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.

中文翻译：

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棘轮集成式气动执行器（RIPA）：受肌节肌肉收缩启发的大行程软线性执行器。

气动人工肌肉（PAM）具有广泛的机器人应用，尤其是在软机器人中，因为它们能够产生线性力和位移，并具有柔软，轻便，紧凑和安全的特性以及高功率密度。但是，空气的可压缩性会导致PAM出现弹簧状的行为，从而导致一些常见问题，即行程受限，与负载有关的行程长度，难以维持其不受干扰的长度以及精确压力控制系统的必要性。为了解决这些问题，本研究借鉴了生物软线性致动器（一种肌肉）的灵感，并提出了一种棘轮集成式气动致动器（RIPA）。利用整合在McKibben肌肉两端的两个棘爪和插入肌肉中间的灵活齿条，RIPA通过重复加压和减压循环来累积McKibben肌肉多个小冲程的位移，从而实现大冲程长度。该循环模仿了肌节的横桥模型，肌节是骨骼肌的基本单位，在该模型中，肌肉会积累肌球蛋白头部马达的纳米级冲程，从而产生较大的冲程。PAM和肌节管的灵感之间的协同作用使大行程软线性致动器可以从负载产生独立的行程。所提出的致动器不仅能够保持其长度以抵抗意外的机械干扰，而且还可以通过相对简单的系统来控制。在本文中，我们描述了RIPA的设计，并提供了分析模型来预测冲程长度和每个周期的驱动时间。