An overview of stiffening approaches for continuum robots

Continuum robots have become more popular recently due to their scalable dexterity and mobility. However, they may suffer from issues like insufficient stiffness because they are designed to promote their flexibility. To address this issue and further improve their performance in all different application scenarios, stiffness flexibility is essential for this type of robot. Therefore, it is necessary to integrate stiffening techniques into both their mechanical structure and actuation approaches when developing continuum robots. To this end, it is crucial to explore how different stiffening approaches can be applied to various types of continuum robots across diverse applications. The primary goal of this survey paper is to provide a comprehensive review of the state-of-the-art research on stiffening techniques for continuum robots over the last two decades. We thoroughly analyse key techniques related to stiffness tunability mechanisms and stiffening methods. Additionally, we categorise these stiffening approaches on the basis of their properties and seek to understand the factors that limit their performance. This survey paper aims to assist robotic engineers in selecting appropriate stiffening techniques when designing continuum robots and serve as a basis for developing potential next-generation stiffening mechanisms.