Improved Nonlinear Disturbance Observer-Based Command-Filtered Backstepping Control of Clamping Force for Electro-Mechanical Brakes

The electro-mechanical brake (EMB), as a Brake-by-Wire (BBW) system that generates clamping force through a torque motor and mechanical mechanism, features compact structure, fast response, and high control accuracy. This article designs an improved nonlinear disturbance observer-based command-filtered backstepping controller (INDOB-CFBSC) for EMB system, which tracks the clamping force using a clamping force estimator and effectively addresses the nonlinearity and uncertainty of the EMB system. Firstly, an EMB model including the torque motor, gearbox, flexibility-considered ball screw model, pressure-displacement relationship-considered clamping force model and friction is built. Particularly, a clamping force estimation method based on the extended least squares (ELS) is proposed, which transforms the clamping force tracking control into torque motor angular position tracking control. Then, a robust clamping force control strategy, INDOB-CDBSC, is proposed based on the command-filtered backstepping controller (CFBSC) and the improved nonlinear disturbance observer (INDOB). Finally, the test results under different operating conditions demonstrate that the INDOB-CDBSC strategy exhibits excellent tracking performance and robustness in the presence of nonlinearity and uncertainty in the EMB system.