Study On Ultra-precision Aspheric On-machine Measurement And Error Compensation Grinding/Polishing Technology

With the rapid development of modern optical electronics technology, a variety of optoelectronic products are applied in aerospace, astronomy, electronics, laser and optical communication fields; therewith the higher performance requirements are set for aspheric optical components. Especially, a demand of high-quality aspheric mold is put forward in machining accuracy and processing materials. In order to resolve current some key technologies for obtaining ultra-precision form accuracy and surface quality of aspheric glass lens mold, in this paper, ultra-precision grinding, measuring, data processing, error compensation processing and ultra-precision processing software development are studied on the basis of a large number of domestic and foreign literatures.In the first chapter, the present researchs such as ultra-precision processing technology, ultra-precision grinding, measurement, compensation and polishing in domestic and foreign are overviewed. The current existing problems of ultra-precision grinding, measurement and error compensation are analyzed and appropriate solution methods are proposed. These key technologies are discussed acoordingly.The first key technology is to study aspheric form measuring system and data processing methods. In the second chapter, an ultra-precision contact measuring method is proposed to research on the error correction of contact measuring data; some measurement errors generated from the probe size error, axis-symmetrical workpeice error in radius direction, inclined angle error and elastic deformation, are also in-depth analyzed. And then, processing approach of measurement data obtained from measurement system is studied. In order to extract the precise figure features of ground workpeice, a multi-filtration method is firstly used to quickly process uniform or non-uniform intensive measured data for accurately deburring; and then a modified regression filtering method is used to quickly filter and smooth the measurement data. At the same time, FFT method is considered to accelerate data processing.The second key technology focuses on wheel centering error, dimension error and form error compensation in aspheric grinding. In the third chapter, based on common aspheric grinding method, single error compensation method is firstly used to compensate the wheel centering errors in X, Y direction, wheel radius error, wear error in ultra-precision grinding of an axis-symmetrical workpeice. A B-axis angle error and compensation are also proposed for right-angle and arc grinding wheels. The separation handling method of comprehensive errors including X-axis centering error, decline angle error, wear error and radius error are considered. Then in the fourth chapter, based on two-axis or three-axis grinding modes, some factors such as contact measuring principle, the probe size, measurement object are taken fully into account to access to the residual error curve and compensate a comprehensive form error. For two-axis orthogonal arc grinding mode, a new symmetrical residual error compensation method is presented to calculate compensation path of grinding wheel. For two-axis inclined grinding mode, a vector residual error compensation method is proposed to control the grinding path of arc wheel center. For three-axis inclined-single-point grinding mode, a single-point inclined-axis residual error compensation mode is also presented. In addition, speed controlling method is considered under a constant grinding volume condition to further inprove the form accuracy and surface roughness.The third key technology is the development of the measurement and error compensation system software for ultra-precision grinding experiments. In the fifth chapter, system software of small ultra-precision aspheric grinding is developed to program two-axis or three-axis NC program for aspheric grinding and compensation processing. The software includes the following functions:the parameter input module, the measuring module, the surface accuracy analysis and evaluation module, the error compensation module, the trajectory display and simulation processing module. And then, in the sixth chapter, a set of ultra-precision grinding and error compensation experiments for axisymmetric spherical, aspherical molds are conducted. Technical experiments include XZ orthogonal error compensation grinding of spherical surface; XZ inclined-axis compensation for aspherical grinding; XZB inclined-axis error compensation experiment for spherical and aspheric glass lens moulds. The experimental results are analyzed to verify the reasonability of ultra-precision grinding, measurement and error compensation methods. At last, on-machine measured data are compared with the off-machine measured data to verify the high precision of the on-machine measurement system.The fourth key technology is to study ultra-precision inclined polishing of magnetic compound fluid and its error compensation methods. In the seventh chapter, in order to obtain a higher form accuracy and lower surface roughness, eliminat surface and sub-surface damage resulted by ultra-precision grinding of small-scale workpiece, an ultra-precision inclined-axis polishing process with magnetic composite fluid is proposed. The equipment of magnetic composite fluid inclined-polishing was developed, and two-dimensional removal and compensation models are built.