Patent ID: 8009522

Claim:
A focusing servo device, for a focal point of an energy beam emitted by a pick-up unit to fall in an accessible range of a data layer in an disc on a spinning axis direction for data recording and/or reproducing, wherein the pick-up unit further detects an energy beam reflected from the disc and generates a detection result, the focusing servo device comprising: a focusing control unit, receiving the detection result detected from the energy beam as the energy beam being emitted to the disc for data recording and/or reproducing, and providing the control signal based on the detected result to the driving unit when the focusing control unit is operated in a feedback control mode; a driving unit, for receiving the control signal and providing a driving signal to the pick-up unit based on the received control signal, such that the focal point of the energy beam emitted by the pick-up unit moves on the spinning axis direction of the disc; and a focus-searching range decision unit, receiving the control signal applied to the driving unit and calculating extremums of the deviation of the disc during a predetermined period based on the received control signal for recording the extremums when the focusing control unit is operated in the feedback control mode, and outputting a focus-searching range to the focusing control unit to adjust the control signal according to the recorded extremums of the deviation of the disc during the predetermined period in the feedback control mode; wherein, when the detection result indicates that the focal point of the energy beam is fallen in the accessible range while a relationship between a focusing error signal of the detection result and a distance from a object lens to the disc is in a linear range, the focusing control unit is operated in the feedback control mode for adjusting and outputting the control signal based on the detection result, and when the detection result indicates the focal point of the energy beam is out of the accessible range while the relationship is out of the linear range, the focusing control unit is operated in a focus-searching mode for adjusting and outputting the control signal based on the focus-searching range, and the focal point of the energy beam is moved in the focus-searching range output in the feedback control mode, such that the driving unit controls the pick-up unit to search the focal point in a focus-searching range above/below the data layer of the disc on the spinning axis direction of the disc for making the focal point of the energy beam to fall in the accessible range.