Development of In-process Optical Sensor for Ultra Precision Machining

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The aim of this research project was to develop the optical non contact displacement sensor which has following characteristics : (1) high resolution, (2) large measurement range, (3) direct displacement measurement capability for any surfaces and (4) high follow-up speed. The developed sensor comprises a single mode optical fiber coupler and a selfoc lens for setting up a Fizeau type interferometer. The displacement of the object surface is obtained by the measurement of the phase change of the beat signal generated by a frequency modulation of the laser diode.First, the basic performance improvement method of the sensor was discussed. By using the optical isolator, (a) the measurement range was enlarged from 26mm to more than 46mm, and (b) the displacement of the mirror target could be measured in addition to 10 kinds of the rough surfaces. By using triangular modulation method, in comparison with the sawtooth one, (a) the resolution was improved from 20nm to 10nm, and (b) 15.4 mm/s follow-up speed was obtained. The performance of the sensor was independence of object material and roughness.Secondly, By the sensor, the surface roughness was tried to measure. The experimental results shows that the sensor can measure the wave of which the pitch is similar to that of the target.Lastly, the absolute distance sensor which has the same optical devices as the displacement sensor was developed. The absolute distance is calculated from the frequency of the beat signal. The experimental results prove that the sensor can measure the absolute distance from 45mm to 70mm with 2mm accuracy.