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.