Benefits of Real-time EtherCAT Automation Applications
An important component of this game-changing automation control architecture stems from new digital fieldbus standards. Though many industrial systems can use standard TCP/IP Ethernet for communications to the control panel, HMI, or to ERP system, TCP/IP does not provide adequate determinism required for a machine to execute with required precision to guarantee quality.
However, because TCP/IP is so prevalent on factory floor and in offices and in homes around the world, Ethernet component parts like the CAT5 cables and NIC card offer both high quality and low cost. To take advantage of this low cost and open high quality hardware, several large companies like Siemens, Rockwell Automation and Beckhoff sought to create a new, deterministic protocol that was both suitable for high precision equipment that required determinism (or hard real-time) AND could reuse the CAT5 cable and NIC card instead of proprietary cables and I/O cards.
However, because of its superior price/performance characteristics and because it has earned, by far, the largest number of servo drive manufacturers who have now adopted it, EtherCAT stands alone as the leading digital fieldbus standard. To find out more, see this article entitled, 5 Real-Time, Ethernet-Based Fieldbuses Compared.
Here is a summary of the features that EtherCAT drive and IO manufacturers find valuable. EtherCAT is an open, real-time, and deterministic Ethernet fieldbus standard widely regarded as one of the best industrial networks to date. Automation equipment manufacturers can use EtherCAT on their own device implementations to improve performance and flexibility, while end users and automation system designers can implement their own EtherCAT-compliant devices. These additional advantages are other reasons why EtherCAT is quickly gaining ground in motion control and automation applications:
EtherCAT is based on fast “Ethernet on the fly” processing. In a traditional Ethernet network, Ethernet frames (or data packets) are sent to each device; the device then reads the data and sends back a response to the master. This process is repeated for each device in the network until all devices are updated. The total network cycle time is the sum of all the response times and is not deterministic. At times, multiple device messages interrupt one another — requiring the master to arbitrate and organize according to priority and adding delay to the cycle time.
In contrast, an EtherCAT network works more efficiently: A frame is sent from the master and when the first slave device receives the frame, it instantly extracts the data with its address and writes any response data. This means that the frame effectively passes through all the slaves (with negligible delay) and then returns to the master.
In addition to on-the-fly processing, EtherCAT also optimizes bandwidth by allowing outgoing and incoming data for multiple devices to be combined into single Ethernet frames, rather than requiring a frame for each networked device. For networks with many drives, I/Os, and devices, this approach significantly reduces transmission overhead. It is well suited for high-bandwidth applications such as multi-axis servo machine control. Sampling and updating 64 drives and several I/O devices can be done in less than 250 µsec.
EtherCAT: Tight synchronization
Multi-axis motion control networks heavily depend on the synchronization of independent devices to accurately execute multi-dimensional motion trajectories. Synchronizing all devices on a network requires that transmission times between devices — and drifting of clocks on different devices — be calculated and compensated for. To this end, the EtherCAT standard uses distributed clocks. The phase shift between all distributed clocks is less than 0.1 µsec.
Low cost — EtherCAT takes advantage of the mass-produced Ethernet communication devices and cables used by all PCs to minimize cost. Slave devices require a low-cost dedicated controller. Most importantly, EtherCAT achieves the low cost because there are so many Slave vendors that have adopted the EtherCAT standard and therefore the dynamic of having so many vendors competing for the slave devices drives the cost down.
In summary, machine builders are finding tremendous value from EtherCAT because it addresses all their deterministic requirements, offers the best performance, synchronization, AND offers the lowest, breakthrough costs.