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As the national metrology institute (NMI), we are focusing on the development and dissemination of measurement standards, promotion of measurement standards utilization, development of measurement technologies related to measurement standards, legal metrology work and training of experts. Our activity covers engineering, physical, material, and chemical measurement standards. It also covers development of measurement and analytical instrumentation. We also coordinate international activities on metrology standards as a national representative.
Researchers at AIST have developed a high-precision sphericity calibration system of reference spherical lenses with an uncertainty of 4.3 nm. High-precision compact lenses are indispensable for cameras used in smartphones, endoscopes, etc. to obtain high-definition images. To achieve high precision in optical elements such as lenses and mirrors, it is necessary to fabricate the absolute profile of the element with the designed profile at the nanometer level. Therefore, it is necessary to precisely and accurately measure the processed surface profile and evaluate the deviation from the designed profile. The high-precision profile measuring apparatus measures the sample profile by referring to the reference spherical lens with a high sphericity. The sphericity of the reference spherical lens determines the accuracy of the measurement. In the sphericity calibration system using laser interferometer, we have established a system to easily calibrate reference spherical lenses of any f-number used in the industry by a practical method called the random ball test. We have also established an uncertainty evaluation method based on a detailed analysis of measurement errors caused by misalignment of the optical system. By adopting the random ball test and the uncertainty evaluation method, we have realized a calibration system for user's reference spherical lens of any f-number with a measurement uncertainty of 4.3 nm. Through the calibration system for reference spherical lenses used in industry, we will contribute to the development of high-precision optical elements and the advancement of product quality control.
Relation between AIST's sphericity calibration system and reference spherical lenses used in production sites
Researchers at AIST have developed a technique to improve the reliability of shape measurement on industrial products. Several industrial products need to be manufactured with micrometer-order precision. For turbine blades used in generators and engines, the slightest deviation from the designed shape not only affects the efficiency of power generation and rotation, but can also cause trouble during operation. Therefore, the shape of industrial products must be accurately evaluated using a Coordinate Measuring Machine (CMM). However, when curved surfaces with a radius of curvature smaller than a few millimeters are measured with a tactile CMM, errors of a few micrometers can occur due to the data processing in the measurement by use of a probe tip with a finite size of approximately 1 mm in radius. In this research, we have developed a method to reduce measurement variation to the sub-micrometer order by applying morphological operation, which is used for noise reduction in image processing and surface roughness measurement, to the measurement using a tactile CMM. We have also applied the developed method to the measurement of a turbine blade edge profile, and have demonstrated that the measurement variation is reduced. This is expected to improve the reliability of shape measurement on industrial products and lead to assurance of quality and safety, such as dimensional accuracy. Details of this research were published online in Precision Engineering on September 11, 2024.
Conventional and developed method for shape measurement of turbine blades, etc., using tactile coordinate measuring machine
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