Pre-tensioned shape memory actuator

A clamping device comprising a shape memory actuator capable of reliable functioning after long periods of inactivity for providing remote actuation at relatively high loads to mechanisms, a two-way shape memory alloy formed into said actuator and having an original position, said alloy being pre-tensioned to a pre-tensioned position, means for partially compressing said alloy actuator to a position intermediate said original position and said pre-tensioned position whereby said alloy actuator fore-shortens back to its original position when heated and expands back to the intermediate position when cooled, means for applying force to a work object, said actuator being in contact with the applying means whereby said actuator supplies the force to said applying means at its intermediate position under normal temperatures and releases the force to said applying means when heated, the force being supplied again when said actuator is cooled and reverts to its intermediate position.

The method of making a two-way shape memory alloy article comprising the steps of fabricating the article from a shape memory alloy having a predetermined initial length l.sub.o, stretching the article to a length l.sub.s greater than its initial length l.sub.o, compressing the article to a length l.sub.c, heating the article until its length returns to the initial length l.sub.o, and cooling the article until its length expands to the compressed length l.sub.c.

The method of applying a compressive force to a work object comprising the steps of utilizing as part of a clamping device a two-way shape memory alloy actuator, pre-tensioning said alloy actuator to a pre-tensioned position, partially compressing said actuator to a position intermediate its original position and said pre-tensioned position, heating said actuator and allowing said actuator to fore-shorten back to its original position, cooling said actuator to cause it to expand again to its intermediate position, arranging said actuator in the clamping device in order to apply compressive forces to the work object under normal temperatures, heating the actuator to release the compressive forces, and cooling the actuator to again apply the compressive forces to the work object.

The method of treating an alloy in order to impart to its pretensioned properties comprising the steps of fabricating an article from a shape memory alloy having a predetermined initial length l.sub.o, stretching the article to a length l.sub.s greater than its initial length l.sub.o, compressing the article to a length l.sub.c, heating the article until its length returns to the initial length l.sub.o, and cooling the article until its length expands to the compressed length l.sub.c.