Temperature controller, image forming apparatus, and temperature control method

Abstract

To determine an abnormality in a temperature sensor of a fuser or an abnormality in a control circuit side.SOLUTION: A temperature abnormality detection circuit provided in a temperature controller comprises a target temperature determination circuit, a difference operation circuit, a temperature abnormality determination circuit, and a storage circuit. The temperature abnormality detection circuit calculates the current temperature difference from a determination of the presence or absence of temperature abnormality according to the state of response of a detected temperature from a temperature sensor and a detected temperature acquired by the temperature sensor and a WAE temperature estimated value when the temperature abnormality is determined to be present, and determines whether an abnormality is present in the temperature sensor or an abnormality is present in a control circuit side from a result of comparison between the temperature difference and a preset threshold.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a temperature control device and an image forming apparatus equipped with the temperature control device. [Background technology]

[0002] The image forming apparatus includes a fuser that applies heat and pressure to a recording medium onto which a toner image has been transferred, thereby fixing the toner image to the recording medium. The fuser includes a fixing rotor (heat roller), a pressure member (press roller), a heating member (lamp, IH heater, etc.), and a temperature sensor. The temperature sensor detects the surface temperature of the heat roller. A controller that controls the fuser increases or decreases the amount of power supplied to the heating member based on a detection signal (temperature sensor signal) from the temperature sensor, thereby controlling the surface temperature of the heat roller to a target value.

[0003] A temperature control device that controls a fixing unit is equipped with an abnormality detection device that detects an abnormality or malfunction of the fixing unit based on a detection signal from a temperature sensor. For example, Patent Document 1 describes a technology that determines that there is an abnormality in the heating means or detection means when, for example, the maximum output value continues for a set time or longer even if the control result of the heating unit does not result in an abnormal value. When the detected temperature of the heat roller of the fixing unit obtained from the temperature sensor exceeds a preset range, the temperature control device first determines that there is an abnormality in the fixing unit and checks for damage to the temperature sensor or heat source or an abnormality in the wiring of the fixing unit. After determining that there is no abnormality in the fixing unit, it then determines whether there is a malfunction in the control circuit (triac, etc.). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-308948 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem that an embodiment of the present invention aims to solve is to provide a temperature control device and an image forming device equipped with such a temperature control device that can compare the current temperature difference calculated from the difference between the detected temperature acquired by the temperature sensor and the WAE temperature estimated value with a threshold value, and determine from the comparison result whether the abnormality is in the temperature sensor or in the circuit. [Means for solving the problem]

[0006] In one embodiment, the temperature control device includes a heater power supply circuit, a temperature sensor, a control signal generation circuit, a temperature estimation circuit, and a temperature abnormality detection circuit. The temperature control device supplies power to a heater of a fixing unit, thereby controlling the temperature of a temperature control target to which heat is propagated from the heater to reach a predetermined target temperature. The heater power supply circuit supplies power to the heater. The temperature sensor measures a detected temperature from the temperature control target. The temperature estimation circuit estimates a temperature estimate of the temperature control target based on the detected temperature, the heat capacity of the heater based on the power supplied to the heater, and the thermal resistance of the fixing unit. The control signal generation circuit outputs a power pulse for controlling the power supplied by the heater power supply circuit based on the estimated temperature of the temperature control target estimated by the temperature estimation circuit and the target temperature. When the temperature detected by the temperature sensor is determined to be an abnormally low temperature or an abnormally high temperature by comparing it with a first threshold value, the temperature abnormality detection circuit compares the current temperature difference calculated from the current detected temperature and the temperature estimated value with a threshold value calculated from the detected temperature and the temperature estimated value of the temperature sensor under normal conditions, and determines whether the abnormality is in the temperature sensor or in the circuit based on the comparison result. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram conceptually illustrating an example of the overall configuration of an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is a block diagram showing an example of a configuration for performing WAE control and abnormal temperature detection. [Figure 3] FIG. 3 is a diagram illustrating an example of the configuration of the fixing unit. [Figure 4]FIG. 4 is a diagram showing an example of the arrangement of heaters and temperature sensors. [Figure 5] FIG. 5 is a cross-sectional view showing the configuration of the heater unit. [Figure 6] FIG. 6 is a cross-sectional view showing the configuration of the heat transfer member and the heater unit. [Figure 7] FIG. 7 is a flowchart for explaining the WAE control. [Figure 8] FIG. 8 is a diagram showing the temperature characteristics of the fixing unit under WAE control. [Figure 9] FIG. 9 is a block diagram showing an example of the configuration of an abnormal temperature detection device. [Figure 10] FIG. 10 is a flowchart for explaining abnormal temperature detection. [Figure 11] FIG. 11 is a diagram showing temperature characteristics when the temperature detected by the temperature sensor becomes abnormally high. [Figure 12] FIG. 12 is a diagram showing temperature characteristics when the temperature detected by the temperature sensor becomes abnormally low. DETAILED DESCRIPTION OF THE INVENTION

[0008] A temperature control device according to one embodiment includes a heater current control circuit and a temperature anomaly detection circuit. The temperature control device controls the temperature of a fuser mounted in an image forming apparatus using weighted average control with estimated temperature (WAE). The heater current control circuit controls the temperature of the fuser using a control signal that combines a fuser temperature estimate (WAE temperature estimate) calculated during operation by WAE control and a temperature detected by a temperature sensor. As described below, WAE control is a technology that simulates the temperature of a temperature-controlled component as a thermal CR circuit. The WAE temperature estimate is calculated by estimating the surface temperature of the film unit, which corresponds to the heat roller to be heated, based on the heat capacity (C) of the film unit, which corresponds to the heat roller to be heated, the thermal resistance (R) of the fuser, and the energy input to the fuser.

[0009] The temperature abnormality detection circuit also determines whether the detected temperature acquired by the temperature sensor provided in the fixing unit is an abnormally low temperature or an abnormally high temperature based on a first threshold value Tth1. If the detected temperature is an abnormally low temperature or an abnormally high temperature, the current temperature difference is calculated from the current detected temperature and the WAE temperature estimate. This current temperature difference is compared with a second threshold value Tth2, which is an allowable temperature range with set upper and lower limits (hereinafter referred to as the allowable temperature range). If the current temperature difference is greater or smaller than the allowable temperature range defined by the second threshold value Tth2, it is determined that there is an abnormality in the circuit. If the current temperature difference does not reach the second threshold value Tth2 and is within the allowable temperature range, it is determined that there is an abnormality in the temperature sensor.

[0010] An image forming apparatus equipped with a temperature control device according to an embodiment will be described below with reference to the drawings. Fig. 1 is a conceptual diagram showing an example of the overall configuration of the image forming apparatus according to this embodiment, and Fig. 2 is a block diagram showing an example of the configuration of the temperature control device.

[0011] The image forming apparatus 1 is, for example, a multifunction printer (MFP) that performs various processes such as image formation while conveying a recording medium P such as printing paper. Alternatively, the image forming apparatus 1 is a solid-state scanning printer (e.g., an LED printer) that can perform various processes such as image formation while conveying the recording medium P and scans an LED array. These image forming apparatuses 1 are configured to receive toner from a toner cartridge and form an image on the recording medium P using the received toner. The toner may be a single color toner or a multi-color toner such as cyan, magenta, yellow, and black. Alternatively, the toner may be an erasable toner that erases when heat is applied after printing.

[0012] As shown in FIG. 1, the image forming apparatus 1 includes a housing 11, a communication interface 12, a system controller 13, a heater power control circuit 14, a display unit 15, an operation interface 16, multiple paper trays 17, a paper output tray 18, a conveying unit 19, an image forming unit 20, a fixing unit 21, a main power switch 24, and a temperature abnormality detection circuit 25.

[0013] The housing 11 is the main body of the image forming apparatus 1. The housing 11 houses a communication interface 12, a system controller 13, a heater energization control circuit 14, a display unit 15, an operation interface 16, a plurality of paper trays 17, a paper output tray 18, a conveying unit 19, an image forming unit 20, a fixing unit 21, a processor 22, and a temperature abnormality detection circuit 25. The temperature control device 26 is composed of the heater energization control circuit 14, the temperature abnormality detection circuit 25, a heater unit 73, and a temperature sensor unit 74, and controls the temperature of the fixing unit 21.

[0014] First, the configuration of the control system of the image forming apparatus 1 will be described. The communication interface 12 is a connection device that enables communication with other devices such as higher-level devices (external devices). The communication interface 12 includes, for example, a network connection terminal for wired connection using a LAN connector or the like. Furthermore, the communication interface 12 may have a function for wireless communication with other devices in accordance with standards such as Bluetooth (registered trademark) or Wi-fi (registered trademark).

[0015] The system controller 13 controls the entire image forming apparatus 1. The system controller 13 includes, for example, a processor 22 and a memory . The memory 23 may be a read-only nonvolatile memory such as a ROM (Read Only Memory), a nonvolatile memory that can be written to and read from at any time such as a flash ROM, a solid state drive (SSD), or a hard disk drive (HDD), or a volatile memory that can be written to and read from at any time such as a random access memory (RAM), or any combination thereof. The memory 23 stores programs, data used in the programs, etc. The memory 23 also functions as a working memory. That is, the memory 23 temporarily stores data being processed by the processor 22, programs executed by the processor 22, etc.

[0016] The processor 22 is an arithmetic element such as a CPU (Central Processing Unit), and executes arithmetic processing. The processor 22 functions as a control unit capable of performing various operations by executing programs stored in the memory 23. The processor 22 also uses data stored in the memory 23 to perform various arithmetic processing and processing related to judgment.

[0017] Also, for example, the processor 22 generates a print job based on an image acquired from an external device via the communication interface 12. The processor 22 stores the generated print job in the memory 23. This print job includes image data indicating an image to be formed on a recording medium P. The image data may be data for forming an image on one sheet of recording medium P, or may be data for forming images on multiple sheets of recording medium P. The print job also includes information indicating whether color printing or monochrome printing is to be performed. Furthermore, the print job may also include information such as the number of copies to be printed (number of page sets), the number of sheets to be printed per copy (number of pages), etc.

[0018] Based on the generated print job, the processor 22 also generates print control information for controlling the operations of the conveying unit 19, the image forming unit 20, and the fixing unit 21. The print control information includes information indicating the timing of paper feed. The processor 22 transmits the print control information to the heater energization control circuit 14.

[0019] Moreover, the processor 22 executes a program stored in the memory 23, thereby functioning as a controller (engine controller) that controls the operations of the conveying unit 19 and the image forming unit 20. That is, the processor 22 controls the conveyance of the recording medium P by the conveying unit 19, and the formation of an image on the recording medium P by the image forming unit 20.

[0020] The image forming apparatus 1 may be provided with an engine controller and a system controller 13 separately. In this case, the engine controller controls the conveyance of the recording medium P by the conveyance unit 19 and the formation of an image on the recording medium P by the image forming unit 20. In this case, the system controller 13 supplies the engine controller with information required for control operations.

[0021] The image forming apparatus 1 also includes a power conversion circuit that uses AC voltage from the AC power source AC to supply DC voltage to each component within the image forming apparatus 1. The power conversion circuit supplies the system controller 13 with DC voltage required for the operation of the processor 22 and memory 23. The power conversion circuit also supplies the image forming unit 20 with DC voltage required for image formation. The power conversion circuit also supplies the conveying unit 19 with DC voltage required for conveying the recording medium P. The power conversion circuit also supplies the heater energization control circuit 14 with DC voltage for driving the heater unit 73 of the fixing device 21.

[0022] The heater current control circuit 14 generates power PC and supplies it to the heater unit 73 of the fixing device 21. The display unit 15 includes a display that displays a screen in response to a video signal input from the system controller 13. A graphic controller or the like may be used instead of the system controller 13. The display of the display unit 15 displays, for example, a screen for various settings of the image forming apparatus 1. The main power switch 24 is a switch that, when turned on or off, supplies or cuts off power to drive the image forming apparatus 1. When the main power switch 24 is turned on, the image forming apparatus 1 starts up, and when the main power switch 24 is turned off, the image forming apparatus 1 stops driving. When the main power switch 24 is turned on or off, the fixing unit 21 also starts or stops.

[0023] The operation interface 16 is connected to the operation members described below. The operation interface 16 supplies operation signals to the system controller 13 in response to the operation of the operation members. The operation members are, for example, a touch sensor, a numeric keypad, a paper feed key, various function keys, or a keyboard. The touch sensor acquires information indicating a specified position within a certain area. The touch sensor is configured as a touch panel integral with the display unit 15, and inputs a signal indicating a touched position on the screen displayed on the display unit 15 to the system controller 13.

[0024] The multiple paper trays 17 are detachably attached to the housing 11, and each cassette is a cassette that stores recording media P of the same size or different sizes. The paper trays 17 supply the recording media P to a conveying unit 19. The paper output tray 18 is a tray that supports the recording media P that have been output from the image forming apparatus 1.

[0025] Next, a configuration for conveying the recording medium P of the image forming apparatus 1 will be described. The conveying unit 19 is a mechanism that conveys the recording medium P within the image forming apparatus 1. As shown in Fig. 1, the conveying unit 19 includes a plurality of conveying paths. For example, the conveying unit 19 includes a paper feed conveying path 31 and a paper discharge conveying path 32.

[0026] The paper feed conveying path 31 and the paper discharge conveying path 32 are each composed of multiple motors, multiple rollers, and multiple guides. The multiple motors rotate their shafts under the control of the system controller 13, thereby rotating rollers that are driven by the rotation of the shafts. The multiple rollers move the recording medium P by rotating. The multiple guides prevent the recording medium P from skewing during conveyance.

[0027] The paper feed conveying path 31 picks up the recording medium P from each paper tray 17 by a pickup roller 33 and supplies each of the picked-up recording media P to the image forming unit 20 . The discharge conveyance path 32 is a conveyance path that discharges the recording medium P on which an image has been formed from the housing 11. The recording medium P discharged by the discharge conveyance path 32 is stored in the discharge tray .

[0028] Next, the image forming unit 20 will be described. The image forming section 20 forms an image on a recording medium P based on a print job generated by the processor 22. The image forming section 20 includes a plurality of process units 41, a plurality of exposure devices 42, and a transfer mechanism 43. The image forming section 20 includes an exposure device 42 for each process unit 41. The plurality of process units 41 and the plurality of exposure devices 42 each have the same configuration.

[0029] First, the process unit 41 will be described. The process unit 41 is connected to toner cartridges that supply different color toners and forms a toner image. Multiple process units 41 are provided for each color of toner, corresponding to color toners such as cyan, magenta, yellow, and black. The toner cartridge includes a toner storage container and a toner delivery mechanism. The toner storage container is a container that supplies the stored toner. The toner delivery mechanism is a mechanism composed of a screw and the like that delivers the toner from the toner storage container.

[0030] Below, a set of a process unit 41 and an exposure device 42 will be described as a representative example. The process unit 41 includes a photosensitive drum 51 , a charger 52 , and a developing unit 53 . The photosensitive drum 51 is a photosensitive member that is composed of a cylindrical drum and a photosensitive layer formed on the outer peripheral surface of the drum. The photosensitive drum 51 is rotated at a constant speed by a drive mechanism that is composed of gears, a belt, etc.

[0031] The main charger 52 uniformly charges the surface of the photosensitive drum 51. For example, the main charger 52 uses a charging roller to apply a voltage (development bias voltage) to the photosensitive drum 51, thereby charging the photosensitive drum 51 to a uniform negative potential (contrast potential). The charging roller rotates in accordance with the rotation of the photosensitive drum 51 while applying a predetermined pressure to the photosensitive drum 51.

[0032] The developing unit 53 is a device that attaches toner to the photosensitive drum 51. The developing unit 53 includes a developer container, a stirring mechanism, a developing roller, a doctor blade, an auto toner control (ATC) sensor, and the like. The developer container is a container that receives and stores toner delivered from the toner cartridge. A carrier is stored in the developer container beforehand. The toner delivered from the toner cartridge is stirred with the carrier by the stirring mechanism to form a developer in which the toner and carrier are mixed. The carrier is stored in the developer container when the developing unit 53 is manufactured.

[0033] The developing roller rotates in a developer container, depositing developer onto its surface. The doctor blade is a component positioned at a predetermined distance from the surface of the developing roller. The doctor blade partially removes the top portion of the developer deposited on the surface of the rotating developing roller. This forms a layer of developer on the surface of the developing roller with a constant thickness that corresponds to the distance between the doctor blade and the surface of the developing roller.

[0034] 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 system controller 13 determines the concentration ratio of the toner to the carrier remaining in the developer container (toner concentration ratio) based on the voltage detected by the ATC sensor. Based on the toner concentration ratio, the system controller 13 operates a motor that drives the toner cartridge's delivery mechanism, causing the toner to be delivered from the toner cartridge to the developer container of the developing unit 53.

[0035] Next, the exposure unit 42 will be described. The exposure unit 42 includes a plurality of light-emitting elements. The exposure unit 42 forms a latent image on the photosensitive drum 51 by irradiating the charged photosensitive drum 51 with light from the light-emitting elements. The light-emitting elements are, for example, light-emitting diodes (LEDs). One light-emitting element is configured to irradiate one point on the photosensitive drum 51 with light. The plurality of light-emitting elements are arranged in the main scanning direction, which is a direction parallel to the rotation axis of the photosensitive drum 51.

[0036] The exposure unit 42 forms a latent image of one line on the photosensitive drum 51 by irradiating the photosensitive drum 51 with light using a plurality of light-emitting elements arranged in the main scanning direction. Furthermore, the exposure unit 42 forms a latent image of multiple lines by continuously irradiating the rotating photosensitive drum 51 with light.

[0037] In the process unit 41 having the above-described configuration, an electrostatic latent image is formed on the surface of the photosensitive drum 51, which has been charged by the electrostatic charger 52, when light is irradiated from the exposure device 42. Furthermore, when the layer of developer formed on the surface of the developing roller approaches the surface of the photosensitive drum 51, the toner contained in the developer adheres to the latent image formed on the surface of the photosensitive drum 51. As a result, a toner image is formed on the surface of the photosensitive drum 51.

[0038] Next, the transfer mechanism 43 will be described. The transfer mechanism 43 transfers the toner image formed on the surface of the photosensitive drum 51 onto the recording medium P. The transfer mechanism 43 includes, for example, a primary transfer belt 61, a secondary transfer opposing roller 62, a plurality of primary transfer rollers 63, and a secondary transfer roller 64.

[0039] The primary transfer belt 61 is an endless belt wound around a secondary transfer opposing roller 62 and a plurality of winding rollers. The primary transfer belt 61 has an inner surface (inner peripheral surface) that contacts the secondary transfer opposing roller 62 and the plurality of winding rollers, and an outer surface (outer peripheral surface) that faces the photosensitive drum 51 of the process unit 41.

[0040] The secondary transfer opposing roller 62 is rotated using a motor as a drive source. By rotating, the secondary transfer opposing roller 62 transports the primary transfer belt 61 in a predetermined transport direction. The multiple winding rollers are configured to be freely rotatable. The multiple winding rollers rotate in accordance with the movement of the primary transfer belt 61 by the secondary transfer opposing roller 62.

[0041] Each of the multiple primary transfer rollers 63 brings the primary transfer belt 61 into contact with the photosensitive drum 51 of the process unit 41. Specifically, each of the multiple primary transfer rollers 63 is provided at a position facing the corresponding photosensitive drum 51 of the process unit 41 with the primary transfer belt 61 sandwiched therebetween. The primary transfer rollers 63 come into contact with the inner circumferential surface of the primary transfer belt 61, displacing the primary transfer belt 61 toward the photosensitive 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 photosensitive drum 51.

[0042] The secondary transfer roller 64 is disposed at a position facing the secondary transfer opposing roller 62 with the primary transfer belt 61 sandwiched therebetween. The secondary transfer roller 64 contacts the outer peripheral surface of the primary transfer belt 61 and applies pressure to it. This forms a transfer nip where the secondary transfer roller 64 and the outer peripheral surface of the primary transfer belt 61 are in close contact with each other. When the recording medium P passes through the transfer nip, the secondary transfer roller 64 presses the recording medium P passing through the transfer nip against the outer peripheral surface of the primary transfer belt 61. The secondary transfer roller 64 and the secondary transfer opposing roller 62 rotate to sandwich and transport the recording medium P supplied from the paper feed transport path 31. As a result, the recording medium P passes through the transfer nip.

[0043] In the transfer mechanism 43 configured as described above, when the outer circumferential 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 circumferential surface of the primary transfer belt 61. If the image forming section 20 includes multiple process units 41, the toner images are transferred onto the outer circumferential surface of the primary transfer belt 61 from the photosensitive drums 51 of the multiple process units 41. The transferred toner image is transported by the primary transfer belt 61 to a transfer nip where the secondary transfer roller 64 and the outer circumferential surface of the primary transfer belt 61 are in close contact with each other. If a recording medium P is present in the transfer nip, the toner image transferred to the outer circumferential surface of the primary transfer belt 61 is transferred to the recording medium P at the transfer nip.

[0044] Next, the fixing device 21 of this embodiment will be described. Fig. 3 is a diagram showing a cross-sectional configuration of the fixing device 21. Fig. 4 is a diagram showing an example of the configuration of a heater unit. Fig. 5 is a cross-sectional configuration diagram of the heater unit shown in Fig. 3. Here, the cross-sectional configuration of the fixing device 21 in the X-axis direction perpendicular to the conveyance direction of the recording medium P is shown. The fixing unit 21 is mainly composed of a film unit 71 corresponding to a heat roller and a pressure roller 72.

[0045] The pressure roller 72 contacts the film unit 71, which is the temperature control target, to form a nip N. The pressure roller 72 rotates on its axis due to a drive source such as a motor, and the film unit 71 rotates following the rotation of the pressure roller 72. The recording medium P is transported by this rotation and rotation. At this time, the pressure roller 72 presses the toner image TI from the back side of the recording medium P that has entered the nip N.

[0046] The pressure roller 72 includes a core 101 and an elastic layer 102. The core 101 is formed in a cylindrical shape from a metal material, such as stainless steel. The elastic layer 102 is provided on the outer circumferential surface of the core 101.

[0047] Both ends of the core 101 in the X-axis direction are rotatably supported by bearings or the like provided on each end. The core 101 is rotated by a motor and a drive mechanism. This drive mechanism is provided with, for example, an elliptical cam member. When this cam member rotates, it moves the core 101 in the radial direction, and can switch between an abutting state in which the core 101 abuts against the film unit 71 and a separated state in which the abutment is released.

[0048] The elastic layer 102 is made of an elastic material such as silicone rubber and is formed to have a constant thickness. A release layer is formed on the outer peripheral surface of the elastic layer 102. This release layer is made of a resin material such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer).

[0049] The pressure roller 72 is brought into contact with the film unit 71 by a cam member, and is pressed by an elastic member such as a pressure spring, thereby forming a nip N between the pressure roller 72 and the film unit 71. The pressure of this nip N is a pressure that allows for fixing processing, and is preferably 400 N, for example. The state in which this nip N is formed is referred to as the contact state between the pressure roller 72 and the film unit 71.

[0050] The separated state of pressure roller 72 and film unit 71 is used when a recording medium P jams inside fixing device 21 during operation. That is, the cam member is rotated to separate pressure roller 72 and film unit 71, thereby removing recording medium P. Similarly, when fixing device 21 is in a standby state, separating pressure roller 72 from film unit 71 prevents plastic deformation of tubular film 111, which will be described later.

[0051] The film unit 71 has a cylindrical film (cylindrical body) 111, a heater unit 73, a support member 112, a stay 113, and a temperature sensor unit 74. This film unit 71 heats the toner image TI on the recording medium P that has entered the nip N. Here, in FIG. 4, to clearly show the positions of the heater unit 73 and other components, a substrate 145 (described later) is shown in two locations.

[0052] The tubular film 111 has a cylindrical shape and is formed into a laminated structure of, from the inner periphery, a base layer, an elastic layer, and a release layer. Of these, the base layer is formed of a resin such as polyimide or a metal such as nickel or stainless steel. The elastic layer is formed of an elastic material such as silicone rubber. The release layer is formed of a material such as PFA resin. To shorten the warm-up time of the fixing device 21, the thicknesses of the elastic layer and the release layer are appropriately set during design so that their thermal capacities are not too large. To improve the frictional sliding of the film unit 71 against the heater unit 73 and the support member 112, a coating may be applied to the inner periphery of the tubular film 111 (the surface of the base layer). Furthermore, heat-resistant grease may be applied to the inner periphery of the tubular film 111.

[0053] 4 or 5, the heater unit 73 of the fixing device 21 has a substrate 145, a glass layer 146, a heating element set (heater) 147, a glass coating 148, and a heater power supply circuit 149. In this embodiment, the heater unit 73 has a heat transfer member 144 provided on the substrate 145. The heater power supply circuit 149 is configured using a power semiconductor element such as a triac, for example.

[0054] Of these, substrate 145 is formed in the shape of a rectangular plate using a metal material such as stainless steel or a ceramic material such as aluminum nitride. Hereinafter, the surface on a first side in the thickness direction of substrate 145 will be referred to as first surface 152, and the surface on a second side opposite to the first side in the thickness direction of substrate 145 will be referred to as second surface 153.

[0055] Substrate 145 is disposed inside tubular film 111 (diametrically inside tubular film 111). Substrate 145 extends in the X-axis direction parallel to the axis of tubular film 111. Glass layer 146 is electrically insulating and covers first surface 152 of substrate 145.

[0056] Heating element set 147 includes first heater 155, second heater 156, and third heater 157. As shown in Fig. 4, first to third heaters 155, 156, and 157 are formed on first surface 158, which is the surface of glass layer 146 opposite to substrate 145. First to third heaters 155, 156, and 157 are each disposed within tubular film 111.

[0057] These first to third heaters 155, 156, and 157 are heating resistors each formed in the shape of a rectangular plate. For example, the first to third heaters 155, 156, and 157 are formed by screen printing silver, a palladium alloy, or the like on the glass layer 146. As shown in Fig. 4, the first heater 155 is disposed in the center, and the third heater 157 and the second heater 156 are disposed on the left and right sides along the X-axis direction. In Fig. 4, the center of the heating element set 147 is indicated by a line M.

[0058] The resistance value of the first heater 155 is smaller than the resistance values ​​of both the second heater 156 and the third heater 157. The resistance value of the second heater 156 and the resistance value of the third heater 157 are approximately the same value. As shown in Fig. 4, as a first system, a first heater 155 is connected to the heater energization control circuit 14 by a wiring 162 via a first contact 160. As a second system, second and third heaters 156 and 157 are connected to the heater energization control circuit 14 by wirings 163 and 164 via a second contact 161. The second and third heaters 156 and 157 are electrically connected in parallel by the wirings 163 and 164. These contacts 160 and 161 and the respective wirings 162, 163, and 164 are formed on the glass layer 146 by screen printing using silver or the like as a material. The first to third heaters 155, 156, and 157 are grounded by wiring 166.

[0059] The first to third heaters 155, 156, and 157 are controlled by driving power from a heater power supply circuit 149 controlled by a heater energization control circuit 14. As shown in Fig. 4, in this embodiment, the circuits are separated into a first system for the first heater 155 and a second system for the second and third heaters 156 and 157, so that the first heater 155 and the second and third heaters 156 and 157 can be controlled individually.

[0060] The ratio of the resistance value of the first heater 155 to the overall resistance value of the second and third heaters 156, 157 is preferably in the range of 1:3 to 1:7, and more preferably in the range of 1:4 to 1:6.

[0061] As shown in Fig. 5, glass coating 148 is laminated and formed so as to cover heating element set 147 and each wiring on first surface 158 of glass layer 146. For simplicity, only first heater 155 and wiring 162 are shown in the cross-sectional configuration of Fig. 5. This glass coating 148 has the function of protecting heating element set 147 and the like, and improving the sliding property between tubular film 111 and heater unit 73. In heater unit 73 configured as described above, glass coating 148 is disposed on surface 73a (FIG. 6) that contacts tubular film 111 from the radially inner side of tubular film 111.

[0062] Next, the structure of the film unit 71 will be described. As shown in FIG. 3, the support member 112 has a plate shape extending in the X-axis direction. A plurality of through holes 118, 119, each having a different diameter, are formed in the support member 112 at intervals in the X-axis direction. Only one of the through holes 118, 119 is shown in FIG. Parts of the first and second temperature sensors 171, 172 are fitted into and fixed in the through hole 118. The heater unit 73 and the heat transfer member 144 are fitted into and fixed in the through hole 119. The first and second temperature sensors 171, 172 are arranged so as to be in close contact with the second surface 144b of the heat transfer member 144. In other words, the support member 112 supports the heater unit 73 via the heat transfer member 144.

[0063] The support member 112 is made of a material that has rigidity, heat resistance, and heat insulation properties. For example, the support member 112 is made of a resin material such as silicone rubber, fluororubber, polyimide resin, polyphenylene sulfide (PPS), polyethersulfone (PES), or liquid crystal polymer.

[0064] Support member 112 abuts against the inner circumferential surface of tubular film 111 at both ends in the Y-axis direction. Support member 112 is maintained by stay 113 extending in the X-axis direction. Stay 113 has a U-shaped cross section perpendicular to the X-axis direction and is formed from a steel plate material or the like. The U-shaped opening of stay 113 is erected on support member 112. Both ends of stay 113 in the X-axis direction are fixed to housing 11 of image forming apparatus 1. This supports film unit 71 on image forming apparatus 1. Stay 113 improves the bending rigidity of film unit 71.

[0065] Stay 113 is formed, for example, by bending a steel plate with a thickness of 2.0 mm. By providing flanges near both ends of stay 113 in the X-axis direction, it is possible to restrict movement of tubular film 111 in the X-axis direction.

[0066] Next, the temperature sensor unit 74 provided in the fixing unit 21 will be described. 3, the temperature sensor unit 74 is provided inside the fixing unit 21. In this embodiment, a configuration having a plurality of temperature sensors is shown, but the present invention is not limited to this, and a configuration in which a single temperature sensor is provided to perform temperature control and abnormality detection may also be used.

[0067] 4, temperature sensor unit 74 includes first and second temperature sensors 171 and 172 disposed on first and second heaters 155 and 156, respectively, and third and fourth temperature sensors 173 and 174 disposed so as to contact the inner circumferential surface of tubular film 111. Thermistors are used as an example of first through fourth temperature sensors 171, 172, 173, and 174. Thermistors are common electronic components, and are configured, for example, such that the sensor body is housed in a case and the temperature-sensing portion is exposed. The first through fourth temperature sensors 171, 172, 173, and 174 are driven, for example, by DC power.

[0068] 3, for example, portions of the first and second temperature sensors 171, 172 are fitted into the through-hole 118 of the support member 112 and are in contact with the first heater 155. The first and second temperature sensors 171, 172 detect the temperatures of the first and second heaters 155, 156. The first and second temperature sensors 171, 172 are each connected to the heater energization control circuit 14 and the temperature abnormality detection circuit 25 by a pair (two) of wires.

[0069] Third and fourth temperature sensors 173 and 174 are disposed so as to contact the inner surface of tubular film 111, respectively, and detect the surface temperature of the inside of tubular film 111. Third and fourth temperature sensors 173 and 174 are also connected to heater energization control circuit 14 and temperature abnormality detection circuit 25 by pairs of wires, respectively. First through fourth temperature sensors 171, 172, 173, and 174 are connected to heater energization control circuit 14 and temperature abnormality detection circuit 25 by pairs of wires 175, 176, 177, and 178, respectively.

[0070] These first to fourth temperature sensors 171, 172, 173, and 174 output the detected temperature Td as a potential difference between a pair of wires to the heater energization control circuit 14 and the temperature abnormality detection circuit 25. The detected temperature Td may be an average value of the temperatures detected by each of the first to fourth temperature sensors 171, 172, 173, and 174, or a value weighted according to the arrangement position of the temperature sensor. The WAE temperature estimate, described below, is calculated based on the design values ​​(center values) of the parameters of the fixing unit 21. The actual measured detected temperature of the fixing unit 21 varies depending on the individual temperature due to manufacturing errors, etc., resulting in a certain degree of discrepancy (deviation). Such discrepancy can be eliminated by correcting within the control range of the design value.

[0071] Next, the heat transfer member 144 and the heater unit 73 will be described with reference to Fig. 6. Fig. 6 is a cross-sectional view showing the configuration of the heat transfer member 144 and the heater unit 73. The heat transfer member 144 is made of a metal material with high thermal conductivity, such as copper. The outer shape of the heat transfer member 144 is the same as the outer shape of the substrate 145 of the heater unit 73. The heat transfer member 144 has a groove 181 on a first surface 144a in the Z-axis direction. In the spatial region defined by the groove 181, the first surface 144a of the heat transfer member 144 and the heater unit 73 are spaced apart. The surface of the heat transfer member 144 other than the groove 181 is a contact portion 182 that comes into contact with the heater unit 73.

[0072] When printing begins in image forming apparatus 1, heating element set 147 heats tubular film 111 to the fixing temperature. When heating element set 147 starts to heat from room temperature, temperature distribution T1 at the beginning of heat generation becomes a mountain shape as shown by the dashed line. Furthermore, when warming-up is complete and tubular film 111 is maintained at the fixing temperature, temperature distribution T2 of heating element set 147 becomes a trapezoid shape as shown by the dashed line.

[0073] These temperature distributions T1 and T2 indicate the temperature distribution in the Y-axis direction on the second surface 73b of the heater unit 73 in the Z-axis direction. As shown by temperature distribution T1, the temperature distribution on the second surface 73b of the heater unit 73 is mountain-shaped. A temperature peak position 73P coincides with the center of the heating element set 147 in the Y-axis direction. The groove portion 181 of the heat transfer member 144 is formed to cover the temperature peak position 73P of the heater unit 73.

[0074] If groove portion 181 is not formed at temperature peak position 73P, heat transfer member 144 will abut against temperature peak position 73P of heater unit 73. In this case, most of the heat from heater unit 73 will be transferred to heat transfer member 144, and not to tubular film 111.

[0075] In contrast, when groove 181 is formed at temperature peak position 73P, much of the heat from heater unit 73 is transferred to tubular film 111 without being transferred to heat transfer member 144. This allows tubular film 111 to be heated efficiently, thereby shortening the time until printing begins. In the Z-axis direction shown in FIG. 6, the depth Hg of groove 181 is desirably 20 to 50% of the thickness Ht of heat transfer member 144. Furthermore, the width Wg of groove 181 may be greater than the width Wh of heating element set 147. This allows much of the heat generated in heating element set 147 to be more easily transferred to tubular film 111 without being immediately transferred to heat transfer member 144. Therefore, tubular film 111 is heated efficiently.

[0076] The heat generating element set 147 is formed to be longer in the X-axis direction than the recording medium P, which has the largest size in the X-axis direction. The groove portion 181 is formed to be longer in the X-axis direction than the heat generating element set 147. The heat transfer member 144 is formed to be longer in the X-axis direction than the groove portion 181. In other words, the heat transfer member 144 extends outward from the heat generating element set 147 in the X-axis direction. The cross-sectional area of ​​the YZ cross section (cross section perpendicular to the X-axis direction) of the heat transferring member 144 in at least a part of the outer region in the X-axis direction of the heat generating element set 147 is defined as the first cross-sectional area. Specifically, the cross-sectional area of ​​the YZ cross section of the heat transferring member 144 in the outer region in the X-axis direction of the groove portion 181 is defined as the first cross-sectional area (the cross-sectional area at the location where the abutment portion 182 is located). On the other hand, the cross-sectional area of ​​the YZ cross section of the heat transferring member 144 in the inner region in the X-axis direction of the heat generating element set 147 is defined as the second cross-sectional area (the cross-sectional area at the location where the groove portion 181 is located). The heat transfer member 144 is formed so that the first cross-sectional area is larger than the second cross-sectional area (first cross-sectional area>second cross-sectional area).

[0077] The heat transfer member 144 also has a contact portion 182 that contacts the heater unit 73 in an outer region of the groove portion 181 in the X-axis direction. The contact portion 182 is an area where the groove portion 181 is not formed. Therefore, the first cross-sectional area of ​​the YZ cross section of the contact portion 182 is larger than the second cross-sectional area of ​​the inner region (region where the groove portion 181 is formed) of the heat generating element set 147 described above (first cross-sectional area > second cross-sectional area). This makes the heat capacity of the contact portion 182 larger than the heat capacity of the region where the groove portion 181 is formed.

[0078] The heating element set 147 generates heat over an area wider than the size of the recording medium P in the X-axis direction. When the recording medium P passes through the fixing device 21, heat from the heater unit 73 is transferred to the recording medium P. Therefore, the area through which the recording medium P passes is cooled, but the area that the recording medium P does not pass through is not cooled. Both ends in the X-axis direction of the heater unit 73, which are the area that does not pass through, tend to become hot.

[0079] The heat transfer member 144 has abutting portions 182 in the outer region in the X-axis direction of the groove portions 181. Heat from both ends of the heater unit 73 in the X-axis direction is easily transferred from the abutting portions 182 to the heat transfer member 144. Therefore, a temperature rise at both ends of the heater unit 73 in the X-axis direction is suppressed.

[0080] The heat transfer member 144 abuts against the second surface 73b of the heater unit 73 at the entire periphery of the groove portion 181 via a frame-shaped abutment portion 182. Therefore, the groove portion 181 is sealed by the heater unit 73. The heat transfer member 144 has a plurality of through holes 183 arranged at regular intervals in the X-axis direction. These through holes 183 penetrate the heat transfer member 144 along the Z-axis direction and open to the inner surface of the groove portion 181. When the support member 112 is arranged in the Z-axis direction of the heat transfer member 144, through holes communicating with the through holes 183 of the heat transfer member 144 are also formed in the support member 112. Air in the groove portion 181 that has become highly pressurized due to a temperature rise is discharged to the outside through these through holes 183. Therefore, the abutment portion 182 of the heat transfer member 144 is prevented from lifting up from the heater unit 73. As a result, heat from heater unit 73 is transferred to heat transfer member 144 via frame-shaped contact portion 182. Furthermore, multiple through holes 183 are formed to open outward along the X-axis direction of heat generating element set 147. Therefore, the thermal condition in the Z-axis direction of heat generating element set 147 becomes approximately uniform along the X-axis direction. As a result, tubular film 111 arranged in the Z-axis direction of heat generating element set 147 is heated approximately uniformly along the X-axis direction.

[0081] 2 to 4, the heater energization control circuit 14 that performs WAE control will be described. The heater energization control circuit 14 includes a temperature estimation circuit 81, an estimation history storage circuit 82, a high-frequency component extraction circuit 83, a coefficient addition circuit 84, a target temperature output circuit 85, a difference comparison circuit 86, a control signal generation circuit 87, and a power supply circuit 88.

[0082] The heater power supply control circuit 14 generates power PC and outputs it to a heater power supply circuit 149 of the heater unit 73 of the fixing device 21. The heater power supply circuit 149 adjusts the amount of heat generated in accordance with the amount of power PC, and controls the temperature of the film unit 71. Furthermore, the heater energization control circuit 14 receives a detected temperature Td detected by the temperature sensor unit 74. The detected temperature Td may be an average value of the detected temperatures detected by the first to fourth temperature sensors 171, 172, 173, and 174 described above, or may be an average value obtained by weighting (multiplying by a coefficient) the detected temperatures according to the positions of the temperature sensors.

[0083] The temperature estimation circuit 81 performs a temperature estimation process to estimate the surface temperature of the film unit 71. The temperature estimation circuit 81 generates a temperature estimation result EST based on the detected temperature Td, the estimated history PREV, and the energization pulse Ps at the start of WAE control. Alternatively, the temperature estimation circuit 81 may be configured to generate the temperature estimation result EST based on the detected temperature Td, the estimated history PREV, the energization pulse Ps, and the voltage (rated voltage) applied to the heater unit 73 when the energization pulse Ps is ON.

[0084] The estimation history holding circuit 82 holds a history of the temperature estimation results EST. The estimation history holding circuit 82 outputs to the temperature estimation circuit 81 an estimation history PREV that is a history of the temperature estimation results EST (past temperature estimation results EST). The high frequency component extraction circuit 83 performs high pass filtering to extract high frequency components from the temperature estimation result EST. The high frequency component extraction circuit 83 outputs a high frequency component HPF, which is a signal indicating the extracted high frequency components, to the coefficient addition circuit .

[0085] The coefficient addition circuit 84 performs a coefficient addition process to correct the detected temperature Td from the temperature sensor unit 74. The detected temperature Td and the high-frequency component HPF from the high-frequency component extraction circuit 83 are input to the coefficient addition circuit 84. The coefficient addition circuit 84 corrects the detected temperature Td based on the high-frequency component HPF. Specifically, the coefficient addition circuit 84 multiplies the high-frequency component HPF by a preset coefficient and adds the result to the detected temperature Td to calculate a WAE temperature estimate. The coefficient addition circuit 84 outputs the WAE temperature estimate to the difference comparison circuit 86 and the temperature abnormality detection circuit 25. The target temperature output circuit 85 outputs a preset target temperature TGT to the difference comparison circuit 86.

[0086] The difference comparison circuit 86 performs a difference calculation process. The difference comparison circuit 86 calculates the difference DIF between the target temperature TGT from the target temperature output circuit 85 and the WAE temperature estimated value from the coefficient addition circuit 84, and outputs it to the control signal generation circuit 87.

[0087] Based on the difference DIF, the control signal generation circuit 87 generates an energization pulse Ps, which is a pulse signal for controlling energization of the heater unit 73. The control signal generation circuit 87 outputs the energization pulse Ps to the power supply circuit 88 and the temperature estimation circuit 81.

[0088] Based on the energization pulse Ps, the power supply circuit 88 outputs a power PC, which is a control signal, to a heater power supply circuit 149 of the heater unit 73. The heater power supply circuit 149 receives power from the power source and switches between a power supply state and a power non-supply state to the first to third heaters 155, 156, and 157, thereby controlling heating by the heater unit 73. The power supply circuit 88 may be configured integrally with the heater power supply circuit 149 in the fixing device 21.

[0089] As described above, the heater energization control circuit 14 adjusts the amount of power supplied to the heater unit 73 of the fixing device 21 based on the detected temperature Td, the estimated temperature history PREV, and the energization pulse Ps. This type of control is called WAE (Weighted Average Control with Estimated Temperature) control. The temperature estimation circuit 81, the estimated history storage circuit 82, the high-frequency component extraction circuit 83, the coefficient addition circuit 84, the target temperature output circuit 85, the difference comparison circuit 86, and the control signal generation circuit 87 of the heater energization control circuit 14 can be configured not only by electrical circuits, but also by software (programs) stored in the processor 22. In this case, each circuit is constructed as a functional block.

[0090] Next, the temperature abnormality detection circuit 25 will be described with reference to FIG. The temperature abnormality detection circuit 25 is composed of a target temperature determination circuit 91, a difference calculation circuit 92, a temperature abnormality determination circuit 93, and a memory circuit 94. In the following explanation, an example is shown in which each circuit is composed of an electric circuit, but it is also possible to compose each circuit by software (program) stored in the processor 22. In this case, each circuit is constructed as a functional block.

[0091] The temperature abnormality detection circuit 25 compares the detected temperature Td acquired by the temperature sensor unit 74 provided in the fixing unit 21 with a first threshold value, which will be described later, to determine whether the detected temperature Td is an abnormally high temperature or an abnormally low temperature. When it is determined that the detected temperature Td is an abnormally high temperature or an abnormally low temperature, the current temperature difference Tc is calculated from the detected temperature Td and the WAE temperature estimate value. The current temperature difference Tc is compared with a threshold value (a second threshold value, which will be described later) to determine whether the current temperature difference is equal to or greater than the threshold value and, based on the response status of the detected temperature detected by the temperature sensor when the heater is turned on and off, whether the abnormality is in the temperature sensor or in the circuitry including the heater current control circuit.

[0092] The target temperature determination circuit 91 compares the detected temperature Td detected by the temperature sensor unit 74 with a first threshold value Tth1, which is an allowable temperature range including a preset target temperature TGT. The first threshold value Tth1 is a threshold value used to determine whether the detected temperature Td is an abnormally high temperature or an abnormally low temperature. A detected temperature Td that exceeds the allowable temperature range defined by the first threshold Tth1 is determined to be an abnormally high temperature or an abnormally low temperature. For example, in FIG. 11, if the first threshold Tth1, which is used to determine an abnormally high temperature, is set to 240°C, when the detected temperature Td exceeds 240°C, it is determined to be an "abnormally high temperature."

[0093] 12, for example, if the first threshold Tth1, which is used to determine a low temperature abnormality, is set to 40°C, and the detected temperature Td falls below 40°C, the temperature is determined to be an "abnormally low temperature." In the example described above, the allowable temperature range of the first threshold Tth1 is set to 240°C for the abnormally high temperature on the high side and 40°C for the abnormally low temperature on the low side. However, the allowable temperature range is not limited to these set temperatures and may be set arbitrarily or based on design specifications. Furthermore, the set temperatures may be changed as appropriate depending on the installation environment and the status of the device. If the determination result is not a temperature abnormality and the change in the detected temperature Td is within the allowable temperature range and below the target temperature, the target temperature determination circuit 91 outputs an instruction signal to the system controller 13 to instruct the heater to turn on or stop heating.

[0094] When the system controller 13 receives a command signal to heat the heater, it controls the heater power supply circuit 149 to start supplying power to the heater unit 73 or to increase the amount of power supplied. On the other hand, if the comparison result shows that the detected temperature Td is within the allowable temperature range and is equal to or higher than the target temperature, the target temperature determination circuit 91 outputs a command signal to the system controller 13 to stop heating by the heater. When the system controller 13 receives a command signal to stop heating by the heater, it controls the heater power supply circuit 149 to stop supplying power to the heater unit 73 or to supply a reduced amount of power. Note that the system controller 13 may indirectly control the heater power supply circuit 149 via the heater energization control circuit 14.

[0095] Furthermore, the target temperature determination circuit 91 outputs the detected temperature Td to the difference calculation circuit 92 when the detected temperature Td exceeds the upper or lower limit of the allowable temperature range of the first threshold value. The difference calculation circuit 92 calculates the current temperature difference Tc by subtracting the detected temperature Td from the WAE temperature estimated value from the coefficient addition circuit 84 of the heater energization control circuit 14. The calculated current temperature difference Tc is output to the temperature abnormality determination circuit 93.

[0096] The memory circuit 94 pre-stores at least a first threshold value Tth1 and a second threshold value Tth2. The first threshold value Tth1 is used to determine whether the detected temperature Td is an abnormally high temperature or an abnormally low temperature. In this example, the first threshold value Tth1 is set to 240°C as the set temperature at which the upper and lower limits of the allowable temperature range are determined to be abnormally high temperatures, and to 40°C as the set temperature at which the upper and lower limits of the allowable temperature range are determined to be abnormally low temperatures. The second threshold Tth2 is a threshold that sets a temperature range for the temperature difference between the WAE temperature estimated value under normal conditions and the temperature detected by the temperature sensor. This second threshold Tth2 is used to determine whether there is an abnormality on the control circuit side or the temperature sensor side by comparing the detected temperature Td and the temperature difference Tc between the WAE temperature estimated value under normal conditions. In the following description, the second threshold Tth2 is set as a judgment criterion, for example, within an allowable temperature range of ±50°C for the temperature difference between the WAE temperature estimated value under normal conditions and the temperature detected by the temperature sensor.

[0097] In the above example, the allowable temperature range of the first threshold Tth1 is set to 240°C for the abnormally high temperature on the high temperature side and 40°C for the abnormally low temperature on the low temperature side, and the second threshold Tth2 is set to ±50°C, but the allowable temperatures are not limited to these set temperatures and may be set arbitrarily or based on design specifications. Furthermore, the set temperatures may be configured to be changeable as appropriate depending on the installation environment and conditions of the device.

[0098] When the detected temperature Td is determined to be an abnormally high temperature or an abnormally low temperature based on the first threshold, the temperature abnormality determination circuit 93 compares the current temperature difference Tc with the second threshold Tth2 read from the memory circuit 94. In this comparison, the temperature abnormality determination circuit 93 determines whether the current temperature difference Tc is equal to or greater than the second threshold Tth2 (temperature difference Tc≧second threshold Tth2).

[0099] If the temperature anomaly determination circuit 93 determines that the current temperature difference Tc does not exceed the allowable temperature range of the second threshold value Tth2 (within the allowable temperature range), it determines that there is an abnormality in the temperature sensor unit. That is, the temperature sensor responds by rising or falling in temperature in response to temperature changes caused by turning the heater on and off, but the temperature change is slower than normal, and the target temperature may not be reached even if the supplied power is increased. For example, this may occur when the detection point of the temperature sensor, which should be in contact with the object to be measured, is separated from the object to be measured, or when the output value is reduced due to a temperature sensor malfunction. In such cases, the detected temperature Td is often lower than normal.

[0100] On the other hand, if the temperature anomaly determination circuit 93 determines that the current temperature difference Tc is greater or smaller than the allowable temperature range of the second threshold value Tth2, it determines that there is an abnormality on the circuit side. That is, since the output value of the temperature sensor follows the temperature change and changes more than normal, it is considered to be an abnormality on the circuit side. When there is an abnormality on the circuit side, it can first be assumed that either the heater energization control circuit 14 or the heater power supply circuit 149 has failed.

[0101] If the temperature abnormality determination circuit 93 determines that a malfunction has occurred, it outputs a signal indicating the occurrence of an abnormality to the system controller 13. The system controller 13 notifies an operator that repair is required. After notifying a service call, the operator or the system controller 13 stops operation of the image forming apparatus 1.

[0102] Next, the WAE control will be described in detail with reference to the flowchart shown in Fig. 7. Here, Fig. 8 is a diagram showing the temperature characteristics of the detected value of the temperature sensor actually measured under normal conditions and the WAE temperature estimated value.

[0103] First, the heater energization control circuit 14 sets various initial values ​​(ACT1). For example, the heater energization control circuit 14 sets the coefficient in the coefficient adding circuit 84 and the target temperature TGT of the target temperature output circuit 85 based on a signal from the system controller 13.

[0104] The temperature estimation circuit 81 of the heater energization control circuit 14 acquires the detected temperature Td from the temperature sensor unit 74, the estimated history PREV (the most recent WAE temperature estimate) from the estimation history storage circuit 82, and the energization pulse Ps from the control signal generation circuit 87 (ACT2). In Figure 8, during the warm-up period after the heater is turned on, the detected temperature (output value) of the temperature sensor rises from room temperature to approximately 150°C, after which the warm-up is completed and the temperature remains constant at around 150°C. The actual surface temperature of the film unit 71 exhibits fine wavy fluctuations.

[0105] Furthermore, if the temperature sensor unit 74 has a slightly slow response to temperature changes due to its own heat capacity or the characteristics of the temperature-sensitive material, the detected temperature Td may be detected in a delayed or smoothed state relative to the WAE temperature estimate value.

[0106] Next, the temperature estimation circuit 81 performs a temperature estimation process (ACT3). That is, the temperature estimation circuit 81 generates a temperature estimation result EST based on the detected temperature Td, the estimation history PREV, and the energization pulse Ps. The temperature estimation circuit 81 outputs the temperature estimation result EST to the high-frequency component extraction circuit 83 and the estimation history storage circuit 82.

[0107] In general, heat transfer can be equivalently expressed by the CR time constant of an electric circuit. Heat capacity is replaced by a capacitor C. Heat transfer resistance is replaced by a resistor R. Furthermore, a heat source is replaced by a DC voltage source. The temperature estimation circuit 81 estimates the amount of heat given to the film unit 71 by applying the amount of current flowing to the heater unit 73 and the heat capacity of the film unit 71 to a CR circuit in which the values ​​of each element are set in advance. The temperature estimation circuit 81 estimates the surface temperature of the film unit 71 based on the amount of heat given to the film unit 71, the detected temperature Td, and the estimation history PREV, and outputs the temperature estimation result EST.

[0108] The temperature estimation circuit 81 repeatedly turns on and off from the DC voltage source based on the energization pulse Ps, and the CR circuit operates in response to the input voltage pulse, generating an output voltage. This makes it possible to estimate the heat propagated to the surface of the film unit 71, which is the temperature control target. Note that the heat from the film unit 71 flows out to the external environment via the space within the fixing unit 21 (the external circuit of the film unit 71). For this reason, the temperature estimation circuit 81 further includes a CR circuit for estimating the heat flow from the film unit 71 to the external environment. The temperature estimation circuit 81 may also further include a CR circuit for estimating the amount of heat flowing from the film unit 71 to the space within the fixing unit 21.

[0109] Next, the high-frequency component extraction circuit 83 performs high-pass filtering to extract high-frequency components from the temperature estimation result EST (ACT 4). The high-frequency component HPF, which is a signal indicating the high-frequency components from the temperature estimation result EST, tracks changes in the actual surface temperature of the film unit 71. Next, the coefficient addition circuit 84 performs a coefficient addition process to correct the detected temperature Td (ACT 5). The coefficient addition circuit 84 multiplies the high frequency component HPF by a preset coefficient, and adds the high frequency component HPF multiplied by the coefficient to the detected temperature Td to calculate a WAE temperature estimation value.

[0110] The coefficient addition circuit 84 uses the coefficient to adjust the value of the high-frequency component HPF to be added to the detected temperature Td, thereby calculating the WAE temperature estimate. For example, if the coefficient is 1, the coefficient addition circuit 84 directly adds the high-frequency component HPF to the detected temperature Td. Also, if the coefficient is 0.1, for example, the coefficient addition circuit 84 adds one-tenth the value of the high-frequency component HPF to the detected temperature Td. In this case, the effect of the high-frequency component HPF is almost eliminated, and the detected temperature Td becomes closer to the detected temperature Td. Also, if the coefficient is 1 or greater, for example, the effect of the high-frequency component HPF can be more strongly expressed. Experimental results have shown that the coefficient set in the coefficient addition circuit 84 should not be too extreme, but should be close to 1.

[0111] In WAE control, minute temperature changes in the surface temperature of the film unit 71 are estimated based on the detected temperature Td and the high-frequency component HPF of the temperature estimation result EST. The WAE temperature estimate is a value that appropriately tracks the surface temperature of the film unit 71. The difference comparison circuit 86 calculates the difference DIF between the target temperature TGT and the WAE temperature estimated value from the coefficient addition circuit 84, and outputs it to the control signal generation circuit 87 (ACT6).

[0112] The control signal generation circuit 87 generates an energization pulse Ps based on the difference DIF. The control signal generation circuit 87 outputs the energization pulse Ps to the power supply circuit 88 and the temperature estimation circuit 81 (ACT7). The power supply circuit 88 outputs power PC, which is a control signal, to the heater power supply circuit 149 of the heater unit 73 based on the energization pulse Ps.

[0113] The difference DIF indicates the relationship between the target temperature TGT and the estimated WAE temperature. For example, if this relationship is such that the estimated WAE temperature is equal to or greater than the target temperature TGT, then the amount of current supplied to the heater unit 73 is reduced and the film unit surface temperature is lowered by narrowing the width of the current supply pulse Ps or by reducing its frequency. On the other hand, if this relationship is such that the estimated WAE temperature is less than the target temperature TGT, then the amount of current supplied to the heater unit 73 is increased and the film unit surface temperature is raised by widening the width of the current supply pulse Ps or by increasing its frequency.

[0114] The difference DIF can be used to determine not only the vertical relationship between the WAE temperature estimate and the target temperature TGT, but also how far apart they are. For example, if the difference DIF (absolute value) is large, the difference between the WAE temperature estimate and the target temperature TGT is large, so the above-mentioned control may be changed significantly. Also, for example, if the difference DIF (absolute value) is small, the difference between the WAE temperature estimate and the target temperature TGT is small, so the above-mentioned control may be performed more gradually.

[0115] The processor 22 of the system controller 13 determines whether to terminate the WAE control (ACT8). If the processor 22 determines in ACT8 that the WAE control should be continued rather than terminated (ACT8: NO), the processor 22 proceeds to the processing of ACT2 described above. On the other hand, if the processor 22 determines that the WAE control should be terminated in response to the device being shut down by turning the main power switch 24 OFF (ACT8: YES), the processor 22 terminates the processing routine.

[0116] In this way, when processing a certain cycle (current cycle), the heater energization control circuit 14 performs WAE control based on the values ​​in the previous cycle (energization pulse Ps and temperature estimation result EST: estimation history PREV) and the detected temperature Td in the current cycle. That is, the heater energization control circuit 14 inherits the values ​​in the next cycle. The heater energization control circuit 14 recalculates the temperature estimation calculation based on the history of the previous calculation. Therefore, the heater energization control circuit 14 is constantly performing calculations during operation. The heater energization control circuit 14 stores the calculation results in a memory or the like and reuses them in the calculation of the next cycle.

[0117] Next, temperature control including temperature abnormality detection by the temperature abnormality detection circuit 25 of this embodiment will be described with reference to the flowchart shown in Fig. 10. In this example, the temperature abnormality detection circuit 25 is installed in the image forming apparatus 1. Fig. 11 is a diagram showing temperature characteristics when the temperature detected by the temperature sensor unit 74 becomes abnormally high, and Fig. 12 is a diagram showing temperature characteristics when the temperature detected by the temperature sensor unit 74 becomes abnormally low.

[0118] First, the image forming apparatus 1 is started by turning on the main power switch 24 (ACT11). The system controller 13 of the image forming apparatus 1 initializes each component to execute printing. At this time, the heater energization control circuit 14 supplies power to the heater unit 73 to heat the first through third heaters 155, 156, and 157 of the film unit 71, thereby starting warm-up for starting printing. As the warm-up begins, WAE control is started, and an estimated WAE temperature value is calculated (ACT12). At this time, as shown in FIG. 7, the detected temperature Td detected by the temperature sensor unit 74 rises from room temperature, and the estimated WAE temperature value rises from 0°C.

[0119] Next, after the warm-up is completed, the temperature abnormality detection circuit 25 acquires the detected temperature Td from the temperature sensor unit 74 and inputs it to the target temperature determination circuit 91 (ACT13). The target temperature determination circuit 91 compares the detected temperature Td detected by the temperature sensor unit 74 with a preset target temperature TGT and determines whether the detected temperature Td is lower than the target temperature TGT (ACT14). In this determination, if the detected temperature Td is lower than the target temperature (ACT14: YES), the target temperature determination circuit 91 outputs an instruction signal to the system controller 13 to heat the heater (ACT15). In response to the instruction signal to heat the heater, the system controller 13 controls the heater power supply circuit 149 to start (ON) the supply of power to the heater unit 73 or to increase the amount of power supplied.

[0120] On the other hand, if it is determined in ACT14 that the detected temperature Td is equal to or higher than the target temperature (ACT14: NO), the target temperature determination circuit 91 outputs an instruction signal to the system controller 13 to stop heating by the heater (ACT16). Upon receiving the instruction signal to stop heating by the heater, the system controller 13 controls the heater power supply circuit 149 to stop (OFF) the supply of power to the heater unit 73 or to supply a reduced amount of power. Note that the system controller 13 may output an instruction signal to turn the heater ON / OFF to the heater power supply circuit 149 via the heater energization control circuit 14.

[0121] Next, the target temperature determination circuit 91 determines whether the detected temperature Td is within a predetermined first threshold allowable temperature range, i.e., whether the detected temperature Td is an abnormally low temperature or an abnormally high temperature (ACT17). Here, if the temperature determined to be an abnormally high temperature within the allowable temperature range is set to, for example, 240°C, when the detected temperature Td exceeds 240°C, it is determined to be an "abnormally high temperature" (ACT17: YES). Similarly, if the temperature determined to be an abnormally low temperature is set to, for example, 40°C, when the detected temperature Td falls below 40°C, it is determined to be an "abnormally low temperature." If the detected temperature Td is determined to be an abnormally low temperature or an abnormally high temperature, the process proceeds to ACT18. On the other hand, if the detected temperature Td is within the allowable temperature range of the first threshold (40°C≦Td≦240°C), it is determined to be operating normally (ACT17: NO), and the process returns to ACT12. Subsequently, the heater is turned on or off by WAE control, and the WAE estimate is calculated.

[0122] Furthermore, the target temperature determination circuit 91 may start determining whether the detected temperature Td exceeds the allowable temperature range of the first threshold value from the start of warm-up or after warm-up is completed. The first threshold value used for this determination may be separately set as a threshold value for the allowable temperature range for warm-up. Next, if the determination in ACT17 (YES) above indicates that the detected temperature Td is an abnormally low temperature or an abnormally high temperature, the difference calculation circuit 92 calculates the difference between the detected temperature Td and the WAE temperature estimated value from the coefficient addition circuit 84 of the heater energization control circuit 14 to obtain the current temperature difference Tc. The obtained current temperature difference Tc is output to the temperature abnormality determination circuit 93.

[0123] 12, the abnormally low temperature of the detected temperature Td has temperature characteristics in which the main temperature sensor detection value measured by the second temperature sensor 171 that detects the temperature of the first heater 155 and the side temperature sensor detection value measured by the second temperature sensor 172 that detects the temperature of the second heater 156 decrease linearly. Similarly, the abnormally high temperature of the detected temperature Td has temperature characteristics in which the main temperature sensor detection value and the side temperature sensor detection value measured by the second temperature sensor 172 increase linearly, as shown in FIG.

[0124] Next, the temperature abnormality determination circuit 93 compares the current temperature difference Tc with the second threshold value Tth2 read from the memory circuit 94, and determines whether the current temperature difference Tc is equal to or greater than the second threshold value Tth2 (temperature difference Tc≧second threshold value Tth2) (ACT 18). Here, the second threshold value Tth2 is set to a temperature width of ±50°C as an allowable temperature range, based on the temperature difference obtained during normal operation, as described above.

[0125] If the temperature anomaly determination circuit 93 determines in ACT18 that the current temperature difference Tc does not exceed the allowable temperature range of the second threshold value Tth2 (ACT18: NO), i.e., if +50°C > current temperature difference Tc > -50°C, it determines that there is an abnormality in the temperature sensor unit (ACT19). This determination is based on the fact that the temperature sensor responds by rising or falling in temperature in response to temperature changes caused by the heater being turned on or off, but the temperature change is slower than normal, and the target temperature may not be reached even if the supplied power is increased. Such cases may include, for example, when the temperature sensor's detection point, which should normally be in contact with the object being measured, is separated from the object being measured, or when the temperature sensor's output is reduced due to a fault. In such cases, the detected temperature Td is often lower than normal.

[0126] On the other hand, if the temperature abnormality determination circuit 93 determines in ACT18 that the current temperature difference Tc is equal to or greater than the allowable temperature range of the second threshold value Tth2 (ACT18: YES), that is, if the current temperature difference Tc is greater than or equal to +50°C or less than or equal to -50°C, it determines that there is an abnormality on the circuit side (ACT20). That is, the temperature sensor follows the temperature change, but the change is greater than normal, so it is considered to be an abnormality on the circuit side. If there is an abnormality on the circuit side, it can be assumed that either the heater energization control circuit 14, which controls output and outputs power, or the heater power supply circuit 149 has failed.

[0127] If the temperature abnormality determination circuit 93 determines that a malfunction has occurred, it outputs a signal indicating the occurrence of an abnormality to the system controller 13. The system controller 13 notifies the operator that repair is required (ACT21). After notifying a service call, the operator or the system controller 13 stops operation of the image forming apparatus 1 (ACT22) and ends the routine.

[0128] As described above, the temperature control device of this embodiment includes an on-board temperature abnormality detection circuit that can determine whether the detected temperature Td acquired by the temperature sensor in the fixing unit is an abnormally low temperature or an abnormally high temperature. If the detected temperature Td is an abnormally low temperature or an abnormally high temperature, the current temperature difference Tc is calculated from the current detected temperature and the WAE temperature estimate, and this current temperature difference is compared with the second threshold value Tth2. If the current temperature difference is greater than or less than the allowable temperature range of the second threshold value Tth2, an abnormality is determined to exist in the control circuit. If the current temperature difference Tc does not reach the second threshold value Tth2 and is within the allowable temperature range, an abnormality is determined to exist in the temperature sensor. The control circuit side mainly includes the heater energization control circuit 14, but may also include the heater power supply circuit 149 and other components.

[0129] Although one aspect and several embodiments of the present invention have been described, these aspects and embodiments are presented as examples and are not intended to limit the scope of the invention. These novel aspects and embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These aspects and embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0130] 1...image forming apparatus, 11...casing, 12...communication interface, 13...system controller, 14...heater energization control circuit, 15...display unit, 16...operation interface, 17...paper tray, 18...paper output tray, 19...conveyor unit, 20...image forming unit, 21...fuser, 22...processor, 23...memory, 24...main power switch, 25...temperature abnormality detection circuit, 26...temperature control device, 31...paper feed transport path, 32...paper output transport path, 33...pickup roller, 41...process unit, 42...exposure unit, 43...transfer mechanism, 51...photosensitive drum, 52...electric charger, 53...developer, 61...primary transfer belt, 62...secondary transfer opposing roller, 63...primary transfer roller, 64...secondary transfer roller, 71...film unit, 72...pressure roller, 73...heater temperature sensor unit, 74...temperature sensor unit, 81...temperature estimation circuit, 82...estimation history storage circuit, 83...high frequency component extraction circuit, 84...coefficient addition circuit, 85...target temperature output circuit, 86...differential comparison circuit, 87...control signal generation circuit, 88...power supply circuit, 91...target temperature judgment circuit, 92...differential calculation circuit, 93...temperature abnormality judgment circuit, 94...memory circuit, 101...core metal, 102...elastic layer, 111...cylindrical film, 112...support member, 113...stay, 118...through hole, 119...through hole, 144...heat transfer member, 144a...surface, 145...substrate, 146...glass layer, 147...heat generating element set, 148...glass coating, 149...heater power supply circuit, 155, 156, 157...heater, 172, 173, 174...temperature sensor, 181...groove portion, 182...contact portion.

Claims

1. A temperature control device that controls a temperature control target to which heat is propagated from a heater of a fixing unit to reach a preset target temperature by supplying power to the heater, a heater power supply circuit that supplies power to the heater; a temperature sensor for measuring a detected temperature from the temperature control target; a temperature estimation circuit that estimates a temperature of the temperature-controlled object based on the detected temperature, a heat capacity and a current pulse of the heater based on current supplied to the heater, and a thermal resistance of the fixing unit; a control signal generation circuit that outputs the current pulse for controlling the power supplied by the heater power supply circuit based on the estimated temperature of the temperature-controlled object estimated by the temperature estimation circuit and a target temperature; a temperature abnormality detection circuit that, when the detected temperature acquired by the temperature sensor is an abnormally low temperature or an abnormally high temperature, compares a current temperature difference calculated from the current detected temperature and a temperature estimate value with a threshold value calculated from the detected temperature and temperature estimate value of the temperature sensor in normal times, and determines whether the abnormality is in the temperature sensor or in the circuitry based on the comparison result; A temperature control device comprising:

2. 2. The temperature control device according to claim 1, wherein the temperature estimation circuit estimates the temperature of the temperature control object based on a CR circuit in which the heat capacity of the temperature control object is replaced with a capacitor and the heat transfer resistance is replaced with a resistor, the current pulse, and the immediately preceding temperature estimation value.

3. The temperature abnormality detection circuit a storage circuit that stores a first threshold value and a second threshold value, each of which has an allowable temperature range; a target temperature determination circuit that determines whether the detected temperature is an abnormally low temperature or an abnormally high temperature that exceeds the lower limit or upper limit of the allowable temperature range by comparing the detected temperature with the first threshold value; a difference calculation circuit that calculates a current temperature difference from a current detected temperature and a temperature estimate value when the detected temperature is the abnormally low temperature or the abnormally high temperature; 2. The temperature control device according to claim 1, further comprising: a temperature abnormality determination circuit that determines whether the abnormality is in the temperature sensor or in the circuit based on whether the current temperature difference is within the allowable temperature range of the second threshold by comparing it with the second threshold.

4. 4. The temperature control device according to claim 3, wherein the temperature abnormality detection circuit determines that there is an abnormality in the circuit when the current temperature difference is greater than or smaller than the allowable temperature range of the second threshold, and determines that there is an abnormality in the temperature sensor when the current temperature difference does not reach the second threshold and is within the allowable temperature range.

5. a heat transfer member disposed between the heater and the temperature sensor in contact with each other; The temperature control device according to claim 1 , wherein the heat transfer member has a groove portion that defines a spatial region between the contact surface with the heater.

6. An image forming apparatus comprising the temperature control device according to claim 1 .

Images