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.)−136−Synthesiology - English edition Vol.11 No.3 (2018) This technology has been filed for patent and registered as intellectual property (Patent No. 2073658, 1996.7).3 Development of defect inspection system for inner wall surfaces of machined holeWhat triggered machined hole inspection was technological consultation from an automobile parts manufacturer in Hiroshima around 1998, about the inspection of minute aws and defects in the inner walls of automobile hydraulic master cylinders that were parts manufactured by the company. The target was a cylindrical part with an inner diameter of 25 mm, depth of 150 mm, and a mirror-polished inner wall. Since it was hard to view the inner wall by visual inspection and minute defects were often missed, Okada decided to conduct the inspection using laser beams. Since the target part was cylindrical and rotatable, the device shown in Fig. 8 was made as a prototype.[6] If there were no defects when the nely focused laser beam is irradiated onto the inspected surface, the laser beam reflects off without scattering. On the other hand, if there was a defect, the light that hit the defect scatters widely outside the specular reflection light. We realized that if optical bers were installed in a position in which specular reflection light could be received and a position in which only scattered light could be received, the two lights could be separated. Therefore, the specular reection light and scattered/diffracted light were separately received with optical ber bundles with a diameter of 0.5 mm arranged along the circumference of two concentric circles of a diameter of 5 mm and 15 mm from the center of the reected laser beam.Figure 9 shows the panorama images of light intensity data that are shown in a circumferential direction and sampled at 0.2 mm intervals. The image in (a) is the light intensity of the specular reection light and (b) is the light intensity image including the scattered and diffracted light. The (a) image clearly shows spiral indentation defects caused by broken cutting bites, and (b) shows a scratch. It was shown that various defects could be detected at high sensitivity by using specular reflection light and scattered light. The black and grey holes are oil holes and are not defects.Around the same time, President Shitanaka of Sigma Corporation, an automobile parts manufacturer in Kure City, saw the laser defect inspection system that was exhibited at a patent fair. He became interested in semiconductor lasers and requested whether this device could be used for external defect inspection for mass-produced automobile parts with cylindrical shapes. Sigma mass produced small automobile parts and was working on automating inspection with the aim of zero shipment of defective products. It was looking (Abrasion)(Scratch)(Normal)Fig. 7 Differences in diffraction pattern by aw types and examples of measurement by multi-segmentation planar detectorFig. 8 Inspection system for inner wall surfaces of machined holesInspection surfaceMirrorOptical bersSpecular reection lightIncident laser beamLensDiracted lightHydraulic master cylinderInspection probe

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