Temperature control device and image forming device

Abstract

The present application provides a temperature control device and an image forming apparatus that can reduce costs and prevent overshoot and temperature fluctuations. The temperature control device, according to one embodiment, controls the temperature of a temperature-controlled object, which transfers heat from a heater, by supplying power to the heater. The device includes a temperature estimation unit and a control signal generation unit. The temperature estimation unit estimates the temperature of the temperature-controlled object based on power supplied to the heater. The control signal generation unit outputs a power pulse for controlling the power supplied to the heater based on the temperature estimation result and the temperature detection result of the temperature-controlled object by a temperature sensor.

Description

Technical Field

[0001] Embodiments of the present invention relate to a temperature control device and an image forming apparatus. Background Art

[0002] An image forming apparatus includes a fuser that applies heat and pressure to the print medium, thereby fixing the toner image to the print medium. The fuser includes a fixing rotating body (heat roller), a pressure member (pressure roller), a heating member (such as a lamp or IH heater), and a temperature sensor. The temperature sensor detects the surface temperature of the heat roller.

[0003] The controller for controlling the fixing device increases or decreases the amount of current supplied to the heater 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.

[0004] If there is a deviation (or time lag) between the temperature detected by the temperature sensor and the surface temperature of the heated roller, overshoot and temperature fluctuations may occur. Therefore, to prevent overshoot and temperature fluctuations, a highly responsive temperature sensor (such as a thermopile) is required. However, highly responsive temperature sensors have the problem of high cost. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a temperature control device and an image forming apparatus that can suppress costs and prevent overshoot and temperature fluctuation.

[0006] A temperature control device according to one embodiment controls the temperature of a temperature-controlled object by supplying power to a heater, whereby heat from the heater is transferred to the temperature-controlled object. The temperature control device includes a temperature estimator and a control signal generator. The temperature estimator estimates the temperature of the temperature-controlled object based on power supplied to the heater. The control signal generator outputs a power pulse for controlling the power supplied to the heater based on the temperature estimation result and the temperature detection result of the temperature controlled object by a temperature sensor.

[0007] An image forming device according to one embodiment includes a fuser and a temperature control unit, wherein the fuser has a fuser rotating body and a heater, the fuser rotating body heats a toner image formed on a medium to fix the toner image on the medium, the heater heats the fuser rotating body, the temperature control unit controls the temperature of the fuser rotating body by supplying power to the heater, and heat from the heater is transferred to the fuser rotating body, the temperature control unit includes: a temperature estimation unit that estimates the temperature of the fuser rotating body based on power supply to the heater; and a control signal generation unit that outputs a power pulse for controlling the power supplied to the heater based on the temperature estimation result and the temperature detection result of the fuser rotating body by a temperature sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a diagram for explaining a configuration example of an image forming apparatus according to an embodiment.

[0009] Figure 2 This is a diagram for explaining a configuration example of a heater energization control circuit according to one embodiment.

[0010] Figure 3 This is a diagram for explaining an operation example of the heater energization control circuit according to one embodiment.

[0011] Figure 4 This is a diagram for explaining an operation example of the heater energization control circuit according to one embodiment.

[0012] Figure 5 This is a diagram for explaining an operation example of a heater energization control circuit according to an embodiment.

[0013] Figure 6 This is a diagram for explaining an operation example of a heater energization control circuit according to an embodiment.

[0014] Description of Reference Numerals

[0015] 1… Image forming device, 11… Housing, 12… Communication interface, 13… System controller, 14… Heater energization control circuit, 15… Display unit, 16… Operation interface, 17… Paper tray, 18… Paper discharge tray, 19… Conveyor unit, 20… Image forming unit, 21… Fuser, 22… Processor, 23… Memory, 31… Paper feed path, 32… Paper discharge path, 33… Pickup roller, 41… Processing unit, 42… Exposure device, 43… Transfer mechanism, 51… …photosensitive drum, 52…charger, 53…developer, 61…primary transfer belt, 62…secondary transfer relative roller, 63…primary transfer roller, 64…secondary transfer roller, 71…heat roller, 72…pressure roller, 73…heater, 74…temperature sensor, 81…temperature estimation unit, 82…estimation history holding unit, 83…high-frequency component extraction unit, 84…coefficient addition unit, 85…target temperature output unit, 86…difference comparison unit, 87…control signal generation unit, 88…power supply circuit. DETAILED DESCRIPTION

[0016] Hereinafter, a temperature control device and an image forming apparatus according to an embodiment will be described with reference to the drawings.

[0017] Figure 1 It is an explanatory diagram for explaining a configuration example of the image forming apparatus 1 according to one embodiment.

[0018] The image forming apparatus 1 is, for example, a multifunction peripheral (MFP) that performs various processes such as image formation while conveying a recording medium such as a print medium. The image forming apparatus 1 is, for example, a solid-state scanning printer (e.g., an LED printer) that uses a scanning LED array to perform various processes such as image formation while conveying a recording medium such as a print medium.

[0019] For example, the image forming apparatus 1 receives toner from a toner cartridge and forms an image on a print medium using the received toner. The toner may be a monochromatic toner or a color toner such as cyan, magenta, yellow, or black. Furthermore, the toner may be a decolorizable toner that is decolorized upon heating.

[0020] like Figure 1 As shown, the image forming apparatus 1 includes a housing 11 , 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 discharge tray 18 , a conveying unit 19 , an image forming unit 20 , and a fixing unit 21 .

[0021] The housing 11 is the main body of the image forming apparatus 1 and 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 discharge tray 18 , a conveying unit 19 , an image forming unit 20 , and a fixing unit 21 .

[0022] First, the configuration of a control system of the image forming apparatus 1 will be described.

[0023] The communication interface 12 is an interface for communicating with other devices. For example, the communication interface 12 is used to communicate with a host device (external device). For example, the communication interface 12 may be configured as a LAN connector. Alternatively, the communication interface 12 may wirelessly communicate with other devices using standards such as Bluetooth (registered trademark) or Wi-Fi (registered trademark).

[0024] The system controller 13 controls the image forming apparatus 1. The system controller 13 includes, for example, a processor 22 and a memory 23.

[0025] The processor 22 is a computing element that performs arithmetic processing. The processor 22 is, for example, a CPU. The processor 22 performs various processes based on data such as programs stored in the memory 23. The processor 22 functions as a control unit capable of performing various operations by executing the programs stored in the memory 23.

[0026] The memory 23 is a storage medium that stores programs and data used by the programs. In addition, the memory 23 also functions as a working memory. That is, the memory 23 temporarily stores data being processed by the processor 22 and programs being executed by the processor 22.

[0027] The processor 22 performs various information processing 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.

[0028] A print job includes image data representing an image to be formed on a print medium P. The image data may be used to form an image on a single sheet of print medium P or may be used to form images on multiple sheets of print medium P. Furthermore, a print job includes information indicating whether to print in color or in monochrome. Furthermore, a print job may include information such as the number of copies (page sets) and the number of sheets (pages) to be printed per copy.

[0029] Based on the generated print job, the processor 22 generates print control information for controlling the operations of the conveyor 19, the image forming unit 20, and the fixing unit 21. The print control information includes information indicating the timing of paper feeding. The processor 22 supplies the print control information to the heater energization control circuit 14.

[0030] Furthermore, the processor 22 functions as a controller (engine controller) that controls the operations of the transport unit 19 and the image forming unit 20 by executing programs stored in the memory 23. Specifically, the processor 22 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.

[0031] It should be noted that the image forming apparatus 1 may also include an engine controller separately 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 information necessary for control by the engine controller to the engine controller.

[0032] The image forming apparatus 1 also includes a power conversion circuit (not shown) that uses the AC voltage of an AC power supply (AC) to supply a DC voltage to various components within the image forming apparatus 1. The power conversion circuit supplies the DC voltage required for the operation of the processor 22 and the memory 23 to the system controller 13. Furthermore, the power conversion circuit supplies the DC voltage required for image formation to the image forming unit 20. Furthermore, the power conversion circuit supplies the DC voltage required for transporting print media to the transport unit 19. Furthermore, the power conversion circuit supplies the DC voltage required for driving the heater of the fuser 21 to the heater energization control circuit 14.

[0033] The heater energization control circuit 14 is a temperature control device (temperature control unit) that controls the power supply to the heater of the fuser 21, which will be described later. The heater energization control circuit 14 generates power PC for energizing the heater of the fuser 21 and supplies the power PC to the heater of the fuser 21. The heater energization control circuit 14 will be described in detail later.

[0034] The display unit 15 includes a display that displays a screen based on a video signal input from the system controller 13 or a display control unit such as a graphic controller (not shown). For example, the display unit 15 displays screens for various settings of the image forming apparatus 1 .

[0035] The operation interface 16 is connected to an operating component (not shown). The operation interface 16 supplies operation signals corresponding to the operation of the operating component to the system controller 13. Examples of the operating component include a touch sensor, a keypad, a power button, a paper feed button, various function keys, or a keyboard. The touch sensor acquires information indicating a designated position within a certain area. The touch sensor is integrally formed as a touch panel with the display unit 15, and thus inputs a signal indicating the touched position displayed on the screen of the display unit 15 to the system controller 13.

[0036] The plurality of paper trays 17 are cassettes that respectively accommodate printing media P. The paper trays 17 are configured to be able to supply the printing media P from the outside of the housing 11 . For example, the paper trays 17 are configured to be able to be pulled out from the housing 11 .

[0037] The paper discharge tray 18 is a tray that supports the print medium P discharged from the image forming apparatus 1 .

[0038] Next, a configuration for conveying the printing medium P in the image forming apparatus 1 will be described.

[0039] The transport unit 19 is a mechanism for transporting the printing medium P within the image forming apparatus 1. Figure 1 As shown, 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.

[0040] The paper feed path 31 and paper discharge path 32 each include multiple motors, rollers, and guides (not shown). Under control of the system controller 13, the motors rotate shafts, which in turn rotate rollers in conjunction with the shafts. The rotation of the rollers moves the print medium P. The guides control the direction in which the print medium P is conveyed.

[0041] The paper feed conveying path 31 receives print media P from the paper tray 17 and supplies the received print media P to the image forming unit 20. The paper feed conveying path 31 includes pickup rollers 33 corresponding to each paper tray. Each pickup roller 33 receives the print media P from the paper tray 17 into the paper feed conveying path 31.

[0042] The paper discharge transport path 32 is a transport path for discharging the print medium P on which an image is formed from the housing 11 . The print medium P discharged from the paper discharge transport path 32 is supported by the paper discharge tray 18 .

[0043] Next, the image forming section 20 will be described.

[0044] The image forming unit 20 is a component that forms an image on the printing medium P. Specifically, the image forming unit 20 forms an image on the printing medium P based on a print job generated by the processor 22 .

[0045] The image forming unit 20 includes a plurality of process units 41, a plurality of exposure devices 42, and a transfer mechanism 43. The image forming unit 20 includes an exposure device 42 in each process unit 41. Note that the plurality of process units 41 and the plurality of exposure devices 42 have the same configuration, and therefore, each process unit 41 and each exposure device 42 will be described separately.

[0046] First, the processing unit 41 will be described.

[0047] The processing unit 41 is a component that forms a toner image. For example, multiple processing units 41 are provided for each type of toner. For example, multiple processing units 41 correspond to color toners such as cyan, magenta, yellow, and black. Specifically, each processing unit 41 is connected to a toner cartridge containing a different color of toner.

[0048] The toner cartridge includes a toner container and a toner delivery mechanism. The toner container is a container that stores toner. The toner delivery mechanism is a mechanism composed of a screw and the like that delivers the toner in the toner container.

[0049] The process unit 41 includes a photosensitive drum 51 , a charger 52 , and a developer 53 .

[0050] The photosensitive drum 51 is a photosensitive member including a cylindrical drum and a photosensitive layer formed on the outer peripheral surface of the drum. The photosensitive drum 51 is rotated at a constant speed by a driving mechanism (not shown).

[0051] The charger 52 uniformly charges the surface of the photosensitive drum 51. For example, the charger 52 uses a charging roller to apply a voltage (development bias) to the photosensitive drum 51, thereby giving the photosensitive drum 51 a uniform negative potential (contrast potential). The charging roller rotates as the photosensitive drum 51 rotates while applying a predetermined pressure to the photosensitive drum 51.

[0052] The developing device 53 is a device that causes toner to adhere to the photosensitive drum 51. The developing device 53 includes a developer container, a stirring mechanism, a developing roller, a doctor blade, an automatic toner control (ATC) sensor, and the like.

[0053] The developer container receives and holds the toner delivered from the toner cartridge. A carrier is pre-stored within the developer container. The toner delivered from the toner cartridge is stirred with the carrier by a stirring mechanism, forming a developer mixture of the toner and carrier. The carrier is housed within the developer container during the manufacturing of the developer unit 53.

[0054] The developing roller rotates within the developer container, causing the developer to adhere to its surface. A doctor blade is a component positioned at a predetermined distance from the surface of the developing roller. The doctor blade removes a portion of the developer adhering to the surface of the rotating developing roller. This forms a developer layer on the surface of the developing roller with a thickness corresponding to the distance between the doctor blade and the surface of the developing roller.

[0055] The ATC sensor is, for example, a magnetic flux sensor having a coil that detects the voltage generated in the coil. The detection voltage of the ATC sensor varies depending on the density of the magnetic flux from the toner in the developer container. Specifically, the system controller 13 determines the concentration ratio of the toner remaining in the developer container relative to the carrier (toner concentration ratio) based on the detection voltage of the ATC sensor. Based on the toner concentration ratio, the system controller 13 activates a motor (not shown) that drives the toner cartridge's delivery mechanism, thereby delivering toner from the toner cartridge to the developer container of the developer 53.

[0056] Next, the exposure device 42 will be described.

[0057] The exposure device 42 includes multiple light-emitting elements. The exposure device 42 forms a latent image on the charged photosensitive drum 51 by irradiating light from the light-emitting elements. Examples of the light-emitting elements include light-emitting diodes (LEDs). Each light-emitting element irradiates light at a single point on the photosensitive drum 51. The multiple light-emitting elements are arranged in a direction parallel to the rotation axis of the photosensitive drum 51, i.e., in the main scanning direction.

[0058] The exposure device 42 irradiates light onto the photosensitive drum 51 using a plurality of light emitting elements arranged in the main scanning direction, thereby forming a latent image corresponding to one line on the photosensitive drum 51. The exposure device 42 continuously irradiates light onto the rotating photosensitive drum 51, thereby forming a plurality of lines of latent images.

[0059] In the above configuration, when light is irradiated from the exposure device 42 onto the surface of the photosensitive drum 51, which has been charged by the charger 52, an electrostatic latent image is formed. When the developer layer 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.

[0060] Next, the transfer mechanism 43 will be described.

[0061] The transfer mechanism 43 is a structure that transfers the toner image formed on the surface of the photoconductive drum 51 to the printing medium P.

[0062] The transfer mechanism 43 includes, for example, a primary transfer belt 61 , a secondary transfer counter roller 62 , a plurality of primary transfer rollers 63 , and a secondary transfer roller 64 .

[0063] The primary transfer belt 61 is an endless belt that is wound around a secondary transfer counter roller 62 and a plurality of winding rollers. The inner surface (inner circumference) of the primary transfer belt 61 contacts the secondary transfer counter roller 62 and the plurality of winding rollers, while the outer surface (outer circumference) faces the photosensitive drum 51 of the process unit 41.

[0064] The secondary transfer counter roller 62 is rotated by a motor (not shown). The rotation of the secondary transfer counter roller 62 transports the primary transfer belt 61 in a predetermined transport direction. The plurality of winding rollers are configured to be freely rotatable. The plurality of winding rollers rotate as the primary transfer belt 61 is moved by the secondary transfer counter roller 62.

[0065] The plurality of 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 primary transfer rollers 63 are arranged to correspond to the photosensitive drums 51 of the process units 41. Specifically, the primary transfer rollers 63 are positioned so as to face the photosensitive drums 51 of the corresponding process units 41, with the primary transfer belt 61 interposed therebetween. The primary transfer rollers 63 contact the inner circumference of the primary transfer belt 61, displacing the primary transfer belt 61 toward the photosensitive drums 51. This causes the primary transfer rollers 63 to bring the outer circumference of the primary transfer belt 61 into contact with the photosensitive drums 51.

[0066] The secondary transfer roller 64 is positioned opposite the primary transfer belt 61. The secondary transfer roller 64 contacts the outer circumference of the primary transfer belt 61 and applies pressure. This creates a transfer nip where the secondary transfer roller 64 and the outer circumference of the primary transfer belt 61 are in close contact. When the print medium P passes through the transfer nip, the secondary transfer roller 64 presses the print medium P against the outer circumference of the primary transfer belt 61.

[0067] The secondary transfer roller 64 and the secondary transfer counter roller 62 rotate to sandwich the print medium P fed from the paper feed path 31 and convey the print medium P. As a result, the print medium P passes through the transfer nip.

[0068] In the above configuration, when the outer peripheral surface of the primary transfer belt 61 contacts the photosensitive drum 51, the toner image formed on the surface of the photosensitive drum is transferred to the outer peripheral surface of the primary transfer belt 61. If the image forming unit 20 includes multiple process units 41, the primary transfer belt 61 receives the toner image from the photosensitive drums 51 of the multiple process units 41. The toner image transferred to the outer peripheral surface of the primary transfer belt 61 is conveyed by the primary transfer belt 61 to the transfer nip where the secondary transfer roller 64 is in close contact with the outer peripheral surface of the primary transfer belt 61. If a print medium P is present in the transfer nip, the toner image transferred to the outer peripheral surface of the primary transfer belt 61 is transferred to the print medium P at the transfer nip.

[0069] Next, the fixing structure of the image forming apparatus 1 will be described.

[0070] The fuser 21 fixes the toner image onto the print medium P to which the toner image has been transferred. The fuser 21 operates under the control of the system controller 13 and the heater energization control circuit 14. The fuser 21 includes a fixing rotating body, a pressure member, and a heating member. The fixing rotating body is, for example, a heat roller 71. The pressure member is, for example, a pressure roller 72. The heating member is, for example, a heater 73 that heats the heat roller 71. Furthermore, the fuser 21 includes a temperature sensor (thermistor) 74 that detects the surface temperature of the heat roller 71.

[0071] The heat roller 71 is a fixing rotating body rotated by a motor (not shown). It comprises a hollow metal core and an elastic layer formed on the outer circumference of the core. Heat roller 71 is heated by a heater 73 located inside the hollow core. Heat generated inside the core is transferred to the outer surface of the heat roller 71 (i.e., the surface of the elastic layer).

[0072] The pressure roller 72 is positioned opposite the heat roller 71. The pressure roller 72 includes a metal core with a predetermined outer diameter and an elastic layer formed on the outer circumference of the core. The pressure roller 72 applies pressure to the heat roller 71 using stress from a tension member (not shown). This pressure from the pressure roller 72 to the heat roller 71 creates a gap (fusing nip) between the pressure roller 72 and the heat roller 71. The pressure roller 72 is rotated by a motor (not shown). The rotation of the pressure roller 72 causes the print medium P entering the fusing nip to move and press the print medium P against the heat roller 71.

[0073] The heater 73 generates heat using the power PC supplied from the heater power control circuit 14. The heater 73 is, for example, a halogen heater. The heater 73 energizes the halogen lamp heater, which serves as a heat source, using the power PC supplied from the heater power control circuit 14. The electromagnetic waves radiated from the halogen lamp heater heat the inner side of the core of the heat roller 71. Alternatively, the heater 73 may be, for example, an IH heater.

[0074] The temperature sensor 74 detects the temperature of the air near the surface of the heat roller 71. Multiple temperature sensors 74 may be provided. For example, multiple temperature sensors 74 may be arranged parallel to the rotation axis of the heat roller 71. It is important to note that the temperature sensor 74 only needs to be located at a position where it can detect temperature changes on the heat roller 71. The temperature sensor 74 supplies a temperature detection signal Td indicating the detection result to the heater energization control circuit 14.

[0075] With the above configuration, the heat roller 71 and the pressure roller 72 apply heat and pressure to the print medium P passing through the fixing nip. The heat from the heat roller 71 melts the toner on the print medium P, and the pressure from the heat roller 71 and the pressure roller 72 spreads the toner onto the surface of the print medium P. This fixes the toner image to the print medium P that has passed through the fixing nip. The print medium P that has passed through the fixing nip is guided into the paper discharge path 32 and discharged outside the housing 11.

[0076] Next, the heater energization control circuit 14 will be described.

[0077] The heater energization control circuit 14 controls energization of the heater 73 of the fixing device 21 . The heater energization control circuit 14 generates energization power PC for energizing the heater 73 of the fixing device 21 and supplies the energization power PC to the heater 73 of the fixing device 21 .

[0078] like Figure 2 As shown, the heater energization control circuit 14 includes a temperature estimation unit 81, an estimation history storage unit 82, a high-frequency component extraction unit 83, a coefficient addition unit 84, a target temperature output unit 85, a difference comparison unit 86, a control signal generation unit 87, and a power supply circuit 88. Furthermore, the temperature detection result Td is input from the temperature sensor 74 to the heater energization control circuit 14.

[0079] The temperature estimation unit 81 performs a temperature estimation process to estimate the surface temperature of the heat roller 71. The temperature estimation unit 81 receives the temperature detection result Td from the temperature sensor 74, the estimated history PREV from the estimation history storage unit 82 (described later), and the power pulse Ps from the control signal generation unit 87 (described later). The temperature estimation unit 81 generates a temperature estimation result EST based on the temperature detection result Td, the estimated history PREV, and the power pulse Ps. Alternatively, the temperature estimation unit 81 may generate a temperature estimation result EST based on the temperature detection result Td, the estimated history PREV, the power pulse Ps, and the voltage (rated voltage) supplied to the heater 73 when the power pulse Ps is on. The temperature estimation unit 81 outputs the temperature estimation result EST to the estimated history storage unit 82 and the high-frequency component extraction unit 83.

[0080] The estimation history holding section 82 holds the history of the temperature estimation results EST. The estimation history holding section 82 outputs an estimation history PREV, which is the history of the temperature estimation results EST (the past temperature estimation results EST), to the temperature estimation section 81.

[0081] The high-frequency component extraction unit 83 performs high-pass filtering to extract the high-frequency component of the temperature estimation result EST and outputs the high-frequency component HPF, which is a signal representing the extracted high-frequency component, to the coefficient addition unit 84 .

[0082] The coefficient addition unit 84 performs a correction process, namely, coefficient addition, to correct the temperature detection result Td. The temperature detection result Td from the temperature sensor 74 and the high-frequency component HPF from the high-frequency component extraction unit 83 are input to the coefficient addition unit 84. The coefficient addition unit 84 corrects the temperature detection result Td based on the high-frequency component HPF. Specifically, the coefficient addition unit 84 multiplies the high-frequency component HPF by a predetermined coefficient and adds the result to the temperature detection result Td to calculate a corrected temperature value WAE. The coefficient addition unit 84 outputs the corrected temperature value WAE to the difference comparison unit 86.

[0083] The target temperature output unit 85 outputs the preset target temperature TGT to the difference comparison unit 86 .

[0084] The difference comparison unit 86 performs a difference calculation process. The difference comparison unit 86 calculates the difference DIF between the target temperature TGT from the target temperature output unit 85 and the corrected temperature value WAE from the coefficient addition unit 84 , and outputs the calculated difference DIF to the control signal generation unit 87 .

[0085] Based on the difference DIF, the control signal generating unit 87 generates a energizing pulse Ps as a pulse signal for controlling energization of the heater 73. The control signal generating unit 87 outputs the energizing pulse Ps to the power supply circuit 88 and the temperature estimating unit 81.

[0086] The power circuit 88 supplies power PC to the heater 73 based on the energizing pulse Ps. The power circuit 88 uses a DC voltage supplied from a power conversion circuit (not shown) to energize the heater 73 of the fuser unit 21. For example, based on the energizing pulse Ps, the power circuit 88 switches between supplying and not supplying the DC voltage from the power conversion circuit to the heater 73, thereby supplying power PC to the heater 73. Specifically, the power circuit 88 changes the duration of power supply to the heater 73 of the fuser unit 21 according to the energizing pulse Ps.

[0087] Note that the power supply circuit 88 may be integrally formed with the fixing device 21. That is, the heater energization control circuit 14 may supply energization pulses Ps to the heater 73 of the fixing device 21 instead of supplying energization power PC to the heater 73.

[0088] As described above, the heater energization control circuit 14 adjusts the amount of power supplied to the heater 73 of the fuser 21 based on the temperature detection result Td, the estimated temperature history PREV, and the energization pulse Ps. Thus, the heater energization control circuit 14 controls the surface temperature of the heat roller 71 heated by the heater 73. This type of control is referred to as weighted average control with estimated temperature (WAE control). It should be noted that the temperature estimation unit 81, estimated history storage unit 82, high-frequency component extraction unit 83, coefficient addition unit 84, target temperature output unit 85, difference comparison unit 86, and control signal generation unit 87 of the heater energization control circuit 14 can each be configured as an electrical circuit or as software.

[0089] Hereinafter, WAE control will be described in detail.

[0090] Figure 3 This is a flowchart for explaining WAE control. Figure 4 as well as Figure 5 This is an explanatory diagram for explaining various signals and the like in WAE control. Figure 4 as well as Figure 5 The horizontal axis represents time. Figure 4 as well as Figure 5 The vertical axis represents temperature.

[0091] The heater energization control circuit 14 sets various initial values ​​(ACT 11 ). For example, based on a signal from the system controller 13 , the heater energization control circuit 14 sets the coefficients in the coefficient adding section 84 and the target temperature TGT of the target temperature output section 85 .

[0092] The temperature estimation unit 81 of the heater energization control circuit 14 acquires the temperature detection result Td from the temperature sensor 74 , the estimation history PREV from the estimation history holding unit 82 , and the energization pulse Ps from the control signal generating unit 87 ( ACT 12 ).

[0093] like Figure 4As shown, there is a discrepancy between the temperature detection result Td and the actual surface temperature of the heat roller 71. The surface temperature of the heat roller 71 fluctuates in a subtle cycle due to intermittent heating by the heater 73. In contrast, the temperature sensor 74 may have poor responsiveness to temperature changes due to its own heat capacity and the characteristics of its temperature-sensing material. In particular, the cheaper the temperature sensor, the worse its responsiveness tends to be. As a result, the temperature detection result Td does not accurately track the actual surface temperature of the heat roller 71. In other words, the temperature detection result Td is detected by the temperature sensor 74 with a delay relative to the surface temperature of the heat roller 71. Furthermore, the temperature detection result Td does not reproduce the subtle fluctuations in the surface temperature of the heat roller 71 and is detected by the temperature sensor 74 in a smoothed state.

[0094] The temperature estimation unit 81 performs temperature estimation processing (ACT 13 ). Specifically, the temperature estimation unit 81 generates a temperature estimation result EST based on the temperature detection result Td, the estimation history PREV, and the energization pulse Ps. The temperature estimation unit 81 outputs the temperature estimation result EST to the high-frequency component extraction unit 83 and the estimation history storage unit 82 .

[0095] Heat transfer can be equivalently represented by the CR time constant of an electrical circuit. The heat capacity is replaced by a capacitor C. The resistance to heat transfer is replaced by a resistor R. The heat source is replaced by a DC voltage source. The temperature estimation unit 81 estimates the amount of heat supplied to the heat roller 71 based on the amount of current supplied to the heater 73, the heat capacity of the heat roller 71, and other factors, using a CR circuit with pre-set values ​​for each component. Based on the amount of heat supplied to the heat roller 71, the temperature detection result Td, and the estimated history PREV, the temperature estimation unit 81 estimates the surface temperature of the heat roller 71 and outputs a temperature estimation result EST.

[0096] The temperature estimation unit 81 repeatedly turns on and off the DC voltage source based on the energizing pulse Ps, and operates the CR circuit according to the input voltage pulse to generate an output voltage, thereby estimating the heat transferred to the surface of the heat roller 71 to be controlled.

[0097] It should be noted that the heat from the heat roller 71 flows out to the external environment through the space within the fuser 21 (outside the heat roller 71). Therefore, the temperature estimation unit 81 further includes a CR circuit for estimating the heat outflow from the heat roller 71 to the external environment. Alternatively, the temperature estimation unit 81 may further include a CR circuit for estimating the amount of heat flowing from the heat roller 71 to the space within the fuser 21.

[0098] like Figure 4 As shown, the temperature estimation result EST appropriately follows the actual change in the surface temperature of the heat roller 71. However, the temperature estimation result EST is a simulation result, and therefore the absolute value may differ from the actual surface temperature of the heat roller due to different conditions.

[0099] The high-frequency component extraction unit 83 performs high-pass filtering processing to extract the high-frequency components of the temperature estimation result EST (ACT 14). Figure 4 As shown, the high-frequency component HPF appropriately follows the actual change in the surface temperature of the heat roller 71 , and is a signal representing the high-frequency component of the temperature estimation result EST.

[0100] The coefficient addition unit 84 performs a coefficient addition process (ACT 15) to correct the temperature detection result Td. The coefficient addition unit 84 multiplies the high-frequency component HPF by a predetermined coefficient and adds the multiplied high-frequency component HPF to the temperature detection result Td to calculate the corrected temperature value WAE. In other words, the coefficient addition unit 84 adjusts the value of the high-frequency component HPF added to the temperature detection result Td by the coefficient to calculate the corrected temperature value WAE.

[0101] For example, if the coefficient is 1, coefficient addition unit 84 directly adds the high-frequency component HPF to the temperature detection result Td. Alternatively, if the coefficient is 0.1, for example, coefficient addition unit 84 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 temperature detection result Td approaches that of the high-frequency component HPF. Furthermore, if the coefficient is 1 or greater, for example, the effect of the high-frequency component HPF is more pronounced. The coefficient set in coefficient addition unit 84 is not an extreme value; experimental results indicate that a value near 1 is appropriate.

[0102] Figure 5 This is an explanatory diagram for explaining an example of the actual surface temperature of the heat roller 71, the temperature detection result Td, and the correction temperature value WAE. In the WAE control, the fine temperature change of the surface temperature of the heat roller 71 is estimated based on the temperature detection result Td and the high frequency component HPF of the temperature estimation result EST. Figure 5 As shown, the correction temperature value WAE becomes a value that appropriately follows the surface temperature of the heat roller 71 .

[0103] The difference comparison unit 86 calculates the difference DIF between the target temperature TGT from the target temperature output unit 85 and the corrected temperature value WAE from the coefficient addition unit 84 , and outputs the calculated difference DIF to the control signal generation unit 87 ( ACT 16 ).

[0104] The control signal generating unit 87 generates a energizing pulse Ps based on the difference DIF. The control signal generating unit 87 outputs the energizing pulse Ps to the power supply circuit 88 and the temperature estimation unit 81 (ACT 17). The power supply circuit 88 supplies energizing power PC to the heater 73 based on the energizing pulse Ps.

[0105] The difference DIF reflects the relationship between the target temperature TGT and the corrected temperature value WAE. For example, if the corrected temperature value WAE exceeds the target temperature TGT, the amount of current supplied to the heater 73 is reduced by narrowing the width of the energizing pulse Ps or reducing its frequency, thereby lowering the heat roller surface temperature. Alternatively, if the corrected temperature value WAE is less than the target temperature TGT, the amount of current supplied to the heater 73 is increased by increasing the width of the energizing pulse Ps or increasing its frequency, thereby raising the heat roller surface temperature.

[0106] It should be noted that the difference DIF not only allows one to determine the relative position of the corrected temperature value WAE and the target temperature TGT, but also the extent of the deviation. For example, if the difference DIF (the absolute value) is large, the deviation between the corrected temperature value WAE and the target temperature TGT is large, thus allowing the aforementioned control to be significantly altered. Alternatively, if the difference DIF (the absolute value) is small, the deviation between the corrected temperature value WAE and the target temperature TGT is small, thus allowing the aforementioned control to be performed more smoothly.

[0107] The processor 22 of the system controller 13 determines whether to end the WAE control (ACT 18). If the processor 22 determines to continue the WAE control, the process jumps to ACT 12. Otherwise, if the processor 22 determines to end the WAE control, the process ends. Figure 3 processing.

[0108] As described above, when the heater energization control circuit 14 performs WAE control during a certain cycle (the cycle in question), it does so based on the values ​​from the previous cycle (the energization pulse Ps and the temperature estimation result EST: the estimation history PREV) and the temperature detection result Ts from the current cycle. In other words, the heater energization control circuit 14 inherits the values ​​from the next cycle. The heater energization control circuit 14 performs temperature estimation calculations again based on the history of the previous calculation. Therefore, the heater energization control circuit 14 constantly performs calculations during operation. The calculation results are stored in memory, etc., and are reused in calculations in the next cycle.

[0109] Figure 6 It is an explanatory diagram for explaining a cycle of processing in the heater energization control circuit 14 . Figure 6 The horizontal axis represents time. For example, the temperature estimation unit 81 performs temperature estimation at time t(n), performs the next temperature estimation at t(n+1), which is dt earlier than that, and performs the next temperature estimation at t(n+2), which is dt earlier. In this way, the temperature estimation unit 81 repeatedly performs temperature estimation. In each cycle of temperature estimation, the temperature estimation unit 81 uses the previous temperature estimation result EST for the new temperature estimation.

[0110] At time t(n), the temperature detection result Td at time t(n), the energizing pulse Ps at the previous time t(n-1), and the temperature estimation result EST (estimated history PREV) at the previous time t(n-1) are input to the temperature estimation unit 81. The temperature estimation unit 81 processes the input signals and outputs the temperature estimation result EST at time t(n). The high-frequency component extraction unit 83, coefficient addition unit 84, difference comparison unit 86, and control signal generation unit 87 process the input signals and output the energizing pulse Ps at time t(n).

[0111] At time t(n+1), the temperature detection result Td newly detected at time t(n+1), the energization pulse Ps at time t(n), and the estimated history PREV, which is the temperature estimation result EST at time t(n), are input to the temperature estimation unit 81. The temperature estimation unit 81 processes the input signals and outputs the temperature estimation result EST at time t(n+1). The high-frequency component extraction unit 83, coefficient addition unit 84, difference comparison unit 86, and control signal generation unit 87 process the input signals and output the energization pulse Ps at time t(n+1).

[0112] At time t(n+2), the temperature detection result Td newly detected at time t(n+2), the energization pulse Ps at time t(n+1), and the estimated history PREV, which is the temperature estimation result EST at time t(n+1), are input to the temperature estimation unit 81. The temperature estimation unit 81 processes the input signals and outputs the temperature estimation result EST at time t(n+2). The high-frequency component extraction unit 83, coefficient addition unit 84, difference comparison unit 86, and control signal generation unit 87 process the input signals and output the energization pulse Ps at time t(n+2).

[0113] It should be noted that the time interval dt may be a fixed value or may be set during the initial value setting of ACT 11. For example, the time interval dt may be set to 100 [msec].

[0114] As described above, the image forming apparatus 1 includes: a fuser 21 having a heat roller 71 that heats and fixes a toner image formed on a medium to the medium, and a heater 73 that heats the heat roller 71; and a temperature control device (heater energization control circuit 14). The heater energization control circuit 14 controls the temperature of the heat roller 71, to which heat is transferred from the heater 73, by supplying power to the heater 73. The heater energization control circuit 14 includes a temperature estimation unit 81 that estimates the temperature of the heat roller 71 based on the power supplied to the heater 73. Furthermore, the heater energization control circuit 14 includes a control signal generation unit that outputs an energization pulse for controlling the power supplied to the heater 73 based on the temperature estimation result and the temperature detection result of the heat roller 71 by the temperature sensor 74.

[0115] With this configuration, the temperature control device can track the surface temperature of the heat roller 71 based on the temperature estimation result, even when the temperature sensor 74 has poor responsiveness to the temperature detection of the heat roller 71. This reduces the cost of the temperature sensor 74 and prevents overshoot and temperature fluctuations.

[0116] The control signal generating unit 87 also performs a weighted average of the temperature estimation result and the temperature detection result of the heat roller 71 by the temperature sensor 74 , and outputs an energizing pulse for controlling the power supplied to the heater 73 based on the weighted average result.

[0117] The image forming apparatus 1 further includes a high-frequency component extraction unit 83 that extracts high-frequency components from the temperature estimation result. The control signal generation unit 87 outputs an energizing pulse based on the temperature detection result and the high-frequency components. This allows the absolute value of the surface temperature of the heat roller 71 to be accurately estimated based on the temperature detection result, while also estimating subtle temperature variations in the surface temperature of the heat roller 71 based on the high-frequency components of the temperature estimation result. This allows the heater 73 to be energized based on the accurate estimation of the surface temperature of the heat roller 71. As a result, overshoot and temperature fluctuations can be prevented.

[0118] It should be noted that the functions described in the above embodiments are not limited to hardware configurations, but can also be implemented by using software to enable a computer to read a program describing each function. In addition, each function can also be configured by appropriately selecting either software or hardware.

[0119] While several embodiments have been described, these embodiments are provided for illustrative purposes only and are not intended to limit the scope of the invention. These new embodiments may be implemented in various other ways and may be omitted, replaced, or modified without departing from the spirit of the invention. These embodiments and their variations are intended to be included within the scope and spirit of the invention and are also intended to be included within the invention set forth in the claims and their equivalents.

Claims

1. A temperature control device that controls the temperature of a temperature-controlled object by supplying power to a heater of a fuser, wherein heat from the heater is transferred to the temperature-controlled object, the temperature control device comprising: a temperature estimating unit that estimates the temperature of the temperature-controlled object based on the energization of the heater and generates a temperature estimation result; a high-frequency component extraction unit for extracting a high-frequency component of the temperature estimation result; and The control signal generating unit outputs an energizing pulse for controlling the power supplied to the heater based on a temperature detection result of the temperature control target by a temperature sensor and the high-frequency component.

2. The temperature control device according to claim 1, wherein The temperature estimation unit 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 by a capacitor and the resistance to heat transfer is replaced by a resistor, and the energization pulse.

3. The temperature control device according to claim 1 or 2, wherein: The temperature estimation unit outputs the temperature estimation result based on the history of the temperature estimation result, the energization of the heater, and the temperature detection result.

4. An image forming apparatus comprising a fixing device and a temperature control unit, The fixing device includes a fixing rotating body and a heater. The fixing rotating body heats a toner image formed on a medium to fix the toner image on the medium. The heater heats the fixing rotating body. The temperature control unit controls the temperature of the fixing rotating body by supplying power to the heater, and the heat from the heater is transferred to the fixing rotating body. The temperature control unit includes: a temperature estimation unit that estimates the temperature of the fixing rotating body based on the energization of the heater and generates a temperature estimation result; a high-frequency component extraction unit for extracting a high-frequency component of the temperature estimation result; and The control signal generating section outputs an energizing pulse for controlling the power supplied to the heater based on a temperature detection result of the fixing rotating body by a temperature sensor and the high-frequency component.

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