Modeling locomotion of a soft-bodied arthropod using inverse dynamics

Abstract

Most bio-inspired robots have been based on animals with jointed, stiff skeletons. There is now an increasing interest in mimicking the robust performance of animals in natural environments by incorporating compliant materials into the locomotory system. However, the mechanics of moving, highly conformable structures are particularly difficult to predict. This paper proposes a planar, extensible-link model for the soft-bodied tobacco hornworm caterpillar, Manduca sexta, to provide insight for biologists and engineers studying locomotion by highly deformable animals and caterpillar-like robots. Using inverse dynamics to process experimentally acquired point-tracking data, ground reaction forces and internal forces were determined for a crawling caterpillar. Computed ground reaction forces were compared to experimental data to validate the model. The results show that a system of linked extendable joints can faithfully describe the general form and magnitude of the contact forces produced by a crawling caterpillar. Furthermore, the model can be used to compute internal forces that cannot be measured experimentally. It is predicted that between different body segments in stance phase the body is mostly kept in tension and that compression only occurs during the swing phase when the prolegs release their grip. This finding supports a recently proposed mechanism for locomotion by soft animals in which the substrate transfers compressive forces from one part of the body to another (the environmental skeleton) thereby minimizing the need for hydrostatic stiffening. The model also provides a new means to characterize and test control strategies used in caterpillar crawling and soft robot locomotion.

A proprioceptive neuromechanical theory of crawling

“…It also suggests alternative design of bioinspired robotic systems by replacing global coordination and actuation by decentralized modules where most of the control effort is replaced by elementary interactions of the body with the substrate that can trigger switch-like behaviour and thus lead to coordinated locomotion [24]. …”

Design, fabrication and control of soft robots

“…Likewise, the caterpillar has provided an ideal model for mobile soft robots 73 . The study of these systems for the development and implementation of soft robotic systems, has also, in turn, reflected back on our understanding of the mechanics and control of the associated natural systems 74 .…”

“…1). Notably, studies of caterpillars have led to a soft robotic systems 20,73 , as well as a further understanding of the control of motion in these animals 74 . An understanding of worm biomechanics also led to a bioinspired worm design composed of flexible materials and actuated by shape memory actuators (SMAs) 88 , and an annelid inspired robot actuated by dielectric elastomer 22 .…”

Design and Locomotion Control of a Soft Robot Using Friction Manipulation and Motor–Tendon Actuation

“…The former approach will comprise of modeling of the physical robot, the actuators and the robot-environment interaction. Physical soft robot modeling has been researched using lumped modeling [20,42], continuum modeling [22] and finite element methods [43]. These approaches tend to ignore the soft continuum properties, are restricted to specific shapes or computationally expensive.…”