SLA} SE] rt Ad of Ol ATA AA BA ALAELS] 412] 9t alo} Design and Control of Cost-Effective Electrostatic Suspension Systems SAL sa aS 7\ AAS A ##t† Truyen The Le Design and Control of Cost-Effective Electrostatic Suspension Systems Aen AS o] EES FHV} Bo] HOE AS 2011 xỉ 02 4 SAL] Sa a} 7]2]2'§3} BSS Truyen The Le Truyen The Le 2] ^Atlld4+ Bata (21) AAA A ASF (21) ALATA A gan (1) AJALS] ] a+ (SÙ 2]ALs] A 4) 7-5 (21) =A] 5† ct2) 7| Al ALS Ab 3 S††} 2011 tì 02 J Thesis for the Degree of Doctor of Philosophy Design and Control of Cost-Effective Electrostatic Suspension Systems By Truyen The Le Supervisor: Prof. Jong Up Jeon Department of Mechanical and Automotive Engineering Graduate School University of Ulsan February 2011 Design and Control of Cost-Effective Electrostatic Suspension Systems By Truyen The Le Supervisor: Prof. Jong Up Jeon Submitted to the Graduate School of the University of Ulsan In partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy At Department of Mechanical and Automotive Engineering, University of Ulsan, Ulsan, Korea February 2011 Design and Control of Cost-Effective Electrostatic Suspension Systems This certifies that the dissertation of Truyen The Le is approved by Committee Chairman Prof. KYU YEOL PARK Committee Member Prof.
JONG UP JEON Committee Member Prof. OCK TAECK LIM Committee Member Prof. YOUNG SOO SUH Committee Member Dr. KEE BONG CHOI ACKNOWKEGMENTS I would like to express heartfelt gratitude to my supervisor, Prof.
Jong Up Jeon for his guidance, advice and support during my study in University of Ulsan. I would like to thank Professors in the committee, Prof. Kyu Yeol Park, Prof. Ock Taeck Lim, Prof.
Young Soo Suh and Dr. Kee Bong Choi for their suggestion and comments throughout the research. I would like to express special gratitude to my wife and my children, Linh Giang & Anh Quan, whose patience and support have been invaluable during my study. I would like to express gratitude to my parents, sisters and brothers for their encouragement and support.
I would like to thank all members in MEMS Lab., University of Ulsan for their friendship. February, 2011 TRUYEN THE LE CONTENTS 1.4 Squeeze film air bearing 5 1.7 Scope of the Work and Outline of the Thesis 10 DYNAMIC MODEL OF ONE DEGREE OF FREEDOM ELECTROSTATIC SUSPENSION SYSTEM 12 2.3 Dynamic equation 17 THE COVENTIONAL ELECTROSTATIC SUSPENSION SYSTEM 18 3.1 Proportional-Integral-Derivative (PID) controller 19 3.2 Design of feedback control by using technique back-stepping 23 3.3 Sub-conclusion | 30 DEVELOPMENT OF COST-EFFECTIVE ELECTROSTATIC SUSPENSION SYSTEMS 4.1 Principle of operation 33 4.2 Simple on-off control 34 4.3 Bang-bang time optimal control 36 4.1 State space representation 36 4.4 Delay controller 58 il 4.2 Design of delay controller and stability analysis 58 4.5 Variable structure controller 78 4.1 Design of variable structure controller 79 4.6 Sub-conclusion 3 97 - NOVEL ELECTROSTATIC SUSPENSION SYSTEM USING MOVABLE ELECTRODE 5.2 Principle of operation 101 5.1 The dynamic equation of suspended object 102 5.2 The dynamic modeling of the suspension system 106 5.1 Design of Genetic-PID controller 110 5.2 Continuous proximate time optimal control 114 5.1 Design and manufacturing of mechanical amplifier 126 5.2 Design of mechanical amplifier-piezo actuator-movable electrode 130 5.3 Novel suspension system 133 5.4 Design of voltage amplifier 134 5.5 Determining of voltage supplied to electrodes 137 5.1 Experimental results obtained by PID control 142 5.2 Experimental results obtained by proximate time optimal control 143 5.7 Sub-conclusion 4 144 iil FINAL CONCLUSION 145 REFERENCES 149 APENDIX 1 152 APENDIX 2 154 IV Symbols and abbreviations Symbols F electrostatic force Fa damping force F Ủy damping force in case suspended object is silicon wafer Fa damping force in case suspended object is aluminum disk F linearized value of F” ự electrode voltage V linearized value of V" Vo bias voltage z gap length between electrode and suspended object Z linearized value ofz” Z de displacement of movable electrode Z2 displacement of suspended object Z| velocity of suspended object A area of electrode m mass of suspended object 6 permittivity of air n viscosity of air La linearization constant ky linearization constant Z0 suspended gap ky damping coefficient k2 electric coefficient K time delay Ker critical time delay Š static displacement of PZT đãa strain coefficient Vcc operating voltage of PZT Von charge supplied voltage Vorr discharge supplied voltage RS, _ recoverable set H gain factor of mechanical amplifier ro radius of suspended object P(r) _ pressure in a thin film Kp ___ proportional gain Kì integral gain Kp _ derivative gain Abbreviations TOC Time optimal control PZT Piezo actuator GA Genetic Algorithm HDD Hard disk driver PID _ Proportional-Integral-Derivative DOF Degree of freedom VỊ Chapter 1 INTRODUTION In manufacturing processes for highly integrated semiconductor devices and liquid crystal displays (LCD), contamination of product surfaces by dust particles is a major factor restricting the product yield. Mechanical grips cause damage and scatter particulates that are detrimental to the fabrication processes. In addition, the direct contact and friction between the object and other materials not only produce dust particles during fabrication processes but also give the transported object a charge, which attracts dust particles from the working environment.
Therefore, it is necessary to handle the sample without any physical contact with other materials. Especially, in recent years fabrication processes in vacuum environment become important. More importantly these dry space processes remove significant sources of contaminants thus eliminating many manufacturing steps. For instance, approximately 25% of the process steps in semiconductor fabrication require vacuum process, many MEMS devices such as inertial sensor, accelerometers and mechanical resonators need a high vacuum environment to improve their performance, and a packaging process in a low pressure environment improves the mechanical quality factor because it reduces air damping significantly.
However, the handling of substrates having extreme small size which are moved from process to process during fabrication cannot be accomplished with the vacuum suction method which is used in ambient air. Therefore, demands of handling object without mechanical contact in vacuum environment are also increasing. Levitation is the process by which an object is suspended against gravity, in a stable position, without physical contact. For levitation on Earth, first, a force is required directed vertically upwards and equal to the force of gravity.
Second, for any small displacement of suspended object, a returning force should appear to stabilize 1t. Many kind of levitation have been studied and applied to industrial such as aerodynamic, acoustic, optical, squeeze film air bearing, magnetic, and electrostatic levitation.1 AERODYNAMIC LEVITATION [1] In aerodynamic levitation a spherical specimen is lifted by a fluid jet. Stability in the vertical direction results from the divergence of the jet, which leads to a decreasing drag with increasing height. In the transverse direction this levitation is stable because the jet is deflected toward an off-axis specimen.
This asymmetry, or the increased Bernoulli force at the side where the flow is faster, produces a centering force that leads to stable levitation of a ball even by a tilted jet of water or air. A further application of aerodynamic levitation is the contact-free positioning of non conducting samples under the condition of microgravity 1n space.2 ACOUSTIC LEVITATION [1, 5] Acoustic levitation uses sound traveling through a fluid, usually a gas, to balance the force of gravity. On Earth, this can cause objects and materials to hover unsupported in the air. A basic acoustic levitator has two main parts, a transducer which is a vibrating surface that makes sound, and a reflector.
The transducer and reflector have concave surfaces to help focus the sound. A sound wave travels away from the transducer and bounces off the reflector. First, the wave, like all sound, is a longitudinal pressure wave. In a longitudinal wave, movement of the in the waves is parallel to the direction the waves travels.
Second, the wave can bounce off of surfaces. It follows the law of reflection, which states that the angle of incidence, the angle at which something strikes a surface, equals the angle of reflection, the angle at which it leaves the surface. In other words, a sound wave bounces off a surface at the same angle at which it hits the surface. A sound wave that hits a surface head-on at a 90 degree angle will reflect straight back off at the same angle.
Finally, when a sound wave reflects off of a surface, the interaction between its compressions and rarefaction causes interference. Compressions that meet other compressions amplify one another, and compressions that meet rarefactions balance one another out. Sometimes, the reflection and interference can combines to create a standing wave. Standing sound waves have defined nodes, or areas of minimum pressure, and antinodes, or areas of maximum pressure.
Imagine a river with rocks and rapids. The water is calm in some part of the river, and it is turbulent in others. Floating debris and foam collect in calm portion of the river. In order for a floating object to stay still in a fast-moving part of the river, it would need to be anchored or propelled against the flow of the water.
This is essentially what an acoustic levitator does, using sound moving through a gas in place of water. By placing a reflector the right distance away from transducer, the acoustic levitator creates a standing wave. When the orientation of the wave is parallel to the pull of gravity, portions of the standing wave have a constant downward pressure and other have a constant upward pressure. The nodes have very little pressure.
In space, where there is little gravity, floating particles collect in the standing wave’s nodes, which are calm and still. On Earth, objects collect just below the nodes, where the acoustic radiation pressure, or the amount of pressure that a sound wave, can exert on a surface, balance the pull of gravity. Sample Object PRESSURE DISTRIBUTION Transducer Fig.2 Principle of acoustic levitation Acoustic Reflector e ye Levitatec sample | “fm Resonant plate ma Ba Xx >2 transducer Fig.3 Acoustic levitation [1] In typical experiments, the high-intensity ultrasonic field is that of a standing wave of 20 to 40 kHz generated by a piezoelectric transducer.3 OPTICAL LEVITATION [1] Optical levitation was developed in the early seventies by Athhur Ashkin and is the precursor of the optical tweezers. The governing physical processes are the same, springing from photon momentum transfer.
In optical levitation, the gravitational force is balanced by photon pressure produced by a vertically directed focused laserbeam. Close to the focus the intensity 1s strong enough to slow down and hold tiny particles in a stable trap. Particles can then be manipulated and moved by moving the laserbeam or the surrounding. Levitated sample Lens Laser bearr Fig.4 Optical levitation in a vertical laser beam [1] 1.4 SQUEEZE FILM AIR BEARING [1] A squeeze film bearing 1s a special kind of air cushion which seems well suited to micro machine application.
It simply operates by a rapid oscillation of one of two surfaces with a gas between them. Levitated Gas film object Z= Zc sinwt Shaker plate P Weight External force Fig.5 Squeeze film gas levitation [1] In the Fig.5, the shaker plate exhibits sine wave movement.5 MAGNETIC LEVITATION [1,3] Truly stable levitation without consumption of energy is possible only in magnetic fields. Several types of magnetic levitation have been successfully tested. I) Levitation by strongly repulsive magnets must be combined with rollers for horizontal guidance or with controlled electromagnets.
2) Levitation with superconductors may be based on the pole diamagnetism 1n the Meissner state that allows stable levitation superconductor in magnetic fields generated. 3) The levitation may rely on the repulsion between a superconducting magnet and a conducting plate or guide way which it moves. The repulsion originates from the eddy currents in the plate that cause both lift and drag. 4) Levitation may use the eddy currents generated in a conducting plate by an ac coil.