Yonghui Hu

Vision-Based Target Tracking and Collision Avoidance for Two Autonomous Robotic Fish

A new type of vision-based autonomous robotic fish capable of 3-D locomotion is developed in this paper. Based on our robotic fish prototype, the forces and moments acting on its fins and body are analyzed, and the governing motion equations are derived. We further investigate a decentralized control method in target-tracking and collision-avoidance task for two autonomous robotic fish. Most of previous work on the task strategies of autonomous robots is focused on terrestrial robots and seldom deals with underwater applications due to the uncertainties and complexity in a hydro environment. To address this challenge in such an underwater task, a situated-behavior-based decentralized control is employed on each robotic fish according to its visual data. On dealing with motion planning of the fish during target tracking and collision avoidance, a control law by a combination of an attractive force toward a target and a repulsive force for collision avoidance is utilized. Experimental results of the task performed by two autonomous robotic fish validate the effectiveness of the proposed method.

Mechanical design and motion control of a biomimetic robotic dolphin

This paper addresses the design, construction and control issues of a novel biomimetic robotic dolphin equipped with mechanical flippers, based on an engineered propulsive model. The robotic dolphin is modeled as a three-segment organism composed of a rigid anterior body, a flexible rear body and an oscillating fluke. The dorsoventral movement of the tail produces the thrust and bending of the anterior body in the horizontal plane enables turning maneuvers. A dual-microcontroller structure is adopted to drive the oscillating multi-link rear body and the mechanical flippers. Experimental results primarily confirm the effectiveness of the dolphin-like movement in propulsion and maneuvering.

Construction and Central Pattern Generator-Based Control of a Flipper-Actuated Turtle-Like Underwater Robot

This paper deals with the construction and control of a turtle-like underwater robot with four mechanical flippers. Each flipper consists of two joints generating a rowing motion by a combination of lead-lag and feathering motions. With cooperative movements of four flippers, the robot can propel and maneuver in any direction without rotation of its main body and execute complicated three-dimensional movements, including ascending, submerging, rolling and hovering. The control architecture is constructed based on a central pattern generator (CPG). A model for a system of coupled nonlinear oscillators is established to construct a CPG and has been successfully applied to the eight-joint turtle-like robot. The CPGs are modeled as nonlinear oscillators for joints and inter-joint coordination is achieved by altering the connection weights between joints. Rowing action can be produced by modulating the control parameters in the CPG model. The CPG-based method performs elegant and smooth transitions between swimming gaits, and enhanced adaptation to the transient perturbations due to nonlinear characteristics. The effectiveness of the proposed method is confirmed via simulations and experimental results.

An adjustable scotch yoke mechanism for robotic dolphin

This paper describes the design, construction, and performance analysis of an adjustable Scotch yoke mechanism mimicking the dorsoventral movement for dolphin-like robots. Since dolphins propel themselves by vertical oscillations following a sinusoidal path with alterable amplitudes, a two- motor-driven Scotch yoke mechanism is adopted as the main propulsor to generate sinusoidal oscillations, where leading screw mechanism and rack and pinion mechanism actuated by the minor motor are incorporated to independently change the length of the crank actuated by the major motor. Meanwhile, the output of the Scotch yoke, i.e., reciprocating motion, is converted into the up-and-down oscillation via rack and gear transmission. A motion control scheme based on the novel Scotch yoke is then formed and applied to achieve desired propulsion. Preliminary tests in a robotics context finally confirm the feasibility of the developed mechanism in mechanics and propulsion.

Underwater target following with a vision-based autonomous robotic fish

This paper is concerned with vision-based target following control of an autonomous, ostraciiform swimming robotic fish. Based on the successful development and effective swimming locomotion control of the robotic fish prototype, we further investigate the utility of the onboard digital camera in target following task, the output of which can be processed with the embedded processor. To treat the degradation of underwater images, a modified continuously adaptive mean shift (Camshift) algorithm is employed to keep visual lock on the moving target. A fuzzy logic controller is designed for motion regulation of a hybrid swimming pattern, which employs synchronized pectoral fins for thrust generation and tail fin for steering. A simple target following task is designed via an autonomous robotic fish swimming after a manually controlled robotic fish with fixed distance. Experimental results verify the effectiveness of the proposed methods.

Optimized design and implementation of biomimetic robotic dolphin

This paper describes an overall design procedure for a free-swimming, radio-controlled, multi-link biomimetic robotic dolphin mimicking dorsoventral movement. The swimming performance of the robotic dolphin is determined by its morphological parameters and kinematic parameters. The thrust is produced by the up-down-motioned fluke, and the turning is achieved by its left-right-sided body deflecting. A 4-link, 550 mm-long robotic dolphin prototype is successfully developed in our laboratory and its basic motion abilities are measured and some data are analyzed which show some promising performance in aquatic environment

Construction and control of biomimetic robotic dolphin

This paper is concerned with the design, construction, and control of a biomimetic robotic dolphin equipped with mechanical flippers, based on a simplified engineered propulsive model. The robotic dolphin is modeled as a three-segment organism composed of rigid anterior body, flexible rear body, and an oscillating fluke. The dorsoventral movement of the tail produces the thrust, and bending of the body in the horizontal plane enables turning maneuvers. A dual-microcontroller structure is proposed to drive the oscillating multi-link rear body and the mechanical flippers. Swimming performance of the prototype robotic dolphin is tested, and the results confirm the effectiveness of the dolphin-like movement in propulsion and maneuvering

Development and control of dolphin-like underwater vehicle

This paper is concerned with prototype development and motion control of a dolphin-like underwater robot. The propulsion and maneuvering of the robotic dolphin are realized with the flapping motion of the mechanical flippers and the combined heaving and pitching motions of the fluke. Mechanical design and control of the flipper apparatus and the flexible tail mechanism are presented. Through coordinated control of the propulsors, several swimming movements are designed. Preliminary experimental results verify the effectiveness of the proposed design scheme.

Towards development of link-based robotic dolphin: Experiences and lessons

This paper focuses on technical endeavors to develop bio-inspired dolphin-like robots, involving dynamic modeling, mechanical design, as well as motion control. The inspiration and motivation comes from the remarkable swimming abilities of dolphins together with some promising applications in aquatic environments. The thrust in dolphin-like movements in a robotics context can be generated by the up-down-motioned fluke, while the turning is achieved by left-right-sided deflections. Based upon three generations of link-based robotic prototypes, experiences and lessons accumulated in the course of producing these accomplishments are summarized, which provide insight into unraveling the efficient and agile propulsive mechanisms associated with Grays paradox. Comparative results are finally offered to demonstrate significant differences between biological dolphin and actual robots.

Modeling and Control of a Link-Based Dolphin-Like Robot Capable of 3D Movements

This paper focuses on a three-dimensional (3D) dynamic model for a self-propelled, multilink dolphin-like robot to predict the dynamic behaviors of the bio-inspired artificial dolphin system within the framework of multibody dynamics. The propulsive structure involves a multilink tail and an oscillating fluke cooperatively achieving dorsoventral oscillations, as well as a pair of mechanical flippers performing flapping movements, which can actually be simplified as an open-chain, tree-like multibody with a mobile base. The Schiehlen method is further utilized to formulate the equations of the motion on the basis of a well-integrated kinematic and dynamic analysis of propulsive elements. A rough comparison between simulations and experiments on forward swimming and combined motions verifies the effectiveness of the formed model and corresponding locomotion control method.