Abstract: This paper introduces the hardware composition and control method of a servo system composed of a permanent magnet synchronous motor, a frequency converter, and a PLC, and points out several issues that need attention during the operation of the system. Keywords: Permanent magnet motor, frequency converter, PLC 0 Introduction Servo systems composed of permanent magnet synchronous motors are often used in applications requiring fast, accurate, and precise position control. The motors are small in size, lightweight, highly efficient, and have no rotor overheating issues. The short fiber cart's fiber bundle dropping device at Luoyang Petrochemical uses two permanent magnet synchronous motors to drive the roller frame trolley in a left-right reciprocating motion and the rollers in a back-and-forth reciprocating motion, respectively, thus ensuring the even distribution of the fiber bundles in the fiber buckets on the rollers. This paper provides a detailed introduction to the system composed of a Siemens 6FK permanent magnet synchronous motor, a Siemens 6SE70 series small AC-DC-AC frequency converter, and an S7-300 PLC, and points out problems encountered during operation and maintenance for reference. 1 Basic Situation A simplified schematic diagram of the dropping device is shown in Figure 1. The entire production area is divided into three zones: the bucket inlet zone, the bucket unloading zone, and the operating zone. In the operating area, the trolley reciprocates left and right, with proximity switch B8 serving as its travel center calibration point. The rollers move back and forth, with proximity switch B15 serving as its travel center calibration point. In the can loading area, when an empty can is placed in the loading position by the transport trolley, proximity switch B2 illuminates, and the can loading motor starts. The can loading motor stops when the empty can reaches proximity switch B1. When the selected cycle time for the yarn tow dropping into the can is reached, the trolley quickly calibrates to the middle position and brakes to a stop; the rollers, with their variable speed, drag the full can forward. After reaching the maximum forward travel set, the can loading motor starts, and the empty can is loaded onto the roller rack. When the rollers move backward, dragging both the full and empty cans, photoelectric switch B13 activates, starting the can unloading motor and guiding the full can to the unloading area. When photoelectric switch B13 detects the gap between the full and empty cans, the roller motor brakes and begins to move backward. When the full can reaches proximity switch B3, both the can loading and unloading motors stop simultaneously. A complete production cycle ends, and the timing restarts. For details, please click: Application of Servo System of Permanent Magnet Synchronous Motor in Short Fiber