Commercial Hard Disk Drives Research Articles

Design of a probabilistic robust track-following controller for hard disk drive servo systems

This paper addresses the design of robust track-following dynamic output feedback controller for hard disk drives (HDDs) in face of parameter uncertainties which can enter into problem description in a possibly non-linear way. The design is performed in a probabilistic framework where the uncertain parameters are treated as random variables and the design specification is met with a given probability level. In particular, a sequential algorithm based on gradient iteration is employed to find a probabilistic robust feasible solution to the formulated problem. The design procedure is computationally tractable and its computational complexity does not depend on the number of uncertain parameters. Our case study allows natural frequency and damping ratio to vary within 8% and 10% from their nominal values for rigid body and all resonance modes. The designed controller achieves robustness in the presence of these uncertainties. Furthermore, the designed controller is implemented in real time on a commercial HDD.

Integrated servo-mechanical control systems design using Nyquist plots for high-performance mechatronics

In this paper, an integrated servo-mechanical control systems design method using Nyquist plots is proposed for high-performance mechatronic systems. The proposed technique is used to analyze stability, performance, and robustness of the control system, considering control and mechanical specifications under one unified framework. The desired stability and performance specifications such as gain and phase margins, infinity norm of sensitivity transfer function, mechanical characteristics, and robustness against plant uncertainties, etc., are transformed into disc regions in the developed technique. The proposed methodology is used to design and analyze a control system for a voice coil motor actuated hard disk drive (HDD) targeted to provide stronger disturbance rejection capabilities on the identified critical resonant mode at 9,146 Hz. The designed controller is implemented in a commercial HDD, and experimental results show that the disturbance at the frequency of critical resonant mode is attenuated by ź7 dB for stronger vibration control.

A Numerical Investigation of Particle Trajectory Inside Hard Disk Drives

This work investigates the particle trajectory in a turbulent flow field and the interaction of particles with the disk surfaces in enclosed hard disk drives (HDDs) through numerical simulation. Two different models of commercial HDDs are used, and two types of particle with sphere and tetrahedral shapes are examined. The results indicate that both HDDs exhibit similar impact distribution patterns on the disk surface. Due to high turbulence intensity caused by the obstruction of the arm, the particles tend to impact areas located near the arm which spreads from the middle to the outer radius of the disk. At each layer of the disk, impact counts increase from the innermost radius to the outermost radius, with the highest impact counts occur at the outermost radius. The simulation results provide useful information and can be used as a guideline in the design of HDDs and the arrangement of air filters inside HDDs.

Singular Perturbation Control for Vibration Rejection in HDDs Using the PZT Active Suspension as Fast Subsystem Observer

Currently, position sensors other than the read/write head are not embedded into current hard disk drives (HDDs) due to signal-to-noise ratio and nanometer resolution issues. Moreover, a noncollocated sensor fusion creates nonminimum phase zero dynamics which degrades the tracking performance. In this paper, the singular perturbation theory is applied to decompose the voice coil motor's (VCM's) and induced PZT active suspension's dynamics into fast and slow subsystems, respectively. The control system is decomposed into fast and slow time scales for controller designs, and control effectiveness is increased to tackle more degrees-of-freedom via an inner loop vibration suppression with measured high-frequency VCM's and PZT active suspension's dynamics from the piezoelectric elements in the suspension. Experimental results on a commercial HDD with a laser doppler vibrometer show the effective suppression of the VCM and PZT active suspension's flexible resonant modes, as well as an improvement of 39.9% in 3sigma position error signal during track following when compared to conventional notch-based servos

Perpendicular Magnetic Recording Integration and Robust Design

We have investigated the effects of stray magnetic field upon a perpendicular magnetic recording (PMR) system, which consists of a single pole type head and a double-layered perpendicular medium. We found that fields in the plane of the disk could cause serious External magnetic flux concentrates around the edges of a return pole and can cause very large fields to appear in the medium. In addition, the writing operation significantly enhances this We called this kind of erasure corner erasure. Experimental 2.5-inch hard disk drives (HDDs) were used to study the combined effect of the external field and write field. We checked SER degradation after applying an in-plane field of 0.8 kA/m (10 Oe). With no write-current applied, there is no degradation. However, as little as 0.8 kA/m (10 Oe) applied during writing causes severe degradation equivalent to that produced by a 4.0 kA/m (50 Oe) field applied when the head is reading on-track. It is concluded that the realization of PMR in commercial HDD would require new transducer designs to solve these problems. We devised a new return pole design which has a stepped-back wing to improve the robustness against in-plane stray fields. The alternative design greatly reduces the concentration of magnetic flux at the edges of return pole. Consequently, the stepped wing structure achieves about twice the robustness of the conventional rectangular return pole. A method was developed to allow external field sensitivity to be carefully checked. The method allows the degraded areas of data to be associated with the exact feature on the head that caused the problem

Modeling and compensation of nonlinearities and friction in a micro hard disk drive servo system with nonlinear feedback control

Friction and nonlinearities result in large residual errors and deteriorate the performance of head positioning of hard disk drive (HDD) servo systems and other mechanical servo systems. Thus, it is highly desirable to characterize the behaviors of nonlinearities and friction in the servo systems. This paper presents a fairly comprehensive modeling and compensation of friction and nonlinearities of a typical voice-coil-motor (VCM) actuator used in commercial HDDs, and the design of an HDD servo system using an enhanced nonlinear control technique. Our contributions are two-fold: We will first obtain a complete model of the VCM actuator including friction and nonlinear characteristics through a careful examination of the configuration and structure of the actual system and through a thorough analysis of its physical effects together with its time-domain and frequency-domain responses. We will then proceed to design a servo system for the hard drive using an enhanced composite nonlinear feedback (CNF) control technique with a simple friction and nonlinearity compensation scheme. The enhanced CNF technique has a feature of removing the uncompensated portion of friction and nonlinearities without sacrificing the overall tracking performance. Simulation and experimental results for both the modeling and the servo design show that our approach is very effective and successful. In particular, our experimental results show that the enhanced CNF control has outperformed the conventional proportional-integral-derivative (PID) control in settling time by 76%. We believe that this approach can be adopted to solve other servomechanism problems.

A simulation and control design environment for single-stage and dual-stage hard disk drives

We describe an integrated tool for the design and evaluation of the performance of different control algorithms and strategies, applied to hard disk drives (HDDs) with single-stage actuators and dual-stage actuators. The tool is composed of a set of procedures for the computer-aided design of servocontrollers and a HDD simulator. In order to perform realistic simulations, each part of the HDD is described with high level of detail. As for the mechanics, the usual inertia plus resonance model of the voice coil motor (VCM) has been enriched with nonlinear friction modeling and, in case of DSAs, with the dynamic coupling between primary and secondary actuator. The nonlinear friction model has been tuned on experimental data, using an experimental system presented in the paper. As for the electronics, the VCM driver model is included and quantizations in the position error signal measurement and computation are explicitly considered. Also, in order to evaluate the tracking performance of different servocontrollers, repetitive run outs and nonrepetitive run outs are included. Such disturbances have been obtained from commercial HDDs, with a procedure that is detailed in the paper. The simulator is then validated by comparing simulation and experimental results, both in open-loop and closed-loop conditions, thus, confirming the effectiveness of the developed tool.

FINITE ELEMENT ANALYSIS OF FLEXURAL VIBRATIONS IN HARD DISK DRIVE SPINDLE SYSTEMS

This paper is concerned with the flexural vibration analysis of the hard disk drive (HDD) spindle system by means of the finite element method. In contrast to previous research, every system component is here analytically modelled taking into account its structural flexibility and also the centrifugal effect particularly on the disk. To prove the effectiveness and accuracy of the formulated models, commercial HDD systems with two and three identical disks are selected as examples. Then their major natural modes are computed with only a small number of element meshes as the shaft rotational speed is varied, and subsequently compared with the existing numerical results obtained using other methods and newly acquired experimental ones. Based on such a series of studies, the proposed method can be concluded as a very promising tool for the design of HDDs and various other high-performance computer disk drives such as floppy disk drives, CD ROM drives, and their variations having spindle mechanisms similar to those of HDDs.

Vibration Analysis of Hard Disk Drive System

This paper relates to the flexural vibration analysis of the hard disk drive (HDD) spindle systems by means of the finite element method. In contrast to previous researches, every system componebt is here analytically modeled taking into account its flexibility and also the centrifugal effect particularly for the disk. To prove the effectiveness and accuracy of the proposed method, commercial HDD spindle systems with two and three identical disks are chosen as examples. Then, their major flexural natural modes are computed employing only a small number of element meshes as the shaft rotaional speed is varied, and compared with the bumerical or experimental results.