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The Design of Moving Magnet Actuators for Large-Range Flexure-Based Nanopositioning

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The Design of Moving Magnet Actuators for Large-Range Flexure-Based Nanopositioning THE DESIGN OF MOVING MAGNET ACTUATORS FOR LARGE-RANGE FLEXURE-BASED NANOPOSITIONING by David B. Hiemstra A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Engineering (Mechanical Engineering) at The University of Michigan Advisor: Professor Shorya Awtar i © David B. Hiemstra 2014 All Rights Reserved ii ACKNOWLEDGEMENTS Shorya, it will take me the rest of my life to learn all of what you have taught me and see all the ways you have helped me grow. Thank you. Thank you to many people who collaborated with me during this work, including Gaurav Parmar1, Cory Welch, Yangbing Lou, Zhen Wu, Yi Chen, Yilong Wen, and Adrian Adames. Your help, discussions, insights, support, and machine shop time spent with me on this project are invaluable. Everyone else who supported me during this adventure, especially my family, the Precision Systems Design Laboratory, and all my friends—thank you. 1 A certain portion of this work was done in collaboration with Gaurav Parmar in the Precision Systems Design Laboratory at the University of Michigan. This portion has been published in a journal paper in IEEE/ASME Transactions on Mechatronics [83]. iii TABLE OF CONTENTS ACKNOWLEDGEMENTS ............................................................................................ iii TABLE OF CONTENTS ................................................................................................ iv LIST OF FIGURES ......................................................................................................... ix LIST OF TABLES .......................................................................................................... xv ABSTRACT ..................................................................................................................... 16 CHAPTER 1 : Introduction and Motivation ............................................................... 18 1.1 Lorenz-force electromagnetic actuators ..................................................... 19 1.1.1 Moving magnet actuators (MMA) ...................................................... 20 1.1.2 Voice coil actuators (VCA) ................................................................ 22 1.1.3 Characteristics of Lorentz force actuators .......................................... 24 1.1.4 Applications ........................................................................................ 25 1.2 Nanopositioning ......................................................................................... 27 1.2.1 Large range flexure based nanopositioning ........................................ 27 1.2.2 Research goals and impact .................................................................. 30 1.2.3 Challenges in achieving large range nanopositioning ........................ 32 1.3 Design specifications .................................................................................. 34 1.3.1 Motion range ....................................................................................... 36 1.3.2 Motion quality ..................................................................................... 36 1.3.3 Speed ................................................................................................... 37 1.3.4 Temperature stability .......................................................................... 43 1.3.5 Additional considerations ................................................................... 43 1.4 Thesis outline ............................................................................................. 44 CHAPTER 2 : Actuators for Large Range Nanopositioning...................................... 46 2.1 Actuator comparison based on literature survey ........................................ 48 2.2 Actuator comparison using performance indices ....................................... 51 2.2.1 Maximize first natural frequency ........................................................ 57 2.2.2 Maximize scanning frequency ............................................................ 60 2.2.3 Minimize rise time in point to point positioning application .............. 65 2.2.4 Minimize power consumption ............................................................ 66 iv 2.2.5 Minimize positioning resolution ......................................................... 67 2.2.6 Conclusion .......................................................................................... 68 2.3 Piezoelectric actuators ................................................................................ 68 2.3.1 Piezoelectric stack actuators ............................................................... 70 2.3.2 Piezoelectric stacks with amplification mechanism ........................... 71 2.3.3 Comparison between electromagnetic and piezoelectric actuators .... 80 2.4 Piezomotors ................................................................................................ 84 2.4.1 Quasi-static piezomotors ..................................................................... 85 2.4.2 Dynamic piezomotors ......................................................................... 88 2.4.3 Ultrasonic piezomotors ....................................................................... 89 2.5 Magnetorestrictive actuators ...................................................................... 91 2.6 Electromagnetic actuators .......................................................................... 92 2.6.1 Voice coil actuators............................................................................. 94 2.6.2 Moving magnet actuators .................................................................... 99 2.6.3 Multi-phase electromagnetic actuators (linear motors) .................... 103 2.6.4 Additional electromagnetic actuator types ........................................ 104 2.7 Conclusion ................................................................................................ 105 CHAPTER 3 : Prior art concerning moving magnet actuators ............................... 106 3.1 Common MMA architectures ................................................................... 106 3.1.1 Slotting .............................................................................................. 107 3.1.2 Traditional MMA architecture .......................................................... 110 3.1.3 Linear motor MMA architecture ....................................................... 111 3.1.4 “Air” core MMA architecture ........................................................... 113 3.1.5 Slotted MMA (compressor architecture) .......................................... 115 3.2 Additional MMA architectures and design ideas ..................................... 118 3.3 Voice coil actuator designs ....................................................................... 127 3.4 Coil design ................................................................................................ 130 CHAPTER 4 : Design considerations and methodologies ........................................ 134 4.1 Actuator design considerations ................................................................ 134 4.1.1 Force uniformity over stroke ............................................................ 134 4.1.2 Armature reaction ............................................................................. 139 4.1.3 Shorted turn ....................................................................................... 141 4.1.4 Wire selection ................................................................................... 142 4.1.5 Magnetic saturation of circuit components ....................................... 143 4.1.6 Magnet material ................................................................................ 144 4.1.7 Radial instability ............................................................................... 149 v 4.1.8 Thermal management........................................................................ 150 4.1.9 Actuator design considerations map ................................................. 150 4.2 System design considerations ................................................................... 153 4.2.1 Open-loop bandwidth........................................................................ 153 4.2.2 Actuator force ................................................................................... 153 4.2.3 Actuator force uniformity ................................................................. 154 4.2.4 Mechanical load on flexure bearing .................................................. 154 4.2.5 Thermal management........................................................................ 155 4.2.6 System design considerations map ................................................... 156 4.3 Design methodologies .............................................................................. 158 4.4 Figures of merit ........................................................................................ 160 CHAPTER 5 : Dynamic Actuator Constant .............................................................. 162 5.1 Derivation ................................................................................................. 163 5.2 Impact on motion system performance .................................................... 170 CHAPTER 6 : Electromagnetic modeling of an MMA ............................................. 176 6.1 Model neglecting magnetic fringing ........................................................ 180 6.2 Models incorporating
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