Modal Testing Using Tracking-Interferometers

Abstract

Modal testing is performed for the characterization of structure dynamics, diagnostics, and condition monitoring. Modal analysis is also used for the detection of sources of vibrations, design optimizations and as comparison data to improve computation results. For open surfaces in the automotive and aerospace industries, the modal testing is often performed using scanning laser vibrometers. In the case of partially closed structures such as machine tools, vibration measurement is typically conducted using three-axial accelerometers. This paper presents a novel approach to performing modal analyses using a single laser tracking-interferometer. First, tracking-interferometers are introduced – followed by an explanation of the modal testing using this device. A holistic measurement method for modal testing is introduced and the individual functionalities are explained as follows. The principle for three-dimensional dynamic measurement is discussed and the performance of the tracking-interferometer measurements in beam direction and in lateral directions are benchmarked against alternative measurement methods. Three-dimensional measurements are presented, including the coordinate transformation and modal analysis results of a machining center. Dynamic measurements and tracking-interferometer-aided geometric model design are presented along with the multiangulation-based position detection for the interferometer head.