Industrial Ethernet has become the de facto standard for manufacturing information networking, and the market is requesting Ethernet connectivity for servo drives. Ethernet offers high-speed data throughput at 10-100 times faster than fieldbus solutions. It uses standard off-the-shelf components and cabling and offers consistent IT implementation from office to the machine level. The problem is that Industrial Ethernet is characterized by high bandwidth and low hardware costs, but is not deterministic. Office communications and certain single-axis motion applications can tolerate delays and data re-transmissions, but that would be disastrous for coordinated multi-axis robots or high-speed machine tools.
The Sercos automation bus, on the other hand, is optimized for high-speed deterministic motion control, which is required for the exact synchronization of multiple drives. Sercos also defines a protocol structure and includes an ample variety of profile definitions for control of motion and I/O devices.
Sercos III is the open, IEC-standardized third-generation of Sercos that "right engineers" Industrial Ethernet for real-time control, combining the best of both Ethernet and previous Sercos designs to provide the highly deterministic bi-directional real time motion and I/O control required by modern production equipment. It overcomes the wasted bandwidth in other TCP/IP-based Ethernet bus solutions, because it is based directly on Ethernet frames, defining a new, registered EtherType for Sercos. In addition to real-time communications between all drives and the motion control, Sercos III provides rich I/O communication capabilities, while also enabling other protocols, such as EtherNet/IP, TCP/IP, UDP and others, to be transmitted over the same Ethernet network efficiently in parallel with Sercos real-time communication. Sercos III is a truly a universal automation bus for machine production and system implementation.
Sercos III offers several fundamental performance and technology benefits for OEMS and end-users:
- Cycle times as low as 31.25 microseconds.
- High speed: it uses Fast Ethernet (100 Mb/s).
- Support for either line or ring topologies; in addition hierarchical, synchronized and real-time coupled network structures can be implemented.
- Support for up to 511 slave devices in one network, with multiple networks possible in a system.
- Bumpless cable break recovery in ring mode within 25 usec.
- Advanced cross communications—both slave-to-slave and controller-to-controller (sometimes called machine-to-machine).
- Capable of hot-plugging devices and network segments—adding machine or line components to a network with synchronization up and running, without having to reset the network or cycle power.
- Support for safety functions up to SIL3 according to IEC 61508 via CIP Safety for Sercos.
- I/O profile that provides an XML-based device and profile description language for I/O device configuration.
- Energy profile that defines parameters and commands for the reduction of energy consumption in a uniform vendor-independent manner.
- Encoder profile that provides a standard method to integrate encoders into a Sercos III network.
- Lower hardware costs.
There are several key advantages that manufacturers, systems engineers and machine builders can leverage when using Sercos III—advantages that enable drive and control systems with vastly improved flexibility and performance.