Focus pull-in behavior analysis in a blu-ray disk and various control approaches to enhance the performance of it

The focus pull-in behavior analysis in a Blu-Ray disk (BD) and various control approach to improve the performance of it are discussed. The focus pull-in work, which locks the beam spot of an optical pick-up to the information layer in an optical disk, is an essential work in an optical disk drive (ODD), and the error tolerance of it depends on the kind of an ODD. In a BD system, the focus pull-in work should be done within a very narrow beam height region (λ/NA = 0.4765 μm) and a very short period. Therefore, the moment of the focus pull-in is a transient phenomenon, and more careful analysis of it is necessary. In this paper, the focus full-in work is analyzed in depth, and various control approaches to improve the focus pull-in performance are discussed. First, various detected servo signal during the focus pull-in work are summarized briefly. Then, a novel swing arm type actuator which is developed by our center for a small form factor BD is introduced. Finally, three control approaches to perform the focus pull-in are designed and applied to the system: (i) conventional lead-lag, (ii) fuzzy control, (iii) sliding mode control. From the experiments results, we find that two control approaches, fuzzy control and sliding mode and, have more good focus pull-in performances than the conventional lead-lag approach.