A Six-degree-of-freedom Laser Vibrometer, Part I: Theoretical Development

The operational principle and evaluation of a novel multi-dimensional vibration transducer is discussed in this paper. The measurement system can determine three translational and three rotational displacements of a vibrating structure by sensing the positions of three light beams reflected by a tetrahedral target. Computation of target pose from light beam positions is achieved with an iterative algorithm. Part I of this work develops the operational principle of the technique. An optimization analysis is used to define feasible system geometries. The most feasible configuration had three photodetectors and three lasers placed equidistantly around concentric circles. A better performance was predicted with the laser circle having a larger diameter than the photodetector circle. The practical implementation and experimental evaluation of this measurement technique is discussed in Part II of this work.