(Article written for Industrial Ethernet Book November 2010)
All the pundits predict that Industrial Ethernet use is expected to grow by double-digit percentages year on year. CPLA’s Steve Jones says that when you dig down into the numbers, you have to start asking yourself whether there is some resistance to its adoption. Answering his own question, he reckons that CC-Link IE technology has gone further than most to meet the demands of designers and maintenance technicians.
THE CONTINUING DRIVE to improve productivity will encourage more automation networking – of that there is little doubt. Initiatives driving this growth include lean working, improvement to takt times (takt time sets the pace for industrial manufacturing lines), increased track and trace type legislation, and product lifecycle management production (PLM).
Delivering the mass customisation demanded by market forces requires joined-up thinking, and connected manufacturing promises to deliver the required value chain transparently. ERP systems are required to make information available backwards into the supply chain, as well as forwards to customers.
Simply put, everyone wants to see what’s going on (see box). As a result, networks will become ever more important and the information they handle will take on the same order of importance as industrial control functions. So who will look after these networks?
End-users have seen standard Ethernet as a way of communicating shop floor data to the top floor ERP/information systems. As a model, Enterprise IT with its standard network backbone is what attracted plant managers to consider a similar approach for their industrial or manufacturing applications. However, unlike the popular automation networks such as CC-Link and Profibus, standard Ethernet will not deliver the performance needed for modern complex manufacturing. This is especially true for applications needing deterministic (predictable) response times.
There are many different ways to provide determinism in Ethernet and this may explain the rash of Industrial Ethernet protocols introduced over the last few years. It can be argued that Industrial Ethernet does not need to be deterministic and that providing enough bandwidth will adequately cope with most situations, a truism for many applications. However, determinism is certainly required for some, so it makes sense to use a deterministic network provided there are no inherent disadvantages in doing so.
While the majority of industrial Ethernet protocols will meet the network performance needs of most users, they frequently bring unwanted complexity as part of the package. The required skills base can adversely affect downtime, maintenance and the ability to make network configuration changes. Perhaps this partly explains why some users have delayed the move from traditional fieldbus to an Ethernet-based equivalent?
Easier to maintain
Skilled control engineers are increasingly rare on the shop floor. For many companies, having a shortage of engineers to handle advanced automation equipment will lead to serious problems. Few companies can presently afford an army of specialist engineers to maintain the networks; the trend is to employ generalists and bring in experts when required – often their suppliers’ support engineers. If companies cannot afford to shut down production while awaiting the attendance of a control consultant, then the networking technology must become easier to use and maintain. New plant and equipment needs to be as simple as possible, with easy-to-use field devices requiring little or no personnel training. For quick response to problems, easy system self diagnostics and cause identification that don’t rely on an engineer’s intuition or experience are crucially important.
CC-Link on Industrial Ethernet
The CC-Link Partner Association (CLPA), using a decade of accumulated knowledge, developed the CC-Link IE to deal with the skills base question. To be taken into consideration were certain clear requests from system designers and maintenance technicians.
From designers, suggestions included:
- High speed communication enabling sharing of large amounts of data in real time, reduced takt times and predictable performance;
- Reduced costs by using commercially available Ethernet equipment;
- Simplified network configuration for faster implementation/model changes;
- Simple connectivity to enable stations to be accessed from anywhere, even across multiple networks;
- Choice of network topologies and cabling options to reduce cost of ownership;
- • High network availability. Maintenance technicians suggested:
- The flexibility to allow easy addition of new stations, and for making network changes;
- Engineering tools to make wiring problems and errors easy to diagnose;
- Hot swap of devices and station additions without stopping the network;
- Minimise problems caused by EMI.
As a result, CLPA introduced CC-Link IE in 2008. Gigabit operation ensured that the network met the throughput performance aims. However, although speed is important, ease of use is perhaps its major benefit.
As well as high throughput of control and communication data, CC-Link IE enables plant engineers with little or no underlying Ethernet or network configuration knowledge to maintain the system. Automated troubleshooting, flexible topologies, determinism and resistance to electrical noise have also been integrated. In addition, CC-Link IE has been designed to use common off-the-shelf (COTS) Ethernet tools and networking devices.
Looking at performance, CC-Link IE’s innovative characteristics minimise network downtime and loss of data. At a controller level, if the network master fails, the standby function automatically switches to a nominated standby master to maintain network communications. Up to 26 standby masters can be assigned and, if required, each can have a completely different operating programme to suit a specific failure situation. A hot-swap function enables networked slave and master stations to be removed without stopping a running network. When replaced, it automatically returns the reconnected station to the data link without the network needing to be reset.
Largely because of cabling problems, EMI can cause intermittent and unreliable operation in some networks. Uniquely, it is thought, the CCLink conformance test includes stringent EMI radiation and immunity tests to minimise these issues.
On the set-up side, the system’s devices do not need special station description files when configuring the network, so if a CC-Link device is replaced, it isn’t necessary to find the appropriate configuration file, or go into the network and update the system information.
A station bypass feature allows the network setup to be created in the network master, with hardware stations being added later when required. New stations can be activated without stopping or resetting the network, saving lost production or additional software writing and commissioning time.
The CC-Link IE control network allows each station to share control data through the network shared memory; in user applications, communication design is possible simply by reading from, or writing to the shared memory. Any device connected to the network can send and receive data from the shared memory, so no specific CC-Link IE protocol knowledge is required. Simple configuration and network diagnosis without having to consider the complexities of Ethernet TCP/IP operation allows the total costs to be reduced from introduction through to operation and maintenance.
Simply specifying the station and network numbers from which data is obtained allows the routing of CC-Link IE field network transient communications, providing seamless communication with all stations regardless of the network’s physical configuration. As a benefit, control programs can be created as if the entire system is a single network.
The pros and cons of various network topologies
Several different networking topologies are available and each has advantages and disadvantages. Most Industrial Ethernets are suitable for use on one, or sometimes two, topologies. However, the CC-Link IE field network can build an optimal network according to each station’s layout by combining line, ring, star or mixed topologies. Duplex fibre rings are also available for PLC to PLC networks when ultra high speed and reliability are required.
If a network has been designed from the outset to be deterministic, what happens if changes are made?
The CC-Link IE field network’s token passing based on 1Gbps high speed Ethernet makes advanced real-time performance a reality. This results in greater communication throughput, and provides deterministic data exchange and constant link scan time by eliminating data collisions.
When adding stations to CC-Link IE Field, they can be connected freely, either to the empty port of another network station, or to a layer two switch. This enables a flexible adding of stations without being aware of the connected port. Figure 2 demonstrates the addition of connected devices; intelligent managed switches are not needed. Where a star topology is preferred, only an unmanaged layer two switch is needed, avoiding extra cost.
Connecting TCP/IP devices
For Ethernet TCP/IP compatible devices, such as RFID readers and bar code scanners, connection to an Ethernet adaptor using Seamless Messaging Protocol (SLMP) is all that’s required to add these devices to a CC-Link IE network
Since the SLMP is a simple client and server type protocol, it can be easily implemented into the firmware of third party vendors’ Fast Ethernet TCP/IP devices. They are then connected to CC-Link IE Field via the Ethernet adaptor.
So as to guarantee a stable data transfer cycle for cyclic real-time information, CC-Link IE assigns a transmission bandwidth for transient (peer-to-peer) message communication without adversely affecting cyclic communication. This assures high-speed determinism for high quality production operations, while still allowing for significant amounts of non real-time messaging. It also supports predictive maintenance programmes and online diagnostics.
In the following example, the CC-Link IE field network uses its high speed transmission rates to acquire the health data of devices periodically while the cyclic transmission for control is performed.
Detailed information, such as sampling motor load current data, can be acquired during the high-speed control without affecting the network’s deterministic behaviour. This supports health of system predictive maintenance and equipment diagnosis programmes by network PCs (see Fig. 4). CC-Link IE also supports Equipment Engineering System (EES), which is widely used in the semiconductor industry to monitor equipment settings and behaviour.
The Transport Layer Security (TLS) protocol that maintains privacy between communicating applications and their users over the Internet overcomes the once critical issue of implementing secure connections to production and information systems.
Using this enabling technology, embedded devices servers are available that allow wired Ethernet or Wi-Fi connection between a machine or process and the Internet. Users can resolve problems remotely and detect and correct potential problems before they become critical (or even known).
Remote monitoring and diagnostics can provide sufficient bandwidth to offer a wide range of bi-directional support functions including video information either for monitoring or providing online support. Using a standard web browser or dedicated software, specialist support engineers no longer need to be on site, or even in the same country to implement solution.
The aim of CC-Link IE was to simplify the implementation and adaptation of industrial Ethernet networking. What it actually delivers is a flexible, high performance automation network that integrates many unique features that simplify use, minimise downtime and reduce total cost from introduction through to operation and maintenance.
In meeting the demands of both designers and maintenance technicians, CC-Link IE retains all the advantages of a proprietary automation network, but is based on an open, flexible Gigabit Ethernet based platform. At the top end, it can support ERP systems using TCP/IP and at field level, it happily integrates Fast Ethernet TCP/IP devices or sensors.
It offers a choice of topologies and uses standard Ethernet techniques, tools and equipment. Users can select their optimal network including ring, star, line and mixed line and star topologies – simple really!
Enterprise Resource Planning and the network
ERP is an integrated computer-based system that manages internal and external resources, including financial, materials, human resources and tangible assets (buildings, computer equipment, production machines and automation equipment). ERP is designed to ease information flow between all of an organisation’s business functions and manage connection to external stakeholders. ERP, therefore, consolidates all business operations into a uniform enterprise-wide system.
ERP systems are conventionally built on a centralised database using a common computing platform. They may either be distributed across modular hardware and software units that provide services and communication on a LAN, or reside on a centralised server. The way an ERP system is organised allows businesses to assemble modules from different vendors without needing to place copies of expensive computer systems in areas that don’t need their full capacity.
An ERP system software package should feature the following: all modules should have the same look and feel; the software should be integrated and operate in real time; and all applications should access a single database to prevent redundant data and many different data definitions. Finally, users must be able to access any information without needing extra system integration work to be carried out.
ERP systems are highly dependent on access to reliable real-time data. In many industrial environments, such data is often difficult to collect and verify for accuracy. It may be sourced from many interfaces, including distributed and quality control systems. A properly implemented process information infrastructure can reveal otherwise hidden plant capacity, show energy wastage, minimise down time and provide production information to the ERP system. This optimises business profitability.