简体中文
Why study EtherCAT (the future star of Industrial Ethernet)
EtherCAT Is an industrial Ethernet communication protocol, the performance is far better than the traditional fieldbus, such as CAN, Profibus, etc.
In the field of industrial automation, servo motion control system, as the core component of robot and CNC equipment, is particularly important. At present, the progress of technology in various fields promotes the continuous improvement of the demand for industrial equipment. The industrial fieldbus used in the traditional servo control system is limited by the old protocol technology and hardware specifications, resulting in more and more difficult to meet the data transmission speed, real-time and other aspects to meet the gradually increasing system bus data transmission demand. The application of the multi-axis servo control system based on the new fieldbus technology has become a trend in the field of automation control.
In the previous industrial network, the traditional fieldbus is the most widely used technology in the industrial network. According to IEC 61158, fieldbus is defined as a digital, serial, bidirectional, multi-node data bus between field equipment or instrument installed in the production process area and the automatic control device or system in the control room. The purpose of the IEC61158 international standards is to unify the existing multiple bus standards into a common standard. If so, then on the one hand, manufacturers can be more convenient production equipment, on the other hand, users can easily choose suitable functional equipment without having to be trapped in the products under the single bus standard. But the fact is that the major companies did not form a consensus, the result is still a scuffle. Big companies after years of development, due to their respective bus products have occupied a certain market share, do not worry about incompatibility between multiple bus products will affect sales, and does not change to the user choose equipment, users can't really according to their own cost and need to consider choose equipment, but more rely on the requirements of choose equipment standard, flexibility is poor. These have hindered the further development of industrial control and automation systems, and the congenital deficiency of the traditional fieldbus needs to be solved urgently. In addition to compatibility, in the previous industrial network, the traditional fieldbus has mutual connection, connectivity, operation and control, and so on need to be solved, and the traditional fieldbus its transmission performance, response time, rate and other aspects can not meet the people standards in the industrial aspect.
Therefore, the development of a better industrial communication technology in the field of automatic communication has become an urgent demand in the field of automatic communication.
Among many communication technologies, Ethernet technology used in the field of computer communication has attracted people's attention. Ethernet has the advantages of easy connection, convenient connectivity, and the price is relatively ideal, the transmission speed can meet the standards required by industrial control, these advantages make it the first choice for the development of industrial networks. General industrial Ethernet is defined as: technically compatible with commercial Ethernet, but must meet the product design on the industrial field of real time, reliability, interoperability, anti-interference, essential security, environment, adaptability, etc of needs, is developed after the fieldbus, is widely recognized as promising a kind of industrial communication network. Industrial Ethernet adopts TCP / IP protocol and is compatible with IEEE 802.3 standard, but adds a unique protocol (IEEE 802.3/IEEE 802.3u usually) in the application layer.
Although, the traditional Ethernet technology uses media access as a competitive shared media technology (CSMA / CD) has a high efficiency on intermittent transmission and sudden long message transmission. However, Ethernet has great randomness and cannot bear large network load. When the number of nodes increases and the data traffic increases, the efficiency of Ethernet decreases a lot. Data indicate that the effective bandwidth utilization rate of Ethernet does not exceed 40%. Therefore, the Ethernet cannot be used directly for automated communication, and its transmission mode needs to be modified.
Compared with commercial Ethernet, the technical characteristics of industrial Ethernet are reflected in the special requirements for the following aspects.① High real-time performance and good time certainty.② Transfer information is mostly short frame information, and information exchange frequently.③ Strong fault tolerance, good reliability and security.④ The control network structure is highly decentralized.⑤ The control network protocol is simple, practical, with high work efficiency.⑥ The intelligence of the control equipment and the autonomy of the control function.⑦ Efficient communication with the information network, easy to achieve the integration with the information network.⑧ Equipment reliability and environmental adaptability.⑨ Long-distance transmission.⑩ bus power supply.
There are three ways to realize industrial Ethernet, namely, TCP / IP mode, Ethernet mode, and modified Ethernet mode.among, The TCP / IP approach still uses the traditional TCP / IP protocol stack for communication, Reduce the uncertainty during data transfer by reasonable scheduling in the upper layer, In this way, Mobus / TCP, Ethernet / IP and other protocols for data transmission is not high; Ethernet approach with standard Ethernet devices, Such a transmission of ordinary Ethernet data can still use the TCP / IP protocol, While process data for transmitting control signals are transmitted using specialized protocols, In this way are Ethernet Powerlink, PROFINet RT and China EPA (Ethernet for Plant Automation), Can achieve a relatively high real-time performance; Modified Ethernet mode for data transmission by a modified Ethernet protocol, And using specialized hardware to process the data, Such that the response time is less than 1ms, Its real-time and non-real-time data are also transmitted separately, Avoid data message conflicts completely, Proprotocols as SERCOS-III, PROFINetIRT and EtherCAT, EtherCAT Technology is an industrial Ethernet technology proposed and realized by German BECKHOFF Automation, Is currently the fastest industrial Ethernet solution.
(Figure:: comparison of broadband utilization)
It can be seen that the EtherCAT has an excellent effective data rate
A complete EtherCAT system can be divided into main station and from station two parts, main station using standard ethernet equipment data transmission, from station using dedicated control chip processing data, support line, tree or star topology structure, with high performance, flexibility and cost advantage, EtherCAT protocol compared with common field bus protocol has the following characteristics:
(1) EtherCAT has a wide range of adaptability, whether it is a simple 16-bit microprocessor or a complex PC system, as long as the control unit with an ordinary Ethernet controller can constitute the EtherCAT main station.
(2) EtherCAT is a special Ethernet protocol, and the data using this protocol can use the commonly used Ethernet devices, which can save the cost of equipment update.
(3) The EtherCAT can flexibly choose the slave station type, whether a complex node with a microprocessor or a simple node with only a 2-bit I / O can be used as a EtherCAT slave station.
(4) EtherCAT The data transmission rate is high, and by (2) the protocol data meets the standard Ethernet protocol, which can be transmitted through the standard Ethernet, and the Ethernet bandwidth can be fully utilized for user data transmission.
(5) EtherCAT Data refresh cycle is short, using special hardware to process data, data refresh cycle is very small, less than 100 μ s, can be used for devices with high response requirements.
(6) EtherCAT has good synchronization performance. The synchronization between devices is completed by the relevant registers of the dedicated hardware, and the clock synchronization accuracy between each station equipment can be controlled within 1 μ s.
Therefore, various industrial Ethernet technologies based on Ethernet for industrial transmission were developed, which is one of the most popular industrial Ethernet standards today.
