## 5 Case Study
### What-If Analysis  
In this section, a _what if_ analysis that involves the generation and subsequent evaluation of several scenarios is presented. In the first stage, the proposed approach is used to generate several collaborative workplaces starting from different sets of inputs. In particular, three input parameters are fixed on three levels in order to create 27 different combinations. Consequently a critical assessment of them is carried out through some criteria in order to find out the best configuration and combination of parameters. Afterwards, the impact of the selected parameters on the performances of the system is evaluated. For this purpose,  
Figure 9: The HRC workplace layout obtained by means of the proposed approach: **(a)** the workplace showed in the 3D environment; **(b)** 3D enlargement showing the several resources that are part of the workplace; **(c)** 2D view highlighting the several task centers and the main workspaces. four Key Performance Indicators (KPIs) of the workplace are evaluated by means of specific functions. Then, an utility value given by the combination of that functions is obtained by means of the Simple Multi-Attribute Rating Technique (SMART) [62; 63; 64]. This technique is a synthetic value that combines several non-homogeneous quantities and provides an utility value through four steps:  
* Assigning a weight to each function or performance by means of a comparison among them;
* Making the output value of each function dimensionless and on a normalized scale making the best of each function corresponded to the maximum in the normalized scale;
* Multiplying the dimensionless values and the weights;
* Summing the results obtained in the previous step. The output value of this technique is a weighted combination of the other performances and the highest value identifies the best configuration among to the different combinations of parameters. The input parameters of this analysis, selected as control factors, are:  
1. Minimum distance: the minimum distance among the resources;
2. Robot speed: the speed adopted by the robot to carry out the inspection;
3. Logistic spaces: the relative position of the logistic spaces. According to the ISO 13854 [57], the minimum distance among the resources must not be lower than 500 mm. In the context of the spatial optimization, it represents the lower limit. On another hand, according to the designing and production purposes, it could be required this value higher to guarantee specific needs. Indeed, even tough the optimization algorithm points to the minimization of the distances, there is always a minimum value to be guaranteed, not only due to the safety, but also for the working exigences. Then, the robot speed influences several key aspects of the workplace such as the timing, the safety, the proximity of the human to the robot, and the collaborative time. Finally, the relative position of the logistic spaces, as explained in Section 4.1.1 can be set at the same side, consecutive sides or opposite sides in a single workplace, with an impact on the logistic optimization that depends on the manufacturing context. The selected parameters belong to a specific domain of the collaborative workplace (Table 1). The _minimum distance_ is a safety requirement, the _robot speed_ is a technical parameter related to the active resource, and the _logistic spaces_ is a logistic parameter. All these parameters, or factors, are presented in Table 5 with the selected values and description. By the combination of these factors, a Design of Experiments (DoE) is made with a total of 27 combinations. Such configurations need to be evaluated through different performances with a set of functions. Consequently, an utility value is calculated for each configuration with the SMART method in order to provide a representative score. The proposed functions are: (i) the impact on space, (ii) the HRC relevance, (iii) the time cycle, and (iv) the initial investment cost. Three of that functions need to be minimized whereas the HRC relevance to be maximized.