Towards Full Actuation: Reconfigurable Micro Underwater Robots

Abstract

Exploration and monitoring of hazardous environments, such as legacy nuclear storage ponds, constitute safety-critical missions to be performed by small-scale underwater robots. These monitoring tasks require fully actuated robot platforms in order to allow for hovering while inspecting objects of interest in detail. A severe bottleneck arises from the restricted access points commonly encountered in these surveillance missions that pose strict limitations on the vehicle dimensions. However, small-scale underwater robots usually possess underactuated propulsion systems and are, thus, only partially suitable for these missions. In this work, we investigate and exploit the idea of reconfigurability. Following the idea of the whole is more than the sum of its parts, we daisy-chain multiple small-scale underwater robots with revolute joints to enable shape reconfigurations. In combination with a centralized sliding mode control scheme, the robot platform is able to change its shape depending on the current task, see Fig. 1. While the straight configuration fits well through tight passages such as inspection holes, the robot can reconfigure itself towards a triangular shape that enables the neutrally buoyant robot to hover at areas of interest, e. g. for inspection tasks. Finally, we examine our proposed concept in a series of simulations and experiments. Moreover, we demonstrate the performance of key elements such as reconfiguration and navigation, discuss their limitations, and point out future directions.