Electric avenue

Are hydraulics and pneumatics being killed off by electric alternatives in motion-control applications? Ben Hargreaves finds that it’s more a case of evolution than revolution.

All-electric machines are fast becoming the fashion. If a company perceives itself as being at the cutting edge, it’s more than likely to be going for electric systems in its factory.

There are signs that hydraulic and pneumatic systems, the bedrock on which motion-control applications have rested for generations, are under threat from the development of viable electromechanical alternatives. But the consensus is that the new kid on the block will not be taking over quite yet.

Engineers in a wide variety of sectors are becoming increasingly aware of the advantages of electric systems. Some industries are even making fundamental changes to their traditional ways of working to accommodate a greater amount of electric kit. The imminent switch from a 14V to 42V architecture in the automotive industry is a prime example: the change may herald the complete replacement of systems that rely on hydraulics with electric versions.

In April German machine tool company Demag Ergotec launched its first all-electric drive injection-moulding machine, the IntElect Directdrive. Previous Demag machines were driven purely by hydraulics, or were electro-hydraulic hybrids. ‘Precision is the main driver for the adoption of electric alternatives,’ said Nigel Flowers, technical director at the firm’s UK subsidiary. ‘There are numerous benefits associated with these electric machines,’ he added. ‘They are less noisy, and feature greatly improved energy consumption – typically they use 40 per cent less energy than hydraulic machines. Most importantly, they have higher levels of repeatability.’

Electric actuators and cylinders offer a repeatability in the order of ±0.013mm. They are easier to install and maintain than their hydraulic and pneumatic counterparts as they are cleaner and more reliable. They also have readily predictable life-cycles. According to Flowers, certain industries have created a greater demand for these all-electric machines. This is particularly true of the medical sector, where all-electric drive systems are well suited to clean room environments.

But it’s not just in high-end or very specialised applications that systems such as the IntElect are making their mark. ‘All-electric technology has become more affordable. Historically it was too expensive for trade shop moulders and so on, but it’s now within their reach. We’ve become better at manufacturing the machines, which is driving down the total cost.’

SMC Pneumatics is another company that has branched out into electric systems, offering a full range of electric actuators to complement its well-established pneumatic offerings. Are these actuators now often replacing their pneumatic predecessors? ‘Not as a matter of course,’ said Nick Pittwood, SMC’s newly appointed UK sales manager. ‘There are no clear-cut applications where we would definitely choose an electric actuator over a pneumatic one. But increasingly we are finding ourselves in a position where we could go with either an electric or a pneumatic actuator solution. This is particularly the case in the medical and electronics sectors.’

‘Electric actuators work very well in clean, quiet environments,’ said Pittwood. ‘They are also good for applications that involve extremes of speed: either a very high speed, or even a very low speed, or a precise control speed. Those are applications where electric actuators really come into their own. They are also ideal when you need high positional accuracy or repeatability.’

The availability of electric actuators, Pittwood said, can open up new markets to companies formerly reliant on pneumatics technology. ‘One of the big benefits of electric actuators is that they don’t rely on compressed air. So you can open up to the machine builder some markets that would have eluded them because of this reliance: offices, hospitals, clinics and so on.’

So with these changes in the market, are the days of pneumatic and hydraulic control systems numbered? As is often the case in engineering, it’s not that simple. Electric motors produce very small torques compared to their size and weight, making them unsuitable for use in applications where small but very powerful systems are required – robotics for example. Where extremely heavy loads (greater than 25,000N) are to be moved, hydraulics still represents the best option. Pneumatic systems are an economical solution when very light loads must be moved rapidly and repeatedly from a fixed location to another fixed location.

‘The pneumatic system comes into its own in straightforward applications, where cost and simplicity make the pneumatic solution attractive,’ said Mike Stoneman, director of engineering at KV Automation. ‘In general, the pneumatic product is more robust in industrial and transport environments. More and more pneumatic products will, without maintenance, outlive the machines on which they are to be installed.’

But what about the headaches associated with the installation of a pneumatics system? ‘Increasingly the pneumatic supplier will provide a modular system that can be pre-tested and supplied in a ready-to-install condition, thus taking away the need to understand the more complex interactions of the pneumatic control system.’

Pittwood said that, though the company’s electric actuator business is growing, he isn’t worried about the effect it will have on SMC’s traditional product portfolio. ‘Electric actuators are a relatively recent addition to our range, and I would expect that growth trend with any new product.’ SMC is also currently bringing out hybrid electro-pneumatic solutions – a move that reflects another significant demand from the market.

Stoneman too remains unconcerned that electric solutions are beginning to threaten pneumatics. ‘There are many new, less traditional applications for pneumatic products and systems. We have seen business increasing over the past few years, rather than being lost to electrical solutions. It’s just that many such applications do not include the use of the conventional actuator.’

Nor does Flowers believe that the day of the hydraulic machine is over – yet. Despite the development of the IntElec, his company still views its original hydraulic machines as an important part of its injection-moulding range. ‘There is still a place for them,’ he said, ‘although they may well move into very different market segments to the ones they operate in now.’

The problem afflicting hydraulics, Flowers said, is that following many years of development of servo valves and pump technology, only incremental improvements in performance are now possible. ‘It’s difficult to see where we’re going to go with the hydraulic machines from here. We’ve got a very mature drive system there.

‘With all-electric drives, on the other hand, we’re at the beginning of the development cycle. There are much greater gains to be made. If you project forward three or four years we will see considerable growth in all-electric machines.’

SMA actuators

Pneumatic, hydraulic and electric actuators aren’t the only kinds available. An alternative comes in the form of shape memory alloys (SMAs).

Discovered by Swedish physicist Arne Olander in 1932 when he was working on an alloy of gold and cadmium, SMAs can be plastically deformed when cool and then heated to return to their original shape – a phenomenon known as Shape Memory Effect (SME). Researchers demonstrated in the 1950s that SMAs could be used to perform mechanical tasks. In 1961 a further breakthrough was made when US naval researchers discovered that an alloy of nickel and titanium also exhibited SME.

To perform as an actuator SMAs must go through a cycle of heating, cooling and deformation, limiting their early use to temperature regulation systems where the environmental temperature could be used for thermal actuation. In the 1970s the first commercial products to employ SMAs began to appear. In 1982 Sharp incorporated SMA actuators into electric oven dampers, while Matsushita Electric Company designed SMA-actuated louvres for air-conditioners. Today SMA actuators are of great interest to the robotics industry because of their excellent force-to-weight ratio, compact size, simplicity and silent operation.