Study On Tool Path Planning In Diamond Turning Of Freeform Optical Surface

Compared to rotationally symmetric surfaces, freeform optical surfaces can improve the optical performance; reduce the size of the optical system and make optical system lightweight. Therefore, freeform optical surfaces have extensively application requirements in a number of different industrial fields, such as aerospace, national defense, scientific instruments, and et al. The diamond turning based on fast tool servo (FTS) is been recognized as a high-efficiency, high-precision and low-cost processing method. In recent years, there are some substantive researches processes have been made, but there are some problems still not been solved. In this thesis, focusing on the diamond turning of freeform optical surface based on FTS, the methods and influences of tool path planning are emphatically studied. The research contents of this thesis are as follows:(1) The selections of the contour shape and the geometric parameters of diamond tool nose are discussed, which provide the theoretical basis for selecting FTS tool. According to the existing FTS systems such as single axis linear FTS, single axis rotary FTS, two-axis orthogonal linear FTS and two-axis linear and rotary FTS, the tool path planning algorithms for diamond turning of freeform optical surface base on different motion forms of FTS are analyzed and proposed. The algorithms are validated by three typical optical surfaces, and the tool paths of the optical surfaces under different motion forms of FTS are analyzed and compared.(2) The technology process of optical freeform surface generation is discussed. The method which generates the waiting process surface of FTS turning by the best-fit conic surface is proposed, and the fitting algorithm of the best-fit conic surface is generated. According to the cutting principle, the motion forms of FTS and cutting technology parameters are taken into consideration, the three-dimensional (3D) surface topography prediction model of diamond turning of the optical freeform surface based on FTS turning is proposed. And the evaluation mechanism of the optical freeform surface after processing is determined:separating the geometrical form of the surface topography by Gaussian filter, then evaluating the surface topography by comprehensive utilization of Two-dimensional (2D) profile analysis and 3D topography analysis.(3) By 3D topography analysis, the influences laws of the surface roughness and the cutting technology parameters such as spindle speed, feed speed and tool nose radius are analyzed, which provide the theoretical basis for selecting those cutting technology parameters. By 2D profile analysis, the influences laws of the surface quality and the motion forms of FTS are analyzed. From the angle of surface quality, the existing FTS systems are analyzed and compared. And the phenomenon of misdistribution of the optical freeform surface quality based on FTS turning is pointed out. In order to solve this problem, a tool path planning method using in two-axis FTS which controls the scallop-height is proposed.