Small Robot : 

7 Path Follower



A Path Follower is self controlled Robot, which follows in a path, which is a wide white or black line. The width of the path is generally more than the width of the Robot. Like Line Follower, here also, many types of sensors may be used to read the path. The Small Robot uses IR (Infra-Red) sensors, to read the path. Four pairs of IR LEDs and IR sensors (shaped as LED) are used here to read the Path. All the four IR sensing pairs are arranged in a row, perpendicular to the path, two on each side of the Small Robot. The Small Robot always try to position within the path, by following the edge of the path.

To read four input pins for IR sensors, ATTNY84 micro-controller is selected, which have 14 pins. Out of 14 pins, four pins are used for sensing the line and four pins are required to control the two motors, through the motor driver (L293D).

(refer Small Robot Base Frame for motor control codes).

In general, Path Followers are used in industries for material handling. The robot moves within the two lines earmarked for its movement. The programming is to move the Robot within two thick lines, which forms as a path, which may have sharp and smooth curves.

The Small Robot is programmed here to follow various path shapes, like sharp bends, sharp turns, sharp curves etc. The coding may be modified for individuals requirement.

A model path used to test the Small Robot is shown below, having various line shapes.


About Path Sensing:

The Path Follower uses IR (Infra-red) sensing system to read the presence of Path. An IR LED emits IR light on the bottom surface. The IR light reflects from the surface and falls on an IR sensor (in LED shape), placed near to the IR LED. The IR sensor is connected in reverse biased, which varies its internal resistance, depending on the brightness of reflected IR light. The internal resistance of the IR sensor decreases with increase in falling IR light.

So, when the surface below the IR sensor is white, more reflected light falls on the IR sensor, which makes least internal resistance. Similarly, if the surface is black, least light reflects on the IR sensor, which makes highest internal resistance. Due to change in the resistance of IR sensor, the voltage at the junction of the IR sensor and fixed resistance varies, which are connected in series with power supply and ground. A typical IR LED + IR sensor pair arrangement with the circuit diagram is shown below.

Total four such IR sensing pairs are required for Path Following Small Robot, and soldered on a PCB, then fixed in front of the Small Robot. All the IR LEDs and IR sensors are 3 mm size. Maintain the gap between. the two successive IR sensors at each extreme end should be just less than the line width of the path. The distance between the mid of the two extreme IR sensors shall be approximately equal to the width of the path. So, that, the Path Follower tries to keep the itself within the path.

The IR sensor PCB, with 4 IR pairs, shall be fitted in front of the Small Robot, as shown below, with a clearance adjustment arrangement (from surface) , to adjust the sensitivity with black and white surfaces.


Working of Path Follower:

Making of Small Robot as Path Follower is simple and easy. One PCB is required for IR sensing board, with 4 pairs of IR LEDs and IR sensors explained above. Another PCB with micro-controller ATTINY84 is used as control system for the Path Follower based on the varying voltages obtained from four IR sensors.

The varying voltages from the IR sensor board are read as four digital inputs by the micro-controller. Then, the programmed logic makes the Small Robot to follow middle two IR sensor. In case, the Small Robot reads that, any IR sensor is out of path, the required output code is sent through the four motor control pins, to turn the Small Robot accordingly, else Small Robot moves in straight path. Similarly, in case of sharp turns, smooth turns, the Small Robot turns accordingly.

The complete circuit diagram of Control Board with ATTINY84, is available below. Use jumper wires to connect S1, S2, S3 & S4 pins from Sensor Board to Control board consecutively.

The shorting jumper, J1 is provided to select the path colour as BLACK or WHITE. Either Red or Yellow LED glows by selecting the shorting jumper position, for White or Black path.

A button switch, SW1 on control board, is useful to start the Path Follower, after switching ON the power supply to the Control Board.


Download file from above link and remove .TXT extension.

Once Small Robot's Base Frame is made, then, various control systems for Small Robot are developed and available for selection, using 'Previous' and 'Next' buttons here.