Multi-body structural effects on the head-disk interface during operational shocks in hard disk drives

Over the past decades, there has been an increase in the demand for hard disk drives (HDDs) used in mobile computing devices. The work performance of a HDD mainly depends on its ability to withstand external disturbances in such applications. Studies of the HDD’s responses and failures during external shocks can be very beneficial for improving the HDD’s designs. Multi-body operational shock (op-shock) models are developed to study the HDDs’ responses during external shocks. Four models which include different components (a disk, a spindle motor, a base plate, a pivot and a head actuator assembly) are introduced in this study to investigate the effects of various components on the drives’ operating performance. It is found that the models must include certain critical components in order to give results for performance reliability when subjected to operational shocks.     

A study of non-operational dynamic responses of disk in 3.5 in. hard disk drive to impact load

Hard disk drives have to be designed to sustain operational and non-operational shock. There are many analytical models and numerical schemes proposed and many experiments conducted for analyzing the transient impact responses of hard disk drives. The existing researches have been focused on the slider-suspension responses at the head-disk interface in which the linear models have been used and the effects of spindle motor have been ignored. In this study, the complex vibrations of disk of 3.5 in. hard disk drive (HDD) under shock are experimentally investigated. The hammer impact test and linear drop test are conducted for the HDD to study the effect of shock on the disk responses. The results show that the nonlinear rock modes substantially contribute to the vibrations of disk when HDD is under shock impact. The nonlinear properties of the disk responses and the mode damping ratio are evaluated by using empirical mode decomposition approach.     

Experimental set-up for simultaneously measuring changes in LD temperature and flying height of HAMR-HGA

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.     

Effect of disk support system dynamics on the stability of head–disk interface during an operational shock in a mobile hard disk drive

There has been a substantial increase in the demand of hard disk drives (HDD) for mobile electronic devices like laptop, camcorders, etc. Mobile HDDs are often subjected to harsh working environments and hence require higher shock resistance for better reliability performance. In this paper, we develop a model for the mobile disk drive to numerically investigate the dynamics of the head–disk interface (HDI) during an operational shock. The results show that the disk and its support system design have a strong influence on the shock resistance. This study can help improve the HDD components and air bearing design for a better shock performance.     

Non-operational shock analysis and design of head gimbal assembly in spinning data storage devices

The work presented in this paper was motivated by the experimental observation of de-bonding phenomena between head gimbal assembly (HGA) and suspension for a commercial 3.5-in. enterprise HDD under non-operational 250?G shock test, which leads to revisit design of HGA/suspension with objective placed on withstanding shocks between the head slider and the suspension. In this study experimental observation and numerical finite element studies were conducted to understand such effect on the mechanical failure of HGA when it is subjected to non-operational shock in parked position on ramp. It was observed that by changing flexure angle in HGA, shock stress can be reduced. FEA simulation results have been presented to verify the findings.     

Shock analysis of non-operating hard disk drives based on a multibody dynamic formulation

Dropping, striking, or bouncing a hard disk drive (HDD) against a hard surface can damage it internally without external evidence of damage. Contact with a hard ground will lift the slider off the disk surface and then slap back on the surface. A drive that is subjected to this type of shock may fail on initial use or the reliability of the drive may degrade over time. Therefore, industry has a lot of interest on the shock conditions that cause a slider to lift off the disk surface. Finite element software such as ANSYS/LS-DYNA is often used to analyze this shock problem. However, this method consumes a great amount of time. It is also difficult to perform design parameter studies because it requires re-analysis of the model of the entire HDD system when certain design variables are changed. This paper presents a flexible multi-body dynamics formulation to analyze the shock problem of non-operating HDDs. Governing equations of motion of the voice coil motor (VCM)–actuators assembly and the disks–spindle system are derived using a Lagrangian formulation. By introducing constraint equations between the slider and the disk surface, the shock response of the whole HDD system has been obtained. Numerical results show that the method is reasonable and the acceleration amplitude which makes the slider lift off can be determined in a significantly shorter time than by the conventional approach. Finally, the effect of drive parameters on shock resistance, such as shock duration and slider resting location are analyzed.     

Analysis of slip characteristics between dimple and flexure in hard disk drives

A mobile hard disk drive (HDD) is often faced with inevitable mechanical problems because of the portability of the drive. Then, almost HDD use much faster emergency parking system to protect the system from these problems. However, very fast emergency parking causes a large ramp contact, which could create dimple-flexure interactions such as a dimple-flexure slip, head-gimbal assembly vibration, unexpected slider motion. These dimple-flexure interactions largely affect the flyability of a slider. As such, dimple-flexure interactions are one of the most important factors in designing a mobile HDD. Therefore, in this study, we characterized the dimple-flexure slip among dimple-flexure interactions and analyzed it using a combination of experiments and finite element modeling. We evaluated the feasibility of dimple-flexure slip and verified the main cause of dimple-flexure slip. We also investigated the relationship between dimple-flexure slips and ramp contact during emergency parking. Finally, we designed the finite element ramp contact simulation, and analyzed dynamic characteristics for the dimple-flexure slip.     

Shock response analysis of hard disk drive using flexible multibody dynamics formulation

Recent development of the shock analysis on the HDD is briefly reviewed. A flexible multi-body dynamics formulation is developed to simulate the shock response of the HDD. If one component in the HDD is changed, only mode shapes and frequencies of that component should be re-calculated and then used to obtain the system’s response. Steady state Reynolds equation is solved to obtain the air pressure on the slider and disk for various slider positions. An air pressure table is formed and used to model the non-linear air bearing during the simulation. Responses of flying height for different direction and shock duration time are analyzed. Results show that the flying state of the slider is more sensitive to the shock with shorter duration time.     

Numerical simulation of thermal flying height control sliders in heat-assisted magnetic recording

Heat assisted magnetic recording (HAMR) is one of the most promising techniques to extend the recording density in hard disk drives beyond 1?Tb/in². Although the diameter of the spot on the disk that is heated by the laser beam is very small, on the order of nanometers, high local temperatures on the disk and the heat dissipated in the slider during the light delivery process can cause thermal deformations of both the disk and the slider, thereby affecting the flying characteristics at the head-disk interface. In this paper, a finite element model is developed which incorporates a HAMR optical system into a thermal flying height control (TFC) slider with dual heater/insulator elements to study the effect of heat dissipation in the wave guide on the thermal deformation and flying characteristics of a HAMR-TFC slider. In addition, the power input of the laser and design parameters of the heaters are investigated.     

Simulation of temperature around laser-heating media in heat-assisted magnetic recording

Heat-assisted magnetic recording (HAMR) is a new approach, which makes the head write data easily under a low magnetic field using a laser to heat the magnetic media to reduce its coercivity, thus, it is considered to be the next generation of higher recording areal density technology. In this paper, a three-dimensional HAMR finite-element model of hard disk drive (HDD) is developed. The temperature distributions around the laser-heating area on disk surface are investigated when the HDD is filled with air and helium. The cooling effects of the disk rotation and the heat convection in head-disk interface (HDI) are also analyzed.     

Microdrive operational and non-operational shock and vibration testing

Commercially available microdrives were tested using linear and rotary shock and vibration testing equipment. Several microdrives designed with different slider and disk configurations were tested to track hard and soft errors as well as head/disk failures. The shock amplitude for operational and non-operational shock was gradually increased to determine the maximum shock that a microdrive could withstand before failure. After failure, the microdrive was examined to determine whether a mechanical failure occurred or whether the failure was due to a magnetic hard/soft error. During a shock event, the displacement and frequency of the vibrations of the microdrive were examined at various locations on the arm and suspension. A scanning laser Doppler vibrometer (LDV) was also used to determine the amplitude and frequency of the vibrations of the front cover and to investigate whether these vibrations contribute to failure of the head/disk interface. A finite element model of the disk drive was also developed to simulate the shock response. The maximum amplitude for failure to occur was determined numerically for operational and non-operational conditions using a pulse width of 2 ms. A comparison of experimental and numerical results is given.     

Efficient simulation of hard disk drive operational shock response using model order reduction

The complex structure, coupled mechanical and fluidic energy domains, and inherent nonlinearity of air bearing between slider and disk involved in the hard disk drive (HDD) are normally presented as a large scale problem which will result in very heavy computational costs in terms of intensive computation and time consuming for HDD research communities and industries to carry out the transient dynamic simulation for HDD design verification, performance analysis, and optimization by using the traditional full-order models, such as finite element model (FEM). This paper presents a method of application of model order reduction (MOR) technique to dramatically reduce the computation time for HDD transient shock performance analysis while capturing the behaviors of original problem faithfully. The reduced models are obtained by performing MOR directly to the FEMs through Krylov subspace and Arnoldi algorithm. The transient operational shock response results of the reduced models of a head suspension assembly (HSA) subjected to half-sine shock pulse demonstrate that the reduced models can dramatically reduce total computation by at least three orders and have very good agreement with those simulated from the original large problem by full-order FEM.     

Optimal dimple point of SFF HDD suspension for improving the unloading performance

The hard disk drive (HDD) using load/unload (L/UL) technology includes the benefits which are increased areal density, reduced power consumption and improved shock resistance than those of contact-start-stop. Dynamic L/UL has been widely used in portable HDD and will become the key technology for developing the small form factor HDD. The main design objectives of the L/UL mechanisms are no slider-disk contact or no media damage even with contact during L/UL, and a smooth and short unloading process. In this paper, we focus on pitch static attitude (PSA), roll static attitude (RSA), force position and dimple point. PSA and RSA are very important parameters in L/UL system and stability of slider is mainly determined by PSA and RSA. Dimple point is also important indicator. Also, we should consider lift-off force. The lift-off force, defined as the minimum air bearing force, is another very important indicator of unloading performance. The large amplitude of lift-off force increases the ramp force, the unloading time, the slider oscillation and contact-possibility. Therefore, to minimize lift-off force, we find the robust dimple point in L/UL performance.     

Numerical analysis of off-track vibration of head gimbal assembly in hard disk drive caused by the airflow

The problem of flow-induced vibration of head gimbal assembly (HGA) in hard disk drive (HDD) is analyzed by means of numerical models. Flow field is calculated in a fraction of physical domain called extended wedge-like domain. For this purpose, appropriate inlet and outlet boundary conditions are specified. The aerodynamic disturbances generated by the slider are studied by performing flow calculations for the cases of with and without slider. It is observed that the slider blocks the airflow causing a high-pressure region in the proximity of the leading surface of the slider. In addition, significant vortical structures are found being generated by the side surfaces of the slider. A finite element model is developed for calculating the response of HGA to the aerodynamic excitations. It is found that the flow disturbances generated by the slider play a significant role in the off-track vibration of the HGA.     

Experimental study of the flow-structure interactions in an air- or helium-filled hard disk drive geometry

The increased rotating speed of the hard disk drive (HDD) causes an unsteady flow field between each stack of disks and leads to flow induced vibration on the slider suspension unit (SSU). This flow induced vibration can reduce the positioning accuracy of the SSU and lead to failure to read or write data. Therefore, reduction of turbulence kinetic energy around the SSU is an important step to improve the performance of the HDD. Several modifications have been investigated in air to decrease the direct effect of unsteady flows on the SSU (e.g. spoiler, damper, or divider in the region upstream of the arm). However, these methods are not fundamental solutions for reducing the vibrations on the SSU. Since the HDDs currently in use are filled with air, helium was selected to compare the flow pattern due to the differing inertial property. To visualize the flow pattern, particle image velocimetry (PIV) measurements were performed at the inter-disk mid-plane between a pair of disks near the arm and the SSU. The geometry is an expanded 2× model simulating Seagate cheetah 2.5-inch drive. For both the air and the helium filled drives, measurements have been performed for two different locations of the SSU for two different angular velocities of 1,000 and 3,000 rpm, corresponding to 5,000 and 15,000 rpm in the commercial drive. The results reveal that the flow patterns of the air and the helium flow are quite similar. However, with respect to the turbulence intensity around the SSU, the helium flow shows a drastic decrease compared with that of the air flow, resulting in much reduced positioning errors. As such, helium-filled drives have merit and should be looked into.     

Numerical simulation of shock response of disk-suspension-slider air bearing systems in hard disk drives

 As non-traditional applications of hard disk drives emerge, their mechanical robustness during the operating state is of greater concern. A procedure for simulating the shock responses of a disk-suspension-slider air bearing system is proposed in this paper. A finite element model of the system is developed and modified, and it is used to obtain the dynamic normal load and moments applied to the air bearing slider. The dynamic load and moments are then used as input data for the air bearing dynamic simulator to calculate the dynamic flying attitudes. We obtain not only the responses of the structural components, but also the responses of the air bearing slider. The procedure is convenient for practical application, because it separates the work into two essentially uncoupled steps. It is used to simulate the shock response of a drive. The system modeled is linear if the load dimple of the suspension maintains contact with the slider, but it is non-linear if the dimple separates due to a strong shock. The air bearing has different responses for upward and downward shocks. Slider-asperity contacts occur when a strong shock is applied. Received: 5 July 2001 / Accepted: 11 December 2001     

硬盘驱动磁头偏置误差检测算法的研究

在硬盘装配过程中,通常需要对磁头间的磁头偏置误差进行预校准,并实施有效的补偿措施以减少磁头切换时的寻址误差,提高读写效率。然而,由于剧烈震动或不当操作等因素的影响,校准好的磁头偏置可能偏离预校准值,从而导致硬盘寻址或读写性能的下降以及伺服启动时间的延长。提出了一种在硬盘正常启动过程中快速有效的磁头偏置的检测和补偿算法,设计了与磁盘扇区绑定磁头偏置滤波方案。实验表明此方法可以快速有效地识别磁头偏置,并启动相应的校准操作,提高了硬盘在剧烈震动后的伺服性能。     

Elastic contact mechanics-based contact and flash temperature analysis of impact-induced head disk interface damage

Shock-induced impulsive slider-disk contact during operation poses a major challenge for modern hard disk drives (HDD). The high contact pressure and surface temperature that are usually associated with such impact could lead to the loss of data or even catastrophic failure of the head-disk interface, rendering the HDD inoperable. In this work, an elastic contact mechanics-based analysis was performed to investigate the impact between a slider corner and a disk surface. First, the analysis uses a homogeneous, smooth contact based on Hertzian impact theory, and trends of critical contact parameters were discussed for various combinations of impact velocities and slider corner radii. From these results, disk plastic failure was identified based on the mean contact pressure. Then, a similar approach was adopted to extend the impact analysis to consider the effects of mechanical properties and thickness of various layers, adhesion, and roughness on the severity of slider-disk impact. Lastly, flash temperatures during the impact were calculated for various conditions, and it was found that thermal erasure could occur under current head-disk impact conditions.     

The evolution of load/unload technology

 Load/unload (L/UL) has recently replaced contact start-stop (CSS) technology in major segments of the hard disk-drive (HDD) industry. Although L/UL has existed since the earliest HDDs, recent implementations use fixed ramp L/UL systems, which are considerably simpler than earlier versions. L/UL offers multiple advantages over CSS, including practically unlimited start-stop cycles and improved shock robustness. However, disk damage can occur in L/UL drives due to head-disk contacts, and a variety of parameters including vertical L/UL speed and slider corner radius should be optimized to minimize damage. Tight control of key tolerances is essential to maximize available disk real estate and minimize the required disk spacing to accommodate L/UL. Power-off retract systems for L/UL must produce higher retract torque than those for CSS designs, leading to new retract circuit designs. Received: 6 July 2001/Accepted: 21 September 2001     

Thermal analysis of helium-filled enterprise disk drive

Enterprise hard disk drives (HDDs) are widely used in high-end storage systems for data center. One of key performance requirements for enterprise HDDs is data access rate, which demands very high rotational speed (e.g. 15 k rpm or more) to permit fast access time. To reach such high speed, the disk spindle motor draws more power to spin and hence the temperature of HDD enclosure increases due to large windage loss. It has been known, temperature rise is one of the most fundamental factors that affect the reliability of the disk drive. In order to develop high reliable enterprise HDDs, thermal management of enterprise HDDs needs to be optimized to improve heat dissipation. One possible approach is to fill disk drive with helium because of its lower density and higher thermal conductivity. This paper investigates thermal performances of helium-filled enterprise disk drives through FEM simulations with experimental validations. Windage loss and heat convection of the HDD filled with helium and air are analysed. The simulated and measured temperature distributions of one commercial enterprise HDD with helium-filled and helium-air mixture are compared with those of an air-filled one. The results show 41% reduction of temperature rise of HDD enclosure can be achieved by filling with helium in comparison with that of air-filled HDD. It is also projected that in terms of equivalent cooling capability like air-filled HDD at 15 k rpm, helium-filled HDD spindle can spin up to 19 k rpm, which will greatly increase data access rate by 25% for future enterprise applications.