Development of the tracking laser vibrometer: Performance and uncertainty analysis

This work presents the development of a laser tracking Doppler vibrometer ( TLDV), which is based on a laser scanning vibrometer improved for tracking the same point of a bladed disk during a complete circular rotation, so tha t a Lagrangian approach can be applied to vibration measurement of a rotati ng object. The TLDV is presented and applied to the measurement of vibratio n velocity map of a rotating object. Measurements have been carried out on a bladed disk rotating up to 62 rps. This article discusses the development of the measurement system, with particular attention to the problems of me asurement uncertainty and laser spot positioning accuracy. Results of TLDV measurements performed under different conditions of rotation and of vibrat ion are presented. An analytical model of the measurement system was develo ped in order to evaluate its behavior and analyze its accuracy on the posit ioning and uncertainty of the measured data. In this way it was possible to identify the most critical elements in the system and to guide its optimiz ation. The misalignment between the optic axis of the tracking system and t he rotation axis of the object is the most relevant source of uncertainty, inducing the presence of pseudovibrations at the frequencies of rotation an d causing relative motion of the laser beam on the target surface, which tu rns out to be a positioning error and a source of speckle noise on the lase r vibrometer signal. A comparison between static measurement and numerical analysis has been performed, so that capabilities of the tracking technique were highlighted. (C) 2000 American Institute of Physics. [S0034-6748(00)0 0412-3].