In DVD focus servo system, the skew of the disc induces periodic disturbance whose frequency is the same with the rotationfrequency of the disc.
在DVD聚焦伺服系统中，光盘翘曲会导致产生与光盘转动频率相同的周期性扰动。
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At the same time optical rotation of the particles was realized. The rotationfrequency was measured by CCD camera and quadrant photodiode detector (QD).
Time domain synchronous averaging can reduce the signal not coherent to rotationfrequency effectively, and extract the repetitive signals directly related to machine operation condition.