Analytical Redundancy and Fuzzy Inference in AUV Fault Detection and Compensation
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Authors
Healey, A. J.
Subjects
Center for Autonomous Vehicle Research
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Date of Issue
1998
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Abstract
This paper will address the results of a recent study developing model based techniques using analytical redundancy in the production of observation residuals that are processed for the on-line, real time detection of dynamic faults during the operation of AUVs. AUVs are being developed for oceanographic survey, as well as military, missions. Now that underwater navigation to sufficient precision within cost limits is possible, the remaining technical issue is to improve the reliability of the mission completion. Increasing mission reliability implies many things-some having nothing to do with automatic fault detection. However, assuming that the vehicle is equipped with highly reliable sensor suites, connections, and computing components, it is of interest to see if unexpected faults could be detected reliably so that system reconfiguration could be accomplished to allow missions to be continued in some fashion. A survey of fault detection methods indicates that alarms can be easily monitored if signals are static. This is done using ‘limits and trends’ analysis with thresholds set for various levels of severity. With dynamic signals, such as those induced by an actuator fault in the form of a stuck fin, or a loose fin, or fouling of a propeller, the transient nature of the signal makes limits and trends analysis invalid. In these cases, signals are sought that include servo error, and the residual error in observation filters. Designing observation filters builds analytical redundancy into the decision making. Additionally, since there is always the difficulty of separating the fault response from disturbance response, operation near the surface under waves requires the development of a wave detector. A fault detection architecture is proposed that is based on using simple detection circuits that look for fault signal magnitude as well as length of time persisting in the fault mode that produces the fault declaration. Adjustments in the threshold parameters are able to distinguish between wave disturbance and fault condition. The architecture allows for the recommended accommodation response using a fuzzy inference system linking residual fault declaration signals as inputs that are mapped to recommended actions using fuzzy rules. Example responses are discussed, and in particular, the fault detection and accommodation due to loss of control at low speed under wave action with stuck fins, is given.
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Conference Paper
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Proceedings Oceanology 1998, Brighton, March 11-14, 1998 pp.45-50
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Citation
Healey, A. J., "Analytical Redundancy and Fuzzy Inference in AUV Fault Detection and Compensation", Proceedings Oceanology 1998, Brighton, March 11-14, 1998 pp.45-50
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.