High performance HDD servo system using GA based fixed structure robust loop Shaping control

High aerial density is needed for improving the capacity in Hard Disk Drive (HDD). In order to achieve this task, tracking performance and robustness of HDD servo system need to be improved. H_¿ robust controller is one of the most popular techniques for the mentioned problem; however, order of this controller is usually higher than that of the plant, making it difficult to implement practically. To overcome this problem, this paper proposes a new technique for designing a robust controller for HDD with Voice Coil motor (VCM) actuator. The control design problem, H_¿ loop shaping with structured controller, is solved by GA. Infinity norm of the transfer function from disturbances to states is used as the cost function in our optimization problem. The proposed technique does not only solve the problem of complicated and high order controller but also still retains the robust performance of conventional H_¿ control technique. In addition, structured pre-filter is also designed by GA to enhance the performance in terms of time-domain tracking. Simulation results in a HDD control system show the effectiveness of the proposed technique.