Laser Diameter Measurement System Based On FPGA Pulse Counting

As an effective non-contact detection method, laser scanning diameter measurement technology is widely used on object diameter online measuring in both domestic and foreign industry, with which high-speed, high precision, non-contact measurement of cylindrical objects can be achieved. Non-contact characteristic and non-interference on the measured object, making it ideal for online measurement of objects, is conducive to the production of automation and intelligence.Contra pose the problem which the design, installation and maintenance of scanning lens in laser scanning diameter measurement requires high standard and measurement accuracy are influenced greatly by ambient temperature, laser scanning system for diameter measuring of non-scanning is in-depth studied and realized. Differential preamplifier is designed, optoelectronic conjugate method of boundary detection is achieved and multiple frequency phase shift method of pulse width measurement is presented and completed.The main contents are as follows:1,The optical system design and analysis are completed by in-depth study of the technical characteristics of laser scanning system for diameter measuring of non-scanning object lens. Laser diameter measurement system based on FPGA pulse counting is constructed by connecting to current experimental platform.2,Differential preamplifier circuit is designed by the use of AD620 instrument amplifier. The circuit is proved that it has great differential-mode gain, common mode rejection ratio, stability and input bandwidth, is suitable to extract weak signal. The boundary of the received optoelectronic signal is analyzed. Contrasts to half-intensity method boundary detection, optoelectronic conjugate circuit is studied and realized and circuit design with more accurate detection of boundary is obtained. In the simulation software Protues, simulation experiments show that this method has good stability and adaptability.3,Measurement of pulse width is achieved by using direct counting method. In order to improve accuracy of measurement, the paper presents a new counting method——multiple frequency phase shift, which can be achieved in Xilinx FPGA. In Xilinx ISE 10.1 software, the code is designed. The simulation shows that the method can improve the accuracy of the counting and reduce error.4,The control circuit is designed and realized by AT89S52. Corresponding control programs and display programs are compiled. Connected to a computer through the RS232, the system provides the possibility of further expansion.5,The system error is analyzed. The recommendations for further improvement are given, such as multi-segment calibration method, some non-functional parameters are added to monitor whether the system is running which can reduce the problems of system maintenance on the condition that the system is not running.