JP2008304503A - Fixing device, and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device and an image forming device, capable of avoiding a fixing belt from becoming an abnormally high temperature, having superior cost benefit and fixing quality. <P>SOLUTION: This fixing device/image forming device is provided with the endless fixing belt tension-laid over from a fixing roller to a heat roller 63, a thermostat 82 for blocking the electric power source of a heating element, when the fixing belt gets to the abnormally high temperature; a frame 66 having a hole 68a inserted with an end part of the heat roller 63; a bearing 91 for holding the heat roller 63 in a prescribed position in the hole 68a; and a protrusion 95, located in an inner circumferential side of the hole 68a and formed in a side arranged with the fixing roller, and the protrusion 95 abuts against the outer circumferential face of the heat roller 63 and maintains the space between the heat roller 63 and the thermostat 82 to be within a prescribed range, when the bearing 91 is softened by heat of the heating roller 63 and when the heat roller 63 is pulled to a fixing roller side by a tension of the fixing belt. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixing device that performs fixing by a belt method, and an image forming apparatus including the fixing device.

  Conventionally, as a fixing device, a heat roller type fixing device that fixes a toner transferred to a recording medium by a transfer device by a heat roller and a pressure roller with a built-in heater is generally used. This type of fixing device is often used in electrophotographic apparatuses such as copying machines, printers, and multifunction machines. This fixing device includes a heat roller provided with a halogen heater or the like inside. The heat roller is heated to a predetermined temperature by a halogen lamp, and the pressure of the pressure roller is applied to the recording medium by heat and pressure. The carried toner is melted and fixed.

  However, the heat roller type fixing device has a narrow nip width, which is sufficient for monochrome images that can be fixed in a short time. However, a sufficient nip width is sufficient for recent full-color color images. It could not be provided and could lead to poor fixing. Further, since the heat roller has a shape in which the outside of the metal core is covered with silicon rubber that is thick and has low heat conductivity, the heat capacity is large, and the heat roller type requires time for warming up and cannot be quick started. That is, most of the energy required for fixing is spent on melting the toner at the nip, but in the heat roller type, the pressure applied to the pressure roller is increased, or the diameter of the heat roller and the pressure roller is increased. However, there is a limit in securing a sufficient nip width for fixing a color image.

  Therefore, a belt-type fixing device has been proposed in place of the conventional heat roller type (see, for example, Patent Document 1). In the belt-type fixing device of this (Patent Document 1), heat is transmitted to the fixing belt stretched between the heat roller and the fixing roller by the heating element heating the heat roller. The surface temperature of the fixing belt is controlled to a constant temperature by a temperature detector and a temperature controller. The fixing belt is structured to receive heat only when it is in contact with the heat roller. After the fixing belt is heated to a high temperature, the recording medium onto which the toner image is transferred is transferred to the fixing belt and the pressure roller. It is fixed by passing it through the pressure contact part.

  In addition to this, a belt type fixing device for fixing by electromagnetic induction has also been proposed (for example, see Patent Document 2). The belt-type fixing device of this (Patent Document 2) is provided with a pressure roller that stretches a fixing belt between a support roller and a fixing roller so as to be rotatable, and is pressed against the fixing roller via the fixing belt. A nip portion is formed at a contact portion between the pressure roller and the fixing belt. The fixing belt includes a heat generating layer that is heated by electromagnetic induction of an electromagnetic induction heating device, and the heat generating layer is a mesh member made of a fibrous member containing at least a metal such as iron, stainless steel, silver, platinum, or gold. Is formed. In addition, in the point of heating a belt locally for a quick start and ensuring a nip width, any belt system of (patent documents 1 and 2) does not change.

  In such a belt type fixing device, when the phenomenon that the heating element runs away for some reason and becomes abnormally high temperature occurs, in addition to a fast rising speed, especially when a thermal fuse with a slow reaction speed is used, the fixing belt The temperature will reach an extremely high temperature in a short time. In view of this, a belt fixing device and an image forming apparatus having the belt fixing device that deal with such a problem have been proposed (see Patent Document 3 as a reference example).

In the belt fixing device of this (Patent Document 3), a thermistor is provided at the center of the heat roller, and a thermostat as a means for preventing excessive temperature rise is provided outside the minimum paper passing region 100 mm away from the axial direction of the heat roller. It is what was done. By the reliable operation of the thermostat, the temperature at the end of the heat roller is prevented from rising above the limit.
JP 2002-214963 A JP 2005-189404 A JP 2002-296955 A

  As described above, the heat roller type fixing device has a narrow nip width and cannot secure a sufficient nip width for a color image, resulting in a fixing failure and a large heat capacity. I couldn't start it.

  In this respect, the belt-type fixing device of (Patent Documents 1 and 2) can have a large nip width, and even a color image is less likely to cause fixing failure and can be quickly started. Further, the fixing device of the belt type of (Patent Document 3) is provided with a thermostat as a means for preventing excessive temperature rise, and the operation of the thermostat prevents the heating element from running away for some reason and causing an abnormally high temperature. To do.

  However, in the fixing device of (Patent Document 3), a thermistor must be provided at the center of the heat roller, and a thermostat must be provided outside the minimum paper passing area 100 mm away in the axial direction of the heat roller. In this case, a thermistor and a thermostat must be arranged between the fixing roller and the heat roller inside the endless belt, and it is inevitable to provide an auxiliary roller to secure a space for accommodating these. This left problems both in terms of manufacturing cost and in terms of downsizing the fixing device.

  To avoid this, installing the thermostat close to the heat roller (non-contact) on the outer periphery of the endless fixing belt can solve the above-mentioned problems, but the bearing deforms when the temperature becomes excessively high due to temperature runaway. When (softening), the heat roller is pulled toward the fixing roller by the tension of the belt, and the thermostat may move away from the surface of the heat roller. was there.

  Therefore, in order to solve such a problem, the present invention can avoid the fixing belt from becoming abnormally high temperature, is excellent in economical efficiency and fixing quality, and has a compact and fail-safe structure fixing device. An object is to provide an image forming apparatus provided.

  The fixing device of the present invention is stretched between a heat roller having a heating element, a pressure roller facing the pressure roller, and a surface layer made of an elastic layer, and the fixing roller and the heat roller, and is heated by the heat of the heat roller. An endless fixing belt, an overheating prevention means that is disposed in the vicinity of the heat roller and that is stretched over the stretched fixing belt, shuts off the power source of the heating element when the temperature becomes abnormally high, and a hole into which the end of the heat roller is inserted A frame provided on the outer periphery of the heat roller, a bearing for holding the heat roller at a predetermined position in a hole in the frame, and an inner peripheral side of the hole in the frame on the side where the fixing roller is disposed. The protrusion is provided on the fixing roller side by the tension of the fixing belt on which the heat roller is stretched without the bearing being softened by the heat of the heat roller. When stretched Tsu, and maintains a gap between the heat roller and the overheat prevention means in contact with the outer peripheral surface of the heat roller in a predetermined range.

  The image forming apparatus of the present invention also has an image forming unit capable of forming and developing an electrostatic latent image on a photosensitive member, and a transfer capable of transferring a toner image developed by the image forming unit to a recording medium. And a fixing device.

  According to the fixing device of the present invention and the image forming apparatus provided with the fixing device, even if the heat roller for heating the fixing belt runs out of temperature, it is possible to reliably detect the temperature and avoid an abnormally high temperature. Therefore, a fail-safe structure having excellent fixing quality, compactness and high reliability can be obtained.

  According to the first aspect of the present invention, a heat roller having a heating element, a fixing roller facing the pressure roller and having a surface layer made of an elastic layer, and stretched between the fixing roller and the heat roller, An endless fixing belt heated by the heat roller, an overheating prevention means that is placed in the vicinity of the heat roller and shuts off the power to the heating element when the tensioned fixing belt becomes abnormally hot, and the end of the heat roller is inserted A frame having a hole to be formed, a bearing provided on the outer periphery of the heat roller to hold the heat roller at a predetermined position in the hole in the frame, and the inner peripheral side of the hole in the frame on which the fixing roller is disposed The protrusion is formed on the fixing belt by the tension of the fixing belt on which the heat roller is stretched without being able to hold the heat roller by the bearing whose softening is caused by the heat of the heat roller. When pulled to the side, a fixing device and maintains the distance between the heat roller and the overheat prevention means contacts the outer peripheral surface of the heat roller and those within a predetermined range. With this structure, when the bearing softened by the heat of the heat roller cannot hold the heat roller and is pulled by the tension of the fixing belt on which the heat roller is stretched, the heat roller is fixed by the overheated and melted bearing. When moving in the contracting direction, the protrusion provided on the moving direction side comes into contact with the outer peripheral surface of the heat roller to prevent the movement. For this reason, the distance between the heat roller and the excessively rising prevention means can be maintained within a predetermined range by contacting the outer peripheral surface of the heat roller, and the heat roller becomes hot for some reason, and the bearing is softened. However, the thermostat can always operate normally with respect to the temperature of the heat roller, and can be a fail-safe fixing device that is excellent in economy and fixing quality, is compact and has high reliability.

  According to a second aspect of the present invention, in the invention according to the first aspect, the protrusions maintain the distance between the surface of the fixing belt in contact with the heat roller and the over-rise prevention means within a predetermined range. Device. With this configuration, the over-rise prevention means can always receive the heat of the fixing belt at an appropriate interval, so that the over-rise prevention means can be fixed even when the heat roller becomes hot and the bearing is softened. It can always operate normally with respect to the belt temperature.

  According to a third aspect of the present invention, there is provided the fixing device according to the first or second aspect, wherein at least two protrusions are formed at a predetermined interval on the inner peripheral side of the frame. With this configuration, even if the bearing is softened and the heat roller moves, the outer peripheral surface of the heat roller is received at two or more protrusions, that is, at two or more positions. The heat roller can be reliably positioned within a predetermined range.

  According to a fourth aspect of the present invention, in any one of the first, second, and third aspects, the height of the protrusion corresponds to a difference between the diameter of the heat roller and the diameter of the hole. The fixing device characterized by the above. With this configuration, the height corresponds to the distance from the outer peripheral side of the heat roller to the inner peripheral side of the hole, that is, the height corresponding to the radial distance existing between the outer peripheral surface of the heat roller and the inner peripheral side of the hole. Therefore, even if the bearing is softened, the heat roller will not move in the space when the protrusion hits the outer peripheral surface of the heat roller, so the position of the heat roller should be fixed within a predetermined range. Can do.

  A fifth aspect of the present invention is the fixing device according to any one of the first, second, third to fourth aspects, wherein the protrusion is covered with a bearing. With this configuration, while the temperature of the heat roller is kept normal, the bearing does not soften and covers the protrusion, so the tip of the protrusion does not contact the heat roller and the heat roller is damaged. Can be prevented.

  According to a sixth aspect of the present invention, in any one of the first, second, third, fourth, and fifth aspects, the frame is swingable about a support shaft, and the fixing belt is attached to the frame. And a biasing member for applying an appropriate tension to the fixing device. With this configuration, the tension of the fixing belt can be automatically adjusted by the swingable frame and the urging member, and since the tension applied to the fixing roller is constant and stable, fixing failure does not occur.

  According to a seventh aspect of the present invention, there is provided an image forming portion capable of forming and developing an electrostatic latent image on a photoreceptor, and a transfer capable of transferring a toner image developed by the image forming portion to a recording medium. And an image forming apparatus comprising the fixing device according to any one of claims 1, 2, 3, 4, 5, and 6. With this structure, when the bearing softened by the heat of the heat roller cannot hold the heat roller and is pulled by the tension of the fixing belt on which the heat roller is stretched, the heat roller is fixed by the overheated and melted bearing. When moving in the contracting direction, the protrusion provided on the moving direction side comes into contact with the outer peripheral surface of the heat roller to prevent the movement. For this reason, the distance between the heat roller and the excessively rising prevention means can be maintained within a predetermined range by contacting the outer peripheral surface of the heat roller, and the heat roller becomes hot for some reason, and the bearing is softened. However, the thermostat can always operate normally with respect to the temperature of the heat roller, and the image forming apparatus having a fail-safe structure that is excellent in economy and fixing quality, is compact, and has high reliability.

(Embodiment 1)
Hereinafter, a fixing belt type fixing device according to a first embodiment of the present invention and an image forming apparatus such as a copying machine, a printer, and a multi-function machine including the fixing belt will be described with reference to the drawings. The fixing device and the image forming apparatus of the present invention may be any apparatus that forms an image by an electrophotographic process in which an image is formed using toner and fixes the image using a fixing belt.

  FIG. 1 is a configuration diagram of an image forming apparatus according to Embodiment 1 of the present invention, FIG. 2 is a configuration diagram of a fixing device according to Embodiment 1 of the present invention, and FIG. 3 is a heat of the fixing device according to Embodiment 1 of the present invention. 4 is an overall perspective view when the roller is exposed, FIG. 4 is an overall perspective view when the fixing device according to the first embodiment of the present invention is disassembled, and FIG. 5 is a fixing belt of the fixing device according to the first embodiment of the present invention. FIG. 6 is a configuration diagram at the time of abnormal temperature of the fixing device according to the first embodiment of the present invention, and FIG. 7 is a detailed perspective view when the fixing device according to the first embodiment of the present invention is disassembled.

  8 is an external view of a bent frame piece of the fixing device according to the first embodiment of the present invention, FIG. 9 is an overall perspective view of a bearing of the fixing device according to the first embodiment of the present invention, and FIG. 10 is an embodiment of the present invention. FIG. 11 is a cross-sectional view showing details of the fixing device according to the first embodiment of the present invention, and FIG. 12 is a first embodiment of the present invention. FIG. 13 is an explanatory diagram showing the relationship between the protrusion and the heat roller during temperature runaway of the fixing device according to Embodiment 1 of the present invention. is there. The image forming apparatus according to the first embodiment is an image forming apparatus that forms a color image by an electrophotographic process.

  First, reference numeral 1 shown in FIG. 1 denotes a tandem color image forming apparatus, which forms a color image on a recording medium that is fed through a conveyance path A such as a sheet or an OHP (Over Head Projector) sheet. In FIG. 1, reference numeral 2 denotes an electrostatic latent image formed on the photosensitive member 21 for each color of yellow (Y), magenta (M), cyan (C), and black (B). This is an image forming unit that forms toner images with supplied toner and performs primary transfer to the intermediate transfer belt 31 in order. Reference numeral 3 denotes an intermediate transfer belt unit for secondary transfer of toner images, which are primarily transferred and stacked in the order of YMCB, onto a recording medium by a secondary transfer roller 51, and 4 denotes each photoconductor 21 with respect to the image forming unit 2. LSU (Laser Scanning Unit) 5 for forming an electrostatic latent image on the toner image, 5 is a secondary transfer portion for transferring the toner image formed on the intermediate transfer belt 31 to the recording medium, and 6 is a toner image transferred to the recording medium. 2 is a fixing unit according to the first embodiment for fixing Reference numeral 7 denotes a recording medium cassette for storing recording media such as paper and OHP, and 8 denotes a discharge unit for discharging the recording medium after color image formation. Details of these will be described later.

  The LSU 4 scans the drum of the photosensitive member 21 of each color with an image signal read by a scanner or the like, or a laser beam modulated by an image signal output from an external computer as a printer, and the electrostatic latent image of each color of YMCB. An image is formed on each photoconductor 21.

  Now, if the explanation of FIG. 1 is further continued, 9 is a pick-up roller that can take out the recording medium one by one from the cassette 7 and send it out to the conveying path A, and 10 is a registration sensor (not shown) that detects the positional deviation. This is a registration roller that corrects the tip position by applying resistance to the recording medium being conveyed. Reference numeral 11 denotes a discharge roller for discharging the recording medium on which the color image has been formed to the discharge unit 8. Reference numeral 12 denotes a double-sided printing in which the recording medium is reversed by manual feed after printing on one side, and then registered again. It is a conveying roller for returning to the inlet side of the roller 10.

  Next, details of the image forming unit 2 will be described. Reference numeral 21 denotes a photoreceptor for each color of YMCB. The photoconductor 21 is provided with an organic photoconductor (OPC) layer on the outer periphery of a cylindrical drum. The surface of the photoconductor 21 is scanned with laser light as described above, and is charged by a charger 23 (described later). An electrostatic latent image is formed on the surface of the charged photosensitive drum. Reference numeral 22 denotes a bottle containing toner of each color of YMCB. Inside the bottle 22, a stirring panel for stirring the toner is provided.

  Reference numeral 23 in FIG. 1 denotes a charger for uniformly charging the photoconductor 21 and is provided close to the photoconductor 21 for each color of YMCB. Reference numeral 24 denotes a developing roller provided for each color of YMCB that supplies toner of each color to the surface of the photoreceptor 21, and reference numeral 25 denotes a primary transfer roller to which a bias voltage is applied for transfer. A cleaning unit 26 includes a cleaning blade and a collection bottle provided around the photosensitive member 21. After the primary transfer is performed, the cleaning blade scrapes the residual toner remaining on the photoreceptor 21 and collects the toner in a toner recovery bottle.

  Here, the operation of the image forming unit 2 will be described in detail. In the image forming unit 2, the charger 23 uniformly charges the photosensitive member 21, and this charging is performed uniformly by scanning the laser beam from the LSU 4. Only the charge necessary for toner image formation remains among the charged charges, and the toner (usually negatively charged) supplied from the developing roller 24 is attached to the formed electrostatic latent image. Further, a bias voltage having a polarity opposite to that of toner (usually positive) is applied to the primary transfer roller 25, and the toner image on the photosensitive member 21 rotated by the action of the electric field is primarily transferred to the intermediate transfer belt 31. Is done. The bias voltage is voltage controlled so that transfer can be performed in the order of YMCB.

  Therefore, the intermediate transfer belt unit 3 that secondarily transfers the primary transferred toner image to a recording medium will be described. In FIG. 1, 31 is an intermediate transfer belt, 32 is a driving roller, 33 is a driven roller, and 34 is a belt cleaning unit having the same configuration as the cleaning unit 26. The intermediate transfer belt unit 3 includes an endless intermediate transfer belt 31, two rollers, a driving roller 32 and a driven roller 33 that stretch the intermediate transfer belt 31, and the intermediate transfer belt 31 sandwiched between the photosensitive member 21. And four primary transfer rollers 25 of YMCB. In addition to the driving roller 32 and the driven roller 33, a tension adjusting roller (not shown) may be separately provided to adjust the tension of the intermediate transfer belt 31.

  Now, the intermediate transfer belt 31 to which toner of four colors or less in the order of YMCB forms an image and adheres in layers is pulled and driven by the driving roller 32, and is driven around the driven roller 33 and the driving roller 32. Circulated. During this rotation operation, the toner image formed by the image forming unit 2 is transferred to the recording medium in the secondary transfer unit 5, and after the secondary transfer, the remaining toner is scraped off by the belt cleaning unit 34. Then, the charge is eliminated, and the primary transfer and the secondary transfer are performed again by repeating this process.

  Next, the secondary transfer unit 5 for secondary transfer of the toner image to the recording medium will be described. Reference numeral 51 shown in FIG. 1 denotes a secondary transfer roller constituting the secondary transfer unit 5. A driven roller 33 is also involved in this secondary transfer. The recording medium whose leading edge position is corrected by the registration roller 10 is fed between the secondary transfer roller 51 and the driven roller 33, and the toner image on the intermediate transfer belt 31 is secondarily transferred. Note that the transfer unit of the present invention includes the intermediate transfer belt unit 3 and the secondary transfer unit 5.

  The secondary transfer roller 51 of the secondary transfer unit 5 has a configuration in which a conductive elastic foam layer such as silicon rubber is formed on the outer periphery of a core metal such as stainless steel. A voltage having a polarity opposite to that of the toner is applied to the core of the secondary transfer roller 51, and the toner charged on the intermediate transfer belt 31 is transferred to the recording medium. The toner image is an unfixed state in which toners of four colors or less of YMCB are sequentially attached. Therefore, the toner is melted and fixed in the fixing unit 6.

  The fixing belt type fixing unit 6 according to the first embodiment will be described. First, the overall configuration of the fixing unit 6 will be described. 2 shows the configuration of the fixing device according to the first embodiment, FIG. 3 shows the appearance when the heat roller of the fixing device is exposed, and FIG. 4 shows the appearance when the fixing device is disassembled. 5 shows a cross section of the fixing belt, FIG. 6 shows a configuration of the fixing device at an abnormal temperature, and FIG. 7 shows a detailed configuration when the fixing device is disassembled.

  1 to 7, reference numeral 61 denotes an endless fixing belt. As shown in FIG. 5, the fixing belt 61 is basically composed of three layers described below. 61a is a surface-layer fluororesin that adheres to the toner surface while flexibly changing its shape according to the unevenness of the toner formed by the adhesion of the toner onto the recording medium, and has a property of being hard to adhere to the toner. For example, a release layer such as PFA or PTFE, 61b is an elastic layer such as silicon rubber provided on the inside of the release layer 61a and elastically absorbing unevenness of toner formed on the recording medium, and 61c is an elastic layer 61b. It is a support layer which consists of thermosetting resins, such as a polyimide which supports. The reason why the thermosetting resin is used for the support layer 61c is to apply tension (tensile force) by using a tensile force by thermosetting so that the fixing belt 61 used at a high temperature does not relax.

  1 to 7, reference numeral 62 denotes a fixing roller. 62 a is an elastic layer made of silicon rubber or the like of the fixing roller 62, and 62 b is a core metal of the fixing roller 62. Reference numeral 63 denotes a heat roller that stretches the fixing belt 61 together with the fixing roller 62 and rotates the fixing belt 61. The heat roller 63 is prevented from slipping by the action of a drive gear 94 described later. Furthermore, 62b is a metal core, and 63b is a locking groove. A pressure roller 64 presses the recording medium together with the fixing roller 62, 64a is an elastic layer such as silicon rubber, and 64b is a core metal of the pressure roller 64. The fixing roller 62 is driven by the rotation of the pressure roller 64 driven by a gear train (not shown). Since the heat roller 63 does not have an elastic layer, the heat transfer speed is fast and the time required for warming up can be shortened.

  1 to 7, reference numeral 65 denotes a heating element such as a halogen lamp which is provided in the heat roller 63 and can heat the fixing belt 61 via the cored bar 63a. Reference numeral 66 denotes a frame that rotatably supports the heat roller 63 around which the fixing belt 61 is circulated, and reference numeral 67 denotes a support shaft that rotatably supports the frame 66. 68 is a bent frame piece (see FIGS. 3 and 4) of the frame 66, 68a is a bearing hole (hole of the present invention) for supporting a bearing 91 (described later) provided on the bent frame piece 68, Reference numeral 68b denotes a support hole that is provided in the bent frame piece 68 and that supports the frame 66 so as to be able to swing through the support 67 having a round bar shape. The bent frame piece 68 is not limited to a configuration in which a part of the frame 66 is bent, but may be a configuration that is provided on the frame 66 and can support the bearing 91.

  Reference numeral 69 denotes a biasing member such as a spring for applying tension to the fixing belt 61. The fixing belt 61 stretched between the fixing roller 62 and the heat roller 63 can always set the fixing belt 61 to the best tension by the action of the urging member 69. The nip width is further pressurized by another urging member (not shown).

  By the way, in order to maintain the fixing temperature of the fixing unit 6, the temperature of the fixing belt 61 is controlled to around 170 ° C., which is about 160 ° C. to 170 ° C. in the temperature range. In FIG. 2, reference numeral 81 denotes a thermistor for controlling the temperature. The temperature detected by the thermistor 81 is fed back, and the temperature of the fixing belt 61 is maintained at around 170.degree. The thermistor 81 is provided in contact with the inner peripheral side of the fixing belt 61 and feeds back a temperature with high detection accuracy.

  However, as long as it is a machine, it cannot be said that there is no possibility of temperature runaway due to the stability of control for some reason. Therefore, apart from the thermistor 81, an excessive rise prevention means for preventing the fixing belt 61 from overheating abnormally is provided. 2, 3, and 4 are provided in a non-contact manner (for example, at an interval of about 0.7 mm) in the vicinity of the heat roller 63 on the outer peripheral side of the fixing belt 61, and if a temperature runaway occurs. This is a thermostat (an excessive rise prevention means of the present invention) that immediately shuts off the power supply. The thermostat 82 is provided in the primary circuit of the power source and directly shuts off the power source. On the other hand, the thermistor 81 is provided in the secondary circuit. The reason why the thermostat 82 is provided in a non-contact manner on the outer periphery of the fixing belt 61 is that if the temperature is detected by contacting the thermostat 82, the outer surface of the fixing belt 61 (release layer 61a, elastic layer 61b) is damaged. This is because fixing defects such as streaks occur based on the scratches.

  In the first embodiment described above, when a temperature runaway occurs for some reason and exceeds an abnormally high temperature, for example, 250 ° C., the bearing is deformed as shown in FIG. 6, and the frame 66 is energized. The member 69 rotates around the support shaft 67 to the side opposite to the fixing roller 62. At this time, since the heat roller 63 is pulled to the fixing roller 62 side by the tension of the fixing belt 61, the thermostat 82 fixed on the frame 66 moves away from the surface of the heat roller 63, and an abnormal temperature is detected by expanding the gap. A delay occurs, and a delay occurs in the start and response of the control operation.

  Note that this is not limited to the case where the bearing is only made of resin, and the same problem occurs if the bearing causes displacement at the center position of the heat roller 63 due to the action of heat. Therefore, the fixing device according to the first embodiment provides a fail-safe structure in such a case.

  Therefore, the fixing device according to the first embodiment is provided with a stopper for suppressing the displacement of the heat roller 63 within a predetermined range. 3 and 4, reference numeral 91 denotes a bearing made of a resin such as PPS, PEEK, or polyamideimide, and 91a denotes a bearing frame insertion portion. The bearing 91 is integrally formed into a shape having a bearing frame insertion portion 91a that can be inserted into the bearing hole 68a. Accordingly, the weight of the fixing device is light, excellent in economic efficiency, and easy to manufacture. Further, reference numeral 92 denotes a detent flange that prevents the fixing belt 61 from shifting to one end side of the bearing 91 and being inclined obliquely. By providing the offset flange 92, the fixing belt 61 is prevented from being skewed and broken.

  Reference numeral 93 is a retaining ring for preventing the heat roller 63 from moving in the axial direction, and 94 is a drive gear for rotating the heat roller 63 in the bearing 91 to prevent slippage. The drive gear 94 is configured such that rotation of a drive motor (not shown) is transmitted by a gear train to a plurality of output destinations through a plurality of paths, and the heat roller 63 is one of the output destinations. It is rotated by the rotation of the motor. The heat roller 63 is supported by bearings 91 fixed to the two bent frame pieces 68 of the frame 66, and the end opposite to the drive gear 94 is locked to the locking groove 63b by a retaining ring 93, thereby preventing the heat roller 63 from coming off. Done. In the two bearings 91, the respective bearing frame insertion portions 91 a are inserted into the bearing holes 68 a of the bent frame pieces 68, and the detent flange 92 disposed inside the bearing 91 is positioned at a fixed position in the longitudinal direction of the fixing belt 61. It is held and locked so as not to slip.

  4 and 7 to 13, reference numeral 95 denotes a protrusion that is provided inside the bearing hole 68 a of each bent frame piece 68 and functions as a stopper of the heat roller 63. Accordingly, the protrusion 95 is provided on the inner periphery of the bearing hole 68a on the side where the fixing roller 62 is disposed. Then, the heat roller 63 is prevented from being deformed by heat and the center of the heat roller 63 being displaced toward the fixing roller 62 side. In addition, it is preferable to provide at least two protrusions 95. If possible, two protrusions 95 may be provided, one functioning as a main stopper, and the other functioning as a secondary stopper for stabilizing the heat roller 63. If the two protrusions 95 are made to function as equivalent stoppers without attaching a master / slave to the heat roller 63, the outer periphery of the heat roller 63 enters the gap between the protrusions 95, and the amount of displacement inevitably increases. However, if such a difference in role as a stopper is given to the protrusion 95, one of them functions as a stopper earlier, and overheating of the heat roller 63 can be detected more reliably and quickly.

  In order to provide such a master / slave stopper function, the belt tension side (traction side) protrusion 95 may be brought close to the line connecting the heat roller 63 and the fixing roller 62 (by changing the distance). That is, the main stopper may be placed near this line, and the secondary stopper may be placed away from this. In other words, there is a difference in angle between the line connecting the heat roller 63 and the fixing roller 62 and the projections 95 during normal operation, a small angle with respect to the main stopper on the belt tension side, and a small angle with respect to the secondary stopper. For example, a large angle should be given. However, even when arranged equally, it has excellent properties in terms of stability other than the control purpose.

  Reference numeral 96 denotes a notch formed in the bearing frame insertion portion 91a, and can receive the protrusion 95. The height of the protrusion 95 corresponds to the difference in diameter between the heat roller 63 formed coaxially and the bearing hole 68a, which corresponds to the thickness of the bearing frame insertion portion 91a. However, the height of the protrusion 95 is smaller than the thickness by a minute width, and a small relief Δ as shown in FIG. 11 is provided so that the heat roller 63 does not contact the protrusion 95 during normal operation. ing. FIG. 8 shows the external appearance of the protrusion 95, and FIG. 9 shows the external appearance of the notch 96 of the bearing 91. FIG. 10 shows a state where the protrusion 95 is inserted into the notch 96. 11 shows a detailed cross section of FIG. 2, FIG. 12 shows the relationship between the protrusion 95 and the heat roller 63 during normal operation, and FIG. 13 shows the relationship between the protrusion 95 and the heat roller 63 during temperature runaway. Yes.

  Now, the function of the protrusion 95 will be described with reference to FIGS. 12 and 13. When there is no temperature runaway as shown in FIG. 12, there is a clearance Δ between the bearing 91 and the protrusion 95, and the heat The roller 63 does not come into contact with the protruding portion 95. However, as shown in FIG. 13, when temperature runaway occurs (for example, the temperature exceeds 200 ° C. considerably), the resin bearing 91 is deformed (softened), and the frame 66 is supported by the force of the biasing member 69. Since the heat roller 63 is rotated toward the fixing roller 62 side by the tension of the fixing belt 61, the heat roller is rotated from the thermostat 82 relatively fixed on the frame 66. 63 is pulled away, but in the fixing device of the first embodiment, the bearing 91 is deformed, and at the same time, the relief Δ disappears, and the protrusion 95 functions as a stopper. As a result, the thermostat 82 is not separated from the surface of the fixing belt 61 on the heat roller 63, and there is no delay in detection of abnormal temperature, no delay in control operation start, and response. The fixing device according to the first embodiment has a further fail-safe structure of the fixing device provided with the thermostat 82.

  As described above, according to the fixing device and the image forming apparatus of the first embodiment, even if the heat roller that heats the fixing belt runs out of temperature, it is possible to reliably detect the temperature and avoid an abnormally high temperature. Since resin is used for the roller bearings, it is economical, light and easy to mold, and the nip width can be increased due to the fixing belt system. Further, the size of the fixing unit can be made sufficiently small, and a compact fixing device and image forming apparatus can be obtained.

  In addition, the tension of the fixing belt can be automatically adjusted by using a swingable frame and a biasing member, and the tension applied to the fixing roller is constant. Since the urging member and the detent flange are provided, the fixing belt does not skew and the parts are not damaged.

  With these configurations, it is possible to improve the reliability of the fail-safe fixing device and the image forming apparatus provided with the over-rise prevention means, and to further improve the reliability of the fail-safe fixing device and the image forming apparatus. Can be provided.

  The present invention can be applied to an image forming apparatus that forms an image by an electrophotographic process using toner and a fixing device thereof.

1 is a configuration diagram of an image forming apparatus according to Embodiment 1 of the present invention. 1 is a configuration diagram of a fixing device according to Embodiment 1 of the present invention. 1 is an overall perspective view when a heat roller of a fixing device according to Embodiment 1 of the present invention is exposed. FIG. 2 is an overall perspective view of the fixing device according to the first embodiment of the present invention when disassembled. Sectional drawing of the fixing belt of the fixing device in Embodiment 1 of the present invention. 1 is a configuration diagram of the fixing device at an abnormal temperature according to Embodiment 1 of the present invention. FIG. 3 is a detailed perspective view of the fixing device in the first embodiment of the present invention when disassembled. 1 is an external view of a bent frame piece of a fixing device according to Embodiment 1 of the present invention. 1 is an overall perspective view of a bearing of a fixing device according to Embodiment 1 of the present invention. 1 is a perspective view of a bearing when a fixing device of an image forming apparatus according to Embodiment 1 of the present invention is assembled. Sectional drawing which shows the detail of the fixing device in Embodiment 1 of this invention Explanatory drawing which shows the relationship between the projection part and heat roller at the time of normal driving | operation of the fixing device in Embodiment 1 of this invention. Explanatory drawing which shows the relationship between the projection part at the time of the temperature runaway of the fixing device in Embodiment 1 of this invention, and a heat roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Image forming part 3 Intermediate transfer belt unit 4 LSU
DESCRIPTION OF SYMBOLS 5 Secondary transfer part 6 Fixing part 7 Recording medium cassette 8 Ejection part 9 Pickup roller 10 Registration roller 11 Ejection roller 12 Conveyance roller 21 Photoconductor 22 Bottle 23 Charger 24 Developing roller 25 Primary transfer roller 26 Cleaning part 31 Intermediate transfer belt 32 Drive roller 33 Follower roller 34 Belt cleaning unit 51 Secondary transfer roller 61 Fixing belt 61a Release layer 61b Elastic layer 61c Support layer 62 Fixing roller 62a Elastic layer 62b Core metal 63 Heat roller 63a Core metal 63b Locking groove 64 Pressure roller 64a Elastic layer 64b Core metal 65 Heating element 66 Frame 67 Support shaft 68 Bending frame piece 68a Bearing hole 68b Support shaft hole 69 Energizing member 81 Thermistor 82 Thermostat 91 Bearing 91a Bearing frame insertion portion 92 Detent flange 93 Retaining Ring 94 Drive Gear 95 Protrusion 96 Notch

Claims (7)

A heat roller having a heating element;
A fixing roller facing the pressure roller and having an elastic layer as a surface layer;
An endless fixing belt stretched between the fixing roller and the heat roller and heated by the heat of the heat roller;
An over-rise prevention means that is disposed in the vicinity of the heat roller and shuts off the power source of the heating element when the stretched fixing belt becomes abnormally hot,
A frame having a hole into which an end of the heat roller is inserted;
A bearing provided on an outer periphery of the heat roller to hold the heat roller at a predetermined position in a hole in the frame;
A protrusion formed on the inner peripheral side of the hole of the frame and on the side where the fixing roller is disposed,
The protruding portion is formed when the bearing is softened by heat of the heat roller and the bearing cannot hold the heat roller, and the heat roller is pulled to the fixing roller side by the tension of the stretched fixing belt. The fixing device is configured to maintain a distance between the heat roller and the over-rise prevention means within a predetermined range by contacting an outer peripheral surface of the heat roller. The fixing device according to claim 1, wherein the protrusion maintains a distance between a surface of the fixing belt contacting the heat roller and the over-rise prevention unit within a predetermined range. The fixing device according to claim 1, wherein at least two of the protrusions are formed at a predetermined interval on an inner peripheral side of the frame. The fixing device according to claim 1, wherein a height of the protrusion corresponds to a difference between a diameter of the heat roller and a diameter of the hole. The fixing device according to claim 1, wherein the protrusion is covered with the bearing. The frame is swingable about a support shaft, and the frame is provided with a biasing member for applying an appropriate tension to the fixing belt. The fixing device according to claim 4. An image forming unit capable of forming and developing an electrostatic latent image on a photoreceptor, a transfer unit capable of transferring a toner image developed by the image forming unit to a recording medium, and An image forming apparatus comprising the fixing device according to claim 3, 4, 5, or 6.