Wall-climbing drones have many applications, including structural health monitoring of civil structures, such as bridges and high-rise buildings, cleaning of solar panels to improve power generation efficiency, and airplane visual inspections. For these applications, the drone requires a high-payload capacity, and consequently the size and weight of the drone increase. The drone also should not damage the target structures considering the purpose of its mission. Our previous versions of a wall-climbing drone could have high-impact force on the surface where the drone perches and on the platform itself because of the impact caused by a fast pose change and landing speed. In order to overcome this potential risk, a mechanism and a control algorithm for perching on a vertical surface through low-speed pose change are proposed in this paper. The drone platform is based on an X-configuration quadcopter, and a tilt-rotor mechanism is incorporated into the two axes, such that the front thrusters and the rear thrusters are paired. The vertical soft landing mechanism using the tilt-rotors is validated by the experimental tests of the prototype.

Wind turbines need annual inspections to investigate their states which may have damages, such as cracks, erosion, bonding defects, cavities and delamination. Wind blades inspection, however, is a difficult process which needs specialized equipment and well-trained technicians to perform it manually. In addition, most approaches to inspect require pre-installed infrastructures like ropes or other platforms, so they are not appropriate for a close investigation and has a low preference. To overcome these problems, the need for a wall-climbing robot has emerged. In this paper, we suggest a MAV (Micro Aerial Vehicle) type wall-climbing robot that has four rotors to make thrust force for tlying and four wheels for wall-climbing so that it can tly, stick, and move on a vertical and non-tlat surface. The overall inspection process has two parts; macro and micro inspections. The main concept was verified throughout simulations.

Urban structures need constant maintenance and inspection of the structural health condition and safety of the users, however, to access the structure is getting harder and harder due to their enormous height and size. In order to deal with this problem, though many researchers have developed several robots for wall-climbing there is no guaranteed solution yet. One of the critical reasons why existing wall-climbing robots haven't been available in the field is the risk of accidental fall due to operational failure from the harsh environment like strong wind and surface's unpredictable condition. Therefore, we tried to develop a drone-type wall-climbing aerial robot platform that can approach to any place of the structure by flying and sticking to the target place with pose change and perching mechanism. The robot is equipped with a locomotion mechanism like other wall-climbing robots to move on the vertical surface of the structure. This paper deals with installing the wall-climbing mechanism on the aerial robot, its pose change and wall sticking mechanism, and locomotion on the vertical surface of an urban structure.

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Nowadays, the evaluation of structural safety and serviceability is becoming more essential due to the deterioration of civil infrastructures. In particular, the structural displacement which provides important information on structural conditions is considered one of the important indicators for the health monitoring of structures. To estimate the structural displacement, this paper proposes a one-way projection-type six degree-of-freedom (DOF) displacement measurement system based on vision and laser sensors, named one-way ViSP (Visually Servoed Paired structured light system). The system is composed of a transmitter and a receiver, which are facing to each other. The transmitter consists of a 1D laser range finder, two lasers, and a 2-DOF manipulator, while the receiver consists of a screen and a camera. The one-way ViSP estimates relative displacements between a transmitter and receiver by measuring the coordinates of three projected beam spots and a distance. Besides the advantages such as high accuracy in 6-DOF displacement measurement, low cost, and real-time monitoring possibilities, the one-way ViSP can cover large areas such as dams and inclined planes by using multiple receivers. Through various simulations and experiments, it is shown that the one-way ViSP has high accuracy in 6-DOF displacement estimation.