An Integrated, Computer-Based Method for Rapid-Prototyping Weapons-Scale Marine Propulsors Using Stereolithography

The present work describes an integrated, two-phase computer-based method for fabricating marine propulsors using stereolithography. This new methodology seamlessly integrates stereolithography rapid prototyping techniques with the hydrodynamic design, structural design, and prototype testing of advanced marine propulsors in order to greatly increase the design process efficiency and reduce development time. Its use as applied to the design, fabrication, and testing of advanced propulsor prototypes for small weapon’s-scale undersea vehicles (e.g., Unmanned Underwater Vehicles (UUVs), lightweight and heavyweight torpedoes, etc.) is described in order to demonstrate specific strengths of the new method.

The Optimization of Threshold Value of the Relational Degree in Grey Theory Method for Fault Diagnosis

In this paper, optimization of the threshold value of the relational degree in Grey Theory method for fault diagnosis is considered. With an emphasis on minimizing both the error rate and miss rate of fault diagnosis, new ideas are proposed to determine the optimal range of the threshold value. A practical example is given to demonstrate the feasibility of the proposed method.

Effect of Multimaterial Layering on the Response of a Generic Hull Structure

The dynamic response of a basic, generic, multilayered, composite vehicle hull with a large, circular opening for the turret assembly has been compared with that of an equivalent single-layer, basic metallic hull with identical geometry to assess the influence of a multilayered, composite armor panel structure on the modal response. Both models, without the engine block, mountings, transmission, and base support system consisting of tracks, wheels, sprockets, torsion bars, etc., were generated using PATRAN 3 to facilitate computational modal analysis and comparative evaluation of the influence of multilayered construction on the free vibrational response.

An Open Architecture Framework for the Integration of Virtual Prototyping Software Tools

The use of virtual prototyping tools typically results in products with lower costs, better quality, and shorter development cycles. However, there are many interface/configuration problems that occur in the process of obtaining a design solution using the typical gamut of virtual prototyping tools. This paper presents the architecture, design, and implementation of a framework to support the integration of the multiple software systems used in the virtual prototyping of mechanical components. Some of the virtual prototyping software systems considered in the implementation of this framework were customer input systems, solid modeling systems, finite-element systems, knowledge-based systems, NC code generator systems, and virtual assembly systems. There is a pressing need for the different software systems to talk to each other while transferring the required data at varying levels of abstraction without compromising data integrity. Of special significance is the fact that the philosophy of the framework is widely applicable to any mechanical system, and is almost independent of specific software utilities. Thus, this design incorporates a clear path towards expansion to encompass other independent tools/systems. The architecture was designed using object-oriented methods. The framework was very successfully demonstrated for a well-defined subset of software systems being used at Isothermal Systems Research (ISR) Inc., a leader in proprietary spray cooling systems for multi-chip modules. This framework effectively supports the strong industry push towards integrated design, manufacturing, and virtual prototyping. The work presented in this paper was supported by an SBIR grant from the Department of Commerce, DOC contract 50-DKNB-5-00117.

COVIRDS: Shape Modeling in a Virtual Reality Environment

Rapid shape creation and visualization of solid models remains a tedious task despite advances in the field of Computer Aided Design (CAD)/Solid Modeling. CAD systems require a significant level of detail, such as vertices, edges, and faces to be specified by the user, even before the simplest of shapes can be created and viewed. In addition, most CAD systems have an essentially 2D interface for designing artifacts. This makes artifact visualization, for example by interactive rotation, difficult since all manipulations have be achieved by 2D translation of the mouse or by typing in the required angles of rotation. The limited visualization capability and the requirement to create shapes through the specification of low level entities is especially cumbersome in the concept shape design stage. This paper describes the Conceptual Virtual Design System, COVIRDS, a tool for product concept design. COVIRDS provides an intuitive voice and hand input-based interface for modeling of products using a ‘construction’ approach. Product shape models are created by ‘attaching’ simpler parametrically defined ‘Shape Elements’ to other elements to create more complex models. Voice commands are used to instantiate shape elements and change their parameters, for example, the width, length and height of a block element. 3D hand input is used for positioning shape elements during element attachment. The voice and hand input-based interface together with a stereoscopic visual display facilitates rapid creation and visualization of concept shape models.

Generic Modular Operations for Virtual Manufacturing Process Engineering

In order to address the computational costs of modeling and analyzing manufacturing processes, a novel approach to virtual manufacturing process engineering using generic modular operations is presented. Relying on a state based representation of operation control for a simplified virtual manufacturing workcell, the valid states for each sequence of generic modular operations are aggregated and both operation state and processing constraints applied to specify the subtasks required to complete each step in a product’s process plan. By adopting this state based control approach, virtual process engineering provides a direct mechanism to map virtual process representations onto actualized processes. Using these generic modular operations and their temporal and processing dependencies, the computationally complex elements of virtual manufacturing process simulation can be directly identified and an architecture for virtual process development specified. Examples from both machining and assembly processes are provided.

A Generic Framework for Internet-Based Supply-Chain Interaction

To remain competitive in the global marketplace, manufacturing companies are transforming their organizational structure and operational philosophy from one based on vertical-integration to one based on core competencies. This trend has resulted in an economy wherein practically every manufacturing company has become dependent on a supply-chain of vendors in order to serve its customers. In the context of this distributed manufacturing environment, the Internet and related technologies such as Java, VRML and intelligent WWW agents are creating fundamentally new approaches to supply-chain interactions that offer greater flexibility in identifying suppliers and the ability to dramatically reduce the response time within a supply-chain for processing requests-for-quotation (RFQs) and orders from customers. In this paper, we describe a generic framework for Internet-based customer-vendor interactions, and present a computer-integrated system for rapid and effective processing of RFQs in such an Internet-based supply-chain. We also identify some key research challenges within this framework that need to be overcome for Internet-based supply-chain interaction to be successful.

Improved Interaction and Visualization of Finite Element Data for Virtual Prototyping

This paper discusses the properties of possible virtual prototyping systems using finite element analysis and reports on a prototype implementation of such a system in order to illustrate the concepts. Virtual reality user interfaces will improve some existing applications and lead to new application domains. Several crucial points such as overall system architecture, speed and intuitivity of interaction, and visualization quality of results are identified and possible solutions are suggested. This includes a flexible virtual hand interaction with adjustable finger size. In particular a level of detail technique for finite element data based on element shape functions is presented which can greatly improve visualization quality as compared to common visualization approaches. This level of detail technique provides a flexible tool to adjust the exactness of visualization to rendering time (i.e., degree of interactivity) constrains. The concepts are currently being implemented within a testbed called VEIFEL (Virtual Environment Investigation of Finite ELement data). A report of this work and of resulting experiences is given.

Multimedia and Virtual Reality for the Control of a Multiple Wheeled Mobile Robot System

This paper describes the application of multimedia and virtual reality technology to a multiple wheeled mobile robot system. The system is designed for teleoperation of a variety of highway maintenance and construction tasks, such as automated highway pavement crack sealing. Each robot is tethered to a support truck through linkages, and has its own embedded controller for motion control and posture sensing. A host computer is dedicated to communicate with the robots and to provide a multimedia interface to the operator. A video camera is mounted above the robots’ workspace and live video is taken to the host computer’s video capture card which supports video overlay. The live video of the robot workspace is then overlaid on the robots’ control window and provides an augmented reality for crack detection, path planning, and robot monitoring. By mapping live video on the computer generated interactive robot animation, the operator can simply control any robot through finger motion on a touch screen. The host computer can also provide a virtual environment providing the operator with a sense that he is sitting on the robot, allowing the robot to be easily controlled with a joystick. This paper shows the manner in which fast growing and inexpensive multimedia PC technology, virtual reality concepts, and the newest programming tools like Visual C++ 4.0 and OpenGL 1.1 for Windows 95/NT can be used to build an integrated interactive monitoring and control interface allowing ease in teleoperation of a multiple robot system thus significantly improving operational performance.

Modeling and Pressure-Based Force Control of a Hydraulic Actuator

A dynamic model of a hydraulic actuator/spool valve combination is developed using the bond graph method. Feedback linearization is used to develop a force controller for the system using hydraulic pressure in each chamber of the actuator along with piston position and velocity as feedback. The use of a feedforward term to compensate for the seal friction within the actuator provides for a stable and accurate controller. Velocity control is achieved through calculation of the reference force required to overcome the seal friction and produce the acceleration required to reach the desired velocity. It is shown that the use of such a force controller allows for an acceptable transition from velocity to force control when the piston comes in contact with an external surface.