Abstract: This paper introduces the application of programmable logic controller (PLC) in a missile loading system, elaborates on the control requirements of the entire system, and presents the hardware composition and software flowchart of the system, highlighting the reliability of the PLC system. Keywords: Missile loading system; PLC; Control; Reliability Abstract: This paper introduces the application of PLC on a missile loading system. The controlling requirements of the whole system are described in detail, and the structure of the hardware system and the flow chart of the software system are given. The reliability of the PLC controlling system is emphasized. Key Words: Missile loading system; PLC; Control; Reliability 1 Introduction Missile loading equipment is one of the missile assembly equipment, used for the insertion and removal of missiles from their containers. It is an important piece of equipment for inserting missiles after final assembly and testing, and for removing missiles when troubleshooting is required. Its main functions include: 1) The equipment has the ability to safely and quickly load missiles into the missile canister and smoothly remove them from the canister; 2) The equipment has dual drive functions, namely electric and manual; 3) The equipment has a protection function; when the thrust or pull exceeds the set limit, the equipment automatically cuts off the power and alarms. Commonly used electrical control systems employ relay-contactor control, but due to its high failure rate, unreliable operation, and difficult maintenance, it is not used in this system. Instead, programmable logic controller (PLC) control is adopted as the preferred control method in modern mechatronics technology to achieve automatic control of the loading speed. This control system is not only simple in circuitry, highly reliable, easy to maintain, and easy to debug on-site. 2. Composition and Control Requirements of the Loading Equipment System 2.1 Main Components As shown in Figure 1, the system consists of two parts: a missile support frame and a missile canister support frame. The support frame is composed of a base, linear rolling guide rail, motor, clutch, handle, etc. Through the drive mechanism, the missile and missile canister can move longitudinally on their respective support frames to complete the loading task. [align=center] Figure 1 Layout Diagram of Loading Equipment[/align] 2.2 System Control Requirements The missile loading equipment is required to have both electric and manual drive functions. The missile's movement speed is freely adjustable in three levels, achieved by controlling a three-speed motor, while the missile canister's movement speed is only a single speed. At the same time, both should be able to switch directly between inching and continuous operation as needed for control. In addition to automatic control, manual operation is also provided, using a handwheel mechanical drive to enable manual operation in case of power failure, overload, or overtravel termination. 3. Loading System Design 3.1 Hardware Design 3.1.1 PLC Selection and Input/Output Point Determination Based on the above control requirements, the OMRON CPM2AH-30CDR-A product is selected. It features a compact and high-speed design, providing 30 I/O points, including 18 relay inputs and 12 relay outputs. [align=center] Figure 2 PLC Hardware Wiring Diagram[/align] The basic PLC configuration requirements for this system are 14 digital inputs and 9 digital outputs. Figure 2 shows the hardware wiring diagram. The components include: SB1 power start switch, SB2 emergency stop switch, SB3 selector switch for pusher motor and ammunition box motor, SB4 pusher speed conversion switch, SB5 jog forward switch, SB6 jog backward switch, SB7 continuous forward switch, SB8 continuous backward switch, SB9 overload pressure signal input, SQ1 and SQ2 pusher stroke limit proximity switches, SQ3 and SQ4 ammunition box stroke limit proximity switches, KM1 ammunition box motor forward contactor, KM2 ammunition box motor reverse contactor, KM3 pusher motor low-speed contactor, KM4 pusher motor medium-speed contactor, KM5 and KM6 pusher motor high-speed contactors, KM7 pusher motor forward contactor, KM8 pusher motor reverse contactor, and HL1 power indicator light. 3.1.2 Handheld Control Box Design Based on the control requirements, the handheld control box is designed as shown in Figure 3. [align=center] Figure 3 Distribution of Control Keys on the Handheld Box[/align] 1) When the system requires jogging operation, pressing the jog button starts the motor, and releasing the button stops the motor. 2) When the system requires continuous operation, the button must be pressed continuously for 3 seconds before it takes effect (this function is implemented through ladder logic programming) to prevent accidental operation. 3) The pusher motor and the cartridge motor are controlled by a single switch, which is interlocked, thus ensuring that the handheld control box cannot control both motors simultaneously. 4) When the pusher motor is selected, if the speed setting is not low, the motor cannot operate. It must go through the low speed setting to transition to the medium or high speed setting, preventing excessive starting current of the motor. 3.1.3 Missile Loading Thrust and Pull Force Test System To prevent damage caused by excessive push and pull forces during missile loading and unloading, an overload protection device is designed. A push and pull force detection system developed using a microcontroller and force sensor is used to test and display the magnitude of the driving force during the missile's entry and exit from the cartridge in real time. The alarm limit force can be adjusted and set in real time as needed. The initial driving force limit is set to 5500N. When the limit is exceeded, the pressure signal is transmitted to the PLC, which issues a command to automatically cut off the power supply to the drive motor to protect the loading safety. [align=center] Figure 4 Driving Force Detection Figure 5 System Software Flowchart[/align] 3.1.4 Missile Loading Stroke Protection System During the operation of the loading equipment, in order to prevent damage caused by the movement of the traction trolley beyond the working range during operations such as pushing the missile and the missile box, four proximity switches are arranged at both ends of the missile and missile box support frame to collect stroke overtravel information and input it into the controller PLC to cut off the power supply in time and realize over-limit protection. When the proximity switches are open, it is in manual operation mode. Turn the handle to make it move away from the limit position in the opposite direction so that the system can work normally. 3.2 Software Design 3.2.1 Software Flowchart According to the motion flow and control requirements of the system, the program is written to realize the control of motor operation and corresponding actuators. The programming software is CX-Programmer V5.0 developed by OMRON for ladder diagram programming. It can run under the Windows system and can realize ladder diagram programming, monitoring and control functions, ensuring the stability and accuracy of the system. The software flowchart is shown in Figure 5. 3.2.2 Software Setup and Operation The OMRON CPM2A CPU unit can communicate with a laptop via the RS-232C port. Start the CX-Programmer software, create a new "Loading Control" document, set the correct "Device Model" and "Network Type," and enter the programming interface. Write a ladder diagram program adapted to the system based on the pre-allocated I/O table, as shown in Figure 6. After the program is compiled correctly, upload it to the laptop via the communication cable. The program can then be run to achieve PLC control. If changes are needed, the program can be downloaded from the PLC to the laptop for offline modification or edited online. 3.2.3 Common Troubleshooting During Programming and Debugging 1) Troubleshooting the inability of the laptop to communicate with the CPU module: Check if the CPU communication switch on the PLC is in the "ON" position; check if the peripheral port setting in the software is in "RS-232C" mode; replace the communication cable or CPU module. 2) Handling methods for input signals but no output signals: Re-load the program into the CPU to prevent the CPU from having no program or the program being lost; check if the PLC is working in "run" or "monitor" state; check the program to ensure it is written correctly; ensure communication is fault-free. 3) Handling methods for electrical equipment not operating: Check if the output wiring is correct; check if there are any forced input/output points in the program; replace the electrical equipment. [align=center] Figure 6 Ladder diagram program interface[/align] 3.3 Other anti-interference measures 1) A 1:1 isolation transformer is used at the power input terminal to better reduce electrical noise; 2) Twisted pair cables are used for the PLC power supply line to prevent interference from the power line; 3) Arc extinguishing devices are installed between the motor power lines to prevent electric arcs between the contactor contacts, achieving the purpose of explosion protection. 4 Conclusion The use of the OMRON CPM2AH programmable controller for automatic control of the missile loading system has achieved significant results in terms of system reliability, simplified operation methods, and flexible functions, achieving good practical results. References: [1] Cheng Zhou. Electrical Control and PLC Principles and Applications. Beijing: Electronic Industry Press, 2003 [2] Lü Jinhua, Jiang Hanhong. Ship Engine Room Monitoring System Based on PLC [J]. Microcomputer Information. 2005, 24: 81-82+138 [3] CPM2A Programmable Controller Operation Manual, 2002 [4] Cao Hui, Huo Gang. Programmable Controller System Principles and Applications. Beijing: Electronic Industry Press, 2003