## 2 State of the Art and Related Work
### Assistance Systems
#### 2.1.2 Cognitive Assistance Systems  
With the primary objective of mental relief for the employee, the field of CASs in manufacturing is primarily concerned with the context-sensitive provision of process-relevant information during the assembly or disassembly of variant-rich products down to batch size 1 [22]. Within this context, CASs are often combined with physical assistance systems (e.g., cobots in human-robot collaboration [5; 12]), or sensorial assistance systems, as mentioned in Section 2.1.1. In addition to assembly, research approaches in the field of maintenance [23], repair [24], overhaul [25] and logistics [26] can also be found. From an economic perspective, CASs may help to ensure an error-free and efficient process execution, thus saving time and additional rework costs. Examining the possible output devices shown in Figure 1, different stationary projection-based approaches utilizing light [7], laser [11; 27], and video projectors [22; 28; 29] as a component within their assistance systems can be found in the respectively cited literature. A shared characteristic of these approaches is their limited scope of application due to the coverage of the devices, rendering them as non-directly transferable to components with larger dimensions. Given this constraint, these applications are often installed at spatially limited workstations (such as assembly tables). In order to cover larger work areas, additional devices must be purchased, increasing cost and control efforts. In addition, projection-based systems are always susceptible to occlusions. Therefore, the devices are typically ceiling-mounted directly over the component to avoid employee coverage of the projection surface. However, if the position of the projector cannot be oriented in such a way that occlusions can be avoided, this problem can also be countered with multiple devices, all with varying positions and projection angles. Solutions based on mobile devices such as augmented reality glasses, with the HoloLens as a market-ready solution, allow the coverage of larger workspaces as well as a more immersive display of information due to their location flexibility, as shown in [30; 31]. Nevertheless, localizing the AR glasses within space is a challenging task. Equipping the manufacturing and assembly environment with stationary reference markers (ArUco markers, April tags) for localization is infeasible within some domains, such as aircraft manufacturing, due to the requirement for installation, calibration and residue-free removal. Here, model-based (CAD) and feature-based (SLAM) methods represent an alternative for localization. However, the latter two methods have limitations in terms of accuracy in large-scale work environments [32]. Another as yet unsolved problem of Augmented Reality devices is \"Simulator Sickness\", which describes a form of motion sickness during the prolonged use of immersive applications [33]. Since the requirements for CASs can vary diversely given different production scenarios, the design of them is frequently individualized. In addition to the selection of a suitable modality and the appropriate output device, factors such as the degree of support, adaptability to human needs (for example, the employee's level of qualification), or the differing production environments compose roles that should not be neglected [34; 35]. In summary, CASs may serve the paradigms of the efficient, networked factory as well as that of human-centered production, enabling flexible processes that can fundamentally meet product and process variations while ensuring high quality. In this paper, we focus on stationary projection systems--more precisely light projection systems. For challenging work environments, such as those described in Section 1.1 using the example of aircraft production, the strengths of these systems come to fruition.