## 2 Methodological Framework
### Ergonomics Assessment  
Once the simulation is completed, numerical data are analyzed in order to perform the ergonomics assessment (step 5 in Figure 1). In a manufacturing scenario, as anticipated in Section 1, it is necessary to investigate the biomechanical overload, a source of injury risks, that is principally caused by working postures, exerted forces, MMH and repetitive actions with upper limbs. Many methods, tools and screening procedures have been developed over the years [3], some of which already implemented in different software codes for production process simulation. Many of them are according to the standards ISO 11,226 [31] and ISO 11228-1,2,3 [32; 33; 34] that regulate the whole procedure of occupational ergonomics monitoring.  
After selecting the four risk indexes (one for each risk factor), numerical data are used for evaluating them (step 5.1 in Figure 1) for each acquired cycle. If the average values of the four indexes fall within the low risk area, the control phase is carried out by applying the following Equation (1) to each evaluated index:  
\[\mathrm{I}_{\sigma}\leq\mathrm{I}_{\mathrm{t}}-\mathrm{I}_{\mu} \tag{1}\]  
where \(I_{\mu}\) and \(I_{\sigma}\) are the average and the standard deviation values of the evaluated index respectively, with respect to investigated working cycles, and \(\mathrm{I}_{\mathrm{t}}\) is the threshold value of the index for accessing the medium risk area.  
If Equation (1) is satisfied, the framework suggests continuing the production (step 6 in Figure 1).  
If none of the indexes fall within the risk area or if the Equation (1) is not satisfied, it is necessary furtherly investigating about the working task focusing on the critical factor.  
This important step should be conducted by experienced ergonomists or by occupational physicians, since they have the appropriate know how for a proper identification and resolution of the critical issues.  
Let us analyze in detail about the investigation (step 5.2 in Figure 1).  
In case the working posture risk index does not fall within the low risk area, it is advisable to investigate, by observation or by studying the temporal history of postural angles, the postures assumed by the operator, identifying the sub-phases of the work cycle that mostly contribute to the value of the index.  
About the exerted forces, if these exceed the maximum applicable value, as reported in specific tables by [PERSON] and [PERSON] [35], it is necessary to investigate the posture assumed during the force exertion, as well as the intensity and the duration of the application.  
MMH is evaluated when the weight of the handled object is at least 3.5 kg; if the risk index exceeds the low risk area threshold, the investigations are different, depending on the kind of handling:  
* for lifting operations, the attention has to be paid to the initial and final altimeters of the handling, as well as the type of gripping and frequency;* for maintenance and carrying, the focus has to be on the distance travelled by the operator, together with the type of grip and frequency;
* for pushing/pulling actions, the investigation will be focused of the type and on the characteristics of the adopted cart, the distance covered by the worker and the frequency.  
If the threshold value is exceeded by the index related to repetitive actions with upper limbs, the investigation will be focused on the number of technical actions, the possible awkward postures of the joints, the types of grip, the frequencies of actions and the recovery times.  
Once the critical issues (step 5.3 in Figure 1) have been identified, it is advisable to discuss the possibility of making changes to the station layout or to the operations to be carried out.  
After the discussion and testing of possible solutions, by means of numerical simulation, the ergonomist will deal with the decision-making process (step 6 in Figure 1) in order to improve the production process.