Dielectric heating device

Abstract

To uniformly heat a heating object with a longer length.SOLUTION: A dielectric heating device 10 comprises a power supply circuit 4 that supplies a high-frequency power generated in a power supply part 1 to an opposing long electrode 5. The power supply circuit 4 includes a first step line path 41 and a second step line path 42 that are hierarchically connected to between the power supply part 1 and the electrode 5. The first step line path 41 is divided into two at a left and a right of a long direction of the electrode 5 in an output end SP1 of the power supply part 1, and each tip end is corresponded to a center position of a dimension of 1 / 2 of a long direction of the electrode 5. The second step line path 42 is divided into two at the left and the right of the long direction of the electrode 5 in each tip end of the first step line path 41. Each tip end is corresponded to the center position of a dimension of 1 / 4 of the long direction of the electrode 5.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an apparatus for dielectrically heating an object to be heated placed between opposing electrodes with high frequency power. [Background technology]

[0002] Conventionally, there has been a demand for applying dielectric heating to longer objects, but uniform heating in the length direction is not easy, and various countermeasures have been considered. For example, a high-frequency heating device is known that produces laminated materials by applying adhesive between multiple thin wooden boards, laminating them, and bonding them together by dielectric heating (for example, Patent Document 1). Patent Document 1 describes that when using long electrodes to produce longer laminated materials, a multi-point power supply method is adopted in consideration of the distribution of the high-frequency electric field. Specifically, small electrode plates are arranged in series at a predetermined interval, and each is connected to an individual high-frequency oscillator circuit, and high-frequency heating operations are alternately switched to perform heating and bonding treatment over the entire length.

[0003] Non-Patent Documents 1 and 2 state that when a high-frequency voltage is applied to a long electrode, the voltage at a position farther from the power supply point becomes higher, and is maximum at the end, etc. In addition, since the amount of heat generated in the heated object is proportional to the square of the voltage, it is preferable that the voltage within the electrode surface is more uniform in order to suppress uneven heating. In order to achieve voltage uniformity, a two-point power supply configuration and the voltage gradient characteristics in that case are shown. In addition, when the electrode is long for the wavelength used, depending on the product processing conditions and the required accuracy for the heating balance in the longitudinal direction, there is a limit to the uniformity of the voltage in the longitudinal direction with two-point power supply. For example, a device has been proposed in which a four-point power supply system is configured and two points are alternately heated in a time-division manner or the work is shifted by 1 / 4 of the dimension to perform heating operation over the entire length.

[0004] Patent Document 2 proposes a high-frequency dielectric heating device in which high-voltage electrodes and earth electrodes are arranged alternately opposite each other to form multiple heating layers, and in order to reduce the difference in the electrical path length from the power source to the high-voltage electrodes in each layer, the electrical path between them is configured in a so-called tournament shape, making the voltage applied to the high-voltage electrodes in each layer approximately equal, thereby enabling equal heating in each heating layer (see paragraphs 0022-0024, Figures 6, and 8-10). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-276309 [Patent Document 2] JP 2019-75363 A [Non-patent literature]

[0006] [Non-Patent Document 1] Kanemichi Tomoda, Electric Heating Classroom "High Frequency Dielectric Heating Equipment and Applications" P58-P67, "Electric Heating" No.70, 1993 [Non-Patent Document 2] Dielectric Heating Special Committee "High Frequency Wood Processing Technical Standards" No. 38 (1)-(18), "Technical Report of the Institute of Electrical Engineers of Japan" February 1960 Summary of the Invention [Problem to be solved by the invention]

[0007] In the case of Patent Document 1, in which the electrode plate is divided into multiple parts, multiple high-frequency oscillator circuits are required, resulting in a large structure. In addition, when a multi-point power supply structure is adopted to suppress voltage unevenness as in Non-Patent Documents 1 and 2, the dimensions of the long laminated lumber to be produced are multiple or varied, so in reality, there is a limit to how much a two-point power supply structure such as that illustrated in Non-Patent Documents 1 and 2 can handle. In addition, in the case of a four-point power supply system, although the heating balance problem can be improved to some extent by incorporating a switching device, the pressurized state of the work pressing part must be released once in the process of shifting the work at the time of switching, and it is necessary to consider the impact on the cycle time and the switching schedule.

[0008] In addition, the tournament shape shown in Patent Document 2 relates to an electric path between a power source and each high-voltage electrode on each layer, and power is supplied to each high-voltage electrode from a single point on the edge of the high-voltage electrode, which differs from the technique of supplying power to multiple points on a single electrode surface to adjust the voltage to a uniform level across the surface.

[0009] The present invention has been made in consideration of the above, and provides a dielectric heating device that uses hierarchical power supply lines to enable as uniform heating as possible of a longer heating object. [Means for solving the problem]

[0010] The dielectric heating device of the present invention includes a power supply circuit which supplies high frequency power generated in a power supply unit to opposing long electrodes, the power supply circuit having at least a first stage line and a second stage line which are hierarchically connected between the power supply unit and the electrodes, the first stage line being branched into two to the left and right in the longitudinal direction of the electrode at the output end of the power supply unit, with each end corresponding to a central position of each 1 / 2 of the longitudinal dimension of the electrode taking a predetermined dimension into consideration, and the second stage line being branched into two to the left and right in the longitudinal direction of the electrode at each end of the first stage line, with each end corresponding to a central position of each 1 / 4 of the longitudinal dimension of the electrode.

[0011] According to the present invention, the first-stage line and the second-stage line constitute a so-called two-tiered tournament power supply circuit, and in the embodiment in which the second-stage line is connected to the electrode, high-frequency power is supplied to the center position of each 1 / 4 dimension in the longitudinal direction of the electrode, suppressing the difference in voltage level on the electrode surface and enabling uniform heating. In the embodiment in which the second-stage line constitutes a line in the middle of the power supply circuit and the final-stage line is connected to the electrode, the ends of the second-stage line are divided and arranged in the longitudinal direction of the electrode, thereby suppressing the difference in voltage level on the electrode surface in the final-stage line connected to the electrode.

[0012] The first-stage line has a first-stage 2-branch path arranged parallel to the longitudinal direction of the electrode from the output end of the power supply unit, and a first-stage connection path extending from the first-stage 2-branch path toward the surface of the electrode. This configuration makes it easy to manufacture a power supply line with balanced impedance.

[0013] In addition, the first-stage two-branch path has its tip coincident with the center position of each half of the longitudinal dimension of the electrode, This configuration makes it easy to adjust the impedance.

[0014] Moreover, the first stage two-branch path has each tip shifted by a preset adjustment dimension from the center position of each 1 / 2 dimension of the electrode in the longitudinal direction. With this configuration, it is possible to manufacture a power supply line with an adjusted impedance balance, and uniform heating of a longer workpiece is possible. Also, since the impedance balance is adjusted not in the final stage but in the first stage two-branch path, it is easier to adjust the balance in the entire longitudinal direction. The adjustment dimension may be set in advance by conducting tests or the like.

[0015] In addition, the shapes of the first-stage line and the second-stage line are symmetrical with respect to the center of the electrode in the longitudinal direction. With this configuration, when a workpiece is symmetrical in the longitudinal direction, a symmetrical power supply circuit can be configured accordingly, making it easy to design the circuit.

[0016] The ends of the final stage lines connected to the electrodes, which are the final stages in the hierarchy, have a multi-point power supply shape branched in the width direction of the electrodes. With this configuration, the difference in voltage level is suppressed in the width direction of the electrodes, and the temperature balance is more uniform on the front surface of the workpiece.

[0017] The power supply circuit further has a third-stage line, which is branched into two at each end of the second-stage line in the longitudinal direction of the electrode, one to the left and one to the right, and each end corresponds to the center position of the electrode in the longitudinal direction, which is 1 / 8 of the dimension. According to this configuration, the power supply circuit has at least two stages, but for objects with strict uniform heating conditions, a third-stage line can be further provided to meet the demand for maintaining the quality of the heated object. Effect of the Invention

[0018] According to the present invention, by performing multipoint power supply to the electrode surface via at least the first stage line and the second stage line that are hierarchically connected, it is possible to heat even longer workpieces as uniformly as possible. [Brief description of the drawings]

[0019] [Figure 1] 1 shows a schematic circuit diagram of a dielectric heating device according to the present invention, in which (A) is a two-tier (four-point power supply) type of so-called tournament type according to a first embodiment, and (B) is a three-tier (eight-point power supply) type of so-called tournament type according to a second embodiment. [Diagram 2] FIG. 1 shows comparative example A1; (A) is an oblique view showing the right half of the power supply circuit and the electrode (as viewed from the central power supply port SP1); (B) is a partial view showing a vertical cross section of the central part of the electrode; (C) is a top view showing the right half of the electrode; and (D) is a temperature distribution diagram over the entire longitudinal direction of the object to be heated (workpiece). [Diagram 3] FIG. 1 shows comparative example B1; (A) is a perspective view showing the right half of the power supply circuit and the electrode, (B) is a top view showing the right half of the electrode, and (C) is a temperature distribution diagram over the entire longitudinal direction of the workpiece. [Figure 4]FIG. 1 shows comparative example C1; (A) is an oblique view showing the right half of the power supply circuit and the electrode, (B) is a top view showing the right half of the electrode, and (C) is a temperature distribution diagram over the entire longitudinal direction of the workpiece. [Diagram 5] FIG. 1 shows comparative example D1; (A) is an oblique view showing the right half of the power supply circuit and the electrode, (B) is a top view showing the right half of the electrode, and (C) is a temperature distribution diagram over the entire longitudinal direction of the workpiece. [Figure 6] FIG. 1 shows comparative example E1; (A) is an oblique view showing the right half of the power supply circuit and the electrode, (B) is a top view showing the right half of the electrode, and (C) is a temperature distribution diagram over the entire longitudinal direction of the workpiece. [Figure 7] FIG. 1 shows comparative example H1; (A) is a perspective view showing the right half of the power supply circuit and the electrode, (B) is a top view showing the right half of the electrode, and (C) is a temperature distribution diagram over the entire longitudinal direction of the workpiece. [Figure 8] FIG. 11 shows comparative example H3; (A) is an oblique view showing the right half of the power supply circuit and the electrode, (B) is a top view showing the right half of the electrode, and (C) is a temperature distribution diagram over the entire longitudinal direction of the workpiece. [Figure 9] FIG. 1 shows comparative example I1; (A) is an oblique view showing the right half of the power supply circuit and the electrode, (B) is a top view showing the right half of the electrode, and (C) is a temperature distribution diagram over the entire longitudinal direction of the workpiece. [Figure 10] FIG. 1 shows embodiment F1, where (A) is an oblique view showing the right half of the power supply circuit and the electrode, (B) is a top view showing the right half of the electrode, and (C) is a temperature distribution diagram over the entire longitudinal direction of the workpiece. [Figure 11] FIG. 1 shows an example G1, in which (A) is an oblique view showing the right half of the power supply circuit and the electrode, (B) is a top view showing the right half of the electrode, and (C) is a temperature distribution diagram over the entire longitudinal direction of the workpiece. [Figure 12] 13 is a chart showing the power supply configurations and temperature uniformity of all comparative examples. [Figure 13] 13 is a chart showing power supply configurations and temperature uniformity for all examples. [Figure 14] 13 is a chart showing a summary of the limit length of the workpiece for each power supply form and temperature uniformity in the comparative example. [Figure 15] 13 is a table showing a summary of the limit length of the workpiece for each power supply form and temperature uniformity in the examples. [Figure 16] FIG. 16 corresponds to FIG. 14 and FIG. 15, and is a table showing a summary of the limit lengths of the workpiece when the temperature uniformity is set to within 15° C. [Figure 17] FIG. 16 corresponds to FIG. 14 and FIG. 15, and is a table showing a summary of the limit lengths of the workpiece when the temperature uniformity is set to within 30° C. [Figure 18] FIG. 12 is a partial perspective view showing another embodiment of the power supply circuit in FIG. 11, in which connection paths connected to electrodes are arranged in a tournament power supply structure in the width direction of the electrodes. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Fig. 1 shows a schematic circuit diagram of a dielectric heating device according to the present invention, where (A) is a two-tier (four-point feed) type of so-called tournament type according to the first embodiment, and (B) is a three-tier (eight-point feed) type of so-called tournament type according to the second embodiment. Note that for ease of explanation, the housing structure surrounding the device is omitted in Fig. 1.

[0021] Dielectric heating device 10 mainly comprises a power supply unit 1, a power supply circuit 4, and an electrode 5. Power supply unit 1 comprises a high-frequency oscillator 2 and a matching circuit 3. Although omitted from Fig. 1, a control unit generally comprises a processor and performs overall control of the heating operation and the matching adjustment operation. High-frequency oscillator 2 generates a predetermined high-frequency power and supplies it to electrode 5 via the matching circuit 3 and power supply circuit 4.

[0022] In this embodiment, the high-frequency oscillator 2 outputs high-frequency power at a predetermined output level with a frequency of 13.56 MHz. The frequency and output level can be appropriately selected depending on the material and size of the object to be heated (workpiece W) and the application. For example, the frequency can be several MHz to several hundreds of MHz, and in practice, a high-frequency range including 13.56 MHz, 27.12 MHz, and 40.6 MHz can be applied. The output level can be preferably several hundreds of W to several tens of kilowatts (W) depending on the application. The matching device 3 is composed of, for example, an LC circuit, and uses the measurement results of a known matching sensor (not shown) to change at least one component of the LC in conjunction with the impedance change to achieve impedance matching between the power supply side and the load side, thereby maintaining efficient dielectric heating. The output end of the power from the power supply unit 1 is shown as a power supply port SP1 in the left-right direction of Fig. 1 (A), Fig. 10 (A), and Fig. 11 (A), i.e., in the center of the longitudinal direction of the electrode 5. In FIG. 1, the output end of the power supply unit 1 corresponds to the center of the electrode 5 in the longitudinal direction.

[0023] The electrode 5 has a pair of opposing plate-like upper and lower electrodes 51 and 52 having a predetermined dimension in the longitudinal direction (left-right direction in FIG. 1). In this embodiment, the upper electrode 51 is a positive electrode, and the lower electrode 52 is a negative electrode. One of the upper electrode 51 and the lower electrode 52 is preferably configured to be able to be raised and lowered by a lifting mechanism (not shown), and clamps the work W to be heated with a required pressure. As the work W, for example, two upper and lower wooden boards (upper work W1 and lower work W2) are used, and an adhesive is applied to the middle of the thickness direction to stack them, and dielectric heating is performed in a pressed state between the upper electrode 51 and the lower electrode 52 to bond them together, thereby producing a laminated material.

[0024] In the first embodiment shown in Fig. 1(A), the power supply circuit 4 has a structure in which a first stage line 41 and a second stage line 42, each made of a metal plate, are connected in a hierarchical manner, while a dielectric heating device 10' of a second embodiment shown in Fig. 1(B) has a structure in which a third stage line 43 made of a metal plate is further connected in a hierarchical manner to the first stage line 41 and the second stage line 42. In both embodiments, each tip of the final stage line is connected to an electrode 51. Hereinafter, the first stage line 41, the second stage line 42 and the third stage line 43 will be referred to as a tournament type or tournament power supply, as appropriate.

[0025] 1(A), first-stage line 41 is branched into two on the left and right in the longitudinal direction of electrode 5 (left and right direction in FIG. 1), and has a length extending from the branching point to a center position of each half the dimension in the longitudinal direction of electrode 5. More specifically, first-stage line 41 has two branched paths 411 that are branched into two at power supply port SP1, which is the output end of power supply unit 1, i.e., at the center in the longitudinal direction of electrode 5, and extend in parallel to the left and right in the longitudinal direction of electrode 5, and connection paths 412 that extend from each tip of two branched paths 411 toward electrode 5 by a predetermined length, for example taking into account the insulation distance.

[0026] The second-stage line 42 is branched into two on the left and right sides in the longitudinal direction of the electrode 5 at each of the left and right ends of the first-stage line 41, and has a length extending from each branch point to a center position of each ¼ dimension in the longitudinal direction of the electrode 5. More specifically, the second-stage line 42 has a two-branch path 421 that is divided into two at the end of the connection path 412 of the first-stage line 41 and extends in parallel to the left and right in the longitudinal direction of the electrode 5, and a connection path 422 that extends a predetermined length from each end of the two-branch path 421 toward the electrode 5 side.

[0027] In the first embodiment, each end of the connecting path 422 of the second-stage line 42 is connected to four locations on the surface of the upper electrode 51, starting from the left side in the longitudinal direction, at the center positions of each 1 / 4 dimension of the longitudinal direction of the electrode 5, i.e., 1 / 8, 3 / 8, 5 / 8, and 7 / 8 (hereinafter referred to as four-point tournament power supply as necessary).

[0028] The dielectric heating device 10' of the second embodiment shown in Fig. 1(B) includes a third-stage line 43. The third-stage line 43 has two branch paths 431 that are branched at the end of each connection path 422 of the second-stage line 42 and extend in parallel to the left and right in the longitudinal direction of the electrode 5, and a connection path 432 that extends a predetermined length from each end of the two branch paths 431 toward the electrode 5 side. In the second embodiment, the end of each connection path 432 of the third-stage line 43 is connected to eight points on the surface of the upper electrode 51, i.e., 1 / 16, 3 / 16, 5 / 16, 7 / 16, 9 / 16, 11 / 16, 13 / 16, and 15 / 16 from the left side in the longitudinal direction, which are center positions of each 1 / 8 dimension in the longitudinal direction of the electrode 5 (hereinafter, referred to as 8-point tournament power supply as necessary).

[0029] Here, the aforementioned Non-Patent Documents 1 and 2 state that when high-frequency power is applied to a certain position (power supply point) on a long electrode surface, the voltage on the electrode surface is at its lowest level at the power supply point, and the voltage gradually increases the further away from the power supply point, reaching its maximum voltage at the furthest edge, making it easier to heat. Furthermore, "Kumagaya Saburo, Fujimoto Sanji, Industrial Electronics Equipment Series 22 "High-Frequency Heating Equipment," pp. 47-50, Nikkan Kogyo Shimbun, published in 1966" states that, in general, the degree of heating at any point in the longitudinal direction on the electrode surface is determined by the square of the ratio between the power supply point voltage (minimum level) V1 and the maximum voltage Vm, which corresponds to the square of the cosine of the ratio (i.e., 2πl / λ) of the length l (el) of the object to be heated and its internal wavelength λ, i.e., (V1 / Vm) 2 =cos 2 It is described that the cosine value is expressed as (2πl / λ). Therefore, if uniform heating is to be performed in the longitudinal direction of the electrode, for example, within 80%, it can be seen that the cosine value should be 0.9, that is, the length l (l) of the object to be heated should be about λ / 14. For example, in the case of general wood (such as pine), the dielectric wavelength λ is 16.47 m at a high frequency of 13.56 MHz, and therefore λ / 14 is 1.177 m. This means that in order to heat this wood uniformly, the length is limited to 1.177 m with a single point power supply, and when power is supplied to the middle part of the electrode excluding both ends, it appears symmetrically on both sides, that is, it is doubled to 2.354 m. If the workpiece is longer, it can be handled by increasing the number of power supply points (by applying multi-point power supply).

[0030] Comparative Examples and Examples Next, a description will be given of the results of a simulation experiment on the heating temperatures of the power supply methods of the comparative example and the embodiment. The temperature distribution of the workpiece W was analyzed using simulation software Femtet (registered trademark) (manufactured by Murata Software Co., Ltd.).

[0031] Figures 2 to 9 are representative examples of each comparative example group, and Figures 10 and 11 are representative examples of each embodiment group. Figure 12 is a list chart showing the power supply form and temperature uniformity of all comparative examples in each comparative example group, and Figure 13 is a list chart showing the power supply form and temperature uniformity of all embodiments in each embodiment group. Figure 14 is a chart showing a summary of the workpiece limit length for each power supply form and temperature uniformity of each comparative example, and Figure 15 is a chart showing a summary of the workpiece limit length for each power supply form and temperature uniformity of each embodiment.

[0032] The tests in the comparative examples and the examples will be described below in order. The simulation test conditions were as follows: upper and lower workpieces W1 and W2: wood "pine", dielectric constant: 1.8 except for some, heating time: 10 minutes, electrode width: 800 mm, workpiece width: 400 mm, workpiece height (electrode spacing): 200 mm, initial temperature: 25°C, output: 100 KW, frequency: 13.56 MHz, wavelength in air (dielectric constant: 1): 22.124 m, 1 / 4 wavelength: 5.531 m. Various adhesives can be used, but here, an aqueous polymer isocyanate adhesive with a curing temperature of 60°C was used. This adhesive can achieve uniform adhesion with a temperature variation of, for example, 20% or less. In the heating test at 100°C described later, a resorcinol resin adhesive with a curing temperature of 80°C was used.

[0033] As shown in Figures 11 and 12, the evaluation item "uniformity" was expressed with ◎, ◯, △, and ×. Temperature variation was calculated as the sum of the difference (ratio %) between the average temperature and the minimum temperature and the difference (ratio %) between the average temperature and the maximum temperature. From the calculation results, ◎ was within 10%, ◯ was within 15%, △ was within 20% (all of which had "uniformity"), and × was over 20% (no "uniformity").

[0034] (1) Test of Comparative Example Group A The comparative example A group is a two-point power supply form in which power is supplied to each center position of the electrode divided into two equal parts in the longitudinal direction. Comparative example A1 in FIG. 2 has an electrode length of 12 m and a work length of 11 m. (A) is a perspective view showing the right half of the power supply circuit and the electrode (as seen from the central power supply port SP1), (B) is a partial view showing a vertical cross section of the center of the electrode, (C) is a top view showing the right half of the electrode, and (D) is a temperature distribution diagram in the entire longitudinal direction of the heated object (work). In comparative example A1, the initial temperature of 25°C rises by 34°C near the center, while it rises by 68°C near both the left and right ends. The temperature variation exceeds 20%, as shown in No. A1 in the first row of FIG. 12 as 78.9%, and the "uniformity" item in the diagram is indicated by an x.

[0035] In addition, in Fig. 12, in the case of Comparative Example A2, when the electrode length was 9 m and the work length was 8.25 m, the temperature variation exceeded 20%, and the "Uniformity" item in the chart was indicated with an X. In Fig. 12, in the case of Comparative Example A4, when the electrode length was 12 m and the work length was also 8.25 m, the temperature variation exceeded 20%, and the "Uniformity" item in the chart was indicated with an X.

[0036] In addition, in Fig. 12, in the case of Comparative Example A3, when the electrode length is 6 m and the workpiece length is 5.5 m, the temperature variation is within 20%, and the "Uniformity" item in the chart is indicated by a circle. In addition, in Fig. 12, in the case of Comparative Example A5, when the electrode length is 12 m and the workpiece length is 5.5 m, the temperature variation is within 20%, and the "Uniformity" item in the chart is indicated by a circle. As a result of the above, it is considered that with two-point power supply, uniform heating is possible if the workpiece is 5.5 m or less in length.

[0037] (2) Test of Comparative Example Group B The comparative example B group is a four-point power supply configuration in which power is supplied to each of the central positions of the electrode divided into four equal parts. More specifically, the power supply circuit B1 is arranged such that a power supply plate b0 parallel to the electrode 5 is arranged from the power supply port SP1 on the central side, and a connection path b1 is vertically extended from the power supply plate b0 to the upper electrode and connected to the upper electrode. In the comparative example B1 in FIG. 3, the electrode length is 12 m and the work length is 11 m, (A) is a perspective view showing the right half of the power supply circuit and the electrode, (B) is a top view showing the right half of the electrode, and (C) is a temperature distribution diagram in the entire longitudinal direction of the work. In the comparative example B1, the temperature rose by 21°C near the center, while the temperature rose by 74°C near both the left and right ends, the temperature variation exceeded 20%, and the "uniformity" item in the diagram was indicated by an x.

[0038] In addition, in Fig. 12, Comparative Example B2 is when the electrode length is 12 m and the work length is 8.25 m, Comparative Example B3 is when the electrode length is 12 m and the work length is 5.5 m, and Comparative Example B4 is when the electrode length is 9 m and the work length is 8.25 m. In all cases, the temperature variation exceeded 20%, and the "uniformity" item in the chart was indicated with an x. As a result of the above, it is considered that the four-point power supply in the form of Fig. 3 cannot heat a work length of 5.5 m even.

[0039] (3) Test of Comparative Example Group C The comparative example C group differs from the configuration of the power supply circuit B1 in that the two connection paths c1 on the center side have a narrow elongated shape and are bent in the planar direction, for example, repeatedly bent into a rectangular shape to form a longer length. In this example, the connection path c1 on the center side is formed, for example, with a width dimension of 1 / 4 and a length twice as long in the longitudinal direction as the connection path b1 (see FIG. 3). By forming the connection path c1 on the center side to be longer, the component of inductance L is increased, and the impedance between the connection path c1 on the end side is balanced. The comparative example C1 in FIG. 4 has an electrode length of 12 m and a work length of 11 m. (A) is a perspective view showing the right half of the power supply circuit and the electrode, (B) is a top view showing the right half of the electrode, and (C) is a temperature distribution diagram in the entire longitudinal direction of the work. In Comparative Example C1, the temperature rose by 35° C. near the center, while the temperature rose by 52° C. near both ends. The temperature variation exceeded 20%, and the "uniformity" item in the graph was marked with an "X."

[0040] In addition, in FIG. 12, Comparative Example C2 is when the electrode length is 12 m and the work length is 8.25 m, and Comparative Example C3 is when the electrode length is 12 m and the work length is 5.5 m. In both cases, the temperature variation is within 20%, and the "uniformity" item in the chart is indicated by △ and ◯. As a result of the above, it is considered that uniform heating is possible if the work length is 8.25 m or less by adjusting the impedance balance (applied voltage balance) of the connection path c1 between the end side and the center side with four-point power supply. In this case, the shape design and production of the connection path d1 become complicated.

[0041] (4) Comparative Example D Group Test The comparative example D group is different in that the two connection paths d1 on the center side have the same width dimension as the connection paths d1 on the end sides compared to the shape of the power supply circuit C1. The connection path d1 on the center side is formed in a rectangular shape and long, thereby increasing the component of inductance L and balancing the impedance with the connection path d1 on the end sides. The connection path d1 on the center side is formed four times longer in the longitudinal direction than the connection path d1 on the end sides. Comparative example D1 in FIG. 5 has an electrode length of 12 m and a work length of 11 m. (A) is a perspective view showing the right half of the power supply circuit and the electrode, (B) is a top view showing the right half of the electrode, and (C) is a temperature distribution diagram in the entire longitudinal direction of the work. In comparative example D1, the temperature rose by 38°C near the center, while the temperature rose by 48°C near both ends, the temperature variation exceeded 20%, and the "uniformity" item in the diagram was indicated by x.

[0042] In addition, in FIG. 12, Comparative Example D2 is when the electrode length is 12 m and the work length is 8.25 m, Comparative Example D3 is when the electrode length is 12 m and the work length is 5.5 m, and Comparative Example D4 is when the electrode length is 12 m and the work length is 2.75 m. In all cases, the temperature variation is within 20%, and the "uniformity" item in the chart is indicated by a circle. As a result of the above, it is considered that uniform heating is possible if the work length is 8.25 m or less by adjusting the impedance balance of the connection path d1 between the end side and the center side with a four-point power supply. In this case, the shape design and manufacturing of the connection path d1 become complicated.

[0043] (5) Test of Comparative Example Group E The comparative example E group includes comparative examples E1 to E3 and comparative examples E4 to E6. In the comparative examples E1 to E3, the connection path e1 on the center side is set to a predetermined length Δ, in this example, 120 cm uniformly, from the intermediate position O, which is 1 / 4 of the original electrode length, toward the end side. In the comparative examples E4 to E6, the position of the connection path e1 is set according to the length of the workpiece W.

[0044] First, in Comparative Example E1 in FIG. 6, the electrode length is 12 m and the work length is 11 m. (A) is a perspective view showing the right half of the power supply circuit and the electrode, (B) is a top view showing the right half of the electrode, and (C) is a temperature distribution diagram in the entire longitudinal direction of the work. In Comparative Example E1, the temperature rose 36°C near the center, while the temperature rose 49°C near both ends. The temperature variation exceeded 20%, and the "uniformity" item in the diagram was indicated by an x. In addition, in FIG. 12, Comparative Example E2 was when the electrode length was 12 m and the work length was 8.25 m, and Comparative Example E3 was when the electrode length was 12 m and the work length was 5.5 m. In both cases, the temperature variation exceeded 20%, and the "uniformity" item in the diagram was indicated by an x. As a result of the above, it was found that, with four-point power supply, even if the central connection path e1 was changed to 120 cm toward the end compared to Comparative Examples B1 to B3, uniform heating was not possible, as in the case of Comparative Examples B1 to B3.

[0045] Next, in FIG. 12, in Comparative Example E4, the electrode length is 12 m, the work length is 8.25 m, and the central connection path e1 is adjusted by 200 mm toward the center from the original intermediate position of 1 / 4 of the electrode length. In Comparative Example E4, the temperature variation exceeds 20%, and the "uniformity" item in the diagram is indicated by ×. In Comparative Example E5, the electrode length is 12 m, the work length is 5.5 m, and the central connection path e1 is adjusted by 400 mm toward the center from the original intermediate position of 1 / 4 of the electrode length. In Comparative Example E5, the temperature variation is within 20%, and the "uniformity" item in the diagram is indicated by △. In Comparative Example E6, the electrode length is 9 m, the work length is 8.25 m, and the central connection path e1 is adjusted by 800 mm toward the end from the original intermediate position of 1 / 4 of the electrode length. In Comparative Example E6, the temperature variation was within 20%, and the "Uniformity" item in the chart was marked with a circle. As a result of the above, it is considered that uniform heating is possible if the workpiece W is 8.25 m or less in length by adjusting the central connection path e1 to an appropriate length toward the end or center depending on the length of the workpiece W. In this case, it becomes complicated to adjust the attachment position of the connection path e1 depending on the workpiece length.

[0046] (6) Comparative Example H Group Test The comparative example H group includes comparative examples H1, H2 and comparative examples H3, H4. Comparative examples H1 and H2 are single-point feed from the center, and comparative examples H3 and H4 are single-point feed from the end.

[0047] First, in comparative example H1 in Fig. 7, the electrode length is 6 m and the work length is 5.5 m. (A) is a perspective view showing the right half of the power supply circuit and the electrode, (B) is a top view showing the right half of the electrode, and (C) is a temperature distribution diagram in the entire longitudinal direction of the work. In comparative example H1, the temperature rose 34°C near the center, while the temperature rose 56°C near both ends, with the temperature variation exceeding 20%, and the "uniformity" item in the diagram is indicated by ×. In addition, in Fig. 12, comparative example H2, in the case of an electrode length of 3 m and a work length of 2.75 m, the temperature variation was within 20%, and the "uniformity" item in the diagram is indicated by ◎.

[0048] Next, in Comparative Example H3 in FIG. 8, the electrode length is 3 m, the workpiece length is 2.75 m, (A) is a perspective view showing the right half of the power supply circuit and the electrode, (B) is a top view showing the right half of the electrode, and (C) is a temperature distribution diagram in the entire longitudinal direction of the workpiece. In Comparative Example H3, the power supply side rose by 29°C and the other end rose by 57°C, the temperature variation exceeded 20%, and the "uniformity" item in the diagram was indicated by ×. In addition, in Comparative Example H4 in FIG. 12, the electrode length was 1.625 m, the workpiece length was 1.375 m, the temperature variation was within 20%, and the "uniformity" item in the diagram was indicated by ◯. As a result of the above, with one-point power supply, uniform heating was possible when the workpiece W was 2.75 m or less.

[0049] (7) Test of Comparative Example Group I The comparative example I group is an eight-point power supply type in which power is supplied to each center of the electrode 5 divided into eight equal parts through a connection path i1 of the same length. In the comparative example I1 in FIG. 9, the electrode length is 12 m and the work length is 11 m. (A) is a perspective view showing the right half of the power supply circuit and the electrode, (B) is a top view showing the right half of the electrode, and (C) is a temperature distribution diagram in the entire longitudinal direction of the work. In the comparative example I1, the temperature rose by 6°C near the center and 85°C at the end, the temperature variation exceeded 20%, and the item "uniformity" in the diagram was indicated by x. In addition, in FIG. 12, the comparative example I2 was when the electrode length was 12 m and the work length was 8.25 m, and the comparative example I3 was when the electrode length was 12 m and the work length was 5.5 m. In both cases, the temperature variation exceeded 20%, and the item "uniformity" in the diagram was indicated by x. In Comparative Example I4, the electrode length was 6 m and the work length was 5.5 m. Unlike Comparative Example I3, the temperature variation was within 20%, and the "Uniformity" item in the chart was marked with a circle. As a result of the above, it was found that with 8-point power supply, when the electrode was as long as 12 m, uniform heating was not possible even if the work length was 5.5 m.

[0050] (8) Test of Example F Group In the example F group, the electrode 5 was divided into four equal parts in the length direction, and power was supplied to each center in the same manner as in Figure 1(A), i.e., four-point tournament power supply was performed. Example F1 in Figure 10 has an electrode length of 12 m and a work length of 11 m, (A) is a perspective view showing the right half of the power supply circuit and the electrode, (B) is a top view showing the right half of the electrode, and (C) is a temperature distribution diagram over the entire work in the longitudinal direction. In example F1, the temperature rose by 47°C near the center and 43°C at the ends, with temperature variation within 10%, and the "uniformity" item in the diagram is indicated by ◎.

[0051] In FIG. 13, in Example F2, when the electrode length is 12 m and the work length is 8.25 m, the temperature variation is within 20%, and the "uniformity" item in the chart is indicated by △. In FIG. 13, in Example F3, when the electrode length is 12 m and the work length is 5.5 m, the temperature variation is within 20%, and the "uniformity" item in the chart is indicated by ◯. In FIG. 13, in Example F4, when the electrode length is 12 m and the work length is 11 m, and the work material has a dielectric constant εr twice that of the work of Example F1, the temperature variation exceeds 20%, and the "uniformity" item in the chart is indicated by ×. In FIG. 13, in Example F5, when the electrode length is 12 m and the work length is 2.75 m, the temperature variation is within 20%, and the "uniformity" item in the chart is indicated by ◎. In FIG. 13, in Example F6, when the electrode length is 13 m and the work length is 12 m, the temperature variation is within 20%, and the "uniformity" item in the chart is indicated by ◯. In FIG. 13, in Example F7, when the electrode length is 14 m and the work length is 13 m, the temperature variation exceeds 20%, and the "uniformity" item in the chart is indicated by ×. In FIG. 13, Example F8 is an improved version of Example F7, in which the electrode length is 14 m and the work length is 13 m, and when the connection path 412 of the first stage line 41 is moved 100 mm from the middle position of the two branch paths 421 to the center side (as shown by the arrow in FIG. 10 (A)), the temperature variation is within 20%, and the "uniformity" item in the chart is indicated by △. In Example F8, instead of adjusting the connection position with the electrode 5, the connection points between the first stage line 41 and the second stage line 42 are adjusted to achieve impedance balance, making it possible to achieve temperature balance as much as possible even when the workpiece is long. As a result of the above, with the four-point tournament power supply, it is somehow possible to heat the workpiece uniformly even if it is 13 m long.

[0052] In addition, a workpiece having the same configuration and shape as in Example F1 (electrode length 12 m, workpiece length 11 m) was heated to about 100°C in the same heating time, i.e., an example for evaluating "uniformity" with respect to other heating temperatures was added. In this additional example, a power level 1.66 times (=70°C / 45°C) higher than that of Example F1 was applied. The results showed an average rise of 74.67°C, with a maximum rise of 78.99°C near the center and a minimum rise of 72.37°C in a wide range toward the end. The temperature variation was within 20%, and the "uniformity" item in the chart was equivalent to 〇. In addition, the maximum and minimum temperature difference was 1.66 times that of Example F1, and it was recognized that the power level and the maximum and minimum temperature difference corresponded. In addition, 70°C is a heating temperature range that can be applied to wood bonding, etc., and 100°C is a heating temperature range that can be applied to wood bonding and wood drying.

[0053] (9) Test of Example G Group In the example G group, the electrode 5 was divided into eight equal parts, and eight-point tournament power supply was performed at each center, similar to that in Fig. 1(B). Example G1 in Fig. 11 has an electrode length of 12 m and a work length of 11 m, (A) is a perspective view showing the right half of the power supply circuit and the electrode, (B) is a top view showing the right half of the electrode, and (C) is a temperature distribution diagram over the entire longitudinal direction of the work. In example G1, the temperature was 39°C near the center and rose to around 44°C over a wide area on the end side, with temperature variation within 20%, and the "uniformity" item in the diagram is indicated by ◎.

[0054] In Fig. 13, in Example G2, the electrode length was 12 m, the work length was 11 m, and the material of the work had a dielectric constant εr twice that of the work in Example G1, but the temperature variation was within 20%, and the "uniformity" item in the chart was shown as ◯. This is thought to be because, in Example F4, which also had an electrode length of 12 m, a work length of 11 m, and a work material with a dielectric constant εr twice that of the work in Example G1, and used a four-point tournament power supply, the "uniformity" was ×, but in Example G2, the impedance balance was further improved by the eight-point tournament power supply, and the uniformity was improved.

[0055] In Figure 13, Example G3 has an electrode length of 12 m, a work length of 11 m, and a work material with a dielectric constant εr three times that of the work in Example G1, and the temperature variation exceeds 20%, and the "Uniformity" item in the chart is indicated by an X. This is thought to be because the dielectric constant εr of the work became three times larger, so the wavelength within the work became 1 / 3, i.e., the range of uniform heating became 1 / 3.

[0056] In FIG. 13, in Example G4, when the electrode length was 15 m and the work length was 14 m, the temperature variation exceeded 20%, and the "uniformity" item in the graph was marked with an "X."

[0057] In FIG. 13, Example G5 is an improved version of Example G4, with an electrode length of 15 m and a work length of 14 m. Example G5 is characterized by the fact that, as shown for reference in FIG. 11(A), when the connection path 412 of the first stage line 41 is moved 200 mm from the middle position of the two branch paths 421 to the end side (as shown by the arrow in FIG. 11(A)), the temperature variation is within 20%, and the "uniformity" item in the chart is improved to ◎. In this Example G5, it is considered that the impedance balance is further improved and uniformity is improved by adjusting the position of the first stage connection path 412 without touching the connection path 432, that is, by adjusting the connection point between the first stage line 41 and the second stage line 42.

[0058] In Fig. 13, in Example G6, when the electrode length was 14 m and the work length was 13 m, the temperature variation exceeded 20%, and the "Uniformity" item in the chart was indicated with an X. In Fig. 13, in Example G7, when the electrode length was 13 m and the work length was 12 m, the temperature variation was within 20%, and the "Uniformity" item in the chart was indicated with a △.

[0059] In FIG. 13, in Example G8, when the electrode length was 16 m and the work length was 15 m, the temperature variation exceeded 20%, and the "uniformity" item in the graph was marked with an "X."

[0060] In FIG. 13, Example G9 is an improved version of Example G8, with an electrode length of 16 m and a work length of 15 m. Example G9 is characterized by the fact that, as shown for reference in FIG. 11(A), when the connection path 412 of the first stage line 41 is moved 200 mm from the middle position of the two branch paths 421 to the end side (as shown by the arrow in FIG. 11(A)), the temperature variation is within 20%, and the "uniformity" item in the chart is indicated by a circle. In this Example G9, it is considered that the impedance balance is further improved by adjusting the position of the first stage connection path 412 without touching the connection path 432, that is, by adjusting the connection point between the first stage line 41 and the second stage line 42, and the uniformity is improved.

[0061] Next, a consideration will be made based on the summary of the comparative examples and the working examples shown in Fig. 14 and Fig. 15. In the comparative examples, as shown in Fig. 14(C), under the operating frequency and the dielectric constant of the workpiece, it was recognized that the workpiece length that could be uniformly heated was up to 2.75 m with one-point power supply, and up to twice that length, 5.5 m, with two-point power supply, and uniform heating was possible within a temperature variation of 20%. In addition, in the four-point power supply, it was recognized that the length and width dimensions and the connection position with the electrode of the central connection paths c1, d1, and e1 in the comparative examples C, D, and E were adjusted to achieve inductance balance, thereby enabling uniform heating up to about three times that length, 8.25 m. In addition, among the eight-point power supply shown in the comparative example I in Fig. 9(A), the electrode length of the comparative example I4 is shorter at 6 m compared to the comparative example I3 with an electrode length of 12 m, and therefore the interval between each connection path i1 is shorter, and therefore the voltage rise between them is smaller, and as a result, it is considered that the temperature unevenness is small and uniform heating is possible with a workpiece length of 5.5 m.

[0062] In contrast, in the examples, as shown in Fig. 15(C), the work length that can be uniformly heated is up to 12m with four-point tournament power supply, and in Example F8, in which the position of the branch point is adjusted, it is up to 13m by balancing the impedance, and it was confirmed that uniform heating with a temperature variation of 20% or less was possible. In addition, with eight-point tournament power supply, it was confirmed that uniform heating was possible up to 12m, and further, by adjusting the position of the branch point as shown in Examples G5 and G9, it was confirmed that uniform heating was possible even at 14m and 15m by balancing the impedance. Therefore, it became possible to apply uniform heating to a longer workpiece compared to the same four-point power supply shown in the comparative example.

[0063] 14 and 15 are tables showing the comparative limit lengths of the workpieces between the comparative example and the working example when the evaluation standard for "uniformity" is 20%, but here, we will confirm and consider the relationship between the limit lengths of the workpieces between the comparative example and the working example when the evaluation standard is other than 20%. Fig. 16 is a table corresponding to Figs. 14 and 15, showing a summary of the limit lengths of the workpieces when the temperature uniformity is within 15°C, and Fig. 17 is a table corresponding to Figs. 14 and 15, showing a summary of the limit lengths of the workpieces when the temperature uniformity is within 30°C.

[0064] In the comparative example shown in Figure 16(A) with four-point power supply (width and length adjustment) and a work length of 8.25 m, the temperature variation was 16.60% (see Figure 14), and in the comparative example with four-point power supply (position adjustment) and a work length of 5.5 m, the temperature variation was 17.20% (see Figure 14).In the case of Figure 14, both were shown as ◯, but in the case of "uniformity" which has an evaluation standard of 15%, they moved to ×. On the other hand, in the example shown in Fig. 16(B) with 4-point tournament power supply and a work length of 8.25 m, the temperature variation was 16.30% (see Fig. 15), and in the example with 4-point tournament power supply (branch point adjustment) and a work length of 13 m, the temperature variation was 19.30% (see Fig. 15), and in the example with 8-point tournament power supply and a work length of 12 m, the temperature variation was 18.10% (see Fig. 15). In the case of Fig. 15, all were shown as ◯, but in the "uniformity" with an evaluation standard of 15%, they changed to ×. Based on the above, in both the comparative example and the example, it was recognized that in response to the change in the evaluation standard from 20% to 15%, the short workpieces were almost uniformly heated, while some of the long workpieces, for example 12 m and 13 m, changed from ◯ to ×.

[0065] Next, in the comparative example shown in Fig. 17(A) with four-point power supply (length adjustment) and a work length of 11 m, the temperature variation was 22.5% (see Fig. 14), and in the comparative example shown in Fig. 14 with four-point power supply (position adjustment), the temperature variation was 30.0% (see Fig. 14), and in the case of Fig. 14, both were marked as ×, but in the case of "uniformity" with an evaluation standard of 30%, they moved to ◯. On the other hand, in the example shown in Fig. 17(B) with four-point tournament power supply and a work length of 13 m, the temperature variation was 21.7% (see Fig. 15), and in the example shown in Fig. 15 with eight-point tournament power supply and a work length of 13 m, the temperature variation was 22.6% (see Fig. 15), and in the case of Fig. 15, both were marked as ×, but in the case of "uniformity" with an evaluation standard of 30%, they moved to ◯. According to the above, in response to the change in the evaluation standard from 20% to 30%, an extension (from 8.25 m to 11 m) was observed in the workpiece limit length for some heating methods in the comparative example, and an extension (from 12 m to 13 m) was observed in the workpiece limit length for some heating methods in the examples, and it was recognized that the workpiece limit length for "uniformity" was extended in both the comparative example and the examples. In this way, the workpiece limit length changes in a similar manner in the comparative example and the examples depending on the level of the evaluation standard for "uniformity", and therefore the workpiece limit length in the examples can be made longer than in the comparative example.

[0066] When setting the evaluation criteria for "uniformity," for example, in the case of "thawing," it is desirable to set the temperature variation small, whereas in the case of "drying," since power is absorbed where there is moisture, a certain degree of temperature variation is acceptable, and so the criteria can be set taking such circumstances into consideration.

[0067] Fig. 18 is a diagram showing another embodiment of the power supply circuit of Fig. 11, and is a partial perspective view showing a structure in which connection path 4320 connected to electrode 51 supplies power in a tournament manner in the width direction of electrode 51. When the length of the object to be heated is long, for example, 10 m, the width dimension may be about 600 to 1000 mm, or about 20000 mm. With this width size, voltage changes not only in the length direction of electrode 51 but also in the width direction, i.e., heating unevenness in the width direction, become an issue, so it is desirable to adopt a multi-point power supply structure in the width direction, preferably a tournament power supply structure.

[0068] 18, a connection path 4320 is formed at the tip of the third-stage line 43. The connection path 4320 has a tournament power supply structure. The connection path 4320 includes an upright portion 4321 extending from above the middle position of the electrode 51 in the width direction toward the electrode 51 surface, and a two-branched piece portion 4322 that is branched in two in the width direction from the lower end of the upright portion 4321 and has each tip extending to the center position of each half of the width direction of the electrode 51. The connection path 4320 also includes a first connection piece portion 432f that stands upright on the electrode 51 surface from the tip of the two-branched piece portion 4322 that extends to one side in the width direction, and a second connection piece portion 432b that stands upright on the electrode 51 surface from the tip of the two-branched piece portion 4322 that extends to the other side in the width direction.

[0069] By employing the connection path 4320, it is possible to suppress the variation in the voltage level in the width direction of the electrode. Although a tournament power supply structure is employed at each end of the third-stage line 43 in Fig. 18, it may be employed at each end of the second-stage line 42. In addition to the two-point or four-point tournament power supply structure, a multi-point power supply system including two-point power supply, as shown in the comparative example described above, may be applied in the width direction as long as it is possible to supply a more uniform voltage in the width direction.

[0070] The present invention is applicable to the dielectric heating bonding of laminated materials described in the first and second embodiments, as well as to any other dielectric heating treatment for long objects that require uniform heating in the length direction. For example, the present invention is applicable to bonding of laminated lumber, as well as bonding, drying, alteration, and thawing of various objects to be heated, as long as the object is long and uneven heating is an issue.

[0071] In addition, in this embodiment, four-point tournament feeding and eight-point tournament feeding are shown, but a circuit configuration with multi-point feeding including 16-point tournament feeding may be used depending on the range of uniform heating according to the heating purpose, etc. Furthermore, in cases where the shape of the workpiece is not symmetrical in the longitudinal direction, the shape of the electrodes or the tournament shape of the feeding circuit do not need to be symmetrical in the longitudinal direction, and the positions and intervals of the connection paths 412, etc. may be designed in advance and used appropriately depending on the amount of heat required, so that heating balance can always be maintained. [Explanation of symbols]

[0072] 10,10' Dielectric heating device 1 Power supply section 4 Power supply circuit 41 First stage track 42 Second stage track 43 3rd stage track 411,421,431 2-way intersection 412,422,432,4320 Connections 5 electrodes 51 Upper electrode 52 Lower electrode Double work W1 Upper work W2 Lower work

Claims

1. A power supply circuit is provided to supply high frequency power generated by a power supply unit to the opposing long electrodes, the power supply circuit has at least a first stage line and a second stage line hierarchically connected between the power supply unit and the electrode, the first stage line is branched into two on the left and right sides in the longitudinal direction of the electrode at the output end of the power supply unit, and each tip corresponds to a center position of each half of the longitudinal dimension of the electrode with a predetermined dimension added; The second stage line is branched into two at each end of the first stage line, to the left and right in the longitudinal direction of the electrode, and each end corresponds to the center position of each 1 / 4 of the longitudinal dimension of the electrode.

2. The dielectric heating device according to claim 1, wherein the first stage line has a first stage 2 branch path arranged parallel to the longitudinal direction of the electrode from the output end of the power supply unit, and a first stage connection path extending from each end of the first stage 2 branch path toward the surface of the electrode.

3. 3. The dielectric heating device according to claim 2, wherein each of the first-stage two branch paths has its tip coincident with a center position of each half of the longitudinal dimension of the electrode.

4. 3. The dielectric heating device according to claim 2, wherein each of the first-stage two branch paths has an end shifted by a preset adjustment dimension from a center position of each half dimension in the longitudinal direction of the electrode.

5. 2. The dielectric heating device according to claim 1, wherein the shapes of the first stage line and the second stage line are symmetrical with respect to a center in the longitudinal direction of the electrode.

6. 2. The dielectric heating device according to claim 1, wherein each end of a final stage line connected to the electrode, which is the final stage in the hierarchy, has a multi-point feeding shape branched in the width direction of the electrode.

7. The power supply circuit further includes a third stage line, The third stage line is branched into two at each end of the second stage line, to the left and right in the longitudinal direction of the electrode, and each end corresponds to a central position of a dimension that is 1 / 8 of the longitudinal direction of the electrode.

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