Abstract: Variable frequency speed control in dyeing machine control offers advantages such as simplified configuration, clear logic, and reduced costs. This paper also details the application of the Huichuan MD330 frequency converter in dyeing machines. Keywords: Dyeing machine, constant tension, constant linear speed, frequency conversion control, common DC bus . I. Introduction Dyeing machines are suitable for the current market demand for dyeing various types of fabrics in small batches. They can be used for intermittent production and have promising development prospects with increasingly widespread applications. Dyeing machine control requires functions such as automatic track recording, automatic counting, automatic reversing, automatic turning, automatic stopping, and anti-drip liquid control. Throughout the process, the tension and linear speed of the fabric must be kept constant, thus requiring a high level of automation. Most traditional domestic dyeing machines use dual DC motor control, which can only achieve an approximate constant tension control effect. Some machines use a single frequency converter, employing asynchronous motor DC braking for unwinding and contactors to switch between the frequency converter and DC braking for winding and unwinding. Analyzing the principles of these solutions, they are all approximate results under conditions of significant error, therefore the control effect is not entirely satisfactory. Imported high-end roll dyeing machines sometimes use servo control, and sometimes expensive engineering-grade frequency converters, achieving relatively ideal results. However, this poses a significant cost burden for domestic users. This article uses an engineering example to illustrate how Huichuan's tension control-specific frequency converter can accurately and ingeniously fulfill the process requirements of a roll dyeing machine. CLM158 Giant Roll Dyeing Machine Technical Specifications: ◆ Width: 1800-3600mm; ◆ Maximum Roll Diameter: 1500mm; ◆ Speed: 20-150m/min; ◆ Maximum Temperature: 98℃; ◆ Tension Adjustment Range: 300～1000N [align=center] Figure 3[/align] [align=center] Figure 4[/align] Figure 4 is a schematic diagram of the roll dyeing machine in operation, which is a typical center roll control system. Undyed fabric is first wound onto one of the rollers by a fabric feeding motor. A proximity switch for counting is installed on the roller's drive shaft. The control system records the number of passes for the entire roll. After winding, one end of the fabric is manually wound onto the other roller. Once tightly wrapped, normal operation begins. Both rollers rotate in the same direction. The control requirement is to maintain constant tension on the fabric and consistent time the fabric spends in the dye bath, i.e., a constant linear velocity. This is a drive system without linear velocity feedback, but the linear velocity does change with the roller radius. Therefore, the control system needs to adapt to this unique requirement. The Huichuan MD330 frequency converter provides an ideal drive platform for high-performance control of the dyeing machine. Actual usage at various dyeing machine manufacturers and end-users in Jiangsu Province shows that dyeing machines controlled by the MD330 balance control performance and cost requirements, providing an excellent solution for product upgrades in this industry. The following example, using the CLM158 giant constant tension dyeing machine for flat-width silk, cotton, nylon, rayon, and synthetic silk fabrics, illustrates the application of the Huichuan MD330 high-performance vector control frequency converter in this industry. II. Electrical System of the Dyeing Machine Using a Dedicated Tension Control Frequency Converter The control of the dyeing machine can be divided into two parts: temperature control and drive control. This article focuses on the drive control part, which relates to tension and linear speed control. [align=center]Figure 5[/align] The control system of this dyeing machine uses a Siemens controller and a touch screen as the human-machine interface. It mainly performs the setting of tension and linear speed, the measurement of fabric thickness, and the control of related logical actions. The frequency converter and PLC communicate via RS-485. The advantage of using communication is that it allows for real-time access to information on the main variables of the frequency converter, reduces wiring, and makes the entire system appear more streamlined. A wiring diagram is shown in Figure 5. As shown in the diagram, the two frequency converters are identical and operate in closed-loop vector control mode. Since the dyeing machine operates at very low frequencies (1-3Hz) for extended periods when the roll is nearly full, using a higher line count encoder helps improve control performance at low speeds. Considering heat dissipation, a dedicated frequency converter motor is required. At the fabric loading moment, the PLC records the total number of turns of the fabric roll on the roller. The operator then measures the diameter of the fabric roll and inputs this value into the HMI. Based on the diameter and total number of turns, the PLC can accurately calculate the thickness of a single layer of fabric. This method yields very little error in obtaining fabric thickness. The fabric thickness is transmitted via RS-485 communication to the MD330 tension control frequency converter as the most basic control parameter. Simultaneously, the required tension and dyeing speed for each type of fabric are also set on the HMI and then transmitted to the frequency converter via the PLC. The MD330 boasts powerful functionality. Besides standard tension control functions such as inertia compensation, roll diameter calculation, friction compensation, and taper calculation, it also features an automatic reel-changing function designed for winding control in industries like cable and printing/packaging: pre-drive. This function automatically calculates the matching angular velocity based on the relationship between linear speed and roll diameter. Using this function, we can first achieve constant linear speed control, a requirement for dyeing machines. The principle is as follows: based on the set linear speed, the initial diameter of the fabric, and the fabric thickness, we can obtain a matching motor rotation speed. When the diameter changes, the inverter automatically subtracts one layer of fabric thickness for each rotation of the roller, resulting in a new diameter. Using this new diameter, the inverter can calculate the required matching linear speed, and so on, ensuring a constant fabric linear speed. Constant tension control utilizes the torque control function of the vector control inverter. It calculates the required torque in real-time based on the set tension value, taper, compensation amount, and roll diameter, thereby indirectly controlling the strip tension. This control method is suitable for high tension control at lower speeds, and the roll dyeing machine is a typical example of this type of system. In this system, the frequency converter receives the tension setpoint transmitted from the PLC via 485, and then calculates the diameter based on the fabric thickness using recursive calculation. The tension setpoint multiplied by the radius and divided by the transmission ratio of the mechanical system gives the torque required by the motor. In this system, assuming the unwinding is set to speed mode, it always operates in pre-drive mode, calculating the required motor speed based on the change in roller diameter to ensure a constant linear speed of the fabric. The winding always operates in torque control mode. When one direction is almost finished dyeing, it is only necessary to switch the winding/unwinding control mode and pre-drive of the two frequency converters. This is precisely a set of logically opposite signals, which can be obtained using a relay. As can be seen from the working principle of the roll dyeing machine, the unwinding motor is always in generator mode. The usual practice is to use a braking unit and braking resistor to dissipate the energy generated by braking as heat. For equipment like the roll dyeing machine that operates in generator mode year after year, this method results in a significant waste of electrical energy. Huichuan frequency converters can easily support a common DC bus. In practice, we directly connected the PN buses of two frequency converters in parallel. This way, the energy generated during normal braking returns to the driven motor through the parallel bus. To account for the possibility that both motors might be in generator mode during rapid deceleration, a braking resistor is still connected in parallel to one of the frequency converters. This resistor operates for a short time with very low energy consumption. The large resistor box previously located below the dyeing machine control cabinet can now be completely eliminated, saving energy and avoiding a large heat source, thus improving system reliability. III. Conclusion After optimizing the parameter values, the system achieved a very stable speed of 150 m/min during equipment testing, completely solving the problem of insufficient continuity and stability in tension control using the original DC motor. To ensure the safety of the components, a tension sensor was installed on the transition roller at the bottom of the dyeing vat in the first system to monitor the fabric tension. The data from the sensor shows that the tension control of this system is very stable, with fluctuations of less than 5% in steady state and less than 15% during rapid acceleration and deceleration. The effect of the taper coefficient in control can also be seen from the sensors, and these performance and functions are things that the original DC motor could not achieve. Using a common bus configuration, the equipment efficiency is 90-95%, and the power saving rate is about 40%. Moreover, the electrical components of this system are simple and the logic is clear, balancing control requirements and cost, making it a truly cost-effective solution. Dyeing machines using this control scheme are already being used in batches in Fujian, Huaibei, Jiangyin, and other places. References: 1. MD330 Modular Frequency Converter User Manual, 2004, Shenzhen Huichuan Technology Co., Ltd. 2. Electrical Variable Frequency Speed ​​Regulation Design Technology, Du Jincheng, 2001, Beijing, China Electric Power Press.