Abstract: At present, the advanced tunnel kiln firing process has been widely adopted in the production of building ceramics. During the firing process of tunnel kiln, completing the top car work at fixed time and location is one of the important means to ensure the firing quality. This article discusses the PLC control of the entire tunnel kiln top car process. Keywords: tunnel kiln, top car machine, PLC, control Abstract: Currently, in the production process of construction ceramics, the more advanced tunnel kiln is generally used for firing. The process of firing ceramics in a tunnel kiln, with fixed times and fixed points for each firing point, is a crucial method for ensuring firing quality. This article discusses the PLC control of the entire tunnel kiln firing process. Key words: tunnel kiln, top car machine, PLC, control 0. Introduction Currently, the construction ceramics industry commonly uses tunnel kiln firing technology. In the process of firing ceramics in a tunnel kiln, in addition to strictly controlling the physical parameters such as temperature and pressure at each controlled point (car position), accurately and timely completing the top car and return car cycles is also a necessary link to ensure firing quality. With the development of computer technology, especially the widespread application of programmable logic controller (PLC) technology, the control of the top car process has been realized through PLC automatic control, thereby greatly improving the reliability of the system and ensuring the steady improvement of product quality. This article takes the top car control process of the building ceramics tunnel kiln in Tangshan Ceramics Factory as an example to discuss the application of PLC in the sequential control of tunnel kilns. 1. The Top Car Process Tunnel kilns are continuous firing production devices. Through orderly top car operations combined with strict control of each controlled point within the kiln, each blank (semi-finished product) completes the firing process required by the firing curve during its "flow" from the kiln head to the kiln tail. In other words, from a macroscopic perspective, the parameters of each controlled point are constant in the control of the tunnel kiln. However, for the blanks being fired within the kiln, they must strictly follow the requirements of the firing curve and pass through each controlled point on time to achieve the ideal fired product. In summary, to ensure that the fired blanks pass through all controlled points on time according to the requirements of the firing curve, the kiln cars within the kiln must circulate and flow in a timely and orderly manner. Currently, the commonly used technology is a timed top car control process based on logic control. A schematic diagram of the top car process in a tunnel kiln is shown in Figure 1. [align=center]Figure 1: Schematic diagram of the top car process in a tunnel kiln[/align] Since the control methods for the kiln tail and kiln head are exactly the same, to save space, this article only discusses the control of the kiln head, and assumes that the kiln tail can fully meet the requirements of various control signals needed for kiln head control. The process of the top car process is as follows: Set the following sequence: Top car timing reaches T0↑ → Kiln car arrives in front of the trolley 13XK↑ → Trolley accurately positioned in the return line direction 1XK↑ → 9XK and 10XK simultaneously↑ → Oil pump starts → No kiln car on the trolley 11XK↓ → Clamping device is in the released state 12XK↓ → 1DT↑ → Pusher starts pushing the kiln car onto the trolley → 13XK↓ → When the kiln car arrives in position 11XK↑ → 2DT↑ → Pusher returns → Pusher returns to position 14XK↑ → Pusher stops → Electromagnetic clamping device clamps the kiln car → After clamping, 12XK↑ → Trolley motor starts at low speed forward, trolley moves slowly towards the kiln head → 2XK↑ → Trolley motor switches to high speed forward → When approaching the kiln head 3XK↑ → Switches to low speed forward, continues moving towards the kiln head → When 4XK↑, enters the positioning and alignment state State → After successful alignment, 9XK and 10XK simultaneously ↑ → Carriage motor stops → Kiln door motor starts forward to open the kiln door → After opening to the correct position, 7XK ↑ → Kiln door motor stops and engages the brake → Clamping device releases 12XK ↓ → 3DT ↑ → Top car advances, pushing the kiln car into the kiln → When the top car is in position, 6XK ↑ → 3DT ↓ → 4DT ↑ → Top car returns → When returned to the correct position, 5XK ↑ → 4DT ↓ → Top car stops → Kiln door motor starts in reverse to close the kiln door → After closing to the correct position, 8XK ↑ → Kiln door motor stops → Carriage motor starts in reverse high speed → Carriage quickly returns → 2XK ↑ → Switches to reverse low speed → 1XK ↑ → Enters reverse alignment positioning → 9XK and 10XK simultaneously ↑, positioning ends, carriage stops → Manually pushes the kiln car to position 13XK → Waits for the next timer to expire. 2. System Hardware Design This system only involves the control of on/off signals, therefore, the Toshiba EX40-PLUS controller is used. The EX40 has 40 basic I/O points, including 24 inputs and 16 outputs. The maximum relay output current can reach 2A, fully meeting the control requirements of this system. The system's hardware schematic is shown in Figure 2. To ensure the system's safe and reliable operation, in addition to interlocking in the ladder diagram, hardware interlocking is also implemented for the contactors used for rising, falling, high-speed, low-speed, forward, and backward movements in the hardware wiring. The EX40's input terminals use a common-drain wiring method, and its power supply is provided internally by the PLC. This system uses relay output mode, with external power supply. The contactors are powered by 220V AC, while the electromagnets and indicator lights are powered by 24V DC. The allocation of each I/O point in the system is shown in Tables 1 and 2. Table 1: System Input Allocation Table 2: System Output Allocation Figure 2: System Hardware Schematic Figure 2 is the hardware wiring diagram of this system. Wiring for alarm indicators, etc., is omitted in the figure. Except for X0 and X16, which are pushbuttons, all input switches are limit switches. 3. System Software Design This system adopts a sequential control method based on a timer principle. The system control structure is simple, the ladder diagram is easy to design and debug, and it is convenient for maintenance and repair. The system flowchart is shown in Figure 3. [align=center] Figure 3: Control System Software Flowchart[/align] As can be seen from the flowchart shown in Figure 3, the system software design mainly includes: system startup and main control formation; trolley travel and positioning control; kiln door opening and closing control; top car machine operation control and some timeout alarm control, etc. The system ladder diagram is omitted. 3. Conclusion This system uses a micro PLC as the control device, especially the EX40-PLUS large-screen programmer, which can easily edit and modify the ladder diagram program, and can also realize online debugging and monitoring of program operation. References: [1] Yang Changneng, Fundamentals and Applications of Programmable Logic Controllers [M], Chongqing: Chongqing University Press, 1990. [2] Wang Zhaoyi, Programmable Logic Controller Tutorial [M], Beijing: Machinery Industry Press, 1993. [3] Guan Yujun, Electrical Control System of PC Light Rail Drilling Machine [J], Proceedings of the 1999 National Conference on Control and Decision, 1999. [4] Yao Yugui et al., Design of Tunnel Kiln for Building Ceramic [M], Beijing: China Building Industry Press, 1979.