JP2024086719A - Heating device having a thermal switch - Google Patents

Abstract

[Problem] To provide a heating device having a thermal switch. [Solution] The heating device of one embodiment includes a substrate (71), a heating element (72) provided on the substrate and extending in the longitudinal direction between a pair of electrodes, and a thermal switch (75) located between the pair of electrodes in the longitudinal direction, the thermal switch including a deformable conductor that moves away from the heating element when the temperature is below a threshold temperature and deforms to contact the heating element when the temperature reaches the threshold temperature. [Selected Figure]

Description

The image forming system includes a transport device that transports the print medium, a photoconductor on which an electrostatic latent image is formed, a developing device that develops the electrostatic latent image, a transfer device that transfers the toner image to the print medium, a fixing device that fixes the toner image to the print medium, and a discharge device that discharges the print medium.

1 is a schematic diagram of an exemplary imaging device that can be used to implement various examples disclosed herein. FIG. 1 is a perspective view of an exemplary fixing device. FIG. 4 is a cross-sectional view of the fixing device taken along line IV-IV in FIG. 3. FIG. 1 is a perspective view of an exemplary heating device. 1A is an exemplary top view of a thermal switch when at a first temperature; FIG. 1B is a side view of the thermal switch; and FIG. 4A is an exemplary side view of a thermal switch when at a second temperature, and FIG. 4B is a front view thereof; 4A is an exemplary side view of a thermal switch when at a third temperature, and FIG. 4B is a front view thereof; 5A to 5C are cross-sectional views showing the operation of the heating device. 4 is a diagram showing a schematic diagram of an electrical connection relationship between a plurality of heat-sensitive switches and a heating element. FIG. FIG. 11 is a cross-sectional view showing a modified example of the heating device. FIG. 13 is a side view showing a modified example of the thermal switch.

Below, a heating device having a thermal switch, a fixing device including the heating device, and an image forming apparatus including the fixing device will be described with reference to the drawings. Note that in describing the drawings, identical elements or elements having the same functions will be given the same reference numerals and duplicated descriptions will be omitted. The drawings may be partially simplified or exaggerated to facilitate understanding, and the dimensional ratios and angles, etc. are not limited to those shown in the drawings.

The image forming apparatus according to the present disclosure is, for example, a printer or other image forming apparatus. This image forming apparatus includes a fixing device that fixes a toner image to a print medium. As described below, the fixing device includes a heating device that heats the print medium. When the paper onto which the toner image has been transferred passes through a fixing nip area formed between a rotating body and a pressure roller, the fixing device applies pressure to the paper while heating it, thereby fixing the toner image to the paper.

Image forming devices may be capable of forming images on different sizes of paper. When a small size paper is passed through the fixing nip area, the rotating body has a paper passing portion that contacts the paper and a non-paper passing portion that does not contact the paper. Since the heat of the fixing belt is not absorbed by the paper in the non-paper passing portion, the temperature of the non-paper passing portion may become excessively high if the rotating body is heated uniformly in the longitudinal direction. Such a partial temperature rise can cause malfunctions in the parts of the fixing device. The heating device disclosed herein has a function of automatically controlling the heating area of the rotating body according to the size of the paper.

FIG. 1 is a schematic diagram of an exemplary image forming apparatus. The image forming apparatus 1 shown in FIG. 1 is an apparatus for forming a color image using each of the colors cyan, magenta, yellow, and black. The image forming apparatus 1 includes a conveying device 10 for conveying a print medium, paper 5, a plurality of developing devices 20C, 20M, 20Y, and 20K for developing an electrostatic latent image (hereinafter, when it is not necessary to distinguish between the individual components, they will be referred to as "developing devices 20"). A transfer device 30 for secondary transfer of the toner images of each color onto the paper 5, a plurality of photoconductors 40C, 40M, 40Y, and 40K on whose surfaces electrostatic latent images are formed (hereinafter, when it is not necessary to distinguish between the individual components, they will be referred to as "photoconductors 40"). A fixing device 50 for fixing the laminated toner image onto the paper 5, and a discharge device 60 for discharging the paper 5. The conveying device 10, the developing device 20, the transfer device 30, the photoconductor 40, the fixing device 50, and the discharge device 60 are housed within the housing 15 of the image forming device 1.

The conveying device 10 conveys paper 5, which is the print medium on which an image is formed, on a conveying path 12. The paper 5 is stored in a stack in a cassette 7, and is picked up and conveyed by a paper feed roller 11. The conveying device 10 causes the paper 5 to reach the transfer area 13 via the conveying path 12 at the timing when the toner image to be transferred to the paper 5 reaches the transfer area 13.

The developing devices 20C, 20M, 20Y, and 20K are provided for each color. Each developing device 20 is equipped with a developing roller 45 that carries toner on the photoconductor 40. The developing device 20 uses a two-component developer containing toner and carrier as the developer. In other words, in the developing device 20, the toner and carrier are adjusted to a desired mixture ratio, and then mixed and stirred to uniformly disperse the toner and prepare a developer with an optimal charge. This developer is carried by the developing roller 45. Then, when the developer is transported to the development area facing the photoconductor 40 by the rotation of the developing roller 45, the toner contained in the developer carried by the developing roller 45 moves to the electrostatic latent image formed on the peripheral surface of the photoconductor 40, and the electrostatic latent image is developed.

The transfer device 30 transports the toner image formed by the developing device 20 to the transfer area 13 where the toner image is secondarily transferred to the paper 5. The transfer device 30 includes an intermediate transfer belt 31 onto which the toner image is primarily transferred from the photoreceptor 40, a tension roller 34 that tensions the intermediate transfer belt 31, idler rollers 35 and 36, a drive roller 37 that drives the intermediate transfer belt 31, primary transfer rollers 32C, 32M, 32Y, and 32K that respectively hold the intermediate transfer belt 31 together with the photoreceptors 40C, 40M, 40Y, and 40K, and a secondary transfer roller 33 that holds the intermediate transfer belt 31 together with the drive roller 37.

The photoconductors 40C, 40M, 40Y, and 40K are also called electrostatic latent image carriers, photoconductor drums, etc. The photoconductors 40C, 40M, 40Y, and 40K are provided for each color. Each photoconductor 40 is provided along the direction of movement of the intermediate transfer belt 31. A developing device 20, a charging device 41, an exposure unit 42, and a cleaning device 43 are provided around the photoconductor 40.

The charging device 41 is, for example, a charging roller that contacts the photoreceptor 40, and uniformly charges the surface of the photoreceptor 40 to a predetermined potential. The exposure unit 42 exposes the surface of the photoreceptor 40 charged by the charging device 41 according to the image to be formed on the paper 5. This changes the potential of the portion of the surface of the photoreceptor 40 exposed by the exposure unit 42, and an electrostatic latent image is formed. The developing devices 20C, 20M, 20Y, and 20K develop the electrostatic latent image formed on the photoreceptor 40 with toner supplied from the toner tanks 18C, 18M, 18Y, and 18K provided opposite the respective developing devices 20, and generate a toner image. The toner tanks 18C, 18M, 18Y, and 18K are filled with cyan, magenta, yellow, and black toner, respectively. The cleaning device 43 collects the toner remaining on the photoreceptor 40 after the toner image formed on the photoreceptor 40 is primarily transferred to the intermediate transfer belt 31.

The fixing device 50 fixes the toner image, which has been secondarily transferred from the intermediate transfer belt 31 to the paper 5, to the paper 5 by passing the paper 5 through the fixing nip area 14. The fixing device 50 includes a fixing belt 51, which is a rotatable rotating body, and a pressure roller 52 that is pressed against the outer circumferential surface of the fixing belt 51. The fixing belt 51 and the pressure roller 52 are housed in a casing 53. A fixing nip area 14 is formed between the fixing belt 51 and the pressure roller 52. The fixing belt 51 includes a heating device 70 that heats the paper 5. The heating device 70 heats the paper 5 that passes through the fixing nip area 14. The toner image is melted and fixed to the paper 5 by applying pressure to the paper 5 while heating it in the fixing nip area 14.

The discharge device 60 is equipped with discharge rollers 62, 64 for discharging the paper 5 on which the toner image has been fixed by the fixing device 50 to the outside of the device.

The image forming device 1 further includes a control device 80. The control device 80 is a computer equipped with a processor, a memory unit, an input device, a display device, etc., and has the function of controlling the overall operation of the image forming device 1. The memory unit of the control device 80 stores a control program for controlling various processes executed by the image forming device 1 by the processor.

Figure 2 is a perspective view of an exemplary fixing device 50, and Figure 3 is a cross-sectional view of the fixing device 50. As described above, the fixing device 50 includes a fixing belt 51 which is a rotating body, a pressure roller 52 which is in pressure contact with the fixing belt 51, and a heating device 70 which heats the fixing belt 51. The fixing belt 51 is a belt having a substantially cylindrical shape made of an elastic material such as resin. The fixing belt 51 extends along an axis 16 and is supported by a casing 53 so as to be rotatable around the axis 16 (see Figure 1).

The pressure roller 52 has a generally cylindrical or columnar shape and extends parallel to the axis 16 adjacent to the fixing belt 51. The pressure roller 52 has, for example, a core 65, an elastic layer 66, and a release layer 67. The core 65 extends parallel to the axis 16, and both ends thereof are rotatably supported by the casing 53. The elastic layer 66 is made of an elastic material and covers the outer peripheral surface of the core 65. The release layer 67 is made of a resin composition and covers the outer peripheral surface of the elastic layer 66. The pressure roller 52 is in pressure contact with the fixing belt 51 to form a fixing nip region 14 between the fixing belt 51 and the pressure roller 52.

The pressure roller 52 is connected to a drive motor. The driving force of the drive motor is transmitted to the pressure roller 52, causing the pressure roller 52 to rotate. The pressure roller 52 rotates while being pressed against the fixing belt 51, causing the fixing belt 51 to rotate. The rotation speed of the pressure roller 52 is controlled by the control device 80 controlling the operation of the drive motor.

Figure 4 is a cross-sectional view of the fixing device 50 taken along line IV-IV in Figure 3. As shown in Figures 3 and 4, a heating device 70 for heating the fixing belt 51 is provided inside the fixing belt 51. The heating device 70 includes a substrate 71, a heating element 72, a heater holder 73, a support member 74, and a plurality of heat-sensitive switches 75.

Figure 5 is a perspective view of the heating device 70. For ease of explanation, the heater holder 73 and the support member 74 are omitted in Figure 5 to illustrate the heating device 70. The substrate 71 is, for example, a ceramic substrate such as alumina having high thermal conductivity, and transmits heat generated in the heating element 72 to the fixing belt 51. As shown in Figures 4 and 5, the substrate 71 has a substantially rectangular shape extending in a direction parallel to the axis 16. In the following explanation, the direction parallel to the axis 16 is sometimes referred to as the "longitudinal direction", and the direction perpendicular to the longitudinal direction along the surface of the substrate 71 is sometimes referred to as the "width direction".

The heating element 72 is a resistive heating element that generates heat when power is supplied. The heating element 72 is made of, for example, an alloy containing silver and palladium, or a ceramic such as SiC. The heating element 72 is provided on the substrate 71 and extends in the longitudinal direction. As shown in FIG. 5, the width of the heating element 72 in the width direction is smaller than the width of the substrate 71 in the width direction.

4, the heating element 72 includes a first end 81, a second end 82 opposite to the first end, and a central portion 83 disposed between the first end 81 and the second end 82 in the longitudinal direction. A first electrode 76 is connected to the longitudinal end of the first end 81. A second electrode 77 is connected to the longitudinal end of the second end 82. The first electrode 76 and the second electrode 77 are made of a conductor such as a metal, and constitute a pair of electrodes of the heating element 72. That is, the heating element 72 extends in the longitudinal direction between the first electrode 76 and the second electrode 77. The upper surface of the heating element 72 may be covered with an insulating film, except for a plurality of contacts 200 (areas facing the contact portions 92 of the thermal switch 75) described later.

The first electrode 76 is connected to the power source 68 through the first conductor path 78. The second electrode 77 is electrically grounded through the second conductor path 79. The first conductor path 78 and the second conductor path 79 are electrically unconnected. Therefore, when a voltage is applied from the power source 68 to the first electrode 76, a current flows through the entire length of the heating element 72, and the heating element 72 generates heat between the first electrode 76 and the second electrode 77. The heat generated by the heating element 72 is transferred to the paper 5 placed in the fixing nip area 14 via the substrate 71 and the fixing belt 51, and the toner image on the paper 5 is fixed.

The heater holder 73 is provided on the heating element 72. The heater holder 73 is made of, for example, a resin having high heat resistance and electrical insulation properties, and holds a plurality of thermal switches 75 by clamping them.

The support member 74 extends in the longitudinal direction inside the fixing belt 51 and supports the heater holder 73. The support member 74 is, for example, a metal member with a U-shaped cross section, and both ends of the support member 74 are fixed to the casing 53. The substrate 71 is supported by the support member 74 via the heater holder 73, and is fixed inside the fixing belt 51. Therefore, when the toner image is fixed to the paper 5, the fixing belt 51 rotates while sliding against the substrate 71.

As shown in Figs. 4 and 5, the multiple heat-sensitive switches 75 are arranged spaced apart from each other in the longitudinal direction between the first electrode 76 and the second electrode 77. The multiple heat-sensitive switches 75 have the function of controlling the range in which current flows through the heating element 72. The multiple heat-sensitive switches 75 include multiple first heat-sensitive switches 84 arranged opposite the first end 81 of the heating element 72, and multiple second heat-sensitive switches 85 arranged opposite the second end 82 of the heating element 72.

The first heat-sensitive switches 84 include heat-sensitive switches 101, 102, 103, 104, 105, and 106. The heat-sensitive switches 101 to 106 are arranged in this order from the center 83 of the heating element 72 toward the first electrode 76, with a gap between them. The second heat-sensitive switches 85 include heat-sensitive switches 111, 112, 113, 114, 115, and 116. The heat-sensitive switches 111 to 116 are arranged in this order from the center 83 of the heating element 72 toward the second electrode 77, with a gap between them. The first heat-sensitive switches 84 and the second heat-sensitive switches 85 are arranged at positions according to a predetermined paper size.

For example, the distance W1 between the thermal switch 101 and the thermal switch 111 in the longitudinal direction corresponds to the width of the first size paper 5, which is the smallest size of the multiple sizes of paper 5 that can be printed by the image forming device 1. The distance W2 between the thermal switch 102 and the thermal switch 112 in the longitudinal direction corresponds to the width of the second size paper 5, which is larger than the first size. Similarly, the distance W3 between the thermal switch 103 and the thermal switch 113, the distance W4 between the thermal switch 104 and the thermal switch 114, the distance W5 between the thermal switch 105 and the thermal switch 115, and the distance W6 between the thermal switch 106 and the thermal switch 116 correspond to the widths of the third size larger than the second size, the fourth size larger than the third size, the fifth size larger than the fourth size, and the sixth size larger than the fifth size, respectively. For example, the first size, second size, third size, fourth size, fifth size, and sixth size correspond to A6S size, A5S size, B5S size, A4S size, B4S size, and A4L size, respectively.

The plurality of first thermal switches 84 are electrically connected to the first electrode 76 of the heating element 72 and the power source 68 through the first conductor path 78. The second thermal switch 85 is electrically grounded through the second conductor path 79. In other words, the first conductor path 78 is connected to the first electrode 76 and the plurality of first thermal switches 84, and the second conductor path 79 is connected to the second electrode 77 and the plurality of second thermal switches 85.

The configuration of each heat-sensitive switch 75 will be described. Fig. 6(a) is a top view of the heat-sensitive switch 75 when it is at a first temperature, Fig. 6(b) is a side view of the heat-sensitive switch 75, and Fig. 6(c) is a front view of the heat-sensitive switch 75 as viewed from the longitudinal direction. The first temperature is, for example, room temperature (20°C). As shown in Figs. 6(a) to 6(c), each of the multiple heat-sensitive switches 75 includes a deformable conductor 86 that can be reversibly deformed in response to temperature, and a support 87 that supports the deformable conductor 86.

As shown in FIG. 6(c), the support 87 includes a pair of legs 93 in contact with the substrate 71 and a bridge 94 supported by the pair of legs. The pair of legs 93 are erected on the substrate 71 across the heating element 72 in the width direction of the substrate 71. As shown in FIG. 3, at least a portion of the pair of legs 93 may be sandwiched between the substrate 71 and the heater holder 73. The bridge 94 is bridged between the pair of legs 93 above the heating element 72 so as not to come into contact with the heating element 72. The support 87 transfers heat from the substrate 71 to the deformable conductor 86. Therefore, the support 87 is made of a metal or the like having high thermal conductivity.

The deformable conductor 86 includes a bimetal plate 91 and a contact portion 92. The bimetal plate 91 extends longitudinally from a bridge 94 of the support 87. That is, one end of the bimetal plate 91 is connected to the bridge 94 of the support 87, and the other end of the bimetal plate 91 is a free end. The contact portion 92 is provided at the free end of the bimetal plate 91.

As shown in FIG. 6(b), the bimetal plate 91 is formed by bonding together a first plate 121 having a relatively high coefficient of thermal expansion and a second plate 122 having a relatively low coefficient of thermal expansion. By bonding together the first plate 121 and the second plate 122 having different coefficients of thermal expansion, the bimetal plate 91 bends in response to an increase in temperature. When the temperature of the bimetal plate 91 is at the first temperature, as shown in FIG. 6(b) and FIG. 6(c), the contact portion 92 of the deformable conductor 86 is positioned away from the heating element 72.

When the heat of the substrate 71 is transferred to the bimetal plate 91 through the support 87 and the temperature of the bimetal plate 91 reaches the second temperature, as shown in FIG. 7(a) and FIG. 7(b), the bimetal plate 91 bends toward the heating element 72 due to the difference in the thermal expansion coefficients of the first plate 121 and the second plate 122. The second temperature is higher than the first temperature and is lower than the threshold temperature. The threshold temperature is a temperature determined by the designer, and is, for example, 220°C. As shown in FIG. 7(a) and FIG. 7(b), at the second temperature, the contact portion 92 of the deformable conductor 86 is spaced apart from the heating element 72.

On the other hand, when the temperature of the bimetal plate 91 reaches the third temperature, as shown in FIG. 8(a) and FIG. 8(b), the bimetal plate 91 bends further toward the heating element 72, and the contact portion 92 of the deformable conductor 86 comes into contact with the heating element 72. The third temperature is a temperature equal to or higher than the threshold temperature. When the deformable conductor 86 comes into contact with the heating element 72, the thermal switch 75 and the heating element 72 are electrically connected.

As described above, the deformable conductor 86 deforms to move away from the heating element 72 when its temperature is below the threshold temperature, and to contact the heating element 72 when its temperature reaches the threshold temperature. That is, the heating element 72 has a plurality of contacts 200 with which the deformable conductors 86 of the plurality of heat-sensitive switches 75 contact each other. As shown in FIG. 4, the plurality of contacts 200 of the heating element 72 are arranged in the longitudinal direction corresponding to the positions of the plurality of heat-sensitive switches 75. More specifically, the deformable conductors 86 of the heat-sensitive switches 101 to 106 can contact the contacts 201, 202, 203, 204, 205, and 206 of the plurality of contacts 200 of the heating element 72. The deformable conductors 86 of the heat-sensitive switches 111 to 116 can contact the contacts 211, 212, 213, 214, 215, and 216 of the plurality of contacts 200 of the heating element 72.

When each of the first heat-sensitive switches 84 comes into contact with a corresponding one of the contacts 201-206, the contact is electrically connected to the first electrode 76. That is, when one of the first heat-sensitive switches 84 comes into contact with a corresponding one of the contacts 201-206, the contact is shorted to the first conductor path 78. When each of the second heat-sensitive switches 85 comes into contact with a corresponding one of the contacts 211-216, the contact is electrically connected to the second electrode 77. That is, when one of the second heat-sensitive switches 85 comes into contact with a corresponding one of the contacts 211-216, the contact is shorted to the second conductor path 79.

The operation of the heating device 70 when the paper 5 passes through the fixing nip area 14 of the fixing device 50 will be described with reference to Figures 4 and 9. When the paper 5 passes through the fixing nip area 14, power is supplied from the power source 68 to the heating element 72. At this time, if the size of the paper 5 passing through the fixing nip area 14 is the largest size among the multiple sizes of paper 5 that can be printed by the image forming device 1, the deformable conductors 86 of the multiple heat-sensitive switches 75 are separated from the heating element 72 as shown in Figure 4. As a result, a current flows through the heating element 72 between the first electrode 76 and the second electrode 77, and the heating element 72 generates heat over the entire longitudinal area.

On the other hand, if the width of the paper 5 passing through the fixing nip area 14 is smaller than the overall length of the heating element 72, the heat transferred from the heating element 72 to the substrate 71 is not taken away by the paper 5, and the temperature of the fixing belt 51 rises in the non-paper passing portion that does not contact the paper 5. For example, if the size of the paper passing through the fixing nip area 14 is the third size corresponding to the distance W3, the temperature of the substrate 71 becomes excessively high outside the area between the contact points 203 and 213 of the heating element 72. If the temperature of the substrate 71 becomes excessively high, there is a risk of damage to components such as the heating element 72 and the heater holder 73.

In contrast, in the heating device 70, the temperature of the substrate 71 rises outside the area between the contacts 203 and 213, which correspond to the non-paper passing portion. For example, when the temperatures of the heat sensitive switches 104 and 105 of the first heat sensitive switches 84 and the heat sensitive switches 114 and 115 of the second heat sensitive switches 85 reach a threshold temperature, the deformable conductors 86 of the heat sensitive switches 104, 105, 114 and 115 deform and come into contact with the contacts 204, 205, 214 and 215 of the heating element 72, respectively, as shown in FIG. 9.

Figure 10 shows a schematic diagram of the electrical connection between the multiple heat-sensitive switches 75 and the heating element 72. As shown in Figure 10, when the heat-sensitive switches 104, 105 come into contact with the contacts 204, 205 of the heating element 72, the contacts 204, 205 of the heating element 72 are electrically connected to the first conductor path 78 via the heat-sensitive switches 104, 105, causing an electrical short circuit. Similarly, when the heat-sensitive switches 114, 115 come into contact with the contacts 214, 215 of the heating element 72, the contacts 214, 215 of the heating element 72 are electrically connected to the second conductor path 79 via the heat-sensitive switches 114, 115, causing an electrical short circuit.

Because current selectively flows through paths with small electrical resistance, when an electrical short occurs in the heating element 72, as shown by the arrows in FIG. 10, the current from the power source 68 is introduced from the first conductor path 78 through the heat-sensitive switch 104 to the contact 204 of the heating element 72, and passes through the heating element 72 in the region 130 between the contact 204 and the contact 214. The current that passed through the heating element 72 is output from the contact 214 through the heat-sensitive switch 114 to the second conductor path 79. That is, the current supplied from the power source 68 bypasses the region 131 between the first electrode 76 and the contact 204, and the region 132 between the contact 214 and the second electrode 77, and flows only through the region 130 between the contact 204 and the contact 214. Therefore, heating of the region 131 and the region 132 corresponding to the non-paper passing portion is stopped, and the region 130 corresponding to the paper passing portion can be selectively heated. This prevents the non-paper passing areas of the fixing belt 51 from being overheated.

After the third size paper 5 has passed through the fixing nip area 14, if a paper 5 larger than the third size passes through the fixing nip area 14 and the temperature of the thermal switches 104, 105, 114, 115 falls below the threshold temperature, the deformable conductors 86 of the thermal switches 104, 105, 114, 115 return to positions away from the contacts 204, 205, 214, 215 of the heating element 72. As a result, the heating range of the heating element 72 is expanded. In other words, the deformable conductors 86 of the multiple thermal switches 75 reversibly deform according to the temperature.

As described above, in the heating device 70, when small-sized paper is passed through the fixing nip area 14, some of the multiple thermal switches 75 are electrically coupled to the heating element 72 in response to the temperature at each position on the substrate 71, and the current path is automatically controlled so that the current selectively flows to the area corresponding to the paper-passing portion, bypassing the area of the heating element 72 corresponding to the non-paper-passing portion. This limits the heat generation range of the heating element 72 to the area corresponding to the paper-passing portion, preventing the temperature of the non-paper-passing portion of the fixing belt 51 from becoming excessively high.

It is to be understood that not all aspects, advantages, and features described herein are necessarily achieved or included in any one particular example and embodiment. Indeed, while various examples have been described and illustrated herein, it should be apparent that other examples can be modified in arrangement and detail. We claim all modifications and variations that fall within the spirit and scope of the subject matter claimed herein.

For example, in FIG. 4, the heating device 70 includes a plurality of first heat-sensitive switches 84 arranged on the first end 81 of the heating element 72 and a plurality of second heat-sensitive switches 85 arranged on the second end 82 of the heating element 72, but the heating device 70 may include only one first heat-sensitive switch 84 and one second heat-sensitive switch 85.

The heating device 70 may be provided with either the first heat-sensitive switch 84 or the second heat-sensitive switch 85. There are two methods for passing small-sized paper 5 through the fixing nip area 14: aligning the center of the paper 5 with the center of the fixing belt 51 in the longitudinal direction, and aligning an edge of the paper 5 with one end of the fixing belt 51 in the longitudinal direction. When aligning an edge of the paper 5 with one end of the fixing belt 51, a non-paper passing portion is formed only at the other end of the fixing belt 51. In this case, even if a heat-sensitive switch is installed only on the other end side in the longitudinal direction, it is possible to prevent the non-paper passing portion from being excessively heated.

The heating device 70 may be provided with only one heat-sensitive switch 75. For example, as shown in FIG. 11, the heating device 70 may be provided with only one heat-sensitive switch 75. When the edge of the paper 5 is aligned with one end of the fixing belt 51, even if only one heat-sensitive switch 75 is provided, the range in which the heating element 72 generates heat can be controlled according to two different sizes of paper 5.

Figure 12 is a side view showing a modified example of the thermal switch 75. As shown in Figure 12, the surface of the contact portion 92 of the deformable conductor 86 is covered with a conductive protective layer 135 containing silicon carbide (SiC) or titanium nitride (TiN). Silicon carbide and titanium nitride have high abrasion resistance, so that abrasion of the contact portion 92 can be suppressed when the contact portion 92 of the deformable conductor 86 repeatedly comes into contact with the contact 200 of the heating element 72.

The deformable conductor 86 does not necessarily have to have the bimetal plate 91, so long as it is deformable so as to move away from the heating element 72 when its temperature is below the threshold temperature and to contact the heating element 72 when its temperature reaches the threshold temperature. For example, the deformable conductor 86 may have a heat-sensitive shape memory alloy or a conductive shape memory polymer instead of the bimetal plate 91.

8(a) and 8(b), the contact portion 92 of the deformable conductor 86 is in point contact with the heating element 72, but the contact portion 92 may have a line or surface extending in the width direction and may be in line or surface contact with the entire width of the heating element 72 at the corresponding position. The various embodiments described above can be combined to the extent that no contradictions exist.

Claims (15)

A substrate;
a heating element provided on the substrate and extending in a longitudinal direction between a pair of electrodes;
a thermal switch located between the pair of electrodes in the longitudinal direction;
Equipped with
A heating device, wherein the thermal switch includes a deformable conductor that deforms away from the heating element when the temperature is below a threshold temperature and into contact with the heating element when the temperature reaches the threshold temperature. The heating device according to claim 1, wherein the heat-sensitive switch is one of a plurality of heat-sensitive switches arranged at intervals in the longitudinal direction at positions according to a predetermined paper size. the pair of electrodes includes a first electrode connected to a first end of the heating element and a second electrode connected to a second end of the heating element;
3. The heating device of claim 2, wherein the plurality of thermal switches includes a first thermal switch arranged opposite the first end of the heating element, and a second thermal switch arranged opposite the second end of the heating element. the first thermal switch is electrically connected to the first electrode;
The heating device of claim 3 , wherein the second thermal switch is electrically connected to the second electrode. The first electrode is electrically connected to a power source that supplies power to the heating element;
The heating device of claim 4 , wherein the second electrode is electrically grounded. the first thermal switch and the second thermal switch are capable of contacting a first contact and a second contact of the heating element, respectively;
the first thermal switch electrically connects the first contact to the first electrode when the first thermal switch comes into contact with the first contact of the heating element;
The heating device according to claim 3 , wherein the second thermal switch electrically connects the second contact to the second electrode when the second thermal switch comes into contact with the second contact of the heating element. The thermal switch is
a support for supporting the deformable conductor, the support including legs contacting the substrate and a bridge spaced apart from the heating element;
a bimetal plate extending from the bridge and bending toward the heating element in response to an increase in temperature transmitted through the support;
The heating device of claim 1 . The heating device according to claim 7, wherein the deformable conductor is provided on the bimetal plate and includes a contact portion that contacts the heating element in response to bending of the bimetal plate, and the surface of the contact portion is covered with a protective layer containing silicon carbide or titanium nitride. A rotatable rotor;
a rotatable pressure roller that is in pressure contact with the rotating body;
a heating device for heating the rotating body, the heating device including a substrate, a heating element provided on the substrate and extending in a longitudinal direction between a pair of electrodes, and a thermal switch located between the pair of electrodes in the longitudinal direction;
Equipped with
The thermal switch includes a deformable conductor that deforms away from the heating element when the temperature is below a threshold temperature and deforms into contact with the heating element when the temperature reaches the threshold temperature. The fixing device according to claim 9, wherein the thermal switch of the heating device is one of a plurality of thermal switches arranged at intervals in the longitudinal direction at positions corresponding to a predetermined paper size. The pair of electrodes of the heating device includes a first electrode connected to a first end of the heating element and a second electrode connected to a second end of the heating element,
11. The fixing device of claim 10, wherein the plurality of thermal switches include a first thermal switch arranged opposite the first end of the heating element, and a second thermal switch arranged opposite the second end of the heating element. the first thermal switch is electrically connected to the first electrode;
The fixing device according to claim 11 , wherein the second thermal switch is electrically connected to the second electrode. The thermal switch is
a support for supporting the deformable conductor, the support including legs contacting the substrate and a bridge spaced apart from the heating element;
a bimetal plate extending from the bridge and bending toward the heating element in response to an increase in temperature transmitted through the support;
The fixing device according to claim 9 . a transfer device that transfers the toner image onto a print medium;
a fixing device for fixing the toner image to the print medium;
Equipped with
The fixing device is
A rotatable rotor;
a rotatable pressure roller that is in pressure contact with the rotating body;
a heating device for heating the rotating body, the heating device including a substrate, a heating element provided on the substrate and extending in a longitudinal direction between a pair of electrodes, and a thermal switch located between the pair of electrodes in the longitudinal direction;
Equipped with
The thermal switch includes a deformable conductor that deforms away from the heating element when the temperature is below a threshold temperature and deforms into contact with the heating element when the temperature reaches the threshold temperature. 15. The image forming apparatus according to claim 14, wherein the thermal switch is one of a plurality of thermal switches arranged spaced apart from one another in the longitudinal direction at positions according to a predetermined paper size.

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