Research On Three-dimensional Profile Measurements Based On Confocal Chromatic Sensor

Profile measurement technology is developing rapidly with the improvement of motion control and sensor technology.Confocal chromatic measurement is a new sensor type,which is very suitable for high precision optical measurement,with high accuracy and small interference.Based on the surface measurement of optical lens,a 3-D contour scanning tester is designed.A whole closed-loop motion platform and a white light co-focusing sensor are adopted.Layout and assembly of the mechanical system was accomplished,and electrical system was established.Servo motor tricyclic PID control strategy was adjusted to realize high precision contour tracking.Motion and scan integrated interface software was written,and hardware trigger was used to solve the synchronization problem of the system.Multi-tread access technology was used to realize the interaction of sensor test and read process.As for the data post-processing analysis,sphere point cloud datum were fitted to spherical surface.The global point cloud based on linear least square method is performed to get the initial results of geometric distance and radius.Levenberg-Marquardt nonlinear least squares fitting is used to optimize the results.This paper discusses the influence of sampling area size,sampling density and point cloud error on fitting accuracy in small segment angle sphere.A robust gaussian regression filter is performed to filtrate the fluctuation errors and abnormal data points.Error transformation function of fitting radius uncertainty and random error uncertainty is proposed.For spherical center position problem,this paper puts forward a strategy,namely,first using the orthogonal scanning to roughly determine the central area,and then using the contour scanning and fitting to precisely determine the center position.This method gives attention to both efficiency and precision of the measurement process.The above methods were verified through Monte Carlo simulation and experiment.The scanning system can realize the basic test process and achieve the test precision,efficiency and other functional parameters.