JP2005011620A - Microwave oven - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve efficiency of an equipment type microwave oven. <P>SOLUTION: The microwave oven has a heating chamber 1 of a lengthwise and breadthwise symmetrical shape fitted with a vertical part 3c at the center of its top face and a waveguide 3 reaching a horizontal part 3a where a magnetron is mounted through a 45° bent part, and a stirrer wing 4 is made rotated on a center axis of the heating chamber. With this, an electric field of lengthwise and breadthwise symmetry is obtained in the heating chamber 1, and the waveguide 3 has only a 45° deflection at maximum in a direction of travel, endowed with high-pass characteristics, so that there is an effect of a high efficiency obtained if only an appropriate operating point is set. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００１１】
但しφは、陰極の中心をｚ軸とした円筒座標ρφｚにおける円周方向成分であり、Ｖｋはｋ次高調波の振幅である。波形のフーリエ解析で知られる如く、高調波成分が無ければ正弦波形状であり、無限の高調波成分の存在により台形形状をなす訳である。この式における高調波とは円周方向φにおけるものであり、時間変化はあくまでもｃｏｓωｔで表現される単一周期である。電子流はこの電界に同期して周回運動を行っている。ただし、同期周回する為には必ずしも同一角速度である必要はない。整数ｋ倍の角速度で周回する電子流も存在し得る。マグネトロンのπ型姿態における電子流の角速度と電界の角周波数との間にはｄφ／ｄｔ＝４ωの関係があるから、電子流中のｋ次高調波成分ｋφは、角周波数ｋωの電界にも同期し得る。電子流のアドミッタンスＹｅの中身には以上の理由から、ｋωに対応する成分が含まれると考えられる。従って発振条件Ｙｅ＋Ｙｃ＝０から、回路アドミッタンスＹｃにもｋω対応成分が必須と言える。
【００１２】
この点、図２のマグネトロン測定装置に用いられている直線状導波管は、高域通過特性を持つから、基本周波数ωだけでなく、ｋωの高調波領域も減衰無しに通過する。一方、図７の、コールドインピーダンス法で適切な動作点に設定したにも関わらず効率が低い従来例は、一端が短絡されたＴ型分岐構造であるから、当業者には１／４波長チョークの原理として良く知られる様に、アンテナの軸から短絡端までの距離が１／４波長に等しい周波数及びその奇数次高調波は通過しない。つまりＴ型分岐は帯域通過特性を有する。帯域外の高調波領域では飛び飛びの遮断領域を持つと考えられる。例えば、通過しない周波数のｎ倍がマグネトロンの発振周波数のｍ次高調波と一致あるいは接近した場合である。その結果回路アドミッタンスＹｃの高調波領域には飛び飛びのゼロ点が存在する事になる。これが、２、４５０±１５ＭＨｚ程度の微弱信号で見る限り最大出力が出る条件を満たしているにも関わらず図７の従来例の効率が低い事の原因であると推測される。
【００１３】
この推測は、Ｔ分岐構造を用いず、高調波領域も通過可能な構成にすれば効率向上が図れる事を示唆するものである。Ｔ分岐構造は導波管を直角に曲げる必要上、採用されたものであるから、Ｔ分岐を用いずに直角に曲げる方法が必要となる。最初に考えられるのは、Ｌ字形状に曲げられた導波管を用いる事であるが、この方式も高域通過ではなく、帯域通過特性を持つ。一般に導波管はＨ０１モードで用いられるから進行方向に垂直な電界が発生している。一方、良く知られる如く金属表面では電界の平行成分はゼロであるから、Ｌ字形状に曲げられた面上ではこのＨ０１モードの電界はゼロとなる。つまりＨ０１モード進行波に対する短絡点として機能する訳である。進行波の全エネルギーが短絡されるのではないが、周波数によって短絡点までの位相が異なり、場合によって大きな影響を受ける可能性がある。従って周波数特性を持つのである。
【００１４】
これを裏付けるように、当業者の経験的知識として、過去にはＬ字状直角曲げ導波管を用いると吸い込みを起こすと言われた時期があった。これはガラス管製マグネトロンが採用されていた当時、反射波が大きいと、アンテナ周囲のガラス管が部分加熱を受けて溶け、空気が浸入してマグネトロン破壊に至る現象を吸い込みと呼び、Ｌ字状直角曲げ導波管では頻度が高い経験に基づく経験則である。
【００１５】
短絡点を持たない形状としては、急激に直角に曲げず、大きな半径の円周状に緩やかに曲げる形状が最も望ましいが、民生機器としてあまり実用的ではない。次善の方法として４５度曲げ導波管、つまり隣接する二つの壁面角度が１３５度である部分を二箇所連続して設ける方式が考えられる。これならばＨ０１モード進行波の電界に対して壁面は４５度の角度を持つので、短絡点とはならない。４５度曲げ導波管も周波数特性が皆無ではないが、短絡点を有する場合と比較して十分小さいと言える。前述の吸い込み現象の解決策として、４５度曲げ導波管が推奨されていた事を付記する。
【００１６】
【課題を解決するための手段】
本発明は上記課題を解決するため、マグネトロンと、略前後左右対称形状の加熱室と、両者を結ぶ導波管と、スタラー羽根及び駆動機構とを有し、導波管は水平部、垂直部及び両者を結ぶ４５度曲げ部とから成り、垂直部は加熱室の天面中央に、水平部は加熱室天面外部に位置せしめ、マグネトロンを取り付け、スタラー羽根の回転軸を加熱室中央に設け、前記４５度曲げ部から外部駆動機構に結合させたものである。
【００１７】
上記発明によれば加熱室が略前後左右対称形状であり、導波管の垂直部及びスタラー羽根の回転軸が共に加熱室の中央に設けたので加熱室内は前後左右対象電界分布が得られる。また導波管は直線及び４５度曲げ形状で形成されるので、高域通過性能を有し、マグネトロンを適切な動作点で動作させれば高効率が得られる。
【００１８】
【発明の実施の形態】
本発明の請求項１にかかる電子レンジはマグネトロンと、略前後左右対称形状の加熱室と、両者を結ぶ導波管と、スタラー羽根及び駆動機構とを有し、導波管は水平部、垂直部及び両者を結ぶ４５度曲げ部とから成り、垂直部は加熱室の天面中央に、水平部は加熱室天面外部に位置せしめ、マグネトロンを取り付け、スタラー羽根の回転軸を加熱室中央に設け、前記４５度曲げ部から外部駆動機構に結合させたものである。
【００１９】
そして、加熱室が略前後左右対称形状であり、導波管の垂直部及びスタラー羽根の回転軸が共に加熱室の中央に設けたので加熱室内は前後左右対象電界分布が得られる。また導波管は直線及び４５度曲げ形状で形成されるので、高域通過性能を有し、マグネトロンを適切な動作点で動作させれば高効率が得られる。
【００２０】
本発明の請求項２にかかる電子レンジは加熱室天面中央に凹部を設け、導波管の垂直部及びスタラー羽根は共に凹部に収納したものである。
【００２１】
そして、凹部の高さは設計上、往々にして３０ｍｍ前後、つまり２、４５０ＭＨｚの約１／４波長近辺になり兼ねない。そうなると導波管と凹部との不連続による反射波と、凹部と加熱室との不連続による反射波との位相差が９０度となり、一方を打ち消す方法を施せば他方が増大する為、インピーダンスの整合が困難となり、必然的に効率低下を招いてしまう。導波管垂直部を凹部内部に設ける事によりこの１／４管内波長線路をバイパスし、導波管と加熱室との不連続のみによる反射波に限定できるので、通常の設計業務に帰着し、効率向上が望める。
【００２２】
本発明の請求項３にかかる電子レンジは導波管の４５度曲げ部に金属を取り付け、両者を貫通して加熱室中心に一致した孔を開け、この孔にスタラー羽根の誘電体製軸を勘合させたものである。
【００２３】
そして、垂直な円柱形状のスタラー軸を４５度傾斜部分通過させた事により導波管垂直部の上部空間で駆動機構に接続可能となる。４５度傾斜面を円形軸が接触せずに通過するにはおきな楕円形状の孔が必要となり、その孔を通しての漏洩電波が懸念されるが、スタラー軸と勘合する丸孔が開けられた金属製スタラー受け６が取り付けられるので漏洩を減少させることができる。
【００２４】
【実施例】
以下、本発明の実施例について図面を用いて説明する。
【００２５】
（実施例１）
図１は本発明の実施例１の正面方向から見た主要部断面図である。
【００２６】
図１において、金属板で構成され、略直方体の形状を持つ加熱室１の天面中央に、円錐台形の凹部２を設け、そのさらに上面中央に導波管３の垂直部３ｃを結合する。この中央にアルミナ磁器製のスタラー軸４ａを貫通させ、その下部は導波管垂直部３ｃ直下でアルミナ磁器製の支持板４ｂに固定され、その先端は金属製スタラー羽根４ｃを保持する。スタラー軸上端はステンレスバネ鋼製でＴ字形状を有する受動レバー４ｄが取り付けられる。導波管３の垂直部３ｃ上部は凹部２外部で４５度傾斜面を持つ４５度部３ｂに続き、さらにその先は水平部３ａとなる。水平部３ａは凹部外部で４５度未満の角度で二箇所曲げられ、略Ｚ字形状を形成して位置を下げ、先端にマグネトロン５が取り付けられる。
【００２７】
４５度部３ｂの中央には楕円形の孔が開けられ、この孔を塞ぐ位置に、この孔と同軸の丸孔を持つ金属製のスタラー軸受け６が固定される。前記スタラー軸４ａの上端はこの両者を貫通して外部に突き出し、スタラー軸受け６の上部で前述の受動レバー４ｄが固定される。スタラーモーター７はその出力軸をスタラー軸４ａと一致させて固定され、出力軸先端には逆Ｌ字形の駆動レバー８が取り付けられ、前記受動レバー４ｄと勘合する。凹部２はガラス板９で塞がれ、その下にはシーズヒーター１０が取り付けられる。
【００２８】
次に動作、作用について説明すると、マグネトロン５で発生したマイクロ波は導波管３の水平部３ａから前述の略Ｚ字型部及び４５度傾斜部３ｂを経て、垂直部３ｃに達する。この垂直部３ｃから放射され、加熱室１内部に置かれた食品に到達、吸収される。吸収されずに反射される一部分は逆の経路を経てマグネトロン５に戻る。導波管３の進行途中には進行波に対して４５度以下の壁面のみを有し、進行波を短絡する様な、電界と平行な壁面が進行方向に無いので高域通過特性を持ち、前述の様に適切な動作点に設計すれば高効率が得られる。
【００２９】
円錐台形状たる凹部２の高さを３０ｍｍ程度に設定した場合、導波管垂直部３ｃを省略すると前述のコールドインピーダンス法で測定した動作点が広範囲に拡大し、効率及び出力が大幅に低下する。垂直部３ｃを設ける事により動作点が狭まり、効率、出力が増加するのである。
【００３０】
加熱室１が略直方体であり、その天面中央に導波管垂直部３ｃが設けられているので加熱室内部には前後左右対象な電界分布が期待できる。前後左右対称を維持する為、スタラー軸４ａは同じく加熱室中央及び導波管垂直部の中央に位置する。４５度曲げ部３ｂを設け、垂直部３ｃの上部に空間が生じた事によりスタラー軸４ａの先端が導波管の外部に突き出せ、スタラーモーター７と結合する事が可能となった。
【００３１】
本実施例ではスタラー空間として凹部２を設けているが、これを省略し、平坦な加熱室天面中央から導波管の垂直部３ｃを直接下方に向ける事も可能である。またマグネトロン５は加熱室１の天面上に配置したが、導波管の水平部３ａを右に伸ばし、マグネトロン５を加熱室の右側に配置する事もできる。
【００３２】
いずれにしろ本発明の主旨は、略前後左右対象形状の加熱室の天面中央に、進行方向に対して４５度以下の曲げのみで構成された導波管の終端を、前後左右対称状態で取り付けたものであり、それにより加熱室内部の前後左右対象電界分布と、高効率とを同時に得るものである。
【００３３】
【発明の効果】
以上説明したように本発明の請求項１に係る電子レンジは、マグネトロンと、略前後左右対称形状の加熱室と、両者を結ぶ導波管と、スタラー羽根及び駆動機構とを有し、導波管は水平部、垂直部及び両者を結ぶ４５度曲げ部とから成り、垂直部は加熱室の天面中央に、水平部は加熱室天面外部に位置せしめ、マグネトロンを取り付け、スタラー羽根の回転軸を加熱室中央に設け、前記４５度曲げ部から外部駆動機構に結合させたものである。
【００３４】
そして、加熱室が略前後左右対称形状であり、導波管の垂直部及びスタラー羽根の回転軸が共に加熱室の中央に設けたので加熱室内は前後左右対象電界分布が得られる。また導波管は直線及び４５度曲げ形状で形成されるので、高域通過性能を有し、マグネトロンを適切な動作点で動作させれば高効率が得られるという効果がある。
【００３５】
また、請求項２に係る電子レンジは加熱室天面中央に凹部を設け、導波管の垂直部及びスタラー羽根は共に凹部に収納したものである。
【００３６】
そして、凹部の高さは設計上、往々にして３０ｍｍ前後、つまり２、４５０ＭＨｚの約１／４波長近辺になり兼ねない。そうなると導波管と凹部との不連続による反射波と、凹部と加熱室との不連続による反射波との位相差が９０度となり、一方を打ち消す方法を施せば他方が増大する為、インピーダンスの整合が困難となり、必然的に効率低下を招いてしまう。導波管垂直部を凹部内部に設ける事によりこの１／４管内波長線路をバイパスし、導波管と加熱室との不連続のみによる反射波に限定できるので、通常の設計業務に帰着し、効率向上が望めるという効果がある。
【００３７】
また、請求項３に係る電子レンジは導波管の４５度曲げ部に金属を取り付け、両者を貫通して加熱室中心に一致した孔を開け、この孔にスタラー羽根の誘電体製軸を勘合させたものである。
【００３８】
そして、垂直な円柱形状のスタラー軸を４５度傾斜部分通過させた事により導波管垂直部の上部空間で駆動機構に接続可能となる。４５度傾斜面を円形軸が接触せずに通過するにはおきな楕円形状の孔が必要となり、その孔を通しての漏洩電波が懸念されるが、スタラー軸と勘合する丸孔が開けられた金属製スタラー受け６が取り付けられるので漏洩を減少させることができるという効果がある。
【図面の簡単な説明】
【図１】本発明の実施例１における電子レンジの要部断面図
【図２】動作原理説明に用いた、マグネトロン動作測定装置の断面図
【図３】動作原理説明に用いたスミス図表を示す図
【図４】動作原理説明に用いたマグネトロンの等出力線図
【図５】スミス図表上に描いた動作点を示す図
【図６】マグネトロン陽極とその電圧との関係図
【図７】従来の電子レンジの要部断面図
【符号の説明】
１ 加熱室
３ａ 導波管水平部
３ｂ 導波管４５度曲げ部
３ｃ 導波管垂直部
４ スタラー羽根
４ａ スタラー軸
４ｄ 受動レバー（駆動機構）
５ マグネトロン
７ スタラーモーター（駆動機構）
８ 駆動レバー（駆動機構）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an equipment type combined with a microwave oven, particularly a full-scale oven.
[0002]
[Prior art]
A conventional microwave oven of this kind is generally as shown in FIG. In this microwave oven, as shown in FIG. 7, the waveguide 3 is coupled to the center of the upper surface of the truncated cone-shaped recess 2 provided at the center of the top surface of the heating chamber 1, and is constituted by a shaft 4a and a blade 4b. The shaft 4a of the antenna 4 is inserted into the waveguide 3, and the blade 4b is rotated inside the recess 2 (see, for example, Patent Document 1).
[0003]
Equipment-type full-scale ovens, especially those used in Europe and the United States, are heated like a method that burns off dirt at a high temperature of about 500 ° C. or a method that employs a surface-treated metal having a catalytic action on the wall surface. As the material constituting the chamber, a metal lined with a heat insulating material is required. When combined with a microwave oven, the space for supplying microwaves and stirring functions is naturally a part without metal, and the larger the part, the lower the heating performance and thermal efficiency of the oven. . In that regard, in the conventional example, the metal-free portion is limited to the concave portion 2 at the center of the top surface of the heating chamber 1, so that it has a function of a microwave oven while having a full-fledged function as an oven. Is possible.
[0004]
[Patent Document 1]
JP 59-42795 A
[Problems to be solved by the invention]
However, the microwave oven combined with the above-described conventional full-scale oven has a problem that the heating efficiency is low although the magnetron is operated at an appropriate operating point. It is generally said that the main cause is that the wall is enameled or the sheathed heater in the heating chamber absorbs microwaves, but it is said that quantitative analysis is sufficient. It is difficult, and I do not think that the existence of other causes has been fully examined.
[0006]
The appropriate operating point is common knowledge to those skilled in the art, but is confirmed by the following procedure. First, the magnetron output is measured in advance with a magnetron operation measuring apparatus as shown in FIG. The relationship between the insertion information and the output value of the metal rod insertion device 10 in which the insertion depth and position of the metal rod are variable at the time of measurement is grasped, and then the weakness in the range of about 2,450 ± 15 MHz from the antenna position of the magnetron 5 The signal is radiated, the load impedance is calculated from the intensity and phase of the reflected signal, the metal rod insertion information is drawn on the Smith diagram as shown in FIG. 3, the output value is placed on it, and the iso-output line as shown in FIG. Prepare what you drew as. Then, the load impedance viewed from the position of the magnetron antenna of FIG. 7 is measured by the same method, and the impedance change locus accompanying the rotation of the stirrer blade is drawn on the Smith diagram as shown in FIG. That the maximum output area matches this trajectory is said to be an appropriate operating point.
[0007]
The magnetron measuring apparatus shown in FIG. 2 is basically provided with a magnetron 5 at one end of a linear standard waveguide 3 having a rectangular cross section, and a non-reflective terminal 11 at the other end. The directional coupler 12 is inserted, and the directional coupler 12 is provided with a power measuring device 13. The frequency of the weak signal used for impedance measurement is about 2,450 ± 15 MHz because the peak value of the actual transmission frequency of the magnetron is about that level. This series of methods is commonly called the cold impedance method and is widely used because it is easy and excellent in reproducibility. In this cold impedance method, it can be confirmed that the condition that the maximum output is obtained is satisfied as long as the weak signal of about 2,450 ± 15 MHz is seen.
[0008]
However, as can be inferred from the cold name, there is one way to see the operating point when the magnetron called hot is actually operated. The reproducibility is inferior due to fluctuations in the operating state due to heat generation, etc., coupled with the handling of high voltage, but it is rarely used recently, but cold and hot do not give the same result, cold does not necessarily reflect the actual operation It is also said that not.
[0009]
Therefore, in order to verify the measurement by the cold method, I will unravel the oscillation principle of the magnetron. In general, as one method of expressing the oscillation condition by a mathematical expression, there is a method using the fact that the sum of admittances seen from a certain point on both sides is zero, and this is used for a magnetron. The oscillation condition is Ye + Yc = 0, where Ye is the admittance when viewing the inner electron flow from the anode surface and Yc is the combined admittance of the outer anode circuit and the external connection load. First consider Ye. In a π-type configuration, which is a normal configuration in a magnetron in which a widely used anode is divided into eight, the phase transition θ between adjacent resonators is equal to π radians, and the potential between the anode and the cathode is trapezoidal as shown in FIG. The AC electric field Vac is represented by the following infinite series sum.
[0010]
[Expression 1]

[0011]
Where φ is a circumferential component in cylindrical coordinates ρφz with the center of the cathode as the z axis, and Vk is the amplitude of the k-order harmonic. As known from Fourier analysis of the waveform, if there is no harmonic component, it has a sinusoidal shape, and it has a trapezoidal shape due to the presence of infinite harmonic components. The harmonics in this equation are those in the circumferential direction φ, and the time change is a single period expressed by cos ωt. The electron stream makes a circular motion in synchronization with this electric field. However, it is not always necessary to have the same angular velocity in order to go around synchronously. There may also be an electron stream that circulates at an integer k times the angular velocity. Since there is a relationship of dφ / dt = 4ω between the angular velocity of the electron flow and the angular frequency of the electric field in the π-type configuration of the magnetron, the k-order harmonic component kφ in the electron flow is also applied to the electric field of the angular frequency kω. Can synchronize. The contents corresponding to kω are considered to be included in the contents of the admittance Ye of the electron flow for the above reasons. Therefore, since the oscillation condition Ye + Yc = 0, it can be said that a component corresponding to kω is essential for the circuit admittance Yc.
[0012]
In this respect, since the linear waveguide used in the magnetron measuring apparatus of FIG. 2 has high-pass characteristics, not only the fundamental frequency ω but also the harmonic region of kω passes without attenuation. On the other hand, the conventional example shown in FIG. 7 having a low efficiency despite being set to an appropriate operating point by the cold impedance method has a T-type branch structure in which one end is short-circuited. As is well known as the principle of the above, a frequency whose distance from the antenna axis to the short-circuited end is equal to a quarter wavelength and its odd-order harmonics do not pass. That is, the T-type branch has band pass characteristics. It is considered that the out-of-band harmonic region has a jump-off region. For example, this is a case where n times the frequency that does not pass coincides with or approaches the mth harmonic of the oscillation frequency of the magnetron. As a result, a jumping zero point exists in the harmonic region of the circuit admittance Yc. This is presumed to be the reason why the efficiency of the conventional example of FIG. 7 is low despite satisfying the condition that the maximum output is obtained as far as the weak signal of about 2,450 ± 15 MHz is seen.
[0013]
This estimation suggests that the efficiency can be improved by using a configuration in which the T-branch structure is not used and the harmonic region can pass. Since the T-branch structure is adopted in order to bend the waveguide at a right angle, a method of bending at a right angle without using the T-branch is necessary. The first idea is to use a waveguide bent into an L shape, but this method also has a band pass characteristic, not a high pass. Generally, since the waveguide is used in the H01 mode, an electric field perpendicular to the traveling direction is generated. On the other hand, as is well known, since the parallel component of the electric field is zero on the metal surface, the electric field of the H01 mode is zero on the surface bent into an L shape. That is, it functions as a short-circuit point for the H01 mode traveling wave. Although the total energy of the traveling wave is not short-circuited, the phase up to the short-circuit point differs depending on the frequency and may be greatly affected in some cases. Therefore, it has frequency characteristics.
[0014]
To support this, there has been a time in the past that it has been said that if an L-shaped right-angled bending waveguide is used, suction will occur if one skilled in the art knows. When a glass tube magnetron was used at the time, when the reflected wave was large, the glass tube around the antenna melted by partial heating, and the phenomenon of air intrusion leading to magnetron destruction was called L-shaped. It is an empirical rule based on high-frequency experience in a right-angle bending waveguide.
[0015]
A shape that does not have a short-circuit point is most preferably a shape that does not bend suddenly at a right angle but gently bends to a large radius of circumference, but is not very practical as a consumer device. As a suboptimal method, a 45-degree bent waveguide, that is, a method in which two adjacent portions having a wall angle of 135 degrees are continuously provided is considered. In this case, since the wall surface has an angle of 45 degrees with respect to the electric field of the H01 mode traveling wave, it does not become a short circuit point. The 45-degree bent waveguide is not completely free of frequency characteristics, but it can be said to be sufficiently small as compared with the case of having a short-circuit point. As a solution to the above-described suction phenomenon, it is added that a 45-degree bent waveguide has been recommended.
[0016]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention has a magnetron, a heating chamber having a substantially longitudinal left-right symmetric shape, a waveguide connecting the two, a stirrer blade, and a drive mechanism. And a 45-degree bend connecting the two, the vertical part is located at the center of the top surface of the heating chamber, the horizontal part is located outside the top surface of the heating chamber, a magnetron is attached, and the rotation axis of the stirrer blade is provided at the center of the heating chamber The 45-degree bent portion is coupled to an external drive mechanism.
[0017]
According to the above invention, the heating chamber has a substantially symmetric shape in the front-rear and left-right directions, and the vertical portion of the waveguide and the rotation axis of the stirrer blade are both provided in the center of the heating chamber. Further, since the waveguide is formed in a straight line and a 45-degree bent shape, it has a high-pass performance, and high efficiency can be obtained by operating the magnetron at an appropriate operating point.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
A microwave oven according to a first aspect of the present invention includes a magnetron, a heating chamber having a substantially front / rear left / right symmetric shape, a waveguide connecting the two, a stirrer blade, and a drive mechanism. The vertical part is located at the center of the top surface of the heating chamber, the horizontal part is located outside the top surface of the heating chamber, a magnetron is attached, and the rotation axis of the stirrer blade is at the center of the heating chamber. The 45-degree bent portion is connected to an external drive mechanism.
[0019]
The heating chamber has a substantially symmetrical shape in the front-rear direction, and the vertical portion of the waveguide and the rotation axis of the stirrer blade are both provided in the center of the heating chamber. Further, since the waveguide is formed in a straight line and a 45-degree bent shape, it has a high-pass performance, and high efficiency can be obtained by operating the magnetron at an appropriate operating point.
[0020]
The microwave oven according to claim 2 of the present invention is provided with a recess at the center of the top surface of the heating chamber, and both the vertical portion of the waveguide and the stirrer blade are accommodated in the recess.
[0021]
The height of the concave portion is often about 30 mm in design, that is, it may be around about ¼ wavelength of 2,450 MHz. Then, the phase difference between the reflected wave due to the discontinuity between the waveguide and the concave portion and the reflected wave due to the discontinuity between the concave portion and the heating chamber becomes 90 degrees, and if one is canceled, the other will increase. Matching becomes difficult and inevitably decreases efficiency. By providing the waveguide vertical part inside the recess, this quarter-wavelength wavelength line can be bypassed and limited to the reflected wave due only to the discontinuity between the waveguide and the heating chamber, resulting in normal design work. Increased efficiency can be expected.
[0022]
In the microwave oven according to claim 3 of the present invention, a metal is attached to the 45-degree bent portion of the waveguide, a hole is formed through the both to coincide with the center of the heating chamber, and the dielectric shaft of the stirrer blade is provided in this hole. It is something that has been combined.
[0023]
Then, by passing the vertical cylindrical stirrer shaft through the inclined portion of 45 degrees, it becomes possible to connect to the drive mechanism in the upper space of the waveguide vertical portion. A special elliptical hole is required to pass through the 45-degree inclined surface without contact with the circular shaft, and there is a concern about leakage radio waves through the hole, but a metal with a round hole that fits into the stirrer shaft. Leakage can be reduced because the stirrer receiver 6 is attached.
[0024]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[0025]
(Example 1)
FIG. 1 is a cross-sectional view of the main part of the first embodiment of the present invention viewed from the front direction.
[0026]
In FIG. 1, a frustoconical recess 2 is provided at the center of the top surface of the heating chamber 1 made of a metal plate and having a substantially rectangular parallelepiped shape, and a vertical portion 3c of the waveguide 3 is coupled to the center of the top surface. An alumina porcelain stirrer shaft 4a is passed through the center, and a lower portion thereof is fixed to an alumina porcelain support plate 4b directly under the waveguide vertical portion 3c, and a tip thereof holds a metal stirrer blade 4c. The stirrer shaft upper end is attached with a passive lever 4d made of stainless spring steel and having a T-shape. The upper part of the vertical part 3c of the waveguide 3 continues to the 45 degree part 3b having a 45 degree inclined surface outside the concave part 2, and further to the horizontal part 3a. The horizontal portion 3a is bent at two locations outside the concave portion at an angle of less than 45 degrees, forms a substantially Z shape, lowers the position, and the magnetron 5 is attached to the tip.
[0027]
An elliptical hole is formed in the center of the 45 degree portion 3b, and a metal stirrer bearing 6 having a round hole coaxial with the hole is fixed at a position for closing the hole. The upper end of the stirrer shaft 4 a penetrates both of these and protrudes to the outside, and the above-mentioned passive lever 4 d is fixed to the upper portion of the stirrer bearing 6. The stirrer motor 7 is fixed so that its output shaft coincides with the stirrer shaft 4a, and an inverted L-shaped drive lever 8 is attached to the tip of the output shaft to engage with the passive lever 4d. The concave portion 2 is closed with a glass plate 9, and a sheathed heater 10 is attached below it.
[0028]
Next, the operation and action will be described. The microwave generated by the magnetron 5 reaches the vertical portion 3c from the horizontal portion 3a of the waveguide 3 through the above-described substantially Z-shaped portion and the 45 ° inclined portion 3b. It is radiated from the vertical portion 3c and reaches and is absorbed by the food placed inside the heating chamber 1. A portion reflected without being absorbed returns to the magnetron 5 through the reverse path. In the middle of traveling of the waveguide 3, it has only a wall surface of 45 degrees or less with respect to the traveling wave, and has a high-pass characteristic because there is no wall surface parallel to the electric field in the traveling direction so as to short-circuit the traveling wave High efficiency can be obtained by designing to an appropriate operating point as described above.
[0029]
When the height of the concave portion 2 having a truncated cone shape is set to about 30 mm, if the waveguide vertical portion 3c is omitted, the operating point measured by the above-described cold impedance method is expanded over a wide range, and the efficiency and output are greatly reduced. . By providing the vertical portion 3c, the operating point is narrowed, and the efficiency and output are increased.
[0030]
Since the heating chamber 1 is a substantially rectangular parallelepiped, and the waveguide vertical portion 3c is provided at the center of the top surface, an electric field distribution that is subject to front, rear, left and right can be expected in the heating chamber. In order to maintain front / rear left / right symmetry, the stirrer axis 4a is also located at the center of the heating chamber and the vertical portion of the waveguide. Since the 45-degree bent portion 3b is provided and a space is generated above the vertical portion 3c, the tip of the stirrer shaft 4a protrudes outside the waveguide and can be coupled to the stirrer motor 7.
[0031]
In this embodiment, the concave portion 2 is provided as the stirrer space, but this can be omitted and the vertical portion 3c of the waveguide can be directly directed downward from the center of the flat top surface of the heating chamber. Although the magnetron 5 is disposed on the top surface of the heating chamber 1, the horizontal portion 3a of the waveguide can be extended to the right and the magnetron 5 can be disposed on the right side of the heating chamber.
[0032]
In any case, the gist of the present invention is that the end of the waveguide formed only by bending at 45 degrees or less with respect to the traveling direction at the center of the top surface of the heating chamber of the substantially front / rear / right / left target shape is symmetrical in the front / rear / left / right state. It is attached, and thereby, the front / rear / left / right target electric field distribution inside the heating chamber and high efficiency are obtained at the same time.
[0033]
【The invention's effect】
As described above, the microwave oven according to the first aspect of the present invention includes a magnetron, a heating chamber having a substantially front / rear left / right symmetric shape, a waveguide connecting the both, a stirrer blade, and a drive mechanism, The tube consists of a horizontal part, a vertical part, and a 45-degree bent part connecting the two. The vertical part is located at the center of the top of the heating chamber, the horizontal part is located outside the top of the heating chamber, a magnetron is attached, and the stirrer blade is rotated. A shaft is provided in the center of the heating chamber, and is coupled to the external drive mechanism from the 45 ° bent portion.
[0034]
The heating chamber has a substantially symmetrical shape in the front-rear direction, and the vertical portion of the waveguide and the rotation axis of the stirrer blade are both provided in the center of the heating chamber. In addition, since the waveguide is formed in a straight line and a 45-degree bent shape, it has high-pass performance, and there is an effect that high efficiency can be obtained if the magnetron is operated at an appropriate operating point.
[0035]
The microwave oven according to claim 2 is provided with a recess at the center of the top surface of the heating chamber, and the vertical portion of the waveguide and the stirrer blade are both accommodated in the recess.
[0036]
The height of the concave portion is often about 30 mm in design, that is, it may be around about ¼ wavelength of 2,450 MHz. Then, the phase difference between the reflected wave due to the discontinuity between the waveguide and the concave portion and the reflected wave due to the discontinuity between the concave portion and the heating chamber becomes 90 degrees, and if one is canceled, the other will increase. Matching becomes difficult and inevitably decreases efficiency. By providing the waveguide vertical part inside the recess, this quarter-wavelength wavelength line can be bypassed and limited to the reflected wave due only to the discontinuity between the waveguide and the heating chamber, resulting in normal design work. There is an effect that improvement in efficiency can be expected.
[0037]
Further, in the microwave oven according to claim 3, a metal is attached to the 45-degree bent portion of the waveguide, a hole is formed through the both to coincide with the center of the heating chamber, and the dielectric shaft of the stirrer blade is fitted into this hole. It has been made.
[0038]
Then, by passing the vertical cylindrical stirrer shaft through the inclined portion of 45 degrees, it becomes possible to connect to the drive mechanism in the upper space of the waveguide vertical portion. A special elliptical hole is required to pass through the 45-degree inclined surface without contact with the circular shaft, and there is a concern about leakage radio waves through the hole, but a metal with a round hole that fits into the stirrer shaft. Since the stirrer receiver 6 is attached, there is an effect that leakage can be reduced.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a main part of a microwave oven according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view of a magnetron operation measuring apparatus used for explaining the operation principle. FIG. 3 is a Smith chart used for explaining the operation principle. [Fig. 4] Fig. 5 is an iso-power diagram of the magnetron used to explain the operation principle. [Fig. 5] Fig. 6 is a diagram showing the operating points drawn on the Smith diagram. [Fig. 6] Fig. 7 is a diagram of the relationship between the magnetron anode and its voltage. Sectional view of the main part of the microwave oven [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Heating chamber 3a Waveguide horizontal part 3b Waveguide 45 degree bending part 3c Waveguide vertical part 4 Staller blade 4a Staller shaft 4d Passive lever (drive mechanism)
5 Magnetron 7 Staller motor (drive mechanism)
8 Drive lever (drive mechanism)

Claims (3)

It has a magnetron, a heating chamber having a substantially symmetric shape in the front-rear direction, a waveguide connecting the two, a stirrer blade, and a drive mechanism. The waveguide includes a horizontal portion, a vertical portion, and a 45-degree bent portion between the two. The vertical part is located in the center of the top surface of the heating chamber, the horizontal part is located outside the top surface of the heating chamber, the magnetron is attached, the rotation axis of the stirrer blade is provided in the center of the heating chamber, and the external drive mechanism from the 45 degree bending part Microwave oven that is combined with. The microwave oven according to claim 1, wherein a concave portion is provided in the center of the top surface of the heating chamber, and the vertical portion of the waveguide and the stirrer blade are both accommodated in the concave portion. The electron according to claim 1 or 2, wherein a metal is attached to a 45-degree bent portion of the waveguide, a hole is formed through the both to coincide with the center of the heating chamber, and a dielectric shaft of the stirrer blade is fitted into the hole. range.

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