1. Introduction In modern industrial automation production, various devices need to exchange information and coordinate to complete automatic control functions, which requires network support. Based on this, Rockwell Automation has introduced an open network composed of Ethernet, ControlNet, and DeviceNet. DeviceNet is a low-cost communication link that connects programmable controllers directly to "smart" devices such as sensors, buttons, motor starters, simple operator interfaces, and frequency converters via a single wire. It is easy to install and debug and has been widely used in industrial automation production systems. ControlNet typically transmits large amounts of I/O and peer-to-peer communication information, exhibiting determinism and repeatability. It tightly connects controllers and I/O devices, enabling multiple controllers to share input data and achieve peer-to-peer communication. Ethernet, using TCP/IP as its transmission protocol, is an open information network. As the highest layer of the automation network, it can process and manage data and information collected in the field. When implementing network control, Rockwell Automation's SLC500 series programmable controllers can be used to easily connect DeviceNet to Ethernet. This paper introduces an experimental AC speed control system based on Rockwell Automation's open network, enabling a PC to control and monitor the inverters in the underlying device network using only an Ethernet network card. This system has a simple network structure and does not use a control network, but this simple and effective method can be extended to the design of other automation systems. 2 Ethernet Integrated Control System 2.1 Introduction Rockwell Automation's three-layer network structure provides an ideal solution for industrial automation. In complex process control systems, multiple controllers and human-machine interfaces require a large amount of data transmission, making a control network essential. Its producer/consumer data exchange method enhances network transmission speed. However, in situations where multiple controllers do not need coordinated control, the control network can be simplified, making control simpler and easier to maintain. A programmable logic controller (PLC) can replace the control network, connecting the device network and Ethernet. This effectively reduces costs and achieves effective network control. 2.2 Device Network Fieldbus The device network fieldbus is a low-cost, high-performance industrial device network with the following characteristics: The device network uses the internationally standardized Controller Area Network (CAN) protocol, establishing the device network's application protocol. It features open technical specifications and inexpensive communication components, resulting in significantly lower development costs compared to other fieldbuses. The device network utilizes a manufacturer/consumer communication model, improving network communication efficiency. Any device on the device network (manufacturer) only needs to send a message once; other devices (consumers) can accept and use the message if needed. The I/O messages provided by the device network are suitable for data with high real-time requirements and control orientation. However, the transmission speed of the device network is not high, with three speed options: 500Kbps, 250Kbps, and 125Kbps. Up to 64 devices can be connected to the network. Devices can be freely connected or disconnected during adjustment and diagnostics, and the Device Manager software allows for flexible management and debugging of the device network. 2.3 Industrial Ethernet Rockwell Automation's Industrial Ethernet supports both real-time and non-real-time messages. Real-time message exchange is based on the manufacturer/consumer communication model and can be used for real-time I/O control. Ethernet uses a carrier sense/error detection communication protocol. To reduce network collisions, the following aspects should be considered: To reduce packet collisions on Ethernet, full-duplex switched Ethernet can be used. This makes real-time I/O packet transmission more stable. Due to the existence of IP broadcast packets, using IGMP snooping multicast filtering technology can more effectively utilize network bandwidth. Port mapping technology between Ethernet and the underlying network is a prerequisite for achieving real-time transmission. 3 Design of AC Speed ​​Control Remote Control System 3.1 The structure of the experimental system is shown in Figure 1. The 1203-GK5 is an intelligent communication module that can connect various SCANport devices to DeviceNet. The 1305 frequency converter has a SCANport interface, so the 1305 frequency converter can be connected to the DeviceNet via the 1203-GK5. The DeviceNet and Ethernet are connected together through SLC500. SLC500 is a general term for a series of small programmable controllers. The one used here must have a 5/05 processor and use the 1747-SDN module. The 1747-SDN module is a scanning module on the device network, scanning and detecting devices on the network. The 5/05 processor has an Ethernet interface and can be directly connected to the Ethernet. Thus, the SLC500 is the sole device connecting the device network and the Ethernet. Figure 1 shows the system structure. 3.2 Network Data Transmission: The accompanying software RSNetWorx for Devicenet can be used to easily configure the device network. When setting up the 1747-SDN scanning module, the author chose discrete I/O to assign input/output mapping tables to the inverters on the network, and the refresh time can be set to 2ms. After configuring the device network, the PC on the Ethernet can use the RSlogix 500 programming software to program the SLC500. By controlling the SLC's input/output files O0 and I1, simple control bit settings such as forward rotation, reverse rotation, jogging, and error clearing can be achieved for the inverter. However, to achieve visualized monitoring and control by the host computer, a graphical human-machine interface (HMI) software like RSview32 must be used. The transmission of control and feedback data is entirely handled by the I/O mapping table between ports. As shown in Figure 2, commands from the PC are transmitted to the SLC, changing the corresponding input/output files O0 and I1. The scanning module 1747-SDN, based on the established I/O mapping table, maps the data in O0 and I1 to the corresponding 1203-GK5 communication modules on the device network, and then directly maps them to the frequency converters via the SCANport interface. The frequency converters on the device network communicate with the scanning module 1747-SDN in a polling manner. The 1747-SDN sends a query message to a frequency converter, and the queried frequency converter sends a response message to the 1747-SDN. The 1747-SDN then scans the entire device network according to the pre-set scan list. This establishes a port mapping channel. A similar channel is also established when providing feedback on the frequency converter's operating parameters. One scan cycle can scan all devices on the network and refresh their input/output mapping status. Since the O0 and I1 files in the SLC each have 32 words, 31 of which are usable, and each inverter has 2 to 10 adjustable input/output words, similar port mapping can be achieved through the MO (output) and MI (input) files of the SLC when there are many inverters on the network. The MO and MI files each have 150 words. 4. Experimental System Operation Results and Analysis After configuring the host industrial control computer using RSview32 HMI software and RSlinx communication software, it can collect data transmitted from the SLC. It also monitors and controls the inverters on the network by manipulating the O0 or I1 files. RSview32 provides a visual graphical representation of the entire system's changes as curves. Figure 3 shows the inverter's output current, voltage, and frequency curves during the entire process of DC braking immediately after the motor reaches the given frequency during no-load start-up. A 2.2kW squirrel-cage motor is used, and the frequency converter is 1305-BA09A with a power of 4kW. The frequency converter settings are as follows: acceleration time is 2s; given frequency is 30Hz; DC braking voltage is 30V, and time is 2s. Figure 3 shows the DC braking state curve of the frequency converter. The voltage and current during braking can be clearly observed in Figure 3. Correspondingly, Figure 4 shows the process of free stopping. It can be seen that when stopping in this way, the output voltage and current of the frequency converter are both zero, and the motor stops based on inertia. Figure 4 shows the free stopping state curve of the frequency converter. RSview32 is a convenient system control software, but its refresh time is 50ms, so the accuracy of the displayed curve is not high. There is a certain lag in the response of the lower-level device network to the upper-level industrial control computer commands, but this solution can meet the needs of most real-time control systems. The transmission speed of the device network is 125Kbps, and the time for each scan is less than 10ms. The main delay is on the Ethernet. Instead of using routers, the Ethernet system uses a simple hub connection, failing to utilize IGMP snooping multicast filtering technology to effectively prevent network collisions. Therefore, the uncertainty of Ethernet data transmission latency increases the 50ms delay. During system testing, the SLC500 can be programmed using RSlogix500 software on a PC. Complex motor coordination control can be achieved by reading and writing O0 or I1 files (already mapped to the frequency converter). RSview32 can then be used to monitor and control the entire operation process through an intuitive graphical interface. This AC speed control remote control device is stable and reliable, demonstrating the concept and significance of network control. The system configuration method can serve as a reference for remote control system design.