a tutorial on robotics part i.pdf
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A Tutorial on Robotics
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What Is Robotics ? The word robotics is used to collectively define a field in
engineering that covers the mimicking of various human
characteristics
Sound concepts in many engineering disciplines is needed for
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It finds its uses in all aspects of our life
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What A Robot Can Mean ? An automatic industrial machine replacing the human in
hazardous work environment
An automatic mobile sweeper machine at a modern home
An automatic toy car for a child to play with
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mac ne remov ng m nes n a war e a y tse anmany more
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What Do We Mean Here ? Here we are aiming at design and prototyping of mobile
robots capable of controlled locomotion
It may be human controlled or automatic
It must be able to perform certain tasks we set for it
The task must be achieved within some iven limitations
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Basic Parts Of Our Mobile Robot Locomotion system
Power supply system Actuators
Sensory devices for feedback
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Sensor Data processing unit
Control system
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Locomotion System As the name suggests a mobile robot must have a system to
make it move
This system gives our machine the ability to move forward,
backward and take turns
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Locomotion System The concept of locomotion invariably needs rotational
motion e.g. a wheel driven by some power source
This involves conversion of electrical energy into mechanical
energy, which we can easily achieve using electrical motors
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speed and torque
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Power, Torque and Speed A simple equation: Power is the product of Torque and
Angular velocity
P = X
This implies that if we want more torque (pulling capacity)
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versa
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Another Simple Relation The dc motors (tape motors) available have very high speed
of rotation which is generally not needed. But what they lack
is torque output
For reduction in speed and increase in pulling capacity we
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These are governed by: 1 X r1 = 2 X r2
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Wheeled Locomotion Systems Differential drive
Car type drive Skid steer drive
Articulated drive
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Synchronous drive Pivot drive
Dual differential drive
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Differential Drive
This is the most commonly used form of locomotion systemused in mobile robots as its the simplest and easiest toim lement
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It has a free moving wheel in the front accompanied with a leftand right wheel.The two wheels are separately powered
When the wheels move in the same direction the machine
moves in that direction. Turning is achieved by making thewheels oppose each others motion, thus generating a couple
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Differential Drive Cont
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Black arrows denote the direction of wheel. The green ones show
robot movement
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Differential Drive Cont
In-place (zero turning radius) rotation is done by turning thedrive wheels at the same rate in the opposite direction
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modifying the angular velocity and/or direction of the drivewheels
Total of two motors are required, both of them are responsible
for translation and rotational motion
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Differential Drive An Analysis
Simplicity and ease of use makes it the most preferred systemby beginners
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.
The differences in motors and frictional profile of the twowheels cause them to move with slight turning effect
The above drawback must be countered with appropriate
feedback system. Suitable for human controlled remote robots
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Car Type Drive This is the car type drive and the most common in real world
but not in robot world
It is characterized by a pair of driving wheels and a separate
pair of steering wheels
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But translation and rotation are interlinked hence this system
faces severe path planning problem
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Car Type Drive Cont
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Disadvantages Of Car Type Drive The turning mechanism must be accurately controlled. A
slight inaccuracy may cause large odometry errors
The system is Non Holonomic hence path planning is
extremely difficult as well as inaccurate
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Holonomic Systems
A Non-Holonomic system is one in which the actuators do not
directly control one or more of the degrees-of-freedom of the
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,
much more complicated than in a Holonomic system
Any robot architecture that allows for direct and, possibly
simultaneous, motion along the x and y axes would be
Holonomic
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Skid Steer Drive
A close relative of the differential drive system
It is mostly used in tracked machines e.g. tanks. Also finds
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The left and right wheels are driven independently
Steering is accomplished by actuating each side at a differentrate or in a different direction, causing the wheels or tracks to
slip, or skid, on the ground
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Skid Steer Drive Cont
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Differences With Differential Drive Multiple drive wheels on each side give increased traction.
The effect is even greater for tracked machines
Skidding causes the wheels to loose contact with the surface
beneath and position tracking becomes difficult
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drive system
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Articulated Drive
In this mechanism the machine chassis (body) is deformed toachieve rotation in contrast to the steering wheels in car typedrive
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Articulated Drive Cont Two actuators (motors) are needed. One to drive the wheels
and the other to change the pivot angle
This system shares most of its features with the car type
mechanism
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Synchronous Drive As the name suggests, it uses synchronous rotation of its
wheels to achieve motion & turns
It is made up of a system of motors. One set of which drive
the wheels and the other set turns the wheels in a
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The two sets can be directly mechanically coupled as they
always move in the same direction with same speed
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Synchronous Drive Cont
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The direction of motion is given by black arrow. The alignment
of the machine is shown by green arrow
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Advantages of Synchronous Drive The use of separate motors for translation and
wheel turning guarantees straight line motionwithout the need for dynamic feedback control
This s stem is somewhat com lex in desi nin
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but further use is much simpler
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Pivot Drive
The most unique type of Locomotion system
It is composed of a four wheeled chassis and a platform that can
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e ra se or owere
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Pivot Drive Cont The wheels are driven by a motor for translation motion in a
straight line
For rotation one motor is needed to lower/raise the platform
& another to rotate the chassis around the platform
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as accurate in place turns to a desired heading
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Complexity of Pivot Drive
The system is quite complex in design
A still more complex design uses only two motors. The wheels
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an e p a orm ro a on are coup e o a s ng e mo or. en
in translation the platform has no effect as it is above ground.
And when turning, the wheels are off the ground due to the
lowered platform
The machine is restricted to only in place turns. This may bean hindrance in some cases
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Dual Differential Drive It offers the flexibility of the differential drive along with a
fairly better accuracy in movement
The design is achieved using a unique arrangement of gears
It guarantees straight line translation along with spot turning
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Dual Differential Drive Cont
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Power Supply System Suitable power source is needed to run the robots
Mobile robots are most suitably powered by batteries
The weight and energy capacity of the batteries may become
the determinative factor of its performance
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