Patent ID: 7226365

Claim:
A shaft structure having an adjustable stiffness comprising in combination: a flexible, elongated shaft having defined therein an elongated enclosed cavity; and means for regulating pressure in said cavity by changing the volume of said cavity, whereby the stiffness of said shaft is regulatable by said pressure in said cavity, including longitudinally slidably movable piston means and platen means in said shaft, spring biasing means located between said piston and said platen means, and jackscrew means mounted in said shaft and coupled to said platen means so as to threadingly displace said platen means; whereby said piston means assumes a longitudinal location in said shaft such that forces on longitudinally opposed sides thereof are about equal and when said platen means is moved longitudinally by said jackscrew, the force on the longitudinally adjacent side of said piston means is changed and said piston means longitudinally moves responsively to a different location where the forces on longitudinally opposed sides of said piston means are again about equal.