JP7622522B2 - Heating device, fixing device, image forming apparatus - Google Patents

Description

The present invention relates to a heating device, a fixing device, and an image forming device.

The heating device, which fixes the toner on the paper by heat, is provided with a fixing belt as a rotating member and a planar heating member with a resistance heating element on a substrate. The heating member is provided along the length of the fixing belt and heats the fixing belt to a predetermined fixing temperature.

In such a fixing device, a temperature detection member is provided to detect the temperature of the heating member. By controlling the flow of electricity to the heating member based on the detection result of this temperature detection member, the fixing belt can be heated to an appropriate temperature.

For example, in the fixing device of Patent Document 1 (JP 2018-169417 A), the heating section where the heating element heats has a curved section that is curved with the same curvature as the circumferential surface of the pressure roller. A temperature detection section abuts against this curved section to detect the temperature of the heating section. Then, the temperature of the heating element is controlled based on the temperature detected by the temperature detection section.

The goal is to create a stable contact state for the temperature detection element.

In order to solve the above problems, the present invention provides a heating device comprising a rotating member, a planar heating member, a temperature detection member, and a biasing member, wherein the temperature detection member has an elastic member and a temperature detection element, the biasing member biases the temperature detection element toward a protrusion, the temperature detection element has the elastic member provided on one side thereof and abuts on the other side thereof, which is the heating member side, against a curved portion of the protrusion that protrudes toward the temperature detection element side , the heating member has a base material and a resistive heating element, and the protrusion is provided on the base material .

The heating device of the present invention can achieve a stable contact state of the temperature detection element against the protrusion.

FIG. 1 is a schematic diagram of an image forming apparatus. 1 is a side cross-sectional view of a fixing device according to an embodiment of the present invention. FIG. FIG. 4 is a plan view of the heater showing the placement of the thermistor. FIG. 2 is a diagram showing a thermistor and its peripheral configuration. 1 is a diagram showing a thermistor having a different configuration from that of the present embodiment and its peripheral configuration. 7A and 7B are diagrams showing the present embodiment, a thermistor having a different configuration from that shown in FIG. 6, and its peripheral configuration. 8 is a diagram showing a state in which a temperature detection element in the thermistor of FIG. 7 is misaligned. FIG. 6 is a diagram showing a state in which a temperature detection element in the thermistor of FIG. 5 is misaligned. FIG. 2 is a plan view showing a specific configuration of a thermistor. FIG. 2 is a side view showing a specific configuration of a thermistor. FIG. 13 is a diagram showing a modified example of the thermistor of the present invention. 14 is a diagram showing a state in which the temperature detection element of the thermistor of FIG. 13 is misaligned. FIG. 1 is a side cross-sectional view of a fixing device having a heat equalizing member.

The present invention will be described below with reference to the attached drawings. In each drawing for explaining the present invention, components such as parts and components having the same function or shape are given the same reference numerals as far as they can be distinguished, and the description will be omitted after the first description. In the following description, a fixing device that fixes a toner image by heat will be exemplified as an example of a heating device equipped with a temperature detection member.

Figure 1 is a schematic diagram of an image forming device according to one embodiment of the present invention.

The image forming device 100 shown in FIG. 1 has four imaging units 1Y, 1M, 1C, and 1Bk that are detachable from the image forming device main body. Each imaging unit 1Y, 1M, 1C, and 1Bk has the same configuration except that it contains a developer of a different color, yellow, magenta, cyan, or black. These color developers correspond to the color separation components of a color image. Each imaging unit 1Y, 1M, 1C, and 1Bk has a drum-shaped photoconductor 2 as an image carrier, a charging device 3, a developing device 4, and a cleaning device 5. The charging device 3 charges the surface of the photoconductor 2. The developing device 4 supplies toner as a developer to the surface of the photoconductor 2 to form a toner image. The cleaning device 5 cleans the surface of the photoconductor 2.

The image forming apparatus 100 also includes an exposure device 6, a paper feeder 7, a transfer device 8, a fixing device 9, and a paper discharge device 10. The exposure device 6 exposes the surface of each photoconductor 2 to light and forms an electrostatic latent image on that surface. The paper feeder 7 supplies paper P as a recording medium to a paper transport path 14. The transfer device 8 transfers the toner image formed on each photoconductor 2 to the paper P. The fixing device 9 fixes the toner image transferred to the paper P to the surface of the paper P. The paper discharge device 10 discharges the paper P outside the apparatus. Each imaging unit 1, photoconductor 2, charging device 3, exposure device 6, transfer device 8, etc. constitute an image forming means for forming an image on paper.

The transfer device 8 has an endless intermediate transfer belt 11 as an intermediate transfer body, four primary transfer rollers 12 as primary transfer members, and a secondary transfer roller 13 as a secondary transfer member. The intermediate transfer belt 11 is stretched by a plurality of rollers. The primary transfer rollers 12 transfer the toner images on the photoconductors 2 to the intermediate transfer belt 11. The secondary transfer rollers 13 transfer the toner images transferred onto the intermediate transfer belt 11 to the paper P. Each of the plurality of primary transfer rollers 12 contacts the photoconductors 2 via the intermediate transfer belt 11. As a result, the intermediate transfer belt 11 and each photoconductor 2 come into contact with each other, and a primary transfer nip is formed between them. Meanwhile, the secondary transfer roller 13 contacts one of the rollers that stretch the intermediate transfer belt 11 via the intermediate transfer belt 11. As a result, a secondary transfer nip is formed between the secondary transfer roller 13 and the intermediate transfer belt 11.

A pair of timing rollers 15 is provided on the paper transport path 14 between the paper feeder 7 and the secondary transfer nip (secondary transfer roller 13).

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

When an instruction to start a printing operation is given, in each of the imaging units 1Y, 1M, 1C, 1Bk, the photoconductor 2 is rotated clockwise in FIG. 1, and the surface of the photoconductor 2 is charged to a uniform high potential by the charging device 3. Next, the exposure device 6 exposes the surface of each photoconductor 2 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 exposed area, forming an electrostatic latent image. Toner is then supplied from the developing device 4 to this electrostatic latent image, and a toner image is formed on each photoconductor 2.

The toner images formed on each photoconductor 2 rotate with the rotation of each photoconductor 2 and reach the primary transfer nip (the position of the primary transfer roller 12). The toner images are then transferred to the intermediate transfer belt 11, which rotates counterclockwise in FIG. 1, so that they overlap one another. The toner images transferred onto the intermediate transfer belt 11 are then transported to the secondary transfer nip (the position of the secondary transfer roller 13) with the rotation of the intermediate transfer belt 11. The toner images are transferred to the paper P that has been transported at the secondary transfer nip. This paper P is supplied from the paper supply device 7. The paper P supplied from the paper supply device 7 is stopped once by the timing roller 15, and then transported to the secondary transfer nip in accordance with the timing at which the toner image on the intermediate transfer belt 11 reaches the secondary transfer nip. Thus, a full-color toner image is carried on the paper P. After the toner image is transferred, the toner remaining on each photoconductor 2 is removed by each cleaning device 5.

The paper P with the transferred toner image is transported to the fixing device 9, which fixes the toner image onto the paper P. The paper P is then discharged from the device by the paper discharge device 10, completing the printing process.

Next, we will explain the configuration of the fixing device.

2, the fixing device 9 according to the present embodiment includes a fixing belt 20 as a rotating member or fixing member, a pressure roller 21 as an opposing rotating member or pressure member, a heater 22 as a heating member, a heater holder 23 as a holding member, a stay 24 as a support member, and a plurality of thermistors 25 as temperature detection members. The fixing belt 20 is an endless belt. The pressure roller 21 contacts the outer peripheral surface of the fixing belt 20 to form a fixing nip (nip portion) N between the fixing belt 20 and the pressure roller 21. The heater 22 heats the fixing belt 20. The heater holder 23 holds the heater 22. The stay 24 supports the heater holder 23. The thermistor 25 detects the temperature of the substrate 50. In other words, the heater 22 is a member to be detected whose temperature is detected by the thermistor 25 (or thermostat). The direction perpendicular to the plane of the paper in Fig. 2 is the longitudinal direction of the fixing belt 20, pressure roller 21, heater 22, heater holder 23, stay 24, etc., and hereinafter, this direction will be simply referred to as the longitudinal direction. Note that this longitudinal direction also corresponds to the width direction of the paper being transported, the belt width direction of the fixing belt 20, and the axial direction of the pressure roller 21. Note that in Fig. 2, the thermistor 25 is depicted as a rectangle for simplicity, and the detailed configuration of the thermistor 25 will be described later.

The fixing belt 20 has a cylindrical substrate made of polyimide (PI) with an outer diameter of 25 mm and a thickness of 40 to 120 μm. This cylindrical substrate includes the inner peripheral surface of the fixing belt 20. A release layer made of fluorine-based resin such as PFA or PTFE with a thickness of 5 to 50 μm is formed on the outermost layer of the fixing belt 20 to improve durability and ensure releasability. An elastic layer made of rubber or the like with a thickness of 50 to 500 μm may be provided between the substrate and the release layer. The substrate of the fixing belt 20 is not limited to polyimide, and may be a heat-resistant resin such as PEEK or a metal substrate such as nickel (Ni) or SUS. The inner peripheral surface of the fixing belt 20 may be coated with polyimide, PTFE, or the like as a sliding layer.

The pressure roller 21 has an outer diameter of, for example, 25 mm and is composed of a solid iron core 21a, an elastic layer 21b formed on the surface of the core 21a, and a release layer 21c formed on the outside of the elastic layer 21b. The elastic layer 21b is made of silicone rubber and has a thickness of, for example, 3.5 mm. To improve releasability, it is desirable to form a release layer 21c made of a fluororesin layer having a thickness of, for example, about 40 μm on the surface of the elastic layer 21b.

When the pressure roller 21 is urged toward the fixing belt 20 by the urging means, the pressure roller 21 is pressed against the heater 22 via the fixing belt 20. This forms a fixing nip N between the fixing belt 20 and the pressure roller 21. The pressure roller 21 is also configured to be driven to rotate by the driving means, and when the pressure roller 21 rotates in the direction of the arrow in FIG. 2, the fixing belt 20 is rotated accordingly.

The heater 22 is a planar heating member that is provided longitudinally across the width of the fixing belt 20. The heater 22 is composed of a plate-shaped base material 50, a resistance heating element 51 provided on the base material 50, an insulating layer 52 that covers the resistance heating element 51, and the like. The heater 22 is in contact with the inner circumferential surface of the fixing belt 20 on the insulating layer 52 side. Therefore, the heat generated by the resistance heating element 51 is transferred to the fixing belt 20 via the insulating layer 52.

The heater holder 23 and the stay 24 are disposed on the inner periphery of the fixing belt 20. The stay 24 is made of a metal channel material, and both ends are supported by both side plates of the fixing device 9. The heater holder 23 and the heater 22 are supported by the stay 24, so that the heater 22 can reliably receive the pressing force of the pressure roller 21 when the pressure roller 21 is pressed against the fixing belt 20. This allows a fixing nip N to be stably formed between the fixing belt 20 and the pressure roller 21.

The heater holder 23 is desirably made of a heat-resistant material because it is prone to becoming hot due to the heat of the heater 22. For example, if the heater holder 23 is made of a heat-resistant resin with low thermal conductivity such as LCP, the transfer of heat from the heater 22 to the heater holder 23 is suppressed. This allows the heater 22 to efficiently heat the fixing belt 20.

In the fixing device 9 according to this embodiment, when a printing operation is started, the pressure roller 21 is driven to rotate, and the fixing belt 20 starts to rotate. In addition, the fixing belt 20 is heated by supplying power to the resistance heating element 51 of the heater 22. Then, when the temperature of the fixing belt 20 reaches a predetermined target temperature (fixing temperature), as shown in FIG. 2, a sheet P carrying an unfixed toner image is transported between the fixing belt 20 and the pressure roller 21 (fixing nip N), and the unfixed toner image is heated and pressurized to be fixed to the sheet P. The fixing belt 20 is a heated member that is heated by the heater 22.

Next, the detailed configuration of the heater 22 will be described. In the following description, the fixing belt 20 side (fixing nip N side) of the heater 22 will be referred to as the "front side," and the heater holder 23 side will be referred to as the "back side."

The heater 22 is constructed by stacking a plate-shaped substrate 50, a conductor layer including a resistance heating element 51, and an insulating layer 52. The conductor layer is provided on the front side of the substrate 50. The insulating layer 52 covers the front side of the conductor layer.

As shown in FIG. 3, the conductor layer is composed of a plurality of heat generating portions 60, a plurality of electrode portions 61, and a plurality of power supply lines 62. The heat generating portions 60 are composed of planar resistive heating elements. The electrode portions 61 are provided on both longitudinal end sides of the substrate 50. The power supply lines 62 connect the electrode portions 61 and the heat generating portions 60. Furthermore, at least a portion of each electrode portion 61 is not covered by the insulating layer 52 and is exposed. This ensures connection between the electrode portions 61 and the connector.

The substrate 50 is made of an insulating material such as ceramics, such as alumina or alumina nitride, or glass. The substrate 50 may also be made of a metal material, such as stainless steel (SUS), iron, copper, or aluminum, and an insulating layer may be provided between the substrate 50 and the conductor layer to ensure insulation. Metal materials are suitable for reducing costs because they are durable against rapid heating and easy to process. Among these, aluminum and copper are preferred because they have high thermal conductivity and are less likely to cause temperature unevenness. Stainless steel also has the advantage of being cheaper to manufacture than these. The substrate 50 has a protrusion, which will be described later, on the back side of the plate material.

The insulating layer 52 is made of heat-resistant glass. Other materials that can be used for the insulating layer 52 include ceramics and polyimide (PI).

Each heating portion 60 can be formed, for example, by applying a paste made of silver palladium (AgPd) and glass powder to the substrate 50 by screen printing or the like, and then firing the substrate 50. In addition to these, the heating portion 60 may be made of a resistive material such as a silver alloy (AgPt) or ruthenium oxide (RuO ₂ ).

The power supply line 62 is made of a conductor with a smaller resistance value than the heat generating portion 60. The power supply line 62 and the electrode portion 61 can be made of materials such as silver (Ag) or silver palladium (AgPd). The power supply line 62 and the electrode portion 61 can be formed by screen printing these materials, for example.

In this embodiment, the heating section 60, the electrode section 61, and the power supply line 62 are made of an alloy such as silver or palladium, and have a PTC characteristic (positive temperature coefficient of resistance). The PTC characteristic is a characteristic in which the resistance value increases as the temperature increases (when a constant voltage is applied, the heater output decreases). By using the heating section 60 with the PTC characteristic, the heater can be started up quickly at low temperatures with high output, and can be prevented from overheating at high temperatures with low output. For example, if the TCR coefficient of the PTC characteristic is about 300 to 4000 ppm/degree, the heater can be kept at a low cost while ensuring the resistance value required for the heater. More preferably, the TCR coefficient is 500 to 2000 ppm/degree. The TCR coefficient can be calculated by measuring the resistance value at 25 degrees and 125 degrees. For example, if the temperature rises by 100 degrees and the resistance value increases by 10%, the TCR coefficient is 1000 ppm/degree.

In this embodiment, three heat generating sections 60 are provided along the longitudinal direction of the substrate 50. One of the three heat generating sections 60 is a central heat generating section 60A serving as a first heat generating section located in the longitudinal center of the substrate 50, and the remaining two are end heat generating sections 60B serving as second heat generating sections located on both longitudinal sides of the central heat generating section 60A. The central heat generating section 60A and the end heat generating section 60B are configured to be capable of being controlled to generate heat independently of each other.

In FIG. 3, the multiple electrode parts 61 are, from the left, the first electrode part 61A, the second electrode part 61B, the third electrode part 61C, and the fourth electrode part 61D. When a voltage is applied to the second electrode part 61B and the fourth electrode part 61D, only the central heating part 60A generates heat. When a voltage is applied to the first electrode part 61A and the second electrode part 61B, only the end heating part 60B on the left side of FIG. 3 generates heat, and when a voltage is applied to the second electrode part 61B and the third electrode part 61C, only the end heating part 60B on the right side of FIG. 3 generates heat. In addition, the first electrode part 61A and the third electrode part 61C are connected in parallel externally so that a voltage can be applied simultaneously. Then, by applying a voltage to these electrode parts 61A, 61C and the second electrode part 61B, it is possible to heat both end heating parts 60B simultaneously. The arrows in FIG. 3 indicate the direction of current flowing in the longitudinal direction of each heat generating portion 60A, 60B.

If the width of the paper passing through is equal to or less than the width L1 of the central heating section 60A, only the central heating section 60A is heated. If the width of the paper passing through is greater than the width L1 of the central heating section 60, each end heating section 60B is heated in addition to the central heating section 60A. In this way, the size of the heating area can be changed according to the size of the paper passing area. Furthermore, it is preferable to match the width L1 of the central heating section 60A to the width of a small size paper (e.g., A4 paper width: 215 mm), and match the width L2 of the heating area including one end heating section 60B to the other end heating section 60B to the width of a large size paper (e.g., A3 paper width: 301 mm). This results in almost no non-paper passing area on the heating sections 60A and 60B, thereby improving printing productivity.

Figure 4 is a diagram showing the positional relationship between multiple thermistors 25A-25C, heat generating sections 60A and 60B, and paper passage areas W1 and W2. The paper passage area indicated by W1 in Figure 4 is the widthwise passing area when paper P1, which has a width smaller than the width L1 of central heat generating section 60A, passes through the fixing nip N. The paper passage area indicated by W2 in the figure is the widthwise passing area when paper P2, which has a width larger than the width L1 of central heat generating section 60A, passes through the fixing nip N. In addition, thermistors 25A, 25B, and 25C will be referred to below for convenience as the first thermistor 25A, the second thermistor 25B, and the third thermistor 25C.

The temperature detection element 251A of the first thermistor 25A is disposed within the width L1 of the central heat generating portion 60A, and further within the small size paper passing area W1. This arrangement allows the first thermistor 25A to detect the temperature of the paper passing area in the central heat generating portion 60A when paper P1 or paper wider than this is passed through. Furthermore, if there are multiple types of paper with widths smaller than the width L1 of the central heat generating portion 60A, the temperature detection element 251A can be disposed within the paper passing area of the smallest paper among them. This allows the first thermistor 25A to detect the temperature of paper passing areas of all sizes that pass over the central heat generating portion 60A.

The temperature detection element 251B of the second thermistor 25B is arranged outside the width L1 of the central heating section 60A and within the large-size paper passage area W2. In other words, the temperature detection element 251B of the second thermistor 25B is arranged to correspond to the paper passage area where the large-size paper P2 passes over the edge heating section 60B when the large-size paper P2 passes. With this arrangement, the second thermistor 25B can detect the temperature of the paper passage area at the edge heating section 60B when the large-size paper P2 passes. Also, when there are multiple types of paper that pass over the edge heating section 60B, the temperature detection element 251B can be arranged within the paper passage area of the smallest width paper. This allows the second thermistor 25B to detect the temperature of paper passage areas of all sizes that pass over the edge heating section 60B.

The temperature detection element 251C of the third thermistor 25C is positioned outside the small-size paper passage area W1 and within the width L1 of the central heating section 60A. In other words, the temperature detection element 251C of the third thermistor 25C is positioned in correspondence with the non-paper passage area where the small-size paper P1 does not pass over the central heating section 60A when the small-size paper P1 is passed through. This positioning allows the third thermistor 25C to detect the temperature of the non-paper passage area in the central heating section 60A when the small-size paper P1 is passed through.

The temperature information detected by each thermistor 25A-25C is sent to a control unit that controls the heat generation of each heat generating unit 60A, 60B, and each heat generating unit 60A, 60B is individually controlled based on the sent temperature information. This controls the temperature of the fixing nip N to a preset target temperature (fixing temperature). However, if small-sized paper is continuously passed through, for example, the temperature of the heater 22 in the non-paper passing area is not consumed much, and the temperature may rise excessively. In such a case, the third thermistor 25C detects that the temperature in the non-paper passing area has reached a predetermined temperature or higher, and the amount of heat generated by the heater 22 is controlled to be reduced. Furthermore, the temperature rise in the non-paper passing area is suppressed by slowing down the paper transport speed, widening the paper transport interval, or stopping image formation.

As described above, the power supply to the heater 22 is controlled based on the detection results of each thermistor 25. Therefore, in order to maintain the fixing belt 20 at an appropriate temperature, it is important that each thermistor 25 accurately detects the temperature of the detected member (heater 22 in this embodiment). The detailed configuration of the thermistor 25 in this embodiment is described below. Note that each thermistor 25 in this embodiment has the same configuration except for the longitudinal arrangement. However, this is not necessarily limited to this, and the configuration described below may be adopted for only one of the thermistors 25. Also, the above-mentioned arrangement of thermistors 25A to 25C is one example, and the arrangement and number are not necessarily limited to this.

As shown in FIG. 5, the thermistor 25 as a temperature detection member includes a temperature detection element 251, an elastic member 252, a holder 253, lead wires, etc.

A coil spring 29 is connected to one surface of the holder 253. The thermistor 25 is biased toward the heater 22 (see the arrow in Figure 5) by the coil spring 29. An elastic member 252 is fixed to the other surface of the holder 253.

The elastic member 252 can be made of rubber or sponge, for example, silicone resin or fluorine resin. The elastic member 252 may also be made of ceramic paper.

The substrate 50 has a protruding portion 53 on the surface facing the temperature detection element 251 that protrudes towards the temperature detection element 251. The protruding portion 53 is arc-shaped. The temperature detection element 251 faces the protruding portion 53 and abuts against the portion of the protruding portion 53 that protrudes most towards the temperature detection element 251. However, the thermistor 25 may have an insulating sheet, and the temperature detection element 251 may abut against the protruding portion 53 via the insulating sheet.

When the fixing belt 20 and the pressure roller 21 are in pressure contact with each other, the pressure of the coil spring 29 presses the temperature detection element 251 against the protrusion 53. This allows the temperature detection element 251 to detect the temperature of the heater 22.

In order for the thermistor 25 to properly detect the temperature of the heater 22, it is important that the temperature detection element 251 is stably abutted against the substrate 50 and that the detection position and detection state of the thermistor 25 relative to the heater 22 are stabilized.

For example, in the fixing device shown in FIG. 6, which has a different configuration from the fixing device of this embodiment, the thermistor 25' is not provided with an elastic member 252, and the holder 253 directly holds the temperature detection element 251. In addition, no protrusion is provided on the back side of the substrate 50, and the temperature detection element 251 abuts against the flat surface of the substrate 50.

In a fixing device configured in this way, the pressure between the temperature detection element 251 and the substrate 50 may become weak, and the temperature detection element 251 may not be in sufficient contact with the substrate 50. In this case, the thermistor 25' may not be able to properly detect the temperature of the heater 22. In response to this, as shown in FIG. 7, by providing a protrusion 53 on the substrate 50, the force pressing the substrate 50 against the temperature detection element 251 can be increased, stabilizing the contact state between the two.

However, the position of the temperature detection element 251 relative to the protrusion 53 varies due to component tolerances, assembly errors, and the like. For this reason, as shown in an exaggerated manner in Figure 8, the relative position of the temperature detection element 251 relative to the protrusion 53 (the position in the vertical direction in Figure 8, the position in the paper transport direction) may shift. Furthermore, since the curvature of the protrusion 53 changes in the vertical direction in Figure 8, if the temperature detection element 251 shifts in position, the temperature detection element 251 will no longer be in proper contact with the substrate 50.

In this embodiment, as shown in FIG. 5, in order to solve the above problems, the base material 50 is provided with a protrusion 53, and the thermistor 25 is provided with an elastic member 252. By providing the base material 50 with the protrusion 53, the force with which the base material 50 is pressed against the temperature detection element 251 can be increased, and the temperature detection element 251 can be stably abutted against the back surface of the base material 50, as in the configuration of FIG. 7 described above. In addition, as shown in FIG. 9, even if the relative position of the temperature detection element 251 with respect to the protrusion 53 is shifted, the temperature detection element 251 can be stably abutted against the back surface of the base material 50. In other words, the elastic member 252 on the side where the pressure of the protrusion 53 is stronger in the vertical direction of FIG. 9 is mainly crushed by the pressure of the protrusion 53 on the thermistor 25. As the elastic member 252 is crushed unevenly from top to bottom, the temperature detection element 251 tilts and faces the side of the surface facing the protrusion 53. For example, in this embodiment, the contact surface of the temperature detection element 251 is inclined in a direction approaching the tangent direction of the curved surface of the protrusion 53. This allows the temperature detection element 251 to stably contact the protrusion 53 even if the temperature detection element 251 is misaligned with respect to the protrusion 53. Note that FIG. 9 shows a case in which the thermistor 25 is misaligned downward with respect to the substrate 50 in FIG. 9, but even if the thermistor 25 is misaligned upward in FIG. 9, the elastic member 252 is similarly crushed, allowing the temperature detection element 251 to stably contact the protrusion 53.

In this manner, in this embodiment, by combining a configuration in which the substrate 50 is provided with a protrusion 53 and a configuration in which the thermistor 25 is provided with an elastic member 252, the temperature detection element 251 can be brought into sufficient contact with the rear surface of the substrate 50, and variations in the contact state due to misalignment between the temperature detection element 251 and the substrate 50 can be suppressed. Therefore, the thermistor 25 can accurately detect the temperature of the heater 22. This allows the temperature of the fixing belt 20 to be appropriately controlled, and prevents excessive heating of the fixing belt 20, excess energy consumption, or deterioration of fixability due to insufficient temperature of the fixing belt 20.

An example of a more detailed configuration of the thermistor 25 is described below with reference to Figures 10 and 11.

10 and 11, the lead wire 255 is connected to one end of the holder 253 in the longitudinal direction (the left-right direction in FIG. 10, the direction perpendicular to the paper surface of FIG. 2). The holder 253 also has an elastic member 252 and a temperature detection element 251 in a narrow portion at the center of the longitudinal direction. A protrusion 253a is provided at each end of the longitudinal direction of the holder 253. The coil spring 29 (see FIG. 5) described above is connected to the protrusion 253a. The holder 253 also has a protrusion 253b that protrudes on the opposite side to the protrusion 253a. The protrusion 253b is a portion that engages with a recess in the heater holder 23 and is positioned in the heater holder 23. The holder 253 is made of a resin material such as LCP (crystalline polymer) that has excellent heat resistance.

The insulating sheet 254 covers the holder 253, the elastic member 252, and the temperature detection element 251 at the center of the longitudinal direction of the holder 253. The insulating sheet 254 is formed from a resin material with good insulation, heat resistance, abrasion resistance, and thermal conductivity, for example, polyimide.

In the thermistor 25 of this embodiment, the temperature detection element 251 abuts against the protrusion via the insulating sheet 254. In this way, the temperature detection element may abut against the protrusion indirectly via another member.

As another embodiment different from the above, as shown in FIG. 12, the temperature detection element 251 has a curved surface 251a that follows the curved surface of the protrusion 53 at the contact portion, which is the surface facing the protrusion 53. This allows the temperature detection element 251 to be more stably contacted with the protrusion 53, and the detection state of the thermistor 25 with respect to the heater 22 can be stabilized. Note that in this embodiment as well, as shown in FIG. 13, even if the relative position of the temperature detection element 251 with respect to the protrusion 53 is shifted, the elastic member 252 is crushed, and the temperature detection element 251 can be stably contacted with the curved surface of the protrusion 53.

In addition, the protrusion 53 that contacts the temperature detection element 251 is not limited to being provided on the substrate 50. For example, in the fixing device 9 shown in FIG. 14, a heat equalizing member (high thermal conductivity member) 26 with a protrusion 53 is provided between the substrate 50 and the thermistor 25.

The heat equalizing member 26 is made of a material with a higher thermal conductivity than the substrate 50, such as aluminum, copper, or SUS. The heat equalizing member 26 is provided in the longitudinal direction and abuts against the substrate 50. This improves the heat transfer efficiency of the substrate 50 in the longitudinal direction, and makes it possible to equalize the temperature of the heater 22 and the fixing belt 20 in the longitudinal direction.

Next, we will explain how to calculate the thermal conductivity. When calculating the thermal conductivity, first, the thermal diffusivity of the target object is measured, and then the thermal conductivity is calculated using this thermal diffusivity.

Thermal diffusivity was measured using a thermal diffusivity/thermal conductivity measuring device (product name: ai-Phase Mobile 1u, ai-Phase Corporation).

In order to convert the thermal diffusivity to thermal conductivity, the density and specific heat capacity values are required. A dry automatic density meter (product name: Accupyc 1330, manufactured by Shimadzu Corporation) was used to measure the density. A differential scanning calorimeter (product name: DSC-60, manufactured by Shimadzu Corporation) was used to measure the specific heat capacity, and sapphire was used as a reference material with a known specific heat capacity. In this example, the specific heat capacity was measured five times, and the average value at 50°C was used. If the density and specific heat capacity are ρ and C, respectively, the thermal conductivity λ can be obtained from the thermal diffusivity α obtained from the thermal diffusivity measurement by the following formula (1).

In this embodiment, as in FIG. 5 of the previous embodiment, the temperature detection element 251 abuts against the elastic member 252 on one side and against the protruding portion 53 of the heat equalizing member 26 on the other side. This allows the temperature detection element 251 to abut against the heat equalizing member 26 in a stable manner. Therefore, the thermistor 25 can accurately detect the temperature of the heat equalizing member 26. This allows the temperature of the fixing belt 20 to be appropriately controlled.

The above describes an embodiment of the present invention, but the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

In the above explanation, the protrusion is an arc-shaped curved portion, but this is not necessarily limited to this. However, forming the protrusion with a curved portion is preferable because it allows the temperature detection element to abut against the protrusion more stably.

The image forming apparatus according to the present invention is not limited to the color image forming apparatus shown in FIG. 1, but may also be a monochrome image forming apparatus, a copier, a printer, a facsimile, or a combination machine of these.

Recording media include paper P (plain paper), as well as cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, overhead projector sheets, plastic film, prepreg, copper foil, etc.

The present invention is not limited to the fixing device described in the above embodiment, but can also be applied to heating devices such as drying devices that dry ink applied to paper, and further to laminators that thermocompression bond a film as a covering member to the surface of a sheet such as paper, and thermocompression devices such as heat sealers that thermocompress the seal portion of packaging material. By applying the present invention to such devices, the temperature detection element can be stably abutted against the detected member. Therefore, the temperature detection member can accurately detect the temperature of the detected member.

1 Image forming apparatus 9 Fixing device 20 Fixing belt (rotating member or fixing member)
21 Pressure roller (opposing rotating member or pressure member)
22 Heater (heating member or detected member)
23 Heater holder 25 Thermistor (temperature detection member)
251 Temperature detection element 251a Curved surface portion (contact portion)
252 Elastic member 254 Holding body 253 Insulating sheet 26 Heat uniformity member (high thermal conductive member)
50: Substrate 51: Resistance heating element 53: Protrusion N: Fixing nip (nip portion)

JP 2018-169417 A

Claims (6)

A rotating member;
A planar heating member;
A temperature sensing member;
A heating device comprising:
The temperature detection member includes an elastic member and a temperature detection element,
The biasing member biases the temperature detection element toward the protrusion,
The temperature detection element is provided with the elastic member on one side thereof, and the other side thereof, which is the heating member side, abuts against a curved portion of the protruding portion protruding toward the temperature detection element side,
The heating member has a substrate and a resistive heating element,
The heating device, wherein the protrusion is provided on the base material . 2. The heating device according to claim 1 , wherein the elastic member is made of sponge. 2. The heating device according to claim 1 , wherein said elastic member is made of ceramic paper. The heating device according to claim 1 , wherein a contact portion of the temperature detection element that contacts the protruding portion has a shape conforming to the protruding portion. 5. The heating device according to claim 1, which is a fixing device for heating and fixing toner on a recording medium. An image forming apparatus comprising the fixing device according to claim 5 .

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