In 2005, SAIC-GM-Wuling Co., Ltd. invested 500 million yuan to build the largest western painting workshop in China. The workshop's electrical control system was designed, manufactured, and installed based on GM North America's CCH1 and CCS2 standards. Advanced production lines, first-class electrical control products, and standardized application software not only ensured safe production in the painting workshop but also maximized the fulfillment of flexible production needs. Electrical Composition The electrical control system network of the western painting workshop (hereinafter referred to as the western painting workshop) is divided into a two-layer architecture. The upper-layer control system is connected via Ethernet (EtherNet), and the lower-layer controlled systems are connected via DeviceNet (DeviceNet). 1. Upper-layer Control System (See Figure 1) Figure 1 Upper-layer Control System Structure Diagram The upper-layer control system equipment includes four major upper-level systems and AB's Logix5561 series PLC. The four upper-level systems are: PMC (Production Monitoring and Control System) server, used to monitor the status of machinery and equipment and the number of vehicles in the workshop area; AVI (Automatic Vehicle Identification System) server, used to track vehicles and exchange data with robots; QAS (Quiet Light System) server, used to help workers on the assembly line complete reliable car assembly tasks within a certain production cycle; and PHS (Process Monitoring System) server, used to monitor the process equipment in the workshop, such as pretreatment and DC power supplies. The central control room computer and field touchscreens form a network, transmitting data via Ethernet to monitor and manage the production line. 2. Lower-level controlled system (see Figure 2) Figure 2 Lower-level control system structure diagram The lower-level controlled system scheme is relatively simple, with a concise structure and convenient maintenance. Its main equipment includes: signal acquisition devices (AB's 1794 FlexI/O, Turck's FDNL8-point input module, etc.); frequency converters (SEW's MFD series frequency converters), which adopt distributed control and have the advantages of reliable operation, convenient maintenance, and safety; and network bridges (Turck's FDN series), used to build a platform for exchanging data between two PLC architecture devices. The lower-level control system adopts DEVICENET fieldbus technology, which has good openness and integrity and has a comprehensive network protocol; the base station and each site in the field are connected into a whole through device network cables, ensuring data reading and writing between PLCs and substations, realizing data information sharing, and thus ensuring fully automated production, sequential start-up, and sequential shutdown. 3. Network Architecture AB's workshop network architecture typically has three layers. The upper-level system communicates via Ethernet; the middle-level system communicates via ControlNet. Here, the middle-level control devices usually refer to the PLCs of each subsystem; the lower-level control system communicates via DeviceNet. In the West Coatings project, only Ethernet and device networks were used. However, according to relevant sources, GM North America already has factories that use Ethernet to control all electrical equipment. Safety First in Production The company always prioritizes safety in production. Considering the inherent dangers of the conveyor system, the workshop is equipped with safety door control systems, light curtain control systems, on-site operation stop buttons, on-site emergency stop buttons, dual-channel safety relays (Pilz brand PNOX series products), and contactors forming a circuit. These safety protection measures effectively ensure safe and efficient production. Here, we will briefly introduce the on-site safety protection circuit of the main control cabinet, taking the area of ​​the topcoat spray booth exit elevator as an example. The logic diagram of the safety protection circuit of the main control cabinet consists of three parts, as shown in Figure 3. When the on-site emergency stop button, light curtain, or safety door is activated, the 380V power supply and 24V DC safety power supply are automatically disconnected; when the on-site operation stop button is activated, the 24V DC safety power supply is disconnected. Taking the E800 safety relay as an example, the reset circuit of the E800 connects the normally closed contacts of two contactors (E828 and E832) in series. When the emergency stop button is pressed, the output of the E800 disconnects, and E828 and E832 also disconnect. When the emergency stop button is pressed again, the E800 receives input and checks the reset circuit. At this time, E828 and E832 must disconnect for the E800 to reset, thus checking whether E828 and E832 are working properly. Figure 3 shows the logic diagram of the safety protection circuit of the main control cabinet , meeting the needs of flexible production . Due to the continuous increase in production and sales, the company's newly developed extended model is in short supply in the market. Given the limited production capacity of the company's eastern factory, we conducted a passability test of the extended vehicle at the western coating plant. The western coating plant's transport system uses a skid conveyor line to transfer the vehicle body and complete the painting process. During the process of moving the extended cart through the workshop, we discovered an interference between the forks of the forklift transfer machine (HYZ-1) and the base spring of the extended cart at the junction of the body skid (BDC skid) and the electrophoresis skid. Therefore, the extended cart needs to be moved 315mm further towards the roller bed process direction, as shown in Figure 4. Figure 4 shows the Xitu mechanical transport system, where the extended cart needs to be moved 315mm further towards the roller bed process direction. To address this, a new clamping device needs to be added to the roller bed, driven by a motor. The specific operating steps of the extended cart are as follows: When the extended cart is in position on the rotating roller bed HXG_18, after the photoelectric detection switch confirms it is an extended cart, it is moved to the position shown in Figure 4. The new clamping device activates, clamping the skid, and then the body is transferred. Here, we use a SEW frequency converter with distributed field control of the motor to drive the clamping device. The SEW frequency converter (MFD series) consists of a base, maintenance switch, frequency converter module, and bus interface module. The SEW frequency converter is controlled by 24V DC, and the cable has 4 cores. Two cores provide 24V DC power to the inductive switch, while the other two cores provide 24V DC safety power. As mentioned in the main control cabinet's safety protection circuit description, the inverter stops outputting if the safety power is lost. The motor brakes used in the workshop are all 220V DC brake coils; no rectifier is needed in the motors. Therefore, the brake wire in the cable from the inverter to the motor is already DC. The SEW inverter's module parameters are adjusted directly on the module. The parameters adjusted in this project include maximum frequency, minimum frequency, acceleration/deceleration time, allowable device network control, allowable over-power operation, allowable individual brake coil opening, allowable motor fast start and thermal protection via TH. Since control is via device network, a station for this device needs to be set up on the back of the bus interface module. After connecting the inverter parameters and field wiring, the field work is complete. Next, AB's RSNetWork software needs to be used to configure the new device. After the above configuration is completed, the SEW inverter can communicate with the CPU via the bus, and the program can be modified for operation. Standardized Application Software The transportation procedures for Xitu are generated based on a common North American standard template. Each piece of equipment in the program corresponds to a standard template. Generating the transportation procedures requires inputting the name, order, and area of ​​each piece of transportation equipment into an Excel spreadsheet. The data type of the equipment is selected from the user-defined data types. The completed Excel spreadsheet is then imported into the Logix5000 programming software, which automatically generates the program. The degree of automation requires only minor modifications from the programmer before it can be used. Taking the extended vehicle modification project as an example, the data type of BSG-3 (see Figure 4) is the user-defined data type ac-LWP (roller bed with auxiliary lifting platform), defined according to the standard template. When using it, we only need to open the Logix5000 programming software, call the ac-LWP module in the User-Defined menu, and the degree of automation requires only minor modifications.