Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-04-14
2001-06-19
Dougherty, Thomas M. (Department: 2832)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S800000
Reexamination Certificate
active
06249076
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an actuator which has a conducting polymer as its active component and is capable of operation outside of a bulk liquid environment.
BACKGROUND ART
Conducting polymers are a class of polymers which structurally feature a conjugated backbone and are electronically conductive. Some common conducting polymers are polyaniline, polypyrrole and polyacetylene. These materials are semi-conductors in their pure form. However, upon oxidation or reduction of the polymer, conductivity is increased. The oxidation or reduction leads to a charge imbalance which, in turn, results in a flow of ions into the material in order to balance charge. These ions or dopants enter the polymer from a surrounding, ionically conductive electrolyte medium. The electrolyte may be a gel, a solid, or a liquid. If ions are already present in the polymer when it is oxidized or reduced, they may exit the polymer.
In addition, it is well known that dimensional changes may be effectuated in certain conducting polymers by the mass transfer of ions into or out of the polymer. In some conducting polymers, the expansion is due to ion insertion between chains, whereas in others interchain repulsion is the dominant effect. Thus, the mass transfer of ions both into and out of the material leads to a contraction or expansion of the polymer. Typical volume changes are on the order of 10%, and linear dimensional changes are hence on the order of 3%. Stresses observed in current conducting polymer materials are on the order of 3 MPa.
Conducting polymer actuators are typically configured by immersion of the polymer in an environment of a bulk liquid electrolyte. Encapsulated conducting polymer actuators known in the art are limited to bilayers comprising multiple conducting polymer films in which a differential contraction and bending is induced.
Copending U.S. patent applications Ser. Nos. 09/130,500, filed Aug. 7, 1998, entitled “Conducting Polymer Driven Rotary Motor,” 09/204,929, filed Dec. 3, 1998, entitled “Method of Manufacture of Polymer Transistors with Controllable Gap,” and 09/263,980, filed Mar. 5, 1999, entitled “Conducting Polymer Generator-Actuator with Energy Storage/Recovery,” disclose other applications for conducting polymers and are hereby incorporated herein by reference.
SUMMARY OF THE INVENTION
In accordance with an embodiment of the present invention, an actuator has an active member, an electrolyte coupled to the surface, and a counter electrode coupled to the electrolyte. The active member has a surface, a member volume, a length, and an axis. The active member includes a polymer. The application of an electrical potential across the electrolyte between the active member and the counter electrode causes the member to exert, essentially along the axis, a force per unit area of at least 10 MPa. Additionally, the actuator may have a flexible skin for separating the electrolyte from an ambient environment.
In accordance with alternate embodiments of the invention, the active member may be a film, a fiber, or a set of substantially parallel fibers. The conducting polymer may, preferredly, be polypyrrole. The electrolyte may be a gel which preferredly includes agar. In another embodiment, the volume of electrolyte is at least five times the member volume. The counter electrode may be a coiled metal wire, a metallic thin film, or a conducting polymer and distributed substantially over the length of the active member. Application of the electrical potential may selectively activate only some of a set of substantially parallel fibers.
In yet another embodiment, the counter electrode may be a second active member. Such an actuator may further be configured so that stresses may be generated by each member in opposite directions along the axis. The members may cause a torque to be applied to a drive arrangement included as part of the actuator embodiment.
In a further embodiment, an actuator has an electrically deformable conducting polymer active member having a surface and an axis, an electrolyte coupled to the surface, a counter electrode coupled to the electrolyte, and a housing. The member, the electrolyte and the counter electrode are located substantially within the housing. The application of an electrical potential across the electrolyte between the member and the counter electrode causes the member to deformessentially along the axis. The housing may be made of polypropylene. The housing may have a wall thickness which is no more than 20% of an actuator dimension measured along a common axis to the thickness measurement normal to the axis.
In a further embodiment, an actuator has an active member which includes a polymer and a plurality of electrically conductive attachment areas spaced at locations along its length, an electrolyte and a counter electrode. The application of an electrical potential across the electrolyte and an area causes the member to deform.
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Hunter Ian W.
Kanigan Tanya S.
Lafontaine Serge
Madden John D.
Bromberg & Sunstein LLP
Dougherty Thomas M.
Massachusetts Institute of Technology
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