US 4,945,727 AGranted

Hydraulic shape memory alloy actuator

OwnerCharles A. Whitehead, Kenneth M. Groominventors

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Abstract

A hydraulic shape memory alloy actuator is provided comprising a uniaxial shape memory alloy wire constructed of Nitinol. The actuator utilizes a pair of hydraulic cylinders in fluid communication with each other, each cylinder containing a hydraulic piston. The first hydraulic piston is moved from a first position to a second position when the wire, connected at one end to the piston and its other to a fixed point, changes from a martensitic to an austenitic state upon heating. The second hydraulic piston responds to the movement of the first hydraulic piston by moving from a rest position to an operating position. Upon cooling the wire to change it from the austenitic state back to the martensitic state, the first piston returns to its original position, with a biasing means being provided to return the second piston to its rest position.

A hydraulic shape memory alloy actuator, comprising:

(a) a first cylinder having fluid therein;
(b) a first piston capable of movement between first and second positions within said first cylinder, said first piston having a fluid contacting surface;
(c) a length of shape memory alloy having a first end connected to said first piston and a second end connected to a fixed point, said alloy capable of changing from a martenistic state to an austenitic state when said alloy is heated above a transition temperature range so as to move said first piston from said first position to said second position, said alloy also capable of changing back to said martenistic state from said austenitic state when said alloy is cooled below said transition temperature range whereby said first piston moves from said second position to said first position, said length of said alloy having a shorter longitudinal dimension in said austenitic state than in said martensitic state;
(d) a second cylinder, said first and second cylinder being in fluid communication with each other;
(e) a second piston capable of movement between a rest and an operating position within said second cylinder, said second piston having a fluid contacting surface, said second piston having said fluid dispersed between it and said first piston, said fluid contacting said fluid contacting surface of said first piston and said fluid contacting surface of said second piston, said fluid communicating the movement of said first piston to said second piston when said first piston moves between said first and second positions, said fluid also communicating the movement of said second piston to said first piston when said alloy changes from said austenitic state to said martenistic state;
(f) biasing means capable of moving said second piston from said operating position to said rest position as said alloy changes from said austenitic state to martenistic state;
and
(g) means for selectively heating said length of shape memory alloy above said transition temperature range.

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Abstract

Claims27