Nanocomposites show promise in various fields, ranging from aerospace vehicles to microelectronics. Specifically, electro-active nanocomposites would enable a whole new set of applications, where the nanocomposite material would exhibit strength, toughness, and electromechanical coupling. The broad goal of this thesis was to investigate potential electromechanical behavior in single walled carbon nanotube (SWNT)-polyimide (PI) composites. The specific objective was to measure and characterize the actuation response of SWNT–PI nanocomposites. Two different polyimides, non-polar CP2, and a weakly piezoelectric polymer (beta-CN) APB-ODPA are used in the study. Electrical and dielectric characterization of the nanocomposites were carried out to better understand the effect of SWNTs on the different physical properties of the composites, and to identify the electroactive mechanism in the resulting composites. (beta-CN) APB-ODPA composites show a higher increase in both conductivity and dielectric constant with SWNT content as compared to the CP2 composites. The effect of SWNTs on remnant polarization (PR) is quantified using the dielectric relaxation tests and Thermally Stimulated Current (TSC) experiments. Both experiments show an increase in the remnant polarization with SWNT content and a higher value for the (beta-CN)APBODPA nanocomposites over CP2 nanocomposites. Actuation tests employing a cantilever bending experiment were carried out on the nanocomposite samples while varying the SWNT content and electric field. The strains are seen to be proportional to the square of the electric field, indicating an electrostrictive response. Strain rate and the coefficient of electrostriction (M1333) values are seen to increase with SWNT content and are higher for (beta-CN) APB-ODPA nanocomposites than the CP2 nanocomposites. Electrostrictive strains can also be expressed as the square of polarization; hence the findings of the dielectric relaxation studies and TSC measurements can be correlated to the measured electrostrictive effect. The cause for the enhancement in dielectric, dielectric relaxation and actuation response of the nanocomposites with the increase in the SWNT content and polarity of the matrix was explored. Among different possible causes special emphasis was given to the importance of the interface between the SWNTs and the matrix and the resulting increase in polarization as the main factor driving the enhancement.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1965. / Typescript. Vita. Description based on print version record. Includes bibliographical references.

This thesis concerns the use of an analogue as an aid to a problem solving program. A -working system, the advantages of the analogue it uses, the mechanisms required, and the interaction of ether forms of knowledge are described. The program, WHISPER, uses a diagram together with procedures for modifying it, as an analogue of a situation involving a stack of arbitrarily shaped rigid bodies. It determines a stack's stability and predicts the motions cf any unstable object by examining the situation's diagram. The analogue is particularly valuable in detecting discontinuities in an object's motion. For example, collisions with other objects or cliffs an object might slide over can be 'seen' in the diagram rather than having to be inferred from a description of the situation. WHISPER uses a simulated parallel processing 'retina' to look at the diagram which is encoded in a two-dimensional array. It consists of a fixed number of processors operating in parallel and communicating only with their immediate neighbours. WHISPER's retina resembles the human retina in some respects. Its resolution decreases away from its center. It can be moved to fixate on different sections of a diagram. A set of domain independent features are extracted from WHISPER's diagrams by procedures, called perceptual primitives, which execute on the parallel processing retina. Example features are: symmetry of an object, similarity of two objects, and contacts of an object with ether objects. In addition to these primitives, the retina can be used to 'visualize1 the rotation of an object without having to move it directly in the diagram The advantages of analogues are classified in terms of two categories according to whether a correspondence exists between the behaviour of the analogue and the behaviour of the external situation, or whether a correspondence exists between the static configurations of the analogue and those of the external situation. Some reasons for the effectiveness of analogues are presented. / Science, Faculty of / Computer Science, Department of / Graduate

University of Macau / Faculty of Science and Technology / Department of Electromechanical Engineering

No description available.

No description available.

No description available.

This thesis describes the modelling and control of an electromechanical brake (EMB) for a drive-by-wire vehicle. The investigation comprised two components on the development, identification and assessment of an EMB model, and the development of an improved control algorithm for an EMB. / The first component of the study began with the examination of a simplified model for an electromechanical disk brake without the positive feedback of brake self-energisation. A methodology was proposed for practical identification of the model parameters on an assembled actuator. Experiments were conducted on a prototype EMB, and for the first time the model fidelity was tested in isolation without a feedback controller acting to reject disturbances. Laboratory tests of the model fidelity were complemented with closed-loop simulations against field data from a brake-by-wire test vehicle. It was determined that the EMB model reasonably predicted the key behaviours of the brake apply, force modulations and lockup due to load-dependent stick-slip friction. The limitations of the model were then identified and extensions were considered to describe secondary effects. / The second component of the study utilised the model to develop an improved control algorithm for an EMB, particularly considering the problem of tracking a brake force command from the driver, or from another vehicle control. Existing EMB controllers were seen to have a limited effectiveness; with a suboptimal handling of actuator nonlinearity, they suffered from problems of the load dependent mechanism friction, and they could not maintain performance throughout the operational envelope. These shortcomings were overcome sequentially by the development of a friction compensation algorithm and a modified control architecture to better manage actuator nonlinearity. To address model uncertainty the modified architecture was incorporated within a robust control design, but this gave an overly conservative brake performance. In a more successful approach, the modified architecture was extended with a model predictive control to optimise the EMB performance and a method for updating the control algorithm was proposed to handle uncertainty and adapt to actuator variation. At each stage experimental tests were conducted on a prototype EMB to demonstrate performance and the incremental improvements achieved. The control improvement was found to be most pronounced for fine manoeuvres whereas large manoeuvres were typically limited by the actuator constraints. / The study outcomes regarding EMB modelling, identification and control are a significant incremental advancement on prior work, and may help to facilitate the development of improved brake-by-wire platforms, anti-lock brake systems and advanced driver assist functions.

Thesis PlanB (M.S.)--University of Wisconsin--Stout, 2008. / Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.