Tendon-Based Stiffening for a Pneumatically Actuated Soft Manipulator

TLDR

Soft robotics offers extended manipulation capabilities compared to rigid links, yet its inherent compliance limits controllable stiffness, prompting exploration of antagonistic muscle‑like mechanisms such as those used by octopus arms. The study introduces a design that enables variable stiffness in a continuum silicon manipulator, targeting applications in minimally invasive surgery. The manipulator uses a hybrid pneumatic‑tendon actuation scheme inspired by octopus muscles, with embedded chambers and integrated tendons that together allow antagonistic stiffness modulation during external force tests. Dual antagonistic actuation improves load‑bearing capacity of soft continuum manipulators, expanding their application range.

Abstract

There is an emerging trend toward soft robotics due to its extended manipulation capabilities compared to traditionally rigid robot links, showing promise for an extended applicability to new areas. However, as a result of the inherent property of soft robotics being less rigid, the ability to control/obtain higher overall stiffness when required is yet to be further explored. In this letter, an innovative design is introduced which allows varying the stiffness of a continuum silicon-based manipulator and proves to have potential for applications in Minimally Invasive Surgery. Inspired by muscular structures occurring in animals such as the octopus, we propose a hybrid and inherently antagonistic actuation scheme. In particular, the octopus makes use of this principle activating two sets of muscles-longitudinal and transverse muscles-thus, being capable of controlling the stiffness of parts of its arm in an antagonistic fashion. Our designed manipulator is pneumatically actuated employing chambers embedded within the robot's silicone structure. Tendons incorporated in the structure complement the pneumatic actuation placed inside the manipulator's wall to allow variation of overall stiffness. Experiments are carried out by applying an external force in different configurations while changing the stiffness by means of the two actuation mechanisms. Our test results show that dual, antagonistic actuation increases the load bearing capabilities for soft continuum manipulators and thus their range of applications.