Image forming apparatus and method for detecting printing paper wrapping around fixing belt

Abstract

To surely detect winding when a printing sheet is wound around a fixing belt.SOLUTION: A heating unit that heats the fixing belt, a pressure roller that presses and passes the print sheet through an outer circumferential surface of the heated fixing belt, a fixing temperature sensor that detects an outer circumferential temperature of a sheet passing region of the fixing belt having a width corresponding to the print sheet as a fixing temperature, and an end temperature sensor that detects an outer circumferential temperature of a region outside the sheet passing region of the fixing belt as an end temperature; A hardware processor that determines presence or absence of winding of the print sheet around the fixing belt, wherein the hardware processor determines that the winding has occurred when a temperature difference between the end temperature and the fixing temperature exceeds a threshold value or when the fixing temperature falls below a predetermined reference during warm-up in which the fixing belt is heated.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus and a method for detecting a print sheet wrapped around a fixing belt, and more particularly to an image forming apparatus having a function for detecting a print sheet wrapped around a fixing belt, and a method for detecting a print sheet wrapped around a fixing belt. [Background technology]

[0002] When a paper jam occurs during printing, wrapping around the heating roller of the fixing device is difficult for the user to completely remove. This requires the user to call a service technician, resulting in significant removal costs and prolonged device downtime. In some cases, if the user turns the device back on after determining that the jam has been removed even though it was not, the remaining paper may heat up and emit smoke. To address this issue, the following fixing device has been proposed to quickly resolve paper jams and reliably detect any remaining paper to avoid problems caused by the remaining paper. This fixing device includes a heating element that heats up using a powered heat source and a non-contact temperature detection device, such as a thermopile, that is located outside of contact with the heating element and detects the heat radiated from the heating element. An abnormality in the wrapping of the recording material is determined by comparing the output state of the non-contact temperature detection device when there is no recording material on the heating element with the output state of the non-contact temperature detection device when there is a recording material on the heating element (see, for example, Patent Document 1).

[0003] Furthermore, a fixing device using a fixing belt is known that detects the temperature of the fixing belt in the paper passing area and outside the paper passing area, and detects whether or not the recording material (printing paper) is wrapped around it based on the temperature difference between the two. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-296953 Summary of the Invention [Problem to be solved by the invention]

[0005] However, it is not easy to reliably detect the wrapping of a recording material (printing paper) by comparing the output state of the non-contact temperature detection means when there is and is not a recording material (printing paper) on the heating element. Furthermore, in order to shorten the warm-up time, fixing devices using a fixing belt with a small heat capacity have become widely used in recent years. Instead of wrapping the fixing belt around a heating roller to apply heat to the fixing belt, these devices heat the fixing belt by arranging a heat source on the inner periphery of the fixing belt.

[0006] Even if the presence or absence of wrapping of printing paper is detected based on the temperature of the fixing belt in the paper passage area and outside the paper passage area, the fixing belt is simply a cylindrical sheet, and if, for example, multiple sheets of printing paper are wrapped around it, the fixing belt will sag. If the fixing belt sags, a temperature sensor that is supposed to detect the temperature of the fixing belt when wrapping occurs outside the paper passage area of ​​the fixing belt may not be able to detect the correct temperature. As a result, it becomes impossible to reliably detect that wrapping of printing paper has occurred. The present invention has been made in consideration of the above circumstances, and provides a method for reliably detecting wrapping of a print sheet around a fixing belt when the wrap occurs. [Means for solving the problem]

[0007] This invention provides an image forming apparatus comprising a fixing belt that is wider than a printing paper, a heating unit that is positioned on the inner side of the fixing belt and heats the fixing belt, a pressure roller that presses the printing paper against the outer surface of the heated fixing belt and passes it through, a fixing temperature sensor that detects the outer temperature of the paper passage area of ​​the fixing belt that is width corresponding to the printing paper as the fixing temperature, an end temperature sensor that detects the outer temperature of the fixing belt outside the paper passage area as the end temperature, and one or more control units that control the heating of the fixing belt by the heating unit based on the fixing temperature and determine whether the printing paper has wrapped around the fixing belt, wherein the control unit determines that the wrapping has occurred when the temperature difference between the end temperature and the fixing temperature exceeds a threshold value or when the fixing temperature drops below a predetermined standard during warm-up while the fixing belt is being heated.

[0008] From a different perspective, the present invention provides a method for detecting wrapping of print paper around a fixing belt, the method comprising the steps of: a control unit of an image forming apparatus heating the fixing belt using a heating unit arranged on the inner side of the fixing belt, the heating unit being wider than the print paper; a step of using a pressure roller to press the print paper against the outer surface of the heated fixing belt and pass it through; a step of using a fixing temperature sensor to detect the outer temperature of a paper passage area of ​​the fixing belt having a width corresponding to the print paper as a fixing temperature; a step of using an edge temperature sensor to detect the outer temperature of the fixing belt outside the paper passage area as an edge temperature; and a wrapping determination step of controlling heating of the fixing belt by the heating unit based on the fixing temperature and determining whether the print paper has wrapped around the fixing belt, wherein the wrapping determination step determines that wrapping has occurred if the temperature difference between the edge temperature and the fixing temperature exceeds a threshold value or if the fixing temperature drops below a predetermined standard during warm-up while the fixing belt is being heated. [Effects of the Invention]

[0009] In the fixing device of this invention, the control unit determines that the winding has occurred not only when the temperature difference between the end temperature and the fixing temperature exceeds a threshold value, but also when the fixing temperature drops below a predetermined standard during warm-up while the fixing belt is being heated, so that winding can be reliably detected when printing paper wraps around the fixing belt. The method of detecting the wrapping of the print paper around the fixing belt according to the present invention also has the same effect. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view showing a configuration of an image forming apparatus according to this embodiment. [Figure 2] 2 is a schematic cross-sectional view showing the configuration of a fixing device included in the image forming apparatus shown in FIG. [Figure 3] 3 is a perspective view showing an example of the arrangement of a fixing belt, a pressure roller, a fixing temperature sensor, and an edge temperature sensor in the fixing device shown in FIG. 2. FIG. [Figure 4] FIG. 2 is a block diagram showing the electrical configuration of the image forming apparatus shown in FIG. [Figure 5] 10A and 10B are waveform diagrams showing an example of changes in the fixing temperature and edge temperature when a paper jam and wrapping of print paper occur in an embodiment. [Figure 6] FIG. 6 is a waveform diagram showing a part of the waveform diagram of FIG. 5 in an enlarged time scale. [Figure 7] 10 is a first flowchart showing the flow when a control unit executes a process related to determining whether wrapping of print paper has occurred in an embodiment. [Figure 8] 10 is a second flowchart showing the flow when the control unit executes processing related to determining whether wrapping of print paper has occurred in the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in more detail below with reference to the accompanying drawings. Note that the following description is given by way of example only in all respects and should not be construed as limiting the present invention. Image forming device FIG. 1 is a schematic cross-sectional view showing a configuration of an image forming apparatus 100 according to an embodiment of the present invention.

[0012] The image forming apparatus 100 is a multifunction machine having a copy function, a scanner function, a facsimile function, and a printer function. The image forming apparatus 100 transmits an image of an original document read by the image reading device 120 to an external device, and forms an image of an original document read by the image reading device 120 or an image received from an external device on a recording medium such as paper in color or monochrome by the image forming unit 110.

[0013] The image forming section 110 includes a fixing device 100, a developing device 111, a photosensitive drum 112, an intermediate transfer belt device 113, a secondary transfer device 114, an optical scanning device 115, a paper feed section 116, and a paper discharge tray 117.

[0014] Image forming unit 110 handles image data corresponding to color images using black (K), cyan (C), magenta (M), and yellow (Y), or monochrome images using a single color (e.g., black). Image forming unit 110 is provided with four developing devices 111 and four photosensitive drums 112 for forming four types of toner images, each corresponding to black, cyan, magenta, and yellow.

[0015] A charger, a primary transfer roller, and a drum cleaning device are arranged around the photosensitive drum 112. An optical scanning device 115 exposes the charged surface of the photosensitive drum 112 to light to form an electrostatic latent image. The developing device 111 develops the electrostatic latent image on the surface of the photosensitive drum 112 to form a toner image on the surface of the photosensitive drum 112. The toner images of each color formed on the surface of the photosensitive drum 112 are sequentially transferred and superimposed onto the intermediate transfer belt device 113. The secondary transfer device 114 sandwiches and transports printing paper from a paper feed unit 116 through a transfer nip formed between the secondary transfer device 114 and the intermediate transfer belt device 113. As the printing paper passes through the transfer nip, the toner image is transferred from the intermediate transfer belt device 113 to the printing paper. The printing paper is then transported to the fixing device 10.

[0016] The fixing device 10 includes a rotatable fixing belt 11 and a pressure roller 12. The fixing device 10 sandwiches a print sheet, onto which a toner image has been transferred at a transfer nip, between the fixing belt 11 and the pressure roller 12, and applies heat and pressure to fix the toner image to the sheet. Although not shown in FIG. 1, the fixing device 10 also includes components other than the fixing belt 11 and the pressure roller 12. Details of the fixing device 10 will be described later.

[0017] The paper feed unit 116 is equipped with a paper feed cassette that holds printing paper used for image formation, and is provided below the optical scanning device 115. The printing paper is pulled out of the paper feed unit 116 by a pickup roller and transported to the secondary transfer device 114 via the paper transport path. After the toner is transferred by the secondary transfer device 114 as described above, the printing paper is transported to the fixing device 10, where the toner is fixed to the printing paper. The printing sheet that has passed through the fixing device 10 is discharged to the paper output tray 117.

[0018] <Fixing device> FIG. 2 is a schematic cross-sectional view showing the configuration of a fixing device 10 according to an embodiment. FIG. 3 is a perspective view showing an example of the arrangement of the fixing belt 11, pressure roller 12, fixing temperature sensor 14, and edge temperature sensor 15 in the fixing device 10 shown in FIG. 2. As shown in FIG. 2, the fixing device 10 includes the fixing belt 11 and the pressure roller 12. The fixing device 10 also includes a heating unit 13 inside the fixing belt 11. The heating unit 13 includes a base 13B, a fixing pad 13P, a sliding sheet 13S, a heater 13H as a heat source, and a reflector 13R. The fixing device 10 also includes a non-contact fixing temperature sensor 14 that detects the temperature inside the paper passage region PR of the fixing belt 11 and a contact-type edge temperature sensor 15 that detects the temperature outside the paper passage region PR of the fixing belt 11. The fixing device 10 also includes a peeling plate 16.

[0019] The fixing belt 11 is an endless, flexible belt formed in a cylindrical shape. The fixing belt 11 has a configuration in which a release layer is provided on the surface of a strip-shaped base material formed of, for example, a synthetic resin such as polyimide or a metal such as nickel. The inner diameter of the fixing belt 11 is, for example, 30 mm, and the thickness is, for example, 30 μm.

[0020] The pressure roller 12 is disposed in a position facing the base 13B with the fixing belt 11 sandwiched therebetween. The pressure roller 12 is disposed so as to rotate about a rotation axis extending in the width direction of the fixing belt 11. At the fixing nip N between the pressure roller 12 and the fixing belt 11, the fixing belt 11 is pressed against the base 13B by the pressure roller 12. The pressure roller 12 can be configured such that the surface of a cylindrical core material formed of a metal such as aluminum is covered with an elastic material such as rubber.

[0021] A driving force from a driving source such as a motor (not shown) is transmitted to the pressure roller 12 via gears or the like. The pressure roller 12 is driven to rotate by this driving force. As the pressure roller 12 is driven to rotate, the fixing belt 11 is driven to rotate in the circumferential direction. The printing paper PP passes through the fixing nip N between the pressure roller 12 and the fixing belt 11 along the paper transport direction S indicated by the arrow in FIG. 2. The peeling plate 16 is disposed downstream of the fixing nip N in the paper transport direction S to physically prevent the printing paper PP from wrapping around the fixing belt 11. However, since there is no member to regulate the position of the peeling plate 16 on the inner periphery of the fixing belt 11, where the leading edge of the peeling plate 16 is close, and there is a small gap between the leading edge of the peeling plate 16 and the fixing belt 11, wrapping cannot be completely prevented.

[0022] The base 13B contacts the inner circumferential surface of the fixing belt 11. The cross section of the base 13B is formed in a substantially L-shape. The portion corresponding to the horizontal line of the L and facing the pressure roller 12 across the fixing belt 11 is called the fixed portion, and the portion corresponding to the vertical line of the L is called the upright portion. A fixing pad 13P and a sliding sheet 13S are provided outside the fixed portion of the base 13B. The fixing pad 13P is a long plate-shaped member extending in the width direction of the fixing belt 11 and is made of, for example, synthetic resin. The base 13B contacts the inner circumferential surface of the fixing belt 11 via the fixing pad 13P and the sliding sheet 13S. The lengths of the base 13B, the fixing pad 13P, and the sliding sheet 13S are substantially equal to the length of the fixing belt 11 in the width direction. When the pressure roller 12 rotates, the fixing belt 11 rotates circumferentially, but the positions of the fixing pad 13P and the sliding sheet 13S do not move. A lubricant may be applied to the surface of the sliding sheet 13S to reduce the frictional force between the sliding sheet 13S and the fixing belt 11.

[0023] Heater 13H is a member that heats fixing belt 11 and is installed so as to extend along the width direction of fixing belt 11. Heater 13H may be, for example, a lamp heater such as a halogen lamp. However, the heater is not limited to this and may be, for example, a resistor or one that applies the principle of induction heating.

[0024] Reflector 13R is a thin plate-like member that covers the surface of base 13B facing heater 13H. Fixing belt 11 is heated by heat radiated from heater 13H and heat reflected by reflector 13R to a predetermined range relative to the target temperature of 160°C, for example. The thickness of fixing belt 11 is on the order of 10 μm, and its heat capacity is very small compared to, for example, pressure roller 12, so the temperature difference between the inner and outer surfaces can be considered to be substantially the same.

[0025] The fixing temperature sensor 14 detects the temperature of the paper passage region PR of the fixing belt 11 without contact. The edge temperature sensor 15 is a contact-type temperature sensor that detects the temperature of the edge of the fixing belt 11, which is outside the paper passage region PR. The paper passage region PR is the region in the width direction of the fixing belt 11 that comes into contact with the print paper PP at the fixing nip N, an example of which is shown in FIG. 3. Note that FIG. 3 also illustrates the heater 13H, but does not illustrate the base 13B. In FIG. 3, dashed lines indicate the positions of both ends in the width direction of the widest print paper PP that passes through the fixing nip N, on both the left and right sides of the fixing belt 11 and the pressure roller 12. The area between the dashed lines is the paper passage region PR corresponding to the widest print paper PP. When multiple sizes of print paper PP with different widths pass through the fixing nip N, the fixing temperature sensor 14 is positioned in a position that corresponds to the paper passage region PR for all sizes of print paper PP. In the example of FIG. 3, it is positioned approximately in the center of the width direction of the fixing belt 11. On the other hand, the edge temperature sensor 15 is disposed at a position outside the paper passing area PR for any size of print paper PP, i.e., at the edge of the fixing belt 11 in the example of FIG.

[0026] Electrical configuration of the image forming apparatus FIG. 4 is a block diagram showing the electrical configuration of the image forming apparatus 100 shown in FIG. 1, mainly related to fixing control. The image forming apparatus 100 includes a control unit 40 and an operation unit 130 in addition to the components shown in FIG. 1. The control unit 40 may be implemented by one or more control devices / arithmetic units (CPUs (Central Processing Units), SoCs (System on a Chip)). The control unit 40 may also include one or more control circuits. The control unit 40 also includes at least one or more RAMs (Random Access Memories), at least one or more ROMs (Random Access Memories), various interface circuits, and the like. The control unit 40 also includes an HDD (Hard Disk Drive), which is a nonvolatile storage device capable of retaining data even when power is interrupted. The control unit 40 in this embodiment is configured around a processor and memory, and includes an input / output interface circuit, and controls the operation of the image forming apparatus 100. The processor executes a control program pre-stored in the memory to perform processing related to the control of the operation of the image forming apparatus. For example, the control unit 40 causes the printing paper PP supplied from the paper feed unit 116 to be conveyed to the fixing device 10 via the secondary transfer device 114. The control unit 40 also controls the image forming unit 110 to form a toner image and transfer it to the printing paper PP by the secondary transfer device 114.

[0027] To control these functions, the paper feed unit 116 and the image forming unit 110 have sensors, motors, and actuators, as shown in FIG. 4. The sensors include multiple paper detection sensors provided on the transport path along which the print paper PP is transported. The control unit 40 determines whether a paper jam has occurred based on whether each paper sensor detects the leading or trailing edge of the transported print paper PP by a predetermined time. The operation unit 130 includes a display device, such as a liquid crystal display device, that displays information related to the status and operation of the image forming apparatus 100, and a touch panel that detects user operations on the display device. The control unit 40 provides information to the user via the operation unit 130 and accepts user operations.

[0028] Furthermore, the control unit 40 controls the fixing process. The fixing device 10 has a heater 13H, a fixing temperature sensor 14, an edge temperature sensor 15, and a heater control circuit 41H (not shown in FIG. 1). The heater control circuit 41H supplies power from a power source (an AC power source from the power system in the image forming apparatus of FIG. 1) to the heater 13H in response to instructions from the control unit 40. Signals related to detection by the fixing temperature sensor 14 and the edge temperature sensor 15 are input to the control unit 40. Since the fixing belt 11 has a smaller heat capacity than rollers and requires quick response in fixing temperature control, a non-contact temperature sensor with excellent response is used for the fixing temperature sensor 14 in this embodiment. On the other hand, the edge temperature sensor 15, which is intended to detect wrapping of the printing paper PP around the fixing belt 11, does not require as quick response as the fixing temperature control, but rather requires stable detection, so a contact temperature sensor is used in this embodiment.

[0029] The control unit 40 controls the heater control circuit 41H to turn on and off the power supplied to the heater 13H and adjust the on-duty of the power supplied so that the fixing temperature detected by the fixing temperature sensor 14 falls within a predetermined range with respect to the target temperature. The on-duty is the proportion of the half-wave voltage waveform that the heater control circuit 41H applies voltage to the heater 13H out of the half-wave voltage waveform included in a predetermined period when AC power is supplied to the heater 13H, in other words, the proportion of the half-wave voltage that the heater control circuit 41H turns on.

[0030] <Detecting print paper wrapped around the fixing belt> Next, we will describe the process by which control unit 40 detects that print paper has wrapped around fixing belt 11. In this embodiment, control unit 40 determines that print paper has wrapped around fixing belt 11 using the following two methods. First, if the temperature difference between the fixing temperature detected by fixing temperature sensor 14 and the end temperature detected by end temperature sensor 15 exceeds a threshold, it determines that print paper has wrapped around fixing belt 11. Second, if the fixing temperature drops below a predetermined standard while fixing belt 11 is being heated during warm-up, it determines that print paper has wrapped around fixing belt 11.

[0031] FIG. 5 is a waveform diagram showing an example of the transitions in the fixing temperature and edge temperature when the control unit 40 determines in this embodiment that a paper jam has occurred in the fixing device 10 or downstream thereof, or that the print paper has wrapped around the fixing belt 11 using only the first method described above. The horizontal axis represents time (seconds), and the vertical axis represents temperature (°C). Note that FIG. 5 also shows the waveform of the on-duty of the heater 13H and the waveform indicating the on / off state of the rotation drive of the pressure roller 12, superimposed on the waveforms of the fixing temperature and edge temperature. FIG. 6 is a waveform diagram showing an enlarged time portion of the waveform diagram shown in FIG. 5.

[0032] As shown in FIG. 5, at time ST1, the control unit 40 determines that a paper jam has occurred and turns off the heater 13H, stopping the rotation of the pressure roller 12. Then, the operation unit 130 displays a message prompting the user to take action. When the pressure roller 12 stops, the driven fixing belt 11 also stops. When the heater 13H is turned off and no longer heated, the fixing temperature drops rapidly. Because the fixing belt 11 has a small thermal capacity, the fixing temperature detected by the fast-responding non-contact fixing temperature sensor 14 follows suit. On the other hand, the end temperature sensor 15 is a contact sensor and has a slower response than the fixing temperature sensor 14. Furthermore, because heat from the print paper wrapped around the fixing belt 11 is transferred to the end of the fixing belt 11, the change in the fixing temperature is more gradual than that of the fixing temperature.

[0033] After that, the paper is removed from the device. However, in the example shown in Figure 5, the warm-up process begins without the print paper wrapped around the fixing belt 11 being overlooked and removed. When warm-up begins, the pressure roller 12 is driven and the heater 13H is turned on. With the print paper wrapped around the fixing belt 11, the fixing temperature sensor 14 detects the temperature of the outer periphery of the wrapped print paper. Because heat from the heater 13H is supplied not only to the fixing belt 11 but also to the wrapped print paper, the apparent heat capacity of the fixing belt 11 increases, slowing the rise in the fixing temperature. Furthermore, because the heater 13H heats the fixing belt 11 from the inner periphery, it takes time for the heat supplied by the heater 13H to reach the outer periphery of the print paper. Therefore, the rise in the fixing temperature during warm-up is slower than in a normal state without the print paper wrapped around it. Print paper usually wraps around the fixing belt 11 in the paper-passing area, and does not significantly affect the non-paper-passing area where the edge temperature sensor 15 detects the edge temperature. As mentioned above, the edge temperature changes more slowly than the fixing temperature, so the transition of the edge temperature during warm-up does not change significantly from that under normal conditions.

[0034] If the fixing temperature during warm-up is lower than the end temperature by more than a predetermined threshold, the control unit 40 determines that a sheet of paper has wrapped around the fixing belt 11. In the example shown in FIG. 5, at time ST2, the control unit 40 determines that a sheet of paper has wrapped around the fixing belt 11 because the fixing temperature is lower than the end temperature by ΔT1, which is the threshold. The control unit 40 then stops the warm-up, turns off the heater 13H, stops the rotation of the pressure roller 12, and displays a message on the operation unit 130 prompting the user to take action. While the above description indicates that a sheet of paper has wrapped around the fixing belt 11 based solely on the temperature difference between the fixing temperature and the end temperature at time ST2, the occurrence of a sheet of paper may also be determined based on, for example, the cumulative temperature difference or average temperature difference over multiple points in time. In the example shown in FIG. 5, the user attempts to remove the sheet of paper wrapped around the fixing belt 11, but the sheet is not completely removed and warm-up begins. For example, there may be a situation where only one of two sheets of wrapped printing paper is removed, but the other sheet is left behind, or where warm-up begins without the wrapped printing paper being found.

[0035] Then, at ST3, a paper jam occurs, just as in ST1, and the print paper wrapped around the fixing belt 11 is overlooked and warm-up begins while the paper remains wrapped around it. As a result, at ST4, just as in ST2, the fixing temperature is lower than the edge temperature by ΔT2, which is the threshold value, so the control unit 40 determines that paper has become wrapped around the fixing belt 11 and stops warm-up. However, the print paper wrapped around the fixing belt 11 is not removed, meaning that the user starts warm-up while the paper remains wrapped around the fixing belt 11.

[0036] After the paper jam stop in ST1 and ST3, the control unit 40 correctly determined that paper wrapping had occurred based on the temperature difference between the fixing temperature during warm-up and the edge temperature. However, after the paper jam stop in ST5, when warm-up was completed and heater 13H was turned off, the edge temperature detected by edge temperature sensor 15 was lower. That is, it was even lower than the edge temperature when it was determined that paper wrapping had occurred during warm-up after the stop in ST1 and ST3, and the edge temperature was detected to be lower than the actual edge temperature of the fixing belt 11. This is because the fixing belt 11 was deflected by the accumulated paper wrapping around it, creating a gap between the edge temperature sensor 15 and the fixing belt 11 where they should be in contact, or reducing the contact pressure. Thus, even if the fixing temperature was lower than the threshold value and should have been determined to have occurred, if the reference edge temperature was detected lower than the actual value, it could be erroneously determined that paper wrapping had not occurred.

[0037] The inventors noticed that when a cumulative amount of printing paper is wound around the fixing belt 11, the rise in the fixing temperature during warm-up is slower than when the belt is normal or when only one sheet of printing paper is wound around it. As shown by "DP" in Figures 5 and 6, there is a period during which the fixing temperature drops even during warm-up. Even in normal conditions or when only one sheet of printing paper is wound around the fixing belt 11, there is a slight delay between when the heater 13H turns on during warm-up and when the fixing temperature rises. However, compared to this condition, when a thick layer of printing paper is wound around the fixing belt 11, causing deflection, the period during which the fixing temperature drops from when the heater 13H turns on until the fixing temperature rises is clearly longer. Figure 5 shows the periods during which the heater 13H is lit at approximately 100% duty as Hon1 to Hon5. The length of the period during which the fixing temperature drops initially in each period and the amount of temperature drop are clearly greater for Hon5 than for the others. For example, among the waveforms Hon1 to Hon4, the waveform Hon1 has the longest period in which the fixing temperature drops, but the drop period DP in Hon5 is clearly longer. Also, among Hon1 to Hon4, the waveform Hon3 has the largest temperature drop, but the temperature drop in Hon5 is clearly larger. In this embodiment, the control unit 40 determines that the printing paper has wrapped around the fixing belt 11 if the fixing temperature drops for more than a predetermined period or by more than a predetermined amount during warm-up, in which power equal to or greater than a predetermined duty is supplied to the heater 13H.

[0038] As described above, when printing paper wraps around fixing belt 11 and the circumferential surface of fixing belt 11 bends, the contact of end temperature sensor 15 with fixing belt 11 weakens, reducing the temperature difference between the end temperature and the fixing temperature, which can make it impossible to determine that printing paper has wrapped around it. In this embodiment, taking advantage of the fact that it takes time for heat to be transmitted from the inner periphery of fixing belt 11 to the outer periphery of the wrapped printing paper during warm-up, it is possible to determine that wrapping has occurred when the temperature of the outer periphery detected by fixing temperature sensor 14 drops below a reference value.

[0039] <Flowchart> Next, the process of the control unit 40 for determining whether paper wrapping has occurred during warm-up will be described with reference to a flowchart. FIGS. 7 and 8 are flowcharts showing the flow of the process performed by the control unit 40 for determining whether paper wrapping has occurred. As shown in FIG. 7, the control unit 40 waits for the start of warm-up (step S11) after initialization processing after turning on the power or returning from power-saving mode, or when resuming a print job interrupted due to a paper jam or the like, and then starts heating control of the heater 13H using the heater control circuit 41H (step S13). Simultaneously with the start of heating control, the control unit 40 starts monitoring the fixing temperature using the fixing temperature sensor 14 (step S15). The control unit 40 then clears a counter that counts the number of condition determinations for determining whether paper wrapping has occurred (step S17). The control unit 40 then drives the pressure roller 12 to rotate, thereby rotating the fixing belt 11 (step S19). The control unit 40 performs the following determinations during warm-up:

[0040] First, the control unit 40 determines whether or not the print paper has wrapped around the fixing belt 11 using the first wrapping detection method described above, i.e., whether or not the temperature difference between the fixing temperature detected by the fixing temperature sensor 14 and the end temperature detected by the end temperature sensor 15 exceeds a threshold (step S21). If it is determined that wrapping has occurred using the first detection method, the control unit 40 proceeds to step S37 in Fig. 7. Then, a service call is made via a network (not shown), or a message urging a service call is displayed on the operation unit 130 (step S37), and the process ends.

[0041] On the other hand, if the first detection method does not detect the occurrence of wrapping (No in step S21), the control unit 40 then uses the second wrapping detection method to determine whether wrapping of the print paper around the fixing belt 11 has occurred, based on whether the fixing temperature has dropped below a predetermined standard. The determination using the second wrapping detection method is as follows. First, the control unit 40 determines whether the heater control circuit 41H is being controlled to supply power equal to or greater than a predetermined on-duty to the heater 13H (step S23). The control unit 40 determines that wrapping of the print paper has occurred if the fixing temperature has dropped despite the supply of the predetermined power during warm-up. If the on-duty is less than the predetermined on-duty (No in step S23), the control unit 40 determines whether warm-up has ended (step S29). If warm-up has not ended (No in step S29), the process returns to the determination in step S23 and repeats the determination. On the other hand, if the warm-up is complete (Yes in step S29), a reserved print job is executed, if any, and if no print job is reserved, the process waits for an instruction to execute a print job. The process related to determining whether the print paper has wrapped around the printer during the warm-up ends, and if the next warm-up starts, the process resumes from the beginning of FIG.

[0042] If the determination in step S23 above indicates that the on-duty is equal to or greater than the predetermined value (Yes in step S23), the control unit 40 then determines whether the fixing temperature is dropping at a gradient (the amount of temperature change per unit time) greater than or equal to a predetermined gradient (step S25). If the fixing temperature is rising, maintaining its value, or dropping but not by the predetermined gradient (No in step S25), the control unit 40 proceeds to step S29 to determine whether the warm-up is complete. Depending on the result of the determination, the control unit 40 then repeats the determination in step S23 or ends the process. On the other hand, if the fixing temperature is dropping at a gradient greater than or equal to the predetermined gradient (Yes in step S25), the control unit 40 then determines whether the drop in the fixing temperature at a gradient greater than or equal to the predetermined gradient has continued for a period greater than or equal to a predetermined gradient (step S27). Because the pressure roller 12 is rotated in step S19 during the warm-up, heat is transferred to the entire circumference of the wrapped printing paper. Compared to when the pressure roller 12 is not rotating, it takes longer for heat to be transferred from the inner periphery of the fixing belt 11 to the outer periphery of the wrapped print paper. During this time, the temperature of the outer periphery detected by the fixing temperature sensor 14 drops. Using the magnitude and duration of the drop in the fixing temperature as the criteria for judgment, it is possible to determine whether or not the drop in the fixing temperature exceeds the criteria, thereby determining whether wrapping has occurred.

[0043] If the period during which the fixing temperature drops at a rate equal to or greater than the predetermined gradient does not last for a predetermined duration (No in step S27), the control unit 40 proceeds to step S29 and determines whether the warm-up has ended. Depending on the determination result, the control unit 40 repeats the determination in step S23 or terminates the process. On the other hand, if the fixing temperature drops at a rate equal to or greater than the predetermined gradient for a predetermined duration (Yes in step S23), the control unit 40 determines that the occurrence of winding has been detected by the second winding detection method and stops the rotation of the pressure roller 12 (step S31 in FIG. 7). The heater control circuit 41H then turns off the power supplied to the heater 13H, thereby terminating the heating control (step S33). Furthermore, the control unit 40 increments the counter for determining the occurrence of winding, which was cleared in step S17, by one (step S35), and determines whether the counter value exceeds a predetermined value (step S37). For example, the predetermined value is 3. If the counter value exceeds a predetermined value, it is determined that the fixing wrap of the printing paper could not be dealt with by the user, and a service call is made via a network (not shown), or a message prompting a service call is displayed on the operation unit 130 (step S39), and the process ends.

[0044] On the other hand, if the counter value is equal to or less than the predetermined value, the pressure roller 12 is rotated for a predetermined period to repeat the condition determination, thereby promoting cooling of the fixing belt 11 and the pressure roller 12 (step S41). After the predetermined period has elapsed (step S43), the rotation of the pressure roller is stopped (step S45), and the process returns to the determination of step S23 in Fig. 6. The above is the determination process regarding the occurrence of winding during warm-up executed by the control unit 40.

[0045] (Embodiment 2) In the first embodiment, it was described that the end temperature was detected as lower than it actually was due to multiple sheets of printing paper being wrapped around the fixing belt 11, causing the fixing belt 11 to flex. In this embodiment, however, a case will be described in which a skewed printing paper is wrapped around the fixing belt 11. When a skewed printing paper is wrapped around the fixing belt 11, the printing paper is wrapped around not only the paper-passing area of ​​the fixing belt 11 but also the non-paper-passing area. A portion of the wrapped printing paper may be inserted between the fixing belt 11 and the end temperature sensor 15, where the end temperature sensor 15 should be in contact with the fixing belt 11. In this case, the end temperature sensor 15 may detect a temperature lower than the actual temperature at the end of the fixing belt 11 as the end temperature. According to this embodiment, even if the wrapped printing paper is inserted between the end temperature sensor 15 and the fixing belt 11, it is determined that wrapping has occurred if the fixing temperature drops below a predetermined standard while the fixing belt 11 is being heated during warm-up, so wrapping of the printing paper around the fixing belt 11 can be reliably detected.

[0046] (Embodiment 3) In the first embodiment, edge temperature sensor 15 was a contact-type temperature sensor, but in this embodiment, edge temperature sensor 15 is a non-contact-type temperature sensor. Even if edge temperature sensor 15 is a non-contact-type temperature sensor, if deflection occurs in fixing belt 11, the amount of infrared light incident from fixing belt 11 may change compared to normal when there is no deflection, or the air flow at the detection area may change, which may cause the edge temperature to be detected as lower than the actual temperature. Furthermore, as described in the second embodiment, if printing paper that is wound skewed becomes inserted between non-contact-type edge temperature sensor 15 and fixing belt 11, the edge temperature may also be detected as lower than the actual temperature.

[0047] It should be understood that the present invention also includes any combination of the above-described aspects. In addition to the above-described embodiment, various modifications of the present invention are possible. These modifications should not be interpreted as not falling within the scope of the present invention. The present invention should include all modifications that have the meaning equivalent to the scope of the claims and that fall within the scope of the present invention. [Explanation of symbols]

[0048] 10: Fixing device, 11: Fixing belt, 12: Pressure roller, 13: Heating unit, 13B: Base, 13H: Heater, 13P: Fixing pad, 13S: Sliding sheet, 13R: Reflector, 14: Fixing temperature sensor, 15: Edge temperature sensor, 16: Peeling plate, 40: Control unit, 41H: Heater control circuit 100: Image forming apparatus, 110: Image forming section, 120: Image reading device, 111: Developing device, 112: Photosensitive drum, 113: Intermediate transfer belt device, 114: Secondary transfer device, 115: Optical scanning device, 116: Paper feed section, 117: Paper discharge tray, 130: Operation section N: Fixing nip area, PP: Printing paper, PR: Paper passing area

Claims

1. A fixing belt that is wider than the printing paper, a heating section disposed on an inner circumferential side of the fixing belt and configured to heat the fixing belt; a pressure roller that presses the printing paper against the outer peripheral surface of the heated fixing belt and causes the printing paper to pass through; a fixing temperature sensor that detects the temperature of the outer periphery of the fixing belt in a paper passing area having a width corresponding to the width of the printing paper; an edge temperature sensor that detects the temperature of the outer periphery of the fixing belt outside the paper passing area as an edge temperature; one or more control units that control heating of the fixing belt by the heating unit based on the fixing temperature and determine whether the printing paper is wrapped around the fixing belt, The control unit determines that the winding has occurred when the temperature difference between the end temperature and the fixing temperature exceeds a threshold value, or when the fixing temperature drops below a predetermined standard during warm-up while the fixing belt is being heated.

2. the fixing temperature sensor is a non-contact type temperature sensor, 2. The image forming apparatus according to claim 1, wherein the edge temperature sensor is a contact or non-contact temperature sensor.

3. a driving mechanism that drives the pressure roller under the control of the control unit; 2. The image forming apparatus according to claim 1, wherein the control unit rotates the pressure roller by the drive mechanism during the warm-up period, and causes the fixing belt to follow the rotation of the pressure roller.

4. the control unit controls the amount of power supplied to the heating unit to control heating of the fixing belt; 2. The image forming apparatus according to claim 1, wherein it is determined that the wrapping has occurred when the fixing temperature drops below a predetermined standard despite the supply of power greater than a predetermined value to the heating unit.

5. 2. The image forming apparatus according to claim 1, wherein the control unit determines that the fixing temperature has dropped when the second fixing temperature after a predetermined period of time has dropped by more than a predetermined amount from the first fixing temperature at a certain point during the warm-up.

6. A control unit of the image forming apparatus a step of heating the fixing belt using a heating unit disposed on the inner circumferential side of the fixing belt, the heating unit being wider than the printing paper; a step of using a pressure roller to press the printing paper against the outer peripheral surface of the heated fixing belt and passing the printing paper; a step of detecting, as a fixing temperature, the outer peripheral temperature of a paper passing area of ​​the fixing belt having a width corresponding to the printing paper, using a fixing temperature sensor; detecting an outer peripheral temperature of the fixing belt outside the paper passing area as an end temperature using an end temperature sensor; a wrapping determination step of controlling heating of the fixing belt by the heating unit based on the fixing temperature and determining whether or not the printing paper is wrapped around the fixing belt, The wrapping determination step is a method for detecting wrapping of printing paper around a fixing belt, in which the wrapping is determined to have occurred when the temperature difference between the end temperature and the fixing temperature exceeds a threshold value, or when the fixing temperature drops below a predetermined standard during warm-up in which the fixing belt is being heated.

Images