IMPORTANT
INTRODUCTION TO LINE FOLLING ROBOT PROJECT:
A line follower robot is basically a robot designed to follow a ‘line’ or path already predetermined by the user. This line or path may be as simple as a physical black line on the floor or as complex path marking schemes e.g. embedded lines, magnetic markers and laser guide markers. In order to detect these specific markers or ‘lines’, various sensing schemes can be employed. These schemes may vary from simple low cost line sensing circuit to expansive vision systems. The choice of these schemes would be dependent upon the sensing accuracy and flexibility required. From the industrial point of view, line following robot has been implemented in semi to fully autonomous plants. In this environment, these robots functions as materials carrier to deliver products from one manufacturing point to another where rail, conveyor and gantry solutions are not possible. Apart from line following capabilities, these robots should also have the capability to navigate junctions and decide on which junction to turn and which junction ignore. This would require the robot to have 90 degree turn and also junction counting capabilities. To add on to the complexity of the problem, sensor positioning also plays a role in optimizing the robots performance for the tasks mentioned earlier.
Line-following robots with pick- and- placement capabilities are commonly used in manufacturing plants. These move on a specified path to pick the components from specified locations and place them on desired locations. Basically, a line-following robot is a self-operating robot that detects and follows a line drawn on the floor. The path to be taken is indicated by a black line on a white surface. The control system used must sense the line and man oeuvre the robot to stay on course while constantly correcting the wrong moves using feedback mechanism, thus forming a simple yet effective closed- loop system.
MOSFET:
It is a special type of field-effect transistor (FET). Unlike BJT which is 'current controlled', the MOSFET is a voltage controlled device. ... When Gate-Source potential difference is applied, the Drain-Source resistance is reduced, and there will be current flowing through Drain-Source, which is now a closed circuit.
IR Sensor:
An infra-red detector is a photo detector. It detects IR energy emitted by the emitter and converts it into electrical energy.
The main principle involved in the conversion of light energy to electrical energy is PHOTOELECTRIC EFFECT.
IR LED
IR LED emits light, in the range of Infrared frequency. IR light is invisible to us as its wavelength (700nm – 1mm) is much higher than the visible light range. Everything which produce heat, emits infrared like for example our human body. Infrared have the same properties as visible light, like it can be focused, reflected and polarised like visible light.
PhotoDiode
Photodiode is considered as Light dependent Resistor (LDR), means it has very High resistance in absence of light and become low when light falls on it. Photodiode is a semiconductor which has a P-N junction, operated in Reverse Bias, means it start conducting the current in reverse direction when Light falls on it, and the amount of current flow is proportional to the amount of Light. This property makes it useful for IR detection.
H-BRIDGE:
An H-bridge is an electronic circuit which enables DC electric motors to be run forwards or backwards. These circuits are often used in robotics. H-bridges are available as integrated circuits, or can be built from discrete components.The two basic states of a H-bridge. The term "H-bridge" is derived from the typical graphical representation of such a circuit. An H-bridge is built with four switches (solid-state or mechanical). When the switches S1 and S4 (according to the first figure) are closed (and S2 and S3 are open) a positive voltage will be applied across the motor. Opening S1 and S4 switches and closing S2 and S3 switches reverse this voltage reversed, allowing reverse operation of the motor. Using the nomenclature above, the switches S1 and S2 should never be closed at the same time, as this would cause a short circuit on the input voltage source. The same applies to the switches S3 and S4. This condition is known as shoot-through
Operation
The H-Bridge arrangement is generally used to reverse the polarity of the motor, but can also be used to 'brake' the motor, where the motor comes to a sudden stop, as the motors terminals are shorted, or to let the motor 'free run' to a stop, as the motor is effectively disconnected from the circuit. The following table summarizes operation.
H-Bridge Driver:
The switching property of this H-Bridge can be replaced by a Transistor or a Relay or a Mosfet or even by an IC. Here we are replacing this with an IC named L293D as the driver whose description is as given below. The Device is a monolithic integrated high voltage, high current four channel driver designed to accept standard DTL or TTL logic levels and drive inductive loads as and switching power transistors. To simplify use as two bridges each pair of channels is equipped with an enable input. A separate supply input is provided for the logic, allowing operation at a lower voltage and internal clamp diodes are included. This device is suitable for use in switching applications at frequencies up to 5 kHz. The L293D is assembled in a 16 lead plastic package which has 4 center pins connected together and used for heat sinking The L293D is assembled in a 20 lead surface mount which has 8 center pins connected together and used for heat sinking.
Straight direction:
We can expect our robot to move in straight direction when the middle sensors response is low and the remaining two sensors response is high. i.e., according to our arrangement the middle sensor will always be on the line and as the line is white in color it will not reflect the emitted radiation back and the response of the sensor will be low and the response of the remaining two sensors will be high as they will be on the bright surface.
Right curve:
When a right curve is found on the line the responses will change i.e. the response of the first sensor which is to the right will become low as that sensor will be facing the black line and the reaming sensors response will be high. We this data is achieved the control of the wheels is changed i.e. the right wheel is held and the left wheel is made to move freely until the response from the middle sensor becomes low. Then the same process repeats again.
Left curve:
When a left curve is found on the line the response of the left most sensor will be changed from high to low as the sensor will now face the black or the dark surface. Then the control of the wheel changes i.e. by holding the left wheel and allowing the right wheel to move freely until the middle sensor changes it is response from high to low.The same process continues for all the turns and the robot moves continuously until the supply is remove
ADVANTAGES
Robot movement is automatic.
Fit and Forget system.
Used for long distance applications.
Defense applications.
Used in home, industrial automation.
Cost effective.
Simplicity of building
DISADVANTAGES
LFR follows a black line about 1 or 2 inches in width on a white surface.
LFR are simple robots with an additional sensors placed on them.
Needs a path to run either white or black since the IR rays should reflect from the particular path.
Slow speed and instability on different line thickness or hard angles.
CONCLUSION:
In this project we have studied and implemented a Line Following Robot by using
MOSFET for blind people. The programming and interfacing of microcontroller has been mastered during the implementation.
FUTURE SCOPE:
Smarter versions of line followers are used to deliver mails within office building and deliver medications in a hospital.
This technology has been suggested for running buses and other mass transit systems and may end up as a part of autonomous cars navigating the freeway
REFERENCES
[1].www.avrfreaks.com, Microntrollers, Atmel,10-
[2]. septiembre-2001. [11] www.atmel.com
[3]. The 8051 Microcontroller and Embedded Systems Using Assembly and C By Muhammad Ali Mazidi, Janice Gillispie Mazidi & Ro lin D. McKinlay
[5]. Atmel Corp. Makers of the AVR microcontroller
www.atmel.com
[6]. www.electronic projects.com
[7]. www.howstuffworks.com
[8]. Electrikindia.
[9]. EMBEDDED SYSTEM BY RAJ KAMAL
