# A Study on Design and Control of the Multi-Station Multi-Container Transportation System
## 2 Materials and Methods  
### Overall Design  
In this section, a general concept of the ATS using hung conveyors is described, which will provide a better look into the structure and the working principle of the entire system, as well as the method chosen for the control system. As mentioned above, the multi-station transport system includes three separated mechanical modules: the forward motion module, the lifting module, and the line switching module. Each mechanical module carries out its function and operates independently as an absolute unit. A forward motion module consists of suspended conveyors of different lengths paired with each other to create the long travel line between stations. This design also conserves electrical energy, as these numerous conveyors will be unpowered at the same time, but sequentially. The slat top chain with POM material (Acetal) is chosen for the conveyor's design; the frame of the conveyor is made from stainless steel, as it meets both firmness and safety requirement. To hang the conveyors on the beam frame on the ceiling, threaded rods are used. The support frame under the conveyor is made from a V-shaped steel bar. The size of the container is 250 \(\times\) 160 \(\times\) 300 mm, with a maximum capacity of 5 kg, and the weight of the steel container itself is 2 kg. To ensure smooth and efficient operation of the plastic belt chain-conveyor, the recommended operating speed is less than 0.6 m/s. As a result, the plastic chain-conveyor is designed to operate at a speed of 0.4 m/s. The lifting module serves to move the container in upward and downward directions, as shown in Figure 1. The module is driven by vertical chain transmission, carrying a sub-conveyor fastened to its actuator to guide the containers into the suspended conveyor system. The travel distance of the lifting module is 3 m, which ensures its sub-conveyor aligns with the overhead conveyor system as well as maintain enough space for the operating area on the floor. The line switching module redirects the conveyed containers to the switching point, as shown in Figure 2. The ball screw drive is used in this module to ensure a smooth horizontal movement. The area of the Bach Khoa Research Center for Manufacturing Engineering (BK-RECME, Ho Chi Minh City University of Technology (HCMUT), Vietnam) is depicted in Figure 3 with three simulated stations. The element conveyors are designed with the standard length of 1 m, 2 m, and 4 m to determine a completed structure of the forward motion module. The forward motion modules will then be combined with other mechanical modules to design the absolute system. Figure 1: The operation principle of the lifting module. The arrows indicate the travel direction of the container. Figure 2: The top-down view at the switching point. For the control system, a user interface program is built to produce a server, to manage and control the container routes. The program is developed on a C++ platformQt Creator [10]. The database MySQL is chosen for the system. The data from the database will not be transmitted directly to the PLC, but the server. At that time, the server will process the data and send the messages to the PLC to enable the output port, as indicated in Figure 4.  
The RFID reader sends the containers' name tag to the PC via TCP/IP. The type of RFID reader chosen is RDM8540-Q-A, the frequency is 13.56 MHz, and the available reading range is less than 8 cm. The selected reader supports both TCP/IP and Wi-Fi protocols. The PLC CompactLogix 5370 1769-L24 ER-QB1B of Allen Bradley was also chosen for the system. Figure 4: The overall functional block diagram of the control system. Figure 3: The drawing of Bach Khoa Research Center for Manufacturing Engineering (BK-RECME). When scanning the RFID tag mounted on the container lid, the data from the RFID reader will be transmitted to the PC via TCP/IP for processing and deciding if the container is available to move or not. To limit the travel length of the mechanical modules, proximity sensors are used.