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Memory metals challenge traditional drives
Published:  01 January, 2005

Memory metals challenge traditional drives

A German start-up company has developed a novel motion technology that could challenge traditional actuators and drives in a variety of applications, including rotary and linear drives, valves, clutches, brakes and relays. The company, called Spyder Engines, has harnessed the unique characteristics of a new breed of "memory metals" to produce compact, rugged, efficient, quiet and lightweight motion devices, with few moving parts.

The company says that its technology could provide a cheaper alternative to traditional electromechanical, pneumatic and hydraulic motion technologies. It claims that, in some cases, its actuators are 80% smaller and 90% lighter than their conventional counterparts. The picture above shows a conventional actuator (left) and its Spyder equivalent (right).

Spyder`s Oliver Simons predicts, in particular, that the new technology "could kill 95% of solenoid applications".

Memory metals, which change shape when heated to a critical temperature, are not new. But earlier materials tended to develop flaws and to lose their memory properties, limiting their practical use. Spyder claims to have developed a new, high-purity material, based on a titanium-nickel alloy, that is super-elastic and will retain its memory properties for several million cycles, at least.

The breakthrough is not just in the materials, but also in the high-vacuum process used to create them, and in the way the materials are formed into disc-shaped actuation elements designed, using finite element analysis, to optimise the memory effect.

These "Working Wire" elements are actuated by an electrically-generated temperature in the range 60-100°C. The resulting motion is a combination of torque and torsion which provides a considerable force and travel distance with relatively little energy input.

Many of the disc-shaped elements can be combined to achieve the required motion. They can, for example, be linked to form a linear actuator with a stroke of up to 85% of its length. A conventional solenoid-driven actuator, by comparison, produces a stroke that is typically, less than a third of its length.

The light weight of the alloy elements, combined with the small number of parts, results in drives with a high power-to-weight ratio. The paucity of parts also boosts reliability, according to Simons. The acid-proof and corrosion-resistant alloy can be used in tough environments.

Another claimed advantage is high efficiency. Unlike conventional electromagnetic actuators which need to be supplied with energy for their entire operating cycle, the Working Wire elements need only brief pulses of current to operate.

The devices will work from DC or AC supplies from 0.7-220V, and can operate in either monostable or bistable modes. It takes about 100ms to heat them up sufficiently to produce a movement.

Within eight weeks of the technology being unveiled at a German trade show late last year, Spyder was already discussing more than 40 possible applications with potential partners. These range from industrial equipment to household appliances and toys. The first commercial applications are expected to emerge by about March of this year.

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