NASA explores use of artificial muscles in space probes

NASA / Friday February 19, 1999
Artificial muscles that should give space robots animal-like flexibility and manipulation ability will get their first test on a small NASA rover destined to explore an asteroid.

Under development by Dr. Yoseph Bar-Cohen of NASA's Jet Propulsion Laboratory, Pasadena, CA, the artificial muscles are based on a simple, lightweight strip of highly flexible plastic that bends and functions similarly to human fingers when electrical voltage is applied to it.

Bar-Cohen and a small team of scientists and engineers are working to turn these strips into grippers and strings which can grab and lift loads, among many other potential uses. These strips and strings, known as artificial muscles or electroactive polymers (EAPs), have the potential to greatly simplify robotic spacecraft tasks. The technology could lead in the future to the development of insect-like robots that emulate biological creatures.

Years from now, these devices could also conceivably replace damaged human muscles, leading to partially "bionic men" and "bionic women" of the future, according to Bar-Cohen and his fellow researchers. "My hope is someday to see a handicapped person jogging to the grocery store using this technology," said Bar-Cohen, leader of JPL's Nondestructive Evaluation and Advanced Actuator Technologies unit, although such "blue sky" medical applications, even if proven feasible, may be decades away.

In the near-term, two EAP actuators are planned for use as miniature wipers to clear dust off the viewing windows of optical and infrared science instruments on the Mu Space Engineering Spacecraft (MUSES-CN) nanorover. This mission, led by the Japanese space agency ISAS, is designed to land the palm-sized rover on an asteroid following its 2002 launch, and return a sample of the asteroid to Earth.

"That's just the tip of the iceberg when it comes to space applications," Bar-Cohen added. "Electroactive polymers are changing the paradigm about the complexity of robots. In the future, we see the potential to emulate the resilience and fracture tolerance of biological muscles, enabling us to build simple robots that dig and operate cooperatively like ants, soft- land like cats or traverse long distances like a grasshopper."

Unlike human hands, which move by contracting and relaxing muscles, typical robotic arms utilize gears, hydraulics and other expensive, heavy, power-hungry parts. In future planetary exploration missions, where robots will need to perform tasks like collecting and manipulating samples of soil or ice, such mass and complexity becomes a problem. To meet these challenges, Bar-Cohen and his team have developed two types of artificial muscles that respond quickly to small amounts of electricity by lengthening or bending.

The first is a flexible polymer ribbon constructed from chains of carbon, fluorine and oxygen molecules. When an electric charge flows through the ribbon, charged particles in the polymer get pushed or pulled on the ribbon's two sides, depending on the polarity. The net result: The ribbon bends. Using four such ribbons, Bar-Cohen has fashioned a gripper that can pick up a rock.

The second consists of thin sheets wrapped into cigar-like cylinders that stretch when one side of a sheet is given a positive charge and the other a negative charge. These charges cause the wrapped sheet to contract toward the center of the cylinder, and this constriction forces the cylinder to expand lengthwise. When the power supply is turned off, the cylinder relaxes, enabling it to lift or drop loads.

Eight individual researchers or groups from around the world will demonstrate their work on artificial muscles as part of the Society of Photo-Optical Instrumentation Engineers' (SPIE) 6th Annual International Symposium on Smart Structures and Materials in Newport Beach, CA, in early March, with a media session planned for the evening of March 2. Contact Pat Wright of the SPIE (360/676-3290, x609) for further information on this event.