1. Introduction Programmable Logic Controllers (PLCs) are widely used in industrial ceramic production process control due to their powerful functions, high reliability, anti-interference capabilities, simple programming, ease of use, and compact size. However, when ceramic production processes change, special requirements arise, or new problems occur in the production process, the PLC control system or programming scheme should be modified and optimized accordingly. This article discusses the modification of the PLC automatic brick-feeding control system, one of the key pieces of equipment in a glazed tile production line with an annual output of 1 million m2. 2. Brief Introduction to the Brick-Feeding Process As shown in Figure 1, M1 and M2 are belt motors, M4 and M5 are roller table motors, G1-G6 are photoelectric detection tubes, YV1 is a solenoid valve, and BX1 is an operation box. When the billet from the glazing line or bisque line is conveyed by the conveyor belt of motor M1 to position G1 of the photoelectric detection tube, G1 activates, motor M2 rotates, and its conveyor belt transports the billet to the roller table in front of the kiln. If there is no billet at G1, M2 stops; when the billet is delivered to G2, M1 stops; when delivered to G3, M2 stops, and simultaneously, solenoid valve YV1 is energized, the belt support frame of M2 drops, and the billet is driven by the roller table speed-changing motors M4 and M5 in front of the kiln, and transported into the kiln by roller transmission; at G4, YV1 is de-energized, the belt is raised, motor M1 starts, and the above process is repeated. Figure 1 shows the billet loading process flow. 3. Problems and Improvements The ladder diagram of the original control system is shown in Figure 2. An OMRON SP10 small machine was adopted. Based on several months of trial operation, the machine has high reliability and basically meets the usage requirements. However, from the perspective of production process, control method, and actual use, its control system still has the following defects. Figure 2. Monitoring of the arrangement of the blanks. 3.1 Production process: This single-layer roller kiln can be used for both glaze firing and bisque firing. When used for bisque firing, the blanks on the conveyor belt are unglazed blanks with lower mechanical strength than glaze blanks, and the process requires no damage. When used for glaze firing, the process also requires strict prohibition of blank stacking. Therefore, during the conveying process, the operation should be smooth, the transition at the joints should be natural, and the belt should rise and fall slowly. These requirements can be solved by adjusting the conveyor belt and the control method of the motor (such as using frequency conversion speed regulation), as well as modifying the solenoid valves. However, the rollers of the roller table controlled by motors M4 and M5 inevitably bend and deform due to long-term operation in a high-temperature environment, causing the blanks entering the kiln to be arranged in a disordered manner, or even stacked and stuck together, resulting in waste products. Usually, this phenomenon is monitored manually, which is time-consuming and labor-intensive. In Figure 1, the author added two photoelectric detection tubes G5 and G6, which are connected to the alarm circuit and PLC, and successfully realized automatic monitoring, as shown in Figure 2. 3.2 Control Aspects (1) PLC Automatic Stop Failure During trial operation, the machine frequently stopped. The main reason was that the ambient temperature was too high, causing the PLC automatic protection system to activate. High ambient temperature in industrial ceramic kilns is a common problem. However, it has not received enough attention from designers. Although the PLC control cabinet is a certain distance from the low-temperature section of the roller kiln, the PC and the magnetic and other electrical components of the control motor are enclosed in a small space by the control panel, and there is no fan in the cabinet, resulting in poor heat dissipation. The increase in ambient temperature in summer, coupled with the limited ventilation conditions in the production workshop, caused the PC to stop frequently. After adding a fan in the cabinet, there was no more stopping. (2) Problem with the setting of the emergency stop button The emergency stop button SB3 in the original system was set on the control cabinet, which was not convenient for dual-location control and often caused a lot of damage to semi-finished products. Therefore, a button box BX1 was added to Figure 1, which was connected in series with the emergency stop button of the glazing line and SB3, making it convenient to stop and start. Figure 3 Original ladder diagram (3) Frequent jogging of motor M2 affects its lifespan. This production line does not have a large billet storage device. When the billet supply is not continuous, the waiting time of motor M2 is too short, and it starts frequently and heats up. One of them was burned out. The problem lies in the programming. As can be seen from the original ladder diagram (as shown in Figure 3), M2 moves once as soon as there is a billet at G1. It should be changed to stop M1 if the billet reaches G2 and there is a billet at G1; otherwise, M1 continues to rotate to make the billet supply continuous. (4) Further optimization of the control system The original system's solenoid valve YV1 is controlled by the intermediate relay KA1. KA1 has now been removed and is directly controlled by the PC. As can be seen from Figure 1, the photoelectric detection tube G4 controls the lifting and lowering of the support frame of the M2 conveyor belt. If the billets are not neatly arranged, some billets arrive at G4 first, while others have not completely left the M2 conveyor belt, but the support frame starts to rise, damaging the billets. Moreover, once G4 fails, it will cause chaos in the entire system. Removing G4 and replacing it with an internal time relay in the PC not only saves costs and facilitates adjustment, but also increases system reliability. 4. Programming of the Improved System The improved ladder diagram is shown in Figure 4. Figure 4 Improved Ladder Diagram 4. Conclusion Years of practical operation have proven that the improved control system is stable, reliable, and reasonable, improving production efficiency. Therefore, the author believes that only by mastering the characteristics and application methods of PLCs and being familiar with specific production conditions can the advantages of PLCs be fully utilized to effectively serve industrial production.