Fast access control of the head positioning using a digital signal processor

We have developed a new digital servo controller for a 5"hard disk drive which has average access time of 10 ms for a 25 mm stroke. To obtain this fast access speed, we used a state estimator with a new acceleration irajectory model. The estimator and trajectory generator are implemented using a digital signal processor. There are two problems for fast access control: motor coil inductance and the mechanical resonance of the actuator and disk enclosure. To solve these problems and to achieve precise head positioning, we developed the following control method. To solve the voice coil motor inductance and actuator resonance problems, we used a new acceleration trajectory model which is not affected by the coil inductance when the head moves quickly. This design is based on an optinial control theory which minimizes the square of differentiated acceleration. By using this new trajectory model, the high harmonics of actuator drive are damped and the residual vibration ofactuator immediately after access is decreased.