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Lifelike robotic finger movement relies on shape memory alloys

09 October 2015

A US researcher has created a novel robotic finger that moves in a lifelike manner by successively heating and cooling shape memory alloy actuators.

The technology uses both a heating and then a cooling process to operate the robotic finger (images courtesy of Florida Atlantic University)

The work was carried out by Florida Atlantic University's (FAU's) Erik Engeberg using shape memory alloy, a 3D CAD model of a human finger, a 3D printer, and a novel thermal training technique.

“We have been able to thermo-mechanically train our robotic finger to mimic the motions of a human finger like flexion and extension,” says Dr Engeberg. “Because of its light weight, dexterity and strength, our robotic design offers tremendous advantages over traditional mechanisms, and could ultimately be adapted for use as a prosthetic device, such as on a prosthetic hand.”

Using a 3D CAD model of a human finger, which they downloaded from a website, they were able to create a solid model of the finger. With a 3D printer, they created the inner and outer moulds that housed a flexor and extensor actuator and a position sensor.

Both flexor and extensor are made from shape memory alloy (SMA) and are heated via an electrical current - the extensor actuator takes a straight shape when it’s heated, whereas the flexor actuator takes a curved shape when heated. The motions of the finger joints are thus determined by heating and successive cooling of the SMA actuators.

The team was able to demonstrate a rapid flexing and extending motion and the ability of the finger to recover its trained shape more accurately and more completely, confirming the biomechanical basis of its trained shape.

“Because SMAs require a heating process and cooling process, there are challenges with this technology such as the lengthy amount of time it takes for them to cool and return to their natural shape, even with forced air convection,” says Dr Engeberg. “To overcome this challenge, we explored the idea of using this technology for underwater robotics, because it would naturally provide a rapidly cooling environment.”

Since the initial application of this finger will be used for undersea operations, Engeberg used thermal insulators at the fingertip, which were kept open to facilitate water flow inside the finger. As the finger flexed and extended, water flowed through the inner cavity within each insulator to cool the actuators.

“Because our robotic finger consistently recovered its thermo-mechanically trained shape better than other similar technologies, our underwater experiments clearly demonstrated that the water cooling component greatly increased the operational speed of the finger,” adds Dr Engeberg.

Undersea applications using Engeberg’s new technology might help to address some of the difficulties and challenges humans encounter while working at depths. 

The work is published in the journal, Bioinspiration & Biomimetics.

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