Abstract: This paper analyzes the contactor control system used in the original shuttle fabric feeder. By using a small PLC in conjunction with a frequency converter for automatic operation control, downtime caused by contactor damage or other circuit faults can be reduced, thereby ensuring equipment reliability, saving maintenance costs, reducing troubleshooting time, and ensuring equipment operating rate. Keywords: PLC, automatic control, shuttle feeder [b][align=center]The PLC Transformation of the Running Control System for Reciprocal Feeder Zhang Rui Zhou Li[/align][/b] Abstract: An analysis of the contact apparatus control system applied on the reciprocal feeder was conducted. The automatic operation control was achieved through the coordination of a small-size PLC with a frequency converter to reduce closing-down accidents due to contact apparatus damage or other circuit failures, in order to ensure the reliability of equipment operation, save maintenance costs, and reduce fault detection time to guarantee the operating rate of the equipment. Key words: PLC; automatic control; reciprocal feeder 0 Introduction In the pellet production line, the green pellets entering the chain grate need to be screened. A shuttle feeder evenly distributes the green pellets on the wide feed belt, and then they are screened by a small ball screen, thus ensuring that qualified green pellets are evenly distributed on the chain grate. 1. Process Flow The process of the screening and distribution system in pellet production is shown in Figure 1. The material flow on the belt conveyor is less than 0.8 m wide, and after screening by the large ball screen, the material flow is only about 1 m wide. The function of the shuttle distributor is to evenly distribute the original 1 m wide material flow onto the 2.8 m wide distribution belt through reciprocating motion. The qualified green pellets are then evenly distributed onto the grate bed of the chain grate machine through the small ball screen of equal width, and enter the chain grate machine, thus proceeding to the next process. 2. Analysis of Defects in the Original Automatic Control System The original screening and distribution system's automatic control system used conventional contactors combined with proximity switches. The action of the proximity switches controlled the engagement and disengagement of different contactors, realizing the forward and reverse rotation of the motor, thereby causing the distributor to reciprocate. The position of the proximity switches was adjusted to adjust the distributor's stroke, ensuring the material flow was evenly distributed on the wide belt. Frequent engagement and disengagement of the contactor significantly impacts its lifespan, making contactor replacement a crucial part of equipment maintenance. Frequent contactor replacement leads to frequent disconnections and reconnections, and loose wires greatly hinder troubleshooting, significantly extending maintenance time. Furthermore, when restarting the equipment, the direction of rotation (forward or reverse) must be selected based on the stopping position; incorrect selection may cause over-limit operation or shutdown. Although the transmission reduction ratio is considered in the design, frequent forward and reverse starts and stops still exert significant impact on the motor and track during actual operation. Frequent speed changes cannot guarantee uniform material distribution and also affect the motor's lifespan. 3. Modification 3.1 Original Operation Control Diagram (Figure 2) Based on the actual operating status of the equipment, data was statistically analyzed. The modification selected a Mitsubishi Fx-1S-20MR small PLC paired with an Emerson TD1000 frequency converter to control the fabric feeder's operation. This allows for manual and automatic switching; manual mode is inching control, and automatic mode is continuous operation, running at different preset speeds in different areas. Meanwhile, one limit switch is added to the outside of SQ1 and SQ3 in the original operation control system to protect the operating limits. Mechanical limit switches are welded onto the rail outside the limit switches to limit the operating limits of the material feeder, completely preventing cable damage caused by exceeding the limits and avoiding derailment and other accidents due to exceeding limits. 3.2 Advantages of this control method: Using a PLC control system to replace the original conventional wiring method, input and output signals are directly connected to the PLC system and are intuitively displayed on the PLC system panel. This facilitates the implementation of multiple control modes, eliminates cumbersome wiring, reduces the probability of failure, and makes it more intuitive for equipment operators and maintenance personnel to observe the equipment's operating status and simplifies troubleshooting. Furthermore, a memory check function for the stopping position is added to the PLC program design to avoid equipment exceeding limits and other failures due to incorrect selection of the running direction. Replacing contactors with frequency converters to directly control motor operation reduces the number of potential failure points caused by protection systems. It also allows for frequency-adjusted motor speed control, enabling smoother starting and stopping of the motor along a set ramp curve. The switching between forward and reverse rotation is also smoother, and the adjustable operating speed facilitates adjustments to fabric thickness. Furthermore, frequency converters can detect and protect against common faults, displaying fault codes for easy troubleshooting by maintenance personnel. This solution makes fault diagnosis more direct and convenient, significantly reducing maintenance time and workload, while also improving equipment reliability and increasing equipment uptime. 4. Conclusion The industrial application of automatic control systems is becoming increasingly sophisticated and widespread. The use of PLCs is not limited by the number of auxiliary contacts of conventional contactors, making it easier to achieve complex control processes that are difficult or impossible with conventional control methods, thus significantly improving operational reliability. It also allows for more direct observation and monitoring of equipment operating status, facilitating control and monitoring of the entire production process. The application of automatic control systems frees employees from frequent and repetitive tasks, greatly reducing their labor intensity and ensuring work quality. At the same time, it makes it easier to locate fault points, preventing delays caused by wasting a lot of time searching for fault points, shortening maintenance time, and improving equipment uptime.