A new approach to design safe-supported HDD against random excitation by using optimization of rubbers spatial parameters

Hard disk drives (HDDs) of laptop personal computers (LPCs) are devices vulnerable in harsh mechanical environments. Hence, they need to be protected against damages due to vibration in order to have better read/write performance. In the present study, a LPC and its HDD are modeled as a system with two degrees of freedom and the nonlinear optimization method is employed to perform a passive control through minimizing the root mean square of HDD absolute acceleration due to a base random excitation. The presented random excitation is considered as a stationary, zero mean process with Gaussian distribution. In addition, eleven inequality constraints are defined based on geometrical limitations and allowable intervals of lumped modal parameters. The target of the optimization is to obtain optimum modal parameters of rubber mounts and rubber feet as design variables and subsequently propose new characteristics of rubber mounts and rubber feet to be manufactured for HDD protection against random excitation. In this paper, a nonlinear optimization problem is separately solved for three widely-used cases of HDD by using modified constrained steepest descent algorithm (PLBA) which was extended based on sequential quadratic programming. Finally, the genetic algorithm is used to verify results of the PLBA algorithm.

     

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.     

The design and development of suspended handles for reducing hand-arm vibration in petrol driven grass trimmer

The portable petrol driven grass trimmer is identified as a type of machine whose operator can be subjected to large magnitude of hand-arm vibration. These vibrations can cause complex vascular, neurological and musculoskeletal disorder, collectively named as hand-arm vibration syndrome. The vibration total level on the handle of grass trimmer of 11.30 m/s² was measured, and it has reached the exposure limit value of 5.0 m/s² for daily vibration exposure A(8). New suspended handles were designed to reduce the vibration level. Three different prototype handles with rubber mounts were designed. Handles were made of different materials, and the distance of rubber mounts were varied. From the study, it was observed that not all the handles with rubber mounts were effective in reducing hand-arm vibration. The reduction of vibration depended on the handle material and distance installed between rubber mount and vibration transmissibility of handle-isolation system. Subjective ratings of perception of vibration were measured, and the results indicated that operators were not fully aware of the level of vibration. A prototype handle that is made of heavier material results in the lowest hand-arm vibration of 2.69 m/s². The new handle has significantly reduced the vibration total value by 76% compare with the existing commercial handle.

Relevance to industry

Large numbers of workers are employed to perform grass trimming job in many developing countries. This paper presents the effect of handle types (commercial and prototype) on the commonly used grass trimmer.     

动力总成橡胶悬置系统的动力学仿真研究

动力总成悬置系统是汽车振动系统的一个重要子系统,对改善汽车平顺性和舒适性有很大的影响。为了能够提高动力总成橡胶悬置系统的性能,该文针对某国产轿车的橡胶悬置系统,应用机械系统动力学仿真分析软件ADAMS,建立了动力总成橡胶悬置系统六自由度的动力学模型。通过对动力总成橡胶悬置系统在不同工况下的自振频率、振型、系统的能量分布、各悬置元件的平动位移和角位移的计算及分析比较,尤其将悬置元件的平动位移和角位移作为重点比较对象,讨论了悬置元件的安装角度和刚度系数对上述性能参数的影响,并得出了动力总成悬置系统的最佳方案。     

热环境下金属橡胶隔振结构的耗散特性及参数识别

由于金属橡胶的耗散特性对温度非常敏感且显著影响隔振性能,因此,开展热环境下金属橡胶隔振结构的耗散及参数识别研究十分重要.本文设计了一种双层金属橡胶隔振结构,研究了环境温度对该隔振结构耗散特性的影响规律,基于试验数据建立了金属橡胶双层隔振结构的非线性本构模型.首先,在不同温度下对该隔振结构进行了一系列耗散特性试验,绘制了隔振结构在各工况下的耗散特性曲线,计算了隔振结构的耗散系数、耗散能量以及最大变形势能,分析了温度、振幅、频率对金属橡胶双层隔振结构耗散特性的作用规律.然后,使用非线性最小二乘法对隔振结构的参数进行了识别,建立了该金属橡胶隔振结构的非线性泛函本构模型,准确预测了隔振结构在各工况下的耗散特性曲线.     

高速列车浮式地板振动响应有限元分析

针对采用试验方法开发高速列车浮式地板耗时耗力,且试验规模小,不能反映整车的振动效果的问题,基于有限元法进行高速列车振动响应分析.对三明治夹芯理论、蜂窝板理论和等效板理论进行比较,确定采用等效板理论数值模拟某浮式地板中的蜂窝板;利用橡胶材料的超弹性理论拟合橡胶材料参数;建立完整模型模拟实际工况下浮式地板的振动响应,得到浮式地板的隔振效果.结果表明此浮式地板的隔振效果约为90%,满足设计要求.     

Experimental and numerical investigation of shock response in 3.5 and 2.5 in. form factor hard disk drives

The shock performance of the head/disk interface (HDI) of 3.5 and 2.5 in. hard disk drives (HDDs) is investigated. The displacement of the actuator arm, the suspension, and the disk due to linear shock loads is studied experimentally for both non-operating and operating states of the disk drive. A finite element model of the disk drive was developed to simulate the shock response. Numerical simulation results and experimental results are compared and presented.     

Characterization of structural effects from above-ground explosion using coupled numerical simulation

The response of a building structure to a nearby explosion is complicated by the drastic spatial and time variation of the blast load. Existing studies on the structural responses to explosion effects often employ simplified structural model with assumed loading patterns, such as element-based (beam-column, slab) models, single degree of freedom or lumped mass systems. The validity of a simplified approach depends on whether the governing response and failure mechanisms are well represented in the simplified scheme. For such validation more sophisticated models are required. This paper presents a numerical simulation study aiming to characterize the various structural effects of above-ground explosions. A coupled numerical approach with combined Lagrangian and Eulerian methods is adopted to allow for the incorporation of the essential processes, namely the explosion, shock wave propagation, shock wave-structure interaction and structural response, in the same model. The computational domain extends to the soil around the base of the structure, allowing also for an evaluation of the significance of the ground vibration effect. Results show that for a typical above-ground explosion scenario, the critical structural damage is dominated by air shock loading, while the ground shock induces only some additional vibration whose structural effect is minor. The distribution of structural damage tends to be governed by member level effects on the front face of the structure, whereas the global dynamic response of the system appears to be insignificant. Similar modeling approach may be applied to explore other blast-induced complex response phenomena.     

A peak filtering method with improved transient response for narrow-band disturbance rejection in hard disk drives

Peak filtering methods are commonly used in track-following control of hard disk drives (HDDs) to suppress narrow-band disturbances around a specific frequency. When there are significant plant dynamics within the bandwidth of the filter, the closed-loop system is prone to be unstable due to the lightly damped poles of the filter, as well as lightly damped poles of the plant. On the other hand, settling response of such peak filters during shock disturbances is slow, and increases tremendously with decreasing damping ratios. In this article, we present a novel design of peak filters with improved transient responses using a phase scheduling method in addition to varying gain and damping ratio. By doing so, the stability margin of the closed-loop systems during both transient stage and steady-state stage will be improved. The effectiveness of the proposed methodology is verified with extensive simulations and the proposed method is then applied in an integrative servo analysis platform to carry out a scaling exercise to evaluate and predict servo performance to support 10 Terabits/in².     

Study on flow-induced vibration of head–disk assembly mechanisms in actual hard disk drive

Achieving ultra-high magnetic-recording density in hard disk drives (HDDs) requires clarification of flow-induced vibration issues. In particular, it is necessary to reduce the flow-induced disk vibration called disk flutter. Thus far, however, there has been no experimental research related to disk flutter in actual HDDs. For this study, therefore, the disk-flutter issues have been studied experimentally, using an actual 2.5-in. HDD with one disk and two magnetic heads. The aim was to study the effect of operating magnetic-head mechanisms on flow-induced disk flutter. This study evaluated disk flutter as well as static pressure distribution in the actual HDD, by taking measurements while changing the operating modes of the magnetic-head mechanism as well as the number of operating air-bearing sliders. The study demonstrated that the disk-flutter amplitude increases and its frequency decreases when the magnetic-head mechanisms are operating. It was also found that the amount of decrease in the disk-flutter frequency depends on the number of operating air-bearing sliders whose amplitude increase varies with the specific operating mode of the head mechanisms, such as whether it is in track-following or seek modes. In addition, operation of the magnetic-head mechanisms generated non-uniform static pressure distribution within the HDD. These factors suggest that a decrease in disk-flutter frequency results from the slider-coupled vibration and an increase in disk-flutter amplitude results from the static pressure changes as well as air-following changes, as these vary with the actual operation of the disk head mechanism. From these experimental results, it appears that the disk-flutter issues in actual HDDs should be considered as a system that includes the operation of the magnetic-head mechanisms and disk-coupled vibration.     

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.     

倾斜安装电机振动特性研究

因为安装空间和实际运行的需要,电机在倾斜工作状态下容易产生振动超标。该文针对倾斜安装异步电机结构特点,设计了倾斜安装异步电机的振动特性实验装置,分析了含有减振垫的异步电 机系统刚度特性,通过有限元分析计算出了不同厚度减振垫的刚度系数。实验中,采用不同厚度橡胶减振垫进行振动测试分析,结果显示,在倾斜 5°的安装条件下,异步电机共振转速随减振垫刚度的减小而明显减小。该研究结果可为倾斜安装电机与减振器振动特性匹配、设计与安装提供理论参考。     

Statistical energy analysis on vibrational energy transmission in hard disk drive components

One of the problems found in the 2.5 in. hard disk drives (HDDs) in operation is the vibration of the HDD case. Aiming to find crucial information to reduce the vibration transmitted to the outer shell of HDD, the parameters involving vibrational energy transmission through the main components of HDD are identified by the test-based statistical energy analysis (SEA). First, the vibration tests of HDD in the idle mode are performed in order to identify the contribution of the main components; the top cover, the platters, and the actuator arm to the overall vibration of HDD. The SEA parameters including the dissipation loss factors of the individual components and coupling loss factors of the pairs of the components are then experimentally determined in order to calculate the vibration transmission power among the components. The determined parameters, hence, provide some vibrational energy transmission characteristics to facilitate the design of the HDD components to generate less vibration. With some further studies using this concept, the vibration due to shock exerted to the shell of HDD that is transmitted to main components inside the HDD can also be reduced.     

Two-sensor control in active vibration isolation using hard mounts

To isolate precision machines from floor vibrations, active vibration isolators are often applied. In this paper, a two-sensor control strategy, based on acceleration feedback and force feedback, is proposed for an active vibration isolator using a single-axis active hard mount. The hard mount provides a stiff support while an active control system is used to get the desired isolation performance. In our previous work, we showed that a sensor fusion control strategy for active hard mounts can be used to realize three performance objectives simultaneously: providing isolation from floor vibrations, achieving a low sensitivity for direct disturbance forces, and adding damping to internal modes of the supported precision machine. In the present work, an enhanced control strategy is presented, referred to as two-sensor control. We will show that two-sensor control outperforms sensor fusion, because it has more possibilities for loop-shaping and has better stability properties. The two-sensor control strategy is successfully validated on an experimental setup.     

基于等效模态阻尼的复合隔振系统振动计算方法

基于线性黏弹性假设,将应变能阻尼理论推广到复合隔振系统的等效模态阻尼计算中,运用Python和Abaqus编制相应的计算程序,该程序可考虑材料阻尼的频变特性。以多种材料组成的船舶双层复合隔振系统为算例,计算其等效模态阻尼和隔振器等效阻尼系数。分别采用直接积分法和模态叠加法计算系统振动响应,对比设备、筏架、船底壳的振动加速度响应,验证基于等效模态阻尼的模态叠加法的准确性。结果表明,该方法可以准确计算复杂组合模型的模态阻尼,算例的振动响应计算结果一致性较好,用模态叠加法可以大幅提高复合隔振系统稳态振动响应的计算效率。     

HybridPlan: a capacity planning technique for projecting storage requirements in hybrid storage systems

Economic forces, driven by the desire to introduce flash into the high-end storage market without changing existing software-base, have resulted in the emergence of solid-state drives (SSDs), flash packaged in HDD form factors and capable of working with device drivers and I/O buses designed for HDDs. Unlike the use of DRAM for caching or buffering, however, certain idiosyncrasies of NAND Flash-based solid-state drives (SSDs) make their integration into hard disk drive (HDD)-based storage systems nontrivial. Flash memory suffers from limits on its reliability, is an order of magnitude more expensive than the magnetic hard disk drives (HDDs), and can sometimes be as slow as the HDD (due to excessive garbage collection (GC) induced by high intensity of random writes). Given the complementary properties of HDDs and SSDs in terms of cost, performance, and lifetime, the current consensus among several storage experts is to view SSDs not as a replacement for HDD, but rather as a complementary device within the high-performance storage hierarchy. Thus, we design and evaluate such a hybrid storage system with HybridPlan that is an improved capacity planning technique to administrators with the overall goal of operating within cost-budgets. HybridPlan is able to find the most cost-effective hybrid storage configuration with different types of SSDs and HDDs     

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.     

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.     

Evaluation of MEMS capacitive accelerometers

Capacitive based microelectromechanical systems (MEMS) accelerometers are devices that measure acceleration based on a change in capacitance due to a moving plate or sensing element. These devices have been implemented in many commercial applications, such as automobile air bags, navigation, and instrumentation. These devices have been employed in these and many other applications because they generally offer more sensitivity (more mV/g) and more resolution than similar piezoresistive accelerometers. For most commercial applications, the maximum g-sensing level (MGSL) employed in capacitive accelerometers is 500 g_n. However, in many applications, there can be high-frequency components to an acceleration profile that are much higher than the MGSL of an accelerometer. For example, in vibration monitoring of a hard drive, the peak acceleration can be as high as 10 kg_n. The response and recovery times of an accelerometer to such shock over range are important in many critical applications. In this article, three commercial MEMS-based capacitive accelerometers (Silicon Designs, Inc. 1220, Analog Devices ADXL, 181-1000, and Endevco 7290A-100) are evaluated below and above their respective MGSLs. The output of these devices is compared to that of an Endevco piezoresistive 7270-A accelerometer and an Endevco 2270 comparison standard accelerometer. The emphasis on this investigation is to determine the response of these devices to high-g shock levels and to evaluate their failure modes     

Linear protrusion structure on carriage-arm surface for reduction of flow-induced carriage vibration in hard disk drives

One of the major contributors to head positioning errors is carriage vibration in low frequency due to an air flow caused by disk rotation. It is necessary to suppress the disturbance for Hard Disk Drives (HDDs) to have more capacity. We experimentally studied a reduction in the flow-induced carriage vibration using linear protrusion structures by putting wires on carriage arms. This study was carried out using 2.5?inch HDD which has high rotational speed of 10,000?rpm. We measured position error signals (PES) and compared with a conventional carriage. From the experimental results, we found that the linear protrusion structure was effective to reduce the carriage vibration. Leading edge wire configuration and 2 linear protrusion configuration improved average non-repeatable position errors (NRPE) by 6.9% and 6.4%, respectively.