# AR-Assisted Guidance for Assembly and Maintenance of Avionics Equipment
## 1 Introduction  
Advanced aviation equipment such as aircraft has the characteristics of complex product structure, huge numbers of parts, and many assembly relationships, which make its assembly and maintenance difficult [1]. In most of the processes of aircraft assembly and maintenance operations, manual operations are still predominant. The characteristics of aircraft assembly operations require operators to memorize a lot of operation instructions, familiarize themselves with complex operation steps and actions, and master a large number of disassembly operation skills. These tasks have high requirements in terms of the experience and comprehensive literacy of the assembly operators, which also indirectly leads to problems, such as low efficiency and unstable assembly quality [2]. The number of large aircraft parts exceeds one million, and their assembly cycle accounts for about 65% of the total manufacturing cycle [3]. Therefore, assembly efficiency and quality are of great significance for the improvement of production capacity. The traditional manual assembly process is guided by two-dimensional (2D) paper drawings and process manuals to assist workers to complete the assembly work [4]. This method has no obvious guidance, and it is easy to make errors when distinguishing drawings, which will reduce assembly efficiency and quality. We introduce AR technologies to assist in assembly and maintenance. By adding the assembly process, installation location, specification requirements, and other assembly guidance information in the real operating environment, we aim to improve the intuitiveness and safety of assembly guidance, increase assembly efficiency, and realize AR visual intelligent assembly of advanced aviation equipment. At present, some researchers have carried out research on the use of AR technology to assist in assembly and maintenance [5]. [PERSON] et al. proposed an AR-assisted manual wiring production method [6]. Boeing engineers and technicians can use AR glasses to query information about aircraft parts, quickly locate faults, and view maintenance procedures [7]. However, there are still some serious obstacles to achieving efficiency in assembly problems which have not been solved. A typical example of such obstacles is a blind-area assembly problem: in the narrow landing gear and equipment bay triangle area of the aircraft, the assembly parts of some avionics equipment cannot be directly seen and the workers basically rely on hand touch to perform blind assembly, which makes the efficiency and quality of assembly uncontrollable. It is also common for assembly parts to be occluded by other parts such as cables during maintenance [8]. One of the solutions to the above problems is to visually guide the whole process of assembly and maintenance through AR-assisted assembly methods. The key of the AR-assisted method lies in real-time acquisition of the pose of dynamic objects through a 3D tracking approach. This enables the overlay of virtual information onto real objects and automatic recognition of the assembly process and results. The primary goal is to reduce the skill requirements for workers, and improve assembly efficiency [9]. Aiming at the common process of assembly and maintenance of avionics equipment in the equipment bay (including the assembly of bolts, cables, and other parts), this paper proposes a blind-area information perception and AR-guided assembly method based on color and depth data (RGBD). We apply machine vision, AR, and image processing technologies to track the poses of parts in blind areas and identify the assembly stage and guide the operator to efficiently complete assembly and maintenance tasks with AR. The contributions of this paper can be summarized as:  
1. We proposed a pose tracking method for dynamic assembly parts based on RGBD data, aiming at fast, accurate tracking and the robust display of assembly information on parts;
2. We proposed an AR-assisted assembly guidance method for the assembly and maintenance operations in the visual blind area.