Masahiro Yoshida

Analysis of measurement accuracy of quadrilateral hole using optical inner-diameter-measuring machine

We develop a technology for detecting the inner wall (not an edge portion) of a small hole in machine parts such as a die, a nozzle, and a gauge directly and measuring the inner diameter (usually, the inner diameter is 0.3 to 10.0 mm and the length of hole is 1 to 20 mm). Especially, we discuss theoretically and experimentally the measurement error in a gap larger than 0.3 mm of a quadrilateral hole sample using an optical noncontact measuring machine. By projecting a spot image onto the samples inside wall and detecting the reflected image with a CCD camera, the position of the inside wall of the sample can be measured. The inner diameter of the sample can be measured from the distance between the positions of each inside wall. Experimental results show that the measurement error of the gap varies with the gap size of the sample. In a comparison with theoretical simulation results, it is verified that the spherical aberrations of the lens in the measuring machine is the cause of this error. With the maximum spherical aberration of the lens at 50 μm, the maximum measurement error of the gap is +1.0 μm for a 0.3×0.3-mm square hole, and is -0.30 to -0.35 μm for a quadrilateral hole with a gap larger than 0.6 mm. These theoretical results are in good agreement with the experimental results. The measurement error is always negative when the spherical aberration is assumed to be 0.

Development of an automatic detection machine for cracks originating at side faces of ceramic chips

Both surfaces of fine ceramics used for electronic parts are covered with, for example, a resin, a ceramic alumina, or a solder. An automatic optical method for detecting cracks originating at the side faces of ceramic chips, the surfaces of which are covered with the men- tioned materials, is developed and is reported. A laser beam is diffused into the specimen by illumination onto the side faces through an objec- tive lens. When the specimen has a crack near the laser spot, the dif- fused laser light is reflected by the crack and the amount of radiant exitance near the crack is increased. The image of the side face is en- larged by the objective lens and detected by four photomultiplier tubes. It is clarified experimentally that it is possible to recognize the region sur- rounded by a close-ended crack wider than 20 mm and longer than 35 mm, or an open-ended crack longer than 50 mm, by detecting signals higher than the average level. Experimental results revel that the cracks in the ceramic parts can be detected automatically in a production line.

In-process Automatic Detection for Cracks in Dark PZT Plates Using Diffusion of Laser Light.

An automatic in-process detection system for narrow and short cracks in dark PZT plates used for piezoelectric parts has been developed. A crack in a dark PZT plate is difficult to detect because the diffuse reflectance of PZT is very low compared with that of an alumina plate. With this system, the contrast and SN ratio in the crack detection signal are improved. The former is improved by using a polarized beam splitter for separating the incident light beam from the reflected light beam. The latter is improved by illuminating the PZT plate with the optimum radiant flux of a laser and by setting the detection window at an optimum position. The 0.2 mm-long cracks with 1 μm and 3 μ m in width, are detected at 50% detection reliability and 100% detection reliability, respectively, using the laser scanning system developed for the in-process inspection.