Abstract: A hydraulic or pneumatically actuated muscle has an elongated elastomeric tubular bladder covered by a tubular braid. The bladder has a fold or invagination along its length. The process for forming this bladder can employ a fixture in the form of a threaded rod. A tubular elastomer is wrapped into the v-shaped thread on the rod. Then the wrapped rod is subjected to heat to set a fold into the tubing. The invaginate bladder can be subjected to a second, mild heat treatment to reduce curling.

Abstract: A hydraulic or pneumatically actuated muscle has an elongated elastomeric tubular bladder covered by a tubular braid. A fluid conduit supplies hydraulic or pneumatic pressure to the bladder to expand it and thereby shorten the braid. When pressure is relieved, the braid is permitted to elongate, and the bladder constricts radially. To ensure that the bladder has its cross section at a minimum when elongated, the bladder has a fold or invagination along its length. The process for forming this bladder can employ a fixture in the form of a threaded rod.