Soft 3D-Printed Endoskeleton for Precise Tendon Routing in Soft Robotics

Abstract

This paper presents the design, development, and testing of a soft 3D-printed endoskeleton for arbitrary cable routing in tendon-driven soft actuators. The endoskeleton is embedded in a silicone body, and it is fixed to the mold prior to the casting process. It enables tendons to be placed through predefined eyelets, ensuring accurate positioning within the soft body. To minimize its impact on the overall stiffness of the soft body, the endoskeleton was designed with a slim profile, flexible connections, and fabricated using a 3D-printable elastic material (Shore A hardness 50), selected to roughly match the mechanical properties of the surrounding silicone matrix (typically with Shore 00 hardness 20–30). Although the reference geometry in this study is a cylindrical body, the design can be extended to a wide range of soft body shapes and sizes. Key features of the proposed solution include a 3D-printable guide for tendon routing that is (1) fully soft,(2) easy to place, (3) rapidly reconfigurable for arbitrary tendon paths, (4) adaptable to variable soft body geometries, and (5) easy to fabricate with single-step casting. The current work describes the design, manufacturing, simulation, and testing of a case study in which the endoskeleton is employed to reproduce a target pose predicted by FE analysis. The matching is satisfactory and demonstrates the effectiveness of the approach.