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A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 0 1 1 MAKING ROBOT GRIPPERS WITH SHAPE MEMORY POLYMERS A team of researchers at Zhejiang University, China, has created a new type of robot gripper using a shape memory polymer (SMP). Developing a gripper that can pick up and manipu- late objects of nearly any shape, differ- ent sizes, and made from different ma- terials typically requires sophisticated mechanisms and associated software. In this new effort, the researchers have done away with such refinement by tak- ing an entirely different approach. Prior research has shown that when certain polymers are heated, they expand slightly and grow soft. So the researchers created a SMP gripper with a cuboid base shape that softens when heated to 45°C and then hard- ens again when exposed to 25°C. They then affixed the gripper to a simple arm that was able to place the gripper down against a tabletop or lift it just above the table—enough to allow placement of various objects underneath. Testing involved placing an object such as a small steel ball beneath the gripper and then heating the entire ap- paratus in an enclosure to 45°C. After a fewminutes, the polymer had softened. The researchers then lowered the grip- per to the object, allowing the object to be encompassed by the material. The temperature in the enclosure was then reduced to 25°C. The polymer shrank Traditional shape memory alloy gripper, courtesy of N.A. Rad et al. Zhejiang Univer- sity researchers are reinventing this model using polymers. slightly, gripping the object as it firmed. The researchers then raised the gripper and the object it was holding. To set the object back down, the researchers low- ered the gripper to the table and raised the temperature in the enclosure to 45°C. www.zju.edu.cn/english.