Abstract : PLC (Programmable Logic Controller) control of stepper motors is widely used in many industrial control applications. This paper introduces the principle that the PLC sends pulse and direction signals to the stepper motor driver, which then controls the stepper motor's operation. The frequency curve of the stepper motor is studied, and the optimal running speed of a moving cart using PLC control of the stepper motor is analyzed and summarized. Experimental data from an automatic traditional Chinese medicine dispensing system demonstrates the feasibility of optimizing the frequency curve of the stepper motor under PLC control. Keywords : Programmable Logic Controller (PLC); Stepper Motor; Frequency Curve 1 Introduction PLC (Programmable Logic Controller) Roller is a new type of controller developed on the basis of sequential controller and microcomputer controller. Its high reliability, simple and intuitive programming method and increasingly perfect functions have made it widely used in the field of industrial control. Among them, in many automatic control systems, the PLC controls the stepper motor [1,2]. When the PLC sends pulse signal and direction signal, the stepper motor driver receives the pulse signal and direction signal through the pulse output port of the PLC to control the stepper motor to work. One pulse signal can make the stepper motor rotate a fixed angle. Then there must be a certain relationship between the number of pulses and the frequency. The frequency curve of the stepper motor reflects this relationship intuitively. In the development and research of the automatic dispensing system of traditional Chinese medicine, the number of pulses of the stepper motor is controlled by the PLC to ensure that the medicine trolley can accurately reach the medicine trolley to pick up the medicine. The literature [3] proposes the relationship between the stepper motor speed stability, frequency and angle jitter. If the number of pulses and frequency are not set properly, the medicine trolley will not only run slowly, but may also have jitter, noise and other adverse factors, which will accelerate the wear of the machine and affect the working efficiency of the whole system. Therefore, it is necessary to optimize the frequency curve of the stepper motor. [b][align=center]For details, please click: Research on Frequency Curve Optimization Technology of PLC-Controlled Stepper Motor[/align][/b]