Programmable hybrid-drive actuator for compact and bimodal continuum robot modules

Abstract

Continuum robots have emerged as a promising solution for robotic applications ranging from medical interventions to structural inspections. However, their capabilities are often limited by restricted deformation modes and a reduced range of motion, especially when operating near their base due to the minimum length of conventional actuation modules. This study introduces compact hybrid-drive actuator modules that combine tendon-driven actuation with a network of inflatable tubes. This concept allows for building actuators that can switch between either extension and bending deformations or extension and twisting deformations depending on the configuration of the inflatable tubes. An axial tendon routed through the center of each module generates the deformation, while the inflatable tubes provide a controllable deformation bias that defines the actuation mode. This approach diverges from conventional continuum actuators which typically rely on the selective contraction of multiple tendons to achieve different deformation patterns. The use of inflatable tubes as structural elements also enables extreme compressibility, allowing the modules to occupy minimal space when not actuated. The developed bending/extension (B/E) actuator demonstrated a maximum elongation exceeding 660 % and a maximum bending angle of 80°, while the twisting/extension (T/E) actuator achieved a maximum elongation of 600 % and a bidirectional twisting angle of 120°. These modules were assembled into a continuum robot capable of operating effectively near its base, enabled by the combination of high compressibility and multimodal actuation.