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Fluid Bearing Spindles for Data Storage Devices Zhang FLUID BEARING SPINDLES FOR DATA STORAGE DEVICES ZHANG QIDE NATIONAL UNIVERSITY OF SINGAPORE 2003 FLUID BEARING SPINDLES FOR DATA STORAGE DEVICES ZHANG QIDE (B. Eng., M. Eng.) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF MECHANICAL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2003 ACKNOWLEDGEMENTS I wish to express my gratitude to many people who have helped me during this project. The completion and success of the project would not have been possible without their invaluable guidance, support and advice. Firstly, I would like to express my utmost gratitude to my supervisor, Assoc. Prof. S. H. Winoto for his precious encouragement, guidance and fervent assistance whenever I approach him. Next, I would like to thank the late Dr. Chen Shixin of Data Storage Institute (DSI) for his precious advice and fruitful discussions during the process of the project. I would also like to sincerely thank some of the staff of Data Storage Institute, Singapore for their support and assistance in the project, especially to Dr. Liu Zhejie for his advice in electrical motor design. The understanding and support from the management of DSI is greatly appreciated and acknowledged. Finally, the invaluable understanding and support from my wife, my daughter and my family members are forever remembered and cherished. i TABLE OF CONTENTS Acknowledgements ..................................................................................................... i Table of Contents ....................................................................................................... ii Summary.................................................................................................................... iv Nomenclature ............................................................................................................ vi List of Figures..............................................................................................................x List of Tables .............................................................................................................xv Chapter 1 INTRODUCTION....................................................................................1 1.1 Background and Motivation .............................................................1 1.2 Literature Review .............................................................................5 1.2.1 Development of hard disk drives and spindle motors...........6 1.2.2 Development of fluid bearings .............................................9 1.3 Objectives and Scope......................................................................13 1.4 Outline of Thesis ............................................................................15 Chapter 2 FLUID BEARINGS ...............................................................................17 2.1 Classification of Fluid Bearings .....................................................17 2.2 Reynolds Equation..........................................................................17 2.3 Dynamic Coefficients of Fluid Bearings........................................22 2.4 Numerical Solution.........................................................................26 2.4.1 Numerical method...............................................................26 2.4.2 Code validation...................................................................30 2.5 Robust Design of Fluid Bearings....................................................34 2.5.1 Concept of robust design ....................................................36 2.5.2 Taguchi method ..................................................................37 Chapter 3 HYDRODYNAMIC BEARINGS .........................................................42 3.1 Comparison of Different Journal Bearings.....................................42 3.2 Parametric Study of Herringbone Groove Journal Bearing............53 3.3 Characteristics of Thrust Bearings .................................................60 3.3.1 Herringbone grooved thrust bearing...................................60 3.3.2 Spiral grooved thrust bearing..............................................66 3.4 Effect of Machining Tolerance ......................................................71 3.5 Discussion and Conclusions ...........................................................87 Chapter 4 AERODYNAMIC BEARINGS ............................................................88 4.1 Advantages and Disadvantages of Air Bearing..............................88 4.2 Characteristics of Aerodynamic Journal Bearing...........................90 4.3 Characteristics of Aerodynamic Thrust Bearing ............................98 4.4 Optimum Parameters of Aerodynamic Bearing System...............102 4.5 Discussion and Conclusions .........................................................106 Chapter 5 HYBRID BEARING SYSTEMS ........................................................108 5.1 Introductory Remarks...................................................................108 5.2 Hybrid Fluid Bearing System.......................................................109 5.3 Discussion and Conclusions .........................................................111 ii Chapter 6 BI-DIRECTIONAL ROTATING BEARING SYSTEM..................118 6.1 Introductory Remarks...................................................................118 6.2 Characteristics of Bi-Directional Rotating Bearing System.........118 6.3 Discussion and Conclusions .........................................................133 Chapter 7 DEVELOPEMNT AND TEST OF FLUID BEARING SPINDLE MOTOR PROTOTYPES..................................................137 7.1 Prototype of Hydrodynamic Bearing Spindle ..............................137 7.1.1 Specifications....................................................................138 7.1.2 Determination of shaft diameter of journal bearing..........139 7.1.3 Determination of minimum clearance ..............................141 7.1.4 Selection of lubricant........................................................142 7.1.5 Design of bearing system..................................................143 7.1.6 Design of bearing sealing system .....................................146 7.1.7 Further considerations in spindle design ..........................150 7.2 Test of Prototypes.........................................................................154 7.2.1 Test results of hydrodynamic bearing spindle motor........154 7.2.2 Test results of hybrid bearing spindle motor ....................159 7.2.3 Discussion and conclusions ..............................................163 Chapter 8 COMPARISON BETWEEN BALL BEARING AND FLUID BEARING SPINDLES .................................................164 8.1 Effect of Unbalanced Magnetic Force on Spindle Motors...........164 8.1.1 Effect on ball bearing spindle motor.................................165 8.1.2 Effect on fluid bearing spindle motor...............................166 8.1.3 Discussion and conclusions ..............................................169 8.2 Experimental Comparison of Disk Vibration Characteristics ......172 8.2.1 Introductory remarks.........................................................172 8.2.2 Experimental set-up ..........................................................174 8.2.3 Discussion and conclusions ..............................................175 Chapter 9 CONCLUSIONS AND RECOMMENDATIONS.............................183 9.1 Conclusions ..................................................................................183 9.2 Recommendations ........................................................................186 Appendix A ELECTRIC MOTOR DESIGN .....................................................188 A.1 Electromagnetic Design of 8 Poles 9 Slots Motor........................188 A.1.1 Determination of magnet thickness ..................................189 A.1.2 Determination of rotor back iron height ..........................190 A.1.3 Determination of dimensions of stator laminations..........191 A.1.4 Determination of number of turns per phase ....................192 A.1.5 Determination of starting torque.......................................192 A.1.6 Determination of wire gauge ............................................193 A.1.7 Determination of winding resistance ................................194 A.1.8 Estimation of iron loss in stator ........................................195 A.2 Electromagnetic Design of 6 Poles 9 Slots Motor........................198 References................................................................................................................201 iii SUMMARY Four different types of fluid bearing, namely, hydrodynamic bearing, aerodynamic bearing, hybrid fluid bearing and bi-directional rotating fluid bearing are studied in the work. First, hydrodynamic bearings were investigated. The dynamic characteristics of five type journal bearings are studied and compared, and the herringbone grooved journal bearing is selected and recommended as the journal bearing to be used in spindle motors for data storage devices. The optimal design parameters for herringbone grooved journal bearing, herringbone grooved thrust bearing and spiral grooved thrust bearing are identified by parametric studies and can be used in future designs of hydrodynamic bearings. Using Taguchi’s robust design method, effect of parts machining tolerance to the performance of fluid bearings is examined. The relative importance of the individual parameter and its sensitivity
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