JP4322978B2 - Optical encoder - Google Patents

Description

【００２１】
と表される。
また、開口と観測点の距離がある程度以上離れている場合には、フレネル（Fresnel ）回折、さらにある程度以上離れている場合にはフランホーファー（Fraunhofer）回折により、ビーム広がりを計算することができ、それぞれ
【００２２】
【数２】

【００２３】
【数３】

【００２４】
と表される。
このように、面発光レーザ出射光の回折パターンは、（１）式〜（３）式を用いて近似的に計算することが可能であり、開口長（出射窓幅）ａ及び観測面と開口との距離ｒなどを考慮して用いる式を選択する。
【００２５】
本実施の形態は、開口から距離が比較的小さい場合について説明するが、一般に、実際のエンコーダにおいては面発光レーザとスケールの間隔を無限に小さくすることはできず、距離ｒには下限が存在し、実用上はフレネル回折の式（２）が成り立つ範囲であると考えられるので、本実施の形態では上記（２）式を用いて計算を行った。
【００２６】
ここで、ｘ軸方向の開口長をａとし、ｙ軸方向には無限大の幅を持つ開口を用いて、そのｘ軸方向の回折パターンを計算する。この場合、ｙ軸方向の積分領域を−∞〜∞とおくと、（２）式より
【００２７】
【数４】

【００２８】
となり、
【００２９】
【数５】

【００３０】
となる。
実際に回折パターンを計算するには数値計算をする必要があるが、
【００３１】
【数６】

【００３２】
【数７】

【００３３】
で表されるフレネル（Fresnel ）積分を使い、
【００３４】
【数８】

【００３５】
として、ｘ軸方向の積分領域を−ａ／２〜ａ／２とすると、
【００３６】
【数９】

【００３７】
となり、光強度分布は
【００３８】
【数１０】

【００３９】
と表される。
この式は、スリットからの距離ｒ、スリット幅ａおよび波長λによってその形を変えるが、
【００４０】
【数１１】

【００４１】
と定義すると、（１０）式におけるフレネル関数の変数は
【００４２】
【数１２】

【００４３】
となり、ｘ／ａを横軸にとり、ｍをパラメータとして回折の光強度分布を記述できる。
図４に上述の方法で求めた光強度分布を示す。
【００４４】
図４（ａ）は、パラメータｍを変化させることで移動する、回折の光強度を観察する位置（ａ〜ｇ）を示している。図４（ａ）において、スクリーンの背後に記した実線はスリットの幾何学的影、点線はｍ＞１の場合の回折パターンの拡がりを示す。
【００４５】
図４（ｂ）は、ｍを変化させたそれぞれの観察位置（ａ〜ｇ）での回折の光強度分布を、（１０）式によって計算した結果を示す。ｒ＝ｍａ² ／２λであり、横軸がｘ／ａ、縦軸が光強度を示している。図４（ｂ）に書き込んだ記号ａ〜ｇは、図４（ａ）に示した光強度分布の観察位置（ａ〜ｇ）を表している。
【００４６】
以下、本実施の形態に係る光学式エンコーダに適用した場合を具体的に説明する。
図５〜図７に、本実施の形態に係る、面発光レーザ１０を用いた反射式エンコーダの構成を示す。図５は、面発光レーザを用いた反射式エンコーダの斜視図、図６は、光ビームの中心軸を通りＹ軸に垂直な平面における断面図、図７は、Ｘ軸方向から見た側面図を示している。なお、スケール２０は、反射率（または透過率）の大きな部分と反射率（または透過率）の小さな部分が交互に規則的に配置された部材であり、例えば、ガラス基板などの低反射率の基板にＡｌなどの高反射率の薄膜を蒸着し、これをリソグラフィー技術を用いてパターニングすることにより作成できる。
【００４７】
上記構成において、面発光レーザ１０から出射したビームをスケール２０で反射させ、反射光を光検出器３０の受光素子で受光する。スケール２０の移動により反射光の強度が変化するので、光検出器３０の出力からスケールの移動量を検出できる。
【００４８】
スケールに照射される光の強度分布は、先述したように、開口長ａと同じ大きさの窓幅で規定される開口１６に平行な平面波を入射させた場合にほぼ近似できるため、面発光レーザ１０の開口１６の形状，寸法及びスケール２０と開口１６間の距離とで規定される。
【００４９】
本実施の形態では、図７に示すように、光ビームの中心軸上における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、スケール２０のスケールピッチをｐ、スケール面上でピッチ方向と光ビームの中心軸に垂直な平面のなす角をθ、スケール２０のピッチ方向を光ビームの中心軸に垂直な平面に投影した方向における光源の開口長をａとし、光源から距離Ｌのレーザ光出射方向に垂直な平面上における、スケール２０のピッチ方向Ｐをこの平面に投影した方向の光強度分布を、（２）式を用いて計算する。
【００５０】
波長λ＝１μm 、開口長ａ＝３０μm の面発光レーザを用い、Ｌを８５．５μm 〜９００μm の間で変化させたときに得られる光強度分布の数値計算例を図８（ａ），図１２（ａ）〜図２９（ａ）に示す。Ｌ＝ｍａ² ／２λであり、横軸はｘ（μｍ）、縦軸は光強度（ａｒｂ．）を表している。ここで、Ｌ（スケール２０と出射面との距離）が極端に小さい場合には、先述したように（２）式において使用する仮定（近似）が成り立たず、（２）式では光強度分布の計算ができなくなるので、ここで示したＬの最小値（８５．５μm ）付近が、（２）式を適用できるＬの下限値である。
【００５１】
上記した方法で計算される光強度分布を有するスポットが、スケール２０に照射されて得られる反射光の光量は、スケール２０の反射率分布とスポット強度分布との積をＸ軸上で積分すれば得られる。ここでは、計算を簡単にするために、スケール２０の透過部，反射部における反射率をそれぞれ０，１、光検出器３０は反射光量を全て受光できるよう十分大きいものと仮定する。
【００５２】
また、スケール２０が移動した場合に起こる反射光の光量変化は、スケール２０の反射率分布を与える位置を変化させればよい。例えば、図８（ａ）における光強度分布に対して、ｐ＝１０μm のスケール２０を使用したときの反射光量の変化は、スケール２０の反射率分布を図９（ａ）〜（ｅ）のように移動させ、それぞれの反射率分布と図８（ａ）の光強度分布の積を積分すれば求められる。すなわち、図９（ａ）〜（ｅ）中に斜線で記した部分の面積を合計することにより、それぞれのスケール位置における反射光量が求められる。
【００５３】
以上のようにして、スケール２０が１ピッチ分（１０μm ）移動したときに得られる反射光量の変化を図１０に示す。これが、スケール移動時のエンコーダ信号に相当し、この最大値と最小値の差がエンコーダ信号のｐ−ｐ振幅（以下単に振幅と表記する）に相当する。また、図１０中（ａ）〜（ｅ）で示した点は、それぞれ図９（ａ）〜（ｅ）の場合に得られる信号に相当する。
【００５４】
上述した方法で、図８（ａ）に示した光強度分布の場合について、スケールピッチｐを開口長ａと等しい３０μm から２μm 単位で小さく変化させ、それぞれのスケールピッチにおいて、スケール２０を移動させた際に得られるエンコーダ信号の振幅を計算した結果を図８（ｂ）に示す。
【００５５】
図８（ｂ）から、光強度分布とスケールピッチｐがある特定の関係（この場合、ｐ＝１０μm 、および１４μm ≦ｐ≦２２μm ）を満たすときに、ｐ＝ａの場合よりも大きい振幅が得られる場合があることが分かる。このことより、従来の光学式エンコーダよりもスケールピッチを小さくすることが可能であること、すなわち、光源とスケールの間隔Ｌがある一定距離（ａ² ／λ）より小さい場合にも、ｐ≦ａとして、従来よりも高分解能を有するエンコーダが得られる可能性があることがわかる。
【００５６】
ここで、スケールピッチと振幅の関係をより詳細に理解するために、図８（ｂ）において振幅の極大が見られるｐ＝６μm 、１８μm の場合について、光強度分布とスケールピッチの関係を図１１（ａ）〜（ｄ）に示す。これを見ると、振幅が大きい場合には、スケールの隣接する反射部（あるいは透過部）が、光強度分布の極大が見られる位置にそれぞれ一致するか、あるいは近い位置にあることがわかる。
【００５７】
例えば、ｐ＝６μm の場合（図１１（ａ））では、スケール反射部がそれぞれ中央、両側の１番目、３番目の計５カ所の極大値の位置にほぼ一致しており、この場合の反射光量（斜線部の面積の合計）はかなり大きい。一方、スケールが半ピッチ（３μm ）移動した場合（図１１（ｂ））には、以上に示した５カ所の極大値はスケール透過部と一致するために、反射光量は小さくなる。スケールが移動する際の反射光量の最大値と最小値の差がエンコーダ信号の振幅となるため、ｐ＝６μm の場合には大きい振幅が得られることがわかる。
【００５８】
また、ｐ＝１８μm の場合（図１１（ｄ））においては、スケール反射部が両側の１、２、３番目の極大値をすべてカバーする位置にあるため、反射光量が大きくなり、スケール２０が半ピッチ移動した場合（図１１（ｃ））の反射光量の差をとると、大きい振幅が得られる。
【００５９】
以上のように、大きい振幅を得るためには、基本的には、光強度分布の極大が見られる位置にスケール２０の同位相の部分（例えば反射部）がほぼ一致するように（極大値間の距離がスケールピッチｐの整数倍）スケールピッチｐを決定すればよい。但し、光強度分布のプロファイルが必ずしも対称な形でないため、極大値間の距離が必ずしもスケールピッチｐの整数倍となるとは限らず、多少のずれがある方がより大きな振幅を得られる場合もある。
【００６０】
なお、実際にエンコーダを使用する際には、スケール反射光より得られる例えば擬似正弦波信号をさらに電気的に分割してより高分解能を得る方法が一般的に用いられており、エンコーダの高分解能化を検討する場合には、信号分割を含めた分解能を最適化する必要がある。そこで、エンコーダ信号が与えられた際に可能な分割数は、エンコーダ信号の振幅に比例するものと考えられるため、高分解能化を図るためには、エンコーダ信号の振幅を確保しながら、スケールピッチｐを小さくすればよい。
【００６１】
よって、図８（ｂ）のプロット上で、振幅／ｐ（プロット上の点から原点まで引いた直線の傾き）の値が最大となる点において最小分解能を得られると考えられる。この考え方を適応すると、図８（ｂ）の場合には、ｐ＝６μm 付近、及びｐ＝１６〜１８μm 付近において振幅／ｐが最大になり、これらの場合に最小分解能が得られることがわかる。
【００６２】
また、従来の光学式エンコーダ（ｐ＝３０μm ）の場合よりも高分解能が得られる範囲は、プロット上のｐ＝３０μm の点と原点を結んだ線よりも、プロットが上にある場合に相当し、図８（ｂ）の場合には、６μm ≦ｐ≦１０μm 、１４μm ≦ｐ≦２４μm において、従来例よりも高分解能が得られていることが分かる。すなわち、信号分割を考慮すると、ｐ＝３０μm の場合と比較して、振幅の絶対値が小さい場合でも、振幅／ｐが大きければより高分解能が得られることになる。
【００６３】
以下同様にして、図１２（ａ）〜図２９（ａ）に示す光強度分布に対して、エンコーダ信号の振幅を各スケールピッチについて計算した結果を図１２（ｂ）〜図２９（ｂ）に示す。これを見ると、図１２（ｂ）〜図２６（ｂ）においては、それぞれｐ＜ａの範囲で、ｐ＝ａの場合よりも高分解能が得られる条件が見られるが、図２７（ｂ）ではほぼｐ＝ａの場合が高分解能化の最適条件であり、図２８（ｂ），図２９（ｂ）においては、ｐ＞ａにおいて最適条件が存在するものと予想され、少なくともｐ≦ａにおいては、ｐ＝ａが最適条件となることがわかる。
【００６４】
なお、ここまでの説明では、θ＝０の場合について示したが、θ≠０の場合は、図３０に示すように、スケールパターンを光ビームの中心軸に垂直な平面上に投影する場合と等価であるものと仮定し、ｐ・ｃｏｓθを等価的なスケールピッチであるものとすると、同様に最適な分解能が得られる条件を決定することが可能である。ここで、θ＝０の場合はｐ・ｃｏｓθ＝ｐであるため、ｐ・ｃｏｓθを使って全ての場合を表現することが可能である。
【００６５】
以上の説明から明らかなように、光源とスケール２０が比較的近接した場合に関して、ｐ・ｃｏｓθ＜ａで分解能を最適化する条件が得られる。これに関して、以下にＬの値による場合分け（パラメータｍを変化させる）を行い、それぞれに関する最適条件が得られる範囲について説明する。
▲１▼Ｌ＝０．０９５ａ² ／λ〜０．１１ａ² ／λ（図８，図１２，図１４）の場合図８（ａ）はＬ＝０．０９５ａ² ／λ、図１２（ａ）はＬ＝０．１ａ² ／λ、図１３（ａ）はＬ＝０．１１ａ² ／λの場合の光強度分布を示している。
【００６６】
Ｌ＝０．０９５ａ² ／λでは、図８（ａ）に示すように、光軸上に光量の極大値が見られ、さらに、光軸を挟んで両側距離Ｌλ／ａの場所にそれぞれ光量の極小値、光軸両側距離２Ｌλ／ａ、３Ｌλ／ａ、４Ｌλ／ａ付近にそれぞれ極大値が見られる。
【００６７】
ここからＬを増加させると、図１２（ａ）に示すように、次第に光軸上の極大値の光強度は減少し、Ｌ＝０．１１ａ² ／λ付近では、図１３（ａ）に示すように光軸上の極大値はほぼ消滅する。また、光軸両側距離２Ｌλ／ａ、３Ｌλ／ａ、４Ｌλ／ａの極大値は、２Ｌλ／ａの極大値を除いて、光強度がかなり低下する。
【００６８】
以上のように、０．０９５ａ² ／λ≦Ｌ≦０．１１ａ² ／λの範囲においては、光軸上および光軸両側距離２Ｌλ／ａの極大値が支配的であり、これらの極大値付近にそれぞれスケールの同位相の部分（例えば反射部）が配置されるような関係の時に、大きい振幅が得られると考えられる。
【００６９】
以上の考え方で、図８（ｂ），図１２（ｂ）及び図１３（ｂ）を参照して、高分解能化に適した条件を数式で表現すると、
１．６Ｌλ／ａ≦ｐ・ｃｏｓθ≦２．４Ｌλ／ａ
（０．０９５ａ² ／λ≦Ｌ≦０．１１ａ² ／λ）
となる。
▲２▼０．０９５ａ² ／λ≦Ｌ≦０．１３ａ² ／λ（図８，図１２〜図１５）の場合図８（ａ）はＬ＝０．０９５ａ² ／λ、図１２（ａ）はＬ＝０．１ａ² ／λ、図１３（ａ）はＬ＝０．１１ａ² ／λ、図１４（ａ）はＬ＝０．１２５ａ² ／λ、図１５（ａ）はＬ＝０．１３ａ² ／λの場合の光強度分布を示している。
【００７０】
０．０９５ａ² ／λ≦Ｌ≦０．１１ａ² ／λの範囲において、回折パターンは、上記▲１▼に示したように変化する。さらにＬを増加させていくと、図１４（ａ）に示すように、光軸上の極大値は消失して極小値となり、かつ光軸両側距離Ｌλ／ａの位置の極小値は極大値となり、光強度が増加する。また、光軸両側距離２Ｌλ／ａ、３Ｌλ／ａ、４Ｌλ／ａの極大値は観察されるが、光強度は低下する。
【００７１】
そして、さらにＬを増大させていくと、Ｌ＝０．１３ａ² ／λ付近で、図１５（ａ）に示すように光軸両側距離Ｌλ／ａの位置の極大値が支配的になり、それまで支配的であった光軸両側距離２Ｌλ／ａの極大値における光強度を上回る。
【００７２】
以上のように、０．０９５ａ² ／λ≦Ｌ≦０．１３ａ² ／λの範囲においては、少なくとも光軸両側距離２Ｌλ／ａの極大値が支配的であり、この極大値付近にそれぞれスケールの同位相の部分（例えば反射部）が配置されるような関係の時に、大きい振幅が得られると考えられる。
【００７３】
以上の考え方で、図８（ｂ），図１２〜図１５のそれぞれ図（ｂ）を参照して、高分解能化に適した条件を数式で表現すると、
４．６Ｌλ／ａ≦ｐ・ｃｏｓθ≦７．４Ｌλ／ａ
（０．０９５ａ² ／λ≦Ｌ≦０．１３ａ² ／λ）
となる。
▲３▼０．１３ａ² ／λ≦Ｌ≦０．２１ａ² ／λ（図１５〜図１８）の場合
図１５（ａ）はＬ＝０．１３ａ² ／λ、図１６（ａ）はＬ＝０．１５ａ² ／λ、図１７（ａ）はＬ＝０．２ａ² ／λ、図１８（ａ）はＬ＝０．２１ａ² ／λの場合の光強度分布を示している。
【００７４】
Ｌ＝０．１３ａ² ／λからＬの値を増加すると、図１６（ａ）に示すように、いったん光軸両側Ｌλ／ａの位置の極大値が支配的となるが、さらにＬを増加させると、図１７（ａ）に示すように、再び光軸上の極小値が極大値になる。そして、Ｌ＝０．２１ａ² ／λ付近で、図１８（ａ）に示すように光軸上の極大値と光軸両側Ｌλ／ａの位置の極大値の光強度がほぼ等しくなる。
【００７５】
以上のように、０．１３ａ² ／λ≦Ｌ≦０．２１ａ² ／λの範囲においては、光軸両側Ｌλ／ａの位置の極大値が支配的であり、この極大値付近にそれぞれスケールの同位相の部分（例えば反射部）が配置されるような関係の時に、大きい振幅が得られると考えられる。
【００７６】
以上の考え方で、図１５（ｂ）〜図１８（ｂ）を参照して、高分解能化に適した条件を数式で表現すると、 ２Ｌλ／ａ≦ｐ・ｃｏｓθ≦４Ｌλ／ａ
（０．１３ａ² ／λ≦Ｌ≦０．２１ａ² ／λ）
となる。
▲４▼０．２１ａ² ／λ≦Ｌ≦０．３ａ² ／λ（図１８〜図２１）の場合
図１８（ａ）はＬ＝０．２１ａ² ／λ、図１９（ａ）はＬ＝０．２２５ａ² ／λ、図２０（ａ）はＬ＝０．２５ａ² ／λ、図２１（ａ）はＬ＝０．３ａ² ／λの場合の光強度分布を示している。
【００７７】
Ｌ＝０．２１ａ² ／λからＬの値を増加させると、図１９（ａ）〜２１（ａ）に示すように、再び現れた光軸上の極大値の光強度が増加し、支配的になっていく。また、光軸両側Ｌλ／ａの位置の極大値は次第に目立たなくなり、図２１（ａ）に示すように、Ｌ＝０．３ａ² ／λ付近においては、極大値が殆ど見られなくなる。
【００７８】
以上のように、０．２１ａ² ／λ≦Ｌ≦０．３ａ² ／λの範囲においては、光軸上の極大値が支配的であるが、光軸両側Ｌλ／ａの位置の極大値の影響も無視できない。従って、以上の３カ所の極大値付近にそれぞれスケールの同位相の部分（例えば反射部）が配置されるような関係の時に、大きい振幅が得られると考えられる。
【００７９】
以上の考え方で、図１８（ｂ）〜図２１（ｂ）を参照して、高分解能化に適した条件を数式で表現すると、
１．１Ｌλ／ａ≦ｐ・ｃｏｓθ≦１．６Ｌλ／ａ
（０．２１ａ² ／λ≦Ｌ≦０．３ａ² ／λ）
と表される。
▲５▼０．３ａ² ／λ≦Ｌ（図２１〜図２９）の場合
図２１（ａ）はＬ＝０．３ａ² ／λ、図２２（ａ）はＬ＝０．３５ａ² ／λ、図２３（ａ）はＬ＝０．３７５ａ² ／λ、図２４（ａ）はＬ＝０．４ａ² ／λ、図２５（ａ）はＬ＝０．５ａ² ／λ、図２６（ａ）はＬ＝０．５５ａ² ／λ、図２７（ａ）はＬ＝０．６ａ² ／λ、図２８（ａ）はＬ＝０．７５ａ² ／λ、図２９（ａ）はＬ＝１．０ａ² ／λの場合の光強度分布を示している。
【００８０】
Ｌ＝０．３ａ² ／λからＬの値を増加させると、図２２〜図２６のそれぞれ図（ａ）に示すように光軸両側Ｌλ／ａの位置に極小値が現れ、光軸上の極大値がさらに支配的になる。さらに、先に述べたように、Ｌ＝０．６ａ² ／λを越えると、図２７〜図２９に示すように、もはやｐ・ｃｏｓθ＜ａの条件では高分解能化に適した条件は見られなくなり、ｐ・ｃｏｓθ≧ａに最適条件が見られるようになる。
【００８１】
このように、０．３ａ² ／λ≦Ｌ≦０．６ａ² ／λの範囲においては、光軸上の極大値が支配的であるため、この極大値のスポット幅に対してスケールピッチを最適な条件で決定すればよい
以上の考え方で、図２１（ｂ）〜図２６（ｂ）を参照して、高分解能化に適した条件を数式で表現すると、
１．２Ｌλ／ａ≦ｐ・ｃｏｓθ＜ａ
（０．３ａ² ／λ≦Ｌ≦０．６ａ² ／λ）
となる。
【００８２】
以上、▲１▼〜▲５▼の場合分けでは、エンコーダの分解能がスケールピッチｐとエンコーダ信号振幅の商（ｐ／振幅）で決まるものと仮定して、この商（ｐ／振幅）が、ｐ＝ａの時に得られる商よりも小さい場合、即ち、最高の分解能が得られる条件について説明した。このように、本実施の形態においては、従来ｐ・ｃｏｓθ≧ａの条件で使用されてきた光学式エンコーダでは、分解能の限界があったのに対し、従来開示されていなかったｐ・ｃｏｓθ＜ａの条件においてｐ・ｃｏｓθ≧ａの条件の時よりも、高分解能を有するエンコーダを得ることができる。
【００８３】
さらに本実施の形態の光学式エンコーダは、商（ｐ／振幅）が、ｐ＝ａの時に得られる商よりも大きな場合でも使用することが可能である。従って、商（ｐ／振幅）が必ずしも最小でない場合において、エンコーダ信号の振幅が観測される範囲について以下に説明する。
【００８４】
上述したように、エンコーダのスケールピッチｐは、光強度の極大値が現れるｘ軸方向（光ビームの中心軸（ビームの主軸に垂直な方向）の間隔程度に合わせれば良いことが分かっている。更に、この光強度が極大値を有するｘ軸方向の間隔は、例えば図８（ａ），図１６（ａ），図１８（ａ）に示すように、Ｌλ／ａの整数倍である。これは、光の回折理論から説明することができる。
【００８５】
したがって、エンコーダ信号の振幅を観測できるようにするためには、光強度が最大値となるｘ軸方向の間隔Ｌλ／ａの整数倍程度にスケールピッチを設定すれば良いことが導き出される。
【００８６】
説明を簡略化するため、以下のようにファクターｋを定義する。
ｋ≡ｐ／（Ｌλ／ａ）
この考え方に基づくと、スケールピッチｐの最小値は、Ｌλ／ａ程度（ｋ＝１程度に相当）となるはずである。
【００８７】
実際に試算した結果では、図１６（ｂ）〜図２９（ｂ）に示すように、エンコーダ信号の振幅が観測されるスケールピッチｐを数式で表現すると、スケール２０に対するビーム光軸の傾きを考慮して、
０．８Ｌλ／ａ≦ｐ・ｃｏｓθ＜ａ（Ｌ≦０．６ａ² ／λ）
とすればより良い観測ができるが、
０．８Ｌλ／ａ≦ｐ・ｃｏｓθ＜ａ（０．６ａ² ／λ≦Ｌ≦１．０ａ² ／λ）
としても観測することができる。
【００８８】
以上、まとめると、
０．８Ｌλ／ａ≦ｐ・ｃｏｓθ＜ａ（Ｌ≦１．０ａ² ／λ）
とすれば良い。
【００８９】
また、従来、光源（面発光レーザ１０）とスケール２０との間隔Ｌが、ある一定距離（ａ² ／λ）よりも大きい場合、スケールピッチｐが、Ｌλ／ａよりも大きくないとエンコーダ信号を得ることができないと考えられていた。
【００９０】
しかし、図３０（ｂ）及び図３１（ｂ）から明らかなように、スケールピッチｐが、Ｌλ／ａよりも小さい場合でもエンコーダ信号を得ることができることが分かる。なお、図３０（ａ）はＬ＝２．０ａ² ／λ、図３１（ａ）はＬ＝４．０ａ² ／λの場合の光強度分布を示している。
【００９１】
また、図３０（ｂ）及び図３１（ｂ）から明らかなように、スケールピッチｐが０．８Ｌλ／ａの状態からエンコーダ出力が立ち上がり始めており、スケールピッチｐがＬλ／ａよりも小さい場合でもエンコーダ信号を得られることが分かる。
【００９２】
以上の事実に基づいて、光源（面発光レーザ１０）とスケール２０との間隔Ｌが、ａ² ／λよりも大きい場合でもエンコーダ出力を得ることができる条件を数式で表現すると、
０．８Ｌλ／ａ≦ｐ・ｃｏｓθ＜１．０Ｌλ／ａ
（Ｌ≧１．０ａ² ／λ）
となる。
【００９３】
このように、本実施の形態によれば、従来の光学式エンコーダでは使用できるスケールピッチｐに、Ｌ≦ａ² ／λの場合はｐ・ｃｏｓ≧ａ、Ｌ＞ａ² ／λの場合はｐ≧Ｌλ／ａという限界があったのに対し、この制限を越えて、Ｌ≦ａ² ／λの場合はｐ・ｃｏｓ＜ａ、Ｌ＞ａ² ／λの場合はｐ＜Ｌλ／ａの条件を満たすスケールを使用可能であることが分かる。また、このように本実施の形態では、従来の光学式エンコーダの場合よりも小さなピッチのスケールが使用可能なため、所望の分解能を得るためにエンコーダからの出力信号の分割次数をより小さくする（あるいは分割しない）ことが可能となり、信号処理回路の制作が容易となる。
【００９４】
なお、本実施の形態では、反射式のエンコーダに本願発明を適用した場合を説明したが、透過型エンコーダにも同様に適用することができる。
【００９５】
【発明の効果】
このように本発明によれば、従来のエンコーダよりもスケールピッチを小さくすることが可能であり、高分解能を実現することができる。
【図面の簡単な説明】
【図１】図１は、発明の実施の形態に係る面発光レーザの構成を示す図である。
【図２】図２（ａ），（ｂ）は、発明の実施の形態に係る面発光レーザの変形例を示す図である。
【図３】図３は、面発光レーザの開口からの放射光の広がり状態を示す図である。
【図４】図４（ａ）は、回折光強度を観察する位置を示す図、図４（ｂ）は、それぞれの観察位置での光強度分布を示す図である。
【図５】図５は、発明の実施の形態に係る光学式エンコーダの構成を示す斜視図である。
【図６】図６は、発明の実施の形態に係る光学式エンコーダの構成を示す断面図である。
【図７】図７は、発明の実施の形態に係る光学式エンコーダの構成を示す側面図である。
【図８】図８（ａ）は、Ｌ＝０．０９５ａ² ／λの場合の光強度分布を示す図、図８（ｂ）は、Ｌ＝０．０９５ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図９】図９（ａ）〜（ｅ）は、ｐ＝１０μｍのスケールを移動させた際に生じる反射光量の変化状態を示す図であり、図中の斜線は、反射光量を求めるために必要な部分の面積を示している。ずなわち、図中の斜線は、断面を示すものではない。
【図１０】図１０は、ｐ＝１０μｍのスケールを１ピッチ移動させた際に得られる反射光量の変化状態を示す図である。
【図１１】図１１（ａ），（ｂ）は、ｐ＝６μｍのスケールを移動させた際に生じる反射光量の変化状態を示す図、図１１（ｃ），（ｄ）は、ｐ＝１８μｍのスケールを移動させた際に生じる反射光量の変化状態を示す図であり、図中の斜線は、反射光量を求めるために必要な部分の面積を示している。ずなわち、図中の斜線は、断面を示すものではない。
【図１２】図１２（ａ）は、Ｌ＝０．１ａ² ／λの場合の光強度分布を示す図、図１２（ｂ）は、Ｌ＝０．１ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図１３】図１３（ａ）は、Ｌ＝０．１１ａ² ／λの場合の光強度分布を示す図、図１３（ｂ）は、Ｌ＝０．１１ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図１４】図１４（ａ）は、Ｌ＝０．１２５ａ² ／λの場合の光強度分布を示す図、図１４（ｂ）は、Ｌ＝０．１２５ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図１５】図１５（ａ）は、Ｌ＝０．１３ａ² ／λの場合の光強度分布を示す図、図１５（ｂ）は、Ｌ＝０．１３ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図１６】図１６（ａ）は、Ｌ＝０．１５ａ² ／λの場合の光強度分布を示す図、図１６（ｂ）は、Ｌ＝０．１５ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図１７】図１７（ａ）は、Ｌ＝０．２ａ² ／λの場合の光強度分布を示す図、図１７（ｂ）は、Ｌ＝０．２ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図１８】図１８（ａ）は、Ｌ＝０．２１ａ² ／λの場合の光強度分布を示す図、図１８（ｂ）は、Ｌ＝０．２１ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図１９】図１９（ａ）は、Ｌ＝０．２２５ａ² ／λの場合の光強度分布を示す図、図１９（ｂ）は、Ｌ＝０．２２５ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図２０】図２０（ａ）は、Ｌ＝０．２５ａ² ／λの場合の光強度分布を示す図、図２０（ｂ）は、Ｌ＝０．２５ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図２１】図２１（ａ）は、Ｌ＝０．３ａ² ／λの場合の光強度分布を示す図、図２１（ｂ）は、Ｌ＝０．３ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図２２】図２２（ａ）は、Ｌ＝０．３５ａ² ／λの場合の光強度分布を示す図、図２２（ｂ）は、Ｌ＝０．３５ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図２３】図２３（ａ）は、Ｌ＝０．３７５ａ² ／λの場合の光強度分布を示す図、図２３（ｂ）は、Ｌ＝０．３７５ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図２４】図２４（ａ）は、Ｌ＝０．４ａ² ／λの場合の光強度分布を示す図、図２４（ｂ）は、Ｌ＝０．４ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図２５】図２５（ａ）は、Ｌ＝０．５ａ² ／λの場合の光強度分布を示す図、図２５（ｂ）は、Ｌ＝０．５ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図２６】図２６（ａ）は、Ｌ＝０．５５ａ² ／λの場合の光強度分布を示す図、図２６（ｂ）は、Ｌ＝０．５５ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図２７】図２７（ａ）は、Ｌ＝０．６ａ² ／λの場合の光強度分布を示す図、図２７（ｂ）は、Ｌ＝０．６ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図２８】図２８（ａ）は、Ｌ＝０．７５ａ² ／λの場合の光強度分布を示す図、図２８（ｂ）は、Ｌ＝０．７５ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図２９】図２９（ａ）は、Ｌ＝１．０ａ² ／λの場合の光強度分布を示す図、図２９（ｂ）は、Ｌ＝１．０ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図３０】図３０（ａ）は、Ｌ＝２．０ａ² ／λの場合の光強度分布を示す図、図３０（ｂ）は、Ｌ＝２．０ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図３１】図３１（ａ）は、Ｌ＝４．０ａ² ／λの場合の光強度分布を示す図、図３１（ｂ）は、Ｌ＝４．０ａ² ／λの場合のスケールピッチとｐ−ｐ振幅との関係を示す図である。
【図３２】図３２は、スケールのピッチ方向と光ビームの中心軸に垂直な平面のなす角θを説明するための図である。
【図３３】図３３は、従来の光学式エンコーダの構成を示す図である。
【符号の説明】
１０…面発光レーザ
１６…開口
２０…スケール
３０…光検出器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical encoder used for detecting a movement amount of a movable part of an apparatus.
[0002]
[Prior art]
Conventional optical encoders need to assemble and adjust various optical components, making it difficult to reduce the size and cost. On the other hand, as disclosed in, for example, Japanese Patent Application Laid-Open No. 7-306058, the present applicant is able to reduce the size and cost of a surface emitting semiconductor laser (hereinafter referred to as a surface emitting laser) as a light source. A possible optical encoder was developed.
[0003]
FIG. 33 shows a configuration of an optical encoder using a surface emitting laser developed by the present applicant as a light source. This optical encoder is configured such that a beam emitted from the surface emitting laser 10 irradiates the scale 20, and a part of the beam is reflected or transmitted by the scale 20 and detected by the photodetector 30 or 30 ′. ing.
[0004]
In general, in the surface emitting laser, the divergence angle of the outgoing beam determined by the outgoing window width (opening length) a is smaller than that of the conventional edge emitting semiconductor laser. For this reason, in the optical encoder developed by the present applicant, parts such as a collimator lens and an index scale that were necessary for the optical encoder before that are not necessary, and the size and cost can be reduced.
[0005]
[Problems to be solved by the invention]
However, in a conventional optical encoder using a surface emitting laser, a distance L between the light source and the scale is a certain distance (a ² L ≦ a smaller than / λ) ² In the case of / λ, it is assumed that the size of the light spot formed on the scale by the surface emitting laser is substantially equal to the opening length a in the scale pitch direction of the exit window of the surface emitting laser, and therefore the scale pitch p is set. The condition of possible values was limited to p ≧ a. L> a ² In the case of / λ, since it was assumed that the size of the light spot formed on the scale was approximately equal to Lλ / a, the scale pitch p was limited to p ≧ Lλ / a.
[0006]
That is, in the conventional optical encoder, the lower limit is set in the size of the scale pitch p, and the possibility of realizing higher encoder resolution by further reducing the scale pitch has not been considered.
[0007]
On the other hand, higher resolution of encoders is continuously required as a means for realizing higher performance of machine tools, measuring instruments, etc., and higher resolution is indispensable even for small and low-cost optical encoders. .
[0008]
The present invention has been made to solve such problems, and in an optical encoder using a surface emitting laser, when a light source and a scale are arranged relatively close to each other, the conventional optical type is provided. It is an object of the present invention to provide an optical encoder that can further increase the resolution by reducing the scale pitch as compared with the encoder.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, in the optical encoder of the present invention, the distance between the moving scale and the light emitting surface of the surface emitting laser light source at the central axis of the light beam is L, and the wavelength of the light beam is λ, the scale pitch of the moving scale is p, the angle between the pitch direction of the moving scale and a plane perpendicular to the center axis of the light beam is θ, and the pitch direction of the moving scale is a plane perpendicular to the center axis of the light beam When the opening length of the surface-emitting laser light source along the projected direction is a, L ≦ 1.0a ² In the case of / λ, the relationship of p · cos θ <a is satisfied, and L ≧ 1.0a ² In the case of / λ, it is configured to satisfy the relationship of 0.8 Lλ / a <p · cos θ <1.0 Lλ / a.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram showing an example of the structure of a surface emitting laser 10 used as a light source in the present embodiment. As shown in the figure, the surface emitting laser 10 has multilayer thin film mirrors 12 and 13 that sandwich an active layer (light emitting layer) 11 from both sides, and an upper electrode 14 and a lower electrode 15 that sandwich the multilayer thin film mirrors 12 and 13. is doing.
[0011]
Such a surface emitting laser 10 is configured to emit light from the active layer 11 by applying a voltage between the upper and lower electrodes 14 and 15 and injecting a current into the active layer 11. Specifically, since the resonator is formed in the film thickness direction by the active layer 11 and the multilayer thin film mirrors 12 and 13, oscillation occurs in this film thickness direction. Since the upper electrode 14 is removed only in the portion of the emission window 21 from which light is emitted, the light is emitted in a direction perpendicular to the film plane as shown in the figure. Examples of the material constituting the surface emitting laser 10 include GaAs applied to the active layer 11 and p-type or n-type GaAs / AlGaAs laminated film applied to the multilayer thin film mirrors 12 and 13.
[0012]
An advantage of the surface emitting laser 10 having the above-described configuration is that the shape of the opening (in this case, the emission window 21) can be freely designed by patterning the upper electrode 14. In addition, when using back surface side emitted light, the lower electrode 15 is patterned.
[0013]
Since the beam divergence of the radiation light is defined by the shape and size of the aperture (because diffraction is generated by the aperture and beam divergence occurs), the beam divergence can be kept relatively small by the design of the aperture. Therefore, if an encoder is configured using a suitably designed surface emitting laser 10 as a light source, a collimator lens (or a condensing lens) and an index scale used in many conventional optical encoders are not required, and the size is extremely small. A low-cost optical encoder can be realized.
[0014]
Here, a modification of the surface emitting laser 10 is shown in FIGS. Since the basic configuration is the same as that of the surface emitting laser 10 shown in FIG. 1, the same reference numerals are given to the common configurations, and description thereof is omitted. In the modification shown in FIGS. 2A and 2B, a part or all of the multilayer mirror 12 is processed in a mesa shape, and the upper electrode 14 is formed in a mesa shape of the multilayer mirror 12. It is formed so as to surround it. A curve 19 in the figure indicates the emitted light.
[0015]
In the modification shown in FIG. 2A, a part of the region 17 of the active layer 11 is insulated, and a current flow 18 flowing from the upper electrode 14 to the lower electrode 15 through the active layer 11 is a multilayer film. It is limited to a region slightly wider than the vertical section of the mesa portion of the mirror 12. In FIG. 2A, b represents the cross-sectional diameter of the mesa portion, c represents the cross-sectional diameter of the non-insulated region of the active layer 11, and c ≧ b. In the surface emitting laser 10 having such a configuration, when a current is passed between the upper electrode 14 and the lower electrode 15, a region that is not insulated in the active layer 11 emits light strongly. Since the overlapping portion in the vertical direction between the mesa-shaped portion and the multilayer mirror 13 functions most strongly as a light resonator, the spread of the laser beam at the light beam exit end surface is indicated by the overlapping portion of b and c, that is, b. Range. Therefore, the opening length a of the light emitting portion in the case of FIG. 2A corresponds to b.
[0016]
Also, the modification shown in FIG. 2B is different from the configuration shown in FIG. 2A in that c <b. In the surface emitting laser 10 having such a configuration, for the same reason as described above, the spread of the laser beam on the light emitting end surface is an overlapping portion of b and c, that is, a range indicated by c. Therefore, the opening length a of the light emitting part in the case of FIG. 2B corresponds to c.
[0017]
Further, also in the case of the surface emitting laser 10 having a configuration different from those in FIGS. 1 and 2A and 2B, the opening length a is a dimension of a portion corresponding to the spreading width of the emitted light beam on the emission surface. Therefore, in the present embodiment, the spread width of the light beam at the emission end face is described as a uniform opening length a. The spread width of the light beam is such that the intensity of the emitted light beam is 1 / e of the peak intensity on a plane perpendicular to the main axis of the light beam. ² (E is a natural logarithm) It shall refer to the width of a certain area. On the surface perpendicular to the main axis of the outgoing beam, when the size of the aperture length a differs depending on the direction to be measured, the direction of the pitch p of the scale 20 described later is the direction projected on the outgoing end face of the light beam. The measured value is defined as the opening length a. In this embodiment, when simply describing an aperture, it is defined as a region corresponding to the beam spreading width on the light beam exit surface of the surface emitting laser, that is, the aperture length a.
[0018]
Subsequently, the beam spread of the radiation light defined by the size of the opening length a will be described below.
As for the light emitted from the surface emitting laser 10 having the refractive index waveguide structure, as shown in FIG. 3, a plane wave parallel to the opening 16 defined by the window width having the same size as the opening length a is incident. Can be approximated to. With regard to the spread of the beam after passing through the aperture 16, except for the case where the aperture length a and the distance r between the observation surface and the aperture 16 are about 5 times or less of the wavelength, Fresnel-Kirchhoff (Fresnel-Kirchhoff) It can be calculated by diffraction integration.
[0019]
That is, the aperture function is u ₀ (X ₀ , Y ₀ ), Where diffracted light on the observation surface is u (x, y),
[0020]
[Expression 1]

[0021]
It is expressed.
In addition, when the distance between the aperture and the observation point is more than a certain distance, the beam spread can be calculated by Fresnel diffraction, and when more than a certain distance, by Fraunhofer diffraction, Respectively
[0022]
[Expression 2]

[0023]
[Equation 3]

[0024]
It is expressed.
As described above, the diffraction pattern of the surface emitting laser emission light can be approximately calculated using the equations (1) to (3), and the aperture length (emission window width) a, the observation surface, and the aperture The formula to be used is selected in consideration of the distance r to
[0025]
In this embodiment, the case where the distance from the opening is relatively small will be described. However, in general, in an actual encoder, the distance between the surface emitting laser and the scale cannot be made infinitely small, and the distance r has a lower limit. In practice, it is considered that the Fresnel diffraction equation (2) is within the range, and in this embodiment, the calculation is performed using the above equation (2).
[0026]
Here, the opening length in the x-axis direction is set to a, and the diffraction pattern in the x-axis direction is calculated using an opening having an infinite width in the y-axis direction. In this case, if the integration region in the y-axis direction is set to −∞ to ∞,
[0027]
[Expression 4]

[0028]
And
[0029]
[Equation 5]

[0030]
It becomes.
In order to actually calculate the diffraction pattern, it is necessary to perform numerical calculations.
[0031]
[Formula 6]

[0032]
[Expression 7]

[0033]
Using the Fresnel integral represented by
[0034]
[Equation 8]

[0035]
Assuming that the integration region in the x-axis direction is −a / 2 to a / 2,
[0036]
[Equation 9]

[0037]
And the light intensity distribution is
[0038]
[Expression 10]

[0039]
It is expressed.
This equation changes its shape depending on the distance r from the slit, the slit width a, and the wavelength λ.
[0040]
[Expression 11]

[0041]
If defined, the Fresnel function variable in equation (10) is
[0042]
[Expression 12]

[0043]
The diffraction light intensity distribution can be described with x / a on the horizontal axis and m as a parameter.
FIG. 4 shows the light intensity distribution obtained by the above method.
[0044]
FIG. 4A shows the positions (a to g) at which the diffraction light intensity is observed by moving by changing the parameter m. In FIG. 4A, the solid line drawn behind the screen indicates the geometric shadow of the slit, and the dotted line indicates the spread of the diffraction pattern when m> 1.
[0045]
FIG. 4B shows the result of calculating the light intensity distribution of diffraction at each observation position (a to g) where m is changed according to the equation (10). r = ma ² / 2λ, the horizontal axis represents x / a, and the vertical axis represents the light intensity. Symbols a to g written in FIG. 4B represent observation positions (a to g) of the light intensity distribution shown in FIG.
[0046]
Hereinafter, the case where it applies to the optical encoder which concerns on this Embodiment is demonstrated concretely.
5 to 7 show a configuration of a reflective encoder using the surface emitting laser 10 according to the present embodiment. 5 is a perspective view of a reflective encoder using a surface emitting laser, FIG. 6 is a cross-sectional view in a plane passing through the central axis of the light beam and perpendicular to the Y axis, and FIG. 7 is a side view as viewed from the X-axis direction. Is shown. Note that the scale 20 is a member in which portions having a large reflectance (or transmittance) and portions having a small reflectance (or transmittance) are alternately and regularly arranged. For example, the scale 20 has a low reflectance such as a glass substrate. It can be formed by depositing a thin film of high reflectivity such as Al on a substrate and patterning it using a lithography technique.
[0047]
In the above configuration, the beam emitted from the surface emitting laser 10 is reflected by the scale 20, and the reflected light is received by the light receiving element of the photodetector 30. Since the intensity of the reflected light changes due to the movement of the scale 20, the amount of movement of the scale can be detected from the output of the photodetector 30.
[0048]
Since the intensity distribution of the light applied to the scale can be approximately approximated when a plane wave parallel to the opening 16 defined by the window width having the same size as the opening length a is incident, as described above, the surface emitting laser It is defined by the shape and size of the ten openings 16 and the distance between the scale 20 and the openings 16.
[0049]
In the present embodiment, as shown in FIG. 7, the distance between the scale on the central axis of the light beam and the light beam exit surface of the surface emitting semiconductor laser light source is L, the wavelength of the light beam is λ, and the scale pitch of the scale 20 P, the angle between the pitch direction on the scale plane and the plane perpendicular to the central axis of the light beam θ, θ, and the aperture length of the light source in the direction in which the pitch direction of the scale 20 is projected onto the plane perpendicular to the central axis of the light beam. A light intensity distribution in a direction in which the pitch direction P of the scale 20 is projected onto this plane on a plane perpendicular to the laser beam emission direction at a distance L from the light source is calculated using Equation (2).
[0050]
FIG. 8A and FIG. 12 show numerical calculation examples of the light intensity distribution obtained when a surface emitting laser having a wavelength λ = 1 μm and an aperture length a = 30 μm is used and L is changed between 85.5 μm and 900 μm. (A) to FIG. 29 (a). L = ma ² / 2λ, the horizontal axis represents x (μm), and the vertical axis represents light intensity (arb.). Here, when L (the distance between the scale 20 and the exit surface) is extremely small, the assumption (approximation) used in the equation (2) does not hold as described above, and the light intensity distribution in the equation (2) does not hold. Since calculation cannot be performed, the vicinity of the minimum value of L (85.5 μm) shown here is the lower limit value of L to which equation (2) can be applied.
[0051]
The amount of reflected light obtained by irradiating the scale 20 with the spot having the light intensity distribution calculated by the above method can be obtained by integrating the product of the reflectance distribution of the scale 20 and the spot intensity distribution on the X axis. can get. Here, in order to simplify the calculation, it is assumed that the reflectance at the transmission part and the reflection part of the scale 20 is 0 and 1, respectively, and that the photodetector 30 is sufficiently large to receive all the reflected light amount.
[0052]
The amount of reflected light that changes when the scale 20 moves may be changed by changing the position of the scale 20 where the reflectance distribution is given. For example, with respect to the light intensity distribution in FIG. 8A, the change in the amount of reflected light when the scale 20 of p = 10 μm is used indicates the reflectance distribution of the scale 20 as shown in FIGS. 9A to 9E. And the product of each reflectance distribution and the light intensity distribution of FIG. 8A is integrated. That is, the amount of reflected light at each scale position is obtained by summing the areas of the hatched portions in FIGS. 9 (a) to 9 (e).
[0053]
FIG. 10 shows the change in the amount of reflected light obtained when the scale 20 is moved by one pitch (10 μm) as described above. This corresponds to the encoder signal when the scale is moved, and the difference between the maximum value and the minimum value corresponds to the pp amplitude (hereinafter simply referred to as amplitude) of the encoder signal. Further, points indicated by (a) to (e) in FIG. 10 correspond to signals obtained in the cases of FIGS. 9 (a) to (e), respectively.
[0054]
In the case of the light intensity distribution shown in FIG. 8A by the above-described method, the scale pitch p is changed from 30 μm, which is equal to the opening length a, to a small unit of 2 μm, and the scale 20 is moved at each scale pitch. The result of calculating the amplitude of the encoder signal obtained at this time is shown in FIG.
[0055]
From FIG. 8B, when satisfying a certain relationship (in this case, p = 10 μm and 14 μm ≦ p ≦ 22 μm) with the light intensity distribution and the scale pitch p, a larger amplitude than in the case of p = a is obtained. It can be seen that Thus, the scale pitch can be made smaller than that of the conventional optical encoder, that is, the distance L between the light source and the scale is a certain distance (a ² / Λ), it can be seen that an encoder having higher resolution than the conventional encoder may be obtained by setting p ≦ a.
[0056]
Here, in order to understand the relationship between the scale pitch and the amplitude in more detail, the relationship between the light intensity distribution and the scale pitch is shown in FIG. 11 in the case of p = 6 μm and 18 μm where the maximum amplitude is seen in FIG. (A) to (d). From this, it can be seen that, when the amplitude is large, the reflection part (or transmission part) adjacent to the scale is at or close to the position where the maximum of the light intensity distribution is seen.
[0057]
For example, in the case of p = 6 μm (FIG. 11 (a)), the scale reflecting portions substantially coincide with the positions of the local maximum values at the first and third points on the both sides, and the reflection in this case. The amount of light (total of the shaded area) is quite large. On the other hand, when the scale is moved by a half pitch (3 μm) (FIG. 11B), the five maximum values shown above coincide with the scale transmitting portion, so the amount of reflected light becomes small. Since the difference between the maximum value and the minimum value of the reflected light amount when the scale moves is the amplitude of the encoder signal, it can be seen that a large amplitude can be obtained when p = 6 μm.
[0058]
In the case of p = 18 μm (FIG. 11D), the scale reflection part is in a position covering all of the first, second and third maximum values on both sides, so that the amount of reflected light increases and the scale 20 is A large amplitude can be obtained by taking the difference in the amount of reflected light when moving by a half pitch (FIG. 11C).
[0059]
As described above, in order to obtain a large amplitude, basically, an in-phase portion (for example, a reflection portion) of the scale 20 substantially coincides with a position where the maximum of the light intensity distribution is seen (between the maximum values). Is an integer multiple of the scale pitch p) and the scale pitch p may be determined. However, since the profile of the light intensity distribution is not necessarily symmetrical, the distance between the maximum values is not necessarily an integer multiple of the scale pitch p, and a larger amplitude may be obtained if there is a slight deviation. .
[0060]
When actually using an encoder, a method of obtaining a higher resolution by further electrically dividing, for example, a pseudo sine wave signal obtained from scale reflected light is generally used. In the case of considering the optimization, it is necessary to optimize the resolution including the signal division. Therefore, the number of divisions possible when an encoder signal is given is considered to be proportional to the amplitude of the encoder signal. Therefore, in order to achieve high resolution, the scale pitch p is secured while ensuring the amplitude of the encoder signal. Should be reduced.
[0061]
Therefore, it is considered that the minimum resolution can be obtained at the point where the value of the amplitude / p (the slope of the straight line drawn from the point on the plot to the origin) is maximum on the plot of FIG. When this concept is applied, in the case of FIG. 8B, the amplitude / p becomes maximum near p = 6 μm and near p = 16 to 18 μm, and it can be seen that the minimum resolution is obtained in these cases.
[0062]
Further, the range in which higher resolution can be obtained than in the case of the conventional optical encoder (p = 30 μm) corresponds to the case where the plot is above the line connecting the point of p = 30 μm and the origin on the plot. In the case of FIG. 8B, it can be seen that higher resolution is obtained than in the conventional example when 6 μm ≦ p ≦ 10 μm and 14 μm ≦ p ≦ 24 μm. That is, when signal division is taken into consideration, even when the absolute value of the amplitude is small as compared with the case of p = 30 μm, a higher resolution can be obtained if the amplitude / p is large.
[0063]
Similarly, the results of calculating the amplitude of the encoder signal for each scale pitch with respect to the light intensity distributions shown in FIGS. 12 (a) to 29 (a) are shown in FIGS. 12 (b) to 29 (b). Show. As can be seen from FIG. 12B to FIG. 26B, the conditions for obtaining higher resolution than in the case of p = a are observed in the range of p <a, respectively. In FIG. 28 (b) and FIG. 29 (b), it is expected that an optimum condition exists when p> a, and at least p ≦ a. It can be seen that p = a is the optimum condition.
[0064]
In the description so far, the case of θ = 0 has been described. However, in the case of θ ≠ 0, as shown in FIG. 30, the scale pattern is projected onto a plane perpendicular to the central axis of the light beam. Assuming that they are equivalent and assuming that p · cos θ is an equivalent scale pitch, it is possible to determine the conditions under which the optimum resolution can be obtained. Here, since p · cos θ = p when θ = 0, it is possible to express all cases using p · cos θ.
[0065]
As is apparent from the above description, the condition for optimizing the resolution is obtained with p · cos θ <a when the light source and the scale 20 are relatively close to each other. In this regard, the following is a description of the range in which optimum conditions for each of the cases are obtained by dividing the cases according to the value of L (changing the parameter m).
(1) L = 0.095a ² / Λ to 0.11a ² In the case of / λ (FIGS. 8, 12, and 14), FIG. 8A shows L = 0.095a. ² / Λ, FIG. 12A shows L = 0.1a ² / Λ, FIG. 13A shows L = 0.11a ² The light intensity distribution in the case of / λ is shown.
[0066]
L = 0.095a ² At / λ, as shown in FIG. 8 (a), the maximum value of the light amount is seen on the optical axis, and the minimum value of the light amount is located at both side distances Lλ / a across the optical axis. Maximum values are observed near distances 2Lλ / a, 3Lλ / a, and 4Lλ / a, respectively.
[0067]
When L is increased from here, as shown in FIG. 12A, the light intensity at the maximum value on the optical axis gradually decreases, and L = 0.11a. ² In the vicinity of / λ, the maximum value on the optical axis almost disappears as shown in FIG. Further, the local maximum values of the distances 2Lλ / a, 3Lλ / a, and 4Lλ / a on both sides of the optical axis are considerably reduced in light intensity except for the maximum value of 2Lλ / a.
[0068]
As above, 0.095a ² /Λ≦L≦0.11a ² In the range of / λ, the local maximum values of the distance 2Lλ / a on the optical axis and on both sides of the optical axis are dominant, and the in-phase portions of the scale (for example, the reflection portion) are arranged near these local maximum values, respectively. It can be considered that a large amplitude can be obtained when the relationship is difficult.
[0069]
With the above concept, referring to FIG. 8B, FIG. 12B, and FIG. 13B, a condition suitable for high resolution is expressed by a mathematical expression.
1.6 Lλ / a ≦ p · cos θ ≦ 2.4 Lλ / a
(0.095a ² /Λ≦L≦0.11a ² / Λ)
It becomes.
(2) 0.095a ² /Λ≦L≦0.13a ² / Λ (FIGS. 8 and 12 to 15) FIG. 8A shows L = 0.095a. ² / Λ, FIG. 12A shows L = 0.1a ² / Λ, FIG. 13A shows L = 0.11a ² / Λ, FIG. 14A shows L = 0.125a. ² / Λ, FIG. 15A shows L = 0.13a ² The light intensity distribution in the case of / λ is shown.
[0070]
0.095a ² /Λ≦L≦0.11a ² In the range of / λ, the diffraction pattern changes as shown in (1) above. As L is further increased, as shown in FIG. 14A, the maximum value on the optical axis disappears and becomes a minimum value, and the minimum value at the position of the optical axis side distance Lλ / a becomes the maximum value. , The light intensity increases. In addition, the local maximum values of the distances 2Lλ / a, 3Lλ / a, and 4Lλ / a on both sides of the optical axis are observed, but the light intensity decreases.
[0071]
When L is further increased, L = 0.13a ² In the vicinity of / λ, the maximum value of the position of the optical axis side distance Lλ / a becomes dominant as shown in FIG. 15A, and the maximum value of the optical axis side distance 2Lλ / a that has been dominant so far is Exceeds light intensity.
[0072]
As above, 0.095a ² /Λ≦L≦0.13a ² In the range of / λ, at least the local maximum value of the distance 2Lλ / a on both sides of the optical axis is dominant. It is considered that a large amplitude can be obtained.
[0073]
With the above concept, referring to FIG. 8B and FIGS. 12B to 15B, the conditions suitable for high resolution are expressed by mathematical formulas.
4.6 Lλ / a ≦ p · cos θ ≦ 7.4 Lλ / a
(0.095a ² /Λ≦L≦0.13a ² / Λ)
It becomes.
(3) 0.13a ² /Λ≦L≦0.21a ² / Λ (FIGS. 15 to 18)
FIG. 15A shows L = 0.13a. ² / Λ, FIG. 16A shows L = 0.15a ² / Λ, FIG. 17A shows L = 0.2a ² / Λ, FIG. 18A shows L = 0.21a. ² The light intensity distribution in the case of / λ is shown.
[0074]
L = 0.13a ² When the value of L is increased from / λ, as shown in FIG. 16A, the maximum value of the position of Lλ / a on both sides of the optical axis once becomes dominant, but when L is further increased, FIG. ), The local minimum on the optical axis becomes the local maximum again. And L = 0.21a ² In the vicinity of / λ, as shown in FIG. 18A, the light intensity of the local maximum value on the optical axis and the local maximum value at the positions of both optical axis Lλ / a are substantially equal.
[0075]
As described above, 0.13a ² /Λ≦L≦0.21a ² In the range of / λ, the maximum value at the position of Lλ / a on both sides of the optical axis is dominant, and when the relationship is such that the in-phase part of the scale (for example, the reflection part) is arranged near this maximum value. It is considered that a large amplitude can be obtained.
[0076]
With the above concept, referring to FIG. 15B to FIG. 18B, the conditions suitable for high resolution can be expressed by mathematical expressions: 2Lλ / a ≦ p · cos θ ≦ 4Lλ / a
(0.13a ² /Λ≦L≦0.21a ² / Λ)
It becomes.
(4) 0.21a ² /Λ≦L≦0.3a ² / Λ (FIGS. 18 to 21)
FIG. 18A shows L = 0.21a. ² / Λ, FIG. 19 (a) shows L = 0.225a. ² / Λ, FIG. 20A shows L = 0.25a ² / Λ, FIG. 21 (a) shows L = 0.3a ² The light intensity distribution in the case of / λ is shown.
[0077]
L = 0.21a ² When the value of L is increased from / λ, as shown in FIGS. 19A to 21A, the light intensity of the maximum value on the optical axis that appears again increases and becomes dominant. Further, the maximum value at the position of both optical axis Lλ / a gradually becomes inconspicuous, and L = 0.3a as shown in FIG. ² In the vicinity of / λ, the maximum value is hardly seen.
[0078]
As described above, 0.21a ² /Λ≦L≦0.3a ² In the range of / λ, the local maximum on the optical axis is dominant, but the influence of the local maximum on the positions of both sides of the optical axis Lλ / a cannot be ignored. Therefore, it is considered that a large amplitude can be obtained when the same phase portion (for example, a reflection portion) of the scale is arranged in the vicinity of the above three maximum values.
[0079]
With the above concept, referring to FIG. 18 (b) to FIG. 21 (b), a condition suitable for high resolution is expressed by a mathematical expression.
1.1 Lλ / a ≦ p · cos θ ≦ 1.6 Lλ / a
(0.21a ² /Λ≦L≦0.3a ² / Λ)
It is expressed.
▲ 5 ▼ 0.3a ² / Λ ≦ L (FIGS. 21 to 29)
FIG. 21A shows L = 0.3a. ² / Λ, FIG. 22A shows L = 0.35a. ² / Λ, FIG. 23A shows L = 0.375a. ² / Λ, FIG. 24A shows L = 0.4a ² / Λ, FIG. 25 (a) shows L = 0.5a ² / Λ, FIG. 26A shows L = 0.55a. ² / Λ, FIG. 27A shows L = 0.6a ² / Λ, FIG. 28A shows L = 0.75a. ² / Λ, FIG. 29A shows L = 1.0a ² The light intensity distribution in the case of / λ is shown.
[0080]
L = 0.3a ² When the value of L is increased from / λ, a minimum value appears at the position of Lλ / a on both sides of the optical axis as shown in FIG. 22A to FIG. 26A, and the maximum value on the optical axis becomes more dominant. become. Further, as mentioned above, L = 0.6a ² As shown in FIG. 27 to FIG. 29, when it exceeds / λ, the condition suitable for high resolution can no longer be seen under the condition of p · cos θ <a, and the optimum condition can be seen when p · cos θ ≧ a. Become.
[0081]
Thus, 0.3a ² /Λ≦L≦0.6a ² Since the maximum value on the optical axis is dominant in the range of / λ, the scale pitch may be determined under optimum conditions for the spot width of this maximum value.
With the above concept, referring to FIG. 21 (b) to FIG. 26 (b), a condition suitable for high resolution is expressed by a mathematical expression.
1.2Lλ / a ≦ p · cos θ <a
(0.3a ² /Λ≦L≦0.6a ² / Λ)
It becomes.
[0082]
As described above, in the cases (1) to (5), it is assumed that the resolution of the encoder is determined by the scale pitch p and the quotient (p / amplitude) of the encoder signal amplitude. The case where the value is smaller than the quotient obtained when = a, that is, the condition for obtaining the highest resolution has been described. As described above, in the present embodiment, the optical encoder conventionally used under the condition of p · cos θ ≧ a has a limit of resolution, whereas p · cos θ <a that has not been disclosed conventionally. Thus, an encoder having a higher resolution can be obtained than when p · cos θ ≧ a.
[0083]
Furthermore, the optical encoder of the present embodiment can be used even when the quotient (p / amplitude) is larger than the quotient obtained when p = a. Therefore, the range in which the amplitude of the encoder signal is observed when the quotient (p / amplitude) is not necessarily minimum will be described below.
[0084]
As described above, it has been found that the scale pitch p of the encoder may be adjusted to approximately the interval in the x-axis direction (the central axis of the light beam (the direction perpendicular to the main axis of the beam) where the maximum value of the light intensity appears. Further, the interval in the x-axis direction where the light intensity has a maximum value is an integral multiple of Lλ / a as shown in FIGS. 8A, 16A, and 18A, for example. Can be explained from the diffraction theory of light.
[0085]
Therefore, in order to be able to observe the amplitude of the encoder signal, it is derived that the scale pitch should be set to an integer multiple of the interval Lλ / a in the x-axis direction where the light intensity becomes the maximum value.
[0086]
In order to simplify the description, the factor k is defined as follows.
k≡p / (Lλ / a)
Based on this concept, the minimum value of the scale pitch p should be about Lλ / a (corresponding to about k = 1).
[0087]
As a result of actual calculation, as shown in FIGS. 16B to 29B, when the scale pitch p at which the amplitude of the encoder signal is observed is expressed by a mathematical expression, the inclination of the beam optical axis with respect to the scale 20 is taken into consideration. do it,
0.8Lλ / a ≦ p · cos θ <a (L ≦ 0.6a ² / Λ)
Better observation,
0.8Lλ / a ≦ p · cos θ <a (0.6a ² /Λ≦L≦1.0a ² / Λ)
Can be observed as well.
[0088]
In summary,
0.8Lλ / a ≦ p · cos θ <a (L ≦ 1.0a ² / Λ)
What should I do?
[0089]
Conventionally, the distance L between the light source (surface emitting laser 10) and the scale 20 is a certain distance (a ² In the case of larger than / λ), it has been considered that an encoder signal cannot be obtained unless the scale pitch p is larger than Lλ / a.
[0090]
However, as is apparent from FIGS. 30B and 31B, it can be seen that an encoder signal can be obtained even when the scale pitch p is smaller than Lλ / a. FIG. 30A shows L = 2.0a. ² / Λ, FIG. 31A shows L = 4.0a ² The light intensity distribution in the case of / λ is shown.
[0091]
Further, as apparent from FIGS. 30B and 31B, the encoder output starts to rise from the state where the scale pitch p is 0.8 Lλ / a, and even when the scale pitch p is smaller than Lλ / a. It can be seen that an encoder signal can be obtained.
[0092]
Based on the above fact, the distance L between the light source (surface emitting laser 10) and the scale 20 is a ² If the condition for obtaining the encoder output even when larger than / λ is expressed by a mathematical expression,
0.8 Lλ / a ≦ p · cos θ <1.0 Lλ / a
(L ≧ 1.0a ² / Λ)
It becomes.
[0093]
Thus, according to the present embodiment, the scale pitch p that can be used in the conventional optical encoder is set to L ≦ a ² In the case of / λ, p · cos ≧ a, L> a ² In the case of / λ, there was a limit of p ≧ Lλ / a, but beyond this limit, L ≦ a ² In the case of / λ, p · cos <a, L> a ² In the case of / λ, it can be seen that a scale satisfying the condition of p <Lλ / a can be used. Further, in this embodiment, since a scale having a smaller pitch than that of the conventional optical encoder can be used, the division order of the output signal from the encoder is made smaller in order to obtain a desired resolution ( The signal processing circuit can be easily manufactured.
[0094]
In the present embodiment, the case where the present invention is applied to a reflective encoder has been described. However, the present invention can also be applied to a transmission encoder.
[0095]
【The invention's effect】
Thus, according to the present invention, the scale pitch can be made smaller than that of the conventional encoder, and high resolution can be realized.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a surface emitting laser according to an embodiment of the invention.
FIGS. 2A and 2B are diagrams showing a modification of the surface emitting laser according to the embodiment of the present invention.
FIG. 3 is a diagram showing a spread state of the emitted light from the opening of the surface emitting laser.
FIG. 4A is a diagram showing a position where the diffracted light intensity is observed, and FIG. 4B is a diagram showing a light intensity distribution at each observation position.
FIG. 5 is a perspective view showing a configuration of an optical encoder according to an embodiment of the invention.
FIG. 6 is a cross-sectional view showing a configuration of an optical encoder according to an embodiment of the invention.
FIG. 7 is a side view showing the configuration of the optical encoder according to the embodiment of the invention.
FIG. 8 (a) shows that L = 0.095a ² FIG. 8B shows a light intensity distribution in the case of / λ, and L = 0.095a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIGS. 9A to 9E are diagrams showing changes in the amount of reflected light that occurs when the scale of p = 10 μm is moved. The hatched lines in FIG. 9 are used to determine the amount of reflected light. The area of the necessary part is shown. In other words, the diagonal lines in the figure do not indicate a cross section.
FIG. 10 is a diagram illustrating a change state of the amount of reflected light obtained when the scale of p = 10 μm is moved by one pitch.
FIGS. 11 (a) and 11 (b) are diagrams showing changes in the amount of reflected light that occurs when the scale of p = 6 μm is moved; FIGS. 11 (c) and 11 (d) show p = 18 μm. FIG. 6 is a diagram showing a change state of the reflected light amount that occurs when the scale is moved, and the oblique lines in the drawing indicate the area of the portion necessary for obtaining the reflected light amount. In other words, the diagonal lines in the figure do not indicate a cross section.
FIG. 12 (a) shows that L = 0.1a. ² FIG. 12B shows a light intensity distribution in the case of / λ, and L = 0.1a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 13 (a) shows that L = 0.11a. ² FIG. 13B shows a light intensity distribution in the case of / λ, and L = 0.11a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 14 (a) shows that L = 0.125a. ² FIG. 14B shows the light intensity distribution in the case of / λ, and L = 0.125a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 15 (a) shows that L = 0.13a ² FIG. 15B shows a light intensity distribution in the case of / λ, and L = 0.13a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 16 (a) shows that L = 0.15a. ² FIG. 16B shows a light intensity distribution in the case of / λ, and L = 0.15a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 17 (a) shows that L = 0.2a. ² FIG. 17B shows a light intensity distribution in the case of / λ, and L = 0.2a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 18 (a) shows that L = 0.21a. ² FIG. 18B shows a light intensity distribution in the case of / λ, and L = 0.21a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 19 (a) shows that L = 0.225a. ² FIG. 19B shows a light intensity distribution in the case of / λ, and L = 0.225a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 20 (a) shows that L = 0.25a. ² FIG. 20B shows a light intensity distribution in the case of / λ, and L = 0.25a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 21 (a) shows that L = 0.3a. ² FIG. 21B shows a light intensity distribution in the case of / λ, and L = 0.3a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 22 (a) shows that L = 0.35a. ² FIG. 22B shows a light intensity distribution in the case of / λ, and L = 0.35a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 23 (a) shows that L = 0.375a. ² FIG. 23B shows a light intensity distribution in the case of / λ, and L = 0.375a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 24 (a) shows that L = 0.4a. ² FIG. 24B shows a light intensity distribution in the case of / λ, and L = 0.4a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 25 (a) shows that L = 0.5a ² FIG. 25B shows a light intensity distribution in the case of / λ, and L = 0.5a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 26 (a) shows that L = 0.55a. ² FIG. 26 (b) shows the light intensity distribution in the case of / λ, and L = 0.55a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 27 (a) shows that L = 0.6a ² FIG. 27B shows a light intensity distribution in the case of / λ, and L = 0.6a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 28 (a) shows that L = 0.75a. ² FIG. 28B shows a light intensity distribution in the case of / λ, and L = 0.75a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 29 (a) shows that L = 1.0a. ² FIG. 29B shows a light intensity distribution in the case of / λ, and L = 1.0a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 30 (a) shows that L = 2.0a ² FIG. 30B shows a light intensity distribution in the case of / λ, and L = 2.0a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 31 (a) shows that L = 4.0a ² FIG. 31B is a diagram showing the light intensity distribution in the case of / λ, and L = 4.0a. ² It is a figure which shows the relationship between the scale pitch in the case of / (lambda), and pp amplitude.
FIG. 32 is a diagram for explaining an angle θ between a pitch direction of the scale and a plane perpendicular to the central axis of the light beam.
FIG. 33 is a diagram showing a configuration of a conventional optical encoder.
[Explanation of symbols]
10 ... Surface emitting laser
16 ... Opening
20 ... Scale
30. Photodetector

Claims (10)

A moving scale that moves relative to the light source, a surface emitting semiconductor laser light source for irradiating a part of the moving scale, and a light receiving element for receiving reflected light or transmitted light from the moving scale In the optical encoder
The distance between the moving scale and the light beam exit surface of the surface emitting laser light source at the central axis of the light beam is L, the wavelength of the light beam is λ, the scale pitch of the moving scale is p, and the pitch direction of the moving scale Is the angle between the plane perpendicular to the central axis of the light beam and θ, and the aperture length of the surface-emitting laser light source along the direction in which the pitch direction of the moving scale is projected onto the plane perpendicular to the central axis of the light beam is a. ,
When L ≦ 1.0a ² / λ, p · cos θ <a
An optical encoder characterized by satisfying the relationship: 0.8Lλ / a ≦ p · cos θ <a when L ≦ 1.0a ² / λ
The optical encoder according to claim 1, wherein the relationship is satisfied. In the case of 0.095a ² /λ≦L≦0.11a ² / λ,
1.6 Lλ / a ≦ p · cos θ ≦ 2.4 Lλ / a
The optical encoder according to claim 2, wherein the relationship is satisfied. If 0.095a ² /λ≦L≦0.13a ² / λ,
4.6 Lλ / a ≦ p · cos θ ≦ 7.4 Lλ / a
The optical encoder according to claim 2, wherein the relationship is satisfied. In the case of 0.13a ² /λ≦L≦0.21a ² / λ,
2Lλ / a ≦ p · cos θ ≦ 4Lλ / a
The optical encoder according to claim 2, wherein the relationship is satisfied. When 0.21a ² /λ≦L≦0.3a ² / λ,
1.1 Lλ / a ≦ p · cos θ ≦ 1.6 Lλ / a
The optical encoder according to claim 2, wherein the relationship is satisfied. When 0.3a ² /λ≦L≦0.6a ² / λ,
1.2Lλ / a ≦ p · cos θ <a
The optical encoder according to claim 2, wherein the relationship is satisfied. A moving scale that moves relative to the light source, a surface emitting semiconductor laser light source for irradiating a part of the moving scale, and a light receiving element for receiving reflected light or transmitted light from the moving scale In the optical encoder
The distance between the moving scale and the light beam exit surface of the surface emitting laser light source at the central axis of the light beam is L, the wavelength of the light beam is λ, the scale pitch of the moving scale is p, and the pitch direction of the moving scale Is the angle between the plane perpendicular to the central axis of the light beam and θ, and the aperture length of the surface-emitting laser light source along the direction in which the pitch direction of the moving scale is projected onto the plane perpendicular to the central axis of the light beam is a. ,
When L ≧ 1.0a ² / λ, 0.8 Lλ / a ≦ p · cos θ <1.0 Lλ / a
An optical encoder characterized by satisfying the relationship: A moving scale that moves relative to the light source, a surface emitting semiconductor laser light source for irradiating a part of the moving scale, and a light receiving element for receiving reflected light or transmitted light from the moving scale In the optical encoder
The distance between the moving scale and the light beam exit surface of the surface emitting laser light source at the central axis of the light beam is L, the wavelength of the light beam is λ, the scale pitch of the moving scale is p, and the pitch direction of the moving scale Is the angle between the plane perpendicular to the central axis of the light beam and θ, and the aperture length of the surface-emitting laser light source along the direction in which the pitch direction of the moving scale is projected onto the plane perpendicular to the central axis of the light beam is a. ,
P · cos θ <a when 0.6a ² /λ<L≦1.0a ² / λ
An optical encoder characterized by satisfying the relationship: In the case of 0.6a ² /λ<L≦1.0a ² / λ, 0.8 Lλ / a ≦ p · cos θ <a
The optical encoder according to claim 9, wherein the relationship is satisfied.

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