JP3766190B2

JP3766190B2 - Capacitance type 3-axis acceleration sensor

Info

Publication number: JP3766190B2
Application number: JP29260197A
Authority: JP
Inventors: 栄治玉越; 克則長野
Original assignee: 内外ゴム株式会社
Priority date: 1997-10-24
Filing date: 1997-10-24
Publication date: 2006-04-12
Anticipated expiration: 2017-10-24
Also published as: JPH11133055A

Description

【０００１】
【発明の属する技術分野】
本発明は、検出精度を高めうる静電容量形３軸加速度センサに関する。
【０００２】
【従来の技術】
加速度センサは、サーボ形、圧電形、ピエゾ抵抗形、静電容量形などが知られており、近年では例えば地震などの縦揺れ、横揺れなど複数の方向の加速度を同時に検出するために、Ｘ−Ｙ−Ｚの３軸方向でそれぞれ加速度を検出しうる３軸加速度センサが開発されつつある。
【０００３】
静電容量形３軸加速度センサは、特開平４−１４８８３３号公報などで提案され、例えば図１４（ａ）に示すように、固定板ａと、重錘ｃを固着させた可撓板ｂとが向き合ってケース体ｄに固定され、前記固定板ａ、可撓板ｂの向き合う面に、固定電極Ｅ１と変位電極Ｅ２とが設けられている。
【０００４】
前記固定板ａは、例えば剛性が高く撓みを生じにくい材料からなり、前記可撓板ｂは、本例では可撓性を有し、力が加わると容易に撓みを生じる材料で構成されているものを示す。また、前記固定電極Ｅ１は、図１５（ａ）に示すように平面視が円形をなすものであり、他方、変位電極Ｅ２は例えば図１５（ｂ）に示すように５分割した分離電極片、すなわち中央で円形をなす電極ＥＺ１と、この電極ＥＺ１の中心を原点としたときに可撓板ｂの平面方向に沿ったＸ軸方向正負に配された電極ＥＸ１、ＥＸ２と、Ｙ軸方向正負に配された電極ＥＹ１、ＥＹ２とから構成される。
【０００５】
このような加速度センサｓに外部から加速度が与えられると、図１４（ｂ）に示すように、重錘ｃの重心にあたる作用点Ｐに力ＦＸが作用して重錘ｃが変位することにより可撓板ｂが撓む。また固定電極Ｅ１と変位電極Ｅ２との間の電極間距離が変化して両電極間の静電容量値も変化する。この静電容量値の変化をＸ軸方向、Ｙ軸方向、Ｚ軸方向それぞれ下記▲１▼〜▲３▼式の如く検出して加速度を検出しうる。
【０００６】

なお静電容量値Ｃは、誘電率をε、電極の表面積をＳ、電極間距離をｄとすると次の式で与えられる。
Ｃ＝ε・Ｓ／ｄ
【０００７】
【発明が解決しようとする課題】
図１４（ｂ）には、静電容量型３軸加速度センサにＸ軸方向の加速度のみが作用した状態を示したが、通常、可撓板ｂには、剛性の指向性がない材料が選ばれるため、重錘ｃの重心を通る垂直軸が可撓板ｂの厚さの中心を通る可撓板ｂの原点ＯはＺ軸方向には変位せず、該原点Ｏの回りにモーメントが生じるものとみなして良い。そして、重錘ｃは、可撓板ｂの剛性に見合った変位をなして釣り合う。
【０００８】
ここで、電極ＥＸ１およびＥＸ２の表面積をそれぞれＳ２、センサに重力加速度のみが作用する無負荷状態での電極ｅＸ１およびｅＸ２と固定電極ｅ１との間の初期の電極間距離をＤ０とし、力ＦＸが作用することで可撓板ｂが撓み電極ＥＸ１およびＥＸ２に生じる固定電極Ｅ１との電極間距離の変化量をＤＸとすると、Ｘ軸方向の加速度に対応する静電容量値ＣＸは、前記▲１▼式から下記数１のように表しうる。
【数１】

【０００９】
また初期の電極間距離Ｄ０に対する電極間距離の変化量ＤＸの比（ＤＸ／Ｄ０）をｄｘで表すと、上記数１は下記数２のように表しうる。
【数２】

【００１０】
ところが、このような静電容量形３軸加速度センサは、Ｘ軸方向の加速度とＺ軸方向の加速度（本例では上向き）とが同時に負荷されるような加速度を受けた場合、力ＦＸが作用することで電極ＥＸ１およびＥＸ２に生じる電極間距離の変化量をＤＸとし、他方、力ＦＺを受けたときの電極間距離の変化量をＤＺとし、（ＤＺ／Ｄ０）をｄｚで表すと、Ｘ軸方向の静電容量値ＣＸＡは、力ＦＺによりＤＺだけＺ軸方向上向きに変位した変位電極Ｅ２が、さらに、Ｘ軸方向の力ＦＸにより±ＤＸだけ傾斜して変位したＸ軸方向の静電容量値ＣＸ１およびＣＸ２の差で表すことができ、下記数３のように表しうる。
【数３】

【００１１】
このように、上記数３では、数２と異なり、Ｘ軸方向の静電容量値に、Ｚ軸方向の変化率ｄｚの因子が含まれていることが判る。
【００１２】
静電容量値と電極間距離の関係を図１６に示している。図では、横軸に電極間距離ｄを、縦軸にＸ軸方向の静電容量値ＣＸをとっている。電極間距離ｄが、無負荷状態の初期の設定値Ｄ０の場合、Ｘ軸方向の加速度により可撓板ｂの変位量が±ＤＸであったとき、静電容量値ＣＸは、ΔＣ０となる。これに対して、Ｚ軸方向の加速度が同時に作用し、電極間距離ｄが初期の設定値Ｄ０よりＤＺ大きいとき又はＤＺだけ小さいときにＸ軸方向の加速度により可撓板ｂの変位量が±ＤＸであると、それぞれ静電容量値は、ΔＣ＋ｚ、ΔＣ−ｚにばらつくことになる。
【００１３】
このように、電極間の静電容量値は、電極間距離の影響を強く受けるため、静電容量形３軸加速度センサでは、上述のようにＺ軸方向の加速度がＸ軸方向又はＹ軸方向といった水平軸方向の加速度に同時に加わると、その影響により、Ｘ軸方向（又はＹ軸方向）の検出加速度にバラツキが生じ、検出精度が悪化するという問題がある。
【００１４】
このような問題を解決するために、例えば電気的に補正回路を組み込むことや、物理的に水平方向の感度を上げることなどが考えられるが、前者の場合には回路が複雑となり、また回路基板を組み込むためにセンサが大型化するという問題があり、また後者の方法では、基板サイズの大型化などの他、コストの面から見ても望ましいとは言えない。
【００１５】
本発明者らは、静電容量形３軸加速度センサの機械的な構造を改良することにより水平方向の静電容量値からＺ軸方向の加速度の影響を排除する方法について鋭意検討を重ねたところ、センサ本体にＺ軸方向の加速度による変位によって、電極間距離が一方は増加しかつ他方は減少する２つの電極群を設けるとともに、これらの各電極群の静電容量の変化差をとることによって、水平方向の加速度に基づく静電容量からＺ軸方向の加速度の影響を大幅に除去しうることを見出したのである。
【００１６】
以上のように本発明は、電気的補正回路に頼ることなく、センサ出力を向上しつつも垂直方向の加速度が水平方向の加速度と同時に作用した場合であっても水平方向の加速度の検出精度を向上しうる静電容量形３軸加速度センサを提供することを目的としている。
【００１７】
【課題を解決するための手段】
本発明のうち請求項１記載の発明は、重錘と、この重錘が取付られかつこの重錘に作用する加速度による重錘の動きにより変位する変位部を有する可撓板とからなる重錘可撓部材、
この重錘可撓部材の一方の第１の変位面に向き合う第１の静止面を有する第１の固定部、
及びこの重錘可撓部材の他方の第２の変位面に向き合う第２の静止面を有する第２の固定部、
をそれぞれセンサ筐体に固定し、かつ
前記第１の変位面に設けられた第１の変位電極と、第１の静止面に設けられた第１の固定電極とからなる第１の電極群、
及び前記第２の変位面に設けられた第２の変位電極と、第２の静止面に設けられた第２の固定電極とからなる第２の電極群とを配したセンサ本体を具えるとともに、
第１の変位電極と、第１の固定電極の少なくとも一方、第２の変位電極と、第２の固定電極の少なくとも一方は、ともに４つ以上かつ同数しかも電気的に独立した分離電極片からなり、
しかも第１の電極群の第１の変位電極は、第２の電極群の第２の変位電極と、前記第１の電極群の第１の固定電極は、第２の電極群の第２の固定電極とそれぞれ同形とするとともに、
重錘の動きにより前記第１の電極群の第１の変位電極と第１の固定電極との間に生じる静電容量の変化、前記第２の電極群の第２の変位電極と、第２の固定電極との間に生じる静電容量の変化との差を出力することにより加速度を測定する演算部を具えたことを特徴とする静電容量形３軸加速度センサである。
【００１８】
また請求項２記載の発明は、前記第１の変位面は、前記重錘が取り付かない側の可撓板の面であり、かつ第２の変位面が前記重錘の面であることを特徴とする請求項１記載の静電容量形３軸加速度センサである。
【００１９】
また請求項３記載の発明は、前記第１の変位面は、前記重錘が取り付かない側の可撓板の面であり、かつ第２の変位面が前記重錘が取り付く側の可撓板の面であることを特徴とする請求項１記載の静電容量形３軸加速度センサである。
【００２０】
また請求項４記載の発明は、前記分離電極片は、前記可撓板の面と直交しその中心を通る中心線回りの中央電極片と、前記中心線が可撓面と交わる原点を通り前記可撓板面と平行なＸ軸、Ｙ軸側で中央電極片の外側かつ正負の位置に配される正、負の周辺Ｘ軸電極片と、正、負の周辺Ｙ軸電極片との合計５つを含むことを特徴とする請求項１乃至３のいずれか１に記載の静電容量形３軸加速度センサである。
【００２１】
また請求項５記載の発明は、前記中央分離電極片はリング状をなすことを特徴とする請求項４記載の静電容量形３軸加速度センサである。
【００２２】
また請求項６記載の発明は、前記分離電極片が形成されない変位面、又は静止面は、金属材からなることを特徴とする請求項１乃至５のいずれか１に記載の静電容量形３軸加速度センサである。
【００２３】
また請求項７記載の発明は、第１の電極群の中央電極片による静電容量値をＣ１１、正、負の周辺Ｘ軸電極片の静電容量値をＣ１２、Ｃ１４、正、負の周辺Ｙ軸電極片の静電容量値をＣ１３、Ｃ１５、第２の電極群の中央電極片による静電容量値をＣ２１、正、負の周辺Ｘ軸電極片の静電容量値をＣ２２、Ｃ２４、正、負の周辺Ｙ軸電極片の静電容量値をＣ２３、Ｃ２５としたとき、各ＸＹＺ軸方向の加速度に対応する静電容量値をＣＸ、ＣＹ、ＣＺを次式により算出して、前記重錘に作用した加速度を検出することを特徴とする請求項４記載の静電容量形３軸加速度センサである。
ＣＸ＝（Ｃ１２−Ｃ１４）−（Ｃ２２−Ｃ２４）
ＣＹ＝（Ｃ１３−Ｃ１５）−（Ｃ２３−Ｃ２５）
ＣＺ＝（Ｃ１１）−（Ｃ２１）
【００２４】
【発明の実施の形態】
以下、本発明の実施の一形態を図面に基づき説明する。
本発明の静電容量形３軸加速度センサは、図１に示すように、重錘可撓部材２と、この重錘可撓部材２の一方の第１の変位面２ａに向き合う第１の静止面３ａを有する第１の固定部３と、前記重錘可撓部材２の他方の第２の変位面２ｂに向き合う第２の静止面４ｂを有する第２の固定部４とをそれぞれセンサ筐体７に固定している。
【００２５】
前記重錘可撓部材２は、重錘５と、この重錘５が取付られかつこの重錘５に作用する加速度による重錘５の動きにより変位する変位部を有する可撓板６とから構成され、本例では重錘５は前記可撓板６の下面に取り付けされているものを示す。
【００２６】
また本実施形態において、前記第１の変位面２ａは、前記重錘５が取り付かない側の可撓板６の面であり、かつ第２の変位面２ｂが前記重錘５の面、本例では重錘５の下面であるものを例示している。なお本例では、前記第１、第２の固定部３、４、重錘５、可撓板６はいずれもガラス、樹脂、セラミックといった絶縁材料から構成されたものを例示している。
【００２７】
また前記重錘可撓部材２の第１の変位面２ａには、第１の変位電極ｅｆ１が設けられ、この第１の変位面２ａに向き合う第１の静止面３ａには、前記第１の変位電極ｅｆ１から距離を隔てて第１の固定電極ｅ１が形成される。これにより、第１の変位電極ｅｆ１と第１の固定電極ｅ１とが第１の電極群ＥＵを構成しうる。
【００２８】
同様に、前記第２の変位面２ｂには、第２の変位電極ｅｆ２が設けられ、この第２の変位面２ｂに向き合う第２の静止面４ｂには、前記第２の変位電極ｅｆ２から距離を隔てて第２の固定電極ｅ２が形成されている。これにより、第２の変位電極ｅｆ２と第２の固定電極ｅ２とが第２の電極群ＥＤを構成しうる。
【００２９】
このように、センサ本体１は、第１の電極群ＥＵと第２の電極群ＥＤとを具えている。また本発明では、前記第１の変位電極ｅｆ１と、第１の固定電極ｅ１の少なくとも一方、第２の変位電極ｅｆ２と、第２の固定電極ｅ２の少なくとも一方は、ともに４つ以上かつ同数しかも電気的に独立した分離電極片から構成されることを特徴の一つとしている。
【００３０】
本実施形態では、前記第１の固定電極ｅ１と、第２の固定電極ｅ２とを図２（ａ）、（ｂ）に示すように、ともに５つしかも電気的に独立した分離電極片から構成したものを例示している。これらの分離電極片は、図の如く前記可撓板６の面と直交しその中心を通る中心線回りの中央電極片ｅＺ１、ｅＺ２と、前記中心線が可撓板６の面と交わる原点を通り前記可撓板６の面と平行なＸ軸、Ｙ軸側で中央電極片ｅＺ１、ｅＺ２の外側かつ正負の位置に配される正、負の周辺Ｘ軸電極片ｅＸ１、ｅＸ２、及びｅＸ３、ｅＸ４と、正、負の周辺Ｙ軸電極片ｅＹ１、ｅＹ２、及びｅＹ３、ｅＹ４との５つをそれぞれ含むものを例示し、これらは互いに電気的に絶縁されて配置される。
【００３１】
これにより、第１の電極群ＥＵ、第２の電極群ＥＤは、それぞれ分離電極片と変位電極との対によりそれぞれ５組、合計１０組の容量素子を形成しうる。なお第１、第２の変位電極ｅｆ１、ｅｆ２は、本例では図２（ｃ）に示すように、一体型の円盤状にて形成されるものを示す。これらの各電極は、導電性の性質を持つ材料であれば種々のものを用いることができるが、これらは同一の材料で構成するのが望ましく、本例では同じ金属材料で構成される。
【００３２】
また本発明では、前記第１の電極群ＥＵ、第２の電極群ＥＤにおいて、前記可撓板６を挟んで対向する前記分離電極片は、それぞれ同一の形状で構成しているため、例えば第１の電極群ＥＵのＸ軸方向に配された分離電極片ｅＸ１、ｅＸ２と、第２の電極群ＥＤのＸ軸方向に配された分離電極片ｅＸ３、ｅＸ４とは、ともに表面積がＳ２で等しくなる。即ち第１の電極群ＥＵの第１の変位電極ｅｆ１は、第２の電極群ＥＤの第２の変位電極ｅｆ２と、前記第１の電極群ＥＵの第１の固定電極ｅ１は、第２の電極群ＥＤの第２の固定電極ｅ２とそれぞれ同形としいる。
【００３３】
また、本実施形態では、センサに重力加速度のみが作用する無負荷状態において、前記第１の電極群ＥＵの電極間距離Ｄ１は、第２の電極群ＥＤの電極間距離Ｄ２と等しく設定したものを例示している。
【００３４】
そして、このような静電容量型３軸加速度センサは、加速度による重錘５の動きにより前記第１の電極群ＥＵの第１の変位電極ｅｆ１と第１の固定電極ｅ１との間に生じる静電容量の変化と、前記第２の電極群ＥＤの第２の変位電極ｅｆ２と、第２の固定電極ｅ２との間に生じる静電容量の変化との差を出力することにより加速度を測定する演算部（図５〜７に示す）を具えている。
【００３５】
このように、本例ではＺ軸方向の加速度による変位によって、電極間距離が一方は増加しかつ他方は減少する２つの電極群、すなわち第１の電極群ＥＵ、第２の電極群ＥＤを形成し、これらの各電極群の静電容量の差をとることによって、水平方向の加速度に基づく静電容量からＺ軸方向の加速度の影響を大幅に除去しうるのである。すなわち、第１の電極群ＥＵの静電容量値から、第２の電極群ＥＤでの静電容量値を差し引くことにより、Ｘ軸方向及びＹ軸方向の加速度にＺ軸方向の加速度が同時に作用した場合であっても、Ｚ軸方向の加速度がＸ軸方向及びＹ軸方向の静電容量値に与える影響を小にすることができ、検出精度を大幅に高めることができる。
【００３６】
例えば図２（ａ）、（ｂ）に示すように、第１の電極群ＥＵの中央電極片ｅＺ１と変位電極ｅｆ１とによる静電容量値をＣ１１、正、負の周辺Ｘ軸電極片ｅＸ１、ｅＸ２の静電容量値をＣ１２、Ｃ１４、正、負の周辺Ｙ軸電極片ｅＹ１、ｅＹ２の静電容量値をＣ１３、Ｃ１５、第２電極群ＥＤの中央電極片ｅＺ２による静電容量値Ｃ２１、正、負の周辺Ｘ軸電極片ｅＸ３、ｅＸ４の静電容量値をＣ２２、Ｃ２４、正、負の周辺Ｙ軸電極片ｅＹ３、ｅＹ４の静電容量値をＣ２３、Ｃ２５としたとき、各ＸＹＺ軸方向の加速度に対応する静電容量値ＣＸ、ＣＹ、ＣＺの演算は、次の▲４▼〜▲６▼式により行いうる。
ＣＸ＝（Ｃ１２−Ｃ１４）−（Ｃ２２−Ｃ２４） … ▲４▼
ＣＹ＝（Ｃ１３−Ｃ１５）−（Ｃ２３−Ｃ２５） … ▲５▼
ＣＺ＝（Ｃ１１）−（Ｃ２１） … ▲６▼
【００３７】
ここで、本発明の静電容量形３軸加速度センサの検出精度について上記演算式を用いながら説明する。先ず、重錘５が加速度を受けこの重錘５の作用点Ｐに、Ｘ方向の力ＦＸ（図１に示す方向）のみが加わった場合、Ｘ軸上の正負に配された分離電極片ｅＸ１、ｅＸ２、ｅＸ３、ｅＸ４において、分離電極片ｅＸ１、ｅＸ４は変位電極ｅｆ１、ｅｆ２との電極間距離を減じ静電容量値Ｃ１２、Ｃ２４を増大させる一方、分離電極片ｅＸ２、ｅＸ３は変位電極ｅｆ１、ｅｆ２との間の電極間距離を増し、静電容量値Ｃ１４、Ｃ２２を減少させる。
【００３８】
これらの静電容量を算出するに当たり、従来の静電容量形３軸加速度センサと比較するため、可撓板、電極、および重錘の形状、寸法、材質、重量を統一することにより両者の基本的諸元を揃え、また電極（例えば電極の平面の図心位置）に生じる電極間距離の変化量を±ＤＸとすると、本発明のセンサのＸ軸方向の加速度に対応する静電容量値ＣＸは、数４のように表される。なお分離電極片ｅＸ１、ｅＸ２、ｅＸ３、ｅＸ４の表面積をＳ２、誘電率をε、力ＦＸによって生じる電極間距離の変位量を±ＤＸ、初期の電極間距離Ｄ０と前記変位量ＤＸとの比（ＤＸ／Ｄ０）をｄｘとしている。
【数４】

【００３９】
このように、Ｘ軸方向（又はＹ軸方向）の加速度のみが、重錘５に加えられた場合、数２で示した従来の静電容量形３軸加速度センサの静電容量値ＣＸと比較すると、本発明のものは静電容量値（出力）が２倍となり、Ｘ軸方向（又はＹ軸方向）の検出感度が向上していることが判る。
【００４０】
また、Ｚ軸方向の加速度のみが重錘５に加えられた場合、中央電極片ｅＺ１、ｅＺ２の表面積をＳ１、中央電極片ｅＺ１と変位電極ｅｆ１との間及び中央電極片ｅＺ２と変位電極ｅｆ２との間にそれぞれ生じる電極間距離の変化量を±ＤＺとし、初期の電極間距離Ｄ０との比（ＤＺ／Ｄ０）をｄｚで表すと、本発明のセンサの静電容量値ＣＺは、数５のようになる。
【数５】

【００４１】
これに対して、従来のセンサでは、数６のようになる。
【数６】

【００４２】
ここで、ｄｚは通常最大で０．１程度で使用されるのが好ましく、この場合、本実施形態の静電容量形３軸加速度センサは、Ｚ軸方向の静電容量値においても実質的に２倍の出力をうることができる。このように、Ｘ軸方向（又はＹ軸方向）あるいはＺ軸方向の力が、それぞれ独立して加えられた場合、本発明の静電容量形３軸加速度センサは、従来のセンサに比べ出力がともに２倍となり、しかもＺ軸方向の静電容量値については、バラツキも減少していることが判る。
【００４３】
なお、Ｚ軸方向の静電容量値の変化を検出するには、図３に示すように、中央電極片を独立して設けず、４分割した分離電極片ｅＸ１、ｅＸ２、ｅＹ１、ｅＹ２の静電容量値の総和の変化から算出することも可能である。しかし、本実施形態のように中央分離電極片ｅＺ１を有する５分割とした場合には、検出の電気回路が単純化され、小型化に有利であり、また電極の原点に近いほど、他軸の影響を受け難いため、Ｚ軸方向の加速度の検出精度をさらに向上しうる利点がある。
【００４４】
次に、Ｘ軸方向の加速度とＺ軸方向の加速度とが同時に重錘５に負荷された場合について考える。この場合図４に示すように、変位電極ｅｆ１、ｅｆ２がＺ軸方向の力ＦＺにより、上向きの変位量ＤＺを生じさせていると同時に、Ｘ軸方向の力ＦＸにより変位量±ＤＸが生じているものと考えることができる。この場合のＸ軸方向の静電容量値ＣＸＢは数７に示すようになる。
【数７】

【００４５】
ここで、数３に示した従来のセンサの静電容量値ＣＸＡは、本発明のセンサの静電容量値ＣＸＢとを比較するために分母の共通化を図ると、数８のように表すことができる。
【数８】

【００４６】
静電容量形３軸加速度センサは、その構造上、作動範囲において通常、ｄｘ、ｄｚの最大値を０．１程度で使用するのが好ましいため、ｄｘ、ｄｚの最大値を０．１とすると、前記数７、８の式の分母｛（１−ｄｚ）²−ｄｘ²｝｛（１＋ｄｚ）²−ｄｘ²｝は、０．９６〜１．００の範囲をとり得る。また、各分子のうち（ｄｚ²−ｄｘ²）の項は、−０．０１〜０．０１の範囲を取りうる。
【００４７】
また本発明の静電容量形３軸加速度センサと従来のセンサの静電容量値ＣＸＢ、ＣＸＡを比較すると、従来のもの（数８）には、分子において「１」に「２ｄｚ」の因子を加えた形となっている。この「２ｄｚ」は、最大で０．２の値をとるため、最大で±２０％のバラツキを与えるものとなる。
【００４８】
これに対して、本発明の静電容量形３軸加速度センサは、静電容量値ＣＸＢが従来のものに比して２倍になっており、検出感度を向上しうるとともに、従来のセンサに比べ、Ｘ又はＹ軸方向といった水平方向の加速度にＺ軸方向の加速度が同時に加わったような場合でも、従来のＺ軸方向の加速度の影響（２ｄｚ）を排除してＸ軸方向（又はＹ軸方向）の静電容量値を取得することができるため、検出精度を大幅に向上しうる。
【００４９】
次に演算部の回路構成の一例を図５〜７に示す。図５はＸ軸方向の加速度出力、図６はＹ軸方向の加速度出力、図７はＺ軸方向の加速度出力を行うものである。例えば図５において、電極ｅＸ１、ｅｆ１間の静電容量Ｃ１２、電極ｅＸ２、ｅｆ１間の静電容量Ｃ１４、電極ｅＸ３、ｅｆ２間の静電容量Ｃ２２、電極ｅＸ４、ｅｆ２間の静電容量Ｃ２４は、それぞれＣＶ変換器Ｈ１〜Ｈ４により電圧値Ｖ１〜Ｖ４に変換されて出力される。
【００５０】
また、差動増幅器Ａ１は、ＣＶ変換器Ｈ１、Ｈ２により変換された電圧値Ｖ１とＶ２との差の電圧Ｖ５を、また差動増幅器Ａ２は、ＣＶ変換器Ｈ３、Ｈ４により変換された電圧値Ｖ３とＶ４との差の電圧Ｖ６をそれぞれ差動増幅器Ａ３に出力する。差動増幅器Ａ３は電圧Ｖ５とＶ６の差をとり、これをＸ軸方向の加速度に対応する電圧値Ｖ７として出力しうる。
【００５１】
なおＹ軸方向もＸ軸方向の場合と同様、電極ｅＹ１、ｅｆ１間の静電容量Ｃ１３、電極ｅＹ２、ｅｆ１間の静電容量Ｃ１５、電極ｅＹ３、ｅｆ２間の静電容量Ｃ２３、電極ｅＹ４、ｅｆ２間の静電容量Ｃ２５は、それぞれＣＶ変換器Ｈ５〜Ｈ８により電圧値Ｖ１０〜Ｖ１３に変換され、差動増幅器Ａ４は、ＣＶ変換器Ｈ５、Ｈ６により変換された電圧値Ｖ１０とＶ１１との差の電圧Ｖ１４を、また差動増幅器Ａ５は、ＣＶ変換器Ｈ７、Ｈ８により変換された電圧値Ｖ１２とＶ１３との差の電圧Ｖ１５をそれぞれ差動増幅器Ａ６に出力する。また差動増幅器Ａ６は電圧Ｖ１４とＶ１５の差をとり、これをＹ軸方向の加速度に対応した電圧値Ｖ１６として出力する。
【００５２】
またＺ軸方向については、電極ｅＺ１、ｅｆ１間の静電容量Ｃ１１、電極ｅＺ２、ｅｆ２間の静電容量Ｃ２１をそれぞれＣＶ変換器Ｈ９、Ｈ１０により対応する電圧Ｖ１７、Ｖ１８に変換するとともに、差動増幅器Ａ７により電圧Ｖ１７、Ｖ１８の差をとり、これをＺ軸方向の加速度に対応した電圧値Ｖ１９として出力しうる。
【００５３】
そして、センサ本体の前記各電極に所定の配線を施して、上述のような演算動作を行う回路に接続することによって、重錘５に作用した加速度に対応する電圧値を、３次元の各軸方向成分ごとに精度良く取り出すことができる。なおこの演算回路は一例であり、たとえば、前記▲４▼〜▲６▼式を変形して、それに対応した演算回路を組むことも、勿論可能である。
【００５４】
また前記無負荷状態において、第１の電極群ＥＵの第１の固定電極ｅ１と第１の変位電極ｅｆ１との電極間距離Ｄ１と、第２の電極群ＥＤの第２の固定電極ｅ２と第２の変位電極ｅｆ２との電極間距離Ｄ２とは、実質的に等しくすることが望ましい。
【００５５】
図８（ａ）に示す曲線Ｇ１ａは、前記電極間距離をＤ１＝Ｄ２＝Ｄ０とした場合の第１の電極群ＥＵの相対出力を示している。同曲線Ｇ１ｂは、第２の電極群ＥＤの相対出力であり、同曲線Ｇ１は、これらの相対出力の和であり、センサとしての相対出力を示している。図から明らかなとおり、曲線Ｇ１は、加速度センサの実用域であるｄｚ＝０近傍で、出力が非常に安定しており、最も適したものとなっている。
【００５６】
また、曲線Ｇ２ａは、前記電極間距離Ｄ１＝Ｄ２＝２Ｄ０とした場合の第１の電極群ＥＵの相対出力を示している。同曲線Ｇ２ｂは、第２の電極群ＥＤの相対出力であり、同曲線Ｇ２は、これらの相対出力の和であり、センサとしての相対出力を示している。この曲線Ｇ２では、出力が、広範囲に亘り安定するものの出力自体が小さくなる。
【００５７】
なお図８（ｂ）に示す曲線Ｇ３ａは、前記電極間距離Ｄ１＝Ｄ０、Ｄ２＝２Ｄ０としたＤ１≠Ｄ２の場合の第１の電極群ＥＵの相対出力を示し、同曲線Ｇ３ｂは、第２の電極群ＥＤの相対出力であり、同曲線Ｇ３は、これらの相対出力の和であり、センサとしての相対出力を示している。図から明らかなとおり、曲線Ｇ３は、補償が小さくなり、出力の曲線が従来のものに近づくため好ましくない。
【００５８】
また図８（ｂ）に示す曲線Ｇ４ａは、前記電極間距離Ｄ１＝Ｄ０、Ｄ２＝Ｄ０／２としたＤ１≠Ｄ２の場合の第１の電極群ＥＵの相対出力を示し、同曲線Ｇ４ｂは、第２の電極群ＥＤの相対出力であり、同曲線Ｇ４は、これらの相対出力の和であり、センサとしての相対出力を示している。図から明らかなとおり、曲線Ｇ４は、Ｄ２が小さいため、補償が大きすぎ、逆に精度を悪くしている。
【００５９】
したがって、初期の電極間距離Ｄ１、Ｄ２は、ともに等しく設定するとともに、個々のセンサに応じて出力特性（曲線）が安定する値を採用するのが良い。
【００６０】
次に、本発明の他の実施形態について説明する。本実施形態では、図９に示すように、前記第１の変位面２ａは、前記重錘５が取り付かない側の可撓板６の面であり、かつ前記第２の変位面２ｂが前記重錘５が取り付く側の可撓板６の面であることを特徴としている。前記第２の電極群ＥＤは、本例では中央部に重錘５が貫通するものを例示し、このため、第２の固定部４は、重錘５が通る透孔４ｃが形成されるとともに、前記中央電極片ｅＺ１、ｅＺ２が、図１０に示すように前記重錘５の周囲を囲むリング状をなすものを採用している。
【００６１】
この実施形態では、Ｘ軸方向の力が加わって重錘５が可撓板６の原点Ｏの回りに回転したときに生じる、第１、第２の電極群ＥＵ、ＥＤの電極間距離の変化の微小な差異を減じることができ、かつ組立寸法精度や組立加工性を向上しうる点で好ましい。
【００６２】
なお、本例では全ての電極を、図１０に示すような同形の分離電極片にて構成しているが、第１の電極群ＥＵ、第２の電極群ＥＤそれぞれについて、固定電極ｅ１（ｅ２）、又は変位電極ｅｆ１（ｅｆ２）のいずれか一方、に上述の様な分離電極片を具えていれば良い。また、その他の構成については、検出回路を含めて、図１に示す構造の装置と概略同様である。
【００６３】
また図１１、図１２には、本発明の他の実施形態を示している。この例では、第１、第２の固定部３、４、重錘５、可撓板６およびセンサ筐体７が金属材料にて構成されている。また、可撓板６は、本例では、センサ筐体７から放射状にのびる複数本のアーム部材により弾性的に支持されたものを例示する。
【００６４】
また前記アーム部材１２は、図１２に図１１のＡ−Ａ断面を示すように、例えば可撓板６よりも十分に弾性変形しやすいものとすることにより、可撓板６を変形させずアーム部材１２のみが弾性変形することにより可撓板６を変位させることもできる。この場合、可撓板６の変位による電極間距離の変位が線形に変化し易くなり、検出精度の向上にさらに役立つ。またこのように放射状に配されたアーム部材１２を設けることにより、可撓板６の変位をより指向性のないものとしうる結果、さらに検出精度の向上に効果がある。またこの例では、変位電極ｅｆ１、ｅｆ２は、いずれも可撓板６、重錘５自体を電極として用いることができ、構造の簡素化も役立つ。
【００６５】
なお可撓板６と重錘５とは、導電性を有する固着方法、例えば、溶接等により接合するのが好ましい。また第１、第２の固定部３、４には、絶縁材１０、１１を介して分離電極片ｅＸ１などを配している。
【００６６】
以上詳述したが、分離電極片は、重錘可撓部材２に設けても良い。さらに、可撓板６は好ましい可撓性を与えるために、環状又は放射状にスリット等の切り込みを入れたダイヤフラム状のものを使用することができる。
【００６７】
またセンサが、大きな衝撃を受ける場合には、センサ本体の強度を向上させることが望ましく、各部材に金属を使用するのが好ましい。一方、絶縁物として、又加工性や単価などの理由で、樹脂やセラミックスなども使用しうる。これらには、熱膨張率が大きく異なるものがあり、センサが自動車のように使用温度がかなり広範囲にわたるところに使用される場合には、熱膨張の差が電極間距離ｄに与える影響は無視できない。そのため、部材としては、熱膨張率の小さなものが望ましく、また、本例のように熱膨張率の近似した材料で構成することによって、温度による誤差等を減じるのが好ましい。
【００６８】
またセンサの検出精度を考慮すると、前述の変位率ｄｘ、ｄｙ、ｄｚそれぞれを０．１程度以下に抑え込むことが望ましいため、そのように各種構成材料の弾性率、厚さ、支持方式、重錘の形状と質量などを設計することも好ましい。さらに前記分離電極面が形成されない第１ないし第２の変位面、又は第１ないし第２の静止面は、金属材料から構成することもできる。さらに、各電極群における電極の大きさは、重錘が変位したときでも十分に垂直方向で重なり合う大きさとするのが良い。
【００６９】
【実施例】
本発明の静電容量形３軸加速度センサとして、最大１Ｇを測定しうる図１１に示した構造のセンサ（実施例）を試作し、図１４に示した従来構造のセンサ（従来例）と性能を比較した。
【００７０】
図１３は、実施例、従来例の各センサに、Ｘ軸方向の一定の加速度ＡＸを与えつつ、同時に±１Ｇ以内のＺ軸方向の加速度ＡＺを負荷した時のＸ軸方向の相対出力ＣＸを実測した結果を示している。測定にあたっては、両センサとも測定条件は同一とした。
【００７１】
図１３から明らかなように、従来例のセンサでは、Ｚ軸方向の加速度に比例してＸ軸方向の加速度の出力のバラツキが大きくなっていることが判る（ただし、Ｘ軸方向の加速度ＡＸの大きい範囲、とくに０．８〜１．０Ｇの範囲では、Ｚ軸方向加速度ＡＺが小さな値（０．５〜０Ｇ）しか負荷できなかったため、比較的小さなバラツキに止まっている）。また実施例のセンサは、従来例に比べて出力が約２倍となっており、検出感度が向上していること、及びＺ軸方向の加速度が負荷された場合であっても、出力のバラツキが非常に小さく、大幅な検出精度の向上が確認でき、計算式を用いて検証したのとほぼ同様の結果が得られている。
【００７２】
【発明の効果】
以上説明したように、本発明の静電容量形３軸加速度センサによれば、３軸の各方向の加速度検出感度を向上しうる。また、Ｘ軸方向及びＹ軸方向といった水平方向の加速度に、垂直方向（Ｚ軸方向）の加速度が加わったような場合でも水平方向の加速度を、負荷された垂直方向の加速度の影響を実質的に受けることなく、精度良く検出できる。このため、複雑な電気的な補正回路をセンサに組み込む必要がなくなり、センサを小型できかつ構造を簡素化した安価な静電容量形３軸加速度センサを提供することができる。
【図面の簡単な説明】
【図１】本発明の実施形態を示すセンサ本体の断面図である。
【図２】（ａ）は第１の固定電極、（ｂ）は第２の固定電極、（ｃ）は第１、第２の変位電極を示す平面図である。
【図３】分離電極片の他の例を示す平面図である。
【図４】変位電極の変位を説明する線図である。
【図５】Ｘ軸方向の演算部の回路図である。
【図６】Ｙ軸方向の演算部の回路図である。
【図７】Ｚ軸方向の演算部の回路図である。
【図８】（ａ）、（ｂ）は、電極間距離を種々変えたときのセンサ出力を説明するためのグラフである。
【図９】本発明の他の実施形態を示すセンサの断面図である。
【図１０】その分離電極片を示す平面図である。
【図１１】本発明の他の実施形態を示すセンサの断面図である。
【図１２】そのＡ−Ａ断面図である。
【図１３】本発明の性能を示すグラフである。
【図１４】従来の静電容量形３軸加速度センサの断面図であり、（ａ）は無負荷状態、（ｂ）は力ＦＸが作用した状態をそれぞれ示す。
【図１５】（ａ）は固定電極、（ｂ）は変位電極を示す平面図である。
【図１６】静電容量と電極間距離を示すグラフである。
【符号の説明】
１センサ本体
２重錘可撓部材
２ａ第１の変位面
２ｂ第２の変位面
３ａ第１の静止面
３第１の固定部
４第２の固定部
４ｂ第２の静止面
５重錘
６可撓板
７センサ筐体
ｅｆ１第１の変位電極
ｅ１第１の固定電極
ＥＵ第１の電極群
ｅｆ２第２の変位電極
ｅ２第２の固定電極
ＥＤ第２の電極群
ｅＸ１〜ｅＸ４、ｅＹ１〜ｅＹ４、ｅＺ１、ｅＺ２分離電極片
１０Ｘ、１０Ｙ、１０Ｚ演算部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a capacitance type triaxial acceleration sensor capable of improving detection accuracy.
[0002]
[Prior art]
Accelerometers are known as servo type, piezoelectric type, piezoresistive type, capacitance type, etc. In recent years, in order to detect accelerations in multiple directions such as pitch and roll such as earthquakes at the same time, X A triaxial acceleration sensor capable of detecting acceleration in the three axial directions of −YZ is being developed.
[0003]
A capacitance type triaxial acceleration sensor is proposed in Japanese Patent Application Laid-Open No. 4-148833. For example, as shown in FIG. 14A, a fixed plate a and a flexible plate b to which a weight c is fixed are provided. Are fixed to the case body d, and a fixed electrode E1 and a displacement electrode E2 are provided on the facing surfaces of the fixed plate a and the flexible plate b.
[0004]
The fixed plate a is made of, for example, a material having high rigidity and is less likely to bend, and the flexible plate b is made of a material that has flexibility in this example and easily bends when a force is applied. Show things. Further, the fixed electrode E1 has a circular shape in plan view as shown in FIG. 15 (a), while the displacement electrode E2 is a separated electrode piece divided into five parts as shown in FIG. 15 (b), for example. That is, an electrode EZ1 that is circular at the center, electrodes EX1 and EX2 that are arranged positively and negatively in the X-axis direction along the plane direction of the flexible plate b when the center of the electrode EZ1 is the origin, and positive and negative in the Y-axis direction The electrodes EY1 and EY2 are arranged.
[0005]
When acceleration is applied to the acceleration sensor s from the outside, as shown in FIG. 14B, the force FX acts on the action point P corresponding to the center of gravity of the weight c, and the weight c is displaced. The bending plate b bends. Further, the interelectrode distance between the fixed electrode E1 and the displacement electrode E2 changes, and the capacitance value between both electrodes also changes. Acceleration can be detected by detecting this change in capacitance value in the X-axis direction, Y-axis direction, and Z-axis direction according to the following equations (1) to (3).
[0006]

The capacitance value C is given by the following equation where ε is the dielectric constant, S is the surface area of the electrodes, and d is the distance between the electrodes.
C = ε · S / d
[0007]
[Problems to be solved by the invention]
FIG. 14B shows a state in which only the acceleration in the X-axis direction is applied to the capacitance type triaxial acceleration sensor. Usually, a material having no rigid directivity is selected for the flexible plate b. Therefore, the origin O of the flexible plate b whose vertical axis passing through the center of gravity of the weight c passes the center of the thickness of the flexible plate b is not displaced in the Z-axis direction, and a moment is generated around the origin O. It can be regarded as a thing. The weight c balances with a displacement corresponding to the rigidity of the flexible plate b.
[0008]
Here, the surface area of the electrodes EX1 and EX2 is S2, respectively, and the initial inter-electrode distance between the electrodes eX1 and eX2 and the fixed electrode e1 in a no-load state where only gravitational acceleration acts on the sensor is D0, and the force FX is Assuming that the amount of change in the distance between the fixed electrode E1 and the fixed electrode E1 generated on the flexible electrodes EX1 and EX2 by the action of the flexible plate b is DX, the capacitance value CX corresponding to the acceleration in the X-axis direction is ▲ 1 From the formula, it can be expressed as the following formula 1.
[Expression 1]

[0009]
Further, when the ratio (DX / D0) of the change amount DX of the inter-electrode distance to the initial inter-electrode distance D0 is expressed by dx, the above formula 1 can be expressed as the following formula 2.
[Expression 2]

[0010]
However, such a capacitive three-axis acceleration sensor receives a force FX when it receives an acceleration in which an acceleration in the X-axis direction and an acceleration in the Z-axis direction (upward in this example) are simultaneously applied. Then, the change amount of the interelectrode distance generated in the electrodes EX1 and EX2 is DX, and on the other hand, the change amount of the interelectrode distance when receiving the force FZ is DZ, and (DZ / D0) is expressed by dz. The electrostatic capacitance value CXA in the axial direction is an electrostatic capacity value in the X-axis direction in which the displacement electrode E2 that is displaced upward in the Z-axis direction by DZ by the force FZ is further inclined and displaced by ± DX by the force FX in the X-axis direction. It can be expressed by the difference between the capacitance values CX1 and CX2, and can be expressed as the following Equation 3.
[Equation 3]

[0011]
Thus, in the above equation (3), unlike the equation (2), it can be seen that the capacitance value in the X-axis direction includes a factor of the change rate dz in the Z-axis direction.
[0012]
FIG. 16 shows the relationship between the capacitance value and the distance between the electrodes. In the figure, the inter-electrode distance d is taken on the horizontal axis, and the capacitance value CX in the X-axis direction is taken on the vertical axis. When the inter-electrode distance d is the initial set value D0 in the no-load state, when the displacement amount of the flexible plate b is ± DX due to acceleration in the X-axis direction, the capacitance value CX becomes ΔC0. In contrast, when the acceleration in the Z-axis direction acts simultaneously and the inter-electrode distance d is larger than the initial set value D0 by DZ or smaller by DZ, the displacement amount of the flexible plate b is ±± due to the acceleration in the X-axis direction. In the case of DX, the capacitance values vary in ΔC + z and ΔC−z, respectively.
[0013]
As described above, since the capacitance value between the electrodes is strongly influenced by the distance between the electrodes, in the capacitance type triaxial acceleration sensor, the acceleration in the Z-axis direction is in the X-axis direction or the Y-axis direction as described above. If the acceleration is applied simultaneously to the acceleration in the horizontal axis direction, the detection acceleration in the X-axis direction (or Y-axis direction) varies due to the influence, and the detection accuracy is deteriorated.
[0014]
In order to solve such a problem, for example, it is conceivable to electrically incorporate a correction circuit or physically increase the sensitivity in the horizontal direction. However, in the former case, the circuit is complicated, and the circuit board is used. However, the latter method is not desirable from the viewpoint of cost as well as increasing the substrate size.
[0015]
The inventors of the present invention have made extensive studies on a method of eliminating the influence of acceleration in the Z-axis direction from the horizontal capacitance value by improving the mechanical structure of the capacitive three-axis acceleration sensor. The sensor body is provided with two electrode groups in which the distance between the electrodes is increased and the other is decreased by displacement due to the acceleration in the Z-axis direction, and by taking the difference in capacitance of each of these electrode groups The present inventors have found that the influence of acceleration in the Z-axis direction can be largely removed from the electrostatic capacitance based on the acceleration in the horizontal direction.
[0016]
As described above, the present invention increases the detection accuracy of the horizontal acceleration even when the vertical acceleration acts simultaneously with the horizontal acceleration while improving the sensor output without relying on the electrical correction circuit. An object of the present invention is to provide a capacitance type triaxial acceleration sensor that can be improved.
[0017]
[Means for Solving the Problems]
  The invention according to claim 1 of the present invention is a weight comprising a weight and a flexible plate to which the weight is attached and having a displacement portion that is displaced by movement of the weight due to acceleration acting on the weight. Flexible member,
  A first fixed portion having a first stationary surface facing one of the first displacement surfaces of the weight flexible member;
  And a second fixed portion having a second stationary surface facing the other second displacement surface of the weight flexible member,
  Are fixed to the sensor housing, and
  A first electrode group consisting of a first displacement electrode provided on the first displacement surface and a first fixed electrode provided on the first stationary surface;
  And a sensor main body provided with a second electrode group including a second displacement electrode provided on the second displacement surface and a second fixed electrode provided on the second stationary surface. ,
  At least one of the first displacement electrode and the first fixed electrode, at least one of the second displacement electrode, and the second fixed electrode is composed of four or more and the same number of electrically separated separation electrode pieces. ,
  In addition, the first displacement electrode of the first electrode group includes the second displacement electrode of the second electrode group, and the first fixed electrode of the first electrode group includes the second displacement electrode of the second electrode group. The same shape as the fixed electrode,
  A change in capacitance that occurs between the first displacement electrode and the first fixed electrode of the first electrode group due to the movement of the weight, the second displacement electrode of the second electrode group, and a second An electrostatic capacitance type three-axis acceleration sensor comprising an arithmetic unit that measures acceleration by outputting a difference from a change in capacitance generated between the fixed electrode and the fixed electrode.
[0018]
The invention according to claim 2 is characterized in that the first displacement surface is a surface of a flexible plate on the side where the weight is not attached, and the second displacement surface is a surface of the weight. The capacitance type triaxial acceleration sensor according to claim 1.
[0019]
According to a third aspect of the present invention, the first displacement surface is a surface of a flexible plate to which the weight is not attached, and the second displacement surface is a flexible plate to which the weight is attached. 2. The capacitance type three-axis acceleration sensor according to claim 1, wherein
[0020]
According to a fourth aspect of the present invention, the separation electrode piece includes a center electrode piece around a center line orthogonal to the surface of the flexible plate and passing through the center thereof, and an origin where the center line intersects the flexible surface. The total of positive and negative peripheral X-axis electrode pieces and positive and negative peripheral Y-axis electrode pieces arranged on the X-axis and Y-axis sides parallel to the flexible plate surface at the positive and negative positions outside the central electrode piece The electrostatic capacitance type three-axis acceleration sensor according to claim 1, comprising five.
[0021]
According to a fifth aspect of the present invention, in the capacitance type triaxial acceleration sensor according to the fourth aspect, the center separation electrode piece has a ring shape.
[0022]
The capacitance type 3 according to any one of claims 1 to 5, wherein the displacement surface or the stationary surface on which the separation electrode piece is not formed is made of a metal material. It is an axial acceleration sensor.
[0023]
According to the seventh aspect of the present invention, the capacitance value of the central electrode piece of the first electrode group is C11, the capacitance value of the positive and negative peripheral X-axis electrode pieces is C12, C14, and the positive and negative peripheral values. The capacitance value of the Y-axis electrode piece is C13, C15, the capacitance value by the center electrode piece of the second electrode group is C21, the capacitance value of the positive and negative peripheral X-axis electrode pieces is C22, C24, When the capacitance values of the positive and negative peripheral Y-axis electrode pieces are C23 and C25, the capacitance values corresponding to the acceleration in the XYZ-axis directions are calculated by the following formulas, 5. The capacitance type triaxial acceleration sensor according to claim 4, wherein the acceleration acting on the weight is detected.
CX = (C12-C14)-(C22-C24)
CY = (C13-C15)-(C23-C25)
CZ = (C11)-(C21)
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the capacitance-type triaxial acceleration sensor of the present invention includes a weight flexible member 2 and a first stationary face that faces one first displacement surface 2 a of the weight flexible member 2. A sensor housing includes a first fixing portion 3 having a surface 3a and a second fixing portion 4 having a second stationary surface 4b facing the other second displacement surface 2b of the weight flexible member 2. 7 is fixed.
[0025]
The weight flexible member 2 includes a weight 5 and a flexible plate 6 to which the weight 5 is attached and which has a displacement portion that is displaced by the movement of the weight 5 due to the acceleration acting on the weight 5. In this example, the weight 5 is attached to the lower surface of the flexible plate 6.
[0026]
In the present embodiment, the first displacement surface 2a is the surface of the flexible plate 6 on the side where the weight 5 is not attached, and the second displacement surface 2b is the surface of the weight 5, this example. FIG. 6 illustrates the lower surface of the weight 5. In the present example, the first and

second fixing parts

3 and 4, the weight 5 and the flexible plate 6 are all made of an insulating material such as glass, resin or ceramic.
[0027]
A first displacement electrode ef1 is provided on the first displacement surface 2a of the weight flexible member 2, and the first stationary surface 3a facing the first displacement surface 2a has the first displacement surface 2a. A first fixed electrode e1 is formed at a distance from the displacement electrode ef1. Accordingly, the first displacement electrode ef1 and the first fixed electrode e1 can constitute the first electrode group EU.
[0028]
Similarly, a second displacement electrode ef2 is provided on the second displacement surface 2b, and a distance from the second displacement electrode ef2 is provided on the second stationary surface 4b facing the second displacement surface 2b. A second fixed electrode e2 is formed with a gap therebetween. Accordingly, the second displacement electrode ef2 and the second fixed electrode e2 can constitute the second electrode group ED.
[0029]
As described above, the sensor main body 1 includes the first electrode group EU and the second electrode group ED. In the present invention, at least one of the first displacement electrode ef1 and the first fixed electrode e1, the second displacement electrode ef2 and at least one of the second fixed electrodes e2 may be four or more and the same number. One of the features is that it is composed of an electrically independent separation electrode piece.
[0030]
In this embodiment, the first fixed electrode e1 and the second fixed electrode e2 are composed of five separate and electrically independent separation electrode pieces as shown in FIGS. 2 (a) and 2 (b). This is an example. These separation electrode pieces have center electrode pieces eZ1 and eZ2 around a center line orthogonal to the surface of the flexible plate 6 and passing through the center thereof as shown in the figure, and an origin at which the center line intersects the surface of the flexible plate 6. Positive and negative peripheral X-axis electrode pieces eX1, eX2, and eX3, which are arranged outside the central electrode pieces eZ1 and eZ2 on the X-axis and Y-axis side parallel to the surface of the flexible plate 6 and at positive and negative positions, Examples include eX4 and five positive and negative peripheral Y-axis electrode pieces eY1, eY2, and eY3, eY4, respectively, which are arranged to be electrically insulated from each other.
[0031]
As a result, the first electrode group EU and the second electrode group ED can form a total of 10 capacitive elements, each consisting of 5 pairs of pairs of separation electrode pieces and displacement electrodes. In this example, the first and second displacement electrodes ef1 and ef2 are formed in an integrated disk shape as shown in FIG. 2 (c). Various materials can be used for each of these electrodes as long as they have conductive properties. However, these electrodes are preferably made of the same material, and in this example, are made of the same metal material.
[0032]
In the present invention, in the first electrode group EU and the second electrode group ED, the separation electrode pieces facing each other with the flexible plate 6 interposed therebetween are configured in the same shape. The separation electrode pieces eX1, eX2 arranged in the X-axis direction of the first electrode group EU and the separation electrode pieces eX3, eX4 arranged in the X-axis direction of the second electrode group ED are both equal in surface area S2. Become. That isThe first displacement electrode ef1 of the first electrode group EU is the second displacement electrode ef2 of the second electrode group ED, and the first fixed electrode e1 of the first electrode group EU is the second electrode Each of the second fixed electrodes e2 of the group ED has the same shape.
[0033]
In the present embodiment, the interelectrode distance D1 of the first electrode group EU is set equal to the interelectrode distance D2 of the second electrode group ED in a no-load state in which only gravitational acceleration acts on the sensor. Is illustrated.
[0034]
Such a capacitance type triaxial acceleration sensor has a static force generated between the first displacement electrode ef1 and the first fixed electrode e1 of the first electrode group EU due to the movement of the weight 5 due to the acceleration. The acceleration is measured by outputting the difference between the change in capacitance and the change in capacitance generated between the second displacement electrode ef2 of the second electrode group ED and the second fixed electrode e2. An arithmetic unit (shown in FIGS. 5 to 7) is provided.
[0035]
As described above, in this example, two electrode groups in which the distance between the electrodes is increased and the other is decreased due to the displacement due to the acceleration in the Z-axis direction, that is, the first electrode group EU and the second electrode group ED are formed. By taking the difference in capacitance between these electrode groups, the influence of acceleration in the Z-axis direction can be largely removed from the capacitance based on the acceleration in the horizontal direction. That is, by subtracting the capacitance value of the second electrode group ED from the capacitance value of the first electrode group EU, the acceleration in the Z-axis direction acts simultaneously on the acceleration in the X-axis direction and the Y-axis direction. Even in this case, the influence of the acceleration in the Z-axis direction on the capacitance values in the X-axis direction and the Y-axis direction can be reduced, and the detection accuracy can be greatly increased.
[0036]
For example, as shown in FIGS. 2A and 2B, the capacitance value of the central electrode piece eZ1 and the displacement electrode ef1 of the first electrode group EU is C11, and the positive and negative peripheral X-axis electrode pieces eX1, The capacitance value of eX2 is C12, C14, the positive and negative peripheral Y-axis electrode pieces eY1, eY2 are C13, C15, and the capacitance value C21 of the second electrode group ED is the central electrode piece eZ2. When the electrostatic capacitance values of the positive and negative peripheral X-axis electrode pieces eX3 and eX4 are C22 and C24, and the electrostatic capacitance values of the positive and negative peripheral Y-axis electrode pieces eY3 and eY4 are C23 and C25, the XYZ axes The capacitance values CX, CY, and CZ corresponding to the direction acceleration can be calculated by the following equations (4) to (6).
CX = (C12−C14) − (C22−C24) (4)
CY = (C13-C15)-(C23-C25) (5)
CZ = (C11) − (C21) (6)
[0037]
Here, the detection accuracy of the capacitance type triaxial acceleration sensor of the present invention will be described using the above arithmetic expression. First, when the weight 5 is accelerated and only the force FX (direction shown in FIG. 1) in the X direction is applied to the action point P of the weight 5, the separation electrode pieces eX1 arranged positively and negatively on the X axis. , EX2, eX3, eX4, the separation electrode pieces eX1, eX4 reduce the distance between the displacement electrodes ef1, ef2 and increase the capacitance values C12, C24, while the separation electrode pieces eX2, eX3 are the displacement electrodes ef1, The distance between the electrodes with ef2 is increased, and the capacitance values C14 and C22 are decreased.
[0038]
In calculating these capacitances, in order to compare with the conventional capacitance type triaxial acceleration sensor, the shape, size, material, and weight of the flexible plate, electrode, and weight are unified to provide the basics of both. The capacitance value CX corresponding to the acceleration in the X-axis direction of the sensor of the present invention is assumed when the technical specifications are aligned and the change amount of the inter-electrode distance generated at the electrode (for example, the centroid position of the electrode plane) is ± DX. Is expressed as in Equation 4. The surface area of the separation electrode pieces eX1, eX2, eX3, eX4 is S2, the dielectric constant is ε, the displacement amount of the interelectrode distance caused by the force FX is ± DX, and the ratio between the initial interelectrode distance D0 and the displacement DX ( DX / D0) is dx.
[Expression 4]

[0039]
In this way, when only the acceleration in the X-axis direction (or Y-axis direction) is applied to the weight 5, it is compared with the capacitance value CX of the conventional capacitance type three-axis acceleration sensor expressed by Equation 2. Then, it can be seen that the capacitance value (output) of the present invention is doubled and the detection sensitivity in the X-axis direction (or Y-axis direction) is improved.
[0040]
When only the acceleration in the Z-axis direction is applied to the weight 5, the surface area of the central electrode pieces eZ1 and eZ2 is S1, the distance between the central electrode piece eZ1 and the displacement electrode ef1, and the central electrode piece eZ2 and the displacement electrode ef2 When the amount of change in the interelectrode distance that occurs during each period is ± DZ and the ratio (DZ / D0) to the initial interelectrode distance D0 is represented by dz, the capacitance value CZ of the sensor of the present invention is become that way.
[Equation 5]

[0041]
On the other hand, in the conventional sensor, Equation 6 is obtained.
[Formula 6]

[0042]
Here, it is preferable that dz is normally used at a maximum of about 0.1. In this case, the capacitance type triaxial acceleration sensor of the present embodiment is substantially also in the capacitance value in the Z-axis direction. Double output can be obtained. In this way, when forces in the X-axis direction (or Y-axis direction) or Z-axis direction are applied independently, the capacitive three-axis acceleration sensor of the present invention has an output compared to conventional sensors. It can be seen that both of them are doubled and the variation in the Z-axis direction capacitance value is also reduced.
[0043]
In order to detect the change in the electrostatic capacitance value in the Z-axis direction, as shown in FIG. 3, the central electrode piece is not provided independently, and the four separated electrode pieces eX1, eX2, eY1, and eY2 are static. It is also possible to calculate from the change of the total capacitance value. However, in the case of five divisions having the central separation electrode piece eZ1 as in the present embodiment, the detection electric circuit is simplified, which is advantageous for downsizing, and the closer to the origin of the electrode, the other axis Since it is hardly affected, there is an advantage that the detection accuracy of acceleration in the Z-axis direction can be further improved.
[0044]
Next, consider a case where the acceleration in the X-axis direction and the acceleration in the Z-axis direction are simultaneously loaded on the weight 5. In this case, as shown in FIG. 4, the displacement electrodes ef1 and ef2 generate an upward displacement amount DZ by the force FZ in the Z-axis direction, and at the same time, a displacement amount ± DX is generated by the force FX in the X-axis direction. Can be considered. The capacitance value CXB in the X-axis direction in this case is as shown in Equation 7.
[Expression 7]

[0045]
Here, the capacitance value CXA of the conventional sensor shown in Equation 3 is expressed as Equation 8 when the denominator is shared in order to compare with the capacitance value CXB of the sensor of the present invention. Can do.
[Equation 8]

[0046]
Because of the structure of the capacitance type triaxial acceleration sensor, it is usually preferable to use the maximum value of dx and dz at about 0.1 in the operating range. Therefore, assuming that the maximum value of dx and dz is 0.1. , Denominator {(1-dz)²-Dx²} {(1 + dz)²-Dx²} Can take the range of 0.96 to 1.00. In addition, among each molecule (dz²-Dx²) Can take a range of -0.01 to 0.01.
[0047]
Further, when comparing the capacitance values CXB and CXA of the capacitance type triaxial acceleration sensor of the present invention and the conventional sensor, the conventional one (Equation 8) has a factor of “2 dz” to “1” in the numerator. It is an added form. Since this “2dz” takes a value of 0.2 at maximum, it gives a variation of ± 20% at maximum.
[0048]
In contrast, the capacitance type triaxial acceleration sensor of the present invention has a capacitance value CXB that is twice that of the conventional one, which can improve detection sensitivity and In comparison, even when the acceleration in the Z-axis direction is simultaneously added to the acceleration in the horizontal direction such as the X- or Y-axis direction, the influence (2dz) of the conventional acceleration in the Z-axis direction is eliminated, and the X-axis direction (or the Y-axis) (Direction) capacitance value can be acquired, and detection accuracy can be greatly improved.
[0049]
Next, an example of the circuit configuration of the arithmetic unit is shown in FIGS. 5 shows acceleration output in the X-axis direction, FIG. 6 shows acceleration output in the Y-axis direction, and FIG. 7 shows acceleration output in the Z-axis direction. For example, in FIG. 5, the capacitance C12 between the electrodes eX1 and ef1, the capacitance C14 between the electrodes eX2 and ef1, the capacitance C22 between the electrodes eX3 and ef2, and the capacitance C24 between the electrodes eX4 and ef2 are: These are converted into voltage values V1 to V4 by CV converters H1 to H4, respectively, and output.
[0050]
The differential amplifier A1 is a voltage V5 which is a difference between the voltage values V1 and V2 converted by the CV converters H1 and H2, and the differential amplifier A2 is a voltage value converted by the CV converters H3 and H4. A difference voltage V6 between V3 and V4 is output to the differential amplifier A3. The differential amplifier A3 can take the difference between the voltages V5 and V6 and output it as a voltage value V7 corresponding to the acceleration in the X-axis direction.
[0051]
Note that the Y-axis direction is the same as in the X-axis direction, the capacitance C13 between the electrodes eY1 and ef1, the capacitance C15 between the electrodes eY2 and ef1, the capacitance C23 between the electrodes eY3 and ef2, and the electrodes eY4 and ef2. The capacitance C25 between them is converted into voltage values V10 to V13 by CV converters H5 to H8, respectively. The differential amplifier A4 is the difference between the voltage values V10 and V11 converted by the CV converters H5 and H6. The differential amplifier A5 outputs the voltage V14 to the differential amplifier A6, and the differential amplifier A5 outputs the difference voltage V15 between the voltage values V12 and V13 converted by the CV converters H7 and H8, respectively. The differential amplifier A6 takes the difference between the voltages V14 and V15 and outputs the difference as a voltage value V16 corresponding to the acceleration in the Y-axis direction.
[0052]
Regarding the Z-axis direction, the capacitance C11 between the electrodes eZ1 and ef1 and the capacitance C21 between the electrodes eZ2 and ef2 are converted into corresponding voltages V17 and V18 by CV converters H9 and H10, respectively, and differential The difference between the voltages V17 and V18 is obtained by the amplifier A7, and this can be output as a voltage value V19 corresponding to the acceleration in the Z-axis direction.
[0053]
Then, by applying predetermined wiring to each electrode of the sensor body and connecting it to a circuit that performs the above-described calculation operation, the voltage value corresponding to the acceleration acting on the weight 5 can be obtained for each three-dimensional axis. Each direction component can be extracted with high accuracy. Note that this arithmetic circuit is an example. For example, it is of course possible to modify the equations (4) to (6) and construct an arithmetic circuit corresponding thereto.
[0054]
In the no-load state, the interelectrode distance D1 between the first fixed electrode e1 and the first displacement electrode ef1 of the first electrode group EU, the second fixed electrode e2 of the second electrode group ED, and the second It is desirable that the distance D2 between the two displacement electrodes ef2 is substantially equal.
[0055]
A curve G1a shown in FIG. 8A shows the relative output of the first electrode group EU when the distance between the electrodes is D1 = D2 = D0. The curve G1b is the relative output of the second electrode group ED, and the curve G1 is the sum of these relative outputs, indicating the relative output as a sensor. As is apparent from the figure, the curve G1 is the most suitable because the output is very stable in the vicinity of dz = 0, which is the practical range of the acceleration sensor.
[0056]
A curve G2a indicates the relative output of the first electrode group EU when the interelectrode distance D1 = D2 = 2D0. The curve G2b is the relative output of the second electrode group ED, and the curve G2 is the sum of these relative outputs, indicating the relative output as a sensor. In this curve G2, although the output is stable over a wide range, the output itself is small.
[0057]
A curve G3a shown in FIG. 8B shows the relative output of the first electrode group EU when D1 ≠ D2 where the interelectrode distance D1 = D0 and D2 = 2D0, and the curve G3b The curve G3 is the sum of these relative outputs and shows the relative output as a sensor. As is apparent from the figure, the curve G3 is not preferable because the compensation is small and the output curve is close to the conventional one.
[0058]
A curve G4a shown in FIG. 8B shows the relative output of the first electrode group EU when D1 ≠ D2 where the interelectrode distance D1 = D0 and D2 = D0 / 2, and the curve G4b is This is the relative output of the second electrode group ED, and the curve G4 is the sum of these relative outputs and shows the relative output as a sensor. As is clear from the figure, the curve G4 has a small D2, so the compensation is too large, and conversely the accuracy is degraded.
[0059]
Accordingly, it is preferable to set the initial inter-electrode distances D1 and D2 to be equal to each other and to adopt a value at which the output characteristic (curve) is stabilized according to each sensor.
[0060]
Next, another embodiment of the present invention will be described. In the present embodiment, as shown in FIG. 9, the first displacement surface 2a is the surface of the flexible plate 6 on the side where the weight 5 is not attached, and the second displacement surface 2b is the weight. It is a surface of the flexible plate 6 on the side to which the weight 5 is attached. In this example, the second electrode group ED is exemplified by the weight 5 penetrating through the center portion. For this reason, the second fixing portion 4 has a through hole 4c through which the weight 5 passes. The center electrode pieces eZ1 and eZ2 adopt a ring shape surrounding the weight 5 as shown in FIG.
[0061]
In this embodiment, a change in the distance between the electrodes of the first and second electrode groups EU and ED, which occurs when the weight 5 rotates around the origin O of the flexible plate 6 by applying a force in the X-axis direction. This is preferable in that the minute difference can be reduced and the assembly dimensional accuracy and assembly processability can be improved.
[0062]
In this example, all the electrodes are configured by the same-shaped separation electrode pieces as shown in FIG. 10, but the fixed electrode e1 (e2) is used for each of the first electrode group EU and the second electrode group ED. ) Or the displacement electrode ef1 (ef2) may be provided with a separation electrode piece as described above. Other configurations are substantially the same as the apparatus having the structure shown in FIG. 1, including the detection circuit.
[0063]
11 and 12 show another embodiment of the present invention. In this example, the 1st, 2nd fixing |

fixed part

3, 4, the weight 5, the flexible plate 6, and the sensor housing | casing 7 are comprised with the metal material. In the present example, the flexible plate 6 is illustrated as being elastically supported by a plurality of arm members extending radially from the sensor housing 7.
[0064]
Further, as shown in the cross section AA of FIG. 11 in FIG. 12, the arm member 12 is, for example, sufficiently elastically deformable than the flexible plate 6 so that the flexible plate 6 is not deformed. Only the member 12 is elastically deformed so that the flexible plate 6 can be displaced. In this case, the displacement of the distance between the electrodes due to the displacement of the flexible plate 6 easily changes linearly, which is further useful for improving the detection accuracy. Further, by providing the arm members 12 arranged in a radial manner in this manner, the displacement of the flexible plate 6 can be made less directional, and the detection accuracy is further improved. Further, in this example, the displacement electrodes ef1 and ef2 can both use the flexible plate 6 and the weight 5 themselves as electrodes, and the simplification of the structure is also useful.
[0065]
The flexible plate 6 and the weight 5 are preferably joined by a conductive fixing method such as welding. In addition, the first and

second fixing portions

3 and 4 are provided with a separation electrode piece eX1 and the like via insulating

materials

10 and 11, respectively.
[0066]
As described above in detail, the separation electrode piece may be provided on the weight flexible member 2. Further, the flexible plate 6 may be a diaphragm having a slit or the like cut in a ring shape or a radial shape in order to give a preferable flexibility.
[0067]
Further, when the sensor receives a large impact, it is desirable to improve the strength of the sensor body, and it is preferable to use metal for each member. On the other hand, resin, ceramics, etc. can be used as an insulator and for reasons such as processability and unit price. Some of these have greatly different coefficients of thermal expansion, and when the sensor is used in a wide range of operating temperatures, such as an automobile, the influence of the difference in thermal expansion on the inter-electrode distance d cannot be ignored. . Therefore, it is desirable that the member has a small coefficient of thermal expansion, and it is preferable to reduce an error due to temperature by using a material having a similar coefficient of thermal expansion as in this example.
[0068]
Considering the detection accuracy of the sensor, it is desirable to suppress each of the above-mentioned displacement rates dx, dy, dz to about 0.1 or less, and as such, the elastic modulus, thickness, support method, weight of various constituent materials It is also preferable to design the shape, mass and the like. Furthermore, the first or second displacement surface or the first or second stationary surface on which the separation electrode surface is not formed can be made of a metal material. Furthermore, the size of the electrodes in each electrode group should be sufficiently large to overlap in the vertical direction even when the weight is displaced.
[0069]
【Example】
As a capacitance type triaxial acceleration sensor of the present invention, a sensor (Example) having the structure shown in FIG. 11 capable of measuring a maximum of 1 G was prototyped, and the sensor having the conventional structure (Conventional Example) shown in FIG. Compared.
[0070]
FIG. 13 shows the relative output CX in the X-axis direction when a constant acceleration AX in the X-axis direction is given to each sensor of the example and the conventional example, and simultaneously the acceleration AZ in the Z-axis direction within ± 1 G is loaded. The result of actual measurement is shown. In the measurement, the measurement conditions were the same for both sensors.
[0071]
As can be seen from FIG. 13, in the sensor of the conventional example, the variation in the output of the acceleration in the X-axis direction is increased in proportion to the acceleration in the Z-axis direction (however, the acceleration AX in the X-axis direction is increased). In a large range, particularly in the range of 0.8 to 1.0 G, the Z-axis direction acceleration AZ can only be loaded with a small value (0.5 to 0 G), so that the variation is relatively small. In addition, the output of the sensor of the example is about twice that of the conventional example, the detection sensitivity is improved, and even when the acceleration in the Z-axis direction is loaded, the output varies. Is very small, and a significant improvement in detection accuracy can be confirmed. The result is almost the same as that verified using a calculation formula.
[0072]
【The invention's effect】
As described above, according to the capacitance type triaxial acceleration sensor of the present invention, the acceleration detection sensitivity in each direction of the three axes can be improved. In addition, even when the acceleration in the vertical direction (Z-axis direction) is added to the acceleration in the horizontal direction such as the X-axis direction and the Y-axis direction, the horizontal acceleration is substantially affected by the applied vertical acceleration. Can be detected with high accuracy. For this reason, it is not necessary to incorporate a complicated electrical correction circuit in the sensor, and it is possible to provide an inexpensive capacitive three-axis acceleration sensor that can be downsized and simplified in structure.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a sensor body showing an embodiment of the present invention.
2A is a plan view showing a first fixed electrode, FIG. 2B is a second fixed electrode, and FIG. 2C is a first and second displacement electrode;
FIG. 3 is a plan view showing another example of the separation electrode piece.
FIG. 4 is a diagram illustrating displacement of a displacement electrode.
FIG. 5 is a circuit diagram of a calculation unit in the X-axis direction.
FIG. 6 is a circuit diagram of a calculation unit in the Y-axis direction.
FIG. 7 is a circuit diagram of a calculation unit in the Z-axis direction.
FIGS. 8A and 8B are graphs for explaining sensor output when various distances between electrodes are changed.
FIG. 9 is a sectional view of a sensor showing another embodiment of the present invention.
FIG. 10 is a plan view showing the separation electrode piece.
FIG. 11 is a cross-sectional view of a sensor showing another embodiment of the present invention.
FIG. 12 is a cross-sectional view taken along the line AA.
FIG. 13 is a graph showing the performance of the present invention.
14A and 14B are cross-sectional views of a conventional capacitive triaxial acceleration sensor, where FIG. 14A shows a no-load state and FIG. 14B shows a state where a force FX is applied.
15A is a plan view showing a fixed electrode, and FIG. 15B is a plan view showing a displacement electrode.
FIG. 16 is a graph showing capacitance and distance between electrodes.
[Explanation of symbols]
1 Sensor body
Double weight flexible member
2a First displacement surface
2b Second displacement surface
3a First stationary surface
3 First fixing part
4 Second fixing part
4b Second stationary surface
5 weights
6 Flexible plate
7 Sensor housing
ef1 first displacement electrode
e1 first fixed electrode
EU first electrode group
ef2 second displacement electrode
e2 Second fixed electrode
ED Second electrode group
eX1 to eX4, eY1 to eY4, eZ1, eZ2 Separation electrode piece
10X, 10Y, 10Z operation unit

Claims

A weight flexible member comprising a weight and a flexible plate to which the weight is attached and a displacement portion that is displaced by the movement of the weight due to acceleration acting on the weight;
A first fixed portion having a first stationary surface facing one of the first displacement surfaces of the weight flexible member;
And a second fixed portion having a second stationary surface facing the other second displacement surface of the weight flexible member,
A first electrode group consisting of a first displacement electrode provided on the first displacement surface and a first fixed electrode provided on the first stationary surface,
And a sensor main body provided with a second electrode group including a second displacement electrode provided on the second displacement surface and a second fixed electrode provided on the second stationary surface. ,
At least one of the first displacement electrode and the first fixed electrode, at least one of the second displacement electrode, and the second fixed electrode is composed of four or more and the same number of electrically separated separation electrode pieces. ,
In addition, the first displacement electrode of the first electrode group includes the second displacement electrode of the second electrode group, and the first fixed electrode of the first electrode group includes the second displacement electrode of the second electrode group. The same shape as the fixed electrode ,
A change in capacitance that occurs between the first displacement electrode and the first fixed electrode of the first electrode group due to the movement of the weight, the second displacement electrode of the second electrode group, and a second A capacitive three-axis acceleration sensor comprising an arithmetic unit for measuring acceleration by outputting a difference from a change in capacitance generated between the fixed electrode and the fixed electrode.

2. The electrostatic device according to claim 1, wherein the first displacement surface is a surface of a flexible plate on which the weight is not attached, and the second displacement surface is a surface of the weight. Capacitance type 3-axis acceleration sensor.

The first displacement surface is a surface of a flexible plate on a side to which the weight is not attached, and the second displacement surface is a surface of a flexible plate on a side to which the weight is attached. The capacitive three-axis acceleration sensor according to claim 1.

The separation electrode piece includes a central electrode piece around a center line orthogonal to the surface of the flexible plate and passing through the center thereof, and an X axis passing through the origin where the center line intersects the flexible surface and parallel to the flexible plate surface. And a total of five positive and negative peripheral X-axis electrode pieces and positive and negative peripheral Y-axis electrode pieces arranged on the Y-axis side outside the central electrode piece and at positive and negative positions. The capacitive three-axis acceleration sensor according to any one of claims 1 to 3.

5. The capacitance type triaxial acceleration sensor according to claim 4, wherein the central electrode piece has a ring shape.

6. The capacitance type triaxial acceleration sensor according to claim 1, wherein the displacement surface or the stationary surface where the separation electrode piece is not formed is made of a metal material.

The capacitance value of the central electrode piece of the first electrode group is C11, and the capacitance values of the positive and negative peripheral X-axis electrode pieces are C12 and C14. The capacitances of the positive and negative peripheral Y-axis electrode pieces. The values are C13 and C15, the capacitance value by the central electrode piece of the second electrode group is C21, the capacitance values of the positive and negative peripheral X-axis electrode pieces are C22 and C24, and the positive and negative peripheral Y-axis electrodes When the capacitance values of the pieces are C23 and C25, the capacitance values corresponding to the accelerations in the XYZ axis directions are calculated by the following equations to detect the acceleration acting on the weight. 5. The capacitive three-axis acceleration sensor according to claim 4, wherein
CX = (C12-C14)-(C22-C24)
CY = (C13-C15)-(C23-C25)
CZ = (C11)-(C21)