Robotic mechanism for soil penetration inspired by plant root

In this paper we propose a soil penetration robotic system inspired by low friction penetration strategies in plant roots. Growth of cells at the root tip deforms soil, while sloughing cells in the cap create an interface between root and soil to reduce root-soil friction during penetration. A simple prototype, inspired by these root features and based on a tubular shaft and a soft continuum skin, was developed. The skin is kept inside the shaft and slips out and slides on its external body. This outward movement of the skin opens the soil in front of the tip and helps the system to penetrate. The skin covering the external body of shaft imitates the role of sloughing cells and provides low-friction interface between soil and shaft. Interaction between the external skin and soil gives to the system self-anchorage capabilities for the penetration. The performances of our robotic system were characterized during penetration in granular soils. The skin-soil interaction was found to be fundamental for 1) displacing the soil in front of the tip and 2) preventing backward movements of the robot by anchoring the posterior body to the soil. In order to exploit these effects some artificial hairs were added along the skin. The increased hair density (0.012 hairs/mm²) resulted in higher penetration depth of robot (about 30%).