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Plant-inspired inflatable eversion robots with their tip growing behaviour have recently emerged. Because they extend from the tip, eversion robots are particularly suitable for applications that require reaching into remote places through narrow openings. Besides, they can vary their structural stiffness. Despite these essential properties which make the eversion robot a promising candidate for applications involving cluttered environments and tight spaces, controlling their motion especially laterally has not been investigated in depth. In this paper, we present a new approach based on model-based kinematics to control the eversion robot's tip position and orientation. Our control approach is based on Euler-Bernoulli beam theory which takes into account the effect of the internal inflation pressure to model each robot bending segment for various conditions of structural stiffness. We determined the parameters of our bending model by performing a least-square technique based on the pressure-bending data acquired from an experimental study. The model is then used to develop a pose controller for the tip of our eversion robot. Experimental results show that the proposed control strategy is capable of guiding the tip of the eversion robot to reach a desired position and orientation whilst varying its structural stiffness.

Recent progress in soft robotics has seen new types of actuation mechanisms based on apical extension which allows robots to grow to unprecedented lengths. Eversion robots are a type of robots based on the principle of apical extension offering excellent maneuverability and ease of control allowing users to conduct tasks from a distance. Mechanical modelling of these robotic structures is very important for understanding their operational capabilities. In this paper, we model the eversion robot as a thin-walled cylindrical beam inflated with air pressure, using Timoshenko beam theory considering rotational and shear effects. We examine the various failure modes of the eversion robots such as yielding, buckling instability and lateral collapse, and study the payloads and operational limits of these robots in axial and lateral loading conditions. Surface maps showing the operational boundaries for different combinations of the geometrical parameters are presented. This work provides insights into the design of eversion robots and can pave the way towards eversion robots with high payload capabilities that can act from long distances.

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