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In recent years, an increasing number of portable electronic devices, such as portable computers and MP3 digital audio players, have been equipped with hard disk drives (HDDs) to store digital data. In these portable devices, HDDs are exposed to external vibrations and shocks. These external disturbances increase the position error, consequently reducing the performance of the HDDs. We propose adaptive feed forward (FF) control with a single shock sensor to improve the head positioning accuracy in magnetic hard disk drives. Since the transfer function relating the acceleration measured by a shock sensor and the position error signal (PES) depend on the characteristics of the applied force, such as the direction or the frequency, an on-line identification of the relating system is needed. Our proposed scheme applies an adaptive control technique to indirectly identify this relationship, i.e., the coefficients of the finite impulse response (FIR) controller are updated by a gradient algorithm so that the magnitude of the PES is minimized. Our numerical simulations and experiments illustrate the effectiveness of our proposed method.

Abstract-The Naval Postgraduate School is developing a laboratory environment for testing advanced beam control methods for compensation of atmospheric turbulence in adaptive optics for use in a maritime environment. This paper presents a multichannel transverse adaptive filter for beam control. Adaptive filters are useful for such control due to the constantly changing nature of atmospheric turbulence. A multichannel filter is required due to the multiple deformable mirror input commands and wavefront sensor output measurements in the system. The filter is augmented with an integrated bias estimator. Additionally, this paper describes a method for generating horizontal-like atmospheric turbulence by using two liquid crystal spatial light modulators. The development and components of the new laboratory testbed are described, and preliminary simulation results are presented.

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