Image forming device

Abstract

To provide an image forming apparatus that can effectively prevent the occurrence of an image failure due to aggregation of developer immediately after the end of an installation mode in a magnetic one-component developing system.SOLUTION: An image forming apparatus comprises an image carrier, a developing device, a developer storage container, and a control unit. The developing device includes: a developer carrier that carries developer; a stirring and conveying member that conveys the developer while stirring it; and a regulation member that regulates a layer thickness of the developer carried on the developer carrier. The control unit can execute normal supply for supplying the developer from the developer storage container to the developing device according to an amount of the developer consumed in a printing operation, and an installation mode for supplying a larger amount of the developer than the normal supply from the developer storage container to the developing device and rotating the developer carrier in a normal direction for a predetermined time. The control unit executes a developer removal operation for rotating the developer carrier in a direction opposite to the normal direction immediately after the execution of the installation mode.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, or a printer, and more particularly to a method for preventing developer from clogging the gap between a developing roller and a regulating blade of a developing device. [Background technology]

[0002] Conventionally, the development method in image forming devices using electrophotographic processes has mainly been to use powder developers, and the typical process involves visualizing (developing) an electrostatic latent image formed on an image carrier such as a photosensitive drum using the developer, transferring the visible image (toner image) onto a recording medium, and then performing a fixing process.

[0003] One known developer development method is the magnetic one-component development method, which uses a one-component developer consisting only of magnetic toner. In the magnetic one-component development method, a fixed magnet with multiple magnetic poles is placed inside a development roller (developer carrier), and the toner in the development container is carried on the development roller using magnetic carrying force. After that, a thin layer of toner is formed by regulating the layer thickness using a regulating blade (regulating member), and the toner is then ejected onto the photosensitive drum at the development position.

[0004] In magnetic single-component development, sufficient magnetic force is required at the tip of the regulating blade to ensure the stability of the toner layer on the developing roller and improve the ability to charge the toner. However, continuous development operations tend to cause toner to soften and aggregate around the regulating blade within the developing device. Because the magnetic binding force of the softly aggregated toner is different from that of other areas, the toner layer on the developing roller becomes distorted. As a result, image defects such as uneven density and white streaks are likely to occur when halftone images are output.

[0005] Therefore, Patent Document 1 discloses an image forming apparatus in which the developer carrier is rotated in the opposite direction to that during development while the image carrier is stopped, thereby preventing toner accumulated on the developer regulating member from being developed into the image. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-258276 Summary of the Invention [Problem to be solved by the invention]

[0007] In a single-component developing device that uses a magnetic single-component developer, when a user replaces the developing device, a method is known in which toner is initially loaded (installed) into the new developing device from a toner container. The toner at the time of installation has low fluidity and an unstable charge amount, making it prone to toner agglomeration at the regulating blade. Therefore, to prevent image defects from occurring during image formation immediately after installation, it is necessary to eliminate the agglomeration at the end of installation.

[0008] SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an image forming apparatus that can effectively suppress the occurrence of image defects caused by the aggregation of developer immediately after installation in a magnetic one-component development system. [Means for solving the problem]

[0009] To achieve the above object, the first aspect of the present invention is an image forming apparatus including an image carrier, a developing device, a developer storage container, and a control unit. The image carrier has a photosensitive layer formed on its surface. The developing device includes a developing container containing a magnetic one-component developer consisting only of magnetic toner, a developer carrier rotatably supported in the developing container, carrying the developer on its outer circumferential surface, and exposed through an opening of the developer container to face the image carrier, one or more stirring and transporting members rotatably supported in the developing container and transporting the developer in the developer container while stirring it, and a regulating member disposed at a predetermined interval from the developer carrier and forming a regulating portion that regulates the layer thickness of the developer carried on the developer carrier, and develops an electrostatic latent image formed on the image carrier. The developer storage container stores developer to be replenished to the developing device. The control unit controls the driving of the developing device and the replenishment of developer from the developer storage container to the developing device. The control unit can execute a normal replenishment mode in which developer is replenished from the developer storage container to the developing device in accordance with the amount of developer consumed during printing operations, and an installation mode in which a larger amount of developer than the normal replenishment is replenished from the developer storage container to the developing device and the developer carrier is rotated for a predetermined time in the forward direction, which is the rotation direction during image formation. Immediately after executing the installation mode, the control unit executes a developer removal operation in which the developer carrier is rotated in the opposite direction from the forward direction to remove developer remaining between the regulating member and the developer carrier. [Effects of the Invention]

[0010] According to the first aspect of the present invention, by performing a developer removal operation in which the developer carrier is rotated in the reverse direction immediately after the installation mode is executed, the developer that has aggregated near the regulating unit is brought into contact with and mixed with the developer around the stirring and transporting member, and is reliably reset (replaced). This effectively prevents the aggregation of developer at the regulating unit, and prevents image defects such as uneven shading and white streaks in halftone images printed immediately after the installation mode is completed. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic cross-sectional view of an image forming apparatus 100 according to an embodiment of the present invention; [Figure 2] A side cross-sectional view of a developing device 4 mounted in an image forming apparatus 100. [Figure 3] A side cross-sectional view of a toner container 5 mounted in an image forming apparatus 100. [Figure 4] FIG. 1 is a block diagram showing an example of a control path used in an image forming apparatus 100 according to an embodiment of the present invention. [Figure 5] 1 is a flowchart showing a first control example of an installation mode executed in the image forming apparatus 100 of the present embodiment. [Figure 6] FIG. 10 is a side view showing the driving state of the developing device 4 during execution of the install mode. [Figure 7] An enlarged view of the developing roller 25 and the second stirring / conveying screw 24 when the developing roller 25 is rotated in reverse. [Figure 8] 10 is a flowchart showing a second control example of the installation mode executed in the image forming apparatus 100 of the present embodiment. [Figure 9] 1 is a flowchart showing a procedure for performing a developer removal operation after the installation mode is completed in the image forming apparatus 100 of this embodiment. [Figure 10] 1 is a flowchart showing a procedure for setting an execution interval of a developer removal operation after installation is completed in the image forming apparatus 100 of this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 according to one embodiment of the present invention. When performing a printing operation in the image forming apparatus (e.g., a monochrome printer) 100, an electrostatic latent image is formed in an image forming unit 9 within the main body of the image forming apparatus 100 based on document image data transmitted from a personal computer (not shown) (hereinafter abbreviated as PC), and a toner image is formed by the developing device 4 attaching toner to the electrostatic latent image. Toner is supplied to the developing device 4 from a toner container 5. In the image forming apparatus 100, an image formation process is performed on the photosensitive drum 1 while the photosensitive drum 1 is rotated clockwise in FIG. 1.

[0013] In the image forming section 9, a charging section 2, an exposure unit 3, a developing device 4, a transfer roller 7, a cleaning device 8, and a static eliminator (not shown) are arranged along the rotation direction (clockwise) of the photosensitive drum 1. The photosensitive drum 1 is, for example, an aluminum drum with a photosensitive layer laminated on it. The photosensitive layer is not particularly limited, but is preferably made of, for example, amorphous silicon (a-Si), which has excellent durability, or an organic photosensitive layer (OPC), which generates little ozone when charged and can produce high-resolution images.

[0014] The charging unit 2 uniformly charges the photosensitive layer on the surface of the photosensitive drum 1. For example, the charging unit 2 may be a corona discharge device that discharges by applying a high voltage using a thin wire or the like as an electrode. Note that instead of a corona discharge device, a contact-type charging device may be used in which a voltage is applied while a charging member, such as a charging roller, is in contact with the surface of the photosensitive drum 1. The exposure unit 3 irradiates the surface of the photosensitive drum 1, which has been charged by the charging unit 2, with a light beam (e.g., a laser beam) based on image data, and forms an electrostatic latent image on the surface of the photosensitive drum 1 by attenuating the charge.

[0015] The developing device 4 forms a toner image by adhering toner to the electrostatic latent image formed on the surface of the photosensitive drum 1. Note that the developing device 4 contains a one-component developer (hereinafter simply referred to as toner) composed only of a magnetic toner component. The developing device 4 will be described in detail later. The transfer roller 7 transfers the toner image formed on the surface of the photosensitive drum 1 to paper being transported along the paper transport path 11. The cleaning device 8 includes a cleaning roller or blade that makes linear contact with the photosensitive drum 1 in the longitudinal direction, and removes residual toner from the surface of the photosensitive drum 1 after the toner image has been transferred to the paper.

[0016] When forming an image, first the surface of the photosensitive drum 1 is uniformly charged by the charging unit 2. Then, based on image data input in advance, the exposure unit 3 irradiates the photosensitive drum 1 with a laser beam (light beam), thereby forming an electrostatic latent image based on the image data on the surface of the photosensitive drum 1. After that, the developing device 4 attaches toner to the electrostatic latent image to form a toner image.

[0017] As described above, paper is transported at a predetermined timing from paper storage unit 10 via paper transport path 11 and registration roller pair 13 toward image forming unit 9, where the toner image is formed, and the toner image on the surface of photosensitive drum 1 is transferred to the paper by transfer roller 7 in image forming unit 9. The paper with the transferred toner image is then separated from photosensitive drum 1 and transported to fixing unit 12, where the toner image is fixed to the paper by heating and pressure. After passing through fixing unit 12, the paper passes through discharge roller pair 14 and is discharged to paper discharge unit 15.

[0018] FIG. 2 is a side cross-sectional view of the developing device 4 mounted in the image forming apparatus 100. FIG. 2 shows the developing device 4 as seen from the rear side of FIG. 1, and the arrangement of components within the developing device 4 is symmetrical to that in FIG. 1. As shown in FIG. 2, within the developing container 20, a first transport chamber 21 and a second transport chamber 22 are formed by a partition wall 20a formed integrally with the developing container 20. A first agitating and transporting screw 23 is disposed in the first transport chamber 21, and a second agitating and transporting screw 24 is disposed in the second transport chamber 22. A toner supply port 20b is provided at the top of the developing container 20, and toner stored in a toner container 5 (see FIG. 1) is supplied therethrough in accordance with the detection result of a toner sensor 26 that detects the amount of toner in the developing container 20.

[0019] The first agitation / conveyance screw 23 and the second agitation / conveyance screw 24 each have a support shaft around which a spiral blade is provided, and are rotatably supported in parallel to each other in the developing container 20. The partition walls 20a are not present at both ends of the longitudinal direction of the developing container 20 (the direction perpendicular to the plane of FIG. 2 ), which is the axial direction of the first agitation / conveyance screw 23 and the second agitation / conveyance screw 24, allowing toner to be transferred between the first conveying chamber 21 (first agitation / conveyance screw 23) and the second conveying chamber 22 (second agitation / conveyance screw 24). The first agitation / conveyance screw 23 agitates the toner in the first conveying chamber 21 and transports it in a predetermined direction (first direction) to transfer it to the second conveying chamber 22. The second agitation / conveyance screw 24 agitates the toner transferred from the first conveying chamber 21 to the second conveying chamber 22 and transports it in the opposite direction (second direction) to the first agitation / conveyance screw 23, thereby supplying it to the developing roller 25.

[0020] The developing roller 25 is rotatably supported on the developing container 20 in a state parallel to the first stirring / conveying screw 23 and the second stirring / conveying screw 24. A fixed magnet 27 made of a permanent magnet with multiple magnetic poles is fixed inside the developing roller 25. The magnetic force of this fixed magnet 27 causes toner to adhere (be carried) on the surface of the developing roller 25, forming a thin toner layer. A portion of the outer circumferential surface of the developing roller 25 is exposed from the opening 20c of the developing container 20, and the developing roller 25 is disposed so that the exposed portion faces the photosensitive drum 1 (see FIG. 1).

[0021] The developing roller 25, on which the thin toner layer is formed, rotates in accordance with the rotation of the photosensitive drum 1, thereby supplying the toner to the photosensitive layer of the photosensitive drum 1. The first agitating / conveying screw 23, the second agitating / conveying screw 24, and the developing roller 25 are driven to rotate at a predetermined speed by a developing drive motor 35 (see FIG. 4) and a gear train. Magnetic seal members 28 are also provided on both ends of the developing roller 25 to prevent developer leakage from the gap between the developing container 20 and the developing roller 25.

[0022] The regulating blade 29 is formed so that its longitudinal length is larger than the maximum development width of the developing roller 25, and is disposed at a predetermined distance from the developing roller 25 to form a regulating portion 30 that regulates the amount of toner supplied to the photosensitive drum 1. The gap of the regulating portion 30 is set to approximately 0.2 mm to 0.4 mm. The regulating blade 29 is made of a magnetic material or a non-magnetic material such as SUS (stainless steel). Here, a permanent magnet 31 is attached to the magnetic regulating blade 29 to give it magnetism.

[0023] The fixed magnet 27 has multiple (four in this example) magnetic poles consisting of a main pole N1, a regulating pole S1, a transport pole S2, and a pumping pole N2. Since the regulating pole S1 of the fixed magnet 27 faces the regulating blade 29, magnetic field lines are concentrated at the tip of the regulating blade 29, generating a magnetic field in the regulating portion 30 in an attractive direction.

[0024] This magnetic field forms a magnetic brush (toner chain) of linked toner particles between the regulating blade 29 and the developing roller 25. The magnetic brush is regulated by passing through the regulating portion 30, and a thin toner layer is formed on the developing roller 25. By using a magnetic blade for the regulating blade 29, the regulating force is increased not only by the gap between the regulating portions 30 but also by the magnetic field generated in the regulating portions 30, and a thin toner layer of several tens of μm is formed on the developing roller 25.

[0025] Meanwhile, toner not used to form the thin toner layer accumulates along the side surface on the upstream side (lower side in Figure 2) of regulating blade 29. Thereafter, when developing roller 25 rotates clockwise in Figure 2 and the magnetic brush moves to a position facing photosensitive drum 1, the magnetic brush is given a magnetic field by main pole N1 of fixed magnet 27, causing it to stand up and come into contact with the surface of photosensitive drum 1 to form a toner image.

[0026] When developing roller 25 further rotates clockwise, transport pole S2 applies a magnetic field in a direction along the outer circumferential surface of developing roller 25, and toner not used in forming a toner image is collected onto developing roller 25 along with the magnetic brush. Furthermore, the magnetic brush detaches from developing roller 25 in the missing portion between transport pole S2 and pumping pole N2 and falls into housing 20. Then, after being stirred and transported by second stirring / transporting screw 24, a magnetic brush is again formed on developing roller 25 by the magnetic field of pumping pole N2.

[0027] 3 is a side cross-sectional view showing the internal configuration of the toner container 5 that supplies toner to the developing device 4. The toner container 5 includes a container vessel 51 that stores toner, a supply spiral 52, and an agitating paddle 53.

[0028] The container 51 has a toner delivery opening 51a that faces the toner supply opening 20b of the developing device 4 (see FIG. 2).

[0029] Supply spiral 52 is rotatably provided at the bottom of container 51, with one end facing toner outlet 51a. Supply spiral 52 is composed of a rotary shaft 52a and conveying blades 52b formed in a spiral shape at a constant pitch on the outer circumferential surface of rotary shaft 52a. When supply spiral 52 rotates in a predetermined direction (counterclockwise in FIG. 3), toner is conveyed toward toner outlet 51a.

[0030] The agitating paddle 53 is composed of a rotating shaft 53a and a paddle-shaped agitating blade 53b that extends radially from the rotating shaft 53a and unfolds in the axial direction. When the agitating paddle 53 rotates in a predetermined direction (counterclockwise in FIG. 3), it agitates the toner in the container 51. The supply spiral 52 and the agitating paddle 53 are rotated by the container drive motor 37 (see FIG. 4).

[0031] 4 is a block diagram showing an example of a control path used in the image forming apparatus 100 of this embodiment. Note that, since various controls are performed on each section of the image forming apparatus 100 when the image forming apparatus 100 is used, the control path for the entire image forming apparatus 100 becomes complex. Therefore, the following description will focus on the parts of the control path that are necessary for implementing the present invention.

[0032] The image input unit 40 receives image data transmitted from a personal computer or the like to the image forming apparatus 100. The image signal input from the image input unit 40 is converted into a digital signal and then sent to the temporary storage unit 94.

[0033] The operation unit 70 is provided with a liquid crystal display unit 71 and an LED 72 that indicates various states, and is configured to indicate the state of the image forming apparatus 100, the image formation status, and the number of copies to be printed. Various settings for the image forming apparatus 100 are made using a printer driver on a personal computer.

[0034] In addition, the operation unit 70 is provided with a start button that the user uses to instruct the start of image formation, a stop / clear button that is used when stopping image formation, and a reset button that is used to reset various settings of the image forming apparatus 100 to their default states.

[0035] The transmitting / receiving unit 80 communicates with the outside world using a telephone line or an internet line. More specifically, the transmitting / receiving unit 80 receives a print command including image data transmitted from a host device such as a personal computer. The received image data is stored in the temporary storage unit 94.

[0036] The control unit 90 includes at least a CPU (Central Processing Unit) 91 as a central processing unit, a ROM (Read Only Memory) 92 as a read-only memory, a RAM (Random Access Memory) 93 as a readable and writable memory, a temporary memory 94 that temporarily stores image data and the like, a counter 95, a plurality of (here, two) I / Fs (interfaces) 96 that transmit control signals to each device in the image forming apparatus 100 and receive input signals from the operation unit 50, and a calculation unit 97. The control unit 90 can be placed anywhere in the image forming apparatus 100.

[0037] The ROM 92 stores data that will not change while the image forming apparatus 100 is in use, such as control programs for the image forming apparatus 100 and numerical values ​​necessary for control. The RAM 93 stores necessary data generated during the control of the image forming apparatus 100 and data temporarily required for the control of the image forming apparatus 100. The RAM 93 (or ROM 92) also stores the cumulative number of printed sheets since the installation mode was executed, the cumulative driving time of the development drive motor 35, and other data that are used when executing reverse rotation control of the development roller 25, which will be described later. The temporary storage unit 94 temporarily stores the image signal that is input from the image input unit 40 and converted into a digital signal. The counter 95 cumulatively counts the number of printed sheets.

[0038] Furthermore, the control unit 90 transmits control signals from the CPU 91 to each part and device in the image forming apparatus 100 via the I / F 96. Furthermore, signals indicating the state of each part and device and input signals are transmitted from each part and device to the CPU 91 via the I / F 96. Examples of each part and device controlled by the control unit 90 include the image forming unit 9, the fixing unit 12, the developing drive motor 35, the container drive motor 37, the image input unit 40, the operation unit 70, and the transmitting / receiving unit 80.

[0039] In the image forming apparatus 100 of this embodiment, when the toner in the developing device 4 runs out, the developing device 4 is removed and replaced with an unused developing device 4, and an installation mode is executed in which a larger amount of toner is supplied from the toner container 5 to the developing device 4 than when toner is replenished during image formation (normal replenishment). Alternatively, even if the developing device 4 has not been replaced, the installation mode may be executed to stabilize the charge state of the toner, for example, when the toner container 5 is replaced and new toner is replenished.

[0040] In the install mode, a fixed amount of toner is supplied from the toner container 5 to the developing device 4, and the first agitating / conveying screw 23, the second agitating / conveying screw 24, and the developing roller 25 are rotated for a fixed period of time in the same direction (forward direction) as during image formation. This stabilizes the charge amount of the toner supplied into the developing device 4.

[0041] The toner supplied to the developing device 4 during toner installation has low fluidity and an unstable charge amount. Therefore, when the above-described installation mode is executed, the toner remaining in the regulating section 30 will soften and aggregate due to the continued forward rotation of the developing roller 25 for a certain period of time, causing clogging. Therefore, in this embodiment, a developer removal operation can be executed to remove the toner (developer) remaining in the regulating section 30 during installation mode. The developer removal operation will be described in detail below.

[0042] In the developer removal operation, when no image is being formed, the developing roller 25 is rotated a predetermined amount (predetermined angle) in the opposite direction to that during image formation (counterclockwise in FIG. 2). This causes a force in the rotation direction of the developing roller 25 to act on the aggregated toner adhering to the tip of the regulating blade 29. As a result, the aggregated toner detaches from the tip of the regulating blade 29. The aggregated toner detached from the tip of the regulating blade 29 comes into contact with and mixes with the toner in the second transport chamber 22 due to the reverse rotation of the developing roller 25, and is removed from the surface of the developing roller 25.

[0043] At this time, if the reverse rotation angle of the developing roller 25 is small (the amount of reverse rotation is small), the effect of removing toner aggregates will be insufficient, and if the reverse rotation angle is large (the amount of reverse rotation is large), toner may leak from the opening 20c of the developing container 20 where the developing roller 25 is exposed. Therefore, it is preferable to specify the reverse rotation angle (amount of reverse rotation) of the developing roller 25 when performing the developer removal operation.

[0044] 7, the upper limit of the reverse rotation angle of the developing roller 25 is set to an angle θ1 at which a position R1 (first opposing position) facing the downstream end in the reverse rotation direction of the toner presence area in the second transport chamber 22 at the start of reverse rotation moves to the lower edge 20d of the opening 20c of the developing container 20. The lower limit of the reverse rotation angle of the developing roller 25 is set to an angle at which a position R2 (second opposing position) facing the regulating blade 29 at the start of reverse rotation moves to a height h of the upper surface (agent surface) of the toner present in the second transport chamber 22 of the developing container 20 when the second stirring / transporting screw 24 is stopped.

[0045] By specifying the upper and lower limits of the reverse rotation angle of the developing roller 25 as described above, it is possible to effectively remove the toner Tg that has softly aggregated in the regulating section 30 while preventing toner leakage from the opening 20c of the developing container 20.

[0046] 5 is a flowchart showing a first control example of the installation mode executed in image forming apparatus 100 of this embodiment. The first control example of the installation mode will be described along the steps of FIG. 5, with reference to FIGS. 1 to 4 and FIGS. 6 and 7, which will be described later, as needed.

[0047] When the install mode is started (step S1), the control unit 90 detects the amount of toner in the developing device 4 by the toner sensor 26 (step S2). The detection result of the toner sensor 26 is sent to the control unit 90.

[0048] Next, the control unit 90 supplies a predetermined amount of toner from the toner container 5 to the developing device 4 in accordance with the detection result of the toner sensor 26 (step S3). For example, when no toner is detected in the developing device 4, the control unit 90 determines that the developing device 4 has been replaced with an unused one, and sends a control signal to the container drive motor 37 to supply the initial amount of toner from the toner container 5 to the developing device 4. On the other hand, when toner is detected in the developing device 4, the control unit 90 determines that the installation mode has been executed to stabilize the charge state of the toner, and sends a control signal to the container drive motor 37 to supply toner until the amount of toner in the developing device 4 reaches a specified level.

[0049] The control unit 90 drives the developing device 4 to rotate in the forward direction in parallel with the supply of toner (step S4). FIG. 6 is a side view showing the driving state of the developing device 4 during execution of the install mode. The control unit 90 sends a control signal to the developing drive motor 35, which rotates the first agitating and conveying screw 23, the second agitating and conveying screw 24, and the developing roller 25 in the same direction as during image formation (forward direction, clockwise in FIG. 6), as shown in FIG. 6. By continuing this forward rotation drive for a predetermined period of time, the charge amount of the toner in the developing device 4 is increased to a level at which printing is possible.

[0050] Next, the control unit 90 determines whether the installation mode has ended (step S5). If the installation mode is still in progress (No in step S5), the process returns to step S3 and continues to supply toner and drive the developing device 4 in the forward direction. If the installation mode has ended (Yes in step S5), the developing roller 25 is rotated in the reverse direction (step S6), and the process ends.

[0051] 7 is an enlarged view of the vicinity of the developing roller 25 and the second agitating / conveying screw 24 when the developing roller 25 is rotated in reverse. As shown in FIG. 7, the position R2 of the developing roller 25 facing the regulating blade 29 at the start of the reverse rotation is reversed to a height h of the upper surface of the toner T in the second conveying chamber 22 when the second agitating / conveying screw 24 is not driven. This ensures that the aggregated toner Tg present in the regulating portion 30 at the start of the reverse rotation comes into contact with and is mixed with the toner T in the second conveying chamber 22.

[0052] 5, by rotating the developing roller 25 in the reverse direction at the end of the installation mode, as shown in FIG. 7, the toner Tg that has softly aggregated near the regulating unit 30 when the developing roller 25 starts to rotate in the reverse direction comes into contact with and mixes with the transported toner T around the second stirring / conveying screw 24 as the developing roller 25 rotates in the reverse direction and then rotates forward again after the reverse rotation, thereby reliably resetting (replacing) the toner in the regulating unit 30. This effectively suppresses toner aggregation in the regulating unit 30, and can suppress image defects such as uneven shading and white streaks in halftone images printed immediately after the installation mode ends.

[0053] 8 is a flowchart showing a second control example of the install mode executed in image forming apparatus 100 of this embodiment. The second control example of the install mode will be described along the steps of FIG. 8, with reference to FIGS. 1 to 4, 6, and 7 as necessary. The steps (steps S1 to S4) from when the install mode is started, to when the amount of toner in developing device 4 is detected, when a predetermined amount of toner is supplied from toner container 5 to developing device 4 according to the detection result, and when developing device 4 is driven to rotate in the forward direction in parallel with the supply of toner, are the same as those in the first control example shown in FIG.

[0054] Next, the control unit 90 determines whether a predetermined time (e.g., 10 minutes) has elapsed since the start of toner supply and forward rotation of the developing device 4 (step S5). If the predetermined time has elapsed (Yes in step S5), the control unit 90 rotates the developing roller 25 in the reverse direction as shown in Fig. 7 (step S6). If the predetermined time has not elapsed (No in step S5), the control unit 90 determines whether the installation mode has ended (step S7).

[0055] If the installation mode continues (No in step S7), the process returns to step S3 and continues to supply toner and drive the developing device 4 in the forward direction. Then, if the predetermined time has elapsed again (Yes in step S5), the developing roller 25 is rotated in the reverse direction (step S6). The above steps S3 to S7 are repeated until the installation mode ends. If the installation mode ends (Yes in step S7), the developing roller 25 is rotated in the reverse direction (step S8) as in the first control example, and the process ends.

[0056] 8, by rotating the developing roller 25 in the reverse direction at predetermined intervals not only when the installation mode ends but also while the installation mode is running, toner that has softly aggregated near the restricting portion 30 is reset during the installation mode. This makes it possible to end the installation mode without causing soft aggregation of toner, and more effectively suppress image defects such as uneven shading and white streaks in halftone images printed immediately after the installation mode ends.

[0057] Incidentally, even if the developing roller 25 is rotated in the reverse direction at the end of the installation mode as described above to remove the toner that has softly agglomerated near the regulating portion 30, if the developing operation is continued after the end of the installation mode, the toner is likely to softly agglomerate around the regulating portion 30 in the developing device 4. Therefore, even after the end of the installation mode, it is preferable to execute a developer removing operation for rotating the developing roller 25 in the reverse direction to reset the toner that has softly agglomerated around the regulating portion 30 every time the number of printed sheets reaches a predetermined number.

[0058] FIG. 9 is a flowchart showing an execution procedure of the developer removing operation after the end of the installation mode executed in the image forming apparatus 100 of the present embodiment. The developer removing operation after the end of the installation mode will be described along the steps of FIG. 9 while referring to FIGS. 1 to 4, FIG. 6, and FIG. 7 as necessary.

[0059] First, the control unit 90 determines whether or not a print command has been received (step S1). If a print command has not been received (No in step S1), the printing standby state is continued. If a print command has been received (Yes in step S1), printing is executed (step S2). Also, the counter 95 counts the cumulative number of printed sheets N from the immediately preceding developer removing operation (step S3).

[0060] Next, the control unit 90 determines whether or not the cumulative number of printed sheets N has become equal to or greater than a threshold value N1 (for example, 100 sheets) after the printing is completed (step S4). If N < N1 (No in step S4), the process returns to step S1 and the printing standby state is continued.

[0061] If N ≧ N1 (Yes in step S4), the developing roller 25 is rotated in the reverse direction as shown in FIG. 7 (step S5). Then, N is reset (N = 0) (step S6), and the process returns to step S1, and the same procedure is repeated thereafter.

[0062] Next, a method for determining the threshold value of the cumulative number of printed sheets N, which serves as a trigger for reversely rotating the developing roller 25, will be described. The toner immediately after the installation mode ends has low fluidity and an unstable charge amount. Therefore, soft aggregation of the toner in the regulation unit 30 is likely to occur. Thereafter, as the developing operation is performed, the toner in the developing container 20 is agitated and its fluidity gradually improves, and the charge amount also becomes stable.

[0063] Also, when the elapsed time after the installation mode ends becomes even longer, the fluidity of the toner decreases due to deterioration of the toner caused by endurance printing, and soft aggregation of the toner in the regulation unit 30 is likely to occur again.

[0064] Therefore, in the present embodiment, when the developing drive time after the installation mode ends becomes longer, the threshold value is increased. That is, when the developing drive time becomes longer, the execution frequency of the reverse rotation operation of the developing roller 25 is decreased. Also, when the developing drive time after the installation mode ends becomes even longer, the threshold value is decreased again. That is, when the developing drive time becomes even longer, the execution frequency of the reverse rotation operation of the developing roller 25 is increased again.

[0065] FIG. 10 is a flowchart showing a procedure for setting the execution interval of the developer removal operation after the installation mode ends, which is executed in the image forming apparatus 100 of the present embodiment. In the control example of FIG. 10, the threshold value of the cumulative number of printed sheets N immediately after the installation mode ends is set to N1 (= 30 [sheets]).

[0066] First, the control unit 90 determines whether a print command has been received (step S1). If a print command has not been received (No in step S1), the print standby state is continued. If a print command has been received (Yes in step S1), printing is executed (step S2). Also, the developing drive time T after toner installation ends is measured (step S3).

[0067] Next, the control unit 90 determines whether the developing drive time T has become equal to or longer than a predetermined time T1 (a first predetermined value, for example, 1 hour) (step S4). If T < T1 (No in step S4), the process returns to step S1 and the print standby state is continued.

[0068] When T≥T1 (Yes in step S4), next, it is determined whether the development driving time T has become equal to or longer than a predetermined time T2 (a second predetermined value, for example, 10 hours) (step S5). When T1≤T<T2 (No in step S5), the threshold value N2 (N2>N1, for example, N2 = 100 [sheets]) of the cumulative number of printed sheets N that triggers the reverse rotation operation of the developing roller 25 is set (step S6). Then, the process returns to step S1, and the developer removal operation after toner installation shown in FIG. 9 is executed using the threshold value N2.

[0069] When T≥T2 in step S5 (Yes in step S5), the threshold value N2 of the cumulative number of printed sheets N that triggers the reverse rotation operation of the developing roller 25 is set to N1 (step S7). Then, the setting of the execution interval of the developer removal operation is terminated, and thereafter, the developer removal operation after toner installation shown in FIG. 9 is executed using the threshold value N1.

[0070] According to the control examples shown in FIGS. 9 and 10, immediately after the end of the installation mode in which soft aggregation of toner in the regulation unit 30 is likely to occur, the threshold value of the cumulative number of printed sheets N that triggers the reverse rotation operation of the developing roller 25 is set to N1 (= 30 [sheets]). Therefore, the execution frequency of the reverse rotation operation of the developing roller 25 increases. Therefore, soft aggregation of toner in the regulation unit 30 immediately after the end of the installation mode can be effectively suppressed.

[0071] On the other hand, as the elapsed time after the end of the installation mode becomes longer, the agitation of the toner in the developing container 20 progresses, the fluidity of the toner increases, and the charge amount becomes stable. Therefore, when the development driving time after the end of the installation mode becomes equal to or longer than the predetermined time T1, the threshold value of the cumulative number of printed sheets N is set to N2 (= 100 [sheets]), and the execution frequency of the reverse rotation operation of the developing roller 25 is lowered. Thereby, the frequency of the reverse rotation operation of the developing roller 25 is set to the minimum frequency necessary for suppressing soft aggregation of toner in the regulation unit 30, and soft aggregation of toner in the regulation unit 30 can be suppressed without significantly reducing the image forming efficiency (productivity).

[0072] As the time that has passed since the installation mode ended becomes even longer, the fluidity of the toner decreases as the toner deteriorates, making it more likely that the toner will agglomerate in the restriction unit 30. Therefore, when the development drive time after the installation mode ended reaches or exceeds the predetermined time T2, the threshold value for the cumulative number of printed sheets N is again set to N1 (=30 sheets), and the frequency of the reverse rotation operation of the development roller 25 is increased. This makes it possible to effectively suppress the agglomeration of the toner caused by the toner deterioration due to the long-term printing.

[0073] In FIG. 10, the development drive time T after the end of the installation mode is used as a trigger for changing the threshold value of the cumulative number of printed sheets N for executing the reverse rotation operation from N1 to N2 (or from N2 to N1), but the cumulative number of printed sheets N' after the end of the installation mode can also be used instead of the development drive time.

[0074] Here, the relationship between the number of prints and the development drive time differs depending on whether the printing is continuous or single-shot (intermittent) printing. For example, in the case of continuous printing, the development drive time T is 1 hour for 2 to 3k sheets, and in the case of single-shot printing, the development drive time T is 1 hour for 1k sheets. Therefore, if the cumulative number of prints N' after the end of the installation mode is used as a trigger for changing the threshold for the cumulative number of prints N from N1 to N2 (or from N2 to N1), it is preferable to change the threshold for the cumulative number of prints N' between continuous printing and single-shot printing.

[0075] Also, in Figure 10, when the development drive time after the end of the installation mode reaches or exceeds a predetermined time T2, the threshold value for the cumulative number of printed sheets N at which the reverse rotation operation is performed is changed from N2 to N1 again, but the threshold value may also be changed to a threshold value that is smaller than N2 and different from N1.

[0076] The present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention. For example, in the above embodiment, the fixed magnet 27 disposed in the developing roller 25 of the developing device 4 has a four-pole configuration with two north poles and two south poles, but the present invention is also applicable to a fixed magnet 27 with a five-pole or three-pole configuration.

[0077] Furthermore, in the above embodiment, a toner sensor 26 is provided to detect the amount of toner in the developing container 20, and toner is supplied (normal replenishment) from the toner container 5 to the developing device 4 in accordance with the detection result of the toner sensor 26, but a toner replenishment method that does not use the toner sensor 26 may also be used. Specifically, it is also possible to apply a leveling method (volume replenishment method) in which, when toner in the developing device 4 is consumed by a printing operation and the toner volume decreases, toner equivalent to the decrease is replenished from the toner container 5 to the developing device 4.

[0078] Furthermore, the present invention is not limited to monochrome printers such as those shown in FIG. 1, but can also be applied to various image forming apparatuses equipped with a developing device using a magnetic single-component development system, such as digital or analog monochrome copiers, color printers, color copiers, and facsimiles. [Industrial Applicability]

[0079] The present invention can be applied to an image forming apparatus using a magnetic single-component developing device, and can provide an image forming apparatus that can effectively suppress image defects caused by toner aggregation around a regulating member immediately after developer installation. [Explanation of symbols]

[0080] 1 Photosensitive drum (image carrier) 4. Developing device 5 Toner container (developer storage container) 9 Image forming unit 20 Developer container 20c opening 23 First stirring and conveying screw (stirring and conveying member) 24 Second stirring and conveying screw (stirring and conveying member) 25 Developing roller (developer carrier) 26 Toner sensor (developer amount detection sensor) 27 Fixed Magnet 29 Regulating blade (regulating member) 30 Regulatory Department 90 Control Unit 100 Image forming device

Claims

1. an image carrier having a photosensitive layer formed on its surface; a developer container containing a magnetic one-component developer consisting of only magnetic toner; a developer carrier that is rotatably supported by the developer container, carries the developer on its outer circumferential surface, and is exposed through an opening of the developer container to face an image carrier; one or more stirring and conveying members rotatably supported by the developing container and configured to stir and convey the developer in the developing container; a regulating member that is disposed at a predetermined interval from the developer carrying member and forms a regulating portion that regulates the layer thickness of the developer carried on the developer carrying member; a developing device for developing an electrostatic latent image formed on the image carrier; a developer storage container for storing the developer to be replenished to the developing device; a control unit that controls driving of the developing device and supplying the developer from the developer storage container to the developing device; Equipped with The control unit normal replenishment of the developer from the developer storage container to the developing device in accordance with the amount of the developer consumed by a printing operation; an install mode in which a larger amount of the developer than the normal replenishment is replenished from the developer storage container to the developing device and the developer carrier is rotated for a predetermined time in a forward direction, which is a rotation direction during image formation; the control unit, immediately after the execution of the installation mode is completed, executes a developer removal operation in which the developer carrier is rotated in a direction opposite to the forward direction to remove the developer remaining between the regulating member and the developer carrier.

2. 2. The image forming apparatus according to claim 1, wherein the control unit executes the developer removal operation every time a predetermined time elapses during execution of the installation mode.

3. the control unit continues the developer removal operation every time the number of printed sheets reaches a predetermined number even after the installation mode has ended, 3. The image forming apparatus according to claim 1, wherein the frequency of the developer removal operation is reduced after the cumulative operating time or cumulative number of prints of the developing device after execution of the installation mode reaches a first predetermined value.

4. 4. The image forming apparatus according to claim 3, wherein the control unit increases the frequency of the developer removal operation again after the cumulative driving time or the cumulative number of printed sheets reaches a second predetermined value that is greater than the first predetermined value.

5. 5. The image forming apparatus according to claim 1, wherein an upper limit value of the reverse rotation angle of the developer carrier during the developer removal operation is an angle at which a first opposing position of the developer carrier, which faces the downstream end of the developer presence area in the developing container in the reverse rotation direction, moves to the edge of the opening when the reverse rotation starts, and a lower limit value of the reverse rotation angle is an angle at which a second opposing position of the developer carrier, which faces the regulating member when the reverse rotation starts, moves to the upper surface of the developer present in the vicinity of the developer carrier in the developing container when the stirring and transporting member is stopped.

Images