Airbus collected data from tens of thousands of embedded sensors during A380 test flights

Miniaturisation: the big issues

Automated manufacturing and precision engineering are driving demand for ever-smaller components that are also smarter and save money.

Smaller, lighter, faster is the mantra that Peter Dent, managing director of LEMO UK, cites as the reason behind the demand for miniaturisation in the design industry. Though this demand is not a new phenomenon, all areas of design engineering are now meeting the challenge of miniaturisation for use in aeronautics, automotive, medical industrial automation and consumer products, to optimise performance, and reduce operating and maintenance costs.

In the electronics field, computer processing power that once took up whole rooms has been reduced to the size of handheld devices. In mechanical design, equipment has been getting smaller for the last two decades, to fit more functionality into a vehicle or aircraft without incurring performance penalties.

Furthermore, in the aircraft industry, pneumatic and hydraulic systems are being replaced by electric systems for the beneficial purposes of lighter weight and lower maintenance costs. “A typical avionics box, 20 years ago would weigh about 10–15kg,” explains Dent. “Today, the work of ten such boxes is performed by one rack and ruggedised card file.”

In other industries, such as the defence market, the move to electric and hybrid-electric vehicles is driven by the power-to-weight ratio benefit this technology brings. It has introduced a new generation of connectors that did not exist 20 years ago, such as those used in unmanned vehicles and drones. There is also a new generation of connectors in the medical sector: portable devices continue to increase in complexity but there is a need for such devices to be light in weight to be carried, or in the case of some military projects, worn on the body.

Industry 4.0

The shift to the smart, automated factory, dubbed Industry 4.0, is another driver for miniaturisation as more automation and intelligence are introduced into the whole supply chain. The main cost of automation is energy, so its rising cost, together with legislation to reduce energy consumption, are driving development in all areas.

“In emerging economies, low-cost labour is becoming scarce, and automation is a viable alternative,” adds Dent. “Miniaturised components are also making human assembly impractical in some cases. In mature economies, the key driver for this increased automation is energy efficiency.”

Connector design has also changed with the march of miniaturisation. Dent says the connector used to be treated as a mechanical part, but now shrinking the size focuses the design effort on its electrical properties. Similarly, CAD (computer aided design) tools were used to develop connectors, but now CAD tools are used for the mechanics while electrical simulation software looks at the electrical performance parameters.

This throws up its own design challenges. As parts are placed closer together, there are electromagnetic compatibility issues. It can also lead to non-uniform heat distribution which can cause disruptive thermal effects.

The connector used to dictate the size of the enclosure, but today contact technology has evolved to increase pin counts at reduced spacing for greater density. Dent recalls that in the 1980s, a typical aircraft connector pitch would be 2.54mm, reducing to 1.90mm 20 years ago and it is now at 1.25mm or less.

“The Airbus 350 was created with around 6,000 sensors generating 2.5TB of data a month,” says Sudhir Sharma, high-tech electronics programme director at Ansys. “The next Airbus 380 is forecast to have 20,000 sensors, generating three times the data volume.”

Dent maintains there is an ergonomic limit to connector miniaturisation. “A medical connector size will be limited by the fact that it will have to be handled by medical staff. There are also practical questions in automation, such as how a part will be assembled and handled during manufacture.”

He adds: “The next evolution will be new materials and processes, as graphene, nanotube and amorphous materials will be used for their conduction characteristics, weight and strength properties.”

Sensor needs

The number of sensors used in factory equipment has increased, and the reduction in size means that more nodes can be monitored and new parameters measured in the manufacturing process, without increasing the size of the machine. “Measuring the part after manufacture produces an unacceptable yield of 80 per cent,” says Chris Jones, managing director of Micro Epsilon, who attributes the reduction in size to integrated electronics.

The electronics, sometimes called conditioning electronics, or the part of the sensor that converts the measurement signal to the output signal, has reduced in size by a factor of 10 in recent years. For example, an eddy current displacement sensor which five years ago would have used microelectronics on a PCB measuring 100 x 50mm, now uses one that is 10mm square.

For Jones, miniaturisation will lead to increased intelligence. “Our sensors know when they are not measuring as accurately as they can and they adjust themselves,” he adds. “We measure things like temperature, expansion, movement and then correct for that, and output the correct signal, without the customer even knowing it”.

While few sensors are used in the engines of aircraft today, Jones speculates that this will change in future, bringing benefits that have not previously been possible. “Integrating miniature sensors in critical parts of the engine means you can have better condition monitoring to predict wear and predict maintenance and schedule maintenance,” he notes.

This is the case in the automotive industry as engineers can embed miniature sensors in the engine to monitor more parameters during development, letting them see which parts are wearing out more quickly so they can design an engine for greater life expectancy and greater efficiency.

The role of software

Simulation software verifies designs at a miniature scale. The performance of MEMS (microelectromechanical systems), such as gyroscopes, accelerometers, speakers and microphones used in smart watches and phones, can be difficult to measure.

“Microscopic technologies are needed to ensure that a microscopic probe does not disturb the function of the device, but these are expensive, so simulation software is used,” explains Bjorn Sojdin, vice president of product management at software company, COMSOL. “Miniaturised devices are counter-intuitive; in a device where temperature is not important, when that device is miniaturised, temperature becomes very important.

“As things start to be tightly integrated, the mechanical performance can be affected. As devices shrink, more physical phenomena, and some we cannot see [at full size], come into play,” he warns.

Software also analyses the mechanical load pattern on, for example, wearable devices or the electro-kinetic flow for medical devices, such as a lab-on-a-chip.

Miniaturisation means that precise assembly is vital as there is less room for manoeuvre. “This can only be realised with precision alignment and connectivity,” explains LEMO UK’s Dent.

Mechanical engineering

A completely different set of challenges faces ball bearing production. “A big driver in bearings in an industry like aerospace is power density,” observes Nick Dowding, business development manager, Barden Bearings, which is part of Schaeffler. Each additional motor on an aircraft adds weight, so it must be small and light.

The same applies in the medical industry as miniaturised, automated, robotic surgery uses miniature tools. Dowding explains that this creates a demand for mechanical components with a smaller footprint, such as the 0.75mm ceramic ball bearing for use in surgical equipment such as a bone saw, where the end is a rotating tip that cuts through the bone. The use of ceramic makes the ball bearing small but with the required stiffness for the cutting operation.

Replacing steel with ceramic is not a new concept, and machine techniques have been adapting to make the bearing small. “This goes hand-in-hand with the design process,” explains Dowding. “Most bearings are designed for a specific application, so to make it as small as possible means working at the edge as far as performance of materials and accuracy are concerned.”

Barden Bearings uses Bearinx modelling software, developed by its parent company, Schaeffler, to model performance in the reduced size. As the reduction may increase a ball bearing’s internal stresses which can generate more heat, the software analyses both stress friction and heat generation.

Dowding says the relationship with the customer is key. As miniaturisation pushes a part’s performance, it is important to know the exact conditions in which it will be used.

Materials and processes

As well as ceramic, steel alloy is used as a material for miniaturised ball bearings, as it can operate in high temperatures and is easy to manufacture.

A homogenous structure is used in the ‘iglidur’ tribopolymer bearings made by polymer components business Igus. These are lighter and smaller than their traditional metallic counterparts, yet accommodate the same loads. Igus director Rob Dumayne says these bearings are cost effective because they are self-lubricating, so they do not require any additional lubrication and maintenance.

Coatings are also vital, as they can strengthen a miniaturised part and reduce friction. They must be applied at sub-micron thicknesses to ensure there is no change in the geometry of the part.

Finally, Dowding suggests that alternative production methods may need to be developed if miniature bearings are to be made accessible in high volumes for the consumer market. He suggests the possibility of forming small bearing parts from sheet steel, rather than solid materials, for example.

Overall, it is clear that miniaturisation is enabling a number of markets to realise energy, economic, space and weight savings while also creating improved products. It brings together engineering skills, materials and process innovation with manufacturing skills to create a smaller, lighter, more efficient world.

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