Asgari Morteza, Hall Patrick T, Moore Bradley S, Crouch Dustin L
Annu Int Conf IEEE Eng Med Biol Soc. 2020 Jul;2020:4926-4929. doi: 10.1109/EMBC44109.2020.9175633.
Wearable, mechanically passive (i.e. spring-powered) exoskeletons may be more practical and affordable than active, motorized exoskeletons for providing continuous, home-based, antigravity movement assistance for people with shoulder disability. However, the biomechanical moment due to gravity is a nonlinear function of shoulder elevation angle and, thus, challenging to counteract proportionally across the shoulder elevation range of motion with a spring alone. We designed, fabricated, and tested an integrated spring-cam-wheel system that can generate a nonlinear moment to proportionally compensate for the expected antigravity moment at the shoulder. We then incorporated the proposed system in a benchtop model and a novel wearable passive cable-driven exoskeleton that was intended to counteract half of the gravitational moment during shoulder elevation movements. The rotational moment measured from the benchtop model closely matched the theoretical moment during simulated positive shoulder elevation. However, a larger moment (up to 12.5% larger) was required during simulated negative shoulder elevation to stretch the spring to its initial length due to spring hysteresis and friction losses. The wearable exoskeleton prototype was qualitatively tested for assisting shoulder elevation movements; we identified several aspects of the prototype design that need to be improved before further testing on human participants. In future studies, we will quantitatively evaluate human kinematics and neuromuscular coordination with the exoskeleton to determine its suitability for assisting patients with shoulder disability.
对于为肩部残疾患者提供持续的、居家的反重力运动辅助而言，可穿戴的机械被动式（即弹簧驱动）外骨骼可能比主动式电动外骨骼更实用且更经济实惠。然而，由于重力产生的生物力学力矩是肩部抬高角度的非线性函数，因此，仅用一个弹簧在整个肩部抬高运动范围内按比例抵消该力矩具有挑战性。我们设计、制造并测试了一种集成的弹簧 - 凸轮 - 轮系统，该系统能够产生非线性力矩，以按比例补偿肩部预期的反重力力矩。然后，我们将所提出的系统纳入一个台式模型和一种新型的可穿戴被动缆索驱动外骨骼中，该外骨骼旨在抵消肩部抬高运动期间一半的重力矩。在模拟的正向肩部抬高过程中，从台式模型测得的旋转力矩与理论力矩紧密匹配。然而，在模拟的负向肩部抬高过程中，由于弹簧滞后和摩擦损耗，需要更大的力矩（最大大12.5%）来将弹簧拉伸至其初始长度。对可穿戴外骨骼原型进行了定性测试，以辅助肩部抬高运动；我们确定了原型设计在对人类参与者进行进一步测试之前需要改进的几个方面。在未来的研究中，我们将定量评估使用该外骨骼时的人体运动学和神经肌肉协调性，以确定其对辅助肩部残疾患者的适用性。
