1. Introduction Rotary screen printing machines are multi-part coordinated electrical drive systems. Due to their advantages of high speed and low cost, they are widely used in the printing and dyeing industry. The rotary screen printing process requires strict synchronous movement between the printing screens and between the screens and the feed belt. The quality of this synchronization directly affects the printing quality. Therefore, designing and developing a high-performance rotary screen printing machine controller is crucial. The printing conveyor belt is driven by a drive motor, running at a stable linear speed. Each printing screen is driven by a stepper motor to track the feed belt, quickly reaching the same speed. After rapid adjustment, the zero-position marks of each screen converge. At this point, the fabric enters the printing machine and begins the production process. During steady-state operation, each screen must not only automatically adjust for errors caused by belt speed variations and its own interference, but also determine its optimal convergence point based on previous errors. Traditional printing machines suffer from low system reliability (e.g., limitations in distributed design and CPU computing power) and high cost, making them unsuitable for the ever-changing market demands. Therefore, designing and developing a high-performance rotary screen printing machine controller is crucial for developing a new type of rotary screen printing machine. 2 Working Process and Control Structure [align=center][img=567,300]http://www.ca800.com/uploadfile/maga/plc2008-7/wyl-1.jpg[/img] Figure 1 Working principle diagram of a rotary screen printing machine[/align] The rotary screen printing machine consists of four units: a fabric feeding unit, a printing unit, a drying chamber unit, and a fabric unloading unit. Its working principle is shown in Figure 1. The fabric enters the machine under the transmission of the fabric feeding motor, is fed onto the printing guide belt, and is adhered to the printing guide belt. When the fabric passes through the printing rotary screen, the synchronous movement of the printing guide belt and the printing rotary screen causes various printing dyes to be transferred to the fabric through the printing rotary screen, thus completing the printing process. After printing, the fabric is sent to the drying chamber in a relaxed state for drying treatment. Finally, the dried fabric is sent out of the machine by the fabric unloading unit, thus completing the entire printing process. Rotary screen printing machines are multi-axis motion machines, so a stable printing guide speed and a high-performance rotary screen position control system are key to ensuring the printing accuracy of the rotary screen printing machine. 3. Control System Design In the past, distributed rotary screen printing machine controllers were used. This approach has the advantages of being easy to decompose and handle complex problems, and local failures are less likely to cause the entire system to collapse. However, distributed control has disadvantages such as complex installation, high cost, poor anti-interference, and low reliability. However, a centralized rotary screen printing machine controller using an FPGA and a microcontroller can improve the system's reliability and control accuracy. This control scheme has advantages such as convenient installation, wide adaptability, easy implementation of control algorithms, good anti-interference, high reliability, good interchangeability, and small plate size. The overall system design block diagram is shown in Figure 2. [align=center][img=567,300]http://www.ca800.com/uploadfile/maga/plc2008-7/wyl-1.jpg[/img] Figure 2 Schematic diagram of the rotary screen control system[/align] In the actual printing process, there are many reasons for misprinting. From an overall analysis, misalignment is caused by two main factors: first, the nonlinear characteristics of the mechanical parts; and second, the different transmission characteristics of different transmission chains between the circular mesh and the guide belt, and between the circular meshes themselves, leading to asynchronous positioning and misalignment. The misalignment caused by the nonlinear characteristics of the mechanical parts is determined by the machining characteristics and remains fixed after machining. Replacing traditional mechanical transmission tracking control technology with electronic gear technology, dynamic tracking is achieved by modifying the electronic gear algorithm. Electronic gears can achieve real-time adjustment of the electronic gear ratio, improving operational reliability and flexibility, and reducing accumulated errors. 4. Design of Electronic Gears The accuracy of the servo system is determined by the number of encoder lines, while electronic gear settings allow the command pulse to be set to any value. The function of electronic gears is to implement the function of mechanical gears using electronic circuits. Just as mechanical gears change transmission speed (increasing or decreasing speed), electronic gears similarly adjust the frequency of command pulses (see Figure 3). [align=center][img=567,300]http://www.ca800.com/uploadfile/maga/plc2008-7/wyl-1.jpg[/img] Figure 3[/align] The instruction device sends pulses, which are processed by a 4x frequency multiplication before entering the electronic gear circuit, and then output to the pulse receiving device. By using different electronic gear ratios in the electronic gear circuit, a linear relationship is maintained between the frequencies of the output pulse and the input pulse (the ratio is equal to the electronic gear ratio). When the electronic gear ratio is fixed, the output pulse frequency changes with the input pulse frequency. Based on the above theoretical principles, an electronic gear can be designed using Quartus II, as shown in Figure 4. Altera's Quartus II programmable logic software belongs to the fourth-generation PLD development platform, providing a design environment for programmable logic. [align=center][img=567,300]http://www.ca800.com/uploadfile/maga/plc2008-7/wyl-1.jpg[/img] Figure 4 Electronic Gear Design Based on Quartus II[/align] 5 Conclusion To ensure error-free printing, the control system must guarantee synchronization between the rotary screens within the error range, and simultaneously ensure that the rotary screen speed and the guide belt speed remain constant. This paper proposes a centralized control system using an FPGA and a microcontroller, which reduces system interference and thus improves printing accuracy. The design and debugging have been successful. Actual operation and testing results show that the system functions are basically realized, and the accuracy meets the design requirements.