Investigation of three-dimensional vibration measurement by a single scanning laser Doppler vibrometer

Abstract

A scanning laser Doppler vibrometer (SLDV) has been widely used in noncontact vibration measurement. This paper presents a novel investigation of three-dimensional (3D) vibration measurement by a single SLDV sequentially placed at three different positions, where 3D vibration is defined as three vibration components along axes of a specified measurement coordinate system (MCS), which can give more precise knowledge of structural dynamic characteristics. A geometric model of the SLDV is proposed and a vibrometer coordinate system (VCS) based on the geometric model is defined and fixed on the SLDV. The pose of a SLDV with respect to a MCS is expressed in the form of a translation vector and a direction cosine matrix from the VCS to the MCS, which can be calculated by four or more target points with known coordinates in both the MCS and the VCS. An improved method based on the least squares method and singular value decomposition is proposed to obtain the pose of the SLDV. Compared with an inverse method, the proposed method can yield an orthogonal direction cosine matrix and be applicable to a two-dimensional (2D) structure. Effects of the number of target points on the accuracy and stability of the proposed method are investigated. With three direction cosine matrices of three different positions obtained by the proposed method, measured vibration velocities along laser line-of-sight directions can be transformed to vibration components along axes of the MCS. An experiment was conducted to measure 3D vibration

A novel algorithm for determining the pose of a scanning laser Doppler vibrometer

“…Cuihong Liu, Chaoping Zang 1 and Biao Zhou structures [9,10], because of the advantage of its non-contact characteristics. Furthermore, in order to distinguish in-plane and out-of-plane vibration components when the structure has 3D vibration, the 3D vibrational characteristics of structures were measured by using three SLDVs [11][12][13], where three laser beams coming from three SLDVs simultaneously are directed onto a target point and measure its velocity. The measured velocities from the three SLDVs can be transformed into the 3D displacement of structures and can then be used to calculate the dynamic strain distributions [14].…”

Impact monitoring of CFRP composites with acoustic emission and laser Doppler vibrometry

“…Laser Doppler Vibrometry (LDV) is a method of measuring the velocity of surface displacement on a structure. It does this by analysing the change in frequency and phase within the backscattered laser reflected from a surface; this change is the result of structural vibration causing Doppler shift within the laser [19]. Researchers have used LDV for a range of NDT applications, including modal analysis [20,21] and acoustoultrasonic inspection [22][23][24], however to the best knowledge of the authors, not for assessing high frequency AE from impact damage in composites.…”

“…Laser Doppler Vibrometry (LDV) is a method of measuring the velocity of surface displacement on a structure. It does this by analysing the change in frequency and phase within the backscattered laser reflected from a surface; this change is the result of structural vibration causing Doppler shift within the laser [19].…”

Low-frame-rate single camera system for 3D full-field high-frequency vibration measurements

“…Complex arrangements (i.e., Polytec PSV-500-3D [10]), based on three separate SLDV sensors, were developed to overcome this limitation by simultaneously measuring the same target point to obtain 3D velocity information. Alternatively, a single SLDV can be sequentially placed at three different position to measure structures under steady vibrations [11].…”