As a field control network technology, fieldbus is regarded as the extension of public data network in the field of motion control. Its rise provides a new opportunity for the development of automatic control technology itself. Fieldbus can use a variety of media (a variety of wired and wireless mode) to transmit digital signals. In two wires can be connected to dozens of automatic control equipment, can save a lot of cables, slot frame, connecting parts. Reduce the workload of system design, installation and maintenance. Fieldbus forms a complete control system which is really scattered in the field, improves the reliability of the control system and enriches the information content of the control equipment. It creates conditions for the control information to enter the public data network, communicates the connection between the field control equipment and the higher control management network, facilitates the integration of the control network and the data network, facilitates the remote transmission of signals and remote automatic control.
1. Fieldbus is a control system framework
Fieldbus control system is a new generation of decentralized control system based on fieldbus technology, which has flat network structure, openness, interoperability, complete dispersion of conventional control functions, and unified control strategy configuration method.
2. Typical application of fieldbus motion control system:
PC+ independent digital motion controller + actuator = open motion control system
Touch screen + independent digital controller + actuator = open motion control system
These two structures are the development direction of servo control system and motion control technology. It can make full use of the resources of PC and touch screen, complete the development of user applications by the third-party software, and send the generated program instructions to the motion controller, which continuously translates the updated position command (motion curve) and sends it to the driver through the communication main line, and the motor driver will transmit the control electricity to the motor, so as to complete the positioning required by the command. In a multi-axis system, a single controller can control multiple motors or drivers. Servo motor is the main executive component, complete the specific action. The bus connects scattered measurement and control devices with communication ability and drive control devices as network nodes to form a control network that can communicate with each other and complete automatic control tasks together
The Ethernet industrial automation system is developing towards network and intelligent real-time control, so the communication has become the key, and the user's demand for unified communication protocol and network is increasingly urgent. On the other hand, the rapid development of Intranet/Internet and other information technologies requires enterprises to realize comprehensive seamless information integration from the field control layer to the management level, and provide an open infrastructure. As for the uncertainty and real-time performance of Ethernet is poor, has been the use of intelligent hub, active switching function, priority introduction and duplex wiring, and so on, basically solved. By increasing the data transmission rate, carefully choosing the network topology and limiting the network load, the probability of data collision can be minimized.
There are also a number of international organizations working to push Ethernet into control. This standard will enable the network to see "objects".
Embedded networked motion control system (NCS) Motion control (servo) is to control and manage the position and speed of mechanical moving parts in real time, so that they can move according to the expected trajectory and specified motion parameters. Open structure motion control system is a kind of modular, reconfigurable, extensible hardware and software system.
The figure above shows the architecture of embedded motion controller. It can be seen from the figure that motion controller is divided into two main parts: network communication module and motion control module. The network communication module directly connects to the Internet, and obtains control commands from the console according to the pre-determined communication protocol, and then gives the commands to the motion control module. The motion control module is directly connected with the motor driver. After analyzing and judging the command, the corresponding motor control signal is sent to the motor. In addition, the result of the command execution is also returned to the network communication module, which then returns to the console over the network.
Embedded motion controller main features:
1. Motion axis expansion The Daughter Board is used to expand motion axis on the controller. Multiple controllers can be networked using Fiber Optic Network to control more axes. Stepper shaft (pulse + direction) and servo shaft (analog instruction + position feedback) can be mixed configuration.
2. Digital input and output expansion
3. Expansion of analog input and output
4. Position feedback interface extension (A/B/Z, SSI, SIN/COS)
5. Fieldbus interface extension: CAN, SERCOS, EtherNet, ProfiBus, DeviceNet, ModBUS, HostLink, etc
"Field devices with embedded Ethernet and embedded Internet servers will soon be a reality," predicts Horst Kohlbert, network product manager at Siemens Energy & Automation, suggesting that industrial Ethernet is about to enter the field control level.
Ethernet is the best solution to control network in the future, and it will become the dominant fieldbus, but fieldbus technology will not easily quit the existing market, and various fieldbuses can learn from each other to further improve. All kinds of fieldbuses have a certain technical focus and application field complementarity, more authoritative in a certain aspect. The coexistence of multiple fieldbuses is not conducive to the investment of users and manufacturers. A large number of bus standards equals no standards. The blooming and flourishing development of fieldbus technology.
Network control system requires that the field bus used in the control field is a digital interconnection network with high network performance, which has interoperability and openness. Digital interconnection is the basic characteristic of network. Interoperability requires the adoption of uniform standards and protocols. Openness means that technology is open and widely used. Now it is a foregone conclusion that multiple fieldbus standards coexist.
Different companies, for their own interests, control the development of standards, so that fieldbus is not widely used. At present, Ethernet technology is the most in line with the characteristics of network control system fieldbus technology, so many companies have introduced Ethernet into industrial control network.
Germany's Jetter AG's Automation system, Israel's ELMO's MAESTRO, British company TRIO's innovative idea, it is based on 100Mb/s Ethernet distributed intelligent control system, declared that "the network is the controller" view.
1. Take advantage of British TRIO controller expansion
2. Extend with Israeli MAESTRO controller
Its characteristics are:
(1) The structure similar to the Internet, the real-time transmission of data does not need programming, do not need to consider the hierarchy of the network;
(2) For users, there is only one set of data and one program, and all the data only needs to be expressed once in the network. Both programs and data can be reused, and the network plays the role of a real server;
(3) There is only one Ethernet bus for direct communication from the sensor to the factory management;
(4) It can be connected to the Internet to realize the global networking of the whole factory;
(5) Ethernet is not only a system bus connecting to various intelligent modules, but also a field bus connecting to field equipment. There is no difference between internal and external communication here. Hub technology is integrated in each controller, and the internal communication is separated from the external communication by allocating address space.
Back in 1998, Foxboro successfully used Ethernet I/O from its Micro-I/A automation system in Bayer AG's Chlor-alkali plant. Ethernet integrates all field equipment, controllers, and PC workstations into a highly reliable, low-cost, real-time control information network.
Industrial Ethernet network can be Profibus, Devicnet, modbus, controlnet, canopen protocol to TCP/IP, the application of a variety of different protocols in the same network, and let them and the same host at the same time dialogue, But it doesn't really solve the problem of universal standards.
