Abstract: An axially contractable actuator which includes an elongated hollow enclosure (14) formed by a fluid impermeable substantially non-elastic material and having a plurality of protrusions each with respective bases having more than three sides. Each base side (48) of a protrusion is attached to a base side (48) of an adjacent protrusion by a flexible seam of continuous fold (55). Each protrusion is foldable about a plane dividing the protrusion into two parts from an axially-extended condition in which the base sides are substantially parallel, to an axially-contracted condition in which the protrusion encloses a volume larger than that enclosed in the axially-extended condition. A pair of axially-aligned end terminations (18) are formed at each end of the enclosure with one of the end terminations being hollow.

Abstract: An actuator has a first connection point and a second connection point at opposite ends and is contractable along an axis extending between the connection points. The actuator has at least one hollow enclosure with an opening for admitting a pressurized fluid. A simultaneously radially expandable, axially contractable constraining means cooperates with the enclosure. The constraining means converts radial expansion of the actuator into axial contraction when pressurized fluid is admitted into the enclosure. In a preferred form, the constraining means comprises a network of non-stretchable, flexible tension links.

Abstract: An actuator has a first connection point and a second connection point at opposite ends and is contractable along an axis extending between the connection points. The actuator has at least one hollow enclosure with an opening for admitting a pressurized fluid. A simultaneously radially expandable, axially contractable constraining means cooperates with the enclosure. The constraining means converts radial expansion of the actuator into axial contraction when pressurized fluid is admitted into the enclosure. In a preferred form, the constraining means comprises a network of non-stretchable, flexible tension links.