In today's era of rapid industrial development, building modern production lines has become an urgent priority to improve production efficiency, ensure the coordination and rational utilization of all aspects of the production line, and reduce labor costs. This article takes the mechanical transportation system in the Jiangling painting workshop as an example to explain how to achieve mechanical transportation automation using PLC as the core, and the key points that need attention.
The painting process begins at the welding exit, proceeds through electrophoresis and drying, then the lifting equipment is changed, sealant is applied, and the equipment is transferred back to the skid for topcoat and waxing processes. Each process step involves a cycle of visual inspection and rework, and finally the equipment is transferred to the skid for final assembly.
To ensure the safety of the entire system, emergency stop button boxes are first installed at the entrances and exits of each process chain. Because the topcoat process is flammable and explosive, explosion-proof isolation barriers are used instead of ordinary sensors. Secondly, in addition to installing limit switches in the hardware, interlocking programs are also written at the bottom layer to prevent operators from operating the equipment in an unsafe state.
The challenges in achieving automation lie in the interaction of vehicle model information between the transportation system and the process robots, the sorting of vehicle models in the storage area, and the automatic path selection in the rework area.
To rationally allocate the load of each control system, and to ensure a clear system structure and convenient maintenance, this scheme adopts a tree-structured design for the system's power and network:
The solution divides the entire system into several areas, each with an MCP and a PLC. The MCP is then connected to the RCPs in its area via a fiber optic network, ensuring network stability, which in turn ensures the stability of the entire production line. Finally, the fiber optic switch converts the signal to Ethernet and connects it to devices such as frequency converters and remote I/O. At the same time, various electrical devices, including motor overload protection switches, relays, and contactors, are also installed in each MCP or RCP.
The PLC program uses sensors installed on the production line to determine the position of the trolley, record the trolley model information, and push the recorded model information in real time based on the conveying status. To prevent errors in the push, RFID reader/writer stations are also set up at key workstations to write the model information into the RFID tag on the trolley using a reader/writer. In the topcoat painting section, the accurate model information is then read from the RFID and handed over to the robot.
This system has six repair workshops, each equipped with a button box to indicate whether the work in that workshop is complete. A button box is also located at the inspection station, allowing operators to record the condition of the chassis by selecting buttons. Leveraging the flexibility of RSLogix programming, the system automatically and systematically selects routes based on vehicle type, inspection station scoring, and the vehicle's status in the storage area, leading to the appropriate repair workshop and overcoming a major challenge.
