Technology Talk
Real-Time Ethernet - a difficult choice
Ethernet on its way towards the real-time world
Only after it had been established throughout the office world, Ethernet did enter the world of automation. The deciding factor was the call for continuous data availability from the field level up to the plant control level. Due to initial problems concerning the real-time capability non-real-time critical PLC applications or connections of CNC controls to PC based operating elements, were the first to be replaced by Ethernet and that in these cases the desired data continuity up to the control level was in fact achieved. However, at the “lower” field level, conditions are becoming more and more critical as the communication with sensors, actuators or drives poses much higher requirements with regard to the real-time capability of data and signal communications. In order to be competitive at the field level, the “Industrial Ethernet” had to overcome two hurdles: 1. It had to become faster as not meeting real-time requirements may lead to disastrous consequences. 2. It had to be cheap in order to be able to prevail over massive competition from established fieldbus system.
Apart from products of other suppliers, basically 3 so-called Industrial-Ethernet solutions are currently available on the market or are being developed:
- Powerlink (ETHERNET Powerlink, developed at B&R and organised in the EPSG)
- Ethercat (Ethernet for Control Automation Technology of Beckhoff organised in the ETG)
- PROFINET (Siemens /PNO)
A difficult choice
In this situation, the decision in favour of one of the available solutions requires much background knowledge and a sense of possible developments of technological trends. For manufacturers of machines it is usually neither possible nor economical and even does not make sense to build up this know-how themselves. Thus the role of the control partner as a consultant of the manufacturer of machines becomes increasingly important.
The developers at ECKELMANN AG have made a decision in favour of the Powerlink solution and have been members of the Ethernet Powerlink Standardization Group, or EPSG for short, since 1 November 2003. Meanwhile ECKELMANN has also joined the EPSG working group of safety.
-> PLC, motion and CNC solutions with Ethernet
Arguments in favour of POWERLINK
To summarize the arguments in favour of Ethernet Powerlink from the point of view of ECKELMANN AG:
- Conformity with standards such as Fast Ethernet
- Suitable for hardest real-time requirements thanks to a jitter < 1micros
- Robust and future-oriented, proven in series machine construction
- Continuous data communication through all levels for vertical integration
- Simple application and seamless integration in IT structures
- Availability and distribution, use of Standard Ethernet Chips
There is no doubt that Ethernet-based CNC solutions will in the future also prevail in areas where hard real-time capability is required, for example in the communication link between CNC and drives. However, ECKELMANN AG has adopted a double strategy and further sticks to the CANbus and the CANopen® communication protocol (down to the device specifications according to CANopen®). This is indispensable to ensure flexibility in meeting machine manufacturers’ needs.
According to this double strategy, ECKELMANN AG also offers the customer a choice between Ethernet, CAN or parallel operation of both technologies in the case of the Embedded Controller ExC66, which is currently being developed. The development and production costs are minimized through the strategy of using a universal hardware platform for a great number of control functions (CNC, PLC and motion control) and communication standards (CAN, Ethernet and others).
Link for further information:
 Control Solutions on the Basis of Real-Time Ethernet
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