Image forming apparatus and heater control device

Abstract

This provides a configuration that allows the heater to stop heating properly even if the ambient temperature around the sensor module 3801 exceeds the temperature at which the sensor module 3801 operates normally. [Solution] The temperature sensor unit 210 includes a substrate 3800, a sensor module 3801 placed on the substrate 3800 to detect the temperature of the upper belt, and a thermistor 3811 placed on the substrate 3800 to detect the temperature around the sensor module 3801. The control unit stops heating the heater when the sensor module 3801 detects a temperature of first predetermined temperature or higher, and the temperature detected by the thermistor 3811 is less than a second predetermined temperature. Furthermore, the control unit stops heating the heater regardless of the output value of the sensor module 3801 when the thermistor 3811 detects a temperature of second predetermined temperature or higher.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus including a fixing device that heats a sheet on which an image is formed by discharging ink to fix the image on the sheet, and a heater control device that controls a heater.

Background Art

[0002] Patent Document 1 describes a configuration in which the temperature of a heater is measured using a sensor disposed on the heater that heats a belt, and when an abnormal temperature rise is detected, the energization control of the heater is changed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, when a temperature sensor for detecting temperature is disposed near the heater, there is a risk that the periphery of the temperature sensor becomes high temperature. For this reason, there is a risk that the temperature around the temperature sensor becomes equal to or higher than the temperature at which the temperature sensor operates normally. In this case, even if the object to be heated such as a belt heated by the heater has an abnormal temperature rise, the energization control of the heater, specifically, the stop of heating of the heater cannot be appropriately performed.

[0005] An object of the present invention is to provide a configuration that can appropriately stop the heating of the heater even when the temperature around the temperature sensor becomes equal to or higher than the temperature at which the temperature sensor operates normally.

Means for Solving the Problems

[0006] One aspect of the present invention is an image forming apparatus comprising: an image forming unit that ejects ink to form an image on a sheet; a fixing device that heats the sheet on which the image has been formed by the image forming unit to fix the image on the sheet; and a control unit, wherein the fixing device comprises: a rotating endless belt; a nip portion forming member that forms a nip portion for gripping and conveying a sheet between itself and the belt; a heater that is positioned non-contact with the belt to heat the belt; and a temperature sensor unit that detects the temperature of the belt, wherein the temperature sensor unit comprises: a substrate; a first temperature sensor positioned on the substrate to detect the temperature of the belt; and a second temperature sensor positioned on the substrate to detect the temperature around the first temperature sensor, wherein the control unit stops heating the heater when the first temperature sensor detects a temperature of a first predetermined temperature or higher and the temperature detected by the second temperature sensor is less than a second predetermined temperature, and stops heating the heater regardless of the output value of the first temperature sensor when the second temperature sensor detects a temperature of a second predetermined temperature or higher.

[0007] One aspect of the present invention is a heater control device for controlling a heater that heats an object to be heated, comprising: a temperature sensor unit for detecting the temperature of the object to be heated; and a control unit for controlling the heater based on the output value of the temperature sensor unit, wherein the temperature sensor unit comprises a substrate, a first temperature sensor disposed on the substrate for detecting the temperature of the object to be heated, and a second temperature sensor disposed on the substrate for detecting the temperature around the first temperature sensor, and the control unit stopping the heating of the heater when the first temperature sensor detects a temperature of a first predetermined temperature or higher, and stopping the heating of the heater regardless of the output value of the first temperature sensor when the second temperature sensor detects a temperature of a second predetermined temperature or higher. [Effects of the Invention]

[0008] According to the present invention, even if the temperature around the temperature sensor exceeds the temperature at which the temperature sensor operates normally, the heater heating can be appropriately stopped. [Brief explanation of the drawing]

[0009] [Figure 1] A schematic cross-sectional view showing the image forming system of the first embodiment. [Figure 2] A schematic cross-sectional view showing a fixing belt unit according to the first embodiment. [Figure 3] (a) Block diagram relating to fixing control of the upper fixing belt system according to the first embodiment, (b) Block diagram of the temperature sensor unit according to the first embodiment. [Figure 4] A flowchart relating to the fixing control of the upper fixing belt system according to the first embodiment. [Figure 5] (a) A plan view and a side view of the temperature sensor according to the first embodiment; (b) A schematic diagram showing the field of view of the temperature sensor; (c) A graph showing the relationship between the field of view and measurement accuracy. [Figure 6] (a) A schematic diagram showing the relationship between the heater and the belt in the width direction according to the first embodiment, and a diagram showing the distribution of radiant intensity in the width direction of the heater, (b) A graph showing the relationship between heating time and belt temperature. [Figure 7] (a) A schematic diagram showing the arrangement of the temperature sensor unit and fan according to the first embodiment, and a diagram showing the distribution of radiant intensity in the width direction of the heater; (b) A schematic diagram showing the positional relationship between the belt and the temperature sensor unit when viewed from the upstream side to the downstream side in the rotation direction of the belt; (c) A graph showing the relationship between the heating time and the belt temperature at each position of the belt when the belt is continuously heated by the heater. [Figure 8] (a) A diagram showing the distribution of ambient temperature in the flow path where the temperature sensor unit 210 according to the first embodiment is located, and (b) A diagram showing the distribution of ambient temperature in the flow path where the temperature sensor units 220 and 230 are located. [Figure 9] Circuit diagram of a circuit board constituting a temperature sensor unit according to the first embodiment. [Figure 10] A graph showing the PWM duty cycle at various belt temperatures. [Figure 11] A graph showing the relationship between the detected temperature of the thermistor and the thermistor's resistance value, and the relationship between the detected temperature of the thermistor and the divided voltage according to the first embodiment. [Figure 12] Circuit diagram of the over-temperature detection HW according to the second embodiment. [Figure 13] (a) Graph showing the temporal transition of the temperature information signal detected by the CPU when the temperature of the belt is being normally controlled, (b) when the temperature of the belt is not being normally controlled, and (c) when the fan has failed. [Figure 14] Flowchart of the control for determining the cause of heater shutdown according to the second embodiment.

Mode for Carrying Out the Invention

[0010] <First Embodiment> The first embodiment will be described with reference to FIGS. 1 to 11. First, the schematic configuration of the image forming system of this embodiment will be described with reference to FIG. 1.

[0011] [Image Forming System] The image forming system (image forming apparatus) 1 of this embodiment uses an inkjet recording method in which ink is ejected to form an image on a sheet, and is a so-called sheet-fed inkjet recording apparatus that forms an ink image on a sheet using two liquids, a reaction liquid and ink. The sheet may be any recording material capable of receiving ink, such as paper like ordinary paper or thick paper, plastic film like overhead projector sheets, special-shaped sheets like envelopes or index paper, and cloth.

[0012] As shown in FIG. 1, the image forming system 1 of this embodiment 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. The sheet S supplied from the feeding module 1000 is subjected to various processes as it is conveyed along the conveyance path within each module, and is finally discharged to the stacking module 7000.

[0013] Note that the feeding module 1000, printing module 2000, drying module 3000, fixing module 4000, cooling module 5000, reversing module 6000, and loading module 7000 may each have a separate housing, and these housings may be connected to form an image forming system. Alternatively, the feeding module 1000, printing module 2000, drying module 3000, fixing module 4000, cooling module 5000, reversing module 6000, and loading module 7000 may be arranged in one housing.

[0014] The feeding module 1000 has storage bins 1100a, 1100b, and 1100c for accommodating the sheet S, and the storage bins 1100a to 1100c are provided so as to be pullable out toward the front side of the apparatus for accommodating the sheet S. The sheet S is fed one by one by a separation belt and a conveyance roller in each of the storage bins 1100a to 1100c and is conveyed to the printing module 2000. Note that the number of the storage bins 1100a to 1100c is not limited to three, and there may be one, two, or four or more.

[0015] The printing module 2000 as an image forming unit has a pre-image registration correction unit (not shown), a printing belt unit 2010, and a recording unit 2020. The sheet S conveyed from the feeding module 1000 is corrected in inclination and position by the pre-image registration correction unit and is conveyed to the printing belt unit 2010. The recording unit 2020 is arranged at a position facing the printing belt unit 2010 with respect to the conveyance path. The recording unit 2020 is an inkjet recording unit that forms an image by discharging ink onto the sheet S from above by a recording head with respect to the conveyed sheet S. A plurality of recording heads for discharging ink are arranged along the conveyance direction. In the present embodiment, in addition to four colors of Y (yellow), M (magenta), C (cyan), and Bk (black), there are a total of five line-type recording heads corresponding to the reaction liquid. The sheet S is adsorbed and conveyed by the printing belt unit 2010, thereby ensuring a clearance with the recording head.

[0016] The number of ink colors and recording heads are not limited to the five mentioned above. The inkjet method can employ methods using heating elements, piezoelectric elements, electrostatic elements, MEMS (Micro Electro Mechanical Systems) elements, etc. Each color of ink is supplied to the recording head from an ink tank (not shown) via an ink tube. The ink contains, based on the total mass of the ink, resin components in an amount of "0.1% to 20.0% by mass," water, water-soluble organic solvents, colorants, waxes, additives, etc.

[0017] As the sheet S, on which an image has been formed by the recording unit 2020, is transported by the print belt unit 2010, an inline scanner (not shown) positioned downstream of the recording unit 2020 in the transport direction of the sheet S detects any misalignment or color density of the image formed on the sheet S. Based on this image misalignment and color density, corrections are made to the image and density formed on the sheet S.

[0018] The drying module 3000, acting as a drying device, dries the sheet S by blowing hot air onto the sheet S on which an image has been formed by ejecting ink. The drying module 3000 includes a decoupling section 3200, a drying belt unit 3300, and a hot air blowing section 3400. The drying module 3000 reduces 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 image-formed sheet S is transported to the decoupling section 3200 located within the drying module 3000. In the decoupling section 3200, the wind pressure from the wind blown from above creates a frictional force between the sheet S and the belt, and the sheet S is transported by the belt. In this way, by transporting the sheet S placed on the belt by frictional force, displacement of the sheet S is prevented when the sheet S is transported between the print belt unit 2010 and the decoupling section 3200. The sheet S, transported from the decoupling unit 3200, is carried by suction on the drying belt unit 3300, and hot air is blown onto it from the hot air blowing unit 3400 located above the belt to dry the ink and reaction liquid applied to the sheet S.

[0019] In this way, the drying module 3000 heats the ink and reaction solution applied to the sheet S, promoting the evaporation of moisture and suppressing the occurrence of so-called cockling, where ink splatters on the sheet S and creates a border-like line around it. Any device capable of heating and drying can be used for the drying module 3000, but a hot air dryer or heater is preferred. As for the heater, heating by electric heating wire or infrared heater is preferred from the standpoint of safety and energy efficiency. In addition to the method of applying hot air, the drying method may also be configured by combining a method of irradiating the surface of the sheet S with electromagnetic waves (ultraviolet or infrared rays, etc.) or a conduction heat transfer method by contact with a heating element.

[0020] The fixing module 4000, as a fixing system, includes a fixing belt unit 4100 as a fixing device. The fixing belt unit 4100 fixes the ink to the sheet S, which has been transported from the drying module 3000, by passing it between a heated upper fixing belt system and a lower fixing belt system. A detailed explanation of the fixing belt unit 4100 will be given later.

[0021] The cooling module 5000 has multiple cooling units 5001, which cool the high-temperature sheet S transported from the fixing module 4000. The cooling units 5001, for example, draw outside air into the cooling box with a fan to increase the pressure inside the cooling box, and then blow air out from the cooling box through nozzles under pressure onto the sheet S to cool the sheet S. The cooling units 5001 are arranged on both sides of the transport path of the sheet S, and both sides of the sheet S are cooled.

[0022] The cooling module 5000 is provided with a transport path switching unit 5002. The transport path switching unit 5002 switches the transport path of the sheet S depending on whether the sheet S is being transported to the inversion module 6000 or to the double-sided transport path for double-sided printing in which images are formed on both sides of the sheet S.

[0023] The inversion module 6000 has an inversion unit 6400. The inversion unit 6400 inverts the front and back sides of the conveyed sheet S, changing the orientation of the sheet S when it is discharged to the loading module 7000. The loading module 7000 has a top tray 7200 and a loading unit 7500, and loads the sheet S conveyed from the inversion module 6000.

[0024] During double-sided printing, the sheet S is transported by the transport path switching unit 5002 to the transport path below the cooling module 5000. The sheet S then passes through the double-sided transport path of the fuser module 4000, drying module 3000, print module 2000, and feed module 1000, and is returned to the print module 2000. The double-sided transport section of the fuser module 4000 is provided with a reversal unit 4200 that reverses the front and back sides of the sheet S. Once returned to the print module 2000, an image is formed on the other side where no image has been formed, and the sheet S is discharged to the loading module 7000 via the drying module 3000, fuser module 4000, cooling module 5000, and reversal module 6000.

[0025] [Fastener belt unit] Next, the fixing belt unit 4100 of this embodiment will be described with reference to Figure 2. As shown in Figure 2, the fixing belt unit 4100 as a fixing device comprises an upper fixing belt system 10 and a lower fixing belt system 20, and a nip portion N is formed when the upper belt 301 of the upper fixing belt system 10 and the lower belt 40 of the lower fixing belt system 20 are pressed together. The sheet S is held and conveyed by the nip portion N, and pressure and heat are applied at that time to fix the image formed by the ink to the sheet S. Either the upper belt 30 or the lower belt 40 corresponds to a belt or a first belt, and the other corresponds to a nip portion forming member or a second belt that forms the nip portion between itself and the belt.

[0026] The image forming system 1 of this embodiment prints (forms an image) onto a sheet S with ink, and then dries and fixes the moisture in the ink. The upper fixing belt system 10 and the lower fixing belt system 20 are fixing systems in which the printed sheet S is conveyed between the heated upper belt 30 and lower belt 40, and the print is fixed. The upper belt 30 and lower belt 40 are rotated by their respective drive motors (not shown), and the sheet S is conveyed in the direction of the arrow.

[0027] In this embodiment, since ink is applied to the upper surface of the sheet S, heaters 110, 120, and 130 are positioned on the upper belt 30 side that contacts the upper surface. Heaters 140 and 150 are also positioned on the lower belt 40 side to heat the sheet S itself, which has the ink applied to it. By nipping (long nipping) the sheet S over a long distance in the sheet transport direction on both the upper belt 30 and the lower belt 40 and heating it, the ink applied to the sheet S penetrates into the sheet, achieving high print quality. One of heaters 110, 120, or 130 corresponds to the first heater, and the other one corresponds to the second heater. Similarly, one of heaters 140 or 150 corresponds to the first heater, and the other one corresponds to the second heater.

[0028] The upper anchoring belt system 10 includes an endless upper belt 30, a plurality of tension rollers for tensioning the upper belt 30, heaters 110, 120, 130, reflectors 112, 122, 132 as reflective members, temperature sensor units 210, 220, 230, a temperature sensor unit 310 for temperature control of the upper belt 30, a rotation detection sensor 410, and the like. At least one of the plurality of tension rollers is a drive roller 610 driven by a motor (not shown) that rotates the endless upper belt 30. The upper belt 30 rotates in the direction of arrow R1 in Figure 2 by the drive roller 610.

[0029] The rotation detection sensor 410 is a sensor that detects whether the upper belt 30 is rotating, and is positioned on the driven roller 611, one of the multiple tension rollers, which rotates in conjunction with the rotation of the upper belt 30. The reason why the rotation detection sensor 410 is positioned on the driven roller 611 is that if the rotation detection sensor 410 were positioned on the drive roller 610, the drive roller 610 would rotate even if the upper belt 30 is not being rotated by the drive roller 610 due to slipping or other reasons, and the motor would still be running, leading to a false detection that the upper belt 30 is rotating. For this reason, in this embodiment, the rotation detection sensor 410 is positioned on the driven roller 611. When the rotation of the upper belt 30 stops, the rotation detection sensor 410 detects the cessation of rotation, and the heating of the heaters 110, 120, and 130 is stopped.

[0030] Heaters 110, 120, 130 and reflectors 112, 122, 132 are positioned inside the upper belt 30. Heaters 110, 120, and 130 are covered by reflectors 112, 122, and 132, respectively, and heat the upper belt 30 directly below the heaters 110, 120, and 130. That is, the heaters 110, 120, and 130 are positioned non-contact with the upper belt 30 and along the width direction of the upper belt 30, intersecting the rotation direction of the upper belt 30, and heat the upper belt 30 by radiating heat. The reflectors 112, 122, and 132 are positioned along the width direction, respectively, and reflect the radiant heat from the heaters 110, 120, and 130 towards the area of ​​the upper belt 30. Furthermore, the regions in which reflectors 112, 122, and 132 reflect the radiant heat from heaters 110, 120, and 130 correspond to the first region for the heater corresponding to the first heater and the second region for the heater corresponding to the second heater.

[0031] Furthermore, the reflectors 112, 122, and 132 are arranged to cover the sides of the heaters 110, 120, and 130, except for the side facing the upper belt 30. That is, the reflectors 112, 122, and 132 are formed such that the heaters 110, 120, and 130 are positioned inside the reflectors, the side of the nip portion N of the heaters 110, 120, and 130 is open, and both ends of the heaters 110, 120, and 130 in the width direction are covered. As a result, the radiant heat from the heaters 110, 120, and 130 is efficiently directed toward the nip portion N by the reflectors 112, 122, and 132.

[0032] The regions in which the reflectors 112, 122, and 132 reflect the radiant heat from the heaters 110, 120, and 130 are located within the nip portion N on the inner surface of the upper belt 30, directly heating the nip portion N with radiant heat. This allows for efficient heat transfer to the sheet S passing through the nip portion N. One of the reflectors 112, 122, and 132 corresponds to the first reflecting member, and the other one adjacent to the first reflecting member corresponds to the second reflecting member.

[0033] The temperature sensor units 210, 220, and 230 are safety sensors that detect the temperature of the area of ​​the upper belt 30 heated by the radiant heat of the heaters 110, 120, and 130, and cut off the power supply to the heaters 110, 120, and 130 when the detected temperature exceeds a threshold temperature (above a first predetermined temperature). In this embodiment, the threshold temperature, which is the first predetermined temperature, is set to 150°C. This 150°C temperature is set to prevent deformation of the upper belt 30, and is not limited to this temperature as it can be determined according to the material of the belt. The temperature sensor units 210, 220, and 230 are also located outside the reflectors 112, 122, and 132. Of the temperature sensor units 210, 220, and 230, the temperature sensor unit that detects the temperature of the first area corresponds to the first temperature sensor unit, and the temperature sensor unit that detects the temperature of the second area corresponds to the second temperature sensor unit.

[0034] The temperature sensor unit 310 is a sensor that detects the temperature of the upper belt 30 and adjusts the temperatures of the heaters 110, 120, and 130. The temperature sensor unit 310, which adjusts the temperature of the upper belt 30, is positioned downstream of the heaters 110, 120, and 130 in the rotational direction of the upper belt 30, and faces the outer surface of the upper belt 30, and detects the temperature of the upper belt 30 at this position. The heaters 110, 120, and 130 are then controlled so that the detected temperature reaches a predetermined temperature (100°C in this embodiment). This achieves high print quality. This 100°C temperature is the temperature at which the ink fixes to the printing medium, and is not limited to this temperature as it is determined according to the ink material.

[0035] In this configuration, if the heaters 110, 120, and 130 exceed their upper temperature limit, the upper belt 30 may deform, requiring the heating of the heaters 110, 120, and 130 to be stopped. However, if this temperature detection were to be performed by the temperature sensor unit 310 used to adjust the temperature of the upper belt 30, it would take time from temperature detection to stopping the heaters. Therefore, in this embodiment, when the heaters 110, 120, and 130 exceed their upper temperature limit, the temperature sensor units 210, 220, and 230 detect the temperature directly beneath the heaters, allowing heating by the heaters 110, 120, and 130 to be stopped quickly.

[0036] In this embodiment, by providing two types of sensor units to the upper fixing belt system 10, even when a long nip configuration is adopted, the temperature of the sheet S can be accurately adjusted to a predetermined temperature, and even when the heaters 110, 120, and 130 exceed the upper limit temperature, the heaters 110, 120, and 130 can be stopped without deforming the upper belt 30. Furthermore, considering the case where the temperature sensor units 210, 220, and 230 fail, and the temperature sensor unit 310 that controls the temperature of the upper belt 30 also fails, a thermostat 510 is placed on the drive roller 610 downstream of the heaters 110, 120, and 130 in the rotational direction of the upper belt 30.

[0037] When the temperature of the upper belt 30 exceeds a certain level, the thermostat 510 also heats the drive roller 610, which is detected by the thermostat 510. When the temperature of the drive roller 610 exceeds a certain level, the AC lines of the heaters 110, 120, and 130 are cut off by the thermostat 510 (see Figure 3 below). In this way, even if the temperature sensor units 210, 220, 230, and 310 fail, the thermostat 510 can safely cut off the AC lines, making it possible to realize a safe fixing system.

[0038] The lower anchoring belt system 20 includes an endless lower belt 40, a plurality of tension rollers for tensioning the lower belt 40, heaters 140, 150, reflectors 142, 152 as reflective members, temperature sensor units 240, 250, a temperature sensor unit 320 for temperature control of the lower belt 40, and a rotation detection sensor 420. At least one of the plurality of tension rollers is a drive roller 620 driven by a motor (not shown) that rotates the endless lower belt 40. The lower belt 40 rotates in the direction of arrow R2 in Figure 2 by the drive roller 620.

[0039] The rotation detection sensor 420 is a sensor that detects whether the lower belt 40 is rotating, and is positioned on the driven roller 621, one of the multiple tension rollers, which rotates in conjunction with the rotation of the lower belt 40. When the rotation of the lower belt 40 stops, the rotation detection sensor 420 detects the cessation of rotation, and the heating of the heaters 140 and 150 stops.

[0040] Heaters 140, 150 and reflectors 142, 152 are positioned inside the lower belt 40. Heaters 140, 150 are covered by reflectors 142, 152, respectively, and heat the lower belt 40 directly beneath the heaters 140, 150. That is, the heaters 140, 150 are positioned non-contact with the lower belt 40 and along the width direction of the lower belt 40, intersecting the rotation direction of the lower belt 40, and heat the lower belt 40 by radiating heat. The reflectors 142, 152 are positioned along the width direction, respectively, and reflect the radiant heat from the heaters 140, 150 towards the area of ​​the lower belt 40. Furthermore, the regions in which reflectors 142 and 152 reflect the radiant heat from heaters 140 and 150 correspond to the first region for the heater corresponding to the first heater and the second region for the heater corresponding to the second heater.

[0041] Furthermore, the reflectors 142 and 152 are positioned to cover the sides of the heaters 140 and 150, except for the side facing the lower belt 40. Specifically, the reflectors 142 and 152 are formed such that the heaters 140 and 150 are positioned inside the reflectors, the side of the nip portion N of the heaters 140 and 150 is open, and both ends of the heaters 140 and 150 in the width direction are covered. As a result, the radiant heat from the heaters 140 and 150 is efficiently directed towards the nip portion N by the reflectors 142 and 152.

[0042] The region in which the reflectors 142 and 152 reflect the radiant heat from the heaters 140 and 150 is the region within the nip portion N on the inner circumferential surface of the lower belt 40, so that the nip portion N is directly heated by the radiant heat. This allows heat to be efficiently transferred to the sheet S passing through the nip portion N. One of the reflectors 142 and 152 corresponds to the first reflective member, and the other corresponds to the second reflective member.

[0043] The temperature sensor units 240 and 250 are safety sensors that detect the temperature of the area of ​​the lower belt 40 heated by the radiant heat of the heaters 140 and 150, and cut off the power supply to the heaters 140 and 150 when the detected temperature exceeds a threshold temperature (150°C or higher in this embodiment). This 150°C temperature is set to prevent deformation of the lower belt 40, and is not limited to this temperature as it is determined according to the material of the belt. The temperature sensor units 240 and 250 are also positioned outside the reflectors 142 and 152. Of the temperature sensor units 240 and 250, the temperature sensor unit that detects the temperature of the first area corresponds to the first temperature sensor unit, and the temperature sensor unit that detects the temperature of the second area corresponds to the second temperature sensor unit.

[0044] The temperature sensor unit 320 is a sensor that detects the temperature of the lower belt 40 and adjusts the temperature of the heaters 140 and 150. The temperature sensor unit 320 that adjusts the temperature of the lower belt 40 is positioned downstream of the heaters 140 and 150 in the rotational direction of the lower belt 40 and faces the outer surface of the lower belt 40, and detects the temperature of the lower belt 40 at this position. The heaters 140 and 150 are then controlled so that the detected temperature reaches a predetermined temperature (100°C in this embodiment). This achieves high print quality. This 100°C temperature is the temperature at which the ink fixes to the printing medium, and is not limited to this temperature as it is determined according to the ink material.

[0045] Similar to the upper anchoring belt system 10, if the heaters 140 and 150 reach a temperature higher than the upper limit, the lower belt 40 may deform, requiring the heating of the heaters 140 and 150 to be stopped. However, if this temperature detection were to be performed by the temperature sensor unit 320 used to adjust the temperature of the lower belt 40, it would take time from temperature detection to stopping the heaters 140 and 150. Therefore, in this embodiment, when the heaters 140 and 150 reach a temperature higher than the upper limit, the temperature sensor units 240 and 250 detect the temperature directly below the heaters 140 and 150, allowing heating by the heaters 140 and 150 to be stopped quickly.

[0046] Thus, in this embodiment, by providing two types of sensor units to the lower fixing belt system 20, even when a long nip configuration is adopted, the temperature of the sheet S can be adjusted to a predetermined temperature with high precision, and even when the heaters 140 and 150 reach a temperature higher than the upper limit temperature, the heaters 140 and 150 can be stopped without deforming the lower belt 40. Furthermore, considering the case where the temperature sensor units 240 and 250 fail and the temperature sensor unit 320 that controls the temperature of the lower belt 40 also fails, a thermostat 520 is placed on the drive roller 620 downstream of the heaters 140 and 150 in the rotational direction of the lower belt 40.

[0047] When the temperature of the lower belt 40 exceeds a certain level, the drive roller 620 on which the thermostat 520 is located is also heated. When the temperature of the drive roller 620 exceeds a certain level, the AC lines of the heaters 140 and 150 are cut off by the thermostat 520. In this way, even if the temperature sensor units 240, 250, and 320 fail, the thermostat 520 can safely cut off the AC lines, making it possible to achieve a safe fixing system.

[0048] [Heater control configuration for the upper anchoring belt system] Next, the control configuration of the heaters 110, 120, and 130 of the upper anchoring belt system 10 will be described using Figure 3(a). Figure 3(a) is a hard block diagram of the upper anchoring belt system 10 of this embodiment. The control configuration of the upper anchoring belt system 10 consists of a control unit 1700, a relay 1200, a power supply unit 1300, an operating unit 1400, heaters 110, 120, and 130, temperature sensor units 210, 220, and 230, a temperature sensor unit 310, a rotation detection sensor 410, and a thermostat 510.

[0049] Furthermore, the control unit 1700 includes a CPU (Central Processing Unit) 1100 as a heater control unit, FETs (Field Effect Transistors) 111, 121, and 131 as power supply control units, and over-temperature detection hardware 211, 221, and 231 as switching units. The control unit 1700, Relay 1200, temperature sensor units 210, 220, and 230, temperature sensor unit 310, rotation detection sensor 410, and thermostat 510 constitute a heater control device 1600 that controls the heaters 110, 120, and 130 of the upper fixing belt system 10.

[0050] The CPU 1100 controls the power supplied to heaters 110, 120, and 130 by driving FETs 111, 121, and 131 with ON / OFF control. Power is supplied to each heater 110, 120, and 130 from power supply 1300. FETs 111, 121, and 131 are positioned between power supply 1300 and heaters 110, 120, and 130, and adjust the voltage applied from power supply 1300 to each heater based on control by the CPU 1100. In other words, FETs 111, 121, and 131 control the power supply from power supply 1300 to heaters 110, 120, and 130, respectively.

[0051] The CPU 1100 adjusts the power supplied to the heaters 110, 120, and 130 by feeding back temperature information from the temperature sensor unit 310 for temperature control. In other words, the CPU 1100 controls the temperature of the upper belt 30 by driving the FETs 111, 121, and 131 based on the temperature (detection result) detected by the temperature sensor unit 310.

[0052] The over-temperature detection HW211, 221, and 231 can switch the state of FETs 111, 121, and 131 between an energized state, where FETs 111, 121, and 131 can supply power from the power supply 1300 to each heater 110, 120, and 130 (powered on), and a shut-off state, where FETs 111, 121, and 131 do not supply power from the power supply 1300 to each heater 110, 120, and 130, based on the output values ​​of the temperature sensor units 210, 220, and 230. The over-temperature detection HW211, 221, and 231 switch from the energized state to the shut-off state when the temperature detected by the temperature sensor units 210, 220, and 230 exceeds a threshold temperature (150°C or higher in this embodiment). In other words, the over-temperature detection HW211, 221, and 231 stop driving the FETs 111, 121, and 131 when they detect that the temperature of the temperature sensor units 210, 220, and 230 is above a threshold temperature. The over-temperature threshold temperature is set to prevent deformation depending on the material of the belt, and in this embodiment it is set to 150°C, but this is not limited to that.

[0053] If any of the over-temperature detection hardware (HW211, 221, or 231) detects a temperature of 150°C or higher, it stops controlling the corresponding FETs (FETs 111, 121, or 131). For example, if the temperature of the temperature sensor unit (210) is detected by the over-temperature detection hardware (HW211), the control of FET 111 is stopped, but the control of the other FETs (121 and 131) is not stopped by the hardware circuit. The CPU (1100) detects the interrupt signal from the over-temperature detection hardware (HW211) and stops FETs 121 and 131 in software. In the above explanation, the FETs are stopped by the CPU, but they could also be stopped by the hardware circuit. The thermostat (510) disconnects the AC line from the Relay (1200) when the temperature of the upper belt (30) exceeds a certain temperature.

[0054] The rotation detection sensor 410 detects when the upper belt 30 stops rotating and shuts off the Relay 1200, thereby stopping the heating of the heaters 110, 120, and 130. The CPU 1100 is connected to an operation unit 1400, which functions as a notification unit. The operation unit 1400 is for operating the image forming system 1 and is, for example, an operation panel with a touch panel capable of inputting and displaying information. In addition to the touch panel, the operation unit 1400 may also have physical buttons such as a start button. In this embodiment, the display unit of the operation unit 1400 has a function to notify the user of various information, such as error information. Error information may include, for example, a shutdown due to overheating of the upper belt 30. Furthermore, the CPU 1100 may also notify an external terminal, such as a personal computer connected to the image forming system 1, of various information, such as error information of the fixing belt unit 4100. In this case, the CPU 1100 functions as a notification unit.

[0055] Figure 3(b) is a block diagram of the temperature sensor unit 210. The temperature sensor units 220 and 230 are similar. The temperature sensor unit 210 consists of a circuit board 3800, a sensor module 3801, an ambient temperature detection unit 3817, a temperature information correction unit 3816 that corrects the temperature information output by the sensor module 3801 according to the ambient temperature detection unit 3817, and a connector 3806 that outputs the temperature information after the temperature information correction unit 3816 has corrected the output. Details of each will be described later.

[0056] [Fixing control of the upper fixing belt system] Next, the fixing control of the upper fixing belt system 10 will be explained using Figure 4. When fixing control is started, the CPU 1100 controls the drive motor of the upper belt 30 and rotates the upper belt 30. The CPU 1100 also turns on RELAY 1200 (S101). The CPU 1100 uses the rotation detection sensor 410 to determine whether the upper belt 30 is rotating (S102). If the CPU 1100 determines that the upper belt 30 is rotating (Y in S102), it proceeds to S103; if it determines that it is not rotating (N in S102), it proceeds to S105.

[0057] In the case of Y in S102, the CPU 1100 controls the temperatures of heaters 110, 120, and 130 based on the temperature values ​​read from the temperature sensor unit 310 (S103). In this embodiment, the CPU 1100 controls the temperatures of heaters 110, 120, and 130 by controlling the FETs 111, 121, and 131 with a duty cycle of the PWM control signal.

[0058] Next, the CPU 1100 determines whether the temperature values ​​read from the temperature sensor units 210, 220, and 230 are equal to or greater than the threshold temperature (S104). If the value of at least one sensor in the temperature sensor units 210, 220, and 230 is equal to or greater than the threshold temperature (150°C in this embodiment) (Y in S104), the process proceeds to S105. On the other hand, if the temperature values ​​read by the CPU 1100 from the temperature sensor units 210, 220, and 230 are lower than the threshold temperature (N in S104), the process proceeds to S102. In S105, the CPU 1100 stops the heaters 110, 120, and 130 by turning off the FETs 111, 121, and 131.

[0059] [Temperature sensor unit configuration] Next, the configurations of temperature sensor units 210, 220, and 230 will be explained using Figures 5(a) to 5(c). Since the configurations of temperature sensor units 210, 220, and 230 are the same, the following explanation will focus on temperature sensor unit 210 as a representative example. Figure 5(a) is an external view of temperature sensor unit 210, with the top figure being a top view and the bottom figure being a side view. Figures 5(b) and 5(c) illustrate the field of view of temperature sensor unit 210.

[0060] The sensor module 3801 is a package with a sensor module built inside, mounted on the circuit board 3800, and has a detection window 3802 on its top. The temperature sensor unit 210 absorbs infrared radiation emitted from the object to be measured through the detection window 3802 and converts the absorbed infrared energy into an electrical signal, thereby enabling non-contact temperature detection. The temperature sensor unit 210 can also output the results detected by the sensor module 3801 from the connector 3806. In this embodiment, the sensor module 3801, which actually detects the temperature, is located at the very edge of the circuit board 3800 among the components mounted on the circuit board 3800.

[0061] Figure 5(b) schematically shows the field of view of the temperature sensor unit 210. The detection window 3802 not only allows infrared rays to pass into the sensor module 3801, but also acts as a lens. That is, the temperature sensor unit 210 has a constant field of view 3804 and detects the temperature of the object to be measured 3803 within the field of view 3804 without contact.

[0062] Figure 5(c) is a diagram illustrating the definition of the field of view 3804. The temperature measurement accuracy is defined as 100% when the object to be measured 3803 is located on the center line 3805 of the field of view 3804. Next, the object to be measured 3803 is moved away from the center line 3805 without changing the distance from the temperature sensor unit 210. The angle θ formed between the object to be measured 3803 and the center line 3805 when the temperature measurement accuracy decreases to 50% due to the movement is defined as the field of view 3804. Note that the value of 50% in this embodiment is merely an example and is not limited to 50%.

[0063] [Heater configuration] Next, the configuration of heaters 110, 120, and 130 will be explained using Figures 6(a) and 6(b). In this embodiment, heaters 110, 120, and 130 have the same light distribution, differing only in the power of the two heaters in a single heating section. Therefore, heater 110 will be described as a representative example below. Figure 6(a) is a schematic diagram of heater 110 and the upper belt 30 viewed from the upstream side to the downstream side in the sheet conveying direction, and a graph showing the radiant intensity of heater 110 at a position in the belt width direction. The belt width direction is the direction perpendicular to the sheet conveying direction and is shown as the x-axis in the figure. The sheet conveying direction is shown as the y-axis, and the height direction as the z-axis. In this embodiment, heating unevenness in the belt width direction is suppressed by distributing the light of heater 110 so that the radiant intensity is higher in the end regions 2501 and 2503 in the belt width direction than in the central region 2502 in the belt width direction.

[0064] Figure 6(b) is a graph showing the relationship between heating time and the temperature of the upper belt 30 when the upper belt 30 is continuously heated by the heater. The horizontal axis represents time, and the vertical axis represents the temperature of the upper belt 30. Graph 2504 shows the temperature rise in the end regions 2501 and 2503 in the belt width direction, and graph 2505 shows the temperature rise in the central region 2502 in the belt width direction. Because the radiation intensity is distributed so that the end regions 2501 and 2503 have a higher radiation intensity than the central region 2502, the temperature rises with a steeper slope in graph 2504. The dashed line 2506 shown in the figure is the limit temperature set to prevent the belt from deforming, and this temperature is determined according to the belt material. Therefore, the threshold temperature for overheat detection is set so that the belt does not exceed the limit temperature of the dashed line 2506. Although the configurations of heaters 110, 120, and 130 are the same in this example, their configurations may be different. For example, of the two heaters in one heating element, one heater may have the aforementioned light distribution, while the other heater has a light distribution with a flat radiation intensity in the belt width direction. Alternatively, both heaters may have a flat radiation intensity distribution. Alternatively, both heaters may have a flat radiation intensity and be of different lengths.

[0065] [Placement of temperature sensor unit] Next, the arrangement of the temperature sensor units 210, 220, and 230 will be explained using Figures 7(a) to 7(c). Figure 7(a) is a diagram showing the arrangement of the temperature sensor units 210, 220, and 230 and the fans 1500 and 1501 in this embodiment, and shows the arrangement of the upper belt 30, heaters 110, 120, 130, temperature sensor units 210, 220, 230, and fans 1500 and 1502 when viewed from above the upper fixing belt system 10. Note that in Figure 7(a), the portion of the upper belt 30 located above the reflectors 112, 122, and 132 is shown as a transparent view.

[0066] The fans 1500 and 1501, which generate airflow, are positioned outside the upper belt 30 in the width direction. Furthermore, fans 1500 and 1501 are positioned only at one end of the upper belt 30 in the width direction. Fan 1500 blows air in the direction of arrow 1500a, generating airflow between reflectors 112 and 122 with respect to the rotation direction of the upper belt 30. Similarly, fan 1501 blows air in the direction of arrow 1501a, generating airflow between reflectors 122 and 132 with respect to the rotation direction of the upper belt 30.

[0067] The temperature sensor unit 210, which detects the temperature of the upper belt 30 heated by heater 110, is located between reflectors 112 and 122 and is positioned close to the fan 1500 with respect to the center 2200 in the belt width direction. The temperature sensor unit 220, which detects the temperature of the upper belt 30 heated by heater 120, is located between reflectors 122 and 132 and is positioned close to the fan 1501 with respect to the center 2200 in the belt width direction. The temperature sensor unit 230, which detects the temperature of the upper belt 30 heated by heater 130, is located between reflectors 122 and 132 and is positioned close to the fan 1501 with respect to the center 2200 in the belt width direction. The areas detected by each temperature sensor unit are represented by dashed lines 2201, 2202, and 2203, respectively, and in this embodiment, they are arranged to detect the belt temperature directly below heaters 110, 120, and 130.

[0068] Figure 7(b) shows the positional relationship between the upper belt 30 and the temperature sensor unit 210 when viewed from the upstream to the downstream side in the belt conveying direction. The temperature sensor unit 210, positioned on the upper belt 30, is positioned diagonally (from the back to the front of the paper in the figure) to detect the area of ​​the upper belt 30 corresponding to the central area 2502 of the heater 110, and is positioned to detect the belt temperature at a position offset from the center 2200 in the belt width direction towards the fan 1500. The positions of the temperature sensor units 220 and 230 when viewed from the upstream to the downstream side in the belt conveying direction are the same as those of the temperature sensor unit 210.

[0069] Figure 7(c) shows the relationship between heating time and belt temperature at various points on the belt when the belt is continuously heated by the heater. The horizontal axis represents time, and the vertical axis represents belt temperature. Graph 1602 shows the temperature change in region 1802 directly below the heater 110. Graph 1603 shows the temperature change in region 1803 directly below the heater 110. As shown in Figure 7(a), region 1802 is within the region of the upper belt 30 corresponding to the central region 2502 of the heater 110, and region 1803 is within the region of the upper belt 30 corresponding to the end region 2501 of the heater 110. The difference in the slope of temperature rise between graphs 1602 and 1603 is due to the difference in the light distribution of the heater 110. The light distribution of the heater is weaker in the central region 2502 compared to the end region 2501. Therefore, the slope of temperature rise is also lower in the central region 2502.

[0070] In order for the upper belt 30 not to reach the limit temperature 2006 set to prevent belt deformation, it is necessary to consider the difference in the slope of temperature rise with respect to the region 1802 detected by the temperature sensor unit 210. In this embodiment, the temperature of region 1802 when region 1803, which has a higher rate of temperature rise, reaches the limit temperature 2006 must be set as the over-temperature detection threshold 2204.

[0071] [Temperature distribution] Next, we will describe the ambient temperature distribution in the flow path where the temperature sensor units 210, 220, and 230 are located. As mentioned above, temperature sensor unit 210 is located between reflectors 112 and 122, and temperature sensor units 230 and 220 are located between reflectors 122 and 132. Figure 8(a) shows the ambient temperature distribution between reflectors 112 and 122. As explained in Figure 7(a), an airflow is formed between reflectors 112 and 122 from fan 1500 in the direction of arrow 1500a, so outside air blows in near fan 1500. Therefore, the ambient temperature near fan 1500 is lower. Then, each time air moves in the direction of arrow 1500a, the air is warmed by the heat from heaters 110 and 120 transmitted through reflectors 112 and 122, so the ambient temperature is higher at positions farther from fan 1500.

[0072] Similarly, Figure 8(b) shows the ambient temperature distribution between reflectors 122 and 132. As explained in Figure 7(a), an airflow is formed between reflectors 122 and 132 from fan 1501 in the direction of arrow 1501a, so outside air blows in near fan 1501. Therefore, the ambient temperature near fan 1501 is lower. Then, each time air moves in the direction of arrow 1501a, the air is warmed by the heat from heaters 120 and 130 transmitted through reflectors 122 and 132, so the ambient temperature is higher at positions farther from fan 1501.

[0073] Therefore, in this embodiment, as described above, the temperature sensor units 210, 220, and 230 are positioned upstream of the airflow direction with respect to the center 2200 in the width direction of the upper belt 30 by fans 1500 and 1501. This allows cooler air to be directed at the temperature sensor units 210, 220, and 230, enabling efficient cooling of the temperature sensor units 210, 220, and 230. Thus, in this embodiment, in a configuration in which the belt is directly heated using a reflector and heater, and the belt temperature is detected using a non-contact temperature sensor unit, the temperature sensor is positioned upstream of the airflow path, thus suppressing the temperature sensor unit from becoming overheated. Although the above description has focused on the upper anchoring belt system 10, the control configuration and arrangement of each component are the same for the lower anchoring belt system 20 as for the upper anchoring belt system 10.

[0074] [Circuit configuration of the temperature sensor unit] Next, the circuit configuration of the temperature sensor unit 210 will be explained using Figures 9 to 11. The same applies to the other temperature sensor units 220, 230, 240, and 250. Figure 9 is a circuit diagram of the circuit board 3800 that constitutes the temperature sensor unit 210, Figure 10 is a graph of the output voltage of the voltage divider circuit, and Figure 11 is a graph showing the relationship between the detected temperature of the thermistor 3811 in the temperature sensor unit 210 and the resistance value of the thermistor 3811.

[0075] Here, since the temperature sensor unit 210 is located near the heater 110, it is expected that the temperature near the temperature sensor unit 210 will become high. In this embodiment, as described above, a fan 1500 is installed to cool the temperature sensor unit 210. However, if, for example, the airflow from the fan 1500 does not become as designed due to a decrease in airflow due to a malfunction of the fan 1500, defects during assembly, or vibrations during transportation, and the temperature of the sensor module 3801 of the temperature sensor unit 210 and the circuit board 3800 on which the sensor module 3801 is mounted exceeds the temperature at which they can operate normally, there is a risk that the heater 110 may not be able to be stopped properly. Therefore, in this embodiment, a thermistor 3811 that detects the temperature around the sensor module 3801 is placed on the circuit board 3800 as shown below.

[0076] As shown in Figure 9, the circuit board 3800 of the temperature sensor unit 210 is equipped with a sensor module 3801 as a first temperature sensor, a connector 3806, a temperature information correction unit 3816, and an ambient temperature detection unit 3817. The ambient temperature detection unit 3817 consists of a thermistor 3811 as a second temperature sensor and a resistor 3812, and outputs a voltage that fluctuates with temperature by voltage division. In this embodiment, the thermistor 3811 is an NTC (Negative Temperature Coefficient) thermistor, and its resistance decreases as the temperature rises. Therefore, the voltage of the signal created by voltage division between the resistor 3812 and thermistor 3811 decreases as the temperature rises. The sensor module 3801 and thermistor 3811 are arranged on the circuit board 3800, and the thermistor 3811 detects the temperature around (nearby) the sensor module 3801.

[0077] The temperature information correction unit 3816, which serves as the correction unit, includes a voltage divider circuit 3810, a comparator 3813, an inverting circuit 3814, and a gate circuit 3815. The voltage divider circuit 3810 is composed of resistors 3810a and 3810b. The voltage divider circuit 3810 creates a threshold voltage by dividing a 5V power supply. In this embodiment, the resistance value of resistor 3810a is 600Ω and the resistance value of resistor 3810b is 210Ω, resulting in a threshold voltage of approximately 1.3V. The comparator 3813 compares the threshold voltage from the voltage divider circuit 3810 with the voltage divided by the resistor 3812 and thermistor 3811 of the ambient temperature sensing unit 3817. If the threshold voltage is lower, it outputs 5V (High), and if the threshold voltage is higher, it outputs 0V (Low). The inverting circuit 3814 logically inverts the output of the comparator 3813. In other words, when the output of comparator 3813 is High, the output of the inverter circuit 3814 is Low, and when the output of comparator 3813 is Low, the output of the inverter circuit 3814 is High.

[0078] The gate circuit 3815 masks the temperature information output from the sensor module 3801. The masking is performed only when the inverting circuit 3814 outputs High. This period is when the thermistor 3811 is below a certain predetermined resistance value, that is, when the thermistor 3811 detects a temperature above a predetermined value (above the second predetermined temperature). The temperature information is masked only during this period, and outside of this period, the output from the sensor module 3801 is used as the 210 output of the temperature sensor unit.

[0079] Specifically, the temperature information correction unit 3816 corrects the output value to be output to the over-temperature detection HW211 based on the output value of the sensor module 3801 and the output value of the thermistor 3811. More precisely, if the temperature detected by the thermistor 3811 is less than a predetermined value, the temperature information correction unit 3816 outputs the output value of the sensor module 3801, and if the temperature detected by the thermistor 3811 is equal to or greater than the predetermined value, it outputs an output value corresponding to a temperature above the threshold temperature, regardless of the output value of the sensor module 3801.

[0080] In this embodiment, the predetermined value (second predetermined temperature) is lower than the threshold temperature (first predetermined temperature). This is because the sensor module 3801 detects the temperature of the upper belt 30 region, which becomes hot when heated by the heater 110, while the thermistor 3811 detects the temperature of the surrounding area where the sensor module 3801 is located, at a position away from the upper belt 30 which is the object heated by the heater 110, and therefore detects different objects. Furthermore, the predetermined value is set to a temperature within the range of temperatures in which the temperature sensor unit 210 operates normally.

[0081] The uncorrected temperature information output from the sensor module 3801 is output as a PWM (Pulse Width Modulation) signal. Figure 10 shows the relationship between the PWM signal and the detected temperature at each temperature. In this embodiment, the temperature range detectable by the detection window 3802 of the sensor module 3801 is from 0°C to 300°C. Depending on the temperature detected by the sensor module 3801 from the detection window 3802, the PWM duty cycle (the ratio of the High interval to the period) is output from the sensor module 3801 of the temperature sensor. Figure 10 shows examples where the temperature of the upper belt 30 detected by the sensor module 3801 is 300°C, 225°C, 150°C, and 75°C. When the High interval (Duty) is 100% of one period, that is, it remains High, it represents the maximum temperature of 300°C. When the High interval is 75% of one period, it represents 225°C, which is 75% of 300°C. Similarly, a Duty of 50% represents 150°C, and a Duty of 25% represents 75°C.

[0082] Figure 11 shows a graph of the temperature detected by thermistor 3811, the resistance value of thermistor 3811, and the voltage generated by voltage division between resistor 3812 and thermistor 3811. The solid line represents the resistance value of thermistor 3811, and the dotted line represents the voltage generated by voltage division between resistor 3812 and thermistor 3811. In this circuit, the power supply is 5V, and the resistance value of resistor 3812 is 600Ω. As the temperature detected by thermistor 3811 rises, the resistance value decreases, and therefore the voltage generated by voltage division also decreases. On the other hand, the threshold voltage created by the voltage divider circuit 3810 is constant regardless of temperature (dotted line in the figure). The intersection point P of the dashed line and the dotted line of this threshold voltage is the point at which the output of comparator 3813 switches, that is, the boundary temperature at which the ambient temperature of substrate 3800 becomes unable to operate normally. The predetermined temperature is the temperature T (approximately 86°C) obtained by drawing a dashed line from intersection point P. In other words, in this embodiment, the predetermined value (second predetermined temperature) is 86°C. In this embodiment, the rated temperature of the connector 3806 mounted on the circuit board 3800 is assumed to be 95°C, and considering the variations in the resistance values ​​of each circuit and resistor, the predetermined value is set to a temperature lower than 95°C.

[0083] When the output from the inverting circuit 3814, which is input to the gate circuit 3815, is High (i.e., the thermistor 3811 detects a temperature of 86°C or higher), the output of the gate circuit 3815 is fixed at High. In other words, the PWM signal output from the sensor module 3801 is masked to High and output from the connector 3806. Masking to High here means that the temperature information (output value) output from the temperature sensor unit 210 will be 300°C. When the temperature information is corrected to 300°C and output from the temperature sensor unit 210 in this way, the heater 110 stops lighting up via the over-temperature detection HW211 and FET111.

[0084] Specifically, the control unit 1700 stops heating the heater 110 when the sensor module 3801 detects a temperature above a threshold temperature (above a first predetermined temperature, 150°C or above in this embodiment) and the temperature detected by the thermistor 3811 is below a predetermined value (below 86°C, below a second predetermined temperature in this embodiment). On the other hand, the control unit 1700 stops heating the heater 110 regardless of the output value of the sensor module 3801 when the thermistor 3811 detects a temperature above a predetermined temperature (above a second predetermined temperature). Specifically, the FET 111 shuts down the over-temperature detection HW211 when the sensor module 3801 detects a temperature above a threshold temperature and when the thermistor 3811 detects a temperature above a predetermined temperature.

[0085] As described above, in this embodiment, the thermistor 3811 is placed on the same substrate 3800 as the sensor module 3801, and the temperature around the sensor module 3801 is detected by the thermistor 3811. If the temperature detected by the thermistor 3811 is above a predetermined value, there is a risk that the sensor module 3801 may not operate properly, so heating of the heater 110 is stopped regardless of the output value of the sensor module 3801. Therefore, even if the temperature around the sensor module 3801 exceeds the temperature at which the sensor module 3801 operates properly, heating of the heater 110 can be appropriately stopped. In other words, the thermistor 3811 is placed near the sensor module 3801, and the temperature information that the temperature sensor unit 210 ultimately outputs is corrected based on the temperature detected by the thermistor 3811. This makes it possible to safely stop the heater 110 with fewer signal lines before the temperature near the temperature sensor unit 210 becomes an unexpected temperature and the output temperature information can no longer be guaranteed.

[0086] <Second Embodiment> A second embodiment will be described using Figures 12 to 14. In the first embodiment described above, a method for safely stopping the system by correcting the temperature information when the vicinity of the temperature sensor unit 210 experiences an abnormal rise in temperature was described. However, in the first embodiment, it is not possible to determine whether the upper belt 30 itself has risen in temperature or whether the vicinity of the temperature sensor unit 210 has risen in temperature. In this embodiment, a method for determining whether the upper belt 30 or the vicinity of the temperature sensor unit 210 has risen in temperature will be described. Note that the other configurations and operations are the same as in the first embodiment described above, so the same components are denoted by the same reference numerals, and their descriptions and illustrations are omitted or simplified. The following description will focus on the differences from the first embodiment. In the following description, the temperature sensor unit 210 will be described. The same applies to the other temperature sensor units 220, 230, 240, and 250.

[0087] Figure 12 is a block diagram of the over-temperature detection HW211 of this embodiment. The over-temperature detection HW211 includes a smoothing circuit 2114, a threshold generation circuit 2111, a comparator 2112, and a latch circuit 2113. The smoothing circuit 2114 smooths the PWM signal from the temperature sensor unit 210 and converts it into a temperature information signal converted to a voltage according to the duty cycle. The temperature information signal is sent to the CPU 1100 and the comparator 2112.

[0088] The threshold generation circuit 2111 generates a threshold voltage for determining whether to stop the heater when the temperature information signal reaches a threshold temperature. In this embodiment, as in the first embodiment, the threshold voltage is set to the voltage corresponding to 150°C. The comparator 2112 compares the threshold voltage with the temperature information signal and outputs High if the voltage of the temperature information signal is equal to or greater than the threshold voltage, and Low if the voltage of the temperature information signal is less than the threshold voltage. When the comparator 2112 transitions from Low to High, the output (Q) of the latch circuit 2113 transitions from High to Low and holds Low. The output of the latch circuit 2113 is connected to the FET 111, and when the output of the latch circuit goes Low, the heater 110 stops. This prevents overheating by the heater 110.

[0089] Figures 13(a) to 13(c) are graphs showing the temporal progression of the temperature information signal detected by the CPU 1100. Figure 13(a) is a graph showing the case when the temperature of the upper belt 30 is being controlled normally. The dotted line in the figure represents the threshold voltage generated by the threshold generation circuit 2111. In order to perform temperature control within a range that does not exceed this threshold voltage, the voltage of the temperature information signal is controlled so as not to exceed the threshold voltage.

[0090] Figure 13(b) is a graph showing the case where the heater 110 stops and heating ceases due to the inability to control the temperature of the upper belt 30 for some reason. If the heater 110 cannot be controlled, the upper belt 30 will continue to heat up and eventually exceed 150°C. This moment occurs when the voltage of the temperature information signal exceeds the threshold voltage, which is the timing of R, the intersection of the dotted and solid lines in the figure. Subsequently, the output of the latch circuit 2113 becomes an output that stops the heater 100, and the drive of the heater 110 stops. As a result, the temperature of the upper belt 30 decreases, and the voltage of the temperature information signal also decreases.

[0091] Figure 13(c) is a graph showing the case where the fan 1500 fails and the temperature near the temperature sensor unit 210 rises to over 86°C before the temperature of the upper belt 30 rises. Because the fan 1500 fails, the temperature near the temperature sensor unit 210 rises, and as explained in the first embodiment, the output of the temperature sensor unit 210 is corrected, and the duty cycle of the PWM signal from the temperature sensor unit 210 becomes 100%. This timing is point S in Figure 13(c), and the voltage of the temperature information signal rises sharply. As a result, the heater 110 stops. Subsequently, since the heater 110 stops, the temperature near the temperature sensor unit 210 also decreases, so the correction is released, and the temperature of the upper belt 30 itself can be detected as the voltage of the temperature information signal.

[0092] Figure 14 is a flowchart showing the operation of the CPU 1100 to determine the cause of heater 110's shutdown. Since the CPU 1100 controls the shutdown causes of other heaters 120 and 130 in a similar manner, the control for heater 110 will be explained as an example. This flowchart starts simultaneously with the activation of heater 110 and continues until heater 110 is shut down.

[0093] The CPU 1100 acquires temperature information from the temperature information signal of the over-temperature detection HW211 and sets that temperature to Tn (S1200). Then, the CPU 1100 stores the information stored in Tn as To (S1201). This is so that Tn is retained as the previously acquired temperature information. Next, the CPU 1100 acquires temperature information from the temperature information signal and sets it to Tn (S1202). As a result, the latest temperature information is stored in Tn.

[0094] The CPU 1100 determines whether Tn exceeds the threshold temperature Tth (S1203). Here, Tth is the temperature at which the belt performance can be guaranteed, and in this embodiment, as in the first embodiment, it is set to 150°C, the temperature at which the belt does not deform. If it determines that Tn is less than Tth (N in S1203), the CPU 1100 determines whether to continue printing (S1205). If it determines to continue printing (Y in S1205), the CPU 1100 waits for a predetermined period (100 msec in this embodiment) (S1206). This 100 msec is the period during which the CPU 1100 samples temperature information. After that, the CPU 1100 executes the flow from S1201 again.

[0095] On the other hand, if the CPU 1100 determines in S1203 that Tn is greater than or equal to Tth (Y in S1203), the CPU 1100 determines whether Tn-To is greater than or equal to DTth (S1204). Here, DTth is the threshold for the amount of temperature information fluctuation over a sampling period (a predetermined period, 100 msec in this embodiment). When an abnormality occurs in the control of the heater 110, the temperature information rises most rapidly when the heater 110 is lit at maximum power. In reality, this temperature information is the temperature of the region 1802 (Figure 7(a)) directly below the heater 110 on the upper belt 30, and in reality, the temperature rise has a certain gradient. In this embodiment, the amount of temperature fluctuation over a 100 msec sampling period when the heater 110 is lit at maximum power is set to 80°C. That is, DTth becomes 80°C.

[0096] On the other hand, if the temperature near the temperature sensor unit 210 rises and the temperature information is masked by the resistance fluctuation of the thermistor 3811 mounted on the substrate 3800, the temperature information is instantly corrected to 300°C. Therefore, the amount of temperature fluctuation is detected as a fluctuation amount exceeding DTth during the CPU 1100's sampling period of 100 msec. If the CPU 1100 determines in S1204 that Tn-To is greater than or equal to DTth (Y in S1204), the CPU 1100 determines that there is an error due to an increase in the temperature near the temperature sensor unit 210 (S1208), and then stops the heater 110 (S1209). The CPU 1100 then displays on the control panel 1400 (Figure 3), which acts as a notification unit, that the heater 110 has stopped heating due to a rise in the ambient temperature around the temperature sensor unit 210.

[0097] In response to this, if the CPU 1100 determines in S1204 that Tn-To is less than DTth (N in S1204), it determines that there is an overheating error in the upper belt 30 (S1207), and then stops the heater (S1209). The CPU 1100 then displays on the control panel 1400 that the heater 110 has stopped heating due to overheating of the upper belt 30. In other words, in this embodiment, when the control unit 1700 stops heating the heater 110, the control unit 1400 notifies (in this case, displays) information based on the amount of change in the output value of the sampling period of the temperature sensor unit 210, regarding whether the heater 110 has stopped heating due to overheating of the upper belt 30 or due to a rise in the ambient temperature of the temperature sensor unit 210. The notification may be made by voice or by a lamp.

[0098] In this embodiment, by determining the amount of temperature fluctuation during the sampling period of the temperature sensor unit 210, it is possible to determine whether the temperature of the upper belt 30 actually rose based solely on temperature information, or whether the temperature near the temperature sensor unit 210 rose. This allows for accurate fault location determination with fewer signals while ensuring the safety of the device.

[0099] <Other Embodiments> In the embodiments described above, the present invention was explained in the case where it is applied to a fixing device (fixing belt unit) of an image forming system, but it is not limited to this. For example, the present invention can also be applied to fixing devices such as electrophotographic image forming apparatuses that use toner, and the same effects as in each embodiment can be obtained.

[0100] Furthermore, in the embodiments described above, the heater control device 1600 was described in the case where the object to be heated by the heater is a belt, but the object to be heated is not limited to a belt. For example, the present invention can also be applied to a temperature sensor unit that detects the temperature of a roller when the object to be heated is a roller. [Explanation of Symbols]

[0101] 1. Image forming system (image forming apparatus) 30... Upper belt 40... Lower belt 110, 120, 130, 140, 150... Heater 111, 121, 131...FET (Power Supply Control Unit) 112, 122, 132, 142, 152... Reflectors (reflective materials) 210, 220, 230, 240, 250... Temperature sensor unit 211, 221, 231... Overheat detection hardware (switching unit) 1100...CPU (Heater Control Unit) 1300...Power supply (power supply section) 1400...Operation Unit (Notification Unit) 1500, 1501...fan 1600... Heater control device 1700... Control Unit 3801... Sensor module (first temperature sensor) 3811...Thermistor (second temperature sensor) 4100... Fixing belt unit (fixing device) N...nipple area

Claims

1. An image forming unit that ejects ink to form an image on a sheet, A fixing device that heats a sheet on which an image has been formed by the image forming unit to fix the image onto the sheet, It comprises a control unit and, The fixing device is A rotating endless belt, A nip portion forming member that forms a nip portion for gripping and conveying the sheet between itself and the belt, A heater is positioned in non-contact with the belt and heats the belt, The system includes a temperature sensor unit for detecting the temperature of the belt, The temperature sensor unit comprises a substrate, a first temperature sensor disposed on the substrate for detecting the temperature of the belt, and a second temperature sensor disposed on the substrate for detecting the temperature around the first temperature sensor. The control unit, When the first temperature sensor detects a temperature of a first predetermined temperature or higher, and the temperature detected by the second temperature sensor is less than the second predetermined temperature, the heating of the heater is stopped. When the second temperature sensor detects a temperature equal to or higher than the second predetermined temperature, the heating of the heater is stopped regardless of the output value of the first temperature sensor. An image forming apparatus characterized by the following features.

2. The system further includes a notification unit that, when the control unit stops heating the heater, notifies information regarding the stopping of heating the heater based on the amount of change in the output value of the temperature sensor unit over a predetermined period. The image forming apparatus according to feature 1.

3. The system further includes a power supply that provides power to the aforementioned heater, The control unit, The heater control unit that controls the heater, A power supply control unit that controls the supply of power from the power source to the heater, The power supply control unit has a switching unit that switches the state of the power supply control unit between an energized state in which the power supply control unit can supply power from the power supply to the heater, and a shut-off state in which the power supply control unit does not supply power from the power supply to the heater, based on the output value of the temperature sensor unit. The switching unit switches the state of the power supply control unit to the shut-off state when the first temperature sensor detects a temperature of the first predetermined temperature or higher, and when the second temperature sensor detects a temperature of the second predetermined temperature or higher. The image forming apparatus according to feature 1.

4. The temperature sensor unit further includes a correction unit that corrects the output value to be output to the switching unit based on the output value of the first temperature sensor and the output value of the second temperature sensor. The correction unit outputs the output value of the first temperature sensor if the temperature detected by the second temperature sensor is less than the second predetermined temperature, and outputs an output value corresponding to a temperature of the first predetermined temperature or higher, regardless of the output value of the first temperature sensor, if the temperature detected by the second temperature sensor is equal to or greater than the second predetermined temperature. The image forming apparatus according to feature 3.

5. The second temperature sensor is a thermistor. The image forming apparatus according to feature 1.

6. The fixing device further includes a heater positioned inside and a reflective member that reflects the radiant heat of the heater toward the belt region, The temperature sensor unit is positioned outside the reflective member and detects the temperature of the area. The image forming apparatus according to feature 1.

7. When the heater is referred to as the first heater, the region as the first region, the reflective member as the first reflective member, and the temperature sensor unit as the first temperature sensor unit, A second heater is positioned in non-contact with the belt and heats the belt, The second heater is positioned on the inside, and a second reflecting member reflects the radiant heat of the second heater toward the second region of the belt, The system further comprises a second temperature sensor unit disposed on the outside of the second reflective member for detecting the temperature of the second region, The control unit, When the first temperature sensor detects a temperature above the first predetermined temperature, the heating of the first heater and the second heater is stopped. When the second temperature sensor detects a temperature equal to or higher than the second predetermined temperature, the heating of the first heater and the second heater is stopped. The image forming apparatus according to feature 6.

8. The system further includes a fan that generates airflow between the first reflective member and the second reflective member in the direction of rotation of the belt, At least one of the first temperature sensor unit and the second temperature sensor unit is positioned between the first reflective member and the second reflective member with respect to the rotational direction of the belt. The image forming apparatus according to feature 7.

9. When the aforementioned belt is designated as the first belt, The nip-forming member is a rotating, endless second belt. The image forming apparatus according to feature 1.

10. A heater control device that controls a heater for heating an object to be heated, A temperature sensor unit for detecting the temperature of the object to be heated, The system includes a control unit that controls the heater based on the output value of the temperature sensor unit, The temperature sensor unit comprises a substrate, a first temperature sensor disposed on the substrate for detecting the temperature of the object to be heated, and a second temperature sensor disposed on the substrate for detecting the temperature around the first temperature sensor. The control unit, When the first temperature sensor detects a temperature of a first predetermined temperature or higher, the heating of the heater is stopped. When the second temperature sensor detects a temperature equal to or higher than the second predetermined temperature, heating of the heater is stopped regardless of the output value of the first temperature sensor. A heater control device characterized by the following features.

Images