Structural health monitoring robot using paired structured light

The displacement measurement in structural health monitoring (SHM), though important, was not popular due to inaccessibility and the huge size of the civil infrastructures. The frequently employed approaches use accelerometer, strain gauge, PZT, GPS, LVDT(Linear Variable Differential Transformer) etc., where most of them indirectly measure the displacement, require high cost, and are not so practical to install and maintain. Thus the development of SHM system that directly measures the displacement of the structure using low-cost sensors can be very helpful. In this paper, a multiple paired structured light (SL) system is proposed to be used as a structural displacement measurement. The proposed paired SL module is quite cheap to implement and can directly measure the accurate relative displacement between any two locations. Based on some simulations, a minimal configuration of the paired SL module is proposed. And the steepest descent and extended Kalman filtering-based displacement estimation methods are proposed by deriving a kinematic equation and its constraints. After building a prototype of the paired SL module, some real experiments are performed to test the feasibility of the system for the long-span structural displacement monitoring. The proposed system is expected to act also as a visual inspection and active sensing system if the mobility of the robot is utilized.