## 2 Methods
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Domain Group**} & \multirow{2}{*}{**Ergonomic Indicator**} & \multicolumn{3}{c}{**Score Level According to RULA**} \\ \cline{3-5}  & & **Low** & **Medium** & **High** \\ \hline \multirow{5}{*}{Upper Quadrant (**UQ**)} & Trunk bending angle (degree) & (0\({}^{\circ}\)–15\({}^{\circ}\)) & (15\({}^{\circ}\)–30\({}^{\circ}\)) & (\(>\)30\({}^{\circ}\)) \\ \cline{2-5}  & Left or right elbow angle (degree) & (0\({}^{\circ}\)–15\({}^{\circ}\)) & (15\({}^{\circ}\)–40\({}^{\circ}\)) & (\(>\)45\({}^{\circ}\)) \\ \cline{2-5}  & Left or right shoulder (degree) & (20\({}^{\circ}\)–45\({}^{\circ}\)) & (45\({}^{\circ}\)–90\({}^{\circ}\)) & (\(>\)90\({}^{\circ}\)) \\ \cline{2-5}  & Neck bending or rotation angle (degree) & (0\({}^{\circ}\)–10\({}^{\circ}\)) & (10\({}^{\circ}\)–20\({}^{\circ}\)) & (\(>\)20\({}^{\circ}\)) \\ \cline{2-5}  & Forearm rotation angle (degree) & (0\({}^{\circ}\)–90\({}^{\circ}\)) & (\(>\)90\({}^{\circ}\)) & (\(>\)90\({}^{\circ}\) and crossed) \\ \cline{2-5}  & Spine (degree) & (0\({}^{\circ}\)–20\({}^{\circ}\)) & (20\({}^{\circ}\)–60\({}^{\circ}\)) & (\(>\)60\({}^{\circ}\)) \\ \cline{2-5}  & \multicolumn{3}{c}{The value is calculated considering the ulnar or radial deviation (inward or outward rotation) according to the RULA and Health Safety Executive guidelines (2014)} & (0\({}^{\circ}\)) The wrist is not subject to rotation. & (+15\({}^{\circ}\); \(-\)15\({}^{\circ}\)) & (\(>\)15\({}^{\circ}\)) \\ \hline \multirow{5}{*}{Stereotypy, loads, typical actions (**TA**)} & Arm position for material withdrawal & (Without extending an arm) & (Extending an arm) & (Two hands needed) \\ \cline{2-5}  & Trunk rotation (degree) & (0\({}^{\circ}\)–45\({}^{\circ}\)) & (45\({}^{\circ}\)–90\({}^{\circ}\)) & (\(>\)90\({}^{\circ}\)) \\ \hline \multirow{2}{*}{Repetition of the same movements (**RM**)} & This parameter refers to high repetition of the same movements & (From 25\% to 50\% of the cycle time) & (From 51\% to 80\% of the cycle time) & (\(>\)80\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The ergonomic domains and criticality index. A knowledge base contains all information about a system and allows other entities to process input data and obtain outputs. This information can be divided into (i) a database and (ii) a rule base. The former contains the descriptions of all variables, including membership functions, while the latter contains the inference rules. * Since the input data are almost always crisp and the fuzzy system works on \"fuzzy\" sets, a conversion is required to translate standard numeric data into fuzzy data. The operation that implements this transformation is called fuzzification. It is conducted using membership functions of the variables being processed. To defuzzify the input value, the membership degree is set for each linguistic term of the variable. * The phase in which the returned fuzzy values are converted into usable numbers is called defuzzification. In this phase, we start with a particular fuzzy set obtained through inference. This fuzzy set is often irregularly shaped due to the combination of the results of various rules, and a single sharp value must be found that best represents it [52]. The resulting values represent the final output of the system and are used as control actions or decision parameters. In this study, the fuzzy engine (FE) is implemented using the Fuzzy Logic Toolbox in Matlab2023b. The FE processes five variables, which are outlined in [40] and Table 2. These variables define the measure of postural stress for the upper quadrant, in particular, for the elbow, shoulder, neck and trunk, while another index refers to high repetition of the same movements. After the identification of the EO\({}_{\text{i}}\)s, the human pose for each EO\({}_{\text{i}}\) is analyzed and the joint angle is automatically determined considering the RULA method and the data in Table 2. This joint angle is the input value for the criticality index calculation.