Researchers) KONDO Yohan, Senior Researcher, HIRAI Akiko, Group Leader, KAWASHIMA Natsumi, Researcher, BITOU Youichi, Deputy Director, Research Institute, Length Standards Group, Research Institute for Engineering Measurement, National Metrology Institute of Japan, KATSUBE Toshiharu, Panasonic Production Engineering Co., Ltd.
Researchers at AIST, in collaboration with Panasonic Production Engineering Co., Ltd., have developed a sphere diameter measurement technology that achieves the world's highest level of accuracy.
In recent years, in fields where high-definition images are essential, such as in-vehicle cameras and endoscopes, optical components increasingly adopt free-form geometries to enhance optical performance. For free-form lenses and mirrors, it is crucial not only to minimize surface profile deviation to the nano-level but also to ensure that the absolute shape, including the radius of curvature, aligns with the design shape at the nano-level. Achieving this requires not only nano-level processing technology but also shape measurement technology that matches or surpasses the precision of nano-level processing.
The accuracy of absolute shape measurement in profilometers of optical components such as free-form lenses and mirrors, depends on the calibration accuracy of the sphere diameter used as a reference for the measuring instrument. Until now, the calibration accuracy of sphere diameter has had an uncertainty of approximately 100 nm to 200 nm, which is not superior to the measurement resolution and repeatability of free-form surface profilometers. In this study, we developed a sphere diameter calibration method using a micro-coordinate measuring machine(µ-CMM) equipped with a low-contact force probe system and a silicon gauge block as the reference. This method enabled measurement of sphere diameters with an uncertainty of 15 nm. By using this sphere as a reference for free-form surface profilometers, it is expected to improve the accuracy of free-form surface measurements.
Details of this research were published in Precision Engineering on December 7, 2024.
In advanced industries and fundamental research, achieving optical components with shape accuracy guaranteed at the nano-level is becoming increasingly essential. For example, enhancing the precision of spherical and aspherical lens shapes is a constant demand for improving the performance of compact camera lenses used in smartphones, in-vehicle camera lenses supporting advanced driver assistance systems (ADAS) and autonomous driving (AD), and lenses for endoscopes. In the field of semiconductor lithography equipment and fundamental scientific fields, such as synchrotron radiation facilities utilizing X-rays, focusing mirrors required in these applications have evolved from spherical to non-axisymmetric and aspheric shapes, with the demanded shape accuracy reaching nano-level precision. The design of these optical components is becoming more complex each year, evolving towards free-form shapes aimed at minimizing aberrations. To realize free-form optical components with nano-level precision, not only advanced polishing and processing technologies but also highly accurate shape measurement and evaluation techniques are indispensable. For example, if the deviation of a fabricated lens from its design shape can be accurately measured, ultra-precision processing technologies can be developed to correct those deviations at the nano-level.
Journal: Precision Engineering
Title: Two-point diameter calibration of a sphere by a micro-coordinate measuring machine using a silicon gauge block as a reference standard
Authors: Yohan Kondo, Akiko Hirai, Toshiharu Katsube, Natsumi Kawashima, and Youichi Bitou
DOI: https://doi.org/10.1016/j.precisioneng.2024.12.003