Design Of A Laser Tracking System

The laser tracking system for 3D coordinate measurement based on multi-lateration principle possesses many advantages, such as high accuracy, large measuring range, and capability of flexible and real-time measurement,over traditional methods. Recently, its applications have been extended to many industry fields, especially for large engineering construction measurement in aerospace, aeronautics, vessel manufacturing, and large-scale machine assembly. The multi-lateration principle also has other advantages, including the capabilities of self-calibration, self-recovering of lost information, error separation and compensation, and system rearrangement. Countries all over 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.The multi-lateration principle can be expressed as follows. Multiple laser interferometers are utilized to track the position of a target. The coordinates of the target are determined based on the lateral displacements measured by these interferometers, rather than the angular displacements in some other methods. The primary advantages of this principle are its high measurement accuracy and capability of self-calibration. This dissertation is focused on the study of optical tracking system, the key element in the measurement system. The dissertation covers the following aspects concerning the main work and creative research in the project.The design of optical diagram of tracking laser interferometer based on the laser interferometer for straightness measurement.When laser interferometers are used for measuring linear displacement, the returned laser beam should be directed to the optical receiver located at an offset with reference to outgoing laser beam. The traditional solution is utilizing a proper optical diagram outside the laser head, including the usage of polarized beam splitter and λ/4 plate. However, this method needs a large number of optical elements, which are difficult to get well adjusted, and requires high quality λ/4 plates. After a comprehensive study on the HP5529 laser interferometer for straightness measurement, it was proved that this type of interferometer can be easily used to measure the lateral displacement. In this manner, the optical diagram is greatly simplified.The development of laser tracking head with dual-axis independent drive Laser tracking head is the key element of the measurement system. A tracking head with dual-axis independent drive has been developed which is compatible to the commercially available laser interferometers. It is simple, versatile, and capable of 3-D tracking measurement. With the improved tracking head, the standard deviation of the measurement uncertainty was reduced to 0.49 μm.A detail accuracy analysis of the laser tracking headErrors of the laser tracking head have significant effects on the final measurement uncertainty of the system. The major error sources include the eccentricity of the incident beam with reference to the rotational center of the tracking mirror, departure of the rotational center from the mirror surface, and the error motion of the rotational center. The concept of equivalent base point is proposed in the dissertation. After careful analysis, it is found that eccentricity of the incident beam less than 0.5mm has negligible effect on measurement accuracy. However departure of the rotational center from the mirror surface, and the error motion of the rotational center are vital to high accuracy. The adjustment of laser tracking headAs for the improved generation II laser tracking head, a novel method for lens surface off-center measurement is brought out. Detailed adjustment procedures are presented in the context.The development of servo tracking systemA servo tracking circuit including current loo...