Research On The 3D Measurement Method With Structured Light Based On Digital Grating Projection

The three-dimensional measurement technology of phase-shift structured light has shown great application prospects in the fields of industrial manufacturing and reverse engineering,due to the characteristics of high precision,non-contact,and large field of view.This work is focused on the research of the three-dimensional measurement method of digital raster projection,in which the key technologies such as structured light coding,camera and projector calibration and Gamma error correction in the three-dimensional measurement system are studied in depth.The main work includes the following aspects:(1)Acquisition of package phase and phase unwrapping of the measured object.The mathematical model is established based on the composition and principle of the digital grating three-dimensional measurement system,the mapping relationship between height and phase is demonstrated,and the phase resolution method of Gray code combined with phase shift and multifrequency heterodyne principle is deeply analyzed.The corresponding experimental analysis and research using the gray code combined with phase shift method as the phase unwrapping method are carried out.The experimental results show that it has high spatial resolution and good robustness.According to the relationship between the number of the phase-shift steps and the measurement accuracy shown by the experimental results,comprehensively considering the advantages and disadvantages of the calculation accuracy and the calculation amount,the 16-step phase shift method has the advantages of high calculation precision and strong operability to obtain the parcel phase and the phase unwrapping with Gray code combined with phase shift method in practice.(2)Calibration of camera and projector based on digital grating 3D measurement system.The distortion of the camera's imaging model and camera lens is analyzed according to the calibration principle of the camera and projector in the digital grating three-dimensional measurement system.Based on the principle of Zhang Zhengyou's calibration method,the improved calibration procedure completes the experiment of simultaneous calibration of both the camera and the projector,the experimental results show that the calibration method has high precision.(3)Phase error correction due to Gamma nonlinear effect.The main error sources of the digital grating three-dimensional measurement system are analyzed,the phase error caused by the Gamma nonlinear effect in the three-dimensional measurement system is mainly studied.The relationship between the Gamma coefficient and the higher-order phase error component is deduced.A concise method of pre-calibration for the system Gamma value is demonstrated.Finally,an analysis experiment was performed,and the results indicate that the range of the phase error was reduced by about 50% by the Gamma correction.(4)Setup and analysis of the 3D measurement system experiment.The experimental platform for three-dimensional measurement system of structured light is completed,with the supporting program codes.The codes integrate the functions of collection,calibration and three-dimensional reconstruction,and provide the convenient human-computer interaction interface,which enables multi-dimensional observation of the results after three-dimensional reconstruction.The threedimensional reconstruction for the object to be tested(standard sphere and toy plaster)is achieved by the experimental platform,and the measurement error of the system is about 0.26 mm,and the three-dimensional morphology of the measured surface can be restored well through the threedimensional reconstruction.