Design Optimization of a Variable Stiffness Robotic Gripper with Passive Restoration Fabricated by Multimaterial 3D Printing

Abstract

Advancements in additive manufacturing and novel materials have accelerated developments in soft robotics, enabling enhanced designs with embedded functionality and passive adaptability. However, developing practical grippers while balancing compliance, structural rigidity, and controlled mechanical behavior remains a challenge. This work presents a multimaterial robotic gripper primarily fabricated via fused filament fabrication, integrating thermoplastic polyurethane (TPU), and conductive polylactic acid (c‐PLA) in a functionally layered structure. TPU serves as soft interfaces for grasped objects, compliant spring elements for passive finger restoration and a flexible housing for embedded sensing components. c‐PLA provides the rigid backbone and forms the basis for variable stiffness joints, where Joule‐heating is applied via embedded nichrome wires. Integrated thermistors enable the gripper to self‐monitor joint temperatures, facilitating active regulation of stiffness in real time. To enhance thermal response, a detachable additively manufactured cooling channel directs forced convection across heated joints, significantly reducing cooling times. The gripper achieves multiple gripping configurations using a single cable‐tendon system, with experimental results demonstrating reliable adaptation to objects of varying size, shape, and rigidity. This work outlines a practical, accessible approach to creating selectively stiffening, self‐monitoring grippers, offering a versatile platform for adaptive manipulation in robotic automation.