Papers by Author: Masahiko Fukuta

Abstract: Large aperture lenses with high surface quality are demanded for professional imaging products such as single-lens reflex cameras and astronomical telescopes. Large aperture optical lenses are shaped by ultra-precision grinding and finished by prolonged polishing. However, the prolonged polishing process leads to deterioration of the form accuracy. In order to reduce the amount of polishing, ductile-mode ultra-precision grinding is demanded. In this study, a rubber bonded wheel, which has a low elastic modulus, is used for grinding of spherical glass BK7, and influence of the hardness of the rubber bonded wheel and abrasive chip thickness on brittle fracture and surface roughness are experimentally investigated.

Abstract: Large-aperture lens used for single-lens reflex cameras is generally produced by both ultra-precision grinding and polishing because a mass-produced lens by molding process can hardly achieve the required form accuracy and surface quality. Recently, grinding process of an optical glass should make surface quality as high as possible in order to reduce removal amount in polishing process. Accordingly, evaluation of subsurface damage induced under various grinding conditions has been required because subsurface damage leads to crack initiation or deterioration of the performance. However, evaluation method of subsurface damage on the spherical glass lens after grinding has not yet been established.In this study, the quantitative evaluation method by applying wet-etching of hydrofluoric acid (HF) is proposed, then its validity is verified. From the experimental results, we clarify to evaluate the subsurface damage by examining the surface transition according to etching time.

Abstract: The demand for large aperture lenses with high surface quality and form accuracy used for single-lens reflex cameras has been increasing. Generally, large aperture glass lenses are produced by ultra-precision grinding. Considering the increasing global competition, the grinding process has to be improved. However, highly efficient grinding causes worse surface quality, which leads to much polishing and ultimately results in lower form accuracy. Thus in this study, aiming at the realization of highly efficient and precise grinding of glass lenses, cross grinding of optical glass BK7 is carried out. As a first step of the study, the influence of grinding conditions on the surface quality is investigated experimentally.

Abstract: This paper presents the dynamic response of an air-bearing displacement sensor for on-machine surface form measurement of micro structures. The on-machine measurement system has some merits in terms of measurement efficiency and re-machining for error compensation after measurement. On the other hand, the performance of the contact type measurement system based on stylus methods is dominated by the dynamic characteristics of the system because the system is subject to random vibrations of the machine tool including the spindle during measurement. Therefore, the dynamic response of the system is useful for analyzing the mechanical vibrations of the practical on-machine measurement system. In this paper, the equation of motion for the air-bearing displacement sensor to the excited input displacement is derived and the displacement behavior of the system by using a PZT actuator is investigated within certain frequency ranges experimentally for identifying the dynamics of the system.

Abstract: The requirement of the ultra-precision machine tools for ductile cutting of hard brittle materials was examined experimentally. One of the essential factors of achieving ductile mode cutting was not only high-resolution feedback control but also the dynamic performance of the machine tool in forming solid immersion lens of monocrystalline silicon. We also proposed newly developed method for ultra-precision machine tools, which does not have enough high dynamic performance in order to achieve ductile mode cutting of the hard brittle materials. An additional device consisted of air slider on the machine tool was applied to cutting of glass in order to keep stable ductile mode cutting. We fabricated high-value added structure, which are designed a diffraction grating, consisted of micro groove on a borosilicate crown glass surface with the developed device.