Development of In-process Optical Sensor for Ultra Precision Machining

本研究项目的目的是研制具有以下特点的光学非接触式位移传感器：(1)分辨率高；(2)测量范围大；(3)可直接测量任意表面的位移；(4)跟踪速度快。该传感器由单模光纤耦合器和用于建立菲佐干涉仪的自聚焦透镜组成。通过测量激光二极管调频产生的拍频信号的相位变化，得到物体表面的位移。通过使用光学隔离器，(A)测量范围从26 mm扩大到46 mm以上；(B)除了可以测量10种粗糙表面外，还可以测量镜面目标的位移。采用三角调制法，与锯齿法相比，(A)分辨率从20 nm提高到10 nm，(B)跟踪速度达到15.4 mm/S。该传感器的性能与物体材料和粗糙度无关。其次，利用该传感器对表面粗糙度进行测量。实验结果表明，该传感器可以测量出与目标的俯仰相似的波。最后，研制了与位移传感器具有相同光学器件的绝对距离传感器。绝对距离是根据差拍信号的频率计算的。实验结果表明，该传感器可以测量45~70 mm的绝对距离，测量精度为2 mm。

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.