Three-dimensional Shape Measurement Method Research Articles

346 マイクロ気液二相流における壁面に付着した液滴の三次元形状計測(T06-4 マイクロ・ナノ熱流体システム(4) 計測,大会テーマセッション,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

In order to develop an efficient micro heat exchanger and micro fuel cell, a number of studies of two phase flow such as liquid-gas in micro scale have been reported. In the micro scale, since surface tension became dominant, micro droplet or liquid film on a wall affects the dynamics of fluid. In the paper, in order to improve measurement accuracy of the three-dimensional shape measurement method for droplet based on a micro laser induced fluorescence technique, experimental conditions such as micro fabrication method, concentration of fluorescence dye, and intensity of excitation light were optimized. The technique was applied to a micro droplet on a wall resulting in achievement of high spatial and temporal resolution. The measurement accuracy of the present method was 0.57μm in comparison to a laser microscope. The result indicated that the present method is suitable for investigation of two phase flow in micro scale.

Flexible calibration procedure for fringe projection profilometry

A novel calibration method for whole field three-dimensional shape measurement by means of fringe projection is presented. Standard calibration techniques, polynomial-and model-based, have practical limitations such as the difficulty of measuring large fields of view, the need to use precise z stages, and bad calibration results due to inaccurate calibration points. The proposed calibration procedure is a mixture of the two main standard techniques, sharing their benefits and avoiding their main problems. In the proposed method, an absolute phase is projected over marked planes placed at unknown positions. The corresponding absolute phase and marks positions are recovered for each plane location. Using Zhang's calibration method, internal camera parameters (also called intrinsic parameters) and the spatial position for each plane are computed. Later on, a polynomial fit of depth with respect to the phase is performed. To obtain the absolute position of an object point, the depth coordinate is obtained by means of the polynomial calibration and its absolute phase. Then the lateral coordinates are computed from the depth, the internal parameters, and the pixel coordinates of the imaged point. Experimental results comparing the proposed method with the standard polynomial-based calibration are shown, demonstrating the feasibility of the proposed technique.

Micro-three dimensional shape measurement method based on shadow Moiré using scanning electron microscopy

A novel, precise, three-dimensional shape measurement method using scanning electron microscopy (SEM) and Moiré topography has been proposed. The possibility for measurement of wavelength order using this method is discussed based on results of experiments to confirm the principle. In these experiments, a high-resolution method based on the new measurement method is proposed, employing fringe scanning technology for the shadow Moiré. The optical system is constructed with a SEM using backscattering electrons, a grating holder that can shift the position of the grating, and a grating having a pitch of 120 µm. Measured results using a bearing ball as a sample show that high resolution measurements of around one micrometre can be performed using the fringe scanning method and the new measurement arrangement. An error analysis of the method is performed to enable improvement of the measuring accuracy.

D303 水中3次元形状計測法の開発

The purpose of this study is to develop the technology of measuring three-dimensional shapes precisely such as sunken ships and undersea harbor structure. The visible image acquired by the sound measurement and TV camera mounted on the ROV is used for measurement of the submarine topography and investigation of the sunken ship, etc.. However, the more detailed three-dimensional shape information compared to the ultrasonic image analysis is required concerning the inspection of the accident cause of the sunken ship. In this paper, the method for irradiating the object with dot matrix pattern of the green laser as a three-dimensional shape measurement method with small attenuation in water is proposed together with the technique which measures the three-dimensional shape of submerged object by scanning the single dot point at high speed on the object surface.

Trapezoidal phase-shifting method for three-dimensional shape measurement

We propose a novel structured light method, namely a trapezoidal phase-shifting method, for 3-D shape measurement. This method uses three patterns coded with phase-shifted, trapezoidal-shaped gray levels. The 3-D information of the object is extracted by direct calculation of an intensity ratio. Compared to traditional intensity-ratio-based methods, the vertical or depth resolution is six times better. Also, this new method is significantly less sensitive to the defocusing effect of the captured images, which makes large-depth 3-D shape measurement possible. If compared to sinusoidal phase-shifting methods, the resolution is similar, but the data processing speed is at least 4.5 times faster. The feasibility of this method is demonstrated in a previously developed real-time 3-D shape measurement system. The reconstructed 3-D results show similar quality to those obtained by the sinusoidal phase-shifting method. However, since the data processing speed is much faster (4.6 ms per frame), both image acquisition and 3-D reconstruction can be done in real time at a frame rate of 40 fps and a resolution of 532×500 points. This real-time capability allows us to measure dynamically changing objects, such as human faces. The potential applications of this new method include industrial inspection, reverse engineering, robotic vision, computer graphics, medical diagnosis, etc.

Dynamic 3-D shape measurement method based on FTP

In this paper, we propose a method for dynamic three-dimensional (3-D) shape measurement based on Fourier transform profilometry. A sequence of dynamic deformed fringe images can be grabbed by a CCD camera and saved on a disk rapidly. By a Fourier transform, filtering and inverse Fourier transform, a sequence of phase-maps can be obtained. By unwrapping these phase maps in 3-D phase space, we can obtain the shape of the dynamic object at different times. In this paper we also propose the algorithm of a phase difference between two deformed fringes, and the 3-D phase unwrapping method based on the phase difference algorithm. The computer simulation and experiment results show that this method can efficiently deal with the dynamic 3-D shape measurement.

Shape measurement of small objects using LCD fringe projection with phase shifting

This paper describes the use of optical fringe projection method for three-dimensional shape measurement of small objects. In this method, sinusoidal linear fringes are projected on the object surface by a programmable liquid crystal display (LCD) projector and a long working distance microscope (LDM). The image of the fringe pattern is captured by another LDM and a CCD camera and processed by phase-shifting technique. A simple procedure is described which enables calibration of the optical setup for subsequent quantitative measurement of unknown object shapes. The method developed can also be applied to the measurement of the warp of a small component under thermal loading. This method is relatively simple and accurate, and is capable of conducting fully automated measurements.

Improvement of measurement accuracy in shadow moiré by considering the influence of harmonics in the moiré profile

A method for high-resolution three-dimensional shape measurement for a shadow moiré system is proposed. To increase the resolving power of the method, the problem caused by the harmonics of the moiré profile needs to be solved. It is well known that moiré fringes in a shadow moiré system have a nonsinusoidal profile caused by harmonics. The influence of the harmonics in moiré profile on the measurement accuracy of the method is discussed. The method is improved to eliminate the error caused by the harmonics in the moiré profile. Both simulation and experimental results show that the improved method can effectively reduce the influence of harmonics.

A slit laser scanning moire method and a simple method for distinguishing between depression and elevation

Three-dimensional shape measurement is a very important subject for the shape recognition of three-dimensional objects. Moire topography is a very useful method for three-dimensional shape measurement because the moire image is formed as a contour line image and it includes three-dimensional shape information. However, in practical use, moire topography has several problems, such as the formation of high-contrast and uniform moire images in an illuminated room, a method for distinguishing between depression and elevation, and a simple method for extracting three-dimensional shape data by image processing. This paper presents a new moire formation method using slit laser scanning and the image accumulation properties of a TV camera, a simple method for distinguishing between depression and elevation, and an automatic image processing measurement system. This new moire method enables the formation of a moire image in an illuminated room, which is a realistic industrial environment. The proposed method for distinguishing between depression and elevation is based on a binary image distinguished by whether the gradient of the measuring surface is positive or negative. This binary image is formed by processing the video signal from a deformed grating image at the same time as the moire image is formed.