Abstract : This paper introduces a control system for a plastic window welding and cleaning production line based on CAN bus. The characteristics and design applications of CAN bus, the system's hardware structure, and control principles are discussed. Due to the adoption of all-digital CAN network technology, data transmission is secure and accurate, and the system is stable and reliable. Keywords : CAN bus; PCC; IPC; PANELWARE; protocol; fieldbus 1. Introduction With the continuous application of computer technology, communication technology, and network technology in industrial production and process control, the requirements for field signal transmission and data exchange in industrial control processes are becoming increasingly stringent. Because all-digital signal systems have advantages over traditional analog signals, such as strong anti-interference capability, high speed, and short construction cycle, digital fieldbuses have rapidly become a focus in the current industrial control field. Currently, there are various fieldbus technologies on the market, such as HART, PROFIBUS, and FF. Among them, CAN (Controller Area Network) fieldbus is a fieldbus standard launched by the German company BOSCH. According to the requirements of the ISO organization's OSI (Open Systems Interconnection) standard, it has a physical layer, a data link layer, and an application layer. The CAN bus is based on the token protocol and is physically a bus structure. The formulation of the protocol includes key technologies such as priority, state change and control transfer. This article introduces a production line control system based on the CAN bus, and specifically describes the actual application and characteristics of the automatic control products of B&R Company of Austria in the plastic door and window welding and cleaning production line through the CAN network. 2. Basic characteristics of CAN bus 2.1 Characteristics of modern industrial systems (1) Openness of the system. An open system means that the communication protocol is open, and the equipment of different manufacturers can be interconnected into a system and information exchange can be realized. Here, openness refers to the consistency and openness of relevant standards, emphasizing the consensus and compliance with standards. An open system gives the right to system integration to the user. Users can combine products from different suppliers into systems of any size according to their own needs and considerations. (2) Interoperability and interoperability. Refers to the realization of information transmission and communication between interconnected devices and the mutual replacement of equipment with similar performance from different manufacturers. (3) Intelligence and functional autonomy of field equipment. It distributes functions such as sensing measurement, compensation calculation, engineering quantity processing and control to field equipment. Therefore, the basic functions of automatic control can be completed by field equipment alone, and the operating status of the equipment can be diagnosed at any time. (4) Highly distributed system structure. It constitutes a new fully distributed control system architecture. It fundamentally changes the existing distributed control system architecture, simplifies the system structure, and improves reliability. (5) Adaptability to field environment. The system has strong error correction capability and can meet safety and explosion protection requirements. 2.2 Advantages of fieldbus (1) Saves hardware quantity and investment. (2) Saves installation costs. (3) Saves maintenance costs. (4) Users have a high degree of initiative in system integration. (5) Improves the accuracy and reliability of the system. (6) Simple design and easy reconfiguration. 2.3 Characteristics of CAN bus technology From the perspective of physical structure, CAN belongs to bus communication network, similar to BITBUS and RS485, but with essential differences. It is a network specifically used in the field of industrial automation, different from Ethernet and other management and information processing networks. Its physical characteristics and network protocol characteristics emphasize the underlying monitoring and control of industrial automation. It adopts the latest technology and unique design, and its reliability and performance exceed those of outdated field communication technologies such as RS485 and BITBUS. CAN has the following main characteristics: (1) CAN cards can be plugged into PC, XT, and AT compatible machines, which can be conveniently used to form a distributed monitoring system. (2) CAN can work in a multi-master mode. Any node on the network can actively send information to other nodes on the network at any time, without master or slave distinction, and the communication mode is flexible. This feature can also be used to easily form a (fault-tolerant) multi-machine backup system. (3) CAN uses non-destructive priority-based arbitration, which can meet different real-time requirements and effectively avoid bus conflicts. (4) CAN can transmit and receive data in several ways, such as point-to-point, point-to-multipoint (group), and global broadcast. (5) CAN adopts a short frame structure, with each frame containing 8 effective bytes, which results in short transmission time, low probability of interference, and short retransmission time. (6) Each frame of CAN information has CRC check and other error detection measures to ensure that the data error rate is extremely low. (7) Identification of fault nodes for temporary errors and permanent faults and automatic removal of fault nodes. (8) NRZ encoding/decoding method and bit stuffing (insertion) technology. (9) The communication medium uses twisted pair cable, with no special requirements. 3. Design and principle of the control system of plastic window production line (Figure 1) [align=center] Figure 1 System structure diagram[/align] 3.1 Design of control system The requirements of the plastic window production line are that the CNC three-axis welding machine, cooling center and CNC four-axis corner cleaning and seam cleaning machine are integrated into one unit, and the processing data and working status information are shared. According to the requirements of the factory, the welding machine and the cleaning machine can work at the same time to realize assembly line production, or they can be set to work separately. For this purpose, each welding machine and the cleaning machine is equipped with a human-machine interface to monitor the equipment operation status in real time. The actual production plan, based on the arrangements of the production scheduler, utilizes a dedicated data processing software package to generate instruction floppy disks to manage equipment operation. Each shift, operators only need to insert the floppy disk into the computer's floppy drive to achieve automated processing according to the processing parameters on the disk. As shown in Figure 1, the production line control system uses a complete set of automation system equipment from B&R to implement CAN fieldbus data processing. The welding machine uses the PROVIT2000 industrial control computer as the monitoring device. A PANELWARE (Human Machine Panel) is installed on the cleaning machine. The welding machine controller is PCC1, and the cleaning machine controller is PCC2. On the CAN network, the master station is the industrial computer, the programmable controller PCC, and the PANELWARE, and data communication between the master stations is achieved through the CAN network. The slave station is a transmission device, consisting of a servo driver (for servo motor positioning) and a frequency converter (for AC motor speed regulation). The slave station takes different station numbers, which are set sequentially as 1, 2, 3 (3-axis servo drive for welding), 4 (frequency converter to realize robot arm movement), 5, 6, 7, 8 (4-axis servo drive for cleaning). 3.2 Control Principle 3.2.1 Welding Machine Control Principle The control principle of the welding machine is as follows: The industrial control computer reads the information from the floppy disk and transmits it to the programmable computer controller PCC1 via the CAN bus. The operator places the pre-cut PVC profiles into the processing position. PCC1, based on the processing parameters, uses B&R's dedicated NCACTION function to transmit data through the CAN network, controlling the designated slave servo driver for linear positioning motion, and coordinating with other IO port outputs to achieve the heating and welding requirements. At the same time, the status information of the cleaning machine PCC2 is read through the NET2CAN function. If normal, the welded window frame is conveyed to the cooling center via the conveyor belt; if abnormal, the conveying is paused to prevent the stacked window frame from cooling in the cooling center, and then the robot arm transfers it to the cleaning machine to clean the fillet weld. 3.2.2 Cleaning Machine Control Principle: The cleaning machine control principle is as follows: PCC2 obtains the welding profile serial number based on the NET2CAN data exchange with PCC1, and displays the real-time working status on the human-machine panel via the CAN network. Using the B&R FRAME DRIVER frame communication software package, it simulates the CAN communication protocol of the multi-frequency variable motor, controlling the motor to achieve the reciprocating motion of the robotic arm. The robotic arm pulls the cooled window frame from the cooling center to the designated processing area, and then the pusher pushes the window frame into the triangular processing area. PCC2, based on the processing parameters, uses the NCACTION function to control the four designated slave servo drives via the CAN network to achieve CNC curve positioning according to linear or circular interpolation requirements. Combined with other workpiece actions, it achieves the purpose of cleaning inner corners, outer corners, and gaps. Simultaneously, the current status is written to the welding machine controller PCC1 via the NET2000 CAN-Write function to ensure information sharing of the processing status. 4. System Features (1) The production line master station is an industrial control computer, a human-machine panel, two PCC programmable controllers, and seven ACOPOS servo drives and one frequency converter drive. It has a very high system integration. (2) The master stations use B&R's general CAN network PVI transmission protocol. Different communication stations are set in the software to facilitate the interconnection between systems. The networking is simple and clear. (3) When the series products are used as slave stations, only the DIP switch needs to be set as the slave address. The dedicated CAN communication function is used with the master station, which has the advantages of reliability, high speed and simplicity. (4) When communicating with other products via CAN network, the B&R's unique free communication software package (FRAME DRIVER) can be used according to the CAN network communication protocol provided by the other party. Based on the communication object, data format and transmission rate, the other party's protocol can be compiled to achieve mutual connection and bidirectional data exchange. (5) The controller PCC and the servo and frequency converter drive are connected by CAN bus, saving a large number of signal lines required in the past. Meanwhile, the controller can save a lot of encoder signal acquisition modules and output control modules. (6) Due to the adoption of all-digital CAN network technology, data transmission is safe and accurate, avoiding the disadvantages of low accuracy and susceptibility to external environmental interference of analog signals. 5. Conclusion The production line has been successfully developed by Jinan Tianchen Machinery Co., Ltd., and has undergone strict testing in the factory. The operation effect is good. It also participated in the International Building Materials and Equipment Exhibition held in Beijing in September 2000 and was affirmed by the experts and representatives present.