Heating device and image forming apparatus

Abstract

To prevent a delay in detection of temperature rise in a heating device caused by a variation in temperature in a longitudinal direction of a heating body.SOLUTION: A heater 22 comprises: a first heat generation unit 60A that includes at least two resistance heating elements 59; a second heat generation unit 60B that includes at least two resistance heating elements 59 located on both ends of the heater 22 with respect to the first heat generation unit 60A; a first electrode unit 61A that is connected with the first heat generation unit 60A through a plurality of electric conductors; a second electrode unit 61B that is connected with the first heat generation unit 60A and the second heat generation unit 60B through the electric conductors; and a third electrode unit 61C that is connected with the second heat generation unit 60B through the electric conductors. The first electrode unit 61A and the second electrode unit 61B are arranged on one side with respect to the center line C0 of a heating area C of the heater 22, and a thermistor 35A is arranged at a position corresponding to the resistance heating element 59 included in the first heat generation unit 60A, the resistance heating element 59 being on one side with respect to the middle position C0 of the heating area C.SELECTED DRAWING: Figure 15

Description

[Technical field]

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

[0002] 2. Description of the Related Art Known heating devices mounted in image forming apparatuses such as copiers and printers include a fixing device that fixes toner on paper by heat and a drying device that dries ink on paper.

[0003] For example, Patent Document 1 listed below discloses a fixing device that includes a heating element (heater) on a longitudinal substrate, the heating element including a resistance heating element, electrode portions, and conductors that electrically connect these.

[0004] In a heating element having such a conductor provided on a substrate, when the resistance heating element is made to generate heat, the conductor also generates a small amount of heat when electricity is passed through the conductor, so strictly speaking, the heat distribution of the entire heating element is affected by the heat generated by the conductor.

[0005] Therefore, depending on the heat distribution of the conductor, there is a risk that the temperature distribution of the heater may vary due to this. Therefore, in a heating device equipped with such a heater, measures are required to suppress problems caused by the temperature variation of the heater due to the heat generated by the conductor. Summary of the Invention [Problem to be solved by the invention]

[0006] There was a problem that the temperature deviation between one side and the other side in the longitudinal direction of the heating body delayed the detection of the temperature rise within the heating device. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the present invention provides a heating device including a heater and a plurality of temperature detection means, wherein the heater includes a first heating section including at least two resistive heating elements, a second heating section including at least two resistive heating elements located on both ends of the heater in a longitudinal direction relative to the first heating section, a plurality of conductors, a first electrode section connected to the first heating section via the conductors, a second electrode section connected to the first heating section and the second heating section via the conductors, and a third electrode section connected to the second heating section via the conductors, and wherein, when a region from a resistive heating element located on one side to a resistive heating element located on the other side among all the resistive heating elements included in the heater in the longitudinal direction is defined as a heating region, in the longitudinal direction, the first electrode section is located on one side with respect to a central position of the heating region, and in the longitudinal direction, the first temperature detection means as the temperature detection means is located at a position corresponding to the resistive heating element included in the first heating section and located on one side with respect to the central position of the heating region. The second temperature detection means as the temperature detection means is a resistive heating element included in the second heating portion, and is disposed at a position corresponding to the resistive heating element disposed on the other side of the center position of the heating area, and the second electrode portion is connected to each of the resistive heating elements of the first heating portion and the second heating portion via the conductor in order from the resistive heating element furthest on the other side in the longitudinal direction to one side in the longitudinal direction, and the arrangement of all the temperature detection means provided in the thermal device is asymmetric between the one side and the other side in the longitudinal direction with respect to the center position of the heating area. It is characterized by: Effect of the Invention

[0008] According to the present invention, a temperature rise in the heating device can be detected at an earlier stage. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram of a fixing device. [Diagram 3] FIG. [Figure 4] FIG. [Diagram 5] FIG. [Figure 6] FIG. [Figure 7] FIG. [Figure 8] FIG. [Figure 9] FIG. 4 is a perspective view showing a state in which a connector is connected to the heater. [Figure 10] FIG. 4 is a diagram showing power supply to a heater. [Figure 11] FIG. 11 is a diagram showing a normal current path in the heater of FIG. [Figure 12] 11 is a diagram showing a current path when unintended current shunting occurs in the heater of FIG. 10. FIG. [Figure 13] 11 is a diagram showing the amount of heat generated in the power supply lines for each block when unintended current shunting occurs in the heater of FIG. 10. FIG. [Figure 14] 11 is a diagram showing the amount of heat generated by power supply lines for each block when electricity is supplied to all heat generating parts in the heater of FIG. 10. FIG. [Figure 15] FIG. 4 is a diagram showing the longitudinal arrangement of thermistors. [Figure 16] 11 is a side view of the fixing device in the case where a temperature detection unit is provided on the outer circumferential side of the fixing belt. [Figure 17] 11 is a diagram showing a heater having a different configuration from that shown in FIG. 10 and power supply to the heater. [Figure 18] FIG. 18 is a diagram showing the amount of heat generated in the power supply lines for each block when unintended current shunting occurs in the heater of FIG. 17. [Figure 19] 18 is a diagram showing the amount of heat generated by power supply lines for each block when electricity is passed through all heat generating parts in the heater of FIG. 17. FIG. [Figure 20] FIG. 2 is a plan view showing the short-side dimension of a heater and the short-side dimension of a resistance heating element. [Figure 21] 13(a) and 13(b) are plan views showing modified examples of the heater. [Figure 22] FIG. 13 is a diagram showing the configuration of another fixing device. [Diagram 23] FIG. 13 is a diagram showing the configuration of another fixing device. [Figure 24] FIG. 13 is a diagram showing the configuration of still another fixing device. [Diagram 25] FIG. 13 is a diagram showing a heater in which a third electrode portion is disposed on the other side in the longitudinal direction. [Figure 26] 1 shows a heater in which the first heating portion is composed of two resistive heating elements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and the duplicated description will be appropriately simplified or omitted. In the following description of each embodiment, the heating device will be described as a fixing device that fixes toner by heat.

[0011] A monochrome image forming apparatus 1 shown in Fig. 1 is provided with a photoconductor drum 10. The photoconductor drum 10 is a drum-shaped rotating body capable of carrying toner as a developer on its surface, and rotates in the direction of the arrow in the figure. Around the photoconductor drum 10, there are a charging roller 11 that uniformly charges the surface of the photoconductor drum 10, a developing device 12 including a developing roller 7 that supplies toner to the surface of the photoconductor drum 10, and a cleaning blade 13 that cleans the surface of the photoconductor drum 10.

[0012] An exposure unit is disposed above the photoconductor drum 10. The exposure unit emits laser light Lb based on image data, and the surface of the photoconductor drum 10 is irradiated via a mirror 14.

[0013] Further, a transfer means 15 including a transfer charger is disposed at a position facing the photoconductor drum 10. The transfer means 15 transfers the image on the surface of the photoconductor drum 10 onto a sheet P.

[0014] A paper feed section 4 is located at the bottom of the image forming apparatus 1, and is made up of a paper feed cassette 16 that stores paper P as a recording medium, a paper feed roller 17 that conveys the paper P from the paper feed cassette 16 to the conveying path 5, etc. A registration roller 18 is disposed downstream of the paper feed roller 17 in the conveying direction.

[0015] The fixing device 9 includes a fixing belt 20 that is heated by a heating element, which will be described later, a pressure roller 21 that can apply pressure to the fixing belt 20, and the like.

[0016] Hereinafter, the basic operation of the image forming apparatus 1 will be described with reference to FIG.

[0017] When a printing operation (image forming operation) is started, first, the surface of the photoconductor drum 10 is charged by the charging roller 11. Then, a laser beam Lb is irradiated from an exposure unit based on image data, and the potential of the irradiated portion is reduced to form an electrostatic latent image. Toner is supplied from a developing device 12 to the surface portion of the photoconductor drum 10 on which the electrostatic latent image has been formed, and the electrostatic latent image is visualized as a toner image (developer image). Then, the toner and the like remaining on the photoconductor drum 10 after transfer is removed by a cleaning blade 13.

[0018] On the other hand, when a printing operation is started, at the bottom of the image forming apparatus 1, the paper P accommodated in the paper feed cassette 16 is sent to the conveying path 5 by the paper feed roller 17 of the paper feed unit 4 being driven to rotate.

[0019] The paper P sent to the transport path 5 is timed by the registration rollers 18 and transported to the transfer section, which is the opposing section between the transfer means 15 and the photosensitive drum 10, at a timing that will face the toner image on the surface of the photosensitive drum 10, and the toner image is transferred by the application of a transfer bias by the transfer means 15.

[0020] The paper P onto which the toner image has been transferred is transported to the fixing device 9, where it is heated and pressed by the heated fixing belt 20 and the pressure roller 21, thereby fixing the toner image onto the paper P. Then, the paper P onto which the toner image has been fixed is separated from the fixing belt 20, transported by a pair of transport rollers provided downstream of the fixing device 9, and discharged onto a paper output tray provided outside the device.

[0021] Next, the configuration of the fixing device 9 will be described in more detail.

[0022] As shown in FIG. 2, the fixing device 9 according to the present embodiment includes a fixing belt 20 as a belt member or fixing member, a pressure roller 21 as an opposing member or pressure member that contacts the outer peripheral surface of the fixing belt 20 to form a nip portion N, and a heating unit 19 that heats the fixing belt 20. The heating unit 19 also includes a planar heater 22 as a heating body, a heater holder 23 as a holding member that holds the heater 22, a stay 24 as a support member that supports the heater holder 23, and a thermistor 35 as a temperature detection means. The fixing belt 20, the pressure roller 21, the heater 22, the heater holder 23, and the stay 24 extend in a direction perpendicular to the paper surface of FIG. 2 (see the direction of the double-headed arrow B in FIG. 3), and hereinafter, this direction is referred to as the longitudinal direction of each member (however, it is also the axial direction of the pressure roller 21), or the longitudinal direction of the heating unit 19 or the fixing device 9. This longitudinal direction is also the width direction of a sheet of paper passed through the fixing device 9.

[0023] The fixing belt 20 is composed of an endless belt member, and has a cylindrical substrate made of polyimide (PI) having an outer diameter of 25 mm and a thickness of 40 to 120 μm. A release layer made of fluorine-based resin such as PFA or PTFE and having a thickness of 5 to 50 μm is formed on the outermost surface of the fixing belt 20 in order to increase durability and ensure releasability. An elastic layer made of rubber or the like having 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.

[0024] 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. In order to improve the release property of the surface of the elastic layer 21b, it is desirable to form the release layer 21c made of a fluororesin layer having a thickness of, for example, about 40 μm.

[0025] The fixing belt 20 is pressed toward the pressure roller 21 by a pressure mechanism and is pressed against the pressure roller 21. As a result, a nip N is formed between the fixing belt 20 and the pressure roller 21. The pressure roller 21 functions as a drive roller that is rotated by a driving force transmitted from a driving means provided in the image forming apparatus body. Meanwhile, the fixing belt 20 is configured to rotate in accordance with the rotation of the pressure roller 21. When the fixing belt 20 rotates, the fixing belt 20 slides against the heater 22. Therefore, in order to improve the sliding property of the fixing belt 20, a lubricant such as oil or grease may be interposed between the heater 22 and the fixing belt 20.

[0026] The heater 22 is provided longitudinally in the direction of the rotation axis or the longitudinal direction of the fixing belt 20, and is in contact with the inner circumferential surface of the fixing belt 20 at a position corresponding to the pressure roller 21. The heater 22 is a member for heating the fixing belt 20 as a member to be heated, and for heating the fixing belt 20 to a predetermined fixing temperature.

[0027] Unlike the present embodiment, the heat generating section 60 may be provided on the opposite side of the substrate 50 from the fixing belt 20 side (the heater holder 23 side). In that case, since the heat of the heat generating section 60 is transferred to the fixing belt 20 via the substrate 50, it is desirable that the substrate 50 be made of a material with high thermal conductivity such as aluminum nitride. Furthermore, in the configuration of the heater 22 according to the present embodiment, an insulating layer may be further provided on the surface of the substrate 50 opposite to the fixing belt 20 (the heater holder 23 side).

[0028] The heater 22 may be in non-contact with the fixing belt 20 or indirectly in contact with the fixing belt 20 via a low friction sheet or the like, but in order to increase the efficiency of heat transfer to the fixing belt 20, it is preferable to have the heater 22 in direct contact with the fixing belt 20 as in this embodiment. The heater 22 can also be in contact with the outer circumferential surface of the fixing belt 20, but since there is a risk that the fixing quality will decrease if the outer circumferential surface of the fixing belt 20 is damaged by contact with the heater 22, it is preferable that the surface with which the heater 22 comes in contact is the inner circumferential surface of the fixing belt 20.

[0029] The heater holder 23 and the stay 24 are disposed inside the fixing belt 20. The stay 24 is made of a metal channel material, and both ends thereof are supported by both side walls of the fixing device 9. Since the surface of the heater holder 23 opposite to the heater 22 side is supported by the stay 24, the heater 22 and the heater holder 23 are maintained without being significantly deflected by the pressure force of the pressure roller 21, and a fixing nip N is formed between the fixing belt 20 and the pressure roller 21 as a nip portion.

[0030] The heater holder 23 is desirably formed of a heat-resistant material because it is likely to become hot due to the heat of the heater 22. For example, when the heater holder 23 is formed of a heat-resistant resin with low thermal conductivity such as LCP, the heat transfer from the heater 22 to the heater holder 23 is suppressed, and the fixing belt 20 can be heated efficiently.

[0031] The thermistor 35 is provided at a position facing the heat generating unit 60 on the rear surface of the substrate 50. The temperature of the fixing belt 20 is controlled to a desired temperature by controlling the power supplied to the heater 22 by a heating control means based on the temperature detected by the thermistor 35. The heating control means refers to a microcomputer including a CPU, ROM, RAM, an I / O interface, and the like. However, when paper is being passed, etc., the temperature of the fixing belt 20 is controlled to a desired temperature by appropriately supplying additional power in consideration of the heat dissipated by the paper passing, in addition to the detected temperature.

[0032] When the printing operation is started, power is supplied to the heater 22, which causes the heat generating section 60 to generate heat and heat the fixing belt 20. Also, the pressure roller 21 is rotated and the fixing belt 20 starts to rotate. Then, when the temperature of the fixing belt 20 reaches a predetermined target temperature (fixing temperature), as shown in Fig. 2, the paper P carrying the unfixed toner image is transported between the fixing belt 20 and the pressure roller 21 (fixing nip N) (see the direction of arrow A in Fig. 2), and the unfixed toner image is heated and pressurized to be fixed to the paper P.

[0033] FIG. 3 is a perspective view of the fixing device, and FIG. 4 is an exploded perspective view thereof.

[0034] 3 and 4, the device frame 40 of the fixing device 9 includes a first device frame 25 consisting of a pair of side walls 28 and a front wall 27, and a second device frame 26 consisting of a rear wall 29. The pair of side walls 28 are disposed at one end side and the other end side in the longitudinal direction, and both end sides of the fixing belt 20, the pressure roller 21, and the heating unit 19 are supported by the both side walls 28. A plurality of engagement protrusions 28a are provided on each side wall 28, and the first device frame 25 and the second device frame 26 are assembled together by engaging each engagement protrusion 28a with an engagement hole 29a provided in the rear wall 29.

[0035] Each side wall portion 28 is provided with an insertion groove 28b for inserting the rotating shaft of the pressure roller 21 and the like. The insertion groove 28b opens on the rear wall portion 29 side and is a butting portion that does not open on the opposite side. A bearing 30 that supports the rotating shaft of the pressure roller 21 is provided at the end on the butting portion side. The pressure roller 21 is rotatably supported by both side wall portions 28 by mounting both ends of the rotating shaft to the bearings 30.

[0036] Further, a drive transmission gear 31 is provided as a drive transmission member on one end side of the rotation shaft of the pressure roller 21. The drive transmission gear 31 is arranged in a state where it is exposed outside the side wall portions 28 with the pressure roller 21 supported by the side wall portions 28. As a result, when the fixing device 9 is mounted on the image forming apparatus main body, the drive transmission gear 31 is connected to a gear provided on the image forming apparatus main body, and is in a state where it can transmit a drive force from a drive source. Note that the drive transmission member that transmits the drive force to the pressure roller 21 may be, in addition to the drive transmission gear 31, a pulley that stretches a drive transmission belt or a coupling mechanism.

[0037] A pair of flanges 32 that support the fixing belt 20, the heater holder 23, the stays 24, etc. are provided at both ends of the heating unit 19 in the longitudinal direction. A guide groove 32a is provided in each flange 32. The flanges 32 are assembled to the side wall portion 28 by inserting the guide groove 32a along the edge of the insertion groove 28b of the side wall portion 28.

[0038] A pair of springs 33 serving as urging members are in contact with each flange 32. The stays 24 and the flanges 32 are urged toward the pressure roller 21 by each spring 33, whereby the fixing belt 20 is pressed against the pressure roller 21, and a fixing nip is formed between the fixing belt 20 and the pressure roller 21.

[0039] As shown in FIG. 4, a hole 29b is provided on one end of the rear wall 29 constituting the second device frame 26 in the longitudinal direction as a positioning portion for positioning the fixing device body relative to the image forming device body. On the other hand, a protrusion 101 is provided on the image forming device body as a positioning portion. The protrusion 101 is inserted into the hole 29b of the fixing device 9, so that the protrusion 101 and the hole 29b fit together, and the fixing device body is positioned in the longitudinal direction relative to the image forming device body. No positioning portion is provided on the end of the rear wall 29 opposite to the end where the hole 29b is provided. This prevents the longitudinal expansion and contraction of the fixing device body due to temperature changes from being restricted.

[0040] FIG. 5 is a perspective view of the heating unit 19, and FIG. 6 is an exploded perspective view thereof.

[0041] As shown in Figs. 5 and 6, the heater holder 23 has a rectangular accommodating recess 23a on the fixing belt side (the surface on the front side in Figs. 5 and 6) for accommodating the heater 22. The accommodating recess 23a is formed to have substantially the same shape and size as the heater 22, but the longitudinal dimension L2 of the accommodating recess 23a is set to be slightly longer than the longitudinal dimension L1 of the heater 22. In this way, the accommodating recess 23a is formed to be slightly longer than the heater 22, so that the heater 22 and the accommodating recess 23a do not interfere with each other even if the heater 22 expands in its longitudinal direction due to thermal expansion. In addition, the heater 22 is held in the accommodating recess 23a by being sandwiched together with the heater holder 23 by a connector, which will be described later, as a power supply member.

[0042] The pair of flanges 32 have a C-shaped belt support portion 32b that is inserted inside the fixing belt 20 to support the fixing belt 20, a flange-shaped belt regulation portion 32c that contacts an end face of the fixing belt 20 to regulate longitudinal movement (deviation), and support recesses 32d into which both end sides of the heater holder 23 and the stay 24 are inserted to support them. By inserting the belt support portions 32b into both end sides of the fixing belt 20, the fixing belt 20 is supported in a so-called free belt manner in which basically no tension is generated in the circumferential direction (belt rotation direction) when the belt is not rotating.

[0043] As shown in Figures 5 and 6, a positioning recess 23e is provided as a positioning portion at one end of the heater holder 23 in the longitudinal direction. A fitting portion 32e of a flange 32 shown on the left side of Figures 5 and 6 fits into this positioning recess 23e, thereby positioning the heater holder 23 and the flange 32 in the longitudinal direction. On the other hand, the flange 32 shown on the right side of Figures 5 and 6 does not have a fitting portion 32e, and is not positioned in the longitudinal direction relative to the heater holder 23. In this way, by positioning the heater holder 23 relative to the flange 32 only on one side in the longitudinal direction, even if the heater holder 23 expands and contracts in the longitudinal direction due to temperature changes, the expansion and contraction is not restricted.

[0044] 6, steps 24a are provided on both longitudinal end sides of the stay 24 to restrict movement of the stay 24 relative to each flange 32. Each step 24a abuts against the flange 32 to restrict longitudinal movement of the stay 24 relative to the flange 32. However, at least one of these step portions 24a is disposed with a gap (backlash) between it and the flange 32. In this way, by disposing at least one step portion 24a with a gap between it and the flange 32, even if the stay 24 expands and contracts in the longitudinal direction due to temperature changes, the expansion and contraction is not restricted.

[0045] FIG. 7 is a plan view of the heater 22, and FIG. 8 is an exploded perspective view thereof.

[0046] 8, the heater 22 has a base material 50, a first insulating layer 51 provided on the base material 50, a conductor layer 52 having a heat generating portion 60 and the like provided on the first insulating layer 51, and a second insulating layer 53 covering the conductor layer 52. In this embodiment, the base material 50, the first insulating layer 51, the conductor layer 52 (heat generating portion 60), and the second insulating layer 53 are laminated in this order toward the fixing belt 20 side (fixing nip N side), and heat generated from the heat generating portion 60 is transferred to the fixing belt 20 via the second insulating layer 53 (see FIG. 2).

[0047] The substrate 50 is a longitudinal plate material made of a metal material such as stainless steel (SUS), iron, or aluminum. In addition to metal materials, ceramics, glass, and the like can also be used as the material of the substrate 50. When an insulating material such as ceramics is used for the substrate 50, the first insulating layer 51 between the substrate 50 and the conductor layer 52 can be omitted. On the other hand, metal materials are excellent in durability against rapid heating and are easy to process, so they are suitable for reducing costs. Among metal materials, aluminum and copper are particularly preferable in that 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 materials.

[0048] Each of the insulating layers 51 and 53 is made of an insulating material such as heat-resistant glass, etc. Alternatively, ceramic, polyimide (PI), etc. may be used as the material.

[0049] The conductor layer 52 is composed of a heating section 60 having a plurality of resistance heating elements 59, a plurality of electrode sections 61, and a plurality of power supply lines 62 serving as conductors that electrically connect these. Each resistance heating element 59 is electrically connected in parallel to any two of the three electrode sections 61 via the plurality of power supply lines 62 provided on the base material 50. In this embodiment, the arrangement direction of the plurality of resistance heating elements 59 is the same as the longitudinal direction of the heater 22.

[0050] The resistance heating element 59 is formed by applying a paste 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 the above, the material of the resistance heating element 59 can be a silver alloy (AgPt) or ruthenium oxide (RuO 2 ) resistive material may be used.

[0051] The power supply line 62 is made of a conductor having a resistance value smaller than that of the resistance heating element 59. As a material for the power supply line 62 and the electrode portion 61, silver (Ag) or silver palladium (AgPd) can be used, and the power supply line 62 and the electrode portion 61 are formed by screen printing such a material.

[0052] FIG. 9 is a perspective view showing a state in which the connector 70 is connected to the heater 22. As shown in FIG.

[0053] 9, the connector 70 has a resin housing 71 and a plurality of contact terminals 72 provided on the housing 71. Each contact terminal 72 is made of a leaf spring, and a harness 73 for power supply is connected to it.

[0054] As shown in Fig. 9, the connector 70 is attached so as to sandwich the heater 22 and the heater holder 23 from the front and back sides together. In this state, the contact portions 72a provided at the tip of each contact terminal 72 elastically contact (pressure weld) with the corresponding electrode portions 61, thereby electrically connecting the heat generating portion 60 to the power source provided in the image forming apparatus via the connector 70. This enables power to be supplied from the power source to the heat generating portion 60. Note that in order to ensure connection with the connector 70, at least a portion of each electrode portion 61 is not covered by the second insulating layer 53 and is exposed (see Fig. 7).

[0055] As shown in FIG. 10, in this embodiment, among the multiple resistance heating elements 59 arranged in the longitudinal direction of the base material 50, a first heating section 60A composed of the resistance heating elements 59 other than those at both ends and a second heating section 60B composed of the resistance heating elements 59 at both ends are configured to be able to control heat generation independently. Specifically, each of the resistance heating elements 59 other than those at both ends constituting the first heating section 60A is connected to a first electrode portion 61A provided on one end side in the longitudinal direction of the base material 50 via a first power supply line 62A. Also, each of the resistance heating elements 59 constituting the first heating section 60A is connected to a second electrode portion 61B provided on the end side opposite to the first electrode portion 61A via a second power supply line 62B. On the other hand, each of the resistance heating elements 59 at both ends constituting the second heating section 60B is connected to a third electrode portion 61C (different from the first electrode portion 61A) provided on one end side in the longitudinal direction of the substrate 50 via a third power supply line 62C or a fourth power supply line 62D. Also, each of the resistance heating elements 59 at both ends is connected to the second electrode portion 61B via a second power supply line 62B, similar to each of the resistance heating elements 59 of the first heating section 60A. In other words, the second electrode portion 61B is connected by merging the power supply lines (second power supply line 62B) extending from all of the resistance heating elements 59.

[0056] Further, each of the electrode units 61A to 61C is connected to a power source 64 via the connector 70 described above, and is supplied with power from the power source 64. A switch 65A is provided between the electrode unit 61A and the power source 64 as a switching unit, and the application of a voltage can be switched on and off by turning the switch 65A on and off. Similarly, a switch 65C is provided between the electrode unit 61C and the power source 64 as a switching unit, and the application of a voltage can be switched on and off by turning the switch 65C on and off. Furthermore, the ON / OFF of these switches 65A and 65C and the timing of the power supply to the heater 22 are controlled by a control circuit 66 as a control unit. The control circuit 66 also performs these controls based on the detection results of various sensors in the image forming apparatus. For example, the timing of passing a paper sheet can be determined based on the detection results of sensors provided at the entrance and exit of the fixing nip N, and the power supply to the heater 22 and the switching of the switches 65A and 65C can be performed.

[0057] When a voltage is applied to the first electrode portion 61A and the second electrode portion 61B, the resistive heating elements 59 other than those at both ends are energized, and only the first heating portion 60A is heated. On the other hand, when a voltage is applied to the second electrode portion 61B and the third electrode portion 61C, the resistive heating elements 59 at both ends are energized, and only the second heating portion 60B is heated. Also, when a voltage is applied to all the electrodes 61A to 61C, it is possible to heat both (all) the resistive heating elements 59 of the first heating portion 60A and the second heating portion 60B. For example, when a relatively small width paper of A4 size (paper passing width: 210 mm) or less is passed through, only the first heating portion 60A is heated, and when a relatively large width paper of more than A4 size (paper passing width: 210 mm) is passed through, the second heating portion 60B is heated in addition to the first heating portion 60A, so that a heating area according to the paper width can be obtained.

[0058] Incidentally, in order to further reduce the size of the image forming device and the fixing device, it is important to reduce the size of the heater, which is one of the components arranged inside the fixing belt. That is, by reducing the size of the heater in its short-side direction (the direction of the arrow Y in FIG. 10: the direction intersecting the longitudinal direction B along the surface on which the heat generating parts 60A and 60B of the heater 22 are provided, or the direction perpendicular to the longitudinal direction B of the heater 22 and different from the thickness direction of the heater 22, which is the direction perpendicular to the paper surface of FIG. 10), the diameter of the fixing belt can be reduced, and thus the fixing device and the image forming device can be reduced in size. Specifically, the following three methods can be given as methods for reducing the size of the heater in the short-side direction.

[0059] One method is to reduce the size of the heat generating portion (resistance heating element) in the short-side direction. However, when the heat generating portion is reduced in the short-side direction, the width of the heating area in which the fixing belt is heated is reduced, and therefore, when the same amount of heat is to be provided to the fixing belt, the problem of a higher peak temperature rise occurs. When the peak temperature rise value becomes high, there is a risk that the temperature of an overheating detection device such as a thermostat or fuse provided on the back surface of the heater exceeds the heat resistance temperature, or that the overheating detection device malfunctions. In addition, when the peak temperature rise value becomes high, the efficiency of heat transfer from the heater to the fixing belt also decreases, which is undesirable from the viewpoint of energy efficiency. As described above, there are circumstances that make it difficult to adopt the method of reducing the size of the heat generating portion in the short-side direction.

[0060] The second method is to reduce the size of the portion in the short direction where the heating part, the electrode part, and the power supply line are not provided. However, this method reduces the gap between the heating part and the power supply line and between the electrode part and the power supply line, so there is a risk that insulation cannot be ensured. In view of the current heater structure, it is difficult to further reduce the gap between the heating part and the power supply line and between the electrode part and the power supply line.

[0061] The remaining third method is to reduce the size of the power supply line in the short direction. This method is more feasible than the above two methods. However, when the power supply line is reduced in the short direction, the resistance value of the power supply line increases, which may cause unintended current shunting on the conductive path of the heater. In particular, when the resistance value of the heating part is reduced in order to increase the heat generation amount of the heating part in order to meet the high speed of the image forming apparatus, the resistance value of the power supply line and the resistance value of the heating part become relatively close to each other, which may cause unintended current shunting. As a method for avoiding such unintended current shunting, it is possible to secure the cross-sectional area and suppress the increase in the resistance value of the power supply line by increasing the thickness direction (the direction intersecting the long direction and the short direction) by the amount of reduction in the power supply line in the short direction. However, in that case, it becomes difficult to screen print the power supply line, which forces a change in the method of forming the power supply line. For this reason, it is difficult to adopt a solution of making the power supply line thicker. Therefore, in order to reduce the size of the heater in the short direction, it is necessary to reduce the size of the power supply line in the short direction in anticipation of an increase in resistance, and to take separate measures against unintended current shunting that may occur as a result.

[0062] Hereinafter, unintended current shunting and the resulting problems will be described using a heater having the same layout as the heater 22 described above as an example.

[0063] In the heater 22 shown in FIG. 11, when a voltage is applied to the first electrode portion 61A and the second electrode portion 61B to heat only each resistive heating element 59 of the first heating portion 60A, a current typically flows through the first power supply line 62A, passes through each resistive heating element 59 other than those at both ends, and flows through the second power supply line 62B.

[0064] However, when the difference between the resistance values ​​of the power supply line and the heat generating part becomes small due to an increase in the resistance value of the power supply line associated with the above-mentioned miniaturization and a decrease in the resistance value of the heat generating part associated with an increase in the amount of heat generated, an unintended branching of the current occurs as shown in Fig. 12. That is, a part of the current that passed through the second resistance heating element 59 from the left in Fig. 12 flows in the opposite direction to the second electrode part 61B at the branch part X of the second power supply line 62A. Then, the branched current passes through the leftmost resistance heating element 59 in Fig. 12, and further passes through the third power supply line 62C, the third electrode part 61C, the fourth power supply line 62D, and the rightmost resistance heating element 59 in this order, before joining the second power supply line 62B.

[0065] Thus, in the heater 22 shown in FIG. 12, the portion of the second power supply line 62B extending from the branch portion X to the left side of the figure, the resistive heating elements 59 at both ends that constitute the second heating portion 60B, the third electrode portion 61C, and the portion including the third power supply line 62C and the fourth power supply line 62D constitute a branched conductive path E3 that allows current to flow through an unintended path.

[0066] Furthermore, such unintended branching can occur when electricity is applied to the first heat generating portion 60A if the conductive path of the heater 22 has at least a first conductive portion E1 connecting the first heat generating portion 60A and the third electrode portion 61C, a second conductive portion E2 extending from the first heat generating portion 60A in a first direction S1 (right side in FIG. 12) of the longitudinal direction of the heater 22 and connected to the second electrode portion 61B, and a branch conductive path E3 branching from the second conductive portion E2 in a second direction S2 (left side in FIG. 12) opposite to the first direction S1 and connected to the second conductive portion E2 or the second electrode portion 61B without passing through the first conductive portion E1. In other words, the above-mentioned shunting may occur when current is applied to the first heat generating part 60A under three conditions: "the first electrode part (first electrode part 61A) is connected to the resistive heating element 59 at the center in the longitudinal direction," "the second electrode part (third electrode part 61C) is connected to the resistive heating elements 59 at both ends in the longitudinal direction," and "the power supply lines extending from the resistive heating elements 59 join and are connected to the third electrode part (second electrode part 61B)." In this embodiment, the second heat generating part 60B and the first electrode part 61A are provided on the branched conductive path E3, but unintended shunting may occur even in a conductive path not provided with the second heat generating part 60B and the first electrode part 61A, or in a conductive path provided with a conductive member other than these.

[0067] When unintended current shunting occurs, the current flows through a previously unanticipated path, causing heat generation from the power supply line to cause variations in the temperature distribution of the heater 22. For example, in the heater 22 shown in Fig. 13, if 20% of the current flows evenly from the first electrode portion 61A to each resistance heating element 59 of the first heating portion 60A, and if the current passing through the second resistance heating element 59 from the left in the figure is shunted by 5% at the branch portion X beyond that, the amount of heat generated in the power supply line in each block divided by the resistance heating elements 59 will be as shown in the table in the figure.

[0068] Here, the portion of each power feeder extending in the short direction of the heater 22 is short and the amount of heat generated in this portion is small, so this amount of heat is ignored and only the amount of heat generated in the portion of each power feeder extending in the longitudinal direction of the heater 22 is calculated. Specifically, the amount of heat generated in the portion of each first power feeder 62A, second power feeder 62B, and fourth power feeder 62D extending in the longitudinal direction of the heater 22 is calculated. In addition, since the amount of heat generated (W) is expressed by the following formula (1), the amount of heat generated shown in the table of FIG. 13 is calculated as the square of the current (I) flowing through each power feeder for convenience. Therefore, the numerical values ​​of the amount of heat generated shown in the table of FIG. 13 are merely simply calculated values ​​and differ from the actual amount of heat generated.

[0069]

number

[0070] 13, the calculation method of the calorific value will be specifically described. In the first block, the current flowing through the first power feed line 62A is 100%, and the current flowing through the fourth power feed line 62D is 5%, so the total value of the squares of these, 10025 (10000+25), is the total calorific value of the power feed lines in the first block. In the second block, the current flowing through the first power feed line 62A is 80%, the current flowing through the second power feed line 62B is 5%, and the current flowing through the fourth power feed line 62D is 5%, so the total value of the squares of these, 6450 (6400+25+25), is the total calorific value of the power feed lines in the second block. In the other blocks, the calorific values ​​are calculated in a similar manner.

[0071] 13, the total heat generation amount of each block is asymmetrical with respect to the fourth block in the center of the heat generation area due to the unintended current division, and the heat generation amount on one side in the longitudinal direction is greater than that on the other side. However, the first and seventh blocks are non-paper passing areas where paper does not pass.

[0072] Even when all heat generating parts are energized, the amount of heat generated in the longitudinal direction of the heater 22 is asymmetrical due to the difference in the magnitude of the current flowing through the conductive parts. In other words, when attempting to miniaturize the heater 22 as described above, it is difficult to make the amount of heat generated in the longitudinal direction of the heater 22 symmetrical because the arrangement of the electrode parts and conductive parts is also restricted. Also, when attempting to increase the speed of the device as described above, the value of the current flowing through the conductive parts increases, and the difference between the left and right becomes large, so that the difference cannot be ignored. The case where all heat generating parts are energized will be described below.

[0073] As shown in FIG. 14, when all the heat generating parts are energized, 20% of the current also flows through the resistance heating elements 59 at both the left and right ends and the power feed lines 62C and 62D connected thereto, which is different from the above case. On the other hand, the value of the current flowing through the power feed line 62A is the same as before. In this case, in the first block, the current flowing through the first power feed line 62A is 100%, and the current flowing through the fourth power feed line 62D is 20%, so the total value of the squares of these, 10400 (10000+400), is the total heat generation amount of the power feed lines in the first block. In the second block, the current flowing through the first power feed line 62A is 80%, the current flowing through the second power feed line 62B is 20%, and the current flowing through the fourth power feed line 62D is 20%, so the total value of the squares of these, 7200 (6400+400+400), is the total heat generation amount of the power feed lines in the second block. The heat generation amounts of the other blocks are calculated in the same manner.

[0074] As shown in the table and graph at the bottom of Figure 14, the total heat generation amount of each block is asymmetrical with respect to the fourth block in the center of the heat generation area. In particular, the second power supply line 62B connected to all the resistance heating elements 59 has a large current value of 120% downstream, i.e., in the seventh block, and the heat generation amount on the other side in the longitudinal direction is larger than that on the one side. In this embodiment, the length of each block is set to be the same so that small size paper and large size paper can be heated evenly.

[0075] In the above partial or full current-carrying case, the amount of current in the second power supply line 62B increases from one longitudinal side to the other. When a current flows from the second electrode portion 61B to the first electrode portion 61A or the third electrode portion 61C, the resistive heating element 59 on the other longitudinal side is disposed upstream in the current direction, and the resistive heating element 59 on the one side is disposed downstream.

[0076] As described above, in the heater 22 of this embodiment, one longitudinal side (left side in FIG. 10) is the side where the amount of heat generated by the heater 22 is large when electricity is applied to the first heat generating portion 60A and unintended current division occurs (in the case of FIG. 13). Also, the other longitudinal side (right side in FIG. 10) is the side where the amount of heat generated is large when electricity is applied to the first heat generating portion 60A and the second heat generating portion 60B (in the case of FIG. 14).

[0077] Such asymmetric variation in the heat generation amount of the power supply lines causes variation in temperature along the longitudinal direction of the heater 22. If the temperature of the heater 22 varies along the longitudinal direction, the detection results of the temperature detection means provided in the fixing device 9 will differ depending on which longitudinal position is detected. Therefore, an arrangement that takes into account the above-mentioned temperature deviation will be required. In the following explanation, the arrangement of the thermistor 35 described above will be explained as one of the temperature detection means provided in the fixing device.

[0078] As shown in FIG. 15, the fixing device of this embodiment has a first thermistor 35A, a second thermistor 35B, and a third thermistor 35C. The longitudinal arrangement of each thermistor 35 will be described below. The region C in FIG. 15 is a longitudinal heat generation region by all the resistance heating elements 59 provided in the heater 22, and is hereinafter also simply referred to as the heat generation region C of the heater 22. The heat generation region C of the heater 22 refers to a region from (the position of one end in the longitudinal direction of) the resistance heating element 59 arranged on the furthest side in the longitudinal direction among all the resistance heating elements 59 provided in the heater 22 to (the position of the other end in the longitudinal direction of) the resistance heating element 59 arranged on the furthest side in the longitudinal direction. Moreover, the line C0 is a line indicating the center position of the heat generation region C, and is hereinafter also simply referred to as the center position C0.

[0079] The first thermistor 35A is disposed within a region CA, which is a region facing the resistance heating element 59 of the first heating section 60A, on one side of the central position C0 in the longitudinal direction. That is, the first thermistor 35A is disposed facing (at a corresponding position) the resistance heating element 59 on the side where the heat generation amount is large in the first heating section 60A during partial energization and when an unintended shunt current flows (as in FIG. 13). In this embodiment, as an example, the first thermistor 35A is disposed facing the resistance heating element 59 disposed at one end side in the longitudinal direction of the region CA among the resistance heating elements 59 of the first heating section 60. Note that the above-mentioned "the thermistor 35 is disposed at a position corresponding to the resistance heating element 59" means that the temperature detection portion of the thermistor 35 and at least a part of the resistance heating element 59 overlap in the longitudinal direction.

[0080] The second thermistor 35B is disposed opposite the resistance heating element 59 of the second heat generating portion 60B on the other longitudinal side of the central position C0. In other words, the second thermistor 35B is disposed opposite the resistance heating element 59 of the second heat generating portion 60B on the side that generates a larger amount of heat when fully energized (in the case of FIG. 14).

[0081] The third thermistor 35C is disposed on the central side in the longitudinal direction. In other words, the third thermistor 35C is disposed opposite the resistance heating element 59 that is closer to the central position C0 than the other thermistors 35, and particularly in this embodiment, the third thermistor 35C is disposed opposite the resistance heating element 59 at the central position C0.

[0082] When the amount of heat generated on one side of the heater 22 in the longitudinal direction is greater than that on the other side, for example, as shown in Fig. 13, when the first heat generating unit 60A is energized in the heater configuration of Fig. 10 and unintended current division occurs, the first thermistor 35A can detect the temperature on the one side of the heater 22 in the longitudinal direction where the amount of heat generated is greater. Then, the output of the heater 22 is controlled using the detection result of the first thermistor 35A. This makes it possible to detect a rise in temperature of the heater 22 at an earlier timing and reduce the output of the heater 22, or to detect an abnormal rise in temperature of the heater 22 and cut off the power supply to the heater 22, thereby improving the safety of the fixing device.

[0083] Incidentally, when the fixing device performs a fixing operation on a small-sized paper, the temperature of the non-paper passing area, which is the end side of the heater 22 and the fixing belt 20 in the longitudinal direction, becomes higher than that of the center side, which is a so-called end temperature rise. For example, when a fixing operation is performed on a paper with a width of the range H2, if the first heat generating unit 60A is energized and the range H1 is set as the heating area of ​​the heater 22, the ranges H3 on both sides of the range H1 become the non-paper passing areas. In the non-paper passing areas, the heat of the fixing belt 20 is not taken by the paper, and the temperature of the fixing belt 20 and the heater 22 rises at this position in the longitudinal direction. In this embodiment, in order to prevent an excessive temperature rise in the non-paper passing areas on the end side in the longitudinal direction, the output of the heater 22 is reduced to reduce the productivity of the fixing device. The control circuit also uses the detection result of the third thermistor 35C on the longitudinal center side to determine the end temperature rise. In addition, since the third thermistor 35C can measure the temperature of the paper passing area which is the coldest whether full or partial current is applied, it is possible to control using the third temperature detection means to ensure fixing performance while preventing problems caused by temperature rise by detecting using the first or second temperature detection means.

[0084] Even if the above-mentioned end temperature rise occurs, the end temperature rise can be detected earlier by providing the first thermistor 35A on the side where the heat generation in the longitudinal direction is large, especially in the area that becomes a non-paper passing area when a small size paper is passed. Then, the control circuit 66 (see FIG. 10) controls the output of the heater 22 based on the detection result of the first thermistor 35A, enabling more accurate temperature control.

[0085] When the heat generation amount of the other side in the longitudinal direction of the heater 22 is greater than that of the other side, for example, as shown in Fig. 14, when all heat generating parts in the heater configuration of Fig. 10 are energized, the second thermistor 35B arranged opposite the second heat generating part 60B can detect the temperature of the other side in the longitudinal direction, which is the side where the heat generation amount of the heater 22 is greater. Then, the output of the heater 22 is controlled using the detection result of the second thermistor 35B. This makes it possible to detect a rise in temperature of the heater 22 at an earlier timing to reduce the output of the heater 22, or to detect an abnormal rise in temperature of the heater 22 to cut off the power supply to the heater 22, thereby improving the safety of the fixing device.

[0086] In the above embodiment, the third electrode portion 61C is disposed on one side in the longitudinal direction, which is the same side as the first electrode portion 61A, but this is not limiting, and for example, the third electrode portion 61C may be disposed on the other side in the longitudinal direction, which is the opposite side to the first electrode portion 61A, as shown in Fig. 25. In this embodiment as well, the thermistors are disposed in the same manner as in the above embodiment.

[0087] Also, as in FIG. 13 of the embodiment described above, in this embodiment, when the first heat generating portion 60A is energized and unintended current division occurs, the amount of heat generated on one side of the heater 22 in the longitudinal direction increases. Therefore, the first thermistor 35A can detect the temperature of the side of the heater 22 where the amount of heat generated is large. Also, as in FIG. 14 of the embodiment described above, when all heat generating portions are energized, the amount of heat generated on the other side of the heater 22 in the longitudinal direction increases. Therefore, the second thermistor 35B can detect the temperature of the side of the heater 22 where the amount of heat generated is large. As a result, in each case, the temperature rise of the heater 22 can be detected at an earlier timing to reduce the output of the heater 22, or the abnormal temperature rise of the heater 22 can be detected to cut off the power supply to the heater 22, thereby improving the safety of the fixing device. Also, the third thermistor 35C can measure the temperature of the paper passing area where the amount of heat generated is the smallest when fully energized and when partially energized, so that the fixing performance can be guaranteed.

[0088] In the above embodiment, the first heating section 60A has five resistive heating elements 59, but the present invention is not limited to this. For example, as shown in FIG. 26, the first heating section 60A may be composed of two resistive heating elements 59 arranged on one side and the other side in the longitudinal direction with respect to the central position C0. In this case, among the resistive heating elements 59 constituting the first heating section 60A, the first thermistor 35A is arranged at a position corresponding to the resistive heating element 59 on one side in the longitudinal direction from the central position C0. Among the resistive heating elements 59 constituting the second heating section 60B, the second thermistor 35B is arranged at a position corresponding to the resistive heating element 59 on the other side in the longitudinal direction from the central position C0. As in the above embodiment, when the first heating section 60A is energized and an unintended shunt occurs, the first thermistor 35A can detect the temperature of the side of the heater 22 that generates a larger amount of heat, and when all the heating sections are energized, the second thermistor 35B can detect the temperature of the side of the heater 22 that generates a larger amount of heat. Therefore, in each case, the temperature rise of the heater 22 can be detected at an earlier timing to reduce the output of the heater 22, or an abnormal temperature rise of the heater 22 can be detected to cut off the power supply to the heater 22, thereby improving the safety of the fixing device.

[0089] In addition, although the above describes an example of a temperature detection means in which the present invention is applied to the thermistor 35 for temperature control, the present invention may also be applied to a thermostat that detects the temperature of the heater 22 or the fixing belt 20 when the temperature rises abnormally and cuts off the power supply to the heater 22. In other words, by arranging the thermostat in the same manner as the first thermistor 35A and the second thermistor 35B described above, it is possible to detect an abnormal rise in temperature of the heater 22 at an early stage and cut off the power supply to the heater 22 in each case.

[0090] In the above embodiment, the present invention has been exemplified by a temperature detection unit that faces the heater 22 and detects its temperature. By providing the temperature detection unit facing the heater 22, the fixing device 9 can be made smaller. However, the present invention is not limited to this, and a temperature detection unit that faces the fixing belt 20 as a belt member and detects its temperature may be provided.

[0091] 16, for example, a non-contact temperature detection means 36 is provided on the fixing belt 20 so as to face the outer circumferential surface of the fixing belt 20. The temperature detection means 36 may be, for example, a non-contact thermistor or a thermopile.

[0092] The temperature detection means 36 of this embodiment can also be arranged in the longitudinal direction in the same manner as the first thermistor 35A and the second thermistor 35B of the above-mentioned embodiment, and can be arranged at positions corresponding to each of the resistive heating elements 59 described above.

[0093] When the temperature detection means 36 is provided in the same arrangement as the first thermistor 35A, as in the above-mentioned embodiment, when the first heat generating portion 60A is energized in the heater configuration of FIG. 10 and unintended current shunting occurs, the temperature of the fixing belt 20 on one side in the longitudinal direction, which is the side where the amount of heat generated by the heater 22 is large, can be detected by the temperature detection means 36. Then, by controlling the output of the heater 22 using the detection result of the temperature detection means 36, it is possible to detect a rise in temperature of the fixing belt 20 at an earlier timing and reduce the output of the heater 22, or to detect an abnormal rise in temperature of the fixing belt 20 and cut off the power supply to the heater 22, thereby improving the safety of the fixing device. Also, as mentioned above, the end temperature rise can be detected earlier.

[0094] When the temperature detection means 36 is provided in the same arrangement as the second thermistor 35B, the temperature of the fixing belt 20 on the other side in the longitudinal direction, which is the side where the amount of heat generated by the heater 22 is large, can be detected by the temperature detection means 36 in the same manner as in the above-described embodiment when all heat generating parts in the heater configuration of FIG. 10 are energized. Then, by controlling the output of the heater 22 using the detection result of the temperature detection means 36, it is possible to detect the temperature rise of the fixing belt 20 at an earlier timing and reduce the output of the heater 22, or to detect an abnormal temperature rise of the fixing belt 20 and cut off the power supply to the heater 22, thereby improving the safety of the fixing device. Of course, the temperature detection means 36 facing the outer circumferential surface of the fixing belt 20 can be provided at each position in the longitudinal direction, like the first to third thermistors 35A to 35C in FIG. 15.

[0095] The layout of the heater 22 is not limited to the configuration shown in FIG. 10. The present invention can be applied to a heater 22 in which a temperature deviation occurs in the heater 22 or fixing belt 20 between one side and the other side in the longitudinal direction.

[0096] For example, as another example of a heater to which the present invention is applied, the heater 22 shown in Fig. 17 differs from the above-mentioned embodiment in that all electrode portions are provided on one side in the longitudinal direction. That is, compared to the heater 22 in Fig. 10 etc., it differs in that the second electrode portion 61B is provided on one side in the longitudinal direction. Also, as shown in Fig. 17, since the second electrode portion 61B is provided on one side in the longitudinal direction, the power supply line directly connected to the second electrode portion 61B extends to the other side in the longitudinal direction, turns back, and is connected to each resistance heating element 59.

[0097] In this embodiment, of the power supply lines connecting these second electrode portions 61B and each resistive heating element 59, the portion from the portion connected to each resistive heating element 59 to the folded portion on the other side of the longitudinal direction is referred to as the second power supply line 62B, and the portion from the portion extending to one side of the longitudinal direction continuous with the folded portion to the second electrode portion 61B is referred to as the fifth power supply line (conductor) 62E.

[0098] Even in such a heater 22, when electricity is applied only to the first heat generating portion 60A, and when electricity is applied to both the first heat generating portion 60A and the second heat generating portion 60B, the temperature deviation in the longitudinal direction as described above occurs.

[0099] First, when electricity is applied only to the first heat generating portion 60A, as shown in FIG. 18, an unintended shunt current occurs toward the third power supply line 62C. Therefore, the total heat generation amount of each block is asymmetrical with respect to the fourth block in the center of the heat generating area, and the heat generation amount on one side in the longitudinal direction is greater than that on the other side. However, the first block and the seventh block are non-paper passing areas through which paper does not pass. Also, when electricity is applied to the first heat generating portion 60A and the second heat generating portion 60B, as shown in FIG. 19, the total heat generation amount is asymmetrical with respect to the fourth block, and the heat generation amount on the other side in the longitudinal direction is greater than that on one side.

[0100] In the above partial or full current-carrying case, the amount of current in the second power supply line 62B increases from one longitudinal side to the other. When a current flows from the second electrode portion 61B to the first electrode portion 61A or the third electrode portion 61C, the resistive heating element 59 on the other longitudinal side is disposed upstream in the current direction, and the resistive heating element 59 on the one side is disposed downstream.

[0101] In the above heater 22, the same effect as in the above embodiment can be obtained by arranging a temperature detection means at a position corresponding to the first thermistor 35A or the second thermistor 35B in the longitudinal direction. That is, in the case of FIG. 18, by controlling the output of the heater 22 using the detection result of the first thermistor 35A, it is possible to detect a rise in temperature of the heater 22 at an earlier timing to reduce the output of the heater 22, or to detect an abnormal rise in temperature of the heater 22 and cut off the power supply to the heater 22, thereby improving the safety of the fixing device. Also, as described above, the end temperature rise can be detected earlier. Furthermore, in the case of FIG. 19, by controlling the output of the heater 22 using the detection result of the second thermistor 35B, it is possible to detect a rise in temperature of the heater 22 at an earlier timing to reduce the output of the heater 22, or to detect an abnormal rise in temperature of the heater 22 and cut off the power supply to the heater 22, thereby improving the safety of the fixing device.

[0102] The present invention is particularly suitable for heaters that are small in size in the short side direction. That is, when trying to reduce the short side dimension of the heater 22 as described above, it is necessary to reduce the short side dimension of the power supply line, and the amount of heat generated from the power supply line becomes relatively large, which increases the influence. Specifically, it is preferable to apply the present invention to a heater 22 in which the ratio (R / Q) of the short side dimension R of the resistance heating element 59 to the short side dimension Q of the heater 22 (substrate 50) shown in FIG. 20 is 25% or more. Furthermore, it is more preferable to apply the present invention to a heater 22 in which the short side dimension ratio (R / Q) is 40% or more. By applying the present invention to such a small heater 22, a greater effect can be expected.

[0103] Next, the experimental results of the temperature deviation occurring between the center side and the end side of the heater 22 in the longitudinal direction when the ratio (R / Q) of the short side dimensions is changed will be described. In the experiment, heaters 22 having the above-mentioned configuration were prepared with the above-mentioned short side dimension ratios (R / Q) of 20% or more and less than 25%, 25% or more and less than 40%, 40% or more and less than 70%, and 70% or more and less than 80%, respectively, and a predetermined voltage was applied to all resistance heating elements of the heater under the condition of a single heater, and the surface temperatures of the center side and the end side of the heater in the longitudinal direction were measured using an infrared thermography FLIR T620 manufactured by FLIR Systems. The above experimental results are shown in Table 1. In the results of Table 1, the temperature difference between the center side and the end side was marked as ○ when it was less than 2°C, △ when it was 2°C or more and less than 5°C, and × when it was 5°C or more. In addition, if the ratio of the short side dimensions (R / Q) is set to 80% or more, there will be no space to place the power supply wires unless the short side dimension of the heater is made extremely large, so this was not included in the experiment.

[0104] [Table 1]

[0105] As shown in Table 1, the temperature difference between the center and the end of the heater increased as the ratio of the short-side dimensions (R / Q) increased. Specifically, the result was ◯ when the ratio was 20% or more and less than 25%, but changed to △ when the ratio was 25% or more and less than 40%, and changed to × when the ratio was 40% or more and less than 70%, and when the ratio was 70% or more and less than 80%. As can be seen from these results, the temperature unevenness in the longitudinal direction of the heater becomes noticeable when the ratio of the short-side dimensions (R / Q) is 25% or more, and is particularly noticeable when the ratio is 40% or more. Therefore, it is preferable to apply the above-mentioned configuration of this embodiment to a heater with such a dimensional ratio to suppress the temperature deviation.

[0106] In addition, a resistance heating element having PTC characteristics may be used to suppress the temperature variation of the heater 22 described above. The PTC characteristics are characteristics in which the resistance value increases as the temperature increases (when a constant voltage is applied, the heater output decreases). By using a heating section having PTC characteristics, it is possible to achieve high output at low temperatures and suppress excessive temperature rise with low output at high temperatures. For example, if the TCR coefficient of the PTC characteristics is set to about 300 to 4000 ppm / degree, it is possible to reduce costs while ensuring the resistance value required for the heater. It is more preferable to set the TCR coefficient to 500 to 2000 ppm / degree.

[0107] The temperature coefficient of resistance (TCR) can be calculated using the following formula (2). In formula (2), T0 is a reference temperature, T1 is an arbitrary temperature, R0 is a resistance value at reference temperature T0, and R1 is a resistance value at arbitrary temperature T1. For example, in the heater 22 described above shown in FIG. 7, if the resistance value between the first electrode portion 61A and the second electrode portion 61B is 10Ω (resistance value R0) at 25°C (reference temperature T0) and 12Ω (resistance value R1) at 125°C (arbitrary temperature T1), the temperature coefficient of resistance is 2000 ppm / °C from formula (2).

[0108]

number

[0109] The heater to which the present invention is applied is not limited to the heater 22 having a block-shaped (rectangular) resistance heating element 59 as shown in FIG. 7 and the like, but may also be applied to a heater 22 having a resistance heating element 59 shaped like a folded straight line as shown in FIG. 21(a) or FIG. 21(b), or a heater having a resistance heating element of another shape. In the figure, the colored parts indicate the resistance heating element 59. FIG. 21(a) shows an example in which the power supply lines 62A and 62D formed along the longitudinal direction of the heater 22 partially extend in a direction intersecting the longitudinal direction. On the other hand, FIG. 21(b) shows an example in which the resistance heating element 59 is formed including the areas bent from the power supply lines 62A and 62D formed along the longitudinal direction of the heater 22 in a direction intersecting the longitudinal direction.

[0110] Further, in addition to the fixing device described above, the present invention is also applicable to fixing devices as shown in Figures 22 to 24. The configuration of each fixing device shown in Figures 22 to 24 will be briefly described below.

[0111] 22, a pressure roller 90 is disposed on the opposite side of the pressure roller 21 with respect to the fixing belt 20, and the fixing belt 20 is sandwiched and heated by the pressure roller 90 and the heater 22. On the other hand, on the pressure roller 21 side, a nip forming member 91 is disposed on the inner periphery of the fixing belt 20. The nip forming member 91 is supported by a stay 24, and the fixing nip N is formed by sandwiching the fixing belt 20 between the nip forming member 91 and the pressure roller 21.

[0112] 23, the above-mentioned pressure roller 90 is omitted, and in order to ensure the circumferential contact length between the fixing belt 20 and the heater 22, the heater 22 is formed in an arc shape in accordance with the curvature of the fixing belt 20. The rest of the configuration is the same as that of the fixing device 9 shown in FIG.

[0113] Finally, the fixing device 9 shown in FIG. 24 will be described. The fixing device 9 is composed of a heating assembly 92, a fixing roller 93 as a fixing member, and a pressure assembly 94 as an opposing member. The heating assembly 92 has the heater 22 and heating unit 19 described in the previous embodiment, and a heating belt 120 as a belt member. The fixing roller 93 is composed of a solid iron core 93a, an elastic layer 93b formed on the surface of the core 93a, and a release layer 93c formed on the outside of the elastic layer 93b. A pressure assembly 94 is provided on the opposite side of the heating assembly 92 side of the fixing roller 93. The pressure assembly 94 has a nip forming member 95 and a stay 96 arranged therein, and a pressure belt 97 rotatably arranged so as to include the nip forming member 95 and the stay 96. Then, a paper P is passed through the fixing nip N2 between the pressure belt 97 and the fixing roller 93, and heated and pressurized to fix an image.

[0114] In the fixing device 9 shown in FIG. 24, the heating assembly 92 heats the fixing roller 93. Therefore, if there is a difference in the amount of heat generated between one side and the other side in the longitudinal direction of the heater 22 (depth direction in the figure) as described above, a difference in temperature will also occur between one side and the other side in the longitudinal direction of the fixing roller 93.

[0115] 22 to 24, by providing a temperature detection means at a position facing the heater 22 or the fixing belt 20 (heating belt 120) and in a position corresponding to the first thermistor 35A or the second thermistor 35B in the longitudinal direction, it is possible to detect a rise in temperature of the heater 22 or the fixing belt 20 (heating belt 120) at an earlier timing to reduce the output of the heater 22, or to detect an abnormal rise in temperature of the heater 22 or the fixing belt 20 (heating belt 120) to cut off the power supply to the heater 22, thereby improving the safety of the fixing device. Also, an increase in the end temperature can be detected earlier.

[0116] Furthermore, 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, laminators that thermocompress the surface of a sheet such as paper with a film as a covering member, and thermocompression devices such as heat sealers that thermocompress the seal portion of a packaging material. By applying the present invention to such devices, an abnormal temperature rise in the heating body or heated member can be detected at an earlier timing and the power supply to the heating body can be cut off, thereby improving the safety of the heating device.

[0117] Examples of recording media include paper P (plain paper), as well as cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheets, plastic film, prepreg, copper foil, and the like. [Explanation of symbols]

[0118] 1. Image forming device 9 Fixing device (heating device) 19 Heating unit 20 Fixing belt (heated member or belt member or fixing member) 21 Pressure roller (opposing member or pressure member) 22 Heater (heating element) 35 Thermistor (temperature detection means) 36 Temperature detection means 59 Resistance heating element (heating element) 60 Heating Part 61 Electrode section 62 Power supply line (conductor) 66 Control circuit (control section) A Paper feeding direction C Heating area by all resistive heating elements C0 Center position of heat generation area N Fixing nip (nip part) P Paper (recording medium or heated object) Q Heater short side dimension R Short side dimension of the resistance heating element Y Heater short side direction [Prior art documents] [Patent documents]

[0119] [Patent Document 1] JP 2016-62024 A

Claims

1. A heating body; A heating device equipped with a plurality of temperature detection means, The heating body is A first heating portion including at least two resistive heating elements; a second heating section including at least two resistive heating elements each located closer to both ends of the heating body in the longitudinal direction than the first heating section; A plurality of conductors; a first electrode portion connected to the first heat generating portion via the conductor; a second electrode portion connected to the first heat generating portion and the second heat generating portion via the conductor; a third electrode portion connected to the second heat generating portion via the conductor; In the longitudinal direction, when a region from the resistive heating element arranged on the most one side to the resistive heating element arranged on the most other side among all the resistive heating elements included in the heating element is defined as a heat generating region, In the longitudinal direction, the first electrode portion is disposed on one side with respect to a center position of the heat generating region, In the longitudinal direction, the first temperature detection means as the temperature detection means is a resistive heating element included in the first heating portion, and is disposed at a position corresponding to the resistive heating element disposed on one side of the center position of the heating area, and the second temperature detection means as the temperature detection means is a resistive heating element included in the second heating portion, and is disposed at a position corresponding to the resistive heating element disposed on the other side of the center position of the heating area, the second electrode portion is connected to each of the resistance heating elements of the first heating portion and the second heating portion via the conductor in order from the resistance heating element closest to the other side in the longitudinal direction to the one side in the longitudinal direction, A heating device, characterized in that all of the temperature detection means provided in the heating device are arranged asymmetrically on one side and the other side in the longitudinal direction with respect to a central position of the heat generation region.

2. 2. The heating device according to claim 1, The temperature detection means is a heating device arranged at a position corresponding to the endmost resistive heating element on the one side among the resistive heating elements of the first heating portion.

3. In the heating device according to claim 1 or 2, The temperature detection means is a heating device arranged at a position corresponding to the endmost resistive heating element on the other side among the resistive heating elements of the second heating portion.

4. The heating device according to claim 1 , wherein the first heat generating portion has a plurality of resistive heating elements electrically connected in parallel.

5. In the heating device according to any one of claims 1 to 4, The heating device further comprises a temperature detection means provided at a position corresponding to the centralmost resistance heating element in the longitudinal direction among the resistance heating elements.

6. The heating device according to any one of claims 1 to 5, wherein the conductor connecting the first heat generating portion or the second heat generating portion to the second electrode portion includes a portion in which the amount of current increases from one side to the other side in the longitudinal direction.

7. 7. The heating device according to claim 1, wherein the heater heats a rotatable endless belt member.

8. 8. The heating device according to claim 7, wherein said temperature detection means detects the temperature of said belt member.

9. 9. The heating device according to claim 8, wherein the temperature detection means is disposed opposite to and in non-contact with the belt member.

10. 10. The heating device according to claim 9, wherein the temperature detection means is a non-contact thermistor.

11. 10. The heating device according to claim 9, wherein said temperature sensing means is a thermopile.

12. The heating device according to claim 1 , wherein the temperature detection means is disposed opposite the heating body.

13. If a direction perpendicular to the longitudinal direction of the heating body and different from the thickness direction of the heating body is defined as a short direction, 13. The heating device according to claim 1, wherein a ratio of a short-side dimension of the resistance heating element to a short-side dimension of the heating element is 25% or more.

14. If a direction perpendicular to the longitudinal direction of the heating body and different from the thickness direction of the heating body is defined as a short direction, 13. The heating device according to claim 1, wherein a ratio of a short-side dimension of the resistance heating element to a short-side dimension of the heating element is 40% or more.

15. 15. The heating device according to claim 1, which is a fixing device for fixing an image on a recording medium.

16. An image forming apparatus comprising the heating device according to claim 1 .

17. The heating device according to claim 1 ; An image forming apparatus including a control unit for controlling power supply to the heating body, When the first heat generating portion is energized, the first temperature detecting means detects the temperature and the control unit controls the heating body; an image forming apparatus, wherein when the first heat generating portion and the second heat generating portion are energized, the second temperature detecting means detects the temperature and the control portion controls the heater;

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