| Comparing with traditional methods, the laser tracking system for 3D coordinate measurement based on multi-station principle possesses many advantages, such as high accuracy, large measuring range, and capability of flexible and real-time measurement. Furthermore, the multi-station principle also has other advantages, including the capability of self-calibration, self-recovering of lost information, error separation and compensation, and system rearrangement. The study on the design and test for this system has been initially developed in our research group, and it is sponsored by the National Science Foundation of China (NSFC) with project contract No. 59875064.Based on multi-station principle, a flexible 3D coordinate measuring system consisting of four laser tracking interferometers has been developed to measure 3D coordinates of the target retroreflector. This dissertation focuses on the study of laser tracking system, which is the key element of the measuring system, and covers the following aspects of the main work in the project.1. The optical diagram of tracking laser interferometer based on the laser interferometer for straightness measurement has been improved. Some former used optical parts are replaced, and some new ones are added. These changes make the laser spot circular and almost immune to the environment light.2. A photoelectric detection circuit has been developed. Based on the principle of the two dimensional PSD, the detection circuit with zero point and gain adjustment functions, including weak current amplifying, addition, subtraction and division functions, is designed. According to the experimental data, the voltage–displacement curve is linear in an about 4cm2 area near the center of the PSD.3. An analog control system of the laser tracking system has been put forward. The analog system is based on the closed loop position control. The PID model of the closed loop position control is established on the base of models of the links composing the loop. The DC motor selection, PWM drive circuit and PID regulator circuit are completed. The experiment proves that the the tracking speed of the system exceeds 0.2 m/s.4. A digital control system of the laser tracking system is designed. The digital control system consists of current loop, speed loop, and position loop. The motor controller forms the current and speed loops, and PSD signals are sampled by the data acquisition card. Through the PI operation, control signals are sent to the motor controller by a CAN bus.5. The measuring software is compiled. The data acquisition system of the laser interferometer is set up, and the measuring software based on VC is programmed to measure the relative displacement of the target retroreflector. Furthermore, a synchronous data acquisition system of three laser interferometers is realized. In order to enable the data acquisition module of the PSD singals to work with the control module, a measuring module is programmed by Labview. The above three modules compose the overall software of the digital control system.6. The error of the cat's eye retro-reflector has been measured. The main optical error sources of the cat's eye retro-reflector are analysed, and associated experiment setup and data processing method are described. Experiment results show that the maximum optical error of the measured cat's eye retro-reflector CER75 made by Leica company is approximately 4μm.
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