'Point-and-click' plant integration

Getting intelligent devices to communicate with each other and higher level systems can be major challenge. Gary Provis argues that Component Based Automation offers the solution

There are currently two challenges facing the manufacturing sector: how to achieve the mass-customisation that is being demanded by consumers and, at the machine/plant level, how to get intelligent devices from different suppliers to communicate with each other. Meanwhile, there are ongoing pressures on machine builders to reduce the lead times for new equipment, and to improve efficiencies through the maximum reuse of knowledge and the minimum time spent on documentation.

If mass-customisation is attempted using a centralised control philosophy, the PLC (programmable controller) algorithms soon become unwieldy. Decentralised control using distributed intelligence, on the other hand, is far better at coping with the demand for continual changes to device configurations. Furthermore, distributed intelligence lends itself to easier machine development because individual modules can be built and tested in isolation, which vastly reduces the on-site commissioning time.

Although some of the larger automation companies have positioned themselves as one-stop-shops for the customer's entire automation needs - from the PLC down to the sensors - it is common to find machines that have components from several different suppliers. Or for large, complex plant where several machines from diverse sources have been integrated together, it is likely that the individual suppliers will each have their own preferred automation vendors. In these circumstances, the problem is often in getting the intelligent devices to communicate with each other - without having to allocate a disproportionate amount of resources to programming and debugging.

Open standards

The solution that Siemens advocates is known as Component Based Automation (CBA). At the heart of this concept is the open-standard ProfiNet communications protocol, which allows Profibus-based systems to be linked with Ethernet-based systems, thereby providing users in the office environment with complete access to data from even the most basic of automation devices. ProfiNet was first proposed by the Profibus user organisation as a cross-vendor communications, automation and engineering model for use with distributed intelligent devices.

Within the concept of CBA, a 'component' is an encapsulated, reusable software module that conforms to the requirements of IEC 61499 (the standard for the application of function blocks in distributed industrial/process measurement and control systems - currently in the form of Publicly Available Specifications). A component can be created for any intelligent device, which, today, might include PLCs, drives, pumps, or intelligent sensors such as vision systems.

In practice, each device will first be programmed using its own vendor's configuration software. By simply pressing the appropriate key (depending on the software tool, of course), an encapsulated component can then be created. This will contain the device's application and have inputs and outputs for events and data. Once all the components have been created, another software tool (such as the Siemens SIMATIC iMAP, which is believed to be the first such package available) is used to link the event and data inputs and outputs of the various components. Because the components are object-orientated, they are effectively vendor-independent, which is why the iMAP or other engineering tool is able to link them all so easily. The iMAP software uses a simple graphical interface so the user just 'points and clicks' to join the various components, rather like using an on-screen soldering iron to wire the components together.

CBA results in a substantial reduction in the programming overhead that is normally associated with building the communications interfaces between intelligent devices. In addition, it allows the machine builder to build, program and test the various machine modules independently, then connect them together physically and in software so that the whole can be tested. Alternatively, if several companies are working in parallel on different modules, the separate modules can be programmed and tested before they are brought together.

Reduced lead times

One of the most important results of this is that lead times can be shortened significantly. Any problems tend to be highlighted - and overcome - much earlier, and the amount of time required for on-site commissioning is much reduced because a good deal of the work has already been done in advance. Furthermore, a large proportion of the documentation is completed automatically as part of the configuration process, helping to save time for the engineer who would otherwise have to do this tedious task during and after the engineering. If any changes are subsequently found to be necessary, the documentation is also updated automatically, which might not be the case for processes reliant upon the diligence of individual engineers.

One of the advantages of using the ProfiNet approach is that existing Profibus networks can easily be connected to the system by using ProfiNet proxies. These hardware devices act as a link between the Profibus network and the higher-level Ethernet, thereby providing an essential bridge from the intelligent devices on the shop floor to the office-based management systems. ProfiNet can also be used with motion control applications (ProfiDrive) and safety-orientated applications (ProfiSafe) in exactly the same way as for a conventional Profibus network.

When the equipment is operational, a further set of benefits is available. Data from the intelligent devices can be shared anywhere on the network, and this includes upwards, to office-based applications. Managers can therefore monitor the performance of the plant down to as fine a level of granularity as could possibly be wanted, which helps in planning maintenance or seeking greater efficiencies. It also allows output levels to be viewed in real-time and, ultimately, for the data to be available to enable mass-customisation to take place.

After the project has been completed, there are still more benefits to be gained from CBA. For instance, the components are reusable so, even if the next machine or system is radically different, the same basic components could still be used again. Linking the components together in a different arrangement is simply a matter of 'point-and-click' graphical on-screen engineering.

Typical applications for CBA will be those where there is distributed intelligence with non-time-critical data exchanges between the intelligent devices and automation controllers. The automotive industry is one example, especially for assembly lines, conveyor systems and paint shops. Another is the food industry, where complex processing and packaging operations need to be linked. Indeed, almost any type of production line consisting of a series of connected machines could benefit, or even a system as apparently straightforward as a series of linked conveyors.

The beauty of component based automation is that it combines the benefits of distributed intelligence with the advantages offered by software component technology. As a result, both configuration and commissioning overheads are reduced, and plant operators gain the data visibility that allows the plant to be operated as flexibly as consumers are now demanding; mass customisation is now truly feasible.

Siemens Automation & Drives
h108@industrialnetworking.co.uk