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The many degrees of freedom of continuum robots (CRs) enable unique applications in the search and rescue, medical and aerospace industries. However, the many motors required result in unwieldy external actuation packs and additional weight. Underactuation can achieve any pose with four motors by locking sections through clutching of cables. Existing underactuated (UA) solutions are characterized by lengthy joint locking times, add significant weight and are not scalable. In this article, a novel design and motion strategy is introduced, with shape memory alloy wires to control clutches that lock cables for section locking. In addition to using conventional smooth cables, beaded cables are proposed for improved clutching strength. The workspace of the design is analyzed, and design tools are proposed to optimize bead pitch. Finally, the operation of the proposed UA CR is demonstrated on a prototype that achieves a mean repeatability of 1.41mm, equivalent to 0.43% of the backbone length. Section locking is achieved in 1 s and section unlocking is achieved in 5 s.
Bishop et al. (Tue,) studied this question.