  Shape change enables new capabilities for robots. One class of robots capable
of dramatic shape change is soft growing "vine" robots. These robots usually
feature global actuation methods for bending that limit them to simple,
constant-curvature shapes. Achieving more complex "multi-bend" configurations
has also been explored but requires choosing the desired configuration ahead of
time, exploiting contact with the environment to maintain previous bends, or
using pneumatic actuation for shape locking. In this paper, we present a novel
design that enables passive, on-demand shape locking. Our design leverages a
passive tip mount to apply hook-and-loop fasteners that hold bends without any
pneumatic or electrical input. We characterize the robot's kinematics and
ability to hold locked bends. We also experimentally evaluate the effect of
hook-and-loop fasteners on beam and joint stiffness. Finally, we demonstrate
our proof-of-concept prototype in 2D. Our passive shape locking design is a
step towards easily reconfigurable robots that are lightweight, low-cost, and
low-power.
