Image forming apparatus

An image forming apparatus includes a forming unit, a supply unit, a first measurement unit, a control unit, a second measurement unit, an adjustment unit, and a changing unit. The forming unit forms a toner image on an image carrier using developer which is contained in a developer container and includes toner and a magnetic carrier. The supply unit supplies the toner to the developer container. The first measurement unit measures a density of the toner in the developer contained in the developer container. The control unit controls the supply unit such that the density measured by the first measurement unit approaches a target density. The second measurement unit measures an image density formed by the forming unit. The adjustment unit adjusts a development contrast potential so that a formation density measured by the second measurement unit approaches a predetermined appropriate density with regard to the toner image formed by the forming unit under a predetermined condition. The changing unit is configured to change a target density if the adjustment unit is not able to adjust the development contrast potential so that the formation density measured by the second measurement unit approaches the appropriate density.

FIELD

Embodiments described herein relate generally to an image forming apparatus.

BACKGROUND

An image forming apparatus is known as one of apparatuses used in workplaces in order to construct office environments, remote work environments, or the like.

In electrographic image forming apparatuses, a formation density of an image may be changed in accordance with various conditions such as a change in a surrounding environment such as humidity and a degradation of an image carrier or the like.

Therefore, to compensate for the change in the formation density of the image, it is desirable to appropriately perform control such that an image can be formed at a given formation density.

DETAILED DESCRIPTION

In general, according to one embodiment, an image forming apparatus includes a forming unit, a supply unit, a first measurement unit, a control unit, a second measurement unit, an adjustment unit, and a changing unit. The forming unit forms a toner image on an image carrier using developer which is contained in a developer container and includes toner and a magnetic carrier. The supply unit supplies the toner to the developer container. The first measurement unit measures a density of the toner in the developer contained in the developer container. The control unit controls the supply unit such that the density measured by the first measurement unit approaches a target density. The second measurement unit measures an image density formed by the forming unit. The adjustment unit adjusts a development contrast potential so that a formation density measured by the second measurement unit approaches a predetermined appropriate density with regard to the toner image formed by the forming unit under a predetermined condition. The changing unit is configured to change a target density if the adjustment unit is not able to adjust the development contrast potential so that the formation density measured by the second measurement unit approaches the appropriate density.

Hereinafter, embodiments will be described with reference to the drawings. In the following embodiments, a multi-function peripheral (MFP) including an image forming apparatus as a printer will be described as an example.

First, a configuration of the MFP according to an embodiment will be described.

FIG.1is a diagram schematically illustrating a mechanical configuration of an MFP100according to the embodiment.

As illustrated inFIG.1, the MFP100includes a scanner101and a printer102.

The scanner101reads an image of a document and generates image data corresponding to the read image. The scanner101generates image data corresponding to an optical image reflected from a reading surface of the document, for example, using an image sensor such as a charge-coupled device (CCD) line sensor. The scanner101scans a document placed on a document platen using an image sensor moving along the document. Alternately, the scanner101scans the document conveyed an auto document feeder (ADF) using a fixed image sensor.

The printer102forms an image on a medium on which an image is to be formed in accordance with an electrographic scheme. The medium is generally a print sheet such as a cut sheet. Accordingly, a print sheet is used as a medium in the following description. Here, as the medium, a sheet material other than a cut sheet may be used or a sheet material such as a resin other than paper may be used. The printer102has a color printing function of printing a color image on a print sheet and a monochromic printing function of printing a monochromic image on a print sheet. The printer102forms a color image by superimposing element images, for example, using toner of three colors of yellow, magenta, and cyan or toner of four colors of black in addition to yellow, magenta, and cyan. The printer102forms a monochromic image, for example, using toner of black. Here, the printer102may have only one of the color printing function and the monochromic printing function. The printer102may additionally have a function of forming a monochromic image using decoloring toner by heating.

In an example configuration illustrated inFIG.1, the printer102includes a sheet feeding unit1, a printing engine2, a fixing unit3, an automatic double-sided unit (ADU)4, and a sheet discharging tray5.

The sheet feeding cassettes10-1,10-2, and10-3accommodate print sheets in a piled state. The print sheets accommodated in the sheet feeding cassettes10-1,10-2, and10-3may be types of print sheets of which sizes and materials are different or may be the same type of print sheets. The sheet feeding unit1may also include an input tray.

The pickup rollers11-1,11-2, and11-3pick up the print sheets from the sheet feeding cassettes10-1,10-2, and10-3, respectively, one by one. The pickup rollers11-1,11-2, and11-3send the picked-up print sheets to the conveyance rollers12-1,12-2, and12-3.

The conveyance rollers12-1,12-2, and12-3convey the print sheets sent by the pickup rollers11-1,11-2, and11-3to the conveyance rollers13via a conveyance path formed by guide members and the like (not illustrated).

The conveyance rollers13further convey the print sheet sent from any of the conveyance rollers12-1,12-2, and12-3and send the print sheet to the resist rollers14.

The resist rollers14correct a tilting of the print sheet. The resist rollers14adjust a timing at which the print sheet is sent to the printing engine2.

The sheet feeding cassettes, the pickup rollers, and the conveyance rollers are not limited to three sets, but any number of sets may be provided. If an input tray is provided, any one set of feeding cassette and pickup and conveyance rollers paired with the feeding cassette may not be provided.

The printing engine2includes a belt20, support rollers21,22, and23, image forming units24-1,24-2, and24-3,24-4, toner bottles25-1,25-2,25-3, and25-4, supply mechanisms26-1,26-2,26-3, and26-4, an exposure unit27, and a transfer roller28.

The belt20has an endless shape and is supported by the support rollers21,22, and23so that a state illustrated inFIG.1is held. The belt20is rotated counterclockwise inFIG.1as the support rollers21are rotated. The belt20temporarily carries an image of toner which is to be formed on the print sheet on a surface (hereinafter referred to as an image carrier surface) located outside. That is, the belt20is an example of an image carrier. In the belt20, for example, semiconductive polyimide is used from the viewpoint of heat resistance and abrasion resistance.

Each of the image forming units24-1to24-4includes a photoreceptor, a charging roller, a developing unit, a transfer roller, and a cleaner and forms an image in conformity with an electrographic scheme in cooperation with the exposure unit27. The image forming units24-1to24-4are located along the belt20so that axial directions of the photoreceptors are parallel to each other. The image forming units24-1to24-4have the same structure and operation except for colors of toner to be used. The image forming unit24-1forms an element image, for example, using the toner of black. The image forming unit24-2forms an element image, for example, using the toner of cyan. The image forming unit24-3forms an element image, for example, using the toner of magenta. The image forming unit24-4forms an element image, for example, using the toner of yellow. Thus, each of the image forming units24-1to24-4is an example of the forming unit. The image forming units24-1to24-4form the element images of the colors so that the element images are piled on the image carrying surface of the belt20. Accordingly, the image forming units24-1to24-4form color images in which the element images of the colors are piled on the image carrying surface of the belt20if the image forming unit24-1is passed.

The toner bottles25-1to25-4contain the toner to be supplied to the image forming units24-1to24-4, respectively. That is, the toner bottle25-1contains, for example, the toner of black. The toner bottle25-2contains, for example, the toner of cyan. The toner bottle25-3contains, for example, the toner of magenta. The toner bottle25-4contains, for example, the toner of yellow.

The supply mechanisms26-1to26-4supply the toner contained in the toner bottles25-1to25-4to the image forming units24-1to24-3, respectively. The supply mechanisms26-1to26-4include pipe lines connected to the image forming units24-1to24-4from the toner bottles25-1to25-4and conveyance mechanisms moving the toner to the pipe lines, and are simplified as indicated by dotted lines inFIG.1.

The exposure unit27exposes the photoreceptors of the image forming units24-1to24-4in accordance with image data indicating the element images of the colors. As the exposure unit27, a laser scanner, a light-emitting diode (LED) head, or the like is used. The exposure unit27includes, for example, a semiconductor laser element, a polygon mirror, an image forming lens system, and a mirror if the laser scanner is used. In this case, the exposure unit27causes, for example, a laser beam emitted from the semiconductor laser element in accordance with the image data to be selectively incident on the photoreceptors of the image forming units24-1to24-4by switching an emission direction by a mirror. The exposure unit27scans the foregoing laser beam in the axial direction (a depth direction inFIG.1) of the photoreceptor by the polygon mirror.

The transfer roller28is disposed in parallel to the support roller23and pinches the belt20with the support roller23. The transfer roller28pinches a print sheet sent from the resist rollers14with the image carrier surface of the belt20. Then, the transfer roller28transfers the images of the toner formed on the image carrier surface of the belt20to the print sheet using an electrostatic force. That is, a transfer unit is formed by the support roller23and the transfer roller28. The toner which is not transferred to the print sheet remains on the image carrier surface of the belt20in some cases. Therefore, the toner attached to the image carrier surface of the belt20after the toner is passed between the support roller23and the transfer roller28is removed by a cleaner (not illustrated) until the toner reaches the image forming unit24-4.

Thus, the printing engine2forms an image on the print sheet sent by the resist rollers14in conformity with the electrographic scheme.

The fixing unit3includes a fixing roller30and a pressure roller31.

The fixing roller30accommodates a heater in a hollow roller formed of, for example, a heat-resistive resin. The heater is, for example, an induction heating (IH) heater, but any other type of heater may be used appropriately. The fixing roller30fixes the toner to the print sheet by melting the toner attached to the print sheet sent from the printing engine2.

The pressure roller31is provided with pressurized against the fixing roller in parallel to the fixing roller30. The pressure roller31pinches the print sheet sent from the printing engine2with the fixing roller30to press the print sheet against the fixing roller30.

The ADU4includes a plurality of rollers and selectively performs the following two operations. A first operation is an operation of sending the print sheet passing through the fixing unit3toward the sheet discharging tray5as it is. The first operation is performed if one-sided printing or double-sided printing is completed. A second operation is an operation of temporarily conveying the print sheet passing through the fixing unit3toward the sheet discharging tray5and then switching back and sending the print sheet to the printing engine2. The second operation is performed if an image is completed on only one side in the double-sided printing.

The sheet discharging tray5receives the print sheet on which the image is formed and which is discharged.

FIG.2is a partial breakaway diagram illustrating a configuration of main units of the image forming units24-1to24-4.

The image forming unit24-1to24-4have the same configuration. Therefore, only the configuration of the image forming unit24-1is illustrated inFIG.2and the configuration of the image forming units24-2to24-4are not illustrated and will not be described.

The image forming unit24-1is configured such that a charging roller242, a developing unit243, a transfer roller244, and a cleaner245are disposed around a photoreceptor241. The image forming unit24-1includes a high-voltage power supply246.

The photoreceptor241is configured such that a photosensitive layer is formed by applying a photosensitive conductive material to a curved surface of a base in which a conductor such as aluminum is formed in a cylindrical shape. The surface of the photoreceptor241on which the photosensitive layer is formed is referred to as a photosensitive surface. The photoreceptor241is rotatably supported by a casing of the image forming unit24-1at a posture directed at an axial direction in the depth direction ofFIG.2.

In the charging roller242, a conductor such as a conductive rubber is formed in a columnar shape. The charging roller242is rotatably supported by a casing or the like of the image forming unit24-1at a posture directed at an axial direction in the depth direction ofFIG.2. A curved surface of the charging roller242comes into contact with or approaches the photosensitive surface of the photoreceptor241. The charging roller242is supplied with a charging voltage from the high-voltage power supply246and uniformly charges the photosensitive surface of the photoreceptor241. Instead of the charging roller242, for example, another type of electrostatic charger such as a scorotron system may be used to uniformly charge the photosensitive surface of the photoreceptor241.

The developing unit243includes a casing2431, a developing sleeve2432, mixers2433and2434, and a doctor blade2435.

The casing2431forms a space where developer is contained inside. That is, the casing2431functions as a developer container that contains the developer. The inner space of the casing2431is partitioned into partitions SEA and SEB. The partitions SEA and SEB are connected via an aperture which is not illustrated inFIG.3. Appropriate developer in the developing unit243is of a 2-component type in which toner and magnetic carrier are mixed.

The developing sleeve2432is formed in a columnar shape and is rotatably supported by the casing2431at a posture directed at an axial direction in a depth direction ofFIG.3and in a state where a part of the developing sleeve2432is located in the partition SEA. The developing sleeve2432includes a magnet formed magnetic poles alternately in a circumferential direction along the circumferential surface. The developing sleeve2432is supplied with a developing bias from the high-voltage power supply246and attaches the toner to the photosensitive surface of the photoreceptor241electrostatically in accordance with an electrostatic latent image formed on the photosensitive surface. A potential difference between a potential of the developing sleeve2432formed with the supplied developing bias and a potential of the photosensitive surface of the photoreceptor241after exposure is referred to as a development contrast potential. As the development contrast potential is larger, more toner is attached to the photosensitive surface of the photoreceptor241.

The mixers2433and2434are configured such that a stirring bar is mounted on a rotational shaft. The mixer2433is rotatably supported by the casing2431at a posture directed at the axial direction of the rotational shaft in the depth direction ofFIG.2and in a state where the mixer2433is located near the bottom of the partition SEA. The mixer2434is rotatably supported by the casing2431at a posture directed at the axial direction of the rotational shaft in the depth direction ofFIG.2and in a state where the mixer2434is located near the bottom of the partition SEB. In the mixers2433and2434, the stirring bars are rotated in areas indicated by circles inFIG.2with rotation around the rotational shaft.

The mixer2433protrudes in front ofFIG.2from the developing sleeve2432and the toner supplied to the image forming unit24-1by the supply mechanism26-1is sent to the periphery of the protrusion portion. The toner sent in this way is mixed with the developer contained in the partition SEA. The developer is sent from the partition SEA to the partition SEB with the rotation of the mixer2433. The developer is sent from the front ofFIG.2to the rear ofFIG.2in the partition SEB with the rotation of the mixer2434, and then is sent from the partition SEB to the partition SEA in the rear ofFIG.2. The developer is carried from the rear ofFIG.2to the front ofFIG.2in the partition SEA with the rotation of the mixer2433. During this process, the developer is stirred and charged as the toner and the magnetic carrier are uniformly mixed.

The doctor blade2435is formed in a plate form and is fixed to the casing2431in a state where the tip end approaches the curved surface of the developing sleeve2432. The doctor blade2435limits an amount of developer moved outside of the casing2431from the partition SEA with the rotation of the developing sleeve2432.

The transfer roller244is formed in a columnar shape and is rotatably supported by the casing or the like of the image forming unit24-1at a posture directed at the axial direction in the depth direction ofFIG.2. The transfer roller244faces the photoreceptor241and pinches the belt20with the photosensitive surface of the photoreceptor241. The belt20is not illustrated inFIG.2. The transfer roller244is supplied with the transfer bias from the high-voltage power supply246and electrostatically transfers the toner attached to the photosensitive surface of the photoreceptor241to the belt20.

The cleaner245includes a cleaning blade of which a tip end comes into contact with or approaches the photosensitive surface of the photoreceptor241. The cleaner245scrapes off the toner remaining on the photosensitive surface by the cleaning blade to collect the toner.

FIG.3is a block diagram schematically illustrating a configuration related to control of the MFP100. InFIG.3, the same elements as those illustrated inFIG.1are denoted by the same reference numerals, and detailed description thereof will be omitted.

The MFP100includes a communication unit103, a system controller104, and an operation panel105in addition to the scanner101and the printer102.

The communication unit103performs a process of communicating with an information terminal such as a computer apparatus and an image terminal such as a facsimile apparatus via a communication network such as a local area network (LAN) and a public communication network.

To implement an expected operation of the MFP100, the system controller104generally controls each unit provided in the MFP100. The expected operation of the MFP100is, for example, an operation of implementing various functions implemented by a known MFP.

The operation panel105includes an input device and a display device. The operation panel105inputs an instruction if an operator gives the instruction with the input device. The operation panel105displays various types of information of which the operator is notified on the display device. As the operation panel105, for example, a touch panel, any of various switches, any of various lamps, or the like can be used singly or in appropriate combination.

The fixing unit3, the ADU4, the image forming units24-1to24-4, the exposure unit27, and the transfer roller28provided in the printer102, as described above, are control target elements. In addition to these elements, the printer102includes a motor group6as a control target element. The motor group6incudes a plurality of motors that rotate a roller provided in the ADU4and various rotators provided in the pickup rollers11-1,11-2, and11-3, the conveyance rollers12-1,12-2, and12-3, the conveyance rollers13, the resist rollers14, the support roller21, the transfer roller28, the fixing roller30, and the image forming units24-1to24-4. The motor group6also includes a toner conveyance motor that individually operates a conveyance mechanism provided in each of the supply mechanisms26-1to26-4.

The printer102further includes a sensor group7, a printer controller81, a forming controller82, an exposure controller83, a transfer controller84, a fixing controller85, a reversing controller86, and a motor controller87.

The sensor group7includes various sensors that monitor operation states of the apparatus. As illustrated inFIG.1, the sensor group7includes an attachment amount sensor71faced the image carrier surface of the belt20between the image forming unit24-1and the transfer roller28. The attachment amount sensor71measures an amount of toner attached to the image carrier surface of the belt20, that is, an attachment amount of toner to the belt20in an image forming operation. As the attachment amount sensor71, for example, an optical sensor measuring the attachment amount as a reflection amount of light can be used. The attachment amount sensor71is an example of a second measurement unit. As illustrated inFIG.2, the sensor group7includes a density sensor72mounted on the bottom of the partition SEB of the casing2431. The density sensor72measures a density of the toner in the developer. The density sensor72is an example of a first measurement unit.

The printer controller81generally controls each unit provided in the printer102to implement an expected operation of the printer102under the control of the system controller104.

The forming controller82, the exposure controller83, the transfer controller84, the fixing controller85, the reversing controller86, and the motor controller87all operate under the control of the printer controller81to control operations of the image forming units24-1to24-4, the exposure unit27, the transfer roller28, the ADU4, and the motor group6.

FIG.4is a block diagram illustrating a configuration of main units of the image controller82.

The forming controller82includes a processor821, a main storage unit822, an auxiliary storage unit823, a communication unit824, an image forming unit825, an interface unit826, and a transmission path827.

The processor821, the main storage unit822, and the auxiliary storage unit823are connected via the transmission path827to configure a computer that performs information processing to control the image forming units24-1to24-4.

The processor821corresponds to a central portion of the computer. The processor821implements information processing to be described below in accordance with an information processing program such as an operating system, middleware, and an application program.

The main storage unit822corresponds to a main storage portion of the computer. The main storage unit822includes a nonvolatile memory area and a volatile memory area. The main storage unit822stores an information processing program in the nonvolatile memory area. The main storage unit822stores data necessary to perform a process by the processor821to control each unit in the nonvolatile memory area or the volatile memory area in some cases. The main storage unit822uses the volatile memory area as a work area where data can be appropriately rewritten by the processor821.

The auxiliary storage unit823corresponds to an auxiliary storage portion of the computer. As the auxiliary storage unit823, for example, known storage devices such as electric erasable programmable read-only memory (EEPROM), a hard disc drive (HDD), and a solid-state drive (SSD) can be used singly or in plural combination. The auxiliary storage unit823stores data used for the processor821to perform various processes or data generated in a process by the processor821. The auxiliary storage unit823stores an information processing program. The auxiliary storage unit823stores measurement pattern data DAA to be described below as the data used for the processor821to perform various processes.

The communication unit824communicates with the printer controller81.

Four image forming unit825corresponding to the image forming units24-1to24-4are provided in the forming controller82. The four image forming units825process element images formed by the corresponding image forming units as processing targets. That is, for example, the image forming unit825corresponding to the image forming unit24-1processes a black element image as a processing target. InFIG.4, only one image processing unit825is illustrated and the other three image processing units825are not illustrated. If print target image data indicates a color image, the four image processing units825generate element image data indicating an element image of each color and supply the element image data to the exposure unit27to perform exposure in accordance with the element image of each color.

The interface unit826performs interface processing to control the high-voltage power supply246by the processor821.

The transmission path827includes an address bus, a data bus, and a control signal line and transmits data and control signals transmitted and received between the connected units.

Next, an operation of the MFP100that has the foregoing configuration will be described. Content of various operations and various processes to be described below is an example, an order of some of the operations and the processes can be appropriately changed, some of the operations and the processes can be appropriately omitted, or other operations and processes can be appropriately added.

Operations different from operations of the same type of known MFP will be described below and the other operations will not be described. A characteristic operation of the MFP100according to the embodiment is an operation of the forming controller82.

If an image is formed by carrying out work involved in an image formed in the MFP100, the toner in the developer contained in the inner space of the casing2431is consumed and toner density is changed in the developing unit243provided in each of the image forming units24-1to24-4. A change in a toner density is indicated as a change in magnetic permeability in the developer. Accordingly, the density sensor72measures a toner density as magnetic permeability related to the developer present near the bottom of the partition SEB in the inner space of the casing2431and outputs a measurement value of the toner density (hereinafter referred to as a density measurement value).

FIG.5is a diagram illustrating a relationship between a toner density and a density measurement value.

The density measurement value inFIG.5indicates a standardized value so that the density measurement value is “100” if the toner density is a target value (hereinafter referred to as a density target value).

As the toner density decreases, a ratio of the magnetic carrier in the developer conversely increases. Therefore, magnetic permeability increases and the density measurement also increases, as illustrated inFIG.5.

In the forming controller82, at a predetermined density adjustment timing, the processor821starts information processing to adjust the toner density related to the developer contained in the developing unit243(hereinafter referred to as a density adjustment process) in accordance with an information processing program stored in the main storage unit822or the auxiliary storage unit823. The density adjustment timing is assumed to be a timing after a process of forming an image is started, as an example. Here, the density adjustment timing may be appropriately determined by, for example, a designer or the like of the MFP100. The processor821sets each of the image forming units24-1to24-4and individually performs the density adjustment process. Here, the density adjustment process of which a target is the image forming unit24-1will be described. Accordingly, all various devices in description of the following density adjustment process are devices related to the image forming unit24-1. That is, for example, in description of the “density sensor72,” the density sensor72refers to the density sensor72provided in the developing unit243of the image forming unit24-1.

FIG.6is a flowchart illustrating a density adjustment process.

In ACT11, the processor821acquires a density measurement value output by the density sensor72.

In ACT12, the processor821determines a toner supply time for adjusting a toner density to a density target value. That is, the processor821determines, as a supply time, a time necessary for the supply mechanism26-1to supply an amount of toner supplied to the developing unit243in order to compensate for a difference between density measurement value acquired in ACT11and a density measurement value output by the density sensor72if the toner density is the density target value. For example, the processor821determines the supply time as a time obtained through predetermined calculation. However, for example, a specific process of determining the supply time, such as a process of determining the supply time with reference to a data table indicating a relationship between the density measurement value and the supply time, may be determined appropriately by, for example, the designer or the like of the MFP100.

In ACT13, the processor821starts the toner conveyance motor. Specifically, the processor821requests the printer controller81to start the corresponding toner conveyance motor. In accordance with an instruction from the printer controller81in response to this request, the motor controller87starts driving the toner conveyance motor provided in the motor group6. If the toner conveyance motor operates and the supply mechanism26-1is driven, the supply mechanism26-1supplies an amount of toner per unit time from the toner bottle25-1to the developing unit243. Thus, the supply mechanism26-1and the toner conveyance motor corresponding to the supply mechanism26-1form a supply unit that supplies the toner to the developing unit243provided in the image forming unit24-1.

In ACT14, the processor821waits for the supply time determined in ACT12after the toner conveyance motor is started in ACT13. If the processor821can confirm that the supply time passes, YES is determined and the process moves to ACT15.

In ACT15, the processor821stops the toner conveyance motor. Specifically, the processor821requests the printer controller81to stop the corresponding toner conveyance motor. In accordance with an instruction from the printer controller81in response to this request, the motor controller87ends the driving of the toner conveyance motor.

Then, the processor821thus ends the present density adjustment process. The processor821repeats the foregoing density adjustment process every density adjustment timing to compensate for a change in the toner density involved in the toner consumed in the image forming and maintain the toner density so that the toner density does not considerably deviate from the density target value.

Thus, the processor821performs the density adjustment process based on the information processing program, so that a computer including the processor821as a central portion functions as a control unit that controls the toner supply to approach the toner density to the density target value.

On the other hand, the processor821starts information processing to adjust the development contrast potential (hereinafter referred to as a contrast adjustment process) every predetermined contrast adjustment timing in accordance with the information processing program stored in the main storage unit822or the auxiliary storage unit823. The contrast adjustment timing is assumed to be, for example, a timing after end of the image forming work after the accumulated number of times the image is formed after completion of the previous contrast adjustment process reaches a given number such as several thousands. That is, the processor821starts the contrast adjustment process in a state where the image forming work is not performed. Here, the contrast adjustment timing may be determined appropriately by, for example, the designer or the like of the MFP100.

FIG.7is a flowchart illustrating a contrast adjustment process.

In ACT21, the processor821forms a measurement pattern. For example, the processor821starts operations of the image forming units24-1to24-4, then reads the measurement pattern data DAA stored in the auxiliary storage unit823, and gives the measurement pattern data DAA to the image processing unit825. A measurement pattern indicated by the measurement pattern data DAA is considered to be a pattern in which an image with a density value determined in advance for each color is formed in an area on the image carrier surface of the belt20passing through a measurement position by the attachment amount sensor71. Any density value may be determined by, for example, the designer or the like of the MFP100.

The measurement pattern data DAA is processed by the image forming unit825and is then supplied to the exposure unit27. The measurement pattern is formed on the image carrier surface of the belt20through a known forming operation by the image forming units24-1to24-4and the exposure unit27. If the area where the measurement pattern is formed on the image carrier surface of the belt20passes through the measurement position by the attachment amount sensor71, an attachment amount of toner of each color is sequentially measured by the attachment amount sensor71.

If the measurement pattern is formed, the processor821does not send a print sheet between the support roller23and the transfer roller28. That is, the measurement pattern is not printed on the print sheet.

In ACT22, the processor821acquires each measurement value of the attachment amount related to the above-described measurement pattern in the attachment amount sensor71(hereinafter referred to an attachment amount measurement value). The processor821may calculate a difference between an output value of the attachment amount sensor71on the image carrier surface of the belt20in a toner-unattached state and an output value of the attachment amount sensor71if the area where the measurement pattern is formed passes through the measurement position by the attachment amount sensor71, and may acquire the difference as an attachment amount measurement value.

Processes after the contrast adjustment process are performed on each of the image forming units24-1to24-4as a target. Since all the processes are the same process, only a process performed on the image forming unit24-1as a target will be described below. Accordingly, all various devices in description of the following contrast adjustment process are devices related to the image forming unit24-1.

In ACT23, the processor821confirms whether the attachment amount measurement value acquired in ACT22is within a predetermined target range. The target range is determined in consideration of a margin to some extent using an attachment amount for implementing a density value formed in the measurement pattern (hereinafter referred to as an appropriate attachment amount) as a reference. The specific target range may be appropriately determined, for example, by the designer of the MFP100. If the processor821can confirm that the attachment amount measurement value is in the target range, YES is determined and the present contrast adjustment process ends as it is. That is, in this case, the development contrast potential is not adjusted.

If the processor821cannot confirm that the attachment amount measurement value is in the target range, NO is determined in ACT23and the process moves to ACT24.

In ACT24, the processor821determines the adjusted development contrast potential (hereinafter referred to as an adjusted potential). That is, for example, the processor821compensates for a difference between the attachment amount measurement value corresponding to an appropriate attachment amount and the attachment amount measurement value acquired in ACT22and determines the development contrast potential for implementing the appropriate attachment amount as an adjusted potential.

FIG.8is a diagram illustrating a concept for determining an adjusted potential.

FIG.8illustrates a relationship between the development contrast potential and the attachment amount measurement value at a certain time. The attachment amount measurement value inFIG.8indicates a value standardized so that an attachment amount measurement value corresponding to the appropriate attachment amount is “100”.

A development contrast potential PCUR is a development contrast potential if the attachment amount measurement value acquired in ACT22is measured. A development contrast potential PADJ is an adjusted potential. That is, in the example ofFIG.8, the development contrast potential PADJ lower than the development contrast potential PCUR is determined as the adjusted potential.

In ACT25, the processor821confirms that the adjusted potential determined in ACT24is too high to the extent that the adjusted potential exceeds a range in which the development contrast potential can be adjusted. Here, in the embodiment, the development contrast potential is adjusted by changing a development bias, as will be described below. However, there is a limitation of a range in which the development bias can be changed depending on the specification of the high-voltage power supply246and there is a restriction of an adjustable range of the development contrast potential. Accordingly, if the adjusted potential is equal to or less than a predetermined maximum potential of the adjustable range of the development contrast potential, the processor821determines that the adjusted potential is not too high, determines NO, and moves to ACT26.

It is assumed that, in consideration of deterioration in image quality or the like, the adjustable range of the development contrast potential is set to be narrower than an adjustment range implemented by a change in a development bias in a changeable range of the development bias depending on the specification of the high-voltage power supply246.

In ACT26, the processor821confirms that the adjusted potential determined in ACT24is too low to the extent that the adjusted potential exceeds a range in which the development contrast potential can be adjusted. Accordingly, if the adjusted potential is equal to or greater than the predetermined minimum potential of the adjustable range of the development contrast potential, the processor821determines that the adjusted potential is not too low, determines NO, and moves to ACT27.

InFIG.8, PMAX and PMIN indicate a maximum potential and a minimum potential of the development contrast potential, respectively. Thus, the adjusted development contrast potential PADJ in the example ofFIG.8is equal to or less than the maximum potential PMAX and equal to or greater than the minimum potential PMIN. Thus, in the case of the example ofFIG.8, the processor821determines NO in one of ACT25and ACT26and moves to ACT27.

In ACT27, the processor821controls the high-voltage power supply246such that the development bias is changed to change the development contrast potential to the adjusted potential determined in ACT24. Then, the processor821thus ends the present contrast adjustment process.

A potential of the photosensitive surface of the photoreceptor241after exposure (hereinafter referred to as a post-exposure potential) is changed in accordance with deterioration in the photoreceptor241. Accordingly, the processor821determines the present post-exposure potential and then adjusts the development bias in accordance with magnitude causing a potential difference corresponding to the adjusted potential from the determined post-exposure potential. The processor821, for example, determines the post-exposure potential based on a print number for which the photoreceptor241is used.

If the attachment amount measurement value is acquired after the development contrast potential is completed as the adjusted potential, the attachment amount measurement value indicates an attachment amount close to the appropriate measurement value. That is, the development contrast potential is adjusted so that the attachment amount measurement value is close to the appropriate attachment amount. Thus, if the processor821performs the contrast adjustment process based on the information processing program, a computer including the processor821as a central portion functions as a control unit.

Meanwhile, if the adjusted potential is greater than the maximum potential PMAX, the processor821determines that the adjusted potential is too high, determines YES in ACT25, and moves to ACT28.

In ACT28, the processor821confirms whether the present density target value in the density adjustment process is a predetermine upper limit value. The upper limit value will be described below. Then, if the density target value is not the upper limit, the processor821determines NO and moves to ACT29.

In ACT29, the processor821increases the density target value by a predetermined amount. For example, if the present density target value is N %, the processor821increases the density target value by N+1%. Here, the increase amount here may be determined appropriately by the designer or the like of the MFP100. Then, the processor821thus ends the present contrast adjustment process.

Conversely, if the adjusted potential is less than the minimum potential PMIN, the processor821determines that the adjusted potential is too low, determines YES in ACT26, and moves to ACT30.

In ACT30, the processor821confirms whether the present density target value in the density adjustment process is a predetermined lower limit value. The lower limit value will be described below. If the density target value is not the lower limit value, the processor821determines NO and moves to ACT31.

In ACT31, the processor821decreases the density target value by a predetermined amount. For example, if the present density target value is N %, the processor821decreases the density target value to N−1%. Here, the decrease amount may be determined appropriately by the designer or the like of the MFP100. Then, the processor821thus ends the present contrast adjustment process.

In this way, the processor821changes the target density in the toner density adjustment by increasing or decreasing the density target value. That is, if the processor821performs the contrast adjustment process based on the information processing program, a computer including the processor821as a central portion functions as a changing unit.

FIG.9is a diagram illustrating a relationship between a development contrast potential and an attachment amount measurement value at a certain time.

A relationship between the development contrast potential and the attachment amount is changed in accordance with a change in a surrounding environment such as humidity or all conditions such as deterioration in the image carrier, for example, as illustrated inFIGS.8and9.

In the example ofFIG.9, the adjusted development contrast potential PADJ is less than the minimum potential PMIN. In this case, the processor821determines that the density target value is too low, determines YES in ACT26, and moves to ACT30. If the density target value is not the lower limit value, the density target value is decreased.

If the density target value is decreased, the toner density of the developer contained in the developing unit243is decreased through the subsequent density adjustment process. The decrease in the toner density is implemented by consuming the toner in the image forming work performed without supplying the toner in the density adjustment process. Here, the steep decrease in the toner density may be achieved by forming an image on the belt20without being involved in the image forming work and recovering the toner attached to the belt20by the cleaner (not illustrated).

FIG.10is a diagram illustrating a state of a change in the attachment amount measurement value made as a toner density decreases.

If only the toner density is changed among various image forming conditions, the attachment amount of the toner to the belt20decreases as the toner density decreases. Accordingly, as illustrated inFIG.10, if the toner density decreases, the attachment amount measurement value decreases. Accordingly, the development contrast potential for implementing the appropriate attachment amount increases from a potential PAPA before the decrease in the toner density to a potential PAPB after the decrease in the toner density. The potential PAPB is in an adjustable range of the development contrast potential. That is, the adjustment of the toner attachment amount by the adjustment of the development contrast potential can continue.

Here, if the change in the toner density is repeated and the change amount of the toner density with respect to a reference value, there is concern of required image quality being unmaintainable. Accordingly, an upper limit value and a lower limit value of a target value of the toner density are determined in advance within a range in which the required image quality is maintainable. The upper limit value and the lower limit value are assumed to be, for example, +2% and −2% of an initial value of the target value of the toner density. However, the upper limit value and the lower limit value may be determined appropriately by, for example, the designer or the like of the MFP100.

If the processor821moves from ACT25to ACT28because the adjusted potential is too high in the state where the toner density is set to the upper limit value, the processor821moves to ACT29. Further, because the density target value cannot be increased, the processor821determines YES in ACT28and moves to ACT32.

If the processor821moves from ACT26to ACT30because the adjusted potential is too low in the state where the toner density is set to the lower limit value, the processor821moves to ACT31. Further, because the density target value cannot be decreased, the processor821determines YES in ACT30and moves to ACT32.

In ACT32, the processor821performs a notification process of notifying a predetermined notification destination that the adjustment reaches a limitation in the contrast adjustment process. The notification destination is assumed to be a manager belonging to an organization using the MFP100, a maintenance person responsible for maintenance of the MFP100, a management operator responsible for management work of the MFP100. The notification destination may be determined fixedly by the designer or the like of the MFP100or may be able to be set appropriately in accordance with a desire of a user or the like.

Here, if the notification process is performed, there is a situation where the MFP100cannot adjust a formation density of an image any more, and thus there is concern of image quality of a subsequently formed image deteriorating. Therefore, it is desirable to set the maintenance person or the management operator as a notification destination and request speedy maintenance. Here, the notification destination may be a user actually using the MFP100.

The notification process may be performed by any of various methods of notifying a remote notification destination, such as transmission of an electronic mail, a push notification to an information terminal, and an upload of predetermined data for notification to a server. Here, the notification process is not limited to the method of notifying a remote notification destination, but a method of notifying a direct operant of the MFP100, such as display of a screen on the operation panel105, may be adopted. Which notification process is performed may be determined fixedly by the designer or the like of the MFP100or may be able to be set appropriately in accordance with a desire of a user or the like. If the notification process is completed, the processor821thus ends the present contrast adjustment process.

For example, if data for notification (hereinafter referred to as notification data) is uploaded to a server, for example, the processor821generates the notification data and requests the system controller104to upload the notification data via the printer controller81. The system controller104uploads the notification data to the server via the communication unit103in response to this request. However, the processor821may give only a notification request to the printer controller81. In this case, the printer controller81generates notification data and requests the system controller104to upload the notification data. Alternatively, the processor821may give only a notification request to the system controller104. In this case, the system controller104may generate notification data and upload the notification data to a server. That is, the notification process may be performed in cooperation with the formation controller82, and the printer controller81and the system controller104or may be performed in cooperation with the forming controller82and the system controller104.

If the processor821moves to ACT32, the development contrast potential is not adjusted. However, by performing maintenance on the MFP100in response to a request from a a notification person receiving by the foregoing notification process or by the determination of a person by herself or himself receiving the notification, the MFP100can quickly return to a state where an appropriate image can be formed.

As described above, the MFP100adjusts the attachment amount of toner on the image carrier involved in the image formation so that the attachment amount is in a target range around the appropriate attachment amount through the adjustment of the development contrast potential, while maintaining the toner density to the target density. In a situation where the development contrast potential at which the attachment amount of the toner is around the appropriate attachment amount cannot be set, the MFP100can adjust the toner density by changing the target density of the toner density adjustment to set the development contrast potential at which the attachment amount of the toner is around the appropriate attachment amount by adjusting the toner density. Accordingly, it is possible to keep the attachment amount of toner to the belt20in the image formation for a long time around the appropriate attachment amount, compared to a case in which only the development contrast potential or only the toner density is adjusted.

Incidentally, if the target density is changed, it is necessary to wait for progress of the supply of the toner or consumption to some extent until the target density is changed and then the toner density becomes around the target density, and thus it takes some time. In particular, if the target density decreases and an arrival of the toner density at the target density is awaited due to consumption of the toner in execution of normal image forming work, there is concern of much time being required until the toner density becomes the target density. Independently of normal image forming work, an image is formed on the belt20. If the toner is steeply consumed, a time until the toner density becomes the target density can be shortened, but the toner may be wasted. However, in the MFP100, the development contrast potential is mainly adjusted. Therefore, the attachment amount can reliably approach the appropriate attachment amount in a short time and the toner is not wasted.

In the MFP100, the upper limit value and the lower limit value of the density target value are determined in advance and the target density is not changed beyond the upper limit value and the lower limit value. Accordingly, it is possible to prevent the toner density from forming an image with poor quality as a result that the toner density is considerably distant from the appropriate density.

In the MFP100, if the density target value reaches the upper limit value or the lower limit value, and thus cannot be changed when the density target value should be changed, a predetermined notification destination is notified of this. Accordingly, it is possible to encourage a state in which the appropriate image is formed by maintenance or the like.

The embodiment can be modified in the following various forms.

The attachment amount toner attached to the photoreceptor241may be measured.

Any of various apparatuses such as a copy machine, a printer, and a facsimile apparatus other than the MFP can perform the foregoing process as long as the apparatus forms an image in conformity with the electrographic scheme.

Some or all of the functions implemented by the processor821in information processing in the foregoing embodiment can also be implemented by hardware such as a logical circuit performing information processing which is not based on a program. Each of the foregoing functions can be implemented by hardware such as the foregoing logical circuit in combination of software control.