Research On Polishing Path Planning For CCOS Of Aspheric

In recent years, as the rapid development of manufacturing industry and opticalindustry in China, the high precision aspheric demand is increasing. As the final stepof processing, polishing plays an important role in manufacturing aspheric surface.Computer controlled optical surfacing(CCOS) is widely applied in asphericprocessing, for its advantages such as the tool head fits the optical surface well，thefull use of computer high repetition accuracy and fast execution,and so on. Polishingpath planning, which is the important research direction of CCOS, directly affects themachining accuracy and machining efficiency of aspheric surface. So, it is veryimportant to plan a good polishing path for production and processing of asphericsurface.Usually the analysis of the machining accuracy affected by the polishing pathbased on two-dimensional space, for which ignores the changes of aspheric curvature,three-dimensional space and other factors. In order to make the analysis of thepolishing path more comprehensive, according to the characteristics of the CCOS, theHertz contact theory was introduced. And the quality evaluation method of polishingpath by the analysis of the removal area generated by path was proposed.Modeling and Simulation of the removal area was established for rotationsymmetric aspheric. With quadric aspheric and high order aspheric as an example, themost commonly used Archimedes spiral path was analyzed by simulation. Theanalysis results show that the generally used Archimedes spiral path fails to ensuregood machining accuracy due to the contact changes of the removal area betweenadjacent tool paths. And the concept of overlap rate was introduced to quantitativelydescribe the varying contact.A novel spiral tool path planning with uniform-overlap-rate was proposed by establishing the changing relation between spiral and overlap rate, and the simulationresults verify the effectiveness of the algorithm. Through detailed analysis of theimpact factors of the change of uniform-overlap-rate, the aspheric surface is dividedinto3types. Different sprial algorithms were given according to different types ofaspheric, which ensure both the processing precision and the algorithm simplicity atthe same time.According to the characteristics of ultra-precision four-axis polishing machine,the optimization algorithm of spiral path and concentric circles path was proposed forfreeform optics surfaces. The algorithm improves the stability of polishing angle andgreatly reduces the error due to the varying projection path interval, which ensuresthat the paths keep the approximately circular characteristic. In the case ofthree-mirror freeform optical system, the optimization effect of the algorithm has beenverified and the path was applied to the polishing.