Design of a NonLinear Observer for a Laboratory Antilock Braking System

In this paper a nonlinear observer is presented in order to estimate the angular velocity of both upper and lower wheels of a PC controlled ABS Laboratory setup, from Inteco Ltd. The system simulates the dynamics of a quarter car model. In order to accomplish this, it includes two attached wheels. The angular velocity of the upper wheel simulates the angular velocity of a vehicle's wheel, while the lower wheel simulates the road surface. In the observer design, it is assumed that the angular velocity of the vehicle's wheel is known, since a sensor is installed on the system, as in a real vehicle, so that the longitudinal velocity can be determined with this information. The proposed nonlinear observer considers the Pacejka's "magic formula" to calculate the contact force. This formula allows the observer to estimate the states in both the linear and nonlinear regions. The stability of the observer is proved and validated with simulations, and experimentally with the Antilock Braking System Laboratory setup.