Feitian Zhang

Miniature Underwater Glider: Design and Experimental Results

The concept of gliding robotic fish combines gliding and fin-actuation mechanisms to realize energy-efficient locomotion and high maneuverability. Such robots hold strong promise for mobile sensing in versatile aquatic environments. In this paper, we present the design and implementation of a miniature glider, a key enabling component for gliding robotic fish. The steady-state glide equation is first presented and then solved numerically for given net-buoyancy and movable mass displacement. Scaling analysis is conducted to understand the tradeoff between the glide performance and energy cost. Comprehensive design for the glider is provided. Experimentation and modeling analysis are further conducted to investigate the impacts of movable mass displacement, net buoyancy, and wing size on the gliding performance.

Miniature underwater glider: Design, modeling, and experimental results

The concept of gliding robotic fish combines gliding and fin-actuation mechanisms to realize energy-efficient locomotion and high maneuverability, and holds strong promise for mobile sensing in versatile aquatic environments. In this paper we present the modeling and design of a miniature fish-like glider, a key enabling component for gliding robotic fish. The full dynamics of the glider is first derived and then reduced to the sagittal plane, where the lift, drag, and pitch moment coefficients are obtained as linear or quadratic functions of the attack angle based on computational fluid dynamics (CFD) analysis. The model is used to design the glider by accommodating stringent constraints on dimensions yet meeting the desired specification on speed. A fully untethered prototype of underwater glider is developed, with a weight of 4 kg and length of 40 cm. With a net buoyancy of 20 g, it realizes a steady gliding speed of 20 cm/s. The volume and net buoyancy of this glider are less than 10% and 5%, respectively, of those of reported gliders in the literature, and its speed per unit net buoyancy is over 9 times of those other vehicles. Experimental results have shown that the model is able to capture well both the steady glide behavior under different control inputs, and the dynamics during transients.

Tail-Enabled Spiraling Maneuver for Gliding Robotic Fish

Gliding robotic fish, a new type of underwater robot, combines both strengths of underwater gliders and robotic fish, featuring long operation duration and high maneuverability. In this paper, we present both analytical and experimental results on a novel gliding motion, tail-enabled three-dimensional (3D) spiraling, which is well suited for sampling a water column. A dynamic model of a gliding robotic fish with a deflected tail is first established. The equations for the relative equilibria corresponding to steady-state spiraling are derived and then solved recursively using Newton’s method. The region of convergence for Newton’s method is examined numerically. We then establish the local asymptotic stability of the computed equilibria through Jacobian analysis and further numerically explore the basins of attraction. Experiments have been conducted on a fish-shaped miniature underwater glider with a deflected tail, where a glidinginduced 3D spiraling maneuver is confirmed. Furthermore, consistent with model predictions, experimental results have shown that the achievable turning radius of the spiraling can be as small as less than 0.4 m, demonstrating the high maneuverability. [DOI: 10.1115/1.4026965]

Design and development of an LED-based optical communication system for autonomous underwater robots

Mobile networking and collaboration of underwater robots is of interest in many applications such as oceanography, environmental monitoring, and underwater surveillance. In this paper, an LED-based underwater optical communication system is designed and implemented for such applications. In contrast with laser-based communication systems, the characteristics of small size and low cost of the LED-based systems are very appealing, especially for small underwater robots. The presented system has a sound balance among desired characteristics of small size (in the order of centimeters), low energy consumption (500 mW on average), and median communication distance (20-30 m, in comparison with several meters available from most similar LED-based systems). The system design is described including the realization of the transmitter and the receiver, as well as the methods for achieving robustness to noise. System performance is experimentally tested in terms of signal strength and waveform shape versus communication distance and transmitting frequency. Experiments on data transmission is conducted to check the bit error rate under different baud rates. The experimental results show that the presented system has a good balance between communication performance and robustness.

Steady spiraling motion of gliding robotic fish

A gliding robotic fish is developed for promising applications in aquatic environment monitoring. The design concept combines the strengths of both underwater gliders and robotic fish, featuring long operation duration and high maneuverability. This paper presents both analytical and experimental results for the three-dimension spiraling motion, an essential working pattern of the gliding fish for detecting pollution in a water column. A dynamic model of the gliding robotic fish with actuated tail is established. Then the steady-state spiraling equations are derived and solved recursively using Newtons method. The gliding fish prototype is tested in experiments. Both model prediction and experimental results show that the spiraling motion has very low energy consumption, and the gliding fish can achieve high maneuverability with a turning radius less than 1 m, 2.5% of the reported turning radius of a typical underwater glider.

Autonomous Sampling of Water Columns Using Gliding Robotic Fish: Algorithms and Harmful-Algae-Sampling Experiments

Gliding robotic fish, which is a hybrid of underwater gliders and robotic fish, is energy efficient and highly maneuverable and holds strong promise for long-duration monitoring of underwater environments. In this paper, a novel scheme is proposed for autonomously sampling multiple water columns using gliding robotic fish. The scheme exploits energy-efficient spiral-down motion to sample each water column, followed by sagittal-plane glide-up toward the direction of the next water column. Once surfacing, the robot uses Global Positioning System guidance to reach the next column location through swimming. To enhance the path-tracking performance, a two-degree-of-freedom controller involving H∞ control is used in the spiral motion, and a sliding-mode controller is employed to regulate the yaw angle during glide-up. The sampling scheme has been implemented on a gliding robotic fish prototype, “Grace,” and verified first in pool experiments and then in field experiments involving the sampling of harmful algae concentration in the Wintergreen Lake, Michigan.

Passivity-based controller design for stablization of underwater gliders

The problem of stabilizing steady gliding is very critical for an underwater glider, which is subject to many non-negligible disturbances from the aquatic environment. Traditional control methods like PID control, LQR control or torque control, can not provide simultaneously easy controller implementation and fast convergence speed for stabilization. In paper we propose a new nonlinear, passivity-based controller for the stablization problem. The controller is designed based on an approximation of a reduced model that is obtained through singular perturbation analysis, and consequently, it does not require full state feedback and is thus easy to implement. The local stability of the closed-loop full system is established through linearization. Simulation results are provided to demonstrate that the proposed controller achieves rapid convergence in stabilization.

Localization of source with unknown amplitude using IPMC sensor arrays

The lateral line system, consisting of arrays of neuromasts functioning as flow sensors, is an important sensory organ for fish that enables them to detect predators, locate preys, perform rheotaxis, and coordinate schooling. Creating artificial lateral line systems is of significant interest since it will provide a new sensing mechanism for control and coordination of underwater robots and vehicles. In this paper we propose recursive algorithms for localizing a vibrating sphere, also known as a dipole source, based on measurements from an array of flow sensors. A dipole source is frequently used in the study of biological lateral lines, as a surrogate for underwater motion sources such as a flapping fish fin. We first formulate a nonlinear estimation problem based on an analytical model for the dipole-generated flow field. Two algorithms are presented to estimate both the source location and the vibration amplitude, one based on the least squares method and the other based on the Newton-Raphson method. Simulation results show that both methods deliver comparable performance in source localization. A prototype of artificial lateral line system comprising four ionic polymer-metal composite (IPMC) sensors is built, and experimental results are further presented to demonstrate the effectiveness of IPMC lateral line systems and the proposed estimation algorithms.

Autonomous sampling of water columns using gliding robotic fish: Control algorithms and field experiments

Gliding robotic fish, a hybrid of underwater gliders and robotic fish, are energy-efficient and highly maneuverable, and hold strong promise for long-duration sampling of underwater environments. In this paper a novel systematic autonomous water-column-based sampling scheme for gliding robotic fish is proposed to measure the three-dimensional spatial distributions of variables of interest in aquatic environments. The scheme exploits energy-efficient spiral-down motion to sample each water column, followed by sagittal-plane glide-up towards the direction of next water column. Once surfacing, the robot uses GPS guidance to reach the next column location through swimming. To enhance the path tracking performance, a two-degree-of-freedom controller involving H∞ control is used in the spiral motion, and a sliding-mode controller is employed to regulate the yaw angle during glide-up. The sampling scheme has been implemented on a gliding robotic fish prototype, “Grace”, and verified first in pool experiments, and then in field experiments involving the sampling of harmful algae concentration in the Wintergreen Lake, Michigan.

Gliding robotic fish for mobile sampling of aquatic environments

Aquatic ecosystems and processes exhibit a high degree of spatial and temporal heterogeneity, which presents significant challenges for their monitoring. In this paper we report a novel underwater robot, called gliding robotic fish, as an emerging platform for mobile sensing in aquatic environments that can potentially provide high spatiotemporal coverage. The robot represents a hybrid of an underwater glider and a robotic fish, and is capable of exploiting gliding to achieve energy-efficient locomotion while using a fish-like active tail to achieve high maneuverability. Preliminary field-test results are presented, where the robot was used to sample the Kalamazoo River and the Wintergreen Lake in Michigan for concentrations of crude oil and harmful algae, respectively.