Roundness measuring system for small balls

针对计划用于测量小球的圆度测量系统的主轴，研制了一种带有主动固有限制器的气体静压轴承。主动固有限制器(简称AIR)是由首席研究员发明的，并被整合到几个空气静压轴承和导轨中，以提高它们的性能。空气由具有通孔的压电致动器组成，当致动器嵌入轴承表面时，该孔的一端足够小以起到孔口的作用。当传感器检测到轴承表面气隙的变化时，空气控制系统的计算机计算压电致动器的电源电压，以改变轴承表面的压力，减少主轴的位移和振动。主轴气体静压轴承的主要技术指标为：外径140 mm，高度86 mm。主轴的径向和推力轴承表面各有8个气隙，在没有采用主动控制系统的情况下，主轴的回转精度约为0.2 mm。利用空气进行主动控制，使旋转精度提高到20-30 nm。轴承在空气作用下的频率响应表明，在低频段(小于20赫兹)可以看到空气对轴承动刚度的影响。然而，由于圆度的计划分辨率为1 nm，因此对于圆度测量机的主轴来说，测量的回转精度是不够的。回转精度不高的主要原因是主轴轴承面的几何误差。为了提高主轴的几何精度，人们已经做了很多努力，但是，主轴的回转精度并没有得到提高。

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.