| The3D object surface measurement is playing an increasingly important role in the field of the scientific research, automatic online testing, forensic analysis, robot vision. The demands on the3D shape measurement are getting higher and higher, mainly focusing on the accuracy, the resolution, the degree of automation and the practicability.In this paper, the basic principle of the law of projection grating phase shift method is studied, including the N-step fixed step method, the equal step method and the FTP method. The performance and the suitability of these methods are summarized:the N-step fixed step method can be used to measure the whole large area, having high accuracy and achieving a good balance between the measurement range and the accuracy but having high requirement for the accuracy of the phase shifting device; the equal step method has the requirement for the equality ofall the phase shifting value and has no requirement fora determined phase shifting value; the FTP method needs only one single deformation fringe but fuzzes detailed information on the object’s surface.The principles of several frequency domain filters that are used in the FTP method are studied, including the ideal filter, the Gaussian filter, the flap-top Gaussian filer. Their performances are concluded:the ideal filter cuts off all the frequency components higher than the cut-off frequency and results in ringing effect; the Gaussian filter has slow convergence and filters some of the useful base frequency component to filter the zero frequency component and the high frequency component totally; the flap-top Gaussian filter can filter the zero frequency component and the high frequency component, keeping most of the useful base frequency component. At the same time, the phase unwrapping method based on the modulation quality map is studied. Several factors that influence the measurement’s accuracy are studied by the way of simulation, including the fringe’s period, the gray level, the error of phase shifting and the error of quantization and then the regular pattern that can be used to direct the measurement experiment is concluded. A3D shape measurement and demonstration instrument based on the dual-CCD is designed. The phase shifting method and the FTP met hod are integrated on this instrument. This instrument based on the white light can be used in the Holds of aetual measurement experiment teaching and automatic demonstration. This instrument runs by3patterns: automatic pattern, semiautomatie pattern and measurement pattern. The measurement of3D shape is conducted automatically without manual intervention in the automatic pattern and semiautomatic pattern. The user can conduct the3D shape measurement experiment in the measurement pattern. The MVC pattern is used in its software system, thus resulting in high maintainability and expansibility and clear framework. |
