A Modular Soft Gripper with Enhanced In-Hand Manipulation Capabilities

Carlos Relaño, Alberto Rodríguez-Sanz, Lisbeth Karina Mena López, Concepción Alicia Monje Micharet

Abstract Soft robotic grippers offer exceptional adaptability and safety for grasping diverse objects. However, achieving dexterous in-hand manipulation remains a significant challenge. Traditional tendon-driven designs are optimized for stable holding but lack the intrinsic degrees of freedom (DoF) required for dexterous object reorientation, often relying instead on complex hybrid mechanisms or repeated regrasping. This study presents a novel modular soft robotic gripper specifically designed to bridge the gap between stable grasping and active, continuous in-hand manipulation. The system features three independently actuated soft fingers, each providing three DoF through a combination of asymmetric tendon-driven bending and active base rotation. A core principle of this design is an asymmetric soft joint that exploits passive geometric blocking to provide direction-dependent compliance and mechanical protection against excessive deformation. By decoupling the bending and spatial reorientation motions, the gripper generates coordinated kinematic patterns across the fingers. Experimental validation demonstrates the system's ability to robustly grasp objects spanning a wide spectrum of sizes and stiffnesses using a unified actuation strategy. Furthermore, the gripper successfully performs complex in-hand manipulation tasks, specifically, continuous object rotation along its axis without releasing the initial grasp. These results indicate that the proposed modular architecture significantly extends the dexterity of purely tendon-driven soft grippers while preserving their inherent compliance, scalability, and mechanical simplicity.