Line Following Robot with obstacle avoidance (Lejos NXT)

The robot has to traverse an arena to reach a destination area. The destination lies towards the southern region of the arena. There is a path in the arena which leads to the destination. The path is black in colour over a white surface. This path ends in a red coloured region which is the destination. The trajectory of this path is variable (such as straight, zig-zag, circular etc.). There are obstacles of different shapes and sizes along the path. While traversing, the robot has to avoid any collision with those obstacles and keep following the path. If a yellow coloured strip is found on the path by the robot that would mean there is a junction point ahead wherein two or more paths diverge. The robot has to decide which way to go to reach the destination.

Algorithms

We use three different algorithm to implement our program that we are going to discus one by one but here it is the overall algorithm containing all the algorithm in one.

until destination reached

      drive to ward destination

          if robot found obstacle

              until robot found target path

                   follow obstacle contour

             end

         end if

         if robot found junction

              until robot found target position

                    follow junction contour

              end

         end if

end

Line Following algorithm

In this algorithm we use two light sensors and as a result our robot encounters four conditions

    1.   If the side sensor sees white and the center sensor sees white, the robot is 
           right outside the path, so it should turn right.

2. If the side sensor sees white and the center sensor sees black, the robot is right over the path, so it should run forward.
3. If the side sensor sees black and the center sensor sees white, the robot is outside to the right part of the path , so it should turn to left.
4. If the side sensor sees black and the center sensor sees white, the robot is outside to the right part of the path , so it should turn to left.

Obstacle detection

if Obstacle found then

    check left and right path for no obstacle

    if no obstacle to the left side of the path

          turn the robot left

          until robot found target path

                move outside the path in curve and

                turn away from the obstacle

          end

   else if no obstacle to the right side of the path

          turn the robot right

          until robot found target path

                move outside the path in curve and

                turn away from the obstacle

         end

   else

         report no path

   end if

end if

Junction Algorithm

If the yellow strip found

       move forward until the robot completely crossed the yellow strip

       rotate 180 degree and move forward until finding the yellow strip and store the compass value

       rotate until the compass reading become 180.

       rotate to left side until getting a black strip other than the incoming path and store the compass -               reading

       rotate back to 180 degree

       find the right side path similarly and store the compass reading

       Take the nearest path (left or right) by comparing the stored compass readings.

In the junction the robot will rotate back to the incoming path. And reads the compass value. Then it rotates until the compass value become 180. Then it will slowly rotates left side until either a black strip is found or reaches to 0 degree. If any path, other than incoming path, found it will stores that compass value. Similarly it will calculate the path on right side also. Then robot takes the path which is near to the 180 degree, i.e south.

System requirement

Hardware :

core components we had used to build the robot are:

1. Color sensor: The Color Sensor enables our robot to distinguish not only between black and white, and also a range of bright and pastel colors.
2. Ultrasonic sensor: The Ultrasonic Sensor is able to detect an object and measure its proximity in inches or centimeters.
3. Compass sensor :the Compass Sensor is able to measure the earth's magnetic field and calculates a magnetic heading to tell which direction our robot is facing
4. Servo motor: We use two servo motor to move the robot and one servo motor to rotate the ultrasonic sensor within 0-180 degree to detect obstacle.
5. Lego brick: The NXT Intelligent Brick, it is the robot’s “brain,” features a powerful 32-bit microprocessor and Flash memory, plus support for Bluetooth and USB 2.0

software :

Java SE Development kit 32 bit

NXT USB Driver 32bit

leJOS NXJ 0.8.5beta win32

eclipse java indigo SR1 win32