Generalized sinusoidal trajectory for seek servomechanism of hard drives

Abstract

A hard disk drive moves a transducer across a disk surface so that the transducer has an essentially generalized sinusoidal acceleration trajectory. A digital signal processor known as a controller is used to control the movement of a transducer. The function of a controller is to move the transducer from its present track to a target track in accordance with a seek routine and a servo control routine. During the seek routine the controller moves the transducer in accordance with a generalized sinusoidal current trajectory, which is devised to be a current profile for the seek control to move a transducer from one position to another position robustly and as fast as possible. To form the generalized sinusoidal trajectory, a constant acceleration phase is inserted in the middle of the acceleration phase and also a constant deceleration phase is inserted in the middle of the deceleration phase. For seeks without coast mode, the current trajectory can be divided into five phases based on seeking status. Excluding the phases for constant acceleration and constant deceleration, the current profile becomes a full cycle of sinusoidal wave. Therefore, the generalized sinusoidal waveform is a generalization of the standard sine wave, which has the capability to stay at its design peak for certain duration of time. As a seek trajectory for current, the generalized sinusoidal waveform has three distinguishable characteristics. First, the seek trajectory is capable of a fast seek time design. Second, this seek trajectory is more manageable and smooth than the classical bang-bang control. Third, this seek trajectory provides smooth transition from phase to phase. The current profile is flexible, general and powerful to achieve descent seek performance. When the duration of constant acceleration and constant deceleration is equal to one half of the total seek time, the trajectory reduces to bang-bang curve. When there are no constant acceleration phase and constant deceleration phase, the trajectory reduces to the simple one-frequency sinusoidal wave. Compared to the classical bang-bang control, the generalized sinusoidal waveform has a narrower frequency spectrum, which is less likely to excite mechanical resonance and, therefore, generates lower acoustic noise. The generalized sinusoidal waveform is a new class of trajectories, which has a transducer movement time falling in a range between the sine wave and bang-bang curve depending on its design parameters.

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