Temperature control device and image forming apparatus

Abstract

The present invention provides a temperature control device and an image forming apparatus that can prevent the occurrence of temperature ripple while suppressing an increase in processing load. [Solution] A temperature control device according to one embodiment is a temperature control device that controls the temperature of a temperature-controlled object from which heat is transmitted from a heater by supplying power to the heater, and comprises a temperature estimation unit, a duty cycle generation unit, and a signal generation unit. The temperature estimation unit estimates the temperature of the temperature-controlled object based on the duty cycle value. The duty cycle generation unit generates a duty cycle value based on the temperature estimation result by the temperature estimation unit, the temperature detection result of the temperature-controlled object by the temperature sensor, and the target temperature. The signal generation unit outputs an energizing pulse to control the power supplied to the heater based on the duty cycle value.

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 print medium by applying heat and pressure to the print medium with a fixing device. The fixing device includes a fixing rotating body (heat roller), a pressing member (press roller), a heating member (lamp or IH (Induction Heating) heater, etc.), and a temperature sensor. The temperature sensor detects the temperature of the surface of the heat roller.

[0003] A controller that controls the fixing device controls the surface temperature of the heat roller to reach a target value by increasing or decreasing the amount of electricity supplied to the heater based on a detection signal (temperature sensor signal) from the temperature sensor.

[0004] If a deviation (or time lag) occurs between the temperature detected by the temperature sensor and the surface temperature of the heat roller, overshoot, temperature ripple, etc. may occur. Therefore, in order to prevent the occurrence of overshoot and temperature ripple, a temperature sensor with good responsiveness (for example, a thermopile, etc.) is required. However, a temperature sensor with good responsiveness has a problem of high cost.

[0005] For such problems, a technique for predicting the surface temperature of a heat roller based on an energization pulse has been studied. However, when the frequency of the energization pulse is high, high-speed sampling becomes essential because time accuracy for detecting the change in the pulse is required. Then, the processing load on a processing circuit such as a CPU (Central Processing Unit) increases.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] The problem that this invention aims to solve is to provide a temperature control device and an image forming apparatus that can prevent the occurrence of temperature ripple while suppressing an increase in processing load. [Means for solving the problem]

[0008] A temperature control device according to one embodiment controls the temperature of a temperature-controlled object from which heat is transmitted by a heater by supplying power to the heater, and comprises a temperature estimation unit, a duty cycle generation unit, and a signal generation unit. The temperature estimation unit estimates the temperature of the temperature-controlled object based on a duty cycle value. The duty cycle generation unit generates a duty cycle value based on the temperature estimation result by the temperature estimation unit, the temperature detection result of the temperature-controlled object by a temperature sensor, and the target temperature. The signal generation unit outputs an energizing pulse to control the power supplied to the heater based on the duty cycle value. [Brief explanation of the drawing]

[0009] [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 configuration of a heater energization control circuit according to one embodiment. [Figure 3] Figure 3 is a diagram illustrating a heat circuit that represents heat transfer for obtaining temperature estimation results according to one embodiment. [Figure 4] Figure 4 is a diagram illustrating an example of the operation of a heater energization control circuit according to one embodiment. [Figure 5] Figure 5 is a diagram illustrating an example of the operation of a heater energization control circuit according to one embodiment. [Figure 6]Figure 6 is a diagram illustrating an example of the operation of a heater energization control circuit according to one embodiment. [Figure 7] Figure 7 is a diagram illustrating an example of the operation of a heater energization control circuit according to one embodiment. [Figure 8] Figure 8 is a diagram illustrating an example of a target temperature in one embodiment. [Figure 9] Figure 9 is a diagram illustrating the relationship between the difference DIF and the duty cycle value DUTY according to one embodiment. [Figure 10] Figure 10 is a diagram illustrating the energizing pulse train generated by a heater energizing control circuit according to one embodiment. [Figure 11] Figure 11 is a diagram illustrating the relationship between the duty cycle value and generated power, and the relationship between the energizing pulse train and generated power, according to one embodiment. [Figure 12] Figure 12 is a diagram illustrating an example of duty cycle value sampling according to one embodiment. [Modes for carrying out the invention]

[0010] 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.

[0011] The 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. The 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.

[0012] 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, for example, a color toner such as cyan, magenta, yellow, and black. Further, the toner may be a decolorizing toner that decolorizes when heat is applied.

[0013] 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, 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.

[0014] 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 display unit 15, the operation interface 16, the plurality of paper trays 17, the paper discharge tray 18, the conveyance unit 19, the image forming unit 20, and the fixing unit 21.

[0015] 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 in accordance with a standard such as Bluetooth (registered trademark) or Wi-fi (registered trademark).

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

[0017] The processor 22 is an arithmetic element that executes arithmetic processing. The processor 22 is, for example, a CPU. The processor 22 performs various processes based on data such as programs stored in the memory 23. The processor 22 functions as a control unit capable of executing various operations by executing the programs stored in the memory 23.

[0018] The processor 22 performs various information processes by executing the programs stored in the memory 23. For example, the processor 22 generates a print job based on an image acquired from an external device via the communication interface 12. The processor 22 stores the generated print job in the memory 23.

[0019] The print job includes image data indicating an image to be formed on the 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 a plurality of print media P. Further, the print job includes information indicating whether it is color printing or monochrome printing. The print job may include information such as the number of printed copies (number of page sets) and the number of printed sheets per copy (number of pages).

[0020] Also, the processor 22 generates print control information for controlling the operations of the conveyance unit 19, the image forming unit 20, and the fixing unit 21 based on the generated print job. The print control information includes information indicating the timing of paper feeding. The processor 22 supplies the print control information to the heater energization control circuit 14.

[0021] Also, the processor 22 functions as a controller (engine controller) that controls the operations of the conveyance unit 19 and the image forming unit 20 by executing the programs stored in the memory 23. That is, the processor 22 controls the conveyance of the print medium P by the conveyance unit 19 and the formation of an image on the print medium P by the image forming unit 20, etc.

[0022] Memory 23 is a storage medium that stores programs and data used by those programs. Memory 23 also functions as working memory; that is, it temporarily stores data being processed by processor 22 and programs executed by processor 22.

[0023] 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.

[0024] 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 of the fuser 21 to the heater power control circuit 14.

[0025] The heater power supply control circuit 14 is a temperature control device (temperature control unit) that controls the supply of power to the heater of the fuser 21, which will be described later. The heater power supply control circuit 14 generates the power supply PC to power the heater of the fuser 21 and supplies it to the heater of the fuser 21. A detailed explanation of the heater power supply control circuit 14 will be given later.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] The output tray 18 is a tray that supports the printing medium P discharged from the image forming apparatus 1.

[0030] 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.

[0031] 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 move the printing medium P by rotating. The multiple guides control the transport direction of the printing medium P.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] A toner cartridge comprises a toner container and a toner delivery mechanism. The toner container is a container that holds the toner. The toner delivery mechanism is a mechanism consisting of a screw or the like that delivers the toner from the toner container.

[0038] 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).

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

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

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

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

[0046] In the 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.

[0047] 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.

[0048] The transfer mechanism 43 includes, for example, a primary transfer belt 61, a secondary transfer opposing roller 62, and a plurality of primary transfer rollers 63 and secondary transfer rollers 64.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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. Furthermore, the fuser 21 is equipped with a temperature sensor (thermal sensor) 74 that detects the temperature of the heat roller 71.

[0056] 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.

[0057] 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 moves the printing medium P that has entered the fixing nip and presses the printing medium P against the heat roller 71.

[0058] The heater 73 is a device that generates heat using the power supply PC provided by the heater power supply 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 by electromagnetic waves emitted from the halogen lamp heater when the power supply PC provided by the heater power supply control circuit 14 energizes the halogen lamp heater, which is the heat source. Alternatively, the heater 73 may be, for example, an induction heater.

[0059] The temperature sensor 74 detects the temperature of the heat roller 71. Here, it is described that the temperature sensor 74 detects the surface temperature of the heat roller 71. The temperature sensor 74 may also detect the temperature of the air near the surface of the heat roller 71. There may be multiple temperature sensors 74. For example, multiple temperature sensors 74 may be arranged parallel to the rotation axis of the heat roller 71. Note that the temperature sensors 74 only need to be positioned in a location where they can detect changes in the surface temperature of the heat roller 71. The temperature sensor 74 supplies the temperature detection result Td of the heat roller 71 detected by the temperature sensor 74 to the heater power supply control circuit 14. The temperature detection result Td is the surface temperature of the heat roller 71 detected by the temperature sensor 74. The temperature detection result Td may also refer to a signal indicating the surface temperature of the heat roller 71 detected by the temperature sensor 74.

[0060] 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.

[0061] Next, the heater power supply control circuit 14 will be described. The heater power supply control circuit 14 supplies power to the heater 73 by controlling the power supply to the heater 73 of the fuser 21. By supplying power to the heater 73, the heater power supply control circuit 14 controls the surface temperature of the heat roller 71 from which heat is transmitted from the heater 73. The heater power supply control circuit 14 generates the power supply PC to power the heater 73 of the fuser 21 and supplies it to the heater 73 of the fuser 21.

[0062] As shown in Figure 2, the heater power supply control circuit 14 includes a temperature estimation unit 81, an estimation history retention unit 82, a high-frequency component extraction unit 83, a coefficient addition unit 84, a target temperature output unit 85, a difference comparison unit 86, a control duty generation unit 87, an external limit unit 88, a duty pulse conversion unit 89, and a power supply circuit 90. The heater power supply control circuit 14 also receives the temperature detection result Td from the temperature sensor 74 as input.

[0063] The temperature estimation unit 81 performs temperature estimation processing to estimate the surface temperature of the heat roller 71. The temperature estimation unit 81 receives the temperature detection result Td from the temperature sensor 74, the estimated history PREV from the estimation history holding unit 82, and the duty cycle value LD from the external limit unit 88 as input.

[0064] The estimated history PREV is the history of temperature estimation results EST by the temperature estimation unit 81. The estimated history PREV may also refer to a signal indicating the history of temperature estimation results EST by the temperature estimation unit 81. The history of temperature estimation results EST by the temperature estimation unit 81 includes multiple past temperature estimation results EST. The temperature estimation result EST is the surface temperature of the heat roller 71 estimated by the temperature estimation unit 81 based on at least the duty cycle LD. The temperature estimation result EST may also refer to a signal indicating the surface temperature of the heat roller 71 estimated by the temperature estimation unit 81 based on at least the duty cycle LD.

[0065] The duty cycle value LD is a duty cycle value based on the duty cycle value DUTY. The duty cycle value LD may also refer to a signal indicating a duty cycle value based on the duty cycle value DUTY. The duty cycle value LD may be the same value as the duty cycle value DUTY, or it may be a different value from the duty cycle value DUTY. If the external limit unit 88 does not limit the duty cycle value DUTY, the duty cycle value LD is the same value as the duty cycle value DUTY. If the external limit unit 88 limits the duty cycle value DUTY, the duty cycle value LD is the duty cycle value after the limit imposed by the external limit unit 88, and is a different value from the duty cycle value DUTY.

[0066] The duty cycle value DUTY is the duty cycle value generated by the control duty cycle generation unit 87. The duty cycle value DUTY may also refer to the signal indicating the duty cycle value generated by the control duty cycle generation unit 87.

[0067] The temperature estimation unit 81 estimates the surface temperature of the heat roller 71 based on the duty cycle value LD and generates the temperature estimation result EST. The temperature estimation unit 81 outputs the temperature estimation result EST to the estimation history holding unit 82 and the high-frequency component extraction unit 83. As described above, the duty cycle value LD is a duty cycle value based on the duty cycle value DUTY. Therefore, estimating the surface temperature of the heat roller 71 based on the duty cycle value LD is one example of estimating the surface temperature of the heat roller 71 based on the duty cycle value DUTY. As described above, the duty cycle value LD may also be the duty cycle value after being limited by the external limit unit 88. Therefore, estimating the surface temperature of the heat roller 71 based on the duty cycle value LD includes estimating the surface temperature of the heat roller 71 based on the duty cycle value after being limited by the external limit unit 88.

[0068] In a typical example, the temperature estimation unit 81 estimates the surface temperature of the heat roller 71 based on the estimated history PREV and the duty cycle value LD, and generates a temperature estimation result EST. Estimating the surface temperature of the heat roller 71 based on the estimated history PREV and the duty cycle value LD is an example of estimating the surface temperature of the heat roller 71 based on the estimated history PREV and the duty cycle value DUTY. Estimating the surface temperature of the heat roller 71 based on the estimated history PREV and the duty cycle value after being limited by the external limit unit 88 includes estimating the surface temperature of the heat roller 71 based on the estimated history PREV and the duty cycle value after being limited by the external limit unit 88.

[0069] The estimated history storage unit 82 stores the estimated history PREV. The estimated history storage unit 82 outputs the estimated history PREV to the temperature estimation unit 81.

[0070] The high-frequency component extraction unit 83 performs high-pass filtering to extract the high-frequency components of the temperature estimation result EST. For example, the high-frequency component extraction unit 83 cancels the DC component of the temperature estimation result EST and extracts only the high-frequency components. The high-frequency component extraction unit 83 generates a high-frequency component HPF and outputs the high-frequency component HPF to the coefficient summing unit 84. The high-frequency component HPF is the high-frequency component of the temperature estimation result EST extracted by the high-frequency component extraction unit 83. The high-frequency component HPF may also refer to a signal indicating the high-frequency component of the temperature estimation result EST extracted by the high-frequency component extraction unit 83.

[0071] The coefficient addition unit 84 performs a coefficient addition process, which is a correction of the temperature detection result Td. The coefficient addition unit 84 receives the temperature detection result Td from the temperature sensor 74 and the high-frequency component HPF from the high-frequency component extraction unit 83 as inputs. The coefficient addition unit 84 corrects the temperature detection result Td based on the high-frequency component HPF and generates a corrected temperature value WAE. The corrected temperature value WAE is the value obtained by correcting the temperature detection result Td based on the high-frequency component HPF, and is the estimated surface temperature of the heat roller 71. The corrected temperature value WAE may also refer to a signal indicating the value obtained by correcting the temperature detection result Td based on the high-frequency component HPF. The coefficient addition unit 84 outputs the corrected temperature value WAE to the difference comparison unit 86.

[0072] Specifically, the coefficient addition unit 84 multiplies the high-frequency component HPF by a preset coefficient K. The coefficient addition unit 84 adds the value obtained by multiplying the high-frequency component HPF by the coefficient K to the temperature detection result Td. The coefficient addition unit 84 calculates the value obtained by (Td + K × HPF) as the corrected temperature value WAE. Since the high-frequency component HPF is based on the temperature estimation result EST, it can be said that the corrected temperature value WAE is based on the temperature estimation result EST and the temperature detection result Td. The coefficient addition unit 84 is an example of a calculation unit that calculates the corrected temperature value WAE.

[0073] For example, when the coefficient K is 1, the coefficient summer 84 directly adds the high-frequency component HPF to the temperature detection result Td. Also, for example, when the coefficient K is 0.1, the coefficient summer 84 adds one-tenth of the value of the high-frequency component HPF to the temperature detection result Td. In this case, the effect of the high-frequency component HPF is almost eliminated, and the result becomes closer to the temperature detection result Td. Furthermore, for example, when the coefficient K is 1 or greater, the effect of the high-frequency component HPF can be expressed more strongly. Experiments have shown that the coefficient K set in the coefficient summer 84 should not be an extreme value, but rather a value close to 1 is preferable.

[0074] The target temperature output unit 85 performs output processing to output a preset target temperature TGT to the difference comparison unit 86. The target temperature TGT is the target value of the surface temperature of the heat roller 71. The target temperature TGT may also refer to a signal indicating the target value of the surface temperature of the heat roller 71. The target temperature TGT can be changed by rewriting it according to a command from the processor 22. The target value of the surface temperature of the heat roller 71 may be stored in the memory 23.

[0075] For example, the target temperature (TGT) is set for each printing process. For example, the target temperature TGT 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 TGT 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 heat roller 71 drops more easily when printing on cardboard than when printing on plain paper. When the printing medium P is cardboard, the target temperature TGT is higher than that associated with plain paper, taking into account the amount of heat absorbed from the heat roller 71 by the cardboard. This makes it easier for the surface temperature of the heat roller 71 to maintain a predetermined temperature. When the printing medium P is thinner than plain paper, the target temperature TGT is lower than that associated with plain paper. In another example, the target temperature (TGT) varies depending on the status of the printing process. Examples of target temperatures (TGT) depending on the printing process status will be discussed later.

[0076] The difference comparison unit 86 performs difference calculation processing. The difference comparison unit 86 receives the corrected temperature value WAE from the coefficient addition unit 84 and the target temperature TGT from the target temperature output unit 85 as inputs. The difference comparison unit 86 compares the target temperature TGT with the corrected temperature value WAE. Based on the comparison between the target temperature TGT and the corrected temperature value WAE, the difference comparison unit 86 calculates the difference DIF. The difference DIF is the difference between the target temperature TGT and the corrected temperature value WAE. The difference DIF may also refer to a signal indicating the difference between the target temperature TGT and the corrected temperature value WAE. The difference comparison unit 86 outputs the difference DIF to the control duty cycle generation unit 87. The difference comparison unit 86 is an example of a comparison unit.

[0077] Here, the difference DIF is explained as the value obtained by subtracting the target temperature TGT from the corrected temperature value WAE, but the reverse is also possible. In this example, if the corrected temperature value WAE is lower than the target temperature TGT, the difference DIF is a negative value. If the corrected temperature value WAE is higher than the target temperature TGT, the difference DIF is a positive value. The difference DIF reflects the relationship between the target temperature TGT and the corrected temperature value WAE.

[0078] The control duty generation unit 87 performs a duty value generation process to generate a duty value DUTY. The control duty generation unit 87 receives the difference DIF from the difference comparison unit 86 as input. The control duty generation unit 87 generates a duty value DUTY based on the difference DIF. The duty value DUTY is the duty value corresponding to the difference DIF. When the corrected temperature value WAE is equal to the target temperature TGT, the duty value DUTY is the center value (reference value) of the duty. When the corrected temperature value WAE is lower than the target temperature TGT, the control duty generation unit 87 increases the duty value above the center value of the duty in order to increase the amount of current supplied to the heater 73. The duty value DUTY is a value higher than the center value of the duty. On the other hand, when the corrected temperature value WAE is higher than the target temperature TGT, the control duty generation unit 87 decreases the duty value above the center value of the duty in order to reduce the amount of current supplied to the heater 73. The duty value DUTY is a value lower than the center value of the duty. The duty cycle value DUTY is a real number. For example, the duty cycle value may have a resolution of 0 to 100. The control duty cycle generation unit 87 outputs the duty cycle value DUTY to the external limit unit 88. The control duty cycle generation unit 87 is an example of a duty cycle generation unit.

[0079] As described above, the corrected temperature value WAE is based on the temperature estimation result EST and the temperature detection result Td. The difference DIF is the difference between the target temperature TGT and the corrected temperature value WAE. Therefore, generating the duty cycle value DUTY based on the difference DIF involves generating the duty cycle value based on the temperature estimation result EST, the temperature detection result Td, and the target temperature TGT.

[0080] The external limit unit 88 performs a limiting process to restrict the duty cycle value DUTY. The external limit unit 88 receives system protection information LMT from the processor 22 and the duty cycle value DUTY from the control duty cycle generation unit 87. The external limit unit 88 reflects the system protection information LMT in the duty cycle value DUTY and generates a duty cycle value LD based on the duty cycle value DUTY. Reflecting the system protection information LMT in the duty cycle value DUTY includes applying the system protection information LMT to the duty cycle value DUTY. If the duty cycle value DUTY does not satisfy the limit indicated by the system protection information LMT, the external limit unit 88 restricts the duty cycle value DUTY by reflecting the system protection information LMT in the duty cycle value DUTY. If the duty cycle value DUTY satisfies the limit indicated by the system protection information LMT, the external limit unit 88 does not restrict the duty cycle value DUTY even if the system protection information LMT is reflected in the duty cycle value DUTY. The external limit unit 88 outputs the duty cycle value LD to the temperature estimation unit 81 and the duty cycle pulse conversion unit 89. The external limit unit 88 is an example of a limit unit.

[0081] System protection information LMT is information for limiting the duty cycle to protect the image forming apparatus 1. System protection information LMT may also refer to a signal indicating information for limiting the duty cycle to protect the image forming apparatus 1. System protection information LMT can be changed by commands from the processor 22.

[0082] For example, the system protection information LMT 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 DUTY exceeds the upper limit of the duty cycle value, the duty cycle value DUTY does not meet the limit indicated in the system protection information LMT. If the duty cycle value DUTY is less than the lower limit of the duty cycle value, the duty cycle value DUTY does not meet the limit indicated in the system protection information LMT. If the duty cycle value DUTY 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 DUTY meets the limit indicated in the system protection information LMT.

[0083] 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 DUTY is 90. Since the duty cycle value DUTY exceeds the upper limit of the duty cycle value, the duty cycle value DUTY does not satisfy the limit indicated in the system protection information LMT. The external limit unit 88 limits the duty cycle value DUTY by reflecting the system protection information LMT to the duty cycle value DUTY. The external limit unit 88 generates a duty cycle value LD based on the duty cycle value DUTY. The duty cycle value LD 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 DUTY is 80. Since the duty cycle value DUTY 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 DUTY satisfies the limit indicated in the system protection information LMT. Even if the external limit unit 88 reflects the system protection information LMT to the duty cycle value DUTY, it does not limit the duty cycle value DUTY. The external limit unit 88 generates a duty cycle value LD based on the duty cycle value DUTY. The duty cycle value LD is the same as the duty cycle value DUTY 80.

[0084] In another example, system protection information LMT is information instructing a stop to avoid danger to the image forming apparatus 1. If the duty cycle value DUTY is a value other than 0, the duty cycle value DUTY does not satisfy the limit indicated by the system protection information LMT. In this case, the external limit unit 88 limits the duty cycle value DUTY by reflecting the system protection information LMT in the duty cycle value DUTY. The external limit unit 88 generates a duty cycle value LD based on the duty cycle value DUTY. The duty cycle value LD is the limited duty cycle value. The limited duty cycle value is 0. If the duty cycle value DUTY is 0, the duty cycle value DUTY satisfies the limit indicated by the system protection information LMT. In this case, even if the external limit unit 88 reflects the system protection information LMT in the duty cycle value DUTY, it does not limit the duty cycle value DUTY. The external limit unit 88 generates a duty cycle value LD based on the duty cycle value DUTY. The duty cycle value LD is 0, the same as the duty cycle value DUTY.

[0085] The duty pulse conversion unit 89 performs a generation process to generate energizing pulses Ps for controlling the power supplied to the heater 73 based on the duty cycle value LD. The energizing pulses Ps are pulse signals for controlling the power supplied to the heater 73. The energizing pulses Ps are the gate signals of the triac. The duty cycle value LD from the external limit unit 88 is input to the duty cycle pulse conversion unit 89. The duty cycle pulse conversion unit 89 converts the duty cycle value LD into an energizing pulse train. The duty cycle pulse conversion unit 89 generates energizing pulses Ps that constitute the energizing pulse train. The duty cycle pulse conversion unit 89 outputs the energizing pulses Ps to the power supply circuit 90. The duty cycle pulse conversion unit 89 is an example of a signal generation unit that generates energizing pulses Ps.

[0086] As described above, the duty cycle value LD may be the duty cycle value after being limited by the external limit unit 88. Therefore, generating and outputting energizing pulses Ps based on the duty cycle value LD includes generating and outputting energizing pulses Ps based on the duty cycle value after being limited by the external limit unit 88. Generating and outputting energizing pulses Ps based on the duty cycle value LD is an example of generating and outputting energizing pulses Ps based on the duty cycle value DUTY.

[0087] The duty pulse conversion unit 89 may select a duty pattern based on the duty value LD and generate energizing pulses Ps 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.

[0088] The duty pulse conversion unit 89 may generate energizing pulses Ps asynchronously with the system operation. Specifically, the duty pulse conversion unit 89 may adjust the pulse frequency and the output time of the energizing pulses Ps to match the AC voltage frequency of 50Hz / 60Hz. The duty pulse conversion unit 89 acquires the AC voltage phase and performs synchronous output processing to output energizing pulses Ps that constitute an energizing pulse train in synchronization with the AC voltage, based on the AC voltage phase. The duty pulse conversion unit 89 outputs energizing pulses Ps in synchronization with the zero-crossing of the AC voltage.

[0089] The power supply circuit 90 supplies power PC to the heater 73 based on the energizing pulse Ps. The power supply circuit 90 energizes the heater 73 of the fuser 21 using an AC voltage supplied from an AC voltage source (not shown). The power supply circuit 90 supplies power PC to the heater 73 by switching, for example, based on the energizing pulse Ps, between a state where the AC voltage from the AC voltage source is supplied to the heater 73 and a state where it is not supplied. That is, the power supply circuit 90 changes the energizing time of the heater 73 of the fuser 21 in accordance with the energizing pulse Ps.

[0090] The power supply circuit 90 may be integrated with the fuser 21. That is, the heater power supply control circuit 14 may be configured to supply power supply pulses Ps to the power supply circuit of the heater 73 of the fuser 21, rather than supplying power PC to the heater 73.

[0091] As described above, the heater power supply control circuit 14 adjusts the amount of power supplied to the heater 73 of the fuser unit 21. This allows the heater power supply control circuit 14 to control the surface temperature of the heat roller 71 heated by the heater 73. This type of control will be referred to here as Weighted Average control with Estimate temperature (WAE control).

[0092] The temperature estimation unit 81, estimation history holding unit 82, high-frequency component extraction unit 83, coefficient addition unit 84, target temperature output unit 85, difference comparison unit 86, control duty generation unit 87, external limit unit 88, and duty pulse conversion unit 89 of the heater power supply control circuit 14 may each be configured by an electrical circuit or by software. If configured by 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.

[0093] This section describes a thermal circuit that represents heat transfer to obtain the temperature estimation result (EST). Figure 3 is a diagram illustrating the thermal circuit that represents heat transfer to obtain the temperature estimation result EST. Heat transfer can be represented by a thermal circuit equivalent to the CR time constant of an electrical circuit (where C is a capacitor and R is a resistor). A thermal circuit is composed of V, C, and R elements.

[0094] The heat source V1 is equivalent to a DC voltage source in an electrical circuit. The heating resistance R1 is equivalent to a variable resistor in an electrical circuit. The heating resistance R1 uses the duty cycle LD as a variable factor. For example, if the duty cycle value indicated by duty cycle LD is 100%, the heating resistance R1 remains R. Here, for example, let's assume R is 100Ω. If the duty cycle value indicated by duty cycle LD is 0%, the heating resistance Ra is assumed to be 100Ω × 10,000,000 (an extremely large value). If the duty cycle value indicated by duty cycle LD is greater than 0 and less than 100, the heating resistance R1 is assumed to be 100Ω × (duty cycle LD / 100). The heater capacitance C1, together with the heating resistance R1, forms the first CR time constant circuit. The heater capacitance C1 refers to the estimated history PREV from a small time interval dt ago and updates to the temperature at the current time.

[0095] 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, together with the heat dissipation resistance R2, forms a second CR time constant circuit. The unit capacitance C2 is updated to the current temperature by referring to the estimated history PREV from dt.

[0096] 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 V2 is equivalent to a DC voltage source in an electrical circuit. The relationship between the heat source V1 and the ambient temperature V2 is heat source V1 ≥ ambient temperature V2. Specifically, the relationship between the heat source V1 and the ambient temperature V2 before startup is heat source V1 = ambient temperature V2, and the relationship between the heat source V1 and the ambient temperature V2 during operation is heat source V1 > ambient temperature V2.

[0097] For example, the temperature estimation unit 81 performs a real-time simulation of the thermal circuit described above using the energy conservation law based on the estimated history PREV and the duty cycle LD. The temperature estimation unit 81 derives the C1 voltage (temperature) as an estimate of the surface temperature of the heat roller 71 through the real-time simulation of the thermal circuit. The temperature estimation unit 81 generates the C1 voltage (temperature) as the temperature estimation result EST for the current time.

[0098] The following provides a detailed explanation of WAE control. Figure 4 is a flowchart illustrating WAE control. Figures 5 and 6 are explanatory diagrams illustrating the various signals in WAE control. The horizontal axis in Figures 5 and 6 represents time. The vertical axis in Figures 5 and 6 represents temperature.

[0099] The heater power control circuit 14 acquires the internal temperature of the image forming apparatus 1 (ACT1). Since the internal temperature changes slowly, the frequency of acquiring the internal temperature by the heater power control circuit 14 does not need to be high.

[0100] The heater power supply control circuit 14 obtains the current temperature detection result Td from the temperature sensor 74 (ACT2).

[0101] As shown in Figure 5, there is a difference between the temperature detection result Td and the actual surface temperature of the heat roller 71. The surface temperature of the heat roller 71 changes in a fine cycle because heating by the heater 73 is performed intermittently. In contrast, the temperature sensor 74 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 Td does not accurately track the actual surface temperature of the heat roller 71. That is, the temperature detection result Td is detected by the temperature sensor 74 with a delay relative to the surface temperature of the heat roller 71. Furthermore, the temperature detection result Td does not reproduce the fine changes in the surface temperature of the heat roller 71 and is detected by the temperature sensor 74 in a smoothed state.

[0102] The temperature estimation unit 81 obtains the estimation history PREV from the estimation history retention unit 82 (ACT3). The difference comparison unit 86 obtains the target temperature TGT from the target temperature output unit 85 (ACT4). The temperature estimation unit 81 obtains the parameters corresponding to the V, C, and R elements that constitute the thermal circuit as described above (ACT5).

[0103] The temperature estimation unit 81 calculates the heat inflow (ACT6). In ACT6, for example, the temperature estimation unit 81 calculates the heat inflow based on the input values ​​V1 and R and the duty cycle LD. The heat inflow can be calculated as I = R / V1 × (100 / duty cycle LD). When the duty cycle value indicated by duty cycle LD is 0%, the heating resistance R1 becomes infinite, and the heat inflow from the input side is 0. On the other hand, when the duty cycle value indicated by duty cycle LD is 100%, I = R / V1, and the heat inflow from the input side is at its maximum.

[0104] The temperature estimation unit 81 obtains Vb, which is a value equivalent to the surface temperature of the heat roller 71, from the acquired estimation history PREV (ACT7). The temperature estimation unit 81 calculates the increase in Vb after dt due to heat inflow from the energy conservation law (ACT8). The temperature estimation unit 81 obtains Ve, which is a value equivalent to the internal temperature of the image forming apparatus 1, from the acquired estimation history PREV (ACT9).

[0105] The temperature estimation unit 81 calculates the heat outflow rate (ACT10). In ACT10, for example, the temperature estimation unit 81 calculates the temperature difference (Vb-Ve) between the surface temperature of the heat roller 71 and the temperature inside the housing. The temperature estimation unit 81 then calculates the heat outflow rate, which is defined by the heat dissipation resistance R2, based on the temperature difference (Vb-Ve). The temperature estimation unit 81 calculates the decrease in Vb after dt due to heat outflow from the energy conservation law (ACT11).

[0106] The temperature estimation unit 81 calculates Vc after dt (ACT11). Vc after dt corresponds to the temperature estimation result EST. In ACT11, for example, the temperature estimation unit 81 calculates Vc after dt using the formula Vc = Vc history value + Vb increase - Vb decrease. The Vc history value is the value of Vc before dt. In other words, Vc after dt is obtained by adding the value obtained by subtracting the decrease in Vb from the increase in Vb to the value of Vc before dt.

[0107] As shown in Figure 5, the temperature estimation result EST appropriately tracks the actual surface temperature change of the heat roller 71. However, since the temperature estimation result EST is a simulation result, the absolute value may differ from the actual surface temperature of the heat roller due to differences in conditions, etc.

[0108] The high-frequency component extraction unit 83 takes the time derivative of Vc, which corresponds to the temperature estimation result EST, and extracts the change (ACT12). The high-frequency component extraction unit 83 integrates the differential value to form a high-pass filter (ACT13). The high-frequency component extraction unit 83 cancels the DC component of the temperature estimation result EST using the high-pass filter and extracts only the high-frequency component. The high-frequency component extraction unit 83 generates a high-frequency component HPF. As shown in Figure 5, the high-frequency component HPF appropriately tracks the actual surface temperature changes of the heat roller 71.

[0109] The coefficient addition unit 84 obtains the current temperature detection result Td from the temperature sensor 74 (ACT15). The coefficient addition unit 84 calculates the corrected temperature value WAE (ACT16). In ACT16, for example, the coefficient addition unit 84 determines the value obtained by (Td + K × HPF) as the corrected temperature value WAE.

[0110] Figure 6 is an explanatory diagram illustrating an example of the actual surface temperature of the heat roller 71, the temperature detection result Td, and the corrected temperature value WAE. In WAE control, the fine temperature changes of the surface temperature of the heat roller 71 are estimated based on the temperature detection result Td and the high-frequency component HPF of the temperature estimation result EST. Therefore, as shown in Figure 6, the corrected temperature value WAE is a value that appropriately tracks the surface temperature of the heat roller 71.

[0111] The estimated history retention unit 82 overwrites the estimated history PREV with the temperature estimated result EST (ACT17). The difference comparison unit 86 calculates the difference DIF based on a comparison between the target temperature TGT and the corrected temperature value WAE (ACT18).

[0112] The control duty generation unit 87 generates the duty cycle value DUTY based on the differential DIF (ACT19).

[0113] The external limit unit 88 reflects the system protection information LMT in the duty cycle value DUTY and limits the duty cycle value (ACT20). In ACT20, for example, the external limit unit 88 generates a duty cycle value LD based on the duty cycle value DUTY by reflecting the system protection information LMT in the duty cycle value DUTY.

[0114] The duty pulse conversion unit 89 converts the duty cycle value LD into a current pulse train (ACT21). The duty pulse conversion unit 89 generates current pulses Ps that constitute the current pulse train. The duty cycle pulse conversion unit 89 outputs energizing pulses Ps that constitute an energizing pulse train in synchronization with the AC voltage (ACT22).

[0115] The processor 22 of the system controller 13 determines whether or not it has received a command to stop WAE control (ACT23). If the processor 22 has not received a command to stop WAE control, processing transitions from ACT23 to ACT2. If the processor 22 has received a command to stop WAE control, processing terminates.

[0116] As described above, when the heater power control circuit 14 processes a certain cycle (the current cycle), it performs WAE control based on the values ​​from the previous cycle (duty cycle value LD and temperature estimation result EST: estimation history PREV) and the temperature detection result Ts from the current cycle. In other words, the heater power control circuit 14 inherits the values ​​in the next cycle. The heater power control circuit 14 recalculates the temperature estimation calculation based on the history of the previous calculation. Therefore, the heater power control circuit 14 is constantly performing calculations while in operation. In the heater power control circuit 14, the calculation results are stored in memory or the like and reused in the calculation of the next cycle.

[0117] Figure 6 is an explanatory diagram illustrating the processing cycle in the heater energization control circuit 14. The horizontal axis in Figure 6 represents time. For example, the temperature estimation unit 81 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 temperature estimation unit 81 repeatedly performs temperature estimation processing. In the temperature estimation processing of each cycle, the temperature estimation unit 81 uses the previous temperature estimation result EST to estimate the new temperature.

[0118] At time t(n), the temperature detection result Td at time t(n), the duty cycle value LD at the previous time t(n-1), and the temperature estimation result EST (estimated history PREV) at the previous time t(n-1) are used. The temperature estimation unit 81 processes the input signal and outputs the temperature estimation result EST at time t(n). The high-frequency component extraction unit 83, coefficient addition unit 84, target temperature output unit 85, difference comparison unit 86, control duty cycle generation unit 87, external limit unit 88, and duty pulse conversion unit 89 process the input signal, and the duty pulse conversion unit 89 outputs the energizing pulse Ps at time t(n).

[0119] At time t(n+1), the newly detected temperature detection result Td at time t(n+1), the duty cycle value LD at time t(n), and the estimated history PREV, which is the temperature estimation result EST at time t(n), are used. The temperature estimation unit 81 processes the input signal and outputs the temperature estimation result EST at time t(n+1). The high-frequency component extraction unit 83, coefficient addition unit 84, target temperature output unit 85, difference comparison unit 86, control duty cycle generation unit 87, external limit unit 88, and duty pulse conversion unit 89 process the input signal, and the duty pulse conversion unit 89 outputs the energization pulse Ps at time t(n+1).

[0120] At time t(n+2), the temperature detection result Td newly detected at time t(n+2), the duty cycle value LD at time t(n+1), and the estimated history PREV, which is the temperature estimation result EST at time t(n+1), are input to the temperature estimation unit 81. The temperature estimation unit 81 processes the input signals and outputs the temperature estimation result EST at time t(n+2). The high-frequency component extraction unit 83, coefficient addition unit 84, target temperature output unit 85, difference comparison unit 86, control duty cycle generation unit 87, external limit unit 88, and duty pulse conversion unit 89 process the input signals, and the duty pulse conversion unit 89 outputs the energization pulse Ps at time t(n+2).

[0121] 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].

[0122] This section describes the target temperature (TGT) according to the status of the printing process. Figure 8 is an explanatory diagram illustrating an example of a target temperature (TGT) according to the status of the printing process. The horizontal axis in Figure 8 represents time. The vertical axis in Figure 8 represents temperature. The solid line represents the target temperature (TGT). The dashed line represents the actual surface temperature of the heat roller 71.

[0123] The printing process status includes various statuses related to the printing process. For example, the printing process status includes, but is not limited to, inrush current prevention, start-up heating, ready, printing started, printing in progress, and energy-saving ready. The target temperature (TGT) for each status is different from one another. The target temperature (TGT) for each status may be predetermined or variable.

[0124] In the inrush current prevention status, the target temperature (TGT) is set to rise gradually to prevent a sudden surge of current. In the startup heating status, the target temperature (TGT) is set higher to quickly reach the standard temperature suitable for printing. In the ready status, the target temperature (TGT) is set slightly lower than the target temperature (TGT) in the startup heating status to save energy after the printer is ready to print. In the print start status, the target temperature (TGT) is set higher than the target temperature (TGT) in the printing status from a little before printing to prevent a temperature drop at the beginning of printing. In the printing status, the target temperature (TGT) is set to the standard temperature suitable for printing. In the energy-saving ready status, if the ready state is to be maintained for a long time, the target temperature (TGT) is set lower than the target temperature (TGT) in the ready status.

[0125] This section explains the relationship between the difference (DIF) and the duty cycle (DUTY). Figure 9 illustrates the relationship between the difference (DIF) and the duty cycle (DUTY). The horizontal axis of Figure 9 represents the difference (DIF). The vertical axis of Figure 9 represents the duty cycle (DUTY). The solid line shows the relationship between the difference (DIF) and the duty cycle (DUTY).

[0126] Here, the center value of the duty cycle, DUTY, when the difference DIF is 0, is set to 45%. The maximum value of the difference DIF is set to 1, and the minimum value of the difference DIF is set to -1. The duty cycle DUTY is set to 0 when the difference DIF is at its maximum value. The duty cycle DUTY is set to 100 when the difference DIF is at its minimum value. The relationship between the difference DIF and the duty cycle DUTY is expressed as a linear function based on the above settings. In this example, the duty cycle DUTY = 45 - difference DIF × slope (45 / 1).

[0127] When the corrected temperature value WAE is lower than the target temperature TGT, the duty cycle value DUTY is higher than the center value of the duty cycle. On the other hand, when the corrected temperature value WAE is higher than the target temperature TGT, the duty cycle value DUTY is lower than the center value of the duty cycle. The control duty cycle generation unit 87 generates the duty cycle value DUTY based on the differential DIF for each processing cycle, using the relationship between the differential DIF and the duty cycle value DUTY as illustrated in Figure 9.

[0128] The energizing pulse train generated by the duty pulse conversion unit 89 will now be described. Figure 10 is a diagram illustrating the energized pulse train generated by the duty pulse conversion unit 89. Here, the energizing pulse train is represented by 10 pulses. Each pulse is 10ms long. Each cell represents one pulse. The shaded cell represents the energizing pulse Ps, which indicates a "1" signal for conduction (on). The white cell represents a "0" signal for interruption (off). When the duty cycle is 0%, all 10 cells representing the energizing pulse train are white. Therefore, in a 100ms energizing pulse train, 100% of the 100ms are "0" signals. When the duty cycle is 20%, the 10 cells representing the energizing pulse train contain 2 shaded cells. Therefore, in a 100ms energizing pulse train, 20% of the 100ms are "1" signals and 80% of the 100ms are "0" signals. When the duty cycle is 50%, the 10 cells representing the energizing pulse train contain 5 shaded cells. Therefore, in a 100ms energized pulse train, 50% of the signals are "1" and 50% are "0". When the duty cycle is 50%, the 10 cells representing the energized pulse train contain 8 diagonal cells. Therefore, in a 100ms energized pulse train, 80% of the signals are "1" and 20% are "0". When the duty cycle is 100%, all 10 cells representing the energized pulse train contain diagonal cells. Therefore, in a 100ms energized pulse train, 100% of the signals are "1".

[0129] This section explains the relationship between the duty cycle and the generated power, and between the energizing pulse train and the generated power. Figure 11 is a diagram illustrating the relationship between the duty cycle and the generated power, and between the energizing pulse train and the generated power. The horizontal axis in Figure 11 represents the duty cycle. The vertical axis in Figure 11 represents the energy.

[0130] The relationship between the duty cycle and the generated power, and between the pulse train and the generated power, shows that the duty cycle and the pulse train are proportional. This is the case when the resistance of the heat roller 71 is constant. If the resistance of the heat roller 71 changes, the relationship between the duty cycle and the amount of power may be corrected using a table. Even in that case, the relationship between the duty cycle and the pulse train remains proportional. Therefore, it can be seen that the duty cycle can be used instead of the energizing pulse Ps in order for the temperature estimation unit 81 to generate the temperature estimation result EST.

[0131] Let's look at an example of sampling duty cycle values. Figure 12 is a diagram illustrating an example of duty cycle value sampling according to one embodiment. As can be seen from the comparison between the duty cycle value shown in Figure 12 (Duty Cycle Value LD) and the duty cycle detection result, the processor uses a self-generated duty cycle value, allowing it to detect the duty cycle value without delay. Furthermore, as can be seen from the sampling interval shown in Figure 12, the processor does not require high-speed sampling because it uses a self-generated duty cycle value.

[0132] Next, the WAE control described above will be explained using a specific numerical example. The parameters corresponding to the V, C, and R elements that constitute the thermal circuit illustrated in Figure 3 are as follows. The heat source V1 is 500 + 273 (Kelvin). The ambient temperature V2 is 25 + 273 (Kelvin). The heating resistance R1 is assumed to be 10 (Ω). The heat dissipation resistance R2 is 2 (Ω). The ambient air resistance R3 is 5 (Ω). The heater capacity C1 is 10 (F). The unit capacity C2 is 100 (F).

[0133] In this case, the values ​​for WAE control are as follows: The temperature estimation result EST is 126 + 273 (Kelvin). The temperature detection result Td is 115 + 273 (Kelvin). The high-frequency component HPF is 5 (Kelvin). The coefficient K is 1. The corrected temperature value WAE is Td + K × HPF = 115 + 273 + 5 × 1. The target temperature TGT is 118 + 273 (Kelvin). The difference DIF is WAE - TGT = 2. The duty cycle value DUTY is 48. When the energizing pulse train is represented by 10 pulses, the duty cycle value LD is 50. In this case, 5 of the 10 pulses representing the energizing pulse train are energizing pulses Ps. When the energizing pulse train is represented by 100 pulses, the duty cycle value LD is 48. In this case, 48 of the 100 pulses representing the energizing pulse train are energizing pulses Ps.

[0134] The temperature estimation unit 81 may also take AC voltage fluctuations into consideration. Assuming the AC voltage is 100V, E1 is 400Ω and R1 is 100Ω. The duty cycle, indicated by LD, is assumed to be 100%. In this case, the input power is E1 × E1 / R1 = 1600 (Watts). Assuming the AC voltage is 110V, E1 is 400 × 110 / 100 = 440 and R1 is 100Ω. The duty cycle, indicated by LD, is assumed to be 100%. In this case, the input power is E1 × E1 / R1 = 1936 (Watts). Assuming the AC voltage is 90V, E1 is 400 × 90 / 100 = 360 and R1 is 100Ω. The duty cycle, indicated by the duty cycle LD, is assumed to be 100%. In this case, the input power is E1 × E1 / R1 = 1296 (Watts).

[0135] As described above, the image forming apparatus 1 includes a fuser 21 having a heat roller 71 that heats and fixes a toner image formed on a printing medium P onto the printing medium P, and a heater 73 that heats the heat roller 71, and a temperature control device (heater power supply control circuit 14). The heater power supply control circuit 14 controls the temperature of the heat roller 71, from which heat is transmitted from the heater 73, by supplying power to the heater 73. The heater power supply control circuit 14 includes a temperature estimation unit 81 that estimates the temperature of the heat roller 71. The heater power supply control circuit 14 includes a control duty generation unit 87 that generates a duty cycle value DUTY based on the temperature estimation result EST from the temperature estimation unit 81, the temperature detection result Td of the heat roller 71 from the temperature sensor 74, and the target temperature TGT. The heater power supply control circuit 14 includes a duty pulse conversion unit 89 that outputs a power supply pulse Ps to control the power supplied to the heater 73 based on the duty cycle value DUTY. The temperature estimation unit 81 estimates the temperature of the heat roller 71 based on the duty cycle value DUTY.

[0136] The temperature estimation unit 81 estimates the temperature of the heat roller 71 based on the history of the temperature estimation result EST and the duty cycle value DUTY.

[0137] The control duty generation unit 87 calculates the duty cycle value DUTY based on the difference DIF between the target temperature TGT and the corrected temperature value WAE based on the temperature estimation result EST and the temperature detection result Td.

[0138] With this configuration, the temperature control device can achieve simple feedback control that is effective for WAE control and can speed up the feedback control. The temperature control device enables highly accurate temperature control through WAE control and feedback control that is effective for WAE control. As a result, the temperature control device can reduce the cost of the temperature sensor 74 and prevent temperature ripple and the like. Furthermore, since the temperature control device estimates the temperature of the heat roller 71 based on the duty cycle value DUTY, it does not require a mechanism to detect changes in pulses even when the frequency of the energizing pulse is high. Therefore, the temperature control device does not require high-speed sampling, and thus the increase in processing load can be suppressed. Consequently, the temperature control device can be implemented with an inexpensive processor. The temperature control device is easy to implement with firmware.

[0139] The heater energization control circuit 14 includes an external limit unit 88 that limits the duty cycle value DUTY. The duty pulse conversion unit 89 outputs an energization pulse Ps based on the duty cycle value after it has been limited by the external limit unit 88. The temperature estimation unit 81 estimates the temperature of the heat roller 71 based on the duty cycle value after it has been limited.

[0140] With this configuration, the temperature control device can avoid danger to the image forming apparatus 1 by limiting the duty cycle value (DUTY).

[0141] The temperature control device described above 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 thermal melting 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 achieved, which can lead to improved yield of manufactured products, improved crystal quality (reduction in crystal defect rate), and improved performance of alloys.

[0142] 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.

[0143] 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]

[0144] 1…Image forming apparatus, 11…Housing, 12…Communication interface, 13…System controller, 14…Heater power supply control circuit, 15…Display unit,…Operation interface, 17…Paper tray, 18…Paper output tray, 19…Conveyor unit, 20…Image forming unit, 21…Fuser, 22…Processor, 23…Memory, 31…Paper feed transport path, 32…Paper output transport path, 33…Pickup roller, 41…Process unit, 42…Exposure unit, 43…Transfer mechanism, 51…Photosensitive drum, 52…Charging chip 53...Garger, 61...Primary transfer belt, 62...Secondary transfer opposing roller, 63...Primary transfer roller, 64...Secondary transfer roller, 71...Heat roller, 72...Press roller, 73...Heater, 74...Temperature sensor, 81...Temperature estimation unit, 82...Estimated history retention unit, 83...High frequency component extraction unit, 84...Coefficient addition unit, 85...Target temperature output unit, 86...Difference comparison unit, 87...Control duty generation unit, 88...External limit unit, 89...Duty pulse conversion unit, 90...Power supply circuit.

Claims

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, The temperature control device is A temperature estimation unit that estimates the temperature of the temperature-controlled object, A duty cycle generation unit generates a duty cycle value based on the temperature estimation result from the temperature estimation unit, the temperature detection result of the temperature-controlled object from the temperature sensor, and the target temperature. A signal generation unit that outputs energizing pulses to control the power supplied to the heater based on the duty cycle value, It is equipped with, The temperature estimation unit estimates the temperature of the temperature-controlled object based on the duty cycle value.

2. The temperature control device according to claim 1, wherein the temperature estimation unit estimates the temperature of the temperature-controlled object based on the history of the temperature estimation results and the duty cycle value.

3. The unit further includes a limit section that limits the duty cycle value, The signal generation unit outputs the energizing pulse based on the duty cycle value after the limiting by the limit unit. The temperature estimation unit estimates the temperature of the temperature-controlled object based on the limited duty cycle value. The temperature control device according to claim 1.

4. The temperature control device according to claim 1, wherein the duty cycle generation unit calculates the duty cycle value based on the difference between the target temperature and the corrected temperature value based on the temperature estimation result and the temperature detection result.

5. 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, The system comprises a temperature control unit that controls the temperature of the fixing rotating body to which heat is transmitted from the heater by supplying power to the heater, The temperature control unit, A temperature estimation unit for estimating the temperature of the fixing rotating body, A duty cycle generation unit generates a duty cycle value based on the temperature estimation result from the temperature estimation unit, the temperature detection result of the fixing rotating body from the temperature sensor, and the target temperature. A signal generation unit that outputs energizing pulses to control the power supplied to the heater based on the duty cycle value, It is equipped with, The image forming apparatus comprises a temperature estimation unit that estimates the temperature of the fixing rotating body based on the duty cycle value.

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