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This paper presents a simulation study on the coupling effects of air bearing dynamics and suspension vibrations due to slider-disk contact or disk waviness. A simulator is developed to include the interactions between the air bearing, the slider-suspension assembly and slider-disk contact by considering the suspension, slider and air bearing as a whole system. From the simulation, the dynamic motion of read/write head in both flying-height (FH) and off-track directions, even on-track direction, can be obtained. It is helpful to characterize dynamics of head positioning and understand the interactions between the head disk interface (HID!) components. In addition, the effects of contact intensity, surface roughness, skew, and disk waviness on the read/write head positioning in both FH and off-track directions are investigated. The mechanisms of these factors' effects on the dynamic stability of read/write head positioning in both FH and off-track directions are also discussed in the paper. [ABSTRACT FROM AUTHOR]

This paper is concerned with the nonrepeatable runout (NRRO) compensation problem for hard disk drives. After standard servo control, several visible frequency components remain in the spectrum of nonrepeatable position error signal (NRPES). The dominant ones among these frequency components contribute a lot to the track mis-registration (TMR). In this paper, we propose an adaptive compensation scheme for the time-varying dominant frequency component of NRRO. The frequency of the dominant component is estimated online by the least mean squares (LMS) algorithm within a short time window. Based on the frequency estimate, the basis function algorithm is applied to adaptively identify the time-varying magnitude and phase of the dominant component. With the identified frequency, magnitude, and phase, an estimate of the dominant component is constructed and then canceled by the control signal. This scheme is further extended to compensating for multiple frequency components. The performance of this compensation scheme is demonstrated by simulation on a realistic hard disk drive model. [ABSTRACT FROM AUTHOR]

Information about several papers discussed at the IEEE International Magnetics conference is presented. The conference was of outstanding scientific and technical quality. The conference featured several personalities in the electrical and computer engineering industry including Ryusuke Hasegawa, Michael McHenry and Hiroaki Muraoka.

In this paper, we compare the positioning accuracy of helium- and air-filled drives. We report the PES spectra of the both drives and calculate the mechanical disturbance. The results reveal that almost all disturbances in higher rpm drives are flow induced vibrations and that disturbances in helium-filled drives are dramatically smaller. The experimental positioning error of helium-filled drives is less than half of that of air-filled drives. The static and dynamic fluid computations explaine these experimental results. [ABSTRACT FROM AUTHOR]

Most hard disk drives that apply the ramp load/unload technology unload the heads at the outer edge of the disk while the disk is rotating. During the unloading process, slider-disk contacts may occur by lift-off force and rebound of the slider. The main issue of this paper is to prevent the slider-disk contact by rebound, and we apply a disk bump to the unloading process. To do so, first, the ranges of bump dimension are determined. Second, the stability of each bump is checked by dynamic simulation. Finally, unload analyses are performed for stable bump designs. As a result of these analyses, we investigate proper bump design and position for the unloading process. Through this research, we propose the optimal bump design to improve the unloading performance. We can also identify to remove rebound contact by applying a bump on disk to the unloading process. [ABSTRACT FROM AUTHOR]

During servo track writing (STW), the timing jitter in clocking process can induce significant errors on servo pattern, which is known as phase-in error. In this paper, we measured the timing jitter on our STW setup and modeled the jitter sources in frequency domain. With the timing jitter models, the typical phase-locked loop system is taken as a typical closed-loop control system and H∞ loop shaping and H2 control method are used to design the loop filter with objective to minimize the timing jitter. It is shown that timing jitter can be significantly reduced with loop filter designed with the H2 method. [ABSTRACT FROM AUTHOR]

In sensorless operation of spindle motors in hard disk drives (HDD), open-looped starting is used to spin up the motor from standstill to a speed that is high enough to reliably detect back-electromotive force (back-EMF) generated in the armature windings. Then the back-EMF zero-crossing points (ZCP) will be used to detect speed and position for closed-looped control. This paper studies three open-looped starting modes for spindle motor. Six-step, which is currently used in HDD, twelve-step, and sine wave starting are illustrated and compared. The simulation results show that twelve-step and sine wave starting can obtain much better starting performance for spindle motors. [ABSTRACT FROM AUTHOR]

This paper has two specific goals to achieve. The first goal is to address major challenges encountered in design and development of miniature hydrodynamic bearings for small form factor hard disk drive spindle motors. These challenges include extremely small thickness of the spindle motors, mass productivity of tiny bearing parts, and bearing reliability and performance in relation to changes in atmospheric pressure. To overcome these challenges, we have developed a prototype hydrodynamic bearing that is resistant to environ- mental changes, free from oil film disruption, and tolerant of variations in processing precision. The prototype hydrodynamic bearing has two special features: an oil circulation function and a gas/liquid separation function. The oil circulation function is achieved by using asymmetric hydrodynamic grooves together with circulation passages. The gas/liquid separation function is achieved by using tapered capillary seals in the circulation passages. As a result of these two special features, the prototype hydrodynamic bearing can successfully expel air bubbles out of the bearing, thus enhancing the performance and reliability of the hydrodynamic bearing. The second goal is to evaluate the prototype hydrodynamic bearing in a miniature spindle motor for small form factor hard disk drives. Two specific bearing designs are evaluated. The first bearing design is a pushing type that generates no low-pressure area. However, the flow rate increases at high temperature. The second design is just the opposite. It is a pulling type design that generates a low-pressure area. But the flow rate is constant and is independent of temperature changes. To accommodate manufacturing tolerances, a parametric study is conducted to identify the effects of manufacturing tolerance on bearing performance. [ABSTRACT FROM AUTHOR]

In this paper, vibration of 1.8-in hard disk drive (HDD) spindle motors is studied experimentally and theoretically. In the experimental study, vibration of 1.8-in HDD motors is measured at 5 °C, 25 °C, and 70 °C in a thermal chamber. Experimental results reveal two important phenomena. First, vibration of 1.8-in HDD spindle motors is dominated by a (0,0) unbalanced mode that has a significant bending deformation of the base plate. Second, the natural frequency of the (0,0) unbalanced mode and the static gain of the frequency response function change significantly as the ambient temperature varies. To explain these experimental observations, we apply a mathematical model developed at the University of Washington to analyze the vibration of the 1.8-in HDD spindle motors. The analysis shows that (0,0) unbalanced mode shifts its natural frequency because membrane stresses are developed in the base plate during temperature changes as a result of a significant mismatch of coefficients of thermal expansion between the base plate and the fixture. Moreover, the change of the static gain results from reduction of fluid-dynamic bearing coefficients as the temperature varies. [ABSTRACT FROM AUTHOR]

This paper proposes a finite-element method (FEM) with mode superposition to analyze the shock response of a flexible hard disk drive (HDD) composed of a spinning disk-spindle system with fluid dynamic bearings (FDBs), a head-suspension-actuator with pivot bearings and air bearings, and a base plate with complicated geometry. The proposed method is applied to a 2.5-in HDD. The displacements of the head, spinning disk, and arm are calculated, and they are also measured by experiments. This research shows that the numerical results match well with the experimental ones. It also investigates the head-disk motion due to operational shock. [ABSTRACT FROM AUTHOR]

This paper reviews the present state of understanding of lubricant-slider interactions in a rigid disk drive. As slider flying heights are rapidly approaching the intrinsic limit of a disk topography (1-3 nm), it has become apparent that disk-slider clearance of less than a nanometer can be achieved, at least on a laboratory setup. We will discuss the implication of such low spacing on the lubricant film behavior, and provide general physical arguments that attempt to highlight lubricant attributes that are relevant under those clearance conditions. [ABSTRACT FROM AUTHOR]

Write fault protection performance determines the data integrity performance in hard disk drives (HDDs). It is also a critical factor in projection of new HDD products to determine the adequate servo sector number. For HDDs with a shock sensor, the write fault protection performance is rather uniform with respect to different shock disturbance. However, this is not the case when shock sensors are not available and only off-track thresholds are used to detect external shock loads. The write fault protection performance may be dependent on many factors, such as shock form and amplitude, the timing of the shock, the sampling frequency, etc. This paper studied the relationship between the write fault protection performance and shock disturbance in HDDs without shock sensors. Simulations showed that when the shock timing is random, the write fault protection performance is inversely proportional to the shock amplitude. [ABSTRACT FROM AUTHOR]

The paper presents a simplified analytical method to design a small two-pole slotless brushless dc motor. Using only a few approximations, the motor analytical model is formulated to generate a system of equations. The system can be solved analytically, producing a motor design for given specifications. The method is used to design a motor with the specifications 150 W, 10 000 rpm, and 18 V. [ABSTRACT FROM AUTHOR]

This paper introduces an improved tabu-based vector optimal algorithm for multiobjective optimal designs of electromagnetic devices. The improvements include a division of the entire search process, a new method for fitness assignment, a novel scheme for the generation and selection of neighborhood solutions, and so forth. Numerical results on a mathematical function and an engineering multiobjective design problem demonstrate that the proposed method can produce virtually the exact Pareto front, in both parameter and objective spaces, even though the iteration number used by it is only about 70% of that required by its ancestor. [ABSTRACT FROM AUTHOR]

The magnetic hard disk drive (HDD) has become a cost-effective means to meet the expanding demands for large data storage capacities in portable electronic devices. A particular problem an HDD faces in such applications is periodic disturbances caused by different kinds of external forces. In this paper, an adaptive controller based on an algorithm proposed by Brown has been developed and applied to identify and reject unknown periodic disturbances in a mobile HDD. Numerical simulations and experiments are conducted and superior convergence properties of the proposed method are shown compared with a method taken from the literature called frequency Chasing Peak Filter. It is found that the convergence rate of the proposed method is less susceptive to the error in the initial frequency estimate in the frequency range of interest. The effect of unaddressed frequency components on the convergence and performance of the controller is also discussed. [ABSTRACT FROM AUTHOR]

This paper presents a systematic, semi-automated method for identifying parameters and parametric uncertainty for a set of dual-stage hard disk drives. A modal analysis technique is selected to extract parameters from a batch of frequency response data. In order to avoid redundancy in modal parameters, two methods are presented to reduce model order. One method combines experimental data to directly extract fewer parameters. The second method uses an optimized model truncation methodology. Finally, convex optimization and singular value decomposition are employed to obtain a minimally conservative, lower-order approximation of uncertain parameters. The result is a reduced-order state space model with parametric uncertainty to be used in robust H2 control synthesis for a track-following hard disk drive servo. [ABSTRACT FROM AUTHOR]

This paper compares the turning and stationary groove configurations of oil lubricated journal bearings used in hard disk drive (HDD) spindle motors under transient contact conditions, such as at startup and shutdown. With rapidly expanding applications for HDDs, spindle motors are required to have lower friction and wear while driving more disks, and be downsized at the same time. It has been known for some time that the turning groove bearing outperforms the stationary groove bearing with regard to friction torque in steady-state operations. However, the friction and wear of the two configurations under the transient contact conditions are still not well understood. To clarify this, we used a model previously proposed and validated experimentally to determine the motion of the turning member in the bearing by simultaneously solving the nonlinear differential equations of motion, the pressure-compliance relationship of elastic-plastic roughness contact, and the average flow Reynolds equation. The different characteristics of the turning and stationary groove configurations are then discussed for both herringbone groove and multi-taper bearings. [ABSTRACT FROM AUTHOR]

In this paper, we numerically study the lubricant migration on a flying slider air-bearing surface in a hard disk drive. The lubricant dynamics is based on a continuum thin film lubrication theory with inter-molecular forces and a precursor film model. It includes air- bearing pressure, air-bearing shear stress, the Laplace pressure, the disjoining pressure, and the shear stress caused by the surface free energy gradient. Using this model we investigate the lubricant migration behavior on a modern negative pressure type slider surface. We also reveal the correlation between the lubricant migration behavior and the air-bearing shear stress. We further perform the lubricant migration analysis for various different slider designs, radii, and skew angles. [ABSTRACT FROM AUTHOR]

In order to find an applicable power supply used in electric guns, there have been two types of the magnetic flux compression linear generator (MFCLG) that use the solenoids as the stators. That is to say, a piston armature or a solenoid armature is used within the stator. Although they can amplify the current theoretically, they can only compress the component of the magnetic flux. So their efficiency is low, and there exist some difficulties, which is difficult to solve in terms of the engineering technology. In addition, the use of the solenoid armature leads to the increment of the ineffective part of the solenoid. A kind of the rail stator augmentation MFCLG is presented here. It separates the combustion chamber-cylinder and the generating channel into two independent parts, and with an antirecoil device. The combustion chamber is extended as a cylinder. Within it the piston pushes the stator-armature package to move forward through the connecting rod along the generating channel consisted of the rails. This can compress the magnetic flux to generate the large electric current to be used by electric guns. If we fill the integrated fuel into the combustion chamber, we can realize the successive pulse operation. The separation of the combustion chamber-cylinder and the channel can avoid the high temperature burning gases from entering the channel to cause ablation. The basic mathematic model of this type of the generator is given and its physical properties are analyzed in this paper. It is found that it can compress the magnetic flux perpendicularly and has higher efficiencies for compression and conversion. It can produce large current with sufficient pulse width to supply the electric guns. Besides, a self-excitation method for this type of generator is also put forward, which can omit the seed power source. Instead, it uses the chemical energy that drives and compresses the magnetic flux to generate the electric current to produce the initial seed magnetic flux used by it. [ABSTRACT FROM AUTHOR]

Presents a study that examined the techniques used in developing an electronic book about electromagnetics. Background on problem-based learning as a teaching method; Application of engineering tools in developing the electronic book; Results and implications.

The generation and measurement of static and time-varying magnetic fields using electromagnetic coils is a common method in various fields. Multiple applications require special geometries, e.g., complex structures on curved surfaces. The fabrication of such complex saddle coils on curved surfaces without special equipment is challenging and requires time-consuming techniques and lot of experience to produce coils with high accuracy. The novel approach uses dedicated slits in a tubular structure to guide and self-fixate the windings of the desired coil structure and allows a fast and easy fabrication with high accuracy and without special skills. In this article, an introduction into the basic idea is given followed by a generalization for arbitrary nested saddle-coil structures. Finally, a first 3-D printed prototype is presented. [ABSTRACT FROM AUTHOR]

Information about several papers discussed at the 41st IEEE International Magnetics Conference is presented. The highlight of the conference was the plenary session which featured informative address on "Magnetic Data Storage and Where It Is Taking Us." The conference featured several personalities in the electrical and computer engineering industry including Mark H. Kryder, H. Neal Bertram and Jai M. Menon.

Particle-induced damage on perpendicular recording media can be categorized as physical damage to the media and magnetic erasures with limited physical damage. Component-level tests were developed in order to measure particle robustness of air bearing designs for these two failure modes. A published model for air bearing interactions with a particle was extended to include the full slider surface and allow particles to slide along the slider air bearing features. The model and test results correlate for hard particle scratching. Specific air bearing features and properties can be modified in order to improve dramatically the air bearing particle robustness for hard particle scratches and particle-induced magnetic erasures. [ABSTRACT FROM AUTHOR]

After introducing our previous study of bouncing instability of a flying head slider, we numerically investigated slider dynamics in the near-contact region taking the root-mean-square value and frequency roll-off factor of the micro-waviness as parameters by using 2-degrees-of-freedom slider model, random micro-waviness model and lubricated rough-surface-contact characteristics model. We found that the slider exhibits self-excited bouncing vibration with a frequency close to the lower pitch frequency under small microwaviness but tends to exhibit forced vibration with a resonant frequency in the upper pitch mode as the amplitude of microwaviness increases. If the amount of microwaviness and destabilized sources are reduced sufficiently, there is a contact sliding condition without self-excited and forced bouncing vibration. [ABSTRACT FROM AUTHOR]

In regards to servo-writing with perpendicular recording, we investigated servo-write quality and servo performance, and found that the premagnetization conditions, the magnetic-flux flow mechanism, and head structure strongly affect the servo-write quality. In response to these findings, we clarified that the flux flows through the writer to the reader are one of the root causes of servo-signal deterioration. In addition, we found that the flux amount is related to the magnetization switching ratio (MSR)—a one sided magnetization pole per writer-pole area. On the other hand, the reader can absorb flux even if it is far from the flux source. This means that not only the reader element but also the adjacent structure can absorb flux from the flux source. [ABSTRACT FROM AUTHOR]

The spreading characteristics of novel alkanolamine-terminated perfiuoropolyether (PFPE) films on carbon surfaces were investigated experimentally by using a scanning micro-ellipsometer. The apparent diffusion coefficients of the novel lubricants were studied in order to evaluate the spreading speed and they were compared with the conventional Z-dol, Z-tetraol, and A20H lubricants. It was found that the mobility of a lubricant is lower when the number of OH end groups is higher. It was also found that the mobility of the alkanolamine-terminated PFPE films was lower than that of conventional lubricants with the same number of OH end groups as that of the alkanolamine-terminated lubricants and that the mobility tendency of the lubricants has a good correlation with their viscosity tendency. In addition, the mobility of ZDPA with a dipropylamine end group (no OH end group) has peculiar characteristics. Its mobility is higher than that of Z-dol when the film thickness of the lubricant exceeds that of one monolayer. However, it is lower than that of Z-dol when the film thickness of the lubricant is less than that of one monolayer. This may be due to the unique interaction between the ZDPA amine group and the carbon overcoat. [ABSTRACT FROM AUTHOR]

Recent progress in the development of patterned magnetic recording media is presented, focusing on the results of patterned media fabricated by a self-assembled mask process. Several issues such as fabrication process, flyability, and signal processing have been discussed so far. However, recent progress seems to resolve these problems. A fabrication process using nano-imprint lithography is a possible solution in terms of productivity. Good results for flyability have been reported for discrete track recording media. Certain advantages with respect to signal processing have been reported. Although problems remain to be resolved, patterned media is expected to be commercialized following the introduction of the discrete track media, as a high density perpendicular magnetic recording media. [ABSTRACT FROM AUTHOR]

A reliability model for the hard disk drive (HDD) is developed, focusing on head-disk separation as the primary independent variable. The model is structured to incorporate the theoretical effects of environmental factors, plus empirical dependence on the product operating mode. An experimental method based on magnetic spacing loss theory is used to characterize the head-media separation as a function of temperature, altitude, humidity, and HTDD operating mode. A statistical model based on these empirical data is developed to predict HDD reliability for various operating conditions. The predictions of the model are verified experimentally through comparison with HDD product reliability test data. [ABSTRACT FROM AUTHOR]

Head and medium designs to support areal densities of 400 Gb/in² were investigated using micromagnetic modeling. The use of side shields allows the track pitch to be reduced, but only by about 10 nm. Reducing the main pole width also permits higher track densities, but the erase band width does not reduce significantly with the pole width reduction. In addition, the erase band width increases at higher linear densities and forms an increasing fraction of the total track width. [ABSTRACT FROM AUTHOR]

To achieve disk drive recording densities greater than one terabit per square inch, future head-media spacings (HMSs) will need to be less than 7 nm. This will place severe demands on the metrology tools used to measure the thickness and topographies of the contributors to the head-media spacing. Here, we first review some of the metrologies used for characterizing overcoats, lubricants, and topographies and discuss some of the limits that will make it difficult to achieve a sub-7-nm HMS. We next show new results for measuring lubricant redistribution on disk surfaces after contact with a small pad on the slider and present a new method for determining wear rates of these slider contact pads. [ABSTRACT FROM AUTHOR]

The effect of magnetic "preconditioning" on the recording performance of perpendicular media is investigated. Furthermore, the dependence of the magnetic write width (MWW) of shielded-pole heads (SPH) on soft-underlayer (SUL) type and thickness (tSUL) and the recording performance of perpendicular media with thin SULs are examined. The MWW dependence on SUL structure is influenced by the pole-to-trailing shield spacing. For a wide-gap (∼80 nm) SPH, thick single-layer, SULs are preferred. For a narrow-gap (∼50 mn) SPH, MWW is less sensitive to the SUL type. For both narrow and wide-gap SPH and for media with an antiferromagnetically-coupled SUL, MWW is reduced for tSUL < 100 nm. Comparable performance is achieved relative to media with tSUL 150 nm. [ABSTRACT FROM AUTHOR]

The emigration genetic algorithm, which is a genetic-based algorithm, is proposed to obtain the Pareto optimal solution of vector optimal designs of electromagnetic devices. The proposed algorithm differs from the traditional ones in its design of an emigration operator as well as the inclusion of some useful approaches such as the fitness sharing, clustering, and elitism strategy. Detailed numerical results on three different multiobjective design problems are reported to demonstrate the effectiveness advantages of the proposed algorithm for solving practical engineering multi-objective optimal design problems. [ABSTRACT FROM AUTHOR]

An investigation into the cogging torque in a four-pole interior-magnet brushless machines having either a six-slot stator and a short-pitched nonoverlapping winding or a 12-slot stator and a full-pitched overlapping winding is described. It is shown by finite-element analyses and measurements that, by appropriately defining the pole-arc to pole-pitch ratio, the optimal pole-arc to pole-pitch ratio for minimum cogging torque, which has been derived for surface-mounted magnet machines, is equally applicable to interior-magnet machines. [ABSTRACT FROM AUTHOR]