Modeling Simulation And Error Analysis Of 3D Shape Measurement Method Of Specular Surface

Specular surfaces have wide applications in various fields,such as new energy,illumination,aerospace and biomedical engineering.Shape deviation of the specular surfaces has a great influence on visual appearance and technical performance.Therefore,it is essential to develop a stable method for specular surface measurement.Phase measuring deflectometry?PMD?-based methods are widely used to obtain the 3D shapes of specular surfaces because they offer the advantages of a large dynamic range,high measurement accuracy,full-field and noncontact operation,and automatic data processing.However,the existence of random noise,uneven illumination,the shape of the object to be measured is not typical,complicated system calibration and other expected factors will add difficulty to analyze algorithm and find ideal system parameter in actual measurementsIn order to analyze the PMD system simply and quickly,this thesis presents a simulated direct PMD?DPMD?measurement system.The principle of the simulated specular measurement system is based on a combination of DPMD and a pinhole imaging model.It is therefore can calculate the coordinate relationships between the two Liquid Crystal Display?LCD?screens and the reference plane,the test surface and the reference plane,and the Charge-Coupled Device?CCD?plane and the reference plane.Then the proposed system can simulate the fringe projected on reference plane and the test surface and the fringe captured by CCD camera in different system parameters.After calculation of the unwrapped phase,the height of the test surface can be calculated using calibration formula of DPMD measurement system.Simulated results indicate that the simulated system has high accuracy,and it provides an ideal platform for the ana lysis of system parameters and error.When the LCD screen is not parallel or the LCD screen is not parallel to the reference mirror,the application method of the simulated DPMD measurement system is given.The effects of the four system parameters on the measurement results have been analyzed with the simulated DPMD measurement system.Simulated and actual experiments were carried out.The results showed that with increasing distance?d between the two LCD screens,the angle?between the camera's optical axis and the reference mirror,the RMS errors of the measurement results decrease gradually.However,with increasing distance d between the LCD₁'screen?virtual image of screen LCD₁?and the reference mirror,the period P of the fringe pattern,the RMS error of the measurement results gradually increase.An actual experimental system has been setup with appropriate system parameters.A manufactured artificial step with multiple discontinuous specular surfaces and a concave mirror were measured by the system.The maximum absolute error and the maximum mean square root error of the reconstructed step surface are 0.023mm and 0.023mm,respectively.The systematic error of the concave mirror is 0.0239mm.These experimental results demonstrate that the DPMD measurement system can obtain the required depth data of specular objects that have discontinuous surfaces and curved surfaces with high precision.