| 摘要 |
A housing (10, 46, 64, 90, 100) has an internal opening in which a thin recess is defined for receiving a heat expansible polymer (30) and a heating element (24). In some embodiments, an insert (14, 98, 102) is inserted into the housing bore such that the thin recess is defined therebetween. In other embodiments, the recess is defined between the housing and a force receiving surface of a piston (40, 60). When the heating element is heated, the polymer expands, forcing the piston to extend. When heating is stopped, the polymer cools allowing the piston to retract. In the embodiment of FIG. 4, the retraction is accelerated by a second polymer and heating element region (54). In other embodiments, a transmission arrangement (72, 74, 78; 124, 126, 128) is provided for converting the relatively high force, low travel of the heated polymer to a higher travel lower force output. In one embodiment, the heating element is resistance heating wire (32) which is surrounded by a covering (36) of electrically insulating material which is porous to the melted polymer.
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