THE LATEST RESEARCH AND DEVELOPMENT NEWS IN MANUFACTURING AND TECHNOLOGYTECH FRONT NASA JPL Gecko Grippers are No Mean Feet t R
esearchers at NASA’s Jet Propulsion Laboratory (JPL; Pasadena, CA) are taking a cold-blooded approach to solving a sticky problem, namely how to effectively
and repeatedly grip smooth surfaces in space. You can’t Vel- cro every surface, and adhesives lose their stickiness if used multiple times. How then to get, say, astronauts in a space station climbing the walls? JPL engineer Aaron Parness and his colleagues found an attractive solution in the foot of the gecko, the little lizard that effortlessly clings to walls with feet that, surprisingly, don’t produce any sort of chemical adhesive. What those feet do have are tiny hairs that allow the gecko to stick to even the smoothest of surfaces at will. There’s nothing like glue and the hairs aren’t acting as hooks of some sort. So what’s the catch? Between the gecko’s feet and the wall is a concept called van der Waals forces. When the gecko applies pressure to bend those tiny hairs against a surface, a slight electri- cal fi eld is created because electrons orbiting the nuclei of atoms are not evenly spaced, so there are positive and negative sides to a neutral molecule. The positively charged part of a molecule attracts the negatively charged part of its neighbor, resulting in “stickiness.” Even in extreme temperature, pressure and radiation conditions, these forces persist. Parness and other JPL researchers used that concept to create a material with synthetic hairs much thinner than a human hair. When a force is applied to make the tiny hairs bend, the material sticks to a desired surface. “This is how the gecko does it, by weighting its feet,” Par- ness said. “The grippers don’t leave any residue and don’t require a mating surface on the wall the way Velcro would.” The newest generation of grippers can support more than 150 N of force, the equivalent of 35 lb (16 kg). In a microgravity fl ight test last year through NASA’s
Space Technology Mission Directorate’s Flight Opportuni- ties Program, the gecko-gripping technology was used to
grapple a 20-lb (10-kg) cube and a 250-lb (100-kg) person. The gecko material was separately tested in more than 30,000 cycles of turning the stickiness “on” and “off” when Parness was in graduate school at Stanford University in Palo Alto, CA. Despite the extreme conditions, the adhesive stayed strong. Researchers have more recently made three sizes of hand-operated “astronaut anchors,” which could one day be given to astronauts inside the International Space Station. The anchors are made currently in footprints of 2.5 × 10
Rendering of how LEMUR (Limbed Excursion Mechanical Utility Robot) could inspect and maintain installations on the International Space Station using the gecko-inspired gripping system.
cm, 5 × 15 cm and 7.6 × 20 cm. They would serve as an experiment to test the gecko adhesives in microgravity for long periods of time and as a practical way for astronauts to attach clipboards, pictures and other hand-held items to the interior walls of the station. Parness and his team are also testing a LEMUR 3 climb-
ing robot, which has gecko-gripper feet, in simulated micro- gravity environments. The team thinks robots like this could inspect and make repairs on the exterior of the space station. For testing, the robot maneuvers across mock-up solar and radiator panels to emulate that environment.
October 2015 |
AdvancedManufacturing.org 35
Image courtesy NASA/JPL-Caltech
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