Fixing device and image forming apparatus

Abstract

To easily check the attachment in a normal posture of an urging member that urges a heat-sensitive element in a direction approaching a planar heater.SOLUTION: A thermistor 40 (heat-sensitive element) is provided, which is in contact with a surface of a planar heater 24 on the opposite side of a surface forming a nip part. Further provided are a compression spring 47 (urging member) that urges the thermistor 40 in a direction approaching the planar heater 24, and a stay 30 that supports a holder 23 to hold the compression spring 47. A hook-shaped part 47a (interlocking part) interlocks with a change in the posture of the compression spring 47 held inside the stay 30, and projects to the outside from a penetration part 30a of the stay 30.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a fixing device equipped with a planar heater, and an image forming apparatus equipped with the fixing device, such as a copying machine, a printer, a facsimile machine, or a combination machine thereof. [Background technology]

[0002] BACKGROUND ART Conventionally, in fixing devices in image forming apparatuses such as copiers and printers, there have been known devices that use a planar heater (heat generating resistor) as heating means for heating a fixing belt (see, for example, Patent Document 1).

[0003] In detail, the fixing device of Patent Document 1 is composed of a fixing belt, a pressure roller (pressure rotating body), a planar heater (heater) that is pressed against the pressure roller via the fixing belt, a holder (heater holder) that holds the planar heater, a stay that holds and reinforces the holder, and a heat-sensitive element (thermostat, thermistor) that detects excessive temperature rise and temperature of the planar heater. The pressure roller is then driven to rotate by a driving means, and the fixing belt is also rotated (co-rotated) in accordance with the rotation of the pressure roller due to frictional resistance with the pressure roller at the nip portion. The fixing belt is then heated by a planar heater whose temperature is controlled by a thermal element, and the toner image on the sheet being transported toward the nip portion is fixed onto the sheet by receiving heat and pressure at the nip portion.

[0004] On the other hand, Patent Document 1 discloses a technique for forming an opening on the side of a stay in order to prevent a short circuit between the stay and the thermostat and to reduce the size of the stay. Summary of the Invention [Problem to be solved by the invention]

[0005] In conventional technology, when a biasing member such as a compression spring that biases a heat-sensitive element such as a thermistor or thermostat toward a surface heater is installed inside a stay, it is difficult to confirm whether the biasing member is installed in the correct position.

[0006] This invention has been made to solve the above-mentioned problems, and aims to provide a fixing device and an image forming device that make it easy to confirm that the urging member that urges the thermal element in the direction toward the planar heater is installed in the correct position. [Means for solving the problem]

[0007] The fixing device of this invention comprises a planar heater extending in the width direction, a fixing belt heated by the planar heater, a pressure rotating body that forms a nip portion through which a sheet is transported by being pressed against the planar heater via the fixing belt, a holder that holds the planar heater, a heat-sensitive element that directly or indirectly contacts or faces the surface of the planar heater opposite the surface that forms the nip portion, a biasing member that biases the heat-sensitive element in a direction approaching the planar heater, and a stay that supports the holder and holds the biasing member, and the linkage portion that links to a change in posture of the biasing member held inside the stay is configured to either protrude to the outside from a penetration portion of the stay or be located in the penetration portion. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a fixing device and an image forming apparatus in which it is easy to confirm that the urging member that urges the thermal element in the direction toward the planar heater is installed in the correct position. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention; [Figure 2] FIG. 2 is a diagram illustrating a configuration of a fixing device. [Figure 3] FIG. 2 is a top view of the fixing device as viewed in the width direction. [Figure 4] FIG. 2 is a schematic side view showing the fixing belt and the guide member in the width direction. [Figure 5] FIG. 2 is a view showing the plane heater in the width direction. [Figure 6] FIG. 2 is an enlarged view showing the vicinity of a planar heater and a thermistor. [Figure 7] FIG. 10 is an enlarged view showing the vicinity of a sheet heater and a thermistor in a fixing device as a comparative example. [Figure 8] 10 is an enlarged view showing the vicinity of a planar heater and a thermistor in a fixing device according to a first modified example. FIG. [Figure 9] 10 is an enlarged view showing the vicinity of a sheet heater and a thermistor in a fixing device according to a second modified example. FIG. [Figure 10] 11 is an enlarged view showing the vicinity of a sheet heater and a thermistor in a fixing device according to a third modified example. FIG. [Figure 11] FIG. 10 is an enlarged view showing the vicinity of a planar heater and a thermistor in a fixing device according to a fourth modified example. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and redundant explanations will be appropriately simplified or omitted.

[0011] First, the overall configuration and operation of an image forming apparatus 1 will be described with reference to FIG. 1, the image forming apparatus 1 in this embodiment is a tandem color printer. Four toner bottles 102Y, 102M, 102C, and 102K corresponding to the respective colors (yellow, magenta, cyan, and black) are detachably (replaceably) installed in a bottle storage section 101 located at the top of the image forming apparatus main body 1. An intermediate transfer unit 85 is disposed below the bottle storage section 101. Opposite to the intermediate transfer belt 78 of the intermediate transfer unit 85, image forming sections 4Y, 4M, 4C, and 4K corresponding to each color (yellow, magenta, cyan, and black) are arranged side by side.

[0012] Each of the image forming units 4Y, 4M, 4C, and 4K is provided with a photosensitive drum 5Y, 5M, 5C, and 5K, respectively. Also, a charging unit 75, a developing unit 76, a cleaning unit 77, a charge removing unit, etc. are provided around each of the photosensitive drums 5Y, 5M, 5C, and 5K. Then, an image forming process (charging process, exposure process, developing process, transfer process, cleaning process) is performed on the surface of each of the photosensitive drums 5Y, 5M, 5C, and 5K, and an image of each color is formed on the surface of each of the photosensitive drums 5Y, 5M, 5C, and 5K.

[0013] The photosensitive drums 5Y, 5M, 5C, and 5K are rotated by a motor in the clockwise direction in Fig. 1. Then, at the position of the charging unit 75, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K are uniformly charged (charging process). Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the irradiation position of the laser light L emitted from the exposure unit 3, and an electrostatic latent image corresponding to each color is formed by exposure scanning at this position (this is the exposure process).

[0014] Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach positions facing the developing unit 76, where the electrostatic latent images are developed to form toner images of the respective colors (developing step). Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach positions facing the intermediate transfer belt 78 and first transfer bias rollers 79Y, 79M, 79C, and 79K, and at these positions the toner images on the photosensitive drums 5Y, 5M, 5C, and 5K are transferred onto the intermediate transfer belt 78 (this is the primary transfer step). At this time, a small amount of untransferred toner remains on the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K.

[0015] Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach a position facing the cleaning unit 77, at which point the untransferred toner remaining on the photosensitive drums 5Y, 5M, 5C, and 5K is mechanically collected by the cleaning blade of the cleaning unit 77 (cleaning process). Finally, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach positions facing the charge removal units, where the residual potential on the photosensitive drums 5Y, 5M, 5C, and 5K is removed. Thus, a series of image forming processes performed on the photosensitive drums 5Y, 5M, 5C, and 5K is completed.

[0016] Thereafter, the toner images of each color formed on each photosensitive drum through the development process are transferred in a superimposed manner onto the surface of the intermediate transfer belt 78. In this way, a color image is formed on the intermediate transfer belt 78. Here, the intermediate transfer unit 85 is composed of the intermediate transfer belt 78, four primary transfer bias rollers 79Y, 79M, 79C, and 79K, a secondary transfer backup roller 82, a cleaning backup roller 83, a tension roller 84, and an intermediate transfer cleaning section 80. The intermediate transfer belt 78 is stretched and supported by three rollers 82 to 84, and is moved endlessly in the direction of the arrow in FIG. 1 by the rotational drive of one roller 82.

[0017] The four primary transfer bias rollers 79Y, 79M, 79C, and 79K sandwich the intermediate transfer belt 78 between themselves and the photosensitive drums 5Y, 5M, 5C, and 5K, respectively, to form primary transfer nips. A transfer bias opposite in polarity to the toner is applied to the primary transfer bias rollers 79Y, 79M, 79C, and 79K. The intermediate transfer belt 78 then travels in the direction of the arrow and passes through the primary transfer nips of the primary transfer bias rollers 79Y, 79M, 79C, and 79K in sequence. In this way, the toner images of each color on the photosensitive drums 5Y, 5M, 5C, and 5K are primarily transferred onto the intermediate transfer belt 78 in a superimposed manner.

[0018] Thereafter, the intermediate transfer belt 78, onto which the toner images of each color have been transferred and superimposed, reaches a position facing the secondary transfer roller 89. At this position, the secondary transfer backup roller 82 sandwiches the intermediate transfer belt 78 between itself and the secondary transfer roller 89, forming a secondary transfer nip. The four-color toner images formed on the intermediate transfer belt 78 are then transferred onto the sheet P that has been transported to the position of this secondary transfer nip. At this time, untransferred toner that has not been transferred to the sheet P remains on the intermediate transfer belt 78. Thereafter, the intermediate transfer belt 78 reaches the position of the intermediate transfer cleaning unit 80. At this position, untransferred toner on the intermediate transfer belt 78 is collected. Thus, the series of transfer processes performed on the intermediate transfer belt 78 is completed.

[0019] Here, the sheet P transported to the position of the secondary transfer nip is transported from the feeding section 12 arranged below the image forming apparatus main body 1 via a transport path arranged on the side of the image forming apparatus main body 1 (on which a paper feed roller 97, a pair of registration rollers 98, a fixing device 20, etc. are arranged). More specifically, a plurality of sheets P such as paper are stacked and stored in the feeding section 12. When the paper feed roller 97 is rotated counterclockwise in FIG. 1, the topmost sheet P is fed toward between the pair of registration rollers 98.

[0020] The sheet P conveyed to the registration roller pair 98 stops temporarily at the roller nip position of the registration roller pair 98, which has stopped rotating. Then, the registration roller pair 98 is rotated in synchronization with the color image on the intermediate transfer belt 78, and the sheet P is conveyed toward the secondary transfer nip. In this way, the desired color image is transferred onto the sheet P.

[0021] Thereafter, the sheet P onto which the color image has been transferred at the secondary transfer nip position is conveyed to the position of the fixing device 20. Then, at this position, the color image transferred onto the surface is fixed onto the sheet P by the heat and pressure of the fixing belt 21 and the pressure roller 31 (fixing process). Then, the sheet P sent out from the fixing device 20 is discharged from the device through a discharge port A by a pair of discharge rollers 99. The sheets P discharged from the discharge port by the pair of discharge rollers 99 are sequentially stacked on a stack unit 100 as output images. In this way, a series of image forming processes (printing operations) in the image forming apparatus is completed. The image forming apparatus 1 in this embodiment is provided with a double-sided conveying path for conveying the sheet P after single-sided printing toward the secondary transfer nip when printing on both sides of the sheet P. In addition, the image forming apparatus 1 in this embodiment is provided with an opening / closing cover 110 that can rotate around a support shaft 110a along with part of the double-sided path, and the fixing device 20, which is exposed when the opening / closing cover 110 is open, can be attached and detached to the image forming apparatus main body 1.

[0022] Next, the configuration and operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail with reference to FIGS. The fixing device 20 is a device that heats and conveys the sheet P (a sheet carrying unfixed toner). 2 to 4, the fixing device 20 is composed of a fixing belt 21 as a fixing rotor, a planar heater 24 as a heating means (heat source), a pressure roller 31 as a pressure rotor, a thermistor 40 as a heat-sensitive element, a bracket 41 that holds the thermistor 40, a compression spring 47 as a biasing member, and the like.

[0023] Here, the fixing belt 21 is an endless belt member that contacts the outside of the pressure roller 31 and rotates in accordance with the rotation of the pressure roller 31. The fixing belt 21 is a thin, flexible endless belt that rotates (rotates in a driven manner) in the direction of the arrow (counterclockwise) in Fig. 2. The fixing belt 21 has a base layer, an elastic layer, and a release layer laminated in this order from the inner circumferential surface (the surface that comes into contact with the planar heater 24), and the overall thickness is set to 1 mm or less. The base material layer of the fixing belt 21 has a thickness of 30 to 50 μm and is made of a metal material such as nickel or stainless steel, or a resin material such as polyimide. The elastic layer of the fixing belt 21 has a thickness of 100 to 300 μm and is made of a rubber material such as silicone rubber, foamed silicone rubber, fluororubber, etc. By providing the elastic layer, minute irregularities are prevented from being formed on the surface of the fixing belt 21 at the fixing nip, heat is transferred uniformly to the toner image on the sheet P, and the occurrence of an orange peel image is suppressed. The release layer of the fixing belt 21 has a layer thickness of 5 to 50 μm and is made of a material such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, PES (polyethersulfone), etc. Providing the release layer ensures releasability (separability) for toner (toner image). In this embodiment, the fixing belt 21 is formed with an elastic layer, but it is also possible to use a fixing belt in which a release layer (surface layer) is formed on a base layer without forming an elastic layer.

[0024] On the inside (inner peripheral surface side) of the fixing belt 21, a sheet heater 24, a holder 23, a stay 30, a thermistor 40, a bracket 41, a compression spring 47, and the like are provided. Here, the sheet heater 24 is disposed so as to extend in the width direction (the direction perpendicular to the plane of FIG. 2, the left-right direction in FIGS. 3 and 4, and the up-down direction in FIG. 5). The sheet heater 24 is in pressure contact with the pressure roller 31 via the fixing belt 21 on the inside (inner peripheral surface side) of the fixing belt 21, forming a nip portion (fixing nip) through which the sheet P is conveyed. That is, the sheet heater 24 is disposed so as to be in sliding contact with the inner peripheral surface of the fixing belt 21. The sheet heater 24 is in pressure contact with the pressure roller 31 via the fixing belt 21, thereby forming a nip portion through which the sheet P is conveyed. In this way, the sheet heater 24 functions as a member (nip portion-forming member) that forms the nip portion (fixing nip). Note that, in order to reduce sliding resistance with the fixing belt 21, the surface of the sheet heater 24 may be covered with a sheet-like member or provided with a surface layer made of a low-friction material such as PTFE. Furthermore, a resistor pattern 26 (see FIG. 5, etc.) is formed on the portion of the sheet heater 24 that comes into sliding contact with the inner circumferential surface of the fixing belt 21. Electric power is supplied to the resistor pattern 26 (heating resistor) from a power supply unit (not shown), and the resistor pattern 26 generates heat due to its resistance, thereby heating the fixing belt 21. In this way, the sheet heater 24 also functions as a heating means (heat source) that heats the fixing belt 21.

[0025] In this embodiment, the sheet heater 24 is held by a holder 23 (holding member). The holder 23 has a recess formed therein, and the sheet heater 24 is fitted into the recess, thereby holding the sheet heater 24 across the width. The holder 23 is held by a stay 30 while holding the planar heater 24. The stay 30 holding the planar heater 24 and the holder 23 has both widthwise ends held by a housing 43 of the fixing device 20 via flange members 42 (see FIG. 3, etc.). The stay 30 is also configured to hold a compression spring 47, which will be described in detail later.

[0026] In this way, the fixing belt 21 is directly heated by the planar heater 24 (resistor pattern 26) installed inside the fixing belt 21. Then, heat is applied to the toner image on the sheet P from the surface of the heated fixing belt 21. Here, the output control of the planar heater 24 is performed based on the temperature detection results of the thermistor 40 that is in direct contact (or indirectly via another member) with the planar heater 24. In this embodiment, no temperature sensor is provided that directly detects the surface temperature of the fixing belt 21, and the thermistor 40 controls the temperature of the planar heater 24, thereby indirectly controlling the surface temperature (fixing temperature) of the fixing belt 21 to a desired temperature. The configurations and operations of the sheet heater 24 and the thermistor 40 will be described in more detail later with reference to FIGS.

[0027] Referring to FIG. 4, the pair of flange members 42 guide both widthwise ends of the fixing belt 21 from the inner peripheral surface side so that the fixing belt 21 is maintained in a substantially cylindrical position. More specifically, the two flange members 42 are made of a heat-resistant resin material or the like, and are held so as to be slidable in a direction to form a nip portion (fixing nip) at both widthwise ends of the housing 43 of the fixing device 20. The flange members 42 are provided with a guide portion 42a for holding the fixing belt 21 while maintaining the substantially cylindrical posture of the fixing belt 21, a stopper portion for restricting movement of the fixing belt 21 in the widthwise direction (toward the belt), and the like. In addition, in this embodiment, as shown in Figure 3, the fixing belt 21 (and the planar heater 24 and holder 23) is configured to be pressed against the pressure roller 31 by pressure applied by the pressure lever 52 (pressure mechanism 51) via the flange member 42. The flange members 42 are arranged at both ends in the width direction within a circumferential range excluding the fixing nip so as not to interfere with the formation of the fixing nip by the planar heater 24 . Furthermore, in this embodiment, the only members that come into contact with the inner circumferential surface of the fixing belt 21 are the flange members 42 that come into loose contact at both ends in the width direction, and the planar heater 24; there are no other members (belt guides) that come into contact with the inner circumferential surface and guide the rotation of the fixing belt 21.

[0028] In this embodiment, the stay 30 is installed inside the fixing belt 21 so as to contact the pressure roller 31 via the planar heater 24 (and the holder 23) and the fixing belt 21. The stay 30 reinforces the strength of the planar heater 24 (and the holder 23) that forms the fixing nip, and is installed on the housing 43 (or the holder 23) by screw fastening or the like. The stay 30 contacts the pressure roller 31 via the planar heater 24 (and holder 23) and the fixing belt 21, thereby preventing the planar heater 24 (and holder 23) from being significantly deformed in the fixing nip due to the pressure of the pressure roller 31. To fulfill the above-mentioned functions, the stay 30 is preferably made of a metal material with high mechanical strength, such as stainless steel or iron.

[0029] The holder 23 may be made of a resin material or a metal material, but is preferably made of a resin material (such as liquid crystal polymer (LCP), polyamideimide (PAI), polyethersulfone (PES), polyphenylene sulfide (PPS), polyethernitrile (PEN), polyetheretherketone (PEEK), etc.) that is rigid enough not to bend significantly even when subjected to the pressure of the pressure roller 31 and has thermal and heat insulating properties. In this embodiment, the holder 23 is made of a liquid crystal polymer (LCP).

[0030] Referring to Figure 2, the pressure roller 31 as a pressure rotating body has an elastic layer 33 provided on a core metal 32 (shaft portion), and is driven to rotate in a predetermined direction (clockwise in Figure 2) by a drive motor (not shown). The core metal 32 of the pressure roller 31 is a hollow structure made of a metal material. The elastic layer 33 of the pressure roller 31 is made of a material such as foamed silicone rubber, silicone rubber, or fluororubber. A thin release layer made of PFA, PTFE, or the like may be provided on the surface of the elastic layer 33. The pressure roller 31 presses against the fixing belt 21 to form a desired nip (fixing nip) between the two members. Referring to FIG. 3, the pressure roller 31 is provided with a gear 45 that meshes with the drive gear of the drive motor, and the pressure roller 31 is driven to rotate in the direction of the arrow (clockwise) in FIG. 2. Both widthwise ends of the pressure roller 31 are rotatably supported by a housing 43 of the fixing device 20 via bearings.

[0031] The normal operation of the fixing device 20 configured as described above will now be briefly described. When the power switch of the device main body 1 is turned on, power is supplied to the planar heater 24, and the pressure roller 31 starts to rotate in the direction of the arrow in Fig. 2. As a result, the frictional force with the pressure roller 31 at the fixing nip causes the fixing belt 21 to rotate (co-rotate) in the direction of the arrow in Fig. 2. Thereafter, the sheet P is fed from the feeding section 12, and an unfixed color image is carried (transferred) onto the sheet P at the position of the secondary transfer roller 89. The sheet P carrying the unfixed image (toner image) is conveyed in the direction of arrow Y10 in FIG. 2 while being guided by a guide plate, and is sent into the nip portion (fixing nip) between the fixing belt 21 and the pressure roller 31, which are in a pressure-contact state. The toner image is fixed onto the surface of the sheet P by heating from the fixing belt 21 heated by the planar heater 24 and by the pressing force of the planar heater 24 (and the holder 23) reinforced by the stay 30 and the pressure roller 31. Thereafter, the sheet P sent out from the fixing nip is transported in the direction of the arrow Y11.

[0032] Referring to Figure 5, the planar heater 24 in this embodiment is formed of a substrate 25 (base portion), a resistor pattern 26 (heating resistor), a conductor pattern 27 (relay portion), a power supply electrode 28 as an electrode, and the like. At least the front surface (the surface facing the inner circumferential surface of the fixing belt 21 in the nip portion) of the base material 25 is made of an insulating material. In this embodiment, the base material 25 is entirely made of an insulating material (in this embodiment, aluminum nitride (AIN)). The resistor pattern 26 is formed on the front surface of the substrate 25. Similarly, the conductor pattern 27 is also formed on the front surface of the substrate 25. The resistor pattern 26 functions as a heating resistor that generates heat due to the resistance when a current flows through it (is energized). The resistor pattern 26 is formed by applying a paste prepared to have a desired resistance value to the surface of the substrate 25 by screen printing or the like, and then baking the applied paste to form a pattern. The conductor pattern 27 is electrically connected to the resistor pattern 26 (and the power supply electrode 28), and functions as a relay section that passes the current input from the power supply electrode 28 to the resistor pattern 26. The conductor pattern 27 is formed by applying a paste made of a highly conductive material to the surface of the substrate 25 by screen printing or the like, and then baking the paste to form a pattern. The power supply electrode 28 is electrically connected to the conductor pattern 27 and is formed so as to be connectable to a connector (not shown) that serves as an external terminal. Therefore, even if a surface layer having insulating properties and low friction is formed over the entire surface of the sheet heater 24, only the power supply electrode 28 will be exposed from the surface layer so as to be able to supply power. Power supply electrode 28 is made of a silver-based material such as silver (Ag) or silver palladium (AgPd) in order to reduce heat generation due to current flow. In this embodiment, power supply electrode 28 is formed by printing on the surface of substrate 25 by screen printing and then baking.

[0033] Also, referring to Figure 6 etc., the thermistor 40 in this embodiment is a heat-sensitive element (temperature detection means) that directly (or indirectly via another member such as a heat-equalizing member) contacts the surface (top surface in Figure 6) opposite to the surface that forms the nip portion (fixing nip) of the planar heater 24. The thermistor 40 is biased by a compression spring 47 as a biasing member in a direction in which it abuts against the planar heater 24 (to the right in FIG. 2, downward in FIG. 6), which will be explained in detail next. Furthermore, in this embodiment, the thermistor 40 (and the compression spring 47) is installed in one location in the center in the width direction, but the number and installation location are not limited to this.

[0034] The configuration and operation of the characteristic fixing device 20 in the image forming apparatus 1 of this embodiment will be described in detail below. As previously explained using Figures 2, 6, etc., the fixing device 20 in this embodiment is equipped with a planar heater 24 (heater) extending in the width direction, a fixing belt 21 heated by the planar heater 24, a pressure roller 31 (pressurizing rotor) that forms a nip portion through which the sheet P is transported by being pressed against the planar heater 24 via the fixing belt 21, and a holder 23 that holds the planar heater 24 across the width direction.

[0035] In addition, the fixing device 20 is provided with a thermistor 40 as a heat-sensitive element that directly or indirectly contacts the surface opposite to the surface that forms the nip portion (fixing nip) of the planar heater 24 (the left side surface in Figure 2, the top surface in Figure 6). The fixing device 20 also includes a compression spring 47 as a biasing member that biases the thermistor 40 (thermal element) in a direction approaching the planar heater 24, and a stay 30 that supports the holder 23 and holds the compression spring.

[0036] 6 etc., the stay 30 is a metal plate that has been bent to have a substantially U-shaped cross section, and is formed to fit into a recess formed in the holder 23 that holds the planar heater 24. Also, the thermistor 40 held by a bracket 41 and a compression spring 47 are installed inside the stay 30. The holder 23 is also formed with a hole for installing the thermistor 40 that contacts the sheet heater 24 (a loose hole that leaves a slight gap between the thermistor 40 and the holder 23).

[0037] On the other hand, the thermistor 40 is held by a bracket 41 made of a resin material so as to fit into a recess formed in the bracket 41. The bracket 41 is formed with a pillar-shaped portion 41a (boss portion) that protrudes in a direction away from the thermistor 40. The pillar-shaped portion 41a is inserted into the inner periphery of one end side (the lower end portion in FIG. 6) of the compression spring 47. The other end (the upper end in FIG. 6) of the compression spring 47 abuts against the inner ceiling surface (the upper inner wall surface in FIG. 6) of the stay 30. As a result, the compression spring 47 is held inside the stay 30 between the ceiling surface of the stay 30 and the surface of the bracket 41 (the upper surface in FIG. 6 where the base of the columnar portion 41a is located) (the distance is set to be shorter than the free length of the compression spring 47).

[0038] Here, in the fixing device 20 of this embodiment, a hook-shaped portion 47a (end-shaped processed portion) as an interlocking portion that interlocks with the change in posture of a compression spring 47 (urging member) held inside the stay 30 is configured to protrude to the outside from the through portion 30a (formed on the ceiling surface) of the stay 30. More specifically, the hook-shaped portion 47a serving as the interlocking portion is a portion formed as part of the compression spring 47 (biasing member). The hook-shaped portion 47a is formed into a substantially rectangular hook shape by bending (end shape processing) the other end (tip end) of the compression spring 47, and is formed to be smaller than the inner diameter (spring inner diameter) of the spring body of the compression spring 47. The hook-shaped portion 47a is disposed so as to protrude from the inside to the outside of the stay 30 through the through-hole 30a.

[0039] If the posture of the spring body of the compression spring 47 changes (for example, due to improper installation such as buckling, oblique placement, or missing parts), the posture of this hook-shaped portion 47a (interlocking portion) changes accordingly, and the spring will no longer protrude normally from the through-hole 30a. In other words, if the hook-shaped portion 47a protrudes normally from the through-hole 30a, the compression spring 47 is set normally in the stay 30 without buckling, oblique placement, missing parts, or the like. 7 as a comparative example, in the case where the compression spring 147 does not have an interlocking portion and the ceiling surface of the stay 130 does not have a through-hole, the compression spring 147 is likely to be set properly inside the stay 130 due to an assembly error, as shown in FIG. 7. Since such improper installation of the compression spring 147 inside the stay 130 cannot be confirmed from the outside of the stay 130, the device is assembled into the fixing device 20 and the fixing process is performed with the improper installation left unattended. In such a case, the thermistor 40 does not contact the sheet heater 24 with the correct contact force or at the correct contact position, and the fixing temperature control based on the detection result of the thermistor 40 is not performed properly, resulting in problems such as poor fixing. In contrast, in the present embodiment, it is possible to easily check whether the compression spring 47 is properly set within the stay 30 without buckling, being positioned at an angle, or being missing, thereby reducing the occurrence of such defects.

[0040] Referring now to Figure 6, in this embodiment, the hole diameter M of the through portion 30a of the stay 30 is set to be larger than the outer diameter N of the hook-shaped portion 47a (interlocking portion) of the compression spring 47 (M>N). By configuring it in this manner, it is possible to reduce the problem of the hook-shaped portion 47a abutting against the through portion 30a and causing the spring force (spring force) of the compression spring 47 to change from the target value, compared to when the hole diameter M of the through portion 30a and the outer diameter N of the hook-shaped portion 47a (interlocking portion) are formed to be equal (M=N).

[0041] 2, in this embodiment, the amount of protrusion of hook-shaped portion 47a (interlocking portion) of compression spring 47 is determined so that it does not come into contact with the inner circumferential surface of fixing belt 21. That is, a sufficient gap is provided between the tip of the hook-shaped portion 47a protruding from the stay 30 and the inner circumferential surface of the fixing belt 21 that faces the tip. This prevents the hook-shaped portion 47a from sliding against the fixing belt 21, thereby preventing the fixing belt 21 and the compression spring 47 from being damaged.

[0042] <Variation 1> As shown in Figure 8, the fixing device 20 in variant example 1 also uses a portion formed as part of the compression spring 47 as a linkage portion that protrudes from the through-hole 30a of the stay 30 and protrudes in conjunction with changes in the posture of the compression spring 47. More specifically, a folded portion 47b is formed as an interlocking portion by folding back the spring wire toward the other end at one end (the lower end in FIG. 8) of the compression spring 47. The folded portion 47b is formed so as to protrude from the inside to the outside of the stay 30 through the through-hole 30a. Even with this configuration, it is easy to confirm that the compression spring 47 is attached in the stay 30 in the correct position.

[0043] <Variation 2> As shown in FIG. 9, in the fixing device 20 of the second modified example, a cap 48 is attached to the other end of the compression spring 47 (urging member) as an attachment member, and protrudes from the through-hole 30a of the stay 30 to function as a linkage part that protrudes in conjunction with changes in the posture of the compression spring 47. Specifically, the cap 48 serving as the mounting member is a generally shaft-shaped member made of a resin material, and the shaft portion on one end thereof is fitted onto the inner periphery of the compression spring 47. The cap 48 also has a flange portion formed in the center thereof with an outer diameter larger than the hole diameter of the through-hole 30a, and this flange portion determines the position in the biasing direction (upward in Figure 4) of the compression spring 47. The shaft portion on the other end of the cap 48 protrudes from the through-hole 30a to the outside of the stay 30 and functions as an interlocking portion. Even with this configuration, it is easy to confirm that the compression spring 47 is attached in the stay 30 in the correct position.

[0044] <Variation 3> As shown in Figure 10, in the fixing device 20 of variant example 3, a protruding columnar portion 41a (inserted into the inner periphery of the compression spring 47) as part of the bracket 41 holding the thermistor 40 (thermal element) protrudes from the through-hole 30a of the stay 30 and functions as a linkage portion that protrudes in conjunction with changes in the posture of the compression spring 47. In detail, as shown in Figure 10, the columnar portion 41a is inserted upward from the top surface of the bracket 41 over the entire inner periphery of the compression spring 47, and is further formed so as to protrude outside the stay 30 through the through-hole 30a. Even with this configuration, it is easy to confirm that the compression spring 47 is attached in the stay 30 in the correct position.

[0045] <Variation 4> As shown in Figure 11 (A), the fixing device 20 in variant example 4 is configured so that the hook-shaped portion 47a, which serves as an interlocking portion that is interlocked with the change in posture of the compression spring 47 (urging member) held inside the stay 30, is positioned (inserted) in the through-hole 30a of the stay 30 rather than protruding outward from the through-hole 30a. That is, unlike that shown in Figure 6, the hook-shaped portion 47a of the compression spring 47 does not completely protrude outward from the through-hole 30a, but is loosely inserted into the through-hole 30a so as to be able to interfere with the through-hole 30a. Even in such a case, by visually checking whether the hook-shaped portion 47a is positioned in the through-hole 30a, it is possible to easily check whether the compression spring 47 is properly set within the stay 30 without buckling, being positioned at an angle, or being missing. FIG. 11(B) shows a modified example corresponding to FIG. 8, in which a folded portion 47b as an interlocking portion is positioned at the through portion 30a. FIG. 11(C) shows a modified example corresponding to FIG. 9, in which a cap 48 (attachment member) as an interlocking part is positioned at the through part 30a. FIG. 11(D) shows a modified example corresponding to FIG. 10, in which a columnar portion 41a serving as an interlocking portion is positioned at the through portion 30a. Furthermore, even when configured as shown in Figures 11(B) to (D), it is easy to check whether the compression spring 47 is properly set within the stay 30 without buckling, being placed at an angle, or being missing.

[0046] As described above, the fixing device 20 (image forming apparatus 1) in this embodiment includes a sheet heater 24 extending in the width direction, a fixing belt 21 heated by the sheet heater 24, a pressure roller 31 (pressure rotating body) that forms a nip portion through which the sheet P is conveyed by being pressed against the sheet heater 24 via the fixing belt 21, and a holder 23 that holds the sheet heater 24. The fixing device 20 also includes a thermistor 40 (thermal element) that directly contacts (or indirectly contacts or faces) the surface of the sheet heater 24 opposite the surface that forms the nip portion. The fixing device 20 also includes a compression spring 47 (biasing member) that biases the thermistor 40 toward the sheet heater 24, and a stay 30 that supports the holder 23 and holds the compression spring 47. The hook-shaped portion 47a (interlocking portion), which is interlocked with the change in posture of the compression spring 47 held inside the stay 30, is configured to protrude to the outside from the through-hole 30a of the stay 30 (or to be positioned at the through-hole 30a). This makes it easy to confirm that the compression spring 47 (biasing member) that biases the thermistor 40 (heat-sensitive element) in a direction approaching the sheet heater 24 is attached in the correct position.

[0047] In this embodiment, the present invention is applied to an image forming apparatus 1 equipped with a fixing device 20 using a pressure roller 31 as a pressure rotating body. However, the present invention can also be applied to an image forming apparatus equipped with a fixing device using a pressure belt as a pressure rotating body. In this embodiment, the thermistor 40 is used as the heat-sensitive element, which is in direct or indirect contact with the surface of the sheet heater 24 opposite the surface that forms the nip portion, but a thermostat can also be used as such a heat-sensitive element. Also, a non-contact thermistor or thermopile that faces the surface of the sheet heater 24 opposite the surface that forms the nip portion with a gap therebetween can also be used as the heat-sensitive element. In these cases, the same effect as that of this embodiment can be obtained.

[0048] It is to be noted that the present invention is not limited to the present embodiment, and it is clear that the present embodiment can be appropriately modified within the scope of the technical concept of the present invention in addition to the modifications suggested in the present embodiment. Furthermore, the number, position, shape, etc. of the components are not limited to the present embodiment, and the number, position, shape, etc. of the components can be any number, position, shape, etc. that is suitable for implementing the present invention.

[0049] In this specification, the term "sheet" is defined to include not only paper but also all sheet-shaped recording media such as coated paper, label paper, OHP sheets, and film sheets that are the objects to be transported. [Explanation of symbols]

[0050] 1 Image forming apparatus (image forming apparatus main body), 20 Fixing device, 21 Fixing belt (fixing rotating body), 23 holder (holding member), 24 Planar heater (heating means), 30 Stay (reinforcing member), 30a Penetration, 31 pressure roller (pressure rotating body), 40 Thermistor (heat-sensitive element, temperature detection means), 41 bracket (support member), 41a Columnar part (interlocking part), 47 compression spring (biasing member), 47a Hook-shaped portion (interlocking portion), 47b Folded processing part (interlocking part), 48 Cap (mounting member, interlocking part), P sheet (recording medium).

[0051] The present invention can also be embodied in a combination of Supplementary Notes 1 to 8, as follows. (Appendix 1) a plane heater extending in the width direction; a fixing belt heated by the planar heater; a pressure rotating body that is in pressure contact with the planar heater via the fixing belt to form a nip portion through which a sheet is conveyed; a holder for holding the planar heater; a heat-sensitive element that directly or indirectly contacts or faces a surface of the planar heater opposite to a surface that forms the nip portion; a biasing member that biases the heat-sensitive element in a direction toward the planar heater; a stay that supports the holder and holds the biasing member; Equipped with a fixing device characterized in that an interlocking portion that is interlocked with a change in the posture of the urging member held inside the stay is configured to protrude to the outside from a through-hole of the stay or to be located in the through-hole. (Appendix 2) 2. The fixing device according to claim 1, wherein the interlocking portion is a portion formed as a part of the urging member. (Appendix 3) 2. The fixing device according to claim 1, wherein the interlocking portion is an attachment member attached to the biasing member. (Appendix 4) The fixing device described in Appendix 1, characterized in that the interlocking portion is a columnar portion that is inserted into the inner peripheral portion of the compression spring serving as the urging member and protrudes as part of a bracket that holds the thermal element. (Appendix 5) 5. The fixing device according to any one of claims 1 to 4, wherein the hole diameter of the through portion is larger than the outer diameter of the interlocking portion. (Appendix 6) The fixing device according to any one of Supplementary Note 1 to Supplementary Note 5, wherein the interlocking portion has a protruding amount determined so as not to come into contact with the inner circumferential surface of the fixing belt. (Appendix 7) 7. The fixing device according to claim 1, wherein the heat-sensitive element is a thermistor or a thermostat. (Appendix 8) An image forming apparatus comprising the fixing device according to any one of Supplementary Notes 1 to 7. [Prior art documents] [Patent documents]

[0052] [Patent Document 1] Japanese Patent Publication No. 2022-140086

Claims

1. a plane heater extending in the width direction; a fixing belt heated by the planar heater; a pressure rotating body that is in pressure contact with the planar heater via the fixing belt to form a nip portion through which a sheet is conveyed; a holder for holding the planar heater; a heat-sensitive element that directly or indirectly contacts or faces a surface of the planar heater opposite to a surface that forms the nip portion; a biasing member that biases the heat-sensitive element in a direction toward the planar heater; a stay that supports the holder and holds the biasing member; Equipped with a fixing device characterized in that an interlocking portion that is interlocked with a change in the posture of the urging member held inside the stay is configured to protrude to the outside from a through-hole of the stay or to be located in the through-hole.

2. 2. The fixing device according to claim 1, wherein the interlocking portion is a portion formed as a part of the biasing member.

3. 2. The fixing device according to claim 1, wherein the interlocking portion is an attachment member attached to the biasing member.

4. 2. The fixing device according to claim 1, wherein the interlocking portion is a columnar portion that is inserted into an inner periphery of a compression spring serving as the biasing member and that protrudes as part of a bracket that holds the thermal element.

5. 2. The fixing device according to claim 1, wherein the hole diameter of the through portion is larger than the outer diameter of the interlocking portion.

6. 2. The fixing device according to claim 1, wherein the interlocking portion has a protruding amount determined so as not to come into contact with the inner peripheral surface of the fixing belt.

7. 2. The fixing device according to claim 1, wherein the heat-sensitive element is a thermistor or a thermostat.

8. An image forming apparatus comprising the fixing device according to claim 1.

Images