BiFlex: A Passive Bimodal Stiffness Flexible Wrist for Manipulation in Unstructured Environments

2025-04-11

AI Summary

Addressing the challenge of simultaneously achieving high-precision manipulation and collision safety in unstructured human–robot collaborative environments, this paper proposes a passive dual-mode stiffness flexible wrist mechanism. The core innovation is a novel sensor-free, passive stiffness-switching mechanism based on soft buckling honeycomb structures, enabling autonomous, adaptive transitions between high- and low-stiffness states without sensors or active control. The mechanism features a modular mechanical interface compatible with mainstream grippers—including Panda, Robotiq, and BaRiFlex. Experimental results demonstrate that the wrist sustains a 500 g load stably under ≤1 cm fingertip deflection. In surface wiping, precise pick-and-place, and confined-space grasping tasks, it significantly simplifies control logic while enhancing operational robustness and contact safety.

Technology Category

• Intelligent Robots: Manipulation
• Humans and AI: Interaction Techniques and Devices
• Computer Vision: Biometrics, Face, Gesture & Pose

Application Category

• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs

Abstract

Robotic manipulation in unstructured, humancentric environments poses a dual challenge: achieving the precision need for delicate free-space operation while ensuring safety during unexpected contact events. Traditional wrists struggle to balance these demands, often relying on complex control schemes or complicated mechanical designs to mitigate potential damage from force overload. In response, we present BiFlex, a flexible robotic wrist that uses a soft buckling honeycomb structure to provides a natural bimodal stiffness response. The higher stiffness mode enables precise household object manipulation, while the lower stiffness mode provides the compliance needed to adapt to external forces. We design BiFlex to maintain a fingertip deflection of less than 1 cm while supporting loads up to 500g and create a BiFlex wrist for many grippers, including Panda, Robotiq, and BaRiFlex. We validate BiFlex under several real-world experimental evaluations, including surface wiping, precise pick-and-place, and grasping under environmental constraints. We demonstrate that BiFlex simplifies control while maintaining precise object manipulation and enhanced safety in real-world applications.

Problem

• Balancing precision and safety in robotic manipulation
• Overcoming traditional wrists' stiffness and control limitations
• Enabling adaptable compliance for unstructured environments

Innovation

• Passive bimodal stiffness flexible wrist
• Soft buckling honeycomb structure design
• Simplifies control with precise manipulation