Lenze explores benefits of Ethernet systems

Increasingly complex drive tasks are forcing a switchover to industrial Ethernet buses, prompting the question: which system will come out on top?

The theoretical answer is still being debated, but, in the end, it will be practical situations and actual tasks that determine which industrial Ethernet bus is used, according to Lenze, a manufacturer and distributor of servo motors, drives and couplings.

Field buses quickly reach the limits of their performance, especially when confronted with complex applications.

With a maximum bandwidth of 1Mbit/s and a maximum line length of 25m between different devices, the technology already seems to be old fashioned.

Extensive plants with numerous network nodes and large amounts of data can no longer be set up economically using conventional field buses.

Although there are currently 26 different industrial Ethernet solutions, three of them have asserted themselves and are to be found in the majority of applications.

These are Profinet, Powerlink and EtherCAT; in Europe, they have good prospects of complementing field buses and, in the long term, replacing them.

All three Ethernet systems can be used within machines and systems in which a central processor controls several drives that perform different movements from one another.

Neither a particularly large bandwidth nor real time are required.

The communication system is more likely to be based on the solution that the manufacturer of the controller prefers.

The Siemens Profinet IO is said to come out on top in the market for simple drive tasks in which a number of drives receive commands from a PLC.

This system performs around as fast as Profibus.

It is a configuration used particularly in large plants (such as car production) in which a plant PLC controls numerous conveyor drives.

Profisafe can also be used to transmit additional safety information to the drives.

The synchronisation of numerous axes is much more demanding, however.

This form of application is said to be best tackled with a decentralised architecture in which an intelligent drive acts as master and generates the control movements.

The position of the master must be reliably transmitted in real time to the drives working in slave mode and the publisher-subscriber concept is particularly suitable for the kind of cross communication that this requires.

This principle, familiar with CAN, also uses the Powerlink industrial Ethernet bus.

It offers a bandwidth of 100Mbit/s and allows lines of up to 100m between two network nodes.

Vertical communication is facilitated using asynchronous communication channels.

Powerlink supports all of the CANopen device profiles, simplifying migration towards Ethernet.

The bus does not require any special hardware and it uses standard Ethernet controllers.

Powerlink's performance is dependent on the processors used and the memory with which the automation components are equipped.

Three-dimensional movements are best dealt with by means of a central control architecture in which a powerful controller calculates and executes, in real time, the paths for all of the axes, which must be coordinated exactly.

This is the domain of EtherCAT combined with powerful industrial PCs.

Special ASICs process data quickly and keep node costs down.

According to Lenze, users may have to be patient while their Gbit Ethernet is adapted and a new ASIC version is ready, but EtherCAT interfaces have the advantage that the resources - those of the slave system, for example - are burdened much less than with a pure software solution.

As a result of the summation frame method that it uses, EtherCAT is said to transmit data particularly efficiently.

With its minimal overhead, the entire bandwidth is used even for small amounts of data.

It is also possible to modify data while running so that hold-ups are only short.

EtherCAT is also suitable for numerous topologies and combinations, facilitating the wiring of complex plants.

It also handles the CANopen protocol, simplifying the process of making a switch.

Lenze claims that it has a suitable solution in its portfolio for every kind of architecture, which means that users are free to choose the control architecture and communication buses they want.

For example, in the company's L-force automation world, the 9400 frequency inverters have a communication module for Profinet RT.

The 8400 series of L-force inverter drives will soon also be given Profinet RT facilities.

The company mainly uses EtherCAT interfaces for its PC-based control systems and these are already available for the 9400 inverter family and other series of devices and in future for the 8400 inverter series.

Ethernet technology continues its rise to power, bringing greater TCP/IP transparency, boosted vertical integration and easier access to new technologies such as web and wireless systems.

That is why the Profinet, Powerlink and EtherCAT industrial Ethernet buses form the basis for many new automation concepts, according to Lenze.

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