Image forming apparatus, carrier discharge method, and program

Abstract

To provide an image forming apparatus, a carrier discharge method, and a program with which a defective carrier in a developer can be appropriately reduced to stabilize image quality.SOLUTION: An image forming apparatus has: a developing device that can supply a developer including a toner and a carrier to an image carrier; and a control unit that controls an operation of an image forming unit including the developing device. The developing device has: a developer storage unit that stores the developer; a developer supply unit that supplies the developer according to the concentration of toner in the developer storage unit; and a developer carrier that supplies the developer to the image carrier. The control unit executes carrier discharge processing of selectively discharging a defective carrier according to a ratio of the defective carrier in the developer stored in the developer storage unit.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus that uses a two-component developer for development, a carrier discharge method, and a program. [Background technology]

[0002] In image forming devices (printers, copiers, facsimiles, etc.) that utilize electrophotographic process technology, a laser beam based on image data is irradiated (exposed) onto a uniformly charged photoconductor, forming an electrostatic latent image on the surface of the photoconductor. Then, toner is supplied to the photoconductor, making the electrostatic latent image visible as a toner image. This toner image is indirectly transferred to a recording material, for example, via an intermediate transfer member, and then heated and pressed in a fixing unit. Through these steps, an image is formed on the recording material.

[0003] There are two types of development methods for forming a toner image on a photoreceptor: one-component development, which uses only toner as the main component of the developer, and two-component development, which uses toner and carrier as the main components of the developer. It is known that in two-component development, the carrier's charging performance deteriorates due to the accumulation of mechanical and thermal stress caused by contact with the toner, which reduces the particle size of the carrier, and the carrier's surface becoming soiled due to toner adhesion. Hereinafter, carriers that do not have the desired charging performance suitable for development are referred to as "defective carriers," and carriers that can exhibit the desired charging performance are referred to as "normal carriers."

[0004] If there is an excess of defective carrier in the developer, the carrier will be supplied to the photoconductor along with the toner. When the image is transferred from the photoconductor to a receiving material (e.g., an intermediate transfer belt), the carrier is pressed against the photoconductor at the transfer nip, which can leave small carrier marks on the photoconductor surface and damage the surface. Furthermore, when the carrier is transferred onto the recording material, image defects (white spots) occur, resembling fireflies where the toner is missing in those areas.

[0005] Therefore, in two-component development systems, trickle development is widely adopted to stabilize the charge level of the developer, for example, by supplying new developer while discharging excess developer (see, for example, Patent Document 1). The developer discharged by trickle development includes not only defective carrier but also normal carrier. In Patent Document 1, the surface of the stirring screw is formed from a magnetized material, so that normal carrier, which has high charging performance and is held by the stirring screw by magnetic attraction, is mainly used for development, and when the developer is discharged, defective carrier that has fallen off the stirring screw by centrifugal force is discharged. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-118149 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the method described in Patent Document 1, defective carrier that has fallen off the stirring screw is not immediately discharged but remains in the developing container, and may adhere to the stirring screw again, be transported, and be used for development. In other words, the method described in Patent Document 1 cannot be said to be able to sufficiently separate and discharge defective carrier. Furthermore, while sufficient separation can be achieved by enlarging the developing container to prevent the fallen defective carrier from adhering again to the stirring screw, issues such as increased costs arise due to the larger size of the developing device, which reduces business viability.

[0008] There is also a method of electrically developing carrier instead of toner onto a photosensitive member and recovering it, but when developing and discharging defective carrier, a high voltage is applied, which may result in discharging not only defective carrier but also normal carrier, which may increase development costs.

[0009] An object of the present invention is to provide an image forming apparatus, a carrier discharging method, and a program that can appropriately reduce defective carrier in a developer and stabilize image quality. [Means for solving the problem]

[0010] The image forming apparatus according to the present invention comprises: a developing device capable of supplying a developer containing toner and a carrier to an image carrier; a control unit that controls the operation of an image forming unit including the developing device, The developing device is a developer storage section that stores the developer; a developer supply unit that supplies the developer in accordance with the toner concentration in the developer container; a developer carrier that supplies the developer to the image carrier; The control unit executes a carrier discharge process for selectively discharging defective carriers in accordance with a ratio of defective carriers in the developer contained in the developer container.

[0011] The carrier discharge method according to the present invention includes the steps of: A carrier discharge method for controlling the amount of defective carrier in a developing device capable of supplying a developer containing toner and carrier to an image carrier, comprising: acquiring a ratio of defective carriers in the developer contained in a developer container of the developing device; and selectively discharging the defective carriers in accordance with the proportion of the acquired defective carriers.

[0012] The program according to the present invention comprises: A program for causing a computer to execute a process for controlling the amount of defective carrier in a developing device capable of supplying a developer containing toner and carrier to an image carrier, the program comprising: A process of acquiring a ratio of defective carriers in the developer accommodated in a developer accommodating section of the developing device; and selectively discharging the defective carriers in accordance with the acquired proportion of the defective carriers. [Effects of the Invention]

[0013] According to the present invention, it is possible to appropriately reduce defective carrier in the developer and stabilize image quality. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing a schematic overall configuration of the image forming apparatus main body. [Figure 2] FIG. 2 is a diagram showing the main parts of a control system of the image forming apparatus. [Figure 3] FIG. 3 is a cross-sectional view showing an example of the internal configuration of the developing device. [Figure 4] FIG. 4 is a diagram showing an example of carrier adhesion ranks relative to the proportion of defective carriers. [Figure 5] FIG. 5 is a diagram showing an example of the carrier adhesion rank setting table. [Figure 6] FIG. 6 is a diagram showing an example of particle size distribution of carrier in the replenished developer. [Figure 7] FIG. 7 is a diagram showing an example of the relationship between the particle diameter of the carrier and the number of rotations of the roller. [Figure 8] FIG. 8 is a diagram showing the particle size distribution of the carrier discharged when the developing roller is driven at the calculated rotation speed. [Figure 9] FIG. 9 is a diagram showing the particle size distribution of the carrier in the developer after the carrier discharging process is performed. [Figure 10] FIG. 10 is a diagram showing an example of a change in the proportion of defective carrier in a developer during printing processing. [Figure 11] FIG. 11 is a flowchart showing an example of processing in the defective carrier discharge mode. [Figure 12] 12A and 12B are diagrams showing changes in the proportion of defective carriers and changes in the carrier adhesion rank when printing is performed in the defective carrier discharge mode. [Figure 13]FIG. 13 is a diagram showing the number of dents on the photosensitive drum when printing is performed at a printing rate of 10% in the defective carrier discharge mode. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0016] Fig. 1 is a diagram showing the overall configuration of an image forming apparatus 1 according to an embodiment of the present invention, Fig. 2 is a diagram showing the main parts of a control system of the image forming apparatus 1.

[0017] 1 and 2 is an intermediate transfer type color image forming apparatus that uses electrophotographic process technology. The image forming apparatus 1 primarily transfers toner images of each color (Yellow, M, C, and K) formed on a photosensitive drum 213 onto an intermediate transfer belt 221, and then superimposes the four color toner images on the intermediate transfer belt 221, and then secondarily transfers the images onto a recording material, thereby forming an image.

[0018] In this embodiment, the image forming apparatus 1 employs a vertical tandem system in which photosensitive drums 213 corresponding to the four colors CMYK are arranged in series in the running direction (vertical direction) of the intermediate transfer belt 221, and each color toner image is transferred sequentially to the intermediate transfer belt 221 in a single step.

[0019] As shown in Figures 1 and 2, the image forming apparatus 1 includes an image reading unit 11, an operation display unit 12, an image processing unit 13, a paper feeding unit 14, a paper discharge unit 15, a recording material conveying unit 16, an image forming unit 20, and a control unit 30.

[0020] The control unit 30 controls the image forming apparatus 1 as a whole by controlling the image reading unit 11, the operation display unit 12, the image processing unit 13, the paper feeding unit 14, the paper discharge unit 15, the recording material conveying unit 16, and the image forming unit 20 according to their respective functions.

[0021] The control unit 30 includes a CPU (Central Processing Unit) 31 as an arithmetic / control device, a ROM (Read Only Memory) 32 as a main storage device, and a RAM (Random Access Memory) 33. The ROM 32 stores basic programs and basic setting data. The ROM 32 also stores programs for implementing image formation processing, such as a program for a defective carrier discharge mode. The CPU 31 reads out a program corresponding to the processing content from the ROM 32, loads it into the RAM 33, and executes the loaded program to control the operation of each functional block of the image forming apparatus 1.

[0022] In this embodiment, the functions of each functional block are realized by cooperation between the hardware components constituting the functional blocks and the control unit 30. Note that the control unit 30 may execute a program to realize some or all of the functions of each functional block. Furthermore, some or all of the processing performed by the control unit 30 may be executed by electronic circuits such as a DSP (Digital Signal Processor), an ASIC (Application Specific Integrated Circuit), or a PLD (Programmable Logic Device) provided depending on the processing.

[0023] The image reading unit 11 includes an automatic document feeder 111 and an original image scanning device (scanner) 112. The automatic document feeder 111 is called an ADF (Auto Document Feeder).

[0024] The automatic document feeder 111 transports documents placed on a document tray using a transport mechanism and sends them to the document image scanning device 112. The automatic document feeder 111 can continuously read images (including both sides) of multiple documents placed on the document tray.

[0025] The original image scanning device 112 reads an original document transported from the automatic document feeder 111 onto the contact glass or an original document placed on the contact glass. Specifically, the original image scanning device 112 optically scans the original document, forms an image of the light reflected from the original document on the light receiving surface of an imaging element (e.g., a CCD (Charge Coupled Device)), and reads the original image. The image reading unit 11 generates input image data based on the reading result by the original image scanning device 112. The input image data is subjected to predetermined image processing in the image processing unit 13.

[0026] The operation display unit 12 is configured with, for example, a flat panel display with a touch panel. The flat panel display may be a liquid crystal display, an organic EL display, etc. The operation display unit 12 has a display unit 121 and an operation unit 122.

[0027] The display unit 121 displays various operation screens, image states, operation statuses of various functions, etc. in accordance with a display control signal input from the control unit 30.

[0028] The operation unit 122 includes various operation keys such as a numeric keypad, a start key, etc. The operation unit 122 accepts various input operations by the user and outputs operation signals to the control unit 30. The user can operate the operation display unit 12 to make settings related to image formation, such as document settings, image quality settings, magnification settings, application settings, output settings, and recording material settings.

[0029] The image processing unit 13 includes a circuit for performing digital image processing on input image data according to initial settings or user settings. For example, the image processing unit 13 performs gradation correction based on gradation correction data under the control of the control unit 30. The image processing unit 13 also performs various correction processes on the input image data, such as color correction, shading correction, and density correction. The image forming unit 20 is controlled based on the image data that has undergone these processes.

[0030] The image forming unit 20 includes an image creating unit 21, an intermediate transfer unit 22, and a fixing unit 23. The image creating unit 21 forms a toner image using color toners of Y, M, C, and K components based on input image data. The intermediate transfer unit 22 transfers the toner image formed by the image creating unit 21 onto a recording material. The fixing unit 23 fixes the transferred toner image onto the recording material.

[0031] Specifically, the imaging unit 21 is made up of four imaging units 21Y, 21M, 21C, and 21K, one for the Y component, one for the M component, one for the C component, and one for the K component. Because the imaging units 21Y, 21M, 21C, and 21K have similar configurations, for ease of illustration and explanation, the common components are denoted by the same reference numerals, and when distinguishing between them, the reference numerals are suffixed with Y, M, C, and K. Note that in Figure 1, only the components of the imaging unit 21Y for the Y component are denoted by reference numerals, and the components of the other imaging units 21M, 21C, and 21K are not denoted by reference numerals.

[0032] The image forming unit 21 includes an exposure device 211, a developing device 212, a photosensitive drum 213, a charging device 214, and a drum cleaning device 215. Although not shown, the image forming unit 21 may also include a charge removing device for removing residual charges remaining on the surface of the photosensitive drum 213 after the primary transfer.

[0033] The photosensitive drum 213 is, for example, a negatively charged organic photoconductor (OPC). The photosensitive drum 213 has a configuration in which an undercoat layer (UCL), a charge generation layer (CGL), and a charge transport layer (CTL) are sequentially laminated on the circumferential surface of an aluminum conductive cylinder (aluminum tube).

[0034] The charge generation layer is made of an organic semiconductor in which a charge generation material (e.g., phthalocyanine pigment) is dispersed in a resin binder (e.g., polycarbonate). The charge generation layer generates pairs of positive and negative charges when exposed to light by the exposure device 211. The charge transport layer has a structure in which a hole transport material (electron-donating nitrogen-containing compound) is dispersed in a resin binder (e.g., polycarbonate resin). The charge transport layer transports the positive charges generated in the charge generation layer to the surface of the charge transport layer.

[0035] The charging device 214 is configured by a corona discharge generator such as a scorotron charging device, a corotron charging device, etc. The charging device 214 uniformly charges the surface of the photosensitive drum 213 to a negative polarity by corona discharge.

[0036] The exposure device 211 is composed of, for example, an LED print head (LPH). The LPH has an LED array, an LPH drive unit (driver IC), a lens array, etc. The LED array has multiple light emitting diodes (LEDs) arranged in a line. The LPH drive unit drives each LED. The lens array focuses the light emitted from the LED array onto the photosensitive drum 213. One LED in the LED array corresponds to one dot of the image.

[0037] The exposure device 211 irradiates the photosensitive drum 213 with light corresponding to an image of each color component. Positive charges generated in the charge generation layer of the photosensitive drum 213 upon receiving the light irradiation are transported to the surface of the charge transport layer, thereby neutralizing the surface charge (negative charge) of the photosensitive drum 213. As a result, an electrostatic latent image of each color component is formed on the surface of the photosensitive drum 213 due to a potential difference with the surroundings.

[0038] The developing device 212 contains a developer of each color component (for example, a two-component developer containing a toner and a magnetic carrier) and causes the toner of each color component to adhere to the surface of the photosensitive drum 213, thereby visualizing the electrostatic latent image and forming a toner image. Specifically, a developing bias voltage is applied to a developer carrier (for example, developing rollers 51 and 52, see FIG. 3), and an electric field is formed between the photosensitive drum 213 and the developer carrier. The potential difference (bias voltage) between the photosensitive drum 213 and the developer carrier causes the charged toner on the developer carrier to move to and adhere to the exposed portion of the surface of the photosensitive drum 213. This makes the electrostatic latent image on the photosensitive drum 213 visible. The detailed configuration of the developing device 212 will be described later.

[0039] The drum cleaning device 215 removes the residual toner remaining on the surface of the photosensitive drum 213 after the primary transfer.

[0040] The intermediate transfer unit 22 includes an intermediate transfer belt 221, a primary transfer roller 222, a plurality of support rollers 223, a belt cleaning device 225, a secondary transfer roller 226, and the like.

[0041] The intermediate transfer belt 221 is an image carrier that carries a toner image, and is a transfer object onto which the toner image on the photosensitive drum 213 is transferred. The intermediate transfer belt 221 is an endless belt that is stretched in a loop shape around a plurality of support rollers 223. At least one of the plurality of support rollers 223 is a drive roller, and the others are driven rollers. The rotation of the drive roller causes the intermediate transfer belt 221 to run at a constant speed.

[0042] The primary transfer rollers 222 are disposed opposite the photosensitive drums 213 of the respective color components on the inner peripheral side of the intermediate transfer belt 221. The primary transfer rollers 222 are pressed against the photosensitive drums 213 with the intermediate transfer belt 221 sandwiched therebetween, thereby forming a primary transfer nip for transferring a toner image from the photosensitive drums 213 to the intermediate transfer belt 221.

[0043] Support roller 223 includes an opposing roller 224 disposed opposite secondary transfer roller 226. Secondary transfer roller 226 is disposed on the outer peripheral surface side of intermediate transfer belt 221 and is pressed against opposing roller 224 with intermediate transfer belt 221 sandwiched therebetween. This forms a secondary transfer nip for transferring a toner image from intermediate transfer belt 221 to a recording material.

[0044] At the primary transfer nip, the toner images on the photosensitive drums 213 are primarily transferred onto the intermediate transfer belt 221 in a sequentially overlapping manner. Specifically, by applying a primary transfer voltage to the primary transfer roller 222, a charge of the opposite polarity to that of the toner is applied to the inner circumferential surface side of the intermediate transfer belt 221 (the side that contacts the primary transfer roller 222). The toner images are electrostatically transferred from the photosensitive drums 213 to the intermediate transfer belt 221.

[0045] Thereafter, when the recording material passes through the secondary transfer nip, the toner image on the intermediate transfer belt 221 is secondarily transferred onto the recording material. Specifically, by applying a secondary transfer voltage to the secondary transfer roller 226, a charge of the opposite polarity to that of the toner is applied to the back side of the recording material (the side that contacts the secondary transfer roller 226). The toner image is electrostatically transferred from the intermediate transfer belt 221 to the recording material. The recording material onto which the toner image has been transferred is transported towards the fixing unit 23.

[0046] The belt cleaning device 225 has a belt cleaning blade (reference numeral omitted) that comes into sliding contact with the surface of the intermediate transfer belt 221. The belt cleaning device 225 removes untransferred toner remaining on the surface of the intermediate transfer belt 221 after the secondary transfer.

[0047] The fixing section 23 includes an upper fixing section 231, a lower fixing section 232, a heating source 233, and a pressure contact / separation section (not shown). The upper fixing section 231 has a fixing surface side member arranged on the fixing surface side of the recording material (the surface on which the toner image is formed). The lower fixing section 232 has a back surface side support member arranged on the back surface side of the recording material (the surface opposite the fixing surface). The heating source 233 heats the fixing surface side member. The pressure contact / separation section presses the back surface side support member against the fixing surface side member.

[0048] The recording material onto which the toner image has been secondarily transferred and which has been transported along the paper path is heated and pressurized when passing through the fixing unit 23. This fixes the toner image onto the recording material.

[0049] The paper feed unit 14 has a paper feed tray 141 and a manual paper feed unit 142. The paper feed tray 141 stores sheets of paper (standard paper, special paper) identified based on basis weight, size, etc., for each preset paper type. The paper feed tray 141 and the manual paper feed unit 142 are provided with a plurality of paper feed roller units (reference numerals omitted). A large-capacity external paper feed device (not shown) can be connected to the manual paper feed unit 142. The external paper feed device may be capable of feeding continuous paper such as roll paper, for example. The paper feed unit 14 sends the recording material fed from the paper feed tray 141 or the manual paper feed unit 142 to the recording material transport unit 16.

[0050] The paper discharge section 15 has a paper discharge transport roller section 151 etc. The paper discharge section 15 discharges the recording material sent from the recording material transport section 16 to the outside of the apparatus.

[0051] The recording material conveying section 16 includes a main conveying section 161, a switchback conveying section 162, a conveying section for back side printing 163, and a paper path switching section (not shown). A part of the recording material conveying section 16 may be incorporated into a single unit together with the fixing section 23, for example, and may be detachably attached to the image forming apparatus 1.

[0052] The main transport section 161 has a recording material transport element that sandwiches and transports the recording material. The recording material transport element includes, for example, a plurality of transport roller units (reference numbers omitted) including a loop roller unit and a registration roller unit. The main transport section 161 transports the recording material fed from the paper feed section 14 and passes it through the image forming section 20 (intermediate transfer section 22, fixing section 23). The main transport section 161 also transports the recording material sent from the image forming section 20 (fixing section 23) toward the paper discharge section 15 or the switchback transport section 162.

[0053] The switchback conveyance section 162 temporarily stops the recording material sent out from the fixing section 23, reverses the conveyance direction, and conveys the recording material to the paper discharge section 15 or a conveyance section 163 for back-side printing.

[0054] The back-side printing transport section 163 circulates and transports the recording material switched back by the switchback transport section 162 to the main transport section 161. The recording material is passed through the main transport section 161 with the back side facing the image formation surface.

[0055] A paper path switching unit (not shown) is disposed downstream in the recording material transport direction of the fixing unit 23. The paper path switching unit switches the paper path depending on whether the recording material sent out from the fixing unit 23 is discharged as is, discharged after being inverted, or transported to the back-side printing transport unit 163. Specifically, the control unit 30 controls the operation of the paper path switching unit (not shown) based on the processing content of the image formation process (single-sided / double-sided printing, face-up / face-down paper discharge, etc.).

[0056] The recording material fed from the paper feed unit 14 is transported to the image forming unit 20 by the main transport unit 161. Then, as the recording material passes through the secondary transfer unit, the toner images on the intermediate transfer belt 221 are transferred all at once to the first side (front side) of the recording material, and a fixing process is performed in the fixing unit 23. The recording material on which the image has been formed is discharged to the outside of the apparatus (in this embodiment, the paper discharge unit 1B) by the paper discharge unit 15. When images are to be formed on both sides of the recording material, the recording material on which the image has been formed on the first side is sent to the switchback transport unit 162. Then, the recording material is turned over by returning to the main transport unit 161 through the back side printing transport unit 163, and an image is formed on the second side (back side).

[0057] The specific configuration of the developing device 212 will be described in detail below. Here, the description will be made using an orthogonal coordinate system (X, Y, Z). Figure 3 is a cross-sectional view showing an example of the internal configuration of the developing device 212.

[0058] 3, the X-axis direction is the insertion direction when the developing device 212 is attached to the image forming apparatus 1, and the Z-axis direction is the vertical direction. The positive side of the X-axis direction is referred to as the "rear side," and the negative side is referred to as the "front side." Developer is replenished and discharged from the developing device 212, for example, at the rear side of the image forming apparatus 1.

[0059] The developing device 212 is, for example, a circulating overflow type developing device that replenishes developer from a developer supply port (not shown) and discharges excess developer from a developer discharge port (not shown). Note that the developing device 212 may also be a liquid surface overflow type.

[0060] 3, the developing device 212 includes a first developing roller 51, a second developing roller 52 (developer carrier), a developing container 53 (developer storage section), a first stirring screw 55, a second stirring screw 56, a recovery roller 57, and a recovery screw 58. The developing device 212 also includes a developing roller driving section 61 (see FIG. 2), a toner concentration sensor 62, and a developer supply section 63 (for example, a toner bottle). The operation of each component of the developing device 212 is controlled by, for example, the control section 30.

[0061] The developing container 53 has a box shape that is long in the X-axis direction and contains a developer. The developing container 53 is made of, for example, a metal material or a hard resin material. The developing container 53 is open toward the first developing roller 51 and the second developing roller 52. The developing container 53 is disposed so that the opening of the developing container 53 faces the first developing roller 51 and the second developing roller 52 in the Y-axis direction.

[0062] A regulating plate 59 (regulating member) is disposed at the opening of the developing container 53. The regulating plate 59 is disposed facing the first developing roller 51 at a predetermined distance from the first developing roller 51. The regulating plate 59 is a plate-shaped member made of a magnetic material such as stainless steel, and extends parallel to the first developing roller 51.

[0063] The developing container 53 is partitioned by a partition wall 531 into an agitation chamber 53A that agitates the developer and a developing chamber 53B that supplies the developer to the first developing roller 51 and the second developing roller 52. A flow port (not shown) is formed in the partition wall 531 near the front end. The developing container 53 also has a developer supply port (not shown) and a developer discharge port (not shown) at the rear end.

[0064] The first agitating screw 55 and the second agitating screw 56 extend in the X-axis direction and are arranged side by side in the Y-axis direction with the partition wall 531 sandwiched between them. The first agitating screw 55 and the second agitating screw 56 are supported by bearing portions (not shown) provided on the rear and front sides of the developing container 53, respectively.

[0065] A predetermined clearance is provided between the first stirring screw 55 and the second stirring screw 56 and between the developer container 53. The second stirring screw 56 is positioned vertically lower than the second developing roller 52 and between the catch pole and regulating pole of the second developing roller 52.

[0066] Although not shown, the first stirring screw 55 and the second stirring screw 56 each have a shaft and a blade formed in a spiral shape around the shaft. The first stirring screw 55 and the second stirring screw 56 are driven to rotate so that the developer is transported in mutually opposite directions.

[0067] The first stirring screw 55 conveys the developer from the rear side to the front side while stirring the developer. The developer is transferred from the stirring chamber 53A to the developing chamber 53B through a flow port (not shown) provided in the partition wall 531.

[0068] The second stirring screw 56 transports the developer from the front side to the back side while stirring it. The developer is circulated and transported through a circulation port (not shown) provided in a partition wall (not shown). The blades of the second stirring screw 56 are formed, for example, in a forward winding, reverse winding, and forward winding, and the reverse winding portion circulates the developer toward the stirring chamber 53A.

[0069] The first developing roller 51 and the second developing roller 52 are so-called magnet rollers, each having a fixed, non-rotatable magnet body (not shown) and a cylindrical transport sleeve (not shown) rotatably arranged around the magnet body. The first developing roller 51 and the second developing roller 52 are arranged in a stepped manner in a substantially vertical direction. The magnet body has multiple magnetic poles (catch poles and regulating poles). These multiple magnetic poles form a magnetic field (magnetic lines of force) for transporting the developer by the transport sleeve. Hereinafter, when the first developing roller 51 and the second developing roller 52 are not distinguished from each other, they may be referred to as "developing rollers 51, 52."

[0070] The developer supplied to the transport sleeve stands up along the magnetic field lines formed by the magnet, for example, to form a so-called magnetic brush. The developer is transported as the transport sleeve rotates and is regulated to a constant thickness by passing through a gap with a regulating plate 59. The toner carried on the transport sleeve is supplied to the photosensitive drum 213, thereby developing an electrostatic latent image on the photosensitive drum 213. Toner not used in development is collected by a collection roller 57 and a collection screw 58 and transported, for example, to the stirring chamber 53A or the developing chamber 53B.

[0071] The developing roller driving unit 61 is a driving source that drives the developing rollers 51 and 52 at a predetermined rotation speed. The developing roller driving unit 61 can drive the developing rollers 51 and 52 independently of each other. The control unit 30 controls the developing roller driving unit 61 to rotate the developing rollers 51 and 52 at a predetermined rotation speed. The rotation speeds of the developing rollers 51 and 52 may be the same or different.

[0072] The toner concentration sensor 62 is installed, for example, inside the developing container 53. The toner concentration sensor 62 detects the toner concentration of the developer in the developing container 53. The control unit 30 controls the developer supply unit 63 based on the detection result of the toner concentration sensor 62, and performs a developer supply process. The developer supply process may be a process of supplying either toner or carrier, or a process of supplying both at the same time.

[0073] In the developing device 212, a portion of the developer is supplied to the developing rollers 51 and 52 during the process of circulating and transporting the developer by the first stirring screw 55 and the second stirring screw 56. Furthermore, a portion of the developer that has passed through the developing chamber 53B is not circulated and is discharged into a developer recovery flow path (not shown) through a developer discharge port (not shown). Meanwhile, based on the detection result of the toner concentration sensor 62, developer is appropriately replenished from the developer replenishing unit 63 to the developing container 53. In this way, in the developing device 212, the developer in the developing container 53 is replenished and discharged using a known trickle development technique.

[0074] In addition, the image forming apparatus 1 according to the present embodiment has a defective carrier discharge mode as a function for appropriately reducing the amount of defective carrier in the developer. In the defective carrier discharge mode, a carrier discharge process is executed to selectively discharge defective carrier depending on the proportion of defective carrier in the developer contained in the developing container 53. By selectively discharging defective carrier, only the amount of defective carrier is reduced while maintaining the amount of normal carrier.

[0075] Specifically, in the carrier discharge process, the rotation speed of the developing rollers 51 and 52 is controlled to utilize centrifugal force to selectively fly and discharge defective carrier carried on the developing rollers 51 and 52. By performing the carrier discharge process according to the proportion of defective carrier and appropriately reducing the defective carrier in the developer, it is possible to suppress image defects caused by defective carrier and stabilize image quality. Furthermore, because the defective carrier is completely discharged outside the developing container 53, the separated defective carrier does not return to the developer and be used for development, as in Patent Document 1.

[0076] Defective carrier is carrier that does not have the desired charging performance suitable for development. Defective carrier includes carrier whose particle size has become small due to the accumulation of mechanical stress or thermal stress caused by contact with toner, carrier whose surface has been soiled by the adhesion of toner, and carrier whose particle size is small from the beginning of replenishment. In this embodiment, carrier whose particle size is equal to or smaller than a predetermined value is particularly treated as defective carrier.

[0077] The particle size that is considered to be a defective carrier can be set as appropriate. For example, using the average particle size of the carrier as a standard, carriers having a particle size of 75% or less of the average particle size can be treated as defective carriers. Here, in a developer in which the average particle size of the carrier is 33 μm, carriers having a particle size of 25 μm or less are treated as defective carriers.

[0078] Fig. 4 shows an example of carrier adhesion rank relative to the proportion of defective carrier (small diameter carrier with a particle size of 25 μm or less). The proportion of defective carrier is expressed as the weight of defective carrier relative to the total weight of carrier in the developer. The carrier adhesion rank is an index that indicates the degree of influence of carrier adhesion on image quality.

[0079] Figure 4 shows the results of forming 10 consecutive images on an A3-sized recording material at a printing rate of 100%, and visually checking and ranking the number of fireflies (white spots) present in the image. The carrier adhesion rank "3" is the acceptable level for customers who are not too concerned about image quality, and the evaluation is done on a 5-point scale.

[0080] As shown in Figure 4, the smaller the proportion of defective carriers, the better the image quality and the higher the carrier adhesion rank. On the other hand, as the proportion of defective carriers increases, the image quality decreases and the carrier adhesion rank decreases.

[0081] As can be seen from Figure 4, for example, to maintain a carrier adhesion rank of "5", the proportion of defective carriers must be controlled to 3 wt% or less. Also, for example, to maintain a carrier adhesion rank of "4", the proportion of defective carriers must be controlled to 7 wt% or less. To maintain a carrier adhesion rank of "3", the proportion of defective carriers must be controlled to 13 wt% or less. Hereinafter, the upper limit of the proportion of defective carriers that can maintain a specified carrier adhesion rank is referred to as the "tolerable limit" of defective carriers.

[0082] The carrier adhesion rank is set, for example, according to the customer's usage conditions. The carrier adhesion rank is set, for example, based on the image quality level required by the customer and the average print rate. For example, if the customer has fairly strict requirements for image quality and a fairly high print rate (i.e., fireflies in the image are easily noticeable), the carrier adhesion rank is set to "4" according to the adhesion rank setting table shown in Figure 5, since the print rate is "medium" and the image quality requirement is "medium." In this case, according to Figure 4, the allowable limit value for defective carrier is 7 wt%. The customer's usage conditions may also include productivity, how the image forming apparatus 1 is used, etc.

[0083] The carrier discharge process is performed at an appropriate timing according to the carrier adhesion rank set by the customer. Specifically, the carrier discharge process is performed so that the proportion of defective carrier does not exceed the allowable limit. For example, if the carrier adhesion rank is set to "4," the carrier discharge process is performed before the proportion of defective carrier reaches the allowable limit of 7 wt%.

[0084] 6 is a diagram showing an example of particle size distribution of carrier particles in a replenished developer, in which the average particle size of the carrier particles is 33 μm.

[0085] As shown in FIG. 6, even initial developer that has not been used for development contains a certain amount of defective carrier with a particle size of 25 μm or less. In the example shown in FIG. 6, the proportion of defective carrier is approximately 11%. As shown in FIG. 4, if development is performed using the initial developer as is, the carrier adhesion rank will be 3.5 or less. In other words, it is easy to predict that the proportion of defective carrier in the developer in the developer container 53 will be high immediately after developer is replenished from the developer replenishment unit 63. Therefore, it is preferable to perform a carrier discharge process prior to the printing process immediately after developer is replenished from the developer replenishment unit 63.

[0086] Note that "immediately after developer is replenished" refers to the first time developer is replenished from the developer replenishment section 63 to the developing container 53, for example, when replacing a toner bottle, and does not include the time immediately after developer is replenished by trickle development.

[0087] In the carrier discharge process according to this embodiment, developing rollers 51 and 52 are rotated at a higher rotation speed than that used in normal printing processes, and centrifugal force is used to fly out defective carrier from developing rollers 51 and 52, and the defective carrier is selectively discharged outside developing container 53. Since this can be achieved by simply increasing the rotation speed of developing rollers 51 and 52, it can be applied to existing image forming devices, and there is no need to increase the size of developing device 212 itself in order to improve the discharge performance of defective carrier.

[0088] The rotation speed of the developing rollers 51 and 52 during the carrier discharge process can be calculated from the balance of the magnetic attraction force, gravity, and centrifugal force acting on the carrier carried at a specific position on the developing rollers 51 and 52.

[0089] The specific position is a position where the rotational component of the magnetic attractive force calculated from the magnetic flux density distribution of the magnet bodies of the developing rollers 51 and 52 is small and the radial component is not directed toward the inside of the developing container 53. In calculating the number of rotations, the position of the carrier is based on the position of the carrier carried on the developing rollers 51 and 52 that is closest to the photosensitive drum 213. The magnetic susceptibility of the carrier is proportional to the cube of the radius of the particle diameter.

[0090] FIG. 7 is a diagram showing an example of the relationship between carrier particle size and roller rotation speed. FIG. 7 shows the rotation speeds calculated as described above for four types of carrier particle size. According to FIG. 7, when the rotation speed of developing rollers 51 and 52 is set to about 1022 rpm, carrier particles with a particle size of 25 μm or less are discharged. When the rotation speed of developing rollers 51 and 52 is set to about 1333 rpm, carrier particles with a particle size of 30 μm or less are discharged.

[0091] When the rotation speed of the developing rollers 51 and 52 in the normal printing process is faster than 642 rpm (for example, 665 rpm), the carrier particles with a particle size of about 18 μm will be naturally discharged in the normal printing process.

[0092] Fig. 8 is a diagram showing the particle size distribution of the carrier discharged when the developing rollers 51 and 52 are driven at a predetermined rotation speed. Fig. 8 shows the particle size distribution when the rotation speed of the developing rollers 51 and 52 is set to the normal rotation speed of 665 rpm under bias development conditions, and the particle size distribution when the rotation speed of the developing rollers 51 and 52 is set to 1674 rpm, 1022 rpm, and 665 rpm under normal development conditions.

[0093] Here, the bias development conditions are conditions for development without charging the photosensitive drum 213. In other words, under the bias development conditions, the entire surface of the photosensitive drum 213 is an image portion, and the printing rate is 100%.

[0094] On the other hand, normal development conditions are conditions in which toner is deposited on an image area (electrostatic latent image) formed by exposing the uniformly charged photosensitive drum 213. In other words, under normal development conditions, toner is deposited on the portion of the surface of the photosensitive drum 213 where the image area is formed. Here, the printing rate is set to 100%.

[0095] As shown in Figure 8, when the carrier discharge process is performed under bias development conditions at a normal rotation speed (665 rpm), the particle size distribution of the carrier shows a tendency similar to that of the carrier in the developer before use (see Figure 6). The bias development conditions are considered to be effective in efficiently discharging the carrier, but the defective carrier is not selectively discharged, and a large amount of normal carrier is also discharged.

[0096] On the other hand, the results of the carrier discharge process under normal development conditions show that defective carrier particles with small particle diameters can be discharged by increasing the rotation speed of the developing rollers 51 and 52 beyond the normal rotation speed (665 rpm). However, if the rotation speed of the developing rollers 51 and 52 is too high, a large amount of normal carrier particles will also be discharged. In other words, to selectively discharge defective carrier particles with particle diameters of 25 μm or less, it is preferable to set the rotation speed (1022 rpm in FIG. 7) calculated as described above for carrier particles with particle diameters of 25 μm or less. In other words, by setting the rotation speed of the developing rollers 51 and 52 according to the particle diameter of the defective carrier particles to be discharged (here, 25 μm or less), the defective carrier particles can be selectively discharged. Furthermore, by discharging the carrier particles under bias development conditions, the defective carrier particles can be efficiently discharged.

[0097] In this embodiment, the developer carrier includes a first developing roller 51, the amount of developer that can be carried of which is regulated by a regulating plate 59, and a second developing roller 52, to which developer is supplied from the first developing roller 51. In this case, it is preferable to set the rotation speed of the second developing roller 52 in the carrier discharging process according to the particle size of the defective carrier to be discharged, and to set the rotation speed of the first developing roller 51 to be smaller than the rotation speed of the second developing roller 52. This reduces the stress that the developer carried by the first developing roller 51 receives when passing through the gap between the first developing roller 51 and the regulating plate 59, while allowing the defective carrier to be selectively discharged by the second developing roller 52.

[0098] Fig. 9 shows the particle size distribution of carrier in developer after the carrier discharge process has been performed. Fig. 9 shows the particle size distribution of carrier after the carrier discharge process has been performed for one minute under bias development conditions with the rotation speed of developing rollers 51 and 52 set to 1022 rpm. Fig. 9 also shows the particle size distribution of carrier before the carrier discharge process (the same as Fig. 6) as a comparative example.

[0099] As shown in Figure 9, by performing the carrier discharge process, defective carrier particles with a particle size of 25 μm or less can be selectively discharged, and the amount of defective carrier particles in the developer can be significantly reduced. Specifically, in Figure 9, the proportion of defective carrier particles is 2 wt%, which is a reduction of about 9 wt% compared to the default.

[0100] FIG. 10 shows an example of the change in the proportion of defective carrier in a developer as a result of printing. FIG. 10 shows printing performed at print rates of 2%, 5%, and 10% using a trickle development method with a developer having a carrier proportion (AR rate) of 5%. FIG. 10 also shows, as a comparative example, a case where only toner is replenished (no trickle) using a developer having a carrier proportion of 0%. The number of printed pages in FIG. 10 is counted from the point in time when the developer replenishment unit 63 was replaced (0 kp).

[0101] As shown in Figure 10, the proportion of small-diameter defective carriers in the developer decreases at a constant rate from the beginning of printing (when the developer supply unit 63 is replaced) and saturates, regardless of the print rate. The same is true when there is no trickle. Furthermore, the higher the print rate, the larger the amount of developer replenished and the greater the number of defective carriers, so the proportion of defective carriers at saturation becomes larger.

[0102] That is, in a conventional image forming apparatus, for example, when the print rate is 10%, the proportion of defective carriers is constant at 8 wt%, and according to Fig. 4, it is difficult to maintain the proportion of defective carriers at or below the allowable limit value for carrier adhesion ranks "4" or "5." In contrast, in this embodiment, by performing a carrier discharge process according to the proportion of defective carriers, it is possible to reduce the proportion of defective carriers to or below the allowable limit value (for example, 2 wt%, see Fig. 9).

[0103] By performing the carrier discharge process at the beginning of printing, the proportion of defective carrier is reduced to below the allowable limit. As the printing process progresses and the number of printed pages increases, developer is replenished by trickle development, so the proportion of defective carrier increases from the initial value. Therefore, even after performing the carrier discharge process at the beginning of printing, it is preferable to perform the carrier discharge process at an appropriate timing so that the proportion of defective carrier does not exceed the allowable limit.

[0104] The timing of the carrier discharge process is determined based on the usage information of the image forming apparatus 1 and the carrier adhesion rank set by the customer. The usage information of the image forming apparatus 1 includes the print rate, the size of the recording material, the number of printed sheets, etc. The usage information of the image forming apparatus 1 may also be the number of times (amount of replenishment) that developer is replenished by trickle development.

[0105] For example, when the carrier adhesion rank is high, the allowable limit of defective carriers is smaller than when the carrier adhesion rank is low, so the proportion of defective carriers reaches the allowable limit with a smaller number of printed sheets. Therefore, when the usage information (printing rate and recording material size) of the image forming apparatus 1 is the same, the interval (number of printed sheets) between executions of the carrier discharge process can be shortened as the carrier adhesion rank is higher, and can be lengthened as the carrier adhesion rank is lower.

[0106] Furthermore, for example, when the print rate is high, the number of times developer is replenished by trickle development increases and the rate of increase in the proportion of defective carriers increases, compared to when the print rate is low, so the proportion of defective carriers reaches the allowable limit with a small number of printed sheets. Therefore, for the same carrier adhesion rank, the interval (number of printed sheets) between executions of the carrier discharge process can be shortened as the print rate increases and lengthened as the print rate decreases. The same can be said for the size of the recording material.

[0107] In this way, by determining the timing of the carrier discharge process based on the usage information of the image forming apparatus 1 and the carrier adhesion rank set by the customer, it is possible to reduce downtime due to the carrier discharge process and improve productivity. Furthermore, although a considerable amount of toner is discharged along with the carrier during the carrier discharge process, unnecessary discharge of toner is also reduced.

[0108] 11 is a flowchart showing an example of processing in the defective carrier discharge mode. This processing is realized, for example, by the CPU 31 of the control unit 30 executing a program stored in the ROM 32 when the image forming apparatus 1 is powered on. Note that whether or not to execute the defective carrier discharge mode can be selected by the user as appropriate.

[0109] In step S101 of Fig. 11, the control unit 30 determines whether or not it is immediately after developer has been replenished. Immediately after developer has been replenished means, for example, immediately after the developer replenishment unit 63 has been replaced. If it is immediately after developer has been replenished ("YES" in step S101), the process proceeds to step S104. If it is not immediately after the developer replenishment unit 63 has been replaced ("NO" in step S101), the process proceeds to step S102.

[0110] In step S102, the control unit 30 estimates the proportion of defective carriers in the developer contained in the developing container 53. Specifically, the proportion of defective carriers can be estimated based on usage information of the image forming apparatus 1. For example, by experimentally obtaining how much the proportion of defective carriers changes with the number of printed pages for each print rate and recording material size, it is possible to estimate the proportion of defective carriers based on the average print rate, recording material size, and number of printed pages up to the current point in time.

[0111] In step S103, the control unit 30 determines whether the proportion of defective carriers is equal to or greater than a threshold value. The threshold value is set, for example, according to the carrier adhesion rank set by the customer so that the proportion of defective carriers does not exceed an allowable limit. For example, if a carrier adhesion rank of "4" is set, the allowable limit value is 7 wt% according to FIG. 4. Therefore, taking into consideration that the proportion of defective carriers increases with the printing process, the threshold value is set slightly smaller than 7 wt%. If the proportion of defective carriers is equal to or greater than the threshold value ("YES" in step S103), the process proceeds to step S104. If the proportion of defective carriers is less than the threshold value ("NO" in step S103), the process from step S101 or S102 onwards is repeated.

[0112] In step S104, the control unit 30 executes a carrier discharge process. The carrier discharge process is executed, for example, between print jobs. In the carrier discharge process, the developing rollers 51 and 52 are rotated for a predetermined time (for example, one minute) at a higher rotation speed than that in a normal printing process. This allows defective carrier in the developer to be selectively discharged outside the developing container 53. According to FIG. 9, after the carrier discharge process, the proportion of defective carrier is reduced to about 2%.

[0113] Since the amount of defective carrier discharged in the carrier discharge process reaches saturation after a certain time has passed, the rotation time of the developing rollers 51 and 52 is appropriately set according to the amount of defective carrier to be discharged. The discharged defective carrier is carried on the photosensitive drum 213, for example, and is collected by the drum cleaning device 215.

[0114] In addition, the image forming apparatus 1 may be provided with a carrier recovery unit that electrically or magnetically recovers the discharged defective carrier, or the air volume of a duct that recovers scattered toner may be increased so that the defective carrier is recovered through the duct.

[0115] Fig. 12A is a diagram showing the change in the proportion of defective carriers when printing is performed at a printing rate of 10% in the defective carrier discharge mode. Fig. 12B is a diagram showing the change in carrier adhesion rank when printing is performed at a printing rate of 10% in the defective carrier discharge mode. Note that Figs. 12A and 12B show a comparative example in which the defective carrier discharge mode is not performed.

[0116] As shown in Figures 12A and 12B, by performing the carrier discharge process at the beginning of printing, the proportion of defective carrier at the beginning of printing is significantly reduced, and an image quality level of carrier adhesion rank "5" can be maintained from the beginning of printing.

[0117] Furthermore, as the number of printed pages increases, developer is replenished by trickle development, and the proportion of defective carrier increases, but by performing carrier discharge processing at the appropriate time before the proportion of defective carrier reaches the allowable limit, the proportion of defective carrier can be reduced and recovered. Therefore, although the carrier adhesion rank gradually decreases as the number of printed pages increases, it is possible to always maintain an image quality level of carrier adhesion rank "4" or "5."

[0118] 13 is a diagram showing the number of dents on the photosensitive drum 213 when printing is performed at a printing rate of 10% in the defective carrier discharge mode. In FIG. 13, a case where the defective carrier discharge mode is not performed is shown as a comparative example.

[0119] From FIG. 13, it can be seen that by printing in the defective carrier discharge mode, the proportion of defective carriers can be reduced, and the number of dents on the photosensitive drum 213 caused by defective carriers can be reduced.

[0120] As described above, the image forming apparatus 1, the carrier discharging method, and the program according to the embodiment have the following features either alone or in appropriate combination.

[0121] That is, the image forming apparatus 1 includes a developing device 212 capable of supplying a developer containing toner and carrier to a photosensitive drum 213 (image carrier), and a control unit 30 that controls the operation of the image forming unit 21 that includes the developing device 212. The developing device 212 includes a developing container 53 (developer container) that contains the developer, a developer replenishing unit 63 that replenishes the developer according to the toner concentration in the developing container 53, and developing rollers 51 and 52 (developer carriers) that supply the developer to the photosensitive drum 213. The control unit 30 executes a carrier discharge process that selectively discharges defective carrier according to the proportion of defective carrier in the developer contained in the developing container 53.

[0122] The carrier discharge method according to the embodiment is a carrier discharge method for controlling the amount of defective carrier in a developing device 212 capable of supplying a developer containing toner and carrier to a photosensitive drum 213 (image carrier), and includes a process of acquiring the proportion of defective carrier in the developer contained in a developing container 53 (developer container) of the developing device 212 (steps S101 and S102 in FIG. 11), and a process of selectively discharging the defective carrier according to the acquired proportion of defective carrier (steps S103 and S104).

[0123] The program according to the embodiment is a program that causes the control unit 30 (computer) to execute a process for controlling the amount of defective carrier in the developing device 212, which can supply a developer containing toner and carrier to the photosensitive drum 213 (image carrier), and includes a process for acquiring the proportion of defective carrier in the developer contained in the developing container 53 (developer container) of the developing device 212 (steps S101 and S102 in FIG. 11), and a process for selectively discharging the defective carrier according to the acquired proportion of defective carrier (steps S103 and S104).

[0124] According to the image forming apparatus 1, carrier discharging method, and program of the embodiment, defective carrier is selectively discharged according to the proportion of defective carrier, thereby appropriately reducing the amount of defective carrier in the developer and stabilizing image quality. Furthermore, it is possible to prevent dents caused by defective carrier from forming on the surface of the photosensitive drum 213. Furthermore, since there is no need to increase the size of the developing device 212 in order to improve the discharge performance (separability) of defective carrier, it also contributes to business viability.

[0125] Furthermore, in the image forming apparatus 1, the control unit 30 executes a carrier discharge process when the developer is first replenished from the developer replenishing unit 63 to the developer container 53 (developer storage unit). This ensures that defective carriers can be reduced even at the beginning of printing when the proportion of defective carriers is relatively high, thereby stabilizing image quality.

[0126] Furthermore, in the image forming apparatus 1, the control unit 30 determines the timing of the carrier discharge process based on usage information of the image forming apparatus 1 and a carrier adhesion rank set according to the customer's usage situation. Specifically, the control unit 30 estimates the proportion of defective carriers based on the print rate and number of printed pages, which are usage information of the image forming apparatus 1, and determines the timing of the carrier discharge process by comparing the estimated proportion of defective carriers with a threshold set according to the carrier adhesion rank. This allows the carrier discharge process to be performed under conditions optimal for the customer, reducing downtime due to the carrier discharge process and maximizing contributions to image quality stability and business viability while minimizing the impact on productivity.

[0127] Furthermore, in the image forming apparatus 1, the control unit 30 controls the rotation speed of the developing rollers 51 and 52 (developer carriers) in the carrier discharge process according to the particle size of the defective carrier to be discharged. This allows the defective carrier to be selectively discharged by utilizing centrifugal force.

[0128] Furthermore, in image forming apparatus 1, developing device 212 further includes a regulating plate 59 (regulating member) that regulates the amount of developer supplied to developing rollers 51 and 52 (developer carriers). The developer carriers include a first developing roller 51 (first developer carrier) whose amount of developer it can carry is regulated by regulating plate 59, and a second developing roller 52 to which developer is supplied from first developing roller 51. Control unit 30 sets the rotation speed of second developing roller 52 in the carrier discharge process according to the particle size of the defective carrier to be discharged, and sets the rotation speed of first developing roller 51 to be smaller than the rotation speed of second developing roller 52. This reduces stress on the developer carried by first developing roller 51 when it passes through the gap between first developing roller 51 and regulating plate 59, thereby suppressing carrier degradation.

[0129] Furthermore, in the image forming apparatus 1, the control unit 30 controls the rotation time of the developing rollers 51 and 52 (developer carriers) in the carrier discharge process, thereby enabling the carrier discharge process to be carried out efficiently and improving productivity.

[0130] Furthermore, in the image forming apparatus 1, the control unit 30 performs the carrier discharge process under bias development conditions, thereby making it possible to efficiently discharge defective carrier without wasting toner.

[0131] Furthermore, the image forming apparatus 1 includes a drum cleaning device 215 (carrier recovery unit) that can recover discharged defective carrier, thereby preventing the discharged defective carrier from scattering and adversely affecting image formation.

[0132] The invention made by the inventor has been specifically described above based on an embodiment, but the present invention is not limited to the above embodiment and can be modified within the scope of the gist thereof.

[0133] For example, although the present invention is applied to an electrophotographic color image forming apparatus, the present invention can also be applied to a monochrome image forming apparatus.

[0134] In the embodiment, the developer carrier is composed of two developing rollers 51 and 52, but the number of developing rollers constituting the developer carrier may be one, or three or more. If the number of developing rollers is large, more defective carrier will be discharged during the printing process, so the interval between carrier discharge processes can be lengthened, which is expected to improve productivity.

[0135] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0136] 1. Image forming device 20 Image forming unit 30 Control Unit 212 Developing device 213 Photosensitive drum (image carrier) 51 First developing roller (first developer carrier) 52 Second developing roller (second developer carrier) 53 Developer container (developer storage section) 61 Developing roller drive unit 62 Toner density sensor 63 Developer supply unit

Claims

1. a developing device capable of supplying a developer containing toner and a carrier to an image carrier; a control unit that controls the operation of an image forming unit including the developing device, The developing device is a developer storage section that stores the developer; a developer supply unit that supplies the developer in accordance with the toner concentration in the developer container; a developer carrier that supplies the developer to the image carrier; the control unit executes a carrier discharge process for selectively discharging the defective carrier in accordance with a ratio of the defective carrier in the developer contained in the developer container. Image forming device.

2. the control unit executes the carrier discharge process when the developer is first replenished from the developer replenishing unit to the developer accommodating unit. The image forming apparatus according to claim 1 .

3. the control unit determines the timing of execution of the carrier discharge process based on usage information of the image forming apparatus and a carrier adhesion rank set according to the customer's usage status. The image forming apparatus according to claim 1 .

4. the control unit estimates the proportion of defective carriers based on the print rate and the number of printed sheets, which are usage information of the image forming apparatus, and compares the estimated proportion of defective carriers with a threshold value set according to the carrier adhesion rank, to determine the timing of execution of the carrier discharge process. The image forming apparatus according to claim 3 .

5. the control unit controls the number of rotations of the developer carrier in the carrier discharge process in accordance with the particle diameter of the defective carrier to be discharged. The image forming apparatus according to claim 3 .

6. the developing device further includes a regulating member that regulates the amount of developer supplied to the developer carrier; the developer carrier includes a first developer carrier whose amount of the developer that can be carried is regulated by the regulating member, and a second developer carrier to which the developer is supplied from the first developer carrier; the control unit sets the rotation speed of the second developer carrier in the carrier discharge process in accordance with the particle size of the defective carrier to be discharged, and sets the rotation speed of the first developer carrier to be smaller than the rotation speed of the second developer carrier. The image forming apparatus according to claim 5 .

7. the control unit controls a rotation time of the developer carrier during the carrier discharge process.

7. The image forming apparatus according to claim 5 or 6.

8. the control unit executes the carrier discharge process under bias development conditions.

7. The image forming apparatus according to claim 5 or 6.

9. a carrier recovery unit capable of recovering the discharged defective carrier; The image forming apparatus according to claim 1 .

10. A carrier discharge method for controlling the amount of defective carrier in a developing device capable of supplying a developer containing toner and carrier to an image carrier, comprising: acquiring a ratio of defective carriers in the developer contained in a developer container of the developing device; and selectively discharging the defective carriers in accordance with the proportion of the acquired defective carriers. Carrier discharge method.

11. A program for causing a computer to execute a process for controlling the amount of defective carrier in a developing device capable of supplying a developer containing toner and carrier to an image carrier, the program comprising: A process of acquiring a ratio of defective carriers in the developer accommodated in a developer accommodating section of the developing device; and selectively discharging the defective carriers in accordance with the ratio of the acquired defective carriers. program.

Images