SPINE Gripper: A Twisted Underactuated Mechanism-based Passive Mode-Transition Gripper

2026-01-11

arXiv.org

AI Summary

This work proposes a single-actuator passive gripper that overcomes the complexity and low reliability of conventional multi-functional grippers, which typically rely on multiple actuators or active control to switch between grasping and in-hand rotation modes. The design introduces a novel non-coplanar motion generation mechanism based on a Torsional Underactuated Mechanism (TUM), which leverages mechanically encoded force transmission logic to automatically transition between stable grasping and bidirectional in-hand rotation solely based on input torque magnitude—eliminating the need for sensors or controllers. Integrated with a mechanical friction generator and supported by analytical modeling, the gripper achieves multi-degree-of-freedom functionality under a single input. Experiments demonstrate high grasping success rates, adaptive friction modulation, consistent axial contraction, and successful execution of tasks such as bolt manipulation and object reorientation, validating the feasibility of purely mechanical multifunctional manipulation.

Technology Category

• Intelligent Robots: Manipulation
• Multiagent Systems: Mechanism Design
• Computer Vision: Multi-modal Vision

Application Category

• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Economics, Online Markets and Human Computation: Trust and reliance of crowd workers and data experts on GenAI
• Search and Retrieval-Augmented AI: Retrieval-Augmented Generation (RAG) and multi-modal RAG

Abstract

This paper presents a single-actuator passive gripper that achieves both stable grasping and continuous bidirectional in-hand rotation through mechanically encoded power transmission logic. Unlike conventional multifunctional grippers that require multiple actuators, sensors, or control-based switching, the proposed gripper transitions between grasping and rotation solely according to the magnitude of the applied input torque. The key enabler of this behavior is a Twisted Underactuated Mechanism (TUM), which generates non-coplanar motions, namely axial contraction and rotation, from a single rotational input while producing identical contraction regardless of rotation direction. A friction generator mechanically defines torque thresholds that govern passive mode switching, enabling stable grasp establishment before autonomously transitioning to in-hand rotation without sensing or active control. Analytical models describing the kinematics, elastic force generation, and torque transmission of the TUM are derived and experimentally validated. The fabricated gripper is evaluated through quantitative experiments on grasp success, friction-based grasp force regulation, and bidirectional rotation performance. System-level demonstrations, including bolt manipulation, object reorientation, and manipulator-integrated tasks driven solely by wrist torque, confirm reliable grasp to rotate transitions in both rotational directions. These results demonstrate that non-coplanar multifunctional manipulation can be realized through mechanical design alone, establishing mechanically encoded power transmission logic as a robust alternative to actuator and control intensive gripper architectures.

Problem

• underactuated gripper
• passive mode transition
• in-hand manipulation
• mechanical intelligence
• torque-based switching

Innovation

• Twisted Underactuated Mechanism
• passive mode transition
• mechanically encoded logic
• single-actuator gripper
• in-hand manipulation