# Projection-Based Augmented Reality Assistance for Manual Electronic Component Assembly Processes
## 4 Usability Test  
With the aim of evaluating the benefits of the AR extension compared to the previous system, a system usability scale (SUS) survey was made, which compares the usability between the two systems. On one hand, the original system presented in [22], where instructions are only displayed on the  
Figure 5: Conceptual scheme of the projection mapping pipeline. Virtual content (left) is transferred to the camera image (\(T_{track}\)), and then, this content is transformed again (\(H_{calib}\)) to the projector image area that is subsequently projected. See text for details. Figure 6: Example of virtual content that is projected (highlighted in white) in the printed circuit board during the component assembly process. The projection is more clearly seen live, so we provided the bottom row that has zoomed-in versions of the top images to see the projections in these images with more quality. screen. On the other hand, the proposed system, where instructions are displayed both in the screen and on the board directly via the projector. SUS survey is a ten-item scale test giving a global view of subjective assessments of usability [27], which is used as a standard survey for usability tests. The proposed test consists of mounting the same PCB with the aid of both solutions, the original and the proposed ones, wherein every mounted process is timed and the number of mounting errors is measured. Finally, the SUS test was completed. A total of 21 people were surveyed. They were between 20-45 years old; there were 15 men and six women, one of them color-blind. They did not have any experience in PCB assembly. This was done in order to emulate a newcomer to the production line, since rotation of personnel is common. The test was performed in a laboratory where a replica of the manufacturing production workspace was located. They were divided into three groups: seven participants for each group. Group 1 used the original system in the first place and later the proposed one. Contrarily, Group 2 used the proposed system first and original system second. Groups 1 and 2 did not have any experience mounting the electronic board; thus, it was fair to assume that the first mounting would take longer than the second, as the users had more experience for the second mounting. For this reason, Group 3 was created. This group had already mounted the PCB using a different solution, so they already had some knowledge of the PCB when using both processes. This grouping was done in order to measure time efficiency among processes, but it did not have any impact from the usability point of view. Figure 7 displays the SUS scores. The higher the score, the more usable the systems is. The systems achieved average values of 80 and 90 out of 100, respectively. Although a SUS score interpretation is not straightforward, [PERSON] et al. [28] concluded that any system above 68 can be considered usable; he also proposed an adjective scale, where a mean SUS score of around 70 is considered good, one around 85.5 is considered excellent and one around 90.9 is referred as the best imaginable. Thus, both systems are highly usable, but the use of augmented reality is preferable. As mentioned, mounting times were measured in order to get some objective insights about system efficiency; see Figure 8. As predicted, for Groups 1 and 2, the first mounting was usually the more time consuming one. However, for Group 3, where participants started both mountings with the same experience, the proposed solution yielded lower mounting times for all participants. In addition, the feedback provided by the two systems prevented the users from making any errors. Figure 7: Distributions of SUS scores. Blue represents the original system and Yellow the proposed one. Black lines mark the average value of both distributions. These results show that the AR system is even faster and more comfortable than the previous system.