Temperature control device and image forming apparatus

Abstract

To provide a temperature controller and an image forming apparatus that can reduce processing time.SOLUTION: A temperature controller according to an embodiment controls the temperature of a temperature control target to which heat is propagated from a heater by supplying power to the heater. The temperature controller is provided with a temperature estimation unit, and an adjustment unit. The temperature estimation unit estimates the temperature of a portion of the temperature control target not facing a medium based on energization to the heater. The adjustment unit adjusts the conveyance speed of the medium based on the estimated temperature of the portion not facing the medium.SELECTED DRAWING: Figure 8

Description

Technical Field

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

Background Art

[0002] An image forming apparatus includes a fixing device that fixes a toner image on a printing medium by applying heat and pressure to the printing medium by the fixing device. The fixing device includes a fixing rotating body (heat roller), a pressing member (press roller), a heating member (such as a heater), and a temperature sensor. The temperature sensor detects the surface temperature of the heat roller.

[0003] The image forming apparatus controls the surface temperature of the heat roller to reach a target value by increasing or decreasing the energization amount to the heater based on the detection signal (temperature sensor signal) of the temperature sensor.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As an example, consider a scenario where an image forming apparatus performs printing on a postcard and then on a portrait-oriented A4 sheet of paper. When the image forming apparatus performs printing on a postcard, the heat roller has two parts: one that faces the postcard and one that does not. Since temperature sensors are expensive, it is difficult to install many temperature sensors in an image forming apparatus. Therefore, the image forming apparatus can detect the surface temperature of the part that faces the postcard, but it cannot detect the surface temperature of the part that does not face the postcard. The part that faces the postcard loses heat from the printing medium and is controlled by the image forming apparatus to reach a target temperature. On the other hand, the part that does not face the postcard does not lose heat from the printing medium, so it accumulates heat and becomes hotter than the part that faces the printing medium.

[0006] Since the width of A4 portrait paper is greater than the width of a postcard, the portion of the A4 portrait paper that does not face the postcard is the portion that faces the A4 portrait paper. If the portion that does not face the postcard becomes too hot, a part of the A4 portrait paper will be heated to a temperature higher than the target temperature. This will negatively affect the fixing of the toner image on the A4 portrait paper. However, if the image forming apparatus performs the printing process on the postcard at a low speed, the surface temperature of the portion that does not face the postcard will decrease over time. Therefore, by performing low-speed printing, the image forming apparatus can prevent the portion that does not face the postcard from becoming too hot.

[0007] However, as mentioned above, the image forming apparatus cannot detect the surface temperature of parts of the postcard that are not in contact with it. Since the image forming apparatus cannot determine when to adjust the printing speed based on the surface temperature of parts of the postcard that are not in contact with it, it is necessary to perform low-speed printing from the beginning. Therefore, the processing time for the image forming apparatus to perform the printing process on the postcard becomes longer.

[0008] The problem that this invention aims to solve is to provide a temperature control device and an image forming apparatus that can shorten processing time. [Means for solving the problem]

[0009] A temperature control device according to one embodiment controls the temperature of a temperature-controlled object to which heat is transmitted from a heater by supplying power to the heater. The temperature control device comprises a temperature estimation unit and an adjustment unit. The temperature estimation unit estimates the temperature of a portion of the temperature-controlled object that does not come into contact with the medium, based on the power supplied to the heater. The adjustment unit adjusts the transport speed of the medium based on the estimated temperature of the portion that does not come into contact with the medium. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a diagram illustrating an example of the configuration of an image forming apparatus according to one embodiment. [Figure 2] Figure 2 is a diagram illustrating an example of the positional relationship between a heat roller, a heater, and multiple temperature sensors according to one embodiment. [Figure 3] Figure 3 is a diagram illustrating an example of the temperature distribution in a heat roller during the transport of A3 portrait paper according to one embodiment. [Figure 4] Figure 4 is a diagram illustrating an example of the temperature distribution in a heat roller during the transport of A4 portrait paper according to one embodiment. [Figure 5] Figure 5 is a diagram illustrating an example of the temperature distribution in a heat roller during postcard transport according to one embodiment. [Figure 6] Figure 6 is a diagram illustrating an example of the temperature distribution in a heat roller during envelope transport according to one embodiment. [Figure 7] Figure 7 is a diagram illustrating an example of the configuration of a heater energization control circuit according to one embodiment. [Figure 8] Figure 8 is a diagram illustrating an example of the configuration of a control circuit for a center according to one embodiment. [Figure 9] Figure 9 is a diagram illustrating a first thermal circuit that represents heat transfer for obtaining a first temperature estimation result according to one embodiment. [Figure 10]Figure 10 is a diagram illustrating a second thermal circuit that represents heat transfer for obtaining a second temperature estimation result according to one embodiment. [Figure 11] Figure 11 is a diagram illustrating an example of the configuration of a side control circuit according to one embodiment. [Figure 12] Figure 12 is a flowchart illustrating an example of WAE control operation by a center control circuit according to one embodiment. [Figure 13] Figure 13 is a diagram illustrating an example of WAE control operation by a center control circuit according to one embodiment. [Figure 14] Figure 14 is a diagram illustrating an example of WAE control operation by a center control circuit according to one embodiment. [Figure 15] Figure 15 is a diagram illustrating the processing cycle in a control circuit for a center according to one embodiment. [Figure 16] Figure 16 is a flowchart illustrating an example of the operation of print speed control in a control circuit for a center according to one embodiment. [Modes for carrying out the invention]

[0011] Hereinafter, a temperature control device and an image forming apparatus according to one embodiment will be described with reference to the drawings. Figure 1 is an explanatory diagram illustrating an example of the configuration of an image forming apparatus 1 according to one embodiment.

[0012] Image forming apparatus 1 is, for example, an MFP (Multifunction Peripheral) that performs various processing such as image formation while transporting a printing medium P. Image forming apparatus 1 is, for example, a solid-state scanning printer (e.g., an LED printer) that scans an LED (Light Emitting Diode) array that performs various processing such as image formation while transporting a printing medium P. Printing medium P is a printable medium. Printing medium P includes not only sheets such as paper, but also postcards or envelopes, etc. Printing medium P is an example of a medium. Image forming apparatus 1 is an example of a temperature control device.

[0013] For example, the image forming apparatus 1 is configured to receive toner from a toner cartridge and form an image on a print medium P using the received toner. The toner may be a single-color toner, or may be a color toner such as cyan, magenta, yellow, and black. Further, the toner may be a decoloring toner that decolors when heat is applied.

[0014] As shown in FIG. 1, the image forming apparatus 1 includes a housing 11, a communication interface 12, a system controller 13, a heater energization control circuit 14, a display unit 15, an operation interface 16, a plurality of paper trays 17, a paper discharge tray 18, a conveyance unit 19, an image forming unit 20, and a fixing unit 21.

[0015] The housing 11 is the main body of the image forming apparatus 1. The housing 11 houses the communication interface 12, the system controller 13, the heater energization control circuit 14, the plurality of paper trays 17, the conveyance unit 19, the image forming unit 20, and the fixing unit 21. The housing 11 is provided with the display unit 15, the operation interface 16, and the paper discharge tray 18.

[0016] First, the configuration of the control system of the image forming apparatus 1 will be described. The communication interface 12 is an interface for communicating with other devices. The communication interface 12 is used, for example, for communication with a host device (external device). The communication interface 12 is configured as, for example, a LAN (Local Area Network) connector or the like. Further, the communication interface 12 may perform wireless communication with other devices according to a standard such as Bluetooth (registered trademark) or Wi-fi (registered trademark).

[0017] The system controller 13 controls the image forming apparatus 1. The system controller 13 includes, for example, a processor 22 and a memory 23.

[0018] The processor 22 is an arithmetic element that performs calculations. The processor 22 is, for example, a CPU (Central Processing Unit). The processor 22 performs various processes based on data such as programs stored in the memory 23. The processor 22 functions as a control unit capable of performing various operations by executing programs stored in the memory 23. The processor 22 is an example of a processing circuit.

[0019] The processor 22 performs various information processing by executing programs stored in memory 23. For example, the processor 22 generates a print job based on an image acquired from an external device via the communication interface 12. The processor 22 stores the generated print job in memory 23.

[0020] A print job includes image data that represents the image to be formed on a print medium P. The image data may be data for forming an image on one print medium P, or data for forming an image on multiple print mediums P. Furthermore, a print job includes information indicating whether it is a color print or a monochrome print. A print job may also include information such as the number of copies to be printed (number of page sets) and the number of pages per copy.

[0021] 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 supplies the print control information to the heater power supply control circuit 14.

[0022] 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 printing medium P by the transport unit 19 and the formation of an image on the printing medium P by the image forming unit 20.

[0023] Memory 23 is a storage medium that stores programs and data used by those programs. Furthermore, memory 23 functions as working memory. That is, memory 23 temporarily stores data being processed by processor 22 and programs executed by processor 22. For example, memory 23 includes RAM (Random-Access Memory).

[0024] The image forming apparatus 1 may also be configured to include an engine controller separate from the system controller 13. In this case, the engine controller controls the transport of the printing medium P by the transport unit 19 and the formation of images on the printing medium P by the image forming unit 20. In this case, the system controller 13 supplies the engine controller with the information necessary for control by the engine controller.

[0025] Furthermore, the image forming apparatus 1 includes a power conversion circuit (not shown) that uses the AC voltage of an AC power supply to supply DC voltage to various components within the image forming apparatus 1. The power conversion circuit supplies the DC voltage necessary for the operation of the processor 22 and 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 printing medium P 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.

[0026] The heater power supply control circuit 14 independently controls the power supply to the center heater 73-1 and the two side heaters 73-2, which are included in the heater 73 of the fuser unit 21. The center heater 73-1 and the side heaters 73-2 are examples of heaters. The heater power supply control circuit 14 generates and supplies the power supply PC to the center heater 73-1. The heater power supply control circuit 14 generates and supplies the power supply PS to the two side heaters 73-2. The power supply PC and power supply PS are examples of power. A detailed explanation of the heater power supply control circuit 14 will be given later.

[0027] The display unit 15 includes a display that shows a screen in response to video signals input from a display control unit such as a system controller 13 or a graphics controller (not shown). For example, the display of the display unit 15 shows screens for various settings of the image forming apparatus 1.

[0028] The operation interface 16 includes an operating component. The operation interface 16 supplies an operation signal to the system controller 13 in response to the operation of the operating component. The operating component is, for example, a touch sensor, a numeric keypad, a power key, a paper feed key, various function keys, or a keyboard. The touch sensor 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.

[0029] Each of the multiple paper trays 17 is a cassette that holds a print medium P. The paper trays 17 are configured to be able to receive the print medium P from outside the housing 11. For example, the paper trays 17 are configured to be able to be pulled out from the housing 11.

[0030] The output tray 18 is a tray that supports the printing medium P discharged from the image forming apparatus 1.

[0031] Next, we will describe the configuration for transporting the printing medium P in the image forming apparatus 1. The transport unit 19 is a mechanism for transporting the printing 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.

[0032] The paper feed path 31 and the paper discharge path 32 are each composed of multiple motors, multiple rollers, and multiple guides (not shown). The multiple motors rotate their shafts based on the control of the system controller 13, thereby rotating the rollers that are linked to the rotation of the shafts. The multiple rollers transport the printing medium P by rotating. The multiple guides control the transport direction of the printing medium P.

[0033] The paper feed transport path 31 takes in the printing medium P from the paper tray 17 and supplies the taken printing medium P to the image forming unit 20. The paper feed transport path 31 is equipped with a pickup roller 33 corresponding to each paper tray. Each pickup roller 33 takes in the printing medium P from the paper tray 17 into the paper feed transport path 31.

[0034] The paper output transport path 32 is a transport path that discharges the printed medium P on which the image has been formed from the housing 11. The printed medium P discharged by the paper output transport path 32 is supported by the paper output tray 18.

[0035] Next, the image forming unit 20 will be described. The image forming unit 20 is configured to form an image on the printing medium P. Specifically, the image forming unit 20 forms an image on the printing medium P based on a print job generated by the processor 22.

[0036] 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. Since the plurality of process units 41 and the plurality of exposure units 42 each have the same configuration, each process unit 41 and exposure unit 42 will be described separately.

[0037] First, let's explain the process unit 41. The process unit 41 is configured to form a toner image. For example, multiple process units 41 are provided for each type of toner. For example, multiple process units 41 correspond to color toners such as cyan, magenta, yellow, and black. Specifically, each process unit 41 is connected to a toner cartridge containing a different color toner.

[0038] A toner cartridge comprises a toner container and a toner dispensing mechanism. The toner container is a container that holds the toner. The toner dispensing mechanism is a mechanism consisting of a screw or the like that dispenses the toner from the toner container.

[0039] The process unit 41 includes a photosensitive drum 51, a charging charger 52, and a developing unit 53. The photosensitive drum 51 is a photoreceptor comprising 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 (not shown).

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

[0041] The developing unit 53 is a device that deposits toner onto the photosensitive drum 51. The developing unit 53 includes a developer container, an agitation mechanism, a developing roller, a doctor blade, and an automatic toner control (ATC) sensor, etc.

[0042] The developer container is a container that receives and stores the toner dispensed from the toner cartridge. A carrier is pre-packaged inside the developer container. The toner dispensed from the toner cartridge is mixed with the carrier by an agitation mechanism, forming a developer mixture of toner and carrier. The carrier is placed inside the developer container during the manufacturing of the developer unit 53.

[0043] The developing roller rotates within the developer container, thereby applying developer to its surface. The doctor blade is a component positioned at a predetermined distance from the surface of the developing roller. The doctor blade removes a 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 with a thickness corresponding to the distance between the doctor blade and the surface of the developing roller.

[0044] 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 a motor (not shown) that drives the toner cartridge delivery mechanism, causing the toner to be delivered from the toner cartridge to the developer container of the developer unit 53.

[0045] 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.

[0046] 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.

[0047] In the above configuration, when light from the exposure unit 42 is shone onto the surface of the photosensitive drum 51, which has been charged by the charging charger 52, an electrostatic latent image is formed. 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.

[0048] Next, the transcription mechanism 43 will be explained. The transfer mechanism 43 is configured to transfer the toner image formed on the surface of the photosensitive drum 51 to the printing medium P.

[0049] 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 secondary transfer rollers 64.

[0050] 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.

[0051] The secondary transfer opposing roller 62 is rotated by a motor (not shown). By rotating, the secondary transfer opposing roller 62 conveys the primary transfer belt 61 in a predetermined conveying direction. The multiple winding rollers are configured to rotate freely. The multiple winding rollers rotate in accordance with the movement of the primary transfer belt 61 by the secondary transfer opposing roller 62.

[0052] Multiple primary transfer rollers 63 are configured to bring the primary transfer belt 61 into contact with the photosensitive drum 51 of the process unit 41. The multiple primary transfer rollers 63 are provided to correspond to the photosensitive drums 51 of the multiple process units 41. Specifically, each of the multiple primary transfer rollers 63 is provided at a position 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.

[0053] The secondary transfer roller 64 is positioned opposite the primary transfer belt 61. The secondary transfer roller 64 contacts the outer circumferential surface of the primary transfer belt 61 and applies pressure. This forms a transfer nip where the secondary transfer roller 64 and the outer circumferential surface of the primary transfer belt 61 are in close contact. When the printing medium P passes through the transfer nip, the secondary transfer roller 64 presses the printing medium P passing through the transfer nip against the outer circumferential surface of the primary transfer belt 61.

[0054] The secondary transfer roller 64 and the secondary transfer opposing roller 62 rotate to transport the printing medium P supplied from the paper feed transport path 31 while gripping it. This allows the printing medium P to pass through the transfer nip.

[0055] In the above configuration, 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 includes a plurality of process units 41, the primary transfer belt 61 receives toner images from the photosensitive drums 51 of the plurality of process units 41. The toner image transferred to the outer surface of the primary transfer belt 61 is transported by the primary transfer belt 61 to the transfer nip where the secondary transfer roller 64 and the outer surface of the primary transfer belt 61 are in close contact. If a printing 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 printing medium P at the transfer nip.

[0056] Next, the configuration related to fixing in the image forming apparatus 1 will be described. The fuser 21 fixes the toner image onto the printing medium P onto which the toner image has been transferred. The fuser 21 operates based on the control of the system controller 13 and the heater power supply control circuit 14. The fuser 21 comprises a fixing rotating body, a pressurizing member, and a heating member. The fixing rotating body is, for example, a heat roller 71. The heat roller 71 heats the toner image formed on the printing medium P and fixes it onto the printing medium P. The pressurizing member is, for example, a press roller 72. The heating member is, for example, a heater 73 that heats the heat roller 71. The heater 73 includes a center heater 73-1 and two side heaters 73-2, as will be described later. Furthermore, the fuser 21 is equipped with temperature sensors (thermal sensors) 74-1 and 74-2 to detect the temperature of the heat roller 71. The positional relationship between the heat roller 71, the heater 73, and the temperature sensors 74-1 and 74-2 will be described later.

[0057] The heat roller 71 is a fixing rotating body that rotates with a motor (not shown). The heat roller 71 has a hollow metal core and an elastic layer formed on the outer circumference of the core. The inside of the hollow metal core of the heat roller 71 is heated by a heater 73 positioned inside the core. The heat generated inside the core is transferred to the surface of the heat roller 71 (i.e., the surface of the elastic layer), which is on the outside.

[0058] The press roller 72 is positioned opposite the heat roller 71. The press roller 72 has a core made of metal with a predetermined outer diameter and an elastic layer formed on the outer circumference of the core. The press roller 72 applies pressure to the heat roller 71 due to stress applied from a tension member (not shown). The pressure applied from the press roller 72 to the heat roller 71 forms a nip (fixing nip) where the press roller 72 and the heat roller 71 are in close contact. The press roller 72 is rotated by a motor (not shown). As the press roller 72 rotates, it transports the printing medium P that has entered the fixing nip and presses the printing medium P against the heat roller 71.

[0059] The heater 73 is a device that generates heat through the electric current supplied from the heater power control circuit 14. For example, the center heater 73-1 generates heat through the electric current PC supplied from the heater power control circuit 14. The two side heaters 73-2 generate heat through the electric current PS supplied from the heater power control circuit 14. The heater 73 is, for example, a halogen heater. The heater 73 generates heat inside the core metal of the heat roller 71 through electromagnetic waves emitted from the halogen lamp heater by the electric current supplied from the heater power control circuit 14, which is the heat source. Alternatively, the heater 73 may be, for example, an induction heater.

[0060] Temperature sensors 74-1 and 74-2 detect the temperature of the heat roller 71. Here, it is described that temperature sensors 74-1 and 74-2 detect the surface temperature of the heat roller 71. The surface temperature of the heat roller 71 is just one example of the temperature of the heat roller 71. Temperature sensors 74-1 and 74-2 may also detect the temperature of the air near the surface of the heat roller 71. Note that temperature sensors 74-1 and 74-2 only need to be positioned in a location where they can detect changes in the surface temperature of the heat roller 71.

[0061] The temperature sensor 74-1 supplies the temperature detection result TdC of the heat roller 71 detected by the temperature sensor 74-1 to the heater power supply control circuit 14. The temperature detection result TdC is the surface temperature of the heat roller 71 detected by the temperature sensor 74-1. The temperature detection result TdC may also refer to a signal indicating the surface temperature of the heat roller 71 detected by the temperature sensor 74-1.

[0062] The temperature sensor 74-2 supplies the temperature detection result TdS of the heat roller 71 detected by the temperature sensor 74-2 to the heater power supply control circuit 14. The temperature detection result TdS is the surface temperature of the heat roller 71 detected by the temperature sensor 74-2. The temperature detection result TdS may also refer to a signal indicating the surface temperature of the heat roller 71 detected by the temperature sensor 74-2.

[0063] With the above configuration, the heat roller 71 and press roller 72 apply heat and pressure to the printing medium P as it passes through the fuser nip. The toner on the printing medium P is melted by the heat supplied by the heat roller 71 and applied to the surface of the printing medium P by the pressure supplied by the heat roller 71 and press roller 72. As a result, the toner image is fixed to the printing medium P as it passes through the fuser nip. The printing medium P that has passed through the fuser nip is introduced into the paper output transport path 32 and discharged into the paper output tray 18.

[0064] Next, the positional relationship between the heat roller 71, the heater 73, and the temperature sensors 74-1 and 74-2 will be explained. Figure 2 is a diagram illustrating an example of the positional relationship between the heat roller 71, the heater 73, and the temperature sensors 74-1 and 74-2.

[0065] The longitudinal direction of the heat roller 71 is parallel to the direction perpendicular to the transport direction of the printing medium P. The longitudinal size of the heat roller 71 is larger than the width of an A3 portrait sheet of paper. An A3 portrait sheet of paper is the widest printing medium P that can be used in the image forming apparatus 1.

[0066] The heater 73 is mounted parallel to the longitudinal direction of the heat roller 71. The longitudinal size of the heater 73 is approximately the same as the longitudinal size of the heat roller 71. One longitudinal end of the heater 73 is at approximately the same position as one longitudinal end of the heat roller 71. The other longitudinal end of the heater 73 is at approximately the same position as the other longitudinal end of the heat roller 71.

[0067] The heater 73 has a center heater 73-1 and side heaters 73-2 on each side. The longitudinal size of the center heater 73-1 is smaller than the width of A3 portrait paper and larger than the width of A4 portrait paper. The center heater 73-1 heats the portion of the heat roller 71 that is opposite to the center heater 73-1. For example, the portion of the heat roller 71 that is opposite to the center heater 73-1 is the portion of the heat roller 71 that is opposite to the center heater 73-1 in the longitudinal direction of the heat roller 71. The portion of the heat roller 71 that is opposite to the center heater 73-1 is the central portion of the heat roller 71 in the longitudinal direction. The portion of the heat roller 71 that is opposite to the center heater 73-1 is the portion of the heat roller 71 that receives heat from the center heater 73-1. The side heaters 73-2 heat the portion of the heat roller 71 that is opposite to the side heaters 73-2. For example, the portion of the heat roller 71 facing the side heater 73-2 is the portion of the heat roller 71 that faces the side heater 73-2 in the longitudinal direction. The portion of the heat roller 71 facing the side heater 73-2 is the end portion of the heat roller 71 in the longitudinal direction. The portion of the heat roller 71 facing the side heater 73-2 is the portion of the heat roller 71 to which heat is transmitted from the side heater 73-2.

[0068] The temperature sensor 74-1 detects the surface temperature of a first position on the heat roller 71. The first position is the portion of the heat roller 71 facing the center heater 73-1, regardless of the width of the printing medium P, that faces the printing medium P. For example, the portion of the heat roller 71 facing the printing medium P is the portion facing the printing medium P in the longitudinal direction of the heat roller 71. For example, the first position is the center position in the longitudinal direction of the heat roller 71. Therefore, the temperature detection result TdC is the surface temperature of the portion of the heat roller 71 facing the printing medium P, as detected by the temperature sensor 74-1.

[0069] The temperature sensor 74-2 detects the surface temperature of a second position on the heat roller 71. The second position is the part of the heat roller 71 that faces a single side heater 73-2 and is the part of the heat roller 71 that faces a vertical A3 sheet of paper. Therefore, the temperature detection result TdS is the surface temperature of the part of the heat roller 71 that faces a vertical A3 sheet of paper, as detected by the temperature sensor 74-2.

[0070] Furthermore, the heater power supply control circuit 14 only needs to control the power supply to each of the two side heaters 73-2 in the same way based on the temperature detection result TdS from the temperature sensor 74-2. Therefore, the fuser 21 only needs to include one temperature sensor 74-2 that detects the surface temperature of the portion of the heat roller 71 facing either of the two side heaters 73-2.

[0071] Next, we will explain the temperature distribution in the heat roller 71 according to the type of printing medium P. This section explains the case where the print medium P is A3 portrait paper. Figure 3 illustrates an example of the temperature distribution in the heat roller 71 during the transport of A3 portrait-oriented paper.

[0072] The width of a portrait A3 sheet of paper is greater than the length of the center heater 73-1. Therefore, the portrait A3 sheet of paper faces the entire portion of the heat roller 71 that is facing the center heater 73-1. The portrait A3 sheet of paper faces a portion of the heat roller 71 that is facing the two side heaters 73-2. The heater power control circuit 14 supplies power PC to the center heater 73-1. The center heater 73-1 generates heat due to the power PC, heating the portion of the heat roller 71 that is facing the center heater 73-1. The heater power control circuit 14 supplies power PS to the two side heaters 73-2. The two side heaters 73-2 generate heat due to the power PS, heating the portions of the heat roller 71 that are facing the two side heaters 73-2.

[0073] In the heat roller 71, the portion facing the center heater 73-1 is the portion that is heated and faces the A3 portrait paper. In the portion of the heat roller 71 facing the two side heaters 73-2, there is a portion that is heated and faces the A3 portrait paper, and a portion that is heated and does not face the A3 portrait paper. The portion that is heated and faces the A3 portrait paper is shown in light gray. The portion that is heated and does not face the A3 portrait paper is shown in dark gray. The temperature of the portion that is heated and faces the A3 portrait paper is the target temperature controlled by the heater energization control circuit 14. The temperature of the portion that is heated and does not face the A3 portrait paper is higher than the target temperature because heat is not lost by the A3 portrait paper, and therefore heat is stored. Note that the size of A4 landscape and A3 portrait paper are the same, so the example of the temperature distribution in the heat roller 71 when transporting A4 landscape paper is the same as the example of the temperature distribution in the heat roller 71 when transporting A3 portrait paper described above.

[0074] This section explains the case where the print medium P is A4 portrait-oriented paper. Figure 4 illustrates an example of the temperature distribution in the heat roller 71 during the transport of A4 portrait-oriented paper.

[0075] The width of a portrait A4 sheet of paper is smaller than the length of the center heater 73-1. Therefore, the portrait A4 sheet of paper faces only a portion of the heat roller 71 that is facing the center heater 73-1. The portrait A4 sheet of paper does not face the entire portion of the heat roller 71 that is facing the two side heaters 73-2. The heater power control circuit 14 supplies power PC to the center heater 73-1. The center heater 73-1 generates heat due to the power PC, heating the portion of the heat roller 71 that is facing the center heater 73-1. The heater power control circuit 14 does not supply power PS to the two side heaters 73-2. The two side heaters 73-2 do not heat the portion of the heat roller 71 that is facing the two side heaters 73-2.

[0076] In the heat roller 71, the part facing the center heater 73-1 has a heated part that faces the A4 portrait paper and a heated part that does not face the A4 portrait paper. The part of the heat roller 71 facing the two side heaters 73-2 is an unheated part that does not face the A4 portrait paper. The heated part that faces the A4 portrait paper is shown in light gray. The heated part that does not face the A4 portrait paper is shown in dark gray. The unheated part that does not face the A4 portrait paper is shown with diagonal lines. The temperature of the heated part that faces the A4 portrait paper is the target temperature controlled by the heater energization control circuit 14. The temperature of the heated part that does not face the A4 portrait paper is higher than the target temperature because heat is not lost by the A4 portrait paper, and heat is stored. The temperature of the unheated part that does not face the A4 portrait paper is room temperature.

[0077] This section explains the case where the printing medium P is a postcard. Figure 5 illustrates an example of the temperature distribution in the heat roller 71 during postcard transport.

[0078] The width of the postcard is smaller than the length of the center heater 73-1. Therefore, the postcard faces only a portion of the heat roller 71 that is facing the center heater 73-1. The postcard does not face the entire portion of the heat roller 71 that is facing the two side heaters 73-2. The heater power control circuit 14 supplies power PC to the center heater 73-1. The center heater 73-1 generates heat due to the power PC and heats the portion of the heat roller 71 that is facing the center heater 73-1. The heater power control circuit 14 does not supply power PS to the two side heaters 73-2. The two side heaters 73-2 do not heat the portion of the heat roller 71 that is facing the two side heaters 73-2. In the heat roller 71, the portion facing the center heater 73-1 has a heated portion that faces the postcard and a heated portion that does not face the postcard. The portion of the heat roller 71 facing the two side heaters 73-2 is an unheated portion that does not face the postcard. The heated portion that faces the postcard is shown in light gray. The heated portion that does not face the postcard is shown in dark gray. The unheated portion that does not face the postcard is shown with diagonal lines. The temperature of the heated portion that faces the postcard is the target temperature controlled by the heater energization control circuit 14. The temperature of the heated portion that does not face the postcard is higher than the target temperature due to heat storage, as heat is not lost by the postcard. The temperature of the unheated portion that does not face the postcard is room temperature. Note that the area of ​​the heated portion that does not face the postcard is larger than the area of ​​the heated portion that does not face the A4 portrait paper as illustrated in Figure 4.

[0079] This section explains the case where the printing medium P is an envelope. Figure 6 illustrates an example of the temperature distribution in the heat roller 71 during envelope transport.

[0080] The width of the envelope is smaller than the length of the center heater 73-1. Therefore, the envelope faces only a portion of the heat roller 71 that faces the center heater 73-1. The envelope does not face the entire portion of the heat roller 71 that faces the two side heaters 73-2. The heater power control circuit 14 supplies power PC to the center heater 73-1. The center heater 73-1 generates heat due to the power PC and heats the portion of the heat roller 71 that faces the center heater 73-1. The heater power control circuit 14 does not supply power PS to the two side heaters 73-2. The two side heaters 73-2 do not heat the portion of the heat roller 71 that faces the two side heaters 73-2.

[0081] In the heat roller 71, the portion facing the center heater 73-1 has a heated portion that faces the envelope and a heated portion that does not face the envelope. The portion of the heat roller 71 facing the two side heaters 73-2 is an unheated portion that does not face the envelope. The heated portion that faces the envelope is shown in light gray. The heated portion that does not face the envelope is shown in dark gray. The unheated portion that does not face the envelope is shown with diagonal lines. The temperature of the heated portion that faces the envelope is the target temperature controlled by the heater energization control circuit 14. The temperature of the heated portion that does not face the envelope is higher than the target temperature due to heat storage, as heat is not lost by the envelope. The temperature of the unheated portion that does not face the envelope is room temperature. Note that the area of ​​the heated portion that does not face the envelope is larger than the area of ​​the heated portion that does not face the A4 portrait paper as illustrated in Figure 4.

[0082] Next, the heater power supply control circuit 14 will be described. Figure 7 is a diagram illustrating an example of the configuration of the heater energization control circuit 14. The heater power supply control circuit 14 includes a center control circuit 14-1 and a side control circuit 14-2.

[0083] The center control circuit 14-1 supplies power PC to the center heater 73-1 by controlling the power supply from the fuser 21 to the center heater 73-1. By supplying power PC to the center heater 73-1, the center control circuit 14-1 controls the surface temperature of the heat roller 71 to which heat is transferred from the center heater 73-1. For example, the heat roller 71 to which heat is transferred from the center heater 73-1 is the part of the heat roller 71 that faces the center heater 73-1. The center control circuit 14-1 supplies power PC to the center heater 73-1 regardless of the width size of the printing medium P to be printed.

[0084] The side control circuit 14-2 supplies energizing power PS to the two side heaters 73-2 of the fuser 21 by controlling the power supply to the two side heaters 73-2. By supplying energizing power PS to the two side heaters 73-2, the side control circuit 14-2 controls the surface temperature of the heat roller 71 to which heat is transmitted from the two side heaters 73-2. For example, the part of the heat roller 71 to which heat is transmitted from the two side heaters 73-2 is the part of the heat roller 71 that faces the two side heaters 73-2. The side control circuit 14-2 switches between running or stopping the power supply to the two side heaters 73-2 depending on the width size of the printing medium P to be printed. When the printing medium P to be printed faces a part of the heat roller 71 that faces the two side heaters 73-2, the side control circuit 14-2 runs the power supply to the two side heaters 73-2. If the printing medium P to be printed does not face the portion of the heat roller 71 that is facing the two side heaters 73-2, the side control circuit 14-2 stops supplying power to the two side heaters 73-2.

[0085] Next, the control circuit 14-1 for the center will be described. Figure 8 is a diagram illustrating an example of the configuration of the center control circuit 14-1. In the explanation of Figure 8, the portion of the heat roller 71 that faces the center heater 73-1 and is in contact with the printing medium P is referred to as the portion of the heat roller 71 that faces the printing medium P. The portion of the heat roller 71 that does not face the printing medium P and is in contact with the center heater 73-1 is referred to as the portion of the heat roller 71 that does not face the printing medium P.

[0086] As shown in Figure 8, the center control circuit 14-1 includes a first temperature estimation unit 81-1, a first estimation history retention unit 82-1, a high-frequency component extraction unit 83-1, a coefficient addition unit 84-1, a target temperature output unit 85-1, a difference comparison unit 86-1, a control duty generation unit 87-1, an external limit unit 88-1, a duty pulse conversion unit 89-1, a power supply circuit 90-1, a second temperature estimation unit 91-1, a second estimation history retention unit 92-1, a first difference calculation unit 93-1, a temperature correction unit 94-1, and a second difference calculation unit 95-1. The center control circuit 14-1 also receives the temperature detection result TdC from the temperature sensor 74-1 as input.

[0087] The first temperature estimation unit 81-1 performs a temperature estimation process to estimate the surface temperature of the portion of the heat roller 71 that faces the printing medium P. The first temperature estimation unit 81-1 estimates the surface temperature of the portion of the heat roller 71 that faces the printing medium P by real-time simulation of the thermal circuit. The first temperature estimation unit 81-1 receives the first estimation history PREVC from the first estimation history holding unit 82-1 and the duty cycle LDC from the external limit unit 88-1 as inputs.

[0088] The first estimated history PREVC is the history of the first temperature estimation result ESTC by the first temperature estimation unit 81-1. The first estimated history PREVC may also refer to a signal indicating the history of the first temperature estimation result ESTC by the first temperature estimation unit 81-1. The history of the first temperature estimation result ESTC by the first temperature estimation unit 81-1 includes a plurality of past first temperature estimation results ESTC. The first temperature estimation result ESTC is the surface temperature of the portion of the heat roller 71 facing the printing medium P, estimated by the first temperature estimation unit 81-1 based on at least the duty cycle LDC. The estimated surface temperature of the portion of the heat roller 71 facing the printing medium P may also be referred to as the estimated surface temperature of the portion of the heat roller 71 facing the printing medium P. The first temperature estimation result ESTC is also the temperature used to control the estimated surface temperature of the portion of the heat roller 71 facing the printing medium P. The first temperature estimation result ESTC may also refer to a signal indicating the surface temperature of the portion of the heat roller 71 facing the printing medium P, which is estimated by the first temperature estimation unit 81-1 based at least on the duty cycle LDC.

[0089] The duty cycle value LDC is the duty cycle value based on the duty cycle value DUTYC. The duty cycle value LDC may also refer to a signal indicating the duty cycle value based on the duty cycle value DUTYC. The duty cycle value LDC may be the same value as the duty cycle value DUTYC, or it may be a different value from the duty cycle value DUTYC. If the external limit unit 88-1 does not limit the duty cycle value DUTYC, the duty cycle value LDC is the same value as the duty cycle value DUTYC. If the external limit unit 88-1 limits the duty cycle value DUTYC, the duty cycle value LDC is the duty cycle value after the limit imposed by the external limit unit 88-1, and is a different value from the duty cycle value DUTYC.

[0090] The duty cycle value DUTYC is the duty cycle value generated by the control duty cycle generation unit 87-1. The duty cycle value DUTYC may also refer to the signal indicating the duty cycle value generated by the control duty cycle generation unit 87-1.

[0091] The first temperature estimation unit 81-1 estimates the surface temperature of the portion of the heat roller 71 facing the printing medium P based on the duty cycle value LDC. Based on the estimation, the first temperature estimation unit 81-1 generates a first temperature estimation result ESTC. The first temperature estimation unit 81-1 outputs the first temperature estimation result ESTC to the first estimation history holding unit 82-1, the high-frequency component extraction unit 83-1, and the first difference calculation unit 93-1. As described above, the duty cycle value LDC is a duty cycle value based on the duty cycle value DUTYC. Therefore, estimating the surface temperature based on the duty cycle value LDC is one example of estimating the surface temperature based on the duty cycle value DUTYC. As described above, the duty cycle value LDC may also be the duty cycle value after being limited by the external limit unit 88-1. Therefore, estimating the surface temperature based on the duty cycle value LDC includes estimating the surface temperature based on the duty cycle value after being limited by the external limit unit 88-1. The energizing pulse PsC is generated based on the duty cycle value LDC. Therefore, estimating the surface temperature based on the duty cycle LDC is one example of estimating the surface temperature based on the energization of the center heater 73-1.

[0092] In a typical example, the first temperature estimation unit 81-1 estimates the surface temperature of the portion of the heat roller 71 facing the printing medium P based on the first estimated history PREVC and duty cycle LDC. Estimating the surface temperature based on the first estimated history PREVC and duty cycle LDC is an example of estimating the surface temperature based on the first estimated history PREVC and duty cycle DUTYC. Estimating the surface temperature based on the first estimated history PREVC and duty cycle LDC includes estimating the surface temperature based on the first estimated history PREVC and the duty cycle value after being limited by the external limit unit 88-1. Estimating the surface temperature based on the first estimated history PREVC and duty cycle LDC is an example of estimating the surface temperature based on the first estimated history PREVC and the energization of the center heater 73-1.

[0093] The first temperature estimation unit 81-1 may use an energizing pulse PsC instead of the duty cycle LDC. The energizing pulse PsC is an example of energizing the center heater 73-1.

[0094] The first estimated history storage unit 82-1 stores the first estimated history PREVC. The first estimated history storage unit 82-1 outputs the first estimated history PREVC to the first temperature estimation unit 81-1.

[0095] The high-frequency component extraction unit 83-1 performs high-pass filtering to extract the high-frequency components of the first temperature estimation result ESTC. For example, the high-frequency component extraction unit 83-1 cancels the DC component of the first temperature estimation result ESTC and extracts only the high-frequency components. The high-frequency component extraction unit 83-1 generates a high-frequency component HPFC and outputs the high-frequency component HPFC to the coefficient addition unit 84-1. The high-frequency component HPFC is the high-frequency component of the first temperature estimation result ESTC extracted by the high-frequency component extraction unit 83-1. The high-frequency component HPFC may also refer to a signal indicating the high-frequency component of the first temperature estimation result ESTC extracted by the high-frequency component extraction unit 83-1.

[0096] The coefficient addition unit 84-1 performs a coefficient addition process to correct the first temperature estimation result ESTC. The coefficient addition unit 84-1 receives the temperature detection result TdC from the temperature sensor 74-1 and the high-frequency component HPFC from the high-frequency component extraction unit 83-1 as inputs. The coefficient addition unit 84-1 obtains the first temperature correction result WAEC based on the high-frequency component HPFC and the temperature detection result TdC. The first temperature correction result WAEC is the corrected temperature of the part of the heat roller 71 facing the printing medium P. The corrected temperature of the part of the heat roller 71 facing the printing medium P is the temperature obtained by correcting the first temperature estimation result ESTC. The first temperature correction result WAEC is the value obtained by correcting the temperature detection result TdC based on the high-frequency component HPFC in order to correct the first temperature estimation result ESTC. The first temperature correction result WAEC may also refer to a signal indicating the corrected temperature of the part of the heat roller 71 facing the printing medium P. The coefficient addition unit 84-1 outputs the first temperature correction result WAEC to the difference comparison unit 86-1 and the temperature correction unit 94-1.

[0097] Specifically, the coefficient addition unit 84-1 multiplies the high-frequency component HPFC by a preset coefficient KC. The coefficient addition unit 84-1 adds the value obtained by multiplying the high-frequency component HPFC by the coefficient KC to the temperature detection result TdC. The coefficient addition unit 84-1 calculates the value obtained by (TdC + KC × HPFC) as the first temperature correction result WAEC. The high-frequency component HPFC is based on the first temperature estimation result ESTC. Therefore, calculating the first temperature correction result WAEC based on the high-frequency component HPFC and the temperature detection result TdC is an example of calculating the first temperature correction result WAEC based on the first temperature estimation result ESTC and the temperature detection result TdC. The coefficient addition unit 84-1 is an example of a calculation unit that calculates the first temperature correction result WAEC.

[0098] For example, when the coefficient KC is 1, the coefficient addition unit 84-1 directly adds the high-frequency component HPFC to the temperature detection result TdC. Also, for example, when the coefficient KC is 0.1, the coefficient addition unit 84-1 adds one-tenth of the value of the high-frequency component HPFC to the temperature detection result TdC. In this case, the effect of the high-frequency component HPFC is almost eliminated, and the result becomes close to the temperature detection result TdC. Also, for example, when the coefficient KC is 1 or greater, the effect of the high-frequency component HPFC can be expressed more strongly. Experiments have shown that the coefficient KC set in the coefficient addition unit 84-1 should not be an extreme value, and a value close to 1 is preferable. The first temperature correction result WAEC is a value that appropriately follows the surface temperature of the part of the actual heat roller 71 that faces the printing medium P.

[0099] The target temperature output unit 85-1 performs output processing to output a preset target temperature TGTC to the difference comparison unit 86-1. The target temperature TGTC is the target surface temperature of the portion of the heat roller 71 that faces the printing medium P. The target temperature TGTC may also refer to a signal indicating the target temperature. The target temperature TGTC can be changed by rewriting it according to a command from the processor 22. The target temperature TGTC may also be stored in the memory 23.

[0100] For example, the target temperature TGTC is set for each printing process. For example, the target temperature TGTC varies depending on the quality of the printing medium P used in each printing process. For instance, quality refers to thickness. Generally, the target temperature TGTC is set so that a predetermined temperature can be maintained when the printing medium P is plain paper. The amount of heat absorbed from the heat roller 71 by the printing medium P as it passes through the fuser 21 increases with thicker cardboard than with plain paper. The surface temperature of the part of the heat roller 71 facing the printing medium P decreases more easily when printing on cardboard than when printing on plain paper. When the printing medium P is cardboard, the target temperature TGTC is higher than the target temperature TGTC associated with plain paper, taking into account the amount of heat absorbed from the heat roller 71 by the cardboard. This makes it easier to maintain a predetermined temperature at the surface of the part of the heat roller 71 facing the printing medium P. When the printing medium P is thinner than plain paper, the target temperature TGTC is lower than the target temperature TGTC associated with plain paper.

[0101] In another example, the target temperature TGTC varies depending on the status of the printing process. The printing process status includes various states related to the printing process. For example, printing process statuses include, but are not limited to, inrush current prevention, start-up heating, ready, printing start, printing in progress, and energy-saving ready. The target temperature TGTC for each status is different from one another. The target temperature TGTC for each status may be predetermined or variable.

[0102] The difference comparison unit 86-1 performs difference calculation processing. The difference comparison unit 86-1 receives the first temperature correction result WAEC from the coefficient addition unit 84-1 and the target temperature TGTC from the target temperature output unit 85-1 as inputs. The difference comparison unit 86-1 compares the target temperature TGTC with the first temperature correction result WAEC. Based on the comparison between the target temperature TGTC and the first temperature correction result WAEC, the difference comparison unit 86-1 calculates the first difference DIFC. The first difference DIFC is the difference between the target temperature TGTC and the first temperature correction result WAEC. The first difference DIFC may also refer to a signal indicating the difference between the target temperature TGTC and the first temperature correction result WAEC. The difference comparison unit 86-1 outputs the first difference DIFC to the control duty cycle generation unit 87-1. The difference comparison unit 86-1 is an example of a comparison unit.

[0103] Here, the first difference DIFC is explained as the value obtained by subtracting the target temperature TGTC from the first temperature-corrected result WAEC, but the reverse is also possible. In this example, if the first temperature-corrected result WAEC is lower than the target temperature TGTC, the first difference DIFC is a negative value. If the first temperature-corrected result WAEC is higher than the target temperature TGTC, the first difference DIFC is a positive value. The relationship between the target temperature TGTC and the first temperature-corrected result WAEC is reflected in the first difference DIFC.

[0104] The control duty generation unit 87-1 performs a duty value generation process to generate a duty value DUTYC. The control duty generation unit 87-1 receives a first difference DIFC from the difference comparison unit 86-1 as input. The control duty generation unit 87-1 generates a duty value DUTYC based on the first difference DIFC. The duty value DUTYC is the duty value corresponding to the first difference DIFC. If the first temperature correction result WAEC is equal to the target temperature TGTC, the duty value DUTYC is the center value (reference value) of the duty. If the first temperature correction result WAEC is lower than the target temperature TGTC, the control duty generation unit 87-1 increases the duty value above the center value of the duty in order to increase the amount of current supplied to the center heater 73-1. The duty value DUTYC is a value higher than the center value of the duty. On the other hand, if the first temperature correction result WAEC is higher than the target temperature TGTC, the control duty generation unit 87-1 reduces the duty value from the center value of the duty in order to reduce the amount of current supplied to the center heater 73-1. The duty value DUTYC is a value lower than the center value of the duty. The duty value DUTYC is a real number. For example, the duty value may have a resolution of 0 to 100. The control duty generation unit 87-1 outputs the duty value DUTYC to the external limit unit 88-1. The control duty generation unit 87-1 is an example of a duty generation unit.

[0105] As described above, the first temperature correction result WAEC is based on the first temperature estimation result ESTC and the temperature detection result TdC. The first difference DIFC is the difference between the target temperature TGTC and the first temperature correction result WAEC. Therefore, generating the duty cycle DUTYC based on the first difference DIFC includes generating the duty cycle based on the first temperature estimation result ESTC, the temperature detection result TdC, and the target temperature TGTC.

[0106] The external limit unit 88-1 performs limiting processing to restrict the duty cycle value DUTYC. The external limit unit 88-1 receives system protection information LMTC from the processor 22 and the duty cycle value DUTYC from the control duty generation unit 87-1. The external limit unit 88-1 reflects the system protection information LMTC in the duty cycle value DUTYC and generates the duty cycle value LDC based on the duty cycle value DUTYC. Reflecting the system protection information LMTC in the duty cycle value DUTYC includes applying the system protection information LMTC to the duty cycle value DUTYC. If the duty cycle value DUTYC does not satisfy the limit indicated by the system protection information LMTC, the external limit unit 88-1 restricts the duty cycle value DUTYC by reflecting the system protection information LMTC in the duty cycle value DUTYC. If the duty cycle value DUTYC satisfies the limit indicated by the system protection information LMTC, the external limit unit 88-1 does not restrict the duty cycle value DUTYC even if the system protection information LMTC is reflected in the duty cycle value DUTYC. The external limit unit 88-1 outputs the duty cycle value LDC to the first temperature estimation unit 81-1, the duty cycle pulse conversion unit 89-1, and the second temperature estimation unit 91-1. The external limit unit 88-1 is an example of a limit unit.

[0107] System protection information LMTC is information for limiting the duty cycle to protect the image forming apparatus 1. System protection information LMTC may also refer to a signal indicating information for limiting the duty cycle to protect the image forming apparatus 1. System protection information LMTC can be changed by commands from the processor 22.

[0108] For example, the system protection information LMTC contains information on at least one of the upper and lower limits of the duty cycle value. The upper limit of the duty cycle value is determined based on the power or current that can be supplied to the heater 73. The lower limit of the duty cycle value can be set arbitrarily. If the duty cycle value DUTYC exceeds the upper limit of the duty cycle value, the duty cycle value DUTYC does not meet the limit indicated in the system protection information LMTC. If the duty cycle value DUTYC is less than the lower limit of the duty cycle value, the duty cycle value DUTYC does not meet the limit indicated in the system protection information LMTC. If the duty cycle value DUTYC is greater than or equal to the lower limit and less than or equal to the upper limit of the duty cycle value, the duty cycle value DUTYC meets the limit indicated in the system protection information LMTC.

[0109] For example, suppose the upper limit of the duty cycle value is 85 and the lower limit is 0. Let's consider the case where the duty cycle value DUTYC is 90. Since the duty cycle value DUTYC exceeds the upper limit of the duty cycle value, the duty cycle value DUTYC does not satisfy the limit indicated in the system protection information LMTC. The external limit unit 88-1 limits the duty cycle value DUTYC by reflecting the system protection information LMTC in the duty cycle value DUTYC. The external limit unit 88-1 generates the duty cycle value LDC based on the duty cycle value DUTYC. The duty cycle value LDC is the duty cycle value after the limit. The duty cycle value after the limit is 85, which corresponds to the upper limit of the duty cycle value. Let's consider the case where the duty cycle value DUTYC is 80. Since the duty cycle value DUTYC is greater than or equal to the lower limit of the duty cycle value and less than or equal to the upper limit, the duty cycle value DUTYC satisfies the limit indicated in the system protection information LMTC. The external limit unit 88-1 does not limit the duty cycle value DUTYC, even if the system protection information LMTC is reflected in the duty cycle value DUTYC. The external limit unit 88-1 generates the duty cycle value LDC based on the duty cycle value DUTYC. The duty cycle value LDC is the same as the duty cycle value DUTYC, 80.

[0110] In another example, system protection information LMTC is information instructing a stop to avoid danger to the image forming apparatus 1. If the duty cycle value DUTYC is a value other than 0, the duty cycle value DUTYC does not satisfy the limit indicated by the system protection information LMTC. In this case, the external limit unit 88-1 limits the duty cycle value DUTYC by reflecting the system protection information LMTC in the duty cycle value DUTYC. The external limit unit 88-1 generates the duty cycle value LDC based on the duty cycle value DUTYC. The duty cycle value LDC is the limited duty cycle value. The limited duty cycle value is 0. If the duty cycle value DUTYC is 0, the duty cycle value DUTYC satisfies the limit indicated by the system protection information LMTC. In this case, even if the external limit unit 88-1 reflects the system protection information LMTC in the duty cycle value DUTYC, it does not limit the duty cycle value DUTYC. The external limit unit 88-1 generates the duty cycle value LDC based on the duty cycle value DUTYC. The duty cycle value LDC is the same as the duty cycle value DUTYC, which is 0.

[0111] The duty pulse conversion unit 89-1 performs a generation process to generate energizing pulses PsC for controlling the energizing power PC supplied to the center heater 73-1 based on the duty cycle value LDC. The energizing pulses PsC are pulse signals for controlling the energizing power PC supplied to the center heater 73-1. The energizing pulses PsC are gate signals of a triac. The duty cycle value LDC from the external limit unit 88-1 is input to the duty cycle pulse conversion unit 89-1. The duty cycle pulse conversion unit 89-1 converts the duty cycle value LDC into an energizing pulse train. The duty cycle pulse conversion unit 89-1 generates energizing pulses PsC that constitute the energizing pulse train. The duty cycle pulse conversion unit 89-1 outputs the energizing pulses PsC to the power supply circuit 90-1. The duty cycle value LDC is based on the first temperature compensation result WAEC. Therefore, generating an energizing pulse PsC based on the duty cycle value LDC is an example of generating an energizing pulse PsC based on the first temperature correction result WAEC. The duty cycle pulse conversion unit 89-1 is an example of a signal generation unit that generates an energizing pulse PsC.

[0112] As described above, the duty cycle value LDC may be the duty cycle value after being limited by the external limit unit 88-1. Therefore, generating and outputting an energizing pulse PsC based on the duty cycle value LDC includes generating and outputting an energizing pulse PsC based on the duty cycle value after being limited by the external limit unit 88-1. Generating and outputting an energizing pulse PsC based on the duty cycle value LDC is an example of generating and outputting an energizing pulse PsC based on the duty cycle value DUTYC.

[0113] The duty pulse conversion unit 89-1 may select a duty pattern based on the duty value LDC and generate an energizing pulse PsC according to the selected duty pattern. The duty pattern is a pattern corresponding to the duty value. The duty pattern represents an energizing pulse sequence composed of a number of "0" or "1" values ​​corresponding to the duty value. "1" indicates a conduction (on) signal. "0" indicates a cutoff (off) signal. The number of "1" values ​​varies depending on the duty value. The duty pattern may be stored in the memory 23.

[0114] The duty pulse conversion unit 89-1 may generate energizing pulses PsC asynchronously with the system operation. Specifically, the duty pulse conversion unit 89-1 may adjust the pulse frequency and the output time of the energizing pulses PsC to match the AC voltage frequency of 50Hz / 60Hz. The duty pulse conversion unit 89-1 acquires the AC voltage phase and performs synchronous output processing to output energizing pulses PsC that constitute an energizing pulse train in synchronization with the AC voltage, based on the AC voltage phase. The duty pulse conversion unit 89-1 outputs energizing pulses PsC in synchronization with the zero-crossing of the AC voltage.

[0115] The power supply circuit 90-1 supplies power PC to the center heater 73-1 based on the energizing pulse PsC. The power supply circuit 90-1 energizes the center heater 73-1 of the fuser 21 using an AC voltage supplied from an AC voltage source (not shown). The power supply circuit 90-1 supplies power PC to the center heater 73-1 by switching, for example, based on the energizing pulse PsC, between a state where the AC voltage from the AC voltage source is supplied to the center heater 73-1 and a state where it is not supplied. That is, the power supply circuit 90-1 changes the energizing time of the center heater 73-1 of the fuser 21 in accordance with the energizing pulse PsC.

[0116] The power supply circuit 90-1 may be integrated with the fuser 21. That is, the center control circuit 14-1 may be configured to supply energizing pulses PsC to the power supply circuit of the center heater 73-1 of the fuser 21, rather than supplying energizing power PC to the center heater 73-1.

[0117] As described above, the center control circuit 14-1 adjusts the amount of power supplied from the fuser 21 to the center heater 73-1. This allows the center control circuit 14-1 to control the surface temperature of the heat roller 71, from which heat is transferred by the center heater 73-1. This type of control will be referred to here as Weighted Average control with Estimate temperature (WAE control).

[0118] The second temperature estimation unit 91-1 performs a temperature estimation process to estimate the surface temperature of the portion of the heat roller 71 that does not come into contact with the printing medium P. The second temperature estimation unit 91-1 estimates the surface temperature of the portion of the heat roller 71 that does not come into contact with the printing medium P by real-time simulation of the thermal circuit. The portion of the heat roller 71 that does not come into contact with the printing medium P differs depending on the type of printing medium P. The second temperature estimation unit 91-1 receives the second estimation history PREVC-1 from the second estimation history holding unit 92-1 and the duty cycle LDC from the external limit unit 88-1 as input.

[0119] The second estimated history PREVC-1 is the history of the second temperature estimation result ESTC-1 by the second temperature estimation unit 91-1. The second estimated history PREVC-1 may also refer to a signal indicating the history of the second temperature estimation result ESTC-1 by the second temperature estimation unit 91-1. The history of the second temperature estimation result ESTC-1 by the second temperature estimation unit 91-1 includes multiple past second temperature estimation results ESTC-1. The second temperature estimation result ESTC-1 is the surface temperature of the part of the heat roller 71 that does not face the printing medium P, estimated by the second temperature estimation unit 91-1 based at least on the duty cycle LDC. The estimated surface temperature of the part of the heat roller 71 that does not face the printing medium P may also be referred to as the estimated surface temperature of the part of the heat roller 71 that does not face the printing medium P. The second temperature estimation result ESTC-1 is also the temperature used to determine high temperature of the part of the heat roller 71 that does not face the printing medium P. The second temperature estimation result ESTC-1 may also refer to a signal indicating the surface temperature of the portion of the heat roller 71 that does not face the printing medium P, which is estimated by the second temperature estimation unit 91-1 based at least on the duty cycle LDC.

[0120] The second temperature estimation unit 91-1 estimates the surface temperature of the portion of the heat roller 71 that does not face the printing medium P, based on the duty cycle value LDC. Based on the estimation, the second temperature estimation unit 91-1 generates a second temperature estimation result ESTC-1. The second temperature estimation unit 91-1 outputs the second temperature estimation result ESTC-1 to the second estimation history holding unit 92-1 and the first difference calculation unit 93-1. Estimating the surface temperature based on the duty cycle value LDC is an example of estimating the surface temperature based on the duty cycle value DUTYC. Estimating the surface temperature based on the duty cycle value LDC includes estimating the surface temperature based on the duty cycle value after being limited by the external limit unit 88-1. Estimating the surface temperature based on the duty cycle value LDC is an example of estimating the surface temperature based on the energization of the center heater 73-1.

[0121] In a typical example, the second temperature estimation unit 91-1 estimates the surface temperature of the portion of the heat roller 71 that does not face the printing medium P, based on the second estimated history PREVC-1 and the duty cycle value LDC. Estimating the surface temperature based on the second estimated history PREVC-1 and the duty cycle value LDC is an example of estimating the surface temperature based on the second estimated history PREVC-1 and the duty cycle value DUTYC. Estimating the surface temperature based on the second estimated history PREVC-1 and the duty cycle value LDC includes estimating the surface temperature based on the second estimated history PREVC-1 and the duty cycle value after being limited by the external limit unit 88-1. Estimating the surface temperature based on the second estimated history PREVC-1 and the duty cycle value LDC is an example of estimating the surface temperature based on the second estimated history PREVC-1 and the energization of the center heater 73-1.

[0122] The second temperature estimation unit 91-1 may use an energizing pulse PsC instead of the duty cycle value LDC.

[0123] The second estimated history storage unit 92-1 stores the second estimated history PREVC-1. The second estimated history storage unit 92-1 outputs the second estimated history PREVC-1 to the second temperature estimation unit 91-1.

[0124] The first difference calculation unit 93-1 performs difference calculation processing. The first difference calculation unit 93-1 receives the first temperature estimation result ESTC from the first temperature estimation unit 81-1 and the second temperature estimation result ESTC-1 from the second temperature estimation unit 91-1 as inputs. Based on the first temperature estimation result ESTC and the second temperature estimation result ESTC-1, the first difference calculation unit 93-1 calculates the second difference DIFC-1. The second difference DIFC-1 is the difference between the first temperature estimation result ESTC and the second temperature estimation result ESTC-1. The second difference DIFC-1 may also refer to a signal indicating the difference between the first temperature estimation result ESTC and the second temperature estimation result ESTC-1. Here, the second difference DIFC-1 is explained as the value obtained by subtracting the first temperature estimation result ESTC from the second temperature estimation result ESTC-1. Since the second temperature estimation result ESTC-1 is higher than the first temperature estimation result ESTC, the second difference DIFC-1 is a positive value. The first difference calculation unit 93-1 outputs the second difference DIFC-1 to the temperature correction unit 94-1. The first difference calculation unit 93-1 is an example of a calculation unit that calculates the second difference DIFC-1.

[0125] Here, the first temperature estimation result ESTC and the second temperature estimation result ESTC-1 are real-time simulations of the same thermal circuit. Therefore, the second difference DIFC-1 can have a smaller error compared to the actual difference. The actual difference is the difference between the surface temperature of the part of the actual heat roller 71 that faces the printing medium P and the surface temperature of the part of the actual heat roller 71 that does not face the printing medium P. Therefore, the accuracy of determining the second temperature correction result WAEC-1, which will be described later, is improved.

[0126] The temperature correction unit 94-1 performs an addition process to correct the second temperature estimation result ESTC-1. The temperature correction unit 94-1 receives the first temperature correction result WAEC from the coefficient addition unit 84-1 and the second difference DIFC-1 from the first difference calculation unit 93-1. Based on the first temperature correction result WAEC and the second difference DIFC-1, the temperature correction unit 94-1 calculates the second temperature correction result WAEC-1. The second temperature correction result WAEC-1 is the corrected temperature of the part of the heat roller 71 that does not face the printing medium P. The corrected temperature of the part of the heat roller 71 that does not face the printing medium P is the temperature obtained by correcting the second temperature estimation result ESTC-1. The second temperature correction result WAEC-1 is a value obtained by adding the second difference DIFC-1 to the first temperature correction result WAEC. The second temperature correction result WAEC-1 may also refer to a signal indicating the corrected temperature of the part of the heat roller 71 that does not face the printing medium P. Since the second difference DIFC-1 is a positive value, the second temperature correction result WAEC-1 is a larger value than the first temperature correction result WAEC. The temperature correction unit 94-1 outputs the second temperature correction result WAEC-1 to the second difference calculation unit 95-1. The second difference DIFC-1 is based on the first temperature estimation result ESTC and the second temperature estimation result ESTC-1. Therefore, determining the second temperature correction result WAEC-1 based on the first temperature correction result WAEC and the second difference DIFC-1 is an example of determining the second temperature correction result WAEC-1 based on the first temperature estimation result ESTC, the second temperature estimation result ESTC-1, and the first temperature correction result WAEC. The temperature correction unit 94-1 is an example of a calculation unit that determines the second temperature correction result WAEC-1.

[0127] Here, the second temperature estimation result ESTC-1 appropriately tracks the surface temperature changes of the parts of the actual heat roller 71 that do not come into contact with the printing medium P. However, since the second temperature estimation result ESTC-1 is a simulation result, there is a possibility of differences due to a certain bias. The first temperature correction result WAEC is data to which a high-pass filter has been applied to cancel out the bias. The temperature correction unit 94-1 can address the bias by adding the second difference DIFC-1 to the first temperature correction result WAEC. Therefore, the second temperature correction result WAEC-1 is a value that appropriately tracks the surface temperature of the parts of the actual heat roller 71 that do not come into contact with the printing medium P.

[0128] The second difference calculation unit 95-1 performs difference calculation processing. The second difference calculation unit 95-1 receives the second temperature correction result WAEC-1 and the upper limit temperature Tmax from the temperature correction unit 94-1. The upper limit temperature Tmax is a threshold value that is the upper limit of the surface temperature of the part of the heat roller 71 that does not face the printing medium P. The upper limit temperature Tmax can be changed by rewriting it according to a command from the processor 22. The upper limit temperature Tmax may be stored in the memory 23.

[0129] The second difference calculation unit 95-1 calculates the third difference DIFC-2 based on the second temperature correction result WAEC-1 and the upper limit temperature Tmax. The third difference DIFC-2 is the difference between the second temperature correction result WAEC-1 and the upper limit temperature Tmax. Here, the third difference DIFC-2 is explained as the value obtained by subtracting the second temperature correction result WAEC-1 from the upper limit temperature Tmax. If the second temperature correction result WAEC-1 exceeds the upper limit temperature Tmax, the third difference DIFC-2 is a negative value. If the second temperature correction result WAEC-1 is less than or equal to the upper limit temperature Tmax, the third difference DIFC-2 is a positive value.

[0130] The second difference calculation unit 95-1 outputs a print speed adjustment command CPM to the processor 22 for adjusting the print speed based on the third difference DIFC-2. As the print speed decreases, the time required for printing increases. For example, the print speed includes the transport speed of the printing medium P. As the transport speed decreases, the time required for printing increases. The transport speed of the printing medium P is an example of the transport speed of the medium. Outputting a print speed adjustment command CPM is an example of adjusting the print speed. The second difference calculation unit 95-1 is an example of an adjustment unit that adjusts the print speed.

[0131] Here, the third difference DIFC-2 is based on the second temperature correction result WAEC-1. The second temperature correction result WAEC-1 is based on the first temperature correction result WAEC and the second difference DIFC-1. The second difference DIFC-1 is based on the first temperature estimation result ESTC and the second temperature estimation result ESTC-1. Therefore, outputting a print speed adjustment command CPM based on the third difference DIFC-2 is an example of outputting a print speed adjustment command CPM based on the second temperature estimation result ESTC-1. Outputting a print speed adjustment command CPM based on the third difference DIFC-2 is an example of outputting a print speed adjustment command CPM based on the first temperature estimation result ESTC and the second temperature estimation result ESTC-1. Outputting a print speed adjustment command CPM based on the third difference DIFC-2 is an example of outputting a print speed adjustment command CPM based on the first temperature estimation result ESTC, the second temperature estimation result ESTC-1, and the first temperature correction result WAEC. Outputting a print speed adjustment command CPM based on the third difference DIFC-2 is an example of outputting a print speed adjustment command CPM based on the second temperature correction result WAEC-1.

[0132] If the second temperature correction result WAEC-1 transitions from a temperature below the upper limit temperature Tmax to a temperature above the upper limit temperature Tmax, the second difference calculation unit 95-1 outputs a print speed adjustment command CPM. The case where the second temperature correction result WAEC-1 transitions from a temperature below the upper limit temperature Tmax to a temperature above the upper limit temperature Tmax is an example of a case where the second temperature correction result WAEC-1 exceeds the upper limit temperature Tmax. In this example, the print speed adjustment command CPM is a command to adjust the print speed from the first print speed to the second print speed.

[0133] The first printing speed is the printing speed when the second temperature correction result WAEC-1 is below the upper limit temperature Tmax. For example, the first printing speed includes the first transport speed of the printing medium P. The second printing speed is the printing speed when the second temperature correction result WAEC-1 is above the upper limit temperature Tmax. The second printing speed is lower than the first printing speed. For example, the second printing speed includes the second transport speed of the printing medium P. The second transport speed is lower than the first transport speed. Outputting a printing speed adjustment command CPM to adjust the printing speed from the first printing speed to the second printing speed is one example of adjusting to lower the printing speed.

[0134] The second printing speed may be a fixed printing speed regardless of the second temperature correction result WAEC-1, or it may vary depending on the second temperature correction result WAEC-1. In the latter example, the second difference calculation unit 95-1 may determine the second printing speed such that it slows down as the second temperature correction result WAEC-1 deviates from the upper limit temperature Tmax. The second difference calculation unit 95-1 may also determine the second printing speed based on a table or function that associates temperature and printing speed.

[0135] If the second temperature correction result WAEC-1 continues to exceed the upper limit temperature Tmax, the second difference calculation unit 95-1 may output a print speed adjustment command CPM in accordance with the change in the second temperature correction result WAEC-1. In this example, the print speed adjustment command CPM is a command to adjust the print speed to a second print speed corresponding to the second temperature correction result WAEC-1. The second difference calculation unit 95-1 may determine the second print speed to become slower as the second temperature correction result WAEC-1 deviates from the upper limit temperature Tmax.

[0136] If the second temperature correction result WAEC-1 transitions from a temperature above the upper limit temperature Tmax to a temperature below the upper limit temperature Tmax, the second difference calculation unit 95-1 may output a print speed adjustment command CPM. In this example, the print speed adjustment command CPM is a command to adjust the print speed from the second print speed to the first print speed.

[0137] As described above, the second temperature estimation unit 91-1, the second estimation history holding unit 92-1, the first difference calculation unit 93-1, the temperature correction unit 94-1, and the second difference calculation unit 95-1 are circuits for determining high temperatures in the portion of the heat roller 71 that does not face the printing medium P. The high temperature determination circuits are applied to the feedback loop of the WAE control described above. The second temperature estimation unit 91-1 uses the duty cycle value LDC generated by the WAE control. The first difference calculation unit 93-1 uses the first temperature estimation result ESTC generated by the WAE control. The temperature correction unit 94-1 uses the first temperature correction result WAEC generated by the WAE control. In this way, the center control circuit 14-1 can add only the processing necessary for high temperature determination to the WAE control without changing the processing for WAE control. Therefore, the center control circuit 14-1 can reduce the processing load compared to when processing for high temperature determination is performed independently of the processing for WAE control.

[0138] The components of the center control circuit 14-1 may be composed of electrical circuits or software. If composed of software, it may be implemented by a processor 22 or a processor different from processor 22 executing a program stored in memory. The processor is, for example, a processing circuit such as a CPU.

[0139] We will now describe the first thermal circuit that represents the heat transfer required to obtain the first temperature estimation result ESTC, and the second thermal circuit that represents the heat transfer required to obtain the second temperature estimation result ESTC-1. It is generally known that a thermal circuit operates in an equivalent manner to an electrical circuit in which thermal resistance is replaced by electrical resistance and thermal capacitance is replaced by electrical capacitance. A thermal circuit consists of elements E, C, and R. E is the voltage source. C is the capacitive component. R is the resistive component.

[0140] Here, there are two paths through which heat escapes from the surface of the heat roller 71. The first path is through which the heat slowly escapes to the outside via the fuser 21. The second path is through which heat is transferred to the printing medium P when the heat roller 71 is pressed tightly against the printing medium P, and the printing medium P is discharged to the output tray 18 while still hot. The ease with which heat escapes through the second path varies depending on the thickness of the printing medium P and the printing speed.

[0141] Figure 9 is a diagram illustrating the first thermal circuit. The heat source E1 is equivalent to a DC voltage source in the electrical circuit. The heating resistance R1 is equivalent to a variable resistor in the electrical circuit. The heating resistance R1 uses a duty cycle LDC as a variable factor. The duty cycle LDC is a control signal that changes the resistance value of the heating resistance R1, which adjusts the inflow of heat. For example, if the duty cycle indicated by the duty cycle LDC is 100%, the heating resistance R1 is set to the resistance value corresponding to when the energizing pulse PsC is 100%. If the duty cycle indicated by the duty cycle LDC is 0%, the energizing pulse PsC corresponds to 0. Therefore, the heating resistance R1 is an extremely large value. If the duty cycle indicated by the duty cycle LDC is greater than 0 and less than 100%, the heating resistance R1 is set to a value corresponding to the ratio of the duty cycles. The heater capacity C1 is updated to the current temperature by referring to the first estimated history PREVC from a small time interval dt prior.

[0142] The heat dissipation resistance R2 is the resistance value when heat escapes from the heat roller 71 into the space inside the fuser 21. The unit capacitance C2 is updated to the current temperature by referring to the first estimated history PREVC from before dt.

[0143] The ambient air resistance R3 is the resistance value of the path through which heat escapes from the space inside the fuser 21 (outside the heat roller 71) to the outside air. The ambient temperature E2 is equivalent to a DC voltage source in an electrical circuit. The relationship between the heat source E1 and the ambient temperature E2 is heat source E1 ≥ ambient temperature E2. Specifically, the relationship between the heat source E1 and the ambient temperature E2 before startup is heat source E1 = ambient temperature E2, and the relationship between the heat source E1 and the ambient temperature E2 during operation is heat source E1 > ambient temperature E2.

[0144] The paper heat dissipation resistance R4 is the resistance value when heat escapes to the printing medium P.

[0145] For example, the values ​​are as follows: E1 is 2500 (Kelvin). R1 ​​has a minimum of 80 (Ω) and a maximum of 100000 (Ω). C1 is 10 (F). R2 is 20 (Ω). C2 is 100 (F). R3 is 10 (Ω). R4 is 20 (Ω). E2 is 25 (Kelvin). The duty cycle LDC is 0-100%.

[0146] For example, the first temperature estimation unit 81-1 performs a real-time simulation of the first thermal circuit as described above using the energy conservation law, based on the first estimated history PREVC and the duty cycle LDC. The first temperature estimation unit 81-1 derives the C1 voltage (temperature) from the real-time simulation of the first thermal circuit. The first temperature estimation unit 81-1 generates the C1 voltage (temperature) as the first temperature estimation result ESTC at the current time.

[0147] Figure 10 is a diagram illustrating the second thermal circuit. The second thermal circuit has the same configuration of E, C, and R elements as the first thermal circuit. The heater capacitance C1 is updated to the current temperature by referring to the second estimated history PREVC-1 from a small time interval dt prior. The unit capacitance C2 is updated to the current temperature by referring to the second estimated history PREVC-1 from dt prior. The resistance value of the paper heat dissipation resistor R4 in the second thermal circuit is different from the resistance value of the paper heat dissipation resistor R4 in the first thermal circuit.

[0148] Here, we will explain the difference between the resistance value of the paper heat dissipation resistor R4 in the first heat circuit and the resistance value of the paper heat dissipation resistor R4 in the second heat circuit. In the heat roller 71, the part facing the printing medium P loses a large amount of heat due to the printing medium P, so heat escapes through the printing medium P. For this reason, a small value is set for the paper heat dissipation resistor R4 in the first heat circuit. On the other hand, in the part of the heat roller 71 that does not face the printing medium P, heat is not lost due to the printing medium P, so heat does not escape through the printing medium P. For this reason, a relatively larger value is set for the paper heat dissipation resistor R4 in the second heat circuit than for the paper heat dissipation resistor R4 in the first heat circuit.

[0149] For example, the values ​​are as follows: E1 is 2500 (Kelvin). R1 ​​has a minimum of 80 (Ω) and a maximum of 100000 (Ω). C1 is 10 (F). R2 is 20 (Ω). C2 is 100 (F). R3 is 10 (Ω). R4 is 100 (Ω). E2 is 25 (Kelvin). The duty cycle LDC is 0 to 100%. Thus, the values ​​of each element E, C, and R in the second thermal circuit are the same as the values ​​of each element E, C, and R in the first thermal circuit, except for the value of the paper heat dissipation resistor R4.

[0150] For example, the second temperature estimation unit 91-1 performs a real-time simulation of the second thermal circuit as described above, using the energy conservation law, based on the second estimated history PREVC-1 and the duty cycle LDC. The second temperature estimation unit 91-1 derives the C1 voltage (temperature) from the real-time simulation of the second thermal circuit. The second temperature estimation unit 91-1 generates the C1 voltage (temperature) as the second temperature estimation result ESTC-1 at the current time.

[0151] When the surface temperature of the portion of the heat roller 71 facing the printing medium P is controlled to reach the target temperature, the surface temperature of the portion of the heat roller 71 not facing the printing medium P increases. The second temperature estimation unit 91-1 can estimate the surface temperature of the portion of the heat roller 71 not facing the printing medium P through real-time simulation. The second temperature estimation result ESTC-1 is higher than the first temperature estimation result ESTC.

[0152] Next, the control circuit 14-2 for the side will be explained. Figure 11 is a diagram illustrating an example of the configuration of the side control circuit 14-2. As shown in Figure 11, the side control circuit 14-2 includes a temperature estimation unit 81-2, an estimation history retention unit 82-2, a high-frequency component extraction unit 83-2, a coefficient addition unit 84-2, a target temperature output unit 85-2, a difference comparison unit 86-2, a control duty generation unit 87-2, an external limit unit 88-2, a duty pulse conversion unit 89-2, and a power supply circuit 90-2.

[0153] The side control circuit 14-2 differs from the center control circuit 14-1, which receives the temperature detection result TdC from the temperature sensor 74-1, in that it receives the temperature detection result TdS from the temperature sensor 74-2. The side control circuit 14-2 also differs from the center control circuit 14-1, which supplies energizing power PC to the center heater 73-1, in that it supplies energizing power PS to the two side heaters 73-2. In other respects, the WAE control by the side control circuit 14-2 is the same as the WAE control by the center control circuit 14-1, so the explanation is omitted. The temperature estimation unit 81-2 is the same as the first temperature estimation unit 81-1 described above. The estimation history holding unit 82-2 is the same as the first estimation history holding unit 82-1 described above. The high-frequency component extraction unit 83-2 is the same as the high-frequency component extraction unit 83-1 described above. The coefficient addition unit 84-2 is the same as the coefficient addition unit 84-1 described above. The target temperature output unit 85-2 is the same as the target temperature output unit 85-1 described above. The difference comparison unit 86-2 is the same as the difference comparison unit 86-1 described above. The control duty generation unit 87-2 is the same as the control duty generation unit 87-1 described above. The external limit unit 88-2 is the same as the external limit unit 88-1 described above. The duty pulse conversion unit 89-2 is the same as the duty pulse conversion unit 89-1 described above. The power supply circuit 90-2 is the same as the power supply circuit 90-1 described above.

[0154] The following describes the WAE control using the center control circuit 14-1 in detail. Figure 12 is a flowchart illustrating an example of WAE control operation by the center control circuit 14-1. Figures 13 and 14 are diagrams illustrating the various signals in WAE control by the center control circuit 14-1. The horizontal axis in Figures 13 and 14 represents time. The vertical axis in Figures 13 and 14 represents temperature. In the descriptions of Figures 12, 13, and 14, the notation "surface temperature of the heat roller 71" refers to the surface temperature of the portion of the heat roller 71 that faces the printing medium P, among the portion that faces the center heater 73-1.

[0155] The center control circuit 14-1 acquires the internal temperature of the image forming apparatus 1 (ACT1). Since the change in internal temperature is slow, the frequency of acquiring the internal temperature by the center control circuit 14-1 does not need to be high.

[0156] The control circuit 14-1 for the center acquires the current temperature detection result TdC from the temperature sensor 74-1 (ACT2).

[0157] As shown in Figure 13, there is a difference between the temperature detection result TdC and the actual surface temperature of the heat roller 71. The actual surface temperature of the heat roller 71 changes in a fine cycle because heating by the center heater 73-1 is performed intermittently. In contrast, the temperature sensor 74-1 may have poor responsiveness to temperature changes due to its own heat capacity and the characteristics of the temperature-sensing material. In particular, inexpensive temperature sensors tend to have poor responsiveness. As a result, the temperature detection result TdC does not accurately track the actual surface temperature of the heat roller 71. That is, the temperature detection result TdC is detected by the temperature sensor 74-1 with a delay relative to the surface temperature of the heat roller 71. Furthermore, the temperature detection result TdC is detected by the temperature sensor 74-1 in a smoothed state, without reproducing the fine changes in the surface temperature of the heat roller 71.

[0158] The first temperature estimation unit 81-1 obtains the first estimation history PREVC from the first estimation history holding unit 82-1 prior to dt (ACT3). The difference comparison unit 86-1 obtains the target temperature TGTC from the target temperature output unit 85-1 (ACT4).

[0159] The first temperature estimation unit 81-1 acquires the values ​​of the parameters corresponding to the E, C, and R elements that constitute the first thermal circuit as described above (ACT5). The first temperature estimation unit 81-1 generates a first temperature estimation result ESTC by real-time simulation of the first thermal circuit (ACT6). As shown in Figure 13, the first temperature estimation result ESTC appropriately tracks the actual surface temperature change of the heat roller 71. However, since the first temperature estimation result ESTC is a simulation result, the absolute value may differ from the actual surface temperature of the heat roller 71 due to differences in conditions, etc.

[0160] The high-frequency component extraction unit 83-1 constitutes a high-pass filter (ACT7). The high-frequency component extraction unit 83-1 cancels the DC component of the first temperature estimation result ESTC using the high-pass filter and extracts only the high-frequency component. The high-frequency component extraction unit 83-1 generates the high-frequency component HPFC. As shown in Figure 13, the high-frequency component HPFC appropriately tracks the changes in the surface temperature of the actual heat roller 71.

[0161] The coefficient adder 84-1 obtains the current temperature detection result TdC from the temperature sensor 74-1 (ACT8). The coefficient summing unit 84-1 calculates the first temperature-corrected result WAEC (ACT9). In ACT9, for example, the coefficient summing unit 84-1 obtains the value obtained by (TdC + KC × HPFC) as the first temperature-corrected result WAEC.

[0162] Figure 14 illustrates an example of the actual surface temperature of the heat roller 71, the temperature detection result Td, and the first temperature correction result WAEC. In WAE control, the fine temperature changes of the surface temperature of the heat roller 71 are estimated based on the temperature detection result TdC and the high-frequency component HPFC of the first temperature estimation result ESTC. Therefore, as shown in Figure 14, the first temperature correction result WAEC is a value that appropriately tracks the actual surface temperature of the heat roller 71.

[0163] The first estimated history retention unit 82-1 overwrites the first estimated history PREVC with the first temperature estimated result ESTC (ACT10).

[0164] The difference comparison unit 86-1 calculates the first difference DIFC (ACT11) based on a comparison between the target temperature TGT and the first temperature correction result WAEC.

[0165] The control duty generation unit 87-1 generates a duty cycle value DUTYC based on the first differential DIFC (ACT12).

[0166] The external limit unit 88-1 reflects the system protection information LMTC in the duty cycle value DUTYC and limits the duty cycle value (ACT13). In ACT13, for example, the external limit unit 88-1 generates the duty cycle value LDC based on the duty cycle value DUTYC by reflecting the system protection information LMTC in the duty cycle value DUTYC.

[0167] The duty pulse conversion unit 89-1 converts the duty cycle value LDC into a current pulse train (ACT14). The duty pulse conversion unit 89-1 generates current pulses PsC that constitute the current pulse train. The duty cycle pulse conversion unit 89-1 outputs an energizing pulse PsC (ACT15) that forms an energizing pulse train in synchronization with the AC voltage.

[0168] The power supply circuit 90-1 supplies power PC to the center heater 73-1 based on the energizing pulse PsC (ACT16).

[0169] The center control circuit 14-1 determines whether or not it has received a stop command for WAE control (ACT17). If the center control circuit 14-1 has not received a stop command for WAE control (ACT17, NO), the process transitions from ACT17 to ACT2. If the center control circuit 14-1 has received a stop command for WAE control (ACT17, YES), the process ends.

[0170] As described above, when the center control circuit 14-1 processes a certain cycle (the current cycle), it performs WAE control based on the values ​​from the previous cycle (duty cycle value LDC and first temperature estimation result ESTC: first estimation history PREVC) and the temperature detection result TsC for the current cycle. In other words, the center control circuit 14-1 inherits the values ​​in the next cycle. The center control circuit 14-1 recalculates the temperature estimation calculation based on the history of the previous calculation. Therefore, the center control circuit 14-1 is constantly performing calculations while in operation. In the center control circuit 14-1, the calculation results are stored in memory, etc., and reused in the calculation of the next cycle.

[0171] Figure 15 is a diagram illustrating the processing cycle in the center control circuit 14-1. The horizontal axis in Figure 15 represents time. For example, the first temperature estimation unit 81-1 performs temperature estimation processing at time t(n), then performs the next temperature estimation processing at t(n+1) after time has advanced by dt, and then performs temperature estimation processing again at t(n+2) after time has advanced by another dt. In this way, the first temperature estimation unit 81-1 repeatedly performs temperature estimation processing. In the temperature estimation processing of each cycle, the first temperature estimation unit 81-1 uses the previous first temperature estimation result ESTC to estimate the new temperature.

[0172] At time t(n), the temperature detection result TdC at time t(n), the duty cycle value LDC from the previous time t(n-1), and the first temperature estimation result ESTC (first estimation history PREVC) from the previous time t(n-1) are used. The first temperature estimation unit 81-1 processes the input signal and outputs the first temperature estimation result ESTC at time t(n). The high-frequency component extraction unit 83-1, coefficient addition unit 84-1, target temperature output unit 85-1, difference comparison unit 86-1, control duty cycle generation unit 87-1, and external limit unit 88-1 process the input signal. The external limit unit 88-1 outputs the duty cycle value LDC at time t(n).

[0173] At time t(n+1), the first estimated history PREVC, which consists of the newly detected temperature detection result TdC at time t(n+1), the duty cycle value LDC at time t(n), and the first temperature estimation result ESTC at time t(n), is used. The first temperature estimation unit 81-1 processes the input signal and outputs the first temperature estimation result ESTC at time t(n+1). The high-frequency component extraction unit 83-1, coefficient addition unit 84-1, target temperature output unit 85-1, difference comparison unit 86-1, control duty cycle generation unit 87-1, and external limit unit 88-1 process the input signal. The external limit unit 88-1 outputs the duty cycle value LDC at time t(n+1).

[0174] At time t(n+2), the first estimated history PREVC, which consists of the newly detected temperature detection result TdC at time t(n+2), the duty cycle value LDC at time t(n+1), and the first temperature estimation result ESTC at time t(n+1), is used. The first temperature estimation unit 81-1 processes the input signal and outputs the first temperature estimation result ESTC at time t(n+2). The high-frequency component extraction unit 83-1, coefficient addition unit 84-1, target temperature output unit 85-1, difference comparison unit 86-1, control duty cycle generation unit 87-1, and external limit unit 88-1 process the input signal. The external limit unit 88-1 outputs the duty cycle value LDC at time t(n+2).

[0175] The above time interval dt may be a fixed value or it may be configured to be set in the initial value settings. For example, the time interval dt may be set to 100 [msec].

[0176] The example of WAE control operation by the side control circuit 14-2 is the same as the example of WAE control operation by the center control circuit 14-1 described above, so its explanation is omitted.

[0177] The operation of the print speed control in the center control circuit 14-1 will be described below. The printing speed control is based on the determination of high temperature in the portion of the heat roller 71 that does not come into contact with the printing medium P.

[0178] Figure 16 is a flowchart illustrating an example of the operation of the print speed control in the center control circuit 14-1. If the width of the printing medium P to be printed is less than the size of the portion of the heat roller 71 facing the center heater 73-1, the center control circuit 14-1 performs print speed control. If the width of the printing medium P to be printed is less than the size of the portion of the heat roller 71 facing the center heater 73-1 and also less than a predetermined size, the center control circuit 14-1 may perform print speed control. For example, if the printing medium P to be printed is a postcard or envelope, the center control circuit 14-1 may perform print speed control. If the printing medium P to be printed is A4 portrait, the center control circuit 14-1 does not need to perform print speed control. If the width of the printing medium P to be printed is greater than or equal to the size of the portion of the heat roller 71 facing the center heater 73-1, the center control circuit 14-1 does not perform print speed control. The processor 22 may detect the width of the printing medium P to be printed based on the printing medium P to be printed specified by the user in the operation interface 16. The processor 22 is an example of a detection unit that detects the width size of the printing medium P to be printed.

[0179] The second temperature estimation unit 91-1 acquires the values ​​of the parameters corresponding to the E, C, and R elements that constitute the second thermal circuit as described above (ACT21). The second temperature estimation unit 91-1 generates a second temperature estimation result ESTC-1 by real-time simulation of the second thermal circuit (ACT22).

[0180] The first difference calculation unit 93-1 calculates the second difference DIFC-1 based on the first temperature estimation result ESTC and the second temperature estimation result ESTC-1 (ACT23).

[0181] The temperature correction unit 94-1 determines a second temperature correction result WAEC-1 based on the first temperature correction result WAEC and the second difference DIFC-1 (ACT24).

[0182] The second difference calculation unit 95-1 calculates the third difference DIFC-2 based on the second temperature correction result WAEC-1 and the upper limit temperature Tmax (ACT25). The second difference calculation unit 95-1 determines, based on the third difference DIFC-2, whether the second temperature correction result WAEC-1 exceeds the upper limit temperature Tmax (ACT26). If the second temperature correction result WAEC-1 exceeds the upper limit temperature Tmax (ACT26, YES), the process transitions from ACT26 to ACT27. If the second temperature correction result WAEC-1 is less than or equal to the upper limit temperature Tmax (ACT26, NO), the process transitions from ACT26 to ACT28.

[0183] The second difference calculation unit 95-1 outputs a print speed adjustment command CPM to the processor 22 (ACT27) to adjust the print speed from the first print speed to the second print speed. The second difference calculation unit 95-1 may also output a print speed adjustment command CPM to adjust the print speed to a second print speed corresponding to the second temperature correction result WAEC-1, in response to the change in the second temperature correction result WAEC-1. The processor 22 adjusts the print speed based on the print speed adjustment command CPM. For example, the processor 22 adjusts the transport speed of the printing medium P by the transport unit 19.

[0184] The center control circuit 14-1 determines whether or not it has received a stop command for WAE control (ACT28). If the center control circuit 14-1 has not received a stop command for WAE control (ACT28, NO), the process transitions from ACT28 to ACT21. If the center control circuit 14-1 has received a stop command for WAE control (ACT28, YES), the process ends.

[0185] The processor 22 may perform the same processing as the second difference calculation unit 95-1. In this case, the processor 22 obtains the second temperature correction result WAEC-1 from the temperature correction unit 94-1. The processor 22 calculates the third difference DIFC-2 based on the second temperature correction result WAEC-1 and the upper limit temperature Tmax. The processor 22 adjusts the printing speed based on the third difference DIFC-2. In this example, the processor 22 is an example of an adjustment unit that adjusts the printing speed.

[0186] In addition, in ACT26, the second temperature correction result WAEC-1 may transition from a temperature exceeding the upper limit temperature Tmax to a temperature below the upper limit temperature Tmax. In this case, the second difference calculation unit 95-1 may output a print speed adjustment command CPM to the processor 22 to adjust the print speed from the second print speed to the first print speed.

[0187] According to this embodiment, the image forming apparatus 1 can adjust the printing speed based on the second temperature estimation result ESTC-1. As a result, the image forming apparatus 1 does not need to perform low-speed printing from the beginning, thus reducing the processing time for the printing process. For example, when printing 100 sheets, the image forming apparatus 1 can perform high-speed printing for the first 20 sheets and low-speed printing for the remaining 80 sheets. When printing 3 sheets, the image forming apparatus 1 can perform high-speed printing for the 3 sheets.

[0188] According to this embodiment, the image forming apparatus 1 can be adjusted to reduce the printing speed when the second temperature correction result WAEC-1 exceeds the upper limit temperature Tmax. As a result, the image forming apparatus 1 can prevent the temperature of the heated portion of the heat roller 71 that does not face the printing medium P from exceeding the upper temperature limit Tmax and becoming excessively high. Therefore, even if the image forming apparatus 1 performs printing on A4 portrait paper after printing on a postcard, for example, the fixing of the toner image on the A4 portrait paper will not be adversely affected.

[0189] According to this embodiment, the image forming apparatus 1 can determine a second temperature correction result WAEC-1 based on the first temperature estimation result ESTC, the second temperature estimation result ESTC-1, and the first temperature correction result WAEC. The image forming apparatus 1 can adjust the printing speed based on the second temperature correction result WAEC-1. As a result, the image forming apparatus 1 can apply a circuit for determining high temperature in the portion of the heat roller 71 that does not face the printing medium P to the WAE control feedback loop. Therefore, the center control circuit 14-1 can reduce the processing load for high temperature determination.

[0190] According to this embodiment, the temperature detection result TdC is the temperature of the portion of the heat roller 71 that faces the printing medium P, as detected by the temperature sensor 74-1. As a result, the image forming apparatus 1 can obtain the second temperature correction result WAEC-1 without detecting the temperature of the part of the heat roller 71 that does not face the printing medium P. Therefore, the image forming apparatus 1 does not need to increase the number of temperature sensors for high temperature detection.

[0191] This embodiment may be represented as follows: [1] A temperature control device that controls the temperature of a temperature-controlled object to which heat is transmitted from the heater by supplying power to the heater, A temperature estimation unit estimates the temperature of the portion of the temperature-controlled object that does not come into contact with the medium, based on the energization of the heater. An adjustment unit adjusts the transport speed of the medium based on the estimated temperature of the portion not in contact with the medium, A temperature control device equipped with the following: [2] The temperature control device according to [1], wherein if the estimated temperature of the portion not in contact with the medium exceeds an upper limit, the adjustment unit adjusts to reduce the transport speed. [3] A temperature estimation unit that estimates the temperature of the portion of the temperature-controlled object that faces the medium based on the energization of the heater, A calculation unit that determines a corrected temperature of the portion facing the medium based on the estimated temperature of the portion facing the medium and the temperature of the temperature-controlled object detected by the temperature sensor, A signal generation unit generates energizing pulses for controlling the power supplied to the heater based on the corrected temperature of the portion facing the medium, A calculation unit that determines the corrected temperature of the portion not facing the medium based on the estimated temperature of the portion facing the medium, the estimated temperature of the portion not facing the medium, and the corrected temperature of the portion facing the medium, Equipped with, The adjustment unit adjusts the transport speed based on the corrected temperature of the portion that does not come into contact with the medium. The temperature control device described in [1]. [4] The temperature control device according to [3], wherein the temperature of the temperature-controlled object detected by the temperature sensor is the temperature of the portion of the temperature-controlled object that is facing the medium, as detected by the temperature sensor. [5] An image forming apparatus that controls the temperature of a fixing rotating body from which heat is transmitted by supplying power to a heater, A fuser having a fixing rotating body that heats and fixes a toner image formed on a medium onto the medium, and a heater that heats the fixing rotating body, A temperature estimation unit estimates the temperature of the portion of the fixing rotating body that does not come into contact with the medium, based on the energization of the heater, An adjustment unit adjusts the transport speed of the medium based on the estimated temperature of the portion not in contact with the medium, An image forming apparatus comprising the following:

[0192] It should be noted that the above-mentioned temperature control device is not limited to being applied to the image forming apparatus 1. The temperature control device can be applied to various devices that utilize heat. For example, the temperature control device can be applied to photocopiers, multifunction printers, or printers that use heat to melt toner. The temperature control device can be applied to furnaces that maintain a constant temperature or gradually change the temperature, and to single-crystal material manufacturing machines that pull up and grow crystals from a melting furnace. The temperature control device can be applied to color thermal printers that change color depending on the temperature. The temperature control device can be applied to melting furnaces that manufacture alloys. In the case of photocopiers or color thermal printers, improved print quality can be expected, such as cleaner printing and no change in color over time even with mass printing. In the case of melting furnaces, precise temperature control can be performed, which can lead to improved yield of manufactured products, improved crystal quality (reduction in crystal defect rate), and improved performance of alloys.

[0193] Furthermore, the functions described in each of the above embodiments are not limited to being implemented using hardware; they can also be realized by loading a program containing each function into a computer using software. Additionally, each function may be configured using either software or hardware, as appropriate.

[0194] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0195] 1…Image forming apparatus, 11…Housing, 12…Communication interface, 13…System controller, 14…Heater power supply control circuit, 14-1…Center control circuit, 14-2…Side control circuit, 15…Display unit, 16…Operation interface, 17…Paper tray, 18…Output tray, 19…Transport unit, 20…Image forming unit, 21…Fuser, 22…Processor, 23…Memory, 31…Paper feed transport path, 32…Output transport path, 33…Pickup roller, 41…Process unit, 42…Explorer, 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…Press roller, 73…Heater, 73-1…Center heater, 73-2…Side heater, 74-1…Warm Temperature sensor, 74-2…Temperature sensor, 81-1…First temperature estimation unit, 81-2…Temperature estimation unit, 82-1…First estimation history retention unit, 82-2…Estimation history retention unit, 83-1…High frequency component extraction unit, 83-2…High frequency component extraction unit, 84-1…Coefficient addition unit, 84-2…Coefficient addition unit, 85-1…Target temperature output unit, 85-2…Target temperature output unit, 86-1…Difference comparison unit, 86-2…Difference comparison unit, 87-1…Control Duty cycle generation unit, 87-2... Control duty cycle generation unit, 88-1... External limit unit, 88-2... External limit unit, 89-1... Duty pulse conversion unit, 89-2... Duty pulse conversion unit, 90-1... Power supply circuit, 90-2... Power supply circuit, 91-1... Second temperature estimation unit, 92-1... Second estimation history retention unit, 93-1... First difference calculation unit, 94-1... Temperature correction unit, 95-1... Second difference calculation unit.

Claims

1. A temperature control device that controls the temperature of a temperature-controlled object by supplying power to a heater, thereby transferring heat from the heater to a medium and applying heat to the medium, A temperature estimation unit estimates the temperature of a portion of the temperature-controlled object that does not come into contact with the medium, based on energizing pulses for controlling the power supplied to the heater. An adjustment unit adjusts the transport speed of the medium by a transport unit that transports the medium, based on the estimated temperature of the portion not in contact with the medium. A temperature estimation unit estimates the temperature of the portion of the temperature-controlled object that faces the medium, based on the energization of the heater, A calculation unit that determines a corrected temperature of the portion facing the medium based on the estimated temperature of the portion facing the medium and the temperature of the temperature-controlled object detected by the temperature sensor, A signal generation unit generates energizing pulses for controlling the power supplied to the heater based on the corrected temperature of the portion facing the medium, A calculation unit that determines the corrected temperature of the portion not facing the medium based on the estimated temperature of the portion facing the medium, the estimated temperature of the portion not facing the medium, and the corrected temperature of the portion facing the medium, It is equipped with, The adjustment unit is a temperature control device that adjusts the transport speed based on the corrected temperature of the portion that does not come into contact with the medium.

2. The temperature control device according to claim 1, wherein if the estimated temperature of the portion not in contact with the medium exceeds an upper limit, the adjustment unit adjusts to reduce the transport speed.

3. The temperature control device according to claim 1, wherein the temperature of the temperature-controlled object detected by the temperature sensor is the temperature of the portion of the temperature-controlled object facing the medium, as detected by the temperature sensor.

4. An image forming apparatus that controls the temperature of a fixing rotating body to which heat is transmitted from a heater by supplying power to the heater, A fuser having a fixing rotating body that heats and fixes a toner image formed on a medium onto the medium, and a heater that heats the fixing rotating body, A temperature estimation unit estimates the temperature of a portion of the fixing rotating body that does not come into contact with the medium, based on energizing pulses for controlling the power supplied to the heater. An adjustment unit adjusts the transport speed of the medium based on the estimated temperature of the portion not in contact with the medium, A temperature estimation unit estimates the temperature of the portion of the fixing rotating body that faces the medium based on the energization of the heater, A calculation unit that determines a corrected temperature of the portion facing the medium based on the estimated temperature of the portion facing the medium and the temperature of the fixing rotating body detected by a temperature sensor, A signal generation unit generates energizing pulses for controlling the power supplied to the heater based on the corrected temperature of the portion facing the medium, A calculation unit that determines the corrected temperature of the portion not facing the medium based on the estimated temperature of the portion facing the medium, the estimated temperature of the portion not facing the medium, and the corrected temperature of the portion facing the medium, It is equipped with, The adjustment unit is an image forming apparatus that adjusts the transport speed based on the correction temperature of the portion that does not come into contact with the medium.

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