Harry E. Stephanou

Consideration of Impedance Matching Techniques for Efficient Piezoelectric Energy Harvesting

This study investigates multiple levels of impedance-matching methods for piezoelectric energy harvesting in order to enhance the conversion of mechanical to electrical energy. First, the transduction rate was improved by using a high piezoelectric voltage constant (g) ceramic material having a magnitude of g33 = 40 times 10-3 V m/N. Second, a transducer structure, cymbal, was optimized and fabricated to match the mechanical impedance of vibration source to that of the piezoelectric transducer. The cymbal transducer was found to exhibit ~40 times higher effective strain coefficient than the piezoelectric ceramics. Third, the electrical impedance matching for the energy harvesting circuit was considered to allow the transfer of generated power to a storage media. It was found that, by using the 10-layer ceramics instead of the single layer, the output current can be increased by 10 times, and the output load can be reduced by 40 times. Furthermore, by using the multilayer ceramics the output power was found to increase by 100%. A direct current (DC)-DC buck converter was fabricated to transfer the accumulated electrical energy in a capacitor to a lower output load. The converter was optimized such that it required less than 5 mW for operation.

Micro and Mesoscale Robotic Assembly

Abstract Some of the challenges associated with Microsystems assembly are examined in this paper and illustrated with examples of ongoing research at the authors’ institution. One of the basic challenges in precision assembly is the need for very high accuracy over a large range of motion. This challenge is addressed through a “multiscale” approach, which involves the design of assembly tools and processes at multiple scales, and their integration into coherent system architectures. Parallelism is an important aspect of this architecture, with the goal of enabling high-throughput, fault-tolerant assembly at moderate cost. The modularity of the architecture is also important, given the need to frequently reconfigure microsystem assembly cells for small-batch production. This paper presents several concepts for the development of multiscale robotic tools for the assembly of microsystems. Numerical simulations and experimental results are used to illustrate the relevance of the proposed approaches. Extensions to manipulation at the nanoscale are briefly discussed. At the conclusion are some guidelines for the design of multiscale assembly systems.

Robotic deployment of sensor networks using potential fields

Deploying large numbers of sensors has been receiving a lot of attention for detection of hazardous biological or chemical substances in public buildings, airports, shallow water harbors, etc. The sensor-carrying robots are in fact agents that facilitate the repositioning of network nodes in order to increase their coverage and accuracy. Wireless network communication is an essential technology in transmitting the sensed and telemetry information between robots, but it has traditionally been addressed separately from mobile robot navigation. In this work we propose to use a potential field framework to control the behavior of the mobile sensor nodes by combining classical robotic team concepts (obstacle avoidance, goal attainment, flight formation, environment mapping and coverage) with traditional sensor network concepts (node energy minimization, optimal data rate and congestion control, routing in ad-hoc networks). Simulation results are used to illustrate the proposed concepts, and an experimental mobile sensor fleet is built at the authors institution.

Perspectives on imperfect information processing

It is argued that many applications of expert-system and decision-support-system technologies will require an appropriate blend of the features of each of these technologies. Such a system is termed a knowledge support system. One of its inherent characteristics is that the knowledge will come from multiple sources and perspectives and will be inherently uncertain, imprecise, incomplete, inconsistent, and otherwise imperfect. Major approaches for the representation of imperfect knowledge and their use in approximate reasoning algorithms for knowledge support systems are described.

μ 3 : Multiscale, Deterministic Micro-Nano Assembly System for Construction of On-Wafer Microrobots

One of the major issues enduring with micro-scale mechanics has been to design high fidelity miniature machines capable of performing complex operations. Though achieved in some proportion through conventional in-plane and out-of-plane designs, the efficacy of such micro-electromechanical systems (MEMS) structures is highly limited due to complicate fabrication and inadequate robustness. On the other hand, the use of precise robots to assemble MEMS parts of comparatively simpler design to build 3D micromechanical structures has recently emerged as a viable approach. Such modular assemblies of microscale parts typically utilize minimum energy connectors that are multifunctional, e.g., mechanical, electrical etc. The μ3 is a 3D microassembly station consisting of 19 DOF arranged into 3 micromanipulators, with additional microgrippers and stereo microscope vision. The platform is capable of motion resolutions of 3nm and is small enough to be used inside of a scanning electron microscope (SEM) for nano-manipulation. In this paper we discuss how systematic identification and calibration of the station, combined with appropriate part connector designs can lead to multi-degree of freedom active MEMS robots assembled on a wafer

Micropeg manipulation with a compliant microgripper

This paper presents analytical, simulation and experimental results from a study of compliant insertion tasks in microassembly. Gripper compliance is desirable to compensate for positional errors and to prevent the breakage of a gripper during assembly tasks. An analytical model is derived to study the motion and force profiles during compliant insertion. Thermal bimorph microgrippers with a compliant tip are designed and fabricated using a silicon DRIE process, and are mounted on a precision motion stage. A series of micropeg manipulation tasks such as pick up, rotation, and insertion are successfully performed. Finally, a comb structure is integrated in the gripper to calculate insertion force by measuring the deflection of a gripper, which is essential for automated microassembly.

Manipulability and stability of a tentacle based robot manipulator

A massively redundant, tentacle-based robot manipulator is proposed as an alternative to dextrous manipulation by an arm/hand combination. The tentacle is advantageous because it is an all-in-one arm and gripping device capable of a wide variety of configurations and grasps, while maintaining the mechanics of serial manipulators. A method for evaluating the forces and velocities imparted to an arbitrary object by a robot hand is reviewed and extended to include the case where several serial manipulators each come in contact with an object at multiple joints. From this analysis, a quantitative evaluation of grasp manipulability and stability is developed that accounts for multiple object contacts for each serial manipulator in the system. A method of applying both precision and power grasps to three-dimensional objects using a tentacle is presented that allows for easy transition between the two by merely curling or uncurling links from around the object. This method helps reduce the number of complexity of grasp configurations. Numerical simulations of different tentacle manipulators and grasps are given.<<ETX>>

Dynamic modeling and input shaping of thermal bimorph MEMS actuators

Thermal bimorphs are a popular actuation technology in MEMS (micro-electro-mechanical systems). Their operating principle is based on differential thermal expansion induced by Joule heating. Thermal bimorphs, and other thermal flexure actuators have been used in many applications, from micro-grippers, to micro-optical mirrors. In most cases open-loop control is used to difficulties in fabricating positioning sensors together with actuator. In this paper we present several methods for extracting reduced-order thermal flexure actuator models based on experimental data, physical principles, and FEA simulation. We then use the models to generate optimal driving signals using input shaping techniques. Both simulation and experimental results are included to illustrate the efficacy of our approach. This framework can also be applied to other types of MEMS actuators, including electrostatic comb drives.

A Multiscale Assembly and Packaging System for Manufacturing of Complex Micro-Nano Devices

Reliable manufacturability has always been a major issue in commercialization of complex and heterogeneous microsystems. Though successful for simpler and monolithic microdevices such as accelerometers and pressure sensors of early days, conventional surface micromachining techniques, and in-plane mechanisms do not prove suffice to address the manufacturing of todays wide range of microsystem designs. This has led to the evolution of microassembly as an alternative and enabling technology which can, in principle, build complex systems by assembling heterogeneous microparts of comparatively simpler design; thus reducing the overall footprint of the device and providing high structural rigidity in a cost efficient manner. However, unlike in macroscale assembly systems, microassembly does not enjoy the flexibility of having ready-to-use manipulation systems or standard off-the-shelf components. System specific designs of microparts and mechanisms make the fabrication process expensive and assembly scheme diverse. This warrants for a modular microassembly cell which can execute the assembly process of multiple microsystems by reconfiguring the kinematics setup, end-effectors, feedback system, etc.; thus minimizing the cost of production. In this paper, we present a multiscale assembly and packaging system (MAPS) comprising of 20 degrees of freedom (DoFs) that can be arranged in several reconfigurable micromanipulation modules depending on the specific task. The system has been equipped with multiple custom-designed microgrippers and end-effectors for different applications. Stereo microscopic vision is achieved through four high-resolution cameras. We will demonstrate the construction of two different microsystems using this microassembly cell; the first one is a miniature optical spectrum analyzer called microspectrometer and the second one is a MEMS mobile robot/conveyor called Arripede.

Real-time robot motion control with circulatory fields

This paper introduces a new feedback algorithm for steering a point robot through an obstacle field. The key innovation is the use of a circulatory field to rotate the robot path around the obstacles instead of the common potential field which repels the robot. This idea is motivated by a charged particle in a magnetic field generated by a current flowing around the obstacle. In constrast, the potential field approach is associated with a repulsive static electric field generated by charges of the same polarity as the robot, on the obstacle. The circulatory field does not generate any spurious local minimum as it does not change the total energy of the system. By combining with an attractive potential field associated with the desired destination, this method achieves global convergence while avoiding collisions with obstacles.