Reliability-based design optimization of slider air bearings

This paper presents a design methodology for determining configurations of slider air bearings considering the randomness of the air-bearing surface (ABS) geometry by using the iSIGHT. A reliability-based design optimization (RBDO) problem is formulated to minimize the variations in the mean values of the flying heights from a target value while satisfying the desired probabilistic constraints keeping the pitch and roll angles within a suitable range. The reliability analysis is employed to estimate how the fabrication tolerances of individual slider parameters affect the final flying attitude tolerances. The proposed approach first solves the deterministic optimization problem. Then, beginning with this solution, the RBDO is continued with the reliability constraints affected by the random variables. Reliability constraints overriding the constraints of the deterministic optimization attempt to drive the design to a reliability solution with minimum increase in the objective. The simulation results of the RBDO are listed in comparison with the values of the initial design and the results of the deterministic optimization, respectively. To show the effectiveness of the proposed approach, the reliability analyses are simply carried out by using the mean value first-order second-moment (MVFO) method. The Monte Carlo simulation of the RBDO’s results is also performed to estimate the efficiency of the proposed approach. Those results are demonstrated to satisfy all the desired probabilistic constraints, where the target reliability level for constraints is defined as 0.8.     

Shape optimum design of slider bearings using inverse method

This study aims to develop an algorithm for designing the optimum shape of slider bearing and pressure distribution using an inverse method. The proposed algorithm only needs to obtain the load and moment conditions in order to simultaneously estimate the slider bearing shape and the pressure distribution. The algorithm is developed from the Reynolds integral, and from force and moment balance equations. The least-squares error method, variational method, Gauss–Seidel method and Newton–Raphson method are employed to calculate the optimum shape of slider bearing. Simulation results reveal that as the degree of the shape polynomial function increases, there are corresponding gains in the maximum pressure, load and torque are, and a corresponding decline in the minimum film thickness. On the other hand, the lower the degree of the objective shape polynomial function is, the more accurate the estimated slider bearing shape and pressure distribution are. With increases in degree of polynomial and number of grid points, the errors in the estimated slider bearing shape and pressure distribution can be reduced. The initial guessed values of the coefficients for the estimated slider bearing shape (C_j), the position of the maximum pressure (X_m) and the outlet film thickness (H₀) have notable effects upon the estimated results for the present algorithm. Moreover, the greatest error of initial guessed value is that of C_j, followed by X_m, and then H₀. The estimated pressure distributions are more accurate than the estimated values for film thickness. Consequently, the present algorithm is capable of providing accurate results for slider bearing shape and pressure distribution.     

Refined simulation of friction power loss in crank shaft slider bearings considering wear in the mixed lubrication regime

Friction reduction is a fundamental factor in decreasing fuel consumption of internal combustion engines. During the design stage of the engine the simulation of friction in the crank mechanism plays a vital role to develop optimum solutions. Due to the interaction of oil and elastic structures with rough surfaces in slider bearings, complex simulation models have to be used for representing the relevant physical behavior. The following article is focused on crank shaft slider bearings of large engines.The article describes a procedure evaluated by measurements showing how to model wear profiles of slider bearings to reach a high quality friction forecast. A fundamental influencing factor of bearing friction is given by the mixed lubrication regime and it is considered in the simulation model as part of asperity contact friction and hydrodynamic friction. Further effects result from the compliance in radial and width directions of the bearing structure and the wear of the bearing surface. Furthermore, the specific operating conditions of the slider bearing such as load, temperature, shaft speed and oil characteristics are essential and have to be taken into account.The objective of this investigation is to propose the wear profile of the bearing surface for the simulation model to be treated iteratively, where simulation results for the amount of mixed lubrication are successively assessed. For this purpose an iterative procedure is introduced and validated by measurements on a slider bearing test rig.The applied simulation method is based on elastic multi-body systems; the lubrication film contact is calculated based on Reynolds differential equation via the pressure balance calculated iteratively in the time domain. The model accounting for the mixed lubrication regime is based on the theory of Greenwood and Tripp.     

3D thermohydrodynamic analysis of a textured slider

Analysis of a 3D inlet textured slider bearing with a temperature dependent fluid is performed. Numerical simulations are carried out for a laminar and steady flow. Hot and cold lubricant mixing in the groove is modelled and examined for different operating conditions. Thermohydrodynamic performance of the bearing is analyzed for different texture lengths.Results show that texture has a stronger and positive influence on load carrying capacity when thermal effects are considered. This beneficial effect is at a maximum for the longest dimples with a length shorter than the pad length. Texture is also beneficial for the load carrying capacity when the sliding speed and inlet flow rate are varied. The load carrying capacity of the slider can be increased by up to 16% in severe operating conditions (high sliding speed).     

Hydrodynamic lubrication of rough slider bearings with couple stress fluids

The combined effects of couple stresses and surface roughness on the performance characteristics of hydrodynamic lubrication of slider bearings with various film shapes, such as plane slider, exponential, secant and hyperbolic, are studied. A stochastic random variable with non-zero mean, variance and skewness is used to mathematically model the surface roughness of the slider bearing’s. The Stokes couple stress fluid model is used to characterize the rheological behavior of the lubricant with polymer additives. The modified expressions for the bearing characteristics, namely pressure, load carrying capacity, center of pressure, frictional force are obtained for the general lubrication film shape on the basis of Stokes microcontinuum theory for couple stress fluids. Results are computed numerically for various film shapes under consideration. It is observed that, for all the lubricant film shapes under consideration, the negatively skewed surface roughness increases the load carrying capacity, frictional force and temperature rise, while it reduces the coefficient of friction. On the contrary, the reverse trend is observed for positively skewed surface roughness. Further, these effects are more pronounced for the couple stress fluids.     

Film height optimization of dynamically loaded hydrodynamic slider bearings

A method is presented to determine the optimal surface shape distribution for a hydrodynamic slider bearing. This is the surface shape distribution that is able to carry a prescribed load while maintaining a maximum separation between the surfaces. This method is first derived for a bearing with constant load and sliding speed. It is subsequently extended for a bearing with periodic load and sliding speed. Results for slider bearings with different shapes, loads and speeds are presented. It is shown that the numerical procedure developed in this paper is numerically more efficient than a reference optimization method.     

Contact force measurement using acoustic emission analysis and system identification methods

Acoustic emission (AE) signals were used to investigate the contact force occurring at the head/disk interface of a computer hard drive. The AE sensor was calibrated directly using the “ball drop method” and indirectly using system identification. For the indirect calibration, a high bandwidth laser Doppler vibrometer (LDV) was used. The transfer function was established from the harmonic response derived at different vibration modes and frequencies. A finite element method based transient response simulation of impact was used to estimate the velocity and stress response of the slider. In our experiments, contact forces were found to be in the range of 5–25 mN for nano sliders and 2–10 mN for pico sliders.     

Optimal film shape for two-dimensional slider bearings lubricated with couple stress fluids

The shape of a slider bearing is one of the major geometric conditions influencing the performance of the bearing. The aim of this study is to design the optimum shapes of the surfaces of sliders to meet the load and center of pressure demands specified by the designers. The design strategy uses COMSOL Multiphysics software package to solve the modified Reynolds equation derived on the basis of stokes microcontinuum theory. The sequential quadratic programming (SQP) is used to optimize the shape of the slider bearing. Results show that designers seeking to effectively reduce friction should consider a reducing the aspect ratio since it is the most significant parameter affecting optimal friction. In addition, slider bearings should be optimized with a polynomial profile of order 6 to reduce the computational effort and yield a solution that is very close to the solution of higher order polynomials.     

Optimal design of slider shape for satisfying load demands under specified operation conditions

Optimal designs of sliders are performed in this study in order to meet the desired load demands under specified operation conditions. An optimization method is developed based on conjugate gradient method in conjunction with a direct problem solver which is built to provide numerical solutions for pressure distributions within the fluid film between the slider and the moving surfaces for various geometric conditions. The desired load demands considered in this study are categorized into two kinds: (1) pressure distribution within the fluid film and (2) resultant forces plus centers of load. In this report, compressible-flow model is employed in construction of the direct problem solver. For validation, the direct problem solver is verified by the existing solutions for some special cases. Effects of the bearing numbers on the shape design are evaluated for these two kinds of load demands. Results show that the surface shape of a slider can be designed to meet the load demands under different specified operation conditions accurately by using the present optimization method.     

An analytical approach for analysis and optimisation of slider bearings with infinite width parallel textures

This paper introduces an analytical approach to study the textured surfaces in hydrodynamic lubrication regime. For this purpose, a method of integrating the Reynolds equation for slider bearings with surface discontinuities is presented. By introducing appropriate dimensionless parameters, analytical relations for various texture profiles in both indented and projected forms are delivered. These relations express the nature of mathematical dependence between textured bearing performance measures and geometrical/operational parameters. An optimisation procedure is employed to achieve the optimum texturing parameters promoting maximum load capacity, load capacity to lubricant flow rate ratio and minimum friction coefficient for asymmetric partially textured slider bearings.     

Hard disc drive air bearing design: modified DIRECT algorithm and its application to slider air bearing surface optimization

Hard disk drives continue to increase in areal data density. This requires air bearing sliders with lower and lower flying heights (FH). Also the uniformity of the FH and the flatness of the roll profile with radius become more critical as the FH gets lower. By using modern optimization techniques, it is possible to optimize slider air bearing surface (ABS) designs according to multiple design goals. In this paper, we discuss two modifications to the DIRECT algorithm: one to handle tolerance and one to deal with hidden constraints. Some numerical experiments were carried out using these modifications and the modified DIRECT algorithm was applied to slider ABS optimization. The results show that these two modifications can improve the efficiency of the DIRECT algorithm and they also provide more flexibility in slider ABS optimization.     

B样条曲线参数重载的非线性整体逼近拟合法

论述了一种新的自由曲线的非线性拟合算法,此算法应用最小二乘法来获得最佳拟合曲线。解析和数值积分法的结合使用实现了曲线整体逼近,从而避免了对原曲线采点取样,B样条的曲线表达使之适用于各种复杂曲线的拟合。此算法结合渐进式逼近法可满足不同拟合精度要求,相对于传统的采点插值,或取样近似法,此方法更简洁、快速,拟合效果更佳。     

Ultra-low-flying-height design from the viewpoint of contact vibration

The design of a head-disk interface for ultra-low flying height has been studied from the viewpoint of contact vibration. It is known that a super-smooth disk is necessary for a slider to fly at an ultra-low flying height; however, such a disk increases the friction force, which potentially increases the vibration of the slider. To solve this problem, the head-disk interface must be optimized to reduce this increased vibration. It has been shown that a large pitch angle and center-pad-mounted read/write elements have advantages in terms of slider/disk contact. It has also been found that a micro-texture on the air bearing surface can prevent contact vibration. Moreover, a frequency-shift-damping slider was found to damp the vibration effectively. To further investigate these findings, numerical simulation and modeling of slider dynamics during contact have been performed. Their results revealed two zones of contact vibration: a stable zone and an unstable zone.     

机器视觉在硬盘磁头组装件生产中的应用

依靠传统工艺技术来生产越来越小的超小型磁头组装件,已经越来越困难。机器视觉技术的引入很好地解决了传统工艺所不能解决的问题。本文简述了机器视觉原理,介绍在磁头组装件生产中成功利用机器视觉技术,实现磁头与焊接球之间的精密焊接工艺,该工艺的实现使制造超小型磁头成为可能。     

Nonlinear modeling and dynamic analysis of flexible structures undergoing overall motions employing mode approximation method

This paper presents a nonlinear modeling method for dynamic analysis of flexible structures undergoing overall motions that employs the mode approximation method. This method, different from the naive nonlinear method that approximates only Cartesian deformation variables, approximates not only deformation variables but also strain variables. Geometric constraint relations between the strain variables and the deformation variables are introduced and incorporated into the formulation. Two numerical examples are solved and the reliability and the accuracy of the proposed formulation are examined through the numerical study.     

Possibility of surface force effect in slider air bearings of 100 Gbit/in hard disks

The recording density has been increasing in a high rate of 60% per year in the last 10 years. In the next several years it is expected that the recording density will be 100 Gbit/in² and then 1000 Gbit/in². It is said that a spacing of about 5 nm will be necessary for 100 Gbit/in². For two solid surfaces with such a small spacing, it is expected reasonably that the surface force will come into action. In this paper, numerical analysis was conducted to explore the possibility of the surface force for the slider air bearing working with respect to the glide avalanche. The numerical results show that surface force reduces the stiffness of the slider air bearing and the load carrying capacity as well. It is worth noting that, although the decrease in the load carrying capacity may not be significant, the reduction in the stiffness may be critical for many cases. The reduction in the stiffness of slider air bearings due to the surface force may be one of the most important mechanisms of the glide avalanche. The predicted take-off height to overcome the surface force is about several nano-meters. Increasing the pitch angle tends to decreases the take-off height. A lubricant film of about 1 nm will reduce the risk of the glide avalanche in some extent, but increasing the film thickness has little effect.     

Particle monitoring method using acoustic emission signal for analysis of slider/disk/particle interaction

One of the most important reliability issues in an information storage device is the contamination problem. The slider and disk can be damaged by the particles intruded into the slider/disk interface (SDI). In this work, in order to monitor the slider/disk interaction due to particle injection the acoustic emission (AE) method, which is typically utilized for the detection of slider contact, was used. The raw as well as frequency spectrum of the AE signal were obtained during the particle injection test. The particles were artificially injected inside the test apparatus to simulate the effect of contamination on the slider/disk interaction. SiC and polystyrene particles were used for the tests. As a result, the 1st torsional and bending mode frequencies of the nano-slider were observed when 1 μm SiC particles and 60 nm polystyrene particles were injected into the SDI. Also, it was shown that the particle behavior at the SDI can be predicted from the characteristics of the AE raw signal.     

直流喷雾隔爆型消防水炮炮头结构设计及流场仿真分析

消防水炮在现代消防灭火作战中起着越来越重要的作用,炮头是消防水炮产生射流的关键部件,其结构参数直接影响消防水炮的射流性能。为研究消防水炮炮头对射流特性的影响,设计了一种直流喷雾两用型隔爆消防水炮炮头。利用Fluent流场仿真软件对炮头直流射流和喷雾射流这两种射流方式进行了仿真分析,同时具体分析了炮头喷嘴出口直线段长度、喷嘴开度及喷嘴内径等结构参数对射流特性的影响。相关结论可为消防水炮灭火提供一定的理论指导。     

Nearmiss Count Between Flying Head and Magnetic Disk by Detecting Electrical Potential of Voltage-Applied Slider

A simple in-situ measurement of flying head dynamics is developed, making use of weak conductive sliders and media as capacitance and resistance sensors. This method is confirmed to detect such abnormal functioning occurring in the head-medium interface as nearmiss, contact or crash. Flying head dynamics are quantitatively studied, using a simple and effective method wherein the slider is excited by externally pressurized air flow. Without this disturbance, the nearmiss count is almost zero, with the number tending to increase up to a resonant frequency governed by the slider inertia and air film stiffness with increasing disturbance, presenting a maximum value at a disk velocity of 3 to 5 m/s.     

使用薄膜湿敏元件的湿度控制器的设计

介绍了一种以Ｔａ２Ｏ５薄膜ＭＯＳ型湿敏元件为核心的湿度控制电路。该电路性能稳定,易于调节,应用广泛。