Travelling Wave Generation in Soft Robotics

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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.