Developmental Study on Control of Large Telescope System

7.5米工程计划使用20厘米厚度的薄半月板镜。这样薄的镜子很容易因自重而变形。因此，它的目的是控制镜面的支撑力，并通过使用执行器来控制镜面。采用有限元法对反射镜自重引起的挠度进行了计算。研究发现，在50kg的最大载荷下，需要390个支撑点左右，支撑力精度必须达到1x10^<-4>。结果表明，由滚珠丝杠和弹簧组成的执行机构是最可靠的执行机构。滚珠丝杠由马达旋转并推动弹簧将垂直运动转化为力。力是用测力元件测量的。将计算值与力信号的差值反馈给电机以抵消差值。对测试执行器进行了大量的构造和测试。对称重传感器和几个机械部件进行修改，使轴向支撑力的误差最小为（+-）5g（最大），相当于音叉式称重传感器本身的精度。由此得出结论，该驱动器设计可用于镜面控制。

The use of thin meniscus mirror of 20-cm thickness is scheduled for the 7.5-m projectg. Such a thin mirror is easily deformed by a self weight.d It is, therefore, intended to control the supporting fprce of the mirror and to control the mirror surface by the use of actuators. Deflection calculations of the mirror due to the self wight were carried out by the finite element method. It was found that about 390 support points are needed and the accuracy of the supporting force must be as high as 1x10^<-4> for the meximum load of 50-kg. It was concluded that the actuator consisting of a ball-screw and a spring is the most reliable device. The ball-srew is rotated by a motor and pushes the spring transforming the vertical motion to a force. The force is measured by a load-cell. The difference of force signal from the calculated value is fed back to the motor to cancel the difference. The test actuator was constructd and tested extensively. Modifying the load cell and several mechanical parts, the error in the axial support force was made as small as (+-) 5 g (max), which was eauivalent to the accuracy of the tuning-fork type load cell itself. Thus, it is concluded that this design of actuator can be used for controling the mirror surface.