## 3 Case Study  
The proposed bi-objective model is applied to a numeric case study exemplifying an operative industrial setting. It refers to the manufacturing of five products through a set of six tasks. Three RMCs, indicated from 1 to 3, and five RMTs, indicated from A to E, are present, i.e., RMTs A and D are in RMC 1, RMT B is in RMC 2, and RMTs C and E are in RMC 3. Moreover, a set of three auxiliary module types exists, including a total of 12 module units, i.e., four module units per type. Additional information about part work cycles, production volumes, and the auxiliary modules assembly and disassembly times are in Appendix A. The compatibility matrix among tasks, RMTs, and auxiliary modules is in Table 1. This matrix shows the task execution modes, i.e., the RMT/RMTs needed for their processing, the required modules (in round brackets), and the unitary processing times, expressed in seconds (in squared brackets). As example, task 5 can be processed on RMT B equipped with the auxiliary modules of type 1 and 2 and a unitary processing time equal to 0.12 s or on RMT D equipped with the auxiliary modules of type 1 and 2 and a unitary processing time equal to 0.108 s.  
The part travel times among the available RMCs are in the next Table 2, expressed in minutes. The return routing policy is adopted to connect RMCs. Other relevant data are the parameter \(MAX\), set to a value equal to 20 units, and the parameter \(T\), equal to 120 periods. Tables 3 and 4 show the OCRA parameters for the ergonomic risk assessment [20; 21]. The values of the technical actions for both the assembly and disassembly tasks refer to the most stressed arm. The values for the OCRA parameters in Table 3 are based on the characteristics of the repetitive tasks required to accomplish the manual operations in the reference RMS, e.g., the assembly and the disassembly of the auxiliary modules. Punctual values are from the ISO 11228-3 standard [26]. The force multiplier \(FMAM_{mr}\) refers to the force exertions required during the manual task. Repetitive tasks with \(FMAM_{mr}=1\) require very weak force exertions, e.g., the assembly of the auxiliary modules type 2 and 3 in Table 3. Moderate force is necessary in case of \(FMAM_{mr}=0.35\), e.g., the assembly of the auxiliary module type 1 in Table 3. The posture multiplier \(PMAM_{mr}\) is equal to 1 when awkward postures or movements of the upper limbs, e.g., pinch or wrist extension, are present for less than one third of the cycle time. Lower values of such multipliers identify the presence of awkward postures for a relevant part of the cycle time. When the cycle time is shorter than 15 s, or when the manual task requires the performance of the same technical actions for at least 50% of the cycle time, the repetitiveness multiplier \(RPMA_{mr}\) is equal to 0.7, e.g., the assembly of the auxiliary module type 2 in Table 3. Otherwise, \(RPMA_{mr}=1\), e.g., the assembly of auxiliary modules type 1 and 2 in Table 3. The additional multiplier \(AMAM_{mr}\) considers the presence of additional factors that may increase the ergonomic risk for the investigated task. Such factors include the use of vibrating tools, the use of gloves that may affect the handling ability, gestures implying countershocks, requirement for absolute accuracy, high pace determined by the machinery operation, localized compressions of the anatomical structures, and the exposure to cold surfaces and environments. The value of \(AMAM_{mr}\) is lower than 1 if one or more additional factors are present, e.g., the assembly of auxiliary modules type 1 and 2 in Table 3. Otherwise, \(AMAM_{mr}=1\), e.g., the assembly of auxiliary module type 3 in Table 3.