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

Abstract

A scanning laser Doppler vibrometer (SLDV) directs the laser beam scanning over an object by using a galvanometer scanner system, which comprises two orthogonal mirrors and two driving motors. Hence, a control algorithm for the galvanometer scanner is essential to precisely direct the laser beam to the desired position. In this paper, a novel and easy-to-implement algorithm is put forward to determine the pose (orientation and position) of an SLDV. Firstly, a mathematical model is established to correlate the coordinates of the laser spot in the galvanometer mirrors’ coordinate system (MCS) and the rotation angles of the X and Y mirrors. Then, the spatial relationship between the MCS and the tested structure’s coordinate system (TSCS) is identified using an appropriate set of fitted polynomials through a number of reference points. The polynomial coefficients are derived by computing the Moore–Penrose pseudoinverse of the matrix composed of the coordinates of the reference points. Integrated into an SLDV, this algorithm has a strong capacity for dealing with complex testing objects with curved surfaces. Taking a compressor blade as an example, the novel algorithm was applied to an SLDV to direct the laser beam scanning over the measurement points arranged on the blade surface. Results show that the position of the laser spot controlled using the proposed algorithm is accurate, with the maximum deviation from the actual measurement points arranged on the surface being less than 1 mm. The mode shapes of the blade and the modal assurance criterion values also illustrate the feasibility and accuracy of the algorithm for determining the pose of the SLDV. The work presented in this paper has excellent potential for the further development of SLDVs.

An adaptive continuous scanning laser Doppler vibrometry technique for measuring vibrational mode shapes of structures with holes

“…where n is the total number of holes, A i , B i , C i , D i are the four endpoints of the ith hole respectively. The presence of each rectangular hole results in a repetition of equation (15). At the same time, based on the requirement of minimum repetition rate, each additional measuring point also needs to be non-repetitive with the existing points, in other words, these two equations cannot be established at the same time:…”

“…Since high-resolution results can be obtained, it has been used for model updating, fault diagnostics [13], and health monitoring [14]. Liu et al [15,16] transformed the normalized rectangular scan path into an arbitrary continuous scanning path based on the method of using reference points to establish a mapping relationship to test irregularly shaped leaves. Weekes et al [17] controlled the scanning mirrors using arbitrary functions created using knowledge of the tested surface to test 2D surfaces with complex holes, and then also performed 3D CSLDV tests on irregularly twisted blades.…”

Method using singular value decomposition and whale optimization algorithm to quantitatively detect multiple damages in turbine blades

“…29 Chen et al 30 propose a new method of modal shapes testing in WT blade using a high spatial resolution 3D SLDV. Liu et al 31 propose the algorithm which is applied to an SLDV to improve the accuracy of modal parameter measurements. Vuye et al 32 apply the 3D-SLDV to measure the 3D-displacement of the blade and calculate the dynamic strain.…”

Removing speckle noise from the signals of a laser Doppler vibrometer on moving platforms (LDVom) by ensemble empirical mode decomposition

“…A single-point LDV [14] only acquires vibrations at one point, and the setup should move when measuring another point. The SLDV measurement [15][16][17][18] is an ensemble of single-point measurements with the setup simplified by rotating mirrors. However, it requires long-time acquisition at each point, which is timeconsuming.…”