JP4140218B2

JP4140218B2 - Inspection method and apparatus for laser welds

Info

Publication number: JP4140218B2
Application number: JP2001258658A
Authority: JP
Inventors: 良介三高; 長生 ▲濱▼田
Original assignee: Matsushita Electric Works Ltd
Current assignee: Panasonic Electric Works Co Ltd
Priority date: 2001-08-28
Filing date: 2001-08-28
Publication date: 2008-08-27
Anticipated expiration: 2021-08-28
Also published as: JP2003065985A

Description

【０００１】
【発明の属する技術分野】
本発明は、本発明は被検査物となる２片の金属を重ね合わせ、その一方の面よりレーザーをスポット照射して溶接したレーザー溶接部の溶接不良を、溶接中のモニタリングではなく、溶接後のオフライン検査により検出する方法、特に電子部品リードなどの薄く小さい部材の微細なレーザー溶接部のオフライン検査方法及びその装置に関するものである。
【０００２】
【従来の技術】
従来、レーザー溶接部の検査方法としては、特開平５−７１９３２号記載の検査方法のように、スリット状のレーザー光をレーザー溶接部に投影し、当該レーザー光の反射光をレーザー投影方向とは異なる方向からカメラにより観測することによりレーザー溶接部の立体形状を取得する、いわゆる光切断法による立体形状計測を用いた方法がある。
【０００３】
また、赤外線カメラを用いたレーザー溶接部の検査方法としては、特開平５−３４２０４号、特開平８−１２２０５１号、特開昭５２−５９０４６号記載の検査方法のように、レーザー溶接部に加熱を行う過程あるいは加熱後（溶接熱による加熱を含む）の冷却過程において、赤外線カメラによりレーザー溶接部周辺の温度分布を計測することにより溶着部の大きさを測定する方法がある。
【０００４】
【発明が解決しようとする課題】
上記従来の立体形状計測による検査方法は、フィラーを用いた突き合わせ溶接やすみ肉溶接などのようにレーザー溶接部が大きく盛り上がる溶接方法においては有効であるが、レーザーによるスポット溶接、特に電子部品のリード部分などの微細な溶接においては溶接に伴う形状の変化が極めて微小であるため精度の高い３次元形状計測方法が必要となり、適用が困難である問題があった。
【０００５】
また後者のレーザースポット溶接されたレーザー溶接部に加熱を行う過程あるいは加熱後（溶接熱による加熱を含む）の冷却過程において、温度分布を測定する従来方法においては、レーザー溶接部がある程度の質量（熱容量）を持つ場合には有効な方法であるが、例えば電子部品のリード部分などの極めて薄く質量の小さい部材のレーザー溶接部においては加熱による温度の変化が極めて短時間の間に起こるため、赤外線画像によって正確に温度分布を計測することが困難になる問題があった。
【０００６】
本発明は、上記の従来例の問題点に鑑みて発明したものであって、その目的とするところは、溶接後のオフライン検査により、特に電子部品リードなどの薄く小さい部材の微細なレーザー溶接部の検査を精度良く行うことができ、検査の信頼性を向上させることができると共に、良否判定精度を高めることができるレーザー溶接部の検査方法及びその装置を提供することにある。
【０００７】
【課題を解決するための手段】
上記課題を解決するために本発明にあっては、被検査物６となる２片の金属を重ね合わせ、その一方の表面にレーザーをスポット照射して溶接したレーザー溶接部１を溶接後に検査する方法において、溶接後雰囲気温度まで冷却したレーザー溶接部１を赤外線カメラ２で撮像し、得られた赤外線画像における輝度の差を被検査物６表面の赤外線放射率の差を表す指標とみなして溶接部領域３を検出する第１の過程と、上記溶接部領域３の形状、上記溶接部領域３内での赤外線画像の輝度値の分布パターン、上記分布パターンをもとに抽出された特徴量の少なくとも１つをもとに溶接の良否を判定する第２の過程とを有することを特徴としており、このように構成することで、赤外線画像の明るさの差（遠赤外線放射率の差）を利用して、レーザー溶接部１と未溶接部の表面性状の違いを検出することができ、簡易な方法でレーザー溶接部１の溶接状態を検査できるようになる。しかも、溶接中のモニタリングではなく、溶接後のオフライン検査により検出するので、特に電子部品リードなどの薄く小さい部材の微細なレーザー溶接部１の検査を精度良く行うことができる。
【０００８】
また、少なくともレーザー溶接部１の外周部では熱の影響により表面粗さが大きくなり、赤外線放射率が高くなることを利用して、赤外線画像において明るく見える部分を検出し、当該部分の外周輪郭より内側を溶接部領域３として検出するので、加熱を行うことなくレーザー溶接部１を検出できるようになる。
【０００９】
また、検出された溶接部領域３の大きさを基準値と比較することにより溶接の良否を判定するのが好ましく、この場合、簡易な方法で溶接状態の判定ができるようになる。
【００１０】
また、検出された溶接部領域３内部の明るく見える外周輪郭の内側に所定の基準値以上の大きさを持つ暗部４があれば良品と判定するのが好ましく、この場合、十分な入熱量が与えられた時は中央部に鏡面状の特徴を生じることを利用して溶接状態の良否を簡易に判定できるようになる。
【００１１】
また、上記赤外線カメラ２により検出された溶接部領域３内部で明るく見える外周輪郭の内側に所定の基準値以上の大きさを持つ暗部４があれば良品候補とし、上記良品候補に赤外線を照射し、上記赤外線源５の正反射を捉える方向に第２の赤外線カメラ２ａを配置して観測した時、溶接部領域３中央の輝度が高くなる場合に良品と判定するのが好ましく、この場合、能動的に照射した赤外線光の正反射成分を捉える第２の赤外線カメラ２ａを付加するだけで、穴あき欠陥と良品を区別できるようになる。
【００１２】
また、被検査物６に赤外線を照射する赤外線源５と被検査物６を撮像する赤外線カメラ２を、上記赤外線源５から照射された赤外線の正反射光を赤外線カメラ２で捉えることができるような位置関係になるように配設し、まず赤外線源５を消灯して撮影した赤外線画像を用いて検出された溶接部領域３内部で明るく見える外周輪郭の内側に所定の基準値以上の大きさを持つ暗部４があれば良品候補とし、次に赤外線源５を点灯して観測した時、溶接部領域３中央の輝度が高くなる場合に良品と判定するのが好ましく、この場合、良品候補を抽出するカメラと良否判定を行うカメラを兼用でき、簡易な装置構成にて穴あき欠陥と良品を区別できるようになる。
【００１３】
また、良品候補に複数の方向から赤外線を照射していずれかの正反射光を捉えることができれば良品とするのが好ましく、この場合、赤外線源５を複数用いることで、仮りに溶接部領域３中央の鏡面部分の向きが安定しない場合にも穴あき欠陥と良品を正しく区別できるようになる。
【００１４】
また、良品候補を斜め方向から赤外線カメラ２で観測するようにし、赤外線画像において溶接部領域３中央に正反射光が捉えられれば良品とし、溶接部領域３中央からずれた位置に正反射光が捉えられれば不良とするのが好ましく、この場合、上下の溶接片８，９の段差が小さい場合にも特別の装置を付加することなく穴あき欠陥と良品を正しく区別できるようになる。
【００１５】
また、被検査物６全体を一様に加熱したうえで検査を行うのが好ましく、この場合、被検査物６を一様に加熱するようにすることで赤外線画像のＳ／Ｎ比が改善される。
【００１６】
また、正確に溶接状態の良否判定をするために、上記方法で良品候補と判断された被検査物６について、上下の溶接片８，９の間に電圧を与えることによってレーザー溶接部１にジュール熱を発生させた状態で赤外線カメラ２により撮像し、上記溶接部領域３内での輝度値の変化を基準値と比較することによりレーザー溶接部１の良否を判定するのが好ましい。また、上記方法で良品候補と判断された被検査物６について、下側の溶接片９のみを加熱しながら上方より赤外線カメラ２で撮像し、上記溶接部領域３内での輝度値の変化を基準値と比較することによりレーザー溶接部１の良否を判定するのが好ましい。
【００１７】
また、下側の溶接片９に通電することにより下側の溶接片９にジュール熱を発生させるのが好ましく、この場合、下側の溶接片９の下側に発熱体を設置できない構造の検査物でも、検査が可能になる。
【００１８】
また、下側の溶接片９に高周波磁界を与えて渦電流を発生させることにより加熱するのが好ましく、この場合、下側の溶接片９の下側に発熱体を設置できない構造の検査物でも、検査が可能になる。
【００１９】
また、高さ計測装置により上記レーザー溶接部１近辺の少なくとも２点Ｈ₁，Ｈ₂の高さ情報を取得し、上記溶接部領域３の輝度値とともに高さ情報を併用して良否判定を行うのが好ましく、この場合、高さ情報を併用することにより穴あき欠陥と良品の区別など画像情報だけでは分かりにくい溶接状態の判定を高い信頼度で行えるようになる。
【００２０】
さらに、本発明に係るレーザー溶接部１の検査装置は、赤外線カメラ２（２ａ）と、赤外線カメラ２（２ａ）からの出力信号を量子化して画像として記憶する画像取り込み装置１０と、上記のいずれかの検査方法により赤外線画像を処理して溶接欠陥検査を行う画像処理装置１１とにより構成されているので、赤外線画像の明るさの差（遠赤外線放射率の差）を利用して、レーザー溶接部１と未溶接部の表面性状の違いを画像処理装置１１にて検出することができ、簡易な構造でレーザー溶接部１の溶接状態を検査できるようになる。
【００２１】
【発明の実施の形態】
以下、本発明を添付図面に示す実施形態に基づいて説明する。
【００２２】
図１は、本発明の方法によりレーザー溶接の良否判定をオフラインで行う検査装置の構成を示す図である。この検査装置は、被検査物６となる２片の金属（溶接片８，９）を重ね合わせ、その一方の表面にレーザーをスポット照射して溶接したレーザー溶接部１の溶接状態を溶接後に検査するものであり、詳しくは、検査対象となる溶接片８，９を溶接後雰囲気温度に冷却し、その後レーザー溶接部１付近を赤外線カメラ２により撮像する。ここで、溶接後雰囲気温度まで冷却とは、充分に放熱された状態のことであり、冷却過程ではない。赤外線カメラ２からの撮像データは、画像取り込み装置１０に取り込まれる。画像取り込み装置１０は、撮像データを画像に変換するための量子化装置１４と、画像を格納する画像メモリ１５とで構成されており、画像処理装置１１により上記画像を解析することにより検査・判定が行なわれる。具体的には、レーザー溶接部１と未溶接部の表面粗さの違いによって生じる遠赤外線放射率の差を利用することにより赤外線画像から溶接部領域３（図２）を抽出し、さらに上記溶接部領域３内側の輝度値を用いて溶接状態を判別することにより、立体形状の変化が微小で温度分布による検査も困難な微細部品のレーザー溶接部１の検査を行うものである。また、放射率だけでは判別が付きにくい場合であっても、レーザー溶接部１の温度を能動的に変化させたり、３次元計測装置を併用することでさらに正確な溶接状態検査が可能になる。以下、具体的に説明する。
【００２３】
図２（ａ）は、溶接後雰囲気温度まで冷却した被検査物６のレーザー溶接部１を図１のように上方から撮像して得られた赤外線画像の一例を示している。また、レーザー溶接部１の３次元形状を図２（ｂ）に示す。図２（ａ）（ｂ）中のＡ部は熱影響をうけていない部分、Ｂ部が熱影響を受けたレーザー溶接部１である。図２（ｂ）に示すようにＡ部は平坦な金属表面であり、表面は鏡面に近い状態であるのに対し、Ｂ部は熱影響により金属が溶融し、ヒダ状の立体構造を持った表面となっている。
【００２４】
図２に示すレーザー溶接部１は上記Ｂ部の直径が数百μｍ程度の小さなものである。このような微細なレーザースポット溶接を行う上下の溶接片８，９は、それぞれ、厚さ数十〜数百μｍ程度と薄く熱容量が小さいため、加熱・冷却に伴う温度変化が極めて急激となってしまう。このため、加熱・冷却時の温度分布を利用して溶着部（ナゲット）のサイズを計測することが非常に困難である。また、レーザー溶接部１が微細であるため、レーザー溶接部１の３次元形状の変化も極めて小さく（数μｍ程度の凹凸）、その３次元形状を計測して良否判定することも困難である。そこで本発明では、このような微細な凹凸の変化を検出するために、赤外線放射率の変化を利用する。すなわち図２（ａ）および（ｂ）に示すＢ部では熱影響により表面粗さが大きくなり、Ａ部に比べて赤外線の放射率が高くなっている。そのため、図２（ａ）に示す赤外線画像においてＢ部はＡ部に比べて明るく写る。この現象を利用して、赤外線画像からレーザー溶接部１を抽出し、熱影響の程度を評価することが可能になる。
【００２５】
しかして、電子部品などの微細なレーザースポット溶接による熱影響部では表面性状（表面粗さ）が変化するものの、凹凸は極めて微細で３Ｄ（３次元）計測による検査は極めて困難であるが、本発明に係るレーザー溶接部１の検査方法によれば、赤外線画像の明るさの差（遠赤外線放射率の差）を利用することにより、また溶接中のモニタリングではなく、溶接後のオフライン検査により検出することにより、レーザー溶接部１と未溶接部の表面性状の違いを検出することができるため、簡易な方法でレーザー溶接部１の溶接状態検査が可能になると共に、画像処理による非破壊検査により、接合不十分な状態の確認作業の自動化が可能になる。従って、例えば、電子部品リードなどの薄く小さい部材の微細なレーザー溶接部１の検査を精度良く行えるようになる。さらに、赤外線カメラ２と、赤外線カメラ２からの出力信号を量子化して画像として記憶する画像取り込み装置１０と、赤外線画像を処理して溶接欠陥検査を行う画像処理装置１１とにより構成される検査装置を用いることで、簡易な装置構成でレーザー溶接部１の溶接状態検査が可能になる。
【００２６】
次に、レーザー溶接部１の溶接部領域の抽出及び検査手順の一例を説明する。図３はレーザー溶接部１の溶接部領域の抽出方法の一例を示し、図４はレーザー溶接部１の抽出手段を含む検査手順を説明するフローチャートである。図４のステップｎ１で図２（ｂ）の画像を二値化し、ステップｎ２で図３の連結領域Ｂ’を抽出する。この図３の連結領域Ｂ’は図２（ｂ）のＢ部に相当する。その後、図４のステップｎ３で連結領域Ｂ’の外周輪郭より内側の部分を溶接部領域３として設定し、さらにステップｎ５で当該溶接部領域３内における明度パターンを解析することにより溶接の良否判定を行う。このように赤外線放射率の高い部分を溶接部領域３として抽出することにより、加熱を行うことなくレーザー溶接部１を検出することができる。
【００２７】
ここで、図４のステップｎ４に示す溶接部領域３内部の輝度値をもとに良否判定を行う過程について説明する。まず第１の方法として溶接部領域３の面積を利用する方法が挙げられる。図５にレーザー溶接の際の入熱量と溶接部領域３（熱影響部）の面積の関係を示す。レーザー溶接においては、溶接入熱量が大きいほど溶接部領域３の面積も大きくなることから、図５のグラフを利用して上記過程で抽出された溶接部領域３の面積をもとに入熱量を推定することができる。図５のグラフをもとに、十分な溶接を行うのに必要な入熱量範囲Ｄ１に対する熱影響部面積範囲Ｓ１を求めておき、レーザー溶接部１の赤外線画像から抽出された溶接部領域３の面積がＳ１の範囲内であれば良品と判定する。このように、溶接時の入熱量と溶接部領域３の面積との関係をもとに溶接状態の良否を判定することによって、簡易な方法で溶接状態の判定ができる。
【００２８】
次に、良否判定を行う第２の方法について説明する。レーザースポット溶接においては、十分な入熱量が与えられた良品においては溶融する金属の量が多いため、図６に示すように溶接部領域３中央において溶融金属が溜まり、中央部が鏡面状となる。このため、良品のレーザー溶接部１を撮影した赤外線画像においては、図７（ａ）に示すように表面粗さが粗く赤外線放射率が高いため白く写るＢ部の内側に、上記鏡面状の部分（鏡面であるため赤外線放射率が低いＣ部）が黒く写る特徴が現れる。そこで、図７（ｂ）に示すように、二値化した赤外線画像において当該溶接部領域３の内側にある基準値以上の大きさを持つ黒色部領域Ｃが観測される場合には良品であると判断する。しかして、十分な入熱量が与えられた時は中央部に鏡面状の特徴を生じることを利用して溶接状態の良否を判定するので、簡易な方法で溶接状態の判定ができる。
【００２９】
ところで、上述した各欠陥検査方法においては、若干の虚報（欠陥を良品と判断する）が発生する可能性がある。上記方法における虚報発生原因とその対策方法について以下に説明する。
【００３０】
レーザー溶接時の不良の一つとして、入熱量が不足している場合に、図８（ａ）の溶接片８，９の断面図に示すように、上側の溶接片８が加熱され、垂れ下がって下側溶接片９に充分接触し、下側溶接片９を加熱溶融させるまでの段階で上側の溶接片８だけが溶融してしまい、中央に穴２０があいてしまう穴あき欠陥が存在する。この場合、赤外線画像においては、穴が開くことによりレーザー溶接部１の外周径が大きくなり、また穴から熱影響を受けていない下側の溶接片９が見えるため、図８（ｂ）に示すように溶接部領域３の内側に黒色部２１が観測されてしまうことにより、上記のいずれの方法による検査においても良品と誤判断されてしまう。
【００３１】
このような虚報をなくすよう構成された装置を図９（ａ）に示す。図９（ａ）の装置は、検査対象となる溶接片８，９のレーザー溶接部１付近を上方から撮像する赤外線カメラ２に加えて、当該レーザー溶接部１に指向性のある赤外光を斜め方向から照射する赤外線源５と、赤外線源５に対して溶接片８，９を挟んで対向し、赤外光がレーザー溶接部１で正反射した光を捕捉できる位置に配設された第２の赤外線カメラ２ａを設けたものである。ここで図１０（ａ）は上方カメラでは良品と判断されてしまう穴あき欠陥を上記第２の赤外線カメラ２ａで撮像した状態を示し、図１０（ｂ）は良品を上記第２の赤外線カメラ２ａで撮像した状態を示す。図１０（ａ）（ｂ）を比較すればわかるように、穴あき欠陥では図１０（ａ）のように、鏡面状の部分（下側の溶接片９）が下の位置にあるため上記赤外線源５からの光が届かず、図１１（ａ）に示すように撮影した赤外線画像では溶接部領域３中央は暗い暗部４となって写る。これに対して図１０（ｂ）の良品の場合はレーザー溶接部１中央の鏡面部で正反射された赤外光が第２の赤外線カメラ２ａに入射するので、図１１（ｂ）に示すように赤外線画像において溶接部領域３中央が白く写る。この違いを利用し、まず図９（ａ）に示す赤外線カメラ２により上方からレーザー溶接部１を観測し、溶接部領域３中央で輝度が低い部分があった場合には当該レーザー溶接部１を良品の候補とし、次に当該良品の候補について第２の赤外線カメラ２ａによって撮影された画像において溶接部領域３中央で輝度が高くなる場合にはじめて良品として決定することにより、上記虚報を排除することができる。また、能動的に照射した赤外線光の正反射成分を捉える第２の赤外線カメラ２ａを付加することによって、穴あき欠陥と良品を区別することができる。
【００３２】
また、上記のように第２の赤外線カメラ２ａを設ける代わりに、図９（ｂ）に示すように上記第２の赤外線カメラ２ａに相当する位置に配設された赤外線カメラ２を１台だけ使用するようにしてもよい。この場合、まず第１回目の撮像時には赤外線源５を消灯して撮影し、溶接部領域３を抽出したのち溶接部領域３中央に暗部４（鏡面部分）が観測されるものを良品候補とする。次に当該良品候補に対して赤外線源５を点灯した状態で撮影を行い、上記検査方法と同様中央部の輝度が高くなった場合に良品として決定する。しかして、１台の赤外線カメラ２で良品候補を抽出するカメラと良否判定を行うカメラを兼用する構成としたので、簡易な装置構成により穴あき欠陥と良品を区別することができる。
【００３３】
上記虚報対策方法をさらに発展させた検査方法ついて以下に述べる。図９（ａ）および（ｂ）の装置では、レーザー溶接部１中央に生じている鏡面部分が傾いていた場合は、第２の赤外線カメラ２ａに赤外線光の正反射成分が届かず、誤って不良品と判断してしまう可能性がある。そこで、図１２の検査装置では、赤外線源５を複数設けてある。これによりレーザー溶接部１中央に生じている鏡面部分が傾いていた場合にも、いずれかの赤外線源５からの赤外光が当該鏡面部で正反射して上記第２の赤外線カメラ２ａへ入射することができるようになり、レーザー溶接部１中央の鏡面部分の向きが安定しない場合にも良品を不良品と判断してしまう誤りが少なくなり、穴あき欠陥と良品を正しく区別することができる。この方法は、第２の赤外線カメラ２ａを複数設けたり、赤外線源５と赤外線カメラ２の少なくとも一方を移動させながら撮像し、赤外線源５と赤外線カメラ２の位置関係が変化していく中でいずれかの場所において鏡面部で赤外線源５からの正反射赤外光が赤外線カメラ２に入射するように構成しても構わない。
【００３４】
また、上記虚報対策方法をさらに発展させた別の検査方法について以下に説明する。図１３（ａ）のように上側の溶接片８が薄い場合や、同（ｂ）のように上下の溶接片８，９の隙間が狭い場合には、上側の溶接片８上面と穴から見えている下側の溶接片９上面の段差が小さく、斜めから照射した赤外光が下側の溶接片９上面で正反射して第２の赤外線カメラ２ａに入射してしまい、良品と誤判断されてしまう可能性がある。ここで図１４（ａ）は段差の小さい穴あき欠陥の赤外線画像を示し、図１４（ｂ）は良品の赤外線画像を示す。図１３（ａ）又は（ｂ）に示したような穴あき欠陥品の場合は、下側の溶接片９上面で反射した赤外光の一部が段差で遮られるために、図１４（ａ）のように溶接部領域３の中心からずれた位置に正反射成分Ｅが観測される。一方これに対して、図１４（ｂ）に示した良品の場合には、溶接部領域３とその中央の鏡面部分に段差がないため、図１４（ｂ）のように上記正反射成分Ｅは溶接部領域３の中央に観測される。これを利用し、レーザー溶接部１に赤外線を照射し、第２の赤外線カメラ２ａで赤外線の正反射成分を観測することにより良否判定を行うにあたり、溶接部領域３の中央部分で正反射成分が観測された場合のみを良品とすることにより、さらに虚報を発生しにくい検査方法が実現できる。また上下の溶接片８，９の段差が小さい場合にも特別の装置を付加することなく穴あき欠陥と良品を正しく区別することができる。
【００３５】
なお、穴あき欠陥と良品を区別するためのより直接的な方法としては、図１５に示すように少なくともある２点Ｈ₁，Ｈ₂の高さを計測できる３次元計測装置７を併用し、上記レーザー溶接部１において周辺部と中心部のそれぞれ少なくとも２点Ｈ₁，Ｈ₂の高さ情報を取得し、両者の差が小さければ良品とし、両者の差が大きければ穴あき欠陥と判定するようにしてもよい。穴あき欠陥の場合は２点Ｈ₁，Ｈ₂の差が大きくなるが、良品の場合は小さくなることを利用することにより、穴あき欠陥と良品の区別など画像情報だけでは分かりにくい溶接状態の判定をさらに高い信頼度で行うことができる。勿論、２点Ｈ₁，Ｈ₂には限らず、３点以上の高さを計測してもよいものである。
【００３６】
以上の検査方法において、対象とする被検査物６は溶接後雰囲気温度まで冷却した状態で撮影を行うようにしていたが、冷却した後で被検査物６全体を一様に加熱してから検査を行うようにしてもよい。ちなみに、熱影響をうけていない未溶接部分は、鏡面に近いため高温にしても赤外線放射の増加量は少ないが、熱影響を受けたレーザー溶接部（熱影響部）では、熱影響により金属が溶融し、ヒダ状の立体構造を持った表面となっているため、高温になるほど多くの赤外線を放射する。そのため、被検査物の温度が高い方が上記検査において赤外線画像におけるＳ／Ｎ比が高くなり、検査の信頼性が向上することがわかる。このことから被検査物６を一様に加熱するようにすることでレーザー溶接部１の明るい部分と、暗部（鏡面部分）との差が大きくなり、明暗パターンがはっきりするようになり、画像処理による検査の信頼性の向上を図ることができる。
【００３７】
次に、上記のようにレーザー溶接部１を溶接後雰囲気温度まで冷却した後に、表面性状にともなう赤外線反射特性の差を用いて良否判定を行う方法において、さらにレーザー溶接部１に局所的に熱を与える方法を併用することにより、さらに精度の高い良否判定を行うことができる。以下説明する。
【００３８】
先ず図１６は局所加熱を伴う第１の検査方法を説明する図である。図１６は図１の検査装置のうち溶接片８，９の周辺のみを示す図であり、撮像装置の構成は図１と同一である。本方法においては、上下の溶接片８，９の各々に電極２２ａ，２２ｂが付けられており、電圧が印加できるようになっている。この両電極２２ａ，２２ｂ間にある一定時間だけ電圧を印加すると、レーザー溶接部１はその抵抗に応じてジュール熱を発生し温度が上昇するが、レーザー溶接部１がきちんと溶着している良品では上下の溶接片８，９間の電気抵抗が小さいので、温度上昇が小さい。これに対して溶接不良（穴開き欠陥等）の場合は絶縁状態にあって全く温度上昇が生じないか、逆に接触抵抗が大きいため大きな温度上昇を示す。これを利用し、上下の溶接片８，９間に一定時間電圧を印加してレーザー溶接部１の温度上昇（具体的には赤外線画像における溶接部領域３内の輝度値の変化量）を赤外線カメラ２により測定し、それが予め定められた上限値と下限値の間にあれば良品と判断する。なお、上記輝度値の変化の観測においては、まず常温状態で上記方法により溶接部領域３を抽出しておき、当該領域内での輝度の平均値を加熱前後で比較する等の方法により温度上昇の大きさを評価するようにすればよい。このようにレーザー溶接部１に直接通電を行ってジュール熱による温度上昇を観測するようにしたので、外観だけで判断する場合より正確に溶接状態の良否判定ができる。
【００３９】
次に、加熱を伴う第２の検査方法を図１７に示す。図１７は図１の検査装置のうち溶接片８，９の周辺のみを示す図であり、撮像装置の構成は図１と同一である。本例では、下側の溶接片９の下面に発熱体２３を接触させ、下側の溶接片９のみを加熱している。これにより発熱体２３から下側の溶接片９を経て上側の溶接片８へ熱伝導が生じるが、溶着部では良好な熱伝導を生じるのに対して、非溶着部では隙間があるため熱伝導が起こりにくい。これを利用して、下側の溶接片９を加熱しながら上方に配設された赤外線カメラ２によりレーザー溶接部１の温度変化（具体的には赤外線画像における溶接部領域３内の輝度値の変化量）を観測し、温度上昇がある基準値より大きければ良品であると判断することができる。つまり下側の溶接片９を加熱して上側の溶接片８へ熱伝導が生じる状態を観測するようにしたので、外観だけで判断する場合より正確に溶接状態の良否判定ができる。なお、上記輝度値の変化の観測においては、局所加熱を伴う第１の検査方法と同じようにまず常温状態で上記方法により溶接部領域３を抽出しておき、当該領域内での輝度の時間変化を求めるようにすればよい。なお、下側の溶接片９を加熱するにあたって、下側の溶接片９に発熱体２３を接触させる方法以外に、下側から熱風や炎で加熱する方法も可能である。
【００４０】
ところで、例えば電子部品などのように下側の溶接片９がすでに構造物に取り付けられた状態にあり、下側の溶接片９を熱伝導によって加熱することができない場合がある。このような場合には、図１８に示すように、下側の溶接片９の両端に電極を取り付け、電圧を印加することにより下側の溶接片９自体にジュール熱を発生させる方法、或いは、下側の溶接片９の下部から高周波磁界を与え、渦電流を発生させてＩＨ（induction heating）加熱する方法などにより加熱を行う方法を採用してもよいものである。
【００４１】
【発明の効果】
上述のように請求項１記載の発明にあっては、被検査物となる２片の金属を重ね合わせ、その一方の表面にレーザーをスポット照射して溶接したレーザー溶接部を溶接後に検査する方法において、溶接後雰囲気温度まで冷却したレーザー溶接部を赤外線カメラで撮像し、得られた赤外線画像における輝度の差を被検査物表面の赤外線放射率の差を表す指標とみなして溶接部領域を検出する第１の過程と、上記溶接部領域の形状、上記溶接部領域内での赤外線画像の輝度値の分布パターン、上記分布パターンをもとに抽出された特徴量の少なくとも１つをもとに溶接の良否を判定する第２の過程とを有しているので、電子部品などの微細なレーザースポット溶接による熱影響部では表面性状（表面粗さ）が変化するものの、凹凸は極めて微細で３Ｄ（３次元）計測による検査は極めて困難であるが、本発明に係るレーザー溶接部の検査方法によれば赤外線画像の明るさの差（遠赤外線放射率の差）を利用することによりレーザー溶接部と未溶接部の表面性状の違いを検出することができるため、簡易な方法でレーザー溶接部の溶接状態検査が可能になる。しかも、溶接中のモニタリングではなく、溶接後のオフライン検査により検出するので、特に電子部品リードなどの薄く小さい部材の微細なレーザー溶接部の検査を精度良く行うことができるものである。
【００４２】
また、少なくともレーザー溶接部の外周部では熱の影響により表面粗さが大きくなり、赤外線放射率が高くなることを利用して、赤外線画像において明るく見える部分を検出し、当該部分の外周輪郭より内側を溶接部領域として検出する方法を採用したので、赤外線放射率の高い部分を溶接部領域として抽出することにより、加熱を行うことなくレーザー溶接部を検出することができる。
【００４３】
また請求項２記載の発明は、請求項１記載の効果に加えて、検出された溶接部領域の大きさを基準値と比較することにより溶接の良否を判定する方法を採用したので、溶接時の入熱量と溶接部領域の面積との関係をもとに溶接状態の良否を判定することで、簡易な方法で溶接状態の判定ができるものである。
【００４４】
また請求項３記載の発明は、請求項１記載の効果に加えて、検出された溶接部領域内部の明るく見える外周輪郭の内側に所定の基準値以上の大きさを持つ暗部があれば良品と判定する方法を採用したので、十分な入熱量が与えられた時は中央部に鏡面状の特徴を生じることを利用して溶接状態の良否を判定することで、簡易な方法で溶接状態の判定ができる。
【００４５】
また請求項４記載の発明は、請求項１記載の効果に加えて、上記赤外線カメラにより検出された溶接部領域内部で明るく見える外周輪郭の内側に所定の基準値以上の大きさを持つ暗部があれば良品候補とし、上記良品候補に赤外線を照射し、上記赤外線源の正反射を捉える方向に第２の赤外線カメラを配置して観測した時、溶接部領域中央の輝度が高くなる場合に良品と判定する方法を採用したので、能動的に照射した赤外線光の正反射成分を捉える赤外線カメラを付加することによって、穴あき欠陥と良品を区別することができる。
【００４６】
また請求項５記載の発明は、請求項１記載の効果に加えて、被検査物に赤外線を照射する赤外線源と被検査物を撮像する赤外線カメラを、上記赤外線源から照射された赤外線の正反射光を赤外線カメラで捉えることができるような位置関係になるように配設し、まず赤外線源を消灯して撮影した赤外線画像を用いて検出された溶接部領域内部で明るく見える外周輪郭の内側に所定の基準値以上の大きさを持つ暗部があれば良品候補とし、次に赤外線源を点灯して観測した時、溶接部領域中央の輝度が高くなる場合に良品と判定する方法を採用したので、良品候補を抽出するカメラと良否判定を行うカメラを兼用する構成としたので、簡易な装置構成により穴あき欠陥と良品を区別することができる。
【００４７】
また請求項６記載の発明は、請求項４又は請求項５記載の効果に加えて、良品候補に複数の方向から赤外線を照射していずれかの正反射光を捉えることができれば良品とする方法を採用したので、赤外線源を複数用いることで、仮りに溶接部領域中央の鏡面部分の向きが安定しない場合にも穴あき欠陥と良品を正しく区別することができる。
【００４８】
また請求項７記載の発明は、請求項４又は請求項５記載の効果に加えて、良品候補を斜め方向から赤外線カメラで観測するようにし、赤外線画像において溶接部領域中央に正反射光が捉えられれば良品とし、溶接部領域中央からずれた位置に正反射光が捉えられれば不良とする方法を採用したので、上下の溶接片の段差が小さい場合にも特別の装置を付加することなく穴あき欠陥と良品を正しく区別することができる。
【００４９】
また請求項８記載の発明は、請求項１〜７のいずれかに記載の効果に加えて、被検査物全体を一様に加熱したうえで検査を行う方法を採用したので、被検査物を一様に加熱するようにすることで赤外線画像のＳ／Ｎ比を改善し、検査の信頼性を向上させることができる。
【００５０】
また請求項９記載の発明は、請求項１記載の効果に加えて、上記方法で良品候補と判断された被検査物について、上下の溶接片の間に電圧を与えることによってレーザー溶接部にジュール熱を発生させた状態で赤外線カメラにより撮像し、上記溶接部領域内での輝度値の変化を基準値と比較することによりレーザー溶接部の良否を判定する方法を採用したので、レーザー溶接部に直接通電を行ってジュール熱による温度上昇を観測するようにしたので、外観だけで判断する場合より正確に溶接状態の良否判定ができる。
【００５１】
また請求項１０記載の発明は、請求項１記載の効果に加えて、上記方法で良品候補と判断された被検査物について、下側の溶接片のみを加熱しながら上方より赤外線カメラで撮像し、上記溶接部領域内での輝度値の変化を基準値と比較することによりレーザー溶接部の良否を判定する方法を採用したので、下側の溶接片を加熱して上側の溶接片へ熱伝導が生じる状態を観測することにより、外観だけで判断する場合より正確に溶接状態の良否判定ができる。
【００５２】
また請求項１１記載の発明は、請求項１０記載の効果に加えて、下側の溶接片に通電することにより下側の溶接片にジュール熱を発生させる方法を採用したので、下側の溶接片の下側に発熱体を設置できない構造の検査物でも、請求項１０の方法による検査が可能になる。
【００５３】
また請求項１２記載の発明は、請求項１０記載の効果に加えて、下側の溶接片に高周波磁界を与えて渦電流を発生させることにより加熱する方法を採用したので、下側の溶接片の下側に発熱体を設置できない構造の検査物でも、請求項１０の方法による検査が可能になる。
【００５４】
また請求項１３記載の発明は、請求項１〜請求項１２のいずれかに記載の効果に加えて、高さ計測装置により上記レーザー溶接部近辺の少なくとも２点の高さ情報を取得し、上記溶接部領域の輝度値とともに高さ情報を併用して良否判定を行う方法を採用したので、高さ情報を併用することにより穴あき欠陥と良品の区別など画像情報だけでは分かりにくい溶接状態の判定を高い信頼度で行うことができる。
【００５５】
また請求項１４記載の発明は、赤外線カメラと、赤外線カメラからの出力信号を量子化して画像として記憶する画像取り込み装置と、請求項１〜請求項１３のいずれかの検査方法により赤外線画像を処理して溶接欠陥検査を行う画像処理装置とにより構成されているので、赤外線画像の明るさの差（遠赤外線放射率の差）を利用して、レーザー溶接部と未溶接部の表面性状の違いを画像処理装置にて検出することができ、簡易な構造でレーザー溶接部の溶接状態を検査することができるものである。
【図面の簡単な説明】
【図１】本発明の一実施形態において用いられる検査装置の構成を示す図である。
【図２】（ａ）は同上の赤外線画像の一例を示す図、（ｂ）はレーザー溶接部の物理的構造を説明する図である。
【図３】同上の溶接部領域の抽出方法を説明する図である。
【図４】同上の検査処理手順を説明するためのフローチャートである。
【図５】同上のレーザー入熱量と熱影響部面積との関係を示すグラフである。
【図６】同上の良品のレーザー溶接部の物理的構造を説明する図である。
【図７】（ａ）（ｂ）は同上の良否判定方法の原理を説明する図である。
【図８】（ａ）は同上の穴あき欠陥による虚報の発生を説明する図、（ｂ）はその赤外線画像の一例を示す図である。
【図９】（ａ）は穴あき欠陥を判別するための装置構成を示す図、（ｂ）は他の装置構成を示す図である。
【図１０】同上の穴あき欠陥と良品の判別方法の原理を説明する図である。
【図１１】（ａ）（ｂ）は穴あき欠陥と良品の赤外線画像の違いを説明する図である。
【図１２】穴あき欠陥を判別するための他の実施形態の装置構成を示す図である。
【図１３】（ａ）（ｂ）は同上の穴あき欠陥を判別するための他の方法を説明する図である。
【図１４】（ａ）（ｂ）は同上の穴あき欠陥を判別するための更に他の方法を説明する図である。
【図１５】（ａ）は穴あき欠陥を判別するための更に他の実施形態の装置構成を示す図、（ｂ）は溶接部の高さ情報の２点を説明する図である。
【図１６】局所加熱を伴う溶接部検査方法の装置構成を示す図である。
【図１７】局所加熱を伴う他の溶接部検査方法の装置構成を示す図である。
【図１８】下側の溶接片の両側に電圧を与えて下側の溶接片自体を発熱させる場合を説明する図である。
【符号の説明】
１レーザー溶接部
２赤外線カメラ
２ａ第２の赤外線カメラ
３溶接部領域
４暗部
５赤外線源
６被検査物
８上側の溶接片
９下側の溶接片
１０画像取り込み装置
１１画像処理装置[0001]
BACKGROUND OF THE INVENTION
The present invention is based on the fact that the present invention superimposes welding defects of a laser welded portion where two pieces of metal to be inspected are overlapped and laser-spotted from one surface is welded instead of monitoring during welding. In particular, the present invention relates to an off-line inspection method and apparatus for fine laser welding of thin and small members such as electronic component leads.
[0002]
[Prior art]
Conventionally, as a method for inspecting a laser welded portion, as in the inspection method described in JP-A-5-71932, slit-like laser light is projected onto a laser welded portion, and the reflected light of the laser light is referred to as a laser projection direction. There is a method using three-dimensional shape measurement by a so-called light cutting method, in which a three-dimensional shape of a laser weld is obtained by observing with a camera from different directions.
[0003]
In addition, as a method for inspecting a laser welded portion using an infrared camera, the laser welded portion is heated as inspected in Japanese Patent Laid-Open No. 5-34204, Japanese Patent Laid-Open No. 8-122051, and Japanese Patent Laid-Open No. 52-59046. There is a method of measuring the size of the welded part by measuring the temperature distribution around the laser welded part with an infrared camera in the process of performing the process or the cooling process after heating (including heating by welding heat).
[0004]
[Problems to be solved by the invention]
The above-described conventional inspection method using three-dimensional shape measurement is effective in welding methods in which a laser welded portion is greatly raised, such as butt welding or fillet welding using a filler, but laser spot welding, particularly a lead portion of an electronic component. In the fine welding such as the above, since the change of the shape accompanying the welding is extremely small, a highly accurate three-dimensional shape measuring method is required, which is difficult to apply.
[0005]
In the latter method of measuring the temperature distribution in the latter process of heating the laser spot welded by laser spot welding or in the cooling process after heating (including heating by welding heat), the laser weld has a certain mass ( This is an effective method when it has a heat capacity). For example, in a laser welded part of a very thin and low mass member such as a lead part of an electronic component, the temperature change due to heating occurs in a very short time. There is a problem that it is difficult to accurately measure the temperature distribution by the image.
[0006]
The present invention has been invented in view of the problems of the above-described conventional example, and the object is to perform an off-line inspection after welding, in particular, a fine laser welded portion of a thin and small member such as an electronic component lead. It is an object of the present invention to provide a method and an apparatus for inspecting a laser welded part capable of accurately performing the inspection of the laser welding, improving the reliability of the inspection and improving the accuracy of the quality determination.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, in the present invention, two pieces of metal to be inspected 6 are overlapped, and laser welding spot 1 is welded by spot-irradiating laser on one surface thereof, and then inspection is performed after welding. In the method, the laser welded part 1 cooled to the ambient temperature after welding is imaged with an infrared camera 2, and the difference in brightness in the obtained infrared image is regarded as an index representing the difference in infrared emissivity on the surface of the object 6 to be welded. The first process of detecting the region 3, the shape of the welded region 3, the distribution pattern of the luminance value of the infrared image in the welded region 3, and the feature amount extracted based on the distribution pattern And a second process for determining whether welding is good or not based on at least one, and by configuring in this way, a difference in brightness of infrared images (difference in far-infrared emissivity) is obtained. Use It can detect the difference in the surface properties of the unwelded portion and over the welded portion 1, it becomes possible to inspect the weld state of the laser welding unit 1 in a simple manner. In addition, since detection is performed not by monitoring during welding but by offline inspection after welding, it is possible to accurately inspect the fine laser welded portion 1 of a thin and small member such as an electronic component lead.
[0008]
Further, by utilizing the fact that the surface roughness is increased due to the influence of heat and the infrared emissivity is increased at least in the outer peripheral portion of the laser welded portion 1, a portion that appears bright in the infrared image is detected, and the outer peripheral contour of the portion is detected. Inside is detected as weld zone 3 So The laser weld 1 can be detected without heating.
[0009]
Moreover, it is preferable to determine the quality of the welding by comparing the detected size of the weld region 3 with a reference value. In this case, the welding state can be determined by a simple method.
[0010]
Further, if there is a dark part 4 having a size equal to or larger than a predetermined reference value inside the outer peripheral contour that appears bright inside the detected welded part region 3, it is preferably determined as a non-defective product. In this case, a sufficient amount of heat input is given. When this is done, it is possible to easily determine whether the welding state is good or not by utilizing a mirror-like feature at the center.
[0011]
Further, if there is a dark part 4 having a size equal to or larger than a predetermined reference value inside the outer peripheral contour that appears bright inside the welded part region 3 detected by the infrared camera 2, it is determined as a good product candidate, and the good product candidate is irradiated with infrared rays. When the second infrared camera 2a is arranged and observed in the direction in which the regular reflection of the infrared source 5 is captured, it is preferable to determine that the product is good when the brightness at the center of the welded region 3 is high. By simply adding the second infrared camera 2a that captures the specular reflection component of the irradiated infrared light, it is possible to distinguish the perforated defect from the non-defective product.
[0012]
In addition, the infrared ray source 5 that irradiates the inspection object 6 with the infrared ray and the infrared camera 2 that images the inspection object 6 can capture the infrared specularly reflected light emitted from the infrared source 5 with the infrared camera 2. Are arranged so as to be in a proper positional relationship, and the size is equal to or larger than a predetermined reference value on the inner side of the outer peripheral contour that appears bright inside the welded region 3 detected using an infrared image taken with the infrared source 5 turned off. If there is a dark part 4 having a non-defective product, it is preferably determined to be a good product when the brightness at the center of the welded region 3 increases when the infrared source 5 is turned on and observed. It is possible to use both the camera to be extracted and the camera to perform pass / fail judgment, and to distinguish between perforated defects and non-defective products with a simple device configuration.
[0013]
In addition, it is preferable that the non-defective product is irradiated with infrared rays from a plurality of directions and any specularly reflected light can be captured. In this case, by using a plurality of infrared sources 5, the weld region 3 is temporarily used. Even when the orientation of the central mirror surface portion is not stable, it becomes possible to correctly distinguish a perforated defect from a good product.
[0014]
Further, a good product candidate is observed with the infrared camera 2 from an oblique direction, and if a regular reflection light is captured at the center of the welded region 3 in the infrared image, a good product is obtained, and the specularly reflected light is displaced from the center of the welded region 3. If it is captured, it is preferable that it is defective. In this case, even when the difference in level between the upper and lower weld pieces 8 and 9 is small, it becomes possible to correctly distinguish the perforated defect from the non-defective product without adding a special device.
[0015]
Further, it is preferable to perform the inspection after the entire inspection object 6 is heated uniformly. In this case, the S / N ratio of the infrared image is improved by heating the inspection object 6 uniformly. The
[0016]
Further, in order to accurately determine the quality of the welded state, a voltage is applied between the upper and lower weld pieces 8 and 9 for the inspected object 6 determined as a good product candidate by the above-described method, whereby the laser welded portion 1 is subjected to joule. It is preferable to determine the quality of the laser welded portion 1 by taking an image with the infrared camera 2 in a state where heat is generated and comparing the change in the luminance value in the welded region 3 with a reference value. Further, the inspection object 6 determined to be a good product candidate by the above method is picked up by the infrared camera 2 from above while heating only the lower welding piece 9, and the change in luminance value in the welded region 3 is detected. It is preferable to determine the quality of the laser weld 1 by comparing with a reference value.
[0017]
In addition, it is preferable to generate Joule heat in the lower welding piece 9 by energizing the lower welding piece 9, and in this case, an inspection of a structure in which a heating element cannot be installed under the lower welding piece 9 Even things can be inspected.
[0018]
Further, it is preferable to heat the lower weld piece 9 by applying a high-frequency magnetic field to generate an eddy current. In this case, even a test object having a structure in which a heating element cannot be installed below the lower weld piece 9 Inspection becomes possible.
[0019]
Further, at least two points H in the vicinity of the laser weld 1 are measured by a height measuring device. ₁ , H ₂ It is preferable to determine the quality by using the height information together with the brightness value of the weld region 3, and in this case, by using the height information in combination, it is preferable to distinguish the perforated defect from the non-defective product This makes it possible to determine the welding state, which is difficult to understand with only image information, with high reliability.
[0020]
Furthermore, the inspection apparatus for the laser welding part 1 according to the present invention includes an infrared camera 2 (2a), an image capturing device 10 that quantizes an output signal from the infrared camera 2 (2a) and stores it as an image, Since the image processing apparatus 11 is configured to process the infrared image by the inspection method and inspect the welding defect, laser welding is performed using the difference in the brightness of the infrared image (difference in the far-infrared emissivity). The difference in surface properties between the part 1 and the unwelded part can be detected by the image processing apparatus 11, and the welding state of the laser welded part 1 can be inspected with a simple structure.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on embodiments shown in the accompanying drawings.
[0022]
FIG. 1 is a diagram showing a configuration of an inspection apparatus that performs off-line determination of laser welding by the method of the present invention. This inspection apparatus superimposes two pieces of metal (welding pieces 8 and 9) to be inspected 6 and inspects the welding state of the laser welded portion 1 welded by spot irradiation with a laser on one surface thereof after welding. Specifically, the welded pieces 8 and 9 to be inspected are cooled to the atmosphere temperature after welding, and then the vicinity of the laser welded portion 1 is imaged by the infrared camera 2. Here, cooling to the ambient temperature after welding means a state in which heat is sufficiently dissipated and is not a cooling process. Image data from the infrared camera 2 is captured by the image capturing device 10. The image capturing device 10 includes a quantization device 14 for converting captured image data into an image and an image memory 15 for storing the image. The image processing device 11 analyzes the image to inspect and determine. Is done. Specifically, the weld region 3 (FIG. 2) is extracted from the infrared image by utilizing the difference in the far-infrared emissivity caused by the difference in surface roughness between the laser welded portion 1 and the unwelded portion. By discriminating the welding state using the luminance value inside the partial region 3, the laser welded portion 1 is inspected for a fine part in which the change in the three-dimensional shape is small and the inspection by the temperature distribution is difficult. Further, even when it is difficult to discriminate only by emissivity, a more accurate welding state inspection can be performed by actively changing the temperature of the laser welded portion 1 or using a three-dimensional measuring device in combination. This will be specifically described below.
[0023]
FIG. 2A shows an example of an infrared image obtained by imaging the laser welded portion 1 of the inspection object 6 cooled to the ambient temperature after welding as shown in FIG. Moreover, the three-dimensional shape of the laser weld 1 is shown in FIG. In FIG. 2A and FIG. 2B, the part A is a part that is not affected by heat, and the part B is the laser welded part 1 that is affected by heat. As shown in FIG. 2 (b), part A is a flat metal surface and the surface is close to a mirror surface, while part B has a fold-like three-dimensional structure due to the metal being melted by heat. It is the surface.
[0024]
The laser welded portion 1 shown in FIG. 2 is a small one having a diameter of the B portion of about several hundred μm. Since the upper and lower weld pieces 8 and 9 for performing such a fine laser spot welding are thin and have a small heat capacity of about several tens to several hundreds of μm, the temperature change accompanying heating and cooling becomes extremely rapid. End up. For this reason, it is very difficult to measure the size of the welded portion (nugget) using the temperature distribution during heating and cooling. Further, since the laser welded portion 1 is fine, the change in the three-dimensional shape of the laser welded portion 1 is extremely small (unevenness of about several μm), and it is difficult to measure the three-dimensional shape and determine whether it is good or bad. Therefore, in the present invention, a change in infrared emissivity is used in order to detect such a minute change in unevenness. That is, the surface roughness of the portion B shown in FIGS. 2 (a) and 2 (b) is increased due to thermal effects, and the infrared emissivity is higher than that of the portion A. Therefore, in the infrared image shown in FIG. 2A, the B part appears brighter than the A part. By utilizing this phenomenon, it becomes possible to extract the laser weld 1 from the infrared image and evaluate the degree of thermal influence.
[0025]
However, although the surface properties (surface roughness) change in the heat-affected zone due to fine laser spot welding such as electronic parts, the unevenness is extremely fine and inspection by 3D (three-dimensional) measurement is extremely difficult. According to the inspection method of the laser welded part 1 according to the invention, it is detected by using the difference in the brightness of the infrared image (difference in the far-infrared emissivity) and not by monitoring during welding but by offline inspection after welding. By doing so, it is possible to detect the difference in surface properties between the laser welded portion 1 and the unwelded portion, so that it is possible to inspect the welding state of the laser welded portion 1 by a simple method and to perform nondestructive inspection by image processing. In addition, it is possible to automate the confirmation work of the insufficient bonding state. Therefore, for example, the inspection of the fine laser welded portion 1 of a thin and small member such as an electronic component lead can be performed with high accuracy. Furthermore, an inspection apparatus including an infrared camera 2, an image capturing device 10 that quantizes an output signal from the infrared camera 2 and stores the image as an image, and an image processing device 11 that processes the infrared image to inspect a welding defect. By using this, it is possible to inspect the welding state of the laser welded portion 1 with a simple apparatus configuration.
[0026]
Next, an example of the extraction and inspection procedure of the weld zone of the laser weld 1 will be described. FIG. 3 shows an example of a method for extracting a welded portion region of the laser welded portion 1, and FIG. 4 is a flowchart for explaining an inspection procedure including an extracting means for the laser welded portion 1. At step n1 in FIG. 4, the image in FIG. 2B is binarized, and at step n2, the connected region B ′ in FIG. 3 is extracted. The connection region B ′ in FIG. 3 corresponds to the B portion in FIG. Thereafter, in step n3 of FIG. 4, the portion inside the outer peripheral contour of the connection region B ′ is set as the weld region 3, and further in step n5, the lightness pattern in the weld region 3 is analyzed to determine the quality of the weld. I do. Thus, by extracting a part with a high infrared emissivity as the welded part region 3, the laser welded part 1 can be detected without heating.
[0027]
Here, the process of performing the pass / fail determination based on the luminance value inside the weld zone 3 shown in Step n4 of FIG. 4 will be described. First, as a first method, there is a method using the area of the welded region 3. FIG. 5 shows the relationship between the amount of heat input during laser welding and the area of the weld zone 3 (heat affected zone). In laser welding, the larger the welding heat input, the larger the area of the weld zone 3. Therefore, the amount of heat input is determined based on the area of the weld zone 3 extracted in the above process using the graph of FIG. 5. Can be estimated. Based on the graph of FIG. 5, the heat affected zone area range S1 with respect to the heat input range D1 necessary for sufficient welding is obtained, and the weld zone 3 extracted from the infrared image of the laser weld 1 is obtained. If the area is within the range of S1, it is determined as a non-defective product. Thus, by determining the quality of the welding state based on the relationship between the amount of heat input during welding and the area of the welded region 3, the welding state can be determined by a simple method.
[0028]
Next, a second method for determining pass / fail is described. In laser spot welding, a good product to which a sufficient amount of heat input is given has a large amount of metal to be melted. Therefore, as shown in FIG. 6, the molten metal accumulates in the center of the weld zone 3 and the center becomes a mirror surface. . For this reason, in the infrared image which image | photographed the good laser welding part 1, as shown to Fig.7 (a), since the surface roughness is rough and infrared emissivity is high, the said mirror-like part is shown inside B part which appears white The feature that the portion (C portion having a low infrared emissivity because it is a mirror surface) appears black appears. Therefore, as shown in FIG. 7B, it is a non-defective product when a black part region C having a size equal to or larger than a reference value inside the welded part region 3 is observed in the binarized infrared image. Judge. Therefore, when a sufficient amount of heat input is given, the quality of the welded state is determined using the occurrence of a mirror-like feature at the center, so the welded state can be determined by a simple method.
[0029]
By the way, in each of the defect inspection methods described above, there is a possibility that some false information (determining a defect as a non-defective product) may occur. The cause of the false alarm occurrence in the above method and the countermeasure method will be described below.
[0030]
As one of the defects at the time of laser welding, when the heat input amount is insufficient, as shown in the cross-sectional view of the weld pieces 8 and 9 in FIG. There is a perforated defect in which only the upper weld piece 8 is melted until the lower weld piece 9 is sufficiently in contact and the lower weld piece 9 is heated and melted, and a hole 20 is formed at the center. In this case, in the infrared image, the outer diameter of the laser welded portion 1 is increased by opening the hole, and the lower weld piece 9 that is not affected by heat from the hole can be seen. As described above, when the black portion 21 is observed inside the welded portion region 3, it is erroneously determined to be a non-defective product in the inspection by any of the above methods.
[0031]
An apparatus configured to eliminate such false information is shown in FIG. The apparatus shown in FIG. 9 (a) adds directional infrared light to the laser welded portion 1 in addition to the infrared camera 2 that images the vicinity of the laser welded portion 1 of the welded pieces 8 and 9 to be inspected from above. An infrared source 5 that irradiates from an oblique direction is opposed to the infrared source 5 with the weld pieces 8 and 9 interposed therebetween, and is disposed at a position where infrared light can capture light that is specularly reflected by the laser weld 1. 2 infrared cameras 2a are provided. Here, FIG. 10 (a) shows a state in which a defect with a hole that is judged as a non-defective product by the upper camera is imaged by the second infrared camera 2a, and FIG. 10 (b) shows a non-defective product by the second infrared camera 2a. Shows the state of imaging. As can be seen by comparing FIGS. 10 (a) and 10 (b), in the case of a holed defect, as shown in FIG. 10 (a), the mirror-like part (lower welding piece 9) is at the lower position, so that the infrared The light from the source 5 does not reach, and in the infrared image taken as shown in FIG. On the other hand, in the case of the non-defective product shown in FIG. 10B, the infrared light specularly reflected by the mirror surface at the center of the laser weld 1 is incident on the second infrared camera 2a. In the infrared image, the center of the weld region 3 appears white. Utilizing this difference, first, the laser welded portion 1 is observed from above with the infrared camera 2 shown in FIG. 9A, and if there is a low-luminance portion at the center of the welded region 3, the laser welded portion 1 is The above-mentioned false information is eliminated by determining the product as a good product and then determining the product as a good product only when the brightness is high at the center of the weld region 3 in the image taken by the second infrared camera 2a. Can do. Further, by adding the second infrared camera 2a that captures the specular reflection component of the infrared light that is actively irradiated, it is possible to distinguish the perforated defect from the non-defective product.
[0032]
Further, instead of providing the second infrared camera 2a as described above, only one infrared camera 2 disposed at a position corresponding to the second infrared camera 2a is used as shown in FIG. 9B. You may make it do. In this case, at the time of the first imaging, the infrared source 5 is turned off and the image is taken, and after extracting the welded part region 3, the dark part 4 (mirror surface part) is observed at the center of the welded part region 3 as a good product candidate. . Next, the non-defective product is photographed in a state where the infrared source 5 is turned on, and is determined as non-defective when the luminance in the central portion becomes high as in the above inspection method. However, since the single infrared camera 2 is used as a camera that extracts a good product candidate and a camera that performs pass / fail judgment, a perforated defect and a good product can be distinguished by a simple device configuration.
[0033]
The inspection method, which is a further development of the above-mentioned false alarm countermeasure method, will be described below. In the apparatus of FIGS. 9A and 9B, when the mirror surface portion generated in the center of the laser welded portion 1 is tilted, the specular reflection component of the infrared light does not reach the second infrared camera 2a, and it is mistakenly made. There is a possibility that it will be judged as a defective product. Therefore, in the inspection apparatus of FIG. 12, a plurality of infrared sources 5 are provided. As a result, even when the mirror surface portion generated at the center of the laser welded portion 1 is inclined, the infrared light from any one of the infrared light sources 5 is regularly reflected by the mirror surface portion and enters the second infrared camera 2a. It is possible to reduce the number of errors in which a non-defective product is judged as a defective product even when the direction of the mirror surface portion at the center of the laser welded portion 1 is not stable, and it is possible to correctly distinguish between a perforated defect and a good product. . In this method, a plurality of second infrared cameras 2a are provided, or imaging is performed while moving at least one of the infrared source 5 and the infrared camera 2, and the positional relationship between the infrared source 5 and the infrared camera 2 changes. The specular reflection infrared light from the infrared source 5 may enter the infrared camera 2 at the mirror surface at such a location.
[0034]
Further, another inspection method, which is a further development of the above-mentioned false alarm countermeasure method, will be described below. When the upper weld piece 8 is thin as shown in FIG. 13A or when the gap between the upper and lower weld pieces 8 and 9 is narrow as shown in FIG. 13B, the upper weld piece 8 is visible from the upper surface and the hole. The lower step of the lower weld piece 9 is small and the infrared light irradiated obliquely is reflected from the upper surface of the lower weld piece 9 and is incident on the second infrared camera 2a. There is a possibility of being. Here, FIG. 14A shows an infrared image of a perforated defect having a small step, and FIG. 14B shows an infrared image of a good product. In the case of a perforated defective product as shown in FIG. 13 (a) or (b), a part of the infrared light reflected on the upper surface of the lower welding piece 9 is blocked by the step, so that FIG. The specular reflection component E is observed at a position deviated from the center of the weld zone 3 as shown in FIG. On the other hand, in the case of the non-defective product shown in FIG. 14 (b), there is no step between the welded region 3 and the central mirror surface portion, so that the regular reflection component E is as shown in FIG. 14 (b). Observed in the center of the weld zone 3. Using this, when irradiating the laser welding part 1 with infrared rays and observing the infrared specular reflection component with the second infrared camera 2a, it is determined whether the specular reflection component is present at the center of the welded region 3. By making a good product only when it is observed, it is possible to realize an inspection method that is less likely to generate false information. Further, even when the difference in level between the upper and lower weld pieces 8 and 9 is small, it is possible to correctly distinguish the perforated defect from the non-defective product without adding a special device.
[0035]
As a more direct method for distinguishing perforated defects from non-defective products, there are at least two points H as shown in FIG. ₁ , H ₂ In combination with a three-dimensional measuring device 7 that can measure the height of the laser welding portion 1, at least two points H in the peripheral portion and the central portion in the laser welding portion 1 ₁ , H ₂ If the difference between the two is small, it is determined as a non-defective product, and if the difference between the two is large, it may be determined as a perforated defect. 2 points for holes with holes ₁ , H ₂ By utilizing the fact that the difference is small in the case of a non-defective product, it is possible to make a determination of a welding state that is difficult to understand only by image information such as discrimination between a perforated defect and a non-defective product with higher reliability. Of course, 2 points H ₁ , H ₂ However, the height of three or more points may be measured.
[0036]
In the above inspection method, the object to be inspected 6 was photographed in a state where it was cooled to the ambient temperature after welding, but after cooling, the entire object to be inspected 6 was uniformly heated and then inspected. May be performed. By the way, the unwelded part that is not affected by heat is close to the mirror surface, so the amount of increase in infrared radiation is small even at high temperatures. However, in laser-welded parts (heat-affected parts) that are affected by heat, Since the surface is melted and has a fold-like three-dimensional structure, more infrared rays are emitted as the temperature rises. Therefore, it can be seen that the higher the temperature of the inspection object, the higher the S / N ratio in the infrared image in the above inspection, and the reliability of the inspection is improved. Therefore, by uniformly heating the object 6 to be inspected, the difference between the bright portion and the dark portion (mirror surface portion) of the laser welded portion 1 becomes large, and the light / dark pattern becomes clear, and image processing is performed. It is possible to improve the reliability of the inspection.
[0037]
Next, after the laser welded portion 1 is cooled to the post-weld ambient temperature as described above, the laser welded portion 1 is further locally heated in the method of performing pass / fail judgment using the difference in the infrared reflection characteristics associated with the surface properties. By using the method of giving the value together, it is possible to perform the pass / fail judgment with higher accuracy. This will be described below.
[0038]
First, FIG. 16 is a diagram for explaining a first inspection method involving local heating. FIG. 16 is a diagram showing only the periphery of the weld pieces 8 and 9 in the inspection apparatus of FIG. 1, and the configuration of the imaging apparatus is the same as that of FIG. In this method, electrodes 22a and 22b are attached to the upper and lower weld pieces 8 and 9, respectively, so that a voltage can be applied. When a voltage is applied between the electrodes 22a and 22b for a certain period of time, the laser welded portion 1 generates Joule heat according to its resistance and the temperature rises. However, in a non-defective product in which the laser welded portion 1 is properly welded, Since the electrical resistance between the upper and lower weld pieces 8, 9 is small, the temperature rise is small. On the other hand, in the case of poor welding (such as a hole defect), the temperature is not increased at all due to the insulation state, or conversely, the contact resistance is large, resulting in a large temperature increase. By utilizing this, a voltage is applied between the upper and lower weld pieces 8 and 9 for a certain period of time to increase the temperature of the laser welded portion 1 (specifically, the amount of change in the luminance value in the welded region 3 in the infrared image). If it is measured by the camera 2 and is between a predetermined upper limit value and lower limit value, it is determined as a non-defective product. In the observation of the change in the brightness value, first, the weld region 3 is extracted by the above method in a room temperature state, and the temperature rises by a method such as comparing the average brightness value in the region before and after heating. What is necessary is just to evaluate the magnitude | size of. Thus, since the laser welding part 1 is directly energized and the temperature rise due to Joule heat is observed, the quality of the welded state can be determined more accurately than when only the appearance is determined.
[0039]
Next, a second inspection method involving heating is shown in FIG. FIG. 17 is a view showing only the periphery of the weld pieces 8 and 9 in the inspection apparatus of FIG. 1, and the configuration of the imaging apparatus is the same as that of FIG. In this example, the heating element 23 is brought into contact with the lower surface of the lower welding piece 9 and only the lower welding piece 9 is heated. As a result, heat conduction occurs from the heating element 23 to the upper welding piece 8 through the lower welding piece 9, but good heat conduction occurs in the welded portion, whereas there is a gap in the non-welded portion. Is unlikely to occur. By utilizing this, the temperature change of the laser welded portion 1 (specifically, the brightness value in the welded portion region 3 in the infrared image is detected by the infrared camera 2 disposed above while heating the lower welding piece 9. The amount of change) is observed, and if the temperature rise is larger than a certain reference value, it can be determined that the product is good. That is, since the lower welding piece 9 is heated to observe the state in which heat conduction occurs to the upper welding piece 8, the quality of the welded state can be determined more accurately than when only the appearance is determined. In the observation of the change in the brightness value, the welded region 3 is first extracted by the above method in the normal temperature state in the same manner as in the first inspection method involving local heating, and the brightness time in the region is measured. Find change. In addition, when heating the lower welding piece 9, the method of heating with a hot air or a flame from the lower side is also possible besides the method of making the heat generating body 23 contact the lower welding piece 9.
[0040]
By the way, there is a case where the lower welding piece 9 is already attached to the structure, such as an electronic component, and the lower welding piece 9 cannot be heated by heat conduction. In such a case, as shown in FIG. 18, electrodes are attached to both ends of the lower weld piece 9 and a voltage is applied to generate Joule heat in the lower weld piece 9 itself, or A method of heating by applying a high frequency magnetic field from the lower part of the lower welding piece 9 to generate an eddy current and heating by IH (induction heating) may be adopted.
[0041]
【The invention's effect】
As described above, in the first aspect of the present invention, a method of inspecting a laser welded portion, which is formed by superimposing two pieces of metal to be inspected and spot-irradiating a laser on one surface thereof after welding. In this case, the laser welded portion cooled to the ambient temperature after welding is imaged with an infrared camera, and the difference in brightness in the obtained infrared image is regarded as an index indicating the difference in infrared emissivity on the surface of the object to be detected. Based on at least one of the first process, the shape of the weld region, the distribution pattern of the brightness value of the infrared image in the weld region, and the feature value extracted based on the distribution pattern And the second process of judging the quality of the welding, the surface properties (surface roughness) change in the heat-affected zone due to the fine laser spot welding of electronic parts, etc., but the unevenness is extremely fine. Inspection by D (three-dimensional) measurement is extremely difficult, but according to the inspection method for laser welds according to the present invention, laser welding is performed by utilizing the difference in brightness of infrared images (difference in far-infrared emissivity). Since it is possible to detect the difference in surface properties between the welded portion and the unwelded portion, it is possible to inspect the welding state of the laser welded portion by a simple method. In addition, since detection is performed not by monitoring during welding but by offline inspection after welding, it is possible to accurately inspect a fine laser welded portion of a thin and small member such as an electronic component lead.
[0042]
Ma Little At least the outer peripheral part of the laser welded part is affected by heat, and the surface roughness increases and the infrared emissivity increases. Since the method of detecting as the weld zone is adopted, the laser weld zone can be detected without heating by extracting the portion having a high infrared emissivity as the weld zone.
[0043]
Also Claim 2 The described invention Claim 1 In addition to the effects described above, a method of judging the quality of welding by comparing the size of the detected welded area with a reference value was adopted, so the relationship between the heat input during welding and the area of the welded area By determining the quality of the welding state based on the above, it is possible to determine the welding state by a simple method.
[0044]
Also Claim 3 The described invention Claim 1 In addition to the effects described above, a method for determining that there is a dark part with a size greater than or equal to a predetermined reference value inside the outer peripheral contour that appears bright inside the detected welded part area has been adopted. Is given, it is possible to determine the welding state by a simple method by determining whether the welding state is good or not by utilizing the occurrence of a mirror-like feature at the center.
[0045]
Also Claim 4 The described invention Claim 1 In addition to the effects described above, if there is a dark part having a size greater than or equal to a predetermined reference value inside the outer peripheral contour that appears bright inside the welded region detected by the infrared camera, it is determined as a non-defective product candidate, and infrared rays are applied to the good product candidate. When the second infrared camera is placed in the direction of capturing the regular reflection of the infrared source and observed, the method of determining that the brightness is high when the brightness at the center of the weld zone is high is used. By adding an infrared camera that captures the specular reflection component of the irradiated infrared light, it is possible to distinguish perforated defects from non-defective products.
[0046]
Also Claim 5 The described invention Claim 1 In addition to the effects described above, an infrared source that irradiates an object to be inspected and an infrared camera that images the object to be inspected, such that infrared specularly reflected light emitted from the infrared source can be captured by the infrared camera. A dark part having a size greater than a predetermined reference value inside the outer contour that appears bright inside the welded part area, which is detected using an infrared image taken by turning off the infrared light source and arranged in a positional relationship. If there is a non-defective product candidate, then when the infrared source is turned on and observed, the brightness of the center of the weld zone is determined to be good. Since the camera is also used as a camera, it is possible to distinguish a perforated defect from a non-defective product with a simple device configuration.
[0047]
Also Claim 6 The described invention Claim 4 or claim 5 In addition to the effects described above, a non-defective product candidate is used if it can capture any specularly reflected light by irradiating non-defective products with infrared rays from multiple directions. Even when the direction of the mirror surface portion at the center of the partial area is not stable, it is possible to correctly distinguish the perforated defect from the good product.
[0048]
Also Claim 7 The described invention Claim 4 or claim 5 In addition to the effects described above, non-defective products can be observed with an infrared camera from an oblique direction, and if regular reflection light is captured at the center of the welded area in the infrared image, it is determined to be non-defective and specularly reflected at a position shifted from the center of the welded area. Since the method of determining that the light is captured is adopted, it is possible to correctly distinguish the perforated defect from the non-defective product without adding a special device even when the step difference between the upper and lower weld pieces is small.
[0049]
Also Claim 8 The described invention Claims 1-7 In addition to the effect described in any one of the above, since the method of performing inspection after heating the entire object to be inspected uniformly is adopted, the infrared image can be obtained by heating the object to be inspected uniformly. The / N ratio can be improved and the reliability of inspection can be improved.
[0050]
Also Claim 9 The described invention Claim 1 In addition to the effects described above, an object to be inspected as a good product candidate by the above method is imaged with an infrared camera in a state where Joule heat is generated in the laser weld by applying a voltage between the upper and lower weld pieces. Because the method of judging the quality of the laser weld by comparing the change in brightness value in the weld zone with the reference value is adopted, the laser weld is directly energized and the temperature rise due to Joule heat is observed. Since it was made to do, the quality determination of a welding state can be performed more correctly than the case where it judges only by an external appearance.
[0051]
Also Claim 10 The described invention Claim 1 In addition to the effects described above, the inspected object determined as a good product candidate by the above method is picked up by an infrared camera from above while heating only the lower welding piece, and the change in luminance value in the welded region Since the method of judging the quality of the laser welded part by comparing the value with the reference value is adopted, by heating the lower weld piece and observing the state in which heat conduction occurs to the upper weld piece, only the appearance It is possible to determine the quality of the welding state more accurately than when determining.
[0052]
Also Claim 11 The described invention Claim 10 In addition to the effects described above, a method of generating Joule heat in the lower weld piece by energizing the lower weld piece has been adopted, so that a heating element cannot be installed under the lower weld piece. Even for inspection objects Claim 10 Inspection by this method becomes possible.
[0053]
Also Claim 12 The described invention Claim 10 In addition to the effects described above, a heating method was adopted by applying a high-frequency magnetic field to the lower weld piece to generate eddy currents, so inspection of a structure where a heating element could not be installed under the lower weld piece Even things Claim 10 Inspection by this method becomes possible.
[0054]
Also Claim 13 The invention described in claims 1 to Claim 12 In addition to the effect described in any of the above, the height measurement device acquires height information of at least two points in the vicinity of the laser welded portion, and uses the height information together with the luminance value of the welded region to determine whether or not Since the method of performing is used, it is possible to perform the determination of the welding state, which is difficult to understand by only the image information, such as discrimination between the holed defect and the non-defective product, by using the height information together.
[0055]
Also Claim 14 The invention described is an infrared camera, an image capturing device that quantizes an output signal from the infrared camera and stores the image as an image, and claims 1 to Claim 13 Because it is composed of an image processing device that inspects welding defects by processing infrared images by any of the inspection methods described above, a laser utilizing the difference in brightness of infrared images (difference in far-infrared emissivity) The difference in surface properties between the welded portion and the unwelded portion can be detected by an image processing apparatus, and the welding state of the laser welded portion can be inspected with a simple structure.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an inspection apparatus used in an embodiment of the present invention.
FIG. 2A is a diagram showing an example of the above infrared image, and FIG. 2B is a diagram for explaining a physical structure of a laser welded portion.
FIG. 3 is a diagram for explaining a method of extracting a welded portion region as described above.
FIG. 4 is a flowchart for explaining the inspection processing procedure of the above.
FIG. 5 is a graph showing the relationship between the laser heat input and the heat-affected zone area.
FIG. 6 is a view for explaining the physical structure of a good laser welded part.
FIGS. 7A and 7B are diagrams for explaining the principle of the pass / fail judgment method of the above.
FIG. 8A is a diagram for explaining generation of a false alarm due to a holed defect, and FIG. 8B is a diagram showing an example of an infrared image thereof.
9A is a diagram showing a device configuration for discriminating perforated defects, and FIG. 9B is a diagram showing another device configuration.
FIG. 10 is a diagram for explaining the principle of a method for discriminating between perforated defects and non-defective products.
FIGS. 11A and 11B are diagrams for explaining a difference between a perforated defect and a non-defective infrared image. FIGS.
FIG. 12 is a diagram showing an apparatus configuration of another embodiment for discriminating a hole defect.
FIGS. 13A and 13B are diagrams for explaining another method for discriminating the holed defect.
FIGS. 14A and 14B are views for explaining still another method for discriminating the holed defect.
FIG. 15A is a diagram showing a device configuration of still another embodiment for discriminating perforated defects, and FIG. 15B is a diagram for explaining two points of height information of a welded portion.
FIG. 16 is a diagram showing an apparatus configuration of a weld inspection method with local heating.
FIG. 17 is a diagram showing a device configuration of another welded portion inspection method involving local heating.
FIG. 18 is a diagram illustrating a case where voltage is applied to both sides of the lower weld piece to cause the lower weld piece itself to generate heat.
[Explanation of symbols]
1 Laser weld
2 Infrared camera
2a Second infrared camera
3 Weld zone
4 Dark areas
5 Infrared source
6 Inspection object
8 Upper weld piece
9 Lower welding piece
10 Image capture device
11 Image processing device

Claims

In the method of superimposing two pieces of metal to be inspected and spot-irradiating laser on one surface and welding a laser welded part after welding, the laser welded part cooled to the ambient temperature after welding is an infrared camera. The first step of detecting the weld region by regarding the difference in luminance in the obtained infrared image as an index indicating the difference in the infrared emissivity of the surface of the inspection object, the shape of the weld region, A distribution pattern of the luminance value of the infrared image in the weld region, a second process of determining whether the welding is good or not based on at least one of the feature values extracted based on the distribution pattern , At least at the outer periphery of the laser weld, the surface roughness increases due to the effect of heat, and the infrared emissivity is increased, so that the portion that appears bright in the infrared image is detected. Inspection method of laser welds, characterized in that from the amount of the outer peripheral edge is detected inside the weld region.

2. The method for inspecting a laser weld according to claim 1, wherein the quality of the weld is determined by comparing the detected size of the weld region with a reference value .

2. The method for inspecting a laser weld according to claim 1, wherein if there is a dark part having a magnitude greater than or equal to a predetermined reference value inside the outer peripheral contour that appears bright inside the detected weld area , the laser weld is inspected.

If there is a dark part with a size greater than or equal to a predetermined reference value inside the outer peripheral contour that appears bright inside the welded region detected by the infrared camera, it is determined as a good product candidate, and the good product candidate is irradiated with infrared light, and the infrared source when the direction to catch the specular reflection was observed a second infrared camera arranged, the inspection method of laser welding of claim 1, wherein the determining to be nondefective when the brightness of the weld area center is higher .

The infrared source that irradiates the inspection object with the infrared light source and the infrared camera that images the inspection object are arranged so that the infrared camera can capture the regular reflected light of the infrared light emitted from the infrared source. First, if there is a dark part with a size greater than a predetermined reference value inside the outer peripheral contour that appears bright inside the welded region detected using the infrared image taken with the infrared source turned off, 2. The method for inspecting a laser weld according to claim 1, wherein when the infrared light source is turned on and observed, the product is determined to be non-defective when the brightness at the center of the weld zone increases .

6. The method for inspecting a laser welded portion according to claim 4, wherein the good product candidate is judged as good if it can irradiate infrared rays from a plurality of directions and capture any specularly reflected light .

A good product candidate is observed from an oblique direction with an infrared camera. The method for inspecting a laser weld according to claim 4 or 5, wherein:

The method for inspecting a laser welded portion according to any one of claims 1 to 7, wherein the inspection is performed after uniformly heating the entire object to be inspected .

The inspection object determined as a good product candidate by the above method is imaged by an infrared camera in a state where Joule heat is generated in the laser weld by applying a voltage between the upper and lower weld pieces, and within the weld region. The method for inspecting a laser weld according to claim 1, wherein the quality of the laser weld is determined by comparing a change in luminance value with a reference value .

Inspecting an object to be inspected as a good product candidate by the above method, taking an image with an infrared camera from above while heating only the lower welding piece, and comparing the change in luminance value in the weld area with a reference value. The method for inspecting a laser welded portion according to claim 1, wherein the quality of the laser welded portion is determined by :

11. The method for inspecting a laser weld according to claim 10, wherein Joule heat is generated in the lower weld piece by energizing the lower weld piece .

The method for inspecting a laser weld according to claim 10, wherein heating is performed by applying a high-frequency magnetic field to the lower weld piece to generate an eddy current .

The height measurement device acquires height information of at least two points in the vicinity of the laser welded portion, and performs quality determination using the height information together with the luminance value of the welded region. The method for inspecting a laser weld according to claim 12 .

An infrared camera, an image capturing device that quantizes an output signal from the infrared camera and stores the image as an image, and an image processing that performs a weld defect inspection by processing an infrared image by the inspection method according to any one of claims 1 to 13. An apparatus for inspecting a laser welding part, characterized in that the apparatus is constituted by a device.