The Linear Motion Masterclass 2008

The Linear Motion Masterclass – which successfully kicked off Eureka's series of Design Days – ran again in 2008.

Delegates discovered that the subject of linear motion 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.

Workshop expertise

In addition to the keynote speakers, the event’s four sponsors each ran a workshop covering the main linear motion technologies. These were linear motors (covered by Aerotech); bearings and chains (Igus); encoders (Renishaw); and ballscrews (Steinmeyer).

Aerotech focused on a precision medical application. Vascular stents are produced by using lasers to burn holes in tiny stainless steel tubes – turning the tubes into ‘chicken wire’. Ron Rekowski explained how linear motors were designed into the machine that makes the stents, to improve the accuracy and repeatability.

Igus took delegates through the basics of plastic bearings and chains. The key feature of both types of product is that they are self-lubricating – so are maintenance-free. Justin Leonard revealed that the longest cable chain in operation currently extends to 500m – supporting power cables on a crane in Singapore.

Renishaw used its XL-80 laser interferometer to give a detailed demonstration of how laser calibration can support the design process, in its ‘machine structure’ workshop. “Errors in machine movement can affect process accuracy and impact on quality, yield and throughput,” said the company’s Gary Swan.

Steinmeyer explained the importance of accuracy in linear drives, addressing the keys to positioning, and showed that ballscrews – a product first launched 50 years ago – can remain fresh. Its ETA+ product manages to run more smoothly than a standard ballscrew – but the modifications allowing this are secret and have not been patented.

“Even an expert would not be able to tell what the difference is,” said managing director Alex Beck.