| In modern servo control system practice, it is common to come across the control tasks and the periodic disturbance, which are of repetitive nature. So,it is frequently needed to track or reject the unknown periodic exogenous signals with a known period when designing the servo control systems. For the high accuracy control of such systems, the repetitive control (RC) algorithm matches the periodic characteristics, which is distinguished by its high control accuracy, simple structure, easy implementation, insensitiveness to parameter variation, little online computation burden, as well as its fitness for high-speed motion control. As a result, the repetitive control has drawn much attention and currently has been widely used in various control systems with repetitive nature, ever since its introduction to the control community.However, in the track-following servo system of an optical disk drive, the eccentricity of optical disk will cause periodic disturbances on TE(tracking errors) signals.Considering the pertinency between the RC theory and the eccentric periodic disturbances, the RC theory is utilized to the DVD tracking servo system in this paper. And great steady-state performances are reached as a result.Firstly, the design problem of continuous-time RC systems is studied.After introducing the basic RC theory,this paper studies the the steady-state and transient performances,disturbance rejection and robustness, and analyzes the influence of introducing the low-pass filter to the servo system. Then, based on these analysises, a design method for plug-in RC systems and optimization of parameters are proposed,meanwhile the design index reflecting the tradeoff of steady-state accuracy and transient response property is determined.Then, the analysis and design of discrete-time RC systems are systematicaly studied. In view of the drawbacks of the existing Prototype Repetitive Controler (PTRC), such as the sensitiveness to parameter variations and poor stability robustness,a new type of robust PTRC is proposed, where a zero phase shift filter is introduced as the repetitive control gain to settle the conflict between stability robustness and steady-state performance. As a result, the modified PTRC systems benefit from broadened bandwidth and improved tracking accuracy.Finally, the design of DVD tracking servo system with repetitive control is studied.In the beginning,the run-out problem in the DVD tracking servo system is presented and the restrictions of ECMA-267 specification are analyzed.Then a diagram of DVD tracking servo system is proposed to solve the run-out problem. In detail,based on the stability of repetitive controller, this paper promotes a mapped method to determine and optimize the parameters of repetitive controller. And through an experiment, it is verified that the designed repetitive controller has a remarkable performance to attenuate the periodic disturbance while preserving the overall stability. |
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