Abstract : This article introduces the multi-speed requirements of the drive motor during workpiece processing and conveying, and analyzes the hardware connection, inverter parameter settings, and PLC programming of the control system composed of a programmable logic controller (PLC) and a frequency converter (VDC). It demonstrates that this is a practical and advanced control technology. Keywords : Conveyor line; PLC; Frequency converter; Control system 1 Introduction With the changes in industrial structure and the development of automatic control technology, programmable logic controllers (PLCs) and frequency converters have become dominant in various high-performance mechanical systems. The combination of a frequency converter and a squirrel-cage induction motor can achieve significant energy savings, high speed regulation accuracy, a wide speed range, and comprehensive protection functions. It also simplifies maintenance and facilitates automatic control of the system. In the automated production process of machining, the conveying of mechanical parts is a crucial link. The transport of parts on the automatic conveyor line requires the drive motor to have multiple operating speeds, and the speed changes during transport require fully automatic control. Therefore, using a PLC and frequency converter for control is the most economical and reasonable approach. 2. Control Requirements and Hardware Connection For rotating loads such as conveyors, roller conveyors, and feeding platform vehicles, the load torque is not significantly related to the speed. For these constant torque loads, frequency converters are used for speed regulation, making the motor operation energy-saving. As the speed of the asynchronous motor controlled by the frequency converter decreases, the motor's output power decreases, and the input power of the frequency converter decreases proportionally, thus reducing energy consumption. Furthermore, when using frequency converter drives, even if the power supply frequency is different, the machinery does not need to be changed, ensuring that the maximum output capacity remains constant, thus standardizing and simplifying the machinery. Figure 1 shows the frequency-speed variation curve of the asynchronous motor of the feeding platform for conveying mechanical parts in a processing plant. Based on the speed variation requirements, the frequency converter's JOG (jog), 2nd speed, and 3rd speed inputs control eight frequency levels. The frequencies for speeds 2, 3, 5, and 7 are set to 10, 15, 25, and 35 Hz, respectively. The 2nd and 3rd acceleration/deceleration time inputs control the frequency converter's acceleration/deceleration time. The acceleration/deceleration reference frequency is set to 50 Hz, and the acceleration/deceleration times for speeds 1, 2, and 4 are set to 20, 10, and 5 seconds, respectively. [b][align=center]For details, please click: PLC-based Variable Frequency Control System for Conveyor Production Line[/align][/b]