The line follower is one of the self operating robot that follows a line that drawn on the floor. The basic operations of the line following are as follows:
Capture line position with optical sensors mounted at front end of the robot. Most are using several number of photo-reflectors, and some leading contestants are using an image sensor for image processing. The linesensing procss requires high resolution and high robustness.
Steear robot to track the line with any steearing mechanism. This is just a servo operation, any phase compensation will be required to stabilize tracking motion by applying digital PID filter or any other servo argolithm.
Control speed according to the lane condition. Running speed is limited during passing a curve due to friction of thetire and the floor.
There are two line styles, white line on the black floor and black line on the white floor. Most contest are adopting the first one in line width of between 15 and 25 millimeters.
Right image shows bottom view and side view of the built line following robot. All mechanical and electrical parts are mounted on a proto board, and it also constitutes thechasis.
The line following robot is upheld in three points of two driving wheels and a free wheel. The driving wheels are made with a 7 mm dia ball bearing and a rubber tire. The free wheel is a 5 mm dia ball bearing attached loosely. To drive driving wheels, two tiny vibration motors that used for cellular phone, pager or any mobile equipment are used. Its shaft is pressed onto the tire with a springplate, the output torque is transferred to the wheels.
The steearing mechanism is realized in differential drive that steear the robot by difference in rotation speed between the left wheel and the right wheel. It does not require any additional actuator, only controling the wheel speed will do.
Controller- ATmega8 (Atmel)
Line sensor Six photo-reflectors
Power supply Two CR2032lithium cells(One is for controller, the other is for motors)
Motor Two micromotors for left wheel and right wheel
Dimensions 45(L), 33(W), 12.5(H) [mm]
Weight 15 grams (Body:8g, Cells:7g)
Performance 53 centimeter per second at oval course
An Atmel ATmega8 is used for the controller and it is powered by a lithium coin cell. The other lithium coin cell is for only motors.Separating the power supply into two cells is to avoid accidental reset of the microcontroller due to voltage dip by motor start current. Six photo-reflectors are mounted at front end of the chasis. They sense reflection rate of the floor under them. Motors are driven in PWM to control rotation speed lineary.
To detect a line to be followed, most contestants are using two or more numberof poto-reflectors. Its output current that proportional to reflection rate of the floor is converted to voltage with a resister and tested it if the line is detected or not. However the threshold voltage cannot be fixed to any level because optical current by ambent light is added to the output current like the image shown right.
Most photo-detecting modules for industrial use are usingmodurated light to avoid interference by the ambient light. The detected signal is filtered with a band pass filter and disused signals are filtered out. Therefore only the modurated signal from the light emitter can be detected. Of course the detector must not be saturated by ambient light, this is effective when the detector is working in linear region.
In this project, pulsed light is used to cancelambient light. This is suitable for arraied sensors that scanned in sequence to avoid interference from next sensor. The microcontroller starts to scan the sensor status, sample an output voltage, turn on LED and sample again the output voltage. The difference between the two samples is the optical current by LED, output voltage by the ambient light is canceled. The other sensors are also...