Anti-windup compensator for improved tracking performance of differential drive mobile robot

Differential drive mobile robot (DDR) is one type of wheeled mobile robots with a specific wheel configuration where two fixed wheels are controlled by the motors and a castor wheel is added to mechanically support its movements. For tracking purposes, the controller and the motors play a very important role to ensure it does not deviate far from targeted locations or path. As most motors exhibit nonlinear behavior, modeling them is not straightforward. The performance of the DDR is also affected by the physical limitations of the motors. In this work, the motors are modeled as a multivariable Hammerstein structure with noninvertible static nonlinearities in series with a linear time invariant system. This work also focuses on both dynamic and kinematic models of the DDR where a proportional-integral (PI) controller is designed to achieve the desired specifications in the linear region. In order to account for the nonlinear effects from the motors which are mainly influenced by their bounded velocity capability, a static anti- windup compensator (AWC) is implemented which is activated when the controller output exceeds the bound. Via this strategy, a significant improvement on the tracking performance of the DDR can be observed via simulations especially when the desired path involves curvatures.