Multiple ViSPs (visually servoed paired structured light systems) for 6-DOF structural displacement estimation

Recently, structural health monitoring has gained great attention due to the deterioration of aging structures and rapid growth of massive structures. To monitor the structural conditions, a visually servoed paired structured light system (ViSP) for estimating 6-DOF relative displacement has been developed. The system is composed of two sides facing with each other, each with one or two lasers with a 2-DOF manipulator, two cameras, and a screen. By calculating the positions of the projected laser beams and rotation angles of the manipulators, the relative displacement can be estimated. To estimate the movement of the massive structure, entire structure is partitioned and the displacement at each partition is estimated by the each ViSP. In the multiple ViSPs, the movement of the entire structure can be estimated by multiplying the estimated displacements in a cascaded manner. However, it has a major problem that the error is propagated due to the multiplication. Therefore, a displacement error back-propagation (DEBP) method which uses the Newton-Raphson method inspired from the error-back propagation method is proposed. In this paper, the details of the ViSP and DEBP method are described.