SERCOS III
After all MDTs and ATs are transmitted, Sercos III nodes allow the remaining time in the cycle to be used as an UC (Unified Communication) Channel, which can be used to exchange data using other formats, such as IP.
Sercos is purposely designed to provide open access at all ports for other protocols between cyclic real-time messages.
All Sercos III telegrams conform to the IEEE 802.3 and ISO/IEC 8802-3 MAC (media access control) frame format.
The AT is issued by the master but is populated by each other device with appropriate response data (feedback values, input states, etc.).
Sercos III supports standard IEEE 802.3 and ISO/IEC 8802-3 100BASE-TX or 100BASE-FX (100 Mbit/s baseband) full duplex physical layer (PHY) entities.
All of the functionality required to configure a Sercos III interface is contained in a stack that is available in both “hard” and “soft” versions.
The hard version is widely used for embedded applications (such as drives, I/O modules, and micro-controller based motion control), where: The hardware stack is available in several different forms.
A standard Ethernet controller can be used for applications with line topology, bus cycle times greater than 500 us, and microsecond range synchronization.
Applications with higher synchronization requirements and lower bus cycle times can be implemented using a TTS-capable Ethernet controller with a suitable real-time operating system.
A product that uses an Arduino board as a rapid prototype platform for an application, plus a corresponding shield (add-on module) with a Sercos EasySlave FPGA, plus other peripheral components, is available.
Sercos III is designed in such a way that no additional network infrastructure (standard Ethernet switches, Hubs, etc.)
The idents define over 700 standardized parameters that describe the interaction between electric, pneumatic, and hydraulic control systems, drives, and other peripheral devices using universal semantics.
They were later grouped into application sets to aid in the selection of pertinent incidents required for a given industry, such as the “Pack Profile” for use with packaging machinery.
During the development of the Sercos III specification, this methodology was further refined to group the incidents logically by device class.
Disadvantages to this method are that delays are induced due to the multiple cycles required, and the master’s processing load is increased as it must actively participate in the function, although it contributes nothing.
Time stamping transmits event-controlled results, such as specific measured data, and switches outputs independently from the cycle.
Sercos III does not define whether a port should operate in cut-through switching or store-and-forward mode when handling UC frames.
Likewise, Sercos III does not define whether a port should intelligently process UC telegrams, such as learning the network topology.
The time allotted for UC traffic is dictated by the amount of data transmitted during the real-time portion of the cycle.
Using the same example of 8 axes but with a cycle time of 62.5 μs, the effective bandwidth available for UC frames would be 40 Mbit/s and the MTU would be reduced to 325.
[11] This provides interoperability at the safety level with all networks based upon the Common Industry Protocol (CIP), including DeviceNet and EtherNet/IP.
Depending on the situation (e.g., scheduled or unscheduled breaks, machine components not needed in the current production process) standardized commands can be issued by the control to switch connected components (drives, I/O, sensors) into energy-saving conditions, up to complete shut-down, reducing their energy consumption.
Shortly before the end of the interruption, Sercos Energy provides for the re-initialization of components in stand-by condition, to make them available again.
Sercos Energy provides mechanisms for unintended breaks caused by machine errors and missing parts.
In these situations, target components can be carefully brought into energy-saving modes while errors are being fixed or during a wait for new parts.
This makes the functions and parameters of Sercos III devices available to OPC UA, independent of any vendor.
The OPC UA server functionality can be implemented into machine control or directly into a Sercos field device, such as a drive, sensor, or I/O module.
I/O Link is a digital interface for the connection of sensors and actuators to higher-level automation busses, such as Sercos III.
An IO-Link-to-Sercos mapping guide[13] is available to assist manufacturers in integrating IO-Link into a Sercos III network.
Conformance testing verifies that both controls and peripheral devices comply with Sercos standards and can operate interoperably in networks with products from multiple vendors.
