Triple-Stage Servo Control And Active Vibration Rejection For Hard Disk Drives

With the recent breakthrough in magnetic recording technology and the increasing demand for data areal density in hard disk drives(HDDs),higher precision is required to achieve ultra-high precision positioning of read/write heads.In recent years,some researchers have proposed a triple-stage actuation in order to further enhance the servo performance.Triple-stage actuating system provides a new way to improve the servo bandwidth and to suppress the high-frequency disturbance due to the fact that there is an additional actuator with better characteristics in high frequency.But in the meantime,due to the limited stroke and available control input,the control design is a big challenge.Based on the Bode integral theorem,stability and robustness,this dissertation studies the track-following control design of the triple-stage servo system for HDDs,the basic track-following robust control design methodologies and the new strategy of vibration control,which provides the theoretical basis for the application of the triple-stage servo system,and has important academic and engineering significance.In this dissertation,we first analyze the principle of the triple-stage actuating sys-tem to improve the performance of the closed-loop system,and give the performance comparison among the three actuation configurations under the variance constraints.We firstly introduce the Bode integral theorem,and uses this theorem to analyze the basic principle that the triple-stage actuation on HDDs can improve the performance of closed-loop system.The optimization problem of minimizing the variance of the system output under the control input and actuator stroke variance constraints is then explored.Simulation results show that the triple-stage configuration can obtain higher bandwidth and smaller position error signal(PES)in theory than the dual and single cases.Moreover,the robust control design methodologies for minimizing the PES in the triple-stage configuration is studied,and the sensitivity-decoupling design and the ?-synthesis design of the triple-stage actuation system track-following control are given respectively.Firstly,due to the characteristics of the three actuators' uncertainty distri-bution,the uniqueness of the sensitivity-decoupling design of the triple-stage actuation system is first determined,and the simple loop shaping method is used to simulate and compare the low frequency disturbance attenuation and servo bandwidth.Then,based on the ?-synthesis design,a controller tuning methodology is proposed and applied to the track-following control design of the triple-stage HDDs.Aiming at the aperiodic vibration problem of HDDs,a fast algorithm for suppress-ing vibration is proposed.Firstly,a vibration suppression structure with feedforward control is proposed.The Wiener solution of using the experimental measurement data to derive the vibration suppression problem is then given.Two fast convergence feed-forward control algorithms are proposed and analyzed to solve the problem that the convergence rate of filtered-x least mean square(Fx-LMS)is slow when the filter input is highly correlated.The analysis results show that the orthogonalization-x algorithm can always improve the convergence rate compared with Fx-LMS algorithm,but the orthogonalization-a algorithm can only be better than Fx-LMS conditionally.For the broadband disturbance,a spectrum separation solution is proposed to sup-press the high frequency vibration by involving the third actuator.An adaptive feed-forward control algorithm based on frequency segmentation is proposed to identify the system and compensate for external vibration.The algorithm starts from the first re-gion and simultaneously identifies the parameters of the feedforward controller and the lower order model of the actuator.The parameters freeze up after the convergence and then move to the next region until the controller parameters and the actuator model pa-rameters are obtained for all the regions.Simulation results verify the effectiveness of the proposed algorithm.Aiming at the periodic vibration of HDDs,a vibration suppression algorithm based on active disturbance rejection control(ADRC)and perturbation estimation theory is proposed.When the perturbation frequency is known,the basic ADRC with one-order higher extended state observer can not take the advantage of the known frequency in-formation to achieve perfect compensation.In this dissertation,an adaptive ADRC based on internal model is proposed,which can realize the perfect estimation of the disturbance under simple assumptions by using the known information.Firstly,the al-gorithm and proof for integral cascaded systems are given,and then generalized to more general single-input-single-output systems.The validity of the proposed method is veri-fied by simulations and comparison with the basic ADRC,and the periodic perturbation compensation in an HDD is also verified by simulation.The detailed analysis and simulation of a direct adaptive algorithm for periodic vibration of the triple-stage HDDs are given.In order to avoid the matrix inversion and reduce the computational complexity,an improved algorithm of the direct adaptive feedforward control is presented.The periodic characteristics of the sine and cosine tables with known frequencies at digital time implementation is analyzed.The simu-lation and comparison of the vibration suppression under the single/dual/triple-stage configurations of the HDDs are carried out.On the one hand,the effectiveness of the proposed algorithm is verified,and on the other hand,it reveals the superiority of the triple-stage configuration.The experimental setup is improved,extended and tested and multiple measure-ment experiments based on the improved experimental setup are given.The implemen-tation techniques and results of periodic/aperiodic vibration compensation of the HDDs are illustrated at the end.