The Research On Auto Chassis' Key Points Measurement Based On The Technology Of Laser Scanning

The Auto Chassis' Key Points Laser Scanning System is a measuring system based on laser scanning combined with the feature target. It can measure the three- dimensional size of the key location point on auto chassis.With the development of the motor technology, opt-electronic technology and computer science, the three-dimensional coordinate measuring technique basing on laser scanning technology shows its advantage and becomes a more and more important measuring method with convenience and high efficiency and accuracy. So it gets widely appliance in various fields as an efficient measurement, such as distance measurement, surface shape of work piece, structural parameters of components, Archaeology, Biological Medicine, Reverse Engineering and car body size measurements. This thesis introduces a system, which is based on four-beam laser scanning, scanning the feature target and measuring the three-dimensional size of the critical point beneath a car. The system extracts the information of feature target using optical, laser, mechanical, electronic and precision measurement theory and technology comprehensively, in order to obtain the location information of key point. It is non-contacted and strong anti-interference, and has a simple structure and a large measuring range with high speed and accuracy; it can conduct real-time and multi-point measurement. This thesis focuses on the improvement of accuracy and stability of the system, implementation of four-beam measurement and disposal of collected information.The main content of this thesis includes:1).This thesis deeply analyzes the measuring principle of the system, including the principle of four-beam laser scanning, identification of target and directional reflection. Sets up the four-beam laser platform and optimizes the performance of the system according its mathematical model and structure.2).The thesis adopts DC brushless motor and studies its performance. And also analyzes the factors related to the stability of motor speed. According to motor performance, it carries out steady speed control of precision based on speed loop and electric current loop, and introduces the peripheral control circuit met the requirement of the motor. This circuit, which is simple but owns many advantages such as multiple function, strong controlling ability, easy debugging, and widely used, has been validated by tests. 3).The thesis also considers data acquisition and processing, and designs a data acquisition and processing module on the system. CPLD and AVR are introduced to realize the software and hardware of the module with a 40MHz crystal as the clock. The circuit has solved the problem which is caused by the competition of the four signals in a simple and ingenious way. At last, I finish the software related to CPLD and AVR.4).The thesis fulfils the preliminary design for PC software, and realizes the preliminary debugging and PC display. The system has a intuitive display and a friendly interface.5).The thesis sets up the system calibration method and conducts preliminary calibration on the base of it. The error of the system has been analyzed. It also measures the chassis model and analyzes the data obtained.