Research and industrial applications of active disturbance rejection control to fast tool servos

Fast tool servos play crucial roles in machining workpieces with noncircular cross sections or non-rotationally symmetric surfaces, by actuating the cutting tool to complete desired tracking motions with high accuracy and at high speed, in the presence of time-varying cutting force disturbance and nonlinear plant parameters. To this end, two active disturbance rejection solutions are developed to control the shear stress and normal stress electromagnetically driven linear actuators. Given the reference trajectories of the cutting tool, the feed-forward strategy is combined the active disturbance rejection design with the linear and nonlinear extended state observers. The tracking accuracy and dynamic stiffness are analyzed using classic frequency response method for the linear controller; and the existence of limit cycles associated with the nonlinear controller is investigated using the describing function method. The proposed control strategies for the fast tool servos have found successful applications in precision machining an engine piston with elliptical cross sections and ultra-precision machining two dimensional micro-structured surfaces. The results show that both the novel concept and the easy-to-use algorithms make the active disturbance rejection control a tool of choice with a promising future in this industry.