| Micro vision inspection technology has gradually become an ideal micro displacement measurement method due to its advantages of visual measurement form,simultaneous measurement of multiple degrees of freedom of movement,high precision,simple installation conditions,non-contact measurement and no influence on the structure and position of micro components.With the continuous development of science and technology,micro visual servo system plays an increasingly important role in micro cutting-edge technology fields such as biomedical engineering,micro machining,micro assembly,etc.However,the inherent nonlinear characteristics of the system as well as the inevitable internal uncertainties and external disturbances in practice have a great influence on the motion accuracy and closed-loop stability of the system,which restrict the motion control performance of the system.This dissertation focuses on the application of active disturbance rejection control(ADRC)method to the micro visual servo system built by the laboratory itself,aiming to make the system have good anti-disturbance ability and realize high-precision motion.Aiming at the problems of low sampling rate and output feedback delay caused by micro vision inspection,the traditional ADRC method is improved to enhance the anti-disturbance ability of the system and improve the motion accuracy.The specific research contents are as follows:(1)An imaging model is proposed and the parameters are calibrated through active motion based on the self-built micro visual servo system.Then the dynamic model of the whole system is proposed and identified through an experimental method to obtain a linear approximate transfer function model of the system,which lays the foundation of subsequent ADRC design.(2)A single rate linear discrete ADRC controller is designed by using the current observer instead of the predictive observer and used in the control of micro visual servo system with modeling errors and external disturbances.The effectiveness of the controller is verified through experiments.(3)Aiming at the problem of the low output sampling rate of micro vision inspection method due to the limitation of camera frame rate,processor load capacity,image processing algorithm speed and other factors makes the anti-disturbance ability of the system weakened,so that the effective suppression of high frequency external disturbance higher than Nyquist frequency cannot be realized,a multi-rate ADRC design based on hold interpolation is proposed.The linear interpolation principle of the first-order hold is used to construct an output predictor to estimate inter-sample outputs,so that the extended state observer(ESO)can be operated at higher sampling rate to realize the multiple relationship between the input and the output sampling rate,which can make the system realize effective suppression of high frequency external disturbance higher than Nyquist frequency,enhance the anti-disturbance capability,reduce the output oscillation and improve the motion accuracy.The stability conditions of closed-loop system are given by using Routh criterion and the advantages of this method are verified through a series of comparative experiments.(4)Aiming at the problem of the inevitable output feedback delay of micro vision inspection method caused by image acquisition,transmission and processing makes the system output produce larger oscillation,a predictive multi-rate ADRC design based on the compensation of Smith predictor is proposed.On the basis of previous work,Smith predictor is used to compensate the time delay of the system to obtain an approximate output with no delay at the current moment,and the delay term is removed from the characteristic equation of the closed-loop system in order to improve the motion performance of the system.The effectiveness of this method is verified through experiments. |
