Such an actuator could exert a large force at small displacement.

Bending actuators of a proposed type would partly resemble ordinary bending actuators, but would include simple additional components that would render them capable of exerting large forces at small displacements. Like an ordinary bending actuator, an actuator according to the proposal would include a thin rectangular strip that would comprise two bonded layers (possibly made of electroactive polymers with surface electrodes) and would be clamped at one end in the manner of a cantilever beam. Unlike an ordinary bending actuator, the proposed device would include a rigid flat backplate that would support part of the bending strip against backward displacement; because of this feature, the proposed device is called a backed bending actuator.

When an ordinary bending actuator is inactive, the strip typically lies flat, the tip displacement is zero, and the force exerted by the tip is zero. During activation, the tip exerts a transverse force and undergoes a bending displacement that results from the expansion or contraction of one or more of the bonded layers. The tip force of an ordinary bending actuator is inversely proportional to its length; hence, a long actuator tends to be weak.

A Backed Bending Actuator would resemble an ordinary bending actuator except that it would include a backplate that would enable a large displacement together with a large force at small displacements.

Taking all of these effects into account, the cantilever-beam equations show that F_b would be approximately inversely proportional to d^1/2 for d less than a calculable amount, denoted the transition displacement (d_t). For d < d_t, part of the strip would be pressed against the backplate. Therefore, the force F_b would be very large for d at or near zero and would decrease as d increases toward d_t. At d > d_t, none of the strip would be pressed against the backplate and F_b would equal the tip force F of the corresponding ordinary bending actuator. The advantage of the proposal is that a backed bending actuator could be made long to obtain large displacement when it encountered little resistance but it could also exert a large zero-displacement force, so that it could more easily start the movement of a large mass, throw a mechanical switch, or release a stuck mechanism.

 

This work was done by Robert C. Costen and Ji Su of Langley Research Center. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Mechanics category.

LAR-16441

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