Top: Technology Focus
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Ruari McCallion examines practical wireless control solutions in terms of auto manufacturing and what the future holds for this technology.
It would be something of a finance officer’s dream if automated factories could be controlled from central points, either onsite or – even better – remotely, controlling everything from supply lines to the delivery of finished product. At a more modest level, the idea that production staff could use wireless communications to free themselves from fixed workplaces, going wherever they could be best deployed, has considerable appeal. Receiving communications by radio, these employees would monitor remote wireless machines, each adaptable to different models or tasks as various products came down the line, with die or tool changeovers made automatically.
Wish away: that kind of future isn’t here yet – and it’s questionable whether it would make sense anyway, for the immediate future, at least.
“At the end of the day, it comes down to companies choosing solutions which have costs commensurate with what they seek to do,” says Tim Whittaker of Cambridge Consultants, a leading technology and innovation company. For a number of reasons, flexible machinery with automated, radio-controlled changeovers just doesn't appear on the agenda. Some are obvious, in as much as a machine is deliberately programmed to perform a particular task with a particular tool or die. Change the task and you may need to change the tool and that’s going to require human intervention and while on site, they may as well reprogram the equipment.
Other issues aren’t as immediately apparent, but they’re just as important – or maybe even more of a hurdle. Power, for example. Wireless equipment may, by design, take advantage of battery power, but due to these finite power supplies, the systems have limited lifespans. If the application is of a critical nature, reliability has to be paramount and a fixed power supply line could be a better solution.
Other hurdles: the manufacturing process has a lot of things happening simultaneously, making monitoring and control both complex and expensive. And there’s interference. It’s unlikely to be the local taxi company breaking into your transmissions, but production facilities have too much going on at any one time to risk any break in communications.
“There are a lot of things against you. Dirt, various pollutants, from water upwards; interference from other things, like electrical machinery, welding and heating equipment, and so on. At the end of the day, there are a lot of problems to solve,” says Whittaker. However, if this all seems rather doom and gloom for wireless control, it's not. Setting realistic parameters and clarifying what cannot be done can define the role of wireless technology. There are a lot of applications already using wireless; indeed, the technology has made some activities much less dangerous – and even made ongoing monitoring of equipment in hazardous areas possible where previously it was not. For example, the use of wireless actuators is already quite widespread. Put simply, it’s essentially a question of assessing and understanding what is realistic, now and in the near future. Yet the paradox remains that the growth of wireless equipment is not driven by advances in radio itself, with advances being more of a reaction to a perceived need.
“What has helped radio is the proliferation of smaller, cheaper microprocessors,” continues Whittaker. “Radio is governed by the laws of physics and they don’t change. What has changed is the ability of devices to work in various mediums.”
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The simplest example of wireless activation is probably in your pocket right now – the car key fob. “It’s very simple and engineered to the lowest possible price. The protocol for dealing with interference or failure is the human holding it. If they press the button and don’t see the car’s lights flash, they’ll try again until they do,” he said. It’s not a very high form of intelligence but it’s intelligence nonetheless. “For a human being, it’s innate;for a machine, it has to be programmed or taught. You can extend the principle. A ‘reliable’ radio link requires some intelligence within the solution, (to) keep trying until it gets through. Try different wavebands or slow down the modulation, for example.”
That’s the equivalent of pressing the key fob button until the lights flash. Lights flashed? Yes. Mission complete? Yes. Stop trying. The most widespread use of wireless controls is on these yes/no actuators. If the product is there, then package it, punch it, weld it, bend it, whatever is required and the machine is programmed to do. It is this ubiquitous nature of wireless-enabled processing units that makes the spread of radio control possible.
“They’re being routinely built-in to equipment, including wifi in laptops. We’re now using them as a matter of course and, on the whole, it works pretty well and it’s all to do with computing. Advances in radio have happened, they’re being built better – or the same, but cheaper – but it’s really all about IT,” says Whittaker. But there are still issues that must be dealt with. "For example, if you want to control a particular valve in a petrochemical plant, the chances are that, no matter how good the radio is, something will interfere. You can switch bandwidths and still encounter problems. If something is dangerous if it fails, then the better solution is to put in hard-wired connections. On the other hand, in various places you may be able to get away with if you don’t have a reading from failed sensors. In a nuclear power plant, for example, you may wish to install radiation monitoring. A hard-wire solution could cost $10,000 per metre to install but it wouldn’t kill you if you didn’t have all the readings, all the time. If wireless gives 99.9 per cent reliability over six months, then the optimum solution could be to get someone to go round and change the batteries every so often."
However, while 99.9 per cent is acceptable in monitoring terms, in manufacturing, that’s a failure rate of 1,000 ppm, which isn’t good enough. And the cumulative effect of thousands of sensors across a facility, collecting millions of readings a year, could also cause problems. Losing a day’s radiation readings in an otherwise clean corridor at a nuclear power station may not be critical; losing a day’s production most certainly is.
“Shell is keen to know the state of all its electrical motors at its new gas control centre in Norway – there are thousands of them. They’re looking seriously at using small motors that will monitor vibration and heat,” Whittaker explains. This, though, is a fairly simple application, with the only significant concern being power supply. Manufacturing is different. “In industrial control, you can use radio for high-integrity control over a range of up to 100 metres. Over longer distances, you can only do so if you have a really unique feature and the object has to be completely untethered, for example, a supply cart. You take a close look at the resulting problems if something goes wrong and take appropriate precautions – for example, if the radio fails, the cart simply stops.”
It’s the same within a robot envelope. People aren’t allowed to pass these borders, but you take the inherent dangers into account and the likelihood of something going wrong, then non-wired solutions could offer a suitable solution.
While the main progress in wireless applications has resulted from advances in IT, the radio development people have also been working on improving their product. We’ve all heard of wifi and Bluetooth, the later named after a 10th Century Scandinavian king. The latest in this list is ZigBee. Designed not as a competitor to Bluetooth, it is more of a complementary operation with different parameters.
Bluetooth is designed as a ‘short-range wireless specification for connecting mobile products’, with short-range meaning anywhere up to 10 metres (Bluetooth can transfer data at up to 1,000m, but rarely is this distance permissible). To communicate, both devices are required to support the same profile. Bluetooth uses the IEEE 802.15.1 standard, which allows a relatively high data transfer, with speeds of up to three Mbps, with the data transmitted in digital packets, reducing the possibility of interference from machinery and atmospheric conditions.
The ZigBee Alliance’s mission statement describes itself as the drive to ‘enable reliable, cost-effective, low-power, wirelessly-networked, monitoring and control products based on an open global standard’. As such, ZigBee also uses digital packets, but with different parameters. Using IEEE 802.15.4, setting specifications for ‘low data rate wireless connectivity with fixed, portable and moving devices with no battery or very limited battery consumption requirements’. Although the range is again, typically 10m, the data transfer rate is generally much lower – a maximum of 250kbps, though this is balanced with the possibility of longer ranges for lower data transmission. In comparison, a wireless local area network (WLAN) can transmit up to 54Mbps under the 802.11g standard at ranges up to 40 metres, but are better-suited to information transmission rather than monitoring such equipment as sensors.
One of the desirable features for wireless protocols is scalability – the ability to easily expand the network. On that score, ZigBee would appear to have the upper hand over Bluetooth, the latter limited to eight devices connected by an ad-hoc network. With its universal standard, ZigBee is suited to so-called ‘mesh’ networks, decentralized, many-to-many communications among multiple devices. Hypothetically, any authorized wireless device could serve as an access point or repeater in a mesh wireless network. There is an analogy with the internet, which has no central point of control but has nodes, or URL web addresses, that can be accessed at any time by any authorized device, whether PC, laptop or mobile phone. The difference is that the internet carries massive amounts of information, whereas ZigBee and wireless networks generally carry much less data, with packets of up to 1,500 bytes. Additionally, Bluetooth devices have only two roles: master or slave. ZigBee, though, enables devices to fulfill a number of roles, including master/co-ordinator, router on the mesh or end node, according to Adaptive Wireless Solutions. The mesh gives users flexibility and improves the reliability of the network by allowing multiple possible transmission paths. Should one be blocked or is experiencing interference, it can try others until it gets through, with range conceivably extended through the use of multiple-hop stages.
ZigBee is currently used in applications such as condition-based maintenance, environmental monitoring (such as humidity management in data centres), in intensive monitoring for plant commissioning and shutdown, which are short-term, intense activities, in security and asset protection, automated meter reading, and in industrial operational control, primarily in OEE functions for optimisation of equipment utilisation – in other words, computer-based maintenance. Adaptive Solutions also sees future uses in assembly line workflow and inventory management.
Bluetooth is currently used in short-range machine-to-machine communication – in a 'here it comes/I have received it/process being undertaken/expect it soon/process completed' setup – and it’s also useful for intermittent connections, for example, in maintenance or condition checks. While it has its limitations, particularly on the requirement to set up individual machines on the same profile, its greater data capacity could be beneficial for processing telemetry, data synchronisation and linking back office functions with process control. The devices need to be connected to the mains or to be regularly recharged, but Bluetooth facilitates the use of handheld computers, laptops and PDAs to acquire and transmit more and deeper information.
The two principle attractions of current wireless systems are the freedom of movement accorded to operators, especially with Bluetooth systems, and the low cost. Instead of wires carried from control, through nodes to application points, the installation of wireless sensors and controls is relatively cheap. But that is balanced by security and reliability issues. Information security is not as strong as some would make out, with directional antennas having ‘back lobes’, radiating energy from the rear of the unit allowing unauthorised access to the network. Ceiling-mounted antennae can also transmit RF signals beyond the intended area. Part of the system integrator’s job is to evaluate vulnerabilities and advise on them, though the 802.11 standard has inbuilt security features and enhancements, with a variety of firewall, encryption and authentication products available.
As wireless technology develops, its applications become more widespread, user-friendly and practical. ABB Robotics has done a lot of work on WISA – wireless interface for sensors and actuators – and has recently announced new products and applications that take the industry another step forward. Wyless plc., announced in January 2008 that it had been selected by ABB to provide a remote service which will enable production lines to maintain round-the-clock operation, using the Wyless global wireless data network to implement pro-active maintenance, reducing downtime and lifetime costs across its whole installed base of 160,000 robots.
“We provide our customers with a wireless global network, based on GPRS,” said Wyless’ Charles Martin. “Our system provides the ability for companies to manage assets, communicating from outside, to ensure they’re operating as they should be. Asset management is one angle: remote workers log in to see how individual machines are working. GPRS is a common technology for monitoring equipment, such as pumps and meters, which they need to see in real time and get information back to the central source. It could be expensive to send personnel out to inspect and repair high-value machines, so monitoring is vital. On the other hand, you could have low-value machines with vital data – for example, temperature monitors – and remote technology can be used to control and talk to the machines and keep them operating properly. You can use our network to transmit updates for firmware and software, check the condition of the machines and plan maintenance for the most convenient time.”
The same system can monitor the ongoing care, operation and maintenance of the machines as they are run on-site. “The company gets real-time feedback. The user interface provides information and data back, which can enable the supplier to help optimise the way it’s used.” One can imagine the sort of help that would be with warranty claims. The Wyless/ABB remote service package logs each robot's key performance data and transmits it to an ABB service centre via GPRS. If there is a problem, the robot can automatically alert the central database, which will trigger an SMS to the identified engineer. He can remotely access the detailed error log and identify the exact fault. But there’s no need to wait for an alert - the engineer can verify status and access maintenance information at any time through ABB’s 'MyRobot' website.
The company’s WISA concept incorporates wireless sensors, proximity switches and sensor pads, which also offer wireless power and cable-free operation. This solution incorporates the ability to monitor and control robot turntables and handling applications; robot cells; modular assembly systems; assembly machines, such as presses, with frequent tool and device changes; and complex movements such as cage stranders, material handling and robot grippers. It’s suitable for small and larger machines and, as there are no cables at all – not even for power – installation is relatively simple. Lifetime costs should be kept to a minimum as both power and data transmission is zero-wear, plus a single machine or cell can have a collection of devices, all operating together through a mesh.
It wasn’t that long ago that wireless, while it held out a lot of promise for the future, could only effectively deliver simple monitoring and actuation functions. As the technology becomes more advanced and reliable – and is more integrated with IT – its effectiveness and cost becomes more practical, even for smaller operations.