Research On On-machine Measurement And Compensation Machining Technology For Small Aspheric Surface

In recent years,with the development of science and manufacturing technology and the growth of market demand,aspheric optical elements have been widely used in the instruments and systems of national defense,aerospace,civil communication,astronomy,laser and other cutting-edge fields due to their good optical characteristics.High precision aspherical machining is inseparable from the measurement of aspherical surface.Off-line measurement is the most widely used measurement method at present.Off-line measurement technology is easy to lead to secondary clamping and repeated positioning error,increase non-machining time,reduce machining efficiency and accuracy,so it is difficult to meet the requirements of high precision and high efficiency in aspheric surface machining.While on-machine measurement can effectively solve the problems caused by the off-line measurement,which is divided into non-contact on-machine measurement and contact on-machine measurement.Non-contact measurement has low accuracy and is susceptible to environmental factors,while contact measurement has high accuracy and reliable measurement data,which is suitable for ultra-precision machining of aspheric surface.Research on key technologies of aspherical on-machine measurement was carried out based on the self-developed optical aspheric ultra-precision composite machining machine in this paper.Contact on-machine measurement system with the main component of small diameter ruby probe,linear porous air bearing and capacitive displacement sensor was developed based on the principle of contact on-machine measurement.The concept of aspheric surface and surface shape evaluation parameters were analyzed and introduced,and the on-machine measurement method and the working principle of on-machine measurement device were revealed.Contact pointby-point scanning method was adopted to measure the workpiece surface.The resolution of the on-machine measurement device can reach 10 nm and the measurement range can reach 250μm.The analysis and processing methods of on-machine measurement data were studied.The sources and classification of measurement errors were analyzed.The measurement system errors were studied,the correlative mathematical error models were established and the influence of the correlative error was analyzed.Adaptive measurement method is used to plan the measurement trajectory.In addition,the measurement data denoising,filtering,fitting and other related processing methods were studied.Aspheric surface measurement and compensation machining software was developed with Visual C#2013 as the development tool.Modular design idea was adopted.The software is composed of two modules: aspheric machining module and aspheric measuring and correcting module.Each module has an independent structure and function.It can realize high-precision automatic measurement and compensation machining of aspheric workpiece.A single point diamond ultra precision cutting experiments for C3604 brass spherical and aspherical surface were carried out.The on-machine measurement and compensation machining experiments were also carried out.After compensation machining,the spherical surface form accuracy reaches PV 231.4 nm,the aspheric surface form accuracy reaches PV 206 nm.Compared with the off-line measurement results,the measuring accuracy of the on-machine measurement system and the validity of compensation machining are verified.