Fieldbus control network
Fieldbus, as a field control network technology, is considered an extension of public data networks in the field of motion control. Its rise has provided new opportunities for the development of automation technology itself. Fieldbus can transmit digital signals using various media (multiple wired and wireless methods). Up to dozens of automation devices can be connected to just two wires, saving a significant amount of cabling, cable trays, and connectors. This reduces the workload of system design, installation, and maintenance. Fieldbus forms a truly distributed, complete control system in the field, improving the reliability of the control system and enriching the information content of the control devices. It creates conditions for control information to enter the public data network, connecting field control devices and their connections to higher-level control management networks, facilitating the integration of integrated control and management networks with data networks, and enabling remote signal transmission and remote automatic control.
1. Fieldbus is a control system framework.
Fieldbus control systems are a new generation of distributed control systems built on fieldbus technology, characterized by a flattened network structure, openness, interoperability, completely decentralized conventional control functions, and a unified control strategy configuration method.
2. Typical applications of fieldbus motion control systems:
PC + Independent Digital Motion Controller + Actuator = Open Motion Control System
Touchscreen + Independent Digital Controller + Actuator = Open Motion Control System
The two structures described above represent the development direction of servo control systems and motion control technology. They fully utilize the resources of PCs and touchscreens, with third-party software developing the user application program. The generated program instructions are then transmitted to the motion controller, which continuously translates and generates updated position commands (motion curves) and sends them down to the driver via a communication bus. The motor driver then transmits control current to the motor, thus completing the required positioning. In a multi-axis system, one controller can control multiple motors or drivers. The servo motor is the primary actuator, performing the specific actions. The bus connects distributed measurement and control devices and drive control devices with communication capabilities as network nodes, forming a control network that can communicate information and jointly complete the automatic control task.
Fieldbus control bus data transmission method
Development Trends of Fieldbus Motion Control Systems
New Force in Fieldbus Development
Ethernet industrial automation systems are evolving towards networked, intelligent, and real-time control, making communication crucial. Users increasingly demand unified communication protocols and networks. On the other hand, the rapid development of information technologies such as Intranet/Internet requires enterprises to achieve comprehensive and seamless information integration from the field control layer to the management layer, providing an open infrastructure. The uncertainties and poor real-time performance inherent in Ethernet have been largely resolved through the use of intelligent hubs, the implementation of active switching functions, the introduction of priority systems, and full-duplex cabling. By increasing data transmission rates, carefully selecting network topology, and limiting network load, the probability of data collisions can be minimized.
Currently, some international organizations are working to promote Ethernet into the control field. This standard will enable networks to see "objects".
Frontiers of Fieldbus Applications
Embedded networked motion control systems (NCS) utilize motion control (servo) to manage the position, speed, and other parameters of mechanical moving parts in real time, ensuring they move according to a predetermined trajectory and specified motion parameters. An open-architecture motion control system is a modular, reconfigurable, and expandable hardware and software system.
The diagram above illustrates the architecture of an embedded motion controller. As shown, the controller is divided into two main parts: a network communication module and a motion control module. The network communication module connects directly to the Internet and receives control commands from the console according to a pre-defined communication protocol, then passes these commands to the motion control module. The motion control module connects directly to the motor driver; after analyzing and judging the commands, it generates corresponding motor control signals and transmits them to the motor. Furthermore, the results of command execution are also returned to the network communication module, which then relays them back to the console via the network.
Key features of embedded motion controllers:
1. Motion axis expansion is achieved using a daughterboard on the controller. Multiple controllers can be networked using FiberOpticNetwork to control more axes. Stepper axes (pulse + direction) and servo axes (analog commands + position feedback) can be configured in combination.
2. Digital input/output expansion
3. Analog input and output expansion
4. Location feedback interface expansion (A/B/Z, SSI, SIN/COS)
5. Fieldbus interface expansion: CAN, SERCOS, Ethernet, ProfiBus, DeviceNet, ModBUS, HostLink, etc.
"Embedded Ethernet field devices and embedded Internet servers will soon become 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 for future control networks and will become the dominant fieldbus. However, fieldbus technology will not easily exit the existing market. Various fieldbuses can complement each other's strengths and weaknesses, leading to further improvements. Each fieldbus has its own technological focus and application area, exhibiting strong complementarity and authority in certain aspects. The coexistence of multiple fieldbuses is detrimental to both user and manufacturer investments. Numerous bus standards are tantamount to having no standards at all. This reflects the flourishing development and diversification of fieldbus technology.
Networked motion control system (NCS)
Networked control systems require fieldbuses used in the control field to be high-performance digital interconnected networks with interoperability and openness. Digital interconnection is a fundamental characteristic of networks. Interoperability requires the use of unified standards and protocols. Openness refers to the technology being publicly available and widely used. Currently, the coexistence of multiple fieldbus standards is a settled matter.
Different companies, driven by their own interests, have monopolized the standard-setting process, hindering the widespread adoption of fieldbus technology. Currently, Ethernet technology is the most suitable for the characteristics of fieldbuses in network control systems, and therefore many companies have already introduced Ethernet into their industrial control networks.
"The network is the controller."
The automation systems from Germany's JetterAG, Israel's ELMO's MAESTRO, and the UK's TRIO are innovative, featuring distributed intelligent control systems based on 100Mb/s Ethernet, proclaiming the idea that "the network is the controller."
1. Expanding using the UK TRIO controller
2. Expand using the Israeli MAESTRO controller
Its characteristics are:
(1) Similar to the Internet structure, real-time data transmission does not require programming and does not need to consider the network hierarchy;
(2) For users, there is only one set of data and one program. All data only needs to be expressed once in the network. Both the program and the data can be reused. 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 level;
(4) It can be connected to the Internet to achieve global networking of the entire factory;
(5) Ethernet is both a system bus connecting various intelligent modules and a field bus connecting field devices. There is no difference between internal and external communication. Hub technology is integrated into each controller, and internal communication is separated from external communication by allocating address space.
As early as 1998, Foxboro successfully used Ethernet I/O in its Micro-I/A automation system for the chlor-alkali plant of Bayer AG in Germany. Ethernet integrated all field devices, controllers and PC workstations into a highly reliable, low-cost real-time control information network.
While industrial Ethernet networks can convert protocols such as Profibus, Devicenet, Modbus, ControlNet, and CANopen to TCP/IP, applying multiple different protocols to the same network and allowing them to communicate with the same host at the same time, it does not truly solve the problem of universal standards.
TCP/IP
TheTechnology-TCP/IPStack&Ethernet
EthernetDaughterFunctionalBlockDiagram
System Components Based on Ethernet and Fieldbus 1
