Linear progression

Astronomy and electronics are two beneficiaries of cutting edge linear motion technology. Lou Reade reports from the Linear Motion Masterclass

Delegates at Eureka’s recent masterclass on Linear Motion discovered that the subject can encompass the very big and the very small – from precision optics to the far reaches of the universe.
The ability to ensure micron accuracy for a part that is 2m wide was used to good effect in a free-form grinding machine – called BoX – developed by Cranfield University and a number of partners. It is used to make very precise mirrors for a new generation of enormous telescopes.
“We are working on the James Webb Space Telescope,” said Professor Paul Shore, who leads the university’s Precision Engineering Centre and was a key figure in the development of BoX.
JWST is an infrared, ground-based telescope – due to go into service in 2013 – that will scan the skies for clues to the origins of the universe. Its 6.5m diameter primary mirror owes a lot to Cranfield University.
Delegates at the event learnt that BoX has one rotary and two linear axes, and has the accuracy of a “top quality” coordinate measuring machine (CMM), said Prof Shore. But the energy needed to remove material from the surface can be a blessing and a curse – with Prof Shore referring to excess energy as the “enemy of precision”. For this reason, the design must be able to handle distortion and deformation.
“A key issue of this machine was to have low moving mass,” said Prof Shore.
And even those who think astronomy pointless can take heart from the likely next step of such components – at the heart of future energy systems.
“The technologies used in ground-based telescopes will allow us to have fusion energy,” said Prof Shore. “Large optics are the ‘wear components’ for the potential clean energy of the future.”
At the same event, Dutch manufacturing giant Philips unveiled details of its linear motion research – including a new architecture that allows a linear motor to move in two axes simultaneously.
The technology, dubbed NForcer, has been covered previously in Eureka. Dr Georgo Angelis, senior scientist at Philips Applied Technologies, explained the technology – and its implications – to delegates.
“It’s an off-the-shelf solution,” he said. “It enables standard ironless linear motors to simultaneously provide movement along two axes – rather than along the conventional single axis.”
A very simple concept is at the heart of the patent: by moving the position of the forcer so that it sits totally within the magnet track – rather than extending beyond it – it can be made to move in two directions. Benefits include: more compact design; lower moving mass (allowing higher acceleration and speed); and reducing the number of motors and electronic drive modules.
The concept has been shown at the heart of a pick-and-place machine – and is likely to find use in the electronics industry. Philips will license the technology to interested parties – which could include machine builders and even linear motor manufacturers.

Tom Shelley

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