Method and apparatus for sensing and damping vibration

Abstract

A shape memory alloy used for both sensing and damping vibration of a structure. In one embodiment, a flat bar (12) is mounted from one end on its edge so that its other end vibrates from side-to-side at its natural resonant frequency. A vibration damping wire (30) extending longitudinally along one surface of the bar is mounted under tension between spaced apart standoffs (32); a sense wire (42) is similarly mounted along the opposite surface of the bar. The vibration damping wire and sense wire comprise a nickel-titanium (Nitinol) alloy, having a relatively high specific damping coefficient. Absorption of kinetic energy by the vibration damping wire when it is stretched by deflection of the bar greatly reduces the time required to passively damp vibration of the bar, compared to its undamped resonant time. the vibration damping wire is heated above a transition temperature by an electrical current pulse while relaxed to restore it to its unstretched length. The sense wire changes resistance in proportion to stress applied to the wire so that a voltage drop across the sense wire corresponds to the vibrational displacement of the bar. The voltage drop signal is used to control application of the current pulse in synchronization with the vibratory motion of the bar. To actively damp vibration of the bar, the pulse of electrical current is applied to heat the Nitinol alloy above its transition temperature so that it resumes a foreshortened memory shape as the bar's vibratory deflection tries to stretch the vibration damping wire. The vibration damping wire thus applies a force to the bar in opposition to its vibration. Other embodiments include a cylinder (52) and a vibration damped strut assembly (80). In these latter two embodiments, vibration damping wires and sense wires are disposed internally within the structure. A digital control (110) or analog vibration damping control (200) controls the application of current pulses to heat a selected vibration damping wire above the transition temperature in phase with the signal produced by the sensor wire.