Article ID: 24-00428
Tapping inspections of structures are commonly performed manually by technicians. However, in the case of nuclear structures and other hazardous environments, maintaining a safe distance from the inspection target is preferable. Additionally, there is a growing demand for automated inspection methods. This study proposes a novel remote tapping inspection method that eliminates the need for close proximity to the object. Our approach employs a String-Shoot Impactor, a device inspired by a string shooter toy, which propels a looped string into the air using rollers. By attaching a 4 mm diameter stainless steel ball to the string, we enable remote tapping of inspection targets. In this study, remote tapping tests were conducted from a distance of 2 meters, and the impact sounds were analyzed using frequency spectrum mapping. The results successfully distinguished defect areas from intact regions in a concrete specimen with a 300 mm diameter void defect. To further extend the inspection range, a high-speed String-Shoot Impactor was developed. The previous device, driven by a speed control motor with a maximum rotation speed of 1400 rpm, achieved a maximum launch velocity of 9.2 m/s. By replacing this motor with a brushless motor capable of 4000 rpm, the launch velocity was increased to 26 m/s, enabling an inspection distance of up to 3 meters. Additionally, the impactor was redesigned with three rollers, improving string retrieval performance and stabilizing the launching mechanism. Mounting the impactor on a tripod allowed smooth adjustment of the impact point, enhancing usability. The results demonstrate that this method enables remote tapping inspections from distances of several centimeters to several meters and can be applied in various orientations, from horizontal to vertical. Furthermore, by integrating the device into a suspended inspection setup, it becomes possible to inspect structures that are difficult to access from the ground.
