JPS6093647A - Reproducing optical system control means of optical type disc player - Google Patents

Abstract

PURPOSE:To execute stable tracking servo by moving an objective lens and a beam splitter out of a reproducing optical system in the tracking direction of a disc by an equal distance in accordance with a servo control signal. CONSTITUTION:When the objective lens 5 and the beam splitter 3 are moved in the tracking direction by DELTAx, a branch point on which the optical path of light flux from a collimator lens 2 is converted by the beam splitter 3 is moved from a point (a) to a point a', i.e. by a distance DELTAx, because a polarized light separating plane 3a is moved as shown by the dashed line. Since the objective lens 5 is also moved by the same distance DELTAx in accordance with the movement of the beam splitter 3, the center of light flux made incident on the objective lens 5 coincides with the center of the lens 5, so that the light distribution of refected light from a disc 6 is prevented from remarkable change.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reproduction optical system control mechanism for an optical disc player.

Conventionally, a reproducing optical system for an optical disc player having a configuration as shown in FIG. 1 has been known. In the same figure, reference numeral 1 denotes a semiconductor laser as a light source. The laser light emitted from the semiconductor laser 1 is converted into a parallel beam by a collimating lens 2, and this parallel beam is reflected by the polarization separation surface 3a of the beam splitter 3 to convert the optical path. be done. Then, this optical path-converted light flux is transferred to a quarter-wave plate 4.
, and is imaged onto the information recording surface of the disk 6 by the objective lens 5. Also, this disk 6
The reflected light returns to the objective lens 5 and passes through the quarter-wave plate 4.
and reaches the beam splitter 3. Furthermore, this reflected light passes through the polarization separation surface 3a of the beam splitter 3 due to the polarization effect of the quarter-wave plate 4, and is condensed by the condenser lens 7, and the optical path is split into two by the half mirror 8. be done. A cylindrical lens 9 is arranged on one of the optical paths, and the focused light reaches the light-receiving surface of the light-receiving element 1o. A signal for detecting the amount of deviation from the recording surface can be obtained. Based on this signal, servo control of the objective lens 5 in the focusing direction (direction of arrow a in FIG. 1) can be performed. Further, the focused light along the other optical path divided by the half mirror 8 reaches the light receiving element 11, and from this light receiving element 11, the light is transmitted from the light receiving element 11 in order to accurately rack the pitch 1 row on the information recording surface of the disk 6. Move the objective lens 5 in the tracking direction (direction indicated by the arrow in Figure 1)
A signal for servo control can be obtained.

The method of obtaining control signals for the tracking servo in this way is generally called the far-field method.
Although this method has the advantage of reducing the number of optical system components compared to a three-beam method using a diffraction grating, the image forming position of the objective lens 5 may be affected by disturbances such as eccentricity of the disk 6. When the center of the pit row shifts, for example, if the objective lens 5 is moved to the normal tracking position of the pit row by servo operation, the optical axis of the reflected light from the disk 6 will shift and the light intensity distribution on the light receiving element ll will be significantly changed. The disadvantage was that it fluctuated. That is, as shown in FIG. 2, when the servo control signal is obtained and the objective lens 5 is moved by the amount of movement ΔX to the position shown by the broken line, the position of the beam splitter 3 remains unchanged, so the center of the light beam incident on the objective lens is also shifted from the center of the previous lens, so the center of the beam of reflected light that is reflected from the information recording surface of the disk 6 and returns to the objective lens 5 is 2 points from the center of the beam of light incident on the objective lens 5.
The beam shifts by an amount of 8X, and the center of the beam of light focused by the condenser lens 7 also changes accordingly. Furthermore, in the case of the far-field method, generally, the imaging position of the light converged by the condenser lens 7 is slightly shifted from the light receiving surface of the light receiving element 11, so the deviation of the center of the light beam of the converged light by the condenser lens 7 is This results in a significant change in the light amount distribution on the light receiving surface of the light receiving element 11. In addition, since the beam of light incident on the objective lens 5 normally has a Gaussian distribution, if the center of the beam of light deviates from the center of the lens, the distribution of the amount of light reflected from the disk 6 will change significantly. Naturally, such a change in the light amount relationship has a negative effect on the tracking servo control signal, which in turn leads to instability of the water control.

In order to eliminate such drawbacks, a method has been proposed in which instead of servo control of only the objective lens 5, servo control is performed for the entire reproduction optical system. However, with this method, the objects to be controlled for high-speed control are wide-ranging, and the drive system for that purpose is naturally large, resulting in a limited range of application and a significant increase in costs. was there.

This invention has been made to eliminate these conventional drawbacks, and by suppressing as much as possible the changes in the light quantity relationship due to the driving of the controlled object, it is possible to perform stable tracking servo and to achieve this with a simple configuration. An object of the present invention is to provide a playback optical system control mechanism for an optical disc player that can be realized in the following manner.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 3 shows the main parts of the reproducing optical system for explaining the state of the optical path, and is similar to FIG. 2, and other details of the structure are as shown in FIG. 1. Therefore, the same reference numerals are used for each component to avoid duplication in the explanation of omitted components and the explanation of components similar to the conventional example.

In the configuration of the present invention, the objective lens 5 and the beam splitter 3 are movable by equal distances in the 1-racking direction of the disk 6 in response to a servo control signal. This moving direction is also a direction parallel to the optical path of the parallel light beam whose optical path has been changed by the polarization separation surface 3a of the beam splitter 3. Furthermore, the angle between the light beam entering the polarization separation surface 3a of the beam splitter 3 from the collimating lens 2 and the polarization separation surface 3a is ll1845°, and the angle between the light beam of this incident light and the light beam reflected by the polarization separation surface 3a is 1845 degrees. The angle formed is approximately a right angle.

Because of this configuration, if the objective lens 5 and beam splitter 3 do not move, the reflected light that is emitted from the collimating lens 2 and reflected by the polarization separation surface 3a of the beam splitter 3 passes through the objective lens 5. disk 6
The reflected light returns along the same optical path as the incident light and travels straight toward the condenser lens 7. That is, the light amount distribution on the light receiving surface of the light receiving element 11 does not change.

Then, the objective lens 5 and beam splitter 3
Assuming that the light beam from the collimating lens 2 is moved by 8X in the racking direction, the beam splitter 3 changes the optical path of the light beam from the collimating lens 3, and the branch point is shifted from point i because the polarization separation surface 3a has moved as shown by the broken line. Move to point 7', ie by distance ΔX. On the other hand, in this case beam splitter 3
As the objective lens 5 moves, the objective lens 5 also moves by the same distance ΔX, so the center of the light flux incident on the objective lens 5 coincides with the center of the lens, and the light flux incident on the objective lens 5 has a predetermined light intensity distribution. Even if it does, it will not have any effect. Note that since the position of the condenser lens 7 remains unchanged, the center of the light beam incident thereon will be shifted by ΔX from the center of the lens, but this shift amount ΔX is 28X compared to 28X in the conventional case. Since the change in the amount of light reaching the light-receiving element 1 is also 1/1, the amount of change in the amount of light reaching the light-receiving element 1 is also significantly reduced.

As explained above, according to the present invention, the objective lens and beam splitter of the reproduction optical system can be moved by the same distance in the tracking direction of the disk according to the servo control signal, so that The control signal can be obtained more accurately than in the conventional configuration, and more stable servo operation can be ensured. Further, since the objective lens and the beam splitter are simply controlled so as to drive them, there is no structural complexity compared to the conventional example, and an increase in cost can be avoided.

[Brief explanation of drawings]

FIG. 1 is an optical system layout diagram explaining a conventional reproduction optical system control mechanism, FIG. 2 is a main part optical system layout diagram explaining optical path changes due to movement of an objective lens, and FIG. 3 is a reproduction diagram according to the present invention. FIG. 3 is a layout diagram of the main optical system for explaining the optical system control mechanism for use in the optical system. ■... Light source, 2... Collimating lens, 3... Beam splitter, 5... Objective lens, 6 - Disk,
7... Condensing lens, 11... Light receiving element. Figure 1 10 Figure 2 Figure 3

Claims (1)

[Claims] a collimating lens that converts the light emitted from the light source into a parallel beam; a beam splitter that converts the optical path of the beam from the collimating lens; an objective lens that forms an image of the beam whose optical path has been changed by the beam splitter on a disk; A reproducing optical system that focuses the reflected light and irradiates it onto a light-receiving element for information detection, and a condensing lens that is arranged on an extension of the straight optical path formed by the objective lens and the beam splitter. In an optical system control mechanism for playback of an optical disc player configured to be controllable by obtaining a tracking servo control signal based on the output of an element, a parallel light beam from the collimating lens is converted into an optical path at right angles by the beam splinter. and the objective lens and the beam splitter are moved an equal distance from each other in a direction in which the objective lens and the beam splitter are tracking the disk and perpendicular to the optical path of the light beam whose optical path has been changed by the beam splitter, in accordance with the control signal. An optical system control mechanism for playback of an optical disc player, characterized by: