Papers by Keyword: Shape Measurement

Abstract: The previous research confirms that the shape of measurement objects influences the measurement results, and the influences can be reduced by aligning the normal of the measurement object with the laser projection axis when using a laser displacement meter for 3D shape measurement [1]. but when the laser projection axis aligns with the normal of the measurement object, calculated based on the design value, the influence of the tilt of the measurement object is omitted if the measurement object has machining or mounting errors. This paper proposes a high-precision shape measurement method for on-machine measurement that considers machining errors and validated its effectiveness.

Abstract: A phase difference image using phase-shifting digital holography, which is applied for non-contact shape measurement, contains speckle noises and filtering to reduce them is inevitable for its application. We have developed a new filter which causes less deformation than commonly used filters.

Abstract: Phase difference image using phase-shifting digital holography is one of the prospective methods for non-contact shape measurement. For the application, filtering of the obtained image is needed to reduce the speckle noise. Conventional filter, e.g. moving average filter, causes loss of the shape information especially around the region with high steepness. To solve this problem novel filter has been developed that kept steepness of the shape in noise reduction. The filtered data were compared with conventionally filtering ones and the former was closer to the data observed by a laser measuring microscope.

Abstract: Optical interferometry methods are widely used for measuring microdisplacement with nanometer accuracy. However, most commercially available optical interferometry systems are large and expensive for manufacturing applications. In this study, we report the development of a low-cost portable optical interferometry microscope for factory use. The light source was a tungsten–halogen white lamp with an optical filter. The microscope has an objective lens with a numerical aperture of 0.3, a magnifying power of 10, and field depth of 3.056 μm. Interference images were collected with an NTSC CCD-video camera. The resolution of the interference image is 320 × 240 pixels and stored in BMP format. To obtain phase shifted interferometry images, a piezoelectric actuator was used to monitor the table movement along the optical axis. The total cost of all system parts is approximately 7000 to 8000 US dollars. To evaluate the basic performance of the developed interferometry microscope, we measured a steel ball, the penetration mark of a Rockwell scale hardness indenter, and a gauge block surface with a bump. The developed interferometry microscope can measure continuous and gently sloping surfaces. The processing time is approximately 10–20 s.

Abstract: A 3D shape measurement system based on a laser rangefinder and a two-dimensional MEMS mirror is presented in this paper. According to the requirement of surface profile measurement, the 3D shape measurement system is mainly composed of a laser module, a two-dimensional MEMS mirror, a ranging module, an orientation module and an image composition module. Based on the MEMS scanning technology and phase shift ranging method, the surface profile of the target can be acquired by the measurement system. For the coupled scanning mode, the scanning pattern is simulated in Lissajous figure and the condition of covering all the field of view is analyzed. The simulation results show that the 3D shape measurement system based on the laser rangefinder and the two-dimensional MEMS mirror can realize the measurement the surface profile of the target in all the field of view.

Abstract: Sampling Moire method is one of the convenient phase analysis methods. The accuracy of phase difference analysis is from 1/100 to 1/1000 of the grating pitches. This method is useful for a real-time measurement because the phase analysis can be performed from a single-shot image. In this paper, we developed a sampling moire camera which can analyze grating phase in real time. This camera is composed of a CMOS sensor and a FPGA. A two-dimensional grating image taken by the CMOS sensor was analyzed by the FPGA in real time. An application on a real-time deformation measurement of a cantilever is demonstrated.

Abstract: As technology development, projected digital fringe pattern is widely used in measuring three- dimensional (3D) shape, even in the presence of surface discontinuities. This paper investigates the reliability and accuracy of two multi-frequency phase unwrapping algorithms by experimental means. The first, which unwraps through a sequence of phase maps produced with exponentially change in spatial frequency with time, is found to be less robust and accuracy than the second, which only use three different frequency to beat new frequency for unwrapping the phase. Through experiment, the best frequency, adjacent ratio for the first method and frequency difference for the second method are proposed for the high efficiency and accuracy measurement.

Abstract: This paper aimed to use a novel optic interferometric fringe projection to measure the three-dimensional shape of small object with high resolution. In this method, the projecting fringe pattern, which has a sinusoidal density distribution, good contrast and equal spacing, is generated by a spherical wave incident into a triangle-section prism. Project the fringe onto the subject under test, the image of the deformed fringe pattern modulated by object surface is captured by a high-speed CMOS camera and processed by the Fourier Transform technique to extract the phase distribution which is related to height information. An experimental system is set to conduct 3-D shape measurement and the result shows the validity of the proposed method. The projecting system is simple and compact, which helps to realize the integration and miniaturization of the system.

Abstract: We previously proposed a real-time shape measurement method using two-component synthesis grating projection. In the method, phase unwrapping of the projected grating is performed by using aliasing of the Fourier spectrum of the grating images. It requires only 5 images obtained for one-cycle phase-shifting. Each phase in the two-component can be extracted from only 5 phase-shifted grating images. In this paper, we propose a real-time shape measurement system. The theory, the algorithm for the analysis and the experimental results are shown.

Abstract: The authors have been developing some novel methods to measure shape, deformation, stress and strain of structures using optical methods and image processing as follows: (1) Phase analysis methods using Fourier, wavelet or Gabor transforms, etc., (2) Real-time 2-D strain measurement using moiré interferometry, (3) Scanning moiré method using thinning-out of scanning lines and a DMD camera (4) Strain rate distribution measurement by a high-speed video camera, (5) Real-time integrated phase-shifting method, (6) Shape measurement methods using multi-reference planes, a linear image sensor, or a frequency modulated grating, and (7) Windowed phase-shifting digital holographic interferometry (WPSDHI). Theories of these methods and some applications are introduced. The most accurate result is 88 picometer standard deviation of errors using the WPSDHI.