Modeling Simulation And Experimental Verification Of 3D Shape Measurement Method Of Composite Surface

The optical measurement methods based on full-field phase calculation are widely used to obtain three-dimensional(3D)shape of the object surfaces due to the advantages of non-contact,automatic data processing and fast acquisition.Existing full-field fringe projection profilometry(FPP)and phase measuring deflectometry(PMD)are applied to measure 3D shape of diffuse objects and specular objects,respectively.However,in industrial applications and daily life,there are many composite objects consisting of diffuse surfaces and specular surfaces.The rapid measurement of surface shapes is the key factor to ensure the processing quality and function of such objects.To this end,this dissertation proposes a method of measuring the 3D shape of composite surfaces based on the combination of direct PMD(DPMD)and FPP.Due to the complexity of the actual measurement system,the tedious processes of adjustment,and the influence of ambient light noise,it is difficult to directly verify the method and find the best system parameters configuration.Therefore,a virtual composite surface measurement system based on DPMD measurement principle,FPP measurement principle and pinhole imaging model is established for simulation,and then an experimental system is built to verify the simulation conclusions of the virtual measurement system.The main research contents of this dissertation include:First,by establishing the coordinate relations among the fringe projection equipment(displays and digital projector),reference surface,measured composite surface and camera in the composite measurement system,the projection and acquisition processes of the reference fringes on the reference surface and the deformed fringes on the measured surface in the actual composite measurement system are simulated.Then,the phase demodulation and unfolding of the acquired fringe patterns are carried out,and the relationship between the phase and depth of the composite surface is used to reconstruct the 3D shape of the virtual composite surface,which verifies the effectiveness of the proposed method for measuring the 3D shape of the composite surface.At the same time,in order to guide the actual measurement system to set reasonable system parameters,the relationships between the five system parameters and Root Mean Square(RMS)error of measurement results are analyzed by simulation based on the established virtual system.The simulation results show that RMS of composite surface measurement results decrease with the increase of the distance ?d between the two Liquid Crystal Display(LCD)screens,the angle?between Charge-Coupled Device(CCD)camera optical axis and the normal of the reference plane,and the angle?between Digital Light Processing(DLP)projector optical axis and the normal of the reference plane.However,the RMS of composite surface measurement results increase with increasing of the distance d between the LCD₁'and the reference plane,the period P of the projected fringe.Finally,the actual measurement system is built to verify the simulation conclusions of the virtual measurement system.The experimental results are consistent with the conclusions of the simulation experiments.An actual measurement system with optimized parameters is used to measure a composite step with known dimensions.The maximum absolute error of the measurement results is 0.031 mm.The measurement results show that the composite surface measurement system established in this dissertation can simultaneously,accurately and efficiently obtain the 3D shape of the discontinuous composite surface.