![]() ![]() Because a primary requirement for survival on land is the ability to cope with internal and external mechanical forces (i.e., self-loading and wind-induced drag forces), the shape, size, internal structure, and behavior of plants provide opportunities to transfer organic mechanical strategies to the construction of engineered artifacts, such as robots.Īn important “proof of (evolutionary) concept” is convergence-when different unrelated organisms solve the same problem using similar methods. Consequently, extinct as well as living species can be viewed as evolutionary experiments that have either failed or that have passed the test of selection. Vascular plants evolved ~350 million years ago and have been subjected to intense natural selection for this period of time (Niklas, 2016). This convergence in the form and function of different plant grasping organs (modified stems, leaves, and even roots) manifests different anatomical and morphological solutions for constructing thin continuum robots. Of particular relevancy to robotic applications is the fact that stems bearing tendrils and tendril-like structures and stems with the ability to intertwine have evolved multiple times in phylogenetically unrelated plant lineages, which provides circumstantial evidence for convergent adaptive evolution by means of natural selection. This “existence of proof” in the natural world provides many insights into potential innovative robotic solutions to similar problems. In particular, numerous climbing plants grow and deploy tendrils or tendril-like structures on their very thin stems, and use these organs to reach out to and stabilize stems via connection with structures in their surrounding environments (Putz and Mooney, 1992 Bohn et al., 2015 Schnitzer et al., 2015), or they intertwine individual stems to form braid-like structures to bridge gaps between supports. To meet them, plants have evolved a variety of structures and growth strategies. Many plants experience similar challenges. Although necessary to enable their envisioned applications the thin profile (lengths of a meter or more, with length to diameter ratio of 100 or more) of these structures renders them highly susceptible to undesired and uncontrollable shape changes as a consequence of external loading (gravity, air currents, environmental contact, etc.). ![]() The challenge of shape regulation is magnified in long, thin variants of continuum robots (Walker, 2013b). However, regulating the shape of these robots can be challenging, given that only a finite number of actuators can be applied to control the (theoretically infinite) degrees of freedom present in the backbones. This feature allows them to adapt to and penetrate cluttered and tight spaces. Continuum robots feature continuous, compliant backbones that can change shape (bend and often extend/contract) at all locations along the structure. In recent years, however, the need to navigate within narrow, sensitive, and congested environments has motivated the development of a new class of “tongue, trunk, and tentacle” robots, collectively termed continuum robots (Walker, 2013a). The rigidity of the links and the ability to directly control the joint angles have enabled accuracy and repeatability that has made robots highly successful in numerous applications, notably in assembly operations within highly structured factory environments. Traditionally, the structures of robotic appendages (arms, legs, fingers) have been based on interconnected rigid links, with the shape of the structures variable at only a small, finite number of locations (joints) (Siciliano and Khatib, 2016). ![]()
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