Image forming apparatus

Abstract

To provide an image forming apparatus that can determine toner end indicating whether a toner container has become empty at an appropriate timing without providing a toner density sensor for detecting the amount of toner in a developing device, and can reduce the frequency at which image forming processing is interrupted by execution of image quality adjustment processing in a state where the amount of toner remaining in the toner container is reduced.SOLUTION: In a first period that is a period from when a first cumulative printing rate exceeds a predetermined first reference value until when initial image quality adjustment processing is executed, a control unit executes first processing of performing only the image quality adjustment processing for every first interval that is a predetermined interval, and in a second period that is a period later than the time point when the initial image quality adjustment processing is executed after the first cumulative printing rate exceeds the first reference value, executes the image quality adjustment processing at a second interval shorter than the first interval, and executes second processing of causing a remaining amount determination processing unit to execute determination processing.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present disclosure relates to an electrophotographic image forming apparatus such as a copying machine, a multifunction machine, a printer, or a facsimile machine. [Background technology]

[0002] An electrophotographic image forming apparatus generally forms a toner image on a photosensitive drum by a developing device, and then transfers the toner image formed on the photosensitive drum directly to a printing sheet by a transfer device, or transfers the toner image to an intermediate transfer body, and then transfers the toner image transferred to the intermediate transfer body to a printing sheet by a transfer device.The toner image transferred to the printing sheet is then heated and melted by a fixing device, and fixed to the sheet.

[0003] In such image forming devices, toner is consumed as the toner image is formed, so a separate toner container is provided to store toner to be replenished to the developing device. However, when the toner container runs out of toner, toner cannot be replenished to the developing device, resulting in a problem of a reduced amount of toner in the developing device and a low density toner image. Patent Document 1 therefore discloses a technology for changing the frequency of image stabilization control to maintain an appropriate toner image density depending on the amount of toner remaining in the toner container, more specifically, a technology for increasing the frequency of image stabilization control when the amount of toner remaining in the toner container becomes low.

[0004] Patent document 1 discloses an image forming device that is configured to suppress a decrease in image density and quality during periods when the remaining toner amount in a toner container is low by increasing the frequency of image stabilization control (referred to as "image quality adjustment processing" in this disclosure) when it is calculated based on the dot count of the formed image that the remaining amount of toner in the toner container is below a threshold value. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-002537 Summary of the Invention [Problem to be solved by the invention]

[0006] The image forming apparatus disclosed in Patent Document 1 always performs image stabilization control at the same timing, meaning that image stabilization control is performed at the same timing whether a high-density toner image (such as a photograph) that consumes a lot of toner is formed or a low-density toner image (such as a text document) that consumes a little toner, resulting in the problem that image stabilization control cannot be performed at an appropriate timing according to the amount of toner consumed.In addition, the determination of whether the toner in the toner container has run out (toner end determination) is performed by a toner concentration sensor that detects the amount of toner (toner concentration) in a separately provided developing device, which results in a problem of increased costs.

[0007] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide an image forming apparatus that can reduce the frequency of image formation process interruptions due to image quality adjustment processes being performed when the toner remaining in a toner container is low. It also aims to provide an image forming apparatus that can perform toner end determination, i.e., whether a toner container is empty, at an appropriate timing without providing a toner concentration sensor that detects the toner amount in a developing device. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, an image forming apparatus according to the present disclosure is an image forming apparatus that forms an image on a sheet, and includes: a toner container that stores toner therein; a developing means that forms a toner image on the surface of an image carrier using the toner supplied from the toner container; a developing power supply that supplies a developing bias that is a predetermined voltage to the developing means; an image sensor that detects the image density of the toner image; and a control unit that is capable of executing an image forming process that forms the toner image on the surface of the image carrier based on image data that is electronic data of the image to be formed on the sheet; and an image quality adjustment process that forms an image quality adjustment toner image that is a predetermined toner image on the surface of the image carrier and adjusts a value of the developing bias based on image density information detected by the image sensor, and the control unit calculates a sheet printing rate, which is the ratio of the area of the toner image formed during the image forming process to the area of the sheet, from the image data. and a remaining amount determination processing unit that determines whether or not the toner remains in the toner container based on image density information of the image quality adjustment toner image detected by the image sensor when the image quality adjustment processing is being performed, wherein during a first period which is a period from when the first cumulative printing rate exceeds a predetermined first reference value until a first image quality adjustment processing is performed, a first process that performs only the image quality adjustment processing is performed at first intervals which are predetermined intervals, and during a second period which is a period after the first image quality adjustment processing is performed after the first cumulative printing rate exceeds the first reference value, the image quality adjustment processing is performed at second intervals which are shorter than the first intervals, and a second process that performs determination processing by the remaining amount determination processing unit.

[0009] According to the above-described configuration, it is possible to timely determine whether the toner container is empty without providing a toner concentration sensor in the developing device, and it is also possible to reduce the frequency of image formation process interruptions due to image quality adjustment processing being performed when the toner container is low in toner.

[0010] In the image forming apparatus according to the present disclosure, the control unit may further have a second cumulative printing rate calculation unit that calculates a second cumulative printing rate by adding and accumulating the sheet printing rates of the image newly formed in the image forming process after the image quality adjustment process is performed each time the image forming process is performed during the second period, and the first interval may be determined by the number of processed sheets, which is the number of sheets to be subjected to the image forming process, and the second interval may be determined by the value of the second cumulative printing rate.

[0011] In the image forming apparatus according to the present disclosure, the control unit may further include a second cumulative printing rate calculation unit that calculates a second cumulative printing rate by adding and accumulating the sheet printing rate of the image newly formed in the image formation process after the image quality adjustment process is performed each time the image formation process is performed during the second period, and a continuation determination unit that determines whether, during the image formation process during the second period, the state is a first state in which next image data, which is the image data for the next image formation process, is present, or a second state in which the next image data is not present, and that determines whether or not to perform the second process during the second period based on the results of the second cumulative printing rate calculation unit and the continuation determination unit.

[0012] In the image forming apparatus according to the present disclosure, the control unit may be characterized in that, during the second period, if the continuation judgment unit determines that the image forming process is in the second state and the value of the second cumulative printing rate reaches a second reference value that is smaller than the first reference value, the control unit executes the second process, and if the continuation judgment unit determines that the image forming process is in the first state and the value of the second cumulative printing rate reaches a third reference value that is larger than the second reference value and smaller than the first reference value, the control unit executes the second process.

[0013] In the image forming apparatus according to the present disclosure, the third reference value may be equal to or less than twice the value of the second reference value.

[0014] In the image forming apparatus according to the present disclosure, the remaining amount determination processing unit may be characterized in that, during the image adjustment process, even if the value of the development bias is changed to form the image quality adjustment toner image, if the image density of the formed image quality adjustment toner image detected by the image sensor does not reach the target density, the remaining amount determination processing unit determines that there is no toner in the toner container.

[0015] In the image forming device according to the present disclosure, the image forming device may further include a display unit, and when the remaining amount determination processing unit determines that there is no toner remaining in the toner container, the control unit may display a message on the display unit indicating that the toner container is empty. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is an explanatory diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a diagram illustrating an image forming unit of the image forming apparatus shown in FIG. [Figure 3] 3A and 3B are diagrams illustrating a toner container attached to the image forming apparatus according to the embodiment. [Figure 4A] FIG. 3 is a cross-sectional view showing the positional relationship between the photosensitive drum and the image sensor, as viewed from the front side. [Figure 4B] FIG. 2 is a side view seen from the right side to show the configuration of the image sensor. [Figure 5] 1 is a schematic configuration diagram showing a part of a control unit and devices included in an image forming apparatus according to an embodiment of the present invention; [Figure 6] FIG. 4 is a diagram showing the relationship between the surface potential of the photosensitive drum and the developing bias. [Figure 7] 5A and 5B are diagrams illustrating image quality adjusting toner images and detection signals in an image sensor in the present embodiment. [Figure 8] 4 is a flowchart showing various operations performed by a control unit according to the present embodiment. [Figure 9]6 is a flowchart showing the operation of a remaining amount determination process performed by a control unit according to the present embodiment. [Figure 10] FIG. 10 is an explanatory diagram showing a schematic configuration of another image forming apparatus according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, a monochrome multifunction peripheral that forms a single-color image (monochrome image) on a sheet P, which is a recording medium, will be described as an example of an image forming apparatus according to the present disclosure. (Image forming device) Fig. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus 10 according to an embodiment of the present disclosure. Fig. 2 is a schematic explanatory diagram illustrating a part of the image forming unit 3 shown in Fig. 1.

[0018] 1 and 2 are views of the image forming apparatus 10 as viewed from the front, with the arrow X in the figures indicating the width direction of the image forming apparatus 10, with the direction indicated by the arrow being the right side and the opposite side being the left side. The arrow Y indicates the front-to-rear direction of the image forming apparatus 10, with the direction indicated by the arrow (dot) being the front side and the opposite side being the rear side. The arrow Z indicates the up-down direction, with the direction indicated by the arrow being the up side and the opposite side being the down side. Figure 3 is a perspective view of the toner container 41 as viewed from the rear side.

[0019] The image forming apparatus 10 includes a document transport unit 1, a document reading unit 2, an image forming unit 3, a paper feeding unit 4, and a sheet transport unit 5.

[0020] The document transport unit 1 is a document transport device 13 that transports documents T placed on a document placement table 11 capable of placing a plurality of documents to a document reading position 12 one by one.

[0021] The document reading unit 2 is a document reading device 17 that includes a document placing table 14 made of a transparent material (such as glass) on which the document T is placed, a scanning optical unit 15 that is arranged below the document placing table 14 and can scan in the left-right direction of the image forming device 10, and an imaging unit 16 that images the document placed on the document placing table 14 via the scanning optical unit 15.

[0022] The imaging unit 16 captures an image of the original T sent to the original reading position 12 by the original transport device 13 using the scanning optical unit 15, or scans the original T placed on the original placing table 14 using the scanning optical unit 15 and captures the image using the imaging unit 16, thereby reading and converting the image into electronic data.

[0023] The paper feed section 4 is a storage section for the sheets P on which the images are to be formed, and the sheet transport section 5 transports the sheets P stored in the paper feed section 4 to the image forming section 3.

[0024] The image forming unit 3 forms an image on a sheet P based on image data that has been scanned by the document reading device 17 and converted into electronic data, or image data sent from a personal computer or the like. The image forming unit 3 includes a photosensitive drum 30, a charging device 31, an exposure device 34, a developing device 36, a transfer device 45, a discharge device 48, a cleaning device 50, a toner container 41, and a fixing device 54.

[0025] The photosensitive drum 30 includes a grounded conductive cylindrical member and a photosensitive layer formed on the outside of the cylindrical member. The photosensitive layer is made of a photoconductor that is insulating in the dark and becomes conductive in the irradiated area when irradiated with light. The photosensitive drum 30 is rotated in the direction of arrow R1 in the figure by a drive source (not shown) provided in the main body of the image forming apparatus 10.

[0026] The charging device 31 includes a charging roller 32 having a conductive shaft and a conductive elastic layer formed on the outside of the shaft. The charging roller 32 is disposed so that the surface of the conductive elastic layer contacts the surface of the photosensitive drum 30, and is supported so as to rotate as the photosensitive drum 30 rotates. A charging power supply 33 that outputs a charging bias, which is a predetermined voltage or current, is connected to the conductive shaft. The charging power supply 33 supplies the charging bias to the surface of the photosensitive drum 30, charging the surface of the photosensitive drum 30 to a predetermined potential (for example, approximately -600 V). The charging power supply 33 is provided in the main body of the image forming apparatus 10.

[0027] The exposure device 34 has a light-emitting unit (e.g., a laser diode) and exposes the surface (photosensitive layer) of the photosensitive drum 30 based on the image data for printing. The exposed area, which is the area exposed to the light emitted from the light-emitting unit, has a lower resistance value and a lower surface potential, and an electrostatic latent image according to the image data for printing is formed.

[0028] The surface potential of the exposed area is closer to ground potential than the non-exposed area, which is the other area that is not exposed, and is, for example, about −50 to −100 V. The exposure device 34 of the present disclosure is a scanning type exposure device that scans the photosensitive drum 30 in the longitudinal direction with a light beam emitted from a light-emitting unit.

[0029] The developing device 36 includes a developer tank 40 that contains developer containing toner and a developing roller 38 that carries a portion of the developer on its surface and supplies the toner to the photosensitive drum 30. The developing roller 38 rotates in the direction of arrow R2 in the figure by a drive source (not shown). A development power source 39 is also connected to the developing roller 38.

[0030] A predetermined voltage, for example, a developing bias DVb of −400 V, is supplied to the developing roller 38 from a developing power supply 39. The toner contained in the developing device 36 is charged to a predetermined negative charge, and when this developing bias DVb is supplied to the developing roller 38, a potential difference occurs between the electrostatic latent image formed on the photosensitive drum 30 and the toner is developed in the exposed area (see FIG. 6).

[0031] By carrying out the above process, a toner image is formed on the photosensitive drum 30. As will be described in detail later, the development power supply 39 is configured to be able to change the value of the development bias DVb supplied to the development roller 38, and is provided in the main body of the image forming apparatus 10.

[0032] The developing device 36 is connected to a toner container 41 (toner cartridge) that contains toner therein. Fig. 3 is a perspective view of the toner container 41 as seen from the rear side.

[0033] The toner container 41 is detachable from the image forming device 10, and as shown in FIG. 3, has an outlet 41a for discharging the toner stored therein, a transport section 42 for transporting the stored toner sequentially toward the outlet 41a, and a terminal 41b provided with a memory means (not shown) for storing the type and amount of toner stored therein (a predetermined sheet printing rate for a sheet of a predetermined size) and the corresponding image forming device 10.

[0034] When toner container 41 is attached to image forming device 10, terminal 41b is connected to a connection terminal provided on the main body of image forming device 10, and toner container detection device 44 provided on image forming device 10 can detect that toner container 41 has been attached and the contents stored in the memory unit of terminal 41b.

[0035] When toner container 41 is attached to image forming apparatus 10, discharge port 41a is connected to developing device 36, and when conveying section 42 provided inside toner container 41 is rotated via gear 42a by toner supply device 43 having a toner supply motor (not shown), toner stored inside is sent to discharge port 41a and supplied to developing device 36. Note that toner container 41 is provided with a movable shutter 41c, and when toner container 41 is removed from image forming apparatus 10, discharge port 41a is configured to be covered by a biasing member (not shown).

[0036] The transfer device 45 includes a transfer roller 46 having a conductive shaft and a conductive elastic layer formed on the outside of the shaft. A transfer bias, which is a predetermined current, is applied to the conductive shaft of the transfer roller 46 from a transfer power source 47. The transfer roller 46 abuts against the photosensitive drum 30 and rotates together with the photosensitive drum 30 when the photosensitive drum 30 is rotated by a drive source (not shown). The transfer roller 46 transfers the toner image formed on the photosensitive drum 30 to the sheet P when the sheet P fed from the paper feed unit 4 is nipped and conveyed between the transfer roller 46 and the photosensitive drum 30 in a transfer nip region NT, which is the abutment portion between the transfer roller 46 and the photosensitive drum 30. The transfer power source 47 is also provided in the main body of the image forming apparatus 10.

[0037] The static eliminator 48 has a light source and irradiates the surface of the photosensitive drum 30 before it is cleaned by the cleaning device 50, thereby eliminating the surface potential on the photosensitive drum 30 to a ground potential (e.g., a value close to 0 V), and erasing the electrostatic latent image formed on the photosensitive drum 30.

[0038] Residual toner, which is toner that remains on the photosensitive drum 30 without being transferred to the sheet P by the transfer device 45, is removed from the photosensitive drum 30 by a cleaning device 50 and collected by a discharge device (not shown) into a collection container provided in the image forming apparatus 10. The cleaning device 50 has a cleaning blade 51 that comes into contact with the photosensitive drum 30 and scrapes off the residual toner adhering to the surface of the photosensitive drum 30.

[0039] After being neutralized by the neutralization device 48 and cleaned by the cleaning device 50, the roller is ready to be charged by the charging device 31.

[0040] By repeating the above process, the image forming unit 3 forms a toner image on the photosensitive drum 30, and forms (transfers) the image onto the sheet P.

[0041] The fixing device 54 sandwiches the sheet P onto which the toner image has been transferred between a heating roller 56 incorporating a heat source and a pressure roller 58, and fixes the toner image on the sheet P by heating and pressure-feeding the toner image on the sheet P.

[0042] The paper feed section 4 has a paper feed device 60 having a sheet stacking section 62 capable of stacking one or more sheets P, and a paper feed roller 64 that conveys the sheets P stacked on the sheet stacking section 62 one by one.

[0043] The sheet conveying section 5 conveys the sheets P sent one by one from the paper supply section 4 to the transfer device 45 and then to the fixing device 54, and conveys the sheets P with the toner image fixed by the fixing device 54 to the paper discharge tray 78. The sheet conveying section 5 has a first conveying path C1, and conveying rollers 72, registration rollers 74, paper discharge rollers 76, etc. arranged along the first conveying path C1.

[0044] The registration roller 74 temporarily stops the sheet P conveyed from the paper feed device 60 and resumes conveying the sheet P so that it coincides with the timing at which the toner image formed on the photosensitive drum 30 reaches the transfer nip area NT.

[0045] The sheet conveying section 5 has a second conveying path C2 for sending the sheet P again to the registration rollers 74 when an image is to be formed on the opposite side of the sheet P on which an image has been formed (so-called double-sided printing). When double-sided printing is performed, the rotation direction of the sheet P on which an image has been formed is reversed while it is being conveyed by the discharge rollers 76, and the sheet P being conveyed is switched back and sent to the second conveying path C2 for double-sided printing. The sheet P conveyed to the second conveying path C2 is conveyed toward the registration rollers 74 by the conveying rollers 80.

[0046] The above is the basic configuration of the image forming apparatus 10 in this embodiment.

[0047] An image sensor 52 that detects the image density of the toner image formed on the photosensitive drum 30 is provided upstream of the transfer nip area NT in the rotation direction of the photosensitive drum 30. Figures 4A and 4B are diagrams showing the image sensor 52, with Figure 4A being a front view of the image sensor 52 as viewed in the axial direction of the photosensitive drum 30 and Figure 4B being a side view of the image sensor 52 as viewed from a direction intersecting the axial direction of the photosensitive drum 30.

[0048] The image sensor 52 has a light-emitting section 52a and a light-receiving section 52b, and is composed of a reflective optical sensor that emits light from the light-emitting section 52a toward the surface of the photosensitive drum 30 and receives the light reflected from the surface of the photosensitive drum 30 at the light-receiving section 52b. (General configuration of the control unit) FIG. 5 is a schematic diagram showing a part of the devices and control unit included in the image forming apparatus according to this embodiment.

[0049] The image forming apparatus 10 according to this embodiment includes the above-described charging device 31, exposure device 34, developing device 36, transfer device 45, fixing device 54, toner supply device 43, toner container detection device 44, and image sensor 52. The image forming apparatus 10 further includes a drive device 70 including a drive source for rotating the above-described photosensitive drum 30, developing roller 38, etc., a communication unit 71 for receiving image data for image formation processing from an external terminal (such as a personal computer or a mobile terminal), a display unit 73 for displaying information necessary for operating the image forming apparatus 10, and a control unit 20 for controlling the above-described devices and sensors. The control unit 20 is connected to each of the above-described devices and sensors via a bus line or the like. The display unit 73 may be a touch panel.

[0050] The control unit 20 has a processing unit 21 and a storage unit 22. The processing unit 21 is a microcomputer such as a CPU mounted on the image forming apparatus 10, and the storage unit 22 includes a non-volatile memory such as a ROM mounted on the image forming apparatus 10 and a volatile memory such as a RAM.

[0051] The processing unit 21 controls the operation of the image forming apparatus 10 by loading a control program stored in advance in the ROM of the storage unit 22 onto the RAM of the storage unit 22 and executing it. The processing unit 21 also has an image formation processing unit 23 that controls the operation of the image forming apparatus 10 to perform processing to form an image on a sheet P, an image quality adjustment processing unit 24 that adjusts the image quality of the image formed on the sheet P, a near-end determination processing unit 25 that determines whether the remaining amount of toner used for image formation is nearing empty, a remaining amount determination processing unit 26 that determines whether the toner has run out, a first cumulative printing rate calculation unit 27, a second cumulative printing rate calculation unit 28, and a continuation determination unit 29, all of which are control processing units that perform predetermined processing by executing the control program.

[0052] For example, based on image data received from the document reading unit 2 or a personal computer PC connected via the communication unit 71, the image forming processing unit 23 controls the charging device 31, the exposure device 34, the developing device 37, and the driving device 70 to form a toner image on the surface of the photosensitive drum 30, and controls the transfer device 45 to transfer the toner image formed on the surface of the photosensitive drum 30 to the sheet P, thereby forming an image (toner image) on the sheet P. The image forming processing unit 23 also calculates a sheet printing rate α (described later) from the image data of the toner image formed on the surface of the photosensitive drum 30, and controls the toner supply device 43 to supply an amount of toner according to the sheet printing rate α from the toner container 41 to the developing device 36.

[0053] The image quality adjustment processing unit 24, near-end determination processing unit 25, remaining amount determination processing unit 26, first cumulative printing rate calculation unit 27, second cumulative printing rate calculation unit 28, and continuation determination unit 29 will be described later. (Image quality adjustment processing) Before describing the image quality adjustment processing unit 24 and the image quality adjustment process, the developing bias DVb in the developing device 36 and the potential of the electrostatic latent image formed on the surface of the photosensitive drum 30 will be described.

[0054] 6 is a diagram in which the horizontal axis represents the circumferential position of the photosensitive drum 30 and the vertical axis represents the surface potential of the photosensitive drum 30. The surface of the photosensitive drum 30 is charged to a predetermined potential V0 (e.g., −600 V) by the charging device 31. The area of the photosensitive drum 30 exposed by the exposure device 34 becomes conductive and drops to a potential close to ground potential (e.g., −80 V), called the exposure potential VL. Here, the area indicated by the symbol A in FIG. 6 is the non-exposed area A of the photosensitive drum 30, and the area indicated by the symbol B is the exposed area B.

[0055] The value of the developing bias DVb supplied to the developing roller 38 is set to a voltage value between a predetermined potential V0, such as −400 V, and the exposure potential VL. By setting the value of the developing bias DVb in this manner, toner is not supplied to the non-exposed area A, but toner can be supplied to the exposed area B. Note that the larger the difference ΔD between the developing bias DVb and the exposure potential VL, the more toner is supplied to the exposed area B, resulting in higher image density. However, the charge amount of the toner may change over time or due to environmental changes. In such cases, even if the same developing bias DVb is supplied to the developing roller 38, the amount of toner developed may change, resulting in a change in image density. Therefore, to always maintain the same image density, it is necessary to adjust the developing bias DVb.

[0056] The adjustment of this developing bias DVb is the image quality adjustment process.

[0057] Next, the image adjustment process performed by the image quality adjustment processor 24 will be described.

[0058] The image quality adjustment processing unit 24 performs image quality adjustment processing to adjust the value of the developing bias DVb at predetermined intervals so that the density of the toner image is neither too high nor too low.

[0059] During the image quality adjustment process, the image quality adjustment processing unit 24 controls the charging device 31, the exposure device 34, and the developing device 36 to form an image quality adjustment toner image TP, which is a predetermined toner image, on the surface of the photosensitive drum 30, and detects the image density using the image sensor 52.

[0060] FIG. 7 is a diagram showing the shape of the image quality adjusting toner image TP in a plan view, and the detection area φS of the image sensor 52 and the detection signal of the light receiving portion 52b.

[0061] The detection area φS is an area where the light receiving section 52b can measure the image density, and has a diameter of 1 mm.

[0062] The image quality adjusting toner image is a so-called patch image having a rectangular shape larger than the detection area φS, for example, 10 mm square, and is formed under exposure conditions that allow toner to be developed over the entire 10 mm square area.

[0063] The curve indicated by the symbol e in the figure shows the detection signal of the light receiving section 52b, with the vertical axis representing the detection voltage Vp (unit: V).

[0064] The light receiving section 52b of the image sensor 52 has a characteristic that the magnitude of the detection signal changes according to the amount of detected light.

[0065] The light emitting portion 52a of the image sensor 52 has its light emission amount adjusted so that the detection voltage Vp of the light receiving portion 52b becomes 3V when nothing is present on the surface of the photosensitive drum 30.

[0066] Since the light emitted from the light-emitting element 52a is diffused or absorbed on the surface of the toner image, the denser the toner image (the more toner there is), the less light reaches the light-receiving element 52b, and the closer the detection voltage Vp is to 0V.

[0067] Here, the area indicated by C in FIG. 7 indicates the image density information of the image quality adjusting toner image, and the density of the image quality adjusting toner image can be determined by reading the value of the detected voltage Vp in the area indicated by C.

[0068] For the image quality adjusting toner image TP, the target density Pd is specified as a voltage value, for example, 0.2 V. During image quality adjustment processing, if the detected value of the light receiving element 52b is less than 0.2 V, it can be determined that the density is darker than the target density, and if it is greater than 0.2 V, it can be determined that the density is lighter than the target density. (Here, the value of the target density Pd is the value detected by the light receiving element 52b when the image sensor 52 reads the image quality adjusting toner image TP, which has been measured and confirmed in advance, and is determined experimentally.) Therefore, when the image density of the image quality adjustment toner image TP detected by the image sensor 52 is lighter than the target density Pd, the image quality adjustment processing unit 24 adjusts the value of the developing bias DVb to increase ΔD in Fig. 6 so that the image density of the image quality adjustment toner image satisfies the target density Pd. Also, when the image density of the image quality adjustment toner image TP detected by the image sensor 52 is darker than the target density Pd, the image quality adjustment processing unit 24 adjusts the value of the developing bias DVb to decrease the value of ΔD in Fig. 6, thereby reducing the value of the developing bias DVb within a range that does not fall below the target density Pd.

[0069] The control unit 20 performs this image quality adjustment process by the image quality adjustment processor 24 at a predetermined first interval (for example, every time the value of the number of processed sheets η, which is the cumulative number of sheets on which images have been formed since the previous image quality adjustment process, reaches 300 sheets), thereby enabling stable image formation without density fluctuations. The period during which this image quality adjustment process is performed at the first interval will be referred to as the first period.

[0070] During the first period, a first process for performing image quality adjustment processing is executed every time a predetermined first interval elapses. (First cumulative print rate and near-end judgment) As described above, the image quality adjustment process by the image quality adjustment processor 24 is performed to form stable images without density fluctuations, but when the amount of toner remaining in the toner container 41 attached to the image forming apparatus 10 becomes low, the amount of toner supplied to the developing device 36 decreases or becomes unstable, which may result in the formation of pale images. For this reason, when the toner in the toner container 41 is consumed and approaches empty, it is desirable to shorten the interval at which the image quality adjustment process is performed.

[0071] The control unit 20 includes a near-end determination processing unit 25 and a first cumulative printing rate calculation unit 27 to determine whether the toner container 41 is nearly empty.

[0072] The near-end determination processor 25 determines whether the toner in the toner container 41 has been consumed and is nearing empty based on the calculation result of the first cumulative printing rate calculator 27. Here, near-end refers to a state in which the amount of toner in the toner container 41 has reached a predetermined remaining amount of toner. By setting the near-end in this manner, it becomes possible to recognize that the amount of toner remaining in the toner container 41 is low.

[0073] When the toner container detection device 44 detects that the toner container 41 has been attached to the main body of the image forming device 10, the near-end determination processing unit 25 reads information on the amount of toner contained in the toner container 41 from the memory unit of the terminal 41b.

[0074] The amount of toner stored in the storage unit of terminal 41b of toner container 41 according to this embodiment is specified so that, for an image having a sheet coverage rate α of, for example, 5%, which is the ratio of the area of a toner image to the area of a sheet of a predetermined size, such as A4 size, image formation is possible on 10,000 sheets. In other words, for images with a sheet coverage rate α of less than 5%, image formation processing can be performed on a larger number of sheets, but for images with a sheet coverage rate α of more than 5%, image formation processing can be performed on only a smaller number of sheets. Therefore, the amount of toner remaining in toner container 41 cannot be accurately predicted based solely on the information on the number of sheets on which image formation processing has been performed.

[0075] Therefore, after the near-end determination processing unit 25 detects that a new toner container 41 has been installed based on the toner amount information read from the memory unit of the terminal 41b of the toner container 41, the first cumulative printing rate calculation unit 27 calculates the sheet printing rate α, which is the ratio between the area of the toner image formed during the image formation process and the area of the sheet on which the toner image is formed, from the image data, and calculates a first cumulative printing rate β1 by adding up the sheet printing rates α obtained each time the image formation process is performed.

[0076] When the value of the first cumulative printing rate β1 reaches a predetermined first reference value U1, in this case 45,000%, the near-end determination processing unit 25 determines that the toner container 41 is close to empty (near-end).

[0077] Here, the value of the first reference value U1, 45,000%, is the first cumulative printing rate β1 when 9,000 sheets with a sheet printing rate of 5% are image-formed. In other words, since the toner container 41 can process images on 10,000 sheets with a sheet printing rate of 5%, this means that 90% of the toner has been consumed and 10% of the toner remains as it was when the container was new. This first reference value is stored in advance in the memory unit 22.

[0078] Since the first reference value is set in advance as described above, the near-end determination processing unit 25 can determine that the toner container is in a near-end state, meaning that 10% of the toner remains, by checking the value of the first cumulative printing rate β1 (can detect the near-end).

[0079] When the near-end determination processing unit 25 detects the near-end state as described above, the control unit 20 changes the interval at which the image quality adjustment processing is performed so that the interval at which the image quality adjustment processing is performed is a second interval that is shorter than the first interval (for example, every time the number of sheets on which images have been formed reaches 50 sheets). By controlling in this way, stable image formation without density fluctuations can be performed even when the amount of toner remaining in the toner container 41 is low and density changes are likely to occur.

[0080] The amount of toner contained in toner container 41 is 150 g in mass. This can be calculated by multiplying the amount of toner consumed per sheet with a sheet printing rate of 5% (e.g., 0.015 g), which was previously determined through an experiment, by 100,000, but it is difficult to measure the actual mass of toner consumed. Therefore, by using the above-mentioned first cumulative printing rate β1, it becomes possible to easily predict the amount of toner remaining in toner container 41.

[0081] As described above, during the second period, which is the period after the near-end determination processing unit 25 detects the near-end, by performing the image quality adjustment processing at a second interval that is shorter than the first interval, it is possible to prevent a decrease in the density of the toner image even if the amount of toner remaining in the toner container 41 becomes low.However, if the toner in the toner container 41 runs out during the image formation process and becomes empty, the amount of toner in the developer tank 40 may become insufficient, resulting in a decrease in the image density.

[0082] To prevent this, in the prior art described above, a toner concentration sensor is provided in developing device 36 to detect the amount of toner in developing tank 40, and if the toner concentration sensor does not indicate a predetermined amount of toner even when toner supply device 43 is driven, it is determined that toner container 41 is empty (toner end) and the image formation process is stopped. However, as mentioned above, the need to provide a toner concentration sensor poses the problem of increased costs.

[0083] For this reason, the control unit 20 of this embodiment includes a remaining amount determination processing unit . (Remaining amount determination process) The remaining amount determination processing unit 26 performs a remaining amount determination process to determine whether the toner in the toner container 41 has run out at the timing when the image quality adjustment process is performed during a second period that is the period after the near-end determination processing unit 25 detects the near-end.

[0084] Here, the remaining amount determination processor 26 determines that the toner container 41 is empty (toner end) if the image density of the image quality adjusting toner image does not reach the target density Pd even when the development bias DVb is adjusted during the image quality adjustment process (even when the potential difference ΔD in FIG. 6 is increased). More specifically, if the image density of the image quality adjusting toner image does not reach the target density Pd during the image quality adjustment process, the toner supply device 43 is forcibly driven for a predetermined time. That is, the toner supply device 43 is driven for a predetermined time to forcibly supply toner from the toner container 41 to the developing device 36, and then the image quality adjustment process is performed again. Then, if the image density of the image quality adjusting toner image does not reach the target density Pd even after the toner supply device 43 is forcibly driven, the toner container 41 is determined to be empty.

[0085] The remaining amount determination processor 26 performs the remaining amount determination process described above each time the image quality adjustment process is performed during the second period. This makes it possible to determine whether the toner container 41 is empty without providing a toner concentration sensor for detecting the toner amount in the developer tank 40. (Second cumulative printing rate calculation unit) As described above, by performing the remaining amount determination process during the image quality adjustment process during the second period, it is possible to effectively prevent a decrease in image density and detect the end of the toner container 41, but the control unit 20 in this embodiment is further provided with a second cumulative printing rate calculation unit 28. Then, based on the calculation result of the second cumulative printing rate calculation unit 28, it is determined whether or not to perform the second process in which the image quality adjustment process and the remaining amount determination process are performed.

[0086] In this way, by providing the second cumulative printing rate calculation unit 28, it is possible to perform the remaining amount determination process at a more appropriate timing during the second period.

[0087] The second cumulative printing rate calculation unit 28 calculates, from the image data, a sheet printing rate α, which is the ratio between the area of the toner image formed after the image quality adjustment process is performed in the second period and the area of the sheet on which the toner image is formed, and calculates a second cumulative printing rate β2 by adding up the sheet printing rates α obtained each time the image formation process is performed.

[0088] The storage unit 22 stores a second reference value U2 that is smaller than the first reference value U1.

[0089] Here, the value of the second reference value U2 is, for example, 125%, which is smaller than the value of the first reference value U1, 45,000%.

[0090] In this way, if, for example, toner images with a sheet printing rate of 5% are formed continuously during the second period, the remaining amount determination process is performed when images have been formed on 25 sheets (the value of the second cumulative printing rate β2 is 125%).As another example, if toner images with a sheet printing rate of 50% are formed continuously, the remaining amount determination process is performed when images have been formed on 3 sheets (the value of the second cumulative printing rate β2 is 150%).Therefore, it becomes possible to perform the remaining amount determination process at an appropriate timing according to the actual amount of toner consumed. (Continuation determination section) The control unit 20 of this embodiment further includes a continuation determination unit 29. During the image formation process in the second period (or the first period), the continuation determination unit 29 determines whether the state is a first state K1, which indicates that next image data, which is image data for the next image formation process, is present (received by the image formation processing unit 23), or a second state K2, which indicates that the next image data is absent (not received by the image formation processing unit 23). Then, during the second period, the control unit 20 determines whether to perform the second process, including the remaining amount determination process and the image quality adjustment process, based on the results of the second cumulative printing rate calculation unit 28 and the continuation determination unit 29. Specifically, when the value of the second cumulative printing rate β2 reaches the second reference value U2, the determination result of the continuation determination unit 29 indicates that there is no image data for the next image formation process, and the control unit 20 performs the second process, including the remaining amount determination process and the image quality adjustment process.

[0091] By doing this, it becomes possible to perform the image formation process and the remaining amount determination process at the time when the image formation process is completed (second state K2), and it is possible to reduce the waiting time required to wait for these processes to complete (there is no waiting time because the process is performed after the image formation process is completed). Furthermore, the control unit 20 of this embodiment stores a third reference value U3 that is greater than the second reference value U2 and less than the first reference value U1 in the storage unit 22. Here, the value of the third reference value U3 is, for example, 250%.

[0092] Here, even if the value of the second cumulative printing rate β2 exceeds the second reference value during the image formation process in the second period, if the continuation determination unit 29 determines that there is next image data for the next image formation process (if the first state K1), the control unit 20 continues the image formation process. Then, when the continuation determination unit 29 determines that the second state K2 has been reached, or when the second cumulative printing rate β2 reaches the third reference value, the control unit 20 executes the second process including the image quality adjustment process and the remaining amount determination process.

[0093] By controlling in this manner, the frequency of interrupting the image forming process during the second period can be reduced, and the toner end can be detected with high accuracy. (Display) In the image forming device 10 of this embodiment, when the remaining amount determination processing unit 26 detects that the toner is out, the image forming process is stopped or the reception of image data is stopped, and a message indicating that the toner container 41 is empty is displayed on the display unit 73 to notify the operator that the toner container 41 needs to be replaced.

[0094] By configuring in this way, it becomes possible to notify the user that the toner is out of stock and to suggest that the toner container 41 be replaced.

[0095] Here, the image forming process, image quality adjustment process, and remaining amount determination process that the control unit 20 of this embodiment performs in the processing unit 21 will be described with reference to FIG.

[0096] FIG. 8 is a flowchart showing various operations that the control unit 20 performs in the processing unit 21.

[0097] When executing the image forming process, in step S1, the control unit 20 performs a process of reading the first cumulative printing rate β1, the second cumulative printing rate β2, and the number of processed sheets η, which is the cumulative number of sheets on which images have been formed since the previous image quality adjustment process, from the storage unit 22. Then, the process proceeds to the next step S2.

[0098] In step S2, the control unit 20 calculates the sheet printing rate α based on the image data and controls the image forming apparatus 10 to form an image on the sheet P. Then, the control unit 20 adds the sheet printing rate α to each of the first cumulative printing rate β1 and the second cumulative printing rate β2, and stores the results again in the memory unit 22. The number of processed sheets η is also incremented and stored in the memory unit 22. Then, the process proceeds to the next step S3.

[0099] In step S3, the control unit 20 determines whether the first cumulative printing rate β1 is equal to or greater than the first reference value U1 stored in the memory unit 22. If the value of the first cumulative printing rate β1 is equal to or greater than the first reference value U1, the process proceeds to step S9. On the other hand, if the value of the first cumulative printing rate β1 is not equal to or greater than the first reference value U1, the process proceeds to step S4.

[0100] In step S4, the control unit 20 checks the value of the number of processed sheets η, and if the value of the number of processed sheets η is 300 or more, the process proceeds to step S5. On the other hand, if the value of the number of processed sheets η is not 300 or more, the process proceeds to step S6.

[0101] In step S5, the control unit 20 performs the image quality adjustment process, then resets the value of the number of processed sheets η, and the process proceeds to step S6.

[0102] In step S6, the control unit 20 determines whether there is next image data, which is image data for the next image formation, using the continuation determination unit 29. If there is next image data, the process proceeds to step S2, where the next image formation process is performed. On the other hand, if there is no next image data, the process proceeds to step S7.

[0103] In step S7, the control unit 20 checks the value stored in the flag variable Pexe. If the value of the flag variable Pexe is 1, the control unit 20 proceeds to step S8. On the other hand, if the value of the flag variable Pexe is not 1, the control unit 20 completes the image forming process.

[0104] In step S8, the control unit 20 performs image quality adjustment processing and remaining amount determination processing, resets the value of the second cumulative printing rate β2, and then completes the image forming processing.

[0105] As described above, when the first cumulative printing rate β1 is smaller than the first reference value U1, the first process (image quality adjustment process) is performed when the number of processed sheets η becomes equal to or greater than 300. This allows images to be formed with a stable image density at all times.

[0106] Next, the process when the value of the first cumulative printing rate β1 is equal to or greater than the first reference value U1 will be described.

[0107] If the first cumulative printing rate β1 is equal to or greater than the first reference value U1 in step S3, the value of the number of processed sheets η is checked in step S9. If the value of the number of processed sheets η is equal to or greater than 300, the process proceeds to step S11. On the other hand, if the value of the number of processed sheets η is not equal to or greater than 300, the process proceeds to step S10.

[0108] In step S4, the control unit 20 checks the value of the number of processed sheets η, and if the value of the number of processed sheets η is 300 or more, the process proceeds to step S10. On the other hand, if the value of the number of processed sheets η is not 300 or more, the process proceeds to step S11.

[0109] In step S10, the control unit 20 executes the first process (last), resets the number of processed sheets η, and proceeds to step S6.

[0110] In step S11, the control unit 20 checks the value of the second cumulative printing rate β2. If the value of the second cumulative printing rate β2 is equal to or greater than the second reference value U2 (e.g., 125%), the process proceeds to step S12. On the other hand, if the value of the second cumulative printing rate β2 is not equal to or greater than the second reference value U2, the process proceeds to step S6.

[0111] In step S12, the control unit 20 checks the value of the second cumulative printing rate β2. If the value of the second cumulative printing rate β2 is equal to or greater than the third reference value U3 (e.g., 250%), the process proceeds to step S14. On the other hand, if the value of the second cumulative printing rate β2 is not equal to or greater than the third reference value U3, the process proceeds to step S13.

[0112] In step S13, the control unit 20 changes the value of the flag variable Pexe to 1 (the default value is 0), and the process proceeds to step S6.

[0113] In step S14, the control unit 20 performs the second process (image quality adjustment process and remaining amount reversal process), then resets the second cumulative printing rate β2, and the process proceeds to step S6.

[0114] As described above, when the first cumulative printing rate β1 is greater than the first reference value U1, the second process (image quality adjustment process and remaining amount determination process) is performed based on the value of the second cumulative printing rate β2 and the determination result of the continuation determination unit 29. This allows the image quality adjustment process and remaining amount determination process to be performed at shorter intervals than when the first cumulative printing rate β1 is less than the first reference value U1, so that even if the remaining toner amount becomes low and the image density tends to become low, it is possible to always form images with a stable image density. In addition, the remaining amount determination of whether toner has run out can be performed accurately because it is performed when a predetermined amount of toner has been consumed.

[0115] The remaining amount determination process performed by the control unit 20 in the processing unit 21 will be described with reference to FIG.

[0116] As described above, the control unit 20 performs the image quality adjustment process and the remaining amount determination process when the second process is performed.

[0117] FIG. 9 is a flowchart showing the operation performed by the control unit 90 during the second process.

[0118] The control unit 20 performs image quality adjustment processing in step S21. That is, the control unit 20 forms an image quality adjustment toner image TP, reads the image density of the formed image quality adjustment toner image TP with the image sensor 52, and then proceeds to the next step S22.

[0119] In step S22, the control unit 20 ends the process if the detection value of the image quality adjusting toner image TP by the image sensor 52 satisfies the target density, and if the target density is not satisfied, the process proceeds to step S23.

[0120] In step S23, control unit 20 drives toner supply device 43 for a predetermined time to perform a supply operation to supply toner to developing device 36. Then, control unit 20 executes the image quality adjustment process again, reads image quality adjustment toner image TP with image sensor 52, and proceeds to step S24.

[0121] In step S24, the control unit 20 ends the process if the detection value of the image quality adjusting toner image TP by the image sensor 52 satisfies the target density, and if the target density is not satisfied, the process proceeds to step S25.

[0122] In step S25, the control unit 20 displays on the display unit 73 that there is no toner in the toner container 41, i.e., that the toner container 41 is in a toner end state, and then stops the process by entering an acceptance stop state in which acceptance of image formation processing is stopped thereafter.

[0123] The control unit 20 can perform the remaining amount determination process by performing the above operations.

[0124] In other words, it becomes possible to appropriately determine whether or not toner remains in the toner container 41 without providing the developing device with a toner concentration sensor that detects the amount of toner. (Color multifunction printer) Although a monochrome multifunction peripheral has been described as an example of the image forming apparatus according to the present disclosure, the present disclosure may also be applied to a color multifunction peripheral that forms multicolor images (color images).

[0125] A color multifunction peripheral differs from a monochrome multifunction peripheral in that the image forming unit includes a plurality of photosensitive drums and an intermediate transfer device.

[0126] FIG. 10 is a cross-sectional view showing a schematic configuration of a color image forming apparatus 100 according to an embodiment of the present disclosure.

[0127] The color image forming apparatus 100 includes multiple image stations ST, each including a photosensitive drum 130, a charging device 131, a developing device 136, a static eliminator 148, and a cleaning device 150, to form a toner image for each color. (Each developing device 136 is connected to a corresponding development power supply, not shown.) The apparatus also includes an exposure device 134 that exposes each photosensitive drum 130 to light, toner containers 141 that supply toner to the developing devices 136 of each color, toner supply devices (not shown) corresponding to each toner container 141, and an intermediate transfer device 190 having an intermediate transfer body 191 (image carrier) to which the toner image formed on each photosensitive drum 130 is intermediately transferred. In the color image forming apparatus 100, an image sensor 152 detects the image density of the toner image intermediately transferred to the intermediate transfer body 191, and a transfer device 145 transfers the toner image intermediately transferred to the intermediate transfer body 191 onto a sheet P.

[0128] In such a configuration, the toner image formed at each image station ST is transferred to an intermediate transfer body 191, and the image density of the toner image transferred to the intermediate transfer body 191 is detected by an image sensor 152, thereby enabling control similar to that of the image forming device 10 (monochrome image forming device).

[0129] In other words, by arranging the image sensor 152 facing the intermediate transfer body 191, it is possible to measure the image density of the toner image formed by each developing device 136 with one sensor, and thus to perform a remaining amount determination process to determine the remaining toner amount in each toner container 141.

[0130] The configuration disclosed in any of the above-described embodiments can be applied in combination with the configuration disclosed in other embodiments, as long as no contradiction arises. Furthermore, the embodiments disclosed in this specification are examples, and the embodiments of the present disclosure are not limited thereto and can be modified as appropriate within the scope of the present disclosure. [Explanation of symbols]

[0131] 10 Image forming device 20 Control Unit 22 Memory section 23 Image forming processing section 24 Image quality adjustment processing section 25 Remaining amount determination processing unit 26 First cumulative printing rate calculation section 27 Second cumulative printing rate calculation section 28 Continuation Judgment Section 30 Photosensitive drum (image carrier) 36 Developing device 37 Development power supply 41 Toner container 43 Toner supply device 44 Toner container detector 52 Image Sensor 72 Display section V0 Surface potential of the non-image area of the photosensitive drum VL Surface potential of the image area of the photoconductor drum DVb Development Bias α Sheet printing rate β1 First cumulative printing rate β2 Second cumulative printing rate U1 First standard value U2 Second standard value U3 Third standard value

Claims

1. An image forming apparatus for forming an image on a sheet, a toner container containing toner; a developing unit that forms a toner image on the surface of an image carrier using the toner supplied from the toner container; a development power supply that supplies a development bias, which is a predetermined voltage, to the developing means; an image sensor for detecting the image density of the toner image; a control unit capable of executing an image forming process of forming the toner image on the surface of the image carrier based on image data that is electronic data of the image to be formed on the sheet, and an image quality adjustment process of forming an image quality adjustment toner image that is a predetermined toner image on the surface of the image carrier, and adjusting the value of the developing bias based on image density information detected by the image sensor, The control unit a first cumulative printing rate calculation unit that calculates a sheet printing rate, which is a ratio between an area of the toner image formed during the image forming process and an area of the sheet, from the image data, and calculates a first cumulative printing rate by adding up the sheet printing rates obtained each time the image forming process is performed; a remaining amount determination processing unit that determines whether or not the toner remains in the toner container based on image density information of the image quality adjustment toner image detected by the image sensor during the image quality adjustment processing, During a first period, which is a period until the first cumulative print rate exceeds a predetermined first reference value and the first image quality adjustment process is performed, a first process that performs only the image quality adjustment process is performed at first intervals, which are predetermined intervals; An image forming apparatus characterized in that, during a second period that is a period after the first time the image quality adjustment process is performed after the first cumulative printing rate exceeds the first reference value, the image quality adjustment process is performed at a second interval that is shorter than the first interval, and a second process that performs a judgment process by the remaining amount judgment processing unit is executed.

2. The control unit a second cumulative printing rate calculation unit that calculates a second cumulative printing rate by adding and accumulating the sheet printing rate of the image newly formed in the image forming process after the image quality adjustment process is performed each time the image forming process is performed during the second period, the first interval is defined by the number of sheets to be processed, which is the number of sheets to be processed for image formation, 2. The image forming apparatus according to claim 1, wherein the second interval is defined by the value of the second cumulative printing rate.

3. The control unit a second cumulative printing rate calculation unit that calculates a second cumulative printing rate by adding and accumulating the sheet printing rate of the image that is newly formed in the image forming process after the image quality adjustment process is performed each time the image forming process is performed during the second period; and a continuation determination unit that determines whether, during the second period, the image forming process is in a first state where next image data, which is the image data for a next image forming process, exists or a second state where the next image data does not exist, 2. The image forming apparatus according to claim 1, wherein during the second period, it is determined whether or not to perform the second process based on results of the second cumulative printing rate calculation unit and the continuation determination unit.

4. The control unit In the second period, When the continuation determination unit determines that the image forming process is in the second state during the image forming process, if the value of the second cumulative printing rate has reached a second reference value that is smaller than the first reference value, the second process is executed; 4. The image forming apparatus according to claim 3, wherein, when the continuation determination unit determines that the image forming process is in the first state during the image forming process, if the value of the second cumulative printing rate reaches a third reference value that is greater than the second reference value and less than the first reference value, the second process is performed.

5. 5. The image forming apparatus according to claim 4, wherein the third reference value is equal to or less than twice the value of the second reference value.

6. 6. An image forming apparatus according to claim 1, wherein the remaining amount determination processing unit determines that there is no toner in the toner container if, during the image adjustment process, even if the value of the development bias is changed to form the image quality adjustment toner image, the image density of the formed image quality adjustment toner image detected by the image sensor does not reach the target density.

7. The image forming apparatus further includes a display unit, 7. The image forming apparatus according to claim 6, wherein the control unit displays a message on the display unit indicating that the toner container is empty when the remaining amount determination processing unit determines that there is no toner remaining in the toner container.

Images