Three-dimensional Profile Measurement Research Articles

Absolute Measurement of Aspheric Surfaces Using White-Light Interferometry

White-light interferometric technique has been widely applied in the measurement of three-dimensional profiles and roughness with high-precision. Based on the characteristic of interferometric technique, a new method combined with image location and a three-dimensional stage is proposed to achieve the non-contact absolute shape measurement for aspheric and spherical surface in a slarge range. The interference fringes vary with the horizontal displacement of the measured surface, the surface information was obtained by locating the transformation of the maximal intensity in the interferograms. Two main influence factors are discussed; they are performance of the inerferimetric microscope and the stage. Since the performance of the stage directly determines the measurement precision, a three-dimensional displacement stage with a large range and a high precision was developed. Some experiments were carried out to verify the performance of the three-dimensional displacement stage and the validity of the new measurement method with satisfactory results.

Random depth access full-field low-coherence interferometry applied to a small punch test

In small punch testing, with approximate preknowledge of the sample deformation, profile measurement need only be made at selected locations in depth. To date, profilometry through full-field low-coherence interferometry has not been applied to small punch testing—conventional methods typically measure the maximum displacement as the sample is deformed, ignoring useful shape and profile information. A modification of full-field low-coherence interferometry is presented, where a digital stepper motor is combined with piezoelectric transducer scanning to achieve random depth access three-dimensional micrometer profile measurement. Offering a rapid, inexpensive, and functional machine vision system, the measurement technique is applied to a small punch test.

A Laser Sensor Technique for Measuring 3D Surfaces Based on the Polarized Heterodyne Astigmatic Principle

A laser measurement technique based on polarized heterodyne astigmatic principle is proposed for high precision three-dimensional (3D) profile measurement. In the presented system, the defocus astigmatic signal coming from the polarized reflection of the detected 3D surface is used to determine the position of the surface. The work of tracing, scanning and processing of the detected 3D surface is performed by combining the system with an ultra precision laser coordinate measuring machine (CMM). Compared with the current heterodyne astigmatic measuring technique, a polarization incidence and Glan-Thompson prism (GP) is used in the novel polarized heterodyne astigmatic measuring method. The anti-interference ability of the optical sensing system is significantly improved. The undesired influence on the measurement results, caused by fluctuation of surrounding brightness, by the intensity disturbance of the laser source, and by the multi-reflection among optical elements, is effectively restrained. Experimental results show that the stability of the optical sensing system is better than 2%. The resolution of the system is better than 0.005µm.

A New Three-Dimensional Profilometer for Surface Profile Measurement Using Digital Fringe Projection and Phase Shifting

The development of a three-dimensional surface profilometer using digital fringe projection technology and phase-shifting principle is presented. Accurate and high-speed three-dimensional profile measurement plays a key role in determining the success of process automation and productivity. By integrating a digital micromirror device (DMD) with the developed system, exclusive advantages in projecting flexible and accurate structured-light patterns onto the object surface to be measured can be obtained. Furthermore, the developed system consists of a specially designed micro-projecting optical unit for generating flexibly optimal structured-light to accommodate requirements in terms of measurement range and resolution. Its wide angle image detection design also improves measurement resolution for detecting deformed fringe patterns. This resolves the problem in capturing effective deformed fringe patterns for phase shifting, especially when a coaxial optical layout of a stereomicroscope is employed. Experimental results verified that the maximum error was within a reasonable range of the measured depth. The developed system and the method can provide a useful and effective tool for 3D full field surface measurement ranging from µm up to cm scale.

Instantaneous Measurement of 3D Profiles by Projecting Coded Grating

A three-dimensional profile measurement system based on a projection coded grating technique is presented. The system uses a designing and decoding technique for grey coded gratings. The coded grating has black, white and grey stripes. The period triples a conventional grating. It greatly increases the height measuring range without any decrease in stripe separation. The shape of object can be obtained from only one grating image. The system is suitable for instantaneous measurement of moving objects including human face. The technique proposed permits rapid 3D measurement and no moving parts are involved in the system. The hardware is relatively simple. Special data processing software is developed. Results of a practical example confirm the effectiveness of the proposed method.

광산란 거친표면의 고정밀 삼차원 형상 측정을 위한 점회절 간섭계

최근 전자산업계에 새롭게 널리 생산되는 마이크로 전자부품들은 왜곡이 최소화된 정밀한 외관 형상을 갖도록 제조되고 관리되지만, 측정 대상의 표면이 가시광 영역에서 광산란되는 특징을 가짐으로 인해, 기존의 피죠나 마이켈슨 형태의 비교간섭법으로는 고정밀의 삼차원 형상측정이 용이하지 아니하였다. 본 논문에서는 광섬유를 이용한 새로운 개념의 점회절 간섭계를 제안하고, 이를 광산란 거친표면의 대표적인 제품인 칩패키지와 실리콘 웨이퍼의 삼차원 형상 측정에 적용하였다. 측정결과 66 mm 측정영역에서 측정 형상오차 PV(peak-to-valley value) 5.6 <TEX>$\mu\textrm{m}$</TEX>, 분산값(<TEX>$\sigma$</TEX>) 1.5 <TEX>$\mu\textrm{m}$</TEX>를 획득함으로써 기존의 비교 간섭 측정법에 비해 더욱 향상된 측정 정밀도를 획득하였다. We present a new point-diffraction interferometer, which has been devised for the three-dimensional profile measurement of light scattering rough surfaces. The interferometer system has multiple sources of two-point-diffraction and a CCD camera composed of an array of two-dimensional photodetectors. Each diffraction source is an independent two-point-diffraction interferometer made of a pair of single-mode optical fibers, which are housed in a ceramic ferrule to emit two spherical wave fronts by means of diffraction at their free ends. The two spherical wave fronts then interfere with each other and subsequently generate a unique fringe pattern on the test surface. A He-Ne source provides coherent light to the two fibers through a 2<TEX>${\times}$</TEX>l optical coupler, and one of the fibers is elongated by use of a piezoelectric tube to produce phase shifting. The xyz coordinates of the target surface are determined by fitting the measured phase data into a global model of multilateration. Measurement has been performed for the warpage inspection of chip scale packages (CSPs) that are tape-mounted on ball grid arrays (BGAs) and backside profile of a silicon wafer in the middle of integrated-circuit fabrication process. When a diagonal profile is measured across the wafer, the maximum discrepancy turns out to be 5.6 <TEX>${\mu}{\textrm}{m}$</TEX> with a standard deviation of 1.5 <TEX>${\mu}{\textrm}{m}$</TEX>.

Measurement of three-dimensional profiles with multi structure linear lighting

In reverse engineering, it is very challenging to acquire the 3D profile information of an object rapidly with high accuracy. This becomes even harder to measure the profile of a large object, such as an automobile body press part as it has a wide scope and is not easy to realize. A new non-contact measuring method using multi structure linear lighting (or multi light-knife) based on laser scanning measurement technology is presented in this paper. The principle of the multi light-knife is first presented. To improve the accuracy of the measuring device developed in this work, a virtual net mapping and the least square theory is applied to calibrate the measuring device of the multi light-knife in the whole measuring field. When the device is used to measure automobile body press parts, a route planning method is used to ease the contradiction between measuring accuracy and the range of measurement. System calibration is achieved by compensating the platform error. Experiments on a rear view mirror case show that the multi light-knife is a very effective device and can become a very promising way to acquire the 3D profile information of large objects.

Absolute interferometer for three-dimensional profile measurement of rough surfaces.

We present a new interferometer system devised for surface-profile metrology with multiple two-point-diffraction sources that are made from a pair of single-mode optical fibers. The diffraction interferometer system performs an absolute profile measurement by projecting multiple fringe patterns on the object surface and then fitting the measured phase data into a global model of multilateration. Test measurement results demonstrate that the proposed profiling method is suited for rough surfaces with excessive surface irregularities, which are difficult to measure with conventional two-arm interferometers.

Spectral interference Mirau microscope with an acousto-optic tunable filter for three-dimensional surface profilometry.

A nonmechanical scanning Mirau-type spectral interference microscope has been developed for the measurement of three-dimensional surface profiles of discontinuous objects. An acousto-optic tunable filter (AOTF) is used as a high-resolution spectral filter, which scans the optical frequency of the broadband light emitted from a superluminescent diode. To generate spectral fringes that make full use of the limited coherence length of the filtered light we unbalanced the Mirau interferometric system by positioning the reference mirror nearly halfway between the top and the bottom of the step height. When the frequency of the broadband light source is scanned by an AOTF, the interference fringes move in opposite directions on the top and the bottom of the object. To uniquely determine the sign of the fringe movement over the large area of the object, we developed a three-dimensional Fourier-transform technique, and from the detected sign of the fringe movement and phase information, we determined the three-dimensional step height. Experimental results of the measurement of 100-microm step height are presented. The main advantages of the proposed system are that it provides nonmechanical scanning and a large measurement range without ambiguity in the sign of the phase.

Three-dimensional surface profile measurement of a moving object by a spatial-offset phase stepping method

This study proposes a new method for measuring the 3-D surface profile of an object moving at constant speed. A sinusoidal grating pattern is projected on a moving object. Then, grating patterns that are deformed according to the profile of the object are acquired by three linear array sensors. Since a linear array sensor records light intensity along an original grating line, the resultant image forms a fringe pattern that represents the profile of the object. Using three images obtained by the three linear array sensors, the phase distribution of the fringe pattern is calculated by a phase stepping method without any phase stepping devices. Consequently, the profile of the moving object can be evaluated from the phase of the fringes, since the value of the phase is simply proportional to the height of the object. Experimentation demonstrates that the accuracy is about 4.3% for the wrapped phase range of 2π rad with a speckle pattern present. The proposed method can be used for inspection of moving objects such as products on an assembly line.

Development of Laser Range-Imaging Vehicle Sensor.

Laser range finder technology-based three-dimensional vehicle profile and size measurements are useful for vehicle detection and classification in electronic toll collection (ETC). First this paper briefly makes a comparative study of conventional vehicle detectors employing range measurement technologies to summarize the requirements for vehicle classification in ETC. Secondly two overseas laser range vehicle profilers are presented as typical examples of the ETC application. Newly developed laser range finder to classify vehicles for domestic ETC is also introduced. The developed sensor successfully acquired the shapes of vehicles in detail and measure the both of height and width of them with sufficient accuracies for toll collection at actual tollgate.

Fast algorithms for data reduction in modern optical three-dimensional profile measurement systems with MMX technology

Confocal microscopy and white-light interferometry are two promising methods for the three-dimensional microstructure analysis of technical and biologic specimens. For both methods the specimen is scanned through the focus position by means of an actuator. A large series of intensity frames is acquired. These data are used for the final calculation of the topography. We demonstrate that the multimedia extended (MMX) instruction set, which is implemented in modern Intel microprocessors, can be used for effective real-time preprocessing and for fast evaluation algorithms. So this new technique enables the implementation of more-complex algorithms with acceptable run times even on standard computer technology. The possibilities of the MMX instruction set are discussed for confocal microscopy and for white-light interferometry.

Two-Wavelength Phase-Shifting Projection $Moir\acute{e}$ Topography for Measurement of Three-Dimensional Profiles with High Step Discontinuities

[] technique is now being extensively investigated as a fast non-contact means of three-dimensional profile measurement especially for reverse engineering. One problem with technique is so called -ambiguity problem that limits the maximum step height difference between two neighboring sampling points to be less than half the equivalent wavelength of fringes. In this investigation, a new two-wavelength scheme of projection topography is proposed and tested to cope with the -ambiguity problem. Experimental results are discussed to assess the new method in measuring large objects with high step discontinuities.

格子パターン投影法を用いた反射物体の表面形状計測 （第２報） 楕円面鏡の計測

This paper describes a grating projection method for three-dimensional profile measurement of specular objects and the method is utilized to measure a concave-shaped mirror that is difficult to measure using conventional non-contact methods in short time. A "deformed grating pattern" is observed when the reference grating is projected onto a mirror-like surface. This pattern formed by the surface reflection is captured by a CCD camera and analyzed on the basis of phase shifting technique to give three-dimensional profile of the specimen. Experimental results are shown with respect to an ellipsoidal mirror to verify the principle proposed here.

Development of optical noncontact sensor for measurement of three-dimensional profiles using depolarized components of scattered light

Development of optical noncontact sensor for measurement of three-dimensional profiles using depolarized components of scattered light

Absolute interferometric distance measurement using a FM-demodulation technique

We propose an interferometric method for measuring absolute distances larger than the wavelength. A laser diode is used as a light source. The principle of operation is based on multiple-wavelength interferometry that uses a modulated light source. This method uses the fact that the wavelength of light emitted by the laser diode can be varied by means of the injection current. The modulation of the injection current in combination with the optical heterodyne technique causes a high-frequency phase-modulated detector signal. The phase deviation of the signal is a measure of the optical path difference in the interferometer. By FM demodulation of the detector output with a phase-locked loop demodulator, the optical path difference can be determined directly without the classical ambiguity problem of interferometry. The measuring range in the experiments was limited to 50 mm by the maximum travel range of the used specimen translation stage. Because of the inherent light sensitivity of the method described, the rangefinder can be used for three-dimensional profile measurements on a wide variety of objects, even on diffuse scattering surfaces.

An experimental investigation of the end-hat effects in a crossed-field amplifier via three-dimensional electron density measurements

In situ three-dimensional electron density profile measurements have been made for the first time to study the end-hat space-charge region in a crossed-field amplifier. It has been found that a separated electron population exists in that region and is detached from the main beam when the end-hats are biased positively with respect to the sole. An investigation into the vacuum electric field profile and the overall device performance versus end-hat bias has suggested that such an electron population may be caused by a redistribution of the beam electrons by the axial and radial end-hat electric field. >

Interferometric profiler for rough surfaces

Conventional interferometric methods of surface profiling are limited in the magnitude of surface height that can be accurately measured because of phase ambiguity errors on steep local slopes. Other optical methods that have been developed for surface profiling frequency suffer from poor height resolution and low measurement speed for three-dimensional profiles. Contact profilometers such as stylus-based instruments suffer from slow measurement speed, especially when three-dimensional profiles of the surface are required. Stylus tips can also scratch delicate surfaces duringthe course ofthe measurement. A new method of optical, noncontact profiling of rough surfaces is described that utilizes interferometric techniques as well as digital signal-processing algorithms to produce fast, accurate, and repeatable three-dimensional surface profile measurements.

Moire topography for three-dimensional profile measurement using the interference fringes of a laser

Resolution-variable moiré topography for measuring the three-dimensional profile of an object is described. With this method, moiré fringes are formed by projecting two sets of interference fringes of laser beams on an object. The interference fringes are formed using a Mach-Zehnder interferometer and are divided into two sets by a beamsplitter. The image, including the moiré fringes, which are formed in accordance with the object depth, is detected by an image sensor. The effectiveness of this method is demonstrated by practically measuring the profiles of a small object. The intervals between adjacent moiré fringes could be experimentally changed from 0.16 to 1.6 mm. The advantage ofthis method is that the interval between moiré fringes can be easily changed continuously by a mechanical operation.

Features and Applications of the Laser Scanning Microscope

Abstract Features and applications of the laser scanning microscope are described, focusing on confocal imaging, the image contrast enhancement effect and three-dimensional surface profile measurement. A longitudinal resolution of 0·01 μm is obtained using a surface profilometer with a position-sensitive detector.