Image forming apparatus

Abstract

To provide an image forming apparatus capable of preventing a temperature sensor for detecting the temperature of a heating belt for heating a developer on a recording medium from reaching a high temperature, and capable of detecting the temperature of the heating belt without using a highly heat-resistant temperature sensor which leads to cost increase.SOLUTION: An image forming apparatus comprising: a rotatable heat belt configured to heat a developer on a recording material; a heater disposed in non-contact with the heat belt and configured to heat the heat belt; and a temperature sensor disposed in a region not overlapping the heat belt in a cross section orthogonal to a conveyance direction of the recording material and configured to detect an surface temperature of the heat belt.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine having a plurality of these functions. [Background technology]

[0002] In an inkjet recording type image forming apparatus, a method is known in which a recording medium to which ink as a developer has been applied is dried to evaporate the water, and then the image is fixed by applying heat and pressure.

[0003] The conventional fixing method that applies heat and pressure is heat roller fixing, in which the recording medium is passed between a heat roller and a pressure roller. In this heat roller fixing system, a safety measure is known in which a thermistor lightly contacting the heat roller detects abnormal heating and cuts off the power supply to the heater.

[0004] In recent years, with the trend toward higher speeds and higher productivity in image forming devices, fusing systems have been proposed that use a pair of heating belts instead of heating rollers, allowing for a longer nip distance. In order to quickly heat the recording medium that enters the nip, these fusing systems use an on-demand fusing method in which a heater directly heats the belt. While this on-demand fusing method offers good thermal efficiency and fast heating speed, it also quickly reaches a temperature at which the belt will deform if abnormal overheating occurs, so it is necessary to quickly detect abnormal overheating.

[0005] In the fixing system described in Patent Document 1, in order to detect abnormal heating of the belt heating surface, a temperature sensor placed on the heating area of ​​the heater is used to measure the temperature of the object to be heated, and if the temperature exceeds a predetermined temperature, the power supply to the heater is stopped. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-136392 Summary of the Invention [Problem to be solved by the invention]

[0007] In the method of heating the belt with a heater, a non-contact temperature sensor may be used to detect the temperature of the belt being heated. However, when using a non-contact temperature sensor, the temperature sensor itself must be placed close enough to the belt. In this case, the temperature sensor itself is exposed to a high-temperature environment due to the influence of heat from the belt.

[0008] Therefore, in order to accurately detect the temperature even in such a high-temperature environment, it is necessary to use a highly heat-resistant sensor, which leads to a problem of increased costs.

[0009] The present invention has been developed in consideration of the above circumstances, and aims to provide an image forming apparatus that can prevent the temperature sensor for detecting the temperature of the heating belt that heats the developer on the recording medium from becoming too high, and that can detect the temperature of the heating belt without using a highly heat-resistant temperature sensor that would increase costs. [Means for solving the problem]

[0010] In order to achieve the above object, the present invention provides an image forming apparatus having a rotatable heating belt that heats developer on a recording medium, a heater that is arranged in non-contact with the heating belt and heats the heating belt, and a temperature sensor that is arranged in an area that does not overlap with the heating belt in a cross section perpendicular to the transport direction of the recording medium and detects the surface temperature of the heating belt. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an image forming apparatus that can prevent the temperature sensor for detecting the temperature of the heating belt that heats the developer on the recording medium from becoming too high, and can detect the temperature of the heating belt without using a highly heat-resistant temperature sensor that would increase costs. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic front cross-sectional view of an image forming system according to a first embodiment of the present invention. [Figure 2] 1 is an overall configuration diagram of a fixing system according to a first embodiment of the present invention. [Figure 3] 1 is a circuit block diagram of an upper fixing belt system according to a first embodiment of the present invention. [Figure 4] 4 is a flowchart of the CPU in FIG. 3 according to the first embodiment of the present invention. [Figure 5] FIG. 1 is an explanatory diagram illustrating a configuration of a temperature sensor according to a first embodiment of the present invention. [Figure 6] FIG. 3 is an explanatory diagram illustrating the heating intensity distribution of a heater according to the first embodiment of the present invention. [Figure 7] FIG. 2 is an explanatory diagram illustrating the arrangement of temperature sensors and fans according to the first embodiment of the present invention. [Figure 8] FIG. 3 is an explanatory diagram showing the ambient temperature distribution at the temperature sensor position according to the first embodiment of the present invention. [Figure 9] FIG. 10 is a diagram illustrating the overall configuration of a fixing system according to a second embodiment of the present invention. [Figure 10] FIG. 10 is a circuit block diagram of an upper fixing belt system according to a second embodiment of the present invention. [Figure 11] FIG. 10 is an explanatory diagram illustrating the arrangement of temperature sensors and fans according to a second embodiment of the present invention. [Figure 12] FIG. 10 is an explanatory diagram illustrating the arrangement of temperature sensors according to a second embodiment of the present invention. [Figure 13] FIG. 10 is an explanatory diagram illustrating the arrangement of temperature sensors according to a third embodiment of the present invention. [Figure 14]FIG. 10 is an explanatory diagram illustrating the arrangement of temperature sensors according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Note that the components described in the following embodiments are merely examples, and various conditions such as the configuration, function, dimensions, materials, shape, and relative arrangement of the device to which the present invention is applied can be appropriately modified or changed without departing from the spirit of the present invention, and are not limited to the following embodiments.

[0014] [First embodiment] FIG. 1 is a schematic cross-sectional front view of an image forming system according to a first embodiment of the present invention.

[0015] 1, an inkjet recording system 100 as an image forming system of this embodiment uses an inkjet recording method in which ink as a developer is ejected to form an image on a sheet as a recording medium, and is a so-called sheet-fed inkjet recording device that forms an ink image on a sheet using two liquids, namely, a reaction liquid and ink. The sheet may be any recording material that can accept ink, such as plain paper, cardboard, plastic film for overhead projectors, specially shaped sheets such as envelopes and index paper, or cloth.

[0016] 1, the inkjet recording system 100 of this embodiment is an example of an image forming apparatus, and includes a feeding module 1000, a printing module 2000, and a drying module 3000. The inkjet recording system 100 further includes a fixing module 4000, a cooling module 5000, an inverting module 6000, and a stacking module 7000. A sheet supplied from the feeding module 1000 undergoes various processes as it is transported along a transport path within each module, and is finally discharged to the stacking module 7000.

[0017] The feeding module 1000 to the stacking module 7000 may each have a separate housing, and these housings may be connected to form the inkjet recording system 100. Alternatively, the feeding module 1000, print module 2000, drying module 3000, fixing module 4000, cooling module 5000, reversing module 6000, and stacking module 7000 may be arranged in a single housing.

[0018] The feeding module 1000 has storage cabinets 1100a, 1100b, and 1100c for storing sheets, and the storage cabinets 1100a, 1100b, and 1100c are provided so that they can be pulled out toward the front of the apparatus to store sheets. Sheets are fed one by one in each storage cabinet 1100a, 1100b, and 1100c by a separation belt and a transport roller, and then transported to the print module 2000. The number of storage cabinets 1100a, 1100b, and 1100c is not limited to three, and the number may be one, two, four, or more.

[0019] A print module 2000, which is an example of an image forming unit, has a pre-imaging registration correction unit (not shown), a print belt unit 2200, and a recording unit 2300, and forms an image by ejecting ink onto a sheet. The sheet transported from the feeding module 1000 has its tilt and position corrected by the pre-imaging registration correction unit (not shown) and is then transported to the print belt unit 2200. The recording unit 2300 is disposed opposite the print belt unit 2200 with respect to the transport path.

[0020] The recording unit 2300 is an inkjet recording unit that forms an image by ejecting ink onto a conveyed sheet from above using a recording head. Multiple recording heads that eject ink are arranged along the sheet conveyance direction. In this embodiment, in addition to the 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 liquids. The sheet is attracted and conveyed by the print belt unit 2200, ensuring clearance between the sheet and the recording heads.

[0021] The number of ink colors and recording heads is not limited to the five mentioned above. The inkjet method can be a method using a heating element, a piezoelectric element, an electrostatic element, or a MEMS (Micro Electro Mechanical Systems) element. Each color of ink is supplied to the recording head from an ink tank (not shown) via an ink tube. The ink contains 0.1% to 20.0% by mass of a resin component, water, a water-soluble organic solvent, coloring material, wax, additives, etc., based on the total mass of the ink.

[0022] When the sheet on which an image is formed by the recording unit 2300 is transported by the print belt unit 2200, it is detected by an inline scanner (not shown) that is arranged downstream of the recording unit 2300 in the sheet transport direction. Here, the misalignment and color density of the image formed on the sheet are detected, and the image to be formed on the sheet, its density, etc. are corrected based on the misalignment and color density of the image.

[0023] The drying module 3000 is an example of a drying device that dries a sheet on which an image has been formed by ejecting ink by blowing hot air onto the sheet. The drying module 3000 has a decoupling section 3200, a drying belt unit 3300, and a hot air blowing unit 3400. The drying module 3000 reduces the liquid content of the ink and reaction liquid applied to the sheet in order to improve the fixation of the ink to the sheet by the subsequent fixing module 4000.

[0024] The sheet on which the image is formed is transported to the decoupling unit 3200 arranged in the drying module 3000. In the decoupling unit 3200, frictional force is generated between the sheet and the belt by the wind pressure of the air blown from above, causing the sheet to be transported by the belt. In this way, the sheet placed on the belt is transported by frictional force, thereby preventing the sheet from shifting as it is transported between the print belt unit 2200 and the decoupling unit 3200.

[0025] The sheet transported from the decoupling section 3200 is adsorbed and transported by the drying belt unit 3300, and the ink and reaction liquid applied to the sheet S are dried by hot air blowing from the hot air blowing unit 3400 arranged above the belt.

[0026] In this way, the drying module 3000 heats the ink and reaction liquid applied to the sheet, promoting evaporation of the water, thereby preventing the ink applied to the sheet from absorbing the ink and causing the sheet to locally stretch and wrinkle, a phenomenon known as cockling. As a heater for heating the air, heating by, for example, an electric heating wire or an infrared heater is preferred from the standpoints of safety and energy efficiency. Furthermore, the drying method may be a combination of a method of applying hot air, a method of irradiating the sheet surface with electromagnetic waves (such as ultraviolet or infrared rays), or a method of conductive heat transfer by contact with a heating element.

[0027] The fixing module 4000 has a fixing belt unit 4100. The fixing belt unit 4100 heats and fixes the ink on the sheet S by passing the sheet S, on which an image is formed and which is transported from the drying module 3000, between an upper belt unit and a lower belt unit which serve as heated heating belts.

[0028] The cooling module 5000 has a plurality of cooling units 5001, which cool the high-temperature sheet conveyed from the fixing module 4000. The cooling units 5001 use, for example, a fan to draw outside air into a cooling box to increase the pressure inside the cooling box, and the pressure causes air to be blown out from the cooling box through a nozzle onto the sheet, thereby cooling the sheet. The cooling units 5001 are arranged on both sides of the sheet conveyance path and cool both sides of the sheet.

[0029] A transport path switching unit is provided in the cooling module 5000. The transport path switching unit switches the transport path of the sheet depending on whether the sheet is transported to the reversing module 6000 or to a double-sided transport path for double-sided printing, in which images are formed on both sides of the sheet.

[0030] The reversing module 6000 has a reversing unit that reverses the front and back of the conveyed sheet, and changes the front and back orientation of the sheet when it is discharged to the stacking module 7000.

[0031] The stacking module 7000 has a top tray 7200 and a stacking portion 7500, and stacks the sheets conveyed from the reversing module 6000.

[0032] During double-sided printing, the sheet is conveyed to a conveyance path below the cooling module 5000 by a conveyance path switching unit of the cooling module 5000. The sheet then passes through a double-sided conveyance path of the fixing module 4000, drying module 3000, print module 2000, and feeding module 1000, and is returned to the print module 2000. The double-sided conveyance unit of the fixing module 4000 is provided with an inverting unit 4200 that inverts the sheet. An image is formed with ink on the other side of the sheet that has not been image-formed, and the sheet is then discharged from the drying module 3000 through the inverting module 6000 and onto the stacking module 7000.

[0033] 2 is an overall configuration diagram including the upper fixing belt system 10 and the lower fixing belt system 20 of the fixing module 4000 in FIG. 1. The inkjet recording apparatus forms an inkjet image on a sheet S, and dries the moisture in the inkjet to fix the image. The upper fixing belt system 10 and the lower fixing belt system 20 are fixing systems in which the sheet S on which an image has been formed is transported between the heated upper belt 30 and the lower belt 40, and the ink on the sheet S is heated to fix the image to the sheet S.

[0034] 2, upper belt 30 and lower belt 40 are rotationally driven by motor 710 shown in FIG. 3, and sheet S is transported in the direction of arrow H. In an inkjet recording device, since ink is applied to the upper surface of sheet S, heaters 110, 120, and 130 are provided on the upper belt 30 side that nips the upper surface. In addition, heaters 140 and 150 are provided on the lower belt 40 side to heat the sheet S itself on which ink has been applied. By nipping and heating sheet S with both upper belt 30 and lower belt 40 for a long time, the ink applied to sheet S penetrates, achieving high print quality.

[0035] The upper fixing belt system 10 is made up of heaters 110, 120, 130, temperature sensors 210, 220, 230, and a temperature sensor 310 that adjusts the temperature of the upper belt 30.

[0036] The rotation detection sensor 410 is a sensor that detects whether the upper belt 30 is rotating, and is disposed on the driven roller. The rotation detection sensor 410 is disposed on the driven roller because if the rotation detection sensor 410 were disposed on the drive roller, the drive roller would rotate and a false detection would occur if the motor was running even when the upper belt 30 was not attached, so the rotation detection sensor 410 is disposed on the driven roller. When the rotation of the upper belt 30 stops, the rotation detection sensor 410 detects this and stops heating by the heaters 110, 120, and 130.

[0037] Heaters 110, 120, and 130 are covered with reflectors and heat the upper belt 30 directly below them. Temperature sensors 210, 220, and 230 are safety sensors that detect the temperature of the belt area of ​​the upper belt 30 heated by heaters 110, 120, and 130, and check whether the temperature exceeds a predetermined temperature of 150°C. This predetermined temperature of 150°C is set so that the upper belt 30 does not deform, and is determined depending on the material of the belt. Therefore, this predetermined temperature does not prevent a different predetermined temperature from being set depending on the material of the belt.

[0038] The temperature sensor 310 detects the temperature of the upper belt 30 and adjusts the heating temperature of the heaters 110, 120, and 130 for the upper belt 30. The temperature sensor 310 that adjusts the heating temperature for the upper belt 30 is located downstream of the heaters 110, 120, and 130 in the rotation direction of the upper belt 30, and adjusts the temperature of the upper belt 30 to 100°C, thereby achieving high print quality. This temperature of 100°C is the temperature at which ink is fixed to the sheet S, and is determined depending on the ink material, so it does not prevent other temperatures from being set depending on the ink material.

[0039] Here, when the belt area of ​​upper belt 30 heated by heaters 110, 120, 130 reaches a high temperature of 150°C or higher, which is high enough to cause deformation of the belt, it takes time to stop heaters 110, 120, 130 using temperature sensor 310, which adjusts the heating temperature of heaters 110, 120, 130 for upper belt 30. Therefore, by using temperature sensors 210, 220, 230 to detect the temperature of the belt area directly below heaters 110, 120, 130, when the belt area of ​​upper belt 30 heated by heaters 110, 120, 130 reaches a high temperature of 150°C or higher, which is high enough to cause deformation of the belt, driving of heaters 110, 120, 130 can be stopped immediately.

[0040] By providing two types of sensors in this way, even when a long nip configuration is adopted, it is possible to accurately adjust the temperature of the upper belt 30 to a predetermined temperature, and it is also possible to stop the heaters 110, 120, 130 without deforming the belt even if the heaters 110, 120, 130 reach a predetermined temperature (150°C) or higher.

[0041] Furthermore, in consideration of the possibility that temperature sensors 210, 220, 230 fail and also temperature sensor 310, which regulates the temperature of upper belt 30, fails, thermostat 510 is disposed on roller 610, which is located downstream of heaters 110, 120, 130 in the rotation direction of upper belt 30. When the temperature of upper belt 30 reaches or exceeds a certain level, thermostat 510 also heats roller 610 on which thermostat 510 is disposed, and when the temperature of roller 610 reaches or exceeds the certain level, thermostat 510 cuts off the AC lines to heaters 110, 120, 130.

[0042] In this way, even if the temperature sensors 210, 220, 230, 310 fail, the thermostat 510 safely disconnects the AC line, thereby realizing a safe fixing system.

[0043] The lower fixing belt system 20 is made up of heaters 140 and 150, temperature sensors 240 and 250, and a temperature sensor 320 that adjusts the temperature of the lower belt 40.

[0044] The rotation detection sensor 420 is a sensor that detects whether the lower belt 40 is rotating, and is disposed on the driven roller. When the rotation of the lower belt 40 stops, the rotation detection sensor 420 detects this and stops heating by the heaters 140 and 150.

[0045] Heaters 140, 150 are covered with reflectors and heat the lower belt 40 directly below heaters 140, 150. Temperature sensors 240, 250 are safety sensors that detect the temperature of the belt area of ​​lower belt 40 heated by heaters 140, 150, and check whether the temperature exceeds a predetermined temperature of 150°C. This predetermined temperature of 150°C is set so that lower belt 40 does not deform, and is determined according to the material of the belt, so it does not prevent other predetermined temperatures from being set depending on the material of the belt.

[0046] Temperature sensor 320 is a sensor that detects the temperature of lower belt 40 and adjusts the heating temperature of heaters 140, 150 for lower belt 40. Temperature sensor 320 that adjusts the heating temperature for lower belt 40 is located downstream of heaters 140, 150 in the rotation direction of lower belt 40, and adjusts the temperature of lower belt 40 to 100°C to achieve high print quality. This temperature of 100°C is the temperature at which ink is fixed to sheet S, and is determined depending on the ink material, so it does not prevent other temperatures from being set depending on the ink material.

[0047] Here, when the belt area of ​​the lower belt 40 heated by the heaters 140, 150 reaches a high temperature of 150°C or higher, which is high enough to cause deformation of the belt, it takes time to stop the heaters 140, 150 using the temperature sensor 320 for adjusting the heating temperature of the lower belt 40. Therefore, by using the temperature sensors 240, 250 to detect the temperature of the belt area directly below the heaters 140, 150 that has reached a high temperature of 150°C or higher, which is high enough to cause deformation of the belt, the driving of the heaters 140, 150 can be stopped immediately.

[0048] By providing two types of sensors in this way, even when a long nip configuration is adopted, it is possible to accurately adjust the temperature of the lower belt 40 to a predetermined temperature, and it is also possible to stop the heaters 140, 150 without deforming the belt even if the heaters 140, 150 reach a predetermined temperature (150°C) or higher.

[0049] Furthermore, in consideration of the possibility that temperature sensors 240, 250 may fail and temperature sensor 320, which regulates the temperature of lower belt 40, may also fail, thermostat 520 is disposed on roller 620, which is located downstream of heaters 140, 150 in the direction of rotation of lower belt 40. When the temperature of lower belt 40 reaches or exceeds a certain level, thermostat 520 also heats roller 620 on which thermostat 520 is disposed, and when the temperature of roller 620 reaches or exceeds the certain level, thermostat 520 cuts off the AC lines to heaters 140, 150.

[0050] In this way, even if the temperature sensors 240, 250, 320 fail, the thermostat 520 safely disconnects the AC line, thereby realizing a safe fixing system.

[0051] FIG. 3 is a circuit block diagram of the upper fixing belt system 10 in FIG.

[0052] In Figure 3, the upper fixing belt system 10 is composed of a CPU 1100, a Relay 1200, FETs 111, 121, 131, overheating detection circuits 211, 221, 231, heaters 110, 120, 130, temperature sensors 210, 220, 230, temperature sensor 310, rotation detection sensor 410, a motor 710 that rotates the upper belt 30, and a motor drive circuit 711 that drives the motor 710.

[0053] CPU 1100 drives FETs 111, 121, 131 by controlling the ON / OFF of FETs 111, 121, 131 to control heaters 110, 120, 130. Temperature sensors 210, 220, 230 are connected to overheating detection circuits 211, 221, 231, and when the surface temperature of upper belt 30 detected by temperature sensors 210, 220, 230 reaches or exceeds a predetermined temperature of 150°C, this is detected by overheating detection circuits 211, 221, 231. This predetermined temperature of 150°C is set so that the belt does not deform, and is determined depending on the material of the belt, so it does not prevent a different predetermined temperature from being set depending on the material of the belt.

[0054] When any of the overheating detection circuits 211, 221, 231 detects a predetermined temperature of 150° C. or higher, the corresponding FET 111, 121, 131 stops the power supply to the corresponding heater 110, 120, 130. That is, for example, when the overheating detection circuit 211 detects that the temperature detected by the temperature sensor 210 has reached the predetermined temperature of 150° C. or higher, the FET 111 stops the power supply to the heater 110, but the overheating detection circuit 211 does not stop the power supply to the heaters 120, 130 from the other FETs 121, 131. Meanwhile, the CPU 1100 detects the interrupt signal from the overheating detection circuit 211 and stops the power supply from the FETs 121 and 131 to the heaters 120 and 130 in a software manner.

[0055] In this embodiment, the CPU 1100 stops the power supply to the other FETs by software, but it may be stopped by a hardware circuit. The thermostat 510 cuts off the AC line from the relay 1200 when the temperature exceeds a predetermined temperature.

[0056] Next, the operation of the upper fixing belt system 10 will be described with reference to the flowchart of the CPU 1100 in FIG.

[0057] When the fixing control is started, the motor driving circuit 711 drives the motor 710 to rotate the upper belt 30 in step S101.

[0058] In addition, in step S102, RELAY1200 is turned ON.

[0059] Next, in step S103, CPU 1100 determines whether upper belt 30 is rotating using rotation detection sensor 410. If it is determined that upper belt 30 is rotating, the process proceeds to step S104, and if it is determined that upper belt 30 is not rotating, the process proceeds to step S106.

[0060] In step S104, the CPU 1100 controls the heating temperatures of the heaters 110, 120, and 130 for the upper belt 30 based on the temperature value read from the temperature sensor 310. The CPU 1100 controls the heating temperatures of the heaters 110, 120, and 130 for the FETs 111, 121, and 131 using the duty width of the PWM control signal.

[0061] Next, in step S105, if the temperature value read from the temperature sensors 210, 220, and 230 is equal to or higher than the predetermined temperature of 150°C, which is the threshold temperature that deforms the upper belt 30, the CPU 1100 proceeds to step S106, and if the temperature value is lower than the predetermined temperature of 150°C, which is the threshold temperature, the CPU 1100 returns to step S103.

[0062] In step S106, the CPU 1100 turns off the FETs 111, 121, and 131 to stop the heaters 110, 120, and 130.

[0063] Figure 5 is an explanatory diagram explaining the configuration of temperature sensor 210, where Figure 5(A) is an outline drawing of temperature sensor 210, and Figures 5(B) and 5(C) are explanatory diagrams explaining the field of view of temperature sensor 210.

[0064] 5(A), package 3801 is a package with a sensor module built in, mounted on substrate 3800, and has detection window 3802 at the top. Temperature sensor 210 absorbs infrared rays emitted from the object to be measured through detection window 3802 and converts the absorbed infrared energy into an electrical signal, thereby enabling non-contact temperature detection. Temperature sensor 210 is also capable of outputting the results detected by package 3801 from connector 3806. In this embodiment, package 3801, which actually detects temperature, is arranged at the end-most part of substrate 3800 among the components mounted within substrate 3800.

[0065] Figure 5(B) is a diagram that schematically shows the viewing angle of temperature sensor 210. In Figure 5(B), detection window 3802 not only allows infrared rays to pass into package 3801, but also functions as a lens. That is, temperature sensor 210 has a fixed viewing angle 3804, and detects the temperature of measurement object 3803 within viewing angle 3804 without contact.

[0066] Fig. 5(C) is a diagram for explaining the definition of field of view 3804. In Figs. 5(B) and 5(C), the temperature measurement accuracy is defined as 100% when measurement object 3803 is located on center line 3805 of field of view 3804. Next, measurement object 3803 is moved from center line 3805 without changing the distance from temperature sensor 210. When this movement causes the temperature measurement accuracy to drop to 50%, the angle θ formed by measurement object 3803 and center line 3805 is defined as field of view 3804. Note that this value of 50% is merely an example and is not limited to 50%.

[0067] The same applies to the temperature sensors 220 and 230.

[0068] FIG. 6 is an explanatory diagram illustrating the heating intensity distribution of the heater 110. As shown in FIG.

[0069] FIG. 6A is a positional relationship diagram of the heater 110 and the upper belt 30 viewed from the upstream side toward the downstream side in the sheet conveying direction, and a graph showing the heating intensity at a position in the belt width direction perpendicular to the rotation direction of the upper belt 30. The belt width direction is the direction perpendicular to the sheet conveying direction and is illustrated as the X-axis in FIG. 6. The sheet conveying direction is illustrated as the Y-axis, and the height direction is illustrated as the Z-axis. In the following description, the X, Y, and Z axes all represent the same direction. In FIG. 6A, in this embodiment, the heater 110 is configured so that the heating intensity is higher in end regions 2501 and 2503 of the upper belt 30 in the width direction than in a central region 2502, thereby suppressing uneven heating in the belt width direction.

[0070] FIG. 6(B) is a graph showing the relationship between heating time and belt temperature when the upper belt 30 is continuously heated by the heater 110. The horizontal axis represents time, and the vertical axis represents belt temperature. Graph 2504 shows the temperature increase in end regions 2501 and 2503 of the upper belt 30 in the width direction, and graph 2505 shows the temperature increase in the central region 2502 of the upper belt 30 in the width direction. In FIG. 6(B), the upper belt 30 is configured so that the end regions 2501 and 2503 are heated more intensely than the central region 2502, so the temperature increase in graph 2504 is at a steeper slope. The dashed line 2506 shown in the figure is the limit temperature set to prevent the belt from deforming, and is a temperature determined according to the belt material. The threshold for detecting excessive temperature rise is set so that the belt does not exceed limit temperature 2506.

[0071] The same applies to the heaters 120 and 130.

[0072] FIG. 7 is an explanatory diagram for explaining the arrangement of the temperature sensors 210, 220, and 230 and the arrangement of the fans 1500 and 1501 as air blowing means in this embodiment.

[0073] 7A shows the arrangement of upper belt 30, heaters 110, 120, 130, temperature sensors 210, 220, 230, and fans 1500, 1502 when viewed from above the upper fixing belt system 10. In FIG. 7A, fan 1500 takes in air and sends it in the direction of arrow 1500a, forming an airflow between reflectors 160 and 161. Fan 1501 also takes in air in the same way and sends it in the direction of arrow 1501b, forming an airflow between reflectors 161 and 162.

[0074] Temperature sensor 210, which detects the temperature of the belt heated by heater 110, is located between reflectors 160 and 161, and is arranged at a position closer to fan 1500 than center 2500 with respect to center 2500 in the width direction of upper belt 30. Temperature sensor 220, which detects the temperature of the belt heated by heater 120, is located between reflectors 161 and 162, and is arranged at a position closer to fan 1501 than center 2500 with respect to center 2500 in the width direction of upper belt 30. Temperature sensor 230, which detects the temperature of the belt heated by heater 130, is located between reflectors 161 and 162, and is arranged at a position closer to fan 1501 than center 2500 with respect to center 2500 in the width direction of upper belt 30. The detection areas of each temperature sensor are represented by dashed line areas 2110, 2111, and 2112, respectively, and in this embodiment, the temperature sensors are arranged to detect the surface temperatures of the belt positions in the ranges directly below the areas irradiated by heaters 110, 120, and 130 on upper belt 30.

[0075] 7(B) is a diagram showing the positional relationship between upper belt 30 and temperature sensor 210 when viewed from the upstream side to the downstream side in the sheet conveying direction of upper belt 30. In Fig. 7(B), temperature sensor 210 arranged on upper belt 30 is arranged diagonally downward (diagonally downward from the back to the front of the page in Fig. 7) so as to be able to detect the temperature within a central region 2502 in the width direction of upper belt 30, and is arranged at a position so as to detect the belt temperature at a position biased toward fan 1500 from center 2500 in the width direction of upper belt 30.

[0076] The temperature sensors 220 and 230 are also positioned in the same manner when viewed from the upstream side to the downstream side of the sheet conveying direction on the upper belt 30.

[0077] FIG. 7(C) is a graph showing the relationship between heating time and belt temperature at various positions on the upper belt 30 when the upper belt 30 is continuously heated by the heater 110. The horizontal axis represents time, and the vertical axis represents belt temperature. In FIG. 7(C), graph 1602 represents the temperature change at belt position 1802 directly below the heater 110 shown in FIG. 7(A). Graph 1603 represents the temperature change at belt position 1803 directly below the heater 110 shown in FIG. 10(A). The difference in the gradient of the temperature rise between graphs 1602 and 1603 is due to differences in the heating intensity distribution of the heater 110. The heating intensity of the heater is weaker in a central region 2502 of the upper belt 30 in the width direction than in an end region 2501 of the upper belt 30 in the width direction. Therefore, the gradient of the temperature rise is also lower.

[0078] To prevent the upper belt 30 from reaching the critical temperature 2006, it is necessary to consider the difference in the gradient of the temperature rise between the belt position 1802 detected by the temperature sensor 210 and the belt position 1803. Based on the above, in this embodiment, the temperature at the belt position 1802 when the belt position 1803, which has a higher temperature rise rate, reaches the critical temperature 2006, is set as the excessive temperature rise detection threshold 2204.

[0079] The same applies to the temperature sensors 220 and 230.

[0080] FIG. 8 is an explanatory diagram showing the ambient temperature distribution between reflectors 160 and 161 and between reflectors 161 and 162 where temperature sensors 210, 220, and 230 are located.

[0081] Fig. 8(A) shows the ambient temperature distribution between reflector 160 and reflector 161. In Fig. 8(A), an airflow is formed from fan 1500 in the direction of arrow 1500a, so outside air is blown in to the area close to fan 1500. Therefore, the ambient temperature near fan 1500 is lower. Then, as the air moves in the direction of arrow 1500a, it is heated by the heat from heaters 110 and 120 that is transmitted through the reflectors, so the ambient temperature becomes higher the farther it is from fan 1500.

[0082] Fig. 8(B) shows the ambient temperature distribution between reflectors 161 and 162. As in the case of Fig. 8(A), outside air is blown into the area close to fan 1501, so the ambient temperature in the vicinity of fan 1501 is low.

[0083] In this way, by arranging the temperature sensor on the upstream side of the air flow relative to the center of the belt width direction of the upper belt 30, it is possible to suppress a rise in temperature near the temperature sensor, and it becomes possible to perform temperature detection more stably.

[0084] Second Embodiment Next, a second embodiment of the present invention will be described.

[0085] In the first embodiment, each heater is provided with one temperature sensor that detects the temperature directly below it. In this embodiment, multiple temperature sensors are used for each heater to detect temperature. By providing multiple temperature sensors, the heaters can be safely stopped even if one temperature sensor fails, thereby improving robustness.

[0086] The basic configuration and operation of this embodiment are the same as those of the first embodiment, and therefore these will be used interchangeably. In the drawings referred to in the following explanation, configurations similar to those of the first embodiment will be given the same reference numerals and will not be described again.

[0087] Fig. 9 is an overall configuration diagram including the upper fixing belt system 10 and the lower fixing belt system 20 of the fixing module 4000 of Fig. 1 in this embodiment. The overall configuration diagram of this embodiment shown in Fig. 9 differs from the overall configuration diagram of the first embodiment shown in Fig. 2 in that there are three temperature sensors (210a, 210b, 210c, 220a, 220b, 220c, 230a, 230b, 230c, 240a, 240b, 240c, 250a, 250b, 250c) for detecting the belt temperature directly below each heater. Other configurations are the same as those of the first embodiment.

[0088] FIG. 10 is a circuit block diagram of the upper fixing belt system 10 of the fixing system of FIG. 2 in this embodiment. The circuit block diagram of this embodiment shown in FIG. 10 differs from the circuit block diagram of the first embodiment shown in FIG. 3 in that there are three temperature sensors (210a, 210b, 210c, 220a, 220b, 220c, 230a, 230b, 230c, 240a, 240b, 240c, 250a, 250b, 250c) for detecting the belt temperature directly below each heater. In addition, overheating detection circuits 211, 221, and 231 are configured to be able to control the power supply to the heaters based on inputs from the three temperature sensors. Other configurations are the same as those in the first embodiment.

[0089] 11 is an explanatory diagram illustrating the arrangement of temperature sensors 210a, 210b, 210c, 220a, 220b, 220c, 230a, 230b, and 230c in this embodiment, and the arrangement of fans 1500 and 1501. The explanatory diagram of this embodiment shown in FIG. 10 differs from the explanatory diagram of the first embodiment shown in FIG. 7 in that the number of temperature sensors that detect the belt temperature directly below each heater has increased.

[0090] 11(A) shows the arrangement of upper belt 30, heaters 110, 120, 130, temperature sensors 210a, 210b, 210c, 220a, 220b, 220c, 230a, 230b, 230c, and fans 1500 and 1502 when viewed from above the upper fixing belt system 10. In FIG. 11(A), fan 1500 takes in air and sends it in the direction of arrow 1500a, forming an airflow between reflectors 160 and 161. Fan 1501 also takes in air in the same way and sends it in the direction of arrow 1501b, forming an airflow between reflectors 161 and 162.

[0091] Temperature sensors 210a, 210b, and 210c that detect the temperature of the belt heated by heater 110 are located between reflectors 160 and 161, and are arranged at positions closer to fan 1500 than center 2500 with respect to center 2500 in the width direction of upper belt 30. Temperature sensors 220a, 220b, and 220c that detect the temperature of the belt heated by heater 120 are located between reflectors 161 and 162, and are arranged at positions closer to fan 1501 than center 2500 with respect to center 2500 in the width direction of upper belt 30. Temperature sensors 230a, 230b, and 230c that detect the temperature of the belt heated by heater 130 are located between reflectors 161 and 162, and are arranged at positions closer to fan 1501 than center 2500 with respect to center 2500 in the width direction of upper belt 30. The areas detected by each temperature sensor are represented by dashed line areas 2110a, 2110b, 2110c, 2111a, 2111a, 2111b, 2111c, 2112a, 2112b, and 2112c, respectively, and in this embodiment, they are positioned to detect the surface temperature of the belt position within the range directly below the area irradiated by heaters 110, 120, and 130.

[0092] 11(B) is a diagram showing the positional relationship between upper belt 30 and temperature sensors 210a, 210b, and 210c when viewed from the upstream side to the downstream side in the sheet conveying direction of upper belt 30. In FIG. 11(B), temperature sensors 210a, 210b, and 210c arranged on upper belt 30 detect the belt temperature diagonally downward (diagonally downward from the back of the page in FIG. 11 to the front). Temperature sensor 210a detects the belt temperature in a central region 2502 in the width direction of upper belt 30, and temperature sensors 210b and 210c detect the belt temperature in an end region 2501 in the width direction of upper belt 30. All temperature sensors are arranged to detect the belt temperature at a position biased toward fan 1500 from center 2500 in the width direction of upper belt 30.

[0093] The temperature sensors 220a, 220b, and 220c and the temperature sensors 230a, 230b, and 230c are also positioned in the same manner when viewed from the upstream side to the downstream side of the upper belt 30 in the sheet conveying direction.

[0094] 11(C) is a graph showing the relationship between heating time and belt temperature at each position on the upper belt 30 when the upper belt 30 is continuously heated by the heater 110. The horizontal axis represents time, and the vertical axis represents belt temperature.

[0095] Since the heater configuration of this embodiment is the same as that of the first embodiment, graph 1602 showing the temperature change at belt position 1802 immediately below heater 110 shown in Fig. 11(A) and graph 1603 showing the temperature change at belt position 1803 immediately below heater 110 are the same as Fig. 7(C). The difference in the gradient of the temperature rise between graph 1602 and graph 1603 is due to the difference in the heating intensity distribution of heater 110. The heating intensity of the heater is weaker in central region 2502 in the width direction of upper belt 30 than in end regions 2501 in the width direction of upper belt 30. Therefore, the gradient of the temperature rise is also lower.

[0096] In this embodiment, to prevent the upper belt 30 from reaching the critical temperature 2006, it is necessary to consider the difference in slope of the temperature rise between belt position 1802 detected by temperature sensor 210a and belt position 1803. Based on the above, in this embodiment, the temperature at belt position 1802 when belt position 1803, which has a higher temperature rise rate, reaches the critical temperature 2006 is set as the excessive temperature rise detection threshold 2204 (threshold A). Furthermore, because temperature sensors 210b and 210c detect the temperature at belt position 1803 in the end region in the width direction of the upper belt 30, that is, in end region 2501 in the width direction of the upper belt 30 where the heating intensity distribution of the heater is high, the threshold for excessive temperature rise detection is set as the critical temperature 2006 (threshold B).

[0097] The same applies to the temperature sensors 220a, 220b, 220c, 230a, 230b, and 230c.

[0098] In the case of a temperature distribution in the width direction of the belt, as in this embodiment, by configuring the temperature to detect the hottest point in the temperature distribution, it becomes possible to set a threshold value that does not directly exceed the belt's limit temperature. If the hottest point cannot be detected, the heater can be stopped before the belt's limit temperature is reached by setting a detection threshold value different from the temperature at the temperature sensor position so that the belt's limit temperature is not exceeded.

[0099] Next, the arrangement of the temperature sensors will be described with reference to FIG.

[0100] In FIG. 12, temperature sensors 210a, 210b, and 210c are identical and arranged in the width direction of upper belt 30. However, in reality, the substrates constituting temperature sensors 210a, 210b, and 210c have lengths. Therefore, to enable temperature detection in end region 2501 in the width direction of upper belt 30 using two temperature sensors, package 3801 is mounted on the end of substrate 3800, and temperature sensors 210b and 210c are arranged rotated 180° as shown in FIG. 12. This reduces the distance 1700 between packages 3801, enabling detection with two temperature sensors even if the area to be measured by the temperature sensors is narrow. The area to be measured by the temperature sensors is, for example, the end of the belt. This is because the end of the belt is prone to become hot when paper is continuously passed through it, since paper is not passed through the end of the belt.

[0101] The same applies to the temperature sensors 220a, 220b, 220c, 230a, 230b, and 230c.

[0102] Third Embodiment Next, a third embodiment of the present invention will be described.

[0103] In the first and second embodiments, fans 1500 and 1501 are used to form airflows between reflectors 160 and 161, and between reflectors 161 and 162, where the temperature sensors are arranged, and the temperature sensors are arranged in positions close to the fans, thereby suppressing temperature rise near the temperature sensors and enabling stable belt temperature detection.

[0104] In contrast to this, this embodiment is configured so that the temperature sensor can stably detect the belt temperature without using the airflow from the fans 1500 and 1501 .

[0105] The basic configuration and operation of this embodiment are the same as those of the first embodiment, and therefore these will be used interchangeably. In the drawings referred to in the following explanation, configurations similar to those of the first embodiment will be given the same reference numerals, and their explanations will be omitted.

[0106] FIG. 13 is an explanatory diagram illustrating the arrangement of the temperature sensors 210, 220, and 230 of this embodiment.

[0107] 13A shows the arrangement of the upper belt 30, heaters 110, 120, 130, and temperature sensors 210, 220, 230 when viewed from above the upper fixing belt system 10. In FIG. 13A, the temperature sensors 210, 220, 230 are each arranged in an area that does not overlap with the upper belt 30 in a cross section perpendicular to the sheet conveying direction, and are configured to detect the surface temperature of an end area 2501 of the upper belt 30 in the width direction. The areas detected by each temperature sensor are represented by dashed line areas 2210, 2211, 2212, respectively. The temperature sensors 210, 220, 230 are arranged so as to detect the surface temperature of the belt at a position outside the range directly below the area irradiated by the heaters 110, 120, 130, respectively, which are immediately downstream of the heaters 110, 120, 130 in the rotation direction of the upper belt 30.

[0108] 13(B) is a diagram showing the positional relationship between the upper belt 30 and the temperature sensor 210 when viewed from the upstream side to the downstream side in the sheet conveying direction of the upper belt 30. In Fig. 13(B), the temperature sensor 210, which is arranged in an area that does not overlap with the upper belt 30 in a cross section perpendicular to the sheet conveying direction, is arranged so as to detect the surface temperature of an end area 2501 in the width direction of the upper belt 30 from diagonally above.

[0109] The temperature sensors 220 and 230 are also positioned in the same manner when viewed from the upstream side to the downstream side of the sheet conveying direction on the upper belt 30.

[0110] FIG. 13(C) is a graph showing the relationship between heating time and belt temperature at various positions on the upper belt 30 when the upper belt 30 is continuously heated by the heater 110. The horizontal axis represents time, and the vertical axis represents belt temperature. In FIG. 13(C), graph 2201 represents the temperature rise at position 2102 in the belt end region immediately below the heater 110 shown in FIG. 13(A). Graph 2202 represents the temperature rise at position 2103 in the belt center region immediately below the heater 110. Graph 2203 represents the temperature rise at position 2104 in the belt end region immediately downstream of the heater 110 in the rotation direction of the upper belt 30, as detected by temperature sensor 210. The difference in the slope of the temperature rise between graphs 2201 and 2202 is due to the difference in the heating intensity distribution of the heater. The difference in the slope of the temperature rise between graphs 2201 and 2203 is the difference in the temperature transmission time depending on the distance from the position of the heated area in the belt end region directly below the heater 110 to the position of the belt end region immediately downstream in the direction of rotation of the upper belt 30 detected by the temperature sensor 210.

[0111] To prevent the upper belt 30 from reaching the critical temperature 2006, it is necessary to consider the difference in the rate of temperature rise between the position 2104 of the belt end region detected by the temperature sensor 210 and the position 2102 of the belt end region directly below the heater 110. Based on the above, in this embodiment, the time when the graph 2201, which has the highest rate of temperature rise, reaches the critical temperature 2206 is set as time 2220, and the temperature of the graph 2203 at time 2220 is set as the overheating detection threshold 2204.

[0112] Note that the relationship between the temperature rise rates of each region and the relationship between the limit temperature and the threshold temperature for detecting excessive temperature rise in this embodiment are merely examples, and are not limited to these. For example, the limit temperature 2206 and the excessive temperature rise detection threshold 2204 may be set to low values ​​with a safety margin.

[0113] [Fourth embodiment] Next, a fourth embodiment of the present invention will be described. The basic configuration and operation of this embodiment are similar to those of the first and third embodiments, and therefore these will be incorporated herein by reference. In the drawings referred to in the following description, the same components as those of the first and third embodiments will be designated by the same reference numerals, and their description will be omitted.

[0114] Fig. 14 is an explanatory diagram illustrating the arrangement of temperature sensors 210, 220, and 230 of this embodiment. The difference between the arrangement of the temperature sensors of this embodiment shown in Fig. 14 and the arrangement of the temperature sensors of the third embodiment shown in Fig. 13 is that in this embodiment, the temperature sensors 210, 220, and 230 are arranged to detect the surface temperatures of the belt positions directly below the heaters 110, 120, and 130, respectively.

[0115] 14(A) shows the arrangement of the upper belt 30, heaters 110, 120, 130, and temperature sensors 210, 220, 230 when viewed from above the upper fixing belt system 10. In Fig. 14(A), the temperature sensors 210, 220, 230 are each arranged in an area that does not overlap with the upper belt 30 in a cross section perpendicular to the sheet conveying direction, and are configured to detect the surface temperature of the belt position within a range directly below the area irradiated by the heaters 110, 120, 130 in an end area 2501 in the width direction of the upper belt 30.

[0116] FIG. 14B is a diagram showing the positional relationship between the upper belt 30 and the temperature sensor 210 when viewed from the upstream side to the downstream side in the sheet conveyance direction of the upper belt 30. In FIG. 14B, the temperature sensor 210, which is disposed in an area that does not overlap with the upper belt 30 in a cross section perpendicular to the sheet conveyance direction, is disposed so as to detect the surface temperature of an end region 2501 in the width direction of the upper belt 30 from diagonally above. Compared to the third embodiment in FIG. 13 , the temperature sensor 210 is disposed so as to directly view the belt end region, which is the heated region directly below the heater 110, and to prevent the heater 110 from entering the detection region 2101. Therefore, the depression angle of the temperature sensor 210 with respect to the upper belt 30 is larger than in the third embodiment. When the depression angle of the temperature sensor 210 is larger, a wider belt region is included in the detection region 2101. Therefore, it is necessary to use a temperature sensor 210 with a narrow detection area 2101, or to provide a margin for detecting excessive temperature rise, taking into account that a wide range of belt temperatures is detected.

[0117] The temperature sensors 220 and 230 are also positioned in the same manner when viewed from the upstream side to the downstream side of the sheet conveying direction on the upper belt 30.

[0118] Fig. 14(C) is a graph showing the relationship between heating time and belt temperature at each position on the upper belt 30 when the upper belt 30 is continuously heated by the heater 110. The horizontal axis represents time, and the vertical axis represents belt temperature. In Fig. 8(C), graph 2201 represents the temperature rise at position 2102 in the belt end region directly below the heater 110. Graph 2202 represents the temperature rise at position 2103 in the central region directly below the heater 110. The difference in the slope of the temperature rise between graphs 2201 and 2202 is due to the difference in the heating intensity distribution of the heater.

[0119] In this embodiment, the temperature sensor 210 detects the temperature at a position 2102 in the belt end region immediately below the heater 110, where the rate of temperature rise is the highest. Therefore, the limit temperature 2006 of the upper belt 30 and the excessive temperature rise detection threshold 2204 are the same temperature.

[0120] Note that the relationship between the limit temperature and the threshold temperature for detecting excessive temperature rise in this embodiment is merely an example, and is not limited to this. For example, the excessive temperature rise detection threshold 2204 may be set to a value lower than the limit temperature 2206 by providing a safety margin. [Explanation of symbols]

[0121] 10...Upper belt fixing system 20...Lower belt fixing system 30...Upper belt 40...Lower belt 100...Inkjet recording system 100...Image forming apparatus 110, 120, 130, 140, 150...Heater 210, 220, 230, 240, 250, 310, 320...Temperature sensors 510, 520...thermostat 1100...CPU 1500, 1501... Fan 4000...Fixing module

Claims

1. a rotatable heating belt for heating the developer on the recording medium; a heater disposed in a non-contact manner with the heating belt for heating the heating belt; a temperature sensor disposed in a region that does not overlap with the heating belt in a cross section perpendicular to the conveying direction of the recording medium, the temperature sensor detecting a surface temperature of the heating belt; An image forming apparatus comprising:

2. 2. The image forming apparatus according to claim 1, wherein the temperature sensor detects the surface temperature of the heating belt in a width direction perpendicular to a rotation direction of the heating belt.

3. 2. The image forming apparatus according to claim 1, wherein the temperature sensor detects the surface temperature of an end region of the heating belt in a width direction perpendicular to the rotation direction of the heating belt.

4. 4. The image forming apparatus according to claim 3, wherein the heater has a first heating region with a first heating intensity and a second heating region with a heating intensity weaker than the first heating intensity, and the end region is a region heated by the first heating region of the heater.

5. 2. The image forming apparatus according to claim 1, further comprising a control unit for controlling the operation of the heater based on the detection result of the temperature sensor.

6. 6. The image forming apparatus according to claim 5, wherein the control means cuts off the power supply to the heater when the temperature detected by the temperature sensor is equal to or higher than a predetermined temperature.

7. 2. The image forming apparatus according to claim 1, wherein the temperature sensor detects the surface temperature of the heating belt at a position within the range irradiated by the heater.

8. 2. The image forming apparatus according to claim 1, wherein the temperature sensor detects the surface temperature of the heating belt at a position outside the range irradiated by the heater.

9. 9. The image forming apparatus according to claim 8, further comprising a control means for cutting off the power supply to the heater when the temperature sensor detects that the surface temperature of the heating belt at a belt position outside the range irradiated by the heater is equal to or higher than a predetermined temperature.

10. 10. The image forming apparatus according to claim 9, wherein the predetermined temperature is set based on the difference between the rate of increase in the surface temperature of the belt position on the heating belt within the range irradiated by the heater and the rate of increase in the surface temperature of the belt position on the heating belt outside the range irradiated by the heater, as detected by the temperature sensor.

Images