Development of Picometer Positioning System and its Application for Ultraprecision Machining

针对新一代超精密机床，提出了一种三模皮计定位系统。定位系统有粗、精、超精三种定位模式。采用扭辊摩擦驱动机构和普通交流伺服电机实现长行程纳米定位的粗定位模式。亚纳米定位的精细模式也由扭辊摩擦驱动机构执行，但该机构由压电作动器驱动。采用在静压导轨中加入有源固有限流器（AIR）的超精细模式实现了皮米级定位。两个三模式定位单元垂直布置，定位系统的每一模式由带有微型计算机的DSP（运动控制器）控制。在粗模式下测得定位分辨率为5nm，在细模式下测得定位分辨率为0.2nm。在超精细模式下，当前定位分辨率为25pm。为了提高三模picometer定位系统的性能，设计了一种主动气动静压耦合，其中推力轴承表面的气膜厚度由主动固有限位器（AIRs）控制，轴承的推力刚度可以是无穷大的。因此，在隔离TFD的横向振动的同时，主动气动静压耦合作为刚性耦合工作。主动联轴器也可以用作精细定位装置。最后，我们期望在适当的时候实现皮米级的定位分辨率，并且在本研究中获得的技术知识将有助于超精密机床定位技术的改进。

For ultraprecision machine tool of the next generation, a tri-mode picometer positioning system is proposed. The positioning system has three positioning modes, namely coarse, fine and ultra-fine mode. The coarse mode for nanometer positioning with long stroke is executed by a twist-roller friction drive (TFD) mechanism and an ordinary AC servomotor. The fine mode for sub-nanometer positioning is also executed by the twist-roller friction drive mechanism, however the mechanism is driven by a piezoelectric actuator. The ultra-fine mode using an active inherent restrictor (AIR) incorporated into the aerostatic guideway realizes the picometer positioning.Two tri-mode positioning units are arranged in perpendicular, and each mode of the positioning system is controlled by a DSP (motion controller) with a microcomputer. Measured positioning resolution in the coarse mode is 5nm and that in the fine mode is 0.2nm. In the ultra-fine mode, current positioning resolution is 25pm.For improving the performance of the tri-mode picometer positioning system, we devise an active aerostatic coupling, where the air film thickness on the thrust bearing surface is controlled by the active inherent restrictors (AIRs) and the thrust stiffness of the bearing can be infinite. Therefore, while isolating the lateral vibration from the TFD, the active aerostatic coupling operates as a rigid coupling. The active coupling can also be used as a fine positioning device.To conclude our research, we expect that the picometer order of positioning resolution will be realized in due course, and the technological knowledge obtained in this research will contribute to the improvement of the positioning technology for ultraprecision machine tools.