Shaking’s all over

An elegant yet simple anti-vibration device is under development at BAE System’s Advanced Research Centre in Chelmsford, Essex.

Dubbed SmartSpring, the new mounting system uses a blend of passive spring elements and digitally controlled electromagnetic actuators to isolate harmful vibrations.

The problems generated by vibrating machinery are far-reaching. Noise and vibration can cause damaging fatigue in structures, reduce passenger comfort in all sorts of vehicles, and, in marine vessels, modal vibrations sometimes generate acoustic signatures that can trigger mines.

Traditional solutions are fraught with trade-offs and compromises. For example, to isolate machinery vibration from the base with a conventional passive anti-vibration mounting system (e.g. elastomer rubber blocks) the blocks would ideally be as soft as possible. But, the softer they are, the more the machine can move around, which obviously limits how soft you can make the mounting.

There are also a number of active systems around, but, says SmartSpring project leader Martin Whittemore, as well as being prohibitively expensive, many of these have significant technical limitations.

With no existing scalable solution that could be applied right across the board – from the engine room of a Destroyer to the factory floor – Whittemore believes that SmartSpring could be the solution the world’s been waiting for.

The culmination of over a decade of studied, evolutionary collaboration, the concepts behind SmartSpring are relatively simple explains Whittemore. ‘We’ve moved away from the compromise you have to make with the passive system and now use a composite smart spring mount – a passive spring in parallel with an electromagnet, or a series of electromagnets.’

This combination generates a supporting force that is independent of the load displacement to create a zero-stiffness composite mount. The zero-stiffness concept is based on the approach of using a series of force and accelerometer sensors to calculate and support an object from its centre of gravity. In doing this, there are no forces transmitted through the mount due to any excited resonance from the supported object.

The power requirements for the system are, says Whittemore, quite modest, and one of the big advantages is that – barring the amplifier, which drives the magnet and the control algorithms – the device is made from off the shelf components (COTS). This, he adds, makes the system easier to retrofit – a requirement that has defined the project from the beginning.

Another key benefit of the mountings is that their performance doesn’t deteriorate with age. Because they’re software controlled, the software can effectively be continuously upgraded to compensate for changes in the materials.

Whittemore says that the SmartSpring will make its first appearance in a marine application where the acoustic signature requirement is a pressing issue. Discussions are underway, certain people are said to ‘very interested’ and a planned application is a couple of years away.

Once this has been achieved, Whittemore is confident that the technology will fulfil its wider potential.

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