VIETNAM NATIONAL UNIVERSITY, HANOI COLLEGE OF TECHNOLOGY Phan Huu Phu SENSING MICROGRIPPER WITH PID CONTROL SYSTEMS MASTER THESIS Hanoi - 2008 LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com VIETNAM NATIONAL UNIVERSITY, HANOI COLLEGE OF TECHNLOGY Phan Huu Phu SENSING MICROGRIPPER WITH PID CONTROL SYSTEMS Major: Electronics and Telecommunications Technology Concentration: Electronics Engineering Code: 60 52 70 MASTER THESIS SUPERVISOR: Dr. Chu Duc Trinh Hanoi - 2008 LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com 2 TABLE OF CONTENTS DECLARATION.5 LIST OF ABBREVIATIONS .1 MANIPULATION IN MICRO-WORLD .2 MICRO-GRIPER FOR MICRO-MANIPULATION .4 Polymeric electrothermal microgripper .3 MICRO-MANIPULATION WITH A FEEDBACK SYSTEM .14 CHAPTER 2 SENSING MICROGRIPPER .2 FORCE-SENSING CANTILEVER.3 SILICON-POLYMER ELECTROTHERMAL MICROGRIPPER.5 THE SENSING MICROGRIPPER CHARACTERISTICS .1 Electrothermal actuator characteristics.2 Sensing cantilever beam characteristics .3 Response frequency of the sensing microgripper .27 CHAPTER 3 BUILDING PID CONTROL FUNCTION .1 FEEDBACK LOOP CONTROL .2 BUILDING A PID TRANSFER FUNCTION FOR THE SENSING MICROGRIPPER SYSTEM .1 Transfer function of sensing microgripper .2 Transfer function of driver circuit .3 Open-loop control .5 Proportional – Integral control.6 Proportional – Derivative control.7 Proportional – Derivative – Integral control .34 CHAPTER 4 ELECTRICAL DESIGN .2 PROCESS SELECTION AND SIMULATION .3 Silicon-level simulation .4 Analog-only simulation .5 Mixed Analog/Digital simulation .3 SYSTEM BLOCK DIAGRAM .1 Voltage reference generator.2 The high temperature detector: .4 Bias current generator.3 Digital to Analog converter (DAC) .5 FULLY SCHEMATIC OF SYSTEM AND SIMULATION RESULTS .62 LUAN VAN CHAT LUONG download : add luanvanchat@agmail.62 CHAPTER 5 PHYSICAL DESIGN .1 INTRODUCTION OF LAYOUT .2 MOS transistor layout .2 SYSTEM FLOOR PLAN .72 CHAPTER 6 CONCLUSION & FUTURE WORKS.1 Finishing the system layout .76 LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com 6 List of Abbreviations AFM: Atomic Force Microscope AlN: Aluminum Nitride Bi-CMOS: Bipolar junction transistors and CMOS technology CAD: Computer Aid Design CMOS: Complementary Metal-Oxide-Semiconductor CTE: Thermal expansion coefficient DAC: Digital-to-Analog Converter DC: Direct Current DIMES: Delft Institute of Microsystems and Nanoelectronics DOFs: Degrees(s) of Freedom DRC: Design Rules Checking ERC: Electrical Rules Check ESD: Electro Static Discharge FIB-cut: Focused ion beam-cut GDSII: Graphic Data System II IC: Integrated Circuits LSB: Least Significant Bit LSI: Large-Scale Integration LVS: Layout versus Schematic MEMS: Micro-Electro-Mechanical systems MIS: Minimally Invasive Surgery MOSFET: Metal-Oxide Semiconductor Field-Effect Transistor NMOS: N-channel Metal-Oxide Semiconductor Field-Effect Transistor PID: Proportional Integral Derivative PLI: Photolithographic Invariance PMOS: P-channel Metal-Oxide Semiconductor Field-Effect Transistor PSRR: Power supply rejection ratio PTAT: Proportional to Absolute Temperature PVDF: Polyvinylidene Flouride PZT: Lead Zirconate Titanate SEM: Scanning Electron Microscope SOI: Silicon on Insulator SPICE: Simulation Program Integrated Circuit Emphasis TC: Temperature Coefficients UVLO: Under Voltage Lock-Out ZnO2: Zinc peroxide LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com 7 Chapter 1 Introduction 1.1 Manipulation in micro-world The dominant physical principles in the micro-world can be quite difference from those of the macro-world. When the size of the object is less than 1mm, adhesive forces between the manipulation tool and the object such as surface tension, electrostatic and van der Waals forces can be significant compared to the gravitational force [23]. Manipulation of micro-particles can be done using several physical principles and methods.
For manipulation of a micro-structure under specific ambient conditions or liquid; suction, cryogenic, electrostatic, and friction are the most often considered methods. Friction principle is chosen for addressing the micro-manipulation of small objects presented in this thesis. Like the human hand, friction manipulation uses at least two fingers applies on two sides of a clamped object. A friction manipulator can old an object due to the friction force between the tools and the object surfaces.
This friction method is the most widely used in micro-manipulation because of size, cost, reliability, and fabrication aspect in particular.2 Micro-griper for micro-manipulation In the recent years, microgrippers have been widely researched as they are in great demand in many research and application areas, such as advanced micro-assembly, micromanipulation, micro-robotic, minimally invasive and living cell surgery. For the development of microgrippers fabricated using integrated circuits (IC) or IC compatible technology, electrostatic, piezoelectric and electro-thermal actuation are generally used.1 Electrostatic microgripper The electrostatic principle is based on the distance change between a fixed electrode and a suspended one when the voltage applied to these two electrodes changes. The first successful electrostatic microgripper based on bulk and surface silicon micro- machining techniques was presented in 1992 (see Fig. The 12 µm thick and 1500 µm long polysilicon microgripper is overhanging from a supporting silicon cantilever.
The microgripper jaw displacement is 10 µm at an applied voltage of 45 V, with a basic frequency of 5 kHz. A monolithically fabricated electrostatic microgripper has been recently presented [7]. A lateral comb drive has been chosen to actuate this gripper. This microgripper can manipulate glass or copolymer spheres of size ranging from 20 to 90 µm with an applied force up to 380 µ at an applied voltage of 140 V.
The main limitation of this device is the high voltage, the large size and the complicated electronic circuit typical of the electrostatic method. LUAN VAN CHAT LUONG download : add luanvanchat@agmail.1: The schematic design of a polysilicon electrostatic microgripper (adapted from [3]) 1.2 Piezoelectric microgripper Piezoelectric materials (such as PZT, AIN, and ZnO2) are capable of producing stress and/or strain when an electric field is applied. Piezoceramic elements have been used to build microgrippers (see Fig. However, piezoelectric actuator fabrication processes are generally not IC compatible and are difficult to miniaturize.
Piezoelectric actuators also require a high actuation voltage and produce small displacements.2: Schematic drawing of a piezoelectric microgripper [22].3 Electrothermal microgripper A thermostat consist a bi-metallic strip, which is made of two thin metallic pieces of difference materials that are bonded together. As the temperature of the strip changes, two pieces change length at difference rates, forcing the strip to bend. Based on the LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com 9 Timoshenko’s bi-metal thermostat theory, an electrothermal microgripper (see Fig.3) is fabricated using doped silicon and a special bonding technique [9]. This structure consists of a silicon cantilever beam with a doped layer on top.
Out of plane bending is obtained when a current is induced though the doped layer.3: Schematic drawing of a typical bi-material cantilever actuator. The doped-silicon expands when applying a current, therefore the cantilever bends downwards (adapted from [9]).4: Schematic drawing of a typical flexure actuator: (a) single hot arm configuration and (b) two hot arms configuration LUAN VAN CHAT LUONG download : add luanvanchat@agmail.5: A microgripper product of Zyvex company: (a) the entire device is about 650 µm long, 270 µm wide, 50 µm thick. The initial gap between the two jaws is 36 µm and the maximum opening is 80 µm; [(b) and (c)] the grippers being used to manipulate a FIB-cut coupon [13]. Since the well-known flexure thermal actuator (see Fig.4(a)) was introduced in 1992 [10], the actuator has received wide interest as they can produce a large displacement, a large force and use IC compatible fabrication process.
The flexure thermal actuator consists of a thin arm with higher electrical resistance than its thick arm. The thin arm (hot arm) gets more heat than the thick one and consequently elongates more than the thick arm and in-plane bending occurs. A configuration more efficient in terms of power consumption uses two hot arm thermal actuators (see Fig. The electrical current just passes through two hot arms.
As there is no electrical current in cold arm and flexure, the efficiency of power consumption is improved compared with the single hot arm structure. This principle is also used in the Zyvex gripper shown in Fig. The limitations of these devices are the extremely high operating temperature and high power consumption.4 Polymeric electrothermal microgripper Recently, polymeric electrothermal microgrippers have been extensively researched as they are capable of producing large displacements at a lower drive voltage and operating temperature [19]. Based on the above-mentioned flexure thermal actuator, polymeric microgrippers are developed using a polymer layer with a thin metal heater on top [19].
The structures have a large displacement at low operational temperature and low power consumption due to the large thermal expansion coefficient (CTE) of the polymer.6 shows the schematic design of a developed polymeric microgripper using SU8 with a thin metal layer (Cr/Au) on top as a heater [19]. The microgripper jaw displacement is 12 µm at an applied voltage of about 2 V and an operational temperature of less than 100 0C. This microgripper has been designed to manipulate cells in air and also in fluid solutions. LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com 11 In these polymeric microgrippers the metal heater is deposited on top of a high thermal expansion coefficient polymer layer.
The interface between the heat source and the polymer layer is limited by the surface area of the metal layer, and the heat transfer along the vertical dimension is not effective. Since the polymer layers have low thermal conductivity, these devices can generate limited movement. Moreover, the unintentional vertical movement couples and interferes with the desired lateral movement [19].7: Schematic drawing of a fabricated SU8 microgripper (adapted from [19]).3 Micro-manipulation with a feedback system When manipulating micro-objects, operating on living cells or in minimally invasive surgery (MIS), enhanced dexterity, accuracy and speed are considerably improved when the force on the objects can be sensed and controlled in real-time. The development of miniaturized manipulators with force control is also of great interest in micro-robotics and micro-assembly.
Manipulation of micro-objects with traditional microgrippers without a built in force sensor normally requires a camera inserted into the system to obtain visual feedback. This approach results in a two-dimensional image. Depth perception of the contact between the manipulating tool and the object being manipulated is lost, making it difficult to identify the position of the tool [16]. Moreover only displacement, and not force, can be detected.
A microgripper with a built-in force sensor can address this limitation and is therefore suitable for holding objects firmly, whilst avoiding any squeezing of delicate objects.1 Force sensor The contact forces between living cells in a laboratory or between micro-particles and a manipulator are generally in the nano-Newton to mili-Newton range. Cantilever force sensors are generally used to measure force in this range. LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com 12 The bending of the cantilever is related to the applied force. By monitoring the deflection of the beam, the amplitude of the applied force can be detected.
Several force-sensing methods, such as capacitive, piezoelectric, optical laser detection, and piezoresistive can be used [30]. The capacitive method is based on the capacitance change which occurs when the structure is deformed, and is widely used in micro-accelerometers and harsh environment sensors. An example of a capacitive force sensor (see Fig.8) is shown in [29]. It has two degrees of freedom (2-DOF) and uses silicon on insulator (SOI) wafers.
This sensor is capable of measuring forces up to 490 µN with a resolution of 0.01 µN along the x -axis and up to 900 µN with resolution of 0.24 µN along the y- axis. Complete isolation between the two electrodes is a limitation of capacitive force sensors, so normally SOI wafers are used. Alternatively, trench isolation can be used. However, it is difficult to control the etching area to obtain a completely isolated structure.
Moreover, the capacitive method requires a complicated fabrication process and complex electronic circuitry.8: Schematic drawing of a capacitive force sensor in two dimensions (adapted from [29]). A two-dimensional piezoelectric force sensor is presented in [28] (see Fig. It consists of two perpendicular pieces of polyvinylidene fluoride (PVDF) material. This structure is symmetric in the vertical and lateral dimensions, with resolution and sensitivity in the µN range.
However, the PVDF cannot be patterned optically. The two pieces have to be glued perpendicularly to each other, resulting in a rather large sensor structure. With this approach, the sensor cannot be miniaturized and the fabrication process is not IC-compatible. The piezoelectric method also requires complicated electronic circuits for processing the signal.