Adaptive nonlinear controller design for differential-drive mobile platforms

Most differential drive platforms are equipped with two independent motors and casters. Possible misalignment between the platform direction and caster orientations and the unbalanced motor dynamics are some of the factors that make it difficult to properly drive the platforms. We present an adaptive nonlinear controller system that reduces the effect of disturbances on the platform motion. The controller system has two main parts: (1) a kinematic controller based upon Lya-punov´s stability theory and (2) a dynamic compensator based upon the reference model approach in order to allow robust trajectory tracking. Both controllers have been implemented and tested on two different types of powered wheelchairs. The results suggest that the proposed nonlinear controllers provide better trajectory tracking performance than well-known PID controllers.