# Human-Robot Interaction for Improving Fuselage Assembly Tasks: A Case Study
## 4 Results and Discussion  
According to Step 1 of the procedure in Figure 1, the working times of human, in HRI configuration, were estimated relying on the current manual configuration of the workstation. For privacy reasons, it is not possible to report the operations' times, but it can be useful to know that the assembling operations of the whole fuselage composite panel require about 3 working shifts. The analysis proposed in this study aims to evaluate if the completion time would decrease in HRI configuration. Moreover, a scale factor (SF) will be used in order to show the difference between the two configurations, as described in Table 2.  
In detail, without loss of generality, the working time values (T) reported in this section, is equivalent to the scaled real working time values (RT), according to the following Equation (2):  
\[\text{T}=\text{RT}\times\text{SF} \tag{2}\]  
By applying Equation (2), the working time to assemble the whole panel (\(T_{a}\)) is 15 hours. For estimating the working times in HRI configuration (Step 2 of procedure in Figure 1), about humans, several studies assess that in presence of robots, which may have predictable or unpredictable motions [41], humans are negatively influenced by the presence a robot [42; 43], so the human working times for each operation have increased in a range between 10-20% of the estimated time, according to the type of operation. About the robots, KUKA estimated a mean reduction of working times, when a task is performed by a robot, of about 30% with respect to humans' times [44]. Consequently, for the tasks performed by robot (namely drilling, countersinking, inspection and riveting), the working times (T\({}_{\text{R}}\)) values are assumed to be reduced of 30% with respect to the previously estimated working time, according to Equation (3). \[\text{T}_{\text{R}}=\text{RT}\times\text{SF}\times 0.70 \tag{3}\]  
Figure 5: Workstation schematic layout. Other robots' operations, such as the referencing of the working zone, the moving times, the end-effector tool changing times, etc., depend on the robots' characteristics. On each digital robot the real robot controller was implemented to define the minimum and maximum linear speeds, the joints' rotation speed and other important parameters. Two types of cycle were implemented to simulate two different assembling scenarios. The first one cannot be considered as HRI, since the human and robots never work at the same time: when human is performing a task, the robot is passive and vice versa. In the second case, human and robots share the same working zone by respecting the constraints imposed by ISO-TS 15066 and their operations can be performed simultaneously, as shown in Table 3, representing part of the working cycle where same colors identify operations performed simultaneously. Simulations were performed considering both simultaneous and separated working tasks. The working times of Table 3 consider also the time required for human's micro-movement, such as walking, raise an arm, grasp an object, etc., which are implemented in Tecnomatix Process Simulate, based on MTM (method and time measurement) tables. Results provided by the simulations are shown in Table 4 where there is a comparison between the different configurations: only manual, human and robot in sequential performing and HRI. The implementation of robots in the workstation drastically reduces the working time for assembling the whole panel. This time is furtherly reduced in HRI configuration, where the difference with the manual configuration is almost the 50%. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Only Manual** & **Human–Robot** & **HRI** \\ \hline
**Time to Assemble (h)** & 15 & 8.78 & 7.86 \\
**Reduced Time (h)** & 0 & 6.22 & 7.14 \\
**\% of Reduced Time** & 0 & 41.5\% & 47.6\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Simulation results.