Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-05-25
2001-09-25
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044250, C369S053190
Reexamination Certificate
active
06295256
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to focusing bias adjusting apparatus and method in an optical recording medium playing apparatus.
2. Description of the Related Art
To accurately read recording information from an optical disc such as CD (Compact Disc), DVD (Digital Versatile Disc), or the like, it is necessary to vertically irradiate a reading beam onto a recording surface of the optical disc. If a warp occurs in the optical disc itself or an error of a mechanism system is large, however, the reading beam cannot be vertically irradiated onto the recording surface of the optical disc and information reading precision deteriorates.
A recording medium playing apparatus for reproducing the recording information from the optical disc is, therefore, provided with a tilt servo control apparatus for detecting a tilt occurring between a pickup as information reading means and the optical disc, inclining the whole pickup by an angle corresponding to the detected tilt, or performing a tilt correcting process corresponding to the tilt to a read signal read out by the pickup, thereby suppressing the deterioration of the information reading precision.
As a tilt servo control apparatus, an apparatus using a liquid crystal panel inserted onto an optical axis in order to execute the tilt correction is known (for example, JP-A-11-3531). In the case of the apparatus, the liquid crystal panel is divided into a plurality of regions and a phase difference is given to a laser beam passing through each region of the liquid crystal panel so as to maximize a level of the read signal derived by the pickup.
Since the irradiation laser beam needs to be focused onto the recording surface of the optical disc in order to accurately read the recording information from the optical disc, an optical disc player is provided with a focusing servo control apparatus for generating a focusing error signal on the basis of each photodetecting level of a plurality of split photodetectors of the pickup and controlling a position in the optical axial direction of an objective lens so as to reduce a level of the focusing error signal. In the focusing servo control apparatus, generally, the focusing error signal is not set to a reference level (for example, 0) in an in-focus state because of an error of an optical system but includes a DC component as an offset component in the focusing error signal. A focusing bias adjustment, therefore, for forcibly setting the offset component in the focusing error signal to 0 is executed so that the focusing error signal is set to the reference level in the in-focus state.
The focusing bias adjustment is generally executed as an initial operation just after the optical disc was set to the disc player. Since the tilt servo control operation is performed by the tilt servo control apparatus even during the playback of the disc, however, if the tilt correction is executed by the tilt servo control operation, since the focusing bias adjustment executed as an initial operation is based on the photodetecting level of each photodetector of the pickup before the tilt correction is executed, there is such a problem that an adjustment value is deviated from a true adjustment value as a result and is not proper. The problem also similarly occurs in the case where an apparatus in which an optical device other than the liquid crystal panel is inserted into the optical system of the pickup so as to maximize the level of the read signal derived by the pickup is used as a tilt servo control apparatus.
OBJECTS AND SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide focusing bias adjusting apparatus and method in an optical recording medium playing apparatus, in which a proper focusing bias adjustment result can be obtained even when a tilt occurs between a pickup and an optical recording medium such as an optical disc or the like.
According to the invention, there is provided a focusing bias adjusting apparatus in an optical recording medium playing apparatus, comprising: an optical pickup having an optical system for irradiating a laser beam onto an optical recording medium and detecting light reflected from the optical recording medium by a split type photodetector; focusing servo control means for generating a focusing error signal on the basis of each output signal of the photodetector and moving an objective lens in the pickup in an optical axial direction of the laser beam in accordance with the focusing error signal; focusing bias adjusting means for making a focusing bias adjustment in order to remove an offset component in the focusing error signal; tilt servo control means for adjusting the optical system so as to maximize a read signal as a sum signal of each output signal of the photodetector in order to compensate a tilt angle which is defined by a normal at the irradiating position of the laser beam on a recording surface of the optical recording medium and the optical axial direction of the laser beam; and readjustment control means for controlling the focusing bias adjusting means so as to execute the focusing bias adjustment again when the adjusting operation of the optical system is performed by the tilt servo control means after completion of the focusing bias adjustment by the focusing bias adjusting means.
According to the invention, there is also provided a focusing bias adjusting apparatus in an optical recording medium playing apparatus, comprising: an optical pickup having an optical system for irradiating a laser beam onto an optical recording medium and detecting light reflected from the optical recording medium by a split type photodetector; focusing servo control means for generating a focusing error signal on the basis of each output signal of the photodetector and moving an objective lens in the pickup in an optical axial direction of the laser beam in accordance with the focusing error signal; focusing bias adjusting means for making a focusing bias adjustment in order to remove an offset component in the focusing error signal; tilt servo control means for adjusting the optical system so as to maximize a read signal as a sum signal of each output signal of the photodetector in order to compensate a tilt angle which is defined by a normal at the irradiating position of the laser beam on a recording surface of the optical recording medium and the optical axial direction of the laser beam; discriminating means for discriminating whether a starting condition of the focusing bias adjustment is satisfied or not when the tilt servo control means executes the adjusting operation of the optical system after completion of the focusing bias adjustment by the focusing bias adjusting means; and readjustment control means for controlling the focusing bias adjusting means so as to executing the focusing bias adjustment again when the discriminating means determines that the starting condition of the focusing bias adjustment is satisfied.
According to the invention, there is further provided a focusing bias adjusting method in an optical recording medium playing apparatus, comprising the steps of: making a focusing bias adjustment to remove an offset component in a focusing error signal based on each output signal of a split type photodetector in an optical pickup; and thereafter, making a tilt adjustment of the optical system so as to maximize a read signal as a sum signal of each output signal of the photodetector in order to compensate a tilt angle which is defined by a normal at the irradiating position of a laser beam from the optical pickup on a recording surface of the optical recording medium and an optical axial direction of the laser beam, wherein the focusing bias adjustment is executed again when a tilt adjusting operation of the optical system of the optical pickup is performed after completion of the focusing bias adjustment.
According to the invention, there is further provided a focusing bias adjusting method in an optical recording medium playing apparatus, comprising the steps of: m
Bradshaw Alex
Kimikawa Yuichi
Kimura Motoi
Nozaki Morio
Yamazaki Hitoshi
Edun Muhammad
Morgan & Lewis & Bockius, LLP
Pioneer Corporation
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