Thickness is an important property of plates, and hence should be measured sometimes. It can be calculated from the point clouds measured by some three-dimensional measurement techniques. During the calculation, for any point from one set of point clouds, its matching point should be searched one by one from the other set of point clouds, which is a time-consuming process. To accelerate the thickness calculation, a new strategy characterized by space gridding and direction alignment is presented. It can dramatically reduce the searching scope, and hence improve the thickness calculation efficiency. Experiments showed that the presented method can improve the thickness calculation efficiency by tens of times.
Reasonable bearing preload can sufficiently ensure the good performance of bearing. Traditionally, rigid and constant preloads are used to apply uniform forces on the bearing. However, considering the machining errors, assembly errors and load conditions, the uniform preload actually manifests as a non-uniform load distribution in ball bearing. The work presents a method to analyze the bearing characters under the different preload conditions. Under non-uniform preload the bearing outer ring is rotated at a small angle with respect to inner ring. In this occasion, the stresses and deformations of rolling elements at different azimuth angles diverse from each other. As a result, the bearing stiffness is also different from that under uniform preload. In this paper, the bearing deformation and stiffness under different uniform and non-uniform preloads are analyzed using nonlinear finite element method. The results show that the relationship between axial stiffness and axial preload are nonlinear. The bearing angular stiffness increases nonlinearly with the equivalent moment under non-uniform preload.
An approach based on a novel technique, called ensemble empirical mode decomposition, is proposed to adaptively reduce noise and remove background intensity from a two-dimensional fringe pattern. It can solve the mode-mixing problem of the original empirical mode decomposition caused by the existence of intermittent noise in fringe signals. Then a strategy is developed to automatically identify and group the resulting intrinsic mode functions for the purpose of eliminating noise and background of the fringe pattern. This approach is applied to process the simulated and practical fringe patterns, compared with Fourier transform and wavelet methods.
A method combining the spatial and temporal fringe analysis techniques is proposed to extract the phase from shadow moiré interferogram with random phase shift. The proposed method first determines the grating translation difference based on the spiral phase transform technique. Then the initial phase shift is estimated. After that a generalized iterative least-squares method is developed to retrieve the accurate phase map using three interferogram frames. The proposed method relaxes the restriction on phase shift calibration between frames and provides stable and correct convergence in a fast way. Simulation and experiment demonstrate the effectiveness of this method. It shows our method possesses a superior performance than the existing typical phase-shifting algorithm. The proposed method is suitable for phase-shifting shadow moiré.
Thermal design is highly related to the performance of space cameras as temperature changes cause thermal displacements of the cameras' optical and mechanical systems, consequently affecting imaging quality. However, most existing thermal design methods for space cameras focus on several thermal design parameters without a comprehensive and quantitative analysis. Therefore, we proposed an optimization thermal design method for space cameras based on thermo-optical analysis and the Taguchi method. We first established the thermal balance equations of space cameras, and by analyzing the thermal design parameters in the equations, we identified the key parameters that affect the temperature field, thermal displacements, and imaging quality of the camera. Furthermore, we evaluated the influence of each thermal design parameter on imaging quality based on the integrated thermo-optical analysis. Thereafter, we applied the Taguchi method to quantitatively calculate the effect of each thermal design parameter on imaging quality. Finally, we implemented an optimal thermal control scheme for space cameras based on the results of the Taguchi method. The experimental results demonstrated that the proposed method is reliable and efficient and would be beneficial to researchers working on the thermal design of optical instruments.
The computation of the disparity for the pixels in the weak texture area has always been a difficult task in stereo vision. The non-local method based on a minimum spanning tree (MST) provides a solution to construct content-adaptive support regions to perform cost aggregation. However, it always introduces error disparity in slanted surfaces and is sensitive to noise and highly textural regions. The window-based methods are not effective for information dissemination. To overcome the problem mentioned above, this paper proposes an approximate geodesic distance tree filter, which utilizes geodesic distance as a pixels similarity metric and recursive techniques to perform the filtering process. The filtering process is performed recursively in four directions (namely from top-left, top-right, and vice versa), which make our filter with linear complexity. Our filter has advantages in the sense that: (1) the pixel similarity metric is approximated geodesic distance; (2) the computational complexity is linear to the image pixel. Due to these reasons, the proposed method can properly cope with cost aggregation in the textureless regions and preserve the boundary of disparity maps. We demonstrate the strength of our filter in several applications.
The aspherical measuring technology that based on computer-generated hologram (CGH) was introduced. The advantage of this method is that the phase shifts can be controlled digitally, no any mechanical moving and rotating element. By changing CGH coding which displayed on the Liquid Crystal Display (LCD), the wavefront and phase shifts in measuring system were induced. Based on the characteristics of aspherical measurement and LCD structure, the CGH encode technology used in LCD was discussed. Then a new encode method which applied to aspherical measurement was put forward. In this method, the LCD modulates functions of amplitude and phase was coexistent, and the character of LCD diffraction frequency spectrum was considered, and phase hologram was applied. This aspherical measuring technology is more flexible than usual method. In this paper, the hologram encode method based on LCD were illuminated in detail. In order to verify the correction of encode technology, the aspherical surface with standard wavefront was generated by coaxial hologram reconstruct system when hologram encode image was displayed on SONY LCX023 LCD, it interfere with the standard spherical wavefront, then the interferogram was sampled to computer by Charge Coupled Device (CCD) and A/D transfer, the wavefront of hologram reconstruct was obtained by image process finally. All calculation is completed by Matlab. An aspherical measuring system based on LCD was built experimentally. Both the theoretical analysis and experimental results demonstrate the feasibility of this approach.
Image filter is to remove the noise of images and try to protect the useful information as much as possible. Edge preserving & noise smoothing is to smooth the polluted image without influencing the detail spatial texture and its spatial structure much. We introduced SAS (separating the contribution of land surface and atmosphere) algorithm zhao proposed in remote sensing inversion area to image filtering area. The test result shows that the new algorithm reveals more powerful capability on protecting spatial texture protection than other algorithms.
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