Microcontroller-based implementation of adaptive structural control

An adaptive filtering technique is developed for the control of structures with lightly damped modes. The technique is based on a feedback control strategy that uses tuned second-order filters to add damping to structural resonances. A single-mode system is analyzed to determine the effect of the filter parameters on the closed-loop structural damping. The analysis demonstrates that the closed-loop damping is linearly related to the filter damping for gain margins greater than two and that the closed-loop damping is highly sensitive to changes in the filter frequency. The sensitivity of the closed-damping to errors in the filter frequency motivates the use of a phase-lock loop to identify the structural frequency during transient vibration. The feedback compensator is implemented on a digitally-programmable analog filter whose parameters are set by a microcontroller. The adaptive algorithm is demonstrated on a flexible composite beam with a variable tip mass. Adding or subtracting mass to the tip of the beam varies the first structural mode from 24 Hz to 11 Hz. Control experiments demonstrate that the closed-loop damping is reduced from 21% to 4% critical when the filter parameters are not adapted to the structural frequency. In contrast, the adaptive filter is able to maintain between 14% and 21% critical damping in the structural mode as the frequency varies from 24 Hz to 11 Hz.