The pneumatic-electrical dynamic in motion control

22 September, 2016

The benefits of automated motion control are becoming increasingly well-recognised, with both electrical and mechanical developments having made major technological strides over the past few years. Chris Walsh, UK sales manager, Asco Numatics, reflects that in the past, pneumatic equipment was often less compatible with a control system. This often resulted in the mechanical engineers of yesteryear having separate pneumatic systems – sometimes with banks of solenoids – communicating with the electrical system.

“Historically the fluid power components were designed into a machine for its movements on one page and the intelligent control was kept separate,” he explained. “The two technologies were effectively brought together by using an electro-pneumatic interface – for example solenoid valves and PLC in a control cabinet. Today, pneumatics and electrical devices are commonly conceived together as part of a fully generic machine design; control of both is considered as one. Pneumatic actuators are now often controlled by intelligent solenoid valves which are typically part of a fieldbus system; sometimes with proportional control, with feedback diagnostics networking within a multifaceted factory control platform and able to send wireless data through the extranet.”

Achieving the required result

Richard Edwards, technical director, IMI Precision Engineering, considers that the technology behind most engineering solutions has to involve some level of compromise with regard to fluid power and electrical application. “Typically it’s about deciding on the best choice of technologies to achieve the required end result,” he said, adding that there are well-recognised advantages and disadvantages in both electric and pneumatic actuation. “For example, the advantages of electric actuation include the fact that you don’t need a compressed air supply, which, if you don’t already have one will need sourcing and installing. The ongoing operating cost of an electric actuator may prove to be less than a pneumatic alternative, but the acquisition cost is typically more expensive.

An electric actuator will generally provide a greater level of precision and will offer the flexibility to stop it part way along its stroke. The ability to profile the speed and the force applied throughout the stroke of the actuator can be vital for some applications. However, the changes taking place in the world of pneumatic actuation – such as linear transducers and proportional control – are impressive.”

With regard to specific equipment, Giorgio Guzzoni, product manager, Metal Work SpA, believes electric actuators are the right solution for motion control when it is necessary to position accurately at unspecified values, and control speed and/or acceleration ramps. He adds that both technologies – pneumatic actuators and electric actuators – have come together in what are commonly known as electric cylinders. These are electric actuators housed in structures that have the shape of a cylinder.

Guzzoni also makes the point that despite the increasing prevalence of electrical motion control, pneumatics continues to play a highly significant role. “It wouldn’t be incorrect to say that 95 per cent of cases with movement requirements can be solved with the conventional, reliable, cost-effective and simple pneumatic cylinder,” he said. “The position reached can be checked by a similarly conventional magnetic sensor. Anybody who produces pneumatic components can sleep soundly in bed at night.”

Something that has seen some of the most rigorous development in recent times is the modern industrial robot. Edwards considers one of the advantages of a robot over a special-purpose piece of equipment is its inherent flexibility and its ability to be reprogrammed to undertake a range of different tasks. This is where Edwards believes electronic and electrical actuation systems come to the fore. However, in areas such as end-of-arm tooling, he believes pneumatics can play a highly significant role; for example, a vacuum system to pick up items such as metal sheets or car body parts. “In this way, robotics can be a good example of a hybrid electrical-pneumatic application,” he said.

Maintenance, repair and replacement

From a maintenance, repair or replacement perspective, Edwards comments that when providing solutions into developing countries pneumatic solutions can have an advantage because they are easy to understand and can often be maintained with simple tools. “On the other hand, if something electrical breaks down you may need to fly in a service engineer a considerable distance in order to replace them,” he added.

In terms of lifecycle of a pneumatic actuator, Edwards points out that users will generally see a progressive deterioration in performance towards the end of its life. “It will start to get stiff and may start to leak,” he said. “However, through condition monitoring users can keep on top of this type of issue and, for example, allow the machine to finish a run before servicing it over the weekend. In the case of an electric actuator, it may operate effectively throughout its lifecycle, but if it fails, it may do so without warning and the machine will immediately cease to function until a replacement actuator is fitted. So, depending on the application this can be a consideration when choosing pneumatic or electric actuation.”

Keeping safe

From a safety perspective, Edwards points out that many mining applications are largely or completely pneumatic in order to reduce the risk of a spark inside a potentially explosive atmosphere. “This can be more convenient than trying to encase everything within an electric application,” he said.

With regard to regulatory requirements concerning safety, Edwards believes it can be an advantage to have both pneumatics and electric control options in place in order to eliminate the potential for a single failure mode. “In this way, companies that deploy an electric solution with a pneumatic backup or vice versa, can rest easier if they lose their power supply,” he said.

Industry 4.0

The motion control industry is increasingly looking at the potential of connectivity concepts such as the Internet of Things (IoT) and Industry 4.0. In this regard, Walsh makes the point that fluid power product portfolios are now becoming more and more aligned with high-end control system functionality. “Cross-protocol communications is becoming a must and rapid data-exchange of all components is expected with Industry 4.0,” he said.

In terms of maintenance, Edwards comments that as engineers become more aware of the potential for connected communication between devices and more conscious of the benefits that could potentially be gained through, for example, a better preventative maintenance or condition monitoring regime, he believes Industry 4.0 will increasingly become the norm.

Pushing the innovation envelope

In terms of other recent innovations within the motion control arena, Walsh explains that there have been a number of enhancements regarding fieldbus technology in pneumatics, positioning feedback in pneumatics actuators (for example, electronic linear transducers within the cylinder) and inbuilt diagnostics in pneumatic valve manifolds (for example, measuring valve speed to predict seal failure).

Walsh has also seen the introduction of products that provide ease of set-up and commissioning for systems engineers; one example being self-addressing fieldbus systems. Additionally, Walsh points to components designed to be easily added-to or changed. “All these developments can provide easier and faster operation, lower labour requirements, and require easier maintenance resulting in less downtime,” he said.

Edwards commented that although a large slice of IMI Precision Engineering’s business involves industrial automation, there is a growing range of applications that don’t lend themselves to simple categorisation. “For example, I recently visited a customer that is producing a system that can fire projectiles and a net in order to capture drones for the purpose of airport security,” he explained. “The company uses a pneumatic cannon to launch the projectile to catch the drones.” Edwards added that electric actuation is also advancing. “As technology changes the costs are coming down and the power density that they can achieve is going up,” he said.

The right solution

Edwards’ view is that pneumatics and electrics shouldn’t be viewed primarily as two technologies in competition with each other. “It really boils down to what is deemed to be the best solution for the end-user’s specific application,” he said. “If you try to sell the wrong technology you may win the business but you’re going to cause yourself and your customer problems further down the road.”

Similarly, Guzzoni stressed that it doesn’t pay to use a sledge hammer to crack a nut – the important thing is to engage the support of technicians that have the right level of knowledge and experience to help companies make the best choices when sourcing motion control solutions.

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