Developing device, process cartridge, and image forming apparatus

Abstract

To reduce the occurrence of trouble in which developer remains on a surface of a flexible sheet member.SOLUTION: A developing device is provided with a developing roller 26a (developer carrier) that forms a developing area opposite to a photoreceptor drum 21 (image carrier), and develops a latent image formed on a surface of the photoreceptor drum 21 in the developing area while rotating in a predetermined rotation direction (normal direction). The developing device is further provided with a flexible sheet member 26r that is held by a case member 26s to face the developing roller 26a with a gap therebetween on an upstream side in the rotation direction (normal direction) of the developing area, and is in contact with the photoreceptor drum 21 at a leading end 26r1 on the side of a free end. At a predetermined timing in a non-developing process, a "control mode" is executed for rotating the developing roller 26a in a direction opposite to the rotation direction (normal direction) to remove developer Gx remaining on a surface of the flexible sheet member 26r.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a developing device that develops a latent image formed on an image carrier such as a photosensitive drum, and to a process cartridge and an image forming apparatus that include the same. [Background technology]

[0002] Conventionally, in developing devices installed in image forming devices such as copiers and printers, a technique has been known in which a flexible sheet member (entrance seal) is installed upstream of the development area in order to prevent toner scattering (see, for example, Patent Document 1).

[0003] More specifically, the developing device in Patent Document 1 is provided with an entrance seal support member (case member) that covers the lower side (upstream side of the development area) of the developing roller (developer carrier) that faces the photosensitive drum (image carrier). An entrance seal (flexible sheet member) is attached to the entrance seal support member (case member) so that the leading end of the free end abuts against the photosensitive drum. The entrance seal installed in the developing device in this way reduces the problem of toner being blown out upstream of the development area.

[0004] On the other hand, Patent Document 1 discloses a technology in which an electromagnet is installed on an entrance seal support member (case member) in order to reduce the problem of developer (toner) accumulating on the surface of the entrance seal (flexible sheet member). Summary of the Invention [Problem to be solved by the invention]

[0005] In the conventional technology, developer accumulates on the surface of the flexible sheet member (entrance seal).The developer accumulated on the flexible sheet member then suddenly moves to the developer carrier, resulting in abnormal images such as toner-dropped images. In contrast, the technology of Patent Document 1 is expected to mitigate the above-mentioned problems by providing an electromagnet in the case member (support member) to create a magnetic field that prevents developer from adhering to the flexible sheet member (entrance seal). However, this method requires extra space and costs to install the electromagnet.

[0006] This invention has been made to solve the above-mentioned problems, and aims to provide a developing device, a process cartridge, and an image forming apparatus that are less likely to experience the problem of developer accumulating on the surface of a flexible sheet member. [Means for solving the problem]

[0007] The developing device of the present invention includes a developer carrier that forms a development area facing an image carrier and develops a latent image formed on the surface of the image carrier in the development area while rotating in a predetermined rotation direction; a flexible sheet member that is held by a case member so as to face the developer carrier with a gap therebetween on the upstream side of the rotation direction relative to the development area, and whose tip on the free end side abuts against the image carrier; a developing case facing the developer carrier with a gap therebetween, the developing case being located downstream of the developing area in the rotation direction; a control mode in which the developer carrying member is rotated in a direction opposite to the rotation direction at a predetermined timing during a non-developing step to remove developer remaining on the surface of the flexible sheet member; and the control mode rotates the developer carrier in the reverse direction at least until the developer on the developer carrier that contacts the developing case reaches the position of the flexible sheet member. It is something. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a developing device, a process cartridge, and an image forming apparatus that are less likely to suffer from the problem of developer remaining on the surface of a flexible sheet member. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention; [Figure 2] FIG. [Figure 3] FIG. 2 is a longitudinal view of the developing device. [Figure 4] 10A and 10B are diagrams illustrating the operation of the developing roller during the developing process. [Figure 5] 10A and 10B are diagrams illustrating the operation of the developing roller in a cleaning mode. [Figure 6] 4 is a timing chart showing an example of drive control of a developing roller. [Figure 7] 10 is a timing chart showing drive control of the developing roller according to Modification 1. [Figure 8] 10 is a flowchart showing control in a cleaning mode according to a second modification. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and redundant explanations will be appropriately simplified or omitted.

[0011] First, the overall configuration and operation of an image forming apparatus 1 will be described with reference to FIG. The image forming apparatus 1 in this embodiment is a tandem color image forming apparatus in which a plurality of process cartridges 20Y, 20M, 20C, and 20BK are arranged side by side so as to face an intermediate transfer belt 40. In addition, a developing device 26 (see FIG. 2) is installed so as to face the photosensitive drums 21 of the plurality of process cartridges 20Y, 20M, 20C, and 20BK.

[0012] In Figure 1, 1 indicates the main body of a color copier as an image forming device, 2 indicates a document transport unit that transports a document to a document reading unit 3, 3 indicates a document reading unit that reads image information from the document, and 4 indicates a writing unit (exposure unit) that emits laser light based on input image information. Also, 20Y, 20M, 20C, and 20BK indicate process cartridges corresponding to the respective colors (yellow, magenta, cyan, and black), and 40 indicates an intermediate transfer belt onto which toner images of multiple colors are transferred in an overlapping manner. Also, 61 denotes a paper feed device in which sheets P such as paper are stored, 65 denotes a secondary transfer roller that transfers the toner image formed on the intermediate transfer belt 40 to the sheet P, and 66 denotes a fixing device that fixes the unfixed image on the sheet P. Also, 70 denotes a toner container for replenishing toner of each color to each developing device 26 corresponding to the multiple process cartridges 20Y, 20M, 20C, and 20BK, and 80 denotes a waste toner collection container in which untransferred toner collected by the cleaning device 23 (see Figure 2) or the intermediate transfer belt cleaning device 81 is collected as waste toner.

[0013] 2, each of the process cartridges 20Y, 20M, 20C, and 20BK integrates a photosensitive drum 21 as an image carrier, a charging device 22, and a cleaning device 23. When each of the process cartridges 20Y, 20M, 20C, and 20BK reaches the end of its life, it is removed from the image forming apparatus main body 1 and replaced with a new one. Each developing device 26 is disposed opposite the photosensitive drum 21 of each process cartridge 20Y, 20M, 20C, and 20BK. When the developing device 26 reaches the end of its life, it is removed from the image forming apparatus main body 1 and replaced with a new one. The operation of attaching and detaching the developing device 26 to and from the image forming apparatus main body 1 and the operation of attaching and detaching the process cartridges 20Y, 20M, 20C, and 20BK to and from the image forming apparatus main body 1 can be performed separately and independently. A toner image of each color (yellow, magenta, cyan, black) is formed on the photosensitive drum 21 (image carrier) of each of the process cartridges 20Y, 20M, 20C, and 20BK.

[0014] Hereinafter, the operation of the image forming apparatus during normal color image formation will be described. First, the document is transported from the document table by the transport rollers of the document transport unit 2 and placed on the contact glass of the document reading unit 3. Then, the document reading unit 3 optically reads the image information of the document placed on the contact glass. Then, the image information for each color of yellow, magenta, cyan, and black is sent to the writing unit 4. Then, from the writing unit 4, laser light L (exposure light) based on the image information for each color is irradiated onto the surface of the photosensitive drum 21 (see FIG. 2) of the corresponding process cartridge 20Y, 20M, 20C, 20BK.

[0015] Meanwhile, each of the four photosensitive drums 21 rotates clockwise in FIGS. 1 and 2. First, the surface of each photosensitive drum 21 is uniformly charged at a position facing the charging device 22 (charging roller) (charging process). In this way, a charging potential is formed on the photosensitive drum 21. Thereafter, the charged surface of each photosensitive drum 21 reaches a position where a laser beam is irradiated by each writing unit 4, and an electrostatic latent image based on image information is formed at that position (exposure process).

[0016] The laser light corresponding to the yellow component is irradiated onto the surface of the photosensitive drum 21 of the first process cartridge 20Y from the left side of the drawing. At this time, the laser light of the yellow component is scanned in the direction of the rotation axis (main scanning direction) of the photosensitive drum 21 by a polygon mirror rotating at high speed. In this way, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 21 after it has been charged by the charging device 22. Similarly, the cyan laser light is irradiated onto the surface of the photosensitive drum 21 of the process cartridge 20C, which is the second from the left on the paper, and an electrostatic latent image of the cyan component is formed. The magenta laser light is irradiated onto the surface of the photosensitive drum 21 of the process cartridge 20M, which is the third from the left on the paper, and an electrostatic latent image of the magenta component is formed. The black laser light is irradiated onto the surface of the photosensitive drum 21 of the process cartridge 20BK, which is the fourth from the left on the paper, and an electrostatic latent image of the black component is formed.

[0017] 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 26. Then, toner of each color is supplied from each developing device 26 onto the photosensitive drum 21, and the latent image on the photosensitive drum 21 is developed (this is the developing process). Thereafter, the surfaces of the photosensitive drums 21 after the development process reach positions facing the intermediate transfer belt 40. Here, primary transfer rollers 24 are installed at each of the facing positions so as to abut against the inner circumferential surface of the intermediate transfer belt 40. Then, at the positions of the primary transfer rollers 24, the toner images of each color formed on the photosensitive drums 21 are transferred onto the intermediate transfer belt 40 in order, superimposed on top of each other (this is the primary transfer process).

[0018] After the primary transfer process, the surfaces of the photosensitive drums 21 reach a position facing the cleaning devices 23. The cleaning devices 23 then collect untransferred toner remaining on the photosensitive drums 21 (this is the cleaning process). The untransferred toner collected by the cleaning devices 23 passes through a waste toner transport path (not shown) and is collected in the waste toner collection container 80. Thereafter, the residual potential on the surface of the photosensitive drum 21 is removed at the position of the charge removal device, and a series of image forming processes on the photosensitive drum 21 is completed.

[0019] Meanwhile, the surface of the intermediate transfer belt 40 onto which the images of each color on the photosensitive drum 21 are transferred and superimposed runs in the direction of the arrow in the figure and reaches the position of the secondary transfer roller 65. Then, at the position of the secondary transfer roller 65, the full-color image on the intermediate transfer belt 40 is secondarily transferred onto the sheet P (secondary transfer process). Thereafter, the surface of the intermediate transfer belt 40 reaches the position of the intermediate transfer belt cleaning device 81. Then, the untransferred toner on the intermediate transfer belt 40 is collected by the intermediate transfer belt cleaning device 81, and the series of transfer processes on the intermediate transfer belt 40 is completed. The untransferred toner collected by the intermediate transfer belt cleaning device 81 passes through a waste toner transport path (not shown) and is collected in a waste toner collection container 80 .

[0020] Here, the sheet P conveyed to the position of the secondary transfer roller 65 is conveyed from the paper feeder 61 via the registration roller 64 and the like. More specifically, a sheet P fed by a paper feed roller 62 from a paper feed device 61 that stores sheets P passes through a conveyance path and is then guided to the position of a registration roller 64. The sheet P that has reached the position of the registration roller 64 is conveyed toward the position of a secondary transfer roller 65 in synchronization with the toner image on the intermediate transfer belt 40.

[0021] Thereafter, the sheet P onto which the full-color image has been transferred is guided to the position of the fixing device 20. Then, in the fixing device 20, the color image is fixed onto the sheet P at the nip between a fixing roller and a pressure roller. After the fixing process, the sheet P is discharged as an output image outside the apparatus main body 1 by a discharge roller 69, and then stacked on the discharge tray 5, completing a series of image forming processes (printing).

[0022] Next, the image forming unit of the image forming apparatus will be described in detail with reference to FIGS. The four image forming units installed in the image forming apparatus main body 1 have almost the same structure except for the color of the toner used in the image forming process, so they are illustrated without the alphabetical symbols (Y, M, C, BK) for components such as process cartridges and developing devices.

[0023] As shown in FIG. 2, the process cartridge 20 mainly includes a photosensitive drum 21 as an image carrier, a charging device 22, and a cleaning device 23 housed integrally in a case. The photosensitive drum 21 is a negatively charged organic photosensitive member, and is formed by providing a photosensitive layer and the like on a drum-shaped conductive support. The charging device 22 is a charging roller made of a conductive core metal and a medium-resistance elastic layer coated on the outer periphery thereof. A predetermined voltage is applied to the charging device 22 (charging roller) from a power supply unit, thereby uniformly charging the surface of the opposing photosensitive drum 21. The cleaning device 23 is equipped with a cleaning blade 25a and a cleaning roller 25b that come into contact with the photosensitive drum 21. The cleaning blade 25a is made of a rubber material such as urethane rubber, and comes into contact with the surface of the photosensitive drum 21 at a predetermined angle and with a predetermined pressure. The cleaning roller 25b is a brush roller with brush bristles arranged around a core metal.

[0024] As shown in Figures 2 and 3, the developing device 26 is mainly composed of a developing roller 26a as a developer carrier, a first transport screw 26b1 (first transport member) facing the developing roller 26a, a second transport screw 26b2 (second transport member) facing the first transport screw 26b1 via a partition member 26e, and a doctor blade 26c as a developer regulating member facing the developing roller 26a to regulate the amount of developer carried on the developing roller 26a. In addition, in the developing device 26 in this embodiment, a flexible sheet member 26r is provided opposite the developing roller 26a at a position upstream of the development area and downstream of the doctor blade 26c, which will be described in detail later.

[0025] The developing device 26 contains a developer (two-component developer) made up of carrier and toner. In this embodiment, the average particle size of the toner is set to about 5.2 μm, the average particle size of the carrier is set to about 35 μm, the toner concentration is set to about 7 wt %, and the amount of developer in the developing device 26 is set to about 250 g.

[0026] The developing roller 26a is configured to form a developing area by facing the photosensitive drum 21 with a small gap W therebetween. As shown in Fig. 3, the developing roller 26a is composed of a magnet 26a1 that is fixed inside and forms multiple magnetic poles H1 to H5 (see Fig. 4, etc.) on the outer circumferential surface of the roller, and a sleeve 26a2 that rotates around the magnet 26a1.

[0027] 4, the drawing-up magnetic pole H5 acts on the carrier as a magnetic body, drawing up the developer G accommodated in the first transport path B1 (see FIG. 2) onto the developing roller 23a. A portion of the developer G carried on the developing roller 23a is scraped off at the position of the doctor blade 26c (see FIG. 2) and returned to the first transport path B1. Meanwhile, at the position of the doctor blade 26c where the magnetic force of the drawing-up magnetic pole H5 acts, the developer G carried on the developing roller 26a passes through the doctor gap between the doctor blade 26c and the developing roller 26a, and becomes raised at the position of the main magnetic pole H1, becoming a magnetic brush in the development area and sliding against the photosensitive drum 21. In this way, the toner in the developer G carried on the developing roller 26a adheres to the latent image on the photosensitive drum 21. After that, the developer G that has passed the position of the main magnetic pole H1 is transported between the upper developer case 26k (developer case) and the developer by multiple transport magnetic poles H2 and H3, and then transported to the position of the developer releasing magnetic pole H4. Then, at the position of the developer releasing magnetic pole H4, a repulsive magnetic field (a magnetic field that acts in a direction away from the developing roller 26a) acts on the carrier, causing the developer G carried on the developing roller 26a after the development process to be detached from the developing roller 26a. The detached developer G falls into the first transport path B1 and is transported downstream of the first transport path B1 by the first transport screw 26b1 (see FIGS. 2 and 3).

[0028] 2 and 3, the transport screws 26b1 and 26b2 as transport members transport the developer contained inside the developing device 26 in the longitudinal direction to form a circulation path (the circulation path indicated by the dashed arrow in FIG. 3). That is, a developer circulation path is formed by a first transport path B1 formed by the first transport screw 26b1 and a second transport path B2 formed by the second transport screw 26b2. The first transport path B1 and the second transport path B2 are separated by a partition member 26e (wall portion), and both longitudinal end portions of the two transport paths B1 and B2 communicate with each other via communication openings 26f and 26g. Specifically, referring to FIG. 3, the upstream end of the first transport path B1 in the transport direction communicates with the downstream end of the second transport path B2 in the transport direction via the first communication opening 26f. Furthermore, the downstream end of the first transport path B1 in the transport direction communicates with the upstream end of the second transport path B2 in the transport direction via the second communication opening 26g. In other words, the partition member 26e is disposed at a position excluding both longitudinal end portions.

[0029] The first transport screw 26b1 (first transport path B1) is disposed opposite the developing roller 26a, and the second transport screw 26b2 (second transport path B2) is disposed opposite the first transport screw 26b1 (first transport path B1) via a partition member 26e. The first transport screw 26b1 transports the developer in the longitudinal direction while supplying the developer toward the developing roller 26a and recovering the post-development developer that has been released from the developing roller 26a. The second transport screw 26b2 agitates and mixes the post-development developer transported from the first transport path B1 with fresh toner supplied from the supply port 26d while transporting them in the longitudinal direction. In this embodiment, the two conveying screws 26b1 and 26b2 are arranged side by side in the horizontal direction. Each of the two conveying screws 26b1 and 26b2 has a screw portion wound around a rotating shaft, and is driven to rotate at a rotation speed of about 600 rpm.

[0030] 2 and other figures, developing device 26 in this embodiment has a filter 26t installed in an opening 26k1 that connects the inside of the device with the outside of the device. More specifically, an opening 26k1 (ventilation path) penetrating from the inside to the outside is formed in the ceiling of the upper developer case 26k (developer case) of the developing device 26. A filter 26t is provided to close the opening 26k1. The filter 26t is used to collect toner and allow ventilation. In other words, an opening 26k1 for sending air from the inside to the outside of the developing device 26 is formed in the developing upper case 26k. The filter 26t is installed at the opening 26k1. The filter 26t is made of a mesh that is smaller than the particle size of the toner and carrier, and is formed so that only air can pass through.

[0031] Here, the gap W (casing gap) between the developing roller 26a and the upper developing case 26k on the downstream side of the developing area is set to be within the range of 0.6 to 1.0 mm. If the casing gap W is too small, the developer carried on the developing roller 26a after the development process will not be transported smoothly to the gap W between the developing roller 26a and the developing upper case 26k, and will easily overflow and leak out of the developing device 26. On the other hand, if the casing gap W is too large, it becomes difficult for the developer carried by the developing roller 26a to slide against the inner surface of the developing case 26k, making it difficult for a suction airflow toward the inside of the developing device 26 due to the pump action, and toner scattering from the developing device 26 (toner scattering around the development area) becomes more likely to occur. By maintaining the casing gap W within an appropriate range, it is possible to reduce developer leakage and toner scattering. Furthermore, the internal pressure of the developing device 26 tends to increase due to the suction airflow in the casing gap W described above, and if the internal pressure increases, toner will scatter from the gaps in the developing device 26. In contrast, in this embodiment, the opening 26k1 in which the filter 26t is installed is provided, so that the toner is collected and prevented from scattering to the outside, while only allowing ventilation, thereby suppressing an increase in the internal pressure of the developing device 26. In other words, toner scattering due to an increase in the internal pressure of the developing device 26 is prevented. In this embodiment, a flexible sheet member may be provided so as to fit into the gap (casing gap W) between the developing roller 26a and the upper developing case 26k.

[0032] The image forming process described above will now be further explained, focusing on the development process. Developing roller 26a rotates in a predetermined rotation direction (counterclockwise direction indicated by the arrow in FIG. 2). As shown in FIG. 3, the developer in developing device 26 is circulated in the longitudinal direction while being stirred and mixed with toner supplied from toner container 70 through toner supply port 26d via the toner supply path by rotation of first transport screw 26b1 and second transport screw 26b2, which are arranged with partition member 26e interposed therebetween (circulation in the direction of the dashed arrow in FIG. 3). The toner, which has been frictionally charged and attracted to the carrier, is then lifted up onto the developing roller 26a together with the carrier by the developer lift-up pole H5 formed on the developing roller 26a. The developer carried on the developing roller 26a is transported in the direction of the arrow in FIG. 2 until it reaches a position facing the doctor blade 26c. The developer on the developing roller 26a is then adjusted to an appropriate amount at this position and then transported to a position facing the photosensitive drum 21 (the development area). The toner is then attracted to the latent image formed on the photosensitive drum 21 by the electric field formed in the development area. The developer remaining on the developing roller 26a then reaches above the first transport path B1 as the sleeve rotates and is detached from the developing roller 26a at this position. The electric field in the development area is formed by a predetermined voltage (development bias) applied to the developing roller 26a by a development power supply and a surface potential (latent image potential) formed on the surface of the photosensitive drum 21 during the charging and exposure processes.

[0033] The toner in the toner container 70 is appropriately replenished into the developing device 26 from the replenishing port 26d via a toner replenishing path (not shown) as the toner in the developing device 26 is consumed. The consumption of the toner in the developing device 26 is detected by a toner concentration sensor (not shown) that magnetically detects the toner concentration of the developer in the developing device 26 (the proportion of toner in the developer). The supply port 26d is provided at one end of the second transport screw 26b2 in the longitudinal direction (the left-right direction in FIG. 3), above the second transport screw 26b2 (second transport path B2).

[0034] The configuration and operation of the developing device 26 (image forming apparatus 1), which is a feature of this embodiment, will be described in detail below. As previously described with reference to FIGS. 2 and 3, the developing device 26 is provided with a developing roller 26a as a developer carrier and an upper developing case 26k as a developing case. The developing roller 26a, which serves as a developer carrier, faces the photosensitive drum 21, which serves as an image carrier, to form a developing area, and develops the latent image formed on the surface of the photosensitive drum 21 in the developing area while rotating in a predetermined rotation direction (counterclockwise (arrow direction) in Figures 2 and 4, which is the forward direction). The upper developer case 26k as a developer case is a casing that faces the developing roller 26a across a gap (casing gap W) on the downstream side of the developing area in the rotation direction (counterclockwise in FIGS. 2 and 4).

[0035] Referring to FIG. 2, in this embodiment, the developing device 26 is provided with a casing (housing) including a lower developing case 26j in addition to the above-described upper developing case 26k. The developing lower case 26j is a casing that serves as the base of the developing device 26, and rotatably holds the developing roller 26a and the conveying screws 26b1 and 26b2, as well as holds the doctor blade 26c. On the other hand, the upper developer case 26k (developer case) is arranged to cover the upper side of the developing roller 26a (developer carrier). The upper developer case 26k is configured to be detachable from the lower developer case 26j, which holds the developing roller 26a, the conveying screws 26b1 and 26b2, and the doctor blade 26c, by snapping or screwing.

[0036] 2, 4, etc., in the developing device 26 in this embodiment, a flexible sheet member 26r (entrance seal) is held by a case member 26s (holding member) so as to face the developing roller 26a (developer carrier) with a gap in the rotation direction upstream of the development region (upstream of the rotation direction of the developing roller 26a during the developing process). A tip 26r1 (see FIG. 4) on the free end side of the flexible sheet member 26r abuts against the photosensitive drum 21 (image carrier) (including a state in which the portion including the tip 26r1 abuts against the photosensitive drum 21). 4 with respect to the development region (the position where the developing roller 26a faces the photosensitive drum 21), and is downstream of the doctor blade 26c in the direction of rotation, and is held by the lower development case 26j via the doctor blade 26c so as to face the developing roller 26a. The facing surface of the case 26s (the surface facing the developing roller 26a) is formed so as to follow the curvature of the developing roller 26a (so that the gap with the developing roller 26a is approximately constant). A flexible sheet member 26r is attached to the surface facing the case member 26s via double-sided tape, etc. A tip 26r1 of the flexible sheet member 26r (the tip on the free end side protruding from the case member 26s) comes into sliding contact with the surface of the photosensitive drum 21.

[0037] In this embodiment, a substantially rectangular urethane sheet with a thickness of about 0.1 mm is used as the flexible sheet member 26r. In addition, in this embodiment, the case member 26s is configured to be held in the lower developing case 26j via the doctor blade 26c, but the method of holding the case member 26s is not limited to this, and for example, the case member 26s can be configured to be held directly in the lower developing case 26j, or the case member 26s can be configured as a part of the lower developing case 26j (developing case).

[0038] 5(A), in the developing device 26 (image forming apparatus 1) in this embodiment, during a non-developing step (when the developing step associated with the printing operation is not being performed), a "control mode" is executed in which the developing roller 26a (developer carrier) is rotated in the opposite direction (the direction of the arrow (clockwise) in FIG. 5(A)) to the rotation direction during the developing step, thereby removing the developer Gx remaining on the surface of the flexible sheet member 26r. Hereinafter, this control mode will be referred to as a "cleaning mode" as appropriate. Specifically, in this embodiment, a developing motor (not shown) is provided to drive the developing device 26 (developing roller 26a, first and second transport screws 26b1, 26b2). This developing motor is a bidirectional motor that rotates forward during the normal developing process (printing) and in the reverse direction during the cleaning mode (control mode). In this embodiment, a development motor (not shown) is provided separately from the motor that rotates and drives the photosensitive drum 21, etc., but it is also possible to configure the development device 26 to be rotated and driven together with the photosensitive drum 21, etc. by a single motor.

[0039] By executing the "cleaning mode (control mode)" in this manner, the problem of developer Gx accumulating on the surface of flexible sheet member 26r (the surface facing developing roller 26a) is less likely to occur, and the occurrence of abnormal images such as toner-dropped images is reduced. Moreover, in this embodiment, it is possible to reduce the accumulation of developer Gx on the surface of flexible sheet member 26r without requiring additional space or cost compared to the case where an electromagnet or the like is installed in case member 26s.

[0040] More specifically, the surface (opposing surface) of the flexible sheet member 26r is less affected by the magnetic poles (particularly the scooping magnetic pole H5 and the main magnetic pole H1) of the developing roller 26a (magnet 26a1). Furthermore, the amount of developer on the developing roller 26a is regulated at the position of the doctor blade 26c adjacent to the flexible sheet member 26r. Therefore, the developer G on the developing roller 26a does not stand upright at the position of the flexible sheet member 26r, and as shown in FIG. 4, the developer G on the developing roller 26a almost never comes into contact with the surface of the flexible sheet member 26r. For this reason, once the developer Gx adheres to the surface of the flexible sheet member 26r, the developer Gx on the flexible sheet member 26r is hardly removed by the forward rotation of the developing roller 26a. On the other hand, when the developing roller 26a is rotated in the reverse direction, as shown in Figure 5(A), the developer G that has formed spikes at the magnetic poles (main magnetic pole H1, first transport magnetic pole H2, etc.) on the downstream side (downstream side during forward rotation) is transported backward to the position of the doctor blade 26c and is blocked at the doctor gap (the gap between the developing roller 26a and the doctor blade 26c).The blocked developer G then comes into contact with the developer Gx on the flexible sheet member 26r, and the developer Gx on the flexible sheet member 26r is removed (cleaned) as if scraped off, and is collected (carried) on the developing roller 26a.

[0041] Based on this mechanism, in order to improve cleaning performance in the cleaning mode (control mode), it is preferable to reverse the rotation of the developing roller 26a so that the developer G that has formed spikes at the magnetic pole on the downstream side of the flexible sheet member 26r (downstream side during forward rotation) is transported to the position of the flexible sheet member 26r (doctor blade 26c). In this embodiment, the cleaning mode (control mode) rotates the developing roller 26a in the reverse direction at least until the developer G on the developing roller 26a in contact with the upper developing case 26k (developing case) reaches the position of the flexible sheet member 26r. In other words, the execution time of the cleaning mode (control mode) (the time it takes to reverse the developing roller 26a) is set to exceed the time it takes for the developer G on the developing roller 26a, which is in contact with the upper developing case 26k (developing case), to reach the position of the flexible sheet member 26r. Specifically, in this embodiment, since sufficient cleaning performance cannot be achieved if the developer G that has formed spikes at the position of the main magnetic pole H1 is transported backward to the position of the flexible sheet member 26r, the developer G that has formed spikes at the position of the first transport magnetic pole H2 is transported backward to the position of the flexible sheet member 26r.

[0042] Furthermore, as explained above, in the developing device 26 of this embodiment, the developer G carried on the developing roller 26a (developer carrier) does not come into contact with the surface (opposing surface) of the flexible sheet member 26r during the normal development process (printing), but comes into contact with the surface of the flexible sheet member 26r during the cleaning mode (control mode). This ensures good developability during the development process, while improving cleanability during the cleaning mode.

[0043] In addition, in this embodiment, the above-mentioned "predetermined timing (the timing for executing the cleaning mode)" is the timing immediately after the rotation of the development roller 26a (developer carrier) in the forward direction (rotation direction) is stopped after the development process (after a series of print jobs are completed), as shown in Figure 6. This allows the developer Gx that has just adhered to the surface of the flexible sheet member 26r after the development step to be efficiently removed without affecting the development step (printing). Note that the range of the "development process (printing)" shown in Figure 6 (and Figure 7 described later) also includes the time allowance (start-up time, shutdown time) taken before and after the actual development process is performed.

[0044] Now, referring to Figures 5(B) and 6, in this embodiment, the "cleaning mode (control mode)" is set to rotate the developing roller 26a (developer carrier) in the reverse direction (the direction of the arrow in Figure 5(A)), and then rotate the developing roller 26a in the forward direction (the same rotation direction as during the development process). That is, when the cleaning mode starts, the developing roller 26a is first rotated in the reverse direction (clockwise) as shown in FIG. 5(A), and then the developing roller 26a is rotated in the forward direction (counterclockwise) as shown in FIG. 5(B). This control is performed because if the development process (printing) is performed immediately after the development roller 26a has been reversed, there is a possibility that the developer Gx removed from the flexible sheet member 26r and collected on the development roller 26a may affect the image (cause an abnormal image). In this embodiment, after the developing roller 26a has rotated in the reverse direction and before the next development process (printing) is started, the developing roller 26a is rotated in the forward direction, and the developer Gx collected on the developing roller 26a is mixed and dispersed with the developer G that was flowing normally (mainly the developer G in the first and second transport paths B1 and B2), thereby reducing the occurrence of abnormal images as described above.

[0045] In particular, in this embodiment, the "cleaning mode (control mode)" is set to rotate the developing roller 26a in the forward direction (the same rotation direction as during the development process) immediately after the reverse rotation of the developing roller 26a (developer carrier) has ended, as shown in FIG. 6. When the developing roller 26a is rotated in the forward direction at such timing, the developer Gx collected on the developing roller 26a is dispersed immediately after the developing roller 26a finishes rotating in the reverse direction, which is useful when there is a long time until the start of the next developing process (print job).

[0046] <Variation 1> As shown in Figure 7, in the developing device 26 (image forming device 1) in variant example 1, similar to the drive control of the developing roller 26a shown in Figure 6, in the cleaning mode (control mode), the developing roller 26a is rotated in the reverse direction after the development process and then rotated in the forward direction. However, the "cleaning mode (control mode)" in variant example 1 is set to rotate the developing roller 26a in the forward direction (the same rotation direction as during the developing process) just before the next developing process is started (just before the developing process for forming the first image in the next print job is started, which is the timing just before the latent image corresponding to the first image reaches the developing area). That is, in the cleaning mode of variant 1, the developing roller 26a is not rotated forward immediately after the developing roller 26a has finished rotating in the reverse direction, but is rotated forward after the developing roller 26a has finished rotating in the reverse direction and before the next print job is started. When the developing roller 26a is rotated in the forward direction at such timing, no time is required to rotate the developing roller 26a in the forward direction immediately after the developing roller 26a has finished rotating in the reverse direction. This is therefore useful when the time until the start of the next developing step (print job) is short and the time to rotate the developing roller 26a in the forward direction can be secured without waste in accordance with the warm-up operation of the image forming apparatus 1 that is performed before the start of the next print job.

[0047] <Variation 2> In the developing device 26 (image forming device 1) in variant example 2, the "cleaning mode (control mode)" adjusts the execution frequency (execution time or number of executions) according to the cumulative driving time (which can also be replaced with "cumulative travel distance") of the developing roller 26a (developer carrier) and the cumulative image area (the proportion of the image per unit area) of the image formed on the surface of the photosensitive drum 21 (image carrier). The reason for this control is that the amount of developer remaining (adhering) on ​​the surface of the flexible sheet member 26r increases as the cumulative driving time of the developing roller 26a increases, and also because the amount of developer remaining (adhering) on ​​the surface of the flexible sheet member 26r increases as the cumulative image area (amount of toner used) increases. Therefore, in Modification 2, the execution time of the cleaning mode (mainly the time during reverse rotation) is adjusted based on the cumulative drive time of the developing roller 26a measured by the counter in the control unit and the cumulative image area grasped by the writing unit 4 (see FIG. 2) and the control unit. Specifically, the execution time of the cleaning mode is adjusted to be longer as the cumulative drive time or cumulative image area increases. This makes it possible to efficiently reduce the problem of developer G staying on the surface of the flexible sheet member 26r, regardless of the cumulative driving time or cumulative image area. The cumulative drive time and cumulative image area are reset each time the cleaning mode is executed. An example of control in the cleaning mode in Modification 2 will be described below with reference to FIG. First, when printing starts (step S1), information regarding the cumulative drive time and cumulative image area is acquired by the control unit (step S2), and then, based on the acquired information, the execution time of the cleaning mode is determined (step S3). After printing is completed, the cleaning mode is executed for the execution time determined in step S3 (step S4), and this flow ends.

[0048] As described above, the developing device 26 in this embodiment is provided with a developing roller 26a (developer carrier) that forms a development area facing the photosensitive drum 21 (image carrier) and develops a latent image formed on the surface of the photosensitive drum 21 in the development area while rotating in a predetermined rotational direction (forward direction). The flexible sheet member 26r is held by a case member 26s so as to face the developing roller 26a with a gap therebetween, upstream of the rotational direction (forward direction) relative to the development area, and has a free end 26r1 that abuts against the photosensitive drum 21. During the non-development step, a "control mode" is executed in which the developing roller 26a is rotated in the direction opposite to the rotational direction (forward direction) at a predetermined timing to remove the developer Gx remaining on the surface of the flexible sheet member 26r. This makes it possible to prevent the developer G from accumulating on the surface of the flexible sheet member 26r.

[0049] In the present embodiment, the developing device 26 is not a component of the process cartridge 20, but is a unit that can be attached to and detached from the image forming apparatus main body 1 independently. However, the developing device 26 can also be one of the components of the process cartridge 20, and configured to be attached and detached from the image forming apparatus main body 1 as a process cartridge. In such a case, the same effect as that of this embodiment can be obtained. In this application, a "process cartridge" is defined as a unit that integrates at least one of a charging device that charges an image carrier, a developing device that develops a latent image formed on the image carrier, and a cleaning device that cleans the image carrier, with an image carrier, and is configured to be detachable from the image forming apparatus main body.

[0050] In this embodiment, the present invention is applied to a developing device 26 in which two transport screws 26b1 and 26b2 (transport members) are arranged side by side in the horizontal direction and a doctor blade 26c is arranged below a developing roller 26a. However, the configuration of the developing device to which the present invention is applied is not limited to this, and the present invention can also be applied to, for example, a developing device in which three or more transport members are arranged side by side in the horizontal direction, a developing device in which multiple transport members are arranged side by side in the vertical direction, or a developing device in which a doctor blade is arranged above a developing roller. In such cases, the same effect as that of this embodiment can be obtained.

[0051] It is clear that the present invention is not limited to the present embodiment, and that within the scope of the technical concept of the present invention, each embodiment may be appropriately modified in addition to what is suggested in each embodiment. Furthermore, the number, position, shape, etc. of the components are not limited to the present embodiment, and the number, position, shape, etc. of the components may be any number, position, shape, etc. that is suitable for implementing the present invention. [Explanation of symbols]

[0052] 1 Image forming apparatus (image forming apparatus main body), 20, 20Y, 20M, 20C, 20BK process cartridges, 21 photosensitive drum (image carrier), 26 developing device, 26a developing roller (developer carrier), 26c Doctor blade (developer control member), 26j Developing case, 26k developing case (developing case), 26r flexible sheet member; 26r1 tip (free end side tip), 26s Case material (retaining material), G Developer, Gx Retained developer. [Prior art documents] [Patent documents]

[0053] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-69190

Claims

1. a developer carrier that forms a development area facing the image carrier and develops a latent image formed on the surface of the image carrier in the development area while rotating in a predetermined rotation direction; a flexible sheet member held by a case member so as to face the developer carrier with a gap therebetween, upstream of the developing region in the rotation direction, and having a free end that contacts the image carrier; a developing case facing the developer carrier with a gap therebetween, the developing case being located downstream of the developing area in the rotation direction; Equipped with a control mode is executed in which the developer carrying member is rotated in a direction opposite to the rotation direction at a predetermined timing during a non-developing step, and the developer remaining on the surface of the flexible sheet member is removed; A developing device characterized in that the control mode rotates the developer carrier in the reverse direction at least until the developer on the developer carrier that contacts the developing case reaches the position of the flexible sheet member.

2. A developer carrier that forms a development area facing an image carrier and develops a latent image formed on the surface of the image carrier in the development area while rotating in a predetermined rotation direction; a flexible sheet member held by a case member so as to face the developer carrier with a gap therebetween, upstream of the developing region in the rotation direction, and having a free end that contacts the image carrier; Equipped with a control mode is executed in which the developer carrying member is rotated in a direction opposite to the rotation direction at a predetermined timing during a non-developing step, and the developer remaining on the surface of the flexible sheet member is removed; The developing device is characterized in that the predetermined timing is a timing immediately after the rotation of the developer carrier in the rotation direction is stopped after the developing step.

3. A developing device as described in claim 1 or claim 2, characterized in that the control mode rotates the developer carrier in the reverse direction and then rotates the developer carrier in the rotational direction.

4. A developing device as described in Claim 3, characterized in that the control mode rotates the developer carrier in the rotational direction immediately after the rotation of the developer carrier in the reverse direction has ended.

5. A developer carrier that forms a development area facing an image carrier and develops a latent image formed on the surface of the image carrier in the development area while rotating in a predetermined rotation direction; a flexible sheet member held by a case member so as to face the developer carrier with a gap therebetween, upstream of the developing region in the rotation direction, and having a free end that contacts the image carrier; Equipped with a control mode is executed in which the developer carrying member is rotated in a direction opposite to the rotation direction at a predetermined timing during a non-developing step, and the developer remaining on the surface of the flexible sheet member is removed; The control mode is characterized in that the developer carrier is rotated in the rotation direction after being rotated in the reverse direction and immediately before the next development process is started.

6. A developing device described in any one of claims 1 to 5, characterized in that the execution frequency of the control mode is adjusted according to the cumulative driving time of the developer carrier and the cumulative image area of ​​the image formed on the surface of the image carrier.

7. A developing device described in any one of claims 1 to 6, characterized in that the developer carried on the developer carrier does not contact the surface of the flexible sheet member during the development process, but contacts the surface of the flexible sheet member during the control mode.

8. A process cartridge detachably installed in an image forming apparatus body, 8. A process cartridge comprising the developing device according to claim 1 and the image carrier, the process cartridge being integrally provided with the developing device.

9. An image forming apparatus comprising a developing device according to any one of claims 1 to 7.

Images