The hard disk drive is one of the finest examples of the precision control of mechatronics, with tolerances less than one micrometer achieved while operating at high speed. Increasing demand for higher data density as well as disturbance-prone operating environments continue to test designers' mettle. Explore the challenges presented by modern hard disk drives and learn how to overcome them with Hard Disk Drive: Mechatronics and Control.Beginning with an overview of hard disk drive history, components, operating principles, and industry trends, the authors thoroughly examine the design and manufacturing challenges. They start with the head positioning servomechanism followed by the design of the actuator servo controller, the critical aspects of spindle motor control, and finally, the servo track writer, a critical technology in hard disk drive manufacturing. By comparing various design approaches for both single- and dual-stage servomechanisms, the book shows the relative pros and cons of each approach. Numerous examples and figures clarify and illustrate the discussion.Exploring practical issues such as models for plants, noise reduction, disturbances, and common problems with spindle motors, Hard Disk Drive: Mechatronics and Control avoids heavy theory in favor of providing hands-on insight into real issues facing designers every day.

Hard Disk Drive: Mechatronics and Control

This paper investigates the design of composite nonlinear-feedback (CNF) control law for a hard-disk-drive (HDD) servo system. First, a scaled nonlinear function is introduced for the CNF control law, in which a parameter is scaled by the error between the amplitude of the target reference and the initial value of the system controlled output. The closed-loop system under the scaled function has robust transient performance to the variation of the amplitude of the target reference. Then, the parameters of the selected nonlinear function are tuned by optimal tuning methods. More specifically, the parameter-tuning problem is formulated as an optimization problem, which can be solved efficiently via numerical methods. The simulation and experimental results show that the control law designed using the new approach yields excellent performance for both track seeking and track following in the HDD servo system.

A Hard-Disk-Drive Servo System Design Using Composite Nonlinear-Feedback Control With Optimal Nonlinear Gain Tuning Methods

A nonlinear sliding surface is proposed to improve the transient response for general discrete multiple-input-multiple-output linear systems with matched perturbations. The tracking case is analyzed, and it is shown that the scheme is able to achieve low overshoot and low settling time simultaneously; this is not possible with a linear sliding surface. The control law is based on the discrete-time sliding mode equivalent control and thus eliminates chattering. The control law is proposed based on two approaches: (1) reaching-law-based approach which needs only disturbance bounds and (2) disturbance-observer-based approach. Multirate output feedback is used to relax the need of the entire state vector for the implementation of the control law. A magnetic tape position control application is used to show the effectiveness of the proposed scheme.

High-Performance Tracking Controller for Discrete Plant Using Nonlinear Sliding Surface

Brief paper: Stability analysis and design of reset systems: Theory and an application

Composite nonlinear feedback control for linear singular systems with input saturation

A reset disturbance compensation scheme is developed to reject midfrequency narrowband disturbances, with an application to the hard disk drives (HDDs). Generally, disturbance at the midfrequency band is not effective to reject through the feedback control based on the internal-model principle or high gain control due to phase stability. This paper investigates a reset control scheme and its favorable approximate frequency response using the describing function. The reset control makes its gain-phase frequency response break through the fundamental Bode's constraint of linear time-invariant system and provides a maximal phase lead at desired frequencies without affecting gain's characteristic. With additional phase lead, the issue of phase stability can be solved. A reset midfrequency narrowband compensator is designed by incorporating the reset controller and a narrowband filter. The implementation on a real HDD servo system shows the removal of midfrequency disturbance due to disk vibration is improved by 50% compared with the linear control scheme, resulting in a track misregistration (TMR) reduction of 32%.

Reset Control for Midfrequency Narrowband Disturbance Rejection With an Application in Hard Disk Drives

This paper proposes a dynamic nonlinear control scheme to improve the seek-settling performance in hard disk drive servo system by a combination of a novel designed reference generator and a nonlinear feedback controller. The feedback controller consists of a linear one for short rise time and an associated nonlinear one for small overshoot. In order to improve the settling performance and system stability due to actuator saturation, reference trajectory is designed based on the performance of feedback loop so that the position error signal in the tracking stage is decreased greatly, which effectively avoids the actuator saturation with a high gain feedback control design. A parameterized second-order system is proposed to generate such desired reference trajectory. The stability of the proposed control scheme is proved through appropriate Lyapunov functions. The results in simulation and implementation show that the proposed control design performs better as compared with linear and optimal control laws for both short and long tracking lengths

Dynamic Nonlinear Control for Fast Seek-Settling Performance in Hard Disk Drives

Conventional integral compensation to deal with unknown bias usually leads to long settling process in hard disk drives. This paper proposes a nonlinear proportional integral derivative control scheme to shorten the settling time by reducing the overshoot caused by the integrator, without degradation of other performance specifications. Experiment results show that it is robust against different bias sizes and step sizes. Furthermore, the single-track seek time can scale down well with the track pitch.

A nonlinear control scheme for fast settling in hard disk drives

Nonlinear mid-frequency disturbance compensation in hard disk drives

This paper investigates a time-dependent phase lead reset control (PLRC) scheme which resets the sub-set of states of the systems at a predefined time. A phase lead reset compensator that has a flat gain characteristic is proposed to be used together with the common feedback control design to enlarge the servo bandwidth by increasing the phase stability margin. We also propose to have a reset time slightly earlier than the instants of input zero-crossing in the usual reset control to solve the impulsive effect in the control signal that leads to control signal saturation. Sinusoidal describing function analysis of the proposed control scheme shows that it can relax the Bode's gain-phase constraint. The application of the proposed PLRC to the Hard Disk Drive (HDD) servo system shows that the performance improvement. Our results also show that the large sharp peaks in the control voltage which may lead to track following controller saturation is also avoided.

Ying Li

Papers

Reset Control for Midfrequency Narrowband Disturbance Rejection With an Application in Hard Disk Drives

Dynamic Nonlinear Control for Fast Seek-Settling Performance in Hard Disk Drives

A nonlinear control scheme for fast settling in hard disk drives

Nonlinear mid-frequency disturbance compensation in hard disk drives

Phase Lead Reset Control Design with an Application to HDD Servo Systems