Adaptive motor control to aid mobile robot trajectory execution in the presence of changing system parameters

Abstract

Most of the mobile robot path planning algorithms presented to date, generate intermediate goal coordinates for a mobile robot to pursue, based upon the local environment and the position of the global target. In response to this, we present a general controller for any vehicle which is driven by changing target vectors and show that the restricted speed (or torque) capabilities of the vehicle can be modeled with a nonlinear saturation element. Although the goal attraction path parameters can be optimized so that a vehicle tracks its target in a near time optimal sense, the effect of motor parameter changes or disturbances to the controlled system upon the path of the robot is noted. When the process gain of the robot's motors change, due to temperature changes, run-in time etc., we show that the trajectory of the mobile robot is momentarily affected, before the closed loop control system again places the robot back on to its correct course. A novel method is presented, which manipulates the effective nonlinear speed saturation element, which models the actual speed or torque limitations of any vehicle, in order to remove this problem. Simple modifications can be applied to the derived control system, so that mobile robot adaptive target tracking can take place. The conditions necessary, which can be exploited to allow the response of a mobile robot to be insensitive to changes in motoring parameters are presented, and the method is demonstrated by purposely inducing process gain changes on a real mobile robot.