# Trajectory Planning of Shape-Following Laser Cleaning Robot for the Aircraft Radar Radome Coating
## 1 Introduction  
The maintenance and repair of aircraft radomes play a pivotal role in ensuring the integrity and functionality of aerospace systems. Radomes are subjected to various environmental factors during operation, including climate variations, flight friction, and airflows. These factors contribute to the wear and damage of the radome's surface coatings and bottom paint. Consequently, in the maintenance process, regular treatment of the radome surface coatings is an essential step for preserving its performance. Conventional methods for aircraft paint removal include mechanical cleaning, solvent-based cleaning, and ultrasonic cleaning [1]. While these methods have reached a considerable level of maturity, they also come with significant drawbacks. For instance, chemical and mechanical cleaning methods are labor-intensive, prone to substrate damage, and can generate substantial waste, which leads to environmental pollution [2, 3]. In comparison, laser cleaning technology is regarded as a greener and more promising alternative, particularly in the context of the global manufacturing industry's transformation. This technology operates by inducing a series of optical, thermal, and mechanical changes in a short period, effectively removing contaminants through their coupled effects [4, 5, 6, 7, 8]. Laser cleaning is considered the most promising green cleaning technology of the 21 st century, as it enables minimal damage through precise control of laser parameters [9, 10]. With theadvancements in robotics and computer numerical control (CNC) technology, multi-joint robots have found widespread applications in various fields, including laser cleaning, processing, and welding, due to their high degrees of freedom, exceptional flexibility, and programmability [11; 12; 13]. Path planning for robot machining is a primary requirement for achieving automation in robot-based machining. Researchers have conducted relevant research on robot path planning according to the characteristics of different machining methods. [PERSON] conducted path planning for robot machining using a parameter-optimized surface model [14]. [PERSON] developed an offline programming system based on computer-aided design (CAD) models for robot polishing path planning [15]. [PERSON] proposed a novel software package design based on CAD surface modeling, integrated into the offline programming software RobotStudio(tm) (Product of ABB Company, Sweden), which considered both simple coating models and torch kinematic parameters to generate robot trajectories automatically [16]. [PERSON] utilized reverse engineering techniques to reconstruct the CAD model of an aircraft wing mask and generated scanning trajectories for non-destructive testing with high positioning accuracy [17]. Most of the above studies are based on the CAD models of the workpieces. However, these methods are unable to accurately execute when the CAD model of the workpiece is missing or when the actual surface shape of the workpiece does not match the CAD model data. Point cloud information can clearly reveal the surface features of the inspected workpiece, leading many researchers to utilize point cloud data for robot path planning [18; 19; 20; 21]. [PERSON] et al. indirectly obtained the stereolithography (STL) model of the workpiece using a 3D scanning device and performed laser cleaning path planning through offline programming software, demonstrating the effectiveness of robot laser cleaning [22]. For simple parts, traditional robot path-planning methods can be employed for robot laser cleaning path planning. However, for large, curved surface workpieces, these methods fail to meet the requirements of precise laser cleaning operations and cannot achieve curved surface cleaning. This work focuses on processing point cloud data of aircraft radomes in the absence of CAD models to generate motion trajectory planning for a coating laser cleaning robot.