Three-Fingered Gripper with Flexure Hinges Actuated by Shape Memory Alloy Wires

A three-fingered gripper with flexure hinges actuated by shape memory alloy (SMA) wires was designed and prototyped. The aim of the work was the manipulation of small, almost cylindrical objects, e.g. test tubes, by a device having small overall dimensions. A parametric study of four different, but similar, fingers was conducted with the aim of obtaining a solution with a good amplification ratio and a gripping force almost constant during closure. The use of flexure hinges simplifies the design, but limits the finger range of motion. Moreover, it was possible to find a configuration with sufficient work space. Once the finger geometry was defined, the whole hand was then designed with the aim of producing a compact hand contained in a cylindrical volume (d 65 x h 65 mm), and the first prototype was built. Preliminary tests demonstrated its good dimensioning and the success of some technological solutions. The experimental transmission ratio was almost the same as the theoretical one. Some drawbacks have been highlighted, such as a reduced range of motion and incomplete backstroke; future studies will deal with them.

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