Exploring the Design of a Mechanical Solution for a Self-Burrowing Probe

Abstract

This thesis aims to explore the design of a mechanical solution for a self-burrowing probe for site characterization using a bio-inspired design approach. The biological strategies of a range of organisms known for their burrowing and penetration behavior are presented and several burrowing robots that implement these biological strategies as working principles are reviewed. Existing literature lacks insight in the performance of burrowing robots in real-world site characterization circumstances where the exact composition of the soil is heterogeneous and initially unknown. Additionally, current burrowing robots perform at shallow depth not representative of the full range of depths associated with different site characterization applications. Seven different conceptual designs of a self-burrowing probe are generated using a morphological chart. The strengths, weaknesses, opportunities and threats of the conceptual designs are addressed, and the concepts are compared based on five Key Performance Indicators (KPIs). The KPIs are prioritized to take into account their significance to the feasibility of the design. The earthworm-inspired self-burrowing probe is deemed the most promising conceptual design based on a comparative analysis. An analytical model of the earthworm-inspired self-burrowing probe is presented and used to calculate the resistance and reaction forces mobilized by the probe during the self-penetration step of the locomotion cycle. Three possible applications at varying depths are introduced to analyse the effect of the principal dimensions of the probe on the self-penetration ability. Through the analysis it is shown that the preferred way to improve the performance of the probe is by increasing the total reaction force mobilized by the anchor through. To achieve this, a combination of increasing the anchor length and skin-soil friction coefficient is advised. The total resistance force calculated by the analytical model and the radial limit pressure at the depth of the three different applications are used to explore several actuation means. The analysis motivates the use of a soft robotic solution with integrated actuation using Smart Memory Alloy (SMA) for seafloor characterization application. The more conventional hydraulic and electromagnetic actuation methods are deemed suitable for the probe for cable laying and foundation design applications. A prototype is constructed that translates the abstract working principles of the self-burrowing probe to a rigid mechanical design. Experience gained during this prototyping exercise is presented to guide the detailed design of a self-burrowing probe for site characterization.