Research On Composite Feedback Control Technology For High-performance Servo Systems

The progress of modern industry and the development of control theory constantly promptpeople to seek better positioning servo control methods. Especially for high-performance servosystems, control methods are more demanding. In order to improve the motion controlperformance of servo systems, this thesis is devoted to the exploration of new control methods.An ideal servo control system is expected to have a fast and smooth output transientresponse, together with the steady-state accuracy. However, under the pure linear control, thefast response and smoothness are incompatible, as the fast response is usually accompanied by alarge overshoot. The Composite Nonlinear Feedback (CNF) control can solve the problem of fastand smooth response in servo systems. And it is a new control technology proposed under thestate space framework. The CNF control law consists of a linear feedback part for achieving fastresponse and a nonlinear feedback part for suppressing the overshoot, so as to improve thetransient performance. But CNF originally does not take into account disturbance factorsimpacting on the systems. In the presence of disturbance, the output of systems under the CNFcontrol usually will have a steady state error. In this thesis, a discrete-time robust compositenonlinear feedback (DRCNF) control scheme is proposed, in which a reduced-order observer isadopted to estimate the immeasurable state variables and unknown constant disturbance, andthen used for compensation. DRCNF is mainly for second-order and higher-order systems. Forsimple first-order systems, a new composite feedback control scheme is proposed, which isbased on disturbance estimation and reference input filtering. And a discrete-time nonlineartracking differentiator is used as the input filter.Closed-loop stability with the two control schemes are analyzed theoretically. The DRCNFcontrol scheme is then applied to a servo system modeled by double integrator, and thecomposite feedback control scheme based on disturbance estimation and reference input filteringis applied to a first-order servo system. Studies have shown that these two control schemes bothcan achieve the desired tracking performance. The control scheme towards first-order systems isapplied to an actual XY-table servo system and a good control effect is shown. The design can begeneralized to other practical motion control servo systems.Finally a real-time control prototyping system is developed based on the idea of virtual instrument. The system is built on a desktop computer and a data acquisition card, while thecontrol scheme towards first-order systems is implemented via LabVIEW. The prototypingsystem can accomplish data acquisition, data display and digital control. Experimental tests showthe system has effective functions, a friendly user interface and vivid visual effects. Somepotential for practical application can be expected.