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LINE FOLLOWERROBOTBY:-YASH PATELComputer engineer
INTRODUCTION A line follower, as its name suggests is a robot
that is capable of following a predefined line using sensory
devices. A line follower should have the following essential parts
to it:Locomotion system.Sensor Circuit.Processing unit.
LOCOMOTION SYSTEM Robot locomotionis the collective name for the
various methods thatrobots use to transport themselves from place
to place. A major goal in this field is in developing capabilities
for robots to autonomously decide how, when, and where to move.
Autonomous robot locomotion is a major technological obstacle for
many areas of robotics, such as humanoids.
SENSORY SYSTEMThe most common features for following line for a
robot is reflectance of a surface.Different intensities of
reflection of light from surface makes the robot to follow a line.
Example(white surface reflect light and black will absorb light).To
read that difference we use sensor circuit consists of LEDs(light
emitting diodes) and LDRs(light dependant resistors).An LDR is a
small resistor, the resistance of which depends upon the intensity
of light incident on it. More the intensity of light falling on it,
lesser is its resistance. The resistance usually varies in the
range of about 10k ohms.
WHAT NEXT??We know that what main things will be required but
now how it works?When led throws the light it is reflected detected
by the LDRs on the detection of light it gives output as 1.When no
light is reflected then LDR will return 0 as output.
SYSTEM WHICH IT FOLLOWS
CONT..If robot is following white line on black background.
Left sensorRight sensorLeft motorRight motor111110010110
HOW ITS WORK
MATERIAL REQUIREDArduino board.IR sensors.Jumper wires.4
motors.
IR SensorCircuit for IR Sensors
BEFORE CODINGWHAT IS PID?PID is an acronym for Proportional
Integral Derivative., these terms describe three basic mathematical
functions applied to the errorMain task of the PID controller is to
minimize the error of whatever we are controlling. It takes in
input, calculates the deviation from the intended behaviour and
accordingly adjusts the output so that deviation from the intended
behaviour is minimized and greater accuracy obtained.
WHY TO IMPLEMENTThe idea behind PID control is that we set a
value that we want maintained, either speed of a motor or reading
from a sensor. We then take the present readings as input and
compare them to the setpoint. From this an error value can be
calculated, i.e, (error = setpoint - actual reading). This error
value is then used to calculate how much to alter the output by to
make the actual reading closer to the setpoint.
CONT..If 3 sensors are used then,If the centre sensor detects
the line the robot steers forwardIf the left sensor detects the
line the robot steers right If the right sensor detects the line
the robot steers left.
HOW TO IMPLEMENT IT?TERMINOLOGYThe basic terminology that one
would require to understand PID are:Error - The error is the amount
at which a device isnt doing something right.Proportional (P) - The
proportional term is directly proportional to the error at
present.Integral (I) - The integral term depends on the cumulative
error made over a period of time (t).Derivative (D) - The
derivative term depends rate of change of error.Constant (factor)-
Each term (P, I, D) will need to be tweaked in the code. Hence,they
are included in the code by multiplying with respective
constants.P-Factor (Kp) - A constant value used to increase or
decrease the impact of ProportionalI-Factor (Ki) - A constant value
used to increase or decrease the impact of IntegralD-Factor (Kd) -
A constant value used to increase or decrease the impact of
Derivative
CONT..Position = (Weighted average of reading of sensor)/(sum of
reading of sensors)Error = position set_pointPosition is calculated
for every position of robot on line. Set_point is a fixed point at
which robot is straight on a line.Error is generated by the
difference of two.
PROPOTIONAL ERRORWe would need to simply add the error value to
the output to adjust the robots motion. And this would work, and is
known as proportional control (the P in PID). It is often necessary
to scale the error value before adding it to the output by using
the constant(Kp).Difference = (Target Position) - (Measured
Position)Proportional = Kp*(Difference)But on increasing constant
Kp it will only make robot to follow a line but for large error
robot will start wobbling, to stop that we have to adjust
differential coefficient.
DERIVATIVEIt provides the rate of change of error.It makes us
know how error changes time to time, so that output can be set.Rate
of Change = ((Difference) (Previous Difference))/time
intervalDerivative= Kd *(Rate of Change)
INTEGRALThe integral improves steady state performance, i.e.
when the output is steady how far away is it from the setpoint.It
improves the accuracy of robot to follow the line.Integral =
Integral + Difference//(propotional)Integral = Ki*(Integral)
TermExpressionEffectProportionalKp x errorIt reduces a large
part of the error based on present time error.Integralerror
dtReduces the final error in a system. Cumulative of a small error
over time would help us further reduce the error.DerivativeKd x
derror / dtCounteracts the Kp and Ki terms when the output changes
quickly.
CODE FOR POSITION AND ERROR
CODE FOR MOTOR CONTROL
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