Research On Autofocus Laser Scanning Projection Technology

The laser scanning projection system is widely used in the precision manufacturing and assembly of large-sized components for aircraft,ships and automobiles.This system can accurately project the contour frame of a component to be processed or assembled to the position where it is to be installed,in turn,which assists the worker in completing the positioning,assembly and processing of the target component.To solve problems of the existing laser scanning projection system,such as low positional accuracy of projection graphics,wide projection laser linewidth and inability for accurate and dynamic autofocus based on variation in projection distance,it was devised that dynamic autofocus laser scanning projection system based on differential detection principle.Firstly,the working principle of the laser scanning projection system has been studied.The traditional laser scanning projection system is improved based on this principle,and a dynamic autofocus laser scanning projection system,based on differential detection principle,was designed.It is established that a mathematical model for the projection system based on the high-speed two-dimensional galvanometer device,and it was determined that the coordinate conversion relationship between the galvanometer's horizontal deflection angle H and vertical deflection angle V with the projection point in the projected target coordinate system.Secondly,the working principle of the dynamic autofocus laser scanning projection system based on differential detection principle was studied,also two dynamic autofocus schemes were designed respectively,i.e.,optical lever type and inverted telephoto type.The corresponding mathematical model was derived and the optical system was simulated based on ZEMAX.By comparison,it is concluded that the response of the inverted telephoto dynamic focus system is more sensitive and rational in structure.Thirdly,the feedback light intensity detection system of the symmetric defocused dual detector based on the differential detection principle was studied,the precise convergence of the scanned light spot was realized in the laser scanning projection system,thereby a narrower line width for the laser scanning line frame was obtained and the positioning accuracy of the laser scanning projection graphics was improved.Then,solving method for the center of cooperative targets based on least squares method was studied,and a circle center solving model was established.Furthermore,the solving method for the coordinate transformation parameters suitable for the laser scanning projection system was derived and the system projection model was simulated,and the feasibility of these two solving methods were verified.Finally,according to the above research results,a dynamic autofocus laser scanning projection set-up based on the differential detection principle was built.Thus,the light intensity signal detection experiment,dynamic focus experiment,cooperative target center detection experiment,projection system calibration experiment and standard graphic projection experiment were carried out,in the end,the projection and positioning accuracy of the system were tested.The experimental results show that the convergent spot diameter of the dynamic autofocus laser scanning projection system based on the differential detection principle can reach up to 0.2mm at best on the projection plane at 4.5m,which can improve the positioning accuracy of the developed set-up to 0.1 mm.The center positioning error of the cooperative target is 0.18 mm,which is better than 0.2mm,and meets the design requirements of the experiment.The horizontal shape deviation value of the projection graphics is 0.04 mm,and the vertical shape deviation value is 0.04 mm,both of which meet the design requirements of the experiment;The projection pattern position deviation can basically meet the deviation requirement of 0.4mm..Therefore,it is proved that the developed dynamic focus laser scanning projection system based on the differential detection principle can realize dynamic focusing,system calibration and precise projection function.Various precision detection results also indicate that the system accuracy meets the requirements,can also be applied to the precision manufacturing and assembly of large-sized components in aircraft,ships and automobiles,etc.