Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-07-09
2001-11-27
Tran, Thang V. (Department: 2753)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044290, C369S112240
Reexamination Certificate
active
06324133
ABSTRACT:
RELATED APPLICATION DATA
The present application claims priority to Japanese Application No. P10 203983 filed Jul. 17, 1998, which application is incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical recording and reproducing apparatus and an optical recording and reproducing method, particularly to an optical recording and reproducing apparatus and an optical recording and reproducing method for recording and reproducing information by using two group object lenses.
2. Description of the Related Art
In a recording and reproducing apparatus of an optical record medium, a spot size d on the record medium is represented by the following equation (1) when a wavelength of a light source is designated by notation &lgr; and an aperture number of an object lens is designated by NA (Numerical Aperture).
d=&lgr;/NA
(1)
As is known from Equation (1), the shorter the wavelength &lgr; of a light source and the larger the numerical aperture NA of the object lens, the smaller the spot size d and high density recording is made feasible.
In such a relationship, as a method of increasing the numeral aperture of an object lens, it is known to be effective to use aspherical two group object lenses. JP-A-9-251645 discloses a record medium recording and reproducing apparatus and a record medium recording and reproducing method by an applicant the same as the applicant of this application in which spherical aberration is restrained from occurring by using two group object lenses. When such two group object lenses are used, it becomes necessary to achieve optimization of a distance between the two group object lenses and minimize wave front aberration in order to make best a reproducing signal from a record medium.
In the meantime, a focal depth fd of an object lens specified by mean square error (&lgr;/14) of wave front aberration, is calculated by the following equation (2).
fd=&lgr;/NA
2
(2)
As is known from Equation (2), when an object lens having a high numerical aperture is used, the focal depth fd becomes extremely small. For example, when a numerical value of two group object lenses is set to 0.85, the focal depth fd is reduced to about a half of that in the case of DVD-RAM (object lens numeral aperture NA=0.6). Here, DVD indicates a digital video disk and DVD-RAM indicates a rewritable digital video disk.
Therefore, when an object lens having a high numerical aperture is used, further accurate focusing control is requested and the lens need to follow precisely a change in environmental temperature and an aging change.
As a method of achieving optimization of a distance between two group object lenses and minimizing wave front aberration, Japanese Patent Application No. 8-340903 discloses an optical disk recording and reproducing apparatus and its method by an applicant the same as the applicant of the application in which after integrating two group lenses and carrying out focusing operation of focus servo, a front lens is independently moved in an optical axis direction by which wave front aberration is adjusted to minimize.
Further, as accurate focusing control, Japanese Patent Application No. 9-84090 discloses a focusing control apparatus and its method and an optical disk apparatus by an applicant the same as the applicant of this application in which in focus servo in an optical disk apparatus using an optical head constituted by two group object lenses having a high numerical aperture, by optimizing focus offset, a disk reproducing signal is adjusted to be best.
However, the above-described respective optimization of the distance between lenses of the two group object lenses and optimization of focus offset are carried out based on the same reproducing signal from a record medium and both are separately adjusted. Therefore, a long period of time is required in the adjustment in comparison with a case of an object lens constituted by a single piece of a lens.
SUMMARY OF THE INVENTION
The present invention has been carried out in consideration of the above-described points and it is an object of the present invention to provide an optical recording and reproducing apparatus and an optical recording and reproducing method capable of simultaneously carrying out optimization adjustment of a distance between lenses of two group object lenses and optimization adjustment of focus offset in a short period of time.
In order to resolve the above-described object, according to a first aspect of the present invention, there is provided an optical recording and reproducing apparatus for carrying out either of recording and reproducing of information by irradiating a beam to an optical record medium via two group lenses constituted by a first lens and a second lens, the optical recording and reproducing apparatus comprising first driving means for moving the first lens in an optical axis direction relative to the second lens and second driving means for moving the two group lenses in the optical axis direction, wherein first adjustment for optimizing a distance between the first lens and the second lens by using the first driving means and second adjustment for optimizing a focus offset by using the second driving means are simultaneously carried out by simultaneously driving the first driving means and the second driving means when focus servo is being operated.
According to a second aspect of the present invention, there is provided the optical recording and reproducing apparatus wherein simultaneously with periodically moving the first lens in the optical axis direction relative to the second lens by the first driving means, the two group lenses constituted by the first lens and the second lens are periodically moved in the optical axis direction by the second driving means to thereby carry out the first and the second adjustments.
According to a third aspect of the present invention, there is provided the optical recording and reproducing apparatus wherein a movement period of periodically moving the first lens relative to the second lens is longer than a movement period of periodically moving the two group lenses comprising the first lens and the second lens.
According to a fourth aspect of the present invention, there is provided the optical recording and reproducing apparatus wherein the periodic movements are of sine waveforms.
Such resolving means is applicable similarly to an optical recording and reproducing apparatus for recording or reproducing information by irradiating a beam to an optical record medium via an optical system having a constitution including an object lens comprising one or more of lenses and a relay lens group comprising one or more of lenses in accordance with a fifth through an eighth aspect of the present invention. That is, only the relationship between the first lens and the second lens is replaced by a relationship between the relay lens group and the object lens.
Further, according to a ninth aspect of the present invention, there is provided an optical recording and reproducing method of carrying out either of recording and reproducing of information by irradiating a beam to an optical record medium via two group lenses comprising a first lens and a second lens wherein after focus servo has been operated, first adjustment for optimizing a distance between the first lens and the second lens by moving the first lens in an optical axis direction relative to the second lens and second adjustment for optimizing a focus offset by moving the two group lenses in the optical axis direction are carried out simultaneously.
In this case, that the movements are made periodic as in a tenth aspect of the present invention, that a movement period of the first lens relative to the second lens is made longer than a movement period of the two group lenses according to an eleventh aspect of the present invention and that the periodic movements are of sine waveforms according to a twelfth aspect of the present invention, are simi
Sonnenschein Nath & Rosenthal
Sony Corporation
Tran Thang V.
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