A report presents a study of the use of wavelet-based mathematical models to quantify the responses of humans in control loops. The report begins with a review of the traditional representation of manual control responses by use of transfer functions derived from Fourier transforms, which, the report notes, are not adequate to represent the temporally varying human responses observed in practice. Some basic principles and equations of wavelet transforms are presented.
This work was done by Martin Brenner of Dryden Flight Research Center and Peter M. Thompson and David H. Klyde of Systems Technology, Inc.
This Brief includes a Technical Support Package (TSP).
Wavelet-Based Time-Varying Models of Pilots in Control Loops
(reference DRC-01-56) is currently available for download from the TSP library.
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Overview
The document titled "Wavelet-Based Time-Varying Models of Pilots in Control Loops" (DRC-01-56) from NASA's Dryden Flight Research Center presents a study on modeling pilot behavior in control systems using wavelet transforms. The research focuses on how experimental data can be converted into models that represent the dynamics of pilot control actions, specifically through the estimation of transfer functions for pilot and controlled system responses.
The study involved three types of pilots: a commercial pilot, a NASA Dryden test pilot, and a general aviation pilot. Each pilot participated in a tracking task where they were briefed on the evaluation process and allowed to practice with a baseline configuration before formal evaluations began. The pilots aimed to minimize root mean square (RMS) tracking errors during their tasks, which included periods of free flying and adjustments to the control system configuration.
Key findings from the evaluations are summarized through the analysis of time and frequency responses, particularly using Bode plots. The paper pilot exhibited the smoothest responses, with stability metrics indicating a significant drop in crossover frequency and phase margin during transitions. In contrast, the commercial pilot's responses showed considerable fluctuations, reflecting changes in pilot strategy as they adjusted their feedback loop bandwidth in response to system changes.
The document emphasizes the advantages of wavelet transform techniques over traditional Fourier transform methods for estimating transfer functions. Wavelet transforms allow for a more nuanced analysis of time-varying behaviors, capturing the dynamic nature of pilot control strategies more effectively.
Overall, the research highlights the importance of understanding pilot behavior in control loops, particularly in the context of aerospace applications. The insights gained from this study can inform the design of more adaptive and responsive control systems, ultimately enhancing safety and performance in aviation. The findings also suggest broader implications for the application of wavelet-based modeling techniques in various technological and scientific fields, paving the way for future research and development in human-machine interaction and control systems.
