• The researchers developed their new actuators as part of a project to build “printable robots,” whose plastic components, like the one shown here, could be built in layers by machines that resemble ink jet printers. The metal actuator, fastened to the top of the plastic joint, is a fraction of a millimeter thick.

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  • Rectangular notches carved into the shape-memory alloy increase its electrical resistance, so that only the material around the notches heats up when an electrical current passes through the actuator. The round holes are for bolts that attach the actuator to a mechanical device.

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  • Different configurations of the actuators cause different types of motions. Here, charging the actuators causes a plastic joint to fold in half.

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  • In early prototypes, the actuators are bolted to the devices they control. But the researchers are currently experimenting with methods for pressing the actuators into the plastic components as they harden, to simplify manufacturing.

    Photo: Jason Dorfman/CSAIL

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  • The ability to arrange the actuators in series and in parallel addresses a persistent problem with the use of shape-memory alloys: how to harness their high torque and low weight in larger devices.

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  • In a practical device, sheets of actuators would be attached to both sides of a joint like this one, to control both its opening and its closing.

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  • A different arrangement of the actuators is able to lift a weight of almost 17 grams. The researchers’ theoretical analysis suggests that their shape-memory actuators could exert a force 160 times their own weight.

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  • This device consists of five plastic rings connected by actuators.

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  • The actuators connecting the rings can be activated simultaneously to maximize the force they exert, or separately to exert forces in different directions.

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  • Unencumbered, the actuator expands by roughly 60 percent of its original size. Conventional shape-memory actuators that don’t use springs can expand by roughly 3 percent their original size.

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  • Because the new actuators use less energy than their predecessors, they can be powered by batteries, a capability demonstrated by this wirelessly controlled rolling robot, which moves like the tread of a tank — but without any wheels.

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Slideshow: Mini robotic muscles

Shape-memory alloys yield mechanical devices that produce more torque but weigh much less than comparably sized electric motors.


MIT researchers have found a new way to use shape-memory alloys — metals that change shape when heated — to create small mechanical “muscles” for electronic devices. The mechanical muscles — or actuators — can produce three to six times as much torque as electric motors of similar size but weigh no more than one-20th as much.

Previous experimental actuators have used springs made from shape-memory alloys. But the new actuator is easier to manufacture, since it can be cut out of a flat sheet of metal, and to mount, since the sheet can be bolted to a mechanical device’s moving parts. And since only a small section of the new actuator heats up when electrically charged — as opposed to the entire length of the spring — it should dissipate heat more easily and consume less energy.

Eduardo Torres-Jara, a postdoctoral associate in the lab of Professor of Computer Science and Engineering Daniela Rus, designed the actuators and fabricated them with the help of graduate student Kyle Gilpin and research assistant Josh Karges. The researchers envision the actuators’ use in devices too small for electric motors, such as the moving parts at the tips of minimally invasive surgical devices, or the tiny cameras built into laptops.


Topics: Actuators, Robots, Shape memory

Comments

Can you provide more information about the Mini Robotic Muscles and are they available for private development?
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