Miniature gears are `grown` to order

A German start-up company has developed a novel technique for "growing" the minuscule gears used to create what it claims is the world`s smallest backlash-free precision gear.

Normal gear production techniques were incapable of delivering the precision needed to manufacture the micron-scale gears. So Micromotion – a venture set up by Harmonic Drives and the Institute for Microtechnology Mainz – came up with a new technique that combines lithographic processes normally used to manufacture semiconductor components, with a process it calls "second galvanoforming".

X-ray lithography is used to produce accurate moulds that that can be mass-reproduced using processes such as plastic injection moulding. In a second step, metal is deposited in these moulds to "grow" the gears, which are about 1mm thick and have surface tolerances better than 1µm. According to Graham Mackrell of Heason Technologies, which is selling the micro gears in the UK, the result is "an almost perfect surface finish".

The assembled gearboxes are 8mm in diameter and 1mm deep. They contain a combination of planetary and harmonic gears, to produce a reduction ratio of between 500:1 and 1,000:1, and have a repeatability of a few seconds of arc. The maximum output torque is 10mNm at 100 rpm. Hollow-shaft versions are available.

Mackrell says that the gears are likely to be used in applications where the "ultimate accuracy" is needed. Examples include insulin pumps, photonics systems for aligning optical fibres, and wire diebond machines used to create semiconductor chips.

At present, the gearboxes have to be assembled by skilled personnel, such as watchmakers, and each costs £1,200-1,500. But Mackrell predicts that the price could fall to under £150 for large quantities. The technology could be used to produce even smaller components, he adds.