Non-time based tracking controller for mobile robots

This paper presents a novel design method for a non-time based mobile robot controller so that it can track an arbitrary second differentiable path. The key to the non-time based control method is the introduction of a suitable motion reference other than time, which is directly related to the desired and measurable system output. It enables the construction of control systems with integrated planning capability, in which planning becomes a real-time closed-loop process. This new design method converts a controller designed with traditional time-based approaches to a non-time based controller using a state to reference (STR) projection. This significantly simplifies the design procedure for a non-time based controller. While designing a time-based controller, the curvature is introduced as a parameter to describe the forward velocity of a mobile robot. As a result, for any given differentiable curve, the same time-based controller can be projected to different non-time based controllers based on the selection of non-time based motion reference. The design procedure is therefore simplified significantly. The method is exemplified by a nonholonomic mobile robot tracking control problem. The controller has been implemented and tested for different curves such as sine waves, circles and ellipses. Experimental results demonstrate advantages of the proposed method.