Visual measurement of laser-transferred structural vibrations

Abstract Vision-based vibration measurement techniques are receiving increasing attention as a typical means of non-contact vibration measurement. Vibration measurements of towering structures using vision-based methods often suffer from low spatial resolution of the camera due to the long shooting distance, which in turn limits the ability to recognize small-amplitude vibrations. Such shortcomings can be compensated to some extent by increasing the focal length of the camera, but longer focal length lenses not only increase the cost, but also place higher demands on the stability of the camera itself. With the progress of UAV technology, the spatial resolution of the camera can also be improved by taking close-up shots of large structures with the on-board camera, but the stability of the UAV itself is still difficult to meet the requirements of high-precision vibration measurement. In this paper, a vibration measurement method is proposed by attaching a laser pointer to a towering structure, which converts the structural vibration into the movement of the laser spot on the ground and realizes the accurate measurement of structural vibration by using the camera to detect the movement of the laser spot at a close distance. For ease of analysis, the method is known as laser-assisted visual measurement of structural vibration i.e. LAVM-Vib. Its operating principle is derived firstly. Then its measurement accuracy is examined numerically for different measurement setups. Finally, the method is evaluated by monitoring the vibration of a micro-wind turbine system. The results obtained by LAVM-Vib are close to that of both the laser displacement sensors and accelerometers mounted on the structure, showing satisfactory results in monitoring faults in tower foundations.