Browsing by Author "Edward Grant, Committee Co-Chair"

Now showing 1 - 4 of 4

Design and Use of Pre-Stressed Unimorphs for High-Displacement, High-Load Applications
(2004-11-29) Mulling, James Frederick; Angus I. Kingon, Committee Chair; Ronald O. Scattergood, Committee Member; Edward Grant, Committee Co-Chair
The purpose of this research was threefold: to characterize pre-stressed unimorph actuators fabricated by different routes, to investigate 3-D orientation of the polarization vector through the piezoceramic thickness using piezoresponse force microscopy (PFM), and to design a motor to use the strengths of a compliant actuator. Applications such as robotics need high-force, high displacement actuators with potential for scaling. Pre-stressed unimorphs, typified by THUNDER™ actuators by Face International Corporation, provide larger displacement than traditional unimorph or bimorph actuators because pre-stress introduced during fabrication enhances piezoelectric strain. The fact that these are compliant actuators has important implications for use. This research showed that bond material and thickness, as well as end conditions all affect actuator performance. Substrate material and thickness relative to that of the ceramic element were shown to have more subtle effects than previously reported. The likely signature of performance enhanced by pre-stress was found in load-displacement test data, which showed that the effect appears to be modified as displacement under load interacts with the original actuator curvature due to pre-stress. The novel application of PFM showed that orientation of the polarization vector did indeed vary through the actuator thickness. Internal stress bias has a dominant role in determining orientation of the polarization vector, so much so that effects of initial poling were not seen except at a location likely to be a neutral surface. With overall domain orientation generally out of alignment with the poling direction, piezoelectric strain augmented by a large extrinsic contribution can be expected when electric field is applied in the poling direction. Performance of a linear motor using an inchworm cycle was found to be limited by clamp slip. The passive (unpowered) clamps otherwise had the advantage of simplifying operation. A rotary motor of novel design was tested using several configurations of actuators and other parts. Its chief advantage was that resonant behavior was little affected by load, since actuators and load were indirectly coupled. Characterization yielded a range of torque and speed data, with best performance generally provided by the simplest drive signals and configurations of parts. Design principles allow the motor to generate high torque. Experimental results, although promising, imply that ample opportunity exists to identify and ameliorate performance-limiting factors.
A Neural Network Control System for the Segway Robotic Mobility Platform
(2006-11-08) Forrest, Charles E; Edward Grant, Committee Co-Chair; David Thuente, Committee Co-Chair; John Muth, Committee Co-Chair
An Artificial Neural Network (ANN) is a network of simple processing elements that emulate neurons in the brain. The behavior of such a network is characterized by the synaptic connections between the input data and the processing elements. Here, an ANN was generated and used as part of a control system for a Segway Robotic Mobility Platform (RMP) being trained in obstacle avoidance behavior. The single sensor input to the control system is a SICK laser, a range-finding sensor; the control output is Pulse Width Modulation commands to the RMP's motors. The Segway RMP, neural network maps input sensor data directly to appropriate motor output commands for obstacle avoidance. Obstacle avoidance training was accomplished in a simulated LabView world using supervised reinforcement learning and practices from evolutionary robotics. Synaptic connection strengths were stored in an array called the artificial "chromosome". The chromosome was randomly modified, and the response of the network was compared to a pre-defined desired output. The goal of the genetic algorithm training was to minimize the error between the desired and actual outputs, yet to ensure that local minima were avoided. Once the ANN was trained in simulation, it was transferred to an actual RMP for obstacle avoidance testing in the real world . The benefits of training ANN's for obstacle avoidance tasks in simulation are demonstrated here. In the simulated world, training and testing can be done in virtual environments: offering greater control over environment complexity, testing the robustness of the controllers generated, and filtering the training data set. All of the foregoing reduces the cost of training and lead to the development of an optimized ANN controller for RMP obstacle avoidance. The ANN provided input pattern generalization for smooth motion, improved computational speeds, and added to the body of knowledge for RMP controller development.
A Novel Method for Dynamic Yarn Tension Measurement and Control in Direct Cabling Process
(2006-03-29) Shankam Narayana, Vivek Prasad; Abdelfattah Seyam, Committee Co-Chair; William Oxenham, Committee Co-Chair; George Hodge, Committee Member; Edward Grant, Committee Co-Chair
Yarn tension control is an important parameter for quality and efficiency in textile processes. It has a significant influence on productivity in various processes such as winding, twisting and cabling. There have been several articles based on theoretical models, which discuss the effect of various factors on yarn tension variation in direct cabling, but very few have addressed the possibility of measuring and controlling it practically while the yarn is being twisted. Quality control system manufacturers like TEMCO (Textile Machinery Components) and BTSR (Best Technologies Studies and Research) have come up with smart tension scanning systems that perform online tension monitoring in various textile machines. However, these systems cannot be installed on the direct cabling machine due to their size and cost. The fact that the supply yarn package is housed inside the rotating yarn balloon restrains any wired tension sensor from performing online measurement. As such, there is an immediate need for using a wireless sensing device to perform online yarn tension measurement and execute a control mechanism that will control yarn tension adaptively. The objective of this research is to demonstrate the possibility of applying MEMS (MicroElectroMechanical Systems) technology with radio frequency (RF) transmission to effectively carry out dynamic online measurement for the control of yarn tension. A novel technique to achieve online control using the measured real-time data has been implemented. A device that ensures uniform tension in the yarn has been designed and developed. Ways of measuring twist in the cabled yarn using optical micrometers and digital imaging systems have also been explored, because variation in tension manifests variation in twist. Using the twist values obtained from these sensors, the individual tensions in the component yarns can be adjusted, resulting in the formation of a uniform cabled yarn with equal lengths of both component yarns.
Printing Conductive Inks on Nonwovens: Challenges and Opportunities
(2007-12-15) Karaguzel, Burcak; H. Troy Nagle, Committee Member; Hooman Vahedi Tafreshi, Committee Member; John M. Wilson, Committee Member; Joel Pawlak, Committee Member; Behnam Pourdeyhimi, Committee Chair; Edward Grant, Committee Co-Chair
Flexible printed circuit boards continue to be a high-growth technology in the area of electrical interconnectivity. Over traditional rigid printed circuit boards (PCB's), wire and wire harnesses, flexible circuit boards provide considerable weight, space, and cost savings This study investigates using conductive inks for printing circuits onto flexible nonwoven substrates as a low-cost alternative to traditional PCB manufacturing, because the emerging generation of nonwovens can offer wearability, printability, lightweight, durability and washability. In this study, instead of incorporating conductive paths by weaving or knitting conductive yarns into the structure of the fabrics, conductive inks are used to print directly onto nonwovens by using polymer thick film technology. There are challenges in printing on fabrics such as achieving printing resolution and durability. Spatial geometry of structure is a critical property for print resolution. The traditional woven fabrics exhibit poor digital printability because the ink disperses mostly through the inter-yarn interstices. The spatial resolution is primarily a function of yarn diameter and thread spacing (e.g., end and picks per inch in woven fabrics). Consequently, in woven fabrics, fine spatial resolution is only possible in high density, light weight, densely structures. Even in the case of such light weight structures, the surface texture can be quite rough for printing purposes. Additionally, light weight fabrics can be limited with respect to properties they offer. Other structural factors such as yarn twist and fiber properties are also factors that may affect the absorbency and the wicking of the ink into the structure and therefore, can limit the utility of the printed circuit lines. In contrast, the new generation of durable micro-fiber nonwoven fabrics offers the opportunity to "engineer" the structure surface properties, the network geometry and the capillary structure to optimize their use for printing. Nonwovens offer the ability to easily manipulate pore size and geometry and create an abundance of small capillaries. Today, it is possible to produce heavy fabrics with fine fibers and different surface textures using nonwovens much more cost effectively than their woven or knitted counterparts. As in other fabrics, the ink substrate interaction determines the printability on nonwoven fabrics. In the case of nonwovens, the main parameters affecting the printability are surface energy of the fibers, fabric structure (fiber orientation distribution), fiber size (controlling surface roughness and pore size) and ink viscosity. Fundamentally, because we are dealing with a porous network as opposed to a non-porous film, the interaction of ink droplet with the structure with respect to its movement in-plane as well as through-the-plane determines the quality of the printing that is achieved. Thus, to control the distribution of the ink on and into the fabric, we have to have control over the structure. The first chapter outlines and examines existing technologies in the so-called electronic textiles area. Conductive inks, printing methods and polymer thick film technologies will be discussed in detail. The second chapter focuses on printing conductive inks on different nonwoven substrates. The polymer thick film conductive inks and the printed transmission lines will be characterized to demonstrate the properties of the structures used as substrates for flexible electronics. The performance metrics related to the circuits parameters and the manner in which the ink is distributed onto and into the substrate will be examined. The third chapter mainly focuses on the electrical conductivity and wash durability of the printed circuits. A method to control the durability of the printed circuits will be explored. In the last chapter, the interaction of liquids with different substrates using ink-jet printing will be modeled and discussed. The modeling results of droplet substrate interaction will be presented for some topical geometries.