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Full-Text Articles in Mechanical Engineering

Ultrasonic Nde Of Thick Composites, R. Bruce Thompson, Donald O. Thompson, David K. Holger, David K. Hsu, M. S. Hughes, Emmanuel P. Papadakis, Yu-Min Tsai, Loren W. Zachary Dec 1991

Ultrasonic Nde Of Thick Composites, R. Bruce Thompson, Donald O. Thompson, David K. Holger, David K. Hsu, M. S. Hughes, Emmanuel P. Papadakis, Yu-Min Tsai, Loren W. Zachary

Aerospace Engineering Conference Papers, Presentations and Posters

A series of ultrasonic techniques being developed for the characterization of thick composites are described. Techniques for the in-situ measurements of elastic constants on thick-walled cylinders based on the times of a variety of ultrasonic modes of propagation are first presented, followed by discussion of the determination of the porosity from measurements of the frequency dependence of the attenuation. Two techniques for imaging delamination are then discussed. The first involves inferring size from plots of reflected signal amplitude versus lateral position of the transducer with a model for beam propagation in anisotropic media used to deconvolve the effects of the ...


Integrated System Identification And Adaptive State Estimation For Control Of Flexible Space Structures, Chung-Wen Chen Jul 1991

Integrated System Identification And Adaptive State Estimation For Control Of Flexible Space Structures, Chung-Wen Chen

Mechanical & Aerospace Engineering Theses & Dissertations

Accurate state information is crucial for control of flexible space structures in which the state feedback strategy is used. The performance of a state estimator relies on accurate knowledge about both the system and its disturbances, which are represented by system model and noise covariances respectively. For flexible space structures, due to their great flexibility, obtaining good models from ground testing is not possible. In addition, the characteristics of the systems in operation may vary due to temperature gradient, reorientation, and deterioration of material, etc. Moreover, the disturbances during operation are usually not known. Therefore, adaptive methods for system identification ...


Kinematic Synthesis Of Deployable-Foldable Truss Structures Using Graph Theory, Dirk B. Warnaar Apr 1991

Kinematic Synthesis Of Deployable-Foldable Truss Structures Using Graph Theory, Dirk B. Warnaar

Mechanical & Aerospace Engineering Theses & Dissertations

A graph theoretic approach is applied to the conceptual design of deployable truss structures. The characteristics that relate to the inter-connectivity of the elements of a deployable truss structure can be captured in a schematic representation, called a graph. A procedure is presented that enables the exhaustive generation of these graphs for structures of any given number of nodes and links and which are foldable onto a plane or onto a line.

A special type of truss structures, called truss modules, is presented. Graphs of this class of structures form a subset of the graphs of truss structures. Two procedures ...


Intelligent Control Of A Robotic Arm Using Hierarchical Neural Network Systems, Xavier J. R. Avula, Luis C. Rabelo Jan 1991

Intelligent Control Of A Robotic Arm Using Hierarchical Neural Network Systems, Xavier J. R. Avula, Luis C. Rabelo

Chemical and Biochemical Engineering Faculty Research & Creative Works

Two artificial neural network systems are considered in a hierarchical fashion to plan the trajectory and control of a robotic arm. At the higher level of the hierarchy the neural system consists of four networks: a restricted Coulomb energy network to delineate the robot arm workspace; two standard backpropagation (BP) networks for coordinates transformation; and a fourth network which also uses BP and participates in the trajectory planning by cooperating with other knowledge sources. The control emulation process which is developed using a second neural system at a lower hierarchical level provides the correct sequence of control actions. An example ...


Petri Net Modeling Of A Flexible Assembly Station For Printed Circuit Boards, M. Zhou, Ming-Chuan Leu Jan 1991

Petri Net Modeling Of A Flexible Assembly Station For Printed Circuit Boards, M. Zhou, Ming-Chuan Leu

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Petri net modeling approaches are presented for a flexible workstation for automatic assembly of printed circuit boards. In order to improve the productivity of such a system, the building of mathematical models is a crucial step. Concentrating on the operational aspects, the authors construct ordinary and temporal Petri net models for the AT&T FWS-200 physical flexible workstation. Three outcomes follow from such models. First, designers can have a better understanding of concurrency, synchronization, mutual exclusion, and sequential relations involved in the system control from the graphical representations of Petri nets. Second, the performance analysis of system operations under different ...


Decoupled Dynamics For Control And Estimation, S. N. Balakrishnan Jan 1991

Decoupled Dynamics For Control And Estimation, S. N. Balakrishnan

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Decoupling of the dynamical equations in polar coordinates is used to develop a control scheme for use in target-intercept problems with passive measurements. By defining a pseudo control variable in the radial coordinate, the radial dynamics is made independent of the transverse dynamics. After solving for the radial control, the transverse control is determined through solutions to a two-point boundary value problem. Numerical results from a six degree-of-freedom simulation which used the decoupled control indicate that it is better than the completely Cartesian coordinate control for most of the cases considered. Decoupled control, though, is obtained iteratively through a two-point ...


Hierarchical Neurocontroller Architecture For Intelligent Robotic Manipulation, Xavier J. R. Avula, Luis C. Rabelo Jan 1991

Hierarchical Neurocontroller Architecture For Intelligent Robotic Manipulation, Xavier J. R. Avula, Luis C. Rabelo

Mechanical and Aerospace Engineering Faculty Research & Creative Works

A hierarchical neurocontroller architecture consisting of two artificial neural network systems for the manipulation of a robotic arm is presented. The higher-level neural system participates in the delineation of the robot arm workspace and coordinates transformation and the motion decision-making process. The lower one provides the correct sequence of control actions. The capabilities, including speed, adaptability, and computational efficiency, of the developed architecture are illustrated by an example.