LQG optimal compensation of contact-induced vibration in high density HDD servo systems

In this paper, a linear-quadratic-gaussian (LQG) controller is proposed in the frequency domain for active compensation of contact-induced vibration (CIV) in high density hard disk drive (HDD) servo systems. Such kind of vibration is due to continuous contact of the read/write head with the media in HDDs. Based on the modeling result of CIV dynamics, nominal LQG design is first presented with the aid of coprime factorization technique of transfer functions. To address the robustness of the proposed controller under severe spectral uncertainties of CIV, we convert the optimal LQG design into a minimax problem, which may be solved based on saddle point theory. Different from many other control strategies presented for non-repeatable runout (NRRO), such as basis function method that actually compensates the dominant components in NRRO, the LQG controller can suppress the infinitely many frequency components simultaneously. In the end, numerical simulation is performed to validate the performance of the proposed method in CIV compensation.