Multifinger electroactive-polymer grippers (MEPGs) are simple, compact, lightweight robotic end effectors with fingers that bend and function similarly to human fingers. The fingers are made from electroactive polymers, which are well suited to use in bending-type actuators because they can be formed into various shapes, are flexible and tough, and damp vibrations. In comparison with electroactive ceramics, electroactive polymers are much lighter and exhibit about 100 times as much actuation strain. Like other polymers, electroactive polymers can be mass-produced at relatively low cost.
More specifically, the fingers of MEPGs are made from ion-exchange membrane platinum (IEMP) composite polymers. When a voltage is applied across the thickness of such a finger, electrostriction in the polymer causes the finger to bend; the direction of bending depends on the polarity of the voltage.
The figure illustrates an MEPG with two opposed fingers wired in antiparallel so that they will bend in opposite directions (and thus toward or away from each other) in response to an applied voltage. The angle of bending of a finger can exceed 120°. Typically, a finger is driven with a potential of about 5 V and consumes a power of about 25 mW.
In a typical operational sequence, a voltage of one polarity is applied to spread the fingers apart to clear an object as the hand approaches the object. Once the hand is positioned over the object with a finger on each side, the polarity is reversed to close the fingers around the object. Hooks on the ends of the fingers (somewhat analogous to fingernails) help to secure the grip on the object, which can be picked up and carried once the fingers close around it. In experiments, a two-finger prototype hand lifted a rod with a mass of 1.5 g, and a four-finger prototype hand lifted a rod with a mass of 10.3 g.
This work was done by Yoseph Bar-Cohen, Tianji Xue, Mohsen Shahinpoor, and Shyh-Shiuh Lih of Caltech for NASA's Jet Propulsion Laboratory. In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
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