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Biomimetic fish robot
A Proposal Presented to the Faculty of the Department of Mechatronics Engineering of College of Engineering Bulacan State University

In Partial Fulfilment of the Requirement for the Degree Bachelor of Science in Mechatronics Engineering

By: Fajardo, Jonah Angelo S.

Engr. Erwin Magsakay Subject Instructor

March, 2012

Abstract Biomimetic robots borrow their senses and structure from animals, such as insects, fish and birds. Development of underwater vehicles is one of the areas where biomimetic robots can potentially perform better than conventional robots. In this paper, the biomimetic design and the workspace study of undulating fin propulsion mechanisms are considered and discussed. We are interested in fish with long and/or wide undulating body/fin especially those of anguilliform, amiiform, rajiform, and gymnotiform. Two major mechanism layouts developed to mimetic fin undulations of real fish are compared and discussed. Various kinematics expressions of fin waves are presented and the model¶s limitation is also discussed. For a parametric study, the geometry of a single fin segment of the assembled fin mechanisms and the fin wave generated are first developed. Next, the fin workspace of the single fin segment is derived based on a defined area ratio. By virtue of the obtained fin dimensions, a gymnotiform robot, Nanyang knifefish (NKF-II), has been designed and constructed. With the fin-ray linkages with sliders connecting in series, the fish robot is able to generate arbitrary undulating waveforms. The robot¶s maneuvering and its depth control have also been achieved by the integration of a buoyancy tank with the undulating fin mechanisms. Initial pool testing has been conducted to demonstrate the basic performance of the fish robot underwater.

Chapter 1

Introduction Biomimetic robots borrow their senses and structure from animals, such as insects, fish and birds. It is believed that the bio-inspired systems function better in the unpredictable real world than the controlled artifice of a laboratory. Another reason for the focus in biomimetics propulsion means is the increasing awareness to preserve the environment. The marine ecological environment has been deteriorating because of human interaction with them. One extremely destructive tool used by such human interaction is the propeller, the main propulsion systems used by most current water vehicles. The broadband noise from cavitating propellers of any motorized vessel may have severe acoustic effects on marine wildlife, like changes of behaviour, µmasking¶ of other signals, or causes temporary (or permanent) hearing trauma thus Schools of robotic fish could one day map the ocean
floor, detect pollution or inspect and survey submerged boats or oil and gas pipelines,

1.1 Statement of the Problem
The aim of this thesis is to design a robotic fish by copying as closely as possible the geometry and material properties of a rainbow trout. The underlying hypothesis is that if the geometry, material properties and the actuation signals are resembling the real trout, the kinematics of the robotic trout will be also similar to the real fish to be used as underwater surveillance helper .

1.2 Objectives, Scope and Overview of the Thesis In this thesis, we will substitute complex mechanisms with compliant bodies, using material properties instead of structural composition to gain similar kinematics and desired propulsion results. The main objective is to design this compliant mechanism which implements biomimetic fish-like propulsion, setting the focus on investigating the properties of real fish and using biological data to develop this artificial system. The final result of this thesis is a robotic fish-like underwater vehicle which is able to generate thrust with similar mechanism to a rainbow trout. It will use only a single actuator and will generate fish-like kinematics by oscillating elastic body in water. The tail of the robot is an elastic vibrating system that is generating underwater oscillations similar to a swimming rainbow trout. However, the vibrations are not caused by the muscles in whole body but by an actuator. Therefore finding right properties of this elastic body is essential 12to find right vibrational behaviour. These properties are found by mimicing the properties of a real rainbow trout¶s body.
1.2.1 Problem statement The aim of this thesis is to design a robotic fish by copying as closely as possible the geometry and material properties of a rainbow trout. The underlying hypothesis is that if the geometry, material properties and the actuation signals are resembling the real trout, the kinematics of the robotic trout will be also similar to the real fish. Furthermore, the prototype is then used as an experimental equipment to conduct scientific experiments within a research project FILOSE [3] investigating fish locomotion and sensing. One of the scientific objectives of this project is to investigate how the properties of fish body determine the locomotion efficiency of

fish. Therefore, it is needed to develop a methodology to design tail propulsors rapidly and cheaply with varying material properties. Thus, the problem statement of this thesis is the following: 1. Develop a methodology to design fish tail propulsors and fish robots with specific material properties. 2. Develop a fish robot prototype that copies as closely as possible the geometry, stiffness and stiffness distribution of a rainbow trout. To achieve these goals this thesis comprises the following design steps: 1. Experimental characterization of real fish body properties. Geometry, mass distribution and bending stiffness of fish body is measured. The properties are characterized by: a. b. c. Analytical description of fish geometry that uses elliptical cross-sections and simplifies the geometry without significant loss of precision. Analytical description of mass distribution using linear regression on the experimental data Analytical description of stiffness and stiffness distribution 132. Development of a design process for designing artificial robot fish tails with specified properties. This comprises: a. Development of a composite material model that permits fine-tuning tail¶s properties by combining a stiffer internal beam with softer outer body. b. Finding the boundary values for the stiffer internal and the softer external material and the selection of suitable commercially available materials. c. Experimental characterization of the materials with tensile experiments. d. Design of a fish tail with a specified geometry and material properties by combining the stiffer internal material with the softer external material. 3. Fabrication of the prototype using CNC-made molds and casting silicone rubbers and foams 4. Testing the prototype tail propulsor fabricated in the previous step by measuring its kinematics and generated forces. Comparing the kinematics of the artificial tail to the kinematics of the real rainbow trout. 5. Design of a fish robot prototype using the previously developed tail. The test results confirm that the methodology used in this thesis and the design process permits creating tail propulsors with specified properties. The kinematics of the artificial tail resembles closely the kinematics of the real rainbow trout. Therefore, this design methodology developed in this thesis is fast, cheap and well suitable for fabrication of artificial fish prototypes with predefined properties. The designed robot is meant for using in future experiments with artificial lateral line sensors. It has to swim freely in flowing water environment and has to detect water flowing patterns around its body using flow speed sensors mounted on its body. Thesis is organized in 7 chapters. Chapter 2 will give an overview of work done in building fish-like robots. Brief summary of fish swimming kinematics and dynamics is given. Also a few fish-like underwater robots are described. In chapter 3 a characterization of real rainbow trout is given to use this data in engineering process. In chapter 4 the artificial fish tail using real fish body properties is used to design an artificial passive fish tail with same properties. Chapter 5 describes the performance characterization of this artificial tail when it is actuated with one rotational actuator. In chapter 6 this designed tail is used to design and build an underwater fish-like robot.

2 Background

This chapter gives an overview of current knowlede about locomotion principles in liquid environments.A brief summary of the swimming mechanisms employed by fish is given along with kinematic data and analytical approaches developed to study them. Also an overview of previous work done to implement artificial fish-like propulsion devices is presented.

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