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(19)【発行国】日本国特許庁(JP)
(12)【公報種別】公開特許公報(A)
(11)【公開番号】P2023133155
(43)【公開日】2023-09-22
(54)【発明の名称】対象物に関する寸法データを決定する装置及び方法
(51)【国際特許分類】
G01B 15/02 20060101AFI20230914BHJP
【ＦＩ】
G01B15/02 C
【審査請求】有
【請求項の数】22
【出願形態】ＯＬ
【外国語出願】
(21)【出願番号】P 2023021949
(22)【出願日】2023-02-15
(31)【優先権主張番号】10 2022 105 479.9
(32)【優先日】2022-03-09
(33)【優先権主張国・地域又は機関】DE
(71)【出願人】
【識別番号】511082609
【氏名又は名称】シコラ アーゲー
(74)【代理人】
【識別番号】100080182
【弁理士】
【氏名又は名称】渡辺 三彦
(74)【代理人】
【識別番号】100142572
【弁理士】
【氏名又は名称】水内 龍介
(72)【発明者】
【氏名】シュー トビアス コリャ
(72)【発明者】
【氏名】ボルテ ヒルマー
【テーマコード（参考）】
2F067
【Ｆターム（参考）】
2F067AA21
2F067AA27
2F067BB01
2F067BB06
2F067EE04
2F067HH02
2F067JJ02
2F067RR24
(57)【要約】 （修正有）
【課題】板状の対象物又はストランド状の対象物の寸法データを少ない経費で確実かつ正確に決定する装置及び方法を提供する。
【解決手段】板状の対象物又はストランド状の対象物１８の寸法データを決定する方法は、第１送信機１０によって対象物１８の表面上にテラヘルツ放射されるステップと、放射されたテラヘルツ放射が対象物１８を少なくとも１回通過した後に第１受信機１０により受信されるステップとを含み、キャリア周波数の５％未満の帯域幅を有するテラヘルツ放射を第２送信機１２により複数の時点で対象物１８に放射されるステップと、放射されたテラヘルツ放射は対象物１８を少なくとも１回通過した後に第２受信機１２によって受信されるステップと、対象物１８の寸法は、第１受信機１０により受信されたテラヘルツ放射を考慮した第２受信機１２により受信されたテラヘルツ放射の時間変化及び／又は空間変化から決定するステップとを含む。
【選択図】図１
【解決手段】板状の対象物又はストランド状の対象物１８の寸法データを決定する方法は、第１送信機１０によって対象物１８の表面上にテラヘルツ放射されるステップと、放射されたテラヘルツ放射が対象物１８を少なくとも１回通過した後に第１受信機１０により受信されるステップとを含み、キャリア周波数の５％未満の帯域幅を有するテラヘルツ放射を第２送信機１２により複数の時点で対象物１８に放射されるステップと、放射されたテラヘルツ放射は対象物１８を少なくとも１回通過した後に第２受信機１２によって受信されるステップと、対象物１８の寸法は、第１受信機１０により受信されたテラヘルツ放射を考慮した第２受信機１２により受信されたテラヘルツ放射の時間変化及び／又は空間変化から決定するステップとを含む。
【選択図】図１
【特許請求の範囲】
【請求項1】
板状の対象物（３４）又はストランド状の対象物（１８）、特にパイプ（１８）に関する寸法データ、特に厚さデータを決定する方法であって、
第１送信機（１０）によって、テラヘルツ放射が前記対象物（１８、３４）の表面上の少なくとも１箇所に、少なくとも１つの時点で放射されるステップと、
前記第１送信機（１０）により放射されたテラヘルツ放射は、前記対象物（１８、３４）を少なくとも１回通過した後に、第１受信機（１０）により受信されるステップと、を含み、
テラヘルツ放射のキャリア周波数の５％未満の帯域幅を有するテラヘルツ放射を、第２送信機（１２）により、複数の時点で前記対象物の表面に、及び／又は前記対象物（１８、３４）の表面の複数の位置に放射されるステップと、
前記第２送信機（１２）によって放射されたテラヘルツ放射は、放射が前記対象物（１８、３４）を少なくとも１回通過した後に、第２受信機（１２）によって受信されるステップと、
前記対象物（１８，３４）の寸法は、前記第２送信機（１２）により受信されたテラヘルツ放射から、及び／又は、前記第１受信機（１０）により受信されたテラヘルツ放射を考慮した前記第２受信機（１２）により受信されたテラヘルツ放射の時間変化及び／又は空間変化から決定するステップと、をさらに含むことを特徴とする、方法。
第１送信機（１０）によって、テラヘルツ放射が前記対象物（１８、３４）の表面上の少なくとも１箇所に、少なくとも１つの時点で放射されるステップと、
前記第１送信機（１０）により放射されたテラヘルツ放射は、前記対象物（１８、３４）を少なくとも１回通過した後に、第１受信機（１０）により受信されるステップと、を含み、
テラヘルツ放射のキャリア周波数の５％未満の帯域幅を有するテラヘルツ放射を、第２送信機（１２）により、複数の時点で前記対象物の表面に、及び／又は前記対象物（１８、３４）の表面の複数の位置に放射されるステップと、
前記第２送信機（１２）によって放射されたテラヘルツ放射は、放射が前記対象物（１８、３４）を少なくとも１回通過した後に、第２受信機（１２）によって受信されるステップと、
前記対象物（１８，３４）の寸法は、前記第２送信機（１２）により受信されたテラヘルツ放射から、及び／又は、前記第１受信機（１０）により受信されたテラヘルツ放射を考慮した前記第２受信機（１２）により受信されたテラヘルツ放射の時間変化及び／又は空間変化から決定するステップと、をさらに含むことを特徴とする、方法。
【請求項2】
前記第１送信機（１０）によって放射されるテラヘルツ放射の帯域幅は、該テラヘルツ放射のキャリア周波数の１０％を超える、好ましくは２０％を超えることを特徴とする、請求項１に記載の方法。
【請求項3】
前記第２送信機（１２）によって放射されるテラヘルツ放射の帯域幅は、該テラヘルツ放射のキャリア周波数の３％未満、好ましくは２％未満であることを特徴とする、請求項１又は請求項２に記載の方法。
【請求項4】
前記第１送信機（１０）及び前記第１受信機（１０）が第１送受信機（１０）によって形成されていること、及び／又は前記第２送信機（１２）及び前記第２受信機（１２）が第２送受信機（１２）によって形成されていることを特徴とする、請求項１から請求項３のいずれか一項に記載の方法。
【請求項5】
前記第１送信機（１０）によって放射されるテラヘルツ放射のための第１反射機（２２）が、前記第１送信機（１０）と反対側にある前記対象物（１８、３４）の側に配置されていること、及び／又は、前記第２送信機（１２）によって放射されるテラヘルツ放射のための第２反射機（２４）が、前記第２送信機（１２）と反対側にある前記対象物（１８、３４）の側に配置されていることを特徴とする、請求項１から請求項４のいずれか一項に記載の方法。
【請求項6】
前記第２送信機（１２）及び前記第２受信機（１２）が前記対象物（１８、３４）を中心に回転し、及び／又は前記対象物（１８、３４）に沿って転置され、かつ／あるいは前記対象物（１８、３４）の周囲又は前記対象物（１８、３４）に沿って配置された複数の前記第２送信機（１２）及び前記第２受信機（１２）が設けられることを特徴とする、請求項１から請求項５のいずれか一項に記載の方法。
【請求項7】
前記第２送信機（１２）は、前記対象物（１８、３４）の表面に斜め入射角でテラヘルツ放射を放射することを特徴とする請求項１から請求項６のいずれか一項に記載の方法。
【請求項8】
前記対象物（１８、３４）の寸法が、前記対象物（１８、３４）の屈折率を考慮して決定されることを特徴とする、請求項１から請求項７のいずれか一項に記載の方法。
【請求項9】
前記対象物（１８、３４）の屈折率は、前記第１受信機（１０）によって受信されたテラヘルツ放射から決定されることを特徴とする、請求項８に記載の方法。
【請求項10】
前記対象物の寸法は、前記第１送信機（１０）及び／又は前記第２送信機（１２）によって放射されたテラヘルツ放射の、前記対象物（１８、３４）を通る放射の通過中に生じる位相変化から決定されることを特徴とする、請求項１から請求項９のいずれか一項に記載の方法。
【請求項11】
前記対象物（１８、３４）の欠陥が、特に、前記第２受信機（１２）によって受信されたテラヘルツ放射信号の急速な信号変化に基づいて推測されることを特徴とする、請求項１から請求項１０のいずれか一項に記載の方法。
【請求項12】
板状の対象物又はストランド状の対象物（１８、３４）に関する寸法データを決定するための装置であって、
前記対象物（１８、３４）の表面上の少なくとも１箇所に、少なくとも１つの時点でテラヘルツ放射を放射するように設計されている第１送信機（１０）と、
前記第１送信機（１０）により放射されたテラヘルツ放射が前記対象物（１８，３４）を少なくとも１回通過した後に受信するように設計された第１受信機（１０）と、
テラヘルツ放射のキャリア周波数の５％未満の帯域幅を有するテラヘルツ放射を、複数の時点で前記対象物（１８、３４）の表面に、及び／又は対象物（１８、３４）の表面の複数の場所に放射するように設計されている第２送信機（１２）と、
前記第２送信機（１２）から放射されたテラヘルツ放射が前記対象物（１８，３４）を少なくとも１回通過した後に受信するように設計された第２受信機（１２）と、
前記第２送信機（１２）によって受信されたテラヘルツ放射から、及び／又は、前記第１受信機（１０）によって受信されたテラヘルツ放射を考慮した前記第２受信機（１２）によって受信されたテラヘルツ放射の時間的及び／又は空間的変化から前記対象物（１８、３４）の寸法を決定するように設計された評価装置（２６）と、を備えていることを特徴とする、装置。
前記対象物（１８、３４）の表面上の少なくとも１箇所に、少なくとも１つの時点でテラヘルツ放射を放射するように設計されている第１送信機（１０）と、
前記第１送信機（１０）により放射されたテラヘルツ放射が前記対象物（１８，３４）を少なくとも１回通過した後に受信するように設計された第１受信機（１０）と、
テラヘルツ放射のキャリア周波数の５％未満の帯域幅を有するテラヘルツ放射を、複数の時点で前記対象物（１８、３４）の表面に、及び／又は対象物（１８、３４）の表面の複数の場所に放射するように設計されている第２送信機（１２）と、
前記第２送信機（１２）から放射されたテラヘルツ放射が前記対象物（１８，３４）を少なくとも１回通過した後に受信するように設計された第２受信機（１２）と、
前記第２送信機（１２）によって受信されたテラヘルツ放射から、及び／又は、前記第１受信機（１０）によって受信されたテラヘルツ放射を考慮した前記第２受信機（１２）によって受信されたテラヘルツ放射の時間的及び／又は空間的変化から前記対象物（１８、３４）の寸法を決定するように設計された評価装置（２６）と、を備えていることを特徴とする、装置。
【請求項13】
前記第１送信機（１０）によって放射されるテラヘルツ放射の帯域幅は、該テラヘルツ放射のキャリア周波数の１０％を超える、好ましくは２０％を超えることを特徴とする、請求項１２に記載の装置。
【請求項14】
前記第２送信機（１２）によって放射されるテラヘルツ放射の帯域幅は、該テラヘルツ放射のキャリア周波数の３％未満、好ましくは２％未満であることを特徴とする、請求項１２又は請求項１３に記載の装置。
【請求項15】
前記第１送信機（１０）及び前記第１受信機（１０）は、第１送受信機（１０）によって形成されていること、及び／又は前記第２送信機（１２）及び前記第２受信機（１２）は、第２送受信機（１２）によって形成されていることを特徴とする請求項１２から請求項１４までのいずれか一項に記載の装置。
【請求項16】
前記第１送信機（１０）によって放射されるテラヘルツ放射のための第１反射機（２２）が、前記第１送信機（１０）と反対側にある前記対象物（１８，３４）の側に配置され、及び／又は前記第２送信機（１２）によって放射されるテラヘルツ放射のための第２反射機（２４）が、前記第２送信機（１２）と反対側にある前記対象物（１８，３４）の側に配置されていることを特徴とする、請求項１２から請求項１５までのいずれか一項に記載の装置。
【請求項17】
測定中に前記対象物（１８、３４）を中心に前記第２送信機（１２）及び前記第２受信機（１２）を回転させるため、及び／又は測定中に前記対象物（１８、３４）に沿って前記第２送信機（１２）及び前記第２受信機（１２）を転置するための回転装置及び／又は転置装置が設けられ、かつ／あるいは前記対象物（１８、３４）の周囲又は前記対象物（１８、３４）に沿って配置された複数の前記第２送信機（１２）及び前記第２受信機（１２）が設けられることを特徴とする、請求項１２から請求項１６までのいずれか一項に記載の装置。
【請求項18】
前記第２送信機（１２）は、前記対象物（１８、３４）の表面に斜め入射角でテラヘルツ放射を放出するように配置されていることを特徴とする請求項１２から請求項１７までのいずれか一項に記載の装置。
【請求項19】
前記評価装置（２６）は、前記対象物（１８、３４）の屈折率を考慮して前記対象物（１８、３４）の寸法を決定するようにさらに設計されていることを特徴とする、請求項１２から請求項１８までのいずれか一項に記載の装置。
【請求項20】
前記評価装置（２６）は、前記第１受信機（１０）によって受信されたテラヘルツ放射から前記対象物（１８，３４）の屈折率を決定するようにさらに設計されていることを特徴とする、請求項１９に記載の装置。
【請求項21】
前記評価装置（２６）は、前記第１送信機（１０）及び／又は前記第２送信機（１２）によって放射されたテラヘルツ放射の、前記対象物（１８、３４）を通過する放射の通過中に生じる位相変化から、前記対象物（１８、３４）の寸法を決定するように設計されていることを特徴とする、請求項１２から請求項２０までのいずれか一項に記載の装置。
【請求項22】
前記評価装置（２６）は、特に、前記第２受信機（１２）によって受信されたテラヘルツ放射信号の急速な信号変化に基づいて、前記対象物（１８，３４）の欠陥を推測するように設計されていることを特徴とする、請求項１２から請求項２１までのいずれか１項に記載の装置。
【発明の詳細な説明】
【技術分野】
【0001】
本発明は、板状又はストランド状の対象物に関する寸法データ、特に厚みデータを求める方法であって、テラヘルツ放射が、第１送信機によって、少なくとも１つの時点で対象物の表面の少なくとも１箇所に放射され、第１送信機によって放射されたテラヘルツ放射は、放射が対象物を少なくとも１度通過した後に第１受信機によって受信される。
【0002】
本発明はまた、板状又はストランド状の対象物に関する寸法データを決定するための装置であって、少なくとも１つの時点で対象物の表面の少なくとも１箇所にテラヘルツ放射を放射するように設計された第１送信機と、第１送信機によって放射されたテラヘルツ放射が対象物を少なくとも１度通過した後にそれを受信するように設計された第１受信機と、を備える装置に関するものである。
【背景技術】
【0003】
テラヘルツ放射、いわゆるミリ波を使って、例えばパイプのような板状又は線状の対象物に関する寸法データを測定することができる。このような寸法データには、例えば、直径又は厚さ、特に壁の厚さが含まれる。テラヘルツ放射の信号は、送信機から測定対象物に放射される。放射された信号は、対象物を通過し、対象物の境界面で反射される。その後、テラヘルツ放射が受信機で受信される。測定対象物によって、反射、散乱、吸収、屈折など、放射信号が操作される。その結果、テラヘルツ波の信号が変化することで、対象物について判定することができ、特に、対象物の境界層での反射を評価し、寸法データを決定することができる。さらに、対象物は空気中の伝搬に比べて密度が高いため、テラヘルツ放射信号が遅延する。したがって、放射信号の遅延を測定して材料の配向と屈折率が分かれば、対象物の寸法の絶対値を決定することができる。特に、パイプのような線状の対象物や板状の対象物には、この方法が適用される。
【0004】
しかし、対象物の境界層での反射を評価するためには、個々の境界層を分解できるようなテラヘルツ放射の帯域幅が必要である。測定対象物の寸法が小さい場合（例えば、肉厚が薄い場合）、使用するテラヘルツ放射の帯域幅には厳しい要求がある。必要な帯域幅は、光速を屈折率と分解したい構造（例えば、分解したい境界面の距離）の積の２倍で割った値にほぼ等しい。構造の大きさにもよるが、１００ＧＨｚ程度の帯域幅が必要となることもある。このため、小さな構造を確実に測定するために必要なテラヘルツ帯の送信機と受信機は、複雑でコスト高になる。多くの場合、特別な認可手続きが必要となる。また、この種の送受信機を複数台用意し、例えば測定するパイプの周囲に配置すると、さらに費用がかさむ。これは、測定対象物を放射し、可能な限り完全に測定するために、しばしば望ましいことである。
【0005】
また、対象物の形状の乱れ、特に、吹き溜まり、へこみ、膨らみなどの欠陥が別の問題として生じる。欠陥を検出するために、独国特許出願公開第１０２０１６１０５５９９号明細書（特許文献１）は、テスト対象物からやってきて送受信ユニットに向けられる反射がオブジェクトの欠陥においてのみ起こるように、非垂直角度で測定すべき対象物の境界面にテラヘルツ放射することを提案している。あるいは、測定対象物の境界面による反射を排除するために、主反射光をアパーチャーで抑制してもよい。
【0006】
独国実用新案第２０２０２１１００４１６号明細書（特許文献２）は、搬送方向に搬送されるストランド状製品の欠陥を検出するための評価装置を有する装置を提案し、この評価装置は、少なくとも１つの受信機によって受信されるテラヘルツ放射信号の一時的変化からストランド状製品の欠陥を推測するように設計されている。
【先行技術文献】
【特許文献】
【0007】
【特許文献1】独国特許出願公開第１０２０１６１０５５９９号明細書
【特許文献2】独国実用新案第２０２０２１１００４１６号明細書
【特許文献3】国際公開第２０１６／１３９１５５号
【発明の概要】
【発明を解決しようとする課題】
【0008】
説明した先行技術から基づき、本発明の目的は、冒頭に述べたタイプの方法及び装置を提供することであり、この方法によって、板状の対象物又はストランド状の対象物に関する寸法データを、少ない経費で確実かつ正確に決定することができる。
【課題を解決するための手段】
【0009】
本発明は、独立請求項１及び１２を有する目的を達成する。有利な実施形態は、従属請求項、説明、及び図に開示されている。
【0010】
本発明は、冒頭で述べたタイプの方法に関して、以下の手段によって目的を達成する。
‐テラヘルツ放射の搬送周波数の５％未満の帯域幅を有するテラヘルツ放射を、第２送信機によって、複数の時点及び／又は対象物の表面上の複数の位置で対象物の表面上に放射し、
‐前記第２送信機によって放射されたテラヘルツ放射は、放射が対象物を少なくとも１回通過した後に、前記第２受信機によって受信され、
‐前記第２送信機が受信したテラヘルツ放射から、及び／又は、前記第１受信機が受信したテラヘルツ放射を考慮して前記第２受信機が受信したテラヘルツ放射の時間及び／又は空間変化から、対象物の寸法が決定されること。
‐テラヘルツ放射の搬送周波数の５％未満の帯域幅を有するテラヘルツ放射を、第２送信機によって、複数の時点及び／又は対象物の表面上の複数の位置で対象物の表面上に放射し、
‐前記第２送信機によって放射されたテラヘルツ放射は、放射が対象物を少なくとも１回通過した後に、前記第２受信機によって受信され、
‐前記第２送信機が受信したテラヘルツ放射から、及び／又は、前記第１受信機が受信したテラヘルツ放射を考慮して前記第２受信機が受信したテラヘルツ放射の時間及び／又は空間変化から、対象物の寸法が決定されること。
【0011】
本発明は、冒頭で述べたタイプの装置に関して、以下の手段によって目的を達成する。
－テラヘルツ放射の搬送周波数の５％未満の帯域幅を有するテラヘルツ放射を、複数の時点で、及び／又は、対象物の表面の複数の場所に放射するように設計されている第２送信機と、
－前記第２送信機から送信されたテラヘルツ放射が前記対象物を少なくとも１回透過した後に受信する第２受信機と、
－前記第２送信機によって受信されたテラヘルツ放射から、及び／又は、前記第１受信機によって受信されたテラヘルツ放射を考慮して前記第２受信機によって受信されたテラヘルツ放射の時間的及び／又は空間的変化から対象物の寸法を決定するように設計されている評価装置。
－テラヘルツ放射の搬送周波数の５％未満の帯域幅を有するテラヘルツ放射を、複数の時点で、及び／又は、対象物の表面の複数の場所に放射するように設計されている第２送信機と、
－前記第２送信機から送信されたテラヘルツ放射が前記対象物を少なくとも１回透過した後に受信する第２受信機と、
－前記第２送信機によって受信されたテラヘルツ放射から、及び／又は、前記第１受信機によって受信されたテラヘルツ放射を考慮して前記第２受信機によって受信されたテラヘルツ放射の時間的及び／又は空間的変化から対象物の寸法を決定するように設計されている評価装置。
【0012】
本発明の測定される対象物は、例えば、プラスチックやガラスの対象物であってもよい。板状又はストランド状、例えばパイプ状である。測定中に第１及び第２送受信機を有する装置を通して、特にその長手方向軸に沿ってストランド状の対象物が搬送されてもよい。この目的のために、装置は、搬送装置を構成してもよい。対象物は、生産装置、例えば押出装置から出るかもしれない。測定中、対象物はまだ高温である可能性がある。また、測定中に対象物の固化がまだ完了していない可能性もある。したがって、対象物は、特に、溶融成分から構成されている可能性がある。
【0013】
本発明によれば、テラヘルツ放射、いわゆるミリ波を用いて、対象物を測定することができる。テラヘルツ放射は、例えば、１０ＧＨｚから３ＴＨｚの周波数範囲であってもよい。テラヘルツ放射は、例えば水蒸気などによる干渉の影響をほとんど受けないため、測定が困難な環境、例えば生産設備などにおける対象物、例えばプラスチックの対象物の測定によく適している。そのため、例えば押出装置から出たストランド状の対象物は、例えば水などの冷却流体を当てて冷却される。これにより、水蒸気が発生する。
【発明の効果】
【0014】
本発明は、一方では第１送信機と第１受信機を有する第１測定システム、他方では第２送信機と第２受信機を有する第２測定システムを用いて、対象物の複合測定を実施するというアイデアに基づいている。第２送信機は、テラヘルツ放射の搬送波周波数の５％未満の帯域幅を有するテラヘルツ放射を、対象物の表面の複数の時点及び／又は複数の位置に放射する。テラヘルツ放射の帯域幅は、送信機によって放射されるテラヘルツ放射の下限周波数と上限周波数との差として定義される。周波数限界は、キャリア周波数の上方及び下方、特にキャリア周波数から同じ距離のところにある。第１送信機は、第２送信機よりも大きな帯域幅を有するテラヘルツ放射を放射することができる。好ましくはより大きな帯域幅のために、対象物の屈折率が既知であるか、又は計量的に決定されている場合、対象物に関する寸法データの絶対値が、第１送信機及び第１受信機を用いて決定され得る。この目的のために、対象物の境界層上でのテラヘルツ放射の反射は、それ自体既知の方法で、例えば伝搬時間測定に基づいて評価することができる。本発明によれば、この測定は、より低い帯域幅を有するテラヘルツ放射を対象物の表面の複数の時間及び／又は複数の位置に放射する第２送信機を用いた測定と組み合わされる。放射が対象物を通過する間のテラヘルツ放射の遅延は、狭帯域の第２送信機と第２受信機を用いて測定することができる。特に、異なる時点で放射された放射信号の比較に基づいて、対象物の寸法、特に対象物の寸法変化、例えば対象物の厚さの変化を、第２送信機又は代替的に受信機の測定位置で特定することができる。これは、例えば、放射が対象物を通過する間に対象物によって生じる第２送信機の放射されたテラヘルツ放射の位相変化に基づいて行われ得る。このようにして、厚み変動を検出することができる。板状の対象物であれば、すぐに明確な測定結果が得られる。パイプ状の対象物の場合は、放射が通過したパイプの両壁の厚み変動の和が測定される。例えば第２送信機と第２受信機からなる測定システムよりも稀に測定を実施し、例えば対象物の絶対厚さを測定する第１送信機と第１受信機からなる測定システムと組み合わせて、第２送信機又はその代わりに受信機の測定位置、すなわち第２送信機によって放射される対象物上の位置において、決定された寸法、特に決定された寸法変化、例えば厚さの変化の絶対値を決定することが可能である。また、例えばパイプの絶対厚みの測定値に基づいて、個々のパイプ壁の厚み変動を推測することも可能である。
【0015】
したがって、絶対的な寸法値、特に寸法変化、例えば厚さの変化は、両方の測定システムの組み合わせにおいて、いつでも確実に決定することができる。本発明による測定システムの組み合わせは、例えばより広い帯域幅である第１測定システムは、時々、かつ対象物の表面のいくつかの位置においてのみ絶対的な厚さの測定を実施しなければならないのに対し、第２測定システムを用いた測定は、より頻繁に、かつ対象物の表面のより多くの位置において行われ得るという利点を提供する。それにもかかわらず、寸法データの完全な絶対的決定、例えば寸法変化は、例えば、第１測定システムとの相関関係によって、第２測定システムを用いて対象物を実質的に完全に検出することによって行われうる。第２送受信機からなる第２測定システムは、特に、対象物の境界面における直接的な放射の反射を評価するためではなく、放射の通過中に対象物によって生じるテラヘルツ放射の遅延を評価するために使用される。これに対して、第１測定システムは、特に、対象物の境界面におけるテラヘルツ放射の反射を評価するために使用される。
【0016】
低い帯域幅を有する測定システムは、費用対効果が高いだけでなく、実装が容易であり、評価が容易であり、一般に、承認要件がそれほど厳しくない。本発明による測定システムの組み合わせにより、対象物の包括的な測定、すなわち対象物へのテラヘルツ放射の広範囲な放射は、第２測定システムを用いてのみ行われる必要があるので、全体としてより低い支出を可能にすることができる。例えば、測定対象物の周囲に複数の送受信機を配置する場合、安価な狭帯域の第２送受信機を対象物の周囲に多く配置することができ、より広帯域の送受信機を多く配置することに伴うコストを発生させることはない。逆に、より薄い対象物も同じ帯域幅で測定することができる。
【0017】
原理的には、テラヘルツ放射が、第１送信機によって、ある時点において、対象物の表面の１箇所にのみ放射されることが可能である。しかし、第１送信機が、第２送信機と同様に、複数の時点及び／又は対象物の表面の複数の場所にテラヘルツ放射を放射することもまた可能である。例えば、説明したように、測定中に対象物が装置内を搬送されることも可能である。この場合、移動する対象物に放射されたテラヘルツ放射は、例えば静止した第１送信機又は第２送信機によって、複数の時点で対象物の表面の複数の場所に放射され得る。好ましくは、テラヘルツ放射は、第１送信機からのテラヘルツ放射の場合よりも、第２送信機によって、より多くの時点で、及び／又は、対象物の表面上のより多くの場所に放射される。特に、テラヘルツ放射が、例えば板状の対象物の場合には対象物の搬送方向に対して横方向に、あるいは代替的に、例えばその長手方向に沿って搬送される対象物の全周にわたって、対象物の実質的に全表面に、第２送信機によって放射されることが可能である。第２送信機が搬送方向に対して横方向に、又は代替的に対象物の周囲を十分に速く移動する場合、又は十分な数の第２送信機及びそれに応じて第２受信機が設けられる場合、このようにして、対象物の表面を実質的に完全にカバーし、したがって第２測定システムによる対象物の測定が可能である。第１測定システムによって比較的まれに行われる測定は、第２測定システムによって識別された寸法変化を対応する絶対値に変換するために依然として十分である。
【0018】
説明したように、第１送信機は、好ましくは、第２送信機よりも大きな帯域幅を有する。一実施形態によれば、第１送信機によって放射されるテラヘルツ放射の帯域幅は、テラヘルツ放射のキャリア周波数の１０％を超える、好ましくは２０％を超えていてもよい。また、第１送信機によって放射されるテラヘルツ放射の帯域幅は、１０ＧＨｚ以上、好ましくは２０ＧＨｚ以上であってもよい。第１送信機が放射するテラヘルツ放射の帯域幅は、光速を、屈折率と測定される寸法（例えば壁の厚さ）との積の２倍で割ったものより大きくてもよい。この種の広帯域センサーは、より高い費用を伴う。その代わり、この種の広帯域送信機は、対象物の境界面の短い距離も確実に解像できるため、絶対寸法、例えば対象物の絶対厚みと屈折率を確実に決定することができる。しかしながら、第１送信機が、第２送信機とは独立して動作し、例えば、予め定められた屈折率に基づいて対象物の総厚を決定する狭帯域の送信機でもあることも考えられるだろう。
【0019】
別の実施形態によれば、第２送信機によって放射されるテラヘルツ放射の帯域幅は、テラヘルツ放射のキャリア周波数の３％未満、好ましくは２％未満であってよい。特に、第２送信機のテラヘルツ放射として、ＩＳＭ帯内のテラヘルツ放射を用いることができれば好ましい。ＩＳＭ（Ｉｎｄｕｓｔｒｉａｌ， Ｓｃｉｅｎｔｉｆｉｃ， ａｎｄ Ｍｅｄｉｃａｌ）バンドは、一般に無認可で使用できる周波数帯である。その結果、出費をさらに抑えることができる。ＩＳＭバンドの例としては、１２２ＧＨｚから１２３ＧＨｚの範囲の周波数帯、すなわち１ＧＨｚの帯域幅を有するものが好適である。特に、第２送信機の帯域幅は、光速を、屈折率と測定される構造（例えば壁の厚さ）との積の２倍で割ったものよりも低くてもよく、好ましくは２倍低い。
【0020】
特に実現可能な実施形態によれば、第１送信機及び第１受信機は、第１送受信機によって形成されてもよく、及び／又は第２送信機及び第２受信機は、第２送受信機によって形成されてもよい。このように、対応する送信機及び受信機は、同じ場所に配置されるか、又はむしろ送受信機として統合される。
【0021】
別の実施形態によれば、第１送信機によって放射されたテラヘルツ放射のための第１反射器が、第１送信機と反対側の対象物の側に配置されること、及び／又は、第２送信機によって放射されたテラヘルツ放射のための第２反射器が、第２送信機と反対側の対象物の側に配置されることが提供可能である。反射器のために、テラヘルツ放射は、放射が対象物を通過した後、再び対象物を通過した後にそれぞれの受信機、特にそれぞれの送信機と共に送受信機の形態で設計された受信機によって受信されるような方法で反射される。
【0022】
第２送信機及び第２受信機は、測定中に対象物を中心に回転し、及び／又は対象物の長さを横切ることができる。代替的又は追加的に、対象物の周囲に又は対象物に沿って配置された複数の第２送信機及び第２受信機が設けられることも可能である。既に説明したように、狭帯域第２測定システムは、費用対効果が高く、出費が少ない。従って、前記測定システムは、対象物を中心に迅速に回転させるか、又は、代替的に、転置させることもでき、あるいは、比較的多数の第２送信機及び第２受信機を設けることもできる。その結果、測定中に装置内を移動する対象物に対して、特に包括的なカバー、したがって測定も行われ得る。例えば、複数の第２送信機及び第２受信機が設けられる場合、これらは、静止するように配置されてもよく、十分な数があれば、測定のために対象物の表面を実質的に完全にカバーすることが可能である。また、既に説明したように、同時に回転又は横行する複数の第２送信機及び第２受信機を設けることも考えられる。直線運動、特に横断は、板状の対象物の場合、特に対象物に沿って、即ち長手方向又はむしろ搬送方向に及び／又は長手方向又はむしろ搬送方向に対して横方向に行われることがある。横断と回転を組み合わせた運動も可能であり、例えばストランド状の対象物についての螺旋運動が行われるような場合である。
【0023】
原理的には、第１送信機と第１受信機からなる第１測定システムも、上記で説明した方法で対象物に対して相対的に移動させることができる。また、複数の第１送信機と第１受信機を設けることも考えられる。対応する実施形態は、上記で説明した第２送信機及び第２受信機の場合と同様であってよい。冒頭で説明したように、この点では、それにもかかわらず、対象物の表面の被覆率が低ければ十分である。
【0024】
別の実施形態によれば、第２送信機は、斜めの入射角、すなわち特に放射の通常の入射からずれた入射角で対象物の表面にテラヘルツ放射を放出することができる。原理的には、第２送信機と第２受信機からなる第２測定システムを用いたテラヘルツ放射による対象物の測定中に、例えば対象物による反射によって、追加の信号が発生し得るという問題が生ずる。この種の追加信号は、望ましくない方法で測定結果に影響を与え、特に、対象物を通過する放射の通過による測定された遅延に影響を与える可能性がある。この種の追加信号は、原理的には、求める遅延信号のみが残るように、計算手段によってフィルタリングすることができる。この場合、対象物の寸法、特に境界面間の短い距離ではなく、追加信号の原因となる障害物（例えば境界面）と測定システム（例えば反射器）との間の距離によって定義されるテラヘルツ放射のある帯域幅が必要となる。例えば反射器と対象物との間の対応する距離を選択することにより、追加信号にもかかわらず、比較的小さな帯域幅で信頼性の高い測定が行われることも可能である。しかしながら、上述の実施形態によれば、対象物の放射面に対するビーム経路の傾斜により、対象物の境界面における反射に起因する追加信号が防止されるため、望ましくない信号が防止される。測定系に直接起因する信号を校正することができる。測定信号から不要な成分を取り除くことができるため、計算による信号のフィルタリングが不要になる。そのため、単周波の連続波（ＣＷ）動作まで、最小限の帯域幅で測定することができる。 同時に、反射器などの測定系と対象物との距離を短くすることができ、装置の設置スペースを小さくすることができる。
【0025】
既に説明したように、対象物の（絶対）寸法は、対象物の屈折率を考慮して決定することができる。原理的には、寸法変化の絶対値を決定するために、対象物の材料に対する屈折率は既知であると仮定することができる。しかし、実際には、使用目的によっては、認識できない屈折率の変化が発生する場合がある。例えば、押出成形装置で製造される物品の場合、押出成形機に供給されるプラスチック混合物の未認識の変化により発生することがある。押出成形されたプラスチックは一般に添加物を含んでおり、その添加物の数や組成が異なることがある。そのため、屈折率が一定であると仮定した場合、誤差が生じる可能性がある。
【0026】
したがって、別の実施形態によれば、第１受信機によって受信されたテラヘルツ放射から、対象物の屈折率を決定することが可能である。原則的に、屈折率は、例えば国際公開第２０１６／１３９１５５号（特許文献３）に記載されているように決定することができる。したがって、ビーム経路に対象物がない状態での第１送信機と第１受信機との間のテラヘルツ放射の伝播時間と、既知の壁厚でビーム経路に対象物がある状態での第１送信機と第１受信機との間の伝播時間との比較から、ストランド材料の屈折率を推測することが可能である。第１送信機と第１受信機の位置と、存在する反射器の位置だけが分かっていなければならない。
【0027】
別の実施形態によれば、第１及び／又は第２送信機によって放射されたテラヘルツ放射の、放射の通過中に対象物によって生じる位相変化から、寸法、特に対象物の寸法変化及び／又は決定された寸法又は寸法変化の絶対値を決定することが可能である。対象物によって生じる放射されたテラヘルツ放射の位相変化を評価することによって、本発明に従って寸法を特に信頼性の高い正確な方法で決定することが可能である。位相又はむしろ位相変化を明確に決定するために、特に非常に狭帯域のテラヘルツ放射を使用する場合、ＣＷ動作まで、Ｉチャネル及びＱチャネルを評価する必要がある。このＩ・Ｑ法（同相・直交法）により、高周波の搬送波信号の位相情報を確実に求めることができる。位相変化を評価することで、より正確な測定が可能になるが、原理的には、周波数測定や振幅評価も考えられる。
【0028】
別の実施形態によれば、対象物の欠陥は、特に、第２受信機によって受信されたテラヘルツ放射信号の急速な信号変化に基づいて推測され得る。特に、比較的小さい、特にテラヘルツ放射の波長以下又はほぼ等しい対象物の物質的変化は、欠陥として理解されることになる。この種の欠陥はミー散乱体として作用し、大まかな近似では、すべての方向でほぼ同じ程度に散乱する。つまり、これらの欠陥によって散乱された信号は、散乱された信号全体から見れば小さい。一般的に、わずか１００ｍｍの距離では、１％未満である。１／ｒ2（ｒ＝距離）に比例して減少する。
【0029】
例えばテラヘルツ放射の低い帯域幅によって達成され得る、短い距離及び少ないノイズの場合、散乱信号は、直接検出され、欠陥として解釈され得る。対照的に、例えば、欠陥の直接反射の信号振幅によって欠陥を検出するための上述の文書、独国特許出願公開第１０２０１６１０５５９９号明細書（特許文献１）に示されたアプローチは、特に、反射器によって本ケースで提供され得るような反射面の存在下で、低い感度を有する。これに対して、上記でも説明した独国実用新案第２０２０２１１００４１６号明細書（特許文献２）に記載のアプローチは、テラヘルツ放射の位相変化を追加的かつ実質的に使用し、その結果、測定の感度が著しく改善されている。
【0030】
上述の実施形態は、テラヘルツ放射信号の比較的遅い変化は対象物の寸法変化によって引き起こされ、一方、寸法変化と比較して、小さな欠陥は、回折パターンの文脈で分離されるテラヘルツ放射信号の速い変化を引き起こすという考えに基づいている。これにより、受信したテラヘルツ放射信号に基づいて、寸法変化と欠陥の区別が可能になる。規則的にコヒーレントなテラヘルツ放射信号は、欠陥において回折効果を引き起こし、ビーム光学の観点から期待される放射経路の近くに欠陥がある場合、測定された放射信号も影響を受けるようになる。従って、この種の回折パターンは、欠陥を特定するために、特に振幅と位相の両方に関して評価することができる。
【0031】
欠陥によって直接散乱されるテラヘルツ放射信号は、一般に、場所によって（あるいは、測定対象物又は送信機もしくは代替的に受信機の移動によって、時間と共に）迅速に変化する。正確な実施形態にもよるが、該テラヘルツ放射信号は、典型的には、数ミリメートルの発振長を有する。例えば、テラヘルツ周波数が１２０ＧＨｚで、斜め入射角が２０°の送受信機を使用する場合、約３．７ｍｍの発振長が期待できる。したがって、テラヘルツ放射信号は、例えば局所周波数解析やマッチングフィルタを用いて、より大きな寸法変化による他の信号変化から確実に区別することができる。これは特に、欠陥信号の発振長が欠陥に依存せず、したがって既知であり、したがって、測定対象物又は送信機若しくはこれに代わる受信機の移動速度が既知である場合には、欠陥に起因する信号変化の周波数が既知であるためである。これは、例えば、テラヘルツ放射信号の振幅を考慮する場合には不可能であり、したがって、欠陥に起因する信号パターンの周波数又はそれに代わる位相の評価が好ましい。
【0032】
本発明による方法は、本発明による装置を用いて実施することができる。従って、本発明による装置、特にその評価装置は、本発明による方法を実施するように設計することができる。
【0033】
以下、本発明を例示的な実施形態に基づき、より詳細に説明する。
【図面の簡単な説明】
【0034】
【発明を実施するための形態】
【0035】
図中、特に断りのない限り、同じ参照符号は同じものを指している。
【0036】
図１に示す装置は、テラヘルツ放射のための第１送信機１０と、第１送信機１０によって放射されたテラヘルツ放射のための第１受信機１０とを備える第１送受信機１０を備える。また、テラヘルツ放射用の第２送信機１２と、第２送信機１２が放射するテラヘルツ放射を受信するための第２受信機１２とからなる第２送受信機１２を備えて構成されている。第２送信機１２は、テラヘルツ放射の搬送周波数の５％未満の帯域幅を有するテラヘルツ放射を放射し、それに応じて第２受信機１２によって受信される。対照的に、第１送信機１０は、より大きな帯域幅を有するテラヘルツ放射、特に、テラヘルツ放射のキャリア周波数の１０％を超える、好ましくは２０％を超える帯域幅を有するテラヘルツ放射を放射し、それは、第１受信機１０によってそれに応じて受信される。
【0037】
図１では、測定すべきパイプ１８の２つの対向する壁部１４、１６が高度に概略的に示されており、当該パイプは、例えばプラスチックパイプであり、特に押出装置から出るプラスチックパイプ１８である。パイプ１８は、図１の矢印２０によって示されるように、装置内をその長手軸に沿って搬送されることがある。図１では、パイプ１８の小さな部分のみが示されていることを理解されたい。さらに、第１送受信機１０には、第１送受信機１０に対向するパイプ１８の側に配置される第１反射器２２が割り当てられている。従って、第２送受信機１２には、第２送受信機１２に対向するパイプ１８の側面に配置される第２反射器２４が割り当てられている。さらに、この装置は、評価装置２６を備えており、この評価装置２６は、送受信機１０，１２、特に送受信機１０，１２の送信機１０，１２及び受信機１０，１２に接続されており、評価装置２６によってこれらを制御することができ、特に受信機１０，１２の測定データを評価装置に転送して評価することができるようになっている。この目的のために、送受信機１０、１２は、適切な信号線及び制御線を介して評価装置２６に接続される。
【0038】
テラヘルツ放射は、パイプ１８を測定するために、第１送信機１０によってパイプ１８に放射され、ここで、テラヘルツ放射は、パイプ１８を通過した後に反射器２２によって反射され、パイプ１８をもう一度通過した後に第１送信機１０に戻ってきて、第１受信機１０によって測定信号として受信されるようにする。これを図１では、ビーム経路２８で示す。その際、テラヘルツ放射は、パイプ１８の境界面で反射される。第１受信機１０の測定信号は評価装置２６に転送され、評価装置２６は、例えば伝搬時間測定を使用して、パイプ１８の材料の屈折率を考慮して境界面で反射された放射信号からパイプ１８の絶対寸法データ、例えば壁部１４、１６の壁厚を決定する。屈折率は、パイプ１８について既知であると仮定することができ、又は、上記で説明した方法で評価装置２６によって決定することができる。第１送受信機１０は、静止するように配置され、一定の時間間隔で測定のためのテラヘルツ放射を放射してもよい。
【0039】
この測定プロセスの間、より低い帯域幅のテラヘルツ放射も第２送信機１２からパイプ１８に放射され、このテラヘルツ放射はパイプ１８を通過した後に第２反射器２４で反射され、もう一度パイプ１８を通過して第２送信機１２に戻ってきて第２受信機１２で測定信号として受信される。これを図１では、ビーム経路３０で説明している。図１から分かるように、テラヘルツ放射は、パイプ１８の表面に斜めに入射するように放射される。テラヘルツ放射は、例えば図１に３２で示すように、パイプの境界面で屈折及び反射される。しかし、テラヘルツ放射の入射角度が斜めであるため、これらの反射信号は、第２送受信機１２には戻ってこず、したがって第２受信機１２にも戻ってこない。したがって、実質的にパイプ１８を通過する放射成分のみが、第２受信機１２によって検出及び測定される。測定信号は、今度は、評価装置２６に送信され、評価装置２６は、パイプ１８によって生じるテラヘルツ放射の遅延に基づいて、パイプ１８の時間的及び／又は空間的な寸法変化を決定する。寸法変化を決定するために、特に、パイプ１８によって生じるテラヘルツ放射の位相変化が決定される。寸法変化を時間的及び／又は空間的に検出するために、テラヘルツ放射は、複数の時点で第２送信機１２によって放射され、パイプ１８が長手方向に搬送されることにより、パイプ１８の表面上の複数の場所に放射される。第２送受信機１２は、パイプ１８の周縁の測定を実行するために、測定中にパイプ１８について回転することができる。しかし、パイプ１８の円周上に分散するように複数の第２送受信機１２を配置することも考えられるだろう。
【0040】
評価装置２６は、第１及び２受信機１０，１２の測定信号を相関させ、そこからパイプ１８の決定された寸法変化の絶対値を決定する。本実施例では、測定された寸法データ又はむしろ寸法変化は、厚さデータ又はむしろ厚さの変化である。
【0041】
図２は、板状の対象物３４の測定に基づく図１からの装置を示す。板状の対象物３４は、今度は、例えば、方向２０に装置を通して搬送することができる。測定及び評価は、図１に関して説明したのと実質的に同じ方法で行われる。しかしながら、図１とは異なり、図２の測定信号は、板状の対象物３４に関する明確な寸法データ、特に厚さデータを提供するが、図１では、決定された寸法データ、特に厚さデータは、両方の管壁１４、１６に関する全体的なデータである。図２において、例えば、複数の第２送受信器１２が搬送方向２０に対して横方向に、すなわち図２における描画面内に１つずつ隣り合って配置され、又は第２送受信器１２が測定中にこの方向にトラバースすることが考えられる。このようにして、例えば、測定は、板状の対象物１８、３４の実質的に全幅にわたって行われ得る。
【0042】
図１及び図２に示す両方のアプリケーションシナリオにおいて、特に、第２受信機１２によって受信されたテラヘルツ放射信号の急速な信号変化に基づいて対象物１８、３４の欠陥を推測することによって、測定される対象物１８、３４の欠陥の検出は依然として可能である。
【0043】
これについては、図３に基づいてより詳細に説明する。ここでは、３つの異なる欠陥サイズ（誤差サイズ）について、第２受信機１２の対応する測定信号が示されており、Ｘ軸には、それぞれのケースでミリメートル単位の欠陥の位置が指定されている。図３では、Ｉチャネル、Ｑチャネル、及び振幅の測定信号が、任意の単位で他の上に１つずつプロットされている。第２送信機１２は、ＣＷ動作時に、２．５ｍｍの波長を有するテラヘルツ放射を放出した。グラフの比較から、欠陥での散乱によって生じる測定信号は、特にＩ及びＱ法による位相評価の際に、方位及び距離に加えて、欠陥のサイズ及び形状に関する情報を提供する特徴的な信号形状を生じることが明らかである。図３の下段に示すように、純粋に振幅だけを考慮すると、よりシンプルな信号形状になるが、特にさらなる外乱がある場合には、検出が難しくなる。
【符号の説明】
【0044】
０ 送受信機、第１送信機、第１受信機
１２ 送受信機、第２送信機、第２受信機
１４ パイプの壁
１６ パイプの壁
１８ パイプ、対象物
２０ 搬送方向
２２ 第１反射器
２４ 第２反射器
２６ 評価装置
２８ ビーム経路
３０ ビーム経路
３２ ビーム経路
３４ 対象物
１２ 送受信機、第２送信機、第２受信機
１４ パイプの壁
１６ パイプの壁
１８ パイプ、対象物
２０ 搬送方向
２２ 第１反射器
２４ 第２反射器
２６ 評価装置
２８ ビーム経路
３０ ビーム経路
３２ ビーム経路
３４ 対象物
【図1】
【図2】
【図3】
【外国語明細書】
Device and method for determining dimensional data relating to an object
The invention relates to a method for determining dimensional data, in particular thickness data, relating to a plate-shaped object or a strand-shaped object, in particular a pipe, comprising the steps of: terahertz radiation is emitted by a first transmitter onto at least one location on the surface of the object at at least one point in time, the terahertz radiation emitted by the first transmitter is received by a first receiver after the radiation has passed through the object at least once.
The invention also relates to a device for determining dimensional data relating to a plate- or strand-shaped object, comprising a first transmitter which is designed to emit terahertz radiation onto at least one location on the surface of the object at at least one point in time, a first receiver which is designed to receive the terahertz radiation emitted by the first transmitter after the radiation has passed through the object at least once.
Dimensional data relating to plate-shaped or strand-shaped objects, for example pipes, can be measured using terahertz radiation, so-called millimeter waves. Such dimensional data include, for example, diameters or thicknesses, in particular wall thicknesses. A terahertz radiation signal is emitted by a transmitter onto the object to be measured. The emitted radiation signal passes through the object and is reflected on boundary surfaces of the object. Subsequently, the terahertz radiation is received by a receiver. On account of the object, the radiation signal is manipulated, in particular by means of reflection, scattering, absorption, and refraction. The resulting change of the terahertz radiation signal makes it possible to draw conclusions on the object, wherein, in particular, reflections on boundary layers of the object are evaluated in order to determine dimensional data. Moreover, the object delays the terahertz radiation signal on account of the higher density thereof in relation to propagation in air, and therefore absolute values of the dimensions of the object can be determined if the orientation and refractive index of the material are known by measuring the delay of the radiation signal. This applies, in particular, to plate-shaped or strand-shaped objects such as pipes.
However, in order to evaluate reflections on boundary layers of the object, a bandwidth of the terahertz radiation used that allows for resolution of the individual boundary layer is required. In the case of small dimensions to be measured, for example lower wall thicknesses, this places strict requirements on the bandwidth of the terahertz radiation used. The required bandwidth is approximately equal to the speed of light divided by twice the product of the refractive index and the structure to be resolved, for example a distance of boundary surfaces to be resolved. Depending on the structure size, this may require bandwidths in the range of 100 GHz. This makes the terahertz transmitters and receivers required for reliably measuring small structures complex and cost-intensive. Often, special approval procedures are required. The outlay increases further if multiple transmitters and receivers of this kind are provided, for example arranged around a pipe to be measured. This is often desirable in order to irradiate the object and thus measure it as fully as possible.
Another problem is posed by disturbances in the object geometry, in particular defects such as blowholes, dents, bulges, or the like. In order to detect defects, DE 10 2016 105 599 A1 proposes radiating terahertz radiation onto boundary surfaces of an object to be measured at a non-perpendicular angle, such that reflections coming from the test object and directed at a transmitting and receiving unit only occur at defects of the object. Alternatively, the main reflected radiation may also be suppressed by means of an aperture in order to exclude reflections by the boundary surfaces of the object from the measurement.
DE 20 2021 100 416 U1 proposes a device having an evaluation apparatus for detecting defects of a strand-shaped product conveyed in a conveying direction, which evaluation apparatus is designed to infer a defect of the strand-shaped product from a temporary change of a terahertz radiation signal received by at least one receiver.
Proceeding from the explained prior art, the object of the invention is to provide a method and a device of the type mentioned at the outset, by means of which dimensional data relating to a plate-shaped or strand-shaped object can be determined reliably and precisely with reduced outlay.
The invention achieves the object with the independent claims 1 and 12. Advantageous embodiments are disclosed in the dependent claims, the description, and the figures.
The invention achieves the object for a method of the type mentioned at the outset by means of the steps of:
- terahertz radiation having a bandwidth of less than 5% of the carrier frequency of the terahertz radiation is emitted by a second transmitter onto the surface of the object at multiple points in time and/or onto multiple locations on the surface of the object,
- the terahertz radiation emitted by the second transmitter is received by a second receiver after the radiation has passed through the object at least once,
- a dimension of the object is determined from the terahertz radiation received by the second transmitter and/or from a temporal and/or spatial change of the terahertz radiation received by the second receiver in consideration of the terahertz radiation received by the first receiver.
With regard to a device of the type mentioned at the outset, the invention achieves the object by means of
- a second transmitter which is designed to emit terahertz radiation having a bandwidth of less than 5% of the carrier frequency of the terahertz radiation onto the surface of the object at multiple points in time and/or onto multiple locations on the surface of the object,
- a second receiver which is designed to receive the terahertz radiation emitted by the second transmitter after the radiation has passed through the object at least once,
- an evaluation apparatus which is designed to determine a dimension of the object from the terahertz radiation received by the second transmitter and/or from a temporal and/or spatial change of the terahertz radiation received by the second receiver in consideration of the terahertz radiation received by the first receiver.
The object to be measured according to the invention may, for example, be a plastics or glass object. It is plate-shaped or strand-shaped, for example pipe-shaped. The object may be conveyed through the device having the first and second transmitters and receivers during the measurement, a strand-shaped object along its longitudinal axis, in particular. For this purpose, the device may comprise a conveying apparatus. The object may be exiting a production device, for example an extrusion device. It may still have a high temperature during the measurement. It is also possible that solidification of the object is not yet complete during the measurement. The object may therefore comprise molten components, in particular.
According to the invention, terahertz radiation, so-called millimeter waves, is used to measure the object. The terahertz radiation may, for example, be in a frequency range of from 10 GHz to 3 THz. Terahertz radiation is well suited for measuring objects, for example plastics objects, in difficult measuring environments, for example in production facilities, since terahertz radiation is largely insensitive to interference caused, for example, by water vapor. Therefore, strand-shaped objects exiting extrusion devices, for example, are cooled by applying a cooling fluid, for example water. This produces water vapor.
The invention is based on the idea of carrying out combined measurement of the object using a first measuring system having a first transmitter and first receiver, on the one hand, and a second measuring system having a second transmitter and second receiver, on the other hand. The second transmitter emits terahertz radiation having a bandwidth of less than 5% of the carrier frequency of the terahertz radiation at multiple points in time and/or onto multiple locations on the surface of the object. The bandwidth of the terahertz radiation is defined as the difference between the lower and upper frequency limit of the terahertz radiation emitted by the transmitter. The frequency limits are above and below the carrier frequency, in particular at the same distance from the carrier frequency. The first transmitter can emit terahertz radiation having a greater bandwidth than the second transmitter. On account of the preferably greater bandwidth, absolute values of dimensional data relating to the object can be determined by means of the first transmitter and first receiver if the refractive index of the object is known or has been metrologically determined. For this purpose, reflections of the terahertz radiation on boundary layers of the object can be evaluated in a manner known per se, for example based on propagation time measurements. According to the invention, this measurement is combined with a measurement using a second transmitter that emits terahertz radiation having a lower bandwidth at multiple times and/or onto multiple locations on the surface of the object. A delay of the terahertz radiation during passage of radiation through the object can be measured using the narrow-band second transmitter and second receiver. Based on a comparison of the radiation signals emitted, in particular, at different points in time, a dimension of the object, in particular a dimensional change of the object, for example a change in thickness of the object, can be identified at the measuring position of the second transmitter or, alternatively, receiver. This may, for example, be done based on a phase change of the emitted terahertz radiation of the second transmitter caused by the object during passage of radiation through the object. Thickness fluctuations can be detected in this manner. In the case of a plate-shaped object, a clear measurement is produced straight away. In the case of a pipe-shaped object, the measurement delivers the sum of the thickness fluctuations of both pipe walls through which radiation has passed. In combination with the measuring system consisting of the first transmitter and first receiver, which, for example, carries out a measurement more rarely than the measuring system consisting of the second transmitter and second receiver and, for example, measures the absolute thickness of the object, an absolute value of the determined dimension, in particular of the determined dimensional change, for example a change in thickness, can be determined at the measuring position of the second transmitter or, alternatively, receiver, i.e. the position on the object irradiated by the second transmitter. It is also possible to infer the thickness fluctuations of the individual pipe walls based on the absolute thickness measurement of, for example, a pipe.
Therefore, absolute dimensional values, in particular dimensional changes, for example changes in thickness, can be reliably determined at any time in the combination of both measuring systems. The combination of measuring systems according to the invention offers the advantage that the first measuring system, which is for example of a wider bandwidth, must only carry out an absolute thickness measurement occasionally, and at some locations on the surface of the object, whereas a measurement using the second measuring system can take place more frequently and at more locations on the surface of the object. Nevertheless, complete absolute determination of the dimensional data, for example dimensional changes, may take place by means of, for example, substantially complete detection of the object using the second measuring system by means of the correlation with the first measuring system. The second measuring system consisting of the second transmitter and receiver is used, in particular, not to evaluate the direct radiation reflections on boundary surfaces of the object, but rather the delay of the terahertz radiation caused by the object during passage of radiation. In contrast, the first measuring system is used, in particular, to evaluate reflections of the terahertz radiation on boundary surfaces of the object.
Measuring systems having a lower bandwidth are not only more cost-effective, but also easier to implement, easier to evaluate, and generally have less stringent approval requirements. On account of the combination of measuring systems according to the invention, an overall lower outlay is made possible, since comprehensive measurement of the object, i.e. extensive emission of terahertz radiation onto the object, only needs to be done using the second measuring system. For example, in the case of an arrangement of multiple transmitters and receivers around the object to be measured, the less expensive narrow-band second transmitters and transmitters can be positioned in greater numbers around the object, without incurring the costs associated with a larger number of wider-band transmitters and receivers. Vice versa, thinner objects can be measured at the same bandwidth.
In principle, it is possible for the terahertz radiation to only be emitted by the first transmitter onto one location on the surface of the object at one point in time. However, it is also possible for the first transmitter, like the second transmitter, to also emit terahertz radiation at multiple points in time and/or onto multiple locations on the surface of the object. For example, it is possible, as explained, for the object to be conveyed through the device during the measurement. In this case, terahertz radiation emitted onto the moving object can be emitted onto multiple locations on the surface of the object at multiple points in time by means of a, for example stationary, first transmitter or second transmitter. Preferably, terahertz radiation is emitted by the second transmitter at more points in time and/or onto more locations on the surface of the object than in the case of terahertz radiation from the first transmitter. It is possible, in particular, for terahertz radiation to be emitted by means of the second transmitter onto substantially the entire surface of the object, for example in the case of a plate-shaped object transversely to a conveying direction of the object or, alternatively, in the case of the strand-shaped object over the entire circumference of the object conveyed, for example, along the longitudinal direction thereof. In the case of a sufficiently fast movement of the second transmitter transversely to the conveying direction or, alternatively, around the object, or in the case of a sufficient number of second transmitters and, accordingly, second receivers being provided, in this way, substantially complete coverage of the object surface and thus measurement of the object by the second measuring system is possible. The measurements carried out comparatively more rarely by the first measuring system are still sufficient for converting the dimensional changes identified by the second measuring system into corresponding absolute values.
As explained, the first transmitter preferably has a greater bandwidth than the second transmitter. According to one embodiment, the bandwidth of the terahertz radiation emitted by the first transmitter may be more than 10%, preferably more than 20%, of the carrier frequency of the terahertz radiation. The bandwidth of the terahertz radiation emitted by the first transmitter may also be more than 10 GHz, preferably more than 20 GHz. The bandwidth of the terahertz radiation emitted by the first transmitter may be greater than the speed of light divided by twice the product of the refractive index and the dimension to be measured, for example a wall thickness. A wider-band sensor of this kind is associated with a higher outlay. In exchange, a wider-band transmitter of this kind is capable of reliably resolving even short distance of boundary surfaces of the object and thus of reliably determining the absolute dimensions, for example the absolute thickness of the object and the refractive index. However, it would also be conceivable for the first transmitter to also be a narrow-band transmitter that operates independently of the second transmitter and, for example, determines the total thickness of the object based on a predefined refractive index.
According to another embodiment, the bandwidth of the terahertz radiation emitted by the second transmitter may be less than 3%, preferably less than 2%, of the carrier frequency of the terahertz radiation. It is particularly preferable if terahertz radiation within an ISM band can be used as the terahertz radiation of the second transmitter. ISM (Industrial, Scientific, and Medical) bands are frequency ranges which can generally be used without approval. As a result, the outlay is further reduced. An example of a suitable ISM band is a frequency band in the range of from 122 to 123 GHz, i.e. with a bandwidth of 1 GHz. In particular, the bandwidth of the second transmitter may be lower than, preferably two times lower than, twice the speed of light divided by the product of the refractive index and the structure to be measured, for example the wall thickness.
According to a particularly feasible embodiment, the first transmitter and the first receiver may be formed by a first transceiver and/or the second transmitter and the second receiver may be formed by a second transceiver. The corresponding transmitters and receivers are thus arranged at the same location or rather integrated as transceivers.
According to another embodiment, it can be provided that a first reflector for the terahertz radiation emitted by the first transmitter is arranged on the side of the object that is opposite the first transmitter and/or that a second reflector for the terahertz radiation emitted by the second transmitter is arranged on the side of the object that is opposite the second transmitter. On account of the reflectors, the terahertz radiation is reflected in such a way after the radiation has passed through the object that it is received by the respective receiver after passing through the object once again, in particular the receiver designed in the form of a transceiver together with the respective transmitter.
The second transmitter and the second receiver may rotate about the object and/or traverse the length of the object during the measurement. Alternatively or additionally, it is also possible for multiple second transmitters and second receivers arranged around the object or along the object to be provided. As already explained, the narrow-band second measuring system is cost-effective and of low outlay. Accordingly, said measuring system may also be quickly rotated or, alternatively, transposed relative to the object or, alternatively, a relatively large number of second transmitters and second receivers may be provided. As a result, particularly comprehensive coverage and thus measurement can also take place for an object that is moved through the device during the measurement. For example, if multiple second transmitters and second receivers are provided, these may be arranged so as to be stationary, wherein, with a sufficient number, substantially complete coverage of the object surface is possible for the measurement. It is also conceivable for multiple second transmitters and second receivers to be provided which rotate or traverse at the same time, as already explained. A linear movement, in particular traversal, may in particular take place along the object in the case of a plate-shaped object, namely in the longitudinal direction or rather conveying direction and/or transversely to the longitudinal direction or rather conveying direction. A combined traversing and rotational movement is also possible, such that a helical movement about a, for example strand-shaped, object takes place, for example.
In principle, the first measuring system consisting of the first transmitter and first receiver can also be moved relative to the object in the manner explained above. It would also be conceivable to provide multiple first transmitters and first receivers. The corresponding embodiments may be the same as in the case of the second transmitter and second receiver, as explained above. As explained at the outset, a lower coverage of the object surface is nevertheless sufficient in this respect.
According to another embodiment, the second transmitter may emit terahertz radiation onto the surface of the object at an oblique angle of incidence, i.e. in particular an angle of incidence that deviates from normal incidence of radiation. In principle, the problem arises that additional signals can be caused, for example by reflections by the object, during measurement of the object with terahertz radiation using the second measuring system consisting of the second transmitter and the second receiver. Additional signals of this kind can influence the measurement result in an undesirable manner, in particular the measured delay due to the passage of radiation through the object. Additional signals of this kind can, in principle, be filtered out by computational means, such that only the delay signal that is sought remains. This requires a certain bandwidth of the terahertz radiation that is not, however, defined by the dimensions of the object, in particular short distances between boundary surfaces, but rather by the distance between the disturbances causing the additional signals, for example boundary surfaces, and the measuring system, for example a reflector. By selecting a corresponding distance, for example, between a reflector and the object, a reliable measurement can therefore also take place with a comparatively small bandwidth in spite of additional signals. However, according to the above-mentioned embodiment, undesired signals are prevented in that an inclination of the beam path with respect to the irradiated surface of the object prevents additional signals caused by reflections on boundary surfaces of the object. Signals directly caused by the measuring system can be calibrated out. By being able to remove all undesired components from the measured signal, no further computational signal filtering is required. Accordingly, measurements can take place with a minimal bandwidth through to mono-frequency continuous wave (CW) operation. At the same time, a short distance between the measuring system, for example a reflector, and the object is possible, such that the installation space of the device is reduced.
As already explained, the (absolute) dimension of the object can be determined in consideration of the refractive index of the object. In principle, the refractive index for the material of the object can be assumed to be known for the determination of the absolute values of the identified dimensional changes. However, in practice, unrecognized changes in the refractive index can sometimes occur depending on the intended use. For example, in the case of objects produced in extrusion devices, this can take place due to an unrecognized change in the plastics mixture supplied to the extruder. The extruded plastics generally comprise additives, wherein the number of additives and also the composition of the additives can vary. As a result, errors can occur if the refractive index is assumed to be constant.
According to another embodiment, it is therefore possible to determine the refractive index of the object from the terahertz radiation received by the first receiver. In principle, the refractive index can be determined as described, for example, in WO 2016/139155 A1. Therefore, it is possible to infer the refractive index of the strand material from a comparison of the propagation time of the terahertz radiation between the first transmitter and the first receiver without an object in the beam path with the propagation time between the first transmitter and the first receiver with an object in the beam path at a known wall thickness. Only the position of the first transmitter and first receiver and any reflector present must be known.
According to another embodiment, it is possible to determine the dimension, in particular the dimensional change of the object and/or the absolute value of the determined dimension or dimensional change, from a phase change, caused by the object during passage of radiation, of the terahertz radiation emitted by the first and/or second transmitter. By evaluating a phase change of the emitted terahertz radiation caused by the object, it is possible to determine the dimension in accordance with the invention in a particularly reliable and precise manner. In order to clearly determine the phase or rather phase change, the I channel and the Q channel must be evaluated, in particular when very narrow-band terahertz radiation is used, up to CW operation. By means of this I and Q method (in-phase and quadrature method), the phase information of a high-frequency carrier signal can be determined in a reliable manner. Although the evaluation of the phase change allows for a more accurate measurement, it would, in principle, also be conceivable to carry out a frequency measurement or amplitude evaluation.
According to another embodiment, a defect of the object can be inferred based, in particular, on rapid signal changes of the terahertz radiation signal received by the second receiver. In particular, material changes to the objects that are relatively small, in particular less than or approximately equal to the wavelength of the terahertz radiation, are to be understood as defects. Defects of this kind act as Mie scatterers which, in a rough approximation, scatter approximately to the same extent in all directions. This means that the signal scattered back by these defects is small relative to the overall scattered signal. Typically, at a distance of just 100 mm, it is less than 1%. It decreases proportionally to 1/r2, wherein r = distance.
In the case of short distances and little noise, which can be achieved, for example, by means of a low bandwidth of the terahertz radiation, the scattered signal can be detected directly and interpreted as a defect. In contrast, the approach presented, for example, in the above-mentioned document DE 10 2016 105 599 A1 for detecting defects by means of signal amplitudes of the direct reflection of a defect has a low sensitivity, in particular in the presence of reflective surfaces, as can be provided in the present case by means of the reflector. In contrast, the approach described in DE 20 2021 100 416 U1, which is also explained above, additionally and substantially uses phase changes of the terahertz radiation, as a result of which the sensitivity of the measurement is significantly improved.
The above-mentioned embodiment is based on the idea that relatively slow changes of the terahertz radiation signal are caused by dimensional changes of the object, whereas in comparison to dimensional changes, smaller defects cause faster changes of the terahertz radiation signal that are isolated in the context of a diffraction pattern. This makes it possible to distinguish between dimensional changes on the one hand and defects on the other hand based on the received terahertz radiation signal. The regularly coherent terahertz radiation signals cause diffraction effects at the defects, such that the measured radiation signal is also influenced when the defect is located near to the radiation paths that are expected in terms of beam optics. Accordingly, a diffraction pattern of this kind can be evaluated, specifically with regard to both the amplitude and the phase, in order to identify defects.
The terahertz radiation signal directly scattered by means of a defect generally changes quickly with location (or, alternatively, over time due to the movement of the measured object or of the transmitter or, alternatively, receiver). Depending on the exact embodiment, said terahertz radiation signal typically has an oscillation length of a few millimeters. For example, in the case of a terahertz frequency of 120 GHz and the use of a transmitter and receiver with an oblique angle of incidence of 20°, an oscillation length of approximately 3.7 mm can be expected. Accordingly, the terahertz radiation signal can be reliably distinguished from other signal changes caused by more significant dimensional changes, for example using a local frequency analysis or matching filter. This is in particular because the oscillation length of a defect signal is independent of the defect and is thus known and therefore, in the event of the movement speed of the measured object or of the transmitter or, alternatively, receiver being known, the frequency of the signal changes caused by a defect is known. This is not possible, for example, when considering the amplitudes of the terahertz radiation signal, and therefore an evaluation of the frequency or, alternatively, phase of the signal pattern caused by the defect is preferred.
The method according to the invention can be performed with the device according to the invention. Accordingly, the device according to the invention, in particular the evaluation apparatus thereof, can be designed to carry out the method according to the invention.
The invention will be explained in more detail below based on exemplary embodiments. In the drawings:
Fig. 1 shows a device according to the invention for carrying out the method according to the invention in a first application scenario,
Fig. 2 shows the device from Fig. 1 in a second application scenario, and
Fig. 3 shows graphs for illustrating the defect detection according to the invention.
The same reference signs refer to the same objects in the figures unless indicated otherwise.
The device shown in Fig. 1 comprises a first transceiver 10, comprising a first transmitter 10 for terahertz radiation and a first receiver 10 for the terahertz radiation emitted by the first transmitter 10. The device also comprises a second transceiver 12, comprising a second transmitter 12 for terahertz radiation and a second receiver 12 for receiving the terahertz radiation emitted by the second transmitter 12. The second transmitter 12 emits terahertz radiation having a bandwidth of less than 5% of the carrier frequency of the terahertz radiation, which is accordingly received by the second receiver 12. In contrast, the first transmitter 10 emits terahertz radiation having a greater bandwidth, in particular terahertz radiation having a bandwidth of more than 10%, preferably more than 20%, of the carrier frequency of the terahertz radiation, which is accordingly received by the first receiver 10.
In Fig. 1, two opposing wall portions 14, 16 of a pipe 18 to be measured are shown in a highly schematic manner, said pipe being a plastics pipe, for example, in particular a plastic pipe 18 exiting an extrusion device. The pipe 18 may be conveyed along its longitudinal axis through the device, as illustrated by the arrow 20 in Fig. 1. It should be understood that, in Fig. 1, only a small portion of the pipe 18 is shown. Moreover, the first transceiver 10 is assigned a first reflector 22, which is arranged on a side of the pipe 18 opposite the first transceiver 10. Accordingly, the second transceiver 12 is assigned a second reflector 24, which is arranged on a side of the pipe 18 opposite the second transceiver 12. Moreover, the device comprises an evaluation apparatus 26, which is connected to the transceivers 10, 12, in particular to the transmitters 10, 12 and receivers 10, 12 of the transceivers 10, 12, such that same can be controlled by means of the evaluation apparatus 26 and measurement data, in particular of the receivers 10, 12, can be forwarded to the evaluation apparatus for evaluation. For this purpose, the transceivers 10, 12 are connected to the evaluation apparatus 26 via suitable signal and control lines.
Terahertz radiation is emitted by the first transmitter 10 onto the pipe 18 in order to measure the pipe 18, wherein the terahertz radiation is reflected by the reflector 22 after passing through the pipe 18, such that it arrives back at the first transceiver 10 after passing through the pipe 18 once more and is received as a measurement signal by the first receiver 10. This is shown in Fig. 1 by the beam path 28. In the process, the terahertz radiation is reflected on boundary surfaces of the pipe 18. The measurement signals of the first receiver 10 are forwarded to the evaluation apparatus 26, which determines absolute dimensional data of the pipe 18, for example the wall thicknesses of the wall portions 14, 16, from the radiation signals reflected on the boundary surfaces in consideration of the refractive index of the material of the pipe 18, for example using propagation time measurements. The refractive index can be assumed to be known for the pipe 18 or determined by means of the evaluation apparatus 26 in the manner explained above. The first transceiver 10 may be arranged so as to be stationary and may emit terahertz radiation for a measurement at regular time intervals.
During this measurement process, terahertz radiation of a lower bandwidth is also emitted by the second transmitter 12 onto the pipe 18, wherein this terahertz radiation is reflected by the second reflector 24 after passing through the pipe 18 and arrives back at the second transceiver 12 after passing through the pipe 18 once more and is received as a measurement signal by the second receiver 12. This is illustrated in Fig. 1 by the beam path 30. As can be seen in Fig. 1, the terahertz radiation is emitted at an oblique angle of incidence onto the surface of the pipe 18. The terahertz radiation is refracted and reflected on the boundary surfaces of the pipe, as shown in Fig. 1 by 32, for example. However, due to the oblique angle of incidence of the terahertz radiation, these reflection signals do not arrive back at the second transceiver 12 and thus the second receiver 12. Therefore, substantially only the radiation components that pass through the pipe 18 are detected and measured by the second receiver 12. The measurement signals are, in turn, transmitted to the evaluation apparatus 26, which determines a temporal and/or spatial dimensional change of the pipe 18 based on the delay of the terahertz radiation caused by the pipe 18. In order to determine the dimensional changes, a phase change of the terahertz radiation caused by the pipe 18 is determined, in particular. In order to temporally and/or spatially detect the dimensional changes, the terahertz radiation is emitted by the second transmitter 12 at multiple points in time and, due to the pipe 18 being conveyed in the longitudinal direction, onto multiple locations on the surface of the pipe 18. The second transceiver 12 can rotate about the pipe 18 during the measurement in order to perform a measurement around the circumference of the pipe 18. However, it would also be conceivable to arrange multiple second transceivers 12 so as to be distributed around the circumference of the pipe 18.
The evaluation apparatus 26 correlates the measurement signals of the first and second receiver 10, 12 and determines the absolute values of the determined dimensional changes of the pipe 18 therefrom. In the present case, the measured dimensional data or rather dimensional changes are thickness data or rather changes in thickness.
Fig. 2 shows the device from Fig. 1 based on the measurement of a plate-shaped object 34. The plate-shaped object 34 can, in turn, be conveyed through the device in the direction 20, for example. The measurement and evaluation take place in substantially the same manner as explained with regard to Fig. 1. However, unlike in Fig. 1, the measurement signals in Fig. 2 provide clear dimensional data, in particular thickness data, relating to the plate-shaped object 34, whereas in Fig. 1 the determined dimensional data, in particular thickness data, are overall data for both pipe walls 14, 16. In Fig. 2, it would be conceivable, for example, for multiple second transceivers 12 to be arranged one next to the other transversely to the conveying direction 20, i.e. into the drawing plane in Fig. 2, or for the second transceiver 12 to traverse in this direction during the measurement. In this way, for example, a measurement can take place substantially over the entire width of the plate-shaped object 18, 34.
In both application scenarios shown in Fig. 1 and Fig. 2, detection of defects of the objects 18, 34 being measured is still possible, in particular by inferring a defect of the object 18, 34 based on rapid signal changes of the terahertz radiation signal received by the second receiver 12.
This will be explained in more detail based on Fig. 3. Here, corresponding measurement signals of the second receiver 12 are shown for three different defect sizes (error sizes), wherein the position of the defect in millimeters is specified in each case on the x-axis. In Fig. 3, the measurement signals of the I channel, Q channel, and amplitude are plotted one above the other in arbitrary units. The second transmitter 12 emitted terahertz radiation having a wavelength of 2.5 mm during CW operation. From a comparison of the graphs, it is clear that measurement signals that are caused by scattering at a defect produce a characteristic signal shape which provides information about the size and shape of the defect, in addition to the orientation and distance, in particular during the phase evaluation according to the I and Q method. Considering purely the amplitude, as shown at the bottom of Fig. 3, leads to a much simpler signal shape, which, however, is more difficult to detect, in particular in the presence of further disturbances.
List of Reference Signs
10 Transceiver, first transmitter, first receiver
12 Transceiver, second transmitter, second receiver
14 Pipe wall
16 Pipe wall
18 Pipe, object
20 Conveying direction
22 First reflector
24 Second reflector
26 Evaluation apparatus
28 Beam path
30 Beam path
32 Beam path
34 Object
The invention relates to a method for determining dimensional data, in particular thickness data, relating to a plate-shaped object or a strand-shaped object, in particular a pipe, comprising the steps of: terahertz radiation is emitted by a first transmitter onto at least one location on the surface of the object at at least one point in time, the terahertz radiation emitted by the first transmitter is received by a first receiver after the radiation has passed through the object at least once.
The invention also relates to a device for determining dimensional data relating to a plate- or strand-shaped object, comprising a first transmitter which is designed to emit terahertz radiation onto at least one location on the surface of the object at at least one point in time, a first receiver which is designed to receive the terahertz radiation emitted by the first transmitter after the radiation has passed through the object at least once.
Dimensional data relating to plate-shaped or strand-shaped objects, for example pipes, can be measured using terahertz radiation, so-called millimeter waves. Such dimensional data include, for example, diameters or thicknesses, in particular wall thicknesses. A terahertz radiation signal is emitted by a transmitter onto the object to be measured. The emitted radiation signal passes through the object and is reflected on boundary surfaces of the object. Subsequently, the terahertz radiation is received by a receiver. On account of the object, the radiation signal is manipulated, in particular by means of reflection, scattering, absorption, and refraction. The resulting change of the terahertz radiation signal makes it possible to draw conclusions on the object, wherein, in particular, reflections on boundary layers of the object are evaluated in order to determine dimensional data. Moreover, the object delays the terahertz radiation signal on account of the higher density thereof in relation to propagation in air, and therefore absolute values of the dimensions of the object can be determined if the orientation and refractive index of the material are known by measuring the delay of the radiation signal. This applies, in particular, to plate-shaped or strand-shaped objects such as pipes.
However, in order to evaluate reflections on boundary layers of the object, a bandwidth of the terahertz radiation used that allows for resolution of the individual boundary layer is required. In the case of small dimensions to be measured, for example lower wall thicknesses, this places strict requirements on the bandwidth of the terahertz radiation used. The required bandwidth is approximately equal to the speed of light divided by twice the product of the refractive index and the structure to be resolved, for example a distance of boundary surfaces to be resolved. Depending on the structure size, this may require bandwidths in the range of 100 GHz. This makes the terahertz transmitters and receivers required for reliably measuring small structures complex and cost-intensive. Often, special approval procedures are required. The outlay increases further if multiple transmitters and receivers of this kind are provided, for example arranged around a pipe to be measured. This is often desirable in order to irradiate the object and thus measure it as fully as possible.
Another problem is posed by disturbances in the object geometry, in particular defects such as blowholes, dents, bulges, or the like. In order to detect defects, DE 10 2016 105 599 A1 proposes radiating terahertz radiation onto boundary surfaces of an object to be measured at a non-perpendicular angle, such that reflections coming from the test object and directed at a transmitting and receiving unit only occur at defects of the object. Alternatively, the main reflected radiation may also be suppressed by means of an aperture in order to exclude reflections by the boundary surfaces of the object from the measurement.
DE 20 2021 100 416 U1 proposes a device having an evaluation apparatus for detecting defects of a strand-shaped product conveyed in a conveying direction, which evaluation apparatus is designed to infer a defect of the strand-shaped product from a temporary change of a terahertz radiation signal received by at least one receiver.
Proceeding from the explained prior art, the object of the invention is to provide a method and a device of the type mentioned at the outset, by means of which dimensional data relating to a plate-shaped or strand-shaped object can be determined reliably and precisely with reduced outlay.
The invention achieves the object with the independent claims 1 and 12. Advantageous embodiments are disclosed in the dependent claims, the description, and the figures.
The invention achieves the object for a method of the type mentioned at the outset by means of the steps of:
- terahertz radiation having a bandwidth of less than 5% of the carrier frequency of the terahertz radiation is emitted by a second transmitter onto the surface of the object at multiple points in time and/or onto multiple locations on the surface of the object,
- the terahertz radiation emitted by the second transmitter is received by a second receiver after the radiation has passed through the object at least once,
- a dimension of the object is determined from the terahertz radiation received by the second transmitter and/or from a temporal and/or spatial change of the terahertz radiation received by the second receiver in consideration of the terahertz radiation received by the first receiver.
With regard to a device of the type mentioned at the outset, the invention achieves the object by means of
- a second transmitter which is designed to emit terahertz radiation having a bandwidth of less than 5% of the carrier frequency of the terahertz radiation onto the surface of the object at multiple points in time and/or onto multiple locations on the surface of the object,
- a second receiver which is designed to receive the terahertz radiation emitted by the second transmitter after the radiation has passed through the object at least once,
- an evaluation apparatus which is designed to determine a dimension of the object from the terahertz radiation received by the second transmitter and/or from a temporal and/or spatial change of the terahertz radiation received by the second receiver in consideration of the terahertz radiation received by the first receiver.
The object to be measured according to the invention may, for example, be a plastics or glass object. It is plate-shaped or strand-shaped, for example pipe-shaped. The object may be conveyed through the device having the first and second transmitters and receivers during the measurement, a strand-shaped object along its longitudinal axis, in particular. For this purpose, the device may comprise a conveying apparatus. The object may be exiting a production device, for example an extrusion device. It may still have a high temperature during the measurement. It is also possible that solidification of the object is not yet complete during the measurement. The object may therefore comprise molten components, in particular.
According to the invention, terahertz radiation, so-called millimeter waves, is used to measure the object. The terahertz radiation may, for example, be in a frequency range of from 10 GHz to 3 THz. Terahertz radiation is well suited for measuring objects, for example plastics objects, in difficult measuring environments, for example in production facilities, since terahertz radiation is largely insensitive to interference caused, for example, by water vapor. Therefore, strand-shaped objects exiting extrusion devices, for example, are cooled by applying a cooling fluid, for example water. This produces water vapor.
The invention is based on the idea of carrying out combined measurement of the object using a first measuring system having a first transmitter and first receiver, on the one hand, and a second measuring system having a second transmitter and second receiver, on the other hand. The second transmitter emits terahertz radiation having a bandwidth of less than 5% of the carrier frequency of the terahertz radiation at multiple points in time and/or onto multiple locations on the surface of the object. The bandwidth of the terahertz radiation is defined as the difference between the lower and upper frequency limit of the terahertz radiation emitted by the transmitter. The frequency limits are above and below the carrier frequency, in particular at the same distance from the carrier frequency. The first transmitter can emit terahertz radiation having a greater bandwidth than the second transmitter. On account of the preferably greater bandwidth, absolute values of dimensional data relating to the object can be determined by means of the first transmitter and first receiver if the refractive index of the object is known or has been metrologically determined. For this purpose, reflections of the terahertz radiation on boundary layers of the object can be evaluated in a manner known per se, for example based on propagation time measurements. According to the invention, this measurement is combined with a measurement using a second transmitter that emits terahertz radiation having a lower bandwidth at multiple times and/or onto multiple locations on the surface of the object. A delay of the terahertz radiation during passage of radiation through the object can be measured using the narrow-band second transmitter and second receiver. Based on a comparison of the radiation signals emitted, in particular, at different points in time, a dimension of the object, in particular a dimensional change of the object, for example a change in thickness of the object, can be identified at the measuring position of the second transmitter or, alternatively, receiver. This may, for example, be done based on a phase change of the emitted terahertz radiation of the second transmitter caused by the object during passage of radiation through the object. Thickness fluctuations can be detected in this manner. In the case of a plate-shaped object, a clear measurement is produced straight away. In the case of a pipe-shaped object, the measurement delivers the sum of the thickness fluctuations of both pipe walls through which radiation has passed. In combination with the measuring system consisting of the first transmitter and first receiver, which, for example, carries out a measurement more rarely than the measuring system consisting of the second transmitter and second receiver and, for example, measures the absolute thickness of the object, an absolute value of the determined dimension, in particular of the determined dimensional change, for example a change in thickness, can be determined at the measuring position of the second transmitter or, alternatively, receiver, i.e. the position on the object irradiated by the second transmitter. It is also possible to infer the thickness fluctuations of the individual pipe walls based on the absolute thickness measurement of, for example, a pipe.
Therefore, absolute dimensional values, in particular dimensional changes, for example changes in thickness, can be reliably determined at any time in the combination of both measuring systems. The combination of measuring systems according to the invention offers the advantage that the first measuring system, which is for example of a wider bandwidth, must only carry out an absolute thickness measurement occasionally, and at some locations on the surface of the object, whereas a measurement using the second measuring system can take place more frequently and at more locations on the surface of the object. Nevertheless, complete absolute determination of the dimensional data, for example dimensional changes, may take place by means of, for example, substantially complete detection of the object using the second measuring system by means of the correlation with the first measuring system. The second measuring system consisting of the second transmitter and receiver is used, in particular, not to evaluate the direct radiation reflections on boundary surfaces of the object, but rather the delay of the terahertz radiation caused by the object during passage of radiation. In contrast, the first measuring system is used, in particular, to evaluate reflections of the terahertz radiation on boundary surfaces of the object.
Measuring systems having a lower bandwidth are not only more cost-effective, but also easier to implement, easier to evaluate, and generally have less stringent approval requirements. On account of the combination of measuring systems according to the invention, an overall lower outlay is made possible, since comprehensive measurement of the object, i.e. extensive emission of terahertz radiation onto the object, only needs to be done using the second measuring system. For example, in the case of an arrangement of multiple transmitters and receivers around the object to be measured, the less expensive narrow-band second transmitters and transmitters can be positioned in greater numbers around the object, without incurring the costs associated with a larger number of wider-band transmitters and receivers. Vice versa, thinner objects can be measured at the same bandwidth.
In principle, it is possible for the terahertz radiation to only be emitted by the first transmitter onto one location on the surface of the object at one point in time. However, it is also possible for the first transmitter, like the second transmitter, to also emit terahertz radiation at multiple points in time and/or onto multiple locations on the surface of the object. For example, it is possible, as explained, for the object to be conveyed through the device during the measurement. In this case, terahertz radiation emitted onto the moving object can be emitted onto multiple locations on the surface of the object at multiple points in time by means of a, for example stationary, first transmitter or second transmitter. Preferably, terahertz radiation is emitted by the second transmitter at more points in time and/or onto more locations on the surface of the object than in the case of terahertz radiation from the first transmitter. It is possible, in particular, for terahertz radiation to be emitted by means of the second transmitter onto substantially the entire surface of the object, for example in the case of a plate-shaped object transversely to a conveying direction of the object or, alternatively, in the case of the strand-shaped object over the entire circumference of the object conveyed, for example, along the longitudinal direction thereof. In the case of a sufficiently fast movement of the second transmitter transversely to the conveying direction or, alternatively, around the object, or in the case of a sufficient number of second transmitters and, accordingly, second receivers being provided, in this way, substantially complete coverage of the object surface and thus measurement of the object by the second measuring system is possible. The measurements carried out comparatively more rarely by the first measuring system are still sufficient for converting the dimensional changes identified by the second measuring system into corresponding absolute values.
As explained, the first transmitter preferably has a greater bandwidth than the second transmitter. According to one embodiment, the bandwidth of the terahertz radiation emitted by the first transmitter may be more than 10%, preferably more than 20%, of the carrier frequency of the terahertz radiation. The bandwidth of the terahertz radiation emitted by the first transmitter may also be more than 10 GHz, preferably more than 20 GHz. The bandwidth of the terahertz radiation emitted by the first transmitter may be greater than the speed of light divided by twice the product of the refractive index and the dimension to be measured, for example a wall thickness. A wider-band sensor of this kind is associated with a higher outlay. In exchange, a wider-band transmitter of this kind is capable of reliably resolving even short distance of boundary surfaces of the object and thus of reliably determining the absolute dimensions, for example the absolute thickness of the object and the refractive index. However, it would also be conceivable for the first transmitter to also be a narrow-band transmitter that operates independently of the second transmitter and, for example, determines the total thickness of the object based on a predefined refractive index.
According to another embodiment, the bandwidth of the terahertz radiation emitted by the second transmitter may be less than 3%, preferably less than 2%, of the carrier frequency of the terahertz radiation. It is particularly preferable if terahertz radiation within an ISM band can be used as the terahertz radiation of the second transmitter. ISM (Industrial, Scientific, and Medical) bands are frequency ranges which can generally be used without approval. As a result, the outlay is further reduced. An example of a suitable ISM band is a frequency band in the range of from 122 to 123 GHz, i.e. with a bandwidth of 1 GHz. In particular, the bandwidth of the second transmitter may be lower than, preferably two times lower than, twice the speed of light divided by the product of the refractive index and the structure to be measured, for example the wall thickness.
According to a particularly feasible embodiment, the first transmitter and the first receiver may be formed by a first transceiver and/or the second transmitter and the second receiver may be formed by a second transceiver. The corresponding transmitters and receivers are thus arranged at the same location or rather integrated as transceivers.
According to another embodiment, it can be provided that a first reflector for the terahertz radiation emitted by the first transmitter is arranged on the side of the object that is opposite the first transmitter and/or that a second reflector for the terahertz radiation emitted by the second transmitter is arranged on the side of the object that is opposite the second transmitter. On account of the reflectors, the terahertz radiation is reflected in such a way after the radiation has passed through the object that it is received by the respective receiver after passing through the object once again, in particular the receiver designed in the form of a transceiver together with the respective transmitter.
The second transmitter and the second receiver may rotate about the object and/or traverse the length of the object during the measurement. Alternatively or additionally, it is also possible for multiple second transmitters and second receivers arranged around the object or along the object to be provided. As already explained, the narrow-band second measuring system is cost-effective and of low outlay. Accordingly, said measuring system may also be quickly rotated or, alternatively, transposed relative to the object or, alternatively, a relatively large number of second transmitters and second receivers may be provided. As a result, particularly comprehensive coverage and thus measurement can also take place for an object that is moved through the device during the measurement. For example, if multiple second transmitters and second receivers are provided, these may be arranged so as to be stationary, wherein, with a sufficient number, substantially complete coverage of the object surface is possible for the measurement. It is also conceivable for multiple second transmitters and second receivers to be provided which rotate or traverse at the same time, as already explained. A linear movement, in particular traversal, may in particular take place along the object in the case of a plate-shaped object, namely in the longitudinal direction or rather conveying direction and/or transversely to the longitudinal direction or rather conveying direction. A combined traversing and rotational movement is also possible, such that a helical movement about a, for example strand-shaped, object takes place, for example.
In principle, the first measuring system consisting of the first transmitter and first receiver can also be moved relative to the object in the manner explained above. It would also be conceivable to provide multiple first transmitters and first receivers. The corresponding embodiments may be the same as in the case of the second transmitter and second receiver, as explained above. As explained at the outset, a lower coverage of the object surface is nevertheless sufficient in this respect.
According to another embodiment, the second transmitter may emit terahertz radiation onto the surface of the object at an oblique angle of incidence, i.e. in particular an angle of incidence that deviates from normal incidence of radiation. In principle, the problem arises that additional signals can be caused, for example by reflections by the object, during measurement of the object with terahertz radiation using the second measuring system consisting of the second transmitter and the second receiver. Additional signals of this kind can influence the measurement result in an undesirable manner, in particular the measured delay due to the passage of radiation through the object. Additional signals of this kind can, in principle, be filtered out by computational means, such that only the delay signal that is sought remains. This requires a certain bandwidth of the terahertz radiation that is not, however, defined by the dimensions of the object, in particular short distances between boundary surfaces, but rather by the distance between the disturbances causing the additional signals, for example boundary surfaces, and the measuring system, for example a reflector. By selecting a corresponding distance, for example, between a reflector and the object, a reliable measurement can therefore also take place with a comparatively small bandwidth in spite of additional signals. However, according to the above-mentioned embodiment, undesired signals are prevented in that an inclination of the beam path with respect to the irradiated surface of the object prevents additional signals caused by reflections on boundary surfaces of the object. Signals directly caused by the measuring system can be calibrated out. By being able to remove all undesired components from the measured signal, no further computational signal filtering is required. Accordingly, measurements can take place with a minimal bandwidth through to mono-frequency continuous wave (CW) operation. At the same time, a short distance between the measuring system, for example a reflector, and the object is possible, such that the installation space of the device is reduced.
As already explained, the (absolute) dimension of the object can be determined in consideration of the refractive index of the object. In principle, the refractive index for the material of the object can be assumed to be known for the determination of the absolute values of the identified dimensional changes. However, in practice, unrecognized changes in the refractive index can sometimes occur depending on the intended use. For example, in the case of objects produced in extrusion devices, this can take place due to an unrecognized change in the plastics mixture supplied to the extruder. The extruded plastics generally comprise additives, wherein the number of additives and also the composition of the additives can vary. As a result, errors can occur if the refractive index is assumed to be constant.
According to another embodiment, it is therefore possible to determine the refractive index of the object from the terahertz radiation received by the first receiver. In principle, the refractive index can be determined as described, for example, in WO 2016/139155 A1. Therefore, it is possible to infer the refractive index of the strand material from a comparison of the propagation time of the terahertz radiation between the first transmitter and the first receiver without an object in the beam path with the propagation time between the first transmitter and the first receiver with an object in the beam path at a known wall thickness. Only the position of the first transmitter and first receiver and any reflector present must be known.
According to another embodiment, it is possible to determine the dimension, in particular the dimensional change of the object and/or the absolute value of the determined dimension or dimensional change, from a phase change, caused by the object during passage of radiation, of the terahertz radiation emitted by the first and/or second transmitter. By evaluating a phase change of the emitted terahertz radiation caused by the object, it is possible to determine the dimension in accordance with the invention in a particularly reliable and precise manner. In order to clearly determine the phase or rather phase change, the I channel and the Q channel must be evaluated, in particular when very narrow-band terahertz radiation is used, up to CW operation. By means of this I and Q method (in-phase and quadrature method), the phase information of a high-frequency carrier signal can be determined in a reliable manner. Although the evaluation of the phase change allows for a more accurate measurement, it would, in principle, also be conceivable to carry out a frequency measurement or amplitude evaluation.
According to another embodiment, a defect of the object can be inferred based, in particular, on rapid signal changes of the terahertz radiation signal received by the second receiver. In particular, material changes to the objects that are relatively small, in particular less than or approximately equal to the wavelength of the terahertz radiation, are to be understood as defects. Defects of this kind act as Mie scatterers which, in a rough approximation, scatter approximately to the same extent in all directions. This means that the signal scattered back by these defects is small relative to the overall scattered signal. Typically, at a distance of just 100 mm, it is less than 1%. It decreases proportionally to 1/r2, wherein r = distance.
In the case of short distances and little noise, which can be achieved, for example, by means of a low bandwidth of the terahertz radiation, the scattered signal can be detected directly and interpreted as a defect. In contrast, the approach presented, for example, in the above-mentioned document DE 10 2016 105 599 A1 for detecting defects by means of signal amplitudes of the direct reflection of a defect has a low sensitivity, in particular in the presence of reflective surfaces, as can be provided in the present case by means of the reflector. In contrast, the approach described in DE 20 2021 100 416 U1, which is also explained above, additionally and substantially uses phase changes of the terahertz radiation, as a result of which the sensitivity of the measurement is significantly improved.
The above-mentioned embodiment is based on the idea that relatively slow changes of the terahertz radiation signal are caused by dimensional changes of the object, whereas in comparison to dimensional changes, smaller defects cause faster changes of the terahertz radiation signal that are isolated in the context of a diffraction pattern. This makes it possible to distinguish between dimensional changes on the one hand and defects on the other hand based on the received terahertz radiation signal. The regularly coherent terahertz radiation signals cause diffraction effects at the defects, such that the measured radiation signal is also influenced when the defect is located near to the radiation paths that are expected in terms of beam optics. Accordingly, a diffraction pattern of this kind can be evaluated, specifically with regard to both the amplitude and the phase, in order to identify defects.
The terahertz radiation signal directly scattered by means of a defect generally changes quickly with location (or, alternatively, over time due to the movement of the measured object or of the transmitter or, alternatively, receiver). Depending on the exact embodiment, said terahertz radiation signal typically has an oscillation length of a few millimeters. For example, in the case of a terahertz frequency of 120 GHz and the use of a transmitter and receiver with an oblique angle of incidence of 20°, an oscillation length of approximately 3.7 mm can be expected. Accordingly, the terahertz radiation signal can be reliably distinguished from other signal changes caused by more significant dimensional changes, for example using a local frequency analysis or matching filter. This is in particular because the oscillation length of a defect signal is independent of the defect and is thus known and therefore, in the event of the movement speed of the measured object or of the transmitter or, alternatively, receiver being known, the frequency of the signal changes caused by a defect is known. This is not possible, for example, when considering the amplitudes of the terahertz radiation signal, and therefore an evaluation of the frequency or, alternatively, phase of the signal pattern caused by the defect is preferred.
The method according to the invention can be performed with the device according to the invention. Accordingly, the device according to the invention, in particular the evaluation apparatus thereof, can be designed to carry out the method according to the invention.
The invention will be explained in more detail below based on exemplary embodiments. In the drawings:
Fig. 1 shows a device according to the invention for carrying out the method according to the invention in a first application scenario,
Fig. 2 shows the device from Fig. 1 in a second application scenario, and
Fig. 3 shows graphs for illustrating the defect detection according to the invention.
The same reference signs refer to the same objects in the figures unless indicated otherwise.
The device shown in Fig. 1 comprises a first transceiver 10, comprising a first transmitter 10 for terahertz radiation and a first receiver 10 for the terahertz radiation emitted by the first transmitter 10. The device also comprises a second transceiver 12, comprising a second transmitter 12 for terahertz radiation and a second receiver 12 for receiving the terahertz radiation emitted by the second transmitter 12. The second transmitter 12 emits terahertz radiation having a bandwidth of less than 5% of the carrier frequency of the terahertz radiation, which is accordingly received by the second receiver 12. In contrast, the first transmitter 10 emits terahertz radiation having a greater bandwidth, in particular terahertz radiation having a bandwidth of more than 10%, preferably more than 20%, of the carrier frequency of the terahertz radiation, which is accordingly received by the first receiver 10.
In Fig. 1, two opposing wall portions 14, 16 of a pipe 18 to be measured are shown in a highly schematic manner, said pipe being a plastics pipe, for example, in particular a plastic pipe 18 exiting an extrusion device. The pipe 18 may be conveyed along its longitudinal axis through the device, as illustrated by the arrow 20 in Fig. 1. It should be understood that, in Fig. 1, only a small portion of the pipe 18 is shown. Moreover, the first transceiver 10 is assigned a first reflector 22, which is arranged on a side of the pipe 18 opposite the first transceiver 10. Accordingly, the second transceiver 12 is assigned a second reflector 24, which is arranged on a side of the pipe 18 opposite the second transceiver 12. Moreover, the device comprises an evaluation apparatus 26, which is connected to the transceivers 10, 12, in particular to the transmitters 10, 12 and receivers 10, 12 of the transceivers 10, 12, such that same can be controlled by means of the evaluation apparatus 26 and measurement data, in particular of the receivers 10, 12, can be forwarded to the evaluation apparatus for evaluation. For this purpose, the transceivers 10, 12 are connected to the evaluation apparatus 26 via suitable signal and control lines.
Terahertz radiation is emitted by the first transmitter 10 onto the pipe 18 in order to measure the pipe 18, wherein the terahertz radiation is reflected by the reflector 22 after passing through the pipe 18, such that it arrives back at the first transceiver 10 after passing through the pipe 18 once more and is received as a measurement signal by the first receiver 10. This is shown in Fig. 1 by the beam path 28. In the process, the terahertz radiation is reflected on boundary surfaces of the pipe 18. The measurement signals of the first receiver 10 are forwarded to the evaluation apparatus 26, which determines absolute dimensional data of the pipe 18, for example the wall thicknesses of the wall portions 14, 16, from the radiation signals reflected on the boundary surfaces in consideration of the refractive index of the material of the pipe 18, for example using propagation time measurements. The refractive index can be assumed to be known for the pipe 18 or determined by means of the evaluation apparatus 26 in the manner explained above. The first transceiver 10 may be arranged so as to be stationary and may emit terahertz radiation for a measurement at regular time intervals.
During this measurement process, terahertz radiation of a lower bandwidth is also emitted by the second transmitter 12 onto the pipe 18, wherein this terahertz radiation is reflected by the second reflector 24 after passing through the pipe 18 and arrives back at the second transceiver 12 after passing through the pipe 18 once more and is received as a measurement signal by the second receiver 12. This is illustrated in Fig. 1 by the beam path 30. As can be seen in Fig. 1, the terahertz radiation is emitted at an oblique angle of incidence onto the surface of the pipe 18. The terahertz radiation is refracted and reflected on the boundary surfaces of the pipe, as shown in Fig. 1 by 32, for example. However, due to the oblique angle of incidence of the terahertz radiation, these reflection signals do not arrive back at the second transceiver 12 and thus the second receiver 12. Therefore, substantially only the radiation components that pass through the pipe 18 are detected and measured by the second receiver 12. The measurement signals are, in turn, transmitted to the evaluation apparatus 26, which determines a temporal and/or spatial dimensional change of the pipe 18 based on the delay of the terahertz radiation caused by the pipe 18. In order to determine the dimensional changes, a phase change of the terahertz radiation caused by the pipe 18 is determined, in particular. In order to temporally and/or spatially detect the dimensional changes, the terahertz radiation is emitted by the second transmitter 12 at multiple points in time and, due to the pipe 18 being conveyed in the longitudinal direction, onto multiple locations on the surface of the pipe 18. The second transceiver 12 can rotate about the pipe 18 during the measurement in order to perform a measurement around the circumference of the pipe 18. However, it would also be conceivable to arrange multiple second transceivers 12 so as to be distributed around the circumference of the pipe 18.
The evaluation apparatus 26 correlates the measurement signals of the first and second receiver 10, 12 and determines the absolute values of the determined dimensional changes of the pipe 18 therefrom. In the present case, the measured dimensional data or rather dimensional changes are thickness data or rather changes in thickness.
Fig. 2 shows the device from Fig. 1 based on the measurement of a plate-shaped object 34. The plate-shaped object 34 can, in turn, be conveyed through the device in the direction 20, for example. The measurement and evaluation take place in substantially the same manner as explained with regard to Fig. 1. However, unlike in Fig. 1, the measurement signals in Fig. 2 provide clear dimensional data, in particular thickness data, relating to the plate-shaped object 34, whereas in Fig. 1 the determined dimensional data, in particular thickness data, are overall data for both pipe walls 14, 16. In Fig. 2, it would be conceivable, for example, for multiple second transceivers 12 to be arranged one next to the other transversely to the conveying direction 20, i.e. into the drawing plane in Fig. 2, or for the second transceiver 12 to traverse in this direction during the measurement. In this way, for example, a measurement can take place substantially over the entire width of the plate-shaped object 18, 34.
In both application scenarios shown in Fig. 1 and Fig. 2, detection of defects of the objects 18, 34 being measured is still possible, in particular by inferring a defect of the object 18, 34 based on rapid signal changes of the terahertz radiation signal received by the second receiver 12.
This will be explained in more detail based on Fig. 3. Here, corresponding measurement signals of the second receiver 12 are shown for three different defect sizes (error sizes), wherein the position of the defect in millimeters is specified in each case on the x-axis. In Fig. 3, the measurement signals of the I channel, Q channel, and amplitude are plotted one above the other in arbitrary units. The second transmitter 12 emitted terahertz radiation having a wavelength of 2.5 mm during CW operation. From a comparison of the graphs, it is clear that measurement signals that are caused by scattering at a defect produce a characteristic signal shape which provides information about the size and shape of the defect, in addition to the orientation and distance, in particular during the phase evaluation according to the I and Q method. Considering purely the amplitude, as shown at the bottom of Fig. 3, leads to a much simpler signal shape, which, however, is more difficult to detect, in particular in the presence of further disturbances.
List of Reference Signs
10 Transceiver, first transmitter, first receiver
12 Transceiver, second transmitter, second receiver
14 Pipe wall
16 Pipe wall
18 Pipe, object
20 Conveying direction
22 First reflector
24 Second reflector
26 Evaluation apparatus
28 Beam path
30 Beam path
32 Beam path
34 Object
Claims
1. A method for determining dimensional data, in particular thickness data, relating to a plate-shaped object (34) or strand-shaped object (18), in particular a pipe (18), comprising the steps of:
- terahertz radiation is emitted by a first transmitter (10) onto at least one location on the surface of the object (18, 34) at at least one point in time,
- the terahertz radiation emitted by the first transmitter (10) is received by a first receiver (10) after the radiation has passed through the object (18, 34) at least once,
characterized by the further steps of:
- terahertz radiation having a bandwidth of less than 5% of the carrier frequency of the terahertz radiation is emitted by a second transmitter (12) onto the surface of the object at multiple points in time and/or onto multiple locations on the surface of the object (18, 34),
- the terahertz radiation emitted by the second transmitter (12) is received by a second receiver (12) after the radiation has passed through the object (18, 34) at least once,
- a dimension of the object (18, 34) is determined from the terahertz radiation received by the second transmitter (12) and/or from a temporal and/or spatial change of the terahertz radiation received by the second receiver (12) in consideration of the terahertz radiation received by the first receiver (10).
2. The method according to claim 1, characterized in that the bandwidth of the terahertz radiation emitted by the first transmitter (10) is more than 10%, preferably more than 20%, of the carrier frequency of the terahertz radiation.
3. The method according to any one of the preceding claims, characterized in that the bandwidth of the terahertz radiation emitted by the second transmitter (12) is less than 3%, preferably less than 2%, of the carrier frequency of the terahertz radiation.
4. The method according to any one of the preceding claims, characterized in that the first transmitter (10) and the first receiver (10) are formed by a first transceiver (10) and/or in that the second transmitter (12) and the second receiver (12) are formed by a second transceiver (12).
5. The method according to any one of the preceding claims, characterized in that a first reflector (22) for the terahertz radiation emitted by the first transmitter (10) is arranged on the side of the object (18, 34) that is opposite the first transmitter (10) and/or in that a second reflector (24) for the terahertz radiation emitted by the second transmitter (12) is arranged on the side of the object (18, 34) that is opposite the second transmitter (12).
6. The method according to any one of the preceding claims, characterized in that the second transmitter (12) and the second receiver (12) are rotated about the object (18, 34) and/or transposed along the object (18, 34) and/or in that multiple second transmitters (12) and second receivers (12) arranged around the object (18, 34) or along the object (18, 34) are provided.
7. The method according to any one of the preceding claims, characterized in that the second transmitter (12) emits terahertz radiation at an oblique angle of incidence onto the surface of the object (18, 34).
8. The method according to any one of the preceding claims, characterized in that the dimension of the object (18, 34) is determined in consideration of the refractive index of the object (18, 34).
9. The method according to claim 8, characterized in that the refractive index of the object (18, 34) is determined from the terahertz radiation received by the first receiver (10).
10. The method according to any one of the preceding claims, characterized in that the dimension of the object is determined from a phase change, caused during passage of radiation through the object (18, 34), of the terahertz radiation emitted by the first and/or second transmitter (12).
11. The method according to any one of the preceding claims, characterized in that a defect of the object (18, 34) is inferred based, in particular, on rapid signal changes of the terahertz radiation signal received by the second receiver (12).
12. A device for determining dimensional data relating to a plate- or strand-shaped object (18, 34), comprising
- a first transmitter (10) which is designed to emit terahertz radiation onto at least one location on the surface of the object (18, 34) at at least one point in time,
- a first receiver (10) which is designed to receive the terahertz radiation emitted by the first transmitter (10) after the radiation has passed through the object (18, 34) at least once,
- characterized by a second transmitter (12) which is designed to emit terahertz radiation having a bandwidth of less than 5% of the carrier frequency of the terahertz radiation onto the surface of the object at multiple points in time and/or onto multiple locations on the surface of the object (18, 34),
- a second receiver (12) which is designed to receive the terahertz radiation emitted by the second transmitter (12) after the radiation has passed through the object (18, 34) at least once,
- an evaluation apparatus (26) which is designed to determine a dimension of the object (18, 34) from the terahertz radiation received by the second transmitter (12) and/or from a temporal and/or spatial change of the terahertz radiation received by the second receiver (12) in consideration of the terahertz radiation received by the first receiver (10).
13. The device according to claim 12, characterized in that the bandwidth of the terahertz radiation emitted by the first transmitter (10) is more than 10%, preferably more than 20%, of the carrier frequency of the terahertz radiation.
14. The device according to any one of claims 12 or 13, characterized in that the bandwidth of the terahertz radiation emitted by the second transmitter (12) is less than 3%, preferably less than 2%, of the carrier frequency of the terahertz radiation.
15. The device according to any one of claims 12 to 14, characterized in that the first transmitter (10) and the first receiver (10) are formed by a first transceiver (10) and/or in that the second transmitter (12) and the second receiver (12) are formed by a second transceiver (12).
16. The device according to any one of claims 12 to 15, characterized in that a first reflector (22) for the terahertz radiation emitted by the first transmitter (10) is arranged on the side of the object (18, 34) that is opposite the first transmitter (10) and/or in that a second reflector (24) for the terahertz radiation emitted by the second transmitter (12) is arranged on the side of the object (18, 34) that is opposite the second transmitter (12).
17. The device according to any one of claims 12 to 16, characterized in that a rotating and/or traversing apparatus is provided for rotating the second transmitter (12) and second receiver (12) about the object (18, 34) during the measurement and/or for transposing the second transmitter (12) and second receiver (12) along the object (18, 34) during the measurement and/or in that multiple second transmitters (12) and second receivers (12) arranged around the object (18, 34) or along the object (18, 34) are provided.
18. The device according to any one of claims 12 to 17, characterized in that the second transmitter (12) is arranged such that it emits terahertz radiation at an oblique angle of incidence onto the surface of the object (18, 34).
19. The device according to any one of claims 12 to 18, characterized in that the evaluation apparatus (26) is further designed to determine the dimension of the object (18, 34) in consideration of the refractive index of the object (18, 34).
20. The device according to claim 19, characterized in that the evaluation apparatus (26) is further designed to determine the refractive index of the object (18, 34) from the terahertz radiation received by the first receiver (10).
21. The device according to any one of claims 12 to 20, characterized in that the evaluation apparatus (26) is designed to determine the dimension of the object (18, 34) from a phase change, caused during passage of radiation through the object (18, 34), of the terahertz radiation emitted by the first and/or second transmitter (12).
22. The device according to any one of claims 12 to 21, characterized in that the evaluation apparatus (26) is designed to infer a defect of the object (18, 34) based, in particular, on rapid signal changes of the terahertz radiation signal received by the second receiver (12).
1. A method for determining dimensional data, in particular thickness data, relating to a plate-shaped object (34) or strand-shaped object (18), in particular a pipe (18), comprising the steps of:
- terahertz radiation is emitted by a first transmitter (10) onto at least one location on the surface of the object (18, 34) at at least one point in time,
- the terahertz radiation emitted by the first transmitter (10) is received by a first receiver (10) after the radiation has passed through the object (18, 34) at least once,
characterized by the further steps of:
- terahertz radiation having a bandwidth of less than 5% of the carrier frequency of the terahertz radiation is emitted by a second transmitter (12) onto the surface of the object at multiple points in time and/or onto multiple locations on the surface of the object (18, 34),
- the terahertz radiation emitted by the second transmitter (12) is received by a second receiver (12) after the radiation has passed through the object (18, 34) at least once,
- a dimension of the object (18, 34) is determined from the terahertz radiation received by the second transmitter (12) and/or from a temporal and/or spatial change of the terahertz radiation received by the second receiver (12) in consideration of the terahertz radiation received by the first receiver (10).
2. The method according to claim 1, characterized in that the bandwidth of the terahertz radiation emitted by the first transmitter (10) is more than 10%, preferably more than 20%, of the carrier frequency of the terahertz radiation.
3. The method according to any one of the preceding claims, characterized in that the bandwidth of the terahertz radiation emitted by the second transmitter (12) is less than 3%, preferably less than 2%, of the carrier frequency of the terahertz radiation.
4. The method according to any one of the preceding claims, characterized in that the first transmitter (10) and the first receiver (10) are formed by a first transceiver (10) and/or in that the second transmitter (12) and the second receiver (12) are formed by a second transceiver (12).
5. The method according to any one of the preceding claims, characterized in that a first reflector (22) for the terahertz radiation emitted by the first transmitter (10) is arranged on the side of the object (18, 34) that is opposite the first transmitter (10) and/or in that a second reflector (24) for the terahertz radiation emitted by the second transmitter (12) is arranged on the side of the object (18, 34) that is opposite the second transmitter (12).
6. The method according to any one of the preceding claims, characterized in that the second transmitter (12) and the second receiver (12) are rotated about the object (18, 34) and/or transposed along the object (18, 34) and/or in that multiple second transmitters (12) and second receivers (12) arranged around the object (18, 34) or along the object (18, 34) are provided.
7. The method according to any one of the preceding claims, characterized in that the second transmitter (12) emits terahertz radiation at an oblique angle of incidence onto the surface of the object (18, 34).
8. The method according to any one of the preceding claims, characterized in that the dimension of the object (18, 34) is determined in consideration of the refractive index of the object (18, 34).
9. The method according to claim 8, characterized in that the refractive index of the object (18, 34) is determined from the terahertz radiation received by the first receiver (10).
10. The method according to any one of the preceding claims, characterized in that the dimension of the object is determined from a phase change, caused during passage of radiation through the object (18, 34), of the terahertz radiation emitted by the first and/or second transmitter (12).
11. The method according to any one of the preceding claims, characterized in that a defect of the object (18, 34) is inferred based, in particular, on rapid signal changes of the terahertz radiation signal received by the second receiver (12).
12. A device for determining dimensional data relating to a plate- or strand-shaped object (18, 34), comprising
- a first transmitter (10) which is designed to emit terahertz radiation onto at least one location on the surface of the object (18, 34) at at least one point in time,
- a first receiver (10) which is designed to receive the terahertz radiation emitted by the first transmitter (10) after the radiation has passed through the object (18, 34) at least once,
- characterized by a second transmitter (12) which is designed to emit terahertz radiation having a bandwidth of less than 5% of the carrier frequency of the terahertz radiation onto the surface of the object at multiple points in time and/or onto multiple locations on the surface of the object (18, 34),
- a second receiver (12) which is designed to receive the terahertz radiation emitted by the second transmitter (12) after the radiation has passed through the object (18, 34) at least once,
- an evaluation apparatus (26) which is designed to determine a dimension of the object (18, 34) from the terahertz radiation received by the second transmitter (12) and/or from a temporal and/or spatial change of the terahertz radiation received by the second receiver (12) in consideration of the terahertz radiation received by the first receiver (10).
13. The device according to claim 12, characterized in that the bandwidth of the terahertz radiation emitted by the first transmitter (10) is more than 10%, preferably more than 20%, of the carrier frequency of the terahertz radiation.
14. The device according to any one of claims 12 or 13, characterized in that the bandwidth of the terahertz radiation emitted by the second transmitter (12) is less than 3%, preferably less than 2%, of the carrier frequency of the terahertz radiation.
15. The device according to any one of claims 12 to 14, characterized in that the first transmitter (10) and the first receiver (10) are formed by a first transceiver (10) and/or in that the second transmitter (12) and the second receiver (12) are formed by a second transceiver (12).
16. The device according to any one of claims 12 to 15, characterized in that a first reflector (22) for the terahertz radiation emitted by the first transmitter (10) is arranged on the side of the object (18, 34) that is opposite the first transmitter (10) and/or in that a second reflector (24) for the terahertz radiation emitted by the second transmitter (12) is arranged on the side of the object (18, 34) that is opposite the second transmitter (12).
17. The device according to any one of claims 12 to 16, characterized in that a rotating and/or traversing apparatus is provided for rotating the second transmitter (12) and second receiver (12) about the object (18, 34) during the measurement and/or for transposing the second transmitter (12) and second receiver (12) along the object (18, 34) during the measurement and/or in that multiple second transmitters (12) and second receivers (12) arranged around the object (18, 34) or along the object (18, 34) are provided.
18. The device according to any one of claims 12 to 17, characterized in that the second transmitter (12) is arranged such that it emits terahertz radiation at an oblique angle of incidence onto the surface of the object (18, 34).
19. The device according to any one of claims 12 to 18, characterized in that the evaluation apparatus (26) is further designed to determine the dimension of the object (18, 34) in consideration of the refractive index of the object (18, 34).
20. The device according to claim 19, characterized in that the evaluation apparatus (26) is further designed to determine the refractive index of the object (18, 34) from the terahertz radiation received by the first receiver (10).
21. The device according to any one of claims 12 to 20, characterized in that the evaluation apparatus (26) is designed to determine the dimension of the object (18, 34) from a phase change, caused during passage of radiation through the object (18, 34), of the terahertz radiation emitted by the first and/or second transmitter (12).
22. The device according to any one of claims 12 to 21, characterized in that the evaluation apparatus (26) is designed to infer a defect of the object (18, 34) based, in particular, on rapid signal changes of the terahertz radiation signal received by the second receiver (12).
Abstract
The invention relates to a method for determining dimensional data, in particular thickness data, relating to a plate-shaped object or strand-shaped object, in particular a pipe, comprising the steps of:
- terahertz radiation is emitted by a first transmitter onto at least one location on the surface of the object at at least one point in time,
- the terahertz radiation emitted by the first transmitter is received by a first receiver after the radiation has passed through the object at least once,
characterized by the further steps of:
- terahertz radiation having a bandwidth of less than 5% of the carrier frequency of the terahertz radiation is emitted by a second transmitter onto the surface of the object at multiple points in time and/or onto multiple locations on the surface of the object,
- the terahertz radiation emitted by the second transmitter is received by a second receiver after the radiation has passed through the object at least once,
- a dimension of the object is determined from the terahertz radiation received by the second transmitter and/or from a temporal and/or spatial change of the terahertz radiation received by the second receiver in consideration of the terahertz radiation received by the first receiver.
The invention also relates to a device for determining dimensional data relating to a plate- or strand-shaped object.
The invention relates to a method for determining dimensional data, in particular thickness data, relating to a plate-shaped object or strand-shaped object, in particular a pipe, comprising the steps of:
- terahertz radiation is emitted by a first transmitter onto at least one location on the surface of the object at at least one point in time,
- the terahertz radiation emitted by the first transmitter is received by a first receiver after the radiation has passed through the object at least once,
characterized by the further steps of:
- terahertz radiation having a bandwidth of less than 5% of the carrier frequency of the terahertz radiation is emitted by a second transmitter onto the surface of the object at multiple points in time and/or onto multiple locations on the surface of the object,
- the terahertz radiation emitted by the second transmitter is received by a second receiver after the radiation has passed through the object at least once,
- a dimension of the object is determined from the terahertz radiation received by the second transmitter and/or from a temporal and/or spatial change of the terahertz radiation received by the second receiver in consideration of the terahertz radiation received by the first receiver.
The invention also relates to a device for determining dimensional data relating to a plate- or strand-shaped object.