Liu Yang, Luo Yuhui, Xiao Ting, Liang Jiejunyi
State Key Laboratory of Intelligent Manufacturing Equipment and Technology, Huazhong University of Science and Technology, Wuhan, China.
School of Art, Soochow University, Suzhou, China.
Front Bioeng Biotechnol. 2024 May 30;12:1385076. doi: 10.3389/fbioe.2024.1385076. eCollection 2024.
During activities of daily living (ADLs), the wrist is mainly engaged in positioning and directing the hand. Researches have demonstrated that restoring wrist mobility can significantly enhance the manipulation ability, reduce body distortion caused by motion compensation, and improve the quality of life for amputees. However, most daily activities, particularly the delicate ones, place high demands on the ability of wrist to maintain a certain rotation angle, also known as non-back-drivable ability, which poses a challenge to the design of prosthetic wrists. To address this issue, various solutions have been proposed, including motor holding brakes, high reduction ratio reducers, and worm gears. However, the motor holding brake only functions after a power outage and cannot continuously prevent torque from the load end. The latter two solutions may alter the transmission ratio, resulting in reduced movement speed and transmission efficiency. Therefore, how to design a miniaturized non-back-drivable mechanism without changing the transmission ratio so that the forearm rotational freedom can be locked at any position for any duration is a problem to be solved in the research of prosthetic wrist designs. This paper presents a line-contact based non-back-drivable clutch (NBDC) that does not cause changes in the transmission ratio, ensuring the motion performance of the prosthetic limb. At the same time, it does not introduce additional friction in the forward transmission process, guaranteeing the overall efficiency. Most importantly, it only allows the torque transmitting from the motor to the load, prevents the load reversely from driving back even in a power failure condition, significantly improving the stability, safety, and comfort. Detailed kinematic and static analyses of the working process has been conducted, and transient dynamics simulation has been performed to verify its effectiveness. Through experiments, it is demonstrated that the self-locking torque of the output end could reach approximately 600 Nmm, and the unlocking torque of the input end is about 80 Nmm, which can be effectively integrated in prosthetic wrist rotation joints, contributing to the performance, safety and energy saving of prosthetic joint systems.
在日常生活活动（ADL）中，手腕主要负责手部的定位和导向。研究表明，恢复手腕的活动能力可以显著提高操作能力，减少因运动补偿引起的身体扭曲，并改善截肢者的生活质量。然而，大多数日常活动，尤其是精细活动，对手腕保持一定旋转角度的能力，即所谓的非回驱动能力，有很高的要求，这对假肢手腕的设计构成了挑战。为了解决这个问题，人们提出了各种解决方案，包括电机抱闸、高减速比减速器和蜗轮。然而，电机抱闸仅在停电后起作用，无法持续阻止来自负载端的扭矩。后两种解决方案可能会改变传动比，导致运动速度和传动效率降低。因此，如何设计一种不改变传动比的小型化非回驱动机构，使前臂旋转自由度能够在任何位置锁定任意时长，是假肢手腕设计研究中需要解决的问题。本文提出了一种基于线接触的非回驱动离合器（NBDC），它不会引起传动比的变化，确保了假肢肢体的运动性能。同时，它在前向传动过程中不会引入额外的摩擦，保证了整体效率。最重要的是，它只允许扭矩从电机传递到负载，即使在停电情况下也能防止负载反向驱动，显著提高了稳定性、安全性和舒适性。对工作过程进行了详细的运动学和静态分析，并进行了瞬态动力学仿真以验证其有效性。通过实验表明，输出端的自锁扭矩可达约600Nmm，输入端的解锁扭矩约为80Nmm，可有效集成于假肢手腕旋转关节中，有助于假肢关节系统的性能、安全和节能。
