The obstacle avoidance subsystem is designed based on the IR sensor readings. This function is vital in any autonomous robot for safety and functionality purpose. The conceptual design is to use two front IR sensors to detect any objects/wall in front and compare the readings to identify the nature to avoid respectively.

​

Our initial concept for obstacle avoidance was to use only the front sensors to identify the obstacle nature by comparing the sensor readings obtained from rotation; however there is a vital disadvantage in this method. The mounting distance between the front sensors has to be very accurate to eliminate the undesirable cases. Thus we have modified the sensor arrangement and the control algorithm to improve the accuracy of obstacle identification. 

​

The final obstacle avoidance functionality consists of a FSM (finite state machine) to determine the situation of the robot, and take reasonable action. First the robot will check if there is any obstacles within 7 cm of any of the front sensors. While no object is detected, the robot will continue moving forward; else if any object is found within the range, the robot enters “checking” state. In the “checking” state the robot determines the actions to take depending on the readings from the sensors. The actions are determined using a truth table.

​

There are two situations that the robot can encounter, such as the wall detection and object detection. When only one front sensor detect something, we consider it to be an object and the robot would strafe to avoid it, then resume the path once passed the object. A secondary truth table is used to determine which side to strafe to avoid the obstacle.

​

After the action is determined the desired motion and desired angle of the robot is set to perform the necessary manoeuvre to dodge the object. If there is an instance when both front sensors indicate something within the range, a wall is detected. If a wall is detected, the robot rotates the front ultrasonic sensor combined with the rear side sensor to check for any obstacles beside the robot. If there are no existing object beside the robot, it will perform strafing and turn 180 degrees for SLAM. 

​