A Study of Micro-Grinding and Inspection for Aspheric Glass Lens

This study discussed abrasive machining of aspheric glass lens, with the aim to increase the aspheric lens machining efficiency and reduce the back-end polishing process. The discussions covered "optical lens design", "Taguchi method optimization", "grinding force measurement", and "on-line real-time inspection". A window interface was designed by using Borland C++ Builder for optical glass design. The aspheric design parameters were substituted in it to obtain the machining path. In terms of Taguchi method optimization, the performance of electroformed grinding rod was compared with that of resin grinding rod. Taguchi method was used to look for optimization, and the quality characteristic was surface roughness. After experimental analysis, the optimization results were: using a resin binder grinding rod, the optimum parameter of 50,000 (rpm), forward grinding, feeding at 10 mm/min, grinding depth at 0.02mm, and aspheric lens surface roughness of 0.03μm. In terms of grinding force measurement, an eight-ring strain gage dynamometer was designed to measure the optimum grinding force. The measurement result showed that the grinding force in vertical direction was 3.2kg, and that in horizontal direction is 4kg. In terms of visual inspection, a CCD camera was mounted on the machine, which takes the image of workpiece immediately after it is machined. The form was inspected, and the dismounting error was reduced.

Studies on Mega-Pixel Cell Phone Lenses Based on Aspheric Optics

According to the principle of optical design, two kinds of 2 Mega-pixel cell phone camera lenses are proposed. One is made up of three plastic (3P) lenses; the other is made up of two plastic lenses and one glass (2P1G) lens. The shapes of all lenses are aspheric. By comparison, the overall length of 2P1G lens is much less than that of 3P lens. Furthermore, in FOV the former is 5 degrees larger than the latter. At the same time, in distortion of the maximum field angle, the former is much less. The other aberrations of 2P1G lens are almost same to those of 3P lens. Therefore, in cell phone camera lens design, it’s recommended to adopt one aspheric glass lens to improve the performance and compactness though the cost will become a little higher due to the introduction of aspheric glass lens. However, the cost of aspheric glass lens could be reduced tremendously by a new cost-effective manufacturing method  compression molding technology.

A Framework of Cooperative Design for Aspheric Glass-Lens Mold

The lens molding technology has become a promising fabrication method for glass lens, especially for aspheric glass lens in batch. Because during the real compression molding, the error compensation for mold shape turns very difficult, the mold needs to be repaired repeatedly to meet the requirements of lens molding. To solve this problem, a cooperative design scheme is proposed. However, the scheme is not limited to solving the mold repairing; it also aims to providing the integrated and optimal design for aspheric glass-lens mold. In fact, the cooperative scheme is a collaborative software platform, which integrates with data processing, optical design, finite element analysis, error compensation and mechanical design for lens molding. On this platform, users only need to submit the (camera) lens parameters or measured data of aspheric lens, and then the platform can provide the final mold drawings, which will be input in the CNC software of ultra-precision machine and guide the mold fabrication. Meanwhile, the cooperative platform is Network-based PDM system, so designers could remotely communicate with it and help to finish the mold design jointly. In this case, the cooperative design could tremendously improve the efficiency and accuracy of lens molding.

An Experimental Study on Flow Characteristics of PBK-40 for Glass Molding Press Simulation

Remarkable progress had been made in both technology and production of optical elements including aspheric lens. Especially, requirements for machining glass materials have been increasing in terms of limitation on using environment, flexibility of material selection and surface accuracy. In the past, precision optical glass lenses were produced through multiple processes such as grinding and polishing, but mass production of aspheric lenses requiring high accuracy and having complex profile was rather difficult. Against such a background, the high-precision optical GMP process was developed with an eye on mass production of precision optical glass pasts by molding press. This GMP process can produce with precision and good repeatability special form lenses such as for cameras, video cameras, aspheric lenses for laser pickup, f-θ lens for laser printer and prism, and fine glass parts including diffraction grating and V-grooved base. Generally, GMP process can be classified into batch and progressive type. In these types, because progressive type has many merits in that productivity is higher and repair/retouch of mold is easier than batch type, progressive GMP process is mainly used to produce aspheric glass lenses these days. In this paper, as a fundamental study to develop the multi-cavity mold for higher productivity of progressive GMP process used in fabrication of aspheric glass lens, compression tests for K-PBK40, which is the material of aspheric glass lens, were conducted at high temperature. As a result, flow characteristics of K-PBK40 were obtained for aspheric glass lens press simulation.