On the measurement of angular vibration displacements: a laser tiltmeter

A novel modification and use of the optical geometry which is used as the basis for the Laser Torsional Vibrometer [1] is described. This latter instrument measures the torsional oscillation (or local rotational speed fluctuation) of a rotating component of arbitrary shape and in the presence of solid body vibrations of the component itself. The Laser Torsional Vibrometer relies on the mean speed of rotation of the component to produce a time resolved voltage analogue of the angular velocity. There are many cases of engineering interest however where a component undergoes an angular oscillation about an axis rather than a simple translation or rotation with a unidirectional angular velocity In modal analysis for example where rotational and translation motions are of equal importance the absence of suitable transducers means rotational mobilities are rarely measured [2]. In what follows it is shown how a modification to the optical geometry of the Laser Torsional Vibrometer can produce an instrument which is capable of measuring the local angular or tilt velocity in this situation and will therefore solve this problem.