JPS6371938A - Optical disk device - Google Patents

Abstract

PURPOSE:To prevent noise from entering, which results from that a light spot traverses a track by interposing a light dividing element for dividing a part in which the quantity of light of both edges of a pit is changed from the reflected light into the advancing path of the reflected light and providing a pair of photosensors for tracking only for receiving the light divided by the light dividing element. CONSTITUTION:The part in which the quantity of light is changed by a diffraction produced according to the position of the light spot in the pit 12 of the reflected light from an optical disk 10 is deflected and the light is received only by the photosensors 30a, 30b for tracking. The quantity of light of the reflected light received on the light receiving surfaces of focussing photosensors 28a, 28b, 28c, 28d is not changed according to the position of the light spot in the pit 12. Therefore, even if an optical head 14 is moved diametrically of the optical disk 10 for changing a track and the light spot is traversed on the track, the noise related to the traverse of the track for the light spot does not enter a focussing error signal FE.

Description

Detailed Description of the Invention Technical Field The present invention relates to an optical disc device, and in particular, the distance between an optical head and an optical disc, in other words, the optical spot is determined from a focus error signal indicating the size of the optical spot irradiated from the optical head onto the optical disc. This relates to a technology for removing noise caused by track crossing.

Prior Art In order to read information stored on an optical disk, a light spot is irradiated from an optical head to a pit row of the optical disk, and the size of the light spot is controlled to a predetermined size, and the irradiation position of the light spot is In order to control the position of the light to a predetermined focus row, the reflected light from the front light distribution disk is placed on the light receiving surface of a plurality of optical sensors arranged adjacent to each other, using an astigmatic point whose condensing shape changes as it moves toward the optical axis direction. In addition to condensing the light with aberrations, the relative distance error of the optical head to the optical disk is detected by a change in the received light based on the astigmatism of the optical sensor, and the amount of received light is determined based on the diffraction of the reflected light of the optical sensor. There is an optical disk device of a type that detects a positional error of the optical head with respect to the pit based on the change.

Such an optical disk device usually has a convex lens and a cylindrical lens for forming astigmatism at the condensing point, and a light-receiving surface at the condensing point of the convex lens and the cylindrical lens.
An optical head is usually equipped with four optical sensors adjacent to each other with a cross border as a boundary, and a focusing error signal is created based on the difference between the sums of the outputs of two pairs of diagonally located optical sensors. However, a tracking error signal is created based on the difference between the signals output from one of the two pairs of optical sensors.

Problems to be solved by the invention However, in such a conventional optical disc device,
Since the optical sensor that outputs the signal for creating the tracking error signal and the optical sensor that outputs the signal for creating the focusing error signal are common, the optical head is moved so that the optical spot crosses the trunk of the optical disk. When the optical head is moved, noise caused by the optical spot crossing the track is mixed into the boss focusing error signal due to the relative distance error of the optical head with respect to the optical disk. This noise is close to the frequency of the focusing error signal, and is difficult to distinguish using a filter or the like.

Means for Solving the Problems The present invention has been made against the background of the above circumstances.
The gist of this method is to irradiate a light spot from an optical head to a pit row of an optical disc in order to read out information stored on the optical disc, and to control the size of the light spot to a predetermined size. In order to control the irradiation position in a predetermined pit row, the shape of the convergence of the reflected light from the optical disk changes as it moves in the optical axis direction onto the light receiving surfaces of a plurality of optical sensors arranged adjacent to each other. In addition to focusing each light with astigmatism,
A relative distance error of the optical head with respect to the optical disk is detected based on a change in the amount of light received by the optical sensor based on the astigmatism, and a change in the amount of light received based on the diffraction of the reflected light of the optical sensor detects the pit of the optical head. In an optical disc device of the type that detects a positional error relative to the optical disc, a light splitting element for dividing the reflected light from the optical disc into a portion where the amount of light changes due to diffraction at each edge of the focal point, from the reflected light, A pair of tracking optical sensors are provided which are inserted into the traveling path of the reflected light and which exclusively receive the light split by the light splitting element.

Operation and Effects of the Invention With this method, the light splitting element inserted in the traveling path of the reflected light from the optical disk allows the part of the reflected light whose scene changes due to the diffraction at both edges of the pit to be divided into two parts. The reflected lights are each split, and the split reflected lights are received by a pair of tracking optical sensors, and a tracking error signal is created from the output from the tracking optical sensors. For this reason, the optical sensor that outputs the output signal to create the focusing error signal receives reflected light from which the portion where the light intensity fluctuates due to diffraction has been removed, so the focusing error signal shows that the light spot is tracked. This eliminates the mixing of noise caused by crossing the line.

EXAMPLE Hereinafter, an example of the present invention will be described in detail based on the drawings.

In FIG. 1, on the surface of an optical disc 10, many rows of pits 12 in which news is recorded are formed in the circumferential direction, and the pits 12 form a so-called ring-shaped or spiral-shaped track.

The optical head 14 is mounted so as to be movable in a direction intersecting the track, and a light beam spot for reading information is directed from the optical head 14 to a predetermined pit 12.
It is designed to be irradiated to

The optical head 14 includes an objective lens 16 and a light splitting element 1.
8, a cylindrical lens 20 and a photosensor device 22 are provided. The objective lens 16 faces the surface of the optical disc 10, and receives reflected light from a light beam spot irradiated onto the pit 12 through the objective lens 16 by a light emitting element, a half mirror, etc. (not shown), and the optical sensor device 22.
Focus the light on.

The light splitting element 18 is a transparent flat plate 2, as shown in FIG.
4, a pair of triangular prisms 26a that are fixed on the flat plate 24 and become thicker toward the center of the flat plate 24,
26b, a part of the reflected light from the optical disk 10 is divided by a pair of prisms 26a and 26b and deflected in two directions, and the remaining part is transmitted in the same direction. The portion of the reflected light that is divided by the pair of prisms 26a and 26b is caused by diffraction due to both edges of the pit 12 when the light beam spot irradiated to the pit 12 shifts from the width center to one of the edges. This is the part where the amount of light changes due to the influence of That is, assuming that the direction parallel to the longitudinal direction of the pit 12 is the X direction, and the direction perpendicular to the longitudinal direction of the pit 12 is the Y direction, the pair of prisms 26a and 26b are respectively positioned in the Y direction, and the third As shown in the figure and FIG. 4, the light split by the pair of prisms 26a and 26b is deflected in the Y direction, and if the cylindrical lens 20 were not used, the light would be in the pattern shown in FIG. The light is focused.

As shown in FIG. 6, the optical sensor device 22 includes focusing optical sensors 28a, 28b adjacent to each other for receiving the remaining light that is not split by the light splitting element 18 out of the reflected light from the optical disc 10. 28 c,
28d, and a pair of tracking optical sensors 30a and 30b for respectively receiving the light beams split by the light splitting element 18. Note that among the areas where light is focused on the light-receiving surfaces of the tracking optical sensors 30a and 30b, the shaded areas are areas where the amount of light changes due to diffraction at the side edges of the pits 12. The above-mentioned focusing optical sensors 28 a, 28 b, 28 c, 2
8d are adjacent to each other with a boundary line parallel to the X direction and a boundary line parallel to the Y direction, which are perpendicular to each other, as boundaries,
It forms an approximately square shape as a whole.

The intersection of these mutually perpendicular boundary lines is the objective lens 16.
is located on the optical axis of the The tracking optical sensors 30a, 30b are focusing optical sensors 28a, 28b, 28c.

They are arranged at predetermined intervals on both sides of 28d in the Y direction.

The cylindrical lens 20 has a semi-cylindrical shape, that is, a semi-cylindrical shape, in which a cylinder is divided by a plane parallel to its axis, and allows light in a plane parallel to the axis to pass through as it is, but it passes light in a plane perpendicular to the axis. It is inserted between the light splitting element 18 and the optical sensor device 22. The cylindrical lens 20 is tilted so that the axis thereof passes through the optical axis of the objective lens 16 and is tilted at equal angles in the X direction and the Y direction. As a result, when the distance between the optical head 14 and the optical disk 10 is a predetermined constant distance, the focusing optical sensors 28a, 28b, 28C128 are activated as shown in FIG.
A circular spot is formed on the light receiving surface d. but,
If the actual distance becomes shorter or longer than the above-mentioned certain distance, an elliptical spot is formed as shown in FIGS. 9 and 10. That is, the optical system consisting of the objective lens 16 and the cylindrical lens 20 is configured such that the condensing pattern of the reflected light condensed on the light receiving surfaces of the focusing optical sensors 28 a, 28 b, 28 c, and 28 d does not converge to a single point. , so that astigmatism exists.

FIG. 7 shows a circuit for extracting a focusing error signal and a tracking error signal from the output signal of the optical sensor device 22, in which the output signals of the focusing optical sensors 28a and 28c are added in an adder 32.
Further, the output signals of the focusing optical sensors 28b and 28d are added in an adder 34, and the error between the output signal of the adder 32 and the output signal of the adder 34 is calculated by a differential amplifier 36 as a focusing error signal FE. It is now output. Further, the error in the output signals of the tracking optical sensors 30a and 30b is calculated by a differential amplifier 38, and then output as a tracking error signal TE.

In the optical disc device configured as described above, when the distance between the optical head 14 and the optical disc 1o becomes smaller or larger than when the distance is the constant distance, the focusing optical sensors 28a, 28b, 28C128d are formed on the light receiving surfaces. Since the focused light pattern changes from the circular shape shown in FIG. 8 to the elliptical shape shown in FIG. 9 or 10, the polarity of the focusing error signal is reversed. FIG. 11 shows how the focusing error signal FE changes with the error δ with respect to the predetermined optimum distance between the optical head 14 and the optical disk 10. Therefore, a control device (not shown) drives the optical head 14 or the objective lens 16 so that the focusing error signal FE becomes a predetermined constant value, and constantly forms a spot of an optimal size within the pit 12. .

Furthermore, if the light spot that should be located at the center of the width of the pit 12 shifts in the radial direction of the optical disk 10, the edge of the pit 12 on the shifted side causes diffraction of the light, which is received by the objective lens 16. The amount of reflected light that is let in is reduced. The portion of the reflected light that is reduced due to the above-mentioned diffraction is transmitted to the light splitting element 1.
a tracking optical sensor 30a,
The light is exclusively received by 30b. The amount of light received by the light-receiving surfaces of the pair of tracking optical sensors 30a and 30b is such that when one increases, the other decreases depending on the deviation of the optical spot within the pit 12.
The tracking error signal TE outputted from the pit 12 also shows a positive or negative value with zero when the optical spot is located at the center of the width within the pit 12. Therefore, a control device (not shown) moves the optical head 14 onto the optical disc so that the tracking error signal TE becomes a predetermined constant value.
Always position in the radial direction of 0.

Here, in this embodiment, as described above, of the reflected light from the optical disk 10, the portion whose light amount changes due to diffraction generated in relation to the position of the light spot in the pit 12 is transmitted to the light splitting element 18. Since the light is deflected by the focusing light sensors 28a and 28, the light is deflected by the tracking light sensors 30a and 30b.
b, the scene of the reflected light received by the light receiving surface of 28C128d does not change in relation to the position of the light spot within the pit 12. Therefore, even if the optical head 14 is moved in the radial direction of the optical disk 10 to change the track and the light spot is made to cross the track, the focusing error signal FE does not include the above-mentioned light as shown in FIG. Noise associated with spots crossing tracks is not introduced. Therefore, stable focusing control can be obtained. Incidentally, FIG. 12 is a diagram corresponding to FIG. 11 showing the conventional focusing error signal FE. In the figure, N is the noise associated with the track crossing of the light spot.

Next, another embodiment of the present invention will be described. In the following description, parts common to those in the above-described embodiments are designated by the same reference numerals, and the description thereof will be omitted.

In place of the above-mentioned light splitting element 18, as shown in FIG. 13, a transparent flat plate 44 and a pair of triangular prisms 46a fixed on the flat plate 44 and becoming thinner toward the center of the flat plate 44 are used. , 46b can be used.

According to the light splitting element 48, compared to the light splitting element 18, the direction of deflection of the portion of the reflected light from the optical disk 10 where the amount of light increases or decreases due to the influence of diffraction is reversed.

Further, as shown in FIG. 14, a reflective light splitting element 50 can be used. In the figure, the light splitting element 50 is
a flat plate 52 similar to the flat plate 24 of the light splitting element 18; a reflecting member 54a having the same external shape as the prisms 26a and 26b;
54b, and are arranged in the opposite direction to that shown in the embodiment of FIG. Therefore, portions of the reflected light from the optical disk 10 whose light intensity increases or decreases due to the influence of diffraction are divided by the reflecting members 54a and 54b, deflected in a direction substantially perpendicular to the optical axis, and received by the tracking optical sensors 56a and 56b, respectively. It will be done.

Furthermore, as shown in FIG. 15, the cylindrical lens 20 may be arranged with its axial direction aligned with the Y direction. In this case, in order to obtain the focusing error signal FE, the focusing optical sensors 60a and 6 shown in FIG.
0b, 60c, and 60d are used. The focusing optical sensors 60a, 60b, and 60C160d are arranged adjacent to each other with boundary lines that are inclined at equal angles to the Y axis and perpendicular to each other. In this way, the focusing optical sensors 60a, 6 in FIG.
The reflected light is focused as shown on 0b, 60c, and 60d and on the tracking optical sensors 30a and 30b. Note that the hatched portions in the condensing areas on the tracking optical sensors 30a and 30b indicate portions where the light fit changes due to diffraction, as in the previous embodiment.

Although one embodiment of the present invention has been described above based on the drawings,
The invention also applies in other aspects.

For example, in the optical head 14 of the above embodiment, the configuration related to tracking and focusing has been described, but other optical elements such as a light source and a half mirror for irradiating a light spot onto the optical disk lo may be appropriately arranged. Ru.

Moreover, optical elements such as optical fibers, prisms, mirrors for converting the direction of light, and lenses for improving optical performance may be appropriately disposed between the optical elements.

Note that the above-mentioned embodiment is merely one embodiment of the present invention, and various modifications may be made to the present invention without departing from the spirit thereof.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the configuration of an embodiment of the present invention. FIG. 2 is a perspective view showing the light splitting element of FIG. 1 in detail. FIGS. 3 and 4 are diagrams showing the light condensing action of the light splitting element shown in FIG. 2, respectively. FIG. 5 is a diagram showing a light condensing pattern in the apparatus of FIG. 1. FIG. 6 is a diagram showing the optical sensor device in the apparatus of FIG. 1. FIG. 7 is a diagram showing a circuit for converting the output signal of the optical sensor device of FIG. 6 into a focusing error signal and a tracking error signal. FIGS. 8, 9, and 10 are diagrams respectively showing light condensing patterns on the focusing optical sensor that change as the distance between the optical disk and the optical head changes in the embodiment shown in FIG. be. FIG. 11 is a diagram showing changes in the focusing error signal as the distance between the optical disk and the optical head changes, obtained in the embodiment shown in FIG. FIG. 12 is a diagram corresponding to FIG. 11 of a conventional device. FIG. 13 is a diagram corresponding to FIG. 6 in another embodiment of the present invention. 14 and 15 are diagrams corresponding to FIG. 1 in other embodiments of the present invention, respectively. FIG. 16 is a diagram corresponding to FIG. 6 in the embodiment of FIG. 15. 10: Optical disk 12: Pit 14: Optical head 18. 48. 50: Light splitting element 30a, 30b, 56a, 56b Optical sensor for tracking Applicant: Brother Industries, Ltd. Figure 1 Figure 61 Figure 7 Figure 8 Figure 9 Figure 10 Figure 14 Figure 15 Figure 16

Claims (1)

[Claims] In order to read information stored on an optical disk, a light spot is irradiated from an optical head to a pit row of the optical disk, and the size of the light spot is controlled to a predetermined size, and the light spot is In order to control the irradiation position of the spot in a predetermined pit row, the reflected light from the optical disk is focused onto the light receiving surfaces of a plurality of optical sensors arranged adjacent to each other, and the condensing shape changes as it goes in the optical axis direction. The relative distance error of the optical head with respect to the optical disk is detected based on the change in the amount of light received by the optical sensor based on the astigmatism, and the error is based on the diffraction of the reflected light from the optical sensor. In an optical disc device of the type that detects a positional error of the optical head with respect to the pit based on a change in the amount of received light, a portion of the reflected light from the optical disc whose light amount changes due to diffraction at both edges of the pit is used as the reflected light. A light splitting element is inserted into the traveling path of the reflected light, and a pair of tracking optical sensors are provided to exclusively receive the light split by the light splitting element. optical disk device.