Vol.11 no.3 2019

Research paper : Development and commercialization of laser inspection system to detect surface aws of machined holes (S. OKADA et al.)−141−Synthesiology - English edition Vol.11 No.3 (2018) Sigma became the top selling company of this niche market of defect inspection systems for interior of holes in Japan, but as shown in Table 2, various hole interior inspection systems with diverse methods were sold in Japan. However, there was no uniformity in performance indication, and the user companies were confused. Esaki felt the need for standardization of defect inspection systems and started activity for standardization in Japan. In 2015, a committee for drafting the proposal for standardization was established with the support of the Hiroshima Industrial Promotion Organization. Device manufacturers and user companies were asked to participate, and an application was submitted to the standardization system for the creation of new markets of the Japanese Industrial Standards Committee. The proposal was accepted, and the discussions for standardization are currently in progress.6 Scenario for road to industrial application of semiconductor lasersStarting with technological consultation from a local company, the collaborative research unit launched R&D for a laser defect inspection that was demanded by industry. Figure 16 shows the flow of product realization through technological development at AIST and collaboration with Sigma explained above. First, to realize defect inspection for inner walls of small and glossy cylindrical parts, we developed a high-sensitive inspection system that separated and measured the diffracted light unique to laser beams that were produced by defects. However, just before commercialization, continuation of R&D seemed difficult due to the re-structuring of AIST, but the development and product realization of a laser defect inspection system of a probe rotating type were continued by establishing a research organization called a collaborative research unit. However, due to the Lehman Shock that occurred suddenly, Sigma faced a crisis of retreat from business, but the policy was changed to meet the demands for inspection of the interior of small holes. As a result of developing a high-speed laser defect inspection system for holes with small diameters that matched the demands of companies, business expanded rapidly. Currently, utilizing the standardization system for the creation of new markets, domestic standardization is being conducted by calling on others in the same industry, and we are also preparing for international standardization in anticipation of overseas expansion.There were two large turning points in the development and commercialization of the laser defect inspection system. Difficulties were overcome by the ingenuity of AIST and a local company, and Sigma was able to send out the ANALYZER to the world. The device system was purchased by automobile manufacturers such as Toyota Motor Corporation, Honda Motor Company, Ltd., Mazda Motor Corporation, and others, as well as automobile parts manufacturers including Denso Corporation, Aisin Seiki Co., Ltd., Mitsubishi Heavy Industries, Ltd., and others. Sales are increasing to foreign companies such as Daimler AG.7 Development of next-generation inspection system through collaboration crossing regional centersAIST sets its important goal as the development of Table 2. Commercially available inspection systems for inner wall surfaces of machined holes (from HPs of respective companies)CharacteristicLaser reection typeCamera imaging typeCamera imaging typeLaser reection typeEddy current typeMeasurement principleSigma CorpCompany DCompany CCompany BCompany AName of manufacturerTwo ND probes are arranged facing each other at 180° to detect cavities and cracks, and four air jets are arranged facing each other at 90° to measure interior diameters. It is necessary to change the probe diameter according to the work piece diameter. Applicable diameter of hole: 40 mm or more.Laser beam is irradiated on one of the two optical bers, the beam is focused to 50 μm using the lens at the tip and irradiated perpendicular to the interior metal surface, specular reection light is collected with another ber, and light intensity is measured by PD. The entire inner surface of a hole is inspected by high-speed rotation of a 45° mirror on the probe tip. The focal depth is shallow since the lens is short-focus. Applicable diameter of hole: 2 mm or more.The characteristic is to shoot ne images inside cylinders with a high resolution area camera and light rotation mechanism in which several mirrors are rotated in synch. The structure is complex. Applicable diameter of hole: 60 mm or more.The tip of an acrylic rod is machined into an inverted cone shape, the inner wall surface is illuminated with a ring lamp from the other end, an image of the inner wall projected on the conical surface of the tip is shot with a camera, and defects are inspected by image processing. It is compact and lightweight since there is no rotating part. Applicable diameter of hole: 6 mm ~60 mm.Laser beams are irradiated perpendicularly to the inspection surface using a long-focus lens, part of specular reection light is irradiated on several optical bers that are arranged along the circumference at the probe tip, light intensity is measured by PD, and defects are determined by changes in light intensity. Since a long-focus lens has deep focal depth, there is no reduced sensitivity due to displacement. Applicable diameter of hole: 4 mm or more.

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