JP2003083923A6 - Defect inspection method and device - Google Patents

Abstract

An object of the present invention is to provide a defect inspection method and apparatus capable of detecting an internal defect in an object to be inspected such as a concrete structure and quantitatively detecting information relating to a defective portion.
A heating control unit of a defect control unit applies periodic heat waves to a heating unit. The heating device 17 repeats heating and stopping of the test object. The temperature measuring device 19 measures the surface temperature of the object to be inspected in time series, and outputs the measured data to the data recording means 13 of the defect inspection control device 10. The measurement data recorded by the data recording means 13 which has received the output is judged by the defect judgment means whether or not it is an internal defect, and the result is output as, for example, image data. By repeating the measurement while changing the cycle of the thermal wave, it is possible to quantitatively detect an internal defect in the inspection object.
[Selection diagram] Fig. 1

Description

ただし、ΔＶ_sinは参照波形に同期する赤外線強度の変動振幅を表し、ΔＶ_cosは、参照波形と９０度位相がずれたｃｏｓ波に同期する赤外線強度の変動振幅を表す。なお，Ｎは信号処理における取り込みフレーム数である。
【００５１】表面温度変動が、変動熱負荷の位相と完全に一致している場合には、ΔＶ_cosは０となる。熱拡散などの影響により、表面温度変動が、変動熱負荷の位相からずれる場合には、ΔＶ_cosの成分が表れる。この場合には、次式により温度変動振幅の絶対値ΔＶおよび位相遅れθを求めることができる。
【００５２】
【数２】

ここで、求めたθを、時刻ｔ、単位領域ｉにおける参照波形Ｒ_tとの位相差Ｐ_{t i}と定義する。
【００５３】ＣＰＵ３０は、次の単位領域における位相差を求めるため、ｉに１を加算してｉ＋１とする（ステップＳ５０４）。さらに、ｉが全領域数Ｉを越えるまで（ステップＳ５０５，ＹＥＳ）、ステップＳ５０１〜５０４の処理を繰り返し位相差Ｐ_tiを求める（ステップＳ５０５，ＮＯ）。
【００５４】次に、ＣＰＵ３０は、時刻ｔにΔｔを加算して時刻をｔ＋Δｔとし（ステップＳ５０６）、所定の解析時間Ｔを越えるまで（ステップＳ５０７，ＹＥＳ）、ステップＳ５０１〜５０６を繰り返す（ステップＳ５０７，ＮＯ）。
【００５５】このように、位相差Ｐ_tiを求める信号処理が、赤外線カメラ２３内の赤外線センサの各ピクセル毎つまり全領域数Ｉ回、赤外線カメラ２３が計測した取り込みフレーム数Ｎ回行われる。
【００５６】１−４−２．解析画像の表示
計測データの解析処理を終えたＣＰＵ３０は、時刻Ｔにおける位相差Ｐ_Tｉを各領域について呼び出した後、これに基づいて計測領域全体の画像データを生成し（ステップＳ４０５）、ディスプレイ３３に出力を行う（ステップＳ４０６）。すなわち、ＣＰＵ３０は、入力した位相差を所定の表示色に対応させて画像データを生成し、これを表示する。
【００５７】図６（Ａ）に、上記に示した欠陥検査システムを適用して、人工欠陥を有するコンクリート試験体にかかる欠陥検査を行った場合の画像データの表示の例を示す。なお、この画像は、図６（Ｂ）に示す人工欠陥１〜６を有するコンクリート試験体を計測したものである。前記人工欠陥１〜６は、それぞれ深さと厚さが異なる欠陥をコンクリート中に埋め込まれて作製されている。
【００５８】図６Ａにおいて、右側の列６１に３つ鮮明にコントラスト差として表示されている部分が、人工欠陥４〜６にそれぞれ対応している。なお、人工欠陥１〜３は、左側の列６０に表示されているが、そのコントラストはあまり鮮明ではない。
【００５９】これにより、この検査時に設定された熱波動の加熱条件の一つである加熱期間が、深さ２０ｍｍの人工欠陥４〜６を検出するのに適していたと考えられる。
【００６０】１−５．まとめ図７は、計測領域の単位領域における計測データと参照波形との位相差をグラフで示した例である。赤外線カメラ２３が計測した計測領域のフレームにおける各単位領域ｉにおける位相差Ｐ_tiは、欠陥部の温度変動曲線７１に近似した参照波形Ｒ₇₁と、健全部の温度変動曲線７３に近似した参照波形Ｒ₇₃との位相差で表現することができる。
【００６１】画像データとして表示する位相差は、加熱期間と欠陥の深さによって決定されていると考えられることから、被検査体２０の欠陥に応じた加熱期間を設定する必要がある。
【００６２】２．第２の実施形態
上述したように、画像データとして表示する位相差は、加熱期間と欠陥の深さによって決定されており、検査を行う欠陥の深さに応じて最適な加熱期間を設定する必要がある。図８は、最適な加熱期間を求めることを目的として、加熱条件の一つである加熱期間を変更して前記人工欠陥（図６Ｂ）を繰り返し計測した場合の画像である。
【００６３】図８Ａ〜Ｄに示すように、欠陥深さ２０ｍｍの欠陥４〜６を示すコントラスト差は、期間Ｔが１０〜３０分において鮮明に表示されており、特に、期間Ｔが２０分のときに最も鮮明にコントラスト差が表示されている。
【００６４】また、図８Ｂ〜Ｅに示すように、欠陥深さ３０ｍｍの欠陥１〜３を示すコントラスト差は、期間Ｔが２０〜４０分において鮮明に表示されており、特に、期間Ｔが３０分のときに最も鮮明にコントラスト差が表示されている。
【００６５】上記の結果から考察した、加熱期間と欠陥深さの関係テーブルの例を図９に示す。図９に示すように、各欠陥深さ毎において位相差が最も大きくなるときの加熱期間が、最適な加熱期間であると考えられる。例えば、欠陥深さ「１０ｍｍ」のときの最大位相差は「２．０°」であることより、この欠陥深さを検査する時の最適な加熱期間は、「１０分」である。すなわち、前記最適な加熱期間が、［特許請求の範囲］において示した「相違が顕著となった所定期間」に該当する。
【００６６】したがって、当該関係テーブルを使用することにより、被検査体２０において検査を行う欠陥深さに応じて、加熱期間を設定することができる。これにより、計測回数の低減を図ることができ検査効率の向上が望める。
【００６７】本実施形態においては、加熱期間と欠陥深さの関係テーブルを使用して、検査効率を高めた欠陥検査方法について説明する。
【００６８】２−１．欠陥検査の概要
第１の実施形態においては、人工欠陥を有するコンクリート試験体にかかる欠陥検出を行ったが、本実施形態においては、実際に経年劣化による内部欠陥を有するコンクリート構造物について、本発明による欠陥検査システムを適用した場合について説明する。
【００６９】なお、欠陥検査を行うコンクリート構造物は、前記コンクリート試験体と同条件の材料・環境で作製されたものとし、図９に示した、欠陥の深さと加熱期間の関係を表した参照テーブルを使用するものとする。
【００７０】２−２．欠陥深さの推定方法
まず、検査対象となるコンクリート構造物について、その検査範囲におけるコンクリートの厚さや鉄筋かぶりの厚さを調べ、欠陥検査を行う最大深さを決定する。なお、鉄筋かぶりの厚さを調べる際には、超音波、マイクロ波レーダまたは電磁誘導などを利用した検査装置を使用すればよい。
【００７１】次に、要求される検査効率から計測する回数を決定し、図９の参照テーブルから前記最大深さに対応する加熱期間を決定して計測を行う。例えば、本実施形態においては、調査の結果、最大深さは３０ｍｍと考えられるので参照テーブルにより、加熱期間を１０〜３０分とし、計測回数を１回とした。
【００７２】図１０は、コンクリート構造物に本発明による欠陥検査システムを適用することによって得られた画像データを表示したものである。なお、図１０（Ａ）〜（Ｃ）は、それぞれ加熱期間を１０〜３０分と変更して計測しており、それぞれの画像において画像中央部に欠陥が存在していることが明瞭に表示されている。
【００７３】以下▲１▼〜▲３▼に示すように、これらの画像および前記参照テーブルにより、この欠陥に関する定量的な情報を推定することができる。
【００７４】▲１▼ 図１０（Ａ）では、画像中心の欠陥の輪郭部１０１が全体に対するコントラスト差として鮮明に表示されている。したがって、参照テーブルによりこの範囲の欠陥深さは、１０ｍｍ前後であると推定できる。すなわち、表面から１０ｍｍ前後において欠陥が存在している。
【００７５】▲２▼ 図１０（Ｂ）では、画像中心の欠陥の輪郭部１０３を示すコントラスト差が、図１０（Ａ）と比較すると、中心に向かって拡大するように表示されている。したがって、参照テーブルによりこの範囲の欠陥深さは２０ｍｍ前後であり、この範囲における欠陥は１０ｍｍの範囲の欠陥よりも空洞部がより大きいものであると推定することができる。
【００７６】▲３▼ 図１０（Ｃ）では、画像中心の欠陥の輪郭部１０５を示すコントラスト差が、図１０（Ｂ）と比較すると、さらに中心に向かって拡大するように表示されている。したがって、参照テーブルによりこの範囲の欠陥深さは３０ｍｍ前後であり、この範囲における欠陥は２０ｍｍの範囲の欠陥よりも空洞部がより大きいものであると推定することができる。
【００７７】これにより、この内部欠陥は、コンクリート構造物の表面から深さ１０ｍｍ〜３０ｍｍの位置に存在し、表面から内部への垂直方向に向かって先細りした形状の浮きであることが推定できる。
【００７８】なお、図１１に、今回計測したコンクリート構造物の内部欠陥部分を、採取したときの例を示す。図１１（Ａ）に示すように、この内部欠陥部分は、図１０に示した画像における内部欠陥のコントラスト差の輪郭部とほぼ同形状の輪郭を有している。また、図１１（Ｂ）は、この内部欠陥部の側面を示しており、その厚みは２０〜３０ｍｍであった。
【００７９】このように、本発明を適用した欠陥検査システムを用いてコンクリート構造物の欠陥検査を行うことで、その内部欠陥にかかる深さを同定するとともに、その大きさや厚さなどの内部欠陥の定量的な情報を推定することが可能となる。これにより、欠陥検査における検査効率を高めることができ、欠陥の事故確率に応じて効果的な対策を講じるリスクベースメンテナンスが可能となる。
【００８０】２−３．欠陥検査制御装置におけるフローチャート
図１２に、２−２．に示した欠陥深さの推定方法を利用して内部欠陥を自動推定する欠陥検査制御装置１０におけるフローチャートを示す。
【００８１】まず、欠陥検査制御装置１０であるコンピュータ装置２９において、検出する欠陥の最大深さを入力する（ステップＳ１２０１）。なお、この時入力する最大深さは、２−２．に示すように、コンクリート構造物の事前調査によって決定すればよい。
【００８２】次に、要求される検査効率に基づいて、計測する回数および加熱条件の範囲を入力する（ステップＳ１２０２）。なお、この加熱条件の範囲は、前記最大深さに応じてＣＰＵ３０が自動的に判断するようにしてもよい。
【００８３】欠陥検査制御装置１０において、コンピュータ装置２９のＣＰＵ３０は、信号発生装置２７に対して加熱条件を出力する（ステップＳ１２０３）。ここで加熱条件とは、被検査体２０に熱負荷を与える時間およびその繰り返し回数を与えるものである。なお、振幅は一定値とし、デューティサイクルは５０％としている。
【００８４】前記加熱条件は、信号発生装置２７に与えられた後、波形信号に変換されてリレー装置２５に出力される。リレー装置２５は、入力した波形信号に基づいてヒーター２１を作動させる。これにより、所定の加熱条件で被検査体２０に熱負荷を与える。
【００８５】所定の加熱条件で加熱・加熱停止を行いつつ、赤外線カメラ２３を用いて、特に加熱停止期間における被検査体２０の表面温度を計測する。この計測データは、接続されたコンピュータ装置２９に出力され、ハードディスク３５等に記録される（ステップＳ１２０４）。この計測処理を所定時間毎に繰り返すことにより、加熱停止期間における、計測時刻毎の表面温度の計測データを取得する。なお、計測データは、被検査体２０であるコンクリート構造物における測定領域の各単位領域毎の表面温度データである。
【００８６】所定の繰り返し回数において上記の処理を行った後、計測を終了し、設定された範囲において加熱期間を変更して（ステップＳ１２１０）、ステップＳ１２０３から同様の処理を繰り返す（ステップＳ１２０５，ＮＯ）。なお、本実施形態においては、加熱・加熱停止を行う繰り返し回数を１回としている。
【００８７】設定された範囲の加熱条件での計測を終了すると（ステップＳ１２０５，ＹＥＳ）、ＣＰＵ３０は、計測した各加熱期間において、計測データの解析処理を行う（ステップＳ１２０６）。なお、ステップＳ１２０６に示す計測データの解析処理は、第１の実施形態の図４に示した処理と同様である。
【００８８】各加熱期間における計測データの解析処理を終えたＣＰＵ３０は、時刻Ｔにおける位相差Ｐ_Tｉを各領域について呼び出し、これに基づいて欠陥の有無を判断する。さらに、ＣＰＵ３０は、欠陥であると判断した領域の位相差を示す相関データに基づいて、当該欠陥の存在する深さを判定する（ステップＳ１２０７）。すなわち、各領域の位相差と、加熱期間と欠陥深さの関係を示した参照テーブル１２０とを参照して、欠陥を示していると判断した領域の深さを判定する。
【００８９】次に、ＣＰＵ３０は、計測領域全体の画像データを生成し（ステップＳ１２０８）、図１０に示す画像データをディスプレイ３３に出力する（ステップＳ１２０９）。なお、本実施形態においては、各画面において欠陥部分の深さの値が同時に表示されているものとする（図示せず）。
【００９０】また、ステップＳ１２０７において判定した欠陥深さを利用して、図１３に示すような、欠陥形状の推定画面を同時に表示してもよい。これにより、欠陥部位における定量的な情報を画像データとして表示させ、欠陥検査における検査結果の確認が容易となり、特別な判断知識を有していない者であっても内部欠陥を見いだすことができる。なお、図１３においては、欠陥部位を二次元的に表現しているが、三次元形状として表現してもよい。これにより、より詳細な欠陥に関する情報を取得することができる。
【００９１】３．その他の実施形態
上記実施形態においては、被検査体１としてコンクリート材料を使用しているが、例えば、ＣＦＲＰなどの低熱伝導性材料から構成された複合材料における欠陥検査にも本発明は適用可能である。
【００９２】上記実施形態においては、加熱・加熱停止を行う繰り返し回数を１回としているが、被検査体の性質によっては複数回繰り返してもよい。なお、この場合、被測定物表面における熱源の反射が影響しなければ、加熱・加熱停止期間の両期間における温度変動を連続して計測すればよい。
【００９３】上記実施形態においては、欠陥部位を求める際の特徴量として、計測データから得られる波形と所定の参照波形との位相差を用いたが、他の指標を特徴量として用いてもよい。例えば、計測データの時間変化における温度勾配データ、当該温度勾配データの時間変化データ、計測データについてフーリエ解析を行った場合の周波数成分データ、計測データ波形のピーク値または当該ピーク値への到達時間などを特徴量としてもよい。
【００９４】さらに、これらの特徴量の比較を行う際に、各計測データと所定の参照波形との相関処理によって計測データ同士を間接的に比較しているが、各計測データを直接的に比較してもよい。例えば、各計測データのピーク値を比較すること等がこれに該当する。
【００９５】上記実施形態においては、加熱期間と欠陥深さの関係テーブルを使用して欠陥部位にかかる定量的な情報を取得しているが、さらに欠陥厚さを加えた関係テーブルを使用してもよい。この場合、より精度の高い欠陥検出が可能となる。
【００９６】上記実施形態においては、欠陥検査制御装置１０をコンピュータ装置２９および信号発生装置２７から構成したが、当該欠陥検査制御装置１０を、加熱制御手段１１およびデータ記録手段１３を実現するデータ収集装置と欠陥判断手段１５を実現する欠陥判断装置とを、それぞれ別の装置から構成してもよい。例えば、通信回線を利用してこれらの装置を接続することで、欠陥検査における遠隔操作が可能となる。
【図面の簡単な説明】
【図１】この発明の一実施形態による欠陥検出システムの機能ブロック図を示す図である。
【図２】この発明の一実施形態による欠陥検出システムを実現する装置の構成図を示す例である。
【図３】この発明の一実施形態によるコンピュータ装置のハードウェア構成図を示す例である。
【図４】欠陥検査制御装置におけるフローチャートを示す図である。
【図４ａ】加熱制御のための信号と、被検査体の表面における温度変動曲線との関係を示す図である。
【図５】計測データの解析処理におけるフローチャートを示す図である。
【図６】人工欠陥（Ｂ）と、この人工欠陥を計測したときの画像データの表示画面の例（Ａ）である。
【図７】計測領域の単位領域における計測データと参照波形との位相差をグラフで示した例である。
【図８】加熱期間を変更して、人工欠陥を計測したときの画像データの表示画面の例である。
【図９】欠陥の深さ毎に、加熱期間と位相差との関係を示した参照テーブルの例である。
【図１０】加熱期間を変更して、内部欠陥をもつコンクリート構造物を計測したときの画像データの表示画面のである。
【図１１】計測したコンクリート構造物の内部欠陥部分を、採取したときの例である。
【図１２】参照テーブル使用時の欠陥検査制御装置におけるフローチャートを示す図である。
【図１３】欠陥部位にかかる定量的な情報に基づいて、欠陥の形状を推定した画面の例である。
【符号の説明】
１０・・・欠陥検査制御装置
１１・・・加熱制御手段
１３・・・データ記録手段
１５・・・欠陥判断手段
１７・・・加熱装置
１９・・・温度計測器[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for detecting internal defects in an object to be inspected made of a material having low thermal conductivity such as concrete.
[0002]
2. Description of the Related Art Conventionally, a thermography method is known as a method for examining internal defects such as floating or peeling of a concrete structure. In this conventional thermography method, a local temperature change area on the concrete surface that occurs when a thermal load is applied to a concrete structure or the like is measured by infrared thermography, and the measured data is output as an image to inspect internal defects. Do. That is, the output image expresses the distribution of the measured infrared intensity, and the internal defect can be detected based on the contrast difference between the infrared intensity of the defective part and the infrared intensity of the healthy part.
However, the conventional thermography method can only detect the presence or absence of an internal defect, and cannot obtain quantitative information such as the depth, thickness, or size of a defective portion. In addition, since defect detection is performed based only on the adiabatic temperature field measurement, high-precision detection that is suitable for detecting internal defects with a small heat-insulating effect, such as honeycombs, artificial cracks, and cold joints, is performed. Can't do it.
The present invention has been made to solve such a problem, and detects an internal defect of an object to be inspected made of a low thermal conductive material such as a concrete structure, and detects the internal defect of the defect. An object of the present invention is to provide a defect inspection method and a device capable of quantitatively and accurately detecting information such as depth and shape.
[0005]
Means for Solving the Problems and Effects of the Invention (1) In the defect inspection method according to the present invention, the surface of the object to be inspected is heated simultaneously over the entire measurement area, and at least after the heating is stopped. In the heating suspension period, the time change of the surface temperature is measured for each unit area of the measurement area, and the test object is measured based on a relative difference between the unit areas regarding the time change of the surface temperature in each unit area. It is characterized by finding defects in.
Therefore, measurement can be performed in consideration of the surface reflection heat of the object to be inspected generated in the heating process. That is, since the measurement is performed in the cooling process during the heating stop period, the surface temperature of the inspection object can be measured more accurately. Thereby, the relative difference in the surface temperature between the unit regions can be accurately detected as a defect in the inspection object.
(2) The defect inspection method according to the present invention is characterized in that the object to be inspected is made of a material having low thermal conductivity.
Therefore, the present invention can be applied to defect inspection of concrete structures and composite materials having low thermal conductivity. Further, since the temperature fluctuation is moderate due to the low thermal conductivity, the number of times of measurement can be reduced. For example, even when measuring a plurality of continuous measurement regions, the measurement efficiency can be improved by sequentially performing heating and measurement for each measurement region.
(3) In the defect inspection method according to the present invention, a position of a defect in the inspection object is specified based on a relative difference between the unit regions with respect to a time change of a surface temperature in each unit region. It is characterized by:
Therefore, by clearly expressing the difference between the unit areas, an accurate defect position can be specified.
(4) In the defect inspection method according to the present invention, a relative difference between the unit regions with respect to a time change of the surface temperature in each unit region is presented as a visually recognizable image. And
Therefore, by associating each unit area with a constituent unit of the image data, the entire measurement area can be output as image data, and the defect position can be visually identified. For example, a relative difference between each unit area can be expressed as a contrast difference on image data.
(5) In the defect inspection method according to the present invention, the relative difference is determined based on a comparison between a waveform due to a time change of the surface temperature in each unit area and a characteristic amount in a predetermined waveform. And
Therefore, even if disturbance data is included in the measurement data, highly accurate defect detection can be performed by referring to a predetermined waveform. For example, in the case of a test object such as a concrete structure, disturbance data may be generated due to dirt on the concrete surface such as soot and free lime, solar radiation or reflection, etc. Can be determined.
(6) In the defect inspection method according to the present invention, the comparison of the characteristic amounts is performed by using a specific value indicating a correlation between a waveform due to a time change of the surface temperature in each unit area and a predetermined waveform, or It is characterized in that it is performed based on the difference between the phases of both waveforms.
Therefore, when comparing the feature amounts, information on the defect can be obtained as a quantitative value corresponding to the degree of the comparison result. That is, accurate defect inspection can be performed by using various indices indicated by waveforms as feature amounts.
(7) In the defect inspection method according to the present invention, the heating and the heating stop are performed for a predetermined period, and the measurement is performed while changing the predetermined period. It is characterized in that the depth of a defect is estimated based on a predetermined period that has become prominent.
Therefore, the depth at which the internal defect exists can be accurately estimated. Further, by repeating the measurement while changing the predetermined period, the depth of the internal defect can be more accurately estimated. Further, the size and thickness of the internal defect can be estimated at the same time.
(8) The defect inspection method according to the present invention is characterized in that the depth of a defect is estimated based on a table in which the depth of the defect is previously associated with a predetermined period.
Therefore, a more accurate depth of the internal defect can be estimated with reference to the table. As a result, the number of measurements can be reduced, and the inspection efficiency can be improved.
(9) In the defect inspection control apparatus according to the present invention, a heating control means for issuing a heating start command to a heating apparatus for simultaneously heating the entire surface of the inspection object over the entire measurement area; Data recording means for inputting data from the temperature measuring device and recording as temperature data of each unit area, and, based on the recorded temperature data, a time change of the surface temperature in each unit area between the respective unit areas. And a defect judging means for judging a defect in the inspection object by detecting a relative difference.
Therefore, measurement can be performed in consideration of the surface reflection heat of the test object generated in the heating process. That is, since the measurement is performed in the cooling process during the heating stop period, the surface temperature of the inspection object can be measured more accurately. This makes it possible to accurately detect a defect of the inspection object.
(10) In the data collection device according to the present invention, a heating control means for issuing a heating start command to a heating device for simultaneously heating the entire surface of the object to be measured over the entire measurement area; Data recording means for inputting data from the temperature measuring device and recording the data as temperature data of each unit area.
Therefore, it is possible to perform measurement in consideration of the surface reflection heat of the test object generated in the heating process. That is, since the measurement is performed in the cooling process during the heating stop period, the surface temperature of the inspection object can be measured more accurately.
(11) In the defect judging device according to the present invention, the time of the surface temperature in each unit area is measured based on the temperature data of each unit area of the measurement area recorded after the heating of the surface of the inspection object is stopped. A defect determining unit that detects a relative difference between the unit areas with respect to the change and determines a defect in the inspection object.
Therefore, a defect can be accurately detected based on the measured surface temperature data of the inspection object.
[0027]
Embodiments of the present invention will be described below with reference to the drawings.
1. First embodiment
When a heat load that fluctuates at a constant cycle is applied to an object, a wave-like heat transfer occurs inside the object, and the surface temperature of the object also fluctuates at a constant cycle and amplitude. If a defect exists in the object, the influence of the defect also appears on the surface temperature distribution that fluctuates in a wave-like manner. In the present embodiment, a method will be described in which such surface temperature fluctuations of a constant cycle are measured in time series, and a defect is identified based on a correlation process between the measured data and a predetermined waveform.
For example, the correlation processing is performed by synchronizing the measured data of the surface temperature fluctuation with the given heat load and the reference waveform having the same period, and the difference of the phase lag value from the reference waveform in each unit area ( Phase difference) is output as correlation data. That is, the unit area where the phase difference occurs indicates a portion where the internal defect exists. Therefore, it is possible to perform a defect inspection by converting the correlation data into image data that is easily recognizable, and displaying a portion where an internal defect exists on the image data as a contrast difference.
1-1. Overview of defect inspection system
FIG. 1 is a functional block diagram showing a schematic configuration of a defect inspection system that realizes the present invention. In this figure, a defect inspection control device 10 inputs a heating control means 11 for controlling heating and heating stop to a heating device 17 and measurement data of a surface temperature of an inspection object measured by a temperature measuring device 19. The apparatus includes a data recording unit 13 for recording, and a defect judging unit 15 for reading out the measurement data recorded in the data recording unit 13 and comparing the characteristic amount with a predetermined reference waveform to judge an internal defect.
1-2. Device configuration of the defect inspection system
FIG. 2 shows a configuration diagram of an apparatus for realizing the defect inspection system. The inspection object 20 shows a concrete wall for inspecting an internal defect. A heater 21 for applying a thermal load to the test object 20 is installed to face the test object 20. The heater 21 is connected to a relay device 25 that can adjust the output of the heat load in order to apply a uniform heat load to the device under test 20. By providing the relay device 25, the irradiation amount at the central portion of the heater 21 is adjusted so that the central portion of the test object 20 does not become hotter than the peripheral portion.
The signal generator 27 is connected to the relay device 25 and the computer device 29, and generates a signal for controlling the relay device 25 based on a heating start command received from the computer device 29.
The infrared camera 23 is installed so as to face the device 1 to be inspected and is connected to the computer device 29. The infrared camera 23 measures the surface temperature of the device 1 to be inspected in chronological order. 29.
Receiving the output of the measurement data, the computer 29 records the measurement data by the data recording means 13 and judges the internal defect of the inspection object 20 by the defect judgment means 15 and outputs an image.
The defect inspection control device 10 in FIG. 1 is realized by a computer device 29 and a signal generation device 27. The heating device 17 is realized by the heater 17 and the relay device 25. The temperature measuring device 19 is realized by the infrared camera 23.
1-3. Hardware configuration diagram of computer device
FIG. 3 shows a hardware configuration diagram of the computer device 29. This device includes a CPU 30, a memory 31, a display 33, a hard disk 35 (storage device), a keyboard / mouse 37, and a communication circuit 39.
The communication circuit 39 is a circuit for making a connection with another device. The hard disk 35 stores a program for determining a defect, a reference waveform, a program for displaying an image, and the like.
1-4. Flow chart in the defect inspection control device
FIG. 4 shows a flowchart in the defect inspection control device 10 when performing a defect inspection. First, in the defect inspection control device 10, the CPU 30 of the computer device 29 outputs a preset heating condition to the signal generation device 27 (step S401). Here, the heating condition refers to a time during which a thermal load is applied to the device under test 20 and the number of repetitions. Note that the amplitude is a constant value and the duty cycle is 50%.
The heating conditions are given to a signal generator 27, converted into a waveform signal, and output to a relay device 25. The relay device 25 operates the heater 21 based on the input waveform signal. As a result, a heat load is applied to the device under test 20 under predetermined heating conditions.
While heating and stopping the heating under predetermined heating conditions, the surface temperature of the inspection object 20 is measured by using the infrared camera 23, particularly during the heating stop period.
FIG. 4A shows a relationship between a signal 40 for heating control output from the relay device 25 to the heater 21 and a temperature fluctuation curve 41 on the surface of the test object 20 heated based on the signal 40. That is, the temperature fluctuation data in the measurement period 45 shown in FIG. 4A is measured.
This measurement data is output to the connected computer device 29 and recorded on the hard disk 35 or the like (step S402). By repeating this measurement process every predetermined time, measurement data of the surface temperature fluctuation at each measurement time during the heating stop period is obtained. Note that the measurement data is surface temperature data for each unit area of the measurement area in the test object 20.
After performing the above processing at a predetermined number of repetitions, the measurement is terminated (step S403). In the present embodiment, the number of repetitions of performing the heating and the heating stop is one.
Upon completion of the measurement, the CPU 30 of the computer 29 performs an analysis process of the measured data (step S404).
1-4-1. Analysis processing of measurement data
FIG. 4 is a flowchart of the measurement data analysis process. Here, the surface temperature data of each unit area of the measurement area in the inspection object 20 is represented by K, and the time t and the temperature in the unit area i are represented by K._tiAnd The CPU 30_tiIs called from the hard disk 35 for each area and stored in the memory 31 (step S501).
The CPU 30 calculates the reference waveform R at time t._tIs called from the hard disk 35 (step S502). The reference waveform R_tIs an analog signal having the same cycle as the thermal load applied to the device under test 20.
The CPU 30 calculates the reference waveform R at time t and area i._tPhase difference P_tiIs calculated (step S503). Below, the phase difference P_tiIs shown.
The CPU 30 calculates the reference waveform R_tIs converted into a square wave, and digital data Sin (t) and Cos (t) of a sine wave and a cosine wave having the same frequency are generated.
Next, at time t, temperature K in unit area i_tiIs performed between the digital signal V (t) determined by the above and the reference waveforms Sin (t) and Cos (t).
[0050]
(Equation 1)

Where ΔV_sinRepresents the fluctuation amplitude of the infrared intensity synchronized with the reference waveform, and ΔV_cosRepresents the fluctuation amplitude of the infrared intensity synchronized with the cos wave whose phase is shifted by 90 degrees from the reference waveform. Note that N is the number of frames taken in the signal processing.
If the surface temperature fluctuation is completely in phase with the fluctuating heat load, then ΔV_cosBecomes 0. If the surface temperature fluctuation deviates from the phase of the fluctuating heat load due to the influence of heat diffusion, ΔV_cosAppears. In this case, the absolute value ΔV of the temperature fluctuation amplitude and the phase delay θ can be obtained by the following equations.
[0052]
(Equation 2)

Here, the obtained θ is converted to the reference waveform R at the time t and the unit area i._tPhase difference P_{t i}Is defined.
The CPU 30 adds 1 to i to obtain i + 1 to obtain the phase difference in the next unit area (step S504). Further, the processing of steps S501 to S504 is repeated until i exceeds the total number of areas I (step S505, YES)._tiIs obtained (step S505, NO).
Next, the CPU 30 adds .DELTA.t to the time t to make the time t + .DELTA.t (step S506), and repeats steps S501 to 506 until the predetermined analysis time T is exceeded (step S507, YES) (step S507). , NO).
As described above, the phase difference P_tiIs performed for each pixel of the infrared sensor in the infrared camera 23, that is, for the total number of regions I times, and the number of captured frames measured by the infrared camera 23 N times.
1-4-2. Display of analysis image
After completing the measurement data analysis process, the CPU 30 determines the phase difference P at the time T._TiIs called for each area, and based on this, image data of the entire measurement area is generated (step S405), and output to the display 33 (step S406). That is, the CPU 30 generates image data in correspondence with the input phase difference with a predetermined display color, and displays the image data.
FIG. 6A shows an example of display of image data when a defect inspection is performed on a concrete specimen having an artificial defect by applying the defect inspection system described above. Note that this image is obtained by measuring a concrete specimen having artificial defects 1 to 6 shown in FIG. The artificial defects 1 to 6 are manufactured by embedding defects having different depths and thicknesses in concrete.
In FIG. 6A, three clearly displayed contrast differences in the right column 61 correspond to the artificial defects 4 to 6, respectively. Although the artificial defects 1 to 3 are displayed in the left column 60, the contrast is not so clear.
Thus, it is considered that the heating period, which is one of the heating conditions of the heat wave set at the time of this inspection, was suitable for detecting artificial defects 4 to 6 having a depth of 20 mm.
1-5. Conclusion FIG. 7 is an example in which the phase difference between the measurement data and the reference waveform in the unit area of the measurement area is shown in a graph. Phase difference P in each unit area i in the frame of the measurement area measured by the infrared camera 23_tiIs a reference waveform R approximating the temperature variation curve 71 of the defective portion.₇₁And a reference waveform R approximating the temperature fluctuation curve 73 of the sound part.₇₃And can be expressed by the phase difference.
Since the phase difference displayed as image data is considered to be determined by the heating period and the depth of the defect, it is necessary to set a heating period according to the defect of the inspection object 20.
[0062] 2. Second embodiment
As described above, the phase difference displayed as the image data is determined by the heating period and the depth of the defect, and it is necessary to set an optimal heating period according to the depth of the defect to be inspected. FIG. 8 is an image when the artificial defect (FIG. 6B) is repeatedly measured by changing the heating period, which is one of the heating conditions, for the purpose of finding the optimal heating period.
As shown in FIGS. 8A to 8D, the contrast difference indicating defects 4 to 6 having a defect depth of 20 mm is clearly displayed when the period T is 10 to 30 minutes. Sometimes the contrast difference is most clearly displayed.
As shown in FIGS. 8B to 8E, the contrast difference indicating defects 1 to 3 having a defect depth of 30 mm is clearly displayed in a period T of 20 to 40 minutes. The contrast difference is displayed most clearly in minutes.
FIG. 9 shows an example of a relation table between the heating period and the defect depth, which is considered from the above results. As shown in FIG. 9, the heating period when the phase difference is the largest at each defect depth is considered to be the optimal heating period. For example, since the maximum phase difference when the defect depth is “10 mm” is “2.0 °”, the optimal heating period when inspecting this defect depth is “10 minutes”. That is, the optimal heating period corresponds to the “predetermined period in which the difference is remarkable” shown in [Claims].
Therefore, by using the relation table, the heating period can be set according to the defect depth of the inspection object 20 to be inspected. Thereby, the number of times of measurement can be reduced, and improvement in inspection efficiency can be expected.
In the present embodiment, a description will be given of a defect inspection method in which the inspection efficiency is improved by using a relation table between a heating period and a defect depth.
2-1. Overview of defect inspection
In the first embodiment, the defect detection is performed on the concrete specimen having the artificial defect. However, in the present embodiment, the defect inspection system according to the present invention is used for a concrete structure having an internal defect due to aging. The case where is applied will be described.
The concrete structure to be subjected to the defect inspection is made of the same material and environment as the concrete specimen, and is shown in FIG. 9 showing the relationship between the depth of the defect and the heating period. A table shall be used.
2-2. Defect depth estimation method
First, for the concrete structure to be inspected, the thickness of the concrete and the thickness of the reinforcing bar cover in the inspection range are checked, and the maximum depth at which the defect inspection is performed is determined. In order to check the thickness of the reinforcing bar cover, an inspection device using ultrasonic waves, microwave radar, electromagnetic induction, or the like may be used.
Next, the number of times of measurement is determined from the required inspection efficiency, and the heating period corresponding to the maximum depth is determined from the reference table of FIG. 9 to perform measurement. For example, in the present embodiment, as a result of the investigation, the maximum depth is considered to be 30 mm. Therefore, the heating period is set to 10 to 30 minutes and the number of times of measurement is set to 1 according to the reference table.
FIG. 10 shows image data obtained by applying the defect inspection system according to the present invention to a concrete structure. In FIGS. 10A to 10C, the heating period was changed to 10 to 30 minutes, respectively, and measurement was performed. In each image, it was clearly displayed that a defect was present at the center of the image. ing.
As shown in (1) to (3) below, quantitative information on this defect can be estimated from these images and the reference table.
{Circle around (1)} In FIG. 10 (A), the outline 101 of the defect at the center of the image is clearly displayed as a contrast difference with respect to the whole. Therefore, it can be estimated from the reference table that the defect depth in this range is around 10 mm. That is, a defect exists at about 10 mm from the surface.
{Circle around (2)} In FIG. 10 (B), the contrast difference indicating the outline 103 of the defect at the center of the image is displayed so as to increase toward the center as compared with FIG. 10 (A). Therefore, the depth of the defect in this range is about 20 mm from the reference table, and it can be estimated that the defect in this range has a larger hollow portion than the defect in the range of 10 mm.
{Circle around (3)} In FIG. 10 (C), the contrast difference indicating the outline 105 of the defect at the center of the image is displayed so as to be further enlarged toward the center as compared with FIG. 10 (B). Therefore, the depth of the defect in this range is about 30 mm from the reference table, and it can be estimated that the defect in this range has a larger hollow portion than the defect in the range of 20 mm.
Thus, it can be estimated that the internal defect is a float having a shape that exists at a depth of 10 mm to 30 mm from the surface of the concrete structure and tapers from the surface to the inside in the vertical direction.
FIG. 11 shows an example when the internal defect portion of the concrete structure measured this time is sampled. As shown in FIG. 11A, this internal defect portion has a contour having substantially the same shape as the contour portion of the contrast difference of the internal defect in the image shown in FIG. FIG. 11B shows a side surface of the internal defect portion, and its thickness was 20 to 30 mm.
As described above, by performing the defect inspection of the concrete structure using the defect inspection system to which the present invention is applied, the depth of the internal defect is identified, and the internal defect such as the size and thickness is determined. Can be estimated. As a result, the inspection efficiency in the defect inspection can be increased, and risk-based maintenance in which an effective countermeasure is taken in accordance with the defect accident probability becomes possible.
2-3. Flow chart in the defect inspection control device
FIG. 4 is a flowchart in the defect inspection control apparatus 10 for automatically estimating an internal defect by using the defect depth estimation method shown in FIG.
First, the maximum depth of a defect to be detected is input to the computer 29, which is the defect inspection control device 10 (step S1201). The maximum depth input at this time is 2-2. As shown in the above, it may be determined by a preliminary survey of the concrete structure.
Next, the number of times of measurement and the range of heating conditions are input based on the required inspection efficiency (step S1202). The range of the heating condition may be automatically determined by the CPU 30 according to the maximum depth.
In the defect inspection control device 10, the CPU 30 of the computer device 29 outputs heating conditions to the signal generator 27 (step S1203). Here, the heating condition refers to a time during which a thermal load is applied to the device under test 20 and the number of repetitions. Note that the amplitude is a constant value and the duty cycle is 50%.
The heating conditions are applied to a signal generator 27, converted into a waveform signal and output to a relay device 25. The relay device 25 operates the heater 21 based on the input waveform signal. As a result, a heat load is applied to the device under test 20 under predetermined heating conditions.
While the heating and the heating are stopped under a predetermined heating condition, the surface temperature of the inspection object 20 is measured by using the infrared camera 23, particularly during the heating stop period. The measurement data is output to the connected computer device 29 and recorded on the hard disk 35 or the like (step S1204). By repeating this measurement process every predetermined time, measurement data of the surface temperature at each measurement time during the heating stop period is obtained. The measurement data is surface temperature data for each unit area of the measurement area in the concrete structure that is the inspection object 20.
After performing the above processing at a predetermined number of repetitions, the measurement is terminated, the heating period is changed within the set range (step S1210), and the same processing is repeated from step S1203 (step S1205, NO). ). In the present embodiment, the number of repetitions of performing the heating and the heating stop is one.
When the measurement under the heating conditions in the set range is completed (step S1205, YES), the CPU 30 analyzes the measured data in each measured heating period (step S1206). Note that the measurement data analysis processing shown in step S1206 is the same as the processing shown in FIG. 4 of the first embodiment.
After completing the analysis of the measurement data in each heating period, the CPU 30 determines the phase difference P at the time T._TiIs called for each area, and the presence or absence of a defect is determined based on this. Further, the CPU 30 determines the depth at which the defect exists based on the correlation data indicating the phase difference of the region determined to be a defect (step S1207). That is, the depth of the region determined to indicate a defect is determined with reference to the phase difference of each region and the reference table 120 indicating the relationship between the heating period and the defect depth.
Next, the CPU 30 generates image data of the entire measurement area (step S1208), and outputs the image data shown in FIG. 10 to the display 33 (step S1209). In this embodiment, it is assumed that the value of the depth of the defective portion is simultaneously displayed on each screen (not shown).
Further, using the defect depth determined in step S1207, a defect shape estimation screen as shown in FIG. 13 may be displayed at the same time. As a result, quantitative information on the defective part is displayed as image data, and the inspection result in the defect inspection is easily confirmed, so that even those who do not have special judgment knowledge can find the internal defect. In FIG. 13, the defective portion is represented two-dimensionally, but may be represented as a three-dimensional shape. As a result, more detailed information on defects can be obtained.
3. Other embodiments
In the above embodiment, a concrete material is used as the inspection object 1, but the present invention is also applicable to a defect inspection of a composite material made of a low thermal conductive material such as CFRP.
In the above embodiment, the number of repetitions of heating / stopping the heating is one, but it may be repeated a plurality of times depending on the properties of the test object. In this case, if the reflection of the heat source on the surface of the object to be measured does not affect the measurement, the temperature fluctuation in both the heating and the heating stop periods may be continuously measured.
In the above embodiment, the phase difference between the waveform obtained from the measurement data and the predetermined reference waveform is used as the characteristic amount when determining the defective portion. However, another index may be used as the characteristic amount. . For example, temperature gradient data in the time change of measurement data, time change data of the temperature gradient data, frequency component data when Fourier analysis is performed on the measurement data, the peak value of the measurement data waveform, or the time to reach the peak value, May be used as the feature value.
Further, at the time of comparing these characteristic amounts, the measurement data are indirectly compared with each other by a correlation process between each measurement data and a predetermined reference waveform. However, each measurement data is directly compared. May be. For example, comparing peak values of respective measurement data corresponds to this.
In the above embodiment, the quantitative information on the defect site is obtained by using the relation table between the heating period and the defect depth, but the relation table to which the defect thickness is further added is used. Is also good. In this case, more accurate defect detection becomes possible.
In the above-described embodiment, the defect inspection control device 10 is constituted by the computer device 29 and the signal generation device 27. The defect inspection control device 10 is provided with a data collection device for realizing the heating control means 11 and the data recording means 13. The device and the defect determination device that implements the defect determination unit 15 may be configured by different devices. For example, by connecting these devices using a communication line, remote control in defect inspection becomes possible.
[Brief description of the drawings]
FIG. 1 is a functional block diagram of a defect detection system according to an embodiment of the present invention.
FIG. 2 is an example showing a configuration diagram of an apparatus for realizing a defect detection system according to an embodiment of the present invention.
FIG. 3 is an example showing a hardware configuration diagram of a computer device according to an embodiment of the present invention.
FIG. 4 is a diagram showing a flowchart in the defect inspection control device.
FIG. 4A is a diagram showing a relationship between a signal for heating control and a temperature variation curve on a surface of an inspection object.
FIG. 5 is a diagram showing a flowchart in a measurement data analysis process.
FIG. 6 is an example (A) of an artificial defect (B) and a display screen of image data when the artificial defect is measured.
FIG. 7 is a graph showing an example of a phase difference between measurement data and a reference waveform in a unit area of the measurement area.
FIG. 8 is an example of a display screen of image data when an artificial defect is measured by changing a heating period.
FIG. 9 is an example of a reference table showing a relationship between a heating period and a phase difference for each defect depth.
FIG. 10 is a display screen of image data when a heating period is changed and a concrete structure having an internal defect is measured.
FIG. 11 is an example when a measured internal defect portion of a concrete structure is collected.
FIG. 12 is a diagram showing a flowchart in the defect inspection control device when the reference table is used.
FIG. 13 is an example of a screen on which the shape of a defect is estimated based on quantitative information on a defect site.
[Explanation of symbols]
10. Defect inspection control device
11 ... heating control means
13 Data recording means
15 ... Defect judgment means
17 ・ ・ ・ Heating device
19 ・ ・ ・ Temperature measuring instrument

Claims (11)

Simultaneously heating the surface of the test object over the entire measurement area
At least in the heating stop period after stopping the heating,
For each unit area of the measurement area, measure the time change of the surface temperature,
A defect inspection method, wherein a defect in the inspection object is found based on a relative difference between the unit regions with respect to a time change of a surface temperature in each unit region. The defect inspection method according to claim 1,
The object to be inspected is made of a material having low thermal conductivity. The defect inspection method according to claim 1 or 2,
A position of a defect in the inspection object is specified based on a relative difference between the unit regions with respect to a time change of a surface temperature in each unit region. The defect inspection method according to any one of claims 1 to 3,
A relative difference between the unit areas with respect to a time change of the surface temperature in each unit area is presented as a visually recognizable image. The defect inspection method according to claim 4,
The relative difference is determined based on a comparison between a waveform based on a time change of the surface temperature in each unit area and a feature amount in a predetermined waveform. The defect inspection method according to claim 5,
The comparison of the feature amounts is performed based on a specific value indicating a correlation between both waveforms of the waveform due to the time change of the surface temperature in each unit area and a predetermined waveform, or a phase difference between both waveforms. thing. The defect inspection method according to any one of claims 1 to 6,
The heating and the stop of the heating are performed in a predetermined period, and the measurement is performed by changing the predetermined period, and the depth of the defect is estimated based on the predetermined period in which the difference in the relative temperature change between the unit regions is remarkable. Characterized by that. The defect inspection method according to claim 7,
Furthermore, the depth of the defect is estimated based on a table in which the depth of the defect is previously associated with a predetermined period. Heating control means for issuing a heating start command to a heating device that simultaneously heats the entire surface of the measurement area with respect to the surface of the test object,
Data recording means for inputting data from the temperature measuring device after the heating is stopped and recording the data as temperature data of each unit area,
Defect determination means for detecting a relative difference between the unit regions with respect to a time change of the surface temperature in each unit region based on the recorded temperature data, and determining a defect in the inspection object;
A defect inspection control device comprising: Heating control means for issuing a heating start command to a heating device that simultaneously heats the entire surface of the measurement area with respect to the surface of the test object,
Data recording means for inputting data from the temperature measuring device after the heating is stopped and recording the data as temperature data of each unit area,
A data collection device for defect inspection, comprising: Based on the temperature data of each unit area of the measurement area recorded after the heating of the surface of the inspection object is stopped, a relative difference between the unit areas with respect to a time change of the surface temperature in each unit area is detected and the inspection is performed. Defect determination means for determining a defect in the body,
A defect determination device for defect inspection, comprising:

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