An Active Air Bearing

提出并构造了一种能够控制轴的两个径向运动的空气径向轴承，并证明了其在低轴转速下的良好性能。这一步的研究重点是发生的问题，当轴旋转超过1000 rpm的高速以及解决这些问题的方法。空气涡轮机安装在轴承。通过这种涡轮机，轴以超过1000 rpm的恒定和高速旋转而没有机械接触。为了执行重复控制（稍后提到），安装了两个非接触式磁阻元件。这些元件在轴每转一圈时产生400个脉冲。在初步的实验中，当轴以1000转/分的速度旋转时，获得了0.3 μ m的旋转精度。采用PID-PDD^2型基本控制器，旋转精度提高到0.1 μ m以下。无法达到更好的准确性。剩余的回转误差具有重复性，是由轴和轴承的圆度误差引起的。为了减小误差，在基本控制器的基础上增加了一个重复控制器（32位微处理器）。实验表明，即使在轴向不平衡的情况下，也可以实现优于25 nm的运动精度。此外，还可以实现旋转轴的快速、超精密定位。由于轴承结构的振动，在1000 rpm以上的转速下无法进行控制。通过改变轴并将空气膜厚度从20 μ m减少到10 μ m来解决这个问题。实验表明，在1740 rpm时，无控轴承的旋转精度约为0.6 μ m。基本控制器将精度提高到0.2 μ m以下，重复控制器将精度提高到15 nm以下。

An air journal bearing, capable of controlling two radial motion of its axis was proposed, constructed and its good performance at low axis rotation speed was demonstrated. This step of research focuses on problems which occur, when the axis is rotated at a high speed of more than 1000rpm as well as solutions for these problems.An air turbine was installed in the bearing. By this turbine, the axis is rotated without mechanical contact with a constant and high speed of more than 1000rpm. In order to execute a repetitive control (mentioned later), two noncontact magnetoresistive elements was installed. These elements generate 400 pulses per each revolution of the axis. These pulses express the angle of rotation of the axis.In preliminary experiments, a rotation accuracy of 0.3mum was obtained when the axis is rotating at 1000rpin. By using a basic controller of PID-PDD^2 type, the rotation accuracy was improved to less than 0.lmum. A better accuracy could not be achieved. The remaining rotation error had repeatability and it was caused by roundness errors in the axis and the bearing. In order to reduce the error, a repetitive controller (a 32 bit microprocessor) was added to the basic controller. Experiments showed that, even with a imbalance in the axis, a motion accuracy better than 25nm can be achieved. Moreover, a fast and ultra-precise positioning of the rotating axis is possible.Because of vibrations in the bearing structure, the control was not possible at a rotation speed higher than 1000rpm. This problem was solved by changing the axis and reducing the air film thickness of 20mum to 10mum. Experiments showed that at 1740rpm, the rotation accuracy of the uncontrolled bearing is approximately 0.6mum. This accuracy is improved to less than 0.2mum by the basic controller and to less than 15nm by the repetitive controller.