Image forming apparatus and developer replacement method of image forming apparatus

An image forming apparatus of an exemplary embodiment includes a temperature sensor, a developing unit, a supply unit, and a control unit. The temperature sensor detects a temperature. The developing unit supplies developer to an image carrier and performs development. The supply unit contains developer and supplies the contained developer to the developing unit. The control unit executes developer replacement processing including discharging the developer from the developing unit and supplying the developer contained in the supply unit to the developing unit based on a first ratio which a ratio of a developer supply time during which the supply unit performs supply of the developer for the developing unit and a drive time during which the developing unit is driven and a threshold value obtained based on a detected temperature of a temperature sensor.

FIELD

Embodiments described herein relate to a technology for replacing developer of an image forming apparatus.

BACKGROUND

In the related art, an image forming apparatus using developer of two-component mixture containing a carrier and a toner is known. The carrier is a substance which is stirred with toner particles in a container and which imparts electric charge to the toner particles and conveys the toner to a surface of a photoconductive substance.

In the image forming apparatus, when an image is formed on a sheet in a state where a printing rate is low, a toner inside a developing container may be degraded. In particular, toner for low temperature fixation which is recently provided in a market may be fixed on a sheet at a low temperature while the toner has low thermal resistance characteristics and is easily soluble and thus, an external additive on a surface of toner may be easily embedded into or separated from the toner surface. Especially, when stirring is continued in a state where the developer is not replaced, an external additive is embedded into or separated from the surface of toner as described above and developing capability to an image carrier (photoconductive drum) is lowered.

For that reason, a degraded toner needs to be replaced with a supplying toner regularly (refresh operation). In this context, an image forming apparatus that performs a determination whether a replacement of a toner is needed or not based on a time at which developing is performed or the number of sheets subjected to print processing, and a printing rate per a single sheet, and replaces the toner is known.

However, in the related art, a cumulative counter is reset after the toner replacement operation is performed, without determining whether the degraded toner is sufficiently output. Accordingly, whether effective developing may be performed is uncertain. Although the toner replacement operation is performed, when the degraded toner is not sufficiently output, effective developing may not be performed.

DETAILED DESCRIPTION

An image forming apparatus of an exemplary embodiment includes a temperature sensor, a developing unit, a supply unit, and a control unit. The temperature sensor detects a temperature. The developing unit supplies developer to an image carrier and performs development. The supply unit contains the developer and supplies the contained developer to the developing unit. The control unit executes developer replacement processing of discharging the developer from the developing unit and supplying the developer contained in the supply unit to the developing unit based on a first ratio which is a ratio of a developer supply time during which the supply unit performs supply of the developer for the developing unit and a drive time during which the developing unit is driven and a threshold value obtained based on a detected temperature of a temperature sensor.

A problem to be solved by the present disclosure is to provide an image forming apparatus capable of performing developer replacement with a high accuracy.

In the following, an image forming apparatus of the exemplary embodiment will be described with reference to drawings. In the exemplary embodiment, a two-component developer with toner, of which a glass transition temperature Tg is less than or equal to 50° C., is used in order to cope with low temperature fixation. Other types of developers can be alternatively employed. A glass transition temperature Tg of a normal toner in the related art is approximately 65° C., however, a toner for low temperature fixation of the present exemplary embodiment is regarded as a toner having a fixation temperature of at least less than or equal to 50° C. and more particularly, from approximately 40° C. to 41° C.

FIG. 1illustrates a diagram of an example of an image forming apparatus of an exemplary embodiment. A dotted line within the figure illustrates a unit positioned inside the apparatus.

An image forming apparatus100is, for example, a composite machine (multi function peripheral (MFP)) capable of forming a toner image on a sheet. The image forming apparatus100is equipped with, for example, a printer function, a copy function, a scanner function, and a facsimile function.

The image forming apparatus100includes an image read unit105, a sheet accommodation unit200, an image forming unit250, a sheet discharge unit161, and a control panel104.

The image read unit105reads images from an original sheet placed on a predetermined position. For example, the image read unit105includes an image-capturing element such as a charge coupled device (CCD) or a contact image sensor (CIS). The image read unit105reads an image from the original sheet placed on a predetermined position by the image-capturing element and generates image data. The image read unit105outputs the generated image data to the image forming unit250. The image read unit105may output, for example, the generated image data to a control unit41which will be described later. The image read unit105may transmit the generated image data to other information processing apparatuses through a network, for example.

The control panel104is provided with a display unit and an operation unit. The display unit is a display device such as a liquid crystal display, an organic electro luminescence (EL) display, or the like. The display unit displays various pieces of information about the image forming apparatus100. The operation unit is provided with a plurality of buttons or the like. The operation unit receives user's operation to the plurality of buttons. The control panel104outputs an instruction signal according to the user's operation by the operation unit to the control unit41which will be described later. The control panel104may be a touch panel display in which a display unit and an operation unit are integrally formed.

The image forming unit250forms an image on a surface of a sheet based on the image data generated by the image read unit105(copy function). The image forming unit250may form an image on a surface of a sheet based on image data transmitted by other information processing apparatuses through the network (printer function). The image forming unit250, for example, forms an image on a surface of a sheet with a toner. The formed image is referred to as a toner image, as needed.

In the present exemplary embodiment, the toner includes a decolorable toner and a non-decolorable toner. The non-decolorable toner is, for example, a toner of yellow (Y), magenta (M), cyan (C), and black (K). The decolorable toner is a colored toner similar to the non-decolorable toner. The decolorable toner decolorizes an image at a temperature higher than a temperature at which the non-decolorable toner is fixed on the sheet. Decolorization means that an image formed with a color (including chromatic color as well as achromatic color such as white and black) different from a color of a base of a paper is not visually seen.

The toner of the exemplary embodiment is regarded as a toner for low temperature fixation of Tg of approximately from 40° C. to 41° C. (less than or equal to 50° C.).

The sheet accommodation unit200is provided with a plurality of paper feeding cassettes. Each of paper feeding cassettes accommodates sheets of a predetermined size and type. Each of paper feeding cassettes is provided with a pickup roller which takes the accommodated sheets out one by one.

The sheet accommodated in the sheet accommodation unit200is conveyed to the image forming unit250. The image forming unit250forms an image on the sheet according to an image of an original document read by the image read unit105or print data transmitted from other information processing apparatuses. The sheet on which an image is formed is discharged by the sheet discharge unit161.

FIG. 2illustrates a schematic diagram of a portion of the image forming apparatus100, especially a schematic diagram illustrating mainly the image forming unit250. InFIG. 2, a configuration with toner of one color (for example, yellow (Y)) is illustrated, however, a magenta (M) toner, a cyan (C) toner, a black (K) toner, and a decolorable (D) toner are also similarly configured.

In the periphery of a developing unit60, a photoconductive drum72(image carrier), a charging unit71, an electricity elimination unit75, a cleaning unit76, and a transfer roller73are provided.

The developing unit60is provided with a developer containing unit64, a developing roller63, a first mixer62a, a second mixer62b, and a toner concentration sensor65, and is driven by obtaining power from the developing motor32. The developing unit60supplies developer existing inside the developer containing unit64to a photoconductive drum72. The developing roller63is an example of a supply mechanism. The developing motor32is an example of a power-supplying and driving unit and controls driving of the developing roller63, the first mixer62a, and the second mixer62b. The toner concentration sensor65is an example of a detection unit, receives a voltage for control from the control unit41as an input, and outputs a sensed result to the control unit41.

The developer containing unit64is a container containing developer. The developer is a mixture of a carrier consisting of magnetic fine particles and each toner. When developer particles are stirred by the first mixer62aand the second mixer62b, the toner is charged by friction. Thus, the toner is adhered to the surface of the carrier by an electrostatic force.

The first mixer62a, the second mixer62b, and the developing roller63are disposed inside the developer containing unit64. The first mixer62aand the second mixer62bstir the developer and convey the developer. The second mixer62bis disposed below the developing roller63and supplies the developer contained in the developer containing unit64to the surface of the developing roller63. The developing roller63is rotated in the counterclockwise direction illustrated in the figure by driving of the developing motor32. The developing roller63is made of magnetic substance (magnet) and a positive electrode and a negative electrode are alternately aligned along a circumferential shape by a developing high voltage from a high voltage power supply45. The developer supplied by the second mixer62bis adhered to the surface of the developing roller63according to a magnetic field distribution generated by a configuration of magnetic substance (magnet) arrangement. The magnetic field distribution of the developing roller63is switchable. The developing unit60performs adhesion or release of adhesion of the developer by switching of the magnetic field distribution of the developing roller63.

A photoconductive layer is provided on a surface of the photoconductive drum72. The photoconductive drum72is rotated in a clockwise direction illustrated in the figure by driving of the main motor35. The charging unit71, the developing unit60, the transfer roller73, the cleaning unit76, and the electricity elimination unit75are disposed in the periphery of the photoconductive drum72. The exposure unit75is disposed below the developing device60and the charging unit71.

The charging unit71uniformly charges the surface (photoconductive layer) of the photoconductive drum72by the electrifying high voltage output from the high voltage power supply45. For example, the charging unit71charges the surface of the photoconductive drum72to be in the negative polarity. The charging unit71charges the photoconductive drum72such that only the toner among the developer adhered to the surface of the developing roller63is adhered to the surface of the photoconductive drum72. In this case, an electrostatic latent image is formed on the surface of the photoconductive drum72by an exposure unit75. Accordingly, the toner is adhered to the electrostatic latent image of the photoconductive drum72from the developing roller63. Thus, the toner image is formed on the surface of the photoconductive drum72.

The cleaning unit76removes untransferred toners or the like on the surface of the photoconductive drum72by performing scraping off or the like of the untransferred toners. The cleaning unit76is provided on a stage at the rear of the position (position of the transfer roller73) at which the toner image on the surface of the photoconductive drum72is transferred to an intermediate transfer belt81. In an example ofFIG. 2, the photoconductive drum72rotates in a clockwise direction illustrated in the figure. Thus, the cleaning unit76removes the toner on the surface of the photoconductive drum72after the toner image is transferred to the intermediate transfer belt81from the photoconductive drum72. The toners removed by the cleaning unit76are collected in a waste toner tank and discarded.

The electricity elimination unit75faces the photoconductive drum72passing through the cleaning unit76. The electricity elimination unit75irradiates the surface of the photoconductive drum72with light. Thus, non-uniform charges of the photoconductive layer are made uniform. That is, the photoconductive layer is subjected to elimination of electricity.

The transfer roller73faces the photoconductive drum72by nipping the intermediate transfer belt81between the transfer roller73and the photoconductive drum72and abuts against the surface of the photoconductive drum72by nipping the intermediate transfer belt81between the transfer roller73and the photoconductive drum72. The transfer roller73transfers (primary transfer) the toner image on the surface of the photoconductive drum72onto the intermediate transfer belt81.

The exposure unit75irradiates the surface of the photoconductive drum72with laser light. The emission of the exposure unit75is controlled based on the image data by control of the control unit41. The exposure unit75emits laser light based on the image data. Thus, static electricity patterns (electrostatic latent image) are formed at a position irradiated with laser light on the surface of the photoconductive drum72. The exposure unit75may use light emitting diode (LED) light instead of laser light.

The toner concentration sensor65detects a toner concentration in the developer containing unit64. The toner concentration represents a ratio (toner/carrier) of a toner to a carrier. The toner concentration sensor65outputs the detected value representing the toner concentration to the control unit41.

The transfer unit82is provided with a support roller82aand a secondary transfer roller82bthat nips the sheet from both sides in a thickness direction. The support roller82aobtains power by driving of the main motor35and moves the intermediate transfer belt81in an arrow direction. The position at which the support roller82aand the secondary transfer roller82bface with each other is a secondary transfer position. The transfer unit82receives transfer bias by the control unit41and transfers the toner image being charged on the surface of the intermediate transfer belt81on the surface of the sheet S in the secondary transfer position. Pressure and heat are applied to the sheet S on which the toner image is transferred by the fixing unit as in the related art.

The supply unit31is provided with a toner supply motor31aand a supply mechanism31b. The supply unit31drives the toner supply motor31aaccording to the control instruction output by the control unit41. The toner supply motor31aoperates the supply mechanism31b. The supply mechanism31bis connected to a toner cartridge not illustrated. The supply mechanism31boperates according to driving of the toner supply motor31aand supplies the toner contained in the toner cartridge to the developer containing unit64. The toner supply motor31ais an example of the toner-supplying and driving unit.

The image forming apparatus100includes a temperature sensor401and a humidity sensor402. The temperature sensor401is a thermistor detecting temperatures inside the image forming unit250or the periphery of the outside the image forming unit250. The humidity sensor402detects a relative humidity inside the image forming apparatus100or outside the image forming apparatus100. The temperature sensor401and the humidity sensor402are regarded as a single sensor, respectively, in the present example, however, a plurality of sensors401and sensors402may be installed for every photoconductive substance of each color or the like. The values of the temperature and the humidity detected by the temperature sensor401and the humidity sensor402are output to the control unit41.

The control unit41is a software functional unit. A processor executes a program to cause the software functional unit to function. The processor is, for example, a central processing unit (CPU). The control unit41may also be a hardware functional unit. For example, the control unit41is implemented by a large scale integration (LSI), an application specific integrated circuit (ASIC), or the like.

The storage unit51is implemented by a storage device such as a read only memory (ROM), a random access memory (RAM), a hard disk drive (HDD), a flash memory, or the like.

The storage unit51stores the image data generated by the image read unit105or image data transmitted by other information processing apparatuses through a network. The storage unit51stores the program executed by a processor of the control unit41. The storage unit51stores, for example, pieces of corresponding information corresponding to each piece of identification information of the developing unit60. That is, the storage unit51stores the piece of corresponding information for each color. The piece of corresponding information includes developing unit drive time information (A), toner supply time information (B), replacement rate information (C), initial value information (D), threshold value information (E), setting value information (F), and toner replacement count (T). The storage unit51stores sensor output determination information, toner supply time derivation information, image pattern information, and replacement rate derivation information. These various pieces of information will be described later.

In the following, examination items and results regarding a relationship between the temperature and the relative humidity detected by the sensors401and402and image contrast potential will be described. The image contrast potential means a potential difference between a DC component of the developing bias and the potential after exposure. If the image contrast potential is high, the toner and the carrier of the developer are adhered together to the surface of the photoconductive substance and, carrier development (development processing in a state where a toner as well as a carrier is adhered to the surface of the photoconductive substance) occurs. As a result, a rough image is formed on the sheet.

In the present exemplary embodiment, an examination has been performed for the following 4 patterns. The following respective patterns are performed under a condition that external environment is 30° C./85% RH (relative humidity). The condition is called an HH environment. These numerical values are an example and different results are obtained depending on the type of the image forming apparatus, conditions of individuals, and installed positions of the sensors.

One side printing of a printing rate of 1% is performed continuously on 10,000 sheets. If the continuous printing is performed under the HH environment, a temperature inside a machine body of the image forming apparatus1is increased and a temperature (temperatures of a drum thermistor) of the photoconductive drum reaches 45° C. A relative humidity inside the machine body is decreased due to receiving of an influence of a temperature increase and becomes 55% RH. Under this situation, upper limit sticking (a limit value example: 700 V) of the image contrast potential occurs in magenta and black and the carrier development is generated in magenta and black. The upper limit sticking refers to, in the present example, a state where the image contrast potential is always maintained in the limit value. The toner, of which the developing capability is deteriorated, becomes difficult to reach a desired concentration (adhesion amount) even when the image contrast potential is raised. In adjusting a concentration or the like, a control unit in the related art controls a concentration of toner to become a desired concentration as much as possible and thus, the control unit controls the image contrast potential to become 700 V which is the limit value and as a result, the state is maintained. With this, the upper limit sticking occurs. If the upper limit sticking occurs, the image is formed in a state where the image contrast potential is high and the carrier development occurs.

One side printing of a printing rate of 4% is performed on 10,000 sheets. If the continuous printing is performed under the HH environment, the temperature of the drum thermistor and the relative humidity become 41° C. and 62% RH, respectively. Under this situation, the upper limit sticking does not occur and also the carrier development does not occur.

Following the second pattern, one side printing of a printing rate of 1% is performed on 10,000 sheets. If the continuous printing is performed under the HH environment, the temperature of the drum thermistor and the relative humidity become 45° C. and 77% RH, respectively. Under this situation, the upper limit sticking (700 V) occurs in magenta and black and the carrier development is generated in magenta and black.

Double side printing of a printing rate of 3% is performed on 10,000 sheets. If the continuous printing is performed under the HH environment, the temperature of the drum thermistor and the relative humidity become 44° C. and 81% RH, respectively. Under this situation, the upper limit sticking does not occur and also the carrier development does not occur.

When the printing rate is 1%, the upper limit sticking of the image contrast potential occurs and the carrier development is generated as illustrated in the first and third patterns. When the printing rate is 1%, a replacement amount of toner in approximately 400 g of developer is small and even when printing of 10,000 sheets is performed, approximately half of the toner particles (approximately 20 g) have been continuously stirred in the developing device from the start of printing. With this, external additives are embedded into or separated from the toner surface and the developing capability to the photoconductive substance is lowered. Accordingly, even when the control unit raises image contrast potential to an upper limit (700 V in the present example), a toner does not reach a desired concentration and contrast of an image is stuck at the upper limit. As a result, the carrier development occurs.

In the exemplary embodiment, replacement processing is performed for the toner degraded due to embedding or separation of the external additive of toner described above. That is, when the replacement amount of toner inside the developer containing unit64is small, the control unit41performs processing for replacing the toner inside the developer containing unit64with a new toner. In general, a time period during which the toner (developer), of which consumption is small, resides in the developer containing unit64becomes longer. As a result, the toner (developer) of the developer containing unit64has a tendency that the number of times that toner particles are stirred by a first mixer62aand a second mixer62bbecomes greater and a percentage of crushing is increased. Thus, the developer is degraded. When the degraded developer is used, the image quality is degraded or flecks may occur in the gradation of an image. Accordingly, the control unit41performs the toner replacement processing described above and prevents degradation of the image quality.

For example, the control unit41executes the toner replacement processing based on a ratio of a time during which the supply unit31supplies the toner to the developing unit60and a drive time during which the developing unit60is driven. The toner replacement processing represents processing for discharging the toner from the developer containing unit64of the developing unit60and supplying the toner to the developing unit60from the supply unit31. The time, during which the supply unit31supplies toner to the developing unit60, corresponds to a developer supply time or a toner supply time and the toner replacement processing corresponds to developer replacement processing.

In the following, the toner replacement processing will be described based on a flowchart.FIG. 3illustrates a flowchart of an example of flow of processing by the control unit41in the exemplary embodiment. The processing in the flowchart is repeatedly performed, for example, at a predetermined period.

First, the control unit41determines whether an instruction signal to form an image is received from the control panel104(ACT001) or not. When the instruction signal to form an image is not received (ACT001: No), the control unit41waits until the instruction signal to form an image is received.

On the other hand, when the instruction signal to form an image is received (ACT1001: Yes), the control unit41starts image formation processing (ACT002). The image formation processing refers that the control unit41performs the following processing.

The control unit41drives the developing motor32to operate the first mixer62aand the second mixer62b. The control unit41operates the first mixer62aand the second mixer62bto stir developer inside the developer containing unit64. The control unit41controls the charging unit71such that the surface of the photoconductive drum72is charged while driving the developing motor32and rotating the photoconductive drum72. The control unit41controls the exposure unit75and irradiates the charged photoconductive drum72with laser light of which emission is controlled based on the image data to form the electrostatic latent image. The control unit41drives the second mixer62band supplies the developer contained in the developer containing unit64to the surface of the developing roller63. In this case, the control unit41controls the supply unit31such that a toner amount that amounts to the toner supplied to the surface of the developing roller63is supplied to the developer containing unit64. The supply unit31is controlled by the control unit41to supply the toner contained in the toner cartridge to the developer containing unit64.

The control unit41drives the developing motor32to adhere the toner on the surface of the developing roller63to the electrostatic latent image formed on the surface of the photoconductive drum72. With this, the toner image is formed on the surface of the photoconductive drum72. The control unit41drives the transfer roller73and the support roller82ato move the intermediate transfer belt81. In this case, the control unit41applies a voltage (transfer bias) to the transfer roller73described above and transfers the toner image on the surface of the photoconductive drum72onto the intermediate transfer belt81. The control unit41controls a conveyance unit such that the sheet S accommodated in the sheet accommodation unit200is conveyed to the transfer unit82. The control unit41drives a main motor35or the like to rotate a support roller82aand a secondary transfer roller82band also applies a voltage to the secondary transfer roller82b(transfer bias). With this, the toner image on the intermediate transfer belt81is transferred onto the sheet S in the secondary transfer position of the transfer unit82. The control unit41controls the conveyance unit such that the sheet S onto which the toner image is transferred is conveyed to the fixing unit, the toner image is fixed, and is conveyed to a finisher or the like as in the related art. The control unit41repeats the processing described above until forming of an image is performed on the number of sheets S set by the user.

Description returns to the flowchart ofFIG. 3. The control unit41starts to measure a drive time A of the developing motor32and a drive time B of the toner supply motor31aimmediately after the start of the image forming apparatus (ACT003). ACT003is performed for each color.

In this case, the control unit41determines whether the drive time A of the developing motor32and the drive time B of the toner supply motor31aalready measured are stored in the storage unit51or not. For example, in the last processing, one or both of the drive time A of the developing motor32and the drive time B of the toner supply motor31amay be stored in the storage unit51. For that reason, the control unit41acquires developing unit drive time information A and toner supply time information B from the storage unit51. The control unit41references the acquired developing unit drive time information A to determine whether the drive time A of the developing motor32is stored in the storage unit51or not. The control unit41references the acquired toner supply time information B to determine whether the drive time B of the toner supply motor31ais stored in the storage unit51or not.

When the drive time A of the developing motor32is already stored in the storage unit51, the control unit41cumulatively adds a time A to be measured from now to time information which is already stored. When the drive time B of the toner supply motor31ais already stored in the storage unit51, the control unit41cumulatively adds a time B to be measured from now to time information B which is already stored.

On the other hand, when the drive time A of the developing motor32is not yet stored in the storage unit51, the control unit41newly measures the drive time A of the developing motor32. When the drive time B of the toner supply motor31ais not yet stored in the storage unit51, the control unit41newly measures the drive time B of the toner supply motor31a.

The measurement of the drive time A of the developing motor32and the drive time B of the toner supply motor31adescribed above is performed on each developing unit60. In the present exemplary embodiment, the developing unit60may be provided according to a type of toner. For that reason, the drive time A of the developing motor32and the drive time B of the toner supply motor31aare measured for each type of toner. Processing from ACT003and subsequent Actions is performed for each type of toner of the developing unit60.

Next, the control unit41determines whether the image formation processing is ended or not (ACT004). For example, when forming of an image is not performed on the number of sheets S set by the user, the control unit41determines that the image formation processing is not ended. When forming of an image is performed on the number of sheets S set by the user, the control unit41determines that the image formation processing is ended.

When it is determined that the image formation processing is not ended (ACT004: No), the control unit41waits until the image formation processing is ended. On the other hand, when it is determined that the image formation processing is ended (ACT004: Yes), the control unit41performs the following processing.

The control unit41ends the measurement of the drive time A of the developing motor32and the drive time B of the toner supply motor31astarted in ACT003(ACT005). The control unit41stores the measured drive time A of the developing motor32in the storage unit51as the developing unit drive time information A. The control unit41stores the measured drive time B of the toner supply motor31ain the storage unit51as the toner supply time information B.

FIG. 4illustrates a diagram for explaining a measurement method of the drive time A of the developing motor32and the drive time B of the toner supply motor31a. For example, the drive time A of the developing motor32is derived by cumulatively adding a period of an on state of the developing motor32. Specifically, a pulse length obtained by cumulatively adding a pulse width ranging from a rise to a fall of a rectangular-wave pulse, which indicates an on state of the developing motor32, corresponds to the drive time A of the developing motor32. In the illustrated example, a pulse width al corresponds to the drive time A of the developing motor32. The drive time B of the toner supply motor31ais derived by cumulatively adding a period of an on state of the toner supply motor31a. In the illustrated example, a pulse length obtained by cumulatively adding pulse widths b1, b2, and b3corresponds to the drive time B of the toner supply motor31a.

The developing motor32is in a state of idling even in a period during which the development processing is not performed. The state of idling refers that the developing motor32is driven in a state where the photoconductive drum72is not charged, that is, a state where the charging unit71is not operated. In the following, description will be made by referring a time during which the motor is in a state of idling as an idling time. The control unit41may measure the drive time A of the developing motor32including the idling time so as to perform a calculation of a replacement rate C, which will be described later, with a high accuracy.

Description returns to the flowchart ofFIG. 3. Next, the control unit41calculates a replacement rate C (ACT006). The replacement rate C is a parameter serving as an index when determining whether the toner is replaced or not in the processing which will be described later.

For example, the replacement rate C is defined as a value obtained by dividing the drive time B of the toner supply motor31aby the drive time A of the developing motor32. Accordingly, the control unit41references the developing unit drive time information A and the toner supply time information B stored in the storage unit51to calculate the replacement rate C. The control unit41stores the calculated replacement rate C in the storage unit51as calculated replacement rate information C. In first image forming processing, for example, a default value is stored in the toner supply time information B as the drive time B of the toner supply motor31a. The developing unit drive time information A and toner supply time information B stored in the storage unit51are rewritten in the processing which will be described later.

Next, the control unit41determines whether the drive time A of the developing motor32is greater than or equal to a setting value F which is determined in advance or not (ACT007). The setting value F is stored in the storage unit51as setting value information F. The setting value F, for example, is set as a fixed value D which is a default in the first image forming processing. The fixed value D is stored in the storage unit51as initial value information D.

When the drive time A of the developing motor32is greater than or equal to the setting value F (ACT007: Yes), the control unit41determines that the developing unit60has been driven for a long period of time. On the other hand, when the drive time A of the developing motor32is less than the setting value F (ACT007: No), the control unit41determines that the developing unit60has not been driven for a long period of time, and returns the processing to ACT001.

When it is determined that the developing unit60has been driven for a long period of time, the control unit41acquires the temperature information of a current state detected by the temperature sensor401(ACT007A). The control unit41derives a threshold value E used for a comparison with the replacement rate C based on the acquired temperature information (ACT007B). In the present exemplary embodiment, the threshold value E is derived from the temperature detected by the temperature sensor401according to a correspondence relationship between the detected temperature and the replacement rate threshold value illustrated inFIG. 5. The correspondence relationship illustrated inFIG. 5is stored in the storage unit51as replacement rate derivation information. The replacement rate derivation information may be defined as a function of calculating a threshold value from the detected temperature or embedded into a program executed by the control unit41.

The control unit41determines whether the replacement rate C is less than the threshold value E obtained in ACT007B (ACT008). The control unit41may compare a threshold value (stored as the threshold value information E in the storage unit51) defined in advance with the replacement rate C.

When the replacement rate C is greater than or equal to the threshold value E (ACT008: No), the control unit41changes the setting value F by the following processing. The control unit41rewrites the setting value F into a sum (D+A) obtained by adding the fixed value D and the drive time A of the developing motor32(ACT009). Thereafter, the processing proceeds to ACT020.

On the other hand, when the replacement rate C is less than the threshold value E (ACT008: Yes), the control unit41performs toner replacement processing (ACT010). Details of the toner replacement processing will be described later.

The control unit41increases toner replacement count T by1(Act011) and the setting value F is rewritten into the drive time A of the developing motor32and updates the toner replacement count T of the storage unit51and the setting value information F (ACT012).

The control unit41determines whether the toner replacement processing is performed on even any one color in ACT020(ACT020). The determination is made based on whether the toner replacement count T is increased or based on a flag value, which is not illustrated, indicating whether the toner replacement processing is performed.

When the toner replacement processing is performed (ACT020: Yes), the control unit41performs image quality maintenance control or closed loop control, which is a control for adjusting an operation amount by feed-backing data such as a movement amount (ACT021), and returns the processing to ACT001. Operation of ACT021may adopt processing as in the related art.

Next, the toner replacement processing in ACT010will be described.FIG. 6illustrates a flowchart of an example of flow of the toner replacement processing of the control unit41in the exemplary embodiment.

First, the control unit41starts an toner replacement operation (ACT101). In this case, the control unit41starts to measure the drive time A of the developing motor32and the drive time B of the toner supply motor31a(ACT102).

The control unit41controls the exposure unit75to irradiate the charged photoconductive drum72with laser light of which emission is controlled based on predetermined image pattern data. The predetermined image pattern data is stored in the storage unit51as image pattern information in advance. Thus, a predetermined toner image (electrostatic latent image) is formed on the surface of the photoconductive drum72(ACT103).

The control unit41drives the transfer roller73and the support roller82ato move the intermediate transfer belt81and transfers the toner image on the surface of the photoconductive drum72to the intermediate transfer belt81. The control unit41does not convey the sheet S to the transfer unit82and drives the transfer roller73and the support roller82ato cause the intermediate transfer belt81to be continuously moved. Thus, the toner adhered to the intermediate transfer belt81is removed by a cleaning unit not illustrated. The control unit41may also remove the toner image of the photoconductive drum72without transferring the toner image onto the intermediate transfer belt81. For example, the control unit41rotates the photoconductive drum72continuously without applying a transfer bias to the photoconductive drum72so as to cause the cleaning unit76to remove the toner image of the photoconductive drum72.

Next, the control unit41acquires an output value representing a toner concentration from the toner concentration sensor65(ACT104). Next, the control unit41determines whether the output value acquired from the toner concentration sensor65is a forcible supply level or not (ACT105).

FIG. 7illustrates a diagram of a relationship of a toner concentration to an output value of the toner concentration sensor65. The horizontal axis illustrated inFIG. 7represents a toner concentration and the vertical axis represents an output value of the toner concentration sensor. For example, a unit of the horizontal axis is wt % and a unit of the vertical axis is v. As illustrated inFIG. 7, the relationship between the output value of the toner concentration sensor65and the toner concentration is represented by a linear function F1. The function F1has a tendency that the output value (level) is decreased as the toner concentration is increased. The function F1is stored in the storage unit51in advance as sensor output determination information. The sensor output determination information may also be table data corresponding to the function F1instead of the function F1. The table data corresponding to the function F1may also be embedded into a program referenced by a processor. In the function F1, four threshold values are provided. The four threshold values are an abnormality determination threshold value Thmax, an abnormality determination threshold value Thmin, a forcible supply threshold value Th1, and a supply stop threshold value Th2. Accordingly, output values of the toner concentration sensor65are classified by these four threshold values.

When the output value of the toner concentration sensor65is greater than or equal to the forcible supply threshold value Th1and less than or equal to the abnormality determination threshold value Thmax, the control unit41determines that the output value is the forcible supply level. When the output value of the toner concentration sensor65is less than or equal to the forcible supply threshold value Th1and greater than or equal to the supply stop threshold value Th2, the control unit41determines that the output value is not the forcible supply level. When the output value belongs to conditions other than the condition described above, conditions are handled as exceptional processing in the present exemplary embodiment.

When the output value of the toner concentration sensor65is the forcible supply level (ACT105: Yes), the control unit41starts the forcible supply operation (ACT120). The forcible supply operation is processing continuing supply of the toner until the output value of the toner concentration sensor65becomes less than or equal to the forcible supply threshold value Th1.

In the following, description will be made on the forcible supply operation performed by the control unit41with reference toFIG. 8. As illustrated, the control unit41drives the developing motor32at all times and operates the first mixer62aand the second mixer62bduring the forcible supply operation. Thus, the developing unit60stirs the carrier and newly supplied toner within the developer containing unit64.

The control unit41intermittently drives the toner supply motor31aand causes the supply unit31to supply the toner from the toner cartridge to the developer containing unit64. In this case, the control unit41acquires the output value of the toner concentration from the toner concentration sensor65after the lapse of a predetermined time from a time point at which the toner supply motor31ais driven once. The predetermined time, for example, is set as a time required for sufficiently stirring the supplied toner and the carrier. The control unit41, for example, determines whether the output value of the toner concentration sensor65is less than or equal to the forcible supply threshold value Th1according to the function F1ofFIG. 7described above. That is, the control unit41determines whether the forcible supply operation is to be ended or not (ACT121). When the output value of the toner concentration sensor65is less than or equal to the forcible supply threshold value Th1, the control unit41determines that the forcible supply operation is to be ended. When the output value of the toner concentration sensor65is greater than the forcible supply threshold value Th1, the control unit41determines that the forcible supply operation is not to be ended.

When the forcible supply operation is not to be ended (ACT121: No), the control unit41drives the toner supply motor31aagain. With this, the control unit41causes the supply unit31to supply the toner from the toner cartridge into the developer containing unit64. The control unit41repeats driving of the toner supply motor31aand acquisition of the output value of the toner concentration sensor65until the output value of the toner concentration sensor65becomes less than or equal to the forcible supply threshold value Th1.

On the other hand, when the forcible supply operation is to be ended (ACT121: Yes), the control unit41performs initialization processing (ACT130). The initialization refers to performing the following processing. The control unit41clears a drive time, which is stored in the storage unit51as the developing unit drive time information A, of the developing motor32to zero. The control unit41clears a drive time, which is stored in the storage unit51as the toner supply time information B, of the toner supply motor31ato zero. The control unit41rewrites a setting value stored as the setting value information F in the storage unit51into a fixed value (initial value information D) which is a default. The control unit41rewrites a value of the toner replacement count (T) into an initial value of zero. Thus, the processing of the present flowchart is ended.

On the other hand, when the output value of the toner concentration sensor65is not the forcible supply level (ACT105: No), the control unit41determines a toner supply time (ACT106).

FIG. 9illustrates a diagram of a relationship of an output value of the toner concentration sensor65to a toner supply time. The horizontal axis illustrated inFIG. 9represents an output value of a toner concentration sensor and the vertical axis represents a toner supply time. For example, a unit of the horizontal axis is v and a unit of the vertical axis is s. As illustrated inFIG. 9, a relationship between the toner supply time and the output value of the toner concentration sensor65is represented by a linear function F2. The function F2has a tendency that the toner supply time is decreased as the output value of the toner concentration sensor65is increased. The function F2is an example when a driving amount of the toner supply motor31ais fixed.

The function F2is stored in the storage unit51in advance as toner supply time derivation information. For example, the control unit41substitutes the output value acquired from the toner concentration sensor65into the function F2to determine the toner supply time. The toner supply time derivation information may be table data corresponding to the function F2instead of the function F2. The table data corresponding to the function F2may also be embedded into a program referenced by a processor.

Next, the control unit41drives the toner supply motor31afor the determined supply time and causes the supply unit31to supply the toner from the toner cartridge to the developer containing unit64(ACT107). Next, the control unit41ends the measurement of the drive time A of the developing motor32and the drive time B of the toner supply motor31a(ACT108). The control unit41stores the measured drive time A of the developing motor32in the storage unit51as the developing unit drive time information A. The control unit41stores the measured drive time B of the toner supply motor31ain the storage unit51as the toner supply time information B.

Next, similar to ACT006described above, the control unit41calculates the replacement rate C (ACT109).

The control unit41acquires the temperature information of a current state detected by the temperature sensor401(ACT109A) and derives the threshold value E based on the temperature information and the correspondence relationship ofFIG. 5(ACT109B). The operations of ACT109A and ACT109B are similar to those of ACT007A and ACT007B, respectively.

Next, the control unit41determines whether the calculated replacement rate C is less than the threshold value E obtained in ACT109B or not (ACT110). When the replacement rate C is less than the threshold value E (ACT110: Yes), the control unit41ends the toner replacement operation (ACT111). Next, the control unit41performs the initialization processing of ACT130described above and ends the processing of the present flowchart.

On the other hand, when the replacement rate C is not less than the threshold value E (ACT110: No), the control unit41determines that the replacement of toner is insufficient and returns the processing to ACT101. Thus, a toner concentration within the developer containing unit64is controlled such that the toner concentration falls within a predetermined range.

In the following, description will be made on an exceptional processing based on the output value of the toner concentration sensor65in ACT105. The exceptional processing is different from the processing of the present flowchart. For example, when the output value of the toner concentration sensor65is greater than or equal to the abnormality determination threshold value Thmax, the control unit41determines that an abnormality occurs in the image forming unit250. When the output value of the toner concentration sensor65is less than or equal to the abnormality determination threshold value Thmin, the control unit41determines that an abnormality occurs in the image forming unit250. When it is determined that an abnormality occurs in the image forming unit250, the control unit41stops the processing of the image forming unit250. When it is determined that an abnormality occurs in the image forming unit250, the control unit41outputs information indicating that an abnormality has occurred to the control panel104.

When the output value of the toner concentration sensor65is less than or equal to the supply stop threshold value Th2and greater than or equal to the abnormality determination threshold value Thmin, the control unit41stops the supply of toner.

According to the image forming apparatus100of the exemplary embodiment described above, the drive time B of the toner supply motor31awhen the supply unit31performs the supply of toner is measured. The image forming apparatus100measures the drive time A of the developing motor32when the developing unit60is driven. The image forming apparatus100executes the toner replacement processing based on the replacement rate C which is a ratio of the measured drive time A of the developing motor32and the drive time B of the toner supply motor31a.

For example, the toner replacement processing may be performed by referencing an index different from the present exemplary embodiment in executing the toner replacement processing. For example, when the toner replacement processing is executed using an index such as toner consumption, the following problems may occur. For example, when the first mixer62aand the second mixer62bare driven without supplying the toner to the photoconductive drum72, a change in toner consumption does not occur. However, the toner particles are stirred and damaged, such as being crushed, within the developer containing unit64, and the toner is degraded. In contrast, in the present exemplary embodiment, the replacement rate C is a ratio of the drive time A of the developing motor32and the drive time B of the toner supply motor31a. That is, the replacement rate C is a rate based on a time spanning from a time when the toner is supplied into the developer containing unit64to a time when the toner particles are stirred in the developer containing unit64. Accordingly, the image forming apparatus100of the exemplary embodiment may execute the toner replacement processing with a higher accuracy according to an actual degradation degree.

According to the image forming apparatus100of the exemplary embodiment, for example, the following processing is performed for the toner which is not an execution target of the toner replacement processing. The image forming apparatus100stores the measured drive time A of the developing motor32and the drive time B of the toner supply motor31ain the storage unit51for next processing. The image forming apparatus100calculates the replacement rate C for toner, which is not replaced, by referencing the measured value to the previous measurement time. The image forming apparatus100calculates the replacement rate C for the toner, which is replaced, by referencing the current measured value. Thus, the image forming apparatus100calculates the replacement rate C for each kind of color of a toner (kind of developing unit60). As a result, the image forming apparatus100may independently execute the toner replacement processing for each kind of color of a toner (kind of developing unit60).

In the following, other exemplary embodiments will be described. When the instruction signal instructs to decolorize the sheet S, the control unit41described above sets a temperature of the fixing unit to be higher than the temperature when an image is formed. The control unit41controls the conveyance unit50to convey the sheet S to be decolorized to the fixing unit70. In this case, the developing motor32is driven in association with conveyance of the sheet S. Accordingly, the developer within the developer containing unit64are stirred by the first mixer62aand the second mixer62b.

The control unit41may perform replacement processing of decolorable toner together with decolorizing of the sheet S. For example, the control unit41controls the conveyance unit50to convey the sheet S to the transfer unit82in the toner replacement processing. Thus, a toner image formed by the developing unit60containing the decolorable toner is transferred onto the sheet S to be decolorized. The control unit41conveys the sheet S on which the toner image formed by the decolorable toner is transferred to the fixing unit and performs decolorization processing and toner replacement processing simultaneously. As a result, the image forming apparatus100may implement efficient processing.

According to the image forming apparatus100of at least one of the exemplary embodiments described above, the drive time B of the toner supply motor31awhen the supply unit31performs the supply of toner is measured. The image forming apparatus100measures the drive time A of the developing motor32when the developing unit60is driven. The image forming apparatus100executes the toner replacement processing based on the replacement rate C which is a ratio of the measured drive time A of the developing motor32and the drive time B of the toner supply motor31aand a threshold value obtained based on the detected temperature of the temperature sensor401.

The threshold value (E) of the replacement rate is varied according to the temperature as in the present exemplary embodiment and as a result, image quality may be maintained. When the present exemplary embodiment is applied, in the condition of the first pattern, the drum thermistor temperature becomes 45° C. and the relative humidity becomes 58% RH, and a image in which the upper limit sticking (limit value example: 700 V) of the image contrast potential is not also generated in each color and an image without problem, whose image concentration is within a standard range, may also be obtained.

As having been described above, the image forming apparatus100may perform a replacement of developer (toner) with a high accuracy.