Online State Estimation of a Fin-Actuated Underwater Robot Using Artificial Lateral Line System

A lateral line system is a flow-responsive organ system, with which fish can effectively sense the surrounding flow field, thus serving functions in flow-aided fish behaviors. Inspired by such a biological characteristic, artificial lateral line systems (ALLSs) have been developed for promoting technological innovations of underwater robots. In this article, we focus on investigating state estimation of a freely swimming robotic fish in multiple motions, including rectilinear motion, turning motion, gliding motion, and spiral motion. The state refers to motion parameters, including linear velocity, angular velocity, motion radius, etc., and trajectory of the robotic fish. Specifically, for each motion, a pressure variation (PV) model that links motion parameters to PVs surrounding the robotic fish is first built; then, a linear regression analysis method is used for determining the model parameters. Based on the acquired PV model, motion parameters can be estimated by solving the PV model inversely using the PVs measured by the ALLS. Finally, a trajectory estimation method is proposed for estimating trajectory of the robotic fish based on the ALLS-estimated motion parameters. The experimental results show that the robotic fish is able to estimate its trajectory in the aforementioned multiple motions with the aid of ALLS, with small estimation errors.

I. Introduction

A LATERAL line system (LLS) is a sensory system, which can be found in most species of fish. The major unit of lateral line is neuromast, which is a mechanoreceptive organ enabling fish to respond to mechanical changes in water. It consists of two kinds of neuromasts, named superficial neuromasts and canal neuromasts. Superficial neuromasts are situated on the surface of fish skin, while canal neuromasts are enclosed in subepidermal canals [1]. It has been demonstrated that fish can effectively detect flow velocity and pressure in the surrounding flow field using the LLS [2]. Based on this characteristic, the LLS serves functions in varieties of flow-aided fish behaviors, such as rheotaxis (which specifically refers to turning to face into an oncoming current), obstacle avoidance, schooling, prey localization, etc. [3], [4].