News Column

Patent Issued for Optical Disc Device

February 4, 2014



By a News Reporter-Staff News Editor at Information Technology Newsweekly -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventor Imagawa, Seiji (Yokohama, JP), filed on March 2, 2012, was published online on January 21, 2014.

The assignee for this patent, patent number 8634281, is Hitachi-LG Data Storage, Inc. (Tokyo, JP).

Reporters obtained the following quote from the background information supplied by the inventors: "The present invention relates to an optical disc device, and in particular, to the tracking control and the focus control of the optical disc device.

"Techniques as background arts of this technical field have been disclosed in JP-A-2002-312958, JP-A-2009-140568, JP-A-2001-357542 and JP-A-2009-170035, for example. These Patent Literatures have disclosed a disc having a plurality of data layers and a servo-dedicated layer used for precisely positioning a beam spot on each data layer, an objective lens control method for precisely condensing (focusing) laser spots on the servo layer and the data layer, correction of optical axis shifts of optical beams condensed on the servo layer and the data layer by use of error signals generated from returning light from the servo layer and the data layer, correction of optical axis tilts by use of error signals and shift error signals generated from returning light from the servo layer and the data layer, etc.

"Meanwhile, JP-A-63-26814 disclosing a head positioning technique for a magnetic disc device includes a description 'In cases where a medium defect exists in a prescribed area of the data surface when the head positioning is executed based on servo information recorded on the servo surface and the head positioning is executed again based on servo information recorded in a prescribed area of the data surface, . . . the medium defect is detected, the head positioning control based on the data-surface servo information is stopped, and the control is returned to the positioning operation based on the servo-surface servo information.' (see 'Summary' in JP-A-63-26814)."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventor's summary information for this patent: "By providing a servo layer separately from the data layer, condensing beam spots separately on the servo layer and the data layer, and executing the tracking control on the servo layer as in JP-A-2002-312958, JP-A-2009-140568, JP-A-2001-357542, JP-A-2009-170035, guide tracks on the data layer become unnecessary and a medium having a plurality of data layers can be manufactured at a lower cost. Further, the positions of the beam spots can be controlled precisely by using error signals and shift signals calculated from the returning light from the servo layer and the data layer.

"However, the conventional techniques can lead to performance deterioration in the control of the beam spot positions since the track pitch of the data layer is desired to be less than or equivalent to that in conventional systems in order to secure a sufficient data capacity whereas the tracking control of the data layer is executed not directly but indirectly based on the returning light from the servo layer. Further, while JP-A-63-26814 (magnetic disc device) has disclosed the stoppage of the head positioning control based on the data-surface servo information and the returning of the control to the positioning operation based on the servo-surface servo information upon detection of a medium defect, no description has been given in regard to switching between control systems regarding the beam spots.

"It is therefore the primary object of the present invention to realize high-reliability tracking control and high-reliability focus control in an optical disc device which reproduces or records information by reading or writing data from/to an optical disc having a data layer and a servo layer.

"In accordance with an aspect of the present invention, there is provided an optical disc device employing an optical pickup which reproduces or records information by reading or writing data from/to a disc having a data layer and a servo layer, comprising: an objective lens which moves in a radial direction of the disc and thereby moves focusing positions of first and second beam spots in the radial direction of the disc; a tracking actuator which drives the objective lens in the radial direction of the disc; a first detector which converts reflected light of the first beam spot from the data layer into an electric signal; a second detector which converts reflected light of the second beam spot from the servo layer into an electric signal; a first tracking error signal generating unit which generates a first tracking error signal based on the output of the first detector; a second tracking error signal generating unit which generates a second tracking error signal based on the output of the second detector; a tracking control unit which generates a control signal for positioning the first beam spot or the second beam spot at a prescribed track based on the output of the first tracking error signal generating unit or the second tracking error signal generating unit; a tracking actuator driving unit which drives the tracking actuator based on the output of the tracking control unit; and a tracking error level detecting unit which detects a tracking error level based on the output of the first tracking error signal generating unit or the second tracking error signal generating unit. The tracking control unit drives the tracking actuator based on the output of the first detector in normal data reproduction. The tracking control unit detects that the output of the first tracking error signal generating unit has exceeded a prescribed range based on the output of the tracking error level detecting unit and then operates to drive the tracking actuator based on the output of the second detector. The tracking control unit detects that the output of the second tracking error signal generating unit has come within a prescribed range based on the output of the tracking error level detecting unit and then operates to drive the tracking actuator based on the output of the first detector again.

"In accordance with another aspect of the present invention, there is provided an optical disc device employing an optical pickup which reproduces or records information by reading or writing data from/to a disc having a data layer and a servo layer, comprising: a first control unit which executes tracking control based on reflected light of a first beam spot condensed on the data layer; and a second control unit which executes the tracking control based on reflected light of a second beam spot condensed on the servo layer. The tracking control in data reproduction is performed by executing switching between the first control unit and the second control unit.

"In accordance with another aspect of the present invention, there is provided an optical disc device employing an optical pickup which reproduces or records information by reading or writing data from/to a disc having a data layer and a servo layer, wherein the optical pickup is configured so that the servo negative feedback region of a second focus error signal generated based on reflected light of a second beam spot condensed on the servo layer is wider than the servo negative feedback region of a first focus error signal generated based on reflected light of a first beam spot condensed on the data layer.

"According to the present invention, high-reliability tracking control and high-reliability focus control can be realized in optical disc devices reproducing or recording information by reading or writing data from/to an optical disc having a data layer and a servo layer."

For more information, see this patent: Imagawa, Seiji. Optical Disc Device. U.S. Patent Number 8634281, filed March 2, 2012, and published online on January 21, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=38&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=1899&f=G&l=50&co1=AND&d=PTXT&s1=20140121.PD.&OS=ISD/20140121&RS=ISD/20140121

Keywords for this news article include: Information Technology, Hitachi-LG Data Storage Inc., Information and Data Storage.

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Source: Information Technology Newsweekly


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