Image forming apparatus and method for detecting winding around fixing belt

Abstract

To surely detect winding when a printing sheet is wound around a fixing belt.SOLUTION: The fixing device includes a fixing belt that is wider than a print sheet, a pressure roller that presses the print sheet against a peripheral surface of the fixing belt and allows the print sheet to pass through, a fixing temperature sensor that detects a temperature of a sheet passing region of the fixing belt as a fixing temperature, the sheet passing region being a region having a width corresponding to the print sheet, an end temperature sensor that detects a temperature of the fixing belt excluding the sheet passing region as an end temperature, and a heating unit that heats at least the sheet passing region of the fixing belt. A hardware processor that determines that the print sheet is wound around the fixing belt when a difference between a fixing temperature gradient in which the fixing temperature rises in a certain period during a recovery operation from a paper jam stop and an end temperature gradient in which the end temperature rises in the corresponding period is equal to or larger than a predetermined difference threshold.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] When a jam occurs during printing, with paper wrapped around the fixing belt of the fixing device, it is difficult for the user to completely remove the jam. This requires the user to call a service engineer, resulting in significant removal costs and prolonged device downtime. In some cases, if the device is turned 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, a known method detects the temperature of the fixing belt's center and the non-conveying area along its rotation axis, and determines whether a sheet is wrapped around the fixing belt based on the temperature difference between the detected temperature at the center and the non-conveying area. For example, a thermal belt fixing device has been proposed that includes a non-contact temperature sensor located within the minimum paper feed width (center) of the fixing belt and a contact temperature sensor located in the non-conveying area (non-conveying area). It also includes a control unit that stops the heat source from generating heat if the temperature detected by the non-contact temperature sensor reaches specified temperature A but the temperature detected by the non-contact temperature detection sensor does not reach specified temperature B, and a reflective paper sensor that detects the presence or absence of paper on the belt (see, for example, Patent Document 1).

[0003] However, if a sheet (paper) wrapped around a rotating member (fixing belt) moves into a non-conveying area on the temperature detection side in the direction of the rotation axis, it is impossible to determine whether the sheet is wrapped around the rotating member based on the temperature difference between the detected temperature at the center and the detected temperature in the non-conveying area. To address this issue, a sheet heating device has been proposed that includes a first temperature detection unit that detects the temperature at a first position a first distance away from one end of the non-conveying area, and a second temperature detection unit that detects the temperature at a second position a second distance away from the other end. The presence or absence of wrapping is determined based on the first detected temperature detected by the first temperature detection unit and the second detected temperature detected by the second temperature detection unit after a certain time has elapsed since the start of rotation. This makes it possible to determine whether the sheet is wrapped around the rotating member even if the sheet moves into the non-conveying area on the temperature detection side (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-251488 [Patent Document 2] Japanese Patent Publication No. 2022-099673 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when determining whether a sheet is wrapped around the fixing belt based on the temperature difference between the center and non-conveying areas, as in Patent Document 1, even if the fixing belt is heated with the same amount of heat (energy), the temperature difference can vary significantly depending on the installation environment and the time of use. For example, when the initial temperature is low, such as early morning in the coldest season, and when the initial temperature is high, such as midday in summer, the temperature difference between the center and non-conveying areas after heating will be different. Large variations due to the installation environment and the time of use make it difficult to accurately determine whether a sheet is wrapped around the fixing belt. Furthermore, the configuration of Patent Document 2 requires two sensors to detect the temperatures of one non-transport area and the other non-transport area, in addition to a sensor to detect the temperature of the central area.

[0006] 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 wrapping 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 pressure roller that presses the printing paper against the circumferential surface of the fixing belt and passes the printing paper through it, a fixing temperature sensor that detects the temperature of a paper passage area of ​​the fixing belt that is an area of ​​a width corresponding to the printing paper as the fixing temperature, an end temperature sensor that detects the temperature of the fixing belt excluding the paper passage area as an end temperature, a heating unit that heats at least the paper passage area of ​​the fixing belt, 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 that the printing paper is wrapped around the fixing belt when the difference between the fixing temperature gradient at which the fixing temperature rises during a certain period during recovery operation from a paper jam and the end temperature gradient at which the end temperature rises during the corresponding period is greater than or equal to a predetermined difference threshold.

[0008] From a different perspective, the present invention provides a method for detecting wrapping around a fixing belt, the method comprising the steps of: one or more control units of an image forming apparatus that performs fixing using a fixing belt using a fixing temperature sensor to detect the temperature of a paper passage area of ​​the fixing belt, which is an area of ​​a width corresponding to the printing paper, as the fixing temperature; using an end temperature sensor to detect the temperature of the fixing belt excluding the paper passage area as the end temperature; using a heating unit to heat at least the paper passage area of ​​the fixing belt; controlling the heating of the fixing belt by the heating unit based on the fixing temperature; and determining that the printing paper is wrapped around the fixing belt when the difference between the fixing temperature gradient at which the fixing temperature rises during a certain period during recovery operation from a paper jam and the end temperature gradient at which the end temperature rises during a corresponding period is greater than or equal to a predetermined difference threshold. [Effects of the Invention]

[0009] The fixing device of this invention is equipped with a control unit that determines that printing paper is wrapped around the fixing belt when the difference between the fixing temperature gradient in which the fixing temperature rises during a certain period during recovery operation from a paper jam stop and the end temperature gradient in which the end temperature rises during the corresponding period is greater than a predetermined difference threshold, so that wrapping of printing paper around the fixing belt can be reliably detected. The method of detecting wrapping around a fixing belt according to the present invention also provides the same effects. [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 provided 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]10 is a waveform diagram showing an example of the transition of the fixing temperature and the edge temperature when a paper jam and wrapping of print paper occur in the first embodiment. FIG. [Figure 6] 10 is a first flowchart showing the flow when the control unit executes processing related to determining whether wrapping of print paper has occurred in the first embodiment. [Figure 7] 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 first embodiment. [Figure 8] 10 is an explanatory diagram showing an example of a data table of difference threshold values ​​for different sizes and types of printing paper in the first embodiment. FIG. [Figure 9] FIG. 10 is a waveform diagram showing an example of the transition of the fixing temperature and the edge temperature when a paper jam and wrapping of print paper occur in the second embodiment. [Figure 10] 10 is a first flowchart showing the flow when the control unit executes processing related to determining whether wrapping of print paper has occurred in the second embodiment. [Figure 11] 10 is a second flowchart showing the flow when the control unit executes processing related to determining whether wrapping of printing paper has occurred in the second embodiment. [Figure 12] FIG. 11 is an explanatory diagram showing an example of a data table of edge gradient threshold values ​​for different sizes and types of printing paper in the second embodiment. [Figure 13] FIG. 11 is an explanatory diagram showing an example of a data table of difference threshold values ​​for different sizes and types of printing paper in the second embodiment. [Figure 14] 11 is an explanatory diagram showing an example of a correction value of a difference threshold value when a power is increased / decreased in the third embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in further 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] Image forming apparatus 100 is a multifunction peripheral having a copy function, a scanner function, a facsimile function, and a printer function. It transmits an image of an original document read by image reading device 120 to an external device, and forms an image of the original document read by image reading device 120 or an image received from an external device in color or monochrome on a recording medium such as paper by image forming unit 110. Image forming unit 110 is provided with fixing device 10, developing device 111, photosensitive drum 112, intermediate transfer belt device 113, secondary transfer device 114, optical scanning device 115, paper feed unit 116, and paper discharge tray 117.

[0013] 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 toner images of four colors, each corresponding to black, cyan, magenta, and yellow.

[0014] 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 circumferential surface of the photosensitive drum 112. The toner images of each color formed on the circumferential 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.

[0015] 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.

[0016] Paper feed unit 116 has a paper feed cassette for loading printing paper, and is provided below optical scanning device 115. The printing paper is pulled out from paper feed unit 116 by a pickup roller and transported via a paper transport path to a transfer nip between intermediate transfer belt device 113 and secondary transfer device 114. After toner is transferred onto the printing paper by secondary transfer device 114, the printing paper is transported to fixing device 10, where the toner is fixed to the printing paper. After passing through fixing device 10, the printing paper is discharged onto paper output tray 117.

[0017] <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 pressure roller 12. The fixing device 10 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 within 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. Note that, although a lamp heater has been used as an example of a heat source in this embodiment, the present invention is not limited to a lamp heater. It is also possible to use a ceramic heater with multiple heating elements, a PTC heater with a positive temperature coefficient, an IH heater with an electromagnetic induction coil, etc. Naturally, the arrangement for heating the fixing belt is determined appropriately depending on the characteristics of each heater.

[0018] 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.

[0019] The pressure roller 12 is disposed at 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.

[0020] 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 receives this driving force and is driven to rotate. As the pressure roller 12 rotates, 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, because there is a small gap between the leading edge of the peeling plate 16 and the fixing belt 11, and because there is no member to regulate the position of the peeling plate 16 on the inner circumferential side of the fixing belt 11 where the leading edge of the peeling plate 16 is close, wrapping cannot be completely prevented.

[0021] The base 13B has a substantially L-shaped cross section. 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 on the outside of 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, a heat-resistant 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 is rotated in the circumferential direction, 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 friction with the fixing belt 11.

[0022] 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.

[0023] 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.

[0024] 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 outside the paper passage region PR. The paper passage region PR is the region 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 of the width of the widest print paper PP that passes through the fixing nip N on both 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 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 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.

[0025] 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 transfer nip. The control unit 40 also controls the image forming unit 110 to form a toner image, and causes the secondary transfer device 114 to transfer the toner image onto the printing paper PP.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] <Detecting print paper wrapped around the fixing belt> Next, the process by which the control unit 40 detects that print paper is wrapped around the fixing belt 11 will be described. In this embodiment, the control unit 40 stops printing when it detects a paper jam. When a user removes jammed print paper inside the machine, a recovery operation is performed to resume printing. During this recovery operation, the control unit 40 determines whether print paper is wrapped around the fixing belt 11. The determination that printing should be resumed is based on, for example, the user opening a door or cover of the image forming apparatus 100 to access the jammed print paper and then closing the door or cover. The user removes the jammed print paper inside the machine by following the illustration displayed on the operation unit 130, for example. However, if the entire print paper becomes wrapped around the fixing belt 11 from the leading edge to the trailing edge, the user may not notice the jammed print paper and may assume that all the print paper has been removed, and close the door or cover. To ensure the safety of the user accessing the jammed print paper inside the machine, the control unit 40 controls the heater control circuit 41H to turn off the heater 13H during a paper jam stop. When the return operation begins, the control unit 40 turns on the heater 13H, which had been off. Then, the pressure roller 12 is driven to rotate the fixing belt 11, and the fixing temperature, which had dropped when the heater 13H was turned off, is raised to the target temperature for printing. During this return operation, it is determined that the print paper is wrapped around the fixing belt 11 in the following manner.

[0030] FIG. 5 is a waveform diagram showing an example of the transitions in the fixing temperature and edge temperature when a paper jam and wrapping of print paper occur in this embodiment. The horizontal axis represents time (seconds), and the vertical axis represents temperature. FIGS. 6 and 7 are flowcharts illustrating the flow of the control unit 40 executing a process related to determining whether print paper is wrapped around the fixing belt 11. The flowcharts shown in FIGS. 6 and 7 can be considered as one of multiple tasks executed by the control unit 40 in a multitasking environment. As shown in FIG. 6, the control unit 40 waits for the start of a recovery operation to resume a print job interrupted due to a paper jam or other problem before performing the next process (step S11). Note that the same process as the recovery operation is also performed during warm-up after the initialization process when the power is turned on or after returning from power-saving mode. In the example waveform diagram shown in FIG. 5, the period of 6 to 10 seconds on the horizontal axis corresponds to a state in which printing is interrupted due to a paper jam or other problem, and the user opens the door and removes the jammed print paper inside the machine. When the time on the horizontal axis reaches 10 seconds and the door that was open is closed, the control unit 40 starts the heating control of the heater 13H using the heater control circuit 41H (step S13 shown in FIG. 6).

[0031] The pressure roller 12 is then driven to rotate, causing the fixing belt 11 to rotate (steps S13 and S15). At the same time as starting the heating control, the fixing temperature sensor 14 starts monitoring the fixing temperature (step S15). For a while after the fixing belt 11 starts rotating, the fixing temperature and edge temperature drop even when the heater 13H is heated. In the example waveform diagram shown in FIG. 5, the fixing temperature drops from 165°C to 140°C, and the edge temperature drops from 118°C to 116°C during the 1.5-hour period after the door is closed and the pressure roller starts to be driven. These temperature effects occur because heat is lost from the fixing belt 11 and the printing paper wrapped around it when the pressure roller 12 and the printing paper cooled by heat radiation while the roller is stopped pass through the fixing nip. Therefore, the control unit 40 may wait a predetermined period of time after the start of the recovery operation or warm-up (step S19) before detecting the wrapping of the fixing belt 11. In other words, the detection of wrapping around the fixing belt 11 may be performed after a predetermined period of time has elapsed since the start of heating control of the heater 13H or the start of driving the pressure roller 12. In this way, the presence or absence of wrapping around the fixing belt 11 can be determined after the period during which the fixing temperature and the end temperature drop due to the rotation of the fixing belt has passed, thereby enabling a stable and reliable determination. In the waveform diagram shown as an example in FIG. 5, the determination of whether the print paper is wrapped around the fixing belt 11 begins after the 1.5-second period from 10 seconds to 11.5 seconds on the horizontal axis has passed. However, as will be described below, the control unit 40 begins the determination after waiting for the on-duty of the heater 13H and the end temperature gradient to reach a predetermined state, so it is not necessary to wait for the predetermined period of time to elapse and this is optional.

[0032] In this embodiment, the control unit 40 determines whether the print paper is wrapped around the fixing belt 11 as follows: That is, it confirms that the on-duty of the power supplied to the heater 13H to heat the fixing belt 11 is equal to or greater than a predetermined value X% and that the end temperature gradient, which is the rate at which the end temperature rises per unit time due to heating, is equal to or greater than a threshold value Y (°C / sec) (Yes in step S21). Then, it starts to determine whether the print paper is wrapped around the fixing belt 11. While the on-duty is less than X% or the end temperature gradient is less than Y (°C / sec) (No in step S21), it reserves the start of the determination and waits. Also, even if the on-duty is equal to or greater than the predetermined value X% and the end temperature gradient is equal to or greater than Y (°C / sec), it reserves the determination until this state continues for Z seconds (No in step S23).

[0033] In other words, the determination of whether the print paper is wound around the fixing belt is made during a predetermined period (a period of Z seconds) during which the on-duty is equal to or greater than a predetermined value X% and the end temperature gradient is equal to or greater than Y (°C / sec). According to this aspect, by determining whether the print paper is wound around the fixing belt when the predetermined state continues for a predetermined period, stable and reliable determination becomes possible.

[0034] If the on-duty cycle remains at or above a predetermined value X% and the edge temperature gradient remains at or above Y (°C / sec) for Z seconds (Yes in step S23), the control unit 40 references the data table of difference thresholds shown in FIG. 8 and obtains a predetermined difference threshold for the type and size of print paper that meets the conditions. The type and size of print paper refer to the print paper related to the print job at the time the paper jam occurred before the start of the recovery operation. In the data table shown in FIG. 8, print paper destinations, types, and sizes are grouped, and difference thresholds are set for each group. Print paper sizes are divided into two groups, larger than B5 size and smaller than B5 size, with B5 size (182 mm x 257 mm), which is slightly smaller than A4 size (210 mm x 297 mm), as the dividing line; however, the dividing line size and number of groups are merely examples. In Europe, where B5 size is not used, the borderline size may be A5, which is slightly smaller than A4. In North America, the borderline size may be half letter size (5.5 x 8.5 inches), which is half letter size (8.5 x 11 inches), which is close to A4. The type of print paper related to the waveform diagram in FIG. 5 corresponds to "domestic" and "plain paper 1, recycled paper" in the data table shown in FIG. 8, and the print paper size corresponds to "B5 or larger." Therefore, the control unit 40 acquires the value "12" that meets these conditions as the difference threshold. This difference threshold is shown in bold in FIG. 8 (step S41 shown in FIG. 7). Applying a difference threshold according to the type and size of print paper enables a determination that is more in line with the characteristics of the print paper wrapped around the fixing belt 11 than when a uniform threshold is applied, resulting in a more stable and reliable determination.

[0035] The control unit 40 then calculates the temperature gradient ΔUM of the fixing temperature rise over a period of Z seconds and the temperature gradient ΔUS of the edge temperature rise over the same period. In the example waveform diagram shown in FIG. 5, the Z-second period for calculating the temperature gradient is 2 seconds. The initial fixing temperature during those 2 seconds is 140°C, and the final fixing temperature is 165°C. Therefore, the fixing temperature gradient ΔUM is 165-140=25°C. The initial edge temperature during the same period is 116°C, and the final edge temperature is 130°C. Therefore, the edge temperature gradient ΔUS is 130-116=14°C. The control unit 40 then calculates the difference between these temperature gradients, i.e., ΔUM-ΔUS, and compares it with the difference threshold value acquired in step S41 (step S43). If the temperature gradient difference ΔUM-ΔUS is less than the difference threshold value (Yes in step S43), the control unit 40 determines that a print sheet is wrapped around the fixing belt 11 (step S45). In the example shown in FIG. 5, ΔUM-ΔUS = 25-14 = 11°C. Because the calculated temperature gradient difference is smaller than the difference threshold value (12) acquired in step S41, the control unit 40 determines that print paper is wrapped around the fixing belt 11. Based on this determination, the control unit 40 turns off the heater 13H to stop heating and stops driving the pressure roller 12. Then, a warning is displayed on the operation unit 130 (step S47). This warning indicates that print paper is wrapped around the fixing belt and that the print paper needs to be removed. The wraparound around the fixing belt 11 detected here was an event that occurred after the user, unaware of the condition, assumed that all print paper had been removed, closed the door, and started the recovery operation. Therefore, it is preferable that the warning be a service call warning message indicating the cause of the service call, rather than a request for user action. The control unit 40 then ends the processing of this task.

[0036] On the other hand, if it is determined in step S43 that the temperature gradient difference ΔUM-ΔUS is equal to or greater than the difference threshold value (No in step S43), control unit 40 determines that the fixing belt 11 is in a normal state, with no print paper wrapped around it (step S51). In this case, control unit 40 then determines whether the fixing temperature has risen to a temperature at which printing is possible and the recovery operation has been completed (step S53). If the recovery operation has not yet been completed (No in step S53), the process returns to step S21 in FIG. 6, where it continues to determine whether print paper is wrapped around fixing belt 11. On the other hand, if the recovery operation has been completed (Yes in step S53), control unit 40 performs other tasks, such as executing the resumed print job or waiting for a print job execution request, but ends the task of determining whether print paper is wrapped around fixing belt 11. The above is an example of the process executed by the control unit 40 in this embodiment to determine whether or not a print sheet is wrapped around the fixing belt 11.

[0037] (Embodiment 2) In this second embodiment, even if the print paper is wrapped diagonally around the fixing belt 11 and becomes sandwiched between the end temperature sensor 15 and the fixing belt 11, it can be determined that the print paper is wrapped around the fixing belt 11. In this embodiment, a case will be described where the print paper is wrapped around the fixing belt 11 at an angle. When the print paper is wrapped around the fixing belt 11 at an angle, the print paper wraps around not only the paper-passing area of ​​the fixing belt 11 but also the non-paper-passing area. It is possible that part of the wrapped print paper is inserted between the end temperature sensor 15 and the fixing belt 11 at the part where the end temperature sensor 15 should be in contact with the fixing belt 11. In this case, the end temperature sensor 15 will detect a temperature lower than the actual temperature at the end of the fixing belt 11 as the end temperature.

[0038] FIG. 9 is a waveform diagram showing an example of the transition of the fixing temperature and edge temperature when a paper jam and wrapping of print paper occur in this embodiment, and corresponds to FIG. 5 in embodiment 1. The horizontal axis represents time (seconds) and the vertical axis represents temperature. Also, FIGS. 10 and 11 are flowcharts showing the flow when control unit 40 executes a process related to determining whether print paper is wrapped around fixing belt 11, and correspond to FIGS. 6 and 7 in the embodiment. Processes similar to those in FIGS. 6 and 7 are assigned similar reference numerals, and the explanation of those processes will be simplified.

[0039] 6, the control unit 40 waits for the start of the recovery operation when a print job interrupted due to a paper jam or the like is resumed (step S11), then starts controlling the heating of the heater 13H (step S13) and driving the pressure roller 12 (step S15), and monitors the changes in the fixing temperature and the end temperature (step S17).Furthermore, after waiting a predetermined period from the start of the recovery operation as an optional process (step S19), it waits for the on-duty of the heater 13H to be X% or more and the end temperature gradient to be Y (°C / sec) (step S21), and determines the temperature gradient for a period of Z seconds (step S23).

[0040] If the state in which the on-duty is equal to or greater than a predetermined value X% and the end temperature gradient is equal to or greater than Y (°C / sec) continues for Z seconds (Yes in step S23), the control unit 40 first references a data table relating to a threshold value (end temperature gradient threshold) of the end temperature gradient ΔUS predetermined for the type and size of printing paper, as shown in FIG. 12. Then, the control unit 40 compares the end temperature gradient ΔUS for Z seconds with the end temperature gradient threshold value for the corresponding condition in the data table shown in FIG. 12 (step S31 shown in FIG. 11). If the end temperature gradient ΔUS is equal to or greater than the end temperature gradient threshold value (Yes in step S31), the control unit 40 references Table A of the two difference threshold data tables (Table A and Table B) shown in FIG. 13 as the data table relating to the difference threshold value (step S33). Note that Table A shown in FIG. 13 is the same as the data table relating to the difference threshold value in the first embodiment. Table B has a larger threshold value than Table A. On the other hand, if the end temperature gradient ΔUS is less than the end temperature gradient threshold (No in step S31), table B shown in Fig. 13 is referenced as a data table relating to the difference threshold (step S35). According to this embodiment, different difference thresholds are applied depending on the magnitude of the end temperature gradient during a period of Z seconds, and it is determined whether or not the print paper is wrapped around the fixing belt 11. By doing so, even if the print paper is inserted between the end temperature sensor 15 and the fixing belt 11 and the detected end temperature is higher than the actual temperature, it is possible to reliably detect that the print paper is wrapped around the fixing belt 11.

[0041] In the example shown in Figure 12, the type of printing paper is "domestic" and "plain paper 1, recycled paper", the size of the printing paper is "B5 or larger", and the value "8" that meets the conditions is acquired as the threshold value for the edge temperature gradient (edge ​​temperature gradient threshold = 8°C). On the other hand, in the example of the waveform diagram shown in Figure 9, the edge temperature gradient over Z seconds is 113°C at the beginning and 120°C at the end, so the edge temperature gradient ΔUS = 7°C. Therefore, Edge temperature gradient ΔUS=7℃ < Edge temperature gradient threshold=8℃ Therefore, the control unit 40 refers to table B as a data table relating to the difference threshold in the waveform example of Fig. 9, and acquires the value "20" that satisfies the relevant condition.

[0042] The transition process is the same as in FIG. 7. The control unit 40 calculates the temperature gradient ΔUM of the fixing temperature increase over a period of Z seconds and the temperature gradient ΔUS of the edge temperature increase over the same period. In the waveform diagram example shown in FIG. 9, the Z-second period for calculating the temperature gradient is 2 seconds, the same as in the example of FIG. 5. The fixing temperature during those 2 seconds is 140°C at the beginning and 165°C at the end. Therefore, the fixing temperature gradient ΔUM is 165-140=25°C. Furthermore, the edge temperature during the same period is 113°C at the beginning and 120°C at the end. Therefore, the edge temperature gradient ΔUS is 120-113=7°C. The control unit 40 calculates the difference between these temperature gradients, i.e., ΔUM-ΔUS, and compares it with the difference threshold value acquired in step S41 (step S43). If the temperature gradient difference ΔUM-ΔUS is less than the difference threshold value (Yes in step S43), the control unit 40 determines that the print paper is wrapped around the fixing belt 11 (step S45). In the example shown in FIG. 9, ΔUM-ΔUS=25-7=18°C. The calculated temperature gradient difference is smaller than the difference threshold value (20) of Table B acquired in step S35, so control unit 40 determines that a print sheet is wrapped around fixing belt 11. In accordance with this determination, control unit 40 turns off heater 13H to stop heating, stops driving pressure roller 12, and displays a warning on operation unit 130 (step S47). Then, processing of this task ends.

[0043] On the other hand, if the determination in step S43 above shows that the temperature gradient difference ΔUM-ΔUS is equal to or greater than the difference threshold (No in step S43), the control unit 40 determines that the fixing belt 11 is in a normal state, with no print paper wrapped around it (step S51). In this case, the control unit 40 determines whether the recovery operation is complete (step S53). If the recovery operation is not yet complete (No in step S53), the process returns to step S21 in FIG. 10. If the recovery operation is complete (Yes in step S53), the control unit 40 performs other tasks, such as executing the resumed print job or waiting for a print job execution request, but ends the task of determining whether print paper is wrapped around the fixing belt 11. The above is an example of the process performed by the control unit 40 in this embodiment to determine whether print paper is wrapped around the fixing belt 11.

[0044] (Embodiment 3) The data table of difference thresholds according to the first embodiment shown in Fig. 8 and the data table of difference thresholds according to the second embodiment shown in Fig. 13 define difference thresholds according to the type and size of printing paper. In this embodiment, correction is also described that takes into account the state of the power source (usually a power source from the grid) that supplies power to the heater 13H. The power source that supplies power to the heater 13H normally has a rated voltage, but may be in a state of reduced power or, conversely, increased power depending on the state of the grid power and the surrounding environment in which the image forming apparatus is installed.

[0045] The control unit 40 controls the on-duty of the power supplied to the heater 13H based on the fixing temperature detected by the fixing temperature sensor. However, even with the same on-duty, if the power is reduced during the recovery operation, the fixing temperature gradient and the end temperature gradient, in which the fixing temperature and the end temperature increase, become smaller than when the power is at rated voltage. Conversely, if the power is increased, the fixing temperature gradient and the end temperature gradient become larger than when the power is at rated voltage. The difference ΔUM-ΔUS also shows a similar tendency. Therefore, in this embodiment, the difference threshold is corrected according to the degree of increase or decrease in the power supply voltage so that appropriate judgment results can be obtained even when the power supply voltage fluctuates.

[0046] Fig. 14 shows an example of a data table that determines the value for correcting the differential threshold value according to the level of increase or decrease in the power supply voltage in this embodiment. In Fig. 14, the level of increase or decrease in the power supply voltage is determined to be two levels in the decreasing direction. That is, rated voltage × 106% ≦ V AC < Rated voltage × 111% range: weak increase in voltage, Rated voltage × 111%≦V AC <The range of rated voltage x 121% is defined as a strong power increase. Also, rated voltage x 89% <V AC < Rated voltage ≦ 94% range: weak reduction, rated voltage × 79% <V AC The range of ≦rated voltage × 89% is defined as strong voltage reduction. A correction value for the difference threshold is then defined for each stage. The correction value is applied regardless of whether difference threshold table A or B is used. In other words, it is a correction value common to difference threshold tables A and B. According to this embodiment, when the power supply voltage increases or decreases from the rated voltage, the difference threshold value is corrected depending on whether the power supply voltage is within the rated range or outside the rated range, for example, depending on whether the power supply voltage is in a reduced or increased state and the degree of this reduction or increase. This correction makes it possible to obtain an appropriate determination result as to whether or not print paper has wrapped around fixing belt 11, even if the power supply voltage fluctuates.

[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 pressure roller that presses the printing paper against the peripheral surface of the fixing belt and causes the printing paper to pass through; a fixing temperature sensor that detects the temperature of a paper passage area of ​​the fixing belt, which is an area with a width corresponding to the width of the printing paper, as a fixing temperature; an end temperature sensor that detects the temperature of the fixing belt excluding the paper passing area as an end temperature; a heating section that heats at least a paper passing area of ​​the fixing belt; An image forming apparatus comprising one or more control units that control the heating of the fixing belt by the heating unit based on the fixing temperature, and determine that the printing paper is wrapped around the fixing belt when the difference between the fixing temperature gradient in which the fixing temperature rises during a certain period during recovery operation from a paper jam stop and the end temperature gradient in which the end temperature rises during a corresponding period is greater than or equal to a predetermined difference threshold.

2. 2. The image forming apparatus according to claim 1, wherein the period is a period of a predetermined length, during which the control unit controls heating so that the heating unit emits a heat quantity equal to or greater than a predetermined value per hour, and during which an end temperature gradient equal to or greater than a predetermined lower limit value is obtained.

3. The image forming apparatus according to claim 1, wherein the control unit drives the pressure roller to rotate the fixing belt during recovery from a paper jam, and after a predetermined period of time has elapsed since the start of the drive, determines whether the printing paper is wrapped around the fixing belt using the difference between the fixing temperature gradient and the end temperature gradient.

4. 2. The image forming apparatus according to claim 1, wherein the control unit makes the determination by applying a different difference threshold value depending on at least one of the size and type of printing paper involved in the paper jam.

5. The image forming apparatus according to claim 1 , wherein the control unit makes the determination by applying a different difference threshold value depending on the magnitude of the edge temperature gradient during the period.

6. the heating unit heats the fixing belt with power supplied from a power source; 2. The image forming apparatus according to claim 1, wherein the control unit controls the power supplied to the heating unit and corrects the value of the difference threshold depending on whether the voltage of the power supply is within a rated range or outside the rated range.

7. One or more control units of an image forming apparatus that performs fixing using a fixing belt, a step of detecting, as a fixing temperature, the temperature of a paper passing area of ​​the fixing belt, which is an area having a width corresponding to a printing paper, using a fixing temperature sensor; detecting a temperature of the fixing belt excluding the paper passing area as an end temperature using an end temperature sensor; heating at least a paper passing region of the fixing belt using a heating unit; controlling heating of the fixing belt by the heating unit based on the fixing temperature; and determining that the printing paper is wrapped around the fixing belt when the difference between the fixing temperature gradient in which the fixing temperature rises during a certain period during recovery operation from a paper jam stop and the end temperature gradient in which the end temperature rises during a corresponding period is equal to or greater than a predetermined difference threshold.

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