# AR-Assisted Guidance for Assembly and Maintenance of Avionics Equipment
## 3 Materials and Methods
### User Study
#### 3.5.2 Procedure  
1. Overview and preparation (20-30 min)  
Before starting the experiment, the participants read and signed an informed consent form containing written explanations regarding the experiment and ethical approval. All participants remained in good condition and actively engaged in the experimental process of the system. Then, we gave the participants a preliminary introduction to our system and experimental methodology. Then, the preparation before the experiment was carried out. First, we introduced the assembly parts to the participants, explained the use of the tools, and made them familiar with the operation process through practical cases of assembling bolts with ratchet wrenches and installing and removing aviation cables. For the ARG group, we also taught participants to interact with the AR system using gestures and speech. In this process, we did not disclose the specific experimental task details. 2. Experiment (40-50 min)  
The task of the experiments in this paper involved three items of avionics equipment and one avionics equipment bay (see Figure 11). The size of avionics equipment A is \(200\,\mathrm{mm}\times 200\,\mathrm{mm}\times 300\,\mathrm{mm}\), and the left and right sides are fixed with two M5 bolts each, and there are three cable interfaces in the front. Avionics equipment B is \(300\,\mathrm{mm}\times 250\,\mathrm{mm}\times 300\,\mathrm{mm}\) in size and is fixed with three M5 bolts on both front and rear sides, with five cable interfaces in the front. Avionics equipment C is \(250\,\mathrm{mm}\times 250\,\mathrm{mm}\times 400\,\mathrm{mm}\) in size and is fixed with two M6 bolts at the front and trapezoidal limit slots at the rear, with four cable interfaces at the front. All cable interfaces are of different types. We designed three tasks: 1 Task 1: training the overall assembly process; 2 Task 2: performing the assembly task for avionics equipment A, B, and C (including installing bolts (Subtask 2-1) and cables (Subtask 2-2)); and 3 Task 3: performing the maintenance task for avionics equipment A and B. Before starting, the participants were told to balance efficiency and quality. Figure 10: The participants’ experience with assembly and AR. Task 1: Training  
Task 1 was intended to make the participants understand the assembly process and steps for all the avionics equipment until they believed they were familiar with the assembly process and reported that they had the confidence to start the assembly task. In TG, we provided 2D drawings of the avionics equipment, the assembly order (AO), and the technical requirements. In ARG, we provided 3D rendered and interactive avionics equipment models, 3D animations of the AO, and the technical requirements. Task 2: Assembly  
After completing the training, the participants began to perform the assembly tasks for the three items of avionics equipment. The participants used assembly tools such as ratchet wrenches to assemble the three items of avionics equipment according to the AO (including Task 2-1, loading the avionics equipment into the equipment bay and tightening the bolts, and Task 2-2, installing the cable glands). In TG, we provided 2D drawings, the AO, and the technical requirements for the avionics equipment. In ARG, we provided the assembly guidance information and the technical requirements that could be rendered in 3D and interacted with through AR glasses. Task 3: Maintenance  
The usual maintenance process includes inspection, disassembly, replacement, and assembly. Considering that the inspection and replacement process takes a short time and that the assembly process is similar to Task 2, we conducted experiments on the disassembly process. Upon completion of the assembly, the participants began to perform the disassembly session of the maintenance task. The participants used assembly tools such as ratchet wrenches to perform the experiment according to the maintenance operation process (MOP) to disassemble the specified avionics equipment A and B. In TG, we provided 2D model drawings and the MOP.