## 3 Case Study
### Ergonomic Assessment  
At the end of the simulation, numerical data are analyzed to perform the ergonomic assessment. As stated in Section 2.3, the main sources of injury risks are postures assumed by workers during each cycle of the work shift, exerted forces, MMH and repetitive actions; thus, each of this class has to be investigated by means of different ergonomic assessment methods.  
In this case study, the methods chosen to evaluate each ergonomic category are the most feasible considering the type of working activity performed. They are listed below, with a short description:  
* Working Postures: OWAS (Ovako Working Analysis System) method. It allows evaluating the whole body postures [37]. The method consists in the analysis of the posture to which a risk class is assigned, based on the values of postural angles. There are four classes (no risk, low risk, medium risk and high risk respectively) The index (\(I\)) for the whole cycle is evaluated according to the frequency (\(a\), \(b\), \(c\), \(d\)) with which the four risk classes are found by means of the following equation: \[I=[(a\)1)+(b\(\cdot\)2)+(c\(\cdot\)3)+(d\(\cdot\)4)]\(\cdot\)100 (2)
* Manual Material Handling: NIOSH (National Institute for Occupational Safety and Health) lifting equation, which is useful when manual lifting of loads is carried out [38]. The method is applied only if the weight of the handled object is higher than 3 kg. It assigns a score based on the vertical and horizontal displacements with which the object is handled, as well as the frequency of action and the type of grip. The Lifting Index (\(LI\)) is given by the ratio between the Loaded Weight (\(LW\)) and the Recommended Weight Limit (\(RWL\)): \[LI=LW/RWL\] (3) where \(RWL\) depends on: worker's genre and age, vertical displacement of the object, maximum horizontal distance between the object and the body, angular dislocation of the object with respect to the sagittal plane, grip mode and lifting frequency;
* Repetitive actions: OCRA (Occupational Repetitive Actions) checklist, which is used to evaluate the biomechanical overload of upper limbs related to repetitive actions [39]. The checklist assigns a score based on the number of actions, fatigue (Borg scale), incongruuous shoulder and wrist postures, type of grip, work organization, etc.;
* Force: in order to evaluate forces, a Force Solver based on Snook and [PERSON] tables [35] was used. The tool provides the maximum force that can be exerted with respect to the posture assumed and the direction of application.  
Table 2 reports the risk areas for the selected indexes.  
Figure 6: Posture angles smooth trends over one working cycle for: trunk (**a**), arms (**b**) and elbows (**c**).  
It is worth noting that Equation (1), needed to perform the control phase of ergonomic indexes, is not applicable to all the chosen methods. In fact, Equation (1) is applied only when the index has a variability during the investigated cycles.  
In this application, OWAS and OCRa indexes present variabilities along the working cycles, since fatigue, distractions or other factors may principally affect the working postures assumed by the worker; in contrast, exerted forces and NIOSH indexes remain the same in different cycles, since they depend on the positions of objects and on their weights, which are not variable.