This study introduces an innovative design for a Variable Stiffness 3 Degrees of Freedom actuated wrist capable of actively and continuously adjusting its overall stiffness by modulating the active length of non-linear elastic elements. This modulation is akin to human muscular cocontraction and is achieved using only four motors. The mechanical configuration employed results in a compact and lightweight device with anthropomorphic characteristics, making it potentially suitable for applications such as prosthetics and humanoid robotics. This design aims to enhance performance in dynamic tasks, improve task adaptability, and ensure safety during interactions with both people and objects. The paper details the first hardware implementation of the proposed design, providing insights into the theoretical model, mechanical and electronic components, as well as the control architecture. System performance is assessed using a motion capture system. The results demonstrate that the prototype offers a broad range of motion ($[55, -45]${\deg} for flexion/extension, $\pm48${\deg} for radial/ulnar deviation, and $\pm180${\deg} for pronation/supination) while having the capability to triple its stiffness. Furthermore, following proper calibration, the wrist posture can be reconstructed through multivariate linear regression using rotational encoders and the forward kinematic model. This reconstruction achieves an average Root Mean Square Error of 7.2{\deg}, with an $R^2$ value of 0.9.

翻译：本研究提出一种创新的变刚度三自由度驱动手腕设计，能够通过调节非线性弹性元件的有效长度，主动且连续地改变其整体刚度。这种调节机制类似于人体肌肉的共收缩，且仅需四个电机即可实现。所采用的机械结构使设备紧凑轻巧，并具有拟人化特征，适用于假肢和人形机器人等领域。该设计旨在提升动态任务中的性能表现、增强任务适应性，并确保与人或物体交互时的安全性。本文详细阐述了该设计的首个硬件实现方案，提供了理论模型、机械与电子组件以及控制架构的深入分析。系统性能通过运动捕捉系统进行评估。结果表明，该原型具有大范围的运动能力（屈伸范围为$[55, -45]${\deg}，径向/尺偏范围为$\pm48${\deg}，旋前/旋后范围为$\pm180${\deg}），同时能够将刚度提升至三倍。此外，经过适当标定后，可通过旋转编码器结合正向运动学模型，利用多元线性回归重建手腕姿态。该重建方法的平均均方根误差为7.2{\deg}，$R^2$值为0.9。