Fixing device and image forming apparatus

Abstract

To suppress positional deviation of a temperature detection member in a short side direction of a heat source.SOLUTION: A fixation device comprises: a rotatable endless fixation belt 21; a rotatable pressure member 22 which is brought into contact with an outer peripheral surface of the fixation belt 21 and forms a fixation nip 100; a heat source 25 which heats the fixation belt 21; a temperature detection member 41 which detects a temperature of the heat source 25; and a heat transfer auxiliary member 28 which is interposed between the heat source 25 and the temperature detection member 41. A surface 28a of the heat transfer auxiliary member 28 contacting the temperature detection member 41 is formed into a concave shape having inclined surfaces that are inclined to each other toward a center side from both ends on a cross section in the direction intersecting a longitudinal direction of the heat source 25.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a fixing device and an image forming apparatus. [Background technology]

[0002] 2. Description of the Related Art Image forming apparatuses such as copiers and printers are equipped with a fixing device that fixes a toner image onto a sheet of paper.

[0003] Typically, a fixing device has a pair of rotating bodies that contact each other, and by passing paper between the rotating bodies (the fixing nip), the paper is heated and pressurized, and the toner image on the paper is fixed.

[0004] In recent years, in order to save energy or shorten the warm-up time, a fixing device has been developed in which a fixing belt having a smaller heat capacity than a roller is used as a rotating body, and a plate-shaped heater as a heat source is arranged so as to contact the inner surface of the nip portion of the fixing belt in order to improve heating efficiency. In addition, in this type of fixing device, from the viewpoint of fixing quality and safety, a temperature detection member such as a thermistor or thermostat is used, and the temperature is controlled by detecting the temperature of the heater with the temperature detection member (for example, see Patent Document 1: JP 2019-91028 A). Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, the plate-shaped heater used in the fixing device has a tendency that the temperature is highest at the center in the short side direction (the direction in which the paper passes through the nip) that intersects with the long side direction (the paper width direction) and the temperature decreases from the center toward both ends. For this reason, a temperature detection member such as a thermistor or thermostat is basically disposed in a position that detects the temperature at the center of the short side direction of the heater, where the temperature is higher.

[0006] However, there is a risk that the position of the temperature detection member may shift in the short-side direction of the heater due to an assembly error during manufacturing, or due to vibration or impact during subsequent transportation. If the position of the temperature detection member shifts from the center to one end in the short-side direction of the heater, the temperature detected by the temperature detection member will be lower than the temperature that should be detected, causing the heater to generate more heat than necessary or making it impossible to accurately detect abnormal temperature increases. For this reason, it is necessary to suppress the position shift of the temperature detection member in the short-side direction of the heater. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides a fixing device that includes a rotatable endless fixing belt, a rotatable pressure member that contacts an outer peripheral surface of the fixing belt to form a fixing nip, a heat source that heats the fixing belt, a temperature detection member that detects the temperature of the heat source, and a heat transfer auxiliary member that is interposed between the heat source and the temperature detection member. a biasing member for biasing the temperature detection member in a direction in which the temperature detection member comes into contact with the heat transfer assistance member; a surface of the heat transfer assistance member with which the temperature detection member comes into contact is a concave having inclined surfaces that are inclined from both ends toward a center in a cross section in a direction intersecting the longitudinal direction of the heat source. curved surface Formed into shape The end of the biasing member that biases the temperature detection member is configured to be displaceable together with the temperature detection member in a direction along the concave curved surface shape. It is characterized by the fact that Effect of the Invention

[0008] According to the present invention, it is possible to suppress misalignment of the temperature detection member in the short-side direction (direction intersecting the long-side direction) of the heat source. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a schematic configuration diagram of a fixing device according to the present embodiment. [Diagram 3] FIG. 2 is a plan view of the heater according to the embodiment. [Figure 4] 3 is a cross-sectional view of the fixing device at a position where a thermistor is disposed. FIG. [Diagram 5] FIG. 2 is a cross-sectional view of the fixing device at a position where a thermostat is disposed. [Figure 6] FIG. 2 is a perspective view of a heat equalizing plate according to the embodiment. [Figure 7] 10A and 10B are diagrams for explaining the effect of suppressing positional deviation of the thermistor and the thermostat. [Figure 8] FIG. 4 is an enlarged view showing the contact state between the thermistor and the heat equalizing plate. [Figure 9] FIG. 4 is an enlarged view showing the contact state between the thermostat and the heat equalizing plate. [Figure 10] FIG. 13 is a diagram showing a modified example of a heat equalizing plate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will be described below with reference to the accompanying drawings. In each drawing for explaining the present invention, components such as members and components having the same function or shape are given the same reference numerals as far as they can be distinguished, and the description thereof will be omitted after the first description.

[0011] FIG. 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention.

[0012] 1, the image forming apparatus 1 according to this embodiment is an electrophotographic printer including an image forming section 2, a recording medium supply section 3, a transfer section 4, a fixing section 5, and a recording medium discharge section 6. The image forming apparatus according to the present invention may be a printer, a copier, a facsimile, or a multifunction machine having two or three of these functions.

[0013] The image forming section 2 includes four imaging units 7Y, 7M, 7C, and 7K that form images, and an exposure device 8 that forms an electrostatic latent image on the surface of a photoconductor 10 included in each of the imaging units 7Y, 7M, 7C, and 7K. In addition to the photoconductor 10 as an image carrier, each of the four imaging units 7Y, 7M, 7C, and 7K includes a charging member 11 that charges the surface of the photoconductor 10, a developing device 12 that supplies a developer to the surface of the photoconductor 10, and a cleaning member 13 that cleans the surface of the photoconductor 10. The imaging units 7Y, 7M, 7C, and 7K have the same configuration, except that they contain developers of different colors, yellow (Y), magenta (M), cyan (C), and black (K), which correspond to the color separation components of a color image. The exposure device 8 includes a light source, a polygon mirror, an f-θ lens, a reflecting mirror, and the like.

[0014] The recording medium supply unit 3 is provided with a paper feed tray 18 that stores paper P as a recording medium, and a paper feed roller 19 that sends out paper P one sheet at a time from the paper feed tray 18. The paper P stored in the paper feed tray 18 includes plain paper, thick paper, thin paper, postcards, envelopes, coated paper (coated paper, art paper, etc.), tracing paper, etc. In addition to paper, a resin sheet such as an OHP sheet may also be used as the recording medium.

[0015] The transfer unit 4 is provided with a transfer device 14 that transfers an image onto a sheet P fed from a paper feed tray 18. The transfer device 14 includes an intermediate transfer belt 15, a primary transfer roller 16, and a secondary transfer roller 17. The intermediate transfer belt 15 is an endless belt member that is stretched by a plurality of support rollers. Four primary transfer rollers 16 are provided on the inner side of the intermediate transfer belt 15 corresponding to the respective photoconductors 10. Each primary transfer roller 16 contacts each photoconductor 10 via the intermediate transfer belt 15, thereby forming a primary transfer nip between the intermediate transfer belt 15 and each photoconductor 10. The secondary transfer roller 17 contacts the outer peripheral surface of the intermediate transfer belt 15 to form a secondary transfer nip.

[0016] The fixing section 5 is provided with a fixing device 20 that fixes an image onto the paper P. The fixing device 20 includes an endless fixing belt 21 and a pressure roller 22 as a pressure member. The fixing belt 21 and the pressure roller 22 are in pressure contact with each other, forming a fixing nip therebetween.

[0017] The recording medium ejection section 6 is provided with a pair of ejection rollers 23 for ejecting the paper P outside the apparatus.

[0018] Next, the printing operation of the image forming apparatus will be described with reference to FIG.

[0019] When an instruction to start a printing operation is given, in each of the imaging units 7Y, 7M, 7C, and 7K, the photoconductor 10 starts to rotate, and the surface of the photoconductor 10 is charged to a uniform high potential by the charging member 11. Next, the exposure device 8 irradiates the surface of each photoconductor 10 with laser light based on the image information of the original document read by the original reading device or the print information instructed to be printed from the terminal. This reduces the potential of the portion irradiated with the laser light, and an electrostatic latent image is formed on the surface of each photoconductor 10. Then, toner is supplied from the developing device 12 to this electrostatic latent image, and a toner image is formed on each photoconductor 10.

[0020] The toner images formed on each photoconductor 10 reach a primary transfer nip (the position of primary transfer roller 16) as each photoconductor 10 rotates, and are transferred to the rotating intermediate transfer belt 15 so as to be overlapped in sequence. After the toner images are transferred, the toner remaining on each photoconductor 10 is removed by each cleaning member 13. Then, the toner image transferred onto the intermediate transfer belt 15 reaches a secondary transfer nip (the position of secondary transfer roller 17) as the intermediate transfer belt 15 rotates, and is transferred to the paper P.

[0021] This paper P is supplied from the recording medium supply unit 3. In the recording medium supply unit 3, after an instruction to start a printing operation is given, the paper feed roller 19 rotates to send out the paper P one sheet at a time from the paper feed tray 18. The sent-out paper P is then temporarily stopped by a pair of timing rollers 24, and is then transported to the secondary transfer nip in accordance with the timing at which the toner image on the intermediate transfer belt 15 reaches the secondary transfer nip. In this way, a full-color toner image is transferred onto the paper P.

[0022] The paper P onto which the toner image has been transferred is transported to the fixing unit 5. Then, in the fixing unit 5, the paper P is conveyed while being sandwiched between a fixing belt 21 and a pressure roller 22, so that the toner image is fixed onto the paper P. Thereafter, the paper P is conveyed to the recording medium discharge unit 6, and is discharged outside the apparatus by a paper discharge roller 23. This completes a series of printing operations.

[0023] Hereinafter, the basic configuration of the fixing device 20 according to this embodiment will be described with reference to FIG.

[0024] As shown in FIG. 2, the fixing device 20 according to this embodiment includes a fixing belt 21, a pressure roller 22, a heater 25, a heater holder 26, and a stay 27.

[0025] The fixing belt 21 is disposed on the unfixed image bearing surface side of the paper P, and is a fixing member that fixes the unfixed image on the paper P. The fixing belt 21 is constituted by an endless belt member, and is rotatably held by a pair of belt holding members inserted into both ends in the longitudinal direction of the fixing belt 21. That is, the fixing belt 21 is held by the pair of belt holding members in a so-called free belt state in which basically no tension is applied to the fixing belt 21 when it is not rotating. In addition, a heater 25 is disposed inside the fixing belt 21 as a heat source for heating the fixing belt 21.

[0026] The pressure roller 22 is a rotating body that contacts the outer circumferential surface of the fixing belt 21 to form a fixing nip 100. Specifically, the pressure roller 22 is composed of a core metal, an elastic layer made of foamed silicone rubber, silicone rubber, fluororubber, or the like provided on the surface of the core metal, and a release layer made of PFA, PTFE, or the like provided on the surface of the elastic layer. The pressure roller 22 is pressed toward the fixing belt 21 by a biasing member such as a spring, and is in pressure contact with the outer circumferential surface of the fixing belt 21. As a result, the fixing nip 100 is formed between the fixing belt 21 and the pressure roller 22 (at the contact point).

[0027] The pressure roller 22 is configured to be rotated by a drive source provided in the image forming apparatus body. When the pressure roller 22 is rotated, the drive force is transmitted to the fixing belt 21, so that the fixing belt 21 rotates. Then, the fixing belt 21 is heated by the heater 25, and when the temperature of the fixing belt 21 reaches a predetermined temperature (fixing temperature), the paper P carrying an unfixed image is transported between the fixing belt 21 and the pressure roller 22 (fixing nip 100) as shown in Fig. 2. As a result, the paper P is pressurized and heated as it passes through the fixing nip 100, and the unfixed image is fixed to the paper P.

[0028] The heater 25 is a plate-shaped heater having a base material 30, a first insulating layer 31, a resistance heating element 32, and a second insulating layer 33. The heater 25 is arranged so as to extend across the longitudinal direction of the fixing belt 21 (the paper width direction intersecting the paper conveying direction). The base material 30 is made of a metal material such as stainless steel (SUS), iron, or aluminum. In addition to a metal material, ceramic or glass can also be used as the material of the base material 30. The first insulating layer 31 and the second insulating layer 33 are made of a material such as heat-resistant glass, ceramic, or polyimide. The first insulating layer 31 is laminated on the surface of the base material 30 on the fixing nip 100 side, and the second insulating layer 33 is laminated further on the fixing nip 100 side than the first insulating layer 31. When the base material 30 is made of an insulating material such as ceramic, the first insulating layer 31 can be omitted. The resistance heating element 32 is a heating element interposed between the first insulating layer 31 and the second insulating layer 33. The resistance heating element 32 is formed, for example, by applying a paste made of silver palladium (AgPd) and glass powder to the surface of the base material 30 by screen printing or the like, and then firing the base material 30. Alternatively, the material of the resistance heating element 32 may be a resistance material such as a silver alloy (AgPt) or ruthenium oxide (RuO2).

[0029] Moreover, the heater 25 is disposed so as to contact the inner circumferential surface of the fixing belt 21 at the position of the fixing nip 100. Therefore, when the fixing belt 21 rotates, the fixing belt 21 slides against the heater 25. At this time, in order to increase the sliding property of the fixing belt 21 against the heater 25, a low friction sheet or a lubricant such as grease may be interposed between the heater 25 and the fixing belt 21.

[0030] The heater holder 26 is a heat source holding member that holds the heater 25 inside the fixing belt 21. The heater holder 26 is preferably made of a heat-resistant material because it is likely to become hot due to the heat of the heater 25. In particular, when the heater holder 26 is made of a heat-resistant resin with low thermal conductivity such as LCP or PEEK, the heat resistance of the heater holder 26 is ensured while heat transfer from the heater 25 to the heater holder 26 is suppressed, so that the fixing belt 21 can be heated efficiently.

[0031] The stay 27 is a reinforcing member disposed on the inside of the fixing belt 21. The stay 27 supports the surface of the heater holder 26 opposite to the surface on the fixing nip 100 side, thereby preventing the heater holder 26 from being deflected by the pressure of the pressure roller 22. As a result, the fixing nip 100 of a uniform width is formed between the fixing belt 21 and the pressure roller 22. Moreover, the stay 27 is preferably made of an iron-based metal material such as SUS or SECC in order to ensure its rigidity.

[0032] FIG. 3 is a plan view of the heater 25 according to the present embodiment.

[0033] As shown in FIG. 3, in addition to a plurality of resistance heating elements 32, a plurality of electrode parts 34, and a plurality of power supply lines 35 connecting the resistance heating elements 32 and the electrode parts 34 are provided on the base material 30 of the heater 25. In this embodiment, the plurality of resistance heating elements 32 are configured by a central resistance heating element 32 arranged so as to overlap with the paper passage area of ​​the small size paper P1, and each end resistance heating element 32 arranged on both ends of the paper passage area of ​​the large size paper P2. In addition, each resistance heating element 32 is configured to be able to generate heat independently of each other. Specifically, when the small size paper P1 is passed through, only the central resistance heating element 32 generates heat, and when the large size paper P2 is passed through, in addition to the central resistance heating element 32, each end resistance heating element 32 also generates heat.

[0034] As shown in FIG. 3, a thermistor 41 and a thermostat 42 are disposed on the rear side of the heater 25 (the side opposite to the fixing nip side) as temperature detection members for detecting the temperature of the heater 25.

[0035] The thermistor 41 is a control temperature detection member that detects the temperature of the heater 25 in order to maintain the temperature of the fixing belt at a predetermined temperature at which an image can be fixed. The output of the heater 25 is controlled based on the temperature of the heater 25 detected by the thermistor 41, thereby maintaining the temperature of the fixing belt at a predetermined temperature. The thermistors 41 are, for example, disposed at the center and end sides of the heater 25 in the longitudinal direction (paper width direction).

[0036] The thermostat 42 is a safety device that detects the temperature of the heater 25 and cuts off the power supply to the heater 25 when the temperature of the heater 25 excessively rises due to a malfunction of the thermistor 41 or the like. The thermostat 42 is disposed at a position not overlapping with the thermistor 41 on the central side and end side of the heater 25 in the longitudinal direction.

[0037] Here, in order to detect the temperature of the heater 25 accurately and with good responsiveness, the temperature detection members such as the thermistor 41 and the thermostat 42 are generally disposed in a portion of the heater 25 where the temperature becomes particularly high.

[0038] 3, in the heater 25 according to this embodiment, the resistance heating element 32 is disposed at the center (at or near the center) in the short-side direction of the heater 25, so that the temperature at the center is higher and the temperature at the end tends to be lower than the temperature at the center. Note that in this specification, the "short-side direction" of the heater means the direction B that intersects or is perpendicular to the longitudinal direction A of the heater disposed across the paper width direction, and refers to the same direction as the direction in which the paper passes through the fixing nip (paper passing direction).

[0039] Thus, in this embodiment, the temperature tends to be higher at the center of the heater 25 in the short side direction. For this reason, it is preferable to arrange the thermistor 41 and the thermostat 42 at the center of the heater 25 in the short side direction. However, in the unlikely event that the positions of the thermistor 41 and the thermostat 42 are shifted toward the heater's short side direction (end side), the temperature detected by the thermistor 41 and the thermostat 42 will be lower than the temperature that they should be detected, and this may cause the heater 25 to generate more heat than necessary or make it impossible to accurately detect an abnormal temperature rise. Therefore, in the fixing device according to the present invention, the following configuration is adopted to suppress the thermistor 41 and the thermostat 42 from being shifted toward the heater's short side direction.

[0040] The configuration of the fixing device according to the embodiment of the present invention will be described in detail below. In the following description, unless otherwise necessary, the thermistor and the thermostat will be collectively referred to as "each temperature detection member".

[0041] Fig. 4 is a cross-sectional view of fixing device 20 at a position where thermistor 41 is disposed, and Fig. 5 is a cross-sectional view of fixing device 20 at a position where thermostat 42 is disposed. In Figs. 4 and 5, the up-down direction in Fig. 2 corresponds to the left-right direction.

[0042] As shown in FIG. 4 and FIG. 5, in the fixing device 20 according to the present embodiment, a heat equalizing plate 28 is disposed between the heater 25 and each of the temperature detection members 41 and 42 as a heat transfer auxiliary member. The heat equalizing plate 28 is a heat transfer auxiliary member that contacts the surface (base material 30) of the heater 25 opposite to the fixing nip 100 side of the heater 25 along the longitudinal direction of the heater 25 and transfers the heat of the heater 25 in the longitudinal direction to achieve heat equalization. The heat equalizing plate 28 is made of a metal material with high thermal conductivity. Specifically, the heat equalizing plate 28 is made of copper, aluminum, silver, or the like. By providing such a heat equalizing plate 28, the heat of the high-temperature part of the heater is dispersed to the surrounding low-temperature part, so that the maximum temperature reached by the heater can be suppressed.

[0043] In particular, in a configuration in which the temperature of the heater is detected by a thermistor as in the present embodiment, the thermistor is more susceptible to the heat of the heater than in a configuration in which the temperature of the fixing belt is detected by a thermistor, and therefore the temperature of the thermistor is more likely to rise. For this reason, if the temperature of the non-paper passing area of ​​the heater rises too much when small-sized paper is continuously passed through, for example, there is a risk that the temperature of the thermistor disposed in the non-paper passing area will exceed the heat resistance temperature of the thermistor. However, in this embodiment, even if the temperature of the non-paper passing area rises excessively, the heat equalizing plate 28 is interposed between the thermistor 41 and the heater 25, so that the maximum temperature reached in the non-paper passing area can be suppressed, and the temperature rise of the thermistor 41 can be suppressed, thereby reducing the risk of failure.

[0044] In this embodiment, the temperature detection members 41, 42 are biased toward the heat equalizing plate 28 by the springs 36 serving as biasing members. Therefore, the temperature detection members 41, 42 are in contact with the surface 28a of the heat equalizing plate 28 on the side opposite to the heater 25. Here, the surface 28a of the heat equalizing plate 28 with which the temperature detection members 41, 42 are in contact is formed into an arc-like concave shape in a cross section in a direction intersecting the longitudinal direction of the heater 25 (cross section in the short-side direction B shown in Figs. 4 and 5).

[0045] FIG. 6 shows a perspective view of the heat equalizer plate 28 according to this embodiment.

[0046] 6, the concave surface 28a of the heat equalizing plate 28 with which the temperature detection members 41, 42 come into contact is formed so as to be continuous with the same cross-sectional shape along the heater's longitudinal direction A. Specifically, the concave surface 28 is most recessed at the center 28b in the short-side direction B of the heater 25, and has an inclined surface 28c extending in an arc shape so as to gradually decrease in depth from the center toward both ends in the short-side direction B.

[0047] In this embodiment, since the surface of the heat equalizing plate 28 on the side of the temperature detection members 41 and 42 is formed as the concave surface 28a, even if the positions of the temperature detection members 41 and 42 are shifted from the center in the short-side direction B of the heater to one of the two ends, the temperature detection members 41 and 42 are returned to the center along the inclined surface 28c of the concave surface 28a. That is, as shown in FIG. 7, when the temperature detection members 41 and 42 are shifted from the center 28b in the short-side direction B, the spring 36 presses the temperature detection members 41 and 42 against the inclined surface 28c, thereby generating a force F that tries to return the temperature detection members 41 and 42 to the center 28b following the inclination of the inclined surface 28c. As a result, the temperature detection members 41 and 42 are returned to the center 28b side, so that the positional shift of the temperature detection members 41 and 42 in the short-side direction B of the heater can be suppressed, and the reliability and safety of the temperature management by the temperature detection members 41 and 42 can be improved.

[0048] The smaller the radius of curvature of the inclined surface 28c, the stronger the force F that returns the temperature detection members 41, 42 to the center 28b side, and conversely, the larger the radius of curvature, the weaker the force F that returns the temperature detection members 41, 42 to the center 28b side. For this reason, it is preferable that the radius of curvature R1 of the inclined surface 28c is smaller than the radius of curvature R2 of the fixing belt 21, for example (see FIG. 4 or FIG. 5). Note that the radius of curvature of the fixing belt here means the radius of curvature when the fixing belt is in a circular shape without receiving an external force. In this way, by making the radius of curvature R1 of the inclined surface 28c smaller than the radius of curvature R2 of the fixing belt 21, the inclined surface 28c can effectively maintain the positions of the temperature detection members 41, 42 and return them to their original positions when they are misaligned.

[0049] In addition, even if the position of the thermistor 41 is displaced in the short-side direction B of the heater, the contact pressure of the thermistor 41 against the heat equalizing plate 28 increases at the displaced position, so that the drop in the detected temperature due to the positional displacement can be suppressed. That is, when the position of the thermistor 41 is displaced from the center of the short-side direction of the heater to the end side, the thermistor 41 moves along the inclined surface 28c of the heat equalizing plate 28, and the spring 36 is compressed, so that the elastic repulsive force of the spring 36 increases and the contact pressure of the thermistor 41 against the heat equalizing plate 28 increases. As a result, the degree of adhesion of the thermistor 41 to the heat equalizing plate 28 increases, and the contact area increases, so that the amount of heat transmitted from the heater 25 to the thermistor 41 via the heat equalizing plate 28 increases. This makes it possible to suppress the drop in the detected temperature due to the thermistor 41 being displaced from the center, where the temperature of the heater 25 is high, to the end side, where the temperature is low, and to suppress the decrease in the accuracy of temperature control.

[0050] 8, the thermistor 41 has a thermistor element 41a as a temperature detection element that contacts an object to detect the temperature of the object. For this reason, it is preferable that at least thermistor element 41a is in contact with the concave surface 28a of the heat equalizer plate 28.

[0051] On the other hand, FIG. 9 is an enlarged view showing the state where the thermostat 42 is in contact with the heat equalizing plate 28. As shown in FIG. 9, the thermostat 42 has a bimetal 42a formed by bonding together metal materials having different thermal expansion coefficients. The bimetal 42a is a heat-sensitive current-sensing cutoff element that deforms when the temperature of the heater 25 exceeds a predetermined temperature as the temperature of the heater 25 rises, and cuts off the current to the heater 25. When the bimetal 42a is in contact with the heat equalizing plate 28, the amount of heat transferred from the heater 25 to the bimetal 42a increases, improving the responsiveness when the temperature of the heater 25 rises. However, when the temperature of the heater 25 is controlled in a high temperature range (e.g., 200° C. or higher), the amount of heat transferred to the bimetal 42a becomes too large, and the thermostat 42 may malfunction during a normal temperature rise, cutting off the current to the heater 25. Therefore, in order to reduce the risk of such a malfunction, it is preferable to prevent the amount of heat transferred from the heater 25 to the bimetal 42a from becoming too large.

[0052] 9, the surface of the heat equalizing plate 28 facing the thermostat 42 is formed as a concave surface 28a, so that the bimetal 42a does not come into contact with the heat equalizing plate 28. That is, since the surface of the heat equalizing plate 28 facing the thermostat 42 is not flat but is formed as a concave surface 28a, the housing of the thermostat 42 and the like come into contact with the concave surface 28a of the heat equalizing plate 28, so that the bimetal 42a is disposed in a state where it is floating above the concave surface 28a. In this way, by disposing the bimetal 42a in a state where it does not come into contact with the heat equalizing plate 28, heat transfer to the bimetal 42a is suppressed, and the risk of malfunction of the thermostat 42 can be reduced.

[0053] In addition, in this embodiment, the thermostat 42 is in contact with the concave surface 28a of the heat equalizing plate 28 at a portion other than the bimetal 42a (such as the edge of the housing), so that the necessary heat can be transferred through the contact portion, and good operation of the thermostat 42 can be ensured when the temperature becomes abnormally high. In contrast, if the thermostat 42, including the housing, is not in contact with the heat equalizing plate 28 as a whole, the amount of heat transferred to the thermostat 42 decreases, and there is a risk that the thermostat 42 cannot operate well at an abnormally high temperature. Therefore, in order to ensure good operation of the thermostat 42 at an abnormally high temperature and improve reliability, it is preferable to have the thermostat 42 in contact with the heat equalizing plate 28 at a portion other than the bimetal 42a, as in this embodiment. Thus, in this embodiment, by making the surface of the heat equalizing plate 28 on the side of the thermostat 42 the concave surface 28a, it is possible to reduce the risk of malfunction while maintaining the function of the thermostat 42 as a safety device.

[0054] Although an embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the gist of the invention.

[0055] For example, in the above-described embodiment, the concave surface 28a of the heat equalizing plate 28 has an arc-shaped cross section, but as shown in the example of Fig. 10, the concave surface 28a is not limited to a curved surface such as an arc, and may be a concave shape (V-shaped) having linear inclined surfaces 28c that are inclined toward the center from both ends in the short-side direction B. The concave surface 28a may also have a shape including curved lines and straight lines. Furthermore, the concave surface 28a is not necessarily formed symmetrically with respect to the center in the short-side direction B, and may be formed asymmetrically.

[0056] In addition, the present invention is not limited to a free-belt type configuration in which the fixing belt is rotatably held by a pair of belt holding members as shown in FIG. 2, but can also be applied to a configuration in which the fixing belt is stretched around multiple rollers or the like. [Explanation of symbols]

[0057] 1. Image forming device 20 Fixing device 21 Fixing belt 22 Pressure roller (pressure member) 25 Heater (heat source) 28 Heat equalizing plate (heat transfer auxiliary component) 28a concave 28b center 28c slope 41 Thermistor (temperature detection component) 41a Thermistor element (temperature detection element) 42 Thermostat (temperature sensing component) 42a Bimetal (heat-sensitive current-cutting element) 100 Fixing nip [Prior art documents] [Patent documents]

[0058] [Patent Document 1] JP 2019-91028 A

Claims

1. a rotatable endless fixing belt; a rotatable pressure member that contacts an outer peripheral surface of the fixing belt to form a fixing nip; a heat source for heating the fixing belt; A temperature detection member that detects the temperature of the heat source; a heat transfer assistance member interposed between the heat source and the temperature detection member; a biasing member that biases the temperature detection member in a direction in which the temperature detection member contacts the heat transfer assistance member, a surface of the heat transfer assistance member with which the temperature detection member comes into contact is formed into a concave curved shape having inclined surfaces that are inclined from both ends toward a center in a cross section in a direction intersecting the longitudinal direction of the heat source, The fixing device according to claim 1, wherein an end portion of the biasing member that biases the temperature detection member is configured to be displaceable together with the temperature detection member in a direction along the concave curved surface.

2. A fixing device as described in claim 1, wherein the radius of curvature of the inclined surface is smaller than the radius of curvature of the fixing belt.

3. The temperature detection member has a temperature detection element that contacts an object and detects the temperature of the object, 3. The fixing device according to claim 1, wherein the temperature detection member is in contact with the concave surface of the heat transfer assistance member at least at a portion of the temperature detection element.

4. The temperature detection member has a heat-sensitive current-cutting element that deforms and cuts off current to the heat source when a predetermined temperature is exceeded, 3. The fixing device according to claim 1, wherein the temperature detection member is in contact with the concave surface of the heat transfer assistance member at a portion other than the heat-sensitive current-transfer cutoff element.

5. An image forming apparatus comprising a fixing device described in any one of claims 1 to 4.

Images