Abstract : Based on yarn length, a constant tension control system for the spinning frame was designed using a frequency converter to control the spindle speed. The program was designed and developed according to the state changes. Experimental results show that the design meets the requirements. The product has been put into mass production. Keywords : spinning frame, tension control, frequency converter, programmable controller, state transition diagram. Frequency conversion speed regulation, as a mature high technology, is being applied to spinning frames at an increasingly rapid pace. It plays a positive role in further reducing yarn breakage, hairiness, achieving high quality and high output, reducing energy consumption, and alleviating the labor intensity of workers. Significant results have been achieved in many spinning mills in China. Currently, many spinning machines in operation in China were produced in the 1970s and 1980s. This design is a constant tension control modification for old-style spinning frames to maintain stable tension at each stage of spinning. In the software design, an object-oriented programming approach is adopted, which improves the program's portability, scalability, and work efficiency. 1. Spinning Tension and Design Scheme Spinning tension is further divided into winding tension, air ring tension, and spinning tension. Spinning tension is a fluctuating variable during the spinning process. Under otherwise constant conditions, spinning tension is directly proportional to the square of the spindle speed. Therefore, to ensure uniform tension, the spindle speed can be adjusted; that is, the spindle speed decreases when the tension is high and increases when the tension is low. Currently, transmission devices for achieving spindle speed regulation include conical disc gearboxes, pole-changing AC motors, and frequency converters. Among these, frequency converters offer constant transmission efficiency, rapid speed adjustment response, and are a mature technology. Therefore, it is feasible to use a frequency converter added to the spinning frame to achieve constant tension control. This design involves creating a separate frequency converter control system on top of the original spinning frame control system. During installation, only signals from a few key points in the original system are introduced into the frequency converter control system, achieving immediate and convenient operation. To ensure basic stability of yarn tension throughout the entire doffing process, a fixed-length speed regulation method is adopted for the spindle speed. The entire doffing process is divided into nine stages, with set length intervals. Each interval has a corresponding spindle speed set based on the actual breakage rate in production. The specific data for the nine speed segments can be set by the workshop process engineer. [b][align=center]For details, please click: Application of Variable Frequency Speed ​​Control Technology in Constant Tension Control of Ring Yarn Frames[/align][/b]