JP4094503B2 - Laser ultrasonic inspection apparatus and inspection method - Google Patents

Description

によって表わされる長さにする構成とする。
【００２１】
請求項６の発明は、請求項１記載のレーザー超音波検査装置において、前記第１のレーザー光で発生した超音波信号のうち、前記被検査材の表面を伝播する弾性波の音速をVS、前記被検査材中を伝播する体積波の音速をVB、前記被検査材の厚さをDとしたとき、前記第１のレーザー光の照射位置と前記第２のレーザー光の照射位置の間隔Ｓを、関係式
【数４】

によって表わされる長さにする構成とする。
【００２７】
【発明の実施の形態】
以下、本発明の実施の形態を図面を参照して説明する。
まず、本発明の第１の実施の形態を図１〜図１３を参照して説明する。本実施の形態のレーザー超音波検査装置は図１に示すように、超音波発生用レーザー光源１と、信号変換手段である受信装置RECと、信号処理・表示・記録装置４１と、トリガー発振器１３と、走査機構３８と、走査制御器３９を備えている。
【００２８】
また、超音波発生用レーザー光PLを被検査材３に照射する照射光学系２、および超音波検出用レーザー光ILを被検査材３に照射しその反射光を集光する照射・集光光学系M6を走査テーブル３７に設置し、それらの被検査材３からの距離および各々の相対的な位置関係を保持する。走査テーブル３７は、それを被検査材３上の検査部位まで搬送する上位の走査機構３８に搭載されていてもよい。
【００２９】
走査テーブル３７あるいは走査機構３８は、走査制御器３９で制御され、検査すべき領域を検査可能な範囲で１次元または２次元的に走査する。ここで、検査すべき領域を検査可能な範囲とは、必ずしも検査すべき領域とは一致しなくてもよい。すなわち、例えば水中環境で表面波を用いる場合、送受信点から数mm〜数十mm程度の範囲であれば表面波は伝播し、その領域にき裂があれば、反射波が検出される。同じ理由で、１次元的な走査によって、走査線に沿った２次元的な領域を検査することも可能である。被検査材３が種々の形状をした溶接部を有する場合には、走査は溶接線に沿った１次元あるいはその方向を長手とする２次元走査とする。
【００３０】
走査しながら超音波信号を送受信するが、その計測間隔はトリガー発振器１３で制御される計測タイミングと走査制御器３９で制御される空間的な動作のパラメータの組み合わせで任意に決定できる。しかし、後段の信号解析による材料特性演算に使用するため、信号を計測した相対的な位置関係は既知であるべきである。この場合、位置センサ４０を設置して計測してもよいし、走査段階で走査ピッチを一定間隔とし、そこから位置を算出してもよい。なお、位置センサ４０としては、超音波距離センサ、レーザー距離センサ、エンコーダーなどが用いられる。
【００３１】
位置情報およびタイミング情報は、検出された超音波信号が受信装置RECによって変換された電気信号とともに、材料特性を演算する信号処理・表示・記録装置４１に入力され、信号処理・表示・記録される。ここで、表面伝播モードの解析手法としては、伝播時間解析法や特開２０００−１８０４１８号公報に記載されている表面伝播波のき裂による反射成分あるいは透過成分を解析する方法などが用いられる。体積伝播モードの解析手法としては回折波飛行時間法（TOFD法: Time-of-Flight Diffraction）や開口合成法（SAFT法: Synthetic Aperture Focusing Technique）などを使用する。
【００３２】
被検査材３の表面を伝播する表面伝播モードを主に用いる表面検査について以下に説明する。図２（ａ）に示すように、被検査材３の表面き裂Ｃを超音波発生用レーザー光PLと超音波検出用レーザー光ILで検査する場合を考える。このとき、２本のレーザー光の照射位置間の距離をS、被検査材３を取り巻く周辺媒質の音速をVM、被検査材３の表面伝播弾性波の音速をVS、超音波発生用レーザー光PLあるいは超音波検出用レーザー光ILのいずれかから検査すべき領域までの距離の短い方の長さをLとする。
【００３３】
いま、検出したい信号は、図２（ａ）に示すような、き裂Ｃからの反射信号、または図２（ｂ）に示すような、き裂Ｃを透過する信号であるが、ここでは、より伝播時間の長い反射信号を考える。この反射信号が計測される時刻tSは、超音波発生用レーザー光PLによって超音波が発生した時刻を基準として
【数５】

である。
【００３４】
一方、被検査材３を取り巻く媒質が大気や水など、超音波が伝播可能な物質の場合、被検査材３の表面を経ず、超音波発生用レーザー光PLの照射位置から超音波検出用レーザー光ILの照射位置まで、周辺媒質を経由して伝播する超音波モードも存在する。この超音波モードはノイズとなるが、その振幅は微小なき裂Ｃからの反射信号振幅よりも極めて大きいことがあり、時刻tSに到達する反射信号がこのノイズと時間的に重なることは避けるべきである。したがって、このノイズの到達時刻tNとして
【数６】

すなわち、２つの照射位置間の距離Sは
【数７】

と決めるべきである。
【００３５】
なお、ノイズは周辺媒質中を衝撃波状に伝播し、VMは定数とならない場合があるが、この場合は（３）式で規定されるSよりも短い距離で信号とノイズの重なりは解消されるため、（３）式の関係を保持していれば十分である。逆に、信号の識別を容易にするため、ノイズと反射信号の間に、信号の分離・識別のため等、何らかの余裕が必要な場合にはその分を正の定数Ａとして
【数８】

と決めてもよい。
【００３６】
いずれにせよ、（３）式で表わされるSが最小であり、表面き裂Ｃを検査するためには、超音波発生用レーザー光PLと超音波検出用レーザー光ILの照射位置間の距離Sはそれ以上であるべきである。
【００３７】
被検査材３の内部を伝播する体積伝播モードを用いる裏面あるいは内部検査について以下に説明する。図３に示す通り、被検査材３の裏面あるいは内部に存在する欠陥Ｃを超音波発生用レーザー光PLと超音波検出用レーザー光ILで検査する場合を考える。このとき、２本のレーザー光の照射位置間の距離をS、被検査材３を取り巻く周辺媒質の音速をVM、被検査材３の表面伝播弾性波の音速をVS、被検査材３の体積伝播弾性波の音速をVB、欠陥Ｃが存在し得る最大深さ、すなわち被検査材３の厚さをDとする。
【００３８】
いま、検出したい信号は、欠陥Ｃからの回折あるいは反射信号である。この回折あるいは反射信号が計測される時刻tBは欠陥Ｃの存在位置によるが、最も遠い場合、すなわち裏面のごく近傍に存在する場合には、tBは、超音波発生用レーザー光PLによって超音波が発生した時刻を基準として
【数９】

である。
【００３９】
ここでVB₁、VB₂とは、体積中を伝播する超音波の音速が一意に決まらない（例えば、縦波弾性波（速度VB₁）として欠陥Ｃに到達し、そこで回折する際にモード変換し、横波弾性波（速度VB₂）として検出される場合など）ことを想定している。ここでは簡単のため、送信される超音波モードと受信される超音波モードが同一の場合、すなわち
【数１０】

を考える。
【００４０】
このとき、この信号検出上のノイズとなるのは、時刻
【数１１】

に到達する媒質中を伝播する衝撃波のほか、時刻
【数１２】

に到達する表面弾性波もノイズとなり得る。
【００４１】
ここで周辺媒質が水や大気、被検査材が金属の場合、VS＞VMであるため、実効的に問題となるのは（９）式で表わされる表面弾性波ノイズである。そこで（７）式と（９）式より、距離Sは
【数１３】

となる。
【００４２】
ここで、体積波として縦波を想定した場合、被検査材３が金属材料であれば、多くの場合、VB はほぼ２VSに等しい。この関係を用いると、
【数１４】

となる。
【００４３】
すなわち、裏面あるいは内部に存在する欠陥Ｃを検査するためには、超音波発生用レーザー光PLと超音波検出用レーザー光ILの照射位置間の距離Sは（１０）式で表わされる値以上であるべきであり、その特殊な場合として（１１）式で表わされる距離Sでもよい。
【００４４】
つぎに、走査と計測のタイミングについて説明する。ステップ的な動作の場合、走査動作と信号計測の速度の差から、必ずしも１動作に１計測でなくてもよいが、タイミングは同期させるべきである。図４に一例を示す。図４（ａ），（ｂ）は走査による位置を示したもので、この場合、ｙ軸方向にy0〜y3の４ステップ、Ｘ軸方向にx0〜x8の９ステップの４行×９列の走査を行うことを想定している。
【００４５】
図４（ｃ）のパルスはパルス性の超音波発生用レーザー光の発振タイミングを示しており、この例では１ステップごと、すなわち同じ検査位置において、Sig(x_m,y_n,1)、Sig(x_m,y_n,2)の２回の信号検出を実施し、かつ走査と信号検出が同期している。このように１動作に対して複数回の計測が行える場合には、それらの信号の加算平均処理を行うことでランダムノイズを低減し各位置において計測する信号のS/N比を向上させることができる。
【００４６】
超音波検出信号は、空間的な信号加算処理によって、例えば通常の加算平均処理で除去することの出来ない固定ノイズを低減しS/N比を向上させることができる。その処理の詳細を図５を用いて説明する。
【００４７】
いま、図５（ａ）のように、被検査材３上のき裂Ｃに対し、パルス性の超音波発生用レーザー光PLを図のように４行×９列で走査する場合を考える。このとき、超音波発生用レーザー光PLの照射位置から距離Sだけ離れた位置には超音波検出用レーザー光ILが照射され、超音波発生用レーザー光PLの走査と共に相対的な位置関係を保持したまま、図示したIL(xm,yn)のように走査される。
【００４８】
送信位置PL(xm,yn)、受信位置IL(xm,yn)で送受信した超音波信号をSig(xm,yn)とする。ここで、任意の列xmに着目すると、Sig(xm,y0)から Sig(xm,y4)までの信号は図５（ｂ）のようになる。図中、信号SAWはPL(xm,yn)からIL(xm,yn)まで伝播した表面波信号で、これは距離Sが固定であるため、走査によらず、常に同じ時刻に観察される。信号Fは固定ノイズであり、これは例えば体積波の板厚エコーや被検査材３の形状に依存した表面波の形状エコーである。信号Fも常に同時刻、あるいはつぎに述べる信号Eとは異なる挙動を示す。
【００４９】
信号SAWや信号Fに共通なことは、これらはランダムノイズではなく、超音波に由来する信号であるため、時間的な平均化処理では除去できない点である。これらの信号を平均処理すると、図６（ａ）のような列ごとの平均信号Save（xm）が得られる。ここで、
Sig’(xm,yn)＝Sig(xm,yn)−Save(xm) ・・・（１２）
という差分処理によって、固定ノイズを除去した信号Sig’(xm,yn)を得る（図６（ｂ））。
【００５０】
信号Eはき裂Ｃからの反射エコーで、本検査において検出したい信号である。超音波発生用レーザー光PLおよび超音波検出用レーザー光ILの走査に従い、計測点からき裂Ｃまでの距離が変わるため、この信号の出現時刻は走査と共に変化する。
【００５１】
レーザー光PLあるいはILの照射点から見たき裂Ｃの相対的な位置は未知であるため、出現する時刻を予め知ることはできないが、ｙ方向の走査ピッチをdyとしたとき、この信号の出現時刻はｙ方向の１ステップあたり2dy/VS（但し、VSは表面弾性波の音速）だけシフトする。
【００５２】
したがって、図７（ａ）のように、各信号Sig’(xm,yn)のスタート時刻を2・n・dy/VSだけシフトした信号Sig’’(xm,yn)を加算処理すると、固定時刻、あるいは時間2・n・dy/VSにしたがってシフトしない信号SAWやFの残成分は加算と共に減少し、逆にき裂からのエコー信号Eのみは加算によって増加する。最終的には、この方法によって、４行の信号から、図７（ｂ）に示すような、S/N比の高い第ｍ列の信号Av(xm)が検知される。
【００５３】
この方法は、各プロセスにおいて、適宜信号振幅の規格化処理を行ってもよい。また、表面波信号SAWや固定ノイズFなどが比較的小さい場合には、差分処理（図６（ａ）〜（ｂ））、またはシフト加算処理（図７（ａ）〜（ｂ））のいずれか一方で十分な場合もある。
【００５４】
こうして得られた高いS/N比の信号の振幅情報を色情報に変換し、x軸-t軸からなる空間にプロットした結果（超音波Ｂスキャン）を図８に示す。図８の（ａ）は上記信号処理をしなかった場合、（ｂ）は信号処理をした場合である。信号SAW、F、F’・・・など種々の固定指示の存在により、図８（ａ）ではき裂信号Eは必ずしも明らかでないが、図８（ｂ）では固定指示が除去され、き裂信号Eが認識しやすくなっている。
【００５５】
本実施の形態のレーザー超音波検査装置は、超音波発生用レーザー光源１のパルス発振が、２次元走査する走査機構３８の走査行または走査列ごとに異なる行または各列と同期動作するようにしてもよい。この方法によれば、各行または列ごとには粗い空間サンプリングで計測しても、実質的な空間分解能を向上させることができる。
【００５６】
この方法の詳細を、図９，図１０を用いて説明する。例えば何らかの理由により、図９に示すように走査の複数回（この例では２回）に１回しか計測が同期できない場合を考える。すなわち、y0行の走査においては０、２、４、６、８、列で各々１回ずつ信号計測が行われる。この場合、得られる空間分解能は、走査時点でのサンプリング間隔2dxである。
【００５７】
しかし、図１０に示すように、y1行の走査においては１、３、５、７列で各々１回ずつ計測を行い、つぎに2dy/VSのシフト処理を行ってy0行で計測した時系列信号波形群Sig’’(x_2k,y₀)（k=0・・・4）と、y1行で計測した時系列信号波形群Sig’’(x_2k+1,y₁)（k=0・・・3）とを合わせる。このようにすると、実質的に空間的にdxの間隔で計測したのと同じ結果が得られる。ここで、y0行とy2行、y1行とｙ3行で差分および加算平均処理を行ってもよい。
【００５８】
以上説明したような本発明の第１の実施の形態のレーザー超音波検査装置に備えられる照射光学系２について図１１を参照して説明する。
【００５９】
大気以外の透明な流体媒質環境に設置された被検査材の検査を行う場合、前記特許文献２に記載されている通り、図１に示した照射光学系２もしくは照射・集光光学系M6の少なくとも一方の中の光路の一部または全部を前記流体媒質と同じ材料で充填することで、各光学素子の面における反射を抑制する方法が公知となっている。しかし、この方法は反射防止には有効なものの、媒質と光学素子材料の屈折率の差が小さくなることから、光路が長くなり、ひいては照射光学系全体が大きくなって狭隘部で使用できなくなる場合がある。
【００６０】
そこで本実施の形態においては、光学素子群および光学素子ホルダーなどで構成される照射光学系２もしくは照射・集光光学系M6の少なくとも一方の中の光路の一部または全部に、周囲の流体媒質と光学素子材料の屈折率の差が大きくなる透明流体をあえて充填することで、各光学素子の面において大きな屈折角を得、照射あるいは照射・集光光学系全体を小型化する。さらに、充填した透明流体の流出を防止するため、照射あるいは照射・集光光学系の充填部をシール処理する。
【００６１】
この構成の一例を図１１に示す。これは照射光学系２の例であり、光ファイバー１７によって超音波発生用レーザー光PLを伝送し、照射光学系２によって被検査材３に照射するものである。ここで、被検査材３は超音波発生用レーザー光PLに対して透過度を有する大気以外の流体媒質Ｗ中にあるものとする。
【００６２】
光ファイバー１７は部材ホルダー２６ａによってハウジング２６ｂに固定される。光ファイバー１７から出たレーザー光はレンズ２７ａにより平行ビームとなり、レンズ２７ｂによって被検査材３上に集光照射される。ここで、必要に応じて収差補正用のレンズ２８ａ，２８ｂを用いてもよいし、レンズ２７ａ，２７ｂとして収差の小さい非球面のレンズを用いてもよい。また平行ビームへの整形と被検査材３への集光を一枚のレンズで行うことも仕様によっては可能である。
【００６３】
この照射光学系２の特徴は、内部の光路に、周囲の流体媒質Ｗと異なる、流体媒質Ｗとレンズ２７ａ，２７ｂ、２８ａ，２８ｂの屈折率差よりも屈折率差が大きくなる透明流体Ｇを充填することである。ここで透明流体Ｇの周辺媒質Ｗへの流出、あるいは周辺媒質Ｗの透明流体Ｇへの流入を防止するため、Oリング２９ａ，２９ｂを備えている。シールはOリングだけでなく、例えば周辺流体媒質Ｗが水である場合には、シリコンなど耐水性の樹脂モールド３０ａ，３０ｂを用いることもできるし、また接合効果も期待すべき部位には、耐水性接着剤３１あるいは溶接構造によるシールも考えられる。
【００６４】
なおこの実施例の場合、光ファイバー１７の端面、あるいはレンズ２７ａ，２７ｂ、２８ａ，２８ｂなどの光学面に反射防止コーティングを施したり、光学的に許される場合には、正反射光の復路が往路と一致せぬよう若干の角度を持って設置したりするなどして、超音波発生用レーザー光PLの反射を防止するのも効果的である。
【００６５】
この実施例の照射光学系２において、流体媒質Ｗが水の場合には透明流体Ｇとして酸素を含む混合気体を用いるのがよい。流体媒質Ｗが水の場合、屈折率的には透明流体Ｇとしては不活性ガスなどを用いることもできるが、特に酸素を含む混合気体を用いれば、以下のようなメリットがある。すなわち、光学素子を保持するハウジング２６ｂ等は炭素鋼やステンレス鋼など炭素を含む金属材料で構成することが多いが、そこに比較的高エネルギーのレーザー光が照射された場合、その相互作用によって炭素が発生する。
【００６６】
もし不活性ガスを用いると、この炭素は粉末状になって光学系内を浮遊し、あるいはレンズ２７ａ，２７ｂ、２８ａ，２８ｂなどの光学素子に付着し、光路上のレーザー光の透過率を低下させると共に、場合によってはレンズ２７ａ，２７ｂ、２８ａ，２８ｂなどの損傷につながる。しかし酸素を含む混合気体を用いれば、炭素は酸素と反応して炭酸ガスとなり、粉末浮遊あるいは付着等によるこれらのトラブルの発生を未然に防止することができる。
【００６７】
つぎに照射・集光光学系M6の実施例を図１２を参照して説明する。
屈折率差の大きい透明流体を充填すると光学素子面での反射率が増大するという問題があるが、光学素子面での反射が問題となるのは主に検出側（第２の照射光学系）であり、被検査材３の反射率が低い場合には、検出用光学系で検出される光信号としては素子面からの反射が支配的となって、これらは超音波信号受信において雑音となる。
【００６８】
そこで図１２に示すように、被検査材３に超音波検出用レーザー光ILを伝送する光ファイバー６ａと、被検査材３からの反射成分SLを図示しない検出用光学系に伝送する光ファイバー６ｂを別々に設けることで、検出用光学系に混入する反射成分SLを低減し、S/N比を向上させる。
【００６９】
この場合、被検査材３へ照射される超音波検出用レーザー光ILの往路に戻る反射成分SLを別光路に導くために、偏向ビームスプリッタ（照射光・反射光分岐素子）３２および波長板（照射光・反射光分岐制御素子）３３を設置してある。また波長板３３の面の反射成分が光ファイバー６ｂに向かう光路へ混入するのを防止するため、波長板３３を若干の角度をもって設置するか、あるいは該当面に反射防止コーティングを施してある。
【００７０】
なお、同じ効果は超音波検出用レーザー光ILの照射と被検査材３からの反射成分SLの集光に、異なる２つの光学素子を用いる構成でも得られるが、この場合には２つの光学素子と被検査材表面の３者の位置合わせが必要な上、超音波発生用レーザー光のために１つ、超音波検出用レーザー光のために２つの合計３つの光学素子が被検査材表面に対向していなければならないことから、配置的に小型化が困難であり、狭隘部の検査には適当でない場合が多い。
【００７１】
本発明の第１の実施の形態のレーザー超音波検査装置（図１）に備えられる照射および照射・集光光学系のさらに他の実施例を図１３を用いて説明する。超音波発生用レーザー光PLと超音波検出用レーザー光ILは各々光ファイバー１７，６で伝送される。この２本の光ファイバー１７，６はある所定の位置関係を持ってハウジング２６に固定されており、レーザー光PLとILは同一のレンズ２７によって被検査材３の表面に照射される構成である。
【００７２】
ここで、被検査材３上の照射位置の関係および結像倍率は、２本の光ファイバー１７，６のハウジング２６内の位置関係によって決めることができる。超音波検出用レーザー光ILと反射成分SLは共に光ファイバー６によって伝送されるが、別途、集光用のレンズと光ファイバーを設けて、反射成分SLを別経路で伝送する構成としてもよい。
【００７３】
この実施例によれば、超音波発生用レーザー光PLを被検査材３に照射するための光学素子と、超音波検出用レーザー光ILの照射あるいは集光用の光学素子の少なくともいずれか一方を共用することで、照射および照射・集光光学系を小型化することができる。
【００７４】
以上説明した本発明の第１の実施の形態のレーザー超音波検査装置によれば、広範囲な領域を効率的に検査することができると共に、信号を分布計測することによる計測感度および信頼性の向上が得られる。
また、特に水中などの気体以外の環境下や狭隘部にある被検査材に対して検査を行う場合に、高感度な信号検知および効率的なノイズ低減が可能となる。
【００７５】
つぎに本発明の第２の実施の形態のレーザー超音波検査装置を説明する。本実施の形態のレーザー超音波検査装置は、図１４に示すように、超音波発生用レーザー光源１と、トリガー発振器１３と、切替え制御装置２０と、切替え装置２１と、受信装置RECを備えている。切替え装置２１は、第１の偏向制御素子２３と、第２の偏向制御素子２２-1〜２２-nと、第１のビームスプリッタ２５-1〜２５-nと、第２のビームスプリッタ２４-1〜２４-nを備えている。
【００７６】
また本実施の形態のレーザー超音波検査装置は、超音波発生用レーザー光PLを被検査材３ａ，３ｂまで伝送する光ファイバー１７-1〜１７-nと、超音波検出用レーザー光ILおよびその被検査材３ａ，３ｂ表面における反射光SLを被検査材３ａ，３ｂと受信装置RECの間で伝送する光ファイバー６-1〜６-nと、それらの光ファイバーにレーザー光を入射する入射用光学系CL-1〜CL-nおよびM1-1〜M1-nと、照射光学系２-1〜２-nと、照射・集光光学系M6-1〜M6-nを検査部位の数（ｎ個）備えている。
【００７７】
この実施の形態の超音波レーザー検査装置は、切替え制御装置２０で駆動される切替え装置２１によって超音波発生用レーザー光PLと超音波検出用レーザー光ILをｎ個の光学系に適宜時間的に切替えて入射する。このようにすることで、レーザー超音波検査装置の主要部分である超音波発生用レーザー光源１、超音波検出用レーザー光源、受信用光学系、および信号処理装置などを含む受信装置RECを、ｎ台よりも少ない台数ですませることができる。
【００７８】
超音波発生用レーザー光PLと超音波検出用レーザー光ILの伝送路を切替える手段としては、図示のような電子制御式の偏向制御光学素子２２、２３とビームスプリッタ２４、２５をｎ個組み合わせて行う方法のほか、光を反射するミラーを挿入・引抜き、あるいは回転させる機械的方法、音響光学素子（AOM: Acousto-Optical Modulator）などを用いた光の回折を用いる音響光学的な方法、液晶シャッターのON/OFFを用いた電子光学的な方法などを適用することもできる。
【００７９】
この第２の実施の形態のレーザー超音波検査装置によれば、大型構造物の複数部位、あるいは広範囲をレーザー超音波検査装置そのものを複数台用いることなく効率的に検査することができる。
【００８０】
この第２の実施の形態のレーザー超音波検査装置の変形例として、信号処理装置RECが、被検査材３ａ，３ｂの表面を伝播する弾性波に由来する検査信号を処理する第１の信号処理手段と、被検査材３ａ，３ｂ内部を伝播して裏面に到達する体積波に由来する検査信号を処理する第２の信号処理手段とを備え、第１の信号処理手段の出力信号により被検査材３ａ，３ｂの表面を、第２の信号処理手段の出力信号により被検査材３ａ，３ｂの内部および裏面を検査する構成としてもよい。
【００８１】
例えば溶接部材のような、表裏両面の開口欠陥と内在欠陥が検査対象となるような部材を検査する簡単な方法は、片面ずつアクセスして検査をすることである。しかし、例えば原子炉内構造物のように、狭隘な空間に複雑形状の構造物が設置されているような場合、片面ずつの検査は検査時間がかかる上、両面へのアクセスは必ずしも容易ではなく、そのために部材の分解・解体等をせねばならない場合もある。
【００８２】
一方、レーザー超音波法の一般的特徴は、超音波発生用レーザー光の照射により、被検査材の表面を伝播する表面波、被検査材内部から裏面まで伝播する体積波など種々の超音波モードが同時に発生することであるが、それゆえ、計測された各モードの信号の識別が難しいという問題もある。
【００８３】
本変形例は多モード同時励起というレーザー超音波法の特長を活かしたもので、超音波発生用レーザー光の照射により同時に発生し表面を伝播するモードと体積中を伝播するモードの両方の超音波を計測し、その伝播を個別に解析することで、被検査材の表面、裏面、内部を同時に検査するものである。ここで、表面伝播モードの解析手法としては、伝播時間解析法や特開２０００−１８０４１８号公報に記載されている表面伝播波のき裂による反射成分あるいは透過成分を解析する方法などが使用でき、体積伝播モードの解析手法としてはパルスエコー法や回折波検知法などが使用できる。
【００８４】
つぎに本発明の第３の実施の形態を説明する。この実施の形態のレーザー超音波検査装置は図１５に示すように、超音波発生用レーザー光源１と、切替え装置２１と、切替え制御装置２０と、トリガー発振器１３と、受信装置RECと、入射用光学系CL、M1-1，M1-2と、光ファイバー６-1，６-2，１７と、照射光学系２と、照射・集光光学系M6-1，M6-2を備えている。
【００８５】
この実施の形態は、被検査材３上の検査すべき複数部位がごく近接している場合で、各方向への超音波の伝播を考慮し、超音波発生用あるいは超音波検出用のレーザー光のいずれか一方のみを切替え動作する構成である（図では超音波検出用のレーザー光のみを切替え動作している）。この第３の実施の形態によれば、複数または広大な領域に対して、装置数を増加することなしに効率的かつ高精度な検査を行うことができる。
【００８６】
つぎに本発明の第４の実施の形態を説明する。この実施の形態のレーザー超音波検査装置は図１６に示すように、超音波発生用レーザー光源１-1，１-2と、切替え装置２１と、切替え制御装置２０と、トリガー発振器１３と、受信装置RECと、入射用光学系CL-1，CL-2、M1-1，M1-2と、光ファイバー６-1，６-2，１７-1，１７-2と、照射光学系２-1，２-2と、照射・集光光学系M6-1，M6-2を備えている。
【００８７】
この第４の実施の形態は、超音波発生用あるいは超音波検出用のレーザー光のどちらか片方はｎ台準備し、他方を切替え動作する構成としたものである。図１６では、超音波発生用のレーザー光源をｎ台（図の場合２台）備え、受信装置RECを１台で検査を行う。この場合には、１台目の超音波発生用レーザー光源1-1および２台目の超音波発生用レーザー光源1-2の動作と、切替え装置２１の動作は同期がとられている。
【００８８】
つぎに本発明の第５の実施の形態を説明する。この実施の形態のレーザー超音波検査装置は図１７に示すように、超音波発生用レーザー光源１と、受信装置RECと、トリガー発振器１３と、照射光学系２と、対物レンズM2，M3と、入射用光学系M1と、コリメーターM4と、光ファイバー６，７を備えている。
【００８９】
受信装置RECは、超音波検出用レーザー光源４と、受信用光学系OPと、光検出器９と、信号処理装置１０と、電源装置１１，１２を備えている。受信用光学系OPは、位相共役素子５と、ミラー８と、レンズM5を備えている。信号処理装置１０は、アナログ・デジタル変換部３４と、ゲート部３５と、信号処理部３６ａと、表示・記録部３６ｂとを備えている。
【００９０】
この第５の実施の形態では、アナログ・デジタル変換部３４で取り込まれた信号を信号処理部３６ａおよび表示・記録部３６ｂに伝送する際に、送受信レーザー光PL，ILの照射位置間の距離Sと、被検査材３の厚さDと、検査に使用される超音波伝播時間から計算される、表面伝播弾性波による検査範囲に対応する時刻範囲と、同様に体積伝播弾性波による検査範囲に対応する時刻範囲とをゲート部３５において分離する。したがって、この第５の実施の形態によれば、第1の実施の形態の変形例と同様に被検査材３の表面、内部および裏面の欠陥を同時に検査することができる。
【００９１】
なお、第１の実施の形態において図１１、１２、１３に示した照射あるいは照射・集光光学系は第２〜第５の実施の形態のレーザー超音波検査装置にも備えることができる。
【００９２】
【発明の効果】
本発明によれば、狭隘部に存在する複数あるいは広い面積の検査対象を感度よく効率的に検査することのできるレーザー超音波検査装置および検査方法を提供することができる。
【図面の簡単な説明】
【図１】本発明の第１の実施の形態のレーザー超音波検査装置の構成を示す図。
【図２】超音波が被検査材表面のき裂によって反射する場合（ａ）、およびき裂を透過する場合（ｂ）を示し、本発明の第１の実施の形態のレーザー超音波検査装置の動作を説明する図。
【図３】超音波が被検査材の裏側のき裂によって反射する場合を示し、本発明の第１の実施の形態のレーザー超音波検査装置の動作を説明する図。
【図４】被検査材上のｙ方向走査位置（ａ）、Ｘ方向走査位置（ｂ）の経時変化およびレーザー光の発振タイミング（ｃ）を示し、本発明の第１の実施の形態のレーザー超音波検査装置の動作を説明する図。
【図５】被検査材上の走査位置（ａ）および超音波検出信号（ｂ）を示し、本発明の第１の実施の形態のレーザー超音波検査装置の動作を説明する図。
【図６】超音波検出信号の平均処理（ａ）および差分処理（ｂ）を示し、本発明の第１の実施の形態のレーザー超音波検査装置の動作を説明する図。
【図７】超音波検出信号のシフト加算処理（ａ）およびその結果（ｂ）を示し、本発明の第１の実施の形態のレーザー超音波検査装置の動作を説明する図。
【図８】超音波検出信号を平均処理した場合（ａ）およびシフト加算処理した場合（ｂ）のＢスキャンを示し、本発明の第１の実施の形態のレーザー超音波検査装置の動作を説明する図。
【図９】被検査材上のｙ方向走査位置（ａ）、Ｘ方向走査位置（ｂ）の経時変化およびレーザー光の発振タイミング（ｃ）を示し、本発明の第１の実施の形態のレーザー超音波検査装置の他の動作を説明する図。
【図１０】被検査材上の走査位置を示し、本発明の第１の実施の形態のレーザー超音波検査装置の他の動作を説明する図。
【図１１】本発明の第１の実施の形態のレーザー超音波検査装置に備えられる照射光学系を示す断面図。
【図１２】本発明の第１の実施の形態のレーザー超音波検査装置に備えられる照射・集光光学系を示す断面図。
【図１３】本発明の第１の実施の形態のレーザー超音波検査装置に備えられる照射・集光光学系の他の実施例を示す断面図。
【図１４】本発明の第２の実施の形態のレーザー超音波検査装置の構成を示す図。
【図１５】本発明の第３の実施の形態のレーザー超音波検査装置の構成を示す図。
【図１６】本発明の第４の実施の形態のレーザー超音波検査装置の構成を示す図。
【図１７】本発明の第５の実施の形態のレーザー超音波検査装置の構成を示す図。
【図１８】従来のレーザー超音波検査装置の第１の例を示す図。
【図１９】従来のレーザー超音波検査装置の第２の例を示す図。
【図２０】従来のレーザー超音波検査装置の第３の例を示す図。
【符号の説明】
１，１-1，１-2…超音波発生用レーザー光源、２，２-1，２-n…照射光学系、３，３ａ，３ｂ…被検査材、４…超音波検出用レーザー光源、５…位相共役素子、６，６ａ，６ｂ，６-1，６-2，６-n，７…光ファイバー、８…ミラー、９…光検出器、１０…信号処理装置、１１，１２…電源装置、１３…トリガー発振器、１４，１６…レンズ系、１５…微小レンズアレイ、１７，１７-1，１７-n…光ファイバー、１８…ビームスプリッタ、１９…ミラー、２０…切替え制御装置、２１…切替え装置、２２，２２-1，２２-n…第２の偏向制御素子、２３，２３-1，２３-n…第１の偏向制御素子、２４，２４-1，２４-n…第２のビームスプリッタ、２５-1，２５-n…第１のビームスプリッタ、２６，２６ｂ…ハウジング、２６ａ…部材ホルダー、２６ｃ…レンズ押え、２７，２７ａ，２７ｂ…レンズ、２８ａ，２８ｂ…収差補正レンズ、２９ａ，２９ｂ…Oリング、３０ａ，３０ｂ…樹脂モールド、３１…接着剤、３２…偏向ビームスプリッタ、３３…波長板、３４…アナログ・デジタル変換部、３５…ゲート部、３６ａ…信号処理部、３６ｂ…表示・記録部、３７…走査テーブル、３８…走査機構、３９…走査制御器、４０…位置センサ、４１…信号処理・表示・記録装置、Ｃ…き裂または欠陥、CL，CL-1，CL-2，CL-n…入射用光学系、Ｇ…透明流体、IL…超音波検出用レーザー光、M1，M1-1，M1-2，M1-n…入射用光学系、M2，M3…対物レンズ、M4…コリメーター、M5…レンズ、M6，M6-1，M6-2，M6-n…照射・集光光学系、OP…受信用光学系、REC…受信装置（信号変換手段）、PL，PL-1，PL-2…超音波発生用レーザー光、Sig…超音波信号、SL…反射光、US…超音波、Ｗ…周辺流体媒質。[0001]
BACKGROUND OF THE INVENTION
The present invention provides a crack or defect by irradiating the inspection target with laser light and receiving reflected light when the inspection target that is difficult to contact or approach, such as a small size, high temperature, or moving part, is in an underwater environment or a narrow environment. The present invention relates to a laser ultrasonic inspection apparatus and inspection method that perform non-contact and non-destructive measurement and evaluation of material characteristics such as inspection of a laser.
[0002]
[Prior art]
Laser ultrasonic methods have been proposed as a technique for crack inspection of power plant equipment and structural materials. The outline of this technique is described in the following Non-Patent Document 1 or the like, but in many cases, thermal stress generated by irradiating a material to be inspected with pulsed laser light or vaporization reaction force is used. On the other hand, the receiving point is irradiated with another laser beam that pulsates or continuously oscillates sufficiently long compared to the propagation time of the ultrasonic wave, and by using its straightness and coherence, This is a technique for detecting cracks and the like by receiving induced displacement or vibration velocity. Detection of cracks and intrinsic defects on material surfaces or evaluation of material properties using ultrasonic waves is a well-known technique, but these can be performed in a non-contact manner by laser ultrasonic methods. It is possible and is expected to be applied to various material evaluation fields.
[0003]
Several different optical systems have been proposed as a method for detecting and generating ultrasonic waves in the laser ultrasonic method. In particular, two optical waves using Michelson interferometry, Mach-Zehnder interferometry, Fabry-Perot method, and phase conjugate element are used as detection optical systems. A mixing method, a knife edge method, and the like have been proposed. Here, a configuration block diagram of a typical conventional apparatus is shown in FIG. 18 regarding generation of ultrasonic waves by irradiation with pulsed laser light and detection of ultrasonic waves using a two-wave mixing method using a phase conjugate element (Patent Document 1 below). reference).
[0004]
In the laser ultrasonic inspection apparatus shown in FIG. 18, ultrasonic generation laser light PL pulsated from an ultrasonic generation laser light source 1 for generating ultrasonic waves is passed through an irradiation optical system 2 and predetermined on the surface of the inspection object 3. The position is irradiated with a predetermined beam shape. Here, as the laser light source 1 for generating ultrasonic waves, a Q-switch YAG laser or the like is often used.
[0005]
Due to the interaction between the material to be inspected 3 and the laser beam PL for generating ultrasonic waves, ultrasonic waves US in various modes such as longitudinal waves, transverse waves, and surface waves are generated in the inspected material 3. The ultrasonic wave US causes a phenomenon such as reflection, scattering, diffraction, absorption, and change in sound speed due to a crack, a defect, or a material characteristic of the material 3 to be inspected. Then, when the ultrasonic wave US propagated through a certain propagation process reaches an arbitrary measurement point on the material to be inspected 3, vibration is generated at that part. By measuring and analyzing the vibration signal, it is possible to inspect the material characteristics of the inspection material 3 such as a crack and a defect existing in the inspection material 3.
[0006]
On the other hand, ultrasonic detection laser light IL oscillated from an ultrasonic detection laser light source 4 for detecting ultrasonic waves is incident on the phase conjugate element 5. Here, as the phase conjugate element 5, a ferroelectric crystal (BaTiO _Three , LiNbO _Three Etc.), paraelectric crystals (BSO, etc.) and semiconductors (GaAs, InP, GaP, etc.) are used. The ultrasonic detection laser beam IL that has passed through the phase conjugate element 5 is incident on the first optical fiber 6 by the incident optical system (collimator) M1, and is irradiated to a predetermined measurement point on the inspection object 3 by the objective lens M2. Is done.
[0007]
A part SL of the reflected component of the irradiated ultrasonic detection laser beam IL is condensed by the second objective lens M3, and is passed through the second optical fiber 7 and the second incident optical system (collimator) M4. The light is incident again on the phase conjugate element 5. Normally, when the surface of the material 3 to be inspected is optically rough, the wavefront of the reflected light SL is distorted and the interference efficiency becomes extremely low, and an interference signal cannot be obtained. However, in this optical system arrangement, The reflected light SL interferes due to the phase conjugate effect, and can be detected with relatively high efficiency by the photodetector 9 via the mirror 8 and the lens M5. The detected signal is appropriately signal processed, displayed, and recorded by the signal processing apparatus 10.
[0008]
Here, a PIN type photodiode (PIN-PD) or an avalanche photodiode (APD) is often used as the photodetector 9, and these are applied with a steady bias voltage from the first power supply device 11. Operate. The phase conjugate element 5 is also operated by applying a bias voltage of several kV to several tens of kV from the second power supply device 12, and an operation mode in which this bias voltage is applied in a pulse form to suppress the drift of the element. Has also been proposed. In addition, the trigger oscillator 13 is used to synchronize the operation timing of the laser light source 1 for generating ultrasonic waves and the operation of the second power supply device 12 so that the phase conjugate element 5 can obtain the maximum interference efficiency at the ultrasonic measurement time. Devices have also been proposed.
[0009]
There has also been proposed a method in which the oscillation light PL of the ultrasonic light generation laser light source 1 having a relatively high pulse energy is incident on the optical fiber 17 using the configuration shown in FIG. This is because the micro lens array 15 is used in addition to the first and second lens systems 14 and 16 to diffuse the focal point and to avoid damage to the optical fiber 17. With this configuration, both transmitted and received light can be transmitted. Optical fiber transmission is also possible.
[0010]
On the ultrasonic detection side, as shown in FIG. 20, a single lens M6 is used to irradiate the inspection object 3 with the laser light IL for ultrasonic detection and to collect the reflection component SL on the surface of the inspection object. A structure for performing light is also already known in Patent Document 2 below. In this case, the reflected light SL transmitted through the optical fiber 6 from the inspection object 3 side to the receiving optical system OP is branched from the optical path of the ultrasonic detection laser light IL by the beam splitter 18, and then the phase conjugate element 5. Led to. In order to efficiently branch the reflected light SL and the ultrasonic detection laser light IL, branch control may be performed by deflection using a deflection control optical element such as a wavelength plate and a deflection beam splitter.
[0011]
[Non-Patent Document 1]
Yamawaki: “Laser Ultrasound and Non-contact Material Evaluation”, Journal of the Japan Welding Society, Vol. 64, No. 2, P.104-108 (1995)
[Patent Document 1]
JP 2002-257793 A
[Patent Document 2]
JP 2001-318081 A
[0012]
[Problems to be solved by the invention]
In principle, the laser ultrasonic inspection method is a part where the material to be inspected is difficult to contact, such as high temperatures, high places, high radiation fields, and complicated shapes, or where the proximity is poor and remote non-contact inspection methods are required. It is effective in the case where the laser beam is spatially transmitted, such as a narrow part or the inside of the shield, by applying fiber technology.
[0013]
However, since it is usually required to inspect a plurality of points or a plurality of regions (areas) on the material to be inspected, or both surfaces (front and back surfaces) of the region, these regions are efficiently used. It is desirable to be able to inspect. In addition, in the nuclear power plant field, for example, these parts are often installed in narrow areas under an underwater environment.
[0014]
In particular, when inspecting materials to be inspected in environments other than gases such as underwater or in narrow spaces, signals may be caused by attenuation of ultrasonic components, attenuation of transmitted / received laser light due to medium quality, or insufficient condensing capability. / There is concern about a decrease in the noise ratio (S / N ratio). In particular, when inspecting an object to be inspected in an environment other than gas such as water or in a narrow part, it is necessary to appropriately pass through a narrow path and access a narrow inspection target part.
[0015]
Accordingly, an object of the present invention is to provide a laser ultrasonic inspection apparatus and an inspection method capable of inspecting a plurality of or a wide area inspection object existing in a narrow part with high sensitivity and efficiency.
[0016]
[Means for Solving the Problems]
The invention according to claim 1 is a first laser light source that oscillates a first laser beam, an irradiating means that irradiates a material to be inspected with the first laser beam, and a second that oscillates a second laser beam. A laser light source, an irradiation / condensing means for irradiating the surface of the material to be inspected with the second laser light and receiving a reflection component thereof, and the reflection component collected by the irradiation / condensing means from the first A receiving optical system for optically detecting a signal relating to an ultrasonic wave generated in the inspection object by irradiation of one laser beam, and a signal conversion for converting the ultrasonic signal received by the receiving optical system into an electrical signal Means, The irradiation means and the irradiation / condensing means are controlled and driven, and the irradiation positions of the first and second laser lights on the material to be inspected are synchronized with each other in synchronization with the oscillation of the first laser light. Scanning means for moving and scanning within a predetermined range and a predetermined step size while maintaining the positional relationship; position detecting means for detecting the irradiation positions of the first and second laser beams; Signal processing the output signal of the signal conversion means, From the ultrasonic signal detected at each position accompanying the scan and the position information detected by the position detection means Calculates and displays information on the propagation of ultrasonic waves and the characteristics of the material to be inspected. Show In a laser ultrasonic inspection apparatus equipped with a signal processing means, The first laser light source is a pulsed laser light source that oscillates in a pulse, the scanning by the scanning means is two-dimensional, and the signal processing means is a column or row of detected ultrasonic signals in a two-dimensional array. Average processing for each column or row, a difference processing process for calculating a difference between an average signal for each column or row obtained as a result of the average processing and a measurement signal at each point, and the scanning A spatial averaging process that shifts twice the distance set by the means by a time corresponding to the propagation of the ultrasound signal and overlaps each row or column by a predetermined number less than or equal to the number of scan rows or columns; And the amplitude information of the time series signal waveform group of one column or one row obtained as a result is displayed in a two-dimensional space consisting of an axis corresponding to the column or row and a time axis. The configuration.
[0017]
The invention of claim 2 ,in front The scanning by the scanning means is configured to operate in synchronization with one pulse oscillation of the first laser light source, a plurality of predetermined times, or a predetermined number of times.
[0018]
According to a third aspect of the present invention, the scanning by the scanning means is an operation synchronized with a predetermined plurality of times of pulse oscillation of the first laser light source, and the signal processing means outputs the detected ultrasonic signal to the above-mentioned ultrasonic signal. The same number of times as the number of pulses Make sense The configuration is as follows.
[0019]
Contract Claim 4 According to the present invention, the oscillation of the pulse laser light source operates in synchronization with different columns or rows for each scanning row or column of the scanning means.
[0020]
Claim 5 According to the present invention, in the laser ultrasonic inspection apparatus according to claim 1, the sound velocity of the surrounding environmental medium in which the inspection object is installed is VM, and the inspection target is the ultrasonic signal generated by the first laser light. The acoustic velocity of the elastic wave propagating on the surface of the material is VS, and the region length to be inspected from the side closer to the crack to be detected on the inspected material at the irradiation position of the first laser beam or the second laser beam. When L is L, an interval S between the irradiation position of the first laser beam and the irradiation position of the second laser beam is expressed by a relational expression.
[Equation 3]

It is set as the structure set to the length represented by these.
[0021]
Claim 6 According to the present invention, in the laser ultrasonic inspection apparatus according to claim 1, VS represents a sound velocity of an elastic wave propagating on a surface of the inspection object among ultrasonic signals generated by the first laser light, and the inspection object When the sound velocity of the volume wave propagating in the material is VB and the thickness of the material to be inspected is D, the relationship between the irradiation position of the first laser beam and the irradiation position of the second laser beam is related. formula
[Expression 4]

It is set as the structure set to the length represented by these.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, a first embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, the laser ultrasonic inspection apparatus of this embodiment includes a laser light source 1 for generating ultrasonic waves, a receiving device REC as signal conversion means, a signal processing / display / recording device 41, and a trigger oscillator 13. And a scanning mechanism 38 and a scanning controller 39.
[0028]
Further, the irradiation optical system 2 for irradiating the inspection target material 3 with the laser beam PL for generating ultrasonic waves, and the irradiation / condensing optics for irradiating the inspection target material 3 with the laser beam IL for ultrasonic detection and condensing the reflected light. The system M6 is installed on the scanning table 37, and the distance from the material 3 to be inspected and the relative positional relationship between them are maintained. The scanning table 37 may be mounted on an upper scanning mechanism 38 that conveys the scanning table 37 to an inspection site on the inspection object 3.
[0029]
The scanning table 37 or the scanning mechanism 38 is controlled by a scanning controller 39, and scans a region to be inspected one-dimensionally or two-dimensionally within a testable range. Here, the range in which the area to be inspected can be inspected does not necessarily match the area to be inspected. That is, for example, when surface waves are used in an underwater environment, surface waves propagate if they are in the range of several millimeters to several tens of millimeters from the transmission / reception point, and if there is a crack in the region, reflected waves are detected. For the same reason, it is also possible to inspect a two-dimensional region along the scanning line by one-dimensional scanning. When the material to be inspected 3 has a welded portion having various shapes, the scanning is one-dimensional along the welding line or two-dimensional scanning with the direction as the longitudinal direction.
[0030]
Ultrasonic signals are transmitted and received while scanning, and the measurement interval can be arbitrarily determined by a combination of measurement timing controlled by the trigger oscillator 13 and spatial operation parameters controlled by the scanning controller 39. However, the relative positional relationship in which the signal is measured should be known in order to be used for material property calculation by subsequent signal analysis. In this case, the position sensor 40 may be installed for measurement, or the scanning pitch may be set at a constant interval in the scanning stage, and the position may be calculated therefrom. As the position sensor 40, an ultrasonic distance sensor, a laser distance sensor, an encoder, or the like is used.
[0031]
The position information and the timing information are input to the signal processing / display / recording device 41 for calculating the material characteristics together with the electric signal obtained by converting the detected ultrasonic signal by the receiving device REC, and the signal processing / display / recording is performed. . Here, as a method for analyzing the surface propagation mode, a propagation time analysis method or a method for analyzing a reflection component or a transmission component due to a crack of a surface propagation wave described in Japanese Patent Laid-Open No. 2000-180418 is used. As a method for analyzing the volume propagation mode, the diffraction wave time-of-flight method (TOFD method: Time-of-Flight Diffraction) or the aperture synthesis method (SAFT method: Synthetic Aperture Focusing Technique) is used.
[0032]
A surface inspection mainly using the surface propagation mode that propagates the surface of the material 3 to be inspected will be described below. As shown in FIG. 2A, a case is considered in which the surface crack C of the material 3 to be inspected is inspected with the ultrasonic wave generation laser beam PL and the ultrasonic detection laser beam IL. At this time, the distance between the irradiation positions of the two laser beams is S, the sound velocity of the surrounding medium surrounding the material to be inspected is VM, the sound velocity of the surface propagation elastic wave of the material to be inspected is VS, and the laser beam for generating ultrasonic waves Let L be the length of the shorter distance from the PL or the ultrasonic detection laser beam IL to the region to be inspected.
[0033]
Now, the signal to be detected is a reflected signal from the crack C as shown in FIG. 2 (a) or a signal that passes through the crack C as shown in FIG. 2 (b). Consider a reflected signal with a longer propagation time. The time tS when this reflected signal is measured is based on the time when the ultrasonic wave is generated by the laser beam PL for ultrasonic wave generation.
[Equation 5]

It is.
[0034]
On the other hand, when the medium surrounding the material to be inspected 3 is a substance capable of transmitting ultrasonic waves, such as air or water, the ultrasonic wave is detected from the irradiation position of the laser beam PL for generating ultrasonic waves without passing through the surface of the material to be inspected 3. There is also an ultrasonic mode that propagates through the peripheral medium to the irradiation position of the laser light IL. Although this ultrasonic mode becomes noise, its amplitude may be much larger than the amplitude of the reflected signal from the minute crack C, and it should be avoided that the reflected signal reaching time tS overlaps with this noise in time. is there. Therefore, as the arrival time tN of this noise
[Formula 6]

That is, the distance S between the two irradiation positions is
[Expression 7]

Should be decided.
[0035]
Note that noise propagates through the surrounding medium in the form of a shock wave, and VM may not be a constant. In this case, the overlap between the signal and noise is eliminated at a distance shorter than S defined by equation (3). Therefore, it is sufficient to maintain the relationship of the expression (3). Conversely, in order to facilitate signal identification, if some margin is required between the noise and the reflected signal, such as for signal separation and identification, that amount is set as a positive constant A.
[Equation 8]

You may decide.
[0036]
In any case, in order to inspect the surface crack C, the distance S between the irradiation positions of the ultrasonic wave generation laser beam PL and the ultrasonic wave detection laser beam IL is minimum. Should be more than that.
[0037]
The back surface or internal inspection using the volume propagation mode in which the inside of the inspection object 3 is propagated will be described below. As shown in FIG. 3, a case is considered in which a defect C existing on the back surface or inside of the inspection object 3 is inspected with an ultrasonic wave generation laser beam PL and an ultrasonic wave detection laser beam IL. At this time, the distance between the two laser light irradiation positions is S, the sound velocity of the surrounding medium surrounding the inspection object 3 is VM, the sound velocity of the surface-propagating elastic wave of the inspection object 3 is VS, and the volume of the inspection object 3 The sound velocity of the propagating elastic wave is VB, and the maximum depth at which the defect C can exist, that is, the thickness of the material 3 to be inspected is D.
[0038]
Now, the signal to be detected is a diffraction or reflection signal from the defect C. The time tB at which the diffraction or reflection signal is measured depends on the position of the defect C, but when it is farthest, that is, when it is in the very vicinity of the back surface, tB is detected by the ultrasonic wave generation laser light PL. Based on the time when it occurred
[Equation 9]

It is.
[0039]
Where VB ₁ , VB ₂ The sound velocity of ultrasonic waves propagating in the volume is not uniquely determined (for example, longitudinal elastic waves (velocity VB ₁ ) To defect C, where it undergoes mode conversion when diffracting, and a transverse elastic wave (velocity VB ₂ ), Etc.). Here, for simplicity, when the transmitted ultrasonic mode and the received ultrasonic mode are the same, that is,
[Expression 10]

think of.
[0040]
At this time, the noise in the signal detection is the time
[Expression 11]

In addition to the shock wave propagating in the medium that reaches
[Expression 12]

Surface acoustic waves that reach can also be noise.
[0041]
Here, when the surrounding medium is water or air and the material to be inspected is metal, since VS> VM, the surface acoustic wave noise represented by the equation (9) is effectively problematic. Therefore, the distance S is calculated from the equations (7) and (9).
[Formula 13]

It becomes.
[0042]
Here, when a longitudinal wave is assumed as the volume wave, if the material 3 to be inspected is a metal material, VB is almost equal to 2VS in many cases. Using this relationship,
[Expression 14]

It becomes.
[0043]
That is, in order to inspect the defect C existing on the back surface or inside, the distance S between the irradiation positions of the ultrasonic wave generation laser beam PL and the ultrasonic detection laser beam IL is not less than the value expressed by the equation (10). As a special case, the distance S expressed by the equation (11) may be used.
[0044]
Next, scanning and measurement timing will be described. In the case of a step-like operation, it is not always necessary to make one measurement per operation because of the difference in speed between the scanning operation and the signal measurement, but the timing should be synchronized. An example is shown in FIG. FIGS. 4A and 4B show the positions by scanning. In this case, 4 rows x 9 columns of 4 steps y0 to y3 in the y-axis direction and 9 steps x0 to x8 in the X-axis direction. It is assumed that scanning is performed.
[0045]
The pulse in FIG. 4C shows the oscillation timing of the pulsed ultrasonic wave generating laser beam. In this example, Sig (x _m , y _n , 1), Sig (x _m , y _n , 2) are detected twice, and scanning and signal detection are synchronized. In this way, when multiple measurements can be performed for one operation, random noise can be reduced by performing an averaging process of these signals, and the S / N ratio of the signal measured at each position can be improved. it can.
[0046]
The ultrasonic detection signal can reduce fixed noise that cannot be removed by, for example, a normal addition averaging process and improve the S / N ratio by a spatial signal addition process. Details of the processing will be described with reference to FIG.
[0047]
Now, as shown in FIG. 5A, consider a case where a pulsed ultrasonic wave generation laser beam PL is scanned in 4 rows × 9 columns as shown in FIG. At this time, the ultrasonic detection laser beam IL is irradiated to the position separated by the distance S from the irradiation position of the ultrasonic generation laser beam PL, and the relative positional relationship is maintained together with the scanning of the ultrasonic generation laser beam PL. Then, scanning is performed as shown IL (xm, yn).
[0048]
An ultrasonic signal transmitted / received at the transmission position PL (xm, yn) and the reception position IL (xm, yn) is defined as Sig (xm, yn). Here, focusing on an arbitrary column xm, signals from Sig (xm, y0) to Sig (xm, y4) are as shown in FIG. In the figure, a signal SAW is a surface wave signal propagated from PL (xm, yn) to IL (xm, yn), and this is always observed at the same time regardless of scanning because the distance S is fixed. The signal F is fixed noise, which is, for example, a volume wave thickness echo or a surface wave shape echo depending on the shape of the material 3 to be inspected. The signal F always behaves differently from the same time or the signal E described below.
[0049]
What is common to the signals SAW and F is that they are not random noises but signals derived from ultrasonic waves, and therefore cannot be removed by temporal averaging. When these signals are averaged, an average signal Save (xm) for each column as shown in FIG. 6A is obtained. here,
Sig ′ (xm, yn) = Sig (xm, yn) −Save (xm) (12)
The signal Sig ′ (xm, yn) from which the fixed noise is removed is obtained by the difference processing (FIG. 6B).
[0050]
The signal E is a reflected echo from the crack C and is a signal to be detected in this inspection. As the distance from the measurement point to the crack C changes according to the scanning of the ultrasonic generation laser beam PL and the ultrasonic detection laser beam IL, the appearance time of this signal changes with the scanning.
[0051]
Since the relative position of the crack C as seen from the irradiation point of the laser beam PL or IL is unknown, the time of appearance cannot be known in advance, but this signal appears when the scanning pitch in the y direction is dy. The time is shifted by 2 dy / VS per step in the y direction (where VS is the acoustic velocity of the surface acoustic wave).
[0052]
Accordingly, as shown in FIG. 7A, when the signal Sig ″ (xm, yn) obtained by shifting the start time of each signal Sig ′ (xm, yn) by 2 · n · dy / VS is added, the fixed time Alternatively, the remaining components of the signals SAW and F that do not shift in accordance with time 2 · n · dy / VS decrease with addition, and conversely, only the echo signal E from the crack increases with addition. Finally, this method detects the signal Av (xm) in the m-th column with a high S / N ratio as shown in FIG. 7B from the four rows of signals.
[0053]
In this method, signal amplitude normalization processing may be appropriately performed in each process. When the surface wave signal SAW, the fixed noise F, etc. are relatively small, either the difference processing (FIGS. 6A to 6B) or the shift addition processing (FIGS. 7A to 7B) is performed. On the other hand, it may be sufficient.
[0054]
FIG. 8 shows the result (ultrasonic B scan) obtained by converting the amplitude information of the high S / N ratio signal thus obtained into color information and plotting it in the space consisting of the x-axis and t-axis. 8A shows the case where the signal processing is not performed, and FIG. 8B shows the case where the signal processing is performed. Due to the presence of various fixing instructions such as signals SAW, F, F ′..., The crack signal E is not necessarily clear in FIG. 8A, but the fixing instruction is removed in FIG. E is easy to recognize.
[0055]
The laser ultrasonic inspection apparatus of the present embodiment is configured so that the pulse oscillation of the laser light source 1 for generating ultrasonic waves operates in synchronization with different rows or columns for each scanning row or scanning column of the scanning mechanism 38 that performs two-dimensional scanning. May be. According to this method, even if measurement is performed with coarse spatial sampling for each row or column, substantial spatial resolution can be improved.
[0056]
Details of this method will be described with reference to FIGS. For example, consider a case where the measurement can be synchronized only once for a plurality of scans (in this example, twice) as shown in FIG. 9 for some reason. That is, in the scan of the y0 row, signal measurement is performed once for each of 0, 2, 4, 6, 8, and columns. In this case, the obtained spatial resolution is the sampling interval 2dx at the time of scanning.
[0057]
However, as shown in FIG. 10, in the scan of the y1 row, the time series is measured once in each of the 1, 3, 5, and 7 columns, and then subjected to the 2dy / VS shift process and measured in the y0 row. Signal waveform group Sig '' (x _2k , y ₀ ) (K = 0 ... 4) and time series signal waveform group Sig '' (x _{2k + 1} , y ₁ ) (K = 0 ... 3). In this way, the same result as that measured substantially spatially at intervals of dx can be obtained. Here, the difference and addition averaging processing may be performed on the y0 and y2 rows and the y1 and y3 rows.
[0058]
The irradiation optical system 2 provided in the laser ultrasonic inspection apparatus according to the first embodiment of the present invention as described above will be described with reference to FIG.
[0059]
When inspecting a material to be inspected installed in a transparent fluid medium environment other than the atmosphere, as described in Patent Document 2, the irradiation optical system 2 or the irradiation / collection optical system M6 shown in FIG. A method of suppressing reflection on the surface of each optical element by filling a part or all of the optical path in at least one with the same material as the fluid medium is known. However, although this method is effective for preventing reflection, the difference in the refractive index between the medium and the optical element material becomes small, so the optical path becomes long, and the entire irradiation optical system becomes large and cannot be used in a narrow part. There is.
[0060]
Therefore, in the present embodiment, the surrounding fluid medium is provided in part or all of the optical path in at least one of the irradiation optical system 2 or the irradiation / collection optical system M6 including the optical element group and the optical element holder. And a transparent fluid in which the difference in refractive index between the optical element materials is increased, a large refraction angle is obtained on the surface of each optical element, and the entire irradiation or irradiation / collection optical system is downsized. Furthermore, in order to prevent the filled transparent fluid from flowing out, the filling portion of the irradiation or irradiation / collection optical system is sealed.
[0061]
An example of this configuration is shown in FIG. This is an example of the irradiation optical system 2, in which the ultrasonic generation laser beam PL is transmitted by the optical fiber 17 and is irradiated to the inspection object 3 by the irradiation optical system 2. Here, it is assumed that the material to be inspected 3 is in a fluid medium W other than the atmosphere having transparency to the laser beam PL for generating ultrasonic waves.
[0062]
The optical fiber 17 is fixed to the housing 26b by a member holder 26a. The laser light emitted from the optical fiber 17 is converted into a parallel beam by the lens 27a, and is condensed and irradiated onto the inspection object 3 by the lens 27b. Here, if necessary, aberration correcting lenses 28a and 28b may be used, and aspherical lenses with small aberrations may be used as the lenses 27a and 27b. In addition, depending on the specification, it is possible to perform shaping into a parallel beam and condensing light on the material 3 to be inspected with a single lens.
[0063]
The irradiation optical system 2 is characterized in that a transparent fluid G having a refractive index difference larger than the refractive index difference between the fluid medium W and the lenses 27a, 27b, 28a, and 28b is different from the surrounding fluid medium W in the internal optical path. To fill. Here, in order to prevent the transparent fluid G from flowing out into the peripheral medium W or from flowing into the transparent fluid G, the O-rings 29a and 29b are provided. For example, when the surrounding fluid medium W is water, water-resistant resin molds 30a and 30b such as silicon can be used as seals, and water-resistant resin molds 30a and 30b can be used for parts that should be expected to have a bonding effect. Sealing with the adhesive 31 or a welded structure is also conceivable.
[0064]
In the case of this embodiment, when the end face of the optical fiber 17 or an optical surface such as the lenses 27a, 27b, 28a, 28b is provided with an antireflection coating or optically permitted, the return path of the regular reflection light is the forward path. It is also effective to prevent reflection of the laser beam PL for generating ultrasonic waves by installing it at a slight angle so as not to match.
[0065]
In the irradiation optical system 2 of this embodiment, when the fluid medium W is water, a mixed gas containing oxygen may be used as the transparent fluid G. When the fluid medium W is water, an inert gas or the like can be used as the transparent fluid G in terms of refractive index. However, the use of a mixed gas containing oxygen has the following merits. That is, the housing 26b or the like that holds the optical element is often made of a metal material containing carbon such as carbon steel or stainless steel, but when a relatively high energy laser beam is irradiated thereto, the interaction causes carbon to Occurs.
[0066]
If an inert gas is used, this carbon becomes powdery and floats in the optical system or adheres to optical elements such as lenses 27a, 27b, 28a, and 28b, thereby reducing the transmittance of laser light on the optical path. In some cases, the lenses 27a, 27b, 28a, 28b and the like may be damaged. However, if a mixed gas containing oxygen is used, carbon reacts with oxygen to become carbon dioxide gas, which can prevent the occurrence of these troubles due to powder floating or adhesion.
[0067]
Next, an embodiment of the irradiation / collection optical system M6 will be described with reference to FIG.
When a transparent fluid having a large refractive index difference is filled, there is a problem that the reflectance on the optical element surface increases, but the reflection on the optical element surface is mainly a problem on the detection side (second irradiation optical system). In the case where the reflectance of the material 3 to be inspected is low, reflection from the element surface is dominant as an optical signal detected by the detection optical system, and these become noise in receiving an ultrasonic signal. .
[0068]
Therefore, as shown in FIG. 12, the optical fiber 6a for transmitting the ultrasonic detection laser beam IL to the inspection material 3 and the optical fiber 6b for transmitting the reflection component SL from the inspection material 3 to the detection optical system (not shown) are separately provided. Thus, the reflection component SL mixed in the detection optical system is reduced, and the S / N ratio is improved.
[0069]
In this case, a deflected beam splitter (irradiated light / reflected light branching element) 32 and a wavelength plate (wavelength plate) (in order to guide the reflected component SL returning to the outward path of the ultrasonic detection laser light IL irradiated to the inspection object 3 to another optical path) An irradiation light / reflected light branching control element) 33 is provided. In order to prevent the reflection component on the surface of the wave plate 33 from entering the optical path toward the optical fiber 6b, the wave plate 33 is installed at a slight angle, or an anti-reflection coating is applied to the corresponding surface.
[0070]
The same effect can be obtained with a configuration in which two different optical elements are used to irradiate the ultrasonic detection laser beam IL and collect the reflection component SL from the material 3 to be inspected. And the surface of the material to be inspected must be aligned, and a total of three optical elements on the surface of the material to be inspected, one for ultrasonic wave generation laser light and two for ultrasonic detection laser light Since they must face each other, it is difficult to reduce the size in terms of arrangement, and in many cases, they are not suitable for inspection of narrow portions.
[0071]
Still another example of the irradiation and irradiation / collection optical system provided in the laser ultrasonic inspection apparatus (FIG. 1) according to the first embodiment of the present invention will be described with reference to FIG. The ultrasonic generation laser beam PL and the ultrasonic detection laser beam IL are transmitted by optical fibers 17 and 6, respectively. The two optical fibers 17 and 6 are fixed to the housing 26 with a certain predetermined positional relationship, and the laser light PL and IL are irradiated onto the surface of the inspection object 3 by the same lens 27.
[0072]
Here, the relationship between the irradiation positions on the inspection material 3 and the imaging magnification can be determined by the positional relationship within the housing 26 of the two optical fibers 17 and 6. Although both the ultrasonic detection laser beam IL and the reflection component SL are transmitted by the optical fiber 6, a configuration may be adopted in which a reflection lens SL and an optical fiber are separately provided and the reflection component SL is transmitted by another path.
[0073]
According to this embodiment, at least one of an optical element for irradiating the inspection target material 3 with the laser beam PL for ultrasonic generation and an optical element for irradiating or condensing the ultrasonic detection laser light IL is provided. By sharing, the irradiation and irradiation / condensing optical system can be reduced in size.
[0074]
According to the laser ultrasonic inspection apparatus of the first embodiment of the present invention described above, it is possible to efficiently inspect a wide area and improve measurement sensitivity and reliability by measuring the distribution of signals. Is obtained.
In particular, when an inspection is performed on a material to be inspected in an environment other than a gas such as underwater or in a narrow part, highly sensitive signal detection and efficient noise reduction are possible.
[0075]
Next, a laser ultrasonic inspection apparatus according to the second embodiment of the present invention will be described. As shown in FIG. 14, the laser ultrasonic inspection apparatus of the present embodiment includes a laser light source 1 for generating ultrasonic waves, a trigger oscillator 13, a switching control device 20, a switching device 21, and a receiving device REC. Yes. The switching device 21 includes a first deflection control element 23, second deflection control elements 22-1 to 22-n, first beam splitters 25-1 to 25-n, and second beam splitter 24- 1 to 24-n.
[0076]
The laser ultrasonic inspection apparatus of the present embodiment also includes optical fibers 17-1 to 17-n for transmitting ultrasonic generation laser light PL to the materials to be inspected 3a and 3b, ultrasonic detection laser light IL, and its target. Optical fibers 6-1 to 6-n that transmit the reflected light SL on the surfaces of the inspection materials 3a and 3b between the inspection materials 3a and 3b and the receiving device REC, and an incident optical system CL that makes laser light incident on these optical fibers. -1 to CL-n and M1-1 to M1-n, irradiation optical system 2-1 to 2-n, and irradiation / condensing optical system M6-1 to M6-n (n) I have.
[0077]
In the ultrasonic laser inspection apparatus according to this embodiment, the switching device 21 driven by the switching control device 20 converts the ultrasonic generation laser light PL and the ultrasonic detection laser light IL into n optical systems as appropriate in time. Switch incident. In this way, the receiving device REC including the ultrasonic light source 1 for generating ultrasonic waves, the laser light source for detecting ultrasonic waves, the receiving optical system, and the signal processing device, which is a main part of the laser ultrasonic inspection device, is n The number can be less than the number of units.
[0078]
As means for switching the transmission path between the ultrasonic wave generation laser beam PL and the ultrasonic wave detection laser beam IL, n electronically controlled deflection control optical elements 22 and 23 and beam splitters 24 and 25 as shown in the figure are combined. In addition to the method used, a mechanical method that inserts, pulls out, or rotates a mirror that reflects light, an acousto-optic method that uses light diffraction using an acousto-optical modulator (AOM), a liquid crystal shutter, etc. It is also possible to apply an electro-optical method using ON / OFF.
[0079]
According to the laser ultrasonic inspection apparatus of the second embodiment, it is possible to efficiently inspect a plurality of parts or a wide range of a large structure without using a plurality of laser ultrasonic inspection apparatuses themselves.
[0080]
As a modification of the laser ultrasonic inspection apparatus according to the second embodiment, the signal processing apparatus REC performs first signal processing in which an inspection signal derived from an elastic wave propagating on the surfaces of the materials to be inspected 3a and 3b is processed. Means and a second signal processing means for processing an inspection signal derived from a volume wave that propagates through the inspected materials 3a and 3b and reaches the back surface, and is inspected by an output signal of the first signal processing means The front surfaces of the materials 3a and 3b may be configured to inspect the inside and the back surface of the materials to be inspected 3a and 3b by the output signal of the second signal processing means.
[0081]
For example, a simple method of inspecting a member such as a welded member in which an opening defect and a built-in defect on both front and back surfaces are to be inspected is to access and inspect each side. However, for example, when a complex-shaped structure is installed in a narrow space, such as a reactor internal structure, inspection on each side takes time, and access to both surfaces is not always easy. Therefore, there are cases where it is necessary to disassemble / disassemble the member.
[0082]
On the other hand, the general feature of the laser ultrasonic method is that various ultrasonic modes such as surface waves propagating on the surface of the material to be inspected and volume waves propagating from the inside of the material to be inspected to the back surface by irradiation with laser light for generating ultrasonic waves However, there is also a problem that it is difficult to identify the measured signals of each mode.
[0083]
This modification takes advantage of the laser ultrasonic method of multi-mode simultaneous excitation. Ultrasound in both the mode that propagates through the surface and the mode that propagates in the volume simultaneously when irradiated with laser light for ultrasonic generation. Is measured, and the propagation is individually analyzed to simultaneously inspect the front, back, and interior of the material to be inspected. Here, as a method for analyzing the surface propagation mode, a propagation time analysis method or a method for analyzing a reflection component or a transmission component due to a crack of a surface propagation wave described in JP 2000-180418 A can be used. As an analysis method of the volume propagation mode, a pulse echo method, a diffracted wave detection method, or the like can be used.
[0084]
Next, a third embodiment of the present invention will be described. As shown in FIG. 15, the laser ultrasonic inspection apparatus according to this embodiment includes an ultrasonic wave generation laser light source 1, a switching device 21, a switching control device 20, a trigger oscillator 13, a receiving device REC, and an incident device. Optical systems CL, M1-1, M1-2, optical fibers 6-1, 6-2, 17, an irradiation optical system 2, and irradiation / collection optical systems M6-1, M6-2 are provided.
[0085]
This embodiment is a case where a plurality of parts to be inspected on the inspection object 3 are very close to each other, taking into account the propagation of ultrasonic waves in each direction, and laser light for ultrasonic generation or ultrasonic detection (Only the laser beam for ultrasonic detection is switched in the figure). According to the third embodiment, efficient and highly accurate inspection can be performed on a plurality or a large area without increasing the number of apparatuses.
[0086]
Next, a fourth embodiment of the present invention will be described. As shown in FIG. 16, the laser ultrasonic inspection apparatus of this embodiment includes laser light sources 1-1 and 1-2 for generating ultrasonic waves, a switching device 21, a switching control device 20, a trigger oscillator 13, and a reception. Device REC, incident optical systems CL-1, CL-2, M1-1, M1-2, optical fibers 6-1, 6-2, 17-1, 17-2, irradiation optical system 2-1, 2-2 and irradiation / condensing optical systems M6-1 and M6-2.
[0087]
In the fourth embodiment, n units of either one of the laser beams for ultrasonic generation or ultrasonic detection are prepared, and the other is switched. In FIG. 16, the number of laser light sources for generating ultrasonic waves is n (two in the figure), and inspection is performed with one receiver REC. In this case, the operations of the first ultrasonic generation laser light source 1-1 and the second ultrasonic generation laser light source 1-2 and the operation of the switching device 21 are synchronized.
[0088]
Next, a fifth embodiment of the present invention will be described. As shown in FIG. 17, the laser ultrasonic inspection apparatus of this embodiment includes a laser light source 1 for generating ultrasonic waves, a receiving device REC, a trigger oscillator 13, an irradiation optical system 2, objective lenses M2 and M3, An incident optical system M1, a collimator M4, and optical fibers 6 and 7 are provided.
[0089]
The receiving device REC includes an ultrasonic detection laser light source 4, a receiving optical system OP, a photodetector 9, a signal processing device 10, and power supply devices 11 and 12. The receiving optical system OP includes a phase conjugate element 5, a mirror 8, and a lens M5. The signal processing apparatus 10 includes an analog / digital conversion unit 34, a gate unit 35, a signal processing unit 36a, and a display / recording unit 36b.
[0090]
In the fifth embodiment, when the signal captured by the analog / digital converter 34 is transmitted to the signal processor 36a and the display / recorder 36b, the distance S between the irradiation positions of the transmission / reception laser beams PL and IL is transmitted. And the time range corresponding to the inspection range by the surface-propagating elastic wave calculated from the thickness D of the material to be inspected 3 and the ultrasonic wave propagation time used for the inspection, and the inspection range by the volume-propagating elastic wave as well. The corresponding time range is separated at the gate unit 35. Therefore, according to the fifth embodiment, it is possible to inspect defects on the front surface, the inside, and the back surface of the material to be inspected 3 at the same time as in the modification of the first embodiment.
[0091]
In the first embodiment, the irradiation or irradiation / collection optical system shown in FIGS. 11, 12, and 13 can also be provided in the laser ultrasonic inspection apparatuses of the second to fifth embodiments.
[0092]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the laser ultrasonic inspection apparatus and inspection method which can test | inspect the test object of the multiple or wide area which exists in a narrow part efficiently can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a laser ultrasonic inspection apparatus according to a first embodiment of the present invention.
FIGS. 2A and 2B show a case where an ultrasonic wave is reflected by a crack on the surface of a material to be inspected (a) and a case where the ultrasonic wave is transmitted through a crack (b), and shows a laser ultrasonic inspection apparatus according to the first embodiment of the present invention. FIG.
FIG. 3 is a diagram illustrating the operation of the laser ultrasonic inspection apparatus according to the first embodiment of the present invention, showing a case where ultrasonic waves are reflected by a crack on the back side of the inspection object.
FIG. 4 shows the time-dependent change in the y-direction scanning position (a) and the X-direction scanning position (b) on the material to be inspected and the laser light oscillation timing (c), and the laser according to the first embodiment of the present invention. The figure explaining operation | movement of an ultrasonic inspection apparatus.
FIG. 5 is a view for explaining the operation of the laser ultrasonic inspection apparatus according to the first embodiment of the present invention, showing a scanning position (a) on an inspection object and an ultrasonic detection signal (b).
FIG. 6 is a diagram illustrating the operation of the laser ultrasonic inspection apparatus according to the first embodiment of the present invention, showing average processing (a) and differential processing (b) of ultrasonic detection signals.
FIG. 7 is a diagram illustrating the operation of the laser ultrasonic inspection apparatus according to the first embodiment of the present invention, showing the shift addition processing (a) of the ultrasonic detection signal and the result (b) thereof.
FIG. 8 shows a B-scan when the ultrasonic detection signal is averaged (a) and when shift addition processing is performed (b), and explains the operation of the laser ultrasonic inspection apparatus according to the first embodiment of the present invention. To do.
FIG. 9 shows the change over time in the y-direction scanning position (a) and the X-direction scanning position (b) on the material to be inspected and the laser light oscillation timing (c), and the laser according to the first embodiment of the present invention. The figure explaining other operation | movement of an ultrasonic inspection apparatus.
FIG. 10 is a view for explaining another operation of the laser ultrasonic inspection apparatus according to the first embodiment of the present invention, showing a scanning position on the inspection object.
FIG. 11 is a cross-sectional view showing an irradiation optical system provided in the laser ultrasonic inspection apparatus according to the first embodiment of the present invention.
FIG. 12 is a sectional view showing an irradiation / collection optical system provided in the laser ultrasonic inspection apparatus according to the first embodiment of the present invention.
FIG. 13 is a cross-sectional view showing another example of the irradiation / collection optical system provided in the laser ultrasonic inspection apparatus according to the first embodiment of the present invention.
FIG. 14 is a diagram showing a configuration of a laser ultrasonic inspection apparatus according to a second embodiment of the present invention.
FIG. 15 is a diagram showing a configuration of a laser ultrasonic inspection apparatus according to a third embodiment of the present invention.
FIG. 16 is a diagram showing a configuration of a laser ultrasonic inspection apparatus according to a fourth embodiment of the present invention.
FIG. 17 is a diagram showing a configuration of a laser ultrasonic inspection apparatus according to a fifth embodiment of the present invention.
FIG. 18 is a diagram showing a first example of a conventional laser ultrasonic inspection apparatus.
FIG. 19 is a diagram showing a second example of a conventional laser ultrasonic inspection apparatus.
FIG. 20 is a diagram showing a third example of a conventional laser ultrasonic inspection apparatus.
[Explanation of symbols]
1, 1-1, 1-2 ... laser light source for ultrasonic generation, 2, 2-1, 2-n ... irradiation optical system, 3, 3a, 3b ... inspection object, 4 ... laser light source for ultrasonic detection, DESCRIPTION OF SYMBOLS 5 ... Phase conjugate element, 6, 6a, 6b, 6-1, 6-2, 6-n, 7 ... Optical fiber, 8 ... Mirror, 9 ... Photodetector, 10 ... Signal processing device, 11, 12 ... Power supply device , 13 ... trigger oscillator, 14, 16 ... lens system, 15 ... micro lens array, 17, 17-1, 17-n ... optical fiber, 18 ... beam splitter, 19 ... mirror, 20 ... switching control device, 21 ... switching device 22, 22-1, 22-n, second deflection control element, 23, 23-1, 23-n, first deflection control element, 24, 24-1, 24-n, second beam splitter. , 25-1, 25-n, first beam splitter, 26, 26b, housing, 26a, member holder, 26c, lens. Presser, 27, 27a, 27b ... Lens, 28a, 28b ... Aberration correction lens, 29a, 29b ... O-ring, 30a, 30b ... Resin mold, 31 ... Adhesive, 32 ... Deflection beam splitter, 33 ... Wave plate, 34 ... Analog / digital conversion unit 35 ... Gate unit 36a ... Signal processing unit 36b ... Display / recording unit 37 ... Scanning table 38 ... Scanning mechanism 39 ... Scanning controller 40 ... Position sensor 41 ... Signal processing Display / recording device, C ... crack or defect, CL, CL-1, CL-2, CL-n ... optical system for incidence, G ... transparent fluid, IL ... laser beam for ultrasonic detection, M1, M1-1 , M1-2, M1-n ... incidence optical system, M2, M3 ... objective lens, M4 ... collimator, M5 ... lens, M6, M6-1, M6-2, M6-n ... irradiation / condensing optical system , OP: receiving optical system, REC: receiving device (signal converting means), PL, PL-1, PL-2 ... laser beam for generating ultrasonic waves, Sig Ultrasonic signals, SL ... reflected light, US ... ultrasound, W ... surrounding fluid medium.

Claims (6)

A first laser light source that oscillates a first laser light; an irradiating means that irradiates the material to be inspected with the first laser light; a second laser light source that oscillates a second laser light; By irradiating the first laser light from the irradiation / condensing means for irradiating the surface of the material to be inspected and receiving the reflection component thereof, and the reflection component condensed by the irradiation / condensing means A receiving optical system for optically detecting a signal relating to an ultrasonic wave generated in the material to be inspected, a signal converting means for converting an ultrasonic signal received in the receiving optical system into an electric signal, and the irradiating means; The irradiation and condensing means are controlled and driven, and the relative positions of the irradiation positions of the first and second laser beams on the material to be inspected are maintained in synchronization with the oscillation of the first laser beam. While moving within a specified range and a specified step size. Scanning means for scanning is super first, a position detecting means for detecting the irradiation position of the second laser light, and signal processing an output signal of said signal conversion means is detected at each position due to the scanning in the laser ultrasonic inspection apparatus that includes a signal processing unit that indicates the calculated table information from the position information detected about the characteristics of the inspection member and the ultrasonic propagation in acoustic signal and said position detecting means, said first The laser light source is a pulse laser light source that oscillates in pulses, and scanning by the scanning means is two-dimensional, and the signal processing means uses the detected two-dimensional array of ultrasonic signal columns or rows as the columns. An average processing process that averages every row or row, and a difference processing process that calculates a difference between an average signal for each column or row obtained as a result of the average processing process and a measurement signal at each point A space that is shifted by a time corresponding to the propagation of the ultrasonic signal by a distance twice as large as the step width set by the scanning means, and is overlapped for each row or column by a predetermined number less than the number of scanning rows or columns. And executing the averaging process, and displaying the amplitude information of the time series signal waveform group of one column or one row obtained as a result in a two-dimensional space composed of an axis corresponding to the column or row and a time axis. A featured laser ultrasonic inspection device. Laser greater of scanning by prior Symbol scanning unit according to claim 1, wherein the an operation in synchronization with one or a predetermined plurality of times or a predetermined plurality of component one of the pulse oscillation of the first laser light source Sonographic equipment. The scanning by the scanning means is an operation synchronized with a predetermined plurality of times of pulse oscillation of the first laser light source, and the signal processing means averages the detected ultrasonic signal the same number of times as the number of pulses described above. laser ultrasonic inspection apparatus according to claim 2, wherein Kasho sense to Rukoto. The oscillation of the pulsed laser light source is a laser ultrasonic inspection apparatus according to claim 1, wherein the different column or row and be operated in sync with each scan line or column of said scanning means. 2. The laser ultrasonic inspection apparatus according to claim 1, wherein a sound velocity of a surrounding environmental medium in which the material to be inspected is installed is VM, and a surface of the material to be inspected among ultrasonic signals generated by the first laser light. The acoustic velocity of the propagating elastic wave is VS, and the length of the region to be inspected from the side closer to the crack to be detected on the material to be inspected at the irradiation position of the first laser light or the second laser light is L. Then, an interval S between the irradiation position of the first laser beam and the irradiation position of the second laser beam is expressed by a relational expression.

A laser ultrasonic inspection method characterized in that the length is represented by: 2. The laser ultrasonic inspection apparatus according to claim 1, wherein, among ultrasonic signals generated by the first laser light, the acoustic velocity of an elastic wave propagating through the surface of the inspection material is VS and the sound wave is propagated through the inspection material. When the sound velocity of the volume wave to be applied is VB and the thickness of the material to be inspected is D, the interval S between the irradiation position of the first laser beam and the irradiation position of the second laser beam is expressed as a relational expression.

A laser ultrasonic inspection method characterized in that the length is represented by:

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