【作者】 刘浩；

【导师】 邓磊敏；

【作者基本信息】 华中科技大学 ， 光学工程， 2022， 硕士

【摘要】 激光精密制造技术是航空航天装备迈向高性能、智能化的关键技术,如飞机雷达罩频率选择表面的加工、智能蒙皮上共形电路的制造、超精密磨具表面织构化结构的制备等。为获得较高的加工精度,需要将激光光斑聚焦到极小尺寸,同时也导致了激光聚焦位置处极短的焦深。由于加工过程中存在零件制造误差、安装误差以及材料表面粗糙不平等问题,极易导致激光离焦造成加工质量与精度的下降,因此激光自动对焦技术不可或缺。现有的激光自动对焦技术存在对焦机构运动缓慢、无法兼容振镜系统、无法应用于曲面等问题,严重阻碍了相关技术的发展。针对上述问题,本文提出了一套与现有激光振镜扫描加工系统兼容的自动对焦方法。通过计算设计了动态聚焦模块的光学结构和同轴反馈光探测光学结构,基于高斯光束的q参数和光场振幅分布,定量计算了透过针孔的激光功率随样品离焦量的变化规律,结合ZEMAX软件的仿真和模拟结果,完善了系统设计。基于现场可编程逻辑门阵列(FPGA)对控制硬件进行了设计和开发:利用高速光电探测器和AD转换模块,实现了反馈光信号的探测和处理,基于XY2-100协议实现了音圈电机的高速控制,采用合适的对焦方案,完成了自动对焦模块控制系统的研发。基于搭建的激光自动对焦扫描加工系统,实验测试了系统关键性能指标。该系统的实际对焦范围为12.9mm,对焦范围内光斑半径变化不超过1μm,对焦时间为1～2s。对多种材料进行了对焦精度的研究,结果表明该系统的对焦精度与反馈光信号的强度有关。对于镜面不锈钢板、镜面碳化硅陶瓷等反馈光信号较强的材料,该系统在平面上的对焦误差较小,平均在20μm左右,而对于表面粗糙的覆铝板材料,平面对焦误差在90μm左右。受反馈光信号强度的影响,各类材料在斜面上的对焦误差均会随斜面倾角的增大而增加,提高AD模块的采样率和采样精度有望提高该系统的自动对焦精度。该系统具有与振镜扫描系统兼容性好、对焦机构高速灵活、无需辅助光探测等优点,易于推广到激光三维曲面刻蚀加工应用中。更多还原

【Abstract】 Laser precision manufacturing technology is a key technology for aerospace equipment to move towards high performance and intelligence,such as preparing frequency selective surface structures on the surface of aircraft radomes,manufacturing conformal circuits on intelligent skins,Fabricating textured functional structures on the surface of ultra-precision abrasives,etc.In order to obtain high processing accuracy,the laser spot needs to be focused to a very small size,which also results in an extremely short depth of focus at the laser focusing position.Due to the manufacturing error of parts,installation error and uneven surface of the material during the processing,it is easy to cause the laser defocusing,which will cause the reduction of the processing quality and accuracy.Therefore,the laser autofocus technology is indispensable.The existing laser autofocus technology has problems such as large mechanism,slow speed,inability to scan,and inability to apply to curved surfaces,which seriously hinders the development of related technologies.Aiming at this common problem,this paper proposes a set of automatic focusing method compatible with the existing laser galvanometer scanning processing system.The optical structure of the dynamic focusing module and the optical structure of the coaxial feedback light detection are designed by calculation.Based on the q parameter of the Gaussian beam and the amplitude distribution of the optical field,the variation law of the laser power passing through the pinhole with the defocusing amount of the sample is quantitatively calculated.The simulation and simulation results of ZEMAX software complete the system design.The control hardware is designed and developed based on Field Programmable Logic Gate Array(FPGA).Using the high-speed photodetector and AD conversion module,the detection and processing of the feedback light signal is realized,and the high-speed control of the voice coil motor is realized based on the XY2-100 protocol,and the development of the automatic focusing module control system is completed by adopting the appropriate focusing scheme.Based on the built laser autofocus scanning processing system,the key performance indicators of the system were experimentally tested.the actual focus range of the system is12.9mm,the change of the spot radius within the focus range does not exceed 1μm,and the focusing time is 1～2s.The focusing accuracy of various materials is studied,and the results show that the focusing accuracy is related to the intensity of the feedback light signal.For materials with strong feedback optical signals such as mirror stainless steel plates and mirror silicon carbide ceramics,the system has a small focusing error on the plane,with an average of about 20 μm,while for the rough surface of the aluminum clad plate,the plane focusing error is about 90 μm.Affected by the intensity of the feedback optical signal,the focusing errors of various materials on the inclined plane will increase with the increase of the inclination angle of the inclined plane.Improving the sampling rate and sampling accuracy of the AD module is expected to improve the automatic focusing accuracy of the system.The system has the advantages of good compatibility with galvanometer scanning system,high-speed and flexible focusing mechanism,and no auxiliary light detection.It is easy to be extended to the application of laser three-dimensional surface etching.更多还原