An Active Air Bearing

提出并构造了一种能够控制其轴向两次径向运动的空气轴颈轴承，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轴在超过1000rpm的高速旋转时出现的问题以及这些问题的解决方案。轴承上安装了一个空气涡轮。通过这种涡轮机，轴在没有机械接触的情况下以超过1000rpm的恒定高速旋转。为了执行重复控制（后面会提到），安装了两个非接触式磁阻元件。这些元件每绕轴一圈产生400个脉冲。这些脉冲表示轴的旋转角度。在初步实验中，当轴以1000rpin旋转时，旋转精度为0.3mum。采用PID-PDD^2型基本控制器，将旋转精度提高到小于0 μ m。没有比这更好的精度了。剩余的旋转误差具有重复性，它是由轴和轴承的圆度误差引起的。为了减少误差，在基本控制器上增加了一个重复控制器（一个32位微处理器）。实验表明，即使在轴向不平衡的情况下，也能获得优于25nm的运动精度。此外，旋转轴的快速和超精确定位是可能的。由于轴承结构中的振动，在转速高于1000rpm时不可能进行控制。通过改变轴向，将20mum的气膜厚度减小到10mum，解决了这一问题。实验表明，在1740rpm时，非受控轴承的旋转精度约为0.6mum。该精度通过基本控制器提高到小于0.2 nm，通过重复控制器提高到小于15nm。

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.