Stabilization of Removal Rate in Small Tool Polishing of Glass Lenses

Abstract

The demand for improving the image quality of cameras has increased significantly, especially in industrial fields such as broadcasting, on-vehicle, security, factory automation, and medicine. The surface of glass lenses as a key component of cameras is formed and finished by polishing using small tools. The existing polishing technologies, however, exhibit serious problems including an unstable material removal rate over time. In our previous work, the mechanism of time variation in material removal rate was clarified. Based on the findings, a vibration-assisted polishing method using polishing pads containing titanium dioxide particles was developed for improving the stability of the material removal rate with the accumulated polishing time. Our experiments revealed that the proposed polishing method suppressed the time variation significantly in the material removal rate. The developed polishing pads, however, possessed a short life because of their poor wear resistance; as such, they could not be applied to the mass-production process of lenses. In this study, we applied the vibration-assisted polishing method to the polishing process using commercial polishing pads that exhibit sufficient wear resistance for practical use. To investigate the effect of vibration on the stability of the material removal rate, polishing experiments and the observation of slurry flow on the surface of the polishing pads during the vibration-assisted polishing process were conducted. Based on the findings, a new polishing method utilizing a large-amplitude high-frequency vibration applied to the polishing pressure was developed. In addition, a new polishing method utilizing the overhang of a polishing pad, where the polishing pad was moved to hang over the edge of the workpiece for incorporating periodic dressing processes of the polishing pad surface during the polishing process, was also developed. Our polishing experiments revealed that both the proposed polishing methods improved the stability of the material removal rate significantly over the course of the polishing process.