A Six-degree-of-freedom Laser Vibrometer, Part II: Experimental Validation

Abstract

The operational principle and evaluation of a novel multi-co-ordinate vibration transducer is discussed in this paper. The measurement system can determine three translational and three rotational displacements of a vibrating structure. In Part I of this paper the analytical development of the technique was discussed. In this paper the practical implementation of the technique and its experimental validation will be discussed. A prototype system is presented. Systematic geometric errors from manufacturing tolerances and assembly misalignment were found to induce sufficient crosstalk between the target translation and rotation variables to degrade the data quality. The errors were reduced by applying a Marquardt kinematic calibration to estimate the effective geometric values of the prototype. Laboratory tests yielded a measured static translational displacements accuracy of 50 μm translational and 0·06° rotational displacements. 99% statistical confidence interval precision values of 20 μm for translation and 0·01° for rotation were obtained. The dynamic measurement capabilities of the technique were evaluated via a structural impact test of a cantilever beam. The resulting frequency response and coherence functions where of high quality with expected characteristics. The results from both static and dynamic tests prove the feasibility of the 6-DOF laser vibrometer concept.