A Multirotor-based Approach for Tap-testing Difficult-to-access Structures

Abstract

Despite advances in structural health monitoring (SHM) technology, human-based inspections continue to remain dominate in practice when performing structural assessments. The reasons for this include the high costs associated with installing and maintaining current SHM, confidence decisions makers have in current SHM technology, and the familiarity the structural assessment community has with humanbased visual inspection. One of the major challenges and costs associated with human-based visual inspections is that structures are often difficult to access. They may be located high above waterways, thus requiring that an expensive crane or barge be rented to provide the inspectors a platform from which to conduct their inspection. In some cases inspectors may even need to rappel down the side of a structure in order to gain access, thus introducing additional safety concerns. Some research has been done to address these concerns by using emerging multirotor technology to facilitate visual structural inspections. Multirotors have shown great potential for maintaining state awareness of structures and construction sites, but one issue is that visual inspection is often hampered by mud, corrosion, vegetation, and other debris on the structure. A proper visual inspection often requires that this debris be removed. This limits the effectiveness of current multi-rotor based visual inspection technology. Furthermore, it is not uncommon for structural inspectors to enhance the quality of their inspection by using a conventional hammer to tap-test the structure of interest. The inspector will simply strike the structure and listen for differences in acoustic response that might indicate the presence of damage in structure. In this work we begin exploring the utility of adding a pneumatic hammer to a multi-rotor vehicle that can be used to facilitate structural inspections. The system features acoustic microphones and accelerometers that can be used to quantifiably document the results of the tap test. Perhaps more importantly though, this paradigm involves transmitting the acoustic response directly a remote structural inspector through earphones. The remote structural inspector can then use their expert judgment to select locations to perform additional tap tests. Furthermore, the pneumatic hammer could also be used to remove debris and corrosion from the structure in order to enhance visual inspection. One challenge associated with this technique is the need to remove acoustic noise caused by the multirotor propellers. Strategies for addressing this source of noise will be discussed. An additional question is how the dynamics of the multirotor will be affected when it is subjected to impact loads from the pneumatic hammers. The results of experimental tests will demonstrate the effect of the hammer impulse on the multicopter’s dynamics. doi: 10.12783/SHM2015/119