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
Technology Reporting Office
JPL
Mail Stop 122-116
4800 Oak Grove Drive
Pasadena, CA 91109
(818) 354-2240
Refer to NPO-20103
This Brief includes a Technical Support Package (TSP).
Robots hands with electroactive-polymer fingers
(reference NPO20103) is currently available for download from the TSP library.
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Overview
The document presents a detailed report on the Multifinger Electroactive Polymer Gripper (MEPG), developed by NASA, which showcases a novel approach to robotic gripping mechanisms. The MEPG is designed to mimic the functionality of human fingers, utilizing ionomer fingers that can bend in response to an electric field. This bending action allows the gripper to clamp onto objects effectively, making it suitable for various applications in robotic systems.
Key features of the MEPG include its low-voltage operation, low power consumption (approximately 25 mW), and lightweight construction, which contribute to the development of cost-effective robotic end effectors. The gripper's fingers can bend at angles exceeding 120 degrees, enabling them to open wide enough to encircle objects and avoid obstacles. The gripping action is achieved by reversing the polarity of the electric field, which allows the fingers to close around the object, similar to how a human hand operates.
The document also describes the electronic circuit designed to control the gripper's operation. This circuit produces a 5-volt DC electric field and operates at a controllable rate of about 0.1 Hz, allowing for a slow response that is suitable for demonstration purposes. The circuit generates a square wave cyclic signal, facilitating the opening and closing of the gripper fingers. The design is compact enough to be mounted on the gripper fixture, making it practical for integration into robotic systems.
Figures included in the report illustrate the gripper's configurations, showing both the open and closed positions, as well as the electronic circuit schematic. The report emphasizes the potential applications of the MEPG in future NASA missions and other robotic endeavors, highlighting its ability to lift and manipulate objects effectively.
Overall, the MEPG represents a significant advancement in robotic technology, combining innovative materials and design to create a versatile and efficient gripping solution. This technology not only addresses the critical needs of space exploration but also has broader implications for robotics in various fields, including manufacturing, healthcare, and service industries. The document serves as a technical support package, detailing the invention and its potential impact on future robotic applications.
