JP3978049B2

JP3978049B2 - Inductive position transducer

Info

Publication number: JP3978049B2
Application number: JP2002052704A
Authority: JP
Inventors: 勝三郎辻
Original assignee: Mitutoyo Corp
Current assignee: Mitutoyo Corp
Priority date: 2002-02-28
Filing date: 2002-02-28
Publication date: 2007-09-19
Anticipated expiration: 2022-02-28
Also published as: JP2003254783A

Description

【０００１】
【発明の属する技術分野】
本発明は誘導型位置トランスデューサ、特に読み取りヘッドとスケールとを備え、スケールに対する読み取りヘッドの絶対位置（ＡＢＳ）を検出する位置トランスデューサに関する。
【０００２】
【従来の技術】
従来より、誘導電流を用いた位置トランスデューサ（あるいは磁気エンコーダ）が知られている。位置トランスデューサは対向配置した読み取りヘッドとスケールとを備える。読み取りヘッド側に送信コイル及び受信コイルを備え、スケール側にも受信コイル及び送信コイルを備える。読み取りヘッド側の送信コイルから磁界を発生させ、この磁界によりスケール側の受信コイルに誘導電流を生じさせる。スケール側の送信コイルと受信コイルは接続され、生じた誘導電流により送信コイルから磁界が生じる。読み取りヘッド側の受信コイルは、スケール側の送信コイルから発生した磁界を検出し、検出信号として出力する。検出信号の位相は、読み取りヘッドとスケールとの位置関係に応じて変動するから、検出信号の位相に基づき読み取りヘッドのスケール上の基準ポイントからの位置、すなわち絶対位置を検出することができる。
【０００３】
通常、スケール側には、互いに異なるピッチ（波長）λ１及びλ２を有する送信コイルをスケールの幅方向に並設し、λ１とλ２の位相差に基づき絶対位置を検出する。すなわち、λ１のコイルのみではλ１毎に検出信号の位相が同一となるため、λ１を超える絶対位置を一義的に決定することができない。そこで、λ１とλ２の位相差に基づき、λ１が何周期目かを検出することで絶対位置を検出する。λ１をλｆｉｎｅとし、λ１とλ２の位相差の１周期をλｍｅｄと定義し、λｍｅｄ内にλｆｉｎｅが含まれる数をｎとすると以下の式が成り立つ。
【０００４】
【数１】
λｍｅｄ＝ｎ・λｆｉｎｅ・・・（１）
ｎはλ１とλ２の波長差により決定される値であり、波長差が小さいほどｎは大きくなり絶対位置を検出できる長さ（測定範囲）は増大する。λ１とλ２の位相差の値が、３６０度をｎ等分した範囲のうちどの範囲に入っているかを判定することでλ１の周期数がわかり、（λ１の周期）×（λ１の周期数）＋（λ１の位相）により絶対位置が算出される。
【０００５】
このように２波長型位置トランスデューサでは測定範囲が拡大されるが、同様に３波長型、つまりスケール側にλ１、λ２及びλ３の異なる３波長を有する送信コイルを配置した位置トランスデューサも提案されている。
【０００６】
図７には、このような３波長型位置トランスデューサの構成が示されている。図７（ａ）はスケール側の構成であり、図７（ｂ）は読み取りヘッド（グリッド）側の構成である。実際には、スケールと読み取りヘッドは互いに重なるように対向配置されるが、図では説明の都合上、両者をそれぞれ並べて示している。
【０００７】
スケール側には、波長λ１のコイルが形成されるとともに、波長λ２及びλ３のコイルも形成される。波長λ１のコイルは、中央の送信コイル１０と当該中央送信コイル１０を挟むようにその両側に配置された受信コイル１１から形成される。また、波長λ２及びλ３のコイルは、それぞれ送信コイルと受信コイルを兼用する。すなわち、波長λ２とλ３のコイルは接続され、波長λ２の送信コイル１２にとっての受信コイルは波長λ３の送信コイル１４であり、波長λ３の送信コイル１４に生じた誘導電流で波長λ２の送信コイル１２は磁界を発生させる。波長λ３の送信コイル１４にとっての受信コイルは波長λ２の送信コイル１２であり、波長λ２の送信コイル１２に生じた誘導電流で波長λ３の送信コイル１４は磁界を発生させる。
【０００８】
一方、グリッド側には、波長λ１の受信コイル１１に向けて磁界を発生する送信コイル２０及び波長λ１の送信コイル１０から発生する磁界を検出する受信コイル３０が設けられる。また、λ２の受信コイルに向けて磁界を発生する送信コイル２２及びλ２の送信コイル１２からの磁界を検出する受信コイル３２が設けられる。さらに、λ３の受信コイルに対し磁界を発生する送信コイル２４及び波長λ３の送信コイル１４からの磁界を検出する受信コイル３４が設けられる。グリッドの送信コイル２０はスケールの受信コイル１１に対向し、受信コイル３０は送信コイル１０に対向して磁気結合する。同様に、送信コイル２４は送信コイル１２（波長λ３の送信コイル１４にとっての受信コイル）に対向し、受信コイル３２は送信コイル１２に対向して磁気結合する。送信コイル２２は送信コイル１４（波長λ２の送信コイル１２にとっての受信コイル）に対向し、受信コイル３４は送信コイル１４に対向して磁気結合する。
【０００９】
グリッド側の送信コイル２０、２２、２４には順次駆動電流が時分割で供給され、受信コイル３０、３２、３４はそれぞれの駆動電流によりスケールの送信コイル１０、１２、１４で順次発生した磁界を検出して信号を出力する。λ１でλｆｉｎｅ、λ１とλ２の位相差でλｍｅｄ、λ２とλ３の位相差でλｃｏａを形成する。λｃｏａ内に含まれるλｍｅｄの数をｍとすると、
【数２】
λｃｏａ＝ｍ・λｍｅｄ＝ｍ・ｎ・λｆｉｎｅ＝ｍ・ｎ・λ１・・・（２）
となる。測定範囲はｍ・ｎで決定されるので、２波長λ１、λ２を用いた位置トランスデューサに比べて測定範囲が増大する。
【００１０】
図８には、上述したλｆｉｎｅ、λｍｅｄ、λｃｏａの位置精度が示されている。図において、横軸はスケールの基準ポイントからの位置であり、縦軸は位相である。λｆｉｎｅ、λｍｅｄ、λｃｏａの順で精度が低く（粗く）なり、これらを組み合わせることでλｃｏａの範囲内で絶対位置を一義的に決定できる。
【００１１】
なお、λｆｉｎｅ、λｍｅｄ、λｃｏａは、具体的には以下のように定義される。
【００１２】
【数３】
λｆｉｎｅ＝λ１
λｍｅｄ＝λ２λ１／（λ２−λ１）＝ｎλｆｉｎｅ
λｃｏａ＝λ３λ２／（λ３−λ２）＝ｍλｍｅｄ・・・（３）
ここで、ｍ及びｎは正の整数である。
【００１３】
【発明が解決しようとする課題】
このように、３波長λ１、λ２、λ３を用いることで測定範囲を増大させることが可能であるが、図７に示されるように、λ２とλ３について送信コイルと受信コイルを共通化したとしてもスケールの幅方向に合計５列のコイル群が形成されることとなり、スケールサイズ、ひいては位置トランスデューサのサイズが増大してしまう問題があった。近年、特にＮＣ等においては装置の小型化が図られており、これらの装置に取り付けて位置データを出力する位置トランスデューサにおいても一層の小型及び高精度化が要求されている。
【００１４】
本発明は、上記従来技術の有する課題に鑑みなされたものであり、その目的は、小型かつ高精度の３波長型位置トランスデューサを提供することにある。
【００１５】
【課題を解決するための手段】
上記目的を達成するために、本発明は、磁界発生手段及び磁界検出手段を有する読み取りヘッドと、前記読み取りヘッドに対向配置され、前記磁界発生手段からの磁界により誘導電流を発生する受信コイルと前記誘導電流により磁界を発生させる送信コイルからなる磁気結合コイルが測定方向に沿って所定ピッチλで形成されたスケールとを備え、前記スケールの前記送信コイルからの磁界を前記磁界検出手段で検出して得られる検出信号の位相に基づき前記読み取りヘッドの前記スケールに対する位置を検出する誘導型トランスデューサであって、前記磁気結合コイルは、第１のピッチλ１で前記測定方向に沿って形成された第１送信コイルと、前記第１のピッチλ１と異なる第２のピッチλ２で前記測定方向に沿って形成され、前記第１送信コイルの片側に形成された第２送信コイルと、前記第１のピッチλ１及び第２のピッチλ２と異なる第３のピッチλ３で前記測定方向に沿って形成され、前記第１送信コイルを挟んで前記第２送信コイルの反対側に形成された第３送信コイルと、を有し、前記第１送信コイルは、前記第２送信コイルに接続されるコイルと、前記第２送信コイルに接続されるコイルに隣接して設けられるコイルであって前記第３送信コイルに接続されるコイルと、から構成され、前記第２送信コイル及び前記第３送信コイルは前記第１送信コイルに接続された受信コイルとして機能し、前記第１送信コイルは前記第２送信コイルあるいは前記第３送信コイルに接続された受信コイルとして機能し、前記第１のピッチλ１、第２のピッチλ２、第３のピッチλ３は、λ２＜λ３＜λ１またはλ３＜λ２＜λ１なる大小関係を満たすことを特徴とする。
【００１６】
ここで、前記第１送信コイル、第２送信コイル及び第３送信コイルは、前記スケールの幅方向に並んで形成され、前記第１送信コイルは第２送信コイルと前記第３送信コイルの間に形成されることが好適である。
【００１８】
この場合、前記第１送信コイルからの磁界の検出信号の位相と、前記第１送信コイルからの磁界の検出信号の位相と前記第２送信コイルからの磁界の検出信号の位相との位相差と、前記第１送信コイルからの磁界の検出信号の位相と前記第３送信コイルからの磁界の検出信号の位相との位相差に基づいて前記位置を検出することが好適である。
【００１９】
このように、本発明の位置トランスデューサ（磁気エンコーダ）では、λ１、λ２、λ３の３ピッチ（３波長）のコイルを用いるが、スケール側のコイル配置として送信コイルと受信コイルを互いに兼用させることでスケール幅方向のコイル数を削減し、サイズを縮小化する。すなわち、第１送信コイル（λ１コイル）と第２送信コイル（λ２コイル）を接続してλ２コイルをλ１コイルの受信コイルとして機能させる。すなわち、読み取りヘッド側の送信コイルから生じた磁界はλ２コイルに誘導電流を生じさせ、その誘導電流がλ１コイルに供給されてλ１コイルから磁界を発生させる。同様に、λ１コイルをλ２コイルの受信コイルとして機能させる。第１送信コイルと第３送信コイルとの関係も同様である。このように、３つの送信コイルがそれぞれ接続された送信コイルの受信コイルとしても機能することで、コイル数を削減して小型化することができる。なお、第１送信コイル（λ１コイル）、第２送信コイル（λ２コイル）、第３送信コイル（λ３コイル）は時分割で駆動されるため、送受信を兼用しても問題は生じない。
【００２０】
また、それぞれピッチ（波長）の異なる第１送信コイルと第２送信コイルを接続し、第１送信コイルと第３送信コイルを接続する場合、第１送信コイルのピッチを最小とすると第１送信コイルで接続不能の「浮きコイル」あるいは「歯抜け」が生じ得、このような浮きの部分では位置を検出できないため精度が低下する。そこで、λ１の周期数を検出するにすぎない第２送信コイルあるいは第３送信コイルに浮きあるいは歯抜けを生じさせることで、浮きあるいは歯抜けが精度に与える影響を抑制することができる。λ１の浮きあるいは歯抜けの防止は、λ１のピッチが最大となる波長構成を採用することで得られる。
【００２１】
【発明の実施の形態】
以下、図面に基づき本発明の実施形態について説明する。
【００２２】
図１には、本実施形態に係る３波長型位置トランスデューサ（磁気エンコーダ）の構成が示されている。図１（ａ）はスケール側の構成であり、図１（ｂ）は読み取りヘッド（グリッド）側の構成である。なお、実際にはスケールとグリッドは所定距離だけ離間して対向配置されることは従来装置と同様である。まず、スケール側の構成について説明する。
【００２３】
スケール側には、波長（ピッチ）λ１の送信コイル１０、波長λ２の送信コイル１２、及び波長λ３の送信コイル１４がスケールの幅方向に並んで形成される。波長λ１の送信コイル１０は、波長λ２の送信コイル１２と波長λ３の送信コイル１４との間に配置される。波長λ１の送信コイル１０は波長λ２の送信コイル１２に接続されるコイルと、当該送信コイル１２に接続されるコイルに隣接して設けられるとともに波長λ３の送信コイル１４に接続されるコイルと、から構成される。波長λ２の送信コイル１２は波長λ１の送信コイル１０にとって受信コイルとして機能する。また、波長λ１の送信コイル１０は波長λ２の送信コイル１２にとっての受信コイルとして機能する。同様に、波長λ３の送信コイル１４は波長λ１の送信コイル１０にとっての受信コイルとして機能し、波長λ１の送信コイル１０は、波長λ３の送信コイル１４にとっての受信コイルとして機能する。
【００２４】
一方、グリッド側の構成は以下の通りである。すなわち、送信コイル２０、２２、２４が設けられ、送信コイル２０は波長λ２の送信コイル１２及び波長λ３の送信コイル１４に対向して配置され、送信コイル２２及び２４は波長λ１の送信コイル１０に対向して配置される。また、送信コイル１０に対向して受信コイル３０が配置され、送信コイル１２に対向して受信コイル３２が配置され、送信コイル１４に対向して受信コイル３４が配置されてそれぞれ磁気結合する。
【００２５】
送信コイル２０に駆動電流を供給することで、送信コイル２０から波長λ２の送信コイル１２（波長λ１の送信コイル１０にとっての受信コイル）及び波長λ３の送信コイル１４（波長λ１の送信コイルにとっての受信コイル）に向けて磁界が発生し、波長λ２の送信コイル１２で生じた誘導電流は送信コイル１０を構成するコイルのうち送信コイル１２に接続されたコイルに、波長λ３の送信コイル１４で発生した誘導電流は送信コイル１０を構成するコイルのうち送信コイル１４に接続されたコイルに、それぞれ供給される。波長λ１の送信コイル１０に供給された誘導電流により磁界が生じ、この磁界は波長λ１の送信コイル１０に対向して配置された受信コイル３０で受信され検出信号として出力される。
【００２６】
また、送信コイル２２に駆動電流を供給することにより、送信コイル２２から波長λ１の送信コイル１０に向けて磁界が発生し、波長λ１の送信コイル１０に誘導電流が生じる。この誘導電流は波長λ２の送信コイル１２に供給され、波長λ２の送信コイル１２から磁界が発生して受信コイル３２で受信され検出信号として出力される。
【００２７】
さらに、送信コイル２４に駆動電流を供給することにより、送信コイル２４から波長λ１の送信コイル１０に向けて磁界が発生し、送信コイル１０に誘導電流が生じる。この誘導電流は送信コイル１４に供給される。送信コイル１４は、この誘導電流により磁界を発生し、送信コイル１４に対向して配置された受信コイル３４で受信され検出信号として出力される。送信コイル２０、２２、２４は従来装置と同様に順次駆動される。
【００２８】
スケール側の３波長のコイルは互いに送信コイル及び受信コイルとして機能するため、図７と異なりスケール幅方向に３列だけコイルを形成すればよく、スケールの幅を縮小させることができる。
【００２９】
以下、本実施形態の３波長型位置エンコーダの作用についてより詳細に説明する。
【００３０】
図２〜図４には、送信コイル２０、２２、２４を順次駆動する場合のスケールとグリッドの作用説明図が示されている。図２は、送信コイル２０を駆動する場合の作用説明図である。グリッド側の送信コイル２０はスケール側の送信コイル１２と１４に対向配置し、グリッド側の受信コイル３０はスケール側の送信コイル１０に対向配置する。グリッド側の送信コイル２０を駆動することでスケール側の送信コイル１０から磁界が生じ、この磁界を受信コイル３０で受信し検出信号を出力する。スケール側の送信コイル１０には、送信コイル１２に接続されたコイルには送信コイル１２からの誘導電流が、送信コイル１４に接続されたコイルには送信コイル１４からの誘導電流がそれぞれ供給される。この送信コイル１２に接続されたコイルの周囲に形成される磁界と、送信コイル１４に接続されたコイルの周囲に形成される磁界と、が互いに干渉して強め合うため、送信コイル１０で生じた磁界を検出する受信コイル３０では強度の大きな検出信号が得られる。すなわち、ノイズに強い測定を行うことができる。検出信号の周期はλ１である。
【００３１】
図３は、送信コイル２２を駆動する場合の作用説明図である。グリッド側の送信コイル２２はスケール側の送信コイル１０に対向配置され、グリッド側の受信コイル３２はスケール側の送信コイル１２に対向配置される。送信コイル２２を駆動することにより、送信コイル１０を介して送信コイル１２から磁界が生じ、この磁界を受信コイル３２で検出する。受信コイル３２からの検出信号は、周期λ２の検出信号である。
【００３２】
図４は、送信コイル２４を駆動する場合の作用説明図である。グリッド側の送信コイル２４はスケール側の送信コイル１０に対向配置され、グリッド側の受信コイル３４はスケール側の送信コイル１４に対向配置される。送信コイル２４を駆動することにより送信コイル１０を介してスケール側の送信コイル１４から磁界が生じ、この磁界を受信コイル３４で検出する。受信コイル３４からの検出信号は、周期λ３の検出信号である。
【００３３】
したがって、従来装置と同様に、λ１でλｆｉｎｅ、λ１とλ２の位相差でλｍｅｄ、λ２とλ３の位相差でλｃｏａを構成し、これらλｆｉｎｅ、λｍｅｄ、λｃｏａを用いて絶対位置を検出することができる。
【００３４】
一方、このように３波長λ１、λ２、λ３の送信コイルと受信コイルを兼用してスケールに形成することで、いわゆるコイルの「歯抜け」が生じる問題がある。これは、３つのコイルがそれぞれλ１、λ２、λ３と異なる波長を有するため、λ１のコイルとλ２のコイル、及びλ１のコイルとλ３のコイルを接続する際に、両コイルの位置関係が次第にずれていくためあるところではもはや接続することができず、接続の「飛び」が生じるからである。
【００３５】
図５には、λ１のコイルを中央に配置し、λ２及びλ３のコイルを両側に配置した場合の歯抜けの様子が示されている。例えば、λ１＝１．０２４ｍｍ、λ２＝１．０９２ｍｍ、λ３＝１．０２８ｍｍとすると、λ２のコイルと接続できないλ１コイル、及びλ３と接続できないλ１コイルが生じている（図中「浮きコイル」と示される部分）。このような浮きコイル（あるいは歯抜け）が存在すると、その部分で磁界の周期的分布が乱れてしまい、特に最も高精度の送信コイルである波長λ１の送信コイル１０に生じると検出精度に大きな影響がある。
【００３６】
そこで、本実施形態では、単にλ１＜λ２＜λ３（あるいはλ１＜λ３＜λ２）とするのではなく、波長構成を変更して精度低下を抑制する。
【００３７】
具体的には、スケールの中央に位置するλ１送信コイル１０の波長λ１を最大とし、
λ２＜λ３＜λ１
あるいは
λ３＜λ２＜λ１
とする。このような波長構成とすることで、λ１ではなくλ２あるいはλ３に歯抜けを生じさせることができる。λ２及びλ３はλｍｅｄ及びλｃｏａを算出するためだけのものであるから、許容される誤差はλ１に比べて格段に大きく、したがって歯抜けによる精度低下を抑制することが可能である。具体的には、例えばλ１＝１．０２４ｍｍ、λ２＝０．９６３ｍｍ、λ３＝１．０２０ｍｍとすればよく、これによりλ２の送信コイル１２のみに歯抜けを生じさせることが可能である。図６には、λ２＜λ３＜λ１とした場合のスケール側のコイル構成が示されている。
【００３８】
なお、歯抜けを防止するためにλ１を大きくすると、その分だけ分解能が低下することとなるが、λ１の検出信号はその強度が大きいため十分な検出精度を確保できる。
【００３９】
また、例えばλ２＜λ３＜λ１としてλ２に歯抜けが生じた場合、λ１で定義されるλｆｉｎｅには影響がないものの、λ１とλ２の位相差で定義されるλｍｅｄやλ２とλ３で定義されるλｃｏａの精度が低下する。特に、λｃｏａに関しては精度の低いλ２とλ３を用いているためその影響が大きいと考えられる。そこで、λ２あるいはλ３に歯抜けを生じさせた場合、λｃｏａはλ２とλ３の位相差で定義するのではなく、λ１とλ３の位相差で定義することが好ましい。具体的には、以下のように定義される。
【００４０】
【数４】
λｆｉｎｅ＝λ１
λｍｅｄ＝λ２λ１／（λ２−λ１）
λｃｏａ＝λ３λ１／（λ３−λ１）・・・（４）
このように、本実施形態では、３波長型位置トランスデューサで、スケール側のコイル配置としてスケール幅方向にコイルが３列に並ぶような構成としたので、スケールサイズ、ひいては位置トランスデューサ全体のサイズを縮小化することができる。
【００４１】
また、本実施形態では、３列コイル構成とした場合の、コイルの浮きあるいは歯抜けを最も精度の高いλ１のコイルに生じさせるのではなく、λｍｅｄあるいはλｃｏａを精製するためだけのコイルλ２あるいはλ３に生じさせるような波長構成とし、かつ、λｃｏａをλ２とλ３ではなくλ１とλ３で定義しているため、浮きあるいは歯抜けによる精度低下を効果的に抑制することができる。
【００４２】
【発明の効果】
以上説明したように、本発明によれば検出範囲を増大させるとともに小型かつ高精度の位置トランスデューサを得ることができる。
【図面の簡単な説明】
【図１】実施形態に係る位置トランスデューサのスケールとグリッド構成図である。
【図２】図１において送信コイル２０を駆動した場合の作用説明図である。
【図３】図１において送信コイル２２を駆動した場合の作用説明図である。
【図４】図１において送信コイル２４を駆動した場合の作用説明図である。
【図５】 λ１送信コイルの歯抜け（浮き）説明図である。
【図６】 λ２送信コイルの歯抜け（浮き）説明図である。
【図７】従来の３波長型位置トランスデューサのスケールとグリッド構成図である。
【図８】図７の３波長型位置エンコーダのλｆｉｎｅ、λｍｅｄ、λｃｏａの説明図である。
【符号の説明】
１０，１２，１４送信コイル（スケール側）、２０，２２，２４送信コイル（グリッド側）、３０，３２，３４受信コイル（グリッド側）。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an inductive position transducer, and more particularly to a position transducer that includes a read head and a scale and detects the absolute position (ABS) of the read head relative to the scale.
[0002]
[Prior art]
Conventionally, a position transducer (or magnetic encoder) using an induced current is known. The position transducer includes a read head and a scale that are opposed to each other. A transmission coil and a reception coil are provided on the read head side, and a reception coil and a transmission coil are also provided on the scale side. A magnetic field is generated from the transmitting coil on the read head side, and an induced current is generated in the receiving coil on the scale side by this magnetic field. The transmission coil and the reception coil on the scale side are connected, and a magnetic field is generated from the transmission coil by the induced current generated. The receiving coil on the reading head side detects the magnetic field generated from the transmitting coil on the scale side and outputs it as a detection signal. Since the phase of the detection signal varies depending on the positional relationship between the read head and the scale, the position from the reference point on the scale of the read head, that is, the absolute position can be detected based on the phase of the detection signal.
[0003]
Usually, on the scale side, transmission coils having different pitches (wavelengths) λ1 and λ2 are arranged side by side in the width direction of the scale, and the absolute position is detected based on the phase difference between λ1 and λ2. In other words, since the phase of the detection signal is the same for each λ1 with only the λ1 coil, the absolute position exceeding λ1 cannot be uniquely determined. Therefore, based on the phase difference between λ1 and λ2, the absolute position is detected by detecting the number of periods of λ1. If λ1 is λfine, one period of the phase difference between λ1 and λ2 is defined as λmed, and the number of λfines included in λmed is n, the following equation holds.
[0004]
[Expression 1]
λmed = n · λfine (1)
n is a value determined by the wavelength difference between λ1 and λ2, and as the wavelength difference is smaller, n increases and the length (measurement range) at which the absolute position can be detected increases. By determining which of the ranges obtained by dividing the phase difference between λ1 and λ2 into 360 degrees divided into n, the number of periods of λ1 can be determined, and (period of λ1) × (number of periods of λ1) The absolute position is calculated by + (the phase of λ1).
[0005]
As described above, the measurement range of the two-wavelength position transducer is expanded, but similarly, a three-wavelength type, that is, a position transducer in which transmitter coils having three wavelengths different from λ1, λ2, and λ3 are arranged on the scale side is also proposed. .
[0006]
FIG. 7 shows the configuration of such a three-wavelength position transducer. FIG. 7A shows the configuration on the scale side, and FIG. 7B shows the configuration on the reading head (grid) side. Actually, the scale and the reading head are arranged to face each other so as to overlap each other, but for convenience of explanation, both are shown side by side.
[0007]
On the scale side, a coil having a wavelength λ1 is formed, and coils having wavelengths λ2 and λ3 are also formed. The coil of wavelength λ1 is formed from a central transmission coil 10 and reception coils 11 arranged on both sides of the central transmission coil 10 so as to sandwich the central transmission coil 10. The coils of wavelengths λ2 and λ3 also serve as a transmission coil and a reception coil, respectively. That is, the coils of wavelengths λ2 and λ3 are connected, the receiving coil for the transmitting coil 12 of wavelength λ2 is the transmitting coil 14 of wavelength λ3, and the transmitting coil 12 of wavelength λ2 by the induced current generated in the transmitting coil 14 of wavelength λ3. Generates a magnetic field. The receiving coil for the transmitting coil 14 having the wavelength λ3 is the transmitting coil 12 having the wavelength λ2, and the transmitting coil 14 having the wavelength λ3 generates a magnetic field by the induced current generated in the transmitting coil 12 having the wavelength λ2.
[0008]
On the other hand, a transmission coil 20 that generates a magnetic field toward the reception coil 11 having the wavelength λ1 and a reception coil 30 that detects the magnetic field generated from the transmission coil 10 having the wavelength λ1 are provided on the grid side. Further, a transmission coil 22 that generates a magnetic field toward the reception coil of λ2 and a reception coil 32 that detects a magnetic field from the transmission coil 12 of λ2 are provided. Further, a transmission coil 24 that generates a magnetic field for the reception coil of λ3 and a reception coil 34 that detects a magnetic field from the transmission coil 14 of wavelength λ3 are provided. The grid transmission coil 20 faces the scale reception coil 11, and the reception coil 30 faces the transmission coil 10 and is magnetically coupled. Similarly, the transmission coil 24 faces the transmission coil 12 (a reception coil for the transmission coil 14 having the wavelength λ3), and the reception coil 32 faces the transmission coil 12 and is magnetically coupled. The transmission coil 22 faces the transmission coil 14 (a reception coil for the transmission coil 12 having the wavelength λ2), and the reception coil 34 faces the transmission coil 14 and is magnetically coupled.
[0009]
The transmission coils 20, 22, 24 on the grid side are sequentially supplied with driving currents in a time-sharing manner, and the receiving coils 30, 32, 34 generate magnetic fields that are sequentially generated in the transmission coils 10, 12, 14 of the scale by the respective driving currents. Detect and output a signal. λ1 is formed by λ1, λmed by the phase difference between λ1 and λ2, and λcoa by the phase difference between λ2 and λ3. When m is the number of λmed included in λcoa,
[Expression 2]
λcoa = m · λmed = m · n · λfine = m · n · λ1 (2)
It becomes. Since the measurement range is determined by m · n, the measurement range is increased as compared with the position transducer using the two wavelengths λ1 and λ2.
[0010]
FIG. 8 shows the positional accuracy of the above-mentioned λfine, λmed, and λcoa. In the figure, the horizontal axis is the position from the reference point of the scale, and the vertical axis is the phase. The accuracy decreases (coarse) in the order of λfine, λmed, and λcoa, and by combining these, the absolute position can be uniquely determined within the range of λcoa.
[0011]
Note that λfine, λmed, and λcoa are specifically defined as follows.
[0012]
[Equation 3]
λfine = λ1
λmed = λ2λ1 / (λ2-λ1) = nλfine
λcoa = λ3λ2 / (λ3-λ2) = mλmed (3)
Here, m and n are positive integers.
[0013]
[Problems to be solved by the invention]
As described above, it is possible to increase the measurement range by using the three wavelengths λ1, λ2, and λ3. However, as shown in FIG. 7, even if the transmission coil and the reception coil are shared for λ2 and λ3, As a result, a total of five coil groups are formed in the width direction of the scale, and there is a problem that the scale size and thus the size of the position transducer increase. In recent years, particularly in NC and the like, the size of devices has been reduced, and a position transducer that is attached to these devices and outputs position data is required to be further downsized and highly accurate.
[0014]
The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide a small and highly accurate three-wavelength position transducer.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, the present invention comprises a reading head having a magnetic field generating means and a magnetic field detecting means, a receiving coil disposed opposite to the reading head and generating an induced current by a magnetic field from the magnetic field generating means, A magnetic coupling coil comprising a transmission coil that generates a magnetic field by an induced current is provided with a scale formed at a predetermined pitch λ along the measurement direction, and the magnetic field from the transmission coil of the scale is detected by the magnetic field detection means. An inductive transducer that detects a position of the read head with respect to the scale based on a phase of a detection signal obtained, wherein the magnetic coupling coil is a first transmission formed along the measurement direction at a first pitch λ1. A coil and a second pitch λ2 different from the first pitch λ1 are formed along the measurement direction, and the first transmission A second transmission coil formed on one side of the coil and a third pitch λ3 different from the first pitch λ1 and the second pitch λ2 are formed along the measurement direction and sandwiching the first transmission coil A third transmitter coil formed on the opposite side of the second transmitter coil, the first transmitter coil being connected to the second transmitter coil and the second transmitter coil. A coil provided adjacent to the coil and connected to the third transmission coil, wherein the second transmission coil and the third transmission coil are connected to the first transmission coil. functions as the first transmission coil acts as a receiver coil connected to the second transmission coil or the third transmission coil, wherein the first pitch .lambda.1, second pitch .lambda.2, third pitch λ3 is λ2 <λ3 <and satisfies the .lambda.1 or λ3 <λ2 <λ1 becomes magnitude relation.
[0016]
Here, the first transmission coil, the second transmission coil, and the third transmission coil are formed side by side in the width direction of the scale, and the first transmission coil is between the second transmission coil and the third transmission coil. Preferably it is formed.
[0018]
In this case, the phase difference between the phase of the magnetic field detection signal from the first transmission coil and the phase of the magnetic field detection signal from the first transmission coil and the phase of the magnetic field detection signal from the second transmission coil; Preferably, the position is detected based on a phase difference between the phase of the magnetic field detection signal from the first transmission coil and the phase of the magnetic field detection signal from the third transmission coil.
[0019]
As described above, in the position transducer (magnetic encoder) of the present invention, coils having three pitches (three wavelengths) of λ1, λ2, and λ3 are used. However, as the coil arrangement on the scale side, the transmitting coil and the receiving coil are used together. Reduce the number of coils in the scale width direction and reduce the size. That is, the first transmission coil (λ1 coil) and the second transmission coil (λ2 coil) are connected to cause the λ2 coil to function as a reception coil of the λ1 coil. That is, the magnetic field generated from the transmission coil on the read head side generates an induced current in the λ2 coil, and the induced current is supplied to the λ1 coil to generate a magnetic field from the λ1 coil. Similarly, the λ1 coil is caused to function as a receiving coil of the λ2 coil. The relationship between the first transmission coil and the third transmission coil is the same. In this way, the number of coils can be reduced and the size can be reduced by functioning also as a reception coil of the transmission coil to which the three transmission coils are respectively connected. Since the first transmission coil (λ1 coil), the second transmission coil (λ2 coil), and the third transmission coil (λ3 coil) are driven in a time-sharing manner, there is no problem even if both transmission and reception are performed.
[0020]
Further, when the first transmitter coil and the second transmitter coil having different pitches (wavelengths) are connected, and the first transmitter coil and the third transmitter coil are connected, the first transmitter coil is assumed to have the minimum pitch of the first transmitter coil. In this case, a “floating coil” or “missing tooth” that cannot be connected can occur, and the position cannot be detected at such a floating portion, so that the accuracy is lowered. Therefore, by causing the second transmission coil or the third transmission coil, which only detects the number of periods of λ1, to cause a float or a missing tooth, the influence of the lift or the missing tooth on the accuracy can be suppressed. Prevention of λ1 lift or tooth loss can be obtained by adopting a wavelength configuration that maximizes the pitch of λ1.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0022]
FIG. 1 shows the configuration of a three-wavelength position transducer (magnetic encoder) according to this embodiment. FIG. 1A shows the configuration on the scale side, and FIG. 1B shows the configuration on the reading head (grid) side. Actually, the scale and the grid are arranged to face each other with a predetermined distance as in the conventional apparatus. First, the configuration on the scale side will be described.
[0023]
On the scale side, a transmission coil 10 having a wavelength (pitch) λ1, a transmission coil 12 having a wavelength λ2, and a transmission coil 14 having a wavelength λ3 are formed side by side in the width direction of the scale. The transmission coil 10 having the wavelength λ1 is disposed between the transmission coil 12 having the wavelength λ2 and the transmission coil 14 having the wavelength λ3. A coil transmitter coil 10 of the wavelength λ1 is connected to the transmitter coil 12 of the wavelength .lambda.2, a coil with provided adjacent to the coil is connected to the transmitter coil 14 of the wavelength λ3 which is connected to the transmission coil 12, from Composed . The transmission coil 12 having the wavelength λ2 functions as a reception coil for the transmission coil 10 having the wavelength λ1. The transmission coil 10 having the wavelength λ1 functions as a reception coil for the transmission coil 12 having the wavelength λ2. Similarly, the transmission coil 14 having the wavelength λ3 functions as a reception coil for the transmission coil 10 having the wavelength λ1, and the transmission coil 10 having the wavelength λ1 functions as a reception coil for the transmission coil 14 having the wavelength λ3.
[0024]
On the other hand, the configuration on the grid side is as follows. That is, the transmission coils 20, 22, and 24 are provided, the transmission coil 20 is disposed to face the transmission coil 12 having the wavelength λ2 and the transmission coil 14 having the wavelength λ3, and the transmission coils 22 and 24 are disposed on the transmission coil 10 having the wavelength λ1. Opposed to each other. A receiving coil 30 is disposed facing the transmitting coil 10, a receiving coil 32 is disposed facing the transmitting coil 12, and a receiving coil 34 is disposed facing the transmitting coil 14 to be magnetically coupled.
[0025]
By supplying a drive current to the transmission coil 20, the transmission coil 20 transmits the transmission coil 12 having the wavelength λ2 (reception coil for the transmission coil 10 having the wavelength λ1) and the transmission coil 14 having the wavelength λ3 (reception for the transmission coil having the wavelength λ1). The induced current generated in the transmission coil 12 having the wavelength λ2 is generated in the transmission coil 14 having the wavelength λ3 in the coil connected to the transmission coil 12 among the coils constituting the transmission coil 10 . The induced currents are respectively supplied to coils connected to the transmission coil 14 among the coils constituting the transmission coil 10 . A magnetic field is generated by the induced current supplied to the transmission coil 10 having the wavelength λ1, and this magnetic field is received by the reception coil 30 disposed opposite to the transmission coil 10 having the wavelength λ1 and output as a detection signal.
[0026]
Further, by supplying a drive current to the transmission coil 22, a magnetic field is generated from the transmission coil 22 toward the transmission coil 10 having the wavelength λ1, and an induced current is generated in the transmission coil 10 having the wavelength λ1. This induced current is supplied to the transmission coil 12 having the wavelength λ2, and a magnetic field is generated from the transmission coil 12 having the wavelength λ2, and is received by the reception coil 32 and output as a detection signal.
[0027]
Further, by supplying a drive current to the transmission coil 24, a magnetic field is generated from the transmission coil 24 toward the transmission coil 10 having the wavelength λ1, and an induced current is generated in the transmission coil 10. This induced current is supplied to the transmission coil 14. The transmission coil 14 generates a magnetic field by this induced current, and is received by the reception coil 34 disposed opposite to the transmission coil 14 and output as a detection signal. The transmission coils 20, 22, and 24 are sequentially driven as in the conventional apparatus.
[0028]
Since the three-wavelength coils on the scale side function as a transmitting coil and a receiving coil, it is only necessary to form coils in three rows in the scale width direction unlike FIG. 7, and the scale width can be reduced.
[0029]
Hereinafter, the operation of the three-wavelength position encoder of the present embodiment will be described in more detail.
[0030]
2 to 4 are diagrams for explaining the operation of the scale and the grid when the transmission coils 20, 22, and 24 are sequentially driven. FIG. 2 is a diagram for explaining the operation when the transmission coil 20 is driven. The transmission coil 20 on the grid side is disposed to face the transmission coils 12 and 14 on the scale side, and the reception coil 30 on the grid side is disposed to face the transmission coil 10 on the scale side. By driving the transmission coil 20 on the grid side, a magnetic field is generated from the transmission coil 10 on the scale side, and this magnetic field is received by the reception coil 30 and a detection signal is output. The transmission coil 10 of the scale side, induced current from the connected transmission coil 12 to the coil in transmission coil 12, an induced current is supplied from the transmitting coil 14 to the coil connected to the transmitter coil 14 . The magnetic field formed around the coil connected to the transmission coil 12 and the magnetic field formed around the coil connected to the transmission coil 14 interfere with each other and strengthen each other . The receiving coil 30 that detects the magnetic field can obtain a detection signal having a high intensity. That is, measurement that is resistant to noise can be performed. The period of the detection signal is λ1.
[0031]
FIG. 3 is an operation explanatory diagram when the transmission coil 22 is driven. The transmission coil 22 on the grid side is disposed to face the transmission coil 10 on the scale side, and the reception coil 32 on the grid side is disposed to face the transmission coil 12 on the scale side. By driving the transmission coil 22, a magnetic field is generated from the transmission coil 12 via the transmission coil 10, and this magnetic field is detected by the reception coil 32. The detection signal from the receiving coil 32 is a detection signal with a period λ2.
[0032]
FIG. 4 is a diagram for explaining the operation when the transmission coil 24 is driven. The transmission coil 24 on the grid side is disposed to face the transmission coil 10 on the scale side, and the reception coil 34 on the grid side is disposed to face the transmission coil 14 on the scale side. By driving the transmission coil 24, a magnetic field is generated from the transmission coil 14 on the scale side via the transmission coil 10, and this magnetic field is detected by the reception coil 34. The detection signal from the reception coil 34 is a detection signal with a period λ3.
[0033]
Therefore, as in the conventional apparatus, λ1 is composed of λfine, λmed is composed of the phase difference between λ1 and λ2, λcoa is composed of the phase difference of λ2 and λ3, and the absolute position can be detected using these λfine, λmed, and λcoa. .
[0034]
On the other hand, there is a problem that so-called “tooth missing” of the coil is caused by using the transmitting coil and the receiving coil of the three wavelengths λ1, λ2, and λ3 in the scale as described above. This is because the three coils have different wavelengths from λ1, λ2, and λ3, respectively, and when the λ1 coil and the λ2 coil, and the λ1 coil and the λ3 coil are connected, the positional relationship between the two coils gradually shifts. This is because it is no longer possible to connect at some point, and a “jump” of connection occurs.
[0035]
FIG. 5 shows a state of missing teeth when the coil of λ1 is arranged in the center and the coils of λ2 and λ3 are arranged on both sides. For example, if λ1 = 1.024 mm, λ2 = 1.092 mm, and λ3 = 1.028 mm, a λ1 coil that cannot be connected to the λ2 coil and a λ1 coil that cannot be connected to λ3 are generated (“floating coil” in the figure). Part shown). When such a floating coil (or missing tooth) is present, the periodic distribution of the magnetic field is disturbed at that portion, and particularly when it occurs in the transmission coil 10 having the wavelength λ1, which is the most accurate transmission coil, the detection accuracy is greatly affected. There is.
[0036]
Therefore, in the present embodiment, instead of simply setting λ1 <λ2 <λ3 (or λ1 <λ3 <λ2), the wavelength configuration is changed to suppress a decrease in accuracy.
[0037]
Specifically, the wavelength λ1 of the λ1 transmission coil 10 located at the center of the scale is maximized,
λ2 <λ3 <λ1
Or λ3 <λ2 <λ1
And By adopting such a wavelength configuration, it is possible to cause tooth loss in λ2 or λ3 instead of λ1. Since λ2 and λ3 are only for calculating λmed and λcoa, the allowable error is much larger than that of λ1, and therefore it is possible to suppress a decrease in accuracy due to missing teeth. Specifically, for example, λ1 = 1.024 mm, λ2 = 0.963 mm, and λ3 = 1.020 mm may be set, and this can cause tooth loss only in the transmission coil 12 of λ2. FIG. 6 shows the coil configuration on the scale side when λ2 <λ3 <λ1.
[0038]
If λ1 is increased in order to prevent tooth loss, the resolution will be reduced by that amount. However, since the detection signal of λ1 has a high strength, sufficient detection accuracy can be ensured.
[0039]
Also, for example, when a missing tooth occurs in λ2 with λ2 <λ3 <λ1, there is no effect on λfine defined by λ1, but it is defined by λmed defined by the phase difference between λ1 and λ2, and by λ2 and λ3. The accuracy of λcoa decreases. In particular, λcoa is considered to have a large influence because λ2 and λ3 having low accuracy are used. Therefore, when tooth loss occurs in λ2 or λ3, λcoa is preferably defined not by the phase difference between λ2 and λ3, but by the phase difference between λ1 and λ3. Specifically, it is defined as follows.
[0040]
[Expression 4]
λfine = λ1
λmed = λ2λ1 / (λ2-λ1)
λcoa = λ3λ1 / (λ3-λ1) (4)
As described above, in this embodiment, the three-wavelength type position transducer is configured so that the coils are arranged in three rows in the scale width direction as the coil arrangement on the scale side, so that the scale size and thus the size of the entire position transducer are reduced. Can be
[0041]
Further, in the present embodiment, when the three-row coil configuration is used, the coil λ2 or λ3 is used only for refining λmed or λcoa, instead of causing the coil floating or tooth loss to occur in the λ1 coil with the highest accuracy. And λcoa is defined not by λ2 and λ3 but by λ1 and λ3, so that a decrease in accuracy due to floating or missing teeth can be effectively suppressed.
[0042]
【The invention's effect】
As described above, according to the present invention, a detection range can be increased and a small and highly accurate position transducer can be obtained.
[Brief description of the drawings]
FIG. 1 is a scale and grid configuration diagram of a position transducer according to an embodiment.
FIG. 2 is an operation explanatory diagram when a transmission coil 20 is driven in FIG. 1;
FIG. 3 is an operation explanatory diagram when a transmission coil 22 is driven in FIG. 1;
FIG. 4 is an operation explanatory diagram when a transmission coil 24 is driven in FIG. 1;
FIG. 5 is an explanatory diagram of tooth missing (lifting) of a λ1 transmission coil.
FIG. 6 is an explanatory diagram of tooth missing (floating) of a λ2 transmission coil.
FIG. 7 is a scale and grid configuration diagram of a conventional three-wavelength type position transducer.
8 is an explanatory diagram of λfine, λmed, and λcoa of the three-wavelength position encoder of FIG. 7;
[Explanation of symbols]
10, 12, 14 Transmitting coil (scale side), 20, 22, 24 Transmitting coil (grid side), 30, 32, 34 Receiving coil (grid side).

Claims

A read head having magnetic field generating means and magnetic field detecting means;
A magnetic coupling coil is formed at a predetermined pitch λ along the measurement direction. The receiving coil is opposed to the reading head and generates a receiving coil that generates an induced current by a magnetic field from the magnetic field generating unit and a transmitting coil that generates a magnetic field by the induced current. Scaled,
An inductive transducer for detecting a position of the read head relative to the scale based on a phase of a detection signal obtained by detecting a magnetic field from the transmission coil of the scale by the magnetic field detection means,
The magnetic coupling coil is:
A first transmission coil formed along the measurement direction at a first pitch λ1,
A second transmission coil formed along the measurement direction at a second pitch λ2 different from the first pitch λ1, and formed on one side of the first transmission coil;
A third pitch λ3 different from the first pitch λ1 and the second pitch λ2 is formed along the measurement direction, and is formed on the opposite side of the second transmission coil with the first transmission coil interposed therebetween. 3 transmitter coils;
Have
The first transmission coil includes a coil connected to the second transmission coil, a coil provided adjacent to a coil connected to the second transmission coil, and a coil connected to the third transmission coil. Consists of
The second transmission coil and the third transmission coil function as a reception coil connected to the first transmission coil, and the first transmission coil is a reception coil connected to the second transmission coil or the third transmission coil. Function as
The inductive position transducer characterized in that the first pitch λ1, the second pitch λ2, and the third pitch λ3 satisfy a magnitude relationship of λ2 <λ3 <λ1.

A read head having magnetic field generating means and magnetic field detecting means;
A magnetic coupling coil is formed at a predetermined pitch λ along the measurement direction. The receiving coil is opposed to the reading head and generates a receiving coil that generates an induced current by a magnetic field from the magnetic field generating unit and a transmitting coil that generates a magnetic field by the induced current. Scaled,
An inductive transducer for detecting a position of the read head relative to the scale based on a phase of a detection signal obtained by detecting a magnetic field from the transmission coil of the scale by the magnetic field detection means,
The magnetic coupling coil is:
A first transmission coil formed along the measurement direction at a first pitch λ1,
A second transmission coil formed along the measurement direction at a second pitch λ2 different from the first pitch λ1, and formed on one side of the first transmission coil;
A third pitch λ3 different from the first pitch λ1 and the second pitch λ2 is formed along the measurement direction, and is formed on the opposite side of the second transmission coil with the first transmission coil interposed therebetween. 3 transmitter coils;
Have
The first transmission coil includes a coil connected to the second transmission coil, a coil provided adjacent to a coil connected to the second transmission coil, and a coil connected to the third transmission coil. Consists of
The second transmission coil and the third transmission coil function as a reception coil connected to the first transmission coil, and the first transmission coil is a reception coil connected to the second transmission coil or the third transmission coil. Function as
The inductive position transducer according to claim 1, wherein the first pitch λ1, the second pitch λ2, and the third pitch λ3 satisfy a relationship of λ3 <λ2 <λ1.

The position transducer according to claim 1 or 2,
The first transmission coil, the second transmission coil, and the third transmission coil are formed side by side in the width direction of the scale, and the first transmission coil is formed between the second transmission coil and the third transmission coil. An inductive position transducer characterized by the above.

The position transducer according to any one of claims 1 to 3,
A phase of a magnetic field detection signal from the first transmission coil;
A phase difference between the phase of the magnetic field detection signal from the first transmission coil and the phase of the magnetic field detection signal from the second transmission coil;
An inductive position transducer that detects the position based on a phase difference between a phase of a magnetic field detection signal from the first transmission coil and a phase of a magnetic field detection signal from the third transmission coil.