Papers by Author: Yutaka Yamagata

Abstract: Micro-aspheric lenses molded by micro-aspheric ceramic molds are increasing in the optical systems such as digital cameras and blu-ray players. To finish the molds with high accuracy and low surface roughness, in this paper, the micro-aspheric mold made of Electroless nickel plating are polished by using the newly developed 5-axis magnetostrictive vibration-assisted polishing machine. The magnetostrictive vibrating polisher generates a lateral vibration at 9.2 kHz with amplitude of 30 μm. The polishing pressure is controlled by a balance adjustment mechanism and the polishing load is controllable within a range of 2 mN ~ 20 mN with a resolution of 2 mN. The motion resolution of the X-Y-Z table is 0.1 μm in each direction. The C-axis rotary table is mounted on a B-axis tilting table and the workpiece is mounted on the C-axis rotary table with a vacuum chuck. According to the polishing experiments, the form accuracy was improved to 200 nm P-V and the surface roughness was reduced to 10 nm Rz (1 nm Ra).

Abstract: Micro structured glass lenses are highly required in new fields such as Micro channels, Fresnel lenses for solar panels and Wafer Level Cameras (WLC). The glass lenses are moulded bypress moulding with micro ceramics moulds made of tungsten carbides (WC). In this paper, a new Vibration Assisted Polishing (VAP) method is proposed and developed by using circular vibration of the magnetostrictive vibrating polisher. The polisher is composed of a magnetostrictive vibrator and a small polishing tool, and the small polishing tool is mounted on the head of the magnetostrictive vibrator. The concrete design of the magnetostrictive vibrating polisher is assisted by the finite element method (FEM) and through vibration mode analysis, the 4th mode is selected. It generates a circular vibration trace at a frequency of 9.2 kHz with a radius of 30 μm. The polisher is fixed in a 5-axis (X, Y, Z, B and C) controlled polishing system. Through some fundamental polishing experiments, the shapes of the removal function is acquired and surface roughness is reduced to 9 nm Rz (1 nm Ra).

Abstract: Demand for glass Fresnel lenses is increasing in solar panel manufacture in order to increase power efficiency. Glass lenses are usually moulded using a glass moulding method with tungsten carbide moulds. In this study, large Fresnel lens moulds made of tungsten carbide are tested to be ground by a simultaneous 2-axis (Y, Z) controlled grinding method. The resinoid bonded diamond wheel is trued with a rare metal truer to increase the sharpness of the wheel edge. In the grinding test of the tungsten carbide mould, a form accuracy of less than 0.8 μm P-V and surface roughness of 18 nm Rz are obtained, and it is clarified that the proposed grinding method is useful for Fresnel grinding.

Abstract: Demands of glass Fresnel lens is increasing in solar panel in order to increase power efficiency. Glass lens is usually molded by glass molding method with tungsten carbide molds. In this study, large Fresnel lens molds made of tungsten carbide are tested to be ground by simultaneous 2-axis (Y, Z) controlled grinding method. The resinoid bonded diamond wheel was trued with a rare metal truer to improve the sharpness of the wheel edge. In the grinding test of the tungsten carbide mold, a form accuracy of less than 0.8 μm P-V and surface roughness of 18 nm Rz were obtained, and it is clarified that the proposed grinding method is useful for the Fresnel grinding.