem type image forming apparatus.

The image forming apparatus 1 includes a scanner unit 2, an image processing unit 3, an exposure unit 4, an intermediate transfer body 10, a cleaning blade 11, image forming units 12 to 16, primary transfer rollers 17-1 to 17-5, a paper feed unit 20, a secondary transfer unit 30, a fixing device 32, a paper discharge unit 33, and a control unit (not shown). Hereinafter, the primary transfer roller 17 will be simply referred to as a primary transfer roller when it is not distinguished.

In the following description, since a sheet is conveyed from the paper feed unit 20 to the paper discharge unit 33, the paper feed unit 20 side is set upstream in the sheet conveying direction, and the paper discharge unit 33 side is set downstream in the sheet conveying direction. Note that a direction orthogonal to the sheet conveying direction is a sheet width direction.

The transfer in the image forming apparatus 1 includes a first transfer step and a second transfer step. In the first transfer step, the primary transfer rollers 17 transfer the images formed by the toners on the photosensitive drums of the respective image forming sections to the intermediate transfer body 10. In the second transfer step, the secondary transfer section 30 transfers the image to the sheet by the toner of each color laminated on the intermediate transfer body 10.

The scanner section 2 reads an image formed on a sheet. For example, the scanner section 2 reads an image on a sheet and generates image data of three primary colors of red (R), green (G), and blue (B). The scanner unit 2 outputs the generated image data to the image processing unit 3.

The image processing section 3 converts the image data into color signals of the respective colors. For example, the image processing section 3 converts the image data into 4-color image data (color signals) of yellow (Y), magenta (M), cyan (C), and black (K). The image processing section 3 controls the exposure section 4 based on the color signal of each color.

The exposure unit 4 irradiates (exposes) the photosensitive drum of the image forming unit with light, and the exposure unit 4 includes an exposure light source such as a laser L ED.

The intermediate transfer body 10 is an endless belt. The intermediate transfer body 10 rotates in the arrow a direction of fig. 2. The surface of the intermediate transfer body 10 forms an image of toner.

The cleaning blade 11 removes the toner adhering to the intermediate transfer body 10.

The image forming sections 12 to 16 form images using toners of respective colors (5 colors in the example shown in fig. 2). The image forming sections 12 to 16 are provided in order along the intermediate transfer body 10.

The primary transfer rollers 17(17-1 to 17-5) are used for transferring the toner images formed by the image forming sections 12 to 16 to the intermediate transfer body 10.

The paper feed unit 20 feeds sheets.

The secondary transfer section 30 includes a secondary transfer roller 30a and a secondary transfer counter roller 30 b. The secondary transfer section 30 transfers the toner image formed on the intermediate transfer body 10 onto a sheet.

In the secondary transfer section 30, the intermediate transfer body 10 and the secondary transfer roller 30a are in contact with each other. The intermediate transfer body 10 and the secondary transfer roller 30a may be spaced apart from each other from the viewpoint of improving the paper jam.

The fixing device 32 fixes the toner image transferred onto the sheet by heating and pressing. The sheet on which the image is formed by the fixing device 32 is discharged from the sheet discharge portion 33 to the outside of the apparatus. The assembly including the intermediate transfer member 10, the primary transfer rollers 17-1 to 17-5, the secondary transfer section 30, and the photoconductive drums 12b to 16b described later is sometimes referred to as an image transfer device.

Next, the image forming sections 12 to 16 will be described.

The image forming sections 12 to 15 respectively store toners of respective colors corresponding to four colors for color printing. The four colors for color printing are yellow (Y), magenta (M), cyan (C), and black (K). The four-color toner for color printing is a non-achromatic toner. The image forming portion 16 contains a color erasing toner. The image forming units 12 to 15 are different from the toner contained in the image forming unit 16, but have the same configuration. Hereinafter, the image forming units 12 to 16 will be described as a representative of the image forming unit 12, and the other image forming units 13 to 16 have the same configuration, and the description thereof will be omitted.

The image forming unit 12 includes a developing device 12a, a photoconductive drum 12b, a charger 12c, and a cleaning blade 12 d.

The developing device 12a contains developer. The developer contains a toner. The developing device 12a causes toner to adhere to the photosensitive drum 12 b. For example, the toner is used as a two-component developer combined with a carrier. For example, iron powder or ferrite particles having a particle size of several tens of μm are used as the carrier. In the embodiment, a two-component developer containing a non-magnetic toner is used.

The photosensitive drum 12b is a specific example of an image carrier (image carrier assembly). The photosensitive drum 12b has a photosensitive body (photosensitive region) on the outer peripheral surface. For example, the photoreceptor is an Organic photoconductor (OPC: Organic Photo Conductor).

The charger 12c uniformly charges the surface of the photosensitive drum 12 b.

The cleaning blade 12d removes the toner adhering to the photosensitive drum 12 b.

Next, the operation of the imaging section 12 will be generally described.

The photosensitive drum 12b is charged at a predetermined potential by a charger 12 c. Subsequently, the photosensitive drum 12b is irradiated with light from the exposure unit 4. This changes the potential of the region of the photoconductive drum 12b to which light is applied. An electrostatic latent image is formed on the surface of the photosensitive drum 12b due to this change. The electrostatic latent image on the surface of the photosensitive drum 12b is developed by the developer of the developing device 12 a. An image developed by the toner (hereinafter referred to as "developed image") is formed on the surface of the photosensitive drum 12 b.

The developed image formed on the surface of the photosensitive drum 12b is transferred to the intermediate transfer member 10 by the primary transfer roller 17-1 facing the photosensitive drum 12b (first transfer step). The developed image formed on the intermediate transfer member 10 is transferred to a sheet by the secondary transfer portion 30 (secondary transfer step).

Next, the developing device 12a will be described.

Fig. 3 is a sectional view of the developing device 12a of the embodiment. Fig. 4 is a plan view of the developing device 12a of the embodiment. Fig. 3 shows a cross section viewed from the sheet width direction of the developing device 12 a. The left-right direction in fig. 3 is directed toward the rotation direction of the intermediate transfer body 10 (arrow a). Hereinafter, the left side in fig. 3 is referred to as the upstream side in the rotating direction of the transfer medium, and the right side in fig. 3 is referred to as the downstream side in the rotating direction of the transfer medium. Shading of the cross-section is omitted in fig. 3.

As shown in fig. 3 and 4, the developing device 12a includes a developing container 60, a developing roller 63, a first mixer 61, and a second mixer 62. The left-right direction of fig. 4 is toward the sheet width direction. The illustration of the developing roller 63 is omitted in fig. 4. In the figure, one side in the rotation axis direction of the first mixer 61 and the second mixer 62 is indicated by an arrow X1, and the other side in the rotation axis direction is indicated by an arrow X2. In the figure, the rotation center line of the first mixer 61 is indicated by a line O1, and the rotation center axis of the second mixer 62 is indicated by a line O2.

The developing container 60 contains the developer D. The developer D contains a carrier as a magnetic body and a toner as a coloring material. The developing container 60 is formed to linearly extend in the longitudinal direction. The developing container 60 has a sheet width direction as a longitudinal direction. The developing container 60 has a substantially rectangular cross-sectional shape. The developing container 60 is disposed adjacent to the photosensitive drum 12b (see fig. 2). The photosensitive drum 12b is arranged with the axial direction along the sheet width direction. The developing container 60 is disposed so that the longitudinal direction thereof is parallel to the axial direction of the photosensitive drum 12 b.

The developing container 60 includes an opening 60h on a side facing the photosensitive drum 12 b. The opening 60h faces the photosensitive drum 12b in the radial direction of the photosensitive drum 12 b. The developing roller 63 is disposed at a position facing the opening 60h inside the developing container 60. The developing roller 63 is disposed with its axial direction along the sheet width direction.

The developing roller 63 is disposed in parallel with the photosensitive drum 12 b. The developing roller 63 is opposed to the photosensitive drum 12b in the radial direction through the opening 60 h. Both end portions of the developing roller 63 in the axial direction are rotatably supported by the developing container 60. The developing roller 63 carries the developer D on the outer circumferential surface. The developing roller 63 carries the developer D by the magnetic force of the magnetic body.

Inside the developing container 60, a first mixer 61 and a second mixer 62 in a shaft shape are disposed. The first mixer 61 and the second mixer 62 are arranged axially along the sheet width direction. The first mixer 61 and the second mixer 62 are disposed in parallel with each other. The first mixer 61 is disposed on the upstream side in the rotating direction of the transfer body. The second mixer 62 is disposed on the downstream side in the rotating direction of the transfer body.

A first conveyance chamber 60a for accommodating the first mixer 61 is formed on the upstream side of the developing container 60 in the rotating direction of the transfer body. A second conveyance chamber 60b in which a second mixer 62 is disposed is formed on the downstream side of the developing container 60 in the rotating direction of the transferred body. The first conveyance chamber 60a and the second conveyance chamber 60b are formed so that the vertical width is larger than the transfer body rotation direction width in the cross section of fig. 3.

A first mixer 61 is housed in a lower portion of the first conveyance chamber 60 a. A second mixer 62 is housed in a lower portion of the second conveyance chamber 60 b. The developing roller 63 is accommodated in an upper portion of the second conveyance chamber 60 b. The developing roller 63, the first mixer 61, and the second mixer 62 are driven to rotate in cooperation with each other by a drive source not shown.

Inside the developing container 60, a partition wall 65 is provided that partitions the first conveying chamber 60a and the second conveying chamber 60 b. The first transfer chamber 60a and the second transfer chamber 60b are adjacent to each other with a partition wall 65 interposed therebetween. The partition wall 65 is provided along the vertical direction.

Communication ports 60c and 60d for communicating the first conveyance chamber 60a and the second conveyance chamber 60b with each other are formed on both sides of the partition wall 65 in the sheet width direction (the rotation axis direction). The communication ports 60c, 60D can circulate the developer D between the first conveyance chamber 60a and the second conveyance chamber 60 b. The communication ports 60c and 60d are formed in a rectangular shape, for example. Hereinafter, the communication port 60c on one side in the rotation axis direction is referred to as a first communication port 60c, and the communication port 60d on the other side in the rotation axis direction is referred to as a second communication port 60 d.

The first mixer 61 includes a shaft portion 61a extending in the rotation axis direction, and a helical blade (stirring blade) 61b formed on the outer periphery of the shaft portion 61 a. The helical blade 61b is provided over the entire length of the first mixer 61 except for a part of the first mixer 61 on one side in the rotation axis direction. The end portion on the rotation axis direction side of the first mixer 61 is provided to extend more on the rotation axis direction side than the end portion on the rotation axis direction side of the second mixer 62.

The second mixer 62 includes a shaft 62a extending in the rotation axis direction and a helical blade (stirring blade) 62b formed on the outer periphery of the shaft 62 a. The helical blades 62b are provided over the entire length of the second mixer 62.

Fig. 4 is a plan view of the inside of the developing container 60. The developing container 60 includes an end wall portion 66 that closes one end in the rotational axis direction of the first and second conveyance chambers 60a and 60b, and a cylindrical wall portion 67 that is provided so as to protrude from the end wall portion 66 toward one side in the rotational axis direction. The cylindrical wall portion 67 is disposed coaxially with the first mixer 61 on the side of the first mixer 61 in the rotational axis direction. The cylindrical wall portion 67 has a bottomed cylindrical shape that is open to the end wall portion 66 side (the other side in the rotation axis direction). In the cylindrical wall portion 67, a third chamber 60e is provided outside the circulation path of the developer D.

The first communication port 60c is formed between the end portion on the one side in the rotation axis direction of the spiral blade 61b of the first mixer 61 and the end portion on the one side in the rotation axis direction of the spiral blade 62b of the second mixer 62.

The second communication port 60d is formed between the end portion on the other side in the rotation axis direction of the helical blade 61b of the first mixer 61 and the end portion on the other side in the rotation axis direction of the helical blade 62b of the second mixer 62.

The first mixer 61 conveys the developer D to the side of the rotational axis direction (the side indicated by the arrow X1 in the figure). The second mixer 62 conveys the developer D to the opposite side (the other side in the rotational axis direction, the side indicated by the arrow X2 in the figure) of the first mixer 61.

A toner replenishing device, not shown, for replenishing toner to the developing device 12a is provided above the developing device 12 a. This toner replenishing container replenishes toner into the developing device 12a when the toner in the developing device 12a is consumed by development.

The developer D agitated and conveyed in the developing device 12a is passed through a toner concentration detector, not shown, to detect the toner concentration. When the toner concentration detected by the toner concentration detector is less than or equal to a predetermined value, the toner is supplied from the toner supply device into the developing device 12 a. This toner is agitated with the developer D in the developing device 12a to increase the toner concentration of the developer D. Thereby, the toner concentration of the developer D in the developing device 12a is maintained constant.

The carrier is also replenished simultaneously with the toner from the toner replenishing device. These replenishments may cause an excessive amount of the developer D in the developing device 12 a. These extra developer D overflows from a discharge port 67a provided on one side in the rotational axis direction of the developing container 60, and is discharged to the outside of the developing container 60. Thereby, the developer amount in the developing device 12a is maintained fixed, and the old deteriorated carrier in the developing device 12a is gradually replaced with a new carrier. The discharge port 67a is provided at a lower portion of the cylindrical wall portion 67.

Fig. 5 is a perspective view of the first mixer 61 of the developing device 12a of the embodiment. Fig. 6 is a plan view of the periphery of the conveyance reducing portion 74 according to the embodiment described below. Fig. 7 is a front view of the periphery of the conveyance reducing portion 74 according to the embodiment described below.

As shown in fig. 5 to 7, the helical blade 61b of the first mixer 61 is roughly divided into a first conveying section 71, a second conveying section 72, and a third conveying section 73.

The first conveying portion 71 is provided in a range from a portion overlapping the first communication port 60c in the rotation axis direction on one side in the rotation axis direction of the first mixer 61 to an end portion on the other side in the rotation axis direction of the first mixer 61. For example, the first conveying section 71 is formed by winding two helical blades (first blade sections 71a) having a pitch of 26 mm. The minimum interval of the first paddle parts 71a of the first conveying part 71 is 13 mm. The minimum interval of 13mm is the minimum pitch of the first conveying section 71.

The second conveying section 72 is provided further toward the rotation axis direction side (the downstream side in the conveying direction of the first conveying section 71) than the rotation axis direction side end portion of the first conveying section 71. The second conveying portion 72 is provided to be rotatable together with the first conveying portion 71. The second conveying portion 72 conveys (presses back) the developer D in the direction opposite to the conveying direction (upstream side) of the first conveying portion 71. For example, the second conveying section 72 is formed by winding one reverse spiral blade (second blade section 72a) having a pitch of 3 mm. For example, the rising height of the second blade portion 72a of the second conveying portion 72 from the shaft portion 62a is the same as the rising height of the first blade portion 71a of the first conveying portion 71 from the shaft portion 62 a.

The third conveying portion 73 conveys the developer D, which has passed over the second conveying portion 72 and reached one side in the rotation axis direction (the downstream side in the conveying direction of the first conveying portion 71), to the discharge port 67 a. The third conveying section 73 is provided to be rotatable together with the first conveying section 71 and the second conveying section 72, and conveys the developer D in the same direction (downstream side) as the conveying direction of the first conveying section 71. For example, the third conveying section 73 is formed by winding a helical blade (third blade section 73a) having a pitch of 10 mm. For example, the rising height of the third blade portion 73a of the third conveying portion 73 from the shaft portion 61a is lower than the rising height of the first blade portion 71a of the first conveying portion 71 from the shaft portion 61 a. The third conveying portion 73 is disposed in the cylindrical wall portion 67 of the developing container 60 (in the third chamber 60 e).

A conveyance reducing portion 74 that reduces the conveyance amount of the developer D is provided between the first conveyance portion 71 and the second conveyance portion 72. For example, the conveyance reducing portion 74 is formed only by the shaft portion 61a without including the helical blade 61 b. The conveyance reducing portion 74 is provided at a position overlapping with the first communication port 60c on one side in the rotation axis direction. The conveyance reducing portion 74 causes the developer D to accumulate at a portion where the first communication port 60c on one side in the rotation axis direction faces the first mixer 61.

The second conveying portion 72 is disposed at a position avoiding the first communication port 60c on one side in the rotation axis direction with respect to the rotation axis direction (a position not overlapping with the first communication port 60c in the rotation axis direction). With this arrangement, the developer D can easily move toward the second mixer 62 through the first communication port 60c on one side in the rotation axis direction.

The width of the conveyance reducing section 74 in the direction of the rotation axis is set to be between 1/2-3/2 of the minimum pitch of the first conveyance section 71. Preferably, the width of the conveyance reducing portion 74 in the rotation axis direction is set to be substantially the same as the minimum pitch of the first conveyance portion 71. The term "substantially the same" means, for example, a degree that the width of the conveyance reducing unit 74 in the rotation axis direction allows the minimum pitch 13mm of the first conveyance unit 71 to be increased or decreased by about ± 10%.

As shown in fig. 6 and 7, the developing container 60 of the developing device 12a includes a space forming portion 75 above the conveyance reducing portion 74. The space forming portion 75 is formed in a rectangular box shape and is open downward. The space forming portion 75 forms an open space 75a therein. The space forming portion 75 has an open space 75a facing the conveyance reducing portion 74 from above.

The space forming section 75 is provided so as to straddle the conveyance reducing section 74 and the second conveying section 72 in the rotational axis direction of the first mixer 61. The space forming portion 75 faces the conveyance reducing portion 74 and the second conveyance portion 72 from above. The space forming section 75 is provided so as to span the entire width of the conveyance reducing section 74 and at least half of the second conveying section 72 in the rotational axis direction of the first mixer 61.

Next, a change in the developer amount (saturated residual developer amount) in the developing container 60 when various conditions are changed will be described.

Fig. 8 is a graph showing a relationship between the saturated residual developer amount of the developing device 12a and the rotational speed of the mixer according to the embodiment, based on the length of the conveyance reducing portion 74 in the rotational axis direction.

In the example of fig. 8, the first mixer 61 that changes the length of the conveyance reducing unit 74 in the rotation axis direction is used. In the example of FIG. 8, the mixer rotation speed is changed within a range of 200 to 600rpm (normal rotation range). At this time, 400g of the developer D was first charged into the developing container 60, and after the developing device 12a was driven for 1 hour, the amount of the developer (saturated residual developer amount) in the developing container 60 was measured.

The developer D is a two-component developer D obtained by mixing a toner having a particle size of 3 to 7 μm and a carrier having a particle size of 25 to 50 μm. In the case of this test, the apparent bulk density of the developer D was 1.7g/cm³。

Hereinafter, in the figure, the saturated residual developer amount when the length in the rotation axis direction of the conveyance reducing unit 74 is 7mm is indicated by a line L, the saturated residual developer amount when the length in the rotation axis direction of the conveyance reducing unit 74 is 13mm is indicated by a line L, the saturated residual developer amount when the length in the rotation axis direction of the conveyance reducing unit 74 is 19.5mm is indicated by a line L.5, and the saturated residual developer amount when the length in the rotation axis direction of the conveyance reducing unit 74 is 23.5mm is indicated by a line L.23.5, respectively.

In the example of fig. 8, the length in the rotation axis direction of the conveyance reducing portion 74 is less than 6.5mm (1/2 corresponding to the minimum pitch of 13mm of the first paddle portion 71a of the first conveying portion 71). In this case, the conveyance speed of the developer D by the first conveyance section 71 is excessively higher than the conveyance speed of the developer D by the second conveyance section 72. In this case, when the first mixer 61 rotates at a high speed of 600rpm, most of the large amount of the developer D conveyed by the first conveying portion 71 passes over the second conveying portion 72. The developer D that has passed over the second conveying portion 72 reaches the extension chamber in the cylindrical wall portion 67, is conveyed to the third conveying portion 73, and is discharged from the discharge port 67a to the outside of the developing container 60.

The conveyance amount of the developer D is reduced around the conveyance reducing portion 74, and therefore, a developer pool is generated. Due to this developer accumulation, pulsation is likely to occur in the rotation cycle of the first paddle parts 71a having the minimum pitch of 13mm in the first conveying section 71. Therefore, more developer D is easily discharged from the discharge port 67 a.

In the example of fig. 8, it is seen that the length of the conveyance reducing portion 74 in the rotation axis direction is greater than 19.5mm (3/2 with the minimum pitch of 13mm for the first paddle portions 71a of the first conveying portion 71). In this case, a large amount of the developer D accumulates around the conveyance reducing portion 74. In this case, when the first mixer 61 is rotated at a low speed of 200rpm, the developer D is discharged from the discharge port 67a in a large amount.

In order to stably obtain the discharge performance of the developer D between 200rpm and 600rpm, it is important to set the length of the conveyance reducing unit 74 provided between the first conveying unit 71 and the second conveying unit 72 in the rotational axis direction, and the length of the conveyance reducing unit 74 in the rotational axis direction is preferably 1/2 to 3/2 which is the minimum pitch of the first blade portion 71a of the first conveying unit 71, and further preferably, the minimum pitch is the same as the length of the conveyance reducing unit 74 in the rotational axis direction, and for example, if the amount of the developer in the developing container 60 is less than 220g (indicated by a line L220 in the figure), a conveyance failure may occur at the end of the first mixer 61.

Fig. 9 is a graph showing a relationship between the saturated residual developer amount and the rotation speed of the mixer in the developing device 12a according to the embodiment, in accordance with the arrangement of the first communication port 60 c.

In the figure, a line L91 represents the saturated residual developer amount when the first communication port 60c overlaps half of the second conveying section 72 in the rotational axis direction, and a line L92 represents the saturated residual developer amount when the first communication port 60c avoids (does not overlap) the second conveying section 72 in the rotational axis direction.

When the first communication port 60c overlaps half of the second conveying portion 72 in the rotation axis direction, a large amount of the developer D is discharged when the first mixer 61 rotates at a low speed (200 rpm). When the first mixer 61 is rotated at 200rpm, the developer D is pressed into the second blade portion 72a of the second conveying portion 72 with a small pitch by the pressure of the developer D pressed back from the second mixer 62 side. Then, the conveying ability of the second conveying portion 72 is reduced, and the amount of pushing back of the developer D is reduced. Then, the amount of the developer D discharged from the discharge port 67a increases up to the extension chamber in the cylindrical wall portion 67. As a result, a decrease in the amount of the developer in the developing container 60 was observed. When the first mixer 61 was rotated at a high speed (at 600 rpm), a decrease in the amount of the developer in the developing container 60 was also observed.

From the above, it is understood that the second conveyance section 72 is not suitable for being positioned opposite to the first communication port 60 c. Therefore, in the present embodiment, the second conveying portion 72 is disposed avoiding the first communication port 60c, and the partition wall 65 is opposed to the second conveying portion 72.

Fig. 10 is a graph showing a correlation between the saturated residual developer amount and the rotational speed of the mixer in the developing device 12a according to the embodiment, depending on the presence or absence of the open space 75 a.

In the figure, a line 101 indicates the saturated residual developer amount when the open space 75a is provided above the conveyance reducing unit 74, and a line L102 indicates the saturated residual developer amount when the open space 75a is not particularly provided above the conveyance reducing unit 74 (the upper surface side is flat).

A space forming portion 75 forming an open space 75a is provided above the conveyance weight reducing portion 74 in the direction of gravity. The open space 75a has a height at least 3mm higher than the outer periphery of the second blade portion 72a of the second conveying portion 72. In the case where this open space 75a is not provided, when the first mixer 61 is rotated at a low speed of 200rpm, a large amount of the developer D may be undesirably discharged from the discharge port 67a, resulting in a drop in the amount of the developer in the developing container 60. When the first mixer 61 is rotated at a high speed of 600rpm, the pressure of the conveyance reducing portion 74 is increased, and the developer D is pushed out in a large amount toward the second mixer 62. Then, the developer D circulating in the developing container 60 increases, resulting in an increase in the amount of developer in the developing container 60.

According to the present embodiment, the amount of the developer in the developing container 60 can be maintained at a predetermined amount with high accuracy regardless of the change in the conveying speed of the developer D in response to a wide range of mixer rotation speeds of 200 to 600 rpm.

That is, according to the present embodiment, it is possible to provide the two-component development type developing device 12a that replenishes the developer D containing the carrier and the toner into the developing container 60 and discharges the excessive developer D to the outside of the developing container 60, and the image forming apparatus 1 including the same.

In the developing device 12a and the image forming apparatus 1 according to the embodiment, the first mixer 61 includes the first conveying section 71, the second conveying section 72, the third conveying section 73, and the conveyance reduction section 74.

The first conveying section 71 includes a spiral first paddle part 71a, and conveys the developer D in the first conveying chamber 60a in the rotation axis direction by the rotation of the first paddle part 71 a.

The second conveying section 72 is disposed downstream of the first conveying section 71 in the rotation axis direction, and includes a second paddle section 72a having a reverse spiral shape with respect to the first paddle section 71a, and conveys the developer D to the upstream side of the first conveying section 71 in the rotation axis direction by the rotation of the second paddle section 72 a.

The third conveying portion 73 is disposed downstream of the second conveying portion 72, and conveys the developer D that has entered the downstream side beyond the second conveying portion 72 to the discharge port 67 a.

The conveyance reducing portion 74 is provided between the first conveying portion 71 and the second conveying portion 72, and reduces the conveyance amount of the developer D in the rotation axis direction.

Between the first conveying section 71 and the second conveying section 72, which are opposite to each other in the conveying direction of the developer D, the conveyance reduction section 74 reduces the conveyance amount of the developer D. In particular, when the rotation speed of the first mixer 61 is switched, the developer formed around the conveyance reducing portion 74 accumulates, and the influence on the conveyance amount of the developer D is suppressed.

According to the developing device 12a and the image forming apparatus 1 of the embodiment, the amount of the developer in the developing container 60 can be maintained at a predetermined amount regardless of the change in the conveyance speed of the developer D. Thereby, the amount of the developer D in the developing container 60 can be stabilized, thereby suppressing the occurrence of image defects.

For example, the conveyance reducing unit 74 is not limited to a structure without a spiral blade. The conveyance reducing unit 74 may be configured to include a low bucket conveyor having a lower conveyance capacity than the first conveyance unit 71 and the second conveyance unit 72. For example, the low conveying blade portions may be blade portions having a reduced height from the shaft portion 61a, blade portions extending in the direction of the rotation axis, disk-shaped blade portions having no lead angle, or the like.

The first mixer 61 is not limited to the configuration provided with the conveyance reducing unit, and the second mixer 62 may be provided with the conveyance reducing unit.

According to at least one of the embodiments described above, in the developing device 12a and the image forming apparatus 1, the first mixer 61 includes the first conveying portion 71, the second conveying portion 72, the third conveying portion 73, and the conveyance reducing portion 74, and thus the amount of the developer in the developing container 60 can be maintained at a predetermined amount regardless of the change in the conveying speed of the developer D.

While several embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. These embodiments can be implemented in other various forms, and various omissions, substitutions, and changes can be made without departing from the spirit of the invention. These embodiments and modifications are included in the scope and spirit of the invention, and are also included in the invention described in the claims and the equivalent scope thereof.

Claims (10)

1. A developing device is characterized by comprising:

an image bearing body bearing a developer containing toner;

a housing section having a first conveying chamber and a second conveying chamber, and housing the developer carried by the image carrier; and

a first developer conveying member and a second developer conveying member rotatably provided in the first conveying chamber and the second conveying chamber, respectively, and conveying the developer in the accommodating portion,

the accommodating portion is provided with a discharge port for discharging the excessive developer inside to the outside,

at least one of the first developer conveying member and the second developer conveying member includes:

a first conveying section having a spiral first blade section, the first conveying section conveying the developer in the first conveying chamber in a direction of a rotation axis by rotation of the first blade section;

a second conveying section which is disposed downstream of the first conveying section in the direction of the rotation axis, has a second blade portion having a reverse spiral shape with respect to the first blade portion, and conveys the developer to an upstream side of the first conveying section in the direction of the rotation axis by rotation of the second blade portion;

a third conveying section disposed downstream of the second conveying section and configured to convey the developer that has passed the second conveying section and entered the downstream side to the discharge port; and

and a conveyance reducing unit provided between the first conveyance unit and the second conveyance unit, the conveyance reducing unit reducing a conveyance amount of the developer in a rotation axis direction.

2. The developing device according to claim 1,

the conveyance reducing portion is formed without the first blade portion and the second blade portion.

3. The developing device according to claim 1 or 2, wherein,

the conveyance reducing portion includes a low conveyance blade portion having a conveyance capability lower than the first blade portion and the second blade portion.

4. The developing device according to claim 3,

the blades of the low conveying blade portion are formed smaller than the first blade portion and the second blade portion.

5. The developing device according to claim 1 or 2, wherein,

the conveying directions of the first conveying chamber and the second conveying chamber are opposite to each other and are communicated with each other through the communication ports on two sides of the conveying direction,

the conveyance reducing portion overlaps the communication port in the rotation axis direction.

6. The developing device according to claim 5,

the first conveying portion overlaps with the communication port in the rotation axis direction.

7. The developing device according to claim 1 or 2, wherein,

the conveyance reducing section has a width in the rotation axis direction of 1/2-3/2 that is the pitch of the first blade sections of the first conveyance section.

8. The developing device according to claim 1 or 2, wherein,

the conveyance reduction portion has the same width as the pitch of the first vane portions of the first conveyance portion in the rotation axis direction.

9. The developing device according to claim 1 or 2, wherein,

the storage unit includes a space forming unit at a position overlapping the conveyance reducing unit in the rotation axis direction,

the space forming section forms an open space above the conveyance reducing section, the open space being open to the conveyance reducing section.

10. An image forming apparatus is characterized by comprising:

the developing device according to any one of claims 1 to 9, forming an output image based on image information;

an image transfer device that transfers the output image formed by the developing device onto a recording medium; and

and a fixing device for fixing the image transferred to the recording medium.

Images