Patent Application
20080025169
Exemplary embodiments of the present invention will now be described with reference to the drawings.
A first embodiment of the present invention will be described below with reference to
The configuration of the optical pickup 1 will be described with reference to
The optical pickup 1 has an optical base 2 having disposed thereon a semiconductor laser 3 serving as a light source, a polarizing beam splitter 4 serving as a splitter, a collimator 11, a quarter-wave plate 12, a deflecting mirror 5, an RF servo-sensor 6 serving as a photo detector, an objective-lens actuator 8, a sensor lens 9, and a monitor sensor 13. The objective-lens actuator 8 supports an objective lens 7 in a biaxially drivable fashion in a focusing direction and tracking direction with respect to a recording track of an optical disc 10. The objective-lens actuator 8 has a known structure, such as a four-wire structure, and therefore, the description of the structure thereof will be omitted.
The optical base 2 has an integral main shaft bearing 2a and sub shaft bearing 2b that are engaged with two guide shafts of an optical disc device to be described below, and is slidable along the guide shafts. A light axis that extends from the semiconductor laser 3 to the deflecting mirror 5 via the polarizing beam splitter 4 is disposed slantwise at an angle θ towards the inner periphery of the optical disc 10 with respect to a direction perpendicular to the moving direction of the optical pickup 1. The RF servo-sensor 6 is disposed at the inner periphery side of the optical disc 10 relative to the light axis.
A recording/reproducing method will be described below.
A light beam emitted from the semiconductor laser 3 as divergent light enters the polarizing beam splitter 4 where the beam is split into reflected light and transmitted light. The light beam reflected by the polarizing beam splitter 4 enters the monitor sensor 13 where a monitor output signal used for performing output control of the semiconductor laser 3 is generated.
Generally, the monitor sensor 13 may be of any type capable of detecting the light intensity. For this reason, it is a known fact that the monitor sensor 13 can be disposed at a position near the polarizing beam splitter 4.
On the other hand, the light beam transmitted through the polarizing beam splitter 4 is substantially collimated by the collimator 11. The light beam transmitted through the collimator 11 travels through the quarter-wave plate 12 and then to the deflecting mirror 5 where the light beam is reflected perpendicularly to the disc surface of the optical disc 10, whereby the light beam enters the objective lens 7. The light beam incident on the objective lens 7 is focused onto an information-recording layer (not shown) of the optical disc 10, whereby an information recording operation is performed.
The light beam reflected by the optical disc 10 is condensed by the objective lens 7 and is then reflected at the polarizing beam splitter 4. The light beam reflected by the polarizing beam splitter 4 travels through the sensor lens 9 so as to enter the RF servo-sensor 6 serving as a photo detector. Accordingly, reproduction of an information signal and generation of focusing and tracking servo-error signals are implemented. Since the servo techniques used are known techniques (e.g. focus servo: astigmatic method, and tracking servo: push-pull method), the descriptions thereof will be omitted here.
An optical disc device 21 will now be described with reference to
The optical disc device 21 includes a chassis 22 serving as a base of the overall structure, a spindle motor 23 disposed on the chassis 22 and arranged to hold and rotate the optical disc 10, the optical pickup 1, a feed motor 25 disposed on the chassis 22 and serving as a stepping motor, and a main shaft 26 and a sub shaft 27 serving as guide shafts that support the optical pickup 1. The feed motor 25 has a lead screw 24 arranged to move the optical pickup 1 in the radial direction of the optical disc 10. The feed motor 25, the main shaft 26, and the sub shaft 27 will be defined as traversing means.
A light beam is emitted from the objective lens 7 of the optical pickup 1 towards the optical disc 10 rotated by the spindle motor 23. The optical pickup 1 and the lead screw 24 integrated with a rotary shaft of the feed motor 25 are engaged with each other through a rack member, not shown. A rotational movement of the lead screw 24 is converted to a translational movement so that the optical pickup 1 is moved in the radial direction of the disc along the main shaft 26 and the sub shaft 27 serving as guides. Accordingly, an information recording/reproducing operation can be performed from the inner periphery towards the outer periphery of the optical disc 10.
In comparison to the related art, the amount of protrusion from the plane of projection of the disc is reduced in the structure of the present invention, as shown in
An advantage of disposing the photo detector at the inner periphery side of the optical disc 10 relative to the light axis extending from the light source to the deflecting mirror via the splitter will now be described with reference to
A light emitting point 3a of the semiconductor laser 3 serving as a light source and a light detecting surface 6a of the RF servo-sensor 6 serving as a photo detector are disposed at substantially conjugate positions with respect to the collimator 11. This means that the light emitting point 3a and the light detecting surface 6a are split from the polarizing beam splitter 4 serving as a splitter by substantially the same distance. Consequently, when the light emitting point 3a and the light detecting surface 6a are disposed within the plane of projection of the disc as shown in
The objective lens 7 is shiftable in the moving direction of the optical pickup 1 by a distance Tr. This technique is generally implemented in order to, for example, compensate for displacement of a recording track caused by decentering of the optical disc 10 or to intermittently drive the feed motor 25 of the optical disc device 21 for the purpose of achieving low power consumption. Thus, the deflecting mirror 5 that deflects a light beam upward in a direction perpendicular to the disc surface requires an area circumscribed by a moving range R of the objective lens 7, including the distance Tr, within the plane of projection of the disc. On the other hand, a flip-up surface 5a of the deflecting mirror 5 needs to be perpendicular to a plane A that extends along the light axis of a light beam incident on the deflecting mirror 5 and through the center of the objective lens 7. Accordingly, if a distance of the reflective surface of the deflecting mirror 5 in the light-axis direction is represented as L, a thickness t of the deflecting mirror 5 is expressed as follows:
From
This means that the thickness t of the deflecting mirror 5 decreases with decreasing angle θ. A light beam incident on the deflecting mirror 5 particularly requires a maximum effective diameter in comparison to that on other optical components. For this reason, the thickness t of the deflecting mirror 5 is one of the main factors that determine the thickness of the optical disc device 21.
Accordingly, by disposing the photo detector at the inner periphery side of the optical disc relative to the light axis extending from the light source to the deflecting mirror via the splitter, the optical disc device can be reduced in thickness.
Table 1 below shows design examples for the thickness t of the deflecting mirror 5 with respect to the angle θ. In these design examples, the distance Tr: ±0.3=0.6 mm, and the objective-lens effective diameter: φ3.4 mm.
If the angle θ is greater than 20°, not only will the thickness shown in Table 1 increase, but the spindle motor 23 and the RF servo-sensor 6 can unfavorably interfere with each other, which is apparent from
Furthermore, in order to achieve the advantage of the present invention, the angle θ at least needs to be set greater than 0°.
Accordingly, a suitable angle θ is greater than 0° but equal to or less than 20°. In the first embodiment, the angle θ is set at about 15°.
In the first embodiment, the splitter may alternatively be defined by a half mirror. In that case, the quarter-wave plate 12 is not necessary, so that the number of components can be reduced.
A second embodiment of the present invention will now be described with reference to
The basic concept of the second embodiment is similar to that of the first embodiment. Therefore, components equivalent to those in the first embodiment are indicated by the same reference numerals, and descriptions of those components will not be repeated.
The basic configuration of the optical pickup 1 is similar to that of the first embodiment. In the second embodiment, a light axis that extends from the deflecting mirror 5 to the RF servo-sensor 6 via the polarizing beam splitter 4 is disposed slantwise at an angle θ towards the inner periphery of the optical disc 10 with respect to a direction perpendicular to the moving direction of the optical pickup 1. Furthermore, the semiconductor laser 3 is disposed at the inner periphery side of the optical disc 10 relative to the light axis.
A recording/reproducing method will be described below.
A light beam emitted from the semiconductor laser 3 as divergent light enters the polarizing beam splitter 4 where the beam is split into reflected light and transmitted light. The light beam transmitted through the polarizing beam splitter 4 enters the monitor sensor 13 where a monitor output signal used for performing output control of the semiconductor laser 3 is generated. The light beam reflected by the polarizing beam splitter 4 is substantially collimated by the collimator 11. The light beam transmitted through the collimator 11 travels through the quarter-wave plate 12 and then to the deflecting mirror 5 where the light beam is reflected perpendicularly to the disc surface of the optical disc 10, whereby the light beam enters the objective lens 7. The light beam incident on the objective lens 7 is focused onto an information-recording layer (not shown) of the optical disc 10, whereby an information recording operation is performed.
The light beam reflected by the optical disc 10 is condensed by the objective lens 7 and is then transmitted through the polarizing beam splitter 4. The light beam transmitted through the polarizing beam splitter 4 travels through the sensor lens 9 so as to enter the RF servo-sensor 6 serving as a photo detector. Accordingly, reproduction of an information signal and generation of focusing and tracking servo-error signals are implemented.
The configuration and operation of the optical disc device 21 are the same as those of the first embodiment shown in
In the present invention, a light axis that extends from a light source to a deflecting mirror via a splitter is slanted towards an inner periphery of a disc-shaped recording medium with respect to a direction perpendicular to the moving direction of the optical pickup. Consequently, in comparison to the related art, the amount of protrusion from the plane of projection of the disc-shaped recording medium can be reduced, thereby achieving size reduction of the device.
In addition, a photo detector is disposed at the inner periphery side of the disc-shaped recording medium relative to the light axis extending from the light source to the deflecting mirror via the splitter. Thus, in comparison to a case where the photo detector is disposed at the outer periphery side relative to the light axis, the device can be reduced in thickness.
Alternatively, a light axis that extends from a photo detector to a deflecting mirror via a splitter can be slanted towards the inner periphery of the disc-shaped recording medium with respect to a direction perpendicular to the moving direction of the optical pickup. Consequently, in comparison to the related art, the amount of protrusion from the plane of projection of the disc-shaped recording medium can be reduced, thereby achieving size reduction of the device. In that case, a light source is disposed at the inner periphery side of the disc-shaped recording medium relative to that light axis. Thus, in comparison to a case where the light source is disposed at the outer periphery side relative to the light axis, the device can be reduced in thickness.
Furthermore, on the basis of a similar concept as the first embodiment, disposing the light source at the inner periphery side relative to the light axis extending from the photo detector to the deflecting mirror via the splitter allows for thickness reduction of the optical disc device as compared with a case where the light source is disposed line symmetrical to the light axis.
In the second embodiment, the splitter may alternatively be defined by a half mirror. In that case, the quarter-wave plate 12 is not necessary, which implies that the number of components can be reduced.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures and functions.
This application claims the benefit of Japanese Application No. 2006-203370 filed Jul. 26, 2006, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-203370 | Jul 2006 | JP | national |
