VarWrist: An Anthropomorphic Soft Wrist with Variable Stiffness
Chaozhou Zhang, Min Li, Zhanshuo Yang, Kong Xiangrui, Jiayi Luo, Yushen Liu, Jian Fu, Guanghua Xu, SHAN LUO
AI summary
Problem
Existing robotic wrists struggle to balance flexibility with load-bearing stability, and most fail to replicate the human wrist's dynamic rotation center and variable stiffness required for complex manipulation.
Approach
The researchers designed a soft wrist prototype using three parallel pneumatic bellows to mimic human-like bending and integrated a central fiber jamming module that stiffens the structure on demand via vacuum pressure.
Key results
- Exceeds human wrist range of motion with 81.9° flexion and 78.5° extension
- Achieves 73% higher trajectory similarity to human wrist motion compared to fixed-axis designs
- Delivers a 206% stiffness increase in resting state and 155% in working state via fiber jamming
- Enables a dexterous hand to complete complex grasping tasks impossible with fixed stiffness
Why it matters
This biomimetic design bridges the flexibility-stability trade-off in soft robotics, advancing teleoperation and adaptive end-effector applications.
Abstract
Robotic wrists play a crucial role in enhancing the dexterity and stability of robotic end-effectors. Existing rigid robotic wrists tend to be complex and lack flexibility, while soft robotic wrists often struggle with limited load-bearing capacity and lower accuracy. Human wrists feature multi-degrees of freedom and variable stiffness, which help human hands to accomplish daily tasks. This study presents an innovative anthropomorphic soft robotic wrist, VarWrist, equipped with a fiber jamming variable stiffness module, enabling stiffness adjustment through vacuuming. VarWrist consists of three parallel bellows, utilizing a positive-negative pneumatic actuation strategy to mimic human wrist motion. In addition, the trajectory equation of the rotation center was fitted through modeling. We developed a prototype of VarWrist and assessed its performance. Results indicate that the soft wrist surpasses the motion range of human wrists, achieving flexion (81.9°), extension (78.5°), ulnar deviation (70.5°), and radial deviation (70.5°). The bending motion trajectory showed a 73% increase in similarity to human motion compared to fixed-axis rotation, with VarWrist exhibiting a significant range of variable stiffness (resting state: 206%, working state: 155%). Demonstration experiments confirm that this wrist facilitates a dexterous hand in completing grasping tasks that would be unattainable by the hand alone.