Stiffness-Tuneable Limb Segment with Flexible Spine for Malleable Robots

TL;DR

The paper tackles the challenge of creating low-DOF, stiffness-tunable serial robot links that can adapt topology without sacrificing strength. It introduces a flexible spine integrated with a layer-jamming sheath to form a malleable link that maintains a constant central diameter during bending and remains hollow for cable pass-through. Experimental results show the spine-enabled design achieving up to 31.33 N resisting force at 180°, a 203% improvement over plain layer jamming, and a central-diameter variation of only about 2.1%, indicating reduced buckling and improved maneuverability. This approach advances malleable robots by delivering higher stiffness-on-demand and reliable manual reshaping, with potential to support various topologies and collaborative tasks.

Abstract

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.

Figures (11)

• Figure 1: Malleable robots are reconfigurable serial arms of lower mobility (i.e., less than 6 DOF) with variable workspace, able to be adapted to specialised topologies (e.g., SCARA, spherical, or PUMA-like) as well as to other ad-hoc articulated architectures. These robots are composed of stiffness-tuneable, continuously bending limb segments (malleable links) serially connected with revolute joints; they are characterised by having a continuous body parameter space controlled by a single strategy.
• Figure 2: Sectional view of the developed controllable stiffness link with integrated flexible spine for malleable robots (right). Close-up view showing internal layout and hollow centre (left).
• Figure 3: Double-sided flap pattern specifications for layer jamming sheath with guide holes and slots.
• Figure 4: Neutral spine position (a), compressed spine (b), and extended spine (c).
• Figure 5: ABS rigid spine segment (left) and sectional view of 2-segment spine with integrated flexible ligaments (square planar ligament connections) (right).