Continuum mechanism bends flexibly and locks stiffness for improved control
Design and Characterization of a Variable-Length Continuum Mechanism with Force Locking
Robotics
Summary
Continuum mechanisms can bend and move like a snake, but they can be too soft to handle heavy tasks. The authors designed a new type of bending mechanism that can switch from being flexible to very stiff by tightening rods that lock its shape. This mechanism can bend up to 180 degrees with good accuracy and becomes stiffer when force locking is applied, making it stronger against certain types of pressure. The amount of stiffness can be tuned by adjusting the tension in the rods, giving precise control over how rigid or flexible the mechanism is.
What this means in practice
- •For robotic manipulators: Build robots that can flexibly navigate tight spaces but stiffen to handle heavy objects precisely.
- •For medical device engineers: Develop flexible surgical tools that become rigid on demand for stable manipulation inside the body.
Authors
Katelyn King, Veronica Fish, Allison M. Okamura
Abstract
The utility of flexible continuum mechanisms for dexterous navigation is often impaired by their low stiffness, making them ineffective at manipulation in high-force scenarios. To address this challenge, we propose a novel continuum mechanism that achieves both flexible and rigid behavior by antagonistic extension and contraction of a rod-driven continuum helical structure. The helical design combines variable-length capacity with force locking for workspace and stiffness enhancement. In this article, we present the detailed design of the proposed mechanism and characterize its performance through experiments that quantify bending and stiffness. The results demonstrate 180 degree bending range of motion with an average distal positioning error of <10%. Further tests demonstrate that force locking directly improves axial stiffness and thus indirectly increases bending stiffness anisotropically, with maximum bending stiffness along load paths with a large axial component. Tensioning the driving rods provides additional stiffness tunability in the force-locked state, where increasing rod tension proportionally increases bending stiffness with a dimensionless gain of 0.56.