## 3 New Methodological Framework  
Figure 1 shows the methodological framework aiming to guide toward the effective design and validation of A3 Ss, which are rising as innovative systems combining the strengths and overcoming the weaknesses of both automated systems and MASs. The framework consists of three main sections: (1) automated assembly systems, on the left, (2) MASs, on the right, and (3) A3 Ss, in the central part, as a joint paradigm.  
In automated assembly systems, controllers, sensors and actuators are interconnected to enable monitoring, control and collaboration and to exchange operational information [37]. The literature classifies these systems in dedicated and flexible assembly systems (FASs). The former is suitable for the production of wide batch sizes and their implementation typically leads to high performances in terms of productivity but low performances in terms of flexibility. To slightly increase flexibility, past literature proposes the FASs characterized by programmable manipulators and by flexible feeder subsystems. However, in such a configuration, the components change largely influences the automation process, causing the need for additional investments and rising management costs [15]. If high flexibility is required, MASs composed of human workers and manual assembly stations can be adopted obtaining a significant decrease in productivity [15]. In addition, unlike the automated systems, the performances of the workers are strongly affected by ergonomic issues that, if not managed properly, can further decrease the productivity levels causing MSDs and absenteeism [38]. In particular, critical conditions occur in assembly systems, e.g., a considerable level of stress, uncomfortable postures and the performance of repetitive movements etc. These conditions lead to the insurgence of work-related MSDs [39]. For these reasons, a strong connection between MASs and ergonomics exists, both in theory and in practice, which needs to be effectively managed.  
Emerging factors such as variable market demand and batches, flexibility and increased product customization and personalization characterize the upcoming Industry 4.0 era, forcing industrial companies to reshape their practices in process and product design and management [2]. In this context, production systems reaching significant levels of both productivity and flexibility are a plus. A3 Ss are an innovative class of MASs including higher automation and collaboration levels to improve and increase the capabilities and skills of the workers who perform the manual work [12]. Humans still represent one of the most flexible components of assembly and manufacturing systems and new manufacturing and assembly systems are designed not to remove but to support and guide them by implementing new technologies, enhancing their skills and overcoming any limitation [40; 41]. A3 Ss rise as integrated systems involving unheard requirements of socio-technical integration and reconfigurability in which hardware, i.e., machines, controllers, sensors and actuators, and the human contribution coexist to benefit of each other's strengths. These goals are achieved thanks to the adaptive and collaborative features of A3 Ss, which allow the assembly system to perform a real-time reconfiguration of its hardware structure, par  
Figure 1: New methodological framework for A3S design and management.  
tially or totally in parallel to the performance of the assembly tasks by the human worker, according to product input data, e.g., work cycle, dimension, and human workers input data, e.g., anthropometric measurements. Such a real-time reconfiguration together with the human contribution allows reaching good performances in terms of productivity and flexibility as well as improvements in the ergonomic work conditions. The next Section 4 exemplifies these concepts introducing a prototypal full-scale A3S, i.e., SASAS.