Design and stability analysis of an underactuated hand with passively rotating fingers

2026-07-21

AI Summary

This work addresses the inherent trade-off between grasping versatility and mechanical complexity in underactuated robotic hands by proposing a novel design that integrates both intra-finger and inter-finger underactuation mechanisms. The hand employs passive revolute joints, two-segment fingers, and a differential transmission to distribute a single actuation input across multiple fingers, while base rotation enables spatially adaptive grasping. A contact-moment-based stability criterion is introduced to support diverse grasp types—including cylindrical, spherical, parallel, and enveloping configurations—without compromising structural simplicity. Experimental results demonstrate that the proposed mechanism achieves high adaptability and reliability in grasping tasks while significantly reducing mechanical complexity and control demands.

Abstract

This paper presents an innovative design and stability analysis of an underactuated robotic finger with spatial mobility, designed to enhance gripping dexterity in robotic hands. The finger architecture incorporates a revolute joint at its base, enabling passive spatial rotation that facilitates both cylindrical and spherical grasping. With only two phalanges per finger, the design simplifies kinematic complexity while supporting precision and enveloping grasps. Stability criteria, based on the moment at the finger base joint induced by contact forces, are introduced to ensure reliable object gripping and prevent ejection during manipulation. The study also examines a differential mechanism that distributes a single actuation torque across multiple fingers, allowing adaptive and coordinated motion. This mechanism enhances the hand's ability to grasp diverse object shapes with minimal pre-grasp adjustments, leveraging passivity for autonomous adaptation. Theoretical findings are experimentally validated using a fully mechanical prototype, demonstrating versatility in performing cylindrical, spherical, parallel, and enveloping grasps. The integration of underactuation-both within individual fingers and among multiple fingers-reduces mechanical complexity, cost, and control demands while preserving functional adaptability. This work advances the development of compliant robotic hands suitable for applications requiring dexterity and robustness, such as agricultural robotics, logistics, assistive technologies, and waste sorting. Future research will focus on automating actuation and refining control strategies to further improve grasp stability and precision, paving the way for autonomous manipulation in unstructured environments.

Problem

• underactuated hand
• passive adaptation
• grasp stability
• spatial mobility
• robotic grasping

Innovation

• underactuation
• passive adaptation
• differential mechanism
• grasp stability
• spatial mobility