Ruifeng Chen

Modified adaptive feedforward runout compensation for dual-stage servo system

This paper applies the modified adaptive feedforward compensation (AFC) scheme to the dual stage servo system for the cancellation of repeatable runout (RRO) and nonrepeatable runout (NRRO). It shows that runout can be effectively compensated or attenuated by assigning runout components to VCM actuator and microactuator properly.

Optimal multirate control design for hard disk drive servo systems

This paper presents a multirate digital controller design for HDD servo systems via direct parameter optimization approach. In order to find a satisfactory multirate controller with good transient and steady state performance, a linear quadratic performance index with stability constraints is introduced. The controller parameters are selected based on the HDD servo system transient response data instead of a detailed plant model. The proposed method can improve the performance of LQG multirate servo designs without knowing the exact plant parameters or noise model. The effect of controller order on system performance is also studied. For a 4th order system studied, it is found that a 4th order controller is sufficient to achieve the optimal performance.

TMR online optimization using quasi-Newton method for HDD servo systems

Presents a direct online parameter optimization method using a quasi-Newton approach to find compensators, which can minimize the measured track mis-registration (TMR) for hard disk drive (HDD) servo systems, without prior knowledge of disturbance/noise models. An optimal controller for a plant with uncertainty can be obtained within a pre-found robust stable region by using the gradient information of TMR with respect to controller parameters based on nominal plant model. The searching time is shorter compared with other non-gradient optimization methods such as random neighborhood search and genetic algorithms. Both simulation and implementation results show the effectiveness of the proposed method. In addition, it is also proved that if the measurement noise is white noise, an optimal controller that minimizes the measured TMR also minimizes the true TMR.

A gradient-based track-following controller optimization for hard disk drive

This paper presents a gradient-based parameter optimization method to find the optimal compensator that minimizes the standard deviation (/spl sigma//sub PES/) of the position error signal (PES) in a hard disk drive servo system. By using the plant response data and the PES gradient information based on the nominal plant model, optimal digital controllers that minimized the 3/spl sigma//sub PES/ of a plant with uncertainty were selected within a pre-found robust stable region. As a result, an optimal track-following controller that minimized the standard deviation of the measured PES (/spl sigma//sub PESm/) was able to be obtained without the prior knowledge of the disturbance and noise model. Furthermore, we proved that if the measurement noise is white, an optimal controller that minimizes the 3/spl sigma//sub PESm/ also minimizes the 3/spl sigma//sub PES/. Both simulation and implementation results suggest that such a gradient-based search process is faster than nongradient optimization methods such as random neighborhood search and genetic algorithms.

An optimal multirate control design with robustness specification for sampled-data HDD servo systems

One major contributor of the track mis-registration in a hard disk drive (HDD) servo system is the position error signal (PES) 3/spl sigma/, or 3 times the standard deviation of the PES. The paper presents an optimal robust multirate control design to minimize 3/spl sigma//sub PES/ in HDD servo systems with stochastic distribution of plant parameters via genetic algorithm and random neighborhood search considering robust stability restrictions. The expected H/sub /spl infin// norm of the sampled-data system was set as the robust performance index and the H/sub /spl infin// norm of weighted complementary sensitivity function of the plant input was set as the robust stability index for the multiplicative perturbation. The genetic algorithm with sharing scheme and tabu list which could improve diversity of solutions and global search ability was employed for a coarse optimization of the controller parameters and random neighborhood search did a fine-tuning of the controller. The numerical results show that, the proposed method could improve the robust performance of the sampled-data HDD servo system considerably while keeping the robust stability.

An intersample ripple free multirate servo controller for disk drive actuators

An intersample ripple free multirate control design is presented. In this paper. The idea is to introduce a constraint in control parameters for the conventional multirate control design approach so that there would be no control chatter, and therefore a reduction of the output ripple. The method is applied to a hard disk drive actuator servo control system. Both simulation and experiment results show that fast response can be achieved and steady state intersample ripples in the plant output are eliminated.