LINE FOLLOWING ROBOT
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ABSTRACT
The line following robot, operates as the name specifies. It is programmed to
follow a dark line on a white background and detect turns or deviations and modify the
motors appropriately. The optical sensor is an array of commercially available IR
reflective type sensors.
The core of the robot is the PIC 16F873 microcontroller. The speed control of the
motors is achieved by the two PWM modules in the μC. The direction control is provided
by 2 I/O pins. The H-Bridge motor driving/control chip takes these signals and translates
it into current direction entering the motor armature. The motors require separate supply
for operation.
The differential steering system is used to turn the robot. In this system, each back
wheel has a dedicated motor while the front wheels are free to rotate. To move in a
straight line, both the motors are given the same voltage (same polarity). To manage a
turn of different sharpness, the motor on the side of the turn required is given lesser
voltage. To take a sharp turn, its polarity is reversed.
The sensor is an array of 7 IR LED-Phototransistor pairs arranged in the form of
an inverted V. The output of each sensor is fed into an analog comparator with the
threshold voltage (used to calibrate the intensity level difference of the line with respect
to the surface). These 7 signals (from each photo-reflective sensor) is given to a priority
encoder, the output of which to the microcontroller.
The control has 6 modes of operation, turn left/right, move left/right, and drift
left/right. The actual action is caused by controlling the direction/speed of the two motors
(the two back wheels), thus causing a turn. The actual implementation is a behavior based
(neural) control with the sensors providing the inputs. The robot can also be programmed
to find the line by pseudo-random movement in case no line is detected by the optical
sensor.
INTRODUCTION
The robots of the movies, such as C-3PO and the Terminator are portrayed as
fantastic, intelligent, even dangerous forms of artificial life. However, robots of today are
not exactly the walking, talking intelligent machines of movies, stories and our dreams.
In the 1970’s scientists proposed that in the year 2000 we would have created
artificial life forms, almost perfect in terms of intelligence and capabilities. The dream of
free and efficient labor made the researchers of the time go on day and night to bring the
dream to existence. But the task was futile due to the lack of compact processors to carry
out the calculations which were oh so necessary. Now in the year 2000, the microprocessor
technology is thousands of times more advanced than what existed back then.
But still the robots of today are no way close to what our movies portray them to be. This
is not only due to drawbacks in processor technology, but also in various other fields such
as vision, motor control so and so forth.
Robots may never make it to our kitchens or living rooms as personal slaves, but
they certainly have made their way to the manufacturing industry, aero-space industry,
and yes to the work benches of robotic hobbyists. Robots are now working in dangerous
places, such as nuclear disposal, space explorers, fire fighting, etc.
The word "robot" originates from the Czech word for forced labor or serf. Robots
are electronic devices intended to perform a desired function. Many refer to them as
"machines", however, a drill press is a machine, yet it requires an operator to perform its
function, where robots can be programmed to do it themselves. Robots have the potential
to change our economy, our health, our standard of living, our knowledge and the world
in which we live. As the technology progresses, we are finding new ways to use robots.
Each new use brings new hope and possibilities, but also potential dangers and risks.
Robotics is not only a science, but it is also an art. The bots we build reflect the ideas and
personalities we portray.
PROBLEM DEFINITION
In the industry carriers are required to carry products from one manufacturing
plant to another which are usually in different buildings or separate blocks.
Conventionally, carts or trucks were used with human drivers. Unreliability and
inefficiency in this part of the assembly line formed the weakest link. The project is to
automate this sector, using carts to follow a line instead of laying railway tracks which are
both costly and an inconvenience.
SCOPE OF STUDY
The robot can be further enhanced to let the user decide whether it is a dark line
on a white background or a white line on a dark background. The robot can also be
programmed to decide what kind of line it is, instead of a user interface. The motor
control could be modified to steer a convectional vehicle, and not require a differential
steering system. The robot could be modified to be a four wheel drive. Extra sensors
could be attached to allow the robot to detect obstacles, and if possible bypass it and get
back to the line. In other words, it must be capable predicting the line beyond the
obstacle. Speed control could also be incorporated. Position and distance sensing devices
could also be built in which can transmit information to a mother station, which would be
useful in tracking a lost carrier.
REVIEW OF LITERATURE
First and foremost, no robot could have been built to completion without a strong
hold on the microcontroller used. Most of the basic, intermediate, and advanced literature
about the PIC microcontroller was found in the book “Programming and Customizing the
PIC Microcontroller” by Myke Predko. His detailed explanation of every topic made it
possible to overcome many problems which were encountered during design and
implementation. The book also provided a programmer for the PIC microcontroller which
was an indispensable tool helping me experiment with algorithms rather than blindly copy
code from the NET.
METHODOLOGY
The first idea was to use optical imaging (CCD cameras) to see the line. This was
later given up due to various reasons including complexity and unavailability of
components. Later a choice was made to use an array of sensors which solved most of
the problems pertaining to complexity.
The resistor values used in the sensor array were experimentally determined rather
than theoretical mathematical design calculations. This was done as the data sheets of
the proximity sensor was not available anywhere and most of the parameters had to be
determined experimentally.
The L293D chip is used as it was a much better option than forming an H-Bridge
out of discrete transistors, which would make the design unstable and prone to risk of
damage.
The PIC microcontroller was used as it is the only device I have a full practical
knowledge about, and most of all a RISC processor which are better suited for realtime
operations. Thus the midrange devices were chosen. The part 16F873 was used
as it has 2 CCP modules which I could use in PWM mode thus simplifying the
software routines which I’d otherwise had to write to generate the PWM control for
the motors.
THE DIFFERENTIAL STEERING SYSTEM
The differential steering system is familiar from ordinary life because it is the
arrangement used in a wheelchair. Two wheels mounted on a single axis are
independently powered and controlled, thus providing both drive and steering. Additional
passive wheels (usually casters) are provided for support. Most of us have an intuitive
grasp of the basic behavior of a differential steering system. If both drive wheels turn in
tandem, the robot moves in a straight line. If one wheel turns faster than the other, the
robot follows a curved path. If the wheels turn at equal speed, but in opposite directions,
the robot pivots.