Department of Industrial and Enterprise Systems Engineering, University of Illinois Urbana-Champaign, Urbana, IL, United States of America.
Bioinspir Biomim. 2018 Apr 18;13(3):036010. doi: 10.1088/1748-3190/aab19c.
Fiber reinforced elastomeric enclosures (FREEs) are soft pneumatic actuators that can contract and generate forces upon pressurization. Typical engineering applications utilize FREEs in their straight cylindrical configuration and derive actuation displacement and forces from their ends. However, there are several instances in nature, such as an elephant trunk, snakes and grapevine tendrils, where a spiral configuration of muscle systems is used for gripping, thereby establishing a mechanical connection with uniform force distribution. Inspired by these examples, this paper investigates the constricting behavior of a contracting FREE actuator deployed in a spiral or coiled configuration around a cylindrical object. Force balance is used to model the blocked force of the FREE, which is then related to the constriction force using a string model. The modeling and experimental findings reveal an attenuation in the blocked force, and thus the constriction force caused by the coupling of peripheral contact forces acting in the spiral configuration. The usefulness of the coiled FREE configuration is demonstrated in a soft arm orthosis for crutch users that provides a constriction force around the forearm. This design minimizes injury risk by reducing wrist load and improving wrist posture.
纤维增强弹性外壳（FREEs）是一种柔软的气动致动器，在加压时可以收缩并产生力。典型的工程应用在其直圆柱配置中利用 FREEs，并从其末端获得致动力和位移。然而，在自然界中有几种情况，例如象鼻、蛇和葡萄藤卷须，其中肌肉系统的螺旋结构用于抓握，从而与均匀的力分布建立机械连接。受这些例子的启发，本文研究了收缩 FREE 致动器在圆柱形物体周围螺旋或缠绕配置下的收缩行为。力平衡用于对 FREE 的阻塞力进行建模，然后使用弦模型将其与收缩力相关联。建模和实验结果揭示了由于螺旋配置中作用的外围接触力的耦合而导致阻塞力和收缩力的衰减。螺旋 FREE 配置的有用性在用于拐杖使用者的软臂矫形器中得到了证明，它在小臂周围提供了收缩力。这种设计通过减少手腕负荷和改善手腕姿势来最大限度地降低受伤风险。
