Image forming apparatus

Abstract

To provide an image forming apparatus that can favorably discharge a deteriorated old toner in a single refresh operation.SOLUTION: An image forming apparatus comprises refresh execution means that forms an image for toner discharge with a uniform image density on the entire surface of a sheet, and executes a refresh operation to cause the image forming apparatus to forcibly consume a toner in a developing device at a predetermined timing. The image for toner discharge is a "discharge visible image" being a visible image with an image density that can be easily visually recognized by a user, and the image density of the "discharge visible image" is set by the user on an operation panel being setting means.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] 2. Description of the Related Art Conventionally, there is known an image forming apparatus equipped with a refresh execution unit that forms a toner expelling image on the entire surface of a sheet and executes a refresh operation at a predetermined timing to forcibly consume toner in a developing device.

[0003] Patent Document 1 describes a toner expelling image formed on the entire surface of a sheet as a "watermark image" with an image density (1% to 5%) that is difficult for a user to see. Summary of the Invention [Problem to be solved by the invention]

[0004] However, the amount of toner forcibly consumed in one refresh operation is small, and there is a risk that the old toner that has deteriorated in the developing device will not be sufficiently discharged. [Means for solving the problem]

[0005] In order to solve the above problem, the present invention provides an image forming apparatus equipped with a refresh execution means that forms a toner expelling image on the entire surface of a sheet and performs a refresh operation at a predetermined timing to forcibly consume toner in a developing device, wherein the toner expelling image is a visible image, and the image forming apparatus has a setting means that allows a user to set the image density of the visible image. [Effects of the Invention]

[0006] According to the present invention, deteriorated old toner can be effectively discharged in one refresh operation. [Brief explanation of the drawings]

[0007] [Figure 1]1 is a schematic perspective front view showing the overall configuration of a color copying machine as an example of an image forming apparatus according to an embodiment of the present invention; [Figure 2] FIG. 2 is a functional block diagram relating to a refresh operation of the color copier. [Figure 3] 5A and 5B are diagrams illustrating timings at which a pixel acquisition unit acquires the number of pixels of each color. [Figure 4] FIG. 4 is a diagram showing an example of a setting screen displayed on a display unit of an operation panel. [Figure 5] FIG. 10 is a diagram showing an example of an image density selection screen for "discharge visible image" displayed on the display unit of the operation panel. [Figure 6] FIG. 10 is a control flow diagram of a refresh operation. [Figure 7] An example of "visible ejection image" formation when printing four sheets continuously is shown. [Figure 8] An example of "visible image ejection" formation during single-sided printing of three consecutive sheets when the user has checked "reverse side input mode" is shown. [Figure 9] FIG. 10 is a control flow diagram of a modified example of a refresh operation. 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] FIG. 1 is a schematic front view showing in perspective the overall configuration of a color copying machine as an example of an image forming apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an electrophotographic color copying machine of an internal paper discharge type, which is exemplified as an image forming apparatus according to an embodiment of the present invention. The Z direction in the drawing is the up-down direction, the Y direction in the drawing is the front-rear direction of the device (also the axial direction), and the X direction in the drawing is the left-right direction of the device.

[0010] This color copier 1 comprises a roughly box-shaped device main body 10 which is the housing for the entire image forming device, and an image reading unit 2 which is located above this device main body 10 and reads an image of an original. Color copier 1 also has an image forming unit 3 which is located within the device main body and records and forms an image on paper as an example of a sheet based on image information read by image reading unit 2 or transmitted from an external device such as a personal computer.

[0011] Between the image reading unit 2 and the image forming unit 3, there is a paper discharge space 12 as a discharge space for discharging paper on which an image has been recorded. At the bottom of the device body 10, there is disposed a paper feed unit 4 for supplying sheets (which means sheet-like recording media including copy paper, resin sheets for overhead projectors, cardboard, postcards, etc., hereinafter referred to as "paper") to a paper transport path as a sheet transport path. Above the image forming unit 3, there is disposed a paper discharge unit for discharging paper on which an image has been recorded to the paper discharge space 12, and between the paper feed unit 4 and the paper discharge unit 5, there is disposed a paper transport path 6.

[0012] The image reading unit 2 has a contact glass 20 as a document table on which a document is placed. It also has a light source 21 that is placed directly below the contact glass 20 and moves to shine light onto the document, an imaging lens 22 that forms an image from the light reflected from the document, and an image sensor 23 such as a CCD that is placed at the imaging position and serves as reading means for reading the document image. The image reading unit 2 also has a plurality of mirrors that reflect the light reflected from the document and direct it to the imaging lens 22.

[0013] In addition, a pressure plate 24 that presses down on the document placed on the contact glass 20 is provided above the image reading unit 2. Note that instead of this pressure plate 24, an automatic document feeder (ADF) that automatically feeds the document onto the contact glass 20 may be installed.

[0014] The image forming unit 3 includes four process cartridges 11Y, 11C, 11M, and 11K corresponding to the four primary color toners: yellow, cyan, magenta, and black. The image forming unit 3 also includes a writing unit 34 located below the four process cartridges 11Y, 11C, 11M, and 11K, which writes latent images onto the respective photosensitive drums (described below). The image forming unit 3 also includes four toner bottles 31Y, 31C, 31M, and 31K, which contain new toner corresponding to the respective process cartridges 11Y, 11C, 11M, and 11K. The image forming unit 3 also includes a transfer unit 32 that transfers the toner images formed by the process cartridges 11Y, 11C, 11M, and 11K onto paper, and a fixing unit 33 that fixes the toner images onto paper.

[0015] The process cartridges 11Y, 11C, 11M, and 11K are detachably mounted to the apparatus main body 10. The process cartridges 11Y, 11C, 11M, and 11K are arranged in the order of yellow, cyan, magenta, and black from the upstream side along the direction of movement of the outer peripheral surface of an intermediate transfer belt 32a (described below, indicated by the arrow Xa in the figure). Each process cartridge 11Y, 11C, 11M, and 11K has a photosensitive drum 7Y, 7C, 7M, or 7K, which is a latent image carrier that rotates clockwise when viewed from the front. The process cartridges also have a charging device, developing devices 30Y, 30C, 30M, and 30K, a cleaning device, and other components mounted around the photosensitive drum.

[0016] The charging devices uniformly charge the outer peripheral surfaces of the photosensitive drums 7Y, 7C, 7M, and 7K by subjecting them to a charging process. The developing devices 30Y, 30C, 30M, and 30K visualize the electrostatic latent images formed on the photosensitive drums 7Y, 7C, 7M, and 7K by a writing unit 34 (described later) into monochrome toner images using toner of the corresponding color. The cleaning devices clean and collect residual toner remaining on the outer peripheral surfaces of the photosensitive drums 7Y, 7C, 7M, and 7K after transfer.

[0017] The writing unit 34 is equipped with a polygon mirror, an fθ lens, etc. The writing unit 34 scans by irradiating a laser beam from a laser emitting device based on image information input from the image reading unit 2, a personal computer, an external scanner, etc. The writing unit 34 selectively exposes the uniformly charged outer peripheral surfaces of the photosensitive drums 7Y, 7C, 7M, and 7K to light, reducing the surface potential of the irradiated portions and forming electrostatic latent images on the photosensitive drums.

[0018] The toner bottles 31Y, 31C, 31M, and 31K are individually filled with new toner of each of the four colors. The toner of each color in the toner bottles 31Y, 31C, 31M, and 31K is replenished to the developing devices 30Y, 30C, 30M, and 30K of the process cartridges 11Y, 11C, 11M, and 11K through a conveying path.

[0019] The transfer unit 32 has an intermediate transfer belt 32a, which is an endless belt made of a multilayer structure of elastic resin, as an intermediate transfer body. The intermediate transfer belt 32a is supported and stretched (meaning that it is stretched while being subjected to tension; the same applies hereinafter) by a plurality of rollers. Specifically, it is supported and stretched by four support rollers 32b, 32c, 32d, and 32e, four primary transfer rollers 32f, and a secondary transfer roller 32g.

[0020] Support roller 32b is a drive roller connected to a drive means and has the function of rotating intermediate transfer belt 32a in the direction of arrow Xa in the figure. Secondary transfer roller 32g is disposed (meaning to be disposed or to be disposed at a determined position, the same applies hereinafter) at a position facing support roller 32b (hereinafter referred to as "drive roller 32b") across intermediate transfer belt 32a. Cleaning device 32h is provided near support roller 32c to scrape off residual toner adhering to the outer peripheral surface of intermediate transfer belt 32a and clean it.

[0021] Considering image degradation due to air gap discharge, each primary transfer roller 32f is positioned slightly downstream in the conveyance direction of the intermediate transfer belt 32a from the position directly facing each photosensitive drum 7Y, 7C, 7M, 7K, where the center-to-center distance between the primary transfer rollers 32f and the intermediate transfer belt 32a is the shortest. Each primary transfer roller 32f functions as a contact-type transfer bias (transfer voltage) application unit. Specifically, each primary transfer roller 32f is connected to a bias power supply and configured to apply (means applying a voltage; the same applies below) a primary transfer bias from the back surface (inner peripheral surface) of the intermediate transfer belt 32a.

[0022] The secondary transfer roller 32g is biased by a biasing means to be pressed against the intermediate transfer belt 32a on the outer periphery of the drive roller 32b, forming a secondary transfer nip between itself and the drive roller 32b. The drive roller 32b serves as a contact-type transfer bias applying means connected to a bias power source. Alternatively, the secondary transfer roller 32g may serve as the transfer bias applying means, in which case a transfer bias of the opposite polarity to that of the toner image to be transferred is applied.

[0023] The fixing unit 33 has a fixing belt 33c, which is an endless belt stretched between a fixing roller 33a and a heating roller 33b, and a pressure roller 33d as a pressure member. The pressure roller 33d is in pressure contact with the fixing belt 33c (this means being in pressure contact; the same applies hereinafter) and forms a fixing nip between the fixing belt 33c and the pressure roller 33d. In this fixing nip, heat and pressure are applied to a sheet of paper conveyed through a paper conveyance path 6 (described below), and the toner image transferred at the secondary transfer nip of the transfer unit 32 described above is melted and adhered to the sheet of paper, thereby being fixed.

[0024] The paper feed unit 4 contains and stocks predetermined paper sheets of different sizes and dimensions, and includes paper feed cassettes 40 and 41 that can be pulled out from the device main body 10, and paper feed rollers 42 and 43 that press the stocked paper sheets from above with a predetermined pressure. Based on a control signal from the control means, the paper feed unit 4 sends out the paper sheets contained in the paper feed cassettes 40 and 41, respectively, to a paper transport path 6, which will be described later, using the paper feed rollers 42 and 43.

[0025] The paper feed unit 4 is also provided with a manual feed tray 44 on which any paper within a predetermined range of transportable dimensions is placed, and a paper feed roller 45 that feeds out this paper. The paper feed unit 4 is configured to feed out the paper placed on the manual feed tray 44 to a paper transport path 6, which will be described later, by rotating the paper feed roller 45.

[0026] The paper discharge unit 5 has a paper discharge tray 5a formed as a slope on the device body 10 below the paper discharge space 12 between the aforementioned toner bottles 31Y, 31C, 31M, and 31K and the image reading unit 2. The paper discharge unit 5 also has a pair of paper discharge rollers 5b that discharges (ejects) paper that has passed through the fixing unit 33 onto the paper discharge tray 5a from a paper transport path 6 (described later). Thus, the color copier 1 of this embodiment is an internal paper discharge type paper discharge unit that has the function of stacking paper discharged by the pair of paper discharge rollers 5b onto the paper discharge tray 5a.

[0027] The paper transport path 6 has a normal transport path 6a of a vertical transport type (vertical path type) that transports paper from the paper feed unit 4 located at the bottom of the device body 10 to the paper discharge unit 5 located at the top of the device body 10 from bottom to top. It also has a reverse transport path 6b that reverses paper for double-sided printing. These transport paths can be switched with a switching claw 6c, which guides paper to the reverse transport path 6b. The paper guided to the reverse transport path 6b is transported to the upper part 6e of the reverse transport path 6b by a pair of reverse transport rollers 6d, and then reversed in a switchback manner by the pair of reverse transport rollers 6d reversing. The paper is then transported to the normal transport path 6a just before a pair of registration rollers 6f, which will be described later.

[0028] The normal conveying path 6a and the reverse conveying path 6b are provided with a plurality of conveying roller pairs spaced apart according to the minimum paper size, and the paper is conveyed by rotating while being sandwiched between these conveying roller pairs. In addition, the normal conveying path 6a is provided with a registration roller pair 6f below the secondary transfer nip, and this registration roller pair 6f adjusts the timing of conveying the paper to the secondary transfer nip based on commands from the control means.

[0029] In addition, on the left side of the paper feed cassette 40 in the figure, there is arranged a waste toner container 18 that stores waste toner removed by the cleaning devices of each process cartridge 11Y, 11C, 11M, and 11K and waste toner removed by the cleaning device 32h of the transfer unit 32.

[0030] If the toner consumption in the developing device is low, the amount of old toner that remains in the developing device and deteriorates increases. When the amount of old toner increases, the image becomes more likely to become grainy and have holes in it, resulting in a decrease in image quality. To prevent this decrease in image quality, the color copier 1 performs a refresh operation (also called a forced consumption operation) that forcibly consumes the toner in the developing device 30 at a predetermined timing, expelling the old toner and replacing it with new toner, thereby keeping the toner in the developing device fresh.

[0031] Conventionally, when a refresh operation is performed, a predetermined latent image pattern is formed on the surface of the photosensitive drum 7. By developing this latent image pattern with toner in the developing device 30, old toner in the developing device 30 is expelled and the toner in the developing device 30 is refreshed.

[0032] The developed spit pattern image is not transferred to paper, but is removed by the cleaning device of the process cartridge 11 and becomes waste toner, which is then stored in the waste toner container 18. As a result, if images with a low image area ratio continue to be printed and refreshing operations are required frequently, the waste toner container 18 quickly becomes full, posing a problem of having to be replaced more frequently. Furthermore, conventionally, refreshing operations are performed after the print job is completed, which causes extra image formation and is one factor in shortening the life of the process cartridge 11.

[0033] Patent Document 1 describes a toner-removal image that is formed on the entire surface of a sheet of paper as a "watermark image" with an image density of 1 to 5% that is difficult for users to see. This prevents the toner constituting the toner-removal image from becoming waste toner, reducing the frequency of replacing the waste toner container 18. However, in Patent Document 1, the "watermark image" formed on the entire surface of the sheet of paper has a low image density of 1 to 5%, resulting in a small amount of toner being forcibly consumed in one refresh operation. In particular, for the colors K and M, which are easily visible on white paper, the image density becomes very low, resulting in a "watermark image" that is difficult for users to see, and almost no toner is consumed in one refresh operation. As a result, there is a risk that degradation of image quality caused by degraded old toner cannot be resolved.

[0034] Therefore, in this embodiment, the toner expulsion image formed on the entire surface of the paper is a "visible image" (hereinafter referred to as "expulsion visible image") with an image density that is easily recognizable by the user, and the amount of toner forcibly consumed in one refresh operation is increased. As will be described later, the image density of the "expulsion visible image" in this embodiment is greater than 5% and less than 30%. This allows the deteriorated old toner to be expelled effectively, eliminating the degradation of image quality caused by the deteriorated old toner.

[0035] However, if the toner expulsion image is a "visible expulsion image" with an image density that is easily recognizable by the user, some users may be dissatisfied with the "visible image" formed on the entire paper surface. For this reason, in this embodiment, the image density of the "visible expulsion image" can be set to the user's preferred image density. This makes it possible to prevent users from being dissatisfied with the "visible expulsion image" as a toner expulsion image formed on the paper. The following describes the characteristics of this embodiment with reference to the drawings. Note that in this embodiment, the "user" is not limited to the user who actually uses the color copier 1, but also includes, for example, the representative of the department to which the user belongs and the manager of the color copier 1.

[0036] FIG. 2 is a functional block diagram relating to the refresh operation of the color copier 1. As shown in FIG. 2, color copier 1 includes control unit 60, which serves as control means. Control unit 60 includes a CPU 60a, ROM 60b, RAM 60c, printer control unit 63, image reading control unit 64, storage control unit 65, operation panel control unit 61, and communication control unit 68. Control unit 60 also includes a refresh execution unit 62, image area cumulative average calculation unit 67, and pixel acquisition unit 69. The components that make up control unit 60 are connected via a bus.

[0037] The control unit 60 controls the entire color copier 1. 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.

[0038] The printer control unit 63 of the control unit 60 functions as an interface for the CPU 60a to control each piece of hardware (process cartridge, transfer unit 32, writing unit 34, fixing unit 33, etc.) of the image forming unit 3. The image reading control unit 64 functions as an interface for the CPU 60a to control the image reading unit 2.

[0039] 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 color copier 1.

[0040] Storage 51 is a readable / writable nonvolatile storage device such as a HDD. This storage 51 stores programs for controlling the entire color copier 1, various application programs, data for managing consumable parts, etc. Storage 51 also stores the image density of the "discharge visible image" set by the user, information on the size of the paper stocked in paper feed cassettes 40 and 41, and the average cumulative image area calculated by image area average cumulative calculation unit 67.

[0041] 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 color copier 1 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.

[0042] The pixel acquisition unit 69 acquires the number of pixels of each color to be printed on paper at 0.1-second intervals from the start of operation of the developing device, based on the image data. The acquired pixel counts are temporarily stored in the print count memory. Note that the acquisition interval for the pixel counts of each color is not limited to 0.1 seconds and can be set appropriately depending on the configuration of the device.

[0043] The image area cumulative average calculation unit 67 calculates the cumulative average image area for each color. The image area cumulative average is the average image area for the past 100 seconds when the developing device is driven for 0.1 seconds. The calculation formula for the image area cumulative average is as follows:

[0044]

number

[0045] The "cumulative average image area (i-1)" is the cumulative average image area before calculation (the previous value). The "image area (i)" is the latest image area. The "image area (i)" is calculated based on the number of pixels stored in the print count memory. The cumulative average image area is calculated each time the number of pixels stored in the print count memory is updated. During a print job, the number of pixels is acquired at 0.1 second intervals, and the number of pixels in the print count memory is updated at 0.1 second intervals, so the cumulative average image area for each color is also calculated at 0.1 second intervals.

[0046] 3 is a diagram illustrating the timing at which the pixel acquisition unit 69 acquires the number of pixels of each color. The dotted lines in FIG. 3 indicate the timing at which the pixel acquisition unit 69 acquires the number of pixels of each color. At timings A1 to A5 in Fig. 3, pixel acquisition unit 69 acquires the number of pixels, and image area cumulative average calculation unit 67 calculates the image area cumulative average A(i). Specifically, at timing A1 in the figure, the number of pixels of each color in range B0 (the paper conveyance range for 0.1 seconds from the start of driving of the developing device) is acquired, and image area (i) in the range of B0 is calculated by image area cumulative average calculation unit 67. Then, image area cumulative average A(i) is calculated based on Equation 1 above. Furthermore, at timing A2 in the figure, the number of pixels of each color in range B1 in the figure is acquired, and image area (i) in the range of B1 and image area cumulative average A(i) are calculated.

[0047] If the developing device is new, the decision to perform the refresh operation is not made until the 1st to 999th pixel count acquisition, but is made from the 1000th pixel count acquisition onwards. If the developing device is new, it contains only new toner, so even if the refresh operation is not performed until the 1000th pixel count acquisition, there will be no degradation in image quality due to degraded old toner.

[0048] Note that for the 1st to 999th pixel acquisitions, the "1000" in the above equation (1) is changed to the current pixel acquisition count, and the cumulative image area average is calculated, so that the "cumulative image area average (i-1)" can be used when calculating the 1000th cumulative image area average. Alternatively, the cumulative image area average may not be calculated for the 1st to 999th pixel acquisitions, and a preset default "cumulative image area average (i-1)" may be used when calculating the 1000th cumulative image area average. With this configuration, there is a risk of a large discrepancy with actual usage conditions until further use, but it has the advantage of simplifying control.

[0049] 2 determines whether or not to perform a refresh operation based on the image area cumulative average A(i) calculated by the image area cumulative average calculation unit 67. The refresh execution unit 62 functions as a refresh execution means.

[0050] The external communication I / F 53 shown in FIG. 2 communicates with external devices such as PCs (personal computers) via a network line or the like. The external communication I / F 53 receives image data to be printed that is sent to the color copier by application software installed on the PC. The image density of the "discharge visible image" can also be set from the application software installed on the PC, and the external communication I / F 53 also receives the set image density. The external communication I / F 53 also sends information about the status of the color copier to the PC, such as the amount of toner remaining to display in the application software and information about the size of paper stocked in the paper feed cassette.

[0051] FIG. 4 is a diagram showing an example of a setting screen displayed on the display unit 50a of the operation panel 50. As shown in FIG. The screen shown in Fig. 4 can be displayed, for example, by tapping the settings icon on the home screen displayed on the display unit 50a of the operation panel 50 and then tapping "Adjust / Manage" from the settings top screen that appears. By tapping "Waste Toner Save" from the settings screen shown in Fig. 4, settings such as the image density of the "visible toner discharge image" that is formed on the entire page as a toner discharge image can be configured.

[0052] FIG. 5 is a diagram showing an example of an image density selection screen for the "discharge visible image" displayed on the display unit of the operation panel 50. As shown in FIG. 5, the selection screen displays a "discharge visible image" and "no print," which have different image densities. The image density of the "discharge visible image" in this embodiment is a halftone image exceeding 5% and not exceeding 30%, and the user sets the image density of the "discharge visible image" within this image density range.

[0053] When the user taps one of the three "discharge visible images" with different image densities, the image density of the tapped "discharge visible image" is set. In this way, the operation panel 50 functions as a setting means for the user to set the image density of the "discharge visible image."

[0054] In FIG. 5, the selection screen displays a plurality of preset "discharge visible images" with different image densities on the display unit 50a, allowing the user to select one from among them. However, a section may be provided on the selection screen where the user can manually set the image density of the "discharge visible image," allowing the user to manually set the image density of the "discharge visible image." For example, by providing a section on the selection screen where the user can directly input the image density of the "discharge visible image," the image density of the "discharge visible image" can be manually set from the selection screen. Alternatively, the selection screen may be provided with a bar with a gradation of image density and a slidable arrow pointing to the position of the bar. The user may then manually set the image density of the "discharge visible image" by moving the arrow to the position of the image density on the bar they wish to set. Furthermore, the image density of the "discharge visible image" for each of Y, M, C, and K may be set by the user.

[0055] On the other hand, if "No Printing" is selected, no "visible toner spit image" is formed on the paper. In this case, as in the conventional method, a band-shaped solid image toner spit pattern is formed between sheets or after the print job is completed, and then removed by a cleaning device. The image density of the "discharge visible image" can also be set using application software installed on the PC.

[0056] As shown in Fig. 5, the selection screen has a place to check "reverse side input mode." When the user checks "reverse side input mode" as shown in Fig. 5, a "discharge visible image" is formed on the reverse side of the paper during a single-sided print job in which a print image (an image printed based on image data received from a personal computer, document reader, etc.) is formed on only one side of the paper. Note that the "reverse side input mode" may be such that the user can select between a mode in which a "discharge visible image" is formed only on the reverse side of a blank sheet of paper, and a mode in which a "discharge visible image" is formed on the front side of a sheet of paper on which a print image has been formed and on the reverse side of the blank sheet of paper.

[0057] FIG. 6 is a control flow diagram of the refresh operation. When a print job is started (S1), the cumulative average image area A(i) for each color stored in storage is obtained (S2). If the calculated cumulative average image area A(i) exceeds the discharge threshold B (No in S3), a lot of toner has been consumed, there is little old toner in the developing device, and there is no need to update the toner in the developing device. Therefore, if the calculated cumulative average image area A(i) is equal to or greater than the discharge threshold B (No in S3), the refresh operation is not performed, and a "discharge visible image" with the image density set by the user is not formed on the entire surface of the paper. In this embodiment, the discharge threshold B is 32.2 [cm 2 This ejection threshold value B is the cumulative average image area A when an image with an image area of about 5% is formed on an A4 sheet of paper.

[0058] On the other hand, if the calculated image area cumulative average A(i) is equal to or less than the discharge threshold B (YES in S3), toner consumption is low, there is a lot of old toner in the developing device, and the image is more likely to have grainy or worm-like features, which may result in a decrease in image quality. Therefore, a refresh operation is performed (S4). Specifically, a "discharge visible image" with an image density set by the user is formed on the entire surface of the paper as a toner discharge image, along with the printed image. Note that if there are multiple colors for which the image area cumulative average A(i) is equal to or less than the discharge threshold B, the "discharge visible image" is formed using the toner of the color with the smallest value of the image area cumulative average A(i). If there is a next sheet of paper (No in S5), the above-described steps S2 to S4 are executed at the timing when image formation on the next sheet of paper starts.

[0059] FIG. 7 shows an example of the formation of a "visible spit image" when printing four sheets continuously. 7, at the start of image formation on sheets 1 to 3, the cumulative average image area A(i) of any of the colors Y, M, C, and K is equal to or less than the discharge threshold B, and a "discharge visible image" with the image density set by the user is formed on the entire surface of the paper. On the other hand, at the start of image formation on sheets 4, the cumulative average image area A(i) for all colors is equal to or less than the discharge threshold B, so no refresh operation is performed and no "discharge visible image" is formed on the paper.

[0060] As described above, the "spit-out visible image" is a halftone image with an image density of more than 5% and not more than 30%. By making the "spit-out visible image" a halftone image with an image density of 30% or less, it is possible to prevent the "spit-out visible image" from making a typical printed image difficult to see.

[0061] Furthermore, in this embodiment, the "visible toner expulsion image" used as the toner expulsion image has an image density exceeding 5%, making it visible to the user. This allows for a larger amount of toner to be forcibly consumed in a single refresh operation than when a "watermark image" having an image density of 5% or less, which is difficult for the user to see, as described in Patent Document 1, is used. This allows for efficient expulsion of old toner, and the refresh operation effectively eliminates degradation of image quality caused by old toner. Furthermore, because the "visible toner expulsion image" is formed on paper, the toner constituting the "visible toner expulsion image" does not become waste toner and be collected in the waste toner container 18. This reduces the frequency with which the waste toner container 18 needs to be replaced.

[0062] Furthermore, by allowing the user to set the image density of the "discharge visible image," a "discharge visible image" with an image density that is acceptable to the user is formed over the entire surface of the paper. This reduces user dissatisfaction with the "discharge visible image," even if the toner discharge image has an image density that the user can recognize.

[0063] FIG. 8 shows an example of "discharge visible image" formation during single-sided printing on three consecutive sheets when the user has checked "reverse side input mode." The color copier 1 of this embodiment performs double-sided printing using the interleaf method, which is a method in which an image is printed on the front side of a sheet of paper between printing on the front side and printing on the back side of the next sheet of paper. As shown in Figure 5, if the user checks the "reverse side input mode" displayed on the selection screen, even for a single-sided print job, the paper with an image formed on its front side is transported to the reverse transport path 6b, and a "discharge visible image" is formed on the back side of the blank paper. This makes it possible to prevent degradation of the quality of the printed image, such as the color of the printed image formed on the front side of the paper, due to the "discharge visible image."

[0064] On the other hand, as shown in Figure 7, by forming a "visible ejection image" on the front side of the paper together with the printed image, productivity can be improved compared to forming a "visible ejection image" on the back side of blank paper.

[0065] FIG. 9 is a control flow diagram of a modified refresh operation. As shown in Figure 9, in the refresh operation of the modified example, when the image area cumulative average A(i) becomes equal to or less than the discharge threshold B and it is determined that a refresh operation is necessary (Yes in S13), the refresh execution unit 62 calculates the amount of toner required for forced consumption based on the image area cumulative average A(i) to make the toner in the developing device fresh (refresh) (S14).

[0066] Next, the refresh execution unit 62 calculates the amount of toner consumed in forming a "discharge visible image" with the image density set by the user. If the amount of toner consumed in forming the "discharge visible image" + α is less than the calculated amount of toner required for forced consumption (No in S15), the image density of the "discharge visible image" is made β% darker than the image density set by the user (S17). This allows deteriorated old toner to be effectively discharged in a single refresh operation.

[0067] On the other hand, if the toner amount consumed in forming the "discard visible image" plus α is greater than the calculated required toner amount for forced consumption (No in S16), the image density of the "discard visible image" is made β% lighter than the image density set by the user (S19). This makes it possible to reduce unnecessary toner consumption.

[0068] The range (β%) within which the image density set by the user can be changed is set so that the user will not easily notice the change in image density. Since the functionality of image density differs for each color, it is preferable to set the range (β%) within which the image density can be changed for each color. The user may also be able to set the allowable range for image density change on the selection screen shown in FIG. 5.

[0069] The "α" in the "toner amount + α" is set to, for example, half the amount of toner that increases or decreases when the image density is changed by β%. For example, if the amount of toner required for forced consumption is slightly greater than the amount of toner consumed, the amount of toner increased by increasing the image density by β% will be too much compared to the amount of toner that is lacking, resulting in wasted toner. Also, if the amount of toner required for forced consumption is slightly less than the amount of toner consumed, the amount of toner reduced by decreasing the image density by β% will be too much compared to the amount of toner that is excessive, resulting in insufficient toner being discharged. As described above, by setting "α" to half the amount of toner that increases or decreases when the image density is changed by β%, it is possible to suppress wasted toner consumption when the image density is changed and to effectively discharge old toner. The value of "α" is merely an example, and may be, for example, the amount of toner that increases or decreases when the image density is changed by β%. Also, the toner density that is changed within the range of β% may be set based on the difference between the amount of toner required for forced consumption and the amount of toner that is actually consumed.

[0070] 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.

[0071] The above description is merely an example, and each of the following aspects provides unique effects. (Aspect 1) In an image forming device such as a color copier 1 that is equipped with a refresh execution means such as a refresh execution unit 62 that forms a toner expulsion image on the entire surface of a sheet and executes a refresh operation at a predetermined timing to forcibly consume toner in a developing device, the toner expulsion image is a visible image such as a "toner expulsion visible image," and the device has a setting means such as an operation panel 50 that allows a user to set the image density of the visible image. According to this, the toner expulsion image formed on the entire surface of the sheet is a "visible image" with an image density that is easily visible to the user, so the image density can be made higher than when a "watermark image" with an image density that is difficult for the user to see is used, and the amount of toner that is forcibly consumed can be increased. As a result, with one refresh operation, deteriorated old toner in the developing device can be effectively discharged, and the deterioration of image quality due to deteriorated old toner can be effectively suppressed. Furthermore, since the user can set the image density of the "visible image," it is possible to form a "visible image" with an image density that suits the user's preference over the entire surface of the sheet. This makes it possible to prevent the user from feeling dissatisfied with the "visible image" formed on the sheet.

[0072] (Aspect 2) In aspect 1, refresh execution means such as refresh execution unit 62 executes a refresh operation when the cumulative average value of image area within a predetermined time (0.1 seconds in this embodiment) while the developing device is in operation is less than a threshold value. This effectively prevents deterioration of the quality of the printed image due to degraded old toner the next time printing is performed.

[0073] (Aspect 3) In the first or second embodiment, the visible image, such as the "spit-out visible image," is a halftone image having an image density of more than 5% and not more than 30%. As a result, as described in the embodiment, it is possible to prevent a printed image formed on a sheet or other paper (an image printed based on image data received from a personal computer, document reading unit, etc.) from becoming difficult to see due to visible images such as a "discharge visible image."

[0074] (Aspect 4) In any of aspects 1 to 3, when a refresh execution means such as the refresh execution unit 62 executes a refresh operation, it calculates the amount of toner required to refresh the toner in the developing device, and when the amount of toner forcibly consumed at the image density of a visible image such as a "discharge visible image" set by the user is less than the required amount of toner, it forms a visible image with an image density higher than the image density set by the user. According to this, as explained with reference to FIG. 9, it is possible to effectively expel deteriorated old toner with one refresh operation.

[0075] (Aspect 5) In any of aspects 1 to 4, when a refresh execution means such as the refresh execution unit 62 executes a refresh operation, it calculates the amount of toner required to refresh the toner in the image device, and when the amount of toner forcibly consumed at the image density of a visible image such as a "discharge visible image" set by the user is greater than the required amount of toner, it forms a visible image with an image density lighter than the image density set by the user. This makes it possible to reduce unnecessary toner consumption, as described with reference to FIG.

[0076] (Aspect 6) In any of the first to fifth aspects, the setting means such as the operation panel 50 has a back-side input mode for forming a visible image such as a "spit-out visible image" only on the back side of a blank sheet in a single-sided print job. According to this, as explained using Figures 7 and 8, if the user places importance on the quality of the printed image, the user can switch to the back side input mode and prevent a visible image such as a "spit-out visible image" from being formed on the front side of the sheet on which the printed image is formed. [Explanation of symbols]

[0077] 1: Color copier 3: Image forming unit 7: Photosensitive drum 11: Process cartridge 18: Waste toner container 30: Developing device 34: Write unit 40: Paper cassette 41: Paper cassette 50: Operation panel 50a: Display section 51: Storage 53: External communication I / F 60: Control section 61: Operation panel control section 62: Refresh execution unit 63: Printer control unit 64: Image reading control unit 65: Storage control unit 67: Image area cumulative average calculation unit 68: Communication control section 69: Pixel acquisition unit [Prior art documents] [Patent documents]

[0078] [Patent Document 1] Patent No. 6686479

Claims

1. An image forming apparatus having a refresh execution means for forming a toner expelling image on the entire surface of a sheet and forcibly consuming toner in a developing device at a predetermined timing, the toner-removing image is a visible image, An image forming apparatus comprising: a setting unit for allowing the user to set the image density of the visible image.

2. 2. The image forming apparatus according to claim 1, The image forming apparatus is characterized in that the refresh execution unit executes the refresh operation when a cumulative average value of image area within a predetermined time while the developing device is in operation is less than a threshold value.

3. 2. The image forming apparatus according to claim 1, The image forming apparatus is characterized in that the visible image is a halftone image having an image density of more than 5% and not more than 30%.

4. 2. The image forming apparatus according to claim 1, The refresh execution means calculates the amount of toner required to refresh the toner in the developing device when performing a refresh operation, and when the amount of toner forcibly consumed at the image density of the visible image set by the user is less than the required amount of toner, forms a visible image with an image density darker than the image density set by the user.

5. 2. The image forming apparatus according to claim 1, The refresh execution means calculates the amount of toner required to refresh the toner in the developing device when performing a refresh operation, and when the amount of toner forcibly consumed at the image density of the visible image set by the user is greater than the required amount of toner, forms a visible image with an image density lighter than the image density set by the user.

6. 2. The image forming apparatus according to claim 1, An image forming apparatus having a back-side input mode for forming the visible image only on the back side of a blank sheet in a single-sided printing job.

Images