# Robotized Mobile Platform for Non-Destructive Inspection of Aircraft Structures
## 1 Introduction
These mechanisms also use different locomotion mechanisms such as driven wheels [27], tracks [28], propulsion impellers [29], legs [30] and moving suction pads [31], etc. However, reports of laboratory mobile systems equipped with advanced NDT equipment such as UT, ECT, IRT, and radiography are rare. Commercial examples, such as the mobile NDT inspection robot with magnetic adhesive system presented in [16], delivered by Eddyfi Technologies (Scorpion 2 dry) or remotely operated vacuum-enabled robot (ROVER), developed by Boeing, and the mobile robot for fuselage inspection (MORFI), developed by Lufthansa Technik, with an implemented IRT inspection system, have demonstrated their utility in aircraft inspections [20]. In most reported cases, the mobile platforms are tested under laboratory conditions while the robots are tested without NDT equipment, which only is estimated as part of the system's payload. An interesting overview of the potential applications of wall climbing robots and their prototypes with different adhesive mechanisms is discussed in [32] where magnetic and negative pressure adhesive systems are found to be particularly suitable for NDT purposes. Additional design considerations for mobile NDT systems can be found in [33]. The authors conclude that there are no robot wall climbing solutions which meet all of the requirements such as high mobility and speed, high payload, reliability and safety, usability in terms of energy consumption and maneuverability. On the other hand, they indicate that specialized solutions tailored for specific environments often offer the best balance for meeting demanding requirements. Despite the variety of robotic systems used for NDT, in this study, we focus on a dedicated solution. Current needs in inspections for the Polish military aircraft ground maintenance sector and difficulties in manual inspections encouraged the authors of this study to develop a mobile platform (MP) with interchangeable sensing systems, which allows for the inspection of various types of aircraft structures, both metallic and polymer-matrix composite, with various angles of inclination. The objective of the development of the mobile platform was to find a low-cost solution for the automation of existing inspection techniques by their implementation onto this platform. In this study, we described the process of conceptual design and detailed design of MP as well as building a prototype and its testing during inspection of various aircraft structures. Based on the published outcomes of suitability of different wall climbing robotsfor NDT inspections [32; 33] we mainly focused on the consideration of the mechanism of adhesion based on negative pressure generation. Such solutions based on vacuum, suction pads or thrust are not or less constrained by the material of the inspected surface and still remain a subject of many ongoing studies and adaptations to specific requirements. For instance, in [34; 35], the thrust adhesion mechanism is detailed designed using numerical simulations. The article [36] presents research about the detailed design and optimization of the suction pads for a robot with multiple legs. Another study on a control system for the robot based on the suction pads mechanism for aircraft skin inspection is presented in [37]. A pair of flexible vacuum suction feet is presented in [38]. This solution has the ability to avoid obstacles. In the study [39], a conceptual design and detailed design plan for a robot that utilizes a vacuum approach and incorporates advanced 3D printing technology is presented. A hybrid mechanism that combines locomotion and adhesive mechanisms is presented in the article [40]. The authors take advantage of the propulsion impellers for this purpose. In [41], a square rotational-flow adsorption unit is tested and used to maintain negative pressure and adsorption force by using the air's rotational inertia effect. Article [42] presents numerical and experimental studies on the negative pressure mechanism for underwater solutions.