Thermally Tunable Deformation Wave on a Bistable Lattice to Enhance Soft-Bodied Climbing Robots

This article presents a method for modifying the propagation speed of deformation waves on a thermoplastic bistable lattice, which consists of multiple bistable structures mechanically connected in a chain. This can be achieved by altering the energy difference between its stable states using thermal bending. Unlike traditional methods requiring material or structural changes, the proposed approach dynamically switches the propagation speed without disassembly. In contrast to magnetic and pneumatic control methods, the thermally tunable bistable lattice requires no external magnetic field, pumps, or tubing and adds minimal extra mass, enabling in situ and local retuning of the propagation speed while preserving a simple, compact system architecture. A caterpillar-like robot, composed of four pairs of oppositely arranged legs, each actuated by a bistable structure, was used to demonstrate the efficacy of the proposed method. The robot achieves crawling locomotion using only a single motor, as the leg movements are sequentially triggered through mechanical propagation of deformation, with the propagation speed tunable via the thermal treatment. Experimental results showed that slower wave propagation enhanced locomotion on a 45° incline by increasing rail grip, achieving a climbing speed of 0.95 mm/s. These results highlight the unique advantages of thermally tunable bistable lattices over conventional actuation schemes and contribute to the development of soft robots capable of adaptive locomotion in unstructured environments such as pipeline/conduit inspection and endoluminal/endoscopic navigation.