  Robotic arms built from stiffness-adjustable, continuously bending segments
serially connected with revolute joints have the ability to change their
mechanical architecture and workspace, thus allowing high flexibility and
adaptation to different tasks with less than six degrees of freedom, a concept
that we call malleable robots. Known stiffening mechanisms may be used to
implement suitable links for these novel robotic manipulators; however, these
solutions usually show a reduced performance when bending due to structural
deformation. By including an inner support structure this deformation can be
minimised, resulting in an increased stiffening performance. This paper
presents a new multi-material spine-inspired flexible structure for providing
support in stiffness-controllable layer-jamming-based robotic links of large
diameter. The proposed spine mechanism is highly movable with type and range of
motions that match those of a robotic link using solely layer jamming, whilst
maintaining a hollow and light structure. The mechanics and design of the
flexible spine are explored, and a prototype of a link utilising it is
developed and compared with limb segments based on granular jamming and layer
jamming without support structure. Results of experiments verify the advantages
of the proposed design, demonstrating that it maintains a constant central
diameter across bending angles and presents an improvement of more than 203% of
resisting force at 180 degrees.
