## 4 Use Case
### VR Model  
According to the proposed approach, the real scenario is created in virtual reality to visualize the designed process and to evaluate this layout, for instance, in terms of the robots working range, among others. Figure 7 shows the creation of the virtual reality environment: Figure 7a is the original area of the facilities, Figure 7b is the 3D point cloud resulting from scanning this area with _FARO Focus3D X130 HDR_, and Figure 7c is the _Blender_-resulting virtual environment ready for its use in virtual reality. The VR model is completed adding the virtual model of all the components of the cell (robots, conveyor belt, tables, parts, etc.). Finally, the physical behavior of the elements and the human interaction is implemented using _Unity3D_. The final result is shown in Figures 8 and 9, where the high quality of the 3D reconstruction to create the immersive effect in the VR interface can be noticed.  
Using this virtual scenario, the process has been simulated and evaluated for the virtual commissioning via applying lean automation concepts and verifying that the design fulfills the requirements. Different work models were defined, assuming a distribution of tasks between the operator and the collaborative robots. Each of these models was mainly characterized by the layout, the logic of behavior, and the parameters associated with production management. The manual process without robots was also evaluated. After analyzing and comparing the models in terms of (1) efficiency and optimization, (2) reduction of movements and transportation, and (3) possibility of future extensions, these are the main conclusions which validate the designed process (including elements, layout, flowchart, etc.):  
1. Efficiency and optimization: * The parts are inspected previously to the assembly of the covers, avoiding spending time and wasting materials on wrong parts. * The operator receives instructions to continue his/her tasks in parallel with robot's tasks. It is not necessary to wait. * The buffer avoids bottlenecks. * The robot discards automatically the wrong parts. The operator does not have to wait for the inspection result. * If a part is pending, it is requested at the end of the batch, increasing process flexibility and avoiding confusions to the operator. * If all the tasks are done manually without any automation, the operator will spend time in repetitive tasks, the inspection will be subjective, and materials will be wasted, among other inefficiencies. Thus, it will not be the optimal situation.
2. Reduction of movements and transportation: * Containers and trays are close to the operator in order to reduce movements. * The conveyor belt permits the transportation of the completed batches from the assembly area to the delivery area, avoiding the use of a mobile platform or an automatic guided vehicle (AGV).
3. Possibility of future extensions: * New workstations can be added. * Augmented reality can be used as HMI instead of the current screen. For this purpose, it is necessary to locate QR-codes in the real scenario. Their possible location has been studied in the virtual scenario as it can be appreciated in Figure 8(a).