Image forming apparatus

Abstract

To provide an image forming apparatus that can reduce the frequency to replace a waste toner container.SOLUTION: An image forming apparatus executes, at a specific timing, an image forming operation without toner supply that is image forming control while inhibiting toner supply to form an image to be transferred to a transfer paper that is a recording material, with toner supply performed by a toner supply device that is toner supply means being stopped. The image forming operation without toner supply performs adjustment of an image forming condition for setting a developing bias, an electrification bias, and the amount of exposure on the basis of a detection result from a toner concentration sensor that is toner concentration detection means (S24). When the detection result from the toner concentration sensor becomes equal to or less than a prescribed toner concentration (NO in S20, S29), or when one of the electrification bias, the developing bias, and the amount of exposure becomes equal to or more than an upper limit (NO in S23), the image forming apparatus ends the image forming operation without toner supply and resumes toner supply control (S21, S24, S30).SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] The following image forming apparatus has been known. Specifically, the image forming apparatus includes a latent image carrier that is uniformly charged by a charging device to which a charging bias is applied and then exposed by an exposure device to form a latent image on the surface; a developing device that carries developer containing toner and carrier in a developer container on the surface of the developer carrier and transports the developer to a development area facing the latent image carrier, and applies a developing bias to the developer carrier to form a developing electric field in the development area that moves the toner to the latent image on the latent image carrier. The image forming apparatus also includes a toner concentration detection unit that detects the toner concentration in the developer in the developing device, a toner supply unit that supplies toner to the developing device, and a toner supply control unit that controls the toner supply unit based on the detection result of the toner concentration detection unit so that the toner concentration in the developer in the developing device reaches a target toner concentration. The image forming apparatus then develops the latent image using the developing device, resulting in a toner image that is finally transferred to a recording material to form an image.

[0003] Patent Document 1 describes a method for performing forced toner consumption control, which forms a forced toner consumption pattern that is not transferred to a recording material with toner replenishment by a toner replenishment means stopped at specific times, such as when the power is turned on, when image quality adjustment control (process control) is being executed, or when an operation display unit receives an instruction to execute toner refresh control. According to this, it is described that by stopping toner replenishment and performing forced toner consumption control, it is possible to efficiently consume deteriorated toner in a developing device. Summary of the Invention [Problem to be solved by the invention]

[0004] However, there is a risk that the waste toner container for storing the waste toner will have to be replaced more frequently. [Means for solving the problem]

[0005] In order to solve the above-mentioned problems, the present invention provides a development device comprising: a latent image carrier that is uniformly charged by a charging device to which a charging bias is applied, and then has its surface exposed by an exposure device to form a latent image on the surface; a developing device that carries developer from a developer container that contains developer including toner and carrier on the surface of the developer carrier, transports the developer to a development area facing the latent image carrier, and applies a development bias to the developer container to form a development electric field in the development area that moves the toner to the latent image on the latent image carrier; toner concentration detecting means that detects the toner concentration in the developer in the developer container; toner replenishing means that replenishing toner to the developing device; and toner replenishing control means that controls the toner replenishing means based on the detection result of the toner concentration detecting means so that the toner concentration in the developer in the developer container becomes a target toner concentration, In an image forming apparatus that forms an image by finally transferring a toner image obtained by developing the latent image using a developing device onto a recording material, the apparatus implements toner replenishment prohibition image formation control, which forms an image to be transferred onto the recording material at a specific timing while toner replenishment by the toner replenishment means is stopped, and during the toner replenishment prohibition image formation control, the developing bias, the charging bias, and the exposure amount when exposing the surface of the latent image carrier by the exposure device are set based on the detection result of the toner concentration detection means, and when the detection result of the toner concentration detection means shows that the toner concentration in the developer in the developing device is equal to or lower than the specified toner concentration which is set lower than the target toner concentration, or when one of the charging bias, the developing bias, and the exposure amount is equal to or higher than an upper limit value, the toner replenishment prohibition image formation control is terminated. [Effects of the Invention]

[0006] According to the present invention, the frequency of replacing the waste toner container can be reduced. [Brief explanation of the drawings]

[0007] [Figure 1]FIG. [Figure 2] FIG. 2 is an enlarged explanatory view of one of four image forming units to which the present invention can be applied. [Figure 3] FIG. 4 is a schematic diagram illustrating an image quality adjustment pattern on an intermediate transfer belt. [Figure 4] 5A and 5B are schematic diagrams showing an example of an image quality adjustment pattern formed on an intermediate transfer belt when image adjustment is performed in parallel with a printing operation. [Figure 5] FIG. 2 is a schematic diagram showing a state in which a toner bottle is installed in a toner supply device. [Figure 6] FIG. 2 is a functional block diagram of a copying machine according to an embodiment. [Figure 7] FIG. 10 is a control flow diagram of conventional toner refresh control. [Figure 8] FIG. 3 is a control flow diagram of the present embodiment. [Figure 9] 10 is a graph showing the relationship between the toner concentration in the developing device and the developing capacity. [Figure 10] FIG. 4 is a graph showing the relationship between image density and developing bias. [Figure 11] 1A is a graph showing the toner concentration and developing bias conditions under which no defects occur in an image in a low-temperature, low-humidity environment, and FIG. 1B is a graph showing the toner concentration and developing bias conditions under which no defects occur in an image in a high-temperature, high-humidity environment. [Figure 12] 9 is a graph showing the change in toner concentration in the developing device when an image is formed to be transferred onto transfer paper in accordance with the control flow diagram shown in FIG. 8 . DETAILED DESCRIPTION OF THE INVENTION

[0008] The best mode for carrying out the present invention will be described below with reference to the drawings. Note that a person skilled in the art can easily modify or alter the present invention within the scope of the claims to create other embodiments, and these modifications and alterations are included within the scope of the claims. The following description is an example of the best mode for carrying out the present invention and does not limit the scope of the claims.

[0009] Hereinafter, an embodiment of a tandem color copier (hereinafter referred to as copier 500) as an image forming apparatus to which the present invention can be applied will be described. FIG. 1 is a schematic diagram of the copier 500. The copier 500 includes an image reading unit 12 above a printer unit 100 as the main body of the image forming apparatus, and a paper feed unit 7 below the printer unit 100. The image reading unit 12 includes a document reading unit 4 and a document transport unit 3. The document transport unit 3 transports documents to the document reading unit 4, and the document reading unit 4 reads image information from the transported documents. The paper feed unit 7 includes a paper feed cassette 26 that stores transfer paper P, which is a recording medium, and a paper feed roller 27 that feeds the transfer paper P in the paper feed cassette 26 toward the printer unit 100. The dashed dotted line in FIG. 1 indicates the transport path of the transfer paper P within the copier 500.

[0010] The top of the printer section 100 is a paper output tray 30 on which transfer paper P with an output image formed thereon is stacked. The printer section 100 includes four imaging units 6 (Y, M, C, K) as imaging sections that form toner images of each color (yellow, magenta, cyan, black), and an intermediate transfer unit 10. Each imaging unit 6 (Y, M, C, K) includes a drum-shaped photoconductor 1 (Y, M, C, K) as an image carrier on which the toner image of each color is formed, a writing section 15 such as an exposure device that writes an electrostatic latent image on the surface of each photoconductor 1 (Y, M, C, K), and a developing device 5 (Y, M, C, K) that develops the electrostatic latent image on the surface of each photoconductor 1 (Y, M, C, K).

[0011] The intermediate transfer unit 10 includes an intermediate transfer belt 8 and primary transfer bias rollers 9 (Y, M, C, K). The intermediate transfer belt 8 is an intermediate transfer body onto which the toner images of each color formed on the surface of each photoconductor 1 (Y, M, C, K) are transferred in an overlapping manner, forming a color toner image on its surface. The primary transfer bias rollers 9 (Y, M, C, K) are primary transfer means that transfer the toner images formed on the surfaces of each photoconductor 1 (Y, M, C, K) to the intermediate transfer belt 8.

[0012] The printer unit 100 includes a secondary transfer bias roller 19 for transferring the color toner image on the intermediate transfer belt 8 onto the transfer paper P. It also includes a pair of registration rollers 28 for adjusting the timing at which the transfer paper P sent out by the paper feed roller 27 is transported to the secondary transfer nip where the intermediate transfer belt 8 and the secondary transfer bias roller 19 face each other. The printer unit 100 also includes a fixing device 20 above the secondary transfer nip for fixing an unfixed toner image on the transfer paper P. Toner bottles 11 (Y, M, C, K) of each color are arranged below the paper discharge tray 30 and above the intermediate transfer unit 10 within the printer section 100. The toner bottles 11 (Y, M, C, K) of each color contain toner of each color (yellow, magenta, cyan, black) to be supplied to the respective developing devices 5 (Y, M, C, K).

[0013] FIG. 2 is an enlarged explanatory diagram of one of four imaging units 6 (Y, M, C, K) to which the present invention can be applied. The four imaging units 6 (Y, M, C, K) are substantially identical in configuration and operation except for the color of toner used in the image formation process. Therefore, in the following description, the reference symbols Y, M, C, and K indicating corresponding colors will be omitted as appropriate. As shown in FIG. 2, the imaging unit 6 is a process cartridge that integrally supports the photosensitive element 1 and the developing device 5. This process cartridge is detachable from the main body of the copier 500. The imaging unit 6 also includes a photosensitive element cleaning device 2, a lubricant applicator 13, and a charging device 14 around the photosensitive element 1, in addition to the developing device 5. In the imaging unit 6 of this embodiment, the photosensitive element cleaning device 2 is configured to perform cleaning using a cleaning blade 2a, and the charging device 14 is configured to perform charging using a charging roller 14a.

[0014] The developing device 5 has a first agent-containing chamber 5a in which a first transport screw 152 serving as developer transport means is disposed. It also has a toner concentration sensor 155 consisting of a magnetic permeability sensor serving as toner concentration detection means, a second transport screw 153 serving as developer transport means, a developing roller 151 serving as a developer carrier, and the like. It also has a second agent-containing chamber 5b in which a doctor blade 154 serving as a developer regulating member and the like are disposed.

[0015] The toner concentration sensor 155 detects the toner concentration of the developer passing through a predetermined detection point located downstream in the developer circulation direction from a point facing the toner supply port 5c in the first agent storage chamber 5a (hereinafter referred to as the "supply position").

[0016] The two developer chambers forming the circulation path contain a developer consisting of a magnetic carrier and negatively charged toner. The first transport screw 152 is driven to rotate by a drive means, thereby transporting the developer in the first developer chamber 5a toward the front in a direction perpendicular to the plane of the paper in Figure 2. The developer transported to the end of the first developer chamber 5a by the first transport screw 152 then enters the second developer chamber through a communication port.

[0017] The second transport screw 153 in the second agent-containing chamber 5b is rotationally driven by a drive means to transport the developer toward the rear in a direction perpendicular to the plane of the paper in Fig. 2. Above the second transport screw 153, a developing roller 151 is disposed in a position parallel to the second transport screw 153. This developing roller 151 is configured to include a magnetic roller fixedly disposed within a developing sleeve made of a non-magnetic sleeve that rotates counterclockwise in Fig. 2 (the direction of arrow B in the figure).

[0018] A portion of the developer transported by the second transport screw 153 is drawn up onto the surface of the developing sleeve by the magnetic force generated by the magnet roller. The doctor blade 154, which is disposed so as to maintain a predetermined gap between the surface of the developing sleeve and the developer layer, regulates the developer layer thickness, and the developer is then transported to the developing region facing the photoreceptor 1, where toner adheres to the electrostatic latent image on the photoreceptor 1. This adhesion forms a toner image on the photoreceptor 1. The developer, from which the toner has been consumed during development, is returned to the second transport screw 153 as the developing sleeve rotates. The developer transported by the second transport screw 153 to the end of the second agent-containing chamber 5b returns to the first agent-containing chamber 5a through a communication port provided in the partition wall separating the two agent-containing chambers. In this manner, the developer is circulated within the developing device.

[0019] The detection result of the toner concentration of the developer by the toner concentration sensor 155 is sent as an electrical signal to the control unit 60 (see FIG. 6), which will be described later. The control unit 60 converts the output voltage from the toner concentration sensor 155 into the toner concentration of the developer. The control unit 60 compares the output voltage from the toner concentration sensor 155 with a target voltage value Vtref, which is a target value for the output voltage stored in the storage 51 (see FIG. 6). Then, the control unit 60 drives the toner supply device 41 to supply an amount of toner according to the comparison result from the toner supply port 5c, and an appropriate amount of toner is supplied from the toner bottle 11 to the developer in the first agent storage chamber 5a (toner supply control). As a result, the toner concentration of the developer in the first agent storage chamber 5a is maintained within a predetermined range near the target toner concentration.

[0020] The following describes the operation of the copying machine 500 of this embodiment during normal color image formation. First, when a document is set on the document table of the document transport unit 3 and the start button is pressed, the document is transported from the document table by the transport rollers of the document transport unit 3 and placed on the contact glass of the document reading unit 4. Then, the document reading unit 4 optically reads the image information of the document placed on the contact glass.

[0021] More specifically, the document reading unit 4 scans the image of the document on the contact glass while irradiating it with light emitted from an illumination lamp. The light reflected from the document is then imaged on a color sensor via a group of mirrors and a lens. The color image information of the document is read by the color sensor in units of RGB (red, green, and blue) color separation light, and then converted into electrical image signals. Furthermore, the image processing unit performs color conversion processing, color correction processing, spatial frequency correction processing, and other processing based on the RGB color separation image signals, thereby obtaining color image information of yellow, magenta, cyan, and black.

[0022] Then, the image information for each color of yellow, magenta, cyan, and black is sent to the writing unit 15. Then, the writing unit 15 emits laser light L based on the image information for each color toward the corresponding photoconductor 1 (Y, M, C, K).

[0023] Meanwhile, the four photoconductors 1 (Y, M, C, K) each rotate clockwise in FIGS. 1 and 2 (the direction of arrow A in FIG. 2). First, the surfaces of the photoconductors 1 (Y, M, C, K) are uniformly charged where they face the charging roller 14a of the charging device 14 (charging process). Thus, the surfaces of the photoconductors 1 (Y, M, C, K) reach a charged potential. Then, the charged surfaces of the photoconductors 1 (Y, M, C, K) reach the irradiation position of the laser light L. In the writing section, four light sources emit laser light L corresponding to an image signal, one for each color. Each laser light L passes through a separate optical path for each color component (yellow, magenta, cyan, black) and is irradiated onto the surface of each photoconductor 1 (Y, M, C, K) (exposure process).

[0024] The laser light L corresponding to the yellow component is irradiated onto the surface of the yellow photoconductor 1Y, which is the first from the left side of the paper in Figure 1. At this time, the laser light L of the yellow component is scanned in the direction of the rotation axis (main scanning direction) of the yellow photoconductor 1Y by a polygon mirror rotating at high speed. In this way, an electrostatic latent image corresponding to the yellow component is formed on the surface of the yellow photoconductor 1Y after it has been charged by the charging device 14.

[0025] Similarly, the laser light L corresponding to the magenta component is irradiated onto the surface of the magenta photoconductor 1M, which is the second from the left in Fig. 1, to form an electrostatic latent image corresponding to the magenta component. The laser light L for the cyan component is irradiated onto the surface of the cyan photoconductor 1C, which is the third from the left in Fig. 1, to form an electrostatic latent image for the cyan component. The laser light L for the black component is irradiated onto the surface of the black photoconductor 1K, which is the fourth from the left in Fig. 1, to form an electrostatic latent image for the black component.

[0026] Thereafter, the surfaces of the photoconductors 1 (Y, M, C, K) on which the electrostatic latent images of each color have been formed reach positions facing the developing devices 5. Then, the toner of each color is supplied from the developer on the developing rollers 151 of the developing devices 5 (Y, M, C, K) that contain the developer consisting of the toner of each color and a carrier onto the surfaces of the photoconductors 1 (Y, M, C, K), and the latent images on the photoconductors 1 (Y, M, C, K) are developed (developing process). The direction of transport of the developer by the developing rollers 151 is counterclockwise, as indicated by arrow B.

[0027] After passing through the area facing the developing device 5, the surfaces of the photoconductors 1 (Y, M, C, K) each reach the area facing the intermediate transfer belt 8. Here, a primary transfer bias roller 9 (Y, M, C, K) is installed at each of the facing areas so as to abut against the inner circumferential surface of the intermediate transfer belt 8. The photoconductors 1 (Y, M, C, K) and the primary transfer bias rollers 9 (Y, M, C, K) face each other across the intermediate transfer belt 8, forming a primary transfer nip. Then, at this primary transfer nip, the toner images of each color formed on each photoconductor 1 (Y, M, C, K) are transferred onto the intermediate transfer belt 8 in a sequentially overlapping manner (primary transfer process).

[0028] After passing through the primary transfer nip, the surface of the photoconductor 1 reaches a position facing the photoconductor cleaning device 2. At the position facing the photoconductor cleaning device 2, untransferred toner remaining on the photoconductor 1 is scraped off and collected by a cleaning blade 2a (photoconductor cleaning process). After passing the portion facing the photoconductor cleaning device 2, the surface of the photoconductor 1 passes through a charge removal section where residual charge is removed, completing a series of image formation processes on the photoconductor 1 and preparing for the next image formation operation.

[0029] Meanwhile, the color toner images on the four photoreceptors 1 (Y, M, C, K) are transferred and superimposed, and the intermediate transfer belt 8 carrying the color toner images moves counterclockwise in FIG. 1 and reaches the secondary transfer nip, which is the position facing the secondary transfer bias roller 19. Also, transfer paper P fed by a paper feed roller 27 from a paper feed cassette 26 containing transfer paper P passes through a conveyance guide and is guided to a pair of registration rollers 28, where it strikes the pair of registration rollers 28 and stops. Having struck the pair of registration rollers 28, the transfer paper P is conveyed toward the secondary transfer nip in time with the color toner image formed on the intermediate transfer belt 8 moving toward the secondary transfer nip. Then, the color toner image carried on the intermediate transfer belt 8 is transferred onto the transfer paper P at the secondary transfer nip (secondary transfer process).

[0030] After passing through the secondary transfer nip, the surface of the intermediate transfer belt 8 reaches the area facing the intermediate transfer belt cleaning device. At this area, the residual toner adhering to the intermediate transfer belt 8 is collected by the intermediate transfer belt cleaning device, and the series of transfer processes on the intermediate transfer belt 8 is completed.

[0031] The untransferred toner scraped off the surface of the photosensitive member 1 by the cleaning blade 2a passes through a recovered toner transport path and is collected in a waste toner container. In addition, the untransferred toner scraped off the surface of the intermediate transfer belt 8 by the intermediate transfer belt cleaning device and the toner of the pattern image for process control also pass through a recovered toner transport path and are collected in a waste toner container.

[0032] The transfer paper P onto which the color toner image has been transferred at the secondary transfer nip is guided to the fixing device 20. In the fixing device 20, the color image is fixed onto the transfer paper P by heat and pressure at the fixing nip formed by a fixing roller and a pressure roller. After passing through the fixing device 20, the transfer paper P is discharged as an output image outside the printer unit 100 by a pair of paper discharge rollers 25 and stacked on a paper discharge tray 30, completing the series of image formation processes.

[0033] Four toner bottles 11 (Y, M, C, K) that individually accommodate Y toner, C toner, M toner, and K toner are arranged above the intermediate transfer unit 10. The Y, C, M, and K toners in the toner bottles 11 (Y, M, C, K) are supplied as needed to the developing devices 5 (Y, M, C, K) of the imaging units 6 (Y, M, C, K) by a toner supply device. The toner bottles 11 (Y, M, C, K) are detachable from the printer body independently of the imaging units 6 (Y, M, C, K).

[0034] In order to stabilize image quality over time and in response to environmental changes, the copying machine 500 performs image density adjustment control, known as process control, at predetermined timings. FIG. 3 is a schematic diagram illustrating the image quality adjustment pattern on the intermediate transfer belt.

[0035] The image quality adjustment pattern is a gradation pattern and is made up of a plurality of toner patches with different image densities. The image quality adjustment patterns are formed at positions (the center and both ends in the width direction) of the intermediate transfer belt 8 facing the optical sensor. In the example shown in Fig. 3, image quality adjustment patterns for black, cyan, magenta, and yellow are formed from top to bottom.

[0036] The optical sensor unit 40 has a plurality of optical sensors 40R, 40C, and 40F as image density detection means arranged at predetermined intervals in the belt width direction of the intermediate transfer belt 8. Each optical sensor outputs a signal according to the light reflectance of the intermediate transfer belt 8 and the image quality adjustment patterns PtK, PtC, PtM, and PtY on the intermediate transfer belt 8, and detects the amount of toner adhesion. The copier 500 adjusts image creation conditions such as the development bias based on the detected amount of toner adhesion.

[0037] The optical sensors 40R and 40F, which are positioned to face the widthwise end regions of the intermediate transfer belt 8, are positioned outside the paper passage area. This allows the copier 500 to perform image quality adjustments such as image density adjustment during printing. Specifically, as shown in FIG. 4, an image quality adjustment pattern is formed outside the paper passage area, and the amount of toner attached to the image quality adjustment pattern is detected by the optical sensors 40R and 40F. Then, based on the amount of toner attached detected by the optical sensors 40R and 40F, the developing bias and the like are adjusted to adjust the image density and the like. The image quality adjustment pattern in this case may be just one solid image patch.

[0038] Next, the toner supply device 41 will be described. 5 is a schematic diagram showing a state in which a toner bottle is installed in a toner supply device 41. In this embodiment, there is a toner supply device and a toner bottle for each of the colors Y, M, C, and K, but the four toner supply devices 41 and toner bottles 11 (Y, M, C, and K) have almost the same structure except for the color of toner used in the image creation process. For this reason, the following description will omit the symbols Y, M, C, and K that indicate corresponding colors as appropriate.

[0039] The toner supply device 41 is composed of a toner transport path that transports the toner in the toner bottle 11 to the developing device 5, a bottle-side drive unit 43, a sub-hopper-side drive unit 44, etc. The toner transport path has a transport nozzle 42a, a vertical transport path 42b, a sub-hopper 42c, and a toner drop transport path 42d.

[0040] 5 and is attached to the printer unit 100, the conveying nozzle 42a of the toner supply device 41 is inserted into the container tip side of the toner bottle 11 in conjunction with the attachment operation. This allows communication between the inside of the toner bottle 11 and the inside of the conveying nozzle 42a.

[0041] The toner bottle 11 is a substantially cylindrical toner bottle. It is mainly composed of a non-rotatable container front cover 11a and a container body 11c integrally formed with a container gear 11b. The container body 11c is held rotatably relative to the container front cover 11a.

[0042] A rotational drive force is input from bottle-side drive unit 43, which is composed of a drive motor, drive gears, etc., to container gear 11b provided on container body 11c. As a result, container body 11c is driven to rotate in the direction of arrow A in Fig. 5. As container body 11c itself rotates, toner contained inside container body 11c is transported from left to right in Fig. 5 along the longitudinal direction of the container body by spiral protrusion 11d formed in a spiral shape on the inner circumferential surface of container body 11c.

[0043] A pumping unit is provided on the container front cover side (right side in the figure) of the container body 11c, which pumps up the toner transported to the container front cover side by the rotation of the container body 11c. This pumping unit pumps up the toner above the transport nozzle 42a inserted into the toner bottle 11, and drops it into a nozzle opening provided at the toner container side end of the transport nozzle 42a, thereby supplying the toner into the transport nozzle 42a.

[0044] A conveying screw 142a is disposed within the conveying nozzle 42a, and when rotational drive is input from the bottle-side drive unit 43 to the conveying screw gear 43a, the conveying screw 142a rotates and conveys the toner supplied into the conveying nozzle 42a in the horizontal direction. The downstream end of the conveying nozzle 42a in the conveying direction is connected to the vertical conveying path 42b, and the toner conveyed by the conveying screw 142a falls under its own weight down the vertical conveying path 42b to a sub-hopper 42c where it is temporarily stored.

[0045] Two agitating members 142b, 142c are disposed inside the sub-hopper 42c. A toner drop transport path 42d is connected to the bottom of the sub-hopper 42c, and a transport coil 142d is disposed in the toner drop transport path 42d. When rotational drive is input from the sub-hopper side drive unit 44, the toner temporarily stored in the sub-hopper 42c is agitated by the two agitating members and then transported to the developing device 5 by the transport coil 142d.

[0046] Control unit 60 (see FIG. 6) compares the output voltage from toner concentration sensor 155 with target voltage value Vtref, and controls sub-hopper-side drive unit 44 so that the amount of toner corresponding to the comparison result is replenished (toner replenishment control). Furthermore, when a toner amount detection sensor provided in sub-hopper 42c that detects the amount of toner in sub-hopper 42c detects that there is no toner, control unit 60 drives bottle-side drive unit 43 to start the process of replenishing toner to sub-hopper 42c. When the toner amount detection sensor detects that there is toner, control unit 60 stops driving bottle-side drive unit 43, and stops the replenishment of toner to sub-hopper 42c.

[0047] FIG. 6 is a functional block diagram of the copying machine 500. 6, the copier 500 includes a control unit 60. The control unit 60 includes a CPU 60a, a ROM 60b, a RAM 60c, a printer control unit 63, an image reading control unit 64, a storage control unit 65, an operation panel control unit 61, and a communication control unit 68. The control unit 60 also includes an average toner consumption calculation unit 67 and a pixel acquisition unit 69. The units that make up the control unit 60 are connected via a bus.

[0048] The control unit 60 controls the entire copier 500. The CPU 60a starts the OS using a boot program stored in the ROM 60b. The CPU 60a then executes the control programs stored in the storage 51 and the ROM 60b on the OS. The RAM 60c is used as a temporary storage area such as the main memory or work area of ​​the CPU 60a.

[0049] The printer control unit 63 of the control unit 60 functions as an interface for the CPU 60a to control each piece of hardware in the printer unit 100 (the image forming unit 6, the toner supply device 41, the intermediate transfer unit 10, the fixing device 20, etc.). The image reading control unit 64 functions as an interface for the CPU 60 a to control the image reading unit 12 . The storage control unit 65 functions as an interface for the CPU 60a to control the storage 51, which is a storage means provided in the copying machine 500.

[0050] Storage 51 is a readable / writable nonvolatile storage device such as an HDD. This storage 51 stores programs for controlling the entire copier 500, various application programs, data for managing consumable parts, and the like. Storage 51 also stores the average toner consumption per unit travel distance of each color developing device calculated by average toner consumption calculation unit 67, and a counter N that counts the number of consecutive executions of print jobs for which toner replenishment control, described later, has been stopped. It also stores a refresh threshold B for determining whether to execute a print job for which toner replenishment control, described later, has been stopped, and the like.

[0051] The operation panel control unit 61 functions as an interface for the CPU 60a to control the operation panel 50. The communication control unit 68 functions as an interface for controlling the external communication I / F 53 that the copier 500 has. The operation panel 50 includes an input unit such as a touch panel or hard keys that accepts user operation instructions, and a display unit such as an LCD or CRT.

[0052] The pixel acquisition unit 69 acquires the number of pixels of each color to be printed on the transfer paper based on the image data. The acquired pixel counts are temporarily stored in the print count memory 52 (Y, M, C, K). The acquisition cycle for the pixel counts of each color is the travel distance of the developing device for one A4-sized page.

[0053] The average toner consumption calculation unit 67 calculates the average toner consumption per unit travel distance of each color developing device (hereinafter referred to as average toner consumption). The average toner consumption is the travel distance of the developing device over a fixed period of time. In this embodiment, the travel distance of the developing device over a fixed period of time is set to the travel distance of the developing device for 50 A4 pages, but the travel distance over a fixed period of time may be set according to the characteristics of the developer and developing unit.

[0054] To calculate the average toner consumption, first, the amount of toner consumed is calculated based on the print count (number of pixels) for the travel distance of the developing device for one A4-sized page, which is temporarily stored in the print count memory 52 (Y, M, C, K). Next, the currently calculated amount of toner consumption is added to the previously calculated average toner consumption. The latest average toner consumption is then calculated by dividing this by the travel distance of the developing device over a certain period (50 A4-sized pages). Note that any indicator that can grasp how much toner has been consumed in the developing device over a specified period of time is acceptable, and is not limited to the average toner consumption. For example, the average image area ratio per unit travel distance of the developing device, the average toner consumption per unit operating time of the developing device, the average image area ratio per unit operating time of the developing device, etc. may be calculated.

[0055] The external communication I / F 53 communicates with external devices such as a PC (personal computer) via a network line, etc. The external communication I / F 53 receives image data to be printed that is sent to the copier 500 by application software installed on the PC.

[0056] When the consumption of toner in the developing device is low, a large amount of degraded toner remains in the developing device. When a large amount of degraded toner remains, the image becomes more likely to become grainy and have holes in it, resulting in a decrease in image quality. To suppress this decrease in image quality, toner refresh control (also called forced consumption control) has conventionally been performed. Toner refresh control (also called forced consumption control) is a control that forcibly consumes degraded toner in the developing device 5 at a predetermined timing, expelling the degraded toner and replacing it with non-degraded toner, thereby keeping the toner in the developing device fresh.

[0057] FIG. 7 is a control flow diagram of conventional toner refresh control. When the printing operation is completed (Yes in S1 to S4), the control unit 60 causes the average toner consumption calculation unit 67 to calculate the average toner consumption per unit travel distance of the developing device for each color (hereinafter referred to as average toner consumption) (S5). If the calculated average toner consumption for all colors exceeds the toner refresh threshold B (No in S6), a large amount of toner has been consumed, there is little degraded toner in the developing device, and there is no need to refresh the toner in the developing device. Therefore, if the calculated average toner consumption A is equal to or greater than the refresh threshold B (No in S6), toner refresh control after the printing operation is not executed.

[0058] On the other hand, if there is a color for which the calculated average toner consumption A is less than the refresh threshold B (YES in S6), toner consumption for that color is low, and there is a lot of degraded toner in the developing device of that color, which may result in image irregularities and insect holes, resulting in a decrease in image quality. Therefore, toner refresh control is performed after the printing operation is completed, and a spit-out pattern is created for each color for which the average toner consumption A is less than the refresh threshold B, and the toner of that color is spit out. As a result, the degraded toner is consumed, and the developing device of that color is replenished with undegraded toner from the toner replenishment device 41, replacing the toner in the developing device with undegraded toner. The created spit-out pattern is not transferred to the transfer paper, but is removed by the intermediate transfer belt cleaning device or the photosensitive member cleaning device 2.

[0059] As described above, in conventional printers, the created spit pattern is not transferred to the transfer paper, but is removed by the intermediate transfer belt cleaning device or the photoconductor cleaning device 2 as waste toner, which is then collected in the waste toner container. As a result, if images with low image coverage continue to be produced and toner refresh control is frequently performed, the waste toner container quickly becomes full, requiring frequent replacement. Furthermore, conventional toner refresh control is performed after a print job is completed, which causes extra image formation, thereby shortening the life of the imaging unit, etc. Furthermore, because it is performed after a print job is completed, the next print job cannot be started until the toner refresh control is completed, which could result in increased waiting times for the user.

[0060] Furthermore, with the conventional control shown in Figure 7, if all old, deteriorated toner in the developing device is ejected by creating a single ejection pattern, there is a risk of cleaning failure occurring. In particular, if all four colors fall below the refresh threshold B and the four-color ejection patterns are input to the cleaning device, a large amount of toner will be removed by the cleaning device, making cleaning failure more likely to occur. Therefore, the ejection pattern is designed to eject a small amount of toner, and the flow shown in Figure 7 is executed multiple times to gradually eject the deteriorated toner.

[0061] In conventional control, during a print job after toner refresh control, the above-mentioned toner replenishment control (control that compares the output voltage from toner concentration sensor 155 with a target voltage value and replenishes the developing device with an amount of toner according to the comparison result) is performed. As a result, after toner refresh control, the undegraded toner replenished to the developing device is mixed with the old, degraded toner that has not been ejected. Therefore, during toner refresh control after a print job, undegraded toner is also consumed, which creates the problem of not being able to efficiently eject degraded toner.

[0062] Therefore, in this embodiment, when the calculated average toner consumption amount A becomes less than the refresh threshold value B, toner replenishment control is stopped and normal printing is performed until the toner concentration in the developing device reaches the lowest possible level at which no problems occur, and the deteriorated toner in the developing device is discharged. The following describes in detail the characteristics of this embodiment.

[0063] FIG. 8 is a control flow diagram of this embodiment. The control shown in FIG. 8 is performed for each color. First, when the control unit 60 receives a print job (S11), it acquires the average toner consumption amount A, the toner concentration T of the developing device, and the counter N that counts the number of consecutive print jobs for which toner replenishment control has been stopped (S12). The average toner consumption amount A and the counter N are acquired by reading them from the storage 51. The toner concentration T of the developing device is acquired from the toner concentration sensor 155 of the developing device.

[0064] Next, the control unit 60 checks whether the acquired counter N is 0 (S13). If the acquired counter N is 0 (YES in S13), it determines that the previous print job was performed as a normal image formation operation, in which images are formed while toner replenishment control is performed. If the previous print job was a normal image formation operation, it checks whether the average toner consumption amount A is less than the refresh threshold value B (S14).

[0065] If the average toner consumption A is equal to or greater than the refresh threshold B (NO in S14), there is little degraded toner in the developing device, so an image is formed by normal image formation while performing toner replenishment control (S15, S16). On the other hand, if the average toner consumption A is less than the refresh threshold B (YES in S14), there is a risk that there is a lot of degraded toner that has remained in the developing device for a long time. Therefore, the toner replenishment control is stopped, and an image formation operation (hereinafter referred to as an image formation operation without toner replenishment) is performed to expel the degraded toner in the developing device (S22-S24).

[0066] If the acquired counter N is not 0 and the previous print job was performed using an image formation operation without toner replenishment (No in S13), it is checked whether the toner concentration T in the developing device is equal to or lower than the specified toner concentration (S20). Note that in the flow shown in Fig. 8, even if the answer is YES in S14, the step S20 is executed to check whether the toner concentration T in the developing device is equal to or lower than the specified toner concentration, but this step S20 may be omitted. This is because, if the answer is YES in S14, toner replenishment control has been executed up until that point to maintain the toner concentration in the developing device at the target toner concentration, and the toner concentration has not fallen below the specified toner concentration.

[0067] The specified toner concentration is a toner concentration lower than the target toner concentration during toner replenishment control. It is set within a range in which the decrease in image density due to a decrease in toner concentration T can be recovered by adjusting image forming conditions such as the development bias, and in which carrier adhesion to the latent image does not occur. In this embodiment, the specified toner concentration is set to the lower limit of the range in which the target toner concentration for toner replenishment control can be set. By setting the specified toner concentration to the lower limit of the range in which the target toner concentration for toner replenishment control can be set, an image is formed on the transfer paper using image formation without toner replenishment until the image quality is affected by insufficient toner concentration. This allows degraded toner in the developing device to be effectively discharged, and most of the toner in the developing device can be replaced with undegraded toner after toner replenishment is resumed.

[0068] If the toner concentration T exceeds the specified toner concentration (YES in S20), the image forming conditions (development bias, charging bias, and exposure amount) are adjusted based on the toner concentration T (S22).

[0069] FIG. 9 is a graph showing the relationship between toner concentration T in the developing device and developability γ (development γ). As shown in FIG. 9, as toner concentration T in the developing device decreases, developability γ decreases accordingly. This decrease in developability γ results in a low image density. FIG. 10 is a graph showing the relationship between image density and development bias. The solid line in FIG. 10 represents the case when toner concentration T in the developing device is α, and the dashed line represents the case when toner concentration is β (α > β). As shown by the solid line in FIG. 10, when toner concentration T is α, a target image density can be achieved by setting the development bias to Vb1. However, as shown by the dashed line in FIG. 10, a decrease in toner concentration T reduces developability γ, resulting in an image density lower than the target image density even when the development bias Vb1 is applied to the developing roller. When toner concentration is β, increasing the development bias from Vb1 to Vb2 increases the development field (development potential = development bias - exposure potential of the photoconductor surface), achieving the desired developability γ. As a result, the target image density can be achieved.

[0070] Therefore, in this embodiment, as shown in FIG. 8, if the toner concentration T exceeds the specified toner concentration (YES in S20), the developing potential, which is the developing electric field, is adjusted based on the toner concentration T (S22). First, the control unit 60 determines the developing bias based on the toner concentration detected by the toner concentration sensor 155. Specifically, a table correlating the toner concentration with the developing bias Vb that will achieve the target image density at that toner concentration is stored in the storage 51. The control unit 60 identifies the developing bias that will achieve the target image density at the detected toner concentration based on the toner concentration T detected by the toner concentration sensor 155 and the table stored in the storage, and sets the identified developing bias. Next, the control unit 60 sets the charging bias and exposure amount based on the set developing bias. The charging bias is set to a charging bias that will achieve a desired background potential (the difference between the potential of the background portion (unexposed portion) of the photoconductor surface and the developing bias potential). The exposure amount is set to an exposure amount that will achieve a desired post-exposure potential on the photoconductor surface with that charging bias.

[0071] If the set developing bias, charging bias, and exposure amount do not exceed the settable upper limit (NO in S23), an image formation operation without toner replenishment is carried out (S25 to S27).

[0072] When printing using this image creation operation without toner replenishment, an image quality adjustment pattern is formed outside the paper passing area after every few sheets are printed, and the developing bias and other parameters are adjusted based on the amount of toner adhesion detected by optical sensors 40R and 40F to adjust the image density, etc. This prevents degradation of image quality due to degraded toner and maintains good images.

[0073] When image formation for one page of transfer paper is completed in the image formation operation without toner replenishment (S27), the control unit 60 redetects the toner concentration T in the developing device (S28). If the toner concentration T in the developing device is not equal to or lower than the specified toner concentration (YES in S20 or YES in S29) and the development bias, charging bias, and exposure amount to be set are all equal to or lower than their upper limit values ​​(YES in S23), the next image formation (printing) will also be performed in the image formation operation without toner replenishment.

[0074] On the other hand, if the toner concentration T is equal to or lower than the specified toner concentration in S20 or S29 (NO in S20, NO in S29), there is a risk of image quality problems occurring if image formation is performed without further toner replenishment, so toner replenishment control is resumed (S21, S30). Also, if any of the set development bias, charging bias, and exposure amount is equal to or higher than the upper limit (NO in S23), image quality cannot be maintained by adjusting the image formation conditions, so toner replenishment control is resumed (S24).

[0075] When toner supply control is resumed, as described above, an amount of toner corresponding to the comparison result between the output voltage of the toner concentration sensor 155 and the target voltage value Vtref is supplied from the sub-hopper to the developing device, and the toner concentration in the developing device is restored to the target toner concentration.

[0076] It is preferable to execute the above-described image quality adjustment control and adjust the image forming conditions (development bias, charging bias, and exposure amount) at the first timing when the toner concentration in the developing device reaches the target toner concentration after toner replenishment control is resumed. This changes the image forming conditions corresponding to the decreased toner concentration to the image forming conditions corresponding to the target toner concentration, thereby improving the quality of the image formed by normal image forming operation.

[0077] Thus, in this embodiment, image formation continues without replenishment of undegraded toner in the developing device until the toner concentration T falls below the specified toner concentration or any one of the developing bias, charging bias, and exposure amount reaches or exceeds its upper limit after the average toner consumption A falls below the refresh threshold B. As a result, images are formed using the toner remaining in the developing device, efficiently consuming degraded toner in the developing device, until the toner concentration falls below the specified toner concentration or any one of the developing bias, charging bias, and exposure amount reaches or exceeds its upper limit, making it impossible to form a good image. Then, once the toner concentration falls below the specified toner concentration or any one of the developing bias, charging bias, and exposure amount reaches or exceeds its upper limit, toner replenishment control resumes, and undegraded toner is replenished until the toner concentration in the developing device returns to the target toner concentration. This refreshes the toner in the developing device with toner that is almost undegraded.

[0078] If images with low image area ratios continue to be produced during image formation without toner replenishment when toner replenishment control is stopped, the average toner consumption amount A will be less than the refresh threshold value B during the next image formation after toner replenishment control is restarted. As a result, there is a risk that an image will be formed again during image formation without toner replenishment when toner replenishment control is stopped, even though there is almost no degraded toner left in the developing device.

[0079] Therefore, it is preferable to calculate the average toner consumption amount A as follows. That is, calculation of the average toner consumption amount A is stopped during image formation without toner replenishment. Then, when toner replenishment control is resumed (S21, S27), the amount of toner replenished to the developing device to restore the target toner concentration is calculated as the amount of toner consumed over the travel distance of the developing device over a predetermined period (equivalent to one A4-sized page). Specifically, as described above, the average toner consumption amount is calculated by adding the amount of replenished toner to the previously calculated average toner consumption amount and dividing the result by the travel distance of the developing device over a predetermined period (equivalent to 50 A4-sized pages). This allows the calculated average toner consumption amount to correspond to the deterioration state of the toner in the developing device. However, without being limited to this, the average toner consumption amount may be changed to a specified value when toner replenishment control is resumed.

[0080] During normal image formation, in which toner replenishment control is performed, once the developing device has traveled a distance corresponding to one A4-sized page (S16), the average toner consumption is calculated (S17). If the print job is continuing (NO in S18), it is checked whether the calculated average toner consumption A is less than the refresh threshold B (S14). If the calculated average toner consumption is equal to or greater than the refresh threshold B (NO in S14), image formation (normal image formation) continues while toner replenishment control is performed (S15-S18). On the other hand, if the calculated average toner consumption is less than the refresh threshold B (YES in S14), the process switches to image formation without toner replenishment, in which toner replenishment control is stopped (S22-S29).

[0081] If, at the end of the print job, a normal image formation operation is being performed in which images are formed while toner replenishment control is being performed (YES in S18), the counter N is updated to 0 (S19), and the calculated average toner consumption amount A is stored in storage. On the other hand, if, at the end of the print job, an image formation operation without toner replenishment is being performed in which toner replenishment control is stopped and images are formed (YES in S31), the counter N is incremented (updated to N+1) (S32). As a result, at the time of the next print job, if the counter N is not 0, it can be determined that an image formation operation without toner replenishment was being performed at the end of the previous job, and the image formation operation without toner replenishment will continue until the toner concentration T falls below the specified toner concentration, or any one of the developing bias, charging bias, and exposure amount reaches or exceeds an upper limit value.

[0082] In this way, in this embodiment, deteriorated toner in the developing device can be expelled and replaced with undeteriorated toner without performing refresh control. This prevents extra image creation and reduces the lifespan of the imaging unit, etc., compared to conventional methods in which refresh control is performed after a print job is completed. Furthermore, the next print job can be started immediately after a print job is completed, eliminating the need for the user to wait. Furthermore, compared to methods in which a spit pattern that is not transferred to the transfer paper is created to expel deteriorated toner in the developing device, the time it takes for the waste toner container to fill up can be extended, reducing the need for frequent replacement.

[0083] The specified toner concentration used to determine whether to restart toner supply control is preferably changed based on the device environment. Figure 11(a) is a graph showing the conditions for toner concentration TC and developing bias Vb that do not cause image defects in a low-temperature, low-humidity environment (10°C, 15%). Figure 11(b) is a graph showing the conditions for toner concentration TC and developing bias Vb that do not cause image defects in a high-temperature, high-humidity environment (27°C, 80%). The establishment window in Figure 11 is the condition for toner concentration TC and developing bias Vb that does not cause image defects.

[0084] A1 and B1 in Figure 11 indicate the boundaries at which poor pumping to the developing roller occurs. If the toner concentration TC is higher than A1 or B1, there is too much toner, and the magnetic force generated by the magnetic roller of the developing roller will not be able to properly pump the developer onto the surface of the developing sleeve.

[0085] A2 and B2 are the boundaries where density unevenness known as "dark at the leading edge" occurs. "Dark at the leading edge" is an abnormal image where the leading edge of a solid image becomes dark for one revolution of the developing roller. If the toner concentration TC is higher than A2 and B2, "dark at the leading edge" occurs.

[0086] A3 and B3 indicate the boundaries where a "halo image" occurs. A "halo image" is an abnormal image where the dot reproducibility of a halftone image adjacent to a solid image deteriorates and the image appears white. This "halo image" is caused by the effects of the edge electric field that occurs at the edge of the solid image, and by the effect of scraping off toner adhering to the photosensitive drum as the magnetic brush, which has consumed toner in developing the solid latent image, passes the rear edge of the halftone due to countercharging. If the toner concentration TC is higher than A3 or B3, a "halo image" will occur.

[0087] A4 and B4 indicate the boundaries at which "solid carrier adhesion" occurs, where carrier adheres to a solid image. When the relationship between toner concentration TC and development bias Vb is above A4 and B4, "solid carrier adhesion" occurs.

[0088] A5 and B5 are boundaries where development becomes impossible due to lack of toner, and if the toner concentration TC is lower than A5 or B5, development becomes impossible due to lack of toner. A6 and B6 indicate the boundaries of negative development, and if the development bias Vb is lower than A6 and B6, negative development becomes impossible. A7 and B7 are boundaries where "edge carrier adhesion," in which carrier adheres to the edge of an image, occurs. When the relationship between the toner concentration TC and the developing bias Vb is above A7 and B7 in the figure, "edge carrier adhesion" occurs.

[0089] A8 in Figure 11(a) is the lower limit at which a desired image density can be obtained, and if the relationship between toner concentration TC and developing bias Vb is below A8 in the figure, the desired image density cannot be obtained. B8 in Figure 11(b) is the upper limit at which a desired image density can be obtained, and if the relationship between toner concentration TC and developing bias Vb is above B8 in the figure, the desired image density cannot be obtained.

[0090] As shown in Figures 11(a) and 11(b), the toner concentration TC at boundaries A5 and B5, where development becomes impossible due to insufficient toner, is the lowest toner concentration (lower limit) within the range (the range within which the target toner concentration can be set) without causing defects. However, as shown in Figure 11(a), in a low-temperature, low-humidity environment (10°C, 15%), the allowable range of the development bias Vb at the toner concentration TC at boundary A5 without causing image defects is narrow. Therefore, if the specified toner concentration for resuming toner replenishment control is set to the toner concentration TC at boundary A5 in a low-temperature, low-humidity environment (10°C, 15%), the following problem may occur. That is, when the development bias Vb is varied by process control near the toner concentration TC at boundary A5, the development bias Vb may exceed boundary A4, resulting in "solid carrier adhesion." Therefore, in a low-temperature, low-humidity environment, the specified toner concentration is set slightly higher than the toner concentration TC at boundary A5 (X in Figure 11(a)).

[0091] On the other hand, as shown in Figure 11(b), in a high-temperature, high-humidity environment (27°C, 80%), even if the specified toner concentration is set to the toner concentration TC at boundary B5 (the lower limit of the settable range for the target toner concentration) where development becomes impossible due to insufficient toner, the allowable range of the development bias Vb without image defects is wide. Therefore, even if the development bias Vb is varied by process control near the toner concentration TC at boundary B5, "solid carrier adhesion" is unlikely to occur. Therefore, in a high-temperature, high-humidity environment, the toner concentration TC at boundary B5 (the lower limit of the settable range for the target toner concentration) is set to the specified toner concentration (X in Figure 11(b)).

[0092] Note that since the toner concentration sensor 155 has a detection error, in reality, as shown in Figures 11(a) and (b), in the range of X1, the toner concentration sensor 155 detects that the toner concentration has reached the specified toner concentration, and toner replenishment control is resumed.

[0093] A table associating temperature and humidity with the above-mentioned specified toner concentration is stored in storage 51, and control unit 60 detects the temperature and humidity inside the device using a temperature and humidity detection sensor, which is an environment detection means, when a print job starts. Then, by setting the specified toner concentration corresponding to the temperature and humidity detected from the table stored in storage 51 as the specified toner concentration, it is possible to set the specified toner concentration according to the device environment.

[0094] Furthermore, the upper limit value of the developing bias (S23 in the flow of Fig. 8) that determines whether to resume toner replenishment control may be set to the upper limit value of the developing bias that establishes the establishment window shown in Fig. 11. As shown in Fig. 11, the upper limit value of the developing bias that establishes the establishment window differs for each environment and each toner concentration, so the control unit 60 sets the upper limit value of the developing bias based on the temperature and humidity detected by the temperature and humidity detection sensor, which is the environment detection means, and the toner concentration detected by the toner concentration sensor 155.

[0095] FIG. 12 is a graph showing the change in toner concentration in the developing device when an image is formed to be transferred onto a transfer paper in accordance with the control flow diagram shown in FIG. 12, up until time t1, normal image formation is performed while performing toner replenishment control, and the toner concentration in the developing device is maintained at approximately the target toner concentration. After image formation with a low image area ratio continues for a while, at time t1, when the calculated average toner consumption amount A falls below the refresh threshold B, the toner replenishment control is stopped and the image formation is switched to without toner replenishment.

[0096] By switching to image formation operation without toner replenishment, image formation (development) is performed without replenishment of toner to the developing device, and the toner concentration in the developing device decreases. Then, at time t2, when the toner concentration in the developing device falls below the specified toner concentration, toner replenishment control is resumed. This increases the toner concentration in the developing device and restores it to the target toner concentration. After that, the image to be transferred to the transfer paper is formed by normal image formation operation, in which toner replenishment control is performed so that the toner concentration in the developing device is maintained at the target toner concentration.

[0097] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to such specific embodiments, and unless otherwise specifically limited in the above description, various modifications and variations are possible within the spirit and scope of the present invention as set forth in the claims. In the above description, when the average toner consumption A per unit travel distance of the developing device is less than the refresh threshold B, the system switches to image formation without toner replenishment and expels degraded toner from within the developing device. However, for example, the system may switch to image formation without toner replenishment when the idle period (the period during which the developing device is stopped) exceeds a threshold. The developing device may have a gap between the developing roller and the case, or an exhaust port for exhausting air that enters the case through the gap between the developing roller and the case as the developing roller rotates. The toner in the developing device is more susceptible to deterioration due to contact with air than toner in a toner bottle or sub-hopper. Therefore, by switching to image formation without toner replenishment when the idle period (the period during which the developing device is stopped) exceeds a threshold, the degraded toner in the developing device is expelled, and by resuming toner replenishment control after the expulsion (when the toner concentration is less than the specified toner concentration), the toner in the developing device can be refreshed from degraded toner to undegraded toner.

[0098] The above description is merely an example, and each of the following aspects provides unique effects. (Aspect 1) a latent image carrier such as a photoreceptor 1 that is uniformly charged by a charging device 14 to which a charging bias is applied and then exposed to light by an exposure device such as a writing unit 15 to form a latent image on the surface; a developing device 5 that carries the developer in a developer storage unit that stores developer containing toner and carrier on the surface of a developer storage unit such as a developing roller 151, transports the developer to a development area facing the latent image carrier, and applies a development bias to the developer storage unit to form a development electric field (development potential) in the development area that moves the toner to the latent image on the latent image carrier; a toner concentration detection means such as a toner concentration sensor 155 that detects the toner concentration in the developer in the developer storage unit; a toner supplying means such as a toner supplying device 41 that supplies toner to the developing device 5; and a toner concentration detection means that detects whether the toner concentration in the developer in the developer storage unit reaches a target toner concentration based on the detection result of the toner concentration detection means. In an image forming apparatus which forms an image by finally transferring a toner image obtained by developing a latent image with a developing device 5 onto a recording material, the apparatus implements toner replenishment prohibition image formation control, which forms an image to be transferred onto the recording material at a specific timing with toner replenishment by the toner replenishment means stopped, and during replenishment prohibition image formation control, the developing bias, charging bias, and exposure amount when exposing the surface of the latent image carrier with the exposure device are set based on the detection result of the toner concentration detection means, and when the detection result of the toner concentration detection means shows that the toner concentration in the developer in the developing device is equal to or lower than a specified toner concentration which is set lower than the target toner concentration, or when one of the charging bias, developing bias, and exposure amount is equal to or higher than an upper limit, the toner replenishment prohibition image formation control is terminated. In Patent Document 1, the forced toner consumption pattern is not transferred to a recording material, but is removed by a cleaning device that cleans the surface of the intermediate transfer belt, and the toner that constituted the removed forced toner consumption pattern is stored in a waste toner container as waste toner. As a result, there is a risk that the waste toner container will quickly become full and will have to be replaced more frequently. In aspect 1, an image to be transferred to a recording material is formed without toner being replenished to the developing device. Therefore, the image to be transferred to the recording material is created using degraded toner in the developing device until the toner concentration reaches or falls below a specified level, allowing the degraded toner to be consumed efficiently. Furthermore, in this aspect, since degraded toner is consumed in the creation of an image to be transferred to a recording material, the time until the waste toner container becomes full can be extended, and the frequency of replacing the waste toner container can be reduced, compared to Patent Document 1, in which degraded toner is consumed in the creation of a forced toner consumption pattern that is not transferred to a recording material. In addition, when toner replenishment prohibited image formation control is used to form an image to be transferred to a recording material while toner replenishment by the toner replenishment means is stopped, the development bias, charging bias, and exposure amount can be adjusted based on the detection results of the toner concentration detection means, thereby suppressing a decrease in the image density of the toner image transferred to the recording material due to a decrease in toner concentration in the development device and maintaining a good image. In addition, the toner replenishment prohibition image formation control is terminated when the toner concentration detection means detects that the toner concentration in the developer in the developing device is equal to or lower than the target toner concentration, which is set to a lower value, thereby allowing toner replenishment control to be resumed before solid carrier adhesion or toner depletion occurs.Furthermore, the toner replenishment prohibition image formation control is also terminated when one of the charging bias, developing bias, and exposure amount exceeds its upper limit, allowing toner replenishment control to be resumed before the decrease in image density due to the decrease in toner concentration in the developing device can no longer be compensated for by adjusting the charging bias, developing bias, and exposure amount.This allows for the maintenance of high-quality images.

[0099] (Aspect 2) In the first aspect, the specific timing is the timing when the average toner consumption amount A per unit travel distance of the developing device 5 becomes smaller than the threshold value. As a result, as described in the embodiment, toner replenishment prohibition image formation control such as image creation operations can be performed at a time when the toner in the developing device 5 is not being consumed much and there is a risk of toner remaining in the developing device for a long time and degrading.

[0100] (Aspect 3) In the second aspect, the average toner consumption amount is calculated based on the number of pixels of an image formed on a recording material during a period in which the developing device 5 travels a predetermined travel distance. According to this, as explained in the embodiment, the average toner consumption amount A per unit travel distance of the developing device 5 can be calculated.

[0101] (Aspect 4) In any of the first to third aspects, the specified toner concentration is the lower limit of the range that can be set as the target toner concentration. As explained in the embodiment, this allows for toner replenishment-prohibited image formation control, such as image formation without toner replenishment, to be performed until the toner concentration in the developing device 5 reaches the lowest possible level where insufficient toner concentration does not affect the image, and allows for efficient discharge of deteriorated toner from within the developing device. Therefore, after the toner concentration falls below the specified toner concentration and toner replenishment control is resumed, the toner in the developing device can be almost undegraded, allowing for efficient refreshing of the toner in the developing device.

[0102] (Aspect 5) In any of the first to fourth embodiments, the specified toner concentration is changed depending on the environment. According to this, as explained in the embodiment, it is possible to maintain a good image even when the toner concentration in the developing device decreases.

[0103] (Aspect 6) In any of aspects 1 to 5, when toner replenishment-prohibited image formation control, such as image formation operation without toner replenishment, is executed, the development bias is determined based on the detection results of the toner concentration detection means, and the charging bias and exposure amount are set based on the determined development bias. This allows the development bias, charging bias, and exposure amount to be set to a desired development potential and a desired background potential, as described in the embodiment. [Explanation of symbols]

[0104] 1: Photoreceptor 2: Photoconductor cleaning device 5: Developing device 5a: First agent storage chamber 5b: Second agent storage chamber 5c: Toner supply port 6: Imaging unit 11: Toner bottle 12: Image reading unit 13: Lubricant application device 15: Writing section 40: Optical sensor unit 41: Toner supply device 42a: Conveying nozzle 42b: Vertical conveying path 42c: Subhopper 42d: Toner drop transport path 43: Bottle side drive unit 43a: Conveying screw gear 44: Sub-hopper side drive unit 50: Operation panel 52: Print count memory 60: Control section 67: Average toner consumption calculation unit 69: Pixel acquisition unit 100: Printer section 142: Carrying coil 142a: Conveying screw 142b: stirring member 142d: Carrying coil 151: Developing roller 152: First conveying screw 153: Second transport screw 154: Doctor Blade 155: Toner density sensor 500: Copier [Prior art documents] [Patent documents]

[0105] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-105147

Claims

1. a latent image carrier that is uniformly charged by a charging device to which a charging bias is applied, and then has its surface exposed by an exposure device to form a latent image on its surface; a developing device that carries the developer in a developer storage unit, which stores developer containing toner and carriers, on the surface of a developer carrier and transports the developer to a development area facing the latent image carrier, and applies a development bias to the developer carrier to form a development electric field in the development area that moves the toner to the latent image on the latent image carrier; and a toner concentration detecting means for detecting a toner concentration in the developer in the developer container; a toner supply means for supplying toner to the developing device; a toner supply control means for controlling the toner supply means based on the detection result of the toner concentration detection means so that the toner concentration in the developer in the developer accommodating portion becomes a target toner concentration; In an image forming apparatus, the toner image obtained by developing the latent image by the developing device is finally transferred onto a recording material to form an image, performing a toner replenishment inhibited image formation control at a specific timing, in which an image to be transferred onto the recording material is formed in a state in which toner replenishment by the toner replenishment means is stopped; During the toner replenishment prohibition image formation control, the developing bias, the charging bias, and the exposure amount when the surface of the latent image carrier is exposed by the exposure device are set based on the detection result of the toner concentration detection means, An image forming apparatus characterized in that the toner replenishment prohibition image formation control is terminated when the detection result of the toner concentration detection means shows that the toner concentration in the developer in the developing device is equal to or lower than a specified toner concentration that is set lower than the target toner concentration, or when one of the charging bias, the developing bias, and the exposure amount is equal to or higher than an upper limit value.

2. 2. The image forming apparatus according to claim 1, The image forming apparatus is characterized in that the specific timing is a timing when an average amount of toner consumed per unit travel distance of the developing device becomes smaller than a threshold value.

3. 3. The image forming apparatus according to claim 2, The image forming apparatus according to claim 1, wherein the average toner consumption amount is calculated based on the number of pixels of an image formed on the recording material during a period in which the developing device has traveled a predetermined travel distance.

4. 2. The image forming apparatus according to claim 1, The image forming apparatus is characterized in that the specified toner density is a lower limit value of a range that can be set as the target toner density.

5. 2. The image forming apparatus according to claim 1, The image forming apparatus is characterized in that the specified toner concentration is changed depending on the environment.

6. 2. The image forming apparatus according to claim 1, An image forming apparatus characterized in that, when the toner replenishment prohibition image formation control is executed, the developing bias is determined based on the detection result of the toner concentration detection means, and the charging bias and the exposure amount are set based on the determined developing bias.

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