VaLeNS: Design of a Novel Variable Length Nested Soft Arm

Over the last decade, soft continuum arms (SCAs) have successfully demonstrated the compliance and dexterity needed to operate in unstructured environments and handle fragile objects. However, their inherent soft compliance limits their performance in situations where stiffness and force transfer is required. In this letter, we present a compact design architecture, which is a hybrid between soft arms and rigid links known as Variable Length Nested Soft (VaLeNS) arm. The design architecture involves a novel SCA nested inside a concentric rigid tube. The SCA can undergo a combination of spatial bending ($B$) and bidirectional axial twist ($R^2$), and can extrude out or retract back into the rigid tube with varying length. The resulting configuration is shown to modulate stiffness up to a factor of ten and exhibits enhanced workspace and dexterity. Furthermore, the VaLeNS arm mounted on a rigid robotic platform allows for bifurcation of the overall workspace into rigid and soft, and can achieve high reachability in constrained environments. The letter demonstrates the effectiveness of the VaLeNS arm system in manipulation tasks that require both the rigid and soft attributes. This design architecture is deemed useful in agricultural applications and in physical human robot interaction.