JPS6224859B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus servo device for an optical information reading device, and more particularly to a focus servo device for an irradiation light converging lens in an information reading device for an optical video disc.

As shown in FIG. 1A, which is a partial plan view, and FIG. Pit 17 consisting of
The pits (recesses) are arranged to form concentric or spiral tracks, and information is recorded by the length and spacing of these pits 17. In order to increase the reflectance of light, a reflective film 7 made of, for example, a vapor-deposited film of aluminum is applied to the surface on which the pits 17 are arranged, and a protective film 18 is further applied thereon.

Information is read from the disk by entering light from the surface of the disk base 6 on the side where the pits 17 are not present and demodulating the reflected light from the reflective film 7, which is modulated depending on the presence or absence of the pits 17. be exposed. Such an information recording disk reading device is provided with a so-called lens focus servo device in order to always accurately focus incident light on the information recording surface of the disk.

FIG. 2 shows a schematic diagram of a conventional focus servo device, in which a light beam irradiated from a light source 1 such as a helium neon laser passes through a collimator lens 2, a beam splitter 3, and a movable mirror 4. , is focused very close to the information recording surface 7 of the disk 6 by the converging lens 5. The disk 6 is rotated at high speed by a motor 14. The reflected light that has read the information recorded on the disk 6 follows the opposite path, is separated by the beam splitter 3, and is converted into an electrical signal by a photoelectric conversion element.

It is impossible to manufacture the disk substrate 6 completely flat, and when it is attached to the shaft of the motor 14, it is usually attached at an angle. Therefore, the recording surface 7 will move up and down as the disk 6 rotates. In order to read information correctly, the converging lens 5 must move up and down following the above-mentioned fluctuations of the recording surface, and must always converge the light beam very close to the recording surface 7. For this purpose, a cylindrical lens 8 is placed on the way where the reflected light from the disk 6 is converged by the converging lens 5, and a light receiving element 9 is placed after that.
The light receiving elements 9 are 9a, 9 as shown in FIG.
Consisting of four independent light receiving elements b, 9c, and 9d, straight lines passing through the centers of the light receiving surfaces of the light receiving elements 9a, 9b and 9c, 9d are at right angles to each other, and one of the straight lines is at the center of the cylinder of the cylindrical lens 8. It is placed in the same direction as the axis. Taking advantage of the property that the position on the optical axis where the bundle of rays passing through this lens 8 converges is different in a plane including the generatrix of this cylindrical lens 8 and in a plane orthogonal thereto, the four light-receiving elements 9 are By detecting and measuring the shape of the beam of light projected onto the light receiving surfaces of the light receiving elements 9a to 9d,
The relationship between the recording surface 7 and the focal position of the converging lens 5 is determined.

In other words, when the convergence point of the incident light by the lens 5 is precisely located on the recording surface of the disk, the reflected light passes through the cylindrical lens 8 and forms an approximately square (fourth
The light-receiving surface of the light-receiving element 9 is arranged at the position shown in FIG. b). In that state, the outputs Va, Vb, and
Vc and Vd are each equal, so the following equation holds.

Va + Vb = Vc + Vd Therefore, as shown in Figure 3, Va + Vb and Vc + Vd
The output V of the differential amplifier 10 having each differential input as V becomes zero. As a result, the output of the amplifier 11 and the output of the lens driving device 12 become zero, so the position of the lens 5 is not varied.

Next, as shown in FIG. 5, when the incident light is converged at the rear of the recording surface 7, that is, when the distance between the recording surface 7 and the converging lens 5 is short, the shape of the light ray on the light receiving surface of the light receiving element 9 is It becomes like b, and then,
Va+Vb>Vc+Vd, and the output of the differential amplifier 10 becomes V<O.

On the other hand, when the incident light is converged at the front of the recording surface 7 as shown in FIG. >O. Therefore, if Z=O when the recording surface 7 is at the position where the incident light is converged and Z>O when it approaches the converging lens, the output V of the differential amplifier 10 will be as shown by the dotted line 20 in FIG. The output of the differential amplifier 10 is amplified by the amplifier 11 as an error signal, and then converted into a displacement by the drive device 12. Automatic focus control is performed by controlling the position of the converging lens 5 via the holder 13.

In the focus servo device as described above, when the movable recorder 4 or the converging lens 5 is correctly positioned and the convergent light is correctly projected onto the track of the pit 17, that is, when tracking is performed correctly, Pitt 17
The track is the light receiving element 9a, 9b or 9
The light is projected as a dark stripe on a straight line passing through the centers of the light receiving surfaces 9d and 9d, and as long as the converging lens 5 is in focus, the output of the light receiving element 9 is zero. However, if tracking is not done correctly,
A difference occurs between Va+Vb and Vc+Vd, resulting in an error signal for the light receiving element 9, which adversely affects the focus servo.

SUMMARY OF THE INVENTION An object of the present invention is to provide a focus servo device that solves the above problems and enables highly accurate focus servo.

The present invention will be explained in detail below.

The focus servo device of the optical information reading device according to the present invention is basically the same as the conventional device shown in FIG. It forms an angle of 45° with respect to the track direction arrow A, that is, with respect to the direction of rotation of the disk 6. In addition, the light receiving elements 9a and 9b
Or the straight line passing through the centers of the light receiving surfaces of 9c and 9d is
It is in the same direction as the axis 8a of the cylindrical lens 8, and the track direction forms an angle of 45° with the straight line as shown in FIG.

Therefore, the reflected light beam passes through the light receiving element 9 as shown at 20.
Projected onto a, 9b, 9c, 9d, pit 17
A dark spot appears at position 17'.

In such a configuration, if tracking is not performed correctly and the track position shifts as shown in No. 10, there will be no difference in the outputs of Va + Vb and Vc + Vd, and as long as focusing is performed correctly, Va + Vb = Vc + Vd. becomes.

Therefore, according to the present invention, a desired focus servo can be performed even if tracking is incorrect, and furthermore, an error signal for tracking servo can be obtained using the Va+Vd and Vb+Vc signals. It is.

On the other hand, in the above-described focus servo device, the positional accuracy of the light-receiving surface of the light-receiving element 9 and the cylindrical lens are strictly required, and the magnitude of the detected error signal cannot be said to be sufficiently large.

Therefore, in the focus servo device according to the present invention, when the incident light is accurately focused on the principal point 30 of the cylindrical lens 8 on the disk recording surface 7 as shown in FIG. The cylindrical lens is placed at or near the position.

The distance between the cylindrical lens 8 and the light receiving element is appropriately selected. The positional relationship of each other component is as follows.
It is the same as that shown in the figure, and its explanation will be omitted.

Therefore, as shown in FIG. 12, when the incident light is accurately focused on the recording surface, the shape of the beam of light on the light receiving surface of the light receiving element 9 is circular as shown in b, and Va+Vb=Vc+Vd. The following relationship holds true, and therefore the output of the differential amplifier 10 becomes zero. the result,
The drive device 12 does not operate and the position of the converging lens 5 is not varied.

Next, when the lens 5 and the recording surface approach each other as shown in FIG.
The equation Vd holds true, so the output V of the differential amplifier 10 satisfies V<O.

On the other hand, as shown in Fig. 14, when the converging lens 5 and the recording surface 7 are separated, as shown in b
Since Va+Vb<Vc+Vd, the output V of the differential amplifier 10 becomes V>O.

Therefore, in the focus servo system according to the present invention, a relationship between the distance Z and the output V of the differential amplifier 10 as shown by the solid line 21 in FIG. 7 is obtained.

Moreover, each element 9a, 9b of the light receiving element 9,
If the size of the shape of the beams projected onto the beams 9c and 9d is determined as shown in FIG. 15, the conventional method shown in FIG.
It will look like the figure. The change in the size of the shape of this light beam becomes the output of the light receiving element 9, and the larger the amount of change (Dcd-Dab), the larger the output of the differential amplifier 10, and the method according to the present invention is better than the conventional method. I know it's good. Furthermore, if a lens with a magnification of approximately 30 to 40 times is used as the convergent lens 5, even if the position of the principal point of the cylindrical lens 8 shifts by 1 mm in the optical axis direction, the distance between the reflective film 7 and the convergent lens 5 will be approximately Since the deviation is only 1 μm, there is no need to assemble the cylindrical lens 8 with particularly high precision.
Furthermore, as is clear, the distance between the cylindrical lens 8 and the light receiving element 9 does not require precision.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the shape of a video disc, where a is a partial plan view, b is a partial sectional view, Fig. 2 is a schematic diagram of a conventional focus servo device, and Fig. 3 is a photodetector and differential amplifier. Figure 4a shows the relationship between the cylindrical lens and the light-receiving element when the convergent lens is focused on the recording surface in Figure 2, and Figure 4b shows the relationship between the cylindrical lens and the light-receiving element when the convergent lens is focused on the recording surface in Figure 2; Figure 5a shows the relationship between the cylindrical lens and the light-receiving element when the recording surface approaches the converging lens in Figure 2, and Figure 5b shows the shape of the ray bundle on the light-receiving surface. , Figure 6a shows the relationship between the cylindrical lens and the light-receiving element when the recording surface is separated from the converging lens in Figure 2, b shows the shape of the light beam on the light-receiving surface, and Figure 7 shows the difference. The eighth figure shows the relationship between the dynamic force and the position of the recording surface and the converging lens.
10 are diagrams showing the shape and position of a light beam projected onto a light receiving element in a focus servo device according to the present invention, FIG. 11 is a schematic diagram showing another embodiment of the present invention, and FIG. Figure a shows the relationship between the cylindrical lens and the light-receiving element when the converging lens is focused on the recording surface in Figure 11, b shows the shape of the light beam on the light-receiving surface, and Figure 13 a Fig. 11 shows the relationship between the cylindrical lens and the light receiving element when the recording surface approaches the converging lens, and b
is a diagram showing the shape of the light beam on the light receiving surface, Figure 14a
shows the relationship between the cylindrical lens and the light-receiving element when the recording surface is separated from the convergent lens in the 11th section, and b
15 is a diagram showing an example of the shape of a ray bundle on the light-receiving surface of a light-receiving element, and FIG. 16 is a diagram showing the shape of a ray bundle on the light-receiving surface of a conventional device. Figure 17 shows the relationship between the distance and the size of the shape of the light beam on the light receiving surface, and FIG. 17 shows the relationship between the distance between the recording surface and the converging lens and the size of the shape of the light beam on the light receiving surface in the present invention. FIG. Explanation of symbols of main parts, 5...Convergent lens, 6
... Recording medium, 7 ... Recording surface, 8 ... Cylindrical lens, 9 ... Light receiving element, 10 ... Differential amplifier, 11
...Amplifier, 12...Driver, 30...Principal point of lens.

Claims (1)

[Scope of Claims] 1. A converging lens for converging irradiated light onto the recording surface of a recording disk having a recording surface having concentric or spiral information recording tracks, and reflection emitted from the recording surface and passing through the converging lens. a cylindrical lens that transmits light; a light receiving unit that receives the light that has passed through the cylindrical lens; and a focus of the converging lens that is adjusted to be positioned on the recording surface of the recording medium in response to an output of the light receiving unit. means, the principal point of the cylindrical lens is placed at or near a position where the reflected light is converged by the converging lens, and the light receiving means emits from the position where the reflected light is converged, and the principal point of the cylindrical lens A focus servo device for an optical information reading device, which is characterized in that it receives divergent light that has passed through. 2. The light receiving means is composed of four independent light receiving elements arranged symmetrically with respect to two orthogonal dividing lines, and arranged so that one of the dividing lines is substantially parallel to the direction of the information recording track. A focus servo device according to claim 1, characterized in that: 3. The focus according to claim 1 or 2, wherein the cylindrical axis of the cylindrical lens is arranged at an angle of approximately 45 degrees with respect to the direction of the information recording track. Servo device.