Temperature Control Device

Abstract

To provide a temperature control device capable of preventing occurrences of overshooting and temperature ripple, while suppressing costs.SOLUTION: A temperature control device comprises a temperature estimation section and a frequency generation section. A temperature generation section estimates a temperature of a temperature control object on the basis of a frequency of a drive signal of an inverter to which an induction heating coil is connected. The frequency generation section generates a frequency of a drive signal on the basis of a temperature estimation result according to the temperature estimation part, a temperature detection result of a temperature control object according to a temperature sensor, and a target temperature of the temperature control object.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] FIELD OF THE INVENTION An embodiment of the present invention relates to a temperature control device. [Background technology]

[0002] The image forming apparatus includes a fuser that fuses a toner image to a print medium by applying heat and pressure to the print medium. For example, the fuser is an induction heating (IH) fuser. The induction heating fuser includes an induction heating coil, a fuser belt, a pressure roller, and a temperature sensor. The temperature sensor detects the surface temperature of the fuser belt.

[0003] A controller that controls the fixing unit controls the surface temperature of the fixing belt to a target value based on a detection signal from the temperature sensor (temperature sensor signal).

[0004] If there is a discrepancy (or time lag) between the temperature detected by the temperature sensor and the actual surface temperature of the fixing belt, overshoot, temperature ripple, etc. may occur. Therefore, to prevent the occurrence of overshoot and temperature ripple, a temperature sensor with good response (for example, a thermopile) is required. However, a temperature sensor with good response has the problem of being expensive. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-119653 Summary of the Invention [Problem to be solved by the invention]

[0006] The problem to be solved by the present invention is to provide a temperature control device that can prevent the occurrence of overshoot and temperature ripple at a reduced cost. [Means for solving the problem]

[0007] A temperature control device according to one embodiment includes a temperature estimator and a frequency generator. The temperature estimator estimates the temperature of a temperature-controlled object based on the frequency of a drive signal from an inverter connected to an induction heating coil. The frequency generator generates the frequency of the drive signal based on the temperature estimation result from the temperature estimator, the temperature detection result of the temperature-controlled object by the temperature sensor, and a target temperature of the temperature-controlled object. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram for explaining an example of the configuration of an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of the configuration of a temperature control circuit according to an embodiment. [Figure 3] FIG. 3 is a diagram for explaining an example of the operation of the temperature control circuit according to one embodiment. [Figure 4] FIG. 4 is a diagram for explaining an example of the operation of the temperature control circuit according to one embodiment. [Figure 5] FIG. 5 is a diagram for explaining an example of the operation of the temperature control circuit according to one embodiment. [Figure 6] FIG. 6 is a diagram for explaining an example of the operation of the temperature control circuit according to one embodiment. [Figure 7] FIG. 7 is a diagram for explaining an example of a frequency generation process of the temperature control circuit according to an embodiment. [Figure 8] FIG. 8 is a diagram for explaining an example of conversion processing of the temperature control circuit according to an embodiment. [Figure 9] FIG. 9 is a diagram for explaining an example of correction processing of the temperature control circuit according to an embodiment. [Figure 10] FIG. 10 is a diagram illustrating a driving pulse signal according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] A temperature control device according to an embodiment will be described below with reference to the drawings. 1 is an explanatory diagram for explaining an example of the configuration of an image forming apparatus 1 according to an embodiment. The image forming apparatus 1 is an example of a temperature control device.

[0010] The image forming apparatus 1 is, for example, an MFP (Multifunction Peripheral) that performs various processes such as image formation while transporting a print medium P. The image forming apparatus 1 is, for example, a solid-state scanning printer (for example, an LED printer) that scans an LED (Light Emitting Diode) array that performs various processes such as image formation while transporting the print medium P.

[0011] For example, the image forming device 1 is configured to receive toner from a toner cartridge and form an image on a print medium using the received toner. The toner may be a single color toner or a color toner such as cyan, magenta, yellow, or black. The toner may also be a decolorizable toner that is decolorized when heat is applied.

[0012] As shown in FIG. 1, the image forming apparatus 1 includes a housing 10, a power conversion circuit 11, a communication interface 12, a system controller 13, a temperature 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, and a fixing unit 21.

[0013] The housing 10 is the main body of the image forming apparatus 1. The housing 10 houses a power conversion circuit 11, a communication interface 12, a system controller 13, a temperature 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, and a fixing unit 21.

[0014] First, the configuration of the control system of the image forming apparatus 1 will be described. The power conversion circuit 11 supplies DC voltage to various components within the image forming apparatus 1 using AC voltage from an AC power source AC that supplies power to the image forming apparatus 1.

[0015] The communication interface 12 is an interface for communicating with other devices. The communication interface 12 is used, for example, for communication with a higher-level device (external device). The communication interface 12 is configured, for example, as a LAN (Local Area Network) connector. The communication interface 12 may also be configured to perform wireless communication with other devices in accordance with standards such as Bluetooth (registered trademark) or Wi-fi (registered trademark).

[0016] The system controller 13 controls the image forming apparatus 1. The system controller 13 includes, for example, a processor 22 and a memory 23.

[0017] The processor 22 is a computing element that executes arithmetic processing. The processor 22 is, for example, a CPU (Central Processing Unit). The processor 22 performs various processes based on data such as programs stored in the memory 23. The processor 22 executes the programs stored in the memory 23, thereby functioning as a control unit that can execute various operations.

[0018] The processor 22 performs various information processes by executing programs stored in the memory 23. 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.

[0019] A print job includes image data that indicates an image to be formed on a print medium P. The image data may be data for forming an image on one sheet of print medium P, or data for forming images on multiple sheets of print medium P. Furthermore, a print job includes information indicating whether color printing or monochrome printing is to be performed. A 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.

[0020] 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 supplies the print control information to the temperature control circuit 14.

[0021] 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 conveying of the print medium P by the conveying unit 19 and the formation of an image on the print medium P by the image forming unit 20, etc.

[0022] The memory 23 is a storage medium that stores programs, data used by 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.

[0023] The image forming apparatus 1 may be configured to include an engine controller separate from the system controller 13. In this case, the engine controller controls the transport of the print medium P by the transport unit 19 and the formation of an image on the print medium P by the image forming unit 20. In this case, the system controller 13 supplies the engine controller with information necessary for control by the engine controller.

[0024] The temperature control circuit 14 controls the temperature of the fixing unit 21, which will be described later. The temperature control circuit 14 will be described in detail later. For example, the temperature control circuit 14 includes a processor 24 and a memory 25. Like the processor 22, the processor 24 is an arithmetic element that executes arithmetic processing. The processor 24 performs various processes based on data such as programs stored in the memory 25. The processor 24 executes the programs stored in the memory 25 to realize each unit, which will be described later, and to perform various operations. Like the memory 23, the memory 25 is a storage medium that stores programs, data used in the programs, and the like.

[0025] The display unit 15 includes a display that displays a screen in response to a video signal input from a display control unit such as the system controller 13 or a graphics controller (not shown). For example, the display of the display unit 15 displays a screen for various settings of the image forming apparatus 1.

[0026] The operation interface 16 is connected to operation members (not shown). 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 power key, 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 the touched position on the screen displayed on the display unit 15 to the system controller 13.

[0027] Each of the multiple paper trays 17 is a cassette that stores print media P. The paper trays 17 are configured so that print media P can be supplied from outside the housing 10. For example, the paper trays 17 are configured so that they can be pulled out from the housing 10.

[0028] The paper discharge tray 18 is a tray that supports the print medium P discharged from the image forming apparatus 1.

[0029] Next, a configuration for transporting the print medium P in the image forming apparatus 1 will be described. The transport unit 19 is a mechanism that transports the print medium P within the image forming apparatus 1. As shown in Fig. 1, the transport unit 19 includes a plurality of transport paths. For example, the transport unit 19 includes a paper feed transport path 31 and a paper discharge transport path 32.

[0030] The paper feed conveying path 31 and the paper discharge conveying path 32 are each composed of multiple motors, multiple rollers, and multiple guides (not shown). The multiple motors rotate their shafts under the control of the system controller 13, thereby rotating rollers that are linked to the rotation of the shafts. The multiple rollers move the printing medium P by rotating. The multiple guides control the conveying direction of the printing medium P.

[0031] The paper feed conveying path 31 takes in the print medium P from the paper tray 17 and supplies the taken-in print medium P to the image forming unit 20. The paper feed conveying path 31 is provided with pickup rollers 33 corresponding to each paper tray. Each pickup roller 33 takes in the print medium P from the paper tray 17 into the paper feed conveying path 31.

[0032] The paper discharge transport path 32 is a transport path that discharges the print medium P on which an image has been formed from the housing 10. The print medium P discharged by the paper discharge transport path 32 is supported by the paper discharge tray 18.

[0033] Next, the image forming unit 20 will be described. The image forming unit 20 is configured to form an image on the print medium P. Specifically, the image forming unit 20 forms an image on the print medium P based on a print job generated by the processor 22.

[0034] 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. Note that the plurality of process units 41 and the plurality of exposure devices 42 each have the same configuration, so one process unit 41 and one exposure device 42 will be described below.

[0035] First, the process unit 41 will be described. The process unit 41 is configured to form a toner image. For example, a plurality of process units 41 are provided for each type of toner. For example, the plurality of process units 41 correspond to color toners such as cyan, magenta, yellow, and black, respectively. Specifically, toner cartridges containing toners of different colors are connected to each process unit 41.

[0036] The toner cartridge includes a toner container and a toner delivery mechanism. The toner container is a container for storing toner. The toner delivery mechanism is a mechanism including a screw and the like for delivering toner from the toner container.

[0037] 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 includes 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 (not shown).

[0038] 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 with the rotation of the photosensitive drum 51 while applying a predetermined pressure to the photosensitive drum 51.

[0039] 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.

[0040] 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 mixed with the carrier by a 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.

[0041] The developing roller rotates in the developer container, causing developer to adhere 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 some of the developer adhering to the surface of the rotating developing roller. This forms a layer of developer on the surface of the developing roller whose thickness corresponds to the distance between the doctor blade and the surface of the developing roller.

[0042] 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 (not shown) 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.

[0043] 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.

[0044] 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.

[0045] In the above configuration, when light is irradiated from the exposure device 42 onto the surface of the photosensitive drum 51 charged by the electrostatic charger 52, an electrostatic latent image is formed. 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.

[0046] Next, the transfer mechanism 43 will be described. The transfer mechanism 43 is configured to transfer the toner image formed on the surface of the photosensitive drum 51 onto the print medium P.

[0047] 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.

[0048] The primary transfer belt 61 is an endless belt wound around the 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.

[0049] The secondary transfer opposing roller 62 is rotated by a motor (not shown). As the secondary transfer opposing roller 62 rotates, it 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.

[0050] The multiple primary transfer rollers 63 are configured to bring the primary transfer belt 61 into contact with the photosensitive drums 51 of the process units 41. The multiple primary transfer rollers 63 are provided to correspond to the photosensitive drums 51 of the multiple process units 41. Specifically, the multiple primary transfer rollers 63 are provided at positions facing the photosensitive drums 51 of the corresponding process units 41, with the primary transfer belt 61 sandwiched between them. The primary transfer rollers 63 come into contact with the inner circumferential surface of the primary transfer belt 61, and displace the primary transfer belt 61 toward the photosensitive drums 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 drums 51.

[0051] The secondary transfer roller 64 is disposed in a position facing the primary transfer belt 61. The secondary transfer roller 64 contacts and applies pressure to the outer peripheral surface of the primary transfer belt 61. 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 printing medium P passes through the transfer nip, the secondary transfer roller 64 presses the printing medium P passing through the transfer nip against the outer peripheral surface of the primary transfer belt 61.

[0052] The secondary transfer roller 64 and the secondary transfer opposing roller 62 rotate to sandwich and transport the print medium P supplied from the paper feed transport path 31. This causes the print medium P to pass through the transfer nip.

[0053] In the above configuration, 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 unit 20 includes multiple process units 41, the primary transfer belt 61 receives toner images from the photosensitive drums 51 of the multiple process units 41. The toner image transferred to the outer circumferential surface of the primary transfer belt 61 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 print 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 print medium P at the transfer nip.

[0054] Next, the fixing-related configuration of the image forming apparatus 1 will be described. The fixing device 21 is an induction heating type fixing device that fixes the toner image onto the print medium P. The fixing device 21 operates under the control of the system controller 13 or the temperature control circuit 14.

[0055] The fixing unit 21 includes a pressure roller 70 , a pressure pad 71 , a magnetic shunt alloy position adjusting mechanism 72 , an aluminum member 73 , a magnetic shunt alloy 74 , a ferrite core 75 , an induction heating coil 76 , a fixing belt 77 , a frame 78 , and a temperature sensor 79 .

[0056] The pressure roller 70 is positioned so as to face the fixing belt 77 on the circumference. The longitudinal width of the pressure roller 70 is wider than the width of the print medium P being transported. The longitudinal direction of the pressure roller 70 is perpendicular to the rotation direction of the pressure roller 70. The pressure roller 70 contacts the fixing belt 77 by springs at both ends. The pressure roller 70 has a metal core with an elastic layer such as a rubber layer on the outside. The pressure roller 70 has a release layer on its surface. The pressure roller 70 is driven to rotate. The pressure roller 70 may be driven by the fixing belt 77. The pressure roller 70 may have a one-way clutch to eliminate a speed difference between the pressure roller 70 and the fixing belt 77.

[0057] The pressure pad 71 is located inside the fixing belt 77. The pressure pad 71 presses the fixing belt 77 toward the pressure roller 70. A fixing nip is formed between the fixing belt 77 and the pressure roller 70. The shape of the part of the pressure pad 71 that faces the pressure roller 70 is the same as the outer circumferential shape of the pressure roller 70. The longitudinal width of the pressure pad 71 is wider than the width of the print medium P being transported. The longitudinal direction of the pressure pad 71 is parallel to the longitudinal direction of the fixing belt 77, which corresponds to the direction perpendicular to the rotation direction of the fixing belt 77. The pressure pad 71 has a low-friction sheet between it and the pressure roller 70 to improve sliding properties. The pressure pad 71 is made of heat-resistant resin. The heat-resistant resin is, for example, polyether ether ketone (PEEK) or phenolic resin.

[0058] The magnetic shunt alloy position adjustment mechanism 72 is fixed to a frame 78. The magnetic shunt alloy position adjustment mechanism 72 is a mechanism for adjusting the position of the magnetic shunt alloy 74. The magnetic shunt alloy position adjustment mechanism 72 has a spring. The magnetic shunt alloy position adjustment mechanism 72 adjusts the position of the magnetic shunt alloy 74 by the force of the spring.

[0059] The aluminum member 73 is connected to the magnetic shunt alloy position adjusting mechanism 72. The aluminum member 73 shields the magnetic field generated by the induction heating coil .

[0060] The magnetic shunt alloy 74 faces the induction heating coil 76 across the fixing belt 77. For example, the longitudinal width of the magnetic shunt alloy 74 is greater than the longitudinal width of the fixing belt 77. The longitudinal direction of the magnetic shunt alloy 74 is parallel to the longitudinal direction of the fixing belt 77. The magnetic shunt alloy 74 is a sheet made of a temperature-sensitive magnetic material. The inductance value of the magnetic shunt alloy 74 is almost constant below the saturation temperature, but drops sharply above the saturation temperature.

[0061] The ferrite core 75 is located outside the induction heating coil 76. The ferrite core 75 shields the magnetic field generated by the induction heating coil 76.

[0062] Induction heating coil 76 is located outside fixing belt 77. Induction heating coil 76 generates a magnetic field when power is supplied from inverter 82 (described later). The power supplied to induction heating coil 76 is also called IH power. Induction heating coil 76 is an example of an element related to temperature control of a temperature control target.

[0063] The fixing belt 77 is an endless belt. It rotates counterclockwise in FIG. 1. The longitudinal width of the fixing belt 77 is wider than the width of the print medium P being transported. The fixing belt 77 has multiple layers. The fixing belt 77 has a conductive layer that generates heat due to the magnetic field of the induction heating coil 76. For example, the conductive layer is made of a conductive material such as iron, nickel, or copper. The fixing belt 77 may have a Cu layer laminated on a Ni layer. The fixing belt 77 has an elastic layer on the conductive layer. The fixing belt 77 has a release layer on the conductive layer. The release layer is a layer that comes into direct contact with the toner. The release layer is preferably made of a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA) or the like, which has good release properties.

[0064] The frame 78 is positioned inside the fixing belt 77. The frame 78 holds the pressure pad 71.

[0065] The temperature sensor 79 detects the surface temperature of the fixing belt 77. The surface of the fixing belt 77 is an example of a temperature control target. The surface temperature of the fixing belt 77 is an example of the temperature of the fixing belt 77. The temperature of the fixing belt 77 is an example of the temperature of a temperature control target. For example, the temperature sensor 79 is located on the outside of the fixing belt 77. The temperature sensor 79 may be located at the center of the fixing belt 77 in the longitudinal direction. The temperature sensor 79 may be located at an end of the fixing belt 77 in the longitudinal direction. The temperature sensor 79 may be located downstream of the heating unit formed by the magnetic shunt alloy 74 and the induction heating coil 76, and upstream of the fixing nip formed between the fixing belt 77 and the pressure roller 70. The number of temperature sensors 79 is not limited to one, and may be multiple. The temperature sensor 79 may be a contact-type thermistor.

[0066] With the above configuration, the fixing belt 77 and pressure roller 70 apply heat and pressure to the print medium P passing through the fixing nip. The toner on the print medium P melts due to the heat applied by the fixing belt 77, and is applied to the surface of the print medium P due to the pressure applied by the fixing belt 77 and pressure roller 70. This causes the toner image to be fixed onto the print medium P that has passed through the fixing nip. The print medium P that has passed through the fixing nip is introduced into the discharge transport path 32 and is discharged outside the housing 10.

[0067] The fixing device 21 may be configured with a belt having the same function as the pressure roller 70 instead of a roller such as the pressure roller 70. The fixing device 21 may be configured with a roller having the same function as the fixing belt 77 instead of a belt such as the fixing belt 77.

[0068] The automatic temperature adjustment function of the fixing unit 21 configured as above will be described. When the induction heating coil 76 is driven at high frequency by an inverter 82 (described later), a combined inductance is generated among the magnetic shunt alloy 74, the induction heating coil 76, and the fixing belt 77. A resonance phenomenon occurs due to the combined inductance and a resonant capacitor 83 (described later). When the resonant frequency and the frequency driving the induction heating coil 76 are appropriate, a large amount of power is supplied to the induction heating coil 76. Now, let's consider a case where a narrow print medium P passes through the fixing unit 21. The print medium P absorbs heat from the portion of the fixing belt 77 through which the print medium P passes. Meanwhile, the portion of the fixing belt 77 through which the print medium P does not pass accumulates heat and becomes hot. In this case, the magnetic shunt alloy 74 reacts to the high temperature and changes its inductance value. As a result, the relationship between the resonant frequency and the frequency driving the induction heating coil 76 changes, suppressing heat generation in the high-temperature portion of the fixing belt 77. As a result, the longitudinal ends of the fixing belt 77 do not reach abnormally high temperatures.

[0069] Next, the temperature control circuit 14 will be described. The temperature control circuit 14 controls the temperature of the fixing unit 21 . FIG. 2 is a diagram for explaining an example of the configuration of the temperature control circuit 14 according to an embodiment. The temperature control circuit 14 includes a converter 81 , an inverter 82 and a resonant capacitor 83 .

[0070] The converter 81 is a circuit that converts the AC voltage of the AC power supply AC into a DC voltage. For example, the converter 81 is a diode bridge. The converter 81 is connected to the AC power supply AC. The converter 81 is connected to an inverter 82.

[0071] The inverter 82 is a circuit that converts the DC voltage converted by the converter 81 into an AC voltage. The inverter 82 supplies power to the induction heating coil 76 to drive it. For example, the inverter 82 is a half-bridge inverter including switches 821 and 822. The inverter 82 is connected to the converter 81. The inverter 82 is connected to a series resonant circuit consisting of a resonant capacitor 83 and the induction heating coil 76. The series resonant circuit is connected between a node MA of the inverter 82 and GND. The node MA is the node between the switches 821 and 822. When a high-frequency alternating signal is supplied to the gates of the switches 821 and 822, a high-frequency alternating voltage is generated between the node MA of the inverter 82 and GND. The series resonant circuit resonates with the high frequency, and a large amount of power is supplied to the induction heating coil 76. This large amount of power is used for induction heating based on the magnetic field generated by the induction heating coil 76.

[0072] For example, the switches 821 and 822 are power semiconductors such as IGBTs (Insulated Gate Bipolar Transistors) or SiC (silicon carbide). The inverter 82 is not limited to a half-bridge inverter, and may be a full-bridge inverter, a half-wave voltage resonant inverter, a quasi-resonant inverter, or the like.

[0073] The temperature control circuit 14 includes a temperature estimation unit 801, an estimation history storage unit 802, a high-frequency component extraction unit 803, a coefficient addition unit 804, a target temperature output unit 805, a difference comparison unit 806, a frequency generation unit 807, a conversion unit 808, a correction unit 809, a pulse generation unit 810, an insulating buffer 811, and an insulating buffer 812. The temperature control circuit 14 acquires a temperature detection result Td from a temperature sensor 79. The temperature detection result Td indicates the surface temperature of the fixing belt 77 detected by the temperature sensor 79. The temperature control circuit 14 acquires a voltage value ACV of the AC voltage of the AC power supply AC. For example, the voltage value ACV is an effective value. Since the AC power supply AC generally has a fluctuation range, the voltage value ACV fluctuates within a predetermined range. When the voltage value ACV fluctuates, the IH power changes. Therefore, it can be said that the heating operation of the induction heating coil 76 depends on the voltage value ACV. Assuming that the duty control for the inverter 82 is the same, the amount of heat generated by the fixing belt 77 when the voltage value ACV is 90 V is less than when the voltage value ACV is 100 V. On the other hand, the amount of heat generated by the fixing belt 77 when the voltage value ACV is 110 V is greater than when the voltage value ACV is 100 V.

[0074] The temperature estimation unit 801 performs a temperature estimation process to estimate the surface temperature of the fixing belt 77. The temperature estimation unit 801 receives an estimation history PREV from an estimation history storage unit 802 (described later) and a power estimation result ESTPB from a correction unit 809 (described later). The estimation history PREV is a history of temperature estimation results EST generated by the temperature estimation unit 801 every minute time dt. The temperature estimation result EST indicates the surface temperature of the fixing belt 77 estimated by the temperature estimation unit 801. The power estimation result ESTPB indicates an estimated value of the currently generated IH power corresponding to a voltage value ACV corresponding to a frequency FRQ. The power estimation result ESTPB is an example of a power estimation result indicating an estimated value of the IH power corresponding to the frequency FRQ. The frequency FRQ indicates the frequency of a drive pulse signal of the inverter 82 connected to the induction heating coil 76. For example, the frequency FRQ is an analog voltage or a digital value representing the frequency. The drive pulse signal is an example of a drive signal. The drive pulse signal includes high-frequency drive pulse signals PU and PD that alternately output high levels.

[0075] The temperature estimation unit 801 estimates the surface temperature of the fixing belt 77 based on the estimated history PREV and the power estimation result ESTPB. Estimating the surface temperature of the fixing belt 77 based on the estimated history PREV and the power estimation result ESTPB is an example of estimating the surface temperature of the fixing belt 77 based on the power estimation result ESTPB by the correction unit 809. The power estimation result ESTPB is based on the frequency FRQ, as will be described later. Therefore, estimating the surface temperature of the fixing belt 77 based on the estimated history PREV and the power estimation result ESTPB is an example of estimating the surface temperature of the fixing belt 77 based on the frequency FRQ. The power estimation result ESTPB and the frequency FRQ are related to the power supply to the induction heating coil 76. Therefore, estimating the surface temperature of the fixing belt 77 based on the estimated history PREV and the power estimation result ESTPB is an example of estimating the surface temperature of the fixing belt 77 based on the power supply to the induction heating coil 76.

[0076] For example, the temperature estimation unit 801 estimates the temperature change amount of the surface temperature of the fixing belt 77 every dt based on the power estimation result ESTPB at the current time. The temperature estimation unit 801 adds the temperature change amount to the temperature estimation result EST for dt before the current time, which is included in the estimation history PREV. The temperature estimation unit 801 estimates the surface temperature of the fixing belt 77 at the current time based on the addition of the temperature change amount to the temperature estimation result EST for dt before the current time. The temperature estimation unit 801 reuses the temperature estimation result EST for dt before the current time to obtain the temperature estimation result EST for the current time, which is dt ahead. The temperature estimation unit 801 outputs the temperature estimation result EST to the estimation history storage unit 802 and the high-frequency component extraction unit 803.

[0077] The estimation history holding unit 802 holds the history of the temperature estimation result EST. The estimation history holding unit 802 outputs the estimation history PREV to the temperature estimation unit 801.

[0078] The high-frequency component extraction unit 803 performs high-pass filtering to extract high-frequency components from the temperature estimation result EST. For example, the high-frequency component extraction unit 803 cancels DC components from the temperature estimation result EST and extracts only the high-frequency components. The high-frequency component extraction unit 803 outputs a high-frequency component HPF, which is a signal indicating the extracted high-frequency components, to the coefficient addition unit 804.

[0079] The coefficient addition unit 804 performs a coefficient addition process to correct the temperature detection result Td. The coefficient addition unit 804 receives the temperature detection result Td from the temperature sensor 79 and the high-frequency component HPF from the high-frequency component extraction unit 803. The coefficient addition unit 804 corrects the temperature detection result Td based on the high-frequency component HPF. Specifically, the coefficient addition unit 804 calculates a corrected temperature value WAE based on the temperature detection result Td and the high-frequency component HPF. The high-frequency component HPF is based on the temperature estimation result EST. Therefore, it can be said that the corrected temperature value WAE is based on the temperature estimation result EST and the temperature detection result Td. The coefficient addition unit 804 is an example of a calculation unit that calculates the corrected temperature value WAE. The coefficient addition unit 804 outputs the corrected temperature value WAE to the difference comparison unit 806.

[0080] The target temperature output unit 805 performs an output process of outputting a preset target temperature TGT to the difference comparison unit 806. The target temperature TGT is a target value for the surface temperature of the fixing belt 77. The target temperature TGT can be changed by rewriting it according to a command from the processor 22. The target temperature TGT may be stored in the memory 23 or the memory 25.

[0081] For example, the target temperature TGT is set for each printing process. In one example, the target temperature TGT varies depending on the quality of the printing medium P used in each printing process. For example, the quality is thickness. Generally, the target temperature TGT is determined so as to maintain a predetermined temperature when the printing medium P is plain paper. The amount of heat removed from the fixing belt 77 by the printing medium P as it passes through the fixing device 21 is greater for thick paper than for plain paper. The surface temperature of the fixing belt 77 is more likely to drop when printing on thick paper than when printing on plain paper. When the printing medium P is thick paper, the target temperature TGT is higher than the target temperature TGT associated with plain paper, taking into account the amount of heat removed from the fixing belt 77 by the thick paper. This makes it easier to maintain the surface temperature of the fixing belt 77 at a predetermined temperature. When the printing medium P is thinner than plain paper, the target temperature TGT is lower than the target temperature TGT associated with plain paper.

[0082] In another example, the target temperature TGT varies depending on the status of the printing process. The status of the printing process includes various statuses related to the printing process, such as, but not limited to, inrush current prevention, startup heating, ready, start printing, printing, and energy saving ready.

[0083] In the inrush current prevention status, the target temperature TGT is set to increase in stages to prevent a sudden large current from flowing. In the startup heating status, the target temperature TGT is set higher to quickly reach the reference temperature suitable for printing. In the ready status, the target temperature TGT is set slightly lower than the target temperature TGT in the startup heating status to save energy after print preparation is complete. In the print start status, the target temperature TGT is set higher than the target temperature TGT in the printing status from shortly before printing to prevent the temperature from dropping at the beginning of printing. In the printing status, the target temperature TGT is set to a reference temperature suitable for printing. In the energy saving ready status, if the ready state continues for a long time, the target temperature TGT is set lower than the target temperature TGT in the ready status.

[0084] The difference comparison unit 806 performs a difference calculation process. The difference comparison unit 806 compares the target temperature TGT from the target temperature output unit 805 with the corrected temperature value WAE from the coefficient addition unit 804. The difference comparison unit 806 calculates a difference DIF based on a comparison between the target temperature TGT and the corrected temperature value WAE. The difference DIF is an example of a comparison result by the difference comparison unit 806. The difference comparison unit 806 is an example of a temperature comparison unit. Here, the difference DIF is described as being the value obtained by subtracting the corrected temperature value WAE from the target temperature TGT, but the opposite may also be true. If the corrected temperature value WAE is lower than the target temperature TGT, the difference DIF is a positive value. If the corrected temperature value WAE is higher than the target temperature TGT, the difference DIF is a negative value. The difference DIF reflects the relationship between the target temperature TGT and the corrected temperature value WAE. The difference comparison unit 806 outputs the difference DIF to the frequency generation unit 807.

[0085] The frequency generation unit 807 performs a frequency generation process to generate a frequency FRQ. The frequency generation unit 807 generates the frequency FRQ based on the difference DIF. Generating the frequency FRQ includes determining the frequency FRQ. For example, when the corrected temperature value WAE is higher than the target temperature TGT, the frequency generation unit 807 increases the frequency FRQ more than when the corrected temperature value WAE is equal to the target temperature TGT. This is to reduce the induction power. When the corrected temperature value WAE is lower than the target temperature TGT, the frequency generation unit 807 decreases the frequency FRQ more than when the corrected temperature value WAE is equal to the target temperature TGT. This is to increase the induction power. The difference DIF is based on the target temperature TGT and the corrected temperature value WAE. Therefore, generating the frequency FRQ based on the difference DIF is an example of generating the frequency FRQ based on the temperature estimation result EST by the temperature estimation unit 801, the temperature detection result Td by the temperature sensor 79, and the target temperature TGT. The frequency generating unit 807 outputs the frequency FRQ to the converting unit 808 and the pulse generating unit 810 .

[0086] The conversion unit 808 performs a conversion process to convert the frequency FRQ into a power estimation result ESTPA. The power estimation result ESTPA indicates an estimated value of the currently generated IH power corresponding to the frequency FRQ when the voltage value ACV is assumed to be 100 V. The power estimation result ESTPA is an example of a power estimation result indicating an estimated value of the IH power corresponding to the frequency FRQ. Converting the frequency FRQ into the power estimation result ESTPA is an example of estimating the IH power based on the frequency FRQ. The conversion unit 808 is an example of a power estimating unit that estimates the IH power. The conversion unit 808 outputs the power estimation result ESTPA to the correction unit 809 based on the conversion from the frequency FRQ to the power estimation result ESTPA.

[0087] The correction unit 809 performs a correction process to correct the power estimation result ESTPA based on the voltage value ACV. Correcting the power estimation result ESTPA based on the voltage value ACV includes converting the power estimation result ESTPA to a power estimation result ESTPB based on the voltage value ACV. Correcting the power estimation result ESTPA based on the voltage value ACV is an example of estimating IH power based on the voltage value ACV. The correction unit 809 is an example of a power estimation unit that estimates IH power. The correction unit 809 outputs the power estimation result ESTPB to the temperature estimation unit 801.

[0088] The pulse generating unit 810 performs a pulse generation process to generate a pulse signal based on the frequency FRQ. The pulse signal includes a first pulse signal and a second pulse signal of a high frequency that alternately output a high level. The second pulse signal is a pulse train in which the high and low levels of the first pulse signal are inverted. The first pulse signal and the second pulse signal are pulse trains with a predetermined duty corresponding to the frequency FRQ. The first pulse signal and the second pulse signal are pulse trains that alternate between a high period and a low period according to the predetermined duty. For example, the predetermined duty is 50%. If the first pulse signal and the second pulse signal include a dead time, the predetermined duty may be a value smaller than 50%. The dead time includes a time during which both the first pulse signal and the second pulse signal are low between the time when the first pulse signal transitions from high to low and the time when the second pulse signal transitions from low to high. The dead time includes the time during which both the first pulse signal and the second pulse signal are Low between the time when the second pulse signal transitions from High to Low and the time when the first pulse signal transitions from Low to High. The pulse generating unit 810 outputs the first pulse signal to the insulating buffer 811. The pulse generating unit 810 outputs the second pulse signal to the insulating buffer 812. The pulse signals are an example of drive signals, as they are the source of drive pulse signals including the drive pulse signals PU and PD.

[0089] The insulating buffer 811 converts the first pulse signal into a gate voltage of the switch 821 of the inverter 82 to generate a drive pulse signal PU, and supplies the drive pulse signal PU to the gate of the switch 821 . The insulating buffer 812 converts the second pulse signal into a gate voltage of the switch 821 of the inverter 82, and supplies the resulting drive pulse signal PD to the gate of the switch. The drive pulse signal PD is a pulse train in which the High and Low levels of the drive pulse signal PU are inverted. The drive pulse signals PU and PD are pulse trains with a predetermined duty corresponding to the frequency FRQ. The drive pulse signals PU and PD are pulse trains that repeat a High period and a Low period according to the predetermined duty. Note that, since the inverter 82 is described here as a half-bridge inverter, two drive signals are supplied to the inverter 82, but this is not limited thereto. If the inverter 82 were a full-bridge inverter, four drive signals would be supplied to the inverter 82.

[0090] As described above, the temperature control circuit 14 adjusts the IH power based on the temperature detection result Td, the estimated history PREV, and the frequency FRQ. As a result, the temperature control circuit 14 controls the surface temperature of the fixing belt 77 by induction heating based on the magnetic field generated by the induction heating coil 76. This type of control is referred to here as weighted average control with estimated temperature (WAE control).

[0091] The temperature estimation unit 801, estimation history storage unit 802, high frequency component extraction unit 803, coefficient addition unit 804, target temperature output unit 805, difference comparison unit 806, frequency generation unit 807, conversion unit 808, correction unit 809 and pulse generation unit 810 of the temperature control circuit 14 are not limited to being realized by software, but may also be configured by hardware using electrical circuits.

[0092] The WAE control will be explained in detail below. Fig. 3 is a flowchart for explaining the output of frequency FRQ in WAE control. Fig. 4 and Fig. 5 are explanatory diagrams for explaining each signal in WAE control. The horizontal axis of Fig. 4 and Fig. 5 represents time. The vertical axis of Fig. 4 and Fig. 5 represents temperature.

[0093] The temperature control circuit 14 generates a trigger to start processing every dt (ACT1). In ACT1, for example, the temperature control circuit 14 starts counting by a timer based on an instruction to start WAE control from the system controller 13. The temperature control circuit 14 ends counting by a timer based on an instruction to end WAE control from the system controller 13. While the image forming apparatus 1 is operating, the temperature control circuit 14 generates a trigger at intervals of dt based on the counting by the timer.

[0094] The temperature control circuit 14 acquires the temperature detection result Td (ACT 2). In ACT 2, for example, the temperature control circuit 14 acquires the temperature detection result Td from the temperature sensor 79.

[0095] The temperature control circuit 14 acquires the voltage value ACV (ACT 3). In ACT 3, for example, the temperature control circuit 14 acquires the voltage value ACV from a voltage detection unit that detects the voltage value ACV.

[0096] The temperature control circuit 14 acquires the target temperature TGT (ACT 4). In ACT 4, for example, the temperature control circuit 14 acquires the target temperature TGT based on a signal from the system controller 13.

[0097] The temperature estimation unit 801 performs temperature estimation processing (ACT5). For example, the temperature estimation unit 801 acquires the power estimation result ESTPB at the current time from the correction unit 809. The temperature estimation unit 801 acquires the temperature estimation result EST dt before the current time as the estimation history PREV from the estimation history storage unit 802. The temperature estimation unit 801 estimates the surface temperature of the fixing belt 77 based on the estimation history PREV and the power estimation result ESTPB. The temperature estimation unit 801 outputs the temperature estimation result EST to the estimation history storage unit 802 and the high-frequency component extraction unit 803 based on the estimation of the surface temperature of the fixing belt 77.

[0098] 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. Heat sources are replaced by voltage sources. The temperature estimation unit 801 simulates a CR circuit in real time, with each element value preset. The temperature estimation unit 801 uses the power estimation result ESTPB based on the frequency FRQ. The power estimation result ESTPB corresponds to the voltage value applied to the CR circuit. In other words, since the IH power increases as the frequency FRQ decreases, the temperature estimation unit 801 simulates this by increasing the voltage applied to the CR circuit. On the other hand, since the IH power decreases as the frequency FRQ increases, the temperature estimation unit 801 simulates this by decreasing the voltage applied to the CR circuit. The temperature estimation unit 801 estimates the amount of heat applied to the fixing belt 77 based on the CR circuit and the power estimation result ESTPB. The temperature estimation unit 801 estimates the surface temperature of the fixing belt 77 based on the amount of heat given to the fixing belt 77 and the estimation history PREV. In this way, the temperature estimation unit 801 estimates the surface temperature of the fixing belt 77 based on the CR circuit and the power estimation result ESTPB.

[0099] As shown in FIG. 4, there is a discrepancy between the temperature detection result Td and the actual surface temperature of the fixing belt 77. The actual surface temperature of the fixing belt 77 changes in a short cycle because the driving frequency of the induction heating frequently changes. In contrast, the temperature sensor 79 may have poor response to temperature changes due to its own heat capacity and the characteristics of the temperature-sensitive material. This is particularly true for less expensive temperature sensors. As a result, the temperature detection result Td does not accurately track the actual surface temperature of the fixing belt 77. In other words, the temperature detection result Td is detected by the temperature sensor 79 with a delay relative to the actual surface temperature of the fixing belt 77. Furthermore, the temperature detection result Td is detected by the temperature sensor 79 in a smoothed state, without reproducing the small changes in the actual surface temperature of the fixing belt 77.

[0100] 4, the temperature estimation result EST appropriately tracks the change in the actual surface temperature of the fixing belt 77 caused by the frequency of the drive pulse signal (or the IH power based thereon) supplied to the inverter 82. However, because the temperature estimation result EST is a simulation result, there is a possibility that the absolute value will differ from the actual surface temperature of the fixing belt 77 due to differences in conditions, etc.

[0101] The high-frequency component extraction unit 803 performs high-pass filtering (ACT6). In ACT6, for example, the high-frequency component extraction unit 803 extracts high-frequency components from the temperature estimation result EST. As shown in FIG. 4, the high-frequency component HPF appropriately tracks changes in the actual surface temperature of the fixing belt 77. The high-frequency component extraction unit 803 outputs the high-frequency component HPF to the coefficient addition unit 804.

[0102] The coefficient addition unit 804 performs a coefficient addition process (ACT7). In ACT7, for example, the coefficient addition unit 804 acquires the temperature detection result Td acquired by the temperature control circuit 14 in ACT2. The coefficient addition unit 804 acquires the high frequency component HPF from the high frequency component extraction unit 803. The coefficient addition unit 804 calculates a corrected temperature value WAE based on the temperature detection result Td and the high frequency component HPF. In a typical example, the coefficient addition unit 804 multiplies the high frequency component HPF by a preset coefficient KA. The coefficient addition unit 804 adjusts the value of the high frequency component HPF to be added to the temperature detection result Td using the coefficient KA. The coefficient addition unit 804 adds the high frequency component HPF multiplied by the coefficient KA to the temperature detection result Td. The coefficient addition unit 804 calculates the corrected temperature value WAE based on the addition process.

[0103] For example, if the coefficient KA is 1, the coefficient adder 804 directly adds the high-frequency component HPF to the temperature detection result Td. Also, if the coefficient KA is 0.1, for example, the coefficient adder 804 adds one-tenth the value of the high-frequency component HPF to the temperature detection result Td. In this case, the effect of the high-frequency component HPF is almost eliminated, and the corrected temperature value WAE becomes closer to the temperature detection result Td. Also, if the coefficient KA is 1 or greater, for example, the corrected temperature value WAE can more strongly express the effect of the high-frequency component HPF. Experiments have shown that the coefficient KA set by the coefficient adder 804 should not be an extreme value, but should be close to 1.

[0104] 5 is an explanatory diagram illustrating an example of the actual surface temperature of the fixing belt 77, the temperature detection result Td, and the corrected temperature value WAE. In WAE control, the temperature control circuit 14 estimates minute temperature changes in the surface temperature of the fixing belt 77 based on the temperature detection result Td and the high-frequency component HPF of the temperature estimation result EST. Therefore, as shown in FIG. 5, the corrected temperature value WAE is a value that appropriately tracks the actual surface temperature of the fixing belt 77.

[0105] The difference comparison unit 806 performs a difference calculation process (ACT8). For example, in ACT8, the difference comparison unit 806 acquires the target temperature TGT from the target temperature output unit 805. The difference comparison unit 806 acquires the corrected temperature value WAE from the coefficient addition unit 804. The difference comparison unit 806 compares the target temperature TGT with the corrected temperature value WAE. Based on the comparison between the target temperature TGT and the corrected temperature value WAE, the difference comparison unit 806 calculates a difference DIF by subtracting the corrected temperature value WAE from the target temperature TGT. The difference comparison unit 806 outputs the difference DIF to the frequency generation unit 807.

[0106] The frequency generation unit 807 performs frequency generation processing (ACT 9). In ACT 9, for example, the frequency generation unit 807 acquires the difference DIF from the difference comparison unit 806. The frequency generation unit 807 generates the frequency FRQ based on the difference DIF. The frequency generation unit 807 may also generate the frequency FRQ based on the difference DIF and the voltage value ACV. An example of the frequency generation processing by the frequency generation unit 807 will be described later. The frequency generation unit 807 outputs the frequency FRQ to the conversion unit 808. The frequency generation unit 807 holds the frequency FRQ until the timing arrives to output the frequency FRQ to the pulse generation unit 810.

[0107] The conversion unit 808 performs a conversion process (ACT10). In ACT10, for example, the conversion unit 808 acquires a frequency FRQ from the frequency generation unit 807. The conversion unit 808 converts the frequency FRQ into a power estimation result ESTPA. An example of the conversion process by the conversion unit 808 will be described later. The conversion unit 808 outputs the power estimation result ESTPA to the correction unit 809.

[0108] The correction unit 809 performs a correction process (ACT11). In ACT11, for example, the correction unit 809 acquires the power estimation result ESTPA from the conversion unit 808. The correction unit 809 acquires the voltage value ACV acquired by the temperature control circuit 14 in ACT3. The correction unit 809 corrects the power estimation result ESTPA based on the voltage value ACV. The correction unit 809 acquires the power estimation result ESTPB based on the correction of the power estimation result ESTPA. An example of the correction process by the correction unit 809 will be described later. The correction unit 809 outputs the power estimation result ESTPB to the temperature estimation unit 801.

[0109] The temperature control circuit 14 determines whether dt has passed (ACT12). If dt has not passed (ACT12, NO), the temperature control circuit 14 waits until dt has passed. If dt has passed (ACT12, YES), the frequency generation unit 807 outputs the frequency FRQ to the pulse generation unit 810 (ACT13). In ACT12, for example, the frequency generation unit 807 outputs the frequency FRQ generated at intervals of dt to the pulse generation unit 810 at intervals of dt. Furthermore, the value of the frequency FRQ output by the frequency generation unit 807 is held by the frequency generation unit 807 until it is updated after the next interval of dt has passed.

[0110] The temperature control circuit 14 determines whether or not to execute the WAE control stop process (ACT14). In ACT14, for example, the temperature control circuit 14 stops the WAE control based on an instruction to stop the WAE control from the system controller 13. If the temperature control circuit 14 does not execute the WAE control stop process (ACT14, NO), the process transitions from ACT14 to ACT1. The temperature control circuit 14 repeats the process illustrated in FIG. 3 every dt while the image forming apparatus 1 is in operation. If the temperature control circuit 14 executes the WAE control stop process (ACT14, YES), the temperature control circuit 14 ends the process illustrated in FIG. 3.

[0111] FIG. 6 is a flowchart for explaining the output of the drive pulse signal in the WAE control. The pulse generating unit 810 acquires the frequency FRQ from the frequency generating unit 807 (ACT14). In ACT14, for example, the pulse generating unit 810 acquires the frequency FRQ from the frequency generating unit 807 at intervals of dt.

[0112] The pulse generating unit 810 generates a first pulse signal based on the frequency FRQ (ACT 15). In ACT 15, for example, the pulse generating unit 810 generates a first pulse signal with a duty of 50% corresponding to the frequency FRQ. If the frequency FRQ is 50 kHz, one period is 20 μs. Of the 20 μs period, the pulse generating unit 810 allocates 10 μs as High and 10 μs as Low.

[0113] The pulse generating section 810 generates a second pulse signal based on the frequency FRQ (ACT 16). In ACT 16, for example, the pulse generating section 810 generates the second pulse signal by inverting the High and Low of the first pulse signal.

[0114] The pulse generating unit 810 inserts a dead time into the pulse signal (ACT 17). In ACT 17, for example, the pulse generating unit 810 inserts a dead time into a first pulse signal with a duty of 50% to generate a first pulse signal with a duty of 48%. The pulse generating unit 810 inserts a dead time into a second pulse signal with a duty of 50% to generate a second pulse signal with a duty of 48%. The dead time is provided to prevent a short circuit when the switches 821 and 822 of the inverter 82 are turned on simultaneously. The pulse generating unit 810 outputs the first pulse signal to the insulating buffer 811. The pulse generating unit 810 outputs the second pulse signal to the insulating buffer 812.

[0115] The insulating buffer 811 outputs a drive pulse signal PU, and the insulating buffer 812 outputs a drive pulse signal PD (ACT18). For example, in ACT18, the insulating buffer 811 acquires a first pulse signal from the pulse generating unit 810. The insulating buffer 811 converts the first pulse signal into a gate voltage of the switch 821 of the inverter 82, thereby supplying the drive pulse signal PU to the gate of the switch 821. The insulating buffer 812 acquires a second pulse signal from the pulse generating unit 810. The insulating buffer 812 converts the second pulse signal into a gate voltage of the switch 821 of the inverter 82, thereby supplying the drive pulse signal PD to the gate of the switch.

[0116] The temperature control circuit 14 determines whether or not to execute the WAE control stop processing (ACT19). In ACT19, for example, the temperature control circuit 14 stops the WAE control based on an instruction to stop the WAE control from the system controller 13. If the temperature control circuit 14 does not execute the WAE control stop processing (ACT19, NO), the processing transitions from ACT19 to ACT14. The temperature control circuit 14 repeats the processing illustrated in FIG. 6 at intervals of dt while the image forming apparatus 1 is in operation. If the temperature control circuit 14 executes the WAE control stop processing (ACT19, YES), the temperature control circuit 14 ends the processing illustrated in FIG. 6.

[0117] An example of frequency generation processing by the frequency generation unit 807 will be described. FIG. 7 is a graph of a function for each voltage value ACV showing the relationship between the control amount and the frequency of the drive pulse signal of the inverter 82.

[0118] The horizontal axis represents the control amount of the IH power. The control amount is a power increase / decrease coefficient that indicates the degree of increase / decrease in the IH power. The control amount may be the value of the difference DIF itself, or a value correlated with the difference DIF. As the difference DIF increases, the control amount also increases. A control amount of 0 indicates that the corrected temperature value WAE is the same as the target temperature TGT, so the IH power can remain as it is. A positive control amount indicates that the corrected temperature value WAE is lower than the target temperature TGT, so the IH power needs to be increased. A negative control amount indicates that the corrected temperature value WAE is higher than the target temperature TGT, so the IH power needs to be decreased. The vertical axis represents the frequency of the drive pulse signal of the inverter 82, which corresponds to the frequency FRQ.

[0119] Because the inverter 82 utilizes the LC resonance phenomenon, the relationship between the frequency FRQ and the IH power is nonlinear. Therefore, as shown in FIG. 7, a function is prepared that indicates the relationship between the controlled variable and the frequency of the drive pulse signal of the inverter 82. The solid line indicates a graph of the function when the voltage value ACV is 100V (also referred to as the FRQ100 function). The dashed line indicates a graph of the function when the voltage value ACV is 110V (also referred to as the FRQ110 function). The dashed line indicates a graph of the function when the voltage value ACV is 90V (also referred to as the FRQ90 function). Although FIG. 7 shows three functions according to the voltage value ACV, four or more functions according to the voltage value ACV may be prepared.

[0120] Due to the characteristics of the inverter 82, the frequency FRQ in a situation where the control amount is positive and the IH power needs to be increased must be lower than the frequency FRQ when the control amount is 0. Due to the characteristics of the inverter 82, the frequency FRQ in a situation where the control amount is negative and the IH power needs to be decreased must be higher than the frequency FRQ when the control amount is 0.

[0121] As shown in the following example, the frequency generator 807 generates a frequency FRQ based on the difference DIF and the voltage value ACV. The frequency generator 807 selects a function associated with the voltage value ACV from among multiple functions based on the voltage value ACV. The frequency generator 807 determines a control amount based on the difference DIF. The frequency generator 807 determines a frequency FRQ corresponding to the control amount based on the selected function. For example, when the voltage value ACV is 90 V, the frequency generator 807 selects the FRQ90 function. The frequency generator 807 determines a frequency FRQ corresponding to the control amount based on the FRQ90 function. The frequency FRQ determined according to the control amount based on the FRQ90 function is lower than the frequency FRQ determined according to the same control amount based on the FRQ100 function. The decrease in IH power associated with the voltage value ACV being 90 V, which is lower than the frequency FRQ when the voltage value ACV is 100 V, is offset by an increase in IH power associated with lowering the frequency FRQ when the voltage value ACV is 90 V compared to the frequency FRQ when the voltage value ACV is 100 V.

[0122] The frequency generation unit 807 generates the frequency FRQ based on the voltage value ACV, thereby generating the frequency FRQ according to fluctuations in the voltage value ACV. This allows the frequency generation unit 807 to generate the frequency FRQ for appropriately controlling the IH power even if the voltage value ACV fluctuates.

[0123] It is preferable, but not limited to, that the frequency generation unit 807 generate the frequency FRQ based on the difference DIF and the voltage value ACV. The frequency generation unit 807 may generate the frequency FRQ based on the difference DIF without considering the voltage value ACV. In this example, the frequency generation unit 807 may use the FRQ100 function when the voltage value ACV is 100V.

[0124] The frequency generating unit 807 may refer to table data instead of a function to generate the frequency FRQ. The table data may be data that associates the controlled variable with the frequency of the drive pulse signal of the inverter 82. The table data may include data for each voltage value ACV that associates the controlled variable with the frequency of the drive pulse signal of the inverter 82. The table data may be stored in the memory 25.

[0125] An example of the conversion process performed by the conversion unit 808 will be described. FIG. 8 is a graph showing the relationship between the frequency of the drive pulse signal of the inverter 82 and the IH power as a function for each voltage value ACV. The horizontal axis represents the frequency of the drive pulse signal of the inverter 82, which corresponds to the frequency FRQ. The vertical axis represents the IH power.

[0126] The solid line shows a graph of the function when the voltage value ACV is 100V (also called the F2P100 function). The dashed line shows a graph of the function when the voltage value ACV is 110V (also called the F2P110 function). The dashed line shows a graph of the function when the voltage value ACV is 90V (also called the F2P90 function).

[0127] Since the inverter 82 utilizes the LC resonance phenomenon, the relationship between the frequency FRQ and the IH power is nonlinear: as the frequency FRQ decreases, the IH power increases, and as the frequency FRQ increases, the IH power decreases.

[0128] The conversion unit 808 converts the frequency FRQ into a power estimation result ESTPA, as shown in the following example: The conversion unit 808 acquires, as the power estimation result ESTPA, the IH power corresponding to the frequency FRQ based on the F2P100 function when the voltage value ACV is 100 V.

[0129] The conversion unit 808 may refer to table data instead of the function to convert the frequency FRQ into the power estimation result ESTPA. The table data is data that associates the frequency of the drive pulse signal of the inverter 82 with the IH power. The table data may be stored in the memory 25.

[0130] An example of the correction process performed by the correction unit 809 will be described. FIG. 9 is a graph of a function for each voltage value ACV showing the relationship between the IH power before correction and the IH power after correction.

[0131] The horizontal axis represents the IH power before correction. The IH power before correction corresponds to the power estimation result ESTPA. The vertical axis represents the IH power after correction. The IH power after correction corresponds to the power estimation result ESTPB.

[0132] The solid line shows a graph of the function (function with a slope of 1) when the voltage value ACV is 100V. The dashed line shows a graph of the function (function with a slope of 1.1) when the voltage value ACV is 110V. The dashed-dotted line shows a graph of the function (function with a slope of 0.9) when the voltage value ACV is 90V. While FIG. 9 shows three functions according to the voltage value ACV, four or more functions according to the voltage value ACV may be prepared.

[0133] The correction unit 809 corrects the power estimation result ESTPA based on the voltage value ACV, as exemplified below. Based on the voltage value ACV, the correction unit 809 selects a function associated with the voltage value ACV from among multiple functions. Based on the selected function, the correction unit 809 converts the pre-correction IH power corresponding to the power estimation result ESTPA into corrected IH power. The correction unit 809 acquires the corrected IH power obtained by converting the pre-correction IH power corresponding to the power estimation result ESTPA as the power estimation result ESTPB.

[0134] For example, assume that the IH power before correction corresponding to the power estimation result ESTPA is 1000 W. If the voltage value ACV is 90 V, the correction unit 809 converts 1000 W to 900 W based on a function associated with the voltage value ACV. The correction unit 809 acquires 900 W as the power estimation result ESTPB. The power estimation result ESTPB is less than the power estimation result ESTPA. On the other hand, if the voltage value ACV is 110 V, the correction unit 809 converts 1000 W to 1100 W based on a function associated with the voltage value ACV. The correction unit 809 acquires 1100 W as the power estimation result ESTPB. The power estimation result ESTPB is more than the power estimation result ESTPA.

[0135] Correction unit 809 corrects power estimation result ESTPA based on voltage value ACV, thereby estimating IH power according to fluctuations in voltage value ACV. This allows correction unit 809 to prevent power estimation result ESTPB from deviating from the IH power actually used for heat generation, even if voltage value ACV fluctuates. Because the accuracy of IH power estimation by correction unit 809 is improved, temperature estimation result EST by temperature estimator 801 is prevented from deviating from the actual surface temperature of fixing belt 77.

[0136] The coefficient KB by which the IH power before correction is multiplied is not limited to a fixed value corresponding to the voltage value ACV that represents a linear relationship as illustrated in Fig. 9. The coefficient KB may be expressed as an arbitrary function for each voltage value ACV.

[0137] The correction unit 809 may correct the power estimation result ESTPA by referring to table data instead of a function. The table data may be data that associates the IH power before correction obtained by actual measurement with the IH power after correction for each voltage value ACV. The table data may be stored in memory 25.

[0138] An example of the drive pulse signal will be described. FIG. 10 is a diagram illustrating an example of a drive pulse signal. In FIG. 10, the upper part shows the drive pulse signal PU, and the lower part shows the drive pulse signal PD. The horizontal axis represents time, and the vertical axis represents voltage. When the frequency FRQ is 50 kHz, one period of the drive pulse signals PU and PD is 20 μs. The drive pulse signals PU and PD are pulse signals with a duty of 48%, which is the original signal duty of 50% minus the dead time. The drive pulse signals PU and PD alternately output high.

[0139] In the above example, the conversion unit 808 and the correction unit 809 are shown as separate functions, but this is not limiting. The temperature control circuit 14 may include a power estimation unit that estimates the IH power based on the frequency FRQ and the voltage value ACV, instead of the conversion unit 808 and the correction unit 809. Estimating the IH power based on the frequency FRQ and the voltage value ACV includes converting the frequency FRQ into a power estimation result ESTPB that corresponds to the voltage value ACV.

[0140] In this example, multiple functions are prepared that indicate the relationship between the frequency of the drive pulse signal of the inverter 82 and the IH power, as illustrated in Fig. 8. Fig. 8 shows three functions according to the voltage value ACV, but four or more functions according to the voltage value ACV may also be prepared.

[0141] The power estimation unit estimates the induction power based on the frequency FRQ and the voltage value ACV, as shown in the following example. Based on the voltage value ACV, the power estimation unit selects a function associated with the voltage value ACV from among a plurality of functions. The power estimation unit converts the frequency FRQ into induction power based on the selected function. The power estimation unit acquires the induction power obtained by converting the frequency FRQ based on the selected function as the power estimation result ESTPB.

[0142] For example, when the voltage value ACV is 90V, the power estimation unit selects the F2P90 function. The power estimation unit obtains a power estimation result ESTPB corresponding to the frequency FRQ based on the F2P90 function. The power estimation result ESTPB obtained corresponding to the frequency FRQ based on the F2P90 function is lower than the power estimation result ESTPB obtained corresponding to the same frequency FRQ based on the F2P100 function. When the voltage value ACV is 110V, the power estimation unit selects the F2P110 function. The power estimation unit obtains a power estimation result ESTPB corresponding to the frequency FRQ based on the F2P110 function. The power estimation result ESTPB obtained corresponding to the frequency FRQ based on the F2P110 function is higher than the power estimation result ESTPB obtained corresponding to the same frequency FRQ based on the F2P100 function.

[0143] The power estimation unit may refer to table data instead of the function to estimate the IH power based on the frequency FRQ and the voltage value ACV. The table data may include data for each voltage value ACV that associates the frequency of the drive pulse signal of the inverter 82 with the IH power. The table data may be stored in memory 25.

[0144] In the above example, the temperature estimation unit 801 estimates the surface temperature of the fixing belt 77 based on the estimated history PREV and the power estimation result ESTPB, but the present invention is not limited to this. The temperature estimation unit 801 may estimate the surface temperature of the fixing belt 77 based on the estimated history PREV and the power estimation result ESTPA.

[0145] In the above example, the system controller 13 and the temperature control circuit 14 are shown separately, but this is not limiting. The system controller 13 may include some or all of the functions of the temperature control circuit 14. In this example, the processor 22 may implement some or all of the functions of the temperature control circuit 14 implemented by the processor 24. The memory 23 may store the programs stored in the memory 25, data used in the programs, etc.

[0146] As described above, the temperature control device according to the embodiment includes a temperature estimation unit that estimates the temperature of the temperature-controlled object based on the frequency of a drive signal of an inverter connected to an induction heating coil. The temperature control device also includes a frequency generation unit that generates a frequency of the drive signal based on the temperature estimation result by the temperature estimation unit, the temperature detection result of the temperature-controlled object by the temperature sensor, and the target temperature of the temperature-controlled object.

[0147] The temperature control device may further include a power estimation unit that estimates the power supplied to the induction heating coil based on the frequency of the drive signal. In this example, the temperature estimation unit estimates the temperature of the temperature-controlled object based on the power estimation result by the power estimation unit.

[0148] The temperature control device may include a high-frequency component extraction unit that extracts high-frequency components from the temperature estimation result. The temperature control device may include a calculation unit that calculates a corrected temperature value based on the temperature detection result and the high-frequency components. The temperature control device may include a temperature comparison unit that compares the target temperature with the corrected temperature value. In this example, the frequency generation unit generates a frequency of the drive signal based on the comparison result by the temperature comparison unit.

[0149] With this configuration, the temperature control device can track the surface temperature of the temperature-controlled object based on the temperature estimation result even if the temperature sensor has poor response to temperature detection of the temperature-controlled object. This allows the temperature control device to reduce the cost of the temperature sensor and prevent overshoot and temperature ripple.

[0150] The program may be transferred in a state where it is stored in the device according to the embodiment, or in a state where it is not stored in the device. In the latter case, the program may be transferred via a network or in a state where it is recorded on a recording medium. The recording medium is a non-transitory tangible medium. The recording medium is a computer-readable medium. The recording medium may be in any form, such as a CD-ROM or a memory card, as long as it is capable of storing the program and is computer-readable.

[0151] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel 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 embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0152] 1...image forming apparatus, 10...casing, 11...power conversion circuit, 12...communication interface, 13...system controller, 14...temperature 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...processor, 25...memory, 31...paper feed path, 32...paper output 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, 70...pressure roller, 71...pressure pad, 72...magnetic shunt alloy position adjustment mechanism, 73...aluminum member, 74...magnetic shunt alloy, 75...ferrite core, 76...induction heating coil, 77...fixing belt, 78...frame, 79...temperature sensor, 81...converter, 82...inverter, 83...resonance capacitor, 801...temperature estimation unit, 802...estimation history storage unit, 803...high frequency component extraction unit, 804...coefficient addition unit, 805...target temperature output unit, 806...difference comparison unit, 807...frequency generation unit, 808...conversion unit, 809...correction unit, 810...pulse generation unit, 811...insulation buffer, 812...insulation buffer, 821...switch, 822...switch.

Claims

1. a temperature estimation unit that estimates the temperature of a temperature-controlled object based on the frequency of a drive signal of an inverter connected to the induction heating coil; a frequency generating unit that generates a frequency of the drive signal based on a temperature estimation result by the temperature estimating unit, a temperature detection result of the temperature control object by a temperature sensor, and a target temperature of the temperature control object; A temperature control device comprising:

2. a power estimation unit that estimates the power supplied to the induction heating coil based on the frequency of the drive signal; the temperature estimation unit estimates the temperature of the temperature control target based on the power estimation result by the power estimation unit; The temperature control device according to claim 1 .

3. the power estimation unit estimates the power supplied to the induction heating coil based on a voltage value of an AC voltage; The temperature control device according to claim 2 .

4. The temperature control device according to claim 2 , wherein the temperature estimation unit estimates the temperature of the temperature-controlled object based on a CR circuit and the power estimation result.

5. a high frequency component extracting unit that extracts high frequency components from the temperature estimation result; a calculation unit that calculates a corrected temperature value based on the temperature detection result and the high-frequency component; a temperature comparison unit that compares the target temperature with the corrected temperature value; Furthermore, the frequency generating unit generates a frequency of the drive signal based on a comparison result by the temperature comparing unit. The temperature control device according to any one of claims 1 to 4.

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