Focusing servo device, optical disc recording/reproducing device and focus-searching method

An optical disc recording/reproducing device, comprising:

• a pick-up unit for making a focal point of one light beam emitted by the pick-up unit to fall on a data layer of an optical disc, detecting a reflected light beam reflected from the optical disc as the one light beam is emitted upon the disc, and generating a detection result based on the reflected light beam;
• and
• a focusing servo device, comprising:
• a focusing control unit, receiving the detection result detected from the reflected energy beam as the energy beam being emitted from the pick-up unit to the disc for data recording and/or reproducing and providing the control signal to the driving unit when the focusing control unit is operated in a feedback control mode;
• a driving unit, receiving the control signal and providing a driving signal to the pick-up unit based on the control signal, such that the focal point of the light beam emitted by the pick-up unit is moved on the spinning axis direction of the optical 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 light beam is fallen in an accessible range above/below the data layer of the optical disc on the spinning axis direction of the optical disc 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 that the focal point of the light 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 output in the feedback control mode, and the focal point of the energy beam is moved in the focus-searching range, such that the driving unit controls the pick-up unit to search the focal point within a focus-searching range above/below the data layer of the optical disc on the spinning axis direction of the optical disc for making the focal point of the light beam to fall in the accessible range.

A focus-searching method for making a focal point of an energy beam in an disc recording/reproducing device to fall in an accessible range of a data layer of an disc on a spinning axis direction of the disc for performing data recording and/or reproducing, the focus-searching method comprising:

• when 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 such that the disc recording/reproducing device being operated in a feedback control mode, recording a position deviation of the focal point of the energy beam during the predetermined period,
• determining a focus-searching range based on the recorded position deviation of the focal point of the energy beam in the feedback control mode,
• wherein the focus-searching range is determined by a focus-searching upper limit and a focus-searching lower limit determined by the position deviation;
• and
• when the focal point of the energy beam is departed from the accessible range of the data layer in the disc while the relationship is out of the linear range such that the disc recording/reproducing device being operated in a focus-searching mode, moving the focal point of the energy beam in the focus-searching range determined in the feedback control mode for making the focal point of the energy beam to fall in the accessible range of the data layer in the disc.