JP2019023680A - Heater and fixing device - Google Patents

Abstract

To provide a fixing device that can change an area where a resistance heating layer generates heat according to a width size of a recording material, and can prevent an abnormal temperature rise of a heater.SOLUTION: A fixing device heats a fixing belt with a heater 600 in contact with an inner surface of the fixing belt. The heater 600 consists of a heating element (shaded portion in figure) and a conductive pattern formed on a substrate, and electrodes (641, 651, 661, 671). A control circuit 100 acquires width size information on a recording material, controls on/off of switches 643, 653, 663, 673 according to the width size information, and disconnects part of electrical connection of a conductive path, and thereby controls such that a heating area of the heating element becomes a heating area suitable for fixing the recording material. A plurality of thermistors (TH) 630 being temperature detection means are provided on the back face of the heater 600.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a heater used for heating a toner image on a recording material, and a fixing device including the heater. The heater and the fixing device of the present invention are used in an image forming apparatus such as a copying machine, a printer, a fax machine, and a multifunction machine having a plurality of these functions.

  2. Description of the Related Art Conventionally, in an image forming apparatus, a method of fixing a toner image on a recording material by forming a toner image on the recording material and then applying heat and pressure with a fixing device is generally used.

  On the other hand, in response to the recent demand for energy saving and quick start, a fixing device of a type in which a heater is brought into contact with the inner surface of a thin belt to heat the belt has been proposed (Patent Document 1).

  Further, Patent Document 1 discloses a configuration in which a region where the heater generates heat is changed according to the width size of the recording material. FIG. 13 is a circuit diagram of the fixing device described in Patent Document 1. In this fixing device, electrodes 1027 (1027a to 1027f) are arranged side by side in the longitudinal direction of the substrate 1021, and the resistance heating layer 1025 is heated by energizing the resistance heating layer 1025 (1025a to 1025e) from each electrode.

  In this fixing device, each electrode is connected to a wiring layer 1029 (1029a, 1029b) formed on the substrate. Specifically, the wiring layer 1029b connected to the electrode 1027b and the electrode 1027d extends to one end in the longitudinal direction of the substrate. The wiring layer 1029a connected to the electrode 1027c and the electrode 1027e extends to the other end in the longitudinal direction of the substrate. Furthermore, the electrode 1027a and the wiring layer 1029b can be connected to the wiring member at one end in the longitudinal direction of the substrate, and the electrode 1027f and the wiring layer 1029a can be connected to the wiring member at the other end in the longitudinal direction of the substrate. It has become.

  An insulating layer for protecting each wiring is not provided at both ends in the longitudinal direction of the substrate, and the wiring layers 1029a and 1029b and the electrodes 1027a and 1027f are exposed. Therefore, the resistance heating layer 1025 is connected to the power supply circuit by the wiring member coming into contact with the exposed portions of the wiring layers 1029a and 1029b and the electrodes 1027a and 1027f. The power supply circuit includes an AC power supply and switches 1033 (1033a, 1033b, 1033c, 1033d), and the connection pattern of each wiring can be changed by turning on and off the switch 1033.

  That is, the wiring layers 1029a and 1029b are connected to either the power supply terminal 1031a side or the power supply terminal 1031b side according to the connection pattern in the power supply circuit, and the heat generation area of the resistance heat generation layer 1025 is changed according to the sheet width size. ing.

JP 2012-37613 A

  By the way, Patent Document 1 does not describe where the thermistor serving as the temperature detecting means is arranged in the longitudinal direction, but there is one thermistor in the longitudinal direction of the heater.

  However, in the heater in which the longitudinal heat generation distribution can be changed independently, if the number of thermistors arranged in the heater is one, the temperature of each heating element cannot be detected. Even when a plurality of thermistors are arranged in the longitudinal direction, if the thermistor fails, the probability is sufficiently low, but when the heater is heated abnormally, the life of the fixing belt at that location is shortened. There is a possibility that.

  SUMMARY OF THE INVENTION The present invention provides a fixing device capable of preventing an abnormal temperature rise of a heater in a heater capable of changing a region where a resistance heating layer generates heat according to the width size of a recording material.

A rotatable endless belt heated by a heating element, and a fixing nip portion that sandwiches and conveys and heats a sheet-like recording material on which an unfixed toner image is formed by pressing and elastically deforming the endless belt are formed. A nip forming member;
A connector connected to the terminal of the power supply;
A board extending along the longitudinal direction to which the connector is attached so as to sandwich the front and back thereof; and
A plurality of electrodes provided on a substrate with which the connector contacts;
A conductor path provided in the longitudinal direction of the substrate from the electrode;
A plurality of branch paths connecting the conductor path and the heating element;
A plurality of heating elements provided to electrically connect a plurality of adjacent branch paths;
In the fixing device composed of a heater unit having a heating element temperature detecting means for detecting the temperature of the heating element, the heating element to be lit is changed according to the width of the recording material to be passed,
A plurality of the heating element temperature detecting means are arranged so as to overlap in a recording material conveyance direction perpendicular to the width direction of the recording material.

  According to the present invention, there is provided a fixing device capable of preventing an abnormal temperature rise of a heater in a heater capable of changing a region in which a resistance heating layer generates heat according to the width size of a recording material.

1 is a diagram illustrating an image forming apparatus according to Embodiment 1. FIG. FIG. 3 is a cross-sectional view illustrating the fixing device according to the first exemplary embodiment. FIG. 3 is a front view illustrating the fixing device according to the first exemplary embodiment. FIG. 3 is a heater circuit diagram according to the first embodiment. The figure explaining the heat_generation | fever method and switching method of the heater 600. FIG. FIG. 3 is a diagram illustrating a configuration of a heater according to the first embodiment. FIG. 6 is a diagram for explaining a temperature rise in a non-sheet passing portion of the fixing device in Embodiment 1. The heater circuit diagram of Example 2. FIG.

  Embodiments according to the present invention will be described below. In the following embodiments, a laser beam printer using an electrophotographic process will be described as an example.

[Example 1]
[Image forming apparatus]
FIG. 1 is a cross-sectional view of a printer 1 which is an image forming apparatus of this embodiment. The printer 1 is an image forming apparatus in which the toner image formed on the photosensitive drum 11 in the image forming unit 10 is transferred to the recording material P and then the image is fixed on the recording material P by the fixing device 40.

  As shown in FIG. 1, the printer 1 includes an image forming unit (image forming station) 10 that forms toner images of each color of Y (yellow), M (magenta), C (cyan), and Bk (black). Yes. The image forming unit 10 includes four photosensitive drums 11 (11Y, 11M, 11C, and 11Bk) corresponding to the colors Y, M, C, and Bk in order from the left side of FIG. Around each photosensitive drum 11, a charger 12, an exposure device 13, a developing device 14, a primary transfer blade 17, and a cleaner 15 are arranged.

  Hereinafter, a procedure for forming a Bk color toner image will be described, but a procedure for forming other color toner images is also the same. A photosensitive drum 11 as an electrophotographic photosensitive member is rotationally driven in the direction of an arrow by a driving source (not shown). Around the photosensitive drum 11, a charger 12, an exposure device 13, a developing device 14, a primary transfer blade 17, and a cleaner 15 are sequentially arranged along the rotation direction.

  Next, a procedure until a toner image is formed on the recording material P will be described. After the surface of the photosensitive drum 11 is uniformly charged by the charger 12, it is exposed according to the image information by the exposure device 13, thereby forming an electrostatic latent image. Then, the toner is developed in the portion exposed to the laser beam by the developing device 14, and a toner image is formed on the photosensitive drum 11. At this time, the same process is performed for the other colors.

  The toner image on each photosensitive drum 11 is primarily transferred to the intermediate transfer belt 31 by the primary transfer blade 17, and the toner remaining on the photosensitive drum 11 is removed by the cleaner 15. Thus, the photosensitive drum 11 is ready for the next image formation.

  On the other hand, the recording material P placed on the feeding cassette 20 or the multi-feed tray 25 is fed one by one by a feeding mechanism (not shown) and fed to the registration roller pair 23. The registration roller pair 23 temporarily stops the recording material P, and when the recording material P is skewed with respect to the transport direction, the direction is straightened and synchronized with the toner image on the intermediate transfer belt 31. The recording material P is fed between the intermediate transfer belt 31 and the secondary transfer roller 35. The secondary transfer roller 35 transfers the toner image on the intermediate transfer belt 31 to the recording material P.

  The recording material P to which the toner image has been transferred is conveyed to the fixing device 40, and a toner image permanently fixed on the recording material P is formed by heating and pressing.

[Fixing device]
Next, the fixing device 40 will be described. 2 is a cross-sectional view of the fixing device 40, and FIG. 3 is a diagram illustrating a front view of the fixing device 40. The belt unit 60 that heats the image on the recording material P is configured to heat a flexible thin fixing belt 603 by a heater 600 that contacts the inner surface.

  As shown in FIG. 2, the fixing belt 603 has a nip portion N formed by the pressure of the heater 600 and the pressure roller 70, and sandwiches and conveys the recording material P fed to the nip portion N. At this time, the heat generated by the heater 600 is applied to the recording material P via the fixing belt 603, and the toner image T on the recording material P is fixed to the recording material P.

  The belt unit 60 is a unit for heating and pressing an image on the recording material P, and is provided in parallel with the pressure roller. The belt unit 60 includes a heater 600, a heater holder 601, a support stay 602, and a fixing belt 603.

  The heater 600 presses the fixing belt 603 toward the pressure roller 70 so that the nip portion N has a desired width. The heater 600 includes a substrate 610 and a resistance heating element 620 (hereinafter referred to as a heating element 620) on the substrate 610, and is fixed to a recess on the lower surface of the heater holder 601. In this embodiment, the heating element 620 is provided on the back side of the substrate 610 (the side not in contact with the fixing belt 603). However, the present invention is not limited to this, and the front side (the side in contact with the fixing belt 603). ) May be provided.

  A polyimide layer having a thickness of about 10 μm is provided as a sliding layer on the surface side of the substrate 610, and by reducing the frictional resistance between the fixing belt 603 and the heater 600, wear on the inner surface of the fixing belt 603 is suppressed. It can be done. Further, a lubricant such as grease may be applied to the inner surface of the fixing belt 603 in order to reduce the rubbing resistance.

  The fixing belt 603 is a cylindrical belt for heating and pressurizing the toner image on the recording material at the nip portion N. In this embodiment, a substrate provided with an elastic layer 603b and a release layer 603c on a base material 603a is used.

  Specifically, a cylindrical member made of a nickel alloy having an outer diameter of 30 mm, a length of 340 mm, and a thickness of 30 μm is used as the base material 603a. Furthermore, a silicone rubber layer having a thickness of 400 μm is formed as an elastic layer 603b on the base material 603a, and a fluororesin tube having a thickness of about 20 μm is coated as a release layer 603c on the elastic layer 603b.

  A heater holder 601 (hereinafter referred to as a holder 601) is a member that holds the heater 600 in a state of being pressed toward the fixing belt 603. Further, the holder 601 has a semicircular cross-sectional shape and has a function of regulating the rotation trajectory of the fixing belt 603. The holder 601 is made of highly heat-resistant resin or the like, and in this embodiment, Zenite 7755 (trade name) manufactured by DuPont is used.

  The support stay 602 is a member that supports the heater 600 via the holder 601. The support stay 602 is desirably made of a material that is not easily bent even when a large load is applied. In this embodiment, SUS304 (stainless steel) is used.

  As shown in FIG. 3, the support stay 602 is supported by the flanges 411a and 411b at both ends in the longitudinal direction. The flanges 411a and 411b are collectively referred to as a flange 411. The flange 411 regulates the movement of the fixing belt 603 in the longitudinal direction and the shape in the circumferential direction. A heat-resistant resin or the like is used for the flange 411, and PPS (polyphenylene sulfide) is used in this embodiment. A pressure spring 415 is provided between the flange 411 and the pressure arm 414 in a contracted state.

  With the above configuration, the elastic force of the pressure spring 415 is transmitted to the heater 600 via the flange 411 and the support stay 602. The fixing belt 603 is pressed against the pressure roller 70 with a predetermined pressing force, and a nip portion N having a predetermined width is formed. In this embodiment, the applied pressure is about 156.8 N on one end side and the total applied pressure is about 313.6 N (32 kgf).

  The connectors 700a and 700b are power supply members that are electrically connected to the heater 600 in order to apply a voltage to the heater 600, and are detachably attached to both ends of the heater 600 in the longitudinal direction.

  As shown in FIG. 2, the pressure roller 70 is a member that forms the nip portion N by being pressed by the fixing belt 603. The pressure roller 70 has a multilayer structure in which an elastic layer 72 is provided on a metal core 71 and a release layer 73 is provided on the elastic layer 72.

  As the metal core 71, stainless steel, SUM (sulfur and sulfur composite free-cutting steel), or aluminum can be used. As the elastic layer 72, silicone rubber, sponge rubber layer, or elastic foam rubber can be used. As the release layer 73, a fluororesin material can be used.

  The pressure roller 70 of this embodiment comprises a stainless steel core 71, an elastic layer 72 of foamed silicone rubber, and a release layer 73 of a fluororesin tube. The outer diameter is about 25 mm, and the longitudinal length of the elastic layer is 330 mm.

  As shown in FIG. 3, the cored bar 71 of the pressure roller 70 is rotatably held via the side plate 41 and the bearings 42a and 42b, and a gear G is provided at one end of the cored bar 71, and the motor M driving force is transmitted to the cored bar 71. As shown in FIG. 2, the pressure roller 70 driven by the motor M is driven to rotate in the direction of the arrow, and the driving force is transmitted to the fixing belt 603 at the nip portion N to be driven to rotate. In this embodiment, the motor M is controlled by the control circuit 100 so that the surface speed of the pressure roller 70 is 200 mm / sec.

  Thermistors (TH) 630a to 630k as temperature detecting means shown in FIG. 4 are temperature sensors that are provided on the back side of the heater 600 and detect the temperature of the heater 600. The thermistor 630 is connected to the control circuit 100 via an A / D converter (not shown), and transmits an output corresponding to the detected temperature to the control circuit 100.

  The control circuit 100 is a circuit that includes a CPU that performs calculations associated with various controls and a nonvolatile medium such as a ROM. A program is stored in the ROM, and various controls are executed by the CPU reading and executing the program. The control circuit 100 is electrically connected to the power source 110 so as to control energization of the power source 110.

  Further, the control circuit 100 reflects the temperature information acquired from the thermistor 630 in the energization control of the power supply 110. That is, the control circuit 100 controls the power supplied to the heater 600 based on the output of the thermistor 630. In this embodiment, a method of adjusting the amount of heat generated by the heater 600 by performing wave number control or phase control on the output of the power supply 110 is used. When the toner on the recording material is fixed, the heater 600 has a predetermined value. Maintained at temperature.

  The thermistors 630a to 630j are about 2 [mm] in length and width. The thermistor 630k is a thermistor for adjusting the temperature of the heater at the center, and has a higher detection resolution than the thermistors 630a to 630j. The location of the thermistor will be described in detail later.

  The image forming apparatus of the present embodiment can produce 30 A4 landscape paper per minute.

[heater]
Next, the configuration of the heater 600 will be described in detail. FIG. 5 is a diagram for explaining a heater heating method and a heating region switching method, and FIG. 6 is a configuration diagram of the heater used in this embodiment.

  As shown in FIG. 5A, in the heater 600 of this embodiment, a branch path 715a, a branch path 715b, and a branch path 715c are connected to the first conductor path 710. On the other hand, a branch path 725d, a branch path 725e, and a branch path 725f are connected to the second conductor path 720.

  The branch paths 715a, 715b, 715c connected to the first conductor path 710 and the branch paths 725d, 725e, 725f connected to the second conductor path 720 are alternately arranged in the longitudinal direction, and resistance heat is generated between the branch paths. A body is provided for electrical connection. When the voltage V is applied between the first conductor path 710 and the second conductor path 720, a potential difference is generated between the adjacent branch paths, and the resistance heating element generates heat due to the generation of the current indicated by the arrows in the drawing.

  Further, as shown in FIG. 5B, when the switch SW is provided between the branch path 725e and the branch path 725f and the switch is turned off, the branch path 715b and the branch path 715c have the same potential. The heating element 620 between 715c does not generate heat.

  That is, in the heater of the present embodiment, only a part of the heating element can generate heat by disconnecting a part of the electrical connection of the conductor path. In the case where a plurality of heating elements arranged in the longitudinal direction are energized to generate heat, a configuration in which the branch paths are arranged so that the current directions of adjacent heating elements are staggered as in the present invention is preferable.

  As another arrangement of the heat generating element and the second branch path, there is a configuration in which branch paths having different polarities are connected to both ends of the heat generating element so that the direction of current is the same in the longitudinal direction. However, since two branch paths are required between adjacent heating elements, a short circuit may occur between the branch paths. In addition, since the width of the branch path between the heat generating elements becomes wider, the non-heat generating portion becomes larger, and temperature unevenness occurs in the heater 600 and the fixing belt 603 in the longitudinal direction. Therefore, the structure which arrange | positions a heat generating body and a branch path so that it may serve as the branch path between adjacent heat generating bodies like this invention is desirable.

  Next, the heater 600 of this embodiment will be described in detail with reference to FIG. The heater 600 includes a substrate 610, a heating element 620 formed on the substrate 610, conductor patterns (640, 650, 660, 670, 642, 652, 662, 672), electrodes (641, 651, 661, 671), and the like. The heating element 620 and the insulating coating layer (not shown) covering the conductor pattern. The insulating coat layer preferably has a thermal conductivity in the range of 0.55 to 0.75 [W / m * K].

  The substrate 610 is a member that determines the size and shape of the heater 600, and a ceramic material such as alumina or aluminum nitride having excellent heat resistance, thermal conductivity, and electrical insulation is used as the material. In this embodiment, alumina having a length in the longitudinal direction of 400 mm, a length in the short direction of 8.0 mm, and a thickness of about 1 mm is used. The thermal conductivity of the heater is 20 [W / m * K]. The heat conductivity of the heater is preferably in the range of 20 to 32 [W / m * K].

  A heating element 620 and a conductor pattern are formed on the substrate 610 by screen printing. In the present embodiment, a silver paste that is a low resistivity material or an alloy paste in which a small amount of palladium is mixed with silver is used as the conductor pattern. The heating element 620 is made of a silver-palladium alloy paste so as to have a desired resistance value.

  Further, the heating element 620 and the conductor pattern are covered with an insulating coating layer (not shown) made of heat-resistant glass, and are electrically protected so as not to cause a leak or a short circuit. Electrodes 641, 651, 661, and 671 that are electrically connected to the power source 110 are provided on the longitudinal ends of the substrate 610. Further, the substrate 610 is provided with a heating element 620 and branch paths (642, 652, 662, 672). The branch paths are the common conductor path 640, the first counter conductor path 650, the second counter conductor path 660a, the third counter conductor path 660b, the fourth counter conductor path 670a, and the fifth counter conductor path 670b. It is a conductor path that is electrically connected.

  The heating element 620 (620a to 620r) is formed on the substrate 610 as one heating element. The heating element 620 of this example has a width (length in the short direction) of about 1.5 to 3.5 mm, a thickness of about 20 μm, a length in the longitudinal direction of about 320 mm, and an A4 size (width size). 297 mm) has a length that can heat the entire area of the recording material P. The total resistance of the heating element 620 is about 10Ω.

  On the heating element 620, six common branch paths 642a to 642j are stacked at equal intervals in the longitudinal direction, so that the heating element 620 is divided into nine sections by the common branch paths 642a to 642j. Note that the length of each section of the heating element 620 is about 17.8 mm. Furthermore, branch paths 642, 652, 662, and 672 are stacked in each section of the heating element 620, and the heating element 620 is divided into 18 sections 620a to 620r.

  The branch paths 642, 652, 662, 672 are provided so as to be orthogonal to the heating element 620. The resistance value of the common branch path 642 and the opposing branch paths 652, 662, and 672 is significantly smaller than the resistance value of the heating element. For this reason, the branch path hardly generates heat. Therefore, when the width of the branch path (length in the longitudinal direction) increases, unevenness in the amount of heat generated in the heating element 620 occurs.

  As a result, a temperature drop occurs in the branch path, and the gloss of the image on the recording material becomes non-uniform. This phenomenon is attributed to the fact that the toner on the recording material cannot be heated and melted sufficiently because the temperature of the fixing belt 603 at the portion facing the branch path is low, resulting in low gloss. The common branch path 642 is electrically connected to the terminal 110a on one side of the power source 110 via the first conductor path 640 and the like.

  The opposing branch paths 652, 662, and 672 are electrically connected to the terminal 110b on the other side of the power supply 110 via the opposing conductor paths 650, 660, and 670. That is, the common branch path and the opposite branch path are alternately arranged in the longitudinal direction of the heating element 620. The common conductor path 640 is formed along the longitudinal direction of the substrate 610 and is connected to each common branch path 642, and one end is connected to the common electrode 641.

  Similarly, the first counter conductor path 650, the second counter conductor path 660a, the third counter conductor path 660b, the fourth counter conductor path 670a, and the fifth counter conductor path 670b are formed along the longitudinal direction of the substrate 610. . The first opposing conductor path 650 is connected to the opposing branch path 652 (652a to 652c), and one end is connected to the electrode 651. The second and third opposing conductor paths 660a and 660b are connected to the opposing branch paths 662a to 662d, respectively, and one end is connected to the electrode 661. The fourth and fifth opposing conductor paths 670a and 670b are connected to the opposing branch paths 672a and 672b, respectively, and one end is connected to the electrode 671.

  The electrode 641 is juxtaposed on one end side in the longitudinal direction of the substrate, while the electrodes 651, 661, 671 are juxtaposed on the other end side in the longitudinal direction of the substrate and insulated to ensure electrical connection with the connector 700. The coating layer is not provided, and is provided outside the region in contact with the fixing belt 603 in an exposed state.

  As described above, in the heater 600 of this embodiment, the power source 110 and the heating element 620 are electrically connected via the connector, the electrode, the common conductor path, the opposing conductor path, and the branch path.

[Power supply to the heater]
Next, a method for supplying power to the heater 600 will be described with reference to FIG. First, the power source 110 is a circuit that supplies power to the heater 600. In this embodiment, a commercial power supply having an effective value of single-phase alternating current of about 100 V is used, and a power supply terminal 110a and a power supply terminal 110b are provided. Note that the power source 110 may be a DC power source as long as it has a function of supplying power to the heater 600.

  The control circuit 100 is electrically connected to each switch for controlling the switch 643, the switch 653, the switch 663, and the switch 673. The switch 643 is a switch (relay) provided between the power supply terminal 110 a and the electrode 641, and switches whether the power supply terminal 110 a and the electrode 641 are connected (ON, OFF) according to an instruction from the control circuit 100. Do. The switch 653 is a switch provided between the power supply terminal 110 b and the electrode 651, and switches whether to connect the power supply terminal 110 b and the electrode 651 in accordance with an instruction from the control circuit 100.

  Similarly, the switch 663 is a switch provided between the power supply terminal 110b and the electrode 661, and switches whether to connect the power supply terminal 110b and the electrode 661 in accordance with an instruction from the control circuit 100.

  Similarly, the switch 673 is a switch provided between the power supply terminal 110b and the electrode 671, and switches whether to connect the power supply terminal 110b and the electrode 671 in accordance with an instruction from the control circuit 100.

  As the job execution instruction is received, the control circuit 100 acquires the width size information of the recording material P, and controls on / off of the switches 643, 653, 663, 673 according to the width size information, and the heating element 620 The heat generation area is controlled to be a heat generation area suitable for fixing the recording material P.

  Next, a method for changing the heat generation area of the heat generating element 620 according to the size of the recording material P in the width direction will be described.

  First, when the recording material P is a large size such as A4 horizontal size (size in the width direction of 297 mm), the control circuit 100 controls the heating element 620 so that the heating width A generates heat. Specifically, the control circuit 100 turns on all of the switch 643, the switch 653, the switch 663, and the switch 673. In this case, the heater 600 is supplied with power from the electrodes 641, 651, 661, and 671, and the heating element In 620, all of the 18 small sections 620a to 620r generate heat. At this time, the heater 600 generates heat in all regions of the heating element of about 320 mm, so that the heater 600 is in a heat generation state suitable for fixing the recording material P of A4 horizontal size.

  Next, when the recording material P is a medium size such as A4 vertical size (size 210 mm in the width direction), the control circuit 100 controls the heat generating width B as the heat generating element 620 to generate heat. Specifically, since the control circuit 100 turns on the switch 643 and the switches 653 and 663 and turns off the switch 673, the heater 600 is supplied with power from the electrodes 641, 651 and 661, and the heating element 620 Of the 18 small sections, 14 sections from 620c to 620p generate heat. At this time, since the heater 600 generates heat in an area of about 249 mm, the heater 600 is in a heat generation state suitable for performing the fixing process of the recording material P of A4 vertical size. Therefore, even when the recording material fixing process such as A4 vertical size is performed, the heater 600 does not generate heat in a portion where the recording material does not pass, so that useless power is not used.

  Next, when the recording material P is a small size such as a postcard size (size 100 mm in the width direction), the control circuit 100 controls the heating element 620 so that the heating width C generates heat. Specifically, the control circuit 100 turns on the switch 643 and the switch 653 and turns off the switches 663 and 673, so that the heater 600 is supplied with power from the electrodes 641 and 651 and has 18 heating elements 620. Of these small sections, six sections from 620 g to 620 l generate heat. At this time, since the heater 600 generates heat in an area of about 107 mm, the heater 600 is in a heat generation state suitable for fixing the postcard-sized recording material P. Accordingly, even when a recording material having a small size in the width direction such as a postcard size is fixed, the heater 600 does not generate heat in a portion where the recording material does not pass, and thus wasteful power is not used.

  As shown in FIG. 4, the feature of the present embodiment is that temperature detection means (thermistors) are arranged on each heating element group, specifically, the heating elements at the extreme ends of the heating ranges A, B, and C. In addition, a plurality of thermistors are arranged in the conveyance direction of the recording material P. The temperature of the non-sheet passing portion region of each heating element group can be detected, the fixing belt can be prevented from becoming high temperature, and the life of the fixing belt can be prevented from being shortened. The cause of shortening the life of the fixing belt is that the adhesive between the base material of the fixing belt and the elastic layer is thermally deteriorated, and the elastic layer of the fixing belt is peeled off from the base material of the fixing belt.

  In this embodiment, the fixing belt surface temperature is controlled to be 230 [° C.] or less. Specifically, if the surface temperature of the fixing belt exceeds 230 [° C], the heater energization control is changed, or the productivity (the number of recording materials transported per unit time) is reduced and the non-sheet passing portion temperature is reduced. It is controlled not to exceed 230 [℃].

  Specifically, as shown in FIG. 7, when passing A4R (vertical) size paper, the heat of the heater is reduced in the non-sheet passing area, which is the difference between the paper edge and the heating end of the heater. It is easy to heat up without being robbed by paper.

  By arranging the temperature detecting means 630c and 630h at the locations as shown in FIG. 7, it is possible to detect an abnormal temperature rise of the heater and prevent the fixing belt from being shortened. Further, since the temperature detection unit 630c ′ is arranged so as to overlap with 630c in the width direction of the paper, and 630h is arranged so as to overlap with 630h, in the unlikely event that the temperature detection unit 630c fails, it is 630c ′, and 630h fails In such a case, control can be performed at 630 h ′, and the life of the fixing belt can be prevented from being shortened.

  According to the method in this embodiment, 630c and 630c ′ are arranged so as to overlap in the longitudinal direction of the paper, so that 630c and 630c ′ detect substantially the same temperature before and after the failure as compared with the case where they do not overlap. There are advantages you can do.

  For example. The failure of the temperature detection element 630C can be determined as a failure when the temperature difference between 630C ′ and 630h exceeds a predetermined temperature difference. Considering the case of passing through other paper widths, the temperature detection means is arranged as shown in FIG.

  The heater of the present embodiment has a configuration having only three regions of the heat generating region A, the heat generating region B, and the heat generating region C. However, the present invention is not limited to this configuration. Needless to say, this is applicable.

  As described above, the heater of this embodiment can change the heat generation region of the resistance heat generation layer according to the width size of the sheet, and can provide a fixing device that can prevent an abnormal temperature rise of the heater.

[Second Embodiment]
A fixing device according to a second embodiment of the present invention and an image forming apparatus including the same will be described. Since the configuration of the image forming apparatus is the same as that of the first embodiment, the description thereof will be omitted, and only the configuration of the fixing device will be described here. Also in the fixing device, the same parts as those in the first embodiment are omitted.

  In this embodiment, in addition to the first embodiment, a temperature detecting element is also added to the inner surface of the fixing belt 603 as shown in FIG. Actually, the heater unit 60 is built in the fixing belt 603. Specifically, in the arrangement of the temperature detection elements, 630 a ″ is added at a position corresponding to 630 a in the longitudinal direction of the recording material P. In addition, 630c ', 630e', 630k ', 630f', 630h ', and 630j' are added with the same idea.

  With such a configuration, when 630a, 630a ′ fails, it can be controlled by 630a ″, and the fixing belt can be prevented from shortening its life, so that it is more reliable than the first embodiment. Increase.

  In addition, when two heaters 630a and 630a ′ cannot be arranged due to a problem such as a narrow heater width, a method of arranging 630a ″ on the heater side and 630a ″ on the film side may be considered.

40 fixing device 60 heater unit 70 pressure roller 100 control circuit 110 power supply 110a, 110b power supply terminal 400 high heat conduction member 600 heater 603 fixing belt 610 substrate 620 resistance heating element 630 temperature detection means (thermistor)
640 Common conductor path 650, 660, 670 Counter conductor path 641, 651, 661, 671 Electrode 642 Common branch path 652, 662, 672 Counter branch path 700 Connector

Claims (4)

A rotatable endless belt heated by a heating element, and a fixing nip portion that sandwiches and conveys and heats a sheet-like recording material on which an unfixed toner image is formed by pressing and elastically deforming the endless belt are formed. A nip forming member;

A connector connected to the terminal of the power supply;
A board extending along the longitudinal direction to which the connector is attached so as to sandwich the front and back thereof; and
A plurality of electrodes provided on a substrate with which the connector contacts;
A conductor path provided in the longitudinal direction of the substrate from the electrode;
A plurality of branch paths connecting the conductor path and the heating element;
A plurality of heating elements provided to electrically connect a plurality of adjacent branch paths;
The heating element to be turned on is changed according to the width of the recording material to be passed in the fixing device comprising a heater unit having a heating element temperature detecting means for detecting the temperature of the heating element,
A plurality of the heating element temperature detecting means are arranged so as to overlap in a recording material conveyance direction perpendicular to the width direction of the recording material.   2. The fixing device according to claim 1, wherein a plurality of the temperature detection units are arranged so that the temperatures of the plurality of heating elements can be detected. When heating the maximum width sheet that can be used in the apparatus, power is supplied to all of the plurality of electrodes,
3. The fixing device according to claim 1, wherein when a sheet having a width narrower than the maximum width sheet is heated, power is supplied to only some of the plurality of electrodes.   The belt inner surface temperature detecting means for detecting the temperature of the inner surface of the endless belt is disposed so as to overlap with the heating element temperature detecting means in a recording material transport direction perpendicular to the width direction of the recording material. The fixing device according to any one of 1 to 3.