大口径光学望远镜油垫非线性干扰的检测与抑制

研究了静压油垫带来的非线性干扰对大口径天文光学望远镜跟踪精度的影响。分析了油垫干扰的成因;综合采用加速度计法和编码器法,精确测得了油垫的非线性干扰频率;通过分析油垫开启前后的振动曲线、编码器位置曲线及其快速傅里叶变换（FFT）曲线,提出了油垫液压振动是一种窄带干扰。然后,采用Notch数字滤波器,将陷波频率设置在主要干扰频率处来抑制油垫液压振动干扰。给出了滤波器的具体设计过程及其Bode图和零极点图。当需要调整油膜厚度时,可改变Notch参数来适应干扰频率的变化。最后,给出了带Notch滤波器的控制系统和滤波结果。仿真和2.5 m天文望远镜的实验结果表明：通过检测并抑制油垫0.825 Hz的主要干扰,望远镜可在保证运动控制系统原有的稳定性和响应能力的情况下,方位轴跟踪精度达到RMS值为0.0837″,PV值为0.571″。相对于脉动衰减装置,该方法灵活、简单、通用性好。

Detection and suppression of oil pad nonlinear disturbance for large optical telescope

This paper explores the effect of nonlinear disturbance of a static pressure oil pad in an optical astronomical telescope on the tracking accuracy. Firstly, the causes of oil pad disturbance are analyzed and the frequencies of nonlinear disturbances are measured accurately with accelerometers and an encoder. By analysis of the vibration curve of the accelerometer, the position curve and Fast Fourier Transfer(FFT) curve of the encoder when the oil pad is turning on or turning off, it points out that the vibration of oil pad is narrow band interference. Then, a Notch filter is proposed to suppress the oil pad disturbance by setting the central frequency at the main disturbance frequency. The design process of the proposed method is discussed in detail. The bode diagram and the zero-pole map of Notch filter are given. When oil film thickness needs to be changed, the Notch frequency band can be adjusted flexibly by changing the parameters of Notch filter. Finally, the control system with Notch filter is implemented and filtering results are shown. Simulation and experimental results of tracking and pointing on a 2.5 m astronomical optical telescope indicate that the tracking precision of the azimuth system is 0.083 7″RMS and 0.571″PV by measuring and eliminating the main noise at 0.825 Hz .As comparing with pressure fluctuation attenuation devices, the proposed method shows the advantages of convenience, flexibility and good universality.