10-01-2011, 04:13 PM
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Submitted by:-
Pankaj Kumar
Ashutosh Singh
Sameer Kumar
Gaurav kumar
Bhagwan thakur
INTRODUCTION:-
This simple robot is designed to be able to follow a black line on the ground without getting off the line too much. The robot has two sensors installed underneath the front part of the body, and two DC motors drive wheels moving forward. A circuit inside takes an input signal from two sensors and controls the speed of wheels’ rotation. The control is done in such a way that when a sensor senses a black line, the motor slows down or even stops. Then the difference of rotation speed makes it possible to make turns. For instance, in the figure on the right, if the sensor somehow senses a black line, the wheel on that side slows down and the robot will make a right turn.
THEORY OF OPERATION:-
How to sense a black line The sensors used for the project are Reflective Object Sensors, 0PB710F that are already ready in the Electronic Lab. The single sensor consists of an infrared emitting diode and a NPN Darlington phototransistor. When a light emitted from the diode is reflected off an object and back into the phototransistor, output current is produced, depending on the amount of infrared light, which triggers the base current of the phototransistor. In my case, the amount of light reflected off a black line is much less than that of a white background, so we can detect the black line somehow by measuring the current. (This current is converted to voltage.)
ii) How to control a DC motor
Instead of applying a constant voltage across a DC motor, we repeat switching on and off the motor with a fixed voltage (Vcc) applied to the motor. This is done by sending a train of PWM (Pulse Width Modulation) pulses to a power MOSFET in order to turn it on and off. Then, the motor sees the average voltage while it depends on duty cycle of PWM pulses. The speed of rotation is proportion to this average voltage.
By PWM method, it’s easier to control the DC motor than by directly controlling the voltage across it. All we have to do is to modulate pulse width, in ord
CONCLUSION:-
For a test, I held my robot in the air and I approached a white paper to sensors. Then, both wheels rotated as expected and they slowed down when either the paper moved away or sensors passed across a black line. Next, I put it down on the track, but unfortunately, it didn’t move. I found the torque of motors not enough to drive my robot. Even though the chosen DC motor was slowest and gave highest torque among other DC motors in the lab, it wasn’t enough. For solving this problem, I will have to find a suitable DC motor with large torque.
Overall, the robot project wasn’t successful, but it was quite a fun to go through all the process. I also realized that there were many things to consider practically such as installation of motors, building up a circuit by soldering and putting all parts together. This experience hopefully would be helpful in the future work
