JP3560692B2 - Optical encoder - Google Patents

Description

一方、Ｌ＜ａ^２ ／λの場合は、おおよそ下記数２に示す（２）式で与えられる。
【００２３】
【数２】

スケールにおける光ビームの反射（または透過）の明暗を良好な信号振幅（受光量を示す出力信号波形において極大値と極小値の差を信号振幅と定義する。）で検出するためには、スケールのピッチｐはＰ方向のビーム径Ｗより大きい方が望ましい。従って、信号振幅の大きな出力信号を得るためには、
Ｌ≧ａ^２ ／λの場合には、下記（３）式
ｐ・ｃｏｓθ≧λ・Ｌ／ａ …（３）
（但し、−π／２＜θ＜π／２，ψ＝０）
Ｌ＜ａ^２ ／λの場合には、下記（４）式
ｐ・ｃｏｓθ≧ａ …（４）
（但し、−π／２＜θ＜π／２，ψ＝０）
とすることが望ましい。
【００２４】
以上、図７においては、θ≠０かつψ＝０の場合について示しているが、図８にθ＝０かつψ≠０の場合について示す。これ以外の各種定義は図７に対するものと同一であるため、ここでは省略する。本図の場合、スケール上のレーザビームのＰ方向のビーム径Ｗ（半値全幅）は、ψによらず一定であるため（図８（Ａ）の正面図参照）、Ｌがａに対して十分に大きい場合（望ましくは、Ｌ≧ａ^２ ／λの範囲）は、Ｗはおおよそ下記数３に示す（５）式で与えられる。
【００２５】
【数３】

一方、Ｌ＜ａ^２ ／λの場合は、おおよそ下記数４に示す（６）式で与えられる。
【００２６】
【数４】

【００２７】
図７の場合と同様に、信号振幅の大きな出力信号を得るためには、スケールのピッチｐはＰ方向のビーム径Ｗより大きい方が望ましい。従って、Ｌ≧ａ^２ ／λの場合には、下記（７）式とし、
ｐ≧λ・Ｌ／ａ（但し、θ＝０，−π／２＜ψ，π／２） …（７）
Ｌ＜ａ^２ ／λの場合には下記（８）式とすることが望ましい。
【００２８】
ｐ≧ａ（但し、θ＝０，−π／２＜ψ，π／２） …（８）
以上のように、θ＝０，ψ≠０の場合は、ψの値によらず、式（５）〜（８）が成り立つことがわかる。
【００２９】
また、図示しないが、θ≠０，ψ≠０の場合については、図８の例で示すようにψの値に依存しないため、式（１）〜（４）がθ，ψの値によらず成り立つといってよい。
【００３０】
以上は極めて粗い概算であるが、以下に回折積分を用いたスケール面上の光強度分布の厳密な計算例を図９に示す。開口長ａの光源の出射窓から出射される平面波の距離Ｌにおける光強度分布｜Ａ｜^２ は、Ｌが大きい時（Ｌ≧ａ^２ ／λ）には、出射窓に対応した瞳関数を空間的にフーリエ変換することにより下記数５に示す（９）式で表される。
【００３１】
【数５】

但し、出射ビームの中心をｘの原点とし、この出射面に平行にｘ軸を考える。また、Ｃはｘに依存しない定数である。
【００３２】
図９は波長λ＝１μｍ、開口幅ａ＝１０μｍ、スケールと開口の距離Ｌ＝１００μｍで計算したものであるが（縦軸はＣ＝１として正規化されている）、スポット系は半値全幅で約１０μｍとなり、光量プロファイルは図のようになる（リニアスケールと開口のなす角θは小さいと仮定し計算上無視している。また、これ以後の計算でもθ＝０の場合については記載するが、θ≠０の場合のピッチｐをｐ・ｃｏｓθと置きかえて考えればよい。）
このスポットがリニアスケールに当った場合の反射光の光量は、リニアスケールの反射率分布とスポット強度分布の積をｘ軸上で積分すれば得られる（光検出器は反射光量すべてを受光できるほど十分大きいとする）。リニアスケールの反射率分布を計算上フーリエ級数で表現し、このスケールが矢印の方向に１０μｍ／ｓで移動した場合の光検出器で得られる信号光量を求めたものを図１０、図１１に示す。ここで、図１０はスケール反射率分布、図１１は検出器の受光量を示す。
【００３３】
これはスケールピッチｐ＝２０，１５，１０μｍについて計算した結果であるが、ピッチに対応した周期的な信号が得られ、この信号波形と変位量の関係を用いて、（例えば、この信号の周期をカウントしたり、あるいは、信号を変位の信号に電子的に変換すること等により）スケールの変位量を計測できる。
【００３４】
ピッチが細かくなるにつれ信号振幅（スケールから１００％反射する場合と無反射の場合の出力信号の差を１として正規化している）は小さくなる。図１０、図１１条件では、（１）式、（２）式よりビーム径Ｗはスケール上で、およそＷ＝１０μｍであるが、図１０、図１１の結果よりおよそこれと同じピッチ、即ちｐ≧Ｗの範囲であれば信号振幅が０．１程度以上が得られることがわかり、これがエンコーダの出力信号の信号振幅を一定以上に設計するための指針になると考えられる。
【００３５】
図１２にスケールピッチｐに対する信号振幅の変化を示す。図中の○印は図１０のそれぞれのｐに対応する。ｐ＝１０の場合は条件式（３）の条件の下限となる（ｐ＝Ｌλ／ａが成立する）。この場合には図よりわかるように信号振幅は全体光量の１／１０程度となり、以下の説明ではこの（信号振幅が０．１になる）状態を実用的な信号振幅の下限とみなすことにする。なお、光検出器のＳ／Ｎが高い場合には、さらに、信号振幅が０．０１でも使用可能である。この結果より先の概算による（３）式の条件が極めて妥当なものであることがわかる。
【００３６】
さらに、Ｌ＜ａ^２ ／λの場合にはビーム径Ｗがおよそａであることもあわせて考慮することにより、エンコーダの仕様が与えられたときに、出力信号が良好なＳ／Ｎを持つための設計条件が上記（３），（４）式により与えられる。図１３では、仮にλ＝１μｍ，Ｌ＝１００μｍの条件下でスケールピッチｐ≦３０μｍとして、信号振幅が０．１以上になるための開口長ａの範囲を示す。図１４では一例として、λ＝１μｍ，ａ＝５μｍ，１０μｍ，１５μｍが与えられた時に、スケールのピッチｐを３０μｍ以下で使用することを前提とした、（信号振幅が０．１以上となる）望ましいｐとＬの範囲を各々のａに対して斜線で示す。このように、面発光半導体レーザを光源に用いることにより、レーザ光の出射窓の径ａを広範に設計できるので、上記のようにして適切なＬ，λ，ｐ，ａの構造パラメータを決定することにより、所定の分解能をもったエンコーダが実現できる。特に、スケールピッチの細かいエンコーダをレンズを省略して実現することができるため、高分解能な光学式エンコーダの小型化や製作の簡略化が可能となる。
【００３７】
（実施例１）
図１５（Ａ），（Ｂ）を参照する。ここで、図１５（Ａ）は光学式エンコーダの側面図、図１５（Ｂ）は斜視図を示す。図１５のように部分的に凹部１３１ を形成した誘電体基板１３２ 上に面発光レーザ（発光素子）１３３ 及び受光素子１３４ がそれぞれ別個に接着されており、特に面発光レーザ１３３ は凹部１３１ の斜面上に置かれている。なお、図中の符番１３５ はリニアスケールである。
【００３８】
次に、この実施例１に係る光学式エンコーダの作用を説明する。面発光レーザ１３３ を出射した光はリニアスケール１３５ で反射され、０次回折光（すなわち反射光）が受光素子１３４ で受光される。面発光レーザは、先に述べたように開口の大きさその他を適切に選ぶことによりスポット広がりをある程度抑えることができ、このため従来のようなビーム整形のためのコリメータレンズなしで高分解能なエンコーダを構成することができる。なお、図１５ではスケールの移動方向とピッチの方向は紙面に平行な方向で示されているが、これらを紙面に垂直な方向としてもよい。このスケールの移動方向，ピッチ方向に関する自由度は本特許の他の実施例においても同様である。
【００３９】
従って、次のような効果がある。
部品点数が減り低コストかつ小型、薄型のエンコーダが実現できる。また、基板とスケールを平行に配置することができエンコーダ全体を小型にすることができる。更に、０次回折光を受光することにより、高次回折光を受光する場合に較べて、スケールのピッチ精度、反射率精度などに依存しにくい許容度の大きい信号検出ができる。なお、この実施例１においては、誘電体基板上に受光素子、発光素子を配置しているが、基板は誘電体に限られるわけではなく、半導体を用いてもよい。
【００４０】
半導体基板を用いる場合には受光素子または発光素子を基板上に一体形成することができるため、素子を新たに基板に接合する手間が省け製作プロセスが簡略化できるという効果がある。また、半導体基板中に信号処理回路を形成すれば、回路系も含めたより一層の小型化が可能になる。
【００４１】
以上、実施例１については、基板の一部に凹部を設けその斜面に斜めに発光素子を配置する構成をとっているが、平坦な基板を用いてもよい。
（実施例２）
図１６（Ａ），（Ｂ）を用いて説明する。
【００４２】
この実施例２は実施例１と同様の構成において、凹部を形成しない平坦な誘電体基板１３２ を用い、発光素子１３３ 及び受光素子１３４ を該基板表面に形成したものである。この基板は図１６のように傾斜台座１４１ 上に取付けられ、リニアスケール１３５ に対して斜めに配置される。発光素子１３３ から出射した光はリニアスケール１３５ で反射され、受光素子１３４ で受光される。この実施例２の場合は平坦な基板を使用するため、実施例１に比べて基板に凹部を形成する工程を省略できるという効果がある。
【００４３】
この場合にも、むろん実施例１と同様に、半導体基板を用いてもよい。また、この構成の場合には基板として化合物半導体を用い、表面上に気相成長法により結晶成長を行い受光素子および発光素子を一体形成してもよい。
【００４４】
なお、上記実施例１，２の各構成は、当然、各種の変形、変更が可能である。実施例１，２に共通して可能な変形例を図１７に実施例３として示す。
（実施例３）
図１７は面発光レーザ光源１３３ の開口１３３ ａを楕円形状にした例である。円形開口では十分なＳ／Ｎ比の信号が期待できない場合は、このような方法でスケールの分解能を落すことなく信号光量を増やし、Ｓ／Ｎ比を向上させることができる。なお、この実施例３では楕円形状の開口となっているが長方形の開口でも同様の効果を期待できる。図１７は実施例１に対応した図であるが、実施例２についても無論同様の変形が可能である。
【００４５】
また、これまでの実施例ではスケール移動量のみが検知され移動している向きは判別できなかったが、構成の若干の変形で簡単に移動の向き判別の機能を付け加えることができる。そのような例を以下実施例４として図１８に示す。
【００４６】
（実施例４）
実施例４の構成を図１８に示す。この実施例４は実施例１と同様の構成において、受光素子１３４ を１３４ ａ，１３４ ｂに２分割したものである。一定の間隙を有してこのように受光素子を２分割することにより、受光素子に入射する信号光の位相を図１９に示すようにπ／２だけずらすことができる。受光素子１３４ ａに入射する信号に対して受光素子１３４ ｂに入射する信号の位相は、スケールが図中右方向に移動する場合はπ／２進み、左方向に移動する場合はπ／２遅れるので、信号処理により両者の位相関係を判別することにより移動の向きの判別ができる。なお、この２つの信号の位相差は必ずしもπ／２に設定する必要はなく、位相差がｎπ（ここで、ｎ＝０，±１，±２…）とならないような一定の値であれば移動の向きの判別が可能である。
【００４７】
また、このような向き判別機能は１次元に限られるわけではなく、受光素子を４分割することにより容易に２次元に拡張できる。なお、実施例４についても、当然ながら基板材料、スポット形状等については実施例１〜３と同様の変形が可能である。
【００４８】
これまでの実施例ではスケールの１次元的な変位量しか検出できなかったが、若干の構成変更により２次元的な変位検出を可能にすることができる。これを以下の実施例５として図２０に示す。
【００４９】
（実施例５）
反射率または透過率の異なる２次元的なパターンを形成したスケール１８１ に対して、面発光半導体レーザ光源からのビームを照射し、この時の反射光または透過光を受光素子４３_１ ，または受光素子４３_２ で受光する。前記移動スケールと面発光半導体レーザ光源の光ビーム出射面との距離をＬ、光ビームの波長をλ、互いに異なる特定方向のスケールピッチを各々ｐ_ｘ ，ｐ_ｙ 、レーザ光の出射方向に垂直な平面と前記２つの特定方向のなす角をθ_ｘ ，θ_ｙ 、前記移動スケールの各々のピッチ方向に対する前記光源の開口長を各々ａ_ｘ ，ａ_ｙ としたとき、
Ｌ≧ａ_ｘ ^２ ／λの場合に、ｐ_ｘ ・ｃｏｓθ_ｘ ≧λ・Ｌ／ａ_ｘ 、
Ｌ≧ａ_ｙ ^２ ／λの場合に、ｐ_ｙ ・ｃｏｓθ_ｙ ≧λ・Ｌ／ａ_ｙ 、
Ｌ＜ａ_ｘ ^２ ／λの場合に、ｐ_ｘ ・ｃｏｓθ_ｘ ≧ａ_ｘ 、
Ｌ＜ａ_ｙ ^２ ／λの場合に、ｐ_ｙ ・ｃｏｓθ_ｙ ≧ａ_ｙ
（但し、−π／２＜θ_ｘ ＜π／２、−π／２＜θ_ｙ ＜π／２）
の関係を満たすように設計することによりエンコーダからの出力の信号振幅を適正なレベルに設計できる。面発光半導体レーザ光源を用いることにより、レーザ光の出射窓の径や形状を広範に設計できるので、レンズを必ずしも必要とせずに互いに異なる特定方向の所定の分解能をもったエンコーダが実現できる。また、特定方向のスケールピッチの細かいエンコーダをレンズを省略して実現することができるため、高分解能な光学式エンコーダの小型化や製作の簡略化、低コスト化が可能となる。
【００５０】
以下、この発明に係る光学式エンコーダについてまとめると、次に示す構成，作用，効果を有する。
１．
（構成）光源に対して相対的に移動し、反射率または透過率の異なる領域が規則的に形成された移動スケールと、この移動スケールの一部を照射するための面発光半導体レーザ光源と、前記移動スケールからの反射光または透過光を受光するための受光素子を具備することを特徴とする光学式エンコーダ。
【００５１】
（作用）この発明においては、面発光半導体レーザ光源から放射された光をスケールに照射し、スケールで反射または透過された光を受光素子により受光し、スケールで反射または透過された光を受光素子により受光し、スケールの変位量を計測する。
【００５２】
（効果）面発光半導体レーザ光源に用いることにより、レーザ光の出射窓の径を広範に設計できるので、レンズや固定スリットを必ずしも必要とせずに所定の分解能をもったエンコーダを実現できる。特に、スケールピッチの細かいエンコーダをレンズを省略して実現することができるため、高分解能な光学式エンコーダの小型化や製作の簡略化、低コスト化が可能となる。
【００５３】
２．
（構成）前記面発光半導体レーザ光源と前記移動スケールは、前記面発光半導体レーザ光源から出射するレーザビームが、レンズや固定スリット等のビーム成形のための光学部品を介さないで、直接、移動スケールを照射するように配置されている前記１．記載の光学式エンコーダ。
【００５４】
（作用）この発明においては、面発光半導体レーザ光源から放射された光をスケールに照射し、スケールで反射または透過された光を受光素子により受光し、スケールで反射又は透過された光を受光素子により受光し、スケールの変位量を計測する。
【００５５】
（効果）レンズや固定スリットを必要とせずに所定の分解能をもったエンコーダを実現できるため、高分解能な光学式エンコーダの小型化や製作の簡略化、低コスト化が可能となる。
【００５６】
３．
（構成）光源に対して相対的に移動し、反射率または透過率の異なる領域が規則的に形成された移動スケールと、この移動スケールの一部を照射するための面発光半導体レーザ光源と、前記移動スケールからの反射光または透過光を受光するための受光素子を具備する光学式エンコーダにおいて、
前記移動スケールと面発光半導体レーザ光源の光ビーム出射面とのレーザ光の出射の中心軸上における距離をＬ、光ビームの波長をλ、スケールピッチをｐ、前記移動スケール面上でスケールのピッチ方向をＰ、前記移動スケール面上でピッチ方向Ｐと垂直な方向をＱ、レーザ光出射方向に垂直な平面と前記方向Ｐ，Ｑのなす角をそれぞれθ，ψ、スケールのピッチ方向Ｐをレーザ光出射方向に垂直な平面に投影した方向の前記光源の開口長をａとしたとき、Ｌ≧ａ^２ ／λの場合に、
ｐ・ｃｏｓθ≧λ・Ｌ／ａ
（但し、−π／２＜θ＜π／２、−π／２＜ψ＜π／２）
の関係を満たすことを特徴とする光学式エンコーダ。
【００５７】
（作用）この発明においては、面発光半導体レーザ光源から放射された光をスケールに照射し、スケールで反射または透過された光を受光素子により受光し、スケールの変位量を計測する。
【００５８】
（効果）Ｌ≧ａ^２ ／λの場合に、面発光半導体レーザ光源を用いることにより、レーザ光の出射窓の径を広範に設計できるので、レンズや固定スリットを必ずしも必要とせずに所定の分解能をもったエンコーダを実現できる。特に、スケールピッチの細かいエンコーダをレンズを省略して実現することができるため、高分解能な光学式エンコーダの小型化や製作の簡略化、低コスト化が可能となる。
【００５９】
４．
（構成）光源に対して相対的に移動し、反射率または透過率の異なる領域が規則的に形成された移動スケールと、この移動スケールの一部を照射するための面発光半導体レーザ光源と、前記移動スケールからの反射光または透過光を受光するための受光素子を具備する光学式エンコーダにおいて、
前記移動スケールと面発光半導体レーザ光源の光ビーム出射面とのレーザ光の出射の中心軸上における距離をＬ、光ビームの波長をλ、スケールピッチをｐ、前記移動スケール面上でスケールのピッチ方向をＰ、前記移動スケール面上でピッチ方向Ｐと垂直な方向をＱ、レーザ光出射方向に垂直な平面と前記方向Ｐ，Ｑのなす角をそれぞれθ，ψ、スケールのピッチ方向Ｐをレーザ光出射方向に垂直な平面に投影した方向の前記光源の開口長をａとしたとき、Ｌ＜ａ^２ ／λの場合に、
ｐ・ｃｏｓθ≧ａ
（但し、−π／２＜θ＜π／２、−π／２＜ψ＜π／２）
の関係を満たすことを特徴とする光学式エンコーダ。
【００６０】
（作用）この発明においては、面発光半導体レーザから放射された光をスケールに照射し、スケールで反射または透過された光を受光素子により受光し、スケールの変位量を計測する。
【００６１】
（効果）Ｌ＜ａ^２ ／λの場合に、面発光半導体レーザ光源を用いることにより、レーザ光の出射窓の径を広範に設計できるので、レンズや固定スリットを必ずしも必要とせずに所定の分解能をもったエンコーダを実現できる。特に、スケールピッチの細かいエンコーダをレンズを省略して実現することができるため、高分解能な光学式エンコーダの小型化や製作の簡略化、低コスト化が可能となる。
【００６２】
５．
（構成）光源に対して相対的に移動し、反射率または透過率の異なる領域が規則的に形成された移動スケールと、この移動スケールの一部を照射するための面発光半導体レーザ光源と、前記移動スケールからの反射光または透過光を受光するための受光素子を具備する光学式エンコーダにおいて、
前記移動スケールと面発光半導体レーザ光源の光ビーム出射面とのレーザ光の出射の中心軸上における距離をＬ、光ビームの波長をλ、互いに異なる特定方向のスケールピッチを各々ｐ_ｘ ，ｐ_ｙ 、レーザ光の出射方向に垂直な平面と前記２つの特定方向のなす角をθ_ｘ ，θ_ｙ 、前記移動スケールの各々のピッチ方向に対する前記光源の開口長を各々ａ_ｘ ，ａ_ｙ としたとき、
Ｌ≧ａ_ｘ ^２ ／λの場合に、ｐ_ｘ ・ｃｏｓθ_ｘ ≧λ・Ｌ／ａ_ｘ 、
Ｌ≧ａ_ｙ ^２ ／λの場合に、ｐ_ｙ ・ｃｏｓθ_ｙ ≧λ・Ｌ／ａ_ｙ 、
Ｌ＜ａ_ｘ ^２ ／λの場合に、ｐ_ｘ ・ｃｏｓθ_ｘ ≧ａ_ｘ 、
Ｌ＜ａ_ｙ ^２ ／λの場合に、ｐ_ｙ ・ｃｏｓθ_ｙ ≧ａ_ｙ
（但し、−π／２＜θ_ｘ ＜π／２、−π／２＜θ_ｙ ＜π／２）
の関係を満たすことを特徴とする光学式エンコーダ。
【００６３】
（作用）この発明においては、面発光半導体レーザ光源から放射された光を、反射率または透過率の異なる２次元的なパターンを形成したスケールに照射し、スケールで反射または透過された光を受光素子により受光し、スケールの変位量を２次元的に計測する。
【００６４】
（効果）面発光半導体レーザ光源を用いることにより、レーザ光の出射窓の径を広範に設計できるので、レンズや固定スリットを必ずしも必要とせずに所定の分解能をもったエンコーダを実現できる。特に、スケールピッチの細かいエンコーダをレンズを省略して実現することができるため、高分解能な光学式エンコーダの小型化や製作の簡略化、低コスト化が可能となる。
【００６５】
６．
（構成）前記面発光レーザ光源が基板上に部分的に形成された傾斜面上に配置されていることを特徴とする前記１．〜前記５．いずれか記載の光学式エンコーダ。但し、基板の傾斜面は、化学エッチング、機械的な切削加工など、どのような方法によって形成してもよい。
【００６６】
（作用）こうした構成の光学式エンコーダにおいては、薄膜表面から光が放射される構造の半導体光源が基板上に部分的に形成された傾斜面に設置されており、この光源から放射した光をスケールに反射させ、その反射光を、受光素子により受光する。
【００６７】
（効果）従って、基板をスケールに対して平行に配置することができ、エンコーダ全体の厚さを薄くすることができる。
７．
（構成）前記受光素子が光源から放射された光のスケールによる反射光の０次回折光を受光する位置に配置されていることを特徴とする前記１．〜前記６．いずれか記載の光学式エンコーダ。
【００６８】
（作用）こうした構成の光学式エンコーダにおいては、薄膜表面から光が放射される構造の半導体光源が基板上に部分的に形成された傾斜面に設置されており、この光源から放射した光をスケールに反射させ、その０次回折光を受光素子により受光する。
【００６９】
（効果）従って、０次回折光を受光することにより、スケールのピッチ精度、反射率精度などに依存しない許容度の大きい信号検出ができる。
８．
（構成）光源からの出射光のビーム形状がスケールの移動方向に対して垂直な方向に主軸を持つ楕円形または長方形となっていることを特徴とする前記１．〜前記７．いずれか記載の光学式エンコーダ。
【００７０】
（作用）こうした構成の光学式エンコーダにおいては、光源から放射した楕円形の放射光をスケールに反射させ、その反射光を、受光素子により受光する。
（効果）従って、スケールの分解能を落とすことなく信号光量を増やすことができ、Ｓ／Ｎ比の良い信号検出ができる。
【００７１】
【発明の効果】
以上詳述した如くこの発明によれば、従来必要としたレンズや固定スリットを省略して極めて小形，薄型で部品点数を少なくできるとともに、光源とレンズの光学的な調整の手間がなく極めて低コストで生産でき、更には構成の若干の変形で簡単に移動方向の判別機能を付け加えることができる信頼性の高い光学式エンコーダを提供できる。
【図面の簡単な説明】
【図１】従来の光学式エンコーダの説明図。
【図２】従来の他の光学式エンコーダの説明図。
【図３】面発光レーザの構造を示す模式図。
【図４】リニアスケールを用いた場合の光学式エンコーダの説明図。
【図５】ロータリースケールを用いた場合の光学式エンコーダの説明図。
【図６】リニアスケールを用いた、図４のエンコーダとは異なる他の光学式エンコーダの説明図。
【図７】この発明の光学式エンコーダの構造を示す模式図。
【図８】本発明に係る、図７の光学式エンコーダとは異なる他の光学式エンコーダの構造を示す模式図を示し、図８（Ａ）は正面図、図８（Ｂ）は側面図。
【図９】リニアスケール上の光強度分布図。
【図１０】スケールピッチに対するスケール反射率の特性図で、図１０（Ａ）はスケールピッチ（ｐ）が２０μｍの場合、図１０（Ｂ）はｐ＝１５μｍの場合、図１０（Ｃ）はｐ＝１０μｍの場合。
【図１１】スケールピッチに対する受光量の特性図で、図１１（Ａ）はｐ＝が２０μｍの場合、図１１（Ｂ）はｐ＝１５μｍの場合、図１１（Ｃ）はｐ＝１０μｍの場合。
【図１２】スケールピッチｐと信号振幅の関係を示す図。
【図１３】エンコーダの成立する範囲を示す図。
【図１４】移動スケールと面発光半導体レーザの光ビーム出射面との距離Ｌとスケールピッチとの関係を示す特性図であり、図１４（Ａ）は光ビームの波長λ：１μｍ，光源の開口長ａ：５μｍの場合、図１４（Ｂ）はλ：１μｍ，ａ：１０μｍの場合、図１４（Ｃ）はλ：１μｍ，ａ：１５μｍの場合。
【図１５】この発明の実施例１に係る光学式エンコーダの説明図であり、図１５（Ａ）は側面図、図１５（Ｂ）は斜視図。
【図１６】この発明の実施例２に係る光学式エンコーダの説明図であり、図１６（Ａ）は側面図、図１６（Ｂ）は斜視図。
【図１７】この発明の実施例３に係る光学式エンコーダの斜視図。
【図１８】この発明の実施例４に係る光学式エンコーダの斜視図。
【図１９】受光される信号を計算したグラフ。
【図２０】この発明の実施例５に係る光学式エンコーダの説明図。
【符号の説明】
３１…活性層（発光層）、
３２…多層薄膜ミラー、
３３…上部電極、
３４…下部電極、
４１…面発光レーザ、
４２，５１，１３５ ，１８１ …スケール、
４３，４３_１ ，４３_２ …光検出器、
１３１ …凹部、
１３２ …誘電体基板、
１３３ …面発光レーザ、
１３４ ，１３４ａ，１３４ｂ…受光素子、
１３５ …リニアスケール、
１４１ …傾斜台座。[0001]
[Industrial applications]
The present invention relates to an optical encoder used for detecting a moving amount of a movable portion of a device.
[0002]
[Prior art]
Conventional optical encoders are composed of components such as a light source such as a semiconductor laser, a photodetector (or light receiving element), a diffraction grating, a collimator lens (or a condensing lens), and have a structure that is difficult to miniaturize. I was Such examples include, for example, JP-A-61-42677 and "Nikkei Mechanical, 1988.7.25, p.54", each of which is shown in FIGS.
[0003]
(1) Japanese Patent Application No. 61-42677 (see Fig. 1)
Light emitted from the laser 1 is converted into parallel light by the collimator lens 2 and is incident on the diffraction grating 4 that moves through the beam splitter 3. The light diffracted by the diffraction grating 4 is reflected by the mirrors 5 and 5 ', overlapped again by the beam splitter 3 and detected by the photodetector 6, and the amount of movement of the diffraction grating 4 can be known from the intensity change. . However, this configuration requires many members such as the laser 1, the collimator lens 2, and the beam splitter 3 as shown in FIG. 1, and the whole encoder becomes considerably large in size, which is not suitable for being incorporated in a small device or the like.
[0004]
Although a diffraction grating is used for the scale in FIG. 1, an encoder that detects only lightness and darkness of the scale using a scale in which high-reflectance portions and low-reflectance portions are alternately arranged without using a diffraction effect is also known. Also known as In this case, since the pitch of the scale cannot be made too small, the resolution as an encoder is reduced, but the mirrors 5 and 5 'for interference are not required, and the size can be reduced. However, also in this case, when a normal stripe type semiconductor laser is used as the light source, the collimator lens is an essential member and cannot be omitted conventionally.
[0005]
(2) "Nikkei Mechanical, 1988.7.25, p.54" (see FIG. 2)
The light beam emitted from the light source 21 is shaped into a parallel beam by the collimator lens 2, passes through the fixed scale 22 and the moving scale 23 having the same scale pitch as this, and reaches the light receiving unit 24. When the moving scale is displaced, the degree of overlap between the fixed scale and the permeable portion of the moving scale changes. Therefore, the light receiving section can measure the amount of displacement by utilizing the fact that the output signal changes in accordance with the amount of movement.
[0006]
As described above, in the configuration shown in FIG. 1, the beam splitter, the lens, the mirror, and the like need to be arranged, and in the configuration shown in FIG. 2, the lens and the two scales need to be arranged with high spatial precision. Therefore, it is difficult to manufacture, the size must be large, and the cost is high.
[0007]
[Problems to be solved by the invention]
As described above, the encoder according to the related art has a problem that it is difficult to miniaturize the encoder because a general semiconductor laser of an edge emission type is used.
The present invention has been made in view of such circumstances, and has as its object to provide an optical encoder that can be reduced in size.
[0008]
[Means for Solving the Problems]
The present invention relates to a moving scale that moves relatively to a light source and has regions having different reflectances or transmittances regularly formed, and a surface-emitting semiconductor laser light source for irradiating a part of the moving scale. An optical encoder comprising a light receiving element for receiving reflected light or transmitted light from the moving scale,
The distance on the central axis of laser light emission between the moving scale and the light beam emitting surface of the surface emitting semiconductor laser light source on the central axis is L, the wavelength of the light beam is λ, the scale pitch is p, and the pitch of the scale on the moving scale surface The direction is vector P (hereinafter, vector P is simply referred to as P), the angle between the plane perpendicular to the laser light emission direction and the direction P is θ, and the pitch direction P of the scale is the plane perpendicular to the laser light emission direction. When the aperture length of the light source in the direction projected to is a,
When L ≧ a ² / λ,
p · cos θ ≧ λ · L / a
When L <a ² / λ,
p · cos θ ≧ a
(However, -π / 2 <θ <π / 2, -π / 2 <ψ <π / 2) it is an optical encoder characterized by satisfying the relationship (hereinafter, the light receiving element and the photodetector be described as a synonym).
[0009]
Further, the distance L on the central axis of the laser beam emission between the moving scale and the light beam emission surface of the surface emitting semiconductor laser light source on the center axis, the wavelength of the light beam is λ, and the scale pitches in different specific directions are p _x , respectively . p _y, the angle between a plane perpendicular said two specific direction to the outgoing direction of the laser beam theta _x, theta _y, respectively a _x an opening length of the light source with respect to the pitch direction of each of said movable _scale, and a _y When
When L ≧ a _x ² / λ,
_{p · cosθ x ≧ λ · L} / a x
When L ≧ a _y ² / λ,
p · cos θ _y ≧ λ · L / a _{y
(However, -π / 2 <θ x <} π / 2, -π / 2 <θ y <π / 2) is an optical encoder and satisfies the relationship.
[0010]
Further, the distance on the central axis of laser light emission between the moving scale and the light beam emission surface of the surface-emitting semiconductor laser light source on the central axis is L, the wavelength of the light beam is λ, and the scale pitches in different directions from each other are p _x , p _y, the angle between a plane perpendicular said two specific direction to the outgoing direction of the laser beam theta _x, theta _y, respectively a _x an opening length of the light source with respect to the pitch direction of each of said movable _scale, and a _y When
In the case of L _<a ^{x 2} / λ,
p · cos θ _x ≧ a _x
When L <a _y ² / λ,
p · cos θ _y ≧ a _{y
(However, -π / 2 <θ x <} π / 2, -π / 2 <θ y <π / 2) is an optical encoder and satisfies the relationship.
[0011]
[Action]
In the present invention, light emitted from a semiconductor light source having a structure in which light is emitted from a thin film surface is reflected (or transmitted) on a scale, and the reflected light (or transmitted light) is received by a light receiving element (the aperture shape of the light source). The conditions that should be met are described in detail in the Examples section). Here, the “substrate” may be either a dielectric substrate or a semiconductor substrate.
[0012]
By using a surface emitting laser light source as a light source, it is possible to appropriately design the size and shape of the beam exit window of several μm or several hundred μm. Therefore, a sharp beam can be emitted from the beam exit window of several μm or several hundred μm by controlling the beam divergence angle, so that the collimator lens as shown in FIGS. 1 and 2 can be omitted. . In addition, by using the narrow and sharp beam of the surface emitting laser light source, the beam can be spatially narrowed with respect to the moving scale. Therefore, a fixed scale is not always necessary as in the example of FIG. There is no need for highly accurate placement and holding of the moving scale. Further, a high-resolution encoder can be realized by detecting the brightness of reflected light or transmitted light from a scale using a thin and sharp beam of a surface emitting laser light source.
[0013]
As a result, an extremely small, thin, and simple configuration can realize a high-resolution encoder. Further, since a lens and many other optical components are not required, the trouble of optically adjusting the optical components from the light source to the light receiving element is simplified, and an extremely low-cost encoder can be realized.
[0014]
【Example】
Embodiments will be described below, but before that, the principle of the invention common to each embodiment will be described. FIG. 3 is a diagram showing an example of the structure of a surface emitting laser used as a light source in this embodiment. As shown in the figure, a multilayer thin-film mirror 32 is formed at both ends with an active layer (light-emitting layer) 31 interposed therebetween, and the upper and lower electrodes 33 and 34 sandwich this. When a voltage is applied between the upper electrode 33 and the lower electrode 34, a current is injected into the active layer 31, and the active layer 31 emits light. Since the resonator is formed in the film thickness direction by the active layer 31 and the multilayer thin film mirror 32, oscillation occurs in this direction, and light is emitted in a direction perpendicular to the film plane as shown in the figure (light is emitted). The upper electrode is removed only at the portion where the light is applied.) As a material for realizing these structures, for example, GaAs is used for the active layer 31, and a p-type or n-type GaAs / AlGaAs laminated film is used for the multilayer thin film mirror 32.
[0015]
An advantage of the laser having this structure is that the shape of the opening (light emission port) can be freely designed by patterning the upper electrode. Since the beam spread of the radiated light is determined by the shape and size of the aperture (diffraction occurs due to the aperture and beam spread occurs), the beam spread can be suppressed to a relatively small value by appropriately designing the aperture. Therefore, if the encoder is configured using a suitably designed surface emitting laser as a light source, the collimator lens (or condensing lens) used in the conventional example becomes unnecessary and an extremely small encoder can be realized.
[0016]
The encoder having such a configuration will be described below based on a specific calculation example. FIG. 2 shows a configuration diagram in the case where an encoder is configured by using a surface emitting laser and omitting a collimator lens. As shown in FIG. 4, the beam emitted from the surface emitting laser 41 is reflected (or transmitted) by the linear scale 42, it is received by the light receiving element of the reflective (or transmissive) optical detector 43 1 light _(or 43 _2). Here, the term “scale” refers to a member in which portions having a large reflectance (or transmittance) and portions having a small reflectance (or transmittance) are alternately and regularly arranged. Such a member can be easily realized, for example, by depositing a thin film of high reflectivity such as Al on a glass substrate and patterning the thin film using lithography technology.
[0017]
Incidentally, in the above configuration, the light detector 43 ₂ for detecting the transmitted light from the light detector 43 ₁ and the scale for detecting the reflected light from the scale operates as an encoder, if one at least one of the following In the embodiment, the case of the reflection type will be described. However, the present invention is not limited to this, and the encoder can be configured in the case of the transmission type with the same configuration.
[0018]
FIG. 4 shows a case where a linear scale is used as the scale. However, as shown in FIG. 5, the rotation of the object can be measured using a rotary scale 51 which rotates relatively to the light source. In the following embodiments, a case where a linear scale is used will be described, but the present invention is not limited to this, and a configuration using a rotary scale with a similar configuration is also possible.
[0019]
Further, FIG. 4, FIG. 5, the light receiving surface of the photodetector 43 _1, 43 ₂ with respect to a plane perpendicular to the incident direction of the light beam, respectively, theta _1, but are arranged inclined by theta ₂ This is to suppress fluctuations in sensor output due to feedback of light reflected from the light receiving surface of the photodetector to the surface emitting laser, that is, fluctuations in output due to return light. Therefore, when the effect of the return light from the light receiving surface is small with respect to the sensor output, for example, when a non-reflection film (or a low reflection film) is formed on the light receiving surface, θ ₁ ≠ 0, θ ₂ ≠ 0. You don't have to.
[0020]
As described above, FIG. 4 shows the case where θ ≠ 0 and ψ = 0, but FIG. 6 shows the case where θ = 0 and ψ ≠ 0. This figure posture with respect to the surface emitting laser 41 of the linear scale 42 are different (the theta, expressed in [psi), and a photodetector 43 _1, and 43 ₂ of the light-receiving surface and the light beam incident direction perpendicular to the plane It is the same as FIG. 4 except that the inclination angles are defined as ψ ₁ and ψ _2, and the description of the configuration and the like is omitted.
[0021]
On the other hand, the intensity distribution of light applied to the linear scale is defined by the shape of the opening of the surface emitting laser and the distance between the linear scale and the opening, as described above. As shown in FIG. 7, P represents the pitch direction of the scale on the moving scale surface, Q represents the direction perpendicular to the pitch direction P on the moving scale surface, and represents the plane perpendicular to the laser light emitting direction and the directions P and Q. The angles formed are θ and ψ (where 、 = 0), the laser aperture length in the direction in which the pitch direction P of the linear scale 42 is projected on a plane perpendicular to the laser light emitting direction is a, and the distance between the laser and the linear scale 42 is Assuming that the distance on the central axis of laser light emission is L and the laser wavelength is λ, if L is sufficiently larger than a (preferably, L ≧ a ² / λ), the laser beam on the scale The beam diameter W (full width at half maximum) in the P direction is approximately given by the following equation (1).
[0022]
(Equation 1)

On the other hand, when L <a ² / λ, it is approximately given by the following equation (2).
[0023]
(Equation 2)

In order to detect the brightness of the reflection (or transmission) of the light beam on the scale with a good signal amplitude (the difference between the maximum value and the minimum value in the output signal waveform indicating the amount of received light is defined as the signal amplitude), it is necessary to use the scale. The pitch p is preferably larger than the beam diameter W in the P direction. Therefore, to obtain an output signal with a large signal amplitude,
When L ≧ a ² / λ, the following equation (3) is used: p · cos θ ≧ λ · L / a (3)
(However, -π / 2 <θ <π / 2, ψ = 0)
When L <a ² / λ, the following equation (4): p · cos θ ≧ a (4)
(However, -π / 2 <θ <π / 2, ψ = 0)
It is desirable that
[0024]
As described above, FIG. 7 shows the case where θ ≠ 0 and ψ = 0, but FIG. 8 shows the case where θ = 0 and ψ ≠ 0. The other various definitions are the same as those for FIG. 7, and thus are omitted here. In the case of this drawing, the beam diameter W (full width at half maximum) of the laser beam on the scale in the P direction is constant irrespective of ψ (see the front view of FIG. 8 (A)). Is large (desirably, in the range of L ≧ a ² / λ), W is approximately given by the following equation (5).
[0025]
(Equation 3)

On the other hand, when L <a ² / λ, it is approximately given by the following equation (6).
[0026]
(Equation 4)

[0027]
As in the case of FIG. 7, in order to obtain an output signal having a large signal amplitude, it is desirable that the pitch p of the scale is larger than the beam diameter W in the P direction. Therefore, when L ≧ a ² / λ, the following equation (7) is obtained.
p ≧ λ · L / a (provided that θ = 0, −π / 2 <ψ, π / 2) (7)
When L <a ² / λ, the following equation (8) is desirable.
[0028]
p ≧ a (however, θ = 0, −π / 2 <ψ, π / 2) (8)
As described above, when θ = 0 and ψ ≠ 0, it can be seen that the expressions (5) to (8) hold regardless of the value of ψ.
[0029]
Although not shown, since θ に つ い て 0 and ψ ≠ 0 do not depend on the value of ψ as shown in the example of FIG. 8, the equations (1) to (4) are based on the values of θ and ψ. It can be said that it holds.
[0030]
Although the above is a rough estimate, FIG. 9 shows a strict calculation example of the light intensity distribution on the scale surface using diffraction integration. When the L is large (L ≧ a ² / λ), the light intensity distribution | A | ² of the plane wave emitted from the emission window of the light source having the aperture length a is represented by a pupil function corresponding to the emission window. Expression (9) shown in the following Expression 5 is obtained by performing a Fourier transform.
[0031]
(Equation 5)

However, the center of the output beam is set as the origin of x, and the x-axis is considered parallel to the output surface. C is a constant independent of x.
[0032]
FIG. 9 is a calculation based on the wavelength λ = 1 μm, the aperture width a = 10 μm, and the distance L between the scale and the aperture L = 100 μm (the vertical axis is normalized as C = 1). The light amount profile is as shown in the figure (the angle θ between the linear scale and the aperture is assumed to be small and is ignored in the calculation. In the subsequent calculations, the case of θ = 0 will be described. , Θ ≠ 0, the pitch p may be replaced with p · cos θ.)
The amount of reflected light when this spot hits the linear scale can be obtained by integrating the product of the linear scale reflectance distribution and the spot intensity distribution on the x-axis. Large enough). The reflectance distribution of the linear scale is expressed by a Fourier series for calculation, and the signal light amount obtained by the photodetector when this scale moves at 10 μm / s in the direction of the arrow is shown in FIGS. 10 and 11. . Here, FIG. 10 shows the scale reflectance distribution, and FIG. 11 shows the amount of light received by the detector.
[0033]
This is the result of calculation for the scale pitch p = 20, 15, and 10 μm. A periodic signal corresponding to the pitch is obtained, and the relationship between the signal waveform and the displacement amount is used (for example, the period of this signal Or the amount of displacement of the scale can be measured (eg, by electronically converting the signal to a displacement signal).
[0034]
As the pitch becomes finer, the signal amplitude (the difference between the output signal in the case of 100% reflection from the scale and the output signal in the case of no reflection) is normalized to 1 becomes smaller. Under the conditions of FIGS. 10 and 11, the beam diameter W is approximately W = 10 μm on the scale according to the expressions (1) and (2). However, the results shown in FIGS. It can be seen that a signal amplitude of about 0.1 or more can be obtained in the range of ≧ W, and this is considered to be a guideline for designing the signal amplitude of the output signal of the encoder to a certain value or more.
[0035]
FIG. 12 shows a change in signal amplitude with respect to the scale pitch p. The circles in the figure correspond to each p in FIG. When p = 10, the lower limit of the condition of the conditional expression (3) is satisfied (p = Lλ / a is satisfied). In this case, as can be seen from the figure, the signal amplitude is about 1/10 of the total light amount, and in the following description, this state (the signal amplitude becomes 0.1) is regarded as the lower limit of the practical signal amplitude. . When the S / N ratio of the photodetector is high, it can be used even if the signal amplitude is 0.01. From this result, it can be seen that the condition of the equation (3) based on the above estimation is extremely appropriate.
[0036]
Further, when L <a ² / λ, the beam diameter W is approximately a, so that the output signal has a good S / N when the encoder specification is given. Is given by the above equations (3) and (4). FIG. 13 shows the range of the aperture length a for the signal amplitude to be 0.1 or more, assuming that the scale pitch is p ≦ 30 μm under the conditions of λ = 1 μm and L = 100 μm. In FIG. 14, as an example, when λ = 1 μm, a = 5 μm, 10 μm, and 15 μm are given, it is assumed that the scale pitch p is used at 30 μm or less (the signal amplitude becomes 0.1 or more). Desirable ranges of p and L are indicated by oblique lines for each a. As described above, by using the surface emitting semiconductor laser as the light source, the diameter a of the emission window of the laser light can be designed in a wide range. Therefore, the appropriate structural parameters of L, λ, p, a are determined as described above. Thus, an encoder having a predetermined resolution can be realized. In particular, since an encoder with a fine scale pitch can be realized by omitting the lens, it is possible to reduce the size of the high-resolution optical encoder and to simplify the production.
[0037]
(Example 1)
Referring to FIGS. 15A and 15B. Here, FIG. 15A is a side view of the optical encoder, and FIG. 15B is a perspective view. As shown in FIG. 15, a surface emitting laser (light emitting element) 133 and a light receiving element 134 are separately bonded on a dielectric substrate 132 in which a concave portion 131 is partially formed. Is placed on top. Reference numeral 135 in the figure is a linear scale.
[0038]
Next, the operation of the optical encoder according to the first embodiment will be described. The light emitted from the surface emitting laser 133 is reflected by the linear scale 135, and the zero-order diffracted light (that is, the reflected light) is received by the light receiving element 134. As described above, the surface emission laser can suppress the spot spread to some extent by appropriately selecting the size of the aperture and the like, and therefore, a high-resolution encoder without a collimator lens for beam shaping as in the past. Can be configured. In FIG. 15, the scale moving direction and the pitch direction are indicated by directions parallel to the plane of the paper, but they may be perpendicular to the plane of the paper. The degrees of freedom in the moving direction and pitch direction of the scale are the same in other embodiments of the present invention.
[0039]
Therefore, the following effects are obtained.
The number of parts is reduced, and a low-cost, compact and thin encoder can be realized. Further, the substrate and the scale can be arranged in parallel, and the entire encoder can be reduced in size. Further, by receiving the 0th-order diffracted light, signal detection with a large tolerance that is less dependent on the scale pitch accuracy, the reflectance accuracy, and the like can be performed as compared with the case of receiving the higher-order diffracted light. In the first embodiment, the light receiving element and the light emitting element are arranged on the dielectric substrate. However, the substrate is not limited to the dielectric, and a semiconductor may be used.
[0040]
When a semiconductor substrate is used, the light-receiving element or the light-emitting element can be integrally formed on the substrate, so that there is an effect that the process of newly joining the element to the substrate can be omitted and the manufacturing process can be simplified. Further, if a signal processing circuit is formed in a semiconductor substrate, further downsizing including a circuit system can be achieved.
[0041]
As described above, in the first embodiment, the configuration is such that the concave portion is provided in a part of the substrate and the light emitting element is disposed obliquely on the slope, but a flat substrate may be used.
(Example 2)
This will be described with reference to FIGS.
[0042]
In the second embodiment, a light-emitting element 133 and a light-receiving element 134 are formed on the surface of a substrate similar to the first embodiment except that a flat dielectric substrate 132 having no concave portion is used. This substrate is mounted on the inclined pedestal 141 as shown in FIG. 16 and is arranged obliquely with respect to the linear scale 135. Light emitted from the light emitting element 133 is reflected by the linear scale 135 and received by the light receiving element 134. In the case of the second embodiment, since a flat substrate is used, there is an effect that the step of forming a concave portion in the substrate can be omitted as compared with the first embodiment.
[0043]
Also in this case, a semiconductor substrate may be used as in the first embodiment. In this case, a light receiving element and a light emitting element may be integrally formed by using a compound semiconductor as a substrate and growing a crystal on the surface by a vapor phase growth method.
[0044]
It is to be noted that each configuration of the first and second embodiments can of course be variously modified and changed. A possible modification common to the first and second embodiments is shown in FIG. 17 as a third embodiment.
(Example 3)
FIG. 17 shows an example in which the opening 133a of the surface emitting laser light source 133 has an elliptical shape. If a signal having a sufficient S / N ratio cannot be expected from the circular aperture, the signal light amount can be increased and the S / N ratio can be improved without lowering the resolution of the scale by such a method. Although the elliptical opening is used in the third embodiment, the same effect can be expected with a rectangular opening. FIG. 17 is a diagram corresponding to the first embodiment, but the same modification can be applied to the second embodiment.
[0045]
In the embodiments described above, only the scale movement amount is detected and the moving direction cannot be determined. However, a function of determining the moving direction can be easily added with a slight modification of the configuration. Such an example is shown below as Example 4 in FIG.
[0046]
(Example 4)
FIG. 18 shows the configuration of the fourth embodiment. The fourth embodiment differs from the first embodiment in that the light receiving element 134 is divided into two parts 134a and 134b. By dividing the light receiving element into two parts with a certain gap, the phase of the signal light incident on the light receiving element can be shifted by π / 2 as shown in FIG. The phase of the signal incident on the light receiving element 134b with respect to the signal incident on the light receiving element 134a is advanced by π / 2 when the scale moves rightward in the drawing, and delayed by π / 2 when the scale moves leftward. Therefore, the direction of movement can be determined by determining the phase relationship between the two by signal processing. Note that the phase difference between these two signals does not necessarily need to be set to π / 2, and if the phase difference is a constant value that does not become nπ (here, n = 0, ± 1, ± 2...). It is possible to determine the direction of movement.
[0047]
Further, such a direction discriminating function is not limited to one dimension, but can be easily extended to two dimensions by dividing the light receiving element into four parts. In the fourth embodiment, the same modifications as those in the first to third embodiments can be applied to the substrate material and the spot shape.
[0048]
In the embodiments described above, only one-dimensional displacement of the scale can be detected, but two-dimensional displacement can be detected by slightly changing the configuration. This is shown in FIG. 20 as Example 5 below.
[0049]
(Example 5)
The scale 181 on which a two-dimensional pattern having different reflectance or transmittance is formed is irradiated with a beam from the surface emitting semiconductor laser light source, and the reflected light or transmitted light at this time is received by the light receiving element 43 ₁ or the light receiving element received by 43 _2. The distance between the moving scale and the light beam emission surface of the surface emitting semiconductor laser light source is L, the wavelength of the light beam is λ, and the scale pitches in specific directions different from each other are p _x and p _y , respectively, and are perpendicular to the laser light emission direction. When angles between the plane and the two specific directions are θ _x and θ _y , and aperture lengths of the light source with respect to each pitch direction of the moving scale are a _x and a _y , respectively,
In the case of _{^{L ≧ a x 2 / λ,}} p x · cosθ x ≧ λ · L / a x,
In the case of _{^{L ≧ a y 2 / λ,}} p y · cosθ y ≧ λ · L / a y,
L _<in the case of _{^{a x 2 / λ, p x}} · cosθ x ≧ a x,
L _<in the case of _{^{a y 2 / λ, p y}} · cosθ y ≧ a y
_{(However, -π / 2 <θ x <} π / 2, -π / 2 <θ y <π / 2)
The signal amplitude of the output from the encoder can be designed to an appropriate level by designing so as to satisfy the relationship. By using the surface emitting semiconductor laser light source, the diameter and shape of the emission window of the laser light can be designed in a wide range, so that an encoder having predetermined resolutions in specific directions different from each other without necessarily requiring a lens can be realized. In addition, since an encoder having a fine scale pitch in a specific direction can be realized by omitting a lens, a high-resolution optical encoder can be reduced in size, simplified in manufacturing, and reduced in cost.
[0050]
Hereinafter, the optical encoder according to the present invention has the following configuration, operation, and effect when summarized.
1.
(Structure) A moving scale relatively moved with respect to the light source and in which regions having different reflectances or transmittances are regularly formed, a surface-emitting semiconductor laser light source for irradiating a part of the moving scale, An optical encoder comprising a light receiving element for receiving reflected light or transmitted light from the moving scale.
[0051]
(Function) In the present invention, light emitted from a surface emitting semiconductor laser light source is irradiated on a scale, light reflected or transmitted by the scale is received by a light receiving element, and light reflected or transmitted by the scale is received by a light receiving element. And the displacement of the scale is measured.
[0052]
(Effect) Since the diameter of the emission window of the laser beam can be designed in a wide range by using the surface emitting semiconductor laser light source, an encoder having a predetermined resolution can be realized without necessarily requiring a lens or a fixed slit. In particular, since an encoder with a fine scale pitch can be realized by omitting a lens, it is possible to reduce the size, simplify the production, and reduce the cost of a high-resolution optical encoder.
[0053]
2.
(Structure) The surface-emitting semiconductor laser light source and the moving scale are configured such that a laser beam emitted from the surface-emitting semiconductor laser light source directly moves the laser beam without passing through optical components for beam shaping such as a lens and a fixed slit. 1. The above-described 1. An optical encoder as described.
[0054]
(Function) In the present invention, light emitted from a surface emitting semiconductor laser light source is irradiated on a scale, light reflected or transmitted by the scale is received by a light receiving element, and light reflected or transmitted by the scale is received by a light receiving element. And the displacement of the scale is measured.
[0055]
(Effect) Since an encoder having a predetermined resolution can be realized without requiring a lens and a fixed slit, it is possible to reduce the size, simplify the production, and reduce the cost of a high-resolution optical encoder.
[0056]
3.
(Structure) A moving scale relatively moved with respect to the light source and in which regions having different reflectances or transmittances are regularly formed, a surface-emitting semiconductor laser light source for irradiating a part of the moving scale, An optical encoder including a light receiving element for receiving reflected light or transmitted light from the moving scale,
The distance on the central axis of laser light emission between the moving scale and the light beam emitting surface of the surface emitting semiconductor laser light source on the central axis is L, the wavelength of the light beam is λ, the scale pitch is p, and the pitch of the scale on the moving scale surface The direction is P, the direction perpendicular to the pitch direction P on the moving scale surface is Q, the angle between the plane perpendicular to the laser beam emitting direction and the directions P and Q is θ, ψ, and the scale pitch direction P is laser. Assuming that the aperture length of the light source in the direction projected on the plane perpendicular to the light emission direction is a, when L ≧ a ² / λ,
p · cos θ ≧ λ · L / a
(However, -π / 2 <θ <π / 2, -π / 2 <ψ <π / 2)
An optical encoder characterized by satisfying the following relationship:
[0057]
(Operation) In the present invention, light emitted from a surface emitting semiconductor laser light source is irradiated on a scale, and light reflected or transmitted by the scale is received by a light receiving element, and the displacement of the scale is measured.
[0058]
(Effect) In the case of L ≧ a ² / λ, by using a surface emitting semiconductor laser light source, the diameter of the emission window of the laser light can be designed in a wide range, so that a predetermined resolution can be obtained without necessarily using a lens or a fixed slit. Can be realized. In particular, since an encoder with a fine scale pitch can be realized by omitting a lens, it is possible to reduce the size, simplify the production, and reduce the cost of a high-resolution optical encoder.
[0059]
4.
(Structure) A moving scale relatively moved with respect to the light source and in which regions having different reflectances or transmittances are regularly formed, a surface-emitting semiconductor laser light source for irradiating a part of the moving scale, An optical encoder including a light receiving element for receiving reflected light or transmitted light from the moving scale,
The distance on the central axis of laser light emission between the moving scale and the light beam emission surface of the surface emitting semiconductor laser light source on the central axis is L, the wavelength of the light beam is λ, the scale pitch is p, and the pitch of the scale on the moving scale surface The direction is P, the direction perpendicular to the pitch direction P on the moving scale surface is Q, the angle between the plane perpendicular to the laser beam emitting direction and the directions P and Q is θ, ψ, and the scale pitch direction P is laser. Assuming that the aperture length of the light source in the direction projected on the plane perpendicular to the light emission direction is a, when L <a ² / λ,
p · cos θ ≧ a
(However, -π / 2 <θ <π / 2, -π / 2 <ψ <π / 2)
An optical encoder characterized by satisfying the following relationship:
[0060]
(Operation) In the present invention, light emitted from a surface emitting semiconductor laser is irradiated on a scale, and light reflected or transmitted by the scale is received by a light receiving element, and the displacement of the scale is measured.
[0061]
(Effect) In the case of L <a ² / λ, by using a surface emitting semiconductor laser light source, the diameter of the emission window of laser light can be designed in a wide range, so that a predetermined resolution can be obtained without necessarily using a lens or a fixed slit. Can be realized. In particular, since an encoder with a fine scale pitch can be realized by omitting a lens, it is possible to reduce the size, simplify the production, and reduce the cost of a high-resolution optical encoder.
[0062]
5.
(Structure) A moving scale relatively moved with respect to the light source and in which regions having different reflectances or transmittances are regularly formed, a surface emitting semiconductor laser light source for irradiating a part of the moving scale, An optical encoder including a light receiving element for receiving reflected light or transmitted light from the moving scale,
The distance L on the central axis of laser light emission between the moving scale and the light beam emission surface of the surface emitting semiconductor laser light source on the central axis, the wavelength of the light beam is λ, and the scale pitches in specific directions different from each other are p _x and _py. the a plane perpendicular to the emission direction of the laser beam two an angle in a specific direction theta _x, theta _y, respectively a _x an opening length of the light source with respect to the pitch direction of each of said movable _scale, when the a _y ,
In the case of _{^{L ≧ a x 2 / λ,}} p x · cosθ x ≧ λ · L / a x,
In the case of _{^{L ≧ a y 2 / λ,}} p y · cosθ y ≧ λ · L / a y,
L _<in the case of _{^{a x 2 / λ, p x}} · cosθ x ≧ a x,
L _<in the case of _{^{a y 2 / λ, p y}} · cosθ y ≧ a y
_{(However, -π / 2 <θ x <} π / 2, -π / 2 <θ y <π / 2)
An optical encoder characterized by satisfying the following relationship:
[0063]
(Function) In the present invention, light emitted from a surface emitting semiconductor laser light source is irradiated on a scale on which a two-dimensional pattern having different reflectivity or transmittance is formed, and light reflected or transmitted by the scale is received. Light is received by the element, and the displacement of the scale is measured two-dimensionally.
[0064]
(Effect) By using the surface emitting semiconductor laser light source, the diameter of the emission window of the laser light can be designed in a wide range, so that an encoder having a predetermined resolution can be realized without necessarily requiring a lens or a fixed slit. In particular, since an encoder with a fine scale pitch can be realized by omitting a lens, it is possible to reduce the size, simplify the production, and reduce the cost of a high-resolution optical encoder.
[0065]
6.
(Configuration) The surface emitting laser light source is disposed on an inclined surface partially formed on a substrate. ~ 5. The optical encoder according to any of the above. However, the inclined surface of the substrate may be formed by any method such as chemical etching and mechanical cutting.
[0066]
(Operation) In an optical encoder having such a configuration, a semiconductor light source having a structure in which light is emitted from a thin film surface is installed on an inclined surface formed partially on a substrate, and light emitted from this light source is scaled. And the reflected light is received by a light receiving element.
[0067]
(Effect) Therefore, the substrate can be arranged in parallel to the scale, and the thickness of the entire encoder can be reduced.
7.
(Structure) The light receiving element is arranged at a position for receiving the 0th-order diffracted light of the reflected light by the scale of the light emitted from the light source. ~ 6. The optical encoder according to any of the above.
[0068]
(Operation) In an optical encoder having such a configuration, a semiconductor light source having a structure in which light is emitted from a thin film surface is installed on an inclined surface formed partially on a substrate, and light emitted from this light source is scaled. And the zero-order diffracted light is received by the light receiving element.
[0069]
(Effect) Therefore, by receiving the 0th-order diffracted light, it is possible to detect a signal with a large tolerance that does not depend on the pitch accuracy and the reflectance accuracy of the scale.
8.
(Configuration) The beam shape of the light emitted from the light source is an ellipse or a rectangle having a main axis in a direction perpendicular to the moving direction of the scale. ~ 7. The optical encoder according to any of the above.
[0070]
(Operation) In the optical encoder having such a configuration, the elliptical radiated light emitted from the light source is reflected on the scale, and the reflected light is received by the light receiving element.
(Effect) Therefore, the signal light amount can be increased without lowering the resolution of the scale, and a signal with a good S / N ratio can be detected.
[0071]
【The invention's effect】
As described above in detail, according to the present invention, the lens and the fixing slit, which are conventionally required, are omitted, the size and the number of parts are extremely small and thin, and the number of components is reduced. It is possible to provide a highly reliable optical encoder that can be easily manufactured with a slight modification of the configuration and can easily add a function of determining the moving direction.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a conventional optical encoder.
FIG. 2 is an explanatory diagram of another conventional optical encoder.
FIG. 3 is a schematic view illustrating a structure of a surface emitting laser.
FIG. 4 is an explanatory diagram of an optical encoder when a linear scale is used.
FIG. 5 is an explanatory diagram of an optical encoder when a rotary scale is used.
FIG. 6 is an explanatory diagram of another optical encoder that uses a linear scale and is different from the encoder of FIG. 4;
FIG. 7 is a schematic diagram showing the structure of an optical encoder according to the present invention.
8 is a schematic view showing the structure of another optical encoder according to the present invention, which is different from the optical encoder of FIG. 7, FIG. 8 (A) is a front view, and FIG. 8 (B) is a side view.
FIG. 9 is a light intensity distribution diagram on a linear scale.
10A and 10B are characteristic diagrams of the scale reflectance with respect to the scale pitch. FIG. 10A shows a case where the scale pitch (p) is 20 μm, FIG. 10B shows a case where p = 15 μm, and FIG. = 10 μm.
11A and 11B are characteristic diagrams of the amount of received light with respect to a scale pitch. FIG. 11A shows a case where p = 20 μm, FIG. 11B shows a case where p = 15 μm, and FIG. 11C shows a case where p = 10 μm. .
FIG. 12 is a diagram showing a relationship between a scale pitch p and a signal amplitude.
FIG. 13 is a diagram showing a range in which an encoder is established.
FIG. 14 is a characteristic diagram showing a relationship between a distance L between a moving scale and a light beam emission surface of a surface emitting semiconductor laser and a scale pitch, and FIG. FIG. 14B shows a case where λ is 1 μm and a is 10 μm, and FIG. 14C shows a case where λ is 1 μm and a is 15 μm.
15A and 15B are explanatory diagrams of the optical encoder according to the first embodiment of the present invention. FIG. 15A is a side view, and FIG. 15B is a perspective view.
FIG. 16 is an explanatory diagram of an optical encoder according to Embodiment 2 of the present invention. FIG. 16 (A) is a side view, and FIG. 16 (B) is a perspective view.
FIG. 17 is a perspective view of an optical encoder according to Embodiment 3 of the present invention.
FIG. 18 is a perspective view of an optical encoder according to Embodiment 4 of the present invention.
FIG. 19 is a graph showing calculated signals received.
FIG. 20 is an explanatory diagram of an optical encoder according to Embodiment 5 of the present invention.
[Explanation of symbols]
31 ... active layer (light emitting layer),
32 ... Multilayer thin film mirror,
33 ... upper electrode,
34 lower electrode,
41 ... surface emitting laser,
42, 51, 135, 181 ... scale,
43 _1, 43 2 _... photodetector,
131 ... recess,
132 ... dielectric substrate,
133 ... surface emitting laser,
134, 134a, 134b ... light receiving element,
135 ... linear scale,
141 ... inclined base.

Claims (16)

A moving scale that moves relative to the light source and in which regions having different reflectances or transmittances are regularly formed, a surface-emitting semiconductor laser light source for irradiating a part of the moving scale, and the moving scale An optical encoder including a light receiving element for receiving reflected light or transmitted light from
The distance on the central axis of laser light emission between the moving scale and the light beam emitting surface of the surface emitting semiconductor laser light source on the central axis is L, the wavelength of the light beam is λ, the scale pitch is p, and the pitch of the scale on the moving scale surface The direction is vector P (hereinafter, vector P is simply referred to as P), the angle between the plane perpendicular to the laser light emission direction and the direction P is θ, and the pitch direction P of the scale is the plane perpendicular to the laser light emission direction. Let a be the aperture length of the light source in the direction of projection onto the light source, and if L ≧ a ² / λ,
p · cos θ ≧ λ · L / a
(However, the optical encoder satisfies the relationship of -π / 2 <θ <π / 2, -π / 2 <ψ <π / 2) . A moving scale that moves relative to the light source and in which regions having different reflectances or transmittances are regularly formed, a surface-emitting semiconductor laser light source for irradiating a part of the moving scale, and the moving scale An optical encoder including a light receiving element for receiving reflected light or transmitted light from
The distance on the central axis of laser light emission between the moving scale and the light beam emitting surface of the surface emitting semiconductor laser light source on the central axis is L, the wavelength of the light beam is λ, the scale pitch is p, and the pitch of the scale on the moving scale surface The direction is a vector P (hereinafter, the vector P is simply referred to as P), the angle between the plane P perpendicular to the laser light emitting direction and the direction P is θ, and the pitch direction P of the scale is perpendicular to the laser light emitting direction. Assuming that the aperture length of the light source in the direction projected on the plane is a, when L <a ² / λ,
p · cos θ ≧ a
(However, the optical encoder satisfies the relationship of -π / 2 <θ <π / 2, -π / 2 <ψ <π / 2) . A moving scale that moves relative to the light source and in which regions having different reflectances or transmittances are regularly formed, a surface-emitting semiconductor laser light source for irradiating a part of the moving scale, and the moving scale An optical encoder including a light receiving element for receiving reflected light or transmitted light from
The distance L on the central axis of laser light emission between the moving scale and the light beam emission surface of the surface emitting semiconductor laser light source on the center axis, the wavelength of the light beam is λ, and the scale pitches in specific directions different from each other are p _x and _py. the a plane perpendicular to the emission direction of the laser beam two an angle in a specific direction theta _x, theta _y, respectively a _x an opening length of the light source with respect to the pitch direction of each of said movable _scale, when the a _y , in the case of L ≧ _a ^{x 2} / λ,
_{p · cosθ x ≧ λ · L} / a x
_{(However, -π / 2 <θ x <} π / 2, -π / 2 <θ y <π / 2) optical encoder characterized by satisfying the relationship. A moving scale that moves relative to the light source and in which regions having different reflectances or transmittances are regularly formed, a surface-emitting semiconductor laser light source for irradiating a part of the moving scale, and the moving scale An optical encoder including a light receiving element for receiving reflected light or transmitted light from
The distance on the central axis of emission of the laser light L between the movable scale and the surface emitting semiconductor laser light source of the light beam emitting surface, the wavelength of the light beam lambda, each p _x a different specific direction of the scale _pitches, p _y the a plane perpendicular to the emission direction of the laser beam two an angle in a specific direction theta _x, theta _y, respectively a _x an opening length of the light source with respect to the pitch direction of each of said movable _scale, when the a _y , L ≧ a _y ² / λ,
p · cos θ _y ≧ λ · L / a _{y
(However, -π / 2 <θ x <} π / 2, -π / 2 <θ y <π / 2) optical encoder characterized by satisfying the relationship. A moving scale that moves relative to the light source and in which regions having different reflectances or transmittances are regularly formed, a surface-emitting semiconductor laser light source for irradiating a part of the moving scale, and the moving scale An optical encoder including a light receiving element for receiving reflected light or transmitted light from
The distance on the central axis of emission of the laser light L between the movable scale and the surface emitting semiconductor laser light source of the light beam emitting surface, the wavelength of the light beam lambda, each p _x a different specific direction of the scale _pitches, p _y When the angle between the plane perpendicular to the laser light emission direction and the two specific directions is θ _x , θ _y , and the aperture length of the light source with respect to each pitch direction of the moving scale is a _x , a _y , respectively. , in the case of L _<a ^{x 2} / λ,
p · cos θ _x ≧ a _{x
(However, -π / 2 <θ x <} π / 2, -π / 2 <θ y <π / 2) optical encoder characterized by satisfying the relationship. A moving scale that moves relative to the light source and in which regions having different reflectances or transmittances are regularly formed, a surface-emitting semiconductor laser light source for irradiating a part of the moving scale, and the moving scale An optical encoder including a light receiving element for receiving reflected light or transmitted light from
The distance L on the central axis of laser light emission between the moving scale and the light beam emission surface of the surface emitting semiconductor laser light source on the center axis, the wavelength of the light beam is λ, and the scale pitches in specific directions different from each other are p _x and _py. When the angle between the plane perpendicular to the laser light emission direction and the two specific directions is θ _x , θ _y , and the aperture length of the light source with respect to each pitch direction of the moving scale is a _x , a _y , respectively. , L <a _y ² / λ,
p · cos θ _y ≧ a _{y
(However, -π / 2 <θ x <} π / 2, -π / 2 <θ y <π / 2) optical encoder characterized by satisfying the relationship. The optical encoder according to any one of claims 1 to 6, wherein the surface emitting laser light source is disposed on an inclined surface partially formed on a substrate . 8. The light receiving element according to claim 1, wherein the light receiving element is arranged at a position for receiving a zero-order diffracted light of light emitted from the surface emitting laser light source and reflected by the moving scale. Optical encoder. The beam shape of the light emitted from the surface emitting laser light source is an elliptical shape or a rectangular shape having a main axis perpendicular to the moving direction of the moving scale. The optical encoder according to claim 1. 9. The optical encoder according to claim 1, wherein the shape of the opening of the surface emitting laser light source is elliptical or rectangular . The shape of the opening of the surface-emitting laser light source is an ellipse or a rectangle having a main axis in a direction perpendicular to the inclination direction of the inclined surface formed partially on the substrate. The optical encoder according to claim 7, wherein: The surface emitting laser is arranged such that the shape of the opening of the surface emitting laser light source is an ellipse or a rectangle having a main axis in a direction perpendicular to the moving direction of the moving scale. An optical encoder according to claim 10 . The optical encoder according to any one of claims 1 to 6, wherein the substrate having the surface emitting laser light source is disposed on an inclined surface of the inclined pedestal . 14. The optical encoder according to claim 1, wherein a non-reflective film or a low-reflective film is provided on a light receiving surface of the light receiving element . 2. The optical encoder according to claim 1, wherein the light receiving element is divided into at least two parts, and each detects an incident signal light having a phase different by [pi] / 2 . 2. The optical encoder according to claim 1, wherein the light receiving elements are divided into at least four parts and are arranged two-dimensionally, and each detect an incident signal light having a phase different by [pi] / 2 .

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