Presented by:
Abhishek Karunakar

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Biologically Inspired Robotic Fish
Introduction
Robotic fish is a biomimetic robot obtaining its design inspiration from aquatic animals. Ex : Shark Fish, Eel, Tuna etc.
For long researchers have been interested in the highly efficient propulsion of fish and now have attempted to apply it to underwater robots for fish-like swimming mechanisms
Why Robotic Fish ?
With increased horizons of underwater applications, there is much pressing on efficient equipments for these operations.
Efficiency and propulsive performance for under water applications essentially requires fish-like performance compared to conventional technique.
Evolution has made fishes excellent swimmers. And the design of there structure is naturally refined for efficiency.
How do Fishes Swim ?
The main tools that fishes use to swim efficiently are
Fins : To glide & turn
Air bladder : To move up & down
Stream lined body : To reduce pressure drag
Slime coat : To reduce friction drag
Principle of Robotic Fish swimming
There are four categories of mechanical design for swimming robotic fishes
Changing wave: Body wave from head to tail is used for propelling. A smooth motion of entire body is required with many hinges and joints. Complex control system. Can realize delicate motion, and work well in narrow water area like a coral reef.
Body Foil: Fish pushes the water away behind them by both oscillation of its tail fin and wave motion of the body. Trout and Salmon are fish typical of those using this swimming method.
Oscillating Wing: Fish using this method derive nearly all of its propulsive force from an oscillating wing-shaped tail fin. These fish has a crescent and wing-shaped tail fin. Tuna and Bonito use this method.
Oscillating Plate: Fish using this method oscillate only a tail fin like a plate without moving the body.
For up and down motion
Different techniques can be used for up and down motion as listed below
A water tank (air bladder) and a pump are located in the fish robot. A balance of gravitation and buoyancy is changed by water in and out of the tank. This mode has problems such as delay of a response, handling of compressed air and getting large size by the tank and the pump.
Fish robot with fins (wings) moves up and down using their lift force.
A mechanism for changing angle of up and down direction at its head or tail. The fish robot changes its body to a shape of a wing, and moves up and down by the lift force. Quick response and high dynamic performance
Fish robot moves up and down with changing a direction of tail fin which generates propulsive force
Fish robot has a mechanism moving a weight to forward and back direction.
Turning Modes
The fish robot swings its tail only to one side during a turning. It is considered that this mode is the most fundamental and important turning mode, because the robot can turn with various turning diameter and speed in this mode
The fish robot swims straight, and gets kinetic energy. Next, the fish robot turns its tail to one side, and keeps the posture to the side. Then the fish robot turns by hydrodynamics force. It is considered that this mode gets smaller turning diameter
The fish robot swings its tail to one side rapidly from stationary state. In this turning mode, inertia force and friction force of the moving tail and the body are changed to the moment of rotation
Sensory System
Various Sensors
Photo Sensor: The fish will turn in the direction corresponding to which sensor (left or right) is detecting more light. If both sensors are detecting the same amount of light, then this would indicate that the source of irradiance is straight ahead, and robot will move forward.
Pressure Sensor: The pressure sensors will be used to indicate to the robot the depth at which it is submerged, and may also be used to indicate any agitation of water within its surroundings.
Humidity Sensor: Humidity sensor is useful device to use for detecting whether or not the robot is submerged in water.
Audio Sensor: A microphone can added to allow for detection of audio signals. In order to detect the location of the sound source, a larger surface area as well as many more microphones would be required.
Structure
The structural design should mimic fish body structure
The body should be compact and accommodate all sensors, actuators & motors.
The outer skin should be flexible, chemically inert & light weight
Applications
Aquatic creature behavioral research : Investigating deep-sea fish behaviors
Mining Applications : Deep sea mining
Pollution Rate Study : Water pollution rate inspection
Industrial purpose : Underwater oil pipe leakage detection
Military Reconnaissance
Sea bed exploration : Abyss region
Deep sea Archeology
Advantages
Simple design
Highly Efficient
Autonomous
Excellent disguise
Good mobility
Future Research
Different fishes have different swimming techniques which can be adapted application wise
Robotic fish should be able to find a charging station as real fish look for food.
Sensory system should be improvised to increase autonomous performance
Defense mechanism to protect robotic fish from other aquatic creatures