A Rigid Morphing Mechanism Enabled Earthworm-Like Crawling Robot

Abstract

Inspired by natural earthworms' locomotion mechanism, this paper investigates how the earthworm's muscle works and presents the approach to mimic segmental muscle by employing rigid elements-based morphing structures. Specifically, the proposed earthworm-like robot employs a class of 2D rigid elements and their array to achieve programmable bidirectional 3D deformation, making the formed mechanism precisely controllable and work effectively, thus facilitating the robot's peristaltic locomotion more efficient. To comprehensively investigate the morphing structure and it formed earthworm-like robot, the kinematics, mechanics, deformation-dependent locomotion framework with its adapted model, as well as the factors that affect the optimal velocity are developed and presented. Extensive simulations and experiments on the proposed robot are performed. The results verify the effectiveness of the morphing mechanism and it enabled earthworm-like robot, and the consistency between the proposed locomotion model and the practical tests. The results also prove that regardless of the condition of the contact surface, the optimal phase shift angle can be achieved when each segment approximately contract and relax once in one wavelength period. Our developed prototype achieves a speed of 4.57~9.23 body lengths per minute, which is very competitive compared with most developed earthworm-like robots.

Actuation and design innovations in earthworm-inspired soft robots: A review

“…In contrast, Ref. (Luo et al, 2022). uses a linkage structure to produce large deformation driven by motor.…”

“…The total length of robots used in the laboratory is generally between 10 and 1,000 mm, while the length of robots currently available for practical use is over 1,000 mm. Certain robots ( Shin et al, 2011 ; Luo et al, 2022 ; Tang et al, 2022 ) have demonstrated remarkable locomotion ability that was much faster than the actual earthworm, which are the top-three robots in terms of standardized speed divided by body length. In Ref.…”

“…Currently, these robots constitute an entire rigid body, but if they are covered with a layer of soft material, they can achieve an overall continuous movement and have a shape similar to that of an actual earthworm. The scissor mechanism ( Luo et al, 2016 ) and morphing mechanism (shown in Figure 13A ) ( Luo et al, 2022 ) driven by motor can simulate the circular and longitudinal muscles to enact continuous and consistent movement. A class of rigid elements-based morphing structures employs various 2D scissor elements to achieve 3D deformation.…”

“…A class of rigid elements-based morphing structures employs various 2D scissor elements to achieve 3D deformation. For instance, Luo et al designed a robot using morphing structures ( Luo et al, 2022 ) that delivered a competitive locomotion speed both in absolute speed (122.4 mm s –1 ) and body lengths per minute (4.67–9.42). The outer mesh ( Boxerbaum et al, 2011 ; Daltorio et al, 2013 ; Wang et al, 2018b ) and its derivatives ( Horchler et al, 2015 ) proposed by Horchler et al provided an evolution in the simulation of earthworm.…”

“… Examples of electric-driven multi-segment earthworm-inspired soft robots with continuous deformable structures. (A) Design and deformation of earthworm-like locomotion robot ( Luo et al, 2022 ). Reproduced from Ref.…”