基于Gabor变换的大型望远镜跟踪镜的轴承抖动分析

Bearing jitter analysis based on Gabor transformation for trackingmirror of a large telescope

为了解决传统抖动分析方法在TMT(Thirty Meter Telescope,30m望远镜)三镜轴承上的局限性,提出了利用Gabor变换作为抖动性质及信号特性的评价方法。介绍了多加速度计的位置分布及连接方式,详细说明了加速度计在俯仰轴及方位轴上抖动信号的测试过程。在抖动信号数据处理中比较了时间序列法和周期图法的不足,提出了Gabor变换的新方法,Gabor变换可以截取任意时间段上的频谱信息的性质,在时-频域上分析信号的特征,使抖动分析更加真实可靠。最终在某2m级望远镜轴承上做了抖动测量实验,从实验结果可以看到2s内的频率特性曲线,接近0 Hz的低频扰动比较敏感,50 Hz噪声扰动一直存在,470Hz的高频信号时续时断。当轴承顺时针转动时,1 s时有很明显的噪声信号;轴承反向转动时,1.5s^2s时噪声信号突出,降噪后低频噪声依然存在,但高阶频率被激励,保证了信号的真实性.Gabor变换的信号处理方法对于今后大型光电望远镜轴承抖动检测的研究具有一定借鉴意义。

In order to overcome the limitation of the traditional jitter measurement analysis methodfor TMT（ thirtymeter-telescope） tertiary mirror bearing, a mathematical method for the analysis of jitter properties called Gabor transformation was proposed. The location distribution and connection type of muti-accelerometers were introduced,and the measurement process of jitter signals at pitching axis and azimuth axis with accelerometers was fully illustrated. In jitter signal processing,the disadvantages of the time series analysis method and those of the periodogram method were compared. The new method called Gabor transformation was introduced,Gabor transformation could intercept the property of frequency spectrum information at any time interval,the characteristics of a signal was analyzed in time-frequency domain,it made the jitter analysis more real and reliable. At last,the jitter measurement test was performed on a 2 mlong telescope,the frequency properties curve within 2 s showed that the excitations with lower frequencies close to 0 Hz are more sensitive,the noise excitation with 50 Hz always exists,and the high frequency signal with 470 Hz is on and off;when the bearing rotates clockwise,there is an obvious noise signal within 1 s; when the bearing rotates counterclockwise,noise signals is significant within 1. 5 s-2 s; lower frequency noise signals still exist after denoising,and higher frequency ones are excited,the realness of the signal is guaranteed. Gabor transformation provided a reference for the future bearing jitter detection of large photo-electric telescopes.