JP5572478B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device used in an electrophotographic image forming apparatus and an electrophotographic image forming apparatus using the same.

  As a fixing device used in an electrophotographic image forming apparatus such as a copying machine or a printer, a heat roller fixing type composed of a pair of rollers pressed against each other is generally used. The roller pair includes a fixing roller and a pressure roller. Heating means comprising a halogen heater or the like is disposed in both or one of the roller pairs to heat the roller pair to a predetermined temperature (fixing temperature) suitable for fixing. In a state where the roller pair is heated to the fixing temperature, the recording paper on which the unfixed toner image is formed is passed through the press contact portion (fixing nip portion), and the toner image is fixed by heat and pressure.

  In a color fixing device, it is common to use an elastic roller in which an elastic layer made of silicon rubber or the like is provided on the surface of the fixing roller. By using an elastic roller as the fixing roller, the surface of the fixing roller is elastically deformed corresponding to the unevenness of the unfixed toner image, and comes into contact so as to cover the toner image surface. For this reason, it is possible to satisfactorily heat-fix a color unfixed toner image having a larger amount of toner than monochrome. In addition, color toner tends to be offset more easily than monochrome, but the releasability with respect to the toner can be improved by the effect of releasing the distortion of the elastic layer at the fixing nip portion. Further, since the nip shape of the fixing nip portion is convex toward the toner image surface (so-called reverse nip shape), the sheet peeling performance is improved. Therefore, it is possible to realize a so-called self-strip configuration in which the sheet can be peeled without using a peeling means such as a peeling claw. As a result, image defects caused by the peeling means can be eliminated.

  On the other hand, various configurations have been proposed in which a fixing belt having a small heat capacity is used instead of the fixing roller. This is to shorten the warm-up time. As a device belonging to the configuration, a device in which a fixed resistance heating element is brought into contact with the belt to quickly raise the temperature of the belt has been proposed. Also, a method of selecting a resistance heating layer that should generate heat according to the sheet size is disclosed in order to prevent a temperature rise in the non-sheet passing portion that occurs in the width direction along the roller rotation axis when small size paper is passed. (For example, refer to Patent Documents 1 and 2). In particular, in Patent Document 1, resistance heating layers having different lengths corresponding to a sheet having a full width in the width direction of the roller pair (full width size) and a small size sheet having a smaller width than that are formed on a substrate elongated in the width direction. What is provided for is disclosed. In Patent Document 2, a heating element that generates heat by applying a voltage between two electrodes extending parallel to the longitudinal direction of the substrate along the sheet conveyance direction corresponds to the sheet size in the longitudinal direction of the substrate. By setting the electrode length as described above, a heat generation region corresponding to a full width size sheet and a small size sheet is realized.

JP 2000-77170 A JP 2008-299205 A

  However, as described in Patent Documents 1 and 2, the resistance heating layer is formed on the substrate by providing a resistance heating layer having different lengths corresponding to the full width size and the small size on the substrate to prevent the temperature rise of the non-sheet passing portion. Two are needed for this. The heat generating material used for the resistance heating layer is generally expensive, and there is a problem that forming different resistance heating layers depending on the sheet size leads to an increase in cost. Also, the short resistance heating layer for small size requires less power than the resistance heating layer for full width size. Therefore, the resistance value must be increased. However, in a resistance heating layer having a structure in which current flows along the longitudinal direction of the substrate, the resistance value of the resistance heating layer decreases as the resistivity is maintained and the length in the longitudinal direction of the substrate is shortened. When a voltage is applied, the amount of heat generation becomes excessive. In order to prevent this, it is necessary to make the latter resistivity higher by making the resistivity of the resistance heating layer for the small size different from the resistivity of the resistance heating layer for the full width size. Alternatively, it is necessary to make the latter width narrower by making the width of the resistance heating layer for small size different from the width of the resistance heating layer for full width size.

  However, materials suitable for forming the resistance heating layer are limited, and the adjustable resistivity range is not so wide. As the width of the resistance heating layer is reduced, the current per cross-sectional area increases and the reliability of the resistance heating layer decreases. In addition, there is a problem that the influence of variation in the heat generation width when forming the resistance heat generation layer is increased, and the temperature distribution in the longitudinal direction of the substrate tends to be non-uniform. Although a method of increasing the thickness of the resistance heating layer is also conceivable, it is practical in terms of reliability and cost to realize this with the conventional method of forming the resistance heating layer using a printing method. I couldn't. Furthermore, if a plurality of types of resistance heating elements having different resistivities are formed within the adjustable range, the number of manufacturing steps is increased and the cost burden is increased as compared with the case of forming a plurality of resistance heating elements having the same resistivity. End up.

  On the other hand, a configuration in which a resistor is heated by applying a voltage between two electrodes extending in parallel to the longitudinal direction of the substrate is not conceivable. However, in this configuration, the distance between the electrodes is narrower than the configuration in which the electrodes are arranged at the end in the longitudinal direction of the substrate, and thus a heating element having a high resistivity is required. However, as described above, suitable materials are limited, and the use of such materials increases the length of the resistance heat generating layer and accordingly increases the width of the substrate, which is not very practical. Further, in order to prevent leakage between a plurality of electrodes arranged according to the sheet size, it is necessary to arrange the electrodes with a certain distance, and it is also necessary to separate the resistance heating layer according to the electrode width. For this reason, a non-heat-generating region is formed in the sheet size, and a temperature drop at that portion becomes a problem.

  The present invention has been made in view of the above-described conventional problems, and forms a plurality of resistance heating layers having substantially the same shape according to the resistivity determined according to the material used for the resistance heating layer and the required heat generation amount. Accordingly, an object of the present invention is to obtain a heat generating body with high reliability, low cost and little temperature unevenness, and to provide a fixing device including the heat generating body.

  The first and second aspects of the present invention are a rotatable endless belt, and a first and a second that convey the toner image transferred between the endless belt surface by rotating the endless belt between the inner and outer sides. (1) a substrate extending in the width direction orthogonal to the rotation direction of the endless belt, (2) five or more odd resistance heating layers arranged in the width direction on the surface of the substrate, and (3) adjacent An intermediate electrode layer sandwiched between the corresponding resistance heating layers to form a common electrode, and (4) an end electrode layer provided on the opposite side to the intermediate electrode layer in the resistance heating layer at one end and the other end, and (5 A heating layer for supplying heat to the endless belt, and the wiring layer is formed on one side of the resistance heating layer in the rotation direction. Formed on the first wiring layer and the other side The first wiring layer is connected to every other intermediate electrode layer including the intermediate electrode layer on one end side of the central resistance heating layer, and the second wiring layer is Provided is a fixing device characterized in that it is connected to every other intermediate electrode layer including the intermediate electrode layer on the other end side of the central resistance heating layer.

  According to a second aspect of the present invention, there is provided a fixing device according to the first aspect, wherein the first wiring layer and the end electrode layer on one end side are connected to a first terminal of a power source, and the second wiring layer and the A first connection pattern for connecting the end electrode layer on the other end side to the second terminal of the power source, a first wiring layer and the end electrode layer on the other end side connected to the first terminal of the power source and A power supply circuit capable of switching to a second connection pattern for connecting the wiring layer of 2 and the end electrode layer on the one end side to the second terminal of the power source, and detecting the size in the width direction of the sheet. An image forming apparatus comprising: a switching control unit that switches to a first connection pattern when detected, and switches to a second connection pattern when a small size is detected.

  Thirdly, according to the present invention, a rotatable endless belt, and a first and a second which convey the toner image transferred between the endless belt by rotating the endless belt between the inner and outer sides. (1) a substrate extending in the width direction orthogonal to the rotation direction of the endless belt, (2) five or more odd resistance heating layers arranged in the width direction on the surface of the substrate, and (3) adjacent An intermediate electrode layer sandwiched between the corresponding resistance heating layers to form a common electrode, and (4) an end electrode layer provided on the opposite side to the intermediate electrode layer in the resistance heating layer at one end and the other end, and (5 A heating layer for supplying heat to the endless belt, the total number of the intermediate electrode layer and the end electrode layer being 2 × M (M is an integer of 3 or more) and the wiring Is a first wiring layer formed on one side of the resistance heating layer in the rotation direction, a second wiring layer formed on the other side, and a first wiring layer formed on the same side as the first wiring layer. 3 wiring layers and a fourth wiring layer formed on the same side as the second wiring layer, and the first wiring layer includes one intermediate electrode layer on one end side of the central resistance heating layer. Out of a total of M intermediate electrode layers or end electrode layers arranged in rows, N are connected from the one end or the other end side (N is an integer larger than half of M and smaller than M), and the third wiring layer remains. The second wiring layer is connected to the MN intermediate electrode layers or end electrode layers, and the second wiring layer includes the intermediate electrode layer on the other end side of the central resistance heating layer, and is arranged every other intermediate electrode layer or end. Of the total M of the partial electrode layers, N are connected to the N from the other end or one end, and the fourth wiring layer remains with MN intermediate powers remaining. Provided is a fixing device connected to an extreme layer or an end electrode layer.

  According to a fourth aspect of the present invention, the fixing device according to the third aspect of the present invention, the first and third wiring layers are connected to the first terminal of the power source, and the second and fourth wiring layers are connected to the second power source. A first connection pattern for connecting to the terminal, and a second connection for connecting the first and fourth wiring layers to the first terminal of the power source and connecting the second and third wiring layers to the second terminal of the power source A power supply circuit that can be switched to a pattern and the sheet width size are detected. When a large size is detected, the first connection pattern is switched. When a small size is detected, the sheet is switched to a second connection pattern. An image forming apparatus comprising a switching control unit is provided.

  According to the first invention, the heating element includes five or more odd resistance heating layers arranged in the width direction, the intermediate electrode layer, the end electrode layer, and the wiring layer connected to the intermediate electrode layer. The first wiring layer is connected to every other intermediate electrode layer including the intermediate electrode layer on one end side of the central resistance heating layer, and the second wiring layer is connected to the other of the central resistance heating layer. Since it is connected to every other intermediate electrode layer including the intermediate electrode layer on the end side, the setting range is determined according to the material used for the resistance heating layer, and the shape is almost the same according to the required heating value By forming the plurality of resistance heating layers and supplying power to the end electrode layer and the wiring layer, a heating element with high reliability, low cost, and low temperature unevenness can be obtained. By using the heating element, it is possible to realize a fixing device that has a high temperature rising rate and can generate heat in a region corresponding to the sheet size, but has little variation in heat generation.

  According to the second invention, the power supply circuit that can be switched between the first and second connection patterns, and when the large size is detected, the first connection pattern is switched to and the small size is detected. In some cases, a switching control unit for switching to the second connection pattern is provided, so that when a small size sheet is fixed, a temperature rise in the non-sheet passing portion can be prevented, and a plurality of resistance heating layers having substantially the same shape are formed. However, it is possible to change the number of resistance heating layers for generating large and small sizes. Furthermore, switching between the large size and the small size can be realized with a simple configuration in which the connection between the power supply terminal and the end electrode layer and the wiring layer is switched by the power supply circuit.

  According to the third aspect of the present invention, the heating element is provided in five or more odd resistance heating layers arranged in the width direction, the intermediate electrode layer, the end electrode layer, the intermediate electrode layer, and the end electrode layer. A wiring layer to be connected, and the first wiring layer includes an intermediate electrode layer on one end side of the central resistance heating layer, and the intermediate electrode layer or the end electrode layer arranged in every other one of the total number M of the intermediate electrode layers. N (N is an integer larger than half of M and smaller than M) is connected from one end or the other end, and the third wiring layer is connected to the remaining MN intermediate electrode layers or end electrode layers, The second wiring layer includes an intermediate electrode layer on the other end side of the central resistance heating layer and includes N intermediate electrode layers or end electrode layers arranged in a row. And the fourth wiring layer is connected to the remaining MN intermediate electrode layers or end electrode layers. High reliability and low cost by forming a plurality of resistance heating layers of approximately the same shape according to the resistivity that determines the setting range according to the material used for the heating layer and the required amount of heat generation, and feeding each wiring layer A heating element with little temperature unevenness can be obtained. By using the heating element, it is possible to realize a fixing device that has a high temperature rising rate and can generate heat in a region corresponding to the sheet size, but has little variation in heat generation.

  According to the second invention, the power supply circuit that can be switched between the first and second connection patterns, and when the large size is detected, the first connection pattern is switched to and the small size is detected. In some cases, a switching control unit for switching to the second connection pattern is provided, so that when a small size sheet is fixed, a temperature rise in the non-sheet passing portion can be prevented, and a plurality of resistance heating layers having substantially the same shape are formed. However, it is possible to change the number of resistance heating layers for generating large and small sizes. Furthermore, switching between the large size and the small size can be realized with a simple configuration in which the connection between the power supply terminal and each wiring layer is switched by the power supply circuit.

  In the present invention, the endless belt is for fixing the toner image on the sheet by being heated by a heating element and being sandwiched between the first and second rollers together with the sheet on which the toner image is transferred. As a specific mode, an elastic layer made of silicon rubber or the like is laminated on a polyimito resin or the like as a base material, and a fluorine resin such as PFA or PTFE is formed on the surface as a scientific layer. In an embodiment described later, the endless belt corresponds to the fixing belt 5.

  The first and second rollers rotate by sandwiching the endless belt from inside and outside. The endless belt rotates in a state where it is hung on a first roller and a heating element sandwiching the endless belt from the inside. Alternatively, it may be hung on the first roller and the tension roller. In that case, the heating element is between the first roller and the tension roller and contacts the endless belt.

The heating element is elongated in the width direction perpendicular to the direction in which the endless belt rotates, contacts the endless belt, and supplies heat to the endless belt.
The heating element includes a plurality of resistance heating layers formed in series on the surface of an elongated substrate. The number of resistance heating layers is an odd number of 5 or more. Full-width and small-size sheets are conveyed at a position where the centers in the width direction coincide. The resistance heating layer, the electrode, and the wiring layer on the substrate are formed so that the connection relationship is point-symmetric with respect to the center in the width direction. This is because the heat generation area is made to correspond to the full width size sheet and the small size sheet conveyed with the center as a reference, and the wiring patterns do not intersect on the substrate.

One of the characteristic aspects of the present application is that a small-sized resistive heating layer and / or a plurality of resistive heating layers dedicated to the full width provided respectively on one end side and the other end side thereof are configured. The total number of resistance heating layers is 5 or more. In the three configurations, one resistance heating layer in the center is for a small size, and one resistance heating layer at each end is a dedicated resistance heating layer for the full width size. This is because it is not included in the configuration.
The heating element of the present invention considers forming a resistance heating layer on a substrate using a printing technique. Further, it is considered that the electrodes and the wiring layer are also formed by using a printing method.

  The power supply circuit connects a power supply terminal and a heating element. The specific embodiment uses a wire lotus, that is, an electric wire, a connector and the like and a switch. The switch may be a mechanical switch such as a relay or a semiconductor element such as a solid state relay. On and off must be controllable by a command from a microcomputer or a computer.

  The switching control unit controls the switch in accordance with the sheet size to switch the connection pattern of the power supply circuit. The switching control unit is realized by a microcomputer or a computer executing a control program. The function of this switching control unit may be realized as part of a computer that controls the overall operation of the image forming apparatus.

1 is an explanatory diagram illustrating an overall configuration of an image forming apparatus including a fixing device according to the present invention. It is explanatory drawing which shows the example of a structure of the fixing device of this invention. It is explanatory drawing which shows the 1st structural example of the heat generating body which concerns on this invention. It is explanatory drawing which shows the 1st structural example of the electric power supply circuit which concerns on this invention. It is explanatory drawing which shows the 2nd structural example of the heat generating body which concerns on this invention. It is explanatory drawing which shows the 2nd structural example of the electric power supply circuit which concerns on this invention. It is explanatory drawing which shows the 3rd structural example of the heat generating body which concerns on this invention. It is a 1st explanatory view showing the 3rd example of composition of the power supply circuit concerning this invention. It is the 2nd explanatory view showing the 3rd example of composition of the power supply circuit concerning this invention. It is explanatory drawing which shows the 4th structural example of the heat generating body and electric power supply circuit which concern on this invention. FIG. 3 is an explanatory diagram showing a configuration example different from FIG. 2 of the fixing device of the present invention.

Hereinafter, the present invention will be described in more detail with reference to the drawings. In addition, the following description is an illustration in all the points, Comprising: It should not be interpreted as limiting this invention.
The fixing device in this embodiment fixes a toner image on a recording sheet by heat and pressure to a sheet on which an unfixed toner image is formed. An unfixed toner image is a developer such as a non-magnetic one-component developer (non-magnetic toner), a non-magnetic two-component developer (non-magnetic toner and carrier), or a magnetic developer (magnetic toner) (hereinafter also referred to as toner). ).

<< Configuration of image forming apparatus >>
FIG. 1 is an explanatory diagram showing the overall configuration of an image forming apparatus provided with the fixing device of the present invention.
In FIG. 1, the image forming apparatus 1 is a color multifunction peripheral, and includes first to fourth visible image forming units 51, 52, 53, 54, an intermediate transfer belt 55, a secondary transfer unit 56, a fixing unit 2, and an internal supply. A feeding unit 57 and a manual feeding unit 58 are provided. Then, a toner image is formed using the first to fourth visible image forming units 51, 52, 53, 54, the intermediate transfer belt 55 and the secondary transfer unit 56.

  The first visible image forming unit 51 includes a photoreceptor 59, a charging unit 60, an optical system unit (not shown), a developing unit 61, and a primary transfer unit 62. A charging unit 60, a developing unit 61, and a cleaning unit 63 are disposed around a photoconductor 59 serving as an image carrier. By these units, a toner image is formed on the photoreceptor 59, and the toner image is transferred to the intermediate transfer belt 55. In the optical system unit, the beams from the four laser light sources 64 are arranged so as to reach the four sets of photoconductors 59, 65, 66 and 67. The primary transfer unit 62 is disposed in pressure contact with the first visible image forming unit 51 via the intermediate transfer belt 55.

  The other second to fourth visible image forming units 52, 53 and 54 have the same configuration as the first visible image forming unit 51. The developing unit 61 of each of the units 51, 52, 53, and 54 contains toner of each color of yellow (Y), magenta (M), cyan (C), and black (B).

  The intermediate transfer belt 55 has each color toner image transferred thereon, and the color toner image of each color is superimposed on the surface. The intermediate transfer belt 55 is driven to rotate by tension rollers 68 and 69. A secondary transfer unit 56 is disposed in contact with the tension roller 68 side of the intermediate transfer belt 55. The secondary transfer unit 56 transfers the color toner image formed on the intermediate transfer belt 55 onto the recording paper. Further, the toner remaining on the surface of the intermediate transfer belt 55 after the secondary transfer is collected in a waste toner box 70 that is in contact with the intermediate transfer belt 55 and disposed on the tension roller 69 side.

The fixing unit 2 is a fixing device of the present invention. The fixing unit 2 is disposed on the downstream side of the secondary transfer unit 56. The fixing unit 2 includes a fixing unit 71 and a pressure unit 72. The pressure unit 72 is pressed against the fixing unit 71 with a predetermined pressure by a pressure mechanism (not shown).
Next, an image forming process in the image forming apparatus 1 will be described.
The surface of the photoreceptor 59 is uniformly charged by the charging unit 60. As the charging unit 60, a charging roller system is employed in order to charge the surface of the photoreceptor 59 uniformly and without generating ozone as much as possible.

The optical system unit exposes the surface of the charged photoreceptor 59 with a beam from the laser light source 64. The laser light source 64 is controlled by image information. As a result, an electrostatic latent image corresponding to the image information is formed on the surface of the photoreceptor 59.
The developing unit 61 develops the electrostatic latent image on the photoconductor 59 to form a toner image. The primary transfer unit 62 applies a bias voltage having a polarity opposite to that of the toner, and transfers the formed toner image onto the intermediate transfer belt 55.
The other three sets of second to fourth visible image forming units 52, 53, and 54 operate in the same manner and sequentially transfer the toner images onto the intermediate transfer belt 55.

  The toner image on the intermediate transfer belt 55 is conveyed to the secondary transfer unit 56. A bias voltage having a polarity opposite to that of the toner is applied to the recording paper supplied from the feeding roller 73 of the internal feeding unit 57 or the feeding roller 74 of the manual feed unit 58, and the toner image is transferred to the recording paper. . The recording paper carrying the toner image is conveyed to the fixing unit 2 and sufficiently heated by the fixing unit 71 and the pressure unit 72, so that the toner image is fused to the recording paper and discharged to the outside. The maximum size of recording paper is A3 size, and the heating width by the fixing unit is A4 horizontal size.

≪Configuration of fixing device≫
Next, the configuration of the fixing device in the image forming apparatus 1 will be described. FIG. 2 is an explanatory diagram showing a configuration example of the fixing device of the present invention. The fixing unit 2 includes a fixing roller 3, a pressure roller 4, an endless fixing belt 5, and a heating element 6 for heating the fixing belt 5. The fixing belt 5 is wound around the fixing roller 3 and the heating element 6. The heating element is fixed and slides with the inner surface of the fixing belt. The sheet 13 on which the toner image 14 is transferred passes through the fixing nip portion 12 between the fixing belt 5 and the pressure roller 4 hung on the fixing roller 3. The fixing belt 5 is heated by a heating element 6. When the sheet 13 passes through the fixing nip portion 12, the toner image 14 is melted by the heat from the fixing belt 5 and is cooled and fixed on the sheet 13 after passing through the fixing nip portion.

  The heating element 6 includes a resistance heating layer, and the pressure roller 4 includes a heater lamp. A first thermistor 10 and a second thermistor 11 are provided as temperature sensors for detecting the temperatures of the fixing belt 5 and the pressure roller 4, respectively.

  The fixing roller 3 has a substantially cylindrical shape, and has a two-layer structure in which a metal core and an elastic layer are formed from the center of the substantially cylindrical shape toward the outer periphery. A metal such as iron, stainless steel, aluminum or copper, or an alloy thereof is used for the core metal. A rubber material having heat resistance such as silicon rubber or fluorine rubber is suitable for the elastic layer. In the present embodiment, the diameter of the fixing roller 3 is 30 mm. Stainless steel with a diameter of 20 mm is used for the core metal, and silicon sponge rubber with a thickness of 5 mm is used for the elastic layer.

  The pressure roller 4 has a substantially cylindrical shape, and has a three-layer structure in which a metal core, an elastic layer, and a release layer are formed from the center of the substantially cylindrical shape toward the outer periphery. A metal such as iron, stainless steel, aluminum copper, or an alloy thereof is used for the core metal. A rubber material having heat resistance such as silicon rubber or fluorine rubber is suitable for the elastic layer. A fluororesin such as PFA (a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) or PTFE (polytetrafluoroethylene) is suitable for the release layer. In the present embodiment, the pressure roller 4 has a diameter of 30 mm. For the metal core, iron (STKM) having a diameter of 26 mm and a wall thickness of 1 mm is used. Silicon elastic rubber having a thickness of 1 mm is used for the elastic layer. A PFA tube having a thickness of 50 μm is used for the release layer.

The pressure roller 4 is disposed to face the fixing roller 3 with the fixing belt 5 interposed therebetween. A portion where the fixing roller 3 and the pressure roller 4 are in contact with each other via the fixing belt 5 between the fixing belt 5 and the pressure roller 4 is a fixing nip portion 12.
The heating element 6 includes a substrate 21 on which a resistance heating layer is formed and a heat conducting member 23 made of metal. The surface opposite to the surface on which the resistance heating layer is formed on the substrate 21 is in close contact with the heat conducting member 23. Of the surface of the heat conducting member 23, the surface opposite to the surface where the substrate 21 is in close contact with the heat conducting member 23 is in contact with the fixing belt 5.

The substrate 21 is made of ceramic, glass, an insulating substrate such as a heat-resistant resin such as polyimide, PEEK, or PPS, or a metal substrate such as SUS or aluminum formed with an insulating layer such as glass, ceramic, or polyimide.
The resistance heating layer on the substrate 21 can be made of carbon, semiconductor oxide, glass paste containing silver (Ag) and palladium (Pd), or the like.
As the heat conducting member 23, a high heat conducting ceramic such as aluminum nitride or silicon nitride can be used in addition to a metal such as aluminum. Note that the substrate 21 may be brought into direct contact with the belt without the heat conducting member.

  The portion of the heat conducting member 23 or the substrate 21 that comes into contact with the belt may be coated with amorphous glass or fluororesin to improve the slidability with the belt. In the present embodiment, a glass substrate on which a resistance heating layer made of a silver palladium alloy is formed is in close contact with an aluminum heat conduction member 23 is used as a heating element.

  A heater lamp 7 a is disposed inside the pressure roller 4, and the heater lamp 7 a heats the pressure roller 4. A control unit (not shown) controls the power supply circuit to supply power to the heater lamp from the power supply circuit. The heater lamp 7a emits light with energization, and the entire pressure roller 4 is heated by the radiation of the heater lamp 7a. In the present embodiment, a heater lamp 7a with a rated power of 300 W is used. In this embodiment, the function of the control unit is realized by performing control mainly by the microcomputer executing a control program prepared in advance. The control unit includes an input / output circuit for detecting an operation on the power supply circuit and a sheet size.

  For the heating element, the control unit controls the power supply circuit and supplies (energizes) power to the resistance heating layer on the substrate 21. Along with energization, the resistance heating layer generates heat due to Joule heat, and the heat is transmitted to the substrate 21 and further to the fixing belt 5 through the heat conducting member 23. In the present embodiment, a resistance heating element having a rated power of 1200 W is used for the maximum heat generation amount of the full width size.

  The fixing belt 5 has a diameter of 50 mm when not attached to the fixing unit 2. The fixing belt 5 has a three-layer structure including a base material, an elastic layer, and a release layer. The base material is formed in a hollow cylindrical shape from a heat-resistant resin such as polyimide, or a metal material such as stainless steel and nickel. An elastic layer made of an elastomer material such as silicon rubber, which is excellent in heat resistance and elasticity, is formed on the surface of the base material. On the surface of the elastic layer, a release layer made of a synthetic resin material which is excellent in heat resistance and release properties, for example, a fluororesin such as PFA or PTFE is formed. In the present embodiment, polyimide having a thickness of 50 μm is used as the base material, silicon rubber having a thickness of 150 μm is used as the elastic layer, and a PFA tube having a thickness of 30 μm is used as the release layer.

<< First Embodiment of Heating Element and Power Supply Circuit >>
FIG. 3 is a diagram showing a first detailed configuration example of the heating element 6. The heating element 6 shown in FIG. 3 has five resistance heating layers 25a, 25b, 25c, 25d, and 25e made of silver-palladium alloy on the surface of an elongated alumina ceramic substrate 21. These resistance heating layers are arranged in series in the longitudinal direction of the substrate 21.
An electrode 27a as an end electrode layer is provided on one end side of the resistance heating layer 25a on one end side of the substrate. An electrode 27b as an intermediate electrode layer is provided between the resistance heating layer 25b adjacent to the resistance heating layer 25a. When the power supply voltage is applied between the electrodes 27a and 27b, the resistance heating layer 25a generates heat.

Furthermore, electrodes 27c, 27d, and 27e as intermediate electrodes are formed between the adjacent resistance heating layers 25b and 25c, between 25c and 25d, and between 25d and 25e, respectively. An electrode 27 f as an end electrode is formed on the other end side of the substrate of the resistance heating layer 25.
The electrode 27c on one end side of the central resistance heating layer 25c and the electrode 27e separating the electrode 27d are connected by a wiring layer 29a. The electrode 27d on the other end side of the resistance heating layer 25c and the electrode 27b separating the electrode 27c are connected by a wiring layer 29b.

  Except for the electrodes 27a and 27f as end electrode layers, half of the electrodes 27b to 27e as intermediate electrode layers arranged every other one are connected to the wiring layer 29a, and the remaining half are connected to the wiring layer 29b. . The electrodes 27a to 27f and the wiring layers 29a and 29b are formed on the substrate 21 with a material that is formed of a low resistance silver (Ag) paste and hardly generates heat. The portions of the electrodes 27b to 27e as the intermediate electrode layers are non-heat generation regions, but by making the width in the longitudinal direction of the substrate as small as about 1 mm, it is possible to prevent a local drop in temperature compared to the resistance heat generation layer. .

The wiring layers 29a and 29b are formed on opposite sides of the resistance heating layers 25a to 25e arranged in series. This is so that they do not cross each other.
By making the length, width, and thickness of each resistance heating layer equal, the amount of heat generated by each resistance heating layer can be made equal. Further, in order to correct the heat escape from the edge of the substrate, the resistance heating layers 25a and 25e at the ends are made narrower and narrower than the other resistance heating layers 25b to 25d, or the length in the longitudinal direction of the substrate is reduced. By doing so, the calorific value may be slightly increased.

  An example of a method for manufacturing the heating element 6 will be described. First, a substrate 21 such as ceramic is prepared. A glass paste mainly composed of silver and palladium is applied on the substrate 21 by a technique such as silk printing. Thereby, portions to be the resistance heating layers 25 a to 25 e are patterned on the substrate 21. Next, it is applied by a technique such as silk printing using a low-resistance glass paste mainly composed of silver. As a result, the portions to be the electrodes 27a to 27f and the portions to be the wiring layers 29a and 29b connecting the electrodes are patterned on the substrate 21 and the resistance heating layers 25a to 25e. The substrate 21 patterned on the surface in this manner is baked to finally form a resistance heating layer, electrodes, and wiring. Subsequently, an insulating paste such as glass is applied thereon and fired again. At this time, the insulating paste is not applied to the portions of the end electrodes 27a and 27f and the wiring layers 29a and 29b located at the end of the substrate 21, so that the silver pattern is exposed. This is because a power supply circuit is connected to a portion where the silver pattern is exposed so that power can be supplied by applying a power supply voltage to each of the resistance heating layers 25a to 25e. The above is the method for manufacturing the heating element 6.

Next, a power supply circuit that supplies power to the heating element of FIG. 3 will be described.
FIG. 4 is an explanatory diagram showing a first configuration example of the power supply circuit according to the present invention. The power supply circuit is a circuit that connects between the power source input to the image forming apparatus and the heating element 6. Power is supplied from the first and second power supply terminals. An AC voltage is applied between these power terminals. The power supply circuit connects the end electrodes 27a and 27f and the wiring layers 29a and 29b of the heating element 6 to the power supply terminal. For the connection, a wiring member such as an electric wire or a connector is used.
The power supply circuit connects the power source and the heating element 6 with the first and second connection patterns. The first connection pattern is a connection pattern for fixing a full width sheet (large size). The second connection pattern is a connection pattern for fixing a sheet having a smaller size than the full width size. FIG. 4A shows a first connection pattern, and FIG. 4B shows a second connection pattern.

In FIG. 4A, the first power supply terminal 31a is connected to the end electrode 27a on one end side, and is connected to the wiring layer 29a via the switch 33a. The second power supply terminal 31b is connected to the electrode 27f as the end electrode on the other end side, and is connected to the wiring layer 29b via the switch 33b. The switches 33c and 33d are released.
According to the first connection pattern of FIG. 4A, the electrodes 27a, 27c and 27e are connected to the power supply terminal 31a, and the electrodes 27b, 27d and 27f are connected to the power supply terminal 31b. Therefore, in both of the resistance heating layers 25a to 25e, the electrodes at both ends are connected to the power supply terminals 31a and 31b to generate heat.

In FIG. 4B, the first power supply terminal 31a is connected to the end electrode 27a on one end side, and is connected to the wiring layer 29b via the switch 33c. The second power supply terminal 31b is connected to the electrode 27f as the end electrode on the other end side, and is connected to the wiring layer 29a via the switch 33d. The switches 33a and 33b are released.
According to the second connection pattern of FIG. 4B, the electrodes 27a, 27b and 27d are connected to the power supply terminal 31a, and the electrodes 27c, 27e and 27f are connected to the power supply terminal 31b. Thus, the resistance heat generating layers 25b, 25c and 25d generate heat when the electrodes at both ends are connected to the power supply terminals 31a and 31b. On the other hand, the resistance heating layer 25a does not generate heat because no current flows through it because both electrodes are connected to the power supply terminal 31a. Similarly, the resistance heating layer 25e is not heated because no current flows because both electrodes at both ends are connected to the power supply terminal 31b. That is, in the second connection pattern, the resistance heating layers 25a and 25e at both ends do not generate heat, and the three resistance heating layers 25b, 25c and 25d near the center generate heat.

  Switching between the first and second connection patterns is realized by switching on and off the switches 33a to 33d. The on / off of these switches is controlled by the aforementioned control unit. The control unit detects whether the fed sheet is a full width size or a small size, and switches the switches 33a to 33d to the first connection pattern when the sheet is full width, and changes to the second connection pattern when the sheet is small. Switches 33a to 33d are switched. Thus, the heat generation area is switched according to the sheet size. Therefore, when the small size sheet is fed, the temperature rise at the end can be suppressed.

For example, the interval between the electrodes 27a27f is set to 320 mm in order to correspond to a sheet having a full width size of A4. When the lengths of the resistance heating layers 25a to 25e are all equal, the distance between the electrodes 27b and 27e corresponding to the small size is 192 mm. This is a length suitable for heating a B5 horizontal sheet or an A4 vertical sheet.
Moreover, the resistance heating layers 25a to 25e can be formed with the same width, length, and thickness. That is, it is not necessary to make the resistivity of the resistance heating layer for the small size different from the resistivity of the resistance heating layer for the full width size.

  Here, the connection between the electrodes 27a and 27f and the wiring layers 29a and 29b on the substrate 21 and the wiring outside the substrate is performed by bringing a beryllium copper leaf spring or the like into contact with the electrode on the substrate 21 and the exposed portion of the wiring. Etc. Moreover, a relay switch, a triac switch, etc. can be used as a switch. Commercial power can be used as the power source.

<< Second Embodiment of Heating Element and Power Supply Circuit >>
In the first embodiment, the small size heat generating area is composed of a plurality of resistance heat generating elements, but the full width size heat generating area is obtained by adding one resistance heat generating element to both ends of the small size heat generating area. . In the second embodiment, it is shown that a configuration in which a plurality of resistance heating elements are added to both ends of the small-size heating region can be realized.

FIG. 5 is an explanatory view showing a second configuration example of the heating element according to the present invention.
The substrate 21, the resistance heating layers 25a to 25e, and the electrodes 27a to 27f are the same as the heating element 6 in FIG. Since the total number of electrodes is 6, this embodiment corresponds to the case of M = 3. What is different from FIG. 3 is a wiring layer pattern. The heating element 6 of FIG. 5 includes wiring layers 29c, 29d, 29e, and 29f.

The electrode 27c on one end side of the central resistance heating layer 25c and the electrode 27a separating the electrode 27b are connected by a wiring layer 29c. The electrode 27d on the other end side of the resistance heating layer 25c and the electrode 27f separating the electrode 27e are connected by a wiring layer 29d. Furthermore, the electrode 27e that separates the electrode 27d from the electrode 27c is connected to the wiring layer 29e. The electrode 27b that separates the electrode 27c from the electrode 27d is connected to the wiring layer 29f. That is, this embodiment corresponds to the case where N = 2.
The wiring layers 29c and 29e are formed on the same side with respect to the resistance heating layers 25a to 25e arranged in series. The wiring layers 29d and 29f are formed on the same side with respect to the resistance heating layers 25a to 25e. On the other hand, the wiring layers 29c and 29d are formed on opposite sides of the resistance heating layers 25a to 25e. This is so that they do not cross each other.
By making the length, width, and thickness of each resistance heating layer equal, the amount of heat generated by each resistance heating layer can be made equal.

Next, a power supply circuit that supplies power to the heating element of FIG. 5 will be described.
FIG. 6 is an explanatory diagram showing a second configuration example of the power supply circuit according to the present invention. The power supply and power supply terminals 31a and 31b shown in FIG. 6 are the same as those in FIG. Four switches similar to those in FIG. 4 are used, but the reference numerals 33e to 33h are different from those in FIG. 4 in order to prevent confusion with FIG.
The power supply circuit connects the power source and the heating element 6 with the first and second connection patterns. The first connection pattern is a connection pattern for fixing a full width sheet (large size). The second connection pattern is a connection pattern for fixing a sheet having a smaller size than the full width size. FIG. 6A shows the first connection pattern, and FIG. 6B shows the second connection pattern.

  In FIG. 6A, the first power supply terminal 31a is connected to an electrode 27a as an end electrode on one end side, and is connected to the wiring layer 29e via a switch 33e. The electrode 27c that separates the electrode 27b from the electrode 27a is connected to the electrode 27a by the wiring layer 29c. The second power supply terminal 31b is connected to an electrode 27f as an end electrode on the other end side, and is connected to the wiring layer 29d via a switch 33f. The electrode 27d that separates the electrode 27e from the electrode 27f is connected to the electrode 27f by the wiring layer 29d. The switches 33g and 33h are released.

According to the first connection pattern of FIG. 6A, the electrodes 27a, 27c and 27e are connected to the power supply terminal 31a, and the electrodes 27b, 27d and 27f are connected to the power supply terminal 31b. Therefore, in both of the resistance heating layers 25a to 25e, the electrodes at both ends are connected to the power supply terminals 31a and 31b to generate heat.
In FIG. 6B, the first power supply terminal 31a is connected to an electrode 27a as an end electrode on one end side, and is connected to the electrode 27b via a switch 33g and a wiring layer 29f. The electrode 27c is connected to the electrode 27a through the wiring layer 29c. The second power supply terminal 31b is connected to an electrode 27f as an end electrode on the other end side, and is connected to the electrode 27e via the switch 33h and the wiring layer 29e. The electrode 27d is connected to the electrode 27f through the wiring layer 29d. The switches 33e and 33h are released.

  According to the second connection pattern of FIG. 6B, the electrodes 27a, 27b and 27c are connected to the power supply terminal 31a, and the electrodes 27d, 27e and 27f are connected to the power supply terminal 31b. Therefore, the resistance heating layer 25c generates heat by connecting the electrodes at both ends to the power supply terminals 31a and 31b. On the other hand, the resistance heating layers 25a and 25b are not heated because no current flows because both electrodes are connected to the power supply terminal 31a. Similarly, the resistance heating layers 25d and 25e do not generate heat because no current flows because both electrodes are connected to the power supply terminal 31b. That is, in the second connection pattern, the resistance heating layers 25a, 25b, 25d and 25e at both ends do not generate heat, and only the central resistance heating layer 25c generates heat.

  Switching between the first and second connection patterns is realized by switching on and off the switches 33e to 33h. The on / off of these switches is controlled according to the sheet size by the control unit described above.

  The second embodiment shows that in the configuration having five resistance heating layers as in FIG. 3, a plurality of resistance heating elements can be added to both ends of the small size heating area to make the full width size. It is. Here, for example, when the width of the electrodes 27a27f is set to 320 mm and the lengths of the resistance heating layers 25a to 25e are all equal in order to correspond to a sheet having an A4 width, the width of the electrode 27c corresponding to the small size. Is 64 mm. This is narrower than the L-size vertical width of 89 millimeters and may not be a practical size. However, by combining the first embodiment and the second embodiment, a small size is configured by a plurality of resistance heating layers, and a plurality of resistance heating elements are added to both ends of the small size heating region to increase the full width size. It becomes possible to configure. This is the third embodiment described below.

<< Third Embodiment of Heating Element and Power Supply Circuit >>
According to the third embodiment, it is possible to configure a small size by a plurality of resistance heating layers and add a plurality of resistance heating elements to both ends of the small size heating region to configure the full width size.
FIG. 7 is an explanatory view showing a third configuration example of the heating element according to the present invention.
As shown in FIG. 7, in this embodiment, 19 resistance heating layers 25a to 25s are formed in series in the longitudinal direction of the substrate 21, and 20 electrodes 27a to 27t are formed correspondingly. Yes. That is, this embodiment corresponds to the case where M = 10. Four wiring layers 29c, 29d, 29e and 29f are provided.

  Among the electrodes arranged alternately, including the electrode 27j on one end side of the central resistance heating layer 25j, eight electrodes 27f, 27h, 27j, 27l, 27n, 27p, 27r, and 27t from the other end side are wiring layers. 29c. The remaining electrodes 27b and 27d are connected to the wiring layer 29d. In addition, eight electrodes 27a, 27c, 27e, 27g, 27i, 27k, 27m, and 27o from one end side among the electrodes arranged alternately including the other end side electrode 27k of the resistance heating layer 25j are wiring layers. 29d. Furthermore, the electrode 27e that separates the electrode 27d from the electrode 27c is connected to the wiring layer 29e. The remaining electrodes 27q and 27s are connected to the wiring layer 29f. That is, this embodiment corresponds to the case of N = 8.

  The wiring layer 29c corresponds to the first wiring layer, the wiring layer 29d corresponds to the second wiring layer, the wiring layer 29e corresponds to the third wiring layer, and the wiring layer 29f corresponds to the fourth wiring layer. The first wiring layer is connected to the eight electrodes from the other end side, and the second wiring layer is connected to the eight electrodes from the one end side, and both are alternately connected to the electrodes. Yes. The third wiring layer is connected to the remaining electrode on the other end side without being connected to the first wiring layer, and is alternately connected to the second wiring layer. The fourth wiring layer is not connected to the second wiring layer but is connected to the remaining electrode on one end side, and is alternately connected to the first wiring layer.

The wiring layers 29c and 29e are formed on the same side with respect to the resistance heating layers 25a to 25s arranged in series. The wiring layers 29d and 29f are formed on the same side with respect to the resistance heating layers 25a to 25e. On the other hand, the wiring layers 29c and 29d are formed on opposite sides of the resistance heating layers 25a to 25e. This is so that they do not cross each other.
By making the length, width, and thickness of each resistance heating layer equal, the amount of heat generated by each resistance heating layer can be made equal.

Next, a power supply circuit that supplies power to the heating element of FIG. 7 will be described.
8 and 9 are explanatory diagrams showing a second configuration example of the power supply circuit according to the present invention. The power supply and power supply terminals 31a and 31b shown in FIG. 8 are the same as those in FIG. Four switches similar to those in FIG. 6 are used.

  The power supply circuit connects the power source and the heating element 6 with the first and second connection patterns. FIG. 8 shows a first connection pattern, and FIG. 9 shows a second connection pattern. The first connection pattern shown in FIG. 8 is a connection pattern for fixing a sheet having a full width (large size). The second connection pattern shown in FIG. 9 is a connection pattern for fixing a small-sized sheet narrower than the full width size.

  In FIG. 8, the first power supply terminal 31a is connected to an electrode 27a as an end electrode on one end side, and is connected to electrodes 27q and 27s via a switch 33e and a wiring layer 29f. Further, the electrodes 27c, 27e, 27g, 27i, 27k, 27m, and 27o are connected to each other through the electrode 27a and the wiring layer 29d. The second power supply terminal 31b is connected to the electrode 27t as the end electrode on the other end side, and is connected to the electrodes 27b and 27d via the switch 33f and the wiring layer 29e. The electrodes 27f, 27h, 27j, 27l, 27n, 27p, and 27r are connected through the electrode 27f and the wiring layer 29c. The switches 33g and 33h are released.

  According to the first connection pattern of FIG. 8, odd-numbered electrodes 27a, 27c, 27e, 27g, 27i, 27k, 27m, 27o, 27q and 27s from one end side are connected to the power supply terminal 31a and from the other end side. The odd-numbered, ie, even-numbered electrodes 27b, 27d, 27f, 27h, 27j, 27l, 27n, 27p, 27r, and 27t from one end side are connected to the power supply terminal 31b. Therefore, in any of the resistance heating layers 25a to 25s, the electrodes at both ends are connected to the power supply terminals 31a and 31b to generate heat.

  On the other hand, according to the second connection pattern of FIG. 9, the first power supply terminal 31a is connected to the electrode 27a as the end electrode on one end side, and further, the electrodes 27c, 27e, 27g, 27i, 27k, 27m and 27o are connected. Further, it is connected to the electrodes 27b and 27d through the switch 33g and the wiring layer 29e. The second power supply terminal 31b is connected to an electrode 27t as an end electrode on the other end side, and is further connected to electrodes 27f, 27h, 27j, 27l, 27n, 27p, and 27r through a wiring layer 29c. Further, it is connected to the electrodes 27q and 27s through the switch 33h and the wiring layer 29f. The switches 33e and 33f are released.

  According to the second connection pattern of FIG. 9, the electrodes 27a, 27b, 27c, 27d, 27e arranged in order from one end side are connected to the power supply terminal 31a, and the electrodes 27g, 27i, 27k, 27m and 27o are connected to the power supply terminal 31a. On the other hand, the electrodes 27t, 27s, 27r, 27q, and 27p arranged in order from the other end side are connected to the power supply terminal 31b, and the electrodes 27n, 27l, 27j, 27h, and 27f arranged alternately from the electrode 27p are the power supply terminals. 31b. Therefore, in the resistance heating layers 25e to 25o closer to the center, the electrodes at both ends are connected to the power supply terminals 31a and 31b to generate heat.

  On the other hand, the resistance heating layers 25a to 25d near one end do not generate heat because no current flows because the electrodes at both ends are connected to the power supply terminal 31a. Similarly, the resistance heat generating layers 25p to 25s near the other end are not heated because no current flows because the electrodes on both ends are connected to the power supply terminal 31b.

  Switching between the first and second connection patterns is realized by switching on and off the switches 33e to 33h. The on / off of these switches is controlled according to the sheet size by the control unit described above.

  In this embodiment, the small size is composed of eleven resistance heating layers 25e to 25o, four resistance heating layers 25a to 25d are provided on one end side of the small size heating region, and four resistance heating layers are provided on the other end side. Each layer 25p-25s can be added to form a full width size.

  As is obvious to those skilled in the art, the total number of resistance heating layers is not limited to 19 in this embodiment, and can be increased or decreased if the total number is an odd number. The total number of resistance heating layers is 5 or more. The total number of electrodes provided at both ends of the resistance heating layer, that is, the total number of electrodes including the intermediate electrode layer and the end electrode layer is 6 or more. Therefore, when the total number of electrodes is 2 × M, M is an integer of 3 or more.

  Also, as is obvious to those skilled in the art, the number of resistance heating layers closer to the center is not limited to 11 in this embodiment, and the total number may be an odd number. It can be increased or decreased. By changing the boundary between the wiring layers 29d and 29f and changing the boundary between the wiring layers 29c and 29e, for example, the small size can be changed to nine resistance heating layers near the center or 13 resistance heating layers. Other numbers are also possible.

<< Fourth Embodiment of Heating Element and Power Supply Circuit >>
In each of the first to third embodiments, switching between the full width size and the small size is performed, but in the present invention, the number of sizes that can be switched can be further increased.
FIG. 10 is an explanatory diagram showing a fourth configuration example of the heating element and the power supply circuit according to the present invention. FIG. 10 shows a configuration example that can be switched to three types of sizes, full width size, medium size, and small size. For example, the full width size corresponds to the A4 longitudinal direction, the middle size corresponds to the B4 short direction, and the small size corresponds to the A4 short direction.

The substrate 21, the resistance heating layers 25a to 25s and the electrodes 27a to 27t are the same as the heating element 6 in FIG. The total number of electrodes is 19. What is different from FIG. 7 is the pattern of the wiring layer. 7 includes wiring layers 29c, 29d, 29g, 29h, 29i, and 29j.
Among them, the wiring layers 29c and 29d have the same pattern as in FIG. That is, the wiring layer 29c is connected to the electrodes 27f, 27h, 27j, 27l, 27n, 27p, 27r, and 27t. The wiring layer 29d is connected to the electrodes 27a, 27c, 27e, 27g, 27i, 27k, 27m, and 27o.

On the other hand, unlike FIG. 7, the wiring layer 29g is connected to the electrode 27d. The wiring layer 29h is connected to the electrode 27b, the wiring layer 29i is connected to the electrode 29q, and the wiring layer 29j is connected to the electrode 27s.
Wiring and switches for connecting to the power supply terminals 31a and 31b are arranged outside the heating element 6. There are eight switches from 33e to 33l. Both are controlled by the control unit.

  The electrode 27b can be connected to the power supply terminal 31a via the switch 33g, and can be connected to the power supply terminal 31b via the switch 33f. The electrode 27d can be connected to the power supply terminal 31a via the switch 33k, and can be connected to the power supply terminal 33b via the switch 33j. The electrode 27q can be connected to the power supply terminal 31a via the switch 33i, and can be connected to the power supply terminal 31b via the switch 33l. The electrode 27s can be connected to the power supply terminal 31a via the switch 33e, and can be connected to the power supply terminal 31b via the switch 33h.

When the control unit switches these switches, the region where the resistance heating layer generates heat can be switched to the full width size, the medium size, and the small size.
The concept of switching control is the same as in the first to third embodiments. Each electrode connected to the wiring layer 29d is always in conduction with the power supply terminal 31a. Each electrode connected to the wiring layer 29c is always in conduction with the power supply terminal 31b.

  In the above configuration, to generate heat of the full width size, the electrodes 27q and 27s may be connected to the power supply terminal 31a, and the electrodes 27b and 27d may be connected to the power supply terminal 31b. For this purpose, the switches 33i, 33e, 33f and 33j are closed, and the switches 33l, 33h, 33g and 33k are released.

  In order to switch to medium-sized heat generation, switching may be performed so that the electrode 27s is connected to the power supply terminal 31b and the electrode 27b is connected to the power supply terminal 31a. The electrode 27q is connected to the power supply terminal 31a, and the electrode 27d is kept connected to the power supply terminal 31b. For this purpose, the switches 33i, 33h, 33g and 33j are closed, and the switches 33l, 33e, 33f and 33k are released.

  In order to switch to small size heat generation, the electrodes 27q and 27s may be connected to the power supply terminal 31b and the electrodes 27b and 27d may be connected to the power supply terminal 31a. For this purpose, the switches 33l, 33h, 33g and 33k are closed, and the switches 33i, 33e, 33f and 33j are released. This is the state shown in FIG.

  The following embodiment shows a configuration example that can be switched to three kinds of sizes, full width size, medium size, and small size. As is obvious to those skilled in the art, if the number of wiring layers is increased, the switchable size can be increased from three types. Further, for example, by wiring the wiring layers 29g and 29i, or the wiring layers 29h and 29j with a plurality of electrodes arranged alternately, it is possible to adjust the width of the small size and / or medium size to be narrowed or widened. It is.

  The shape of the resistance heating layer may be determined as follows. The adjustable resistivity range is determined depending on the material used for the resistance heating layer. When forming a resistance heating layer using a printing technique, applicable materials are limited, and a glass paste containing silver and palladium is usually used. The resistivity range is determined by this. On the other hand, the amount of heat generated per unit length in the width direction is determined by the characteristics of the toner used, the specifications of the image forming apparatus, more specifically, the printing speed, the sheet conveyance speed, the warm-up time, and the like. The size and number of sizes to be switched are determined by the type of sheets handled by the image forming apparatus and the printing speed corresponding to each sheet size.

  Therefore, in order to satisfy these various conditions, the designer may determine the total number of resistance heating layers and the shape, ie, thickness, width, and length of each draft heating layer. According to the present invention, each size to be switched can be constituted by one or more resistance heating layers, and an appropriate number of resistance heating layers can be determined according to the size. Then, by making the resistance heating layer shapes substantially the same, it is possible to provide a heating element having stable heating characteristics with little variation.

≪Modification of fixing device≫
FIG. 11 is an explanatory view showing a configuration example different from FIG. 2 of the fixing device of the present invention.
In the fixing device of FIG. 11, a rotatable tension roller 15 is brought into contact with the fixing belt 5, and the heat conducting member 23 of the heating element 6 is brought into contact with a flat portion of the fixing belt 5. According to this configuration, the bending of the fixing belt 5 at the start and end points of the belt winding portion of the heat conducting member 23 is alleviated, and the durability of the belt is improved. Also, the slidability between the heat conducting member 23 and the fixing belt 5 is improved.

  The tension roller 15 preferably has a small heat capacity. Therefore, the tension roller 15 is made of a thin metal such as aluminum, SUS, or iron, or a core metal such as aluminum, SUS, or iron coated with a silicon sponge. In one example, the tension roller is an aluminum cored bar having an outer diameter φ of 12 millimeters and a thickness of 1 millimeter and covered with a silicon sponge.

  In addition to the embodiments described above, there can be various modifications of the present invention. These modifications should not be construed as not belonging to the scope of the present invention. The present invention should include the meaning equivalent to the scope of the claims and all modifications within the scope.

1: image forming apparatus 2: fixing unit 3: fixing roller 4: pressure roller 5: fixing belt 6: heating element 7a: heater lamp 10: first thermistor 11: second thermistor 12: fixing nip 13: sheet 14: Toner image 15: Tension roller 21: Substrate 23: Heat conducting members 25a, 25b, 25c, 25d, 25e,..., 25s: Resistance heating layers 27a, 27b, 27c, 25d, 27e, 27f,. Electrodes 29a, 29b, 29c, 29d,..., 29h: wiring layers 31a, 31b: power supply terminals 33a, 33b, 33c, 33d, 33e, 33f, 33g, 33h,. Visual image forming unit 52: second visible image forming unit 53: third visible image forming unit 54: fourth visible image forming unit 55: intermediate transfer belt 5 : Secondary transfer unit 57: internal feeding unit 58: manual feeding unit 59, 65, 66, 67: photoconductor 60: charging unit 61: developing unit 62: primary transfer unit 63: cleaning unit 64: laser light source 68 , 69: tension roller 70: waste toner box 71: fixing unit 72: pressure unit 73, 74: feeding roller

Claims (2)

A rotatable endless belt; first and second rollers that nipping and rotating the endless belt from both the inner and outer sides and conveying a sheet onto which a toner image has been transferred; A substrate extending in the width direction perpendicular to the rotation direction of the endless belt, (2) sandwiched between five or more odd number of resistance heating layers arranged in the width direction on the surface of the substrate, and (3) adjacent resistance heating layers. An intermediate electrode layer forming a common electrode for the resistance heating layer, (4) an end electrode layer provided on the opposite side to the intermediate electrode layer in the resistance heating layer at one end and the other end, and (5) connected to the intermediate electrode layer. And a heating element that supplies heat to the endless belt, and the wiring layer is formed on one side of the resistance heating layer in the rotation direction and on the other side. A second wiring layer formed on the first wiring The intermediate electrode layer is connected to every other intermediate electrode layer including the intermediate electrode layer on one end side of the central resistive heating layer, and the second wiring layer is on the other end side of the central resistive heating layer A fixing device connected to every other intermediate electrode layer including
A first wiring layer and the end electrode layer on one end side are connected to a first terminal of a power source, and a second wiring layer and the end electrode layer on the other end side are connected to a second terminal of a power source. And the first wiring layer and the end electrode layer on the other end side are connected to the first terminal of the power source, and the second wiring layer and the end electrode layer on the one end side are connected to the second terminal of the power source. A power supply circuit switchable to a second connection pattern connected to
A switching control unit that detects a size in the width direction of the sheet and switches to a first connection pattern when a large size is detected, and switches to a second connection pattern when a small size is detected. Image forming apparatus. A rotatable endless belt; first and second rollers that nipping and rotating the endless belt from both the inner and outer sides and conveying a sheet onto which a toner image has been transferred; A substrate extending in the width direction perpendicular to the rotation direction of the endless belt, (2) sandwiched between five or more odd number of resistance heating layers arranged in the width direction on the surface of the substrate, and (3) adjacent resistance heating layers. An intermediate electrode layer forming a common electrode for the resistance heating layer, (4) an end electrode layer provided on the opposite side of the intermediate heating layer in the resistance heating layer at one end and the other end, and (5) the intermediate electrode layer and the end A heating element that includes a wiring layer connected to the partial electrode layer and supplies heat to the endless belt, and the total number of the intermediate electrode layer and the end electrode layer is 2 × M (M is an integer of 3 or more) And the wiring layer has the resistance in the rotation direction. A first wiring layer formed on one side of the thermal layer, a second wiring layer formed on the other side, a third wiring layer formed on the same side as the first wiring layer, and a second wiring layer An intermediate electrode layer or end having a fourth wiring layer formed on the same side as the wiring layer, the first wiring layer being arranged every other line including the intermediate electrode layer on one end side of the central resistance heating layer MN intermediate electrode layers that are connected to N pieces (N is an integer larger than half of M and smaller than M) from the one end or the other end side among the total M pieces of partial electrode layers, and the third wiring layer remains. Alternatively, a total of M intermediate electrode layers or end electrode layers that are connected to the end electrode layer and that are arranged every other line including the intermediate electrode layer on the other end side of the central resistance heating layer are connected to the end electrode layer. Of these, N are connected from the other end or one end, and are connected to MN intermediate electrode layers or end electrode layers where the fourth wiring layer remains. A fixing device comprising:
A first connection pattern connecting the first and third wiring layers to the first terminal of the power supply and connecting the second and fourth wiring layers to the second terminal of the power supply; and the first and fourth wiring layers A power supply circuit capable of switching to a second connection pattern that connects the first and second wiring layers to the first terminal of the power source and connects the second and third wiring layers to the second terminal of the power source;
A switching control unit that detects a size in the width direction of the sheet and switches to a first connection pattern when a large size is detected, and switches to a second connection pattern when a small size is detected. Image forming apparatus.