Image forming apparatus and image forming method

An image forming apparatus includes a fixing rotator and an opposed rotator pressed against the fixing rotator to form a fixing nip therebetween, through which a recording medium bearing a toner image is conveyed. A heater heats the fixing rotator. A temperature sensor contacts the opposed rotator to detect a temperature of the opposed rotator. A conveyor conveys the recording medium to the fixing nip. A driver drives the conveyor. A controller, operatively connected to the temperature sensor and the driver, controls the driver to drive the conveyor to convey the recording medium to the fixing nip based on the temperature of the opposed rotator detected by the temperature sensor. The controller causes the driver to be ready to drive the conveyor when a change in the detected temperature of the opposed rotator per unit time reaches a predetermined threshold.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Application No. 2014-222641, filed on Oct. 31, 2014, in the Japanese Patent Office, the entire disclosure of which is hereby incorporated by reference herein.

BACKGROUND

Technical Field

Exemplary aspects of the present disclosure relate to an image forming apparatus and an image forming method, and more particularly, to an image forming apparatus for forming a toner image on a recording medium and an image forming method for forming a toner image on a recording medium.

Description of the Background

Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having two or more of copying, printing, scanning, facsimile, plotter, and other functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of a photoconductor; an optical writer emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a developing device supplies toner to the electrostatic latent image formed on the photoconductor to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the photoconductor onto a recording medium or is indirectly transferred from the photoconductor onto a recording medium via an intermediate transfer belt; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.

Such fixing device may include a fixing rotator, such as a fixing roller, a fixing belt, and a fixing film, heated by a heater and an opposed rotator, such as a pressure roller and a pressure belt, pressed against the fixing rotator to form a fixing nip therebetween through which a recording medium bearing a toner image is conveyed. As the recording medium bearing the toner image is conveyed through the fixing nip, the fixing rotator and the opposed rotator apply heat and pressure to the recording medium, melting and fixing the toner image on the recording medium.

SUMMARY

This specification describes below an improved image forming apparatus. In one exemplary embodiment, the image forming apparatus includes a fixing rotator rotatable in a predetermined direction of rotation and an opposed rotator pressed against the fixing rotator to form a fixing nip therebetween, through which a recording medium bearing a toner image is conveyed. A heater heats the fixing rotator. A temperature sensor contacts the opposed rotator to detect a temperature of the opposed rotator. A conveyor conveys the recording medium to the fixing nip. A driver drives the conveyor. A controller, operatively connected to the temperature sensor and the driver, controls the driver to drive the conveyor to convey the recording medium to the fixing nip based on the temperature of the opposed rotator detected by the temperature sensor. The controller causes the driver to be ready to drive the conveyor when a change in the detected temperature of the opposed rotator per unit time reaches a predetermined threshold.

This specification further describes an improved image forming method. In one exemplary embodiment, the image forming method includes detecting a temperature change per second in a temperature of a pressure rotator detected by a temperature sensor; determining that the temperature change per second is 1 degree centigrade per second or smaller for three times consecutively; calculating a difference between the temperature of the pressure rotator detected by the temperature sensor and a reference temperature; storing the difference in a memory; and adding the stored difference to the detected temperature of the pressure rotator.

DETAILED DESCRIPTION OF THE DISCLOSURE

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, in particular toFIG. 1, an image forming apparatus1according to an exemplary embodiment of the present disclosure is explained.

It is to be noted that, in the drawings for explaining exemplary embodiments of this disclosure, identical reference numerals are assigned, as long as discrimination is possible, to components such as members and component parts having an identical function or shape, thus omitting description thereof once it is provided.

FIG. 1is a schematic vertical sectional view of the image forming apparatus1. The image forming apparatus1may be a copier, a facsimile machine, a printer, a multifunction peripheral or a multifunction printer (MFP) having at least one of copying, printing, scanning, facsimile, and plotter functions, or the like. According to this exemplary embodiment, the image forming apparatus1is a color laser printer that forms color and monochrome toner images on recording media by electrophotography. Alternatively, the image forming apparatus1may be a monochrome printer that forms a monochrome toner image on a recording medium.

With reference toFIG. 1, a description is provided of a construction of the image forming apparatus1.

As shown inFIG. 1, the image forming apparatus1includes four image forming devices4Y,4M,4C, and4K situated in a center portion thereof. Although the image forming devices4Y,4M,4C, and4K contain developers in different colors, that is, yellow, magenta, cyan, and black corresponding to color separation components of a color image, (e.g., yellow, magenta, cyan, and black toners), respectively, they have an identical structure.

For example, each of the image forming devices4Y,4M,4C, and4K includes a drum-shaped photoconductor5serving as an image bearer or a latent image bearer that bears an electrostatic latent image and a resultant toner image; a charger6that charges an outer circumferential surface of the photoconductor5; a developing device7that supplies toner to the electrostatic latent image formed on the outer circumferential surface of the photoconductor5, thus visualizing the electrostatic latent image as a toner image; and a cleaner8that cleans the outer circumferential surface of the photoconductor5. It is to be noted that, inFIG. 1, reference numerals are assigned to the photoconductor5, the charger6, the developing device7, and the cleaner8of the image forming device4K that forms a black toner image. However, reference numerals for the image forming devices4Y,4M, and4C that form yellow, magenta, and cyan toner images, respectively, are omitted.

Below the image forming devices4Y,4M,4C, and4K is an exposure device9that exposes the outer circumferential surface of the respective photoconductors5with laser beams. For example, the exposure device9, constructed of a light source, a polygon mirror, an f-θ lens, reflection mirrors, and the like, emits a laser beam onto the outer circumferential surface of the respective photoconductors5according to image data sent from an external device such as a client computer.

Above the image forming devices4Y,4M,4C, and4K is a transfer device3. For example, the transfer device3includes an intermediate transfer belt30serving as an intermediate transferor, four primary transfer rollers31serving as primary transferors, a secondary transfer roller36serving as a secondary transferor, a secondary transfer backup roller32, a cleaning backup roller33, a tension roller34, and a belt cleaner35.

The intermediate transfer belt30is an endless belt stretched taut across the secondary transfer backup roller32, the cleaning backup roller33, and the tension roller34. As a driver drives and rotates the secondary transfer backup roller32counterclockwise inFIG. 1, the secondary transfer backup roller32rotates the intermediate transfer belt30counterclockwise inFIG. 1in a rotation direction D30by friction therebetween.

The four primary transfer rollers31sandwich the intermediate transfer belt30together with the four photoconductors5, forming four primary transfer nips between the intermediate transfer belt30and the photoconductors5, respectively. The primary transfer rollers31are connected to a power supply that applies a predetermined direct current (DC) voltage and/or alternating current (AC) voltage thereto.

The secondary transfer roller36sandwiches the intermediate transfer belt30together with the secondary transfer backup roller32, forming a secondary transfer nip between the secondary transfer roller36and the intermediate transfer belt30. Similar to the primary transfer rollers31, the secondary transfer roller36is connected to the power supply that applies a predetermined direct current (DC) voltage and/or alternating current (AC) voltage thereto.

The belt cleaner35includes a cleaning brush and a cleaning blade that contact an outer circumferential surface of the intermediate transfer belt30. A waste toner drain tube extending from the belt cleaner35to an inlet of a waste toner container conveys waste toner collected from the intermediate transfer belt30by the belt cleaner35to the waste toner container.

A bottle holder2situated in an upper portion of the image forming apparatus1accommodates four toner bottles2Y,2M,2C, and2K detachably attached thereto to contain and supply fresh yellow, magenta, cyan, and black toners to the developing devices7of the image forming devices4Y,4M,4C, and4K, respectively. For example, the fresh yellow, magenta, cyan, and black toners are supplied from the toner bottles2Y,2M,2C, and2K to the developing devices7through toner supply tubes interposed between the toner bottles2Y,2M,2C, and2K and the developing devices7, respectively.

In a lower portion of the image forming apparatus1are a paper tray10that loads a plurality of sheets P serving as recording media. The paper tray10is provided with a feed roller11serving as a conveyor driven by a driver to pick up and feed a sheet P from the paper tray10toward the secondary transfer nip formed between the secondary transfer roller36and the intermediate transfer belt30. The sheets P may be thick paper, postcards, envelopes, plain paper, thin paper, coated paper, art paper, tracing paper, overhead projector (OHP) transparencies, and the like. Optionally, a bypass tray that loads thick paper, postcards, envelopes, thin paper, coated paper, art paper, tracing paper, OHP transparencies, and the like may be attached to the image forming apparatus1.

A conveyance path R extends from the feed roller11to an output roller pair13to convey the sheet P picked up from the paper tray10onto an outside of the image forming apparatus1through the secondary transfer nip. The conveyance path R is provided with a registration roller pair12located below the secondary transfer nip formed between the secondary transfer roller36and the intermediate transfer belt30, that is, upstream from the secondary transfer nip in a sheet conveyance direction A1. The registration roller pair12serving as a conveyor conveys the sheet P conveyed from the feed roller11toward the secondary transfer nip.

The conveyance path R is further provided with a fixing device20(e.g., a fuser or a fusing unit) located above the secondary transfer nip, that is, downstream from the secondary transfer nip in the sheet conveyance direction A1. The fixing device20fixes a toner image transferred from the intermediate transfer belt30onto the sheet P conveyed from the secondary transfer nip. The conveyance path R is further provided with the output roller pair13located above the fixing device20, that is, downstream from the fixing device20in the sheet conveyance direction A1. The output roller pair13ejects the sheet P bearing the fixed toner image onto the outside of the image forming apparatus1, that is, an output tray14disposed atop the image forming apparatus1. The output tray14stocks the sheet P ejected by the output roller pair13.

With reference toFIG. 1, a description is provided of an image forming operation performed by the image forming apparatus1having the construction described above to form a color toner image on a sheet P.

As a print job starts, a driver drives and rotates the photoconductors5of the image forming devices4Y,4M,4C, and4K, respectively, clockwise inFIG. 1in a rotation direction D5. The chargers6uniformly charge the outer circumferential surface of the respective photoconductors5at a predetermined polarity. The exposure device9emits laser beams onto the charged outer circumferential surface of the respective photoconductors5according to yellow, magenta, cyan, and black image data constituting color image data sent from the external device, respectively, thus forming electrostatic latent images thereon. The developing devices7supply yellow, magenta, cyan, and black toners to the electrostatic latent images formed on the photoconductors5, visualizing the electrostatic latent images as yellow, magenta, cyan, and black toner images, respectively.

Simultaneously, as the print job starts, the secondary transfer backup roller32is driven and rotated counterclockwise inFIG. 1, rotating the intermediate transfer belt30in the rotation direction D30by friction therebetween. The power supply applies a constant voltage or a constant current control voltage having a polarity opposite a polarity of the charged toner to the primary transfer rollers31, creating a transfer electric field at each of the primary transfer nips formed between the photoconductors5and the primary transfer rollers31, respectively.

When the yellow, magenta, cyan, and black toner images formed on the photoconductors5reach the primary transfer nips, respectively, in accordance with rotation of the photoconductors5, the yellow, magenta, cyan, and black toner images are primarily transferred from the photoconductors5onto the intermediate transfer belt30by the transfer electric field created at the primary transfer nips such that the yellow, magenta, cyan, and black toner images are superimposed successively on a same position on the intermediate transfer belt30. Thus, a color toner image is formed on the outer circumferential surface of the intermediate transfer belt30. After the primary transfer of the yellow, magenta, cyan, and black toner images from the photoconductors5onto the intermediate transfer belt30, the cleaners8remove residual toner failed to be transferred onto the intermediate transfer belt30and therefore remaining on the photoconductors5therefrom, respectively. Thereafter, dischargers discharge the outer circumferential surface of the respective photoconductors5, initializing the surface potential thereof.

On the other hand, the feed roller11disposed in the lower portion of the image forming apparatus1is driven and rotated to feed a sheet P from the paper tray10toward the registration roller pair12through the conveyance path R. The registration roller pair12conveys the sheet P sent to the conveyance path R by the feed roller11to the secondary transfer nip formed between the secondary transfer roller36and the intermediate transfer belt30at a proper time. The secondary transfer roller36is applied with a transfer voltage having a polarity opposite a polarity of the charged yellow, magenta, cyan, and black toners constituting the color toner image formed on the intermediate transfer belt30, thus creating a transfer electric field at the secondary transfer nip.

As the yellow, magenta, cyan, and black toner images constituting the color toner image on the intermediate transfer belt30reach the secondary transfer nip in accordance with rotation of the intermediate transfer belt30, the transfer electric field created at the secondary transfer nip secondarily transfers the yellow, magenta, cyan, and black toner images from the intermediate transfer belt30onto the sheet P collectively. After the secondary transfer of the color toner image from the intermediate transfer belt30onto the sheet P, the belt cleaner35removes residual toner failed to be transferred onto the sheet P and therefore remaining on the intermediate transfer belt30therefrom. The removed toner is conveyed and collected into the waste toner container.

Thereafter, the sheet P bearing the color toner image is conveyed to the fixing device20that fixes the color toner image on the sheet P. Then, the sheet P bearing the fixed color toner image is ejected by the output roller pair13onto the outside of the image forming apparatus1, that is, the output tray14that stocks the sheet P.

The above describes the image forming operation of the image forming apparatus1to form the color toner image on the sheet P. Alternatively, the image forming apparatus1may form a monochrome toner image by using any one of the four image forming devices4Y,4M,4C, and4K or may form a bicolor or tricolor toner image by using two or three of the image forming devices4Y,4M,4C, and4K.

With reference toFIG. 2, a description is provided of a construction of the fixing device20incorporated in the image forming apparatus1described above.

FIG. 2is a schematic vertical sectional view of the fixing device20. The fixing device20includes a fixing belt21serving as a fixing rotator or a fixing member and a pressure roller22serving as an opposed rotator or a pressure rotator. Inside a loop formed by the fixing belt21are a nip formation pad24, a fixing stay25, a halogen heater23, a heat shield26, and a pair of flanges that supports the nip formation pad24, the fixing stay25, the halogen heater23, and the heat shield26. The pressure roller22is pressed against the nip formation pad24via the fixing belt21to form a fixing nip N between the pressure roller22and the fixing belt21. The fixing stay25supports the nip formation pad24against load or pressure exerted from the pressure roller22to the nip formation pad24. The halogen heater23serves as a heater or a heat source for heating the fixing belt21. The fixing belt21and the components situated inside the loop formed by the fixing belt21, that is, the nip formation pad24, the fixing stay25, the halogen heater23, and the heat shield26, may constitute a belt unit21U detachably attached to the fixing device20. As shown inFIG. 2, the fixing nip N is planar. Alternatively, the fixing nip N may be contoured into a recess, a curve, or other shapes. If the fixing nip N defines a recess or a curve, the curved fixing nip N directs a leading edge of the sheet P toward the pressure roller22as the sheet P is ejected from the fixing nip N, facilitating separation of the sheet P from the fixing belt21and suppressing jamming of the sheet P.

A detailed description is now given of a construction of the pressure roller22.

The pressure roller22is constructed of a metal roller22a, an elastic layer22bcoating an outer circumferential surface of the metal roller22aand being made of silicone rubber, and a release layer22ccoating an outer circumferential surface of the elastic layer22b. The release layer22cis made of tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), polytetrafluoroethylene (PTFE), or the like to facilitate separation of the sheet P from the pressure roller22. As a driving force generated by a driver (e.g., a motor) situated inside the image forming apparatus1depicted inFIG. 1is transmitted to the pressure roller22through a gear train, the pressure roller22rotates in a rotation direction D22.

A spring or the like presses the pressure roller22against the nip formation pad24via the fixing belt21. As the spring presses and deforms the elastic layer22bof the pressure roller22, the pressure roller22produces the fixing nip N having a predetermined length in the sheet conveyance direction A1. Alternatively, the pressure roller22may be a solid roller. However, a hollow roller has a decreased thermal capacity. Further, a heater such as a halogen heater may be disposed inside the pressure roller22.

The elastic layer22bmay be made of solid rubber. Alternatively, if no heater is situated inside the pressure roller22, the elastic layer22bmay be made of sponge rubber. The sponge rubber is more preferable than the solid rubber because it has an increased insulation that draws less heat from the fixing belt21.

A detailed description is now given of a construction of the fixing belt21.

The fixing belt21is an endless belt or film rotatable in a rotation direction D21and made of metal such as nickel and SUS stainless steel or resin such as polyimide. The fixing belt21is constructed of a base layer and a release layer. The release layer constituting an outer surface layer is made of PFA, PTFE, or the like to facilitate separation of toner of a toner image T on the sheet P from the fixing belt21. An elastic layer may be sandwiched between the base layer and the release layer and made of silicone rubber or the like. If the fixing belt21does not incorporate the elastic layer, the fixing belt21has a decreased thermal capacity that improves a fixing property of being heated quickly. However, as the pressure roller22and the fixing belt21sandwich and press the toner image T on the sheet P passing through the fixing nip N, slight surface asperities of the fixing belt21may be transferred onto the toner image T on the sheet P, producing an orange peel mark on the solid toner image T on the sheet P. To address this circumstance, the elastic layer of the fixing belt21has a thickness not smaller than 100 micrometers. As the elastic layer deforms, the elastic layer absorbs slight surface asperities of the fixing belt21, preventing formation of a faulty orange peel image.

A detailed description is now given of a configuration of other components of the fixing device20.

The heat shield26interposed between the halogen heater23and the fixing stay25shields the fixing stay25from heat or light radiated from the halogen heater23, preventing the fixing stay25from being heated by the halogen heater23and thereby reducing waste of energy. Alternatively, instead of the heat shield26, an opposed face of the fixing stay25disposed opposite the halogen heater23may be treated with insulation or mirror finish.

Alternatively, the heater for heating the fixing belt21may be an induction heating (IH) coil, a resistance heat generator, a carbon heater, or the like, instead of the halogen heater23. As the driver drives and rotates the pressure roller22, the driving force of the driver is transmitted from the pressure roller22to the fixing belt21at the fixing nip N, thus rotating the fixing belt21by friction between the pressure roller22and the fixing belt21. Alternatively, the driver may also be connected to the fixing belt21to drive and rotate the fixing belt21. A separator28disposed downstream from the fixing nip N in the sheet conveyance direction A1separates the sheet P ejected from the fixing nip N from the fixing belt21. A temperature sensor27disposed opposite the fixing belt21detects the temperature of the fixing belt21.

A temperature sensor50serving as a temperature detector contacts the pressure roller22to detect the temperature of the pressure roller22.FIG. 3is a sectional view of the temperature sensor50. As shown inFIG. 3, the temperature sensor50includes a detection element50acontacting the pressure roller22.

A description is provided of a control performed by the image forming apparatus1.

FIG. 4is a block diagram of the image forming apparatus1. As shown inFIG. 4, the image forming apparatus1further includes a driver40, a communicator80, and a controller160. The halogen heater23and the temperature sensor50are connected to the controller160.

The driver40drives components that convey the sheet P, that is, conveyors, such as the feed roller11and the registration roller pair12depicted inFIG. 1. The communicator80receives information such as image data from an external terminal90such as a client computer through a network or the like. Alternatively, the communicator80may receive information such as image data from another external terminal90such as a client computer through a server91. Upon receipt of the information, the communicator80sends the information to the controller160.

The temperature sensor50detects the temperature of an outer circumferential surface of the pressure roller22. The temperature sensor50sends the detected temperature of the pressure roller22to the controller160.

The controller160includes an arithmetic portion160aand a memory160b. The arithmetic portion160acalculates a difference between a current temperature and a reference temperature as described below. The memory160bstores the difference calculated by the arithmetic portion160a.

The controller160controls at least one of driving of the driver40and an amount of power supplied to the halogen heater23based on information sent from the communicator80, the temperature sensor50, and the memory160b.

The temperature to allow feeding or conveyance of the sheet P, that is, the reference temperature, varies depending on the type and the thickness of the sheet P. Accordingly, in order to allow the driver40to drive the conveyor to convey the sheet P based on the temperature of the pressure roller22detected by the temperature sensor50, it is necessary to detect the temperature of the pressure roller22precisely.

However, if the temperature sensor50is not positioned relative to a detection object, that is, the pressure roller22, precisely, or if a foreign substance51such as toner and paper dust adhered to the pressure roller22is accumulated between the pressure roller22and the temperature sensor50as shown inFIG. 5, the temperature sensor50may not detect the temperature of the pressure roller22precisely.FIG. 5is a sectional view of the temperature sensor50and the pressure roller22illustrating the foreign substance51.

FIG. 6is a graph showing a relation between the time and the temperature of the pressure roller22. If the temperature sensor50does not detect the temperature of the pressure roller22precisely, the temperature sensor50detects an abnormal temperature Tp2with detection error that is lower than a normal temperature Tp1without detection error as shown inFIG. 6. In the graph shown inFIG. 6, Th represents a control temperature of the fixing belt21and ΔTp1represents a temperature change per second in the normal temperature Tp1of the pressure roller22detected by the temperature sensor50without detection error.

Accordingly, if the controller160is configured to allow feeding or conveyance of the sheet P when the controller160determines that the fixing belt21has stored a sufficient amount of heat based on the temperature of the pressure roller22detected by the temperature sensor50, the controller160may delay start of printing and therefore may increase a waiting time for a user to wait for start of printing.

A description is provided of a configuration of a comparative fixing device.

The comparative fixing device includes an endless fixing belt that is heated quickly. However, if a power supply having a decreased voltage output is configured to supply power to the comparative fixing device, a heater incorporated in the comparative fixing device may receive a decreased amount of power from the power supply when peripherals of the comparative fixing device consume an increased amount of power. Accordingly, the fixing belt may suffer from shortage of heat from the heater and therefore the temperature of the fixing belt may decrease. Consequently, the fixing belt may not be heated to a desired temperature.

Additionally, a small sheet is conveyed over a center of the fixing belt in an axial direction thereof. Accordingly, after a plurality of small sheets is conveyed over the fixing belt continuously, both lateral ends of the fixing belt outboard from the center of the fixing belt in the axial direction thereof may overheat because the plurality of small sheets is not conveyed over both lateral ends of the fixing belt and therefore does not draw heat therefrom. Consequently, the overheated fixing belt may be damaged or broken.

In order to prevent overheating of both lateral ends of the fixing belt, a controller may control the heater based on a temperature of a pressure roller detected by a contact temperature sensor contacting the pressure roller.

However, the contact temperature sensor may include a downsized detection element to improve responsiveness. Hence, the contact temperature sensor may suffer from shifting from the pressure roller or releasing of pressure, resulting in detection error. If the temperature sensor detects the temperature of the pressure roller with detection error, the controller may delay control of the heater based on the detected temperature of the pressure roller, increasing the waiting time for the user to wait for start of printing. Further, the controller may cause the heater to overheat the fixing belt, resulting in damage and breakage of the fixing belt.

To address those circumstances, the controller160depicted inFIG. 4performs controls described below.

A description is provided of various exemplary controls performed by the controller160to determine storage of heat in the fixing belt21based on output of the temperature sensor50that detects the temperature of the pressure roller22.

At least two exemplary controls described below may be combined within an applicable range. Each of flowcharts shown inFIGS. 7 to 11 and 13is an example of a routine control performed by the controller160. Hence, other flowcharts may also be applicable within a scope of the present disclosure to achieve advantages thereof.

With reference toFIG. 7, a description is provided of a first exemplary control performed by the controller160.

FIG. 7is a flowchart showing control processes of the first exemplary control.

If the temperature sensor50detects the abnormal temperature Tp2of the pressure roller22with detection error as shown inFIG. 6, the controller160detects a temperature change ΔTp2per second in the temperature of the pressure roller22detected by the temperature sensor50in step S10. The controller160determines whether or not the temperature change ΔTp2per second is 1 degree centigrade or smaller per second for three times consecutively, for example, in step S11. If the controller160determines that the temperature change ΔTp2per second is not 1 degree centigrade or smaller per second for three times consecutively (NO in step S11), the controller160returns to step S10. Conversely, if the controller160determines that the temperature change ΔTp2per second is 1 degree centigrade or smaller per second for three times consecutively (YES in step S11), the arithmetic portion160aof the controller160depicted inFIG. 4calculates a difference ΔT between a detected temperature Sp2of the pressure roller22detected by the temperature sensor50, that is, a current temperature, and a reference temperature Sp1defining a temperature at which the controller160allows the driver40to drive the conveyor to convey the sheet P in step S12. In step S13, the memory160bof the controller160depicted inFIG. 4stores the difference ΔT. In step S14, the controller160adds the stored difference ΔT to the detected temperature Sp2, finishing the first exemplary control. The controller160allows the driver40to drive the conveyor or causes the driver40to be ready to drive the conveyor based on information, that is, a value, obtained by adding the stored difference ΔT to the detected temperature Sp2. According to this exemplary embodiment, a threshold for the temperature change ΔTp2per second is 1 degree centigrade per second. However, the threshold is not limited to 1 degree centigrade per second.

According to the first exemplary control, the controller160corrects the temperature of the pressure roller22detected by the temperature sensor50. Accordingly, even if the temperature sensor50does not detect the temperature of the pressure roller22precisely, the controller160prevents delay in start of printing due to control based on output from the temperature sensor50, shortening the waiting time for the user.

With reference toFIG. 8, a description is provided of a second exemplary control performed by the controller160.

FIG. 8is a flowchart showing control processes of the second exemplary control.

When the fixing device20is driven initially, that is, when the fixing device20is powered on as a main power supply of the image forming apparatus1is turned on, for example, if the temperature sensor50detects the abnormal temperature Tp2of the pressure roller22with detection error as shown inFIG. 6, the controller160starts the second exemplary control and determines whether or not the image forming apparatus1has received a print job in step S20. The print job defines a series of image forming processes to be performed by the image forming apparatus1upon receipt of an instruction from the user. If the controller160determines that the image forming apparatus1has received the print job (YES in step S20), the controller160finishes the second exemplary control. Conversely, if the controller160determines that the image forming apparatus1has not received the print job (NO in step S20), the controller160detects the temperature change ΔTp2per second in the temperature of the pressure roller22detected by the temperature sensor50in step S21. The controller160determines whether or not the temperature change ΔTp2per second is 1 degree centigrade or smaller per second for three times consecutively, for example, in step S22. If the controller160determines that the temperature change ΔTp2per second is not 1 degree centigrade or smaller per second for three times consecutively (NO in step S22), the controller160returns to step S21. Conversely, if the controller160determines that the temperature change ΔTp2per second is 1 degree centigrade or smaller per second for three times consecutively (YES in step S22), the arithmetic portion160aof the controller160calculates the difference ΔT between the detected temperature Sp2of the pressure roller22detected by the temperature sensor50, that is, the current temperature, and the reference temperature Sp1, that is, the temperature at which the controller160allows the driver40to drive the conveyor to convey the sheet P in step S23. In step S24, the memory160bof the controller160stores the difference ΔT. In step S25, the controller160adds the stored difference ΔT to the detected temperature Sp2, finishing the second exemplary control. The controller160allows the driver40to drive the conveyor or causes the driver40to be ready to drive the conveyor based on information, that is, a value, obtained by adding the stored difference ΔT to the detected temperature Sp2.

According to the second exemplary control, the controller160corrects the temperature of the pressure roller22detected by the temperature sensor50. Accordingly, even if the temperature sensor50does not detect the temperature of the pressure roller22precisely, the controller160prevents delay in start of printing due to control based on output from the temperature sensor50, shortening the waiting time for the user.

With reference toFIG. 9, a description is provided of a third exemplary control performed by the controller160.

FIG. 9is a flowchart showing control processes of the third exemplary control.

When the fixing device20is driven initially, that is, when the fixing device20or the image forming apparatus1is powered on, if the temperature sensor50detects the abnormal temperature Tp2of the pressure roller22with detection error as shown inFIG. 6, the controller160starts the third exemplary control and determines whether or not the image forming apparatus1has received a print job that requests the fixing belt21to store heat in step S30. The print jot that requests the fixing belt21to store heat (hereinafter referred to as the print job requesting heat storage) defines a print instruction or the like, for example. If the controller160determines that the image forming apparatus1has not received the print job requesting heat storage (NO in step S30), the controller160finishes the third exemplary control. Conversely, if the controller160determines that the image forming apparatus1has received the print job requesting heat storage (YES in step S30), the controller160detects the temperature change ΔTp2per second in the temperature of the pressure roller22detected by the temperature sensor50in step S31. The controller160determines whether or not the temperature change ΔTp2per second is 1 degree centigrade or smaller per second for three times consecutively, for example, in step S32. If the controller160determines that the temperature change ΔTp2per second is not 1 degree centigrade or smaller per second for three times consecutively (NO in step S32), the controller160returns to step S31. Conversely, if the controller160determines that the temperature change ΔTp2per second is 1 degree centigrade or smaller per second for three times consecutively (YES in step S32), the arithmetic portion160aof the controller160calculates the difference ΔT between the detected temperature Sp2of the pressure roller22detected by the temperature sensor50, that is, the current temperature, and the reference temperature Sp1, that is, the temperature at which the controller160allows the driver40to drive the conveyor to convey the sheet P in step S33. In step S34, the memory160bof the controller160stores the difference ΔT. In step S35, the controller160adds the stored difference ΔT to the detected temperature Sp2, finishing the third exemplary control. The controller160allows the driver40to drive the conveyor or causes the driver40to be ready to drive the conveyor based on information, that is, a value, obtained by adding the stored difference ΔT to the detected temperature Sp2.

According to the third exemplary control, the controller160corrects the temperature of the pressure roller22detected by the temperature sensor50. Accordingly, even if the temperature sensor50does not detect the temperature of the pressure roller22precisely, the controller160prevents delay in start of printing due to control based on output from the temperature sensor50, shortening the waiting time for the user.

With reference toFIG. 10, a description is provided of a fourth exemplary control performed by the controller160.

FIG. 10is a flowchart showing control processes of the fourth exemplary control.

When the fixing device20is driven initially, that is, when the fixing device20or the image forming apparatus1is powered on, if the temperature sensor50detects the abnormal temperature Tp2of the pressure roller22with detection error as shown inFIG. 6, the controller160starts the fourth exemplary control and determines whether or not the image forming apparatus1has received a print job that requests the fixing belt21to store heat in step S40. The print job that requests the fixing belt21to store heat, that is, the print job requesting heat storage, defines a print instruction or the like, for example. If the controller160determines that the image forming apparatus1has not received the print job requesting heat storage (NO in step S40), the controller160finishes the fourth exemplary control. Conversely, if the controller160determines that the image forming apparatus1has received the print job requesting heat storage (YES in step S40), the controller160detects them temperature change ΔTp2per second in the temperature of the pressure roller22detected by the temperature sensor50in step S41. The controller160determines whether or not the temperature change ΔTp2per second is 1 degree centigrade or smaller per second for three times consecutively, for example, in step S42. If the controller160determines that the temperature change ΔTp2per second is not 1 degree centigrade or smaller per second for three times consecutively (NO in step S42), the controller160returns to step S41. Conversely, if the controller160determines that the temperature change ΔTp2per second is 1 degree centigrade or smaller per second for three times consecutively (YES in step S42), the controller160controls the driver40to drive the conveyor to convey the sheet P in step S43, thus finishing the fourth exemplary control.

According to the fourth exemplary control, the controller160corrects the temperature of the pressure roller22detected by the temperature sensor50. Accordingly, even if the temperature sensor50does not detect the temperature of the pressure roller22precisely, the controller160prevents delay in start of printing due to control based on output from the temperature sensor50, shortening the waiting time for the user.

With reference toFIG. 11, a description is provided of a fifth exemplary control performed by the controller160.

FIG. 11is a flowchart showing control processes of the fifth exemplary control.

When the fixing device20is driven initially, that is, when the fixing device20or the image forming apparatus1is powered on, if the temperature sensor50detects the abnormal temperature Tp2of the pressure roller22with detection error as shown inFIG. 6, the controller160starts the fifth exemplary control and determines whether or not the image forming apparatus1has received a print job that requests the fixing belt21to store heat in step S50. The print jot that requests the fixing belt21to store heat, that is, the print job requesting heat storage, defines a print instruction or the like, for example. If the controller160determines that the image forming apparatus1has not received the print job requesting heat storage (NO in step S50), the controller160finishes the fifth exemplary control. Conversely, if the controller160determines that the image forming apparatus1has received the print job requesting heat storage (YES in step S50), the controller160detects the temperature change ΔTp2per second in the temperature of the pressure roller22detected by the temperature sensor50in step S51. The controller160determines whether or not the temperature change ΔTp2per second is 1 degree centigrade or smaller per second for three times consecutively, for example, in step S52. If the controller160determines that the temperature change ΔTp2per second is not 1 degree centigrade or smaller per second for three times consecutively (NO in step S52), the controller160returns to step S51. Conversely, if the controller160determines that the temperature change ΔTp2per second is 1 degree centigrade or smaller per second for three times consecutively (YES in step S52), the arithmetic portion160aof the controller160calculates the difference ΔT between the detected temperature Sp2of the pressure roller22detected by the temperature sensor50, that is, the current temperature, and the reference temperature Sp1, that is, the temperature at which the controller160allows the driver40to drive the conveyor to convey the sheet P in step S53. In step S54, the memory160bof the controller160stores the difference ΔT. In step S55, the controller160determines that the fixing belt21has stored heat based on a total value obtained by adding the stored difference ΔT to the detected temperature Sp2, thus finishing the fifth exemplary control.

According to the fifth exemplary control, the controller160corrects the temperature of the pressure roller22detected by the temperature sensor50. Accordingly, even if the temperature sensor50does not detect the temperature of the pressure roller22precisely, the controller160prevents delay in start of printing due to control based on output from the temperature sensor50, shortening the waiting time for the user.

A description is provided of a comparative control.

FIG. 12is a flowchart showing the comparative control. In a comparative fixing device configured to control heating of a fixing belt by estimating heating of the fixing belt based on a temperature of a pressure roller detected by a temperature sensor, if the temperature of the pressure roller detected by the temperature sensor exceeds 180 degrees centigrade, for example, a controller degrades productivity of the comparative fixing device to suppress heating of the fixing belt, thus preventing damage to the fixing belt. For example, as shown inFIG. 12illustrating the comparative control, the temperature sensor detects the temperature of an outer circumferential surface of the pressure roller in step S60. The controller determines whether or not the temperature of the pressure roller detected by the temperature sensor is a temperature at which it is necessary to suppress temperature increase of the pressure roller, for example, 180 degrees centigrade or higher, in step S61. If the controller determines that the temperature of the pressure roller detected by the temperature sensor is not 180 degrees centigrade or higher (NO in step S61), the controller returns to step S60. Conversely, if the controller determines that the temperature of the pressure roller detected by the temperature sensor is 180 degrees centigrade or higher (YES in step S61), the controller decreases productivity of printing to 80 percent of a current productivity in step S62, thus finishing the comparative control.

According to the comparative control shown inFIG. 12, even if the temperature sensor detects the temperature of the pressure roller with detection error, the comparative fixing device controls heating of the fixing belt by estimating the temperature of the fixing belt based on the temperature of the pressure roller detected by the temperature sensor. However, the controller does not detect overheating of the fixing belt precisely, resulting in damage or breakage of the fixing belt. Additionally, even if both lateral ends of the fixing belt in an axial direction thereof overheat after a plurality of sheets is conveyed over a center of the fixing belt in the axial direction thereof because the plurality of sheets is not conveyed over both lateral ends of the fixing belt and therefore does not draw heat from both lateral ends of the fixing belt, the comparative fixing device controls heating of the fixing belt by estimating the temperature of the fixing belt based on the temperature of the pressure roller detected by the temperature sensor. However, the controller does not detect overheating of the fixing belt precisely, resulting in damage or breakage of the fixing belt. To address this circumstance, the controller160shown inFIG. 4performs control processes described below.

With reference toFIG. 13, a description is provided of a sixth exemplary control performed by the controller160.

FIG. 13is a flowchart showing control processes of the sixth exemplary control.

If the controller160performs any one of the first to fifth exemplary controls, the controller160starts the sixth exemplary control and the temperature sensor50detects the temperature of the outer circumferential surface of the pressure roller22in step S70. In step S71, the controller160adds the difference ΔT stored in the memory160bto the temperature of the pressure roller22detected by the temperature sensor50. In step S72, the controller160determines whether or not a total value obtained by adding the stored difference ΔT to the detected temperature of the pressure roller22is a temperature at which it is necessary to suppress temperature increase of the pressure roller22, for example, 180 degrees centigrade or higher. If the controller160determines that the total value is not 180 degrees centigrade or higher (NO in step S72), the controller160returns to step S70. Conversely, if the controller160determines that the total value is 180 degrees centigrade or higher (YES in step S72), the controller160decreases productivity of printing to 80 percent of a current productivity in step S73, thus finishing the sixth exemplary control.

According to the sixth exemplary control, the controller160corrects the temperature of the pressure roller22detected by the temperature sensor50. Accordingly, even if the temperature sensor50does not detect the temperature of the pressure roller22precisely, the controller160prevents overheating of both lateral ends of the fixing belt21in an axial direction thereof, thus preventing damage and breakage of the fixing belt21.

The construction and configuration of the fixing device20are not limited to those of the exemplary embodiments described above. The material and dimension of each of the components described above are examples and therefore various materials and dimensions thereof may be selectively used. For example, the fixing device20shown inFIG. 2employs a center conveyance method in which the sheet P is conveyed over a center of the fixing belt21in the axial direction thereof. Alternatively, the fixing device20may employ a lateral end conveyance method in which the sheet P is conveyed along one lateral edge of the fixing belt21in the axial direction thereof. The exemplary embodiments described above are also applicable to the fixing device20employing the lateral end conveyance method.

A description is provided of advantages of the fixing device20.

As shown inFIG. 2, the fixing device20includes a fixing rotator (e.g., the fixing belt21) rotatable in a predetermined direction of rotation and a nip formation pad (e.g., the nip formation pad24) disposed inside the fixing rotator. An opposed rotator (e.g., the pressure roller22) is pressed against the nip formation pad via the fixing rotator to form the fixing nip N between the fixing rotator and the opposed rotator. A heater (e.g., the halogen heater23) heats the fixing rotator directly in a circumferential span on the fixing rotator other than the fixing nip N. As a recording medium (e.g., a sheet P) bearing an unfixed toner image (e.g., a toner image T) is conveyed through the fixing nip N, the toner image is fixed on the recording medium. A temperature detector (e.g., the temperature sensor50) contacting the opposed rotator detects a temperature of the opposed rotator. As shown inFIGS. 1 and 4, a controller (e.g., the controller160) is operatively connected to the temperature detector and a driver (e.g., the driver40) to control the driver to drive a conveyor (e.g., the feed roller11and the registration roller pair12) to convey the recording medium to the fixing nip N based on the temperature of the opposed rotator detected by the temperature detector. The controller allows the driver to drive the conveyor or causes the driver to be ready to drive the conveyor when change in the detected temperature of the opposed rotator per unit time reaches a predetermined threshold.

The controller controls the driver to drive the conveyor based on output of the temperature detector contacting the opposed rotator. Accordingly, the fixing device20prevents increase in the waiting time for the user to wait for start of printing and overheating of the fixing rotator due to detection error by the temperature detector.

According to the exemplary embodiments described above, the fixing belt21serves as a fixing rotator. Alternatively, a fixing roller, a fixing film, a fixing sleeve, or the like may be used as a fixing rotator. Further, the pressure roller22serves as an opposed rotator. Alternatively, a pressure belt or the like may be used as an opposed rotator.

The present disclosure has been described above with reference to specific exemplary embodiments. Note that the present disclosure is not limited to the details of the embodiments described above, but various modifications and enhancements are possible without departing from the spirit and scope of the disclosure. It is therefore to be understood that the present disclosure may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative exemplary embodiments may be combined with each other and/or substituted for each other within the scope of the present disclosure.