Study Of Method On Laser Differential Measurement

The thesis aims to the special areas which require non-contact and online measuring the diameter of workpiece.It researches and studies the diameter measurement method based on the principle of laser differential scanning measurment .Including a series of key technologies such as optical system structure and mechanical structure , beam receiver module, amplification and filter circuit, conjugate boundary detection circuit, FPGA timing circuit, measurement and control software and so on.The main contents in the project:(i) It analyzes and investigates the optical system structure of laser differential scanning measurement in-depth, and compares the characteristics of commonly used lasers. The He- Ne laser was selected as a system light source. Getting the general design principles of the structure of extension and collimation beam by analyzing the beam size of system measurement field in theoretical ; Analyzing the characteristics of the differential scanning rotating mirror structure, which gives the conclusion that the selection of differential characteristic quantities affects the measurement result.(ii) According to the analysis of the border character of the laser diameter measurement signal and the consideration for the actual vibration of the workpiece, the project using the combination of pixel optical transition contact and silicon photodiodes as the receiver module of border laser signal. Which can avoid the impact of the workpiece vibration. The silicon photodiode is selected as a photoelectric signal conversion devices by analyzing of characteristics of commonly used Photoelectric detectors.(iii) Aims to the specific requirements for this system, the design uses two differential amplification and filter circuit to change the light current signal into voltage signal. Which can eliminate the noise impact caused by a number of photodiodes in parallel. The project researches and implements a new detection method of the boundary signal - conjugate boundary detection. The online simulation on Proteus software and hardware verification shows the method has good stability and environmental adaptability.(iv) The project finished high-precision pulse width measurement which based on FPGA digital phase shift .It uses the XC2S50 chip which in the series of Xilinx Spartan II ,writes corresponding VHDL source code in ISE9.1 software environment and implementes pulse count on FPGA hardware system successfully.(v) The project designs the main control system MCU hardware and digital display circuit ,and writes the corresponding data communication program and display control program.The RS232 port helps to implemente serial communication and visualize the measurement results.(vi) The thesis makes a comprehensive analysis of the experimental results and errors of the measurement system, points out the possible error compensation method, and proposes measures to improve the system accuracy.