Nowadays, the evaluation of structural safety and serviceability is becoming more essential due to the deterioration of civil infrastructures. In particular, the structural displacement which provides important information on structural conditions is considered one of the important indicators for the health monitoring of structures. To estimate the structural displacement, this paper proposes a one-way projection-type six degree-of-freedom (DOF) displacement measurement system based on vision and laser sensors, named one-way ViSP (Visually Servoed Paired structured light system). The system is composed of a transmitter and a receiver, which are facing to each other. The transmitter consists of a 1D laser range finder, two lasers, and a 2-DOF manipulator, while the receiver consists of a screen and a camera. The one-way ViSP estimates relative displacements between a transmitter and receiver by measuring the coordinates of three projected beam spots and a distance. Besides the advantages such as high accuracy in 6-DOF displacement measurement, low cost, and real-time monitoring possibilities, the one-way ViSP can cover large areas such as dams and inclined planes by using multiple receivers. Through various simulations and experiments, it is shown that the one-way ViSP has high accuracy in 6-DOF displacement estimation.

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