A Tutorial on Robotics Part I.pdf

7/30/2019 A Tutorial on Robotics Part I.pdf

1/32

A Tutorial on Robotics


2/32

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

..

It finds its uses in all aspects of our life


3/32

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

..

mac ne remov ng m nes n a war e a y tse anmany more


4/32

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

..


5/32

Basic Parts Of Our Mobile Robot Locomotion system

Power supply system Actuators

Sensory devices for feedback

..

Sensor Data processing unit

Control system


6/32

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

..


7/32

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

..

speed and torque


8/32

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)

..

versa


9/32

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

..

These are governed by: 1 X r1 = 2 X r2


10/32

Wheeled Locomotion Systems Differential drive

Car type drive Skid steer drive

Articulated drive

..

Synchronous drive Pivot drive

Dual differential drive


11/32

Differential Drive

This is the most commonly used form of locomotion systemused in mobile robots as its the simplest and easiest toim lement

..

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


12/32

Differential Drive Cont

..

Black arrows denote the direction of wheel. The green ones show

robot movement


13/32

Differential Drive Cont

In-place (zero turning radius) rotation is done by turning thedrive wheels at the same rate in the opposite direction

..

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


14/32

Differential Drive An Analysis

Simplicity and ease of use makes it the most preferred systemby beginners

..

.

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


15/32

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

..

.

But translation and rotation are interlinked hence this system

faces severe path planning problem


16/32

Car Type Drive Cont

..


17/32

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

..


18/32

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

..

,

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


19/32

Skid Steer Drive

A close relative of the differential drive system

It is mostly used in tracked machines e.g. tanks. Also finds

..

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


20/32

Skid Steer Drive Cont

..


21/32

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

..

drive system


22/32

Articulated Drive

In this mechanism the machine chassis (body) is deformed toachieve rotation in contrast to the steering wheels in car typedrive

..


23/32

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

..


24/32

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

..

The two sets can be directly mechanically coupled as they

always move in the same direction with same speed


25/32

Synchronous Drive Cont

..

The direction of motion is given by black arrow. The alignment

of the machine is shown by green arrow


26/32

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

..

but further use is much simpler


27/32

Pivot Drive

The most unique type of Locomotion system

It is composed of a four wheeled chassis and a platform that can

..

e ra se or owere


28/32

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

..

as accurate in place turns to a desired heading


29/32

Complexity of Pivot Drive

The system is quite complex in design

A still more complex design uses only two motors. The wheels

..

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


30/32

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

..


31/32

Dual Differential Drive Cont

..


32/32

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

..

A Tutorial on Robotics Part I.pdf

Documents

Transcript of A Tutorial on Robotics Part I.pdf