Study Of Coordination Control Strategies For Multi-Axial Servo Systems

The increasing complexity of machining parts in manufacturing industry and the practical requirement of ever-higher precision in computer-controlled machine tools,are calling for more intensive research efforts to improve the transient performance and precision in trajectory tracking and contour control.This thesis,taking a biaxial servo system driven by Permanent Magnet Linear Synchronous Motor(PMLSM)as the plant to be controlled,conducts a successive study on single-axis servo tracking control and biaxial cross-coupling control problems,with an aim to reduce the contour error,so that the biaxial servo system can accomplish effective tracking of all kinds of contours.In this thesis,the state of the art of multi-axial servo system at home and abroad is first introduced,and the relevant control strategies are analyzed.Based on the working principles and dynamic equations of PMLSM,the mathematical model of the biaxial servo system is established.Then,the study is carried out on two-dimensional trajectory motion control using an XY biaxial servo system which is driven directly by two PMLSMs configured in a perpendicular structure.Next,the single-axis tracking control strategies for PMLSM are studied.To meet the requirement for fast settling,high precision and robustness in point-to-point tracking tasks,a proximate time-optimal servo(PTOS)control strategy is adopted in the thesis.The PTOS takes advantage of time-optimal control when the system error is large in amplitude,and then transitions into the proportional-derivative control once the error gets small,thus ensures a better robustness while maintaining the rapidness in system response,making it possible for effective applications in practical systems.For single-axis trajectory tracking tasks,a modified version of composite nonlinear control(CNC)is adopted,where a reference generator is included,and an extended state observer(ESO)is designed to estimate the unknown disturbance and unmeasured state variables.The combination of reference generator and ESO-based CNC,provides an effective solution to tracking general trajectory reference signals.To solve the coordination control problem in multi-axial servo system,the thesis analyzes the advantages and disadvantages of existing multi-axial coordination control algorithms,and the variable-gain cross coupling control strategy is chosen for use in biaxial servo system.The control strategy first performs some mathematical transformations on the two single-axial tracking errors to obtain the corresponding contour error,and then a contour error compensator with a proper computation of the compensation gain,is utilized to synthesize a modification signal for each axis,which then will be summed into the control input signal to participate the position control of the corresponding axis.Thus the cross coupling control strategy can alleviate the contour error induced by the mismatch of the biaxial motors.Digital simulation has been conducted in MATLAB/Simulink,and the results are analyzed in details.Finally,an experimental testbench has been constructed,using a high-precision linear motor-driven XY table,a Copley servo drive module,a Mega-fabs servo drive module and a 28335 digital signal controller board.A series of contour following control experiments are then conducted in normal conditions,using the developed single-and bi-axial control strategies,and the effectiveness is verified.