JP4047096B2 - Surface shape measuring apparatus and method - Google Patents

Description

同様に、光線２１の焦点位置の測定座標は次の式で計算できる。
【００４４】

この座標位置は３面の参照ミラーを位置の基準に測定しているので、Ｚスライダの姿勢誤差に影響されない。
【００４５】
以上説明してきた構成において、図６で説明するフローチャートで動作を説明する。
【００４６】
３つの位置マーク球３を取り付けたジグ２に被測定物１を着脱可能に取り付ける（１００）。次に、球中心位置測定手段と自由曲面を測定する接触式プローブの位置合わせを行う必要があるかどうかを判断する（１０１）。これが必要となる場合は、例えば装置を製作した最初の時や、接触式プローブを交換してプローブの位置情報がなくなってしまった時である。
【００４７】
又、前述したように球中心位置測定手段の測定位置、即ち光線２１の焦点位置が接触式プローブ９の真下になるように大体の位置合わせを行うが、非常に精密にこれを調整するのは困難である。そういった意味でも先ず球中心位置測定手段と自由曲面を測定する接触式プローブの位置合わせを行う必要がある。しかし、ひとたび位置合わせを行ってしまえば、位置合わせの必要はなくなる。
【００４８】
位置合わせをする場合は、先ず、位置マーク球３の表面を接触式プローブでトレースしたときの点群を測定する（１０２）。その表面上の点群から最小２乗法等を用いて球中心位置を計算する（１０３）。計算の結果得られた位置をＰａとする。
【００４９】
ここで、この点Ｐａは従来例のように球の頂点ではないことを注意しておく。頂点位置と異なり、球の中心位置はどの方向から測定しても同じ点になる筈である。言い換えると、本発明では従来例と異なり、位置マーク球の位置をどの方向から測定しても同じ結果を与える。
【００５０】
次に、球中心測定手段によって位置マーク球の位置を測定する。接触式プローブで測定した位置マーク球の位置Ｐａと光線２１の焦点位置がほぼ合うように、ＸＹＺ制御装置８を用い、Ｘ，Ｙ，Ｚスライダを動かす（１０４）。この位置において、図２で説明したエラー信号ｅ１２或はｅ３の何れか一方でも出力されていないかを判定する（１１６）。もし、エラーが出力されていれば、位置マーク球が想定した位置にいないか、半導体レーザーが故障した等、何らかの故障があったことになるので、エラー停止する旨、コンピュータ画面等の表示装置に対してエラー表示し（１１７）、停止する。一方、エラーでなければ、信号φ１，φ２，φ３は正しい測定値と考えることができる。
【００５１】
そして、φ１，φ２及びφ３はそれぞれ光線２１の垂直方向と光軸方向の偏差を表しているので、それらが全てゼロになるようにＸＹＺ制御装置８を用い、Ｘ，Ｙ，Ｚスライダを微調整する（１０５）。φ１，φ２，φ３が変化する移動方向と、Ｘ，Ｙ，Ｚスライダの移動方向は異なるが、傾斜しているだけなので、自由度は同じ３である。しかも、直交しており、互いに干渉しにくい独立な３方向と言える。従って、必ず調節することができる。調整残差が十分小さくなった時のＸＹＺスライダの位置、姿勢から図５と（式２）を用いて説明した方法で球の中心位置を求める。
【００５２】
又、このとき、調整し切れなかった信号φ１，φ２，φ３は十分小さくなっている筈であるが、その調整残差をＸＹＺ位置に換算し、ＸＹＺスライダの位置Ｐｂを補正しておけば、なお精密である（１０６）。
【００５３】
位置の差Ｄ＝Ｐａ−Ｐｂを計算し、これを位置補正量とする。これは自由曲面を測定する接触式プローブの位置と、位置マーク球を測定する球中心位置測定プローブの位置補正量を表している（１０７）。
【００５４】
次に、全ての位置マーク球を球中心位置測定手段で測定する。１つ１つの測定は先程説明した手順と同じである。第ｎ番目の位置マーク球を測定する場合について説明する。
【００５５】
先ず、第ｎ位置マーク球中心位置に光線２１の焦点位置を移動させる（１０８）。おおよその位置はジグの設計図面、ジグを測定装置に取り付ける図面等から分かるので、その位置にＸＹＺスライダを移動させることができる。この位置において、図２で説明したエラー信号ｅ１２或はｅ３の何れか一方でも出力されていないか判定する（１１８）。もし、エラーが出力されていれば、位置マーク球が想定した位置にいない等、何らかの故障があったことになるので、エラー停止する旨、コンピュータ画面等の表示装置に対してエラー表示し（１１９）、停止する。
【００５６】
一方、エラーでなければ、信号φ１，φ２，φ３は正しい測定値と考えることができる。次に、信号φ１，φ２，φ３がゼロになるようにＸＹＺスライダの位置を微調整する（１０９）。このときの第ｎ番の球中心位置を計算し、Ｐｎとする（１１０）。このとき、先程求めた位置補正量Ｄを加える。すると、この位置Ｐｎは、あたかも接触式プローブで測定したときの位置に変換されている。しかも、接触式プローブで測定する場合に比べ、表面をトレースする必要がないため測定時間が可成り短い。全部の位置マーク球を測定するまで（１０８）からの動作を繰り返し、終わったら次に進む（１１１）。
【００５７】
３つの球中心位置から１つの直交座標系を決定する（１１２）。この方法は幾つかあるが、例えば３つの点（測定した球中心位置）で定義される平面に直交する方向にＺ軸を取り、そのなかの２点を結ぶ線をＸ軸とし、残りのＹ軸はＸ，Ｚ軸に垂直な軸として定義できる。こうして定義した直交座標系は３つの球に固定されているので、被測定物座標系と呼ぶ。この被測定物座標系から見て、測定すべき自由曲面を含む被測定物１はいつも同じ位置にある。なぜなら、冒頭で述べたように、３球位置マーク３に固定したジグ２に被測定物１が固定されているからである。
【００５８】
次に、自由曲面を接触式プローブでトレースし、自由曲面上の点群を測定する（１１３）。この点群を全て被測定物座標系に座標変換する（１１４）。こうして得られた点群は３球を位置基準としているので、被測定物を測定装置のどこに設置しても、どんな姿勢に設置しても、同じ点群が得られる。次に、最小２乗法を用いて設計形状との差、即ち誤差形状を計算する（１１５）。
【００５９】
以上説明してきた方法によれば、測定時間を短縮することができる。なぜならば３球の測定時間が短くなるからである。前述したように、プローブを用い、球の表面をトレースして位置を測定する場合、三次元的な位置情報が必要なので、断面ではなく、複数断面のトレースが必要となるため、長いトレース長さが必要である。しかも、往復運動を繰り返してトレースする場合にはその加減速に要する時間も無視できない。これに対して本実施形態による方法であれば、光軸２１の中心位置におおよそ位置マーク球が来るようにＸＹＺ軸を移動させ、その後、信号φ１，φ２，φ３に従って微調整するだけで球中心位置が決定できる。球の表面をトレースする必要がないので大幅な時間短縮が可能である。
【００６０】
又、本発明によれば、球の頂点位置ではなく、球の中心位置を測定しているので、被測定物の位置姿勢の影響を受けない。これは、どの方向から中心位置を測定しても同じ点を指し示すという、球の性質を利用しているからである。
【００６１】
更に、本発明によれば、球の測定時間が短縮されるため、全体の測定時間も短縮される。時間と共に変化する温度変形等の誤差を緩和することができるので、結果として測定精度を向上させることができる。
【００６２】
本実施の形態において、光源は半導体レーザー１７としたが、他の点光源でも同じことである。例えば、別に設けたレーザー発信器のレーザー光を光ファイバに入射させ、その出射端を、本実施の形態の半導体レーザー１７の代わりに設置しても同じことである。
【００６３】
本実施の形態において、斜めの光線２１を得るのにプリズム２０を用いているが、これを反射ミラーとしても作用は同じである。
【００６４】
本実施の形態において、自由曲面を測定するプローブは接触式のプローブとして説明してきたが、別に非接触式のプローブであっても同じことである。
【００６５】
本実施の形態においては、ハーフミラー２２で反射した側に光点位置測定手段を、透過した側に焦点位置検出手段（オートフォーカス）を配置したが、逆にしても同じことである。即ち、ハーフミラー２２で反射した側に焦点位置検出手段（オートフォーカス）を、透過した側に光点位置測定手段を配置する。
【００６６】
又、本実施の形態において、ハーフミラー１８での光量損失を改善するためにこれを偏光ビームスプリッタに変更し、レンズ１９との間に４分の１波長板を置くことも考えられる。この場合、半導体レーザーから出射した光は偏光ビームスプリッタで１方向の直線偏光のみが反射され、４分の１波長板で円偏光に変換される。球面で反射した後再び４分の１波長板を通過したとき、先程とは９０度回転した直線偏光に変換されるので、今度は偏光ビームスプリッタを通過する。しかし、その場合でも基本的な作用はこれまで説明してきたことと同じである。
＜実施の形態２＞
図７に本発明の実施の形態２を示す。
【００６７】
前記実施の形態１に対して、プリズム２０を省略し、光線２１の焦点位置がプローブ球中心からずれている点が異なる。他の構成及び作用は実施の形態１と同じなので説明を省略する。
【００６８】
本実施の形態では実施の形態１に対して次の効果がある。
【００６９】
１）光線２１を曲げる必要がないので、少ない光学部品で構成可能である。
【００７０】
２）光線２１の距離を短くできる。言い換えると対物レンズ１９の開口率を上げることができるので、オートフォーカス部、すなわちＺ方向の検出感度を向上することができる。
【００７１】
３）接触式プローブの近傍に障害物であるプリズム２０等の部品を配置する必要がないので、被測定物と測定装置が衝突する可能性が低くなる。従って被測定物の設計制約を緩和することができる。
【００７２】
４）位置マーク球を含む被測定物は接触式プローブと、球中心位置測定手段である光線２１とが両方アプローチできるように設計しておく必要があるが、本実施の形態によれば、両方とも垂直方向だけを考慮すれば良いので、実施の形態１の場合に比べて死角が少ない。実施の形態１では斜め方向と垂直方向との２方向を考慮するからである。
【００７３】
従って、本実施の形態によれば、被測定物の設計制約を緩和することができる。例えば、同図において、左側に配置した２つの球を測定する場合が考え易い。この球は紙面に対して垂直方向にずれて配置してあるので、Ｚ方向から測定することは問題ない。しかし、実施の形態１のように斜めの光線で測定しようとすると球３ａがジグ２の陰となり測定が難しい。
【００７４】
このようなメリットがある反面、図５で説明したスライダの位置姿勢補正は十分に機能しない。図５で姿勢補正が可能なのはプローブの軸上だけだからである。軸上から外れると、スライダ姿勢誤差のうち、垂直Ｚ軸回りの姿勢誤差、所謂ヨーイング誤差の影響が大きくなってくる。従って、本実施の形態では実施の形態１の場合に対してヨーイング誤差が小さいＸＹＺスライダが必要となる。
【００７５】
＜実施の形態３＞
図８に本発明の実施の形態３を示す。
【００７６】
接触式プローブを貫通させる穴のあいた折り曲げミラー３３を設け、球中心位置測定手段の光線２１をプローブの後ろに配置した点が実施の形態１と異なる。作用及び効果は実施の形態１の場合と同じなので説明を省略する。
【００７７】
本実施の形態では実施の形態１，２に対して次の効果がある。
【００７８】
１）位置マーク球を含む被測定物は接触式プローブと、球中心位置測定手段である光線２１とが両方アプローチできるように設計しておく必要があるが、本実施の形態によれば両方とも垂直方向だけを考慮すれば良いので、実施の形態１の場合に比べて死角が少ない。実施の形態１では、斜め方向と垂直方向との２方向を考慮するからである。従って、本実施の形態によれば、被測定物の設計制約を緩和することができる。例えば、同図において、左側に配置した２つの球を測定する場合が考え易い。この球は紙面に対して垂直方向にずれて配置してあるので、Ｚ方向から測定することは問題ない。しかし、実施の形態１のように斜めの光線で測定しようとすると球３ａがジグ２の陰となり測定が難しい。
【００７９】
２）球中心測定位置と接触式プローブが同軸上に配置できるので、実施の形態２で説明したように高精度なＸＹＺスライダは必要ない。
【００８０】
＜実施の形態４＞
図９に本発明の実施の形態４を示す。
【００８１】
球中心位置測定手段を２組設けた点が実施の形態１と異なる。他の部分は実施の形態１と同じなので説明を省略する。
【００８２】
第１の球中心位置測定手段１２ａ及び第２の球中心位置測定手段１２ｂをＺスライダ７に固定して設け、それぞれの測定する光線を２１ａ，２１ｂとし、それぞれの信号を位置測定用アンプ１３ａ，１３ｂに接続し、ＸＹＺコントローラ８に接続する。
【００８３】
以上の構成において、図１０及び図１１で説明するフローチャートで動作を説明する。
【００８４】
３つの位置マーク球３を取り付けたジグ２に被測定物１を着脱可能に取り付ける（１００）。次に、球中心位置測定手段と自由曲面を測定する接触式プローブの位置合わせを行う必要があるかどうかを判断する（１０１）。前述したようにこれが必要となる場合は、例えば装置を製作した最初の時や、接触式プローブを交換してプローブの位置情報がなくなってしまった時である。しかし、ひとたび位置合わせを行ってしまえば、位置合わせの必要はない。
【００８５】
位置合わせをする場合は、先ず、２つの球中心位置測定手段で測定可能な位置マーク球３の表面を接触式プローブでトレースしたときの点群を測定する（１０２）。その表面上の点群から最小２乗法等を用い、球中心位置を計算する（１０３）。計算の結果得られた位置をＰａとする。
【００８６】
次に、第１の球中心測定手段によって位置マーク球の位置を測定する。接触式プローブで測定した位置マーク球の位置Ｐａと光線２１の焦点位置がほぼ合うようにＸＹＺ制御装置８を用い、Ｘ，Ｙ，Ｚスライダを動かす（１０４ａ）。この位置において、図２で説明したエラー信号ｅ１２又はｅ３の何れか一方でも出力されていないかを判定する（１１６ａ）。もし、エラーが出力されていれば、位置マーク球が想定した位置にいないか、半導体レーザーが故障した等、何らかの故障があったことになるので、エラー停止する旨、コンピュータ画面等の表示装置に対してエラー表示し（１１７ａ）、停止する。一方、エラーでなければ、信号φ１ａ，φ２ａ，φ３ａは正しい測定値と考えることができる。
【００８７】
そして、φ１ａ，φ２ａ及びφ３ａはそれぞれ光線２１の垂直方向と光軸方向の偏差を表しているので、それらが全てゼロになるようにＸＹＺ制御装置８を用い、Ｘ，Ｙ，Ｚスライダを微調整する（１０５ａ）。φ１ａ，φ２ａ，φ３ａが変化する移動方向と、Ｘ，Ｙ，Ｚスライダの移動方向は異なるが、傾斜しているだけなので、自由度は同じ３である。しかも、直交しており、互いに干渉しにくい独立な３方向と言える。従って、必ず調節することができる。調整残差が十分小さくなった時のＸＹＺスライダの位置、姿勢から図５と（式２）を用いて説明した方法で球の中心位置を求める。
【００８８】
又、このとき、調整し切れなかった信号φ１ａ，φ２ａ，φ３ａは十分小さくなっている筈であるが、その調整残差をＸＹＺ位置に換算し、ＸＹＺスライダの位置Ｐｂ（ａ）を補正しておけば、なお精密である（１０６ａ）。
【００８９】
位置の差Ｄ（ａ）＝Ｐａ−Ｐｂ（ａ）を計算し、これを位置補正量とする。これは自由曲面を測定する接触式プローブの位置と、位置マーク球を測定する球中心位置測定プローブの位置補正量を表している（１０７ａ）。
【００９０】
次に、第２の球中心測定手段によって位置マーク球の位置を測定する。接触式プローブで測定した位置マーク球の位置Ｐａと光線２１の焦点位置がほぼ合うようにＸＹＺ制御装置８を用い、Ｘ，Ｙ，Ｚスライダを動かす（１０４ｂ）。この位置において、図２で説明したエラー信号ｅ１２又はｅ３の何れか一方でも出力されていないかを判定する（１１６ｂ）。もし、エラーが出力されていれば、位置マーク球が想定した位置にいないか、半導体レーザーが故障した等、何らかの故障があったことになるので、エラー停止する旨、コンピュータ画面等の表示装置に対してエラー表示し（１１７ｂ）、停止する。一方、エラーでなければ、信号φ１ｂ，φ２ｂ，φ３ｂは正しい測定値と考えることができる。
【００９１】
そして、φ１ｂ，φ２ｂ及びφ３ｂはそれぞれ光線２１の垂直方向と光軸方向の偏差を表しているので、それらが全てゼロになるようにＸＹＺ制御装置８を用い、Ｘ，Ｙ，Ｚスライダを微調整する（１０５ｂ）。φ１ｂ，φ２ｂ，φ３ｂが変化する移動方向と、Ｘ，Ｙ，Ｚスライダの移動方向は異なるが、傾斜しているだけなので、自由度は同じ３である。しかも、直交しており、互いに干渉しにくい独立な３方向と言える。従って、必ず調節することができる。調整残差が十分小さくなった時のＸＹＺスライダの位置、姿勢から図５と（式２）を用いて説明した方法で球の中心位置を求める。
【００９２】
又、このとき、調整し切れなかった信号φ１ｂ，φ２ｂ，φ３ｂは十分小さくなっている筈であるが、その調整残差をＸＹＺ位置に換算し、ＸＹＺスライダの位置Ｐｂ（ｂ）を補正しておけば、なお精密である（１０６ｂ）。
【００９３】
位置の差Ｄ（ｂ）＝Ｐａ−Ｐｂ（ｂ）を計算し、これを位置補正量とする。これは自由曲面を測定する接触式プローブの位置と、位置マーク球を測定する球中心位置測定プローブの位置補正量を表している（１０７ｂ）。
【００９４】
次に、全ての位置マーク球を球中心位置測定手段で測定する。１つ１つの測定は先程説明した手順と同じである。第ｎ番目の位置マーク球を測定する場合について説明する。
【００９５】
先ず、第ｎ位置マーク球中心位置に光線２１の焦点位置を移動させる（１０８）。おおよその位置はジグの設計図面、ジグを測定装置に取り付ける図面等から分かるので、その位置にＸＹＺスライダを移動させることができる。
【００９６】
次に、２つの球中心位置測定手段のエラー状態記憶装置ａ，ｂをクリアーしておく（１２０）。
【００９７】
この位置において、次に第１の球中心位置測定手段で位置マーク球の位置を測定する。
【００９８】
図２で説明したエラー信号ｅ１２又はｅ３の何れか一方でも出力されていないか判定する（１１８ａ）。もし、エラーが出力されていれば、エラー状態記憶ａをセットする（１２１ａ）。
【００９９】
一方、エラーでなければ、信号φ１ａ，φ２ａ，φ３ａは正しい測定値と考えることができる。次に、信号φ１ａ，φ２ａ，φ３ａがゼロになるようにＸＹＺスライダの位置を微調整する（１０９ａ）。この時の第ｎ番の球中心位置を計算し、Ｐｎ（ａ）とする（１１０ａ）。このとき、先程求めた位置補正量Ｄ（ａ）を加える。すると、この位置Ｐｎ（ａ）は、あたかも接触式プローブで測定した時の位置に変換されている。
【０１００】
次に、第２の球中心位置測定手段で位置マーク球の位置を測定する。
【０１０１】
図２で説明したエラー信号ｅ１２又はｅ３の何れか一方でも出力されていないか判定する（１１８ｂ）。もし、エラーが出力されていれば、エラー状態記憶ｂをセットする（１２１ｂ）。一方、エラーでなければ、信号φ１ｂ，φ２ｂ，φ３ｂは正しい測定値と考えることができる。
【０１０２】
次に、信号φ１ｂ，φ２ｂ，φ３ｂがゼロになるようにＸＹＺスライダの位置を微調整する（１０９ｂ）。このときの第ｎ番の球中心位置を計算し、Ｐｎ（ｂ）とする（１１０ｂ）。このとき、先程求めた位置補正量Ｄ（ｂ）を加える。すると、この位置Ｐｎ（ｂ）は、あたかも接触式プローブで測定した時の位置に変換されている。
【０１０３】
次に、エラー状態記憶ａ，ｂの状態によって処理を分岐する。
【０１０４】
エラー状態記憶ａ，ｂ共ににエラーかどうかを判定し（１２２）、エラーの場合は球中心位置が測定できなかったことになるので、エラー表示し（１２３）、停止する。そうでないならば次の処理に進み、エラー状態記憶ａ，ｂ共に正常かどうかを判定し（１２４）、もしも両方正常ならば２つの測定値を平均する（１２５）。即ち、Ｐｎ（ａ）とＰｎ（ｂ）を平均し、ｎ番目の位置マーク球の球中心位置とする。
【０１０５】
そうでないならば、正常な方の測定値を採用する（１２６）。即ち、Ｐｎ（ａ）かＰｎ（ｂ）の正常な何れか一方をｎ番目の位置マーク球の球中心位置とする。
【０１０６】
全部の位置マーク球を測定するまで（１０８）からの動作を繰り返し、終わったら次に進む（１１１）。
【０１０７】
３つの球中心位置から１つの直交座標系を決定する（１１２）。この方法は幾つかあるが、例えば３つの点（測定した球中心位置）で定義される平面に直交する方向にＺ軸を取り、そのなかの２点を結ぶ線をＸ軸とし、残りのＹ軸はＸ，Ｚ軸に垂直な軸として定義できる。こうして定義した直交座標系は３つの球に固定されているので、被測定物座標系と呼ぶ。この被測定物座標系から見て、測定すべき自由曲面を含む被測定物１はいつも同じ位置にある。なぜなら、冒頭で述べたように３球位置マーク３に固定したジグ２に被測定物１が固定されているからである。
【０１０８】
次に、自由曲面を接触式プローブでトレースし、自由曲面上の点群を測定する（１１３）。この点群を全て被測定物座標系に座標変換する（１１４）。こうして得られた点群は３球を位置基準としているので、被測定物を測定装置のどこに設置しても、どんな姿勢に設置しても、同じ点群が得られる。次に、最小２乗法を用いて設計形状との差、即ち誤差形状を計算する（１１５）。
【０１０９】
本実施の形態によれば、次のメリットがある。
【０１１０】
１）１つの球中心位置測定手段から見たとき、位置マーク球がジグ等によって陰になり測定できない場合でも、もう１つの球中心位置測定手段から見たときに位置マーク球が陰になっていなければ測定可能である。従って、死角が少なくなり、被測定物の設計制約を緩和することができる。
【０１１１】
２）位置マーク球を２つの球中心位置測定手段で測定可能な場合、２つの測定結果を平均できるので、偶然誤差を軽減できる。従って、測定精度を向上することができる。
【０１１２】
図９に示した本実施の形態によれば、２つの球測定手段は対向する配置で描かれている。即ち、上から見て１８０度離れて配置してあるが、９０度離して配置しても、何度離しても同じことである。
【０１１３】
＜実施の形態５＞
図１２及び図１３に本発明の実施の形態５を示す。
【０１１４】
実施の形態１に対し、非接触球中心位置測定手段の構成が異なる。
【０１１５】
図１２は本実施の形態における球位置測定手段の主要部分である。半導体レーザー１７から出射した光は、ハーフミラー１８で反射し、レンズ１９を通ることによって集光し、プリズム２０で方向を曲げ、集束光ビーム２１を得る。このとき、集束光ビームの焦点位置が、先程の先端球９を有する接触式プローブ１０の真下になるように、先程のレンズ１９とプリズム２０の位置を予め調整しておく。図に示すように、この焦点位置と位置マーク球３の中心位置がほぼ重なった時、先程の集束光ビーム２１は位置マーク球３の表面で反射し、元来た光路を戻っていく。そしてハーフミラー１８を透過し、シリンドリカルレンズ２４を通過しスポットを結ぶ。そのスポット像を観察するカメラ３５を設け、画像処理装置３６に接続する。
【０１１６】
画像処理装置３６に取り込まれたスポット像を図１３に示す。
【０１１７】
これまで説明してきたように、位置マーク球の球中心が集束光ビーム２１の光軸に対して垂直方向にずれると、このスポット像の位置がずれる。このスポット像の位置は画像処理装置３６を用い、スポット像の重心位置を計算すれば求められる。その重心位置を信号φ１，φ２とする。
【０１１８】
又、位置マーク球の球中心が集束光ビーム２１の光軸に沿った方向にずれると、前述したようにスポット像の形が縦長楕円や横長楕円といった具合に形が変わる。そこで、画像処理装置３６を用い、スポット像の縦横サイズＳＸ，ＳＹを測定し、比を計算することにより求めることができる。その計算値をφ３とする。
【０１１９】
更に、カメラに入射した全部の光量を画像処理装置３６で計算し、所定の値よりも光量が低い場合にはエラー信号ｅを出力する。これは実施の形態１で説明した２つのエラー信号ｅ１２とｅ３をＯＲ接続したことと同じ意味である。
【０１２０】
これらの信号φ１，φ２，φ３及びｅを用いて球中心位置を測定することができる。後の説明は実施の形態と同じなので省略する。
【０１２１】
本実施の形態によれば、光学系の構成部品が少ないのでより簡便に実現可能である。
【０１２２】
【発明の効果】
以上説明したように、本発明によれば次の効果がある。
（１）従来例のように位置マーク球表面をトレースする必要がないので、大幅な測定時間短縮が期待できる。
（２）球の頂点ではなく、球の中心を測定しているので、被測定物の位置や姿勢に関係なく同じ測定結果が得られる。なぜなら、球の中心はどの方向から測定しても同じ点だからである。
（３）測定時間が短縮できるので、測定時間内での環境温度変化も小さくなり、測定精度が向上する。
（４）非接触に位置マーク球中心を測定できるので、球の摩耗を心配することがなくなり、摩耗による誤差の増大が無いため、測定精度を向上することができる。
（５）非接触なので位置マーク球の寿命を延ばすことができる。
（６）非接触なので上に、摩耗による測定誤差の増大が無いため精度が向上する。
（７）非接触球中心位置測定手段の測定位置をプローブ軸の延長線上とすることにより、プローブ移動に伴う移動部材の位置、姿勢誤差の影響をプローブと同様に最小限にできる。
（８）非接触球中心位置測定手段を簡便な光学系で実現できる。
（９）位置マーク球が脱落した場合等の異常状態を自動検出、装置を停止することが可能となる。
（１０）位置マーク球の変わりに間違った別部品がついている等、従来では対応が難しかったエラーに対しても安全にエラーを自動検出、装置を停止することが可能となる。
（１１）従来のようにトレースする必要がないので、異常を素早く検出することでエラーの影響を最小限にくい止めることができる。
（１２）安全にエラーを検出し停止できるため、事故防止という点でも有効である。事故を未然に防ぐことで生産設備の稼働率を向上し、生産コストを下げることに繋がる。
（１３）球中心位置測定手段で用いる光の軸とプローブの軸とが同じ方向を向いているので、被測定物は１つの方向についてぶつからない設計をすれば良い。従って、設計制約を緩和できる。
（１４）球中心位置測定手段を２組設けることにより、位置マーク球がジグ等で陰になり測定できない場合でも、もう１つの球中心位置測定手段から見たときに位置マーク球が陰にならなければ測定可能である。従って、死角が少なくなり、被測定物の設計制約を緩和することができる。
（１５）又、位置マーク球を２つの球中心位置測定手段で測定可能な場合、２つの測定結果を平均できるので、偶然誤差を軽減できる。従って、測定精度を向上することができる。
（１６）より簡便な構造で非接触球中心位置測定手段を構成できる。
（１７）非接触球中心位置測定手段の測定位置と、プローブの位置ずれを精密に補正できるので、特に位置マーク球に対する自由曲面の相対位置について測定精度を向上することができる。
（１８）非接触球中心位置測定手段の測定位置とプローブの位置とのずれを精密に位置出しする必要がなくなるので、装置製作コストを下げることができる。
【図面の簡単な説明】
【図１】本発明の実施の形態１を説明する図である。
【図２】本発明の実施の形態１の主要部分を説明する図である。
【図３】本発明の実施の形態１の光学系の第１の模式図である。
【図４】本発明の実施の形態１の光学系の第２の模式図である。
【図５】本発明の実施の形態１の座標位置測定の方法を説明する図である。
【図６】本発明の実施の形態１の動作を説明するフローチャートである。
【図７】本発明の実施の形態１を説明する図である。
【図８】本発明の実施の形態３を説明する図である。
【図９】本発明の実施の形態４を説明する図である。
【図１０】本発明の実施の形態４の動作を説明するフローチャートである。
【図１１】本発明の実施の形態４の動作を説明するフローチャートである。
【図１２】本発明の実施の形態５を説明する図である。
【図１３】本発明の実施の形態１における画像処理を説明する図である。
【図１４】従来の例を説明する図である。
【図１５】従来の例の動作を説明するフローチャートである。
【図１６】従来の例の頂点位置を測定することの問題点を説明する図である。
【符号の説明】
１ 被測定物
２ ジグ
３ 位置マーク球
４ ベース
５ Ｘスライダ
６ Ｙスライダ
７ Ｚスライダ
８ ＸＹＺ制御装置
９ 先端球
１０ 接触式プローブ
１１ プローブ制御用アンプ
１２ 球位置測定手段
１３ 位置測定用アンプ
１４ コラム
１５ Ｘ方向参照ミラー
１６ Ｚ方向参照ミラー
１７ 半導体レーザー
１８ ハーフミラー
１９ レンズ
２０ プリズム
２１ 収束用ビーム
２２ 第２のハーフミラー
２３ 光点位置検出手段（ポジションセンサー）
２４ シリンドリカルレンズ
２５ ４分割フォトダイオード
２６ 引き算回路
２７ 加算回路
２８ 割り算回路
２９ 加算回路
３０ 引き算回路
３１ 加算回路
３２ 割り算回路
３３ 折り曲げミラー
３４ エラー判定回路
３５ カメラ
３６ 画像処理装置
３７ スポット形状[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface shape measuring apparatus capable of accurately measuring an optical element constituted by a free-form surface, for example, a lens, a mirror surface, or a mold for molding an optical element.
[0002]
[Prior art]
14 and 15 show a conventional invention disclosed in Japanese Patent Laid-Open No. 2001-133239.
The shape of the three positioning balls 11 having the same shape placed on the surface of the mold base 1a in close contact with the mold shaft 1b of the lens mold 1 is measured by scanning in the XY coordinate direction with the measurement probe 3. To do. After calculating the vertex coordinates of each positioning sphere 11, the center of the lens mold 1 is calculated based on the plane formed by each vertex coordinate and the perpendicular bisector of each two vertex coordinates. After obtaining the measurement data of the shape of the mold transfer surface 1c, the inclination of the mold transfer surface 1c with respect to the previous plane and the eccentricity of the center of the mold transfer surface 1c with respect to the center 18 of the lens mold 1 And calculate.
The flowchart of FIG. 15 will be described.
[0003]
First, three positioning spheres are installed (S1), and the surface of the positioning sphere is measured using the measurement probe 3 (S2). Next, the Z coordinate of the sphere with respect to the measured XY position is calculated (S3), the difference is calculated (S4), the RMS (Root Mean Square) value is calculated (S6), and the RMS value is reduced. The coordinate conversion is performed (S6), and the process returns to S4 until the RMS value becomes sufficiently small (S7) and repeats (S7). Next, the vertex coordinates of each sphere are calculated (S9), and the plane including the three vertices and the center position of the mold are calculated (S10).
[0004]
Next, the surface of the mold transfer surface is measured using the measurement probe 3 (S11). Next, the Z coordinate of the design shape with respect to the XY position of the measured point is calculated (S12), the difference is calculated (S13), the RMS (Root Mean Square) value is calculated (S14), and the RMS value is small. (S15), until the RMS value becomes sufficiently small (S13), the process returns to S13 and repeats (S16). When the RMS value becomes sufficiently small, the shape of the mold transfer surface is calculated (S17). The inclination and eccentricity of the transfer surface are calculated (S18, S19).
[0005]
[Problems to be solved by the invention]
However, the conventional example has the following drawbacks.
(1) Measurement takes time.
In the conventional apparatus, the surface of three positioning spheres is scanned using a measurement probe,
The center position of the sphere was calculated from the measured coordinates. In this method, it is necessary to measure three spheres using a measurement probe, which takes time. That is, in addition to the measurement time of the mold surface to be measured, the measurement time of three sphere surfaces is required.
In particular, the measurement of the sphere center position by such probe scanning takes time. Moreover, since it is necessary to measure the position of a three-dimensional sphere, information on a plurality of cross sections is required instead of one cross section. Therefore, a long probe scanning distance is required, and when the entire surface is scanned by repeating the reciprocating motion, a wasteful time required for the acceleration / deceleration cannot be ignored.
(2) The measurement result is affected by the mounting posture of the object to be measured.
In the conventional apparatus, the position of the mold is measured by measuring the vertices of three positioning spheres,
Although it can be measured, the position of the sphere apex is affected when the mounting posture changes although the object to be measured, that is, the mold and the three spheres are integrated.
The reason for this will be described with reference to FIG.
[0006]
The amount is Rsin (θ), where R is the radius of the positioning sphere and θ is the inclination angle. For example, if R is 10 mm and θ is 30 degrees, it will be 5 mm. Therefore, in the conventional example, it is a precondition that the three spheres are placed almost in parallel on the XY plane of the apparatus, which is a great obstacle to implementation.
(3) The linear thermal expansion coefficient of an object to be measured that is greatly affected by environmental temperature changes is not always small. This is especially true for molds. Even if the environmental temperature is controlled to be constant and thermal deformation is suppressed, the effect cannot be made zero. In the conventional example, since measurement time is required, the measurement error increases due to the influence of environmental temperature change.
(4) Since the lifetime of the three position mark spheres is short, the measurement accuracy deteriorates.
In order to measure the positions of the three position mark spheres, the surface is traced with a contact probe in the conventional example.
On the other hand, since the position mark sphere must be measured every time the shape of the object to be measured is measured, the number of measurement of the position mark sphere tends to increase. For this reason, wear cannot be ignored, and the measurement error of the position mark sphere gradually increases in the conventional method. Although it is conceivable to change the position mark sphere to a new one each time it is measured, it is not only uneconomical but also difficult to replace when used with adhesive fixation.
(5) Consider a case in which the position mark sphere is not attached due to human error or the like in the conventional example that cannot cope with an error that occurs when measuring the position mark sphere. Although the measuring probe 3 tries to contact the place where the ball is located, it is possible that not only the ball is present but there is another object such as a measured object or a jig. In such a case, there is a possibility of damaging the probe and the object to be measured.
In the conventional example, it is only possible to measure whether or not the position mark sphere, that is, the spherical surface is properly set there, using a probe. Therefore, since the probe must be brought close to the object to be measured and the surface is actually traced, the risk of the probe colliding with something is inevitable if there is the problem described above.
[0007]
Therefore, the first object of the present invention is to shorten the measurement time.
[0008]
The second purpose is to prevent the measurement result from being affected even if the mounting posture of the object to be measured changes.
[0009]
The third purpose is to reduce the influence on the measurement accuracy even if the environmental temperature changes.
[0010]
The fourth object is to extend the life of the position mark sphere by eliminating wear of the position mark sphere, and to prevent an increase in the measurement error of the sphere.
[0011]
The fifth object is to safely stop the measuring device against an error when measuring the position mark sphere.
[0012]
[Means for Solving the Problems]
  In order to achieve the above object, the present invention is a surface shape measuring apparatus for measuring the shape of a free-form surface and a relative position with respect to the position-mark sphere with respect to an object having three or more position mark spheres and a free-form surface. And
  It has a moving member that can move in three dimensions,
  A probe that traces the surface of the object to be measured and measures its shape;
  Provided separately from the probe,The light emitted from the light source is focused on the position mark sphere, and the center position of the position mark sphere is measured from the reflected light from the position mark sphere.The sphere center position measuring means is fixedly arranged.And
  The focal position of the focused light generated from the light source is on the extension line of the probe axis.It is characterized by that.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
[0014]
<Embodiment 1>
1 to 6 show a first embodiment of the present invention.
[0015]
First, description will be made with reference to the overall view of the measuring apparatus in FIG. 1 and the enlarged main portion of FIG.
[0016]
The object to be measured 1 is attached to the jig 2. A position mark ball 3 is attached to the jig 2. As described in Japanese Patent Application Laid-Open No. 11-14906, this jig fixes a position mark sphere and detachably holds an object to be measured.
[0017]
This is attached to the base 4 of the measuring apparatus. In addition to the structure described in Japanese Patent Application Laid-Open No. 10-19504, the measuring device main body is added with the ball position measuring means proposed in this case and its control device.
[0018]
The base 4 is provided with an X slider 5, a Y slider 6, and a Z slider 7 movably in the XYZ triaxial directions, and each is connected to an XYZ control device 8. The Z slider 7 is provided with laser length measuring devices X1, X2, and Z1 for measuring positions, and Y1 and T2 that are perpendicular to the paper surface, although not shown.
[0019]
The Z slider is provided with a contact type probe 10 having a sphere 9 at the tip. This probe has a parallel leaf spring structure as described in, for example, Japanese Patent Laid-Open No. 11-304463, and outputs a signal according to the displacement of the leaf spring. The signal is connected to the XYZ control device 8 via the probe control amplifier 11. Further, the Z-slider is provided with a ball position measuring means 12 which will be described in detail with reference to FIG.
[0020]
A column 14 is provided which is fixed to the base 4 and supports the position measurement reference. A reference mirror 15 which is fixed to the column 14 and serves as a reference in the X direction is provided. The reference mirror 15 is used as a target for the laser length measuring devices X1 and X2.
[0021]
A reference mirror 16 that is fixed to the column 14 and serves as a reference in the Z direction is provided. This reference mirror 16 is used as a target of the laser length measuring machine Z1.
[0022]
Although not shown, similarly, a reference mirror that is fixed to the column 14 and serves as a reference in the Y direction is provided. This reference mirror is used as a target of the laser length measuring devices Y1 and Y2 described above.
[0023]
The output signals of these laser length measuring instruments, i.e., the distance from the reference mirror, are connected to a data processor (not shown) and processed as position information on the surface of the object to be measured. The data processing of this part is the same as that of JP-A-10-19504.
[0024]
Next, the main part of the ball position measuring means will be described with reference to FIG.
[0025]
The light emitted from the semiconductor laser 17 is reflected by the half mirror 18, condensed by passing through the lens 19, and the direction is bent by the prism 20 to obtain a focused light beam 21. At this time, the positions of the lens 19 and the prism 20 are adjusted in advance so that the focal position of the focused light beam is directly below the contact probe 10 having the tip sphere 9. Although it is difficult to make this adjustment very precisely, the adjustment error at this time can be corrected. This method will be described with reference to a flowchart described later.
[0026]
As shown in the figure, when the focal position and the center position of the position mark sphere 3 substantially overlap, the focused light beam 21 is reflected by the surface of the position mark sphere 3 and returns to the original optical path. Then, the light spot detecting means 23, a so-called position sensor, is provided at a position where the light passes through the half mirror 18, is divided into two by the second half mirror 22, and the reflected light is focused.
[0027]
Four signals from the position sensor are passed through two subtraction circuits 26 to obtain two difference signals. That is, this signal represents the position of the light spot. However, this is still affected by fluctuations in the output of the semiconductor laser as the light source. Assuming that the laser output is multiplied by α, the four outputs of the position sensor are also uniformly multiplied by α, and of course, the difference signal is also multiplied by α. Therefore, all four signals from the position sensor are added together by the adding circuit 27, and the difference signal is divided by the dividing circuit 28. Since the difference signal multiplied by α is divided by α, the influence of fluctuations in the output of the semiconductor laser can be eliminated. The light spot position signals thus obtained are denoted by φ1 and φ2, as shown in the figure.
[0028]
Further, the output of the adder circuit 27 is connected to the error determination circuit 34. When the output of the adding circuit 27 is low, there is a possibility that the light beam does not strike the position sensor 23 properly. Therefore, it can be determined whether or not an error condition has occurred by determining whether or not this signal is below a certain predetermined value. The error determination circuit 34 compares the output of the addition circuit 27 with a preset signal level, and outputs an error signal if it is low. This error signal is set to e12 as shown in the figure.
[0029]
Next, it will be described with reference to FIGS. 3 and 4 that the signals φ1 and φ2 measure the positions in the two directions perpendicular to the optical axis 21 among the center positions of the position mark sphere 3.
[0030]
The light emitted from the light source 17 is condensed by the action of the lens 19 and focused at E1. At this time, from the lens formula, if the focal length of the lens 19 is f1,
1 / f1 = 1 / L1 + 2 / L2
The image E1 is reflected by the spherical surface 3. If the radius of the sphere is assumed to be R, it can be considered that the spherical surface has the same effect as a concave lens having a focal length of R / 2, so that the point image is mapped to a position E2 separated by L4.
[0031]
2 / R = 1 / L3 + 1 / L4
Here, as described above, a case where the focal position and the center position of the position mark sphere substantially coincide is considered, so that L3 and L4 are substantially the same distance.
[0032]
This point image passes through the lens 19 again and forms a focal point E3 on the light spot position detecting means 23. That is,
1 / f1 = 1 / L5 + 1 / L6
Consider the case where the spherical surface 3 moves δ in the direction perpendicular to the optical axis in such an optical system arrangement. The state at that time is shown in FIG. Since the point image E1 is the same as the δ movement for the spherical surface 3, E2 moves by δ * (L4 / L3 + 1) with respect to the optical axis.
[0033]
Furthermore, since it is mapped to E3 by the lens 19, the movement δ1 of E3 is
δ1 = δ * (L4 / L3 + 1) * L6 / L5
For example, if L3 = L4 and L6 = L5, then 2δ. That is, the motion perpendicular to the optical axis of the position mark sphere 3 is doubled and can be detected. The signals are φ1 and φ2.
[0034]
On the other hand, the light transmitted through the second half mirror 22 passes through the cylindrical lens 24 and enters the quadrant photodiode 25. This portion is autofocus using so-called astigmatism. Of the four signals of the four-divided photodiode, two opposing signals are added by the adder circuit 29 and the difference is obtained by the subtractor circuit 30. In this way, this signal changes depending on whether the light on the quadrant photodiode is vertically long or horizontally long.
[0035]
However, this is still affected by fluctuations in the output of the semiconductor laser as the light source. If the output of the laser is now multiplied by α, the four outputs of the four-division photodiode are also uniformly multiplied by α, and naturally the sum and difference signals are also multiplied by α. Therefore, all four signals from the four-divided photodiodes are added by the adder circuit 31 and the difference signal is divided by the divider circuit 32. Since the difference signal multiplied by α is divided by α, the influence of fluctuations in the output of the semiconductor laser can be eliminated. The light spot position signal thus obtained is set to φ3 as shown in the figure.
[0036]
Further, the output of the adder circuit 31 is connected to the error determination circuit 34. When the output of the adder circuit 31 is low, there is a possibility that the light beam does not strike the quadrant photodiode 25 properly. Therefore, it can be determined whether or not an error condition has occurred by determining whether or not this signal is below a certain predetermined value. The error determination circuit 34 compares the output of the adder circuit 31 with a preset signal level, and if it is low, generates an error signal. Let this error signal be e3.
[0037]
Next, it will be described that the signal φ3 measures the position in the direction along the optical axis 21 among the center positions of the position mark sphere 3. The schematic diagram is almost the same as FIG. When attention is paid to the action of the last lens 19, E3 becomes a point image when the focus position is exactly matched in E3.
[0038]
However, since the focal position is shifted only in one direction, that is, the direction having the curvature of the cylindrical lens, by the action of the cylindrical lens 24, the shape of the focal point is a vertically long ellipse, a circle, or a horizontally long ellipse with the change of the focus position. Change. This change in the shape of the focus image can be detected by the quadrant photodiode as described above. For example, in the case of a vertically long ellipse, the output in the vertical direction is large, and on the contrary, the output in the horizontal direction is small. Therefore, the signal φ1, which is the difference, has a large value. On the other hand, in the case of a horizontally long ellipse, since the top and bottom are small and the left and right are large, φ1 should have the opposite sign.
[0039]
Then, the position where the signal φ1 is exactly zero is the position where the focus is balanced in the vertical and horizontal directions. Since the focus direction is the direction of the optical axis, the signal φ1 represents the displacement of the position mark sphere in the optical axis direction.
[0040]
Here, once summarized, the displacement of the position mark sphere with respect to the optical axis 21 can be measured by the signal φ3. Two directions perpendicular to the optical axis 21 can be measured with φ1 and φ2. Error signals e12 and e3 indicate an error state.
[0041]
The laser length measuring device described with reference to FIG. 1 measures and corrects the position and orientation of the Z slider, and the method will be described with reference to FIG.
[0042]
For three reference mirrors fixed to the base and arranged orthogonally, the lengths measured by the laser length measuring device are X1, X2, Y1, Y2 and Z1, as shown in the figure. Z1 measures the distance between the Z reference mirror 16 and the contact probe 10. The difference between the mounting height of the X1 and Y1 interferometers and the mounting height of the X2 and Y2 interferometers is L2, and the difference from there to the mounting height of the contact probe 10 is L3. The difference to the position is L4, and the distance from there to the focal position of the light beam 21 is L5. These distances L2 to L3 are lengths determined by the component dimensions of the measuring apparatus. L1 is obtained by subtracting L2 and L3 from the Z1 measurement value.
[0043]
In this configuration, the measurement coordinates of the sphere center position of the contact probe can be calculated by the following equation.

Similarly, the measurement coordinates of the focal position of the light beam 21 can be calculated by the following equation.
[0044]

This coordinate position is not affected by the attitude error of the Z slider because it is measured with the reference mirror of the three surfaces as the position reference.
[0045]
In the configuration described above, the operation will be described with reference to the flowchart described in FIG.
[0046]
The object to be measured 1 is detachably attached to the jig 2 to which the three position mark balls 3 are attached (100). Next, it is determined whether or not it is necessary to align the spherical center position measuring means and the contact probe for measuring the free-form surface (101). This is necessary, for example, when the device is first manufactured or when the contact probe is replaced and the probe position information is lost.
[0047]
In addition, as described above, the positioning is performed so that the measurement position of the sphere center position measuring means, that is, the focal position of the light beam 21 is directly below the contact probe 9, but this is adjusted very precisely. Have difficulty. In this sense, first, it is necessary to align the position of the sphere center position measuring means and the contact probe for measuring the free-form surface. However, once alignment is performed, alignment is no longer necessary.
[0048]
When aligning, first, a point cloud when the surface of the position mark sphere 3 is traced with a contact probe is measured (102). The sphere center position is calculated from the point group on the surface using the least square method or the like (103). The position obtained as a result of the calculation is defined as Pa.
[0049]
Here, it should be noted that this point Pa is not the apex of the sphere as in the conventional example. Unlike the apex position, the center position of the sphere should be the same point no matter what direction it is measured. In other words, unlike the conventional example, the present invention gives the same result regardless of the direction of the position of the position mark sphere.
[0050]
Next, the position of the position mark sphere is measured by the sphere center measuring means. The XYZ controller 8 is used to move the X, Y, and Z sliders so that the position Pa of the position mark sphere measured by the contact probe and the focal position of the light beam 21 are substantially matched (104). At this position, it is determined whether any one of the error signals e12 and e3 described in FIG. 2 is output (116). If an error is output, it means that the position mark sphere is not at the expected position or the semiconductor laser has failed. On the other hand, an error is displayed (117) and the operation stops. On the other hand, if there is no error, the signals φ1, φ2, and φ3 can be considered as correct measured values.
[0051]
Since φ1, φ2 and φ3 represent deviations of the light beam 21 in the vertical direction and the optical axis direction, respectively, the X, Y, and Z sliders are finely adjusted by using the XYZ controller 8 so that they are all zero. (105). The moving direction in which φ1, φ2, and φ3 change and the moving direction of the X, Y, and Z sliders are different, but are only inclined, so the degree of freedom is the same 3. Moreover, they can be said to be three independent directions that are orthogonal and hardly interfere with each other. Therefore, it can be adjusted without fail. From the position and orientation of the XYZ slider when the adjustment residual becomes sufficiently small, the center position of the sphere is obtained by the method described with reference to FIG. 5 and (Equation 2).
[0052]
At this time, the signals φ1, φ2, and φ3 that could not be adjusted should be sufficiently small. However, if the adjustment residual is converted into the XYZ position and the position Pb of the XYZ slider is corrected, It is precise (106).
[0053]
A position difference D = Pa−Pb is calculated and used as a position correction amount. This represents the position of the contact probe for measuring the free-form surface and the position correction amount of the sphere center position measuring probe for measuring the position mark sphere (107).
[0054]
Next, all the position mark spheres are measured by the sphere center position measuring means. Each measurement is the same as the procedure described above. A case where the nth position mark sphere is measured will be described.
[0055]
First, the focal position of the light beam 21 is moved to the center position of the nth position mark sphere (108). Since the approximate position is known from the design drawing of the jig, the drawing for attaching the jig to the measuring device, etc., the XYZ slider can be moved to that position. At this position, it is determined whether any one of the error signals e12 and e3 described in FIG. 2 is output (118). If an error has been output, it means that there has been some trouble, such as the position mark sphere not being in the assumed position. Therefore, an error is displayed on the display device such as a computer screen to stop the error (119). ),Stop.
[0056]
On the other hand, if there is no error, the signals φ1, φ2, and φ3 can be considered as correct measured values. Next, the position of the XYZ slider is finely adjusted so that the signals φ1, φ2, and φ3 become zero (109). The n-th spherical center position at this time is calculated and set as Pn (110). At this time, the position correction amount D previously obtained is added. Then, this position Pn is converted into a position as if measured with a contact probe. Moreover, the measurement time is considerably shorter because the surface does not need to be traced as compared with the case of measuring with a contact probe. The operation from (108) is repeated until all the position mark spheres have been measured, and when completed, the process proceeds to the next (111).
[0057]
One orthogonal coordinate system is determined from the three spherical center positions (112). There are several methods. For example, the Z axis is taken in the direction perpendicular to the plane defined by three points (measured sphere center positions), the line connecting the two points is taken as the X axis, and the remaining Y An axis can be defined as an axis perpendicular to the X and Z axes. Since the orthogonal coordinate system defined in this way is fixed to three spheres, it is called an object coordinate system. When viewed from the measured object coordinate system, the measured object 1 including the free-form surface to be measured is always at the same position. This is because, as described at the beginning, the DUT 1 is fixed to the jig 2 fixed to the three-ball position mark 3.
[0058]
Next, the free-form surface is traced with a contact probe, and a point group on the free-form surface is measured (113). All of these point groups are coordinate-converted into the measured object coordinate system (114). Since the point group obtained in this way is based on the position of three balls, the same point group can be obtained no matter where the measurement object is placed in the measuring apparatus or in any posture. Next, a difference from the design shape, that is, an error shape is calculated using the least square method (115).
[0059]
According to the method described above, the measurement time can be shortened. This is because the measurement time for three balls is shortened. As described above, when measuring the position by tracing the surface of a sphere using a probe, three-dimensional position information is required, so multiple cross-section traces are required instead of a cross-section. is required. Moreover, the time required for acceleration / deceleration cannot be ignored when reciprocating and tracing is repeated. On the other hand, in the method according to the present embodiment, the XYZ axis is moved so that the position mark sphere is approximately at the center position of the optical axis 21, and then the sphere center is simply adjusted by the signals φ1, φ2, and φ3. The position can be determined. Since it is not necessary to trace the surface of the sphere, the time can be significantly reduced.
[0060]
Further, according to the present invention, since the center position of the sphere is measured instead of the vertex position of the sphere, it is not affected by the position and orientation of the object to be measured. This is because the sphere is used in such a manner that the same point is pointed regardless of the center position measured from any direction.
[0061]
Furthermore, according to the present invention, since the measurement time of the sphere is shortened, the overall measurement time is also shortened. Since errors such as temperature deformation that change with time can be relaxed, measurement accuracy can be improved as a result.
[0062]
In this embodiment, the light source is the semiconductor laser 17, but the same applies to other point light sources. For example, the same thing can be said even if laser light from a separately provided laser transmitter is incident on an optical fiber and its emission end is installed instead of the semiconductor laser 17 of the present embodiment.
[0063]
In the present embodiment, the prism 20 is used to obtain the oblique light beam 21, but the operation is the same even if this is used as a reflection mirror.
[0064]
In the present embodiment, the probe for measuring a free-form surface has been described as a contact type probe, but the same applies to a non-contact type probe.
[0065]
In the present embodiment, the light spot position measuring means is disposed on the side reflected by the half mirror 22, and the focal position detecting means (autofocus) is disposed on the transmitted side. That is, the focal position detecting means (autofocus) is arranged on the side reflected by the half mirror 22, and the light spot position measuring means is arranged on the transmitted side.
[0066]
In the present embodiment, in order to improve the light amount loss in the half mirror 18, it may be possible to change this to a polarization beam splitter and place a quarter-wave plate between the lens 19. In this case, the light emitted from the semiconductor laser reflects only linearly polarized light in one direction by the polarization beam splitter, and is converted into circularly polarized light by the quarter wavelength plate. When the light passes through the quarter-wave plate again after being reflected by the spherical surface, it is converted into linearly polarized light rotated by 90 degrees from the previous one, so that it now passes through the polarizing beam splitter. However, even in that case, the basic operation is the same as described above.
<Embodiment 2>
FIG. 7 shows a second embodiment of the present invention.
[0067]
The first embodiment is different from the first embodiment in that the prism 20 is omitted and the focal position of the light beam 21 is shifted from the center of the probe sphere. Since other configurations and operations are the same as those of the first embodiment, description thereof is omitted.
[0068]
The present embodiment has the following effects over the first embodiment.
[0069]
1) Since there is no need to bend the light beam 21, it can be configured with a small number of optical components.
[0070]
2) The distance of the light beam 21 can be shortened. In other words, since the aperture ratio of the objective lens 19 can be increased, the autofocus portion, that is, the detection sensitivity in the Z direction can be improved.
[0071]
3) Since there is no need to dispose the obstacle 20 such as the prism 20 in the vicinity of the contact probe, the possibility of collision between the object to be measured and the measuring device is reduced. Therefore, design restrictions on the device under test can be relaxed.
[0072]
4) The object to be measured including the position mark sphere needs to be designed so that both the contact probe and the light beam 21 as the sphere center position measuring means can approach, but according to the present embodiment, both In both cases, since only the vertical direction needs to be considered, the number of blind spots is smaller than in the case of the first embodiment. This is because the first embodiment considers two directions, the oblique direction and the vertical direction.
[0073]
Therefore, according to the present embodiment, it is possible to relax the design constraints of the device under test. For example, in the figure, it is easy to consider the case of measuring two spheres arranged on the left side. Since the spheres are displaced in the direction perpendicular to the paper surface, there is no problem in measuring from the Z direction. However, if measurement is performed with oblique rays as in the first embodiment, the sphere 3a becomes the shadow of the jig 2 and measurement is difficult.
[0074]
On the other hand, the slider position and orientation correction described with reference to FIG. 5 does not function sufficiently. This is because posture correction is possible only on the probe axis in FIG. When deviating from the axis, the influence of a so-called yawing error, which is a posture error around the vertical Z-axis, increases among slider posture errors. Therefore, in the present embodiment, an XYZ slider having a smaller yawing error than that in the first embodiment is required.
[0075]
<Embodiment 3>
FIG. 8 shows a third embodiment of the present invention.
[0076]
The difference from the first embodiment is that a bending mirror 33 having a hole for penetrating the contact probe is provided, and the light beam 21 of the sphere center position measuring means is arranged behind the probe. Since the operation and effect are the same as those in the first embodiment, the description thereof is omitted.
[0077]
This embodiment has the following effects over the first and second embodiments.
[0078]
1) The object to be measured including the position mark sphere needs to be designed so that both the contact probe and the light beam 21 which is the sphere center position measuring means can approach, both according to the present embodiment. Since only the vertical direction needs to be considered, the number of blind spots is smaller than that in the first embodiment. This is because the first embodiment considers two directions, the oblique direction and the vertical direction. Therefore, according to the present embodiment, it is possible to relax the design constraints of the device under test. For example, in the figure, it is easy to consider the case of measuring two spheres arranged on the left side. Since the spheres are displaced in the direction perpendicular to the paper surface, there is no problem in measuring from the Z direction. However, if measurement is performed with oblique rays as in the first embodiment, the sphere 3a becomes the shadow of the jig 2 and measurement is difficult.
[0079]
2) Since the sphere center measurement position and the contact probe can be coaxially arranged, a highly accurate XYZ slider is not necessary as described in the second embodiment.
[0080]
<Embodiment 4>
FIG. 9 shows a fourth embodiment of the present invention.
[0081]
The difference from Embodiment 1 is that two sets of spherical center position measuring means are provided. Since other parts are the same as those of the first embodiment, description thereof is omitted.
[0082]
The first sphere center position measuring means 12a and the second sphere center position measuring means 12b are fixedly provided on the Z slider 7, the respective light beams to be measured are 21a and 21b, and the respective signals are sent to the position measuring amplifiers 13a, 13b and connected to the XYZ controller 8.
[0083]
In the above configuration, the operation will be described with reference to the flowcharts described in FIGS.
[0084]
The object to be measured 1 is detachably attached to the jig 2 to which the three position mark balls 3 are attached (100). Next, it is determined whether or not it is necessary to align the spherical center position measuring means and the contact probe for measuring the free-form surface (101). As described above, this is necessary when, for example, the device is first manufactured or when the contact probe is replaced and the position information of the probe is lost. However, once alignment is performed, alignment is not necessary.
[0085]
When aligning, first, a point cloud is measured when the surface of the position mark sphere 3 that can be measured by the two sphere center position measuring means is traced by a contact probe (102). The sphere center position is calculated from the point group on the surface using the least square method or the like (103). The position obtained as a result of the calculation is defined as Pa.
[0086]
Next, the position of the position mark sphere is measured by the first sphere center measuring means. The X, Y, and Z sliders are moved using the XYZ control device 8 so that the position Pa of the position mark sphere measured by the contact probe and the focal position of the light beam 21 are substantially matched (104a). At this position, it is determined whether any one of the error signals e12 and e3 described in FIG. 2 is output (116a). If an error is output, it means that the position mark sphere is not at the expected position or the semiconductor laser has failed. On the other hand, an error is displayed (117a) and the operation stops. On the other hand, if there is no error, the signals φ1a, φ2a, and φ3a can be considered as correct measurement values.
[0087]
Since φ1a, φ2a, and φ3a represent deviations in the vertical direction and the optical axis direction of the light beam 21, respectively, the XYZ controller 8 is used to fine-tune the X, Y, and Z sliders so that they are all zero. (105a). Although the moving direction in which φ1a, φ2a, and φ3a change and the moving direction of the X, Y, and Z sliders are different, the degree of freedom is 3 because it is only inclined. Moreover, they can be said to be three independent directions that are orthogonal and hardly interfere with each other. Therefore, it can be adjusted without fail. From the position and orientation of the XYZ slider when the adjustment residual becomes sufficiently small, the center position of the sphere is obtained by the method described with reference to FIG. 5 and (Equation 2).
[0088]
At this time, the signals φ1a, φ2a, φ3a that could not be adjusted should be sufficiently small, but the adjustment residual is converted into the XYZ position, and the position Pb (a) of the XYZ slider is corrected. If so, it is still precise (106a).
[0089]
The position difference D (a) = Pa−Pb (a) is calculated, and this is used as the position correction amount. This represents the position correction amount of the contact-type probe for measuring the free-form surface and the sphere center position measurement probe for measuring the position mark sphere (107a).
[0090]
Next, the position of the position mark sphere is measured by the second sphere center measuring means. The X, Y, and Z sliders are moved using the XYZ controller 8 so that the position Pa of the position mark sphere measured by the contact probe and the focal position of the light beam 21 are substantially matched (104b). At this position, it is determined whether any one of the error signals e12 and e3 described in FIG. 2 is output (116b). If an error is output, it means that the position mark sphere is not at the expected position or the semiconductor laser has failed. On the other hand, an error is displayed (117b) and the operation stops. On the other hand, if there is no error, the signals φ1b, φ2b, and φ3b can be considered as correct measured values.
[0091]
Since φ1b, φ2b, and φ3b represent deviations of the light beam 21 in the vertical direction and the optical axis direction, respectively, the X, Y, and Z sliders are finely adjusted using the XYZ controller 8 so that they are all zero. (105b). Although the moving direction in which φ1b, φ2b, and φ3b change and the moving direction of the X, Y, and Z sliders are different, the degree of freedom is 3 because it is only inclined. Moreover, they can be said to be three independent directions that are orthogonal and hardly interfere with each other. Therefore, it can be adjusted without fail. From the position and orientation of the XYZ slider when the adjustment residual becomes sufficiently small, the center position of the sphere is obtained by the method described with reference to FIG. 5 and (Equation 2).
[0092]
At this time, the signals φ1b, φ2b, and φ3b that could not be adjusted should be sufficiently small, but the adjustment residual is converted into the XYZ position, and the position Pb (b) of the XYZ slider is corrected. If so, it is still precise (106b).
[0093]
The position difference D (b) = Pa−Pb (b) is calculated, and this is used as the position correction amount. This represents the position correction amount of the position of the contact probe for measuring the free-form surface and the sphere center position measurement probe for measuring the position mark sphere (107b).
[0094]
Next, all the position mark spheres are measured by the sphere center position measuring means. Each measurement is the same as the procedure described above. A case where the nth position mark sphere is measured will be described.
[0095]
First, the focal position of the light beam 21 is moved to the center position of the nth position mark sphere (108). Since the approximate position is known from the design drawing of the jig, the drawing for attaching the jig to the measuring device, etc., the XYZ slider can be moved to that position.
[0096]
Next, the error state storage devices a and b of the two sphere center position measuring means are cleared (120).
[0097]
At this position, the position of the position mark sphere is then measured by the first sphere center position measuring means.
[0098]
It is determined whether any one of the error signals e12 and e3 described in FIG. 2 is output (118a). If an error is output, the error state storage a is set (121a).
[0099]
On the other hand, if there is no error, the signals φ1a, φ2a, and φ3a can be considered as correct measurement values. Next, the position of the XYZ slider is finely adjusted so that the signals φ1a, φ2a, and φ3a become zero (109a). The n-th spherical center position at this time is calculated and set as Pn (a) (110a). At this time, the position correction amount D (a) obtained previously is added. Then, this position Pn (a) is converted into a position as if measured with a contact probe.
[0100]
Next, the position of the position mark sphere is measured by the second sphere center position measuring means.
[0101]
It is determined whether any one of the error signals e12 and e3 described in FIG. 2 is output (118b). If an error is output, the error state storage b is set (121b). On the other hand, if there is no error, the signals φ1b, φ2b, and φ3b can be considered as correct measured values.
[0102]
Next, the position of the XYZ slider is finely adjusted so that the signals φ1b, φ2b, and φ3b become zero (109b). The n-th spherical center position at this time is calculated and set as Pn (b) (110b). At this time, the position correction amount D (b) obtained previously is added. Then, this position Pn (b) is converted into a position when measured with a contact probe.
[0103]
Next, the process branches depending on the states of the error state memories a and b.
[0104]
It is determined whether or not there is an error in both of the error state memories a and b (122). If there is an error, the sphere center position cannot be measured. If not, the process proceeds to the next process, and it is determined whether or not both of the error state memories a and b are normal (124). If both are normal, the two measured values are averaged (125). That is, Pn (a) and Pn (b) are averaged to obtain the sphere center position of the nth position mark sphere.
[0105]
If not, the normal measurement is adopted (126). That is, one of normal Pn (a) and Pn (b) is set as the sphere center position of the nth position mark sphere.
[0106]
The operation from (108) is repeated until all the position mark spheres have been measured, and when completed, the process proceeds to the next (111).
[0107]
One orthogonal coordinate system is determined from the three spherical center positions (112). There are several methods. For example, the Z axis is taken in the direction perpendicular to the plane defined by three points (measured sphere center positions), the line connecting the two points is taken as the X axis, and the remaining Y An axis can be defined as an axis perpendicular to the X and Z axes. Since the orthogonal coordinate system defined in this way is fixed to three spheres, it is called an object coordinate system. When viewed from the measured object coordinate system, the measured object 1 including the free-form surface to be measured is always at the same position. This is because the DUT 1 is fixed to the jig 2 fixed to the three-ball position mark 3 as described at the beginning.
[0108]
Next, the free-form surface is traced with a contact probe, and a point group on the free-form surface is measured (113). All of these point groups are coordinate-converted into the measured object coordinate system (114). Since the point group obtained in this way is based on the position of three balls, the same point group can be obtained no matter where the measurement object is placed in the measuring apparatus or in any posture. Next, a difference from the design shape, that is, an error shape is calculated using the least square method (115).
[0109]
According to this embodiment, there are the following merits.
[0110]
1) Even when the position mark sphere is shaded by a jig or the like and cannot be measured when viewed from one sphere center position measuring means, the position mark sphere is shaded when viewed from the other sphere center position measuring means. Otherwise, it can be measured. Accordingly, the blind spots are reduced, and the design constraints of the object to be measured can be relaxed.
[0111]
2) When the position mark sphere can be measured by the two sphere center position measuring means, the two measurement results can be averaged, so that the chance error can be reduced. Therefore, measurement accuracy can be improved.
[0112]
According to the present embodiment shown in FIG. 9, the two sphere measuring means are depicted in an opposing arrangement. That is, they are arranged 180 degrees apart when viewed from above, but they are the same regardless of whether they are arranged 90 degrees apart or many times apart.
[0113]
<Embodiment 5>
12 and 13 show a fifth embodiment of the present invention.
[0114]
The configuration of the non-contact sphere center position measuring unit is different from that of the first embodiment.
[0115]
FIG. 12 shows the main part of the ball position measuring means in the present embodiment. The light emitted from the semiconductor laser 17 is reflected by the half mirror 18, condensed by passing through the lens 19, and the direction is bent by the prism 20 to obtain a focused light beam 21. At this time, the positions of the lens 19 and the prism 20 are adjusted in advance so that the focal position of the focused light beam is directly below the contact probe 10 having the tip sphere 9. As shown in the figure, when the focal position and the center position of the position mark sphere 3 substantially overlap, the focused light beam 21 is reflected on the surface of the position mark sphere 3 and returns to the original optical path. Then, the light passes through the half mirror 18 and passes through the cylindrical lens 24 to form a spot. A camera 35 for observing the spot image is provided and connected to the image processing device 36.
[0116]
A spot image captured by the image processing device 36 is shown in FIG.
[0117]
As described above, when the sphere center of the position mark sphere is shifted in the direction perpendicular to the optical axis of the focused light beam 21, the position of the spot image is shifted. The position of the spot image can be obtained by calculating the position of the center of gravity of the spot image using the image processing device 36. The center of gravity position is defined as signals φ1 and φ2.
[0118]
Further, when the sphere center of the position mark sphere is shifted in the direction along the optical axis of the focused light beam 21, the shape of the spot image is changed to a vertically long ellipse or a horizontally long ellipse as described above. Therefore, the image processing device 36 can be used to measure the vertical and horizontal sizes SX and SY of the spot image and calculate the ratio. The calculated value is φ3.
[0119]
Further, the total amount of light incident on the camera is calculated by the image processing device 36, and an error signal e is output when the amount of light is lower than a predetermined value. This has the same meaning as the OR connection of the two error signals e12 and e3 described in the first embodiment.
[0120]
Using these signals φ1, φ2, φ3 and e, the sphere center position can be measured. Since the subsequent description is the same as that of the embodiment, it is omitted.
[0121]
According to this embodiment, since there are few components of an optical system, it can be realized more simply.
[0122]
【The invention's effect】
As described above, the present invention has the following effects.
(1) Since it is not necessary to trace the surface of the position mark sphere as in the conventional example, it is possible to expect a significant reduction in measurement time.
(2) Since the center of the sphere is measured instead of the top of the sphere, the same measurement result can be obtained regardless of the position and orientation of the object to be measured. This is because the center of the sphere is the same point no matter what direction it is measured.
(3) Since the measurement time can be shortened, the environmental temperature change within the measurement time is also reduced, and the measurement accuracy is improved.
(4) Since the center of the position mark sphere can be measured in a non-contact manner, there is no need to worry about wear of the sphere, and there is no increase in error due to wear, so that measurement accuracy can be improved.
(5) Since it is non-contact, the life of the position mark sphere can be extended.
(6) Since there is no contact, there is no increase in measurement error due to wear, and accuracy is improved.
(7) By setting the measurement position of the non-contact sphere center position measurement means on the extension line of the probe axis, the influence of the position and posture error of the moving member accompanying the probe movement can be minimized as in the probe.
(8) The non-contact sphere center position measuring means can be realized with a simple optical system.
(9) It is possible to automatically detect an abnormal state such as when the position mark ball is dropped and to stop the apparatus.
(10) It is possible to automatically detect an error and stop the apparatus safely even for an error that has been difficult to deal with in the past, such as a wrong part being attached instead of the position mark sphere.
(11) Since there is no need for tracing as in the prior art, it is possible to minimize the influence of errors by detecting abnormalities quickly.
(12) Since an error can be detected and stopped safely, it is also effective in preventing accidents. By preventing accidents, the operating rate of production equipment is improved and production costs are reduced.
(13) Since the axis of the light used in the sphere center position measuring means and the axis of the probe are in the same direction, the object to be measured may be designed not to collide in one direction. Therefore, design constraints can be relaxed.
(14) By providing two sets of sphere center position measuring means, even if the position mark sphere is shaded by a jig or the like and cannot be measured, the position mark sphere is shaded when viewed from the other sphere center position measuring means. Otherwise, it can be measured. Accordingly, the blind spots are reduced, and the design constraints of the object to be measured can be relaxed.
(15) Further, when the position mark sphere can be measured by the two sphere center position measuring means, the two measurement results can be averaged, so that the chance error can be reduced. Therefore, measurement accuracy can be improved.
(16) The non-contact sphere center position measuring means can be configured with a simpler structure.
(17) Since the measurement position of the non-contact sphere center position measuring means and the positional deviation of the probe can be accurately corrected, the measurement accuracy can be improved particularly for the relative position of the free-form surface with respect to the position mark sphere.
(18) Since it is not necessary to precisely position the deviation between the measurement position of the non-contact sphere center position measurement means and the position of the probe, the device manufacturing cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating Embodiment 1 of the present invention.
FIG. 2 is a diagram for explaining a main part of the first embodiment of the present invention.
FIG. 3 is a first schematic diagram of the optical system according to the first embodiment of the present invention.
FIG. 4 is a second schematic diagram of the optical system according to the first embodiment of the present invention.
FIG. 5 is a diagram for explaining a coordinate position measurement method according to the first embodiment of the present invention;
FIG. 6 is a flowchart for explaining the operation of the first embodiment of the present invention.
FIG. 7 is a diagram illustrating Embodiment 1 of the present invention.
FIG. 8 is a diagram for explaining a third embodiment of the present invention.
FIG. 9 is a diagram for explaining a fourth embodiment of the present invention.
FIG. 10 is a flowchart for explaining the operation of the fourth embodiment of the present invention.
FIG. 11 is a flowchart illustrating the operation of the fourth embodiment of the present invention.
FIG. 12 is a diagram for explaining a fifth embodiment of the present invention.
FIG. 13 is a diagram illustrating image processing according to Embodiment 1 of the present invention.
FIG. 14 is a diagram illustrating a conventional example.
FIG. 15 is a flowchart illustrating the operation of a conventional example.
FIG. 16 is a diagram for explaining a problem of measuring a vertex position in a conventional example.
[Explanation of symbols]
1 DUT
2 jigs
3 Position mark sphere
4 base
5 X slider
6 Y slider
7 Z slider
8 XYZ controller
9 tip sphere
10 Contact probe
11 Probe control amplifier
12 Ball position measuring means
13 Position measurement amplifier
14 columns
15 X direction reference mirror
16 Z-direction reference mirror
17 Semiconductor laser
18 half mirror
19 Lens
20 Prism
21 Focusing beam
22 Second half mirror
23 Light spot position detection means (position sensor)
24 Cylindrical lens
25 Quadrant photodiode
26 Subtraction circuit
27 Adder circuit
28 Dividing circuit
29 Adder circuit
30 Subtraction circuit
31 Adder circuit
32 Divide circuit
33 Bending mirror
34 Error judgment circuit
35 cameras
36 Image processing device
37 Spot shape

Claims (7)

A surface shape measuring device for measuring a shape of a free curved surface and a relative position with respect to the position mark sphere with respect to an object to be measured having three or more position mark spheres and a free curved surface,
It has a moving member that can move in three dimensions,
A probe that traces the surface of the object to be measured and measures its shape;
A sphere center position measuring means, which is provided separately from the probe , focuses light generated from the light source on the position mark sphere, and measures the center position of the position mark sphere from the reflected light from the position mark sphere. Arranged ,
Profilometer the focal point of the focused beam generated from said light source and said extension on the near Rukoto probe shaft. The spherical center position measuring means includes a focusing optical system for refocusing the reflected light;
A half mirror for dividing the refocused focused light in two directions;
One of the divided focused lights is focused on the light spot position measuring means to measure the position in two directions perpendicular to the optical axis, and the other is focused on the focus position detecting means to be 1 along the optical axis. 2. The surface shape measuring apparatus according to claim 1, wherein a position in a direction is measured.   The light spot position measuring unit includes a light amount measuring unit for incident light, and a first error determination circuit for generating an error signal when the incident light does not reach a predetermined light amount, and the focal position The detection means includes a light quantity measurement means for incident light, and a second error determination circuit that generates an error signal when the incident light does not reach a predetermined light quantity. 3. The surface shape measuring apparatus according to claim 2, wherein the measurement is interrupted when at least one of the error determination circuits generates an error signal. 4. The sphere center position measuring means includes a folding mirror that reflects light generated from a light source and reflects reflected light formed by reflecting the light from a position mark sphere again. Surface shape measuring device. A surface shape measuring method for measuring a shape of a free-form surface and a relative position with respect to the position-mark sphere with respect to an object to be measured having three or more position mark spheres and a free-form surface, and a movable member movable in three dimensions A probe for measuring the shape by tracing the surface of the object to be measured on the moving member, and focusing the light generated from the light source on the position mark sphere, The center position of the position mark sphere is measured from the reflected light of the two sets of sphere center position measuring means for measuring the center position of the position mark sphere, and the focal position of the focused light generated from the light source is on the extension line of the probe axis. Is fixedly placed,
If both of the two sets of sphere center position measuring means are in error, the measurement is interrupted, if one of them is in error, the measurement result of the normal one is adopted, and if both are normal, the average of the two is used. A surface shape measuring method characterized by adopting The non-contact sphere center position measuring means is provided with a cylindrical lens , and the center of the sphere is determined from the aspect ratio of the obtained spot image by a camera that observes the shape and position of the spot image formed by passing through the cylindrical lens . 3. The surface shape measuring apparatus according to claim 2, wherein the position in the optical axis direction is measured from the position of the center of gravity of the spot image in the direction perpendicular to the optical axis at the center of the sphere. A surface shape measuring method for measuring a shape of a free-form surface and a relative position with respect to the position-mark sphere with respect to an object to be measured having three or more position mark spheres and a free-form surface, and a movable member movable in three dimensions A probe for measuring the shape by tracing the surface of the object to be measured on the moving member, and focusing the light generated from the light source on the position mark sphere. A center position measuring means for measuring the center position of the position mark sphere from the reflected light from the reflected light and fixed so that the focal position of the focused light generated from the light source is on an extension line of the probe axis Arranged,
The center position of a predetermined same position mark sphere is measured in advance by the sphere center position measuring means and the probe, and the difference between the measured values is stored as a correction amount. Thereafter, the position mark sphere is measured by the sphere center position measuring means. A surface shape measuring method, comprising: adding a correction amount to the measured value when measuring the center position of the surface.

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