Control Strategies And Experimental Platform For Two-axis High-speed Direct-drive Servo Feed System

The concept of high-speed machining (HSM) has brought a revolution to thetraditional machine tool industry. Conventional machine tool structure, spindletechnology, servo system and processing techniques have been greatly evolved.Among the evolutions, that of the servo system is most prominent. Direct-drive linearmotor is considered as an optimal choice for high speed servo system due to its highspeed, high efficiency and high accuracy. Nevertheless linear motors also come withthe problem of force ripples produced by the end effect. Moreover direct-drive linearmotor system is more sensitive to external disturbances due to the lack of intermediatetransmission reducers. As a result, the control of a linear motor system is generallymore difficult. Hence, research on the control strategy for linear motor servo systemsis important from both theoretical aspect and practical aspect. This thesis investigatedthe control of a two-axis high-speed direct-drive servo feed system. A force loadingexperimental platform is developed and some control strategies are proposed anddemonstrated. The main content of the thesis includes:The structure and the work principle of a permanent magnet linearsynchronous motor (PMLSM) are firstly analyzed. Then, a mathematicmodel for the PMLSM and the two-axis servo feed system is produced usingthe method of coordinate system transformation.A variable structure sliding mode control (SMC) method and robust controlmethods are presented and are applied to the two-axis servo feed system inclosed-loop. The theory of the sliding mode control is firstly briefly reviewedand is then studied for both the continuous-time system and the discrete-timesystem. The SMC utilizing reaching law method is presented in details. Thedesign method of reaching law is discussed in particular. An integrateddesign procedure based on the pole-placement method for determining thereaching law and the switching surface is proposed. And the procedure isapplied to the mathematical model of the two-axis servo feed system. Someextra control items for correcting control signals are introduced to enhancethe robustness of the tracking controller against the model uncertainty and external disturbance. The effectiveness and robustness properties of aproposed control system with SMC are discussed using Matlab/Simulinksimulations.A controller based on Active Disturbance Rejection Control (ADRC) for thetwo-axis servo feed system is presented. ADRC inherits the error-drivenapproach (or in principle “use error to eliminate the error”) from traditionalPID method but enhances the later with modern control theory. In theresearch, the ADRC structure is analyzed and designed first, and then tunedfor the two axis servo drive system in order to reject the unknowndisturbance. Finally, simulations validate the controllability of the newcontroller.An experimental platform is developed for the direct drive servo feed systemin order to verify and investigate the effect of different control strategies andthe load response of the servo system. The platform is constructed using highperformance double-side type PMLSM, high precision linear encoder,PMAC controller and PLC system, controllable hydraulic loading systemand magnetic loading system. A computer application for SCADA isdeveloped using LabVIEW/G lanuage, while PMAC/PEWIN are employedto control the two axis system. A most prominent feature of this platform isthat the control strategy can be switched online and a variety of load signalto the feed system can be applied.Comprehensive experiments are carried out for both the single-axis linearmotor system and the two-axis feed system. No-load experiments andvarying load experiments are applied for both cases. The characteristics ofthe linear motor and the two-axis feed system are discussed through theanalysis of experimental results. The experiments verify the proposed controlstrategies and implementations.