Circular Path Tracking Control Scheme of the Self-Driving Robot Driven by Two BLDC Motors

This paper presents a real-time circular path-tracking error compensation and positioning control scheme of the self-driving indoor robot driven by two in-wheel type BLDC(Brushless DC) motors without any absolute space position sensors such as GPS. Because of the absolute position sensorless applications, the moving distance and path of the self-driving robot has to be estimated by the motion of an in-wheel BLDC motor. The accurate motion control and the path tracking control of the BLDC motor can reduce the absolute positioning and path tracking error of the robot. If the accurate BLDC motion control is implemented, the non-linear slip between the wheel and path surface, the actual moving trajectory is not the same as the reference trajectory. Furthermore, this error cannot be compensated by the external absolute position sensors at the indoor application. In this paper, the moving position and the trajectory of the self-driving robot are controlled by the hall-position sensor at each in-wheel BLDC motor. The moving distance error and path tracking error are compensated by the heading angle estimation of IMU(Inertial Measurement Unit) sensor. In the proposed method, the actual moving path and trajectory can be estimated by the calculated speed and path by the hall-position sensor of BLDC motor, and compensated by the heading angle error between the estimated heading angle and the reference heading angle of the tracking path. The tracking path error is real-time compensated by the modified reference path using the calculated two wheel moving distance and speed. In the compared experiments, the proposed circular path tracking scheme shows the advanced and improved tracking performance than the conventional control scheme.