Abstract

In recent years the electronics for developing sensor networks have become compact and cheaper. This has led to an interest in creating communities of distributed sensors that can collect and share data over a large area without being physically connected by wires. The Intelligent Systems Center at the University of Missouri-Rolla (UMR) has for several years been using commercial off-the-shelf (COTS) hardware and custom software to develop a system of stationary sensing nodes capable of pre processing their data locally and sharing processed data to produce global details. This distributed sensing and processing array is targeted for use in monitoring a wide variety of infrastructures. It has been laboratory tested for use in civil, automotive, and airframe monitoring. This paper is an overview of the technologies investigated and the level of functionality obtained from each hardware/sensor/target set.The current system consists of a web server, a central cluster and a collection of satellite clusters. The central cluster is a PC104 x86 based computer with the satellite clusters being 8051 based single board computers. The satellite clusters are of the order 6"x5"x2" in size. There is an effort under way to place a short-range radio with a processor and a PZT sensor into a 2"x1.5"x.5" package. Exercises have been carried out to demonstrate the ability of the central clusters to remotely control the satellite clusters and the web server's ability to control the central cluster. Further work is under way to integrate the entire system into a web server attached to the Internet and to a long distance communication device, currently employed is a cellular modem into the monitoring array. The web server communicates over standard phone lines to the central cluster, which is equipped with a cellular modem. The central cluster communicates with the satellite clusters using short-range wireless equipment. Proxim rangelan, Erickson Bluetooth, and Linx Technologies RF modules have all been tested as short-range wireless communication solutions.We have demonstrated a system that consists of a structure with an array of smart sensors, preprocess and collect data, and post this data on a web server for global inspection and manipulation. This will enable data sharing and collaborative data analysis to extend the knowledge of structural health monitoring.

Implementation issues represent an unfamiliar challenge to most control engineers, and many techniques for controller design ignore these issues outright. Consequently, the design of controllers for smart structural systems usually proceeds without regard for their eventual implementation, thus resulting either in serious performance degradation or in hardware requirements that squander power, complicate integration, and drive up cost. The level of integration assumed by the smart patch further exacerbates these difficulties, and any design inefficiency may render the realization of a single-package sensor-controller-actuator system infeasible. The goal of this research is to automate the controller implementation process and to relieve the design engineer of implementation concerns like quantization, computational efficiency, and device selection. Field programmable gate arrays (FPGA) are specifically targeted as a hardware platform because these devices are highly flexible, power efficient, and reprogrammable.The current study develops an automated implementation sequence that minimizes hardware requirements while maintaining controller performance. Beginning with a state space representation of the controller, the sequence automatically generates a configuration bitstream for a suitable FPGA implementation. MATLAB functions optimize and simulate the control algorithm before translating it into the VHSIC hardware description language (VHDL). These functions improve power efficiency and simplify integration in the final implementation by performing a linear transformation that renders the controller computationally friendly. The transformation favors sparse matrices in order to reduce multiply operations and the hardware necessary to support them; simultaneously, the remaining matrix elements take on values that minimize limit cycles and parameter sensitivity. The proposed controller design methodology is implemented on a simple cantilever beam test structure using FPGA hardware. The experimental closed loop response is gathered for an automated FPGA controller implementation. Finally, the integration of FPGA based controllers into a multi-chip module (MCM) is explored, which represents the next step towards the realization of the smart patch.

Wireless network sensors are being implemented for applications in transportation, manufacturing, security, and structural health monitoring. This paper describes an approach for data acquisition for damage detection in structures. The proposed Web-Controlled Wireless Network Sensors (WCWNS) is the integration ofwireless network sensors and a web interface that allows easy remote access and operation from user-friendly HTML screens. The WCWNS is highly flexible in terms of functions and applications. Algorithms and tools for data analysis can be directly installed on and executed from the web server. This means WCWNS will have unlimited capabilities in performing data analysis. Data can be analyzed for damage detection either on site distributed amongst the intelligent sensors or off site either in the web server or at an end users location after downloading from the web server. This feature allows for a variety of health monitoring algorithms to be investigated by researchers of all backgrounds and abilities. In addition, both short-range and long-range communications devices handle data exchange and communications in WCWNS. The system can be setup to operate efficiently in any topological arrangement. Short-range communications devices facilitate fast and low-power local data transfer, while longrange communications devices support high quality long-distance data exchange. The proposed system is demonstrated on an experimental setup.

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