## 2 State of the Art and Related Work
### Assistance Systems  
#### 2.1.1 Classification of Assistance Systems in Manufacturing  
Figure 1 serves as an overview for current research approaches in the field of assistance systems in manufacturing. The classification is based on the three criteria shown: the type  
of assistance (1), the modality used (2), and the technology leveraged in the form of the output device (3). The focus lies in cognitive assistance systems with visual information transfer, and these are marked in blue. Further detailed considerations of other types of assistance systems or alternative modalities within cognitive assistance systems will be omitted, as they are not relevant to the present work (marked in gray as to classify this work in the overall research field). The illustrated classification method for assistance systems represents a combination of criteria commonly used within the pertinent literature, and is explained in more detail here. On the first level, a distinction is made regarding the type of assistance. More on this basic classification can be found in the work of [4; 9]. The general aim of CASs is to support employees in their decision-making, or otherwise, in the execution of work processes with the aid of information, instructions, or feedback, thus imparting relief from mental fatigue. A detailed analysis of this type of assistance system in the context of manufacturing will be part of Section 2.1.2. Sensorial Assistance is intended to assist the worker by extending their capabilities of either acquiring information or focusing their attention on a specific piece of information [10]. Relevant instances often work with systems (mostly cameras) that record and document conditions such as product status [11], or track employee motions [12]. It should be noted that within the relevant literature, the terms \"cognitive\" and \"sensorial\" assistance are not always used in mutual distinction; in many systems, information acquisition, its processing, and its presentation to the human accompany each other, often rendering stringent distinction unnecessary. In several publications, therefore, the terms \"Digital Assistance Systems\" [13] or \"Informational Assistance Systems\" [14] can be found, in which the goal of mental relief is achieved by combining both approaches. Dissimilar to the first two types, Physical Assistance Systems provide not mental, but physical relief. This is realized, for example, by exoskeletons [15] that support specific body regions as a wearable suit, or by cobots that assume particularly unergonomic tasks in a common workflow [16]. The second level of classification relates only to cognitive assistance systems and is based on the modalities of information transfer in the work of [17; 18]. They are derived from the human senses that allow us to perceive information. The most common modalities in which information can be transferred are visual, auditory and haptic. In this work, we focus on cognitive assistance systems with a visual information output that is focused separately. Examples for the the auditory modality can be found in [19], in which the worker is provided corresponding steps by a voice output on an Augmented Reality Glass, enabling hands-free work execution. Haptic information outputs are often realized in manufacturing by using vibration functionalities of a smart watch; e.g., [20] leverages this as a means to convey direct feedback about the quality of the conducted processes. Figure 1: Overview of assistance systems in manufacturing. Focused areas in blue, grey boxes are out of scope. The third classification level pertains to the type of output devices selected and is also proposed as a classification criterion in similar approaches by [9; 21]. In this context, it should be noted that some devices are not only capable of transmitting visual information, but are also capable of serving other modalities. These connecting lines are not drawn in the figure for simplicity.