Department of Mechanical Engineering, Institute of Advanced Machines and Design (IAMD), Institute of Engineering Research, Seoul National University, Seoul, 08826, Republic of Korea.
Bioinspir Biomim. 2020 Mar 25;15(3):036011. doi: 10.1088/1748-3190/ab7762.
Pneumatic artificial muscles (PAMs) have a wide range of robotics applications, especially in soft robots, for their ability to generate linear force and displacement with the soft, lightweight, compact, and safe characteristics as well as high power densities. However, the compressibility of the air causes a spring-like behavior of PAMs, resulting in several common issues of limited stroke, load-dependent stroke lengths, difficulty in maintaining their length against disturbance, and necessity of accurate pressure control system. To address these issues, this study borrows inspiration from a biological soft linear actuator, a muscle, and proposes a ratchet-integrated pneumatic actuator (RIPA). Utilizing two pawls integrated at both ends of a McKibben muscle and a flexible rack inserted in the middle of the muscle, the RIPA achieves a large stroke length by accumulating displacements from multiple small strokes of the McKibben muscle by repeating the cycle of pressurization and depressurization. This cycle mimics the cross-bridge model of a sarcomere, a basic unit of a skeletal muscle, in which a muscle accumulates nanoscale strokes of myosin head motors to generate large strokes. The synergy between a PAM and the inspiration from a sarcomere enabled a large-stroke soft linear actuator that can generate independent strokes from loads. The proposed actuator is not only capable of maintaining its length against unexpected mechanical disturbances but also controllable with a relatively simple system. In this paper, we describe the design of the RIPA and provide analytical models to predict the stroke length and the period per cycle for actuation. We also present experimental results for characterization and comparison with model predictions.
气动人工肌肉（PAMs）在机器人技术中有广泛的应用，特别是在软体机器人中，因为它们具有柔软、轻巧、紧凑和安全的特性，以及高功率密度，能够产生线性力和位移。然而，空气的可压缩性导致 PAMs 具有类似弹簧的行为，从而导致几个常见问题，如有限的行程、负载依赖的行程长度、难以抵抗干扰保持其长度以及需要精确的压力控制系统。为了解决这些问题，本研究从一种生物软体线性执行器，即肌肉中获得灵感，并提出了一种棘轮集成气动执行器（RIPA）。RIPA 在 McKibben 肌肉的两端集成两个棘爪，并在肌肉中间插入一个柔性齿条，通过重复加压和减压的循环，利用 McKibben 肌肉的多次小冲程的累积位移来实现大的行程长度。这个循环模拟了肌节的横桥模型，肌节是骨骼肌的基本单位，其中肌肉通过肌球蛋白头部马达的纳米级冲程累积来产生大的冲程。PAM 与肌节灵感的协同作用使大行程软体线性执行器能够产生与负载无关的独立冲程。该执行器不仅能够抵抗意外的机械干扰保持其长度，而且可以用相对简单的系统进行控制。在本文中，我们描述了 RIPA 的设计，并提供了分析模型来预测行程长度和每个周期的周期。我们还介绍了用于特性描述和与模型预测比较的实验结果。
