JP2005326192A - Three-dimensional shape measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform a precise three-dimensional measurement in a largely changing environment while preventing deterioration of accuracy by vibration, fluctuation or the like of an optical system. <P>SOLUTION: This device is adapted to project interference fringes by two parallel luminous fluxes L<SB>1</SB>and L<SB>2</SB>obtained by separating 0-order light and primary light of laser beam made parallel by a collimator lens 2 and transmitted by a transmission type diffraction grating 3 by a space filter 5 to a measuring object W<SB>1</SB>, image the modulated interference fringes by an imaging element 7, and perform image processing in an imge processor 8. According to this, the deterioration of accuracy by vibration, fluctuation or the like can be avoided due to a common path system in which the two parallel luminous fluxes L<SB>1</SB>and L<SB>2</SB>following the same optical path generate interference fringes based on a displacement quantity by focal position slippage of the 0-order light and primary light in a lens 4a. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a three-dimensional shape measuring apparatus capable of measuring a shape of a large area with high accuracy by projecting interference fringes.

  As a method for measuring the three-dimensional shape of an object, a three-dimensional shape measurement method using lattice pattern projection has been proposed. This technique is a technique proposed in Patent Document 1, in which a lattice pattern is projected onto a measurement target, and a shape is obtained from a lattice pattern modulated according to the shape. As a feature of this method, it is possible to perform in-plane shape batch measurement. In addition, since the measurement range can be greatly changed according to the grating frequency of the pattern to be projected, a wide range of applications from large shapes such as the shape of the human body to shape measurements on the order of μm is possible. The lattice pattern projection method is expected to be applied to a shape inspection apparatus for molded products because of the two features that it is possible to measure the shape in the order of μm and that the measurement time is short because of in-plane collective measurement.

  In order to perform shape measurement on the order of μm by the grating pattern projection method, it is necessary to narrow the projection grating interval to the order of μm. However, when projecting an actual lattice pattern, there is an unsolved problem that the effect of diffraction becomes obvious due to a narrow lattice interval, making it impossible to project an ideal lattice pattern. In the case of narrowing the grating interval of the projection grating, there is a method using interference fringe projection as a method that can avoid the influence of diffraction and project an ideal grating pattern, which is proposed in Patent Document 2.

In this technique, a two-beam interference system including a laser light source 101, a collimating lens 102, a beam splitter 103, and a plane mirror 104 is used as a system that can easily adjust the grating frequency, as shown in FIG. The two light beams L ₁ and L ₂ separated by the beam splitter 103 are crossed at the surface of the object to be measured W ₀ on the holder 105, and the generated interference fringes are imaged by the image sensor 107 through the objective lens 106. The processing device 108 performs image processing.

Such interference fringe projection has the advantage that the projection pattern has a sinusoidal profile in addition to being unaffected by the diffraction. Since the projection pattern is sinusoidal, the measurement resolution can be further increased by using a phase analysis technique represented by the phase shift method. In particular, if the Fourier transform method is used for the phase analysis method, since only one modulation fringe image is required for the analysis, it is possible to cope with measurement such as instantaneous shape measurement and real-time shape measurement. From the above, it can be seen that by measuring interference fringes at intervals of several tens of μm, shape measurement can be performed at a very high speed with a resolution of the order of μm.
JP 2002-224828 A Japanese Patent Publication No. 3-12684

  However, when interference fringe projection is performed by the above-described method, if there is mechanical vibration or thermal fluctuation in the two-beam interference system, vibration / modulation occurs in the projection pattern. For this reason, the measurement accuracy is greatly impaired except in a controlled environment, and measurement cannot be performed in a bad environment such as a production line. Even if it is used as an inspection device separated from the line, there is an unresolved problem that it is required to use in an environment-controlled place or to incorporate an environmental control mechanism in the device itself, which causes high costs was there.

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art. By utilizing common path interference in which two divided light beams share one light beam system, thermal and mechanical properties are obtained. It is an object of the present invention to provide a three-dimensional shape measuring apparatus that can automatically perform three-dimensional shape measurement without impairing measurement accuracy even in an environment where fluctuations exist.

  In order to achieve the above object, a three-dimensional shape measuring apparatus of the present invention includes a laser light source, an optical element that converts laser light from the laser light source into parallel light, and parallel light emitted from the optical element by a light beam sharing means. An interference fringe projection optical system that divides the light into two parallel light beams in the same traveling direction and projects an interference fringe generated at a portion where the two parallel light beams overlap with the object to be measured; And an imaging device that images the modulation fringes on the surface of the object to be measured. The shape of the object to be measured is obtained by calculation based on phase information of the modulation fringes imaged by the imaging device.

  The laser light converted into parallel light is divided into two parallel light beams overlapping on the same optical path by a light beam sharing means using a diffraction grating or the like, and interference fringes are generated by the displacement amount, shift angle or phase difference between them. Therefore, compared to a two-beam interference system in which two divided beams interfere with each other through separate optical paths, the optical system is not affected by thermal and mechanical fluctuations.

  Accordingly, it is possible to realize a highly reliable three-dimensional shape measuring apparatus capable of stably performing high-precision three-dimensional measurement even in an environment with a large change.

  Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram for explaining a first embodiment of the present invention. FIG. 1A is a schematic diagram illustrating the entire three-dimensional shape measuring apparatus. As shown in FIG. 1A, an interference fringe projection system using a shearing interference system, which is a light-sharing means for common path interference for forming interference fringes, is provided. _The modulation interference fringes projected on the surface of ₁ are imaged by the image sensor 7, the modulation fringe image obtained from the image sensor 7 is acquired, and the three-dimensional shape is obtained using the Fourier transform phase analysis method in the image processing device 8. calculate.

  FIG. 1B is a detailed diagram for explaining the shearing interference system shown in FIG. The shearing interference system in FIG. 1B transmits only the transmissive diffraction grating 3, the lens 4a that is a Fourier transform element that forms a Fourier transform image of the diffraction grating, and only the 0th and 1st orders of the Fourier transform image. The spatial filter 5 and a lens 4b, which is an inverse Fourier transform element that performs inverse Fourier transform on the transmitted 0th-order / first-order light, generate interference fringes by the interference of the 0th-order / first-order light.

  As shown in FIG. 1, the laser light emitted from the laser light source 1 is converted into parallel light by a collimating lens 2 that is an optical system, and is incident on a transmissive diffraction grating 3.

  The light transmitted through this diffraction grating is divided into n-order parallel light beams due to the influence of diffraction. At this time, the magnitude of the diffraction angle of the nth-order light with respect to the 0th-order light is determined by the grating interval of the diffraction grating and the wavelength of the laser. Assuming that the grating interval of the diffraction grating is d and the laser wavelength is λ, the diffraction angle θ of the n-order light is expressed by the following equation (1).

ｎ次に分割された平行光束をそのまま照射すると各光束が多重に干渉し、等間隔の格子パターンは投影されない。そのため、透過型回折格子３の後にレンズ４ａを配置して回折光を集光させる。各次の回折光はそれぞれ異なる角度でレンズ４ａに入射するため、焦点位置はそれぞれ異なった位置になる。このときの焦点位置の変位量ΔＨは、レンズ４ａの焦点距離をｆとすると式（２）で表される。

When the n-order-divided parallel light beams are irradiated as they are, the light beams interfere with each other in multiple ways, and the equally spaced lattice pattern is not projected. Therefore, the lens 4a is disposed after the transmissive diffraction grating 3 to collect the diffracted light. Since the respective diffracted lights are incident on the lens 4a at different angles, the focal positions are different from each other. The displacement ΔH of the focal position at this time is expressed by Expression (2), where f is the focal length of the lens 4a.

この焦点位置の分布は、回折格子のフーリエ変換像に対応している。フーリエ変換像は０〜ｎ次が完全に分離して現れるため、焦点位置に空間フィルタ５を配置することで、任意の次数の回折光を抽出することができる。干渉縞を発生させるためには２本の光束のみを抽出すればよい。また、投影光の強度が最大となるとき、測定感度を最も高めることができることから、空間フィルタ５は０次光と１次光のみを透過するように設計する。０次と１次光のフーリエ変換像は隣接しているため、空間フィルタ５はピンホール１つでよい。ピンホールの直径は焦点位置の変位量ΔＨに依存し、その大きさは式（３）で表される。

This distribution of focal positions corresponds to a Fourier transform image of the diffraction grating. Since the Fourier transform image appears with the 0th to nth orders completely separated, diffracted light of an arbitrary order can be extracted by arranging the spatial filter 5 at the focal position. In order to generate interference fringes, only two light beams need be extracted. Further, since the measurement sensitivity can be maximized when the intensity of the projection light is maximized, the spatial filter 5 is designed to transmit only the 0th-order light and the 1st-order light. Since the Fourier transform images of the 0th order and the 1st order light are adjacent, the spatial filter 5 may be a single pinhole. The diameter of the pinhole depends on the amount of displacement ΔH of the focal position, and its size is expressed by equation (3).

空間フィルタ５を透過した０次・１次光は、レンズ４ｂによって逆フーリエ変換され変位量ΔＨを有する平行光束Ｌ₁ 、Ｌ₂ へと戻される。このときのレンズ４ｂはレンズ４ａと同じＦナンバーのものを使用する。この結果、シェアされた０次と１次光が干渉し、干渉縞が被測定物Ｗ₁ に投影される。干渉縞の投影方向は０次と１次光のなす角の二等分線の方向となる。すなわち、０次光と投影光のなす角は式（４）で表される角度となる。

The 0th-order / first-order light transmitted through the spatial filter 5 is inverse Fourier transformed by the lens 4b and returned to the parallel light beams L ₁ and L ₂ having the displacement amount ΔH. The lens 4b at this time uses the same F number as the lens 4a. As a result, the zero-order and first-order light shares interference, the interference fringes are projected onto the object to be measured W _1. The projection direction of the interference fringes is the direction of the bisector of the angle formed by the 0th order and the primary light. That is, the angle formed by the 0th-order light and the projection light is an angle represented by Expression (4).

このときに投影される干渉縞の格子間隔は０次と１次光のなす角から一意に決定される。この格子間隔ｄ_p は、式（５）で表される大きさとなる。

The lattice spacing of the interference fringes projected at this time is uniquely determined from the angle formed between the 0th order and the primary light. The lattice spacing d _p has a size represented by the equation (5).

被測定物Ｗ₁ に対してシアリング干渉縞を投影し、被測定物Ｗ₁ の形状に応じて変調された変調縞を対物レンズ６で撮像素子７に対して結像させる。撮像素子７で撮像された変調縞は画像処理装置８へと取り込まれ、フーリエ変換位相解析により位相情報への変換が行われる。さらに位相のアンラッピング処理を行うことにより、被測定物Ｗ₁ の形状情報が算出される。

Projecting the shearing interference pattern relative to the DUT W _1, it is imaged to the imaging device 7 a modulation pattern that is modulated in accordance with the shape of the workpiece W ₁ by the objective lens 6. The modulation fringes imaged by the image sensor 7 are taken into the image processing device 8 and converted into phase information by Fourier transform phase analysis. Further, the shape information of the workpiece W ₁ is calculated by performing the phase unwrapping process.

  By adopting such a configuration, it is possible to stably perform highly accurate three-dimensional measurement even in a large change environment without being affected by thermal and mechanical fluctuations of the optical system. A shape measuring device can be realized.

  FIG. 2 is a diagram for explaining a second embodiment of the present invention. 2A is a schematic diagram for explaining the entire three-dimensional shape measuring apparatus, and FIG. 2B is a detailed diagram for explaining the shearing interference system shown in FIG. 2A. The three-dimensional shape measuring apparatus shown in FIG. 2 includes a reflective diffraction grating 13, a lens 14a that is a Fourier transform element that forms a Fourier transform image of the diffraction grating, and a space that transmits only the 0th and 1st orders of the Fourier transform image. The filter 15 includes a lens 14b that is an inverse Fourier transform element that performs inverse Fourier transform on the transmitted 0th-order / first-order light, and interference fringes are generated by the interference of the 0th-order / first-order light. 2 (a) and 2 (b), the same members as those in FIGS. 1 (a) and 1 (b) are denoted by the same reference numerals, and the description thereof is omitted.

FIG. 2C is a schematic diagram for explaining the exit angle of the diffracted light by the reflective diffraction grating 13 shown in FIG. FIG. 2 uses a shearing interference fringe projection system with a reflective diffraction grating 13, and the laser light collimated (collimated) by the collimating lens 2 enters the reflective diffraction grating 13 at an angle θ _i . Assuming that the grating interval d of the reflective diffraction grating 13 is, the emission angle θ _d (θ _i −θ _S ) of ± n-order diffracted light at this time is an angle represented by equation (6).

図１の透過型回折格子を使用した場合と同様に、反射型回折格子１３の後にレンズ１４ａを配置して回折光を集光させる。各次の回折光はそれぞれ異なる角度でレンズ１４ａに入射するため、焦点位置はそれぞれ異なった位置になる。このときの焦点位置の変位量ΔＨは、レンズ１４ａの焦点距離をｆとすると式（７）で表される。

As in the case where the transmission type diffraction grating of FIG. 1 is used, a lens 14 a is arranged after the reflection type diffraction grating 13 to collect diffracted light. Since the respective diffracted lights are incident on the lens 14a at different angles, the focal positions are different from each other. The displacement ΔH of the focal position at this time is expressed by Expression (7), where f is the focal length of the lens 14a.

焦点位置に０次光と１次光のみを透過する空間フィルタ１５を設置する。この空間フィルタ１５はピンホール１つで形成される。ピンホールの直径ｒは焦点位置の変位量ΔＨに依存し、その大きさは式（８）で表される。

A spatial filter 15 that transmits only the 0th order light and the 1st order light is installed at the focal position. This spatial filter 15 is formed by one pinhole. The diameter r of the pinhole depends on the focal position displacement amount ΔH, and the size thereof is expressed by Expression (8).

空間フィルタ１５を透過した０次・１次光は、レンズ１４ｂによって平行光束へと戻される。このときのレンズ１４ｂはレンズ１４ａと同じＦナンバーのものを使用する。この結果、シェアされた２本の平行光束Ｌ₁ 、Ｌ₂ が干渉し、干渉縞が被測定物Ｗ₂ に投影される。干渉縞の投影方向は０次と１次光のなす角の二等分線の方向となる。すなわち、０次光と投影光のなす角は式（９）で表される角度となる。

The 0th-order / first-order light transmitted through the spatial filter 15 is returned to a parallel light beam by the lens 14b. At this time, the lens 14b having the same F number as the lens 14a is used. As a result, the two shared parallel light beams L ₁ and L ₂ interfere with each other, and the interference fringes are projected onto the workpiece W ₂ . The projection direction of the interference fringes is the direction of the bisector of the angle formed by the 0th order and the primary light. That is, the angle formed by the 0th-order light and the projection light is an angle represented by Expression (9).

このときに投影される干渉縞の格子間隔は０次と１次光のなす角から一意に決定される。この格子間隔ｄ_p は、式（１０）で表される大きさとなる。

The lattice spacing of the interference fringes projected at this time is uniquely determined from the angle formed between the 0th order and the primary light. The lattice spacing d _p has a size represented by the equation (10).

被測定物Ｗ₂ に対してシアリング干渉縞を投影し、被測定物Ｗ₂ の形状に応じて変調された変調縞を対物レンズ６で撮像素子７に対して結像させる。撮像素子７で撮像された変調縞は画像処理装置８へと取り込まれ、フーリエ変換位相解析により位相情報への変換が行われる。さらに位相のアンラッピング処理を行うことにより、被測定物Ｗ₂ の形状情報が算出される。

Projecting the shearing interference pattern with respect to the measured object W _2, it is imaged to the imaging device 7 a modulation pattern that is modulated in accordance with the shape of the workpiece W ₂ by the objective lens 6. The modulation fringes imaged by the image sensor 7 are taken into the image processing device 8 and converted into phase information by Fourier transform phase analysis. Further, by performing the phase unwrapping process, the shape information of the workpiece W ₂ is calculated.

  By adopting such a configuration, it is possible to stably perform highly accurate three-dimensional measurement even in a large change environment without being affected by thermal and mechanical fluctuations of the optical system. A shape measuring device can be realized. Further, the projection grating interval can be adjusted by adjusting the angle of the reflective diffraction grating.

FIG. 3 is a diagram for explaining a third embodiment of the present invention. FIG. 3A is a schematic diagram for explaining the entire three-dimensional shape measuring apparatus. The three-dimensional shape measuring apparatus shown in FIG. 3 includes a transparent substrate 23 with wedges, and the front and back surfaces of the transparent substrate 23 with wedges. Interference fringes are generated by the interference of the reflected lights L ₁ and L ₂ from. In FIG. 3A, the same members as those in FIG. 1A are denoted by the same reference numerals, and the description thereof is omitted.

FIG. 3 (a) uses a shearing interference fringe projection system by the transparent substrate 23 with wedges shown in FIG. 3 (b), and the laser light collimated (collimated) by the collimating lens 2 is The light enters the transparent substrate 23 with wedges at an angle θ _i . If the transparent substrate 23 with wedges is formed of a material that transmits laser light and has a wedge angle θ _w , the shift angle θ _P formed by the reflected light from the substrate surface and the reflected light from the back surface of the substrate is expressed by the formula ( 11).

このときに投影される干渉縞の格子間隔ｄ_p は、式（１２）で表される大きさとなる。

The lattice spacing d _p of the interference fringes projected at this time has a size represented by Expression (12).

被測定物Ｗ₃ に対してシアリング干渉縞を投影し、被測定物Ｗ₃ の形状に応じて変調された変調縞を対物レンズ６で撮像素子７に対して結像させる。撮像素子７で撮像された変調縞は画像処理装置８へと取り込まれ、フーリエ変換位相解析により位相情報への変換が行われる。さらに位相のアンラッピング処理を行うことにより、被測定物Ｗ₃ の形状情報が算出される。

Projecting the shearing interference pattern with respect to the measured object W _3, it is imaged to the imaging device 7 a-modulated fringe objective lens 6 in accordance with the shape of the workpiece W _3. The modulation fringes imaged by the image sensor 7 are taken into the image processing device 8 and converted into phase information by Fourier transform phase analysis. Further, the shape information of the workpiece W ₃ is calculated by performing the phase unwrapping process.

  By adopting such a configuration, it is possible to stably perform highly accurate three-dimensional measurement even in a large change environment without being affected by thermal and mechanical fluctuations of the optical system. A shape measuring device can be realized. Further, since the spatial filter mechanism is not required as compared with the case where the light beam is divided by diffraction, it is possible to reduce the size of the projection optical system.

FIG. 4 is a diagram for explaining a fourth embodiment of the present invention. 4A is a schematic diagram for explaining the entire three-dimensional shape measuring apparatus, and FIG. 4B is a detailed diagram for explaining the light beam sharing means shown in FIG. 4A. An interference fringe is generated by the interference of the _two light beams L ₁ and L ₂ divided by the polarizing prism 33, which is composed of the polarizing prism 33 and the polarizing plate 34 disposed immediately thereafter. 2 (a) and 2 (b), the same members as those in FIGS. 1 (a) and 1 (b) are denoted by the same reference numerals, and the description thereof is omitted.

  The laser light collimated by the collimating lens 2 enters a polarizing prism (Wollaston prism) 33. The incident parallel light is divided into a p-polarized component and an s-polarized component, and is emitted separately in different directions. The angle formed by the traveling direction of the p-polarized component and the s-polarized component at this time is defined as θ.

  The p-polarized component and the s-polarized component emitted from the polarizing prism 33 are converted into linearly polarized light in the 45 ° direction by the polarizing plate 34 disposed immediately after. As a result, the two light beams become coherent, so that interference fringes are formed. The fringe spacing of the interference fringes at this time is determined according to the angle given by the polarizing prism 33 and is expressed by equation (13).

被測定物Ｗ₄ に対してシアリング干渉縞を投影し、被測定物Ｗ₄ の形状に応じて変調された干渉縞を対物レンズ６で撮像素子７に対して結像させる。撮像素子７で撮像された変調縞は画像処理装置８へと取り込まれ、フーリエ変換位相解析により位相情報への変換が行われる。さらに位相のアンラッピング処理を行うことにより、被測定物Ｗ₄ の形状情報が算出される。

Projecting the shearing interference pattern with respect to the measured object W _4, is imaged to the imaging device 7 a modulated interference fringes by the objective lens 6 in accordance with the shape of the workpiece W _4. The modulation fringes imaged by the image sensor 7 are taken into the image processing device 8 and converted into phase information by Fourier transform phase analysis. Further, the shape information of the workpiece W ₄ is calculated by performing the phase unwrapping process.

  By adopting such a configuration, it is possible to stably perform highly accurate three-dimensional measurement even in a large change environment without being affected by thermal and mechanical fluctuations of the optical system. A shape measuring device can be realized. Further, since the spatial filter mechanism is not required as compared with the case where the light beam is divided by diffraction, it is possible to reduce the size of the projection optical system.

FIGS. 1A and 1B show a first embodiment, in which FIG. 1A is a schematic diagram for explaining an entire three-dimensional shape measuring apparatus, and FIG. 1B is a diagram for explaining a shearing interference system using a transmission diffraction grating. FIG. 9 shows a second embodiment, where (a) is a schematic diagram for explaining the entire three-dimensional shape measuring apparatus, (b) is a diagram for explaining a shearing interference system using a reflective diffraction grating, and (c) is an exit angle of diffracted light. FIG. FIG. 9 shows a third embodiment, in which (a) is a schematic diagram for explaining the entire three-dimensional shape measuring apparatus, and (b) is a schematic diagram for explaining a reflection direction by a transparent substrate with a wedge. FIGS. 4A and 4B show a fourth embodiment, in which FIG. 4A is a schematic diagram for explaining an entire three-dimensional shape measuring apparatus, and FIG. 4B is a diagram for explaining a shearing interference system using a polarizing prism. It is a schematic diagram explaining the three-dimensional shape measuring apparatus by the conventional interference fringe projection.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser light source 2 Collimating lens 3 Transmission type diffraction grating 4a, 4b, 14a, 14b Lens 5, 15 Spatial filter 6 Objective lens 7 Imaging element 8 Image processing apparatus 13 Reflection type diffraction grating 23 Transparent substrate with wedge 33 Polarizing prism 34 Polarizing plate

Claims (5)

  A laser light source, an optical element that converts laser light from the laser light source into parallel light, and parallel light emitted from the optical element are divided into two parallel light beams in the same traveling direction by a light sharing means, An interference fringe projection optical system for projecting an interference fringe generated at a portion where parallel light beams overlap on the object to be measured; and an imaging element for imaging a modulation fringe on the surface of the object to be measured on which the interference fringe is projected; A three-dimensional shape measuring apparatus, wherein the shape of the object to be measured is obtained by calculation based on phase information of the modulation fringes imaged by the image sensor.   A light sharing means, a transmissive diffraction grating, a Fourier transform element that forms a Fourier transform image of the transmissive diffraction grating, a spatial filter that transmits only the 0th order light and the 1st order light of the Fourier transform image, and the 0 The three-dimensional shape measuring apparatus according to claim 1, further comprising a secondary light and an inverse Fourier transform element that performs inverse Fourier transform on the primary light.   A light sharing means, a reflection type diffraction grating, a Fourier transform element that forms a Fourier transform image of the reflection type diffraction grating, a spatial filter that transmits only the 0th order light and the 1st order light of the Fourier transform image, and the 0 The three-dimensional shape measuring apparatus according to claim 1, further comprising a secondary light and an inverse Fourier transform element that performs inverse Fourier transform on the primary light.   The three-dimensional shape measuring apparatus according to claim 1, wherein the light beam sharing means has a transparent substrate with a wedge.   2. The three-dimensional shape measuring apparatus according to claim 1, wherein the light beam sharing means includes a polarizing prism and a polarizing plate disposed immediately after the polarizing prism.

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