# A Five-Step Approach to Planning Data-Driven Digital Twins for Discrete Manufacturing Systems
## 4 Results and Discussion
### Step 3  
The third step is the development of the digital model of the presented case study. In our case, the Siemens Tecnomatix Plant Simulation 14.2 software package was used to develop the digital model. The development started with the definition of the layout of the manufacturing system with all the building blocks. Each type of a building block requires specific parameters to define it. The defined parameters with their values for the conveyor building block are described in the text below and in Figure 13.  
The name of the conveyor is required both to identify the building block (e.g., Conveyor1, Assembly_station1) and for more transparent planning. To determine the correct position and orientation of the conveyor, the tangential angle \(\alpha\) in degrees is required (\(\alpha=-180^{\circ}\) from the starting point). The next parameters are the length (L1 = 2.57 m; L2 = 0.07 m) and the width (W = 0.16 m) of the conveyor, the number of curves (4), the angle of curves (90\({}^{\circ}\)) and the radius (R = 0.2 m) of curves. The required data also includes velocity (0.15 m/s), acceleration (0 m/s\({}^{2}\)) and deceleration (0 m/s\({}^{2}\)) of the conveyor. The information on the number of workstations and their locations is also required. The workstation is defined as the location where the product is involved in a process. In our case study, there are 3 workstations. The location of the workstation is defined as the distance from the starting point (a = 0.45 m; b = 1.67 m; c = 0.45 m). It is also important to have information about the number of different pellets or parts that are transported by the conveyor. In the case study, there are 4 pellets with the same dimensions. The availability of the machine is proportional to the time that the machine is in an operational state, represented by a value between 0 and 100 percent; in our case study, the availability is 100%. The next parameter is MTTR--a measure of maintainability. It is defined as the average time to repair a machine and is 0 s in our case study. The procedure for defining the parameters needed for other building blocks is the same as for the conveyor building block. Then the development of the digital model begins. For the development of the digital model, we followed the procedure described in Section 2.3.2. Mathematical methods and logical dependencies are used to connect the digital models of the building blocks to the digital model of the entire manufacturing system in \begin{table}
\begin{tabular}{c c c c} \hline \hline \begin{tabular}{c} **“Fabrication”** \\ **Building Blocks** \\ \end{tabular} & \begin{tabular}{c} **“Logistics” Building** \\ **Blocks** \\ \end{tabular} & \
\begin{tabular}{c} **“Storage” Building** \\ **Blocks** \\ \end{tabular} &
\begin{tabular}{c} **“Inspection”** \\ **Building Blocks** \\ \end{tabular} \\ \hline Assembly station 1 & \multirow{2}{*}{Conveyor (I)} & \multirow{2}{*}{Pallet (II)} & \multirow{2}{*}{Machine vision (IX)} \\ (X) & & & \\ \hline Assembly station 2 & \multirow{2}{*}{Robot 1 (IV)} & Warehouse for base \\ (XI) & & & \\ \multirow{2}{*}{Robot 2 (V)} & Warehouse for robot \\  & & & \\ \multirow{2}{*}{Robot 2 (V)} & Warehouse for robot \\  & & & \\ \multirow{2}{*}{Buffer for tiles (VII)} & \multirow{2}{*}{Box (VIII)} \\ \end{tabular}
\end{table} 
Table 2: Building blocks of the manufacturing system divided into the four groups. the Siemens Plant Simulation software tool, using the SimTalk programming language. The processes in the digital model should follow each other as defined in Step 2. Figure 12: The sequence of processes in the manufacturing system case study. The result is a functional digital model with all the details of a real system that functions exactly like a real manufacturing system (Figure 14). The feedback loop is not yet established in this step, which means that if there is a change in the real world, the digital model will not change accordingly.