Tendon-driven based extensible soft robot with variable stiffness

Abstract

Extensible soft continuum robots have ubiquitous adoption in confined and intricate environments, owing to their dexterity, wide workspace, and adaptable stiffness. However, their existing designs still encounter challenges such as bulky, limited bending angles, complex modeling and control, and low payload capacity. This article presents a compact design of extensible single-section soft robot-based tendon-driven actuation, consisting of three segments based on a semi-octagon honeycomb pattern. This design is fabricated by varying the soft structure to provide extensibility and variable stiffness by controlling tension and retraction of cables. It consists of three segments; the middle segment, resembling a flexible spring, is sandwiched between two identical segments. A shape estimation using Inertial Measurement Unit (IMU) and motors’ encoders combined with a Constant Curvature assumption, is developed. The design performance is experimentally evaluated by performing workspace reachability, repeatability, payload capability. Additionally, the variable stiffness is verified against external payloads. Furthermore, a design enhancement is carried out to overcome buckling at specific configurations, incorporating flexible hollow hoses embedded within the prototype’s structure. The results verify that the prototype could achieve extension and compression up to 30% and 65% relative to its lengths respectively, high payload capacity reaches 565 gm, and efficient stiffness variation. Moreover, using hollow tubes enhance the payload capability of the robot without significant effect on its original structure.