Magnetron apparatus and manufacturing method for the same

Abstract: In a magnetron apparatus and a manufacturing method of the present invention, the magnetron apparatus comprises an anode cylinder (1), and a plurality of plate-form anode segments (15) radially arranged around a central axis of the anode cylinder inside the anode cylinder. The anode segments (15) are pressed against an inner surface of the anode cylinder (1) by a pin (40) press-fit into the central portion of the anode cylinder (1), and a far-end-side end surface each of the anode segments is secured to the inner surface. A hollow (22) is provided in the central portion of an inner end surface (21) where the anode segments (15) come into contact with the pin (40).

Description: BACKGROUND OF THE INVENTION The present invention relates to a magnetron arrangement for use in the production of magnetron apparatuses for microwave ovens and the like, and to a manufacturing method for the same. A magnetron apparatus is a microwave oscillating tube which operates at a fundamental frequency of, for example, 2,450 MHz, and is used as a high frequency source in electric arrangementes using microwaves such as microwave heaters and microwave discharge lamps. A typical configuration of a magnetron apparatus is such that a cathode and an anode are disposed coaxially cylindrically. More specifically, a magnetron apparatus comprises a coiled cathode, an anode cylinder disposed with the cathode as the central axis, and plural anode segments radially arranged around the central axis in a space inside the anode cylinder for defining a resonant cavity. A magnetron apparatus further comprises a pair of magnetic pole pieces disposed at upper and lower open ends of the anode cylinder and magnetically associated with an annular permanent magnet, plural strap rings for electrically interconnecting the anode segments, and an antenna with one end connected to one of the anode segments for discharging microwaves. In the above-mentioned magnetron apparatus, after the anode cylinder, the anode segments, the antenna, the strap rings and the magnetic pole pieces are integrally assembled as an anode assembly, the cathode is disposed in the central portion of the anode assembly. In a magnetron apparatus, as well known, the assembly precision of the components greatly influences the performance of the apparatus, and the arrangement of the plural anode segments for defining a desired resonant cavity inside the anode cylinder is particularly important. Therefore, it is a technical problem of the magnetron apparatus to coaxially radially secure the plural anode segments with high precision so as to be equally spaced on the inner surface of the anode cylinder with a predetermined distance from the cathode. In a conventional manufacturing method for the magnetron apparatus, a brazing and soldering method is known in which the anode segments are pressed against the inner surface of the anode cylinder by use of a temporary assembling pin and all the anode segments are secured to the inner surface at once with a brazing filler metal as disclosed in, for example, examined and published Japanese patent application TOKKO Sho 57-18823. Hereinafter, the conventional magnetron arrangement and the manufacturing method will be concretely explained with reference to FIG. 16 and FIG. 17. FIG. 16 is a partially cutaway perspektive view showing a configuration of a principal part of an anode assembly in a conventional magnetron arrangement before a brazing filler metal is melted. FIG. 17 is a cross sectional view showing the configuration of the principal part of the anode assembly in the conventional magnetron arrangement after the brazing filler metal is melted. As shown in FIG. 16 and FIG. 17, plural anode segments 52 (52a, 52b, 52c, 52d, ---) are coaxially radially arranged inside an anode cylinder 51. Specifically, for example, ten anode segments 52 are equally spaced inside the anode cylinder 51. Each of the anode segments 52 is formed into a substantial rectangular shape having a longitudinal size of 9.5 mm and a lateral size of 13 mm, for example. In each of the anode segments 52, one end surface on the shorter side is secured to the inner surface of the anode cylinder 51. These anode segments 52 are pressed against the inner surface of the anode cylinder 51 by a jig pin 40, which is a temporarily used assembling pin, shown by the dash and dotted line of the figure, and the above-mentioned one end surface is secured to the inner surface of the anode cylinder 51 by melting a wire-form brazing filler metal 56 (FIG. 16). When a non-illustrated coiled cathode is disposed along the central axis of the anode cylinder 51, each end surfaces of the anode segments 52 on the central side in the direction of the arrangement, i.e. an end surface each of the anode segments 52 opposed to the above-mentioned one end surface (hereinafter, the end surface on the central side will be referred to as an "inner end surface") is situated with a predetermined distance from the cathode, so as to define a desired resonant cavity inside the anode cylinder 51. At opposite end surfaces (i.e., upper surface and lower surface) on the longer side each of the anode segments 52, strap ring grooves 53a and 53b are provided for brazing two pairs of strap rings 54 (54a and 54b) and 55 (55a and 55b). At the upper end surface of each of the anode segments 52 where the strap ring groove 53a is provided, a terminal groove 53c is provided for connecting one end of a non-illustrated antenna. The strap rings 54b and 55a are brazed to every two anode segments 52a, 52c, ---, and the strap rings 54a and 55b are brazed to the remaining anode segments 52b, 52d, ---. A plating layer (not shown) of the brazing filler metal 56 is formed on the surface of each of the strap rings 54 and 55, and when the brazing filler metal 56 is melted to secure the one end surfaces of the anode segments 52 to the inner surface of the anode cylinder 51, the plating layer is also melted, so that the strap rings 54 and 55 are secured to the corresponding anode segments 52. The above-mentioned anode cylinder 51, anode segments 52, strap rings 54 and 55, and antenna (not shown) are made of, for example, oxygen free copper. The jig pin 40 is made of a metal member containing silicon nitride (Si 3 N 4 ), and the surface of a cylindrical portion which comes into contact with the inner end surface of each of the anode segments 52 is formed so as to be as smooth as a mirror finished surface. The brazing filler metal 56 is made of an alloy of silver and copper, and the strap rings 54 and 55 and the antenna (not shown) are made of copper having a silver plating layer provided on the surface thereof. In such a conventional manufacturing method for the magnetron arrangement, first, the plural anode segments 52 and the strap rings 54 and 55 are placed in the respective positions inside the anode cylinder 51 by use of a non-illustrated temporary assembling jig. Then, the jig pin 40 is moved along the central axis of the anode cylinder 51 and press-fit from below into the central portion in the direction of the arrangement of the anode segments 52 (the central portion of the anode cylinder 51) as shown by the arrow Y of FIG. 16. So that the jig pin 40 contacts with the inner end surfaces of the anode segments 52. Thereby, the anode assembly is maintained in a preassembled condition where the one end surface each of the anode segments 52 are pressed against the inner surface of the anode cylinder 51 by the jig pin 40. Hereafter, only the temporary assembling jig is detached, and the brazing filler metal 56 is placed on the end surfaces on the longer side of the anode segments 52 so as to be in contact with the inner surface of the anode cylinder 51 as shown in FIG. 16. After one of the magnetic pole pieces (not shown) is attached to an upper open end of the anode cylinder 51, one end of the antenna (not shown) is attached to one of the anode segments 52. Then, the anode assembly in the preassembled condition is heated to a predetermined temperature (for example, 800 to 900 'C) in a non-illustrated furnace. Thereby, the brazing filler metal 56 is melted and flows into a clearance between the inner surface of the anode cylinder 51 and the one end surface each of the anode segments 52 caused by expansion. At this time, the plating layers on the strap rings 54 and 55 and the antenna (not shown) are also melted. Hereafter, by taking the anode assembly out of the furnace while maintaining the preassembled condition and cooling it, the inner surface of the anode cylinder 51 and the one end surface each of the anode segments 52, the strap ring grooves 53a and 53b and the corresponding strap rings 54 and 55, and the one of the anode segment 52 and the antenna (not shown) are secured. Consequently, after the jig pin 40 is downwardly pulled out, the other of the magnetic pole pieces (not shown) is attached to a lower open end of the anode cylinder 51, and thereby the assembly of the anode assembly is finished. In the conventional magnetron arrangement and the manufacturing method as described above, when the jig pin 40 is press-fit or taken out by moving it in the direction of the central axis, the jig pin 40 comes into contact with and is rubbed against the inner end surface each of the anode segments 52 over the entire surface in the direction of the central axis. That is, in the conventional magnetron arrangement and the manufacturing method, the contact surface of the jig pin 40 and each the anode segments 52 equal the length of the inner end surface in the direction of the central axis, and the length of the contact surface (shown at A in FIG. 16) is long. For this reason, in the conventional magnetron arrangement and the manufacturing method, during the while the jig pin 40 is being press-fit or being taken out, contact pressure exerted on the anode segments 52 through the contact surfaces increases, so that the anode segments 52 are apt to be deformed. When such deformation is caused on the anode segments 52, the molten brazing filler metal 56 does not deposit onto the entire surface of the one end surface each of the anode segments 52 but the anode segments 52 come off due to insufficient brazing. Further, the deformation of the anode segments 52 changes the configuration of the strap ring grooves 53a and 53b, so that deformation of the strap rings 54 and 55 are caused and the strap rings 54 and 55 come off because the strap rings 54 and 55 are not secured to the strap ring grooves 53a and 53b. When the components such as the plural anode segments 52 are mass-produced, it is difficult to form these components so as to have uniform outer dimensions and it is impossible to completely prevent the outer dimensions from varying. For this reason, in the conventional magnetron arrangement and the manufacturing method, there are occasions when the anode and the cathode are short-circuited because of the variation in outer dimension specifically, in the case that the outer dimensions of the anode segments 52 are greater than predetermined outer dimensions and the outer dimensions of the inner surface of the anode cylinder 51 are smaller than predetermined outer dimensions, when the jig pin 40 is press-fit from below, the inner end surface each of the anode segments 52 is extended in the movement direction of the jig pin 40 by stress caused by the press fitting of the jig pin 40, so that copper foil burrs 57 as illustrated in FIG. 18 are caused at the upper end of the inner end surface. As a result, when the cathode is placed along the central axis of the anode assembly (anode cylinder 51), an accident frequently occurs such that the burrs 57 come into contact with the cathode and the contact causes a short circuit. Further, in the case that the anode cylinder 51 or the anode segments 52 are formed to have outer dimensions which are different from predetermined outer dimensions as mentioned above, greater power is necessary when the jig pin 40 is press-fit or taken out, so that dents and scratches are caused also on the jig pin 40 and it is required to replace the jig pin 40 with a new one. Further, in each of the anode segments 52, as has been explained in the above, the strap ring groove 53a and the terminal groove 53c are provided at one of the end surface on the longer side, and the strap ring groove 53b is provided at the other end surface. For this reason, in the conventional magnetron arrangement and the manufacturing method, when the jig pin 40 is press-fit so as to be in contact with the inner end surface each of the anode segments 52, the pressing force which the anode segments 52 receive from the jig pin 40 and the anode cylinder 51 is not uniform in the direction of the central axis. Specifically, when each anode segment 52 is divided into three areas, for example, an upper area Va, a central area Vb and a lower area Vc in the direction of the central axis as shown in FIG. 17, the central area Vb does not include the grooves 53a, 53b and 53c. Thereby, the pressure exerted on the central area Vb is greater than that exerted on the upper and lower areas Va and Vc. When the anode assembly in the preassembled condition is heated, since the anode segments 52 expand and the molten brazing filler metal 56 flows into the clearance between the anode cylinder 51 and the anode segments 52, the pressing force applied on the upper and lower areas Va and Vc by the jig pin 40 is smaller than the pressing force which the central area Vb receives therefrom. Thus, when the pressing force exerted on the anode segments 52 is not uniform in the direction of the central axis, because of the above-mentioned reasons combined with the fact that the surface of the jig pin 40 is as smooth as a mirror finished surface, the anode segments 52 slide over the inner surface and are secured to the inner surface of the anode cylinder 51 with the one end surfaces of the anode segments 52 being inclined from the direction of the central axis. Consequently, in the conventional magnetron arrangement and the manufacturing method, the distance between adjoining two anode segments 52 i.e. the pitch varies as shown at P1, P2 and P3 in FIG. 19, so that the plural anode segments 52 are not equally spaced inside the anode cylinder 51. As has been explained in the above, in the conventional magnetron arrangement and the manufacturing method, deformation of the anode segments 52 and the strap rings 54 and 55 and coming-off of brazed parts due to insufficient brazing are apt to occur, and the burrs 57 and the variation in pitch of the plural anode segments 52 are caused. Therefore, in the conventional magnetron arrangement and the manufacturing method, it has been impossible to define the desired resonant cavity inside the anode assembly 51, so that it is impossible to oscillate microwaves of the fundamental frequency with stability. Further, the magnetron efficiency deteriorates and high-frequency noises are markedly generated. Examples of a conventional magnetron arrangement intended for reducing the contact pressure between the jig pin 40 and the anode segments 52 include one disclosed in unexamined and published Japanese patent application JP-A-1-52365. In the conventional magnetron arrangement, by forming the cylindrical portion of the jig pin 40 so as to have dimensions which are 50 to 70% of the inner end surface each of the anode segments 52, the contact pressure is reduced which is caused when the jig pin 40 is press-fit or taken out. However, in the conventional magnetron arrangement, when the anode segments 52 are pressed against the inner surface of the anode cylinder 51, on the inner end surface each of the anode segments 52 there are produced one area which is pressed by being in contact with the cylindrical portion of the jig pin 40 and the other area which is not pressed because it does not come into contact with the cylindrical portion. Thereby, in the conventional magnetron arrangement, the pressing force which the anode segments 52 receive is unbalanced in the direction of the central axis, so that in addition to the problem that the anode segments are not equally spaced, a new problem arises that the diameter of an inscribed circle defined by the inner end surface each of the plural anode segments 52 varies in the direction of the central axis (the vertical direction). Because of these problems, the conventional magnetron arrangement as shown e.g. in JP-A-1-52365 is not realized and commercialized. From US-A-2 433 339 it is already known to use a temporary assembling jig for placing the plural anode segments in the respective predetermined positions wherein the jig is double tapered so as to leave a hollow mid-height of the vane edges. BRIEF SUMMARY OF THE INVENTION The object of the present invention is to provide a magnetron arrangement and a manufacturing method for the same that can solve the aforementioned problems in the conventional arrangement and can be configured with less cost and has a long life. In order to achieve the above-mentioned object, a magnetron arrangement comprises: an anode cylinder, and a plurality of plate-shaped anode segments radially arranged around the central axis of said anode cylinder inside said anode cylinder and pressed against an inner surface of the anode cylinder by a pin press-fit into the central portion of the anode cylinder, so that a far-end-side end surface each of said anode segments is secured to said inner surface, and is characterized in that each of the anode segments has a hollow at the central portion of its inner end surface which contacts said pin. According to this configuration, a conventionally-used existing assembly jig can be used without any modification. Further, the assembly precision of the magnetron arrangement can be easily improved, so that the magnetron apparatus can be operated with stability. In the magnetron arrangement of another aspect of the present invention, the length of the hollow in the direction of the central axis is 20 to 50% of the length of the inner end surface in the direction of the central axis. According to this configuration, the deterioration of magnetron efficiency can be restrained. In the magnetron arrangement under another aspect of the present invention a chamfered portion is provided on at least one angular portion of the inner end surface in the direction of the central axis. According to this configuration, a magnetron arrangement with higher assembly precision can be obtained. A manufacturing method for a magnetron arrangement of the present invention comprising an anode cylinder and a plurality of plate-shaped anode segments radially arranged around the central axis of said anode cylinder inside said anode cylinder and pressed against an inner surface of said anode cylinder by a pin press-fit into the central portion of said anode cylinder, so that a far-end-side end surface each of said anode segments is secured to said inner surface, is characterized by a step in which a hollow is provided in a central portion of the inner end surface of each of the anode segments which is foreseen to contact said pin; and a step in which the pin is press-fit into the central portion of the anode cylinder and the far-end-side end surface is pressed against and secured to the inner surface of the anode cylinder. According to this configuration, a conventionally-used existing assembly jig can be used as it is without any modification. Further, the assembly precision of the magnetron arrangement can be easily improved, so that the magnetron apparatus produced therewith can be operated with stability. The manufacturing method for the magnetron arrangement under another aspect of the present invention further comprises a step in which the length of the hollow in the direction of the central axis is formed so as to be 20 to 50% of the length of the inner end surface in the direction of the central axis. According to this configuration, the pressure exerted on the anode segments by an assembly member can be sufficiently reduced, so that a magnetron arrangement with high assembly precision can be obtained. The manufacturing method for the magnetron arrangement under another aspect of the present invention further comprises a step in which a chamfered portion is provided on at least one angular portion of the inner end surface in the direction of the central axis. According to this configuration, the insertion pressure of the assembly member exerted on the central portion of the anode cylinder can be further reduced. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross sectional view showing a configuration of a magnetron apparatus. FIG. 2 is a partially cutaway perspective view showing a configuration of a principal part of a magnetron arrangement according to the invention and leading to the production of the magnetron apparatus shown in FIG. 1 before a brazing filler metal is melted. FIG. 3 is a cross sectional view showing the configuration of the principal part of the anode assembly in the magnetron arrangement shown in FIG. 2 after the brazing filler metal is melted. FIG. 4 is a graph showing a relationship between magnetron efficiency and the ratio of a length Hb to a length Ha. FIG. 5 is a view showing a configuration of a modified version of the anode segment shown in FIG. 3. FIG. 6 is a view showing a configuration of another modified version of the anode segment shown in FIG. 3. FIG. 7 is a cross sectional view showing a configuration of a principal part of an anode assembly of a magnetron arrangement in a second embodiment of the present invention. FIG. 8 is a view showing a configuration of a modified version of the anode assembly shown in FIG. 7. FIG. 9 is a view showing a configuration of another modified version of the anode assembly shown in FIG. 7. FIG. 10 is a view showing a configuration of another modified version of the anode assembly shown in FIG. 7. FIG. 11 is a view showing a configuration of another modified version of the anode assembly shown in FIG. 7. FIG. 12 is a graph showing measurement results of the noise level at the fifth harmonic. FIG. 13 is a measurement result showing noise characteristics in the vicinity of the fifth harmonic in the conventional magnetron arrangement shown in FIG. 16. FIG. 14 is a measurement result showing noise characteristics in the vicinity of the fifth harmonic in a magnetron produced by using the arrangement of the first embodiment. FIG. 15 is a measurement result showing noise characteristics in the vicinity of the fifth harmonic in a magnetron produced by using the arrangement of the second embodiment. FIG. 16 is a partially cutaway perspective view showing a configuration of a principal part of an anode assembly in a conventional magnetron arrangement before a brazing filler metal is melted. FIG. 17 is a cross sectional view showing the configuration of the principal part of the anode assembly in the conventional magnetron arrangement after the brazing filler metal is melted. FIG. 18 is an explanatory view showing the generation of burrs in the conventional magnetron arrangement. FIG. 19 is an explanatory view showing the variation in pitch of the anode segments in the conventional magnetron arrangement. DETAILED DESCRIPTION OF THE INVENTION Hereinafter, preferred embodiments of a magnetron arrangement and that of a manufacturing method in accordance with the present invention will be described with reference to the accompanying drawings. FIRST EMBODIMENT FIG. 1 is a cross sectional view showing a configuration of a magnetron. FIG. 2 is a partially cutaway perspective view showing a configuration of a principal part of a magnetron arrangement leading to the production of the magnetron apparatus shown in FIG. 1 before a brazing filler metal is melted. FIG. 3 is a cross sectional view showing the configuration of the principal part of the anode assembly in the magnetron arrangement shown in FIG. 2 after the brazing filler metal is melted. In FIG. 1, the magnetron apparatus comprises an anode cylinder 1, first and second magnetic pole pieces 2 and 3 attached to upper and lower open ends of the anode cylinder 1, respectively, and first and second grommetted metal cylinders 4 and 5 attached to the first and second magnetic pole pieces 2 and 3, respectively. The outer end surface of the first magnetic pole piece 2 is covered with a flange 4a provided at one end of the first metal cylinder 4, and a rim of the flange 4a is secured to the upper open end of the anode cylinder 1. To the other end of the first metal cylinder 4, a microwave output terminal 7 is sealed through an insulating ring 6. Likewise, the outer end surface of the second magnetic pole piece 3 is covered with a flange 5a provided at one end of the second metal cylinder 5, and a rim of the flange 5a is secured to the lower open end of the anode cylinder 1. To the other end of the second metal cylinder 5, a cathode terminal lead stem 8 is sealed. On the periphery of the anode cylinder 1, a plurality of fins 9 are provided in a multiplicity of stages in order to discharge heat generated inside the anode cylinder 1. On the peripheral end surface of the first magnetic pole piece 2, a first annular permanent magnet 10 is placed coaxially with on the flange 4a, and one magnetic pole surface 10a and the first magnetic pole piece 2 are magnetically associated with each other. Similarly, on the peripheral end surface of the second magnetic piece 3, a second annular permanent magnet 11 is placed coaxially with on the flange 5a, and one magnetic pole surface 11a and the second magnetic pole piece 3 are magnetically associated with each other. The other magnetic pole surfaces 10b and 11b of the first and second permanent magnets 10 and 11 are magnetically interconnected by a pot-shaped yoke 12 surrounding the fins 9. In order to prevent leakage of high-frequency noises, a metallic shield case 13 incorporating the above-mentioned stem 8 and a known LC filter circuit member (not shown) is attached to the bottom of the pot-shaped yoke 12. Inside the anode cylinder 1, a coiled cathode 14 disposed along the central axis of the anode cylinder 1 and plural anode segments 15 coaxially radially arranged around the cathode 14 for defining a resonant cavity are provided. The cathode 14 is connected to a pair of cathode terminals 14a and 14b inside the anode cylinder 1. The pair of cathode terminals 14a and 14b are led out of the anode cylinder 1 through the stem 8, and connected to a non-illustrated high-frequency power source. Inside the anode cylinder 1, an antenna 16 with one end connected to the microwave output terminal 7 is connected to one of the a node segments 15. Thereby, the magnetron apparatus discharges a microwave having a fundamental frequency of, for example, 2,450 MHz from the microwave output terminal 7. Here, an anode assembly of the magnetron arrangement of a first embodiment of the present invention will be elucidated in more detail with reference to FIG. 1 to FIG. 3. In FIG. 1 to FIG. 3, the anode assembly is one of the assembly units at the time of manufacture of the magnetron apparatus, and is an integral assembly of the anode cylinder 1, the first and second magnetic pole pieces 2 and 3, the plural anode segments 15, the antenna 16 and two pairs of strap rings 17 (17a and 17b) and 18 (18a and 18b) for interconnecting the plural anode segments 15 inside the anode cylinder 1. Such an anode assembly enables improvement of the assembly precision of the magnetron arrangement. The anode cylinder 1, the anode segments 15 and the strap rings 17 and 18 are made of the same metal material, for example, oxygen free copper, and secured by the brazing and soldering method using a brazing filler material made of an alloy of silver and copper. The antenna 16 is made of, for example, oxygen free copper, and the first and second magnetic pole pieces 17 and 18 are made of a magnetic material such as iron. Inside the anode cylinder 1, the plural, for example, ten anode segments 15 (15a, 15b, 15c, 15d, ---) are equally spaced. Each of the anode segments 15 is formed into a plate shape having a longitudinal size of 9.5 mm, a lateral size of 13 mm, and a thickness size of 2 mm, for example. These anode segments 15 are pressed against the inner surface of the anode cylinder 1 by a jig pin 40, which is a temporarily used assembling pin, shown by the dash and dotted line of the figure, and one end surface on the shorter side is secured to the inner surface of the anode cylinder 1 by melting a wire-form brazing filler metal 19 (FIG. 2). At opposite end surfaces (i.e., upper surface and lower surface) on the longer side of each of the anode segments 15, strap ring grooves 20a and 20b are provided for brazing the two pairs of the strap rings 17 (17a and 17b) and 18 (18a and 18b). At the upper end surface of each of the anode segments 15 where the strap ring groove 20a is provided, a terminal groove 20c is provided for connecting one end of the antenna 16. The strap rings 17b and 18a are brazed to every two anode segments 15a, 15c, ---, and the strap rings 17a and 18b are brazed to the remaining anode segments 15b, 15d, ---. A plating layer (not shown) of the brazing filler metal 19 is formed on the surface of each of the strap rings 17 and 18, and when the brazing filler metal 19 is melted to secure the one end surface each of the anode segments 15 to the inner surface of the anode cylinder 1, the plating layer is also melted, so that the strap rings 17 and 18 are secured to the corresponding anode segments 15. At an end surface of each of the anode segments 15 on the central side in the direction of the arrangement, i.e. an inner end surface 21 opposed to one end surface on the shorter side and in contact with the jig pin 40, a hollow 22 having a rectangular opening configuration is provided in the central portion in the direction of the central axis (shown by the arrow F of the figure) of the anode cylinder 1. Here, the opening configuration is the configuration of the hollow 22 sighted in a thickness direction each of the anode segments 15. The hollow 22 is formed by cutting the inner end surface 21 so as to have a length Hb in the direction of the central axis and a depth D in the direction of the radius of the anode cylinder 1. The length Hb of the hollow 22 is selected so as to be 20 to 50% of a length Ha of the inner end surface 21 in the direction of the central axis. At the inner end surface 21, a chamfered portion may be provided in which at least one of the angular portions 21a and 21b in the direction of the central axis is chamfered. With this configuration, in the magnetron arrangement of this embodiment, the area of contact between the anode segments 15 and the jig pin 40 can be reduced, so that the pressure exerted on the anode segments 15 by the jig pin 40 can be reduced. Consequently, in the magnetron arrangement of this embodiment, the problems can be solved such as the deformation of the anode segments and the coming-off of brazed parts due to insufficient brazing in the conventional magnetron arrangement described previously and the generation of burrs shown in FIG. 18, so that microwaves of the fundamental frequency can be oscillated with stability without any faulty oscillation. Further, in the magnetron arrangement of this embodiment, a conventionally used ordinary assembly jig such as the jig pin 40 can be used without any modification, so that the manufacture cost can be prevented from increasing due to a modification of manufacture equipment. The jig pin 40 is made of an expensive ceramic member containing silicon nitride (Si 3 N 4 ), and the surface of a cylindrical portion which is in contact with the inner end surface 21 is formed so as to be as smooth as the mirror finished surface. The outer diameter of the cylindrical portion is set so that the diameter of an inscribed circle defined by a plurality of coaxially radially arranged anode segments 15 is a value which is decided based on the theory of operation for the magnetron apparatus. Next, technical advantages of the hollow 22 will be explained concretely. In the below-mentioned description, each anode segment 15 is divided into three areas, i.e. a central area Vy having the hollow 22 and upper and lower areas Vx and Vz situated above and below the central area Vy. In the anode segments 15 of this embodiment, excepting the portion of the hollow 22, two portions, i.e. the inner end surface 21 in the upper area Vx and the inner end surface 21 in the lower area Vz are in contact with the jig pin 40. Therefore, the pressure from the jig pin 40 is exerted only on the upper and lower areas Vx and Vz and the area of contact with the jig pin 40 can be reduced. Consequently, in the magnetron arrangement of this embodiment, the anode segments 15 can be well-balancedly supported at the upper and lower two portions divided in the direction of the central axis with respect to the jig pin 40, so that the assembly precision of the magnetron arrangement can be easily improved. Moreover, since the area of contact with the jig pin 40 is reduced, the flatness of the contact surface which comes into contact with the jig pin 40 can be also easily improved, so that the insertion pressure of the jig pin 40 exerted on the central portion in the direction of the arrangement of the anode segments 15 can be reduced. Further, the strap ring grooves 20a and 20b are provided at the end surface on the longer side of each anode segment 15. Thereby, the pressure exerted on the upper and lower areas Vx and Vz by the jig pin 40 is reduced, so that the insertion pressure of the jig pin 40 exerted on the central portion in the direction of the arrangement of the anode segments 15 can be further reduced. Even if unbalance occurs in the pressure from the jig pin 40 in the upper and lower areas Vx and Vz, the unbalance can be absorbed by the portions of the strap ring grooves 20a and 20b. Thus, in the magnetron arrangement of this embodiment, by providing the hollow 22 in the central portion in the direction of the central axis of the inner end surface 21, the pressure exerted on the anode segments 15 by the jig pin 40 can be reduced and uniformized. Consequently, in the magnetron arrangement of this embodiment, the problems of the conventional magnetron arrangement can be solved such as the deformation of the anode segments and the strap rings caused at the time of assembly, the coming-off of brazed parts due to insufficient brazing, the generation of burrs shown in FIG. 18 and the variation in pitch shown in FIG. 19. As a result, in the magnetron apparatus produced by using this arrangement, a stable operation having no faulty oscillation of a predetermined frequency can be performed by use of the conventional ordinary assembly jig as it is. On the contrary, in the conventional magnetron arrangement, as described previously with reference to FIG. 17, when the jig pin 40 is press-fit in the central portion in the direction of the arrangement of the anode segments, the pressing force exerted on the central area Vb is greater than that exerted on the upper and lower areas Va and Vc in the direction of the central axis of the anode segments. Therefore, in the conventional magnetron arrangement, variation in the pitch of the anode segments is caused as illustrated in FIG. 19, so that the plural anode segments are not equally spaced. Next, the depth D and the length Hb of the hollow 22 will be explained in detail. The depth D of the hollow 22 defines the distance from the inner end surface 21 each of the anode segments 15 in a direction toward the inner surface of the anode cylinder 1 (the distance in the direction of the radius) when the anode segments 15 are secured to the anode cylinder 1. The effects of reducing and uniformizing the pressure exerted on the anode segments 15 by the jig pin 40 can be always obtained by providing the hollow 22 so that the portion of the hollow 22 is kept from contact with the jig pin 40. Therefore, the depth D of the hollow 22 may be any depth as long as the portion of the hollow 22 can be always kept from contact with the jig pin 40. Therefore, in view of the deformation of the anode segments 15 at the time of expansion it is necessary that the depth D of the hollow 22 be not less than approximately 0.1 mm. For mass production, in view of the dimensional tolerance of the anode segments 15 and variation due to the press manufacturing method, it is necessary that the depth D be not less than 0.2 mm. The length Hb of the hollow 22 defines the length in the direction of the central axis when the anode segments 15 are secured to the anode cylinder 1. The inventors have found through an examination that it is necessary that the ratio of the length Hb to a length of the anode segments 15 in the direction of the central axis, i.e. the length Ha of the inner end surfaces 21 be not less than 20% in order to improve the assembly precision of the anode assembly by reducing and uniformizing the pressure exerted on the anode segments 15 by the jig pin 40. Further, in view of the fact that the pressure from the jig pin 40 is absorbed by the anode segments 15, it is most desirable to provide the hollow 22 to all the central portions in the direction of the central axis of the anode segments 15 which central portions are not opposed to the strap ring grooves 20a and 20b. That is, as shown in FIG. 3, when the length of the strap ring grooves 20a and 20c is Hc, it is most desirable to form the hollow 22 so that a relationship Hb = Ha - 2 x Hc holds. In the anode segments 15 of a typical magnetron arrangement, since the length Hc is 10 to 30% of the length Ha, the ratio of the length Hb to the length Ha is approximately 40 to 80%. On the other hand, when the hollow 22 is provided at the inner end surface 21 of each of the anode segments 15 in a magnetron arrangement, the distance from the cathode 14 disposed in the central portion in the direction of the arrangement increases at the portion of the hollow 22 during operation of the magnetron apparatus produced by using this arrangement. Thereby, there is a possibility that the magnetron efficiency is reduced. Accordingly, in view of the magnetron efficiency, it is desirable that the length Hb of the hollow 22 be as small as possible. Here, a relationship between magnetron efficiency and the depth D and the length Hb of the hollow 22 obtained through an experiment by the inventors will be elucidated with reference to FIG. 4. FIG. 4 is a graph showing a relationship between magnetron efficiency and the ratio of the length Hb to the length Ha. Graphs 31, 32 and 33 shown in FIG. 4 are results of the experiment when the depth D of the hollow 22 is 0.2 mm, 0.3 mm and 0.4 mm, respectively. As is apparent from the graphs 31, 32 and 33 of FIG. 4, as the ratio of the length Hb of the hollow 22 to the length Ha of the inner end surface 21 is greater, the magnetron efficiency is lower, and as the depth D of the hollow 22 is greater, the deterioration of the magnetron efficiency is greater. In the magnetron apparatus produced by using this arrangement, magnetron efficiency of not less than approximately 70% is required in practical use as well known. Therefore, when the depth D of the hollow 22 is set to 0.2 mm in view of the dimensional tolerante at the time of mass production, it is desirable that the length Hb of the hollow 22 be set to less than 50% of the length Ha of the inner end surface 21. From the above-described examination results that it is apparent that the ratio of the length Hb of the hollow 22 to the length Ha of the inner end surface 21 is desirably selected and set so as to be 20 to 50%. Further, according to an experiment by the inventors, for example, a magnetron apparatus for a microwave oven with an output of 500 to 1000 W was produced by using an arrangement according to the present invention. Therein, the magnetron apparatus (hereinafter, referred to as experimental product 1) had the anode segments 15 in which the length Ha of the inner end surface 21 is 9.5 mm, the depth Hc of the strap ring grooves 20a and 20b is 2.6 mm, the depth D of the hollow 22 is 0.2 mm and the length Hb of the hollow 22 is 4.0 mm (Hb/Ha=42%). In the experimental product 1, results which are sufficient for practical use were obtained such that the assembly precision is sufficient and the magnetron efficiency is approximately 71%. In the above-mentioned description, the opening configuration of the hollow 22 of each anode segments 15 is rectangular. However, the opening configuration may have any configuration as long as there is a predetermined spatial distance in the central portion in the direction of the central axis each of the anode segments 15, and a hollow may have a tapered opening configuration or a circular opening configuration as shown in FIG. 5 and FIG. 6, respectively. At this time, the depth D is a distance from a point in the hollow 22 which is farthest from the inner end surface 21, and the length Hb is the size of the widest part of the hollow 22, i.e. the size of the hollow 22 at the inner end surface 21 each of the anode segments 15. In the above-mentioned description, the anode segments 15 are pressed against the inner surface of the anode cylinder 1 by use of the jig pin 40 having the cylindrical portion which comes into contact with a plurality of the inner end surfaces 21. However, the jig pin 40 is not limited to the one having the cylindrical portion, but any assembly member may be used that is designed so as to come into contact with the inner end surface 21 each of the anode segments 15. MANUFACTURING METHOD In the manufacturing method for the magnetron arrangement of this embodiment, first, the plural anode segments 15 and the strap rings 17 and 18 are placed in the respective predetermined positions inside the anode cylinder 1 by use of a non-illustrated temporary assembling jig. Then, the jig pin 40 is moved along the central axis of the anode cylinder 1 and press-fit from below into the central portion in the direction of the arrangement of the anode segments 15 (the central portion of the anode cylinder 1) as shown by the arrow Y of FIG. 2. So that the jig pin 40 contacts with the inner end surface 21 each of the anode segments 15. Thereby, the anode assembly is maintained in a preassembled condition where the one end surface each of the anode segments 15 is pressed against the inner surface of the anode cylinder 1 by the jig pin 40. Then, only the temporary assembling jig is detached, and the brazing filler metal 19 is put on the end surface on the longer side each of the anode segments 15 so as to be in contact with the inner surface of the anode cylinder 1 as shown in FIG. 2. After the magnetic pole piece 2 is attached to the upper open end of the anode cylinder 1, one end of the antenna 16 is mounted to one of the anode segments 15. Then, the anode assembly in the preassembled condition is heated to a predetermined temperature (for example, 800 to 900 'C) in a non-illustrated furnace. Thereby, the brazing filler metal 19 is melted and flows into a clearance between the inner surface of the anode cylinder 1 and the one end surface each of the anode segments 15 caused by expansion. At this time, the plating layers on the strap rings 17 and 18 and the antenna 16 are also melted. Then, by taking the anode assembly out of the furnace while maintaining the preassembled condition, and cooling it, the inner surface of the anode cylinder 1 and the one end surface each of the anode segments 15, the strap ring grooves 20a and 20b and the strap rings 17 and 18, and the antenna 16 and the one of the anode segments 15 are secured. Then, after the jig pin 40 is downwardly pulled out, the magnetic pole piece 3 is attached to the lower open end of the anode cylinder 1, so that the assembly of the anode assembly is finished. In the manufacturing method for the magnetron arrangement of this embodiment, because of the provision of the hollow 22 in the central portion of the inner end surface 21 each of the anode segments 15, the area of contact between the inner end surface 21 and the jig pin 40 is smaller than in the conventional arrangement, so that the pressure exerted on the anode segments 15 by the jig pin 40 is reduced. Consequently, the pressure exerted on the two pairs of the strap rings 17 and 18 situated at the upper and lower ends in the direction of the central axis each of the anode segments 15 is smaller than in the conventional arrangement, so that the brazing precision improves and the deformation of the strap rings 17 and 18 and the coming-off of brazed parts due to insufficient brazing can be prevented during the while the jig pin 40 being press-fit and taken out. The pressure which the anode segments 15 receive from the jig pin 40 is dispersed and uniformized into the upper and lower areas Vx and Vz in the direction of the central axis because the hollow 22 is provided in the central portion in the direction of the central axis. Further, since the strap ring grooves 20a and 20b are provided in the upper and lower areas Vx and Vz, even if the anode segments 15 expand due to temperature increase at the time of brazing, the expanded portions are absorbed by the strap ring grooves 20a and 20b, so that the pressure is equally exerted. Particularly, since the central area Vy each of the anode segments 15 includes a spatial distance defined by the depth D of the hollow 22 from the jig pin 40, even if outer dimension variation or expansion of the anode segments 15 is caused, no pressure is exerted on the central area Vy by the jig pin 40. Therefore, even if the anode segments 15 expand when heated, the pressures exerted on the upper and lower areas Vx and Vz are similar. Consequently, the anode segments 15 can be pressed against the jig pin 40 always in a stable condition at the two portions of the upper and lower areas Vx and Vz, so that even if the jig pin 40 has a surface which is as smooth as the mirror finished surface, the variation in pitch as illustrated in FIG. 19 is never caused. That is, in the manufacturing method for the magnetron arrangement of this embodiment, the plural anode segments 15 can be equally spaced in the anode cylinder 1, so that a magnetron arrangement suitable for the production of a magnetron apparatus which operates with stability can be obtained. As has been explained in the above, according to the manufacturing method for the magnetron arrangement of the present invention, the assembly precision of the anode assembly can be easily improved without modifying the process from the preassembly to the brazing by use of the conventional ordinary assembly jig as it is without any modification. Particularly, as the jig pin 40 which is expensive because high heat resistance and high wear resistance are required therefor, a conventional temporary assembling pin can be used as it is without any modification, so that the manufacture cost is prevented from greatly increasing. SECOND EMBODIMENT FIG. 7 is a cross sectional view showing a configuration of a principal part of an anode assembly of a magnetron arrangement in a second embodiment of the present invention. In this embodiment, in the configuration of the magnetron arrangement, a chamfered portion is provided in which at least one angular portion of the inner end surface each of the anode segments is chamfered. The other elements and portions are similar to those of the first embodiment, and therefore overlapping descriptions on the similar points are omitted. As shown in FIG. 7, in the magnetron arrangement of this embodiment, a tapered chamfered portion 26 is provided at one angular portion of the inner end surface 21 each of anode segments 25 and 25', and the anode segments 25 and 25' are secured to the inner surface of the anode cylinder 1 so that the chamfered portions 26 are situated at the upper side in the direction of the central axis. That is, in the anode segment 25, the chamfered portion 26 is formed by chamfering an angular portion at which the inner end surface 21 intersects the end surface where the strap ring groove 20a is provided. In the anode segment 25', the chamfered portion 26 is formed by chamfering an angular portion at which the inner end surface 21 intersects the end surface where the strap ring groove 20b is provided. By providing such a chamfered portion 26, in the magnetron arrangement of this embodiment, the area of contact between the jig pin 40 and the anode segments 25 and 25' is smaller than in the first embodiment, so that the pressure exerted on the anode segments 25 and 25' by the jig pin 40 can be reduced. Moreover, as shown in FIG. 8, the anode segments 25 and 25' may be secured to the inner surface of the anode cylinder 1 so that the chamfered portions 26 are situated at the lower side in the direction of the central axis. Further, as shown in FIG. 9 and FIG. 10, the anode segments which are secured to the inner surface of the anode cylinder 1 may be only one kind of the two anode segments 25 and 25'. Moreover, as shown in FIG. 11, an anode segment 27 in which the chamfered portion 26 is provided at the angular portion at each of the upper and lower ends of the inner end surface 21 in the direction of the central axis may be secured to the inner surface of the anode cylinder 1. In the anode assemblies shown in FIG. 7 to FIG. 10, the contact area can be reduced by substantially the same extent. In the anode assemblies shown in FIG. 8 and FIG. 11, since the chamfered portion 26 is situated at the side where the jig pin 40 is inserted, the jig pin 40 is more easily inserted than in the other anode assemblies. In a conventional anode assembly for the magnetron arrangement, typically, anode segments of the same configuration are arranged so that every two anode segments are vertically inverted. However, when the anode segments 25 and 25' shown in FIG. 7 and FIG. 8 are used, it is necessary to select those anode segments 25 and 25' and arranged them alternately. On the other hand, when the anode segments 27 shown in FIG. 11 are used, since the chamfered portion 26 is provided at the angular portion at each of the upper and lower ends of the inner end surface 21, the selection of anode segments is unnecessary, so that the time necessary for assembling the anode assembly can be reduced the most. Further, the contact area can be reduced the most and the insertion of the jig pin 40 is facilitated. Thus, the anode segments 27 are most suitable for practical use. According to an experiment by the inventors, in the anode segments 27 for use in the magnetron apparatus for the microwave oven with an output of 500 to 1000 W, the most desirable result where the magnetron efficiency is the highest was obtained when the chamfered portion 26 of C = 0.2 to 0.6 mm was provided at each of the upper and lower ends of the inner end surface 21. As described above, in the magnetron arrangement of this embodiment, the chamfered portion 26 is provided on at least one angular portion of the inner end surface 21. Thereby, the area of contact between the anode segments and the jig pin 40 is smaller than in the first embodiment, so that the aforementioned deformation of the anode segments and the strap rings 17 and 18, the coming-off of brazed parts due to insuffizient brazing and the generation of burrs due to nonuniformity of components can be further reduced. In the above description, the tapered chamfered portion 26 is provided at the inner end surface 21 which faces the jig pin 40. However, the configuration of the chamfered portion is not limited to the tapered configuration as long as the Dimension in the direction of the central axis of the inner end surface 21 which faces the jig pin 40 can be reduced. For example, a circular chamfered portion may be provided. Further, in the above description, the chamfered portion 26 is provided on at least one of the upper and lower ends of the inner end surface in the direction of the central axis. However, the chamfered portion may be provided at an angular portion which faces the hollow 22 of the inner end surface 21. Test results on noise characteristics of the magnetron apparatus produced by using the arrangement of the present invention will be explained with reference to FIG. 12 to FIG. 15. FIG. 12 is a graph showing measurement results of the noise level at a fifth harmonic. FIG. 13 is a measurement result showing noise characteristics in the vicinity of the fifth harmonic in the conventional magnetron apparatus produced by using the arrangement shown in FIG. 16. FIG. 14 is a measurement result showing noise characteristics in the vicinity of the fifth harmonic in the magnetron apparatus produced by using the arrangement of the first embodiment. FIG. 15 is a measurement result showing noise characteristics in the vicinity of the fifth harmonic in the magnetron apparatus produced by using the arrangement of the second embodiment. In this test, three kinds of magnetron apparatuses, i.e. the aforementioned experimental product 1 obtained by using the first embodiment, an experimental product 2 obtained by using the second embodiment in which the chamfered portion 26 of C = 0.5 mm is provided in each anode segment of the experimental product 1, and an apparatus obtained by using the conventional arrangement shown in FIG. 16 were operated at a fundamental frequency of 2,450 MHz, and noise levels at the fifth harmonic 12.25 GHz and at frequencies in the vicinity thereof were measured. This is because the fifth harmonic of such magnetron apparatuses falls within the frequency range (11.7 to 12.7 GHz) of the satellite broadcasting band on which strict regulation has been imposed in recent years. In this test, it was examined whether the standard of CISPR (International Special Committee on Radio Interference) was satisfied or not. Specifically, the effective radiated power of electromagnetic waves within the frequency range of 11.7 to 12.7 GHz was measured with a half-wave dipole antenna as the reference, and it was examined whether or not the measurement results were not more than 57 dB which is the permissible electric power of the radio frequency radiation jamming wave defined by the standard. As a result, in the experimental products 1 and 2, the measurement results of the noise level at the fifth harmonic were 47 to 51 dB and 43 to 48 dB, respectively, as shown at B and E of FIG. 12, and both were below the permissive value 57 dB and satisfied the CISPR standard. Moreover, it was found that the experimental product 2 having the anode segments 27 provided with the chamfered portion 26 was more effective for reducing the noise level at the fifth harmonic than the experimental product 1. On the contrary, in the apparatus produced by using the conventional arrangement, the measurement results were 55 to 58 dB as shown at A of FIG. 12 and the CISPR standard was not satisfied. Although the present invention has been described in terms of the presently preferred embodiments, it is to be understood that such disclosure is not to be interpreted as limiting.

Claims: A magnetron arrangement comprising: an anode cylinder (1) and a plurality of plate-shaped anode segments (15, 25, 25', 27) radially arranged around the central axis of said anode cylinder inside said anode cylinder, and pressed against an inner surface of said anode cylinder by a pin (40) press-fit into the central portion of said anode cylinder, so that a far-end-side end surface each of said anode segments is secured to said inner surface, characterized in that each of said anode segments has a hollow (22) at the central portion of its inner end surface (21) which contacts said pin. A magnetron arrangement in accordance with claim 1, wherein the length (Hb) of said hollow (22) in the direction of said central axis is 20 to 50% of the length (Ha) of said inner end surface (21) in said direction of said central axis. A magnetron arrangement in accordance with claim 1 or claim 2, wherein a chamfered portion (26) is provided on at least one angular portion of said inner end surface (21) in said direction of said central axis. A manufacturing method for a magnetron arrangement comprising an anode cylinder (1) and a plurality of plate-shaped anode segments (15, 25, 25', 27) radially arranged around the central axis of said anode cylinder inside said anode cylinder and pressed against an inner surface of said anode cylinder by a pin (40) press-fit into the central portion of said anode cylinder, so that a far-end-side end surface each of said anode segments is secured to said inner suface, characterized by a step in which a hollow is provided in a central portion of the inner end surface (21) of each of said anode segments which is foreseen to contact said pin and a step in which said pin is press-fit into the central portion of said anode cylinder and said far-end-side end surface is pressed against and secured to said inner surface of said anode cylinder. A manufacturing method for a magnetron arrangement in accordance with claim 4, further comprising a step in which the length (Hb) of said hollow (22) in the direction of said central axis is formed so as to be 20 to 50% of the length (Ha) of said inner end surface in said direction of said central axis. A manufacturing method for a magnetron arrangement in accordance with claim 4 or claim 5, further comprising a step in which a chamfered portion (26) is provided on at least one angular portion of said inner end surface (21) in said direction of said central axis.

Inventors: NAKANO YASUNOBU, OCHIAI HIROSHI, YOSHIHARA MASANORI, NAKANO, YASUNOBU, OCHIAI, HIROSHI, YOSHIHARA, MASANORI
Applicants: MATSUSHITA ELECTRONICS CORP, MATSUSHITA ELECTRONICS CORPORATION
Application year: 1998
Main classification: H01J23
IPC codes: H01J23