Method of controlling the application of counter-vibration to a structure

The method of controlling the application of counter-vibration to a structure so as to reduce the effect of externally-created sinusoidal vibration thereon, comprising the steps of:

• mounting a vibratory force generator on said structure for applying sinusoidal counter-vibrations to said structure in response to a supplied electrical signal;
• mounting an accelerometer on said structure at a point at which vibration is to be measured, said accelerometer being arranged to produce an output signal having an amplitude, phase and frequency in response to a sensed vibration;
• providing a tunable filter capable of resonating at an electrically-controllable frequency;
• providing an adaptive frequency estimator arranged to produce a tuning signal as a function of said accelerometer output signal;
• supplying said tuning signal to said filter;
• supplying said accelerometer output signal to said filter;
• continuously adjusting the resonant frequency of said filter so as to equal the frequency of said accelerometer output signal so that said accelerometer output signal will be greatly amplified at the output of said filter;
• and
• supplying said resonant filter output signal as an electrical command output signal to said force generator;
• thereby to cause said vibratory force generator to apply counter-vibrations to said structure to reduce the effect of externally-created vibrations at such measurement point.