Chang-Ik Kang

Adaptive and Optimal Rejection of Non-Repeatable Disturbance in Hard Disk Drives

This paper presents an efficient control strategy to reduce the non-repeatable position error signal (PES) components caused by mechanical vibration in hard disk drives. A peak filter is designed that plugs into a servo loop in parallel with the existing controller. Based on the PES, the filters center frequency is adaptively searched for in order to identify a dominant spectral peak. An analytical procedure is proposed to design the filter that minimally affects the stability of control systems and the distortion in the error rejection curve. The performance and practicality of the proposed strategy are demonstrated by simulation and experiment.

Fractional-Order Proportional Derivative Controller Synthesis and Implementation for Hard-Disk-Drive Servo System

In this brief, a fractional-order (FO) proportional derivative (PD) controller is designed in a systematic way based on the frequency responses data model for the hard-disk-drive (HDD) servo system. The open-loop system using the designed FO controller is with a flat-phase feature around the gain crossover frequency, which obtains the robustness to loop-gain variations. Thus, the control performance can be made uniform with more consistency than the optimized traditional integer-order controller when the loop gain changes. The theoretical foundation of the FO controller design is presented first. Thereafter, the implementation details of the designed controller in the real-time HDD servo system are introduced, which are important for the real applications of the FO controllers in practice. From the experimental validation, the presented FO-PD controller and the design synthesis are found to be efficient in improving the track-following control performance for the HDD servo system.

Servo loop gain identification and compensation in hard disk head-positioning servo

The servo loop gain in the track-following servo depends on head flying height, length of magnetic fringing field, and magnetic flux density of actuator. The loop gain variation should be suppressed for uniform servo performance over all track locations. In this paper, we present a new approach to the identification and compensation of servo loop gain. The identification algorithm is based on sinusoidal excitation and measuring open loop frequency response. The experimental results show that loop gain variations can be reduced significantly by applying our identification algorithm.

A new seek servo controller for minimizing power consumption in micro hard disk drives

Recently, the demand for micro hard disk drive that provides high-capacity removable storage for handheld electronic devices is increasing very rapidly. The major concern in the design of seek servo controller in micro disk drives is to reduce power consumption. The input power delivered to the seek servo system is consumed by the transistors of power amplifier and motor coil resistance. In this paper, we present a new seek servo controller for minimizing the power consumption. We use a Fourier decomposition and constrained nonlinear programming to determine the optimum seek profile that minimizes the power consumption. Finally, we present some experimental results using a commercially available micro disk drive.

Pre-filtering and head-dependent adaptive feed-forward compensation for linear vibration in hard-disc-drive

This paper suggests a pre-filtering and head-dependent adaptive feed-forward (AFF) control scheme for vibration compensation in hard-disc-drive (HDD) servo system. First, an AFF algorithm is designed and implemented for the linear vibration compensation in the servo system. In order to improve the vibration compensation performance significantly, a pre-filtering process is added in the AFF scheme. Meanwhile, a head-dependent AFF control strategy is proposed and implemented to accommodate the dynamics variations in HDD servo system. This head-dependent AFF control scheme improves the vibration compensation performance in consistency. The proposed pre-filtering and head-dependent AFF control scheme is validated by the drive level experiments with significant performance improvement for vibration compensation in high density HDD servo system.

Practical frequency shaping of on-track mode controller of HDD servo

The study of desired loop shape and design of on-track mode controller are discussed. The desired loop shape is expressed as the performance shaping function. The controller is designed using loop-shaping technique to maintain stability margins. Simulation and experimental results validate the effectiveness of the proposed controller.