# Comparing Augmented Reality-Assisted Assembly Functions--A Case Study on Dougong Structure
## 2 Related Work
The experimental results showed that AR was faster and more accurate for psychomotor phase activities, was preferred by participants, and was considered to be more intuitive. [PERSON] et al. [13] compared the effects of different AR hardware devices for complex manual assembly tasks, including Microsoft HoloLens 1, desktop computer, and tablet computer based on three quantitative measures. The use of HoloLens AR instructions led to the shortest assembly time and lowest error counts, but has a lower NPS (net promoter score) than the tablet group. They thus suggested improving the wear comfort and the object tracking performance of the HoloLens device. [PERSON] et al. [14] developed AR-assisted functions that provide instant validation for manual assembly using computer vision techniques. Experiments of puzzle assembly were conducted to compare the performance, ease of use, and acceptance of two AR display methods: a mobile device and a projector. Participants of the projector group completed the assembly task faster with slightly fewer errors and lower cognitive load. A possible reason is that the field of view (FOV) provided by the mobile device was static and thus limited the user movements during the assembly process. Previous studies have not fully agreed that AR applications are guaranteed to improve the operational efficiency or quality of the manual assembly of complex objects. A possible reason is that the success of AR-assisted assembly functions depends on how the instructional information is presented to the users and the system's process design [5; 7; 8]. However, most studies agreed that AR-assisted functions should be designed to improve paper-based assembly instructions. The aim in this study is to investigate the effectiveness of AR interactive content designed for manual assembly with two focuses. First, novel AR-assisted functions were designed to overcome the existing limitations of paper-based assembly instructions [15]. These functions include automatic object recognition and result verification that prevent the user from fetching the wrong parts or performing incomplete assembly. The second focus was to clarify whether or not and how AR can improve the operational efficiency or quality of the manual assembly of complex objects. Existing studies have shown mixed results for these issues. The frameworks of two assembly systems were based on a 3D viewer and AR, respectively, which contained a set of functions designed for those purposes. A series of experiments were conducted to compare these two systems with paper-based instructions. Objective measures included the duration of each assembly step and number of various errors recorded during the assembly process. Subjective assessment was conducted through interviews using the NASA-TLX questionnaire. The analysis of the experimental results revealed important factors about the performance of the three media. These findings may work as design guidelines for improving computer-assisted manual assembly of complex products. They also demonstrate the potential of AR as an interface in construction automation.