# Design of Cognitive Assistance Systems in Manual Assembly Based on Quality Function Deployment
## 6 Discussion and Limitations
### Discussion
For this purpose, the existing QFD approach was adapted and expanded to the six-phase CAS-QFD. It is assumed that it is possible using the CAS-QFD for designing cognitive assistance systems (operationality), as the industry example shows. Furthermore, the six-phase method shows how the design is performed (research question 1) and which adaptations of a common QFD method were necessary (research question 2). The method also describes how the design of assistance systems is structured, starting from the assembly process as a preliminary step (research question 3), and how the worker and company requirements are addressed (research question 4) to reach step-by-step the final design of a cognitive assistance system. The evaluation shows that the identified requirements could be fulfilled to a large extent by using CAS-QFD based on the results of the prototype evaluation. The solution hypotheses were confirmed. From the industrial application, we expect that the method will provide the user with a transparent overview of the design steps in each phase. At the same time, alternatives can always be planned and compared with each other to determine their effects. In later phases, it became clear that the context analysis regarding the process and the work system was essential for the later design. Many of ideas and recommendations were based on observed and collaboratively documented influences in the work environment. The participation of the workers, engineers and managers, although time-consuming, was positive in terms of the quality of the requirements and solution strategies. This has already been demonstrated in other areas regarding QFD [115; 116]. Based on the evaluation discussions with the project team, it is assumed that the step-by-step design could reduce complexity (ease of use). This is the advantage of the sequential process of the QFD method, which has already been recognized in other approaches [104; 105; 106; 107; 108]. The research team was able to focus on the essential steps at each phase so that they remained manageable. The ability to proceed in iterations, repeating steps backwards and forwards, including changes, resulted in a robust design with traceable chains of reasoning (efficiency). This is also confirmed by other QFD studies in other fields [117; 118]. The strict separation of requirements and assistance functions as well as technical features prevented the project team from discussing technologies and realizations too early and, therefore, losing focus on the requirements and the optimization of the assembly process. The definition of generic assistance functions (Table 1) proved to be a suitable tool during the evaluation. The defined levels were able to integrate and summarize the content of the assistance, the intensity of the assistance and the automation level to a good extent. Thus, the adaptability of the assistance system could also be discussed and planned based on the following questions; for example: can the system assist differently depending on the complexity of the task and the experience level of the worker? Can the levels be adjusted by the worker himself or are they predefined? The market comparison included in the second phase was rated as helpful since it already became clear and can be discussed transparently whether a company should develop its own assistance system or buy or adapt an available one. The evaluation case study showed that it is challenging to find the right level of abstraction for a complex and long assembly process to consider the most important steps on the one hand and not to overload the method on the other hand. Regarding the worker and company requirements, we found that, in the case of a cognitive assistance system, these can be contradictory to each other. For example, the company has the requirement to increase process control and, at the same time, the worker in the process neither wants to be monitored nor more strongly controlled within the work tasks. The method does not provide a system for resolving such conflicts of requirements.