JP3703017B2 - Spot welding monitoring method and monitoring apparatus - Google Patents

Description

【００４０】
【数２】

【００４１】
但し、ｍは加圧系の質量であり、また、ωは溶接機の加圧機構部の固有振動数であり、いずれも定数として取り扱うことができる。
【００４２】
そこで、上記数１および数２に、仮定した粘性減衰係数Ｃおよびばね定数Ｋを当てはめて評価した結果、振幅および位相差は図３に示すようになる。
【００４３】
この際、完成した図３の電極チップの先端形状と、被溶接材のナゲット形成部の温度との組み合わせの推移は、基準の図３▲１▼から開始して電極チップの先端形状が摩耗して平らになる図３▲２▼へ遷移し、必要な電流密度が得られない程度に摩耗が進んで被溶接材Ｗｐのナゲット形成部の温度が低下する図３▲３▼へと変遷すると考えられる。この▲１▼→▲２▼→▲３▼の状態遷移が通常の溶接作業時における径時変化に対応したものとなる。
【００４４】
一方、電極チップの先端の摩耗が進んでいない場合であったとしても、通電電流が不足すると、電流密度が低下して被溶接材Ｗｐのナゲット形成部の温度が下がる。このとき、通電電流不足により外力(電磁力)も低下するのに伴なって振幅が「小」となる点で他の▲１▼〜▲３▼の状態とは異なる。したがって、この▲４▼の状態は通常の溶接作業時における径時変化とは無関係に発生する。
【００４５】
上記のようにして求めた振幅および位相差の各推移を平面座標上(二次元マップ上)にプロットすると、図４(ａ)に示す軌跡を描いて、溶接不良の発生に至ると推測され、▲１▼から▲２▼への遷移時においては、▲１▼および▲２▼を往復しながら、次第に▲２▼へ遷移する傾向にある。
【００４６】
なお、実際の溶接現場では、偶発的な溶接電流Ｉｗの低下以外にも加圧力Ｆｐの低下が溶接不良を引き起こす要因として挙げられる。この場合、加圧力Ｆｐの低下は、被溶接材Ｗｐへの電極チップ１５の食い込み量が浅くなるために図３▲２▼と等価な状態になると考えられ、したがって、検出した振幅および位相差の座標が図４(ａ)のどの位置にあるかを評価することで、溶接の良否を含む溶接状態を推定することができる。
【００４７】
図５は、本発明に係わるスポット溶接のモニタリング方法およびモニタリング装置の一実施例を示している。
【００４８】
図５に示すように、スポット溶接機１０は、シリンダロッドに加圧軸１７を一体的に設けたエアシリンダ１９と、このエアシリンダ１９に電機絶縁体１４を介して結合された溶接ガンアーム１８と、加圧軸１７と溶接ガンアーム１８に設けられて互いに対向する電極チップ１５，１６を備えており、図示しない重ね合わせた２枚の被溶接材を電極チップ１５，１６で挟んで加圧し、通電による抵抗加熱で両被溶接材を溶着させるものとなっている。加圧軸１７はエアシリンダ１９により空気圧で加圧駆動されるようになっており、他方のガンアーム１８は、少なくとも溶接時において固定状態となっている。
【００４９】
上記スポット溶接機１０は、両電極チップ１５，１６に対する溶接電流、通電時間（サイクル数）および通電角が、溶接制御装置１１で制御され、その出力である１次電流を溶接トランス１２において溶接に必要な電流Ｉｗまで増幅させる。この場合、加圧軸１７、溶接ガンアーム１８、両電極チップ１５，１６および図示しない被溶接材で溶接電流回路が構成される。なお、電極チップ１５，１６の断続的機械減衰振動を検出するための振動センサ２０は、例えば圧電素子を用いた加速度センサを適用し、溶接する際に被溶接材と干渉せず、かつ、電極チップ部分の振動を適切な感度で検出可能な位置にブラケットを用いるか、または直接接着して取り付ける。
【００５０】
上記のスポット溶接機１０を用いて行うスポット溶接のモニタリング装置２１は、電極間電圧Ｖｅを入力して通電タイミング信号φｃを生成する通電角検出回路２１１と、上記振動センサ２０の検出信号Ｖｓを入力してこの検出信号Ｖｓから不必要な周波数成分の除去を行うと共に同検出信号Ｖｓを後段の回路に適正な信号レベルまで増幅させた検出振動信号Ｖｍを出力する振動検出回路２１２と、振動振幅検出回路（振動振幅検出手段）２１３と、振動位相差検出回路（振動位相差検出手段）２１４と、良否判定基準座標設定回路（良否判定基準領域設定手段）２１５と、溶接良否判定回路（溶接良否判定手段）２１６と、電極摩耗判定回路（電極摩耗判定手段）２１７と、判定しきい値調整回路（判定しきい値調整手段）２１８を備えている。
【００５１】
この場合、図８のタイミングチャートに示すように、電極間電圧Ｖｅ（２）は、スポット溶接機１０の通電経路のインダクタンスにより溶接電流Ｉｗ（１）を微分した波形として検出され、この実施例に係わる通電角検出回路２１１では、簡単かつ安価でしかも時間分解能に優れた電極間電圧Ｖｅを検出し、その急峻な電圧変化点のみで細いパルス信号が出るように処理して通電タイミング信号φｃを生成出力している。この際、細いパルス信号の生成には、ハイパスフィルタを適用でき、このようにして得られた細いパルス信号は、はじめの信号Ｐｏが通電開始時期（以下、点弧）に対応し、次の信号Ｐｃが通電停止時期（以下、消弧）に対応して、後段における振動位相差の算出時の基準タイミング信号として使用される。
【００５２】
また、振動振幅検出回路２１３では、入力された振動検出回路２１２からの検出振動信号Ｖｍに基づいて振動振幅値Ａｖを計測して振幅信号Ｊａを出力し、一方、振動位相差検出回路２１４では、入力された通電タイミング信号φｃおよび検出振動信号Ｖｍの位相差ｄθを計測して振動位相差信号Ｊｐを出力するようになっている。
【００５３】
さらに、良否判定基準座標設定回路２１５は、スポット溶接の良否判定の際の判定基準座標Ｊｃを振幅軸およびこれと直交する位相差軸で定められる二次元マップ上に設定出力するものであり、溶接良否判定回路２１６では、良否判定基準座標設定回路２１５が出力する判定基準座標Ｊｃに振動位相差信号Ｊｐおよび振幅信号Ｊａを照らし合わせて溶接良否を判定して判定信号Ｓｊを出力するようになっている。
【００５４】
さらにまた、電極摩耗判定回路２１７では、振動振幅信号Ｊａと電極摩耗判定基準値Ｓｅ’とを比較して電極チップの先端が摩耗したことを判定して、電極摩耗判定信号Ｓｄを出力するようになっており、判定しきい値調整回路２１８では、電極摩耗判定信号Ｓｄを入力し、その電極摩耗判定信号Ｓｄが電極摩耗を示した際に、電極摩耗判定基準値Ｓｅを電極摩耗検知後に設定すべき値に調整するようになっている。
【００５５】
上記モニタリング装置２１の基本処理手順を図６のフローチャートに基づいて説明する。
【００５６】
まず、ステップＳ１において、図５に示すモニタリング装置２１に外部から入力された振幅しきい値Ｓｙ１，Ｓｙ２および位相しきい値Ｓｘに基づいて、図４(ｂ)に示すように、良否判定基準座標を設定する、すなわち、二次元マップ上に、新品電極で溶接した場合のＯＫ領域▲１▼，電極摩耗が進行した場合のＯＫ領域▲２▼，ＮＧ領域▲３▼および通電不良領域▲４▼を設定し、ステップＳ２において、通電タイミング信号φｃを読み込んで溶接電流の通電タイミングを測定し、ステップＳ３において、検出振動信号Ｖｍの振幅Ａｖを測定し、この際、溶接電流の少なくとも１サイクル以上の平均振幅値Ｊａを求め、以降の良否判定において安定した判定結果が得られるようにする。
【００５７】
次に、ステップＳ４において、通電タイミング信号φｃと検出振動信号Ｖｍとを読み込んで、両者の振動位相差ｄθを測定し(図１(ａ)の波形グラフ参照)、この際、溶接電流の少なくとも１サイクル以上の平均位相差Ｊｐを求め、以降の良否判定において安定した判定結果が得られるようにする。
【００５８】
そして、ステップＳ５において、ステップＳ１で設定した良否判定基準座標上に対してステップＳ３，Ｓ４で測定した平均振幅値Ｊａおよび平均位相差Ｊｐの各座標を照合し、まず、ステップＳ６において、平均振幅値Ｊａと振幅しきい値Ｓｙ２とを比較して、平均振幅値Ｊａが通電不良等による溶接不良を起こしているか否かを判定し、振幅しきい値Ｓｙ２＜平均振幅値Ｊａである場合（Ｙｅｓ）は通電不良等による溶接不良を起こしていないと判定して、すなわち、通電不良領域▲４▼にはないと判定して、ステップＳ７に進み、一方、振幅しきい値Ｓｙ２≧平均振幅値Ｊａである場合（Ｎｏ）は通電不良等による溶接不良を起こしていると判定して、すなわち、通電不良領域▲４▼にあると判定して、ステップＳ９において、溶接不良の判定結果を出力する。
【００５９】
次いで、ステップＳ７において、平均振幅値Ｊａおよび平均位相差Ｊｐの各座標がＮＧ領域▲３▼にあるか否かを判定し、この際、振幅しきい値Ｓｙ１≦平均振幅値Ｊａでかつ位相しきい値Ｓｘ≧平均位相差Ｊｐである場合（Ｙｅｓ）はＮＧ領域▲３▼にあると判定して、ステップＳ９において、溶接不良の判定結果を出力し、一方、それ以外である場合（Ｎｏ）はＯＫ領域▲１▼，▲２▼にあると判定し、ステップＳ８において、溶接良好の判定結果を出力する。
【００６０】
次に、電極チップの摩耗判定の処理を開始する。ここで、電極チップ摩耗判定の判定基準値には、図７に示すように、電極チップ摩耗の履歴状態に応じて二通りの値があり、一方は、新品電極あるいは電極先端を新品同様に研磨整形した場合に適用される電極摩耗判定基準値Ｓｅ’(Ｈ)であり、他方は、一旦電極摩耗と判定されてから次の新品電極への交換あるいは電極先端の整形までに適用される電極摩耗判定基準値Ｓｅ’(Ｌ)である。
【００６１】
そこで、まず、ステップＳ１０において、前回の判定で電極チップ摩耗の有無を調べ、既に電極チップ摩耗があった場合（Ｙｅｓ）は、ステップＳ１１において、外部から入力された電極摩耗判定基準値Ｓｅに予め定めた調整係数Ｈを乗じた値を新しい電極摩耗判定基準値Ｓｅ’(Ｌ)とし、一方、電極チップ摩耗がないと判定された場合（Ｎｏ）は、ステップＳ１２において、外部から入力された電極摩耗判定基準値Ｓｅをそのまま電極摩耗判定基準値Ｓｅ’(Ｈ)とする。
【００６２】
次に、ステップＳ１３において、平均振幅値Ｊａと電極摩耗判定基準値Ｓｅ’とを比較し、電極摩耗判定基準値Ｓｅ’＜平均振幅値Ｊａである場合（Ｙｅｓ）は、ステップＳ１４において、電極摩耗と判定し、電極摩耗判定基準値Ｓｅ’≧平均振幅値Ｊａである場合（Ｎｏ）は、ステップＳ１５において、未だ電極チップが摩耗していないと判定する。
【００６３】
以上で一回の溶接における良否判定処理を完了する。なお、続けて次の溶接に備えるために、ステップＳ１４，Ｓ１５からステップＳ２に戻り、次の溶接における新しい振動情報に基づいて上記一連の処理が継続される。
【００６４】
上記したように、この実施例に係わるモニタリング装置２１によれば、通電時の電磁力を加振源とした大振幅の断続的機械減衰振動を検出対象としていることから、信号検出に高度な信号抽出技術を必要とすることなく、金属溶融振動を容易に信号検出することができ、その結果、スポット溶接の良否判定を確実に行うことが可能である。
【００６５】
また、表面コーティング層の溶解振動を検出対象としていないため、様々な鋼材に適用することが可能であり、したがって、スポット溶接の良否モニタリングの適用範囲拡大を促進することが可能であり、加えて、振動振幅値Ｊａおよび位相差Ｊｐの２つの変数を用いて良否の判定を行うため、電極チップの先端形状や溶接電流や加圧力変動が複合的に作用した場合でも、適正に良否判定を行うことができる。
【００６６】
さらに、上記したモニタリング装置２１によれば、電極チップの先端の摩耗具合と相関の高い振動振幅値Ｊａと所定の電極摩耗判定しきい値Ｓｅとを比較することで摩耗検知を行うことができ、加えて、電極摩耗判定後にしきい値Ｓｅを変更することで、信頼性の低下および電極摩耗の見逃しを防止することができる。
【００６７】
図９は、本発明に係わるスポット溶接のモニタリング方法およびモニタリング装置の他の実施例を示している。
【００６８】
図９に示すように、この実施例のモニタリング装置２１’は、電極間電圧Ｖｅを入力して通電タイミング信号φｃを生成する通電角検出回路２１１と、上記振動センサ２０の検出信号Ｖｓを入力してこの検出信号Ｖｓから不必要な周波数成分の除去を行うと共に同検出信号Ｖｓを後段の回路に適正な信号レベルまで増幅させた検出振動信号Ｖｍを出力する振動検出回路２１２と、通電タイミング信号φｃおよび検出振動信号Ｖｍを入力すると共に両信号の位相差ｄθを計測して、前回の位相差に対する変化量を算出して位相変化量信号ΔＪｐを出力する位相変化量検出回路（位相変化量検出手段）２２０と、その位相変化量が所定値以上であった場合にのみその位相変化量を積算して位相差積算信号ΣΔＪｐを出力する位相差積算回路（位相差変化量積算手段）２２１と、外部から入力される溶接不良判定基準値Ｊｂと位相差積算信号ΣΔＪｐとを比較して溶接不良検出信号Ｓｂを出力する溶接不良検出回路（溶接不良検出手段）２２２を備えている。
【００６９】
上記モニタリング装置２１’の基本処理手順を図１０のフローチャートに基づいて説明する。
【００７０】
まず、ステップＳ２１において、図９に示すモニタリング装置２１’に外部から入力された溶接不良判定基準値Ｊｂを設定し、ステップＳ２２において、通電タイミング信号φｃを読み込んで溶接電流の通電タイミングを測定し、ステップＳ２３において、通電タイミング信号φｃと検出振動信号Ｖｍとを読み込んで、両者の振動位相差ｄθを測定し(図１(ａ)の波形グラフ参照)、ステップＳ２４において、数３に示すように、前回の溶接時における振動位相差ｄθに対する変化量を算出して位相変化量信号ΔＪｐを出力する。
【００７１】
【数３】

【００７２】
続いて、ステップＳ２５において、予め求めておいた不感幅Ｃと位相変化量信号ΔＪｐとを比較して、Ｃ≧ΔＪｐである場合（Ｎｏ）は、溶接状態が前回とほぼ同様に良好であると判定し、一方、Ｃ＜ΔＪｐである場合（Ｙｅｓ）は、溶接状態に変化があったと判定して次に進み、合わせて、ステップＳ２６において、その位相変化量信号ΔＪｐの極性が負(０＜ΔＪｐ)である場合（Ｙｅｓ）は、溶接が不良の方向へ変化したと判定し、ステップＳ２７において、その負の位相変化量信号ΔＪｐを前回までの位相変化量信号ΔＪｐに積算して位相差積算信号ΣΔＪｐを得る。
【００７３】
次に、ステップＳ２８において、位相差積算信号ΣΔＪｐとステップＳ２１で設定した溶接不良判定基準値Ｊｂとを比較し、溶接不良判定基準値Ｊｂ＜位相差積算信号ΣΔＪｐである場合（Ｙｅｓ）には、溶接不良に至ったことを検出して、ステップＳ２９において、溶接不良検出信号Ｓｂを出力し、一方、溶接不良判定基準値Ｊｂ≧位相差積算信号ΣΔＪｐである（Ｎｏ）には、溶接状態が不良発生の方向にあるものの不良発生には至っていないと判定し、溶接不良検出信号Ｓｂは出力しない。
【００７４】
以上で一回の溶接における良否判定処理を完了する。なお、続けて次の溶接に備えるために、ステップＳ２９からステップＳ２２に戻り、次の溶接における新しい振動情報に基づいて上記一連の処理が継続される。
【００７５】
上記したように、この実施例に係わるモニタリング装置２１’によれば、ナゲット径の生成と相関の高い位相変化量と、その発生回数とを積算するといった簡単な演算によって、スポット溶接の良否判定を行うことができる。
【００７６】
図１２は、本発明に係わるスポット溶接のモニタリング方法およびモニタリング装置のさらに他の実施例を示している。
【００７７】
図１２に示すように、この実施例によるモニタリング方法およびモニタリング装置２１’’が図５に示すモニタリング方法およびモニタリング装置２１と相違するところは、振動位相差の替わりに振動減衰指標をパラメータとした点にあり、他の構成は図５に示すモニタリング方法およびモニタリング装置２１とおなじである。
【００７８】
すなわち、このモニタリング装置２１’’は、通電角検出回路２１１からの通電タイミング信号φｃと振動検出回路２１２からの検出振動信号Ｖｍとを入力して、図１３に示すように、通電０．５サイクル期間（＝Ｔ）における振動波形の正側振幅値を積分した減衰振動積分信号∫Ｖｍおよびその同一期間（＝Ｔ）内の最大振動振幅Ｖｐを同期間で積分した最大振幅積分信号∫Ｖｐを算出して出力する振動振幅積分回路（振動振幅積分手段）２３０と、減衰振動積分信号∫Ｖｍと最大振幅積分信号∫Ｖｐとの比を計算して振動減衰指標を求めると共に位相差信号Ｊｐに置換する減衰指標算出回路（減衰指標算出手段）２３１を備えている。
【００７９】
次に、このモニタリング装置２１’’の動作を説明する。ここでは、振動振幅積分回路２３０と減衰指標算出回路２３１の動作を計算式で説明し、良否判定手順に関する動作説明は、図６のフローチャートにおいて対応する処理ステップのみ示し、全体の説明は省略する。
【００８０】
まず、振動振幅積分回路２３０の減衰振動積分信号∫Ｖｍおよび最大振幅積分信号∫Ｖｐの計算式は、数４および数５で表される。
【００８１】
【数４】

【００８２】
【数５】

【００８３】
また、減衰指標算出回路２３１の減衰指標Ｉｄ（Ｊｐ）の計算式は、数６で表される。
【００８４】
【数６】

【００８５】
この際、対応する良否判定処理手順のステップは、図６のフローチャートにおけるステップ４の「位相差Ｊｐの測定」であり、この「位相差Ｊｐの測定」に替えて数４，数５および数６の演算処理がなされて良否判定が実行される。
【００８６】
なお、減衰振動積分信号∫Ｖｍの正側振幅についての具体的な説明は省いたが、例えば、交流信号の測定に用いられる一般的な整流回路にて実現できることを補足しておく。
【００８７】
上記したように、この実施例に係わるモニタリング装置２１’’によれば、複雑な振動波形であったとしても、その振動の減衰度合いを示す指標としての実用的な値を簡単に求めることができ、より一層信頼性の高い良否の判定を安定して行うことが可能である。
【００８８】
最後に、本発明に係わるスポット溶接のモニタリング方法およびモニタリング装置による良否判定を板厚０．８ｍｍの溶融合金化亜鉛めっき鋼板の２枚重ね溶接において適用した結果の一例を図２(ｂ)に示す。この例では、２枚の鋼板が溶着していない、いわゆる、剥がれに至る溶接不良を検出するように良否判定基準値を定めたものである。当然ながら、溶接不良には溶着があっても、そのナゲット径が合格値に達しないものもあることから、このような不良を検出するためには、振幅しきい値Ｓｙ１と、位相しきい値Ｓｘを加減することで可能となる。
【００８９】
なお、本発明に係わるスポット溶接のモニタリング方法およびモニタリング装置は、その構成が上記各実施例のみに限定されるものではなく、種々の変形実施が可能である。
【図面の簡単な説明】
【図１】本発明に係わるスポット溶接の原理を示す説明図（ａ）および溶接打点数に対する振動位相差，振幅値およびナゲット径の関係を示すグラフ（ｂ）である。
【図２】振幅軸およびこれと直交する位相差軸で定められる判定基準座標上における電極チップ先端形状の状態遷移を示すグラフ（ａ）および本発明に係わるスポット溶接のモニタリング方法およびモニタリング装置による良否判定を板厚０．８ｍｍの溶融合金化亜鉛めっき鋼板の２枚重ね溶接において適用した結果を示すグラフ（ｂ）である。
【図３】溶接部分における物理現象を説明する図である。
【図４】振幅および位相差の各推移を二次元マップ上にプロットした説明図（ａ）および二次元マップ上に設定した良否判定の判定基準領域を説明する図（ｂ）である。
【図５】本発明に係わるスポット溶接のモニタリング装置の一実施例を説明する基本ブロック図である。
【図６】本発明に係わるスポット溶接のモニタリング装置による基本的な処理手順を説明するフローチャートである。
【図７】電極摩耗判定手段を説明するグラフである。
【図８】通電タイミングを検出する手段を説明するタイミングチャートである。
【図９】本発明に係わるスポット溶接のモニタリング装置の他の実施例を説明する基本ブロック図である。
【図１０】図９に示したスポット溶接のモニタリング装置による基本的な処理手順を説明するフローチャートである。
【図１１】ナゲット径の減少と位相差の変化との間の相関関係を説明するグラフである。
【図１２】本発明に係わるスポット溶接のモニタリング装置のさらに他の実施例を説明する基本ブロック図である。
【図１３】振動波形の減衰指標を求める方法を説明する図である。
【符号の説明】
１０ スポット溶接機
２１，２１’，２１’’ モニタリング装置
２１３ 振動振幅検出回路（振動振幅検出手段）
２１４ 振動位相差検出回路（振動位相差検出手段）
２１５ 良否判定基準座標設定回路（良否判定基準領域設定手段）
２１６ 溶接良否判定回路（溶接良否判定手段）
２１７ 電極摩耗判定回路（電極摩耗判定手段）
２１８ 判定しきい値調整回路（判定しきい値調整手段）
２２０ 位相変化量検出回路（位相変化量検出手段）
２２１ 位相差積算回路（位相差変化量積算手段）
２２２ 溶接不良検出回路（溶接不良検出手段）
２３０ 振動振幅積分回路（振動振幅積分手段）
２３１ 減衰指標算出回路（減衰指標算出手段）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spot welding monitoring method and a monitoring device used for determining whether a welding state is good or not in spot welding for joining welded materials such as various steel plates.
[0002]
[Prior art]
At present, spot welding is widely used for welding steel sheets in various products using steel sheets. Conventionally, in these products, since mild steel sheets have been used as materials to be welded, there are few welding defects, and it has been possible to maintain welding quality relatively stably by managing predetermined welding conditions. However, in recent years, difficult-to-weld materials such as hot-dip galvanized steel sheets with enhanced rust prevention performance have been mainly used as welded materials, and this has led to wear of electrode tips of spot welders. Due to the occurrence of poor welding, there is a problem that it is difficult to manage the welding quality. Therefore, in spot welding, it is necessary to manage not only the welding conditions to be constant but also the quality of the nugget at each hit point with high accuracy.
[0003]
Therefore, various monitoring devices have been proposed to control the quality of the nugget. For example, it can be applied to in-process monitoring of all welding points that are particularly demanding on the production line. There has been a monitoring method for determining whether or not spot welding is good by focusing on the vibration phenomenon. (Japanese Patent Application Nos. 11-352790 and 11-353915)
[0004]
[Problems to be solved by the invention]
However, in spot welding monitoring methods that determine the quality of spot welding based on vibrations that occur during welding, depending on the type and structure of the spot welder, the vibration caused by the metal melting condition may become the mechanical vibration of the spot welder. It may be buried and it may be difficult to judge good or bad. For example, in a spot welder having a saddle-shaped arm generally called a C-type gun, the arm rigidity is low, so that the amplitude of mechanical vibration caused by electromagnetic force acting on the arm portion and electrode tip with energization increases. Become. This mechanical vibration becomes an intermittent vibration accompanied by attenuation synchronized with a frequency twice as large as the energization current frequency. For this reason, it may be difficult for the vibration to be evaluated for pass / fail judgment, that is, the vibration caused by the metal melting state to be buried in the mechanical intermittent vibration of the spot welder and make the pass / fail judgment. There is a problem, and it has been a conventional problem to solve this problem.
[0005]
OBJECT OF THE INVENTION
The present invention has been made in view of the above-described conventional situation. For example, a low-rigidity AC spot welder such as a C-type gun is used to determine whether or not spot welding is good based on vibrations generated during welding. Even if it is, it aims at providing the monitoring method and monitoring apparatus of the spot welding which can perform the quality determination of the stable spot welding.
[0006]
[Means for Solving the Problems]
The spot welding monitoring method according to claim 1 of the present invention generates an electromagnetic force as an excitation source when an AC welding current is applied when performing spot welding quality determination based on vibrations generated during welding. The amplitude value of intermittent mechanically damped vibration in the electrode part of the spot welder is detected, and the phase difference between the AC welding current and intermittent mechanically damped vibration is detected, and is determined by the amplitude axis and the phase difference axis orthogonal thereto. It is configured to set a pass / fail judgment reference area on the two-dimensional map and perform spot welding pass / fail judgment based on the detected amplitude value and phase difference position on the two-dimensional map. As a means to solve the problem.
[0007]
The spot welding monitoring apparatus according to claim 2 of the present invention sets two amplitude threshold values on the amplitude axis and sets one phase difference threshold value on the phase difference axis, and displays it on a two-dimensional map. The following four criteria areas are set: welding good area, welding failure attention area, welding failure area, and welding energization failure area, and the amplitude value of intermittent mechanical damping vibration and the phase difference between AC welding current and intermittent mechanical damping vibration. Is characterized in that the quality of spot welding is judged according to which of the good welding region, the poor welding attention region, the poor welding region, and the poor welding energization region on the two-dimensional map.
[0008]
The spot welding monitoring method according to claim 3 of the present invention is characterized in that the amplitude axis and phase difference axis of the two-dimensional map are set based on the initial amplitude value and initial phase difference at the start of welding.
[0009]
In the spot welding monitoring method according to claim 4 of the present invention, electrode wear is determined when the detected amplitude value of intermittent mechanical damping vibration exceeds a preset electrode wear determination threshold value, and the electrode wear is determined. At this stage, the electrode wear determination threshold value is changed to a value lower than the amplitude fluctuation range of the wear electrode and higher than the amplitude value at the time of a new electrode.
[0010]
The spot welding monitoring method according to claim 5 of the present invention generates an electromagnetic force as an excitation source when an AC welding current is applied when performing spot welding quality determination based on vibrations generated during welding. The phase difference between the intermittent mechanical damping vibration and the AC welding current in the electrode part of the spot welder is detected, and the amount of change is calculated by subtracting the phase difference for this time from the phase difference for the previous time. The amount of change is integrated only when the value is greater than or equal to a predetermined value and the polarity is negative, and when the integrated value falls below a preset pass / fail judgment threshold, it is determined that welding is defective.
[0011]
The spot welding monitoring method according to claim 6 of the present invention generates an electromagnetic force as an excitation source when an AC welding current is applied when performing spot welding quality determination based on vibration generated during welding. Detects the amplitude value of intermittent mechanically damped vibration at the electrode part of the spot welder. As well as Integrating the positive-side amplitude value in the vibration waveform between intermittent periods of continuous mechanically damped vibration and dividing the integration result by the product of maximum positive-side amplitude value and period as an index of the amount of intermittent mechanically damped vibration Calculate the attenuation index The phase difference is replaced, and a pass / fail judgment criterion region is set on the two-dimensional map defined by the amplitude axis and the phase difference axis orthogonal thereto, and the phase difference replaced from the detected amplitude value and vibration attenuation index is set. Based on the position on the 2D map It is characterized in that the quality of pot welding is judged.
[0012]
On the other hand, in the spot welding monitoring apparatus according to claim 7 of the present invention, resistance welding is performed by applying an AC welding current to both electrode tips while pressing the overlapped workpieces (steel plates) with a pair of electrode tips. In spot welding where two workpieces are welded together, a vibration sensor attached to an electrode tip or a gun arm in the vicinity thereof for detecting vibrations generated during welding, and an electrode portion of a spot welder detected by the vibration sensor Vibration amplitude detecting means for detecting the amplitude value of intermittent mechanically damped vibration, vibration phase difference detecting means for detecting a phase difference (delay time) between AC welding current and intermittent mechanically damped vibration, and determination criterion region for pass / fail judgment Is set on a two-dimensional map defined by an amplitude axis and a phase difference axis orthogonal to the amplitude axis, and the detected amplitude value and phase In order to solve the conventional problems described above, the configuration of the spot welding monitoring device is provided with a welding pass / fail judgment means for judging the pass / fail of the nugget formed at the spot welded location in light of the two-dimensional map. As a means of.
[0013]
In the spot welding monitoring apparatus according to claim 8 of the present invention, the pass / fail judgment reference region setting means sets two amplitude threshold values on the amplitude axis and one phase difference threshold value on the phase difference axis. Set and set four determination reference areas, a good welding area, a poor welding attention area, a poor welding area, and a poor welding energization area, on the two-dimensional map, and the welding quality determination means uses the amplitude detected by the vibration amplitude detection means. The quality of spot welding is determined by whether the phase difference detected by the value and the vibration phase difference detection means belongs to the good welding region, the poor welding attention region, the poor welding region, or the poor welding current region on the two-dimensional map. It is characterized by having a configuration for performing.
[0014]
In the spot welding monitoring apparatus according to claim 9 of the present invention, the amplitude axis and the phase difference axis of the two-dimensional map are set based on the initial amplitude value and the initial phase difference at the start of welding. It is a feature.
[0015]
The spot welding monitoring apparatus according to claim 10 of the present invention determines electrode wear when the amplitude value of the intermittent mechanical damping vibration detected by the vibration amplitude detecting means exceeds a preset electrode wear determination threshold value. Electrode wear determination means, and determination to change the electrode wear determination threshold value to a value that is lower than the amplitude fluctuation range of the wear electrode and higher than the amplitude value at the time of a new electrode when it is determined as electrode wear by the electrode wear determination means It is characterized by having a configuration including a threshold value adjusting means.
[0016]
The spot welding monitoring apparatus according to claim 11 of the present invention reduces the nugget diameter {Dn (1) to Dn (4)} as shown in FIG. And the change in phase difference {Jp (1) to Jp (4)}, with a correlation between them, and when an AC welding current is applied, electromagnetic force is generated as an excitation source Vibration phase difference detection means for detecting the phase difference between intermittent mechanically damped vibration and AC welding current in the electrode part of the spot welding machine, and the current phase from the previous phase difference detected by the vibration phase difference detection means. Phase change amount detection means that calculates the amount of change by subtracting the phase difference, and phase difference change amount integration that integrates the change amount only when the change amount detected by the phase change amount detection means is greater than or equal to a predetermined value and the polarity is negative And the phase difference change amount integrating means The present invention is characterized in that a welding failure detection means for determining a welding failure when the amount of change made falls below a preset pass / fail judgment threshold value is provided.
[0017]
According to a twelfth aspect of the present invention, in a spot welding monitoring device for determining whether or not spot welding is good based on vibrations generated during welding, an electromagnetic force is generated as an excitation source when an AC welding current is applied. Vibration amplitude detecting means for detecting the amplitude value of intermittent mechanically damped vibration in the electrode portion of the spot welder, and vibration amplitude integrating means for integrating the positive amplitude value in the vibration waveform during the intermittent period of intermittent mechanically damped vibration; By dividing the integration result by the vibration amplitude integration means by the product of the maximum positive amplitude value and the period, a damping index is calculated as an index of the amount of intermittent mechanical damping vibration. And replace with phase difference An attenuation index calculating means, and a pass / fail judgment reference area setting means for setting a pass / fail judgment reference area on a two-dimensional map defined by an amplitude axis and a phase difference axis orthogonal thereto. , Based on the detected amplitude value and the position on the two-dimensional map of the phase difference replaced from the vibration damping index It is characterized by having a configuration including a welding quality determination means for determining quality of spot welding.
[0018]
【The invention's effect】
According to the first and seventh aspects of the invention, when determining the quality of spot welding based on vibrations generated during welding, for example, in a low-rigidity AC spot welder, it corresponds to the nugget formation situation. Even if the metal melting vibration is buried in the mechanical vibration of the spot welder and cannot be detected easily, it detects the large amplitude intermittent mechanical damping vibration using the electromagnetic force during energization as the excitation source. Further, it is possible to easily detect a metal melting vibration without requiring an advanced signal extraction technique for signal detection, and it is possible to reliably determine whether or not spot welding is good.
[0019]
In addition, since the dissolution vibration of the surface coating layer is not targeted for detection, it can be applied to various steel materials, that is, it is possible to promote the expansion of the application range of spot welding quality monitoring. Since the pass / fail judgment is performed using the two variables of the amplitude value and the phase difference, the pass / fail judgment can be properly performed even when the tip shape of the electrode tip, the welding current, and the pressure fluctuation are combined. This is a very good effect.
[0020]
According to the invention described in claim 2 and claim 8, since it has the above-described configuration, the same effect as that of the invention described in claims 1 and 7 can be obtained, and the threshold value can be easily determined. Therefore, it is possible to obtain an excellent effect that it is possible to make an absolute pass / fail judgment, predict the progress of electrode wear, and make it possible to determine a welding failure due to an unexpected current drop.
[0021]
According to the invention described in claim 3 and claim 9, since it is configured as described above, the same effects as those of the invention described in claims 1, 2 and 7, 8 can be obtained, and various types can be obtained. Therefore, it is possible to cope with the above welding conditions.
[0022]
According to the fourth and tenth aspects of the invention, since the above-described configuration is adopted, the vibration amplitude value having a high correlation with the wear condition of the tip of the electrode tip is compared with a predetermined electrode wear determination threshold value. It is possible to detect wear with high accuracy, and in addition, by changing the threshold value after electrode wear determination, it is possible to prevent a drop in reliability and oversight of electrode wear, and at the time of electrode shaping or The electrode wear alarm can be automatically canceled at the time of electrode replacement, which is an excellent effect.
[0023]
According to the invention described in claim 5 and claim 11, since it has the above-described configuration, spot welding is performed by a simple calculation such as integrating the amount of phase change highly correlated with generation of the nugget diameter and the number of occurrences thereof. It is possible to obtain a very excellent effect of being able to make a pass / fail judgment.
[0024]
According to the sixth and twelfth aspects of the present invention, since the above-described configuration is adopted, even if the vibration waveform is complicated, a practical value as an index indicating the degree of attenuation of the vibration is easily obtained. Therefore, it is possible to obtain a very excellent effect that it is possible to perform the determination of pass / fail with higher reliability stably.
[0025]
【Example】
Hereinafter, a spot welding monitoring method and monitoring apparatus according to the present invention will be described with reference to the drawings.
[0026]
First, the basic principle of pass / fail determination according to the present invention will be described. FIG. 1A shows an example of a basic configuration of a spot welding monitoring apparatus according to the present invention and an example of a vibration waveform of an electrode tip portion detected during energization. In the figure, reference numeral 10 is a spot welder, 11 is a welding control device, and 12 is a welding transformer. It can be seen that the mechanical vibration Vs detected with respect to the welding current waveform Iw has a vibration phase difference (delay time) dθ. Further, when the vibration phase difference dθ is seen in the transition when continuous welding is performed until the welding failure (round frame) occurs with the same electrode tip, as shown in FIG. 1B, the minimum acceptable nugget diameter Dn is obtained. A characteristic that monotonously increases up to about 1100 times, which is the first time, is observed, and when the welding failure (round frame) occurs, a characteristic that decreases conversely is observed. Furthermore, the tendency that the vibration amplitude value Av also increases monotonously is observed.
[0027]
When these transitions of the vibration phase difference dθ and the vibration amplitude value Av are plotted on a plane coordinate (on a two-dimensional map), the locus of the coordinate point is approximately ▲ as shown in FIG. It turned out that it changed with 1 ▼ → ▲ 2 ▼ → ▲ 3 ▼.
[0028]
Here, (1) corresponds to an OK region plotted when a pass nugget diameter is generated by welding with a new electrode, and (2) indicates an OK region plotted when electrode wear progresses. Corresponding (3) corresponds to an NG region plotted when welding failure occurs. In addition, (4) is an energization failure area, and it was found that this area is plotted in an experiment assuming a decrease in energization current when the power supply of the welding power source is insufficient.
[0029]
The present invention focuses on the coordinate points of the vibration phase difference dθ and the vibration amplitude value Av, and the coordinates of the vibration phase difference dθ and the vibration amplitude value Av of the mechanical vibration Vs of the electrode tip portion with respect to the welding current waveform Iw. By monitoring the points, welding defects are detected.
[0030]
The index of the axis of the vibration phase difference dθ in FIG. 1A is obtained by normalizing the vibration phase difference angle (deg) with one cycle (360 deg) of the square wave of the welding current. The vibration amplitude value Av is the average value of the maximum vibration amplitude values Av for each half cycle (180 deg) as the vibration amplitude value Av at the hit point. Furthermore, the X-axis (phase axis) and Y-axis (amplitude axis) in FIG. 2A are normalized with the coordinates when a new electrode can be satisfactorily welded.
[0031]
Here, considering the mechanism of the coordinate locus of the vibration amplitude value Av and the vibration phase difference dθ, FIG. 3 shows the temperature change in the nugget forming portion of the material to be welded, the change in the tip shape of the electrode tip, and the welding point associated therewith. It is quite complicated to represent the actual physical phenomenon when the welding state is “good” and “bad”, and the irregularity factor. Is considered to be a macrophysical phenomenon in an ideal simple model.
[0032]
First, the mechanical elements that act on the electrode tip portion during welding will be briefly described. The electrode tip 15 is strongly subjected to the pressure Fp applied by the pressure cylinder. An electromagnetic force induced by energization of the welding current Iw serves as an excitation source for the electrode tip 15, and an X-axis direction (Fmx) perpendicular to the axis of the electrode tip 15 and a Z-axis direction (Fmz) along the axis. A pulsating force is applied at a frequency twice the welding current Iw. And the molten pool of nugget diameter (melting diameter) Dn is formed in the to-be-welded material Wp by resistance heating. In addition, the electrode tip 15 bites into the workpiece Wp with the applied pressure Fp, and keeps a balance between the rigidity of the workpiece Wp, the combined force of the internal pressure of the molten pool, and the applied pressure Fp.
[0033]
Therefore, how the state changes in the case of poor welding is determined by using typical mechanical parameters of the electrode portion. The new electrode tip 15 causes the temperature of the welded material Wp to reach a sufficiently high temperature necessary for welding. The viscosity damping coefficient C and spring constant K modeled at this time are expressed as temperature functions C (t) and K (t) and the tip shape function C of the electrode tip. (s) and K (s) are evaluated.
[0034]
First, in FIG. 3 (1), the tip shape function C (s) of the electrode tip 15 has a deeper bite into the material to be welded Wp because the tip shape of the electrode tip 15 has a dome shape. Since the projected area in the cross-sectional direction of the workpiece Wp that acts as a resistance force increases, it is assumed to be “medium”, while the temperature function C (t) is the nugget formation portion of the workpiece Wp. Is sufficiently dissolved, so it is assumed that the action of the resistance force against the external force is low and is “small”.
[0035]
Next, the function K (s) of the tip shape of the electrode tip has a large projected area in the cross-sectional direction of the material Wp to be welded, similarly to C (s), and its influence is considered to be larger than C (s). On the other hand, the temperature function K (t) is assumed to be “small” because the spring constant is extremely lowered near the metal melting temperature.
[0036]
That is, in FIG. 3 (1), the viscous damping coefficient C and the spring constant K in the nugget forming portion of the workpiece Wp are “C (s, t) = medium” and “K (s, t) = medium”. Assume.
[0037]
Thereafter, when the electrode tip 15 is worn (FIG. 3 (2)) and when the temperature at the nugget forming portion of the material Wp to be welded is lowered due to the decrease in current density caused by the wear of the electrode tip 15 and the enlargement of the current-carrying area. (FIG. 3 (3)) and the temperature at the nugget formation portion of the work piece Wp cannot be ensured due to insufficient energization even when the tip shape of the electrode tip 15 provides a sufficient current density. 3 (4) is evaluated in the same way as described above, it can be seen that FIGS. 3-2 to 4-4 are in a relative magnitude relationship between the viscous damping coefficient C and the spring constant K. Conceivable.
[0038]
Here, general expressions of the vibration amplitude value and the vibration phase difference with respect to the external force (electromagnetic force) having the viscous damping coefficient C and the spring constant K as variables are expressed by the following equations (1) and (2).
[0039]
[Expression 1]

[0040]
[Expression 2]

[0041]
However, m is the mass of the pressurization system, and ω is the natural frequency of the pressurization mechanism part of the welding machine, both of which can be handled as constants.
[0042]
Therefore, as a result of evaluation by applying the assumed viscous damping coefficient C and spring constant K to the above formulas 1 and 2, the amplitude and phase difference are as shown in FIG.
[0043]
At this time, the transition of the combination of the tip shape of the completed electrode tip of FIG. 3 and the temperature of the nugget forming portion of the material to be welded starts from the reference FIG. The transition to Fig. 3 (2), which is flattened, is considered to change to Fig. 3 (3) where the wear progresses to the extent that the required current density cannot be obtained and the temperature of the nugget formation portion of the work piece Wp decreases. It is done. This state transition of (1) → (2) → (3) corresponds to a change with time in a normal welding operation.
[0044]
On the other hand, even if the wear of the tip of the electrode tip has not progressed, if the energization current is insufficient, the current density is lowered and the temperature of the nugget forming portion of the material to be welded Wp is lowered. At this time, it differs from the other states (1) to (3) in that the amplitude becomes “small” as the external force (electromagnetic force) decreases due to insufficient energization current. Therefore, the state of (4) occurs regardless of the change in diameter during normal welding work.
[0045]
When each transition of the amplitude and the phase difference obtained as described above is plotted on a plane coordinate (on a two-dimensional map), it is estimated that a locus shown in FIG. At the time of transition from (1) to (2), there is a tendency to gradually shift to (2) while reciprocating between (1) and (2).
[0046]
In an actual welding site, in addition to the accidental decrease in the welding current Iw, a decrease in the applied pressure Fp is cited as a factor that causes poor welding. In this case, the decrease in the applied pressure Fp is considered to be equivalent to the state shown in FIG. 3 (2) because the amount of the electrode tip 15 biting into the workpiece Wp becomes shallow, and accordingly, the detected amplitude and phase difference are reduced. By evaluating which position in FIG. 4A the coordinates are in, it is possible to estimate the welding state including the quality of the welding.
[0047]
FIG. 5 shows an embodiment of the spot welding monitoring method and monitoring apparatus according to the present invention.
[0048]
As shown in FIG. 5, the spot welder 10 includes an air cylinder 19 integrally provided with a pressure shaft 17 on a cylinder rod, and a welding gun arm 18 coupled to the air cylinder 19 via an electrical insulator 14. The electrode tip 15, 16 is provided on the pressure shaft 17 and the welding gun arm 18 so as to oppose each other, and two stacked materials to be welded (not shown) are sandwiched between the electrode tips 15, 16 to pressurize them. Both the welded materials are welded by resistance heating. The pressure shaft 17 is driven by air pressure by an air cylinder 19 and the other gun arm 18 is fixed at least during welding.
[0049]
In the spot welder 10, the welding current, energization time (number of cycles) and energization angle for both electrode tips 15 and 16 are controlled by the welding control device 11, and the primary current as the output is welded by the welding transformer 12. Amplify to the required current Iw. In this case, a welding current circuit is constituted by the pressurizing shaft 17, the welding gun arm 18, the two electrode tips 15, 16 and the material to be welded (not shown). The vibration sensor 20 for detecting intermittent mechanically damped vibrations of the electrode tips 15 and 16 applies an acceleration sensor using, for example, a piezoelectric element, and does not interfere with the material to be welded when welding. A bracket is used at a position where vibration of the chip portion can be detected with appropriate sensitivity, or it is attached by direct bonding.
[0050]
The spot welding monitoring device 21 using the spot welding machine 10 receives an energization angle detection circuit 211 that inputs an interelectrode voltage Ve and generates an energization timing signal φc, and a detection signal Vs of the vibration sensor 20. A vibration detection circuit 212 that removes unnecessary frequency components from the detection signal Vs and outputs a detection vibration signal Vm obtained by amplifying the detection signal Vs to an appropriate signal level in a subsequent circuit, and vibration amplitude detection Circuit (vibration amplitude detection means) 213, vibration phase difference detection circuit (vibration phase difference detection means) 214, quality determination reference coordinate setting circuit (quality determination reference area setting means) 215, welding quality determination circuit (welding quality determination) Means) 216, an electrode wear determination circuit (electrode wear determination means) 217, and a determination threshold adjustment circuit (determination threshold adjustment means) 218. That.
[0051]
In this case, as shown in the timing chart of FIG. 8, the interelectrode voltage Ve (2) is detected as a waveform obtained by differentiating the welding current Iw (1) by the inductance of the energization path of the spot welder 10, and this example shows The energizing angle detection circuit 211 detects the interelectrode voltage Ve that is simple, inexpensive and excellent in time resolution, and generates an energization timing signal φc by processing so that a thin pulse signal is output only at the steep voltage change point. Output. At this time, a high-pass filter can be applied to generate a thin pulse signal. The thin pulse signal thus obtained corresponds to the first signal Po corresponding to the energization start timing (hereinafter referred to as ignition), and the next signal Pc is used as a reference timing signal at the time of calculation of the vibration phase difference in the subsequent stage, corresponding to the energization stop timing (hereinafter, arc extinction).
[0052]
The vibration amplitude detection circuit 213 measures the vibration amplitude value Av based on the detected vibration signal Vm from the input vibration detection circuit 212 and outputs the amplitude signal Ja, while the vibration phase difference detection circuit 214 The phase difference dθ between the input energization timing signal φc and the detected vibration signal Vm is measured, and the vibration phase difference signal Jp is output.
[0053]
Further, the pass / fail judgment reference coordinate setting circuit 215 sets and outputs the judgment reference coordinate Jc at the time of spot weld pass / fail judgment on a two-dimensional map defined by an amplitude axis and a phase difference axis orthogonal thereto. In the pass / fail judgment circuit 216, the judgment reference coordinate Jc output from the pass / fail judgment reference coordinate setting circuit 215 is compared with the vibration phase difference signal Jp and the amplitude signal Ja to judge the weld pass / fail and output the judgment signal Sj. Yes.
[0054]
Furthermore, the electrode wear determination circuit 217 compares the vibration amplitude signal Ja and the electrode wear determination reference value Se ′ to determine that the tip of the electrode tip has been worn, and outputs an electrode wear determination signal Sd. The determination threshold adjustment circuit 218 receives the electrode wear determination signal Sd, and sets the electrode wear determination reference value Se after the electrode wear is detected when the electrode wear determination signal Sd indicates electrode wear. It is designed to adjust to a power value.
[0055]
The basic processing procedure of the monitoring device 21 will be described based on the flowchart of FIG.
[0056]
First, in step S1, based on the amplitude threshold values Sy1, Sy2 and the phase threshold value Sx externally input to the monitoring device 21 shown in FIG. 5, as shown in FIG. In other words, on the two-dimensional map, the OK region (1) when welding with a new electrode, the OK region (2), NG region (3), and poor current conduction region (4) when electrode wear progresses In step S2, the energization timing signal φc is read and the energization timing of the welding current is measured. In step S3, the amplitude Av of the detected vibration signal Vm is measured. At this time, at least one cycle of the welding current is measured. An average amplitude value Ja is obtained so that a stable determination result can be obtained in subsequent quality determinations.
[0057]
Next, in step S4, the energization timing signal φc and the detected vibration signal Vm are read and the vibration phase difference dθ between them is measured (see the waveform graph in FIG. 1A). At this time, at least one of the welding currents is measured. An average phase difference Jp equal to or greater than the cycle is obtained so that a stable determination result can be obtained in the subsequent pass / fail determination.
[0058]
In step S5, the coordinates of the average amplitude value Ja and average phase difference Jp measured in steps S3 and S4 are collated with the pass / fail judgment reference coordinates set in step S1, and first, in step S6, the average amplitude is determined. The value Ja is compared with the amplitude threshold value Sy2, and it is determined whether or not the average amplitude value Ja causes a welding failure due to a conduction failure or the like. When amplitude threshold value Sy2 <average amplitude value Ja (Yes) ) Determines that no welding failure has occurred due to a failure in energization or the like, that is, it is determined that the current is not in the current failure region (4), and the process proceeds to step S7, while amplitude threshold value Sy2 ≧ average amplitude value Ja If it is (No), it is determined that a welding failure due to an energization failure or the like has occurred, that is, it is determined that it is in the energization failure region (4), and in step S9, a welding failure is determined. And outputs the determination result.
[0059]
Next, in step S7, it is determined whether or not the coordinates of the average amplitude value Ja and the average phase difference Jp are in the NG region {circle around (3)}. At this time, the amplitude threshold value Sy1 ≦ the average amplitude value Ja and the phase is set. When the threshold value Sx ≧ the average phase difference Jp (Yes), it is determined that it is in the NG region {circle around (3)}, and in step S9, the result of determination of poor welding is output, while other than that (No). Are determined to be in the OK regions {circle around (1)} and {circle around (2)}, and in step S8, a result of determining good welding is output.
[0060]
Next, the electrode tip wear determination process is started. Here, as shown in FIG. 7, there are two kinds of determination values for electrode tip wear determination, depending on the history of electrode tip wear, and one of them is polishing a new electrode or electrode tip like a new one. The electrode wear determination reference value Se ′ (H) applied when the electrode is shaped, and the other is the electrode wear applied after the electrode wear is determined to be replaced with the next new electrode or the electrode tip is shaped. The determination reference value Se ′ (L).
[0061]
Therefore, first, in step S10, the presence or absence of electrode tip wear is checked in the previous determination. If electrode tip wear has already occurred (Yes), in step S11, the electrode wear determination reference value Se input from the outside is set in advance. A value obtained by multiplying the determined adjustment coefficient H is a new electrode wear determination reference value Se ′ (L). On the other hand, when it is determined that there is no electrode tip wear (No), in step S12, an electrode input from the outside The wear determination reference value Se is directly used as the electrode wear determination reference value Se ′ (H).
[0062]
Next, in step S13, the average amplitude value Ja and the electrode wear determination reference value Se ′ are compared. If electrode wear determination reference value Se ′ <average amplitude value Ja (Yes), the electrode wear is determined in step S14. If the electrode wear determination reference value Se ′ ≧ the average amplitude value Ja (No), it is determined in step S15 that the electrode tip is not yet worn.
[0063]
This completes the quality determination process in one welding. In order to prepare for the next welding, the process returns from steps S14 and S15 to step S2, and the series of processes described above is continued based on new vibration information in the next welding.
[0064]
As described above, according to the monitoring device 21 according to this embodiment, since a large-amplitude intermittent mechanical damping vibration using an electromagnetic force during energization as a vibration source is a detection target, a high-level signal is used for signal detection. Without requiring an extraction technique, it is possible to easily detect the signal of the metal melting vibration, and as a result, it is possible to reliably determine whether the spot welding is good or bad.
[0065]
In addition, since the dissolution vibration of the surface coating layer is not targeted for detection, it can be applied to various steel materials, and therefore it is possible to promote the expansion of the application range of spot welding quality monitoring, Since the pass / fail judgment is performed using the two variables of the vibration amplitude value Ja and the phase difference Jp, the pass / fail judgment is properly performed even when the tip shape of the electrode tip, the welding current, and the pressure fluctuation are combined. Can do.
[0066]
Furthermore, according to the monitoring device 21 described above, wear detection can be performed by comparing the vibration amplitude value Ja highly correlated with the wear state of the tip of the electrode tip and the predetermined electrode wear determination threshold value Se, In addition, by changing the threshold value Se after the electrode wear determination, it is possible to prevent the reliability from being lowered and the electrode wear from being overlooked.
[0067]
FIG. 9 shows another embodiment of the spot welding monitoring method and monitoring apparatus according to the present invention.
[0068]
As shown in FIG. 9, the monitoring device 21 ′ of this embodiment inputs an energization angle detection circuit 211 that inputs an interelectrode voltage Ve and generates an energization timing signal φc, and a detection signal Vs of the vibration sensor 20. A vibration detection circuit 212 that removes unnecessary frequency components from the detection signal Vs and outputs a detection vibration signal Vm obtained by amplifying the detection signal Vs to an appropriate signal level in a subsequent circuit, and an energization timing signal φc And a detected vibration signal Vm and a phase difference detection circuit (phase change amount detection means) that measures a phase difference dθ between the two signals, calculates a change amount with respect to the previous phase difference, and outputs a phase change amount signal ΔJp. ) 220 and a phase difference integration circuit (phase difference change) that outputs the phase difference integration signal ΣΔJp by integrating the phase change amount only when the phase change amount is equal to or greater than a predetermined value. (Quantity integrating means) 221 and a welding failure detection circuit (welding failure detection means) 222 that compares the welding failure determination reference value Jb inputted from the outside with the phase difference integration signal ΣΔJp and outputs a welding failure detection signal Sb. ing.
[0069]
The basic processing procedure of the monitoring device 21 ′ will be described based on the flowchart of FIG.
[0070]
First, in step S21, the welding failure determination reference value Jb input from the outside is set to the monitoring device 21 ′ shown in FIG. 9, and in step S22, the energization timing signal φc is read to measure the energization timing of the welding current, In step S23, the energization timing signal φc and the detected vibration signal Vm are read and the vibration phase difference dθ between them is measured (see the waveform graph in FIG. 1A). In step S24, as shown in Equation 3, A change amount with respect to the vibration phase difference dθ at the previous welding is calculated, and a phase change amount signal ΔJp is output.
[0071]
[Equation 3]

[0072]
Subsequently, in step S25, the dead width C obtained in advance and the phase change amount signal ΔJp are compared, and if C ≧ ΔJp (No), the welding state is as good as the previous time. On the other hand, if C <ΔJp (Yes), it is determined that the welding state has changed, and the process proceeds to the next. In addition, in step S26, the polarity of the phase change amount signal ΔJp is negative (0 < If (ΔJp), (Yes), it is determined that the welding has changed in the direction of failure, and in step S27, the negative phase change signal ΔJp is integrated with the previous phase change signal ΔJp to integrate the phase difference. A signal ΣΔJp is obtained.
[0073]
Next, in step S28, the phase difference integrated signal ΣΔJp is compared with the welding failure determination reference value Jb set in step S21. If the welding failure determination reference value Jb <the phase difference integration signal ΣΔJp (Yes), In step S29, the welding failure detection signal Sb is output after detecting that the welding failure has occurred. On the other hand, if the welding failure judgment reference value Jb ≧ phase difference integration signal ΣΔJp (No), the welding state is poor. Although it is in the direction of occurrence, it is determined that no failure has occurred, and the welding failure detection signal Sb is not output.
[0074]
This completes the quality determination process in one welding. In order to prepare for the next welding, the process returns from step S29 to step S22, and the series of processes described above is continued based on new vibration information in the next welding.
[0075]
As described above, according to the monitoring device 21 ′ according to this embodiment, the quality determination of spot welding can be performed by a simple calculation such as adding up the amount of phase change and the number of occurrences highly correlated with the generation of the nugget diameter. It can be carried out.
[0076]
FIG. 12 shows still another embodiment of the spot welding monitoring method and monitoring apparatus according to the present invention.
[0077]
As shown in FIG. 12, the monitoring method and the monitoring device 21 ″ according to this embodiment are different from the monitoring method and the monitoring device 21 shown in FIG. 5 in that a vibration damping index is used as a parameter instead of the vibration phase difference. The other configuration is the same as the monitoring method and the monitoring device 21 shown in FIG.
[0078]
That is, the monitoring device 21 ″ inputs the energization timing signal φc from the energization angle detection circuit 211 and the detected vibration signal Vm from the vibration detection circuit 212, and as shown in FIG. A damped vibration integrated signal ∫Vm obtained by integrating the positive amplitude value of the vibration waveform in the period (= T) and a maximum amplitude integrated signal ∫Vp obtained by integrating the maximum vibration amplitude Vp in the same period (= T) during the same period are calculated. The vibration amplitude integrating circuit (vibration amplitude integrating means) 230 to be outputted and the ratio between the damped vibration integrated signal ∫Vm and the maximum amplitude integrated signal ∫Vp are calculated to obtain the vibration damping index and replaced with the phase difference signal Jp. An attenuation index calculation circuit (attenuation index calculation means) 231 is provided.
[0079]
Next, operation | movement of this monitoring apparatus 21 '' is demonstrated. Here, the operations of the vibration amplitude integration circuit 230 and the attenuation index calculation circuit 231 will be described with calculation formulas, and the operation description regarding the pass / fail determination procedure will be shown only in the corresponding processing steps in the flowchart of FIG. 6, and the entire description will be omitted.
[0080]
First, the calculation formulas of the damped vibration integration signal ∫Vm and the maximum amplitude integration signal ∫Vp of the vibration amplitude integration circuit 230 are expressed by Equations 4 and 5.
[0081]
[Expression 4]

[0082]
[Equation 5]

[0083]
Further, the calculation formula of the attenuation index Id (Jp) of the attenuation index calculation circuit 231 is expressed by Equation 6.
[0084]
[Formula 6]

[0085]
At this time, the step of the corresponding pass / fail judgment processing procedure is “measurement of phase difference Jp” in step 4 in the flowchart of FIG. 6. The pass / fail judgment is executed by performing the above calculation process.
[0086]
Although a specific description of the positive amplitude of the damped vibration integration signal ∫Vm has been omitted, it will be supplemented that it can be realized by, for example, a general rectifier circuit used for measuring an AC signal.
[0087]
As described above, according to the monitoring device 21 ″ according to this embodiment, even if the vibration waveform is complicated, a practical value as an index indicating the degree of vibration attenuation can be easily obtained. Therefore, it is possible to stably perform the determination of pass / fail with higher reliability.
[0088]
Finally, FIG. 2 (b) shows an example of the result of applying the pass / fail judgment by the spot welding monitoring method and the monitoring device according to the present invention in the double lap galvanized steel sheet having a thickness of 0.8 mm. . In this example, the pass / fail judgment reference value is determined so as to detect a so-called weld failure leading to peeling, in which two steel plates are not welded. Of course, even if there is a weld failure, the nugget diameter may not reach the acceptable value. Therefore, in order to detect such a failure, the amplitude threshold value Sy1 and the phase threshold value are detected. This is possible by adjusting Sx.
[0089]
Note that the spot welding monitoring method and monitoring apparatus according to the present invention are not limited to the above embodiments, and various modifications can be made.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram (a) showing the principle of spot welding according to the present invention, and a graph (b) showing a relationship between a vibration phase difference, an amplitude value, and a nugget diameter with respect to the number of welding points.
FIG. 2 is a graph (a) showing a state transition of an electrode tip tip shape on a judgment reference coordinate defined by an amplitude axis and a phase difference axis orthogonal thereto, and the quality of the spot welding monitoring method and monitoring device according to the present invention. It is a graph (b) which shows the result of having applied the determination in the two-ply welding of the hot galvannealed steel plate with a plate thickness of 0.8 mm.
FIG. 3 is a diagram for explaining a physical phenomenon in a welded portion.
FIG. 4A is an explanatory diagram in which transitions of amplitude and phase difference are plotted on a two-dimensional map, and FIG. 4B is a diagram illustrating a determination criterion region for pass / fail judgment set on the two-dimensional map.
FIG. 5 is a basic block diagram for explaining an embodiment of a spot welding monitoring apparatus according to the present invention.
FIG. 6 is a flowchart for explaining a basic processing procedure by the spot welding monitoring apparatus according to the present invention.
FIG. 7 is a graph illustrating electrode wear determination means.
FIG. 8 is a timing chart for explaining means for detecting energization timing.
FIG. 9 is a basic block diagram for explaining another embodiment of the spot welding monitoring apparatus according to the present invention.
10 is a flowchart for explaining a basic processing procedure by the spot welding monitoring apparatus shown in FIG. 9;
FIG. 11 is a graph illustrating a correlation between a decrease in nugget diameter and a change in phase difference.
FIG. 12 is a basic block diagram illustrating still another embodiment of the spot welding monitoring apparatus according to the present invention.
FIG. 13 is a diagram for explaining a method for obtaining an attenuation index of a vibration waveform.
[Explanation of symbols]
10 Spot welder
21,21 ', 21''monitoring device
213 Vibration amplitude detection circuit (vibration amplitude detection means)
214 Vibration phase difference detection circuit (vibration phase difference detection means)
215 Pass / fail judgment reference coordinate setting circuit (pass / fail judgment reference area setting means)
216 Welding quality judgment circuit (welding quality judgment means)
217 Electrode wear determination circuit (electrode wear determination means)
218 judgment threshold value adjustment circuit (judgment threshold value adjusting means)
220 Phase change detection circuit (phase change detection means)
221 Phase difference integration circuit (phase difference change amount integration means)
222 Welding failure detection circuit (welding failure detection means)
230 Vibration amplitude integrating circuit (vibration amplitude integrating means)
231 Attenuation index calculation circuit (attenuation index calculation means)

Claims (12)

  Amplitude value of intermittent mechanically damped vibration at the electrode part of a spot welder that generates electromagnetic force as an excitation source when AC welding current is applied when performing pass / fail judgment of spot welding based on vibration generated during welding Detecting the phase difference between the AC welding current and the intermittent mechanical damping vibration, and setting the pass / fail judgment criteria region on the two-dimensional map defined by the amplitude axis and the phase difference axis orthogonal to the amplitude axis. A spot welding monitoring method comprising: performing spot welding quality determination based on the detected amplitude value and phase difference on a two-dimensional map.   Two amplitude threshold values are set on the amplitude axis and one phase difference threshold value is set on the phase difference axis, and a good welding region, a poor welding attention region, a poor welding region, and a welding are displayed on the two-dimensional map. The four criteria areas for the poor conduction area are set, and the amplitude value of intermittent mechanical damping vibration and the phase difference between the AC welding current and intermittent mechanical damping vibration are the good welding area, the poor welding attention area, The spot welding monitoring method according to claim 1, wherein the quality of spot welding is determined according to which of the poor welding region and the poor welding current region belongs.   The spot welding monitoring method according to claim 1 or 2, wherein an amplitude axis and a phase difference axis of a two-dimensional map are set based on an initial amplitude value and an initial phase difference at the start of welding.   When the detected amplitude value of the intermittent mechanically damped vibration exceeds the preset electrode wear determination threshold value, it is determined as electrode wear, and when it is determined as electrode wear, it is lower than the amplitude fluctuation range of the wear electrode and is a new electrode. The spot welding monitoring method according to claim 1, wherein the electrode wear determination threshold value is changed to a value higher than the amplitude value at the time.   Intermittent mechanically damped vibration and AC welding in the electrode part of a spot welder that generates electromagnetic force as an excitation source when AC welding current is applied when performing pass / fail judgment of spot welding based on vibration generated during welding Detects the phase difference from the current, calculates the amount of change by subtracting the current phase difference from the previous phase difference, and changes only when the calculated change amount is greater than or equal to a predetermined value and the polarity is negative A spot welding monitoring method characterized by integrating a quantity and determining a welding failure when the integrated value falls below a predetermined pass / fail judgment threshold value. Amplitude value of intermittent mechanically damped vibration at the electrode part of a spot welder that generates electromagnetic force as an excitation source when AC welding current is applied when performing pass / fail judgment of spot welding based on vibration generated during welding while detect the intermittent mechanical damping vibrations by dividing by the product of the positive-side amplitude value is integrated and most Taisho side amplitude value and the integration result and the period of the vibration waveform between cadences intermittent mechanical damping vibrations An attenuation index as an index of the amount of attenuation is calculated and replaced with a phase difference, and a detection criterion region for pass / fail judgment is set on a two-dimensional map defined by an amplitude axis and a phase difference axis orthogonal thereto. monitoring method of spot welding and performing quality determination of spot weld on the basis of the position in the amplitude value and two-dimensional map on the phase difference obtained by replacing the vibration damping index.   Intermittent machine in the electrode part of a spot welder that generates electromagnetic force as an excitation source in a spot welding monitoring device that performs spot welding quality judgment based on vibrations generated during welding Vibration amplitude detecting means for detecting the amplitude value of the damped vibration, vibration phase difference detecting means for detecting the phase difference between the AC welding current and the intermittent mechanically damped vibration, and the pass / fail judgment criterion region as the amplitude axis and orthogonal thereto Quality determination reference area setting means for setting on a two-dimensional map determined by a phase difference axis to be welded, and welding quality determination means for determining the quality of spot welding based on the position of the detected amplitude value and phase difference on the two-dimensional map A spot welding monitoring device characterized by comprising:   The pass / fail judgment reference area setting means sets two amplitude threshold values on the amplitude axis and one phase difference threshold value on the phase difference axis, so that a good welding region and poor welding are set on the two-dimensional map. Four determination reference areas, a caution area, a welding failure area, and a welding energization failure area, are set, and the welding quality determination means has two-dimensional amplitude values detected by the vibration amplitude detection means and a phase difference detected by the vibration phase difference detection means. The spot welding monitoring device according to claim 7, wherein the spot welding quality determination is performed according to which of the good welding region, the poor welding attention region, the poor welding region, and the poor welding energization region on the map.   9. The spot welding monitoring device according to claim 7, wherein the amplitude axis and the phase difference axis of the two-dimensional map are set based on an initial amplitude value and an initial phase difference at the start of welding.   Electrode wear determination means for determining electrode wear when the amplitude value of intermittent mechanical damping vibration detected by the vibration amplitude detection means exceeds a preset electrode wear determination threshold value, and electrode wear determination by the electrode wear determination means 10. A determination threshold value adjusting means for changing the electrode wear determination threshold value to a value lower than the amplitude fluctuation range of the wear electrode and higher than the amplitude value at the time of a new electrode at the stage of being applied. The spot welding monitoring device according to claim 1.   Intermittent machine in the electrode part of a spot welder that generates electromagnetic force as an excitation source in a spot welding monitoring device that performs spot welding quality judgment based on vibrations generated during welding Vibration phase difference detection means for detecting the phase difference between the damped vibration and the AC welding current, and a phase change for calculating a change amount obtained by subtracting the current phase difference from the previous phase difference detected by the vibration phase difference detection means. The amount detection means, the phase difference change amount integration means for integrating the change amount only when the change amount detected by the phase change amount detection means is equal to or greater than a predetermined value and the polarity is negative, and the phase difference change amount integration means A spot welding monitoring device, comprising: a welding failure detection means for determining a welding failure when the amount of change made falls below a preset pass / fail judgment threshold. Intermittent machine in the electrode part of a spot welder that generates electromagnetic force as an excitation source in a spot welding monitoring device that performs spot welding quality judgment based on vibrations generated during welding The vibration amplitude detecting means for detecting the amplitude value of the damped vibration, the vibration amplitude integrating means for integrating the positive amplitude value in the vibration waveform during the intermittent period of the intermittent mechanically damped vibration, and the integration result by the vibration amplitude integrating means is maximized. and attenuation index calculating means you substituted out calculate the attenuation index as an indicator of attenuation of intermittent mechanical damping vibrations by dividing by the product of the positive amplitude value and the period of the phase difference, amplitude determination reference area of the quality determination axis and a quality determination reference area setting means for setting on a two-dimensional map defined by the retardation axis orthogonal thereto, the detected amplitude value and the phase which is displaced from the vibration damping index Monitoring device of the spot welding, characterized in that it comprises a welding quality determining means for performing a quality determination of the spot welding on the basis of the position on the two-dimensional map of.

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