Travelling Wave Generation in Soft Robotics

行波在自然生物中非常丰富，它们存在于蠕虫，千足虫，乌贼甚至人体内。在爬行和游泳的生物体中，这种机制通常是它们运动的核心，而粘液纤毛运输在人类生理学中起着关键作用。在机器人系统中产生行波可以为敏感和非常规环境中的新型运动策略以及转移多相物质的能力创造新的机会。然而，生物学上的例子是很难理解的;在这里，大量的微观肌肉纤维被串联激活，产生一个平滑的行波。这种规模的致动和控制对于用当前方法再现是不切实际的，尽管在制造生物启发机器人时通常使用具有减少数量的有源元件（通常<10）的近似，例如伺服驱动乌贼[1]和蠕虫机器人[2][3]。使用离散致动器的这种近似方法的主要缺点是，有源元件的数量与近似的保真度成比例，如果需要平滑波，则会带来复杂性、成本、致动器/阀的数量和控制程度的不期望的增加（图1）。减少不必要的控制、致动器和阀门的程度将通过潜在地实现更软、更便宜和更鲁棒的软机器人来提供益处。虽然目前可以通过单一流体输入进行可编程的形状改变，但是仅通过形态学难以实现对整个机器人的压力进行不均匀的改变（例如，顺序地对不同区域进行充气和放气）。 在这篇博士论文中，将研究使用软机器人技术产生行波的机制，目的是消除当前缩放和低保真度的限制。这将创造出一种新型的柔性行波系统，可用于低冲击运动、输送和蠕动泵送。在这个设计空间的研究差距（如图1所示）将通过回答几个关键问题来解决：如何可以在机器人中同时产生多个波前，而不会伴随着执行器和控制信号的数量增加？行波机制如何与尺寸/长度/宽度成比例？在不同的环境中，运动机制的有效性如何？行波的哪些特性对物质传输有用，这些特性可以集成到机器人系统中吗？最初的工作将集中在Blockworm设计的延续上，该设计仅通过两个致动器在柔软的蠕虫状身体中产生行波[4]（在之前的硕士论文中开发并提交给IEEE International Conference on Soft Robotics 2020）。随着项目的继续，将开始更广泛地关注在软体中产生行波的方法。行波在机器人中的应用是多种多样的。对于单独的运动，行波可以被应用于穿越平坦的地形，诸如土壤、沙子或污泥的介质以及诸如管道或人体的受限通道（以及上述在一个机器人中的可能组合）。这种适应性是软机器人的愿望，可直接应用于手术（例如动脉支架放置），灾难恢复，管道检查，核退役等。除了运动之外，行波还可以用于运输易碎物品，如水果和其他农产品。这些可以是蠕动波，就像在人类气管和胃肠道中发现的那样，或者是一个扁平的分拣台。该原理也可以应用于具有按摩功能的可穿戴设备，例如用于刺激手术后或长途飞行中腿部的血液流动，从而降低深静脉血栓形成的风险。

Travelling waves are abundant in natural organisms, they are found in worms, millipedes, cuttlefish and even within the human body. In crawling and swimming organisms, this mechanism is often central to their locomotion, whilst peristalsis and mucociliary transport play a critical role in human physiology. Generating travelling waves in robotic systems could create new opportunities for novel locomotion strategies in sensitive and unconventional environments and the capacity to translocate multi-phase matter. However, the biological example is a difficult one to follow; here a very large number of microscopic muscle fibres are activated in series to produce a smooth travelling wave. Actuation and control on this scale is impractical to reproduce with current approaches, although, an approximation with a reduced number of active elements (generally <10) is commonly used when making bioinspired robots, such as servo driven cuttlefish [1] and worm robots [2][3]. The main drawback to this approximated approach using discrete actuators is that the number of active elements scales with the fidelity of the approximation, bringing undesirable increases in complexity, cost, number of actuators/valves and degrees of control if a smooth wave is required (Figure 1). Reducing unnecessary degrees of control, actuators and valves would provide benefits by potentially enabling softer, cheaper and more robust soft robots. While programmable shape change is possible with a singular fluidic input at present, making non-uniform changes to pressure throughout the robot (for example, sequentially inflating and deflating different areas) is difficult to achieve through morphology alone. In this PhD, mechanisms for producing a travelling wave using soft robotic technologies will be investigated with the aim of eliminating the current limitations of scaling and low fidelity. This will create a new class of flexible travelling wave systems that can be exploited for low impact locomotion, conveying and peristaltic pumping. Research gaps in this design space (as shown in Figure 1) will be addressed by answering several key questions: How can multiple wave fronts be simultaneously generated in the robot without a concomitant increase in the number of actuators and control signals? How does the travelling wave mechanism scale with size/length/width? How effective is the mechanism for locomotion in various environments? What characteristics of a travelling wave are useful for matter transport and can these be integrated into a robotic system? Initial work will focus on the continuation of the Blockworm design, which generates a travelling wave in a soft worm-like body from only two actuators [4] (developed during the previous masters dissertation and submitted to the IEEE International Conference on Soft Robotics 2020). As the project continues, a wider focus on the methods of generating travelling waves in soft bodies will commence. Applications of travelling waves in robotics are diverse. For locomotion alone, travelling waves can be applied to traverse flat terrain, media such as soil, sand or sludge and confined channels, such as pipes or the human body (and possibly combinations of the above in one robot). Such adaptability is an aspiration of soft robotics with direct application to surgery (e.g. arterial stent placement), disaster recovery, pipe inspection, nuclear decommissioning and more. Outside of locomotion, travelling waves could be used for the transport of fragile items, such as fruit and other produce. These could be peristaltic waves like those found in the human windpipe and gastrointestinal tract, or a flat sorting table. The principle could also be applied to wearable devices in a massaging function, for example used to stimulate blood flow in the legs post-surgery or on long flights, reducing the risk of deep vein thrombosis.