An Active Air Bearing

提出了一种能够控制轴向两个径向运动的气体滑动轴承，并对其在低轴转速下的良好性能进行了验证。这一步的研究重点是当轴以超过1000rpm的高速旋转时出现的问题以及解决这些问题的方法。通过这种涡轮机，轴在没有机械接触的情况下旋转，恒定的高速超过1000rpm。为了执行重复控制(后述)，安装了两个非接触式磁阻元件。这些元件每转一圈就产生400个脉冲。这些脉冲表示了轴的旋转角度。在初步实验中，当轴以1000rins的速度旋转时，旋转精度达到了0.3um。通过采用基本的PID-PDD^2型控制器，使系统的回转精度提高到0.1微米以下。不可能达到更好的准确度。剩余的回转误差具有重复性，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，即使在轴线不平衡的情况下，也可以获得优于25 nm的运动精度。此外，旋转轴的快速和超精密定位是可能的。由于轴承结构的振动，在高于1000rpm的转速下无法进行控制。通过改变轴线，将气膜厚度从20微米减小到10微米，解决了这个问题。实验表明，在1740rpm转速下，无控轴承的旋转精度约为0.6um。基本控制器的精度提高到0.2um以下，重复控制器提高到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.