HGST Japan Ltd.

Kawasaki, Japan

HGST Japan Ltd.

Kawasaki, Japan

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Atsumi T.,HGST Japan Ltd. | Nakamura S.,HGST Japan Ltd. | Furukawa M.,HGST Japan Ltd. | Naniwa I.,HGST Japan Ltd. | Xu J.,HGST Japan Ltd.
IEEE Transactions on Magnetics | Year: 2013

In this paper, we propose a triple-stage actuator system with a thermal actuator to increase a servo bandwidth of a head-positioning control system in hard disk drives. The thermal actuator is good for control in high frequency range because it has little negative impact caused by mechanical resonances. Therefore, the proposed system with a thermal actuator can control the head position beyond the major mechanical resonances caused by a voice coil motor (VCM) or piezoelectric (PZT) actuator. As a result, the servo bandwidth of the proposed triple-stage actuator system can be higher than that of the conventional dual-stage actuator system which consists of the VCM and the PZT actuators. Simulation results of sensitivity functions showed that the disturbance-compensation performance below 2 kHz will be improved by 6 dB with proposed control system. © 1965-2012 IEEE.


Paoletti U.,Hitachi Ltd. | Noma T.,Hitachi Ltd. | Nishiyama N.,HGST Japan Ltd.
IEEE International Symposium on Electromagnetic Compatibility | Year: 2015

A parallel strip line of very small size has been designed in order to study the susceptibility of hard disk drive heads. High accuracy and low cost design is obtained using printed circuit board technology. Details of the design are discussed. A special solution for implementing the termination is proposed. The parallel strip line has been fabricated and its usabilty up to at least 6 GHz has been confirmed in terms of the voltage standing wave ratio and internal to external field ratio. Calibration was conducted by measuring the field across the termination resistors. © 2015 IEEE.


Naniwa I.,HGST Japan Ltd. | Nakamura S.,HGST Japan Ltd.
Microsystem Technologies | Year: 2014

Heat-assisted magnetic recording (HAMR) is a promising technology for overcoming the performance limit of the conventional magnetic head in a hard disk drive. The HAMR-HGA consists of a HAMR-head slider, a suspension, and a laser diode (LD) mounted on the slider. An optical near-field transducer (NFT) and a waveguide are near the write-pole in the head slider. During the HAMR process, current is applied to an LD, and the laser beam is coupled into the waveguide and delivered to the NFT. The NFT further concentrate the focused optical spot and the optical spot locally heats the recording medium, thereby reducing the media coercivity. The temperature of the LD and the slider, however, increases. The slider is, moreover, locally deformed, and the flying-height (FH) changes. Therefore, an experimental set-up to simultaneously evaluate the FH change and LD temperature of the HAMR-HGA was required to develop the HAMR technology. We developed a novel experimental set-up for simultaneously evaluating laser characteristics (power, voltage, and wavelength), the increase in LD temperature, and the FH change of a HAMR-HGA. By using this set-up to measure these characteristics of our prototype, the HAMR-HGA showed that the FH decreased as the LD temperature increased. The LD temperature is directly related to the laser characteristics. The change in laser characteristics affects the read-write performance of HAMR. The FH change also affects the performance. Therefore, the developed experimental set-up should be useful in improving HAMR-HGA. © 2014 Springer-Verlag Berlin Heidelberg.


Yabui S.,HGST Japan Ltd. | Okuyama A.,Tokai University | Atsumi T.,HGST Japan Ltd. | Odai M.,Hitachi Ltd.
Journal of Advanced Mechanical Design, Systems and Manufacturing | Year: 2013

This paper presents an adaptive feed-forward cancellation (AFC) technique with a damping function based on optimized AFC. The proposed AFC includes a mechanical resonance characteristic as an internal model that is realized by using the damping function and that achieves the best performance in the frequency domain. This makes it possible to apply the proposed AFC to suppress not only repeatable run-out (RRO) but also non-repeatable run-out (NRRO) of the head positioning system in hard disk drives. Simulation results showed that the proposed AFC can suppress NRRO such as disk flutter vibration and that the stability of the feedback loop was improved by the damping function. Copyright © 2013 by JSME.


The relationship between natural frequency, damping, the waveform of a feedforward acceleration input, and the transient vibrations of track-seek control is derived theoretically and a target for vibration design of the head actuator of a hard disk drive (HDD) is discussed from the viewpoint of the transient vibrations. When the acceleration feedforward input of the track-seek control is expressed as a polynomial function of time, the transient response of a single degree of freedom system is solved by applying integral by parts to the Duhamel’s integral repeatedly. The results show the transient vibrations are generated at the initial and terminal times of the input and their amplitude depends on the lowest orders of non-zero derivatives of the polynomial. They also show that increasing the damping ratio effectively reduces the transient vibrations for fourth and sixth order polynomials but not for fifth and seventh order polynomials. The results were confirmed by performing a continuous time simulation and analyzing the shock response spectrum. Also discussed is the relationship between the transient vibrations and the seek time and track pitch, which are key parameters associated with the data access time and the HDD capacity. This relationship indicated the requirements needed for vibration design of the head actuator to increase HDD performance and capacity. © 2015 Springer-Verlag Berlin Heidelberg


Yabui S.,HGST Japan Ltd. | Atsumi T.,HGST Japan Ltd. | Nakamura S.,HGST Japan Ltd.
Microsystem Technologies | Year: 2016

This paper introduces an improvement method of convergence behavior for adaptive feed-forward control in hard-disk-drives (HDDs). To increase a data capacity of HDDs, head-positioning-control system must compensate for any disturbances which worsen the positioning accuracy. Especially, it is important to compensate for external disturbances in the head positioning system of 2.5 type HDDs. Previous studies proposed an adaptive feed-forward control method to compensate for the external disturbances. However, the control method have problems with respect to convergence in the adaptive algorithm. To overcome the problems, we have developed design method of initial values for the adaptive feed-forward control by using data-driven design method. The initial values designed by proposed method can improve the convergence behavior for the adaptive algorithm. © 2016 Springer-Verlag Berlin Heidelberg


Furukawa M.,HGST Japan Ltd. | Xu J.,HGST Japan Ltd. | Kato Y.,HGST Japan Ltd. | Wada T.,Hitachi Ltd.
Microsystem Technologies | Year: 2013

We developed a tester consisting of minor-loop and major-loop quasi-static test (QST) units in order to better understand head instabilities under conditions where the head slider was flying on the disk. The minor-loop QST unit, composed of a spin-stand and an electromagnetic coil, was used to understand the mechanism of head instabilities caused by thermal stress due to flying-height control using a thermal actuator and caused by mechanical stress due to contact between the head and disk under flying conditions. The major-loop QST unit was used to investigate head damage in detail. We designed and fabricated the tester and conducted experiments that focused on thermal and mechanical stress. The results confirmed that the new method was effective for studying head instabilities at the head disk interface of hard disk drives (HDDs). © 2013 Springer-Verlag Berlin Heidelberg.


Suzuki K.,Hitachi Ltd. | Ohta M.,HGST Japan Ltd.
Microsystem Technologies | Year: 2013

We proposed a carriage called a two-layer coil carriage that attenuates an out-of-plane mode. The coil of the proposed carriage is divided into two parts that are stacked on one another. The ratio of the current for the two coils can be changed by optimizing the coil coefficients. We have clarified the mechanism of excitation of the out-of-plane mode. We constructed the two-layer coil carriage, and measured the frequency response from the voice coil motor current of the two coils to head displacement. The effectiveness of the proposed carriage in reducing excitation of the coil torsion mode was demonstrated through simulation and experiment. © 2013 Springer-Verlag Berlin Heidelberg.


Eguchi H.,HGST Japan Ltd. | Kobayashi I.,HGST Japan Ltd.
2012 Digest APMRC - Asia-Pacific Magnetic Recording Conference: A Strong Tradition. An Exciting New Look! | Year: 2012

We measured and calculated shock responses due to the thermal stick-slip phenomenon in hard disk drives, and visualized the stress wave propagation. We utilized PZT elements and the response envelopes to observe the propagation. Then we calculate the shock response and compared the results with the measurement. We observed that the stress wave propagated from the stick-slip point, through the actuator to the head. Using this calculation model, we demonstrated shock detection investigation using the shock sensors. We compared the sensor responses attached to the base plate with one on the actuator, and found the response on the actuator decreases due to the cushiony property of the pivot bearing. We proposed to use the lower-natural-frequency sensor if the sensor is on the actuator. © 2012 DSI.


Yabui S.,HGST Japan Ltd. | Atsumi T.,HGST Japan Ltd.
IECON 2015 - 41st Annual Conference of the IEEE Industrial Electronics Society | Year: 2015

This paper presents design method of initial value in adaptive feed-forward control by using support vector machine. The adaptive feed-forward control are implemented to compensate for disturbances induced position error signals in positioning control systems. Although the effectiveness was verified in previous studies, experimental results show that the adaptive control have mainly two problems. The adaptive algorithm requires time to converge the adaptive parameters and the performance may vary in experiments. To overcome the problems, we have developed an improvement method of convergence for adaptive feed-forward control by setting initial values. The experimental results in hard disk drives show that the proposed method can improve the convergence time and the performance variation. © 2015 IEEE.

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