Abstract The application of automatic welding is becoming increasingly widespread, and the demand for welding wire is also increasing. Simultaneously, layer winding equipment is required to adapt to various specifications of welding wire, with precise and reliable movement and a high degree of automation. The application of measurement and control network technology provides a guarantee for realizing the automation of the production process, improving product quality, and ensuring safe production. The layer winding machine measurement and control system based on the Modbus protocol adopts a bus structure and RS-485 serial bus communication. Through real-time precise control via the network, the winding accuracy and automation level are improved. The implementation of active wire opening technology compensates for the shortcomings of similar domestic products. The equipment has been used in the field and has shown stable performance and reliable operation. Keywords Programmable Logic Controller; Frequency Converter; Network Measurement and Control The application of measurement and control network technology provides a guarantee for realizing the automation of the production process, improving product quality, and ensuring safe production. The Modbus communication protocol has the characteristics of strong error detection capability, large data transmission capacity, and good real-time performance, and has become a widely used communication protocol in the field of automation. Through this protocol, control equipment from different manufacturers can be connected to form an industrial network for centralized control and data sharing. Currently, foreign-made layer winding machines are highly automated, with precise automatic wire arrangement, active wire release, and high winding quality, but they are expensive. Domestically developed layer winding machines have unstable automatic wire arrangement and require manual intervention; most rely on passive wire release, resulting in unstable winding quality and low production efficiency, and none utilize network measurement and control. This paper addresses the control scheme for the wire storage mechanism's material level and the layer winding machine measurement and control system based on the ModbuS protocol. It adopts a bus structure and uses real-time precise network control, effectively solving the technical challenges of constant tension layer winding control and active wire release. It achieves adaptive speed control for wire winding, automatic length-based stopping, and other functions, improving the winding accuracy and equipment success rate, while remaining inexpensive. 1. Structure and Function of the Measurement and Control Network With the surge in demand for various brazing wire products (such as welding wire, motor and transformer windings), there is an urgent need for high-precision and highly automated continuous winding equipment to improve productivity and product quality. Therefore, accelerating research into high-precision winding technology based on fully digital AC servo systems is imperative. 1.1 Overall Structure of the Measurement and Control Network The overall structure of the layer winding machine measurement and control system based on the Modbus protocol is shown in Figure 1. It includes a central control unit, a take-up measurement and control unit, a tension measurement and control unit, a guide-opening measurement and control unit, a linear motion unit, and a human-machine interface system. 1.2 Structure and Function of Each Network Node Central Control Unit (PLC): Processes the data transmitted from each unit and controls the execution actions of each unit. Take-up Measurement and Control Unit: Measures the speed of the spindle motor using an encoder, and controls the take-up frequency converter setpoint using the PLC. Tension Measurement and Control Unit: Monitors the position of the floating roller (i.e., the material level) to reflect changes in the welding wire tension. The material level is divided into 9 states, and fuzzy control is used to track and adjust the material level to keep the floating roller in the optimal position. Guide-Opening Measurement and Control Unit: Controls the guide-opening motor according to tension changes to achieve active guide-opening function. Linear Motion Unit: Uses a Delta servo motor as the actuator to maintain the welding wire winding angle. Human-Machine Interface System: Uses a Delta touchscreen to set various production parameters and monitor system operation status. It provides alarm prompts in case of faults and uses an RS-232 interface connection. 2. Introduction to the Communication System The Modbus communication protocol is widely used in industrial control. Its simple and universal protocol structure is supported by most industrial control systems. The Modbus standard defines the application layer message transmission protocol at Layer 7 of the 051 model. It also standardizes the protocol on serial links to facilitate querying and responding between a master node and multiple slave nodes. The Modbus serial link protocol is a master/slave protocol located at Layer 2 of the 051 model. The Modbus application protocol at Layer 7 of the 051 model defines simple Protocol Data Units (PDUs) independent of the communication layers below it. The Modbus protocol mapping for RS-485 bus networks involves the master node initiating a Modbus transaction constructing a Modbus PDU, and then adding additional fields to construct the Modbus serial link communication PDU. Modbus communication is always initiated by the master node. The master node sends query commands to slave nodes and processes the responses. Slave nodes do not actively send data or communicate with other slave nodes unless they receive a request from the master node. The master node initiates only one Modbus transaction at a time. 2.1 Protocol Format The Mdobus protocol defines two serial transmission modes: RTU mode and ASCII mode. It specifies the serial transmission method of message field information bits on the line, and determines how data information is formed into messages and how messages are decoded. This system uses RTU mode. Each SBit byte in the message contains two 4-bit hexadecimal characters, as shown in Table 1. The main advantage of this method is that it can transmit more data than ASCII mode at the same baud rate. Message transmission in this mode must begin with a pause interval of at least 3.5 character times. During transmission, the network device continuously monitors the network bus, including during the pause interval. When the first field (address field) is received, the corresponding device decodes the subsequent transmitted characters. Once there is a pause of at least 3.5 character times, the message ends. 2.2 Check Code (CRC) The host or slave can use the check code to determine whether the received information has an error. The error detection field contains a 16-bit value (implemented using two 8-bit characters). The content of the error detection field is obtained by performing a cyclic redundant detection method on the message content. The CRC field is appended to the end of the message, and the low byte is added first and then the high byte. Therefore, the high byte of the CRC is the last byte of the sent message. Error verification adopts the CRC-16 verification method. The CRC check code is calculated as follows: 2.3 Communication program compilation and parameter setting 2.3.1 Human-machine interaction system 2.3.1.1 Main screen (1) There is a "weight CLR zeroing" button on the operation panel. When this button is pressed, the weight of the wound welding wire is zeroed; if it is held down for more than 35, the cumulative weight is zeroed (the delay function is implemented by the PLC). (2) The main screen has data such as "preset weight, welding wire diameter, wound weight and cumulative weight". (3) There are three sub-screen switching buttons: "user parameters" (see Table 4), "process parameters" and "mechanical parameters". 2.3.1.2 Sub-screen (1) Mechanical parameters: set the center angle input of the wiring and the lag angle input of the wiring. (2) Frequency compensation setting for the lead-out inverter: The frequency compensation value for high material level lead-out, medium-high material level lead-out, medium-low material level lead-out, and low material level lead-out can be set. (3) Angle sensor alarm and wire breakage alarm stop. (4) Welding wire specific gravity setting. 2.3.2 Inverter The inverter is Delta VFD-B series. There is one inverter driving each of the take-up and lead-out motors. The two inverters and the programmable controller comply with the Modbus communication protocol. The parameter settings of the inverter are shown in Table 5. 2.3.3 Programmable controller The programmable controller is Delta DVP-SX model. This machine is a 01-point (4DI+ZDO+ZAI+ZAO) special host with a built-in 2-digit seven-segment display module that directly corresponds to the internal register. The expansion module is DVP06X-H analog input/output hybrid module. The communication program between the programmable controller and the inverter is shown in Figure 2. The flowchart of the master node accessing the slave node is shown in Figure 3. 3. Conclusion Measurement and control systems are increasingly becoming distributed and networked. A Modbus-based network measurement and control system has been fully implemented on the winding machine. An RS-485 serial communication bus is used between the master node and each slave node, simplifying the wiring of the measurement and control network, ensuring stable and reliable signal transmission, and achieving excellent tension control results through the use of fuzzy control algorithms, greatly improving winding accuracy and automation. The measurement and control network can be managed using an enterprise LAN, and remote measurement and control functions can be achieved by connecting to the Internet through a gateway. This integrated development of production process control systems and information management systems enables comprehensive enterprise automation. The equipment operates well in the field, is stable and reliable, and is easy to operate, possessing broad market prospects. References [1] Wen Keqiang. Application of Modbus communication protocol in L(5) and PLC communication [J]. Petrochemical Automation, 2005, 6: 65-68. [2] Song Ye et al. Implementation of PLC communication based on MODBUS protocol [J]. Yunnan Hydropower, 2005, 21(4): 61-63. [3] Yan Heheng et al. Analysis of Modbus key technologies and node development [J]. Automation Technology and Application, 2006, 25(5): 49-51.