As an answer to the growing requirements of the modern automation engineering to the real-time capability of the bus systems and the high costs of the common bus components, several companies began to generate a real-time capable bus system. It is drawn up to the favorable standard components of the Ethernet-standards IEEE 802.3. One of these industrial-Ethernet bus systems is “EtherCAT”, which was initiated by the company Beckhoff Automation and is now further developed by the EtherCAT Technology Group.
EtherCAT – focused on speed
EtherCAT was especially developed for the demands of control systems in the automotive technology. The specialization of EtherCAT stands for Ethernet for Control Automation Technology. Main focus of the development here was real-time capability, synchronization as much exactly as possible and with low costs. The real-time capability of bus systems in the automation are for example demanded at Motion-Control-Tasks. These require real-time capability, pose control, velocity, acceleration or a combination of this all. If a vehicle with an electric motor has to follow a desired speed profile, then the bus system must be real-time capable.
EtherCAT is known as the by far fastest industrial-Ethernet technology, due to its functional principles. In contrast to other technologies, the EtherCAT slave module begins with data interpretation, data handling and data transfer while the message is still passing the module. Common technologies first have to receive, interpret and copy the process information of the whole message. A visualization of the functional principle can be found on the following video by the EtherCAT Technology Group.
Synchronism through distributed clocks
Another important demand, resulting from automation technology, is the exact synchronization of two commands. If it is necessary to perform two physically separated processes at the same time, they have to be synchronized by using a shaft – a mechanical connection. It is also possible to create an “electrical shaft” by starting and rotating two servo motors at the exactly same time and with the exact same moment. EtherCAT makes this possible by using distributed clocks. The main clock, which is located in the slave-device, transmits the current time to the slave clocks which can be readjusted by including the running time the signal had consumed. By using this method, synchronization accuracies of less than 1 µs can be achieved.
Installation structure defines the topology
The topology of a fieldbus system determines the chronological order the devices of the bus cable will run through. All devices can be connected with a cable in a line, built up like a star (master in the center) or realized in a ring. EtherCAT supports nearly all possibilities of topologies plus their combinations with a random number of nodes. As you can see, the topology is not enforced by the bus system, but can be rather chosen by the installation structure. If redundancy is important in the system, you have to use the ring-topology. At a breakdown of the bus system, all devices are still reachable and the erroneous node can rapidly be identified.
Not only fast, but also economically viable!
From the beginning of the development of EtherCAT, the profitability was kept in mind. For the fulfillment of an EtherCAT-master, only an standard Ethernet-card is necessary, that can be found in every modern computer. Even at the construction of the ring-topology it is sufficient to extend the master by a second Ethernet-card. Also the cables are cheap standard products, which are available in nearly every electronics market. The EtherCAT slave controller does exist on ASIC, FPGA and the basis of a micro controller and manages time-critical tasks. Therefore, the performance of the EtherCAT slave components got no high demands anymore, because only the local application like the drive control are given. As a result, the connection costs of additional components can be kept low.
The EtherCAT standard offers great advantages, which is essential in the area of automation technology. Besides meeting hard and soft real-time capable requirements and the synchronous accuracy of less than 1 µs, EtherCAT convinces because of the low acquisition costs of the components and the cabling. Thus, the electronic components of the Robot Makers GmbH supports the EtherCAT standard. The electronic line of the Modular Control System can therefore be used as a slave module to control motors, hydraulic actors or measurement. The central control unit Generic Control Box with its integrated software tool is predestined for the use as an EtherCAT master.