# A Study on Design and Control of the Multi-Station Multi-Container Transportation System
## 4 Discussions  
In Figure 3, the proposed control algorithm is applied in the real system to test the ability to transport containers according to the system built at BK-RECME. During the researching and designing process, the authors considered and solved several problems that resulted in the container being unable to complete the travel routes, such as (1) transition position between two conveyors (Figure 26); (2) perpendicular position between two conveyors (Figure 27); (3) placement of the proximity sensors on the sub-conveyors (Figure 28); (4) the location of the RFID readers to help identify containers entering or leaving the modules (Figure 29); (5) the system can be expanded, so it is necessary to ensure easy installation and a minimum number of inputs/outputs of the control modules. In other words, the system is helped to satisfy the assumptions and constraints set. * For the problem (1), to address the gaps between the conveyors, segmented transfer plates could be used to help fill in the gaps so that the containers can pass through normally. * For the problem (2), this is a featured design of the system; instead of using a curved conveyor, we arrange the conveyors perpendicular to each other, to save space and avoid cumbersome action, in designing the overhead system, as parallel curves will require different curvature radiation. To ensure the containers do not get stuck in transition at the 90-degree turn, additional guiding rails are used to help smooth and adjust the movement of the containers at those positions. * For the problem (3), we design the frame to place the proximity sensor PR12--4 DN [12] for ensuring that the containers will be detected when they pass through. * For the problem (4), the selected RFID reader is RDM8540 TCP/IP + WIFI RFID reader series. It can recognize RFID tags within 8(cm) [13]. When the conveyor module is shut off, the container's inertia may cause the container itself to fall off the conveyor. Therefore, RFID readers need to be placed at the appropriate position in each conveyor module. On the other hand, to ensure the containers are detected, we propose to use more than one RFID reader at each position and more than one RF-tag on each container. * For the problem (5), the system is designed in modules to ensure interchangeability, replaceability, and ability to expand to a larger-scale system. Therefore, the control system would also need to follow the modular design. For each mechanical module, there will be a separate control function. The algorithm built in combination with the model, as in Figure 4, makes it easier to control the system. A special feature is that instead of using one output for each conveyor, which leads to an extremely large number of system outputs, we only use one output for the whole forward motion module, which consists of multiple component conveyors. Based on the built-in model in Figure 3, we decided to combine all the conveyors between the line switching modules and the lifting modules into one control module. The RFID readers will be used to limit the two ends of a module as in Figure 10 and minimize the output for the control module. Figure 26: Transition position between two conveyors. With the following experimental results from Section 3.3, (a) the lifting and line switching modules operate suitably according to the proposed algorithm; (b) the system can help to transport containers corresponding to selected routes, and the control model helps control and manage the data of the whole system. To further clarify this issue, we consider the following comments:  
* As for the experiment (a), during the operation test, we also check the sensor position as mentioned in Section 3.1 to ensure that the conveyor operates in the exact limited range. As for the lifting module, it is also necessary to adjust the position of the limit switches to ensure that the vertical movement of the sub-conveyor does not  
Figure 28: The installation position of proximity sensors on the sub-conveyors. Figure 27: Perpendicular position between two conveyors.