# Simulation on Cooperative Changeover of Production Team Using Hybrid Modeling Method
## Case Study
### Basic Information of Production Cell  
In this case, operators need to conduct the loading, unloading, and changeover operations during the production process. (1) When a machine is idle and there is at least one part to be machined in its queue, the first part needs to be loaded before machining. (2) Every part needs to be unloaded after machining. (3) When converting a line from running one type of parts to another, changeover operations of machines need to be conducted. The loading and unloading time of parts and changeover time of machines are both subject to normal distributions, and the machining time is constant. The loading and unloading skills for the same type of machines are universal, but the changeover skills for machines are related to the process characteristics of the parts. The assumptions and rules in the simulation model are shown in Table 1. \begin{table}
\begin{tabular}{c c} \hline \hline
**Assumptions and Rules** & **Descriptions** \\ \hline \multirow{7}{*}{Production process routes of three types of parts} & TC: M1\(\rightarrow\) M2\(\rightarrow\) M3\(\rightarrow\) M4\(\rightarrow\) M5\(\rightarrow\) M6\(\rightarrow\) M7\(\rightarrow\) M8\(\rightarrow\) \\  & M9\(\rightarrow\) M10; \\  & EC1: M11\(\rightarrow\) M12\(\rightarrow\) M13\(\rightarrow\) M14\(\rightarrow\) M15\(\rightarrow\) M16\(\rightarrow\) \\  & M17\(\rightarrow\) M18; \\  & EC2: M11\(\rightarrow\) M12\(\rightarrow\) M1\(\rightarrow\) M2\(\rightarrow\) M3\(\rightarrow\) M4\(\rightarrow\) M13\(\rightarrow\) \\  & M14\(\rightarrow\) M5\(\rightarrow\) M6\(\rightarrow\) M7\(\rightarrow\) M8\(\rightarrow\) M17\(\rightarrow\) M18. \\  & M3, M4, M5, M6, M13, M14. \\  & S1=[M1, M2, M11, M12]; S2=[M3, M4, M15, M16]; \\  & S3=[M5, M6, M7, M8]; S4=[M9, M10, M13, M14] and \\  & S5=[M17, M18]. \\ \multirow{2}{*}{Parts processing rule} & Parts are removed from processing queues according to first-in-first-out rule. \\  & (1) Changeover tasks are superior to loading and \\  & unloading tasks; \\ Task selection preferences of operators & (2) Tasks of the same type are removed from the task \\  & list according to first-in-first-out rule. \\ \multirow{2}{*}{Coordination rule for task application conflicts} & The task is assigned to the highest skilled operator. \\ \cline{2-2}  & \(\rightarrow\) M10; \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Assumptions and rules in the simulation model. Table 1 shows that parts of types TC and EC1 can be processed simultaneously, while parts of EC2 can only be processed separately due to machine constraints in the process route. The simulation software Anylogic 7.1.2 is selected to build the hybrid model of the production cell. The secondary development such as the cooperative changeover behavior of operator agents is programmed in Java language. The 3D view of the model developed is shown in Figure 4.  
Table 2 shows the personnel skills configuration of the production cell. Each operator has two loading and unloading skills with different skill levels and two assisted changeover skills with different skill levels. Additionally, Operators O2, O3 and O5 have the whole changeovers skills for specific machines. An operator with the required assisted changeover skill can conduct the line-changing operation for a machine cooperatively with another operator who has the required whole changeover skill, but cannot conduct the changeover operation for the machine separately. In Table 2, LN\({}_{\text{Sx}}\)(d\({}_{1}\)) denotes the level d\({}_{1}\) for the Sx-class skill of loading and unloading, W\({}_{\text{My}}\)(d\({}_{2}\)) denotes the level d\({}_{2}\) for the whole changeover skill of machine My, and A\({}_{\text{Mz}}\)(d\({}_{3}\)) denotes the level d\({}_{3}\) for the assisted changeover skill of machine Mz. Table 3 shows the distributions of time taken by operators with Skill Level 5 to complete changeover subtasks of six machines.