Temperature control device and image forming apparatus equipped with temperature control device

Abstract

To provide a temperature control unit that determines the presence or absence of a failure from the correlation between a temperature estimated value and a sensor temperature, and performs temperature control of correcting the sensor temperature to an appropriate target temperature for preventing an increase in the temperature of a fuser, and an image forming apparatus comprising the temperature control unit.SOLUTION: A temperature control unit controls power to be supplied to a heater of a fuser on the basis of a temperature estimated value that is estimated with time so that the temperature of a temperature control target, to which heat is propagated from the heater, reaches a target temperature, and comprises a temperature sensor, a first storage circuit, a second storage circuit, a temperature difference detection circuit, and a target temperature correction circuit. The temperature sensor detects the temperature of the heater. The first storage circuit stores the temperature estimated value. The second storage circuit stores a sensor temperature. The temperature difference detection circuit calculates the actual amount of temperature increase from the temperature difference between the temperature estimated value read out from the first storage circuit and the temperature of the heater read out from the second storage circuit. The temperature correction circuit performs control of reducing the target temperature according to the actual amount of temperature increase.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] An image forming apparatus placed in a workplace or the like includes a fixing device that fixes a toner image on a recording medium by applying heat and pressure to the recording medium on which the toner image has been transferred. This fixing device has a temperature sensor that detects the temperature of the surface of a heat roller (fixing member). The fixing device controls the temperature of the surface of the heat roller to reach a target value by increasing or decreasing the amount of power supplied to a heating member (such as a lamp or an IH heater) based on the detection signal of the temperature sensor.

[0003] When foreign matter is sandwiched between the temperature sensor and the heat roller or toner dirt adheres to the temperature sensor, a situation may occur where even though the temperature sensor itself is normal, an accurate temperature cannot be detected. When the temperature sensor cannot detect an accurate temperature, a difference occurs between the temperature of the heat roller and the temperature detected by the temperature sensor, and an inappropriate target value is set and the temperature is controlled. As a result, the temperature of the fixing device rises, leading to the occurrence of high-temperature offset and service calls, and a state where the image forming apparatus cannot operate temporarily occurs.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The problem that the embodiments of the present invention aim to solve is to provide a temperature control device and an image forming apparatus equipped with a temperature control device that perform temperature control to determine a fault in the detected temperature from the correlation between the calculated temperature estimate and the sensor temperature, and correct the temperature to an appropriate target temperature to prevent the temperature of the fuser from rising. [Means for solving the problem]

[0006] A temperature control device according to one embodiment controls the power supplied to a heater based on a temperature estimate estimated over time so that the temperature-controlled object, from which heat is transmitted by the heater of a fuser, reaches a preset target temperature. The temperature control device comprises: a temperature sensor for detecting the temperature of the heater; a first storage circuit for storing the temperature estimate acquired at any given time; a second storage circuit for storing the sensor temperature detected by the temperature sensor; a temperature difference detection circuit for calculating the actual temperature rise from the temperature difference between the temperature estimate read from the first storage circuit and the heater temperature read from the second storage circuit; and a temperature correction circuit for performing control to lower the target temperature according to the actual temperature rise. The target temperature correction circuit has multiple control correction temperatures correlated with the actual temperature rise, which is the difference between the normal temperature of the temperature-controlled target when the heater temperature rises and the current actual temperature of the temperature-controlled target. It generates a corrected target temperature by subtracting the control correction temperature corresponding to the actual temperature rise from the currently set target temperature. . [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a conceptual diagram showing an example of the overall configuration of an image forming apparatus according to one embodiment. [Figure 2] Figure 2 is a block diagram showing an example of the configuration of a temperature control device. [Figure 3] Figure 3 shows an example of the configuration of a heater unit in a fuser. [Figure 4] Figure 4 is a flowchart illustrating WAE control. [Figure 5] Figure 5 shows the measured temperature and the estimated temperature when a gap is left in the center. [Figure 6] Figure 6 shows the measured temperature and the estimated temperature when a gap is left on the side. [Figure 7]Figure 7 shows the temperature characteristics of the center temperature estimate WAE, the actual temperature of the heat roller, and the sensor temperature. [Figure 8] Figure 8 shows the temperature characteristics of the side temperature estimate WAE, the actual temperature of the heat roller, and the sensor temperature. [Figure 9] Figure 9 shows the correlation of temperature rise based on the temperature characteristics of the center. [Figure 10] Figure 10 shows the correlation of temperature rise based on the temperature characteristics of the side. [Figure 11] Figure 11 shows the setting of the control correction temperature in relation to the actual temperature rise of the heat roller. [Figure 12] Figure 12 shows the correlation between the actual temperature rise of the heat roller, the first temperature rise center, and the control correction temperature. [Figure 13] Figure 13 shows the correlation between the actual temperature rise of the heat roller, the first temperature rise, and the control correction temperature. [Figure 14] Figure 14 is a flowchart illustrating the temperature control of the fuser. [Figure 15] Figure 15 shows a second example of the fuser configuration. [Figure 16] Figure 16 shows an example of the heater unit configuration in the fuser of the second configuration example. [Figure 17] Figure 17 shows a third example configuration of the fuser unit. [Figure 18] Figure 18 shows an example of the heater unit configuration in the fuser of the third configuration example. [Figure 19] Figure 19 shows a fourth example of the fuser configuration. [Figure 20] Figure 20 shows an example of the configuration of the heater unit in the fourth example of a fuser. [Figure 21] Figure 21 shows a fifth example of the fuser configuration. [Figure 22] Figure 22 shows an example of the heater unit configuration in the fuser of the fifth configuration example.

Best Mode for Carrying Out the Invention

[0008] Hereinafter, a temperature control device and an image forming apparatus according to an embodiment will be described with reference to the drawings. FIG. 1 conceptually shows an overall configuration example of the image forming apparatus according to this embodiment, and FIG. 2 is a block diagram showing a configuration example of the temperature control device.

[0009] The temperature control device 101 according to an embodiment cooperates with a heater energization control circuit 14 and a temperature control circuit 25 to control the temperature of the fixing device 21 mounted on the image forming apparatus 1 using the difference between the detected temperature (sensor temperature) of the fixing device 21 detected by the temperature sensor 74 and the temperature estimated value WAE obtained by WAE (Weighted Average control with Estimate temperature) control. Either temperature control (first temperature control) by WAE control or control temperature (second temperature control) by a target value corrected by a correction value having a correlation with the sensor temperature detected by the temperature sensor was selected to control the temperature of the fixing device 21.

[0010] As will be described later, WAE control is a technique for simulating the member temperature of the temperature control target as a thermal CR circuit. It is temperature control using the temperature estimated value WAE of the fixing device obtained by estimating (calculating) the surface temperature of the heat roller that is the temperature control target from the heat capacity (C) of the heat roller to be heated, the thermal resistance (R) of the fixing device, the energy input to the fixing device, and the like.

[0011] The image forming apparatus 1 shown in Figure 1 is a multifunction printer (MFP) that is placed in a workplace or the like and performs various processing such as image formation while transporting a recording medium such as printing paper. Alternatively, the image forming apparatus 1 is a solid-state scanning printer (e.g., an LED printer) that scans an LED array and performs various processing such as image formation while transporting a recording medium. These image forming apparatuses 1 are configured to, for example, receive toner from a toner cartridge and form an image on the recording medium using the received toner. The toner may be a single-color toner, or it may be a multi-color toner such as cyan, magenta, yellow, and black. The toner may also be a decolorizing toner that disappears when heat is applied after printing.

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

[0013] The housing 11 is the main body of the image forming apparatus 1. The housing 11 houses a communication interface 12, a system controller 13, a display unit 15, an operation interface 16, multiple paper trays 17, an output tray 18, a transport unit 19, an image forming unit 20, a fuser 21, a heater power supply control circuit 14, and a temperature control circuit 25. The temperature control device 101, which will be described later, is configured using the heater power supply control circuit 14, the temperature control circuit 25, and the temperature sensor 74 of the fuser 21.

[0014] First, I will explain the configuration of the control system for the image forming apparatus 1. The communication interface 12 is a connection device that enables communication with external peripheral devices (such as host devices). The communication interface 12 includes, for example, a network connection terminal for wired connection using a LAN connector. Furthermore, the communication interface 12 may also have a function to perform wireless communication with other devices in accordance with standards such as Bluetooth® or Wi-Fi®.

[0015] The system controller 13 controls the image forming apparatus 1. The system controller 13 includes, for example, a processor 22 and a memory 23. Memory 23 can be a read-only non-volatile memory such as ROM (Read Only Memory), or a non-volatile memory that can be written to and read at any time, such as flash ROM, SSD (Solid State Drive), and HDD (Hard Disk Drive), or a volatile memory that can be written to and read at any time, such as RAM (Random Access Memory). These can be used in combination as appropriate. Memory 23 stores programs and data used by programs. Memory 23 also functions as working memory. That is, memory 23 temporarily stores data being processed by processor 22 and programs executed by processor 22.

[0016] The processor 22 is an arithmetic circuit that includes arithmetic elements such as a CPU (Central Processing Unit). The processor 22 functions as a control unit that executes various operations by running programs stored in the memory 23. The processor 22 also performs various arithmetic and decision-making processes using the data stored in the memory 23.

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

[0018] Furthermore, the processor 22 generates print control information to control the operation of the transport unit 19, the image forming unit 20, and the fuser unit 21 based on the generated print job. The print control information includes information indicating the timing of paper feeding. The processor 22 transmits the print control information to the heater power supply control circuit 14.

[0019] Furthermore, the processor 22 functions as a controller (engine controller) that controls the operation of the transport unit 19 and the image forming unit 20 by executing a program stored in the memory 23. Specifically, the processor 22 controls the transport of the recording medium P by the transport unit 19 and the formation of an image on the recording medium P by the image forming unit 20. In addition, the processor 22 can also control the temperature of the fuser unit 21 by executing functions equivalent to those of the heater power supply control circuit 14 and the temperature control circuit 25 through program processing, instead of the heater power supply control circuit 14 and the temperature control circuit 25.

[0020] The image forming apparatus 1 may also include an engine controller and a system controller 13 separately. In this case, the engine controller controls the transport of the recording medium P by the transport unit 19 and the formation of images on the recording medium P by the image forming unit 20. In this case, the system controller 13 supplies the engine controller with the information necessary for its control operation.

[0021] Furthermore, the image forming apparatus 1 includes a power conversion circuit that uses the AC voltage of an AC power supply to supply DC voltage to each component within the image forming apparatus 1. This power conversion circuit supplies the DC voltage necessary for the operation of the processor 22 and the memory 23 to the system controller 13. The power conversion circuit also supplies the DC voltage necessary for image forming to the image forming unit 20. The power conversion circuit also supplies the DC voltage necessary for transporting the recording medium to the transport unit 19. The power conversion circuit also supplies the DC voltage for driving the heater 73 of the fuser 21 to the heater energization control circuit 14. The heater 73 is a heating element, and for example, a lamp heater or the like may be used.

[0022] The heater power supply control circuit 14 generates power PC and supplies it to the heater 73 of the fuser 21. This heater power supply control circuit 14 is included as a component of the temperature control device 101 in this embodiment. A detailed description of the heater power supply control circuit 14 will be given later. Furthermore, the temperature control circuit 25 performs control to correct the target temperature of the fuser 21 to the heater power supply control circuit 14, which will be described later.

[0023] The display unit 15 includes a display that shows a screen in accordance with the video signal input from the system controller 13. Alternatively, a graphics controller or the like may be used instead of the system controller 13. For example, the display of the display unit 15 may show screens for various settings of the image forming apparatus 1. The main power switch 24 is a switch that supplies / cuts power to drive the image forming apparatus 1 by ON / OFF operation. Turning the main power switch 24 ON starts the image forming apparatus 1, and turning it OFF stops the image forming apparatus 1 from operating. In addition, the fuser unit 21 is also started / stopped by the ON / OFF operation of this main power switch 24.

[0024] The operation interface 16 is connected to the operation components described below. The operation interface 16 supplies operation signals to the system controller 13 in response to the operation of the operation components. The operation components include, for example, a touch sensor, a numeric keypad, a paper feed key, various function keys, or a keyboard. The touch sensor acquires information indicating a specified position within a certain area. The touch sensor is configured as a touch panel integrated with the display unit 15, and inputs a signal indicating the touched position on the screen displayed on the display unit 15 to the system controller 13.

[0025] Multiple paper trays 17 are detachably mounted on the housing 11 and are cassettes that house recording media P of the same or different sizes, each in its own cassette unit. The paper trays 17 supply the recording media P to the transport unit 19. The output tray 18 is a tray that supports the recording media P discharged from the image forming apparatus 1.

[0026] Next, the heater unit in the fuser 21 of the image forming apparatus 1 will be described. Figure 3 shows an example of the configuration of the heater unit in the fuser 21. In this heater unit, the heater 73 is composed of multiple heat sources, which generate heat using electricity supplied from the heater control circuit 14. In the first configuration example shown in Figures 1 and 3, the heater 73 in the fuser 21 has two heat sources (heat sources): a center heater 73a and a side heater 73b. For example, halogen heaters, lamp heaters, induction heaters, and resistance heaters can be used for the center heater 73a and side heater 73b.

[0027] The heater 73 in this fuser unit 21 consists of two heaters: a center heater 73a and a side heater 73b. The center heater 73a heats the central part (center region C) of the heat roller 71 in the direction of the rotation axis. The side heater 73b heats the peripheral part (side region S) of the heat roller 71 other than the central part in the direction of the rotation axis. The printing medium P is transported in the transport direction F shown in Figure 3. For example, the lengths of the center region C and the side region may be set according to the size of the medium used as the printing medium P.

[0028] The center heater 73a and the side heater 73b generate heat through power supplied by the control of the system controller 13. The power consumption of the center heater 73a and the side heater 73b is, for example, 600W.

[0029] When the system controller 13 performs a fixing process on a printing medium P that is narrow in the direction of rotation of the heat roller 71 (the transport direction F of the printing medium P), it heats the center region C of the heat roller 71. When the system controller 13 heats the center region C of the heat roller 71, it supplies power to the center heater 73a via the heater control circuit 14 and stops supplying power to the side heater 73b.

[0030] Furthermore, when the system controller 13 performs a fixing process on a printing medium P that is wide in the direction of rotation of the heat roller 71 (the transport direction F of the printing medium P), it heats the entire heat roller 71 (both the center region C and the side region S). When the system controller 13 heats the entire heat roller 71, it activates both the center heater 73a and the side heater 73b using the heater control circuit 14.

[0031] The temperature sensors 74a and 74b have contact portions (detection portions) that contact the surface of the heat roller 71 and detect the temperature of the area that the contact portion contacts. The temperature sensors 74a and 74b are, for example, thermistors. The temperature sensors 74a and 74b are arranged parallel to the rotation axis of the heat roller 71. In the first configuration example shown in Figure 3, the temperature sensor 74a detects the temperature of the center region (the central part when divided into three parts in the direction of rotation) C of the heat roller 71 in the direction of rotation. The temperature sensor 74b detects the temperature of the side region (any side part when divided into three parts in the direction of rotation) S of the heat roller 71 in the direction of rotation.

[0032] Each temperature sensor 74a and 74b has a contact portion (detection portion) that contacts the surface of the heat roller 71. Temperature sensor 74a detects the temperature of the center region C of the heat roller 71 by the detection portion contacting the surface of the center region C of the heat roller 71. Temperature sensor 74b detects the temperature of the side region S of the heat roller 71 by the detection portion contacting the surface of the side region S of the heat roller 71.

[0033] Each temperature sensor 74a and 74b supplies a temperature detection result signal indicating the temperature detection result to the temperature control circuit 25 and the heater power supply control circuit 14. When heating the center region C of the heat roller 71, the heater power supply control circuit 14 activates the center heater 73a based on the temperature detected by temperature sensor 74a. When heating the entire heat roller 71, the system controller 13 activates the center heater 73a and the side heaters 73b based on the temperatures detected by temperature sensors 74a and 74b.

[0034] Next, we will describe the configuration for transporting the recording medium P of the image forming apparatus 1. The transport unit 19 is a mechanism for transporting the recording medium P within the image forming apparatus 1. As shown in Figure 1, the transport unit 19 is equipped with multiple transport paths. For example, the transport unit 19 is equipped with a paper feed transport path 31 and a paper discharge transport path 32.

[0035] The paper feed path 31 and the paper discharge path 32 are each composed of multiple motors, multiple rollers, and multiple guides. The multiple motors rotate their shafts based on the control of the system controller 13, thereby rotating the rollers that are driven by the rotation of the shafts. The multiple rollers move the recording medium P by rotating. The multiple guides prevent the recording medium P from tilting during transport.

[0036] The paper feed transport path 31 takes in recording media P from each paper tray 17 using pickup rollers 33 and supplies each of the taken recording media P to the image forming unit 20. The paper output transport path 32 is a transport path that discharges the recording medium P on which the image has been formed from the housing 11. The recording medium P discharged by the paper output transport path 32 is placed in the paper output tray 18.

[0037] Next, the image forming unit 20 will be described. The image forming unit 20 forms an image on the recording medium P based on a print job generated by the processor 22. The image forming unit 20 comprises a plurality of process units 41, a plurality of exposure units 42, and a transfer mechanism 43. The image forming unit 20 includes an exposure unit 42 for each process unit 41. The plurality of process units 41 and the plurality of exposure units 42 each have the same configuration.

[0038] First, let's explain the process unit 41. The process unit 41 is connected to toner cartridges that supply toner of different colors, forming a toner image. Multiple process units 41 are provided for each toner color, corresponding to, for example, cyan, magenta, yellow, and black color toners. The toner cartridge comprises a toner storage container and a toner delivery mechanism. The toner storage container is a container that supplies the toner to be stored. The toner delivery mechanism is a mechanism consisting of a screw or the like that delivers the toner from the toner storage container.

[0039] The following description will use a set of process units 41 and exposure unit 42 as representative examples. The process unit 41 includes a photosensitive drum 51, a charging charger 52, and a developing unit 53. The photosensitive drum 51 is a photosensitive body composed of a cylindrical drum and a photosensitive layer formed on the outer surface of the drum. The photosensitive drum 51 rotates at a constant speed by a drive mechanism consisting of gears and belts.

[0040] The charging charger 52 uniformly charges the surface of the photosensitive drum 51. For example, the charging 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 in accordance with the rotation of the photosensitive drum 51 while applying a predetermined pressure to the photosensitive drum 51.

[0041] The developer unit 53 is a device that deposits toner onto the photosensitive drum 51. The developer unit 53 includes a developer container, an agitation mechanism, a developing roller, a doctor blade, and an automatic toner control (ATC) sensor. The developer container is a container that receives and stores the toner dispensed from the toner cartridge. A carrier is pre-stored inside the developer container. The toner dispensed from the toner cartridge is agitated with the carrier by the agitation mechanism, thereby forming a developer mixture of toner and carrier. The carrier is stored inside the developer container during the manufacturing of the developer unit 53.

[0042] Of these components, the developing roller rotates within the developer container, applying developer to its surface. The doctor blade is positioned at a predetermined distance from the surface of the developing roller. The doctor blade partially removes the top portion of the developer adhering to the surface of the rotating developing roller. This creates a layer of developer on the surface of the developing roller of a certain thickness, corresponding to the distance between the doctor blade and the surface of the developing roller.

[0043] The ATC sensor is, for example, a magnetic flux sensor that has a coil and detects the voltage value generated in the coil. The voltage detected by the ATC sensor changes depending on the density of the magnetic flux from the toner in the developer container. That is, the system controller 13 determines the density ratio of the toner remaining in the developer container to the carrier (toner density ratio) based on the voltage detected by the ATC sensor. Based on the toner density ratio, the system controller 13 operates the motor that drives the toner cartridge delivery mechanism and delivers toner from the toner cartridge to the developer container of the developer unit 53.

[0044] Next, we will describe the exposure unit 42. The exposure unit 42 is equipped with multiple light-emitting elements. The exposure unit 42 forms a latent image on the charged photosensitive drum 51 by irradiating the photosensitive drum 51 with light from the light-emitting elements. The light-emitting elements are, for example, light-emitting diodes (LEDs). Each light-emitting element is configured to irradiate light onto a single point on the photosensitive drum 51. The multiple light-emitting elements are arranged in the main scanning direction, which is parallel to the rotation axis of the photosensitive drum 51.

[0045] The exposure unit 42 forms a single line of latent image on the photosensitive drum 51 by irradiating it with light using multiple light-emitting elements arranged in the main scanning direction. Furthermore, the exposure unit 42 forms multiple lines of latent image by continuously irradiating the rotating photosensitive drum 51 with light.

[0046] In the process unit 41 with the above configuration, when light is shone from the exposure unit 42 onto the surface of the photosensitive drum 51, which has been charged by the charging charger 52, an electrostatic latent image is formed. Furthermore, when the layer of developer formed on the surface of the developing roller comes into close proximity to 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.

[0047] Next, the transcription mechanism 43 will be explained. The transfer mechanism 43 transfers the toner image formed on the surface of the photosensitive drum 51 to the recording medium P. The transfer mechanism 43 includes, for example, a primary transfer belt 61, a secondary transfer opposing roller 62, a plurality of primary transfer rollers 63, and a secondary transfer roller 64.

[0048] The primary transfer belt 61 is an endless belt wound around the secondary transfer opposing roller 62 and a plurality of winding rollers. The inner surface (inner circumferential surface) of the primary transfer belt 61 is in contact with the secondary transfer opposing roller 62 and the plurality of winding rollers, while the outer surface (outer circumferential surface) faces the photosensitive drum 51 of the process unit 41.

[0049] The secondary transfer opposing roller 62 is rotated using a motor as a drive source. By rotating, the secondary transfer opposing roller 62 conveys the primary transfer belt 61 in a predetermined conveying direction. Multiple winding rollers are configured to rotate freely. Multiple winding rollers rotate in accordance with the movement of the primary transfer belt 61 by the secondary transfer opposing roller 62.

[0050] Each of the multiple primary transfer rollers 63 brings the primary transfer belt 61 into contact with the photosensitive drum 51 of the process unit 41. Specifically, each of the multiple primary transfer rollers 63 is positioned opposite the corresponding photosensitive drum 51 of the process unit 41, with the primary transfer belt 61 in between. The primary transfer rollers 63 contact the inner circumferential surface of the primary transfer belt 61, displacing the primary transfer belt 61 toward the photosensitive drum 51. As a result, the primary transfer rollers 63 bring the outer circumferential surface of the primary transfer belt 61 into contact with the photosensitive drum 51.

[0051] The secondary transfer roller 64 is positioned opposite the secondary transfer opposing roller 62, with the primary transfer belt 61 in between. The secondary transfer roller 64 contacts and applies pressure to the outer surface of the primary transfer belt 61. This forms a transfer nip where the secondary transfer roller 64 and the outer surface of the primary transfer belt 61 are in close contact. As the recording medium P passes through, the secondary transfer roller 64 presses the recording medium P passing through the transfer nip against the outer surface of the primary transfer belt 61.

[0052] The secondary transfer roller 64 and the secondary transfer opposing roller 62 rotate to transport the recording medium P supplied from the paper feed transport path 31 while gripping it. This allows the recording medium P to pass through the transfer nip.

[0053] In the transfer mechanism 43 with the configuration described above, when the outer surface of the primary transfer belt 61 comes into contact with the photosensitive drum 51, the toner image formed on the surface of the photosensitive drum is transferred to the outer surface of the primary transfer belt 61. If the image forming unit 20 has multiple process units 41, the toner image is transferred from the photosensitive drums 51 of the multiple process units 41 to the outer surface of the primary transfer belt 61. The transferred toner image is then transported by the primary transfer belt 61 to a transfer nip where the secondary transfer roller 64 and the outer surface of the primary transfer belt 61 are in close contact. If a recording medium P is present at the transfer nip, the toner image transferred to the outer surface of the primary transfer belt 61 is transferred to the recording medium P at the transfer nip.

[0054] The fuser 21 fixes the toner image onto the recording medium P on which the toner image has been transferred. The fuser 21 operates based on the control of the system controller 13 and the temperature control device 101. As described above, the fuser 21 has a temperature sensor 74, a heat roller 71, a pressure roller 72, a heater unit 76, etc. The heat roller 71 is rotated by a drive source such as a motor. The heater 73 generates heat with power PC supplied from the heater power supply control circuit 14. Multiple temperature sensors 74 (74a, 74b) are arranged parallel to the rotation axis of the heat roller 71 and detect the surface temperature of the heat roller 71. The temperature sensor 74 is, for example, a sensor element such as a contact type thermistor, and of course, other temperature sensors may also be used. In this embodiment, the average value of the detection signal output from the temperature sensor 74 per set time (or unit time) is used as one detection signal.

[0055] Next, the temperature control device 101 will be described with reference to Figures 1 and 2. The temperature control device 101 consists of a heater power supply control circuit 14, a temperature control circuit 25, and a temperature sensor 74. In this example, the temperature control circuit 25 is shown as an independent arithmetic processing circuit, but it is not particularly limited and may be provided in the processor 22 of the system controller 13 of the image forming apparatus 1, or in other control circuits. The sensor temperature Td detected by the temperature sensor 74 is input to the heater power supply control circuit 14.

[0056] The heater power supply control circuit 14 generates power PC and supplies it to the heater 73 of the fuser 21. The heater 73 adjusts its heat output according to the amount of power PC, thereby controlling the temperature of the heat roller 71. This heater power supply control circuit 14 adjusts the amount of power supplied to the heater 73 of the fuser 21 based on the sensor temperature Td, the estimated temperature history PREV, and the power supply pulse Ps. This type of control is called WAE (Weighted Average control with Estimated temperature) control. The heater power supply control circuit 14 includes a temperature estimation circuit 81, an estimated history holding circuit 82, a high-frequency component extraction circuit 83, a coefficient addition circuit 84, a target temperature output circuit 85, a difference comparison circuit 86, a control signal generation circuit 87, and a power supply circuit 88. Furthermore, the temperature estimation circuit 81, estimation history holding circuit 82, high-frequency component extraction circuit 83, coefficient addition circuit 84, target temperature output circuit 85, difference comparison circuit 86, and control signal generation circuit 87 of the heater power supply control circuit 14 may each be composed of electrical circuits, or they may be composed of software (programs) and executed by a computer.

[0057] The temperature estimation circuit 81 performs a temperature estimation process to estimate the surface temperature of the heat roller 71. Based on the sensor temperature Td, the estimated history PREV, and the energization pulse Ps, the temperature estimation circuit 81 generates a temperature estimation result EST. This temperature estimation result EST is output to the high-frequency component extraction circuit 83.

[0058] The estimation history retention circuit 82 retains the history of the temperature estimation result EST. The estimation history retention circuit 82 outputs the estimation history PREV, which is the history of the temperature estimation result EST (past temperature estimation result EST), to the temperature estimation circuit 81. The high-frequency component extraction circuit 83 performs high-pass filtering to extract the high-frequency components of the temperature estimation result EST. The high-frequency component extraction circuit 83 outputs the high-frequency component HPF, which is a signal indicating the extracted high-frequency components, to the coefficient summing circuit 84.

[0059] The coefficient addition circuit 84 performs a coefficient addition process, which is a correction, on the sensor temperature Td from the temperature sensor 74. The coefficient addition circuit 84 receives the sensor temperature Td and the high-frequency component HPF from the high-frequency component extraction circuit 83 as inputs. The coefficient addition circuit 84 corrects the sensor temperature Td based on the high-frequency component HPF. Specifically, the coefficient addition circuit 84 multiplies the high-frequency component HPF by a preset coefficient, adds it to the sensor temperature Td, and calculates the temperature estimate WAE. The coefficient addition circuit 84 outputs the temperature estimate WAE to the difference comparison circuit 86.

[0060] The target temperature output circuit 85 outputs a preset target temperature TGT to the difference comparison circuit 86. The difference comparison circuit 86 performs difference calculation processing. The difference comparison circuit 86 calculates the difference DIF between the target temperature TGT from the target temperature output circuit 85 and the estimated value WAE from the coefficient addition circuit 84, and outputs it to the control signal generation circuit 87. In addition, when the difference comparison circuit 86 receives a control switching signal SW from the target temperature correction circuit 94 of the temperature control circuit 25 (described later), it calculates the difference DIF between the sensor temperature Td from the temperature sensor 74 and the target temperature TGT instead of the difference between the target temperature TGT and the estimated value WAE, and outputs it to the control signal generation circuit 87.

[0061] The control signal generation circuit 87 generates an energizing pulse Ps, which is a pulse signal for controlling the supply of power to the heater 73, based on the differential DIF. The control signal generation circuit 87 outputs the energizing pulse Ps to the power supply circuit 88 and the temperature estimation circuit 81.

[0062] The power supply circuit 88 supplies power PC to the heater 73 based on the energizing pulse Ps. The power supply circuit 88 uses the supplied DC voltage to energize the heater 73 of the fuser 21. The power supply circuit 88 supplies power PC to the heater 73 by switching, for example, between a state where DC voltage is supplied to the heater 73 and a state where it is not supplied, based on the energizing pulse Ps. In other words, the power supply circuit 88 varies the energizing time of the heater 73 of the fuser 21 according to the energizing pulse Ps.

[0063] The power supply circuit 88 may be integrated with the fuser 21. That is, the heater power supply control circuit 14 may be configured to supply power pulses Ps to the power supply circuit of the heater 73 of the fuser 21, rather than supplying power PC to the heater 73.

[0064] Next, the temperature control circuit 25 consists of a first memory circuit 91, a second memory circuit 92, a temperature difference detection circuit 93, and a target temperature correction circuit 94. The calculations performed by each circuit constituting the temperature control circuit 25 can be replaced by programs that perform these calculations. These programs are processed by the processor 22 installed in the system controller 13 and can perform the same processing (temperature control and target temperature correction) as the components of the temperature control circuit 25 described later.

[0065] In these configurations, the first memory circuit 91 stores the estimated temperature WAE output from the coefficient summing circuit 84 in the WAE control described later. The second memory circuit 92 stores the sensor temperature Td detected from the temperature sensor 74. The temperature difference detection circuit 93 estimates the actual temperature rise from the temperature difference between the estimated temperature WAE read from the first memory circuit 91 and the sensor temperature Td of the heater 73 read from the second memory circuit 92.

[0066] The target temperature correction circuit 94 outputs a control switching signal SW to the difference comparison circuit 86 based on the temperature rise and the correlation described later, and estimates the control correction temperature, outputting a corrected target temperature Tad, which is the current target temperature reduced, to the target temperature output circuit 85. Specifically, the target temperature correction circuit 94 sets multiple control correction temperatures, as shown in Figure 11, correlated with the actual temperature rise, which is the difference between the normal temperature of the temperature-controlled target when the heater 73 temperature rises and the current actual temperature of the temperature-controlled target. Then, it generates a corrected target temperature Tad by subtracting the control correction temperature (-5℃~) corresponding to the actual temperature rise from the currently set target temperature. The target temperature output circuit 85 outputs a target temperature TGT consisting of the corrected target temperature Tad to the difference comparison circuit 86.

[0067] [WAE control] Next, we will explain WAE control in detail with reference to the flowchart shown in Figure 4. The heater power supply control circuit 14 sets various initial values ​​(ACT1). For example, the heater power supply control circuit 14 sets the coefficient in the coefficient addition circuit 84 and the target temperature TGT of the target temperature output circuit 85 based on the signal from the system controller 13.

[0068] The temperature estimation circuit 81 of the heater power supply control circuit 14 acquires the sensor temperature Td from the temperature sensor 74, the estimated history PREV from the estimation history holding circuit 82, and the power supply pulse Ps from the control signal generation circuit 87 (ACT2). However, if the temperature sensor 74 has a slow response to temperature changes due to the influence of its own heat capacity and the characteristics of the temperature-sensing material, the sensor temperature Td may be detected with a delay relative to the roller temperature estimate, or it may be detected in a smoothed state.

[0069] Next, the temperature estimation circuit 81 performs temperature estimation processing (ACT3). Specifically, the temperature estimation circuit 81 generates a temperature estimation result EST based on the sensor temperature Td, the estimated history PREV, and the energization pulse Ps. The temperature estimation circuit 81 outputs the temperature estimation result EST to the high-frequency component extraction circuit 83 and the estimated history holding circuit 82.

[0070] Generally, heat transfer can be equivalently represented by the CR time constant of an electrical circuit. Heat capacity is replaced by capacitor C. Heat transfer resistance is replaced by resistor R. Also, the heat source is replaced by a DC voltage source. The temperature estimation circuit 81 applies the amount of current supplied to the heater 73 and the heat capacity of the heat roller 71 to a CR circuit with pre-set values ​​for each element to estimate the amount of heat supplied to the heat roller 71. Based on the amount of heat supplied to the heat roller 71, the sensor temperature Td, and the estimated history PREV, the temperature estimation circuit 81 estimates the surface temperature of the heat roller 71 and outputs the temperature estimation result EST.

[0071] The temperature estimation circuit 81 repeatedly energizes and disconnects from a DC voltage source based on the energizing pulse Ps, and the CR circuit operates in accordance with the input voltage pulse, generating an output voltage. This allows the heat propagated to the surface of the heat roller 71, which is the object of temperature control. In other words, the temperature estimation result EST output by the temperature estimation circuit 81 estimates the actual surface temperature of the heated element from the heat capacity (C) of the heated element, the thermal resistance (R) of the fuser, the energy input to the fuser, etc. Therefore, as the surface temperature of the heat roller 71 heats up due to an increase in input energy (supplied power), the temperature estimation result EST also increases. The heat from the heat roller 71 flows out to the external environment through the space inside the fuser 21 (the external circuit of the heat roller 71). Therefore, the temperature estimation circuit 81 is further equipped with a CR circuit to estimate the outflow of heat from the heat roller 71 to the external environment. The temperature estimation circuit 81 may also be further equipped with a CR circuit to estimate the amount of heat flowing from the heat roller 71 to the space inside the fuser 21.

[0072] The high-frequency component extraction circuit 83 performs a high-pass filter process to extract the high-frequency components of the temperature estimation result EST (ACT4). The high-frequency component HPF, which is a signal indicating the high-frequency components of the temperature estimation result EST, tracks the actual surface temperature changes of the heat roller 71. Next, the coefficient addition circuit 84 performs a coefficient addition process, which is a correction, on the sensor temperature Td (ACT5). This coefficient addition circuit 84 multiplies the high-frequency component HPF by a preset coefficient, adds the multiplied high-frequency component HPF to the sensor temperature Td, and calculates the temperature estimate WAE. For example, if the coefficient is 1, the coefficient addition circuit 84 directly adds the high-frequency component HPF to the sensor temperature Td. Also, for example, if the coefficient is 0.1, the coefficient addition circuit 84 adds one-tenth of the value of the high-frequency component HPF to the sensor temperature Td. In this case, the effect of the high-frequency component HPF is almost eliminated, and the result is close to the sensor temperature Td. Also, for example, if the coefficient is 1 or greater, the effect of the high-frequency component HPF can be expressed more strongly. Experimental results have shown that the coefficient set in the coefficient addition circuit 84 should not be an extreme value, but rather a value close to 1.

[0073] In WAE control, the fine temperature changes of the surface temperature of the heat roller 71 are estimated based on the sensor temperature Td and the high-frequency component HPF of the temperature estimation result EST. The temperature estimation value WAE is a value that appropriately tracks the surface temperature of the heat roller 71. The difference comparison circuit 86 calculates the difference DIF between the target temperature TGT, which includes the control correction temperature Tad from the target temperature output circuit 85, and the temperature estimate WAE from the coefficient summing circuit 84, and outputs it to the control signal generation circuit 87 (ACT6).

[0074] The control signal generation circuit 87 generates an energizing pulse Ps based on the differential DIF. The control signal generation circuit 87 outputs the energizing pulse Ps to the power supply circuit 88 and the temperature estimation circuit 81 (ACT7). The power supply circuit 88 supplies power PC to the heater 73 based on the energizing pulse Ps.

[0075] The difference DIF mentioned above shows the relationship between the target temperature TGT and the estimated temperature WAE. For example, if the relationship is estimated temperature WAE > target temperature TGT, the amount of current supplied to the heater 73 decreases by controlling the width or frequency of the energizing pulses Ps, thereby lowering the heat roller surface temperature. Conversely, if the relationship is estimated temperature WAE < target temperature TGT, the amount of current supplied to the heater 73 increases by controlling the width or frequency of the energizing pulses Ps, thereby raising the heat roller surface temperature.

[0076] Furthermore, the differential DIF not only shows the relative position between the temperature estimate WAE and the target temperature TGT, but also indicates how far apart they are. For example, if the differential DIF (absolute value) is large, the discrepancy between the temperature estimate WAE and the target temperature TGT is large, so the aforementioned control may be significantly altered. Conversely, if the differential DIF (absolute value) is small, the discrepancy between the temperature estimate WAE and the target temperature TGT is small, so the above control may be applied more gradually.

[0077] The processor 22 of the system controller 13 determines whether or not to terminate WAE control (ACT8). If the processor 22 determines in ACT8 to continue without terminating WAE control (ACT8:NO), it proceeds to the processing of ACT2 described above. On the other hand, if the processor 22 determines to terminate WAE control in accordance with the shutdown of the device due to the OFF operation of the main power switch 24 (ACT8:YES), it terminates the processing routine.

[0078] Thus, when the heater power control circuit 14 processes a certain cycle (the current cycle), it performs WAE control based on the values ​​from the previous cycle (power pulse Ps and temperature estimation result EST: estimation history PREV) and the sensor temperature Td in the current cycle. In other words, the heater power control circuit 14 inherits the values ​​in the next cycle. The heater power control circuit 14 recalculates the temperature estimation calculation based on the history of the previous calculation. Therefore, the heater power control circuit 14 is constantly performing calculations while in operation. In the heater power control circuit 14, the calculation results are stored in memory or the like and reused in the calculation of the next cycle.

[0079] [Target temperature correction processing] Next, the temperature control of the fuser using the temperature control device of this embodiment will be described. The numerical values, gap distances, temperatures, and temperature estimates for the specifications or designs of the components described below are examples set as appropriate for illustrative purposes and are not particularly limited. In the following description, "center" refers to the central part of the heat roller 71 and the position adjacent to or facing the central part. "Side" refers to the end parts on both sides of the central part of the heat roller 71 and the positions adjacent to or facing the end parts on both sides.

[0080] Figure 5 is a table showing the measured temperature and estimated temperature when a gap is left between the contact surface of the heat roller 71 and the center temperature sensor 74a. These gaps are assumed to be those that occur when foreign matter is trapped or when dirt adheres to the surface. Figure 7 shows the temperature changes of the "estimated temperature WAE center," "actual temperature center of the heat roller," and "sensor temperature center" shown in Figure 5 as temperature characteristics between the heat roller 71 and the center temperature sensor 74a.

[0081] In the temperature detection shown in Figure 5, the target temperature (control temperature) is set to 160°C for each set gap (first gap to third gap). After the heating of the heat roller 71 by warming up is complete and a waiting time of 40 seconds has elapsed since the WAE control started, the temperature is measured for 20 seconds using a thermocouple (actually measuring the heat roller surface temperature), and the average temperature is taken as the detected value. This waiting time is an arbitrary setting time in this embodiment and will vary depending on the type of fuser, and is not limited to any particular time.

[0082] The fuser unit 21 used in this embodiment has the following specifications and characteristics: a heat roller (H / R) 71 with a diameter of Φ30 mm (core metal thickness: 0.6 mm), a pressure roller (P / R) 72 with a diameter of Φ30 mm, a P / R pressure of 150 N, a controlled temperature (standby state) of 160°C for the heat roller center and 155°C for the heat roller side, and a peripheral speed of 210 mm / sec. The recording medium size is A4, and the processing rate per unit time is 45 sheets / minute. As mentioned above, the heat roller 71 is equipped with a center heater 73a that heats the center of the heat roller 71 and side heaters 73b and 73c that heat both ends of the heat roller 71, each of which heats the heat roller 71. The center heater 73a and the side heaters 73b and 73c can also be individually temperature-controlled.

[0083] In the table shown in Figure 5, the "distance between the temperature sensor (center) and the heat roller" is shown in three patterns: a first gap C1 with a gap distance of "0 mm" between the heat roller 71 and the center temperature sensor 74a, a second gap C2 with a gap distance of "0.21 mm", and a third gap C3 with a gap distance of "0.42 mm". These gaps are created by the first gap C1 being in contact, the second gap C2 by layering and sandwiching three pieces of Kapton tape (0.07 mm x 3) which are assumed to be foreign material, and the third gap C3 by layering and sandwiching six pieces of Kapton tape (0.07 mm x 6). In this embodiment, Kapton tape was used as the foreign material, but it is not limited to this, and any material that does not deform or weld due to heat can be used.

[0084] Furthermore, the "actual temperature center of the heat roller" is the temperature measured by attaching an external thermocouple (thermistor) to the central part of the heat roller 71. The "sensor temperature center" is the temperature detected by the temperature sensor 74a located in the central part of the heat roller 71. The "estimated temperature WAE center" is the estimated temperature used for WEA control, output from the coefficient summing circuit 84 in the heater energization control circuit 14 using the sensor temperature Td detected by the temperature sensor 74a across the aforementioned gap. The "first temperature rise center" is the difference between the estimated temperature WAE center and the sensor temperature center. The "second temperature rise center" is the difference between the actual temperature center of the heat roller 71 and the sensor temperature center. The "actual temperature rise center" is the difference between the temperature center of a normal heat roller measured in advance and the actual temperature center of the current heat roller.

[0085] Referring to Figures 5 and 7, the temperature characteristics when a gap occurs between the heat roller 71 and the temperature sensor 74a will be explained. In WAE control, if such a gap occurs, even if the target temperature is set to 160°C, the temperature sensor 74a detects a lower temperature than the actual temperature, increasing the estimated temperature WAE, and heating by the center heater 73a is performed in an attempt to raise the temperature above the current temperature.

[0086] Comparing the first gap C1 (0 mm) and the third gap C3 (0.42 mm), the "sensor temperature center" is 162°C to 163°C, showing a nearly constant temperature. However, the "actual temperature center of the heat roller" obtained from the thermocouple rises from 170.2°C to 189.6°C, and the "estimated WAE center" also rises from 172.9°C to 203.5°C. Therefore, depending on the temperature difference between the estimated WAE center and the sensor temperature center, it can be determined that there is an abnormality such as foreign matter being stuck between the heat roller 71 and the temperature sensor 74a, or dirt adhering to either or both of the heat roller 71 and the temperature sensor 74a.

[0087] Next, Figure 6 is a table showing the measured temperature and estimated temperature when a gap is left between the contact surface of the heat roller 71 and the temperature sensors 74b on both sides. Figure 8 shows the temperature changes of the "estimated temperature WAE side," "actual temperature side of the heat roller," and "sensor temperature side" shown in Figure 6 as temperature characteristics between both ends of the heat roller 71 and the temperature sensors 74b. Note that the temperature detection in Figure 6 is the same as in the example in Figure 5, and after the heat roller 71 has finished warming up and a waiting time of 40 seconds has elapsed since the start of WAE control, the temperature detection by thermocouple is measured for 20 seconds and the average temperature is used as the detected value.

[0088] Each item in the table shown in Figure 6 is the same as the items shown in Figure 5, except that "center" and "side" are different. The "distance between the temperature sensor (side) and the heat roller" has three patterns: a first gap S1 with a gap distance of "0 mm" between the heat roller 71 and the side temperature sensor 74b, a second gap S2 with a gap distance of "0.21 mm", and a third gap S3 with a gap distance of "0.42 mm". As mentioned above, these gaps are created by overlapping and sandwiching Kapton tape, which is assumed to be a foreign object.

[0089] Referring to Figures 6 and 8, the temperature characteristics when a gap occurs between the heat roller 71 and the temperature sensor 74b will be explained. In WAE control, if such a gap occurs, even if the target temperature is set to 155°C, the temperature sensor 74b will detect a temperature lower than the actual temperature. Therefore, the heater 73 will increase the estimated temperature WAE and heat the roller 73 to raise the temperature above the current temperature.

[0090] In Figure 6, comparing the first gap S1 (0 mm) and the third gap S3 (0.42 mm), the "sensor temperature side" shows a nearly constant temperature of 157°C, but the "actual temperature side of the heat roller" obtained from the thermocouple rises from 162°C to 181.2°C, and the temperature estimate WAE side also rises from 183.6°C to 220.7°C. Therefore, when the temperature difference between the temperature estimate WAE side and the sensor temperature side exceeds a pre-set threshold, it can be determined that there is an abnormality such as foreign matter being stuck between the heat roller 71 and the temperature sensor 74b, or dirt adhering to either or both of the heat roller 71 and the temperature sensor 74b.

[0091] Next, Figure 9 is a diagram (correlation diagram) showing the correlation of temperature rise based on the temperature characteristics shown in Figure 5. In Figure 9, the horizontal axis is the "first temperature rise center" shown in Figure 5, and the vertical axis is the "actual temperature rise center". For example, the correlation equation (y=0.63x-6.49) for the linear temperature sensor 74a can be obtained from the correlation shown in Figure 9. The temperature difference detection circuit 93 has a correlation relationship (temperature characteristics of the slope) of temperature rise shown in Figure 9, in which the first temperature rise, which consists of the difference between the temperature estimate WAE and the sensor temperature Td, and the actual temperature rise are correlated. Based on the acquired temperature estimate WAE and sensor temperature Td, the actual temperature rise can be estimated from the correlation shown in Figure 9.

[0092] Similarly, Figure 10 is a correlation diagram showing the correlation of temperature rise based on the temperature characteristics shown in Figure 6. In Figure 10, the horizontal axis represents the "first temperature rise side" shown in Figure 6, and the vertical axis represents the "actual temperature rise side". For example, the correlation equation (y=0.50x-13.78) for the linear temperature sensor 74a can be derived from the correlation shown in Figure 10.

[0093] From the correlations shown in Figures 9 and 10, for example, if the estimated temperature WAE and the sensor temperature are known, the actual temperature of the heat roller 71 and the actual temperature rise can be estimated from the difference between them. Figure 11 shows the setting of the control correction temperature for the actual temperature rise of the heat roller 71. The temperature variation of the temperature sensor 74 used in this embodiment is set to ±5°C relative to the reference temperature. Of course, this value will vary depending on the temperature sensor and is not limited to this value.

[0094] As shown in Figure 11, if the actual temperature rise of the heat roller 71 is estimated to be 0 to ±5°C from the target temperature based on Figures 9 and 10, it is determined to be normal based on the temperature variation described above, and WAE control is continued. However, if the temperature has not risen, such as when the actual temperature drops to -5°C, the heat roller 71 is heated as appropriate.

[0095] Temperature correction is performed when the actual temperature rise exceeds 5°C. That is, WAE control is stopped and the system switches to temperature control based on a target value corrected by a correction value correlated with the sensor temperature Td of the temperature sensor 74. Furthermore, if the actual temperature rise is estimated to be between 5 and 10°C, the control correction temperature is set to -5°C, correcting the target temperature to a value obtained by lowering the current target temperature by -5°C. Similarly, if the actual temperature rise is between 10 and 15°C, the control correction temperature is set to -10°C, correcting the target temperature to a value obtained by lowering the current target temperature by -10°C, and if the actual temperature difference is between 15 and 20°C, the control correction temperature is set to -15°C, correcting the target temperature to a value obtained by lowering the current target temperature by -15°C. Thereafter, for every 5°C change in the actual temperature rise, the target temperature is corrected to a value obtained by lowering the current target temperature by -5°C.

[0096] Next, Figures 12 and 13 are diagrams for setting the control correction temperature. Here, the correlation between the actual temperature rise of the heat roller 71, the first temperature rise (the difference between the temperature estimate WAE and the sensor temperature) and the control correction temperature is shown. Figure 12 shows the correlation between the actual temperature rise of the heat roller 71, the first temperature rise center, and the control correction temperature. Figure 13 shows the correlation between the actual temperature rise of the heat roller 71, the first temperature rise side, and the control correction temperature. Here, instead of WAE control, temperature control (second temperature control) is performed using a target temperature corrected with a control correction temperature correlated with the detected sensor temperature.

[0097] In setting the control correction temperature of the center of the heat roller 71 shown in Figure 12, for example, if the actual temperature rise tb shown in Figure 9 is 5°C, the first temperature rise center will be approximately 18.1°C. Subsequently, the temperature of the first temperature rise center will be approximately 25.9°C when the actual temperature rise is 10°C, approximately 33.8°C when the actual temperature rise is 15°C, and approximately 41.7°C when the actual temperature rise is 20°C.

[0098] In setting the control correction temperature on the side of the heat roller 71 shown in Figure 13, for example, if the actual temperature rise tb shown in Figure 10 is 5°C, the first temperature rise side will be approximately 37.4°C. Subsequently, the temperature on the first temperature rise side will be approximately 47.3°C when the actual temperature rise is 10°C, approximately 57.3°C when the actual temperature rise is 15°C, and approximately 67.2°C when the actual temperature rise is 20°C.

[0099] By referring to FIGS. 12 and 13, both the center or side temperature can estimate the actual temperature rise tb in degrees Celsius from the first temperature rise ta, and further, the control correction temperature can be obtained from the estimated actual temperature rise. As an example, when the first temperature rise center ta, which is the temperature difference between the temperature estimated value WAE center - the temperature of the sensor temperature center obtained by WAE control, is 25°C, if the actual temperature rise tb caused by abnormalities such as dirt adhesion or foreign object entrapment is judged to be rising between more than 5°C and 10°C or less (5 < tb ≤ 10) on the temperature rising side from the target temperature. When the actual temperature rise tb rises in this way, the current WAE control (first temperature control) is stopped, and temperature control (second temperature control) is performed with the target temperature corrected using the control correction temperature correlated with the detected sensor temperature. Specifically, in this example, the correction target temperature obtained by subtracting the control correction temperature -5°C from the current target temperature is set for temperature control.

[0100] Also, in FIG. 13, when the first temperature rise side ta, which is the temperature difference between the temperature estimated value WAE side - the temperature of the sensor temperature side, is 50°C, if dirt adheres to the temperature sensor 74b, the actual temperature rise tb is judged to be rising between more than 10°C and 15°C or less (10 < tb ≤ 15) on the temperature rising side from the target temperature. When the actual temperature rise tb rises in this way, the current WAE control (first temperature control) is stopped, and the correction target temperature obtained by subtracting the control correction temperature -15°C from the current target temperature is set, and the temperature control (second temperature control) using the temperature sensor 74 is switched. Thus, an accurate correction value corresponding to the temperature difference can be obtained from the correlation relationship.

[0101] Next, referring to the flowchart shown in FIG. 14, the temperature control including temperature correction by the temperature control device 101 of the present embodiment will be described. In this example, the temperature control device 101 is assumed to be a configuration example mounted on the image forming apparatus 1.

[0102] First, the image forming apparatus 1 starts up when the main power switch 24 is turned on (ACT 11). The system controller 13 of the image forming apparatus 1 sets each component to its initial state in order to perform printing. At this time, the heater power supply control circuit 14 of the temperature control device 101 supplies power to the heater 73 to heat the heat roller 71, and the warm-up to start printing begins. Once the warm-up is complete, WAE control is started (ACT 12), and the waiting time count begins.

[0103] Next, the system controller 13 determines whether the sensor temperature detected by the temperature sensors 74 (74a, 74b) is 40°C or lower (ACT13). If the sensor temperature is higher than 40°C (NO) as determined by ACT13, it is determined that the presence or absence of dirt or foreign matter attached to the temperature sensor 74 cannot be accurately determined, and therefore the first temperature control by WAE control will be continued, and the control mode will not be switched to the second temperature control mode. The second temperature control, as shown in Figures 5 to 13 above, performs temperature control using a target temperature corrected with a control correction temperature correlated with the detected sensor temperature. On the other hand, if the sensor temperature detected by the temperature sensor 74 is 40°C or lower (YES) as determined by ACT13, it is determined that it is possible to switch to the control mode by the second temperature control mode.

[0104] Next, it is determined whether or not a print command to the recording medium has been received (ACT14). If ACT14 determines that a print command has been received (YES), printing to the recording medium is performed while WAE control continues. On the other hand, if ACT14 determines that a print command has not been received (NO), it is determined whether or not 40 seconds have elapsed since the start of WAE control (ACT15).

[0105] In this ACT15 determination, if the waiting time is less than 40 seconds (NO), the time count continues. If the waiting time has exceeded 40 seconds (YES), the storage of the center and side temperature estimates WAE into the first memory circuit 91 begins. Simultaneously, the storage of the sensor temperature Td detected by the center and side temperature sensors 74a and 74b into the second memory circuit 92 at the same timing as the above temperature estimates WAE (center and side) begins (ACT16). Along with starting these storages, the count of the storage time begins. The sampling timing for these storages is set as appropriate.

[0106] Next, it is determined whether 20 seconds have elapsed since the start of storing the temperature estimate WAE and sensor temperature Td (ACT17). If ACT17 determines that 20 seconds have not elapsed (NO), the storage of the temperature estimate WAE and sensor temperature Td continues. On the other hand, if ACT17 determines that 20 seconds have elapsed (YES), the average values ​​of the temperature estimate WAE and sensor temperature Td during those 20 seconds are calculated and stored in the first storage circuit 91 and the second storage circuit 92 (ACT18). If a print command is received while the temperature estimate WAE and sensor temperature Td are being stored, these storage operations are stopped, printing to the recording medium is performed, and then the waiting time count is restarted.

[0107] Next, the temperature difference detection circuit 93 reads the estimated temperature WAE center from the first memory circuit 91 and the sensor temperature center from the second memory circuit 92 to obtain the first temperature rise center (difference between the estimated temperature WAE and the sensor temperature) taC. It then determines whether this first temperature rise center taC is higher than a preset threshold temperature thC (ACT19). Here, the threshold temperature th is set to "18.1℃" for the center's threshold temperature thC and to "37.4℃" for the side's threshold temperature thS, which will be described later. Of course, these threshold temperatures are set as appropriate and are not limited to them.

[0108] In the determination of ACT19, if the first temperature rise center taC is 18.1°C or less, which is the preset threshold temperature thC (NO), the heat roller 71 and the temperature sensor 74a of the fixing device 21 are determined to be normal, and the WAE control is continued. On the other hand, in the determination of ACT19, if the first temperature rise center taC is higher than the preset threshold temperature of 18.1°C (YES), it is determined that an abnormality such as dirt adhering to the temperature sensor 74a of the center or a foreign object being sandwiched between the heat roller 71 has occurred, and a control switching signal SW is output to the differential comparison circuit 86 to stop the WAE control (first temperature control) of the center (ACT20). Upon receiving this control switching signal SW, the differential comparison circuit 86 stops calculating the difference DIF between the temperature estimated value WAE from the coefficient addition circuit 84 and the target temperature TGT from the target temperature output circuit 85. As a result, the WAE control (first temperature control) of the center stops.

[0109] After stopping the WAE control (first temperature control) of the center, the control is switched to the second temperature control for temperature control by the aforementioned temperature sensor, and control temperature correction (correction for lowering the target temperature) for correcting the target temperature at the center is performed (ACT21). For example, in the target temperature correction circuit 94, when the calculated first temperature rise ta is "20°C" (18.1 < ta ≤ 25.9) using the temperature correlation shown in FIGS. 11 and 12, it corresponds to 5 < tb ≤ 10 as the actual temperature rise, and the control correction temperature of "-5°C" is obtained. Therefore, a corrected target temperature Tad obtained by subtracting -5°C from the current target temperature is calculated and output to the target temperature output circuit 85. The target temperature output circuit 85 outputs the target temperature TGT consisting of the corrected target temperature Tad to the differential comparison circuit 86. The differential comparison circuit 86 calculates the difference DIF between the target temperature TGT and the sensor temperature Td at the center and outputs it to the control signal generation circuit 87.

[0110] Next, in ACT21, when the control temperature correction for correcting the target temperature is performed, the service person is notified that an abnormality has occurred in the temperature control of the fixing device 21 (ACT22). Specifically, the notification content may suggest that there is a problem between the heat roller 71 and the temperature sensor 74.

[0111] Following the notification in ACT22, the first temperature rise side taS is calculated from the difference between the temperature estimate WAE side and the sensor temperature side. It is then determined whether this first temperature rise side taS is higher than the pre-set threshold temperature thS (ACT23). Here, as mentioned above, the threshold temperature thS for the side is set to "37.4℃".

[0112] In this ACT23 judgment, if the first temperature rise on the side taS is below the preset threshold temperature thS of 37.4°C (NO), the heat roller 71 and temperature sensor 74b of the fuser 21 are judged to be normal, and WAE control is continued. On the other hand, in this ACT23 judgment, if the first temperature rise on the side ta is higher than the preset threshold temperature of 37.4°C (YES), it is judged that an abnormality has occurred, such as dirt adhering to the side temperature sensor 74b or foreign matter being stuck between it and the heat roller 71, and a control switching signal SW is output to the difference comparison circuit 86 in order to stop the side WAE control (first temperature control) (ACT24). In this example, even if an abnormality occurs in either of the temperature sensors 74b, both side temperature sensors 74b are treated as if there was an abnormality, and are treated as a single unit.

[0113] Upon receiving this control switching signal SW, the differential comparison circuit 86 stops calculating the difference between the temperature estimated value WAE from the coefficient addition circuit 84 and the target temperature TFT from the target temperature output circuit 85, thereby stopping the WAE control (first temperature control) on the side. Thereafter, the control switches to the aforementioned second temperature control, and performs control temperature correction (correction to lower the target temperature) for correcting the target temperature on the side (ACT25). For example, in the target temperature correction circuit 94, when the calculated first temperature rise ta is "50 °C" (47.3 < ta ≤ 57.3) using the temperature correlation shown in FIGS. 11 and 13, it corresponds to 10 < tb ≤ 15 as the actual temperature rise, and a control correction temperature of "-10 °C" is obtained. Therefore, a corrected target temperature Tad obtained by subtracting -10 °C from the current target temperature is calculated and output to the target temperature output circuit 85. The target temperature output circuit 85 outputs it to the differential comparison circuit 86 as a target temperature TGT consisting of the corrected target temperature Tad. The differential comparison circuit 86 calculates the difference DIF between this target temperature TGT and the sensor temperature Td on the side, and outputs it to the control signal generation circuit 87.

[0114] Next, in ACT25, when control temperature correction for correcting the target temperature is performed, the service technician is notified that an abnormality has occurred in the temperature control of the fixing device 21 (ACT26). As the notification content, specifically, it may be suggested that there is a problem between the heat roller 71 and the temperature sensor 74.

[0115] As described above, according to the temperature control device of the present embodiment, until the service technician responds, the temperature control by the temperature sensor for lowering the target temperature is continuously performed. By configuring the temperature control device in this way, by detecting abnormalities occurring in the temperature sensors on the center and side and performing appropriate temperature control, it is possible to prevent in advance failures such as high-temperature offsets and service calls occurring in the fixing device 21 that cause the device to stop urgently.

[0116] Furthermore, in the flowchart shown in Figure 14, if the dirt adhering to the temperature sensor 74 is removed or any foreign object that was stuck in it is dislodged by passing the recording medium through it, the first temperature rise will fall within the specified temperature range that is judged to be normal. In such cases, a step may be incorporated to return from the judgment of no correction based on the control correction temperature to the second temperature control using the temperature sensor and then to WAE control.

[0117] Furthermore, the image forming apparatus of this embodiment is connected to external devices, such as personal computers located at workplaces like homes or branch offices, via a network such as the Internet, enabling communication and allowing for the printing of various information and the performance of maintenance management through remote control of the personal computer. The aforementioned warning information regarding maintenance management results can also be displayed on the personal computer. [Second example of fuser configuration] Next, a second configuration example of a fuser applicable to the image forming apparatus 1 according to this embodiment will be described. Figure 15 is a diagram showing the second configuration example of the fuser. Figure 16 is a diagram showing the configuration example of the heater unit in the fuser of the second configuration example.

[0118] The fuser 21 includes a temperature sensor 74, a heat roller 71 made of a tubular film as a fixing member, a pressure roller 72, a heater (heater, e.g., a lamp heater) 73, and a heater substrate 75. The pressure roller 72 forms a nip with the heat roller 71. The heat roller 71 and the pressure roller 72 heat the recording medium P that has entered the nip while applying pressure. The temperature sensor 74 uses a contact-type temperature detection element such as a thermistor and includes a center temperature sensor 74a and two side temperature sensors 74b and 74c.

[0119] The heater unit 76 consists of a heater 73 and a heater substrate 75, etc. The heater 73 can be, for example, a halogen heater, a lamp heater, an IH heater, or a resistance heating heater. The heater substrate 75 is formed into a long, narrow rectangular plate shape using a metal material or a ceramic material. The heater substrate 75 is positioned radially inside the heat roller 71. The longer side of the rectangle of the heater substrate 75 is aligned with the axial direction of the heat roller 71.

[0120] In this embodiment, the heater 73 is composed, for example, of a center heater 73a, a side heater 73b, and a side heater 73c, each divided into three sections. These heaters 73a, 73b, and 73c are arranged in a direction perpendicular to the paper transport direction (the longitudinal direction of the heater substrate 75). The center heater 73a is positioned such that its central position coincides with the central position in the width direction (the direction perpendicular to the transport direction) of the recording medium P passing through the nip. The two side heaters 73b and 73c are positioned adjacent to both ends of the center heater 73a in the longitudinal direction.

[0121] Of the heaters 73, the center heater 73a is the first heat source, and the side heaters 73b and 73c are the second heat sources. As shown in Figure 15, the center heater 73a supplies heat to the center region C in a direction perpendicular to the paper transport direction indicated by the arrow. However, even if only the center heater 73a is heated, the temperature of the side region S will also rise due to heat transfer. As shown in Figure 15, the side heaters 73b and 73c supply heat to their respective side regions S in a direction perpendicular to the paper transport direction.

[0122] Furthermore, temperature sensor 74a primarily detects the temperature of the center region C heated by the center heater 73a. Temperature sensors 74b and 74c primarily detect the temperatures of the respective side regions S heated by the side heaters 73b and 73c. ​​Such a fuser 21 can be controlled by the WAE control described above.

[0123] As described above, the WAE control described above is also possible in the fuser 21 shown in Figures 15 and 16. Therefore, the image forming apparatus 1 equipped with the fuser 21 shown in Figures 15 and 16 can also be subjected to temperature control using the WAE estimated value as described above. [Third example of fuser configuration] Next, a third configuration example of a fuser applicable to the image forming apparatus 1 according to this embodiment will be described. Figure 17 is a diagram showing the third configuration example of the fuser. Figure 18 is a diagram showing the configuration example of the heater unit in the fuser of the third configuration example.

[0124] As shown in Figure 17, the fuser 121 includes a temperature sensor 74 (74a, 74b), a tubular film 171 as a fixing member (fixing rotating body), a pressure roller 172, a heater and a heater substrate 175, etc. The pressure roller 172 forms a nip with the tubular film 171. The tubular film 171 and the pressure roller 172 heat the printing medium P that has entered the nip while applying pressure.

[0125] The heater unit includes a heater 173 and a heater substrate 175. The heater substrate 175 is made of a metal or ceramic material. The heater substrate 175 is formed in the shape of an elongated rectangular plate. The heater substrate 175 is positioned radially inside the tubular film 171. The axial direction of the tubular film 171 is the longitudinal direction of the heater substrate 175.

[0126] The heater 173 includes multiple heaters 173a, 173b, and 173c. The heater 173 is positioned on the heater substrate 175 and is provided in contact with the inner surface of the cylindrical film 172. Each of these center heaters 173a, side heaters 173b, and side heaters 173c is a resistor that generates heat when power is supplied from an AC power source.

[0127] The center heater 173a is used to fix toner to the printing medium P whose width (paper width) in the direction perpendicular to the transport direction is the largest. The center heater 173a has a width corresponding to the largest paper width. The center heater 173a is positioned on the upstream and downstream sides of the transport direction of the printing medium P on the heater substrate 175.

[0128] Center heater 173b is shorter than center heater 173a in the direction perpendicular to the transport direction of the printing medium P. Heater 173c is even shorter than center heater 173b in the direction perpendicular to the transport direction of the printing medium P. Center heater 173a is the main heater, and center heaters 173b and 173c are sub-heaters. The main heater and sub-heaters are controlled to be on or off according to the paper width of the printing medium P.

[0129] As described above, the fuser 121 shown in Figures 17 and 18 can also be subjected to the WAE control described above. Therefore, an image forming apparatus equipped with the fuser 121 shown in Figures 17 and 18 can perform temperature control using the WAE estimated value as described above. [Fourth example of fuser configuration] Next, a fourth configuration example of a fuser applicable to the image forming apparatus 1 according to this embodiment will be described. Figure 19 is a diagram showing the fourth configuration example of the fuser. Figure 20 is a diagram showing the configuration example of the heater unit in the fuser of the fourth configuration example. As shown in Figure 19, the fuser 221 includes a temperature sensor 74 (74a, 74b), a tubular film 271 as a fixing member (fixing rotating body), a pressure roller 272, a heater 273, and a heater substrate 275. The pressure roller 272 forms a nip with the tubular film 271. The tubular film 271 and the pressure roller 272 heat the printing medium P that has entered the nip while applying pressure.

[0130] The heater unit includes heaters 273 (273a, 273b) and a heater substrate 275. The heater substrate 275 is made of a metal or ceramic material. The heater substrate 275 is formed in the shape of an elongated rectangular plate. The heater substrate 275 is positioned radially inside the tubular film 271. The axial direction of the tubular film 271 is the longitudinal direction of the heater substrate 275.

[0131] The heater 273 includes a plurality of heaters 273a and 273b. The heater 273 is positioned on the heater substrate 275 so as to be in contact with the inner surface of the cylindrical film 271. Each of the center heater 273a and side heaters 273b is a resistor that generates heat, for example, when power is supplied from an AC power source.

[0132] The center heater 273a has a width corresponding to the maximum width of the printing medium P in a direction perpendicular to the transport direction. As shown in Figure 20, the center heater 273a has a larger width relative to the transport direction in the central part of the center heater 273a and a smaller width relative to the transport direction at the edges. The center heater 273a is a main heater configured to heat the center region C intensively. Heater 273b has a smaller width relative to the transport direction in the central part of the center heater 273b and a larger width relative to the transport direction at the edges. Heater 273b is a sub-heater configured to heat the side regions S intensively. The main heater and sub-heater are controlled to be turned on and off according to the paper width of the printing medium P.

[0133] As described above, the WAE control described above is also possible in the fuser 221 shown in Figures 19 and 20. As a result, the image forming apparatus 1 equipped with the fuser 221 shown in Figures 19 and 20 can perform temperature control using the WAE estimated value as described above. [Fifth example of fuser configuration] Next, a fifth configuration example of a fuser applicable to the image forming apparatus 1 according to this embodiment will be described. Figure 21 is a diagram showing the fifth configuration example of the fuser. Figure 22 is a diagram showing the configuration example of the heater unit in the fuser of the fifth configuration example.

[0134] As shown in Figure 21, the fuser 321 includes a temperature sensor 74 (74a, 74b), a heat roller 371 as a fixing member, a pressure roller 372, and an induction heating coil 373, etc. The pressure roller 372 forms a nip with the heat roller 371. The heat roller 371 and the pressure roller 372 heat the printing medium P that enters the nip while applying pressure.

[0135] The induction heating coil 373 is an example of a heat source for heating the heat roller 371, which serves as a fixing member. The induction heating coil 373 consists of a central coil 373a and end coils 373b. The central coil 373a and end coils 373b are arranged side by side inside the heat roller 371 in a direction perpendicular to the paper transport direction (the rotation axis direction of the heat roller 371). The central coil 373a is positioned so that its center is aligned with the width direction of the printing medium P passing through the nip (in a direction perpendicular to the transport direction). The end coils 373b are arranged side by side on either side of the central coil 373a.

[0136] The central coil 373a is an example of a first heat source. As shown in Figure 22, this central coil 373a heats the center region C of the heat roller 371 in a direction perpendicular to the paper transport direction. The end coil 373b is an example of a second heat source. As shown in Figure 22, the end coil 373b heats the side region S of the heat roller 371 in a direction perpendicular to the paper transport direction.

[0137] The temperature sensors 74a and 74b are contact-type temperature detection devices such as thermistors, similar to the fuser 21 in the first configuration example described above. Temperature sensor 74a detects the temperature of the center region C of the heat roller 371. Temperature sensor 74b detects the temperature of the side region C of the heat roller 371.

[0138] As described above, the fuser 321 shown in Figures 21 and 22 can also be subjected to the WAE control described above. Therefore, in the image forming apparatus 1 equipped with the fuser 321 shown in Figures 21 and 22, temperature control using the WAE estimated value as described above can be implemented.

[0139] Furthermore, this embodiment of the present invention is presented as an example and is not intended to limit the scope of the invention. This embodiment can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. This embodiment and its variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. The original claims of this application are included below. [C1] A temperature control device that controls the power supplied to a heater based on a temperature estimate calculated over time so that the temperature-controlled object, which is heated by the heater of a fuser, reaches a preset target temperature, A temperature sensor for detecting the temperature of the heater, A first memory circuit that stores the temperature estimate obtained at any given time, A second memory circuit that stores the sensor temperature detected by the temperature sensor, A temperature difference detection circuit calculates the actual temperature rise from the temperature difference between the estimated temperature read from the first memory circuit and the heater temperature read from the second memory circuit. A temperature control device comprising: a target temperature correction circuit that performs control to lower the target temperature in accordance with the actual temperature rise; [C2] The temperature control device according to C1, wherein the target temperature correction circuit has a plurality of control correction temperatures correlated with the actual temperature rise, which is the difference between the normal temperature of the temperature-controlled target when the heater temperature rises and the current actual temperature of the temperature-controlled target, and generates a corrected target temperature by subtracting the control correction temperature corresponding to the actual temperature rise from the currently set target temperature. [C3] The temperature control device according to C1, wherein the temperature difference detection circuit has a temperature characteristic in which a first temperature rise, which is the difference between the estimated temperature and the sensor temperature, and the actual temperature rise are correlated, and the actual temperature rise is estimated from the temperature characteristic based on the acquired estimated temperature and the sensor temperature. [C4] The temperature control device further, The temperature control device according to C1, comprising a temperature estimation circuit that estimates the temperature of the temperature-controlled object from the heat capacity of the heater and the thermal resistance of the fuser based on the energization of the heater. [C5] An image forming apparatus comprising the temperature control device described in C1. [C6] A program that causes the processor to execute the processing performed by each circuit of the temperature control device described in C1 to C4. [Explanation of Symbols]

[0140] 1…Image forming apparatus, 11…Housing, 12…Communication interface, 13…System controller, 14…Heater power supply control circuit, 15…Display unit, 16…Operation interface, 17…Paper tray, 18…Paper output tray, 19…Conveyor unit, 20…Image forming unit, 21…Fuser, 22…Processor, 23…Memory, 24…Main power switch, 25…Temperature control circuit, 31…Paper feed transport path, 32…Paper output transport path, 33…Pickup roller, 41…Process unit, 42…Exposure unit, 43…Transfer mechanism, 51…Photosensitive drum, 52…Charging charger, 53…Developer, 61…Primary transfer belt, 62…Secondary transfer opposing roller 63...Primary transfer roller, 64...Secondary transfer roller, 71...Heat roller, 72...Pressure roller, 73...Heater, 73a...Center heater, 73b...Side heater, 73c...Side heater, 74...Temperature sensor, 74a, 74b, 74c...Temperature sensor, 75...Heater substrate, 76...Heater unit, 81...Temperature estimation circuit, 82...Estimation history retention circuit, 83...High frequency component extraction circuit, 84...Coefficient addition circuit, 85...Target temperature output circuit, 86...Difference comparison circuit, 87...Control signal generation circuit, 88...Power supply circuit, 91, 92...Memory circuit, 93...Temperature difference detection circuit, 94...Target temperature correction circuit, 101...Temperature control device.

Claims

1. A temperature control device that controls the power supplied to a heater based on a temperature estimate calculated over time so that the temperature-controlled object, which is heated by the heater of a fuser, reaches a preset target temperature, A temperature sensor for detecting the temperature of the heater, A first memory circuit that stores the temperature estimate obtained at any given time, A second memory circuit that stores the sensor temperature detected by the temperature sensor, A temperature difference detection circuit calculates the actual temperature rise from the temperature difference between the estimated temperature read from the first memory circuit and the heater temperature read from the second memory circuit. The system includes a target temperature correction circuit that controls the temperature to be lowered in accordance with the actual temperature rise, The target temperature correction circuit has a plurality of control correction temperatures correlated with the actual temperature rise, which is the difference between the normal temperature of the temperature-controlled target when the heater temperature rises and the current actual temperature of the temperature-controlled target. The temperature control device generates a corrected target temperature by subtracting the control correction temperature corresponding to the actual temperature rise from the currently set target temperature.

2. The temperature control device according to claim 1, wherein the temperature difference detection circuit has a temperature characteristic in which a first temperature rise, which consists of the difference between the estimated temperature and the sensor temperature, and the actual temperature rise, which consists of the difference between the normal temperature of the temperature-controlled target when the heater temperature rises and the current actual temperature of the temperature-controlled target, are correlated, and the actual temperature rise is estimated from the temperature characteristic based on the acquired estimated temperature and the sensor temperature.

3. The temperature control device further, The temperature control device according to claim 1, comprising a temperature estimation circuit that estimates the temperature of the temperature-controlled object from the heat capacity of the heater and the thermal resistance of the fuser based on the energization of the heater.

4. An image forming apparatus comprising the temperature control device described in claim 1.

5. A program that causes a processor to execute the processing performed by each circuit of the temperature control device described in any one of claims 1 to 3.

Images