A Tutorial on Robotics Part III

7/29/2019 A Tutorial on Robotics Part III

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Copyright Robotix Team, IIT Kharagpur

February 3rd-5th, 2006


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A Tutorial on Robotics

Part III : Control System & Sensors


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Basic Parts Of Our Mobile Robot

Locomotion system

Power supply system

Actuators Sensory devices for feedback

Sensor data processing unit

Control system


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Open Loop Control System

There is no error correction. No way tocheck if the actuator was able to take the

desired action Simple system to design, not very reliable

Requires regular calibration of thesystem

Controller Actuator

O/P

Desired Action

Controller Actuator


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Closed Loop Control System

Desired Action Controller Actuator

O/P

Feedback


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Example : An Air conditioner

Desired Temp. ControllerCooling

Device

Room

Temp

Temperature

Sensor


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Proportional Control

Correction is made depending onthe magnitude of error

If desired output > actual output

new input > previous input Else

new input < previous input

New Input = Previous Input + K (Desired Output- Actual Output)


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Sensors

Analogous to human sensory organs

Eyes, ears, nose, tongue, skin

Sensors help the robot knowing itssurroundings better

Improves its actions and decisionmaking ability

Provides feedback control


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LDR - Light Dependent Resistor

Made of cadmium sulphide

Resistance between two terminals

vary depending on the intensity oflight

Can be used to differentiatecontrast colours


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Thermistor

Manufactured from the oxides of thetransition metals - manganese,cobalt, copper and nickel

Resistor depends on temperature


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IR Photo Diode

Detects presence of Infra Redradiations

Used for obstacle proximity sensing IR Data Communication


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Sensor InterfacingVCC

R4

2K2

R2

1k

R4

2K2

Temperature Detector

0

Digital O/P

Light Intensity Detector

Thermistor

R3

R5

10K

R6

5K

Digital O/P

VCC

LDR

D3

IR LED

R2

1k

0

0

U3A

LM339

5

4

3

12

2

+

-

V+

V-

OUT

R2

100R

R6

5K

Digital O/P

8 - Bit ADC

R5

100K

Digital O/P

VCC

U3A

LM339

5

4

3

12

2

+

-

V+

V-

OUT

0

Bump Detector

8 - Bit ADC

VCC

R3

IR Proximity Detector

D4

Photo Diode


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Shaft Encoder

Shaft Encoders are used to measure therotation of motor shaft

The holes / sectors are counted


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Shaft Encoder Cont

Pulses from thephoto diode arecounted

QuadratureEncoders areused to

determinedirection ofrotation as well


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An Example - Line Follower

A line follower is arobot capable oftracking a line

drawn on a surface Optical sensors

capture the lineposition at the front

end of the robot The robot is steered

to keep it alwaysover the line


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Block Layout of Line Follower

OpticalSensorArray

SteeringController

Left Motor Right Motor


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Controller Layout Diagram


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Optical Reflectors


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Line Following Algorithm

Step1:All the sensors are assignedsome weight such as

Sensor 1 = a1 = 3Sensor 2 = a2 = 2

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

Step2:

Let b1

b6 denote thestate of each sensor. 0for white line and 1 forblack line

Step3:Line Position = aibi

Step4:Vcm is fixed, predetermined

cm is proportional to Lineposition

Step5:Vl = Vcm + (cm / a)Vr = Vcm (cm/ a)a : Separation betweenleft/right wheels


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Thank You

In Part IV : Microcontrollers we willtake up the AVR family ofmicrocontrollers, and discuss someof its features

Serial (RS-232) and Parallel Portcomputer communication will also

be discussed

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A Tutorial on Robotics Part III

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