Temperature control device and image forming device

Abstract

To suppress abnormal rise in a fuser temperature when a temperature detection element fails.SOLUTION: A temperature correction unit of a temperature control device according to one embodiment which controls the temperature of a temperature control object to which heat propagates from a heater by supplying power to the heater calculates a temperature correction value on the basis of a temperature estimation result of a temperature estimation unit that estimates the temperature of the temperature control object on the basis of the electric conduction to the heater and a temperature detection result of the temperature control object by a temperature sensor. A temperature bias correction unit corrects the temperature estimation result using a preset bias value. A failure determination unit determines a failure for the temperature sensor or a transmission path of the temperature detection result on the basis of a difference between the temperature estimation result and the temperature detection result. A selection unit selects either the output of the temperature correction unit or the output of the temperature bias correction unit on the basis of the failure determination result. A signal generation unit outputs an electric conduction pulse in order to control the power supplied to the heater on the basis of the selected output.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] The image forming apparatus includes a fixing unit that applies heat and pressure to the print medium to fix a toner image to the print medium. The fixing unit includes a fixing rotor (heat roller), a pressure member (press roller), a heating member (lamp or induction heating heater, etc.), and a temperature sensor. The temperature sensor detects the temperature of the surface of the heat roller.

[0003] The controller that controls the fixing unit controls the surface temperature of the heat roller to a target value by increasing or decreasing the amount of electricity supplied to the heater based on the detection signal of the temperature sensor (temperature sensor signal). That is, the controller reduces the amount of electricity supplied to the heater when the detected temperature is high, and increases the amount of electricity supplied to the heater when the detected temperature is low.

[0004] For example, if the temperature sensor fails or the transmission path of the detection signal from the temperature sensor to the controller, i.e., the physical wiring, is broken, the detection signal will no longer be input to the controller. The controller will then mistakenly determine that the temperature has dropped and will continue to increase the amount of electricity supplied to the heater. This will cause the temperature of the fuser, including the heat roller, to rise abnormally, putting stress on the fuser components and leading to their failure.

[0005] When the temperature of the fixing unit rises abnormally, a separate thermostat will eventually forcibly cut off the power to the heater, ensuring safety. However, when the power is cut off, the image forming device itself also stops printing at that point. This causes print media that have not yet been ejected to remain in the image forming device and the user must manually remove them. Since the user has no way of knowing that the end of the printing operation of the image forming device is due to a malfunction such as a temperature sensor or a disconnection in the transmission path of the detection signal, the user will assume that it is simply a paper jam, remove the print media, and then restart the image forming device. This causes the same thing to happen again and again, and the user will have to remove the print media from the image forming device many times without being able to complete the printing.

[0006] Furthermore, if the toner is being melted and pressed onto the print medium, that is, if the print medium stops at the fixing unit, even if the print medium is removed, toner residue will remain on the heat roller, and this toner residue will reduce the print quality thereafter.

[0007] The abnormal rise in the temperature of the fixing unit when a failure occurs in the temperature detection element of the heat roller, including the temperature sensor and the transmission path of the temperature detection result, can be prevented by installing multiple temperature detection elements in the image forming apparatus, but this increases the cost of the image forming apparatus. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2014-48422 A Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a temperature control device and an image forming apparatus capable of suppressing an abnormal rise in the temperature of the fixing unit when a failure occurs in a temperature detection element. [Means for solving the problem]

[0010] A temperature control device according to an embodiment is a temperature control device that controls the temperature of a temperature control target to which heat is propagated from a heater by supplying power to the heater, and includes a temperature estimation unit, a temperature correction unit, a temperature bias correction unit, a failure determination unit, a selection unit, and a signal generation unit. The temperature estimation unit estimates the temperature of the temperature control target based on the power supply to the heater. The temperature correction unit calculates a temperature correction value based on the temperature estimation result of the temperature estimation unit and the temperature detection result of the temperature control target by the temperature sensor. The temperature bias correction unit corrects the temperature estimation result of the temperature estimation unit by a preset bias value. The failure determination unit performs a failure determination for the temperature sensor or the transmission path of the temperature detection result based on the difference between the temperature estimation result of the temperature estimation unit and the temperature detection result of the temperature control target by the temperature sensor. The selection unit selects the output of the temperature correction unit or the output of the temperature bias correction unit based on the determination result of the failure determination unit. The signal generation unit outputs an energization pulse for controlling the power supplied to the heater based on the selected output of the temperature correction unit or the temperature bias correction unit. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of an image forming apparatus according to an embodiment. [Diagram 2] FIG. 2 is a diagram for explaining an example of the configuration of a heater energization control circuit according to an embodiment. [Diagram 3] FIG. 3 is a diagram for explaining a thermal circuit representing a heat transfer for obtaining a temperature estimation result according to an embodiment. [Figure 4] FIG. 4 is a diagram for explaining an example of the operation of the heater energization control circuit according to one embodiment. [Diagram 5]FIG. 5 is a diagram for explaining an example of the operation of the heater energization control circuit according to one embodiment. [Figure 6] FIG. 6 is a diagram for explaining an example of the operation of the heater energization control circuit according to an embodiment. [Figure 7] FIG. 7 is a diagram for explaining an example of the operation of the heater energization control circuit according to an embodiment. [Figure 8] FIG. 8 is a diagram for explaining an example of the operation of the heater energization control circuit according to an embodiment. [Figure 9] FIG. 9 is a diagram for explaining an example of the operation of the heater energization control circuit according to an embodiment. [Figure 10] FIG. 10 is a diagram for explaining an example of the operation of the heater energization control circuit according to an embodiment. [Figure 11] FIG. 11 is a diagram for explaining an example of a target temperature in one embodiment. [Figure 12] FIG. 12 is a diagram for explaining the relationship between the difference DIF and the duty value DUTY according to one embodiment. [Figure 13] FIG. 13 is a diagram for explaining an energization pulse train generated by a heater energization control circuit according to an embodiment. [Figure 14] FIG. 14 is a diagram for explaining the relationship between the duty value and the generated power, and between the energizing pulse train and the generated power according to one embodiment. [Figure 15] FIG. 15 is a diagram for explaining an example of sampling of duty values ​​according to an embodiment. [Figure 16] FIG. 16 is a diagram for explaining an example of the operation of the system controller according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A temperature control device and an image forming apparatus according to an embodiment will be described below with reference to the drawings. FIG. 1 is an explanatory diagram for explaining an example of the configuration of an image forming apparatus 1 according to an embodiment.

[0013] 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 type 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.

[0014] For example, the image forming apparatus 1 has a configuration for receiving toner from a toner cartridge and forming an image on a print medium P using the received toner. The toner may be a single color toner or a color toner such as cyan, magenta, yellow, and black. The toner may also be a decolorizable toner that is decolorized when heat is applied.

[0015] As shown in FIG. 1, the image forming apparatus 1 includes a housing 11, a communication interface 12, a system controller 13, a heater current control circuit 14, a display unit 15, an operation interface, multiple paper trays 17, a paper output tray 18, a conveying unit 19, an image forming unit 20, and a fixing unit 21.

[0016] The housing 11 is the main body of the image forming apparatus 1. The housing 11 houses a communication interface 12, a system controller 13, a heater current control circuit 14, a display unit 15, an operation interface 16, a plurality of paper trays 17, a paper output tray 18, a conveying unit 19, an image forming unit 20, and a fixing unit 21.

[0017] First, the configuration of the control system of the image forming apparatus 1 will be described. 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 external device includes, for example, a user terminal such as a personal computer and a server device on a cloud. 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).

[0018] The system controller 13 controls the image forming apparatus 1. The system controller 13 includes, for example, a processor 22 and a memory 23.

[0019] The processor 22 is a calculation element that executes calculation processing. The processor 22 is, for example, a CPU (Central Processing Unit). The CPU may be a multi-core / multi-threaded one, and can execute multiple processes in parallel. The processor 22 may be, for example, an MPU (micro processing unit), an SoC (system on a chip), a DSP (digital signal processor), a GPU (graphics processing unit), an ASIC (application specific integrated circuit), a PLD (programmable logic device), or an FPGA (field-programmable gate array). Alternatively, the processor 22 may be a combination of two or more of these. 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 that can execute various operations by executing the programs stored in the memory 23.

[0020] 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.

[0021] The print job includes image data indicating 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 may be data for forming an image on multiple sheets of print medium P. Furthermore, the print job includes information such as information indicating whether color printing or monochrome printing is to be performed, and information indicating the print medium P to be used for printing. The print job may also include information such as the number of copies to be printed (number of page sets), the number of sheets to be printed per copy (number of pages), etc.

[0022] In addition, the processor 22 generates print control information for controlling the operations of the conveying unit 19, the image forming unit 20, and the fixing unit 21 based on the generated print job. The print control information includes information indicating the timing of paper passing. The processor 22 supplies the print control information to the heater energization control circuit 14.

[0023] 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 control of the conveying unit 19 to convey the print medium P, the control of the image forming unit 20 to form an image on the print medium P, and the like.

[0024] The memory 23 is a storage medium that stores programs, data used in the programs, etc. The memory 23 also functions as a working memory. That is, the memory 23 temporarily stores data being processed by the processor 22, programs executed by the processor 22, etc.

[0025] 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 in the engine controller.

[0026] The image forming apparatus 1 also includes a power conversion circuit (not shown) that uses the AC voltage of the AC power source AC to supply a DC voltage to various components within the image forming apparatus 1. The power conversion circuit supplies the system controller 13 with a DC voltage required for the operation of the processor 22 and the memory 23. The power conversion circuit also supplies the image forming unit 20 with a DC voltage required for image formation. The power conversion circuit also supplies the conveying unit 19 with a DC voltage required for conveying the print medium P. The power conversion circuit also supplies the heater energization control circuit 14 with a DC voltage for driving the heater of the fixing unit 21.

[0027] The heater current control circuit 14 is a temperature control device (temperature control section) that controls current supply to a heater of the fixing device 21, which will be described later. The heater current control circuit 14 generates current supply power PC for energizing the heater of the fixing device 21, and supplies the current supply power to the heater of the fixing device 21. The heater current control circuit 14 will be described in detail later.

[0028] 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 graphic controller (not shown). For example, a screen for various settings of the image forming apparatus 1 is displayed on the display of the display unit 15.

[0029] The operation interface 16 includes an operation member. The operation interface 16 supplies an operation signal corresponding to the operation of the operation member to the system controller 13. The operation member is, for example, a touch sensor, a numeric keypad, a power key, a paper feed key, various function keys, or a keyboard. The touch sensor obtains information indicating a specified position within a certain area. The touch sensor is configured as a touch panel integrally with the display unit 15, and inputs a signal indicating a touched position on the screen displayed on the display unit 15 to the system controller 13.

[0030] Each of the multiple paper trays 17 is a cassette that stores print media P. The paper trays 17 are configured to be able to supply the print media P from outside the housing 11. For example, the paper trays 17 are configured to be able to be pulled out from the housing 11.

[0031] The discharge tray 18 is a tray that supports the print medium P discharged from the image forming apparatus 1.

[0032] Next, a configuration for transporting the print medium P of the image forming apparatus 1 will be described. The transport unit 19 is a mechanism that transports the print medium P inside 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.

[0033] The paper feed path 31 and the paper discharge path 32 are each composed of a plurality of motors, a plurality of rollers, and a plurality of guides (not shown). The plurality of motors rotate their shafts under the control of the system controller 13, thereby rotating rollers linked to the rotation of the shafts. The plurality of rollers move the printing medium P by rotating. The plurality of guides control the transport direction of the printing medium P.

[0034] 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 includes a pickup roller 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.

[0035] The discharge transport path 32 is a transport path that discharges the print medium P on which an image has been formed from the housing 11. The print medium P discharged by the discharge transport path 32 is supported by the discharge tray .

[0036] 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.

[0037] 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 since the plurality of process units 41 and the plurality of exposure devices 42 each have the same configuration, one process unit 41 and one exposure device 42 will be described below.

[0038] 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 having toners of different colors are connected to each process unit 41.

[0039] The toner cartridge includes a toner storage container and a toner delivery mechanism. The toner storage container is a container for storing toner. The toner delivery mechanism is a mechanism including a screw and the like for delivering the toner from the toner storage container.

[0040] 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 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).

[0041] The electric charger 52 uniformly charges the surface of the photosensitive drum 51. For example, the electric charger 52 charges the photosensitive drum 51 to a uniform negative potential (contrast potential) by applying a voltage (development bias voltage) to the photosensitive drum 51 using a charging roller. The charging roller rotates with the rotation of the photosensitive drum 51 while applying a predetermined pressure to the photosensitive drum 51.

[0042] The developing unit 53 is a device that adheres the 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.

[0043] The developer container is a container that receives and stores the toner discharged from the toner cartridge. A carrier is stored in the developer container beforehand. The toner discharged 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.

[0044] The developing roller rotates in the developer container to deposit developer on its surface. The doctor blade is a member disposed at a specified distance from the surface of the developing roller. The doctor blade removes a portion of the developer deposited on the surface of the rotating developing roller. As a result, a layer of developer is formed on the surface of the developing roller, the thickness of which corresponds to the distance between the doctor blade and the surface of the developing roller.

[0045] The ATC sensor is, for example, a magnetic flux sensor having a coil and detecting a voltage value generated in the coil. The detection voltage of 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 remaining in the developer container 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 operates a motor (not shown) that drives the delivery mechanism of the toner cartridge, and sends the toner from the toner cartridge to the developer container of the developing device 53.

[0046] 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.

[0047] The exposure unit 42 forms a latent image of one line on the photosensitive drum 51 by irradiating light onto the photosensitive drum 51 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.

[0048] In the above configuration, when the surface of the photosensitive drum 51 charged by the electrostatic charger 52 is irradiated with light from the exposure device 42, 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] The secondary transfer opposing roller 62 is rotated by a motor (not shown). The secondary transfer opposing roller 62 rotates to transport 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.

[0053] 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 interposed therebetween. The primary transfer rollers 63 come into contact with the inner peripheral surface side 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 peripheral surface of the primary transfer belt 61 into contact with the photosensitive drums 51.

[0054] The secondary transfer roller 64 is disposed at a position facing the primary transfer belt 61. The secondary transfer roller 64 contacts the outer peripheral surface of the primary transfer belt 61 and applies pressure to it. This forms a transfer nip in which 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.

[0055] The secondary transfer roller 64 and the secondary transfer opposing roller 62 rotate to convey the print medium P supplied from the paper feed conveyance path 31 while sandwiching the print medium P between them, causing the print medium P to pass through the transfer nip.

[0056] 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. When the image forming section 20 includes a plurality of process units 41, the primary transfer belt 61 receives the toner images from the photosensitive drums 51 of the plurality of 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. When 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.

[0057] Next, a fixing-related configuration of the image forming apparatus 1 will be described. The fixing device 21 fixes the toner image onto the printing medium P onto which the toner image has been transferred. The fixing device 21 operates under the control of the system controller 13 and the heater energization control circuit 14. The fixing device 21 includes a fixing rotor, a pressure member, and a heating member. The fixing rotor is, for example, a heat roller 71. The heat roller 71 heats the toner image formed on the printing medium P to fix it onto the printing medium P. The pressure member is, for example, a press roller 72. The heating member is, for example, a heater 73 that heats the heat roller 71. The fixing device 21 also includes a temperature sensor (thermal sensor) 74 that detects the temperature of the heat roller 71.

[0058] Heat roller 71 is a fixing rotor rotated by a motor (not shown). Heat roller 71 has a hollow metal core and an elastic layer formed on the outer periphery of the core. Heat roller 71 heats the inside of the hollow core by heater 73 arranged inside the core. The heat generated inside the core is transferred to the outside surface of heat roller 71 (i.e., the surface of the elastic layer).

[0059] The press roller 72 is disposed at a position facing the heat roller 71. The press roller 72 has a core bar formed of metal with a predetermined outer diameter, and an elastic layer formed on the outer periphery of the core bar. The press roller 72 applies pressure to the heat roller 71 by stress applied from a tension member (not shown). When pressure is applied from the press roller 72 to the heat roller 71, a nip (fixing nip) is formed in which the press roller 72 and the heat roller 71 are in close contact with each other. The press roller 72 is rotated by a motor (not shown). As the press roller 72 rotates, it moves the printing medium P that has entered the fixing nip and presses the printing medium P against the heat roller 71.

[0060] The heater 73 is a device that generates heat by the energizing power PC supplied from the heater energization control circuit 14. The heater 73 is, for example, a halogen heater. The heater 73 heats the inside of the core metal of the heat roller 71 by electromagnetic waves radiated from a halogen lamp heater, which is a heat source, when the energizing power PC supplied from the heater energization control circuit 14 is applied to the halogen lamp heater. The heater 73 may also be, for example, an IH heater.

[0061] The temperature sensor 74 detects the temperature of the heat roller 71. Here, the temperature sensor 74 is described as detecting the surface temperature of the heat roller 71. The temperature sensor 74 may detect the temperature of the air near the surface of the heat roller 71. There may be multiple temperature sensors 74. For example, multiple temperature sensors 74 may be arranged parallel to the rotation axis of the heat roller 71. It is sufficient that the temperature sensor 74 is provided at a position where it can detect at least a change in the surface temperature of the heat roller 71. The temperature sensor 74 supplies the temperature detection result Td of the heat roller 71 by the temperature sensor 74 to the heater current control circuit 14. The temperature detection result Td is the surface temperature of the heat roller 71 detected by the temperature sensor 74. The temperature detection result Td may also refer to a signal indicating the surface temperature of the heat roller 71 detected by the temperature sensor 74.

[0062] With the above configuration, the heat roller 71 and the press roller 72 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 heat roller 71, and is applied to the surface of the print medium P by the pressure applied by the heat roller 71 and the press roller 72. 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 paper discharge transport path 32 and discharged to the paper discharge tray 18.

[0063] Next, the heater current control circuit 14 will be described. The heater current control circuit 14 supplies power to the heater 73 by controlling the current supply to the heater 73 of the fixing device 21. The heater current control circuit 14 controls the surface temperature of the heat roller 71 to which heat is propagated from the heater 73 by supplying power to the heater 73. The heater current control circuit 14 generates current supply power PC for energizing the heater 73 of the fixing device 21 and supplies it to the heater 73 of the fixing device 21.

[0064] 2, 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 selection unit 85, a difference comparison unit 86, a control duty generation unit 87, an external limit unit 88, a duty pulse conversion unit 89, a power supply circuit 90, a fault determination unit 91, and a temperature bias correction unit 92. The heater energization control circuit 14 also receives the temperature detection result Td from the temperature sensor 74, and receives the target temperature TGT, system protection information LMT, the fault determination difference DT, and the preset bias value TP from the system controller 13. The heater energization control circuit 14 supplies energizing power PC to the heater 73, and outputs the fault determination result JR to the system controller 13.

[0065] 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 estimated history storage unit 82, and the duty value LD from the external limit unit 88.

[0066] The estimated history PREV is a history of the temperature estimation results EST by the temperature estimation unit 81. The estimated history PREV may also refer to a signal indicating the history of the temperature estimation results EST by the temperature estimation unit 81. The history of the temperature estimation results EST by the temperature estimation unit 81 includes a plurality of past temperature estimation results EST from a small time ago. The temperature estimation results EST are the surface temperature of the heat roller 71 estimated by the temperature estimation unit 81 based on at least the duty value LD. The temperature estimation result EST may also refer to a signal indicating the surface temperature of the heat roller 71 estimated by the temperature estimation unit 81 based on at least the duty value LD.

[0067] The duty value LD is a duty value based on the duty value DUTY. The duty value LD may also refer to a signal indicating a duty value based on the duty value DUTY. The duty value LD may be a duty value having the same value as the duty value DUTY, or may be a duty value having a different value from the duty value DUTY. If the external limit unit 88 does not limit the duty value DUTY, the duty value LD is a duty value having the same value as the duty value DUTY. If the external limit unit 88 limits the duty value DUTY, the duty value LD is a duty value after limitation by the external limit unit 88, and is a duty value having a different value from the duty value DUTY.

[0068] The duty value DUTY is a duty value generated by the control duty generation unit 87. The duty value DUTY may also refer to a signal indicating the duty value generated by the control duty generation unit 87.

[0069] The temperature estimation unit 81 estimates the surface temperature of the heat roller 71 based on the duty value LD and generates a temperature estimation result EST. The temperature estimation unit 81 outputs the temperature estimation result EST to the estimation history storage unit 82 and the high frequency component extraction unit 83. As described above, the duty value LD is a duty value based on the duty value DUTY. Therefore, estimating the surface temperature of the heat roller 71 based on the duty value LD is an example of estimating the surface temperature of the heat roller 71 based on the duty value DUTY. As will be described later, the energizing power PC actually applied to the heater 73 is generated based on the duty value LD, so the temperature estimation calculation by the temperature estimation unit 81 must also be performed using this duty value LD. In other words, in order to obtain a simulation result (temperature) equivalent to the actual operation in the temperature estimation unit 81, it is necessary to perform calculations using the duty value LD. Therefore, as described above, it is desirable to set the duty value LD to a duty value after limiting by the external limit unit 88. Therefore, estimating the surface temperature of the heat roller 71 based on the duty value LD includes estimating the surface temperature of the heat roller 71 based on the duty value after the limiting by the external limit unit 88.

[0070] In a typical example, the temperature estimation unit 81 estimates the surface temperature of the heat roller 71 based on the estimated history PREV and the duty value LD, and generates a temperature estimation result EST. Estimating the surface temperature of the heat roller 71 based on the estimated history PREV and the duty value LD is an example of estimating the surface temperature of the heat roller 71 based on the estimated history PREV and the duty value DUTY. Estimating the surface temperature of the heat roller 71 based on the estimated history PREV and the duty value LD includes estimating the surface temperature of the heat roller 71 based on the estimated history PREV and the duty value after limitation by the external limit unit 88.

[0071] The estimated history storage unit 82 stores the estimated history PREV. The estimated history storage unit 82 outputs the estimated history PREV to the temperature estimation unit 81.

[0072] The high frequency component extraction unit 83 performs high pass filtering to extract high frequency components of the temperature estimation result EST. For example, the high frequency component extraction unit 83 cancels DC components in the temperature estimation result EST and extracts only high frequency components. The high frequency component extraction unit 83 generates a high frequency component HPF and outputs the high frequency component HPF to the coefficient addition unit 84. The high frequency component HPF is the high frequency component of the temperature estimation result EST extracted by the high frequency component extraction unit 83. The high frequency component HPF may also refer to a signal indicating the high frequency component of the temperature estimation result EST extracted by the high frequency component extraction unit 83.

[0073] The coefficient addition unit 84 performs a coefficient addition process to correct the temperature detection result Td. The coefficient addition unit 84 receives the temperature detection result Td from the temperature sensor 74 and the high frequency component HPF from the high frequency component extraction unit 83. The coefficient addition unit 84 corrects the temperature detection result Td based on the high frequency component HPF to generate a corrected temperature value WAE. For example, the coefficient addition unit 84 performs a calculation such as adding the high frequency component HPF and the temperature detection result Td to generate the corrected temperature value WAE. The corrected temperature value WAE is a value obtained by correcting the temperature detection result Td based on the high frequency component HPF, and is an estimated surface temperature of the heat roller 71. The corrected temperature value WAE may also refer to a signal indicating a value obtained by correcting the temperature detection result Td based on the high frequency component HPF. The coefficient addition unit 84 outputs the corrected temperature value WAE to the difference comparison unit 86 via the selection unit 85.

[0074] Specifically, the coefficient addition unit 84 multiplies the high frequency component HPF by a preset coefficient K. The coefficient addition unit 84 adds the value obtained by multiplying the high frequency component HPF by the coefficient K to the temperature detection result Td. The coefficient addition unit 84 obtains a value obtained by (Td+K×HPF) as the corrected temperature value WAE. Since the high frequency component HPF is based on the temperature estimation result EST, 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 84 is an example of a calculation unit that obtains the corrected temperature value WAE.

[0075] For example, when the coefficient K is 1, the coefficient adding unit 84 directly adds the high frequency component HPF to the temperature detection result Td. Also, when the coefficient K is 0.1, for example, the coefficient adding unit 84 adds a value that is one tenth 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 becomes close to Td. Also, when the coefficient K is 1 or more, for example, the effect of the high frequency component HPF can be more strongly expressed. Experiments have shown that the coefficient K set in the coefficient adding unit 84 should not be an extreme value, but a value close to 1 is best.

[0076] The selection unit 85 selects either the corrected temperature value WAE from the coefficient addition unit 84 or the bias corrected temperature value TBC from the temperature bias correction unit 92, and inputs it to the difference comparison unit 86. The selection unit 85 makes this selection based on the failure determination result by the failure determination unit 91. In a normal state where there is no failure in the temperature detection element, such as an abnormality in the temperature sensor 74 itself or a break in the transmission path of the temperature detection result Td, the selection unit 85 inputs the corrected temperature value WAE from the coefficient addition unit 84 to the difference comparison unit 86.

[0077] First, each part will be described below using the normal state as an example. The difference comparison unit 86 performs a difference calculation process. The difference comparison unit 86 receives the corrected temperature value WAE from the selection unit 85 and the target temperature TGT from the system controller 13.

[0078] The target temperature TGT is a target value for the surface temperature of the heat roller 71. The target temperature TGT may also refer to a signal indicating a target value for the surface temperature of the heat roller 71. The target temperature TGT can be changed by a command from the processor 22. The target value for the surface temperature of the heat roller 71 may be stored in the memory 23. The target temperature TGT may also be stored in the heater current control circuit 14. In this case, the target temperature TGT can be changed by being rewritten by a command from the processor 22.

[0079] For example, the target temperature TGT can be set for each printing process. In one example, the target temperature TGT differs depending on the quality of the printing medium P used in each printing process. For example, the quality is thickness. In general, the target temperature TGT is determined so as to maintain a predetermined temperature when the printing medium P is plain paper. When the printing medium P passes through the fixing device 21, the amount of heat taken away from the heat roller 71 by the printing medium P is greater for thick paper, which is thicker than plain paper, than for plain paper. The surface temperature of the heat roller 71 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 taken away from the heat roller 71 by the thick paper. This makes it easier to maintain the surface temperature of the heat roller 71 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.

[0080] In another example, the target temperature TGT varies depending on the status of the printing process. Examples of target temperatures TGT depending on the status of the printing process are described below.

[0081] The difference comparison unit 86 compares the target temperature TGT with the corrected temperature value WAE. The difference comparison unit 86 calculates a difference DIF based on the comparison between the target temperature TGT and the corrected temperature value WAE. The difference DIF is the difference between the target temperature TGT and the corrected temperature value WAE. The difference DIF may also refer to a signal indicating the difference between the target temperature TGT and the corrected temperature value WAE. The difference comparison unit 86 outputs the difference DIF to the control duty generation unit 87. The difference comparison unit 86 is an example of a comparison unit.

[0082] Here, the difference DIF is described as a value obtained by subtracting the target temperature TGT from the correction temperature value WAE, but the opposite is also possible. In this example, when the correction temperature value WAE is lower than the target temperature TGT, the difference DIF is a negative value. When the correction temperature value WAE is higher than the target temperature TGT, the difference DIF is a positive value. The relationship between the target temperature TGT and the correction temperature value WAE appears in the difference DIF.

[0083] The control duty generating unit 87 performs a duty value generating process to generate a duty value DUTY. The difference DIF from the difference comparing unit 86 is input to the control duty generating unit 87. The control duty generating unit 87 generates a duty value DUTY based on the difference DIF. The duty value DUTY is a duty value according to the difference DIF. When the correction temperature value WAE is equal to the target temperature TGT, the duty value DUTY is a center value (reference value) of the duty. When the correction temperature value WAE is lower than the target temperature TGT, the control duty generating unit 87 increases the duty value from the center value of the duty to increase the amount of power supplied to the heater 73. The duty value DUTY is a value higher than the center value of the duty. On the other hand, when the correction temperature value WAE is higher than the target temperature TGT, the control duty generating unit 87 decreases the duty value from the center value of the duty to decrease the amount of power supplied to the heater 73. The duty value DUTY is a value lower than the center value of the duty. The duty value DUTY is a real number. For example, the duty value may have a resolution of 0 to 100. The control duty generating section 87 outputs the duty value DUTY to the external limit section 88. The control duty generating section 87 is an example of a duty generating section.

[0084] As described above, the corrected temperature value WAE is based on the temperature estimation result EST and the temperature detection result Td. The difference DIF is the difference between the target temperature TGT and the corrected temperature value WAE. Therefore, generating the duty value DUTY based on the difference DIF includes generating the duty value based on the temperature estimation result EST, the temperature detection result Td, and the target temperature TGT.

[0085] The external limit unit 88 performs a limiting process to limit the duty value DUTY. The external limit unit 88 receives the system protection information LMT from the processor 22 and the duty value DUTY from the control duty generating unit 87. The external limit unit 88 reflects the system protection information LMT on the duty value DUTY and generates a duty value LD based on the duty value DUTY. Reflecting the system protection information LMT on the duty value DUTY includes applying the system protection information LMT to the duty value DUTY. If the duty value DUTY does not satisfy the restrictions indicated by the system protection information LMT, the external limit unit 88 limits the duty value DUTY by reflecting the system protection information LMT on the duty value DUTY. If the duty value DUTY satisfies the restrictions indicated by the system protection information LMT, the external limit unit 88 does not limit the duty value DUTY even if the system protection information LMT is reflected on the duty value DUTY. The external limit unit 88 outputs the duty value LD to the temperature estimation unit 81 and the duty pulse conversion unit 89. The external limit unit 88 is an example of a limit unit.

[0086] The system protection information LMT is information for limiting the duty value in order to protect the image forming apparatus 1. The system protection information LMT may also refer to a signal indicating information for limiting the duty value in order to protect the image forming apparatus 1. The system protection information LMT can be changed by a command from the processor 22.

[0087] In one example, the system protection information LMT is information on at least one of the upper and lower limit values ​​of the duty value. The upper limit value of the duty value is a value determined based on the power or current that can be supplied to the heater 73. The lower limit value of the duty value can be set arbitrarily. If the duty value DUTY exceeds the upper limit value of the duty value, the duty value DUTY does not satisfy the limit indicated in the system protection information LMT. If the duty value DUTY is less than the lower limit value of the duty value, the duty value DUTY does not satisfy the limit indicated in the system protection information LMT. If the duty value DUTY is equal to or greater than the lower limit value of the duty value and equal to or less than the upper limit value of the duty value, the duty value DUTY satisfies the limit indicated in the system protection information LMT.

[0088] For example, assume that the upper limit value of the duty value is 85 and the lower limit value is 0. A case where the duty value DUTY is 90 will be described. Since the duty value DUTY exceeds the upper limit value of the duty value, the duty value DUTY does not satisfy the limit indicated by the system protection information LMT. The external limit unit 88 limits the duty value DUTY by reflecting the system protection information LMT on the duty value DUTY. The external limit unit 88 generates a duty value LD based on the duty value DUTY. The duty value LD is the duty value after the limit. The duty value after the limit is 85, which corresponds to the upper limit value of the duty value. A case where the duty value DUTY is 80 will be described. Since the duty value DUTY is equal to or greater than the lower limit value and equal to or less than the upper limit value of the duty value, the duty value DUTY satisfies the limit indicated by the system protection information LMT. Even if the external limit unit 88 reflects the system protection information LMT on the duty value DUTY, the duty value DUTY does not limit the duty value DUTY. The external limit unit 88 generates a duty value LD based on the duty value DUTY. The duty value LD is 80, which is the same as the duty value DUTY.

[0089] In another example, the system protection information LMT is information instructing the image forming apparatus 1 to stop in order to avoid danger. When the duty value DUTY is a value other than 0, the duty value DUTY does not satisfy the limit indicated by the system protection information LMT. In this case, the external limit unit 88 limits the duty value DUTY by reflecting the system protection information LMT on the duty value DUTY. The external limit unit 88 generates a duty value LD based on the duty value DUTY. The duty value LD is the duty value after the limit. The duty value after the limit is 0. When the duty value DUTY is 0, the duty value DUTY satisfies the limit indicated by the system protection information LMT. In this case, the external limit unit 88 does not limit the duty value DUTY even if the system protection information LMT is reflected on the duty value DUTY. The external limit unit 88 generates a duty value LD based on the duty value DUTY. The duty value LD is 0, which is the same as the duty value DUTY.

[0090] The duty pulse conversion unit 89 performs a generation process to generate an energization pulse Ps for controlling the power supplied to the heater 73 based on the duty value LD. The energization pulse Ps is a pulse signal for controlling the power supplied to the heater 73. The energization pulse Ps is a gate signal of a triac. The duty pulse conversion unit 89 receives the duty value LD from the external limit unit 88. The duty pulse conversion unit 89 converts the duty value LD into an energization pulse train. The duty pulse conversion unit 89 generates the energization pulse Ps that constitutes the energization pulse train. The duty pulse conversion unit 89 outputs the energization pulse Ps to a power supply circuit 90. The duty pulse conversion unit 89 is an example of a signal generation unit that generates the energization pulse Ps.

[0091] As described above, the duty value LD may be a duty value after limitation by the external limit unit 88. Therefore, generating and outputting the energizing pulse Ps based on the duty value LD includes generating and outputting the energizing pulse Ps based on the duty value after limitation by the external limit unit 88. Generating and outputting the energizing pulse Ps based on the duty value LD is an example of generating and outputting the energizing pulse Ps based on the duty value DUTY.

[0092] The duty pulse conversion unit 89 may select a duty pattern based on the duty value LD, and generate an energizing pulse Ps according to the selected duty pattern. The duty pattern is a pattern corresponding to the duty value. The duty pattern indicates an energizing pulse train consisting of a number of values ​​of "0" or "1" arranged according to the duty value. "1" indicates a conductive (ON) signal. "0" indicates a cut-off (OFF) signal. The number of "1" values ​​varies depending on the duty value. The duty pattern may be stored in the memory 23.

[0093] The duty pulse conversion unit 89 may generate the energizing pulse Ps asynchronously with the system operation. Specifically, the duty pulse conversion unit 89 may adjust the pulse frequency and the emission time of the energizing pulse Ps in accordance with the AC voltage frequency of 50 Hz / 60 Hz. The duty pulse conversion unit 89 acquires the AC voltage phase, and performs a synchronous output process to output the energizing pulse Ps that constitutes an energizing pulse train in synchronization with the AC voltage based on the AC voltage phase. The duty pulse conversion unit 89 outputs the energizing pulse Ps in synchronization with the zero crossing of the AC voltage.

[0094] The power supply circuit 90 supplies energizing power PC to the heater 73 based on the energizing pulse Ps. The power supply circuit 90 energizes the heater 73 of the fixing unit 21 using an AC voltage supplied from an AC voltage source (not shown). The power supply circuit 90 supplies the energizing power PC to the heater 73 by switching between a state in which the AC voltage from the AC voltage source is supplied to the heater 73 and a state in which the AC voltage is not supplied based on the energizing pulse Ps, for example. That is, the power supply circuit 90 changes the energizing time of the heater 73 of the fixing unit 21 according to the energizing pulse Ps.

[0095] The power supply circuit 90 may be integrated with the fixing device 21. In other words, the heater energization control circuit 14 may be configured to supply an energization pulse Ps to the power supply circuit of the heater 73 of the fixing device 21, instead of supplying the energization power PC to the heater 73.

[0096] As described above, the heater energization control circuit 14 adjusts the amount of power supplied to the heater 73 of the fixing unit 21 by using the corrected temperature value WAE, which is a simulation temperature obtained by performing calculations such as adding the high frequency component HPF of the temperature estimation result EST to the temperature detection result Td, instead of the temperature detection result Td, which is the actual measured temperature. In this way, the heater energization control circuit 14 controls the surface temperature of the heat roller 71 heated by the heater 73. Such control that uses a simulation temperature instead of the actual measured temperature is referred to here as Weighted Average control with Estimate temperature (WAE control).

[0097] The failure determination unit 91 performs a process of determining whether or not a failure has occurred in the temperature detection element including the temperature sensor 74 and the transmission path of the temperature detection result Td. The failure determination unit 91 receives the temperature estimation result EST from the temperature estimation unit 81, the temperature detection result Td from the temperature sensor 74, and the failure determination difference DT from the system controller 13.

[0098] The failure determination difference DT is a threshold value for determining whether a failure has occurred. The failure determination difference DT can be changed by a command from the processor 22. The threshold value for failure occurrence determination may be stored in the memory 23. Also, the failure determination difference DT may be stored in the heater energization control circuit 14. In this case, the failure determination difference DT can be changed by rewriting by a command from the processor 22.

[0099] The failure determination unit 91 determines the presence or absence of a failure based on the relationship between the difference between the temperature estimation result EST and the temperature detection result Td and the failure determination difference DT, and generates a failure determination result JR. Specifically, if the difference value between the value of the temperature estimation result EST and the value of the temperature detection result Td is less than or equal to the failure determination difference, the failure determination unit 91 determines that no failure has occurred. If the difference value between the value of the temperature estimation result EST and the value of the temperature detection result Td is greater than the failure determination difference DT, the failure determination unit 91 determines that a failure has occurred. The failure determination unit 91 outputs the failure determination result JR to the selection unit 85 and also outputs it to the system controller 13.

[0100] Explaining with a specific numerical example, for example, assuming that the temperature estimation result EST is 130 degrees, the temperature detection result Td is 125 degrees, and the failure determination difference DT is 40 degrees, since 130 - 125 ≤ 40, the failure determination unit 91 outputs a failure determination result JR indicating no failure, that is, normal.

[0101] Also, for example, assuming that the temperature estimation result EST and the failure determination difference DT are similarly 130 degrees and 40 degrees, and when the temperature detection result Td is an abnormal value of 10 degrees, since 130 - 10 > 40, the failure determination unit 91 outputs a failure determination result JR indicating a failure.

[0102] Note that in this example, it is assumed that the failure determination is performed based on EST - Td ≤ DT and EST - Td > DT, but of course, it may also be determined based on EST - Td < DT and EST - Td ≥ DT.

[0103] The temperature bias correction unit 92 performs a process of bias correction of the temperature estimation result EST from the temperature estimator 81. The temperature bias correction unit 92 receives the temperature estimation result EST from the temperature estimator 81 and the preset bias value TP from the system controller 13.

[0104] The preset bias value TP is a value indicating the amount of bias correction. The preset bias value TP can be changed by a command from the processor 22. The amount of bias correction may be stored in the memory 23. The preset bias value TP may also be stored in the heater energization control circuit 14. In this case, the preset bias value TP can be changed by being rewritten by a command from the processor 22.

[0105] The temperature bias correction unit 92 adds the preset bias value TP to the value of the temperature estimation result EST to generate a bias-corrected temperature value TBC. The temperature bias correction unit 92 outputs the bias-corrected temperature value TBC to the selection unit 85.

[0106] To explain this using a specific numerical example, for example, if the temperature estimation result EST is 130 degrees and the preset bias value TP is -5 degrees, the temperature bias correction unit 92 outputs a bias-corrected temperature value TBC of 125 degrees. This bias-corrected temperature value TBC is approximately the same as the corrected temperature value WAE obtained from the normal temperature detection result Td and the temperature estimation result EST.

[0107] As described above, the selection unit 85 selects one of the corrected temperature value WAE from the coefficient addition unit 84 and the bias-corrected temperature value TBC from the temperature bias correction unit 92 based on the failure judgment result JR from the failure judgment unit 91, and inputs it to the difference comparison unit 86. Specifically, if the failure judgment result JR is a result indicating no failure, i.e., normal, the selection unit 85 selects the corrected temperature value WAE from the coefficient addition unit 84, and inputs it to the difference comparison unit 86. If the failure judgment result JR is a result indicating a failure, the selection unit 85 selects the bias-corrected temperature value TBC from the temperature bias correction unit 92, and inputs it to the difference comparison unit 86.

[0108] The temperature estimation unit 81, the estimation history storage unit 82, the high frequency component extraction unit 83, the coefficient addition unit 84, the selection unit 85, the difference comparison unit 86, the control duty generation unit 87, the external limit unit 88, the duty pulse conversion unit 89, the fault determination unit 91 and the temperature bias correction unit 92 of the heater energization control circuit 14 may each be configured by an electric circuit or by software. When configured by software, they may be realized by the processor 22 or a processor different from the processor 22 executing a program stored in a memory. The processor is, for example, a processing circuit such as a CPU.

[0109] The thermal circuit representing the heat transfer for obtaining the temperature estimation result EST will be described. FIG. 3 is a diagram for explaining a thermal circuit representing a heat transfer for obtaining a temperature estimation result EST. The transfer of heat can be expressed by a thermal circuit equivalent to the CR time constant of an electric circuit (C is a capacitor and R is a resistor). The thermal circuit is composed of the elements V, C, and R.

[0110] The heat source V1 is equivalent to a DC voltage source in an electric circuit. The heating resistor R1 is equivalent to a variable resistor in an electric circuit. The heating resistor R1 corresponds to a physical quantity that indicates the difficulty of heat transmission from the heat source. The heating resistor R1 uses a duty value LD as a variable factor. For example, when the duty value indicated by the duty value LD is 100%, the heating resistor R1 remains R. Here, for example, R is assumed to be 100Ω. When the duty value indicated by the duty value LD is 0%, the heating resistor Ra is assumed to be 100Ω×10,000,000 (an extremely large value). When the duty value indicated by the duty value LD is greater than 0 and less than 100, the heating resistor R1 is assumed to be 100Ω×(duty value LD / 100). The heater capacity C1, which is the heat capacity of the heater 73, is equivalent to the capacity in an electric circuit. The heater capacitance C1 forms a first CR time constant circuit together with the heating resistor R1. The heater capacitance C1 refers to the estimated history PREV from an infinitesimal time dt before, and updates the temperature to the current time.

[0111] The heat dissipation resistance R2 is the resistance value when heat escapes from the heat roller 71 into the space inside the fixing unit 21. The unit capacitance C2, which is the thermal capacity of the fixing unit 21, forms a second CR time constant circuit together with the heat dissipation resistance R2. The unit capacitance C2 refers to the estimated history PREV from an infinitesimal time dt ago, and updates it to the temperature at the current time.

[0112] The outside air resistance R3 is the resistance value of the path through which heat escapes from the space inside the fixing unit 21 (outside the heat roller 71) to the outside air. The outside air temperature V2 is equivalent to a DC voltage source in an electric circuit. The relationship between the heat source V1 and the outside air temperature V2 is heat source V1 ≧ outside air temperature V2. Specifically, the relationship between the heat source V1 and the outside air temperature V2 before startup is heat source V1 = outside air temperature V2, and the relationship between the heat source V1 and the outside air temperature V2 during operation is heat source V1 > outside air temperature V2.

[0113] For example, the temperature estimation unit 81 performs a real-time simulation of the thermal circuit as described above using the law of conservation of energy based on the estimation history PREV and the duty value LD. The temperature estimation unit 81 derives the C1 voltage (temperature) as an estimate of the surface temperature of the heat roller 71 through the real-time simulation of the thermal circuit. The temperature estimation unit 81 generates the C1 voltage (temperature) as the temperature estimation result EST at the current time.

[0114] The operation of the heater current control circuit 14 will now be described in detail. 4 and 5 are flow charts for explaining the main operation of the heater energization control circuit 14. FIG. 6 is a flow chart for explaining the calculation operation of the correction temperature value WAE used in the heater energization control circuit 14 in normal operation, and FIG. 7 is a flow chart for explaining the calculation operation of the bias correction temperature value TBC used in the heater energization control circuit 14 when a failure occurs in the temperature detection element. The operations shown in these FIGS. 4, 5, 6, and 7 are constantly executed while the power supply of the image forming apparatus 1 is on, until a stop command is received from the system controller 13. FIG. 8 and FIG. 9 are explanatory diagrams for explaining each signal in the operation of the heater energization control circuit 14. The horizontal axis of FIG. 8 and FIG. 9 indicates time. The vertical axis of FIG. 8 and FIG. 9 indicates temperature.

[0115] 6, the temperature estimation unit 81 acquires the internal temperature of the image forming apparatus 1 (ACT201). Note that since the internal temperature changes slowly, the temperature estimation unit 81 may not acquire the internal temperature frequently.

[0116] The temperature estimation unit 81 acquires the temperature detection result Td at the current time from the temperature sensor 74 (ACT 202).

[0117] As shown in FIG. 8, there is a difference between the temperature detection result Td and the actual surface temperature of the heat roller 71. The surface temperature of the heat roller 71 changes in a short cycle because the heater 73 heats it intermittently. In contrast, the temperature sensor 74 may have poor response to temperature changes due to its own heat capacity and the characteristics of the temperature-sensitive material. In particular, the cheaper the temperature sensor, the poorer its response tends to be. As a result, the temperature detection result Td does not accurately track the actual surface temperature of the heat roller 71. That is, 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. Also, the temperature detection result Td is detected by the temperature sensor 74 in a smoothed state without reproducing the small changes in the surface temperature of the heat roller 71.

[0118] The temperature estimation unit 81 acquires the estimation history PREV from the estimation history storage unit 82, which is the estimation history from the very short time dt before (ACT 203).

[0119] The temperature estimation unit 81 acquires each parameter corresponding to the V, C, and R elements that configure the thermal circuit as described above (ACT 204).

[0120] The temperature estimation unit 81 calculates the amount of heat inflow (ACT205). In ACT205, for example, the temperature estimation unit 81 calculates the amount of heat inflow based on V1 and R on the input side and the duty value LD. The amount of heat inflow can be calculated by I=R / V1×(100 / duty value LD). When the duty value indicated by the duty value LD is 0%, the heating resistance R1 becomes ∞ and the heat inflow from the input side is 0. On the other hand, when the duty value indicated by the duty value LD is 100%, I=R / V1 and the heat inflow from the input side is the greatest.

[0121] The temperature estimation unit 81 acquires Vb, which is a value equivalent to the surface temperature of the heat roller 71, from the acquired estimated history PREV (ACT 206).

[0122] The temperature estimation unit 81 calculates the increase in Vb after dt due to the heat inflow from the law of conservation of energy (ACT207).

[0123] The temperature estimation unit 81 acquires Ve, which is a value equivalent to the temperature inside the housing of the image forming apparatus 1, from the acquired estimated history PREV (ACT208).

[0124] The temperature estimation unit 81 calculates the amount of heat outflow (ACT209). In ACT209, for example, the temperature estimation unit 81 calculates the temperature difference (Vb-Ve) between the surface temperature of the heat roller 71 and the temperature inside the housing. The temperature estimation unit 81 calculates the amount of heat outflow that is determined by the heat dissipation resistance R2 for the temperature difference (Vb-Ve).

[0125] The temperature estimation unit 81 calculates the drop in Vb after dt due to the heat outflow from the law of conservation of energy (ACT210).

[0126] The temperature estimation unit 81 calculates Vc after dt (ACT211). Vc after dt corresponds to the temperature estimation result EST. In ACT211, for example, the temperature estimation unit 81 calculates Vc after dt by Vc=Vc history value+Vb increase amount-Vb decrease amount. The Vc history value is the value of Vc before dt. In other words, Vc after dt is a value obtained by adding a value obtained by subtracting the decrease amount of Vb from the increase amount of Vb to the value of Vc before dt.

[0127] 8, the temperature estimation result EST appropriately tracks the changes in the actual surface temperature of the heat roller 71. However, because the temperature estimation result EST is a simulation result, there is a possibility that the absolute value may differ from the actual surface temperature of the heat roller due to differences in conditions, etc.

[0128] The high frequency component extracting unit 83 time-differentiates Vc corresponding to the temperature estimation result EST and extracts the change (ACT 212).

[0129] The high frequency component extraction unit 83 integrates the differential value to configure a high pass filter (ACT213). The high frequency component extraction unit 83 cancels the direct current component in the temperature estimation result EST by the high pass filter, and extracts only the high frequency component. The high frequency component extraction unit 83 generates a high frequency component HPF.

[0130] As shown in FIG. 8, the high frequency component HPF appropriately follows the actual change in the surface temperature of the heat roller 71.

[0131] The coefficient adding unit 84 acquires the temperature detection result Td at the current time from the temperature sensor 74 (ACT 214).

[0132] The coefficient adding unit 84 calculates the corrected temperature value WAE (ACT215). In ACT215, for example, the coefficient adding unit 84 obtains a value obtained by (Td+K×HPF) as the corrected temperature value WAE.

[0133] 9 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 corrected temperature value WAE. In the WAE control, the minute temperature changes of the surface temperature of the heat roller 71 are estimated based on the temperature detection result Td and the high frequency component HPF of the temperature estimation result EST. Therefore, as shown in FIG. 9, the corrected temperature value WAE is a value that appropriately tracks the surface temperature of the heat roller 71.

[0134] The estimation history holding unit 82 overwrites the estimation history PREV with the temperature estimation result EST (ACT 216).

[0135] The temperature estimation unit 81, the high frequency component extraction unit 83, and the coefficient addition unit 84 determine whether or not they have received a command to stop WAE control from the system controller 13 via a control line (not shown) (ACT217). If they have not received a command to stop WAE control, the process transitions from ACT217 to ACT202. If the temperature estimation unit 81, the high frequency component extraction unit 83, and the coefficient addition unit 84 receive a command to stop WAE control, they end the process. Note that the system controller 13 may stop the power supply to the temperature estimation unit 81, the high frequency component extraction unit 83, and the coefficient addition unit 84 instead of supplying a command to stop WAE control to them. In such a configuration, ACT217 becomes unnecessary, and the process transitions from ACT216 to ACT202.

[0136] As shown in FIG. 4, in the heater energization control circuit 14, the failure determination unit 91 acquires the current temperature detection result Td from the temperature sensor 74 (ACT101).

[0137] Furthermore, the failure determination unit 91 acquires the temperature estimation result EST calculated by the temperature estimation unit 81 in ACT 211 (ACT 102).

[0138] The failure determination unit 91 determines whether or not a failure has occurred in the temperature detection element based on the acquired temperature detection result Td and temperature estimation result EST and the failure determination difference DT from the system controller 13 (ACT103).

[0139] The failure determination unit 91 outputs the failure determination result JR to the selection unit 85 and the system controller 13 (ACT104).

[0140] The selection unit 85 checks whether the fault judgment result JR is a fault (ACT105). If no fault has occurred, that is, if it is a normal time (NO), the process proceeds from ACT105 to ACT106. On the other hand, if a fault has occurred (YES), the process proceeds from ACT105 to ACT114.

[0141] First, normal operation without any malfunction will be described. If no failure has occurred, the selection unit 85 selects the corrected temperature value WAE calculated in ACT 215 above, and outputs it to the difference comparison unit 86 (ACT 106).

[0142] The difference comparison unit 86 acquires the target temperature TGT from the system controller 13 (ACT107).

[0143] The difference comparison unit 86 calculates the difference DIF based on the comparison between the target temperature TGT and the corrected temperature value WAE output from the selection unit 85 (ACT108).

[0144] The control duty generating section 87 generates a duty value DUTY based on the difference DIF (ACT109).

[0145] The external limit unit 88 reflects the system protection information LMT on the duty value DUTY and limits the duty value (ACT110). In ACT110, for example, the external limit unit 88 generates a duty value LD based on the duty value DUTY by reflecting the system protection information LMT on the duty value DUTY.

[0146] The duty pulse conversion unit 89 converts the duty value LD into an energizing pulse train (ACT111). The duty pulse conversion unit 89 generates energizing pulses Ps that form the energizing pulse train.

[0147] The duty pulse conversion unit 89 outputs an energizing pulse Ps that constitutes an energizing pulse train in synchronization with the AC voltage (ACT112).

[0148] Each part of the heater energization control circuit 14 determines whether or not it has received an operation stop command from the system controller 13 via a control line (not shown) (ACT113). If it has not received an operation stop command, the process transitions from ACT113 to ACT101. If the heater energization control circuit 14 receives an operation stop command, it ends the process. Note that instead of supplying a stop command for the heater energization control circuit 14 to each part of the heater energization control circuit 14, the system controller 13 may stop the power supply to those parts. In such a configuration, ACT113 is unnecessary, and the process transitions from ACT112 to ACT101.

[0149] As described above, when the heater energization control circuit 14 processes a certain cycle (the current cycle), it performs WAE control based on the values ​​in the previous cycle (duty value LD and temperature estimation result EST: estimation history PREV) and the temperature detection result Ts in the current cycle. That is, the heater energization control circuit 14 inherits the values ​​in the next cycle. The heater energization control circuit 14 recalculates the temperature estimation calculation based on the history of the previous calculation. Therefore, the heater energization control circuit 14 is constantly performing calculations during operation. In the heater energization control circuit 14, the calculation results are stored in a memory or the like and are reused in the calculation of the next cycle.

[0150] FIG. 10 is an explanatory diagram for explaining the processing cycle in the heater current control circuit 14. The horizontal axis in FIG. 10 indicates time. For example, the temperature estimation unit 81 performs temperature estimation processing at time t(n), performs the next temperature estimation processing at t(n+1) which is advanced by dt from the time t(n), and performs the next temperature estimation processing at t(n+2) which is advanced by a further dt. In this manner, the temperature estimation unit 81 repeatedly performs temperature estimation processing. In each cycle of temperature estimation processing, the temperature estimation unit 81 uses the previous temperature estimation result EST to estimate a new temperature.

[0151] At time t(n), the temperature detection result Td at time t(n), the duty value LD at the previous time t(n-1), and the temperature estimation result EST (estimation history PREV) at the previous time t(n-1) are used. The temperature estimation unit 81 performs processing based on the input signal and outputs the temperature estimation result EST at time t(n). The high frequency component extraction unit 83, the coefficient addition unit 84, the difference comparison unit 86, the control duty generation unit 87, the external limit unit 88, and the duty pulse conversion unit 89 perform processing based on the input signal, and the duty pulse conversion unit 89 outputs the energization pulse Ps at time t(n).

[0152] At time t(n+1), the temperature detection result Td newly detected at time t(n+1), the duty value LD at time t(n), and the estimation history PREV which is the temperature estimation result EST at time t(n) are used. The temperature estimation unit 81 performs processing based on the input signal, and outputs the temperature estimation result EST at time t(n+1). The high frequency component extraction unit 83, the coefficient addition unit 84, the difference comparison unit 86, the control duty generation unit 87, the external limit unit 88, and the duty pulse conversion unit 89 perform processing based on the input signal, and the duty pulse conversion unit 89 outputs the energization pulse Ps at time t(n+1).

[0153] At time t(n+2), a temperature detection result Td newly detected at time t(n+2), a duty value LD at time t(n+1), and an estimation history PREV which is a temperature estimation result EST at time t(n+1) are input to a temperature estimation unit 81. The temperature estimation unit 81 performs processing based on the input signals, and outputs a temperature estimation result EST at time t(n+2). A high frequency component extraction unit 83, a coefficient addition unit 84, a difference comparison unit 86, a control duty generation unit 87, an external limit unit 88, and a duty pulse conversion unit 89 perform processing based on the input signals, and the duty pulse conversion unit 89 outputs a current application pulse Ps at time t(n+2).

[0154] The infinitesimal time dt may be a fixed value or may be set in the initial value setting. For example, the infinitesimal time dt is set to 100 [msec].

[0155] The target temperature TGT according to the status of the printing process will be described. FIG. 11 is an explanatory diagram for explaining an example of the target temperature TGT according to the status of the printing process. The horizontal axis of Fig. 11 represents time. The vertical axis of Fig. 11 represents temperature. The solid line represents the target temperature TGT. The dashed line represents the actual surface temperature of the heat roller 71.

[0156] The status of the printing process includes various statuses related to the printing process. For example, the status of the printing process includes, but is not limited to, inrush current prevention, startup heating, ready, start printing, printing, and energy saving ready. The target temperature TGT of each status is different from each other. The target temperature TGT of each status may be predetermined or may be variable.

[0157] 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 so that the reference temperature suitable for printing is reached quickly. 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 printing preparations are complete. In the print start status, the target temperature TGT is set higher than the target temperature TGT in the printing status from a little 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 status continues for a long time, the target temperature TGT is set lower than the target temperature TGT in the ready status.

[0158] The relationship between the difference DIF and the duty value DUTY will be described. Fig. 12 is a diagram for explaining the relationship between the difference DIF and the duty value DUTY. The horizontal axis of Fig. 12 represents the difference DIF. The vertical axis of Fig. 12 represents the duty value DUTY. The solid line represents the relationship between the difference DIF and the duty value DUTY.

[0159] Here, the center value of the duty, which is the duty value DUTY when the difference DIF is 0, is set to 45%. The maximum value of the difference DIF is set to 1, and the minimum value of the difference DIF is set to -1. The duty value DUTY when the difference DIF is at its maximum value is set to 0. The duty value DUTY when the difference DIF is at its minimum value is set to 100. The relationship between the difference DIF and the duty value DUTY is expressed as a linear function based on the above settings. In this example, the duty value DUTY = 45 - difference DIF x slope (45 / 1).

[0160] When the correction temperature value WAE is lower than the target temperature TGT, the duty value DUTY is higher than the center value of the duty. On the other hand, when the correction temperature value WAE is higher than the target temperature TGT, the duty value DUTY is lower than the center value of the duty. The control duty generating unit 87 generates the duty value DUTY based on the difference DIF for each processing cycle, using the relationship between the difference DIF and the duty value DUTY illustrated in FIG.

[0161] The energizing pulse train generated by the duty pulse conversion unit 89 will be described. FIG. 13 is a diagram for explaining the energizing pulse train generated by the duty pulse conversion unit 89. As shown in FIG.

[0162] Here, the energization pulse train is represented by 10 pulses. One pulse is 10 ms. Each square represents one pulse. The shaded squares are energization pulses Ps that indicate a "1" signal for conduction (ON). The white squares represent a "0" signal for interruption (OFF). When the duty value DUTY is 0%, the 10 squares representing the energization pulse train are all white. Therefore, a 100 ms energization pulse train is a "0" signal for 100% of the 100 ms. When the duty value DUTY is 20%, the 10 squares representing the energization pulse train include two shaded squares. Therefore, a 100 ms energization pulse train is a "1" signal for 20% of the 100 ms, and a "0" signal for 80% of the 100 ms. When the duty value DUTY is 50%, the 10 squares representing the energization pulse train include five shaded squares. Therefore, in a 100 ms energization pulse train, 50% of the 100 ms is a "1" signal, and 50% of the 100 ms is a "0" signal. When the duty value DUTY is 50%, the 10 squares representing the energization pulse train include 8 shaded squares. Therefore, in a 100 ms energization pulse train, 80% of the 100 ms is a "1" signal, and 20% of the 100 ms is a "0" signal. When the duty value DUTY is 100%, all 10 squares representing the energization pulse train are shaded squares. Therefore, in a 100 ms energization pulse train, 100% of the 100 ms is a "1" signal.

[0163] The relationship between the duty value and the generated power, and between the energizing pulse train and the generated power will be described. FIG. 14 is a diagram for explaining the relationship between the duty value and the generated power, and between the energizing pulse train and the generated power. The horizontal axis of Fig. 14 represents the duty value, and the vertical axis of Fig. 14 represents the amount of power.

[0164] According to the relationship between the duty value and the generated power and between the pulse train and the generated power, it can be seen that the duty value and the pulse train are in a proportional relationship. Note that this is the case when the resistance value of the heat roller 71 is constant. If the resistance value of the heat roller 71 changes, the relationship between the duty value and the amount of power may be corrected using a table. Even in this case, the relationship between the duty value and the pulse train is proportional. Therefore, it can be seen that the duty value can be used instead of the energization pulse Ps in order for the temperature estimation unit 81 to generate the temperature estimation result EST.

[0165] An example of the duty value sampling will be described. FIG. 15 is a diagram for explaining an example of sampling of duty values ​​according to an embodiment. As can be seen from a comparison between the duty value indicated by the duty value LD shown in Fig. 15 and the detection result of the duty value, the processor uses a self-generated duty value, so the duty value can be detected without delay. Also, as can be seen from the sampling interval shown in Fig. 15, the processor uses a self-generated duty value, so high-speed sampling is not required.

[0166] Next, the above-mentioned WAE control will be explained using a specific numerical example. The parameters corresponding to the V, C, and R elements constituting the thermal circuit illustrated in FIG. Heat source V1 is 500+273 (Kelvin). Outside air temperature V2 is 25+273 (Kelvin). Heating resistance R1 is 10 (Ω). Heat dissipation resistance R2 is 2 (Ω). Outside air resistance R3 is 5 (Ω). Heater capacity C1 is 10 (F). Unit capacity C2 is 100 (F).

[0167] In this case, the values ​​in the WAE control are as follows: The temperature estimation result EST is 126+273 (Kelvin). The temperature detection result Td is 115+273 (Kelvin). The high frequency component HPF is 5 (Kelvin). The coefficient K is 1. The corrected temperature value WAE is Td+K×HPF=115+273+5×1. The target temperature TGT is 118+273 (Kelvin). The difference DIF is WAE-TGT=2. The duty value DUTY is 48. When the energization pulse train is expressed by 10 pulses, the duty value LD is 50. In this case, five of the ten pulses that express the energization pulse train are energization pulses Ps. When the energization pulse train is expressed by 100 pulses, the duty value LD is 48. In this case, 48 of the 100 pulses that express the energization pulse train are energization pulses Ps.

[0168] The temperature estimation unit 81 may take AC voltage fluctuations into account.

[0169] When the AC voltage is 100V, E1 is 400 and R1 is 100Ω. The duty value indicated by the duty value LD is 100%. In this case, the input power is E1×E1 / R1=1600 (Watt).

[0170] When the AC voltage is 110V, E1 is 400×110 / 100=440, and R1 is 100Ω. The duty value indicated by the duty value LD is 100%. In this case, the input power is E1×E1 / R1=1936 (Watt).

[0171] When the AC voltage is 90V, E1 is 400×90 / 100=360, and R1 is 100Ω. The duty value indicated by the duty value LD is 100%. In this case, the input power is E1×E1 / R1=1296 (Watt).

[0172] Next, an operation will be described in the case where a failure occurs in a temperature detection element, such as an abnormality in the temperature sensor itself or a break in the transmission path of the temperature detection result. As shown in FIG. 7, the temperature bias correction unit 92 acquires the preset bias value TP from the system controller 13 (ACT301).

[0173] Furthermore, the temperature bias correction unit 92 acquires the temperature estimation result EST calculated by the temperature estimation unit 81 in ACT 211 (ACT 302).

[0174] Then, the temperature bias correction unit 92 calculates a bias corrected temperature value TBC by adding the acquired preset bias value TP and the temperature estimation result EST (ACT303).

[0175] The temperature bias correction unit 92 judges whether or not it has received a command to stop the calculation operation of the bias correction temperature value TBC from the system controller 13 via a control line (not shown) (ACT304). If it has not received a command to stop the calculation operation of the bias correction temperature value TBC, the process transitions from ACT304 to ACT302. If the temperature bias correction unit 92 receives a command to stop the calculation operation of the bias correction temperature value TBC, it ends the process. Note that the system controller 13 may stop the power supply to the temperature bias correction unit 92 instead of supplying a command to stop the calculation operation of the bias correction temperature value TBC to the temperature bias correction unit 92. In such a configuration, ACT304 is unnecessary, and the process transitions from ACT303 to ACT302.

[0176] As shown in FIG. 5, if a failure occurs, the selection unit 85 acquires the bias-corrected temperature value TBC calculated in ACT 303 above (ACT 114).

[0177] Then, the selection unit 85 selects the acquired bias corrected temperature value TBC and outputs it to the difference comparison unit 86 (ACT115).

[0178] The following ACT116 to ACT121 are the same as the above-mentioned ACT107 to ACT112. However, the object for calculating the difference with the target temperature TGT in ACT117 is the bias correction temperature value TBC output from the selection unit 85, whereas the object for calculating the difference with the target temperature TGT in ACT108 is the correction temperature value WAE.

[0179] Then, in ACT122, each part of the heater energization control circuit 14 determines whether or not it has received an operation stop command from the system controller 13 via a control line (not shown), similar to ACT113. If it has not received an operation stop command, the process transitions from ACT122 to ACT114. If it has received an operation stop command, the heater energization control circuit 14 ends the process.

[0180] Next, the operation of the system controller 13 upon receiving the failure determination result JR from the heater energization control circuit 14 will be described. 16 is a flowchart for explaining the operation of the processor 22 relating to failure judgment. The operation shown in FIG. 16 is started when the power supply of the image forming apparatus 1 is turned on.

[0181] The processor 22 transmits an operation start command to the heater energization control circuit 14 (ACT1). That is, the processor 22 starts the operation of the heater energization control circuit 14.

[0182] Then, the processor 22 waits to receive the failure determination result JR from the failure determination unit 91 of the heater energization control circuit 14 (ACT2).

[0183] When the fault judgment result JR is received, the processor 22 checks whether the fault judgment result JR indicates a fault or not (ACT3). If no fault has occurred, that is, if the time is normal (NO), the process transitions from ACT3 to ACT2. On the other hand, if a fault has occurred (YES), the process transitions from ACT3 to ACT4.

[0184] If a failure has occurred, the processor 22 determines whether printing is currently in progress (ACT4). If printing is not in progress (NO), the process transitions from ACT4 to ACT5. On the other hand, if printing is in progress (YES), the process transitions from ACT4 to ACT8.

[0185] First, the case where printing is not in progress will be described. In this case, the processor 22 stops the printing operation (ACT5). That is, the processor 22 stops the operation of each unit involved in the printing operation, including the conveying unit 19, the image forming unit 20, and the fixing unit 21. It can also be said that the processor 22 prohibits subsequent printing operations if printing is not in progress.

[0186] Furthermore, the processor 22 transmits an operation stop command to the heater current control circuit 14 (ACT6). That is, the processor 22 ends the operation of the heater current control circuit 14. It can also be said that the processor 22 prohibits the heater current control circuit 14 from operating thereafter.

[0187] Then, the processor 22 notifies the occurrence of the failure (ACT7) and ends the process. The processor 22 transmits an error notification to notify the occurrence of the failure to, for example, a server device on the cloud via the communication interface 12. This error notification can include an error code indicating that a failure has occurred in a temperature detection element including the temperature sensor 74 and the transmission path of the temperature detection result Td, and a machine ID for identifying the image forming device 1. The server device that receives this error notification can automatically arrange for a serviceman to inspect and repair the image forming device 1.

[0188] Of course, in addition to or instead of this, the processor 22 may also notify the user of the occurrence of the failure by displaying on the display unit 15 a message indicating that a failure has occurred in the temperature detection element including the temperature sensor 74 and the transmission path of the temperature detection result Td, or an error code indicating the failure. Furthermore, if the image forming apparatus 1 is equipped with a speaker, the processor 22 can generate an error sound in addition to this display. The user who has been notified of the occurrence of the failure in this way can arrange for a serviceman to inspect and repair the device.

[0189] Next, the case where printing is in progress will be described. In this case, the processor 22 determines whether the remaining number of prints, that is, the number of unprinted print sheets, is equal to or less than a specified number (ACT8).

[0190] The processor 22 can know the remaining number of copies to be printed based on information stored in the memory 23, such as the number of copies to be printed (number of page sets) and the number of sheets to be printed per copy (number of pages), and based on the number of sheets that have already been printed.

[0191] The specified number of sheets is a small number, such as 5 sheets, that does not affect the print quality so much even if the temperature control is based on the bias correction temperature value TBC instead of the correction temperature value WAE. In the temperature control based on the bias correction temperature value TBC instead of the correction temperature value WAE, the accuracy decreases as time passes, compared to the temperature control based on the correction temperature value WAE. Therefore, it is preferable to keep the temperature control based on the bias correction temperature value TBC for a period in which the accuracy of the temperature control does not decrease so much. In one print set specified by a print job, printing is repeated on each print medium P, each of which takes a certain time, so the elapsed time can be expressed as the number of prints. Therefore, in this embodiment, the time at which the required temperature control accuracy is obtained is specified by the specified number of sheets. The specified number of sheets can be stored in advance in the memory 23 as a plurality of values ​​determined based on conditions such as the required print quality, the print quality performance of the image forming unit 20, and the print medium to be used. The processor 22 selects one of a plurality of specified numbers of sheets based on information stored in the memory 23, such as information indicating whether the print job is color printing or monochrome printing, and information indicating the print medium P to be used for printing.

[0192] For example, if the number of printed sheets is 5, the number of printed sheets indicated in the print job is 10, and the specified number is 5, the processor 22 determines that the number of remaining prints is equal to or less than the specified number. If the number of remaining prints is equal to or less than the specified number (YES), the process transitions from ACT8 to ACT9. If the number of printed sheets is 5, the number of printed sheets indicated in the print job is 100, and the specified number is 5, the processor 22 determines that the number of remaining prints exceeds the specified number. If the number of remaining prints is not equal to or less than the specified number (NO), the process transitions from ACT8 to ACT10.

[0193] If the number of remaining prints is equal to or less than the specified number, the processor 22 continues the printing operation (ACT9). Then, when printing of the remaining number of prints is completed, the process transitions from ACT9 to ACT5 above, and the printing operation is stopped. This ensures that the printing of the print medium P in the middle of printing is completed without stopping at the position of the heat roller 71 of the fixing unit 21, and the print medium P is discharged to the paper discharge tray 18. It can be said that the processor 22 controls the print medium P so that it does not stop at the position of the heat roller 71 when stopping the printing operation using the fixing unit 21.

[0194] Also, if the remaining number of prints exceeds the specified number, the processor 22 continues the printing operation up to the specified number of remaining prints (ACT10). For example, if the number of printed sheets is 5, the number of printed sheets indicated in the print job is 100, and the specified number is 5, the processor 22 prints the sixth to tenth sheets. Note that, in order to increase the printing speed, there is also an image forming apparatus 1 in which the printing operation for the next print medium P is started without waiting for the ejection of the printed print medium P. In the case of such an image forming apparatus 1, the processor 22 controls so that the printing of the next eleventh print medium P is not started at the stage when the tenth print medium P is taken out from the paper tray 17. In this way, when the printing of the tenth sheet, which has reached the specified number, is completed, the process transitions from ACT10 to the above ACT5, and the printing operation is stopped. Therefore, in this case as well, the printing of the print medium P in the middle of printing is completed without stopping at the position of the heat roller 71 of the fixing device 21, and the print medium P is ejected to the paper ejection tray 18.

[0195] In ACT8, it is determined whether the remaining number of prints is equal to or less than a specified number, but it is of course possible to determine whether the remaining number of prints is less than the specified number.

[0196] In this way, if a failure occurs in the temperature detection element including the temperature sensor 74 and the transmission path of the temperature detection result Td during printing, the heater energization control circuit 14 detects the occurrence of the failure based on the temperature estimation result EST for WAE control, and controls energization to the heat roller 71 of the fixing unit 21 based on the bias-corrected temperature value TBC obtained by bias-correcting the temperature estimation result EST with the preset bias value TP, thereby allowing the image forming apparatus 1 to continue the printing operation. Then, the image forming apparatus 1 stops printing at a convenient point, makes an automatic service call to the server device through the communication interface 12, and displays the reason for the error to the user through the display unit 15. A convenient point to stop printing is a point where the print medium P being printed does not stop at the position of the heat roller 71.

[0197] Although the temperature estimating section 81 uses the duty value LD from the external limiting section 88 when estimating the temperature estimation result EST, the energizing pulse Ps from the duty pulse converting section 89 may be used instead.

[0198] In addition, the calculation operation of the bias correction temperature value TBC shown in FIG. 7 has been described as starting when the power is turned on, but it may also be started in response to the failure judgment result JR being judged to be a failure in ACT105.

[0199] As described above, the image forming apparatus 1 includes a fixing unit 21 having a heat roller 71 that heats a toner image formed on a print medium P to fix the toner image on the print medium P, and a heater 73 that heats the heat roller 71, and a temperature control device (heater current control circuit 14). The heater current 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 current control circuit 14 includes a temperature estimation unit 81 that estimates the temperature of the heat roller 71 based on the current supplied to the heater. The heater current control circuit 14 includes a high frequency component extraction unit 83 and a coefficient addition unit 84 as a temperature correction unit that calculates a correction temperature value WAE based on the temperature estimation result EST by the temperature estimation unit 81 and the temperature detection result Td of the heat roller 71, which is the control target, by the temperature sensor 74. The heater energization control circuit 14 includes a temperature bias correction unit 92 that calculates a bias-corrected temperature value TBC by correcting the temperature estimation result EST with a preset bias value TP, a failure determination unit 91 that determines a failure in the temperature sensor 74 or the transmission path of the temperature detection result Td based on the difference between the temperature estimation result EST and the temperature detection result Td, and a selection unit 85 that selects the corrected temperature value WAE or the bias-corrected temperature value TBC based on the determination result of the failure determination unit 91. The heater energization control circuit 14 includes a difference comparison unit 86, a control duty generation unit 87, an external limit unit 88, and a duty pulse conversion unit 89 as signal generation units that output an energization pulse Ps for controlling the power supplied to the heater 73 based on the selected corrected temperature value WAE or bias-corrected temperature value TBC.

[0200] Specifically, if the failure determination result JR from the failure determination unit 91 indicates that there is no failure, the selection unit 85 selects the corrected temperature value WAE, and if it indicates that there is a failure, the selection unit 85 selects the bias corrected temperature value TBC.

[0201] According to this configuration, in a normal state where there is no failure in the temperature sensor 74 or the transmission path of the temperature detection result Td, even if the response of the temperature detection of the heat roller 71 by the temperature sensor 74 is poor, the temperature control device can track the surface temperature of the heat roller 71 based on the temperature estimation result EST and the corrected temperature value WAE based on the temperature detection result Td. This makes it possible to reduce the cost of the temperature sensor 74 and prevent overshoot and temperature ripple. If a failure occurs in the temperature sensor 74 or the transmission path of the temperature detection result Td, the failure determination unit 91 detects this and tracks the surface temperature of the heat roller 71 based on the bias correction temperature value TBC instead of the corrected temperature value WAE based on the temperature detection result Td, that is, ignoring the temperature detection result Td from the inaccurate temperature sensor 74. Therefore, even if a failure occurs in the temperature sensor 74 or the transmission path of the temperature detection result Td, it is possible to suppress an abnormal rise in the temperature of the fixing device. Therefore, since the fixing device 21 does not reach an abnormal temperature, stress is not applied to the parts of the fixing device 21 that may lead to the parts of the fixing device 21 being broken.

[0202] In addition to the temperature sensor 74 that detects the temperature of the heat roller 71 to which heat is transmitted from the heater 73 and outputs the temperature detection result Td, and the heater current control circuit 14, the image forming apparatus 1 is provided with a system controller 13 that prohibits subsequent printing operations when the failure determination result JR of the failure determination unit 91 of the heater current control circuit 14 indicates a failure, unless an image forming operation, i.e., a printing operation, using the fixing unit 21 is being performed.

[0203] With this configuration, the image forming apparatus 1 can prevent printing due to inaccurate temperature control.

[0204] On the other hand, if the failure judgment result JR indicates a failure when printing is instructed for one print set, i.e., multiple sheets of print media P, as specified in the print job, the system controller 13 controls the print media P so that it does not stop at the position of the heat roller 71, and stops the printing operation.

[0205] With this configuration, the print medium P does not stop at the position of the heat roller 71, so there is no need to remove the print medium P that has stopped at the position of the heat roller 71. It is also possible to prevent toner residue from remaining on the heat roller 71, thereby eliminating the risk of toner residue degrading the print quality thereafter.

[0206] Here, when the failure judgment result JR is a failure, if the remaining number of prints in the print set is equal to or less than a predetermined specified number, the system controller 13 continues the printing operation for the print set and then stops the printing operation.

[0207] With this configuration, when the number of remaining prints is small, the image forming apparatus 1 can continue printing by controlling the current supply to the heat roller 71 based on the bias correction temperature value TBC, thereby completing printing while maintaining a certain level of quality.

[0208] On the other hand, when the failure judgment result JR is a failure, if the remaining number of prints in the print set is greater than the specified number, the system controller 13 continues the printing operation on the print media P up to the specified number, and stops the printing operation on the remaining print media P in the print set.

[0209] With this configuration, when there are many remaining prints, the image forming apparatus 1 can continue printing for a specified number of sheets by controlling the current supply to the heat roller 71 based on the bias correction temperature value TBC, so that a certain number of sheets can be printed while maintaining a certain level of quality.

[0210] In addition, the image forming device 1 further includes a communication interface 12 for communicating with an external device, a server device, via a network. If the failure judgment result JR indicates a failure, the system controller 13 transmits an error notification to the server device via the communication interface 12 to notify the occurrence of the failure. The error notification includes an error code indicating that a failure has occurred in the temperature detection element including the temperature sensor 74 and the transmission path of the temperature detection result Td, and a machine ID for identifying the image forming device 1.

[0211] According to this configuration, the image forming apparatus 1 transmits an error notification to the server apparatus, and the server apparatus, upon receiving the notification, can automatically arrange for a service technician to inspect and repair the image forming apparatus 1.

[0212] Alternatively, the image forming apparatus 1 further includes a display unit 15, and when the failure judgment result JR indicates a failure, the system controller 13 causes the display unit 15 to display a message indicating that a failure has occurred in the temperature detection element including the temperature sensor 74 and the transmission path of the temperature detection result Td, or an error code indicating this, as an error indicating the occurrence of a failure.

[0213] With this configuration, the image forming device 1 can notify the user of a malfunction via the display unit 15, and the user, upon seeing this notification, can arrange for a service technician to inspect and repair the image forming device 1.

[0214] The control duty generation unit 87, which constitutes the signal generation unit, generates a duty value DUTY based on the selected correction temperature value WAE or bias correction temperature value TBC and the target temperature TGT, and the duty pulse conversion unit 89, which also constitutes the signal generation unit, outputs an energization pulse Ps for controlling the power supplied to the heater 73 based on the duty value DUTY. The temperature estimation unit 81 estimates the temperature of the heat roller 71 based on the duty value DUTY. The temperature estimation unit 81 estimates the temperature of the heat roller 71 based on the history of the temperature estimation result EST and the duty value DUTY. The control duty generation unit 87 calculates the duty value DUTY based on either the difference DIF between the target temperature TGT and the correction temperature value WAE based on the temperature estimation result EST and the temperature detection result Td, which is calculated by the difference comparison unit 86, which constitutes the signal generation unit, or the difference DIF between the target temperature TGT and the bias correction temperature value TBC obtained by bias-correcting the temperature estimation result EST with the preset bias value TP by the temperature bias correction unit 92.

[0215] According to this configuration, the temperature control device can realize a simple feedback control that is effective for WAE control and can speed up the feedback control when no failure occurs in the temperature sensor 74 or the transmission path of the temperature detection result Td. The temperature control device enables highly accurate temperature control through WAE control and feedback control that is effective for WAE control. As a result, the temperature control device can reduce the cost of the temperature sensor 74 and prevent temperature ripples and the like from occurring. Furthermore, since the temperature control device estimates the temperature of the heat roller 71 based on the duty value DUTY, even if the frequency of the energization pulse is high, there is no need for a mechanism to detect changes in the pulse. Therefore, the temperature control device does not require high-speed sampling, and therefore an increase in the processing load can be suppressed. Therefore, the temperature control device can be realized with an inexpensive processor. The temperature control device is easy to implement firmware. Furthermore, when a failure occurs in the temperature sensor 74 or the transmission path of the temperature detection result Td, it is possible to obtain substantially the same effect, although for a limited time, without using the temperature detection result Td of the temperature sensor 74.

[0216] Further, an external limit unit 88 constituting the signal generating unit limits the duty value DUTY, and a duty pulse converting unit 89 outputs an energizing pulse Ps based on the duty value after the limitation by the external limiting unit 88. A temperature estimating unit 81 estimates the temperature of the heat roller 71 based on the duty value after the limitation.

[0217] According to such a configuration, the temperature control device can prevent danger to the image forming apparatus 1 by limiting the duty value DUTY.

[0218] The above-mentioned temperature control device is not limited to being applied to the image forming apparatus 1. The temperature control device can be applied to various devices that use heat. For example, the temperature control device can be applied to a copying machine, a multifunction machine, or a printing machine that heat-melts toner. The temperature control device can be applied to a furnace that keeps the temperature constant or gradually changes the temperature, and a single crystal material manufacturing machine that pulls crystals from a melting furnace and grows them. The temperature control device can be applied to a color thermal printer that changes color depending on the temperature. The temperature control device can be applied to a melting furnace that manufactures alloys. In the case of a copying machine or a color thermal printer, the printing is beautiful and there is no change in color over time even when printing in large quantities, so that improvement in print quality can be expected. In the case of a melting furnace, since temperature control can be performed precisely, it is possible to expect an improvement in the yield of the manufactured products, improvement in crystal quality (reduction in the crystal defect rate), and improvement in the performance of the alloy.

[0219] The functions described in the above embodiments can be realized not only by hardware but also by software, by loading a program that describes each function into a computer. Also, each function may be realized by selecting either software or hardware as appropriate.

[0220] Although some 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 implemented 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 in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0221] 1...image forming apparatus, 11...housing, 12...communication interface, 13...system controller, 14...heater energization control circuit, 15...display unit, ...operation interface, 17...paper tray, 18...paper output tray, 19...transport unit, 20...image forming unit, 21...fixing unit, 22...processor, 23...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...current imager, 61...primary transfer belt, 62...secondary transfer opposing roller, 63...primary transfer roller, 64...secondary transfer roller, 71...heat roller, 72...press roller, 73...heater, 74...temperature sensor, 81...temperature estimation section, 82...estimation history storage section, 83...high frequency component extraction section, 84...coefficient addition section, 85...selection section, 86...difference comparison section, 87...control duty generation section, 88...external limit section, 89...duty pulse conversion section, 90...power supply circuit, 91...failure determination section, 92...temperature bias correction section.

Claims

1. A temperature control device that controls a temperature of a temperature control target to which heat is propagated from a heater by supplying power to the heater, comprising: a temperature estimating unit that estimates a temperature of the temperature-controlled object based on the power supply to the heater; a temperature correction unit that calculates a temperature correction value based on a temperature estimation result of the temperature estimator and a temperature detection result of the temperature control target by a temperature sensor; a temperature bias correction unit that corrects the temperature estimation result of the temperature estimator by a preset bias value; a failure determination unit that determines a failure of the temperature sensor or a transmission path of the temperature detection result based on a difference between the temperature estimation result of the temperature estimator and a temperature detection result of the temperature control target by a temperature sensor; a selection unit that selects an output of the temperature correction unit or an output of the temperature bias correction unit based on a result of the judgment by the failure judgment unit; a signal generating unit that outputs a current pulse for controlling power supplied to the heater based on the selected output of the temperature correcting unit or the selected output of the temperature bias correcting unit; Equipped with Temperature control device.

2. The selection unit is Selecting an output of the temperature correction unit according to a determination result of the failure determination unit that there is no failure; selecting an output of the temperature bias correction unit according to a determination result of the failure determination unit that a failure has occurred; The temperature control device according to claim 1 .

3. a fixing unit including a fixing rotor that heats a toner image formed on a medium to fix the toner image on the medium, and a heater that heats the fixing rotor; a temperature sensor that detects the temperature of the fixing rotor to which heat is transferred from the heater and outputs the temperature detection result; a temperature control unit that controls a temperature of the fixing rotor to which heat is transferred from the heater by supplying power to the heater, The temperature control unit is a temperature estimating unit that estimates a temperature of the fixing rotor based on the power supply to the heater; a temperature correction unit that calculates a temperature correction value based on a temperature estimation result of the temperature estimation unit and a temperature detection result of the fixing rotor by a temperature sensor; a temperature bias correction unit that corrects the temperature estimation result of the temperature estimator by a preset bias value; a failure determination unit that determines a failure of the temperature sensor or a transmission path of the temperature detection result based on a difference between the temperature estimation result of the temperature estimation unit and a temperature detection result of the fixing rotor by a temperature sensor; a selection unit that selects an output of the temperature correction unit or an output of the temperature bias correction unit based on a result of the judgment by the failure judgment unit; a signal generating unit that outputs a current pulse for controlling power supplied to the heater based on the selected output of the temperature correcting unit or the selected output of the temperature bias correcting unit; A temperature control unit comprising: Equipped with Image forming device.

4. 4. The image forming apparatus according to claim 3, further comprising a controller that, when the judgment result of the failure judgment section of the temperature control section is a failure, prohibits subsequent image forming operations using the fixing unit unless the image forming operation is being performed.

5. The image forming apparatus of claim 4, wherein when the controller is instructed to form an image on a media set including a plurality of media and the judgment result is a failure, the controller controls the media so that the media does not stop at the position of the fixing rotor, thereby stopping the image forming operation.

Images