# Robotized Mobile Platform for Non-Destructive Inspection of Aircraft Structures
## 1 Introduction  
Increasing demands on structural safety and reliability in the aircraft sector stimulate the development of the non-destructive testing (NDT) market, which demonstrates continuous growth, having reached the size of USD 10.3 billion in 2023 and currently being projected to reach USD 18.5 billion in 2028, according to recent reports [1]. Among other factors, the increasing attention on the automation of NDT systems plays a crucial role in the development of new technologies and solutions in this sector, which received confirmation in the mentioned report [1]. This leads to the implementation of the NDT 4.0 concept, which assumes the automation and digitization of NDT systems, including the development of robotized inspection systems with the support of automated processing tools [2; 3]. This is especially important for the aircraft sector during manufacturing quality assurance and in-service inspection [4], where NDT inspections are usually laborious and time-consuming due to the necessity of scanning extended and geometrically complex structures. Introducing the automated NDT systems allows for reducing the inspection time with a simultaneous increase in the accuracy of inspection, which undoubtedly influences the overall lowering inspection costs. This is particularly important during C- and D-checks of aircraft, where the reduction of inspection time will be the most profitable [5]. According to the estimations made in [6], by the implementation of automatized inspection solutions, the overall cost of an aircraft fuselage inspection is expected to be reduced by 10% with a simultaneous reduction in inspection time by 30%. Several solutions within robotic NDT systems are commercially available and widely used in aircraft inspections, especially employing ultrasonic testing (UT), eddy current testing (ECT), and infrared thermography (IRT) techniques due to their accuracy andefficiency, as well as portability. It is worth mentioning manipulators and robotic arms adapted for the purposes of inspections of aircraft parts and structures, e.g., YXLON robotic systems used in X-ray inspections or NSpect robotic ultrasonic scanning systems developed by Genesis for aerospace markets based on FlawInspecta technology; as well as portable inspection systems, like Boeing Mobile Automated Scanner (MAUS), which is a multi-technique system, and includes both UT and ECT. Examples of several other adaptations of robotic arms for NDT inspection are described in [7]. Apart from them, numerous NDT approaches are adapted to automatic inspection performance. An overview of automatic and robotic systems for NDT can be found, e.g., in [8; 9; 10; 11; 12; 13]. Recently, unmanned aerial vehicles (UAVs) have been used for inspection purposes, including aircraft inspections [14; 15; 16]; however, their performance is usually limited to visual inspection only, while most of the structural inspection procedures of aircraft are based on contact techniques. The newest solutions demonstrate the ability to perform contact inspections with UAVs: the authors of [17] demonstrated the technology of a sticking inspection system with implemented equipment for UT evaluation; however, the energy consumption and control of such systems remain challenging questions. The inspection systems based on robotic arms have already proven their effectiveness; however, their significant limitation is the possibility to perform inspections in specialized laboratories only, while in numerous cases there is a need for performing inspections in hangars or even on the aprons. This leads to the necessity of developing mobile systems which can fulfill these demands. Several efforts have been made to implement mobile robotic, including climbing robots with different adhesion mechanisms such as magnetic [18], adhesive [19], bionic [20], electrostatic [21], thrust [22], vacuum [23], and vortex suction [24; 25; 26].