Image forming apparatus

Abstract

To provide an image forming apparatus that can prevent the occurrence of scumming and toner separation after replacement of a toner container.SOLUTION: An image forming apparatus executes, at the timing when a toner bottle 11 that is a toner container is replaced, a toner supply OFF image forming operation that is toner supply inhibition image forming control of performing image formation, while supply of toner, which is performed by a toner supply device that is toner supply means, is stopped, until a detection result from a toner concentration sensor that is toner concentration detection means becomes equal to or less than a first regular toner concentration that is the concentration of toner in developer in a developing device and is set lower than a target toner concentration.SELECTED DRAWING: Figure 12

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; a developing device that carries developer, which contains developer containing toner and carrier, on the 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. 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 supply by a toner supply means stopped 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 supply and executing forced toner consumption control, deteriorated toner in a developing device can be efficiently consumed. Summary of the Invention [Problem to be solved by the invention]

[0004] Due to changes in toner specifications aimed at improving image quality, the base material or external additives of the toner in the toner container may be changed, and toner replacement may result in the replenishment of toner (hereinafter referred to as new toner) with different properties from the toner in the developing device (hereinafter referred to as original toner).As a result, friction between the new toner and the original toner in the developing device may cause one of the two toners with different properties to be charged with a polarity opposite to the normal charging polarity or to become low-charged, which could cause problems such as background scumming and toner falling off. [Means for solving the problem]

[0005] In order to solve the above-mentioned problems, the present invention provides 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; a developing device that carries developer in a developer container containing developer including toner and carrier on a developer carrier, 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 toner to the latent image on the latent image carrier; toner concentration detecting means that detects the toner concentration in the developer in the developing device; toner supplying means that supplies toner from a toner container that contains the toner to the developing device; and a toner concentration detecting means that detects the toner concentration in the developer in the developing device. and a toner supply control means for controlling the toner supply means based on the detection result of the detection means so that the toner concentration in the developer in the developing device becomes a target toner concentration, and the image forming apparatus finally forms an image by transferring the toner image obtained by developing the latent image with the developing device to a recording material, characterized in that, when the toner container is replaced, the toner supply prohibiting image formation control is implemented, in which image formation is performed with toner supply by the toner supply means stopped until the detection result of the toner concentration detection means indicates that the toner concentration in the developer in the developing device becomes equal to or lower than a first specified toner concentration set lower than the target toner concentration. [Effects of the Invention]

[0006] According to the present invention, it is possible to prevent background scumming and toner dropping after replacing a toner container. [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] 5A and 5B are conceptual diagrams illustrating discharge control, which is a feature of the present embodiment. [Figure 8] 10 is a graph showing the relationship between the toner concentration in the developing device and the developing capacity. [Figure 9] FIG. 4 is a graph showing the relationship between image density and developing bias. [Figure 10] 6 is a graph showing an example of the transition of the toner concentration in the developing device and the set developing bias in the discharge control of the present embodiment. [Figure 11] 4A and 4B are diagrams illustrating the inside of the developing device when the toner discharge control of the present embodiment is performed. [Figure 12] FIG. 10 is a flow chart for determining whether to perform discharge control. [Figure 13] FIG. 4 is a control flow diagram of the discharge control of the present embodiment. [Figure 14] (a) is a graph showing the conditions for toner concentration and development bias that do not cause image defects in a low-temperature, low-humidity environment, and (b) is a graph showing the conditions for toner concentration and development bias that do not cause image defects in a high-temperature, high-humidity environment. 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. The printer section 100 also includes a writing section 15 such as an exposure device that writes an electrostatic latent image onto the surface of each drum-shaped photoconductor 1 (Y, M, C, K) that serves as an image carrier on which the color toner image of each imaging unit 6 (Y, M, C, K) is formed. Each imaging unit 6 (Y, M, C, K) includes a developing device 5 (Y, M, C, K) that develops the electrostatic latent image on the surface of the corresponding 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) are disposed above the intermediate transfer unit 10, each serving as a toner container and containing Y toner, C toner, M toner, and K toner, respectively. 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 11 is installed in a toner supply device 41. In this embodiment, there is a toner supply device 41 and a toner bottle 11 for each of the colors Y, M, C, and K, but the four toner supply devices 41 and toner bottles 11 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 toner in a toner bottle 11, which is a toner container, 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] Furthermore, if the toner amount detection sensor does not detect the presence of toner even after the bottle side drive unit 43 has been driven for a predetermined time, it is determined that the toner is out, and a message is displayed on the display unit of the operation panel 50 instructing the user to replace the toner bottle 11.

[0048] 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 components constituting the control unit 60 are connected via a bus.

[0049] 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.

[0050] 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.

[0051] The storage 51 is a readable / writable nonvolatile storage device such as an HDD, etc. The storage 51 stores programs for controlling the entire copier 500, various application programs, data for managing consumable parts, and the like.

[0052] 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.

[0053] 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.

[0054] Toner specifications may be changed for technical reasons, such as improving image quality, in the copier 500. As a result, the base material and external additives of the toner in the replaced toner bottle 11 (hereinafter referred to as new toner) may differ from those of the toner in the developing device 5 (hereinafter referred to as original toner), and the characteristics of the new toner in the toner bottle 11 may differ from those of the original toner in the developing device 5. As a result, when new toner is replenished to the developing device 5, toners with different characteristics may be mixed in the developing device 5. This mixing of toners causes friction between the toners with different characteristics. This friction between two toners with different characteristics may cause one of the toners to be charged with a polarity (positive polarity) opposite to the normal charging polarity (negative polarity) or to become low-charged. This may result in image defects such as background scumming and toner loss.

[0055] Therefore, in this embodiment, when a toner bottle 11 containing new toner with properties different from those of the original toner in the developing device 5 is attached to the printer unit 100, the toner supply operation is stopped, a print job is performed, and discharge control is implemented to discharge the original toner in the developing device 5, thereby preventing the different toners from mixing together. The following describes the characteristic features of this embodiment.

[0056] FIG. 7 is a conceptual diagram of the discharge control, which is a feature of this embodiment. As shown in Figure 7, the discharge control involves performing a series of operations at least once, consisting of a toner supply OFF image formation operation 81 in which toner supply is stopped and an image is formed, and a toner supply ON image formation operation 82 in which an image is formed while toner supply is being continued.

[0057] The toner supply OFF image formation operation 81 is performed until the toner concentration in the developing device 5 reaches a first specified toner concentration that is lower than the target toner concentration for toner supply control during normal operation. This first specified toner concentration is set within a range in which a decrease in image density due to a decrease in toner concentration can be recovered by adjusting the image formation conditions such as the developing bias, and in which carrier adhesion to the latent image does not occur. During the toner supply OFF image formation operation 81, the drive of the sub-hopper side drive unit 44 is stopped, thereby stopping the toner supply to the developing device 5.

[0058] Furthermore, when toner supply OFF image formation operation is started, only the sub-hopper-side drive unit 44 is driven for a predetermined time to discharge the original toner in the sub-hopper to the developing device 5 and empty the sub-hopper 42c. Then, after driving the sub-hopper-side drive unit 44 for the predetermined time, the bottle-side drive unit 43 may be driven to transport new toner in the toner bottle to the empty sub-hopper 42c. This makes it possible to prevent original toner from being replenished from the sub-hopper immediately after the start of toner supply ON image formation operation 82, and to prevent the proportion of original toner in the developing device from increasing after toner supply ON image formation operation.

[0059] In this embodiment, the first specified toner concentration is set to the lower limit of the range of toner concentration targets that can be set for toner replenishment control. By setting the first specified toner concentration to the lower limit of the range of toner concentration targets that can be set for toner replenishment control, images are formed using toner replenishment-off image formation until the very limit at which insufficient toner concentration would affect the image. This allows the original toner in the developing device to be efficiently discharged.

[0060] The image formed during the toner supply OFF image forming operation 81 may be an image that is not transferred to the transfer paper, such as a spit pattern, but is removed by the intermediate transfer belt cleaning device or the photosensitive drum cleaning device 2. However, in this embodiment, an image that is transferred to the transfer paper, such as a copy image or a print image, is used for the following reasons. That is, the toner constituting the image that is not transferred to the transfer paper, such as a spit pattern, is removed by the intermediate transfer belt cleaning device or the photosensitive drum cleaning device 2 and becomes waste toner. Because the waste toner is stored in the waste toner container, the waste toner container may quickly become full, requiring frequent replacement. On the other hand, by forming the image formed during the toner supply OFF image forming operation 81 as an image that is transferred to the transfer paper, such as a copy image or a print image, the time it takes for the waste toner container to become full can be extended, thereby reducing the frequency of replacement. Another advantage is that, compared to an image that is not transferred to the transfer paper, such as a spit pattern, no additional image forming operation is required, thereby minimizing the shortened life of the imaging unit.

[0061] During this toner supply OFF image forming operation 81, the image forming conditions are adjusted based on the toner density in the developing device, and the image density is maintained. FIG. 8 is a graph showing the relationship between the toner concentration T in the developing device 5 and the developability γ (development γ). As shown in FIG. 8, as the toner concentration T in the developing device 5 decreases, the developability γ decreases accordingly. This decrease in developability γ results in a lower image density. FIG. 9 is a graph showing the relationship between image density and the developing bias Vb. The solid line in FIG. 9 represents the case when the toner concentration T in the developing device 5 is α, and the dashed line represents the case when the toner concentration is β (α>β). As shown by the solid line in FIG. 9, when the toner concentration T is α, the target image density can be obtained by setting the developing bias to Vb1. However, as shown by the dashed line in FIG. 9, the decrease in the toner concentration T causes the developability γ to decrease, resulting in an image density lower than the target image density even when the developing bias Vb1 is applied to the developing roller 151. When the toner concentration is β, increasing the developing bias from Vb1 to Vb2 increases the development electric field (development potential = development bias Vb - exposure potential of the photosensitive surface), achieving the desired developability γ. As a result, the target image density can be obtained.

[0062] Therefore, during toner supply OFF image formation operation 81, the image formation conditions are adjusted based on the toner concentration in developing device 5. First, the developing bias Vb is determined based on the toner concentration in developing device 5 detected by toner concentration sensor 155, and the developing potential, which is the developing electric field, is adjusted. Specifically, a table that associates the toner concentration with the developing bias Vb that will obtain a target image density at that toner concentration is stored in storage 51. Control unit 60 identifies the developing bias Vb that will obtain the target image density at the detected toner concentration from the toner concentration detected by toner concentration sensor 155 and the table stored in storage 51, and sets the identified developing bias Vb.

[0063] Next, the charging bias and exposure amount are set based on the set development bias Vb. The charging bias is set to a value that will give a desired background potential (the difference between the potential of the background portion (unexposed portion) of the photosensitive drum surface and the development bias potential). The exposure amount is set to a value that will give a desired post-exposure potential on the photosensitive drum surface with that charging bias.

[0064] The timing for adjusting the image forming conditions is not particularly limited, and may be set as appropriate, for example, every time a predetermined number of images are formed, every time the toner concentration in the developing device drops by a predetermined value, etc. When the toner concentration in the developing device 5 falls below a first specified toner concentration and the limit of the toner supply OFF operation is reached, the toner supply OFF image forming operation 81 is switched to toner supply ON image forming operation 82.

[0065] When the sub-hopper side drive unit 44 is driven to replenish toner to the developing device 5, the developing device 5 must be driven to stir and transport the toner replenished to the developing device 5 using the transport screw, thereby making the toner concentration in the developing device uniform. Therefore, if toner is replenished at times other than when an image is being created, unnecessary operation occurs in the photosensitive member 1, developing device 5, etc., leading to a shortened lifespan. Therefore, in this embodiment, toner is replenished only when an image is being created.

[0066] The toner supply ON image formation operation 82 is performed until the toner concentration in the developing device 5 reaches a second specified toner concentration that is higher than the target toner concentration during toner supply control during normal printing operations. This second specified toner concentration is set within a range that allows the increase in image density due to the increase in toner concentration to be restored by adjusting the image formation conditions such as the developing bias, and that does not cause abnormal images such as "halo images," which are abnormal images in which the dot reproducibility of halftone images adjacent to solid images deteriorates and results in whiteout.

[0067] In this embodiment, the second specified toner concentration is set to the upper limit of the range that can be set as the target toner concentration for toner replenishment control. By setting the second specified toner concentration to the upper limit of the range that can be set as the target toner concentration for toner replenishment control, toner replenishment is performed up to the point where an increase in toner concentration would affect the image. This effectively increases the proportion of new toner in the toner in the developing device 5 after toner replenishment is turned on for image formation. This reduces friction between the new toner and the original toner, preventing one of the two toners from becoming a reversely charged toner with a polarity opposite to the normal charge polarity or a low-charge toner. This reduces image defects such as background scumming and toner loss.

[0068] During toner supply-ON image formation, the toner concentration in the developing device, which had decreased during toner supply-OFF image formation 81, increases due to toner supply. This increases the development capability γ, resulting in a higher image density. Therefore, during toner supply-ON image formation, the image formation conditions are adjusted to maintain the image density. The adjustment of the image formation conditions during toner supply-ON image formation is similar to the adjustment of the image formation conditions during toner supply-OFF image formation. Specifically, based on the toner concentration in the developing device 5 detected by the toner concentration sensor 155 and the table stored in storage 51, the developing bias Vb that will achieve the target image density at the detected toner concentration is identified and set. Next, the charging bias is set based on the set developing bias Vb, and the exposure amount is set based on the set charging bias.

[0069] Then, when the toner concentration in the developing device reaches or exceeds the second specified toner concentration, the toner supply ON image formation operation 82 is terminated. The discharge control of this embodiment performs a series of operations, such as the toner supply OFF image formation operation 81 followed by the toner supply ON image formation operation 82, at least once in succession.

[0070] 10 is a graph showing an example of the change in toner concentration in the developing device and the change in the set developing bias Vb during the toner discharge control of this embodiment. The dashed line in the graph shows the change in toner concentration, and the solid line in the graph shows the change in the developing bias Vb.

[0071] As shown in Figure 10, before toner bottle 11 is replaced with new toner containing toner with properties different from the original toner in developing device 5, normal toner replenishment control (control for replenishing toner so that the toner concentration in the developing device is maintained at the target toner concentration) is performed. Therefore, the toner concentration in the developing device is maintained at approximately the target toner concentration. Before toner bottle 11 is replaced with new toner containing toner with properties different from the original toner in the developing device, developing bias Vb is the developing bias set by the process control described above.

[0072] When the toner bottle 11 is replaced with a new toner containing toner with properties different from the original toner in the developing device 5, the toner discharge control is started, and the toner supply OFF image formation operation 81 is performed, as shown by the dashed line in the figure, the toner concentration in the developing device 5 gradually decreases as the toner in the developing device 5 is consumed by image formation. Meanwhile, the developing bias Vb increases in accordance with the decrease in toner concentration in order to maintain the image density, as shown by the solid line in the figure.

[0073] Then, when the toner concentration in the developing device 5 reaches a first specified toner concentration, the image forming operation 81 with toner supply OFF is switched to the image forming operation 82 with toner supply ON. By switching to the image forming operation 82 with toner supply ON, new toner is replenished into the developing device 5, and the toner concentration in the developing device 5 increases. Accordingly, the developing bias Vb decreases to maintain the image concentration.

[0074] The series of image formation operations, which includes toner supply OFF image formation operation 81 followed by toner supply ON image formation operation 82, should be performed at least once, and preferably three to four times. By performing the series of image formation operations multiple times, it is possible to make 95% or more of the toner in the developing device new, as will be described later.

[0075] FIG. 11 is a diagram illustrating the inside of the developing device 5 when the toner discharge control of this embodiment is being performed. Figure 11(a) shows the time when the toner bottle 11 in the developing device 5 is replaced with a new toner T2 containing new toner T2 with different properties from the original toner T1 in the developing device 5. At this time, all the toner in the developing device is the original toner T1.

[0076] FIG. 11(b) shows the end of the first toner supply OFF image formation operation, and FIG. 11(c) shows the end of the first toner supply ON image formation operation. As shown in FIG. 11(b), image formation is performed with toner supply stopped until the toner concentration in the developing device reaches a first specified toner concentration, which is set at the lower limit of the range of target toner concentrations for toner supply control. This effectively expels the original toner T1 from the developing device 5. As a result, as shown in FIG. 11(c), the proportion of new toner T2 in the developing device increases at the end of the first toner supply ON image formation operation. This selectively causes the new toner T2 to be triboelectrically charged with the carrier, reducing friction between the original toner T1 and the new toner T2. This prevents the occurrence of reversely charged toner and low-charged toner, thereby preventing abnormal images such as background smearing and toner dropping. However, at this point, a certain amount of original toner T1 remains in the developing device 5.

[0077] Figure 11(d) shows the end of the second image formation operation with toner supply OFF, Figure 11(e) shows the end of the second image formation operation with toner supply ON, Figure 11(f) shows the end of the third image formation operation with toner supply OFF, and Figure 11(g) shows the end of the third image formation operation with toner supply ON. As shown in Figures 11(d) to 11(g), by performing the series of operations, toner supply OFF image formation operation 81 → toner supply ON image formation operation 82, multiple times, almost no original toner T1 remains in the developing device. By performing the series of operations three to four times, more than 95% of the toner in the developing device can be converted into new toner T2. This almost eliminates friction between the new toner T2 and the original toner T1, making it possible to sharpen the charge distribution of the toner in the developing device and obtain a good image.

[0078] Unlike the present embodiment, even when a toner bottle 11 containing new toner with different characteristics from the original toner in the developing device 5 is installed in the printer unit 100, new toner is gradually supplied to the developing device 5 as long as normal operation is performed to maintain the toner concentration in the developing device 5 at the target toner concentration. Initially, after replacing the toner bottle 11, the toner in the developing device 5 contains a high proportion of original toner. Therefore, the original toner accounts for the majority of the original toner, forming a normal charge with the carrier. This suppresses friction between the original toner and the new toner, resulting in little reverse-charged or low-charged toner. Subsequently, as new toner is replenished and the proportion of new toner in the developing device 5 gradually increases, friction between the original toner and the new toner becomes more likely, resulting in an increase in reverse-charged or low-charged toner. As a result, image defects such as background scumming and toner loss become more likely. Furthermore, as the proportion of new toner increases, the consumption of original toner slows. As a result, the proportions of original toner and new toner remain roughly the same for a long period of time, creating a state in which friction between the original toner and new toner is likely to occur. This could result in the continued occurrence of image defects such as background scumming and toner loss for a long period of time.

[0079] In this embodiment, too, for a predetermined period during the first toner supply-on image formation operation, the ratio of original toner to new toner is approximately equal, creating a state in which friction between the original toner and new toner is likely to occur, resulting in image defects such as background smearing and toner loss. However, during image formation operation with toner supply on, new toner is continuously supplied to the developing device during image formation so that the toner concentration in the developing device reaches the second specified toner concentration, so the period during which the ratio of original toner to new toner is approximately equal is short. Therefore, the risk of image defects such as background smearing and toner loss occurs only during the predetermined short period during the first toner supply-on image formation operation. This effectively prevents image defects such as background smearing and toner loss, even when a toner bottle 11 containing new toner with characteristics different from those of the original toner in the developing device 5 is installed in the printer unit 100, compared to normal operation in which the toner concentration in the developing device 5 is maintained at the target toner concentration.

[0080] FIG. 12 is a decision flow diagram for carrying out the discharge control. When the toner bottle 11 is replaced, the determination flow for performing the discharge control shown in Fig. 12 begins. When the determination flow begins, the control unit 60 checks whether the characteristics of the new toner in the toner bottle are different from those of the original toner (S1). As described above, whether the toner bottle 11 has been replaced and the characteristics of the new toner are different from those of the original toner can be determined by reading the information stored in the ID chip 71 of the toner bottle 11 with the chip reading unit 72. Note that the user may operate the operation panel 50 to determine whether the toner bottle 11 has been replaced and the characteristics of the new toner are different from those of the original toner.

[0081] If the characteristics of the toner in the toner bottle 11 are the same as those in the developing device (N in S1), the toner discharge control is not performed and normal operation to maintain the toner concentration in the developing device at the target toner concentration is continued.On the other hand, if the characteristics of the toner in the toner bottle are different from those in the developing device (Y in S1), the discharge control is started (S2).

[0082] FIG. 13 is a control flow diagram of the discharge control. When the discharge control is started, first, toner supply OFF image formation operation 81 is performed in which toner supply is turned OFF and image formation is performed (S11). If the toner concentration becomes equal to or lower than a first specified toner concentration (Y in S12), image formation without further toner supply may result in problems with image quality, so toner supply ON image formation operation 82 is started (S16). The timing of determining whether the toner concentration is equal to or lower than the first specified toner concentration may be set appropriately depending on the device configuration, for example, before the start of a print job, after each page is printed, or the like.

[0083] If the developing bias, charging bias, or exposure amount is high when the toner bottle is replaced, adjustment of the image forming conditions based on the toner concentration may cause one of the developing bias, charging bias, or exposure amount to exceed its upper limit before the toner concentration reaches or falls below the first specified toner concentration, making it impossible to obtain a good image. Also, adjustment of the image forming conditions by process control performed during this toner supply OFF image forming operation may cause one of the developing bias, charging bias, or exposure amount to exceed its upper limit.

[0084] Therefore, when the image forming conditions are adjusted based on the toner concentration or by process control during toner supply OFF image forming operation, the control unit 60 checks whether any of the set developing bias, charging bias, and exposure amount is equal to or greater than the upper limit (S13, S14, S15). If any of the set developing bias, charging bias, and exposure amount is equal to or greater than the upper limit (Y in S13, Y in S14, Y in S15), a good image cannot be obtained, and therefore the control unit 60 switches from toner supply OFF image forming operation 81 to toner supply ON image forming operation 82 (S16).

[0085] When switching to toner supply ON image formation operation 82, toner supply control is performed so that the toner concentration becomes the second specified toner concentration during the image formation operation. When toner is supplied until the toner concentration becomes equal to or greater than the second specified toner concentration (Y in S17), further toner supply may cause problems with image quality, so toner supply ON image formation operation 82 is terminated. The timing for determining whether the toner concentration is equal to or greater than the second specified toner concentration may be set appropriately depending on the device configuration, for example, before the start of a print job, after each page is printed, or the like.

[0086] If the developing bias, charging bias, or exposure amount is low when switching to toner supply ON image formation operation 82, adjustment of the image formation conditions based on the toner concentration may cause one of the developing bias, charging bias, or exposure amount to fall below its lower limit before the toner concentration reaches or exceeds the second specified toner concentration, making it impossible to obtain a good image. Also, adjustment of the image formation conditions by process control performed during this toner supply ON image formation operation may cause one of the developing bias, charging bias, or exposure amount to fall below its lower limit.

[0087] Therefore, when the control unit 60 adjusts the image forming conditions based on the toner concentration or by process control during the toner supply ON image forming operation, it checks whether any of the developing bias, charging bias, and exposure amount to be set is equal to or less than the lower limit (S18, S19, S20). If any of the developing bias, charging bias, and exposure amount to be set is equal to or less than the lower limit (Y in S18, Y in S19, Y in S20), it is not possible to obtain a good image, and therefore the toner supply ON image forming operation 82 is terminated.

[0088] Next, after completing the toner supply-ON image formation operation 82, the control unit 60 increments (updates to W+1) the number of operations W stored in the storage 51, which is a series of operations for performing a toner supply-OFF image formation operation followed by a toner supply-ON image formation operation (S21). If the updated number of operations W is less than a specified value (N in S22), the series of operations from the toner supply-OFF image formation operation to the toner supply-ON image formation operation is performed again. On the other hand, if the updated number of operations W is equal to the specified value (Y in S22), the discharge control is terminated and the process returns to normal operation, in which image formation is performed while performing toner supply control to maintain the toner concentration in the developing device at the target toner concentration.

[0089] The first specified toner concentration and the second specified toner concentration are preferably changed based on the device environment. Figure 14(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 14(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.

[0090] A1 and B1 in Figure 14 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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 toner concentration TC and developing bias Vb is above A7 and B7 in the figure, "edge carrier adhesion" occurs.

[0095] A8 in Figure 14(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 14(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.

[0096] As shown in Figures 14(a) and 14(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 14(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 first specified toner concentration 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 exceeds boundary A4, resulting in "solid carrier adhesion." Therefore, in a low-temperature, low-humidity environment, the first specified toner concentration is set to a toner concentration slightly higher than the toner concentration TC at boundary A5 (X1 in Figure 14(a)).

[0097] On the other hand, as shown in Figure 14(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 causing 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 first specified toner concentration (X1 in Figure 14(b)).

[0098] 14(a), in a low-temperature, low-humidity environment, the toner density at boundary A3 where a "halo image" occurs is the highest toner density (upper limit) within the range where no defects occur (the range that can be set to the target toner density). Therefore, in a low-temperature, low-humidity environment, the toner density at boundary A3 is set to the second specified toner density X2.

[0099] 14(b), in a high-temperature, high-humidity environment, the toner concentration at the intersection of boundary B8 and boundary B6 is the highest toner concentration (upper limit) within the range where no defects occur (the range where the toner concentration can be set to the target toner concentration). In a high-temperature, high-humidity environment, the toner concentration TC at the intersection of boundary B8 and boundary B6 has a narrow allowable range for the development bias Vb where no defects occur in the image, so it is preferable to set the second specified toner concentration X2 to a toner concentration that is a predetermined value higher than this toner concentration.

[0100] 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 X-1, the toner concentration sensor 155 detects that the toner concentration has reached the first or second specified toner concentration.

[0101] 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.

[0102] Furthermore, the upper limit value of the developing bias (S13 and S18 in the flow of FIG. 13) that determines whether to terminate the toner supply OFF image formation operation or the toner supply ON image formation operation may be set to the upper limit value or lower limit value of the developing bias that establishes the establishment window shown in FIG. 14. As shown in FIG. 14, since the upper limit value of the developing bias that establishes the establishment window differs for each environment and each toner concentration, the control unit 60 sets the upper limit value of the developing bias in the toner supply OFF image formation operation 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.

[0103] In a high-temperature, high-humidity environment, the lower limit of the developing bias in the image formation operation with toner supply ON is set to the boundary B6 for negative development.In a low-temperature, low-humidity environment, the lower limit of the developing bias in the image formation operation with toner supply ON is set 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.

[0104] 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.

[0105] In the above description, it is detected whether the characteristics of the toner in the toner bottle differ from the characteristics of the toner in the developing device, and if the characteristics differ, the toner is discharged. However, the toner discharge control may be performed when it is detected that the toner bottle 11 has been replaced. This eliminates the need for the user to input the characteristics of the toner in the replaced toner bottle 11, and eliminates the need for an ID chip on the toner bottle or a reader for reading this ID chip.

[0106] Furthermore, in the above description, the discharge control involves performing at least once a toner supply-off image formation operation 81, in which toner supply is stopped and image formation is performed until the toner concentration in the developing device reaches or exceeds a first specified toner concentration, and a toner supply-on image formation operation 82, in which toner supply is stopped and image formation is performed until the toner concentration in the developing device reaches or exceeds a second specified toner concentration. However, the discharge control may be performed only with the toner supply-off image formation operation 81. Because the toner supply-off image formation operation 81 sufficiently discharges the original toner in the developing device, even if normal image formation is performed after the toner supply-off image formation operation while performing toner supply control to maintain the toner concentration in the developing device at the target toner concentration, the proportion of original toner in the developing device can be effectively reduced. This reduces friction between the original toner and new toner in the developing device, preventing abnormal images such as background scumming and toner dropping.

[0107] 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 by an exposure device such as a writing unit 15 to form a latent image; a developing device 5 that carries the developer in a developer storage unit that stores developer containing toner and carrier on a developer carrier 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 carrier 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; and a toner supply unit that supplies toner to the developing device 5 from a toner storage unit such as a toner bottle 11 that stores toner. In an image forming apparatus comprising a toner supply means such as a supply device 41 and a toner supply control means such as a control unit 60 that controls the toner supply means so that the toner concentration in the developer in a developer storage unit becomes a target toner concentration based on the detection result of a toner concentration detection means, and which finally transfers the toner image obtained by developing a latent image with a developing device 5 onto a recording material to form an image, toner supply prohibition image formation control such as a toner supply OFF image formation operation in which image formation is performed with toner supply by the toner supply means stopped until the detection result of the toner concentration detection means indicates that the toner concentration in the developer in the developing device becomes equal to or less than a first specified toner concentration set lower than the target toner concentration is performed when the toner storage unit is replaced. According to aspect 1, when a toner container such as toner bottle 11 is replaced, toner replenishment-disabled image formation control (toner replenishment-off image formation operation 81) is implemented, in which image formation is performed with toner replenishment stopped until the toner concentration in developing device 5 reaches or falls below a first specified toner concentration. As a result, friction occurs between original toner particles until the toner concentration in developing device 5 reaches or falls below the first specified toner concentration, suppressing the generation of oppositely charged toner or lowly charged toner. Then, the original toner in developing device 5 is consumed by image formation, and when the original toner in developing device 5 is sufficiently reduced, new toner is replenished from the replaced toner container to developing device 5. As a result, the proportion of new toner in the developing device after toner replenishment increases, and friction between new toner particles becomes dominant within the developing device, suppressing friction between the original toner and new toner. Therefore, when the characteristics of the new toner in the toner container that has been replaced due to a change in toner specifications for the purpose of improving image quality are different from the characteristics of the original toner in the developing device, one of the two toners with different characteristics in the developing device is prevented from becoming reversely charged or lowly charged, thereby preventing background scumming and toner falling.

[0108] (Aspect 2) In aspect 1, a characteristic change detection means (in this embodiment, consisting of an ID chip 71 and a chip reading unit 72) is provided to detect a change in the characteristics of the toner replenished to the developing device 5, and when a toner container such as a toner bottle 11 is replaced, if the characteristic change detection means detects a change in the characteristics of the toner replenished to the developing device 5, toner replenishment inhibited image formation control such as toner replenishment OFF image formation operation 81 is performed. This makes it possible to prevent toners with different characteristics from being mixed into the developing device.

[0109] (Aspect 3) In aspect 1 or 2, during toner replenishment prohibited image formation control such as toner replenishment OFF image formation operation 81, the development bias, charging bias, and exposure amount when exposing the surface of the latent image carrier by the exposure device are set based on the detection results of a toner concentration detection means such as toner concentration sensor 155, and the toner replenishment prohibited image formation control is terminated if one of the charging bias, development bias, and exposure amount reaches or exceeds an upper limit value before the toner concentration falls below a first specified toner concentration. As described in the embodiment, this makes it possible to suppress a decrease in image density due to a decrease in toner concentration in the developing device. Furthermore, by terminating the toner replenishment prohibition image formation control when one of the charging bias, developing bias, and exposure amount exceeds its upper limit, toner replenishment can be resumed before the decrease in image density due to a 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 a good image quality.

[0110] (Aspect 4) In any of aspects 1 to 3, after performing toner replenishment-prohibited image formation control such as toner replenishment OFF image formation operation 81, toner replenishment is performed by the toner replenishment means until the toner concentration in the developer in the developing device reaches or exceeds a second specified toner concentration set higher than the target toner concentration. This reduces the proportion of original toner in the developing device compared to when toner is replenished so that the toner concentration in the developing device reaches the target toner concentration after toner replenishment-prohibited image formation control, such as toner replenishment-off image formation operation 81, as described in the embodiment. As a result, friction between new toner and original toner can be further reduced, and abnormal images such as background scumming and toner dropping can be prevented.

[0111] (Aspect 5) In aspect 4, after performing toner replenishment-prohibited image formation control such as toner replenishment OFF image formation operation 81, a series of operations is performed multiple times to replenish toner using a toner replenishment means until the toner concentration in the developer in the developing device reaches or exceeds a second specified toner concentration set higher than the target toner concentration. This allows most of the toner in the developing device to be replaced with new toner, as described in the embodiment.

[0112] (Aspect 6) In aspect 4 or 5, when toner is replenished by the toner replenishment means until the toner concentration reaches or exceeds a second specified toner concentration, the development bias, charging bias, and exposure amount when exposing the surface of the latent image carrier by the exposure device are set based on the detection results of the toner concentration detection means, and if one of the charging bias, development bias, and exposure amount falls below a lower limit value before the toner concentration reaches or exceeds the second specified toner concentration, the toner replenishment operation is terminated. This makes it possible to suppress an increase in image density due to an increase in toner concentration in the developing device. Furthermore, by terminating the toner supply operation when one of the charging bias, developing bias, and exposure amount falls below a lower limit, toner supply can be stopped before the increase in image density due to an increase 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 a good image quality.

[0113] (Aspect 7) In any of aspects 1 to 6, toner supply prohibited image formation control such as toner supply OFF image formation operation 81 forms an image to be transferred to a recording material such as transfer paper in a state where toner supply by a toner supply means such as toner supply device 41 is stopped. This reduces the frequency of replacing the waste toner container compared to when, as described in the embodiment, an image that is not transferred to the recording material, such as a discharge pattern, is formed to discharge the toner in the developing device. [Explanation of symbols]

[0114] 1: Photoreceptor 5: Developing device 5a: First agent storage chamber 5b: Second agent storage chamber 5c: Toner supply port 6: Imaging unit 8: Intermediate transfer belt 10: Intermediate transfer unit 11: Toner bottle 14: Charging device 14a: Charging roller 15: Writing section 40: Optical sensor unit 41: Toner supply device 42c: Subhopper 43: Bottle side drive unit 44: Sub-hopper side drive unit 50: Operation panel 51: Storage 60: Control section 71: ID chip 72: Chip reader 81: Toner supply OFF Imaging operation 82: Toner supply ON Imaging operation 100: Printer section 155: Toner density sensor 500: Copier [Prior art documents] [Patent documents]

[0115] [Patent Document 1] Patent No. 6573169

Claims

1. 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; a developing device that carries the developer in a developer storage unit, the developer containing the toner and carrier, on 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 developing device; a toner supplying means for supplying toner from a toner container containing the 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 developing device 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, An image forming apparatus characterized in that, when the toner container is replaced, a toner replenishment prohibition image formation control is implemented in which image formation is performed in a state in which toner replenishment by the toner replenishment means is stopped until the detection result of the toner concentration detection means indicates that the toner concentration in the developer in the developing device is equal to or lower than a first specified toner concentration set lower than the target toner concentration.

2. 2. The image forming apparatus according to claim 1, a characteristic change detection means for detecting a change in the characteristics of the toner supplied to the developing device; an image forming apparatus characterized in that, when the toner storage container is replaced, the characteristic change detection means detects a change in the characteristics of the toner replenished to the developing device, and then the toner replenishment prohibition image formation control is implemented.

3. 2. The image forming apparatus according to claim 1, 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, The image forming apparatus is characterized in that the toner replenishment prohibition image formation control is terminated when one of the charging bias, the developing bias, and the exposure amount reaches or exceeds an upper limit value before the toner concentration falls below the first specified toner concentration.

4. 2. The image forming apparatus according to claim 1, An image forming apparatus characterized in that, after implementing the toner replenishment prohibition image formation control, toner replenishment is carried out by the toner replenishment means until the toner concentration in the developer in the developing device reaches or exceeds a second specified toner concentration set higher than the target toner concentration.

5. 5. The image forming apparatus according to claim 4, An image forming apparatus characterized in that, after implementing the toner replenishment prohibition image formation control, a series of operations of replenishing toner using the toner replenishment means is performed multiple times until the toner concentration in the developer in the developing device becomes equal to or greater than the second specified toner concentration.

6. 5. The image forming apparatus according to claim 4, an image forming apparatus characterized in that, when toner is replenished by the toner replenishment means until the toner concentration reaches or exceeds the second specified toner concentration, 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 results of the toner concentration detection means, and if one of the charging bias, the developing bias, and the exposure amount falls below a lower limit value before the toner concentration reaches or exceeds the second specified toner concentration, the toner replenishment operation is terminated.

7. 2. The image forming apparatus according to claim 1, The image forming apparatus is characterized in that the toner replenishment prohibition image formation control forms an image to be transferred onto the recording material in a state where toner replenishment by the toner replenishment means is stopped.

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