Nanometric Straightness Measurement of Machine Table Using Laser Beam Straight Datum

对激光作为直线基准的实用化和应用进行了可行性研究。利用四象限光电二极管（QPD）和压电补偿器，研制了专门设计的激光束能量中心二维位置传感器/补偿器。该位置传感器/补偿器的分辨率约为3 nm，截止频率约为200 Hz，以激光束为直线基准，结合QPD位置传感器/补偿器，实现了静压气、油滑台上某点直线运动的二维误差测量，测量精度在3 nm以内。载物台直线运动误差大于50 nm /100 mm。然而，误差运动的重复性已被证实是小于几nm。理论上，完整的分析直线运动的滑台可以执行通过测量的三个不同的点上的工作台上的同时错误的运动。这需要三个平行的激光束作为一组基准，它们在所需的精度内对齐。通过一组平行双激光束的实验，部分地证实了该方法的有效性.影响该方法可靠性的最重要因素是激光光路的位置和角度稳定性.在对激光管的热稳定性和光路中的气流采取预防措施的情况下，窄的He-Ne激光束可用作在200 mm的工作距离上精度为3 nm的直线度测量基准线，测量时间约为1分钟。为了扩展所提出的方法的有用性，本质上需要开发高度稳定的激光束。

A feasibility study is made for the utility and the application of laser beam as a straight datum. By using a quadrant photodiode (QPD) and a piezo-compensator, the specially designed two-dimensional position sensor/compensator for the energy center of the laser beam is developed. The resolution of the position sensor/compensator is estimated to be about 3 nm with the cut-off frequency of about 200 Hz.Combining the laser beam as straight datum line with QPD position sensor/compensator, the two-dimensional error in straight motion of a certain point on hydrostatic air and oil slide tables are measured within the accuracy of 3 nm. The slide tables have straight error motion more than 50 nm /100mm. However, the repeatability of the error motion have been confirmed to be less than a few nm.Theoretically, complete analysis of straight motion of a slide table can be executed by measuring the error motion of three different points on the table simultaneously. This call for three parallel laser beams as a set of the datum which are aligned within a required accuracy. The usefulness of the method has been partly confirmed by the experiment using a set of two parallel laser beam.The most important factor affecting the reliability of the proposed method is the positional and angular stability of the laser beam path. Under the precautions against the thermal stability of the laser tube and the air flow in the beam path, a narrow He-Ne laser beam can be used as the metrological datum line of straightness within the accuracy of 3 nm over the working distance of 200 mm for about 1 minute. To extend the usefulness of the method proposed, the development of highly stable laser beam is essentially required.