Phase-change material could let robots be soft or hard-bodied as needed
By Ben Coxworth
July 15, 2014
If you've ever watched an octopus, you may have noticed how they can deliver powerful grasping force when necessary, yet can also squeeze through tiny openings by essentially making themselves "liquid." Now imagine if there were robots that could do the same thing. They could conceivably squirm through debris to reach buried survivors at disaster sites, or even travel through patients' bodies to perform medical procedures. An international team of scientists is working on making such technology a reality, using a combination of polyurethane foam and wax.
Although robots that were in a permanently soft state might have no problem wriggling into tight spaces, they wouldn't be able to deliver much force when performing tasks that involved any kind of manual dexterity. As MIT's Prof. Anette Hosoi explains, it would be like trying to manipulate an object using a bowl of Jell-O. That's why her and colleagues from MIT, Germany's Max Planck Institute for Dynamics and Self-Organization, and Stony Brook University in New York are developing materials that would allow robots to alternate between soft and hard states.
To that end, she's already created a material that consists of a three-dimensional scaffold of polyurethane foam coated in wax. The wax remains hard when at room temperature, allowing the material to support weight and deliver torque. When the wax is heated, however, it becomes soft and pliable, letting the material be squashed down, stretched and otherwise reshaped. As an added bonus, any cracks or chips that appear in the wax while it's cool are melted away when it's heated, bringing it back to its original undamaged state once it cools again.
In order to allow a robot to facilitate the temperature changes, the researchers believe that flexible wires could be run along each of the foam struts. The robot would deliver an electrical current to those wires as needed, causing them to heat the surrounding wax or leaving it to cool.
Besides allowing the robot's whole body to become soft, it would also be possible to heat only selected parts of it. This could allow an otherwise-rigid robot to bend at given "joints" where the wax is warm. It could even be temporarily locked in that position, if the current in that area was subsequently shut off.
Given that wax might not be durable enough for use in practical applications, however, Hosoi is looking into using solder instead. She's also investigating magnetorheological and electrorheological fluids, which consist of particles suspended within a liquid, and that can be made soft or rigid via the application of a magnetic or electric field.
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