Roundness measuring system for small balls

针对小球圆度测量系统的主轴，研制了一种主动固有节流气体静压轴承。主动固有限流器（简称AIR）是由首席研究员发明的，并结合到几个空气静压轴承和导轨，以改善其性能。空气由一个压电致动器具有一个通孔，孔的一端是足够小的功能作为一个孔时，致动器是嵌入在轴承表面。当传感器检测到轴承表面上的气隙变化时，AIR控制系统的计算机计算压电致动器的电源电压，以改变轴承表面上的压力，并减少主轴的位移和振动。主轴空气静压轴承的主要规格为：外径140 mm，高度86 mm。在不采用主动控制系统的情况下，主轴的回转精度约为0.2mm。使用AIR的主动控制将旋转精度提高到20- 30 nm。轴承的频率响应表明，空气对轴承的动刚度的影响可以看到在低频范围内（小于20 Hz）。然而，由于圆度的计划分辨率为1 nm，因此测量的旋转精度对于圆度测量机的主轴来说是不够的。回转精度不足的主要原因是主轴支承面的几何误差。已经进行了一些努力来提高几何精度，然而，主轴的旋转精度不能提高。

An aerostatic bearing with active inherent restrictors is developed for the main spindle of a roundness measuring system planned to measure small balls. The active inherent restrictor (abbreviated AIR) was invented by the head investigator, and incorporated into several aerostatic bearings and guideways for improving their performances. The AIR consists of a piezoelectric actuator having a through hole, one end of the hole is small enough to function as an orifice when the actuator is embedded in the bearing surface. When a sensor detects the change in the air gap on the bearing surface, a computer of the AIR-control system calculates the supply voltage for the piezoelectric actuator to change the pressure on the bearing surface, and to reduce the displacement and vibration of the main spindle. The major specification of the aerostatic bearing for the main spindle is as follows : the outer diameter is 140mm and the height is 86mm. There are eight AIRs on each radial and thrust bearing surface.Without using the active control system, the rotational accuracy of the main spindle is about 0.2mm. Active control using the AIR improves the rotational accuracy to be 20-30nm. The frequency response of the bearing with the AIR shows that the effect of the AIR on the dynamic stiffness of the bearing can be seen in the low frequency range (less than 20Hz). However, the measured rotational accuracy is not enough for the main spindle of the roundness measuring machine because the planned resolution of the roundness is 1nm. The main reason of the lack in the rotational accuracy is the geometrical error of the bearing surface on the spindle. Several efforts have been performed to improve the geometrical accuracy, however, the rotational accuracy of the main spindle can not be improved.