## 5 Experimental Analysis  
This analysis aims at testing the performances of the SASAS prototype in terms of productivity and ergonomic work conditions in a realistic environment, focusing on the assembly process of a horizontal multistage centrifugal electric pump. Figure 6 shows a picture of the reference pump. The product, after the assembly phase, must be inserted into a carter. The developed experimental analysis compares two main assembly configurations, named as in the following:  
* Configuration #1: traditional MAS;
* Configuration #2: SASAS prototype, including Configuration #2.1 (SASAS prototype with manual reconfiguration) and Configuration #2.2 (SASAS prototype with automatic reconfiguration). In Configuration #1, the assembly system works as a fixed, i.e., rigid, workstation, not using the key attribute of self-adaptability to the part and human operator features. In such a configuration, the fast-picking area is as in Figure 3 (left) and the central conveyor is set to a height equal to 0.95 m from the floor. In addition, the components are placed on shelving behind the assembly prototype, at a distance of 2 m, and the additional tools, e.g., screwdrivers, screws, etc., are placed in the fast-picking zone of the SASAS. In Configuration #2, the adaptivity feature is used, making the system able to manually, i.e., Configuration #2.1, and automatically, i.e., Configuration #2.2, reconfiguring in real-time its structure according to the work cycle of the product and to the anthropometric measurements of the human worker performing the assembly process. Figure 6: Reference product used for the lab experimental field-test. The analysis assesses the cycle time, \(\rm T_{c}\), i.e., the time required to complete the whole assembly process, the system average productivity, \(\rm Q=1/T_{c}\), and tracking the REBA ergonomic index. Many tests are performed to collect such performance parameters. In each configuration, the minimum number of tests, n, to get statistical reliability is determined using the formula presented in [48]. Values of parameter n equal to 19.07 in Configuration #1, to 16.65 in Configuration #2.1 and to 56.62 in Configuration #2.2 guarantee a statistical significance. A global number of 60 tests per each configuration is performed, getting the average cycle time in Table 2.  
The average system productivity for the two configurations is in Table 3.  
Results confirm the positive impact coming from the SASAS use. In particular, compared to Configuration #1, i.e., traditional assembly, through the system automatic reconfiguration, i.e., Configuration #2.2, the cycle time decreases by 38.6%, while the productivity increases by 62.8%. To stress the key role played by the collaborative feature in cycle time reduction and productivity increase, a focus on the assembly process of the centrifugal electric pump is proposed, highlighting the specific assembly and reconfiguration tasks in both Configuration #2.1 and #2.2 (Table 4). The most relevant results are in Table 5. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Tasks**} & **Assembly** & \multirow{2}{*}{**Task Description**} & **Manual** & **Automatic** \\  & **/Reconfiguration** & & **Reconfiguration** & **(Collaboration Effect)** \\ \hline \hline \multirow{4}{*}{**\#1**} & Assembly & Pump crankcase picking and drop-off on the central & 10 & 10 \\  & Reconfiguration & & Opening of the fast-picking area & 5.9 & 0 \\  & **Picking of the pump rotor from the fast-picking area** & 11 & 11 \\  & Assembly & & and assembly & 12 & 12 \\  & Reconfiguration & & Closing of the fast-picking area & 5.9 & 0 \\  & Assembly & & Covering operation on the upper surface of the pump & 9 & 9 \\  & Reconfiguration & & Raising of the central roller conveyor & 4.05 & 3.75 \\  & Assembly & & Covering operation on the lower surface of the pump & 8 & 8 \\  & Reconfiguration & & Lowering of the central roller conveyor (0.95 m from & 4.05 & 3.75 \\  & & the floor) & & \\ \hline \hline \end{tabular}
\end{table}