Miniature Electroactive-Polymer Rakes

Unwanted particulate matter in remote instrumentation settings would be removed by simple actuators.

NASA's Jet Propulsion Laboratory, Pasadena, California

Miniature electroactive-polymer rakes (MEARs) are undergoing development for eventual use as simple, lightweight, inexpensive low-power-consumption devices that would remove soil, dust, and/or other loose particulate matter from the surfaces of solid objects. In the original intended application, MEARs is being sought for use, in exploration of remote planets, to expose surfaces of rocks for examination by video cameras and/or other optoelectronic instruments. MEARs could also be used in similar remote-control geological exploration on Earth.

Unlike the tines in an ordinary rake, the tines in a MEAR are actuator fingers that bend under electrical control. Each finger consists mostly of a sandwichlike composite of (1) an inner layer comprising an ion-exchange-polymer membrane between (2) two outer polymeric layers that contain or are coated with gold or platinum and that serve as electrodes. The amount and direction of bending depends on the magnitude and polarity of the potential (typically of the order of several volts) applied between the electrodes. An alternating potential can be applied to obtain a repetitive raking or sweeping action. As described thus far, the MEAR fingers are nearly identical to the bending actuators described in "Robot Hands With Electroactive-Polymer Fingers" (NPO-20103), NASA Tech Briefs, Vol. 22, No. 10 (October 1998), page 78 and "Wipers Based on Electroactive Polymeric Actuators" (NPO-20371), NASA Tech Briefs, Vol. 23, No. 2 (February 1999), page 7b.

Figure 1 is a drawing of a typical MEAR. To enhance the raking action, wires made from aromatic polyamid fibers and bent into sine curves are attached to the tips of the actuator fingers. To prevent the potential accumulation of static electric charges from the rubbing of the fingers and/or sine-shaped wires on other objects, copper ground wires are added to the tips.

Figure 2 schematically depicts a variant of the basic MEAR concept for removing dust from a glass window. In this case, the window would be wiped by either a MEAR with metal-coated fingers or else by a metal-coated electroactive-polymer wiper like those described in the noted previous article about wipers. To remove charged particles and dust from the window, a large positive or negative dc potential difference would be applied between the window frame and the MEAR fingers or wiper. From time to time, the polarity of the applied dc potential would be switched.

Figure 1. A Miniature Electroactive Polymer Rake contains actuator fingers that bend when voltage is applied. Overlapping sine-shaped wires on the tips enhance the raking action. Ground wires (not shown) at the tips prevent the accumulation of static electric charges.

Figure 2. A Window Wiper containing one or more electroactive-polymer actuators and high-voltage circuitry would remove charged particles and dust.

 

This work was done by Yoseph Bar-Cohen and Sean Leary of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com under the Mechanics category.

NPO-20613