Design of a flexible axe foot structure for bionic razor clam soft robot

Abstract This paper presents a novel bionic robot inspired by the axe-foot structure of a razor clam, integrating Kresling structural units and a four-chamber circular trapezoidal module to achieve propulsion, anchoring, and steering functions. The soft axe foot, measuring 330 mm in length and weighing 127.5 g, was first analysed to establish the spatial geometric relationship between the rotation angle and height variation of the Kresling units. Based on the principle of minimum potential energy, the relationship between pneumatic pressure and elastic potential energy was modelled to derive mathematical expressions for output force and torque. Concurrently, a model linking air pressure to the rotation angle was developed, considering the energy conversion between resistance power consumption and energy stored within the structural creases. Furthermore, the nonlinear expansion of the anchoring chamber was investigated using the Mooney-Rivlin hyperelastic model. By assuming constant chamber height and uniform circumferential deformation, the anchoring force was determined via integral solutions. Performance evaluations revealed that at a driving pressure of 20 kPa, the extension response time was 0.58 s and the rotation angle was 405°, and when the input pressure is increased to 60 kPa, the measured output force was 4.6 N. Additionally, the soft axe foot module reached a rotation angle of 86° at an input pressure of 160 kPa. Finally, crawling and obstacle-crossing experiments validated the soft robot’s superior environmental adaptability and motion flexibility, demonstrating its capacity for complex propulsion tasks.