Key Research On Surface Profilometry Based On Laser Scanning Triangulation Using Lateral Synchronization

Intelligent manufacturing has made new demands on the advanced online measurement with the "Made in China 2025" plan unveiled and rapid development of modern industrial equipment manufacturing. Traditional non-synchronized laser triangulation profile measuring system including line structured light sensor has its own limitations, as the horizontal and vertical fields of view and resolution have a fixed relationship partly determined by the sensor geometry, measurement performance is subject to environmental light and multiple reflection interference, the sensor signal-to-noise ratio falls when the object material, color or roughness changes in the measurement field of view. To meet the advanced measurement requirements of high-speed, high-accuracy and robustness, the key technologies of surface profilometry based on laser scanning triangulation using lateral synchronization are studied in this paper. The main research work of this thesis is as follows:1. A surface profilometry based on laser scanning triangulation using lateral synchronization and high-speed rotating polygon mirror is proposed after analysis on the pros and cons of traditional non-synchronized laser triangulation scanning measurement system. The precise synchronization of laser triangulation outgoing beam and scattering beam is fulfilled with a precision-engineered 12-facet polygon mirror scanning subsystem of high stability. To meet the actual measurement requirements, system prototype is made and functionality is verified with precision-designed optical simulation, mechanical design, electrical controls and software algorithms.2. A high-accuracy non-parametric system calibration model based on precision linear guide and laser interferometer is put forward to reduce errors of system nonlinear measurement principle, mechanical manufacturing and mounting of optical elements. System measurement with high-speed, high-precision and high-stability is achieved by the combination of real-time laser spot intensity tracking and improved high-stability subpixel laser spot centroid location algorithm based on Fourier descriptors.3. The theoretical foundation for the advanced high-precision measurement is laid through the detailed analysis on key parts of the system signal processing chain.The laser speckle effect is clarified to be the primary factor affecting the measurement performance of laser triangulation scanning measurement system. The limit-error of laser spot centroid position is derived by using the first-order statistical properties of laser speckle effect, and the theoretical analysis on laser speckle reduction is given by using laser scanning measurement based on rotating polygon mirror. The system measurement uncertainty is evaluated with experiment on standard plane and standard needle gauge to verify the feasibility and accuracy of surface profilometry based on synchronized laser triangulation scanning.