JP2700575B2 - Optical pickup device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical pickup device for positioning a light beam on a recording track formed on an optical storage medium such as an optical disk.

[Prior Art] In recent years, an optical disk storage device using an optical disk having an optical storage medium formed in a disk shape as a storage medium has been proposed. In this optical disk, the data storage surface has, for example, a track width of about 1 μm and a track pitch of 2 μm.
A recording track having a minute structure is formed, and the recording track is irradiated with a laser beam having a spot diameter of about 1 μm.

Then, while rotating the optical disk, the data is stored by modulating the intensity of the laser beam corresponding to the data to be recorded, and the fluctuation of the level of the laser beam reflected from the data storage surface is detected. Is playing back the stored data.

The portion that follows the laser beam to the recording track and narrows the spot diameter to a predetermined size is the optical pickup, and a schematic configuration example is shown in FIG.

In FIG. 1, a laser beam output from a semiconductor laser device 1 is converted into a parallel beam by a coupling lens 2, transmitted through a polarization beam splitter 3,
After being polarized by the objective lens 5, the image is focused on the recording track of the optical disk 6 by the objective lens 5.

The reflected light from the optical disk 6 is again transmitted to the objective lens 5.
After being converted into parallel light through the, the light is further polarized by the 波長 wavelength plate 4, thereby reflected by the polarization beam splitter 3 and imaged by the lens 7 on the quadrant light receiving element 8.

Further, the objective lens 5 is provided with a tracking mechanism for positioning the objective lens 5 in the radial direction of the optical disc 6 and a focusing mechanism for focusing. Hereinafter, the tracking mechanism and the focusing mechanism are collectively referred to as an objective lens moving mechanism.

Then, a servo control unit (not shown) detects a position error and a focus error of the laser beam on the recording track based on the output signal of the four-division light receiving element 8, and according to the detection signal of the error, the tracking mechanism and The focusing mechanism is controlled, and the objective lens 5 is moved in a direction to reduce the position shift and the focus shift of the laser beam on the recording track. Further, recording data is extracted from the output signal of the four-divided light receiving element 8.

The focusing mechanism attached to the objective lens 5 generally uses a lens holder that supports the objective lens 5 that reciprocates in the focusing direction by a linear motor, a voice coil, or the like. As the tracking mechanism, a mechanism that reciprocates in an arc shape in the tracking direction, including a focusing mechanism, using a linear motor, a voice coil, or the like is used.

FIG. 9 shows an example of an objective lens moving mechanism having such a tracking mechanism.

In FIG. 1, the objective lens 5 is housed in a lens holder 20, and the lens holder 20 has focus bobbins 21, 22 around which a driving coil constituting a linear motor serving as a driving source of a focusing mechanism is wound. Also, track bobbins 23 and 24 around which drive coils constituting a linear motor serving as a drive source of the tracking mechanism are wound are attached.

The yokes of the magnetic circuit members 26 and 27 formed integrally with the base 25 are inserted into the focus bobbins 21 and 22,
Also, the yokes of the magnetic circuit members 28, 29 formed integrally with the base 25 are inserted into the track bobbins 23, 24.

The lens holder 20 includes two sets of parallel leaf springs 31, 32,
33 and 34, it is resiliently supported by the rotary supporter 35.
The leaf spring 32 facing the leaf spring 31 is at a position that cannot be seen in the drawing.

The rotation supporter 35 is rotatably supported by a support mechanism (not shown) between a support member 36 rising from the base 23 in an inverted L-shape and the base 25.

A light emitting diode 38 is attached to the rotation supporter 35 via a holding member 37, and a semiconductor position detecting element that receives output light from the light emitting diode 38.
39 is attached to the base 25 via a support member 40.

With the above configuration, when a drive current is supplied to the drive coils wound around the focus bobbins 21 and 22, the lens holder 20 moves in the focusing direction according to the polarity (direction) and strength thereof, and thereby the objective lens 5 in the focusing direction are determined. When a drive current is supplied to the drive coils wound around the track bobbins 23 and 24, the lens holder 20 rotates in the tracking direction around the pins 37 and 39 of the rotation supporter 35 according to the polarity and strength thereof, Thereby, the position of the objective lens 5 in the tracking direction is determined.

Thus, the objective lens 5 is moved in the focusing direction and the tracking direction, respectively.

When the lens holder 20 rotates in the tracking direction, the spot formed by the output light from the light emitting diode 28 moves on the light receiving surface of the semiconductor position detecting element 39, thereby moving the objective lens relative to the reference position. A displacement of the moving mechanism in the tracking direction is detected.

Then, the objective lens moving mechanism is controlled so that the optical axis of the laser beam coincides with the optical axis of the objective lens 5. Further, when a large acceleration is applied, for example, when the optical pickup device including the objective lens moving mechanism is rapidly moved in the tracking direction by a seek mechanism (not shown), the displacement in the tracking direction becomes a value within a certain range. The servo control is performed to prevent an obstacle such as damage to the objective lens moving mechanism.

[Problems to be Solved by the Invention] However, such a conventional apparatus uses a very expensive semiconductor position detecting element to detect a displacement of the objective lens moving mechanism in the tracking direction with respect to the reference apparatus. There has been an inconvenience that the apparatus cost is high.

In addition, since the spot diameter of the light received by the semiconductor position detecting element needs to be within a certain range, it is necessary to use an expensive light emitting diode having a small variation in the emission angle, and the device cost is increased. .

The present invention has been made in view of such circumstances, and has as its object to provide an optical pickup device that can reduce the device cost.

[Means for Solving the Problems] The present invention provides a light emitting element interlocked with the rotation of an objective lens moving mechanism, a cover member provided with a window that covers the light emitting element and has a window for reducing output light from the light emitting element. A light-receiving element that receives light emitted from the cover member and has a light-receiving surface divided into two by a dividing line perpendicular to the moving direction of the input light, and light-receiving elements obtained from the two divided surfaces of the light-receiving element. Signal processing means for detecting displacement of the objective lens moving mechanism in the tracking direction based on the signal difference signal is provided.

[Operation] Therefore, in order to detect the displacement of the objective lens moving mechanism in the tracking direction with respect to the reference position, the light receiving element having the light receiving surface divided into two is used, so that the apparatus cost can be reduced. Further, since the output light from the light emitting element is narrowed down by the cover member, a light emitting element having a large variation in the emission angle can be used, and the apparatus cost can be further reduced.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows an objective lens moving mechanism according to one embodiment of the present invention. In this figure, the same parts as those in FIG. 10 and corresponding parts are denoted by the same reference numerals.

In the figure, a cover member 45 covers the light emitting diode 38, and has a window 46 for restricting the light output from the light emitting diode 38.

A light receiving element 46 having a light receiving surface divided into two is attached to the base member 25 via a holding member 40 at a position where the light emitted from the light emitting diode 38 narrowed by the window 46 is received.

Also, as shown in FIG.
Is such that the dividing line LN that divides the light receiving surface 48 into two is parallel to the direction orthogonal to the direction in which the light emitted from the light emitting diode 38 moves on the light receiving surface 48 when the objective lens moving mechanism rotates in the tracking direction. And so on.

Therefore, as shown in FIGS. 3A to 3C, the spot SP formed by the light emitted from the light emitting diode 38 on the light receiving surface 48 moves according to the displacement of the objective lens moving mechanism in the tracking direction. Thereby, the light receiving surface of the light receiving element 47
Since the amounts of received light 48a and 48b are biased, it is possible to detect the displacement of the objective lens moving mechanism in the tracking direction with respect to the reference position.

For example, as shown in FIG. 4, the light receiving signal Sa from the light receiving surface 48a is applied to the positive input terminal of the differential amplifier 50, and the light receiving surface 48b
Is applied to the minus input terminal of the differential amplifier 50 to form a difference signal SE corresponding to the difference between the received light signal Sa and the received light signal Sb. This difference signal SE is shown in FIG. Thus, it changes according to the displacement in the tracking direction.

Here, the objective lens moving mechanism moves back and forth by several tens of μm from the reference position in the tracking direction, and the moving range DL of the spot SP is very small.
Then, the difference signal SE changes linearly. In this case,
With the objective lens moving mechanism moving to the reference position,
The position of the spot SP with respect to the light receiving surface 48 is set so that the value of the difference signal SE becomes zero.

Therefore, the displacement of the objective lens moving mechanism in the tracking direction can be detected by using the light receiving element 47 which is much cheaper than the semiconductor position detecting element used in the conventional apparatus.

By the way, if a light emitting diode 38 having a large variation in the emission angle can be used, a cheaper light emitting diode 38 can be used, so that the apparatus cost can be further reduced.

For example, a light emitting diode whose emission angle varies about twice
When using No. 38, as shown in FIGS. 6 (a) and (b), the radius of the spot SP1 when the emission angle is the smallest is r
Then, the radius of the spot SP2 when the emission angle is the largest is 2r. Therefore, the area of the spot SP2 is four times the area of the spot SP1.

On the other hand, the total sum for light reception on the light receiving surface 48 is constant, and
Assuming that the output intensities of the spots SP1 and SP2 are broad, the light quantity per unit area is about four times as large for the spot SP1 as for the spot SP2.

Here, when the spots SP1 and SP2 move by a small distance Δx from the center position of the light receiving surface 48, the light receiving surface 48a and the light receiving surface 48 have an area S1 and S2 indicated by oblique lines before and after that.
The area of the spots SP1 and SP2 received at b changes.

 The areas S1 and S2 are respectively expressed as follows.

S1 = 2r · Δx, S2 = 4r · Δx other hand, as described above, the light amount A ₁ per unit area of the spot SP1, the light quantity per unit area of the spot SP2 A ₂
Therefore, before and after the spots SP1 and SP2 move by a small distance Δx from the center position of the light receiving surface 48, the changes ΔP ₁ and ΔP ₂ in the light receiving amounts of the light receiving surfaces 48a and 48b are as follows, respectively. become.

_{ΔP1 = S1 · A 1 = 2r} · Δx · 4A 2 = 8r · Δx · A 2 ΔP 2 = S2 · A 2 = 4r · Δx · A 2 Therefore, [Delta] P ₁ is twice the [Delta] P _2, the spot diameter is small In the case, the change in the amount of received light is larger, and therefore, the rate of change of the difference signal SE is larger.

From the above, the spot SP formed on the light receiving surface 48 is
It is desirable to set the diameter as small as possible.

Therefore, as shown in FIG. 1, the light emitting diode 38 is covered with a cover member 45, and the light emitting diode 38 is
The diameter of the spot SP can be kept substantially constant even when the emission angle of the light emitting diode 38 is large by narrowing the light emitted from the light emitting diode 38.

By controlling the sum signal of the light receiving signal Sa from the light receiving surface 48a and the light receiving signal Sb from the light receiving surface 48b to have a constant value, the difference signal SE takes a value within a certain range. Therefore, the operation of the control system using the difference signal SE is stabilized.

Further, as described above, the light emitting diode 38 is
7, prevents the flare light of the light emitting diode 38 from reflecting on the surface of the base member 25 and entering the light receiving surface 48 of the light receiving element 47, thereby adversely affecting the signal system. can do.

As described above, according to the present embodiment, the displacement of the objective lens moving mechanism in the tracking direction can be detected using the light receiving element having the light receiving surface divided into two, so that the apparatus cost can be reduced.

In addition, as the light emitting element, a light emitting element whose emission angle varies to some extent and which is cheaper can be used, so that the apparatus cost can be further reduced.

The present invention can be similarly applied to an equivalent mechanism other than the mechanism shown in FIG. Further, the present invention can be similarly applied to an optical pickup device having an optical system different from that of FIG.

[Effects of the Invention] As described above, according to the present invention, an inexpensive light receiving element can be used to detect a displacement of an objective lens moving mechanism in a tracking direction with respect to a reference position, and an inexpensive light emitting element can be used. Can be used, so that the effect that the apparatus cost can be greatly reduced is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing an objective lens moving mechanism according to one embodiment of the present invention, FIG. 2 is a schematic perspective view for explaining a positional relationship between a light emitting diode and a light receiving surface of a light receiving element, and FIG. 4A to 4C are schematic diagrams for explaining the principle of detecting the displacement of the objective lens moving mechanism in the tracking direction with respect to the reference position. FIG. 4 shows the displacement of the objective lens moving mechanism in the tracking direction with respect to the reference position. FIG. 5 is a circuit diagram showing a means for forming a difference signal, FIG. 5 is a graph showing an example of a relationship between the difference signal and displacement, and FIGS. 6 (a) and (b) are spot diameters and a change rate of the difference signal. FIG. 7 is a schematic perspective view for explaining another effect of the present invention, FIG. 8 is a schematic view showing an example of an optical system of the optical pickup device, and FIG. FIG. 4 is a schematic perspective view showing a conventional example of an objective lens moving mechanism. . 38 …… Light-emitting diode, 45 …… Cover member, 46 …… Window,
47: Light receiving element, 48, 48a, 48b: Light receiving surface, 50: Differential amplifier.

Claims (1)

(57) [Claims] An objective lens for imaging a light beam on a recording track formed on an optical storage medium is linearly moved in a focus direction and circularly moved in a tracking direction to position the light beam on the recording track. In an optical pickup device provided with an objective lens moving mechanism, a light emitting element interlocked with the rotation of the objective lens moving mechanism, a cover member formed with a window that covers the light emitting element and narrows output light from the light emitting element, A light-receiving element that receives light emitted from the cover member and has a light-receiving surface divided into two by a dividing line perpendicular to the moving direction of the input light, and light-receiving elements obtained from the two divided surfaces of the light-receiving element. Signal processing means for detecting a displacement of the objective lens moving mechanism in a tracking direction with respect to a reference position based on a signal difference signal The optical pickup apparatus according to claim.