A computer-vision based vibration transducer scheme for structural health monitoring applications

Abstract

It is known that the structural health monitoring (SHM) applications rely on the physical data obtained fromin-situmeasurements. In this view, various instruments such as accelerometers, strain gauges, displacement sensors are used to collect data, which are to be used in structural identification applications. Considering the basic requirements like precision, accuracy and applicability for reliable data post-processing, a new scheme for a vibration sensing device is introduced in this study. The proposed sensor scheme is a vibration transducer which combines the fundamental sensing principles of conventional accelerometers and the computer vision techniques. Basically, the transducer consists of a mechanical system as the primary sensor and a camera as the secondary sensor. In conventional piezoelectric (PE) accelerometers, the PE material generates charge or voltage which is proportional to the acceleration applied to the sensor. Subsequently, this charge or voltage is measured and used to determine the imposed accelerations. However, in the proposed vibration transducer, the motion of the seismic mass is directly tracked by a camera and the displacements are extracted using computer vision algorithms. Afterwards, displacement of the seismic mass can be related to the imposed acceleration, velocity and displacement. In this study, the transducer concept was realized practically using two different primary sensors consist of a spring-mass system and a cantilever beam together with a smartphone's camera. The concept was tested on a laboratory structure in order to verify its capabilities in modal identification, damage detection and localization applications. The comparison of the results obtained by the proposed transducer and the conventional accelerometers has shown that the proposed vibration transducer is capable of both identifying modal parameters and detecting damage despite its crude design. Although the sensitivity of the transducer is lower than the conventional accelerometers in its current state, the concept is prone to further improvements.