Surface Shape Measurement Research Articles

Texture Evaluation for Planed Surface of Polyoxymethylene Resin by Measuring Surface Shape and Color with Light and Strain Sensitive Tactile Sensor

Texture Evaluation for Planed Surface of Polyoxymethylene Resin by Measuring Surface Shape and Color with Light and Strain Sensitive Tactile Sensor

High-dynamic-range 3D shape measurement utilizing the transitioning state of digital micromirror device

This paper introduces a novel method for 3D shape measurement of high-contrast surfaces in real-time by taking advantage of the transitioning state of digital micromirror device. We propose to project defocused 1-bit binary patterns for sinusoidal generation to bypass the rigid camera-projector synchronization requirement. Each pattern is capture twice in one projection cycle to obtain two fringe images with different brightness: the first fringe is captured when the camera is totally exposed within the projector’s bright period; the second fringe is captured when part of the projector’s dark period is within the camera exposure. The two fringes will be combined to alleviate the saturation problem. Experiments demonstrate the success of the proposed method by showing the real-time 3D shape measurement capability (image acquisition rate: 166 Hz; 3D frame rate: 14 Hz). Moreover, since 1-bit binary patterns are used, it is potentially applicable to high-speed measurements.

Study on melting and solidification behaviors of tungsten loaded by high heat flux for divertor in tokamak fusion reactor

Tungsten is a candidate as a surface material of divertor in Tokamak fusion reactor. A pulsed high heat flux emitted in plasma disruption and Type I Edge Localized Mode (ELM) is considered to melt the tungsten surface repeatedly. The repetitive phase change can transmute surface characteristics of divertor and then reduce the thermal resistance. For the safety design and the development acceleration of fusion demonstration reactor, investigation and understanding of surface melting and solidification procedure are important. In previous studies, experiments have been conducted by Ueda et al. and the surface after the laser irradiation had the geometry as a crater with a center cone. However, the formation mechanism of the crater was not fully understood. In this paper, two measurement methods are studied. One is an in-situ observation method of tungsten and molybdenum surface during the laser irradiation using high speed video camera, and another is a 3-dimensional measurement of tungsten surface shape after the laser irradiation experiments using a stereoscopic photography technique. In the former, it was confirmed that a molten pool had wavy surface pattern until solidification, and the applicability of the stereoscopic photography technique for the in-situ observation during the laser irradiation was indicated in the latter.

Dynamic microscopic 3D shape measurement based on marker-embedded Fourier transform profilometry.

In recent years, the fringe projection profilometry (FPP) technique has shown great prospects in the field of dynamic 3D measurement of microscopic surface shape. However, under dynamic conditions, it is desirable to use fewer projected patterns to minimize the sensitivity to motion. The commonly used phase-shifting method needs at least three fringe patterns to retrieve the wrapped phase, which depends heavily on the high-speed hardware to alleviate the effect of motion. Besides, to achieve an unambiguous measurement, at least two wrapped phase maps are required to obtain the absolute phase map, resulting in six pattern projections. In this paper, we propose the marker-embedded Fourier transform profilometry (MEFTP), which extends the modified Fourier transform profilometry with two embedded markers suited to assist the phase-unwrapping process. Combining the embedded markers with temporal phase difference information, the absolute phase can be reliably reconstructed with only two projected patterns. Furthermore, since the phase information is only encoded within a single high-frequency fringe, MEFTP is more suitable for measuring fast-moving or surface-changing objects compared with the phase-shifting method. Experiments on both static and dynamic scenes are performed, verifying that our method can achieve an accurate and robust measurement of a vibrating diaphragm at the speed of 200 frames per second.

An experimental platform for real-time measurement of the deformation of nuclear fuel rod claddings submitted to thermal transients.

We report on experimental development and qualification of a system developed to detect and quantify the deformations of the cladding surface of nuclear fuel pellet assemblies submitted to heat transient conditions. The system consists of an optical instrument, based on 2 wavelengths speckle interferometry, associated with an induction furnace and a model pellet assembly used to simulate the radial thermal gradient experienced by fuel pellets in pressurized water reactors. We describe the concept, implementation, and first results obtained with this system. We particularly demonstrate that the optical system is able to provide real time measurements of the cladding surface shape during the heat transients from ambient to high temperatures (up to a cladding surface temperature of 600 °C) with micrometric resolution.

基于条纹反射的超精密车削反射镜的在位面形检测

基于条纹反射的超精密车削反射镜的在位面形检测

Warp Measurement for Large-Diameter Silicon Wafer Using Four-Point-Support Inverting Method

Recently, the production of silicon wafers 450 mm in diameter has begun. However, a precise method for warp measurement of 450 mm wafers has not yet been established. Hence, the authors have developed a four-point-support inverting method to measure the warp shapes of large diameter wafers with high accuracy. The principle of this measurement method is equivalent to that for the three-point-support inverting method developed for warp measurement of 300 mm wafers. In the four-point-support inverting method, surface shape measurement can be performed with decreased deflection due to gravity using an additional central support. In this study, the principle of the proposed measurement method was verified experimentally. It was found that the four-point-support inverting method could measure the warp of a 300 mm wafer with high accuracy, equivalent to that of the three-point-support inverting method. However, in this experiment, a steel ball was used for additional support which caused concern regarding damage to the wafer surface at the point of contact with the support. Hence, a noncontact support method using an air bearing was proposed. It was found that the noncontact support method could measure the warp with accuracy equivalent to the contact support method described previously. Moreover, this study demonstrates the superiority of the four-point-support method to the three-point-support method regarding the repeatability of the warp measurement.

High-frequency background modulation fringe patterns based on a fringe-wavelength geometry-constraint model for 3D surface-shape measurement.

A new fringe projection method for surface-shape measurement was developed using four high-frequency phase-shifted background modulation fringe patterns. The pattern frequency is determined using a new fringe-wavelength geometry-constraint model that allows only two corresponding-point candidates in the measurement volume. The correct corresponding point is selected with high reliability using a binary pattern computed from intensity background encoded in the fringe patterns. Equations of geometry-constraint parameters permit parameter calculation prior to measurement, thus reducing measurement computational cost. Experiments demonstrated the ability of the method to perform 3D shape measurement for a surface with geometric discontinuity, and for spatially isolated objects.

Surface shape measurement by multi-illumination lensless Fourier transform digital holographic interferometry

This paper presents a multi-illumination lensless Fourier transform digital holographic interferometry method for surface shape measurement. In this method, the interference phases with different effective synthetic wavelengths are obtained by tilting the illumination angle several times, and all are wrapped. A Fourier-transform demodulation algorithm employing all these wrapped phases simultaneously is used to determine the object surface shape. No phase unwrapping procedure is required, and the shape information of each point is calculated independently, thereby offering great flexibility for measuring objects with discontinuities surface, such as holes, steps and gaps. Experimental results demonstrate the validity of the principle.

3D surface profilometry based on 2D S-Transform method with optimized window

S-Transform method can be regarded as an extension to the ideas of the Windowed Fourier Transform (WFT) method and the Wavelet Transform (WT) method, which gives consideration to both local frequency concept of WFT and the multi-resolution strategy of WT. It has been introduced in optical 3D shape measurement recently. However, the S-Transform method suffers from poor energy concentration when some kind of signal is treated with. In order to enhance energy concentration to provide more accurate estimation of the instantaneous frequency, a modification to the existing 2D S-Transform is proposed in this paper. Two additional parameters are introduced to respectively optimize the window width in x and y direction. The paper gives the expression of 2D S-Transform with optimized window and its performance in 3D surface reconstruction. The application of proposed method is demonstrated on both simulation and experiment by comparing with traditional 2D S-Transform method. The improved performance of optimized 2D S-Transform for 3D surface shape measurement shows its feasibility and veracity.

Background and amplitude encoded fringe patterns for 3D surface-shape measurement

This paper presents a new fringe projection method for surface-shape measurement that uses background and amplitude encoded high-frequency fringe patterns. The background and amplitude, combined as a codeword, identify the wrapped phase fringe order to partially unwrap the phase to a low frequency. The low-frequency wrapped phase map is then directly used to reconstruct the surface based on geometry constraints without requiring additional images as in other temporal phase-unwrapping methods. Measurements performed on a double-hemisphere, mask, and manikin head, using projected fringe patterns with 48 periods, demonstrated the ability of the method to perform 3D shape measurement with only four projected patterns and captured images, using a single camera and projector.

A REVIEW ON - SOLAR CONCENTRATORS, PERFORMANCE OF SOLAR COLLECTORS & ENERGY STORAGE

Parabolic trough concentrators are one type of concentrators which reflects the sunlight on the receiver (Line type) and gives us wet steam for water. It can be tried with any type of fluid. Presently solar collectors are used for residential and commercial use. These solar collectors require high maintenance and high installation cost, solar concentrators help us in these disadvantages. This review paper concentrates on solar concentrators and various fluids that can be used in receiver. It also focuses on surface shape measurement of solar concentrator in solar thermal power application. In order to capture maximum amount of solar energy it is required to orient the concentrator as per the position of the sun i.e. tracking is required .However some of the concentrators do not track and are referred as fixed concentrators. The objective of the project is to track the receiver instead of solar concentrator.

Surface shape measurement of mirrors in the form of rotation figures by using point diffraction interferometer

The paper deals with the use of a point diffraction interferometer (PDI) to study the surface shape of rotation figures. The relations are given for the correspondence of the coordinates on the surfaces of an ellipsoid, a paraboloid and a hyperboloid as well as on an interferogram. Using PDI and Zygo white-light interferometer (WLI), we experimentally investigated the surface shape of the grazing incidence ellipsoid with the multilayer reflective coating on a wavelength of 0.154 nm with the following parameters: length is 55 mm, half-axis are 6 and 235 mm. The results coincided with an accuracy of 73 nm (RMS) without taking into account the PDI lateral resolution, and with an accuracy of 50 nm (RMS) with taking it into account, which ensures the local angles measurement accuracy of the ellipsoid-shaped reflecting surface at a level of 3 μrad. We think that this difference may be attributed to the limited lateral resolution of PDI and errors of frames stitching of WLI; nevertheless, we do believe that the PDI measurement accuracy is in the range of sub-μrad.

Deflectometric method for optical surface reconstruction

Detailed theoretical analysis of the shape measurement of optical surfaces based on light reflection on the measured surface is provided. Relations are given for computing the parameters of the reflected beam on the measured surface and its record on the light detector. Deflectometric equation is derived for oblique incident beam on the measured surface and the method of its solution is given.

A dual-frequency fringe projection three-dimensional shape measurement system using a DLP 3D projector

A dual-frequency fringe projection system for three-dimensional (3D) surface shape measurement is proposed in this paper. The system includes two cameras, a DLP 3D projector, and a liquid crystal (LC) shutter glasses. The phase information related to the object height is obtained from the dual-frequency temporal method with 3-step phase-shifting algorithm. By using the DLP 3D projector and LC shutter glasses, 3-step phase-shifting high-frequency and low-frequency fringe patterns are captured only 3 times by the two cameras synchronously. The technique of image registration is applied to low-frequency fringe patterns to guarantee the accuracy of low-frequency phase for high-frequency phase unwrapping. Using the equi-phase coordinate method based on two reference planes, the phase-to-height conversion and non-sinusoidal errors reduction are carried out in one go without any extra operation or measurement time. Experimental results demonstrate that the proposed method effectively improves the measuring speed, and it is valid for measuring surface shapes with multi-steps or discontinuities.

Interferometric measurement of surface shape by wavelength tuning suppressing random intensity error.

In this research, the susceptibility of the phase-shifting algorithms to the random intensity error is formulated and estimated. The susceptibility of the random intensity error of conventional windowed phase-shifting algorithms is discussed, and the 7N-6 phase-shifting algorithm is developed to minimize the random intensity error using the characteristic polynomial theory. Finally, the surface shape of the transparent wedge plate is measured using a wavelength-tuning Fizeau interferometer and the 7N-6 algorithm. The experimental results indicate that the surface shape measurement accuracy for the transparent plate is 2.5 nm.

Error-compensating phase-shifting algorithm for surface shape measurement of transparent plate using wavelength-tuning Fizeau interferometer

When measuring the surface shape of a transparent sample using wavelength-tuning Fizeau interferometry, the calculated phase is critically determined by not only phase-shift errors, but also by coupling errors between higher harmonics and phase-shift errors. This paper presents the derivation of a 13-sample phase-shifting algorithm that can compensate for miscalibration and first-order nonlinearity of phase shift, coupling errors, and bias modulation of the intensity, and has strong suppression of the second reflective harmonic effect. The characteristics of the 13-sample algorithm are estimated with respect to Fourier representation in the frequency domain. The phase error of measurement performed using the 13-sample algorithm is discussed and compared with those of measurements obtained using other conventional phase-shifting algorithms. Finally, the surface shape of a fused silica wedge plate obtained using a wavelength tuning Fizeau interferometer and the 13-sample algorithm are presented. The experimental results indicate that the surface shape measurement accuracy for a transparent fused silica plate is 3nm. The accuracy of the measurement is discussed by comparing the amplitudes of the crosstalk noise calculated using other conventional algorithms.

An orthogonal phase-shifting interferometry and its application to the measurement of optical plate

An optical interferometry named orthogonal phase-shifting interferometry (OPSI) was proposed. Compared with other interferometers, OPSI works well at air turbulence and complex environment. Phase recovery method was calculated by Jones matrix for measurement of optical elements surface shape and roughness. In order to control piezo-electric transducer (PZT) shifter, the property between voltage and phase of PZT shifter was calculated. Based on this interferometry, the roughness of an unknown transparent optical plate was measured. The results show that the error of peak to valley (PV) value is 0.0087λ (λ=1064nm) and the error of root mean square (RMS) value is 0.0006λ compared with WYKO(a commercial interferometer of Veeco),and this demonstrates the high stability and precision of the orthogonal phase-shifting interferometry.

Geometric phase shifting digital holography.

A new phase shifting digital holographic technique using a purely geometric phase in Michelson interferometric geometry is proposed. The geometric phase in the system does not depend upon either optical path length or wavelength, unlike dynamic phase. The amount of geometric phase generated is controllable through a rotating wave plate. The new approach has unique features and major advantages in holographic measurement of transparent and reflecting three-dimensional (3D) objects. Experimental results on surface shape measurement and imaging of 3D objects are presented using the proposed method.

Characterization and optimization of illumination vector for contouring surface form and feature using DSPI.

Surface defect or damage is one of the critical factors leading to the failure of engineering materials and structures. The methodologies for the measurement of surface shape and feature or defect have been extensively explored and developed over the past few decades, including both contact and non-contact methods. Speckle pattern interferometry, as a non-contact optical method, has been demonstrated to effectively contour the surface shape through adjusting the illumination vector. However, few studies have been made to investigate the effect of the initial position of the illumination source as well as the source translation direction. In this paper, we report to carry out a study of measuring the surface form and feature using digital speckle pattern interferometry system via a slight translation of illumination source. Through theoretically analyzing the sensitivity factor along with the experimental validation, it is shown that the contouring fringe is more sensitive to the surface height with an off-axis illumination than the paraxial illumination. It is also found that translating the source along axial and lateral direction can be both used for the surface shape re-construction.