  Soft, tip-extending "vine" robots offer a unique mode of inspection and
manipulation in highly constrained environments. For practicality, it is
desirable that the distal end of the robot can be manipulated freely, while the
body remains stationary. However, in previous vine robots, either the shape of
the body was fixed after growth with no ability to manipulate the distal end,
or the whole body moved together with the tip. Here, we present a concept for
shape-locking that enables a vine robot to move only its distal tip, while the
body is locked in place. This is achieved using two inextensible, pressurized,
tip-extending, chambers that "grow" along the sides of the robot body,
preserving curvature in the section where they have been deployed. The length
of the locked and free sections can be varied by controlling the extension and
retraction of these chambers. We present models describing this shape-locking
mechanism and workspace of the robot in both free and constrained environments.
We experimentally validate these models, showing an increased dexterous
workspace compared to previous vine robots. Our shape-locking concept allows
improved performance for vine robots, advancing the field of soft robotics for
inspection and manipulation in highly constrained environments.
