Ethernet POWERLINK

The Ethernet POWERLINK Standardization Group (EPSG) was founded in 2003 in Switzerland as an independent association with a democratic structure.

Ethernet POWERLINK

STANDARDS BODY, TITAN AND PHILOSOPHY

Ethernet POWERLINK was introduced by B&R in 2001. Its goal was to provide standard Ethernet with real-time properties and allow universal solutions all the way down to demanding motion applications. Since that time, the EPSG (Ethernet POWERLINK Standardization Group) has promoted Ethernet POWERLINK and taken responsibility for its openness, continuous improvement, and independence.

ARCHITECTURAL PHILOSOPHY: OPEN SOFTWARE/MODIFIED ETHERNET

Ethernet POWERLINK is a strictly cyclical protocol that organizes the access to a network as well as the synchronization of the devices. The communication cycle is divided into an isochronous phase for time-critical data as well as an asynchronous phase for transferring ad-hoc data. All of the devices on the network can always directly read all of the data from the other devices; detouring over a central bus master is not necessary. This protocol is equally suitable for local as well as remote control designs.

Because Ethernet POWERLINK is a cycle-based real-time system, it superimposes a time slot mechanism over the CSMA/CD mechanism. The master (controller) successively polls the slaves (drives) within an allocated communication cycle period. The remaining cycle time is left over for asynchronous data traffic, such as for configuration of the devices. Data transport occurs via a standard Ethernet telegram, with the Ethertype set to ‘Powerlink’ for the real-time data and to ‘IP’ for the general data. All stations (master and slaves) within a real-time segment interconnect via a standard Ethernet hub.

A special gateway links the real-time segment to the standard Ethernet environment. The IEEE1588 time synchronization method permits different real-time segments to be synchronized in a highly precise way, such as might be required for the control of multiple robots.

The idea behind Ethernet POWERLINK is to find the right balance between common automation demands and those demands that are specific to each application area. This has led to a widely accepted solution that gained some initial traction in the market. However, only a handful of servo drive vendors adopted Powerlink in spite of the fact that countries like China adopted it as a standard. This means that the standard is not actually broadly adopted. The resulting economic benefits were not as compelling because the price for servos remains high. In response to these conditions, the Chinese government has now updated its preferred standard and adopted EtherCAT. Having more vendor choices drives costs down.

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