Optical Measurement of Surface Texture for Practical use in working fluid of an Electric Discharge Machine and Optimization of its Machining Conditions

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The research purposes are to develop the optical measurement system by which the surface texture of relatively smooth surfaces generated by electric discharge machining can be assessed practically in working fluid and to propose the optimizing control system by which the succeeding machining conditions are adequately renewed during a series of machining processes. The measuring principle is based on laser speckling on image plane. The optical measurement unit composed mainly of an oblique incident laser beam and a waterproofed video image sensor was constructed and attached to the electrode holder of a conventional electric discharge machine (EDM). The power stabilized laser source is isolated from the EDM and connected with the measurement unit by light fiber. The optical lens system of image sensor was designed so that the speckle intensity distribution on an image plane can be measured. The intensity distribution detected by the image sensor is digitized and send to a computer for d … More ata processing. The optical information was evaluated experimentally by not only contrast value but also frequency spectrum. It was realized that spectrum data is important in case of low contrast value. It was also demonstrated that the intensity distribution detected is considerably affected by the working fluid depending on its muddiness or impurity. As a practical compensation means of its influence, two reference surfaces were set in a working fluid chamber to obtain temporary bias data. Through the experimental study it was made clear that the surface texture can be assessed optically in spite of its low accuracy. It was noted that the surface texture generated by EDM is geometrically isotropic and its lateral spacing parameters are correlated fairly well with averaged amplitude. The relative positioning between an optical measurement unit and a work surface was changed to an open-loop control method by NC location data because the positioning by use of detected image data is a complicated and time-consuming process. It was judged that the inter-process optical inspection for adaptive control of electrical discharge machining is feasible for practical use although individual machine characteristics must be taken into account. Less