JP2016130841A - Developing device, process cartridge, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device of a multi-stage developing system that suppresses the occurrence of large unevenness in density of an image formed on an image carrier, even when a plurality of developing rollers each have runout; a process cartridge; and an image forming apparatus.SOLUTION: Two developing rollers 23a1 and 23a2 are formed to have a difference in the amount of runout to be a predetermined value or less, and are installed while the positional relationship in the directions of rotation between the rollers is defined so that: when the surface of a photoreceptor drum 21 (point M) when the surface of the first developing roller 23a1 (point R) is brought closest to the surface of the photoreceptor drum 21 reaches an opposite position to the second developing roller 23a2 (second developing area), the surface of the second developing roller 23a2 (point Q) is separated farthest from the surface of the photoreceptor drum 21.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine thereof, a developing device installed therein, and a process cartridge.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, a multi-stage developing system in which a plurality of developing rollers are arranged in parallel so as to face each other along the rotation direction (running direction) of a photosensitive drum (image carrier). A technique using a developing device is known (for example, see Patent Document 1).

Specifically, in Patent Document 1 and the like, a two-component developer (including a case where an additive or the like is added) including a toner and a carrier is accommodated in the developing device. Then, according to the toner consumption in the developing device, the toner is appropriately supplied into the developing device from a toner supply port provided in a part of the developing device. The replenished toner is agitated and mixed together with the developer in the developing device by a conveying member (agitating member) such as a conveying screw. Part of the stirred and mixed developer is supplied to the first developing roller on the upstream side. The developer carried on the first developing roller is regulated to an appropriate amount by a doctor blade (developer regulating member), and then the toner in the developer is exposed at a position facing the photosensitive drum (first development area). It adheres to the latent image on the body drum. Thereafter, a part or all of the developer carried on the first developing roller is supplied to the second developing roller on the downstream side. Then, the toner in the developer carried on the second developing roller adheres to the latent image on the photosensitive drum at a position facing the photosensitive drum (second developing area).
Such a multi-stage developing system developing device can take a long developing time by using a plurality of developing rollers, so that even a high-speed device can form a high-quality image by a good developing process. ing.

On the other hand, in Patent Document 2 and the like, an increase in the shake amount in the developing roller causes image density unevenness corresponding to the rotation period of the developing roller to occur in the image (toner image) formed on the photosensitive drum. A bug has been disclosed. Specifically, when the surface of the developing roller approaches the surface of the photosensitive drum due to shake and the developing gap (the gap between the developing roller and the photosensitive drum) becomes narrow, the image density on the photosensitive drum increases. turn into. On the other hand, if the developing roller surface is moved away from the surface of the photosensitive drum due to the shake and the developing gap is widened, the image density on the photosensitive drum is lowered. Such high and low image densities are formed in a pitch shape corresponding to one rotation (one cycle) of the developing roller.
Patent Document 2 and the like disclose a method for measuring a shake amount in the developing roller.

  A conventional multi-stage development system developing device has a photosensitive drum (image) if it is installed without worrying about the positional relationship in the rotational direction when there is a shake (amount of shake) in each of a plurality of development rollers. There is a possibility that large image density unevenness may occur in the image formed on the carrier.

  Specifically, the surface of the photosensitive drum when the surface of the upstream first developing roller is closest to the surface of the photosensitive drum is the position facing the downstream second developing roller (second developing region). When the surface of the second developing roller comes closest to the surface of the photosensitive drum when the temperature reaches the surface of the photosensitive drum, a developing process for increasing the image density is repeated, and an image having a very high image density is formed. Will be. On the other hand, the surface of the photosensitive drum when the surface of the upstream first developing roller is farthest from the surface of the photosensitive drum is the position facing the downstream second developing roller (second developing region). ), When the surface of the second developing roller is farthest from the surface of the photosensitive drum, a developing process for reducing the image density is repeated, so that an image with a very low image density is obtained. Will be formed. These developing steps are performed in the synchronized rotation cycle of the two developing rollers, resulting in image density unevenness with a large density difference.

  The present invention has been made in order to solve the above-described problems, and an image formed on an image carrier even in a case where a plurality of developing rollers have shakes in a multistage developing type developing device. It is an object of the present invention to provide a developing device, a process cartridge, and an image forming apparatus in which large image density unevenness hardly occurs.

  According to a first aspect of the present invention, there is provided a developing device for developing a latent image formed on the surface of an image carrier that travels in a predetermined direction, along the traveling direction of the image carrier. A plurality of developing rollers arranged side by side so as to face each other, wherein the plurality of developing rollers are formed such that a difference in shake amount between two developing rollers adjacent to each other in the traveling direction is a predetermined value or less; The surface of the image carrier when the surface of the developing roller on the upstream side in the direction is closest to the surface of the image carrier and the developing roller on the downstream side in the traveling direction adjacent to the upstream developing roller. The positions of the developing rollers on the downstream side are set so as to be farthest from the surface of the image carrier when the opposite position is reached.

  According to the present invention, even in a case where a plurality of developing rollers have shakes in a multistage developing type developing device, a large unevenness in image density does not easily occur in an image formed on an image carrier, and the developing device and process A cartridge and an image forming apparatus can be provided.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. It is a schematic block diagram which shows the principal part of an image creation part. It is an enlarged view which shows a developing device. It is the schematic which shows operation | movement of two developing rollers. (A) A table showing the relationship between the amount of shake of the developing roller and the color of the marking, and (B) a table showing a combination of two developing rollers with markings. 6 is a graph showing a change in distance from the photosensitive drum when the developing roller rotates once. It is the schematic which shows a developing roller in the rotating shaft direction. It is a figure which shows the state which determines and sets the positional relationship of a mutual rotating shaft direction from the marking position of two developing rollers. 6 is a graph showing a relationship between a difference in shake amount between two developing rollers and brightness amplitude serving as an index of the degree of image density unevenness. 6 is a graph showing a relationship between a difference in shake amount between two developing rollers and a rank of image density unevenness. It is an enlarged view which shows the principal part of the image development apparatus as a modification. It is a table | surface figure which shows a part of characteristic value of the developing device as a modification.

Embodiment.
Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

First, the overall configuration and operation of the image forming apparatus will be described with reference to FIG.
In FIG. 1, 1 is a tandem color copier as an image forming apparatus, 2 is a writing unit that emits laser light based on input image information, and 4 is a document that reads image information of a document placed on a contact glass 5. A reading unit, 7 is a paper feeding unit for storing a recording medium P such as transfer paper, 9 is a registration roller (timing roller) for adjusting the conveyance timing of the recording medium P, and 14 is formed on the surface of each photosensitive drum 21. A primary transfer bias roller for transferring the toner image superimposed on the intermediate transfer belt 17, 17 an intermediate transfer belt on which toner images of a plurality of colors are transferred, and 18 recording a color toner image on the intermediate transfer belt 17. The secondary transfer bias rollers 20Y, 20M, 20C, and 20BK for transferring onto the medium P are processes corresponding to the respective colors (yellow, magenta, cyan, and black). A cartridge (image forming unit) 21 is a photosensitive drum as an image carrier installed in each color process cartridge 20Y, 20M, 20C, 20BK, 22 is a charging unit that charges the surface of each photosensitive drum 21, and 23 is A developing device that develops an electrostatic latent image formed on the surface of each photoconductive drum 21, 24 is a static eliminator that neutralizes the surface potential of each photoconductive drum 21, and 25 is an unremoved portion remaining on the surface of each photoconductive drum 21. A cleaning unit 30 collects the transfer toner, and a fixing device 30 fixes the toner image (unfixed image) secondarily transferred onto the recording medium P.
Although not shown in FIG. 1, above each process cartridge 20Y, 20C, 20M, 20BK, there are two components including developer (toner and carrier) corresponding to each color (yellow, cyan, magenta, black). Developer supply means (consisting of a developer container 28 and a developer supply device 80) for supplying the developer) to the developing device 23 is installed (see FIG. 2). ).

Hereinafter, an operation during normal color image formation in the image forming apparatus will be described. Note that FIG. 2 can also be referred to for the image forming process performed by the process cartridges 20Y, 20M, 20C, and 20BK.
First, the document reading unit 4 optically reads image information of a document placed on the contact glass 5. Specifically, the document reading unit 4 scans an image of a document on the contact glass 5 while irradiating light emitted from an illumination lamp. Then, the light reflected from the original is imaged on the color sensor via the mirror group and the lens. The color image information of the original is read for each color separation light of RGB (red, green, blue) by the color sensor, and then converted into an electrical image signal. Further, the image processing unit performs color conversion processing, color correction processing, spatial frequency correction processing, and the like based on the RGB color separation image signals, and converts yellow, magenta, cyan, black (black) color image information. obtain.
Then, the image information of each color of yellow, magenta, cyan, and black is transmitted to the writing unit 2. Then, the writing unit 2 emits laser light L (see FIG. 2) based on the image information of each color toward the corresponding photosensitive drum 21.

On the other hand, the four photosensitive drums 21 rotate in the counterclockwise direction in FIGS. First, the surface of the photosensitive drum 21 is uniformly charged at a portion facing the charging unit 22 (a charging step). Thus, a charged potential is formed on the photosensitive drum 21. Thereafter, the surface of the charged photosensitive drum 21 reaches the irradiation position of each laser beam L.
In the writing unit 2, laser light L corresponding to the image signal is emitted from the four light sources corresponding to each color. Each laser beam passes through a separate optical path for each of the yellow, magenta, cyan, and black color components (this is an exposure process).

  The laser beam corresponding to the yellow component is applied to the surface of the photosensitive drum 21 of the first process cartridge 20Y from the left side of FIG. At this time, the yellow component laser light is scanned in the rotational axis direction (main scanning direction, longitudinal direction) of the photosensitive drum 21 by a polygon mirror that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 21 charged by the charging unit 22.

  Similarly, the laser beam corresponding to the magenta component is irradiated on the surface of the photosensitive drum 21 of the second process cartridge 20M from the left side of the paper, and an electrostatic latent image corresponding to the magenta component is formed. The cyan component laser light is applied to the surface of the photosensitive drum 21 of the third process cartridge 20C from the left side of the drawing, thereby forming an electrostatic latent image of the cyan component. The black component laser light is applied to the surface of the photosensitive drum 21 of the fourth process cartridge 20BK from the left side of the drawing, thereby forming an electrostatic latent image of the black component.

Thereafter, the surface of the photosensitive drum 21 on which the electrostatic latent image of each color is formed reaches a position facing the developing device 23. Then, each color toner is supplied from each developing device 23 onto the photosensitive drum 21, and the latent image on the photosensitive drum 21 is developed to form a toner image (this is a developing step).
Thereafter, the surface of the photoconductive drum 21 after the development process reaches a portion facing the intermediate transfer belt 17. Here, a primary transfer bias roller 14 is installed at each facing portion so as to be in contact with the inner peripheral surface of the intermediate transfer belt 17. Then, at the position of the primary transfer bias roller 14, the toner images of the respective colors formed on the photosensitive drum 21 are sequentially superimposed and transferred onto the intermediate transfer belt 17 (this is a primary transfer process).

Then, the surface of the photosensitive drum 21 after the primary transfer process reaches a position facing the cleaning unit 25. The untransferred toner remaining on the photosensitive drum 21 is collected by the cleaning unit 25 (this is a cleaning process).
Thereafter, the surface of the photosensitive drum 21 passes through the static eliminating unit 24, and a series of image forming processes on the photosensitive drum 21 is completed.

On the other hand, the intermediate transfer belt 17 on which the toners of the respective colors on the respective photosensitive drums 21 are transferred (carried) are run in the clockwise direction in the drawing and reach the position facing the secondary transfer bias roller 18. Then, a color toner image carried on the intermediate transfer belt 17 is transferred onto the recording medium P at a position facing the secondary transfer bias roller 18 (secondary transfer step).
Thereafter, the surface of the intermediate transfer belt 17 reaches the position of an intermediate transfer belt cleaning unit (not shown). Then, the untransferred toner attached on the intermediate transfer belt 17 is collected by the intermediate transfer belt cleaning unit, and a series of transfer processes in the intermediate transfer belt 17 is completed.

Here, the recording medium P transported between the intermediate transfer belt 17 and the secondary transfer bias roller 18 (secondary transfer nip) is transported from the paper supply unit 7 via the registration roller 9 and the like. It is a thing.
Specifically, the recording medium P fed by the paper feeding roller 8 from the paper feeding unit 7 that stores the recording medium P is guided to the registration roller 9 after passing through the conveyance guide. The recording medium P that has reached the registration roller 9 is conveyed toward the secondary transfer nip at the same timing.

The recording medium P on which the full color image is transferred is guided to the fixing device 30 by a conveyance belt (not shown). In the fixing device 30, the toner image (color image) on the recording medium P is heated and melted at the nip between the fixing roller (a heater as a heat source is provided) and the pressure roller, and the recording medium P is heated. Fixed on top.
Then, the recording medium P after the fixing process is discharged as an output image outside the image forming apparatus 1 by a paper discharge roller, and a series of image forming processes is completed.

Next, the process cartridge 20 (image forming unit), the developer container 28, and the developer supply device 80 in the image forming apparatus will be described.
Each process cartridge 20Y, 20C, 20M, 20BK has substantially the same structure, and each developer container 28 and each developer replenishing device 80 have substantially the same structure. Therefore, in FIG. The container and the developer replenishing device are illustrated by removing the alphabet (Y, C, M, BK).
FIG. 2 is a schematic configuration diagram showing the process cartridge 20, the developer container 28, and the developer supply device 80 installed in the image forming apparatus main body 1. FIG. 3 is an enlarged view showing the developing device 23 installed in the process cartridge 20.

As shown in FIG. 2, the process cartridge 20 includes a photosensitive drum 21 as an image carrier, a charging unit 22, a developing device 23 (developing unit), and a cleaning unit 25, and is a premix developing unit. System (development system in which carrier is replenished / discharged as appropriate) is adopted.
The photoconductor drum 21 as an image carrier is a negatively charged organic photoconductor, and is rotated (runs) in a predetermined direction (counterclockwise in FIG. 2) by a rotation driving mechanism (not shown).

The charging unit 22 is a charging roller having elasticity, in which a medium-resistance foamed urethane layer in which a urethane resin, carbon black as conductive particles, a sulfurizing agent, a foaming agent, and the like are formed in a roller shape on a core metal. The material of the middle resistance layer of the charging unit 22 is urethane, ethylene-propylene-diene polyethylene (EPDM), butadiene acrylonitrile rubber (NBR), silicone rubber, isoprene rubber, etc. It is also possible to use a rubber material in which a conductive material such as the above is dispersed or a foamed material of these materials. In this embodiment, a charging roller is used as the charging unit 22, but a corona discharge type wire charger can also be used as the charging unit 22.
The cleaning unit 25 is provided with a cleaning blade that presses against the photosensitive drum 21, and mechanically removes and collects untransferred toner on the photosensitive drum 21. The untransferred toner collected inside the cleaning unit 25 is conveyed to the outside of the cleaning unit 25 by a conveyance coil, and is collected as waste toner inside a collection container (not shown) via a discharge path.

The developing device 23 is disposed such that two developing rollers 23a1 and 23a2 as developer carriers are opposed to the photosensitive drum 21 with a gap (hereinafter referred to as “development gap” as appropriate). Thus, development areas where the photosensitive drum 21 and the magnetic brush are in contact with each other are formed in both development gaps. In the developing device 23, a developer G (a two-component developer including additives and the like) containing toner T and carrier C is accommodated. The developing device 23 develops the electrostatic latent image formed on the photosensitive drum 21 (forms a toner image).
Specifically, after the developer G carried on the upstream first developing roller 23a1 is regulated to an appropriate amount by the doctor blade 23c, the toner T in the developer G is opposed to the photosensitive drum 21 (first position). (1 developing area) adheres to the latent image on the photosensitive drum 21. Thereafter, a part or all of the developer G carried on the first developing roller 23a1 is supplied (delivered) to the second developing roller 23a2 on the downstream side. Then, the toner T in the developer G carried on the second developing roller 23a2 adheres to the latent image on the photosensitive drum 21 at a position facing the photosensitive drum 21 (second developing region). As described above, the latent image on the photosensitive drum 21 is attached with toner in the first development area and the second development area, thereby forming a high-quality toner image.

Here, the developing device 23 in the present embodiment is of a premix developing type, and a new developer G (appropriately) is introduced into the developing device 23 from the developer container 28 via the developer supply device 80. The toner T and the carrier C) are supplied, and the deteriorated developer G (mainly the carrier C) is discharged to the outside of the developing device 23, and is collected through a discharge path 70 (not shown; The above-mentioned waste toner is also collected) as a waste developer.
Referring to FIG. 2, developer container 28 contains developer G (toner T and carrier C) to be replenished into developing device 23. The developer container 28 functions to supply new toner T to the developing device 23 and also functions to supply new carrier C to the developing device 23. Specifically, the developer replenishing device 80 is based on the information of the toner concentration (the ratio of the toner in the developer G) detected by a magnetic sensor (not shown) installed in the developing device 23. The conveying screw 82 is rotationally driven, the developer G stored in the storage portion 81 is conveyed toward the dropping path portion 85, and the developer G is dropped from the dropping path portion 85 into the developing device 23 by its own weight. Let them replenish.

Hereinafter, the configuration and operation of the developing device 23 will be described in more detail.
Referring to FIG. 3, the developing device 23 includes two developing rollers 23a1, 23a2 (developer carrying member), three conveying screws 23b1 to 23b3 (conveying member), a doctor blade 23c (developer regulating member), and the like. It is configured. Further, in the developing device 23, three developer conveying portions B1 to B3 (conveying paths) that convey the developer G and form a circulation path are formed.

Two developing rollers (the first developing roller 23a1 and the second developing roller 23a2) are arranged side by side so as to face each other along the rotation direction (traveling direction) of the photosensitive drum 21. Each of the two developing rollers 23a1 and 23a2 is formed by rotating a sleeve formed of a nonmagnetic material such as aluminum, brass, stainless steel, or conductive resin into a cylindrical shape in a clockwise direction in FIG. It is comprised so that. In the sleeves of the developing rollers 23a1 and 23a2, a magnet for forming a magnetic field is fixed so as to cause the developer G to rise on the peripheral surface of the sleeve. The carrier C in the developer G rises in a chain shape on the sleeve so as to follow the normal magnetic field lines emitted from the magnet. The charged toner T is attached to the carrier C that is spiked in a chain shape to form a magnetic brush. The magnetic brush is transferred in the same direction (clockwise) as the sleeve by the rotation of the sleeve.
In the present embodiment, the first developing roller 23a1 and the second developing roller 23a2 are formed with the same outer diameter, and are substantially the same except for the configuration of the magnetic poles of the magnets provided therein. Rotate at the same rotational speed in the direction (clockwise in FIG. 2).
In the present embodiment, the surfaces of the sleeves of the developing rollers 23a1 and 23a2 are subjected to known electromagnetic blasting or sand blasting, and the amount of deflection as the developing roller is relatively large.

  The doctor blade 23c as a developer regulating member opposes the first developing roller 23a1 on the upstream side in the running direction of the photosensitive drum 21, and makes the amount of the two-component developer G carried on the first developing roller 23a1 an appropriate amount. regulate.

The three transport screws 23b1 to 23b3 are formed with a screw portion in a spiral shape on the shaft portion, and the developer G accommodated in the developing device 23 is placed in the longitudinal direction (in the direction perpendicular to the plane of FIG. 3). The direction of rotation of the developing rollers 23a1 and 23a2 coincides with the direction of the rotation axis).
Specifically, the conveyance path (first developer conveyance part B1) by the first conveyance screw 23b1, the conveyance path (second developer conveyance part B2) by the second conveyance screw 23b2, and the conveyance path (by the third conveyance screw 23b3) ( The third developer conveying part B3) is isolated from the wall part. The downstream side of the second developer transport unit B2 and the upstream side of the third developer transport unit B3 communicate with each other via the first relay unit. In addition, the downstream side of the third developer transport unit B3 and the upstream side of the first developer transport unit B1 communicate with each other via the second relay unit. In addition, the downstream side of the first developer transport unit B1 and the upstream side of the third developer transport unit B3 communicate with each other via a dropping path. With such a configuration, a circulation path for circulating the developer G in the longitudinal direction in the developing device 23 is formed by the three developer conveying portions B1 to B3 (conveying screws 23b1 to 23b3).

  Here, a discharge port 23d (see FIG. 2) for discharging a part of the developer G accommodated in the developing device 23 to the outside (discharge path 70) is formed in the wall portion of the third developer conveying portion B3. Can be). In detail, the discharge port 23d is supplied with the developer G into the developing device 23 by the developer replenishing device 80, the amount of the developer in the device increases, and the developer surface (upper surface) of the developer exceeds a predetermined height. The excess developer G is discharged toward the discharge path 70. As described above, the carrier C deteriorated by being contaminated with the base resin of the toner T or the external additive is automatically discharged to the outside of the developing device 23, so that deterioration of the image quality can be suppressed even over time.

  As described above, in the present embodiment, since the premix developing type developing device 23 is used, the speed of deterioration of the carrier C in the developing device 23 is apparently slowed down, and the developer G replacement cycle is prolonged. can do.

Referring to FIG. 2, the developer container 28 in the present embodiment is a substantially box-shaped container, and is provided with a shutter member that opens and closes a discharge port, a conveying screw 285, a stirring member 286, and the like. It has been.
The developer container 28 is attached / detached to / from the developer supply device 80 (image forming apparatus 1) with the substantially horizontal direction as the attachment / detachment direction by a user's manual operation. At the bottom of the developer container 28, a discharge port for discharging the developer G accommodated in the developer container 28 toward the storage part 81 of the developer supply device 80 opens downward. Is formed. Further, the developer container 28 is provided with a shutter member that moves in the same direction as the attaching / detaching direction with respect to the developer supply device 80 to open and close the discharge port.

Hereinafter, the characteristic configuration and operation of the developing device 23 according to the present embodiment will be described.
In the present embodiment, the two developing rollers 23a1 and 23a2 (two developing rollers adjacent to each other along the traveling direction of the photosensitive drum 21) have a predetermined amount of shake difference (in this embodiment, 10 μm.) It is formed to be the following. That is, when the shake amount of the first developing roller 23a1 is X1 and the shake amount of the second developing roller 23a2 is X2, the two developing rollers 23a1, 23a2 are set so that the absolute value of X1-X2 is 10 μm or less. Is selected. Specifically, referring to FIG. 5A, the developing rollers 23a1 and 23a2 have markings S (see FIG. 7) that are divided into four layers and color-coded according to the magnitude of the shake amount. As shown in FIG. 5 (B), the combination is determined by the marking color so that the difference between the shake amounts of the two developing rollers 23a1 and 23a2 is 10 μm or less. Yes.
Here, the “shake amount” of the developing roller is the difference between the maximum value and the minimum value of the shake. For example, the “shake amount” when a shake as shown by the solid line in FIG. 2 μm. For the measurement of the “shake amount”, a known one (for example, one disclosed in Patent Document 2) can be used.

  With reference to FIG. 4, in the present embodiment, the two developing rollers 23 a 1 and 23 a 2 are such that the surface of the first developing roller 23 a 1 (the developing roller on the upstream side in the traveling direction) is in relation to the surface of the photosensitive drum 21. Is the point M on the surface (FIG. 4A) of the photosensitive drum 21 when it is closest. ) Reaches a position (second development region) facing the second development roller 23a2 (a development roller on the downstream side in the running direction adjacent to the first development roller 23a1) as shown in FIG. 4B. In some cases, the second developing roller 23a2 is installed so as to have a positional relationship in the rotational direction so that the surface of the second developing roller 23a2 is farthest from the surface of the photosensitive drum 21.

Specifically, the distance (development gap) between the first developing roller 23a1 and the photosensitive drum 21 changes with the rotation period as shown by the solid line in FIG. The first developing roller 23a1 has the smallest developing gap when the point R on the surface reaches the position facing the photosensitive drum 21, and the point R 'on the surface is the position facing the photosensitive drum 21. The development gap becomes the largest when the value is reached.
Similarly, the distance (development gap) between the second developing roller 23a2 and the photosensitive drum 21 changes with the rotation period as shown by the broken line in FIG. The second developing roller 23 a 2 has the smallest developing gap when the Q ′ point on the surface thereof reaches the position facing the photosensitive drum 21, and the Q point on the surface is the position facing the photosensitive drum 21. The development gap becomes the largest when the value is reached.
As shown in FIG. 4A, the point M on the surface of the photosensitive drum 21 when the point R on the surface of the first developing roller 23a1 reaches the first developing area with the photosensitive drum 21 is As shown in FIG. 4B, when the second developing region is reached, the two developing rollers 23a1, 23a2 are arranged such that the point Q on the surface of the second developing roller 23a2 faces the point M of the photosensitive drum 21. However, the postures (phases) in the rotation direction are adjusted and assembled.

  Specifically, in the present embodiment, the outer diameters of the two developing rollers 23a1 and 23a2 are set to 30.28 mm, respectively, and the outer diameter of the photosensitive drum 21 is set to 100 mm. In FIG. The arc length from point M to point N on 21 is set to 24.5 mm, and the developing rollers 23a1, 23a2 taking into account the linear speed ratio of the developing rollers 23a1, 23a2 with respect to the photosensitive drum 21 in the first and second developing regions. One period is 65.6 mm. Therefore, the angle QON at the second developing roller 23a1 in FIG. 4A is set to 134 ° (= 360 ° × 24.5 / 65.6), so that these conditions are satisfied. The two developing rollers 23a1 and 23a2 are assembled by adjusting the postures (phases) in the rotational direction.

With this configuration, even in the case where the two developing rollers 23a1 and 23a2 are shaken in the multistage developing type developing device 23, large image density unevenness is generated in the image formed on the photosensitive drum 21. It can be made difficult to occur.
Specifically, the surface (point M) of the photoconductive drum 21 when the surface (point R) of the first developing roller 23a1 is closest to the surface of the photoconductive drum 21 is a position facing the second developing roller 23a2 ( When the surface (Q ′ point) of the second developing roller 23a2 comes closest to the surface of the photosensitive drum 21 when reaching the second developing region), a developing process for increasing the image density is repeated. As a result, an image with a very high image density is formed. Further, the surface (point M) of the photosensitive drum 21 when the surface (point R ′) of the first developing roller 23a1 is farthest from the surface of the photosensitive drum is the position (first position) facing the second developing roller 23a2. When the surface (Q point) of the second developing roller 23a2 is farthest from the surface of the photosensitive drum 21 when reaching the second developing region), the developing process for reducing the image density is repeated. Thus, an image having a very low image density is formed. These development steps are performed in the synchronized rotation cycle of the two developing rollers 23a1 and 23a2, and image density unevenness having a large density difference is generated.
On the other hand, in the present embodiment, when an image having a high image density is formed in the first development area, an image having a low image density is formed in the second development area by the configuration as described above. When an image having a low image density is formed in the first development area, an image having a high image density is formed in the second development area, and the image is rotated over the rotation period so as to cancel out the high and low image density in the two development areas. An image having a balanced density can be formed. In other words, even if the two developing rollers 23a1 and 23a2 are shaken, the sum of the image density in the first development area and the image density in the second development area is always almost equal to form an image with little image density unevenness. can do.

Here, referring to FIG. 7, in the present embodiment, the two developing rollers 23a1 and 23a2 are each marked S on the surface (R point, Q ′ point) closest to the surface of the photosensitive drum 21. Is attached. Specifically, in the developing rollers 23a1 and 23a2, the marking S is given by shifting the position to the end in the rotation axis direction without shifting the position in the rotation direction with respect to the position in the rotation axis direction center where the shake is maximum. The
The two developing rollers 23a1 and 23a2 are installed so as to determine the positional relationship in the rotational direction by shifting the positions where the markings S are attached to each other by a predetermined angle when viewed in the rotational axis direction. Specifically, referring to FIG. 8, at the time of assembling the developing device 23, first, the marking S of the first developing roller 23a1 (which is attached to the position corresponding to the R point) is the photosensitive drum 21. The position of the first developing roller 23a1 in the rotational direction is determined so as to be positioned in the horizontal direction on the side. Then, with respect to the developing device 23 in this state, the marking S of the second developing roller 23a2 (which is attached at a position corresponding to the point Q ′) is clockwise with respect to the horizontal direction on the photosensitive drum 21 side. The position of the second developing roller 23a2 in the rotational direction is determined so as to be displaced by a predetermined angle θ (19 ± 5 ° in the present embodiment) in the direction. Specifically, the rotation direction of the developing rollers 23a1 and 23a2 is adjusted so as to adjust the meshing position of the gear train between the gears (not shown) installed at the shaft portions of the two developing rollers 23a1 and 23a2 and the idler gear meshing therebetween. The positional relationship will be adjusted. As a result, the two developing rollers 23a1 and 23a2 can be accurately installed in a desired positional relationship in the rotational direction.
In the present embodiment, in the developing rollers 23 a 1 and 23 a 2, the marking S is given to the surface (R point, Q ′ point) that is closest to the surface of the photosensitive drum 21. On the other hand, the marking S can be given to the surface (R ′ point, Q point) that is farthest away. Even in such a case, the same effect as described above can be obtained.

  Here, as described above with reference to FIG. 5 and the like, in this embodiment, the difference between the shake amounts of the two developing rollers 23a1 and 23a2 is set to be 10 μm or less. Even if the positional relationship in the rotational direction of the two developing rollers 23a1 and 23a2 is adjusted so as to cancel out the image density level in the two developing regions as in the present embodiment, the two developing rollers This is because if the difference between the shake amounts of 23a1 and 23a2 is too large, it is difficult to exert an effect of canceling out the image density. That is, when an image having a high image density is formed in one development area, it is necessary to form an image that is low enough to cancel the image density in the other development area. If an image that is too low to cancel the image density is formed, the image density unevenness cannot be solved as a whole.

  FIG. 9 is a result of an experiment in which the developing device 23 according to this embodiment is used to examine the relationship between the difference between the shake amounts of the two developing rollers 23a1 and 23a2 and the brightness amplitude that is an index of the degree of image density unevenness. Is shown. From the experimental results shown in FIG. 9, it can be seen that by setting the difference between the shake amounts of the two developing rollers 23a1 and 23a2 to be 10 μm or less, the lightness amplitude level is such that the image density unevenness cannot be visually recognized.

FIG. 10 shows an experiment in which the relationship between the difference between the shake amounts of the two developing rollers 23a1 and 23a2 and the rank of the image density unevenness of the actual output image is examined using the developing device 23 according to the present embodiment. The result is shown. In the embodiment, the shake amount of the first developing roller 23a1 is set to 20 μm, and the shake amount of the second developing roller 23a2 is set to 20 μm. In Comparative Example 1, the shake amount of the first developing roller 23a1 is set to 20 μm, and the shake amount of the second developing roller 23a2 is set to 5 μm. In Comparative Example 2, the shake amount of the first developing roller 23a1 is set to 8 μm, and the shake amount of the second developing roller 23a2 is set to 20 μm. In the experiment, a black developing device was used, the pumping amount of the first developing roller 23a1 was set to 31 mg / cm2, and the output image was a halftone image with a halftone dot image area ratio of 75%.
Also from the experimental results of FIG. 10, it can be seen that by setting the difference between the shake amounts of the two developing rollers 23a1 and 23a2 to be small, the rank 5 is obtained in which no image density unevenness occurs. Further, when the difference between the shake amounts of the two developing rollers 23a1 and 23a2 is set to be larger than 10 μm, the image density unevenness becomes a marginal level 3 or an unacceptable level according to the magnitude. It turns out that it becomes two.

In the present embodiment, the two developing rollers 23a1 and 23a2 are connected to the surface of the photosensitive drum 21 (M) when the surface (point R) of the first developing roller 23a1 is closest to the surface of the photosensitive drum 21. When the point) reaches a position facing the second developing roller 23a2 (second developing region), the surface (Q point) of the second developing roller 23a2 is farthest from the surface of the photosensitive drum 21. The positional relationship in the rotational direction of each other was determined and installed.
In contrast, the two developing rollers 23a1 and 23a2 are arranged such that the surface of the photosensitive drum 21 when the surface of the first developing roller 23a1 (point R ′) is farthest from the surface of the photosensitive drum 21 (point M). However, when reaching the position facing the second developing roller 23a2 (second developing region), the surface of the second developing roller 23a2 (Q ′ point) is closest to the surface of the photosensitive drum 21 so that each other. It is also possible to determine and set the positional relationship in the rotation direction.
As shown in FIG. 6, the R point, the Q point, the R ′ point, and the Q ′ point are at positions that are substantially 180 ° out of phase in one cycle (one rotation) of the developing rollers 23a1, 23a2. Even when configured as described above, the configuration is almost the same as that of the present embodiment, and substantially the same effect can be obtained.

Hereinafter, the developing device 23 as a modification will be described with reference to FIGS. 11 and 12.
The developing device 23 as a modification is also configured in the same manner as that of the present embodiment. In particular, the two developing rollers 23a1 and 23a2 are formed so that the difference between the shake amounts is a predetermined value or less, and the surface (point R) of the first developing roller 23a1 is the most relative to the surface of the photosensitive drum 21. When the surface (M point) of the photosensitive drum 21 when approaching reaches the position (second developing region) facing the second developing roller 23a2, the surface (Q point) of the second developing roller 23a2 is the photosensitive drum. The positions are set so as to be farthest from the surface of the 21 with respect to each other in the rotational direction. The two developing rollers 23a1 and 23a2 are both subjected to known electromagnetic blasting or sand blasting on the surface of the sleeve, and a plurality of recesses (irregularities) are regularly or irregularly formed on the outer peripheral surface thereof. Is formed. The concave portions formed on the surfaces of the developing rollers 23a1 and 23a2 in this way greatly affect the amount of developer G pumped up (or transportability) in the developing rollers 23a1 and 23a2. Specifically, when the surface roughness of the developing rollers 23a1 and 23a2 increases (becomes rough), the pumping amount (or transportability) of the developer G becomes larger than when the surface roughness is small.

Here, in the developing device 23 as a modified example, the surface roughness of the first developing roller 23a1 (upstream developing roller) is the surface of the second developing roller 23a2 (downstream developing roller). It is comprised so that it may become large compared with roughness. Specifically, as shown in FIG. 12, the surface roughness of the first developing roller 23a1 (“10-point average roughness Rz” defined by JIS standard) is set to about 70 μm, and the second developing roller 23a2 The surface roughness is set to about 35 μm.
Unlike the second developing roller 23a2, the first developing roller 23a1 is subjected to a large stress due to sliding with the developer G at a position facing the doctor blade 23c (doctor gap). ) Are likely to disappear due to wear over time (the difference in unevenness is likely to be eliminated), and the pumping amount (or transportability) of the developer G tends to decrease over time. Therefore, the occurrence of such a problem can be reduced by setting the surface roughness of the first developing roller 23a1 large in advance.

Further, referring to FIG. 11, the developing device 23 as a modified example has a developing gap H1 between the first developing roller 23a1 (upstream developing roller) and the photosensitive drum 21 (image carrier). It is formed to be larger than the developing gap H2 between the second developing roller 23a2 (downstream developing roller) and the photosensitive drum 21 (H1> H2). Specifically, as shown in FIG. 12, the developing gap H1 of the first developing roller 23a1 is set to about 300 μm, and the developing gap H2 of the second developing roller 23a2 is set to about 260 μm.
Here, “development gaps H1 and H2” are development gaps measured in such a manner that a plurality of locations on the outer peripheral surfaces of the development rollers 23a1 and 23a2 are opposed to the photosensitive drum 21 in consideration of the shake amounts of the development rollers 23a1 and 23a2. Is the average value. That is, in this modification, the outer diameters of the two developing rollers 23a1 and 23a2 are the same, and therefore, the distance W1 (center distance) between the first developing roller 23a1 and the photosensitive drum 21 is the second developing roller. It is set to be larger than the inter-axis distance W2 (center-to-center distance) between 23a2 and the photosensitive drum 21 (W1> W2).

This is because if the concave portions are formed on the surfaces of the developing rollers 23a1 and 23a2 by blasting (spraying) as described above, the shake amounts of the developing rollers 23a1 and 23a2 increase. Specifically, as the surface roughness of the developing rollers 23a1 and 23a2 increases, the amount of shake of the developing rollers 23a1 and 23a2 increases accordingly. Specifically, as shown in FIG. 12, the surface roughness of the first developing roller 23a1 is set to about 70 μm, and the deflection amount is about 25 μm. On the other hand, the surface roughness of the second developing roller 23a2 is set to about 35 μm, and the deflection amount is about 10 μm.
As the shake amount of the developing rollers 23a1 and 23a2 increases, image density unevenness (pitch unevenness) corresponding to the rotation pitch of the developing rollers 23a1 and 23a2 becomes more conspicuous on the image.
If the two developing rollers 23a1 and 23a2 are combined so that the shake amounts are the same, such pitch unevenness is reduced. However, in this modified example, since the surface roughness of the first developing roller 23a1 is set larger than that of the second developing roller 23a2, and the amount of shake increases, pitch unevenness is likely to occur.

  On the other hand, in this modification, the developing gap H1 of the first developing roller 23a1 is set to be larger than the developing gap H2 of the second developing roller 23a2, so that it depends on the amount of shake of the first developing roller 23a1. The sensitivity of pitch unevenness can be reduced. That is, even when the developing roller is largely shaken and pitch unevenness is likely to occur, the pitch unevenness is less likely to be recognized as the development gap becomes larger. In the modification, even if the first developing roller 23a1 is configured to have a large deflection amount, the development gap H1 of the first developing roller 23a1 is set to be large, so that pitch unevenness hardly occurs. Furthermore, since the developing gap H2 of the second developing roller 23a2 is not set large, white spots that occur at the boundary between the high density portion and the low density portion in the image are not deteriorated. Therefore, a good image is formed as a final image subjected to the development process in the first development area and the second development area.

The inventor of the present application conducted an experiment to confirm the effect of the above-described modification.
In the experiment, the developing gaps H1 and H2 of the first and second developing rollers 23a1 and 23a2 are set to 260 μm for the developing device 23 (modified example) having the characteristic values shown in FIG. The developing device (Comparative Example 1) and the developing device (comparative example) in which the developing gap H1 of the first developing roller 23a1 is set to 220 μm and the developing gap H2 of the second developing roller 23a2 is set to 260 μm (comparison) Example 2) was prepared. Then, using each of the developing devices, images having a dot image area ratio of 75% were formed, and image density unevenness (pitch unevenness) of these images was visually evaluated.
As a result, in the modified example, the occurrence of pitch unevenness was not confirmed at all. In Comparative Example 1, the occurrence of pitch unevenness was confirmed, and in Comparative Example 2, the occurrence of even worse pitch unevenness was confirmed.

As described above, in the present embodiment, the two developing rollers 23a1 and 23a2 are formed so that the difference between the shake amounts is a predetermined value or less, and the surface (R point) of the first developing roller 23a1 is the same. When the surface (point M) of the photoconductive drum 21 that is closest to the surface of the photoconductive drum 21 (image carrier) reaches the position facing the second developing roller 23a2 (second developing area), The second developing roller 23a2 is installed with a positional relationship in the rotational direction so that the surface (Q point) is farthest from the surface of the photosensitive drum 21.
Thus, even when the developing rollers 23a1 and 23a2 are each shaken in the multistage developing type developing device 23, it is difficult to cause large image density unevenness in the image formed on the photosensitive drum 21. it can.

In the present embodiment, the present invention is applied to the two-component developing type developing device 23 in which the developer G is supplied from the developer container 28 containing the developer G (two-component developer). . On the other hand, the present invention can naturally be applied to the two-component developing type developing device 23 in which the toner T is supplied from the toner container containing only the toner T.
In the present embodiment, the present invention is applied to the two-component developing type developing device 23 in which a two-component developer is accommodated. On the other hand, the present invention can also be applied to a developing device of a non-contact one-component developing system that contains only toner T (one-component developer). In this case, a plurality of developing rollers are arranged in parallel so as to face the image carrier with a gap.
In the present embodiment, the present invention is applied to the developing device 23 provided with the two developing rollers 23a1 and 23a2. On the other hand, the present invention can naturally be applied to a developing device provided with three or more developing rollers.
Furthermore, the present invention is naturally applied to a developing device (for example, disclosed in Japanese Patent Application Laid-Open No. 2006-235328) configured such that two developing rollers rotate in directions opposite to each other. Can be applied.
Even in such a case, the same effect as in the present embodiment can be obtained.

Further, in the present embodiment, the present invention is applied to the case where the developing device 23 is integrated as the process cartridge 20 together with the photosensitive drum 21 (image carrier), the charging unit 22, and the cleaning unit 25. . However, the application of the present invention is not limited to this, and all or a part of these constituent members 21 to 23 and 25 are each configured as a unit that is detachably attached to the image forming apparatus main body 1. Of course, the present invention can also be applied. In such a case, the same effect as in the present embodiment can be obtained.
In the present application, “process cartridge” means a charging unit (charging device) for charging an image carrier, a developing device (developing unit) for developing a latent image formed on the image carrier, and an image carrier. It is defined as a unit in which at least one of the cleaning unit (cleaning device) for cleaning the top and the image carrier are integrated and detachably installed on the image forming apparatus main body.

  It should be noted that the present invention is not limited to the present embodiment, and it is obvious that the present embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the present embodiment. is there. In addition, the number, position, shape, and the like of the constituent members are not limited to the present embodiment, and the number, position, shape, and the like suitable for implementing the present invention can be achieved.

1 image forming apparatus (image forming apparatus main body),
20, 20Y, 20C, 20M, 20BK Process cartridge,
21 Photosensitive drum (image carrier),
23 Developing device (developing part),
23a1 first developing roller (developing roller, developer carrier),
23a2 second developing roller (developing roller, developer carrier),
23c Doctor blade (developer regulating member),
S marking,
G developer (two-component developer), T toner, C carrier.

JP 2012-42799 A JP 2006-17510 A

Claims (10)

A developing device for developing a latent image formed on the surface of an image carrier traveling in a predetermined direction,
A plurality of developing rollers arranged in parallel so as to face each other along the traveling direction of the image carrier,
The plurality of developing rollers are
Formed so that the difference between the shake amounts of two developing rollers adjacent to each other in the running direction is a predetermined value or less,
When the surface of the developing roller on the upstream side in the traveling direction is closest to the surface of the image carrier, the surface of the image bearing member is adjacent to the developing roller on the upstream side and is developed on the downstream side in the traveling direction. When the position facing the roller is reached, the surface of the developing roller on the downstream side is installed so as to determine the positional relationship in the rotational direction so that the surface is farthest from the surface of the image carrier. Developing device. A developing device for developing a latent image formed on the surface of an image carrier traveling in a predetermined direction,
A plurality of developing rollers arranged in parallel so as to face each other along the traveling direction of the image carrier,
The plurality of developing rollers are
Formed so that the difference between the shake amounts of two developing rollers adjacent to each other in the running direction is a predetermined value or less,
When the surface of the developing roller upstream in the traveling direction is farthest from the surface of the image carrier, the surface of the image bearing member is adjacent to the upstream developing roller and is downstream in the traveling direction. When the position facing the roller is reached, the surface of the developing roller on the downstream side is installed so as to determine the positional relationship in the rotational direction so that it is closest to the surface of the image carrier. Developing device.   The developing device according to claim 1, wherein the predetermined value is 10 μm.   Each of the plurality of developing rollers is marked on the surface closest to or farthest from the surface of the image carrier, and the positions where the markings are attached are shifted by a predetermined angle with respect to the rotation axis direction. The developing device according to claim 1, wherein the developing device is installed by determining a positional relationship in a rotational direction.   The developing device according to claim 4, wherein the marking is hierarchized and color-coded according to the amount of shake of the developing roller. A two-component developer composed of toner and carrier is contained inside,
The plurality of developing rollers are two developing rollers having the same outer diameter rotating at the same rotational speed in the same direction,
The developer regulating member for regulating the amount of the two-component developer carried on the upstream developing roller facing the upstream developing roller in the traveling direction is provided. Item 6. The developing device according to Item 5.   7. The surface roughness of the upstream developing roller is configured to be larger than the surface roughness of the downstream developing roller. Development device.   The gap between the upstream developing roller and the image carrier is formed so as to be larger than the gap between the downstream developing roller and the image carrier. Item 8. The developing device according to Item 7. A process cartridge that is detachably installed on the main body of the image forming apparatus,
9. A process cartridge in which the developing device according to claim 1 and the image carrier are integrated.   An image forming apparatus comprising the developing device according to claim 1 and the image carrier.

Images