JP2019012173A - Heater and fixation device - Google Patents

Abstract

To provide a heater which can alter a region to be heated by a resistance heating layer according to width size of a recording material, and whose heating value is uniform in a longitudinal direction.SOLUTION: The heater comprises: a single connector connected to one terminal and the other terminal of a power source; a substrate 610 which extends along a longitudinal direction, and to which the connector is attached so that front and rear sides of the substrate are sandwiched; plural electrodes 645, 655 and 665 disposed on the substrate abutted on by the connector; conductor paths 650, 660a and 660b arranged along the longitudinal direction of the substrate from the electrodes; plural branching paths connecting the conductor paths with heating elements 620; and the plural heating elements arranged so that the plural neighboring branching paths are electrically connected. In the continuously neighboring heating elements connected to the same electrode, a relation of heating element resistances satisfies R1>R2, when R1 denotes resistance of the heating elements on an electrode side, and R2 denotes resistance of the heating elements on a non-electrode side.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. 15 is a circuit diagram of the fixing device described in Patent Document 1. In FIG. 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, in patent document 1, although the characteristic of a material used for a wiring layer and an electrode, resistance value, etc. are not indicated, silver which is a material with low resistivity as a wiring layer generally used with a heater of the same composition, Alternatively, a mixture of silver and palladium is used. Since the heater used in the fixing device is required to reduce the size of the heater due to the demand for downsizing of the fixing device, the width of the wiring layer is required to be less than 1 mm.

  Further, in the heater used in a general fixing device, the length of the wiring layer in the longitudinal direction is about 350 mm. Therefore, even when the wiring layer is made of a material having a low resistivity as described above, for example, the voltage applied to the electrode 1027c is applied to the electrode 1027e due to the resistance of the wiring layer 1029a between the electrodes 1027c and 1027e. It becomes lower than the voltage. In addition, the voltage applied to the electrode 1027e is lower than the voltage applied to the electrode 1027f due to the resistance of the wiring layer 1029a between the right end of the substrate 1021 and the electrode 1027e.

  This phenomenon also occurs in the wiring layer 1029b. The voltage applied to the electrode 1027d is lower than the voltage applied to 1027b, and the voltage applied to the electrode 1027b is lower than the voltage applied to 1027a. Therefore, for example, the heat generation amount per unit length in the longitudinal direction of the resistance heating element 1025c between the electrode 1027c and the electrode 1027d is smaller than the heat generation amount of the resistance heating element 1025e between the electrode 1027e and the electrode 1027f. For this reason, unevenness occurs in the temperature in the longitudinal direction of the belt heated by the heater (dotted line in FIG. 7), and the gloss of the image on the recording material after the fixing process becomes non-uniform.

  SUMMARY OF THE INVENTION Accordingly, the present invention provides a heater capable of changing a region where the resistance heating layer generates heat according to the width size of the recording material and capable of making the temperature distribution in the longitudinal direction uniform. .

A single connector (700) connected to one terminal of the power supply (110) and the other terminal;
A board (610) extending along the longitudinal direction to which the connector (700) is attached so as to sandwich the front and back thereof; and
A plurality of electrodes (641, 651, 661 (661a, 661b)) provided on a substrate (610) with which the connector (700) contacts;
A conductor path (640, 650, 660) provided from the electrode toward the longitudinal direction of the substrate (610);
A plurality of branch paths (642, 652, 662) connecting the conductor paths (640, 650, 660) and the heating element (620);
A plurality of heating elements 620 (620a to 620l) provided to electrically connect a plurality of adjacent branch paths,
In the adjacent heating elements connected to the same electrode, when the resistance of the heating element on the electrode side is R1 and the resistance of the heating element on the non-electrode side is R2, the relationship of the heating element resistance is R1> R2. A heater characterized by being.

According to the present invention, it is possible to provide a heater capable of changing the region where the resistance heating layer generates heat according to the width size of the recording material and capable of making the temperature distribution in the longitudinal direction uniform. it can.

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 diagram illustrating a heater according to the first embodiment. 1 is a diagram illustrating a fixing device according to a first exemplary embodiment. The figure explaining the resistance value of the heat generating body of the heater of Example 1 and 2. FIG. FIG. 4 is a view for explaining a temperature distribution of the fixing belt according to the first and second embodiments. The figure explaining the heater of a prior art example. FIG. 6 is a diagram illustrating a heater according to a second embodiment. Explanatory drawing of heater heating method and heating area switching method

  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. FIG. 2 is a cross-sectional view of the fixing device 40, FIG. 3 is a front view of the fixing device 40, and FIG.

  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. Therefore, the fixing belt 603 can be efficiently heated and the start-up performance is excellent. 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 603d on the surface side of the substrate 610. 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. You can do it. 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 that heats 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 connector 700 is a power supply member that is electrically connected to the heater 600 in order to apply a voltage to the heater 600, and is detachably attached to one end side in the longitudinal direction of the heater 600.

  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 length of the elastic layer is 330 mm. It is.

  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.

  The thermistor 630 shown in FIG. 5 is a temperature sensor that is provided on the back side of the heater 600 and detects 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 heat generation amount of the heater 600 by performing wave number control on the output of the power supply 110 is used. When fixing the toner on the recording material, the heater 600 is maintained at a predetermined temperature. Is done.

[heater]
Next, the configuration of the heater 600 will be described in detail. FIG. 4 is a configuration diagram of a heater used in this embodiment, and FIG. 10 is a diagram for explaining a heater heating method and a heating region switching method.

  As shown in FIG. 10A, in the heater 600 of this embodiment, the first conductor path 710 is connected to the branch path a715a, the branch path b715b, and the branch path c715c. On the other hand, a branch path d725d, a branch path e725e, and a branch path c725c 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. 10B, when the switch SW is provided between the branch path e725e and the branch path f725f and the switch is turned off, the branch path b715b and the branch path c715c have the same potential, so the branch path b715b and the branch path The heating element 620 between c715c 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 an arrangement of the other heating element and the second branch path, there is a configuration in which branch paths having different polarities are connected to both ends of the heating element so that the direction of the 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, a conductor pattern (640, 650, 660, 642, 652, 662), an electrode (641, 651, 661), a heating element 620, and a conductor. It consists of an insulating coat layer (not shown) that covers the pattern.

  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.

  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. On one end side in the longitudinal direction of the substrate 610, electrodes 641, 651, and 661 that are electrically connected to the power supply 110 are provided.

  Further, the substrate 610 is provided with a heating element 620 and branch paths (642, 652, 662). The branch path is a conductor path that electrically connects the common conductor path 640, the first counter conductor path 650, the second counter conductor path 660a, the third counter conductor path 660b, and the heating element 620.

  The heating element 620 (620a to 620l) 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 2.0 mm (details will be described later), a thickness of about 20 μm, and a length in the longitudinal direction of about 320 mm. 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.

  A heating element in a conventional configuration will be described. On the heating element 620, seven common branch paths 642a to 642g are stacked at equal intervals in the longitudinal direction, so that the heating element 620 is divided into six sections by the common branch paths 642a to 642g. Note that the length of each section of the heating element 620 is about 53.3 mm. Furthermore, six opposing branch paths 662 and 652 are stacked at the center of each section of the heating element 620, and the heating element 620 is divided into 12 sections 620a to 620l. The length of each section is about 26.7 mm.

  In addition, the configuration of the heating element in the present embodiment will be described. On the heating element 620, ten common branch paths 642a to 642l are stacked with a narrower interval in the longitudinal direction, so that the heating element 620 is divided into ten sections by the common branch paths 642a to 642j. . The length of each section of the heating element 620 is about 53.3 mm in the section divided by the common branch paths 642b to 642i connected to the common electrode 655, and the section closest to the electrode 655 is an electrode in the longitudinal direction. The adjacent sections in the direction away from 655 are 38.3 mm, and the section length is shortened by 15 mm in order. Further, nine opposing branch paths 662 and 652 are stacked at the center of each section of the heating element 620, and the heating element 620 is divided into 18 sections 620a to 620r.

  The resistance values of the common branch path 642 and the opposing branch paths 652 and 662 are significantly smaller than the resistance value of the heating element, but have a constant resistance value. For this reason, when the length of the branch path to the heating element (length in the longitudinal direction) increases, the combined resistance value correspondingly increases. For example, in the combined resistance of the heating element 620 and the branch path 652 and the combined resistance of the heating element 620 and the branch path 662, the combined resistance value of the heating element 620 and the branch path 662 is larger. Therefore, unevenness in the amount of heat generation occurs in the longitudinal direction of the heating element, which causes surface temperature unevenness in the longitudinal direction of the heater 600 and the fixing belt 603. As a result, when uneven temperature occurs in the fixing belt 603, the gloss of the image on the recording material becomes non-uniform.

  The common branch path 642 (642a to 642g) is provided so as to be orthogonal to the heating element 620, and is further provided at an odd number from one end in the longitudinal direction of the heating element 620. 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 and 662 are provided so as to be orthogonal to the heating element 620, and are provided evenly from one end in the longitudinal direction of the heating element 620. The opposing branch paths 652 and 662 are electrically connected to the terminal 110b on the other side of the power supply 110 via the opposing conductor paths 650 and 660 and the like.

  That is, the common branch path and the opposite branch path are alternately arranged in the longitudinal direction of the heating element 620. In the present embodiment, the odd-numbered common branch path and the even-numbered counter branch path from one end in the longitudinal direction of the heating element 620 are used, but the present invention is not limited to this configuration. It goes without saying that the same effect can be obtained by using even-numbered common branches and odd-numbered counter branches from one end 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, and the third counter conductor path 660b are also formed along the longitudinal direction of the substrate 610. The first counter conductor path 650 is connected to the counter branch path 652 (652b to 652e), and one end thereof is connected to the electrode 651. The second and third opposing conductor paths 660a and 660b are connected to the opposing branch paths 662a and 662b, respectively, and one ends thereof are connected to the electrodes 661a and 661b, respectively.

  The electrodes 641, 651, 661 are juxtaposed on one end side in the longitudinal direction of the substrate, and are not provided with an insulating coat layer to ensure electrical connection with a connector (not shown), and are exposed to the fixing belt 603. It is provided outside.

  As described above, in the heater 600 of this embodiment, the power source 100 and the heating element 620 are electrically connected via the connector, electrode, common conductor path, opposing conductor path, and 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 the respective switches for controlling the switch A649, the switch B659, and the switch C669. The switch A649 is a switch (relay) provided between the power supply terminal 110a and the electrode 641, and switches whether the power supply terminal 110a and the electrode 641 are connected (ON / OFF) according to an instruction from the control circuit 100. Do. A switch B659 is a switch provided between the power supply terminal 110b and the electrode 651, and switches whether to connect the power supply terminal 110b and the electrode 651 in accordance with an instruction from the control circuit 100. Similarly, the switch 669 is a switch provided between the power supply terminal 110b and the electrodes 661a and 661b, and switches whether to connect the power supply terminal 110b and the electrodes 661a and 661b according to an instruction from the control circuit 100. I do.

  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 switch A649, the switch B659, and the switch C669 according to the width size information. 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 297 mm), the control circuit 100 controls the heat generating body 620 so that the heat generating width B generates heat. Specifically, the control circuit 100 turns on all of the switch A649, the switch B659, and the switch C669. In this case, the heater 600 is supplied with power from the electrodes 641, 651, 661a, and 661b, and the heating element 620 has 12 All of the small sections 620a to 620l 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 small size such as A4 vertical size (size 210 mm in the width direction), the control circuit 100 controls the heat generating width 620 so as to generate heat. Specifically, since the control circuit 100 turns on the switch A649 and the switch B659 and turns off the switch C669, the heater 600 is supplied with power from the electrodes 641 and 651, and the heating element 620 includes twelve small elements. Of the sections, eight sections from 620c to 620j generate heat. At this time, since the heater 600 generates heat in an area of about 213 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. Accordingly, even when the recording material having a small size in the width direction such as A4 vertical size is subjected to the fixing process, 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, the configuration of the heater 600 for equalizing the heat generation amount in the small sections 620a to 620l of the heating element 620, which is a characteristic part of the present embodiment, will be described.

In the heater 600 of this embodiment, a silver paste material, which is a material having a low low resistivity, is used as the common conductor path 640 and the opposing conductor paths 650 and 660. The conductor path has a length in the longitudinal direction of 320 mm. Since it is long and the width is as narrow as 0.4 mm, it has a certain resistance value.
The resistance value R1 of the conductor path from each electrode to the branch path is calculated from the following equation. The width of the conductor path is W1 (short direction of the substrate 610), the height is H1, the resistivity is ρ1, and the distance from the electrode to the branch path is L1.

R1 = ρ1 × L1 / (W1 × H1) Formula (1)
That is, it can be seen that the resistance value R1 of the conductor path increases in proportion to the distance from the electrode to the first branch path.

  Next, the resistance value R2 of the branch path from the contact point between the common conductor path 640, the opposing conductor paths 650 and 660 and each branch path to the other end of the branch path is calculated from the following equation. The width of the branch path (longitudinal direction of the substrate 610) is W2, the height is H2, the resistivity is ρ2, and the length of the branch path is L2.

R2 = ρ2 × L2 / (W2 × H2) Formula (2)
Accordingly, the total resistance R, which is the resistance from the electrode to the end of the branch path, is calculated from the following equation.

R = R1 + R2
R = ρ1 × L1 / (W1 × H1) + ρ2 × L2 / (W2 × H2) Equation (3)
Therefore, when the resistance values of all the common branch paths are the same, the total resistance R increases as the resistance value of the common conductor path 640 increases as the distance from the electrode 641 increases. Therefore, the voltage applied to the heating element Decreases. This phenomenon also occurs in the opposite conductor path, and the voltage applied to the heating element decreases as the distance from the electrodes 651 and 661 increases. For this reason, the heat generation amount of each section of the heat generating element 620 is the largest in the heat generating element 620a located closest to the electrode. The heating value of a certain heating element 620 l is the smallest. Therefore, the temperature of the fixing belt 603 is higher on the electrode side, and the temperature on the opposite side of the electrode is lower (FIG. 7).

  Therefore, as shown in FIG. 8 as the present embodiment, the heater 600 shortens the length of the heating element 620 in the longitudinal direction in a direction away from the electrode, according to the distance from the electrode. As a method of changing the width of the heating element 620, in the central heating elements 620c to 620p connected to the electrode 655, the width of the heating elements 620c and 620d is set as a reference (53.3 mm), and as the position becomes far from the electrode side, The longitudinal length of the heating element 620 is shortened by 15 mm. By doing so, the resistance value Rh of each heating element can be gradually reduced as the electrode side increases and the position becomes farther from the electrode.

  This will be specifically described below. In showing the resistance value of each heat generating body (620a-620l) used in a present Example in FIG. 6, it carried out using the following formula | equation as a calculation method.

Resistance value Rh = R ′ × L / W of each heating element (620a to 620l)
R ′: sheet resistance, L: length in the longitudinal direction of the heating element, and W: length in the width direction of the heating element.

In the present embodiment, a configuration in which R ′ of the heating element is 10Ω / □ and L is 26.7 mm is used.
As described above, as the distance from the electrode is longer, the combined resistance value of the heating element and the branch path increases by the resistance value of the branch path. Therefore, in the present embodiment, the combined resistance of the heating element and the branch path is reduced by decreasing the distance in the longitudinal direction of the branch path as the distance from the electrode increases in the longitudinal direction.

A specific example will be described with reference to FIG. In the heating elements α, β, and γ that are sequentially adjacent to each other in the longitudinal direction from the electrode side, the longitudinal lengths of the heating elements are denoted by Lα, Lβ, and Lγ.
The heating elements α and β are connected to the electrode 651, and the heating element γ is connected to the electrode 661b.

Here, as described above, in the heating element α and the heating element β, the increase Rβ−Rα of the total resistance, which is the resistance from the electrode to the end of the branch path, is calculated by the following equation.
Rβ−Rα = ρ1 + × 1/2 (Lα + Lβ) / (W1 × H1) +
ρ2 × 1/2 (Lα + Lβ) / (W2 × H2) Equation (4)
This increase in resistance value causes the above-described temperature unevenness of the heating element. Therefore, in the present embodiment, the longitudinal length of the heating element β is reduced so that the resistance value of the heating element β is smaller than the resistance value of the heating element α by the same amount as the value of Expression (4). . Specifically, the interval between the branch paths connected to the heating element β adjacent to the heating element α is narrowed by 0.2 mm. As a result, the total resistances of the heating element α and the heating element β are equal, and an increase in resistance value due to the length in the longitudinal direction can be eliminated.

  The said Example is made | formed continuously in the longitudinal direction of the heat generating body connected by the same electrode, and is not applied in the adjacent heat generating body connected to a different electrode. That is, in the longitudinal length of the heating element β and the heating element γ, the above relationship is not necessarily applied, and the heating element γ + 1 adjacent to the heating element γ in the direction away from the electrode in the longitudinal direction is more than the heating element γ. The length in the longitudinal direction is 15 mm shorter.

  As described above, by reducing the length in the longitudinal direction of the heating elements connected to the same electrode by 15 mm, the resistance value decreases as the distance from the electrode increases as shown in FIG. This is due to the fact that the resistance value Rh is different due to the difference in length in the longitudinal direction of the heating element. Therefore, the longer the heating element farther from the electrode, the shorter the longitudinal length (interval interval) of the heating element, so the resistance value Rh becomes smaller. When a voltage is applied to the electrode 655, the heating element 620p located farther from the electrode 655. The power (heat generation amount) when a voltage is applied is improved. Therefore, in the heater of this embodiment, the resistance value Rh is reduced by narrowing the interval between the heating elements located far from the electrodes.

  Next, the temperature distribution in the longitudinal direction of the fixing belt 603 in this embodiment will be described. FIG. 7 is a diagram showing the temperature distribution of the fixing belt when the heater 600 of this embodiment and the conventional heater are used. The temperature distribution when the heater 600 of the present embodiment is used is indicated by a solid line, and the temperature distribution when the heater of the conventional example is used is indicated by a broken line. Note that the horizontal axis in FIG. 7 has the left end of the heating element 620 in FIG. 4 as the origin. In the fixing device of the present embodiment, the temperature at the central portion in the longitudinal direction of the heater 600 is maintained at 220 ° C. by the thermistor 630 as described above. At this time, the temperature of the longitudinal central portion (position 160 mm in FIG. 7) of the fixing belt is maintained at 195 ° C.

  In the case of the heater of the conventional example (FIG. 8), the temperature closer to the electrode is higher than the central portion, and the maximum temperature is about 220 ° C. On the other hand, the temperature on the side far from the electrode is lower than the central portion, and the minimum temperature is about 165 ° C. Accordingly, a temperature difference of about 55 ° C. is generated as the temperature unevenness in the longitudinal direction of the fixing belt 603, and therefore, uneven gloss is generated in the longitudinal direction in the image after the fixing process.

  In the case of the heater of the present embodiment, since the total resistance from the electrodes of the heating elements 620a to 620l to the common branch path is made equal, the distance from the electrode 641 is increased = the heating element when the resistance value R increases. The temperature in the longitudinal direction of the fixing belt 603 becomes uniform at about 195 ° C. without lowering the applied voltage or decreasing the voltage applied to the heating element as the distance from the opposing conductor path electrodes 651 and 661 increases. At this time, gloss unevenness of the image as described above does not occur.

  In addition, the boundaries of the heating elements connected to the different electrodes are respectively set to 210 mm (A4 vertical size of the recording material P) and 297 mm (A4 horizontal size of the recording material P) from the longitudinal center to both ends.

  The heater of the present embodiment has a configuration having only two regions of the heat generating region A and the heat generating region B, but is not limited to this configuration, and can be applied to a configuration having three or more patterns of heat generating regions. Needless to say. In addition, it is conceivable to obtain the same effect by changing the width of the heating element in the conveyance direction as an alternative to this embodiment. The purpose can be achieved more easily and cheaply by using the example.

  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 heater with a uniform heat generation amount in the longitudinal direction.

40 Fixing device 60 Heater unit 70 Pressure roller 100 Control circuit 110 Power supply 110a, 110b Power supply terminal 600 Heater 603 Fixing belt 610 Substrate 620a-620l Resistance heating element 640 Common conductor path 650, 660 Opposite conductor path 645, 655, 665 Electrode 642 Common branch 652, 662 Opposed branch 700 connector

Claims (3)

A single connector (700) connected to one terminal of the power supply (110) and the other terminal;
A board (610) extending along the longitudinal direction to which the connector (700) is attached so as to sandwich the front and back thereof; and
A plurality of electrodes (645, 655, 665) provided on a substrate (610) with which the connector (700) contacts;
A conductor path (640, 650, 660) provided from the electrode toward the longitudinal direction of the substrate (610);
A plurality of branch paths (642, 652, 662) connecting the conductor paths (640, 650, 660) and the heating element (620);
A plurality of heating elements 620 (620a to 620l) provided to electrically connect a plurality of adjacent branch paths,
In the adjacent heating elements connected to the same electrode, when the resistance of the heating element on the electrode side is R1 and the resistance of the heating element on the non-electrode side is R2, the relationship of the heating element resistance is R1> R2. A heater characterized by being. At least an endless fixing belt (603) for heating the image on the sheet;
A pressure member that forms a fixing nip portion by closely contacting the fixing belt (603) to the heater (600);
The fixing device (40) according to claim 1 or 2, further comprising a heater (600) for heating the fixing belt. When heating a sheet of the maximum width size that can be used in the apparatus, power is supplied to all of the plurality of electrodes (645, 655, 665),
2. When heating a sheet having a narrower width than the maximum width sheet, only a part of the plurality of (645, 655, 665) electrodes is fed. The fixing device (40) according to any one of claims 3 to 4.