Image forming device

Abstract

To normally determine a change in toner density without comprising a temperature sensor to accurately control the density of toner included in a developing device.SOLUTION: An image forming apparatus comprises: a toner density value acquisition unit that acquires a toner density value of toner stored in a developing device; a storage unit that stores a density determination reference value being a reference in determining whether to supply toner stored in a toner cartridge to the developing device in comparison with the acquired toner density value and double-sided printing history information obtained when double-sided printing is performed; and a density determination reference value correction unit that corrects the density determination reference value based on the number of double-sided printing stored in the double-sided printing history information. After correcting the density determination reference value, the density of toner is controlled through comparison between the acquired toner density value and the corrected density determination reference value.SELECTED DRAWING: Figure 14

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus having a function of detecting the density of toner used in image formation and controlling the toner density. [Background technology]

[0002] Image forming apparatuses have been used for a long time, and multifunction peripherals that have functions such as document reading (scanning) and network connection in addition to a printing function for printing documents and the like are now in use. In an image forming device, a certain amount of two-component developer consisting of, for example, toner and carrier is supplied to a developing device, the toner is caused to adhere to the surface of a photosensitive drum, and an electrostatic latent image formed on the charged surface of the photosensitive drum is developed, thereby forming a toner image corresponding to the electrostatic latent image. In order to maintain an appropriate toner concentration in the developing device and form a toner image with an appropriate concentration, a toner concentration sensor that constantly detects the toner concentration in the developing device is provided in the developing tank of the developing device.

[0003] As the toner concentration sensor, for example, a sensor (magnetic permeability sensor) that measures the magnetic permeability of a two-component developer is used, and a change in the toner concentration is detected from a change in the measured magnetic permeability. However, the signal value output from the toner concentration sensor may fluctuate due to temperature changes in the developing device or photosensitive drum, changes in the fluidity of the two-component developer, and the like. In particular, in double-sided printing, where an image forming device prints on both sides of a printing sheet, when double-sided printing is performed in large quantities continuously, there is a problem in that the print density gradually decreases due to the influence of changes in the output value of the toner density sensor. Therefore, in order to maintain the density of the printed image appropriately, the following measures have been proposed.

[0004] For example, Patent Document 1 describes an image forming apparatus that is equipped with a temperature sensor that comes into contact with the recording medium being transported, detects the temperature of the recording medium being transported by the temperature sensor, estimates the photosensitive body surface temperature from the correlation between a pre-stored photosensitive body surface temperature and the temperature of the recording medium detected by the temperature sensor, and adjusts the development bias voltage, the voltage applied to the charging charge, etc. based on the estimated photosensitive body surface temperature to maintain an appropriate image density.

[0005] Furthermore, Patent Document 2 describes an image forming device that includes a magnetic permeability sensor provided at the bottom of a developer storage section and a resistance temperature sensor that detects the temperature in the vicinity of the magnetic permeability sensor, and that calculates the remaining amount of developer by correcting the output voltage of the magnetic permeability sensor using a predetermined formula based on the signal output from the resistance temperature sensor. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-107810 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-5277 Summary of the Invention [Problem to be solved by the invention]

[0007] In all of the above-mentioned conventional techniques, a temperature sensor is provided, and the temperature detected by the temperature sensor is used to adjust the developing bias voltage and correct the output of the toner concentration sensor. However, since the developing device must be provided with a temperature sensor in addition to the toner concentration sensor, the configuration of the developing device becomes complicated, and the addition of the temperature sensor increases the production cost.

[0008] In particular, when double-sided printing is performed continuously, in addition to temperature changes in the developing device and photosensitive body, the fluidity of the developer and the degree of stress on the developer due to the operating time of the image forming device and the usage environment such as humidity changes have a significant impact on the output value of the toner concentration sensor, and even if the temperature of the developing device is the same, the output value of the toner concentration sensor may change, making it impossible to properly correct the output value of the toner concentration sensor.

[0009] For example, continuous double-sided printing causes the temperature of the surface of the printing paper to rise during transport, and as the surface temperature of the printing paper rises, the temperatures of the developing device and photosensitive element also rise, and as a result, the temperature of the developer also rises. When the temperature of the developer rises, the fluidity of the developer decreases due to the thermal stress, the carrier density within the detection range of the toner concentration sensor decreases, and the magnetic permeability, which is the output value of the toner concentration sensor, decreases.

[0010] Generally, when the output value of the toner concentration sensor becomes smaller than a predetermined reference value (concentration determination reference value), it is determined that the toner concentration is high, and the supply of toner to the developing device is stopped. Furthermore, when the output value of the toner concentration sensor becomes larger than a predetermined reference value (concentration determination reference value), it is determined that the toner concentration is low, and toner replenishment to the developing device is started.

[0011] As described above, if the magnetic permeability, which is the output value of the toner concentration sensor, decreases as the temperature rises and becomes smaller than a predetermined reference value, the toner concentration will be erroneously detected as high, and the supply of toner to the developing device will be stopped even though the condition does not warrant stopping the supply of toner. When the supply of toner is stopped, the toner concentration in the developing device decreases, and the print density on double-sided printing paper decreases, resulting in images not being printed with the appropriate density.

[0012] Therefore, this invention has been made in consideration of the above circumstances, and its objective is to provide an image forming device that, when performing double-sided printing, can correctly determine changes in toner concentration without having a temperature sensor by correcting the concentration judgment reference value taking into account the printing conditions of double-sided printing, such as the number of double-sided prints, and the output value of the toner concentration sensor, and can accurately control the concentration of the toner contained in the developing device and appropriately control the concentration of the printed image, even without having to have a temperature sensor. [Means for solving the problem]

[0013] This invention provides an image forming apparatus characterized by comprising: a toner concentration sensor provided in a developing device containing a two-component developer consisting of toner and carrier, and outputting a signal corresponding to the concentration of toner contained in the developing device; a toner concentration value acquisition unit that acquires the toner concentration value of toner contained in the developing device using the signal output from the toner concentration sensor; a concentration determination reference value that is compared with the acquired toner concentration value to determine whether to replenish toner contained in a toner cartridge to the developing device; a memory unit that stores double-sided printing history information obtained when double-sided printing is performed; and a concentration determination reference value correction unit that corrects the concentration determination reference value based on the number of double-sided printed sheets stored in the double-sided printing history information.

[0014] The apparatus further includes a double-sided printing number measurement unit that counts the number of double-sided printing sheets, which is the number of sheets of printing paper to be double-sided printed when double-sided printing is performed, and the double-sided printing history information is the number of double-sided printing sheets, and the range of the number of double-sided printing sheets is set as the correction condition.

[0015] The device further includes a concentration determination unit that determines whether or not to supply the toner contained in the toner cartridge to the developing device by comparing the acquired toner concentration value with the corrected concentration determination reference value, and a toner supply unit that supplies the toner contained in the toner cartridge to the developing device, and when the concentration determination unit determines that toner needs to be supplied to the developing device, the toner supply unit supplies the toner contained in the toner cartridge to the developing device.

[0016] The toner concentration sensor further includes a sensor output amplitude value acquisition unit that acquires a sensor output amplitude value, which is the amplitude value of the signal output from the toner concentration sensor, and further corrects the concentration determination reference value corrected by the concentration determination reference value correction unit using the acquired sensor output amplitude value.

[0017] The image forming apparatus further includes an amplitude ratio calculation unit that calculates amplitude ratio information from the ratio between the sensor output amplitude value acquired by the sensor output amplitude value acquisition unit and an amplitude comparison value, which is a sensor output amplitude value acquired using a predetermined standard developer, and that corrects the density determination reference value corrected by the density determination reference value correction unit so as to correspond to the magnitude of the calculated amplitude ratio information.

[0018] Furthermore, when the power supply to the image forming apparatus is turned off and then turned on after a predetermined time or more has elapsed, the density determination reference value is returned to a predetermined initial value that has not been corrected.

[0019] The printing apparatus further includes an average printing rate acquisition unit that calculates the average printing rate when image data read from the document to be printed is printed on printing paper; a recovery judgment unit that judges whether the double-sided printing history information obtained when double-sided printing is requested and the calculated average printing rate satisfy predetermined recovery judgment conditions; and a recovery execution unit that executes a recovery process to replace the toner contained in the two-component developer remaining in the developing device with new toner when the recovery judgment unit judges that the recovery judgment conditions are satisfied, and the recovery judgment unit judges that the recovery judgment conditions are satisfied when it is determined from the double-sided printing history information that double-sided printing has been performed continuously on more than a predetermined number of sheets and the average printing rate is less than the predetermined printing rate.

[0020] The toner concentration sensor further includes a sensor output amplitude value acquisition unit that acquires a sensor output amplitude value, which is the amplitude value of the signal output from the toner concentration sensor, and an amplitude ratio calculation unit that calculates amplitude ratio information from the ratio between the sensor output amplitude value acquired by the sensor output amplitude value acquisition unit and an amplitude comparison value, which is the sensor output amplitude value acquired using a predetermined standard developer, and the recovery determination unit is further characterized in that it determines that the recovery determination condition is met when the calculated amplitude ratio information is equal to or greater than predetermined amplitude ratio comparison information.

[0021] The recovery process is characterized by a solid discharge operation in which each color information is printed on a predetermined number of sheets of printing paper.

[0022] The printing apparatus further comprises an average printing rate acquisition unit that calculates an average printing rate when image data read from the document to be printed is printed on printing paper; a toner remaining amount information acquisition unit that acquires toner remaining amount information corresponding to the remaining amount of toner contained in the toner cartridge; a toner remaining amount determination unit that determines whether the double-sided printing history information obtained when double-sided printing is requested, the calculated average printing rate, and the acquired toner remaining amount information satisfy predetermined toner remaining amount determination conditions; and a toner remaining amount warning unit, wherein the toner remaining amount determination unit determines that the toner remaining amount determination conditions are satisfied when it determines from the double-sided printing history information that double-sided printing has been performed continuously on more than a predetermined number of sheets, and the average printing rate is less than the predetermined printing rate comparison information, and the toner remaining amount information is less than the predetermined toner remaining amount comparison information, and if the toner concentration value does not increase even after toner is replenished from the toner cartridge to the developing device, the toner remaining amount warning unit issues a warning requesting the toner cartridge to be replaced.

[0023] The present invention also provides a toner concentration control method for an image forming apparatus, comprising: a toner concentration value acquisition step for storing a concentration determination reference value serving as a criterion for determining whether to replenish toner contained in a toner cartridge attached to the image forming apparatus to a developing device, and double-sided printing history information obtained when double-sided printing is performed, and acquiring a toner concentration value of the toner contained in the developing device using a signal output from a toner concentration sensor provided in the developing device, the toner concentration value being acquired; a concentration determination reference value correction step for correcting the concentration determination reference value based on the number of double-sided prints stored in the double-sided printing history information; and a concentration control step for controlling the concentration of toner contained in the developing device by comparing the acquired toner concentration value with the corrected concentration determination reference value, wherein a control unit provided in the image forming apparatus sequentially executes the above steps.

[0024] The present invention also provides a toner concentration control method for an image forming apparatus, comprising: a toner concentration value acquisition step of acquiring a toner concentration value of toner contained in the developing device using a signal output from a toner concentration sensor provided in the developing device that stores in advance a concentration determination reference value serving as a reference for determining whether to replenish toner contained in a toner cartridge attached to the image forming apparatus to a developing device; and reference value correction information that associates correction conditions for the concentration determination reference value, which are set using double-sided printing history information obtained when double-sided printing is performed, with the correction value when the correction conditions are satisfied; a concentration determination reference value correction step of correcting the concentration determination reference value with the correction value associated with the correction condition, when double-sided printing history information obtained when double-sided printing is requested satisfies the correction conditions set in the reference value correction information; and a concentration control step of controlling the concentration of toner contained in the developing device by comparing the acquired toner concentration value with the corrected concentration determination reference value, wherein the steps are sequentially executed by a control unit provided in the image forming apparatus.

[0025] Further, this invention is also provided with a method in which the double-sided printing history information is the number of double-sided prints, which is the number of sheets of printing paper to be double-sided printed, and a range of the number of double-sided prints is set as the correction condition, and a double-sided print number measurement step is further provided for counting the number of double-sided prints when double-sided printing is requested prior to the density determination reference value correction step, and the density control step comprises a density determination step for determining whether or not toner contained in the toner cartridge should be replenished to the developing device by comparing the acquired toner density value with the corrected density determination reference value, and a toner supply step for supplying a predetermined amount of toner contained in the toner cartridge to the developing device when it is determined that toner should be replenished to the developing device, and and if the number of double-sided prints counted in the double-sided print count measurement step is within the range of double-sided prints set in the correction conditions of the reference value correction information, the density determination standard value is corrected using a correction value associated with the correction conditions. If the acquired toner concentration value becomes greater than the corrected density determination standard value in the density determination step, the toner contained in the toner cartridge should be replenished to the developing device, and a predetermined amount of toner contained in the toner cartridge is replenished to the developing device in the toner replenishment step. [Effects of the Invention]

[0026] According to this invention, when the double-sided printing history information obtained when double-sided printing is requested satisfies the correction conditions set in the standard value correction information, the density determination standard value correction unit corrects the density determination standard value using the correction value corresponding to the satisfied correction condition, and then controls the density of the toner contained in the developing device by comparing the acquired toner concentration value with the corrected density determination standard value.Therefore, when double-sided printing is performed continuously, by correcting the density determination standard value, it is possible to correctly determine changes in toner concentration, accurately control the concentration of toner contained in the developing device, and appropriately control the density of the printed image, even without providing a temperature sensor in the image forming device. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a block diagram showing the configuration of an image forming apparatus according to an embodiment of the present invention; [Figure 2] 3 is an explanatory diagram of an embodiment of information stored in a storage unit of an image forming apparatus in the present invention; FIG. [Figure 3] 3 is an explanatory diagram of an embodiment of information stored in a storage unit of an image forming apparatus in the present invention; FIG. [Figure 4] 3 is an explanatory diagram of an embodiment of information stored in a storage unit of an image forming apparatus in the present invention; FIG. [Figure 5] 3 is an explanatory diagram of an embodiment of information stored in a storage unit of an image forming apparatus in the present invention; FIG. [Figure 6] 3 is an explanatory diagram of an embodiment of information stored in a storage unit of an image forming apparatus in the present invention; FIG. [Figure 7] 3 is an explanatory diagram of an embodiment of information stored in a storage unit of an image forming apparatus in the present invention; FIG. [Figure 8] 3 is an explanatory diagram of an embodiment of information stored in a storage unit of an image forming apparatus in the present invention; FIG. [Figure 9] 3 is an explanatory diagram of an embodiment of information stored in a storage unit of an image forming apparatus in the present invention; FIG. [Figure 10] 3 is an explanatory diagram of an embodiment of information stored in a storage unit of an image forming apparatus in the present invention; FIG. [Figure 11] 10A and 10B are explanatory diagrams illustrating an example of a comparison of toner density values ​​when the density determination reference value is corrected in accordance with the number of double-sided printed sheets and when the density determination reference value is not corrected. [Figure 12] 10 is a flowchart of an embodiment of an initial setting process for a concentration determination reference value in the present invention. [Figure 13] 4 is a flowchart of an embodiment of a toner supply process in the present invention. [Figure 14] 1 is a flowchart of an embodiment of a printing process in the present invention. [Figure 15] 10 is a flowchart of an embodiment of a process for correcting a concentration determination reference value in the present invention. [Figure 16] 10 is a flowchart of an embodiment of a process for correcting a concentration determination reference value in the present invention. [Figure 17] 1 is a flowchart of an embodiment of a recovery process in the present invention. [Figure 18] 1 is a flowchart of an embodiment of a recovery process in the present invention. [Figure 19] 1 is a flowchart of an embodiment of a process for checking the amount of remaining toner in the present invention. [Figure 20] 1 is a flowchart of an embodiment of a process for checking the amount of remaining toner in the present invention. [Figure 21] 4 is a flowchart of an embodiment of a toner remaining amount determination process in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments.

[0029] <Configuration of image forming device> FIG. 1 shows a block diagram of the configuration of an image forming apparatus according to an embodiment of the present invention. An image forming device (hereinafter referred to as an MFP: Multifunction Peripheral, or multifunction device) 1 is a device that processes image data, and is an electronic device that has, for example, a copying function, a printing function, a document reading (scanning) function, a document editing function, a document saving function, a document sending (fax) function, and a communication function. In the following embodiment, the image forming apparatus 1 of the present invention will be described as having a printing function in particular, but may have other functions.

[0030] In FIG. 1, the image forming apparatus (MFP) 1 of the present invention mainly includes a control unit 11, an operation unit 12, a display unit 13, an image processing unit 14, a toner concentration sensor 15, a toner supply unit 16, a double-sided print count measurement unit 21, a toner concentration value acquisition unit 22, a sensor output amplitude value acquisition unit 23, a concentration determination unit 24, a concentration determination reference value correction unit 25, an amplitude ratio calculation unit 26, an average printing rate acquisition unit 27, a recovery determination unit 28, a recovery execution unit 29, a toner remaining amount information acquisition unit 30, a toner remaining amount determination unit 31, a toner remaining amount warning unit 32, and a memory unit 50. Here, the image processing section 14 is mainly composed of an image input section 14a, an image forming section 14b, and an image output section 14c.

[0031] The control unit 11 is a part that controls the operation of each component such as the operation unit and image processing unit, and is realized mainly by a microcomputer that includes a CPU, ROM, RAM, an I / O controller, a timer, and the like. The CPU organically operates various hardware components based on a control program stored in advance in a ROM or the like, and executes the image forming function, density determining function, and the like of the present invention. Furthermore, the toner concentration control method of the present invention is realized by the control unit 11 sequentially executing predetermined steps.

[0032] Of the above components, in particular, the double-sided print count measurement unit 21, toner concentration value acquisition unit 22, sensor output amplitude value acquisition unit 23, concentration determination unit 24, concentration determination reference value correction unit 25, amplitude ratio calculation unit 26, average print rate acquisition unit 27, recovery determination unit 28, recovery execution unit 29, toner remaining amount information acquisition unit 30, toner remaining amount determination unit 31, and toner remaining amount warning unit 32 are each a functional block of the control unit 11, and the CPU of the control unit 11 operates the necessary hardware based on a predetermined program stored in ROM or the like, and performs each process in a software manner.

[0033] The operation unit 12 is a section where a user of the image forming apparatus inputs information and is an input device for performing predetermined input operations to operate the image forming apparatus. For example, it is a section where information such as characters is input and function selection input is input, and a keyboard, mouse, touch panel, etc. are used. Keys operated by the user include an operation start key, a function selection key, a setting key, and the like. The user can execute a printing function, a document reading function, or a function for setting function settings items by, for example, touching the touch panel or pressing a start key for a function such as printing or reading.

[0034] The display unit 13 is a part that displays information, and displays information necessary for executing each function, the results of the execution of the function, and the like, to inform the user. For example, an LCD, an organic EL display, or the like is used as the display unit 13, and when a touch panel is used as the operation unit 12, the display unit 13 and the touch panel are arranged to overlap each other. The display unit 13 displays, for example, the settings of setting items used for printing, etc. of the image forming device, information necessary to execute printing functions, document reading functions, etc., and operation screens for selected functions, etc., using characters, symbols, figures, images, icons, animations, videos, etc. In particular, in this invention, when it is determined that the toner in the toner cartridge is empty, a warning screen is displayed on the display unit 13, requesting that the toner cartridge be replaced.

[0035] The image processing unit 14 is a unit that executes the image forming function, which is the main function of the image forming apparatus, and is mainly composed of an image input unit 14a, an image forming unit 14b, and an image output unit 14c. Mainly, the image input unit 14a is a unit that inputs specified image data, the image forming unit 14b is a unit that converts the input image data into information that can be printed, etc., and the image output unit 14c is a unit that outputs the formed printing information, etc. onto printing paper, etc.

[0036] The image input unit 14a is a part that inputs image data of a document on which images, characters, figures, etc. are written, and is a part that reads a document placed on a document table, for example. The image input unit 14a is a scanner (reading device) that reads a document on which information is written. In order to read an original, the image forming apparatus 1 includes an original placement table (original table) on which the original is placed, and an original cover that holds the original.

[0037] The image forming apparatus 1 may also include an automatic document feeder (ADF) that allows a plurality of original documents to be placed thereon and automatically transports and reads the original documents one by one. An automatic document feeder is used when continuously reading and printing a large number of documents, and the documents containing images, etc. are read one by one by a scanner, and the input image data of each document is stored in the memory unit 50.

[0038] There are various methods for inputting image information. For example, an interface for connecting an external storage medium such as a USB memory corresponds to the image input unit 14a. An electronic data file such as image information to be input may be stored in an external storage medium such as a USB memory, and the USB memory or the like may be connected to an input interface such as a USB terminal, and the desired electronic data file stored in the USB memory or the like may be read out by performing a predetermined input operation on the operation unit 12, and stored in the storage unit 50 as input image data.

[0039] For example, when printing input image data on a recording medium, the image forming unit 14b generally performs the steps of charging, exposing, developing, transferring, cleaning, de-electrifying, and fixing in succession to form the input image data on the recording medium. An image forming apparatus is equipped with a developing device that develops an electrostatic latent image. The developing device contains a two-component developer consisting of toner and carrier, and toner contained in a toner cartridge is replenished to the developing device. Furthermore, a toner concentration sensor is provided in the developing device to measure the concentration of the toner contained in the developing device.

[0040] In the developing process, toner is supplied from a toner cartridge to a developing device, and the electrostatic latent image formed on the surface of the charged photosensitive drum is developed to form a toner image corresponding to the electrostatic latent image. The toner image formed on the surface of the photosensitive drum is transferred onto a recording medium by a transfer device, and then fixed onto the recording medium by heating by a fixing device. Furthermore, the image forming unit 14b converts the input image data into information in a format that can be transferred or displayed.

[0041] The image output unit 14c is a part that outputs the formed input image data, and corresponds to, for example, a printer that prints information such as input image data, and prints the input image data of the read manuscript on a specified printing paper (paper medium). However, the output of input image data is not limited to printing, but also includes storing input image data of a scanned document, sending input image data of a scanned document by fax, and the like. For example, storing input image data of a scanned document onto an external storage medium such as a USB memory, transmitting input image data to another image forming device or server via a network such as the Internet, and storing the input image data in a specific storage folder are also examples of image output.

[0042] The toner concentration sensor 15 is provided in the developing device and outputs a signal corresponding to the concentration of the toner contained in the developing device. The toner concentration sensor 15 may be, for example, a magnetic permeability sensor. The toner concentration sensor 15 is disposed on the bottom or side of a developing container (developing tank) of the developing device that contains, agitates, and transports two-component developer. The magnetic permeability sensor detects the magnetic permeability of the two-component developer that comes into contact with the magnetic permeability sensor among the two-component developers contained in the developing device, and outputs a signal corresponding to the magnetic permeability. The signal corresponding to this magnetic permeability corresponds to the signal corresponding to the density of the toner contained in the developing device.

[0043] If the toner concentration sensor 15 is a magnetic permeability sensor, it outputs a signal corresponding to the magnetic permeability. Generally, if the toner concentration of the contained developer is high, the output value of the magnetic permeability sensor will be a low value. Conversely, when the toner concentration of the contained developer is low, the output value of the magnetic permeability sensor indicates a high numerical value.

[0044] Furthermore, the toner concentration is continuously measured by the toner concentration sensor 15, and when the output value of the sensor (toner concentration value TD, which will be described later) increases, it is determined that the toner concentration has decreased.

[0045] The output value of the signal output from toner concentration sensor 15 is converted into a digital value, acquired by toner concentration value acquisition unit 22, and stored in storage unit 50 as toner concentration value TD.

[0046] The toner supply unit 16 supplies the toner contained in the toner cartridge to the developing device. The toner discharge port of the toner cartridge is engaged with the toner intake port of the developing device, and by rotating a screw provided in the toner transport path inside the toner cartridge, a predetermined amount of toner is discharged from the toner discharge port and replenished to the developing device.

[0047] As will be described later, when the toner concentration value TD becomes larger than a predetermined concentration determination reference value TH0 (TD>TH0), the toner contained in the toner cartridge is replenished to the developing device. The density determination reference value TH0 is information that serves as a reference for comparing with the acquired toner density value TD to determine whether or not to supply the toner contained in the toner cartridge to the developing device.

[0048] When determining whether to replenish toner by comparing the toner concentration value TD with a predetermined concentration determination reference value TH0, as described above, the output value (toner concentration value TD) of the toner concentration sensor 15 may change depending on the temperature of the developing device, etc., which may result in an incorrect determination of whether toner should be replenished or a delay in the timing of replenishment of toner to the developing device. Therefore, the present invention is characterized in that when double-sided printing is performed, the density determination reference value TH0, which is a numerical value to be compared with the toner density value TD, is corrected based on predetermined conditions. By correcting the density determination reference value TH0, the toner density is determined normally, taking into consideration the number of double-sided prints, the print rate, etc., even if there is a change in the temperature of the developing device, etc., and the toner density in the developing device is controlled to be maintained within a predetermined range.

[0049] The double-sided printing number measurement unit 21 is a unit that counts the number of printing sheets (double-sided printing number) on which double-sided printing is performed when double-sided printing is performed. Generally, when performing double-sided printing, a user of the image forming apparatus uses the operation unit 12 to input a setting indicating that "double-sided printing" is to be performed. When a setting is input indicating that "double-sided printing" is to be performed, printing paper is transported one sheet at a time and double-sided printing is performed, but for example, before a sheet of printing paper that will actually be double-sided printed is transported, 1 is added to the information that counts the number of printing paper sheets (number of double-sided printing sheets). The number of print sheets to be double-sided printed, counted by the double-sided print count measurement unit 21, is stored in the storage unit 50 as the double-sided print sheet count RN.

[0050] The number of double-sided printed sheets RN corresponds to the double-sided printing history information described above, and is used when correcting the density determination reference value TH0. The double-sided printing history information is information obtained when double-sided printing is performed, and includes the double-sided printing ratio in addition to the number of double-sided printed sheets RN. When printing continuously on multiple sheets of printing paper, for example, when double-sided printing and single-sided printing are mixed, the proportion of double-sided printing (RN) is the ratio of the number of sheets of printing paper that have been double-sided printed to the total number of prints NA (RN / NA).

[0051] If the total number of sheets printed on the printing process is 100, of which 80 sheets are double-sided and 20 sheets are single-sided, the double-sided printing ratio is 80%. As will be described later, the double-sided printing number conditions for correcting the density judgment reference value and the recovery conditions for performing recovery processing use the double-sided printing number RN, but the double-sided printing ratio may also be used instead of the double-sided printing number RN. That is, the density determination reference value may be corrected using the double-sided printing ratio, and the presence or absence of recovery processing may be determined. The number of double-sided prints RN and the total number of prints NA may be the number of sheets processed within a predetermined time period in the past.

[0052] The toner concentration value acquisition unit 22 is a part that uses the signal acquired from the toner concentration sensor 15 to acquire the toner concentration value of the toner contained in the developing device. The output value of the toner concentration sensor 15 indicates a numerical value corresponding to the concentration of the toner contained in the two-component developer, and the numerical value obtained by converting this output value into a digital value is obtained as the toner concentration value TD and stored in the memory unit 50.

[0053] The sensor output amplitude value acquiring unit 23 is a part that acquires, from the signal output from the toner concentration sensor 15, an amplitude value that indicates the magnitude of the signal (hereinafter referred to as the sensor output amplitude value). The developer contained in the developing device is constantly stirred and in a state of flow, so the amount of toner that comes into contact with the toner concentration sensor changes, and the output value of the toner concentration sensor also changes. The sensor output amplitude value is numerical data corresponding to the difference between the maximum and minimum output values ​​of the toner concentration sensor. For example, the sensor output amplitude value can be obtained by calculating the difference between the maximum and minimum values ​​of the output waveform period of the toner concentration sensor. For example, the amplitude value may be calculated by averaging the difference between the maximum value and the minimum value in one cycle of the output waveform over a predetermined number of cycles, or may be calculated as the difference between the maximum value and the minimum value over a predetermined number of cycles.

[0054] The sensor output amplitude value is used as information for further correcting the concentration determination reference value TH0 corrected by the concentration determination reference value correcting unit 25, as will be described later. The acquired sensor output amplitude value is stored in the storage unit 50 as sensor output amplitude value information (AM) 53.

[0055] Generally, when double-sided printing is performed continuously, the temperature of the developing device etc. rises, and as the temperature rises, the fluidity of the developer in the developing device decreases, resulting in rough images (faint print). When the fluidity of the developer decreases, the repulsion between the carriers in the two-component developer increases, causing the two-component developer to swell. When the two-component developer is in a swollen state, the density fluctuation of the carrier in the vicinity of the toner concentration sensor becomes large, and therefore the amplitude of the output waveform of the signal output by the toner concentration sensor becomes large. Therefore, by detecting a change in the sensor output amplitude value (the amplitude of the output waveform increasing), it can be determined that the fluidity of the developer is decreasing, and the sensor output amplitude value is used as information for correcting the concentration determination reference value TH0. Furthermore, by using the sensor output amplitude value as information for correcting the density determination reference value TH0, the accuracy of toner density control can be further improved.

[0056] The concentration determining section 24 is a section that determines whether toner should be replenished based on the toner concentration of the developer contained in the developing device. As described above, the toner concentration value TD acquired by the toner concentration value acquisition unit 22 is compared with the predetermined concentration determination reference value TH0 to determine whether or not toner contained in the toner cartridge should be replenished to the developing device.

[0057] In principle, when the acquired toner concentration value TD becomes larger than the concentration determination reference value TH0 (TD>TH0), it is determined that toner should be replenished to the developing device, and the toner replenishment unit 16 replenishes the toner contained in the toner cartridge to the developing device. On the other hand, if the toner concentration value TD is equal to or less than the concentration determination reference value TH0 (TD≦TH0), it is determined that toner should not be replenished to the developing device, and if the toner concentration value TD is equal to or less than the concentration determination reference value TH0 while toner is being replenished to the developing device, the replenishment of toner is stopped. Furthermore, if the density determination reference value TH0 is corrected, the corrected density determination reference value TH0 is compared with the acquired toner density value TD.

[0058] The concentration determination reference value correcting section 25 is a section that determines a correction value for the concentration determination reference value using predetermined conditions, and corrects the concentration determination reference value TH0. In particular, in this invention, when double-sided printing is requested, the density determination reference value TH0 is corrected using double-sided printing history information obtained by double-sided printing and reference value correction information pre-stored in the memory unit 50. Since temperature information of the developing device, photosensitive drum, etc. is not used to correct the density judgment reference value TH0, there is no need to provide a temperature sensor for detecting the temperature of the developing device, etc. Therefore, by not providing a temperature sensor, product costs can be reduced.

[0059] The reference value correction information is information that associates the correction conditions for the density determination reference value set using the double-sided printing history information obtained when double-sided printing is performed with the correction value when the correction conditions are met, and is information (HS1) such as that shown in Figure 3, which will be described later. If the double-sided printing history information obtained when double-sided printing is requested satisfies the correction conditions set in the reference value correction information, the density determination reference value correction unit 25 corrects the density determination reference value TH0 using the correction value associated with the satisfied correction conditions. Thereafter, the density of the toner contained in the developing device is controlled by comparing the acquired toner density value TD with the corrected density determination reference value TH0.

[0060] For example, if the double-sided printing history information is the number of double-sided prints RN, and a range of the number of double-sided prints (double-sided print number condition) is set as the correction condition of the reference value correction information HS1, when double-sided printing is requested, if the number of double-sided prints RN counted by the double-sided print number measurement unit 21 is within the range of the number of double-sided prints set as the correction condition of the reference value correction information HS1, the density judgment reference value TH0 is corrected by the correction value associated with that correction condition.

[0061] As will be described later, the density determination reference value TH0 is corrected based on the reference correction value KH associated with the double-sided number condition satisfied by the double-sided number of sheets RN measured by the double-sided printing number measurement unit 21 and the reference value correction information HS1 stored in advance in association with the double-sided number condition shown in Figure 3. In this way, by changing the density determination reference value TH0, which is a comparison value used to determine whether to replenish toner, depending on the number of sheets of printing paper to be double-sided printed continuously (number of double-sided prints RN), erroneous determination of toner density is suppressed.

[0062] In this case, for example, as shown in the reference value correction information HS1 in FIG. 3, the density determination reference value TH0 is corrected so that the density determination reference value TH0 decreases as the number of double-sided prints RN increases. By changing the concentration determination reference value TH0 to a smaller value, the comparison value for determining whether toner should be replenished or not is set low, and the standard for determining that the toner concentration is high (the standard for deciding to replenish toner) is lowered, making it less likely that the toner concentration will be erroneously determined to be high. Several examples of correcting the concentration determination reference value TH0 will be described in detail later.

[0063] The amplitude ratio calculation unit 26 is a part that calculates an amplitude ratio (hereinafter referred to as amplitude ratio information) corresponding to the sensor output amplitude value acquired by the sensor output amplitude value acquisition unit 23. The amplitude ratio is calculated from the ratio between the acquired current sensor output amplitude value 53 and the amplitude comparison value 63, which is the sensor output amplitude value acquired using a predetermined standard developer. The standard developer means, for example, the developer in the initial state enclosed when the machine is shipped.

[0064] As will be described later, if amplitude ratio information 54, which is the amplitude ratio to be calculated, is AMR, sensor output amplitude value information 53, which is the current sensor output amplitude value, is AM, and amplitude comparison value 63, which is the sensor output amplitude value information obtained using a standard developer, is AM0, then amplitude ratio information 54 (AMR) is calculated by AM / AM0 (AMR=AM / AM0). The amplitude ratio information 54 (AMR) is information for correcting the concentration determination reference value TH0. For example, by using amplitude ratio correction information 64 as shown in FIG. 5, which will be described later, the concentration determination reference value TH0 corrected by the concentration determination reference value correction unit 25 is corrected to correspond to the magnitude of the calculated amplitude ratio information AMR.

[0065] The sensor output amplitude value information 53 itself is used as information for correcting the concentration determination reference value TH0, but there are cases where it is preferable to use the amplitude ratio information 54 rather than the sensor output amplitude value information 53. For example, when the fluidity of the developer decreases and the density variation of the carrier near the toner concentration sensor increases, it is preferable to use the amplitude ratio corresponding to the sensor output amplitude value rather than using the sensor output amplitude value as is. This is because using the amplitude ratio obtained by comparing the reference amplitude value obtained with a standard developer with the current output amplitude value makes it possible to remove the influence of individual differences in the sensor output based on individual differences in the toner concentration sensor and individual differences in the sensor mounting position on the developer tank, thereby making it possible to accurately detect changes in developer density fluctuations. As the carrier density variation increases, the amplitude ratio becomes 100% or more, so the concentration judgment reference value TH0 is corrected using amplitude ratio conditions as shown in FIG. 5, which will be described later. The accuracy of toner concentration control can also be improved by using the amplitude ratio corresponding to the sensor output amplitude value as information for correcting the concentration determination reference value TH0.

[0066] The average printing rate acquisition unit 27 is a part that calculates the average printing rate when image data read from a document to be printed is printed on printing paper. The image data read from the print document contains parts containing information such as text and images, and blank parts with nothing written on them. Since toner is used to print the parts containing information, the percentage of the read image data that contains information such as text (average printing rate) is calculated as information for determining the amount of toner used.

[0067] For example, when a document is placed on the document table and a request is made to print, the document is read and image data is generated, but the image data is divided into a portion with information and a portion without information. The portion with information corresponds to the number of pixels of the scanned document, so the ratio of the number of pixels IMG in the portion with information to the number of images IMG0 in the entire image data is calculated (IMG / IMG0), and this is obtained as the average print rate PR. Generally, in a document in which most of the information is text, the average print ratio PR is about 1% to 10%. The average printing rate PR is used in recovery processing, etc., as will be described later.

[0068] The recovery determination unit 28 is a part that determines whether or not recovery processing should be performed. For example, it is determined whether the double-sided printing history information obtained when double-sided printing is requested and the calculated average printing rate satisfy a predetermined recovery determination condition. Furthermore, the recovery determination unit 28 determines that the recovery determination conditions are met when it determines from the double-sided printing history information that double-sided printing has been performed continuously on more than a predetermined number of sheets and the average printing rate is less than the predetermined printing rate. In this case, the number of double-sided printed sheets RN is used as the double-sided printing history information.

[0069] The recovery process is a process of replacing the toner remaining in the developing device, forcibly consuming the toner by printing a predetermined number of sheets of printing paper, and then replenishing new toner from the toner cartridge. Printing performed in recovery processing is called recovery printing. In the recovery process, for example, a solid discharge operation is performed in which each color information is printed over the entire surface of a predetermined number of sheets of printing paper.

[0070] In particular, when performing continuous double-sided printing, in a low printing state where the average printing rate of information printed on one sheet of printing paper is low, the amount of toner consumed in the developing device is small, so the fluidity of the toner in the developing device is likely to decrease. A decrease in toner fluidity leads to less replacement of toner in the developing device, which promotes an increase in temperature of the developing device, developer, etc., making the printed image more likely to become rough (faint).

[0071] In addition, if the temperature of a developing device or the like rises, the magnetic permeability, which is the output value of the toner concentration sensor, decreases and the output value becomes smaller than a predetermined reference value, the toner concentration may be erroneously determined to be high. Therefore, in order to prevent the image from becoming rough and to suppress erroneous determination of the toner concentration, a recovery process is performed to forcibly consume the toner present in the developing device and replenish it with approximately the same amount of new toner as the consumed toner.

[0072] The determination of whether or not recovery processing should be performed may be made, for example, based on whether or not the number of double-sided printed sheets RN and the average print rate PR satisfy a preset determination condition. Alternatively, as described below, in addition to the determination conditions of the number of double-sided prints RN and the average printing rate PR, the recovery determination conditions may be determined to be met if the amplitude ratio information AMR calculated by the amplitude ratio calculation unit 26 is greater than or equal to a predetermined amplitude ratio comparison information AMR0. Specific examples of the determination conditions will be described later.

[0073] The recovery execution unit 29 is a part that executes the above-mentioned recovery process. When the recovery determination unit 28 determines that the recovery determination conditions are met, a recovery process is executed to replace the toner contained in the two-component developer remaining in the developing device with new toner. For example, recovery printing (solid printing) is performed. By executing the recovery process, the toner present in the developing device is replaced with new toner, which reduces the roughness of the printed image and also reduces erroneous determination of the toner concentration.

[0074] The remaining toner amount information acquiring unit 30 is a part that acquires information (remaining toner amount information) corresponding to the remaining amount of toner contained in the toner cartridge from the toner cartridge. The toner cartridge is equipped with a motor that drives a mechanism for discharging toner to the outside, and by measuring the number of rotations of this motor (number of cartridge rotations), information corresponding to the remaining amount of toner can be obtained.

[0075] The cumulative number of cartridge rotations from when the toner cartridge is new to the present time almost corresponds to the amount of toner remaining in the toner cartridge, so by counting the cumulative number of cartridge rotations, the amount of toner remaining in the toner cartridge can be almost determined. Therefore, the number of cartridge rotations is acquired from the toner cartridge as information equivalent to the remaining amount of toner, and the amount of toner remaining in the toner cartridge is calculated using the accumulated number of acquired cartridge rotations. The calculated remaining amount of toner is stored in the storage unit 50 as remaining toner amount information TR56.

[0076] Alternatively, some toner cartridges are equipped with a memory element that stores information corresponding to the number of cartridge rotations and the amount of remaining toner, so the information corresponding to the number of cartridge rotations and the amount of remaining toner may be read from the memory element of the toner cartridge. The remaining toner amount information TR56 is used in the remaining toner amount confirmation process, which will be described later.

[0077] The remaining toner amount determining section 31 is a section that determines whether or not to perform a remaining toner amount determining process that checks whether the toner in the toner cartridge is almost empty. For example, it is determined whether the double-sided printing history information obtained when double-sided printing is requested, the calculated average printing rate, and the acquired remaining toner information satisfy predetermined remaining toner determination conditions.

[0078] Furthermore, the toner remaining amount determination unit 31 determines that the toner remaining amount determination conditions are met when the double-sided printing history information determines that double-sided printing has been performed continuously on more than a predetermined number of sheets, the average printing rate PR is less than the predetermined printing rate comparison information, and the toner remaining amount information TR56 is less than the predetermined toner remaining amount comparison information. If the toner concentration value does not increase even after toner is replenished from the toner cartridge to the developing device, for example, a toner remaining amount warning unit 32 (described later) issues a warning requesting replacement of the toner cartridge.

[0079] The above-mentioned remaining toner amount determination process mainly determines whether the toner concentration in the developing device will recover when toner is replenished from a toner cartridge, and if the toner concentration does not increase above a predetermined value, the printing process is stopped.

[0080] Generally, a decrease in the amount of toner in a developing device can be determined by checking the output value of a toner concentration sensor. When the amount of toner in the developing device decreases, the toner concentration in the developing device decreases, and the output value (toner concentration value TD) of the toner concentration sensor increases. When the toner density value TD rises above a predetermined value, it is possible to check whether the toner cartridge is empty.

[0081] However, when double-sided printing is performed continuously and the average printing rate of each printing paper is quite low, as mentioned above, the fluidity of the developer decreases, and even though the toner concentration actually decreases, the output value of the toner concentration sensor (toner concentration value TD) does not increase, resulting in an erroneous judgment, and the toner remaining amount determination process to check whether the toner in the toner cartridge is almost empty may not be performed.

[0082] Therefore, in order to avoid erroneous determinations that may occur particularly when double-sided printing is performed continuously, determination is made by the remaining toner amount determination unit 31. As will be described later, the toner remaining amount determination unit 31 may make a determination based on whether the number of double-sided printed sheets RN, the average printing rate PR, and the toner remaining amount information TR satisfy predetermined determination conditions. Alternatively, in addition to the determination conditions for the average printing rate PR, if the amplitude ratio information AMR satisfies a predetermined determination condition, it may be determined that the remaining toner amount determination process is to be performed. Specific examples of the determination conditions will be described later.

[0083] The remaining toner warning unit 32 is a part that notifies a warning that the toner cartridge is low in amount and requests replacement of the toner cartridge when the toner remaining amount determination process determines that the toner cartridge is almost empty. For example, if the toner cartridge is almost empty, a message is displayed on the display unit 13 requesting that the toner cartridge be replaced. Alternatively, the toner cartridge replacement request may be notified by voice, or data indicating a toner cartridge replacement request may be sent to a mobile terminal of the manager of the image forming apparatus.

[0084] The memory unit 50 is a part that stores information and programs necessary to execute each function of the image processing device of the present invention, and generally uses semiconductor memory elements such as ROM, RAM, and flash memory, storage devices such as HDDs and SSDs, and other storage media. For example, non-rewritable memory such as ROM is used to store programs and setting data that never change. In addition, storage devices such as RAM and HDD, which are readable and rewritable memories, can be used to store information that is rewritten when each function of the image processing device is executed, and information that is temporarily stored.

[0085] The memory unit 50 stores, for example, a toner concentration value 51, number of double-sided prints 52, sensor output amplitude value information 53, amplitude ratio information 54, average printing rate 55, remaining toner amount information 56, concentration determination reference value 61, reference value correction information 62, amplitude comparison value 63, amplitude ratio correction information 64, recovery determination information 65, remaining toner amount determination information 66, etc.

[0086] The toner concentration value 51 is information (TD) obtained from the output value of the signal output from the toner concentration sensor 15, and is acquired by the toner concentration value acquisition unit 22 described above.

[0087] The double-sided print number 52 is, in principle, the number of print sheets (RN) on which double-sided printing is performed when double-sided printing is performed continuously, and is counted by the double-sided print number measurement unit 21. However, even if double-sided printing is not performed continuously, if double-sided printing and single-sided printing are mixed, the number of double-sided printed sheets is counted by adding 1 when double-sided printing is performed and subtracting 1 when single-sided printing is performed.

[0088] The sensor output amplitude value information 53 is numerical information (hereinafter also referred to as sensor amplitude value, AM) obtained by measuring the magnitude of the amplitude from the output value of the toner concentration sensor, and is acquired by the sensor output amplitude value acquiring unit 23.

[0089] The amplitude ratio information 54 is information calculated from the currently acquired sensor output amplitude value and the sensor output amplitude value information acquired using the standard developer. As shown in FIG. 4, when the amplitude ratio information 54 is AMR, the sensor output amplitude value information (sensor amplitude value) 53, which is the current sensor output amplitude value, is AM, and the amplitude comparison value 63, which is the sensor output amplitude value information acquired using a standard developer, is AM0, the amplitude ratio information 54 (AMR) is calculated by AM / AM0 (AMR=AM / AM0).

[0090] The average printing rate 55 is the ratio (PR: %) of the portion of the image data read from the print document that contains information such as characters, and is calculated by the average printing rate acquisition unit 27. If the average print rate 55 (PR) is high, there is a lot of information such as text on one document page, and more toner is required to print that document. On the other hand, if the average printing rate 55 (PR) is low, there is relatively little information such as text on a single document, and when printing that document, the amount of toner consumed is small, the amount of toner replenished is small, and the fluidity of the toner is low. For example, when double-sided printing is performed continuously with an average print rate 55 (PR) as low as about 3% or less, it is preferable to perform recovery processing to replace the toner.

[0091] The remaining toner amount information 56 is information (TR) corresponding to the remaining amount of toner in the toner cartridge, and is acquired by the remaining toner amount information acquisition unit 30. If the toner cartridge is provided with a storage medium in which information corresponding to the remaining amount of toner is stored, the remaining toner amount information 56 (TR) is read and acquired from the storage medium of the toner cartridge.

[0092] The density determination reference value 61 is information (TH0) to be compared with the toner density value TD acquired by the toner density value acquisition unit 22. FIG. 2 shows an explanatory diagram of an embodiment of the concentration determination reference value 61. 2, 128 (CNT) is shown as an example of the density determination reference value 61 (TH0). For example, the value obtained with a standard developer is registered as the density determination reference value, and the value obtained by AD converting the output voltage value at the time of acquisition is used. If the toner concentration value TD is relatively high, it indicates that the toner concentration is low. For example, if the toner concentration value TD becomes larger than the concentration determination reference value TH0 (TD>TH0), it means that the concentration of toner in the developing device has decreased, and toner is replenished from the toner cartridge to the developing device.

[0093] The initial value of the concentration determination reference value 61 (TH0) may be stored in advance in the storage unit 50 as a fixed value. However, when a new developer is installed in the developing device, the output value of the toner concentration sensor 15 may be measured, and the toner concentration value TD obtained from this output value may be stored as the initial value of the concentration determination reference value 61 (TH0).

[0094] FIG. 12 shows a flowchart of an embodiment of the initial setting process for the concentration determination reference value. In step S1 of FIG. 12, when a new standard developer is installed, the output value of the toner concentration sensor 15 is measured, and the toner concentration value acquisition unit 22 acquires the toner concentration value TD from this output value. In step S2, the acquired toner concentration value TD is stored as the initial value of the concentration determination reference value 61 (TH0). At this time, the printing operation is disabled unless the operation of acquiring and recording the judgment reference value is performed, thereby checking whether the registration of the judgment reference value has been completed.

[0095] The initial value of the density determination reference value 61 (TH0) is, in principle, a fixed value, and by comparing the density determination reference value TH0 with the toner concentration value TD obtained thereafter, it is determined whether to replenish toner from the toner cartridge to the developing device. In this invention, when double-sided printing is performed continuously, the density determination reference value 61 (TH0) is corrected based on predetermined conditions as will be described later. However, in order to enable the concentration determination reference value TH0 to be returned to its initial value even if the concentration determination reference value TH0 is corrected, the initial value of the concentration determination reference value TH0 is stored in the memory unit 50 so that it will not be changed by any processing other than the initial setting processing.

[0096] FIG. 13 is a flowchart showing an embodiment of the toner supply process. In step S11 of FIG. 13, the output value of toner concentration sensor 15 is measured, and toner concentration value acquisition unit 22 acquires toner concentration value TD from this output value. In step S12, the concentration determination reference value TH0 is read from the storage unit 50. Here, if the concentration determination reference value TH0 is not corrected and remains at its initial value, the initial value of the concentration determination reference value TH0 is read out. On the other hand, if the concentration determination reference value TH0 has been corrected in a correction process for the concentration determination reference value, which will be described later, the corrected concentration determination reference value TH0 is read out.

[0097] In step S13, the acquired toner density value TD is compared with the density determination reference value TH0. In step S14, if the acquired toner concentration is lower than a predetermined reference value, i.e., if the toner concentration value TD is greater than the concentration determination reference value TH0 (TD>TH0), proceed to step S15; otherwise, return to step S11. In step S15, toner is replenished from the toner cartridge to the developing device. Thereafter, the process returns to step S11, and the above-described processing is repeated. The toner supply process shown in FIG. 13 is executed as a task independent of the printing process described later.

[0098] The reference value correction information 62 is information that sets conditions for correcting the concentration determination reference value TH0. FIG. 3 is an explanatory diagram of an example of information (reference value correction information 62) stored in the storage unit of the image forming apparatus. Here, information is shown for correcting the density determination reference value TH0 using the number of double-sided prints RN.

[0099] The reference value correction information 62 in FIG. 3 is made up of a condition relating to the number of double-sided print sheets RN (double-sided sheet number condition) and a reference correction value KH, and the reference correction value KH is set and stored in advance in association with the double-sided sheet number condition. For example, when the number of double-sided prints RN is equal to or greater than 0 and is smaller than a predetermined value N1, H00 is set as the reference correction value KH. Also, when the number of double-sided prints RN is equal to or greater than a predetermined value N1 and smaller than a predetermined value N2, H01 is set as the reference correction value KH.

[0100] The reference value correction information 62 in Fig. 3 also shows specific examples of double-sided sheet count conditions and reference correction values ​​KH. However, the specific values ​​shown in Fig. 3 are merely examples and are not limited to these values. For example, if the number of double-sided prints RN is equal to or greater than 0 and less than 300, the reference correction value KH is set to 0. When the reference correction value KH is 0, it means that the concentration judgment reference value TH0 is not corrected.

[0101] Furthermore, when the number of double-sided prints RN is equal to or greater than 300 sheets and less than 500 sheets, the density determination reference value TH0 is set to be reduced by 10% as the reference correction value KH. When this reference correction value KH is adopted, it means that a value obtained by subtracting 10% from the initial value of the concentration determination reference value TH0 is set as the concentration determination reference value TH0.

[0102] Similarly, when the number of double-sided prints RN is equal to or greater than 500 sheets and less than 750 sheets, the density determination reference value TH0 is set to be reduced by 20% as the reference correction value KH. When this reference correction value KH is adopted, it means that a value obtained by subtracting 20% ​​from the initial value of the concentration determination reference value TH0 is set as the concentration determination reference value TH0. Furthermore, if the number of double-sided prints RN is 750 or more but less than 950, the standard correction value KH is set to reduce the density determination reference value TH0 by 30%, which means that the density determination reference value TH0 is set to a value that is 30% less than the initial value.

[0103] In this way, as the number of double-sided prints RN increases, the density determination reference value TH0 is corrected by setting a value obtained by decreasing the initial value of the density determination reference value TH0 by a predetermined amount. This correction lowers the reference value of the toner concentration for replenishing toner, thereby preventing the toner concentration from being judged as not reaching the replenishment standard even when the toner has actually decreased to the extent that the toner concentration exceeds the replenishment standard, and suppresses erroneous judgment of the toner concentration that may occur when double-sided printing is performed continuously.

[0104] As described above, the amplitude comparison value 63 is the sensor output amplitude value information AM0 obtained using the standard developer. The amplitude comparison value 63 (AM0) is a fixed value that is set and stored in advance in the storage unit 50, and is obtained, for example, by measuring the output waveform period of the toner concentration sensor for the standard developer and calculating the difference between the maximum and minimum values ​​of the waveform. As described above, the amplitude comparison value AM0 is used when calculating the amplitude ratio information 54 (AMR).

[0105] The amplitude ratio correction information 64 is information that sets conditions for correcting the concentration determination reference value TH0, and is information when the concentration determination reference value TH0 is corrected using the amplitude ratio information AMR. FIG. 5 is an explanatory diagram of an example of information (amplitude ratio correction information 64) stored in the storage unit of the image forming apparatus.

[0106] The amplitude ratio correction information 64 in FIG. 5 is made up of conditions (amplitude ratio conditions) related to the amplitude ratio information AMR and a reference correction value KH2, and the reference correction value KH2 is set and stored in advance in association with the amplitude ratio conditions. For example, when the amplitude ratio information AMR is equal to or greater than 0 and equal to or less than a predetermined value N1, H10 is set as the reference correction value KH2. Also, when the amplitude ratio information AMR is greater than the predetermined value N1 and equal to or less than the predetermined value N2, H11 is set as the reference correction value KH2.

[0107] As described above, the density determination reference value TH0 is corrected based on the reference correction value KH corresponding to the number of double-sided prints RN, using the double-sided print count condition of the reference value correction information 62 shown in FIG. 3. Here, however, the density determination reference value TH0 (referred to as the reference correction value) corrected based on the reference correction value KH corresponding to the number of double-sided prints RN is further corrected based on the reference correction value KH2 of the amplitude ratio correction information 64 in FIG. 5. That is, the density determination reference value TH0 (reference correction value) corrected based on the reference correction value KH corresponding to the double-sided printing number RN is further corrected using the amplitude ratio information AMR calculated from the sensor amplitude value.

[0108] Specific examples of amplitude ratio conditions and reference correction values ​​KH are also shown in the amplitude ratio correction information 64 in Fig. 5. However, the specific numerical values ​​shown in Fig. 5 are merely examples, and the present invention is not limited to these numerical values. The specific numerical values ​​of the amplitude ratio condition and the reference correction value KH may be fixed values, but may also be changeable by the manager of the image forming apparatus as needed.

[0109] In the amplitude ratio correction information 64 of FIG. 5, for example, when the amplitude ratio information AMR is equal to or greater than 0 and equal to or less than 100%, 0 is set as the reference correction value KH. When the standard correction value KH is 0, it means that the concentration judgment standard value TH0 is not corrected, and it also means that the reference correction value is not corrected.

[0110] Also, when the amplitude ratio information AMR is greater than 100% and equal to or less than 120%, a correction value of 100% is set to be adopted as the reference correction value KH. A 100% correction value means that 100% of the reference correction value is set as the concentration judgment reference value TH0. In this case, the numerical value of the reference correction value is directly adopted as the concentration determination standard value TH0, and no correction of the reference correction value is performed.

[0111] Also, when the amplitude ratio information AMR is greater than 120% and equal to or less than 150%, a correction value between 85% and 95% is set to be adopted as the reference correction value KH. A correction value between 85% and 95% means that a value between 85% and 95% of the reference correction value is set as the concentration judgment reference value TH0. The range of 85% to 95% is set because the degree of fluidity reduction differs depending on the type of developer. A value between 85% and 95% is selected as the correction value of the reference correction value in correspondence with the actual value of the amplitude ratio information AMR. In this case, the numerical value of the reference correction value is corrected by the amplitude ratio information AMR, and the concentration determination reference value TH0 is further corrected.

[0112] Similarly, when the amplitude ratio information AMR is greater than 150%, a correction value between 75% and 84% is set to be adopted as the reference correction value KH. A correction value between 75% and 84% means that a numerical value between 75% and 84% of the reference correction value is set as the concentration judgment standard value TH0, and a numerical value between 75% and 84% is selected as the correction value of the reference correction value in accordance with the actual numerical value of the amplitude ratio information AMR. In this case as well, the numerical value of the reference correction value is corrected by the amplitude ratio information AMR, and the concentration determination reference value TH0 is further corrected.

[0113] In the amplitude ratio correction information 64 in FIG. 5, the numerical value of N1 of the amplitude ratio condition when the density determination reference value TH0 is not corrected is set to 100%, but this is not limitative. The output value of the toner concentration sensor may vary due to slight fluctuations in fluidity depending on the machine environment in which it is installed, the life of the developer, etc., so taking into account the variation in the output value, a value of N1 may be adopted, for example, as 95%. The reason why 95% is used as the value of N1 is to take into consideration the variation in the sensor output described above, but it is preferable to set a value other than 100%, and a value between 90% and 100% may be set for N1.

[0114] In this way, by utilizing the amplitude ratio information AMR and further correcting the concentration determination standard value TH0 (reference correction value) corrected based on the standard correction value KH corresponding to the number of double-sided prints RN based on the standard correction value KH2 of the amplitude ratio correction information 64 in Figure 5, the degree of fluidity decrease can be detected, thereby improving the accuracy of the correction of the concentration determination standard value TH0 and further suppressing erroneous determination of toner concentration that can occur when double-sided printing is performed continuously.

[0115] The recovery determination information 65 is information indicating the conditions for performing recovery processing. The recovery determination information 65 includes, for example, double-sided sheet number comparison information RN0, printing rate comparison information PR0, and amplitude ratio comparison information AMR0. 6, 7, and 8 are explanatory diagrams showing an example of information (recovery determination information 65) stored in the storage unit of the image forming apparatus. The numerical values ​​of the recovery determination information 65 shown in FIGS. 6 to 8 are merely examples, and the invention is not limited to these numerical values. The numerical value of the recovery determination information 65 may be a fixed value, but may also be changeable by the administrator of the image forming apparatus as needed.

[0116] The amplitude ratio comparison information AMR0 shown in FIG. 6 is information to be compared with the amplitude ratio information AMR. In FIG. 6, 150% is shown as a specific example of the amplitude ratio comparison information AMR0. In this case, if the amplitude ratio information AMR is greater than 150%, which is the amplitude ratio comparison information AMR0, it means that recovery processing should be performed. The flowcharts of the recovery process shown in FIGS. 17 and 18, which will be described later, show cases where the amplitude ratio information AMR is used and cases where it is not used. When amplitude ratio information AMR is used to determine whether or not recovery processing is required, it is possible to actually detect a decrease in developer fluidity and accurately determine whether or not recovery processing is required, thereby suppressing recovery processing and preventing the toner used in recovery printing (solid printing) from being wasted.

[0117] The double-sided sheet number comparison information RN0 shown in FIG. 6 is information to be compared with the double-sided printing sheet number RN, and recovery determination conditions for the double-sided printing sheet number RN are set and stored in advance. FIG. 7 is an explanatory diagram of an example of the double-sided sheet number comparison information RN0 in the recovery determination information 65. The double-sided sheet count comparison information RN0 in FIG. 7 indicates the double-sided sheet count comparison value RNH corresponding to the model performance of the image forming apparatus (MFP model performance) and the recovery determination conditions. If the measured number of double-sided printed sheets RN satisfies the recovery determination condition, it is determined that recovery processing is necessary. However, the decision as to whether or not to actually execute the recovery process is made taking into consideration not only the recovery decision conditions but also the print rate comparison conditions of the print rate comparison information PR0 and the amplitude ratio comparison information AMR0, which will be described later.

[0118] The model performance of the image forming apparatus (MFP model performance) in FIG. 7 shows the number of prints per unit time of the image forming apparatus. For example, "a model that can print 30 or less pages" means that the number of pages printed per minute is 30 or less. Also, "30≦model number of sheets≦44" means that the model can print 30 or more and 44 or less sheets per minute.

[0119] In the double-sided sheet count comparison information RN0 in FIG. 7, for the "models that print 30 or less sheets", the double-sided sheet count comparison value RNH is set to 250 sheets, and RN>250 is set as the recovery determination condition. This means that if the model performance of the image forming apparatus is "a model of 30 sheets or less," and double-sided printing is performed with the number of double-sided print sheets RN exceeding 250, recovery processing should be performed.

[0120] Also, in the double-sided sheet count comparison information RN0 in Figure 7, when the model performance of the image forming device is "30≦model sheet count≦44", the recovery judgment condition is set as RN>500, which means that recovery processing should be performed when double-sided printing is performed with a double-sided printing sheet count RN exceeding 500. Similarly, when the model performance of the image forming device is "45≦model number of sheets≦59", the recovery judgment condition is set to RN>1000, which means that recovery processing should be performed when double-sided printing is performed where the number of double-sided print sheets RN exceeds 1000.

[0121] The printing rate comparison information PR0 shown in FIG. 6 is information to be compared with the average printing rate PR, and printing rate comparison conditions for the average printing rate PR are set and stored in advance. FIG. 8 is an explanatory diagram of an example of the printing rate comparison information PR0 in the recovery determination information 65. The print rate comparison information PR0 in FIG. 8 indicates the print rate comparison conditions and the number of recovery prints. The variable T is the number of print sheets (reference number) when performing recovery processing, and is stored in the storage unit 50 in advance. FIG. 8 also shows specific examples of the number of recovery print sheets when the reference number T is set to 3.

[0122] If the calculated average printing rate PR satisfies the printing rate comparison condition, printing equivalent to so-called solid printing is performed on the number of printing sheets set as the corresponding number of recovery printing sheets. For example, if the average print coverage PR of the scanned document is less than 1%, the number of recovery prints is T+2. This means that when recovery processing is performed if the average print rate PR of the scanned document is less than 1%, recovery printing (solid printing) is performed on T+2 sheets of printing paper. If the reference number of sheets T is 3, recovery printing (solid printing) will be performed on 5 sheets of printing paper.

[0123] Furthermore, if the average print rate PR of the scanned document is 1% or more but less than 2%, the number of recovery prints is T+1, which means that when recovery processing is performed, recovery printing (solid printing) is performed on T+1 sheets of printing paper. If the reference number of sheets T is 3, recovery printing (solid printing) is performed on 4 sheets of printing paper.

[0124] Similarly, if the average print rate PR of the scanned document is 2% or more but less than 3%, the number of recovery prints is T, which means that when recovery processing is performed, recovery printing (solid printing) is performed on T sheets of printing paper. If the reference number of sheets T is 3, recovery printing (solid printing) is performed on 3 sheets of printing paper. Furthermore, if the average print ratio PR of the scanned document is 3% or more, the number of recovery prints is zero, which means that no recovery processing is performed.

[0125] In the printing rate comparison conditions of the printing rate comparison information PR0 in Figure 8, the lower the average printing rate PR, the more pages are printed to perform recovery processing, and if the average printing rate PR is relatively high, at 3% or above, recovery processing is not performed. The reason why the number of prints subjected to recovery processing is increased as the average printing rate PR decreases is that when double-sided printing is performed continuously with a lower average printing rate PR, there is a higher possibility of an incorrect determination of toner concentration due to a decrease in the fluidity of the developer in the developing device. By increasing the number of prints subjected to the recovery process, the toner in the developing device is replaced and the fluidity of the developer in the developing device is improved, thereby preventing erroneous determination of the toner concentration when subsequent double-sided printing is performed.

[0126] The remaining toner amount determination information 66 is information that the remaining toner amount determination unit 31 uses to determine whether or not to perform the remaining toner amount determination process for checking whether the toner in the toner cartridge is almost empty. The remaining toner amount determination information 66 includes, for example, double-sided sheet number comparison information RN1, printing rate comparison information PR1, amplitude ratio comparison information AMR1, and remaining toner amount comparison information TR1.

[0127] 9 and 10 are explanatory diagrams showing an example of information (toner remaining amount determination information 66) stored in the storage unit of the image forming apparatus. FIG. 9 also shows specific numerical values ​​of the printing rate comparison information PR1, the amplitude ratio comparison information AMR1, and the remaining toner amount comparison information TR1. The values ​​of the remaining toner amount determination information 66 shown in FIGS. 9 and 10 are merely examples, and the present invention is not limited to these values. The numerical value of the remaining toner amount determination information 66 may be a fixed value, but may also be changed by the manager of the image forming apparatus as needed.

[0128] The double-sided sheet number comparison information RN1 shown in FIG. 9 is information to be compared with the double-sided printing sheet number RN, and the remaining toner amount determination conditions for the double-sided printing sheet number RN are set and stored in advance. FIG. 10 is an explanatory diagram of an example of the double-sided sheet number comparison information RN1 included in the remaining toner amount determination information 66. The double-sided sheet count comparison information RN1 in FIG. 10 indicates the double-sided sheet count comparison value RNH corresponding to the model performance of the image forming apparatus (MFP model performance) and the remaining toner amount determination conditions. If the measured number of double-sided printed sheets RN satisfies the remaining toner amount determination condition, it is determined that the remaining toner amount determination process is necessary. However, the decision as to whether to actually execute the remaining toner amount determination process is made taking into consideration not only the remaining toner amount determination conditions, but also the printing rate comparison information PR1, the amplitude ratio comparison information AMR1, and the remaining toner amount comparison information TR1.

[0129] The model performance of the image forming apparatus (MFP model performance) in FIG. 10 indicates the number of prints per unit time of the image forming apparatus, similar to the information shown in FIG. 7. The double-sided sheet number comparison value RNH in FIG. 10 is also the same as the numerical value shown in FIG. 7, and the remaining toner amount determination conditions in FIG. 10 indicate the same numerical conditions as the recovery determination conditions in FIG. However, the double-sided sheet number comparison value RNH and the remaining toner amount determination conditions in FIG. 10 may be set to information different from that in FIG.

[0130] The printing rate comparison information PR1 shown in FIG. 9 is information to be compared with the average printing rate PR. In FIG. 9, 2.5% is shown as a specific example of the printing rate comparison information PR1. In this case, if the average printing rate PR is smaller than 2.5%, which is the printing rate comparison information PR1, it is determined that the remaining toner amount determination process should be performed.

[0131] The remaining toner amount comparison information TR1 shown in FIG. 9 is information to be compared with the remaining toner amount information TR. In FIG. 9, 1.0% is shown as a specific example of the remaining toner amount comparison information TR1. In this case, if the remaining toner amount information TR is smaller than 1.0%, which is the remaining toner amount comparison information TR1, it is determined that the remaining toner amount determination process should be performed.

[0132] The amplitude ratio comparison information AMR1 shown in FIG. 9 is information to be compared with the amplitude ratio information AMR. In FIG. 9, 120% is shown as a specific example of the amplitude ratio comparison information AMR1. In this case, if the amplitude ratio information AMR is equal to or greater than 120%, which is the amplitude ratio comparison information AMR1, it is determined that the remaining toner amount determination process should be performed.

[0133] The flowcharts of the remaining toner amount confirmation process shown in FIGS. 19 and 20, which will be described later, show the process in which the amplitude ratio information AMR is used and the process in which it is not used. When the amplitude ratio information AMR is used to determine whether or not to perform the toner remaining amount determination process, it is possible to actually detect a decrease in developer fluidity and check for erroneous detection of the toner concentration sensor output, thereby making it possible to accurately determine whether or not the toner remaining amount determination process needs to be performed. For example, if the amplitude ratio information AMR is smaller than the amplitude ratio comparison information AMR1, the toner remaining amount determination process is not performed, thereby saving toner that would otherwise be consumed in the toner replenishment process in the toner remaining amount determination process shown in Figure 21, which will be described later.

[0134] <Example of printing process of image forming device> Here, an example of printing processing of an image forming apparatus, which includes correction processing of the density determination reference value TH0, will be described. The printing process is mainly performed when a print job is input and a print instruction is entered, according to the settings of the currently set print setting items. In the following example, however, we will explain the printing process when the print setting items are set to print double-sided.

[0135] When the image forming apparatus is powered off, the time elapsed since the power was turned off (power-off elapsed time) is measured, and the time measurement continues even while the power is off. The power-off elapsed time is stored in the non-volatile memory of the storage unit 50. When the power supply to the image forming apparatus is cut off, the printing process is not performed, so the temperature of the developing device and the developer does not rise. If a predetermined time (for example, six hours or more) has passed since the power was turned off, and the image forming device is then turned on and printing processing is started, the thermal history of the developer will have been eliminated and its fluidity will have been restored, so it is thought that erroneous determination of toner concentration, which may occur when performing continuous double-sided printing, will not occur.

[0136] Therefore, when the image forming apparatus is powered on, the time elapsed since the power was turned off is checked. When the image forming apparatus is turned on after a predetermined time has elapsed since the power was turned off, the density determination reference value TH0 is returned to a predetermined uncorrected initial value. That is, immediately after power is turned on when the power has been turned off for a predetermined time or more, the toner concentration is determined using the uncorrected concentration determination reference value TH0.

[0137] FIG. 14 shows a flowchart of an embodiment of the printing process of the image forming apparatus. In FIG. 14, the predetermined time to be compared with the power-off elapsed time is set to six hours, but it is not limited to this time and may be set by the administrator of the image forming apparatus.

[0138] In step S21 of FIG. 14, the image forming apparatus is started up. A user operates the power switch to turn on the image forming apparatus. This activates the hardware and software required to execute the functions of the image forming apparatus.

[0139] In step S22, the power-off elapsed time stored in the storage unit 50 is acquired. In step S23, it is checked whether the time since the power was turned off is six hours or more. If the time since the power was turned off is six hours or more, the process proceeds to step S24; if not, the process proceeds to step S25.

[0140] In step S24, the concentration determination reference value TH0 is initialized and returned to the initial value of the concentration determination reference value TH0 stored in the storage unit 50. Here, information relating to the concentration determination and the correction of the concentration determination reference value may be initialized. For example, the number of double-sided prints RN is initialized to zero. Furthermore, since the image forming apparatus has started up, the power-off elapsed time may be initialized to zero.

[0141] In step S25, it is checked whether print job information is input. For example, a user places a document to be printed on the document table, and inputs settings for print settings such as document size, number of copies to print, double-sided or single-sided printing, printing paper, and reduction ratio, and then performs an input operation to start printing. In step S26, if the above print job information is input, the process proceeds to step S27. If the print job information is not input, the process may return to step S22 or may return to step S25.

[0142] In step S27, the setting contents of double-sided printing among the print setting items are checked. In step S28, if double-sided printing is set, the process proceeds to step S29, and if not, the process proceeds to step S31. In step S29, the number of double-sided prints RN is incremented by 1 (RN=RN+1).

[0143] In step S30, the concentration determination reference value TH0 is corrected. In this correction process, for example, as shown in FIG. 15, which will be described later, the density determination reference value TH0 is corrected using the number of double-sided printed sheets RN. An example of the correction process for the concentration determination reference value TH0 will be described later with reference to FIGS.

[0144] In step S31, the printing process is executed for the input print job. Here, it is assumed that printing is performed for one page of a document. When double-sided printing is set, printing is performed on both sides of the printing paper, and when single-sided printing is set, printing is performed on only one side of the printing paper. In step S32, if there is a next document (page) to be printed, the process returns to step S27, and the processes from step S27 to step S31 are performed to print the next document. In step S32, if there is no next document (page) to be printed, the process returns to step S22.

[0145] If the concentration determination reference value TH0 is corrected to a value different from the initial value in the correction process of the concentration determination reference value TH0 in step S30, the corrected concentration determination reference value TH0 is used as the determination standard for toner concentration in the toner supply process that is executed as a separate task. In this way, by correcting the density determination reference value TH0, it is possible to correctly determine changes in toner density and accurately control the density of toner replenished to the developing device, even without providing a temperature sensor.

[0146] <Example 1 of Correction Process for Concentration Judgment Reference Value> This correction process of the concentration determination reference value is the process executed in step S30 of FIG. Here, the number of double-sided print sheets RN is acquired, and the density determination reference value TH0 is corrected using the reference value correction information HS1 as shown in FIG.

[0147] FIG. 15 shows a flowchart of the first embodiment of the correction process for the concentration determination reference value. In step S41 of FIG. 15, the number of double-sided prints RN stored in the storage unit 50 is acquired. In step S42, the reference value correction information HS1 stored in the storage unit 50 is read out.

[0148] In step S43, the reference value correction information HS1 is used to obtain the reference correction value KH corresponding to the obtained number of double-sided prints RN. That is, the reference correction value KH associated with the double-sided printing number condition to which the acquired double-sided printing number RN belongs is obtained in the reference value correction information HS1. For example, when the reference value correction information HS1 in FIG. 3 is used, if the acquired number of double-sided prints RN is 580, a "20% reduction" is acquired as the reference correction value KH. This means that, as described above, a value obtained by decreasing the initial value of the concentration determination reference value TH0 by 20% is set as the concentration determination reference value TH0.

[0149] In step S44, the concentration determination reference value TH0 is corrected using the acquired reference correction value KH. For example, if a "20% decrease" is acquired as the reference correction value KH, the concentration determination reference value TH0 is changed to a value that is 20% less than the initial value of the concentration determination reference value TH0. However, if "0" is acquired as the reference correction value KH, the concentration determination reference value TH0 is not changed. After the concentration determination reference value TH0 is corrected, the flow returns to that of FIG. 14 and proceeds to step S31.

[0150] Figure 11 shows an explanatory diagram of one example of a comparison of toner concentration (toner concentration of printed image), which indicates the quality of an image printed on printing paper, when the density determination reference value TH0 is corrected according to the number of double-sided prints (with double-sided printing correction) and when the density determination reference value TH0 is not corrected (without double-sided printing correction).

[0151] FIG. 11 shows the number of double-sided printed sheets RN when double-sided printing is performed continuously, and the toner concentration (wt %) of the printed image when double-sided printing is performed. The toner concentration shown is the numerical value when the density determination reference value TH0 is set to a predetermined fixed value and no correction is made (no double-sided printing correction), and the numerical value when the density determination reference value TH0 is corrected in accordance with the number of double-sided prints RN, as in this invention (double-sided printing correction). For example, the toner density of the printed image when the number of double-sided prints RN is 500 sheets corresponds to the toner density of the image printed on the 500th sheet of printing paper when double-sided printing is performed continuously.

[0152] In Figure 11, for example, when the number of double-sided prints RN is zero, i.e., when double-sided printing is not performed, the toner concentration without double-sided printing correction and the toner concentration with double-sided printing correction are both 5.21 (wt%), and there is no difference. The toner concentration of the developer shows good values ​​in both cases.

[0153] However, when the number of double-sided prints RN was 300, i.e., when double-sided printing was performed continuously on 300 sheets of printing paper, the toner concentration of the developer without double-sided printing correction was 5.10 (wt%), which was lower than when double-sided printing was not performed (5.21). In other words, in the case of "no double-sided printing correction," it is possible that the toner was not properly replenished due to the double-sided printing of 300 sheets in a row, which means that the image quality of the printed image is lower than if double-sided printing had not been performed.

[0154] On the other hand, when the number of double-sided printing sheets RN was 300, the toner concentration of the developer with "double-sided printing correction" was 5.44 (wt%), which was not reduced compared to when double-sided printing was not performed (5.21). In other words, when "double-sided printing correction is enabled," even if 300 sheets are printed double-sided in succession, the image quality of the printed image does not become faint because the appropriate amount of toner is replenished, and good image quality is maintained even on the 300th sheet of printed paper, just as if double-sided printing had not been performed.

[0155] As a result, when the density determination reference value TH0 is not corrected (no double-sided printing correction), a large amount of double-sided printing causes the output value of the toner concentration sensor to decrease, resulting in a higher measured toner concentration value, which in turn leads to an incorrect determination of the toner concentration and a failure to replenish proper toner, resulting in a low image quality of the printed image.On the other hand, when the density determination reference value TH0 is corrected (double-sided printing correction), even if the output value of the toner concentration sensor decreases, there is almost no incorrect determination of the toner concentration, and proper toner is replenished, thereby maintaining good image quality of the printed image.

[0156] Similarly, when the number of double-sided prints RN is 500, 750, and 950, the toner density of the printed image without double-sided printing correction (4.74, 4.89, 4.82) is significantly reduced compared to when double-sided printing is not performed (5.21). This means that when a large amount of double-sided printing is done continuously, the quality of the printed images is significantly lower in any case than when double-sided printing is not done. If the toner density of the printed image has decreased to this extent and the image quality of the printed image has become pale, it is conceivable that users who have performed double-sided printing may point out the poor image quality (paleness).

[0157] On the other hand, the toner density of the printed image with "double-sided printing correction" tends to not decrease compared to when double-sided printing is not performed, or if it does decrease, the decrease tends to be quite small. With this level of decrease in toner density, the image quality of the printed image is thought to be at a level where users will not point out poor image quality (lightness). Therefore, in this invention, by correcting the density determination reference value TH0 in accordance with the number of double-sided prints, it is possible to almost completely eliminate erroneous determination of toner density, and to control the toner density with high precision.

[0158] Furthermore, although not shown, when a fluorescent spectrodensitometer is used to irradiate a specified light onto double-sided printed paper and measure a numerical value (ID) corresponding to the amount of toner adhered to the printed paper, in the case of "no double-sided printing correction," a numerical value is measured indicating that the amount of toner adhered is less than when double-sided printing is not performed, which shows that the image quality of the printed image becomes lighter when a large amount of double-sided printing is performed continuously. On the other hand, when "double-sided printing correction is enabled," even when large volumes of double-sided printing are performed continuously, the value (ID) corresponding to the amount of toner adhered to the printing paper is measured to be almost the same as when double-sided printing is not performed, which shows that good print image quality is maintained and toner concentration can be controlled with precision.

[0159] <Example 2 of Correction Processing of Concentration Judgment Reference Value> This correction process of the concentration determination reference value is the process executed in step S30 of FIG. Here, the number of double-sided prints RN and the sensor amplitude acquisition value information AM are acquired, and the density determination reference value TH0 is corrected using the reference value correction information HS1 as shown in FIG. 3 and the amplitude ratio correction information HS2 as shown in FIG. 5.

[0160] FIG. 16 shows a flowchart of the second embodiment of the process for correcting the concentration determination reference value. In step S51 of FIG. 16, the number of double-sided prints RN stored in the storage unit 50 is acquired. In step S52, the reference value correction information HS1 stored in the storage unit 50 is read out.

[0161] In step S53, the reference value correction information HS1 is used to obtain the reference correction value KH corresponding to the obtained number of double-sided prints RN. That is, similarly to step S43 in FIG. 15, the reference correction value KH associated with the double-sided number condition to which the acquired double-sided printing number RN belongs is obtained in the reference value correction information HS1.

[0162] In step S54, the acquired standard correction value KH is used to calculate a reference correction value based on the number of double-sided sheets. The reference correction value based on the number of double-sided sheets corresponds to the corrected density determination reference value TH0 obtained in step S44 of FIG. That is, similarly to step S44 in FIG. 15, the density determination reference value TH0 is corrected using the acquired reference correction value KH, and this corrected density determination reference value TH0 is used as the reference correction value based on the number of double-sided sheets.

[0163] For example, if a "30% reduction" is acquired as the reference correction value KH, a value obtained by reducing the initial value of the density determination reference value TH0 by 30% is calculated as the reference correction value based on the number of double-sided sheets. However, if "0" is acquired as the reference correction value KH, the initial value of the density determination reference value TH0 is set as the reference correction value based on the number of double-sided sheets.

[0164] In step S55, the sensor output amplitude value acquiring unit 23 acquires the sensor output amplitude value information AM. In step S56, the sensor output amplitude value information AM and the amplitude comparison value AM0 are used to calculate the amplitude ratio information AMR (AMR=AM / AM0).

[0165] In step S57, the amplitude ratio correction information HS2 stored in the storage unit 50 is read out in order to correct the reference correction value. For example, the amplitude ratio correction information HS2 shown in FIG. 5 may be read out. In this flowchart, 100% is used as the value of N1 in the amplitude ratio correction information HS2. In steps S58, S59, and S60, the amplitude ratio information AMR is compared based on the amplitude ratio conditions of the amplitude ratio correction information HS2.

[0166] In step S58, when the amplitude ratio information AMR is 100% or less (AMR ≦ 100), proceed to step S61. In step S59, when the amplitude ratio information AMR is greater than 100% and 120% or less (100 < AMR ≦ 120), proceed to step S62. In step S60, when the amplitude ratio information AMR is greater than 120% and 150% or less (120 < AMR ≦ 150), proceed to step S63. When the amplitude ratio information AMR is greater than 150% (150 < AMR), proceed to step S64.

[0167] In step S61, assuming that the reference correction value KH2 corresponding to the case where the amplitude ratio information AMR is 100% or less is zero, no correction based on the amplitude ratio information is performed on the density determination reference value TH0. However, if the density determination reference value TH0 has been corrected in the reference correction value based on the number of double-sided sheets, the corrected density determination reference value TH0 (reference correction value) is adopted. After that, the process ends, returns to the flow of FIG. 14, and proceeds to step S31.

[0168] In step S62, correct the density determination reference value TH0 based on the reference correction value KH2 corresponding to 100 < AMR ≦ 120. When the reference correction value KH2 corresponding to 100 < AMR ≦ 120 is 100%, use the numerical value of 100% of the reference correction value based on the number of double-sided sheets to correct the density determination reference value TH0. That is, directly adopt the reference correction value based on the number of double-sided sheets as the density determination reference value TH0. After the density determination reference value TH0 is corrected, return to the flow of FIG. 14 and proceed to step S31.

[0169] In step S63, correct the density determination reference value TH0 based on the reference correction value KH2 corresponding to 120 < AMR ≦ 150. When the reference correction value KH2 corresponding to 120 < AMR ≦ 150 is 85 - 95%, use the numerical value of 85 - 95 of the reference correction value based on the number of double-sided sheets to correct the density determination reference value TH0. That is, a value between 85% and 95% of the reference correction value based on the number of double-sided sheets is adopted as the density determination reference value TH0. After the density determination reference value TH0 is corrected, return to the flow of FIG. 14 and proceed to step S31.

[0170] In step S64, the density determination reference value TH0 is corrected based on the reference correction value KH2 corresponding to 150 < AMR. When the reference correction value KH2 corresponding to 150 < AMR is 75% - 84%, the density determination reference value TH0 is corrected using a value between 75% and 84% of the reference correction value based on the number of double-sided sheets. That is, a value between 75% and 84% of the reference correction value based on the number of double-sided sheets is adopted as the density determination reference value TH0. After the density determination reference value TH0 is corrected, return to the flow of FIG. 14 and proceed to step S31.

[0171] <Example 1 of Recovery Processing> Two examples of the recovery process are shown below. As the recovery process, either process may be used. However, since it is possible to correctly detect a decrease in fluidity by judging based on the amplitude value of the developer, it is preferable to execute the process of Example 2 shown in FIG. 18.

[0172] In Example 1, the number of double-sided printed sheets RN is obtained, the average printing rate PR is calculated, and it is determined whether to perform a recovery process (toner replacement process) using the recovery determination information 65 as shown in FIGS. 6, 7, and 8 described above. When a recovery process is required, a process of executing a predetermined recovery printing process (solid printing) will be described. The recovery process is executed as a task different from the printing process in FIG. 14. When executing a recovery printing process (solid printing), the printing process is interrupted.

[0173] FIG. 17 shows a flowchart of Example 1 of the recovery process. In step S71 of FIG. 17, the number of double-sided prints RN stored in the storage unit 50 is acquired. In step S72, the double-sided sheet number comparison information RN0 of the recovery determination information 65 stored in the storage unit 50 is read out. For example, double-sided sheet number comparison information RN0 as shown in FIG. 7 is read out.

[0174] In step S73, the double-sided sheet count comparison information RN0 is used to check whether the double-sided print sheet count RN satisfies the recovery determination condition of the double-sided sheet count comparison information RN0. In step S74, if the recovery determination condition is met, the process proceeds to step S75, and if not, the process ends.

[0175] For example, if the model performance of the image forming device indicated by the double-sided print count comparison information RN0 in FIG. 7 is a model of 30 sheets or less, it is determined whether the double-sided print count RN is greater than 250 sheets, and if RN>250, proceed to step S75. On the other hand, if RN≦250, the recovery determination condition is not met, so recovery processing is not performed and processing is terminated. Similarly, the model performance of other image forming apparatuses is checked to see if they satisfy the recovery determination conditions.

[0176] In step S75, the average printing rate PR is calculated. In step S76, the printing rate comparison information PR0 of the recovery determination information 65 stored in the storage unit 50 is read out. For example, the printing rate comparison information PR0 shown in FIG. 8 is read out.

[0177] In the following steps S77, S78, and S79, the printing rate comparison conditions are used to determine whether or not recovery processing should be performed. When recovery processing is performed, recovery printing processing (solid printing) is executed for the number of sheets corresponding to the number of recovery prints. In steps S77, S78, and S79, the average printing rate PR is compared based on the printing rate comparison conditions of the printing rate comparison information PR0.

[0178] In step S77, if the average printing rate PR is less than 1.0% (PR<1.0), proceed to step S80; in step S78, if the average printing rate PR is 1.0% or greater but less than 2.0% (1.0≦PR<2.0), proceed to step S81; in step S79, if the average printing rate PR is 2.0% or greater but less than 3.0% (2.0≦PR<3.0), proceed to step S82; and if the average printing rate PR is 3.0% or greater (3.0≦PR), the process ends without performing recovery processing.

[0179] In step S80, recovery printing processing (solid printing) is executed with the number of recovery prints being the reference value T+2 (for example, 5 in FIG. 8), and the process proceeds to step S83. In step S81, recovery printing processing (solid printing) is executed with the number of recovery prints set to the reference value T+1 (for example, 4 in FIG. 8), and the process proceeds to step S83. In step S82, recovery printing processing (solid printing) is executed with the number of recovery prints being the reference value T (for example, 3 in FIG. 8), and the process proceeds to step S83.

[0180] In step S83, after the recovery printing process (solid printing) is completed, the density determination reference value TH0 and the number of double-sided prints RN are initialized to return the toner density determination to the initial state without correction, as in step S24, and the process ends.

[0181] <Recovery Processing Example 2> Here, we will explain the process of obtaining the number of double-sided prints RN, calculating the average printing rate PR, calculating the amplitude ratio information AMR, and using the recovery determination information 65 as shown in Figures 6, 7, and 8 above to determine whether or not to perform recovery processing (toner replacement processing), and if recovery processing is required, executing a specified recovery printing processing (solid printing). The recovery process in FIG. 18 differs from that in FIG. 17 in that amplitude ratio information AMR is used.

[0182] FIG. 18 shows a flowchart of the recovery process according to the second embodiment. Steps that perform the same processing as in FIG. 17 are assigned the same step numbers as in FIG. First, steps S71 to S74 in FIG. 18 are the same as those in FIG. That is, the double-sided printing number RN is acquired, the double-sided printing number comparison information RN0 is read, and the double-sided printing number RN0 is used to check whether the double-sided printing number RN satisfies the recovery determination condition of the double-sided printing number comparison information RN0. In step S74, if the recovery determination conditions are met, the process proceeds to step S88, and if not, the process ends without performing recovery processing.

[0183] In step S88, it is checked whether the amplitude ratio information AMR is equal to or greater than the amplitude ratio comparison information AMR0 of the recovery determination information 65. If AMR≧AMR0, the process proceeds to step S75; otherwise, the process ends. For example, as shown in FIG. 6, when the amplitude ratio comparison information AMR0 of the recovery determination information 65 is 150%, if AMR≧150, the process proceeds to step S75, and if not, the process ends. Although not shown, before the check in step S88, similar to step S55 described above, sensor output amplitude value information AM is acquired, and similar to step S56, a process is performed to calculate amplitude ratio information AMR using the sensor output amplitude value information AM and amplitude comparison value AM0 (AMR=AM / AM0).

[0184] In step S75, after the average printing rate PR is calculated, the processes from step S76 to step S83 are carried out in the same manner as in FIG. That is, the printing rate comparison conditions are used to determine whether or not recovery processing is to be performed, and if recovery processing is to be performed, recovery printing processing (solid printing) is executed for the number of sheets corresponding to the number of recovery prints.

[0185] <Example 1 of remaining toner amount confirmation process> Two examples of the remaining toner amount confirmation process will be described below. Either process may be used as the remaining toner amount checking process. However, it is preferable to execute the process of the second embodiment shown in FIG. 20, since the decrease in fluidity can be detected more accurately by determining the amplitude value of the developer, and the erroneous detection of the toner concentration sensor can be accurately determined.

[0186] In the first embodiment, the number of double-sided prints RN is acquired, toner remaining amount information TR is acquired, the average printing rate PR is calculated, and the toner remaining amount confirmation process is described, in which the toner remaining amount determination information 66 as shown in Figures 9 and 10 described above is used to determine whether or not to perform the toner remaining amount determination process. When a toner remaining amount determination process is required, the toner remaining amount determination process attempts to replenish toner, and if the toner concentration does not tend to increase, the printing is interrupted and a warning is issued to indicate that the toner in the toner cartridge is almost empty.

[0187] The remaining toner amount confirmation process is executed as a task separate from the printing process of FIG. 14, and when the remaining toner amount determination process is executed, the printing process is temporarily interrupted. The toner remaining amount confirmation process may be performed periodically, such as when the image forming device is started, or may be performed automatically every time a predetermined time has elapsed, or may be performed in response to a predetermined input operation by the user.

[0188] FIG. 19 shows a flowchart of the remaining toner amount confirmation process according to the first embodiment. FIG. 21 shows a flowchart of an embodiment of the remaining toner amount determination process. The remaining toner amount determination process is a process that is performed in step S109 of the remaining toner amount confirmation process.

[0189] In step S101 of FIG. 19, the number of double-sided prints RN stored in the storage unit 50 is acquired. In step S102, the double-sided sheet number comparison information RN1 of the toner remaining amount determination information 66 stored in the storage unit 50 is read out. For example, the double-sided sheet number comparison information RN1 as shown in FIG. 10 is read out. The setting content of the double-sided sheet number comparison information RN1 in FIG. 10 shows the same content as the setting content of the double-sided sheet number comparison information RN0 in FIG. 7, but different setting contents may also be used.

[0190] In step S103, using the double-sided sheet number comparison information RN1, it is checked whether the double-sided print number RN satisfies the toner remaining amount determination condition of the double-sided sheet number comparison information RN1. In step S104, if the toner remaining amount determination condition is satisfied, the process proceeds to step S105; if not, the process proceeds to step S110.

[0191] For example, if the model performance of the image forming apparatus shown in the double-sided sheet number comparison information RN1 in FIG. 10 is a model with 30 sheets or less, it is determined whether the double-sided print number RN is greater than 250 sheets. If RN > 250, the process proceeds to step S105. On the other hand, when RN ≦ 250, the toner remaining amount determination condition is not satisfied, so the process proceeds to step S110 without performing the toner remaining amount determination process. Similarly, for the model performance of other image forming apparatuses, it is also checked whether the toner remaining amount determination condition is satisfied.

[0192] In step S105, the toner remaining amount information acquisition unit 30 acquires the toner remaining amount information TR, and compares the acquired toner remaining amount information TR with the toner remaining amount comparison information TR1 stored in the storage unit 5​​​​​​​For example, when the toner remaining amount comparison information TR1 is 1.0% as shown in FIG. 9, It is determined whether the acquired toner remaining amount information TR is less than 1.0%. If TR < 1.0, the process proceeds to step S107. On the other hand, when TR ≧ 1.0, it is considered that the toner in the toner cartridge has not decreased so much, and the process proceeds to step S110 without performing the toner remaining amount determination process.

[0194] In step S107, the average printing rate PR is calculated. In step S108, the printing rate comparison information PR1 of the toner remaining amount determination information 66 stored in the storage unit 50 is read out, and the average printing rate PR is compared with the printing rate comparison information PR1. For example, the printing rate comparison information PR1 (= 2.5%) as shown in FIG. 9 is read out. When the average printing rate PR is less than the printing rate comparison information PR1 (PR < PR1), the process proceeds to step S109; otherwise, the process proceeds to step S110.

[0195] In step S109, the toner remaining amount determination process shown in FIG. 21 described later is executed, and the process ends. In step S110, since the toner remaining amount determination process is not executed, if there is a print job for which printing has been interrupted, the printing process of that print job is resumed, and the process ends.

[0196] In the toner remaining amount determination process of FIG. 21, in step S121, the toner supply unit 16 supplies toner from the toner cartridge to the developing device. In this case, since only an increase in toner concentration is checked, the amount of toner to be supplied may be small. For example, it may be supplied at about 0.3 wt% as the toner concentration. In step S122, the output value of the toner concentration sensor 15 is measured, and the toner concentration value acquisition unit 22 acquires the toner concentration value TD from this output value. In order to check an increase in toner concentration, the toner concentration value TD is stored as a history. The processes of steps S121 and S122 are repeated for a fixed period of time (for example, 60 seconds), and then the process proceeds to step S123.

[0197] In step S123, it is checked whether the toner density increases. Here, it is checked whether the toner density value TD drops to or exceeds a predetermined value. The predetermined value is set and stored in advance, and is a reference value for determining whether the toner density has increased, and may be set to a value different from the density determination reference value TH0 described above. Alternatively, it is also possible to check the change in the toner concentration value TD stored as history and confirm whether the toner concentration is on the rise. If the toner concentration value TD decreases, it is determined that the toner concentration is increasing.

[0198] In step S124, if the toner concentration does not increase (toner concentration value TD does not decrease), the process proceeds to step S125, and if the toner concentration increases (toner concentration value TD decreases), the process proceeds to step S128. If the toner density increases as a result of replenishing toner from the toner cartridge to the developing device, it is determined that the toner cartridge is not yet empty, and printing can continue. However, if the toner concentration does not increase when the toner is replenished from the toner cartridge to the developing device, the toner cartridge is likely empty, and the printing process is stopped.

[0199] In step S125, it is determined that the toner in the toner cartridge is almost empty, and a warning message requesting replacement of the toner cartridge is displayed. Alternatively, the request to replace the toner cartridge may be notified by voice or by e-mail to the mobile terminal of the administrator. In step S126, since there is a possibility that the toner in the developing device is low and normal printing may not be possible, subsequent printing processing is stopped and the process is terminated. Printing will be suspended until the toner cartridge is replaced with a new one.

[0200] In step S127, if there is a print job whose printing execution has been suspended, the printing process of that print job is resumed, and the process ends.

[0201] As described above, the system uses not only the remaining toner amount information TR obtained from the toner cartridge, but also the number of double-sided printed pages RN and the average printing rate PR to determine that the toner in the toner cartridge is almost empty and that the toner cartridge needs to be replaced, so that a warning requesting toner cartridge replacement can be issued at a more appropriate time before any problems occur in the printed image.

[0202] <Example 2 of remaining toner amount confirmation process> Here, we will explain the toner remaining amount confirmation process, which acquires the number of double-sided prints RN, acquires toner remaining amount information TR, calculates the average printing rate PR, calculates amplitude ratio information AMR, and uses the toner remaining amount determination information 66 shown in Figures 9 and 10 described above to determine whether or not to perform the toner remaining amount determination process. Furthermore, if a toner remaining amount determination process is required, the toner remaining amount determination process attempts to replenish toner, and if the toner concentration does not show an increasing trend, printing is interrupted and a warning is issued indicating that the toner cartridge is almost empty (or a request to replace the toner cartridge).

[0203] FIG. 20 shows a flowchart of the remaining toner amount confirmation process according to the second embodiment. The remaining toner amount confirmation process in FIG. 20 differs from the remaining toner amount confirmation process in FIG. 19 in that amplitude ratio information AMR is calculated and the amplitude ratio information AMR is compared with amplitude ratio comparison information AMR1. In the remaining toner amount confirmation process of FIG. 20, the steps that perform the same processing as the steps in the remaining toner amount confirmation process of FIG. 19 are assigned the same step numbers.

[0204] In FIG. 20, the processes from step S101 to step S108 are the same as the remaining toner amount confirmation process in FIG. It is determined whether the acquired number of double-sided printed sheets RN satisfies the toner remaining amount determination conditions, it is determined whether the acquired toner remaining amount information TR is smaller than the toner remaining amount comparison information TR1, it is determined whether the calculated average printing rate PR is smaller than the printing rate comparison information PR1, and if these three conditions are met, it proceeds to step S111. If any of the above three conditions is not met, the process proceeds to step S110.

[0205] In step S111, it is checked whether the amplitude ratio information AMR is equal to or greater than the amplitude ratio comparison information AMR1 of the remaining toner amount determination information 66. If AMR≧AMR1, the process proceeds to step S109; otherwise, the process proceeds to step S110. For example, as shown in FIG. 9, when the amplitude ratio comparison information AMR1 of the remaining toner amount determination information 66 is 120%, if AMR≧120, the process proceeds to step S109, and if not, the process proceeds to step S110. Although not shown, before the check in step S111, similar to step S55 described above, sensor output amplitude value information AM is acquired, and similar to step S56, a process is performed to calculate amplitude ratio information AMR using the sensor output amplitude value information AM and amplitude comparison value AM0 (AMR=AM / AM0).

[0206] Thereafter, in the same manner as in FIG. 19, in step S109, the remaining toner amount determination process shown in FIG. 21 is executed, and the process ends. In step S110, if there is a print job whose execution has been suspended, the print processing of that print job is resumed, and the process ends.

[0207] As described above, the system uses not only the remaining toner amount information TR obtained from the toner cartridge, but also the number of double-sided prints RN, the average print rate PR, and the amplitude ratio information AMR to determine when the toner in the toner cartridge is almost empty and the toner cartridge needs to be replaced, so that a warning requesting toner cartridge replacement can be issued at a more appropriate time before any problems occur in the printed image. [Explanation of symbols]

[0208] 1. Image forming device (MFP), 11 control section, 12 Operation section, 13 Display section, 14 Image processing unit, 14a image input unit, 14b image forming unit, 14c image output unit, 15 Toner concentration sensor, 16 Toner supply unit, 21 Double-sided printing count measurement unit, 22 toner density value acquisition unit, 23 sensor output amplitude value acquisition unit, 24 Concentration determination section, 25 concentration determination reference value correction unit, 26 Amplitude ratio calculation section, 27 Average printing rate acquisition section, 28 recovery determination unit, 29 Recovery Execution Department, 30 remaining toner amount information acquisition unit, 31 remaining toner amount determination unit, 32 Toner remaining warning unit, 50 storage section, 51 toner density value, 52 double-sided prints, 53 Sensor output amplitude value information, 54 amplitude ratio information, 55 Average printing rate, 56 Toner remaining information, 61 concentration criteria, 62 Reference value correction information, 63 Amplitude comparison value, 64 Amplitude ratio correction information, 65 Recovery determination information, 66 Toner remaining amount determination information

Claims

1. a toner concentration sensor provided in a developing device containing a two-component developer consisting of toner and carrier, the toner concentration sensor outputting a signal corresponding to the concentration of the toner contained in the developing device; a toner concentration value acquisition unit that acquires a toner concentration value of the toner contained in the developing device by using a signal output from the toner concentration sensor; a storage unit that stores a density determination reference value that is used as a reference for determining whether to replenish the toner stored in the toner cartridge to the developing device by comparing the acquired toner density value with the density determination reference value, and double-sided printing history information obtained when double-sided printing is performed; a density determination reference value correcting unit that corrects the density determination reference value based on the number of double-sided printed sheets stored in the double-sided printing history information; a sensor output amplitude value acquisition unit that acquires a sensor output amplitude value that is an amplitude value of a signal output from the toner concentration sensor; an amplitude ratio calculation unit that calculates amplitude ratio information from a ratio between the sensor output amplitude value acquired by the sensor output amplitude value acquisition unit and an amplitude comparison value that is a sensor output amplitude value acquired using a predetermined standard developer, The image forming apparatus is characterized in that the density determination reference value corrected by the density determination reference value correcting section is corrected so as to correspond to the magnitude of the calculated amplitude ratio information.

2. A toner concentration sensor provided in a developing device containing a two-component developer consisting of toner and carrier, the toner concentration sensor outputting a signal corresponding to the concentration of the toner contained in the developing device; a toner concentration value acquisition unit that acquires a toner concentration value of the toner contained in the developing device by using a signal output from the toner concentration sensor; a storage unit that stores a density determination reference value that is used as a reference for determining whether to replenish the toner stored in the toner cartridge to the developing device by comparing the acquired toner density value with the density determination reference value, and double-sided printing history information obtained when double-sided printing is performed; a density determination reference value correcting unit that corrects the density determination reference value based on the number of double-sided printed sheets stored in the double-sided printing history information; An image forming apparatus characterized in that, when the power is turned on after a predetermined time or more has elapsed since the power was turned off, the density determination reference value is returned to a predetermined initial value that has not been corrected.

3. a concentration determination unit that determines whether to supply the toner contained in the toner cartridge to the developing device by comparing the acquired toner concentration value with the corrected concentration determination reference value; a toner supply unit that supplies the toner contained in the toner cartridge to the developing device, 3. The image forming apparatus according to claim 1, wherein when the concentration determination unit determines that toner needs to be replenished to the developing device, the toner replenishment unit replenishes the toner contained in the toner cartridge to the developing device.

4. A toner supply unit that supplies toner contained in a toner cartridge to a developing device; a storage unit that stores double-sided printing history information obtained when double-sided printing is performed; an average printing rate acquisition unit that calculates an average printing rate when image data read from a document to be printed is printed on printing paper; a recovery determination unit that determines whether the double-sided printing history information obtained when double-sided printing is requested and the calculated average printing rate satisfy a predetermined recovery determination condition; a recovery execution unit that executes a recovery process to replace the toner contained in the two-component developer remaining in the developing device with new toner when the recovery determination unit determines that the recovery determination condition is met, The recovery judgment unit judges that the recovery judgment conditions are met when the double-sided printing history information determines that double-sided printing has been performed continuously on more than a predetermined number of sheets, and when the average printing rate is less than a predetermined printing rate.

5. 5. The image forming apparatus according to claim 4, wherein the recovery process includes a solid discharge operation for printing each color information on a predetermined number of sheets of printing paper.

6. A toner concentration sensor provided in a developing device containing a two-component developer consisting of toner and carrier, the toner concentration sensor outputting a signal corresponding to the concentration of the toner contained in the developing device; a toner concentration value acquisition unit that acquires a toner concentration value of the toner contained in the developing device by using a signal output from the toner concentration sensor; a toner supply unit that supplies the toner contained in the toner cartridge to the developing device; a storage unit that stores double-sided printing history information obtained when double-sided printing is performed; an average printing rate acquisition unit that calculates an average printing rate when image data read from a document to be printed is printed on printing paper; a toner remaining amount information acquiring unit that acquires toner remaining amount information corresponding to the remaining amount of toner contained in the toner cartridge; a toner remaining amount determination unit that determines whether the double-sided printing history information obtained when double-sided printing is requested, the calculated average printing rate, and the acquired toner remaining amount information satisfy predetermined toner remaining amount determination conditions; a toner remaining amount warning unit; the toner remaining amount determining unit determines that the toner remaining amount determination condition is satisfied when it determines from the double-sided printing history information that double-sided printing has been performed continuously on more than a predetermined number of sheets, the average printing rate is less than predetermined printing rate comparison information, and the toner remaining amount information is less than predetermined toner remaining amount comparison information; An image forming apparatus as described in any one of claims 1 to 5, characterized in that if the toner concentration value does not increase even after toner is replenished from the toner cartridge to the developing device, the toner remaining warning unit issues a warning requesting replacement of the toner cartridge.

7. A toner concentration control method for an image forming apparatus, comprising: a density determination reference value that is a criterion for determining whether to supply toner contained in a toner cartridge attached to the image forming apparatus to a developing device, and double-sided printing history information obtained when double-sided printing is performed; a toner concentration value acquisition step of acquiring a toner concentration value of the toner contained in a developing device, the toner concentration value being obtained by utilizing a signal output from a toner concentration sensor provided in the developing device, the toner concentration value being obtained by utilizing a signal output from a toner concentration sensor provided in the developing device, the toner concentration value being obtained by utilizing a signal output from the ... a density determination reference value correcting step of correcting the density determination reference value based on the number of double-sided printed sheets stored in the double-sided printing history information; an amplitude ratio calculation step of calculating amplitude ratio information from a ratio between a sensor output amplitude value, which is an amplitude value of a signal output from the toner concentration sensor, and an amplitude comparison value, which is a sensor output amplitude value obtained by using a predetermined standard developer; a density control step of controlling the density of the toner contained in the developing device by comparing the density determination reference value corrected in the density determination reference value correction step with the magnitude of the calculated amplitude ratio information, with the acquired toner density value; A toner concentration control method for an image forming apparatus, characterized in that a control unit provided in the image forming apparatus sequentially executes the above steps.

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