# Projection-Based Augmented Reality Assistance for Manual Electronic Component Assembly Processes
## 2 Related Work  
Visual Computing technologies (including augmented reality) will be key enabling technologies for the smart factories of the future [1]. These technologies have demonstrated good capacities for empowering human operators when performing industrial tasks by providing tools that assist them and improve their comfort and performance [3]. Consequently, the research community has focused on these technologies and several related approaches have been proposed [4]. Next, we mention a few AR works applied to the manufacturing sector.  
Augmented reality has been extensively used in many industrial processes, such as maintenance operations [5]. Some of these solutions [6; 7; 8; 9; 10; 11] are oriented toward assembly tasks, in which an AR technology provides virtual instructions in order to guide the operators. In those solutions, the virtual content is shown in a screen, forcing the operators to constantly change the attention between the physical workspace and the screen. As stated by [12], switching attention between two sources during a maintenance task (for example, between the documentation and the workspace when using a traditional paper based instructions, or between a screen and the workspace) might cause a high cognitive load, which translates into greater probability of errors and an increase of the task completion time. On the contrary, projection based augmented reality (also cited as spatial augmented reality (SAR) [13] in a broader meaning, or just projection mapping) projects the virtual data directly in the physical space. This approach allows the operator to have their hands free and is considered an enabling technology to face the challenge of supporting operators performing tasks [14]. Attracted by these advantages, several SAR works have been developed for industrial environments [15; 16; 17; 18; 19]. Most of these works are focused on providing guidance to the operators, without verifying if the task is correct or not. To face that, [20] proposes an AR system that also verifies the operator task by comparing the status of every step along the maintenance procedure, represented by a captured image, with a reference virtual 3D representation of the expected status, which is converted to an image as well by rendering the virtual 3D data using the tracked real camera location.  
Moreover, as more and more visual computing solutions are integrated into industrial shop floors, the complexity of communication and interaction across different peripherals and industrial devices increases. Nonetheless, [21] has recently proposed a middleware architecture that enables communication and interaction across different technologies without manual configuration or calibration.  
From the works cited above, only [6; 11] deal with PCBs and are focused on a similar domain to our work. However, they only address the part of offering augmented instructions on the screen (without projection). Additionally, compared to all the works cited, our work combines the best characteristics of each of them. Thus, our work has the following strong points:  
* The proposed system verifies if the operator has performed the operation correctly.
* Instructions are simple, so there is no need to create the multimedia content that is projected. The authoring effort is minimized to only set the position of each component in the reference board.
* The projection is done on a flat surface, so the calibration step has been simplified to be easy, fast and automatic (the user only has to put the calibration pattern in the workspace).  
* The proposed system uses advanced visualization techniques (flickering) to deal with reflections when projecting on PCBs.
* The proposed system supports dynamic projection; i.e., the projection is updated in real time when the PCB is moved.
* A normal RGB camera is used; no depth information is required.