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Track misregistration (TMR) in ultra-high density bit-patterned media recording (BPMR) is one of the crucial problems, because it can severely degrade the overall system performance. In practical, TMR can be detected and adjusted by a servo control loop system. However, this paper proposes to utilize multiple readback signals obtained from the optimized positioning of the two side read head closer to the main read head to improve the TMR prediction process in a multitrack multi-head BPMR system with position jitter noise. In addition, we also propose the soft-information exchange and the bit-flipping techniques for the multitrack data detection, so as to improve the bit-error rate (BER) performance of all three data tracks simultaneously. Simulation results indicate that the proposed system is superior to the conventional system, especially, when the amount of TMR and position jitter is high. Furthermore, we also found that the upper and lower read heads, which are moved closer to the center track by 25% of a track pitch, will provide the best BER performance with and without position jitter noise.

The resolution limits of tape head lateral position estimates derived from timing-based servo (TBS) patterns preformatted on perpendicularly oriented barium ferrite tape media are investigated. A set of four new TBS patterns with azimuth angles ranging from 15° to 24° but having, otherwise, identical parameters are compared. Measurements of the standard deviation of the closed-loop position-error signal are compared with resolution estimates based on: 1) the noise floor of the power spectral density of the lateral tape motion measured from the servo pattern during open or closed-loop track-following and 2) an analytical lower bound on the mean-squared estimation error, which depends on the servo readback signal shape and the signal-to-noise ratio. All four servo patterns are shown to achieve nanoscale resolution under realistic operating conditions. The 24° pattern was found to provide the highest performance with a position estimation resolution better than 3.8 nm for a single channel, and better than 2.6 nm when the estimates of two channels are combined.

Perpendicular magnetic recording (PMR) in the hard disk drive is approaching its physical limits. In an earlier work, the dedicated servo (DS) recording system has been proposed to provide continuous position error signal for servo, enable higher servo sampling rate, and improve the overall servo performance. A further benefit is that the DS layer results in surface area savings at the data layer. However, it was also reported that the embedded servo layer introduces baseline variation and non-linear transition shift (NLTS) to the readback signal of the data layer. In this paper, we propose novel signal processing techniques to improve the bit error rate (BER) in DS recording. The synchronous averaging technique is proposed to improve the BER in the presence of baseline variation distortions. Further, the servo and data-dependent noise prediction method is proposed to mitigate the effect of the NLTS. Through the use of these techniques the linear density loss from the conventional PMR media is reduced.

A dual-stage piezoelectric shear-mode actuation scheme aiming at high-density hard disk drive applications is designed, simulated, and experimentally evaluated. In this actuation scheme, a shear-mode piezoelectric single-crystal microactuator is installed between a suspension and a slider for realizing magnetic head nanopositioning in hard disk drives. The piezoelectric single-crystal-based shear-mode microactuator is dedicatedly designed and made of ( $1\,-\,x$ )Pb(Zn1/3Nb2/3)O3PbTiO3 ( $x=0.06$ –0.07) material to meet the technical specifications of servo control for 10 Tbit/in $^{2}$ hard disk drives. The shear displacement of this microactuator under a constant voltage is independent of the dimensions of the microactuator, which has the great promise for further miniaturization and excellent performance consistency control. Theoretical analysis shows that the first intrinsic resonance of the microactuator is around 143 kHz. The shear-mode microactuator has a displacement of 25.4–30.7 nm at 12 V at frequencies up to 60 kHz. After it is installed between a suspension and a slider, and tested on a spin stand, the shear-mode microactuator exhibits a working frequency of 39.1 kHz and a displacement of more than 22 nm at 12 V under the disk flying condition. The technical feature and performance as achieved show that the dual-stage nanopositioning scheme using a shear-mode piezoelectric single-crystal microactuator is promising to meet the requirements of servo control for 10 Tbit/in $^{2}$ hard disk drives.

Off-track condition in magnetic recording systems degrades the system performance. It is typically detected and adjusted by the servo control loop. In this work, we propose an off-track detection based on the readback signals and improve the bit error performance using an asymmetric target depending on the detected off-track direction. Specifically, we investigate the effects of off-track events on the target-shaping equalizer coefficients when the generalized partial-response target (GPR) is fixed. For a 3 t 3 channel matrix of bit patterned media recording (BPMR) system, the asymmetric targets offer the gain of about 1 to 2 dB at BER=10-4 for the TMR level of 20% to 25%.

The paper proposes a control scheme for detecting and compensating the low-frequency vibrations in hard disk drive systems. A vibration detector is proposed, utilizing the down-sampled position error signal (PES). Due to the performance limitation in loop shaping, attenuating low-frequency vibration is usually penalized by high frequency disturbance amplification. This paper proposes an adaptive scheme to intelligently adjust a vibration reduction factor, such that when vibration level is low, the servo loop maintains its normal operation mode, and little or no compensation is carried out. Experiments on hard disk drives on a vibration shaker validated the effectiveness of the proposed compensation scheme.

Lateral motion of the magnetic tape in data storage applications misaligns the flexible medium relative to the recording head and reduces the potential for decreasing data track width and spacing, and thereby the achievable data storage density. In order to reduce the effect of misalignment between the tape and the recording head, the head is mounted on a track-following actuator that can compensate for the position error up to a frequency that is governed partly by its mechanical resonances; this bandwidth is typically 1 kHz or less for conventional voice coil-based actuators. This paper introduces the design and implementation of a track-following actuator that is piezo-electrically actuated in order to potentially achieve a significant increase of bandwidth and positioning precision. A proof-of-concept is prototyped and experimental results are presented. An H∞ controller is designed and implemented to compensate for typical disturbances such as periodic runout of packs and rollers, or non-periodic flange impacts. Preliminary closed loop experimental results with an experimental low lateral motion tape path, and conventional servo format and media demonstrate a reduction in positioning error standard deviation to 74.5 nm, with simulations indicating a potential for further improvement to 20.6 nm with the use of improved media and servo format.

The characterization of novel small size 405 nm blue-laser optical head-like opto-mechanical system for turntable thermal mode lithography system that can provide high quality beam spot profile and real time high precision servo control and feasibility for thermal mode lithography process application are presented. The optical head-like opto-mechanical system consists of a single wavelength laser direct-write blue-laser opto-mechanical module and related servo control main board. An ideally narrow round shape exposure beam spot about 260 nm and high precision power control, focusing servo control are produced for thermal mode inorganic resist exposure. The small size opto-mechanical system combination with thermal mode lithography technology has been successfully applied to fabricate nickel stamper with submicro/nano structure patterns. The minimum pit (or hole) diameter is about 180 nm and ultra-low surface roughness (2 nm) is achieved after electroforming process.

The recording performance of a new magnetic tape based on perpendicularly oriented barium ferrite particles was investigated using a 90-nm-wide giant-magnetoresistive reader and a prototype enhanced-field write head. A linear density of 600 kb/in with a postdetection byte-error rate $ was demonstrated based on measured recording data and a software read channel that used a noise-predictive maximum likelihood detection scheme. Using a new iterative decoding architecture, a user bit-error rate of $ can be achieved at this operating point. To facilitate aggressive scaling of the track density, we made several advances in the area of the track-following servo. First, we developed an experimental low-noise tape transport. Second, we implemented an optimized servo channel that together with an experimental timing-based servo pattern enables the generation of position estimates with nanoscale resolution at a high update rate. Third, we developed a field-programmable gate array-based prototyping platform in which we have implemented the servo channel and an $H_{\infty }$ -based track-following controller, enabling real-time closed-loop track-following experiments. Combining these technologies, we achieved a position-error signal (PES) with a standard deviation of 10.3 nm. This magnitude of PES in combination with a 90-nm-wide reader allows the writing and reading of 177-nm-wide tracks at 600 kb/in, for an equivalent areal density of 85.9 Gb/in $^{2}$ . This paper clearly demonstrates the continued scaling potential of tape technologies based on low-cost particulate media.

In this paper, we investigate the effect of read head profile on the playback signal from data and servo sector in a staggered bit-patterned-media recording system. The scaling of the read head is targeted to achieve better data signal quality while such scaling is shown to have negative effect on the servo signal. A secondary servo burst that uses data samples to generate supplementary PES is then proposed and its feasibility is demonstrated.

This paper proposes a filtering method to smooth the position error signal (PES) contaminated by impulsive disturbances in hard disk drives. The impulsive disturbances, observed as sudden changes in PES, may be distributed separately or consecutively. A nonlinear switched filtering method is developed to remove the impulsive disturbances before the position error signal is fed into the servo controller. It turns out that the proposed filtering algorithm is able to effectively remove impulsive disturbances in the corrupted PES with no impact on the stability and the servo performance of the original servo loop.

A solid immersion lens (SIL)-based near field recording (NFR) device is regarded as the next generation optical storage device that can achieve an areal density over 100 GB/in2 . However, the NFR system is very weak for the external shock due to the extremely small gap between a SIL and a disc. Many researches using a gap servo control were carried out, but the results were too insufficient to satisfy needs of the industry. To solve this problem, we propose a new method using air bearing surface (ABS) to avoid a collision between the SIL and the disc occurred by the external shock. In this paer, we check a feasibility of a ABS on shock resistance in NFR system due to many reasons such as a large mass of moving part, a protrusion of the SIL and a low stiffness of wire. We also design an ABS to avoid effectively the collision between the SIL and the disc and to improve shock resistance of SIL based NFR system. Finally, we investigate the effect of the ABS on shock resistance of optical head for SIL based NFR system.

Tilt error can affect a serious effect to holographic data storage system using angle(polytopic) multiplexing. Because the tolerance about tilt error is very tight it is important to measure the tilt error and compensate it. In this paper, tilt error measurement system with additional red laser and reflection geometry is suggested and servo control experiments are conducted. A servo controller to compensate tilt error is designed using disturbance observer. Amount of tilt is decreased smaller than 0.01 degree and signal-to-noise ratio is increased with the tilt servo controller when 0.216 degree of tilt disturbance is applied.

This paper proposes modifications to enhance the original generalized Kalman-Yakubovic-Popov (G-KYP) lemma-based sensitivity function shaping technique that Q-parameterizes the controller and solves for the desired finite impulse response filter Q(z) using linear matrix inequalities (LMI) optimization. By representing Q(z) with an infinite impulse response filter and including an extra LMI that is derived based on the bounded real lemma into the original LMI optimization algorithm, our modifications avoid such problems as unnecessary increase and decrease in sensitivity gain at various frequency ranges, large sensitivity peak, degradation in noise rejection, and insufficient stability robustness against plant uncertainty. In other words, the proposed scheme achieves a better compromise between disturbance and noise rejection performance and stability robustness. The proposed control design was applied to a servo track writing platform. Experimental results show that the control design based on our proposed scheme further reduces the true PES NRRO 3sigma from 6 nm to 5.7 nm and improves the closed-loop stability robustness by 5.1%.

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.

Narrow-band position error at midfrequencies around the open-loop crossover frequency cannot be effectively reduced by using a conventional peak filter, because the attenuation of sensitivity gains has to be traded off with the associated decrease of phase margin. This paper presents a general second-order filter that can reject narrow-band disturbances at any frequency range. The filter zero is designed to minimally degrade the closed-loop system stability and obtain a smooth sensitivity curve around the disturbance frequency. The paper presents a nonlinear optimization procedure for selecting the filter parameters so that the statistical position error is minimized. Experimental results of a piezoelectrically actuated head positioning control system on a spinstand demonstrate that the add-on filter can further reduce the midfrequency nonrepeatable runout of the position error signal by 8% and preserve the stability margin of the original feedback control system

In a hard disk drive with a dual-stage actuator the standard rotary actuation of the voice coil motor (VCM) is combined with an additional micro- or milli-actuation to accomplish high-bandwidth and highly accurate track following. For extremely high density recording, the servo control algorithm designed for a specific dual-stage actuator needs to maintain high performance track following in lieu of external disturbances and uncertainties in the dynamic response induced by product manufacturing tolerances. Essential in the robust design of a servo control algorithm is to bound these uncertainties and design a robust track following servos accordingly. In this paper, we present an experiment based methodology to characterize and bound the uncertainties in the dynamic response of a dual-stage actuator in the form of an uncertainty model. Subsequently, the uncertainty model is used for the analysis and synthesis of a robust dual-stage servo controller that is able to optimize position error variance in the presence of uncertainty information.

We describe a high-performance servo control system for enhancement of spinstand servo performance. This PC-based system uses a multifunction I/O card for controller output and a high-speed digitizer card capable of sampling the frequency-encoded servo pattern at 500 MS/s. The PC, running under the Linux operating system, uses the Goertzel algorithm decoding scheme to calculate the position error signal (PES) at a 15-kHz update rate for feedback control. The control signal drives a custom-made lead zirconate titanate (PZT) actuator, which moves the suspension and thus the read/write head. A proportional and integral (PI) type servo controller supports a 1.1-kHz servo bandwidth, producing a 21.9% improvement of the positioning accuracy of the spinstand.

This paper proposes a robust track-following controller design method for a dual-stage servo system in magnetic hard disk drives (HDDs). The method formulates the problem of minimizing track misregistration (TMR) in the presence of plant uncertainty and variation as a multiobjective optimization problem. Tracking error minimization is naturally formulated as an H/sub 2/ norm minimization problem, while the robust stability issue is addressed by some H/sub /spl infin// norm bounds. This mixed H/sub 2//H/sub /spl infin// control problem can then be formulated as a set of linear matrix inequalities (LMIs) and be efficiently solved through convex optimization algorithms. To enhance the system's tracking performance and stability robustness, the method explicitly takes attenuation of airflow-excited suspension vibration into consideration by an inner loop fast rate damping and compensation controller that utilizes the output of a strain gauge sensor on the suspension surface. Analysis and simulation show that a system designed by this method can achieve good tracking performance while still keeping stability robustness to plant variation and high-frequency spillover.

Very fast, precise and robust servo algorithm and tracking algorithm for a probe storage system are proposed, which use only probes without any additional high-resolution position sensors. Servo algorithm uses the values read by servo probes as the coordinate of every data bit with one-to-one correspondence so that it provides high accuracy, short seek-time, and robustness. Also the concept of virtual subsection of data field is introduced to reduce the number of the servo probes. Tracking algorithm can detect two-axis position errors used for off-track control and synchronization independently and continuously. By vibrating the scanner and by multiplying two decomposition signals, position errors are modulated and demodulated from probe reading signal. Servo+track code is designed to reduce total number of additional probes for servo and tracking and to have stable noise characteristics.

For magnetic disk drives, we have developed a scheme for synchronous servo with maximum-likelihood (SSML) detection that is synchronous around the entire circumference of the track and utilizes ML estimation to detect head position, clock mark phase, and track addresses. Compared to the conventional asynchronous sector servo scheme, the SSML scheme has many, much shorter, servo areas-typically several hundred-distributed on the disk. This results in higher servo information rate, which will be needed for future high-track-density disk drives with a wide servo bandwidth. We analyze the performance of the SSML scheme, including the format efficiency. We discuss a limitation of the synchronous servo scheme with respect to the number of servo areas, and we show an appropriate region for its application. Feasibility of the SSML scheme has been demonstrated in prototype 2.5-in hard disk drives.

This paper considers a new model-based friction compensator for servo control of hard disk drives (HDDs). Using measured and simulated responses in both time and frequency domains as a guide, an HDD designer can iteratively improve the friction model of the HDD system and verify the correctness of the HDD measurement through this new model. By feeding back the model-based estimated friction forces into the voice coil motor (VCM), the frequency response between the read/write head position and the VCM current can be linearized. This allows the cancellation scheme to be developed and implemented through model-based compensation. Experiments have confirmed that the cancellation scheme is indeed effective in the frequency range of 0-300 Hz. Furthermore, by using a sequence of square waves as references for track-to-track seeking, the overshooting in the time responses can be compared between servo controls with and without compensators for friction.

A phase-stabilized servo controller was developed based on a Nyquist plot for moving-suspension dual-stage actuators. The controller uses the suspension resonances of a PZT microactuator to compensate for the track misregistration (TMR) due to windage disturbance caused by suspension vibration. Experimental results obtained using a prototype 3.5-in hard disk drive show that the crossover frequency of the open loop is 2.0 kHz, and that the root mean square of the TMR due to windage disturbance is reduced by 23% compared to that of a conventional notch-based dual-stage controller.

Hard disk drive (HDD) servo technology for media-level servo track writing (MLSTW) is developed. MLSTW is the process of writing servo signals on magnetic disks before they are assembled in drives. It supplies a solution to achieve low-cost and accurate means of servo-signal writing. The HDD servo controller for MLSTW drives compensates for radial and rotational distortions of the servo signals (e.g., track-address, eccentricities, and servo-signal timing) that are inherent in the MLSTW method. The authors prove that the positioning accuracy is improved and the seek time is unchanged by using the new servo controller for HDDs with MLSTW disks.

Disk runout consists of repeatable runout (RRO) and nonrepeatable runout (NRRO). NRRO is the main cause of track misregistration that prevents a high track density, whereas tracking servo control can compensate for most of RRO. An increase in the disk rotation speed increases the amplitude of disk flutter and, hence, causes head position error. Disk flutter is mainly caused by air disturbance due to disk rotation. In this paper, the displacement spectrum is obtained by integrating the velocity data and removing the low-frequency component associated with integration noise. The axial displacements are converted to radial track misregistration units by modal analysis, the reformed Barasch method, and experimental study of the disk. The interaction between head and disk is precisely solved, and it becomes possible to predict the track misregistration by analyzing the disk flutter and transfer ratio for various disks.

In addition to achieving high areal density, recording with perpendicular media must be compatible with other elements of disk drive recording. These include use of rotary actuation, the need for offtrack capability, stray field immunity, and servo control of the head position. Rotary actuation implies writing and reading with the head skewed at substantial angles relative to the track, while servo requires clean track edges. A soft magnetic underlayer, while improving the perpendicular write efficiency, exacerbates problems with head skew and stray fields. We have performed experiments related to drive integration, at the component level and by building drives incorporating perpendicular media. We report on the effect of head skew on the drive, particularly for servo and data recovery. We report on a beveled probe head design which minimizes the effect of skew on the servo pattern and track squeeze. In a 20 Gbit/in/sup 2/ drive, perpendicular media yields comparable servo and nearly equal areal density performance to longitudinal recording.

Demodulation of the servo tracking signals magnetically printed on hard disks by using a lithographically patterned master disk has been studied. Position signal decoded from the printed servo pattern was successfully demonstrated on a spin stand. Position error evaluated in a prototype drive was 30% track pitch. Pulse timing shift control by compensating the pattern dimension, and introduction of a more sophisticated servo control system for actively controlling the printed pattern eccentricity would be key issues for further improvements.

Track access time is an important parameter for high-performance hard disk drives (HDDs). Presently, the resonances of the head actuator caused by the pivot-bearing stiffness are an even more urgent problem, since these resonances have become the main design factor that limits further reduction of track access time and improvement of the servo control bandwidth in HDDs. Our objective in this paper is to investigate, from a mechanics and dynamics viewpoint, the influence of the driving force waveforms on residual vibrations and to identify the characteristics of the waveform, which will lead to zero or very low residual vibrations. Using a simplified model of a head actuator assembly and finite-element simulation, we show that the residual vibration of the head actuator assembly depends strongly on the waveform and the time duration of the driving impulse force. If suitable waveform and time duration of the seeking impulse force are appropriately chosen, very low track seeking residual vibrations and quick track access can be achieved.

This paper presents common system design considerations imposed on magnetic storage devices that employ MEMS devices for positioning of a magnetic probe device over a magnetic media. The paper demonstrates that active servo control of the probe tip to media separation can be achieved with sub-nanometer accuracy. It demonstrates that reasonable-size capacitive sensors can resolve probe tip motions with a noise floor of roughly 22 picometers, allowing them to be used as position sensors in magnetic force microscope (MFM) readout approaches. In addition, this paper demonstrates that although MEMS media actuators can achieve scanning ranges of /spl plusmn/50 um, the mass of the media sled imposes important access time and data rate constraints on such MEMS-actuated mass storage devices.

This article presents an adaptive resonance compensation scheme for microactuator-based dual-stage servo system in hard disk drives. The approach is to identify the microactuator resonant modes and compensate the model accordingly to a simpler one by pole-zero cancellation. Consequently, the servo controller can be designed based on the compensated fixed model despite actuator resonant mode variations. Simulation and experiment results show that this adaptive compensation scheme can suppress microactuator resonance without priori knowledge of the resonant modes. This approach makes the servo control system robust against microactuator resonance variations.

Algorithms are developed that utilize a single analog-to-digital converter in the read channel of a disk drive for dual purposes: for high-rate data detection and for high-resolution servo position error signal estimation. Iterative algorithms exploit the lower clock rate requirement of a servo field, while dithering takes advantage of the periodic characteristic of the servo position waveform.

A comprehensive time domain simulation tool has been developed to provide a realistic simulation of hard disk drive track following servo performance. It serves as a "virtual drive" which allows the prediction of achievable TPI for future products, and off-track shock/vibration characteristics with a given mechanical platform and servo controller. It also provides a convenient tool for enhancing mechanical and servo designs. The simulation tool has three main modules. The methodology used in identifying them is detailed. The simulator was developed based on drive level and component level measurement of position error signal (PES) and mechanical vibrations, and an electrical noise recovery scheme. Simulation and experimental results have been used to evaluate the accuracy of the simulator.

This paper addresses the design and control issues in a novel single-deck six degree-of-freedom (DOF) magnetic levitation (maglev) stage. The proposed design uses an array of solenoids to levitate and to hold a permanent magnet (PM) carrier in place. The solenoids are excited in a manner to generate restoring force when the platform with PMs is displaced from its equilibrium position. The ANSOFT finite element analysis results help providing insight to the design of the mechanism and the solenoid arrangement for the maglev stage. The study builds the mathematical model for the novel maglev stage and uses computer simulation to tune the PID control parameters. Actual implementation results show that the design is feasible and susceptible to position and altitude control

Timing-Based Servo (TBS) is a unique servo technology developed specifically for linear tape drives. In TBS systems, recorded servo patterns consist of transitions with two different azimuthal slopes, and head position is derived from the relative timing of pulses generated by a narrow head reading the pattern. Position signals are nearly perfectly linear over multiple track widths, and highly immune to errors caused by head wear, head instability, debris, and media defects. Multitrack TBS servo patterns are written in a single pass using a novel multigap horizontal thin film servo writing head. The design of the pattern and its dimensions are optimized to provide sampling rate, noise level, and error rate suitable for the intended application. An all-digital TBS servo channel provides a speed-invariant position signal. Pattern recognition algorithms detect servo signal errors, providing a highly robust servo signal. Test results show approximately I pm linearity and 0.3 /spl mu/m noise level over a width of 400 /spl mu/m width with 18 kHz sampling rate. The TBS pattern allows flexibility for encoding additional information without affecting the position signal. By shifting transitions as little as 0.1 /spl mu/m from their nominal pattern positions, a low error rate serial bitstream can be encoded in the servo track. This technique allows tape longitudinal position to be encoded with a resolution of about 2 mm, allowing efficient and precise tape transport control based on the servo signal alone.

The pivot nonlinearity of a disk drive actuator is a complex phenomenon. Various models and compensation schemes were designed to cope with the nonlinearity. In this paper, a fuzzy logic based actuator pivot nonlinearity model is proposed. The fuzzy model can learn the dynamics of the actuator pivot nonlinearity by training with measured data. After the fuzzy model is trained, it can be augmented into a servo controller design as a disturbance observer to cancel the effects of the pivot nonlinearity. The fuzzy model, its modeling performance and a laboratory implementation to demonstrate its effectiveness in pivot nonlinearity compensation are presented.

We describe an alternating dc track servo pattern as a way to avoid magnetization imbalances within the position error signal (PES) regions of the media in perpendicular recording systems. A spin-stand was used to compare signal amplitude and medium noise between the alternating dc track servo pattern and a conventional dc-track servo pattern. The alternating dc track servo pattern improves the signal amplitude and decreases the residual noise. Therefore, the new servo pattern exhibits a superior signal-to-noise ratio of the PES regions.

The nonlinear response of a conventional actuator which depends on the ball-bearing friction is the main factor for determining the high track density of hard disk drives. We cannot get enough servo loop gain in the low-frequency region with a conventional single actuator because of its hysteresis characteristics. We have developed a new planar piezoelectric microactuator which is lightweight and applicable for a hard disk drive. Also we introduced a two-stage servo controller and realized a high servo bandwidth over 1 kHz and enough tracking-error reduction in the low-frequency region.

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.

A time optimal controller design is proposed for the purpose of steering the read/write head of a magnetic disk drive during a seek manuever. The design includes the development of a switch-on-time (SOT) open loop slew control using a third order model of the voice coil motor. The SOT algorithm employs a look up table of switch times versus angle. A perturbation correction stage is included to tailor the switch times to adjust for variations in the operating characteristic of the disk drive (due, for example to heat buildup, wear, etc.). The design also includes a terminal stage servo control that employs an optimal feedback/feedforward controller which is used to provide precise positioning at the end of the seek maneuver. >

A systematic design procedure is presented that can be used to construct servo controllers for dual-stage actuation in a hard disk drive. The systematic approach is based on optimal control theory using an H/sub /spl infin//-norm-based control design, where servo design specifications are formulated in terms of relatively simple weighting functions. Different possible servo control strategies are designed and compared on performance and energy consumption. Results based on a piezoelectric milli-actuator from Hutchinson Technology Inc. illustrate the design of a dual-stage servo controller that is able to perform high-density track recording, with a significant reduction in power consumption.

A method of designing a multi-rate servo controller for a HDD that operates at a higher sampling frequency than that of the position error signal (PES) is proposed. Multi-rate sampling has an advantage for increasing the track density of a HDD without increasing the overhead of the servo information on the disk. A plant model for a design with a higher sampling rate is obtained by adding a zero-interpolator at the output of the position error signal. The controller is calculated by the H/spl infin/ method to suppress the noise at the PES sampling frequency that is created by the use of multi-rate sampling. The servo bandwidth and margins of the method are studied for 2.5" and 3.5" HDDs, and for an HDD with a dual-stage actuator. The multi-rate sampling is especially effective for the dual-stage actuator because the MEMS actuator's transfer function is very clean.