3D profile measurement is widely used in many areas such as manufacturing, computer-aided design, virtual reality and medical diagnostics. As one of the core technologies in 3D profile measurement, digital fringe pattern projection is a highly sensitive noncontact technique for obtaining the 3D shape of an object. Then the grating pattern deformed by the measured object is captured by CCD cameras and decoded using appropriate algorithms so that the shape of the object can be deduced. In this paper, three sets of phase shift fringe patterns with different frequencies are projected on the surface of the measured object by a DLP projector and the deformed patterns are captured by two cameras. Then the four-step phase shift method is used to obtain the three groups of fringe patterns phases, and the three-frequency heterodyne method is adopted to unwrap the phase and obtain the absolute phase. The causes of the phase errors are analyzed and the subsequent compensation method of gamma correction of grating pattern is proposed to eliminate the main errors. Experiments are carried out and the results verify the accuracy and effectiveness of the proposed methods.
An automatic large-scale 3D coordinate measurement system based on vision guidance is presented. With a high-accuracy total station accomplishing the basic coordinate measurement, a camera mounted on the total station is used to scan the measuring field. The camera can identify the target in the viewing field and provide its azimuth information for the total station to aim at it automatically. Thus high-accuracy non-contact measurement can be accomplished without additional effort for targeting. The results showed that the measurement system can realize automatic large-scale measurement precisely and efficiently which provides an efficient approach for solving automatic large-scale measurement problems.
A complete theory is established for opto-mechanical systems design of the window in this paper, which can make the design more rigorous .There are three steps about the design. First, the universal model of aerodynamic environment is established based on the theory of Computational Fluid Dynamics, and the pneumatic pressure distribution and temperature data of optical window surface is obtained when aircraft flies in 5-30km altitude, 0.5-3Ma speed and 0-30°angle of attack. The temperature and pressure distribution values for the maximum constraint is selected as the initial value of external conditions on the optical window surface. Then, the optical window and mechanical structure are designed, which is also divided into two parts: First, mechanical structure which meet requirements of the security and tightness is designed. Finally, rigorous analysis and evaluation are given about the structure of optics and mechanics we have designed. There are two parts to be analyzed. First, the Fluid-Solid-Heat Coupled Model is given based on finite element analysis. And the deformation of the glass and structure can be obtained by the model, which can assess the feasibility of the designed optical windows and ancillary structure; Second, the new optical surface is fitted by Zernike polynomials according to the deformation of the surface of the optical window, which can evaluate imaging quality impact of spectral camera by the deformation of window.