Research On Control System Of Laser Tracking System

Laser Tracking System(LTS),as a new three dimensional measuring machine,is firstly used in Robot Measurement and Calibration Technology. Flexible coordinate measuring system,based on laser interferometer which is acknowledged as the highest precision device in large area distance measurement,is promised to be the most potential high precision,large-area,contactless, dynamic measurement tool. In our research subject,a single-station LTS is designed on the basis of sphere coordinates measurement principle.The paper is mainly focused on control system design of the single-station LTS.The main content of research work is as follows:1) Theoretical Analysis of controlled object mathematical modelMathematical model is very necessary in high precision and fast response tracking system which can help to analyze the interference mechanism of various disturbance.The controlled object mathematical model is deduced and model parameters are obtained and model precision is evaluated through experiments.2) Analysis of disturbance factors and classification of themAll the disturbance factors are found out and the effort mechanism of them are clarified.All these factors are classified in three groups through their work mechanism:disturbance to current torque(angular acceleration related),disturbance to angular speed,disturbance to distance tracking,which is much helpful for modularization design of three-loops(current loop,speed loop,position loop) and responsibility distribution for every link in the control system.3) Design of current loop and relative experimentsCurrent loop which reflects the robustness and rigidness of current torque determines the tracking performance of angular acceleration.The design demand of current loop can be easily met using traditional digital PID algorithm on account of high sensitivity and fastness of current response.Parameters like frequency bandwidth,response time,tracking error are obtained through experiments and real-time display and statistical analysis of current loop parameters are designed which is very useful for time domain and frequency domain analysis of current loop.4) Design of speed loop and relative experiments Speed loop is a key link in the whole control system and so design of speed loop is the main part of the research work in this paper.Actually,many disturbance factors in system will cause interfere to speed tracking,including linear factors and nonlinear factors(such as friction torque).An important idea in speed design is that all factor causing interfere to speed tracking should be enclosed in speed loop so that speed loop can be equalized as First Order Inertia Link with very short inertia time constant if rigidness and fastness of the speed loop meet design demand.Some advanced control strategy consisting of Fuzzy PI Control,Fuzzy Neural Network Control,Auto Disturbance Rejection Control(ADRC) are adopted in speed loop design and then advantages and disadvantages of them are concluded through their experiment tracking effects.5) Design of position loop and relative experimentsThe typical conflict between the overshot and rapidity in Feedback Control is deeply studied.In ADRC,Tracking Differentiator(TD) serves to solve that problem by arranging transition process of the command input while in Compound Control it is solved by leading signal feedforward.Mechanisms of the above two control strategies are researched and validities of them are evaluated by experiment.6) Compound control in LTSThe relative theory of compound control is studied and put into use in LTS.7) Composition of target speed and Prediction filtering technologyComposition of target speed is a key point in Compound control and Prediction filtering technology is an useful tool in target speed measurement. Theory studies and experiments are carried out in LTS.