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 device. 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 a fixing member. A contact type temperature sensor can directly measure the temperature of the part where the detection part contacts. However, in the manufacturing process of an 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 a 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 laborious 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 one embodiment, the fixing device includes a fixing unit, a temperature sensor, a memory, and a controller. The fixing unit includes a fixing member into which a medium on which a developer image has been transferred comes into contact, and a heat source that supplies heat to the fixing member. The temperature sensor measures the temperature at a detection unit that comes into contact with the surface of the fixing member that comes into contact with the medium. The memory stores a temperature estimate that estimates the temperature of the fixing member and the detected 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 based on the difference between the temperature estimate stored in the memory and the detected temperature of the temperature sensor. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 shows an example of the configuration of an image forming apparatus equipped with a fixing device according to an embodiment. [Figure 2] Figure 2 shows a first example of the configuration of the fuser in the fixing device according to the embodiment. [Figure 3] Figure 3 is a block diagram showing an example of the configuration of a control system in an image forming apparatus equipped with a fixing device according to an embodiment. [Figure 4] Figure 4 shows an example of the configuration of a heater control circuit in a fixing device according to an embodiment. [Figure 5] Figure 5 shows the average values ​​of various temperatures in the center region of the heat roller measured in the ready state of the fixing device according to the embodiment. [Figure 6] Figure 6 shows the average values ​​of various temperatures in the side region of the heat roller measured in the ready state of the fixing device according to the embodiment. [Figure 7] Figure 7 is a graph showing various temperatures in the center region in relation to the size of the air layer acting as a float for the temperature sensor in the fixing device according to the embodiment. [Figure 8] Figure 8 is a graph showing various temperatures in the side region with respect to the size of the air layer acting as a float for the temperature sensor in the fixing device according to the embodiment. [Figure 9]Figure 9 shows the relationship between the WAE estimate, which fluctuates according to the floating of the center temperature sensor of the fixing device according to the embodiment, and the rise in the actual temperature of the center region. [Figure 10] Figure 10 shows the relationship between the WAE estimate, which fluctuates according to the floating of the side temperature sensor of the fixing device according to the embodiment, and the rise in the actual temperature of the side region. [Figure 11] Figure 11 shows the relationship between the temperature detected by the temperature sensor and the actual temperature of the heat roller in the fixing device according to the embodiment. [Figure 12] Figure 12 shows the relationship between the WAE estimate and the detected temperature for the actual temperature rise in the center region of the heat roller of the fixing device according to the embodiment. [Figure 13] Figure 13 shows the relationship between the WAE estimate and the detected temperature for the actual temperature rise in the side region of the heat roller of the fixing device according to the embodiment. [Figure 14] Figure 14 is a flowchart illustrating an example of the operation of the floating detection process for detecting floating of the temperature sensor in the fixing device according to the embodiment. [Figure 15] Figure 15 is a flowchart illustrating an example of the operation of the floating detection process for detecting floating of the temperature sensor in the fixing device according to the embodiment. [Figure 16] Figure 16 shows a second example of the configuration of a fuser used in the fixing device according to the embodiment. [Figure 17] Figure 17 shows an example of the configuration of a heater unit in a fuser, which is a second example of the configuration used in the fuser device according to the embodiment. [Figure 18] Figure 18 shows a third example of the configuration of a fuser used in the fixing device according to the embodiment. [Figure 19] Figure 19 shows an example of the configuration of a heater unit in a fuser, which is a third example of the configuration used in a fuser device according to the embodiment. [Figure 20] Figure 20 shows a fourth example of the configuration of a fuser used in the fixing device according to this embodiment. [Figure 21]FIG. 21 is a diagram showing a configuration example of a heater unit in a fixing device of a fourth configuration example used in the fixing device according to the embodiment. [Figure 22] FIG. 22 is a diagram showing a fifth configuration example of a fixing device used in the fixing device according to the embodiment. [Figure 23] FIG. 23 is a diagram showing a configuration example of a heater unit in a fixing device of a fifth configuration example used in the fixing device according to the embodiment. MODE FOR CARRYING OUT 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 multi-function peripheral (MFP) that performs various processes such as image formation while transporting a recording medium such as a print medium. The image forming apparatus 1 transfers a toner image formed by an electrophotographic method to a print medium as a recording medium, and fixes the toner image on the print medium with a fixing device.

[0009] The image forming apparatus 1 receives toner from a toner cartridge, and prints an image on a print 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 transport 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 operating device 16, multiple paper trays 17, an output tray 18, a transport mechanism 19, an image forming mechanism 20, a fuser 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 via a network. The communication interface 12 is used for communication with external devices. External devices include user terminals that issue print jobs, or servers that act as external management devices. The communication interface 12 is composed of, for example, a LAN connector. The communication interface 12 may also communicate wirelessly with other devices according to standards such as Bluetooth® or Wi-Fi®.

[0013] The controller (system controller) 13 controls and processes data for each part of the image forming apparatus 1. For example, the controller 13 is a computer including a processor, memory, and various interfaces. The controller 13 controls each part and processes data by having the processor execute programs stored in the memory. The controller 13 connects to each part within the housing 11 through various internal interfaces.

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

[0015] The controller 13 includes an engine controller that controls the operation of the transport mechanism 19, the image forming mechanism 20, and the fuser 21. For example, the controller 13 controls the transport of the printing medium P by the transport 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 printing medium P. The controller 13 controls the fixing of the developer image to the printing medium P by the fuser 21. By controlling the operation of the transport 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 printing medium P.

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

[0017] The heater control circuit 14 is a temperature control device that controls the supply of power to the heaters 73 (center heater 731 and side heaters 732) of the fuser 21, which will be described later, based on the control of the controller 13. The heater control circuit 14 generates the energizing power PC1 and PC2 to energize the heaters 73 of the fuser 21. The heater control circuit 14 supplies the energizing power PC1 to the center heater 731 and the energizing power PC2 to the side heaters 732. A detailed explanation of the heater control circuit 14 will be given later.

[0018] The display device 15 includes a display that displays images in response to image signals input from the controller 13 or a display control unit such as a graphics controller. For example, the display device 15 displays guidance or other information in response to instructions from the controller 13. The display device 15 also displays setting screens for various settings in the image forming apparatus 1 on its display.

[0019] The operating device 16 supplies an operation signal to the controller 13 in accordance with the operation performed on the operating device. The operating device may be, 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 integrated with the display device 15. The display device 15 and the operating device 16 may be provided on an operation panel that serves as a user interface.

[0020] The power conversion circuit 22 supplies DC voltage to various parts of the image forming apparatus 1 using 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. The power conversion circuit 22 supplies DC voltage Vdd to the controller 13 and DC power supply voltage Vdc to the heater control circuit 14. The power conversion circuit 22 also supplies the DC voltage necessary for image forming, generated from the AC voltage of the AC power source, to the image forming mechanism 20. The power conversion circuit 22 also supplies the DC voltage necessary for transporting the printing medium P, generated from the AC voltage of the AC power source, to the transport mechanism 19.

[0021] The power supply voltage detection device 23 detects the voltage value of the AC power supply AC supplied from an external power source and outputs a power supply voltage detection result Sv. The configuration of the power supply voltage detection device 23 is not particularly limited. Any device capable of detecting the power supply voltage value is acceptable. The power supply voltage detection device 23 may also detect the voltage value of the DC power supply voltage Vdc converted by the power conversion circuit 22, rather than the voltage value of the AC power supply AC supplied from the power source. The power supply voltage detection result Sv output by the power supply 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. The controller 13 may also transmit the power supply voltage value indicated by the power supply voltage detection result Sv to the host computer via the network using the communication interface 12. In this case, the controller 13 may store destination information such as the host computer's network address in non-volatile memory. The controller 13 may also transmit the power supply voltage value indicated by the power supply voltage detection result Sv to another image forming apparatus connected via the network using the communication interface 12. The controller 13 may also 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 the interface.

[0023] Next, the configuration of the transport system in the image forming apparatus 1 will be described. Each of the multiple paper trays 17 is a cassette that holds a print medium P. The paper trays 17 are configured to be able to receive the print medium P from outside the housing 11. For example, the paper trays 17 are configured to be able to be pulled out from the housing 11. The output tray 18 is a tray that supports the printing medium P discharged from the image forming apparatus 1.

[0024] The transport mechanism 19 is a mechanism for transporting the printing medium P within the image forming apparatus 1. As shown in Figure 1, the transport mechanism 19 has multiple transport paths. For example, the transport mechanism 19 has a paper feed transport path 31 and a paper discharge transport path 32.

[0025] The paper feed path 31 and the paper discharge path 32 are each composed of multiple motors, multiple rollers, and multiple guides. The multiple motors rotate their axes based on the control of the controller 13, thereby rotating the rollers that are linked to the rotation of the axes. The multiple rollers move the printing medium P by rotating. The multiple guides control the transport direction of the printing medium P.

[0026] The paper feed transport path 31 takes in the printing medium P from the paper tray 17 and supplies the taken printing medium P to the image forming mechanism 20. The paper feed transport path 31 is equipped with a pickup roller 33 corresponding to each paper tray. Each pickup roller 33 takes in the printing medium P from the paper tray 17 into the paper feed transport path 31.

[0027] The paper output transport path 32 is a transport path for discharging the printed medium P on which the image has been formed to the outside of the housing 11. The printed medium P discharged by the paper output transport path 32 is supported by the paper output 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 printing medium P. The image forming mechanism 20 forms an image on the printing medium P based on a print job generated by the controller 13. The image forming mechanism 20 comprises 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, each process unit 41 and exposure unit 42 will be described separately.

[0029] First, let's explain the process unit 41. The process unit 41 forms a toner image. For example, multiple process units 41 are provided for each type of toner. For example, multiple process units 41 correspond to color toners such as cyan, magenta, yellow, and black. Specifically, each process unit 41 is connected to a toner cartridge containing a different color toner.

[0030] A toner cartridge comprises a toner container and a toner dispensing mechanism. The toner container is a container that holds the toner. The toner dispensing mechanism is a mechanism consisting of a screw or the like that dispenses the toner from the toner container.

[0031] The process unit 41 includes a photoreceptor drum 51, a charger 52, and a developer 53, among other things. The photoreceptor drum 51 is a photoreceptor comprising a cylindrical drum and a photosensitive layer formed on the outer surface of the drum. The photoreceptor drum 51 rotates at a constant speed by a drive mechanism.

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

[0033] The developer unit 53 is a device that deposits toner onto the photoreceptor drum 51. The developer unit 53 includes a developer container, an agitation mechanism, a developing roller, a doctor blade, an automatic toner control (ATC) sensor, and the like.

[0034] The developer container is a container that receives and stores the toner dispensed from the toner cartridge. A carrier is pre-packaged inside the developer container. The toner dispensed from the toner cartridge is mixed with the carrier by an agitation mechanism, forming a developer mixture of toner and carrier. The carrier is placed inside the developer container during the manufacturing of the developer unit 53.

[0035] The developing roller rotates within the developer container, thereby applying developer to its surface. The doctor blade is a component positioned at a predetermined distance from the surface of the developing roller. The doctor blade removes a portion of the developer adhering to the surface of the rotating developing roller. This creates a layer of developer on the surface of the developing roller with a thickness corresponding to the distance between the doctor blade and the surface of the developing roller.

[0036] The ATC sensor is, for example, a magnetic flux sensor that has a coil and detects the voltage value generated in the coil. The voltage detected by the ATC sensor changes depending on the density of the magnetic flux from the toner in the developer container. That is, the controller 13 determines the density ratio of the toner remaining in the developer container to the carrier (toner density ratio) based on the voltage detected by the ATC sensor. Based on the toner density ratio, the controller 13 operates the motor that drives the toner cartridge delivery mechanism and delivers toner from the toner cartridge to the developer container of the developer unit 53.

[0037] Next, the configuration of the exposure unit 42 will be described. The exposure unit 42 is equipped with multiple light-emitting elements. The exposure unit 42 forms a latent image on the charged photoreceptor drum 51 by irradiating the photoreceptor drum 51 with light from the light-emitting elements. The light-emitting elements are, for example, light-emitting diodes (LEDs). Each light-emitting element is configured to irradiate light onto a single point on the photoreceptor drum 51. The multiple light-emitting elements are arranged in the main scanning direction, which is parallel to the rotation axis of the photoreceptor drum 51.

[0038] The exposure unit 42 forms a single line of latent image on the photoreceptor drum 51 by irradiating it with light using multiple light-emitting elements arranged in the main scanning direction. Furthermore, the exposure unit 42 forms multiple lines of latent image by continuously irradiating the rotating photoreceptor drum 51 with light.

[0039] In the above configuration, when light from the exposure unit 42 is shone onto the surface of the photoreceptor drum 51, which has been charged by the charger 52, an electrostatic latent image is formed. When the layer of developer formed on the surface of the developing roller comes into close proximity to the surface of the photoreceptor drum 51, the toner contained in the developer adheres to the latent image formed on the surface of the photoreceptor drum 51. As a result, a toner image is formed on the surface of the photoreceptor drum 51.

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

[0041] Furthermore, the transfer mechanism 43 includes, for example, a primary transfer belt 61, a secondary transfer opposing roller 62, and a plurality of primary transfer rollers 63 and secondary transfer rollers 64. In the configuration example shown in Figure 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 circumferential surface) of the primary transfer belt 61 is in contact with the secondary transfer opposing roller 62 and the plurality of winding rollers, while the outer surface (outer circumferential surface) faces the photoreceptor 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 conveying direction. Multiple winding rollers are configured to rotate freely. Multiple winding rollers rotate in accordance with the movement of the primary transfer belt 61 by the secondary transfer opposing roller 62.

[0043] Multiple primary transfer rollers 63 are configured to bring the primary transfer belt 61 into contact with the photoreceptor drum 51 of the process unit 41. The multiple primary transfer rollers 63 are provided to correspond to the photoreceptor drums 51 of the multiple process units 41. Specifically, the multiple primary transfer rollers 63 are provided at positions (primary transfer positions) opposite each other, with the photoreceptor drum 51 and primary transfer belt 61 of the corresponding process unit 41 in between. The primary transfer rollers 63 contact the inner circumferential surface of the primary transfer belt 61, displacing the primary transfer belt 61 toward the photoreceptor drum 51. As a result, the primary transfer rollers 63 bring the outer circumferential surface of the primary transfer belt 61 into contact with the photoreceptor drum 51.

[0044] The secondary transfer roller 64 is positioned opposite the primary transfer belt 61 (secondary transfer position). The secondary transfer roller 64 contacts the outer circumferential surface of the primary transfer belt 61 and applies pressure. This forms a transfer nip where the secondary transfer roller 64 and the outer circumferential 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 circumferential surface of the primary transfer belt 61.

[0045] The secondary transfer roller 64 and the secondary transfer opposing roller 62 rotate to transport the printing medium P supplied from the paper feed transport path 31 while gripping it. This allows the printing medium P to pass through the transfer nip.

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

[0047] Next, the configuration of the fuser 21 in the image forming apparatus 1 will be described. The fuser 21 fixes the toner image onto the printing medium P on which the toner image has been transferred. The fuser 21 operates based on the control of the controller 13. The fuser apparatus according to this embodiment is an apparatus comprising a fuser 21, a heater control circuit 14, and a controller 13. The fuser 21 comprises a fixing rotating body as a fixing member, a pressurizing member, a heating member (heat source), and a temperature sensor. Various configurations are possible for the fuser applied to the fuser apparatus according to this embodiment. Here, Figure 1 shows a first example of the configuration of the fuser 21.

[0048] In the first configuration example shown in Figure 1, the fuser 21 includes a heat roller 71, a press roller 72, a heater 73, and a temperature sensor 74. The heat roller 71 is an example of a fixing rotating body (fixing member). The press roller 72 is an example of a pressing member. The heater 73 is an example of a heating member (heat source). The fuser 21 of the first configuration example includes a heater 73 having multiple heat sources. In the first configuration example, the heater 73 has 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] Furthermore, the temperature sensor 74 is an example of a temperature sensor that detects the surface temperature of the heat roller 71. In this embodiment, the fuser 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 that the detection part contacts. In the first configuration example, the temperature sensor 74 has 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 area on the surface of the heat roller 71. The detection part of the temperature sensor 742 contacts the side area on the surface of the heat roller 71.

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

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

[0052] The heat roller 71 is heated on the inside of the core metal by a heater 73, which is a heating element (heat source) positioned inside the hollow core metal. The heat applied to the inside of the core metal is transferred to the surface of the heat roller 71 (the surface of the elastic layer), which is the outside of the core metal. The fixing rotating body may be configured as an endless belt.

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

[0054] The press roller 72 applies pressure to the heat roller 71 due to the stress applied from the tension member. The pressure is, for example, 150 N. The diameter of the press roller 72, the pressure value, and the name of the raw material are examples only and are not limited to these. The pressure applied from the press roller 72 to the heat roller 71 forms a nip (fixing nip) where the press roller 72 and the heat roller 71 are in close contact. The press roller 72 is rotated by a motor. As the press roller 72 rotates, it moves the printing medium P that has entered the fixing nip and presses the printing medium P against the heat roller 71. 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 multiple heat sources, which generate heat using electricity supplied from the heater control circuit 14. In the first configuration example shown in Figures 1 and 2, the heater 73 in the fuser 21 has two heat sources (heat sources): a center heater (first heat source) 731 and a side heater (second heat source) 732. The center heater 731 and the side heater 732 are, for example, halogen lamp heaters equipped with halogen lamps.

[0056] In the first configuration example, the heater 73 in the fuser 21 consists of two heaters: a center heater 731 and a side heater 732. The center heater 731 heats the center region (first region) C, which is the central part of the heat roller 71 in the direction of the rotation axis. The side heater 732 heats the side region (second region) S, which is the peripheral part of the heat roller 71 other than the central part in the direction of the rotation axis. The printing medium P is transported in the transport direction F shown in Figure 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 printing medium P.

[0057] The center heater 731 and the side heater 732 generate heat through power supplied by the control of the controller 13. The power consumption of the center heater 731 and the side heater 732 is, for example, 600W. When the controller 13 performs a fixing process on a printing medium P that is narrow in the direction of rotation of the heat roller 71 (the transport direction F of the printing medium P), it heats the center area C of the heat roller 71. When the controller 13 heats the center area C of the heat roller 71, it activates the center heater 731 without activating the side heater 732 using the heater control circuit 14.

[0058] Furthermore, when the controller 13 performs a fixing process on a printing medium P that is wide in the direction of rotation of the heat roller 71 (the transport direction F of the printing medium P), it 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, it activates both the center heater 731 and the side heater 732 using the heater control circuit 14.

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

[0060] Each temperature sensor 741 and 742 has a detection unit that contacts the surface of the heat roller 71. The center temperature sensor 741 detects the temperature of the center region C of the heat roller 71 by having its detection unit contact 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 by having its detection unit contact the surface of the side region S of the heat roller 71.

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

[0062] The heat roller 71 and press roller 72 apply heat and pressure controlled within a predetermined temperature range to the printing medium P as it passes through the fuser nip. The toner on the printing medium P is fixed to the surface of the printing medium P by the heat from the heat roller 71 and the pressure from the heat roller 71 and press roller 72. As a result, a toner image is fixed to the printing medium P as it passes through the fuser nip. The printing medium P that has passed through the fuser nip is introduced into the paper discharge 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 this embodiment will be described. Figure 3 is a block diagram showing an example of the control system configuration in the image forming apparatus 1. As shown in Figure 3, the image forming apparatus 1 connects a communication interface 12, a heater control circuit 14, a display device 15, an operating device 16, a transport mechanism 19, an image forming mechanism 20, and a fuser 21, etc., to a controller (system controller) 13.

[0064] The controller 13 includes a processor 81, ROM (Read Only Memory) 82, RAM (Random Access Memory) 83, and data memory 84. The controller 13, along with the processor 81, ROM 82, RAM 83, and data memory 84, constitutes a computer. The controller 13 may also include an ASIC, such as an image processing processor.

[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 the operating system or 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 acting as the controller 13. ROM 82 is a non-volatile memory area, and RAM 83 is a volatile memory area. ROM 82 stores the operating system or application programs. ROM 82 stores control data necessary for the processor 81 to perform processing to control each part. RAM 83 is used as a work area where data is rewritten as appropriate by the processor 81. RAM 83 has a work area for storing, for example, image data.

[0067] The data memory 84 is composed of 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 EEPROM (Electric Erasable Programmable Read-Only Memory), HDD (Hard Disk Drive), or SSD (Solid State Drive). The data memory 84 stores data such as configuration data used by the processor 81 when performing various processes. The data memory 84 stores data generated by processes executed by the processor 81. The data memory 84 may also store application programs.

[0068] The controller 13 controls the image forming mechanism 20. For example, the controller 13 controls each process unit 41, the exposure unit 42, and the transfer mechanism 43. For example, the controller 13 controls the on / off switching of the charger 52 of each process unit 41. The controller 13 controls the on / off switching of the laser light that irradiates the photoreceptor drum 51 to the exposure unit 42 of each process unit 41. As a result, an electrostatic latent image is formed on the photoreceptor drum 51.

[0069] Furthermore, the controller 13 controls the on / off switching of the development bias for the developer unit 53 of each process unit 41. As a result, the electrostatic latent image on the photoreceptor drum 51 is developed by the toner supplied from the developer unit 53, and a toner image is formed on the photoreceptor drum 51. The controller 13 controls the primary transfer bias for the transfer mechanism 43 at each primary transfer position. The toner image on the photoreceptor drum 51 is transferred to the primary transfer belt 61 at the primary transfer position. In addition, the controller 13 controls the secondary transfer bias for the transfer mechanism 43 at the secondary transfer position. As a result, the toner image on the primary transfer belt 61 is transferred to the printing medium P.

[0070] Furthermore, the controller 13 controls the fixing device, including the fuser 21. The controller 13 controls the operation of the center heater 731 and the side heaters 732 by the heater control circuit 14 according to the detection results of the temperature sensors 741 and 742. The heater control circuit 14 controls the supply of power to the center heater 731 and the side heaters 732 by operating in response to control instructions from the controller 13. Note that some or all of the components of the heater control circuit 14, which will be described later, may be included in the controller 13.

[0071] The heater control circuit 14 controls the power supply to the center heater 731 and the side heater 732 so that the surface of the heat roller 71 reaches a 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 target value for the center (e.g., 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 target value for the side (e.g., 155°C).

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

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

[0074] In other words, the thermal capacitance of the fuser 21 in the thermal CR circuit is replaced by a capacitor C. The heat transfer resistance is replaced by a resistor R. The heat source is replaced by a DC voltage source. The thermal CR circuit is a circuit that operates in response to an input voltage pulse. The thermal CR circuit operates with an input voltage pulse in which the DC voltage source is repeatedly energized and cut off based on the energization pulse. Such a thermal CR circuit applies the heat generated as an output voltage to the heating element.

[0075] In the thermal CR circuit, the values ​​of each element (C and R) are set based on the amount of current supplied to the heating element and the heat capacity of the fixing rotating body. The amount of heat transmitted to the surface of the fixing rotating body, which is the target of control, can be estimated based on the thermal CR circuit described above. WAE control controls the amount of current supplied to the heating element based on the actual surface temperature of the fixing rotating body estimated from the energy input to the fuser, etc., by simulating the thermal CR circuit. Through such WAE control, the fixing apparatus in the image forming apparatus 1 according to the embodiment controls the surface temperature of the fixing rotating body to reach a target value.

[0076] Furthermore, the image forming apparatus 1 can determine the actual input voltage (input energy) using the power supply voltage detection device 23. This enables the image forming apparatus 1 to perform operation control using the actual input voltage in WAE control.

[0077] Figure 4 shows an example of the configuration 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 Figure 4, the heater control circuit 14 controls the supply of power to the heater 73 of the fuser 21. The heater control circuit 14 generates energizing powers PC1 and PC2 to energize the heater 73 of the fuser 21. The heater control circuit 14 supplies power to the center heater 731 with energizing power PC1 and to the side heater 732 with energizing power PC2.

[0078] The heater control circuit 14 includes a temperature estimation unit 91, an estimation history retention 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. The heater control circuit 14 also receives 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 as input.

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

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

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

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

[0083] The high-frequency component extraction unit 93 performs high-pass filtering to extract the high-frequency components 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 components, to the coefficient summing unit 94.

[0084] The coefficient addition unit 94 performs a coefficient addition process, which is a correction of the temperature detection result Td. The coefficient addition unit 94 receives the temperature detection result Td from the temperature sensor 74 and the high-frequency component HPF from the high-frequency component extraction unit 93 as inputs. 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 the corrected temperature value WAE. The coefficient addition unit 94 outputs the corrected temperature value WAE to the difference comparison unit 96. The coefficient addition unit 94 also outputs the corrected temperature value WAE to the processor 81 of the controller 13.

[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. The difference comparison unit 96 performs difference calculation processing. The difference comparison unit 96 calculates the 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 energizing pulse Ps, which is a pulse signal for controlling the energization of the heater 73, based on the differential DIF. The control signal generation unit 97 outputs the energizing pulse Ps to the power supply circuit 98 and the temperature estimation unit 91.

[0087] The power supply circuit 98 supplies energizing power PC1 and PC2 to the heater 73 based on the energizing 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 fuser 21. For example, the power supply circuit 98 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 energizing pulse Ps. In this way, the power supply circuit 98 supplies energizing power PC1 and PC2 to the heater 73. In other words, the power supply circuit 98 varies the energizing time of the heater 73 of the fuser 21 according to the energizing pulse Ps.

[0088] The power supply circuit 98 receives a lighting control signal from the processor 81 of the controller 13, corresponding to the size of the printing medium P to be fixed. The power supply circuit 98 supplies either power PC1 or both power PC1 and PC2 to the heater 73 according to the lighting control signal from the processor 81, i.e., according to the size of the printing medium P.

[0089] Furthermore, the power supply circuit 98 may be integrated with the fuser 21. The heater control circuit 14 may be configured to supply energizing pulses Ps to the power supply circuit of the heater 73 of the fuser 21, rather than supplying energizing power PC to the heater 73.

[0090] As described above, the heater control circuit 14 adjusts the amount of power supplied to the heater 73 of the fuser 21 based on the heat capacity correction amount Cc, the temperature detection result Td, the power supply voltage detection result Sv, the temperature estimation history PREV, and the energization pulse Ps, thereby adjusting the surface temperature of the heat roller. This allows the heater control circuit 14 to control the power supplied to the heater 73 so that the surface temperature of the heat roller 71 reaches the target temperature.

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

[0092] Furthermore, the heat capacity C of the fuser used in WAE control may be the design standard value. However, in WAE control using the design standard value, there is a possibility that the heat capacity of the fuser may vary from machine to machine, so a heat capacity correction amount Cc may be set for the heat capacity C. For example, the image forming apparatus 1 may have a correction amount table in the data memory 84 that shows the heat capacity correction amount Cc as a correction amount for the heat capacity C. The correction amount table stores the heat capacity correction amount according to the temperature difference set for each machine of the image forming apparatus 1. The temperature difference is the difference between the heater temperature of the fuser 21 estimated by the heater control circuit 14 with the heat capacity correction amount set to "0" and the heater temperature measured in actual measurements.

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

[0094] Next, we will explain the various temperature fluctuations caused by the contact state between the surface of the heat roller 71 and the contact detection part of the temperature sensor 74 (hereinafter simply referred to as the detection part). The detection part of the temperature sensor 74, which is a contact-type sensor, is mounted so as to be in contact with the surface of the heat roller 71. However, due to improper mounting or other reasons, the detection part of the temperature sensor 74 may separate from the surface of the heat roller 71. In the following description, this state in which the detection part of the temperature sensor 74 and the surface of the heat roller 71 are separated will also be referred to as temperature sensor floating. Temperature sensor floating is checked, for example, during the manufacturing process of the image forming apparatus 1, or when the fuser 21 of the image forming apparatus 1 is replaced during operation.

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

[0096] In the actual manufacturing process of the image forming apparatus or the replacement work of the fuser 21, it is assumed that there is no dirt or foreign matter adhering between the contact part 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, then an air layer will exist between the detection part of the temperature sensor 74 and the surface of the heat roller 71. Generally, the thermal conductivity of air is said to be 0.0241 [W / (m·K)], and the thermal conductivity of polyimide is said to be 0.23 [W / (m·K)]. Therefore, the ratio of the thermal conductivity of air to polyimide is 0.1 (0.0241 ÷ 0.23). This indicates that air is about 10 times less efficient at transferring heat than gap tape.

[0097] According to the thermoelectric coefficient ratios mentioned above, a gap tape with a thickness of 0.42 mm can be converted to an air gap of 0.042 mm. If the thickness of one piece of gap tape is 0.007 mm, a gap tape with a thickness of 0.42 mm, equivalent to an air gap of 0.042 mm, can be formed by stacking six pieces of gap tape. Also, a gap tape with a thickness of 0.21 mm, equivalent to an air gap of 0.021 mm, can be formed by stacking three pieces of gap tape.

[0098] Figure 5 shows the average values ​​of various temperatures acquired during the last 20 seconds of a 1-minute period 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 (float of the temperature sensor) between the surface of the heat roller 71 and the contact area of ​​the temperature sensor 741 is changed. The measurement results for various air layers show the actual temperature of the heat roller 71, the temperature detected by the temperature sensor 741, and the estimated center WAE value. The actual temperature of the heat roller 71 was measured using a thermocouple on the surface of the center region C of the heat roller 71.

[0099] In Figure 5, the air gap (float of the temperature sensor) can be set to one of three patterns: "0 mm", "0.021 mm", or "0.042 mm". The "0 mm" air gap state is when the surface of the heat roller 71 is in contact with the detection part of the temperature sensor 741. The "0.021 mm" air gap state is when three gap tapes with a gap of 0.21 mm are placed between the surface of the heat roller 71 and the detection part of the temperature sensor 741. The "0.042 mm" air gap state is when six gap tapes with a gap of 0.42 mm are placed between the surface of the heat roller 71 and the detection part of the temperature sensor 741.

[0100] As shown in Figure 5, the measured temperature (temperature detected by the temperature sensor 741) is almost the same regardless of the presence or absence of an air layer. This is because the center heater 731 is controlled so that the temperature detected by the center temperature sensor 741 reaches the target value. In contrast, the actual temperature (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 it is 0.021 mm, and 170.2°C when there is no air layer. Furthermore, the estimated center WAE is 203.5°C when the air layer is 0.042 mm, 186.4°C when it is 0.021 mm, and 172.9°C when there is no air layer.

[0101] Figure 5 shows the difference between the estimated center WAE value and the temperature detected by the temperature sensor 741 (the difference between the estimated WAE value and the detected temperature), and the difference between the actual temperature in the center region C and the temperature detected by the temperature sensor 741 (the difference between the actual temperature and the detected temperature). In the center region, both the difference between the estimated WAE value and the detected temperature, and the difference between the actual temperature and the detected temperature, increase as the air layer increases (the gap widens).

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

[0103] Furthermore, Figure 5 shows the difference in actual temperature due to the air layer compared to the actual temperature without the air layer. For example, when the air layer is 0.042 mm thick, the actual temperature rise is 19.4°C, and when it is 0.021 mm thick, the actual temperature rise is 8.6°C. These results show that the larger the air layer, the greater the actual temperature rise.

[0104] Figure 6 shows the average values ​​of various temperatures obtained during the last 20 seconds of a 1-minute period in the ready state, with the control temperature of the side region S set to 155°C. The measurement results shown in Figure 6, similar to the measurement results shown in Figure 5, show the actual temperature (temperature measured by a thermocouple on the surface of the side region S of the heat roller 71), the detected temperature (temperature detected by the temperature sensor 742), and the estimated side WAE value for three different air layer configurations.

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

[0106] Figure 6 shows the difference between the estimated side WAE value and the temperature detected by the temperature sensor 742 (the difference between the estimated WAE value and the detected temperature), and the difference between the actual temperature in the side region S and the temperature detected by the temperature sensor 742 (the difference between the actual temperature and the detected temperature). In the side region S as well, both the difference between the estimated WAE value and the detected temperature, and the difference between the actual temperature and the detected temperature, increase as the air layer increases.

[0107] For example, the difference between the estimated WAE 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. As shown in Figure 6, since the detected temperature is a constant value (157°C) regardless of the air layer, the estimated WAE value and the actual temperature increase as the air layer increases.

[0108] Furthermore, Figure 6 shows the difference in actual temperature due to the air layer compared to the actual temperature without the air layer. For example, the actual temperature increase when the air layer is 0.042 mm is 19.2°C. Also, the actual temperature increase when the air layer is 0.021 mm is 11.2°C. These results indicate that, even in the side region, the actual temperature increases as the size of the air layer increases.

[0109] Figure 7 is a diagram showing graphs of various temperatures in relation to the size of the air layer, based on the measurement results shown in Figure 5. In Figure 7, line Cs represents the temperature detected by the temperature sensor 741, line Cr represents the actual temperature of the center region C of the heat roller 71, and line Cw represents the WAE estimate. Figure 7 shows that while the temperature detected by the temperature sensor 741 remains constant, the actual temperature and the WAE estimate increase as the air layer increases.

[0110] Figure 8 is a graph showing the measurement results from Figure 6, with various temperatures as a function of the size of the air layer. In Figure 8, line Ss represents the temperature detected by the temperature sensor 742, line Sr represents the actual temperature of the side region S of the heat roller 71, and line Sw represents the WAE estimate. As shown in Figure 8, similar to Figure 7, the temperature detected by the temperature sensor 742 remains constant, while the actual temperature and the WAE estimate increase as the air layer increases.

[0111] The phenomena shown in Figures 7 and 8 are thought to be caused by the fact that when the temperature sensor 74 (741, 742) is floating, the temperature detected by the temperature sensor 74 becomes lower than the actual temperature of the heat roller 71. The heater control circuit 14 controls the on / off state of the heater to maintain the temperature detected by the temperature sensor 741 at a target value. If the temperature detected by the temperature sensor 741 is lower than the actual temperature, the heater control circuit 14 will overheat the heat roller 71, causing the heater 73 to turn on more times. As a result, the actual temperature of the heat roller 71 and the WAE estimate will rise above the temperature detected by the temperature sensor 74. By utilizing this phenomenon, the controller 13 can detect (determine) the floating of the temperature sensor 74 based on the temperature difference between the temperature detected by the temperature sensor 74 (741, 742) and the WAE estimate.

[0112] Next, we will explain the correlation between the increase in the WAE estimate due to the floating of the temperature sensor 74 and the increase in the actual temperature at the heat roller. Figure 9 shows the relationship between the estimated center WAE value, which fluctuates according to the floating of the center temperature sensor 741, and the rise in the actual temperature in the center region C of the heat roller 71. The horizontal axis in Figure 9 represents the temperature difference between the WAE estimated value shown in Figures 5 and 7 and the detected temperature (the temperature detected by the temperature sensor 741). The vertical axis in Figure 9 represents the temperature increase in the actual temperature (the actual temperature of the center region C of the heat roller 71) shown in Figures 5 and 7. Figure 9 shows that the actual temperature of the center region C rises at a constant rate in accordance with the difference between the WAE estimated value, which rises due to the floating of the temperature sensor 741, and the detected temperature. According to the correlation shown in Figure 9, the correlation equation (y=0.6347x-6.4909) between the difference between the WAE estimated value, which rises due to the floating of the temperature sensor 741, and the detected temperature, and the actual temperature can be obtained.

[0113] Figure 10 shows the relationship between the estimated side WAE value, which fluctuates 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 in Figure 10 represents the temperature difference between the WAE estimated value shown in Figures 6 and 8 and the detected temperature (the temperature detected by the temperature sensor 742). The vertical axis in Figure 10 represents the temperature increase in the actual temperature (the actual temperature of the side region S of the heat roller 71) shown in Figures 6 and 5. Figure 10 shows that the actual temperature of the side region S rises at a constant rate in accordance with the difference between the WAE estimated value, which rises due to the floating of the temperature sensor 742, and the detected temperature. According to the correlation shown in Figure 10, a correlation equation (y=0.5021x-13.782) can be obtained between the difference between the WAE estimated value, which rises due to the floating of the temperature sensor 742, and the detected temperature, and the actual temperature.

[0114] Figure 11 shows the relationship between the temperature detected 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 Figure 11, under normal conditions (when the temperature sensor is not floating), the variation in temperature detected by the temperature sensor 74 is within ±5°C of the actual temperature of the heat roller 71. In contrast, when the temperature sensor is floating, the actual temperature rises compared to normal conditions, so the temperature detected by the temperature sensor 74 becomes more than 5°C higher than the actual temperature. Therefore, if the increase in actual temperature is 5°C or less, it can be determined that the temperature sensor 741 is not floating, and if the increase in actual temperature is more than 5°C, it can be determined that the temperature sensor 741 is floating.

[0115] Figure 12 shows the relationship between the estimated center WAE value and the difference (tac) between the actual temperature rise (tbc) in the center region C and the temperature detected by the center temperature sensor 741. Figure 12 shows the difference between the WAE estimate and the temperature detected by the temperature sensor 741, divided into cases where the actual temperature rise in the center region C is 5°C or less and cases where it is higher than 5°C. According to the correlation formula shown in Figure 9, when the actual temperature rise in the center region C is 5°C, the difference between the center WAE estimate and the temperature detected by the center temperature sensor 741 is 18.1°C.

[0116] As shown in Figure 12, if the difference between the estimated center WAE value and the temperature detected by 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 estimated center WAE value and the temperature detected by the temperature sensor 741 is 18.1°C or less, it can be determined that the temperature sensor 741 is not floating (the contact part is in contact with the heat roller). Also, if the difference between the estimated center WAE value and the temperature detected by 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 estimated center WAE value and the temperature detected by the temperature sensor 741 is higher than 18.1°C, it can be determined that the temperature sensor 741 is floating (the contact part is separated from the heat roller).

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

[0118] According to Figure 13, if the difference between the estimated side WAE value and the temperature detected by 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 estimated side WAE value and the temperature detected by the temperature sensor 742 is 37.4°C or less, it can be determined that the temperature sensor 742 is not floating (the contact part is in contact with the heat roller). Also, if the difference between the estimated side WAE value and the temperature detected by the temperature sensor 742 is higher than 37.4°C, the actual temperature rise in the side region S will be higher than 5°C. Therefore, if the difference between the estimated WAE value and the detected temperature is higher than 37.4°C, it can be determined that the temperature sensor 742 is floating (the contact part is separated from the heat roller).

[0119] Next, we will describe the lift detection process for detecting lifting of the temperature sensors 74 (741, 742) in the fuser 21 of the image forming apparatus 1 according to the embodiment. Figures 14 and 15 are flowcharts illustrating an example of the operation of the lift detection process for detecting lift of the temperature sensors 74 (741, 742) in the fuser 21 of the image forming apparatus 1 according to the embodiment. For example, the controller 13 performs a dirt prediction process by having the processor 81 execute a program for float detection processing. The program for float detection processing executed by the processor 81 is stored in a non-volatile memory such as ROM 82 or data memory 84.

[0120] Here, the floating detection process is performed assuming that there is no contamination inside the fuser 21, such as during the manufacturing process of the image forming apparatus 1 or during the replacement of the fuser 21. For example, the controller 13 performs the floating detection process during the manufacturing process of the image forming apparatus 1 or during the replacement of the fuser 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 the calculation of the center WAE estimate and the side WAE estimate (ACT 11). If the conditions for performing floating detection, such as in the manufacturing process, are met, the controller 13 determines whether the detected temperatures of both temperature sensors 741 and 742 are 40°C or lower (ACT 12).

[0122] If the temperature detected by either temperature sensor 741 or 742 is higher than 40°C (ACT12, NO), the controller 13 notifies that the fuser 21 is too hot to perform float detection (ACT13). If the heat roller 71 is hot (in this case, 40°C or higher) when the power is turned on, the heat capacity of the heating element up to the standby state, the thermal resistance of the fuser, and the energy input to the fuser will change. Therefore, if the heat roller 71 is hot when the power is turned on, the WAE estimate will not be stable. If the WAE estimate is not stable, the float detection by temperature sensors 741 and 742 cannot be correctly determined. As a result, the controller 13 will not perform float detection if the temperature detected by both temperature sensors 741 and 742 is higher than 40°C.

[0123] For example, if the temperature detected by the temperature sensor 74 is higher than 40°C, the controller 13 displays on the display device 15 that the fuser temperature is too high and therefore float detection will not be performed. The controller 13 may also notify an external device via the communication I / F 12 that the fuser temperature 21 is too high and therefore float detection will not be performed. By notifying the operator (worker, service technician, manager, etc.) that the fuser temperature is too high and float detection cannot be performed, the image forming apparatus 1 can prompt the operator to lower the fuser temperature before performing float detection with the temperature sensor.

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

[0125] If a print request is received by the controller 13 between the start of standby and the end of a predetermined time (measurement end time, e.g., 60 seconds) (ACT14, YES), the controller 13 stops the float detection and notifies the controller of the cancellation of float detection due to printing (ACT15). For example, the controller 13 may display the cancellation of float detection due to printing on the display device 15, or it may notify an external device via the communication I / F 12.

[0126] When the controller 13 has elapsed from the start of standby to the start of measurement (40 seconds) (ACT16, YES), it acquires the detected temperatures of the temperature sensors 74 (temperature sensors 741 and 742) at predetermined timings (for example, at predetermined intervals). The controller 13 stores the detected temperatures of the temperature sensors 74 acquired at predetermined timings in the RAM 83 (or data memory 84) (ACT17). For example, the controller 13 stores the detected temperatures of temperature sensor 741 and temperature sensor 742 acquired at predetermined intervals in the RAM 83.

[0127] Furthermore, when the measurement start time (40 seconds) has elapsed from the start of standby (ACT16, YES), the controller 13 acquires WAE estimates (center WAE estimate and side WAE estimate) at predetermined timings (for example, predetermined cycles). The controller 13 stores the WAE estimates acquired at predetermined timings in RAM 83 (or data memory 84) (ACT18). For example, the controller 13 stores the center WAE estimate and side WAE estimate acquired at predetermined cycles in RAM 83.

[0128] The controller 13 continuously saves the temperature detected by the temperature sensor 74 and the WAE estimate value from the start of standby until the measurement end time (60 seconds) has elapsed (ACT19, NO). The controller 13 defines the period from 40 seconds after the start of standby until 60 seconds (the last 20 seconds within the period from the start of standby to 60 seconds) as a predetermined measurement period. The controller 13 saves the temperature detected by the temperature sensor 74 and the WAE estimate value during the predetermined measurement period (the time from the start of measurement to the end of measurement) to the RAM 83.

[0129] For example, the controller 13 stores the detected temperatures and WAE estimates (center WAE estimate, side WAE estimate) of the temperature sensors 74 (741, 742) acquired at predetermined intervals during a predetermined measurement period in the RAM 83. As a result, the RAM 83 stores the detected temperatures of temperature sensor 741, temperature sensors 742, center WAE estimates, and side WAE estimates for the predetermined measurement period.

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

[0131] Furthermore, when 60 seconds have elapsed since the start of standby (ACT19, YES), the controller 13 calculates the average value of the WAE estimates for a predetermined measurement period stored in RAM 83 (ACT21). Specifically, the controller 13 calculates the average value of the center WAE estimates and the average value of the side WAE estimates for the predetermined measurement period.

[0132] Controller 13 calculates the average value of the detected temperature from the center temperature sensor 741 and the average value of the center WAE estimate, and then calculates the difference between these average values ​​(average difference) (ACT22). That is, Controller 13 calculates the difference between the average value of the detected temperature from the center temperature sensor 741 and the average value of the center WAE estimate as the center average difference. After calculating the center average difference, Controller 13 determines whether the center average difference is greater than or equal to the center threshold (threshold for the first region) (ACT23). If the center average difference is not greater than or equal to the center threshold (ACT23, NO), Controller 13 proceeds to ACT25.

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

[0134] If the average difference of the centers is greater than or equal to the threshold for the centers (ACT23, YES), the controller 13 notifies that it has detected a floating of the center temperature sensor 741 (ACT24). For example, if floating of the center temperature sensor 741 is detected, the controller 13 displays on the display device 15 that floating of the center temperature sensor 741 has been detected. This allows the image forming apparatus 1 to notify that floating of the center temperature sensor 741 has been detected using its own display device 15. As a result, the image forming apparatus 1 can prompt nearby operators (workers, service personnel, managers, etc.) to check the mounting status of the center temperature sensor 741 in which floating has been detected.

[0135] Furthermore, the controller 13 may also notify an external device via the communication I / F 12 that it has detected a lift in the center temperature sensor 741. Upon receiving such notification, the external device will inform the image forming apparatus 1 that it has detected a lift in the center temperature sensor 741 (for example, by displaying it on a display device). This allows the image forming apparatus 1 to be notified by an external device located remotely that it has detected a lift in the center temperature sensor 741. As a result, the image forming apparatus 1 can prompt an operator located remotely to confirm the mounting status of the center temperature sensor 741 in which a lift has been detected.

[0136] Furthermore, the controller 13 calculates the difference between the average values ​​of the side temperature sensor 742's detected temperatures and the average values ​​of the side WAE estimates (ACT25). In other words, the controller 13 calculates the difference between the average values ​​of the side temperature sensor 742's detected temperatures and the average values ​​of the side WAE estimates as the side average difference. After calculating the side average difference, the controller 13 determines whether the side average difference is greater than or equal to the threshold for the side (threshold for the second region) (ACT26). If the side average difference is not greater than or equal to the threshold for the side (ACT26, NO), the controller 13 terminates the floating detection process.

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

[0138] If the average difference of the sides is greater than or equal to the threshold for the sides (ACT26, YES), the controller 13 notifies that it has detected a lift in the side temperature sensor 742 (ACT27). For example, if the controller 13 detects a lift in the side temperature sensor 742, it displays on the display device 15 that a lift in the side temperature sensor 742 has been detected. This allows the image forming apparatus 1 to notify that it has detected a lift in the side temperature sensor 742 using its own display device 15. As a result, the image forming apparatus 1 can prompt nearby operators (workers, service personnel, managers, etc.) to check the mounting status of the side temperature sensor 742 in which a lift has been detected.

[0139] Furthermore, the controller 13 may also notify an external device via the communication I / F 12 that it has detected a lift in the side temperature sensor 742. Upon receiving such notification, the external device will announce (for example, display on a display device) that the image forming apparatus 1 has detected a lift in the side temperature sensor 742. This allows the image forming apparatus 1 to be notified by an external device located remotely that a lift in the side temperature sensor 742 has been detected. As a result, the image forming apparatus 1 can prompt an operator located remotely to confirm the mounting status of the side temperature sensor 742 that has been detected as lifted.

[0140] As described above, the image forming apparatus according to the embodiment acquires the temperature detected by the temperature sensor and the WAE estimated value during a predetermined period immediately after power-on. The image forming apparatus calculates the difference between the average value of the temperature detected by the temperature sensor and the average value of the WAE estimated value during the predetermined period. If the difference between the temperature detected by the temperature sensor and the WAE estimated value is greater than or equal to a predetermined threshold, the image forming apparatus detects that the temperature sensor has floated. As a result, the image forming apparatus can detect that the temperature sensor installed in the fuser has floated without using a dedicated jig.

[0141] Furthermore, the image forming apparatus according to the embodiment performs a lift detection process for both the center temperature sensor and the side temperature sensor. When the image forming apparatus detects a lift in either the center temperature sensor or the side temperature sensor, it notifies the operator that a lift in the temperature sensor has been detected. By notifying the operator that a lift in the temperature sensor has been detected, the image forming apparatus can prompt the operator to check the mounting status of the temperature sensor and other relevant information.

[0142] In the embodiments described above, an image forming apparatus 1 equipped with a fuser 21 of the first configuration example shown in Figures 1 and 2 was described. However, the configuration of the fuser applied to the image forming apparatus 1 according to the embodiment is not limited to the first configuration example shown in Figures 1 and 2. The image forming apparatus 1 according to the embodiment is not limited to the fuser 21 of the first configuration example, but can also be fitted with fusers of the second to fifth configuration examples described later.

[0143] The following describes modified examples of the fuser applicable to the image forming apparatus 1 according to this embodiment. First, a second example of a fuser applicable to the image forming apparatus 1 according to this embodiment, namely the fuser 200, will be described. Figure 16 shows an example configuration of a fuser 200, which is a second example of a fuser applicable to the image forming apparatus 1 according to the embodiment. Figure 17 shows an example configuration of the heater unit in the fuser 200.

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

[0145] The heater unit includes a heating element 273 and a heating element substrate 275. The heating element substrate 275 is made of a metal material or a ceramic material. The heating element substrate 275 is formed in the shape of an elongated rectangular plate. The heating element substrate 275 is positioned radially inside the tubular film 271. The heating element substrate 275 has its longitudinal direction aligned with the axial direction of the tubular film 271.

[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 in a direction perpendicular to the paper transport direction (the longitudinal direction of the heating element substrate 275). The central heating element 2731 is positioned so that its center aligns with the width direction of the printing medium P passing through the nip (a direction perpendicular to the transport direction). The first end heating element 2732 and the second end heating element 2733 are arranged side by side on either side of the central heating element 2731.

[0147] The central heating element 2731 is an example of a first heat source. As shown in Figure 17, the central heating element 2731 supplies heat mainly to the center region C in a direction perpendicular to the paper transport direction. However, even if only the central heating element 2731 is heated, the temperature of the side region S will rise. The first end heating element 2732 and the second end heating element 2733 are examples of second heat sources. As shown in Figure 17, the first end heating element 2732 and the second end heating element 2733 supply heat mainly to the side region S in a direction perpendicular to the paper transport direction.

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

[0149] As described above, the fuser 200 shown in Figures 16 and 17 can also be subjected to the WAE control described above. An image forming apparatus equipped with the fuser 200 shown in Figures 16 and 17 can perform temperature sensor floating detection processing based on the difference between the WAE estimated value and the temperature detected by the temperature sensor, as described above. However, the thresholds shown in Figures 12 and 13 cannot be directly applied to an image forming apparatus equipped with the fuser 200. An image forming apparatus equipped with the fuser 200 needs to set center thresholds and side thresholds for each machine, as shown in Figures 12 and 13.

[0150] For example, in an image forming apparatus equipped with a fuser 200, the actual temperature, detected temperature, and WAE estimated value are measured under various conditions (air layer), as shown in Figures 5 and 6. Based on the measured results of the actual temperature, detected temperature, and WAE estimated value for the center and side, the image forming apparatus equipped with the fuser 200 sets thresholds (center threshold and side threshold) for detecting the floating of the temperature sensors 741 and 742. The image forming apparatus equipped with the fuser 200 stores the center threshold and the side threshold in a data memory 84 or the like, and performs the floating detection processing as described above. As a result, even with an image forming apparatus equipped with a fuser 200, the floating of the center temperature sensor and the side temperature sensor can be determined without using a dedicated jig.

[0151] Next, a third example of a fuser applicable to the image forming apparatus 1 according to this embodiment, namely the fuser 300, will be described. Figure 18 shows an example configuration of a fuser 300, which is a third example of a fuser applicable to the image forming apparatus 1 according to the embodiment. Figure 19 shows an example configuration of the heater unit in the fuser 300.

[0152] As shown in Figure 18, the fuser 300 includes temperature sensors 74 (741, 742), a tubular film 371 as a fixing member (fixing rotating body), a pressure roller 372, a heating element 373, and a heating element substrate 375. The pressure roller 372 forms a nip with the tubular film 371. The tubular film 371 and the pressure roller 372 heat the printing medium P that has entered the nip while applying pressure.

[0153] The heater unit includes a heating element 373 and a heating element substrate 375. The heating element substrate 375 is made of a metal material or a ceramic material. The heating element substrate 375 is formed in the shape of an elongated rectangular plate. The heating element substrate 375 is positioned radially inside the tubular film 371. The heating element substrate 375 has its longitudinal direction aligned with the axial direction of the tubular film 271.

[0154] The heating element 373 includes multiple heating elements 3731, 3732, and 3733. The heating element 373 is positioned on the heating element substrate 375 and is provided in contact with the inner surface of the cylindrical film 371. Each heating element 3731, 3732, and 3733 is a resistor that generates heat when power is supplied from an AC power source.

[0155] The heating element 3731 is used to fix toner to the printing medium P whose width (paper width) in the direction perpendicular to the transport direction is the largest. The heating element 3731 has a width corresponding to the largest paper width. The heating element 3731 is positioned on the upstream and downstream sides of the transport direction of the printing medium P on the heating element substrate 375.

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

[0157] As described above, the fuser 300 shown in Figures 18 and 19 can also be subjected to the WAE control described above. An image forming apparatus equipped with the fuser 300 shown in Figures 18 and 19 can perform temperature sensor floating detection processing based on the difference between the estimated WAE value and the temperature detected by the temperature sensor, as described above. However, the thresholds shown in Figures 12 and 13 cannot be directly applied to an image forming apparatus equipped with the fuser 300. An image forming apparatus equipped with the fuser 300 needs to set center thresholds and side thresholds for each machine, as shown in Figures 12 and 13.

[0158] For example, in an image forming apparatus equipped with a fuser 300, the actual temperature, detected temperature, and WAE estimated value are measured under various conditions (air layer), as shown in Figures 5 and 6. Based on the measured results of the actual temperature, detected temperature, and WAE estimated value for the center and side, the image forming apparatus equipped with the fuser 300 sets thresholds (center threshold and side threshold) for detecting the floating of the temperature sensors 741 and 742. The image forming apparatus equipped with the fuser 300 stores the center threshold and the side threshold in a data memory 84 or the like, and performs the floating detection processing as described above. As a result, even with an image forming apparatus equipped with a fuser 300, the floating of the center temperature sensor and the side temperature sensor can be determined without using a dedicated jig.

[0159] Next, a fourth example of a fuser applicable to the image forming apparatus 1 according to this embodiment, namely a fuser 400, will be described. Figure 20 shows an example configuration of a fuser 400, which is a fourth example of a fuser applicable to the image forming apparatus 1 according to the embodiment. Figure 21 also shows an example configuration of a heater unit in the fuser 400.

[0160] As shown in Figure 20, the fuser 400 includes temperature sensors 74 (741, 742), a tubular film 471 as a fixing member (fixing rotating body), a pressure roller 472, a heating element 473, and a heating element substrate 475. The pressure roller 472 forms a nip with the tubular film 471. The tubular film 471 and the pressure roller 472 heat the printing medium P that has entered the nip while applying pressure.

[0161] The heater unit includes a heating element 473 and a heating element substrate 475. The heating element substrate 475 is made of a metal material or a ceramic material. The heating element substrate 475 is formed in the shape of an elongated rectangular plate. The heating element substrate 475 is positioned radially inside the tubular film 471. The heating element substrate 475 has its longitudinal direction aligned with the axial direction of the tubular film 471.

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

[0163] The heating element 4731 has a width corresponding to the maximum width of the printing medium P in a direction perpendicular to the transport direction. As shown in Figure 21, the heating element 4731 has a larger width relative to the transport direction in the central part of the heating element 4731 and a smaller width relative to the transport direction at the ends. The heating element 4731 is a main heater configured to heat the center region C intensively. The heating element 4732 has a smaller width relative to the transport direction in the central part of the heating element 4732 and a larger width relative to the transport direction at the ends. The heating element 4732 is a sub-heater configured to heat the side region S intensively. The main heater and sub-heater are controlled to be switched on and off according to the paper width of the printing medium P.

[0164] As described above, the fuser 400 shown in Figures 20 and 21 can also be subjected to the WAE control described above. An image forming apparatus equipped with the fuser 400 shown in Figures 20 and 21 can perform temperature sensor floating detection processing based on the difference between the WAE estimated value and the temperature detected by the temperature sensor, as described above. However, the thresholds shown in Figures 12 and 13 cannot be directly applied to an image forming apparatus equipped with the fuser 400. An image forming apparatus equipped with the fuser 400 needs to set center thresholds and side thresholds for each machine, as shown in Figures 12 and 13.

[0165] For example, in an image forming apparatus equipped with a fuser 400, the actual temperature, detected temperature, and WAE estimated value are measured under various conditions (air layer), as shown in Figures 5 and 6. Based on the measured results of the actual temperature, detected temperature, and WAE estimated value for the center and side, the image forming apparatus equipped with the fuser 400 sets thresholds (center threshold and side threshold) for detecting the floating of the temperature sensors 741 and 742. The image forming apparatus equipped with the fuser 400 stores the center threshold and the side threshold in a data memory 84 or the like, and performs the floating detection processing as described above. As a result, even with an image forming apparatus equipped with a fuser 400, the floating of the center temperature sensor and the side temperature sensor can be determined without using a dedicated jig.

[0166] Next, a fifth example of a fuser applicable to the image forming apparatus 1 according to this embodiment, namely fuser 500, will be described. Figure 22 shows an example configuration of a fuser 500, which is a second example of a fuser applicable to the image forming apparatus 1 according to the embodiment. Figure 23 shows an example configuration of the heater unit in the fuser 500.

[0167] As shown in Figure 22, the fuser 500 includes temperature sensors 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 that enters the nip while applying pressure.

[0168] The induction heating coil 573 is an example of a heat source for heating the heat roller 571, which serves as a fixing member. The induction heating coil 573 consists of a central coil 5731 and end coils 5732. The central coil 5731 and the end coils 5732 are arranged side by side inside the heat roller 571 in a direction perpendicular to the paper transport direction (the rotation axis direction of the heat roller 571). The central coil 5731 is positioned so that its center is aligned with the width direction of the printing medium P passing through the nip (in a direction perpendicular to the transport direction). The end coils 5732 are arranged side by side on either side of the central coil 5731.

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

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

[0171] As described above, the fuser 500 shown in Figures 22 and 23 can also be subjected to the WAE control described above. An image forming apparatus equipped with the fuser 500 shown in Figures 22 and 23 can perform temperature sensor floating detection processing based on the difference between the WAE estimated value and the temperature detected by the temperature sensor, as described above. However, the thresholds shown in Figures 12 and 13 cannot be directly applied to an image forming apparatus equipped with the fuser 500. An image forming apparatus equipped with the fuser 500 needs to set center thresholds and side thresholds for each machine, as shown in Figures 12 and 13.

[0172] For example, in an image forming apparatus equipped with a fuser 500, the actual temperature, detected temperature, and WAE estimated value are measured under various conditions (air layer), as shown in Figures 5 and 6. Based on the measured results of the actual temperature, detected temperature, and WAE estimated value for the center and side, the image forming apparatus equipped with the fuser 500 sets thresholds (center threshold and side threshold) for detecting the floating of the temperature sensors 741 and 742. The image forming apparatus equipped with the fuser 500 stores the center threshold and the side threshold in a data memory 84 or the like, and performs the floating detection processing as described above. As a result, even with an image forming apparatus equipped with a fuser 500, the floating of the center temperature sensor and the side temperature sensor can be determined without using a dedicated jig.

[0173] Furthermore, the functions described in each of the above embodiments are not limited to being implemented using hardware; they can also be realized by loading a program containing each function into a computer using software. Additionally, each function may be configured using either software or hardware, as appropriate.

[0174] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents.

[0175] The fixing devices according to the above-described embodiment are listed below. [1] A fuser having a fixing member in contact with a medium onto which a developer image has been transferred, and a heat source that supplies heat to the fixing member, A temperature sensor that measures temperature at a detection unit that contacts the surface of the fixing member in which the medium is in contact, A memory that stores the temperature estimate value used to estimate the temperature of the fixing member and the detected temperature detected by the temperature sensor, A controller that determines poor contact between the detection unit of the temperature sensor and the surface of the fixing member based on the difference between the temperature estimate stored in the memory and the temperature detected by the temperature sensor, A fixing device having [2] The memory stores the estimated temperature during a predetermined measurement period in the print standby state and the detected 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 based on the difference between the average value of the temperature estimate during the predetermined measurement period and the average value of the temperature detected by the temperature sensor. [1] Fixing device as described above. [3] The controller determines that there is poor contact between the detection unit of the temperature sensor and the surface of the fixing member if the difference between the average value of the temperature estimate during the predetermined measurement period and the average value of the temperature detected by the temperature sensor is greater than or equal to a predetermined threshold. [2] Fixing device as described above. [4] Furthermore, it has a display device, The controller, when it determines that there is poor contact between the temperature sensor's detection unit and the surface of the fixing member, will indicate that there is poor contact between the temperature sensor's detection unit and the surface of the fixing member. The instructions are displayed on the aforementioned display device. [1] Fixing device as described above. [5] Furthermore, it has a communication interface for communicating with external devices, When the controller determines that there is poor contact between the temperature sensor's detection unit and the surface of the fixing member, it notifies the external device via the communication interface of information indicating poor contact between the temperature sensor's detection unit and the surface of the fixing member. [1] Fixing device as described above. [6] The temperature sensor includes a first temperature sensor for measuring the temperature of a first region in the fixing member, and a second temperature sensor for measuring the temperature of a second region in the fixing member. The controller determines poor contact between the detection unit of the first temperature sensor and the surface of the fixing member based on the difference between a first temperature estimate, which is the result of estimating the temperature of the first region in the fixing member, and the temperature detected by the first temperature sensor, and determines poor contact between the detection unit of the second temperature sensor and the surface of the fixing member based on the difference between a second temperature estimate, which is the result of estimating the temperature of the second region in the fixing member, and the temperature detected by the second temperature sensor. [1] Fixing device as described above. [7] The memory stores a first temperature estimate, the temperature detected by the first temperature sensor, a second temperature estimate, and the temperature detected by the second temperature sensor during a predetermined measurement period in the print standby state. The controller determines poor contact between the detection unit of the first temperature sensor and the surface of the fixing member based on the difference between the average value of the first temperature estimate during the predetermined measurement period and the average value of the temperature detected by the first temperature sensor, and determines poor contact between the detection unit of the second temperature sensor and the surface of the fixing member based on the difference between the average value of the second temperature estimate during the predetermined measurement period and the average value of the temperature detected by the second temperature sensor. [6] Fixing device as described above. [8] The controller determines that there is poor contact between the detection unit of the first temperature sensor and the surface of the fixing member if the difference between the average value of the first temperature estimate during the predetermined measurement period and the average value of the temperature detected by the first temperature sensor is greater than or equal to a threshold for the first region, and determines that there is poor contact between the detection unit of the second temperature sensor and the surface of the fixing member if the difference between the average value of the second temperature estimate during the predetermined measurement period and the average value of the temperature detected by the second temperature sensor is greater than or equal to a threshold for the second region. [7] Fixing device as described above. [9] Furthermore, it has a display device, The controller, when it determines that there is poor contact between the detection unit of the first temperature sensor and the surface of the fixing member, displays a message on the display device indicating poor contact of the detection unit of the first temperature sensor, and when it determines that there is poor contact between the detection unit of the second temperature sensor and the surface of the fixing member, displays a message on the display device indicating poor contact of the detection unit of the second temperature sensor. [6] Fixing device as described above.

[10] Furthermore, it has a communication interface for communicating with external devices, The controller, when it determines that there is poor contact between the detection unit of the first temperature sensor and the surface of the fixing member, notifies the external device via the communication interface of information indicating poor contact between the detection unit of the first temperature sensor and the surface of the fixing member, and when it determines that there is poor contact between the detection unit of the second temperature sensor and the surface of the fixing member, notifies the external device via the communication interface of information indicating poor contact between the detection unit of the second temperature sensor and the surface of the fixing member. [6] Fixing device as described above. [Explanation of symbols]

[0176] 1…Image forming apparatus (fixing apparatus) 12…Communication Interface 13… Controller 14… Heater control circuit 21…Fuser 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 section 92... Estimated history storage unit 93...High-frequency component extraction section 94... Coefficient addition section 95…Target temperature output section 96...Difference comparison section 97...Control signal generation unit 98…Power circuit 200... Fuser 271...Cylindrical film 272... Compression roller 273... Heating element 2731... Central heating element 2732...First end heating element 2733...Second end heating element 275… Heating element substrate 300... Fuser 371...Cylindrical film 372... Compression roller 373... Heating element 375… Heating element substrate 400... Fuser 471...Cylindrical film 472... Pressure roller 473... Heating element 4731... Heating element 4732... Heating element 475… Heating element substrate 500... Fuser 571... Heat Roller 572... Compression roller 573... Induction heating coil 5731... Central coil 5732... End coil.

Claims

1. A fuser having a fixing member in contact with a medium onto which a developer image has been transferred, and a heat source that supplies heat to the fixing member, A temperature sensor that measures temperature at a detection unit that contacts the surface of the fixing member in which the medium is in contact, A memory that stores the temperature estimate value used to estimate the temperature of the fixing member and the detected temperature detected by the temperature sensor, A controller that determines poor contact between the detection unit of the temperature sensor and the surface of the fixing member based on the difference between the temperature estimate stored in the memory and the temperature detected by the temperature sensor, A fixing device having

2. The memory stores the estimated temperature during a predetermined measurement period in the print standby state and the detected 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 based on the difference between the average value of the temperature estimate during the predetermined measurement period and the average value of the temperature detected by the temperature sensor. The fixing device according to claim 1.

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

4. Furthermore, it has a display device, When the controller determines that there is poor contact between the temperature sensor's detection unit and the surface of the fixing member, it displays a message on the display device indicating that there is poor contact between the temperature sensor's detection unit and the surface of the fixing member. The fixing device according to claim 1.

5. Furthermore, it has a communication interface for communicating with external devices, When the controller determines that there is poor contact between the detection unit of the temperature sensor and the surface of the fixing member, it notifies the external device via the communication interface of information indicating 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