Fixing apparatus and image forming apparatus

Abstract

To accurately detect temperature changes in the upper and lower belts while directly heating and maintaining them at predetermined temperatures. [Solution] The fixing module 4000 performs temperature control to maintain the temperature of the upper belt 30 and the lower belt 40 at a predetermined temperature by controlling a plurality of heating units 117, heating unit 127, heating unit 137, heating unit 147 and heating unit 157 based on the temperature detected by temperature sensors 310, 311, 312, 315, 316 and 317, 320, 321 and 322.

Description

【Technical Field】 【0001】 The present invention relates to a fixing device using a heating method and an image forming apparatus including the fixing device. 【Background Art】 【0002】 Conventionally, an inkjet recording type image forming apparatus is known which dries a recording medium to which ink is applied to evaporate moisture, and then applies heat and pressure to the recording medium to fix an image. Conventionally, as a fixing system for applying such heat and pressure to fix an image, a heat roller method in which a recording medium is passed between a heating roller and a pressure roller has been used. In a conventional heat roller type fixing system, an abnormal heating is detected using a thermistor lightly contacting a heating roller, and when an abnormal heating is detected, the power supply to a heater for heating the roller is cut off. 【0003】 In recent years, with the increase in speed and productivity of image forming apparatuses, a fixing system has been used which can lengthen the distance in the conveyance direction of a recording medium in a nip portion by using a pair of heating belts instead of rollers (for example, Patent Document 1). In such a fixing system, in order to quickly heat a recording medium entering the nip portion, an on-demand fixing method is used in which a belt is directly heated by a heater to shorten the rise time. The on-demand fixing method has good thermal efficiency and a high heating rate. On the other hand, since it is necessary to detect a temperature drop after the recording medium has passed and reheat with a heater when the temperature drop is detected, highly accurate temperature detection and control are required. 【0004】 Conventionally, in the on-demand fixing method, temperature detection using a contact type sensor contacting a belt is known. However, when temperature detection is performed using a contact type sensor, there is a possibility that the sensor is worn by sliding the sensor on the belt. When the sensor is worn, uneven temperature or variation in contact pressure occurs, and thus the detected temperature is not stable. 【0005】 In contrast, a conventional on-demand fixing method is known in which a sensor that detects the surface temperature of the belt non-contactually is installed on the outside of the belt just downstream of the paper output opening. By using a non-contact sensor, it is possible to prevent the sensor from being worn down by the belt. [Prior art documents] [Patent Documents] 【0006】 [Patent Document 1] Japanese Patent Publication No. 2018-136392 [Overview of the project] [Problems that the invention aims to solve] 【0007】 However, conventionally, since non-contact sensors are placed on the outside of the belt immediately downstream of the paper output tray, there is a risk of condensation forming on the sensor due to water vapor generated by the heating of the recording medium. In addition, conventionally, the emissivity of the sensor changes due to contamination by paper dust and other substances adhering to the surface of the belt. As a result, conventionally, there is a problem that the detection accuracy of the sensor may decrease. 【0008】 The object of the present invention is to provide a fixing device and an image forming device that can accurately detect temperature changes in the upper and lower belts when directly heating and maintaining them at a predetermined temperature. [Means for solving the problem] 【0009】 The fixing device according to the present invention is a fixing device for fixing an image to a sheet by heating and pressurizing the sheet, and is characterized by comprising: an endless upper belt; an endless lower belt that grips and conveys the sheet together with the upper belt at a nip portion formed by contacting the upper belt; a plurality of heating units for heating the upper belt and the lower belt; a first temperature sensor disposed on the outside of the upper belt and the lower belt and detecting the temperature of the upper belt and the lower belt respectively in a non-contact manner; a second temperature sensor disposed on the inside of the upper belt and detecting the temperature of the upper belt in a non-contact manner; and a control unit that performs temperature control to maintain the temperature of the upper belt and the lower belt at a predetermined temperature by controlling the plurality of heating units based on the temperatures detected by the first temperature sensor and the second temperature sensor. [Effects of the Invention] 【0010】 According to the present invention, when directly heating the upper belt and the lower belt and maintaining them at a predetermined temperature, temperature changes in the upper belt and the lower belt can be accurately detected. [Brief explanation of the drawing] 【0011】 [Figure 1] This is a schematic front view of an image forming apparatus according to Embodiment 1 of the present invention. [Figure 2] This is a front cross-sectional view of a fixing module according to Embodiment 1 of the present invention. [Figure 3] This is a front cross-sectional view of a part of a fixing module according to Embodiment 1 of the present invention. [Figure 4] This is a schematic diagram of a part of the heating section of the fixing module according to Embodiment 1 of the present invention. [Figure 5] This is a partial perspective view of the fixing module according to Embodiment 1 of the present invention. [Figure 6] This is a side cross-sectional view of a fixing module according to Embodiment 1 of the present invention. [Figure 7] This is a block diagram showing the configuration of the upper fixing belt system of the fixing module according to Embodiment 1 of the present invention. [Figure 8] It is a block diagram showing the configuration of the lower fixing belt system of the fixing module according to Embodiment 1 of the present invention. [Figure 9] It is a diagram showing the configuration and characteristics of the heater of the fixing module according to Embodiment 1 of the present invention. [Figure 10] It is a diagram showing a schematic diagram and characteristics of a part of the fixing module according to Embodiment 1 of the present invention. [Figure 11] It is a diagram showing a schematic diagram and characteristics of the heater of the fixing module according to Embodiment 1 of the present invention. [Figure 12] It is a flowchart showing the operation of the fixing module according to Embodiment 1 of the present invention. [Figure 13] It is a flowchart of the error detection process executed by the fixing module according to Embodiment 1 of the present invention. [Figure 14] It is a diagram showing the arrangement position of the temperature sensor of the fixing module according to Embodiment 1 of the present invention. [Figure 15] It is a flowchart of the temperature sensor selection process executed by the fixing module according to Embodiment 2 of the present invention. 【Mode for Carrying Out the Invention】 【0012】 Hereinafter, embodiments will be described in detail with reference to the drawings. 【0013】 (Embodiment 1) <Configuration of the Image Forming Apparatus> The configuration of the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to FIG. 1. Note that FIG. 1 is a view of the image forming apparatus 100 seen from the front. 【0014】 The image forming apparatus 100 uses an inkjet recording method that discharges ink to form an image on a sheet S, and is a so-called sheet-fed inkjet recording apparatus that forms an ink image on the sheet S using two liquids, a reaction liquid and ink. The inkjet recording method can employ a method using a heating element, a method using a piezo element, a method using an electrostatic element, a method using a MEMS (MicroElectro Mechanical Systems) element, or the like. 【0015】 Here, the sheet S is a recording material capable of receiving ink, such as plain paper, cardboard, a sheet with a special shape, or cloth. The sheet with a special shape is a plastic film for an overhead projector, an envelope, an index paper, or the like. 【0016】 Specifically, the image forming apparatus 100 includes a feeding module 1000, a printing module 2000, a drying module 3000, a fixing module 4000, a cooling module 5000, a reversing module 6000, and a stacking module 7000. 【0017】 Each of the feeding module 1000 to the stacking module 7000 of the image forming apparatus 100 may have an individual housing, and those housings may be connected. Alternatively, the image forming apparatus 100 may have the feeding module 1000, the printing module 2000, the drying module 3000, the fixing module 4000, the cooling module 5000, the reversing module 6000, and the stacking module 7000 arranged in one housing. 【0018】 The feeding module 1000 accommodates the sheet S. The feeding module 1000 separates the accommodated sheet S one by one by a separation belt (not shown) and feeds it to the printing module 2000 by a conveying roller (not shown). The feeding module 1000 includes a storage 1100a, a storage 1100b, and a storage 1100c. Note that the number of the storages 1100a, 1100b, and 1100c is not limited to three, and one, two, or four or more may be provided. 【0019】 The storage compartment 1100a houses the sheet S and is provided to be retractable from the front side of the image forming apparatus 100 in order to house the sheet S. 【0020】 The storage compartment 1100b houses the sheet S and is provided to be retractable from the front side of the image forming apparatus 100 in order to house the sheet S. 【0021】 The storage compartment 1100c houses the sheet S and is provided to be retractable from the front side of the image forming apparatus 100 in order to house the sheet S. 【0022】 The print module 2000, as an image forming means, ejects ink onto a sheet S fed by the feeding module 1000 to form an image, and then transports the sheet S with the image formed on it to the drying module 3000. The print module 2000 includes a pre-image registration correction unit (not shown), a print belt unit 2200, and a recording unit 2300. 【0023】 The pre-printing registration correction unit corrects the tilt and position of the sheet S fed by the feeding module 1000, and then transports the sheet S, whose tilt and position have been corrected, to the print belt unit 2200. 【0024】 The print belt unit 2200 ensures clearance between the sheet S and the recording head by using suction to transport the sheet S, which is conveyed by the pre-image registration correction unit. 【0025】 The recording unit 2300 is positioned opposite the print belt unit 2200 with respect to the transport path of the sheet S. The recording unit 2300 forms an image on the sheet S, which is transported by the pre-image registration correction unit, by ejecting ink from above the recording head. Multiple recording heads are arranged along the transport direction of the sheet S (hereinafter simply referred to as the "transport direction"). Here, we exemplify a total of five line-type recording heads: four for Y (yellow), M (magenta), C (cyan), and Bk (black), plus one corresponding to the reaction solution. Note that the number of recording heads is not limited to five; there may be other numbers as well. 【0026】 The drying module 3000, acting as a drying means, dries the sheet S on which an image has been formed, which is transported by the print belt unit 2200, by blowing hot air onto the sheet S. The drying module 3000 dries the sheet S to reduce the liquid content of the ink and reaction solution applied to the sheet S in order to improve the ink fixation to the sheet S by the subsequent fixing module 4000. The drying module 3000 transports the dried sheet S to the fixing module 4000. The drying module 3000 comprises a decoupling unit 3200, a drying belt unit 3300, and a hot air blowing unit 3400. 【0027】 The decoupling section 3200 generates frictional force between the sheet S and the belt due to the wind pressure from the wind blowing from above, thereby transporting the sheet S placed on the belt to the drying belt unit 3300 by the belt. The decoupling section 3200 prevents the sheet S from shifting when it is transported between the print belt unit 2200 and the decoupling section 3200. 【0028】 The drying belt unit 3300 uses suction to transport the sheet S that is being conveyed by the decoupling unit 3200. 【0029】 The hot air blowing unit 3400 is equipped with a heater (not shown) for heating the air and is positioned above the belt. The hot air blowing unit 3400 heats the air with the heater and blows the heated air onto the sheet S, which is being carried by the drying belt unit 3300, thereby drying the ink and reaction liquid applied to the sheet S. As the heater, for example, an electric heating wire or an infrared heater is preferred in terms of safety and energy efficiency when heating the air. In addition to the method of blowing hot air, the drying method may also be a combination of a method of irradiating the surface of the sheet S with electromagnetic waves such as ultraviolet or infrared rays, or a conductive heat transfer method in which a heating element is brought into contact with the sheet S. 【0030】 The fixing module 4000, acting as a fixing device, performs a fixing process to fix ink to the sheet S by heating the sheet S conveyed by the drying module 3000. The fixing module 4000 includes a fixing belt unit 4100 and a reversing unit 4200. 【0031】 The fixing belt unit 4100 is located above the fixing module 4000 and has a substantially linear conveying path for the sheet S. The fixing belt unit 4100 heats and pressurizes the sheet S conveyed by the drying module 3000 while gripping and conveying it to fix the ink to the sheet S. The fixing belt unit 4100 then conveys the ink-fixed sheet S to the cooling module 5000. 【0032】 The reversing unit 4200 reverses the front and back sides of the sheet S being transported by the cooling module 5000, and then transports the reversed sheet S to the drying module 3000. Details of the configuration of the fixing module 4000 will be described later. 【0033】 The cooling module 5000 cools the high-temperature sheet S transported by the fixing module 4000, and transports the cooled sheet S to a transport path to the inversion module 6000 or to a double-sided transport path for double-sided printing where images are formed on both sides. The cooling module 5000 is equipped with a plurality of cooling units 5001. 【0034】 Each of the multiple cooling units 5001, for example, draws outside air into the cooling box with a fan to increase the pressure inside the cooling box, and blows air out of the cooling box through a nozzle under pressure onto the sheet S to cool the sheet S. The multiple cooling units 5001 are arranged on both sides of the conveying path of the sheet S to cool both sides of the sheet S. 【0035】 The inversion module 6000 inverts the front and back sides of the sheet S being transported by the cooling module 5000 and transports it to the loading module 7000. 【0036】 The loading module 7000 loads the sheets S that are transported by the inversion module 6000. The loading module 7000 includes a top tray 7200 and a loading section 7500. 【0037】 The top tray 7200 loads the sheets S that are transported by the inversion module 6000. 【0038】 The loading section 7500 loads the sheets S that are transported by the inversion module 6000. 【0039】 In the image forming apparatus 100 having the above configuration, the sheets S supplied from the feeding module 1000 are transported along the transport path within each module, undergoing various processes as they are transported, and are finally discharged into the loading module 7000. 【0040】 Furthermore, the ink ejected onto the sheet S by the print module 2000 contains 0.1% to 20.0% by mass of resin components, water, water-soluble organic solvents, colorants, waxes, and additives, based on the total mass of the ink. 【0041】 Furthermore, when the sheet S on which the image has been formed in the recording unit 2300 is transported by the print belt unit 2200, it is detected by an in-line scanner (not shown) located downstream of the recording unit 2300 in the transport direction. This in-line scanner detects any misalignment or color density of the image formed on the sheet S. The image forming apparatus 100 corrects the image or density to be formed on the sheet S based on the misalignment or color density detected by the in-line scanner. 【0042】 Furthermore, the drying module 3000 can suppress the occurrence of so-called cockling, which occurs when the sheet S absorbs the applied ink and stretches locally, causing wrinkles, by heating the ink and reaction solution applied to the sheet S to promote the evaporation of moisture. 【0043】 During double-sided printing, a sheet S with an image formed on one side by ink is transported by the transport path switching unit 5002 to a transport path below the cooling module 5000. The sheet S is then returned to the print module 2000 via the double-sided transport path of the fuser module 4000, drying module 3000, print module 2000, and feed module 1000. Upon returning to the print module 2000, an image is formed on the other side of the sheet S with ink, and the sheet is discharged from the drying module 3000 through the inversion module 6000 to the loading module 7000. 【0044】 <Configuration of the fixing module> The configuration of the fixing module 4000 of the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to Figures 2, 3, 5 to 8. 【0045】 The fixing module 4000 comprises an upper fixing belt system 10, a lower fixing belt system 20, a CPU 1100, and a RELAY 1200. 【0046】 The upper anchoring belt system 10 is positioned above the lower anchoring belt system 20 in the vertical direction (downward in Figure 2). The upper anchoring belt system 10 comprises an upper belt 30, a heating section 117, a heating section 127, and a heating section 137. The upper anchoring belt system 10 also comprises a temperature sensor 310, a temperature sensor 311, a temperature sensor 312, a temperature sensor 315, a temperature sensor 316, a temperature sensor 317, a rotation detection sensor 410, a driven roller 430, and a drive roller 450. 【0047】 Here, temperature sensors 310, 311, and 312 are the first temperature sensors, and temperature sensors 315, 316, and 317 are the second temperature sensors. Note that in Figure 2, the descriptions of temperature sensors 311, 312, 316, and 317 have been omitted. 【0048】 The upper belt 30 is made of a material that does not allow moisture to pass through, as moisture is necessary for the ink to penetrate into the sheet S. Therefore, when the sheet S becomes hot, moisture evaporated from the surface of the sheet S escapes through the upper belt 30, which is in contact with the sheet S. Considering heat resistance, sliding properties, airtightness, and durability, the upper belt 30 is exemplified here as being made by coating the surface of a glass fiber base material with PTFE (polytetrafluoroethylene). The thickness of the upper belt 30 is exemplified here as being approximately 0.4 mm. 【0049】 The upper belt 30 is endless and is taut and detachable, supported by multiple tension rollers. The upper belt 30 heats the sheets S conveyed by the drying module 3000 and transports them to the cooling module 5000. 【0050】 Each of the heating units 117, 127, and 137 is positioned along the conveying direction above the nip portion N inside the upper belt 30. Each of the heating units 117, 127, and 137 heats the upper belt 30 from the inside, thereby heating the inner surface of the upper belt 30. Details of the configuration of the heating units 117, 127, and 137 will be described later. 【0051】 Temperature sensor 310 is used to detect the temperature of the upper belt 30 when performing temperature control, and to detect errors such as tears in the upper belt 30. Temperature sensors 311 and 312 are each used to detect errors such as tears in the upper belt 30. 【0052】 Temperature sensors 310, 311, and 312 are each located on the outside of the upper belt 30 and the lower belt 40. Each of the temperature sensors 310, 311, and 312 non-contactually detects the surface temperature of the upper belt 30 and outputs an electrical signal corresponding to the detected surface temperature to the CPU 1100. Each of the temperature sensors 310, 311, and 312 is an infrared sensor that detects infrared rays. 【0053】 Temperature sensors 315, 316, and 317 are sensors used to detect errors such as tears in the upper belt 30. Each of the temperature sensors 315, 316, and 317 is installed on the inside of the upper belt 30. Each of the temperature sensors 315, 316, and 317 detects the surface temperature of the upper belt 30 non-contact and outputs an electrical signal to the CPU 1100 corresponding to the detected surface temperature. Each of the temperature sensors 315, 316, and 317 is an infrared sensor that detects infrared rays. 【0054】 The rotation detection sensor 410 is mounted on the rotation axis of the driven roller 430. The rotation detection sensor 410 is a Hall sensor composed of a magnet whose magnetic force switches according to the rotation of the driven roller 430, and detects the rotation of the upper belt 30 and outputs an electrical signal corresponding to the detected rotation of the upper belt 30 to the CPU 1100. Note that the rotation detection sensor 410 is not limited to the above configuration, and may also be a transmissive sensor that detects a light-shielding state or a light-transmitting state using a physical flag having an edge in the rotation direction of the driven roller 430. 【0055】 The driven roller 430 rotates in accordance with the rotation of the upper belt 30. 【0056】 The drive roller 450, together with the tension roller, tensions the upper belt 30. The drive roller 450 is connected to a drive motor (not shown), and when the drive motor is driven, it rotates, causing the upper belt 30 to rotate due to the frictional force between the surface of the drive roller 450 and the inner surface of the upper belt 30. 【0057】 The lower anchoring belt system 20 is positioned vertically below the upper anchoring belt system 10. The lower anchoring belt system 20 includes a lower belt 40, a heating unit 147, a heating unit 157, a temperature sensor 320, a temperature sensor 321, a temperature sensor 322, a temperature sensor 325, a temperature sensor 326, and a temperature sensor 327. The lower anchoring belt system 20 also includes a rotation detection sensor 420, a driven roller 440, a drive roller 460, a plurality of tension rollers that tension the lower belt 40, and a pad 423. 【0058】 Here, temperature sensors 320, 321, and 322 are the first temperature sensors, and temperature sensors 325, 326, and 327 are the second temperature sensors. Note that in Figure 2, the descriptions of temperature sensors 321, 322, 326, and 327 have been omitted. 【0059】 The lower belt 40 is made of a material that does not allow moisture to pass through, as moisture is necessary for the ink to penetrate into the sheet S. Therefore, when the sheet S becomes hot, moisture evaporated from the surface of the sheet S escapes through the lower belt 40, which is in contact with the sheet S. Considering heat resistance, sliding properties, airtightness, and durability, the lower belt 40 is exemplified here as being made of a material with a thickness of approximately 0.4 mm, with a glass fiber base material coated with PTFE (polytetrafluoroethylene) on the surface. The lower belt 40 is endless and is stretched by multiple tension rollers. 【0060】 The lower belt 40 contacts the upper belt 30 to form a nip portion N. The lower belt 40, together with the upper belt 30, grips and heats the sheet S, which is being transported by the drying module 3000, at the nip portion N, and then transports it to the cooling module 5000. 【0061】 Each of the heating units 147 and 157 is located inside the lower belt 40 and heats the lower belt 40 from the inside. Each of the heating units 147 and 157 heats the lower surface portion 40a of the lower belt 40 that is not in contact with the horizontally extending pad 423 from the inside. Details of the configuration of the heating units 147 and 157 will be described later. 【0062】 Temperature sensor 320 is used to detect the temperature of the lower belt 40 when performing temperature control, and to detect errors such as tears in the lower belt 40. Temperature sensors 321 and 322 are each used to detect errors such as tears in the lower belt 40. 【0063】 Temperature sensors 320, 321, and 322 are each located on the outside of the upper belt 30 and the lower belt 40. Each of the temperature sensors 320, 321, and 322 non-contactually detects the surface temperature of the lower belt 40 and outputs an electrical signal corresponding to the detected surface temperature to the CPU 1100. Each of the temperature sensors 320, 321, and 322 is an infrared sensor that detects infrared rays. 【0064】 Temperature sensors 325, 326, and 327 are sensors used to detect errors such as tears in the lower belt 40. Each of the temperature sensors 325, 326, and 327 is located inside the lower belt 40. Each of the temperature sensors 325, 326, and 327 detects the surface temperature of the lower belt 40 non-contact and outputs an electrical signal to the CPU 1100 corresponding to the detected surface temperature. Each of the temperature sensors 325, 326, and 327 is an infrared sensor that detects infrared rays. 【0065】 The rotation detection sensor 420 is mounted on the rotation axis of the driven roller 440. The rotation detection sensor 420 is a Hall sensor composed of a magnet whose magnetic force switches according to the rotation of the driven roller 440, and detects the rotation of the lower belt 40 and outputs an electrical signal corresponding to the detected rotation of the lower belt 40 to the CPU 1100. Note that the rotation detection sensor 420 is not limited to the above configuration, and may also be a transmissive sensor that detects a light-shielding state or a light-transmitting state using a physical flag having an edge in the rotation direction of the driven roller 440. 【0066】 The driven roller 440 rotates in accordance with the rotation of the lower belt 40. 【0067】 The drive roller 460, together with the tension roller, tensions the lower belt 40. The drive roller 460 is connected to a drive motor (not shown), and when the drive motor is driven, it rotates, causing the lower belt 40 to rotate due to the frictional force between the surface of the drive roller 460 and the inner surface of the lower belt 40. 【0068】 The pad 423 is positioned to form a nip portion N with the upper belt 30 via the lower belt 40. Here, the pressure of the nip portion N is determined by the tension and thickness of the upper belt 30 and the curvature of the pad 423. The pressure of the nip portion N is preferably 1 Pa to 2000 Pa, and more preferably 1 Pa to 200 Pa, because if it is too high, the ink from the sheet S may adhere to the upper fixing belt system 10 and peel off the sheet S. 【0069】 The radius of curvature of the pad 423 should preferably be 50 mm or more, and preferably 100,000 mm or less from the standpoint of manufacturing precision. If the curvature of the pad 423 is large, the difference in the transport path between the front and back sides of the sheet S will increase, which may cause friction between the sheet S and the belt. In addition, if the curvature of the pad 423 is large, the sheet S may retain its curved shape and curl. 【0070】 Based on the above, the tension of the upper belt 30 is exemplified here as 200N, the thickness of the upper belt 30 is exemplified here as 0.3mm, the radius of curvature of the pad 423 is exemplified here as 30000mm, and the pressure of the nip is exemplified here as approximately 16Pa. 【0071】 The CPU 1100, acting as the control unit, controls heating units 117, 127, and 137 based on the temperature indicated by the electrical signals input from temperature sensors 310, 311, 312, 315, 316, and 317. The CPU 1100 performs temperature control to maintain the temperature of the upper belt 30 at a predetermined temperature by controlling heating units 117, 127, and 137. Specifically, the CPU 1100 controls the power supplied to heating units 117, 127, and 137 by controlling the drive of RELAY 1200, FET 111, FET 121, and FET 131. 【0072】 The CPU 1100 controls heating units 147 and 157 based on the temperature indicated by the electrical signals input from temperature sensors 320, 321, 322, 325, 326, and 327. By controlling heating units 147 and 157, the CPU 1100 performs temperature control to maintain the temperature of the lower belt 40 at a predetermined temperature. Specifically, the CPU 1100 controls the power supplied to heating units 147 and 157 by controlling the drive of RELAY 1200, FET 141, and FET 151. 【0073】 The CPU 1100 notifies an error when it determines that an abnormality has occurred based on the electrical signals input from temperature sensors 310, 311, 312, 315, 316, and 317. 【0074】 The CPU 1100 notifies of an error when it determines that there is an abnormality based on the electrical signals input from temperature sensors 320, 321, 322, 325, 326, and 327. The CPU 1100 notifies of the error by, for example, displaying information indicating the abnormality on a display unit (not shown), or by issuing a warning by voice or sound from a speaker (not shown). 【0075】 The CPU 1100 detects that the upper belt 30 has stopped rotating based on an electrical signal corresponding to the rotation of the upper belt 30 input from the rotation detection sensor 410, and stops the operation of the RELAY 1200. By stopping the operation of the RELAY 1200, the CPU 1100 stops heating by the heating units 117, 127, and 137. 【0076】 The CPU 1100 detects that the lower belt 40 has stopped rotating based on an electrical signal corresponding to the rotation of the lower belt 40 input from the rotation detection sensor 420, and stops the operation of the RELAY 1200. By stopping the operation of the RELAY 1200, the CPU 1100 stops heating by the heating units 147 and 157. 【0077】 The CPU 1100 includes a power control unit 1101 and a power ratio calculation unit 1102. 【0078】 The power control unit 1101 controls the power supplied to heaters 110, 120, and 130 by performing PWM control so that the power ratio is calculated by the power ratio calculation unit 1102. 【0079】 The power ratio calculation unit 1102 calculates the power ratio of heaters 110, 120, and 130 based on the electrical signal corresponding to the temperature detected by the temperature sensor 310. 【0080】 The RELAY1200, under the control of the CPU 1100, supplies power to heating units 117, 127, and 137, or stops supplying power to heating units 117, 127, and 137 under the control of the CPU 1100. The RELAY1200, under the control of the CPU 1100, supplies power to heating units 147 and 157, or stops supplying power to heating units 147 and 157 under the control of the CPU 1100. 【0081】 The fixing module 4000 having the above configuration includes a flow path section 116a, which is a space that serves as an air passage, surrounded by a reflector 116, a reflector 126, a reflector 115 of the heating section 117 (described later), and a reflector 125 of the heating section 127 (described later). The fixing module 4000 also includes a flow path section 126a, which is a space that serves as an air passage, surrounded by a reflector 126, a reflector 136, a reflector 125 of the heating section 127 (described later), and a reflector 135 of the heating section 137 (described later). 【0082】 Furthermore, the fixing module 4000 includes a flow path section 146a, which is a space that serves as an air passage, surrounded by a reflector 146, a reflector 156, a reflector 145 of the heating section 147 (described later), and a reflector 155 of the heating section 157 (described later). 【0083】 <Configuration of the heating section> The configurations of the heating units 117, 127, 137, 147, and 157 of the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to Figures 3 and 4. Figure 3 is a front view of a part of the fixing module 4000. 【0084】 The heating unit 117 includes a heater 110, an FET 111, a reflector 115, a temperature sensor 210, and an overheat detection HW211. 【0085】 The heater 110 is a halogen heater capable of receiving higher power. The heater 110 is supported by a support means (not shown) provided on the main body of the image forming apparatus 100. The heater 110 is positioned closer to the upper belt 30 than the focal point 115d of the parabola of the reflector 115, which has a parabolic shape when viewed from the front, and heats the upper belt 30 directly below it in the vertical direction. The heater 110 is positioned so as not to interfere with the detection area 2101 of the temperature sensor 210. 【0086】 The heater 110 consists of two heaters 110a and 110b with different maximum powers. Heater 110a is positioned below heater 110b. Heater 110b has a lower maximum power and is low power compared to heater 110a. 【0087】 FET111 supplies power to heater 110 when turned on by ON / OFF control by CPU1100, and stops supplying power to heater 110 when turned off by ON / OFF control by CPU1100. FET111 also stops supplying power to heater 110 when turned off by over-temperature detection HW211. 【0088】 The reflector 115 has a parabolic shape that is convex upward when viewed from the front, from the apex 115a to the parabolic end 115c, and covers the heater 110. The reflector 115 is made of, for example, a mirror-finished aluminum material, and concentrates the light generated upward from the heater 110 onto the upper belt 30 by reflecting it downward. The reflector 115 has a straight section 115b that extends vertically from the parabolic end 115c toward the upper belt 30. 【0089】 The straight section 115b is provided to secure space for arranging the temperature sensor 210. It is preferable to eliminate the straight section 115b or make it as short as possible. 【0090】 The temperature sensor 210 is a safety sensor used to control the upper belt 30 so that it does not exceed a predetermined temperature. The predetermined temperature is set to prevent the upper belt 30 from deforming due to heat. Here, 200°C is used as an example, but it is not limited to 200°C as it depends on the material of the upper belt 30. The temperature sensor 210 is positioned between the reflector 115 and the reflector 125 of the heating unit 127, which will be described later. The temperature sensor 210 non-contactively detects the temperature of the area of ​​the upper belt 30 heated by the heater 110 and outputs an electrical signal corresponding to the detected temperature to the over-temperature detection HW211. The temperature sensor 210 is an infrared sensor that detects infrared rays. 【0091】 The temperature sensor 210 is located near the reflector 115 on the outside of the reflector 115 because it needs to directly detect the temperature of the area of ​​the upper belt 30 that is heated by the heater 110. The temperature sensor 210 is located near the heater 110b side of the reflector 115. At least a portion of the temperature sensor 210 is located within the flow path section 116a. The temperature sensor 210 is located outside the end of the upper belt 30 in the width direction perpendicular to the conveying direction (the direction perpendicular to the plane of the paper in Figure 2) (hereinafter simply referred to as "width direction"). 【0092】 The over-temperature detection hardware HW211 outputs an electrical signal input from the temperature sensor 210 to the CPU 1100, and hardware-switches off the FET 111 according to the temperature indicated by the electrical signal input from the temperature sensor 210. 【0093】 The heating unit 127 includes a heater 120, an FET 121, a reflector 125, a temperature sensor 220, and an over-temperature detection HW221. Note that the configurations of the FET 121, reflector 125, and over-temperature detection HW221 are identical to those of the FET 111, reflector 115, and over-temperature detection HW211, respectively, and therefore their descriptions are omitted. 【0094】 The heater 120 consists of two heaters 120a and 120b with different maximum power outputs. Heater 120a is positioned below heater 120b. Heater 120b has a lower maximum power output and is low power compared to heater 120a. The heater 120 is positioned so as not to interfere with the detection area of ​​the temperature sensor 220. Note that the configuration of heater 120 other than those described above is the same as that of heater 110, so its explanation is omitted. 【0095】 The temperature sensor 220 is positioned between the reflector 115 and the reflector 125. The temperature sensor 220 non-contactually detects the temperature of the area heated by the heater 120 of the upper belt 30 and outputs an electrical signal corresponding to the detected temperature to the over-temperature detection HW221. The temperature sensor 220 is positioned outside the reflector 125, near the reflector 125, because it needs to directly detect the temperature of the area heated by the heater 120 of the upper belt 30. 【0096】 The temperature sensor 220 is located near the heater 120b side of the reflector 125. At least a portion of the temperature sensor 220 is located within the flow path section 116a. Note that the other configurations of the temperature sensor 220 are the same as those of the temperature sensor 210, so their description is omitted. 【0097】 The heating unit 137 includes a heater 130, an FET 131, a reflector 135, a temperature sensor 230, and an over-temperature detection HW 231. Note that the configurations of the FET 131, reflector 135, and over-temperature detection HW 231 are identical to those of the FET 111, reflector 115, and over-temperature detection HW 211, and therefore their descriptions are omitted. 【0098】 The heater 130 consists of two heaters 130a and 130b with different maximum power outputs. Heater 130a is positioned below heater 130b. Heater 130b has a lower maximum power output and is low power compared to heater 130a. Heater 130 is positioned so as not to interfere with the detection area of ​​the temperature sensor 230. Note that the configuration of heater 130 other than those described above is the same as that of heater 110, so its explanation is omitted. 【0099】 The temperature sensor 230 is positioned between the reflectors 135. The temperature sensor 230 non-contactually detects the temperature of the area heated by the heater 130 of the upper belt 30 and outputs an electrical signal corresponding to the detected temperature to the over-temperature detection HW231. The temperature sensor 230 is positioned outside the reflectors 135, near the reflectors 135, because it needs to directly detect the temperature of the area heated by the heater 130 of the upper belt 30. 【0100】 The temperature sensor 230 is located near the heater 130b side of the reflector 135. At least a portion of the temperature sensor 230 is located within the flow path section 126a. Note that the other configurations of the temperature sensor 230 are the same as those of the temperature sensor 210, so their description is omitted. 【0101】 The heating unit 147 includes a heater 140, an FET 141, a reflector 145, a temperature sensor 240, and an over-temperature detection HW 241. Note that the configurations of the FET 141, reflector 145, and over-temperature detection HW 241 are identical to those of the FET 111, reflector 115, and over-temperature detection HW 211, respectively, and therefore their descriptions are omitted. 【0102】 The heater 140 consists of two heaters 140a and 140b with different maximum power outputs. Heater 140a is positioned below heater 140b. Heater 140b has a lower maximum power output and is low power compared to heater 140a. Heater 140 is positioned so as not to interfere with the detection area of ​​the temperature sensor 240. Note that the configuration of heater 140 other than those described above is the same as that of heater 110, so its explanation is omitted. 【0103】 The temperature sensor 240 is a safety sensor used to control the lower belt 40 so that it does not exceed a predetermined temperature. The predetermined temperature is set to prevent the lower belt 40 from deforming due to heat. Here, 200°C is used as an example, but it is not limited to 200°C as it depends on the material of the lower belt 40. The temperature sensor 240 is positioned between the reflector 145 and the reflector 155 of the heating unit 157, which will be described later. The temperature sensor 240 non-contactively detects the temperature of the area of ​​the lower belt 40 heated by the heater 140 and outputs an electrical signal corresponding to the detected temperature to the over-temperature detection HW241. The temperature sensor 240 is an infrared sensor that detects infrared rays. 【0104】 The temperature sensor 240 is located near the reflector 145 on the outside of the reflector 145 because it needs to directly detect the temperature of the area of ​​the lower belt 40 that is heated by the heater 140. The temperature sensor 240 is located near the heater 140b side of the reflector 145. At least a portion of the temperature sensor 240 is located within the flow path section 146a. The temperature sensor 240 is located outside the end of the lower belt 40 in the width direction. 【0105】 The heating unit 157 includes a heater 150, an FET 151, a reflector 155, a temperature sensor 250, and an over-temperature detection HW 251. Note that the configurations of the FET 151, reflector 155, and over-temperature detection HW 251 are identical to those of the FET 111, reflector 115, and over-temperature detection HW 211, respectively, and therefore their descriptions are omitted. 【0106】 The heater 150 consists of two heaters 150a and 150b with different maximum power outputs. Heater 150a is positioned below heater 150b. Heater 150b has a lower maximum power output and is low power compared to heater 150a. Heater 150 is positioned so as not to interfere with the detection area of ​​the temperature sensor 250. Note that the configuration of heater 150 other than those described above is the same as that of heater 110, so its explanation is omitted. 【0107】 The temperature sensor 250 is positioned between the reflector 145 and the reflector 155. The temperature sensor 250 non-contactually detects the temperature of the area heated by the heater 150 of the lower belt 40 and outputs an electrical signal corresponding to the detected temperature to the over-temperature detection HW251. The temperature sensor 250 is positioned outside the reflector 155, near the reflector 155, because it needs to directly detect the temperature of the area heated by the heater 150 of the lower belt 40. 【0108】 The temperature sensor 250 is located near the heater 150b side of the reflector 155. At least a portion of the temperature sensor 250 is located within the flow path section 146a. Note that the other configurations of the temperature sensor 250 are the same as those of the temperature sensor 240, so their description is omitted. 【0109】 In the configuration where the three heating units 117, 127, and 137 described above are installed together, it is not possible to place all the temperature sensors 210, 220, and 230 close to the low-power heaters 110b, 120b, and 130b. In other words, temperature sensor 230 will be close to the high-power heater 120a. However, in this case, at least temperature sensors 210 and 220 are positioned as far away from the high-power heaters 120a and 130a as possible. 【0110】 Furthermore, reflectors 115, 125, 135, 145, and 155 were designed to have a parabolic shape that is convex upwards when viewed from the front. However, the design is not limited to this, and each reflector may be made into a polygonal shape by connecting multiple members, while approximating the shape of a parabola that is convex upwards when viewed from the front. 【0111】 <Temperature sensor configuration> The configurations of the temperature sensors 210, 220, 230, 240, 250, 310, 311, 312, 315, 316, 317, 320, 321, 322, 325, 326, and 327 of the image forming apparatus 100 according to this embodiment will be described in detail with reference to Figure 9. 【0112】 In Figure 9, Figure 9(a) shows the external shape of the temperature sensor 210, Figure 9(b) shows the field of view θ of the temperature sensor 210, and Figure 9(c) shows the relationship between the temperature measurement accuracy of the temperature sensor 210 and the field of view θ. 【0113】 Since the configurations of temperature sensors 210, 220, 230, 240, 250, 310, 311, 312, 315, 316, 317, 320, 321, 322, 325, 326, and 327 are identical, only the configuration of temperature sensor 210 will be described. 【0114】 The temperature sensor 210 comprises a circuit board 3800, a sensor module 3801, and a connector 3806. 【0115】 The circuit board 3800 has a sensor module 3801 and a connector 3806 mounted on it. 【0116】 The sensor module 3801 is located closest to the edge of the circuit board 3800 among the components mounted on the circuit board 3800. The sensor module 3801 is equipped with a detection window 3802 that acts as a lens. The sensor module 3801 absorbs infrared radiation emitted from the object to be measured 3803 through the detection window 3802, converts the absorbed infrared radiation into an electrical signal, and outputs the converted electrical signal to the outside via the connector 3806. 【0117】 Connector 3806 is mounted on circuit board 3800 and is connected to the destination of temperature sensor 210. 【0118】 The temperature sensor 210, having the above configuration, detects the temperature of the object to be measured 3803 non-contact. Here, the temperature measurement accuracy is defined as 100% when the object to be measured 3803 is located on the center line 3805, as shown in Figure 9(b). The angle between the object to be measured 3803 and the center line 3805 when the temperature measurement accuracy decreases to 50% by moving the object to be measured 3803 away from the center line 3805 without changing the distance to the temperature sensor 210 is defined as the field of view angle θ. Note that the temperature measurement accuracy when setting the field of view angle θ is not limited to 50% but can be any value. 【0119】 <Temperature sensor placement configuration> The arrangement of the temperature sensors 310, 311, 312, 315, 316, 317, 320, 321, 322, 325, 326, and 327 of the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to Figures 2 and 14. 【0120】 In Figure 14, "front" refers to one end of the fixing module 4000 in the width direction (the front side in Figure 2), and "back" refers to the other end of the fixing module 4000 in the width direction (the back side in Figure 2). "Center" is the center of the fixing module 4000 in the width direction. 【0121】 Furthermore, in Figure 14, "top" refers to the upper anchoring belt system 10, "bottom" refers to the lower anchoring belt system 20, "outside" refers to the outside of the upper belt 30 and the outside of the lower belt 40, and "inside" refers to the inside of the upper belt 30 or the inside of the lower belt 40. 【0122】 For example, "Upper Inner" is located approximately 600 mm downstream of "Upper Outer" in the transport direction, and "Lower Inner" is located approximately 500 mm downstream of "Lower Outer" in the transport direction. Also, if "Center" is set to 0 mm, "Front" is located 160 mm in front of "Center," and "Back" is located 160 mm behind "Center." 【0123】 Temperature sensors 310, 311, and 312 are each positioned on the outside of the upper belt 30 with spacing at the center, front, and back in the width direction. Temperature sensors 315, 316, and 317 are each positioned on the inside of the upper belt 30 with spacing at the center, front, and back in the width direction. Temperature sensors 320, 321, and 322 are each positioned on the outside of the lower belt 40 with spacing at the center, front, and back in the width direction. Temperature sensors 325, 326, and 327 are each positioned on the inside of the lower belt 40 with spacing at the center, front, and back in the width direction. 【0124】 Temperature sensors 310, 315, 320, and 325 are positioned at the same location (center) in a direction perpendicular to the conveying direction. Temperature sensors 311, 316, 321, and 326 are positioned at the same location (160 mm in front of the center) in a direction perpendicular to the conveying direction. Temperature sensors 312, 317, 322, and 327 are positioned at the same location (160 mm behind the center) in a direction perpendicular to the conveying direction. 【0125】 Furthermore, this embodiment is not limited to the above arrangement configuration; it is also possible to omit temperature sensors 311, 312, 316, 317, 321, 322, 326, and 327. In other words, a configuration consisting only of temperature sensors 310, 315, 320, and 325 is also possible. 【0126】 <Measures to suppress temperature rise in temperature sensors> The following will be a detailed explanation of measures to suppress temperature rise in the temperature sensors 210, 220, 230, 240, 250, 315, 316, 317, 325, 326, and 327 of the image forming apparatus 100 according to Embodiment 1 of the present invention. 【0127】 First, the measures to suppress temperature rise in temperature sensors 210, 220, 230, 240, and 250 will be explained in detail with reference to Figures 3 to 6. 【0128】 Reflector 115 has been treated with a mirror finish to improve its reflection efficiency, but its temperature rises as it absorbs some of the light from heater 110. The same applies to reflectors 125, 135, 145, and 155 as to reflector 115. 【0129】 As a result, the temperature of the reflector in conventional fuser modules can eventually rise to approximately 300°C. In addition, the temperature of the temperature sensor placed near the conventional reflector may rise to approximately 200°C because the surrounding atmosphere is also heated by the high temperature of the reflector. The heat resistance temperature of the temperature sensor is approximately 110°C, and if the temperature of the temperature sensor placed near the reflector rises to approximately 200°C, there is a risk that the temperature sensor will not be able to accurately detect the temperature. 【0130】 In contrast, in this embodiment, the following measures 1 to 3 are implemented to suppress the temperature rise of temperature sensors 210, 220, 230, 240, and 250. 【0131】 (Countermeasure 1) The temperature sensor 210 is positioned so that it is closer to heater 110b than to heater 100a. As a result, since heater 110b requires less power input than heater 110a, the temperature rise of the temperature sensor 210 can be suppressed. Furthermore, the positions of temperature sensors 220, 230, 240, and 250 are the same as those of temperature sensor 210, so the temperature rise of temperature sensors 220, 230, 240, and 250 can also be suppressed. 【0132】 (Countermeasure 2) Air from the fan 1500 flows into the flow path section 116a on the outside of the reflector 115 via the flow path inlet frame 116b and the flow path inlet unit 116c. Furthermore, a flow path outlet 116d is provided downstream of the air flow path in the flow path section 116a for exhausting the air flowing through the flow path section 116a to the outside of the upper fixing belt system 10. The fan 1500 creates an airflow in the flow path section 116a by sending the intake air in the direction of arrow 1500a. Note that the reflector 116 may be composed of multiple components, and a part of the reflector 115 of an adjacent heating section 127 may also perform this function. 【0133】 Furthermore, at least a portion of the temperature sensor 210 is located within the flow path section 116a. The temperature sensor 210 is also positioned between the reflector 115 and the reflector 125, and is located close to the fan 1500 with respect to the center Q in the width direction of the upper belt 30. As a result, the temperature sensor 210 is sufficiently cooled by the airflow formed in the flow path section 116a. 【0134】 Furthermore, since the arrangement of temperature sensors 220, 230, 240, and 250 is the same as that of temperature sensor 210, temperature sensors 220, 230, 240, and 250 are sufficiently cooled by the airflow. 【0135】 (Countermeasure 3) When multiple heating units 147 and 157 are arranged side by side, the temperature sensor 240 provided on heating unit 147 and the temperature sensor 250 provided on heating unit 157 are positioned between reflectors 145 and 155. In this case, the temperature sensors 240 and 250 are heated up by heat supplied from the adjacent reflectors 145 and 155. 【0136】 In contrast, the temperature sensor 240 is positioned closer to the heater 140b of the reflector 145, which has lower power than the heater 140a, and the temperature sensor 250 is positioned closer to the heater 150b of the reflector 155, which has lower power than the heater 150a. This makes it possible to suppress the temperature rise of the temperature sensors 240 and 250. 【0137】 Furthermore, since the arrangement of temperature sensors 210 and 220 is the same as the arrangement of temperature sensors 240 and 250, it is possible to suppress the temperature rise of temperature sensors 240 and 250. 【0138】 Furthermore, at least a portion of the temperature sensor 240 and at least a portion of the temperature sensor 250 are located in the flow path section 146a. This allows two temperature sensors 240 and 250 to be placed within a single flow path section 146a, enabling efficient cooling of the temperature sensors 240 and 250 with a small number of fans 1500. 【0139】 Furthermore, since the arrangement of temperature sensors 210 and 220 is the same as that of temperature sensors 240 and 250, the temperature sensors 210 and 220 can be efficiently cooled with a small number of fans 1500. 【0140】 Next, the measures to suppress the temperature rise of temperature sensors 315, 316, 317, 325, 326, and 327 will be explained in detail with reference to Figure 2. 【0141】 The conventional problem described above, in which detection accuracy decreases due to changes in emissivity caused by condensation on the IR sensor and contamination by paper dust, can be solved by installing non-contact IR sensors on the inside of the upper and lower belts. However, since non-contact sensors are more susceptible to heat than contact sensors, simply installing non-contact sensors on the inside of the upper and lower belts presents another problem: detection accuracy decreases at high temperatures. 【0142】 In contrast, in this embodiment, the temperature sensors 315, 316, and 317, which are located inside the upper belt 30, are kept away from the heating units 117, 127, and 137, as well as away from the areas heated by the heating units 117, 127, and 137. Furthermore, the temperature sensors 325, 326, and 327, which are located inside the lower belt 40, are kept away from the heating units 147 and 157, as well as away from the areas heated by the heating units 147 and 157. 【0143】 Specifically, temperature sensors 315, 316, and 317 are provided downstream of the upper belt 30 of the nip section N in the direction of rotation, and upstream of the upper belt 30 of the heating section 117, 127, and 137 in the direction of rotation. In addition, temperature sensors 325, 326, and 327 are provided downstream of the lower belt 40 of the nip section N in the direction of rotation, and upstream of the lower belt 40 of the heating section 117, 127, and 137 in the direction of rotation. 【0144】 This makes it possible to suppress the temperature rise of the temperature sensors 315, 316, and 317 located inside the upper belt 30, and the temperature sensors 325, 326, and 327 located inside the lower belt 40. 【0145】 <Operation of the fixing module> The operation of the fixing module 4000 of the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to Figures 2, 3, 7, and 8. 【0146】 The sheet S is held and transported in a nip section N formed by the upper belt 30 and the lower belt 40. By adopting this configuration, uniform pressure can be applied to the sheet S even in a wide nip section N. As a result, even when the temperature of the upper fixing belt system 10 is set to the melting point of wax or the boiling point of water, sufficient heat transfer to the sheet S can be achieved by increasing the contact time between the sheet S and the upper belt 30. 【0147】 On the other hand, if the sheet S is held in the nip section N after sufficient heat has been transferred to the sheet S, the ink on the sheet S may adhere to the upper belt 30 and peel off the sheet S, or the upper belt 30 and the sheet S may rub against each other, causing the image to become distorted. For this reason, it is undesirable for the sheet S to be held in the nip section N for too long, so the time required from when the leading edge of the sheet S in the transport direction enters the nip section N until it exits the nip section N is preferably 0.5 sec to 4 sec. 【0148】 Here, the length of the sheet S on pad 423 in the transport direction is exemplified as 900 mm, and the transport speed of the sheet S is exemplified as 700 mm / sec. Furthermore, the time required from when the leading edge of the sheet S in the transport direction enters the entrance of the nip section N until it exits the exit of the nip section N is exemplified as approximately 1.3 seconds. 【0149】 The heating elements 117, 127, and 137 of the upper fixing belt system 10 directly heat the nip portion N, allowing heat to be efficiently transferred to the sheet S. On the other hand, the heating elements 147 and 157 of the lower fixing belt system 20 cannot directly heat the nip portion N because the pad 423 is provided. In contrast, by positioning the heating elements 147 and 157 facing the lower surface portion 40a of the lower belt 40, the lower belt 40 can be efficiently heated directly. 【0150】 The CPU 1100 controls the power supplied to heaters 110, 120, and 130 based on the detection value of a temperature sensor 310 that detects the surface temperature of the upper belt 30, thereby maintaining the temperature of the upper belt 30 at a predetermined temperature. The CPU 1100 also controls the power supplied to heaters 140 and 150 based on the detection value of a temperature sensor 320 that detects the surface temperature of the lower belt 40, thereby maintaining the temperature of the lower belt 40 at a predetermined temperature. 【0151】 Furthermore, when the rotation detection sensor 410 detects that the upper belt 30 has stopped rotating, the CPU 1100 controls the RELAY 1200 to stop heating by the heating units 117, 127, and 137. Similarly, when the rotation detection sensor 420 detects that the lower belt 40 has stopped rotating, the CPU 1100 controls the RELAY 1200 to stop heating by the heating units 147 and 157. This prevents heating of the upper belt 30 and lower belt 40 when they are stopped rotating, thereby suppressing localized heating of the upper belt 30 and lower belt 40. 【0152】 <Heater heating operation> The heating operation of heaters 110, 120, 130, 140, and 150 of the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to Figures 10 and 11. 【0153】 In Figure 10, Figure 10(a) is a view of the upper belt 30, temperature sensor 210, temperature sensor 220, and temperature sensor 230 from above. Figure 10(b) shows the positional relationship of the upper belt 30, heater 110, and temperature sensor 210 when viewed from the upstream side in the conveying direction. Figure 10(c) shows the temperature changes at each position of the upper belt 30 when the upper belt 30 is continuously heated by the heater 110. 【0154】 In Figure 11, Figure 11(a) shows the positional relationship between the upper belt 30 and the heater 110 as viewed from the upstream side in the conveying direction, and the heating intensity at the position of the heater 110 in the width direction. Figure 11(b) shows the temperature change of the upper belt 30 when the upper belt 30 is continuously heated by the heater 110. 【0155】 Since the heating operations of heaters 110, 120, 130, 140, and 150 are identical, the heating operation of heater 110 will be explained, and the explanations of the heating operations of heaters 120, 130, 140, and 150 will be omitted. 【0156】 In Figures 10 and 11, the y-axis direction is the conveying direction, the x-axis direction is the width direction, and the z-axis direction is the height direction. 【0157】 Figure 10(c) shows the relationship between the heating time at various positions on the upper belt 30 and the temperature of the upper belt 30 when the upper belt 30 is continuously heated by the heater 110, with the horizontal axis representing time and the vertical axis representing the temperature of the upper belt 30. In Figure 10(c), graph 2201 shows the temperature change at the end position 2102 directly below the heater 110, and graph 2202 shows the temperature change at the central position 2103 directly below the heater 110. 【0158】 The difference between the slope of temperature rise in graph 2201 and graph 2202 is due to the difference in light distribution of the heater 110. Furthermore, the temperature sensor 210 detects the temperature at the end position 2102, which is the region with the highest temperature rise rate. Therefore, the limit temperature 2006 of the upper belt 30 and the over-temperature detection threshold temperature 2204 are the same temperature. 【0159】 In the above example, the limit temperature 2006 of the upper belt 30 and the over-temperature detection threshold temperature 2204 were set to the same temperature. However, this is not the only option; for example, a safety margin may be added to the over-temperature detection threshold temperature 2204, making it lower than the limit temperature 2206 of the upper belt 30. 【0160】 Figure 11(b) shows the relationship between heating time and the temperature of the upper belt 30 when the upper belt 30 is continuously heated by the heater 110, with the horizontal axis representing time and the vertical axis representing the temperature of the upper belt 30. Graph 2504 shows the temperature rise in the end regions 2501 and 2503, while graph 2505 shows the temperature rise in the central region 2502. The heater 110 is designed to have a higher heating intensity in the end regions 2501 and 2503 than in the central region 2502. As a result, the temperature rise in graph 2504 is steeper than that in graph 2505. This helps to suppress uneven heating in the x-axis direction. 【0161】 The limit temperature 2506, shown by the dashed line in Figure 11(b), is the temperature set to prevent deformation of the upper belt 30, and is determined according to the material of the upper belt 30. The overheat detection threshold temperature 2204, used to detect whether or not overheating occurs due to heating by the heater 110, must be set so that the upper belt 30 does not exceed the limit temperature 2506. 【0162】 Furthermore, by positioning the heater 110 closer to the upper belt 30 than the focal point 115d, it is possible to reduce the proportion of light reflected by the reflector 115 relative to the light from the heater 110, thereby increasing heating efficiency. However, if the heater 110 and the upper belt 30 are too close together, while the heating efficiency of the upper belt 30 can be increased, the intensity distribution of the light irradiated onto the upper belt 30 becomes more uneven. 【0163】 Furthermore, by arranging the two heaters 110a and heater 110b at different heights in the vertical direction, the degree of bias in the light concentration distribution of heater 110a and heater 110b can be made different. This makes it possible to suppress localized concentration of light when the two heaters 110a and heater 110b are lit simultaneously. 【0164】 <Operation of the temperature sensor> The operation of the temperature sensors 210, 220, 230, 240, and 250 of the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to Figure 10. 【0165】 Temperature sensor 210 detects the temperature of region 2110 in Figure 10(a) of the upper belt 30. Temperature sensor 220 detects the temperature of region 2111 in Figure 10(a) of the upper belt 30. Furthermore, temperature sensor 230 detects the temperature of region 2112 in Figure 10(a) of the upper belt 30. 【0166】 Since the operation of temperature sensors 210, 220, 230, 240, and 250 is identical, the operation of temperature sensor 210 will be explained, and the operation of temperature sensors 220, 230, 240, and 250 will be omitted. 【0167】 The temperature sensor 210, positioned outside the upper belt 30 in the width direction, detects the temperature of the end region 2501 at the width direction end of the upper belt 30 from an oblique angle. As a result, the downward angle of the temperature sensor 210 relative to the upper belt 30 becomes large. When the downward angle of the temperature sensor 210 is large, a wide area of ​​the upper belt 30 is included in the detection area 2101 of the temperature sensor 210. To address this, either a temperature sensor 210 with a narrow detection area 2101 is used, or a temperature sensor 210 with a wide detection area 2101 is used, and the detection result of overheating detected by the temperature sensor 210 is corrected to provide a margin. 【0168】 When the upper belt 30 is normally rotating and temperature control is in operation, the temperature sensor 210 typically continues to detect temperatures of approximately 130°C or lower and never detects temperatures of 200°C or higher. On the other hand, if the rotation detection sensor 420 malfunctions and the upper belt 30 stops rotating, the area around the detection position of the temperature sensor 210 will be continuously heated locally and become very hot. 【0169】 Thus, even if the rotation detection sensor 420 malfunctions and the upper belt 30 stops rotating, the temperature of the hottest part of the upper belt 30 can be directly detected by the temperature sensor 210. This allows the image forming apparatus 100 to be stopped before the upper belt 30 is damaged due to deformation or other reasons, making it possible to realize a safer fixing module 4000. 【0170】 <Operation of the upper fixing belt system> The operation of the upper fixing belt system 10 of the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to Figure 12. 【0171】 The operation shown in Figure 12 begins when the main power supply of the image forming apparatus 100 is turned on. 【0172】 First, the CPU 1100 controls the drive of a drive motor (not shown) to rotate the upper belt 30 and turns on the RELAY 1200 (S101). 【0173】 Next, the CPU 1100 determines whether or not the upper belt 30 is rotating based on the electrical signal input from the rotation detection sensor 410 (S102). 【0174】 When the upper belt 30 is rotating (step S102: Yes), the CPU 1100 controls heaters 110, 120, and 130 based on an electrical signal corresponding to the temperature input from the temperature sensor 310 (S103). Specifically, the CPU 1100 controls heaters 110, 120, and 130 by the duty cycle width of the PWM control signals output to FETs 111, FET 121, and FET 131. In this way, the CPU 1100 performs temperature control to maintain the upper belt 30 at a predetermined temperature. 【0175】 Next, the CPU 1100 determines whether the temperature indicated by the electrical signals input from temperature sensors 210, 220, and 230 is higher than a predetermined threshold temperature (S104). Here, the threshold temperature is exemplified as 200°C. 【0176】 If the CPU 1100 is above the threshold temperature (step S104: Yes), it turns off FETs 111, 121, and 131, stopping heaters 110, 120, and 130 (S105). After that, the CPU 1100 terminates its operation. 【0177】 On the other hand, if the upper belt 30 is not rotating during step S102 (step S102: No), the CPU 1100 skips to step S105. This prevents the upper belt 30 from being locally heated by heaters 110, 120, and 130. 【0178】 Furthermore, if the CPU 1100 is below the threshold temperature during step S104 (step S104: No), it returns to the operation of step S102. 【0179】 Note that the operation of the lower fixing belt system 20 is the same as the operation shown in Figure 12, so a detailed explanation is omitted. In this case, the CPU 1100 controls the heaters 140 and 150 based on an electrical signal corresponding to the temperature input from the temperature sensor 320. The CPU 1100 also stops the heaters 140 and 150 if the temperature detected by the temperature sensor 240 or temperature sensor 250 is higher than the threshold temperature, or if the rotation detection sensor 420 determines that the lower belt 40 is not rotating. 【0180】 <Error detection process> The error detection process performed by the image forming apparatus 100 according to Embodiment 1 of the present invention will be described in detail with reference to Figure 13. 【0181】 The error detection process shown in Figure 13 is initiated when the temperature detected by temperature sensors 310 and 320 rises to a printable temperature and enters standby mode. At this time, the fuser module 4000 transports the sheet S at a transport speed of 700 mm / sec. 【0182】 The error detection process shown in Figure 13 is executed repeatedly at predetermined control cycles. Here, a control cycle of 100 msec is used as an example. 【0183】 First, the CPU 1100 stores the temperature Temp1, indicated by the electrical signal input from the temperature sensor 310, in a memory not shown (S201). 【0184】 Next, the CPU 1100 acquires the temperature Temp2 indicated by the electrical signal input from the temperature sensor 315 after a predetermined time has elapsed since the execution of step S201 (S202). Here, the predetermined time is 0.86 seconds as an example. 【0185】 The predetermined time mentioned above is determined by dividing the distance between temperature sensor 310 and temperature sensor 315 by the transport speed. Temperature sensor 315 detects the temperature after a predetermined time has elapsed since the execution of step S201, thereby enabling it to detect the temperature at the same position on the upper belt 30 where temperature sensor 310 detected the temperature during step S201. 【0186】 Next, the CPU 1100 stores the temperature Temp2 obtained in step S202 into memory (S203). 【0187】 Next, the CPU 1100 calculates the absolute value of the detected temperature difference, ΔTemp1, which is the difference between temperature Temp1 and temperature Temp2 (ΔTemp1 = |Temp1 - Temp2|) (S204). 【0188】 Next, the CPU 1100 determines whether the absolute value ΔTemp1 obtained in step S204 is greater than a predetermined value of 20°C (S205). 【0189】 If the absolute value ΔTemp1 is 20°C or less (step S205: No), the CPU 1100 performs normal temperature control using the temperature sensor 310 (S206), and then terminates the error detection process. 【0190】 On the other hand, if the absolute value ΔTemp1 is greater than 20°C (step S205: Yes), the CPU 1100 increments the count value, which is counted by a counter (not shown). Then, the CPU 1100 refers to the count value and determines whether the absolute value ΔTemp1 is greater than 20°C three times in a row for each control cycle (S207). 【0191】 The CPU 1100 terminates the error detection process if the count value is 2 or less and the absolute value ΔTemp1 is not greater than 20°C for three consecutive times (step S207: No). 【0192】 On the other hand, if the count value is 3 and the absolute value ΔTemp1 is greater than 20°C for three consecutive times (step S207: Yes), the CPU 1100 determines that the detection result for the lower of the two detected temperatures, Temp1 and Temp2, is abnormal. The CPU 1100 then broadcasts error information (S207), and after setting the count value of a counter (not shown) to "0", terminates the error detection process. In this way, by broadcasting error information when the absolute value ΔTemp1 is greater than 20°C for three consecutive times, it is possible to suppress the broadcasting of incorrect error information due to false detections caused by noise. 【0193】 Error information is communicated by prompting cleaning or replacement, or by issuing a warning. The cause of the error is likely a tear or malfunction of the upper belt 30. 【0194】 In this way, by executing the above error detection process, when performing temperature control using the temperature sensor 310, the temperature sensor 315 can confirm whether the detection result of the temperature sensor 310 is normal or abnormal. Furthermore, if the detection result of the temperature sensor 310 is abnormal, the cause of the abnormal detection result of the temperature sensor 310 can be resolved by stopping the temperature control and replacing the upper belt 30, etc. Note that the temperature used as the threshold for determining whether or not to notify error information is not limited to 20°C, but a predetermined temperature other than 20°C can be set, taking into account temperature unevenness in the upper belt 30 or lower belt 40, or variations in detection accuracy. 【0195】 In addition to the above processing, the CPU 1100 executes the error detection process shown in Figure 13 using temperature sensors 320 and 325. The error detection process using temperature sensors 320 and 325 is the same as the above processing except that temperature sensor 320 is used instead of temperature sensor 310 and temperature sensor 325 is used instead of temperature sensor 315, so its explanation is omitted. This allows the temperature sensor 325 to confirm whether the detection result of temperature sensor 320 is normal or abnormal when performing temperature control using temperature sensor 320. 【0196】 When the CPU 1100 performs the above error detection process using temperature sensors 320 and 325, it acquires the temperature Temp2 detected by temperature sensor 325 after a predetermined time has elapsed since the execution of the process in step S201 (S202). Here, the predetermined time is 0.71 seconds as an example. 【0197】 The predetermined time mentioned above is determined by dividing the distance between temperature sensor 320 and temperature sensor 325 by the transport speed. Temperature sensor 325 detects the temperature after a predetermined time has elapsed since the execution of step S201, thereby enabling it to detect the temperature at the same position on the lower belt 40 where temperature sensor 320 detected the temperature during step S201. 【0198】 Furthermore, the CPU 1100 executes the error detection process shown in Figure 13 using temperature sensors 311 and 316. Note that the error detection process using temperature sensors 311 and 316 is the same as the process described above, except that temperature sensor 311 is used instead of temperature sensor 310 and temperature sensor 316 is used instead of temperature sensor 315, so its explanation is omitted. This makes it possible to detect tears in the upper belt 30, etc., using temperature sensors 311 and 316. 【0199】 The CPU 1100 also performs the error detection process shown in Figure 13 for temperature sensors 312 and 317. The error detection process for temperature sensors 312 and 317 is the same as the process described above, except that temperature sensor 312 is used instead of temperature sensor 310 and temperature sensor 317 is used instead of temperature sensor 315, so its explanation is omitted. This makes it possible to detect tears in the upper belt 30, etc., using temperature sensors 312 and 317. 【0200】 The CPU 1100 also performs the error detection process shown in Figure 13 for temperature sensors 321 and 326. The error detection process for temperature sensors 321 and 326 is the same as the process described above, except that temperature sensor 321 is used instead of temperature sensor 310 and temperature sensor 326 is used instead of temperature sensor 315, so its explanation is omitted. This makes it possible to detect tears in the lower belt 40, etc., using temperature sensors 321 and 326. 【0201】 The CPU 1100 also performs the error detection process shown in Figure 13 for temperature sensors 322 and 327. The error detection process for temperature sensors 322 and 327 is the same as the process described above, except that temperature sensor 322 is used instead of temperature sensor 310 and temperature sensor 327 is used instead of temperature sensor 315, so its explanation is omitted. This makes it possible to detect tears in the lower belt 40, etc., using temperature sensors 322 and 327. 【0202】 By performing the above error detection process, temperature changes in the upper belt 30 and lower belt 40 can be accurately detected in the on-demand heating method that directly heats the upper belt 30 and lower belt 40. In addition, the degree of temperature variation detected by temperature sensors 310 and 320 can be understood, and abnormalities can be easily detected. Furthermore, by referring to the temperatures detected by temperature sensors 311, 312, 315, 316, 317, 321, 322, 325, 326, and 327, the detection errors of temperature sensors 310 and 320 can be corrected. As a result, temperature control can be performed with greater accuracy compared to conventional methods. 【0203】 In this embodiment, the upper belt 30 has temperature sensors 315, 316, and 317 positioned inside the upper belt 30 to detect the temperature of the upper belt 30 non-contact. It also has a CPU 1100 that performs temperature control to maintain the temperature of the upper belt 30 at a predetermined temperature by controlling a plurality of heating units 117, 127, and 137 based on the temperatures detected by temperature sensors 310 and 315. 【0204】 Furthermore, the CPU 1100 performs temperature control to maintain the temperature of the lower belt 40 at a predetermined temperature by controlling multiple heating units 147 and 157 based on the temperatures detected by temperature sensors 320 and 325. This allows for accurate detection of temperature changes in the upper belt 30 and lower belt 40 when directly heating and maintaining them at predetermined temperatures. 【0205】 (Embodiment 2) The configuration of the image forming apparatus and fixing module according to Embodiment 2 of the present invention is the same as that shown in Figures 1 to 3 and Figures 5 to 8, so its description is omitted. Also, the configuration of the heating section of the fixing module, the configuration of the temperature sensor, and the arrangement of the temperature sensor according to this embodiment are the same as those shown in Figures 2 to 4, Figure 9, and Figure 14, so their description is omitted. Furthermore, the measures to suppress the temperature rise of the temperature sensor of the fixing module according to this embodiment are the same as the measures to suppress the temperature rise of the temperature sensor in Embodiment 1 described above, so their description is omitted. 【0206】 <Temperature sensor selection process> The temperature sensor selection process performed by the image forming apparatus 100 according to Embodiment 2 of the present invention will be described in detail with reference to Figure 15. 【0207】 In the above embodiment 1, temperature sensor 315 is used to determine whether temperature sensor 310 is abnormal or normal, and temperature sensor 325 is used to determine whether temperature sensor 320 is abnormal or normal. In this embodiment, temperature sensors 315 and 325 are used for temperature control. 【0208】 The temperature sensor selection process shown in Figure 15 is initiated when the temperatures detected by temperature sensors 310 and 320 rise to a printable temperature and enter a standby state. At this time, the fuser module 4000 transports the sheet S at a transport speed of 700 mm / sec. 【0209】 First, the CPU 1100 stores the temperature Temp3, which is the sum of the temperature detected by the temperature sensor 310 and the temperature detected by the temperature sensor 320, in a memory (not shown) (S301). 【0210】 Next, the CPU 1100 obtains the temperature detected by the temperature sensor 315 0.86 seconds after the execution of step S301, and the temperature detected by the temperature sensor 325 0.71 seconds after the execution of step S301 (S302). 【0211】 The temperature sensor 315 detects the temperature 0.86 seconds after the execution of step S301, thereby enabling it to detect the temperature at the same position on the upper belt 30 as the temperature sensor 310 detected in step S301. Similarly, the temperature sensor 325 detects the temperature 0.71 seconds after the execution of step S301, thereby enabling it to detect the temperature at the same position on the lower belt 40 as the temperature sensor 320 detected in step S301. 【0212】 Next, the CPU 1100 stores the temperature Temp4 in memory, which is the sum of the temperature detected by the temperature sensor 320 acquired in step S302 and the temperature detected by the temperature sensor 325 acquired in step S302 (S303). 【0213】 Next, the CPU 1100 calculates the detected temperature difference ΔTemp2, which is the difference between temperature Temp3 and temperature Temp4 (ΔTemp2 = Temp3 - Temp4) (S304). 【0214】 Next, the CPU 1100 determines whether the detected temperature difference ΔTemp2 is less than "0" (S305). 【0215】 The CPU 1100 determines whether the detected temperature difference ΔTemp2 is greater than or equal to 6 (S306) if the detected temperature difference ΔTemp2 is 0 or greater (step S305: No). 【0216】 If the detected temperature difference ΔTemp2 is 6 or less (step S306: No), the CPU 1100 performs normal temperature control using the temperature sensor 310 or temperature sensor 315 selected by executing the previous temperature sensor selection process (S307). After that, the CPU 1100 terminates the temperature sensor selection process. 【0217】 On the other hand, in the process of step S305, the CPU 1100 increments the first count value of a counter (not shown) if the detected temperature difference ΔTemp2 is less than "0" (step S305: Yes). Then, the CPU 1100 refers to the first count value and determines whether the detected temperature difference ΔTemp2 is less than "0" three times in a row for each control cycle (S308). 【0218】 If the first count value is 2 or less and the detected temperature difference ΔTemp2 is not less than "0" for three consecutive times (step S308: No), the CPU 1100 proceeds to the process in step S307. 【0219】 On the other hand, if the first count value is 3 and the detected temperature difference ΔTemp2 is less than "0" for three consecutive times (step S308: Yes), the CPU 1100 selects the temperature Temp4 value detected by temperature sensors 315 and 325 (S309). After that, the CPU 1100 sets the first count value to "0" and then proceeds to the process in step S307. 【0220】 In this process, the CPU 1100 performs temperature control using the temperature sensors 315 and 325 selected in step S309. By selecting temperature sensors 315 and 325 when the detected temperature difference ΔTemp2 is less than "0" for three consecutive times, it is possible to reduce the chance of incorrectly selecting temperature sensors 315 and 325 due to the influence of detection noise. 【0221】 Furthermore, in the process of step S306, the CPU 1100 increments a second count value if the detected temperature difference ΔTemp2 is greater than 6 (step S306: Yes). Then, the CPU 1100 refers to the second count value and determines whether the detected temperature difference ΔTemp2 is greater than 6 three times in a row for each control cycle (S310). 【0222】 If the second count value is 2 or less and the detected temperature difference ΔTemp2 is not greater than 6 for three consecutive times (step S310: No), the CPU 1100 proceeds to the process in step S307. 【0223】 On the other hand, if the second count value is 3 and the detected temperature difference ΔTemp2 is greater than 6 for three consecutive times (step S310: Yes), the CPU 1100 selects the temperature Temp3 detected by temperature sensors 310 and 320 (S311). After that, the CPU 1100 sets the second count value to "0" and then proceeds to the process in step S307. 【0224】 In this process, the CPU 1100 performs temperature control using the temperature sensors 310 and 320 selected in step S311. By selecting temperature sensors 310 and 320 when the detected temperature difference ΔTemp2 is greater than 6 for three consecutive times, it is possible to reduce the chance of incorrectly selecting temperature sensors 310 and 320 due to false detection caused by noise. 【0225】 In this way, since temperature control is performed using the temperature sensor 315 located inside the upper belt 30, the temperature of the upper belt 30 can be stably detected, as it is less susceptible to changes in the shape of the upper belt 30 and the surface properties of dirt adhesion on the upper belt 30. Furthermore, since temperature control is performed using the temperature sensor 325 located inside the lower belt 40, the temperature of the lower belt 40 can be stably detected, as it is less susceptible to changes in the shape of the lower belt 40 and the surface properties of dirt adhesion on the lower belt 40. 【0226】 In the temperature sensor selection process described above, the temperature at the position detected by the temperature sensor 310 on the upper belt 30 decreases by approximately 3°C by the time it reaches the temperature sensor 315 downstream of the temperature sensor 310 in the direction of rotation of the upper belt 30. Similarly, the temperature at the position detected by the temperature sensor 320 on the lower belt 40 decreases by approximately 3°C by the time it reaches the temperature sensor 325 downstream of the temperature sensor 320 in the direction of rotation of the lower belt 40. Therefore, when the temperature sensor 310 is functioning correctly, the temperature sensor 315 will detect a temperature 3°C lower than the temperature detected by the temperature sensor 310. Also, when the temperature sensor 320 is functioning correctly, the temperature sensor 325 will detect a temperature 3°C lower than the temperature detected by the temperature sensor 320. 【0227】 From this point onward, the CPU 1100 selects the temperature sensors 310 and 320, or 315 and 325, that detected high temperatures as normal temperature sensors. Specifically, if the detected temperature difference ΔTemp2 is lower than 0°C, the temperatures detected by temperature sensors 315 and 325 are used for temperature control. If the detected temperature difference ΔTemp2 is greater than 6°C, the temperatures detected by temperature sensors 310 and 320 are used for temperature control. Furthermore, if the detected temperature difference ΔTemp2 is greater than or equal to 0°C and less than or equal to 6°C, the temperature sensors used for temperature control are considered normal, and the previously selected temperature sensors are used for temperature control. 【0228】 Furthermore, the temperature of the upper belt 30 differs in the width direction between the paper-passing region, where heat from the upper belt 30 is transferred to the sheet S as the sheet S passes, and the non-paper-passing region, where heat from the upper belt 30 is not transferred to the sheet S as the sheet S does not pass. The same applies to the lower belt 40. As a result of this temperature difference, heat unevenness occurs on the surfaces of the upper belt 30 and the lower belt 40, and this heat unevenness causes heat transfer between the paper-passing region and the non-paper-passing region as the upper belt 30 and the lower belt 40 move downstream in the rotational direction. 【0229】 Therefore, it is generally preferable to perform temperature control using a temperature sensor 310 located upstream of the upper belt 30 in the rotational direction of the temperature sensor 315 in order to suppress the effects of the above-mentioned temperature transmission. Similarly, it is generally preferable to perform temperature control using a temperature sensor 320 located upstream of the lower belt 40 in the rotational direction of the temperature sensor 325 in order to suppress the effects of the above-mentioned temperature transmission. 【0230】 In the above temperature sensor selection process, Temp3 was set as the sum of the temperatures detected by temperature sensors 310 and 320, and Temp4 was set as the sum of the temperatures detected by temperature sensors 315 and 325. However, the system is not limited to this; Temp3 may be set as the temperature detected by temperature sensor 310 or 320, and Temp4 may be set as the temperature detected by temperature sensor 315 or 325. 【0231】 In this case, in step S306, it is determined whether ΔTemp2 is greater than 3. If ΔTemp2 is greater than 3, the process proceeds to step S310; otherwise, the process proceeds to step S307. In step S310, it is determined three times consecutively whether ΔTemp2 is greater than 3. 【0232】 In this embodiment, the CPU 1100 performs temperature control based on the higher of the temperatures detected by temperature sensors 310 and 320 and temperature sensors 315 and 325. Thus, in this embodiment, it is also possible to perform temperature control using the temperature sensor 315 inside the upper belt 30 and the temperature sensor 325 inside the lower belt 40. 【0233】 As a result, in addition to the effects of Embodiment 1 described above, the temperature of the upper belt 30 can be stably detected by making it less susceptible to the effects of the shape of the upper belt 30 and the adhesion of dirt to the surface of the upper belt 30. Furthermore, the temperature of the lower belt 40 can be stably detected by making it less susceptible to the effects of the shape of the lower belt 40 and the adhesion of dirt to the surface of the lower belt 40. 【0234】 The present invention is not limited to the embodiments described above, and it goes without saying that various modifications are possible without departing from the spirit of the invention. 【0235】 Specifically, in Embodiments 1 and 2 described above, temperature sensors 325, 326, and 327 are provided inside the lower belt 40, but the invention is not limited to this, and temperature sensors 325, 326, and 327 do not need to be provided. Even if temperature sensors 325, 326, and 327 are not provided, the temperature control of the upper belt 30 that contacts the image forming surface of the sheet S can be accurately performed using temperature sensors 315, 316, and 317. 【0236】 Furthermore, in Embodiments 1 and 2 described above, heating units 117, 127, and 137 are provided on the inside of the upper belt 30, while heating units 147 and 157 are provided on the inside of the lower belt 40. However, the invention is not limited to this, and heating units 117, 127, 137, 147, and 157 may be provided on the outside of the upper belt 30 and the lower belt 40. [Explanation of Symbols] 【0237】 10 Upper anchoring belt system 20 Lower anchoring belt system 30 Upper belt 40 Lower belt 100 Image forming apparatus 110 Heater 117 Heating section 120 Heater 127 Heating section 130 Heater 137 Heating section 140 Heater 147 Heating section 150 Heater 157 Heating section 220 Temperature Sensor 230 Temperature Sensor 240 Temperature Sensor 250 Temperature Sensor 310 Temperature Sensor 311 Temperature sensor 312 Temperature Sensor 315 Temperature Sensor 316 Temperature Sensor 317 Temperature Sensor 320 Temperature Sensor 321 Temperature Sensor 322 Temperature Sensor 325 Temperature Sensor 326 Temperature Sensor 327 Temperature Sensor 1100 CPU 4000 Fuser Module

Claims

[Claim 1] A fixing device that heats and pressurizes a sheet to fix an image onto the sheet, An endless upper belt, An endless lower belt that, together with the upper belt, grips and conveys the sheet in a nip portion formed by contacting the upper belt, Multiple heating units for heating the upper belt and the lower belt, A first temperature sensor is positioned outside the upper belt and the lower belt and non-contactively detects the temperature of the upper belt and the lower belt, A second temperature sensor is positioned inside the upper belt and detects the temperature of the upper belt in a non-contact manner. A control unit that performs temperature control to maintain the temperatures of the upper belt and the lower belt at predetermined temperatures by controlling the plurality of heating units based on the temperatures detected by the first temperature sensor and the second temperature sensor, A fixing device characterized by having the following features. [Claim 2] The second temperature sensor is In addition to being positioned on the inside of the upper belt, it is also positioned on the inside of the lower belt. The fixing device according to feature 1. [Claim 3] The control unit, An error is reported when the difference between the temperature detected by the first temperature sensor and the temperature detected by the second temperature sensor exceeds a predetermined value. The fixing device according to claim 1 or 2. [Claim 4] The first temperature sensor is Multiple points are provided in the width direction perpendicular to the sheet transport direction, The second temperature sensor is Multiple locations in the width direction are provided at the same locations where the first temperature sensor is provided, The control unit, If the temperature difference detected by the first temperature sensor and the second temperature sensor, which are provided at the same location in the width direction, exceeds a predetermined value, an error is reported, and the temperature control is performed based on the temperature detected by the first temperature sensor. The fixing device according to feature 3. [Claim 5] The second temperature sensor is The first temperature sensor is provided downstream of the upper belt in the rotational direction, The control unit, The temperature control is performed based on the higher of the temperature detected by the first temperature sensor and the temperature detected by the second temperature sensor. The fixing device according to claim 1 or 2. [Claim 6] The second temperature sensor is Multiple points are provided in the width direction perpendicular to the sheet transport direction. The fixing device according to claim 1 or 2. [Claim 7] The first temperature sensor is Multiple points are provided in the width direction perpendicular to the sheet transport direction. The fixing device according to claim 1 or 2. [Claim 8] The plurality of heating units are The inner surface of the upper belt and the inner surface of the lower belt are heated. The fixing device according to claim 1 or 2. [Claim 9] Each of the aforementioned multiple heating units is Equipped with a halogen heater, The fixing device according to claim 1 or 2. [Claim 10] The first temperature sensor and the second temperature sensor are It is an infrared sensor that detects infrared radiation. The fixing device according to claim 1 or 2. [Claim 11] A fixing device according to claim 1 or claim 2, Image forming means for forming an image on a sheet with ink, A drying means for drying the image formed on the sheet by the image forming means, It has, The fixing device is The image dried by the aforementioned drying means is fixed onto the sheet by heating and pressurizing it. An image forming apparatus characterized by the following:

Images