Adaptive tuned vibration absorber

Abstract

A control algorithm is developed and applied to a previously designed tunable vibration absorber. The adaptive vibration absorber is capable of detecting the frequency of the driving force and tuning itself automatically to that particular frequency. The primary structure was previously designed to obtain a certain natural frequency. The absorber structure was previously designed so that its range of frequencies includes the natural frequency of the primary structure. The primary structure design consists of a cantilever beam with the absorber attachment hardware, and the vibration absorber assembly consists of three rods and a stepper motor.

The control algorithm uses a look-up table and a gradient search to optimize the effectiveness of the absorber for vibration reduction on the primary structure. The look-up table uses an equation, based on experimental data, to transform a given voltage input, directly proportional to the forcing frequency, into an output command necessary to adjust the natural frequency of the absorber. Once the input voltage reaches a steady state, the gradient search routine adjusts the natural frequency of the absorber to ensure the absorber is tuned to the optimal frequency that minimizes the primary structure vibration.

The primary structure with the adaptive absorber offers significant reduction to the vibration amplitudes of the primary structure, as compared to both the primary structure with no absorber and the primary structure with a passive absorber, throughout the 45 Hz to 71 Hz and 73 Hz to 108 Hz range. The primary structure with no absorber has a 1^st mode natural frequency of 72 Hz and offers the lowest vibration amplitudes, as compared to both the primary structure with the adaptive absorber and the primary structure with a passive absorber, throughout the ranges of 30 Hz to 45 Hz and 108 Hz to 130 Hz. The primary structure with the passive absorber offers the lowest vibration amplitudes of the primary structure, as compared to both the primary structure with no absorber and the primary structure with the adaptive absorber, throughout the 71 Hz to 73 Hz range.