Head-positioning control system using thermal actuator in hard disk drives

In this paper, we propose a head-positioning control system with a thermal actuator in hard disk drives (HDDs). The frequency response of the thermal actuator showed that the thermal actuator system has no mechanical resonant mode. Therefore, this head-positioning system with a thermal actuator can control the head-position beyond the major mechanical resonances caused by a voice coil motor (VCM) or suspensions. In this study, the system was a dual-stage actuator system; the first actuator was a VCM, and the second was a thermal actuator. Simulation results for a track-following control in an HDD demonstrated the validity of the proposed method.     

Depletion and harvesting thermal energy from actuator arm electronics in hard disk drives

In this paper, a thermal resistance network model is established for calculating arm electronics (AE) chip junction temperature to ambient. The thermal resistance network is based on heat transfer paths from chip to ambient. This network can be used to predict AE chip junction temperature to ambient under thermal managements. The accuracy of the presented model is also proven through comparing the results of numerical calculation and simulation. A piezoelectric micro-thermal energy harvester is designed and placed on top of AE chip. Finite element analysis (FEA) software is used to establish the model of PZT membrane generator and analyze piezoelectric characteristics of PZT membrane. The relationship between average voltage output and electrode size is shown.     

Separated pivot-shaft actuator for small skew angle in hard disk drives

A large skew angle in a hard disk drive (HDD) adversely affects the flying stability of the head sliders and the off-track capability of the read/write head. A novel actuator in the form of a separated pivot-shaft actuator (SPA) with a small skew angle is proposed in this paper. The SPA was particularly designed for a four-disk 3.5-in. HDD and has a skew angle of ±1.6°, which is approximately one-tenth of that of a conventional voice coil motor. The SPA was numerically analyzed by a finite element method, and its mechanical characteristics were compared with those of a long-arm actuator (LAA) (which is a strong candidate for a small-skew-angle actuator) with respect to the seek performance and frequency response. It was found that the SPA had a higher resonant frequency, which enabled the achievement of a wider servo-bandwidth compared to the LAA, and that the average seek time of the SPA was significantly shorter than that of the LAA.     

Topology optimization of actuator arms in hard disk drives for reducing bending resonance-induced off-tracks

The objective of this work is to find an optimal actuator arm configuration in hard disk drives (HDD’s) for sufficiently small arm bending-induced off-track error by maximizing the fundamental eigenfrequency of arm bending modes subject to a constraint on the mass moment of inertia of arms. By applying the topology optimization method for the purpose, an arm configuration having two balancing holes instead of a single balancing hole in conventional designs was obtained. It is numerically shown that an optimized arm configuration substantially increases the arm bending resonant frequency with little change in the mass moment of inertia of arms in comparison with conventional designs having a single balancing hole. Finally, the performance of an optimized actuator arm is verified by showing that the eigenfrequencies associated with arm bending modes are increased by about 100?Hz and the off-track error by measuring the position error signal (PES) from actual sample drives can be reduced by as much?as?25%.     

Thermal actuator for accurate positioning read/write element in hard disk drive

Flying height control (TFC) sliders with thermal actuation, which make it possible to control head disk spacing, have been introduced in commercial products for compensating the flying height loss and reducing the risk of head disk contacts, thus to increase the bit density (Gupta et al. in ASME J Tribol 123:380–387, 2001; Juang and Bogy in ASME J Tribol 129:570–578, 2007; Kurita et al. in Microsyst Technol 12:369–375, 2006; Shiramatsu et al. in IEEE Trans Magn 42:2513–2515, 2006). However, with the increasing of areal density, it is also necessary to increase the track density. To increase track density, it is required to improve the performances of head positioning system in terms of fast transition from one track to another (track seeking), fast and accurate settling, and precise track following of the target track. Dual-actuator systems (Choe in A thermal driven micro actuator for hard disk drive. In: Proceedings of the APMRC 2010, Nov 10–12, 2010, Singapore, 2010; Bain et al. in Electrothermal actuator for hard disk drive application. In: Proceedings of the APMRC 2010, Nov. 10–12, 2010, Singapore, 2010; Furukawa et al. in Fabrication and test of thermal actuator. In: ISPS 2011, Jun. 13–14, Santa Clara, CA, USA, 2011) have been proposed to meet these requirements. These dual-actuator systems consist of a voice-coil-motor (VCM) as a first-stage actuator and a transducer (piezoelectric, electromagnetic, electrostatic and thermal) as a second-stage actuator. The second-stage actuator could be designed to actuate the movement of suspension (suspension driven), slider (slider driven) or head element (head driven). Most of reported dual-actuator systems were made to be suspension driven or slider driven. Recently, Choe by (A thermal driven micro actuator for hard disk drive. In: Proceedings of the APMRC 2010, Nov. 10–12, 2010, Singapore, 2010) and Bain et al. by (Electrothermal actuator for hard disk drive application. In: Proceedings of the APMRC 2010, Nov. 10–12, 2010, Singapore, 2010) reported to use thermal actuators for driving head movement. They attained a thermal transient of less than 10?μs using 2-D finite element simulation. Using thermal actuators to accurately position read/write element could be a promising technology for mass production for future HDD. This kind of control theme was termed as thermal positioning control (TPC). The objective of TPC actuator design is to achieve large actuation stroke as well as increase frequency bandwidth. In our studies, the design procedure may involve several steps: (1) Fundamental studies with simple TPC slider structure by finite element simulations to explore the feasibility of TPC actuation and estimate working frequency range. Also we may be able to find out the problems which induced by TPC actuator. (2) Prototyped TPC slider, and tested its frequency characteristics to confirm the feasibility and achievability of TPC actuation. (3) Increases TPC actuation stroke and frequency bandwidth by improving TPC slider structures and servo control schemes. This paper explores the feasibility studies of TPC slider by finite element simulation. The principle and structural modeling of slider with TPC heater was first introduced. Then static–static simulation was carried out to study the steady deformation displacement at read/write element and transient analysis was conducted to estimate the deformation displacement response. It was found that 7?nm deformation stroke at read/write element could be attained at steady state with 50?mW input power, and the deformation displacement was about 1.7?nm after power was applied to TPC heater 1.5?ms (frequency of 1?kHz based on first order delay system). Meanwhile, it was found that protrusion on the air bearing surface (ABS) becomes a problem for the slider’s flying performance, thus the ABS design was improved to reduce protrusion’s effect, and cross-talk effect between TFC and TPC actuators was then investigated.     

Human-based evaluation of sound from hard disk drives for noise control

Most recent efforts to reduce the noise produced by hard disk drives (HDDs) have been based on measurable physical quantities such as the sound pressure level. However, given that the purpose of reducing HDD noise is to improve human comfort, it would be better to evaluate noise levels on the basis of human perceptions. To address this issue, we carried out human jury tests on eight HDDs in which people were asked to compare the noise of pairs of HDDs and determine which HDD sounded louder or more annoying. The jury test results were then compared with sound pressure level measurements of the noise produced by the idling HDDs and a discrepancy was found between the human perception of HDD noise and the physical quantities commonly employed for noise control. Psychoacoustic variables such as loudness level showed a better correlation with the jury test results.This research was supported by Samsung Electronics Co., South Korea. The authors gratefully acknowledge the support and encouragement provided by Dr. Young Son and Dr. Yunsik Han.     

Multi-frequency disturbance rejection via blending control technique for hard disk drives

This paper is concerned with the rejection of multiple narrowband disturbances in hard disk drives (HDDs). Inspired by a control blending idea, the multi-frequency disturbance rejection is formulated as a blending control problem. Each disturbance rejection is accomplished by using the H₂ optimal control method. Based on all H₂ optimal controllers, the blending technique is applied to yield a single controller which is capable of achieving rejection of all disturbances. Rejections of two and three disturbances for a 1.8-inch HDD VCM actuator are taken as application examples in the paper. Simulation and experimental results show that the ultimate controller results in a simultaneous attenuation of disturbances with frequencies higher or lower than the closed-loop system bandwidth. Moreover, the method turns out to be able to lift phase and thus prevent phase margin loss when it is used to deal with disturbances near bandwidth.     

Servo signal processing for flying height control in hard disk drives

A novel method of measuring the relative head-medium spacing based on a measurement in the servo sectors is developed and simulated using a read back signal model. The spacing measurement is tested experimentally on a spin stand where the flying height is varied using the resistance heater element in a thermal flying height control slider. In addition, voltage step response measurements were obtained. The data were used to perform system identification and estimate the dynamics of the thermal actuator. The model can potentially be used for thermal flying height control.     

Settling control with reference redesign for dual actuator hard disk drive systems

This paper considers settling control of a recording head for a dual actuator system for hard disk drives consisting of a coarse actuator (voice coil motor, VCM) and a fine actuator (peizoelectric transducer, PZT). The design method proposed in this paper is called the dual actuator reference trajectory re-design (RTRD). In this method, the design is divided into three steps. In the first step, the coarse actuator loop is designed to achieve stability and basic performance. In the second step, the fine actuator path is designed by loop shaping for superior performance of the overall system. Finally, the reference signals are generated for both the coarse and fine actuators by minimizing the square integral of jerk during the transition. The reference signals are updated or redesigned in real time as the recording head approaches the target track for smooth landing and minimal residual vibration. The “soft switching” technique is applied for gradually introducing the fine actuator (PZT actuator), which may shorten the settling time and achieve a smooth settling response. The effectiveness of the proposed approach is evaluated by simulations.     

Active magnetic inertia latch for hard disk drives

In this paper, a new hybrid inertia latch is proposed to improve the shock resistance and the loading time for hard disk drives. The new latch mechanism combines the inertia effect and the magnetic force by additional yoke and magnets, reducing the time required for loading the head to media that is the mechanical limitation of the widely used pawl inertia latch. The operating mechanism of the proposed latch is optimally designed using an electromagnetic simulation, and it is verified by experiments using a prototype. The new latch system reduces the time required for loading the head to media up to 8 ms.     

Self-sensing actuators with passive damping for adaptive vibration control of hard disk drives

A push–pull piezoelectrically actuated devices have been developed for higher bandwidth servo systems as microactuators for fine and fast positioning, while the voice coil motor functions as a large but coarse seeking. However, the current dual-stage actuator design uses piezoelectric patches only and therefore a dual-stage servo system using enhanced active–passive hybrid micro piezoelectric actuators is proposed to improve the existing dual-stage actuators for higher precision and shock resistance, due to the incorporation of passive damping in the design. In this paper, three different configurations of self-sensing actuators (SSAs) incorporating an adaptive mechanism for vibration control of suspensions in dual-stage hard disk drives (HDDs) are investigated. In the piezo-based SSA configuration, the signal sensed due to mechanical deformation is mixed with the control input signal, which would be corrupted due to the variation of the piezoelectric capacitance when a fixed bridge circuit is used. In this study, a self-tuning adaptive compensation is used to combine with the SSA technique to extract the true sensing signal for the vibration control of suspensions in HDDs. An assembled suspension with piezoelectric microactuators is tested to demonstrate the vibration suppression performance of this adaptive structure under an external shock disturbance such as hammer excitation. The experimental results show that the target vibration modes have been suppressed effectively with using the adaptive positive position feedback controller for the enhanced SSAs with passive damping in HDDs.     

Narrowband performance of active control on flow-induced vibrations inside hard disk drives

This paper presents an experimental study of narrowband active control on the flow-induced vibrations (FIV) on the head gimbals assembly (HGA) in a working hard disk drive (HDD). Firstly, experiments with an analog feedback close-loop were conducted as demonstration for narrowband active control on principal peaks in the spectrum of the off-plate FIV on the HGA whose signal was collected with a 1-D laser Doppler vibrometer (LDV). Secondly, the modal testing on the experimental HDD was carried out to find out where the spectrum principal peaks focused in current active control come from. Thirdly, a digital feedback control close-loop was implemented in experiments for narrowband suppression on the focused FIV spectrum peaks on the HGA. In those close-loops, the off-plate HGA vibrations detected by the LDV were used as feedback error signals, then the signals was passed through an analog or digital controller to generate feedback signals to drive a piezoelectric disk to actuate feedback acoustic pressure around the HGA. Active control experiments were conducted in narrow bands on five principal peaks in the HGA off-plate vibration spectrum, around 1,256, 1,428, 2,141, 2,519 and 3,469 Hz, respectively. It is shown that distinct narrowband suppression of at least 10 dB can be achieved on all these HGA vibration peaks.     

A design based on final-state control for residual vibrationless seeking in hard disk drives

A new design method - based on a final-state control (FSC) - for short-span seeking in a hard-disk drive (HDD) has been developed. The short-span seeking is performed by two-degree-of-freedom (2-DOF) control, which uses a feedforward (FF) control input along with a reference trajectory. The design method can directly generate the FF control input, whose derivative at a specified order is minimized and whose power spectrum amplitude is reduced at a specified frequency. The residual vibration caused by mechanical resonance can therefore be reduced by the generated FF control input. Test with a 2.5-in form-factor HDD experimentally confirmed that the developed seeking control significantly reduces the residual vibration in a HDD.     

Track following servo control for rotary piezoelectric motor based primary actuation in hard disk drives

In this paper, we show the tracking performance of a rotary piezoelectric motor based hard disk drive actuator. The actuator is built and modeled for positioning servo in disk drive systems. The Piezo motor replaces the voice-coil-motor based primary actuation. Simulation and experimental results for its servo system proves that it can help to achieve track density of more than 1000?KTPI.     

Aerodynamically induced power loss in hard disk drives

In this paper, the effects of rotational speed, form factor and enclosure conditions on power dissipation in hard disk drives are presented. The aerodynamically dissipated power losses by 3.5, 2.5 and 1 in. hard disks are experimentally measured using a vacuum chamber and compared to theoretical estimations. Experiments in open air without enclosure agree well with theoretical predictions; a 3.5-in. disk satisfies the turbulent model but 1 and 2.5-in. disks match the laminar one, which is inversely proportional to the half power of Reynolds number. Experiments using a single 3.5-in. disk in enclosure show that aerodynamic power loss is proportional to the second power of rotational speed and the fourth power of disk radius, which agrees with the laminar theory rather than turbulent one. It is also shown that the aerodynamic power loss is reduced as the axial gap and radial clearance of enclosure decrease.