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 6.6{\deg}, with an $R^2$ value of 0.93.

翻译：本研究提出一种新型变刚度三自由度驱动手腕的创新设计，该手腕能够通过调节非线性弹性元件的有效工作长度，实现整体刚度的主动连续调节。这种调节机制类似于人体肌肉的共收缩运动，且仅需使用四台电机即可实现。所采用的机械构型使装置具有紧凑轻量化及类人特征，有望应用于假肢和人形机器人等领域。该设计旨在提升动态任务性能、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，深入解析了理论模型、机械与电子元件以及控制架构。系统性能通过运动捕捉系统进行评估。结果表明，该原型可实现大范围运动（屈伸运动$[55, -45]${\deg}，径向/尺偏运动$\pm48${\deg}，旋前/旋后运动$\pm180${\deg}），同时具备三倍刚度调节能力。经适当校准后，可通过旋转编码器结合正向运动学模型，利用多元线性回归方法重构手腕姿态，其平均均方根误差为6.6{\deg}，决定系数$R^2$达到0.93。