Robotics@Techweek’07

What is a Robot?

Electro-mechanical device.

Performs Various tasks.

May be human controlled or automated.

It finds it’s uses in all aspects of our life.

How a Robot Can Help ?

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.

A machine removing mines in a war field all by itself and many more…

Basic Parts of a Robot

Mechanical system

Power supply system

Actuators

Sensory devices for feedback

Sensor Data processing unit

Control system

Mechanical System

The most basic and important part of the robot.

It comprises of chassis, motors, wheels and their placement.

This system decides the locomotion of the robot.

Wheeled Locomotion Systems

Differential drive Car type drive Skid steer drive Synchronous drive Pivot drive

Differential Drive

This is the most commonly used form of locomotion system used in robots as it’s the simplest and easiest to implement.

It has free moving wheel(s) in the front accompanied with a left and right wheel. The two wheels are driven by different motors.

Differential Drive Cont…

Differential Drive: An Analysis

Simplicity and ease of use makes it the most preferred system by beginners

Independent drives makes it difficult for straight line motion. The differences in motors and frictional profile of the two wheels cause them to move with slight turning effect

The above drawback must be countered with appropriate feedback system. Suitable for human controlled remote robots

Car Type Drive

It is characterized by a pair of driving wheels and a separate pair of steering wheels.

The translation and rotation are interlinked, hence this system faces severe path planning problem.

Car Type Drive Cont…

Skid Steer Drive

A close relative of the differential drive system. It is mostly used in tracked machines e.g. tanks.

Also finds application in some four / six wheeled robots

The left and right wheels are driven independently.

Steering is accomplished by actuating each side at a different rate or in a different direction, causing the wheels or tracks to slip, or skid, on the ground.

Skid Steer Drive Cont…

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 synchronous fashion

The two sets can be directly mechanically coupled as they always move in the same direction with same speed

Synchronous Drive Cont…

Pivot Drive

The most unique type of Locomotion system

It is composed of a four wheeled chassis and a platform that can be raised or lowered

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

This system can guarantee perfect straight line motion as well as accurate in – place turns to a desired heading

Power Supply System

Suitable power source is needed to run the robots.

Robots are most suitably powered by batteries.

The weight and energy capacity of the batteries may become the determinative factor of its performance.

Actuators

They convert the electrical energy into meaningful mechanical work

Mechanical output can be rotational or linear (straight line)

Motors provide rotational motion

Electromagnets provide linear motion

Motors are of various kinds

AC Motors : Not used much in robotics

Stepper Motors : For controlled rotation

DC Motors : Finds extensive general use

Servo Motors : DC motor with in built feedback & error compensation

Stepper Motors Used for measured

rotation.

Can be held at a particular position of the shaft.

Ideal for many autonomous robots requiring higher precision.

Stepper Motor Working

0001001001001000Stepping Sequences for Single Coil Excitation

Only one coil is active at a given instant of time

Single Coil Excitation

Stepper Motor Working Cont…

1001001101101100

Stepping Sequences for Double Coil Excitation

Two coils active at any given instant of time

Double Coil Excitation

Problems with Stepper Motors

Very low torque to weight ratio

Torque decreases with increase in the stepping frequency

For sufficiently high stepping speed the stepper motor may skip steps due to overshoot

DC Motors

As the name suggests, a motor which uses a DC (Direct Current) power

Can run in both directions

Speed Controllable

DC Motor Characteristics

DC Motors are high–speed, low-torque devices.

Using gears, the high speed of the motor is traded off into torque

DC Motor Drivers

These are current amplifying circuits.

A low current control signal is converted into a proportionally higher current signal that can drive the motor

DC Motor Direction Control

H – Bridge Circuit Diagram

S1

S3

S2

S4

M1 2

VCC

Power Transistor Switches

H – Bridge Working

S1 S2 S3 S4 Current Direction

Effect

1 0 0 1 1 to 2 Motor spins forward

0 1 1 0 2 to 1 Motor spins backward

1 1 0 0 - Braking Occurs

0 0 0 0 - -

Electronic Direction Control

H – Bridge Circuit Diagram

GND

VCC

NOT GATE

12Q1 Q3

A- +

DC MOTOR

12

LQ4Q2

R

NOT GATE

12

Open Loop Control System

There is no error correction. No way to check if the actuator was able to take the desired action

Simple system to design, not very reliable Requires regular calibration of the system

Controller Actuator

O/PDesired Action Controller Actuator

Closed Loop Control System

Desired Action Controller Actuator

O/P

Feedback

Example : An Air conditioner

Desired Temp. ControllerCooling Device

Room Temp

Temperature Sensor

Sensors

Analogous to human sensory organs Eyes, ears, nose, tongue, skin

Sensors help the robot knowing its surroundings better

Improves its actions and decision making ability

Provides feedback control

Examples

Light Dependent Resistor

Thermistor

IR Photo Sensor

Line Follower

A line follower is a robot capable of tracking a line drawn on a surface

Optical sensors capture the line position at the front end of the robot

The robot is steered to keep it always over the line

Click to view

Optical Reflectors

Sensor InterfacingVCC

R4

2K2

R21k

R4

2K2

Temperature Detector0

Digital O/P

Light Intensity Detector

Thermistor

R3

R5

10K

R6

5K

Digital O/P

VCC

LDR

D3IR LED

R21k

0

0

U3A

LM339

5

4

312

2

+

-

V+V-

OUT

R2100R

R6

5K

Digital O/P

8 - Bit ADC

R5

100K

Digital O/P

VCC

U3A

LM339

5

4

312

2

+

-

V+V-

OUT

0

Bump Detector

8 - Bit ADC

VCC

R3

IR Proximity Detector

D4Photo Diode

Delhi College of Engineering

DescriptionTasks and Arena

Embedded

Control Systems

Power

Mechanical Design

The Vehicle

Test and Performance