A Study On The Improvement Of Laser Tracking System And Self-calibration Based On Locating Stations

The laser tracking system for 3D coordinate measurement based on multi-lateration principle presents many characteristics such as high accuracy, large measuring range, flexible and dynamic measurement. More importantly, the system is capable of self-calibration, recovering the lost information and error compensation by use of redundancy technique. So the system has wide prospective applications in many fields such as robot performance calibration, precision measurement for large dimension and many others. Countries allover the world have invested tremendous resources and manpower to study these topics. As the foremost work on this research in China, the study on the design and test for this system has been started in our research group. This project is sponsored by the National Science Foundation of China (NSFC), under project contract No. 59875064.This thesis is focused on the study of servo tracking system, the key elements of the measurement system. Explanations on the loop operation principle, beam spot position signal extraction, and selection of motor control mode are presented. A servo tracking circuit including current loop, speed loop, and position loop has been developed to assure high accuracy and dynamic performance of the tracking system.In the analog control scheme, the measuring range is limited for the gain coefficient of transfer-function is related to the distance l between the target and tracking head. A method to improve the original scheme is proposed.The thesis has also carried out the research on self-calibration method based on locating stations. Several locating stations are set in the space. The distances between locating stations are calibrated by a specially designed laser interferometric length measuring instrument. The cat-eye can be located at each locating station successively. The distances between the reference points of the tracking systems and locating stations are measured by straight-line method. After all the distances have been measured the positions of the reference points in selected coordinate system can be determined and the self-calibration is realized. Computer simulation result shows that the standard deviations of the calibrated positions of reference points are reduced and it proves that the self-calibration method based on locating stations improves the calibration accuracy.