A review of research on crawling soft robots: bionic mechanisms and actuation motion

Crawling soft robots have attracted widespread attention due to their high adaptability to unstructured environments. However, existing research often focuses on understanding the formation mechanism of their motion capabilities from the perspective of actuation methods or control strategies, resulting in fragmented design logic and a lack of a unified framework. Through comparative analysis across animal, plant, and microbial systems, this paper points out that crawling behavior in different biological systems largely depends on the synergistic effect of morphological deformation and interface friction. Many studies have shown that rectifying periodic, reversible deformation processes into directional net displacement plays a crucial role. Building on this, this paper further analyzes the roles of various actuation technologies in crawling systems, emphasizing that actuation primarily undertakes deformation triggering and modulation functions, and its impact on motion performance is highly dependent on the coupling method with morphological structure and interface conditions. Regarding control and learning methods, this paper discusses the key role of morphological and interface design in reducing control dimensionality and improving system robustness from the perspective of embodied intelligence, a design paradigm in which intelligent behavior emerges from the interaction among morphology, materials, actuation, and environmental constraints rather than solely from computational control. Pointing out that control strategies are more about compensating for and optimizing the structure-generated motion capabilities. Soft crawling robots gain locomotion from coordinated periodic deformation rectification among body morphology, driving timing and interfacial contact instead of single actuator performance. This review further summarizes prospective design rules and research paradigms to build a unified framework for relevant mechanism analysis and practical engineering design. This review provides a unique perspective by systematically examining the coupling among morphology, interfacial friction, and environmental interactions in crawling soft robots, which distinguishes it from previous general reviews on soft robotics and soft actuation systems.