Fixing device

Abstract

To provide a fixing device capable of easily detecting poor contact of a temperature sensor.SOLUTION: According to an embodiment, a fixing device includes a fixing unit, a temperature sensor, a memory and a controller. The fixing unit includes: a fixing member with which a medium transferred with a developer image comes into contact; and a heat source which supplies heat to the fixing member. The temperature sensor measures the temperature through a detection unit that contacts the surface of the fixing member which comes into contact with the medium. The memory stores a temperature estimation value that estimates a temperature of the fixing member, and a detection temperature detected by the temperature sensor. The controller determines poor contact between the detection unit of the temperature sensor and the surface of the fixing member on the basis of a difference between the temperature estimation value stored in the memory and the detection temperature of the temperature sensor.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] Embodiments of the present invention relate to a fixing device.

Background Art

[0002] An image forming apparatus placed in a workplace or the like includes a fixing device that fixes a toner image on a print medium by applying heat and pressure to the print medium with a fixing unit. The fixing device has a temperature sensor that detects the temperature of the surface of a fixing rotating body (fixing member). The fixing device controls the surface temperature of the fixing member to reach a target value based on the detection signal of the temperature sensor.

[0003] In a conventional fixing device, a contact type temperature sensor may be used as a temperature sensor for detecting the temperature of the fixing member. The contact type temperature sensor can directly measure the temperature of the part where the detection part contacts. However, in the manufacturing process of the image forming apparatus, there may be a problem that the detection part of the contact type temperature sensor in the fixing device separates from the fixing member. In the conventional manufacturing process, an inspection method is implemented using a dedicated jig to inspect the contact state between the fixing member and the detection part of the temperature sensor. Such an inspection method using a dedicated jig has a problem of being time-consuming and costly.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a fixing device capable of easily detecting a poor contact of a temperature sensor.

Means for Solving the Problems

[0006] According to an embodiment, the fixing device includes a fixing unit, a temperature sensor, a memory, and a controller. The fixing unit has a fixing member that contacts the medium onto which the developer image is transferred and a heat source that supplies heat to the fixing member. The temperature sensor measures the temperature with a detection unit that contacts the surface of the fixing member where the medium contacts. The memory stores a temperature estimated value for estimating the temperature of the fixing member and a detected temperature detected by the temperature sensor. The controller determines a poor contact between the detection unit of the temperature sensor and the surface of the fixing member based on the difference between the temperature estimated value stored in the memory and the detected temperature detected by the temperature sensor.

Brief Description of the Drawings

[0007]

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DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an image forming apparatus including a fixing device according to an embodiment will be described with reference to the drawings. FIG. 1 is a diagram for explaining a configuration example of an image forming apparatus 1 including a fixing device according to the embodiment. The image forming apparatus 1 is, for example, a digital multifunction peripheral (MFP) that performs various processes such as image formation while conveying a recording medium such as a printing medium. The image forming apparatus 1 transfers a toner image formed by an electrophotographic method to a printing medium as a recording medium, and fixes the toner image on the printing medium with a fixing device.

[0009] The image forming apparatus 1 receives toner from a toner cartridge and prints an image on a printing medium with the received toner. The toner may be a single-color toner, or may be a color toner such as cyan, magenta, yellow, and black. Further, the toner may be a decolorizing toner that decolorizes when heat is applied.

[0010] As shown in FIG. 1, the image forming apparatus 1 includes a housing 11, a communication interface 12, a controller (system controller) 13, a heater control circuit 14, a display device 15, an operation device 16, a plurality of paper trays 17, a paper discharge tray 18, a conveyance mechanism 19, an image forming mechanism 20, a fixing device 21, a power conversion circuit 22, and a power supply voltage detection device 23.

[0011] The housing 11 is the main body of the image forming apparatus 1. The housing 11 houses a communication interface 12, a controller 13, a heater control circuit 14, a display device 15, an operation device 16, a plurality of paper trays 17, a paper discharge tray 18, a conveyance mechanism 19, an image forming mechanism 20, a fixing device 21, a power conversion circuit 22, and a power supply voltage detection device 23.

[0012] The communication interface 12 is an interface for communicating with other devices connected through a network. The communication interface 12 is used for communication with external devices. The external devices are, for example, a user terminal that instructs a print job, or a server as an external management device. The communication interface 12 is composed of, for example, a LAN connector or the like. The communication interface 12 may perform wireless communication with other devices according to standards such as Bluetooth (registered trademark) or Wi-fi (registered trademark).

[0013] The controller (system controller) 13 controls each part of the image forming apparatus 1 and executes data processing and the like. For example, the controller 13 is a computer including a processor, a memory, and various interfaces. The controller 13 performs control and data processing of each part by the processor executing a program stored in the memory. The controller 13 is connected to each part within the housing 11 through various internal interfaces.

[0014] The controller 13 generates a print job based on image data and the like received from an external device via the communication interface 12. The image data included in the print job is data indicating an image to be formed on the print medium P. The image data may be data for forming an image on one print medium P, or may be data for forming an image on a plurality of print media P. Further, the print job may include information indicating print conditions such as information indicating whether it is color printing or monochrome printing.

[0015] The controller 13 includes an engine controller that controls the operations of the conveyance mechanism 19, the image forming mechanism 20, and the fuser 21. For example, the controller 13 controls the conveyance of the print medium P by the conveyance mechanism 19. The controller 13 controls the formation of the developer image by the image forming mechanism 20 and the transfer of the developer image to the print medium P. The controller 13 controls the fixing of the developer image to the print medium P by the fuser 21. By controlling the operations of the conveyance mechanism 19, the image forming mechanism 20, and the fuser 21, the controller 13 forms an image of the image data included in the print job on the print medium P.

[0016] Note that the image forming apparatus 1 may be configured to include an engine controller separately from the controller 13. For example, the image forming apparatus 1 may be provided with an engine controller that controls at least one of the conveyance mechanism 19, the image forming mechanism 20, the fuser 21, etc. separately from the controller 13. The engine controller provided separately from the controller 13 may be configured to acquire information necessary for control from the controller 13.

[0017] The heater control circuit 14 is a temperature control device that controls the energization of the heater 73 (center heater 731 and side heater 732) provided in the fuser 21 described later based on the control of the controller 13. The heater control circuit 14 generates energization powers PC1 and PC2 for energizing the heater 73 of the fuser 21. The heater control circuit 14 supplies the energization power PC1 to the center heater 731 and supplies the energization power PC2 to the side heater 732. A detailed description of the heater control circuit 14 will be given later.

[0018] The display device 15 includes a display that displays an image according to an image signal input from a display control unit such as the controller 13 or a graphic controller. For example, the display device 15 displays a guide or the like according to an instruction from the controller 13. Further, the display device 15 displays a setting screen for various settings in the image forming apparatus 1 on the display.

[0019] The operation device 16 supplies an operation signal corresponding to an operation on the operation device to the controller 13. The operation device is, for example, a touch sensor, a numeric keypad, a power key, various function keys, or a keyboard. The touch sensor acquires information indicating a specified position within a certain area. The touch sensor may be configured as a touch panel integrally with the display device 15. Note that the display device 15 and the operation device 16 may be provided on an operation panel as a user interface.

[0020] The power conversion circuit 22 supplies a DC voltage to each part within the image forming apparatus 1 using an AC voltage from an AC power source such as an external power source. For example, the power conversion circuit 22 generates DC voltages Vdd and Vdc from the AC voltage of the AC power source AC. The power conversion circuit 22 supplies the DC voltage Vdd to the controller 13 and supplies the DC power source voltage Vdc to the heater control circuit 14. Further, the power conversion circuit 22 supplies a DC voltage necessary for image formation, which is generated from the AC voltage of the AC power source AC, to the image forming mechanism 20. The power conversion circuit 22 supplies a DC voltage necessary for conveyance of the print medium P, which is generated from the AC voltage of the AC power source AC, to the conveyance mechanism 19.

[0021] The power source voltage detection device 23 detects the voltage value of the AC voltage of the AC power source AC supplied from an external power source and outputs a power source voltage detection result Sv. The configuration of the power source voltage detection device 23 is not particularly limited. Any device that can detect the power source voltage value may be used. The power source voltage detection device 23 may detect the voltage value of the DC power source voltage Vdc converted by the power conversion circuit 22 instead of the voltage value of the AC voltage of the AC power source AC supplied from the power source. The power source voltage detection result Sv output by the power source voltage detection device 23 is input to the controller 13.

[0022] The controller 13 stores the power supply voltage value indicated by the power supply voltage detection result Sv. Further, the controller 13 may transmit the power supply voltage value indicated by the power supply voltage detection result Sv to the host computer via the network by the communication interface 12. In this case, the controller 13 may store transmission destination information such as the network address of the host computer in a non-volatile memory or the like. Further, the controller 13 may transmit the power supply voltage value indicated by the power supply voltage detection result Sv to another image forming apparatus connected via the network by the communication interface 12. Further, the controller 13 may transmit the power supply voltage value indicated by the power supply voltage detection result Sv to another image forming apparatus connected to the image forming apparatus 1 via an interface.

[0023] Next, the configuration of the conveyance system in the image forming apparatus 1 will be described. The plurality of paper trays 17 are cassettes for accommodating the print medium P. The paper tray 17 is configured to be able to supply the print medium P from the outside of the housing 11. For example, the paper tray 17 is configured to be pullable out from the housing 11. The paper discharge tray 18 is a tray for supporting the print medium P discharged from the image forming apparatus 1.

[0024] The conveyance mechanism 19 is a mechanism for conveying the print medium P in the image forming apparatus 1. As shown in FIG. 1, the conveyance mechanism 19 includes a plurality of conveyance paths. For example, the conveyance mechanism 19 includes a paper feed conveyance path 31 and a paper discharge conveyance path 32.

[0025] The paper feed conveyance path 31 and the paper discharge conveyance path 32 are each constituted by a plurality of motors, a plurality of rollers, and a plurality of guides. The plurality of motors rotate the shaft based on the control of the controller 13, thereby rotating the rollers interlocked with the rotation of the shaft. The plurality of rollers move the print medium P by rotating. The plurality of guides control the conveyance direction of the print medium P.

[0026] The paper feed conveyance path 31 takes in the print medium P from the paper tray 17 and supplies the taken-in print medium P to the image forming mechanism 20. The paper feed conveyance path 31 includes pickup rollers 33 corresponding to each paper tray. Each pickup roller 33 takes in the print medium P on the paper tray 17 into the paper feed conveyance path 31, respectively.

[0027] The paper discharge conveyance path 32 is a conveyance path for discharging the print medium P on which an image has been formed to the outside of the housing 11. The print medium P discharged by the paper discharge conveyance path 32 is supported by the paper discharge tray 18.

[0028] Next, the configuration of the image forming mechanism 20 in the image forming apparatus 1 will be described. The image forming mechanism 20 forms an image on the print medium P. The image forming mechanism 20 forms an image on the print medium P based on the print job generated by the controller 13. The image forming mechanism 20 includes a plurality of process units (image forming stations) 41, a plurality of exposure units 42, and a transfer mechanism 43. The image forming mechanism 20 includes an exposure unit 42 for each process unit 41. Since the plurality of process units 41 and the plurality of exposure units 42 may each have the same configuration, one process unit 41 and one exposure unit 42 will be described respectively.

[0029] First, the process unit 41 will be described. The process unit 41 forms a toner image. For example, the plurality of process units 41 are provided for each type of toner. For example, the plurality of process units 41 correspond to color toners such as cyan, magenta, yellow, and black, respectively. Specifically, a toner cartridge having different color toners is connected to each process unit 41.

[0030] The toner cartridge includes a toner storage container and a toner delivery mechanism. The toner storage container is a container for storing toner. The toner delivery mechanism is a mechanism constituted by a screw or the like for sending out the toner in the toner storage container.

[0031] The process unit 41 includes a photosensitive drum 51, a charger 52, a developing device 53, etc. The photosensitive drum 51 is a photosensitive member including a cylindrical drum and a photosensitive layer formed on the outer peripheral surface of the drum. The photosensitive drum 51 rotates at a constant speed by a driving mechanism.

[0032] The charger 52 uniformly charges the surface of the photosensitive drum 51. For example, the charger 52 applies a voltage (development bias voltage) to the photosensitive drum 51 using a charging roller, thereby charging the photosensitive drum 51 to a uniform negative potential (contrast potential). The charging roller rotates by the rotation of the photosensitive drum 51 while applying a predetermined pressure to the photosensitive drum 51.

[0033] The developing device 53 is a device that attaches toner to the photosensitive drum 51. The developing device 53 includes a developer container, an agitation mechanism, a developing roller, a doctor blade, an auto toner control (ATC) sensor, etc.

[0034] The developer container is a container that receives and stores the toner sent out from the toner cartridge. A carrier is stored in the developer container in advance. The toner sent out from the toner cartridge is agitated with the carrier by an agitation mechanism, thereby constituting a developer in which the toner and the carrier are mixed. The carrier is stored in the developer container during the manufacture of the developing device 53.

[0035] The developing roller rotates in the developer container, thereby attaching the developer to its surface. The doctor blade is a member disposed at a predetermined interval from the surface of the developing roller. The doctor blade removes a part of the developer attached to the surface of the rotating developing roller. Thereby, a layer of developer having a thickness corresponding to the interval between the doctor blade and the surface of the developing roller is formed on the surface of the developing roller.

[0036] The ATC sensor has, for example, a coil and is a magnetic flux sensor that detects the voltage value generated in the coil. The detection voltage of the ATC sensor varies depending on the density of the magnetic flux from the toner in the developer container. That is, the controller 13 determines the concentration ratio (toner concentration ratio) of the toner remaining in the developer container with respect to the carrier based on the detection voltage of the ATC sensor. The controller 13 operates the motor that drives the toner cartridge delivery mechanism based on the toner concentration ratio, and sends toner from the toner cartridge to the developer container of the developing device 53.

[0037] Next, the configuration of the exposure device 42 will be described. The exposure device 42 includes a plurality of light-emitting elements. The exposure device 42 forms a latent image on the photosensitive drum 51 by irradiating light from the light-emitting elements onto the charged photosensitive drum 51. The light-emitting elements are, for example, light-emitting diodes (LEDs) or the like. One light-emitting element is configured to irradiate light at one point on the photosensitive drum 51. The plurality of light-emitting elements are arranged in the main scanning direction, which is a direction parallel to the rotation axis of the photosensitive drum 51.

[0038] The exposure device 42 forms a latent image for one line on the photosensitive drum 51 by irradiating light onto the photosensitive drum 51 with a plurality of light-emitting elements arranged in the main scanning direction. Further, the exposure device 42 forms latent images for a plurality of lines by continuously irradiating light onto the rotating photosensitive drum 51.

[0039] In the above configuration, when light is irradiated from the exposure device 42 onto the surface of the photosensitive drum 51 charged by the charger 52, an electrostatic latent image is formed. When the layer of the developer formed on the surface of the developing roller approaches the surface of the photosensitive drum 51, the toner contained in the developer adheres to the latent image formed on the surface of the photosensitive drum 51. Thereby, a toner image is formed on the surface of the photosensitive drum 51.

[0040] Next, the configuration of the transfer mechanism 43 will be described. The transfer mechanism 43 is configured to transfer the toner image formed on the surface of the photosensitive drum 51 to the printing medium P. The transfer mechanism 43 transfers the toner image formed on the surface of the photosensitive drum 51 to the primary transfer belt 61, and transfers the toner image transferred to the primary transfer belt 61 to the printing medium P.

[0041] Further, the transfer mechanism 43 includes, for example, a primary transfer belt 61, a secondary transfer opposing roller 62, a plurality of primary transfer rollers 63, and a secondary transfer roller 64. In the configuration example shown in FIG. 1, the primary transfer belt 61 is an endless belt wound around the secondary transfer opposing roller 62 and a plurality of winding rollers. The inner surface (inner peripheral surface) of the primary transfer belt 61 contacts the secondary transfer opposing roller 62 and the plurality of winding rollers, and the outer surface (outer peripheral surface) thereof faces the photosensitive drum 51 of the process unit 41.

[0042] The secondary transfer opposing roller 62 is rotated by a motor. By rotating, the secondary transfer opposing roller 62 conveys the primary transfer belt 61 in a predetermined conveyance direction. The plurality of winding rollers are configured to be rotatable freely. The plurality of winding rollers rotate according to the movement of the primary transfer belt 61 by the secondary transfer opposing roller 62.

[0043] The plurality of primary transfer rollers 63 are configured to bring the primary transfer belt 61 into contact with the photosensitive drum 51 of the process unit 41. The plurality of primary transfer rollers 63 are provided corresponding to the photosensitive drums 51 of the plurality of process units 41. Specifically, the plurality of primary transfer rollers 63 are provided at positions (primary transfer positions) where they face each other with the photosensitive drum 51 of the corresponding process unit 41 and the primary transfer belt 61 interposed therebetween. The primary transfer roller 63 contacts the inner peripheral surface side of the primary transfer belt 61 and displaces the primary transfer belt 61 toward the photosensitive drum 51 side. Thereby, the outer peripheral surface of the primary transfer belt 61 is brought into contact with the photosensitive drum 51.

[0044] The secondary transfer roller 64 is provided at a position (secondary transfer position) facing the primary transfer belt 61. The secondary transfer roller 64 contacts the outer peripheral surface of the primary transfer belt 61 and applies pressure thereto. Thereby, a transfer nip is formed in which the outer peripheral surface of the secondary transfer roller 64 and the outer peripheral surface of the primary transfer belt 61 are in close contact. When the printing medium P passes through the transfer nip, the secondary transfer roller 64 presses the printing medium P passing through the transfer nip against the outer peripheral surface of the primary transfer belt 61.

[0045] The secondary transfer roller 64 and the secondary transfer opposing roller 62 rotate to convey the printing medium P supplied from the paper feed conveyance path 31 while sandwiching it. Thereby, the printing medium P passes through the transfer nip.

[0046] In the above configuration, when the outer peripheral surface of the primary transfer belt 61 contacts the photosensitive drum 51, the toner image formed on the surface of the photosensitive drum is transferred to the outer peripheral surface of the primary transfer belt 61. When the image forming mechanism 20 includes a plurality of process units 41, the primary transfer belt 61 receives the toner image from the photosensitive drums 51 of the plurality of process units 41. The toner image transferred to the outer peripheral surface of the primary transfer belt 61 is conveyed by the primary transfer belt 61 to the transfer nip where the outer peripheral surface of the secondary transfer roller 64 and the outer peripheral surface of the primary transfer belt 61 are in close contact. When the printing medium P is present in the transfer nip, the toner image transferred to the outer peripheral surface of the primary transfer belt 61 is transferred to the printing medium P at the transfer nip.

[0047] Next, the configuration of the fixing device 21 in the image forming apparatus 1 will be described. The fixing device 21 fixes the toner image to the printing medium P to which the toner image has been transferred. The fixing device 21 operates based on the control of the controller 13. The fixing device according to the embodiment is assumed to be a device including a fixing device 21, a heater control circuit 14, and a controller 13. The fixing device 21 includes a fixing rotating body as a fixing member, a pressing member, a heating member (heat source), and a temperature sensor. As the fixing device applied to the fixing device according to the embodiment, various configurations can be possible. Here, FIG. 1 shows a first configuration example of the fixing device 21.

[0048] In the first configuration example shown in FIG. 1, the fixing device 21 includes a heat roller 71, a pressure roller 72, a heater 73, a temperature sensor 74, and the like. The heat roller 71 is an example of a rotating body for fixing (fixing member). The pressure roller 72 is an example of a pressing member. The heater 73 is an example of a heating member (heat source). The fixing device 21 of the first configuration example includes a heater 73 having a plurality of heat sources. In the first configuration example, the heater 73 includes a heater (center heater) 731 which is an example of a first heat source and a heater (side heater) 732 which is an example of a second heat source.

[0049] Also, the temperature sensor 74 is an example of a temperature sensor that detects the temperature of the surface of the heat roller 71. In the present embodiment, the fixing device 21 has a plurality of temperature sensors as the temperature sensor 74. Each temperature sensor 74 has a detection part (contact part) that contacts the surface of the heat roller 71, and detects the temperature of the part where the detection part contacts. In the first configuration example, the temperature sensor 74 includes a temperature sensor (center temperature sensor, first temperature sensor) 741 and a temperature sensor (side temperature sensor, second temperature sensor) 742. The detection part of the temperature sensor 741 contacts the central region on the surface of the heat roller 71. The detection part of the temperature sensor 742 contacts the side region on the surface of the heat roller 71.

[0050] FIG. 2 is a cross-sectional view showing a configuration example around the heat roller 71 in the fixing device 21 of the first configuration example shown in FIG. 1. The heat roller 71 is a rotating body for fixing that rotates while being heated by the heater 73. The heat roller 71 has a metal core bar formed in a hollow shape and an elastic layer formed on the outer periphery of the core bar.

[0051] The diameter of the heat roller 71 is, for example, φ30 mm. The core metal is made of aluminum with a thickness of, for example, 0.6 mm. The peripheral speed of the heat roller 71 is, for example, 210 mm / s. The elastic layer is made of, for example, a fluororesin (tetrafluoroethylene resin). The values of the diameter of the heat roller 71, the thickness of the core metal, the peripheral speed, and the raw material names of the core metal and the elastic layer described above are just examples and are not limited thereto.

[0052] The heat roller 71 is heated inside the core metal formed in a hollow shape by a heater 73 as a heating member (heat source) disposed inside the core metal. The heat applied inside the core metal is transmitted to the surface of the heat roller 71 (the surface of the elastic layer), which is the outside of the core metal. Note that the fixing rotator may be configured as an endless belt.

[0053] The press roller 72 is provided at a position facing the heat roller 71. The press roller 72 has a core metal formed of metal with a predetermined outer diameter and an elastic layer formed on the outer periphery of the core metal. The diameter of the press roller 72 is, for example, φ30 mm. The elastic layer of the press roller 72 is made of, for example, silicone rubber or fluororubber.

[0054] The press roller 72 applies pressure to the heat roller 71 by the stress applied from the tension member. The pressure is, for example, 150 N. The values of the diameter and pressure of the press roller 72, as well as the raw material names, are just examples and are not limited thereto. When pressure is applied from the press roller 72 to the heat roller 71, a nip (fixing nip) where the press roller 72 and the heat roller 71 are in close contact is formed. The press roller 72 rotates by a motor. By rotating, the press roller 72 moves the printing medium P that has entered the fixing nip and presses the printing medium P against the heat roller 71. Note that the heat roller 71 and the press roller 72 may each have a release layer on their surfaces.

[0055] The heater 73 is composed of heating elements as a plurality of heat sources that generate heat by the electric power supplied from the heater control circuit 14. The heater 73 in the fixing device 21 of the first configuration example shown in FIGS. 1 and 2 has a center heater (first heat source) 731 and a side heater (second heat source) 732 as two heat sources (heating elements). The center heater 731 and the side heater 732 are, for example, halogen lamp heaters including halogen lamps.

[0056] The heater 73 in the fixing device 21 of the first configuration example is composed of two heaters, the center heater 731 and the side heater 732. The center heater 731 heats a center region (first region) C that is the central portion in the rotation axis direction of the heat roller 71. The side heater 732 heats a side region (second region) S that is the peripheral portion other than the central portion in the rotation axis direction of the heat roller 71. The print medium P is conveyed in the conveyance direction F shown in FIG. 2. For example, the center region C and the side region S may be set according to the size of the medium used as the print medium P.

[0057] The center heater 731 and the side heater 732 generate heat by the electric power supplied under the control of the controller 13 respectively. The power consumption of the center heater 731 and the side heater 732 is, for example, 600 W. When the controller 13 executes the fixing process on the narrow-width print medium P in the rotation axis direction (conveyance direction F of the print medium P) of the heat roller 71, the controller 13 heats the center region C of the heat roller 71. When the controller 13 heats the center region C of the heat roller 71, the controller 13 operates the center heater 731 without operating the side heater 732 by the heater control circuit 14.

[0058] Also, when the controller 13 executes the fixing process on the wide-width print medium P in the rotation axis direction (conveyance direction F of the print medium P) of the heat roller 71, the controller 13 heats the entire heat roller 71 (both the center region C and the side region S). When the controller 13 heats the entire heat roller 71, the controller 13 operates both the center heater 731 and the side heater 732 by the heater control circuit 14.

[0059] The temperature sensors (first temperature sensor) 741 and the temperature sensors (second temperature sensor) 742 have a detection part (contact part) that contacts the surface of the heat roller 71, and detect the temperature of the part where the detection part contacts. The temperature sensors 741 and 742 are, for example, thermistors. The temperature sensors 741 and 742 are arranged in parallel with the rotation axis of the heat roller 71. In the first configuration example shown in FIG. 2, the temperature sensor 741 detects the temperature of the center region (central part when divided into three in the rotation axis direction) C in the rotation axis direction of the heat roller 71. The temperature sensor 742 detects the temperature of the side region (any side part when divided into three in the rotation axis direction) S in the rotation axis direction of the heat roller 71.

[0060] Each of the temperature sensors 741, 742 has a detection part that contacts the surface of the heat roller 71 respectively. The center temperature sensor 741 detects the temperature of the center region C of the heat roller 71 when the detection part contacts the surface of the center region C of the heat roller 71. The side temperature sensor 742 detects the temperature of the side region S of the heat roller 71 when the detection part contacts the surface of the side region S of the heat roller 71.

[0061] Each of the temperature sensors 741, 742 supplies a temperature detection result signal indicating the temperature detection result to the controller 13. When heating the center region C of the heat roller 71, the controller 13 operates the center heater 731 based on the temperature detected by the temperature sensor 741. When heating the entire heat roller 71, the controller 13 operates the center heater 731 and the side heater 732 based on the temperatures detected by the temperature sensors 741, 742.

[0062] The heat roller 71 and the press roller 72 apply heat and pressure controlled within a predetermined temperature range to the print medium P passing through the fixing nip. The toner on the print medium P is fixed on the surface of the print medium P by the heat from the heat roller 71 and the pressure from the heat roller 71 and the press roller 72. Thereby, the toner image is fixed on the print medium P that has passed through the fixing nip. The print medium P that has passed through the fixing nip is introduced into the paper discharge conveyance path 32 and discharged to the outside of the housing 11.

[0063] Next, the configuration of the control system in the image forming apparatus 1 according to the embodiment will be described. FIG. 3 is a block diagram showing a configuration example of the control system in the image forming apparatus 1. As shown in FIG. 3, the image forming apparatus 1 connects a communication interface 12, a heater control circuit 14, a display device 15, an operation device 16, a conveyance mechanism 19, an image forming mechanism 20, a fixing device 21, etc. to a controller (system controller) 13.

[0064] The controller 13 includes a processor 81, a ROM (Read Only Memory) 82, a RAM (Random Access Memory) 83, and a data memory 84. The controller 13 constitutes a computer by the processor 81, the ROM 82, the RAM 83, and the data memory 84. Further, the controller 13 may be provided with an ASIC or the like which is a processor for image processing.

[0065] The processor 81 corresponds to the central part of the computer as the controller 13. The processor 81 controls each part of the image forming apparatus 1 according to an operating system or an application program. The processor 81 is, for example, a CPU (Central Processing Unit).

[0066] ROM 82 and RAM 83 correspond to the main memory portion of the computer as the controller 13. ROM 82 is a non-volatile memory area, and RAM 83 is a volatile memory area. ROM 82 stores an operating system or an application program. ROM 82 stores control data necessary for the processor 81 to execute processes for controlling each part. RAM 83 is used as a work area where data is appropriately rewritten by the processor 81. RAM 83 has, for example, a work area for storing image data.

[0067] The data memory 84 is composed of a rewritable non-volatile memory. The data memory 84 corresponds to the auxiliary storage portion of the computer as the controller 13. The data memory 84 is composed of a storage device such as, for example, an EEPROM (registered trademark) (Electric Erasable Programmable Read-Only Memory), an HDD (Hard Disc Drive), or an SSD (Solid State Drive). The data memory 84 stores data such as setting data used by the processor 81 to perform various processes. The data memory 84 stores data generated by the processes executed by the processor 81. The data memory 84 may store an application program.

[0068] The controller 13 controls the image forming mechanism 20. For example, the controller 13 controls each process unit 41, the exposure device 42, and the transfer mechanism 43. For example, the controller 13 controls the on / off of charging for the charger 52 of each process unit 41. The controller 13 controls the on / off of the laser light irradiated to the photosensitive drum 51 for the exposure device 42 of each process unit 41. Thereby, an electrostatic latent image is formed on the photosensitive drum 51.

[0069] Further, the controller 13 controls the turning on and off of the developing bias for the developing device 53 of each process unit 41. Thereby, the electrostatic latent image on the photoreceptor drum 51 is developed by the toner supplied from the developing device 53, and a toner image is formed on the photoreceptor drum 51. The controller 13 controls the primary transfer bias at each primary transfer position for the transfer mechanism 43. The toner image on the photoreceptor drum 51 is transferred to the primary transfer belt 61 at the primary transfer position. Further, the controller 13 controls the secondary transfer bias at the secondary transfer position for the transfer mechanism 43. Thereby, the toner image on the primary transfer belt 61 is transferred to the printing medium P.

[0070] Also, the controller 13 controls the fixing device including the fixing unit 21. The controller 13 controls the operations of the center heater 731 and the side heater 732 by the heater control circuit 14 according to the detection results of the temperature sensor 741 and the temperature sensor 742. The heater control circuit 14 controls the energization to the center heater 731 and the side heater 732 by operating according to the control instruction from the controller 13. Note that part or all of the configuration of the heater control circuit 14 described later may be a configuration included in the controller 13.

[0071] The heater control circuit 14 controls the energization to the center heater 731 and the side heater 732 so that the surface of the heat roller 71 reaches the set target temperature. For example, the controller 13 sets a target value (control target temperature) for the heater control circuit 14. The heater control circuit 14 supplies power to the center heater 731 while referring to the temperature detected by the temperature sensor 741 so that the center region C of the heat roller 71 reaches the center target value (for example, 160°C). The heater control circuit 14 supplies power to the side heater 732 while referring to the temperature detected by the temperature sensor 742 so that the side region S of the heat roller 71 reaches the side target value (for example, 155°C).

[0072] Further, when the temperature of the center region C of the heat roller 71 reaches the set center high-temperature stop temperature, the heater control circuit 14 cuts off the power supply to the center heater 731. When the temperature of the side region S of the heat roller 71 reaches the set side high-temperature stop temperature, the heater control circuit 14 cuts off the power supply to the side heater 732. The center high-temperature stop temperature and the side high-temperature stop temperature are set and corrected by the controller 13 in the heater control circuit 14.

[0073] Next, the control of the heater 73 of the fixing device 21 in the image forming apparatus 1 according to the embodiment will be described. The image forming apparatus 1 including the fixing device according to the present embodiment controls the heater 73 of the fixing device 21 by WAE (Weighted Average control with Estimate temperature) control. The WAE control is performed assuming that the heat transfer in the fixing device 21 is equivalently represented by the CR time constant of the electric circuit. In the WAE control, the heat capacity in the fixing device 21 is assumed to be C, the resistance of heat transfer is assumed to be R, and a circuit (referred to as a heat CR circuit) with a DC voltage source as the heat source is assumed.

[0074] That is, the heat capacity of the fixing device 21 in the heat CR circuit is replaced by the capacitor C. The resistance of heat transfer is replaced by the resistor R. The heat source is replaced by the DC voltage source. The heat CR circuit is a circuit that operates according to the input voltage pulse. The heat CR circuit operates by the input voltage pulse in which the energization and interruption from the DC voltage source are repeated based on the energization pulse. Such a heat CR circuit applies the heat generated as the output voltage to the heating member.

[0075] In the heat CR circuit, the values (C and R) of each element are set based on the amount of electricity supplied to the heating member and the heat capacity of the fixing rotator, etc. The amount of heat propagated on the surface of the fixing rotator, which is the control target, can be estimated based on the above-described heat CR circuit. The WAE control controls the amount of electricity supplied to the heating member based on the actual surface temperature of the fixing rotator estimated from the input energy to the fixing device, etc., by simulating it as a heat CR circuit. By such WAE control, the fixing device in the image forming apparatus 1 according to the embodiment controls the surface temperature of the fixing rotator to reach the target value.

[0076] Also, the image forming apparatus 1 can specify the actual input voltage (input energy) by the power supply voltage detection device 23. Thereby, the image forming apparatus 1 can perform operation control using the actual input voltage in the WAE control.

[0077] FIG. 4 is a diagram showing a configuration example of the heater control circuit 14 in the image forming apparatus 1 that performs WAE control according to the embodiment. In the configuration example shown in FIG. 4, the heater control circuit 14 controls the energization of the heater 73 of the fixing device 21. The heater control circuit 14 generates energization powers PC1 and PC2 for energizing the heater 73 of the fixing device 21. The heater control circuit 14 supplies power to the center heater 731 by the energization power PC1 and supplies power to the side heater 732 by the energization power PC2.

[0078] The heater control circuit 14 includes a temperature estimation unit 91, an estimation history holding unit 92, a high-frequency component extraction unit 93, a coefficient addition unit 94, a target temperature output unit 95, a difference comparison unit 96, a control signal generation unit 97, and a power supply circuit 98. Further, the temperature detection result Td from the temperature sensor 74 and the power supply voltage detection result Sv stored in the data memory 84 of the controller 13, etc., are input to the heater control circuit 14.

[0079] The temperature estimation unit 91 performs temperature estimation processing to estimate the temperature (WAE estimated value) on the surface of the heat roller 71. In the configuration example shown in FIG. 4, the temperature detection result Td, the power supply voltage detection result Sv, the estimation history PREV, and the energization pulse Ps from the temperature sensor 74 are input to the temperature estimation unit 91. The temperature estimation unit 91 estimates the WAE estimated value based on the temperature detection result Td, the power supply voltage detection result Sv, the estimation history PREV, and the energization pulse Ps. The temperature estimation unit 91 outputs the WAE estimated value, which is the estimated temperature estimation result EST.

[0080] The temperature estimation unit 91 estimates the amount of heat applied to the heat roller 71 by a thermal CR circuit in which the values of each element are set in advance based on the energization amount to the heater 73 and the heat capacity of the heat roller 71, etc. The temperature estimation unit 91 generates the temperature estimation result EST based on the estimated amount of heat applied to the heat roller 71, the temperature detection result Td, the power supply voltage detection result Sv, the estimation history PREV, and the energization pulse Ps. The temperature estimation unit 91 outputs the temperature estimation result EST to the estimation history holding unit 92 and the high-frequency component extraction unit 93.

[0081] In the present embodiment, the temperature estimation unit 91 estimates (calculates) the center WAE estimated value ct and the side WAE estimated value st as the temperature estimation result EST. The center WAE estimated value ct is an estimated value of the temperature on the surface in the center region C of the heat roller 71. The side WAE estimated value st is an estimated value of the temperature on the surface in the side region of the heat roller 71. The temperature estimation unit 91 supplies the center WAE estimated value ct and the side WAE estimated value st to the controller 13.

[0082] The estimation history holding unit 92 holds the history of the temperature estimation result EST. The estimation history holding unit 92 outputs the estimation history PREV, which is the history of the temperature estimation result EST (the past temperature estimation result EST), to the temperature estimation unit 91.

[0083] The high-frequency component extraction unit 93 performs a high-pass filter process to extract the high-frequency component of the temperature estimation result EST. The high-frequency component extraction unit 93 outputs the high-frequency component HPF, which is a signal indicating the extracted high-frequency component, to the coefficient addition unit 94.

[0084] The coefficient addition unit 94 performs a coefficient addition process which is a correction of the temperature detection result Td. The temperature detection result Td from the temperature sensor 74 and the high-frequency component HPF from the high-frequency component extraction unit 93 are input to the coefficient addition unit 94. The coefficient addition unit 94 corrects the temperature detection result Td based on the high-frequency component HPF. Specifically, the coefficient addition unit 94 multiplies the high-frequency component HPF by a preset coefficient and adds it to the temperature detection result Td to calculate a corrected temperature value WAE. The coefficient addition unit 94 outputs the corrected temperature value WAE to the difference comparison unit 96. Also, the coefficient addition unit 94 outputs the corrected temperature value WAE to the processor 81 of the controller 13 as well.

[0085] The target temperature output unit 95 outputs the set target temperature TGT to the difference comparison unit 96. The target temperature TGT is set by the controller 13 in the target temperature output unit 95. The difference comparison unit 96 performs a difference calculation process. The difference comparison unit 96 calculates a difference DIF between the target temperature TGT from the target temperature output unit 95 and the corrected temperature value WAE from the coefficient addition unit 94. The difference comparison unit 96 outputs the calculated difference DIF to the control signal generation unit 97.

[0086] The control signal generation unit 97 generates an energization pulse Ps which is a pulse signal for controlling the energization of the heater 73 based on the difference DIF. The control signal generation unit 97 outputs the energization pulse Ps to the power supply circuit 98 and the temperature estimation unit 91.

[0087] The power supply circuit 98 supplies energization powers PC1, PC2 to the heater 73 based on the energization pulse Ps. The power supply circuit 98 uses the DC power supply voltage Vdc supplied from the power conversion circuit 22 to energize the heater 73 of the fixing unit 21. The power supply circuit 98, for example, switches between a state where the DC power supply voltage Vdc from the power conversion circuit 22 is supplied to the heater 73 and a state where it is not supplied based on the energization pulse Ps. Thereby, the power supply circuit 98 supplies the energization powers PC1, PC2 to the heater 73. In other words, the power supply circuit 98 varies the energization time of the heater 73 of the fixing unit 21 according to the energization pulse Ps.

[0088] Note that a lighting control signal corresponding to the size of the printing medium P to be fixed is input from the processor 81 of the controller 13 to the power supply circuit 98. The power supply circuit 98 supplies the heater 73 with the energization power PC1, or both the energization powers PC1 and PC2, according to the lighting control signal from the processor 81, that is, according to the size of the printing medium P.

[0089] Also, the power supply circuit 98 may be integrally configured with the fixing device 21. The heater control circuit 14 may be configured to supply the energization pulse Ps to the power supply circuit of the heater 73 of the fixing device 21 instead of supplying the energization power PC to the heater 73.

[0090] As described above, the heater control circuit 14 adjusts the amount of electric power to the heater 73 of the fixing device 21 based on the heat capacity correction amount Cc, the temperature detection result Td, the power supply voltage detection result Sv, the estimated temperature history PREV, and the energization pulse Ps. Thereby, the heater control circuit 14 can control the power supplied to the heater 73 so that the surface temperature of the heat roller 71 becomes the target temperature.

[0091] Note that the temperature estimation unit 91, the estimated history holding unit 92, the high-frequency component extraction unit 93, the coefficient addition unit 94, the target temperature output unit 95, the difference comparison unit 96, and the control signal generation unit 97 of the heater control circuit 14 may each be configured by an electric circuit or may be configured by software. Also, part or all of the heater control circuit 14 may be a configuration provided in the controller 13. For example, the controller 13 may be configured to calculate (estimate) the center WAE estimated value and the side WAE estimated value as the WAE estimated value.

[0092] In addition, as the heat capacity C of the fixing device used in the WAE control, the design reference value may be used. In the WAE control using the design reference value, since there may be variations in the heat capacity of the fixing device for each machine body, a heat capacity correction amount Cc for the heat capacity C may be set. For example, the image forming apparatus 1 may provide a correction amount table indicating the heat capacity correction amount Cc as the correction amount for the heat capacity C in the data memory 84. The correction amount table stores the heat capacity correction amount corresponding to the temperature difference set for each machine body of the image forming apparatus 1. The temperature difference is the difference between the temperature of the heater of the fixing device 21 estimated by setting the heat capacity correction amount to "0" by the heater control circuit 14 and the temperature of the heater measured by actual measurement.

[0093] When the heater control circuit 14 estimates the temperature taking into account the heat capacity correction amount Cc, the heater control circuit 14 acquires the heat capacity correction amount Cc of the image forming apparatus 1 based on the correction amount table from the controller 13. When the heat capacity correction amount Cc is input to the heater control circuit 14, the temperature estimation unit 91 estimates the WAE estimated value based on the temperature detection result Td, the power supply voltage detection result Sv, the heat capacity correction amount Cc, the estimation history PREV, and the energization pulse Ps. As a result, the temperature estimation unit 91 can output the WAE estimated value, which is the temperature estimation result EST estimated using the heat capacity correction amount Cc.

[0094] Next, various temperature fluctuations due to the contact state between the surface of the heat roller 71 and the contact detection unit (hereinafter simply referred to as the detection unit) of the temperature sensor 74 will be described. The detection unit of the temperature sensor 74, which is a contact type sensor, is attached so as to contact the surface of the heat roller 71. However, due to poor attachment or the like, the detection unit of the temperature sensor 74 may be separated from the surface of the heat roller 71. In the following description, the state where the detection unit of the temperature sensor 74 and the surface of the heat roller 71 are separated is also referred to as the floating of the temperature sensor. The floating of the temperature sensor is checked, for example, during the manufacturing process of the image forming apparatus 1 or when the fixing device 21 in the operating image forming apparatus 1 is replaced.

[0095] The following describes various temperature data (measurement results) collected when the distance between the detection unit of the temperature sensor 74 and the surface of the heat roller 71 is set under various conditions. The float of the temperature sensor 74 is reproduced by attaching a tape for converting to an air layer (hereinafter referred to as a gap tape) to the detection unit of the temperature sensor 74. The gap tape is, for example, a heat-resistant tape of an insulator formed in a tape shape using polyimide as a material.

[0096] In the actual manufacturing process of the image forming apparatus or the replacement work of the fixing unit 21, it is assumed that there is no dirt or foreign matter adhering between the contact portion of the temperature sensor 74 and the surface of the heat roller 71. If there is no dirt or foreign matter and the temperature sensor 74 is floating, an air layer exists between the detection unit of the temperature sensor 74 and the surface of the heat roller 71. Generally, the thermal conductivity of air is 0.0241 [W / (m·K)], and the thermal conductivity of polyimide is 0.23 [W / (m·K)]. Therefore, the ratio of the thermal conductivity of air to that of polyimide is 0.1 (0.0241÷0.23). This indicates that heat is about 10 times less likely to be transmitted through air than through the gap tape.

[0097] According to the above ratio of thermoelectricity, a gap tape with a thickness of 0.42 mm can be converted into an air layer of 0.042 mm. If the thickness of one gap tape is 0.007 mm, a 0.42 mm gap tape corresponding to an air layer of 0.042 mm can be formed by stacking 6 gap tapes. Also, a 0.21 mm gap tape corresponding to an air layer of 0.021 mm can be formed by stacking 3 gap tapes.

[0098] FIG. 5 shows data indicating the average values of various temperatures obtained in the latter 20 seconds during 1 minute elapse in the ready state (standby state) with the control temperature of the center region C set to 160°C. Figure 5 shows the measurement results when the air layer (the floating of the temperature sensor) between the surface of the heat roller 71 and the contact part of the temperature sensor 741 is changed. As the measurement results for various air layers, the actual temperature of the heat roller 71, the detected temperature of the temperature sensor 741, and the center WAE estimated value are shown. The actual temperature of the heat roller 71 is measured by a thermocouple on the surface of the center region C of the heat roller 71.

[0099] In Figure 5, the air layer (the floating of the temperature sensor) has three patterns: "0 mm", "0.021 mm", and "0.042 mm". The state where the air layer is "0 mm" is a state where the surface of the heat roller 71 and the detection part of the temperature sensor 741 are in contact. The state where the air layer is "0.021 mm" is a state where three gap tapes with a thickness of 0.21 mm are provided between the surface of the heat roller 71 and the detection part of the temperature sensor 741. The state where the air layer is "0.042 mm" is a state where six gap tapes with a thickness of 0.42 mm are provided between the surface of the heat roller 71 and the detection part of the temperature sensor 741.

[0100] According to the measurement results shown in Figure 5, the detected temperature (the detected temperature of the temperature sensor 741) is almost the same regardless of the presence or absence of the air layer. This is because the center heater 731 is controlled so that the detected temperature of the center temperature sensor 741 becomes the target value. In contrast, the actual temperature (the temperature measured by a thermocouple in the center region C of the heat roller 71) is 189.6 °C when the air layer is 0.042 mm, 177.8 °C when the air layer is 0.021 mm, and 170.2 °C when there is no air layer. Also, the center WAE estimated value is 203.5 °C when the air layer is 0.042 mm, 186.4 °C when the air layer is 0.021 mm, and 172.9 °C when there is no air layer.

[0101] In Figure 5, the difference between the center WAE estimated value and the detected temperature of the temperature sensor 741 (the difference between the WAE estimated value and the detected temperature) and the difference between the actual temperature of the center region C and the detected temperature of the temperature sensor 741 (the difference between the actual temperature and the detected temperature) are shown. In the center region, both the difference between the WAE estimated value and the detected temperature and the difference between the actual temperature and the detected temperature increase as the air layer becomes larger (the gap becomes wider).

[0102] For example, the difference between the WAE estimated value and the detected temperature is 40.5°C when the air layer is 0.042 mm, 24.4°C when the air layer is 0.021 mm, and 9.9°C when there is no air layer (when in contact). Also, the difference between the actual temperature and the detected temperature is 26.6°C when the air layer is 0.042 mm, 15.8°C when the air layer is 0.021 mm, and 7.2°C when there is no air layer. In FIG. 5, since the detected temperature is almost a constant value (163 or 162°C) regardless of the air layer, it shows that the WAE estimated value and the actual temperature increase as the air layer becomes larger.

[0103] Also, in FIG. 5, as the increase in the actual temperature due to the air layer, the difference value of the actual temperature with respect to the actual temperature when there is no air layer is shown. For example, when the air layer is 0.042 mm, the actual temperature increase is 19.4°C, and when the air layer is 0.021 mm, the actual temperature increase is 8.6°C. According to these, it shows that the larger the air layer, the higher the actual temperature.

[0104] FIG. 6 is data showing the average values of various temperatures obtained in the latter 20 seconds during 1 minute elapse in the ready state with the control temperature of the side region S being 155°C. The measurement results shown in FIG. 6, similar to the measurement results shown in FIG. 5, show the actual temperature (the temperature measured by the thermocouple on the surface of the side region S of the heat roller 71), the detected temperature (the detected temperature of the temperature sensor 742), and the side WAE estimated value when the air layer is in three patterns.

[0105] According to the measurement results shown in FIG. 6, the detected temperature (the detected temperature of the temperature sensor 742) is almost the same regardless of the presence or absence of the air layer. This is because the side heater 732 is controlled so that the detected temperature of the side temperature sensor 742 becomes the target value. On the other hand, the actual temperature of the side region S is 181.2°C when the air layer is 0.042 mm, 173.2°C when the air layer is 0.021 mm, and 162.0°C when there is no air layer. Also, the side WAE estimated value is 220.7°C when the air layer is 0.042 mm, 209.6°C when the air layer is 0.021 mm, and 183.6°C when there is no air layer.

[0106] In FIG. 6, the difference between the side WAE estimated value and the detected temperature of the temperature sensor 742 (the difference between the WAE estimated value and the detected temperature) and the difference between the actual temperature of the side region S and the detected temperature of the temperature sensor 742 (the difference between the actual temperature and the detected temperature) are shown. Also in the side region S, both the difference between the WAE estimated value and the detected temperature and the difference between the actual temperature and the detected temperature increase as the air layer becomes larger.

[0107] For example, the difference between the WAE estimated value and the detected temperature is 63.7 ° C when the air layer is 0.042 mm, 52.6 ° C when it is 0.021 mm, and 26.6 ° C when there is no air layer. Also, the difference between the actual temperature and the detected temperature is 24.2 ° C when the air layer is 0.042 mm, 16.2 ° C when it is 0.021 mm, and 5.0 ° C when there is no air layer. According to FIG. 6, since the detected temperature is a constant value (157 ° C) regardless of the air layer, it shows that the WAE estimated value and the actual temperature increase as the air layer becomes larger.

[0108] Also in FIG. 6, as the increase in the actual temperature due to the air layer, the difference value of the actual temperature with respect to the actual temperature when there is no air layer is shown. For example, the increase in the actual temperature when the air layer is 0.042 mm is 19.2 ° C. Also, the increase in the actual temperature when the air layer is 0.021 mm is 11.2 ° C. According to these, it shows that also in the side region, as the air layer becomes larger, the actual temperature increases.

[0109] FIG. 7 is a diagram showing a graph of the measurement results shown in FIG. 5 indicating various temperatures with respect to the size of the air layer. In FIG. 7, the line Cs indicates the detected temperature of the temperature sensor 741, the line Cr indicates the actual temperature of the center region C of the heat roller 71, and the line Cw indicates the WAE estimated value. According to FIG. 7, while the detected temperature of the temperature sensor 741 is constant, it shows that the actual temperature and the WAE estimated value increase almost as the air layer becomes larger.

[0110] FIG. 8 is a diagram showing a graph of the measurement results shown in FIG. 6 indicating various temperatures with respect to the size of the air layer. In FIG. 8, line Ss indicates the detected temperature of temperature sensor 742, line Sr indicates the actual temperature of side region S of heat roller 71, and line Sw indicates the WAE estimated value. According to FIG. 8, similar to FIG. 7, while the detected temperature of temperature sensor 742 is constant, it shows that both the actual temperature and the WAE estimated value increase approximately as the air layer becomes larger.

[0111] The phenomena shown in FIGS. 7 and 8 are considered to be caused by the fact that when there is floating of temperature sensor 74 (741, 742), the detected temperature of temperature sensor 74 becomes lower than the actual temperature of heat roller 71. Heater control circuit 14 controls the on / off of the heater so as to maintain the detected temperature of temperature sensor 741 at the target value. If the detected temperature of temperature sensor 741 is lower than the actual temperature, heater control circuit 14 will overheat heat roller 71, and the number of times heater 73 is turned on will increase. As a result, the actual temperature of heat roller 71 and the WAE estimated value will rise above the detected temperature of temperature sensor 74. By utilizing such a phenomenon, controller 13 can detect (judge) the floating of temperature sensor 74 based on the temperature difference between the detected temperature of temperature sensor 74 (741, 742) and the WAE estimated value.

[0112] Next, the correlation between the increase in the WAE estimated value due to the floating of temperature sensor 74 and the increase in the actual temperature in the heat roller will be described. FIG. 9 is a diagram showing the relationship between the center WAE estimated value that varies according to the floating of center temperature sensor 741 and the increase in the actual temperature in center region C of heat roller 71. The horizontal axis shown in FIG. 9 is the temperature of the difference between the WAE estimated value and the detected temperature (the detected temperature of temperature sensor 741) shown in FIGS. 5 and 7. The vertical axis shown in FIG. 9 is the temperature increase of the actual temperature (the actual temperature of center region C of heat roller 71) shown in FIGS. 5 and 7. According to FIG. 9, it shows that the actual temperature of center region C increases at a certain rate according to the difference between the WAE estimated value that increases due to the floating of temperature sensor 741 and the detected temperature. According to the correlation shown in FIG. 9, the correlation formula (y = 0.6347x - 6.4909) between the difference between the WAE estimated value that increases due to the floating of temperature sensor 741 and the detected temperature and the actual temperature is obtained.

[0113] FIG. 10 is a diagram showing the relationship between the side WAE estimated value that varies according to the floating of the side temperature sensor 742 and the change in the actual temperature in the side region S of the heat roller 71. The horizontal axis shown in FIG. 10 is the temperature of the difference between the WAE estimated value shown in FIGS. 6 and 8 and the detected temperature (the detected temperature of the temperature sensor 742). The vertical axis shown in FIG. 10 is the temperature of the increase in the actual temperature (the actual temperature of the side region S of the heat roller 71) shown in FIGS. 6 and 5. According to FIG. 10, it shows that the actual temperature of the side region S rises at a certain rate according to the difference between the WAE estimated value that rises due to the floating of the temperature sensor 742 and the detected temperature. According to the correlation shown in FIG. 10, a correlation formula (y = 0.5021x - 13.782) between the difference between the WAE estimated value that rises due to the floating of the temperature sensor 742 and the detected temperature and the actual temperature is obtained.

[0114] FIG. 11 is a diagram showing the relationship between the detected temperature by the temperature sensor 74 (741 or 742) and the actual temperature of the heat roller 71 (center region C or side region S). As shown in FIG. 11, during normal operation (when there is no floating of the temperature sensor), the variation in the detected temperature by the temperature sensor 74 is within ±5°C with respect to the actual temperature of the heat roller 71. In contrast, when there is floating of the temperature sensor, the actual temperature rises compared to normal, so the detected temperature by the temperature sensor 74 becomes higher than 5°C with respect to the actual temperature. Therefore, if the increase in the actual temperature is 5°C or less, it can be determined that there is no floating of the temperature sensor 741, and if the increase in the actual temperature is higher than 5°C, it can be determined that there is floating of the temperature sensor 741.

[0115] FIG. 12 is a diagram showing the relationship between the difference (tac) between the center WAE estimated value and the detected temperature of the center temperature sensor 741 with respect to the increase in the actual temperature (tbc) in the center region C. FIG. 12 shows the difference between the WAE estimated value and the detected temperature of the temperature sensor 741, divided into the case where the actual temperature rise in the center region C is 5°C or less and the case where it is higher than 5°C. According to the correlation formula shown in FIG. 9, when the actual temperature rise in the center region C is 5°C, the difference between the center WAE estimated value and the detected temperature of the center temperature sensor 741 is 18.1°C.

[0116] As shown in FIG. 12, if the difference between the center WAE estimated value and the detected temperature of the temperature sensor 741 is 18.1°C or less, it is determined that the actual temperature rise in the center region C is 5°C or less. Therefore, if the difference between the center WAE estimated value and the detected temperature of the temperature sensor 741 is 18.1°C or less, it can be determined that the temperature sensor 741 has no float (the contact part is in contact with the heat roller). Also, if the difference between the center WAE estimated value and the detected temperature of the temperature sensor 741 is higher than 18.1°C, it can be determined that the actual temperature rise in the center region C is higher than 5°C. Therefore, if the difference between the center WAE estimated value and the detected temperature of the temperature sensor 741 is higher than 18.1°C, it can be determined that the temperature sensor 741 has a float (the contact part is separated from the heat roller).

[0117] FIG. 13 is a diagram showing the relationship between the difference (tas) between the side WAE estimated value and the detected temperature of the side temperature sensor 742 with respect to the actual temperature rise (tbs) in the side region S. FIG. 13 shows the difference between the WAE estimated value and the detected temperature of the temperature sensor 742, divided into the case where the actual temperature rise in the side region S is 5°C or less and the case where it is higher than 5°C. According to the correlation formula shown in FIG. 10, when the actual temperature rise in the side region S is 5°C, the difference between the side WAE estimated value and the detected temperature of the side temperature sensor 742 is 37.4°C.

[0118] According to FIG. 13, if the difference between the side WAE estimated value and the detected temperature of the temperature sensor 742 is 37.4° C. or less, it can be determined that the actual temperature rise in the side region S is 5° C. or less. Therefore, if the difference between the side WAE estimated value and the detected temperature of the temperature sensor 742 is 37.4° C. or less, it can be determined that the temperature sensor 742 has no floating (the contact part is in contact with the heat roller). Also, if the difference between the side WAE estimated value and the detected temperature of the temperature sensor 742 is higher than 37.4° C., the actual temperature rise in the side region S becomes higher than 5° C. Therefore, if the difference between the WAE estimated value and the detected temperature is higher than 37.4° C., it can be determined that the temperature sensor 742 has floating (the contact part is separated from the heat roller).

[0119] Next, a floating detection process for detecting the floating of the temperature sensors 74 (741, 742) in the fixing device 21 of the image forming apparatus 1 according to the embodiment will be described. FIGS. 14 and 15 are flowcharts for explaining an operation example of a floating detection process for detecting the floating of the temperature sensors 74 (741, 742) in the fixing device 21 of the image forming apparatus 1 according to the embodiment. For example, the controller 13 executes a dirt prediction process by the processor 81 executing a program for the floating detection process. The program for the floating detection process executed by the processor 81 shall be stored in a non-volatile memory such as the ROM 82 or the data memory 84.

[0120] Here, the floating detection process is executed on the premise that there is no dirt in the fixing device 21 such as during the manufacturing process of the image forming apparatus 1 or when replacing the fixing device 21. For example, the controller 13 shall execute the floating detection process during the manufacturing process of the image forming apparatus 1 or during the replacement operation of the fixing device 21 in the image forming apparatus 1.

[0121] In the image forming apparatus 1, when the power is turned on, the controller 13 starts WAE control including calculation of the center WAE estimated value and the side WAE estimated value (ACT11). When the conditions for performing floating detection in the manufacturing process or the like are met, the controller 13 determines whether the detected temperatures of both the temperature sensors 741 and 742 are 40°C or lower (ACT12).

[0122] When the detected temperature of either of the temperature sensors 741 and 742 is higher than 40°C (ACT12, NO), the controller 13 notifies that the floating detection cannot be performed because the fuser 21 is at a high temperature (ACT13). When the heat roller 71 is at a high temperature (here, 40°C or higher) when the power is turned on, the heat capacity of the heating member until the standby state, the thermal resistance of the fuser, and the energy input to the fuser change. For this reason, when the heat roller 71 is at a high temperature when the power is turned on, the WAE estimated value is not stable. If the WAE estimated value is stable, the floating of the temperature sensors 741 and 742 cannot be correctly determined. Accordingly, the controller 13 does not perform the floating detection if the detected temperatures of both the temperature sensors 741 and 742 are higher than 40°C.

[0123] For example, when the detected temperature of the temperature sensor 74 is higher than 40°C, the controller 13 displays on the display device 15 that the floating detection is not performed because the temperature of the fuser is high. Further, the controller 13 may notify an external device via the communication I / F 12 that the floating detection is not performed because the temperature of the fuser 21 is high. By notifying that the floating detection cannot be performed because the fuser is at a high temperature, the image forming apparatus 1 can prompt the operator (worker, service technician, administrator, etc.) to lower the temperature of the fuser and then perform the floating detection of the temperature sensor.

[0124] When the detected temperatures of the temperature sensors 741 and 742 are 40°C or lower (ACT12, YES), the controller 13 executes a warm-up operation. When the warm-up operation is completed, the controller 13 transitions to the ready state. When the controller 13 transitions to the ready state, it monitors the presence or absence of a print request while counting the duration of being in the ready state (the elapsed time since transitioning to the standby state) (ACT13).

[0125] If there is a print request (ACT14, YES) before a predetermined time (measurement end time, e.g., 60 seconds) has elapsed since the start of standby, the controller 13 aborts the float detection and notifies of the abort of the float detection due to print execution (ACT15). For example, the controller 13 may display the abort of the float detection due to print execution on the display device 15, or may notify an external device via the communication I / F 12.

[0126] When the measurement start time (40 seconds) has elapsed since the start of standby (ACT16, YES), the controller 13 acquires the detected temperature of the temperature sensor 74 (temperature sensor 741 and temperature sensor 742) at a predetermined timing (e.g., a predetermined period). The controller 13 stores the detected temperature of the temperature sensor 74 acquired at each predetermined timing in the RAM 83 (or the data memory 84) (ACT17). For example, the controller 13 stores the detected temperatures of the temperature sensor 741 and the temperature sensor 742 acquired at a predetermined period in the RAM 83.

[0127] Also, when the measurement start time (40 seconds) has elapsed since the start of standby (ACT16, YES), the controller 13 acquires the WAE estimated values (center WAE estimated value and side WAE estimated value) at a predetermined timing (e.g., a predetermined period). The controller 13 stores the WAE estimated values acquired at each predetermined timing in the RAM 83 (or the data memory 84) (ACT18). For example, the controller 13 stores the center WAE estimated value and the side WAE estimated value acquired at a predetermined period in the RAM 83.

[0128] The controller 13 continuously executes the storage of the detected temperature of the temperature sensor 74 and the WAE estimated value until the measurement end time (60 seconds) elapses from the start of standby (ACT19, NO). The controller 13 sets the period from 40 seconds after the start of standby to 60 seconds (the last 20 seconds within the 60 seconds from the start of standby) as the predetermined measurement period. The controller 13 stores the detected temperature of the temperature sensor 74 and the WAE estimated value in the RAM 83 during the predetermined measurement period (the time from the start time of measurement to the end time of measurement).

[0129] For example, the controller 13 stores the detected temperature of the temperature sensors 74 (741, 742) and the WAE estimated values (center WAE estimated value, side WAE estimated value) acquired at a predetermined cycle during the predetermined measurement period in the RAM 83. As a result, the detected temperature of the temperature sensor 741, the detected temperature of the temperature sensor 742, the center WAE estimated value, and the side WAE estimated value during the predetermined measurement period are accumulated in the RAM 83.

[0130] When 60 seconds (measurement end time) elapses from the start of standby (ACT19, YES), the controller 13 calculates the average value of the detected temperatures by the temperature sensor 74 during the predetermined measurement period stored in the RAM 83 (ACT20). Specifically, the controller 13 calculates the average value of the detected temperatures of the center temperature sensor 741 and the average value of the detected temperatures of the side temperature sensor 742 during the predetermined measurement period, respectively.

[0131] Also, when 60 seconds elapses from the start of standby (ACT19, YES), the controller 13 calculates the average value of the WAE estimated values during the predetermined measurement period stored in the RAM 83 (ACT21). Specifically, the controller 13 calculates the average value of the center WAE estimated value and the average value of the side WAE estimated value during the predetermined measurement period, respectively.

[0132] When the controller 13 calculates the average value of the detected temperatures of the center temperature sensor 741 and the average value of the center WAE estimated values, it calculates the difference (average difference) between these average values (ACT22). That is, the controller 13 calculates the difference between the average value of the detected temperatures of the center temperature sensor 741 and the average value of the center WAE estimated values as the center average difference. When the controller 13 calculates the center average difference, it determines whether the center average difference is equal to or greater than the center threshold value (the threshold value for the first region) (ACT23). If the center average difference is not equal to or greater than the center threshold value (ACT23, NO), the controller 13 proceeds to ACT25.

[0133] The center threshold value is set by the difference between the center WAE estimated value at which the actual temperature rise in the center region C is 5 °C (the allowable range of temperature variation) or more and the detected temperature of the center temperature sensor 741. For example, the center threshold value is set by the set value shown in FIG. 12 based on the measurement results shown in FIG. 5. The center threshold value is stored in the data memory 84 or the ROM 82.

[0134] When the center average difference is equal to or greater than the center threshold value (ACT23, YES), the controller 13 notifies that the center temperature sensor 741 has been detected as floating. For example, when the center temperature sensor 741 is detected as floating, the controller 13 displays on the display device 15 that the center temperature sensor 741 has been detected as floating. Thereby, the image forming apparatus 1 can notify that the center temperature sensor 741 has been detected as floating using the display device 15 provided therein. As a result, the image forming apparatus 1 can prompt an operator (worker, service technician, administrator, etc.) in the vicinity to check the mounting state of the center temperature sensor 741 in which floating has been detected.

[0135] Further, the controller 13 may notify an external device via the communication I / F 12 that the floating of the center temperature sensor 741 has been detected. When receiving such a notification, the external device notifies (for example, displays on a display device) that the floating of the center temperature sensor 741 has been detected in the image forming apparatus 1. Thereby, the image forming apparatus 1 can notify that the floating of the center temperature sensor 741 has been detected by an external device at a remote location. As a result, the image forming apparatus 1 can prompt an operator at a distant location to check the attachment state of the center temperature sensor 741 in which the floating has been detected.

[0136] Further, when the controller 13 calculates the average value of the detected temperatures of the side temperature sensors 742 and the average value of the side WAE estimated values, the controller 13 calculates the difference (average difference) between those average values (ACT25). That is, the controller 13 calculates the difference between the average value of the detected temperatures of the side temperature sensors 742 and the average value of the side WAE estimated values as the side average difference. When the controller 13 calculates the side average difference, the controller 13 determines whether or not the side average difference is equal to or greater than a side threshold value (a threshold value for the second region) (ACT26). If the side average difference is not equal to or greater than the side threshold value (ACT26, NO), the controller 13 ends the floating detection process.

[0137] The side threshold value is set by the difference between the side WAE estimated value and the detected temperature of the side temperature sensor 742 when the actual temperature rise in the side region S is 5°C (the allowable range of temperature variation) or more. For example, the side threshold value is set by a set value as shown in FIG. 13 based on the measurement results as shown in FIG. 6. The side threshold value is stored in the data memory 84 or the ROM 82.

[0138] When the average difference between sides is equal to or greater than the threshold value for the sides (ACT26, YES), the controller 13 notifies that the floating of the side temperature sensor 742 has been detected (ACT27). For example, when the floating of the side temperature sensor 742 is detected, the controller 13 displays on the display device 15 that the floating of the side temperature sensor 742 has been detected. Thereby, the image forming apparatus 1 can notify that the floating of the side temperature sensor 742 has been detected using the display device 15 provided therein. As a result, the image forming apparatus 1 can prompt an operator (such as a worker, a service technician, or an administrator) in the vicinity to check the mounting state of the side temperature sensor 742 in which floating has been detected.

[0139] Further, the controller 13 may notify an external device via the communication I / F 12 that the floating of the side temperature sensor 742 has been detected. When receiving such a notification, the external device notifies (for example, displays on a display device) that the floating of the side temperature sensor 742 has been detected in the image forming apparatus 1. Thereby, the image forming apparatus 1 can notify that the floating of the side temperature sensor 742 has been detected by an external device located remotely. As a result, the image forming apparatus 1 can prompt an operator in a distant location to check the mounting state of the side temperature sensor 742 in which floating has been detected.

[0140] As described above, the image forming apparatus according to the embodiment acquires the detected temperature of the temperature sensor and the WAE estimated value during a predetermined period immediately after the power is turned on. The image forming apparatus calculates the difference between the average value of the detected temperatures of the temperature sensor and the average value of the WAE estimated values during the predetermined period. If the difference between the detected temperature of the temperature sensor and the WAE estimated value is equal to or greater than a predetermined threshold value, the image forming apparatus detects the floating of the temperature sensor. Thereby, the image forming apparatus can detect the floating of the temperature sensor provided in the fixing device without using a dedicated jig.

[0141] In addition, the image forming apparatus according to the embodiment executes floating detection processing for each of the center temperature sensor and the side temperature sensor. When the center temperature sensor or the side temperature sensor detects, the image forming apparatus notifies the operator that the floating of the temperature sensor has been detected. By notifying the operator that the floating of the temperature sensor has been detected, the image forming apparatus can prompt the operator to check the attachment state of the temperature sensor and the like.

[0142] In the above-described embodiment, the image forming apparatus 1 including the fixing device 21 of the first configuration example shown in FIGS. 1 and 2 has been described. However, the configuration of the fixing device applied to the image forming apparatus 1 according to the embodiment is not limited to the first configuration example shown in FIGS. 1 and 2. The image forming apparatus 1 according to the embodiment can apply fixing devices of the second to fifth configuration examples described later, not limited to the fixing device 21 of the first configuration example.

[0143] Hereinafter, a modification example of the fixing device applicable to the image forming apparatus 1 according to the embodiment will be described. First, the fixing device 200 which is a second example of the fixing device applicable to the image forming apparatus 1 according to the embodiment will be described. FIG. 16 is a diagram showing a configuration example of a fixing device 200 which is a second example of the fixing device applicable to the image forming apparatus 1 according to the embodiment. Further, FIG. 17 is a diagram showing a configuration example of a heater unit in the fixing device 200.

[0144] As shown in FIG. 16, the fixing device 200 includes temperature sensors 74 (741, 742), a cylindrical film 271 as a fixing member, a pressure roller 272, a heating element 273, a heating element substrate 275, and the like. The pressure roller 272 forms a nip with the cylindrical film 271. The cylindrical film 271 and the pressure roller 272 heat the print medium P that has entered the nip while applying pressure.

[0145] The heater unit includes a heating element 273, a heating element substrate 275, etc. The heating element substrate 275 is formed of a metal material, a ceramic material, or the like. The heating element substrate 275 is formed in a long and narrow rectangular plate shape. The heating element substrate 275 is disposed inside the cylindrical film 271 in the radial direction. The heating element substrate 275 has the axial direction of the cylindrical film 271 as its longitudinal direction.

[0146] The heating element 273 includes a central heating element 2731, a first end heating element 2732, and a second end heating element 2733. The three heating elements 2731, 2732, and 2733 are arranged side by side in a direction orthogonal to the paper conveyance direction (the longitudinal direction of the heating element substrate 275). The central heating element 2731 is arranged such that the central position in the width direction (the direction orthogonal to the conveyance direction) of the print medium P passing through the nip coincides. The first end heating element 2732 and the second end heating element 2733 are arranged side by side on both sides of the central heating element 2731.

[0147] The central heating element 2731 is an example of a first heat source. As shown in FIG. 17, the central heating element 2731 supplies heat centered on the center region C in a direction orthogonal to the paper conveyance direction. However, even when only the central heating element 2731 is heated, the temperature of the side region S rises. The first end heating element 2732 and the second end heating element 2733 are examples of a second heat source. As shown in FIG. 17, the first end heating element 2732 and the second end heating element 2733 supply heat centered on the side region S in a direction orthogonal to the paper conveyance direction.

[0148] The temperature sensors 741 and 742 are contact-type temperature detection devices such as thermistors, similar to the first configuration example. The temperature sensor 741 detects the temperature at a position corresponding to the center region C heated by the central heating element 2731. Also, the temperature sensor 742 detects the temperature at a position corresponding to the side region S heated by the end heating element 2732 or 2733.

[0149] As described above, the fixing device 200 shown in FIGS. 16 and 17 can also be subjected to the above-described WAE control. The image forming apparatus including the fixing device 200 shown in FIGS. 16 and 17 can perform the floating detection process of the temperature sensor based on the difference between the above-described WAE estimated value and the detected temperature of the temperature sensor. However, the threshold values as shown in FIGS. 12 and 13 cannot be directly applied to the image forming apparatus including the fixing device 200. The image forming apparatus including the fixing device 200 needs to set the center threshold value and the side threshold value as shown in FIGS. 12 and 13 for each apparatus body.

[0150] For example, in an image forming apparatus including the fixing device 200, as shown in FIGS. 5 and 6, the actual temperature, the detected temperature, and the WAE estimated value are measured under various conditions (air layers). The image forming apparatus including the fixing device 200 sets threshold values (center threshold value and side threshold value) for detecting the floating of the temperature sensors 741 and 742 based on the measurement results of the actual temperature, the detected temperature, and the WAE estimated value for each of the center and the side. The image forming apparatus including the fixing device 200 stores the center threshold value and the side threshold value in a data memory 84 or the like, and performs the floating detection process as described above. Thereby, even in the image forming apparatus including the fixing device 200, the floating of the center temperature sensor and the side temperature sensor can be determined without using a dedicated jig.

[0151] Next, a fixing device 300 which is a third example of a fixing device applicable to the image forming apparatus 1 according to the embodiment will be described. FIG. 18 is a diagram showing a configuration example of a fixing device 300 which is a third example of a fixing device applicable to the image forming apparatus 1 according to the embodiment. FIG. 19 is a diagram showing a configuration example of a heater unit in the fixing device 300.

[0152] As shown in FIG. 18, the fixing device 300 includes a temperature sensor 74 (741, 742), a cylindrical film 371 as a fixing member (fixing rotating body), a pressure roller 372, a heating element 373, a heating element substrate 375, and the like. The pressure roller 372 forms a nip with the cylindrical film 371. The cylindrical film 371 and the pressure roller 372 heat the printing medium P while pressing it as it enters the nip.

[0153] The heater unit includes a heating element 373, a heating element substrate 375, and the like. The heating element substrate 375 is formed of a metal material, a ceramic material, or the like. The heating element substrate 375 is formed in a long and narrow rectangular plate shape. The heating element substrate 375 is disposed inside the cylindrical film 371 in the radial direction. The heating element substrate 375 has the axial direction of the cylindrical film 271 as its longitudinal direction.

[0154] The heating element 373 includes a plurality of heating elements 3731, 3732, 3733. The heating element 373 is provided in a state of being disposed on the heating element substrate 375 so as to contact the inner surface of the cylindrical film 371. Each of the heating elements 3731, 3732, 3733 is a resistor that generates heat by power supply from an AC power source.

[0155] The heating element 3731 is used to fix the toner to the printing medium P having the maximum width of the printing medium P in the direction perpendicular to the conveyance direction. The heating element 3731 has a width corresponding to the maximum paper width. The heating element 3731 is disposed on the heating element substrate 375 on the upstream side and the downstream side in the conveyance direction of the printing medium P.

[0156] The heating element 3732 is a heating element shorter than the heating element 3731 in the direction perpendicular to the conveyance direction of the printing medium P. The heating element 3733 is a heating element even shorter than the heating element 3732 in the direction perpendicular to the conveyance direction of the printing medium P. The heating element 3731 is the main heater, and the heating elements 3732 and 3733 are sub-heaters. The main heater and the sub-heaters are controlled to be turned on and off according to the paper width of the printing medium P.

[0157] As described above, the fixing device 300 shown in FIGS. 18 and 19 can also be subjected to the above-described WAE control. The image forming apparatus including the fixing device 300 shown in FIGS. 18 and 19 can perform the floating detection process of the temperature sensor based on the difference between the above-described WAE estimated value and the detected temperature of the temperature sensor. However, the threshold values as shown in FIGS. 12 and 13 cannot be directly applied to the image forming apparatus including the fixing device 300. The image forming apparatus including the fixing device 300 needs to set the center threshold value and the side threshold value as shown in FIGS. 12 and 13 for each machine body.

[0158] For example, in an image forming apparatus including the fixing device 300, as shown in FIGS. 5 and 6, the actual temperature, the detected temperature, and the WAE estimated value are measured under various conditions (air layers). The image forming apparatus including the fixing device 300 sets threshold values (center threshold value and side threshold value) for detecting the floating of the temperature sensors 741 and 742 based on the measurement results of the actual temperature, the detected temperature, and the WAE estimated value for each of the center and the side. The image forming apparatus including the fixing device 300 stores the center threshold value and the side threshold value in a data memory 84 or the like, and performs the floating detection process as described above. Thereby, even in the image forming apparatus including the fixing device 300, it is possible to determine the floating of the center temperature sensor and the side temperature sensor without using a dedicated jig.

[0159] Next, a fixing device 400 which is a fourth example of a fixing device applicable to the image forming apparatus 1 according to the embodiment will be described. FIG. 20 is a diagram showing a configuration example of a fixing device 400 which is a fourth example of a fixing device applicable to the image forming apparatus 1 according to the embodiment. FIG. 21 is a diagram showing a configuration example of a heater unit in the fixing device 400.

[0160] As shown in FIG. 20, the fixing device 400 includes a temperature sensor 74 (741, 742), a cylindrical film 471 as a fixing member (fixing rotating body), a pressure roller 472, a heating element 473, a heating element substrate 475, and the like. The pressure roller 472 forms a nip with the cylindrical film 471. The cylindrical film 471 and the pressure roller 472 heat the printing medium P while pressing it as it enters the nip.

[0161] The heater unit includes a heating element 473, a heating element substrate 475, and the like. The heating element substrate 475 is formed of a metal material, a ceramic material, or the like. The heating element substrate 475 is formed in a long and narrow rectangular plate shape. The heating element substrate 475 is disposed inside the cylindrical film 471 in the radial direction. The heating element substrate 475 has the axial direction of the cylindrical film 471 as its longitudinal direction.

[0162] The heating element 473 includes a plurality of heating elements 4731, 4732. The heating element 473 is provided in a state of being disposed on the heating element substrate 475 so as to be in contact with the inner surface of the cylindrical film 471. Each of the heating elements 4731, 4732 is, for example, a resistor that generates heat by power supply from an AC power source.

[0163] The heating element 4731 has a width corresponding to the maximum width of the printing medium P in the direction perpendicular to the conveyance direction. As shown in FIG. 21, the heating element 4731 has a large width in the conveyance direction at the central portion in the direction perpendicular to the conveyance direction and a small width in the conveyance direction at the end portions. The heating element 4731 is a main heater configured to preferentially heat the center region C. Further, the heating element 4732 has a small width in the conveyance direction at the central portion in the direction perpendicular to the conveyance direction and a large width in the conveyance direction at the end portions. The heating element 4732 is a sub-heater configured to preferentially heat the side region S. The main heater and the sub-heater are controlled to be turned on and off according to the paper width of the printing medium P.

[0164] As described above, the fixing device 400 shown in FIGS. 20 and 21 can also be subjected to the above-described WAE control. The image forming apparatus including the fixing device 400 shown in FIGS. 20 and 21 can perform the floating detection process of the temperature sensor based on the difference between the above-described WAE estimated value and the detected temperature of the temperature sensor. However, the threshold values as shown in FIGS. 12 and 13 cannot be directly applied to the image forming apparatus including the fixing device 400. The image forming apparatus including the fixing device 400 needs to set the center threshold value and the side threshold value as shown in FIGS. 12 and 13 for each machine body.

[0165] For example, in an image forming apparatus including the fixing device 400, as shown in FIGS. 5 and 6, the actual temperature, the detected temperature, and the WAE estimated value are measured under various conditions (air layers). The image forming apparatus including the fixing device 400 sets threshold values (center threshold value and side threshold value) for detecting the floating of the temperature sensors 741 and 742 based on the measurement results of the actual temperature, the detected temperature, and the WAE estimated value for each of the center and the side. The image forming apparatus including the fixing device 400 stores the center threshold value and the side threshold value in a data memory 84 or the like, and performs the floating detection process as described above. Thereby, even in the image forming apparatus including the fixing device 400, the floating of the center temperature sensor and the side temperature sensor can be determined without using a dedicated jig.

[0166] Next, a fixing device 500 which is a fifth example of a fixing device applicable to the image forming apparatus 1 according to the embodiment will be described. FIG. 22 is a diagram showing a configuration example of a fixing device 500 which is a second example of a fixing device applicable to the image forming apparatus 1 according to the embodiment. FIG. 23 is a diagram showing a configuration example of a heater unit in the fixing device 500.

[0167] As shown in FIG. 22, the fixing device 500 includes a temperature sensor 74 (741, 742), a heat roller 571 as a fixing member, a pressure roller 572, and an induction heating coil 573. The pressure roller 572 forms a nip with the heat roller 571. The heat roller 571 and the pressure roller 572 heat the printing medium P entering the nip while applying pressure thereto.

[0168] The induction heating coil 573 is an example of a heat source for heating the heat roller 571 as a fixing member. The induction heating coil 573 includes a central coil 5731 and an end coil 5732. The central coil 5731 and the end coil 5732 are arranged side by side in a direction orthogonal to the paper conveyance direction (the rotation axis direction of the heat roller 571) inside the heat roller 571. The central coil 5731 is arranged such that the central position in the width direction (the direction orthogonal to the conveyance direction) of the printing medium P passing through the nip coincides. The end coils 5732 are arranged side by side on both sides of the central coil 5731.

[0169] The central coil 5731 is an example of a first heat source. As shown in FIG. 23, the central coil 5731 heats the center region C of the heat roller 571 in a direction orthogonal to the paper conveyance direction. The end coil 5732 is an example of a second heat source. As shown in FIG. 23, the end coil 5732 heats the side region S of the heat roller 571 in a direction orthogonal to the paper conveyance direction.

[0170] The temperature sensors 741 and 742 are contact-type temperature detection devices such as thermistors, similar to the fixing device 21 of the first configuration example. The temperature sensor 741 detects the temperature of the center region C of the heat roller 571. Also, the temperature sensor 742 detects the temperature of the side region C of the heat roller 571.

[0171] As described above, the fixing device 500 shown in FIGS. 22 and 23 can also be subjected to the above-described WAE control. An image forming apparatus including the fixing device 500 shown in FIGS. 22 and 23 can perform the floating detection process of the temperature sensor based on the difference between the above-described WAE estimated value and the detected temperature of the temperature sensor. However, the threshold values as shown in FIGS. 12 and 13 cannot be directly applied to the image forming apparatus including the fixing device 500. The image forming apparatus including the fixing device 500 needs to set the center threshold value and the side threshold value as shown in FIGS. 12 and 13 for each machine body.

[0172] For example, in an image forming apparatus including the fixing device 500, as shown in FIGS. 5 and 6, the actual temperature, the detected temperature, and the WAE estimated value are measured under various conditions (air layers). The image forming apparatus including the fixing device 500 sets threshold values (center threshold value and side threshold value) for detecting the floating of the temperature sensors 741 and 742 based on the measurement results of the actual temperature, the detected temperature, and the WAE estimated value for each of the center and the side. The image forming apparatus including the fixing device 500 stores the center threshold value and the side threshold value in a data memory 84 or the like, and performs the floating detection process as described above. Thereby, even in an image forming apparatus including the fixing device 500, it is possible to determine the floating of the center temperature sensor and the side temperature sensor without using a dedicated jig.

[0173] Note that the functions described in the above embodiments are not limited to being configured using hardware, and can also be realized by causing a computer to read a program describing each function using software. Also, each function may be configured by appropriately selecting either software or hardware.

[0174] Although some embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

[0175] Hereinafter, the fixing device according to the above-described embodiment will be listed. [1] A fixing device having a fixing member with which a medium onto which a developer image has been transferred comes into contact, and a heat source that supplies heat to the fixing member, A temperature sensor that measures temperature with a detection unit that contacts the surface of the fixing member with which the medium comes into contact, A memory that stores a temperature estimated value for estimating the temperature of the fixing member and a detected temperature detected by the temperature sensor, A controller that determines a contact failure between the detection unit of the temperature sensor and the surface of the fixing member based on a difference between the temperature estimated value stored in the memory and the detected temperature detected by the temperature sensor, A fixing device having the above. [2] The memory stores a temperature estimated value and a detected temperature detected by the temperature sensor during a predetermined measurement period in a print standby state, The controller determines a contact failure between the detection unit of the temperature sensor and the surface of the fixing member based on a difference between an average value of the temperature estimated values and an average value of the detected temperatures detected by the temperature sensor during the predetermined measurement period. The fixing device according to [1]. [3] The controller determines that there is a contact failure between the detection unit of the temperature sensor and the surface of the fixing member when a difference between an average value of the temperature estimated values and an average value of the detected temperatures detected by the temperature sensor during the predetermined measurement period is equal to or greater than a predetermined threshold value. The fixing device according to [2]. [4] Furthermore, it has a display device, When the controller determines that there is a poor contact between the detection part of the temperature sensor and the surface of the fixing member, it indicates the poor contact between the detection part of the temperature sensor and the surface of the fixing member and displays the guidance on the display device. The fixing device according to [1]. [5] Furthermore, it has a communication interface for communicating with an external device, and when the controller determines that there is a poor contact between the detection part of the temperature sensor and the surface of the fixing member, it notifies the external device of the information indicating the poor contact between the detection part of the temperature sensor and the surface of the fixing member through the communication interface. The fixing device according to [1]. [6] The temperature sensor includes a first temperature sensor that measures the temperature of a first region on the fixing member and a second temperature sensor that measures the temperature of a second region on the fixing member. The controller determines the poor contact between the detection part of the first temperature sensor and the surface of the fixing member based on the difference between the first temperature estimated value, which is the result of estimating the temperature of the first region on the fixing member, and the detected temperature of the first temperature sensor, and determines the poor contact between the detection part of the second temperature sensor and the surface of the fixing member based on the difference between the second temperature estimated value, which is the result of estimating the temperature of the second region on the fixing member, and the detected temperature of the second temperature sensor. The fixing device according to [1]. [7] The memory stores the first temperature estimated value, the detected temperature of the first temperature sensor, the second temperature estimated value, and the detected temperature of the second temperature sensor during a predetermined measurement period in the printing standby state. The controller determines the poor contact between the detection part of the first temperature sensor and the surface of the fixing member based on the difference between the average value of the first temperature estimated values and the average value of the detected temperatures of the first temperature sensor during the predetermined measurement period, and determines the poor contact between the detection part of the second temperature sensor and the surface of the fixing member based on the difference between the average value of the second temperature estimated values and the average value of the detected temperatures of the second temperature sensor during the predetermined measurement period. The fixing device described in [6]. [8] When the difference between the average value of the first temperature estimated value and the average value of the detected temperature of the first temperature sensor in the predetermined measurement period is equal to or greater than the threshold value for the first region, the controller determines that there is a poor contact between the detection unit of the first temperature sensor and the surface of the fixing member. When the difference between the average value of the second temperature estimated value and the average value of the detected temperature of the second temperature sensor in the predetermined measurement period is equal to or greater than the threshold value for the second region, the controller determines that there is a poor contact between the detection unit of the second temperature sensor and the surface of the fixing member. The fixing device described in [7]. [9] Furthermore, it has a display device. When the controller determines that there is a poor contact between the detection unit of the first temperature sensor and the surface of the fixing member, the controller displays a guidance indicating the poor contact of the detection unit of the first temperature sensor on the display device. When the controller determines that there is a poor contact between the detection unit of the second temperature sensor and the surface of the fixing member, the controller displays a guidance indicating the poor contact of the detection unit of the second temperature sensor on the display device. The fixing device described in [6].

[10] Furthermore, it has a communication interface for communicating with an external device. When the controller determines that there is a poor contact between the detection unit of the first temperature sensor and the surface of the fixing member, the controller notifies the external device of information indicating the poor contact of the detection unit of the first temperature sensor through the communication interface. When the controller determines that there is a poor contact between the detection unit of the second temperature sensor and the surface of the fixing member, the controller notifies the external device of information indicating the poor contact of the detection unit of the second temperature sensor through the communication interface. The fixing device described in [6].

Explanation of Signs

[0176] 1... Image forming apparatus (fixing device) 12... Communication interface 13... Controller 14... Heater control circuit 21... Fixing device 22... Power conversion circuit 23... Power supply voltage detection device 71... Heat roller (fixing member) 72... Press roller 73... Heater 731... Center heater 732... Side heater 74... Temperature sensor 741... Center temperature sensor (first temperature sensor) 742... Side temperature sensor (second temperature sensor) 81... Processor 82... ROM 83... RAM (memory) 84... Data memory (memory) 91... Temperature estimation unit 92... Estimation history holding unit 93... High-frequency component extraction unit 94... Coefficient addition unit 95... Target temperature output unit 96... Difference comparison unit 97... Control signal generation unit 98... Power supply circuit 200... Fixing device 271... Tubular film 272... Pressing roller 273... Heating element 2731... Central heating element 2732... First end heating element 2733... Second end heating element 275... Heating element substrate 300... Fixing device 371... Tubular film 372... Pressing roller 373... Heating element 375... Heating element substrate 400... Fixing device 471... Tubular film 472... Pressing roller 473... Heating element 4731... Heating element 4732... Heating element 475... Heating element substrate 500... Fixing device 571… Heat roller 572… Pressing roller 573… Induction heating coil 5731… Central coil 5732… End coil.

Claims

1. a fixing unit including a fixing member that comes into contact with the medium onto which the developer image has been transferred and a heat source that supplies heat to the fixing member; a temperature sensor that measures a temperature using a detection portion that is in contact with a surface of the fixing member that contacts the medium; a memory for storing a temperature estimate value for estimating a temperature of the fixing member and a detected temperature detected by the temperature sensor; a controller that determines a contact failure between a detection portion of the temperature sensor and a surface of the fixing member based on a difference between the temperature estimated value stored in the memory and the detected temperature of the temperature sensor; A fixing device having the same.

2. the memory stores a temperature estimate value during a predetermined measurement period in a print standby state and a detected temperature detected by the temperature sensor; the controller determines poor contact between a detection portion of the temperature sensor and a surface of the fixing member based on a difference between an average value of the estimated temperature during the predetermined measurement period and an average value of the detected temperature of the temperature sensor. The fixing device according to claim 1 .

3. the controller determines that there is poor contact between a detection unit of the temperature sensor and a surface of the fixing member when a difference between an average value of the estimated temperature during the predetermined measurement period and an average value of the detected temperature of the temperature sensor is equal to or greater than a predetermined threshold value; The fixing device according to claim 2 .

4. Further, the display device is provided. when it is determined that there is poor contact between the detection unit of the temperature sensor and the surface of the fixing member, the controller displays a guide indicating the poor contact between the detection unit of the temperature sensor and the surface of the fixing member on the display device. The fixing device according to claim 1 .

5. Further, the device has a communication interface for communicating with an external device, when it is determined that there is poor contact between the detection unit of the temperature sensor and the surface of the fixing member, the controller notifies the external device via the communication interface of information indicating the poor contact between the detection unit of the temperature sensor and the surface of the fixing member. The fixing device according to claim 1 .

Images