JP3858994B2

JP3858994B2 - Position detection method and apparatus

Info

Publication number: JP3858994B2
Application number: JP2002345958A
Authority: JP
Inventors: 喜彦岡山
Original assignee: Azbil Corp
Current assignee: Azbil Corp
Priority date: 2002-11-28
Filing date: 2002-11-28
Publication date: 2006-12-20
Anticipated expiration: 2022-11-28
Also published as: JP2004177335A; CN1308654C; CN1504721A

Description

【０００１】
【発明の属する技術分野】
本発明は、例えばロールから巻き戻されて一方向に高速に搬送される帯状体の縁部（エッジ）の幅方向における位置変位を高速度に、しかも高精度に検出することのできる位置検出方法および装置に関する。
【０００２】
【関連する背景技術】
フィルムやシート等の物品の縁部（エッジ）の位置を検出する位置検出装置として、物品（検査対象物）に向けて平行光を照射する投光部（光源）と、この投光部に対峙させて設けたＣＣＤ等の受光部（ラインセンサ）とを備えた光学式のものがある。この種の光学式の位置検出装置は、基本的には上記物品により遮られなかった平行光を受光部にて受光し、該受光部における平行光の受光領域と非受光領域（遮光領域）との境界を前記物品（検査対象物）の縁部（エッジ）の位置として検出するものである。
【０００３】
また最近ではレーザ光等の単色平行光を用い、物品（検査対象物）のエッジにおける上記単色平行光のフレネル回折に着目して前記ラインセンサ（受光部）の受光面上における光強度分布から上記物品（検査対象物）の縁部（エッジ）の位置を高精度に検出する装置も提唱されている（例えば特許文献１を参照）。
【０００４】
【特許文献１】
特開平８−２４７７２６号公報
【０００５】
【発明が解決しようとする課題】
ところで単色平行光のフレネル回折によるラインセンサ（受光部）の受光面上における光強度分布を利用して検査対象物のエッジの位置を検出する場合、予め上記光強度分布の特性を高精度に求めておくことが必要である。ちなみに上記フレネル回折による光強度分布は、図８に示すようにエッジ位置近傍で急峻に立ち上がり、エッジ位置から離れるに従って振動しながら収束する。このような光強度分布の特性は、単色平行光の波長をλ、検査対象物のエッジから受光面までの距離をｚ、受光面上でのエッジ位置を［ｘ＝０］としたとき、∫を［ｘ＝０］から［（２／λｚ）^1/2・ｘ］までの積分を示す演算記号として
光強度＝ ( １／２ ) ｛ [ １／２＋Ｓ ( ｘ )] ² ＋ [ １／２＋Ｃ ( ｘ )] ² ｝
Ｓ(ｘ) ＝∫ sin( π／２ )・Ｕ ² d Ｕ
Ｃ(ｘ) ＝∫ cos( π／２ )・Ｕ ² d Ｕ
として表される。但し、Ｕは仮の変数である。そして受光面で収束する光強度を［１.００］とした場合、エッジ位置［ｘ＝０］における光強度（相対値）は［０.２５］となる。
【０００６】
尚、上記関数Ｓ(ｘ),Ｃ(ｘ)については、専ら数学公式集に示されるようにフレネル関数を用いて
Ｓ(ｘ)’≒（１／２）−（１／πｘ）cos(πｘ²／２)
Ｃ(ｘ)’≒（１／２）＋（１／πｘ）sin(πｘ²／２)
としてそれぞれ近似することができる。従って基本的には上記近似式Ｓ(ｘ)’,Ｃ(ｘ)’を用いることにより、前記ラインセンサの各受光セルによる受光強度から前述したエッジ位置を計算することができる。
【０００７】
しかしながら実際に計算してみると、図９に示すように関数Ｓ(ｘ),Ｃ(ｘ)とその近似式Ｓ(ｘ)’,Ｃ(ｘ)’とは、その立ち上がり以降の収束部分（２山目以降）において非常に良好に近似するものの、最初の立ち上がり部分（１山目）において大きなずれがあることが否めない。特にこの最初の立ち上がり部分の特性はエッジ検出において重要な役割を担うものであり、その特性のずれはエッジ位置の検出精度の低下の要因となる。
【０００８】
本発明はこのような事情を考慮してなされたもので、その目的は、フレネル回折による受光面上での光強度分布を、特に最初の立ち上がり部分の特性を高精度に近似し、これによって高精度な位置検出を行い得るエッジ検出方法および装置を提供することにある。
また本発明の別の目的は、複数の受光セルの配列ピッチが粗い安価なラインセンサを用いた場合であっても、エッジ位置の検出を高精度に、しかも高速度に行い得るエッジ検出装置を提供するにある。
【０００９】
【課題を解決するための手段】
上述した目的を達成するべく本発明に係る位置検出方法は、一方向に所定のピッチで配列された複数の受光セルを備えたラインセンサ（受光部）と、このラインセンサに対峙して設けられて該ラインセンサの上記複数の受光セルに向けて単色平行光を投光する投光部と、前記ラインセンサの出力を解析して前記単色平行光の光路に存在する遮蔽物の前記受光セルの配設方向におけるエッジ位置を検出するエッジ検出部とを具備した位置検出装置に適用されるものであって、
特に前記エッジ検出部においては、前記遮蔽物による単色平行光のフレネル回折による前記ラインセンサの受光面上での光強度分布の最初の立ち上がり部分における光強度変化をハイパボリックセカンド関数sech(ｘ)により近似し、このハイパボリックセカンド関数sech(ｘ)を用いて前記ラインセンサの各受光セルによる受光強度を解析して前記遮蔽物のエッジ位置を求めることを特徴としている。
【００１０】
即ち、本発明に係る位置検出方法は、単色平行光のフレネル回折による受光面上での光強度分布の最初の立ち上がり部分、特にその１山目の分布特性が、ａ,ｂ,ｃをそれぞれ係数として
ｙ＝ａ／cosh（ｂｘ＋ｃ）
なるハイパボリックコサイン関数cosh(ｘ)の逆数、つまりハイパボリックセカンド関数sech(ｘ)に極めて良好に近似することを見出してなされている。そしてこのハイパボリックセカンド関数sech(ｘ)を用いて前記ラインセンサの出力（光強度）を解析し、前記フレネル回折による受光面上での光強度分布において光強度（相対値）が［０.２５］となる位置[ｘ＝０]を、前記遮蔽物のエッジ位置として検出することを特徴としている。
【００１１】
好ましくは前記ハイパボリックセカンド関数sech(ｘ)を用いた前記ラインセンサの各受光セルによる受光強度の解析を、例えば
予め規定された基準受光強度［０.２５］の近傍の該基準受光強度より大きい受光強度を得た受光セルおよび上記基準受光強度より小さい受光強度を得た受光セルをそれぞれ求め（第１段階）、
これらの各受光セルの受光面において当該受光強度となる受光位置をハイパボリックセカンド関数sech(ｘ)の逆関数ln ｛ [ １＋ ( １−Ｙ ² ) ^1/2 ] ／Ｙ｝に従ってそれぞれ求めた後（第２段階）、
これらの受光位置から前記基準受光強度となる位置を前記遮蔽物のエッジ位置として求める（第３段階）ことを特徴としている。
【００１２】
また本発明に係る位置検出装置は、一方向に所定のピッチで配列された複数の受光セルを備えたラインセンサと、このラインセンサに対峙して設けられて該ラインセンサの上記複数の受光セルに向けて単色平行光を投光する投光部と、前記遮蔽物による単色平行光のフレネル回折による前記ラインセンサの受光面上での光強度分布に従って前記ラインセンサの出力を解析して、前記単色平行光の光路に存在する遮蔽物の前記受光セルの配設方向におけるエッジの位置を検出するエッジ検出部とを備えたものであって、特に前記エッジ検出部として、
前記ラインセンサの出力から予め規定された基準受光強度［０.２５］の近傍の該基準受光強度より大きい受光強度を得た受光セルと上記基準受光強度より小さい受光強度を得た受光セルとをそれぞれ特定する受光セル特定手段と、
ハイパボリックセカンド関数sech(ｘ)の逆関数ln ｛ [ １＋ ( １−Ｙ ² ) ^1/2 ] ／Ｙ｝により近似した光強度分布に従って前記受光セル特定手段にて特定した各受光セルの受光面において当該受光セルの受光強度となる受光位置をそれぞれ求める受光位置算出手段と、
この受光位置算出手段でそれぞれ求められた受光位置から前記基準受光強度となる位置を前記遮蔽物のエッジ位置として検出する補間演算手段と
を設けたことを特徴としている。
【００１３】
好ましくは前記受光セル特定手段は、前記ラインセンサの出力を予め正規化した後、前記基準受光強度［０.２５］より大きい受光強度を得た受光セルと上記基準受光強度［０.２５］より小さい受光強度を得た受光セルとを、具体的には前記基準受光強度［０.２５］の近傍の受光強度が得られた少なくとも２つの互いに隣接する受光セルＣn,Ｃn-1を特定するように構成することが望ましい。
【００１４】
このように構成された位置検出装置によれば、基準受光強度［０.２５］を挟む受光強度が得られた少なくとも受光セルにおいて当該受光セルの受光強度となる受光位置を、フレネル回折による光強度分布の最初の立ち上がり部分の特性を高精度に近似したハイパボリックセカンド関数sech(ｘ)を用いることでそれぞれ高精度に求めることができるので、これらの受光位置からラインセンサの受光面上におけるエッジの位置、つまり受光強度が［０.２５］となる位置を高精度に求めることができる。しかも上記ハイパボリックセカンド関数sech(ｘ)の逆関数ln ｛ [ １＋ ( １−Ｙ ² ) ^1/2 ] ／Ｙ｝については、これを級数展開やＣＰＵに実装されている命令に従って演算することができるので、その演算処理速度（位置検出速度）を十分に高速化することができる。
【００１５】
尚、ラインセンサの出力の最初にピーク値をとる受光セルとその手前の受光セルをそれぞれ求め、これらの各受光セルの各受光強度から前述したハイパボリックセカンド関数sech(ｘ)の逆関数ln ｛ [ １＋ ( １−Ｙ ² ) ^1/2 ] ／Ｙ｝に従ってエッジ位置を求めることも可能である。このようにしてエッジ位置を検出すれば、例えば検出対象物が半透明体からなり、検出対象物によって単色平行光を完全に遮光することができない場合であっても上記検出対象物の縁部（エッジ）の位置を高精度に検出することが可能となる。
【００１６】
【発明の実施の形態】
以下、図面を参照して本発明の一実施形態に係る位置検出方法および装置について説明する。
図１はこの実施形態に係る位置検出装置の概略構成図であり、基本的には図２に示すように一方向に所定のピッチｐで配列した複数の受光セル１ａを備えたラインセンサ（受光部）１と、このラインセンサ１の受光面に対峙して設けられて該ラインセンサ１の複数の受光セル１ａに向けて単色平行光４を投光する投光部２と、前記ラインセンサ１の出力を解析して前記単色平行光４の光路に位置付けられた、例えば帯状体からなる遮蔽物（検出対象物）７の前記受光セル１ａの配設方向におけるエッジ位置を検出するエッジ検出部３とを備える。
【００１７】
尚、投光部２は、例えばレーザダイオード（ＬＤ）からなる光源２ａが発した単色光（レーザ光）を導く光ファイバ２ｂと、この光ファイバ２ｂを介して導かれた単色光を平行光に変換して投射する投射レンズ（コリメータレンズ）２ｃとを具備したものからなる。このような投光部２は、前記ラインセンサ１と共に所定の隙間を形成したコの字状の筐体５に上記隙間を挟んで互いに対峙させて一体に組み込まれて、１つのセンシングユニットとして形成されている。
【００１８】
前述したエッジ検出部３は、このようなセンシングユニットの隙間を通過する前記遮蔽物（検出対象物）７の端部（エッジ）の位置を、前記ラインセンサ１の出力から検出する役割を担う。具体的には前記エッジ検出部３は、前記単色平行光の一部が遮蔽物（検出対象物）７にて遮られたとき、その端部（エッジ）においてフレネル回折が生じること、そしてフレネル回折を生じて前記ラインセンサ１の受光面に到達する光の強度が、前述した図７に示したようにエッジ位置近傍で急峻に立ち上がり、エッジ位置から離れるに従って振動しながら収束する分布特性を持つことに着目し、受光面上での光強度分布に従って前記遮蔽物７の端部（エッジ）の位置を高精度に検出するように構成される。
【００１９】
基本的には上述したラインセンサ１、投光部２、およびエッジ検出部３を備えて構成される位置検出装置は、例えばロールから巻き戻されて一方向に高速度に走行させて搬送される帯状体（遮蔽物；検出対象物）７の幅方向の位置ずれを、その縁部（エッジ）位置の変化として検出するように設けられる。そして検出した上記帯状体７の縁部（エッジ）の位置を、該帯状体７の走行駆動系にフィードバックすることで、その走行駆動を制御するために用いられる。
【００２０】
さてこのような位置検出装置において、この発明に係る位置検出方法および装置が特徴とするところは、前記エッジ検出部３においてラインセンサ１の出力から遮蔽物７のエッジの位置を検出するに際して、フレネル回折による光強度分布を近似したハイパボリックセカンド関数sech(ｘ)を用いてエッジ位置を算出する点にある。即ち、フレネル回折による前記ラインセンサ１の受光面上での光強度分布を、特にその最初の立ち上がり部分（１山目）における光強度変化をハイパボリックセカンド関数sech(ｘ)により近似し、このハイパボリックセカンド関数sech(ｘ)を用いて近似した光強度分布に従って前記ラインセンサ１の各受光セル１ａによる受光強度を解析して前記遮蔽物７のエッジ位置を求めるようにした点にある。
【００２１】
このフレネル回折による光強度分布のハイパボリックセカンド関数sech(ｘ)による近似について説明すると、前述したようにフレネル関数を用いた場合、光強度分布の最初の立ち上がり部分（１山目）における誤差が非常に大きいと言う問題がある。そこで光強度分布の最初の立ち上がり部分（１山目）だけに着目し、その山の形状（光強度の変化傾向）から２乗の有理関数、ハイパボリックコサイン関数、および指数関数を用いてそれぞれ近似することを試みた。
【００２２】
具体的には２乗の有理関数として
ｙ＝ａ／[(ｘ＋ｂ)²＋ｃ]
ハイパボリックコサイン関数の逆数として
ｙ＝ａ／cosh(ｂｘ＋ｃ)
そして指数関数として
ｙ＝ａ・exp[−ｂ(ｘ＋ｃ)²]
なる３つの関数を考え、これらの各関数に示される係数ａ,ｂ,ｃにそれぞれ適当な値を代入しながらその特性曲線を求めたところ、図３に示すような計算結果が得られた。
【００２３】
ちなみに図３において特性Ａは光強度分布の理論値を示しており、また特性Ｂは上記２乗の有理関数における係数ａ,ｂ,ｃをそれぞれ［０.０５７］,［−０.３８］,［０.０４１７］としたときの光強度ｙの変化、特性Ｃは前記ハイパボリックコサイン関数の逆数における係数ａ,ｂ,ｃをそれぞれ［１.３７］,［６.２９］,［−２.４０］としたときの光強度ｙの変化、そして特性Ｄは前記指数関数における係数ａ,ｂ,ｃをそれぞれ［１.３７］,［１６.３０］,［−０.３８］としたときの光強度ｙの変化をそれぞれ示している。但し、これらの計算は、単色光の波長λを６７０ｎｍ、遮蔽物７のエッジからラインセンサ１の受光面迄の距離ｚを３００ｍｍとして行った。
【００２４】
これらの計算結果に示されるように、ハイパボリックコサイン関数の逆数、即ち、ハイパボリックセカンド関数sech(ｘ)を用いれば、フレネル回折による光強度分布の、特に最初の立ち上がり部分（１山目）の特性を非常に高精度に近似し得ることが明らかとなった。特に所定の基準受光強度［０.２５］となるエッジ位置の理論値に対する誤差が６.７７μｍと非常に小さく、フレネル回折による光強度分布を極めて精度良く近似し得ることを見出した。
【００２５】
ちなみに前記ハイパボリックコサイン関数の逆数を前述したフレネル回折による光強度分布の式に当て嵌めて該光強度分の最初の立ち上がり部分（１山目）までを近似すると、そのハイパボリックセカンド関数sech(ｘ)は
光強度＝１.３７・sech｛１.９８３(２／λｚ)^1/2ｘ−２.３８６｝
として示される。そしてこの近似式は、３桁程度の精度で光強度分布の理論式に一致することが確認できた。
【００２６】
本発明はこのような知見に立脚し、フレネル回折による光強度分布を、特にその最初の立ち上がり部分を上述したハイパボリックセカンド関数sech(ｘ)を用いて近似し、この光強度分布を近似したハイパボリックセカンド関数sech(ｘ)を用いて前述したラインセンサ１の出力から遮蔽物７のエッジ位置を高精度に検出するようにしている。
【００２７】
この際、その計算処理を簡略化し、エッジ位置の検出処理速度の高速化を図るべく次のような工夫をしている。この計算処理のアルゴリズムについて説明すると、ハイパボリックセカンド関数sech(ｘ)を用いて近似される光強度は、前述したように
光強度＝１.３７・sech｛１.９８３(２／λｚ)^1/2ｘ−２.３８６｝
として示される。ここで光強度（相対値）が［０.２５］の位置が（ｘ−ａ）であるとすると、上式から
０.２５＝１.３７・sech（ｘ−ａ）
なる関係を導くことができ、上記位置（ｘ−ａ）は
（ｘ−ａ）＝ sech^-1（０.２５／１.３７）＝１.８６６
として計算することができる。
【００２８】
そこで光強度（相対値）が［０.２５］となる位置を原点とするＸ-Ｙ座標に上述した光強度分布の式を置き換えて光強度ｙを表すと
ｙ＝１ . ３７・sech ｛１ . ９８ ( ２／λｚ ) ^1/2 ｘ−２ . ３９｝
となる。そしてその逆関数を計算すると、
Ｙ＝ｙ／１.３７，Ｘ＝１ . ９８（２／λｚ） ^1/2 ｘ
とおいて、
Ｘ＝２ . ３９− ln ｛ [ １＋ ( １−Ｙ ² ) ^1/2 ] ／Ｙ｝
として表すことができる。
尚、λは単色平行光の波長でその単位は [ ｎｍ ] 、ｚは検査対象物のエッジから受光面までの距離でその単位は [ ｍｍ ] 、またｘは受光面上でのエッジ位置でその単位は [ μｍ ] である。
【００２９】
そこでエッジ検出部３においては、例えば図４に示す手順に従い、先ずラインセンサ１における複数（ｍ個）の受光セル１ａによる各受光強度ｙ1,ｙ2,〜ｙmを上述した係数［１.３７］で除算してＸ-Ｙ座標上での光強度Ｙ1,Ｙ2,〜Ｙmに変換している（ステップＳ１）。そしてこれらの複数の受光セル１ａの内、例えば互いに隣接して前述した基準光強度［０.２５］よりも大きい受光強度を得た受光セルＣnと、上記基準光強度［０.２５］よりも小さい受光強度を得た受光セルＣn-1とをそれぞれ求めている（受光セル特定手段；ステップＳ２）。つまり複数の受光セル１ａ（Ｃ1,Ｃ2,〜Ｃm）間のそれぞれにおいて受光強度が［０.２５］となる、互いに隣接する２つの受光セルＣn,Ｃn-1を求めている。
【００３０】
そしてこれらの各受光セルＣn,Ｃn-1の受光強度Ｙn,Ｙn-1が得られる該受光セルＣn,Ｃn-1の受光面上での位置Ｘn,Ｘn-1を、前述した近似式に従って
Ｘn＝２ . ３９− ln ｛ [ １＋ ( １−Ｙ n ² ) ^1/2 ] ／Ｙ n ｝
Ｘn-1＝２ . ３９− ln ｛ [ １＋ ( １−Ｙ n-1 ² ) ^1/2 ] ／Ｙ n-1 ｝
としてそれぞれ逆変換により計算し（受光位置算出手段；ステップＳ３）、これらの位置Ｘn,Ｘn-1から図５にその概念を示すように受光強度が［０.２５］となる位置（エッジ位置）を補間演算により計算している（補間演算手段；ステップＳ４）。この補間演算については前述した近似式を用いて実行しても良いが、上述した２つの受光セルＣn,Ｃn-1間での光強度の変化が直線的であると見なし得る場合には、単純な直線補間であっても良い。
【００３１】
尚、ここでは隣接する受光セル１ａ間で光強度が［０.２５］となる位置を見出し、その位置をセル境界とする２つの受光セルＣn,Ｃn-1を特定したが、単に上記位置を挟む２つ以上の受光セルを特定しても良い。但し、この場合には必ず前述した近似式を用いて補間演算を行うことで、その演算精度の低下を防止するようにすれば良い。また上述した逆変換については、例えば予めその計算値を記憶したテーブルを用いることで、その演算処理負担を大幅に軽減して瞬時に実行することが可能である。
【００３２】
かくして上述した如くして遮光物７のエッジ位置を検出する位置検出方法および装置によれば、フレネル回折による光強度分布を高精度に近似したハイパボリックセカンド関数sech(ｘ)を用いて、ラインセンサ１の複数の受光セル１ａによる受光強度ｙからその光強度が［０.２５］となる位置Ｘを算出するので、その検出精度を十分に高くすることができる。また自然対数関数（ln関数）は、通常の浮動小数点演算（ＦＰＵ）機能を備えたマイクロプロセッサではその命令の中に含まれているが、このようなＦＰＵ機能を備えていないマイクロプロセッサであっても、例えば上記ハイパボリックセカンド関数sech(ｘ)、特にその逆関数 ln( ｘ ) については、例えば

として級数展開が可能であり、その収束も速いので計算が容易である。従ってエッジ位置の検出を簡単に、しかも高精度に行うことが可能となる等の効果が奏せられる。
【００３３】
またラインセンサ１の出力は、該ラインセンサ１における各受光セル１ａの配列ピッチｐとセル数によって変化する。ちなみに７μｍの配列ピッチｐで５０００セルを備えた分解能の高いイメージセンサを用いた場合には、例えば図６(ａ)に示すように非常に緻密なセンサ出力が得られる。この点、８５μｍの配列ピッチｐで１０２セルを備えた汎用の安価なイメージセンサを用いた場合には、図６(ｂ)に示すように粗いセンサ出力しか得ることができない。しかしセル数が少ない分だけセンサ出力の高速な読み出しが可能である。
【００３４】
しかしこのような分解能の低い安価なラインセンサ１を用いたとしても、前述したように本発明に係る位置検出方法および装置によれば、フレネル回折による光強度分布を高精度に近似したハイパボリックセカンド関数sech(ｘ)を用いるので受光セル１ａ間の受光強度の変化を高精度に補間することができる。従って分解能の低い安価なラインセンサ１を用いてセンサ出力の読み出し速度を十分に速くしながら、簡単な演算処理によってエッジ位置検出を高精度に行うことが可能となる等の実用上多大なる効果が奏せられる。
【００３５】
ところで検出対象物７が完全な遮光体でない場合、例えば半透明体からなる場合には単色平行光を完全に遮光することができない。この場合、ラインセンサ１の出力は検出対象物７を透過した光成分が重畳したものとなり、図７に示すようにその受光強度がラインセンサ１の全受光領域に亘って［０.２５］を上回ることがある。すると前述したアルゴリズムに従ってエッジ位置を検出することができなくなる。
【００３６】
そこでこのような場合には、例えば先ず半透明体からなる検出対象物７にてラインセンサ１の受光領域の全てを覆い、そのときに検出される単色平行光の受光パターンと検出対象物７がないときの単色平行光の受光パターンとの差を求める。そしてこの差に基づいてラインセンサ１の出力に対するオフセットとゲインとを調整する。
【００３７】
具体的には検出対象物７がないときのラインセンサ７の各受光セル１ａの受光強度Ａi（ｉ＝１,２,〜ｍ）と、ラインセンサ７の全受光領域を検出対象物７で覆ったときの該ラインセンサ１の受光強度Ｃi（ｉ＝１,２,〜ｍ）とをそれぞれ求める。そして上記受光強度Ｃi（ｉ＝１,２,〜ｍ）の最低値Ｃminをラインセンサ７の出力に対するオフセットとしてセットし、その上で受光強度Ａi（ｉ＝１,２,〜ｍ）と上記最低値Ｃminとの差の平均値が該ラインセンサ７の最大出力の半値となるようにその出力ゲインを調整する。しかる後、再度、前記単色平行光の出力を得、この出力を［１］とする係数（正規化パラメータ）Ｎi（ｉ＝１,２,〜ｍ）を求める。但し、上記オフセットとゲイン調整は、検出対象物７が半透明体であることに起因してラインセンサ１の出力における明暗の分解能が小さいとき、これを補うことを目的として行われるものであり、分解能が十分に高い場合には必要はない。
【００３８】
その後、実際のエッジ位置の検出においては、その受光パターンＹi（ｉ＝１,２,〜ｍ）を求め、上記係数Ｎi（ｉ＝１,２,〜ｍ）に従ってラインセンサ７の出力を正規化する。そして受光パターンの最初の立ち上がり部分からそのピーク値と、例えばその１つの手前の受光セル１ａの出力値とをそれぞれ求め、これらの各受光値を得た２つの受光セル１ａをそれぞれ特定する。次いで前述した近似式（逆フレネル関数）
Ｘp＝２ . ３９− ln ｛ [ １＋ ( １−Ｙ p ² ) ^1/2 ] ／Ｙ p ｝
Ｘp-1＝２ . ３９− ln ｛ [ １＋ ( １−Ｙ p-1 ² ) ^1/2 ] ／Ｙ p-1]
に従って図７に示すように受光強度Ｙp,Ｙp-1をＸ軸に逆写像する。そして逆写像した受光位置Ｘp,Ｘp-1から図７に示すように受光強度が［０.２５］となるエッジ位置を算出するようにしても良い。
【００３９】
このようにすればラインセンサ１の受光セル１ａでの受光強度が［０.２５］を上回るような場合であっても、つまり検出対象物７が半透明体であるような場合でも、そのエッジ位置を高精度に検出することが可能となる。即ち、この例に示されるように、基準受光強度［０.２５］を挟む受光強度のセルを特定しなくても、例えばそのピーク値をとる受光セル１ａとその手前の受光強度の受光セル１ａとから検出対象物７のエッジ位置を算出することができ、前述した実施形態と同様な効果が奏せられる。
【００４０】
尚、本発明は上述した各実施形態に限定されるものではない。例えばイメージセンサ１が備える受光セル１ａの数やその配列ピッチｐについては、その検出仕様に応じたものを用いれば十分である。またエッジ検出部３については、汎用のマイクロプロセッサを用いて実現すれば良く、前述した演算式をＲＯＭ化して与えるようにしても良い。その他、本発明はその要旨を逸脱しない範囲で種々変形して実施することができる。
【００４１】
【発明の効果】
以上説明したように本発明によれば、フレネル回折による受光強度分布をハイパボリックセカンド関数sech(ｘ)を用いて近似し、この近似式を用いてラインセンサの出力からエッジ位置を計算するので、簡易にして高精度に、しかも高速度にエッジ位置を検出することができる。特に分解能の低い安価なラインセンサを用いた場合であっても、その計測精度を十分に高め得る等の実用上多大なる効果が奏せられる。
【図面の簡単な説明】
【図１】本発明の一実施形態に係る位置検出装置の基本的な構成を示す図。
【図２】ラインセンサにおける受光セルの配列を示す図。
【図３】フレネル回折による光強度分布の理論値と、関数を用いた近似特性とを対比して示す図。
【図４】本発明の一実施形態に係る一検出方法および装置におけるエッジ検出処理の手順の一例を示す図。
【図５】連接する２つの受光セルにおいて求められる受光強度と、これらの受光強度が得られた位置から求められるエッジ位置の関係を示す図。
【図６】ラインセンサの分解能の違いによるセンサ出力の例を示す図。
【図７】検出対象物が半透明体の場合におけるエッジ検出の作用を説明する為の図。
【図８】フレネル回折による光強度分布特性を示す図。
【図９】フレネル回折による光強度分布のフレネル関数を用いた近似における問題点を説明する為の図。
【符号の説明】
１ラインセンサ
２投光部
３エッジ検出部
７遮蔽物（検出対象物）[0001]
BACKGROUND OF THE INVENTION
The present invention provides a position detection method capable of detecting a position displacement in the width direction of an edge portion of a belt-like body that is unwound from a roll and conveyed at high speed in one direction at high speed and with high accuracy. And device.
[0002]
[Related background]
As a position detection device that detects the position of an edge of an article such as a film or sheet, a light projecting part (light source) that irradiates parallel light toward the object (inspection object), and this light projecting part There is an optical type provided with a light receiving portion (line sensor) such as a CCD. This type of optical position detection device basically receives parallel light that is not blocked by the article at the light receiving unit, and receives a parallel light receiving region and a non-light receiving region (light blocking region) in the light receiving unit. Is detected as the position of the edge (edge) of the article (inspection object).
[0003]
Recently, using monochromatic parallel light such as laser light, focusing on the Fresnel diffraction of the monochromatic parallel light at the edge of the article (inspection object), the light intensity distribution on the light receiving surface of the line sensor (light receiving unit) An apparatus for detecting the position of an edge (edge) of an article (inspection object) with high accuracy has also been proposed (see, for example, Patent Document 1).
[0004]
[Patent Document 1]
JP-A-8-247726
[0005]
[Problems to be solved by the invention]
By the way, when detecting the position of the edge of the inspection object using the light intensity distribution on the light receiving surface of the line sensor (light receiving unit) by Fresnel diffraction of monochromatic parallel light, the characteristics of the light intensity distribution are obtained with high accuracy in advance. It is necessary to keep it. Incidentally, the light intensity distribution by Fresnel diffraction rises steeply in the vicinity of the edge position as shown in FIG. 8, and converges while oscillating as the distance from the edge position increases. Such light intensity distribution characteristics are as follows: when the wavelength of monochromatic parallel light is λ, the distance from the edge of the inspection object to the light receiving surface is z, and the edge position on the light receiving surface is [x = 0]. [X = 0] to [(2 / λz)^1/2・ Operation symbol indicating integration up to x]
Light intensity =( 1/2 ) { [ 1/2 + S ( x )] ² + [ 1/2 + C ( x )] ² }
S (x) =∫ sin ( π / 2 ) ・ U ² d U
C (x) =∫ cos ( π / 2 ) ・ U ² d U
Represented as: However, U is a temporary variable. When the light intensity converged on the light receiving surface is [1.00], the light intensity (relative value) at the edge position [x = 0] is [0.25].
[0006]
For the above functions S (x) and C (x), the Fresnel function is used exclusively as shown in the mathematical formulas.
S (x) ′ ≈ (1/2) − (1 / πx) cos (πx²/ 2)
C (x) '≈ (1/2) + (1 / πx) sin (πx²/ 2)
Can be approximated respectively. Therefore, basically, by using the approximate expressions S (x) ′ and C (x) ′, the edge position described above can be calculated from the received light intensity of each light receiving cell of the line sensor.
[0007]
However, when actually calculated, as shown in FIG. 9, the functions S (x), C (x) and the approximate expressions S (x) ′, C (x) ′ are converged after the rise ( Although it approximates very well in the second and subsequent peaks, it cannot be denied that there is a large shift in the first rising portion (first mountain). In particular, the characteristic of the first rising portion plays an important role in edge detection, and the deviation of the characteristic causes a decrease in the detection accuracy of the edge position.
[0008]
The present invention has been made in consideration of such circumstances, and its purpose is to approximate the light intensity distribution on the light receiving surface by Fresnel diffraction, in particular, the characteristics of the first rising portion with high accuracy, thereby increasing the An object of the present invention is to provide an edge detection method and apparatus capable of performing accurate position detection.
Another object of the present invention is to provide an edge detection device capable of detecting an edge position with high accuracy and high speed even when an inexpensive line sensor having a large array pitch of light receiving cells is used. In offer.
[0009]
[Means for Solving the Problems]
In order to achieve the above-described object, a position detection method according to the present invention is provided with a line sensor (light-receiving unit) including a plurality of light-receiving cells arranged at a predetermined pitch in one direction, and facing the line sensor. A light projecting unit that projects monochromatic parallel light toward the plurality of light receiving cells of the line sensor, and an analysis of the output of the line sensor to analyze the output of the light receiving cell of the shielding object present in the optical path of the monochromatic parallel light. It is applied to a position detection device comprising an edge detection unit that detects an edge position in the arrangement direction,
In particular, in the edge detection unit, the light intensity change at the first rising portion of the light intensity distribution on the light receiving surface of the line sensor due to Fresnel diffraction of monochromatic parallel light by the shield is approximated by a hyperbolic second function sech (x). Then, using this hyperbolic second function sech (x), the received light intensity of each light receiving cell of the line sensor is analyzed to obtain the edge position of the shielding object.
[0010]
That is, in the position detection method according to the present invention, the first rising portion of the light intensity distribution on the light receiving surface by Fresnel diffraction of monochromatic parallel light, in particular, the distribution characteristics of the first mountain, are coefficients a, b, and c, respectively. As
y = a / cosh (bx + c)
The hyperbolic cosine function cosh (x), i.e., the hyperbolic second function sech (x) is found to be very well approximated. Then, the output (light intensity) of the line sensor is analyzed using this hyperbolic second function sech (x), and the light intensity (relative value) in the light intensity distribution on the light receiving surface by the Fresnel diffraction is [0.25]. The position [x = 0] is detected as the edge position of the shielding object.
[0011]
Preferably, analysis of received light intensity by each light receiving cell of the line sensor using the hyperbolic second function sech (x), for example,
A light receiving cell that obtains a light receiving intensity larger than the reference light receiving intensity in the vicinity of a predetermined reference light receiving intensity [0.25] and a light receiving cell that obtains a light receiving intensity smaller than the reference light receiving intensity are respectively obtained (first stage). ,
The light receiving position corresponding to the light receiving intensity on the light receiving surface of each of the light receiving cells is an inverse function of the hyperbolic second function sech (x).ln { [ 1+ ( 1-Y ² ) ^1/2 ] / Y}After each (according to step 2)
From these light receiving positions, a position having the reference light receiving intensity is obtained as an edge position of the shielding object (third step).
[0012]
The position detection device according to the present invention includes a line sensor including a plurality of light receiving cells arranged at a predetermined pitch in one direction, and the plurality of light receiving cells of the line sensor provided to face the line sensor. Analyzing the output of the line sensor according to the light intensity distribution on the light receiving surface of the line sensor due to Fresnel diffraction of the monochromatic parallel light by the shielding, An edge detection unit that detects the position of an edge in the arrangement direction of the light receiving cell of the shielding object present in the optical path of monochromatic parallel light, and particularly as the edge detection unit,
A light receiving cell that obtains a light receiving intensity greater than the reference light receiving intensity in the vicinity of a predetermined reference light receiving intensity [0.25] from the output of the line sensor and a light receiving cell that obtains a light receiving intensity smaller than the reference light receiving intensity. A light receiving cell specifying means for specifying each;
Inverse function of hyperbolic second function sech (x)ln { [ 1+ ( 1-Y ² ) ^1/2 ] / Y}A light receiving position calculating means for obtaining a light receiving position that is a light receiving intensity of the light receiving cell on the light receiving surface of each light receiving cell specified by the light receiving cell specifying means according to the light intensity distribution approximated by
Interpolation calculation means for detecting a position that is the reference light reception intensity from the light reception positions respectively obtained by the light reception position calculation means as an edge position of the shielding object;
It is characterized by providing.
[0013]
Preferably, the light receiving cell specifying means normalizes the output of the line sensor in advance, and then obtains a light receiving intensity greater than the reference light receiving intensity [0.25] and the reference light receiving intensity [0.25]. A light receiving cell having a small received light intensity, specifically, at least two adjacent light receiving cells Cn and Cn−1 having a received light intensity in the vicinity of the reference received light intensity [0.25] are specified. It is desirable to configure.
[0014]
According to the position detecting device configured as described above, at least the light receiving cell in which the light receiving intensity sandwiching the reference light receiving intensity [0.25] is obtained, the light receiving position that is the light receiving intensity of the light receiving cell is determined as the light intensity by Fresnel diffraction. Since the hyperbolic second function sech (x) that approximates the characteristics of the first rising part of the distribution with high precision can be obtained with high precision, the position of the edge on the light receiving surface of the line sensor from these light receiving positions. That is, the position where the received light intensity is [0.25] can be obtained with high accuracy. Moreover, the inverse function of the hyperbolic second function sech (x)ln { [ 1+ ( 1-Y ² ) ^1/2 ] / Y}Since it can be calculated according to series expansion or instructions mounted on the CPU, the calculation processing speed (position detection speed) can be sufficiently increased.
[0015]
The light receiving cell having the peak value at the beginning of the output of the line sensor and the light receiving cell in front thereof are respectively obtained, and the inverse function of the above-described hyperbolic second function sech (x) is obtained from the light receiving intensity of each light receiving cell.ln { [ 1+ ( 1-Y ² ) ^1/2 ] / Y}It is also possible to obtain the edge position according to If the edge position is detected in this way, for example, even if the detection object is made of a translucent body and the monochromatic parallel light cannot be completely blocked by the detection object, the edge of the detection object ( The position of the edge) can be detected with high accuracy.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a position detection method and apparatus according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a position detection apparatus according to this embodiment. Basically, as shown in FIG. 2, a line sensor (light reception) including a plurality of light receiving cells 1a arranged in one direction at a predetermined pitch p. Part) 1, a light projecting part 2 provided so as to face the light receiving surface of the line sensor 1 and projecting monochromatic parallel light 4 toward a plurality of light receiving cells 1 a of the line sensor 1, and the line sensor 1 The edge detection unit 3 detects the edge position in the arrangement direction of the light receiving cell 1a of the shield (detection target) 7 made of, for example, a belt-like body, which is positioned in the optical path of the monochromatic parallel light 4 With.
[0017]
The light projecting unit 2 converts an optical fiber 2b that guides monochromatic light (laser light) emitted from a light source 2a made of, for example, a laser diode (LD), and the monochromatic light guided through the optical fiber 2b into parallel light. And a projection lens (collimator lens) 2c for converting and projecting. Such a light projecting unit 2 is integrated into a U-shaped casing 5 that forms a predetermined gap together with the line sensor 1 so as to face each other with the gap therebetween, and is formed as one sensing unit. Has been.
[0018]
The edge detection unit 3 described above plays a role of detecting the position of the end (edge) of the shielding object (detection target) 7 passing through the gap of the sensing unit from the output of the line sensor 1. Specifically, the edge detection unit 3 generates Fresnel diffraction at an end (edge) when a part of the monochromatic parallel light is blocked by a blocking object (detection target) 7, and Fresnel diffraction. The intensity of light reaching the light receiving surface of the line sensor 1 rises steeply in the vicinity of the edge position as shown in FIG. 7 and converges while oscillating as the distance from the edge position increases. The position of the edge (edge) of the shielding object 7 is detected with high accuracy according to the light intensity distribution on the light receiving surface.
[0019]
Basically, the position detection device configured to include the above-described line sensor 1, light projecting unit 2, and edge detection unit 3 is unwound from a roll, for example, and transported while traveling at a high speed in one direction. It is provided so as to detect a positional shift in the width direction of the belt-like body (shielding object; detection target object) 7 as a change in its edge (edge) position. The detected position of the edge (edge) of the strip 7 is fed back to the travel drive system of the strip 7 to be used for controlling the travel drive.
[0020]
In such a position detection apparatus, the position detection method and apparatus according to the present invention is characterized in that when the edge detection unit 3 detects the position of the edge of the shielding object 7 from the output of the line sensor 1, it is Fresnel. The edge position is calculated using a hyperbolic second function sech (x) approximating the light intensity distribution by diffraction. In other words, the light intensity distribution on the light receiving surface of the line sensor 1 due to Fresnel diffraction is approximated by the hyperbolic second function sech (x), particularly the light intensity change at the first rising portion (first mountain). According to the light intensity distribution approximated using the function sech (x), the received light intensity of each light receiving cell 1a of the line sensor 1 is analyzed to obtain the edge position of the shielding object 7.
[0021]
The approximation of the light intensity distribution by Fresnel diffraction using the hyperbolic second function sech (x) will be explained. When the Fresnel function is used as described above, the error at the first rising portion (first mountain) of the light intensity distribution is very large. There is a problem of being big. Therefore, paying attention to only the first rising part (first peak) of the light intensity distribution, approximation is performed using the rational function of the square, the hyperbolic cosine function, and the exponential function from the peak shape (change tendency of the light intensity). I tried to do that.
[0022]
Specifically, as a rational function of square
y = a / [(x + b)²+ C]
As the reciprocal of the hyperbolic cosine function
y = a / cosh (bx + c)
And as an exponential function
y = a · exp [−b (x + c)²]
When the characteristic curves were determined while substituting appropriate values for the coefficients a, b, and c shown in these functions, the calculation results shown in FIG. 3 were obtained.
[0023]
Incidentally, the characteristic A in FIG. 3 indicates the theoretical value of the light intensity distribution, and the characteristic B indicates the coefficients a, b, and c in the squared rational function [0.057], [−0.38], The change of the light intensity y when [0.0417] is set, and the characteristic C is obtained by changing the coefficients a, b, and c in the reciprocal of the hyperbolic cosine function to [1.37], [6.29], and [-2.40], respectively. ] And the characteristic D is the light when the coefficients a, b and c in the exponential function are [1.37], [16.30] and [−0.38], respectively. The change of intensity y is shown, respectively. However, in these calculations, the wavelength λ of monochromatic light is set to 670.nmThe distance z from the edge of the shield 7 to the light receiving surface of the line sensor 1 was set to 300 mm.
[0024]
As shown in these calculation results, if the inverse of the hyperbolic cosine function, that is, the hyperbolic second function sech (x) is used, the characteristics of the light intensity distribution by Fresnel diffraction, particularly the first rising part (first mountain), can be obtained. It became clear that it can be approximated with very high accuracy. In particular, it has been found that the error with respect to the theoretical value of the edge position at which the predetermined reference received light intensity [0.25] is as small as 6.77 μm, and the light intensity distribution by Fresnel diffraction can be approximated with extremely high accuracy.
[0025]
By the way, when the inverse of the hyperbolic cosine function is applied to the above-described formula of the light intensity distribution by Fresnel diffraction and approximated to the first rising portion (first mountain) of the light intensity, the hyperbolic second function sech (x) is
Light intensity = 1.37 · sech {1.983 (2 / λz)^1/2x-2.386}
As shown. It was confirmed that this approximate expression agrees with the theoretical expression of the light intensity distribution with an accuracy of about three digits.
[0026]
Based on such knowledge, the present invention approximates the light intensity distribution by Fresnel diffraction, in particular, the first rising portion using the above-described hyperbolic second function sech (x), and the hyperbolic second approximating this light intensity distribution. Using the function sech (x), the edge position of the shielding object 7 is detected with high accuracy from the output of the line sensor 1 described above.
[0027]
At this time, in order to simplify the calculation process and increase the speed of the edge position detection process, the following measures are taken. The algorithm of this calculation process will be described. The light intensity approximated using the hyperbolic second function sech (x) is as described above.
Light intensity = 1.37 · sech {1.983 (2 / λz)^1/2x-2.386}
As shown. If the position of the light intensity (relative value) [0.25] is (x−a),
0.25 = 1.37.sech (x-a)
The above position (x−a) is
(X−a) = sech^-1(0.25 / 1.37) = 1.866
Can be calculated as
[0028]
Therefore, the light intensity y is expressed by substituting the above formula of the light intensity distribution for the XY coordinates with the origin where the light intensity (relative value) is [0.25].
y =1 . 37 ・ Sech {1 . 98 ( 2 / λz ) ^1/2 x-2 . 39}
It becomes. And calculate its inverseWhen,
Y = y / 1.37, X = 1 . 98 (2 / λz) ^1/2 x
Anyway,
X =2 . 39- ln { [ 1+ ( 1-Y ² ) ^1/2 ] / Y}
Can be represented asit can.
Λ is the wavelength of monochromatic parallel light and its unit is [ nm ] , Z is the distance from the edge of the inspection object to the light receiving surface, and its unit is [ mm ] X is the edge position on the light receiving surface, and its unit is [ μm ] It is.
[0029]
Therefore, in the edge detection unit 3, for example, according to the procedure shown in FIG. 4, first, the received light intensities y1, y2, to ym of the plurality (m) of light receiving cells 1a in the line sensor 1 are expressed by the coefficient [1.37] described above. Dividing and converting into light intensities Y1, Y2 to Ym on the XY coordinates (step S1). Among the light receiving cells 1a, for example, adjacent to each other, the light receiving cell Cn having a light receiving intensity larger than the reference light intensity [0.25] described above, and the reference light intensity [0.25] above. Each of the light receiving cells Cn-1 having a small received light intensity is obtained (light receiving cell specifying means; step S2). That is, two adjacent light receiving cells Cn and Cn-1 having a light receiving intensity of [0.25] in each of the plurality of light receiving cells 1a (C1, C2, to Cm) are obtained.
[0030]
Then, the positions Xn, Xn-1 on the light receiving surface of the light receiving cells Cn, Cn-1 from which the light receiving intensities Yn, Yn-1 of these light receiving cells Cn, Cn-1 are obtained according to the above-described approximate expression.
Xn =2 . 39- ln { [ 1+ ( 1-Y n ² ) ^1/2 ] / Y n }
Xn-1 =2 . 39- ln { [ 1+ ( 1-Y n-1 ² ) ^1/2 ] / Y n-1 }
As shown in FIG. 5, the position (edge position) at which the received light intensity is [0.25] as shown in the concept of FIG. 5 from these positions Xn and Xn-1. Is calculated by interpolation calculation (interpolation calculation means; step S4). This interpolation calculation may be executed using the above-described approximate expression. However, if the change in light intensity between the two light receiving cells Cn and Cn-1 can be regarded as linear, it is simple. Simple linear interpolation may be used.
[0031]
Here, a position where the light intensity is [0.25] between adjacent light receiving cells 1a is found, and two light receiving cells Cn and Cn-1 having the position as a cell boundary are specified. Two or more light receiving cells may be specified. However, in this case, it is only necessary to prevent the calculation accuracy from being lowered by performing the interpolation calculation using the approximate expression described above. Further, the inverse transformation described above can be executed instantaneously, for example, by using a table in which the calculated values are stored in advance, thereby greatly reducing the calculation processing load.
[0032]
Thus, according to the position detection method and apparatus for detecting the edge position of the light shielding object 7 as described above, the line sensor 1 is used by using the hyperbolic second function sech (x) that approximates the light intensity distribution by Fresnel diffraction with high accuracy. Since the position X at which the light intensity is [0.25] is calculated from the received light intensity y by the plurality of light receiving cells 1a, the detection accuracy can be sufficiently increased. The natural logarithm function (ln function) is included in the instruction of a microprocessor having a normal floating point operation (FPU) function, but is not a microprocessor having such an FPU function. For example, the hyperbolic second function sech (x), especially itsInverse function ln ( x ) about,For example

Series expansion is possible, and its convergence is fast, so calculation is easy. Therefore, effects such as being able to detect the edge position easily and with high accuracy can be achieved.
[0033]
The output of the line sensor 1 varies depending on the arrangement pitch p and the number of cells of the light receiving cells 1a in the line sensor 1. Incidentally, when using a high resolution image sensor having 5000 cells with an array pitch p of 7 μm, a very precise sensor output can be obtained as shown in FIG. 6A, for example. In this regard, when a general-purpose inexpensive image sensor having 102 cells with an array pitch p of 85 μm is used, only a rough sensor output can be obtained as shown in FIG. However, the sensor output can be read at a high speed as the number of cells is small.
[0034]
However, even if such an inexpensive line sensor 1 with low resolution is used, according to the position detection method and apparatus according to the present invention, as described above, a hyperbolic second function that approximates the light intensity distribution by Fresnel diffraction with high accuracy. Since sech (x) is used, the change in the received light intensity between the light receiving cells 1a can be interpolated with high accuracy. Therefore, there is a great practical effect such that the edge position can be detected with high accuracy by a simple arithmetic process while sufficiently reading out the sensor output speed by using the inexpensive line sensor 1 with low resolution. Played.
[0035]
By the way, when the detection object 7 is not a complete light-shielding body, for example, when it consists of a translucent body, it is not possible to completely shield monochromatic parallel light. In this case, the output of the line sensor 1 is obtained by superimposing the light component transmitted through the detection object 7, and the received light intensity is [0.25] over the entire light receiving region of the line sensor 1 as shown in FIG. May exceed. Then, the edge position cannot be detected according to the algorithm described above.
[0036]
Therefore, in such a case, for example, first, the detection target 7 made of a translucent body covers the entire light receiving region of the line sensor 1, and the light receiving pattern of the monochromatic parallel light and the detection target 7 detected at that time are detected. The difference from the light receiving pattern of the monochromatic parallel light when there is no light is obtained. Based on this difference, the offset and gain for the output of the line sensor 1 are adjusted.
[0037]
Specifically, the light receiving intensity Ai (i = 1, 2,...) Of each light receiving cell 1a of the line sensor 7 when there is no detection target 7 and the entire light receiving area of the line sensor 7 are covered with the detection target 7. Then, the received light intensity Ci (i = 1, 2,..., M) of the line sensor 1 is obtained. The minimum value Cmin of the light reception intensity Ci (i = 1, 2,... M) is set as an offset with respect to the output of the line sensor 7, and the light reception intensity Ai (i = 1, 2,. The output gain is adjusted so that the average value of the difference from the value Cmin becomes a half value of the maximum output of the line sensor 7. Thereafter, the output of the monochromatic parallel light is obtained again, and a coefficient (normalization parameter) Ni (i = 1, 2,..., M) having this output as [1] is obtained. However, the offset and gain adjustments are performed for the purpose of compensating for the low and bright resolution at the output of the line sensor 1 due to the detection object 7 being a translucent body, This is not necessary when the resolution is sufficiently high.
[0038]
Thereafter, in the actual edge position detection, the light receiving pattern Yi (i = 1, 2,... M) is obtained, and the output of the line sensor 7 is normalized according to the coefficient Ni (i = 1, 2,... M). To do. Then, the peak value and, for example, the output value of the preceding light receiving cell 1a are obtained from the first rising portion of the light receiving pattern, and the two light receiving cells 1a that have obtained the respective light receiving values are specified. Next, the approximate expression (inverse Fresnel function) described above
Xp =2 . 39- ln { [ 1+ ( 1-Y p ² ) ^1/2 ] / Y p }
Xp-1 =2 . 39- ln { [ 1+ ( 1-Y p-1 ² ) ^1/2 ] / Y p-1]
As shown in FIG. 7, the received light intensity Yp, Yp-1 is inversely mapped to the X axis. Then, the edge position at which the received light intensity is [0.25] may be calculated from the reversely mapped received light positions Xp and Xp−1 as shown in FIG.
[0039]
In this way, even when the light receiving intensity at the light receiving cell 1a of the line sensor 1 exceeds [0.25], that is, even when the detection object 7 is a translucent body, the edge thereof is obtained. The position can be detected with high accuracy. That is, as shown in this example, for example, the light receiving cell 1a having the peak value and the light receiving cell 1a having the light receiving intensity in front of the peak light receiving intensity cell having the reference light receiving intensity [0.25] are not specified. Thus, the edge position of the detection object 7 can be calculated, and the same effect as the above-described embodiment can be obtained.
[0040]
In addition, this invention is not limited to each embodiment mentioned above. For example, as for the number of light receiving cells 1a included in the image sensor 1 and the arrangement pitch p thereof, it is sufficient to use those according to the detection specifications. Further, the edge detection unit 3 may be realized using a general-purpose microprocessor, and the arithmetic expression described above may be provided as a ROM. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.
[0041]
【The invention's effect】
As described above, according to the present invention, the received light intensity distribution by Fresnel diffraction is approximated using the hyperbolic second function sech (x), and the edge position is calculated from the output of the line sensor using this approximate expression. Thus, the edge position can be detected with high accuracy and at high speed. In particular, even when an inexpensive line sensor with low resolution is used, there are significant practical effects such as that the measurement accuracy can be sufficiently increased.
[Brief description of the drawings]
FIG. 1 is a diagram showing a basic configuration of a position detection device according to an embodiment of the present invention.
FIG. 2 is a diagram showing an arrangement of light receiving cells in a line sensor.
FIG. 3 is a diagram showing a comparison between a theoretical value of a light intensity distribution by Fresnel diffraction and an approximate characteristic using a function.
FIG. 4 is a diagram showing an example of a procedure of edge detection processing in one detection method and apparatus according to an embodiment of the present invention.
FIG. 5 is a diagram showing a relationship between received light intensity obtained in two light receiving cells connected to each other and edge positions obtained from positions where the received light intensity is obtained.
FIG. 6 is a diagram illustrating an example of sensor output due to a difference in resolution of a line sensor.
FIG. 7 is a diagram for explaining the operation of edge detection when the detection object is a translucent body.
FIG. 8 is a diagram showing light intensity distribution characteristics by Fresnel diffraction.
FIG. 9 is a diagram for explaining a problem in approximation using a Fresnel function of a light intensity distribution by Fresnel diffraction.
[Explanation of symbols]
1 Line sensor
2 floodlight
3 Edge detector
7 Shield (object to be detected)

Claims

A line sensor having a plurality of light receiving cells arranged at a predetermined pitch in one direction, and a monochromatic parallel light projecting toward the plurality of light receiving cells of the line sensor provided opposite to the line sensor A light projecting unit, and an edge detecting unit that analyzes an output of the line sensor and detects an edge position in an arrangement direction of the light receiving cell of the shielding object existing in the optical path of the monochromatic parallel light,
The edge detection unit approximates the light intensity change at the rising portion of the light intensity distribution on the light receiving surface of the line sensor due to Fresnel diffraction of monochromatic parallel light by the shield by a hyperbolic second function sech (x). A position detection method, wherein a second function sech (x) is used to analyze received light intensity of each light receiving cell of the line sensor to obtain an edge position of the shielding object.

Analysis of received light intensity by each light receiving cell of the line sensor using the hyperbolic second function sech (x)
When the output of the line sensor is normalized to [1], a light receiving cell having a light receiving intensity greater than [0.25] and a light receiving intensity smaller than [0.25] were obtained. Find each light receiving cell,
Converting the inverse function ln of the light receiving position where the received light intensity of the light receiving cells in the light-receiving surfaces of the respective light receiving cells hyperbolic second function sech (x) {[1+ ( 1-Y 2) 1/2] / Y} After
The position detection method according to claim 1, wherein a position at which the received light intensity is [0.25] is obtained as an edge position of the shielding object from these light receiving positions.

A line sensor having a plurality of light receiving cells arranged at a predetermined pitch in one direction, and a monochromatic parallel light projecting toward the plurality of light receiving cells of the line sensor provided opposite to the line sensor A light projecting unit, and an edge detecting unit that analyzes the output of the line sensor and detects the position of an edge in the arrangement direction of the light receiving cell of the shielding object present in the optical path of the monochromatic parallel light,
The edge detection unit obtains the edge position of the shielding object from the light intensity distribution on the light receiving surface of the line sensor by Fresnel diffraction of monochromatic parallel light by the shielding object,
A light receiving cell that specifies a light receiving cell having a light receiving intensity greater than [0.25] from a normalized output of the line sensor and a light receiving cell having a light receiving intensity smaller than [0.25]. Cell identification means;
In the light-receiving surface of the light receiving cells that are identified in the light receiving cell identification means according to the light intensity distribution approximated by the inverse function ln {[1+ (1-Y 2) 1/2] / Y} hyperbolic second function sech (x) A light receiving position calculating means for obtaining a light receiving position which is a light receiving intensity of the light receiving cell;
A position detection apparatus comprising: interpolation calculation means for detecting a position having the reference received light intensity as an edge position of the shielding object from the light receiving positions respectively obtained by the light receiving position calculating means.

The light receiving cell specifying means normalizes the output of the line sensor to [1] in advance, and then obtains a light receiving cell that has received light intensity greater than a predetermined reference light reception intensity and a light reception intensity less than the reference light reception intensity. The position detecting device according to claim 3, wherein each of the light receiving cells is specified.

5. The position detecting device according to claim 3, wherein the light receiving cell specifying means specifies at least two adjacent light receiving cells from which a light receiving intensity in the vicinity of [0.25] is obtained.

Analysis of received light intensity by each light receiving cell of the line sensor using the hyperbolic second function sech (x)
After normalizing the output of the line sensor to [1], first, a light receiving cell where the light receiving intensity has a peak value and a light receiving cell in front of it are obtained,
Converting the inverse function ln of the light receiving position where the received light intensity of the light receiving cells in the light-receiving surfaces of the respective light receiving cells hyperbolic second function sech (x) {[1+ ( 1-Y 2) 1/2] / Y} After
The position detection method according to claim 1, wherein a position at which the received light intensity is [0.25] is obtained as an edge position of the shielding object from these light receiving positions.