Sliding-mode control combined with improved adaptive feedforward for wafer scanner

•The general form of an improved adaptive feedforward is proposed for nth-order systems with force ripple.•The dominant frequency components of the force ripple are obtained by experimental analysis based on FFT.•A sliding-mode control method combined with the improved adaptive feedforward is established for precision control of wafer scanner.•The feasibility and effectiveness of the proposed methods are demonstrated by comparative experiments in real application.