Heater, fixing device, and image forming apparatus

Abstract

To suppress deformation of a substrate loaded with a heater.SOLUTION: A heater comprises: a substrate 54a; a heating element 54b1; a heating element 54b2 having almost the same length in a longer direction as the heating element 54b1; a heating element 54b3 having a shorter length in the longer direction than the heating element 54b1 and the heating element 54b2; and a heating element 54b4 having a shorter length in the longer direction than the heating element 54b3. The heating element 54b1, the heating element 54b2, the heating element 54b3 and the heating element 54b4 are arranged on the substrate 54a. The heating element 54b1 is arranged at one end side in a shorter direction of the substrate 54a, whereas the heating element 54b2 is arranged at the other end side in the shorter direction of the substrate 54a. The heating element 54b3 and the heating element 54b4 are arranged in between the heating element 54b1 and the heating element 54b2 in the shorter direction of the substrate 54a. A resistance value of the heating element 54b4 is larger than a resistance value of the heating element 54b3.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a heater, a fixing device and an image forming apparatus, and more particularly to a fixing device and a heater in an image forming apparatus that uses an electrophotographic recording method, such as a laser printer, a copier, or a facsimile. [Background technology]

[0002] The fixing device uses a heating element having a width (hereinafter referred to as maximum width) that is almost the same as the maximum width of the paper that can be conveyed (hereinafter referred to as paper passing) in the nip portion, and heats and fixes the unfixed toner image on the paper to the paper. Meanwhile, users use various sizes of paper, such as A4, B5, A5, etc. When using wide A4 paper, the paper passes through the entire area heated by the heating element having the widest heating element (hereinafter referred to as heating area), so the heating element and fixing device maintain a uniform temperature throughout. Meanwhile, when using narrow A5 paper, the paper does not pass through the entire heating area of ​​the heating element having the widest heating element. That is, the A5 paper passes through part of the heating area, but the A5 paper does not pass through part of the heating area. The area where the paper passes through in the heating area (hereinafter referred to as paper passing area) has a low temperature because heat is taken away by the paper. Meanwhile, the area where the paper does not pass through in the heating area (hereinafter referred to as non-paper passing area) has a high temperature (temperature rise) because heat is not taken away by the paper. This temperature rise in the non-paper passing area may cause image defects. Therefore, for narrow paper, the temperature rise in the non-paper passing area is suppressed by controlling the printer to reduce productivity in advance. In order to suppress this decrease in productivity, for example, in Patent Document 1, a wide heating element and a narrow heating element are provided in the heating element, and the narrow heating element is used when narrow paper is passed through. This reduces the temperature rise in the non-paper passing area, making it possible to maintain high productivity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-162909 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the unlikely event that a part of the device breaks down and excessive power is supplied to one of the heating elements, the substrate of the heating element (hereinafter referred to as the heating element substrate) may be significantly deformed due to a sudden rise in temperature of the heating element. When the heating element substrate is partially heated significantly, some parts experience a large rise in temperature and some parts experience a small rise in temperature. In the parts where the temperature rise is large, the heating element substrate stretches significantly. On the other hand, in the parts where the temperature rise is small, the heating element substrate does not stretch very much. The difference in the stretching between the different parts of the heating element substrate causes distortion (thermal stress) to occur in the heating element substrate. The greater the temperature rise or the temperature gradient occurring in the heating element substrate, the greater the distortion (thermal stress) occurring in the heating element substrate.

[0005] The present invention has been made under these circumstances, and has an object to suppress deformation of a substrate on which a heater is mounted. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0007] (1) A heater comprising a substrate, a first heating element, a second heating element having a longitudinal length substantially the same as that of the first heating element, a third heating element having a longitudinal length shorter than the first heating element and the second heating element, and a fourth heating element having a longitudinal length shorter than the third heating element, wherein the first heating element, the second heating element, the third heating element, and the fourth heating element are disposed on the substrate, the first heating element is disposed at one end side of the substrate in a short side direction, the second heating element is disposed at the other end side of the substrate in the short side direction, the third heating element and the fourth heating element are disposed between the first heating element and the second heating element in the short side direction of the substrate, and a resistance value of the fourth heating element is greater than a resistance value of the third heating element.

[0008] (2) A fixing device that fixes an unfixed toner image carried on a recording material, comprising: a heater; a first rotating body that is heated by the heater; and a second rotating body that forms a nip portion together with the first rotating body. The heater comprises a substrate, a first heating element, a second heating element having a length in a longitudinal direction substantially the same as that of the first heating element, a third heating element having a length in the longitudinal direction shorter than that of the first heating element and the second heating element, and a fourth heating element having a length in the longitudinal direction shorter than that of the third heating element. a fixing device characterized in that the first heating element, the second heating element, the third heating element, and the fourth heating element are arranged on the substrate, the first heating element is arranged on one end side of the substrate in the short side direction, the second heating element is arranged on the other end side of the substrate in the short side direction, the third heating element and the fourth heating element are arranged between the first heating element and the second heating element in the short side direction of the substrate, and a resistance value of the fourth heating element is greater than a resistance value of the third heating element.

[0009] (3) An image forming apparatus comprising: an image forming unit that forms an unfixed toner image on a recording material; and the fixing device according to (2) that fixes the unfixed toner image on the recording material. Effect of the Invention

[0010] According to the present invention, it is possible to suppress deformation of a substrate on which a heater is mounted. [Brief description of the drawings]

[0011] [Figure 1] Overall configuration diagram of an image forming apparatus according to embodiments 1 to 3 [Diagram 2] Control block diagram of an image forming apparatus according to first to third embodiments [Diagram 3] FIG. 1 shows a fixing device and a heater according to embodiments 1 to 3. [Figure 4] FIG. 1 shows a heater according to a first embodiment. [Diagram 5] FIG. 1 is a diagram showing a heater of Comparative Example 1 for comparison with Example 1. [Figure 6] FIG. 1 shows power supply to a heater in Example 1 and Comparative Example 1. [Figure 7] FIG. 1 shows a comparative verification result 1 between Example 1 and Comparative Example 1. [Figure 8] FIG. 2 shows comparative verification results 2 between Example 1 and Comparative Example 1. [Figure 9] FIG. 1 is a diagram showing a modified example of the heater of the first embodiment. [Figure 10] FIG. 1 is a diagram showing a modified example of the heater of the first embodiment. [Figure 11] FIG. 1 is a diagram showing a modified example of the heater of the first embodiment. [Figure 12] Graph showing the relationship between maximum current and power density in Example 2 [Figure 13] Graph showing cross-sectional view of fixing device of Example 3 and corresponding nip pressure DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following examples, passing a sheet through a fixing nip is referred to as "passing the sheet." In addition, an area where the heating element is generating heat and where the sheet does not pass is referred to as a non-sheet passing area (or non-sheet passing section), and an area where the sheet passes is referred to as a sheet passing area (or sheet passing section). Furthermore, a phenomenon in which the temperature of the non-sheet passing area becomes higher than that of the sheet passing area is referred to as non-sheet passing section temperature rise. EXAMPLES

[0013] [Image forming device] Fig. 1 is a configuration diagram showing an in-line type color image forming apparatus, which is an example of an image forming apparatus equipped with the fixing device of the first embodiment. The operation of the electrophotographic type color image forming apparatus will be described with reference to Fig. 1. The first station is a station for forming a yellow (Y) toner image, and the second station is a station for forming a magenta (M) toner image. The third station is a station for forming a cyan (C) toner image, and the fourth station is a station for forming a black (K) toner image.

[0014] In the first station, the photosensitive drum 1a, which is an image carrier, is an OPC photosensitive drum. The photosensitive drum 1a is a metal cylinder on which multiple layers of functional organic materials, such as a carrier generation layer that is photosensitive to light and generates charges, and a charge transport layer that transports the generated charges, are laminated, and the outermost layer has low electrical conductivity and is almost insulated. A charging roller 2a, which is a charging means, is abutted against the photosensitive drum 1a, and as the photosensitive drum 1a rotates, it uniformly charges the surface of the photosensitive drum 1a while rotating in accordance with the rotation of the photosensitive drum 1a. A voltage in which a DC voltage or an AC voltage is superimposed is applied to the charging roller 2a, and the photosensitive drum 1a is charged by generating discharge in a small air gap on the upstream and downstream sides of the rotation direction from the nip portion between the charging roller 2a and the surface of the photosensitive drum 1a. The cleaning unit 3a is a unit that cleans toner remaining on the photosensitive drum 1a after transfer, which will be described later. The developing unit 8a, which is a developing means, is composed of a developing roller 4a, a non-magnetic one-component toner 5a, and a developer coating blade 7a. The photosensitive drum 1a, the charging roller 2a, the cleaning unit 3a, and the developing unit 8a are integrated into a process cartridge 9a that is detachably attached to the image forming apparatus.

[0015] The exposure device 11a, which is an exposure means, is composed of a scanner unit or an LED (light-emitting diode) array that scans laser light using a polygon mirror, and irradiates the photosensitive drum 1a with a scanning beam 12a modulated based on an image signal. The charging roller 2a is connected to a charging high voltage power supply 20a, which is a voltage supply means to the charging roller 2a. The developing roller 4a is connected to a developing high voltage power supply 21a, which is a voltage supply means to the developing roller 4a. The primary transfer roller 10a is connected to a primary transfer high voltage power supply 22a, which is a voltage supply means to the primary transfer roller 10a. The above is the configuration of the first station, and the second, third, and fourth stations have the same configuration. For the other stations, parts having the same functions as the first station are given the same reference numerals, and the suffixes b, c, and d are added to the reference numerals for each station. In the following description, the suffixes a, b, c, and d are omitted except when a specific station is described.

[0016] The intermediate transfer belt 13 is supported by three rollers, a secondary transfer counter roller 15, a tension roller 14, and an auxiliary roller 19, as tension members. A force in a direction to stretch the intermediate transfer belt 13 is applied only to the tension roller 14 by a spring, so that an appropriate tension force is maintained on the intermediate transfer belt 13. The secondary transfer counter roller 15 rotates by receiving a rotation drive from a main motor (not shown), and the intermediate transfer belt 13 wound around the outer periphery rotates. The intermediate transfer belt 13 moves at approximately the same speed in a forward direction (for example, clockwise direction in FIG. 1) as the photosensitive drums 1a to 1d (for example, rotating counterclockwise in FIG. 1). The intermediate transfer belt 13 also rotates in the direction of the arrow (clockwise direction), and the primary transfer roller 10 is disposed on the opposite side of the photosensitive drum 1 with the intermediate transfer belt 13 in between, and rotates following the movement of the intermediate transfer belt 13. The position where the photosensitive drum 1 and the primary transfer roller 10 are in contact with each other across the intermediate transfer belt 13 is called the primary transfer position. The auxiliary roller 19, the tension roller 14, and the secondary transfer opposing roller 15 are electrically grounded. Note that the primary transfer rollers 10b to 10d in the second to fourth stations have the same configuration as the primary transfer roller 10a in the first station, so a description thereof will be omitted.

[0017] Next, the image forming operation of the image forming apparatus of the first embodiment will be described. When the image forming apparatus receives a print command in a standby state, it starts the image forming operation. The photosensitive drum 1, the intermediate transfer belt 13, etc. start to rotate in the direction of the arrow at a predetermined process speed by a main motor (not shown). The photosensitive drum 1a is uniformly charged by the charging roller 2a to which a voltage is applied by the charging high-voltage power supply 20a, and then an electrostatic latent image according to image information is formed by the scanning beam 12a irradiated from the exposure device 11a. The toner 5a in the developing unit 8a is negatively charged by the developer application blade 7a and applied to the developing roller 4a. Then, a predetermined developing voltage is supplied to the developing roller 4a from the developing high-voltage power supply 21a. When the photosensitive drum 1a rotates and the electrostatic latent image formed on the photosensitive drum 1a reaches the developing roller 4a, the electrostatic latent image is visualized by the negative toner adhering thereto, and a toner image of a first color (for example, Y (yellow)) is formed on the photosensitive drum 1a. The stations (process cartridges 9b-9d) for the other colors M (magenta), C (cyan), and K (black) operate in the same way. Electrostatic latent images are formed on the photosensitive drums 1a-1d by exposure while delaying the write start signal from a controller (not shown) at a fixed timing according to the distance between the primary transfer positions of each color. A high DC voltage of the opposite polarity to the toner is applied to each of the primary transfer rollers 10a-10d. Through the above process, the toner images are transferred in order to the intermediate transfer belt 13 (hereinafter referred to as primary transfer), and a multiple toner image is formed on the intermediate transfer belt 13.

[0018] Thereafter, in accordance with the formation of the toner image, the paper P, which is a recording material loaded in the cassette 16, is fed (picked up) by a paper feed roller 17 that is driven to rotate by a paper feed solenoid (not shown). The fed paper P is conveyed to a registration roller (hereinafter referred to as a registration roller) 18 by a conveying roller. The paper P is conveyed to a transfer nip portion, which is a contact portion between the intermediate transfer belt 13 and a secondary transfer roller 25, by the registration roller 18 in synchronization with the toner image on the intermediate transfer belt 13. A voltage of the opposite polarity to that of the toner is applied to the secondary transfer roller 25 by a secondary transfer high voltage power source 26, and the four-color multi-layered toner image carried on the intermediate transfer belt 13 is transferred collectively onto the paper P (onto the recording material) (hereinafter referred to as secondary transfer). Members (e.g., the photosensitive drum 1, etc.) that contributed to the formation of an unfixed toner image on the paper P function as image forming means. Meanwhile, after the secondary transfer is completed, the toner remaining on the intermediate transfer belt 13 is cleaned by a cleaning unit 27. After the secondary transfer is completed, the paper P is transported to a fixing device 50, which is a fixing means, and after the toner image is fixed, the paper P is discharged as an image formed product (print, copy) onto a discharge tray 30. The film 51, nip forming member 52, pressure roller 53, and heater 54 of the fixing device 50 will be described later.

[0019] [Block diagram of image forming device] 2 is a block diagram for explaining the operation of the image forming apparatus, and the printing operation of the image forming apparatus will be explained with reference to this diagram. The host computer PC110 outputs a print command to a video controller 91 inside the image forming apparatus, and is responsible for transferring image data of the print image to the video controller 91.

[0020] The video controller 91 converts image data from the PC 110 into exposure data and transfers it to an exposure control device 93 in the engine controller 92. The exposure control device 93 is controlled by a CPU 94, and turns on and off the exposure data and controls the exposure device 11. When the CPU 94, which is a control means, receives a print command, it starts an image formation sequence.

[0021] The engine controller 92 is equipped with a CPU 94, a memory 95, etc., and performs pre-programmed operations. The high voltage power supply 96 is composed of the charging high voltage power supply 20, the developing high voltage power supply 21, the primary transfer high voltage power supply 22, and the secondary transfer high voltage power supply 26 described above. The power control unit 97 is composed of a bidirectional thyristor (hereinafter referred to as a triac) 56, a heating element switch 57 as a switching means for exclusively selecting a heating element to which power is supplied, etc. The power control unit 97 selects a heating element that generates heat in the fixing device 50 and determines the amount of power to be supplied. The drive unit 98 is composed of a main motor 99, a fixing motor 100, etc. The sensor 101 is composed of a fixing temperature sensor 59 that detects the temperature of the fixing device 50, a paper presence / absence sensor 102 that has a flag and detects the presence or absence of paper P, etc., and the detection result of the sensor 101 is transmitted to the CPU 94. The CPU 94 obtains the detection result of the sensor 101 in the image forming apparatus, and controls the exposure device 11, the high voltage power supply 96, the power control unit 97, and the drive unit 98. As a result, the CPU 94 performs processes such as forming an electrostatic latent image, transferring the developed toner image, and fixing the toner image onto the paper P, thereby controlling the image forming process in which the exposure data is printed as a toner image on the paper P. Note that the image forming apparatus to which the present invention is applied is not limited to the image forming apparatus having the configuration described in Fig. 1, but may be any image forming apparatus capable of printing on paper P of different widths and equipped with a fixing device 50 having a heater 54 described later.

[0022] [Fixing device] The cross section of the fixing device 50 used in the first embodiment is shown in FIG. 3(a), and the back side of the heater 54 is shown in FIG. 3(b). The details will be described below. The fixing device 50 is composed of a cylindrical film 51, a pressure roller 53 that forms a fixing nip N together with the film 51, a heater 54 as a heating body, a nip forming member 52 that holds the heater 54, and a stay 60 for maintaining strength in the longitudinal direction. The film 51, which is a first rotating body, is composed of a 200 μm-thick silicone rubber layer on a 50 μm-thick polyimide base material, and a 20 μm-thick PFA release layer on the silicone rubber layer. The pressure roller 53, which is a second rotating body, is composed of a SUM core metal with an outer diameter of 13 mm, a 3.5 mm-thick silicone rubber elastic layer on the silicone rubber layer, and a 40 μm-thick PFA release layer on the silicone rubber layer. The pressure roller 53 is rotated by a driving source (not shown), and the film 51 is driven by the pressure roller 53 to rotate.

[0023] The heater 54 is provided so as to contact the inner surface of the film 51, and is held by the nip forming member 52, so that the inner circumferential surface of the film 51 and the surface of the heater 54 are in contact with each other. Here, the surface of the heater 54 on which the heating elements 54b1 to 54b4 described later are provided is the front surface, and the surface on which the thermoswitch 58 described later and the like are provided is the back surface. The stay 60 is pressurized at both ends by means not shown, and the pressure roller 53 receives the pressure via the nip forming member 52 and the film 51. As a result, the fixing nip N is formed where the film 51 and the pressure roller 53 are pressed and come into contact with each other. The nip forming member 52 must have rigidity, heat resistance, and heat insulation properties, and is made of a liquid crystal polymer. On the back surface of the heater 54, as shown in FIG. 3(b), a thermoswitch 58 as a safety element and a fixing temperature sensor 59 such as a thermistor as a temperature detection means are arranged in contact with each other.

[0024] The thermoswitch 58 disposed on the rear surface of the heater 54 is, for example, a bimetal thermoswitch, and the heater 54 and the thermoswitch 58 are electrically connected. When the thermoswitch 58 detects that the temperature of the rear surface of the heater 54 has risen excessively (hereinafter referred to as excessive temperature rise), the bimetal inside the thermoswitch 58 operates and can cut off the power supplied to the heater 54. The fixing temperature sensor 59 disposed on the rear surface of the heater 54 is a chip resistor type thermistor. The fixing temperature sensor 59 detects the chip resistance, and the detection result is used to control the temperature of the heater 54. The fixing temperature sensor 59 can also detect excessive temperature rise.

[0025] [heater] FIG. 4 shows the configuration of the heater 54 of the first embodiment, and will be described in detail below. The substrate 54a is a plate-shaped ceramic substrate made of alumina or the like, and has dimensions of, for example, a thickness t of 1 mm, a width W of 6.3 mm, and a length l of 280 mm. Heating elements 54b1, 54b2, 54b3, and 54b4, a conductor 54c which is a conductive path, and contacts 54d1, 54d2, 54d3, and 54d4 for supplying power are formed on the substrate 54a by a printing process. Hereinafter, the heating elements 54b1 to 54b4 may be collectively referred to as heating element 54b. In FIG. 4, the heating element 54b is shown in white, the conductor 54c is shown with diagonal lines, and the contacts 54d1 to 54d4 are shown in black.

[0026] The heating elements 54b are arranged at equal intervals in the order of the heating element 54b1 having the longest length in the longitudinal direction (hereinafter also referred to as width), the heating element 54b3 having the second widest width, the heating element 54b4 having the third widest width, and the heating element 54b2 having the widest width. The heating elements 54b1 and 54b2 have approximately the same width. The interval between the heating elements 54b is, for example, 0.7 mm in the first embodiment. The dimensions of the heating elements 54b1 and 54b2 in the first embodiment are, for example, a thickness t=10 μm, a width W=0.7 mm, and a length l=222 mm. The dimensions of the heating element 54b3 in the first embodiment are, for example, a thickness t=10 μm, a width W=0.7 mm, and a length l=188 mm. The dimensions of the heating element 54b4 in the first embodiment are, for example, a thickness t=10 μm, a width W=0.7 mm, and a length l=154 mm.

[0027] Heating elements 54b1 and 54b2 have a length l of 222 mm and are used when printing A4 paper with a width of 210 mm. Heating element 54b3 has a length l of 188 mm and is used when printing B5 paper with a width of 182 mm. Heating element 54b4 has a length l of 154 mm and is used when printing A5 paper with a width of 148.5 mm.

[0028] The heating element 54b is made of a conductive material mainly composed of silver and palladium, and the conductor 54c and the contacts 54d1 to 54d4 are made of a conductive material mainly composed of silver. The electrical resistance between both ends of the heating element 54b in the longitudinal direction is 20Ω for the longest heating elements 54b1 and 54b2, 30Ω for the second longest heating element 54b3, and 30Ω for the third longest heating element 54b4. One end of the longest heating elements 54b1 and 54b2 is electrically connected to a common contact 54d1, and the other end is electrically connected to a common contact 54d2. The combined electrical resistance of the longest heating elements 54b1 and 54b2 between the contacts 54d1 and 54d2 is 10Ω because the heating elements 54b1 and 54b2 are connected in parallel. Thus, the combined resistance of heating elements 54b1 and 54b2 is 10Ω, which is smaller than the resistance (30Ω) of heating elements 54b3 and 54b4.

[0029] As described above, the heater 54 includes the first heating element 54b1 and the second heating element 54b2, which has a length in the longitudinal direction substantially equal to that of the heating element 54b1. The heater 54 further includes the third heating element 54b3, which has a length in the longitudinal direction shorter than the heating elements 54b1 and 54b2, and the fourth heating element 54b4. The heating element 54b1 is provided at one end of the substrate 54a in the lateral direction, and the heating element 54b2 is provided at the other end of the substrate 54a in the lateral direction. The heating elements 54b3 and 54b4 are provided between the heating elements 54b1 and 54b2 in the lateral direction of the substrate 54a.

[0030] In the first embodiment, the contact 54d1, which is the first contact, is a contact to which one ends of the heating elements 54b1 and 54b2 are electrically connected. The contact 54d2, which is the second contact, is a contact to which the other ends of the heating elements 54b1, 54b2, and 54b3 are electrically connected. The contact 54d3, which is the third contact, is a contact to which one ends of the heating elements 54b3 and 54b4 are electrically connected. The contact 54d4, which is the fourth contact, is a contact to which the other end of the heating element 54b4 is electrically connected.

[0031] In the first embodiment, the width W of each of the heating elements 54b is set to the same width of 0.7 mm, but depending on the performance required for the fixing device 50, it may be difficult to select a conductive material for forming the heating elements 54b with the same width W. In that case, the width W of the heating elements 54b may be varied depending on the performance required for the fixing device 50.

[0032] (Regarding heating elements 54b1 and 54b2) The characteristics of the heating elements 54b1 and 54b2 with the longest width in the heater 54 described above will be described below. If the fixing device 50 can reach a sufficiently heated state where fixing is possible (hereinafter also referred to as a paper passing state) as quickly as possible, printed matter can be provided to the user as quickly as possible. For this reason, it is preferable to maximize the power supply capacity of the longest heating elements 54b1 and 54b2 capable of heating the entire area in the longitudinal direction so that any size of paper P can be selected. The heating elements 54b3 and 54b4, which have a shorter longitudinal length than the longest heating elements 54b1 and 54b2, are used after the fixing device 50 is sufficiently heated by the longest heating elements 54b1 and 54b2. Therefore, since it is only necessary to supplement the amount of power required to fix the toner image to the paper P when the paper is passed, when the heating elements 54b3 and 54b4 are used, it is preferable to set the power supply capacity to be lower than the high power supply capacity of the longest heating elements 54b1 and 54b2.

[0033] The fact that the longest heating elements 54b1 and 54b2 have a high power supply capacity means that there is a high risk of deformation of the substrate 54a in the unlikely event of an equipment failure in which excessive power is supplied to the longest heating elements 54b1 and 54b2. In the first embodiment, the longest heating elements 54b1 and 54b2 are configured as two pieces, with one heating element 54b1 being disposed at one end in the short side direction of the substrate 54a, and the other heating element 54b2 being disposed at the other end in the short side direction of the substrate 54a. As a result, the two longest heating elements 54b1 and 54b2 are disposed symmetrically in the short side direction of the substrate 54a.

[0034] Furthermore, the heating elements 54b1, 54b2 are electrically connected by common contacts 54d1, 54d2, so that the two heating elements 54b1, 54b2 are always supplied with power at approximately the same time. As a result, when power is supplied to the longest heating element 54b1, 54b2, both ends in the short side direction of the heater 54 always generate heat, so that the amount of supplied power can be dispersed and the temperature gradient of the substrate 54a in the short side direction can be reduced.

[0035] As a result, the fixing device 50 can reach a state in which paper can pass through in a short time, and even if an apparatus malfunction occurs and an excessive power supply state occurs, the temperature gradient in the short direction of the substrate 54a can be reduced, thereby reducing the risk of deformation of the substrate 54a.

[0036] (Regarding heating elements 54b3 and 54b4) Next, the characteristics of the two types of heating elements 54b3 and 54b4 that are not the longest will be described below. One end of the heating element 54b3 and the heating element 54b4 is electrically connected by one contact 54d3. On the other hand, the other end of the heating element 54b3 and the heating element 54b4 is electrically connected to a contact 54d2, and the heating element 54b4 is electrically connected to a contact 54d4. In other words, the heating element 54b3 and the heating element 54b4 are configured so that one of them generates heat.

[0037] As described above, the heating element 54b3 is used when printing B5 paper, and the heating element 54b4 is used when printing A5 paper. The width of the paper P (hereinafter referred to as the paper width) and the longitudinal length of the heating elements 54b3 and 54b4 are almost the same length, and the paper P passes through most of the area where the heating elements 54b3 and 54b4 generate heat (hereinafter referred to as the heat generation area). Therefore, most of the heat generated by the heating elements 54b3 and 54b4 can be given to the paper P, so that the temperature rise of the non-paper passing area where the paper P does not pass can be suppressed. This makes it possible to maintain high productivity. In addition, since the longest heating elements 54b1 and 54b2 are responsible for heating the fixing device 50 to a paper passing state, the non-longest heating elements 54b3 and 54b4 only need to supplement the amount of power required to fix the toner image to the paper P when the paper passes. Therefore, the power supply capacity of the heating elements 54b3, 54b4 that are not the longest can be reduced, and the degree of temperature rise of the heating elements 54b3, 54b4 in the event of an abnormality can be reduced.

[0038] In addition, the above-mentioned two types of heating elements 54b3 and 54b4 are arranged between the two longest heating elements 54b1 and 54b2, and the heating elements 54b3 and 54b4 are arranged as close as possible to the center in the short side direction of the substrate 54a. This makes it possible to raise the temperature of both the first end, which is one end in the short side direction of the substrate 54a, and the second end, which is the other end, to the same extent, and to reduce the temperature gradient of the substrate 54a in the short side direction.

[0039] From the above, the power supply capacity of the non-longest heating elements 54b3 and 54b4 is reduced, and the non-longest heating elements 54b3 and 54b4 are arranged as symmetrically as possible in the short-side direction of the substrate 54a. This reduces the temperature gradient in the short-side direction of the substrate 54a even if an excessive power supply state occurs due to an equipment failure, so that the risk of deformation of the substrate 54a can be reduced. In addition, by providing only the longest heating elements 54b1 and 54b2, which require high power supply capacity, with two, and providing the non-longest heating elements 54b3 and 54b4 with only one, which is the minimum required, while taking into consideration symmetry in the short-side direction, it is possible to achieve both miniaturization of the dimensions of the substrate 54a.

[0040] [Comparative Example] Fig. 5 shows heater 200 in Comparative Example 1, and the detailed configuration will be described below. Substrate 207 is a plate-shaped ceramic substrate made of alumina or the like, and has dimensions of thickness t = 1 mm, width W = 6.3 mm, and length l = 280 mm. Heating elements 201, 202, conductor 254, and contacts 203, 204, 205, and 206 are formed on substrate 207 by a printing process. In Fig. 5, heating elements 201, 202 are shown in white, conductor 254 is shown with diagonal lines, and contacts 203 to 206 are shown in black.

[0041] In the heater 200, two heating elements, the heating element 201 with the longest width and the heating element 202 with the second longest width, are arranged on the substrate 207 with a gap of 3.5 mm between them. The dimensions of the heating element 201 are thickness t=10 μm, width W=0.7 mm, and length l=222 mm. The dimensions of the heating element 202 are thickness t=10 μm, width W=0.7 mm, and length l=188 mm. The heating element 201 is used when printing A4 (width 210 mm) paper, and the heating element 202 is used when printing B5 (width 182 mm) paper. The electrical resistance between both ends of the heating elements 201 and 202 in the longitudinal direction is 10 Ω for the heating element 201 with the longest width, and 30 Ω for the heating element 202 with the second longest width. The longest length of heating element 201 is electrically connected at both ends to junctions 203 , 204 via conductors 254 , and the second length of heating element 202 is electrically connected at both ends to junctions 205 , 206 via conductors 254 .

[0042] [Example 1 and Comparative Example 1] FIG. 6(a) shows a power supply circuit of Example 1, and FIG. 6(b) shows a power supply circuit of Comparative Example 1. Using these circuits, a comparative verification between Example 1 and Comparative Example 1 is performed. Each power supply circuit will be described below. In Example 1 of FIG. 6(a), contacts 54d1 to 54d4 are connected to a heating element switch 57 for switching the power supply path. Note that, since the heating element switch 57 switches the power supply path to switch the heating element 54b that generates heat, switching the power supply path is also expressed as switching the heating element 54b. In Example 1, the heating element switch 57 is specifically electromagnetic relays 57a and 57b having a C-contact configuration.

[0043] The electromagnetic relay 57a has a contact 57a1 connected to a first pole of the AC power supply 55 via the triac 56, a contact 57a2 connected to the contact 54d1, and a contact 57a3 connected to the contact 54d3. The electromagnetic relay 57a is controlled by the engine controller 92 to be in one of two states: a state in which the contact 57a1 and the contact 57a2 are connected, and a state in which the contact 57a1 and the contact 57a3 are connected. The electromagnetic relay 57b has a contact 57b1 connected to a second pole of the AC power supply 55, a contact 57b2 connected to the contact 54d2, and a contact 57b3 connected to the contact 54d4. The electromagnetic relay 57b is controlled by the engine controller 92 to be in one of two states: a state in which the contact 57b1 and the contact 57b2 are connected, and a state in which the contact 57b1 and the contact 57b3 are connected.

[0044] 6(a) shows the state in which the electromagnetic relays 57a and 57b are not in operation, with the contacts 57a1 and 57a2 of the electromagnetic relay 57a being connected, and the contacts 57b1 and 57b2 of the electromagnetic relay 57b being connected. When the electromagnetic relays 57a and 57b are not in operation, power is supplied between the contacts 54d1 and 54d2, so that the longest heating elements 54b1 and 54b2 generate heat.

[0045] When the electromagnetic relays 57a and 57b are operated, the contacts 57a1 and 57a3 of the electromagnetic relay 57a are connected, and the contacts 57b1 and 57b3 of the electromagnetic relay 57b are connected. When the electromagnetic relays 57a and 57b are operated, power is supplied between the contacts 54d3 and 54d4, so only the heating element 54b4 generates heat. When only the electromagnetic relay 57a is operated, the contacts 57a1 and 57a3 of the electromagnetic relay 57a are connected, and the contacts 57b1 and 57b2 of the electromagnetic relay 57b are connected. When only the electromagnetic relay 57a is operated, power is supplied between the contacts 54d3 and 54d2, so only the heating element 54b3 generates heat.

[0046] In the comparative example 1 of FIG. 6(b), the contacts 203 to 206 are connected to electromagnetic relays 208 and 209 having a C-contact configuration, which are heating element switches for switching the power supply path. The electromagnetic relay 208 has a contact 208a connected to a first pole of the AC power source 55 via the triac 56, a contact 208b1 connected to the contact 203, and a contact 208b2 connected to the contact 205. The electromagnetic relay 208 is in either one of a state in which the contact 208a and the contact 208b1 are connected and a state in which the contact 208a and the contact 208b2 are connected, under the control of the engine controller 92. The electromagnetic relay 209 has a contact 209a connected to a second pole of the AC power source 55, a contact 209b1 connected to the contact 204, and a contact 209b2 connected to the contact 206. Under the control of the engine controller 92, the electromagnetic relay 209 is placed in one of two states: a state in which the contact 209a is connected to the contact 209b1, and a state in which the contact 209a is connected to the contact 209b2.

[0047] 6(b) shows the state when electromagnetic relays 208 and 209 are not operating, in which electromagnetic relay 208 has contact 208a connected to contact 208b1, and electromagnetic relay 209 has contact 209a connected to contact 209b1. When electromagnetic relays 208 and 209 are not operating, power is supplied between contact 203 and contact 204, so that longest heating element 201 generates heat.

[0048] When electromagnetic relays 208 and 209 are operated, electromagnetic relay 208 connects contacts 208a and 208b2, and electromagnetic relay 209 connects contacts 209a and 209b2. When electromagnetic relays 208 and 209 are operated, power is supplied between contacts 205 and 206, so that only heating element 202 generates heat. Note that the electromagnetic relay may be a contact switch such as an electromagnetic relay with an a-contact configuration or an electromagnetic relay with a b-contact configuration, or a contactless switch such as a solid state relay (SSR), photoMOS relay, or triac.

[0049] [Temperature gradient in Example 1 and Comparative Example 1] (i) In order to estimate the amount of deformation of the substrate when excessive power is supplied to the heating element, the temperature profile of the back of the substrate (position indicated by line A-A') 3 seconds after power application was measured when an AC voltage of 100 V was continuously applied to the heating element in each of Example 1 and Comparative Example 1. The greater the difference between the maximum and minimum values ​​of the temperature profile, the higher the risk of substrate deformation.

[0050] FIG. 7 shows Example 1, Comparative Example 1, etc. in the first column, and the heating pattern of the heater in the second column. Note that the heating element to which power is supplied is shown with vertical stripes. FIG. 7 shows the difference between the maximum and minimum values ​​of the temperature profile (hereinafter referred to as the temperature difference) in the third column, and shows the rear temperature profile (substrate rear temperature profile) corresponding to the position indicated by the line A-A' on the substrate in the fourth column. In the graph of the temperature profile, the horizontal axis indicates the short side direction (temperature short side) [mm] of the substrate, and the vertical axis indicates the temperature (substrate rear temperature) [°C]. Note that symbols are omitted in the figure of the heating pattern for ease of viewing. Note that in the graph of Example 1, Example 1(1) is shown with a solid line, Example 1(2) is shown with a dotted line, and Example 1(3) is shown with a dashed line. Also, in the graph of Comparative Example 1, Comparative Example 1(1) is shown with a solid line, and Comparative Example 1(2) is shown with a dashed line.

[0051] Moreover, Example 1(1) shows a case where power is supplied to the two longest heating elements 54b1 and 54b2 corresponding to A4 paper. Example 1(2) shows a case where power is supplied to the second longest heating element 54b3 corresponding to B5 paper. Example 1(3) shows a case where power is supplied to the shortest heating element 54b4 corresponding to A5 paper. Comparative Example 1(1) shows a case where power is supplied to the longest heating element 201 corresponding to A4 paper, and Comparative Example 1(2) shows a case where power is supplied to the second longest heating element 202 corresponding to B5 paper.

[0052] (Example 1(1)) In Example 1(1), the maximum temperature on the back of the substrate 54a reached 472°C near the heating element 54b1 or heating element 54b2, and the minimum temperature was 391°C between the two heating elements 54b1 and 54b2. The difference between the maximum and minimum temperatures was 81°C, and the temperature gradient in the substrate 54a was small. The longest heating elements 54b1 and 54b2 in Example 1(1) were configured as two elements to distribute the amount of power, and were arranged symmetrically at both ends of the short side of the substrate 54a, and the contacts 54d1 and 54d2 were shared so that the two heating elements 54b1 and 54b2 always generated heat at the same time. This made it possible to reduce the temperature gradient generated in the substrate 54a.

[0053] (Example 1(2)) In Example 1(2), the maximum temperature on the back of substrate 54a reached 271°C near heating element 54b3, and the minimum temperature was 174°C at the end in the short side direction farther from heating element 54b3. The difference between the maximum and minimum temperatures was 97°C, and the temperature gradient in substrate 54a was small. In Example 1(2), the second longest heating element 54b3 was arranged with the minimum necessary power supply capacity and in the approximate center of the short side direction of substrate 54a so as to be as symmetrical as possible with heating element 54b4, thereby making it possible to reduce the temperature gradient occurring in substrate 54a.

[0054] (Example 1(3)) In Example 1(3), the maximum temperature on the back of substrate 54a reached 316°C in the vicinity of heating element 54b4, and the minimum temperature was 196°C at the end in the short direction farther from heating element 54b4. The difference between the maximum and minimum temperatures was 120°C. For the same reasons as those explained in Example 1(2), it was possible to reduce the temperature gradient occurring in substrate 54a.

[0055] (Comparative Example 1(1)) In Comparative Example 1(1), the maximum temperature on the back of substrate 207 reached 673°C near heating element 201, and the minimum temperature was 208°C at the end in the short side direction farther from heating element 201. The difference between the maximum and minimum temperatures was 465°C, and the temperature gradient in substrate 207 was large. In Comparative Example 1(1), there was only one longest heating element 201 that provided the maximum power supply capacity, and it was disposed at one end in the short side direction of substrate 207, resulting in a large temperature rise at one end.

[0056] (Comparative Example 1(2)) In Comparative Example 1(2), the maximum temperature on the back of substrate 207 reached 341°C in the vicinity of heating element 202, and the minimum temperature was 136°C at the end in the short side direction farther from heating element 202. The difference between the maximum and minimum temperatures was 205°C, and the temperature gradient in substrate 207 was large. Since heating element 202 has a lower power supply capacity than heating element 201 in Comparative Example 1(1), the temperature gradient was smaller than in Comparative Example 1(1). However, since heating element 202 is disposed at one end in the short side direction of substrate 207, the temperature rise at one end was large.

[0057] From the above, the maximum temperature difference in Example 1 is 120°C as shown in Example 1(3), whereas the maximum temperature difference in Comparative Example 1 is 465°C as shown in Comparative Example 1(1), and the temperature difference in Comparative Example 1 is more than three times larger than that in Example 1. The substrate elongates more in the high temperature portion and less in the low temperature portion, and the substrate deforms due to the difference in the amount of elongation. In Example 1, the temperature difference is 120°C or less for any heating element 54b, which is sufficiently smaller than that in Comparative Example 1, and it was confirmed that the risk of deformation of substrate 54a is small. Even if the material and dimensions of the substrate are changed, the same effect can be obtained by adopting the configuration shown in Example 1.

[0058] [Productivity of Example 1 and Comparative Example 1] (ii) Figure 8 shows the results of confirming the maximum productivity for B5 paper and A5 paper in Example 1 and Comparative Example 1. Figure 8 shows Example 1 and Comparative Example 1 in the first column, and the heating element patterns in the second column. The heating element patterns also show the widths of B5 paper and A5 paper. Figure 8 shows the maximum productivity when B5 paper is printed continuously in the third column, and the maximum productivity when A5 paper is printed continuously in the fourth column.

[0059] The conditions of the image forming apparatus and the fixing device when checking the productivity are as follows. The paper P that is printed first is hereinafter referred to as the preceding paper, and the succeeding paper that is printed after the paper P is hereinafter referred to as the succeeding paper. The interval between the rear end of the preceding paper and the front end of the succeeding paper is hereinafter also referred to as the paper interval. The image process speed of the image forming apparatus is 200 mm / sec, the interval (paper interval) between the preceding paper and the succeeding paper is 50 mm (0.4 seconds), and the same size of paper P is continuously passed through while maintaining maximum productivity. The paper is passed through while controlling the temperature by the engine controller 92 so that the rear of the substrate is 180°C by the fixing temperature sensor 59 installed on the rear of the substrate. The paper P is B5 (width 182 mm × length 257 mm × thickness 92 μm, basis weight 68 g / m 2 ) size Canon CS680, A5 (width 148.5 mm x length 210 mm x thickness 83 μm, basis weight 64 g / m 2 A Canon PBPAPER of size 100 mm was used. The temperature of the film 51 in the non-paper passing area where the paper P does not pass during paper passing was measured, and if the temperature exceeded 200°C, the gap (paper gap) between the preceding and succeeding sheets was enlarged. The maximum productivity refers to the productivity when the temperature of the film 51 was 200°C or less.

[0060] In the first embodiment, there are a plurality of small-size heating elements 54b3 and 54b4 corresponding to B5 and A5 paper, and the temperature rise of the film 51 is small for any paper P, and adjustment of the paper interval is not required. In the first embodiment, the maximum productivity of B5 paper was 39 sheets / min, and the maximum productivity of A5 paper was 46 sheets / min. On the other hand, in the first comparative example, there is only one type of heating element, the heating element 202 corresponding to B5 paper, so that adjustment of the paper interval is not required when printing B5 paper, and the maximum productivity is 39 sheets / min. However, even when printing A5 paper, the heating element 202 corresponding to B5 paper is used, so the temperature rise of the film 51 is large, and it is necessary to expand the paper interval so as not to cause a temperature rise in the non-paper passing portion, and the maximum productivity is low at 16 sheets / min.

[0061] As described above, according to the first embodiment, the first-length heating element is composed of two heating elements, the first heating element and the second heating element, so that the power input to the first-length heating element can be dispersed. In addition, the first heating element and the second heating element are always supplied with power at the same time, so that the temperature does not rise unevenly at only one end of the short side of the substrate. As a result, even if excessive power is supplied to the first-length heating element in the unlikely event of an equipment failure, the temperature gradient occurring in the short side of the substrate can be reduced. A small temperature gradient means that the distortion (thermal stress) occurring in the substrate can be reduced, and deformation of the substrate can be suppressed.

[0062] Next, the power supply capacity of the third and fourth heating elements, which are shorter in the longitudinal direction than the first length and have different longitudinal lengths, is made smaller than that of the heating elements of the first length. Then, the third and fourth heating elements are arranged between the first and second heating elements in the lateral direction of the substrate, and symmetry in the lateral direction of the substrate is maintained as much as possible. As a result, even if excessive power is supplied to the third or fourth heating element in the unlikely event of an equipment failure, the temperature gradient occurring in the lateral direction in the substrate can be reduced, and deformation of the substrate caused by distortion can be suppressed. Then, since the third and fourth heating elements, which are shorter in the longitudinal direction than the first length and have different longitudinal lengths, are provided, the productivity of multiple types of narrow-width paper can be improved. Finally, by configuring only the heating elements of the first length with two pieces and configuring the other heating elements with short longitudinal lengths with one piece each, the heater can also be made smaller at the same time.

[0063] [Variation 1] In the first embodiment, the configuration in which the two longest heating elements 54b1 and 54b2 are electrically connected in parallel and power is supplied at the same time has been described in detail, but the present invention is not limited to this configuration. FIG. 9(a) is a diagram showing the configuration of the heater 54, and FIG. 9(b) is a diagram showing the heater 54 and the power control unit 97. As shown in FIG. 9(a), the heater may be electrically connected in series in the order of the first contact 54d1, the first heating element 54b1, the second heating element 54b2, and the second contact 54d3. Specifically, the heating element 54b1 has one end connected to the contact 54d1, and the other end connected to the other end of the heating element 54b2 via the conductor 54c without a contact. The heating element 54b2 has one end connected to the contact 54d3, and the other end connected to the other end of the heating element 54b1 via the conductor 54c without a contact. The heating element 54b3 has one end connected to the contact 54d1 and the other end connected to the contact 54d3. The heating element 54b4 has one end connected to the contact 54d3 and the other end connected to the contact 54d4.

[0064] As shown in FIG. 9B, the electromagnetic relay 57a has a contact 57a1 connected to a first pole of the AC power supply 55 via the triac 56, a contact 57a2 connected to a contact 54d1, and a contact 57a3 connected to a contact 54d4. The electromagnetic relay 57a is controlled by the engine controller 92 to be in one of two states: a state in which the contact 57a1 and the contact 57a2 are connected, and a state in which the contact 57a1 and the contact 57a3 are connected. The electromagnetic relay 57b has a contact 57b1 connected to a second pole of the AC power supply 55, a contact 57b2 connected to a contact 54d2, and a contact 57b3 connected to a contact 54d3. The electromagnetic relay 57b is controlled by the engine controller 92 to be in one of two states: a state in which the contact 57b1 and the contact 57b2 are connected, and a state in which the contact 57b1 and the contact 57b3 are connected.

[0065] 9(a) shows the state in which the electromagnetic relays 57a and 57b are not in operation, with the contacts 57a1 and 57a2 of the electromagnetic relay 57a being connected, and the contacts 57b1 and 57b2 of the electromagnetic relay 57b being connected. When the electromagnetic relays 57a and 57b are not in operation, power is supplied between the contacts 54d1 and 54d2, causing the longest heating elements 54b1 and 54b2 to generate heat.

[0066] When only the electromagnetic relay 57b is operated, the contacts 57a1 and 57a2 of the electromagnetic relay 57a are connected, and the contacts 57b1 and 57b3 of the electromagnetic relay 57b are connected. When only the electromagnetic relay 57b is operated, power is supplied between the contacts 54d1 and 54d3, so only the heating element 54b3 generates heat. When only the electromagnetic relay 57a is operated, the contacts 57a1 and 57a3 of the electromagnetic relay 57a are connected, and the contacts 57b1 and 57b2 of the electromagnetic relay 57b are connected. When only the electromagnetic relay 57a is operated, power is supplied between the contacts 54d4 and 54d2, so only the heating element 54b4 generates heat.

[0067] As described above, in the modified example shown in FIG. 9, the contact 54d1, which is the first contact, is electrically connected to one end of the heating element 54b1 and the heating element 54b3. The contact 54d2, which is the second contact, is electrically connected to one end of the heating element 54b4 and the heating element 54b2. The contact 54d3, which is the third contact, is electrically connected to the other end of the heating element 54b3. The contact 54d4, which is the fourth contact, is electrically connected to the other end of the heating element 54b4. And the other end of the heating element 54b1 and the other end of the heating element 54b2 are electrically connected.

[0068] The configuration of FIG. 9 also provides the same effect as in the first embodiment, since the longest heating elements 54b1 and 54b2 are simultaneously supplied with power. It is desirable to make the power supplyable by the longest heating elements 54b1 and 54b2 the same as in the first embodiment, and the electrical resistance between both ends of the first heating element 54b1 and the second heating element 54b2, which are the longest heating elements, may be set to 5Ω. In FIG. 9, the heating elements 54b1 and 54b2 are connected in series, and the combined resistance is 10Ω. The other heating elements may be the same as in the first embodiment. Thus, in the first modification, the combined resistance of the heating elements 54b1 and 54b2 is 10Ω, which is smaller than the resistance (30Ω) of the heating elements 54b3 and 54b4. The effect provided by the heater 54 shown in FIG. 9 is the same as in the first embodiment.

[0069] [Variation 2] In the first embodiment, the case where the non-longest heating elements 54b3 and 54b4 are two pieces is described in detail, but the present invention is not limited to this configuration. For example, as shown in FIG. 10, even if the non-longest heating elements are three pieces, the same effect as described in the first embodiment can be achieved. That is, in the second modification, a fifth heating element 54b5 having a shorter longitudinal length than the fourth heating element 54b4 is provided. The heating elements 54b1 and 54b2 have one end connected to a contact 54d1 which is a common first contact, and the other end connected to a contact 54d2 which is a common second contact. The heating element 54b3 has one end connected to a contact 54d3 which is a third contact, and the other end connected to a contact 54d2. The heating element 54b4 has one end connected to a contact 54d4 which is a fourth contact, and the other end connected to a contact 54d2. One end of the heating element 54b5 is connected to the fifth contact 54d5, and the other end is connected to the contact 54d2. That is, the other ends of all the heating elements 54b1 to 54b5 are connected to the contact 54d2. In addition, in the short side direction of the substrate 54a, the three heating elements 54b3 to 54b5 are disposed between the two heating elements 54b1 and 54b2. In addition, in the short side direction of the substrate 54a, the heating element 54b5 is disposed between the heating elements 54b3 and 54b4.

[0070] The heater 54 shown in Fig. 10 will be described. The longest heating elements 54b1 and 54b2 are arranged at both ends of the substrate 54a in the short direction, and power is supplied simultaneously from common contacts 54d1 and 54d2. Following the first embodiment, the longest heating elements 54b1 and 54b2 each have an electrical resistance of 20 [Ω] at both ends. The length of the heating elements 54b1 and 54b2 in the longitudinal direction is 222 mm.

[0071] The length in the longitudinal direction is 188 mm for the heating element 54b3, 154 mm for the heating element 54b4, and 111 mm for the heating element 54b5. The heating element 54b3 is used when printing B5 paper, the heating element 54b4 is used when printing A5 paper, and the heating element 54b5 is used when printing A6 paper. The electrical resistance at both ends in the longitudinal direction of these heating elements 54b3 to 54b5 that are not the longest is all 30 [Ω]. Thus, in the second modification, the combined resistance of the heating elements 54b1 and 54b2 is 10 Ω, which is smaller than the resistance (30 Ω) of the heating elements 54b3 to 54b5. By increasing the number of types of heating elements that are not the longest to three, it is possible to maximize the productivity of three types of paper: B5 paper, A5 paper, and A6 paper.

[0072] In the case of a non-longest heating element, if an excessive power supply is assumed, the power supplied to each of the heating elements 54b3 to 54b5 is the same. Since the heating element 54b5 has the shortest length in the longitudinal direction, the degree of power concentration is the largest, and the risk of deformation of the substrate 54a during heating is high. In order to eliminate this risk as much as possible, it is preferable to arrange the shortest heating element 54b5 at the center in the lateral direction of the substrate 54ba, and to provide symmetry in the lateral direction. In addition, it is preferable to arrange the heating elements 54b3 and 54b4 as close to the center as possible at both ends in the lateral direction of the heating element 54b5. The effect of the heater 54 shown in FIG. 10 is the same as that of the first embodiment.

[0073] [Variation 3] In the second modification, four contacts are arranged at one end in the longitudinal direction of the substrate 54a, and one contact is arranged at the other end. In the third modification, an example is described in which three contacts are arranged at one end in the longitudinal direction, and two contacts are arranged at the other end. In the third modification, the heating element can be arranged as close to the center as possible in the longitudinal direction of the substrate 54a, and this is a preferable arrangement for achieving a uniform heat distribution in the longitudinal direction.

[0074] In the third modification, the fifth heating element 54b5 is provided, which is shorter in the longitudinal direction than the fourth heating element 54b4. The heating elements 54b1 and 54b2 have one end connected to the contact 54d1, which is a common first contact, and the other end connected to the contact 54d2, which is a common second contact. The heating element 54b3 has one end connected to the contact 54d3, which is a third contact, and the other end connected to the contact 54d2. The heating element 54b4 has one end connected to the contact 54d3, and the other short part connected to the contact 54d4, which is a fourth contact. The heating element 54b5 has one end connected to the contact 54d5, which is a fifth contact, and the other end connected to the contact 54d4. Among the five heating elements, the first heating element 54b1 and the second heating element 54b2 with the longest length and the fourth heating element 54b3 with the second longest length are connected to the second contact 54d2. The fourth heating element 54b3 with the second longest length and the fourth heating element 54b4 with the third longest length are connected to the third contact 54d3. The fourth heating element 54b4 with the third longest length and the fifth heating element 54b5 with the fourth longest length are connected to the fourth contact 54d4. That is, the heating element 54b is connected to a common contact with the heating element 54b with the smallest difference in length from the heating element 54b. In addition, in the short-side direction of the substrate 54a, the three heating elements 54b3 to 54b5 are arranged between the two heating elements 54b1 and 54b2. In addition, the heating element 54b5 is arranged between the heating elements 54b3 and 54b4 in the short-side direction of the substrate 54a.

[0075] The heater 54 shown in Fig. 11 will be described. The longest heating elements 54b1 and 54b2 are arranged at both ends of the substrate 54a in the short direction, and power is supplied simultaneously from common contacts 54d1 and 54d2. Following the first embodiment, the longest heating elements 54b1 and 54b2 each have an electrical resistance of 20 [Ω] at both ends. The length of the heating elements 54b1 and 54b2 in the longitudinal direction is 222 mm.

[0076] The length in the longitudinal direction is 188 mm for the heating element 54b3, 154 mm for the heating element 54b4, and 111 mm for the heating element 54b5. The heating element 54b3 is used when printing B5 paper, the heating element 54b4 is used when printing A5 paper, and the heating element 54b5 is used when printing A6 paper. The electrical resistance at both ends in the longitudinal direction of these heating elements 54b3 to 54b5 that are not the longest is all 30 [Ω]. Thus, in the third modification, the combined resistance of the heating elements 54b1 and 54b2 is 10 Ω, which is smaller than the resistance (30 Ω) of the heating elements 54b3 to 54b5. By increasing the number of types of heating elements 54b that are not the longest to three, it is possible to maximize the productivity of three types of paper: B5 paper, A5 paper, and A6 paper.

[0077] In the case of the heating element 54b that is not the longest, if an excessive power supply is assumed, the power supplied to each of the heating elements 54b3 to 54b5 is the same. Since the heating element 54b5 has the shortest length in the longitudinal direction, the degree of concentration of power is the largest, and the risk of deformation of the substrate 54a during heating is high. In order to eliminate this risk as much as possible, it is preferable to arrange the shortest heating element 54b5 at the center in the lateral direction of the substrate 54ba to provide symmetry in the lateral direction. In addition, it is preferable to arrange the heating elements 54b3 and 54b4 as close to the center as possible at both ends in the lateral direction of the heating element 54b5. The effect of the heater 54 shown in FIG. 11 is the same as that of the first embodiment.

[0078] Conventionally, the resistance of the multiple heating elements was the same, and the power that could be supplied was also the same. Conventionally, when power was continuously supplied to a wide heating element, an excessive temperature rise occurred at one end in the short direction of the substrate. This caused a large temperature gradient in the substrate, and the substrate was likely to be significantly distorted. Furthermore, conventionally, since only one type of narrow heating element was provided, it was difficult to prevent the temperature rise in the non-paper passing area when using paper of multiple sizes, and it was difficult to provide high productivity. In contrast, according to the first embodiment, it is possible to suppress the deformation of the substrate on which the heater is mounted. EXAMPLES

[0079] The shape of the heater 54 in the second embodiment is the same as that in the first embodiment, as shown in FIG. 4, and the description will be omitted. In the second embodiment, the power density (described later) of the shorter heating element 54b4 of the heating elements 54b3 and 54b4 that are not the longest is set higher than the power density of the longer heating element 54b3. The heating elements 54b3 and 54b4 that are not the longest have a wide non-heated area that cannot be heated in the longitudinal direction. The shorter the longitudinal length of the heating element 54b, the wider the non-heated area becomes, and the more likely it is that the heat of the heating element 54b is taken away by the non-heated area. In the vicinity of this non-heated area, the fixing device 50 cannot sufficiently heat the area, and the toner image on the paper P may not be fixed. For this reason, it is preferable that at least the shorter heating element 54b4 has a higher power density than the longer heating element 54b3.

[0080] In addition, of the heating elements 54b3 and 54b4 that are not the longest, the resistance value of the shorter heating element 54b4 is set to be equal to or greater than that of the longer heating element 54b3. This allows the fixing device 50 to operate at a certain current or less regardless of whether the shorter heating element 54b4 or the longer heating element 54b3 is used. This allows the selection of low-rated, low-cost wires and electric elements for connecting the heating elements 54b3 and 54b4 that are not the longest.

[0081] Here, power density is defined as the value (unit: W / mm) obtained by dividing the power generated when 100V is applied to heating element 54b by the length of heating element 54b in the longitudinal direction. The electrical resistance of longer heating element 54b3 is R1, the electrical resistance of shorter heating element 54b4 is R2, the length of longer heating element 54b3 in the longitudinal direction is L1, and the length of shorter heating element 54b4 in the longitudinal direction is L2. In this case, the power of longer heating element 54b3 is "100 2 / R1”, and the power of the shorter heating element 54b4 is “100 2 Since each power is divided by the length of the heating element 54b, the power density of the longer heating element 54b3 is expressed as "100 2 / R1 / L1”, and the power density of the shorter heating element 54b4 is “100 2 / R2 / L2". In the second embodiment, "100 2 / R1 / L1<100 2 This relation can also be expressed as "R1L1>R2L2".

[0082] [Power density and fixability] The power density of the heating element 54b and the conditions for checking whether the toner image can be fixed to the paper P are described below. The image process speed of the image forming apparatus is set to 200 mm / sec, and the interval (paper interval) between the preceding and succeeding paper is set to 0.25 seconds. The paper is passed through while controlling the temperature by the engine controller 92 so that the rear of the substrate 54a is at 180°C using the fixing temperature sensor 59 installed on the rear of the substrate 54a. The fixing device 50 equipped with the heater 54 is kept in a sufficiently cooled state.

[0083] When using the longer heating element 54b3 of the heating elements 54b3 and 54b4 that are not the longest, the size of the heating element is B5 (width 182 mm × length 257 mm × thickness 92 μm, basis weight 68 g / m 2 When using the shorter heating element 54b4, the aforementioned CS680 paper is A5 size (width 148.5 mm x length 210 mm x thickness 92 μm, basis weight 68 g / m2). 2 In each case, 10 sheets are passed continuously. The toner image on the sheet P is formed uniformly over the entire area of ​​the sheet P (the top, bottom, left and right margins are all set to 5 mm), and the toner amount is 1.0 mg / cm 2 Let us assume that.

[0084] The presence or absence of unfixed areas of the toner image on the paper P is checked, and if all of the toner images are fixed, this is deemed to be no problem with fixing, indicated with an "O", and if any areas are not fixed, this is deemed to be a fixing problem, indicated with an "X". Fixability is checked for five types of longer heating elements 54b3 with different power densities, and five types of shorter heating elements 54b4 with different power densities. The check results are shown in Table 1.

[0085] [Table 1] In Table 1, the left table shows the longer heating element 54b3, and the right table shows the shorter heating element 54b4. In each table, the first column shows the longitudinal length of the heating element 54b, the second column shows the power density, and the third column shows the fixability (◯ or ×) described above.

[0086] As shown in Table 1, in the case of the longer heating element 54b3, when the power density was 1.72 [W / mm] or more, all the toner images were fixed to the paper P, and there was no problem with fixation. In addition, in the case of the shorter heating element 54b4, when the power density was 1.8 [W / mm] or more, all the toner images were fixed to the paper P, and there was no problem with fixation. It was also confirmed that the heating element 54b4, which has a wide non-heated area and is short in the longitudinal direction and is prone to losing heat to the non-heated area near the end of the heating element 54b4, requires a higher power density than the heating element 54b3.

[0087] [Maximum current and fixability] Here, the maximum current amount refers to the amount of current that flows when 100V is applied to the heating element 54b. The smaller the value of this maximum current amount, the lower the cost and the lower the rating of the wires and electrical elements that are connected to the heating element 54b can be selected. Figure 12 shows the relationship between the maximum current amount [A] and the power density [W / mm], with a plot of "◯" for cases where there are no fixing problems and "×" for cases where there are fixing problems.

[0088] In the longer heating element 54b3, the plot Lg1 has a fixability of "good" and the smallest maximum current amount. The plot Lg1 has a power density of 1.72 [W / mm] and a maximum current amount of 3.23 [A]. The electrical resistance of the heating element 54b3 at this time is 31 [Ω]. In the shorter heating element 54b4, the plot St1 has a fixability of "good" and the smallest maximum current amount. The plot St1 has a power density of 1.80 [W / mm] and a maximum current amount of 2.78 [A]. The electrical resistance of the heating element 54b4 at this time is 36 [Ω]. That is, the shorter heating element 54b4 of the plot St1 has a higher power density and a higher resistance value than the longer heating element 54b3 of the plot Lg1. In this way, by setting the resistance of the longer heating element 54b3 to 31 [Ω] and the shorter heating element 54b4 to 36 [Ω], it is possible to satisfy the fixing performance and keep the maximum current amount below 3.23 [A]. It is also possible to select low-cost, low-rated wires and electric elements to be connected to the heating element 54b.

[0089] For the shorter heating element 54b4, the conditions of plot St1 are recommended, but the plot St2 indicated by the black circle also has a low power density of 2.09 [w / mm] and a maximum current of 3.23 [A] or less. In this case, the electrical resistance of the shorter heating element 54b4 is 31 [Ω]. Even if the electrical resistance of the longer heating element 54b3 is 31 [Ω] and the electrical resistance of the shorter heating element 54b4 is 31 [Ω], the fixing performance can be satisfied and the maximum current can be kept at 3.23 [A] or less. That is, the shorter heating element 54b4 of plot St2 has a higher power density and the same resistance as the longer heating element 54b3 of plot Lg1. From the above, it is preferable to use the shorter heating element 54b4 in the range from plot St1 to plot St2 in the graph of FIG. 12.

[0090] From the above confirmation results, among the heating elements 54b3 and 54b4 that are not the longest, the power density of the shorter heating element 54b4 is made higher than that of the longer heating element 54b3. Thereby, regardless of which heating element 54b is used, the fixing property in the vicinity of the non-heating regions at both ends of the heating element 54b can be satisfied. Further, by making the resistance value of the shorter heating element 54b4 the same as or greater than that of the longer heating element 54b3, the fixing device 50 can be operated with a current amount below a certain level, and an inexpensive wire harness or the like can be used.

[0091] As described above, according to the second embodiment, deformation of the substrate on which the heater is mounted can be suppressed.

Embodiment

[0092] FIG. 13(a) is a cross-sectional view of the fixing nip portion N of the fixing device 50, showing a part of the film 51, a part of the nip forming member 52, the heater 54, and the pressure roller 53. Let the center of the rotation axis of the pressure roller 53 be C, the position of the shorter heating element 54b4 among the heating elements 54b3 and 54b4 that are not the longest be H1, and the position of the longer heating element 54b3 be H2. Define the distance from the center C to the position H1 as RL1 and the distance from the center C to the position H2 as RL2. In the third embodiment, the heater 54 is arranged at a position where the distance RL1 is smaller than the distance RL2 (RL1 < RL2). The closer the distance between the center C of the pressure roller 53 and the heating element 54b, the greater the amount of collapse of the elastic layer of the pressure roller 53. Therefore, the pressure of the fixing nip portion N at the position H1 can be made higher than that at the position H2.

[0093] FIG. 13(b) shows the profile of the pressure (nip pressure) of the fixing nip portion N in the paper P conveyance direction. In FIG. 13(b), the horizontal axis represents the position in the conveyance direction corresponding to the fixing nip portion N shown in FIG. 13(a), and the vertical axis represents the nip pressure. As shown in FIG. 13(b), in the conveyance direction of the paper P, the nip pressure is the highest at the position of the center C of the pressure roller 53. Also, as shown in FIG. 13(b), it can be seen that the nip pressure at the position H1 is higher than the nip pressure at the position H2.

[0094] As described above, the distance from the center of rotation of the pressure roller 53 to the heating element 54b (heating element 54b4 in FIG. 4 and the heating element 54b5 in FIG. 10) that has the shortest longitudinal length among the third heating element and the fourth heating element 54b is defined as RL1. The distance from the center of rotation of the pressure roller 53 to the other heating elements excluding the shortest heating element among the third heating element and the fourth heating element is defined as RL2. Then, in the third embodiment, the heating element 54b is disposed on the substrate such that the distance RL1 is shorter than the distance RL2 at a predetermined longitudinal position (for example, the center).

[0095] The high nip pressure can reduce the thermal resistance due to contact between the heater 54 and the film 51, and between the film 51 and the pressure roller 53, and can improve the thermal conductivity between the various components. This improved thermal conductivity makes it possible to quickly conduct the excess heat generated by the heater 54 to the pressure roller 53, which has a high thermal capacity, even if excessive power is supplied to the heating element 54b in the unlikely event of a breakdown. In other words, the risk of deformation of the substrate 54a can be reduced.

[0096] The shorter the length of the heat generating element 54b in the longitudinal direction, the wider the non-heated area is, and the more heat is taken away, so it is preferable to set the power density of the shorter heat generating element 54b4 higher than that of the longer heat generating element 54b3. On the other hand, the risk of deformation of the substrate 54a in the event of a failure is somewhat higher. In order to reduce this risk, it is desirable to place the shorter heat generating element 54b4 at a position H1 where the nip pressure is higher. In the third embodiment, even if excessive power is supplied to the shorter heat generating element 54b4, the generated heat can be quickly transferred to the pressure roller 53, etc., and the risk of deformation of the substrate 54a can be reduced. As described above, when the heater 54 described in the first and second embodiments is incorporated into the fixing device 50, the shorter heat generating element 54b4 of the heat generating elements 54b3 and 54b4 that are not the longest is placed closer to the center C of the pressure roller 53 than the longer heat generating element 54b3. This reduces the risk of deformation of the substrate 54a.

[0097] As described above, according to the third embodiment, it is possible to suppress deformation of the substrate on which the heater is mounted. [Explanation of symbols]

[0098] 54 Heater 54b1~54b4 Heating element 54a Substrate

Claims

1. A substrate; A first heating element; a second heating element having a length in a longitudinal direction substantially equal to that of the first heating element; a third heating element having a length in the longitudinal direction shorter than the first heating element and the second heating element; a fourth heating element having a length in the longitudinal direction shorter than that of the third heating element; Equipped with the first heating element, the second heating element, the third heating element, and the fourth heating element are disposed on the substrate; the first heating element is disposed on one end side of the substrate in a short side direction, the second heating element is disposed on the other end side of the substrate in the short side direction, the third heating element and the fourth heating element are disposed between the first heating element and the second heating element in the short-side direction of the substrate, A heater, wherein a resistance value of the fourth heating element is greater than a resistance value of the third heating element.

2. 2. The heater according to claim 1, wherein a combined resistance value of the first heating element and the second heating element is smaller than a resistance value of the third heating element and a resistance value of the fourth heating element.

3. 2. The heater according to claim 1, wherein the first heating element, the third heating element, the fourth heating element, and the second heating element are arranged in this order in the short side direction.

4. 2. The heater according to claim 1, wherein the third heating element and the fourth heating element are arranged symmetrically in a short-side direction of the substrate.

5. a first contact to which one end of the first heating element and one end of the second heating element are electrically connected; a second contact to which the other ends of the first heating element, the second heating element, and the third heating element are electrically connected; a third contact to which one end of each of the third heating element and the fourth heating element is electrically connected; a fourth contact to which the other end of the fourth heating element is electrically connected; The heater of claim 1 , further comprising:

6. a first contact to which one end of the first heating element and one end of the third heating element are electrically connected; a second contact to which one end of the fourth heating element and one end of the second heating element are electrically connected; a third contact to which the other end of the third heating element is electrically connected; and a fourth contact to which the other end of the fourth heating element is electrically connected; Equipped with 2. The heater according to claim 1, wherein the other end of the first heating element and the other end of the second heating element are electrically connected to each other.

7. When the length of the third heating element in the longitudinal direction is L1, the resistance value of the third heating element is R1, the length of the fourth heating element in the longitudinal direction is L2, and the resistance value of the fourth heating element is R2, R1×L1>R2×L2 7. The heater according to claim 1, wherein the following relationship is satisfied:

8. A fixing device that fixes an unfixed toner image carried on a recording material, comprising: A heater and a first rotating body heated by the heater; a second rotating body that forms a nip portion together with the first rotating body; The heater comprises: A substrate; A first heating element; a second heating element having a length in a longitudinal direction substantially equal to that of the first heating element; a third heating element having a length in the longitudinal direction shorter than the first heating element and the second heating element; a fourth heating element having a length in the longitudinal direction shorter than that of the third heating element; Equipped with the first heating element, the second heating element, the third heating element, and the fourth heating element are disposed on the substrate; the first heating element is disposed on one end side of the substrate in a short side direction, the second heating element is disposed on the other end side of the substrate in the short side direction, the third heating element and the fourth heating element are disposed between the first heating element and the second heating element in the short-side direction of the substrate, A fixing device, wherein a resistance value of the fourth heat generating element is greater than a resistance value of the third heat generating element.

9. 9. The fixing device according to claim 8, wherein the first rotating body is a film.

10. the heater is disposed in an internal space of the film, and the film is sandwiched between the heater and the second rotating body, 10. The fixing device according to claim 9, wherein the image on the recording material is heated through the film in a nip portion formed between the film and the second rotating body.

11. The fixing device according to claim 8, characterized in that, at a predetermined position in the longitudinal direction, the distance from the center of rotation of the second rotating body to a heating element having the shortest length in the longitudinal direction among the other heating elements excluding the first heating element and the second heating element is shorter than the distance from the center of rotation of the second rotating body to a heating element other than the shortest heating element among the other heating elements.

12. an image forming unit that forms an unfixed toner image on a recording material; a fixing device according to claim 8 for fixing an unfixed toner image on a recording material; An image forming apparatus comprising:

Images