Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-10-05
2001-06-12
Hindi, Nabil (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S053190, C369S112020
Reexamination Certificate
active
06246648
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technical field of an aberration correcting apparatus for correcting a wavefront aberration (mainly a coma aberration) generated on an information recording surface of an information record medium for an optical information reproduction due to an inclination of an angle formed between the information recording surface and an optical axis of an optical beam for the information reproduction from the right angle. (Hereafter, this inclination is referred to as a tilt, and the amount of this inclination is referred to as a tilt amount.)
2. Description of the Related Art
In such an aberration correcting device, the wavefront aberration caused, for example, in the direction of a radius of an optical disc functioning as an information record medium (hereafter referred to as radial direction) due to the tilt is corrected by: emitting an optical beam for a tilt amount detection onto the optical disc besides the above described optical beam for the information reproduction; receiving the reflected light of the optical beam for the tilt amount detection by using a photodetector divided into two partial detection portions by a division line perpendicular to the radial direction (hereafter, the emitting device for emitting the optical beam for the tilt amount detection and the photodetector are referred to collectively as a tilt sensor); calculating the above described tilt amount from the difference between the detected signals supplied from the respective partial detection portions; and inclining the optical axis of the optical beam for the information reproduction so as to cancel the tilt on the basis of the calculated tilt amount.
In this aberration correcting apparatus, however, it is necessary to cancel the tilt by inclining the optical axis by using a mechanical drive device. Therefore, the aberration correcting apparatus has problems of an increased manufacturing cost, a lowered reliability and a difficulty in a size reduction. These problems occur for the tilt in the rotation direction of the optical disc (hereafter, which referred to as a tangential direction) as well in the same way.
Therefore, as an improvement of the above described mechanical aberration correcting apparatus, there is a method of giving a phase difference or the like to the optical beam for the information reproduction on the basis of the detected tilt amount without using the mechanical tilt canceling device, to thereby optically cancel the wavefront aberration caused by the tilt.
However, according to the above described method of optically canceling the aberration, the tilt itself is not canceled but the wavefront aberration caused by the tilt is canceled. Thus, even if the wavefront aberration is canceled, the tilt itself is not changed. As a result, the detected signal supplied from the tilt sensor is not changed, either.
Therefore, it cannot be determined from the detected signal supplied from the tilt sensor whether the optical correction is insufficient or superfluous. Unlike the above described mechanical aberration correcting apparatus, therefore, a so-called feedback control based on the detected signal of the tilt sensor cannot be conducted. Instead, a so-called feedforward control of estimating the wavefront aberration (i.e., the tilt amount) on the basis of the detected signal supplied from the tilt sensor and conducting the correction is thus execution.
Therefore, if the tilt amount cannot be detected accurately by the tilt sensor, the aberration correction cannot be conducted properly. Thus, there is a problem that the dispersion of sensitivities and offsets or nonlinear characteristics of the partial detection portions in the tilt sensor must be adjusted accurately.
Furthermore, there is a problem that a change is caused in some cases by an elapse of time even or aging even if these values are adjusted accurately in the initial state.
Furthermore, there is a problem that, in the case where both of the tilt in the radial tilt direction and the tilt in the tangential direction are to be corrected, two tilt sensors must be used resulting in a large sized pickup portion.
SUMMARY OF THE INVENTION
The present invention is made in view of the above described problems. It is therefore an object of the present invention to provide an aberration correcting apparatus, which has a high precision and a high reliability and which can be reduced in size without employing an additional separated sensor such as the above described tilt sensor, and an information reproducing apparatus having such an aberration correcting apparatus.
The above object of the present invention can be achieved by an aberration correcting apparatus provided with: a light detection device for irradiating an information record medium, on which record information is recorded, with a light beam, and outputting a light detection signal corresponding to the record information on the basis of a reflection light of the light beam reflected from the information record medium; a tilt detection device for detecting a tilt between an information record surface of the information record medium and an optical axis of the light beam on the basis of the light detection signal; a correction device for correcting a wavefront aberration generated in the light beam due to the tilt; and a driving device for driving the correction device on the basis of the detected tilt.
According to the aberration correcting apparatus, an information record medium is irradiated with the light beam by the light detection device, and the light detection signal corresponding to the record information is outputted on the basis of a reflection light. Then, on the basis of the light detection signal, the tilt between the information record surface of the information record medium and the optical axis of the light beam is detected by the tilt detection device. Then, the wavefront aberration generated in the light beam due to the tilt is corrected by the correction device. Finally, the corrected device is driven by the driving device on the basis of the detected tilt.
Accordingly, since the tilt is detected on the basis of the light detection signal obtained by the irradiation of the light beam for the information reproduction, it is not necessary to emit another light beam exclusive for the tilt detection besides the light beam for the information reproduction, so that the structure of the aberration correcting apparatus can be simplified.
Therefore, it is possible to correct the aberration due to the tilt of the optical axis of the light beam precisely by the structure which is simplified and is reduced in size.
In one aspect of the aberration correcting apparatus, the information record medium is provided with a disc type record medium on which the record information is recorded by forming a spiral or coaxial track. The light detection device outputs as the light detection signal a center detected signal corresponding to the record information forming a center turn of the track on which the record information to be reproduced is recorded, an inner detected signal corresponding to the record information forming an inner turn of the track located adjacent to the center turn at an inner side thereof and an outer detected signal corresponding to the record information forming an outer turn of the track located adjacent to the center turn at an outer side thereof. And that, the tilt detection device provided with at least one of (i) a tangential tilt detection device for detecting a tangential tilt, which is the tilt in a tangential direction of the track on the disc type record medium, on the basis of the center detected signal and (ii) a radial tilt detection device for detecting a radial tilt, which is the tilt in a radial direction of the track on the disc type record medium on the basis of the inner, center and outer detected signals.
According to this aspect, the center detected signal, the inner detected signal and the outer detected signal are outputted by the light detection device.
Hindi Nabil
Pioneer Electronic Corporation
Young & Thompson
LandOfFree
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