JP2022182541A - Fixation device and image formation apparatus - Google Patents

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

The present invention relates to fixing devices and image forming apparatuses.

2. Description of the Related Art An image forming apparatus such as a copier or printer is equipped with a fixing device that fixes a toner image on a sheet of paper.

In general, a fixing device has a pair of rotating bodies that are in contact with each other. By passing a sheet between the rotating bodies (fixing nip), the sheet is heated and pressurized to form a toner image on the sheet. is established.

In recent years, in order to save energy or shorten the warm-up time, a fixing belt with a smaller heat capacity than a roller is used as a rotating body. A fixing device has been developed that is arranged so as to contact the inner surface of the nip portion. In addition, in this type of fixing device, a temperature detection member such as a thermistor or thermostat is used from the viewpoint of fixing quality and safety, and the temperature is controlled by detecting the temperature of the heater with these temperature detection members. (For example, refer to Patent Document 1: Japanese Unexamined Patent Publication No. 2019-91028).

By the way, in the plate-shaped heater used in the fixing device, the temperature on the center side is the highest in the lateral direction (passing direction in which the paper passes through the nip portion) that intersects the longitudinal direction (paper width direction). The temperature tends to decrease from the center side toward both end sides. For this reason, a temperature detecting member such as a thermistor or thermostat is arranged at a position for detecting the temperature of the central side in the width direction of the heater, where the temperature is basically high.

However, there is a possibility that the position of the temperature detecting member may be displaced in the lateral direction of the heater due to an assembly error of parts during manufacturing or vibration or impact during subsequent transportation. If the position of the temperature detection member deviates from the central side to one end side in the short direction of the heater, the temperature detected by the temperature detection member becomes lower than the originally detected temperature. Otherwise, it may generate heat, or it may not be possible to accurately detect an abnormal temperature rise. Therefore, it is necessary to suppress the displacement of the temperature detection member in the short side direction of the heater.

In order to solve the above-described problems, the present invention provides a rotatable endless fixing belt, a rotatable pressure member that contacts the outer peripheral surface of the fixing belt to form a fixing nip, and a heater that heats the fixing belt. a heat source, a temperature detecting member for detecting the temperature of the heat source, and a heat transfer assisting member interposed between the heat source and the temperature detecting member, wherein the temperature detecting member is in contact with the heat transfer assisting member. The surface of the heat transfer assisting member is formed in a concave shape having inclined surfaces that are inclined from both ends toward the center in a cross section in a direction intersecting the longitudinal direction of the heat source. do.

According to the present invention, positional displacement of the temperature detection member in the lateral direction (direction intersecting the longitudinal direction) of the heat source can be suppressed.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention; FIG. 1 is a schematic configuration diagram of a fixing device according to an exemplary embodiment; FIG. It is a top view of the heater concerning this embodiment. 4 is a cross-sectional view of the fixing device at a position where the thermistor is arranged; FIG. 4 is a cross-sectional view of the fixing device at a position where a thermostat is arranged; FIG. It is a perspective view of a heat equalizer plate according to the present embodiment. FIG. 10 is a diagram for explaining how the thermistor and the thermostat are prevented from being misaligned; It is an enlarged drawing which shows the contact state of a thermistor and a heat equalizing plate. It is an enlarged view which shows the contact state of a thermostat and a heat equalizing plate. It is a figure which shows the modification of a heat equalizing plate.

The present invention will be described below with reference to the accompanying drawings. In addition, in each drawing for explaining the present invention, constituent elements such as members and constituent parts having the same function or shape are given the same reference numerals as much as possible, and once explained, the explanation will be repeated. omitted.

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to one embodiment of the present invention.

As shown in FIG. 1, an image forming apparatus 1 according to this embodiment includes 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. It is an electrophotographic printer. Note that the image forming apparatus according to the present invention may be a copier, a facsimile machine, or a multifunction machine having two or three of these functions, in addition to the printer.

In the image forming section 2, four image forming units 7Y, 7M, 7C, and 7K for forming images, and electrostatic latent images are formed on the surfaces of photoconductors 10 provided in the respective image forming units 7Y, 7M, 7C, and 7K. An exposure device 8 is provided. The four image forming units 7Y, 7M, 7C, and 7K include a photoreceptor 10 as an image carrier, a charging member 11 that charges the surface of the photoreceptor 10, and a developing unit that supplies developer to the surface of the photoreceptor 10. A device 12 and a cleaning member 13 for cleaning the surface of the photoreceptor 10 are provided. Each of the image forming units 7Y, 7M, 7C, and 7K contains developers of different colors of yellow (Y), magenta (M), cyan (C), and black (K) corresponding to color separation components of a color image. The configuration is the same except that The exposure device 8 includes a light source, a polygon mirror, an f-θ lens, a reflecting mirror, and the like.

The recording medium supply unit 3 is provided with a paper feed tray 18 that accommodates paper P as a recording medium, and a paper feed roller 19 that feeds out the paper P from the paper feed tray 18 one by one. The paper P accommodated in the paper feed tray 18 includes plain paper, thick paper, thin paper, postcards, envelopes, coated paper (coated paper, art paper, etc.), tracing paper, and the like. Moreover, as a recording medium, a resin sheet such as an OHP sheet may be used instead of paper.

The transfer unit 4 is provided with a transfer device 14 that transfers an image onto the paper P supplied from the paper feed tray 18 . The transfer device 14 includes an intermediate transfer belt 15 , primary transfer rollers 16 and secondary transfer rollers 17 . The intermediate transfer belt 15 is an endless belt member and is stretched by a plurality of support rollers. Four primary transfer rollers 16 are provided inside the intermediate transfer belt 15 so as to correspond to the respective photoreceptors 10 . A primary transfer nip is formed between the intermediate transfer belt 15 and each photoreceptor 10 by bringing each primary transfer roller 16 into contact with each photoreceptor 10 via the intermediate transfer belt 15 . The secondary transfer roller 17 contacts the outer peripheral surface of the intermediate transfer belt 15 to form a secondary transfer nip.

In the fixing section 5, a fixing device 20 for fixing an image on the paper P is provided. The fixing device 20 includes an endless fixing belt 21, a pressure roller 22 as a pressure member, and the like. The fixing belt 21 and the pressure roller 22 are pressed against each other to form a fixing nip therebetween.

A pair of paper discharge rollers 23 for discharging the paper P to the outside of the apparatus is provided in the recording medium discharge section 6 .

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

When there is an instruction to start the printing operation, the photoreceptor 10 starts rotating in each of the image forming units 7Y, 7M, 7C, and 7K, and the charging member 11 charges the surface of the photoreceptor 10 to a uniform high potential. Next, the exposure device 8 irradiates the surface of each photoreceptor 10 with a laser beam based on the image information of the document read by the document reading device or the print information instructed to print from the terminal. As a result, the potential of the portion irradiated with the laser light is lowered, and an electrostatic latent image is formed on the surface of each photoreceptor 10 . Toner is supplied from the developing device 12 to the electrostatic latent image, and a toner image is formed on each photoreceptor 10 .

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

This paper P is supplied from the recording medium supply section 3 . In the recording medium supply unit 3 , after receiving an instruction to start the printing operation, the paper P is fed out one by one from the paper feed tray 18 by rotating the paper feed roller 19 . After being temporarily stopped by a pair of timing rollers 24, the sheet P sent out is conveyed to the secondary transfer nip at the timing when the toner image on the intermediate transfer belt 15 reaches the secondary transfer nip. Thus, a full-color toner image is transferred onto the paper P.

The paper P onto which the toner image has been transferred is conveyed to the fixing section 5 . Then, in the fixing section 5 , the toner image is fixed on the paper P by being conveyed while being nipped by the fixing belt 21 and the pressure roller 22 . After that, the paper P is conveyed to the recording medium ejection section 6 and ejected outside the apparatus by the paper ejection rollers 23 . This completes a series of printing operations.

The basic configuration of the fixing device 20 according to this embodiment will be described below with reference to FIG.

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

The fixing belt 21 is a fixing member that is arranged on the unfixed image carrying surface side of the paper P and fixes the unfixed image on the paper P. As shown in FIG. The fixing belt 21 is composed of an endless belt member, and is rotatably held by a pair of belt holding members inserted at both longitudinal ends thereof. That is, the fixing belt 21 is held by the pair of belt holding members in a so-called free belt state in which tension is basically not applied when the fixing belt 21 is not rotating. A heater 25 as a heat source for heating the fixing belt 21 is arranged inside the fixing belt 21 .

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

Further, the pressure roller 22 is configured to be rotationally driven by a drive source provided in the main body of the image forming apparatus. When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21, whereby the fixing belt 21 is driven to rotate. Then, when the fixing belt 21 is heated by the heater 25 and the temperature of the fixing belt 21 reaches a predetermined temperature (fixing temperature), the paper P carrying the unfixed image is separated from the fixing belt 21 as shown in FIG. It is conveyed between the pressure roller 22 (fixing nip 100). As a result, the paper P is pressurized and heated when passing through the fixing nip 100, and the unfixed image is fixed on the paper P. FIG.

The heater 25 is a plate heater having a substrate 30 , a first insulating layer 31 , a resistance heating element 32 and a second insulating layer 33 . The heater 25 is arranged to extend in the longitudinal direction of the fixing belt 21 (paper width direction crossing the paper conveying direction). The base material 30 is made of a metal material such as stainless steel (SUS), iron, or aluminum. Moreover, as the material of the base material 30, it is also possible to use ceramics, glass, or the like in addition to metal materials. The first insulating layer 31 and the second insulating layer 33 are made of a material such as heat-resistant glass, ceramics, or polyimide. The first insulating layer 31 is laminated on the fixing nip 100 side of the base material 30 , and the second insulating layer 33 is laminated further on the fixing nip 100 side than the first insulating layer 31 . Note that the first insulating layer 31 can be omitted when the base material 30 is made of an insulating material such as ceramic. 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 by, for example, applying a paste prepared by mixing 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 . As the material of the resistance heating element 32, it is also possible to use a resistance material such as silver alloy (AgPt) or ruthenium oxide ( _RuO2 ).

Further, the heater 25 is arranged so as to contact the inner peripheral 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 on the heater 25 . At this time, a low-friction sheet or a lubricant such as grease may be interposed between the heater 25 and the fixing belt 21 in order to increase the slidability of the fixing belt 21 with respect to the heater 25 .

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

The stay 27 is a reinforcing member arranged inside the fixing belt 21 . Since the surface of the heater holder 26 opposite to the surface on the fixing nip 100 side is supported by the stay 27 , the heater holder 26 is prevented from being bent by the pressure applied by the pressure roller 22 . Thereby, a fixing nip 100 having 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.

FIG. 3 is a plan view of the heater 25 according to this embodiment.

As shown in FIG. 3, on the substrate 30 of the heater 25, there are a plurality of resistance heating elements 32, a plurality of electrode portions 34, and a plurality of feeder lines connecting the resistance heating elements 32 and the electrode portions 34. 35 is provided. In the present embodiment, a plurality of resistance heating elements 32 are arranged so as to overlap the sheet passing area of the small size paper P1, and the resistance heating element 32 on the central side of the sheet passing area of the large size paper P2. It is configured by each resistance heating element 32 on the side of the arranged end. Each resistance heating element 32 is configured to generate heat independently of each other. Specifically, when the small size paper P1 is passed, only the central resistance heating element 32 generates heat, and when the large size paper P2 is passed, in addition to the central resistance heating element 32, Each resistance heating element 32 on both end sides also generates heat.

Further, as shown in FIG. 3, a thermistor 41 and a thermostat 42 as temperature detecting members for detecting the temperature of the heater 25 are arranged on the back side of the heater 25 (the side opposite to the fixing nip side).

The thermistor 41 is a temperature detecting member for control that detects the temperature of the heater 25 in order to maintain the temperature of the fixing belt at a predetermined temperature at which the image can be fixed. By controlling the output of the heater 25 based on the temperature of the heater 25 detected by the thermistor 41, the temperature of the fixing belt is maintained at a predetermined temperature. The thermistors 41 are arranged, for example, on the central side and the end side of the heater 25 in the longitudinal direction (paper width direction).

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 is excessively increased due to a failure of the thermistor 41 or the like. The thermostat 42 is arranged at a position that does not overlap the thermistor 41 on the central side and the end side of the heater 25 in the longitudinal direction.

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

As shown in FIG. 3, in the heater 25 according to the present embodiment, the resistance heating element 32 is arranged at the center side (the center and its vicinity) in the width direction of the heater 25, so that the temperature at the center side is The temperature on the edge side tends to be lower than the temperature on the center side. In this specification, the "lateral direction" of the heater means the direction B that intersects or is perpendicular to the longitudinal direction A of the heater arranged across the paper width direction, and the paper passes through the fixing nip. It means the same direction as the direction (paper feeding direction).

As described above, in the present embodiment, the temperature of the central side of the heater 25 in the width direction tends to be high. For this reason, the thermistor 41 and the thermostat 42 are preferably arranged on the center side of the heater 25 in the width direction. However, in the unlikely event that the positions of the thermistor 41 and the thermostat 42 are shifted in the lateral direction (end side) of the heater, the temperature detected by the thermistor 41 and the thermostat 42 becomes lower than the temperature that should be detected. There is a risk that the heater 25 will generate more heat than necessary, or that an abnormal temperature rise will not be detected accurately. Therefore, in the fixing device according to the present invention, the following configuration is adopted in order to suppress the positional deviation of the thermistor 41 and the thermostat 42 in the short side direction of the heater.

Hereinafter, the configuration of the fixing device according to the embodiment of the invention will be described in detail. In the following description, the thermistor and thermostat are collectively referred to as "each temperature detection member" unless necessary.

4 is a cross-sectional view of the fixing device 20 at the position where the thermistor 41 is arranged, and FIG. 5 is a cross-sectional view of the fixing device 20 at the position where the thermostat 42 is arranged. 4 and 5, the up-down direction in FIG. 2 is the left-right direction.

As shown in FIGS. 4 and 5, in the fixing device 20 according to the present embodiment, a heat equalizing plate 28 as a heat transfer auxiliary member is arranged between the heater 25 and the temperature detection members 41 and 42. ing. The heat equalizing plate 28 is in contact with the surface (base material 30) of the heater 25 opposite to the fixing nip 100 side over the longitudinal direction of the heater 25, and transfers the heat of the heater 25 in the longitudinal direction to equalize the heat. It is a heat transfer auxiliary member that aims at The heat equalizing plate 28 is made of a metal material with high thermal conductivity. Specifically, as the material of the heat equalizing plate 28, copper, aluminum, silver, or the like is used. By providing such a heat equalizing plate 28, the heat of the high-temperature portion of the heater is dispersed to the surrounding low-temperature portion, so that the maximum reaching temperature of the heater can be suppressed.

In particular, in a configuration in which the temperature of the heater is detected by a thermistor, as in this 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 the thermistor. tends to be high. For this reason, for example, if the temperature of the non-paper-passing area of the heater rises too much when small-sized paper is continuously passed, the temperature of the thermistor arranged in the paper-non-passing area may exceed the heat resistant temperature of the thermistor. . However, in the present 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 non-paper-passing area can be suppressed, the temperature rise of the thermistor 41 can be suppressed, and the risk of failure can be reduced.

Further, in this embodiment, each of the temperature detection members 41 and 42 is biased toward the heat equalizing plate 28 by a spring 36 as a biasing member. Therefore, the temperature detection members 41 and 42 are in contact with the surface 28a of the heat equalizing plate 28 opposite to the heater 25 side. Here, the surface 28a of the heat equalizing plate 28 with which the temperature detection members 41 and 42 are in contact is a cross section in a direction intersecting the longitudinal direction of the heater 25 (a cross section in the lateral direction B shown in FIGS. 4 and 5). ), it is formed in an arcuate concave shape.

FIG. 6 shows a perspective view of the heat equalizing plate 28 according to this embodiment.

As shown in FIG. 6, the concave surface 28a of the heat equalizing plate 28 with which the temperature detecting members 41 and 42 are in contact is formed continuously with the same cross-sectional shape over the longitudinal direction A of the heater. Specifically, the concave surface 28 is most concave at the center 28b in the short direction B of the heater 25, and has an inclined surface 28c extending in an arc shape so that the depth gradually decreases from the center to both ends in the short direction B. have.

As described above, in the present embodiment, since the surface of the heat equalizing plate 28 on the side of the temperature detecting members 41 and 42 is formed as the concave surface 28a, the positions of the temperature detecting members 41 and 42 are aligned in the lateral direction of the heater. Even if it deviates from the center of B to one side of both ends, the temperature detecting 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 displaced from the center 28b in the lateral direction B, the spring 36 presses the temperature detection members 41 and 42 against the inclined surface 28c. A force F is generated to return the temperature detection members 41 and 42 to the center 28b following the inclination of the surface 28c. As a result, the temperature detection members 41 and 42 are returned to the center 28b side, so that positional deviation of the temperature detection members 41 and 42 in the lateral direction B of the heater can be suppressed. Management reliability and safety can be improved.

The smaller the radius of curvature of the inclined surface 28c, the greater the force F that returns the temperature detection members 41 and 42 toward the center 28b. Force F becomes weaker. Therefore, 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 (see FIG. 4 or FIG. 5). The radius of curvature of the fixing belt here means the radius of curvature of the fixing belt in a circular state without being subjected to external force. By making the radius of curvature R1 of the inclined surface 28c smaller than the radius of curvature R2 of the fixing belt 21 in this way, the temperature detecting members 41 and 42 can be effectively maintained in position by the inclined surface 28c and restored in the event of positional deviation. will be able to perform effectively.

Moreover, even if the position of the thermistor 41 deviates in the lateral direction B of the heater, the contact pressure of the thermistor 41 with respect to the heat equalizer plate 28 increases at the deviated position. can. That is, when the position of the thermistor 41 shifts from the center in the width direction of the heater to the end side, the thermistor 41 moves along the inclined surface 28c of the heat equalizing plate 28, thereby compressing the spring 36. The elastic repulsive force of 36 increases, and the contact pressure of the thermistor 41 against the heat equalizing plate 28 increases. As a result, the thermistor 41 comes into close contact with the heat equalizing plate 28 and the contact area increases, so that the amount of heat transferred from the heater 25 to the thermistor 41 via the heat equalizing plate 28 increases. As a result, it is possible to suppress a decrease in the detected temperature due to the thermistor 41 shifting from the center where the temperature of the heater 25 is high to the end side where the temperature is low, thereby suppressing a decrease in accuracy of temperature control.

Further, as shown in the enlarged view of FIG. 8, the thermistor 41 has a thermistor element 41a as a temperature detection element that detects the temperature of the object by coming into contact with the object. Therefore, it is preferable that at least the thermistor element 41 a is in contact with the concave surface 28 a of the heat equalizing plate 28 .

On the other hand, FIG. 9 is an enlarged view showing a state in which the thermostat 42 is in contact with the heat equalizing plate 28. As shown in FIG. As shown in FIG. 9, the thermostat 42 has a bimetal 42a made by pasting together metal materials with different coefficients of thermal expansion. The bimetal 42a is a heat-sensitive current-breaking element that deforms when the temperature of the heater 25 rises and exceeds a predetermined temperature, and cuts off the current to the heater 25. As shown in FIG. 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, so the responsiveness when the temperature of the heater 25 rises is improved. However, when the temperature of the heater 25 is controlled in a high temperature range (for example, 200° C. or higher), the amount of heat transferred to the bimetal 42a becomes too large, causing the thermostat 42 to malfunction during a normal temperature rise. There is a possibility that the energization to the heater 25 will be interrupted. Therefore, in order to reduce the possibility of such malfunction, it is preferable that the amount of heat transferred from the heater 25 to the bimetal 42a is not excessively increased.

Therefore, in this embodiment, as shown in FIG. 9, the surface of the heat equalizer 28 on the side of the thermostat 42 is formed as a concave surface 28a so that the bimetal 42a does not come into contact with the heat equalizer 28. FIG. That is, since the heat equalizing plate 28 has a concave surface 28a instead of a flat surface, the housing of the thermostat 42 or the like contacts the concave surface 28a of the heat equalizing plate 28, so that the bimetal 42a is lifted from the concave surface 28a. are placed in the same position. By arranging the bimetal 42a in a non-contact state with respect to the heat equalizing plate 28 in this manner, heat transfer to the bimetal 42a is suppressed, and the risk of malfunction of the thermostat 42 can be reduced.

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). is obtained, and good operation of the thermostat 42 can be ensured when the temperature becomes abnormally high. On the other hand, 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 is reduced, and there is a risk that the thermostat 42 will not operate well at abnormally high temperatures. There is Therefore, in order to ensure good operation of the thermostat 42 at an abnormally high temperature and improve reliability, the thermostat 42 is brought into contact with the heat equalizing plate 28 at a portion other than the bimetal 42a as in the present embodiment. is preferred. Thus, in this embodiment, by forming the thermostat 42 side surface of the heat equalizing plate 28 into 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. is possible.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the gist of the invention.

For example, in the above embodiment, the concave surface 28a of the heat equalizer plate 28 has an arcuate cross-sectional shape, but as in the example shown in FIG. A recessed shape (V-shaped) having linear inclined surfaces 28c that incline toward the center from both ends in the direction B may be employed. Moreover, the concave surface 28a may have a shape including a curved line and a straight line. Further, the concave surface 28a is not necessarily formed symmetrically with respect to the center in the lateral direction B, and may be formed asymmetrically.

Further, the present invention is not limited to the configuration of the free belt system in which the fixing belt is rotatably held by a pair of belt holding members as shown in FIG. It is also applicable to a suspended configuration.

REFERENCE SIGNS LIST 1 image forming apparatus 20 fixing device 21 fixing belt 22 pressure roller (pressure member)
25 heater (heating source)
28 heat equalizing plate (heat transfer auxiliary member)
28a concave surface 28b center 28c inclined surface 41 thermistor (temperature detection member)
41a thermistor element (temperature detection element)
42 thermostat (temperature detection member)
42a Bimetal (heat-sensitive current interrupting element)
100 fixing nip

Japanese Patent Application Laid-Open No. 2019-91028

Claims (7)

a rotatable endless fixing belt;
a rotatable pressure member contacting the outer peripheral surface of the fixing belt to form a fixing nip;
a heating source that heats the fixing belt;
a temperature detection member that detects the temperature of the heating source;
A fixing device comprising a heat transfer auxiliary member interposed between the heat source and the temperature detection member,
The surface of the auxiliary heat transfer member with which the temperature detection member is in contact has a concave shape with slanted surfaces slanted from both ends toward the center in a cross section in a direction intersecting the longitudinal direction of the heat source. A fixing device comprising: 2. The fixing device according to claim 1, wherein the temperature detecting member is biased by a biasing member in a direction of contact with the heat transfer assisting member. 3. The fixing device according to claim 1, wherein the inclined surface is curved. The fixing device according to claim 3, wherein the radius of curvature of the inclined surface is smaller than the radius of curvature of the fixing belt. The temperature detection member has a temperature detection element that contacts an object and detects the temperature of the object,
The fixing device according to any one of claims 1 to 4, wherein the temperature detection member contacts the concave surface of the heat transfer assisting member at least at a temperature detection element portion. The temperature detection member has a heat-sensitive current-disconnecting element that deforms when the temperature exceeds a predetermined temperature to cut off the current supply to the heat source,
The fixing device according to any one of claims 1 to 4, wherein the temperature detecting member contacts the concave surface of the heat transfer assisting member at a portion other than the heat-sensitive current interrupting element. An image forming apparatus comprising the fixing device according to claim 1 .

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