This paper describes a novel winding system. Unlike traditional winding systems, it eliminates the need for a winding diameter measurement mechanism and a tensioning frame synchronization device. It simply operates a servo-controlled frequency converter in torque mode and indirectly obtains winding diameter information through calculation to achieve variable tension winding. 1. Introduction Winding systems are widely used in industries such as textiles, printing and dyeing, papermaking, and metallurgy. In most cases, constant tension is required during processing. However, the winding process is different; sometimes it requires a tighter inner section and a looser outer section, necessitating variable tension control where the tension gradually decreases as the winding diameter increases. Constant tension is often related to constant linear velocity, which requires the motor speed to be inversely proportional to the winding diameter. Tension control can be achieved using open-loop or closed-loop methods. Some motors (such as torque motors) possess soft mechanical characteristics; using them to drive the winding mechanism can achieve approximately constant tension operation. Changes in winding diameter can be considered a disturbance; disturbance compensation adjustment can achieve indirect tension control, which is also an approximate form of constant tension control. The most direct and effective method is to use a tension sensor to achieve closed-loop tension adjustment, also known as direct tension control. The tensioning frame commonly used in dyeing and printing machines can also be considered a tension detection element. However, this device is bulky, has poor accuracy, lacks tension display, and is inconvenient to use. The roll diameter (spool diameter) is an essential parameter in the winding system and generally requires some kind of detection device to obtain. Winding tension is a function of the roll diameter and needs to be calculated. This article describes a completely new winding system that utilizes the torque control mode provided by the latest servo controller to achieve constant linear speed and variable tension winding control without the need for a tensioning frame synchronization device. The roll diameter value required for control is obtained through internal calculation by the servo controller, eliminating the need for roll diameter detection, making it a novel and simple method. In the constructed application system, a fieldbus is used to transmit tension setting and roll diameter information between the programmable controller and the servo controller. 2. Speed ​​Control and Torque Control Speed ​​control and torque control are two control modes of the servo controller. Speed ​​control mode is well-known. It provides both a set speed and feedback speed, forming a closed-loop control to ensure the speed stays at the set value, while torque fluctuates with the load. Torque control mode, on the other hand, provides a set torque. The servo controller calculates the actual torque; if the actual torque is lower than the set torque, the speed increases; conversely, it decreases, resulting in a fluctuating speed. Torque control mode is well-suited for winding drives. In winding drives, the linear speed is constant, and the rotational speed decreases as the winding diameter increases. Tension is a given value for the system. Torque mode perfectly meets these requirements. The product of tension and radius is the torque, which serves as the setpoint for torque mode. The rotational speed in torque mode fluctuates precisely to the required linear speed, eliminating the need for linear speed control. Furthermore, without a dedicated detection device, the servo controller (frequency converter) can calculate the winding diameter itself, further simplifying the problem. Figure 1 shows a block diagram of a speed control mode winding system. The system includes a winding diameter measurement component, which calculates the rotational speed setpoint based on the winding diameter. A tensioning bracket is also used to ensure synchronization between motors. Obviously, using the torque control mode of the servo controller (inverter) for the winding drive can eliminate the need for the tensioner, thus simplifying the control system. [IMG=Fig. 1 Speed ​​Mode Winding System]/uploadpic/THESIS/2007/11/2007111614250882598Y.jpg[/IMG] Fig. 1 Speed ​​Mode Winding System 3 Winding Drive with Internal Winding Diameter Calculation As mentioned above, if the servo controller (inverter) has a winding diameter calculation function, then the torque setpoint can be calculated from the external tension setpoint, making the use of torque control mode very convenient. Figure 2 shows a two-servo controller winding system. Servo controller (inverter) 1 transmits the system's operating linear speed to servo controller (inverter) 2. Servo controller (inverter) 2 accepts the externally input tension setpoint and the tension feedback information input from the tension sensor to form a tension closed-loop control. Servo controller (inverter) 2 has an internal winding diameter calculation function and operates in torque control mode. The servo controller (inverter) 2 drives the asynchronous motor to wind the coil at the required tension and automatically floats its speed to the operating linear speed. The following uses the LENZE-9300 series servo controller (inverter) as an example to illustrate the calculation method for the coil diameter. The LENZE-9300 series servo controller (inverter) has more than fifty function blocks internally, capable of performing functions such as addition, subtraction, multiplication, division, and a series of transformations, as well as PID closed-loop regulation. Let v be the linear velocity; ω be the angular velocity; D be the coil diameter; and k be a constant. Then, the coil diameter is calculated according to the following formula: D = k * v / ω = k * ∫v dt / ∫ω dt, where v is the externally input linear velocity value, ω is the angular velocity value known to the servo controller (inverter), and k is a constant determined experimentally. The use of function blocks can be accomplished by setting a series of codes. Figure 3 shows a block diagram for calculating the coil diameter composed of function blocks. [IMG=Figure 2 Torque Mode Winding System with Internal Roll Diameter Calculation]/uploadpic/THESIS/2007/11/2007111614274839038N.jpg[/IMG] Figure 2 Torque Mode Winding System with Internal Roll Diameter Calculation [IMG=Figure 3 Roll Diameter Calculation Signal Flow Diagram Using Function Blocks Inside a Servo-Controlled Frequency Converter]/uploadpic/THESIS/2007/11/2007111614295074206C.jpg[/IMG] Figure 3 Roll Diameter Calculation Signal Flow Diagram Using Function Blocks Inside a Servo-Controlled Frequency Converter 4 Application Example [IMG=Figure 4 Working Principle Diagram of Winding Section in a Wet Felt Production Line]/uploadpic/THESIS/2007/11/2007111614334769648R.jpg[/IMG] Figure 4 Figure 4 shows the working principle diagram of the winding system of a wet-laid felt production line. A total of three LENZE-9300 series servo controllers (frequency converters) (9326) are used to drive three variable frequency asynchronous motors (M) with rotary transformers (R). The roller servo controller (frequency converter) operates in speed mode, with its speed setpoint (1/2 end) coming from the analog output of the production line PLC, and its auxiliary speed setpoint (3/4 end) coming from the tensioning frame signal, thus maintaining synchronization with the production line. The servo controllers (frequency converters) of roll 1 and roll 2 operate in torque mode, with internal roll diameter calculation functions, enabling closed-loop control of the tension setpoint information sent from the PLC via the CAN bus and the actual tension information sent from the tension sensor. There is no need for dedicated speed control of roll 1 and roll 2; they can automatically float their linear speed to the required value. The linear speed information required for roll diameter calculation is sent by the roller servo controller (frequency converter) through a dedicated speed cascade interface X9-X10. Reel 1 and reel 2 work alternately to achieve continuous winding. A shaft-changing motor driven by a LENZE-8215 frequency converter (not shown in the diagram) performs the shaft-changing function. The CAN bus also sends the winding diameter information calculated by the servo controller (frequency converter) to the PLC, which then calculates the tension setting. The winding section requires the reel to be tight inside and loose outside, which necessitates a high initial tension that gradually decreases as the winding diameter increases. This application system fully meets these requirements. Actual operation has proven the reliability of the winding system, achieving dense and neat winding from 86 mm to 1200 mm in diameter, with a winding speed reaching 80 m/min. 5. Conclusion Compared to speed-mode winding, torque-mode winding is simpler. This is primarily because torque-mode winding eliminates the need for a tensioner synchronization mechanism. Furthermore, the servo-controlled frequency converter's internal winding diameter calculation capability eliminates the need for winding diameter detection, further simplifying the system hardware. Although a tension detection circuit was used, it was to improve the accuracy of tension control and was not essential. The use of fieldbus facilitates convenient and fast information exchange between the frequency converter and the PLC. (Proceedings of the 2nd Servo and Motion Control Forum; Proceedings of the 3rd Servo and Motion Control Forum)