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REVIEW ON BIOMEMITIC ROBOFISH
PRIYANSHU SHARMA, Higher Degree Student, BITS - Hyderabad, Hyderabad, Andhra Pradesh, India
sharmapriyanshu20@gmail.com
Dr Daseswara Rao Yendluri, Professor, BITS - Hyderabad, Hyderabad, Andhra Pradesh, India
yvdrao@gmail.com
ABSTRACT
Biomimetic describes an engineering process or system that mimics biology.
The essence of biological data joined along with advances in low-cost, power efficient
computer systems, which supports the emerging development of robots that mimic insect
and sea creatures. Today researchers look forward for biological inspiration to create a new
generation of flying, crawling, and swimming automatons known as biomimetic robot.
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Generation of interest in how other species have adapted to a whole world of
environmental niches, researchers are working to understand and reverse-engineer the
adaptive traits of creatures. This paper would include some features of biomimetic robot
fish like design and implementation, motion control algorithms, posture control and 3D
implementation.
Keywords: biomimetic robots, design, parameters, swimming modes, robofish
1 INTRODUCTION Biomimetic robots form their structure and senses from animals, such as
birds or insects. Features of biomimetic robots are taken from earth's greatest examples of
survival i.e. living organisms. How birds fly, how fish swim, how dolphins locate objects, and
how humans walk might best be discovered and understood by trying to reproduce these
activities in a device. Biomimetic robots are still relatively new, however, and the possible
collaborations among biologists, robotic engineers, and computer scientists have begun.
There are some categories in which these biomimetic robots can be classified as per their
applications, namely mammals, insects, fishes, amphibians find their applications in military,
medical, engineering respectively.
The first basic biomimetic robot was a “lobster”, model was established in 1970 by efforts of
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Joseph Ayers [8], a biological professor at North-eastern University. With the rapid
development in field of biology and computers, it is now possible to understand and imitate
the behaviour of other animals.
Biomimetic fish like robots are gaining popularity as they can be used extensively in under
water investigations and marine applications like checking quality of water i.e. level of
contamination by chemical discharge and oil spills, certain space applications , underground
investigations (snake type features) and certain rescue missions . Some researchers also
think fish robots as effective weapon for ship propulsion which may reduce shoreline
erosion and undermining of submarine installation caused by screws used in ships.
1.1.
Design and implementation of a biomimetic robot
A biomimetic robot fish with tail is made for propulsion along with pectoral fins having three
degree DOF (provided to give flexibility adaptability), and multiple sensors are designed
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based on the analysis of propulsion and manoeuvring mechanisms for carangiform swimming
motion in which undulations of fish movement are limited to the caudal (tail) regions with the
body bending into less than one half of a sinusoidal wave form [1]. A mechanical tail
structure with cams and connecting rods for fitting carangiform fish body wave is designed
based on the propulsion and manoeuvring mechanisms of real fishes, which provides the
main propulsion.
In order to obtain the necessary environmental information, several kinds of sensors (video,
infrared, and temperature, pressure and PH value sensors) are mounted on the robofish
model. To analyse the carangiform propulsive mechanism and the large-amplitude elongated
body theory, a model based on elongated-body theory was put forward as idea to analyse the
irregular amplitude of tail. Several other developments have taken place in the field of
biomimetic robofish, as MIT has successfully developed first free-swimming robotic fish
,which is an eight-link, fish-like machine named as RoboTuna. A fish-like micro robot
prototype which possesses a pair of fins actuated by piezoceramics is being developed in
Nagoya University. Under water robot research on imitating the propulsion mechanical
structure of fish fins and constructed an experiment platform using elastic module, was
conducted by the Harbin Institute of Technology [9].
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The biomimetic robot fish considered in the work [1] is a usual fish-like machines motivated
by BCF (Body and/or Caudal Fin), which imitate the locomotion of fish by controlling the
position of several independent joints.
Design of the tail of the mechanical structure is based on the study that there is a travelling
wave, which travels from the neck to the tail of the fish body. Hence from the carangiform
propulsive wave curve starts from the fish’s centre of inertia to the caudal joint and is given
by equation
ybody (x,t) = [(c1x + c2x2)][sin(kx +ωt)] ………(1)
where , ybody is the transverse displacement of body,
x is thedisplacement along main axis,
k is the body wave number(k =2π/λ),
λ is the body wave length,
c1 is the linear waveamplitude envelope,
c2 is the quadratic wave amplitude envelope
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ω is the body wave frequency (ω=2πf=2π/T).
The fish body curve can also be shown by the graph,
Fig 1 Fish body wave curve
1.1.1 SOME IMPORTANT TAIL PARAMETERS
The tail parameters of the biomimetic
robot fish include the tail fin shape S, relative wavelength R, number of joints N, length of
joints Lj(j=1,2…N), and the position of every joint end P={(xj,yj)},(i=1,2…M; j=1,2…N) in
every sampling cycle. Following conclusions can be drawn [1],
Table 1
PARAMETERS
EFFECTS
Tail fin shape
The propulsive power is mainly provided by the tail in carangiform
mode, a crescent-shaped fin made.
Relative
wavelength reduction of R results in the increase of propulsive efficiency, the
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(R)
increase of velocity, and the reduction of manoeuvrability
Number of Joints (N)
The increase of N results in the increase of the flexibility of fish
body, the reduction of error of curve fitting, and the increase of
manoeuvrability.
Length of Joints
The length of joints reduces gradually, and the flexibility is larger
with the shorter joint. Shorter the joint is, the bigger the torque it can
offer is, the higher the oscillatory tail frequency is. In practice,
L1: L2 = 1: 0.5.
1.1.2 TAIL MECHANICAL STRUCTURE: The mechanical tail structure has two main parts
namely Oscillate part and Drive part. Oscillate part simulates the fish tail motion by two
joints designed according to the tail parameters calculated. The Drive part of the tail is
composed of a pair of cams and two slide bars
= (i=1,2) connected to joints. The tail
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mechanical structure can be shown by the diagram below
Fig 2 Tail mechanical structure
The detailed working of tail with its cam system can be understood by the help of above
diagram. The two cams rotate in reverse directions to push slide bars in the direction of bodyaxis to drive all joints and the tail fin to oscillate. We can implement the position control of
slide bars at all the sampling points, by calculating the appropriate cam shape, which may
drive the tail to fit the carangiform propulsive mechanism. DC motors are adopted instead of
step motors or servo actuators, which may offer more propulsion power to the structure.
1.1.3 PECTORIAL FINS: Fins are very essential for fishes for balance and also to
control the posture. The locomotion of the fish pectoral fins can be simplified to two kinds of
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fundamental motions: rotation and flap. A uniform motion is given to the pectoral fins, thus
corresponding degree of freedom to each motor is three. To change the attack angle, both
pectoral fins roll synchronously, when the motor 2 is made to rotate. Similarly motor 1 and
motor 3 will rotate in forward and backward with certain range of angle to make the left/right
pectoral fin flap continuously. Hence this structure satisfies the manoeuvrability of the
locomotion.
1.1.4 CONTROL SYSTEM ARCHITECTURE: When the robot fish works in underwater
environment, it needs to understand the environment. Hence multiple sensors are equipped
with the robot fish to collect information of its surrounding environment, i.e. water depth,
neighbouring obstacles. In such underwater applications, pressure sensors,
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Fig 3 Pectoral fin structure
a CCD camera, temperature transducer, infrared sensors and a PH value sensor are chosen.
Details of control structure are explained [1].The control system can be roughly understood
by the block diagram,
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Fig 4: block diagram of control system
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Fig 5 prototype of a biomimetic fish
1.1.
VARIOUS FISH SWIMMING MODES
Fish swim either by body and/or caudal fin (BCF) movements or using median and/or paired
fin (MPF) propulsion. MPF is generally employed at slow speeds, as it offers greater
manoeuvrability and better propulsive efficiency, whereas, BCF movements can be used to
achieve greater thrust and accelerations. In the work of Michael Sfakiotakis el all [2], we can
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see an overview of fish swimming and some of the analytical methods that were applied to
some of their propulsive mechanisms. Properties of water like its compressibility and high
density affect the motion of a fish as well as effects in a similar way to a biomimetic robofish.
To study the fish swimming mechanism, following terminologies were extracted from [2];
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Fig 6 Describing type of fins and other features
Table 2
TYPE OF FIN
NAME GIVEN TO THEM
Median and paired fins
short-based or long based,
Normal and parallel to water flow
Span and chord
Swimming involves the transfer of momentum from the fish to the surrounding water (and
vice versa). The main momentum transfer mechanisms are via drag, lift, and acceleration
reaction force.
Swimming locomotion has been classified into two generic categories on the basis of the
movement’s temporal features
(1) Periodic (or steady or sustained) swimming: Periodic swimming is employed by fish
to cover relatively large distances at a more or less constant speed.
(2) Transient (or unsteady) movements: Transient movements last milliseconds and are
typically used for catching prey or avoiding predators.
Some of the important swimming modes based on Breder’s fish classification can be seen in
the given diagram [2]
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Fig 7 swimming modes
Table 3:
TYPE
OF
FORCE
1
Drag Has two components namely , friction and pressure
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force
drag
Friction drag arises as a result of the viscosity of
water in areas of flow with large velocity gradients.
And form drag is caused by the distortion of flow
around solid bodies and depends on their shape.
2 Lift force
Lift forces originate from water viscosity and are
caused by asymmetries in the flow.
3
It is generated by the resistance of the water
acceleration surrounding a body or an appendage when the
or
inertial velocity of the latter relative to the water is
force
changing.
Acceleration reaction is more sensitive to size than
is lift or drag velocity
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Table 4:
Swimming modes
Brief Explanation
ANGUILLIFORM MODE
Whole body participates in large amplitude
undulations. Such swimmers are capable of
backward as well as forward swimming.
Similar movement but amplitude of the
undulation is limited and increase only in
posterior half of the body
Faster than above two mentioned, body
undulations are confined to last third of the
body length and thrust is provided by a rather
stiff caudal fin.
Most efficient, generate thrust by lift based
method , allowing high cruising speed to be
maintained for long period
Locomotion is purely oscillatory BCF mode,
fish that uses this have inflexible bodies and
forage their habitat usually MPF propulsion.
Thrust generation involves the passing of
vertical undulation along the pectoral that are
very large , triangle shaped and flexible
Propulsion is achieved by passing undulation
down board pectoral fins
Undulation of a dorsal fin, while body axis in
many cases held straight while swimming
Upside –down equivalent to amiiform mode,
since propulsion is obtained by undulation of
a long based anal fin.
Both anal and dorsal fins undulate to generate
the propulsion forces
Dorsal and anal fins are flapped as a single
unit, either in phase or alternating to achieve
propulsion.
Propulsion is achieved by oscillatory
movements of pectoral fins .
SUB-CARANGIFORM MODE
CARANGIFORM MODE
THUNNIFORM MODE
OSTRACILFORM MODE
RAJIFORM MODE
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DIODONTIFORM MODE
AMIIFORM MODE
GYMNOTIFORM MODE
BALISTIFORM MODE
TETRADONTIFORM MODE
LABRIFORM MODE
Swimming modes of biomimetic underwater Robots can be classified based
on Breder’s fish classification and can be briefly understood by the diagram [4]
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1.2.
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POSTURE CONTROL
This section deals with the posture control and 3D implementation of a biomimetic robofish
named as TPF-I (Three degree of freedom Pectoral Fin-I) , in which by using barycentre –
adjustor, a particular type of adjustor, the position of centre of gravity of robot fish can be
changed, which then changes the pitching angle. By synthesizing three basic control methods
like speed control, orientation control and pitching control, posture control can be
implemented.
Various researchers are working to develop biomimetic robots having high velocity,
efficiency and manoeuvrability. An eight link, fish-like machine RoboTuna has been
developed by MIT. RoboTuna and subsequent RoboPike projects that exploited external fluid
forces to produce thrust, by utilizing a flexible posterior body and a flapping foil (tail fin)
have attempted to create AUVs with increased energy savings and longer mission duration.
Work done on posture control [3] resulted in a biomimetic fish with three degree of freedom,
TFP-I. A multiple link tail is designed to simulate the carangiform propulsion mechanism.
By changing the central axis of the tail oscillating, orientation control is done. The centre of
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gravity position changes by a moving counterweight, which in turn controls pitching. The
robot fish can descend and ascend at certain velocity. The design of fish discussed[3]is based
on three methods, namely,(i) Changing Gravitation (Buoyancy), (ii)Pectoral fins,
(iii)Changing body shape, (iv) Hanging the Barycentre. In the design that is based on
barycentre, the weight is located in the head part of robot fish, and servo actuator is used to
change its position. The motion of the weight changes the centre of gravity position. Shown
in the figure 8 is the robot fish with barycentre-adjustor and circuit system
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Fig 8 Barycentre-adjustor and control system
For the tail of the robot carangiform propulsive wave curve is considered, and the equation
and obtained graphs can be seen in [3]. The schematic structure of a robofish is given in
figure 9 below that a clear idea about this robo fish.
Fig 9 Schematic structure of robot fish TPF-I
Posture control [5] is briefly discusses about velocity control, orientation control, pitching
control, which requires a good experimental data [3], that is based on effects of velocity,
orientation and pitching control. Hence it can be said that the
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Barycenter-adjustor is used to change the posture and perform the 3-D locomotion by
combining with the tail motion.
1.4. SOME EXAMPLES OF BIOMIMETIC ROBOTS
A hexapod robot uses Shape Memory Alloy (SMA) actuators [5]. In this work an investigation
is made with regard to the characteristics of the SMA actuators and introduces various gaits
used for the six-legged motion. Also discussed are the controller of the robot and the driver
for SMA actuators along with the robot’s performance. Further given are the dimensions and
information about the communication links and required algorithms. Another work done
discusses about the design and implementation of robot fish –PoTuna [6].
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Fig 10: PoTuna robot fish
Design of the flight control algorithms for flapping wing micromechanical flying insects
(MFIs) are done to some extent [7].
2 CONCULSION
In this work an attempt is made to gather basic information about
biomimetic robots, concentrating specially robot fish, discussing the design and its
implementation in 3D. Various type of swimming modes are also shown, also posture control
is shown. Design of PoTuna is also briefly shown. As biomimetic robots is a growing area of
research, as they can be used in so many applications, a robofish is discussed here as it is
being very important for military work, underwater investigations, determining the water
contaminations , temperature study in areas where human divers find difficulty .
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3 REFRENCES
[1] Chao Zhou, Min Tan, Nong Gu, Zhiqiang Cao, Shuo Wang and Long Wang, ―The
Design and Implementation of a Biomimetic Robot Fish‖, International Journal of Advanced
Robotic Systems, Vol. 5, No. 2 (2008)
[2] Michael Sfakiotakis, David M. Lane, and J. Bruce C. Davies, ―Review of Fish Swimming
Modes for Aquatic Locomotion‖, IEEE JOURNAL OF OCEANIC ENGINEERING, VOL.
24, NO. 2, APRIL 1999.
[3] Chao Zhou, Zhiqiang Cao, Shuo Wang and Min Tan, ―The Posture Control and 3-D
Locomotion Implementation of Biomimetic Robot Fish‖, International Conference on
Intelligent Robots and Systems October 9 - 15, 2006.
[4] Won-Shik Chu etall, ―Review of Biomimetic Underwater Robots Using Smart
Actuators‖, International journal of precision engineering and manufacturing.
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[5] Chia-Lun Tien , Yung-Yaw Chen , Jia-Yush Yen , Feng-Li Lian ,‖ Development of Biomimetic Micro-Robot – A Project Review‖, CACS Automatic Control Conference Tainan.
[6] EunJung Kim
and Youngil Youm, ―Design and Dynamic Analysis of Fish-like
Robot:PoTuna‖, ICCAS2003
[7] Xinyan Deng, Luca Schenato, and Shankar Sastry, ―Flapping Flight for Biomimetic
Robotic Insects: Part II—Flight Control Design‖
[8] Linda Dailey Paulson, ―Biomimetic Robots‖ ,IEEE,2004
[9] won-shik chu etall. ―Review of biomimetic underwater robots using
smart actuators‖, International journal of precision engineering and manufacturing vol. 13.
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