Sang-Joon Yoon

Static Analysis of Flying Characteristics of the Head Slider by Using an Optimization Technique

This paper suggests a method to predict the static solution for gas-lubricated slider bearings in a hard disk drive (HDD) by using an optimization technique. The modified Reynolds equation for the hydrodynamic lubrication theory under the slip condition is used to describe the compressible fluid flow within the gas bearing, and a factored implicit finite difference (FIFD) scheme is applied for pressure calculations. An optimization technique is employed to find the solution at which the forces and moments acting on the gas bearing are in a state of equilibrium

Design optimization for optical patterns in a light-guide panel to improve illuminance and uniformity of the liquid-crystal display

Design of an optical pattern in a light-guide panel (LGP) has relied on empirical methods. However, the characteristics of developing liquid-crystal display (LCD) products such as frequent design modifications, various design conditions, and a short development period make it difficult for the empirical design approach to cope with various design requirements for size, shape, and optical performance of the LCD products. The most important tasks for the design of LGPs are improving average illuminance and the uniformity of the backlight unit. To meet these requirements, a design for an incoupling and an outcoupling part of the LGP is presented. These two parts can be designed in two separate phases: the first for the incoupling part and the second for the outcoupling part. The shape of serration in the incoupling part was first determined by design of experiments, and the dot patterns in the outcoupling part were subsequently determined by a density-based approach with progressive quadratic response surface modeling. Using this design approach, the illuminance was increased from 2241 lx in the initial design to 2299 lx in the optimal design, and its uniformity also increased from 38% to 82%.

An Optimum Design of the Transverse Pressure Contour Slider for Enhanced Flying Characteristics

This paper proposes a design method for determining the configuration of a TPC slider by using an optimization technique in order to meet the desired flying characteristics over the entire recording band. The desired flying characteristics considered in this study are to minimize the variation in flying height from a target value, to maintain the pitch angle as large as possible, to keep the roll angle as small as possible. and to keep the outside rail to fly, lower than the inside rail. The design variables selected are left-side step width, pad width, right-side step width, side step depth, front taper height, and pivot offset in the transverse direction of the slider. The sequential quadratic programming (SQP) method in Automated Design Synthesis (ADS) is used to efficiently find the optimum design variables which simultaneously meet all the desired flying characteristics. To validate the suggested design method, a computer program is developed and applied to the configuration design of two TPC slider models positioned by a rotary actuator. The optimum configurations of each slider model are automatically obtained for three different target flying heights with the same predefined skew angle range without any difficulty. This shows the effectiveness of the proposed design method in comparison with the conventional one based on the parametric study.

Design Optimization of the Taper-Flat Slider Positioned by a Rotary Actuator

In this paper, an optimization technique is utilized to find an optimum configuration of the taper-flat slider positioned by a rotary actuator for enhanced static air-bearing characteristics. The aim of optimization consists in simultaneously minimizing the variation in flying height from a target value, maximizing the smallest pitch angle, and minimizing the largest roll angle, over the entire magnetic recording band. As the design variables, the leading edge taper angle and rail width of a taper-flat slider, and the skew angle at the inside track are chosen since they seem to be the most influential parameters on air-bearing characteristics. The optimum design variables are automatically obtained by using the augmented Lagrange multiplier method, and the static characteristics of the optimally designed sliders are found to be superior to those of the taper-flat sliders of typical configuration over the entire recording band. Results obtained for three taper-flat slider models are reported, showing the effectiveness of the proposed design scheme.

Adjoint Design Sensitivity Analysis of Molecular Gas Film Lubrication Sliders

This paper proposes an analytical design sensitivity analysis (DSA) to topological parameters of MGL (molecular gas film lubrication) sliders by introducing an adjoint variable method. For the analysis of slider air bearings, we used the spatial discretization of the generalized lubrication equation based on a control volume formulation. The residual functions for inverse analysis of the slider are considered as the equality constraint functions. The slider rail heights of all grid cells are chosen as design variables since they are the topological parameters determining air bearing surface (ABS). Then, a complicated adjoint variable equation is formulated to directly handle the highly nonlinear asymmetric coefficient matrix and vector in the discrete system equations of slider air bearings. An alternating direction implicit (ADI) scheme is utilized to efficiently solve large-scale problem in special band storage. The simulation results of DSA are directly compared with those of finite-difference approximation (FDA) to show the effectiveness and accuracy of the proposed approach. The overall sensitivity distribution over the ABS is reported, and clearly shows to which section of the ABS the special attention should be given during the manufacturing process. It is demonstrated that the proposed method can reduce more than 99 percent of the CPU time in comparison with FDA, even though both methods give the same results.

Optimizations of air-lubricated slider bearings using the reduced-basis concept

This paper presents an approach to achieve an optimal air bearing surface (ABS) design by using the reduced-basis concept that can effectively reduce the number of design variables. A multicriteria optimization problem is formulated to meet both the desired flying characteristics over the entire recording band and the fast takeoff performance at the landing zone. The optimal solutions of the sliders, whose target flying heights are 12 and 9 nm, are obtained. Due to its efficiency, our proposed method achieves the optimum solution with less than one-tenth of the effort for the conventional optimization method.

Topology Designs of Slider Air Bearings

A new approach for topology designs of slider air bearings in magnetic recording disk drives is suggested by using large-scale discrete variable optimization techniques. Conventional optimization techniques are restricted to the original topology of the slider by modifying the initial designs. To overcome the restriction, a new topology design approach is presented with enhanced mathematical techniques. Topology optimization of slider air bearings typically has a large number of design variables because the finite mesh must be fine enough to represent the shape of the air bearing surface (ABS). To handle a large number of design variables, an efficient strategy for the optimization including the sensitivity analysis must be established. As a gradient-based local optimization algorithm, the sequential unconstrained minimization technique (SUMT) using an exterior penalty function is used, which requires little computational effort and computer memory. For the gradient calculation, the analytical design sensitivity analysis method introducing an adjoint variable is employed. A topology design problem is formulated as a function of the residuals which is calculated by solving the generalized Reynolds equation. A very large number of discrete design variables (=9409) are dealt with, which denote the rail heights at grid cells. To validate the suggested design methodology a developed program is applied to two slider models with one and three trailing rails. The simulation results demonstrated the effectiveness of the proposed design methodology by showing that the optimized topologies have reasonable shapes without any initial designs.

A study on the flying stability of optical flying head on the plastic disks

In the optical drive system, adopting the optical-flying-type head (OFH) flying on a removable plastic disk, the flying stability of the small OFH should be carefully considered to ensure the reliability for the first surface recording. This study gives two simulation results on the flying stability of the OFH: one is the dependence of the flying height and pitch angle variations on the wavelength and amplitude of disk waviness, and the other is the flying stability of the slider and suspension system during the dynamic load/unload process.

Head Slider Designs Considering Dynamic L/UL Systems for 1-in Disk Drives

This paper focuses on air bearing surface (ABS) design optimizations in order to reduce the lift-off force during the unloading process while satisfying the desired static flying performances. Since it takes a huge amount of computational time to solve time-dependent dynamic load/unload (L/UL) equations, an approximate lift-off force is created as a function of the air bearing suction force and flying attitude parameters by the kriging method. The design framework is employed in wrapping effectively and connecting the kriging model and the static analyzer to the optimizer. An optimization problem is formulated to minimize the amplitude of the lift-off force during the unloading process while keeping the flying height, pitch, and roll angles within suitable ranges over the entire recording band as well as reducing the possibility of slider-disk contact in steady state. Then, two different sizes of slider models are optimally designed for L/UL applications with 1-in disk drive. The L/UL simulation results show that the optimized ABS designs have reduced the lift-off force in the loading process by approximately 62% and 11% for pico and femto design respectively, while satisfying desired static flying performance. In addition, results demonstrated that the optimum slider incorporated with the suspension were not only properly unloaded onto the ramp but also smoothly loaded onto the rotating disk. Therefore, it is believed that the proposed design approach works efficiently in ABS designs for L/UL applications.

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.