Zhang Xiaochen, Liu Yi-Xing, Wang Ruoli, Gutierrez-Farewik Elena M
KTH MoveAbility, Department of Engineering Mechanics, KTH Royal Institute of Technology, Stockholm, Sweden.
Department of Women's and Children's Health, Karolinska Institutet, Stockholm, Sweden.
Front Neurorobot. 2024 Aug 21;18:1372763. doi: 10.3389/fnbot.2024.1372763. eCollection 2024.
Wearable exoskeletons are emerging technologies for providing movement assistance and rehabilitation for people with motor disorders. In this study, we focus on the specific gait pathology dropfoot, which is common after a stroke. Dropfoot makes it difficult to achieve foot clearance during swing and heel contact at early stance and often necessitates compensatory movements.
We developed a soft ankle exoskeleton consisting of actuation and transmission systems to assist two degrees of freedom simultaneously: dorsiflexion and eversion, then performed several proof-of-concept experiments on non-disabled persons. The actuation system consists of two motors worn on a waist belt. The transmission system provides assistive force to the medial and lateral sides of the forefoot via Bowden cables. The coupling design enables variable assistance of dorsiflexion and inversion at the same time, and a force-free controller is proposed to compensate for device resistance. We first evaluated the performance of the exoskeleton in three seated movement tests: assisting dorsiflexion and eversion, controlling plantarflexion, and compensating for device resistance, then during walking tests. In all proof-of-concept experiments, dropfoot tendency was simulated by fastening a weight to the shoe over the lateral forefoot.
In the first two seated tests, errors between the target and the achieved ankle joint angles in two planes were low; errors of <1.5° were achieved in assisting dorsiflexion and/or controlling plantarflexion and of <1.4° in assisting ankle eversion. The force-free controller in test three significantly compensated for the device resistance during ankle joint plantarflexion. In the gait tests, the exoskeleton was able to normalize ankle joint and foot segment kinematics, specifically foot inclination angle and ankle inversion angle at initial contact and ankle angle and clearance height during swing.
Our findings support the feasibility of the new ankle exoskeleton design in assisting two degrees of freedom at the ankle simultaneously and show its potential to assist people with dropfoot and excessive inversion.
可穿戴外骨骼是为运动障碍患者提供运动辅助和康复的新兴技术。在本研究中，我们关注中风后常见的特定步态病理——足下垂。足下垂使得在摆动期难以实现足部离地，且在站立初期难以足跟触地，通常需要代偿性动作。
我们开发了一种软踝外骨骼，其由驱动和传动系统组成，可同时辅助两个自由度：背屈和外翻，然后对非残疾人士进行了多项概念验证实验。驱动系统由佩戴在腰带上的两个电机组成。传动系统通过鲍登缆线向前足的内侧和外侧提供辅助力。耦合设计可同时实现背屈和内翻的可变辅助，并提出了一种无动力控制器来补偿设备阻力。我们首先在三个坐姿运动测试中评估了外骨骼的性能：辅助背屈和外翻、控制跖屈以及补偿设备阻力，然后在步行测试中进行评估。在所有概念验证实验中，通过在前足外侧的鞋子上固定重物来模拟足下垂倾向。
在前两个坐姿测试中，两个平面内目标踝关节角度与实际达到的角度之间的误差较小；在辅助背屈和/或控制跖屈时误差<1.5°，在辅助踝关节外翻时误差<1.4°。第三个测试中的无动力控制器在踝关节跖屈期间显著补偿了设备阻力。在步态测试中，外骨骼能够使踝关节和足部节段的运动学正常化，特别是初始接触时的足部倾斜角度和踝关节内翻角度，以及摆动期的踝关节角度和离地高度。
我们的研究结果支持了新的踝外骨骼设计同时辅助踝关节两个自由度的可行性，并显示了其辅助足下垂和过度内翻患者的潜力。
