EtherCAT
EtherCAT ( "Ethernet for Controller and Automation Technology" ) is a project initiated by the company Beckhoff real-time Ethernet. The method disclosed in IEC standard IEC61158 protocol is suitable for hard and soft real-time requirements in automation technology.
The focus of the development of EtherCAT were on short cycle times ( ≤ 100 microseconds ), low jitter for accurate synchronization ( ≤ 1 microseconds ) and low hardware cost.
- 2.1 Master
- 2.2 slave
- 3.1 Control and regulation
- 3.2 Measurement Systems
EtherCAT properties
Principle of operation
The standard Ethernet frame sent by the master ( IEEE 802.3) is not received as with other Industrial Ethernet solutions in every connection, then interpreted and copied over the process data. The EtherCAT slave devices read the data addressed to them while the frame passes through the device. Similarly, input data is inserted in the flow in the telegram. Here, a frame is not received completely, before it is processed, but the processing is started as early as possible. Shipping is also done with a minimum offset of a few bit times.
SVG animation, to see the principle of operation of the EtherCAT
Protocol
Shipped is optimized for process data EtherCAT protocol within a standard Ethernet frames using a proprietary Ethertype ( 0x88A4 ). The EtherCAT telegram may consist of several Subtelegrammen (EtherCAT commands) exist, each serving a particular memory area of up to 4 gigabytes logical process image.
The data sequence is independent of the physical order of the stations in the network, it can be addressed randomly. Broadcast, Multicast and communication between slaves are possible.
Topology
The transmission method of the EtherCAT is based on the full-duplex properties of Ethernet. On the cabling level EtherCAT enables a wide variety of topologies such as line, tree, ring, star, and combinations thereof. Linked to this are different communication characteristics such as line redundancy, Hot Connect segments, replacing devices with network or master redundancy with hot standby.
By combining topology variants with different network architectures such as subordinate or adjacent control systems with continuous synchronization thus results in many ways. Thus one does not need any additional switches.
The Fast Ethernet physics allows a maximum cable length is 100 m between two stations, the E-bus (LVDS ) is provided only for modular devices as the physical layer. For each line section, the signal variation can be individually selected. For longer distances or for complete electrical isolation between two slaves optical waveguides are used. With single-mode fiber up to 20 km between two nodes to be bridged. Since up to 65535 nodes can be connected per network segment, the entire network is almost unlimited.
Synchronization
Accurate synchronization is always a special significance when spatially distributed processes require simultaneous actions, such as where several servo axes are to simultaneously perform coordinated movements.
The most powerful approach for synchronization is the accurate alignment of distributed clocks. The time of the main clock via EtherCAT to the secondary clocks is sent and this readjusted term compensated. With EtherCAT, the main clock is a slave device, so that this no special hardware in the master is required. The synchronization accuracy is significantly less than 1 microseconds, with 300 participants and 120 m cable length deviations of ± 20 ns were achieved.
Performance
Due to the hardware integration in the slave and DMA access to the network card in the master the entire protocol processing is done in hardware and is thus independent of the duration of the protocol stacks, CPU performance or software implementation.
The bandwidth utilization is maximized, as not for each participant and each date a separate frame is always needed. Thus, extremely short cycle times of ≤ 100 microseconds result. By using the full-duplex 100BASE-TX features of effective data rates of over 100 Mbit / s (> 90 percent payload data rate of 2 × 100 Mbit / s) can be achieved.
The EtherCAT technology principle is scalable and not at 100 Mbit / s bound. A future extension to Gigabit Ethernet is possible, but not yet in preparation, because the performance of EtherCAT / s is not a problem even at 100 Mbit.
Diagnosis
The rapid and accurate detection of disturbances is one of many diagnostic features provided EtherCAT.
Bit errors in the transmission can be reliably detected by evaluating the CRC checksum: the 32-bit CRC polynomial has a minimum Hamming distance of 4. In addition to the breaking point detection and localization, protocol, transfer physics and topology of the EtherCAT system enable individual quality monitoring of each individual circuit. The automatic evaluation of the corresponding error counters enables precise localization of critical network sections.
Learn more about this see point monitoring below.
EtherCAT connectivity development for CANopen and SERCOS devices
The device profiles describe the application parameters and the functional behavior of the device, including the device- class-specific state machines. It offered the following software interfaces for existing device profiles. A vendor- side Migration from fieldbus to EtherCAT by adjusting the firmware and the hardware is facilitated significantly.
CAN application protocol over EtherCAT (CoE )
CANopen ™ devices and application profiles are available for a wide range of device classes and applications: Starting from the I / O modules, drives (such as Drive profile CiA 402 standardized as IEC 61800-7-201/301 ), encoder (CiA 406), proportional valves and hydraulic control ( CiA 408), to application profiles. EtherCAT then replaced CAN.
Servo Drive 's profile over EtherCAT ( SoE )
SERCOS interface ™ is a powerful real-time communication interface especially for demanding motion control applications. The SERCOS profile for servo drives and communication technology are standardized in IEC 61800-7. In this standard, also the mapping of the SERCOS Servo Drive profile is included on EtherCAT (IEC 61800-7-304 ).
Other protocols
Ethernet over EtherCAT ( EoE )
All Ethernet devices can be connected within the EtherCAT segment via so-called switch ports. Ethernet frames are tunneled through the EtherCAT protocol as is customary in the Internet protocols (e.g., TCP / IP, VPN, PPPoE ( ADSL), etc.). The EtherCAT network is fully transparent to the Ethernet device and the EtherCAT real-time properties are not affected.
File Access over EtherCAT ( FoE )
This similar to TFTP, very simple protocol allows the access to any data structures in the unit. Thus, for example, a single upload of firmware on devices possible - regardless of whether they support TCP / IP.
Safety over EtherCAT ( FSoE )
Parallel to the development of EtherCAT also a fieldbus-independent safety protocol was developed, which stands for EtherCAT as " Safety over EtherCAT " ( FSoE = Fail Safe over EtherCAT) available. Thus, functional safety can be realized with EtherCAT. Protocol and implementation are TÜV-certified and comply with the Safety Integrity Level 3 according to IEC 61508. Safety over EtherCAT since 2010 61784-3-12 international norm IEC.
This caused Safety over EtherCAT no restriction on transmission speed and cycle time, as EtherCAT is used as a single channel of communication. The transport medium is regarded as a "black channel" and not included in the safety analysis with.
Monitoring
Since EtherCAT standard Ethernet frames used by IEEE 802.3, is any standard Ethernet is monitor tool to observe the EtherCAT communication. In addition, free parser software for Wireshark ( formerly Ethereal, an open source monitoring tool) and the Microsoft Network Monitor, is treated with the mitgeschnittener EtherCAT traffic comfortable and displayed.
Integration
Gateways, existing networks such as CANopen, DeviceNet and Profibus seamlessly integrated into the EtherCAT environment and also provide a stumbling -free migration path from classic fieldbus to EtherCAT. This protects existing investments.
Thanks to the performance of EtherCAT is doing with outsourced fieldbus masters as fast as communicates with the classic, PCI or other backplane buses connected cards. Since decentralized fieldbus interfaces lead to shorter stretches of field buses, these can often even operate at higher baud rates than would have been possible with the classical architecture.
Implementation
Master
Master can be implemented as a software solution to any Ethernet MACs. There is code from different manufacturers and for different operating systems, including several open source projects ( see links).
It is made no great demands on the CPU power of the master due to the displaced mappings in the slave hardware, this gets the data already as a ready -stocked process image.
Slave
In contrast to the standard Ethernet EtherCAT frames are processed by the slaves in the run. This means that on the slave side hardware integrated EtherCAT Slave Controller (ESC ) must be used. ESC are implemented as ASICs or implemented based on FPGA. Since the beginning of 2012 also first standard microprocessors with EtherCAT slave interface are on the market.
For simple devices, no additional microcontroller is required. For more complex devices, the communication performance for EtherCAT is almost independent of the performance of the controller used. The requirements of the microcontroller is therefore specified by the local application, such as the drive control.
Applications
Control and regulation
To manage and control physical processes ensure high data integrity, data security and synchronization is required. EtherCAT has been designed specifically for these applications and meets all requirements for high-speed control.
Measuring systems
Modern measurement systems are characterized by Vielkanaligkeit, synchronicity and accuracy. Due to the features of EtherCAT protocol, an efficient synchronous data throughput is guaranteed. The given through Ethernet Network properties allow a measurement network with distributed measurement modules.
User organization: EtherCAT Technology Group
The EtherCAT Technology Group was founded in 2003 and is relative to the number of its members, now the largest Industrial Ethernet user organization in the world.
It provides its members with implementation support and training services to hosted plug fests (so-called interoperability tests) and driving the development and dissemination of technology with the help of members and offices in Germany, China, Japan, Korea and the United States ahead.
In the ETG for end users together from different industries, machine manufacturer and supplier of high-performance control technology to support the EtherCAT technology and promote. The diversity of industries ensures that EtherCAT for various applications is optimally prepared. The system partners make with their qualified feedback for easy integration of hardware and software components in all required device classes.
The Conformance developed with the assistance of members of ETG test tool ensures interoperability and protocol conformance of EtherCAT devices.
International Organization for Standardization
EtherCAT is IEC standard since 2005. The EtherCAT Technology Group is an official partner of the IEC standardization working groups for digital communication.
Integration into the International Standard IEC 61158 ( protocols and services ) and IEC 61784-2 ( Communications profiles for the specific device classes ) is done. In IEC 61800-7 ( drive profiles and communication ) EtherCAT is standardized as a communication technology for the SERCOS and CANopen drive profile. Also in ISO 15745-4 (device description with XML) EtherCAT is included.
Since September 2007, EtherCAT is also SEMI standard: the E54.20 describes the use of technology in semiconductor and flat panel display manufacturing equipment.