Study On Micro-angle Measuring Basic Technique Of Laser Autocollimation

The technique of photoelectric autocollimation for micro-angle measurement has the advantages of noncontact, working distance independence and high precision. It has been widely used in such important fields as machinery, aerospace and military area, especially in the application of aiming and positioning. For the purpose of aiming and positioning application, the basic techniques of laser autocollimation– a new kind of photoelectric autocollimation are researched in this dissertation.In view of the limitation of the simplified model, this dissertation proposes a modeling method for photoelectric autocollimation system based on vector operation. The model of laser autocollimation system is established. On the basis of this model, the principle of image trace for 2D autocollimation and incremental dimension are discussed. And also the relationship between working distance and measuring range is derived for the actual finite aperture. With its special case, an ideal autocollimation system is put forward. Numerical simulation clearly illustrates the principle error of the simplified model and the image trace while the reflector turning. The analysis result of this model may provide theoretical basis for the development of laser autocollimation.Aiming at ideal autocollimation system, a laser autocollimation system based on LD-PSD is constructed. According to the analysis of the system model and the actual requirements, the scheme design emphasizes on response speed, light intensity dynamic range and stability. To build a LD-PSD laser autocollimation system, contrast experiments with some types of photoelectric detector and light source are carried out. With the theory of Gaussian beam transformation, the optical structure is designed. Differing from the former optical structure of autocollimation, the designed scheme not only meets the requirements of ideal autocollimation system, but also avoids the adoption of high precision reticle.The properties of LD and PSD are analyzed, which are closely related to the performance of laser autocollimation. Via experimental study, a correction method is proposed to improve its dynamic characteristic of light intensity. That correction method uses sum volgate of PSD to compensate the relative sensitivity coefficient. The factors influencing structural stability and photoelectric system stability are analyzed. And then an integrated experiment is implemented to examine the stability of laser autocollimation.On the basis of cross correlation, a signal processing method for laser autocollimation system is presented to improve its anti-interference capability and dynamic adaptability of light intensity. Comparative study on signal processing between synchronization sampling, improved synchronization sampling and cross correlation is conducted. Among these methods, cross correlation has the best property of angle noise and long-time drift. Considering the collimation difficulty in the process of collimating and positioning, this dissertation presents a rapid collimating method using inclination sensor. That method adopts a 2D MEMS inclination sensor with high accuracy for easily and rapidly collimating. The inclination angle sensor is calibrated through a 2D micro table and the absolute level of the rapid collimating system is calibrated with the principle of self-calibration.Finally, a prototype of laser autocollimation system is constructed and several test experiments are implemented on it. The prototype exhibits high precision and high stability for 2D small angle measurement, with the maximum range of±700″, the resolution of 0.1″, the maximum nonlinear error of 0.8″within the range of±150″and drift of 0.4″/4h. By means of rapid collimating, the average collimation time is less than 3 minutes.The main creative contributions of this dissertation are as follows. (1) This dissertation presents a modeling method for photoelectric autocollimation system based on vector operation. The model of laser autocollimation system is established and the concept of ideal autocollimation system is put forward. (2) Aiming at collimating and positioning, a rapid collimating method using inclination sensor is proposed. (3) Based on cross correlation, a signal processing method for laser autocollimation system is presented to improve its anti-interference capability and dynamic adaptability of light intensity. (4) A correction method is proposed to improve dynamic characteristic of light intensity, in which method sum volgate of PSD is used to compensate the relative sensitivity coefficient.