Discovery Magazine

Flexible Body Control Demonstration using Fiber Optic Sensor Arrays

The measurement of the bending modes of a highly flexible aerospace structure is accomplished using state-of-the-art fiber optic sensors. The control of the flexible structure is accomplished using cold gas thrusters as actuators at two different locations within the test article. The scope of the study was defined as follows: (i) Develop numerical models of the test article, including the structural response, actuator models, and transport and conversion delays associated with the fiber optic sensors (ii) Design, model and validate a novel cold gas actuator system, (iii) Develop a test plan and procedure to demonstrate performance of fiber optic sensor control system, and (iv) Final assessment, including experimental assessment, simulations and demonstration of the corresponding analytical tools, as well as an assessment of the viability to utilize fiber optic sensors on current and future aerospace vehicles, including rockets and aircraft.

A complete test article that satisfies the requirements for the study was designed, built and tested extensively. FEM modeling methodology was developed to capture most significant features of the test article. Both classical MIMO PID controllers and an H-infinity MIMO controller were developed to test the use of fiber-Bragg optic grating fiber optic sensor arrays in the real-time control of flexible structures, using both the integrated models of the structure, fiber optic sensor and actuators, as well as experiments for both perturbation of the initial conditions and continuous base excitation. It was demonstrated that the first two modes (the lowest frequency modes) of a slender structure can be robustly controlled using two independent gas actuators, and that robustness can be improved at the expense of performance when the number of available actuators is small. Future work includes the development of virtual inertial sensors using FBG fiber optic sensor arrays, structural on-line modal estimation of time-varying structures, and advanced robust control of flexible structures using robust gain scheduling as in linear parameter-varying control and L1-adaptive control.