Robotix Tutorial 6

TECHNOLOGY ROBOTICS SOCIETY

Indian Institute of Technology, Kharagpur

A TUTORIAL ON ROBOTICSSensors

Copyright © Robotix Team, IIT Kharagpur

Basic Parts Of Our Mobile Robot Locomotion system Power supply system Actuators Sensory devices for feedback Sensor Data processing unit Control system

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

LDR - Light Dependent Resistor Made of cadmium

sulphide Resistance between

two terminals vary depending on the intensity of light

Can be used to differentiate contrast colours

LED – Light Emitting Diodes Used generally with LDRs

to make a complete sensor module.

Act as a source of light for the LDRs.

The main specification of LED are its current rating=20mA, typical cut in voltage=2V,voltage is around 4.5V.

Thermistor Manufactured from the oxides of the

transition metals - manganese, cobalt, copper and nickel

Resistor depends on temperature Commonly available temperature

sensors are LM35,DS1621 thermistor.

IR Photo Diode Detects presence of Infra

Red radiations Used for obstacle proximity

sensing IR Data Communication Used in combination with IR

LEDs

Sensor Interfacing

Light Sensing Module using LED-LDR combination

Sensor Interfacing

Bump Detector Module

An Example - 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

Block Layout of Line FollowerOptical Sensor Array

Steering Controller

Left Motor Right Motor

Line Following AlgorithmStep1:Step1: All the sensors are assigned All the sensors are assigned some weight such assome weight such as

Sensor 1 = a1 = 3Sensor 1 = a1 = 3Sensor 2 = a2 = 2Sensor 2 = a2 = 2Sensor 3 = a3 = 1Sensor 3 = a3 = 1Sensor 4 = a4 = -1Sensor 4 = a4 = -1Sensor 5 = a5 = -2Sensor 5 = a5 = -2Sensor 6 = a6 = -3Sensor 6 = a6 = -3

Step2:Step2:Let b1 – b6 denote the state of each Let b1 – b6 denote the state of each

sensor. 0 for white line and 1 for black linesensor. 0 for white line and 1 for black lineStep3:Step3:

Line Position = Line Position = ΣΣaibiaibi

Step4:Step4:Vcm is fixed, Vcm is fixed,

predeterminedpredeterminedωωcm is cm is

proportional to Line proportional to Line positionposition

Step5:Step5:Vl = Vcm + (Vl = Vcm + (ωωcm / a)cm / a)Vr = Vcm – (Vr = Vcm – (ωωcm / a)cm / a)a : Separation between left/right a : Separation between left/right wheelswheels