Research On Micro-obeject Fringe Project Profilometry System

Micro three-dimensional accurate measurement plays an important role in the micro change of mechanical,electronic,biological and material.Three dimensional measurement method based on grating projection is widely used in the field of non-contact measurement because of its high precision and speed.A micro object measurement system based on grating projection three-dimensional measurement technology is developed to study on three-dimensional reconstruction of micro objects.The key technologies in the measurement process such as the calibration of telecentric lens,the high dynamic range measurement and the phase unwrapping are discussed.The main work in this dissertation is outlined as follows:1.Aiming at the problem that the traditional calibration method is no longer suitable for the telecentric lens,a calibration method based on general imaging model is proposed.Three different poses of the planar target rotating around the fixed axis are utilized to calibration.This method solves multivariate problem of the general imaging model without precise positioning stage and simplified the calibration procedure.In order to improve the accuracy of calibration,LM algorithm is conducted to optimize calibration parameters to reduce the gap between the 3D coordinates obtained by the spatial intersection method and the real coordinates after the first calibration.Finally,the optimized calibration parameters are obtained.And a self convolution blind deblurring method is proposed to solve the defocusing phenomena caused by small depth of field of the telecentric lens and improves the camera calibration accuracy.2.Aiming at the problem that the traditional phase shift method cannot measure the objects with wide range of surface reflection,a new method of high dynamic range three dimensional grating measurement method based on multiple exposure is proposed.Firstly,find the required exposure time range for different objects.In the range of the exposure time,the camera's exposure time is selected and the multiple groups of phase shift gratings are obtained under different exposure conditions.Traditional method of multiple exposure generates a set of high dynamic range gratings by groups of phase shift gratings to obtain a better unwrapped phase without considering the phase unwrapping process.In fact,light or dark areas also affect the traditional gray-code method.The multiple exposure method proposed by this paper fuse the true phase after unwrapping and get the continuous phase information at last.At the same time,to solve the problems in the gray code method,three steps correction method of gray code is put forward and experiments show this method can improve the quality of phase effectively.3.Based on the study of the algorithms in the measurement process,this paper develops a micro object measurement system.Hardware equipment and software system are designed independently.A large number of experiments have been carried out on the system and the results show that the system can obtain the three dimensional data of micro objects with high quality in the 23.7mm×17.78mm field of view.