Focusing errors in optical disk drives comprise significant periodic components and an eventful dc content. The dc component is not explicitly taken into account in many periodic compensation methods. This paper investigates the design of adaptive feedforward cancellation (AFC) and frequency adaptive control technique (FACT) algorithms for periodic components as well as dc disturbance compensation. Both algorithms are applied as a plug-in module to an optical disk drive for demonstrating their facility in the reduction of focusing errors. By making good use of frequency sampling filter (FSF), the real-time harmonic identification can be fulfilled in FACT method for various playing speeds. Analysis and experimental results show that FACT has better properties than AFC in terms of dc cancellation and harmonic independence. It is also shown that AFC fails when both the dc content and harmonics are compensated simultaneously.

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