JPH02154330A - Optical pickup - Google Patents

Abstract

PURPOSE:To improve the position detecting sensitivity by using a cylindrical lens constituted in such a way that the lens can refract light in a required direction only. CONSTITUTION:A cylindrical lens 13 formed of a transparent plastic material is provided at the side section of a mobile member 4 in the tracking direction and a light source 14 and photodetector 15 are provided at a required interval on both sides of the lens 13. The light source 14 and photodetector 15 are fixed to a holding member 16 together with a flexible printed circuit board 17. Then the position of the mobile member 4 in the 2nd direction is detected by means of the photodetector 15 which receives the light passed through the optical member 13. Therefore, the position detecting sensitivity can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup equipped with a position detection device.

[Prior Art] In general, optical pickups used for recording and reproducing information on optical discs such as compact discs and video discs, and optical recording media such as magneto-optical discs are used for recording and reproducing. In order to irradiate a light beam through an objective lens onto an optical disc, etc. in a focused state, and to make it follow the track of the optical disc, etc., the objective lens has a focus direction that is the direction of its optical axis, which is orthogonal to the focus direction. Further, it is supported by the pickup main body so as to be movable in a tracking direction perpendicular to the track direction of the optical disc. Furthermore, such optical pickups have the disadvantage that, during a so-called access operation in which the pickup is moved to a predetermined track at high speed, the objective lens causes unnecessary vibrations due to inertial force or the like in the tracking direction.

Therefore, in order to suppress this unnecessary vibration and perform the access operation accurately, the optical pickup is equipped with a lens position detection device to detect the position of the objective lens, and to quickly perform tracking control. It has been known.

An example of an optical pickup equipped with such a lens position detection device is the one described in Japanese Patent Laid-Open No. 61-276137. In this conventional example, as shown in FIG. 7, a shielding plate 22 in which an opening 21 is formed is fixed to a movable part 24 having an objective lens 23, and the shielding plate 22 has a light source 25 such as an LED and four element detectors. A split photodetector 26 consisting of
It was established between When the movable part 24 moves, the opening 21 of the shielding plate 22 also moves together, and the light beam from the light source 25 moves on the split-type photodetector 26. If the amount of light received by each element detector of the split type photodetector 26 is calculated, the movable part 2
Signals corresponding to the vertical and rotational displacements of the object lens 4, that is, the displacements of the objective lens in the focusing and tracking directions, are obtained. In this way, the lens position is detected.

Furthermore, as shown in FIG. 8, the publication also describes an example in which a lens 27 is provided in the opening 21 of the shielding plate 22 to magnify and extract the movement of the movable part to improve position detection of the movable part. ing.

[Problem to be solved by the invention]

However, in conventional position detection devices, only the light that has passed through the opening of the shielding plate is received by the photodetector, resulting in poor light utilization (poor light detection sensitivity). Therefore, it is possible to make the aperture of the shielding plate larger to improve the light utilization efficiency, but this also requires increasing the light-receiving area of the photodetector, resulting in a disadvantage in terms of component costs. There is a problem with this.

On the other hand, although a lens provided at the opening of the shielding plate can improve the light utilization efficiency, when the movable part moves in the focus direction (usually ±1 cabinet), the light intensity distribution of the light emitted from the light source is not uniform. , there is a problem that the amount of light incident on the lens decreases, resulting in a decrease in photodetection sensitivity (deterioration of linearity of detection sensitivity). This also applies to movement in the tracking direction.

The present invention is proposed to solve the above problems,
The object of the present invention is to provide an optical pickup equipped with a position detection device with high position detection sensitivity.

[Means and effects for solving the problems] In order to achieve the above object, the present invention includes a movable member that holds an optical system, and a movable member that is movably supported in a first direction and a second direction that are orthogonal to each other. an optical pickup having a supporting member and a driving means for driving the movable member, wherein a light source and a photodetector are provided at predetermined positions in a third direction perpendicular to the first direction and the second direction; An optical member that does not have refractive power in the first direction but has refractive power in the second direction and is integrally provided with the movable member is disposed between the light source and the photodetector, and the optical member is disposed between the light source and the photodetector. The position of the movable member in the second direction is detected by a photodetector that receives the transmitted light.

In this way, the position detection sensitivity can be improved by making the optical member having refractive power in one direction movable integrally with the movable member and allowing the light from the light source to be received by the photodetector through the optical member. became.

〔Example〕

FIG. 1 shows a first embodiment of the present invention, in which an objective lens 1 is fixed to the upper surface of the center of a movable member 4, and focus coils 2 are wound around the outer periphery of the movable member. Four formed tracking coils 3 are glued together. The base 5 has outer yokes 6a and 6b and an inner yoke divided in the center? There are two pairs of magnets 8a and 8b inside the outer yokes 6a and 6b.
are fixed to each other, forming two sets of magnetic circuits. A fixing member 9 is fixed to the outside of one outer yoke 6a,
Four round holes 11° and 12 are formed in the fixed member 9 and the movable member 4 on the upper, lower, left and right sides to correspond to each other, and four metal wires 1 are inserted into these holes.
The zero end is inserted and fixed, making the movable member 4 movable in the focusing direction and the tracking direction. Therefore, when current is passed through the focus coil 2 and the tracking coil 3, a driving force is generated by electromagnetic interaction with the magnets 8a and 8b, and the movable member 4 moves in the focusing direction and the tracking direction.

2A and 2B are exploded perspective views of a portion of the optical pickup. The opening 4b formed by the outer peripheral part 4c of the movable member 4 and the cylindrical part (optical system support member) 4d is the outer peripheral part 4c.
and the rib 4a and partition wall 4e formed across the cylindrical portion 4d.
It is divided into four parts. Two pairs of inner yoke here? a,
7b is located there. And the inner yoke? a, 7
The surface b facing the cylindrical portion 4d is chamfered so that the inner yokes 7a, 7b and the center of the objective lens 1 are close to each other.

Since the rib 4a is formed between the cylindrical portion 4d and the outer peripheral portion 4c of the movable member 4 in this manner, the rigidity of the opening 4b is significantly improved compared to the conventional one.

In FIG. 1, a cylindrical lens 13 made of transparent plastic such as PMMA is provided on the side of the movable member 4 in the tracking direction. 15 forms a sensor unit 20. The light 514 and the photodetector 15 are fixed to the holding member 16 together with the flexible printed circuit board 17, and the washer 18,
It is fixed to the base 5 via screws 19.

Next, a position detection device including the sensor unit 1-20 will be explained. As shown in FIG. 3, the cylindrical lens 13 has a positioning fixing part 13a to the movable member 4, a surface roughening part 13d continuous to this, a semicylindrical part 13b, and a surface roughening part 13d continuous to the semicylindrical part 13b. have The light in the X direction that is incident on the semi-cylindrical portion 13b is not refracted in the X direction, but is refracted only in the X direction and transmitted. In addition,
Since the cylindrical lens 13 does not have an opening or the like, it has high rigidity and is less affected by resonance.

FIG. 4 is a plan view of the position detection device, and FIG. 5 is a front view. A light source 14 such as an LED is connected to the lead frame 1
The diverging light from the light emitting part 14a provided in the holding member 16 is made into a substantially parallel light beam by the spherical part 14b formed in the emission direction and emitted.
It is fixed at 6a.

The photodetector 15 includes a lead frame 15c provided with a light receiving section 15a divided into two in the X direction as shown in FIG.
It is fixed in a recess 16c formed in the holding member 16.

Lead frame 14c of the light source 14 and photodetector I5.

15c is fixed to the flexible printed circuit board 17 provided on the back surface of the holding member 16 by soldering.

The optical axis of the light emitted from the light source 14 is connected to the light receiving section 15 of the photodetector 15.
It should almost match the center of a. Sensor unit 20
As shown in FIG. 5, the protrusion 16d formed at the lower part of the holding member 16 is rotatably inserted into the hole 5b formed in the base 5, and the light is emitted from the light source 14, and the cylindrical lens 1
The light beam focused by the light receiving section 15a of the photodetector 15
The light-receiving section 15 is divided into two parts so that the light is irradiated almost in the center of the
Position the sensor unit 20 on the base 5 while rotating the sensor unit 20 using the protrusion 16a of the holding member 16 as a fulcrum so that the differential output of a becomes 0.
Fix it at 8. Note that the preamplifier circuit of the differential output circuit may be provided near the sensor unit 20 in order to reduce the influence of noise.

In this embodiment, the light source 14 and the photodetector 15 are attached to the holding member 1.
6, there is almost no deviation between the optical axis and the center position of the photodetector, which is advantageous for assembly. Further, position adjustment with the cylindrical lens 13 is easy because the light source 14 and the photodetector 15 can be rotated and adjusted as one unit.

Next, referring to FIG. 6, a description will be given of how to obtain a differential output by the photodetector 15. When the movable member 4 is stationary,
A light receiving element 15d of the photodetector 15 is divided into two parts.

15e, the intensity of the irradiated light is the same on the left and right sides as shown in FIG. 6A, so the differential output is O.

When the movable member 4 moves and the objective lens 1 moves in the tracking direction, the light moves in the direction perpendicular to the bisecting line (moves to the right in the drawing) as shown in FIG. 6B.
The differential output changes from 0 to (+) ((-) in the opposite direction). In this way, the position of the objective lens l in the tracking direction appears as the differential output of the photodetector μm5.

The light emitted from the light source 14 passes through the aperture section 16 of the holding member 16.
b is designed to cut off light other than effective light. In addition, the semi-cylindrical part 1 of the cylindrical lens element 3 through which light passes
Since the surface of the surface roughening portion 13d other than 3b is formed to be rough, the light incident on this portion is difficult to reach the photodetector 15, and is hardly affected by anything other than effective light. .

X direction (tracking direction) and Z direction of the semi-cylindrical portion 13b
The dimensions in the direction (focus direction) are such that the light from the light source 14 will not be eclipsed even if the cylindrical lens 13 moves in each direction, and even if the cylindrical lens 13 moves due to the movement of the movable member 4, The light amount and light amount distribution of the photodetector L5 do not change, and the sensitivity of position detection is not affected.

As described above, position detection in the tracking direction is performed. During normal recording and reproduction of optical discs, etc., the differential output of the photodetector 15 is input to the means for sending the optical pickup in the track direction, and the optical pickup itself , so that the amount of movement of only the objective lens 1 does not become too large.

In addition, during access operation, a current is passed through the tracking coil 3 so that the differential output of the photodetector 15 or the value obtained by differentiating this becomes O, and unnecessary vibrations are generated in the objective lens 1 in the tracking direction due to inertial force, etc. In order to ensure that access operations are performed accurately.

The present invention is not limited to the above-described embodiments, and can be modified and modified in many ways. For example, the cylindrical lens 13 is not limited to a plastic molded body, and may be a gradient index lens, a prism, or the like. Further, a COD linear sensor, a position sensor, or the like may be used as the photodetector. Further, the optical system driving method is not limited to the wire-only method, but may be other driving methods. Further, a relay lens or the like may be used instead of the objective lens.

〔Effect of the invention〕

As described above, according to the present invention, by using a cylindrical lens that refracts only in the required direction, the efficiency of light utilization is high, and even if the movable part moves in a direction other than the direction of position detection, light detection is possible. Changes in the amount of light received by the device are small.

Therefore, the position detection sensitivity of the movable part is high and the linearity is also good.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the present invention, FIG.
B is an exploded perspective view of the same part, FIG. 3 is a perspective view of the cylindrical lens, FIG. 4 is a plan view of the photodetector, FIG. 5 is a front view of the same, and FIG. 6 is the photodetector. 7 is a perspective view of an optical pickup according to a conventional example, and FIGS. 8A and 8B are a partial side view and an explanatory view showing another conventional example. ■...Objective lens 4...Movable member 13
...Cylindrical lens 14...Light source I5...
・Photodetector Figure 1 Figure 7 Figure 8 4 by moving in the focus direction.''

Claims (1)

[Claims] 1. A movable member holding an optical system, a support member supporting the movable member so as to be movable in a first direction and a second direction orthogonal to each other, and a driving means for driving the movable member. In the optical pickup, a light source and a photodetector are provided at predetermined positions in a third direction perpendicular to the first direction and the second direction, and a light source and a photodetector are provided in the first direction between the light source and the photodetector. An optical member that has no refractive power but has refractive power in a second direction and is integrally provided with the movable member is provided, and a photodetector that receives light transmitted through the optical member is used to detect the movement of the movable member. An optical pickup characterized by detecting a position in a second direction.