Study On Servomechanism Control For Hard Disk Drive Systems Based On Discrete-time Sliding Mode Control Techniques

Since IBM brought the first disk - the random access memory accounting machine (RAMAC) to market in 1956, the storage capacity and read/write speed have continuously increased along with the development of the techniques of media, read/write head, actuators and semiconducting chips. The problems of R/W head's settling control is definitely important in order to ensure the reliability of read and write performance. Track seeking and track following are two main stages of the hard disk servo system. Researchers have developed kinds of control strategies to implement the servo control from PID control to advanced control methods. Dual-stage actuator has attracted many researchers and engineers for its broader bandwidth compared with single-stage actuator.Sliding mode control (SMC) is an important branch of nonlinear control theory account of its excellent robustness and complete adaptability to the uncertainties and external disturbance, and it is suitable for the control problem of hard disk drive servo system. Considering the current developed control approaches of hard disk drive settling control, the thesis adopted discrete-time sliding mode control in designing of the settling controllers to single-stage actuator and dual-stage actuator respectively. The main results obtained in this thesis are as follows:1. To avoid the shortcoming of traditional discrete-time sliding mode controllers that they have an intensive chattering and can not completely get to the steady-state, an improved discrete-time sliding mode control which has a time-varying discrete-time reaching law was presented. Quadratic Lyapunov function was employed to prove the reachability and asymptotic stability of the sliding surface. The improved control strategy solves the problem of chattering that exists in classical discrete-time sliding mode control and shortens the arrival time.2. For single-stage actuator, we adopted proximate time optimal servomechanismcontrol (PTOS) as track seeking control while employed the proposed discrete-time SMC as track following control. Simulation results show the effectiveness of the acknowledged PTOS as well as the proposed control strategy. Parametric uncertainty was also considered. The proposed SMC and the reported SMC were simulated separately on the hard disk drive model with uncertainty. Results verify the advantages of the proposed sliding mode controller. 3. We also focused on dual-stage actuator hard disk drive system. Different controllers were designed to match the two stages. For Voice Coil Motor (VCM), we introduced an improved PTOS with sliding mode control, and simulation results show that sliding mode PTOS has a shorter response time than traditional PTOS. For Microactuator (MA), which is always a piezoelectric transducer (PZT), we designed the controller by employing the time-varying sliding mode control method. The two controllers were integrated by master-slave loop with decoupling. The affect of periodic external disturbance was shown in simulation results which verified the robustness of the sliding mode control for actuator servo systems.The conclusion and perspective are given at the end of the thesis.